The adsorptive properties of UiO-66 towards organic dyes: A record adsorption capacity for the anionic dye Alizarin Red S

Comparative study of synthesis methods and pH-dependent adsorption of methylene blue dye on UiO-66 and NH2-UiO-66

Metal-organic frameworks (MOFs) are highly promising adsorbents with notable properties such as elevated adsorption capacities and versatile surface design capabilities. This study introduces two distinct synthesis methods, one lasting 1 h and the other 24 h, for UiO-66 and NH2-UiO-66. While both methods yield structures with comparable crystallinity and morphology, the adsorption performance of the cationic methylene blue dye varies at different pH levels. Despite the 24 h synthesis time being optimal for maximum adsorption in both MOFs, the relative difference in NH2-UiO-66 adsorption percentage at different times suggests reduced dependency on synthesis time for this property. Notably, NH2-UiO-66 exhibits consistent and effective performance across three pH levels, warranting further investigation into its adsorption kinetics and isotherm. The achievement of high adsorption efficiency coupled with a significantly reduced synthesis time underscores the importance of developing simplified synthetic methods, essential for enhancing the practical applicability of MOFs in diverse applications.

The effect of the number of SO3- groups on the adsorption of anionic dyes by the synthesized hydroxyapatite/Mg-Al LDH nanocomposite

In this study, a new nanocomposite of hydroxyapatite (HA)/Mg-Al layered double hydroxide (LDH) was successfully formed via a facile co-precipitation method and applied to adsorb three anionic dyes of alizarin red S (ARS), Congo red (CR), and reactive red 120 (RR120) differing in the number of SO3- groups from aqueous solution. Based on a combination of characterization analysis and adsorption experiments, HA/Mg-Al LDH nanocomposite showed better adsorption performance than HA and Mg-Al LDH. Using XRD and TEM analyses, the crystallinity and the presence of nanoparticles were confirmed. According to the SEM investigation, the Mg-Al LDH layers in the nanocomposite structure were delaminated, while HA nanorods were formed at the surface of Mg-Al LDH nanoparticles. The higher BET surface area of the novel HA/Mg-Al LDH nanocomposite compared to HA and Mg-Al LDH provided its superior adsorption performance. Considering an effective amount of adsorbent dosage, pH 5 was selected as the optimum pH for each of the three dye solutions. According to the results from the study of contact time and initial concentration, the pseudo-second-order kinetic (R2 = 0.9987, 0.9951, and 0.9922) and Langmuir isotherm (R2 = 0.9873, 0.9956, and 0.9727) best fitted the data for ARS, CR, and RR120, respectively. Anionic dyes with different numbers of SO3- groups demonstrated distinct adsorption mechanisms for HA and Mg-Al LDH nanoparticles, indicating that the adsorption capacity is influenced by the number of SO3- groups, with HA/Mg-Al LDH nanocomposite offering superior performance toward dyes with higher numbers of SO3- groups. Furthermore, ΔH° less than 40 kJ/mol, positive ΔS°, and negative ΔG° accompanied by the mechanism clarifying show physical spontaneous adsorption without an external source of energy and increase the randomness of the process during the adsorption, respectively. Finally, the regeneration study demonstrated that the nanocomposite could be utilized for multiple adsorption-desorption cycles, proposing the HA/Mg-Al LDH as an economically and environmentally friendly adsorbent in the adsorption of anionic dyes in water treatment processes.

Highly porous organoclay-supported bimetal-organic framework (CoNi-MOF/OC) composite with efficient and selective adsorption of organic dyes

Herein, a highly porous bimetal-organic framework (bi-MOF) based on cobalt and nickel was successfully in situ grown on organoclay (OC) clusters by solvothermal method. Accordingly, the hierarchical porous CoNi-MOF/OC composite with a superior specific surface area of 2046 m²/g and a large pore volume of 0.763 cm³/g was obtained, which facilitated the adsorption of organic dyes. A morphological study using scanning electron microscopy indicated the formation of uniform bi-MOF crystals on the OC plates. Furthermore, the single- and multi-dye adsorption assays were implemented to precisely evaluate the adsorption capacity and selectivity of CoNi-MOF/OC composite to anionic and cationic dyes. The results revealed a high adsorption capacity of 58.61 mg/g at an adsorbent content of 15 mg, initial dye concentration of 20 ppm, and contact time of 25 min for MB, which is superior to several existing clay-based adsorbents. The adsorption kinetics study showed that the adsorption of cationic and anionic dyes onto the CoNi-MOF/OC composite followed the pseudo-second-order kinetic model. Interestingly, the regeneration study showed appropriate reusability and stability of the CoNi-MOF/OC composite for the removal of organic dyes with an almost unchanged structure after four regeneration cycles. The results of this study provide new insights for the rational design and fabrication of next-generation clay-based adsorbent by combining the synergistic advantages of bi-MOF with superior specific surface area and pore volume with organoclay composition and structure.

