No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
The antibacterial effect of heavy metal and cetylpridinium-exchanged montmorillonites
Abstract
The antibacterial effects of Cu2+-, Zn2+-, Ag+-, Ag0- and cetylpridinium-exchanged montmorillonites were tested on Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213 strains which are highly resistant to antibiotics and cause severe infections in hospitalized patients. The exchange reactions were carried out using heavy metal and cetylpridinium (CP) cations in amounts that are equal to or less than the amounts required forming a monolayer on montmorillonite surface. The amounts required for the monolayer formation were determined by conducting batch adsorption experiments. The antibacterial activity of the samples was detected by the disk diffusion method. Cu2+-, Ag+-exchanged and Ag0-covered montmorillonites had a good antibacterial effect against P. aeruginosa and S. aureus as did the Zn2+-exchanged montmorillonite against S. aureus. However, the CP-exchanged montmorillonite was ineffective for both of the bacterial species. Thus, the heavy metal exchanged montmorillonites could be used in pharmaceutical applications, personal care products, in the decontamination of P. aeruginosa reservoirs in hospitals, and also in aqueous based cleaning agents and liquid and bar soaps. Zn2+-exchanged montmorillonite has potentiality to be used as a low cost substitution to silver for applications against S. aureus.
... The adsorption of bacteria (Coliphages T1 and T7 of E. coli) on MMT clay was investigated for the first time by Schiffenbauer M. and Stotzky G. [43]. MMT clay as a natural material has always been worthy of consideration and has attracted intensive attention as a novel support, it absorbs a variety of materials on its surface because it has the advantage of a lamellar structure, a large surface area, and exhibits a negative surface charge (−60 ± 10 mV) [44][45][46], is biologically inert and it is effortless to remove it from the human organism [47]. MMT/metal NPs composites exhibit excellent adsorption, rheological, ion exchange, heat insulators and are heat-resistant, and swelling properties [48,49]. ...
... According to the MIC value, it is apparent that Ag 2 CO 3 /MMT exhibited higher antibacterial performance than the Ag/MMT nanocomposite because Ag 2 CO 3 NPs were found to be well dispersed in MMT, resulting in higher silver ion release [94]. Nevertheless, there is clear argument with others finding that antimicrobial performance depends on silver content [46,95], Later, Bonga et al. synthesized AgNPs on MMT by the chemical reduction of silver nitrate with sodium citrate and measured antibacterial performance towards S. aureus and E. coli. The effect of synthetic parameters, such as higher concentration of reductant, leading to a smaller AgNP size, was investigated [96]. ...
... Özdemir et al. showed that Cu 2+ , Ag + -exchanged, and Ag 0 -covered MMT exhibited excellent antibacterial performance against P. aeruginosa and S. aureus. On the contrary, Zn 2+ /MMT was powerful only against S. aureus, which suggested the potential use of Zn/MMT instead of Ag/MMT for applications towards S. aureus [46]. In another interesting study, the antibacterial (E. ...
One of the crucial challenges of our time is to effectively use metal and metal oxide nanoparticles (NPs) as an alternative way to combat drug-resistant infections. Metal and metal oxide NPs such as Ag, Ag2O, Cu, Cu2O, CuO, and ZnO have found their way against antimicrobial resistance. However, they also suffer from several limitations ranging from toxicity issues to resistance mechanisms by complex structures of bacterial communities, so-called biofilms. In this regard, scientists are urgently looking for convenient approaches to develop heterostructure synergistic nanocomposites which could overcome toxicity issues, enhance antimicrobial activity, improve thermal and mechanical stability, and increase shelf life. These nanocomposites provide a controlled release of bioactive substances into the surrounding medium, are cost effective, reproducible, and scalable for real life applications such as food additives, nanoantimicrobial coating in food technology, food preservation, optical limiters, the bio medical field, and wastewater treatment application. Naturally abundant and non-toxic Montmorillonite (MMT) is a novel support to accommodate NPs, due to its negative surface charge and control release of NPs and ions. At the time of this review, around 250 articles have been published focusing on the incorporation of Ag-, Cu-, and ZnO-based NPs into MMT support and thus furthering their introduction into polymer matrix composites dominantly used for antimicrobial application. Therefore, it is highly relevant to report a comprehensive review of Ag-, Cu-, and ZnO-modified MMT. This review provides a comprehensive overview of MMT-based nanoantimicrobials, particularly dealing with preparation methods, materials characterization, and mechanisms of action, antimicrobial activity on different bacterial strains, real life applications, and environmental and toxicity issues.
... The use of natural and synthetic zeolites, clays, and silicate frameworks as carriers for antimicrobial Ag + and Zn 2+ ions has received increasing attention in the quest to control the transmission of pathogenic microorganisms [28,30,31,[41][42][43][44][45][46][47][48]. Silver ions are soft acids that target DNA and disrupt the chemistry of microbial metalloproteins involved in respiration, membrane structure, replication, and metabolism, by binding with thiol groups [49]. ...
... The uptakes of Ag + and Zn 2+ ions by the container glass-derived tobermorites in the present study are compared with those of other natural and synthetic silicate-based carriers reported in the recent literature in Table 3 [28,30,31,[41][42][43][44][45][46][47][48]. The uptakes of Ag + ions by the green and amber glass-derived tobermorites are within the reported range for zeolite Y [44,45] and greater than those of analcime [41], chabazite [31], and montmorillonite [48]. ...
... The uptakes of Ag + and Zn 2+ ions by the container glass-derived tobermorites in the present study are compared with those of other natural and synthetic silicate-based carriers reported in the recent literature in Table 3 [28,30,31,[41][42][43][44][45][46][47][48]. The uptakes of Ag + ions by the green and amber glass-derived tobermorites are within the reported range for zeolite Y [44,45] and greater than those of analcime [41], chabazite [31], and montmorillonite [48]. However, the extents of Ag + -loading of TG4 and TA4 are inferior to those of zeolites A [30,32] and X [43], ZSM-5 [45], clinoptilolite [47], and the titanosilicate frameworks JDF-L1 and AM-4 [46]. ...
In this study, the layer-lattice calcium silicate hydrate mineral, tobermorite, was synthesized from waste green or amber container glass and separately ion-exchanged with Ag+ or Zn2+ ions under batch conditions. Hydrothermal treatment of stoichiometrically adjusted mixtures of waste glass and calcium oxide in 4 M NaOH(aq) at 125 °C yielded tobermorite products of ~75% crystallinity with mean silicate chain lengths of 17 units after one week. Maximum uptake of Zn2+ ions, ~0.55 mmol g−1, occurred after 72 h, and maximum uptake of Ag+ ions, ~0.59 mmol g−1, was established within 6 h. No significant differences in structure or ion-exchange behavior were observed between the tobermorites derived from either green or amber glass. Composite membranes of the biopolymer, chitosan, incorporating the original or ion-exchanged tobermorite phases were prepared by solvent casting, and their antimicrobial activities against S. aureus and E. coli were evaluated using the Kirby–Bauer assay. S. aureus and E. coli formed biofilms on pure chitosan and chitosan surfaces blended with the original tobermorites, whereas the composites containing Zn2+-substituted tobermorites defended against bacterial colonization. Distinct, clear zones were observed around the composites containing Ag+-substituted tobermorites which arose from the migration of the labile Ag+ ions from the lattices. This research has indicated that waste glass-derived tobermorites are functional carriers for antimicrobial ions with potential applications as fillers in polymeric composites to defend against the proliferation and transmission of pathogenic bacteria.
... Another problem is the tendency of the Cu NPs to agglomerate, which decreases their antibacterial properties. Therefore, loading of Cu on the surface of inorganic carriers to limit the release of copper ions and improve the dispersion of NPs was proposed [13,72,82]. ...
... The antimicrobial properties of N-halamine are related to the oxidation state + I of halide atoms in chloramine (>N-Cl) or bromamine (>N-Br) groups [84].The mechanism of antibacterial action of N-halamine-based materials is explained by the direct transfer of the halogens (e.g. chlorine, bromine) from N-halamine to bacterial cells, and their participation in ionic reactions or combination with another elements, which results in a destruction or inhibition of metabolic processes in the cells [82]. The biocidal activity of PES UF membranes modified with N-halamine grafted HNTs (N-halamine@HNTs) was investigated by Duan et al. [73]. ...
Polymeric membranes are widely applied for water and wastewater treatment. However, the membranes used in the pressure driven membrane processes suffer from the undesired phenomena of fouling and biofouling. That leads to a decrease in productivity and an increase in treatment costs. The membranes used in forward osmosis, being a non – pressure driven process, are less endangered by fouling; nonetheless, due to low permeation they have limited potential in wastewater treatment. To improve the membranes performance with reference to permeability, antifouling/antibiofouling resistance and separation properties the application of various nanomaterials has been proposed. This review presents a progress in the research on the polymer mixed-matrix membranes containing pure and modified halloysite nanotubes (HNTs). The effect of HNTs on the properties and performance of membranes made of polymers such as polysulfone, polyethersulfone, polystyrene and polyvinylidene fluoride is widely discussed. Finally, the key issues to be considered in further research on the mixed-matrix membranes modified with HNTs are proposed.
... Their toxicity makes the heavy metal ions highly efficient antibacterial agents but it also forms a disadvantage in the applications requiring direct contact with other living organisms. Thus, instead of heavy metals, cationic surfactants like quaternary alkyl ammoniums immobilized onto a host material (mostly mineral surfaces) is a recently studied issue in literature (He et al., 2006;Malachová et al., 2009;Özdemir et al., 2010, 2013Ke et al., 2014;Malek and Ramli, 2015;Kleyi et al., 2016;Samlikova et al., 2016). Some new investigations have introduced heavy metal ions to the quaternary ammonium immobilized mineral surfaces to increase the antibacterial effect of the material (Saad et al., 2016;Jou et al., 2016). ...
... Clay minerals with a high surface area, cation exchange capacity, chemical stability, low toxicity, and high availability are commonly used as host materials in immobilization studies (He et al., 2006;Malachová et al., 2009;Özdemir et al., 2010, 2013Ke et al., 2014;Malek and Ramli, 2015;Kleyi et al., 2016;Samlikova et al., 2016). The exchangeable inorganic cations are replaced by organic cations, such as quaternary ammonium compounds to form organo-clays. ...
An organo-montmorillonite was synthesized to generate a two-level antibacterial agent. The material (Mt-CP-SR) was prepared through the adsorption of sodium lauroyl sarcosinate (SR) on montmorillonite modified with cetylpyridinium (Mt-CP) and its structure was characterized by conducting ATR-FTIR, XRD, and SEM analyses. The results of the ATR-FTIR analyses indicated that SR on the surface could be detected when its amount exceeded the CEC of the Mt. The XRD analyses revealed that the adsorption of CP and SR causes the separation of Mt layers into smaller stacks. The adsorption and desorption study of SR onto and from 0.7 CEC Mt-CP were investigated to determine the amount of SR adsorbed at varying initial SR concentrations and the amount of SR released when diluted with water. Around 140 mg of SR could be loaded on one gram of the Mt intercalated with 170 mg of CP. The results indicated that desorption of SR from the surface is gradual and SR and CP have strong interactions on the montmorillonite (Mt) surface. The antibacterial activity of the material was tested against E. coli, S. aureus, and P. aeruginosa. Additionally, the SR solutions and CP + SR solutions in equimolar ratios were subjected to antibacterial tests for comparison purposes. SR proved to be effective against all three bacteria and the MIC values were found as 75 mg/mL for E. coli, 37.5 mg/mL for S. aureus, and 300 mg/mL for P. aeruginosa. The MBC was 300 mg/mL for E. coli and S. aureus. The solutions of CP + SR mixtures were ineffective against P. aeruginosa, whereas, they were effective against S. aureus. The prepared Mt-CP-SR samples were found to be effective against S. aureus and E. coli. These results indicate that the material could be used in antibacterial liquid soaps, in toothpaste formulations, personal care products, and topical applications against acne, and wounds without any negative contribution to the physico-chemical and detergency properties of the materials.
... Silver and copper are known for their antibacterial properties. Most of authors have studied the antibacterial ability of Cu-forms of montmorillonite (Zhou et al., 2004;Hu et al., 2005;Özdemir et al., 2010) and vermiculite (Li et al., 2002). Cu-montmorillonites were studied in connection with their potential utilization in veterinary medicine Hu and Xia, 2006;Tong et al., 2005;Yu et al., 2008). ...
