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Kinetic and thermodynamic studies of neutral dye removal from water using zirconium metal-organic framework analogues
Abstract
A series of isostructural water stable UiO-66-X (X = H, NH2, NO2), one of the most well-known metal-organic framework (MOF) materials, was synthesized by solvothermal synthesis. Their dye adsorption capacity toward a neutral dye, Phenol Red (PR), was investigated for the first time in this research in order to elucidate how the functional group of the organic linker contribute to the adsorption capacity. The operational parameters, i.e. pH, adsorbent concentration, initial dye concentration, contact time and temperature were monitored. The maximum adsorption capacities of UiO-66, UiO-66-NO2 and UiO-66-NH2 were measured to be 19 mg/g, 11 mg/g and 27 mg/g, respectively. The adsorption kinetics of all three adsorbents were similar and fitted best with pseudo-second-order kinetics model. Adsorption isotherms of the adsorbents can be explained by Freundlich model which suggests that the adsorption of PR on the adsorbents can be both physisorption and chemisorption. Thermodynamic studies indicated that the adsorption process in all studied adsorbents was spontaneous, endothermic and entropic-driven which was confirmed by the obtained thermodynamic variables. Functional group of the organic ligand was found to contribute significantly to the adsorption capacity of MOFs. The adsorbent with a functional group that can create more intermolecular forces will enhance the adsorption capacity. Experimentally, UiO-66-NH2 showed the highest adsorption capacity when compared to UiO-66 and UiO-66-NO2.
... As listed in Table 4, the negative value of ∆G at all temperatures indicated that the adsorption process was spontaneous. The results obtained in this study are similar to that of the thermodynamic study of neutral red on a zirconium metal-organic framework [43] and the adsorption of neutral red onto halloysite nanotubes [15]. The absolute value of ∆G increased as the temperature increased. ...
... Thus, the adsorption of neutral red was not an enthalpy-driven process but rather an entropy-driven one. Our findings are supported by the results from other researchers, as similar spontaneous adsorption processes, seen as the result of a negative value of ∆G, were noted to have a positive change in enthalpy ∆H and a positive change in entropy ∆S [15,43]. ...
... As listed in Table 4, the negative value of ΔG at all temperatures indicated that the adsorption process was spontaneous. The results obtained in this study are similar to that of the thermodynamic study of neutral red on a zirconium metal-organic framework [43] and the adsorption of neutral red onto halloysite nanotubes [15]. The absolute value of ΔG increased as the temperature increased. ...
Educational and research laboratories often produce relatively small amounts of highly
diverse organic wastes. Treating waste can contribute significantly to the cost of running laboratories. This study introduced a simple and economical waste management system such that readily available used chromatography-grade inorganic materials, such as silica and alumina (basic and acidic), are utilized to treat remnant dye solutions and solution wastes from educational and small research laboratories. To recycle the adsorbents, they were heated to 600 ◦C, where the adsorbates were combusted. The results showed that acidic alumina is an effective adsorbent material for azo dyes and anionic dyes/stains, as well as textile dyes, with a 98 to 100% removal efficiency. Furthermore, alumina and
silica possess excellent regeneration properties, where the dye removal efficiency of the materials was retained after regeneration at 600 ◦C. The adsorption properties of the materials were compared with those of aliginite and activated biomass from coffee grounds. Kinetic and thermodynamic studies of the sorption processes on the different materials were carried out. Overall, the inorganic materials used were efficient at removing contaminating remnant organic dyes stemming from educational and small research laboratories.
... However, Zr-AZB displayed significant loss in crystallinity after 7 days in suspension, Al-AZB is thus more stable in water than Zr-AZB. However, since the equilibrium adsorption of dyes from water is usually achieved within 24 h (Alqadami et al., 2018;Nanthamathee and Dechatiwongse, 2021), the as-prepared MOFs are highly stable and suitable for the adsorption process. During pH stability tests, Al-AZB showed stability over a wider range of pHs with framework crystallinity being lost at pH above 9 (Fig. 6). ...
... This is similar to previous reports on dye removal via sorption on MOFs (Arora et al., 2019;Gautam et al., 2017;Liu et al., 2016). Nanthamathee and Dechatiwongse stated that the sorption of dyes on MOFs is generally endothermic in nature (Nanthamathee and Dechatiwongse, 2021). They explained that since adsorption takes place in a solution containing both water and dye molecules, water molecules should be desorbed for dye molecules to be adsorbed, otherwise the adsorption becomes negative. ...
... kJ/mol and 21.0-418.4 kJ/mol indicate the dominance of physisorption or chemisorption, respectively, in the overall sorption process (Nanthamathee and Dechatiwongse, 2021). In this regard, it is evident that the uptake of CR on both Al-AZB and Zr-AZB was dominated by chemisorption, which corroborates the deductions of the LM and PSOM discussed previously. ...
The high efficiency of metal-organic-frameworks (MOFs) such as the ZIF, MIL and UiO type species in dye adsorption is well established. Recently, an emerging class of photoresponsive azobenzene-based MOFs has found suitable application in gas adsorption. However, there is a dearth of research on their use in the adsorption of dyes and other water pollutants. In this research, two microporous photoresponsive azobenzene dicarboxylate MOFs of Al³⁺ (Al-AZB) and Zr⁴⁺ (Zr-AZB) were synthesized for the adsorption of congo red (CR) dye. The surface and textural properties of the synthesized MOFs were characterized by FTIR, PXRD, SEM, TGA, BET and pore analysis. Both MOFs were crystalline, thermally stable up to 300 °C and stable in aqueous medium at room temperature. The Al-AZB displayed a higher surface area (2718 m²/g) than the Zr-AZB (1098 m²/g), which significantly impacted the higher adsorption of CR. Besides, pore volumes of 0.86 cm³/g and 0.35 cm³/g were obtained for Al-AZB and Zr-AZB, respectively. The maximum adsorption capacity of Al-AZB and Zr-AZB was 456.6 mg/g and 128.9 mg/g, respectively, with the former superior to other potent adsorbents. The pseudo-second-order and Langmuir models were well correlated with the dye uptake on the MOFs. Thermodynamics revealed random and endothermic sorption of CR dominated by chemisorption, while efficient regeneration and reuse of both MOFs were achieved using dimethylformamide as eluent. The results proved the potency of the synthesized photoresponsive MOFs, as highly efficient and reusable materials for dye adsorption.
... It can be seen in Tables 2 and 3 that by increasing the temperature, the initial adsorption rate K 2 increases. However, at a constant temperature, K 2 decreases along with an increase in the initial concentration of MO [58,59]. Furthermore, under most conditions, K 1 decreases along with an increase in temperature. ...
... The value of n corresponds to adsorption feasibility, in which a value of n > 1 indicates a more favorable adsorption. It can be seen from Table 5 that all the adsorbents have a value of n > 1 [58]. From the calculation of the linear Langmuir isotherm model it was obtained that the maximum adsorption capacity of UiO-66 and Al(M100)@UiO-66 in this study were higher than the other adsorbents (Table 9). ...
... However, excess addition of adsorbent, up to 15 mg, causes a drastic decrease in the adsorption capacity. There exists a threshold for the maximum amount of adsorbent that results in an efficient dye adsorption capacity [58]. Furthermore, excess addition of adsorbent increases the effect of agglomeration of the adsorbent which reduces adsorption sites on the surface [88]. ...
The kinetic, isotherm and thermodynamic parameters of adsorption were investigated to obtain the optimum conditions of adsorption. Error analysis methods such as RMSE and χ² were used to determine the best kinetic equation and isotherm. From the adsorption kinetics study, the linear pseudo second order model showed an effective adsorption mechanism and the most suitable adsorption isotherm was the linear Langmuir isotherm model. Based on the linear Langmuir isotherm model, the maximum adsorption capacities of UiO-66 and Al(M100)@UiO-66 were 233.65 and 268.82 mg/g, respectively. The results showed that the linear method was better suited to take into account the adsorption parameters than the nonlinear method. The resulting R² values of other kinetic models, namely Intraparticle Diffusion and Elovich, were still below that of the linear pseudo second order model and the resulting R² values of other isotherm models, namely Temkin, Dubinin-Radushkevich, and Scatchard, were still below that of the linear Langmuir isotherm model. The adsorption thermodynamic study showed that the adsorption process was exothermic and spontaneous. Other operational parameters such as pH, ionic strength and adsorbent dose were also discussed. Al(M100)@UiO-66 can be regenerated up to four times using a diluted HCI solution.
... Recently, many physical and chemical technologies have been developed to eliminate PFOA from environment such as coagulation, electromembrane process, photochemical oxidation, photocatalysis, microwave degradation, electrochemical degradation and adsorption technology [9] .Since low cost, easy operation, less energy requirement and loose reaction conditions, adsorption technology has attracted great attention [11] .To date, a variety of porous materials have been developed to adsorb PFOA from wastewater, such as mesoporous metal oxides (silica and alumina), microporous minerals (zeolite) and porous carbons (activated carbon, carbon nanotubes and carbon fiber) [9] . Generally, the research results suggested electrostatic interactions, acid-base interactions, pore filling adsorption, hydrogen bonding, hydrophobic interaction and π-π interaction as the main reaction mechanisms [11] . ...
... Recently, many physical and chemical technologies have been developed to eliminate PFOA from environment such as coagulation, electromembrane process, photochemical oxidation, photocatalysis, microwave degradation, electrochemical degradation and adsorption technology [9] .Since low cost, easy operation, less energy requirement and loose reaction conditions, adsorption technology has attracted great attention [11] .To date, a variety of porous materials have been developed to adsorb PFOA from wastewater, such as mesoporous metal oxides (silica and alumina), microporous minerals (zeolite) and porous carbons (activated carbon, carbon nanotubes and carbon fiber) [9] . Generally, the research results suggested electrostatic interactions, acid-base interactions, pore filling adsorption, hydrogen bonding, hydrophobic interaction and π-π interaction as the main reaction mechanisms [11] . Current studies on PFOA adsorption by biochar have shown that the van der Waals and π-π bonds would negligibly affect the adsorption process considering the low polarizability and absence of benzene structure in PFOA [12] . ...
... They can be show some superior characteristics including high specific surface area, abundant unsaturated metallic sites, and high mechanical stability, as well as easy modular synthesis, designable pore structure, and tunable physicochemical properties targeting different adsorbents via variation of metal ions and organic ligands or decoration on synthesized products [14] . In recent decades, MOFs have shown great separation and adsorption potential [11] , and extensively applied to storage/separation, catalysis, sensing, bioimaging and other aspects [13] . At present, MOFs are widely used in environmental engineering [10] , and in particular, its composite materials have been absorbents for various contaminants in water [13] . ...
As a persistent pollutant, PFOA places a serious threat to natural ecosystems and human health for its global distribution and residual. Currently, adsorption technology is a promising approach for PFOA removal. MOFs become a concerned adsorbent attributing to its special designability and easy modular synthesis. Aiming at improving hydrophobic interactions to absorb PFOA, this study was designed to introduce amino group to decorate Zr-based MOF UiO-66. And subsequently introduced GO to modify UiO-66-NH2 to explore the influence of hydrophobicity on PFOA adsorption removal. Based on the performance of the characterization of synthesized products, the adsorption removal effect of PFOA and the corresponding adsorption mechanism were discussed. The results indicate the introduction of the amino group could enlarge the pore size, but also display strong hydrophobic effects, significantly enhance the adsorption capacity(maximum capacity was 1653mg/g). This work not only provides the method of introducing amino group to Zr-based MOFs to strengthen the hydrophobic properties in purpose of removing PFOA efficiently, but also proposes the feasible the reference for tailoring MOFs to remove endurable organic pollutants in water.
... The main diffraction peaks of Zn(BDC) were 7.07°, 10.57°, and 13.27° that had no significant change indicating no structure degradation of Zn(BDC) and keeping their crystallinity even after 24 h in suspension. Since the adsorption equilibrium of the dyes from the water was typically accomplished within 24 h (Alqadami et al. 2018;Nanthamathee and Dechatiwongse 2021), it was concluded that the prepared Zn(BDC) is highly stable and convenient for the adsorption process. ...
