Novel polyvinylidene fluoride nanofiltration membrane blended with functionalized halloysite nanotubes for dye and heavy metal ions removal

Fabrication of eco-friendly nanocellulose-chitosan-calcium phosphate ternary nanocomposite for wastewater remediation

Nanocomposites have emerged as promising materials for pollutant removal due to their unique properties. However, conventional synthesis methods often involve toxic solvents or expensive materials. In this study, we present a novel ternary nanocomposite synthesized via a simple, cost-effective vacuum filtration method. The composite consists of calcium phosphate (CaP), biowaste-derived nanocellulose (diameter <50 nm) (NC), and chitosan (CH). The nanocomposite exhibited exceptional pollutant removal capabilities due to the hybrid approach of combining adsorption and size exclusion that widens and accelerates pollutant removal. When tested with synthetic wastewater containing 10 ppm of Ni ions and 10 ppm of Congo red (CR) dye, it achieved impressive removal rates of 98.7% for Ni ions and 100% for CR dye. Moreover, the nanocomposite effectively removed heavy metals such as Cd, Ag, Al, Fe, Hg, Mo, Li, and Se at 100%, and Ba, Be, P, and Zn at 80%, 92%, 87%, and 97%, respectively, from real-world municipal wastewater. Importantly, this green nanocomposite membrane was synthesized without the use of harmful chemicals or complex modifications and operated at a high flux rate of 146 L/m2.h.MPa. Its outstanding performance highlights its potential for sustainable pollutant removal applications.

An integrated experimental and theoretical approach to probe Cr(vi) uptake using decorated halloysite nanotubes for efficient water treatment

Halloysite nanotubes (HNTs) were surface functionalized using four distinct chemical moieties (amidoxime, hydrazone, ethylenediamine (EDA), and diethylenetriamine (DETA)), producing modified HNTs (H1-H4) capable of binding with Cr(vi) ions. Advanced techniques like FTIR, XRD, SEM, and EDX provided evidence of the successful functionalization of these HNTs. Notably, the functionalization occurred on the surface of HNTs, rather than within the interlayer or lumen. These decorated HNTs were effective in capturing Cr(vi) ions at optimized sorption parameters, with adsorption rates ranging between 58-94%, as confirmed by atomic absorption spectroscopy (AAS). The mechanism of adsorption was further scrutinized through the Freundlich and Langmuir isotherms. Langmuir isotherms revealed the nearest fit to the data suggesting the monolayer adsorption of Cr(vi) ions onto the nanotubes, indicating a favorable adsorption process. It was hypothesized that Cr(vi) ions are primarily attracted to the amine groups on the modified nanotubes. Quantum chemical calculations further revealed that HNTs functionalized with hydrazone structures (H2) demonstrated a higher affinity (interaction energy -26.33 kcal mol-1) for the Cr(vi) ions. This can be explained by the formation of stronger hydrogen bonds with the NH moieties of the hydrazone moiety, than those established by the OH of oxime (H1) and longer amine chains (H3 and H4), respectively. Overall, the findings suggest that these decorated HNTs could serve as an effective and cost-efficient solution for treating water pollution.

Combining phthalimide innate of a positive-charge nanofiltration membrane for high selectivity and rejection for bivalent cations

A positively charged nanofiltration (NF) membrane is known to have exceptional separation performance for bivalent cations in aqueous solutions. In this study, a new NF activity layer was created using interfacial polymerization (IP) on a polysulfone (PSF) ultrafiltration substrate membrane. The aqueous phase combines the two monomers of polyethyleneimine (PEI) and phthalimide, while successfully producing a highly efficient and accurate NF membrane. The conditions of the NF membrane were studied and further optimized. The aqueous phase crosslinking process enhances the polymer interaction, resulting in an excellent pure water flux of 7.09 L·m^-2·h^-1·bar^-1 under a pressure of 0.4 MPa. Additionally, the NF membrane shows excellent selectivity toward inorganic salts, with a rejection order of MgCl₂ > CaCl₂ > MgSO₄ > Na₂SO₄ > NaCl. Under optimal conditions, the membrane was able to reject up to 94.33% of 1,000 mg/L of MgCl₂ solution at an ambient temperature. Further to assess the antifouling properties of the membrane with bovine serum albumin (BSA), the flux recovery ratio (FRR) was calculated to be 81.64% after 6 h of filtration. This paper presents an efficient and straightforward approach to customize a positively charged NF membrane. We achieve this by introducing phthalimide, which enhances the membrane's stability and rejection performance.

