Adsorptive nanocomposite membranes for heavy metal remediation: Recent progresses and challenges

Removal of Heavy Metals from Wastewaters and Other Aqueous Streams by Pressure-Driven Membrane Technologies: An Outlook on Reverse Osmosis, Nanofiltration, Ultrafiltration and Microfiltration Potential from a Bibliometric Analysis

A bibliometric study to analyze the scientific documents released until 2024 in the database Scopus related to the use of pressure-driven membrane technologies (microfiltration, ultrafiltration, nanofiltration and reverse osmosis) for heavy metal removal was conducted. The work aimed to assess the primary quantitative attributes of the research in this field during the specified period. A total of 2205 documents were identified, and the corresponding analysis indicated an exponential growth in the number of publications over time. The contribution of the three most productive countries (China, India and USA) accounts for more than 47.1% of the total number of publications, with Chinese institutions appearing as the most productive ones. Environmental Science was the most frequent knowledge category (51.9% contribution), followed by Chemistry and Chemical Engineering. The relative frequency of the keywords and a complete bibliometric network analysis allowed the conclusion that the low-pressure technologies (microfiltration and ultrafiltration) have been more deeply investigated than the high-pressure technologies (nanofiltration and reverse osmosis). Although porous low-pressure membranes are not adequate for the removal of dissolved heavy metals in ionic forms, the incorporation of embedded adsorbents within the membrane structure and the use of auxiliary chemicals to form metallic complexes or micelles that can be retained by this type of membrane are promising approaches. High-pressure membranes can achieve rejection percentages above 90% (99% in the case of reverse osmosis), but they imply lower permeate productivity and higher costs due to the required pressure gradients.

From environmental issue to purification aid: Novel positively charged functionalized algal biochar as robust modifier of composite nanofiltration membranes

Robust membrane modifiers were achieved for the first time by functionalizing the algal biochar of unique porous structure. The biochar was prepared through the pyrolysis of Cladophora glomerata, the most widespread freshwater macroalga, functionalized by diethylenetriamine and dendrimer poly(amidoamine), and employed to fabricate positively charged composite nanofiltration membranes. The presence of hydrophilic functionalizers of positive charge on the membrane was verified through Fourier transform infrared and energy dispersive X-ray analyses and atomic force microscopy and zeta potential measurements were performed to determine surface roughness and confirm positive charge of the modified membranes. Dispersion of modifiers on the surface and morphology of the were also revealed through field-emission scanning electron microscopy images. It has shown that, compared to the pristine membrane, pure water fluxes were increased by 214% and 185%, and water contact angles were reduced from 66.1° to 39.5° and 43.3° in those modified by biochar functionalized with dendrimer poly(amidoamine) and diethylenetriamine, respectively. More than 90% dye rejections and salt and heavy metals removals were recorded for the membranes possessed 0.6 wt% of modifiers. Finally, a comparative study conducted between the novel modifier introduced in this study and those reported in the literature, indicated that C. glomerata biochar decorated with amine functional groups could be considered as a robust and practical alternative to the common modifiers used to manipulate nanocomposite membranes characteristics.

Biomimetic ZrO2-modified seaweed residue with excellent fluorine/ bacteria removal and uranium extraction properties for wastewater purification

Exploring and developing promising biomass composite membranes for the water purification and waste resource utilization is of great significance. The modification of biomass has always been a focus of research in its resource utilization. In this study, we successfully prepare a functional composite membrane, activated graphene oxide/seaweed residue-zirconium dioxide (GOSRZ), with fluoride removal, uranium extraction, and antibacterial activity by biomimetic mineralization of zirconium dioxide nanoparticles (ZrO2 NPs) on seaweed residue (SR) grafted with oxidized graphene (GO). The GOSRZ membrane exhibits highly efficient and specific adsorption of fluoride. For the fluoride concentrations in the range of 100-400 mg/L in water, the removal efficiency can reach over 99 %, even in the presence of interfering ions. Satisfactory extraction rates are also achieved for uranium by the GOSRZ membrane. Additionally, the antibacterial performance studies show that this composite membrane efficiently removes Escherichia coli (E. coli) and Methicillin-resistant Staphylococcus aureus (MRSA). The high adsorption of F- and U(VI) to the composite membrane is ascribed to the ionic exchange and coordination interactions, and its antibacterial activity is caused by the destruction of bacterial cell structure. The sustainability of the biomass composite membranes is further evaluated using the Sustainability Footprint method. This study provides a simple preparation method of biomass composite membrane, expands the water purification treatment technology, and offers valuable guidance for the resource utilization of seaweed waste and the removal of pollutants in wastewater.

Advancement in nanomaterials for environmental pollutants remediation: a systematic review on bibliometrics analysis, material types, synthesis pathways, and related mechanisms

Environmental pollution is a major issue that requires effective solutions. Nanomaterials (NMs) have emerged as promising candidates for pollution remediation due to their unique properties. This review paper provides a systematic analysis of the potential of NMs for environmental pollution remediation compared to conventional techniques. It elaborates on several aspects, including conventional and advanced techniques for removing pollutants, classification of NMs (organic, inorganic, and composite base). The efficiency of NMs in remediation of pollutants depends on their dispersion and retention, with each type of NM having different advantages and disadvantages. Various synthesis pathways for NMs, including traditional synthesis (chemical and physical) and biological synthesis pathways, mechanisms of reaction for pollutants removal using NMs, such as adsorption, filtration, disinfection, photocatalysis, and oxidation, also are evaluated. Additionally, this review presents suggestions for future investigation strategies to improve the efficacy of NMs in environmental remediation. The research so far provides strong evidence that NMs could effectively remove contaminants and may be valuable assets for various industrial purposes. However, further research and development are necessary to fully realize this potential, such as exploring new synthesis pathways and improving the dispersion and retention of NMs in the environment. Furthermore, there is a need to compare the efficacy of different types of NMs for remediating specific pollutants. Overall, this review highlights the immense potential of NMs for mitigating environmental pollutants and calls for more research in this direction.