Selective removal of heavy metals by Zr-based MOFs in wastewater: New acid and amino functionalization strategy

Zr-based metal-organic frameworks (MOFs) have been developed in recent years to treat heavy metals, e.g. hexavalent chromium Cr⁶⁺ pollution, which damages the surrounding ecosystem and threaten human health. This kind of MOF is stable and convenient to prepare, but has the disadvantage of low adsorption capacity, limiting its wide application. To this end, a novel formic acid and amino modified MOFs were prepared, referred to as Form-UiO-66-NH₂. Due to the modification of formic acid, its specific surface area, pore size, and crystal size were effectively expanded, and the adsorption capacity of Cr⁶⁺ was significantly enhanced. Under optimal conditions, Form-UiO-66-NH₂ exhibited an excellent adsorption capacity (338.98 mg/g), ∼10 times higher than that reported for unmodified Zr-based MOFs and most other adsorbents. An in-depth study on the photoelectronic properties and pH confirmed that the adsorption mechanism of Form-UiO-66-NH₂ to Cr⁶⁺ was electrostatic adsorption. After modification, the improvement of Cr⁶⁺ adsorption capacity by Form-UiO-66-NH₂ was attributed to the expansion of its specific surface area and the increase in its surface charge. The present study revealed an important finding that Form-UiO-66-NH₂ elucidated selective adsorption to Cr⁶⁺ in mixed wastewater containing toxic heavy metal ions and common nonmetallic water quality factors. This research provided a new acid and amino functionalization perspective for improving the adsorption capacity of Zr-based MOF adsorbents while simultaneously demonstrating their pertinence to target contaminant adsorption.

Biocomposite based on zirconium and amine-grafted walnut shell with antibacterial properties for the removal of Alizarin red in water: batch and column studies

Recent progress has been made in the application of novel zirconium-loaded amine-grafted walnut shells as multifunctional adsorbents for the remediation of Alizarin red (AR) and bacteria in aqueous solutions. The morphology and functional groups of ACWNS@Zr were studied using Brunauer-Emmett-Teller (BET) techniques, X-ray diffraction (XRD), pH point of zero charges (pHpzc), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. Adsorption and regeneration tests were carried out in batch and column mode. The ACWNS@Zr had a Langmuir maximum capacity of 415.5 ± 6.1 mg g^-1 at 303 K. The spread plate technique was used to evaluate the adsorbent's antimicrobial properties against Staphylococcus aureus and Escherichia coli. ACWNS@Zr exhibited inhibitory potential towards S. aureus and E. coli in the suspensions by 53.3% and 15.0%, respectively. Electrostatic interaction and complexation interaction could be the key mechanisms governing AR dye removal. Equilibrium isotherms fit Langmuir models better for both batch and column studies, while adsorption kinetics to pseudo-second-order and Thomas models for batch and column studies, respectively. Thermodynamic studies indicated that the adsorption process was endothermic and spontaneous. Furthermore, columns' mass transfer capacity (B) increased as the concentration increased due to the enhanced driving force for AR adsorption onto ACWNS@Zr. Regeneration with NaOH solution of AR-loaded ACWNS@Zr was remarkable.

