Arsenic removal from water by metal-organic framework MIL-88A microrods

Role of microalgae-bacterial consortium in wastewater treatment: A review

In the global effort to reduce CO2 emissions, the concurrent enhancement of pollutant degradation and reductions in fossil fuel consumption are pivotal aspects of microalgae-mediated wastewater treatment. Clarifying the degradation mechanisms of bacteria and microalgae during pollutant treatment, as well as regulatory biolipid production, could enhance process sustainability. The synergistic and inhibitory relationships between microalgae and bacteria are introduced in this paper. The different stimulators that can regulate microalgal biolipid accumulation are also reviewed. Wastewater treatment technologies that utilize microalgae and bacteria in laboratories and open ponds are described to outline their application in treating heavy metal-containing wastewater, animal husbandry wastewater, pharmaceutical wastewater, and textile dye wastewater. Finally, the major requirements to scale up the cascade utilization of biomass and energy recovery are summarized to improve the development of biological wastewater treatment.

High Capacity Arsenate Removal from Real Samples Using Dihydrotetrazine Decorated Zirconium-Based Metal-Organic Frameworks

Zirconium metal-organic frameworks (Zr-MOFs) are potential candidates for decontamination of water resources from harmful pollutants due to their modulable porosity and chemical stability in aqueous solutions. Linker functionalization is an approach for tuning the host-guest chemistry of Zr-MOFs and extends their applications in environmental monitoring. In this work, the structure of UiO-66(Zr) (formulated Zr6(OH)4O4(BDC)6, BDC2- = benzene-1,4-dicarboxylate) was functionalized with dihydrotetrazine group via postsynthesis linker exchange (PSLE) method. The functionalized framework, UiO-66(Zr)-DHTZ, was applied for the removal of arsenate ions from aqueous solutions. The results show that UiO-66(Zr)-DHTZ can adsorb 583 mg g-1 of As(V) at pH = 7 after 2 h, which is significantly higher than that of the UiO-66(Zr). According to X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR), the removal mechanism is based on possible hydrogen bindings between free -C-NH and -C═N- sites of dihydrotetrazine function with -O- and -OH sites of As(V) species. Removal tests in real samples show that UiO-66(Zr)-DHTZ still has a high capacity (220 mg g-1) to As(V) ions in complex matrixes and also can decrease the concentration of As(V) below the detection limit (0.05 ppm) of the inductively coupled plasma optical emission spectroscopy (ICP-OES) method. Since the dihydrotetrazine-decorated UiO-66(Zr)-DHTZ reaches one the highest adsorption capacities to As(V) species, it can be considered a potential candidate for water treatment in real-life applications.

Adsorption behavior and mechanism of modified Fe-based metal-organic framework for different kinds of arsenic pollutants

Arsenic in water environment can present significant threats to human health, and eliminating arsenic pollutants from wastewater is crucial. Based on our previously reported work, this study delved into the adsorption behavior and mechanism of different arsenic contaminants (p-ASA, ROX, As(V), and DMA) on the activated Fe-based metal-organic framework (activated MIL-88A). The results show that activated MIL-88A exhibits exceptional adsorption capabilities toward diverse arsenic pollutants. The adsorption process is endothermic, spontaneous, and viable, and chemical adsorption plays a leading role. The remarkable adsorption capacity of activated MIL-88A to various arsenic pollutants is primarily attributed to coordination, while hydrogen bonding also assumes a significant role in the elimination of p-ASA and ROX. Additionally, we investigated the impact of arsenic molecule shape and size, solution pH, and the existence of specific anions and dissolved organic matter (DOM) on the adsorption of different arsenic pollutants. This study can provide valuable insights for further exploring the selective adsorption of different kinds of arsenic species by Fe-based MOF materials and improving the adsorption efficiency of MOFs.