... Cu-montmorillonites were studied in connection with their potential utilization in veterinary medicine Hu and Xia, 2006;Tong et al., 2005;Yu et al., 2008). The antibacterial influence of Ag/montmorillonites and Ag/vermiculites was less commonly studied (Magaña et al., 2008;Valášková et al., 2010;Özdemir et al., 2010;Malachová et al., 2009). Özdemir et al. (2010) compared the antibacterial effect of Ag-, Cu-and Zn-forms of montmorillonite. ...
Vermiculite (V) from Brazil with aqueous solutions AgNO3 and/or Cu(NO3)2 was used for preparation of nanocomposites V/Ag, V/Cu, V/AgCu and V/CuAg using two procedures and their effect on bacteria was compared. Structural changes were evaluated using X-ray diffraction (XRD) analysis, Infrared spectroscopy (IRS) and Scanning electron microscopy (SEM). Elemental chemical composition was determined using X-ray fluorescence (XRF) analysis and the solutions were analyzed by Atomic emission spectroscopy with inductively coupled plasma (AES-ICP). Antibacterial properties of Ag- and Cu-vermiculites and combined Ag/Cu-vermiculites were tested on two bacteria groups: (1) Gram-positive, G+, (Staphylococcus aureus and Enterococcus faecalis) and (2) Gram-negative, G-, (Pseudomonas aeruginosa and Klebsiella pneumoniae). The samples under antibacterial testing showed different effective times and minimum inhibitory concentration (MIC) values. The Gram-negative bacteria showed higher sensitivity to the prepared samples than Gram-positive bacteria. The combined Cu/Ag vermiculites stopped the bacterial growth at lower MIC value.
... Several biocide materials based on clays, such as clays modified by the sorption of biocide compounds, have been proposed for various applications, including cosmetics, medicine, food, and the detergent industry [2]. Among biocide compounds, alkyltrimethylammonium cations, especially quaternary amines, are commonly employed as organic compounds with antibacterial activity [3][4][5][6]. However, the isolated use of these compounds for wastewater treatment is limited because they are soluble and can become pollutants in the effluent. ...
... The MMT support substrate is highly attractive due to its excellent ion exchange capacity, chemical inertness, natural abundance, cost-effectiveness, nontoxicity, ease of exfoliation to twodimensional nanosheets, and effortless dispersion in almost all solvents. Furthermore, MMT has the advantage of a lamellar structure and a large surface area, exhibits negative surface charge (−63 ± 11 mV), and is also biologically inert [21][22][23]. MMT/metal NP composites exhibit excellent adsorption, rheological, heat-insulator, heat-resistant, and swelling properties [24]. An appealing property of MMT substrates is the propensity to absorb a variety of compounds on their surface. ...
Unlike other antimicrobial agents, Ag-based composites are stable and currently widely used as broad spectral additives, fighting microbial biofilms and other biological threats. The goal of the present study is to develop a green, multifunctional, and robust antibiofilm water-insoluble coating, inhibiting histamine-producing Lentilactobacillus parabuchneri biofilms. Herein, laser-ablated Ag NPs (L-Ag NPs) were incorporated into and onto a montmorillonite (MMT) surface layer with a simple wet chemical method, provided that the electrostatic interaction between L-Ag NPs and MMT clay led to the formation of L-Ag/MMT nanoantimicrobials (NAMs). The use of MMT support can facilitate handling Ag NPs in industrial applications. The Ag/MMT composite was characterized with transmission electron microscopy (TEM) and scanning electron microscopy (SEM), which confirmed the entrapment of L-Ag NPs into MMT clay. The surface chemical composition was assessed with X-ray photoelectron spectroscopy, proving that Ag NPs were in contact with and deposited onto the surface of MMT. The characteristic L-Ag/MMT band was investigated with UV–vis spectroscopy. Following that, the L-Ag/MMT composite was embedded into a biosafe water-insoluble beeswax agent with a spin coating technique. The antimicrobial ion release kinetic profile of the L-Ag/MMT/beeswax coating through an electrothermal atomic absorption spectroscopy (ETAAS) study supported the controlled release of Ag ions, reaching a plateau at 420 ±80 nM, which is safe from the point of view of Ag toxicity. Microbial biofilm growth inhibition was assessed with real-time in situ Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR) in a flow cell assembly over 32 h. The study was further supported by optical density (OD) measurements and SEM on bacteria incubated in the presence of the L-Ag/MMT/beeswax coating.
... Moreover, this result is corroborated by other authors like Jou et al., (2016) [67] and Holesova et al., (2013) [68] which reported that natural clay minerals show no antibacterial effect. Therefore, the antibacterial properties of clay minerals are attributed to coexisting inorganic species such as Zn [56,69,70] and Cu ions [56,[71][72][73]. The total count of bacteria, molds, and yeasts starting from the initial inoculation at the predetermined time intervals are summarized in Table 6, while the logarithmic reduction of CFU and the score for each sample according to the relevant criteria are presented in Table 7. Specifically, CuBentp showed excellent resistance to bacteria and yeasts with similar results to the phenoxyethanol sample, as the total count for bacteria and yeasts was found lower than 100 cfu/g within two days and reduced to a minimum count of <10 cfu/g until the seventh day, thus passing criterion A. Additionally, it demonstrated an adequate reduction of CFU for molds barely missing criterion A with 1.41 instead of 2 log reduction at day 14, overall satisfying criterion B. In this case, the microbiological risk of the product should be assessed during the product development phase, taking into consideration control factors other than the formulation. ...
Pharmaceutical grade bentonite, containing a high amount of montmorillonite, enriched with zinc (Zn) or copper (Cu) (ZnBent and CuBent, respectively) was used as the main component for the creation of formulations for cutaneous use and tested for their antimicrobial capacity. Bentonite (Bent) with added phenoxyethanol (PH) as a preservative and unmodified bentonite were used as control groups. The mineralogical composition, structural state, and physical or chemical properties, before and after the modification of the samples, were characterized utilizing X-ray Diffraction Analysis (XRD), Fourier-Transform Infrared Spectroscopy (FTIR) and X-ray Fluorescence (XRF) techniques, and Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM, SEM-EDS) analyses. In addition, the profile of zinc and copper concentration from two types of surfaces ZnBent and CuBent, and into Phosphate-Buffered Saline (PBS) are discussed. Finally, the formulations in the form of basic pastes were challenged against bacteria, molds, and yeasts, and their performance was evaluated based on the European Pharmacopeia criteria. The Cu-modified bentonite performed excellently against bacteria and yeasts, while the Zn-modified bentonite only showed great results against yeasts. Therefore, Cu-modified bentonite formulations could offer antimicrobial protection without the use of preservatives.
... kaolinite), showed no antibacterial effect. According to the literature, clay minerals are loaded with inorganic species exhibiting antibacterial properties such as copper ions [70,71] and zinc ions [72,73]. However, this observation was not observed for the CuTp and ZnKp pastes that were also found with a microbial load of total anaerobic microbial count >3 × 10 3 cfu/g as well as molds and yeasts 4 × 10 and >3 × 10 2 , respectively, five days after their preparation (Table 7). ...
Six pharmaceutical pastes were prepared using chemically modified kaolin and talc powders. Tests were conducted to determine their structural and chemical characteristics as well as their antimicrobial protection, thus rendering them suitable for cosmetic and pharmaceutical uses. Kaolin and talc were treated chemically via the cation exchange method to load the clay particles with copper and zinc ions, two cations well known for their antimicrobial properties. Mineralogical analyses were conducted by using X-ray diffraction (XRD) before and after the modification, confirming the mineralogical purity of the samples. Scanning electron microscopy was also used in conjunction with energy dispersed spectroscopy (SEM-EDS) to obtain chemical mapping images, revealing the dispersion of the added metals upon the clay minerals surfaces. Moreover, chemical analysis has been performed (XRF) to validate the enrichment of the clays with each metal utilizing the cation exchange capacity. All modified samples showed the expected elevated concentration in copper or zinc in comparison to their unmodified versions. From the X-ray photoelectron spectroscopy (XPS), the chemical state of the samples’ surfaces was investigated, revealing the presence of salt compounds and indicating the oxidation state of adsorbed metals. Finally, the resistance of pastes in microbial growth when challenged with bacteria, molds, and yeasts was assessed. The evaluation is based on the European Pharmacopeia (EP) criteria.
... As a nonmental versatile fine chemical raw material, 4-cumylphenol is an effective chemical substance applied as a fungicide, preservative, and anti-termite agent [18][19][20][21]. Higaki developed a wood preservative containing 4-cumylphenol. ...
As a byproduct from the soybean oil industry, soy meal can be reproduced into value-added products to replace formaldehyde as a plywood adhesive. However, the use of soy meal has been limited by its poor antifungal and antiseptic properties. In this work, three kinds of material, namely nano-Ag/TiO2, zinc pyrithione, and 4-cumylphenol were applied to enhance the mildew resistance of soy meal via breakdown of the cellular structure of mildew. The fungi and mold resistance, morphology, thermal properties, and mechanism of the modified soy meal were evaluated. The success of the antifungal and antiseptic properties was confirmed by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy. The results indicated that all three kinds of material improved the fungi and mold resistance of soy meal, and sample B, which was modified with a compound of nano-Ag/TiO2 and zinc pyrithione, was the effective antifungal raw material for the soy-based adhesives. FTIR indicated that the great improvement of antifungal properties of soy meal modified with 4-cumylphenol might be caused by the reaction between COO– groups of soy protein. This research can help understand the effects of the chemical modification of nano-Ag/TiO2, zinc pyrithione, and 4-cumylphenol on soy meal, and the modified soy meal exhibits potential for utilization in the plywood adhesive industry.
... between the cellular membranes and organic salt that induced the leakage of intercellular components within the microorganisms. This mechanism is similar to that of nanoclays modified with heavy metals [29]. It has been already reported that nanocomposites inhibit the growth of a wide variety of both Gram-positive and Gramnegative bacteria, including major foodborne pathogens (e.g. S. aureus, B. subtilis, and E. coli) [30][31][32]. ...
The present study investigates the effect of thermooxidative and photooxidative aging on the mechanical and bactericidal properties of elastomer nanocomposites (ENs) based on Nanobent ZR2. The mechanical properties and morphologies were analyzed before and after aging. The addition of nanoparticles had a significant effect on the mechanical properties of ENs. Samples containing Nanobent exhibited higher tensile strength before and after aging compared to the reference composition. The addition of nanoparticles attenuated elastomer aging at elevated temperatures and ultraviolet light. Aged nanocomposites showed an inhibitory effect on the growth of bacteria and yeasts. Antibacterial and antifungal activity was only partially reduced after aging using physical methods compared to the activity of probes without aging. Scanning electron microscopy micrograph analysis showed different rough but homogeneous structures, confirming the uniform dispersion of the modified nanoparticles in the elastomer matrix as well as the retention of mechanical properties after the aging process.
... When the Fe 3+saturated montmorillonite impregnated filter paper was used, the E. coli deactivation efficiency improved significantly to 77% and 99% when the 200 mL and 50 mL E. coli containing water samples were filtered, respectively (Fig. 4). The E. coli deactivation efficiencies achieved by the Fe 3+ -saturated montmorillonite impregnated filter paper are comparable with those reported for other types of antibacterial filter papers (Mansur-Azzam et al., 2014;Özdemir et al., 2010;Vyhnalkova et al., 2012). ...
In areas with high exposure to pathogen contaminated water and lack the economic means for water treatment, low cost and convenient point-of-use drinking water disinfection materials/devices are essential. Using a simple craft paper making method, Fe³⁺-saturated montmorillonite impregnated filter paper was constructed to filter live Escherichia coli (E. coli)-spiked water. The Scanning Electron Microscopic images of the E. coli cells in contact with the Fe³⁺-saturated montmorillonite impregnated filter paper showed: 1) Fe³⁺-saturated montmorillonite particles were uniformly coated on the cellulose paper fiber, creating large mineral surface for cell contact; and 2) E. coli cell membrane was dehydrated and damaged, resulting cell deactivation upon contacting with the Fe³⁺-saturated montmorillonite particles impregnated in the paper. The E. coli cells passing through the Fe³⁺-saturated montmorillonite impregnated filter paper were not viable as further confirmed by the microfluidic dielectrophoresis analysis. They remained non-viable at room temperature even after 5 days, as shown by the results from both the Colony Counting test and the Colilert test. More than 99.5% deactivation efficiency was achieved when the ratio of the volume of the E. coli contaminated water to the mass of Fe³⁺-saturated montmorillonite was maintained at <1:1.5 (mL/mg). The Fe³⁺-saturated montmorillonite impregnated filter paper maintained ~74% E. coli deactivation efficiency even after the 8th consecutive use. About 0.52 mg Fe³⁺, which is bioavailable, could be leached into the water for every 2 L E coli-contaminated water that is treated with the filter paper. The treated water could therefore provide iron supplement to a person at a level within the range of the FDA recommended human daily intake of iron. The results from this study has clearly demonstrated promising potential of using the Fe³⁺-saturated montmorillonite impregnated filter paper for low cost (~$0.07/L treated water for this study) and convenient point-of-use drinking water disinfection.