Removal of methyl orange wastewater by Ugi multicomponent reaction functionalized UiO-66-NS

The efficient and rapid removal of organic dyes from wastewater remains a complex and challenging task. In this study, UiO-66-NH₂ was prepared by solvothermal synthesis, and then, UiO-66-NS was prepared by compounding L-cysteine with UiO-66-NH₂ via the Ugi reaction for the efficient removal of methyl orange. UiO-66-NS was prepared by the addition of 1 mmol L-cysteine and showed good adsorption of methyl orange with 92.00% removal. Pseudo-second-order kinetics and Langmuir isotherms more accurately described the adsorption process of UiO-66-NS on methyl orange, which indicated that the adsorption process was dominated by monolayer adsorption of chemical reactions, and the maximum adsorption amounts of UiO-66-NS on methyl orange were 242.72 mg/g at 298 K. In addition, UiO-66-NS exhibited ultrahigh stability in acidic, neutral, and alkaline media (pH = 3-10), but its adsorption of methyl orange after 5 cycles was only 59.53% of the maximum adsorption amount. The adsorption mechanism is primarily electrostatic adsorption of UiO-66-NS with methyl orange, hydrogen bonding, and π-π interactions. This atomically economical Ugi multicomponent reaction provides new ideas for the preparation of structurally designable adsorbents with excellent performance.

A comprehensive review on water remediation using UiO-66 MOFs and their derivatives

Metal-organic frameworks (MOFs) are a versatile class of porous materials offering unprecedented scope for chemical and structural tunability. On account of their synthetic versatility, tunable and exceptional host-guest chemistry they are widely utilized in many prominent water remediation techniques. However, some of the MOFs present low structural stabilities specifically in aqueous and harsh chemical conditions which impedes their potential application in the field. Among the currently explored MOFs, UiO-66 exhibits structural robustness and has gained immense scientific popularity. Built with a zirconium-terephthalate framework, the strong Zr-O bond coordination contributes to its stability in aqueous, chemical, and thermal conditions. Moreover, other exceptional features such as high surface area and uniform pore size add to the grand arena of porous nanomaterials. As a result of its stable nature, UiO-66 offers relaxed admittance towards various functionalization, including synthetic and post-synthetic modifications. Consequently, the adsorptive properties of these highly stable frameworks have been modulated by the addition of various functionalities. Moreover, due to the presence of catalytically active sites, the use of UiO-66 has also been extended towards the degradation of pollutants. Furthermore, to solve the practical handling issues of the crystalline powdered forms, UiO-66 has been incorporated into various membrane supports. The incorporation of UiO-66 in various matrices has enhanced the rejection, permeate flux, and anti-fouling properties of membranes. The combination of such exceptional characteristics of UiO-66 MOF has expanded its scope in targeted purification techniques. Subsequently, this review highlights the role of UiO-66 in major water purification techniques such as adsorption, photocatalytic degradation, and membrane separation. This comprehensive review is expected to shed light on the existing developments and guide the inexhaustible futuristic scope of UiO-66 MOF.

Removal of organic micropollutans by adsorptive membrane

Various emerging organic micropollutants, such as pharmaceuticals, have attracted the interest of the water industry during the last two decades due to their insufficient removal during conventional water and wastewater treatment methods and increasing demand for pharmaceuticals projected to climate change-related impacts and COVID-19, nanosorbents such as carbon nanotubes (CNTs), graphene oxides (GOs), and metallic organic frameworks (MOFs) have recently been extensively explored regarding their potential environmental applications. Due to their unique physicochemical features, the use of these nanoadsorbents for organic micropollutans in water and wastewater treatment processes has been a rapidly growing topic of research in recent literature. Adsorptive membranes, which include these nanosorbents, combine the benefits of adsorption with membrane separation, allowing for high flow rates and faster adsorption/desorption rates, and have received a lot of publicity in recent years. The most recent advances in the fabrication of adsorptive membranes (including homogeneous membranes, mixed matrix membranes, and composite membranes), as well as their basic principles and applications in water and wastewater treatment, are discussed in this review. This paper covers ten years, from 2011 to 2021, and examines over 100 published studies, highlighting that micropollutans can pose a serious threat to surface water environments and that adsorptive membranes are promising, particularly in the adsorption of trace substances with fast kinetics. Membrane fouling, on the other hand, should be given more attention in future studies due to the high costs and restricted reusability.

Nickel and iron-based metal-organic frameworks for removal of organic and inorganic model contaminants

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 q_max of 176.68 mg/g described the experimental data well. The separation factor, K_L, 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.

