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Obtention and characterization of a hybrid nanocomposite monolith by sol–gel process
Abstract
A monolithic porous composite was synthesized by sol–gel process, containing the maximum and significant amount of bentonite that allows its use as a filter bed in aqueous effluents treatment. This process is able to apply on an industrial scale.
The bentonite used was an efficient adsorbent for various contaminant molecules in aqueous media when is operated in a batch stirred tank, but presents difficulty in the separation stage of suspended particles. In this laboratory-scale work, cylindrical monoliths of 9 cm length by 2 cm diameter were made that can be used as a filter bed. The primary composite, silica-resin, was prepared by the sol–gel precursor mixture of the partially hydrolyzed tetraethylorthosilicate and a phenol-formaldehyde resin. Bentonite was added to the pre-gelling, obtaining the silica-resin-bentonite composite, made up the gel which is then dried and cured at 270 °C. The different composites mineralogical and structurally were evaluated. The preliminary performance of the developed bentonite filter bed showed almost 90% adsorption of diphenylamine, a commercial agrochemical widely used as anti-antiscaldant in postharvest treatment of fruit, and showed that the bentonite conserves its adsorption capacity and controls the swelling of the interlayer space which encourages further research studies applied to water treatment.
... The pore diameter distribution for sample B was determined using the BJH method in the desorption isotherm, assuming pores of cylindrical geometry [17], and it presented a unimodal character, with an average pore diameter of 4.18 Å. However, nanocomposite CB presented a uniform distribution in the mesopores range, so it was not possible to report an average diameter [18]. On the other hand, with the activation of both solids, the adsorption and desorption curves did not present changes, and neither did the pore size distribution (not shown in Figure 3). ...
... Figure 5a shows the FTIR spectra of natural bentonite and the activated sample under the most severe conditions (solid B0.5-90). The signals at 465 and 520 cm −1 correspond to Si-O vibrations in the tetrahedral sheets, while the signal observed at 798 cm −1 is characteristic of the Si-O vibration present in quartz [18]. In addition, the signals at 919 cm −1 and 3629 cm −1 are attributed to the Al-OH vibrations of the octahedral layers [20]. ...
... Figure 5b shows the infrared spectra of the CB and CB0.5-90 solids. The CB solid presents the same bands as B, and it also presents two bands at 808 and 1100 cm −1 , which can be attributed to Si-O-Si bonds coming from the condensation of TEOS [18]. The bands observed in both solids remain unchanged, indicating that the acid treatment did not generate important changes in the structure of the solid. ...
Bentonites are natural clays found in abundance in deposits all over the planet and possess certain properties that make them interesting for various industrial applications. Through their activation or acid treatment, they can be used as catalysts in several reactions of interest. However, these materials form colloidal suspensions in water or in aqueous solutions, which makes their separation and recovery difficult and prevents their implementation on an industrial scale. To overcome these limitations, in the present work, a silica-resin-bentonite composite material was synthesized and activated with HNO3. The activated solids were characterized and evaluated in the catalytic reaction of solketal synthesis from glycerol and acetone. The best results were obtained for a composite containing 47 wt.% acidified bentonite at 90 °C, with a HNO3 concentration of 0.5 mol L⁻¹, which was attributed to both its acid site density—3.9 mmol per gram of bentonite—and the acidic strength of these sites.
... Figure 2 shows the infrared spectra of solids CBA and B. The spectra of both solids presented signals at 465 and 520 cm −1 , which corresponded to the Si-O vibrations in the tetrahedral layer. In addition, the signal observed at 798 cm −1 in solid B was related to the Si-O vibration, which is characteristic of quartz, and the signals at 919 cm −1 and 3629 cm −1 were attributed to Al-OH vibrations in the octahedral layers of the bentonite [33]. The bands observed at 1641 and 3460 cm −1 were attributed to the H-OH vibrations of the water adsorbed on the interlayer structure and were observed in both solids [34]. ...
... The X-ray diffraction technique was used to study the structure of the bentonite in the composite and to evaluate the effect of acidification on the bentonite's structure. were attributed to Al-OH vibrations in the octahedral layers of the bentonite [33]. The bands observed at 1641 and 3460 cm −1 were attributed to the H-OH vibrations of the water adsorbed on the interlayer structure and were observed in both solids [34]. ...
... On the other hand, solid CB presented two bands at 808 and 1100 cm −1 , which could be attributed to the Si-O-Si unions from the condensation of TEOS [33]. As can be observed, the acid treatment did not generate important changes in the solid structure. ...
Activated bentonites are low-cost acid catalysts used in several reactions. However, their application at an industrial scale is affected by the formation of colloidal suspensions when these bentonites are in aqueous solutions. In order to overcome these limitations, this work proposes obtaining a catalyst based on a composite containing natural bentonite within a silica–resin structure, which allows separating and re-utilizing the catalyst more easily and without centrifugal filtration requirements. By means of characterization techniques, the present study determined that the activated bentonite composite presented a total specific surface area of ~360 m2 g−1, ~4 mmol of acid sites per gram of bentonite, and sites with strong acid strength, all of which bestowed activity and selectivity in the solketal synthesis reaction from glycerol and acetone, reaching equilibrium conversion within a short reaction time. Furthermore, the present work developed a Langmuir–Hinshelwood–Hougen–Watson kinetic model, achieving an activation energy of 50.3 ± 3.6 kJ mol−1 and a pre-exponential factor of 6.4 × 106 mol g−1 L−1 s−1, which are necessary for reactor design.