Novel MXene-Modified Polyphenyl Sulfone Membranes for Functional Nanofiltration of Heavy Metals-Containing Wastewater

In this work, MXene as a hydrophilic 2D nanosheet has been suggested to tailor the polyphenylsulfone (PPSU) flat sheet membrane characteristics via bulk modification. The amount of MXene varied in the PPSU casting solution from 0-1.5 wt.%, while a series of characterization tools have been employed to detect the surface characteristics changes. This included atomic force microscopy (AFM), scanning electron microscopy (SEM), contact angle, pore size and porosity, and Fourier-transform infrared spectroscopy (FTIR). Results disclosed that the MXene content could significantly influence some of the membranes' surface characteristics while no effect was seen on others. The optimal MXene content was found to be 0.6 wt.%, as revealed by the experimental work. The roughness parameters of the 0.6 wt.% nanocomposite membrane were notably enhanced, while greater hydrophilicity has been imparted compared to the nascent PPSU membrane. This witnessed enhancement in the surface characteristics of the nanocomposite was indeed reflected in their performance. A triple enhancement in the pure water flux was witnessed without compromising the retention of the membranes against the Cu²⁺, Cd²⁺ and Pd²⁺ feed. In parallel, high, and comparable separation rates (>92%) were achieved by all membranes regardless of the MXene content. In addition, promising antifouling features were observed with the nanocomposite membranes, disclosing that these nanocomposite membranes could offer a promising potential to treat heavy metals-containing wastewater for various applications.

Pilot scale nanofiltration membrane fabrication containing ionic co-monomers and halloysite nanotubes for textile dye filtration

Wastewater from the textile industry contains high concentrations of pollutants, so the wastewater must be treated before it is discharged. In addition, the reuse of treated wastewater should be considered from an environmental point of view, as large volumes of wastewater are produced. Since textile wastewater mainly contains dyestuffs, it must be treated effectively using environmentally friendly technologies. Membrane processes are widely used in textile wastewater treatment as they have distinct advantages over conventional wastewater treatment methods. This study reports the pilot-scale manufacturing and characterization of three different NF membranes. Three different types of membranes were fabricated. The fabricated membranes were compared through characterization by surface properties, chemical structure and morphology. Membranes were tested for pure water flux. Then the synthetic wastewater (SWW) was tested for flux and rejection. Lastly, the textile wastewater was tested. The textile wastewater flux of pure piperazine (PIP), 60% S-DADPS and 0.04% halloysite nanotubes (HNTs) were 22.42, 79.58 and 40.06 L m^-2 h^-1. It has been proven that the 60% s-DADPS membrane provides up to four times improvement in wastewater flux and simultaneously. In addition, NF membranes produced using HNT and sDADPS on a pilot scale have brought innovation to the literature with the good results obtained.

Recent Advances on the Fabrication of Antifouling Phase-Inversion Membranes by Physical Blending Modification Method

Membrane technology is an essential tool for water treatment and biomedical applications. Despite their extensive use in these fields, polymeric-based membranes still face several challenges, including instability, low mechanical strength, and propensity to fouling. The latter point has attracted the attention of numerous teams worldwide developing antifouling materials for membranes and interfaces. A convenient method to prepare antifouling membranes is via physical blending (or simply blending), which is a one-step method that consists of mixing the main matrix polymer and the antifouling material prior to casting and film formation by a phase inversion process. This review focuses on the recent development (past 10 years) of antifouling membranes via this method and uses different phase-inversion processes including liquid-induced phase separation, vapor induced phase separation, and thermally induced phase separation. Antifouling materials used in these recent studies including polymers, metals, ceramics, and carbon-based and porous nanomaterials are also surveyed. Furthermore, the assessment of antifouling properties and performances are extensively summarized. Finally, we conclude this review with a list of technical and scientific challenges that still need to be overcome to improve the functional properties and widen the range of applications of antifouling membranes prepared by blending modification.

