A Sm-MOF/GO nanocomposite membrane for efficient organic dye removal from wastewater

Microplastics and dye removal from textile wastewater using MIL-53 (Fe) metal-organic framework-based ultrafiltration membranes

Microplastics (MPs) and other organic matters in textile wastewater have posed a formidable challenge for treatment processes, particularly in the primary stages such as ultrafiltration (UF). UF plays a crucial role in preventing the entry of pollutants into subsequent treatment steps. However, the performance efficiency of UF membranes is compromised by the potential fouling of membrane pores by MPs, dyes and other organic pollutants such as bovine serum albumin (BSA). This study focuses on enhancing UF membrane performance, specifically its antifouling properties, through the development of high-performance membranes using MIL-53(Fe) metal-organic framework (MOF) particles (noted as MIL-53 here). Various concentrations of the MIL-53 (0.05, 0.1, 0.2, and 0.5 wt%) were integrated into the membrane structure through phase inversion process. Streaming zeta potential results confirmed the negatively charged surface of the membranes and their high hydrophilicity was validated through contact angle analysis. FTIR, SEM, EDS, and XRD confirmed the presence of MIL-53 particles on the surface of membranes. The developed membranes were tested for 24 h to assess their antifouling properties, with a subsequent 30-min hydraulic flush to measure their flux recovery ratios. Methylene Blue (MB) dye was used as a cationic dye present in textile wastewater to evaluate the efficiency of the developed membranes in dye removal and the synergistic effects of dye rejection in the presence of organic matters (i.e., MPs and BSA). Since previous studies have not fully addressed the combination of dyes and organic matter, this study thoroughly investigated the effect of particle-type foulants (MPs) and their interactions with dye (MB), as well as water soluble protein-type foulants (BSA) and their interaction with MB. The results indicated that the developed membranes exhibited higher MB rejection when the dye was present with either MP or BSA, along with improved antifouling properties. The optimised UF membrane integrated with 0.1 wt% MIL-53 demonstrated nearly 96% BSA rejection and around 86% MB rejection in the mixed foulant case (BSA-MB). The modified membrane exhibited a substantial increase in water flux from 176 L m-2.h-1 to 327 L m-2.h-1. The findings of this research show the potential of iron-based MOFs in improving the performance of UF membranes and provide a platform for future studies on significant areas such as long-term stability studies and testing with other pollutants found in textile wastewater.

KMnO4-oxidized whole pine needle based adsorbent for selective and efficient removal of cationic dyes

In the present study, we report the chemical modification of the dried and fallen pine needles (PNs) via a simple protocol using KMnO4 oxidation. The oxidized PNs (OPNs) were evaluated as adsorbents using some cationic and anionic dyes. The successful synthesis of OPNs adsorbent was characterized by various techniques to ascertain its structural attributes. The adsorbent showed selectivity for the cationic dyes with 96.11% removal (Pr) for malachite green (MG) and 89.68% Pr for methylene blue (MB) in 120 min. Kinetic models namely, pseudo-first order, pseudo-second order, and Elovich were applied to have insight into adsorption. Additionally, three adsorption isotherms, i.e., Langmuir, Freundlich, and Temkin were also applied. The dye adsorption followed a pseudo-second-order kinetic model with R2 > 0.99912 for MG and R2 > 0.9998 for MB. The adsorbent followed the Langmuir model with a maximum adsorption capacity (qm) of 223.2 mg/g and 156.9 mg/g for MG and MB, respectively. Furthermore, the OPNs showed remarkable regeneration and recyclability up to nine adsorption-desorption cycles with appreciable adsorption for both the dyes. The use of OPNs as an adsorbent for the removal of dyes from wastewater, therefore, provides an ecologically benign, low-cost, and sustainable solution.