Parametric Study of Methyl Orange Removal Using Metal–Organic Frameworks Based on Factorial Experimental Design Analysis

Wastewater treatment plants (WWTPs) are one of the most energy-intensive industries. Every stage of wastewater treatment consumes energy, which is the primary contributor to WWTP costs. Adsorbents and process optimization are critical for energy savings. The removal of dyes from industrial wastewater by adsorption using commercially available adsorbents is inefficient. Metal–organic frameworks (MOFs) have outstanding properties that can improve separation performance over current commercial adsorbents, and thus, these materials represent a milestone in improving dye removal in water treatment methods. In this work, three types of metal–organic frameworks (Fe-BTC, Cu-BTC, and ZIF-8) have been investigated as prospective adsorbents for methyl orange removal from water in batch setups. The results showed that at 15 mg/L MO initial concentration and 100 mg dosage, Fe-BTC had the highest removal efficiency of 91%, followed by ZIF-8 (63%), and finally Cu-BTC (35%), which exhibited structural damage due to its instability in water. Fe-BTC maintained consistent adsorption capacity over a wide range of pH values. Furthermore, a 23 full factorial design analysis was implemented to evaluate the conditions for maximum MO-removal efficiency. The main effects, interaction effects, analysis of variance (ANOVA), and the Pareto chart were reported. The statistical analysis demonstrated that the MOF type was the most significant factor, followed by dosage and initial concentration. The analysis indicated that the type of MOF and dosage had a positive effect on the removal efficiency, while the initial concentration had a negative effect. The two-way and three-way interactions were also found to be significant.

Butane isomers mobility and framework dynamics in UiO-66 (Zr) MOF: Impact of the hydroxyl groups in zirconia cluster

UiO-66 (Zr) is a metal-organic framework (MOF) known for its thermal and chemical stability and wide range of adsorption-based applications. This MOF exhibits high separation selectivity for butane isomers. It has been earlier inferred that the separation performance of the material depends on the hydroxylation state of the zirconia cluster. In this contribution, we apply ²H solid-state NMR to characterize the dynamics of both the MOF organic framework itself and butane isomers in hydroxylated and dehydroxylated forms of UiO-66. It is established that the rate of π-flipping and the amplitude of the phenylene ring plane librations in the framework are higher for the dehydroxylated form. Self-diffusion coefficients of butane isomers have been estimated for both forms of UiO-66. The diffusivity is higher for n-butane in the dehydroxylated form, whereas the diffusion of isobutane is not affected by the presence of OH groups in the zirconia cluster of the MOF. Higher diffusivity of n-butane in dehydroxylated form is accounted for by the larger effective diameter of the window between the adjacent cages in this form, which arises from faster rotation and larger amplitude of framework linker libration. This rationalizes the higher efficiency of the dehydroxylated form of UiO-66(Zr) material for butane isomers separation.

Recent Advances in MOF-Based Adsorbents for Dye Removal from the Aquatic Environment

The adsorptive removal of dyes from industrial wastewater using commercially available adsorbents is not significantly efficient. Metal–organic frameworks (MOFs) offer outstanding properties which can boost the separation performance over current commercial adsorbents and hence, these materials represent a milestone in improving treatment methods for dye removal from water. Accordingly, in this paper, the recent studies in the modification of MOF structures in dye removal from the aquatic environment have been discussed. This study aims to elaborate on the synthetic strategies applied to improve the adsorption efficiency and to discuss the major adsorption mechanisms as well as the most influential parameters in the adsorptive removal of dyes using MOFs. More particularly, the advanced separation performance of MOF-based adsorbents will be comprehensively explained. The introduction of various functional groups and nanomaterials, such as amine functional groups, magnetic nanoparticles, and carbon-based materials such as graphene oxide and CNT, onto the MOFs can alter the removal efficiency of MOF-based adsorbents through enhancing the water stability, dispersion in water, interactions between the MOF structure and the contaminant, and the adsorption capacity. Finally, we summarize the challenges experienced by MOF-based materials for dye removal from water and propose future research outlooks to be considered.