... The positive value of ΔH° for AB adsorption on Zn(BDC) confirms that the process is endothermic, which links an increase in the temperature to increase the adsorption of AB. This is comparable to earlier studies on the sorption of dye on MOFs (Gautam et al. 2017, Arora et al. 2019Nanthamathee and Dechatiwongse 2021). Moreover, the small positive value of ΔH° (< 40 kJ mol −1 ) of AB indicates that the adsorption process was monitored by physical adsorption (Konicki et al. 2017). ...
Green synthesis of metal–organic frameworks (MOFs) has attracted a lot of attention as a crucial step for practical industrial applications. In this work, green synthesis of zinc(II) metal–organic framework (Zn-MOF) has been carried out at room temperature. The Zn metal (node) was extracted from spent domestic batteries, and the linker was benzene di-carboxylic acid (BDC). The characterization of the as-prepared Zn-MOF was accomplished by PXRD, FT-IR spectroscopy, SEM, TEM, TGA, and nitrogen adsorption at 77 K. All the characterization techniques strongly supported that as-synthesized Zn-MOF using metallic solid waste Zn is similar to that was reported in the literature. The as-prepared Zn-MOF was stable in water for 24 h without any changes in its functional groups and framework. The prepared Zn-MOF was tested for the adsorption of three dyes, two anionic dyes, aniline blue (AB), and orange II (O(II)) as well as methylene blue (MB), an example of cationic dye from aqueous solution. AB has the highest equilibrium adsorbed amount, qe, of value 55.34 mg g⁻¹ at pH = 7 and 25 °C within 40 min. Investigation of the adsorption kinetics indicated that these adsorption processes could be described as a pseudo-second-order kinetic model. Furthermore, the adsorption process of the three dyes was described well by the Freundlich isotherm model. According to the thermodynamic parameters, the adsorption of AB on the prepared Zn-MOF was an endothermic and spontaneous process. In contrast, it was non-spontaneous and exothermic for the uptake of O(II) and MB. This study complements the business case development model of “solid waste to value-added MOFs.”
... Also, the ΔG values for all cationic dyes were determined in the range of − 20-0 kJ. mol − 1 , which shows the predominance of physical mechanisms in the adsorption [54]. The ΔH parameter for MBD, MVD, and CVD was determined as − 75.467 kJ.mol − 1 , − 73.591 kJ.mol − 1 , and − 84.927 kJ. ...
... Besides, the amount of adsorption energy (K L ) for the adsorption process of MBD, MVD, and CVD using synthesized magnetic nanocomposite powder was determined to be 2.83 L.mg − 1 , 2.20 L.mg − 1 , and 3.22 L.mg − 1 , respectively, which proves that the adsorption energy of CVD is more than the two others. Freundlich isotherm is another model that assumes a monolayer or multilayer surface adsorption and states that the adsorption process takes place on a heterogeneous surface that has dissimilar active sites with different binding energies [54]. Based on the Freundlich model, for all three types of cationic dyes, the n value was greater than 1, which shows that the adsorption process is physical and fine. ...
A new magnetic nanocomposite clinoptilolite (CLT)/Starch/CoFe2O4 was synthesized using co-precipitation method. The prepared magnetic composite powder was utilized for decontamination of methylene blue dye (MBD), methyl violet dye (MVD), and crystal violet dye (CVD) from water media. The BET analysis showed that CLT modification using starch and CoFe2O4 nanoparticles improved its specific surface and the amount of specific surface area for CLT, CoFe2O4, and CLT/Starch/CoFe2O4 powder was reported to be 18.82 m².g⁻¹, 151.4 m².g-1, and 104.75 m².g⁻¹, respectively. Experimental results showed that pH 9 had a vital role in the adsorption process of all three types. Langmuir and Redlich-Petersen isotherm models were well fitted with experimental data. Also, the maximum adsorption capacity of CVD, MBD, and MVD to the desired composite was determined as 32.84 mg.g⁻¹, 31.81 mg.g⁻¹, and 31.15 mg.g⁻¹, respectively. In addition, the kinetic data of the removal process followed a pseudo-first order (PFO) kinetic model. Negative thermodynamic parameters were indicated that the process is spontaneous and exothermic. Finally, ad(de)sorption experiments' results showed that the synthesized nanocomposite adsorbent has an excellent ability to adsorb cationic dyes after several consecutive cycles.
... kJ/mol and 21.0-418.4 kJ/ mol, respectively [151]. Others propose that chemisorption are associated with values greater than 40.0 kJ/mol Pseudo-first-order, Pseudo-second-order ...
Bromophenol blue is a toxic triphenylmethane dye that is widely used in various industries. The dye-contaminated wastewater released from the industries results in substantial water pollution, causing several health problems and having severe negative consequences for the ecosystem. As a result, its toxic presence in environmental water is a cause for serious concern. Therefore, the removal of wastewater is vital to preserving environmental quality. The adsorption process stands out among several water treatment techniques due to its low cost, efficiency, simplicity, selectivity, and recyclability. Thus, several adsorbents have been applied for the treatment of bromophenol blue-contaminated water via the adsorption technique. This review presents the adsorption of bromophenol blue onto bio-based adsorbents such as biomass, activated carbon, and biochar as well as other potent materials like nanoparticles, polymers, and composite. The isotherm, kinetics, thermodynamics, and mechanism of the adsorption process were all discussed. We also considered the regeneration of the adsorbents and their reusability in the treatment process. Moreover, research gaps in many aspects were discovered, and future research proposals were offered.
... These findings imply that the pseudo second order kinetic model accurately predicted MO adsorption on 40-Hec over the pseudo first order model. MO adsorption was reported to follow the pseudo second order kinetic model on various adsorbents such as LVM [3], UiO-66-X (X = H, NH 2 , NO 2 ) [69], and modified commercial coffee waste (MCWs) [59]. ...
Hectorite modified with cetyltrimethylammonium bromide (CTAB) using a single-step
synthesis and modification produced an efficient adsorbent for water treatment.
Characterization analysis revealed that incorporating CTAB at 5-10 wt/wt increased the basal distances and the mesopore area of hectorite. The high concentration at 20-40 wt/wt deposited CTAB on the external surface of hectorite, consequently reducing the surface area. TGA-DTG analysis revealed that the surface-bound CTAB has lower thermal stability than the interlayered CTAB. CTAB-modified hectorite (40-Hec) showed the adsorption capacity of methyl orange at 164.28 mg/g, with 98.57% removal efficiency, significantly higher than hectorite. The adsorption of methyl orange followed the pseudo-second-order kinetic and the Sips models. The Sips isotherm was suitable to describe the adsorption mechanism by monolayer physisorption. For thermodynamic studies, parameters such as the Gibbs free energy (ΔG˚), the enthalpy (ΔH˚) and the entropy (ΔS˚) revealed that the adsorption of methyl orange on CTAB-modified hectorite is a spontaneous exothermic process and affected by the entropy of adsorption.
... The synthesis of UiO-66-TLA was based on a previously reported one-pot hydrothermal method, with slight modifications. (Nanthamathee and Dechatiwongse, 2021). Briefly, ZrCl 4 (0.3673 g) was dissolved in DMF (14.583 ml), and HCl (2.917 ml) was added, then the mixture was sonicated for 20 min first. ...
A novel metal-organic framework (MOF) UiO-66-TLA (UiO-66-Trimellitic Acid) was synthesized by one-pot method with trimellitic acid as modifier, which can effectively remove the basic dye Basic Blue 3 (BB3) in wastewater. Modification with carboxyl groups facilitates the adsorption of the cationic dye Basic Blue 3. The adsorption of BB3 by the modified UiO-66-TLA was significantly greater than that of its parent MOF. The adsorption capacity of the modified UiO-66-TLA for BB3 (234.23 mg g−1) was 93.2% higher than that of the original UiO-66-NH2 (121.24 mg g−1), this is closely related to the electrostatic interaction of -COOH in trimellitic acid. UiO-66-TLA was successfully synthesized as indicated by various characterization results. The adsorption kinetics conformed to the pseudo-second-order model, and the adsorption isotherm conformed to the Redlich-Peterson isotherm. This indicates that BB3 is a multi-parameter model of monolayer/multilayer arrangement on the adsorbent surface, and its rate-controlling step is chemisorption. The adsorption process was non-spontaneous and belonged to an endothermic reaction, in addition, it has great adsorption stability and regeneration The interaction of the modified UiO-66-TLA with BB3 was mainly affected by mechanisms, such as electrostatic interaction, π–π stacking as well as the abundant functional groups on UiO-66-TLA surface. These results demonstrate that UiO-66-TLA is an efficient, regenerable, water-stable material for the removal of BB3 in solution, with practical implications, suggesting its potential as a dye adsorbent.
... Adsorbents Intraparticle diffusion Elovich of adsorption, while a number greater than one indicates favorable adsorption. According to Table 5, MOFs adsorbents had a n value greater than one [70]. The Cr(VI) highest adsorption capacity on HKUST-1, ZIF-8, and UiO-66 is compared to each other adsorbents in Table 6. ...
Due to the limitation of a sole method for removal of hexavalent chromium (Cr(VI)) which unable to process higher concentrations and limited efficiency of removal. Thus, the integrated reduction and adsorption system was designed by combining microbial fuel cell (MFC) and adsorbent (MOF type HKUST-1, UiO-66, and ZIF-8) to remove Cr(VI). HKUST-1 showed the highest adsorption capacity and Cr(VI) removal percentages compared to other MOF types, reaching 78.616 mg/g and 96.551 % in 90 min (batch adsorption), respectively. In addition, the pseudo-2nd-order kinetic and Langmuir isotherm type matched well with the suggested adsorption mechanism based on the adsorption kinetics and isotherms analysis. On the other hand, the highest power density resulted from the simultaneous integration of MFC adsorption, namely 198 mW/m2, and the removal rate of 99.34 % at 75 mg/L Cr(VI) concentration owing to MOF simultaneously adsorbs by forming a coordinating covalent bond and reducing it with electron donor groups in the organic linker of the MOF. Several important factors influencing the reduction rate of Cr(VI) in the MFC adsorption integration were pH, the Cr(VI) concentration, and substrate at the anode. Moreover, the hydrodynamic effect (agitation) can also increase the performance of the MFC, due to an increase in current leading to a high Cr(VI) removal. Furthermore, the MFC-adsorption integration showed better stability up to five cycles for 35 days. Overall, combining adsorption and MFC for Cr(VI) removal provides promising potency to be explored and developed for the wastewater treatment process.
... The negative value of ΔG° between 25 and 55 °C suggests that the adsorption of CR molecules onto CrZnO is spontaneous and thermodynamically favorable. In addition, the value of ΔG 0 can be utilized to differentiate between chemisorption (− 400 to -80 kJ mol −1 ) and physisorption (− 20 to 0 kJ mol −1 ) processes [71]. In this study, all ΔG 0 values suggest the chemisorption process of CR molecules onto CrZnO nanoparticles. ...
Organic dyes, especially Congo red, are utilized primarily in the textile industry and consequently discharged into water resources that pollute aquatic environments. This study aims to investigate the fabrication of Cr-doped ZnO nanoparticles by sol–gel method to eliminate Congo red dye from wastewater. The obtained Cr-doped ZnO was characterized by scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, and Fourier transform infrared spectroscopy. The Cr-doped ZnO crystallizes within a hexagonal wurtzite structure with a BET surface area equal to 9.5 m². g⁻¹. It is found that the variation of dye concentration and pH influence the removal of Congo red by Cr-doped ZnO. Excellent efficiency of 155.52 mg.g⁻¹ is achieved under optimum operating conditions, i.e., the adsorbent dosage of Cr-doped ZnO (0.400 g/L), contact time of 110 min, and solution pH (7.00). Pseudo-second-order adsorption kinetics and Langmuir isotherm models best fitted Congo red adsorption onto Cr-doped ZnO. The Congo red adsorption mechanism is associated with the chemisorption and hydrogen bond, as indicated by the pH, isotherms, and Fourier transforms infrared spectroscopy studies. The examination of Cr-doped ZnO with other dyes (malachite green, crystal violet, basic fuchsin, methylene blue, and eriochrome black T) suggests the high adsorption capacity of Cr-doped ZnO towards malachite green, crystal violet, and basic fuchsin dyes compared with methylene blue and Eriochrome black T dyes. The findings demonstrate that Cr-doped ZnO nanostructures manifest excellent adsorption capability to remove organic dyes from aqueous solutions.