Metal-Organic Framework-Based Materials for Wastewater Treatment: Superior Adsorbent Materials for the Removal of Hazardous Pollutants

In previous years, different pollutants, for example, organic dyes, antibiotics, heavy metals, pharmaceuticals, and agricultural pollutants, have been of note to the water enterprise due to their insufficient reduction during standard water and wastewater processing methods. MOFs have been found to have potential toward wastewater management. This Review focused on the synthesis process (such as traditional, electrochemical, microwave, sonochemical, mechanochemical, and continuous-flow spray-drying method) of MOF materials. Moreover, the properties of the MOF materials have been discussed in detail. Further, MOF materials' applications for wastewater treatment (such as the removal of antibiotics, organic dyes, heavy metal ions, and agricultural waste) have been discussed. Additionally, we have compared the performances of some typical MOFs-based materials with those of other commonly used materials. Finally, the study's current challenges, future prospects, and outlook have been highlighted.

Environmental occurrence, toxicity and remediation of perchlorate - A review

Perchlorate (ClO4-) comes under the class of contaminants called the emerging contaminants that will impact environment in the near future. A strong oxidizer by nature, perchlorate has received significant observation due to its occurrence, reactive nature, and persistence in varied environments such as surface water, groundwater, soil, and food. Perchlorate finds its use in number of industrial products ranging from missile fuel, fertilizers, and fireworks. Perchlorate exposure occurs when naturally occurring or manmade perchlorate in water or food is ingested. Perchlorate ingestion affects iodide absorption into the thyroid, thereby causing a decrease in the synthesis of thyroid hormone, a very crucial component needed for metabolism, neural development, and a number of other physiological functions in the body. Perchlorate remediation from ground water and drinking water is carried out through a series of physical-chemical techniques like ion (particle) transfer and reverse osmosis. However, the generation of waste through these processes are difficult to manage, so the need for alternative treatment methods occur. This review talks about the hybrid technologies that are currently researched and gaining momentum in the treatment of emerging contaminants, namely perchlorate.

Graphene-Based Metal-Organic Framework Hybrids for Applications in Catalysis, Environmental, and Energy Technologies

Current energy and environmental challenges demand the development and design of multifunctional porous materials with tunable properties for catalysis, water purification, and energy conversion and storage. Because of their amenability to de novo reticular chemistry, metal-organic frameworks (MOFs) have become key materials in this area. However, their usefulness is often limited by low chemical stability, conductivity and inappropriate pore sizes. Conductive two-dimensional (2D) materials with robust structural skeletons and/or functionalized surfaces can form stabilizing interactions with MOF components, enabling the fabrication of MOF nanocomposites with tunable pore characteristics. Graphene and its functional derivatives are the largest class of 2D materials and possess remarkable compositional versatility, structural diversity, and controllable surface chemistry. Here, we critically review current knowledge concerning the growth, structure, and properties of graphene derivatives, MOFs, and their graphene@MOF composites as well as the associated structure-property-performance relationships. Synthetic strategies for preparing graphene@MOF composites and tuning their properties are also comprehensively reviewed together with their applications in gas storage/separation, water purification, catalysis (organo-, electro-, and photocatalysis), and electrochemical energy storage and conversion. Current challenges in the development of graphene@MOF hybrids and their practical applications are addressed, revealing areas for future investigation. We hope that this review will inspire further exploration of new graphene@MOF hybrids for energy, electronic, biomedical, and photocatalysis applications as well as studies on previously unreported properties of known hybrids to reveal potential "diamonds in the rough".

A facile synthesis of CeO2 from the GO@Ce-MOF precursor and its efficient performance in the oxygen evolution reaction