... It combines high cation exchange capacity and specific surface, as well as good stability in acid media. These properties allowed the classical montmorillonite applications as cationic adsorbent [16], and particularly its selectivity toward ammonium ions and alkyl-ammonium salts make it a material with increasing interest in research for biomedicine [17][18][19][20][21][22] and to wastewater treatments [23][24][25]. The ammonium ions or R-ammonium salts selectivity showed by montmorillonite generated the so called organo-montmorillonites, which traditional preparation method for different cationic (ammonium) surfactants used oven heating [24,[26][27][28]. ...
In this work, Montmorillonite (Mt) obtained from Tokat, Reşadiye region having 0.91 mmol/g cation exchange capacity was modified by using Benzethonium Chloride (BZT). Organoclays, from Mt and BTZ, were prepared by using conventional and microwave heating methods and BTZ in amounts equivalent to 50%, 100% or 200% of CEC of clay. The samples were characterized by XRD, ATR-FTIR, SEM, Thermal analyses and Zeta Potential measurements. Kinetic experiments revealed that adsorption kinetic of BTZ was very fast when the BTZ amount was less than 80% of CEC. The adsorption kinetics fitted to pseudo second order kinetic model for BTZ amounts of 80% and 100% CEC. Adsorption behavior of BTZ on montmorillonite was explained by Sips isotherm model. XRD results indicated that the basal spacing of the clay increased up to 2.85 nm with increasing amount of BTZ and a pseudo trimolecular layer formed in the interlayer. The results of Zeta potential measurements and XRD analyses confirmed the distribution of BTZ between external and internal surfaces.
... Because of its costeffectiveness, environmental-friendliness and high-efficiency, Mt and its functionalized derivatives have been widely applied in the field of environmental remediation, such as heavy metal adsorption [14][15][16][17][18]. Mt adsorbing metal ions could be reused through desorption with NaCl [19] or strong acids [14]. Moreover, it has been demonstrated that heavy metal exchanged Mt can serve as an antibacterial reagent [20]. Through the adsorption of H + ions, Mt is able to increase solution pH [21]. ...
... 12,13 On the other hand, the research on the bactericidal properties of heavy metal exchanged montmorillonite (MMT) has increased interest since antibiotic treatment is becoming obsolete, as the overuse of antibiotics has led to an increase of bacteria resistant to antibiotics. 14 In recent years, clay mineral-based antibacterial complexes have been prepared by a series of processes between the clay minerals and antibacterial substances. Recently, Rivera-Garza et al. reported the elimination of the pathogenic microorganisms, E. coli and Enterococcus faecalis from water by silver-loaded clinoptilolite/heulandite mineral. ...
The antibacterial activity of copper-doped montmorillonite nanocomposites (Cu-MMT) has been investigated. Copper loaded clay nanocomposites have been synthesised by alkaline ion exchange processes in media containing copper sulfate at 550°C. Characterisation studies on the composites were done by X-ray diffractometry (XRD), scanning electron microscope (SEM) and absorption spectra analysis. SEM results indicated the diffusion of copper to the inner montmorillonite layer and opening of presenting cracks on its surface. The XRD analysis showed the presence of copper oxide (CuO) structure intercalated within the clay mineral layers. The antimicrobial effects of doped montmorillonite powders against pathogen bacterial strains Escherichia coli and Staphylococcus aureus were tested in broth media. Quantitative test in liquid media clearly showed that copper-doped samples had viable cells reduction ability for testing strains. The excellent antimicrobial activity of the composites was observed on S. aureus. In addition, the composite showed good stability in water and good promise for use in water treatment.
... Although clay-based inorganic materials show high thermal stability, they also have disadvantages, such as the accumulation of harmful heavy metals, mostly in the pseudohexagonal cavities of the silicate layers, resulting in decreased antibacterial activity. In spite of their low thermal stability, the organoclay materials exhibit many advantages compared to inorganic materials, mainly regarding their organophilicity, which results in easy adherence and ability to exterminate a number of bacterial species [32][33][34][35]. The antibacterial behaviour of vermiculite-bound chlorhexidine against selected Gram-positive and Gram-negative bacterial strains has already been demonstrated [36,37]. ...
Infectious stomatitis represents the most common oral cavity ailments. Current therapy is insufficiently effective because of the short residence time of topical liquid or semisolid medical formulations. An innovative application form based on bioadhesive polymers featuring prolonged residence time on the oral mucosa may be a solution to this challenge. This formulation consists of a mucoadhesive oral film with incorporated nanocomposite biomaterial that is able to release the drug directly at the target area. This study describes the unique approach of preparing mucoadhesive oral films from carmellose with incorporating a nanotechnologically modified clay mineral intercalated with chlorhexidine. The multivariate data analysis was employed to evaluate the influence of the formulation and process variables on the properties of the medical preparation. This evaluation was complemented by testing the antimicrobial and antimycotic activity of prepared films with the aim of finding the most suitable composition for clinical application. Generally, the best results were obtained with sample containing 20 mg of chlorhexidine diacetate carried by vermiculite, with carmellose in the form of nonwoven textile in its structure. In addition to its promising physicomechanical, chemical, and mucoadhesive properties, the formulation inhibited the growth of Staphylococcus and Candida; the effect was prolonged for tens of hours.
... Organo-clay derived from HDTMA-modified kaolinite has also recently been proven to increase the adsorption capacity towards chromate anions (Jin et al., 2014). Apart from the improved adsorption capability, organo-clay has also improved the antibacterial activity of unmodified clay (Herrera et al., 2000;Malachová et al., 2009;Maryan and Montazer, in press;Özdemir et al., 2010 because the modifiers (cationic surfactant quaternary ammonium compounds) of organo-clay are known antibacterial agents. ...
This paper discusses the formation of cetylpyridinium bromide (CPB), a cationic surfactant quaternary ammonium compound (QAC), immobilized on kaolinite with different initial CPB concentrations ([CPB]i) and their effect on the antibacterial activity against Escherichia coli. The CPB-immobilized kaolinites were characterized by a CHNS analyzer, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), zeta potential (ZP) analysis and the amount of CPB adsorbed on kaolinite. The antibacterial assay of the samples was studied through the disk diffusion technique (DDT) against E. coli as a model bacterium. The amount of CPB adsorbed on kaolinite did not affect the structure of the parent kaolinite but affected the overall charge of the kaolinite and eventually affected their antibacterial activity. CPB-immobilized kaolinite with [CPB]i above the critical micelle concentration (CMC) possessed antibacterial activity because of reversal of the charge from negative to positive on the kaolinite surfaces, as proven by ZP analysis, which could allow the action of CPB molecules against bacteria cells. This was due to the bilayer formation of surfactant molecules via hydrophobic bonding of their long hydrocarbon chains on the kaolinite surfaces at surfactant concentrations above the CMC value. Therefore, one of the important factors in producing antibacterial agents from surfactant immobilized kaolinite (organo-clay) is by loading excess surfactant on the clay above its CMC level to ensure bilayer formation of surfactant molecules on clay surfaces.
... In the particular case of P. aeruginosa, some studies showed that Zn +2 stimulates protein synthesis in these bacteria, invalidating its biocidal properties [24,25]. However, other research studies assessing the toxicity of metals showed differences in metal resistance profiles between environmental strains and hospital strains [26,27]. ...
... Previous reports have shown that, the modified clay minerals was used as an adsorbent for many different branches of industry e.g. in fluids [3], cement or drilling; in pharmaceutical e.g. nanocomposite [4], [5], removal pathogenic, virus [6], and toxin including heavy metal from aqueous solution [7], or an adsorbent for many hazardous pesticides and herbicides for eliminate pollutant from water and entirely systems [8], [9]. ...
Pesticides daily pollutes soil and water in farmland and environment in ASEAN agricultural developing countries. In this study, pesticide adsorption was studied by bentonite modification, targeting the “organoclay” adsorbent in comparison to native bentonite, which was probably reported to adsorb agricultural pesticide. Commercial bentonite was modified with the berberine containing natural extract from Coscinium fenestratum; the local folk medicine in Thailand. The modified clay by extracted berberine was able to adsorb carbamate pesticide carbaryl with significant rate. HPLC analysis of residue carbaryl after adsorption process showed that it was up to 80% carbaryl adsorption when bentonite was modified by extracted berberine with ratio 1:100 (w/w), whereas commercial bentonite has showed at 70%. Modified bentonite by C. fenestratum extract and berberine revealed by scanning electron microscopy showed that the different transform levels of this clay surface, herein, the highest carbaryl adsorption occurred when berberine/bentonite ratio for modification process was 1/200 (w/w). SEM results also demonstrated that the amount of berberine should be taken into consideration in term of bentonite modification for pesticide adsorption. Coscinium fenestratum plant will be further studied for its contribution to pesticide adsorption material in Thailand.
Nematodes are the most diverse organism after insects on this planet. The nematode community comprises of the population of nematodes with differences in their feeding habits, shape, size, etc. existing in an ecosystem. They are categorized into fungivores, bacteriovores, herbivores, omnivores and predators based on their feeding habits. Soil health can be determined by various characteristics such as stability, resistance to stress, supports biodiversity, nutrient recycling, etc. Nematodes have been exploited as indicators for the evaluation of soil qualities. To keep a check on the soil health, various indices were computed by assessing the nematode community of a particular region viz., maturity index (MI), enrichment index (EI) and structural index (SI). The maturity index is based on the c-p values which are used to decipher the r-strategist and k-strategist in the community. The colonizer was found to be less disturbed by the various activities which have a great effect on other communities, and they are termed as r-strategist. Various models have been used by researchers for carrying out preliminary studies to estimate soil quality. One of these is the soil food web model focused on the nematode community, which is beneficial to soils such as bacteriovores, predators, etc. and other is the fertilizer uses the efficiency model focused on both parasitic and free-living forms of nematodes. Besides this, the Caenorhabditis elegans model was also gained attention from scientists worldwide due to their short generation time, life cycle, and simple culturing of these nematodes in the laboratories. The effect of any metal which is found higher in a particular region can be evaluated with this model. All the indices based on nematode population or community showed a direct or indirect relationship with the soil properties such as nutrients, agricultural practices, plant productivity, etc. Hence, nematodes can be used as bio-indicators for understanding soil health.
This work is an extension to our previous work. Montmorillonite/poly(o-phenylenediamine) (MMT/POPD) Nanocomposites (NC) were synthesized by Riaz et al. 2016 and evaluated for the antimicrobial potential. Antibacterial potential of NC were investigated by the broth microdilution and agar well diffusion methods. Further, effective concentration (EC 50 ) and minimum inhibitory concentration (MIC) of the NC were determined. Intercalation and in-situ polymerization of POPD within MMT was successfully obtained using sonochemical technique. The TEM micrograph of MMT/POPD and POPD/MMT confirmed the size in the range of 20-90 nm and the shape observed was spherical (Riaz et al. 2016). The NC was then checked for antimicrobial activity against four bacterial strains and they showed potent antibacterial activity in both broth and on agar plate. Quantitative test in liquid media clearly showed that NC had viable cells reduction ability for testing strains. Results obtained here concluded that the NC can prevent the infestation of various bacterial pathogens effectively. Therefore, we propose that they are useful as effective and non-cytotoxic biologically active agents and can be used as nanocarriers with dual role i.e. in addition to carrying drugs, carrier will itself act as antibacterial agent. This dual nature of NC could be an alternative to target multi-drug resistant bacterial strains and can further be explored for their mode of action against bacterial pathogens.