Efficient Removal of Nitrate in Neutral Solution Using Zero-Valent Al Activated by Soaking

Nitrate is a contaminant widely found in surface water, and a high concentration of nitrate can pose a serious threat to human health. Zero-valent iron is widely used to reduce nitrate in aqueous solution, but an acidic condition is required. Zero-valent aluminum has a much lower redox potential (E₀(Al³⁺/Al⁰) = -1.662 V) than zero-valent iron (E₀(Fe²⁺/Fe⁰) = -0.44 V), making it a better choice for reduction of nitrate. However, a passive oxide film covering on Al surfaces inhibits its electron transfer. In this work, metal Al powder was activated by a soaking procedure in deionized water. It was found that nitrate in neutral solution can be efficiently and completely reduced by soaked Al, even if the concentration of nitrate-N was up to 100 mg L^-1. Using an optimal soaking time, the soaked Al can remove >90% of nitrate in aqueous solution within ∼2 h at 50 °C. Furthermore, the nitrate reduction efficiency increased with increasing reaction temperature and dosage of Al powder. After reaction, only ∼50% of pristine N content was left in the form of ammonia ions (NH₄⁺) in aqueous solution. Mechanism analyses showed that after soaking, Al particle surfaces were covered by a layer of loose and fine Al(OH)₃ grains, which can shorten the induction time for the beginning of the reaction between inner Al and outside ions or molecules. This is the reason why soaked Al has a high efficiency for nitrate removal. The present results indicate that soaking is an effective way to activate Al to remove nitrate in water.

Research on Improved MOF Materials Modified by Functional Groups for Purification of Water

With the rapid development of urbanization and industrialization, water contamination has gradually become a big problem. Relevant studies show that adsorption is an efficient strategy to treat pollutants in water. MOFs are a class of porous materials with a three-dimensional frame structure shaped by the self-assembly of metal centers and organic ligands. Because of its unique performance advantages, it has become a promising adsorbent. At present, single MOFs cannot meet the needs, but the introduction of familiar functional groups on MOFs can promote the adsorption performance of MOFs on the target. In this review, the main advantages, adsorption mechanism, and specific applications of various functional MOF adsorbents for pollutants in water are reviewed. At the end of the article, we summarize and discuss the future development direction.

Facile monomer interlayered MOF based thin film nanocomposite for efficient arsenic separation

The thin film nanocomposites (TFN) based membranes are sensitive to the synergy between the polymer and nanoparticles. TFN incorporating metal-organic frameworks (MOFs) have shown tremendous enhancement in permeability. This study investigates alternate MOF positioning during TFC fabrication for a highly selective membrane. Co-Zn-based mixed metal-organic framework (mMOF) was interlayered between m-phenylenediamine (MPD) and trimesoyl chloride (TMC) to form a polyamide (PA) selective layer. The practiced method conveniently allowed exact loading of mMOF and thus prevented the loss. Owing to the mMOF's placement between MPD and TMC, an increase in PA cross-linking was observed. The mMOF-MPD monomer compatibility allowed homogeneous distribution and formation of a defect-free PA layer. The surface morphology showed a more pronounced formation of leaves-like features due to interfacial degassing. Neutral solute-based filtration tests determined mean pore size, probability distribution, and MWCO. The incorporation of mMOF led to formation of additional nanochannels in the membrane surface. The perm-selectivity studies performed on a dead-end filtration unit resulted in 94% As⁵⁺ retention with 2.5 times higher permeance than the control. The current study pronounced the viability of the monomer interlayer method to form a highly selective TFN for water separation and related applications.

Machine learning approaches for predicting arsenic adsorption from water using porous metal-organic frameworks

Arsenic in drinking water is a serious threat for human health due to its toxic nature and therefore, its eliminating is highly necessary. In this study, the ability of different novel and robust machine learning (ML) approaches, including Light Gradient Boosting Machine (LightGBM), Extreme Gradient Boosting, Gradient Boosting Decision Tree, and Random Forest was implemented to predict the adsorptive removal of arsenate [As(V)] from wastewater over 13 different metal–organic frameworks (MOFs). A large experimental dataset was collected under various conditions. The adsorbent dosage, contact time, initial arsenic concentration, adsorbent surface area, temperature, solution pH, and the presence of anions were considered as input variables, and adsorptive removal of As(V) was selected as the output of the models. The developed models were evaluated using various statistical criteria. The obtained results indicated that the LightGBM model provided the most accurate and reliable response to predict As(V) adsorption by MOFs and possesses R², RMSE, STD, and AAPRE (%) of 0.9958, 2.0688, 0.0628, and 2.88, respectively. The expected trends of As(V) removal with increasing initial concentration, solution pH, temperature, and coexistence of anions were predicted reasonably by the LightGBM model. Sensitivity analysis revealed that the adsorption process adversely relates to the initial As(V) concentration and directly depends on the MOFs surface area and dosage. This study proves that ML approaches are capable to manage complicated problems with large datasets and can be affordable alternatives for expensive and time-consuming experimental wastewater treatment processes.