Graphical abstract
... MG molecules will be adsorbed if water molecules are being desorbed, that because water molecules have a lower molar volume than MG molecules, they are desorbed off the surface area in greater numbers. This produces a significant quantity of heat; the positive enthalpy value indicates the endothermic nature of the process [131] on the other side, negative enthalpies indicate that the adsorption process is exothermic. On the surface, the ΔH • value of molecules engaged in the adsorption process in the solution was reduced. ...
This comprehensive review focuses on the recent progress related to biochar applications as an efficient removal agent for
malachite green (MG) dye. Recently, biochar has been extensively employed as an effective adsorbent material through its
exceptional characteristics, such as cost-effectiveness, high porosity, large surface area, and mass production. Many strategies
are reported for biochar fabrication, including hydrothermal liquefaction and hydrothermal carbonization, pyrolysis,
and gasification. The reported technologies for biochar synthesis used to remove MG are covered and discussed in detail.
In addition, the key recent applications related to using different biochar adsorbents to remove MG are overviewed and discussed.
The drawbacks related to this topic as well as the current challenges and perspectives are highlighted.
... Chemical structures of various dyes employed.adsorption capacity for UiO-66, UiO-66-NO 2 , and UiO-66-NH 2 was measured to be 19, 11, and 27 mg/g, respectively(Nanthamathee and Dechatiwongse, 2021).Jeyaseelan et al. (Jeyaseelan and Viswanathan, 2021) fabricated La@BTC and Ce@BTC MOFs for superior fluoride adsorption. The synthesized La@BTC and Ce@BTC MOFs showed promising capacities of 4985 and 4930 mg/g, respectively. ...
Metal-organic frameworks (MOFs) are a promising class of porous nanomaterials in the field of environmental remediation. Ni-MOF and Fe-MOF were chosen for their advantages such as structural robustness and ease of synthesis route. The structure of prepared MOFs was characterized using FE-SEM, XRD, FTIR, and N2 adsorption-desorption. The efficiency of MOFs to remove organic model contaminants (anionic Alizarin Red S (ARS) and cationic malachite green (MG) and inorganic fluoride was studied. Fe-MOF and Ni-MOF adsorbed 67, 88, 6% and 32, 5, and 9% of fluoride, ARS, and MG, respectively. Further study on ARS adsorption by Fe-MOF showed that the removal efficiency was high in a wide range of pH from 3 to 9. Moreover, dye removal was directly increased by adsorbent mass (0.1–0.75 g/L) and decreased by ARS concentration (25–100 mg/L). The pseudo-first-order kinetic model and Langmuir isotherm model with a qmax of 176.68 mg/g described the experimental data well. The separation factor, KL, was in the range of 0–1, which means the adsorption process was favorable. In conclusion, Fe-MOF showed remarkable adsorption of organic and inorganic model contaminants.
... kJ/mol and 21.0-418.4 kJ/mol indicates the dominance of physisorption or chemisorption, respectively, in the overall process [87]. Thus, the ∆H o values obtained imply that the adsorption of both EBT and CB onto IBBC was dominated by chemisorption. ...
In a bid to develop efficient biochars, we prepared new biochar by the pyrolysis of Ipomoea batatas feedstock for the ultrasonic-aided adsorption of eriochrome black T (EBT) and celestine blue (CB) dyes. The characterisation of the Ipomoea batatas-derived biochar (IBBC) showed potent functional groups, good thermal stability, porous structure and a point of zero charge of 6.41. The pH of 2.0 and 7.0 was found to be optimum for the uptake of anionic EBT and cationic CB onto IBBC, respectively. A decrease in the surface area of IBBC from 96.35 m²/g to 48.43 m²/g and 32.11 m²/g was obtained after the adsorption of EBT and CB, respectively. Thermogravimetric analysis revealed high thermal stability of IBBC up to 350°C. The Energy dispersive X-ray (EDX) spectrum revealed carbon (52.6%), oxygen (24.5%) and potassium (7.1%) as the major component of the biochar. The elemental analysis showed carbon, hydrogen and nitrogen compositions of 55.4%. 2.6% and 1.2%, respectively. Moreover, a biochar yield of 36.2% was obtained. The adsorption of both dye molecules was well correlated by the Freundlich isotherm, supported by the Scatchard model analysis. Kinetics was well fitted to the film diffusion and pseudo-second-order models, while thermodynamics showed an endothermic and spontaneous dye uptake on IBBC. The adsorption capacity of the biochar for EBT and CB was 59.24 mg/g and 63.69 mg/g respectively. Percentage desorption of 87.5% for EBT and 82.3% for CB was achieved during regeneration of the dye-loaded biochar. Moreover, IBBC showed good potentials to be reused for adsorption. The results revealed the potentials of the novel biochar for efficient adsorption of both cationic and anionic dye species.
... These error functions are the statistical methods and are used to determine the difference between the experimental data and the predicted values. [49][50][51][52][53][54]53] The isotherm parameters and error functions values are given in Table 3. ...
In the present study, Powder Activated Carbon/Maghemite composite (MPCs) was used as an efficient adsorbent for the removal of a textile dye ‘Reactive Blue 19ʹ (RB19) from simulated textile wastewater containing auxiliary chemicals from textile production. The specific morphology, elemental analysis, specific surface area, identification of crystalline phases, magnetic specifications, and surface functional groups of the synthesized MPCs were investigated by using Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray (EDX), Brunaure–Emmett–Teller method (BET), X-ray Diffraction (XRD), Magnetization Saturation Measurement and Fourier Transmission Infrared (FTIR), respectively. The effects of the initial dye concentration, temperature, pH, and the MPCs dosage on the adsorption process were investigated. 0.2 g MPCS was found to be sufficient for the removal of 50 mg/L RB19 with 99.93% removal efficiency. The thermodynamic analysis showed that the adsorption of the RB19 by MPCs was an endothermic process. Eleven adsorption isotherm models were tested to understand the adsorption mechanism. The Vieth-Sladek isotherm model described the adsorption process more effectively among the tested isotherms (R² = 0.991, ERRSQ = 71.3, APE% = 0.172, X² = 0.882). The maximum adsorption capacity of the composite was predicted to be 105.5 mg/g by the Vieth-Sladek isotherm.
The development of new materials that have a high capacity to remove pollutants in water-based media is becoming increasingly important because of the serious contamination of water and the negative impact on biodiversity and public health. The presence of glyphosate in water, the most widely used herbicide worldwide, has triggered alerts owing to the collateral effects it may cause on human health. The main objective of the present study was to investigate the potential of the hybrid material MIL-53(Al)@RH for the adsorption of glyphosate in aqueous solution. The material was obtained following the methodology of MIL-53(Al) synthesis in the presence of hydrolyzed rice husk assisted by microwave. Batch adsorption experiments were carried out to evaluate the adsorbent dosage, pH0 solution effect, contact time, adsorbate concentration, and temperature effect. The results demonstrated that a maximum adsorption capacity of 296.95 mg g-1, at pH0 4 with a ratio of 0.04 g MIL-53(Al)@RH/50 mL of solution, was achieved in 30 min. The Avrami and pseudo-second order models appropriately described the adsorption kinetics and the equilibrium by Langmuir and Sips models. The enthalpy changes (ΔH°) determined propose an endothermic reaction governed by chemisorption, corroborating the kinetic and equilibrium settings. Hydrogen bonds, π*-π interactions, and complexation between the metal centers of MIL-53(Al) and the anionic groups of glyphosate were postulated to be involved as adsorption mechanisms. Finally, for practical application, MIL-53(Al)@RH was packed in a column for a fixed-bed test which revealed that the hybrid can remove glyphosate with an adsorption capacity of 76.304 mg L-1, utilizing 90% of the bed.
17 The integrated reduction and adsorption system was designed by combining microbial fuel 18 cell (MFC) and adsorbent (MOF type HKUST-1, UiO-66, and ZIF-8) to remove Cr(VI). 19 Compared to other MOF types, HKUST-1 had the highest adsorption capacity and Cr(VI) 20 removal percentage, reaching 78,62 mg/g in 90 minutes (batch adsorption). The pseudo-2nd-21 order kinetic and Langmuir isotherm types matched well with the suggested adsorption 22 mechanism based on the adsorption kinetics and isotherms analysis. Because the MFC and 23 adsorption methods were used concurrently, the highest power density was 198 mW per 24 square meter, with a removal rate of 99.34% at 75 mg/L of Cr(VI). Important factors 25 influencing the reduction rate of Cr(VI) in the MFC adsorption integration were pH, the 26 Cr(VI) concentration, and substrate at the anode. Furthermore, the hydrodynamic effect 27 (agitation) can improve MFC performance by increasing current, resulting in high Cr(VI) 28 removal. Electrons from the MFC system were used to start the process of reducing and 29 adsorbing Cr(VI) in the MFC-adsorption integration system. Then, protons from the anode 30 were sent through a proton exchange membrane to the cathode. In addition, the HKUST-1 31 simultaneously adsorbs by forming a coordinating covalent bond and reducing it with 32 electron donor groups in the HKUST-1 organic linker. 33
The contamination of environmental waters with heavy metals and radionuclides is increasing because of rapid industrial and population growth. The removal of these contaminants from water via adsorption onto metal nanoparticles is an efficient and promising technique to abate the toxic effects associated with these pollutants. Among metal nanoparticle adsorbents, zinc oxide nanoparticles (ZnONPs) have received tremendous attention owing to their biocompatibility, affordability, long-term stability, surface characteristics, nontoxicity, and powerful antibacterial activity against microbes found in water. In this review, we considered the adsorption of heavy metals and radionuclides onto ZnONPs. We examined the isotherm, kinetic, and thermodynamic modeling of the process as well as the adsorption mechanism to provide significant insights into the interactions between the pollutants and the nanoparticles. The ZnONPs with surface areas (3.93 to 58.0 m ² /g) synthesized by different methods exhibited different adsorption capacities (0.30 to 1500 mg/g) for the pollutants. The Langmuir and Freundlich isotherms were most suitable for the adsorption process. The Langmuir separation factor indicated favorable adsorption of all the pollutants on ZnONPs. The pseudo-second-order kinetics presented the best for the adsorption of the adsorbates with regression values in the range of 0.986–1.000. Spontaneous adsorption was obtained in most of the studies involving endothermic and exothermic processes. The complexation, precipitation, ion exchange, and electrostatic interactions are the probable mechanisms in the adsorption onto ZnONPs with a predominance of complexation. The desorption process, reusability of ZnONPs as well as direction for future investigations were also presented.
Adsorptive removal of aromatic diamines such as methylenedianiline (MDA) and p-phenylenediamine (PPD) was firstly investigated with nitro-functionalized metal-organic frameworks (MOFs, MIL-101(Cr)-NO2). The MIL-101(Cr)-NO2 showed much better performances in the removal of MDA and PPD, in both adsorption capacity and kinetics, than any other adsorbents. For example, MIL-101(Cr)-NO2 had a much higher maximum adsorption capacity for MDA (1111 mg·g⁻¹) than activated carbon (208 mg·g⁻¹) or a reported adsorbent (391 mg·g⁻¹). Based on experimental results, hydrogen bonding (especially, via the formation of a 6-membered ring (6-MR) between -NO2 of the adsorbent and -NH2 of the adsorbates) could be suggested as the main mechanism to interpret the noticeable adsorption of the diamines. Importantly, this is the first example to confirm that MOFs with nitro group can be a competitive adsorbent to remove organics composed of amino group, especially via making 6-MR through hydrogen bonding. Higher adsorption of MDA than that of PPD over MIL-101(Cr)-NO2 might be explained with π-π interaction between aromatic rings (π-lean aromatics of MOF and π-rich aromatics of the adsorbates). Moreover, MIL-101(Cr)-NO2 could be recycled after simple washing, suggesting the potential use of the MOF in adsorptive purification of contaminated water with organics with amino groups.