The direct application of heavy metal- and quaternary ammonium-based antibacterial agents can cause inconvenience such as irritation, short-term applicability, discoloration of the tissue, and environmental concerns. The immobilization of these agents on montmorillonite (Mnt) was expected to diminish these effects by hindering direct contact of the ions with the target tissues. The objective of the present study was, therefore, to prepare inorgano(I)- and organo(O)-montmorillonites (I/O-Mnt) and to determine their potential uses in such biomedical applications. Na-montmorillonite (Mnt-Na) was modified by hydrothermal and microwave irradiation methods using Cu2+/Zn2+, and quaternary ammonium and/or anionic surfactants. The effect of the structures formed by immobilization on Mnt surfaces on antibacterial activity was investigated. Quaternary ammonium surfactants were cetyltrimethyl ammonium bromide (CTAB) with a linear alkyl chain, cetylpyridinium chloride (CPC) with a single aromatic ring, and benzethonium chloride (BZT) with double aromatic rings. N-lauroyl sarcosinate (SR) was the anionic surfactant. The samples were subjected to thermogravimetric (TGA) and scanning electron microscopy (SEM) analyses. Desorption tests showed that the antibacterial efficacy against Streptococcus mutans stemmed from I/O-Mnt and not from the ions released from the material surfaces to the aqueous phase. The results of the antibacterial studies showed that the existence of a linear alkyl chain and a double aromatic ring were the structural factors causing the greatest antibacterial effect. The time-kill tests revealed that Mnt-CTA, Mnt-BZT, and Mnt-CP-SR were effective against Streptococcus mutans within 5 min of contact. With the new findings, they were identified as possible selective and potent bactericidal agents and promising candidates for biomedical applications.
Enzyme immobilization provides ideal operating conditions for enzymes stabilization and sustainable recycling. In this work, as a kind of clay material, montmorillonite (MTL) was chosen for immobilizing the β-glucosidase extracted from Agrocybe aegirit. The immobilized β-glucosidase via partly cross-linking enzyme aggregates (pCLEAs) formed by self-catalysis provided biocatalysts with satisfactory thermal and pH stability. Compared to the glutaraldehyde cross-linked, the immobilized β-glucosidase (β-G-pCLEAs@MTL) exhibited significantly higher immobilization efficiency (IE) and immobilization yield (IY), which were 80.6% and 76.9%, respectively. The β-G-pCLEAs@MTL also showed better stability and preferable reusability. And the activity of the β-G-pCLEAs@MTL remained 85.0% after 5 cycles and 74.7% after 10 cycles. Therefore, the method based on the pre- crosslinking to form pCLEAs and after-immobilization can effectively improve IY and IE. In addition, MTL seems to be a good alternative carrier to immobilize other enzymes for industrial application.
Kaolinite is a common component of soil. Negatively-charged kaolinite can act as an adsorbent material and it has the ability to adsorb antimicrobial agents. In this study, local natural kaolinite was used to adsorb gentamicin and cationic surfactant molecules. Gentamicin-loaded surfactant-kaolinite (GSK) was prepared firstly by the attachment of cationic surfactant 4.0 mM hexadecyltrimethyl ammonium (HDTMA) on raw kaolinite to produce surfactant-kaolinite (SK), which was then loaded with gentamicin sulphate (50 and 200 mg/L) to yield GSK. Gentamicin-loaded kaolinite (GK) was also prepared and compared. All samples were characterised by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and CHNS elemental analysis. The characterisation results proved that the framework structure of kaolinite was not disrupted after modification with antimicrobial agents. The antibacterial activity of the samples was tested against Gram-negative Escherichia coli (ATCC 11229) and Gram-positive Enterococcus faecalis (ATCC 29212) through disc diffusion technique (DDT). Based on the technique, raw kaolinite did not exhibit antibacterial activity but showed antibacterial activity when HDTMA and/or gentamicin was loaded on kaolinite. In addition, GSK showed better antibacterial activity compared to GK and performed better on Gram-positive bacteria compared to Gram-negative bacteria. As a conclusion, immobilisation of HDTMA on kaolinite proved that kaolinite can act as an adsorbent to adsorb antibiotics and it has the potential to be developed as an enhanced antimicrobial agent.
Antibacterial potential of NC were investigated by the broth microdilution and agar well diffusion methods. Further, effective concentration (EC 50 ) and minimum inhibitory concentration (MIC) of the NC were determined. Intercalation and in-situ polymerization of POPD within MMT was successfully obtained using sonochemical technique.The NC was then checked for antimicrobial activity against four bacterial strains and they showed potent antibacterial activity in both broth and on agar plate. Quantitative test in liquid media clearly showed that NC had viable cells reduction ability for testing strains. Results obtained here concluded that the NC can prevent the infestation of various bacterial pathogens effectively.
Mycotoxins, bacteria, heavy metals and other toxic contaminants in feed have adverse effects on the health of animal. The decontamination of feed to reduce the content of harmful substances before feeding is inevitably needed. Clay minerals are a promising effective feed additive due to their cost-effectiveness and nearly without side effects. Montmorillonite (Mt) has high adsorption for mycotoxins, bacteria, heavy metals in animal feed and body. This review made a comprehensive and critical review of how Mt as an ingredient in animal feed functions. It covers the recent understanding of removing mycotoxins, bacteria and heavy metals onto Mt and the relevant influences of Mt on animal intestinal health, growth performance and product quality. Mt as feed additive can remove mycotoxins and bacteria in feed and gastrointestinal tract of the animal by surface adsorption, electrostatic adsorption and intermolecular force. In addition, Mt can adsorb heavy metals effectively in feed by the exchangeability of interlayer cations and by the swellability due to cation hydration. Modification of Mt by metal ions, metal oxides, and organic cations can improve the adsorption efficiency of mycotoxins, bacteria, heavy metals in vitro and in vivo. Mt and its modified products as feed additive can remarkably enhance the intestinal health and growth performance of livestock, aquatic and poultry. Utilization of Mt as feed additive can effectively improve the quality of milk, egg and meat.
Sodium bentonites have excellent cation exchange capacity (CEC) giving them great power of silver adsorption, which enables their use as precursors of antimicrobial materials. Countries like Brazil, however, do not have natural sources of sodium bentonite, only calcium or polycationic clays that do not show the same adsorption and ion exchange potential. In this study, the adsorption of silver in a polycationic bentonite from Quatro Barras, Brazil, previously subjected to a sodium treatment is evaluated. Samples were first modified with or NaOH and then, subjected to silver impregnation in a batch system under controlled ambient conditions. Antibacterial properties of silver-exchanged clays were evaluated by the disk susceptibility and the minimum inhibitory concentration tests on Escherichia coli and Staphylococcus aureus bacteria. Results show that the sodium treatment with allowed higher concentrations within a shorter time, increasing the pH without compromising the montmorillonite structure, which resulted on greater CEC and swelling values. Such better performance of the samples previously treated with sodium carbonate also caused an enhanced silver adsorption, resulting on a material of greater antibacterial potential. Experimental adsorption data fitted well to Freundlich isotherm.
The main objective of the present study was the preparation and characterization of new cationic/anionic surfactants and Cu2+/Zn2+ modified montmorillonites and the evaluation of their potential applicability as antibacterial agents for topical applications. To evaluate the antibacterial activity of Cu2+ and Zn2+ by synergistic effect, as well as to reduce the well-known toxicity of these metal cations; cetylpyridinium (CP) and N-lauroylsarcosinate (SR) intercalated montmorillonite (Mt-CP-SR) was used as the host material. In addition to their role to capture the metal cations and inhibit their release in any contact medium, these surfactants also increase the efficacy of the material due to their antibacterial properties. The effect of surfactant loading on the adsorption behavior of the metal cations onto the Mt-CP was investigated using SR in two different concentrations, namely 0.7 and 1.0 CEC of sodium montmorillonite (Mt-Na). The samples prepared were characterized using SEM, ATR-FTIR, zeta potential, and XRD analyses and they were subjected to antibacterial tests using the "Standard Method Under Dynamic Contact Conditions" on the Gram positive S. aureus, and Gram negative E. coli. As confirmed with desorption and characterization studies, the addition of Cu2+/Zn2+ onto the Mt-CP-SR yielded double adsorbed amounts compared to that of the Mt-CP, which indicated that Cu2+/Zn2+ bound to SR- interacted with the Mt surface. In contrary of Zn2+ caused no considerable change in the antibacterial effect of the host, Cu2+ addition enhanced the antibacterial activity. The produced antibacterial agents have the potential use in dyes, polymer composites, personal care products, and topical medicinal applications.
A new type of zeolite composite antibacterial agents was prepared by introducing zinc oxide and copper ions into 13X zeolite through the coprecipitation and ion-exchange methods. The structural properties of the tested antibacterial material were characterized and the antibacterial activity was evaluated. In Cu²⁺/ZnO-13X (CZ-13), zinc oxide and copper ions were either embedded in the interlayer space or dispersed on surface of 13X zeolite. Excellent antimicrobial activity of CZ-13 was observed on Escherichia coli (E. coli) and Staphylococcus aureus (S.aureus). In the case of Cu²⁺/ZnO-13X, both MIC and MBC against E.coli were 0.2 mg/mL and 0.8 mg/mL. For S.aureus, CZ-13 also showed similar antibacterial properties. The bacterial cells turned from normal rod-shape into irregular shapes after treatment with the tested CZ-13. An increase of the intracellular enzyme activity after CZ-13 addition suggested that the permeability of the cell membrane increased and bacteria were damaged.
The relationship between antimicrobial properties and structure of montmorillonite (MMT) containing hexadecyltrimethylammonium bromide (HDTMA-Br) and silver (Ag) was determined. HDTMA was adsorbed at the clay interlayer by a cation exchange, through the positive head of the ammonium group. At higher surfactant loadings (100 and 200% cation exchange capacity (CEC); MH1 and MH2 samples, respectively) the prevalence of weak adsorption (Van der Waals forces) was observed; whereas below the clay CEC (50%, MH0.5) strong interactions predominated (cation exchange). These different interactions impacted on antimicrobial activity, increasing bactericidal capacity when the surfactant was more available to diffuse. For organo-montmorillonites (OMMT) and all samples with Ag, zeta potential pointed out electrical charge changes on the outer surface, respect to MMT. XPS analyses showed peaks attributed to clusters formation, silver oxidation, and Ag 0 in MMT-Ag and MH0.5-Ag. The Ag 0 peak was also present in MH1-Ag and MH2-Ag, the later showing an extra peak associated with AgBr. HDMTA + and Ag adsorbed on the MMT acted synergistically against Staphylococcus aureus. This effect was less noticeable for Escherichia coli and the result was attributed to both, E. coli outer envelope which might lower the efficacy of HDMTA + adsorbed on the MMT, and decreasing silver proportions when the surfactant loading increased. MH1-Ag presented the best bactericidal properties, showing synergistic effects against S. aureus, while maintaining activity against E. coli compared to MMT-Ag. Understanding MMT-HDMTA-Ag efficacy contributes to the design of new antimicrobial materials for potential applications in health care.
Effect on antimicrobial activity observed for several types of hybrid materials is described in our chapter. The substrates for functional antimicrobial particles are natural clay minerals and carbon materials for this review limited to graphite/graphene and carbon nanoparticles (nanotubes and fullerenes). Short description of substrate materials and their properties is followed by discussion of the effect of selected most popular antimicrobial metals (silver, copper) and several oxides (zinc, titanium and copper oxides) and it is conferred for Gram positive and Gram negative bacterial strains. The methods for preparation of such particles may vary but the most used are intercalation and decoration methods from solution for the clay minerals. Nanoparticles (NPs) of metals and metal oxides on carbon and nanocarbon materials are prepared using physico-chemical approach. The research confirmed that the shape and size of functional NPs can depend on used substrate, preparation conditions and used method. Interestingly, it was found that Ag-clay sample was as effective as the free Ag+ions. Generally, it was found the size of active surface area, mobility and availability of potential active particles (ions or nanoparticles) and chemical state of them plays an important role in antimicrobial activity.
Production of nonmaterial by an appropriate price and good quality is the main problem in using of nanotechnology. For achieving this discipline, present study proposed a simple and cost effect method. Nanocomposites of bentonite/titanium dioxide nanocomposites were synthesized for using as an antibacterial material by a prompt and simple alkaline ion exchange method. The preparation of nanocomposite was achieved by heating a mixture of TiO2 and bentonite at 500, 600 and 700 °C for 30 and 60 minute. For synthesis of these nanocomposites, no reduction agent or chemical material not used except TiO2 and bentonite. The nanocomposites were characterized by XRD, XRF, SEM and DRS. SEM observations confirmed the formation of TiO2 particles on the clay surfaces with the mean average size of about 96.7-99.6 nm at less than 60 min. The XRD analysis showed the presence of anatase structure of TiO2 nanoparticles within the clay mineral layers. The nanocomposite have antibacterial effect on the S. aureus and E. coli bacteria.