Electrochemical water splitting has enticed fascinating consideration as a key conduit for the advancement of renewable energy systems. Fabricating adequate electrocatalysts for water splitting is fervently preferred to curtail their overpotentials and hasten practical utilizations. In this work, a series of Ce-MOF, GO@Ce-MOF, calcinated Ce-MOF, and calcinated GO@Ce-MOF were synthesized and used as high-proficient electrocatalysts for the oxygen evolution reaction. The physicochemical characteristics of the prepared samples were measured by diverse analytical techniques including SEM, HRTEM, FTIR, BET, XPS, XRD, and EDX. All materials underwent cyclic voltammetry tests and were evaluated by electrochemical impedance spectroscopy and oxygen evolution reaction. Ce-MOF, GO@Ce-MOF, calcinated Ce-MOF, and calcinated GO@Ce-MOF have remarkable properties such as enhanced specific surface area, improved catalytic performance, and outstanding permanency in the alkaline solution (KOH). These factors upsurge ECSA and intensify the OER performance of the prepared materials. More exposed surface active-sites present in calcinated GO@Ce-MOF could be the logic for superior electrocatalytic activity. Chronoamperometry of the catalyst for 15°h divulges long-term stability of Ce-MOF during OER. Impedance measurements indicate higher conductivity of synthesized catalysts, facilitating the charge transfer reaction during electrochemical water splitting. This study will open up a new itinerary for conspiring highly ordered MOF-based surface active resources for distinct electrochemical energy applications.

Metal-organic framework-based materials for the abatement of air pollution and decontamination of wastewater

Developing new and efficient technologies for environmental remediation is becoming significant due to the increase in global concerns such as climate change, severe epidemics, and energy crises. Air pollution, primarily due to increased levels of H₂S, SO_x, NH₃, NO_x, CO, volatile organic compounds (VOC), and particulate matter (PM) in the atmosphere, has a significant impact on public health, and exhaust gases harm the natural sulfur, nitrogen, and carbon cycles. Similarly, wastewater discharged to the environment with metal ions, herbicides, pharmaceuticals, personal care products, dyes, and aromatics/organic compounds is a risk for health since it may lead to an outbreak of waterborne pathogens and increase the exposure to endocrine-disrupting agents. Therefore, developing new and efficient air and water quality management systems is critical. Metal-organic frameworks (MOFs) are novel materials for which the main application areas include gas storage and separation, water harvesting from the atmosphere, chemical sensing, power storage, drug delivery, and food preservation. Due to their versatile structural motifs that can be modified during synthesis, MOFs also have a great promise for green applications including air and water pollution remediation. The motivation to use MOFs for environmental applications prompted the modification of their structures via the addition of metal and functional groups, as well as the creation of heterostructures by mixing MOFs with other nanomaterials, to effectively remove hazardous contaminants from wastewater and the atmosphere. In this review, we focus on the state-of-the-art environmental applications of MOFs, particularly for water treatment and air pollution, by highlighting the groundbreaking studies in which MOFs have been used as adsorbents, membranes, and photocatalysts for the abatement of air and water pollution. We finally address the opportunities and challenges for the environmental applications of MOFs.

Improving stability and separation performance of graphene oxide/graphene nanofiltration membranes by adjusting the laminated regularity of stacking-sheets

The laminated graphene oxide (GO) membranes are promising alternatives in the field of nanofiltration due to their unique stacked interlayer structure and controllable molecular transport channels. However, it is still challenging to obtain satisfactory physical stability and separation performance to meet its practical application. In this study, a novel GO/Gr (graphene) nanofiltration membrane with high stability was engineered by post-hot-pressure treatment, following forward pressure filtration. The impact of GO/Gr loading ratio of the composites nanofiltration membranes for the permeability, selectivity, hydrophilicity and physical stability was investigated. The GO/Gr nanofiltration membranes exhibited high stability and separation performance because of the enhanced regularity and smoothness of the overall stacking layers. It was demonstrated that the satisfactory permeability (12.8-20 L·m^-2·h^-1) of GO/Gr nanofiltration membranes could be achieved. Compared with the pure GO membranes, GO/Gr-0.5 membranes exhibited a higher Na₂SO₄, NaCl, MgCl₂, and MgSO₄ rejection rate of approximately 78.3%, 51.2%, 34.5% and 32.6%, respectively. Meanwhile, the rejection rate (99.5%, 99.9%, 97.3% and 98.6%) of composite membranes for Methylene blue, Congo red, Rhodamine B and Methyl orange could be achieved. This facile way reveals the potential of stacked GO/Gr membranes in developing GO-based nanofiltration membranes.