Polymer Membranes as Innovative Means of Quality Restoring for Wastewater Bearing Heavy Metals

The problem that has aroused the interest of this review refers to the harmful effect of heavy metals on water sources due to industrial development. In this respect, the review is aimed at achieving a literature survey on the outstanding results and advancements in membranes and membrane technologies for the advanced treatment of heavy metal-loaded wastewaters. Particular attention is given to synthetic polymer membranes, for which the proper choice of precursor material can provide cost benefits while ensuring good decontamination activity. Furthermore, it was also found that better removal efficiencies of heavy metals are achieved by combining the membrane properties with the adsorption properties of inorganic powders. The membrane processes of interest from the perspective of industrial applications are also discussed. A noteworthy conclusion is the fact that the main differences between membranes, which refer mainly to the definition and density of the pore structure, are the prime factors that affect the separation process of heavy metals. Literature studies reveal that applying UF/MF approaches prior to RO leads to a better purification performance.

Highly Efficient Elimination of Pb+2 and Al+3 Metal Ions from Wastewater Using Graphene Oxide/3,5-Diaminobenzoic Acid Composites: Selective Removal of Pb2+ from Real Industrial Wastewater

In this study, graphene oxide (GO) was functionalized with 3,5-diaminobenzoic acid (DABA) by a one-step method to produce functionalized graphene oxide (FGO). FGO is a new type of absorbent crystalline substance that has a high surface area and a large porosity site as well as a large number of dentate functional groups which lead to enhanced adsorption performance for heavy metal ions. The adsorption efficiency of FGO for Pb⁺² and Al⁺³ metal ions was extra satisfactory when compared with GO due to the ease of design and the homogeneous structure of FGO. The structure of synthesized GO and FGO was confirmed by different techniques such as FTIR, XRD, TGA, BET nitrogen adsorption-desorption methods, and TEM analyses. The mass of utilized adsorbents, the pH of the medium, the concentration of ionic species in the medium, temperature, and process time were all investigated as variables in the adsorbent procedure. The experimental data recorded that the maximum adsorption efficiency of the 0.5 g/L FGO composite was 99.7 and 99.8% for Pb⁺² and Al⁺³ metal ions, respectively, while in the case of using GO, the maximum adsorption efficiency was 92.6 and 91.9% at ambient temperature in a semineutral medium at pH 6 after 4 h. The adsorption results were in good conformity with the Freundlich model and pseudo-second-order kinetics for Pb⁺² and Al⁺³ metal ions. Also, the reusability study indicates that FGO can be used repeatedly at least for five cycles with a slight significant loss in its efficiency.

Efficient Removal of Eriochrome Black T (EBT) Dye and Chromium (Cr) by Hydrotalcite-Derived Mg-Ca-Al Mixed Metal Oxide Composite