Surface modified Acacia Senegal Gum based spherical hydrogel; fabrication, characterization, and kinetically optimized waste water treatment with remarkable adsorption efficiency

Acacia Senegal Gum hydrogel (HASG) with swollen dimension less than 50 μm were fabricated, and chemically modified with versatile diethylenetriamine (d-amine) to tailor the surface properties for environmental remediation. Negatively charged metal ions, for example, chromate (Cr(III)), dichromate (Cr(VI)), and arsenate (As(V)) were removed from aqueous media by using modified hydrogels (m-HASG). The FT-IR spectra revealed some new peaks due to d-amine treatment. The zeta potential measurements confirm a positively charged surface of HASG upon d-amine modification at ambient conditions. The absorption studies revealed that 0.05 g feed of m-(HASG) possesses 69.8, 99.3, and 40.00% cleaning potential against As(V), Cr(VI), and Cr(III), respectively with 2 h contact time in deionized water. Almost comparable adsorption efficiency was achieved by the prepared hydrogels towards the targeted analytes dissolved in real water samples. Adsorption isotherms, for example, Langmuir, Freundlich and modified Freundlich isotherms were applied to the collected data. Briefly, Modified Freundlich isotherm manifested comparatively agreeable line for the all adsorbents pollutants with highest R² figure. In addition, maximum adsorption capacity (Qm) with 217, 256, and 271 mg g^-1 numerical values were obtained against As(V), Cr(VI), and Cr(III), respectively. In real water samples, 217, 256, and 271 mg g^-1 adsorption capacity was represented by m-(HASG). In brief, m-(HASG) is a brilliant material for environmental application as cleaner candidate towards toxic metal ions.

Chitosan-based hollow nanofiber membranes with polyvinylpyrrolidone and polyvinyl alcohol for efficient removal and filtration of organic dyes and heavy metals

Due to their large specific surface area and numerous diffusion channels, hollow fibers are widely used in wastewater treatment. In this study, we successfully synthesized a chitosan (CS)/polyvinylpyrrolidone (PVP)/polyvinyl alcohol (PVA) hollow nanofiber membrane (CS/PVP/PVA-HNM) via coaxial electrospinning. This membrane demonstrated remarkable permeability and adsorption separation. Specifically, the CS/PVP/PVA-HNM had a pure water permeability of 4367.02 L·m^-2·h^-1·bar^-1. The hollow electrospun nanofibrous membrane exhibited a continuous interlaced nanofibrous framework structure with the extraordinary advantages of high porosity and high permeability. The rejection ratios of CS/PVP/PVA-HNM for Cu²⁺, Ni²⁺, Cd²⁺, Pb²⁺, malachite green (MG), methylene blue (MB) and crystal violet (CV) were 96.91 %, 95.29 %, 87.50 %, 85.13 %, 88.21 %, 83.91 % and 71.99 %, and the maximum adsorption capacities were 106.72, 97.46, 88.10, 87.81, 53.45, 41.43, and 30.97 mg·g^-1, respectively. This work demonstrates a strategy for the synthesis of hollow nanofibers, which provides a novel concept for the design and fabrication of highly efficient adsorption separation membranes.

Advanced Polymeric Nanocomposite Membranes for Water and Wastewater Treatment: A Comprehensive Review

Nanomaterials have been extensively used in polymer nanocomposite membranes due to the inclusion of unique features that enhance water and wastewater treatment performance. Compared to the pristine membranes, the incorporation of nanomodifiers not only improves membrane performance (water permeability, salt rejection, contaminant removal, selectivity), but also the intrinsic properties (hydrophilicity, porosity, antifouling properties, antimicrobial properties, mechanical, thermal, and chemical stability) of these membranes. This review focuses on applications of different types of nanomaterials: zero-dimensional (metal/metal oxide nanoparticles), one-dimensional (carbon nanotubes), two-dimensional (graphene and associated structures), and three-dimensional (zeolites and associated frameworks) nanomaterials combined with polymers towards novel polymeric nanocomposites for water and wastewater treatment applications. This review will show that combinations of nanomaterials and polymers impart enhanced features into the pristine membrane; however, the underlying issues associated with the modification processes and environmental impact of these membranes are less obvious. This review also highlights the utility of computational methods toward understanding the structural and functional properties of the membranes. Here, we highlight the fabrication methods, advantages, challenges, environmental impact, and future scope of these advanced polymeric nanocomposite membrane based systems for water and wastewater treatment applications.