Antimicrobial polyethersulfone ultrafiltration membranes containing zerovalent iron (Fe 0) and magnetite (Fe 3 O 4) nanoparticles were synthesized via phase inversion method using polyethersulfone (PES) as membrane material and nano-iron as nanoparticle materials. Zerovalent iron nanoparticles (nZVI) were prepared by the reduction of iron ions with borohydride applying an inert atmosphere by using N 2 gases. The magnetite nanoparticles (nMag) were prepared via co-precipitation method by adding a base to an aqueous mixture of Fe 3+ and Fe 2+ salts. The synthesized nanoparticles were characterized by scanning electron microscopy, X-ray powder diffraction, and dynamic light scattering analysis. Moreover, the properties of the synthesized membranes were characterized by scanning electron microscopy energy dispersive X-ray spectroscopy and atomic force microscopy. The PES membranes containing the nZVI or nMag were examined for antimicrobial characteristics. Moreover, amount of iron run away from the PES composite membranes during the dead-end filtration were tested. The results showed that the permeation flux of the composite membranes was higher than the pristine PES membrane. The membranes containing nano-iron showed good antibacterial activity against gram-negative bacteria (Escherichia coli). The composite membranes can be successfully used for the domestic wastewater filtration to reduce membrane biofouling.
The antibacterial chlorhexidine/vermiculite (CA/Ver) was successfully prepared through the intercalation process and the stability of CA on the vermiculite matrix and was investigated by stirring in aqueous solutions under the influence of different pH and temperature. The content of CA was determined by total organic carbon (TOC) analysis before and after stability tests. The structure of all samples was characterized by X-ray powder diffraction (XRD) and Fourier–transform infrared spectroscopy (FTIR). The antibacterial activity of prepared CA/Ver samples was evaluated by finding a minimum inhibitory concentration (MIC) against Enterococcus faecalis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. The content of chlorhexidine ranged from 209 to 231.6 mg of CA in 1 g of the whole sample after the intercalation process. After stability study, only a slight outflow of CA from the Ver matrix (< 5%) was noted. The antibacterial test confirmed that the outflow of CA was negligible.
After 30 min of exposition the MIC of organovermiculite samples before and after stability test were the same for Staphylococcus aureus and Escherichia coli with value 3.33 (%; w/v) and the MIC decreased to 0.014 (%; w/v) with longer time of exposition (120 h). A small difference was observed at Enterococcus faecalis where MIC was 10 (%; w/v) after 30 min of exposition for the sample after stability test in neutral pH. However, after 24 h of treatment the MIC value decreased to 0.014 (%; w/v). And finally, bacterial strain Pseudomonas aeruginosa showed a great resistance against antibacterial organovermiculite samples and MIC did not decreased under 10 (%; w/v) even after 5 days of exposition.
The Na⁺ montmorillonite (Mt) was modified with l-cystine, and palladium was loaded via an ion-exchange reaction under microwave irradiation to obtain Pd@Mt. The entire process was conveniently carried out under mild reaction conditions in a matter of hours. The XRD, XPS and ICP-AES results confirmed the successful loading of palladium (0.55 wt%). The so obtained Pd@Mt was subsequently explored as a catalyst for the Suzuki cross-coupling reaction and afforded the corresponding products in good to excellent yields for twenty reactants (in the range of 79–99%, only 3 reactants gave yields below 90%). The catalytic mechanism was investigated and discussed in detail. This supported catalyst could be easily recovered from the reaction mixture by simple filtration or centrifugation. Decreased palladium loss and improved reusability were achieved when the catalyst was recovered by filtration. Notably, this recovery method maintained the observed high yields, showing a > 90% yield for the 6th run. Although palladium ions were reduced to Pd (0) in the cross-coupling reaction, only a small amount of aggregation was observed in the TEM images, where the diameters of the palladium particles on Mt were in nano scale.
The present study examined the adsorption of silver ion in aqueous solution onto natural clinoptilolite zeolite from Futatsui Mine, Akita Prefecture, Japan. The effects of various parameters, i.e., solution pH, adsorbent dosage, adsorption time, silver ion solution concentration, and temperature, on silver ion adsorption process onto clinoptilolite were examined. Additionally, the thermodynamics of the silver ion adsorption process was investigated. The optimum pH for silver adsorption was determined to be around 4.0. The adsorption process could be well described by the Langmuir isotherm model. The calculated maximum adsorption capacity was 0.64 mmol/g. Adsorption kinetics studies were also conducted. The results showed that the adsorption process preferentially followed the pseudo-second-order kinetics model over the pseudo-first-order model. Furthermore, with decreasing aqueous solution temperatures, the adsorption kinetics became slower and the amount of silver ion adsorbed increased. The thermodynamic values, ΔG0, ΔH0, and ΔS0, indicated that adsorption was an exo-thermic and spontaneous process.
The potential application of triethylenetetramine intercalated montmorillonite (TETA-Mt) in mine tailings treatment and AMD (acid mine drainage) remediation was investigated with batch experiments. The structural and morphological characteristics of TETA-Mt were analyzed with XRD, FTIR, DTG-TG and SEM. The inhibition efficiencies of TETA-Mt against heavy metal release from mine tailings when exposed to acid rain leaching was examined and compared with that of triethylenetetramine (TETA) and Mt. Results showed that the overall inhibition by TETA-Mt surpassed that by TETA or Mt for various heavy metal ions over an acid rain pH range of 3–5.6 and a temperature range of 25–40 °C. When mine tailings were exposed to acid rain of pH 4.8 (the average rain pH of the mining site where the mine tailings were from), TETA-Mt achieved an inhibition efficiency of over 90% for Cu²⁺, Zn²⁺, Cd²⁺ and Mn²⁺ release, and 70% for Pb²⁺ at 25 °C. It was shown that TETA-Mt has a strong buffering capacity. Moreover, TETA-Mt was able to adsorb heavy metal ions and the adsorption process was fast, suggesting that coordination was mainly responsible. These results showed the potential of TETA-Mt in AMD mitigation, especially in acid rain affected mining area.
Chlorhexidine acetate-loaded silver-kaolinite (CA-Ag-Kaol) was prepared and characterised, and its application as an antibacterial agent was studied. CA-Ag-Kaol was prepared by the adsorption of chlorhexidine acetate (CA) (0.5 mmol/L) on Ag (50% of the Cation Exchange Capacity (CEC) of kaolinite) on kaolinite. Kaolinite (Kaol), silver-kaolinite (Ag-Kaol), CA-modified kaolinite (CA-Kaol) and CA-Ag-Kaol were characterised by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field-emission scanning-electron microscopy (FESEM), energy dispersive X-ray (EDX) spectroscopy, zeta potential analysis and dispersion behavior measurements. The modification of kaolinite with cationic silver and chlorhexidine ions did not change the structure of kaolinite, and the characterization of the kaolinite samples revealed the successful loading of cationic silver and chlorhexidine ions on the kaolinite. The antibacterial assay of the samples was carried out against Escherichia coli ATCC 11229, Pseudomonas aeruginosa ATCC 15442, Staphylococcus aureus ATCC 6538 and Enterococcus faecalis ATCC 29212 using the disc diffusion technique (DDT) and the minimum inhibition concentration (MIC) technique. Based on the antibacterial assay, CA-Ag-Kaol showed better antibacterial activity than Ag-Kaol and CA-Kaol, and it performed well in both distilled water and a 0.9% saline solution. Gram-positive bacteria were more susceptible to the antibacterial behavior of Ca-Ag-Kaol than Gram-negative bacteria. In conclusion, silver-kaolinite that has been loaded with chlorhexidine acetate can be used as an effective antibacterial agent because of its high antibacterial activity against wide spectrum of bacteria in solutions containing electrolytes (saline solution).
A zeolitic adsorbent was synthesized from waste green tuff stone cake by hydrothermal treatment, and its adsorption of silver ions from aqueous solution was examined for application in silver ion removal from polluted industrial waters and as a bactericide. The waste cake was composed mainly of SiO2 and Al2O3 in the form of silicate and aluminosilicate minerals, such as quartz, anorthite, muscovite and clinochlore. The cake was treated with 0–10 M NaOH solution at 80, 120 and 160°C for 24 h, and analcime, hydroxysodalite and hydroxycancrinite were synthesized. A product with high silver adsorption ability, including analcime, was obtained in 4 M NaOH solution at 160°C. The concentrations of Si and Al in the solution during the reaction in 4 M NaOH solution at 160 °C explain the synthesis of analcime zeolite phase due to the dissolution of quartz and anorthite in the cake, and Ag adsorption of the product depends on analcime zeolite crystals in the product. The optimal pH for silver adsorption for the product was found to be around 5. The equilibrium silver adsorption capacity was measured and extrapolated using the Langmuir and Freundlich isotherm models, and experimental data were found to fit the Langmuir model. The calculated maximum adsorption capacity of 1.10 mmol/g shows that this product is suitable for silver uptake from aqueous media. Adsorption kinetics was tested for pseudo-first- and -second-order reactions, and the rate constants of adsorption for these kinetic models were calculated. Adsorption experiments demonstrated that the adsorption process corresponds to a pseudo-second- rather than -first-order kinetics model. With decreasing aqueous solution temperature, the adsorption kinetics become slower and the amount of silver ion adsorbed increases. The thermodynamic values, ΔG°, ΔH° and ΔS°, indicated that adsorption was an exothermic and spontaneous process.
Catanionic surfactant systems are used as drug-delivery vehicles and as nanocompartments in the formation of biomaterials and nanosized particles. Clay minerals are compatible with organic tissues and also have biomedical applications. The aim of the present study was to combine the properties of catanionic surfactants and clay minerals to obtain new materials with potential uses in medicine, waste-water treatment, and antibacterial applications. The surfactants chosen to make the catanionic surfactant were cetylpyridinium (CP) and lauroyl sarcosinate (SR), which interact strongly in aqueous media and cause specific aggregations such as ion-pair amphiphiles and needle- and leaf-like structures. Aside from the aqueous solution, new ternary systems are formed with different structures and properties through the addition of montmorillonite (Mnt). The surface and interlayer structures of the different Mnt-CP-SR samples prepared by using CP and SR in amounts equal to various ratios of cationic exchange capacity of the clay mineral were studied. They were also compared with the structured surfactant aggregates formed in aqueous media. The Mnt-CP-SR samples were subjected to X-ray diffraction (XRD), thermogravimetric analyses, and zeta-potential measurements to elucidate the interlayer- and external-surface structures. The XRD analyses showed the formation of a compact structure in the interlayer region resulting from the interaction between randomly oriented pyridinium and negatively charged SR head groups. The triple interactions among the Mnt surface, CP, and SR were more complex than the double interactions between the Mnt and cationic surfactant, and the CP played a dominant role in the formation of external and interlayer surface structures regardless of the amount and order of the addition of SR. The new findings support new applications for organoclays in the fields of biomedicine, remediation of polluted water, and nanocomposite materials.
The sorption of Pb2+ and Cu2+ cations from phosphoric acid using a natural zeolite has been studied. The effect of pH =2, initial copper concentration (1-100 mg), sorbent dose (2 g), contact time (5-60 min) and temperature (298 K) was studied.
Antibacterial activity of modified kaolinite and bentonite with antibacterial agents against Pseudomonas aeruginosa was studied. These clays have been modified with only cetyltrimethyl ammonium bromide (CTAB) and copper (Cu) and the combination of both. Characterization of the studied materials with X-Ray Diffraction (XRD), Fourier Transform-Infrared (FTIR) spectroscopy, Energy Dispersive X-ray (EDX) analyzer and Field Emission-Scanning Electron Microscopy (FESEM) revealed the successful preparation of CTAB-clays, Cu-clays and CTAB-Cu-clays without distorting the structure of these clays. From the antibacterial assay of the studied materials by Inhibition Growth Study and Minimum Inhibition Concentration (MIC) technique, CTAB-Cu-clays have been proven to have the highest antibacterial activity due to the synergistic effect of CTAB and Cu as antibacterial agents. It can be concluded that modification of clays with CTAB and Cu can become new alternative powerful antibacterial agent.