... The results indicated that despite using different silica sources, the two materials presented very similar characteristics, evidencing the feasibility of using an inexpensive waste material as silica source in the synthesis of these molecular sieves, once the synthesis conditions have been satisfactorily adjusted [21]. Therefore, some research has been conducted to develop mesoporous silica using low-cost silica resources, including fly ash [22], wheat stem ash [23], bentonite [24], Diatomaceous marl [25], palm kernel shell ash [26] and packaging resin waste [27]. ...
The preparation of an aluminum-mesoporous A1-MCM-41 humidity control material (Al-MHCM) by hydrothermally synthesizing a mixture of thin-film transistor liquid crystal display (TFT-LCD) waste glass and sandblasting (SB) waste was studied. The product has a typical mesoporous structure, with a specific surface area of up to 1013 m²/g, the pore size distribution calculated is 3–4 nm, and the pore volume of 0.97 cm³/g. All the aluminum atoms of the product are in the form of tetrahedral aluminum in the framework, which confirms the successful synthesis of Al-MHCM. Results show that when the hydrothermal synthesis temperature is 105 °C, the product synthesized from a mixture with a Si/Al molar ratio of 41.8 exhibits excellent performance (91.45 m³/m³) in terms of the equilibrium moisture content and moisture adsorption capacity. The results confirm that the equilibrium moisture content of Al-MHCM is better than the rape straw concrete and hemp concrete (9.8–17.8 m³/m³), and that of a diatomite/ground calcium carbonate composite aterial (11.7 m³/m³). The research results are expected to provide a new technology for synthesizing TFT-LCD waste glass and SB waste into novel high value-added humidity control materials.
Nanoclay is a fine-grained crystalline material, which contains a mineral of Alumina and Silica with high aspect ratio and at least one dimension of particle in the nanometer (1 nm=10-9 m) range. Nanoclays have various applications in many fields, including problematic soil treatment, pharmacy, medicine, catalysis, cosmetics, food packaging and textile industry. The raw cost of Nanoclay is high due to its costly manufacturing process that involves heavy chemicals and machinery. Therefore, the aim of the current research is to extract Nanoclay from the montmorillonite rich commercially available Bentonite soil using cost effective method. The process involves the exfoliation of the nano-sized lamina from the staked 2:1 tetrahedral-octahedral laminae of montmorillonite minerals with the help of surfactant. Three different types of surfactant (cationic, non-ionic and anionic) were chosen in the current study to evaluate their effect on the exfoliation process of highly expansive Bentonite soil. A series of chemical processes including solution preparation, sonication, centrifugation, and drying were performed using selected proportion of surfactant and Bentonite soil mixture. Physical and chemical properties of end-product were investigated by performing X-ray diffraction (XRD) technique and scanning electron microscope (SEM) image analysis. Nanoclay of the particle size range of 10 to 15 nm is successfully exfoliated from montmorillonite sheet structure by the chemical interaction between cationic surfactant and Bentonite soil. Non-ionic surfactant was observed to be just intercalated between the sheets of montmorillonite mineral with additional growth of small needle like structures. Anionic surfactant has no prominent effect on the Bentonite soil.
Continuous adsorption of methylene blue from aqueous solutions onto maize
stem ground tissue in column mode was investigated. The study encompassed the
effects of important parameters such as flow rate, initial concentration of
methylene blue, and bed depth on methylene blue removal from model solutions.
The maximum adsorption capacity of the maize stem was 45.9 mg/g at the
initial methylene blue concentration of 20 mg/L, bed height of 6.5 cm and
flow rate of 8 mL/min. It was found that the breakthrough time for reaching
saturation increased with a decrease in the flow rate, and also occurred
earlier for a higher influent concentration. The breakthrough times increased
with the bed depth, thus allowing a larger volume to be treated. The
Adams-Bohart, Yoon-Nelson, Clark and artificial neural network models were
used to predict the breakthrough curves. These models gave excellent
approximations of the experimental behavior.[Project of the Serbian Ministry
of Education, Science and Technological Development, Grant no. 172025]
The application for montmorillonite to deal with toxic metals (including radionuclides) becomes interesting based on its excellent physicochemical properties. In this work, the thermal activation method was utilized to pre-treat montmorillonite before use. The sample was characterized by FTIR, XRD, zeta potential, BET and potentiometric titration to clarify the variation of montmorillonite before and after thermal activation. Batch techniques were used to investigate the sorption ability of montmorillonite to U(VI) under different environmental conditions. The electrical double layer model has been introduced to describe the variation of pre-treated sample as well as the principal mechanism for U(VI) uptake. In addition, the irradiation effects of samples for U(VI) sorption was also investigated. Based on the optimum condition for U(VI) uptake, it can be deduced that the thermally activated montmorillonite has potential application for the removal of U(VI) in wastewater.
We report the sol–gel preparation of SiO2/montmorillonite composite materials and the investigation of the effect of the amount of clay and the TEOS concentration on the textural and structural properties of the composites. Pre-swelling of the clay with cetyltrimethyl ammonium results in solids with a larger mesoporous surface area. A decrease in the gel time and an increase in the surface area were observed upon increasing the amount of clay in the reaction medium. These porous solids showed acidic properties, and their acidities were correlated with the amount of the clay mineral. The obtained composites were functionalized by adding manganese, and their catalytic properties were evaluated in the cyclohexene oxidation reaction.
Graphical Abstract
This work deals with the preparation of epoxy-clay nanocomposites. The results show that the mechanical properties of nanocomposites depend on their compatibility, the epoxy resin used and the purity of the nanoclay. The used bentonite was purified and the effects of the organoclay synthesis and various additives on its characteristics were evaluated. X-ray Diffraction (XRD), X-ray Fluorescence (XRF) and Scanning Electron Microscopy (SEM) were used to analyze the microstructure and the phase composition of the nanoclay. The XRD results revealed that when the modifier addition was increased from 10wt.% to 40 wt.%, the interlayer spacing of the nanoclay increased from 12.43 Å being incompatible with the resin to 20.43 Å making possible to prepare required nanocomposite.