Cr(VI) Adsorption from Aqueous Solution by UiO-66 Modified Corncob

To adsorb hexavalent chromium (Cr(VI)) in polluted water, this paper prepared a UiO-66 (Zr6O4(OH)4(BDC)12) modified granular corncob composite adsorbent by hydrothermal method with in situ loading of UiO-66 on pretreated corncob particles. The physicochemical properties of the synthesized samples were characterized. Batch adsorption experiments were conducted to investigate the adsorption process of aqueous Cr(VI) under various conditions (different ionic strength, pH and co-existing anions). The results showed that UiO-66 was successfully loaded on the modified corncob particles. The isothermal adsorption data of Cr(VI) adsorption by the UiO-66 modified corncob fit well with the Langmuir model with the maximum adsorption capacity of Cr(VI) on UiO-66@Corn+ being 90.04 mg/g. UiO-66 loading could increase Cr(VI) adsorption capacity of Corn+. The kinetic study showed that the equilibrium time for Cr(VI) adsorption on UiO-66 modified corncob was about 180 min and the kinetic data followed the pseudo-secondary kinetic model. The Cr(VI) adsorption capacity on UiO-66@Corn+ decreased with the increasing solution pH, and the optimum pH range was 4–6. The ionic strength has little effect on the Cr(VI) adsorption capacity, but the coexistence of CO32−, SO42− and PO43− in the solution could significantly decrease the equilibrium adsorption capacity of Cr(VI). The adsorption mechanism analysis showed that Cr(VI) was adsorbed on the surface of adsorbents through electrostatic attraction and was reduced further to the less toxic Cr(III) by the electron donor on the surface of adsorbent. The electrostatic interaction was the main force affecting the adsorption of Cr(VI) by UiO-66. UiO-66@Corn+ had an excellent removal efficiency of Cr(VI) and excellent reusability. UiO-66@Corn+ could effectively remove Cr(VI) from water and have a promising application.

Experimental and Density Functional Theory Studies on a Zinc(II) Coordination Polymer Constructed with 1,3,5-Benzenetricarboxylic Acid and the Derived Nanocomposites from Activated Carbon

A coordination polymer with the composition C₁₂H₂₀O₁₆Zn₂ (ZnBTC) (BTC = benzene-1,3,5-tricarboxylate) was synthesized under hydrothermal conditions at 120 °C, and its crystal structure was determined using single-crystal X-ray crystallography. First-principles electronic structure investigation of the compound was carried out using the density functional theory computational approach. The highest occupied molecular orbital, the lowest unoccupied molecular orbital, the energy gap, and the global reactivity descriptors of ZnBTC were investigated in both the gas phase and the solvent phase using the implicit solvation model, while the donor-acceptor interactions were studied using natural bond orbital analyses. The results revealed that ZnBTC is more stable but less reactive in solvent medium. The larger stabilization energy E ⁽²⁾ indicates a greater interaction of ZnBTC in the solvent than in the gas phase. Orange peel activated carbon and banana peel activated carbon chemically treated with ZnCl₂ and/or KOH were used to modify the synthesis of ZnBTC to obtain nanocomposites. ZnBTC and the nanocomposites were characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis, and Fourier transform infrared. The specific surface area (S _BET) and the average pore diameter of the materials were determined by nitrogen sorption measurements using the Brunauer-Emmett-Teller (BET) method, while scanning electron microscopy and transmission electron microscopy were used to observe their morphology and particle size, respectively. The PXRD of all the activated carbon materials exhibited peaks at 2θ values of 12.7 and 13.9° corresponding to a d-spacing of 6.94 and 6.32 Å, respectively. The N₂ adsorption-desorption isotherm of the materials are of type II with nanocomposites showing enhanced S _BET compared to the pristine ZnBTC. The results also revealed that activated carbons from the banana peel and the derived nanocomposites exhibited better porous structure parameters than those obtained from orange peel. The degradation efficiency of methyl orange in aqueous solutions using ZnBTC as a photocatalyst was found to be 52 %, while that of the nanocomposites were enhanced up to 79 %.