Layer-by-layer coating of MIL-100(Fe) on a cotton fabric for purification of water-soluble dyes by the combined effect of adsorption and photocatalytic degradation

Efforts have been made for sustainable development of adsorbents to purify organic contaminants from wastewater. In this study, a MIL-100(Fe) based textile that acts as a reusable adsorbent and photocatalytic agent was developed by synthesizing MIL-100(Fe) onto a cotton fabric by the layer-by-layer (LBL) process using water-based solutions. As the number of LBL cycles increased, the add-on's of MIL-100(Fe) showed a drastic increase up to 8 cycles, then showed gradual increases with further treatments. The overall adsorption performance was enhanced with the increased MIL-100(Fe) add-on's, but the specific adsorption efficiency per unit mass of MIL-100(Fe) was reduced as the LBL cycles increased, implying the reduced average adsorption efficiency with a thicker coating. To examine the reusability of the adsorbent, desorption efficiency of RhB was measured. The desorption after the first-time adsorption was not efficient due to the strong binding inside the pores. For the later cycles of adsorption–desorption, desorption occurred more efficiently, probably because RhB molecules were adhered mostly at the outer surface of the MOF layer. Simultaneously, MIL-100(Fe)@cotton demonstrated the photocatalytic degradation performance against RhB in the presence of H₂O₂ by the Fenton reaction. With the combined effect of adsorption and photodegradation, the developed fabric attained 96% removal efficiency for RhB dissolved in water. This study demonstrates an environmentally responsible process of developing a MIL-100(Fe) coated fabric that is readily available for effective removal of organic foulants in water. This fabrication method can be applied as a scalable manufacturing of metal–organic framework-based photocatalytic adsorbent textiles.

A MIL-100(Fe)-based water purifying textile that functions by dual action of adsorption and photocatalytic activity is designed via a layer-by-layer process without using toxic organic solvents.

Biogenic Synthesis of Cu-Doped ZnO Photocatalyst for the Removal of Organic Dye

The Cu-doped ZnO photocatalysts were prepared with a green and coprecipitation approach by using water hyacinth (Eichhornia crassipes) aquatic plant extract. In the preparation process, different amount of copper precursors such as 1, 2, 3, 4, and 5% of molar ratio were added to zinc nitrate precursors and abbreviated as Cu-ZnO (1%), Cu-ZnO (2%), Cu-ZnO (3%), Cu-ZnO (4%), and Cu-ZnO (5%), respectively. The characterization of the obtained samples was carried out, and the removal of the methylene blue (MB) dye was examined. Out of all catalysts, Cu-ZnO (3%) had the best photocatalytic performance and 89% of the MB dye was degraded. However, the degradation performances of blank (without catalysts), ZnO, Cu-ZnO (1%), Cu-ZnO (2%), Cu-ZnO (4%), and Cu-ZnO (5%) catalysts were 6, 54, 69, 83, 80, and 73%, respectively. Therefore, the use of water hyacinth plant extract with the optimum amount of Cu added to ZnO during the preparation of the catalyst could have a promising application in the degradation of organic pollutants.

Nanotechnology in the Restoration of Polluted Soil

The advancements in nanoparticles (NPs) may be lighting the sustainable and eco-friendly path to accelerate the removal of toxic compounds from contaminated soils. Many efforts have been made to increase the efficiency of phytoremediation, such as the inclusion of chemical additives, the application of rhizobacteria, genetic engineering, etc. In this context, the integration of nanotechnology with bioremediation has introduced new dimensions for revamping the remediation methods. Hence, advanced remediation approaches combine nanotechnological and biological remediation methods in which the nanoscale process regulation supports the adsorption and deterioration of pollutants. Nanoparticles absorb/adsorb a large variety of contaminants and also catalyze reactions by lowering the energy required to break them down, owing to their unique surface properties. As a result, this remediation process reduces the accumulation of pollutants while limiting their spread from one medium to another. Therefore, this review article deals with all possibilities for the application of NPs for the remediation of contaminated soils and associated environmental concerns.

Dye contaminated wastewater treatment through metal–organic framework (MOF) based materials

A complete discussion of MOFs and MOF composites such as MOF-based membranes, magnetic MOFs, and metal–organic gels (MOGs) used for dye removal along with their adsorption efficiency has been done.