The accumulation of carbon dioxide (CO2) within enclosed spaces, along with volatile organic compounds, under certain humidity, temperature, and ventilation conditions is associated with detrimental human health symptoms such as fatigue. Color-based chemical sensing is a promising approach to detect CO2 levels relevant to indoor air quality through producing fast, quantifiable output visible to the naked eye. In a prior work, a colorimetric gas sensor was fabricated through synthesizing the metal-organic framework, ZIF-8, as the adsorbent, followed by post-synthetic mixing with a dye, phenol red (PSP), and primary amine, ethylenediamine (ED). While this sensor (termed PSP-ED/ZIF-8) maintained its structural integrity in atmospheric conditions and exhibited an increasing fuchsia-to-yellow color change with increasing CO2 levels in dry environment, the colorimetric response greatly suffered in the presence of humid CO2. In this work, a significantly improved colorimetric CO2 sensor (referred to as ED/PSP:ZIF-8) is accomplished through directly incorporating phenol red in the ZIF-8 metal and linker precursor solutions and then blending with ethylenediamine. MATLAB-generated color distributions and in-situ ultraviolet-visible (UV-Vis) spectroscopic studies quantitatively demonstrate an enhanced colorimetric gas response of ED/PSP:ZIF-8 compared to that of PSP-ED/ZIF-8 across an important range of CO2 for indoor air quality monitoring (500 – 3500 ppm) and across a range of humidity. The new sensor also exhibits high selectivity to CO2 compared to select volatile organic compounds, such as acetone and ethanol, which contribute to human health symptoms experienced indoors. The enhanced performance is attributed to the proposed incorporation of phenol red within ZIF-8, while maintaining the chemical stability of the MOF.
In this paper, we present the synthesis of [email protected]3O4–MoO3 binary composite were prepared through the facile hydrothermal process. The ultrasonic aided adsorption efficacy was evaluated by studying triphenylmethane dye's adsorption potential. The ultrasonic aided adsorption capacity towards crystal violet was 993.6 mg/g, which is remarkably higher and best fitted with the Langmuir isotherm model and followed pseudo-second-order kinetics. The electrochemical studies working electrode have been prepared with 80 wt% active material, 10 wt% carbon black, and 10% polyvinylidene difluoride to evaluate energy storage characteristics. The [email protected]3O4–MoO3 demonstrated an excellent specific capacitance of 40.94 F/g with better retention and stability, making it a potential cathode material for next-generation electrochemical energy storage devices.
In this review, metal-organic frameworks functionalized with nitro groups (MOF-NO2s) were analyzed, for the first time, in terms of their preparation and applications. MOF-NO2s were obtained by direct synthesis from nitro-functionalized linker precursors and by post-synthetic modification of a pristine MOF without a -NO2 group. Additionally, the applications of MOF-NO2s, specifically in adsorption and catalysis, were discussed. CO2 capture using MOF-NO2s was highly effective due to the polar nitro group which aided in quadrupole–dipole interactions. Furthermore, on account of the electron-withdrawing nitro group, MOF-NO2s were efficient in the adsorption of other gases, such as nitrogen. Similarly, MOF-NO2s were promising for the removal of hazardous organics from water and particulate matter from the air mainly due to the charge separation on the nitro group. MOF-NO2s could be very useful in catalysis that relies on the Lewis acidity because the electron-withdrawing nitro group can increase Lewis acidity. MOF-NO2s can be used in other applications, such as detection of H2S. Based on the analysis of the achievements thus far, the prospects of MOF-NO2s for further research were provided.
In recent years, antibiotics in aqueous solutions have drawn extensive attention due to their harmful effect on human health and the environment. In this study, efficient and rapid adsorption of two antibiotics, including tetracycline (TC) and cefazolin (CFZ) on synthesised montmorillonite (Mt)/nano zero-valent iron (nZVI)/graphene oxide (GO) from aqueous solutions was studied. The prepared adsorbent was characterised by scanning electron microscope (SEM), energy dispersive X-Ray (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and vibrating sample magnetometer (VSM). One-factor-at-a-time (OFAT) method was used to optimise the experimental factors. The maximum removal percentage was achieved at pH of 7, an adsorbent dosage of 0.4 g, contact time of 7 min = TC and 10 min = CFZ, initial concentration of 5 mg L⁻¹, and a temperature of 298 K. The evaluation of isotherm models indicated that the Langmuir isotherm with a coefficient of determination (R²) value of 0.9992 for both antibiotics was selected as the best fitting model to describe the adsorption process. The maximum adsorption capacities (qmax) of Mt-nZVI-GO were obtained at 43.24 mg g⁻¹ for TC and 20.36 mg g⁻¹ for CFZ. Furthermore, the pseudo-second-order (PSO) kinetic model fitted well for TC (R² = 0.9937) and CFZ (R² = 0.9997). Thermodynamic parameters, i.e. adsorption Gibbs free energy (ΔG⁰), standard enthalpy (ΔH⁰), and standard entropy (ΔS⁰) were estimated. It was found that the adsorption had spontaneous and exothermic in nature. The results revealed that Mt-nZVI-GO could be used as a simple, efficient, and eco-friendly adsorbent for the simultaneous removal of contaminants in aqueous media.
Hierarchically porous activated Starbons® derived from starch are found to make excellent adsorbents for methylene blue, even in the presence of other dyes and inorganic salts, highlighting their potential to be used in water purification. The optimal material (S950C90) has a methylene blue adsorption capacity (891 mg g⁻¹) almost nine times higher than that of unactivated S800 and four times higher than that of commercial activated carbon at 298 K. The adsorption of methylene blue onto optimal materials (S950C90 and S800K4) reaches equilibrium within 5 minutes. Adsorption data for all the adsorbents show a good fit to the Freundlich isotherm which allows the Gibbs free energies of adsorption to be calculated. The adsorption capacities increase as the pH of the methylene blue solution increases, allowing the dye to be desorbed by treatment with acidic ethanol and the Starbon® materials reused. Porosimetry and SEM-EDX imaging indicate that methylene blue adsorbs throughout the surface and completely fills all the micropores in the Starbon® adsorbent. The methylene blue adsorption capacities show excellent correlations with both the BET surface areas and the micropore volumes of the materials.
The removal of organic pollutants was examined by new zeolitic imidazolate [email protected] multi-walled carbon nanotubes (ZIF-8/MWCNTs-COOH) nanoadsorbents, which were prepared via controlling the reaction sequence of MWCNTs-COOH with the precursors of ZIF-8. Structural morphology and chemical composition characterizations confirmed the successful preparation of ZIF-8/MWCNTs-COOH nanoadsorbents. The obtained samples manifested a preferable adsorption capacity for Congo red with the maximum adsorption capacity of 1185.58 mg g–1 with an adsorption removal rate of 97.93% at equilibrium adsorption. Further analyses indicated that the adsorption process conformed to the pseudo-second-order kinetic model and Langmuir adsorption isotherm. The thermodynamic analyses were depicted as endothermic, entropy-increasing, and spontaneous. The effects of pH value, interfering ions, and dosage on the adsorption properties are systematically explored. The nanoadsorbent can be expediently reused for eight cycles without a prominent reduction in adsorption activity. The improved performance and high reusability can be ascribed to the increasing specific surface, the presence of electrostatic interaction, hydrogen bonding, and π–π interaction between ZIF-8/MWCNTs-COOH and organic molecules. In addition, the prepared composites also showed a better adsorption performance for tetracycline with the equilibrium adsorption capacity of 471.22 mg g–1 compared to pure ZIF-8 and MWCNTs-COOH.
The agricultural crops are recognized as inexpensive and abundant biomaterials. Their use for the biosorption of pollutants has attracted great concern. Herein, powdered pergularia tomentosa fruit, a locally available biomaterial, was characterized and used for the biosorption of methylene blue in batch mode. FT–IR spectroscopy revealed that the hydroxyls (–OH) were the main groups responsible for the biosorption of methylene blue. SEM depicted a rough and heterogeneous surface with the presence of some cavities. The thermal decompositions of pergularia fruit were observed at 233 °C and 393 °C which were ascribed to the decomposition of cellulose and non-cellulose constituents, and to the depolymerization process. The effect of the operational conditions such as pH, time, dye concentration, adsorbent dose, temperature, and ionic strength on the biosorption performance was carried out. Several classical and statistical models were used to fit the experimental data. The monolayer model with two energies was the most appropriate. This statistical model revealed that two functional groups of the pergularia tomentosa fruit surface contributed to the adsorption of methylene blue. Each group is characterized by a particular energy and a stoichiometric number. The pergularia tomentosa fruit could be anchored by one or more dye molecules per site. The adsorption energy is lesser than 20 kJ/mol. The results confirmed a physio-sorption process. The maximum biosorption was 152 mg/g. The ionic strength disfavored the biosorption system. The results demonstrated that pergularia tomentosa fruit is an attractive candidate for removing cationic dyes from contaminated water.
Dye wastewater pollution is a pervasive problem that hinders sustainable development. Adsorption is a particularly important technique for treating dye wastewater because of its low cost, high efficiency, and operational ease. Moreover, metal-organic frameworks (MOFs) are considered promising materials for the removal of toxic dyes from industrial wastewater because of their exceptionally high porosity, abundant active sites, and receptiveness to functional modification. This review highlights recent advancements in functionally modified MOFs (FM-MOFs) fabricated as adsorbents for effective organic dye removal, and classifies the FM-MOFs based on various modification strategies. In particular, the effects of these functional modification strategies on the adsorption driving forces between the FM-MOF adsorbents and organic dyes are systematically examined. This journal is
A procedure was developed for in situ preparation of a composite material consisting of graphene oxide and a copper-containing metal-organic framework by the reaction between 1,3,5-benzenetricarboxylic acid, graphene oxide, and copper sulfate. The materials obtained were examined by X-ray diffraction, IR spectroscopy, scanning electron microscopy, and energy-dispersive X-ray microanalysis. The composite was used for removing organic dyes Congo Red and Methylene Blue from their aqueous solutions. The samples containing 20% graphene oxide showed the highest adsorption rate. The structure of the composite does not change in the course of the sorption.
Here in, we present a review on the adsorption of dyes and pharmaceuticals from water onto UiO (Universitetet i Oslo) metal-organic frameworks (MOFs). The MOFs possessed distinctive and promising properties, uncommon to other conventional adsorbents, such as ultra-porosity and remarkable stability, worthy of being super adsorbents for pollutants adsorption from water. They have shown prodigious performance towards the adsorption of both dyes and pharmaceuticals from the aqueous medium at both lower and higher concentrations. The vast adsorption efficiency of the MOFs is heavily attributed to their high Brunauer-Emmett-Teller (BET) surface areas and pore volume, providing abundant adsorption sites for the pollutants. The binding affinity of the MOFs for the dyes and pharmaceuticals adsorption has been elucidated by the different interactions such as electrostatic, hydrogen bonding and π-π stacking, often dictated by the surface charged of the target pollutant and the zeta potential on the MOF’s surface. The MOFs have shown higher efficiency even in multi-component systems. The ease for the regeneration of the MOFs using common organic solvents and the impressive performance for repeated cycles has been outstanding. The MOFs were thus regarded as superior over conventional porous adsorbents and commendable for large scale applications.
Removing hazardous organics from water or fuel is important for our clean environment; adsorption over porous materials has been a competitive means to eliminate such organics. Here, the adsorption or removal of hazardous organics with metal-organic framework-based adsorbents was explained, especially adsorption that relies on hydrogen bonding (H-bonding). The bonding details (direction, quantitative contribution, importance of 6-membered rings, and characterizations to support H-bonding) and improved performance via H-bonding were investigated. Finally, prospects for further development or research in the relevant fields were suggested.