Fast and efficient adsorption of palladium from aqueous solution by magnetic metal-organic framework nanocomposite modified with poly(propylene imine) dendrimer

In this study, a magnetic metal-organic framework (MMOF) was synthesized and post-modified with poly(propyleneimine) dendrimer to fabricate a novel functional porous nanocomposite for adsorption and recovery of palladium (Pd(II)) from aqueous solution. The morphological and structural characteristics of the prepared material were identified by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmet-Teller (BET) isotherm, and vibrating sample magnetometer (VSM). The results confirmed the successful synthesis and post-modification of MMOF. Semispherical shape particles (20-50 nm) with appropriate magnetic properties and a high specific surface area of 120 m²/g were obtained. An experimental design approach was performed to show the effect of adsorption conditions on Pd(II) uptake efficiency of the dendrimer-modified magnetic adsorbent. The study showed that the Pd(II) uptake on dendrimer-modified MMOF was well described by the Langmuir isotherm model with the highest uptake capacity of 291 mg/g under optimal condition (adsorbent content of 12.5 mg, Pd ion concentration of 80 ppm, pH = 4, and contact time of 40 min). The adsorption kinetics of Pd(II) ions was suggested to be a pseudo-first-order model. The results revealed a faster adsorption rate and higher adsorption capacity (about 43%) for dendrimer-modified MMOF. Finally, the reusability of the provided adsorbent was evaluated. This work provides a valuable strategy for designing and developing efficient magnetic adsorbents based on MOFs for the adsorption and recovery of precious metals.

Deployment of metal-organic frameworks as robust materials for sustainable catalysis and remediation of pollutants in environmental settings

From metal-organic chemistry, metal-organic frameworks (MOFs) are of supreme interest for catalysis and environmental settings. Owing to anthropogenic sources and booming industrial practices, the most challenging issue is increased water pollution and environmental insecurity. For instance, several types of synthetic dyes are toxic up to a certain extent, as emerging organic contaminants (EOCs) pose adverse environmental and potential health consequences. A gradual increase in the contamination sources and unpredictable environmental changes in terms of anthropogenic pollution severely affect both water availability and distribution. Therefore, the treatment of dyes containing wastewater matrices for water resource generation is one of the most important tasks, which must be addressed effectively. With structural tunability, MOFs have been appearing as a robust tool for remediating toxic pollutants from wastewater matrices. Moreover, the promising functionality, structural tunability, robust catalytic attributes, compatibility, large surface area, stability in water, and ease in surface functionalization make MOFs one of the considerable materials of interest. This review work spotlights the present-day progress related to MOFs and their catalytic and adsorptive chemistry for a sustainable environment. Following a brief introduction, the characteristic rendering MOFs, as adsorbents, are given with prominent examples. Next, several synthesis routes as a roadmap to engineer MOFs are discussed. From the applied perspective, the adsorptive and catalytic potentialities of MOFs as given by addressing sustainable mitigation of toxic dyes. The last section of the work illustrates key challenging issues and future directions by considering the suiting importance of MOFs.

Adsorption of Malachite Green and Alizarin Red S Dyes Using Fe-BTC Metal Organic Framework as Adsorbent

Synthetic organic dyes are widely used in various industrial sectors but are also among the most harmful water pollutants. In the last decade, significant efforts have been made to develop improved materials for the removal of dyes from water, in particular, on nanostructured adsorbent materials. Metal organic frameworks (MOFs) are an attractive class of hybrid nanostructured materials with an extremely wide range of applications including adsorption. In the present work, an iron-based Fe-BTC MOF, prepared according to a rapid, aqueous-based procedure, was used as an adsorbent for the removal of alizarin red S (ARS) and malachite green (MG) dyes from water. The synthesized material was characterized in detail, while the adsorption of the dyes was monitored by UV-Vis spectroscopy. An optimal adsorption pH of 4, likely due to the establishment of favorable interactions between dyes and Fe-BTC, was found. At this pH and at a temperature of 298 K, adsorption equilibrium was reached in less than 30 min following a pseudo-second order kinetics, with k″ of 4.29 × 10⁻³ and 3.98 × 10⁻² g∙mg⁻¹ min⁻¹ for ARS and MG, respectively. The adsorption isotherm followed the Langmuir model with maximal adsorption capacities of 80 mg∙g⁻¹ (ARS) and 177 mg∙g⁻¹ (MG), and K_L of 9.30·10³ L∙mg⁻¹ (ARS) and 51.56·10³ L∙mg⁻¹ (MG).