Engineering of appropriate pore size combined with sulfonic functionalization in a Zr-MOF with reo topology for the ultra-high removal of cationic malachite green dye from an aqueous medium

A Zr-based metal–organic framework with reo topology, denoted as Reo-MOF-1, was fabricated through a solvothermal method capable of efficiently removing the cationic MG dye from an aqueous medium.

Recent advances in metal-organic framework membranes for water treatment: A review

Among many separation membranes reported to date, the favorable polymer affinity and unique physio-chemical performances of metal-organic frameworks (MOFs) including ultra-high surface area, regular and highly controlled porosity have drawn widespread attention in industrial and academic communities. In this comprehensive review, the developmental timeline of MOF containing membranes for water treatment were clarified. The removal efficiencies, elimination mechanisms, as well as possible influencing factors of various MOF containing membranes that applied to water treatment were systematically summarized. The excellent removal performances of MOF containing membranes for various pollutants were determined by the size-exclusion, π-π stacking interaction, electrostatic interaction, hydrogen bonding and so on. Since the progress of engineered MOF containing membranes for practical wastewater treatment applications lags, we further analyzed the potential environmental application of MOF containing membranes from four aspects (stability of MOFs, antifouling performance of membranes, compatibility between MOF fillers and polymer matrix, dispersity of MOF nanoparticles in matrix), hoping to provide some meaningful insights.

Well-designed sophisticated structure of sandwich-like CC@NiAl-LDH@GO@NiCo-LDH material with unique advantages for high performance and practicality hybrid quasi-solid-state supercapacitors

A sandwich-like flexible architecture electrode material composed of NiAl-LDH nanoplates grown on carbon cloths (CC), coupled with GO interlayer and NiCo-LDH nanowire on the interlayer was successfully assembled via hydrothermal and chemical bath deposition (denoted as CC@NiAl-LDH@GO@NiCo-LDH). The promising combination of NiAl-LDH, graphene and NiCo-LDH forming a multilayer structure through electrostatic absorption and in-situ growth process which endow a high mass loading superiority and synergistic effect for supercapacitors. In addition, the interspace inside the sandwich-like architecture constructed by the graphene and the NiAl-LDH/ NiCo-LDH nano-flakes contribute to alleviate of the volume expansion during the cycling process and promote the diffusion rate of ions. The CC@NiAl-LDH@GO@NiCo-LDH material demonstrates excellent electrochemical performance which exhibit remarkable specific capacitance of 2359.8F·g^-1 (14.2F·cm^-2) at 1 A·g^-1 (6 mA·cm^-2) and outstanding capacitance retentions of 93.1% after 1500 cycles. Subsequently, the CC@NiAl-LDH@GO@NiCo-LDH material was used as cathode material to fabricate a hybrid quasi-solid-state supercapacitor that exhibits a high energy density of 52.0 Wh·kg^-1 at 796.7 W·kg^-1 and 38.4 Wh·kg^-1 at 12015 W·kg^-1, revealing its potential and viability for commercial applications. Furthermore, the hybrid quasi-solid-state supercapacitor can be applied under different extreme operating conditions such as bending, twisting, sour/alkali soaking, ice bathing, warm bathing, hammering and cutting conditions. It is predictable that the unique sandwich-like structure will be an extremely promising electrode material for high-performance supercapacitors.

A new approach for ultra-high adsorption of cationic methylene blue in a Zr-sulfonic-based metal-organic framework

A series of Zr-sulfonic-based metal–organic frameworks have been synthesized by the solvothermal method, namely VNU-17 and VNU-23. Particularly, VNU-17 and VNU-23 adopt the sulfonate group (SO₃⁻) moieties densely packed within their structure, which can efficiently uptake MB⁺ from wastewater. The maximum adsorption capacity for MB⁺ onto VNU-23 is up to 1992 mg g⁻¹ at pH = 7, which is more than five times that of activated carbon and possesses the highest value among all the reported MOF materials. In addition, VNU-23 retains the adsorption uptake of MB for at least five cycles. The adsorption isotherms and kinetic studies reveal that MB⁺ dye adsorption onto VNU-23 fits a Langmuir isotherm and the pseudo second order kinetic model. Furthermore, the ultra-high adsorption capacity of VNU-23 for MB dye can be accounted for by the suitable pore/channel size together with electrostatic attraction and π–π interactions. These results indicate that VNU-23 can be utilized as a promising candidate for removing MB⁺ from an aqueous medium.