A novel multi-residue method, magnetic solid-phase extraction combined with LC–MS/MS, was proposed for simultaneous enantiomeric determination of eight chiral pesticides in water and fruit juices. Fe3O4@[email protected] was firstly used to extract and enrich pesticides, showing excellent adsorption capacity, which was proved by adsorption kinetic and thermodynamic experiments. Multiple extraction parameters were optimized by Plackett-Burman and Box-Behnken design. Under optimized conditions, good linearity (1.0–200 ng L⁻¹, R² ≥ 0.9953) for all analytes, detection limits (0.10 to 0.35 ng L⁻¹), quantitation limits (0.35 to 1.00 ng L⁻¹), recoveries (83.68–95.99%), and precision (intra-day RSD ≤ 7.06%, inter-day RSD ≤ 9.40%) were obtained, meeting the requirements of pesticides residues analysis. It is worth mentioning that eight chiral pesticides can be separated quickly within 19 min. The above results indicate that the proposed method with satisfactory sensitivity and accuracy has the potential for routine analysis of chiral pesticide residues in aqueous samples.
The metal-organic frameworks (MOFs) as emerging materials have attracted worldwide attention. In this study, a novel strategy by blending classic MOFs material UiO-66-NH2 to efficiently enhance the thermal stability and thermal aging resistance of silicone rubber (SR) was proposed. The experimental results indicated that very low dosage (0.25–1.5 part) of UiO-66-NH2 addition could effectively increase the thermal-oxidative stability of SR, which was proved by that the values of T5 (temperature at 5% weight loss) and Tm (the maximum thermal decomposition rate temperature) of SR were greatly increased by 43.4 °C and 97.9 °C, respectively. Moreover, the retention rate of elongation at break and tensile strength of SR with 1.5 part UiO-66-NH2 could remain about 72% and 57% after 288 h treatment in 210 °C. The possible heat resistance mechanism was explored by processing torque (PT) and thermogravimetry-mass spectrometry (TG-MS), whose results suggested that even very low addition of UiO-66-NH2 could efficiently inhibit degradation of SR chains and obstruct heat transfer due to its low thermal conductivity. This study provided a novel strategy to enhance thermal stability of rubber materials, and might open up new filed for polymer material processing.
Metal-organic framework (MOF) membranes with sub-nanometer channels have great potential in molecule selective transport, but the scalable and facile fabrication of flexible and thin membranes from stable MOF structures is difficult, which is the key to realizing practical applications. In this work, stable and ultra-small MOF nanoparticles act as "ordered porous monomers"and are interfacially polymerized with organic monomers into ultra-thin and flexible membranes. An ∼150 nm thin MOF active layer can be produced rapidly (<10 minutes) and economically (∼30 USD m-2) on a commercial polymer substrate. With their uniform pore size and thin membrane thickness, the membranes possess a long-lasting dye rejection rate (99.8%) and high water permeance (up to 55.9 L m-2 h-1 bar-1), which is 30 times higher than that of commercial DK nanofiltration membranes. Remarkably, the scalable and stable membrane can maintain the superior separation performance after being rolled up 20 times with a curvature of 200 m-1, suggesting that the flexible membrane could be used to construct a spiral wound membrane module. The strategy adopted here has been extended to other crystalline porous materials such as metal-organic cages for flexible and thin membrane fabrication.
Dye molecules are one of the most hazardous compounds for human and animal health and the excess intake of these materials can create toxic impacts. Several studies show the practicality of the adsorption process for dye uptake from wastewaters. In recent years, various adsorbents were used to be efficient in this process. Among all, polymeric adsorbents demonstrate great applicability in different environmental conditions and attract many researchers to work on them, although there is not enough reliable and precise information regarding these adsorbents. This study aims to investigate some influential parameters such as their type, physical properties, experimental conditions, their capacity, and further modeling along with a comparison with non-polymeric adsorbents. The influence of the main factors of adsorption capacity was studied and the dominant mechanism is explained extensively.
Characterization of the guest-host interactions and the heterogeneity of porous materials is essential across the physical and biological sciences, for example for gas sorption and separation, pollutant removal from wastewater,...
High-silica zeolites have been found to be effective adsorbents for the removal of organic micro-pollutants (OMPs) from impaired water, including various pharmaceuticals, personal care products, industrial chemicals, etc. In this review, the properties and fundamentals of high-silica zeolites are summarised. Recent research on mechanisms and efficiencies of OMP adsorption by high-silica zeolites are reviewed to assess the potential opportunities and challenges for the application of high-silica zeolites for OMP adsorption in water treatment. It is concluded that the adsorption capacities are well-related to surface hydrophobicity/hydrophilicity and structural features, e.g. micropore volume and pore size of high-silica zeolites, as well as the properties of OMPs. By using high-silica zeolites, the undesired competitive adsorption of background organic matter (BOM) in natural water could potentially be prevented. In addition, oxidative regeneration could be applied on-site to restore the adsorption capacity of zeolites for OMPs and prevent the toxic residues from re-entering the environment.
In this report, we present a simple, swift mechanochemical synthesis of metal-organic frameworks (MOFs) using a kitchen grinder. By adopting this tool, we could synthesize ZIF-8, CuBTC and MIL-100(Fe) in multi gram-scale and successfully employed MIL-100(Fe)-KG for the efficient (ca. 98%) removal of organic dye (methylene blue) from aqueous solution. Indeed, we demonstrated the significance of pore window for effective dye adsorption by comparing the adsorption behaviour of ZIF-8-KG and MIL-100(Fe)-KG. We believe that this approach could be of economic interest towards the greener synthesis of porous adsorbents for waste-water treatment.
Metal–organic frameworks (MOFs) are an emerging class of porous materials with potential applications in gas storage, separations, catalysis, and chemical sensing. Despite numerous advantages, applications of many MOFs are ultimately limited by their stability under harsh conditions. Herein, the recent advances in the field of stable MOFs, covering the fundamental mechanisms of MOF stability, design, and synthesis of stable MOF architectures, and their latest applications are reviewed. First, key factors that affect MOF stability under certain chemical environments are introduced to guide the design of robust structures. This is followed by a short review of synthetic strategies of stable MOFs including modulated synthesis and postsynthetic modifications. Based on the fundamentals of MOF stability, stable MOFs are classified into two categories: high-valency metal–carboxylate frameworks and low-valency metal–azolate frameworks. Along this line, some representative stable MOFs are introduced, their structures are described, and their properties are briefly discussed. The expanded applications of stable MOFs in Lewis/Brønsted acid catalysis, redox catalysis, photocatalysis, electrocatalysis, gas storage, and sensing are highlighted. Overall, this review is expected to guide the design of stable MOFs by providing insights into existing structures, which could lead to the discovery and development of more advanced functional materials.
In order to decisively determine the adsorption selectivity of zirconium MOF (UiO-66) towards anionic versus cationic species, the adsorptive removal of the anionic dyes (Alizarin Red S. (ARS), Eosin (E), Fuchsin Acid (FA) and Methyl Orange (MO)) and the cationic dyes (Neutral Red (NR), Fuchsin Basic (FB), Methylene Blue (MB), and Safranine T (ST)) have been evaluated. The results clearly reveal a significant selectivity towards anionic dyes. Such an observation agrees with a plethora of reports of UiO-66 superior affinity towards other anionic species (Floride, PO43 −, Diclofenac sodium, Methylchlorophenoxy-propionic acid, Phenols, CrO42 −, SeO32 −, and AsO4⁻). The adsorption process of ARS as an example has been optimized using the central composite design (CCD). The resultant statistical model indicates a crucial effect of both pH and sorbent mass. The optimum conditions were determined to be initial dye concentration 11.82μg·g− 1, adsorbent amount 0.0248 g, shaking time of 36 min and pH 2. The adsorption process proceeds via pseudo-second order kinetics (R² = 0.999). The equilibrium data were fit to Langmuir and Tempkin models (R² = 0.999 and 0.997 respectively). The results reveals an exceptional removal for the anionic dye (Alizarin Red S.) with a record adsorption capacity of 400 mg·g− 1. The significantly high adsorption capacity of UiO-66 towards ARS adds further evidence to the recently reported exceptional performance of MOFs in pollutants removal from water.
Methylene blue color is a cationic dye which is used in textile industry. Health effects of methylene blue dye discharge into the environment is including toxicity, high color, reduced light penetration in water, high stability, and low degradation capability. So, removing it from the environment is extremely important. The aim of this study was to synthesize Uio-66 MOFs used for adsorption of methylene blue from synthetic sample. The synthesized UiO-66 MOFs were characterized by using XRD, FE-SEM, EDAX, and BET analyses. Various parameters were evaluated such as pH, initial MB concentration, reaction time, and adsorbent dose. The findings showed that the sizes of Uio-66 crystals were between 153 and 213 nm. Total pore volume, BET, and Langmuir surface area were found to be 657, 906 m² g⁻¹, and 0.446 m³ g⁻¹, respectively. Zeta potential of Uio-66 was equal to 6. As a result, at higher than zeta potential point, methylene blue adsorption on Uio-66 is favorable. Maximum adsorption has been achieved at the pH = 9. The maximum adsorption capacity of Uio-66 for methylene blue was 91 mg/g. Optimum dose of Uio-66 was 0.4 g L⁻¹ for methylene adsorption. The Langmuir I isotherm was a fit model to describe the adsorption isotherm. Pseudo-first-order kinetic model was a fit model to describe the adsorption kinetic of MB on Uio-66. The Uio-66 MOF is a promising adsorbent in the adsorption of methylene blue from aqueous solution.
In recent years, the presence of a group of contaminants, termed as emerging contaminants (ECs) has been recognized as significant water pollutants that have adverse effects on human and wildlife endocrine systems. Natural attenuation and conventional treatment processes are not capable of removing these micropollutants which are reported to bioaccummulate in macro invertebrates, other organisms in the aquatic food web and humans. An in-depth review of the state-of-the-art technologies available to remove emerging contaminants (ECs) in water was undertaken. The results of the review show that the majority of the research in recent years has focused on using phase-changing processes, including adsorption in different solid matrices and membrane processes, followed by biological treatment and advanced oxidation processes. This paper focuses on the type of EC being removed, the conditions of the process and the outcomes achieved. The main trends in the field are also highlighted along with perceptive comments and recommendations for further developments as well as the identification of the current knowledge gaps and future research directions related to the application of these technologies for water treatment and restoration.
Zirconium based metal organic frameworks (Zr-MOFs) have become popular in engineering studies due to their high mechanical stability, thermostability and chemical stability. In our work, by using a theoretical kinetic adsorption isotherm, we can exert MOFs to an acid dye adsorption process, experimentally exploring the adsorption of MOFs, their external behavior and internal mechanism. The results indicate their spontaneous and endothermic nature, and the maximum adsorption capacity of this material for acid orange 7 (AO7) could be up to 358 mg·g⁻¹ at 318 K, estimated by the Langmuir isotherm model. This is ascribed to the presence of an open active metal site that significantly intensified the adsorption, by majorly increasing the interaction strength with the adsorbates. Additionally, the enhanced π delocalization and suitable pore size of UiO-66 gave rise to the highest host-guest interaction, which further improves both the adsorption capacity and separation selectivity at low concentrations. Furthermore, the stability of UiO-66 was actually verified for the first time, through comparing the structure of the samples before and after adsorption mainly by Powder X-ray diffraction and thermal gravimetric analysis.
The metal–organic frameworks UiO-66 with amine functional groups were synthesized by microwave irradiation, their structures and properties were characterized. The results show that NH2-UiO-66 can be prepared quickly and well-crystallized by microwave-assisted method within 15 min. The amine-functionalized UiO-66 was octahedral crystals of well defined sizes (500–900 nm) and had a high specific surface area about 924.37 m2 g−1 and micropore range from 2.0 to 11 nm. The amine-functionalized UiO-66 was thermally stable up to 540 °C stability and exhibited a good combination of methylene blue adsorption. The maximum adsorption capacity reached up to 203.95 mg g−1. The kinetics and equilibrium of the adsorption process were found to follow the pseudo-second-order kinetic and Langmuir adsorption model, respectively.