Potential application of spent mushroom compost (SMC) biochar as low-cost filtration media in heavy metal removal from abandoned mining water: a review

Overpopulation and rapid development have put an increasing burden on the environment, leading to various water crisis. Importing water from abandoned mines as an alternative raw water source could be the next answer to alleviate water scarcity problems globally. However, due to its high heavy metals content, there is a need to find an economical and effective method to remove heavy metals before reusing it as potable water source. Biochar, a low-cost and carbon-rich biosorbent, has received increasing attention on its application as a remediating agent to remove heavy metals from water. Previous studies have revealed the potential properties of biochar as a heavy metal removal agent including high cation exchange capacity, high surface area, active surface functional groups, as well as efficient adsorption. Apparently, the most important factor influencing the sorption mechanism is the type of feedstock materials. Spent mushroom compost (SMC), a waste product from mushroom cultivation, has been found as an excellent biosorbent. SMC has received global attention as it is low cost and eco-friendly. It also has been proved as an efficient heavy metals remover from water. Nevertheless, its application as biochar is still scarce. Therefore, this review focuses on the potential of transforming SMC into modified biochar to remove heavy metals, especially from abandoned mining water. The present review emphasizes the current trends in adsorption methods for heavy metal removal from water, assembles data from previous studies on the feedstock of biosorbents to biochars, and discusses the potentials of SMC as a biochar for water treatment.

Electrospun tannin-rich nanofibrous solid-state membrane for wastewater environmental monitoring and remediation

Heavy metal, organic dyes, and bacterial contamination in water endanger human/animals' health, and therefore, the detection, adsorption, and capturing of contaminants are essential for environmental safety. Ligand-rich membranes are promising for sensors, adsorption, and bacterial decontamination. Herein, tannin (TA)-reinforced 3-aminopropyltriethoxysilane (APTES) crosslinked polycaprolactone (PCL) based nanofibrous membrane (PCL-TA-APTES) was fabricated via electrospinning. PCL-TA-APTES nanofibers possess superior thermal, mechanical, structural, chemical, and aqueous stability properties than the un-crosslinked membrane. It changed its color from yellowish to black in response to Fe^2+/3+ ions due to supramolecular iron-tannin network (FeTA) interaction. Such selective sensing has been noticed after adsorption-desorption cycles. Fe³⁺ concentration, solution pH, contact time, and ligand concentration influence FeTA coordination. Under optimized conditions followed by image processing, the introduced membrane showed a colorimetric linear relationship against Fe³⁺ ions (16.58 μM-650 μM) with a limit of detection of 5.47 μM. The PCL-FeTA-APTES membrane could restrain phenolic group oxidation and result in a partial water-insoluble network. The adsorption filtration results showed that the PCL-FeTA-APTES membrane can be reused and had a higher methylene blue adsorption (32.04 mg/g) than the PCL-TA-APTES membrane (14.96 mg/g). The high capture efficiency of nanocomposite against Fe³⁺-based S. aureus suspension than Fe³⁺-free suspension demonstrated that Fe³⁺-bounded bacterium adhered to the nanocomposite through Fe³⁺/TA-dependent biointerface interactions. Overall, high surface area, rich phenolic ligand, porous microstructure, and super-wetting properties expedite FeTA coordination in the nanocomposite, crucial for Fe^2+/3+ ions sensing, methylene blue adsorption-filtration, and capturing of Fe³⁺-bounded bacterium. These multifunctional properties could promise nanocomposite membrane practicability in wastewater and environmental protection.

Polymeric membranes for environmental remediation: A product space model perspective

The development of polymeric membranes from polymers such as polystyrene (PS), polyvinylchloride (PVC), and their associated family has brought great momentum to the environmental remediation universe, mainly due to their surprisingly diverse and multi-purpose nature. Their usage has surged 20 times in the last half-century and is likely to double again in the coming 20 years. As a result, the polymeric materials economy and commercialization of research become increasingly important as a possible option for a country to boost prosperity while decreasing its reliance on limited raw resources and mitigating negative externalities. This transformation demands a systematic strategy, which involves progress beyond improving the existing models and building new avenues for collaboration. In this work, a sophisticated system, i.e., product space model (PSM), has been presented, explicitly appraising the opportunity space for United Kingdom, Italy, Poland, India, Canada, Indonesia, Brazil, Saudi Arabia, Russia and Colombia for their potential future industrialization and commercialization of polymeric membranes for environmental remediation. The results revealed that UK, Italy, Poland and India are at advantageous positions owing to their close proximity of (distance<2) and their placement in Parsimonious policy, which is the most desired quadrant of Policy Map of PSM, Canada and Indonesia have medium level opportunities, while Russia and Saudi Arabia have opportunities with more challenges to fully exploit the unexploited polymers products in terms of membranes for environmental remediation and prove favorable for export diversification, sustainable economic growth, and commercialization.

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.

Synthesis of new functionalized magnetic nano adsorbents and adsorption performance for Hg(II) ions

Fe₃O₄@SiO₂-NH-nNG-SPTZ (including Fe₃O₄@SiO₂-NH-2NG-SPTZ, Fe₃O₄@SiO₂-NH-3NG-SPTZ) were prepared by 2-mercapto-5-(4-pyridyl)-1,3,4-thiadiazole and the reaction products of 3, 6-dichloropyridazine and cyanuric chloride with Fe₃O₄@SiO₂-NH₂ respectively. Fe₃O₄@SiO₂-S-nNG-SPTZ (including Fe₃O₄@SiO₂-S-2NG-SPTZ, Fe₃O₄@SiO₂-S-3NG-SPTZ) were prepared by 2-mercapto-5-(4-pyridyl)-1,3,4-thiadiazole and the reaction products of 3, 6-dichloropyridazine and cyanuric chloride with Fe₃O₄@SiO₂-SH respectively. Four novel adsorbents were characterized by SEM, TEM, FT-IR and XRD. Hg(II) ions removal efficiency of these adsorbents were more than 95%, in 15–20 min, at pH 7.0–8.0. It is easy to separate these adsorbents that adsorb mercury ions from the solution through magnets. These adsorbents have similar adsorption mechanism and have application value in the treatment of mercury ions in sewage and are worth studying.