Clay minerals are commonly used materials in pharmaceutical production both as inorganic carriers or active agents. The purpose of this study is the preparation and characterization of clay/antibacterial drug hybrids which can be further included in drug delivery systems for treatment oral infections. Novel nanocomposites with antibacterial properties were successfully prepared by ion exchange reaction from two types of kaolinite/urea intercalates and chlorhexidine diacetate. Intercalation compounds of kaolinite were prepared by reaction with solid urea in the absence of solvents (dry method) as well as with urea aqueous solution (wet method). The antibacterial activity of two prepared samples against Enterococcus faecalis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa was evaluated by finding the minimum inhibitory concentration (MIC). Antibacterial studies of both samples showed the lowest MIC values (0.01%, w/v) after 1 day against E. faecalis, E. coli and S. aureus. A slightly worse antibacterial activity was observed against P. aeruginosa (MIC 0.12%, w/v) after 1 day. Since samples showed very good antibacterial activity, especially after 1 day of action, this means that these samples can be used as long-acting antibacterial materials. Prepared samples were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The experimental data are supported by results of molecular modelling. C) 2014 Elsevier B.V. All rights reserved.
The nano silicate platelets (NSPs) of 100 x 100 x 1 nm3 in dimension were previously derived from the exfoliation of naturally occurring sodium montmorillonite clay, and revealed for their affinity for adhering onto the surface of bacteria. The unique characteristics of ionic charges (≡Si-O-Na+) and the presence of siloxanol functionalities (≡Si-OH) allowed the organic modification of NSP-tethering poly(hydroxyethyl methacrylate) pendants (HEMA) through a sol-gel and living polymerization. Further modified by attaching nathphalimide-type fluorescence onto NSP-PHEMA, the new class of fluorescent organic-inorganic hybrids (NSP-PHEMA-HA), was prepared and characterized for their photoluminescence (PL) and bacterial trapping properties. In addition, the investigation of PL emission revealed that the fluorescent NSP hybrids could be used to detect bacteria. With the combined features of photoluminescence and physical trapping for bacteria, the NSP hybrids can be employed for the biosensor applications.
Silver loaded montmorillonite (Ag-MMT) was prepared by ion exchange reaction under microwave irradiation. The effects of microwave irradiation time, AgNO3 concentration, and microwave power on the silver content of Ag-MMT were investigated using the Volhard method. The time of ion exchange reaction was found to be greatly shortened under microwave irradiation. The most suitable reaction condition was in 0.2 m AgNO3 under 100% microwave power irradiation for 4 min, and the silver content was determined and was found to be 1.23 wt%. The results of the Fourier transform infrared spectrum (FT-IR) and Ag+ release tests confirmed the successful loading of silver and its good slow-release property. The X-ray diffraction (XRD) patterns and ultraviolet-visible (UV-vis) spectra proved the existence of metallic Ag nanoparticles. The Ag-MMT showing a large inhibition zone, high inhibition ratio, and low minimum inhibitory concentration (MIC) value against Staphylococcus aureus ATCC6535 presented a very good antibacterial property.
The Na+ montmorillonite (MMT) was modified with sulfur containing amino acid (l-cystine, l-cysteine or l-methionine) and characterized by energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectrum (FT-IR). The results showed the modification was smooth and the surface condition of MMT was changed with sulfur containing groups. Then silver was loaded on the modified MMTs via ion-exchange reaction under microwave irradiation, the spectra of X-ray photoelectron spectroscopy (XPS), EDS and FT-IR confirmed the successful loading of massive silver and the strong interaction between sulfur and silver, the silver loaded l-cystine modified MMT (Ag@AA-MMT-3) with a silver content of 10.93 wt% was the highest of all. Further more, the Ag@AA-MMT-3 was under the irradiation of a UV lamp to turn silver ions to silver nano particles (Ag NPs). The XPS, specific surface area (SSA), transmission electron microscopy (TEM), XRD patterns and UV-vis spectra proved the existence of uniform nano scaled metallic Ag NPs. By contrast, the UV irradiated Ag@AA-MMT-3 (Ag@AA-MMT-UV) showed a much better slow release property than Ag@AA-MMT-3 or Ag@MMT. The Ag@AA-MMT-UV showing a large inhibition zone and high inhibition ratio presented very good antibacterial property.
The antibacterial properties of silver modified montmorillonites from Pellegrini Lake, Argentina were tested in growth inhibition of Escherichia coli bacteria. Montmorillonite was first submitted to different treatments: (a) calcination at 550°C for 3h and (b) grinding during 300s. After that, the samples were loaded with silver by ion exchange. Structural characterization was performed by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), and BET specific surface area measurements. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTM) showed that metallic silver nanoparticles precipitates over the clay surface after silver modification. Nevertheless, the displacement of the (001) reflection observed by XRD in the calcined sample, and the diminution in Na+ content evaluated by energy dispersive X-ray spectroscopy (EDXS), indicate that Ag ions were interchanged in the structure of the clays. Both samples showed good antibacterial activity against E. coli, measured by the disk susceptibility and the minimum inhibitory concentration (MIC) tests. The ground montmorillonite required a lower MIC than the thermally treated, although the last one presented a bigger inhibition zone in the disk method. The results shows that the antibacterial activity is generated by the Ag+ present in the clay, as confirmed by X-ray photoelectronic spectroscopy (XPS); however the overall antibacterial properties are affected by the availability of the ionic silver to be in contact with the bacteria.
Ag+–Na+, Zn2+–Na+, and Cu2+–Na+ equilibria for clinoptilolite-rich mineral from Gördes (Western Anatolia) were investigated at 25 °C and 0.1 N total solution normality. While silver exchange was favorable over the whole concentration range, zinc and copper were partially exchanged and preferred only at low concentrations. The standard free energies of exchanges for Ag+–Na+, Zn2+–Na+, and Cu2+–Na+ pairs were found as −6.0, 2.03, and 3.09 kJ/equiv., respectively. From these values, selectivity sequence was determined as Ag+>Na+>Zn2+>Cu2+. Antibacterial activities of the exchanged samples were measured as a function of exchange level against Pseudomonas aeruginosa and Escherichia coli. Considering the selectivity sequence of the clinoptilolite and antibacterial activity results, Ag-clinoptilolite seemed to be promising antibacterial material.
Neste trabalho foi estudada a adsorção de Ag + sobre montmorilonita (MMT) do tipo Wyoming rica em Na + . Os dados de adsorção foram ajustados de acordo com várias isotermas comuns, mas os melhores parâmetros de regressão foram obtidos pelo modelo de Langmuir, indicando que Ag + foi adsorvido na superfície de MMT formando monocamadas. A adsorção de pequenas quantidades de Ag + promoveu o aumento da área superficial específica (SSA) de micro (r = 0.4-0.5 nm) a mesoporos (r = 1.5-3 nm). A intercalação de Ag + em MMT foi observada por difração de raios-X (XRD). Com o aumento da concentração de soluções de nitrato de prata, a quantidade de Ag + em MMT também aumentou e a estrutura em camadas gradualmente sofreu colapso e esfoliação. As amostras de MTT saturadas com Ag + foram tratadas com solução de boro hidreto de sódio para produzir Ag 0 . Foi estimado um tamanho médio de L 111 = 8.5(1) nm dos cristalitos de Ag 0 . As nanopartículas de prata metálica ficaram localizadas na superfície e nas bordas dos cristais de MMT. In this study Ag + adsorption on Na + -rich montmorillonite (MMT) type Wyoming was studied. Adsorption data were fitted with several common isotherms but the best regression parameters were obtained for Langmuir model. It indicates that Ag + was adsorbed on the MMT surface forming a monolayer. By adsorption of small amounts of Ag + enlargement of the specific surface area (SSA) of micro-(r = 0.4-0.5 nm) and mesopores (r = 1.5-3 nm) was found. Intercalation of Ag + into MMT was observed using X-ray diffraction (XRD). With increasing concentration of the silver nitrate solutions the content of Ag + in MMT increased and the layered MMT structure gradually collapsed and exfoliated. The MMT samples saturated with Ag + were treated with the sodium borohydride solutions to produce Ag 0 . The mean size of the Ag 0 crystallites of L 111 = 8.5(1) nm was estimated. The metal silver nanoparticles are assumed to be located at the layer surface and crystal edges of MMT.
Antibacterial fluoromicas were prepared by ion-exchanging fluoromicas with different antibacterial agents including various quaternary ammonium compounds, AgNO3, and norfloxacin. Antibacterial activities of the ion-exchanged fluoromicas were determined against Staphylococcus aureus and Escherichia coli. Minimum inhibitory concentration (MIC) and zone of inhibition (ZOI) tests were performed to determine both antibacterial effectiveness and mode of action associated with the fluoromicas. All treated fluoromicas showed excellent antibacterial activities against both types of bacteria. The antibacterial activities of treated fluoromicas were found to be either better than or the same as those of neat antibacterial agents. The repeated antibacterial activity tests demonstrated the extended activity of these systems.
The introduction of penicillin 50 years ago was followed by an extraordinary period of discovery, exuberant use, and predictable obsolescence. Resistant bacterial strains have emerged and have spread throughout the world because of the remarkable genetic plasticity of the microorganisms, heavy selective pressures of use, and the mobility of the world population. New and more expensive drugs have appeared almost in the nick of time, but it is doubtful that they will keep pace. The problem of resistance to antimicrobial drugs is particularly troublesome in developing countries. The underlying problems are largely economic and societal, and no ready solutions are available. An urgent need exists for more appropriate selection and use of antimicrobial drugs in the developed as well as in developing countries. The focus in developing countries should be on the availability of safe and effective drugs and on the enforcement of more responsible national drug policies. These issues must be addressed by the collective action of governments, the pharmaceutical industry, health care providers, and consumers. The developed countries have an important stake in the ways in which antibiotics are used in developing countries because resistant microorganisms do not recognize national boundaries.
Avian commercial male broiler chicks (n = 240), 1 d of age, were used to investigate the effects of copper-bearing montmorillonite (Cu-MMT) on growth performance, digestive enzyme activities, and intestinal microflora and morphology. The chicks were allocated to 4 treatments, each of which had 5 pens of 12 chicks per pen. The 4 treatments were basal diet only (control group), basal diet + 1.5 g/kg montmorillonite (MMT), basal diet + 36.75 mg/kg Cu, in the form of CuSO4, and basal diet + 1.5 g/kg Cu-MMT. The results showed that supplementation with Cu-MMT significantly improved growth performance compared with the control diet, and that chicks fed with Cu-MMT had higher average daily gain (ADG) than those fed with MMT or CuSO4. Supplementation with Cu-MMT significantly reduced the total viable counts of Escherichia coli and Clostridium in the small intestine and cecum. Supplementation with MMT or CuSO4 had no influence on intestinal microflora. Chicks fed with Cu-MMT had lower viable counts of E. coli in cecal contents than those fed with MMT or CuSO4. The addition of either MMT or Cu-MMT to the diet improved the activities of total protease, amylase, and lipase in the small intestinal contents but had no effect on those in the pancreas. Morphological measurements of the small intestinal mucosa of chicks indicated that dietary addition of MMT or Cu-MMT improved intestinal mucosal morphology.
This chapter describes the beneficial and harmful effects of clay mineral. Clay minerals can be beneficial to human health by serving as active principles or excipients in pharmaceutical preparations, in spas, and in beauty therapy medicine. In some cases, however, these minerals may be harmful to human health. In pharmaceutical formulations, spas and beauty therapy, clay minerals are used for therapeutic purposes and their beneficial effect on human health. In pharmaceutical formulations, these minerals are used as active principles (gastrointestinal protectors, antacids antidiarrhoeaics, dermatological protectors, cosmetics) and excipients (inert bases, delivery systems, lubricants, emulsifiers). In spas and beauty therapy, clay minerals are used in geotherapy, pelotherapy, and paramuds to treat dermatological diseases, alleviate the pain of chronic rheumatic inflammations, moisturize the skin, and combat compact lipodystrophies and cellulite. However, clay minerals can also have an adverse effect on human health when they are inhaled over a very long period. In the lung, clay minerals can cause diverse pathologies such as cancer, mesothelioma, or pneumoconiosis, but the toxicity of these minerals is generally related to the presence of quartz or asbestos from mining operations. The pathogenicity of fibrous clay minerals (sepiolite and palygorskite) is related to the geological conditions of formation.