In this paper, MIL-53 (Fe), was synthesized and the adsorption interaction between this MOF and methyl red (MR) in an aqueous solution was studied. The structural characteristics, surface area, and thermal analysis of the synthesized MIL-53 (Fe) was carried out using XRD, TGA, TEM, and BET methods. The effects of the parameters such as initial concentration, contact time, adsorbent dosage, and temperature on the adsorption capacity were investigated for the determination of the best fit adsorption isotherm, adsorption kinetics, adsorption thermodynamics, and equilibrium time. It was found that the adsorption kinetics obeyed the pseudo-second-order kinetic model and an intraparticle diffusion model was also applied to understand the adsorption mechanism. The Langmuir and Freundlich adsorption isotherm models were also investigated. The results of the adsorption thermodynamics revealed that the adsorption of MR by selected MOF was a spontaneous and exothermic process. MIL-53 (Fe) opens its pores only in the presence of guest molecules. Its flexible structure leads to high adsorption capacities for MR.
Among the large family of metal-organic frameworks (MOFs), Zr-based MOFs, which exhibit rich structure types, outstanding stability, intriguing properties and functions, are foreseen as one of the most promising MOF materials for practical applications. Although this specific type of MOF is still in its early stage of development, significant progress has been made in recent years. Herein, advances in Zr-MOFs since 2008 are summarized and reviewed from three aspects: design and synthesis, structure, and applications. Four synthesis strategies implemented in building and/or modifying Zr-MOFs as well as their scale-up preparation under green and industrially feasible conditions are illustrated first. Zr-MOFs with various structural types are then classified and discussed in terms of different Zr-based secondary building units and organic ligands. Finally, applications of Zr-MOFs in catalysis, molecule adsorption and separation, drug delivery, and fluorescence sensing, and as porous carriers are highlighted. Such a review based on a specific type of MOF is expected to provide guidance for the in-depth investigation of MOFs towards practical applications.
In our efforts toward the rational design and systematic synthesis of porous 3D MOFs, three 3D frameworks of Zn-MOFs ([Zn(BDC)(TIB)]·3H2O (Zn-MOF-1) (TIB = 1,3,5-tri(1H-imidazol-1-ly) benzene and H2BDC = 1,4-dicarboxybenzene), [Zn(BDA)(TIB)2/3]n (Zn-MOF-2) (H2BDA = 4,4′-biphenyl-dicarboxylic acid) and [Zn3(BDC)2(BDA)(TIB)2]n (Zn-MOF-3)) were successfully synthesized, based on different multicarboxylate ligands through solvothermal reactions. The resulting MOFs show similar 3D structures with different pore sizes which lead to distinct selective adsorption for organic dyes. Remarkably, Zn-MOF-1 exhibits an excellent capacity to adsorb CR (congo red) with high selectivity, and it maintains an almost identical adsorption performance after being recycled several times.
In this study UiO-66 and UiO-66-NH2 were synthesized by solvothermal method. The effect of preparation conditions on the quality of UiO-66-NH2 was studied. The obtained material has been characterized by x-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimatric analysis (TGA), scanning electron microscopy (SEM) and nitrogen physisorption measurements (BET). The CO2 and CH4 physisorption measurements were carried out using a high pressure volumetric analyzer (Micromeritics HPVA—100). The results showed that the UiO-66-NH2 of ball shape crystalline had been obtained and characterized by high surface area (BET) up to 876 m2 g−1, specific volume 0.379 cm3 g−1, pore radius 9.5 Å and thermal stability up to 673 K, respectively. The experiments indicated that in comparison with UiO-66 the addition of NH2 is able to increase the CO2 and CH4 storage capacity at 1 bar and 303 K twice from 28.43 cm3 g−1 up to 52 cm3 g−1 and from 6.68 cm3 g−1 to 11.1 cm3 g−1, respectively.
A facile and efficient strategy for the preparation of a hybrid magnetic metal-organic framework HKUST-1 via chemical bonding approach was reported. The composite features both magnetic separation characteristic and high porosity of MOF, making it an excellent adsorbent for removal of hazardous anionic Congo red dye from effluents.
In this paper, a microwave-assisted method in the presence of an additive has been employed to quickly and prepare UIO-66 (MWHAc-UIO-66) in high yield. The microwave/additive method gives rise to a full octahedral morphology of ~250 nm particles and a highest surface area 1533.53 m2 g−1, which is confirmed by the surface area of MWBA-UIO-66 (1661.01 m2 g−1), prepared with benzoic acid as the additive. The adsorption results for a low-concentration of acid chrome blue K show that MW-UIO-66 and MWHAc-UIO-66 have excellent adsorption abilities (~98%), while HHAc-UIO-66 is also satisfactory (~85%), which are far better than activated carbon. Moreover, the saturated adsorption amount of acid chrome blue K for MWHAc-UIO-66 can be up to ~15%. The adsorption of different dyes shows that MWHAc-UIO-66 is attractive to charged dyes. Reusability experiments indicate that sulfuric acid can facilitate dye desorption from MWHAc-UIO-66 instead of a base or salt.
Presently, Malaysia is the third largest rubber producer in the world, whereby the rubber industry is an economically and socially significant industry. Rubber industry consumes large volumes of water, uses chemicals and other utilities and produces enormous amounts of wastes and effluent. Discharge of untreated rubber effluent to waterways resulted in water pollution that affected the human health. With a new global trend towards a sustainable development, the industry needs to focus on cleaner production technology, waste minimization, utilization of waste, resource recovery and recycling of water. The present work aims at highlighting various technologies that currently have been used for treatment of rubber effluent in Malaysia. The work introduces the basis of these processes including their benefits and also problems. It also adheres to the future trends of rubber effluent treatment in Malaysia by reviewing various treatment technologies for natural rubber industry implemented by Thailand, the world largest rubber producer. These new and effective effluent treatment methods would minimize environmental pollution of rubber industry and bring it to become sustainable and environmental friendly.
Advanced oxidation processes (AOPs) constitute important, promising, efficient, and environmental-friendly methods developed to principally remove persistent organic pollutants (POPs) from waters and wastewaters. Generally, AOPs are based on the in situ generation of a powerful oxidizing agent, such as hydroxyl radicals (•OH), obtained at a sufficient concentration to effectively decontaminate waters. This critical review presents a precise and overall description of the recent literature (period 1990–2012) concerning the main types of AOPs, based on chemical, photochemical, sonochemical, and electrochemical reactions. The principles, performances, advantages, drawbacks, and applications of these AOPs to the degradation and destruction of POPs in aquatic media and to the treatment of waters and waste waters have been reported and compared.
Many chemicals used in modern printing processes are either toxic or difficult to decompose, which results in the production of complicated and refractory printing wastewater. In this study, an electrocatalytic technology with different catalytic electrodes was employed to treat a real printing wastewater, and the production rates of hydroxyl radicals were determined. The results indicate that under a voltage gradient of 11 V cm−1, the production concentration of hydroxyl radicals by various electrodes followed a decreasing order of TiO2 > DSA (dimensional sustainable anode with IrO2) > graphite, with the values of 8.21 × 10−3, 5.24 × 10−3, and 0.86 × 10−3 M, respectively. A lower wastewater conductivity could lead to a greater electric voltage thus contributing to a higher removal efficiency of TOC and chroma. At a current density of 50 mA cm−2 and using one pair of electrodes (IrO2 + stainless steel), the TOC and chroma removal efficiencies reached 71% and 53% after 60 min treatment. Under the same operation conditions but using two pairs of electrodes, the removal efficiencies of TOC and chroma were increased to 75% and 82%, respectively. The removal efficiencies of TOC and chroma could be further raised to 90% and 92% if the electrocatalytic effluent was polished by powder activated carbon absorption.
Initial assessment of industrial structure and wastewater characteristics is important for successful environmental management in an industrial district. This is particularly important for the cases where highly polluting industries such leather tanners are of concern. In this study, Biga Leather Tanners District was evaluated. The process characteristics, wastewater amounts, wastewater quality and their variations with time were defined. The district housed 46 tanning plants, processing mainly sheepskins with a total capacity of 66.5 tons skin per day. Process profile was prepared and checked with experimental data. Chemical treatability experiments were conducted to assess the pretreatment alternatives. Chemical precipitation preceded by catalytic air oxidation of sulfide was found to be an optimum pretreatment system providing COD and TKN removals up to 80% together with complete chromium removal, Results of the study were evaluated and discussed.
MIL-100(Fe) shows large adsorption uptakes for both MO and MB,while MIL-100(Cr) can selectively adsorb MB from a MO/MB mixture.This work demonstrates that MOFs are promising adsorbents for dye capture and highlights that the framework metal ions replacement is an efficient way to tailor MOFs for different applications in liquid separation.
A record-high HCHO capture capacity, reaching 49 mg/g, is achieved in about ten minutes, on the defective NH2-UiO-66(Zr) nano-octahedra. The adjacent bifunctional base/acid catalytic centers significantly facilitate the efficient HCHO...
Decontamination of air or other gas streams loaded with low VOC concentrations is a prevalent task for adsorption using zeolites. Emphasizing the importance of adsorber selection, several zeolites varying in type, Si/Al ratio and provider were tested for toluene as representative organic target compound and water as adsorbate both in single and competing adsorption studies. In some cases, the toluene breakthrough is mainly caused by water-driven desorption. It was shown that for adsorption capacity, kinetics and competition behavior not only type and Si/Al ratio of the zeolite are important but also producer-specific parameters such as crystallinity, binder type and content which are usually not explicitly documented. This study offers a basis for the selection of adsorber materials for treatment of gas streams with significant water contents.
In this paper, the treatability of strong wastes originating from an organic chemicals industry was studied. Literature data were evaluated to assess the applicability of conventional and advanced methods of treatment to highly concentrated wastewaters. A detailed treatability study was conducted on the wastewater, which was provided from a small-scale polyester manufacturing plant. The manufacturing process involved only esterification reactions, generating a wastewater with a COD content of over 200,000 mgl−1. The applicable treatment methods to be tested were determined as biological treatment of activated sludge process with low organic loading and chemical oxidation with H2O2. Results of the biological treatability study indicated that 80% COD removal could be obtained with 10 days retention time, provided that the system was fed with a 1/100 diluted raw wastewater. Chemical oxidation of raw wastewater with H2O2 in acid conditions and using ferric chloride as catalyst yielded 70% COD removal. However, the dosage required to obtain this efficiency was about 1 kg H2O2 per m3 of wastewater. With these applications the wastewater was treated to yield a COD of lower than 2000 mg/l. Results of the study were discussed and evaluated considering complexity and cost of treatment.
A highly water stable metal-organic framework (MOF) based on zirconium, i.e. UiO-66, was synthesized and then employed to adsorptive removal of an anionic dye, methyl orange (MO), and a cationic dye, methylene blue (MB), from aqueous solution. In this work, for the first time, the long term stability of UiO-66 in water was investigated for 12 months. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and N2 adsorption/desorption analysis were employed to monitor the textural alteration of UiO-66 during water aging. The results indicated that the structure of UiO-66 was mostly retained and its adsorption capacity toward dyes exhibited minor loss after long term water aging. Experimental data showed that adsorption capacity of UiO-66 toward MO was higher than that of MB, particularly at acidic and neutral environments, due to its stronger electrostatic attraction and π-π stacking. However, the adsorption capacity of UiO-66 changed with pH value of solution due to the alteration of electrostatic interactions caused by the change in zeta potential of the adsorbent. Thermodynamic analysis exhibited that the adsorption of both dyes on UiO-66 was spontaneous. Adsorption of MO on UiO-66 was dominated by enthalpy effects and exhibited stronger interaction compared with MB, while entropy effects governed the adsorption of MB. The adsorption kinetics of UiO-66 was described by pseudo-second-order and Freundlich isotherm model exhibited very good fit with adsorption data. Eventually, it was shown that UiO-66 demonstrated suitable reusability and kept mostly its initial structure as well as adsorption capacity after four consecutive adsorption-desorption experiments.