Adsorptive Membrane for Boron Removal: Challenges and Future Prospects

The complexity of removing boron compounds from aqueous systems has received serious attention among researchers and inventors in the water treating industry. This is due to the higher level of boron in the aquatic ecosystem, which is caused by the geochemical background and anthropogenic factors. The gradual increase in the distribution of boron for years can become extremely toxic to humans, terrestrial organisms and aquatic organisms. Numerous methods of removing boron that have been executed so far can be classified under batch adsorption, membrane-based processes and hybrid techniques. Conventional water treatments such as coagulation, sedimentation and filtration do not significantly remove boron, and special methods would have to be installed in order to remove boron from water resources. The blockage of membrane pores by pollutants in the available membrane technologies not only decreases their performance but can make the membranes prone to fouling. Therefore, the surface-modifying flexibility in adsorptive membranes can serve as an advantage to remove boron from water resources efficiently. These membranes are attractive because of the dual advantage of adsorption/filtration mechanisms. Hence, this review is devoted to discussing the capabilities of an adsorptive membrane in removing boron. This study will mainly highlight the issues of commercially available adsorptive membranes and the drawbacks of adsorbents incorporated in single-layered adsorptive membranes. The idea of layering adsorbents to form a highly adsorptive dual-layered membrane for boron removal will be proposed. The future prospects of boron removal in terms of the progress and utilization of adsorptive membranes along with recommendations for improving the techniques will also be discussed further.

Recent Advances in Adsorptive Nanocomposite Membranes for Heavy Metals Ion Removal from Contaminated Water: A Comprehensive Review

Water contamination is one of the most urgent concerns confronting the world today. Heavy metal poisoning of aquatic systems has piqued the interest of various researchers due to the high toxicity and carcinogenic consequences it has on living organisms. Due to their exceptional attributes such as strong reactivity, huge surface area, and outstanding mechanical properties, nanomaterials are being produced and employed in water treatment. In this review, recent advances in the use of nanomaterials in nanoadsorptive membrane systems for wastewater treatment and heavy metal removal are extensively discussed. These materials include carbon-based nanostructures, metal nanoparticles, metal oxide nanoparticles, nanocomposites, and layered double hydroxide-based compounds. Furthermore, the relevant properties of the nanostructures and the implications on their performance for water treatment and contamination removal are highlighted. The hydrophilicity, pore size, skin thickness, porosity, and surface roughness of these nanostructures can help the water permeability of the nanoadsorptive membrane. Other properties such as surface charge modification and mechanical strength can improve the metal adsorption effectiveness of nanoadsorptive membranes during wastewater treatment. Various nanocomposite membrane fabrication techniques are also reviewed. This study is important because it gives important information on the roles of nanomaterials and nanostructures in heavy metal removal and wastewater treatment.

Modification of silica nanoparticles by 2,4-dihydroxybenzaldehyde and 5-bromosalicylaldehyde as new nanocomposites for efficient removal and preconcentration of Cu(ii) and Cd(ii) ions from water, blood, and fish muscles

Herein, silica nanoparticles were modified by 2,4-dihydroxybenzaldehyde and 5-bromosalicylaldehyde to produce new nanocomposites which were abbreviated as N₁ and N₂, respectively. The synthesized nanocomposites were used for efficient removal and preconcentration of Cu(ii) and Cd(ii) ions from water, blood, and fish muscles. FE-SEM, FT-IR, XRD, CHN elemental analysis, and nitrogen gas sorption analyzer were used to characterize the new nanocomposites. The XRD proved that the synthesized oxide is cristobalite with an average crystallite size of 54.80 nm. Due to the formation of the C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N group, the intensity of the XRD peak at 2θ = 21.9° in the N₁ and N₂ nanocomposites decreased significantly. The FT-IR bands, which appeared at 1603 and 1629 cm⁻¹ in the N₁ and N₂ nanocomposites, are attributable to the bending vibration of CN and/or OH, respectively. Also, the FE-SEM analysis shows the morphology of the silica nanoparticles which were identified as spherical and rod-like with slight agglomeration while the N₁ and N₂ nanocomposites have flaky surfaces due to the formation of CN groups. The maximum Cu(ii) ion adsorption capacities of the N₁ and N₂ nanocomposites are 64.81 and 40.93 mg g⁻¹, respectively. The maximum Cd(ii) ion adsorption capacities of the N₁ and N₂ nanocomposites are 27.39 and 26.34 mg g⁻¹, respectively. The adsorption of Cu(ii) or Cd(ii) ions using the synthesized nanocomposites is spontaneous, chemical, exothermic, and well-matched with the Langmuir equilibrium isotherm. The recovery findings demonstrate that the preconcentration process is accurate, adaptable, and resulted in quantitative separation because % Recovery is more than 95%. Furthermore, the % RSD was less than 3.5%, indicating good reproducibility.