Eriochrome Black T (EBT) and chromium (Cr) are considered to be potential pollutants due to their toxicity and severe impact on the environment. In the current study, hydrotalcite-derived Mg-Ca-Al-LDO mixed metal oxide composite was prepared using a conventional co-precipitation method and explored in terms of the removal of Cr and EBT dye from aqueous solution in a batch mode adsorption process. The prepared Mg-Ca-Al-LDH, Mg-Ca-Al-LDO and spent Mg-Ca-Al-LDO adsorbents were characterized to propose the adsorption mechanism. Different adsorption parameters were examined, such as adsorbent dosage, initial concentration, pH, reaction temperature and contact time. The EBT adsorption kinetic results matched strongly with the pseudo-second-order model for both Cr (R2 = 0.991) and EBT (R2 = 0.999). The Langmuir isotherm model exhibited a maximum adsorption capacity of 65.5 mg/g and 150.3 mg/g for Cr and EBT, respectively. The structure and morphology results obtained after Cr and EBT dye adsorption reveal that the adsorption mechanism is associated with electrostatic interactions and surface complexation of Cr and EBT dye with Mg-Ca-Al-LDO surface functional groups. Moreover, more than 84% of the initial adsorption capacity of EBT and Cr can be achieved on the Mg-Ca-Al-LDO surface after five adsorption/desorption cycles. Finally, the Mg-Ca-Al-LDO mixed metal oxide composite can be potentially used as a cost-effective adsorbent for wastewater treatment processes.

Ganzoury M, Zhang N, de Lannoy CF. Nanocomposite Polymeric Membranes for Organic Micropollutant Removal: A Critical Review

The prevalence of organic micropollutants (OMPs) and their persistence in water supplies have raised serious concerns for drinking water safety and public health. Conventional water treatment technologies, including adsorption and biological treatment, are known to be insufficient in treating OMPs and have demonstrated poor selectivity toward a wide range of OMPs. Pressure-driven membrane filtration has the potential to remove many OMPs detected in water with high selectivity as a membrane's molecular weight cutoff (MWCO), surface charge, and hydrophilicity can be easily tailored to a targeted OMP's size, charge and octanol-water partition coefficient (Kow). Over the past 10 years, polymeric (nano)composite microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) membranes have been extensively synthesized and studied for their ability to remove OMPs. This review discusses the fate and transport of emerging OMPs in water, an assessment of conventional membrane-based technologies (NF, reverse osmosis (RO), forward osmosis (FO), membrane distillation (MD) and UF membrane-based hybrid processes) for their removal, and a comparison to the state-of-the-art nanoenabled membranes with enhanced selectivity toward specific OMPs in water. Nanoenabled membranes for OMP treatment are further discussed with respect to their permeabilities, enhanced properties, limitations, and future improvements.

Synthesis of MgNiCo LDH hollow structure derived from ZIF-67 as superb adsorbent for Congo red

Adsorption materials with large specific surface area and porous structures exert a beneficial impact on improving the adsorption performance. In this work, MgNiCo LDH hollow structure (MNC HS) is fabricated through a simple one-step solvothermal method using ZIF-67 as the sacrificial template. Electron microscopy shows that the MNC HS retains the dodecahedral shape of ZIF-67. The as-prepared sample exhibits efficient adsorption for Congo red (CR) in water, which is due to the hierarchical structure and large specific surface area that provides more adsorption sites and electrostatic interaction. The CR adsorption process fits the pseudo-second-order model better by kinetics simulation; while Langmuir model is more accurate than Freundlich model in describing the adsorption isotherms of CR. The maximum adsorption capacity calculated by the Langmuir model can reach 1194.7 mg g^-1, which is much higher than that of the sample MgNiCo LDH (MNC) synthesized by conventional methods. The cycle tests also show that the as-prepared adsorbent has good stability and recycling ability.

Valorization of food waste as adsorbents for toxic dye removal from contaminated waters: A review

Industrial contaminants such as dyes and intermediates are released into water bodies, making the water unfit for human use. At the same time large amounts of food wastes accumulate near the work places, residential complexes etc. polluting the air due to putrefaction. The need of the hour lies in finding innovative solutions for dye removal from wastewater streams. In this context, the article emphasizes adoption or conversion of food waste materials, an ecological nuisance, as adsorbents for the removal of dyes from wastewaters. Adsorption, being a well-established technique, the review critically examines the specific potential of food waste constituents as dye adsorbents. The efficacy of food waste-based adsorbents is examined, besides addressing the possible adsorption mechanisms and the factors affecting phenomenon such as pH, temperature, contact time, adsorbent dosage, particle size, and ionic strength. Integration of information and communication technology approaches with adsorption isotherms and kinetic models are emphasized to bring out their role in improving overall modeling performance. Additionally, the reusability of adsorbents has been highlighted for effective substrate utilization. The review makes an attempt to stress the valorization of food waste materials to remove dyes from contaminated waters thereby ensuring long-term sustainability.