This study was undertaken to evaluate the effects of mixing BDC-NO2 and BDC-NH2 linkers in the synthesis of Zr-based metal organic frameworks (Zr-MOFs) on their adsorption and separation of CO2 and CH4. UiO-66 with single or binary -NO2 and -NH2 samples were synthesized under solvothermal conditions and activated by solvent exchanging using methanol. Structural analyses of the materials were conducted using FTIR, XRD, TGA, SEM, ¹HNMR and N2 adsorption/desorption techniques and adsorption of CO2 and CH4 at high pressures and different temperatures (273 and 298 K) was investigated. It was found that UiO-66-NH2 exhibited higher CO2 and CH4 adsorption capacities than those of UiO-66-NO2. Addition of -NH2 functional group in UiO-66-NO2 could enhance CO2 and CH4 adsorption due to the extra CO2 adsorption sites of -NH2 functional groups. Addition of -NO2 functional group to UiO-66-NH2 at a low loading could also increase CO2 and CH4 adsorption, however, a high loading of NO2 functional group to UiO-66-NH2 would result in decreased adsorption.
Herein, we report the synthesis and characterization of Ce(III)-doped UiO-66 nanocrystals, revealing their potential to efficiently remove organic dyes such as methylene blue (MB), methyl orange (MO), Congo red (CR), and acid chrome blue K (AC) from aqueous solutions. Specifically, the room-temperature adsorption capacities of Ce(III)-doped UiO-66 equaled 145.3 (MB), 639.6 (MO), and 826.7 (CR) mg g–1, exceeding those reported for pristine UiO-66 by 490, 270, and 70%, respectively. The above behavior was rationalized based on zeta potential and adsorption isotherm investigations, which revealed that Ce(III) doping increases the number of adsorption sites and promotes π-π interactions between the adsorbent and the adsorbate, thus improving the adsorption capacity for cationic and anionic dyes and overriding the effect of electrostatic interactions. The obtained results shed light on the mechanism of organic dye adsorption on metal-organic frameworks, additionally revealing that the synergetic interplay of electrostatic, π-π, and hydrophobic interactions results in the operation of two distinct adsorption regimes depending on adsorbate concentration.
To date, the utilization of metal-organic frameworks (MOFs) is found from numerous fields of applications including separation, storage, sensing, and many other miscellaneous ones. Their feasibility toward wastewater treatment (WWT) for several pollutants (e.g., heavy metal ions, pesticides, volatile organic pollutants (VOCs), and other hazardous chemicals) has not yet been thoroughly evaluated. Here, we attempted to provide the current technical advances associated with MOF-based WWT in reference to conventional materials. Our review emphasized current perspectives on contamination processes in water systems and performance of MOF in diverse WWT applications. © 2018 The Korean Society of Industrial and Engineering Chemistry.
The pollution of surface and groundwater with heavy metals is a serious global concern, both environmentally, as well as with respect to human health. Overabundance of these elements poses severe health risks for humans, and also for other life forms through bioaccumulation along food chains. Therefore, steps should be taken to reduce the amount of such elements in water to acceptable levels. This review looks at metal–organic frameworks (MOFs) which have been recently developed and studied for potential applications in heavy metal removal from water. We provide an overview of the current capabilities and important properties of MOFs used for this purpose.
Emerging contaminants (EC's) are pollutants of growing concern. They are mainly organic compounds such as: pesticides, pharmaceuticals and personal care products, hormones, plasticizers, food additives, wood preservatives, laundry detergents, surfactants, disinfectants, flame retardants, and other organic compounds that were found recently in natural wastewater stream generated by human and industrial activities. A majority of ECs does not have standard regulations and could lead to lethal effects on human and aquatic life even at small concentrations. The conventional primary and secondary water treatment plants do not remove or degrade these toxic pollutants efficiently and hence need cost effective tertiary treatment method. Adsorption is a promising method worldwide for EC removal since it is low initial cost for implementation, highly-efficient and has simple operating design. Research has shown that the application of different adsorbents such as, activated carbons(ACs), modified biochars (BCs), nanoadsorbents (carbon nanotubes and graphene), composite adsorbents, and other are being used for EC's removal from water and wastewater. The current review intends to investigate adsorption process as an efficient method for the treatment of ECs. The mechanism of adsorption has also been discussed.
The adsorption activity of a layered two-dimensional (2D) nickel-based metal-organic framework (Ni-MOF) was investigated for the removal of the harmful methylene blue dye (MB) from water. NiCu-BTC, which has high surface area, was selected as a comparable adsorbent. The morphology and structure of MOF adsorbents were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA)-differential thermal analysis (DTA), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, nitrogen adsorption/desorption, field emission-scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The adsorption studies of MB included kinetic and equilibrium approaches. Nanosheets of Ni-MOF showed analogous adsorption capacity (765.5 mg/g) in comparing with highly porous NiCu-BTC (798.0 mg/g). The adsorption activity of Ni-MOF may be attributed to its layered structure that facilitate the diffusion of dye species to the predominate exposed facet of (100) plane. The adsorption of dye fitted with the Langmuir isotherm and followed the pseudo-second-order kinetic model.
Metal–organic frameworks (MOFs) represent a fascinating class of solid crystalline materials which can be self-assembled in a straightforward manner by the coordination of metal ions or clusters with organic ligands. Owing to their intrinsic porous characteristics, unique chemical versatility and abundant functionalities, MOFs have received substantial attention for diverse industrial applications, including membrane separation. Exciting research activities ranging from fabrication strategies to separation applications of MOF-based membranes have appeared. Inspired by the marvelous achievements of MOF-based membranes in gas separations, liquid separations are also being explored for the purpose of constructing continuous MOFs membranes or MOF-based mixed matrix membranes. Although these are in an emerging stage of vigorous development, most efforts are directed towards improving the liquid separation efficiency with well-designed MOF-based membranes. Therefore, as an increasing trend in membrane separation, the field of MOF-based membranes for liquid separation is highlighted in this review. The criteria for judicious selection of MOFs in fabricating MOF-based membranes are given. Special attention is paid to rational design strategies for MOF-based membranes, along with the latest application progress in the area of liquid separations, such as pervaporation, water treatment, and organic solvent nanofiltration. Moreover, some attractive dual-function applications of MOF-based membranes in the removal of micropollutants, degradation, and antibacterial activity are also reviewed. Finally, we define the remaining challenges and future opportunities in this field. This Tutorial Review provides an overview and outlook for MOF-based membranes for liquid separations. Further development of MOF-based membranes for liquid separation must consider the demands of strict separation standards and environmental safety for industrial application.
Titanium in different amount has been successfully doped into the Zirconium-based metal-organic framework UiO-66 via an in-situ synthesis method, resulting in a series of hybrid UiO-66-nTi MOFs. These materials maintain relatively high crystallinity and excellent structural stability. The addition of titanium has a significant effect on the crystal size and morphology of UiO-66. The UiO-66-nTi MOFs exhibit sphere-like crystal morphology with smaller crystal size and rougher surface comparing to the octahedral UiO-66 crystals. The framework order and porosity of the UiO-66-nTi MOFs slightly decrease due to titanium doping. The UiO-66-nTi MOFs were studied as adsorbents for removal of an organic dye from water. The results demonstrate that these hybrid materials have enhanced adsorption capacity for organic dye Conge red in comparison with the parent UiO-66. UiO-66-2.7Ti with 2.7% titanium doping shows the highest adsorption capacity of 979 mgg1, which is three times higher than that of the parent UiO-66. The strong electrostatic attraction between the positively charged surface of UiO-66-2.7Ti and the negatively charged Congo red molecules was identified as the main driving force for the high adsorption capacity.
Metal-organic frameworks (MOFs) are versatile materials highly regarded for their porous nature. Depending on the synthetic method, various guest molecules may remain in the pores or can be systematically loaded for various reasons. Herein, we present a study that explores the effect of guest molecules on the adsorption and reactivity of the MOF in both the gas phase and solution. The differences between guest molecule interactions and the subsequent effects on their activity are described for each system. Interestingly, different effects are observed and described in detail for each class of guest molecules studied. We determine that there is a strong effect of alcohols with the secondary building unit of UiO MOFs, while Lewis bases have an effect on the reactivity of the –NH2 group in UiO-66-NH2 and adsorption by the coordinatively unsaturated copper sites in HKUST-1. These effects must be considered when determining synthesis and activation methods of MOFs toward various applications.
A novel immobilized-phosphate zirconium-based metal-organic framework composite, denoted as UiO-66-P, was synthesized by a solvothermal method using UiO-66 nanoparticles and Na3PO4 ligands. The products were characterized by powder X-ray diffraction, energy dispersive spectrometry, field emission scanning electron microscopy, thermogravimetric analysis, infrared spectroscopy, zeta potential analysis, and gas adsorption measurements. The UiO-66-P nanocrystals, which comprised negatively charged frameworks, exhibited high stability, excellent porosity, and efficient charge-selective capture and separation of the cationic dye Methylene Blue (MB). An uptake capacity of 91.1 mg g⁻¹ was achieved at room temperature over 24 h when 5 mg of UiO-66-P was immersed in 40 mL of a 500 mg L⁻¹ MB solution. This capacity is much higher than that of UiO-66 (24.5 mg g⁻¹). The adsorption capability of UiO-66-P for MB was improved by 272% compared to that of pristine UiO-66. The effects of variables such as initial pH, MB concentration, and contact time were investigated. In addition, the as-obtained UiO-66 nanocrystals exhibited excellent adsorption capability for the anionic dyes Congo Red, Acid Chrome Blue K, and Methyl Orange.
UiO-66 was modulated by addition of acetic acid or HCl in the precursor solution. The resulting acetic acid-promoted UiO-66has more regular octahedral structures and high surface areas of 892-1090m(2)/g. Anionic dyes (methyl orange (MO) and Congo red (CR)) and cationic dyes (methylene blue (MB) and rhodamine B (RhB)) were examined for the selective dye adsorption on various UiO-66. The acid-promoted UiO-66 exhibits an excellent selective adsorption to anionic dyes, where the adsorption capacities of MO and MB are 84.8 and 13.2mg/g, respectively. However, UiO-66 prepared without acid shows similar adsorption to both anionic dye MO (70.4mg/g) and cationic dye MB (67.5mg/g). Mixed dyes (MO/MB and MO/RhB) adsorption on acid-promoted UiO-66 further proves the selective adsorption to anionic dyes. The adsorption mechanism was studied by testing the Zeta potential of acid-promoted UiO-66, and more positive Zeta potential (hydrogen ions) of UiO-66 is beneficial to the anionic dye adsorption.
A Keggin-type polyoxometalate H3PW12O40 (PW12) was firstly incorporated into the harmless porous metal organic framework MIL-101(Fe) resulting in [email protected] composite material (denoted as PW12@MIL-101). The material was synthesized by a one-pot solvothermal reaction of H3PW12O40, FeCl3·6H2O and terephthalic acid (H2bdc). The composite was characterized by FTIR, XRD, thermogravimetric analysis (TGA), inductively coupled plasma (ICP) spectrometry, SEM, EDS, ³¹P NMR and nitrogen adsorption-desorption isotherms. These results demonstrated the successful insertion of H3PW12O40 within the cavities of MIL-101(Fe). The adsorption rate of the isolated MIL-101 was up to 30.7% and 28.3% for cationic dyes methylene blue (MB) and rhodamine B (RhB), and 82% for anionic dye methyl orange (MO) within 30 min. However, the dye adsorption capacity of MIL-101 has greatly changed by introducing highly electronegative polyoxoanions into the cages of MIL-101. The adsorption rate of PW12@MIL-101 composite was able to reach 99% and 96% for cationic dyes MB and RhB, and 16% for anionic dye MO in the initial 5 min. Surprisingly, the composite not only exhibited a large-scale adsorption capacity of 473.7 mg g⁻¹ for MB, but also could quickly remove 97.3% MB from the dye solution with 1 ppm (1 mg L⁻¹). Furthermore, this material could be easily desorbed for reuse, and the structure of the composite was intact during the adsorption experiment. Thus, it is a promising and environmentally friendly adsorbent for removing cationic organic pollutants in dye-wastewater.