The objective of this study was to develop a treatment system that can effectively reduce the concentration of colloidal particles in raw water that can greatly reduce the cost of treatment and improve the subsequent steps of treatment. Aluminum sulphate (alum) and ferric chloride as a coagulant and anionic polymer as coagulant aid were used in the process that changed the scale of particles from nanoscale to microscale and larger by a physico-chemical process. The influence of PH, temperature, coagulant and coagulant aid dosages on the coagulation process was studied and conditions were optimized corresponding to the best removal of organic matters, viruses, colloids, bacteria, color and decrease in turbidity. 85-98% reduction of turbidity from raw water can be achieved by using the optimum coagulant dosage (8ppm, ferric chloride/10 ppm, alum) in the optimum PH range (9.2, ferric chloride/8.5, alum) in the optimum temperature (20°C, ferric chloride/24°C, alum). Ferric chloride produced better results than alum. Higher dosages did not significantly increase pollutant removal and were not economical. The results provide useful information for raw water treatment.
Hollow spheres of phenolic resin/silica composite are synthesized by macroscopic phase separation of a sorbitan monooleate
surfactant Span 80 during aerosol-assisted spraying. The cavity can be evolved from multiple compartments to single hollow
cavity with the increase of Span 80 content. The composite shell becomes mesoporous due to the release of small molecules
after thermal treatment above 350°C. After further thermal treatment at a higher temperature for example 900°C in nitrogen
or 1,450°C in argon, the carbon/silica composite hollow spheres or crystalline silicon carbide hollow spheres are derived,
respectively. Compared to the pure phenolic resin-based carbon spheres, thermal stability of the carbon-based composite spheres
in air is essentially improved by the introduction of inorganic component silica. The carbon-based composite hollow spheres
combine both performances of easy mass transportation through macropores and high specific surface area of mesopores, which
will be promising to support catalysts for fuel cells.
An overview of nanoclays or organically modified layered silicates (organoclays) is presented with emphasis placed on the
use of nanoclays as the reinforcement phase in polymer matrices for preparation of polymer/layered silicates nanocomposites,
rheological modifier for paints, inks and greases, drug delivery vehicle for controlled release of therapeutic agents, and
nanoclays for industrial waste water as well as potable water treatment to make further step into green environment. A little
amount of nanoclay can alter the entire properties of polymers, paints, inks and greases to a great extent by dispersing 1nm
thick layered silicate throughout the matrices. The flexibility of interlayer spacing of layered silicates accommodates therapeutic
agents which can later on be released to damaged cell. Because the release of drugs in drug-intercalated layered materials
is controllable, these new materials have a great potential as a delivery host in the pharmaceutical field. The problem of
clean water can be solved by treating industrial and municipal waste water with organoclays in combination with other sorbents
like activated carbon and alum. Organoclays have proven to be superior to any other water treatment technology in applications
where the water to be treated contains substantial amounts of oil and grease or humic acid.
The objective of this paper is to give an overview of the colloidal properties of clays and to describe the work performed until the present moment in the area of adsorption of non-ionic polymers onto clay and the rheology of clay suspensions. The review is particularly focused on Na+-montmorillonite clay of the smectite group (Bentonite), due to its high swelling capacity, the ability to adsorb significant amounts of polymer on its surfaces, and the formation of a gel-like structure with yield characteristics and viscoelastic properties at relatively low clay concentrations. A significant amount of research has been performed in these areas with applicability to various fields, such as soil science and drilling fluids, where interaction of organic polymers with the clay surface and the rheological response in the presence of electrolytes under different temperature and pressure conditions are of considerable relevance. In order to understand the interaction of these compounds with the clay surface and the rheological response of the resulting suspensions, it becomes essential to understand the structure of clay minerals, the interaction of clay particles in aqueous medium, the swelling behaviour and electrokinetic properties of Na+-montmorillonite clay. For this reason, the above topics are addressed, along with the general features of stabilisation of colloidal particles and the adsorption mechanism of non-ionic compounds on hydrophilic surfaces. A comprehensive review of the most relevant studies of the adsorption of non-ionic surfactants and polymers onto both silica and clay is presented. Finally, an overview of the rheological behaviour of concentrated suspensions and models used to describe the flow behaviour of clay suspensions is given, along with the effect of electrolytes, polymers, high pressure and high temperature on the flow behaviour of Na+-montmorillonite suspensions.
Excessive use of nitrogenous fertilizers has led to increased nitrate concentrations in groundwater that pose a threat to human health, via nitrate-contaminated potable water, and contribute to eutrophication. The elimination of nitrate from water systems has been thoroughly examined; however, unconventional and low-cost technologies are greatly needed. Clays and clay minerals are widely-used for environmental applications, mostly due to their non-toxicity, worldwide abundance, low cost and physicochemical properties (high surface area, ion exchange capacity, high sorption and catalytic properties). Most are used for the degradation of cationic pollutants, nevertheless, they can be equally efficient at anionic decontamination, depending on the modification process they have undergone, or the materials they are combined with. This review aims to assemble the available literature research on the application of clays and clay minerals as well as the mechanisms that lead to successful removal of nitrate from water. The main characteristics of clays and clay minerals in nitrate uptake are evaluated and the known shortcomings of their application discussed, leading to suggestions for further research.