Frontier Materials for Adsorption of Antimony and Arsenic in Aqueous Environments: A Review

As highly toxic and carcinogenic substances, antimony and arsenic often coexist and cause compound pollution. Heavy metal pollution in water significantly threatens human health and the ecological environment. This article elaborates on the sources and hazards of compound antimony and arsenic contamination and systematically discusses the research progress of treatment technology to remove antimony and arsenic in water. Due to the advantages of simple operation, high removal efficiency, low economic cost, and renewable solid and sustainable utilization, adsorption technology for removing antimony and arsenic from sewage stand out among many treatment technologies. The adsorption performance of adsorbent materials is the key to removing antimony and arsenic in water. Therefore, this article focused on summarizing frontier adsorption materials' characteristics, adsorption mechanism, and performance, including MOFs, COFs, graphene, and biomass materials. Then, the research and application progress of antimony and arsenic removal by frontier materials were described. The adsorption effects of various frontier adsorption materials were objectively analyzed and comparatively evaluated. Finally, the characteristics, advantages, and disadvantages of various frontier adsorption materials in removing antimony and arsenic from water were summarized to provide ideas for improving and innovating adsorption materials for water pollution treatment.

Facile fabrication of amino-functionalized MIL-68(Al) metal-organic framework for effective adsorption of arsenate (As(V))

An amino-functionalized MIL-68(Al) metal–organic framework (amino-MIL-68(Al) MOF) was synthesized by solvothermal method and then characterized by FESEM, XRD, FTIR, EDX-mapping, and BET-BJH techniques. In order to predict arsenate (As(V)) removal, a robust quadratic model (R² > 0.99, F-value = 2389.17 and p value < 0.0001) was developed by the central composite design (CCD) method and then the genetic algorithm (GA) was utilized to optimize the system response and four independent variables. The results showed that As(V) adsorption on MOF was affected by solution pH, adsorbent dose, As(V) concentration and reaction time, respectively. Predicted and experimental As(V) removal efficiencies under optimal conditions were 99.45 and 99.87%, respectively. The fitting of experimental data showed that As(V) adsorption on MOF is well described by the nonlinear form of the Langmuir isotherm and pseudo-second-order kinetic. At optimum pH 3, the maximum As(V) adsorption capacity was 74.29 mg/g. Thermodynamic studies in the temperature range of 25 to 50 °C showed that As(V) adsorption is a spontaneous endothermic process. The reusability of MOF in ten adsorption/regeneration cycles was studied and the results showed high reusability of this adsorbent. The highest interventional effect in inhibiting As(V) adsorption was related to phosphate anion. The results of this study showed that amino-MIL-68(Al) can be used as an effective MOF with a high surface area (> 1000 m²/g) and high reusability for As(V)-contaminated water.

MIL series of metal organic frameworks (MOFs) as novel adsorbents for heavy metals in water: A review

With large specific surface area, abundant adsorption sites, flexible pore structure, and good water stability, Materials of Institute Lavoisier frameworks (MILs) have attracted increasing attention as effective environmental adsorbents. This review systematically analyzes and recapitulates recent progress in the synthesis and application of MIL-based adsorbents for the removal of aqueous heavy metal ions. Commonly used solvothermal, microwave, electrochemical, ultrasonic, and mechanochemical syntheses of MILs are first summarized and compared. Instead of focusing on adsorption process parameters, adsorption performances and governing mechanisms of virgin MILs, functional MILs, MIL-based composites, and carbonized MILs to representative metal(loid) ions (chromium, arsenic, lead, cadmium, and mercury) in water under various conditions are then systematically reviewed and discussed. In the end, this work also outlines prospects and future directions to promote the applications of MILs in treating heavy metal contaminated water.