In this paper, two kinds of metal-organic frameworks (MOFs), MIL-53(Al) and MIL-53(Al)-NH2, were synthesized. Then these MOFs were used to remove methylene blue and malachite green dyes from aqueous solution. Characterizations of MOFs were carried out by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared (FT-IR) spectrometry, and zeta potential. Experimental results showed that MIL-53(Al)-NH2 can rapidly bind to the two kinds of cationic dyes from aqueous solution with high adsorption capacity. However, the adsorption capacity of MIL-53(Al) for cationic dyes is extremely low. The adsorptive selectivity of MIL-53(Al)-NH2 to the cationic dyes resulted from the hydrogen bonding interaction between amimo groups of the dyes molecule and the MIL-53(Al)-NH2, while the extremely low adsorption capacity of MIL-53(Al) for the dyes may be main caused by the ''breathing''behavior of MIL-53(Al). The factors including adsorption time, temperature, and the pH of solution that affected adsorption of the two dyes on MIL-53(Al)-NH2 were studied. Pseudo first-order kinetic, pseudo second-order kinetic, and Weber-Morris models were used to fit the adsorption data, and the pseudo second-order kinetic model showed a better fit for the adsorption of methylene blue and malachite green than that of the pseudo first-order kinetic model. Furthermore, the internal diffusion model which represented by Weber-Morris model was involved in the step of speed control, but it was not the only speed control step, while out-diffusion also played an important role in the adsorption process. The adsorption isotherm and thermodynamics of methylene blue and malachite green on MIL-53(Al)-NH2 were also studied. The adsorption of methylene blue and malachite green dyes on MIL-53(Al)-NH2 can be fitted to both Langmuir and Freundlich isotherm, but the former was better than the latter. The adsorption thermodynamic experiments demonstrated that adsorption reaction was spontaneous and endothermic. Finally, according to the experimental phenomenon, the possible mechanism of adsorption was proposed. Besides, the used adsorbent can be reused for adsorptive removal through simply washing.
Metal-organic frameworks (MOFs) are an emerging class of microporous, crystalline materials with potential applications in the capture, storage, and separation of gases. Of the many known MOFs, MOF-5 has attracted con-siderable attention due to its ability to store gaseous fuels at high densities. Nevertheless, MOF-5 and several other MOFs are known to exhibit limited stability upon exposure to reactive species such as water. The present study quantifies the impact of humid air exposure on the properties of MOF-5 as a function of exposure time, humidity level, and morphology (i.e., powders vs. pellets). Properties examined include hydrogen storage capacity, surface area, and crystallinity. Water adsorption/desorption isotherms are measured using a gravimetric technique; the first uptake exhibits a type V isotherm with a sudden increase in uptake at ~50% relative humidity. For humidity levels below this threshold only minor degradation is observed for exposure times up to several hours, suggesting that MOF-5 is more stable than generally assumed under moderately humid conditions. In contrast, irreversible degradation occurs in a matter of minutes for exposures above the 50% threshold. FTIR spectroscopy indicates that molecular and/or dissociated water is inserted into the skeletal framework after long exposure times. Densification into pellets can slow the degradation of MOF-5 significantly, and may present a pathway to enhance the stability of some MOFs.
The world is faced with increasing demands for high-quality drinking water and for removal of contaminants from municipal, agricultural, and industrial wastewaters. Treatment is required to obtain drinking water from most natural resources as well as from wastewaters with varying amounts of impurities. These impurities may occur in a variety of forms including large particles such as microorganisms or suspended solids or as dissolved or colloidal inorganic and organic substances. This chapter provides an overview of the use of natural zeolites in removal of impurities from water or wastewater (Murphy et al. 1978, Tarasevich 1994, Kallo 1995).
Most technologies using natural zeolites for water purification are based on the unique cation-exchange behavior of zeolites through which dissolved cations can be removed from water by exchanging with cations on a zeolite’s exchange sites (see Pabalan and Bertetti, this volume). The most common cation in waters affecting human and animal health is NH4+. It can be removed by exchanging with biologically acceptable cations such as Na+, K+, Mg2+, Ca2+ or H+ residing on the exchange sites of the zeolite. Fortunately, many natural zeolites (e.g. clinoptilolite, mordenite, phillipsite, chabazite) are selective for NH4+ ( vide infra ), meaning that they will exchange NH4+ even in the presence of larger amounts of competing cations. Clinoptilolite and mordenite are also selective for transition metals (e.g. Cu2+, Ag+, Zn2+, Cd2+, Hg2+, Pb2+, Cr3+, Mo2+, Mn2+, Co2+, Ni2+), which are often present in industrial waters and can be very toxic even in concentration as low as several mg/L. As emphasized in discussions of radioactive waste treatments, both clinoptilolite and mordenite …
Herein, two zirconium(IV)-based MOFs UiO-66 and UiO-66-NH2 had been successfully prepared by a facile solvothermal method and were characterized by X-ray diffraction (XRD), field emission transmission electron microscopy (FETEM), N2 adsorption–desorption (BET), X-ray photoelectron spectroscopy (XPS), and zeta potential. They exhibit small size, large surface area, and can remove cationic dyes from aqueous solution more effectively than anionic dyes. This adsorption selectivity is due to the favorable electrostatic interactions between the adsorbents and cationic dyes. Furthermore, owing to the individual micropore structure of UiO-66-NH2 and its more negative zeta potential resulted from the charge balance for the protonation of –NH2, UiO-66-NH2 displays much higher adsorption capacity for cationic dyes and lower adsorption capacity for anionic dyes than UiO-66.
A series of amine-functionalized mixed-linker metal-organic frameworks (MOFs) of idealized structural formula Zr6O4(OH)4(BDC)6-6X(ABDC)6X (where BDC = benzene-1,4-dicarboxylic acid, ABDC = 2-aminobenzene-1,4-dicarboxylic acid) has been prepared by solvothermal synthesis. The materials have been characterized by thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), and Fourier transform infrared (FTIR) spectroscopy with the aim of elucidating the effect that varying the degrees of amine functionalization has on the stability (thermal and chemical) and porosity of the framework. This work includes the first application of ultraviolet-visible light (UV-vis) spectroscopy in the quantification of ABDC in mixed-linker MOFs.
In this review article the authors presented up to-date development on the application of adsorption in the removal of dyes from aqueous solution. This review article provides extensive literature information about dyes, its classification and toxicity, various treatment methods, and dye adsorption characteristics by various adsorbents. One of the objectives of this review article is to organise the scattered available information on various aspects on a wide range of potentially effective adsorbents in the removal of dyes. Therefore, an extensive list of various adsorbents such as natural materials, waste materials from industry, agricultural by-products, and biomass based activated carbon in the removal of various dyes has been compiled here. Dye bearing waste treatment by adsorption using low cost alternative adsorbent is a demanding area as it has double benefits i.e. water treatment and waste management. Further, activated carbon from biomass has the advantage of offering an effected low cost replacement for non-renewable coal based granular activated carbon provided that they have similar or better adsorption on efficiency. The effectiveness of various adsorbents under different physico-chemical process parameters and their comparative adsorption capacity towards dye adsorption has also been presented. This review paper also includes the affective adsorption factors of dye such as solution pH, initial dye concentration, adsorbent dosage, and temperature. The applicability of various adsorption kinetic models and isotherm models for dye removal by wide range of adsorbents is also reported here. Conclusions have been drawn from the literature reviewed and few suggestions for future research are proposed.
A metal-organic frameworks (MOFs) based on copper-benzenetricarboxylates was applied to the adsorption of methylene blue (MB) from aqueous solution. Cu-BTC [BTC = 1,3,5-benzenetricarboxylatel also known as HKUST-1 is a widely studied MOF. Cu-BTC mainly possessed mesopores, high surface area and big pore volume which is benefit for the adsorption capacity. Characterization of Cu-BTC were achieved by XRD, SEM micrographs, nitrogen adsorption-desorption analysis and FT-IR spectra. The kinetics characteristic and thermodynamic parameters were also analyzed. The experimental isotherms data were analyzed using Langmuir and Freundlich isotherm equations and the results indicated that the Langmuir isotherm showed a better fit for MB adsorption. Thermodynamic parameters were calculated by the Gibbs free energy function, confirming that the adsorption process was spontaneous and accompanied by exothermic. The maximum removal has been achieved at the pH = 7.0. The possible mechanism and the adsorption behavior of the adsorption of MB onto Cu-BTC were investigated. The adsorbent Cu-BTC could be easily regenerated after washing with ethanol. The experimental results suggested that Cu-BTC materials have potential application for the wastewater treatment containing MB dye. (C) 2014 Published by Elsevier Inc.
An amino-functionalised metal-organic framework (MOF), aluminium aminoterephthalate (amino-MIL-101(Al)), has been applied to the adsorptive removal of dyes (cationic methylene blue, MB, and anionic methyl orange, MO) from aqueous solutions in order to examine the effect of the amino group on sorption behaviour. Adsorption isotherms and thermodynamic studies indicated the spontaneous adsorption of MB with a maximum adsorption capacity at 30 [degree]C (762 +/- 12 mg gMOF-1) higher than those observed for MB on other MOFs and most other materials. In contrast, lower adsorption capacities were observed in the adsorption of the same dye on the analogous non-amino-functionalised framework (MIL-101(Al), 195 mg g-1) and in the adsorption of MO by amino-MIL-101(Al) (188 +/- 9 mg g-1), suggesting that an electrostatic interaction between the amino groups of the MOF and the cationic dye MB may have contributed to the high adsorption capacity. The adsorptions of both dyes on amino-MIL-101(Al) were spontaneous, endothermic, and entropy-driven, as is common for dye adsorptions. However, the [capital Delta]S value obtained for the adsorption of MB (346 J mol-1 K-1) was extreme. Further analysis demonstrated that after exposure to MB, the ordered amino-MIL-101(Al) structure was absent, [similar]30% of the Al3+ was lost to solution, and significant changes occurred in the X-ray photoelectron spectrum of the MOF. On the other hand, the MOF structure was intact following the adsorption of MO. Several groups have exploited electrostatic interactions to improve dye adsorption; however, these proved excessive in the case of MB (but not MO) adsorption on amino-MIL-101(Al).
A highly porous metal-organic framework (MOF) material based on chromium-benzenedicarboxylates (MIL-101) was applied to the adsorption of xylenol orange (XO) from aqueous solution. Adsorption kinetics and isotherms were determined from the experimental data, and the results showed that pseudo-second-order kinetic model and Langmuir adsorption isotherm matched well for the adsorption of XO onto MIL-101. Thermodynamic parameters including free energy, enthalpy, and entropy of adsorption were obtained, and all the results were in favor of the adsorption. It was found that the adsorbed amounts decreased with increasing pH value of the XO solution, which indicates that the mechanism may be the charge interactions between the dye stuffs and the adsorbents. The used MIL-101 could be regenerated by washing with a dilute concentration of NaOH solution. Compared with other adsorbents like active carbon and MCM-41, especially in high concentrations of XO, MIL-101 demonstrated a superior dye adsorption capability.
The adsorption of malachite green from aqueous solution on a highly porous metal–organic framework MIL-100(Fe) was studied in view of the adsorption isotherm, thermodynamics, kinetics, and regeneration of the sorbent. The adsorption isotherms of malachite green on MIL-100(Fe) followed the Freundlich model, and MIL-100(Fe) possessed heterogeneous surface caused by the presence of different functional groups on the surface. The adsorption of malachite green on MIL-100(Fe) is controlled by an entropy effect rather than an enthalpy change, and obeyed a pseudo-second-order kinetics. Analysis of the intraparticle diffusion plots revealed that more than one process affected the adsorption, and film (boundary layer) diffusion controlled the adsorption rate at the beginning. Evidence from zeta potential and X-ray photoelectron spectroscopic data showed that the adsorption of malachite green was also driven by electrostatic attraction and the interaction between the Lewis base –N(CH3)2 in malachite green and the water molecule coordinated metal sites of MIL-100(Fe). MIL-100(Fe) gave much higher adsorption capacity for malachite green than other conventional adsorbents such as activated carbon and natural zeolite. The high adsorption capacity, good solvent stability, and excellent reusability make MIL-100(Fe) attractive for the removal of MG from aqueous solution.