The effect of anions on the Na-Cu exchange reactions on montmorillonites is not well understood and discrepancies exist in the literature. This study was conducted to examine the role of anions on the Na-Cu exchange reaction on Wyoming montmorillonite. The copper exchange capacity (CuEC) and Na-Cu exchange reactions on Wyoming montmorillonite were studied in Cl-, ClO4/-, NO3/-, and SO4/2- solution media at a constant total metal charge concentration of 0.0200 mol, L-1. We found that the values of CuEC were similar in Cl-, ClO4/-, NO3/-, and SO4/2- electrolyte media, and the quantity of Cu extracted by Na2-EDTA solution was only 1.0 to 1.2% of the CuEC and was not affected by anions. The apparent adsorbed metal charge, Q, and Vanselow selectivity coefficients, K(v), were determined across a wide range of exchanger phase composition, with Cu2+ occupying 30 to 95% of the charge sites. We found that the values of Q increased with Cu saturation in each of the anionic media, and the increase was not affected by anions. The increase in Q was attributed to decrease in negative adsorption of anions. We observed that K(v) was independent of exchanger composition in each of the four anionic media. The values of K(v) in the SO4/- medium were lower than those in other anionic media because of the complexation reaction between C2+ and SO4/2-. The data showed that C2+ ions were not specifically adsorbed under our experimental conditions and that the exchanger phase behaved as an ideal mixture. It was concluded that no detectable monovalent complexes such as CuCl+ and CuNO3/+ were adsorbed on Wyoming montmorillonite in the Na-Cu exchange reaction.
Calcium montmorillonite (Ca-MMT), sodium montmorillonite (Na-MMT) and acid-activated montmorillonite (AAM), and their Cu2+-exchanged montmorillonites (Cu-MMT), Cu*Ca-MMT, Cu*Na-MMT and Cu*AAM, were used to study the antibacterial activity on Escherichia coli K88. AAM, Na-MMT and Ca-MMT showed some ability to reduce bacterial plate counts by 37.4%, 13.4% and 14.2%, respectively. Exchanging the montmorillonite with Cu2+ enhanced the antibacterial activity. The Cu*AAM, Cu*Na-MMT and Cu*Ca-MMT reduced the bacterial plate counts by 98.6%, 97.5% and 95.6%. Attempts were made to study the desorption of Cu2+ by washing with sterile physiological saline solution for 24 h. The washing solutions did not show a significant reduction of the bacterial counts, while the washed Cu-MMT retained their full antibacterial activity. Results from time-depending studies showed that the reduction of the bacterial counts by Cu-MMT increased during 24 h. The ranking of antibacterial activity of the three Cu-MMT was as Cu*AAM>Cu*Na-MMT>Cu*Ca-MMT. E. coli thrived optimally in a pH range from 5 to 7. Beyond this range, the bacterial counts decreased as the pH reduced the viability of the bacteria. The ranking of antibacterial activity of Cu-MMT was not affected by pH. The mechanism by which bacterial counts are reduced may involve the enhanced affinity of Cu-MMT for E. coli K88 and the antibacterial activity of Cu2+.
The antimicrobial abilities of Cu2+-montmorillonite to E. coli and S. faecalis were investigated. The minimal inhibitory concentration (MIC) and killing concentration of Cu2+-montmorillonite on these two disease-causing species were ∼10 and ∼50 ppm, respectively. The powerful antimicrobial property of the Cu2+-montmorillonite was discussed in brief.
Two experiments were conducted with broiler chickens from 22 to 28days of age. In Experiment 1, the effect of adding enzyme preparations to a maize, soyabean meal and linseed (125gkg−1) basal diet was evaluated. Commercial enzyme complexes (Energex® CT, Luctazyme® aviar and Pectinase Lucta) with high xylanase and pectinase activities were used. The results showed that responses to enzymes in terms of digestibility of protein, amino acids, fat and major fatty acids as well as dietary AME value (AMEn) were not significant. Digesta viscosity value at the jejunal level was not affected by enzyme treatment.In Experiment 2, the effects of substituting demucilaged-linseed for linseed in the basal diet and addition of sepiolite to a diet containing linseed were evaluated. Removal of mucilage was achieved by extracting the seed with hot water (80°C) for 2h. The substitution of demucilaged-linseed for linseed significantly improved the digestibility of fat and major fatty acids as well as AMEn. Moreover, digesta viscosity was markedly reduced (29.6 vs. 4.9cP). Addition of sepiolite to the diet containing linseed had no influence on the nutrient utilization and on intestinal digesta viscosity.
Productive and digestive parameters (feed:gain conversion rates, whole-tract digestibility, intestinal viscosity and kinetics of digesta flow) were determined in broiler chickens fed on three diets of different viscosities, maize (low viscous), wheat–barley (medium viscous) and maize–10g/kg carboxymethyl cellulose (maize–CMC, high viscous) based. The three diets were supplemented with 0, 10 and 20g/kg of sepiolite (EXAL® UE-562), respectively, to examine how soluble non-starch polysaccharides per se influence nutrient digestion, and the extent to which sepiolite supplementation (10 or 20g/kg) could improve dietary OM digestibility and AME content. Broiler chickens fed on maize and barley-wheat showed higher (p
Forty-two castrated male hybrid (Hypor) pigs body weight (12kg BW) were used to investigate the effects of the dietary inclusion of sepiolite at the level of 20gkg−1 of sepiolite on protein and energy balance of growing pigs. Six pigs were slaughtered at the start of the test to determine the initial dry matter, protein, lipid, ash, and energy content of the empty body. The remaining 36 pigs were split into two groups: a control group was fed a basal diet and a sepiolite group was fed the basal diet with 20gkg−1 added sepiolite (Exal®). Six pigs from each treatment were killed at 35 and at 100kg body weight (BW) to determine dry matter, protein, lipids, ash and energy content of the carcasses. The inclusion of sepiolite did not influence, either average daily gain or feed conversion ratio. During the 12 to 35kg BW phase, pigs on the sepiolite diet had improved (P
Silver compounds are of interest because of their antimicrobial and other biological activity. Electrochemical and chemical (e.g., dissolution) properties of silver films of various origins, e.g., sputtered Acticoat antimicrobial silver samples, electrodeposited Ag metal and electrooxidized silver samples in various media have been studied with electrochemical techniques, quartz crystal microbalance (QCM) gravimetry, X-ray diffraction, atomic force microscopy (AFM), and scanning electrochemical microscopy (SECM). Examination of several sputtered antimicrobial silver samples with AFM reveals their nanometer grainy aggregate structures. The electrochemical results suggest that the sputtered antimicrobial films contain both Ag(0) and Ag(I) (in the form of Ag2O, AgOH, or a mixture of these). While the dissolution of metallic Ag or antimicrobial films that were completely reduced to the Ag(0) form is small in aqueous 1.0 M NaClO4 solution, films containing Ag(I) are soluble. The initial dissolution rate of an antimicrobial film in 1.0 M NaClO4 under open-circuit conditions was estimated to be about 3.6 (μg/h)/cm2 in an unstirred condition. The SECM/QCM results suggest that the dissolved silver species contains both Ag(I) and Ag(0), with diffusion coefficients in the range (3.5−4.0) × 10-6 cm2/s. Small clusters containing Ag(0) and Ag(I) (as well as O and H) are proposed for these dissolved silver species.
Several modified clays have been designed and created for selective removal and recovery of heavy metals such as Cd, Cu, Cr, etc. These surfactant−clay complexes were prepared using hectorite or montmorillonite as the base clay. A simple two-step approach has been developed to synthesize these modified-clay complexes through ion exchange and hydrophobic anchoring of several surfactants such as long-chain alkyldiamines, long-chain dialkylamines, and long-chain carboxylic acids onto the clay matrices. The adsorption capacities and affinity constants of the modified clays can be found to approach those of commercial chelating resin (Chelex 100, Bio-Rad). Using cadmium as a model metal and montmorillonite−cetylbenzyldimethylammonium−palmitic acid (M−CBDA−PA) as a model modified-clay complex, the maximum adsorption capacity of the modified clay is found to be 42 ± 0.8 mg/g of clay and the affinity constant is 3.0 ± 0.1 mg/L. The metal adsorption has been shown to be mainly through chemical complexation rather than ion exchange. The immobilization of the metal ions is pH dependent, and thus, pH can act as a molecular switch to regenerate the modified-clay complexes.
The addition of small quantities 1–2% (w/w) of the sepiolite clay EXAL to animal feed increases the feed efficiency and weight of animals. -Chymotrypsin, lipase and -amylase from bovine pancreas adsorbed on to EXAL at different pH values form active stable complexes at enteric pH values. The enzymes are chemisorbed on EXAL by interaction between NH3+ groups of lysines and basic sites of the solid surface. The derivatives obtained are stable, regardless of changes in pH, and the relation between their activity and pH is complementary to that observed with the native enzyme. Therefore, these enzyme-EXAL derivatives are resistant to proteolysis and increase the amount of active digestive enzymes in the intestine. A more efficient utilization of feed would take place in animals that have ingested EXAL than in those which have not ingested the sepiolite.
This chapter discusses the applications of clays and clay materials as drugs. Clay minerals are efficient against several aggressors that cause major disorders of the gut. These beneficial effects of clay minerals (on the gastrointestinal mucosa) are associated with two mechanisms of action: (1) adsorption of the aggressors or their toxic secretions and (2) modification of the thickness and rheological properties of the adherent mucus, reinforcing the natural defenses of the gastrointestinal mucosa. At the surface of the gut, a mucus gel adheres to the epithelial cells of the mucosa. This adherent mucus is dynamic, being continuously secreted by the calceiform cells and regularly eroded by environmental aggressors present in the gut lumen. The mucus gel is largely composed of glycoprotein polymers, lipids, and proteins linked together by covalent bonds. It acts as a physical barrier protecting the mucosa against penetration by extraneous molecules and mechanical injury. By maintaining a pH gradient and competing with the epithelial surface for microorganisms, the mucus gel also acts as a chemical barrier.
The equilibrium isotherms of zinc adsorption onto natural bentonite show that the data correlate well with Freundlich and Langmuir models and that the adsorption is physical in nature. The operating parameters (agitation-speed, solid-liquid ratio, temperature, particle size and initial zinc concentration) influenced the rate of adsorption. The maximum monomolecular capacity eo according to the Langmuir model is 52.91 mg g(-1) for an initial zinc concentration of 300 mg L(-1) at 20 degrees C. (C) 1997 Published by Elsevier Science Ltd.
The activities of antibacterial compounds, such as cetylpyridinium (CP), cetyltrimethylammonium (CTA), silver ions and metallic silver, immobilised on montmorillonite (MMT), were tested in Escherichia coli and Enterococcus faecium bacteria. The results of bacterial growth tests were confirmed by determination of the minimum inhibition concentrations (MICs). Unlike CP and CTA, the intercalated silver ions were easily released from MMT by ion-exchange with Na+ and acted as very effective antibacterial substances in the long term. Their bactericidal and bacteriostatic effects were determined. Generally, antibacterial compounds are effective when they are released from an inorganic carrier. Metallic silver was prepared by reduction of intercalated Ag+ with sodium borohydride. Antibacterial effects of metallic silver were not observed.
The biosorption of the heavy metals most frequently found in polluted environments by Pseudomonas aeruginosa and Bacillus thuringiensis was studied. The effects of these metals on bacterial growth, quantity of dry cells, ammonium assimilation, pigment production, and protein synthesis were investigated. At lower concentrations than the minimal inhibitory concentration (MIC), the metals partially limited bacterial growth and caused an inhibition proportional to the metal concentration applied. The production of bacterial biomass varied according to the nature and concentration of the metals, and to the bacterial strain studied. The biosorption of metals by P. aeruginosa and B. thuringiensis was variable. Mercury and copper appeared to be the elements most adsorbed by bacteria. Citrate noticeably increased the biosorption of chromium by P. aeruginosa (0.07–45.9%) and copper by B. thuringiensis (18.7–33.8%). Metallic cations exerted variable effects on protein synthesis. Zinc stimulated protein synthesis in P. aeruginosa, and cadmium inhibited it significantly in B. thuringiensis. Mercury and cobalt, at concentrations below the MIC, always inhibited the synthesis of pigments in P. aeruginosa. The strong interactions of mercury and copper with organic matter suggest that these undesirable elements might be removed from the environment by bacterial trapping and sequestration. A better understanding of the different forms of metals actually existing in polluted environments (speciation) would be of great interest.
Mingguang palygorskite clays, when modified with the silver and copper ion may be useful in removing bacteria from aqueous solution. The antibacterial effect of these modified clays were investigated using Escherichia coli and Staphylococcus aureus as indicators of fecal contamination of water. Introduction of Ag+ or Cu2+ did not change the crystal structure of the Mingguang palygorskite. It was found that the Mingguang silver and copper palygorskite minerals eliminated the pathogenic microorganisms E. coli and S. aureus from water with the average amount of silver and copper supported on the minerals after 12 h of contact time.