Synthesis of 3D Hollow Layered Double Hydroxide-Molybdenum Disulfide Hybrid Materials and Their Application in Flame Retardant Thermoplastic Polyurethane

The development of high-performance thermoplastic polyurethane (TPU) with high flame retardancy and low toxicity has always been the focus of its research. In this paper, the novel 3D hollow layered double hydroxide/molybdenum disulfide (LDH/MoS₂) hybrid materials were synthesized by hydrothermal method using the MIL-88A as in situ sacrificial template and MoS₂ as synergistic flame retardant. Among all TPU composites, the peak heat release rate, total heat release rate, and total smoke release rate of TPU/NiFeTb-LDH/MoS₂ were reduced by 50.9%, 18.2%, and 35.8% compared with pure TPU, respectively. The results of the thermogravimetric infrared analysis demonstrated that the contents of combustible volatiles (hydrocarbons) and toxic volatiles (CO and HCN) emitted from TPU/LDH/MoS₂ were significantly reduced, indicating that LDH/MoS₂ hybrid materials can dramatically enhance the fire safety of TPU composites. Combined with the analysis of carbon residues and thermal stability of TPU composites, the enhanced flame retardancy and smoke suppression performances are primarily attributed to the catalytic carbonization of LDH and the physical barrier effect of MoS₂.

Research progress of metal organic frameworks and their derivatives for adsorption of anions in water: A review

Anion pollution in water has become a problem that cannot be ignored. The anion concentration should be controlled below the national emission standard to meet the demand for clean water. Among the methods for removing excess anions in water, the adsorption method has a unique removal performance, and the core of the adsorption method is the adsorbent. In recent years, the emerging metal-organic frameworks (MOFs) have the advantages of adjustable porosity, high specific surface area, diverse functions, and easy modification. They are very competitive in the field of adsorption of liquid anions. This article focuses on the adsorption of fluoride, arsenate, chromate, radioactive anions (ReO₄^-, TcO₄^-, SeO₄^2-/SeO₃^2-), phosphate ion, chloride ion, and other anions by MOFs and their derivatives. The preparation methods of MOFs are introduced in turn, the application of different types of metal-based MOFs to adsorb various anions were discussed in categories with their crystal structure and functional groups. The influence on the adsorption of anions is analyzed, including the more common and special adsorption mechanisms, adsorption kinetics and thermodynamics, and regeneration performance are briefly described. Finally, the current situation of MOFs adsorption of anions is summarized, and the outlook for future development is summarized to provide my own opinions for the practical application of MOFs.

Nanomaterials as adsorbents for As(III) and As(V) removal from water: A review

Freshwater demand will rise in the next couple of decades, with an increase in worldwide population growth and industrial development. The development activities, on one side, have increased the freshwater demand. However, the ground water has been degraded. Among the various organic and inorganic contaminants, arsenic is one of the most toxic elements. Arsenic contamination in ground waters is a major issue worldwide, especially in South and Southeast Asia. Various methods have been applied to provide a remedy to arsenic contamination, including adsorption, ion exchange, oxidation, coagulation-precipitation and filtration, and membrane filtration. Out of these methods, adsorption of As(III)/As(V) using nanomaterials and biopolymers has been used on a wide scale. The present review focuses on recently used nanomaterials and biopolymer composites for As(III)/As(V) sorptive removal. As(III)/As(V) adsorption mechanisms have been explored for various sorbents. The impacts of environmental factors such as pH and co-existing ions on As(III)/As(V) removal, have been discussed. Comparison of various nanosorbents and biopolymer composites for As(III)/As(V) adsorption and regeneration of exhausted materials has been included. Overall, this review will be useful to understand the sorption mechanisms involved in As(III)/As(V) removal by nanomaterials and biopolymer composites and their comparative sorption performances.

Robust Al3+ MOF with Selective As(V) Sorption and Efficient Luminescence Sensing Properties toward Cr(VI)