Adsorption process has been widely used for treatment of wastewaters due to its simplicity and lower costs as compared to other traditional technologies. Among the alternative sorbent materials, the use of abundantly available clays for adsorption of organic pollutants has garnered increasing attention worldwide. Clays, in its natural and modified forms, have been extensively employed for the removal of organic contaminants from different wastewaters. The current review appraises the sorption performance of natural and modified clays for environmental remediation applications. The adsorption capacity of phenolic compounds, aromatic compounds, pesticides and herbicides, and other organic contaminants are comprehensively reviewed. The effect of the experimental conditions (pH, initial concentration (Co), surfactant loading, etc.) on the adsorption capacity is also appraised. Furthermore, the adsorption mechanisms, structures, and adsorptive characteristics of natural and modified clay sorbents are included. A statistical analysis of the adsorption isotherms reveals that Langmuir and Freundlich are the most examined models in fitting the experimental adsorption data. In addition, the adsorption kinetics is predominantly based on the pseudo-second-order model. The current review is an attempt to draw a prior knowledge about the technical viability of clay sorption process by assessing outcomes of the studies published between 2000 and 2018.
Copper (Cu(II)) is a very toxic heavy metal that even at low concentration can affect living organisms. Therefore, designing effective materials with high selectivity and cost-efficiency is essential for the control capturing of toxic Cu(II) ions. This study was developed a ligand based composite material for simultaneous Cu(II) detection and removal from wastewater samples. The composite material was fabricated based on the ligand anchoring onto the mesoporous silica by direct coating approach. The application of Cu(II) detection and adsorption was measured at neutral pH region with exhibition of significant color visualization. The experiment conditions were optimized based on contact time, solution acidity, initial Cu(II) concentration and pH value and diverse metal salt concentrations. The results were revealed that the composite material was not affected with the existing foreign ions and the signal intensity was observed only toward the Cu(II) ion. The composite material was able to detected the low level Cu(II) ion as the detection limit was 0.25 µg/L and the adsorption of highest removal capacity was 171.33 mg/g. In addition, the diverse ions were not reduced the Cu(II) ion adsorption significantly, and the composite material has approximately no adsorption capacity for other ions at this pH. The elution of Cu(II) ions from the saturated composite material was desorbed successfully with 0.20 M HCl. The regenerated adsorbent that remained maintained the high selectivity to Cu(II) ions and exhibited almost the same sorption capacity as that of the original adsorbent. However, the sorption efficiency slightly decreased after ten cycles. Therefore, the proposed material offered a cost-effective material and may be considered a viable alternative for effectively toxic Cu(II) ion capturing from water samples without the need for sophisticated instrument.
To explore the approach for further enhancing the dye removal performance of polydopamine (PDA) coated materials, a novel composite of PDA-kaolin with reduced graphene oxide hybridization (PDA-rGO-kaolin) was synthesized and selected as a model adsorbent for methylene blue (MB) removal. The BET characteristic analysis showed that the introduction of rGO significantly increased the surface area of PDA-kaolin by 3.1 times. A series of comparative experiments on PDA-kaolin and PDA-rGO-kaolin towards MB removal in various conditions were carried out. Adsorption experiment indicated that PDA-rGO-kaolin was more satisfactory for MB removal. Kinetic analysis showed that the adsorption followed a pseudo-second-order kinetic model. The adsorption behavior could be better described by Langmuir isotherm model. Compared with PDA-kaolin, PDA-rGO-kaolin showed higher maximum adsorption capacity towards MB (39.663 mg/g). Furthermore, the adsorption of MB molecules on adsorbents was spontaneous and endothermic process according to thermodynamic experiment. Moreover, PDA-rGO-kaolin showed a good regeneration performance for MB removal. These results show that the introduction of graphene is a feasible and efficient method to improve the adsorption performance of PDA coated kaolin composite.
An excellent, concise, and interdisciplinary overview of different classes of emerging pollutants arising, for example, from pharmaceuticals, pesticides, personal care products, and industrial chemicals and their impact on water, soil, and air. Following an introduction to chemical pollutants, with special attention focused on organic compounds and their properties, the book goes on to describe major emerging pollutants grouped according to their applications in different sectors of industrial or economic activity. For each type of compound, the chemical structure, main properties, and source are presented, along with their fate in the environment as pollutants, the latest analytical methods for detection, possible health or ecology consequences, as well as current regulatory laws. New developments, such as nanotechnology as a pollution source, are also included. The book closes with a chapter devoted to conclusions and future perspectives.
Alginate beads, with and without different types of organo-modified clays, were obtained using a calcium chloride (CaCl2) solution. Firstly, raw clays were organo-modified with a cationic surfactant, hexadecyl trimethylammonium (HDTMA). Then, their cationic exchange capacities (CEC) were calculated and they also were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Afterwards, the obtained polymers and clay polymer nanocomposites (CPN) were carefully characterized by means of the same techniques. Later, different phenol and 4-chlorophenol (4CF) aqueous solutions were prepared and put in contact, for different periods of time, with the synthesized CPN. Phenol and 4CF concentrations were measured by means of UV-vis spectroscopy. Results indicated a successful modification of the raw clay with this cationic surfactant and its incorporation into the alginate polymer matrix. Finally, the maximum removal capacities for both phenolic compounds, 4CF and phenol, were found at qe = 0.334 mg·g⁻¹ and qe = 0.118 mg·g⁻¹, respectively.
The effective use of the sorption properties of different clays as sorbents for the removal of dyes from wastewater has currently received much attention because of the eco-friendly nature of clay materials. Dyes are complex class of organic compound having wide range of applications in textile and food industries and a large amount of dyes are wasted, which get mixed in natural water resources. Mixing of dyes in water resources must be prohibited for the safety of natural ecosystem. The adsorbents (natural and modified) have been successfully used for the adsorption of dyes form wastewater. This review article highlights the importance of clay (raw and modified) as an adsorbent for the adsorption of dyes from textile wastewater. Appropriate conditions for clay-dye system and adsorption capacities of a variety of clays are presented and sorption process is critically analyzed. Studies reported the clays as an adsorbent from 2004 to 2016 are included and different properties for the utilization of clay and clay-based adsorbents are discussed. Based on studies, it was found that the clays (natural and modified) are affective adsorbents for the purification of wastewater containing dyes.