Herein, silica nanoparticles were modified by 2,4-dihydroxybenzaldehyde and 5-bromosalicylaldehyde to produce new nanocomposites which were abbreviated as N₁ and N₂, respectively.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

A review of the potential of conventional and advanced membrane technology in the removal of pathogens from wastewater

Consumption of pathogenic contaminated water has claimed the lives of many people. Hence, this scenario has emphasized the urgent need for research methods to avoid, treat and eliminate harmful pathogens in wastewater. Therefore, effective water treatment has become a matter of utmost importance. Membrane technology offers purer, cleaner, and pathogen-free water through the water separation method via a permeable membrane. Advanced membrane technology such as nanocomposite membrane, membrane distillation, membrane bioreactor, and photocatalytic membrane reactor can offer synergistic effects in removing pathogen through the integration of additional functionality and filtration in a single chamber. This paper also comprehensively discussed the application, challenges, and future perspective of the advanced membrane technology as a promising alternative in battling pathogenic microbial contaminants, which will also be beneficial and valuable in managing pandemics in the future as well as protecting human health and the environment. In addition, the potential of membrane technology in battling the ongoing global pandemic of coronavirus disease 2019 (COVID-19) was also discussed briefly.

A comprehensive review on sources, analysis and toxicity of environmental pollutants and its removal methods from water environment

Natural and human anthropogenic activities increase the concentration of the toxic pollutant in the water environment; they could cause harmful effects even in their lower concentration. In humans, toxic pollutants damage the structural and functional properties of essential organs including the heart, liver, kidneys, reproductive systems and pancreas. To avoid the toxicity of the pollutant, they should be removed from the water environment. Since various conventional water/wastewater treatment technologies including precipitation, ion exchange, flocculation, filtration, electrodialysis and membrane separation are employed to reduce the concentration of the pollutant, they have various difficulties in implementation, efficiency and ecological perspective. Therefore, several researchers are now focusing on alternative and eco-friendly approach called biosorption to remove toxic contaminants from the water environment. The biosorption innovation is one of the acclaimed systems for water treatment. The noteworthy endeavours have been made throughout the years to grow profoundly particular and effective biosorbent materials that are more effective, abundantly available, and cost-effective. Biosorption is effectively executed by utilizing both living and dead biomasses of bacteria, fungi and algae. Moreover, agro-waste materials are also utilized as biosorbents due to their excellent surface properties, abundant availability and cost-effectiveness. A variety of physical and chemical treatments enhances the biosorption capabilities of biosorbents via modifying their surface properties. In this review, biosorption mechanism, influencing parameters and application of biosorbent materials towards the removal of toxic pollutants are discussed. The future research opportunities for sustainable wastewater treatment were also explained.

Evaluation of process condition impact on copper and lead ions removal from water using goethite incorporated nanocomposite ultrafiltration adsorptive membranes

Polyacrylonitrile (PAN) adsorptive membrane incorporated with nanosize-goethite (α-FeO(OH)) hydrous metal oxide particles (GNPs), prepared with optimal flux and Cu(II) removal in the previous study, was used to evaluate the process parameter on the Cu(II) removal. Box-Behnken Design (BBD) based on the Response Surface Methodology (RSM) was employed to evaluate the impact of Cu(II) feed solution characteristics such as pH, initial concentration of metal ion, and transmembrane pressure (TMP) on copper removal efficiency. The outcomes indicated that the RSM optimization technique could be utilized as an applicable method to find the optimum condition for the maximum Cu(II) removal with slight variance compared with the experimentally measured data. The effect of each process parameter and the coupling effect of parameters on the Cu(II) removal was assessed. Finally, the optimum condition of pH, Cu(II) concentration, and transmembrane pressure (TMP) to obtain high copper removal efficiency was decided. In the optimum condition of the Cu(II) removal, the removal of lead (Pb(II)) metal ion was evaluated by the same membrane.

Modification of naturally abundant resources for remediation of potentially toxic elements: A review

Water and soil contamination due to potentially toxic elements (PTEs) represents a critical threat to the global ecosystem and human health. Naturally abundant resources have significant advantages as adsorbent materials for environmental remediation over manufactured materials such as nanostructured materials and activated carbons. These advantages include cost-effectiveness, eco-friendliness, sustainability, and nontoxicity. In this review, we firstly compare the characteristics of representative adsorbent materials including bentonite, zeolite, biochar, biomass, and effective modification methods that are frequently used to enhance their adsorption capacity and kinetics. Following this, the adsorption pathways and sites are outlined at an atomic level, and an in-depth understanding of the structure-property relationships are provided based on surface functional groups. Finally, the challenges and perspectives of some emerging naturally abundant resources such as lignite are examined. Although both unamended and modified naturally abundant resources face challenges associated with their adsorption performance, cost performance, energy consumption, and secondary pollution, these can be tackled by using advanced techniques such as tailored modification, formulated mixing and reorganization of these materials. Recent studies on adsorbent materials provide a strong foundation for the remediation of PTEs in soil and water. We speculate that the pursuit of effective modification strategies will generate remediation processes of PTEs better suited to a wider variety of practical application conditions.