In this work, the effects of an anionic biosurfactant, rhamnolipid (RL), and pH on the adsorption and desorption of Cu(2+) ions on Na-montmorillonite were investigated. Adsorption studies were conducted through the addition of Cu(2+) to the dispersions containing pristine- and/or RL-modified clay. In the case of pristine clay, RL was also added simultaneously with the Cu(2+). The effect of pH was studied in the range between 1.0 and 8.0. The highest adsorption capacity was obtained at the pH of 4.7-4.8. Among the models including the Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich isotherms; Langmuir isotherm gave a better fit to the experimental data. The most suitable fit for the adsorption kinetics of Cu(2+) was obtained with a pseudo-second-order model. It was determined that the adsorption capacity of the pristine clay is comparable with that of the activated carbon and the modification of clay with RL causes an increase in the adsorption rate due to the distribution of clay platelets in the solution.
The antimicrobial properties of two new imidazolium and pyridinium chlorides in comparison with three currently in disinfection compounds applied are described. The following research was performed: resistance of organisms to disinfectants and disinfection of hands. The new 3-methyl-n-dodecylthiomethylpyridinium chlorid was the most active compound.
Recent experiments in our laboratory have suggested that certain montmorillonite clays, when exchanged with the cationic surfactant cetylpyridinium (CP), may be useful in removing bacteria from aqueous solution. During an initial study, screening various CP-exchanged products for potential antibacterial activity, three CP-exchanged clays - CP*AAM (acid-activated montmorillonite), CP*STx-1 (Ca(++)-montmorillonite), and CP*SWy-2 (Na(+)-montmorillonite), proved to be the most effective. Binding studies were performed using 1mg each of CP-exchanged AAM, STx-1, and SWy-2 with a standardized Salmonella enteritidis solution containing approximately 40,000 colony forming units (CFU)/ml. The modified clays reduced bacterial numbers 98.1, 97.6, and 95.2%, respectively. In contrast, the parent clays only produced reductions of 39.8, 16.9, and 16.6%, respectively. Attempts were made to desorb CP from the modified clays by washing in sterile physiological saline for 24h. The resulting wash solutions failed to produce any significant reduction in bacterial colony counts; while, the washed clays retained their full antimicrobial activity. These findings suggested that the antibacterial effect of the clays is localized on the clay surface and is not due to CP dissociating from the clay. Electron microscopy revealed that the bacteria adhered to the surface of the CP-exchanged clays, but not the parent clays. Results from timed binding studies showed that the antibacterial effect was stable over the period observed. Rates of binding were positively influenced by increasing temperature, not affected by changes in pH, and negatively influenced by the presence of organic contaminants. The mechanism by which bacterial counts are reduced may involve the enhanced hydrophobicity and affinity of the CP-exchanged clay for Salmonella and the antibacterial activity of CP.
Removal of Cu2+ and Zn2+ from aqueous solutions by sorption on the montmorillonite modified with sodium dodecylsulfate (SDS) was investigated. Experiments were carried out as a function of solution pH, solute concentration, and temperature (25-55 degrees C). The Dubinin-Kaganer-Radushkevick model was adopted to describe the single-solute sorption isotherms. Also, the binary-solute sorption equilibria could be reasonably predicted by the competitive Langmuir model, in which the Langmuir parameters were directly taken from those obtained in single-solute systems. The thermodynamic parameters (DeltaH(o) and DeltaS(o)) for Cu2+ and Zn2+ sorption on the modified clay were also determined from the temperature dependence. The kinetics of metal ions sorption was examined and the pseudo-first-order rate constant was finally evaluated.
Clays (especially montmorillonite and bentonite) are widely used as barriers in landfills to prevent contamination of subsoil and groundwater by leachates containing heavy metals. For this reason it is important to study the adsorption of metals by these clays. The sorption of seven metals (Cd, Cr, Cu, Mn, Ni, Pb and Zn) on Na-montmorillonite was studied as a function of pH and in the presence of ligands, forming complexes of different stabilities with the metals of interest. The continuous column method was used as it better simulates natural conditions. The total capacity of Na-montmorillonite towards these metals was determined. The pH variations influence to a higher extent the concentrations of Cu, Pb and Cd in the effluent. Moreover the results suggest that complex formation hinders the sorption of the metals on the clay, with an increasing influence in the order: Mn < or = Pb < or = Cd < or = Zn < Ni < Cu < Cr. The evaluation of the total capacity of Na-montmorillonite shows that this clay is a good sorbent towards all examined metals.
The aim of this research was to determine the antibacterial properties and mechanisms of Cu(II)-exchanged montmorillonite (MMT-Cu) in vitro. Escherichia coli ATCC K88 and Salmonella choleraesuis ATCC 50020 were chosen as indicators of intestinal tract pathogenic bacteria in weanling pigs. The antibacterial activity of MMT-Cu and MMT were evaluated by determining the minimum inhibitory concentrations (MICs) using two-fold serial dilutions in MH broth, and the amount of Cu2+ released into the broth was measured by an atomic absorption technique. The rate of oxygen consumption was measured using a SP-II-type oxygen electrode analyzer; the structural integrity of cell walls of bacteria was observed by transmission electron microscope (TEM); enzymatic activity of bacteria was examined with a semi-automatic biochemical analyzer. The results showed that MMT-Cu inhibited the growth of E. coli K88 and S. choleraesuis, and the MICs were 1024 and 2048 microg/ml, respectively. The amount of Cu2+ released into the broth was in the range 6.51-45.65 microg/ml. Nevertheless, both tested bacteria still grew in broth containing 32,768 microg/ml of MMT. Treatment with MMT-Cu could lead to significant release of intracellular enzymes from the tested bacteria. Data from oxygen consumption of bacteria showed that MMT-Cu could inhibit the TCA pathway of the bacterial respiration metabolism. These results show that MMT-Cu has an antibacterial activity.
In the present study, attapulgite, kaolinite, and montmorillonite KSF were modified using azeotropic distillation to condense 2-mercaptoethanol with the clay material. The resulting product was used as a coordinating agent to remove selected metal ions, e.g., copper(II), cadmium(II), silver(I), nickel(II), and lead(II) ions from standard aqueous solutions. Batch systems were used, and samples were shaken for two hours, and following filtration, metal content of the filtrate was measured by atomic absorption spectrometry. Without adjusting the pH, better than 90% of the metal ions could be removed.
Montmorillonite (MMT) and its Cu2+-exchanged montmorillonite (Cu-MMT) were used to study the antibacterial activity on Aeromonas hydrophila. The results indicated that MMT had no antibacterial activity. The minimum inhibitory concentration (MIC) and bactericidal concentration (MBC) of Cu-MMT on A. hydrophila are found to be 150 and 600 mg/L, respectively. The continuance of the antibacterial activity of Cu-MMT was much longer than copper sulfate. In order to reveal the mechanism of the antibacterial activity of Cu-MMT, the Cu release from Cu-MMT in tryptic soy broth (TSB) was investigated. In the first 2 h, Cu concentration in the supernatant reaches saturated value, about 1.22-2.27% of the overall Cu in Cu-MMT suspended in the medium. The washed Cu-MMT in TSB for 24 h retained their full antibacterial activity; whereas, the supernatants from the washed pellets showed very little antibacterial activity. These findings suggested that the antibacterial activity of Cu-MMT was mainly localized on the clay surface, and not due to the release of Cu2+ into solution. The excessive positive charge of Cu-MMT would make Cu-MMT attract A. hydrophila with negatively charged cellular wall. In this case, the copper cation would act directly on the bacteria adsorbed on the surface of Cu-MMT, instead of into the medium. The mechanism for the antibacterial activity of Cu-MMT may involve the enhanced affinity of Cu-MMT for A. hydrophila and the antibacterial activity of Cu2+.
The adsorptive properties of natural and Na-enriched bentonite in zinc rich aqueous environment have been studied. The results show that adsorption behavior of both bentonites was strongly depending on the pH. At low pH values, the mechanisms that govern the adsorption behavior of bentonites are dissolution of crystal structure and competition of the metal ions with the H+. Between pH 4 and 7, the basic mechanism is an ion exchange process. The alkaline and alkaline earth metals located in the exchangeable sites of bentonites are replaced with Zn2+ cations present in the aqueous solution. At higher pH values (i.e. pH 8), formation of zinc hydroxyl species may result either participation to the adsorption or precipitation onto the bentonites. Therefore, a rapid increase in the equilibrium removal of zinc was obtained above pH 7. Increase in the initial metal ion concentration led to the increase in equilibrium adsorption to a certain degree; then, a plateau was obtained at higher concentrations. The rate of zinc removal depends also on the solid concentration of the suspension. Reducing the slurry concentration allows particles to get in the more dispersed form, resulting higher available sorption sites for zinc. As a result, the adsorption performance of Na-enriched bentonite is better than the natural bentonite in all physical and chemical changes. The data were fitted both Langmuir and Freundlich isotherms.
A series of novel organoclays with antibacterial activity were synthesized using Ca-montmorillonite and Chlorhexidini Acetas (CA) by ion-exchange. The resultant organoclays were characterized using X-ray diffraction (XRD), high-resolution thermogravimetric analysis (HRTG) and Fourier transform infrared spectroscopy (FTIR). Their antibacterial activity was assayed by so-called halo method. In the organoclays prepared at low CA concentration, CA ions within the clay interlayer adopt a lateral monolayer while a 'kink' state or a special state with partial overlapping of the intercalated CA in the organoclays prepared at 1.0-4.0 CEC. HRTG analysis demonstrates that CA located outside the clay interlayer exists in all synthesized organoclays, resulting from the complex molecular configuration of CA. The dramatic decrease of the surface adsorbed water and interlayer water is caused by the surface property transformation and the replacement of hydrated cations by cationic surfactant. These observations are supported by the results of FTIR. Antibacterial activity test against E. coli demonstrates that the antibacterial activity of the resultant organoclays strongly depends on the content of CA. Meanwhile, the resultant organoclay shows a long-term antibacterial activity that can last for at least one year. These novel organoclays are of potential use in synthesis of organoclay-based materials with antibacterial activity.
The use of an electrochemical reactor operated under different flow conditions to deposit silver from aqueous AgNO(3) solutions and tartaric acid as an organic additive on a commercial activated carbon with ultimate bactericidal applications in water purification processes is presented. The characterization of carbon/silver samples was studied by BET, FTIR, X-ray diffraction, XPS, and SEM techniques. The bactericidal activity of the carbon/silver samples was tested on drinking water samples inoculated with E. coli. A reduction of carbon surface area was detected and was caused by increased amounts of silver deposited on carbon samples. Adherent silver deposits were obtained on the carbon/silver samples. X-ray diffraction studies of carbon with electrodeposited silver showed two different preferential deposition planes, [111] and [220]. The FTIR results confirm the presence of carboxyl, phenolic, quinone, and ether surface groups. The XPS results suggest the formation of Ag(2)O and AgO surface species and confirm the reduction of silver to the metallic form. Antimicrobial activity toward E. coli indicated reductions by up to 7 orders of magnitude in the log CFU/mL in just 10 min contact time and for silver contents of 2.47 wt%.
Stabilization-activation of pancreatic enzymes adsorbed on sepiolite clay
- M J Cabezas
- D Salvador
- J V Sinisteria
Cabezas, M.J., Salvador, D., Sinisteria, J.V., 1991. Stabilization-activation of pancreatic
enzymes adsorbed on sepiolite clay. J. Chem. Technol. Biotechnol. 52, 265-274.
Handbook of Clay Science
- M I Carretero
- C S F Gomes
- F Tateo
Carretero, M.I., Gomes, C.S.F., Tateo, F., 2006. Clays and human health. In: Bergaya, F.,
Theng, B.K.G., Lagaly, G. (Eds.), Handbook of Clay Science. Elsevier Ltd. Chap. 11.5.
Clinical Laboratory Standards Institute, 2005. Performance Standards for Antimicrobial
Susceptibility Testing. 5th International Supplement (M100-S15). CLSI, Wayne, PA.
Clays and Clay Minerals as Drugs. Handbook of Clay Science
- M T Droy-Lefaix
- F Tateo
Droy-Lefaix, M.T., Tateo, F., 2006. In: Bergaya, F., Theng, B.K.G., Lagaly, G. (Eds.), Clays
and Clay Minerals as Drugs. Handbook of Clay Science. Elsevier Ltd. Chapter 11.6.