A comprehensive review on electrospun nanohybrid membranes for wastewater treatment

Electrospinning, being a versatile and straightforward method to produce nanofiber membranes, has shown significant advancement in recent years. On account of the unique properties such as high surface area, high porosity, mechanical strength, and controllable surface morphologies, electrospun nanofiber membranes have been found to have a great potential in many disciplines. Pure electrospun fiber mats modified with different techniques of surface modification and additive incorporation have exhibited enhanced properties compared to traditional membranes and are even better than the as-prepared electrospun membranes. In this review, we have summarized recently developed electrospun nanohybrids fabricated by the incorporation of functional specific nanosized additives to be used in various water remediation membrane techniques. The adsorption, filtration, photocatalytic, and bactericidal capabilities of the hybrid membranes in removing common major water pollutants such as metal ions, dyes, oils, and biological pollutants have been discussed. Finally, an outlook on the future research pathways to fill the gaps existing in water remediation have been suggested.

Design of microstructure for hollow fiber loose nanofiltration separation layer and its compactness-tailoring mechanism

In order to promote the application of membrane technology in the treatment of textile wastewater containing small molecule dye, fabricating a hollow fiber loose nanofiltration (LNF) with a thin and compact separation layer and deepening the understanding of compactness-tailoring mechanism in chemical crosslinking are essential. Firstly, the mechanisms of synergistic crosslinking of PEI-70K and PEI-10K, along with a weakening of the PEI hydration by ethanol, were expounded in primary crosslinking. Then, some LNF separation layers with different compactness were prepared through crosslinking with different crosslinkers to further reduce pore size, which resulted in the efficient removal (~100%) of a small molecular dye (methyl orange (MO), M = 327 g mol^-1). The removal of methyl orange is mainly caused by size sieving. The relationship among the pore size, the M_w of the secondary crosslinkers, and the pore size reduction rate was interpreted by comparing the pore size reduction rate of three secondary crosslinkers with different molecular weights. In addition, the as-prepared separation layer exhibited excellent dimensional stability and solvent resistance. This paper not only provides a reference for fabricating hollow fiber LNF with better purification performance, but also shows their potential in developing solvent resistant nanofiltration.

Simultaneous decontamination of multi-pollutants: A promising approach for water remediation

Water remediation techniques have been extensively investigated due to the increasing threats of soluble pollutants posed on the human health, ecology and sustainability. Confronted with the complex composition matrix of wastewater, the simultaneous elimination of coexisting multi-pollutants remains a great challenge due to their different physicochemical properties. By integrating multi-contaminants elimination processes into one unit operation, simultaneous decontamination attracted more and more attention under the consideration of versatile applications and economical benefits. In this review, the state-of-art simultaneous decontamination methods were systematically summarized as chemical precipitation, adsorption, photocatalysis, oxidation-reduction, biological removal and membrane filtration. Their applications, mechanisms, mutual interactions, sustainability and recyclability were outlined and discussed in detail. Finally, the prospects and opportunities for future research were proposed for further development of simultaneous decontamination. This work could provide guidelines for the design and fabrication of well-organized simultaneous decontaminating system.