Herein, we report the synthesis and characterization of a new robust Al³⁺ metal-organic framework MOF, [Al(OH)(PATP)]·solvent (Al-MOF-1, with PATP^2- = 2-((pyridin-2-ylmethyl)amino)terephthalate). Al-MOF-1 exhibits excellent stability from highly acidic (pH = 2) to basic (pH = 12) aqueous solutions or in the presence of oxoanionic species [As(V) and Cr(VI)]. On the contrary, the related MIL-53(Al) MOF (Al(OH) (BDC), with BDC^2- = terephthalate) shows a partial structure collapse under these conditions, signifying the superior chemical robustness of Al-MOF-1. Al-MOF-1 was proved to be an effective sorbent toward As(V) with efficient sorption capacity (71.9 ± 3.8 mg As/g), rapid sorption kinetics (equilibrium time ≤1 min), and high selectivity in the presence of various competing anions. Furthermore, Al-MOF-1 revealed high sorption capacities for Cr(VI) species in both neutral (124.5 ± 8.6 mg Cr/g) and acidic (63 ± 2 mg Cr/g) aqueous media, combining fast kinetics and relatively good selectivity. The limited porosity (BET = 38 m²/g) and small pores (2-3 Å) of the material indicate that the sorption process occurs exclusively on the external surface of Al-MOF-1 particles. The driving force for the capture of oxoanions by Al-MOF-1 is the strong electrostatic interactions between the oxoanionic species and the positively charged surface of MOF particles. Aiming at a practical wastewater treatment, we have also immobilized Al-MOF-1 on a cotton substrate, coated with polydopamine. The fabric sorbent exhibited highly effective removal of the toxic oxoanionic species from aqueous media under either batch or dynamic (continuous flow) conditions. In addition, Al-MOF-1 was found to be a promising luminescence sensor for detecting trace amounts of Cr(VI) in real water samples, with Cr(VI) being successfully detected at concentrations well below the acceptable limits (<50 ppb). Moreover, Al-MOF-1 was demonstrated to be a sufficient water sensor in organic solvents (LOD ≤0.25% v/v). All the above indicate that Al-MOF-1 represents a multifunctional material with a multitude of potential applications, such as environmental remediation, industrial wastewater treatment, chemical analysis, and water determination in biofuels.

Graphene-supported polyoxometalate entrapped in MIL-88A network with highly efficient conversion of polysulfides in Li-S batteries

Polyoxometalates (POMs) have been demonstrated to have strong anchoring and efficient catalysis for lithium polysulfides (LiPSs). However, the severe aggregation buries the effective active sites of POMs, along with poor...

A comparative study on high-efficient reduction of bromate in neutral solution using zero-valent Al treated by different procedures

Bromate, a toxic by-product of bromide-containing drinking water after disinfecting with ozone, has attracted much attention in the past two decades. Traditional methods to activate zero-valent metals for reducing bromate are to eliminate their surface oxide layer by acid washing. In this work, for the first time, zero-valent Al (ZVAl) was surface treated by the following procedures including soaking, soaking and freeze-drying, soaking and heat-treating, and γ-Al₂O₃ covering Al particle surfaces (GCAP). It was found that all of above surface treated ZVAls have an obvious high efficiency for bromate reduction relative to pristine ZVAl. The bromate reduction rate is GCAP > soaking Al > freeze-drying Al > soaking and heat-treating Al > pristine Al, and using GCAP just 30 min is taken to completely reduce bromate to bromide in neutral solution. Mechanism analyses revealed that Al surface treating or covered by fine γ-Al₂O₃ phase can promote the hydration and breakage of Al surface passive oxide layer, resulting in a fast contact of inner Al with outside ions, leading to a high reduction rate of bromate in neutral solution. XPS analyses indicated that there are no bromate or bromide ions adsorbed on Al particle surfaces, implying that there is a high direct donating efficiency of electrons from inner Al to bromate ions in solution. Furthermore, GCAP has a good reusability and >90% bromate can be reduced even it was reused up to 4 cycles.

Removal of decidedly lethal metal arsenic from water using metal organic frameworks: a critical review

Water contamination is worldwide issue, undermining whole biosphere, influencing life of a large number of individuals all over the world. Water contamination is one of the chief worldwide danger issues for death, sickness, and constant decrease of accessible drinkable water around the world. Among the others, presence of arsenic, is considered as the most widely recognized lethal contaminant in water bodies and poses a serious threat not exclusively to humans but also towards aquatic lives. Hence, steps must be taken to decrease quantity of arsenic in water to permissible limits. Recently, metal-organic frameworks (MOFs) with outstanding stability, sorption capacities, and ecofriendly performance have empowered enormous improvements in capturing substantial metal particles. MOFs have been affirmed as good performance adsorbents for arsenic removal having extended surface area and displayed remarkable results as reported in literature. In this review we look at MOFs which have been recently produced and considered for potential applications in arsenic metal expulsion. We have delivered a summary of up-to-date abilities as well as significant characteristics of MOFs used for this removal. In this review conventional and advanced materials applied to treat water by adsorptive method are also discussed briefly.