The chemical contamination of water from an extensive variety of toxic derivatives, specifically heavy metals, aromatic molecules and dyes, is a genuine ecological issue attributable to their potential human lethality. In this way, there is an earnest need to create advances that can remove harmful toxins found in wastewaters. Among all the reported treatment techniques, adsorption is one of the more prevalent systems for the removal of contaminations from the water. Adsorption is a standout among the most simple and effective strategy for treating industrial effluents, and a valuable device for ensuring nature. The increasing number of publications on adsorption of toxic compounds by modified bentonites demonstrates that there is a recent increasing interest in the synthesis of new low-cost adsorbents used in water treatment. The present review demonstrates the late advancements of nanotechnology in the synthesis of nanoadsorbents containing bentonite and its composites. The primary target of this review is to depict the adaptable way of bentonite and its composite and their capacity to absorb variety of inorganic contaminants, which are available in the water. It is evident from the review that modified bentonite composites (low-cost adsorbents) have demonstrated high removal capabilities for certain inorganic contaminants from water.
Clays have been one of the more important industrial minerals; and with the recent advent of nanotechnology, they have found multifarious applications and in each application, nanoclays help to improve the quality of product, economize on the cost and saves environment. The chapter describes key characteristics of nanoclays and their classification on the basis of the arrangement of “sheets” in their basic structural unit “layer”. Major groups include kaolin–serpentine, pyrophyllite-talc, smectite, vermiculite, mica and Chlorite. The structural, morphological and physicochemical properties of halloystite and montmorillonite nanoclays, representative of the 1:1 and 2:1 layer groups, respectively, are discussed as well. After briefly introducing the surface modification of clay minerals by modifying or functionalizing their surfaces and their incorporation into polymer matrices to develop polymer/clay nanocomposites, techniques that are being employed to characterize these nanoclays, in general, and the sample preparation for these techniques, in particular, are also reviewed in this chapter.
North of Morocco is becoming one of suppliers of tourism sites and agricultural products for Europe. Thus, environmental risks from this region are important for the future of these activities. The presence of pesticides in soils and waters can become a serious environmental problem. Clay minerals can be used for mitigation of this problem. In this work, the adsorption of two fungicides, metalaxyl and tricyclazole, on natural Northern Moroccan clays was investigated using the batch equilibration method and several techniques, such as, X-ray diffraction (XRD), thermal analysis (TGA/DSC), and surface area measurement (BET) were used for clay characterization. The data from kinetic and adsorption studies were fitted to different models. The adsorption kinetics of these fungicides followed a pseudo-second-order model. Adsorption data, higher for metalaxyl than for tricyclazole, were fitted the Freundlich model. A natural stevensite was the clay with the highest adsorption capacities for both fungicides.
A Subcommittee of the IUPAC Commission on Colloid and Surface Chemistry including Catalysis was formed in 1979 to consider the reporting of gas adsorption data. The main objectives of the Subcommittee are: (1) to draw attention to the problems and ambiguities which have arisen in the reporting of physisorption data; (2) to formulate tentative proposals for the standardisation of procedures and terminology. The provisional manual is essentially a discussion document but it contains a set of general conclusions and recommendations including a check list to assist authors in the measurement and presentation of physisorption data.
Thirteen bentonite deposits of North Patagonia, Argentina, were characterised by chemical and differential thermal analysis (DTA), X-ray diffraction, Mössbauer spectroscopy, and Cation Exchange Capacity (CEC) and Specific Surface area (S) determinations. The chemical analysis on <2μm fraction permitted to calculate the nature and degree of isomorphic substitution (octahedral and tetrahedral). Parameters as CEC, S and thermal stability (T) (determined by DTA analyses) were correlated linearly with the degree of tetrahedral isomorphic substitution. These parameters and the mathematical models obtained could be used to predict technological uses of this mineral. Electron microscopy observation showed different modes of particle associations related also, as the precedent parameters, to the degree of tetrahedral isomorphic substitution. The adsorption on bentonite of organic pollutants was evaluated using a fungicide (Thiabendazole) employed in the same region. Fungicide adsorption increased with the degree of tetrahedral isomorphic substitution and consequently with the surface area and CEC values of the samples studied.
Samples of original and thermally treated bentonite at 650 °C 4 h were characterized with chemical analysis, X-ray diffraction, thermal analysis, mercury porosimetry, differential scanning calorimetry, physisorption measurement and scanning electron microscopy. These consequence of the heating have been found. The chemical analysis shows high silica and alumina contents and small quantities of Fe+3, Ca+2 and Mg+2. XRD analysis shown the presence the main minerals are montmorillonite and opal CT, in the subordinate quantity illite. The result of the heating was the decomposition of clay minerals. Further, the increase in silica and alumina contents. A significant changes in the original pore structure have been found. The changes were characterized by the expressed increase in the content of total porosity caused by the achieved occurence of the pores covering pore radius area over 2000 nm. This effect represents the increased openness of the pore structure which may have the significant role in the intensity of alkali-activation process as a factor contributing to the increase of the contact of alkali activator solution with the activated solid. As a possible consequence of the increased openness could be the acceleration of alkali-activation process resulting, for example, in the acceleration of the strength development of binding system based on the thermally treated bentonite.