Promoting the stability and adsorptive capacity of Fe3O4-embedded expanded graphite with an aminopropyltriethoxysilane-polydopamine coating for the removal of copper(ii) from water

In this study, three magnetic graphites, namely, EGF, GAF, and GFA + KH550, were prepared, which were loaded either with Fe₃O₄ or with Fe₃O₄ and PDA or with Fe₃O₄, PDA, and KH550 onto expanded graphite. ATR-FTIR, XRD, XPS, SEM, TEM, and TGA characterization results showed that EGF, GAF, and GFA + KH550 were successfully prepared. Under the same initial copper concentration, the removal rates of copper ions by EGF, GFA, and GFA + KH550 were 86.2%, 96.9%, and 97.0%, respectively and the hazard index reductions of the three adsorbents were 2191 ± 71 (EGF), 1843 ± 68 (GFA), and 1664 ± 102 (GFA + KH550), respectively. Therefore GFA + KH550 exhibited better removal of Cu(ii) than EGF and GFA, for PDA and KH550 provided more adsorption-active sites like –OH and –NH. Here, the adsorption of GFA + KH550 fitted the pseudo-second-order kinetic and Langmuir models well within the testing range, which means that adsorption occurs on a monolayer surface between Cu(ii) and the adsorption sites. The intraparticle diffusion model and various thermodynamic parameters demonstrated that Cu(ii) was adsorbed on GFA + KH550 mainly via external surface diffusion and that the process was both endothermic and spontaneous. Recycling experiments show that GFA + KH550 has a satisfactory recyclability, and the way of direct recovery by magnets exhibits good magnetic induction. GFA + KH550 was applied in lake water and artificial seawater samples, and exhibited better removal of copper than that in DI water under the same environmental conditions for the existence of macromolecular organic matter. Furthermore, the adsorption capacity of copper ions was not relative to the salinity of water. The application of GFA + KH550 demonstrated the potential for application in water treatment procedures.

In this study, three magnetic graphites, namely, EGF, GAF, and GFA + KH550, were prepared, which were loaded either with Fe₃O₄ or with Fe₃O₄ and PDA or with Fe₃O₄, PDA, and KH550 onto expanded graphite.

Nanotechnological approaches as a promising way for heavy metal mitigation in an aqueous system

The ever-rising environmental problems because of heavy metals emerging from anthropogenic activities pose an impending threat to all biota globally. Considering their persistence and possibility in biomagnification, they are prominent among pollutants. There has been an apparent shift of research interest in advancing cost-effective and competent technologies to mitigate environmental contaminants, specifically heavy metals. In the recent two decades, tailored nanomaterials (NMs), nanoparticles, and NM-based adsorbents have been emerging for removing heavy metal pollution on a sustainable scale, especially the green synthesis of these nanoproducts effective and nonhazardous means. Hence, this review explores the various avenues in nanotechnology, an attempt to gauge nanotechnological approaches to mitigate heavy metals in the aqueous system, especially emphasizing the recent trends and advancements. Inputs on remediating heavy metal in sustainable and environmentally benign aspects recommended future directions to compensate for the voids in this domain have been addressed.

Graphene Oxide and Carbon Nanotubes-Based Polyvinylidene Fluoride Membrane for Highly Increased Water Treatment

As contaminated water increases due to environmental pollution, the need for excellent water treatment is increased, and several studies have reported the polyvinylidene fluoride (PVDF)-based water treatment membranes. However, the PVDF membrane has several problems such as low filtration performance, fouling resistance, and difficulty in precisely controlling the morphology of the pores and hydrophilicity. Therefore, we newly produced a water treatment PVDF membrane containing graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) to improve the filtration performance. Surface properties of the fabricated membrane such as morphology, and size of pores, hydrophilicity, and water flux of the membrane were investigated. Additionally, the performance of these membrane filters was evaluated for free residual chlorine, turbidity, chromaticity, magnesium, sulfate, and particulates class 1 according to drinking water management act criteria, respectively. A performance improvement of at least 108.37% was observed compared to the Pure PVDF filter module and anti-fouling effects due to the functional groups of GO and MWCNTs. These results reveal that proposed membrane can accelerate the development of various water filtration applications.