Oxide modified aluminum for removal of methyl orange and methyl blue in aqueous solution

Oxide modified Al exhibited a higher efficiency in removing organic dyes in aqueous solution than pristine Al.

Mixed matrix membranes incorporated with sonication-assisted ZIF-8 nanofillers for hazardous wastewater treatment

Mixed matrix membranes (MMMs) provide a unique pathway to treat hazardous industrial effluents. MMMs containing zeolitic imidazolate framework-8 (ZIF-8) as filler in polydimethoxysilane (PDMS) matrix were synthesized. ZIF-8 was prepared using a modified recipe and characterized by different techniques to evaluate its morphology, thermal stability, surface area, pore volume, and other characteristics. The performance of membranes was evaluated for their application in industrial dye-stuff wastewater treatment and solvent-resistant nanofiltration. The results demonstrated that increase in the percentage of ZIF-8 loading in PDMS led to simultaneous increase in the solvent permeability as well as solute rejection from wastewater. The permeability of MMMs increased up to 32% as compared with neat PDMS membrane. The organic dye rejection was achieved more than 87% with MMMs incorporated with 20% loading of nanofillers. Rejection of MMMs was 22% higher than that of unfilled PDMS membrane due to the effect of reduced polymer swelling and size exclusion of the nanofillers. Membrane swelling tests with toluene and isopropanol demonstrated that nanofiller amount has inverse relation with membrane swelling, which implied that nanofillers were in good interaction with polymer and allowed defect free membranes with higher solute rejections and reduced membrane swelling.

Metal-organic frameworks for aquatic arsenic removal

Effective remediation of arsenic contaminated water remains a critical task from the environmental perspective, owing to the harmful effects of arsenic on human health and the environment. Recently, highly porous metal-organic frameworks (MOFs) with excellent chemical stability and abundant functional groups represent a significant new addition to the area of capturing aquatic arsenic pollutants. This review focuses on the development of MOF-based materials for the efficient removal of toxic arsenic species from aqueous solutions. Aspects related to the materials' characteristics, application performance and interaction mechanisms are systematically studied, referencing the macroscopic experimental behaviors and microscopic spectroscopy analyses. The properties of various MOF-based materials are assessed and compared with those of other conventionally used materials. At last, insights and perspectives are suggested in terms of future research directions and development challenges. Overall, this class of materials demonstrates a promising potential for aquatic arsenic removal, and with a proper up-scaling development might it be used for practical applications in the near future.

Preparation of Magnetic Fe₃O₄/MIL-88A Nanocomposite and Its Adsorption Properties for Bromophenol Blue Dye in Aqueous Solution

Metal-organic frameworks (MOFs) are considered as good materials for the adsorption of many environmental pollutants. In this study, magnetic Fe₃O₄/MIL-88A composite was prepared by modification of MIL-88A with magnetic nanoparticles using the coprecipitation method. The structures and magnetic property of magnetic Fe₃O₄/MIL-88A composite were characterized and the adsorption behavior and mechanism for Bromophenol Blue (BPB) were evaluated. The results showed that magnetic Fe₃O₄/MIL-88A composite maintained a hexagonal rod-like structure and has good magnetic responsibility for magnetic separation (the maximum saturation magnetization was 49.8 emu/g). Moreover, the maximum adsorption amount of Fe₃O₄/MIL-88A composite for BPB was 167.2 mg/g and could maintain 94% of the initial adsorption amount after five cycles. The pseudo-second order kinetics and Langmuir isotherm models mostly fitted to the adsorption for BPB suggesting that chemisorption is the rate-limiting step for this monomolecular-layer adsorption. The adsorption capacity for another eight dyes (Bromocresol Green, Brilliant Green, Brilliant Crocein, Amaranth, Fuchsin Basic, Safranine T, Malachite Green and Methyl Red) were also conducted and the magnetic Fe₃O₄/MIL-88A composite showed good adsorption for dyes with sulfonyl groups. In conclusion, magnetic Fe₃O₄/MIL-88A composite could be a promising adsorbent and shows great potential for the removal of anionic dyes containing sulfonyl groups.