Fabrication of zirconium (IV)-loaded chitosan/Fe3O4/graphene oxide for efficient removal of alizarin red from aqueous solution

Zirconium(IV)-loaded chitosan/Fe₃O₄/graphene oxide (Zr-CMGO) was fabricated and applied to remove alizarin red (AR) from aqueous solution. Characterizations of Zr-CMGO were performed using several techniques. The effects of initial AR pH, coexisted NaCl, contact time and AR concentration were systematically investigated in batch mode. The increased pH had a negative effect on AR adsorption while there was little impact with salinity. Adsorption capacity toward AR reached up to 231 mg/g at 313 K. The kinetic and isotherm analyses indicated that pseudo-second-order kinetic model and Freundlich model could predicted the uptake of AR. In addition, the mechanism of AR adsorption could be mainly complexation, electrostatic force, etc. There is antibacterial activity from test about Zr-CMGO. Furthermore, the two-stage design could be applied for the theoretical support. Based on all results, Zr-CMGO is a novel and selective adsorbent for practical applications.

PPI-Dendrimer-Functionalized Magnetic Metal-Organic Framework (Fe3O4@MOF@PPI) with High Adsorption Capacity for Sustainable Wastewater Treatment

Herein, a magnetic zirconium-based metal-organic framework nanocomposite was synthesized by a simple solvothermal method and used as an adsorbent for the removal of direct and acid dyes from aqueous solution. To enhance its adsorption performance, poly(propyleneimine) dendrimer was used to functionalize the as-synthesized magnetic porous nanocomposite. The dendrimer-functionalized magnetic nanocomposite was characterized by field-emission scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption/desorption isotherms, and vibration sample magnetometer. The obtained results revealed the successful synthesis and functionalization of the magnetic nanocomposite. The adsorbents exhibited good magnetic properties with high saturation magnetization and high specific surface area. The adsorption isotherms and kinetics of anionic dyes were described by the Freundlich and pseudo-second-order models, respectively. It was found that the kinetics of adsorption of both the investigated dyes by the dendrimer-functionalized magnetic composite is considerably faster than the magnetic composite under the same condition. The adsorption capacity of the dendrimer-functionalized magnetic composite for investigated direct and acid dyes was 173.7 and 122.5 mg/g, respectively, which was higher than those of the existing magnetic adsorbents. This work provides new insights into the synthesis and application of hybrid magnetic adsorbents with synergistic properties of nanoporous metal-organic frameworks and dendrimer with a large number of functional groups for the removal of organic dyes.

Facile synthesis of acid-modified UiO-66 to enhance the removal of Cr(VI) from aqueous solutions

The adsorption behavior and mechanism of Cr(VI) on different acid-modified UiO-66s (Form-UiO-66 and Ac-UiO-66) were systematically investigated for the first time through a series of characterizations, and theoretical calculations of batch experiments. The characterization results demonstrate that acid-modified UiO-66 exhibited a larger specific surface area than did unmodified UiO-66. In addition, since the regulator (formic acid) of Form-UiO-66 was the stronger competition, the specific surface area of Form-UiO-66 (1138 m² g^-1) was larger than that of Ac-UiO-66 (915 m² g^-1). Under optimal experimental conditions, the maximum adsorption capacity of Cr(VI) was 243.9 mg g^-1 on Form-UiO-66, and 151.52 mg g^-1 on Ac-UiO-66, which was far higher than on the reported unmodified UiO-66 (36.4 mg g^-1). The results of pH testing, zeta potential, and X-ray photoelectron spectroscopy analysis indicate that Cr(VI) ions were fixed to adsorbent surfaces via electrostatic adsorption. Acid-modified UiO-66 increased the surface active site via the increase in its specific surface area to enhance adsorption capacity of Cr(VI). These results indicated that both the surface charge and specific surface area of the adsorbent primarily determined the Cr(VI) adsorption capacity. Acid modified UiO-66 exhibited enhanced adsorption capacity, stability, and regeneration, compared to traditional adsorbents, and these results provide new insights into adsorption by MOFs.