Recyclable polyurethane foam loaded with carboxymethyl chitosan for adsorption of methylene blue

Novel composite foam (CMCTS-PUF-s) was prepared by immobilizing carboxymethyl chitosan (CMCTS) on polyurethane foam (PUF) in which amino groups in CMCTS reacted with isocyanate groups in polyurethane prepolymer. The adsorption capacity of the optimal composite foam (CMCTS-PUF-5) reached to 118.2 mg/g with 5% CMCTS loading. The removal rate to methylene blue (MB) was up to 97.1%, which was obviously higher than 18.9% of PUF. After recycling for five times, the removal rate still reached 83.2%, which strongly proved the excellent reusability of immobilizing CMCTS modified PUF. The characterization results of FTIR and TG showed that CMCTS was well loaded on PUF by covalent bond. The Young's modulus and tensile strength of CMCTS-PUF-5 were increased by 252% and 97% compared with that of PUF. MIP characterization result showed the porosity of CMCTS-PUF-5 was 73.99% and the pore sizes were mainly distributed between 50 and 150 µm, which provide sufficient diffusion channels and active sites for MB dyes. The adsorption kinetics and isotherm proved pseudo-second-order kinetic model and Langmuir isotherm model could well describe the adsorption process of CMCTS-PUF-5. Therefore, CMCTS-PUF-s presents excellent recoverability, high stability and attractive adsorption efficiency, shows the potential application in future treatment of dye wastewater.

Advances in the Synthesis and Application of Anti-Fouling Membranes Using Two-Dimensional Nanomaterials

This article provides a comprehensive review of the recent progress in the application of advanced two-dimensional nanomaterials (2DNMs) in membranes fabrication and application for water purification. The membranes fouling, its types, and anti-fouling mechanisms of different 2DNMs containing membrane systems are also discussed. The developments in membrane synthesis and modification using 2DNMs, especially graphene and graphene family materials, carbon nanotubes (CNTs), MXenes, and others are critically reviewed. Further, the application potential of next-generation 2DNMs-based membranes in water/wastewater treatment systems is surveyed. Finally, the current problems and future opportunities of applying 2DNMs for anti-fouling membranes are also debated.

Research trends of heavy metal removal from aqueous environments

Heavy metals are a threat against human health. During the last century, with increased industrial activities, many water resources have been contaminated by heavy metals. Meanwhile the number of scientific studies about removing these toxic substances from aqueous environments has increased exponentially. According to bibliometric analysis the number of articles from 2000 to 2019 experienced a 1700% growth rate. China, India and the United States have published the greatest number of top-cited articles on the topic, with China in first place by a large margin. Six clusters of papers (by topic) were identified. From among the processes such as adsorption, membrane filtration, and ion exchange, adsorption has the lion's share of the investigations. Technical and efficiency considerations, as well as environmental impact and cost-effectiveness, were chosen as criteria to compare different methods. According to life cycle assessment, adsorption has the least amount of negative environmental effects compared to other trending methods such as membrane filtration and ion exchange. From a financial viewpoint, utilizing biosorbents and biochars for adsorption are the best options. Unlike other methods which depend on pretreatment processes and have a high energy demand, these sorbents are cost-effective and exhibit acceptable performance.

Pressure-Driven Membrane Process: A Review of Advanced Technique for Heavy Metals Remediation

Pressure-driven processes have come a long way since they were introduced. These processes, namely Ultra-Filtration (UF), Nano-Filtration (NF), and Reverse-Osmosis (RO), aim to enhance the efficiency of wastewater treatment, thereby aiming at a cleaner production. Membranes may be polymeric, ceramic, metallic, or organo-mineral, and the filtration techniques differ in pore size from dense to porous membrane. The applied pressure varies according to the method used. These are being utilized in many exciting applications in, for example, the food industry, the pharmaceutical industry, and wastewater treatment. This paper attempts to comprehensively review the principle behind the different pressure-driven membrane technologies and their use in the removal of heavy metals from wastewater. The transport mechanism has been elaborated, which helps in the predictive modeling of the membrane system. Fouling of the membrane is perhaps the only barrier to the emergence of membrane technology and its full acceptance. However, with the use of innovative techniques of fabrication, this can be overcome. This review is concluded with perspective recommendations that can be incorporated by researchers worldwide as a new problem statement for their work.