Different resol phenol-formaldehyde prepolymer resins have been synthesized with different formaldehyde/phenol ratios. The phenolic resin composition depends on monomer ratio, catalyst, reaction conditions, and residual free monomers. Temperature and pH conditions under which reactions of phenols with formaldehyde are carried out have a profound effect on the characteristics of the resulting products. Three reaction sequences must be considered: formaldehyde addition to phenol, chain growth or prepolymer formation and finally the crosslinking or curing reaction. Two prepolymer types are obtained depending on pH, novolacs in an acidic pH region whereas resols by alkaline reaction. Resol resins are synthesized with a molar excess of formaldehyde (1<F/P<3). These are mono- or polynuclear hydroxymethylphenols which are stable at room temperatures, but are transformed into three dimensional, cross linked, insoluble and infusible polymers by the application of heat. An ATR-FTIR spectrometry technique (ReactIR 4000) with light conduit and diamond-composite sensor was used to perform in-line monitoring of phenol-formaldehyde prepolymer synthesis. This technique was found to be ideal for determining residual free phenol and formaldehyde, individual phenol and formaldehyde conversions and prepolymer composition changes as a function of time when the condensation reaction was carried out. The kinetics data obtained through the ReactIR 4000 in-line reaction analysis system agreed well with those determined by the traditional titration method. ReactIR technology replaces time consuming and inaccurate off-line methodology.
Organically modified clays (‘organo-clays’) have attracted a great deal of interest because of their wide applications in industry and environmental protection. The objective of this study was to synthesize organo-clays using Tunisian smectite saturated with Na+, Ca2 + and Zn2 + ions and the cationic surfactant hexadecyltrimethylammonium bromide (HDTMAB). The effects of initial concentration (0.1–3.0 CEC), contact time (0.5–48 h) and temperature (293–333 K) were studied. The changes in the surfaces and structures of the smectites modified with HDTMA surfactant were characterized using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR).For all clays, the adsorbed HDTMA increased with increasing initial concentration; at high surfactant concentrations, Zn-exchanged clay displayed a high affinity for HDTMA surfactant suggesting that adsorption could be described by a different process. The kinetic adsorption data were modeled using pseudo-first-order and pseudo-second-order equations. It was shown that pseudo-second-order kinetic equation could best describe the adsorption kinetics. The enthalpy (Δ°H) and entropy (Δ°S) of adsorption were calculated from the slope and intercept of the linear plot of Log Kd against 1/T. Calculations on the thermodynamics of adsorption showed that principal contribution to the negative value of Δ°G (− 14 to 14 kJ·mol− 1), is the large positive value of Δ°S (0.06–0.07 kJ·mol− 1·K− 1), whereas Δ°H is positive ranging between 4 and 7 kJ·mol− 1. It follows that adsorption of HDTMA onto smectite was feasible, spontaneous and endothermic process. Different configurations of surfactants within smectite interlayer were proposed based on the d(001) basal spacings which increased with surfactant loading. The presence of symmetrical and asymmetrical vibration bands of the CH2 group in the IR spectrum of the modified clays and the variation of their frequencies and their intensities confirmed the results obtained by XRD.
This chapter discusses the bentonite applications. Bentonites are comprised predominantly of the smectite group of minerals. Calcium montmorillonite is the most predominate of the smectite minerals and is found in many areas of the world. Sodium montmorillonite is relatively rare in occurrence in comparison with calcium montmorillonite. Beidellite is the aluminum montmorillonite and is also relatively rare in occurrence. The smectite minerals occur as extremely fine particles of the order of 0.5 μm or less. Exchangeable cations such as sodium, calcium, and magnesium occur between the silicate layers, associated with water molecules. These elements are exchangeable and the property of exchange capacity is measured in terms of milliequivalents per 100 grams. The property of ion exchange and the exchange reaction are very important in many of the applications in which the smectite minerals are used.
The toxicity characteristic leaching procedure (TCLP, method 1311) (USEPA, 1990) was used to evaluate the effectiveness of nine organoclays in reducing the leachability of pentachlorophenol (PCP) from three highly contaminated (3000-5000 mg kg-1) soils from wood treatment facilities. The soils differed in their PCP, oil and grease, and organic C contents. The organoclays were smectite exchange with quaternary ammonium cations of the form [(CH3)3]NR]+ or [(CH3)2NR2]+ where R is an aliphatic or aromatic hydrocarbon. A cement-based solidification agent (Sorbond) was also added to the soil to evaluate its effects on the leachability of PCP. Organoclays with large (>C10) aliphatic R groups (organophilic organoclays) were compared with those with small aromatic or aliphatic groups (adsorptive organoclays). The adsorptive organoclays were much less effective than the organophilic clays in reducing PCP levels in the TCLP leachate. The organophilic clays dramatically reduced the leachability of PCP from all of the soils. The most effective clay tested was the dimethyldicocoammonium smectite; a 20% addition of this organoclay to the soil resulted in leachable PCP levels below the detection limit (0.2 mg L-1). The addition of Sorbond to the soil increased both the pH (from 4.95 to 12.00) and the PCP concentrations (from 6.8 to 100.8 mg L-1) in the leachate. However, when Sorbond was added with an organophilic clay, the PCP concentration was decreased below detection limits despite the increase in pH. These results demonstrate the potential effectiveness of organoclays for reducing the leaching of PCP from highly contaminated soils.
The papers collected in this issue reveal the diversity of pesticide–clay interactions. The most important bonding mechanisms are shortly described in this introduction. These mechanisms provide the basis for attempts to design new pesticide formulations. Several examples of such formulations are reported.