Heavy metals contamination and associated health risks in food webs-a review focuses on food safety and environmental sustainability in Bangladesh

Heavy metals occur naturally in very small amounts in living organisms, but exposure to their higher concentrations is hazardous. Heavy metals at hazardous levels are commonly found in foodstuffs of Bangladesh, mainly due to the lack of safety guidelines and poor management of industrial effluents. Several lines of evidence suggest that the level of heavy metals in foodstuffs of Bangladesh is higher than the acceptable limits set by World Health Organization/Food and Agriculture Organization. Literature survey revealed that the sources and transport pathways of heavy metals in the ecosystem and the abundance of heavy metals in the food products of Bangladesh are potential threats to food safety. However, an extensive assessment of the toxicity of heavy metals in food webs is lacking. Although widespread heavy metal contamination in various foodstuffs and environmental matrices have been summarized in some reports, a critical evaluation regarding multi-trophic transfer and the health risk of heavy metal exposure through food chain toxicity in Bangladesh has not been performed. This systematic review critically discussed heavy metal contamination, exposure toxicity, research gaps, existing legislation, and sustainable remediation strategies to enhance Bangladesh's food safety. In particular, this study for the first time explored the potential multi-trophic transfer of heavy metals via food webs in Bangladesh. Furthermore, we recommended a conceptual policy framework to combat heavy metal contaminations in Bangladesh.

Sustainable mitigation of heavy metals from effluents: Toxicity and fate with recent technological advancements

Increase in anthropogenic activities due to rapid industrialization had caused an elevation in heavy metal contamination of aquatic and terrestrial ecosystems. These pollutants have detrimental effects on human and environmental health. The majority of these pollutants are carcinogenic, neurotoxic, and are very poisonous even at very low concentrations. Contamination caused by heavy metals has become a global concern for which the traditional treatment approaches lack in providing a cost-effective and eco-friendly solution. Therefore, the use of microorganisms and plants to reduce the free available heavy metal present in the environment has become the most acceptable method by researchers. Also, in microbial- and phyto-remediation the redox reaction shifts the valence which makes these metals less toxic. In addition to this, the use of biochar as a remediation tool has provided a sustainable solution that needs further investigations toward its implementation on a larger scale. Enzymes secreted by microbes and whole microbial cell are considered an eco-efficient biocatalyst for mitigation of heavy metals from contaminated sites. To the best of our knowledge there is very less literature available covering remediation of heavy metals aspect along with the sensors used for detection of heavy metals. Systematic management should be implemented to overcome the technical and practical limitations in the use of these bioremediation techniques. The knowledge gaps have been identified in terms of its limitation and possible future directions have been discussed.

Enhanced Specific Mechanism of Separation by Polymeric Membrane Modification-A Short Review

Membrane technologies have found a significant application in separation processes in an exceeding range of industrial fields. The crucial part that is decided regarding the efficiency and effectivity of separation is the type of membrane. The membranes deal with separation problems, working under the various mechanisms of transportation of selected species. This review compares significant types of entrapped matter (ions, compounds, and particles) within membrane technology. The ion-exchange membranes, molecularly imprinted membranes, smart membranes, and adsorptive membranes are investigated. Here, we focus on the selective separation through the above types of membranes and detect their preparation methods. Firstly, the explanation of transportation and preparation of each type of membrane evaluated is provided. Next, the working and application phenomena are evaluated. Finally, the review discusses the membrane modification methods and briefly provides differences in the properties that occurred depending on the type of materials used and the modification protocol.

Synthesis, characterization, and assessment of novel sulfonated polynorbornene dicarboximides as adsorbents for the removal of heavy metals from water

The occurrence of heavy metals in the natural aquatic systems arising from anthropogenic sources is an issue of global and environmental concern because of their extremely harmful effects to living beings even in rather low concentrations. The synthesis and ring-opening metathesis polymerization (ROMP) of novel norbornene dicarboximides bearing highly aromatic pendant groups, specifically, N-4-tritylphenyl-norbornene-5,6-dicarboximide (2a) and N-2,4,6-(triphenyl)phenyl-norbornene-5,6-dicarboximide (2b), their hydrogenation and further polymer sulfonation to render them adsorbents for the uptake of heavy metal ions from water is reported in this study. The macromolecules were characterized by means of FT-IR, ¹H NMR, and thermal analysis, among others. A thoroughly kinetic and isothermal study of adsorption in single and ternary aqueous solutions of Pb²⁺, Cd²⁺, and Ni²⁺ was performed considering several experimental variables for instance initial metal concentration, contact time and solution pH. In general, the experimental data were adjusted more efficiently to the pseudo-second order kinetic model and to the Freundlich isotherm model, respectively. The maximum removal amounts were found to be 55.7 mg/g for Pb²⁺, 33.9 mg/g for Cd²⁺, and 10.2 mg/g for Ni²⁺ in the sulfonated trityl-bearing polymer 5a while those found for the sulfonated triphenyl-bearing polymer 5b were 31.5 mg/g for Pb²⁺, 26.6 mg/g for Cd²⁺, and 7.0 mg/g for Ni²⁺, respectively. The higher heavy metal removal capacity of polymer 5a was attributed to its also higher degree of sulfonation. The outcomes indicate that these novel sulfonic acid containing polymer-based adsorbents are effective for the uptake of heavy metallic elements from water.