Effect of Co(II) dopant on the removal of Methylene Blue by a dense copper terephthalate

In this research, for the first time, a series of Co(II) doped copper terephthalate (CoX-CuBDC, where X is doping percentage) were successfully synthesized via solvothermal method and were tested for dye removal application. The physical properties of CoX-CuBDC were studied by several techniques including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) surface area analysis. The incorporation of Co(II) dopant leads to isomorphic substitution of Cu(II) in the CuBDC framework with the maximum doping percentage of 22. Doping and parent MOFs which are non-porous were used for removal of Methylene Blue (MB) from aqueous solution. Adsorption capacity of Co22-CuBDC and CuBDC are 52 and 58 mg/g, respectively, both of which are higher than the adsorption capacity recorded from several high porosity MOFs. Adsorption kinetic studies indicate that adsorption process follows pseudo-second order model while the adsorption mechanism is dominated by electrostatic attraction. Overall, even though these materials show non-porous characteristic, it can be used effectively in wastewater treatment application.

Determination and removal of clenbuterol with a stable fluorescent zirconium(IV)-based metal organic framework

A metal organic framework (MOF) based adsorbent of type UiO-66 was hydrothermally prepared and applied to simultaneous sensing and removal of the asthma drug clenbuterol. The MOF possesses a large specific surface area (1460 cm²·g^-1) and a stable structure, and has a large adsorption capacity for clenbuterol (160 mg·g^-1). If clenbuterol binds to the MOF, the fluorescence of the sorbent (best measured at excitation/emission wavelengths of 290/396 nm) is quenched by up to 88%. Based on these findings, a fluorometric assay has been developed for the rapid determination of clenbuterol. The adsorption equilibrium of UiO-66 for CLB can be achieved at 60 min and the adsorption efficiency is above 80%. The method has a linear response in the 4.0 to 40 ng·mL^-1 concentration range, and the lower limit of detection is 0.17 μM. All of this indicates that UiO-66 is promising for simultaneous detection and the removal of CLB in water. Graphical abstract Schematic presentation of the detection and removal of clenbuterol in water medium by a stable fluorescent Zr(IV)-based metal organic framework. This method exhibited a large adsorption capacity for clenbuterol (160 mg/g) and low limit of detection (0.17 μM).

Recent advances on porous organic frameworks for the adsorptive removal of hazardous materials

Environmental pollution is one of the most serious problems facing mankind today, and has attracted widespread attention worldwide. The burgeoning class of crystalline porous organic framework materials, metal-organic frameworks and covalent organic frameworks present promising application potential in areas related to pollution control due to their interesting surface properties. In this review, the literature of the past five years on the adsorptive removal of various hazardous materials, mainly including heavy metal ions, harmful gases, organic dyes, pharmaceutical and personal care products, and radionuclides from the environment by using COFs and MOFs, is summarized. The adsorption mechanisms are also discussed to help understand their adsorption performance and selectivity. Additionally, some insightful suggestions are given to enhance the performance of MOFs and COFs in the adsorptive removal of various hazardous materials.

Fabrication of Fe3O4@UiO-66-SO3H core–shell functional adsorbents for highly selective and efficient removal of organic dyes

A novel magnetic nanocomposite with a core–shell structure was first synthesized and employed as an adsorbent to selectively remove methylene blue.

Revealing the role of the 1T phase on the adsorption of organic dyes on MoS2 nanosheets

Herein, different phases of MoS₂ nanosheets were synthesized, characterized and tested for dye removal from water. The influence of the MoS₂ phases as well as the 1T concentration on the adsorption performance of organic dyes MO, RhB and MB was deeply investigated. The results revealed that the 1T-rich MoS₂ nanosheets have superior adsorption performance compared to other 2H and 3R phases. The kinetic results of the adsorption process demonstrate that the experimental data followed the pseudo-second order equation. Meanwhile, the adsorption of dyes over the obtained materials was fitted with several isotherm models. The Langmuir model gives the best fitting to the experimental data with maximum a adsorption capacity of 787 mg g⁻¹. The obtained capacity is significantly higher than that of all previous reports for similar MoS₂ materials. Computational studies of the 2H and 1T/2H-MoS₂ phases showed that the structural defects present at the 1T/2H grain boundaries enhance the binding of hydroxide and carboxyl groups to the MoS₂ surface which in turn increase the adsorption properties of the 1T/2H-MoS₂ phase.

The high adsorption capacity of dyes onto the 1T-rich MoS₂ samples is due to the strong binding between the hydroxide/carboxyl groups and the 1T active sites. The capacity can be tuned by controlling the ratio between 1T and 2H phases of MoS₂ nanosheets.