A series of Zr-sulfonic-based metal–organic frameworks have been synthesized by the solvothermal method, namely VNU-17 and VNU-23.

Welding partially reduced graphene oxides by MOFs into micro-mesoporous hybrids for high-performance oil absorption

Partially reduced graphene oxides (PRGOs) with a small number of COOH groups remaining at the edges were interlocked by UiO-66-NH2 nanoparticles into hierarchical porous hybrids (PRGO@UiO-66-NH2) during the synthesis of UiO-66-NH2 in the presence of PRGOs, in which the UiO-66-NH2 nanoparticles provide micropores and the interlocked PRGO skeletons provide mesopores. The peak intensity of the functional groups on the PRGO@UiO-66-NH2 hybrids decrease greatly when compared with the GO@UiO-66-NH2 hybrids and the UiO-66-NH2 nanoparticles, and the number of -COOH at the edge of the PRGOs are approximately 6.3% after reduction, which is confirmed by the FT-IR and XPS results. When the PRGO@UiO-66-NH2 hybrids were embedded in their macropores via hydrogen bonding, melamine foams (MFs) were able to effectively absorb a variety of water-immiscible organic solvents from oil/water biphasic mixtures and, at the same time, suppress water infusion due to Cassie-state surface superhydrophobicity with a water contact angle of 154.2° in air. After 10 cycles, the PRGO@UiO-66-NH2-laden MFs exhibited water contact angles of 148.3°, which indicated that the composite MFs had excellent stability and recycling ability after 10 cycles. The PRGO@UiO-66-NH2-laden MFs had an oil absorption capacity of >10 000 wt% of the dry mass of absorbents and water absorption capacity of ≈1.76 wt% of the adsorbate, thus highlighting the high absorption selectivity of oil over water.

Fabrication of UiO-66/MIL-101(Fe) binary MOF/carboxylated-GO composite for adsorptive removal of methylene blue dye from aqueous solutions

This study provides a novel composite as an efficient adsorbent of cationic methylene blue dye. UiO-66/MIL-101(Fe) binary metal organic framework (MOF) was fabricated using a solvothermal technique. Additionally, the developed binary MOF was modified with carboxylated graphene oxide (GOCOOH) using a post-synthetic technique. The as-fabricated UiO-66/MIL-101(Fe)-GOCOOH composite was analyzed by FTIR, XRD, SEM, BET, TGA, XPS and zeta potential analysis. The adsorption performance of UiO-66/MIL-101(Fe)-GOCOOH composite was examined for its aptitude to adsorb cationic MB dye using a batch technique. The obtained data revealed that, the developed UiO-66/MIL-101(Fe)-GOCOOH composite exhibited higher adsorption capacity compared to UiO-66/MIL-101(Fe) binary MOF. Adsorption isotherms and kinetic studies revealed that MB dye adsorption onto UiO-66/MIL-101(Fe)-GOCOOH composite fitted a Langmuir isotherm model (q m = 448.71 mg g-1) and both pseudo 1st order and pseudo 2nd order kinetic models. An intra-particle diffusion model showed that the adsorption process occurs through three steps. Besides, thermodynamic data reflected that the adsorption of MB onto UiO-66/MIL-101(Fe)-GOCOOH composite is an endothermic and spontaneous process and the adsorption involves both physisorption and chemisorption interactions. The as-fabricated UiO-66/MIL-101(Fe)-GOCOOH composite exhibited good reusability and can be considered as a promising reusable adsorbent for the treatment of dye-containing industrial effluents with high efficiency.