The nature of clay fines influences the characteristics of clay–rubber composites. This paper discusses the improvement of properties of clay–rubber composites by acid activation and surface modification of the clay. Acid-treated clays show a higher surface activity and a stronger combining ability with silane coupling agents. The silane modified clay fines reinforce the rubber by increasing the compatibility between rubber and clay.
Literature reveals that the nature of the clay minerals in clay-based polymer nanocomposites (CPN) is often disregarded or only reported in very general terms. The decisive clay mineral properties for high-performance CPN are highlighted. Many aspects should be taken into account when clay minerals are used for the preparation and optimization of CPN. Clay minerals (smectite, kaolinite, sepiolite) differ by class, but there are also differences within each species such as montmorillonite. Even montmorillonites of the same locality can differ in certain properties. The structural details of the clay minerals (composition, compensating cations) must therefore be carefully specified, so even small changes can be of influence in applications such as nanocomposites. The clay mineral particles are often modified to render them compatible with the polymer. In most cases, surfactants are used to render the surface hydrophobic, but this modification generally reduces or impedes delamination of the clay mineral particles into thinner or single layers. The most important step is therefore finding the optimal way of modification and adjusting the hydrophilic–lipophilic balance (HLB) to the polymer matrix. The HLB not only depends on the chemical nature of the surfactants but also on the surfactant/CEC ratio. The aspects discussed clearly indicate that CPN formation is an excellent example of modern Materials Science requiring the cooperation of scientists of different backgrounds, engineers and technologists. It is evident that Clay Technology can only be successful and of strong impact when the actual results of modern Clay Science will be fully established.
In the years 1930—1950 clay mineral identification involved mainly a combination of X-ray powder diffraction and chemical analysis with some assistance from other techniques, notably differential thermal analysis. In the period 1950—1970 additional procedures have emerged including infrared analysis, electron optical methods and a variety of thermal methods. These procedures are now treated in other monographs sponsored by the Mineralogical Society and in many other publications. Despite the availability of other techniques, X-ray diffraction remains a basic tool for studying minerals and we hope that this monograph will continue to serve, as did the previous editions, both those concerned with the more academic aspects of clay mineralogy and also those, such as geologists, civil engineers and soil scientists, for whom identification and quantitative estimation of the minerals in natural clayey materials is a practical requirement.
Montmorillonite–silica nanocomposites were prepared by a sol–gel approach involving hydrolysis reaction of alkoxysilanes (TEOS) and subsequent condensation reaction with hydroxyl groups of the clay, resulting in the formation of the mesoporous silica network and silica nanoparticles covered or attached on the clay surfaces. According to X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and nitrogen adsorption isotherms, the structure and surface properties of the sol–gel-modified clay can be controlled by varying the TEOS/clay mass ratio and/or adding trace amounts of acid as catalyst. In the case of acid-catalyzed procedures, large continuous mesoporous silica was covered on the clay surfaces, resulting in delamination of clay platelets in silica matrix at higher TEOS/clay ratio, and attaching of isolated mesoporous silica on the clay surface at lower TEOS/clay ratio, respectively. In the case of non-catalyzed procedures, silica nanoparticles were attached on the two-dimensional (2D) clay platelets, while the stack order of the clay was maintained regardless of the TEOS/clay ratios. This sol–gel modification approach combines the surface properties of mesoporous silica and nanoparticles with layered clay, while inheriting the structural properties of the pristine clay such as further intercalation with organic compounds and polymers.
This chapter attracts the attention of clay scientists in academe and industry as well as in politics (as research needs funding), and focuses on the importance of clay science to society and the quality of life. The economic benefits seem evident because clays are abundant, widespread, and inexpensive compared with other raw materials. The chapter discusses the industrial and environmental importance of clays and clay minerals. The great variety of physical, chemical, and thermal treatments that may be used to modify clays and clay minerals provide unlimited scope for future applications, particularly in terms of protecting the environment. Because of the multidisciplinary nature of clay science, its teaching is another challenging task. By learning about the mineralogical, physico-chemical, and industrial aspects of clay science, students would not only gain an appreciation of the “scientific method” and the physical environment but also find suitable employment and a fulfilling career.
A continuous adsorption study in a fixed-bed column was carried out by using phoenix tree leaf powder as an adsorbent for the removal of methylene blue (MB) from aqueous solution. The effect of flow rate, influent MB concentration and bed depth on the adsorption characteristics of adsorbent was investigated at pH 7.4. Data confirmed that the breakthrough curves were dependent on flow rate, initial concentration of dye and bed depth. Four kinetic models, Thomas, Adams–Bohart, Yoon–Nelson and Clark, were applied to experimental data to predict the breakthrough curves using nonlinear regression and to determine the characteristic parameters of the column that are useful for process design, while a bed-depth service time analysis (BDST) model was used to express the effect of bed depth on breakthrough curves and to predict the time needed for breakthrough at other conditions. The Thomas and Clark models were found suitable for the description of whole breakthrough curve, while the Adams–Bohart model was only used to predict the initial part of the dynamic process. The data were in good agreement with the BDST model. It was concluded that the leaf powder column can be used in wastewater treatment.
The increasing presence of pesticides in natural ecosystems has stimulated research to look for improved adsorbent materials which can be used to remediate and prevent soil and water contamination by these compounds. Among the different materials that have been assayed as adsorbents of pesticides are natural clay minerals, particularly 2:1 phyllosilicates and their structurally complementary synthetic analogues layered double hydroxides (LDHs). The great
interest in natural clays and LDHs as adsorbent materials is mainly related to the large specific surface areas associated with their layered structure, the ease with which they are obtained or synthesized, and the possibility of modifying their surfaces to increase their affinity for specific adsorbates. This review summarizes the adsorptive properties of natural clays and LDHs for pesticides and related organic compounds. Particular emphasis is given to the surface modification of clay minerals and LDHs with organic ions as a strategy to improve the efficiency of these materials as pesticide adsorbents. Potential applications of unmodified and modified clays and LDHs as adsorbents to prevent and remediate soil and water contamination by pesticides are also discussed.