Fabrication of chitosan-aminopropylsilane graphene oxide nanocomposite hydrogel embedded PES membrane for improved filtration performance and lead separation

In the present study chitosan-aminopropylsilane graphene oxide (CS-APSGO) nanocomposite hydrogel was synthesized and utilized as a hydrophilic additive in different dosages (0.5, 1, 2 and 5 wt%) in fabrication of porous polyethersulfone (PES) membranes via the phase inversion induced process by immersion precipitation method for heavy metal ion and dye removal. The modified membranes were characterized using ATR-FTIR, AFM, SEM, water contact angle, overall porosity and mean pore radius evaluations and zeta potential measurement. The addition of CS-APSGO nanocomposite hydrogel to PES doping solutions enhanced membranes hydrophilicity and consequently pure water flux permeability. Filtration performance of the CS-APSGO embedded membranes showed promising antifouling properties during BSA filtration test (FRR> 90%) and 1 wt% membranes showed the highest pure water flux of 123.8 L/m² h with BSA rejection more than 98% and removal capability more than 82% for lead (II) ion, 90.5% and 98.5% for C.I. Reactive Blue 50 and C.I. Reactive Green 19, respectively. Therefore, the CS-APSGO nanocomposite hydrogel blending in order to modification of PES-based membranes have a noticeable potential in improving filtration performance of blended membranes.

Synthesis of highly fluorescent and water soluble graphene quantum dots for detection of heavy metal ions in aqueous media

Fluorescent graphene quantum dots (GQDs) are nanomaterials which possess unique properties that show great potential in different applications. In this work, GQDs were synthesized using graphene oxide (GO) as precursor via thermal treatment at high temperature. The obtained GQDs were highly fluorescent and were suitable for the determination of heavy metal ions. X-ray diffraction, FTIR spectroscopy, and UV visible spectroscopy confirm the formation of GQDs. TEM images show that formed GQDs have size ranging from 2 to 10 nm. Emission profile of aqueous GQDs was taken by exciting GQDs at different wavelength. The intensity of GQDs remains the same for 4-5 months. Furthermore, as prepared, GQDs were used for selective recognition of Fe³⁺, Pb⁺², and Cr³⁺ from the bunch of different metal ions in aqueous media. Lower limit of detection obtained for Fe³⁺, Cr³⁺ and Pb²⁺ using GQDs were 50, 100 and 100 nM, respectively, which indicates that the GQDs can be utilized as a promising material for sensing of the heavy metal ions. Graphical abstract.

Activation of biochar through exoenzymes prompted by earthworms for vermibiochar production: A viable resource recovery option for heavy metal contaminated soils and water

The industrial revolution and indiscriminate usage of a wide spectrum of agrochemicals account for the dumping of heavy metals in the environment. In-situ/ex-situ physical, chemical, and bioremediation strategies with pros and cons have been adopted for recovering metal contaminated soils and water. Therefore, there is an urgent requirement for a cost-effective and environment-friendly technique to combat metal pollution. Biochar combined with earthworms and vermifiltration is a suitable emerging technique for the remediation of metal-polluted soils and water. The chemical substances (e.g., sodium hydroxide, zinc chloride, potassium hydroxide, and phosphoric acid) have been used to activate biochar, which also faces several shortcomings. Studies reveal that extracellular enzymes have been used to activate biochar which is produced by earthworms and microbes that can alter the surface of the biochar. The present review focuses on the global scenario of metal pollution and its remediation through biochar activation using earthworms. The earthworms and biochar can produce "vermibiochar" which is capable of reducing the metal ions from contaminated water and soils. The vermifiltration can be a suitable technology for metal removal from wastewater/effluent. Thus, the biochar has a trick of producing entirely new options at a time when vermifiltration and other technologies are least expected. Further attention to the biochar-assisted vermifiltration of different sources of wastewater is required to be explored for the large-scale utilization of the process.

A review on the potential of photocatalysis in combatting SARS-CoV-2 in wastewater

Photocatalytic technology offers powerful virus disinfection in wastewater via oxidative capability with minimum harmful by-products generation. This review paper aims to provide state-of-the-art photocatalytic technology in battling transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in wastewater. Prior to that, the advantages and limitations of the existing conventional and advanced oxidation processes for virus disinfection in water systems were thoroughly examined. A wide spectrum of virus degradation by various photocatalysts was then considered to understand the potential mechanism for deactivating this deadly virus. The challenges and future perspectives were comprehensively discussed at the end of this review describing the limitations of current photocatalytic technology and suggesting a realistic outlook on advanced photocatalytic technology as a potential solution in dealing with similar upcoming pandemics. The major finding of this review including discovery of a vision on the possible photocatalytic approaches that have been proven to be outstanding against other viruses and subsequently combatting SARS-CoV-2 in wastewater. This review intends to deliver insightful information and discussion on the potential of photocatalysis in battling COVID-19 transmission through wastewater.

A Way to Membrane-Based Environmental Remediation for Heavy Metal Removal

During the last century, industrialization has grown very fast and as a result heavy metals have contaminated many water sources. Due to their high toxicity, these pollutants are hazardous for humans, fish, and aquatic flora. Traditional techniques for their removal are adsorption, electro-dialysis, precipitation, and ion exchange, but they all present various drawbacks. Membrane technology represents an exciting alternative to the traditional ones characterized by high efficiency, low energy consumption and waste production, mild operating conditions, and easy scale-up. In this review, the attention has been focused on applying driven-pressure membrane processes for heavy metal removal, highlighting each of the positive and negative aspects. Advantages and disadvantages, and recent progress on the production of nanocomposite membranes and electrospun nanofiber membranes for the adsorption of heavy metal ions have also been reported and critically discussed. Finally, future prospective research activities and the key steps required to make their use effective on an industrial scale have been presented

Potential environmental pollution from copper metallurgy and methods of management