The swelling behavior and the structure of composite gels of poly(acrylamide) with incorporated bentonite clay and the products of their reactions with a cationic surfactant, cetylpyridinium chloride, were studied by SAXS and ESR (spin-probe) methods. The ESR data show that the adsorption of CPC on the clay platelets already leads to the formation of the ordered surfactant aggregates with low molecular mobility in the region of surfactant concentrations much below the cmc. A SAXS study demonstrates that further adsorption of the surfactant results in the formation of lamellas, including alternating layers of clay platelets and double layers of CPC. These two steps of the adsorption are accompanied by the strong shrinking of the gel composite. At high concentrations of the surfactant, total overcharging of the surface of the clay particles occurs, resulting in a change in the direction of the electroosmotic transport of water through the gel and in the reswelling of the gel composite. The models of the clay/surfactant complexes in the gel phase are discussed.
The structural changes which occur during the intracrystalline swelling of a well-characterized Wyoming sodium montmorillonite have been investigated using controlled-rate thermal analysis, nitrogen adsorption volumetry, water adsorption and desorption gravimetry, immersion microcalorimetry in water, and X-ray diffraction under controlled humidity conditions. The experimental X-ray powder patterns of the 001 reflections have been compared with the theoretical simulations to determine the structural change of the montmorillonite during hydration and dehydration. 85 refs., 13 figs., 4 tabs.
Reaction of bis(trimethoxysilyl)hexane, (CH3O)3Si(CH2)6Si(OCH3)3, and the protonated salt of 3-aminopropyltriethoxysilane, (C2H5O)3Si(CH2)3NH3+Cl-, with different clay aqueous colloidal dispersions produces a network of clay platelets cross-linked on their edges by the corresponding organosiloxanes. In the case of the α,ω-bridging organosiloxane, where the surface modification of the clay by the silane proceeds on its outer surfaces, cross-linking results in a gel network that extends to the whole volume of the initial aqueous dispersion. Drying of this gel and grinding of the as-formed, relatively hard specimens affords fine hybrid powders consisting of cross-linked clay particles that inherit the swelling, intercalation, and ion-exchange properties of the starting clay. Controlling both the composition of the initial suspension (clay type, solvent, and concentration) and the drying process, enables the fabrication of monolithic clay hybrids. In the case of the protonated aminosiloxane, the surface modification of the clay takes place both within its interlayer space and at its edges. The former leads to the formation of silsequioxane pillars within the clay galleries. The latter produces stiff yet ductile monoliths upon drying via condensation of edge-modified adjacent clay layers. When Laponite and (CH3O)3Si(CH2)3N(CH3)3+Cl- are used, optically transparent monoliths (or clay glasses) are obtained.
We have over the years developed and patented a general technique for the hydrothermal synthesis of clay minerals in the presence of organic, organometallic, and polymeric intercalants. This review will summarize the details for crystallization of modified hectorites along with their characterization and materials applications. Among the several potential uses of these synthetic materials, there are two important applications concerning catalysis and composites. The fate of the template dictates which of these applications is pertinent. First, if the organic molecule or polymer is used with the intention of acting as templates of pore structure, then the organic template is removed after the modified clay has been crystallized. Upon template removal, the now porous materials are examined for their use as potential catalysts and catalyst supports. We have recently proven a correlation between catalyst pore size in the mesoporous range and the size and concentration of a polymeric template that is used. Preliminary hydrodesulfurization catalytic results have been obtained using these materials. If, on the other hand, intercalants are allowed to remain as a part of the structure, then a distinctive class of organic–inorganic composites becomes possible. When polymeric intercalants are used, especially at high concentrations, the materials have relevance to nanocomposite applications. Work in this area has focused on incorporating polymers at higher than 85 wt.% of the nanocomposite.
Some Argentine North Patagonia bentonite deposits have been characterised by chemical and differential thermal analysis (DTA), X-ray diffraction and Isoelectric Point (IEP), Cation Exchange capacity (CEC) and specific surface area (S) determinations.Samples with high degree of tetrahedral isomorphic substitution, and consequently high interlayer cation charge compensation, would be used as organic pollutant adsorbent when the adsorption was a cation exchange mechanism.
Simultaneous sorption of organic compounds and phosphate from water by inorganic–organic bentonites (IOBs) was investigated, which would contribute to the treatment of contaminated water containing both of these contaminants. A series of IOBs were synthesized by intercalating bentonite with both cetyltrimethyl ammonium bromide (CTMAB) and hydroxy-aluminum at their various ratios, and the obtained materials had large basal spacing, low surface area and high organic carbon contents. Sorption experiments with phenol, p-chlorophenol, 2,4-dichlorophenol, 2-naphthol, nitrobenzene, p-nitrotoluene or naphthalene together with phosphate demonstrated that IOBs could simultaneously remove organic compounds and phosphate from water, due mainly to the partition and ligand exchange mechanism, respectively. The sorption capacity of IOBs with organic compounds was retained as those of organobentonites, and the removed amount were in the range of 42–98% for the tested organic compounds. In addition, the removal efficiency of phosphate by IOBs is higher than that by the corresponding hydroxy-aluminum pillared bentonites, and more than 98% phosphate were removed at the initial concentration of 20 mg/L (calculated as P). The coexisting organic compounds had little influence on the sorption of phosphate to IOBs under the experimental conditions. Thus, IOBs could be promising sorbents for simultaneous removal of organic compounds and phosphate from water.