This paper presents the latest overview of the environmental impact of wastes from the non-ferrous metallurgical industry. Ashes, slags and dusts - by-products from mining and metal processing - are sources of toxic metals, such as Pb, Cd, Hg, As, Al, as well as particulate matter. Physical, chemical and biological processes transform industrial wastes and cause water, soil and air pollution. Improperly protected heaps are subject to wind erosion and rain water leaching. Heavy metals and particulate matter are transported over long distances, contaminating the soil, living areas, watercourses, while in combination with mist they create smog. Water erosion releases heavy metals, which are leached into groundwater or surface runoff. This paper focuses on the range of pollution emissions from non-ferrous metallurgy wastes, hazards, mechanisms of their formation and fallouts, on the current state of technology and technological risk reduction solutions. The impact of pollution on human health and the biosphere, and methods of waste reduction in this industry sector are also presented. A sustainable and modern mining industry is the first step to cleaner production.

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.

Electrostatic assembly construction of polysaccharide functionalized hybrid membrane for enhanced antimony removal

There is a growing demand for heavy metal removal by membrane technology in real applications. However, few studies were reported concerning antimony (Sb) removal by membrane technology. Herein, a novel thin film nanocomposite (TFN) membrane comprising an alginate (SA) selective layer and a polyether sulfone (PSF) support membrane incorporating chitosan functionalized iron nanocomposite has been firstly developed for Sb removal via electrostatic self-assembly. The support matrix membrane contained iron nanocomposite (denoted as CIM) retained high water flux and porosity, and it reached a maximum removal capacity of 16.5 and 13.6 mg/g for Sb(III) and Sb(V) with nanofiller loading rate of 20% during static experiments, respectively. The coated SA top layer endowed the hybrid membrane (denoted as SA-CIM) to have a lower membrane flux, and have stronger retention abilities for Sb species than that by CIM during dynamic filtration experiments. The SA-CIM membranes also possess tolerable reversibility towards Sb removal. Benefiting from the negatively-charged dense selective layer and high adsorption capacity of the iron nanocomposites, the SA-CIM membranes demonstrated an enhanced removal capacity for Sb species via steric hindrance effect, electrostatic repulsion and adsorption. Our study offers a simple method to remove Sb by a novel polysaccharide functionalized hybrid membrane.

Toxic metal sequential sequestration in water using new amido-aminoacid ligand as a model for the interaction with polyamidoamines

Polyamidoamines are low cost and easily synthesized materials that may find applications in cations sequestration and water treatment. In this paper a new amido-aminoacid ligand containing methionine has been designed as a monomeric model of the corresponding polyamidoamine. The amido-aminoacid ligand has been synthesized in high yield, by reacting acrylamide and methionine via aza-Michael addition in water and mild temperature conditions. The reaction has been monitored by NMR and Raman spectroscopies and the crystal structure has been determined by X-ray diffraction analysis. The coordination ability of the ligand towards Cu²⁺ cations in water, as well as its affinity for Ni²⁺ and Co²⁺ has been studied by potentiometric and spectrophotometric techniques. The divalent metal cations sequestration from water may occur with sequential selection by changing the pH of the solution. The copper complex with two coordinated ligands has been fully characterized in the solid state by single crystal X-ray diffraction. The results are discussed with a view to use these materials in the treatment of water contaminated by toxic transition metal ions.

Novel adsorptive PVC nanofibrous/thiol-functionalized TNT composite UF membranes for effective dynamic removal of heavy metal ions

The development of efficient strategies for the removal of heavy metal ions from aqueous solutions is rapidly demanded as these contaminants are very toxic and carcinogenic and show detrimental effects on the living creatures. The main focus of the current study is on the preparation and assessment of electrospun adsorptive nanofiber membranes for the removal of toxic Ni(II) and Cu(II) from wastewater in the ultrafiltration process. Hydrothermally synthesized titanate nanotubes (TNT) was modified with thiol functional groups and then directly incorporated to the polyvinyl chloride nanofiber matrices via electrospinning process to fabricate an adsorptive membrane. The as-prepared electrospun nanofiber membranes and the nanoadsorbents were characterized with respect to the physiochemical properties, surface structure and morphology, applying XPS, FTIR, FESEM, EDX and TEM analysis and then, the membranes were evaluated in terms of the removal of the heavy metal ions in a continuous ultrafiltration mode. In adsorptive filtration of the metal ions, the effective factors including nanoadsorbents loading (0.5-1.5 wt%), initial metal ion concentration (60-150 mg/L), feed temperature (~25 °C-45 °C), presence of competing ion and reusability were investigated in the UF system where the membranes containing 1.5 wt% thiol-modified TNT and virgin TNT adsorbents demonstrated excellent removal efficiency compared to the other membranes. The Cu(II) and Ni(II) removal efficiency of the membrane containing 1.5 wt% functionalized TNT was 90% and 86.7%, respectively which was the highest ones. As was expected and due to the uniform dispersion and less aggregation of the modified TNT adsorbents on the large surface area of the electrospun nanofibers, more adsorption capacity of the nanoparticles can be exploited. Moreover, the strong affinity of the thiol functional groups toward the metal cations, these membranes removed metal contaminants more efficiently. Besides, the Cu(II) removal efficiency of the fabricated membranes didn't show any drastic changes in the presence of the competing ions. Furthermore, acceptable performance was achieved for the prepared membranes even after four adsorption/regeneration cycles in the continuous UF experiments, demonstrating the feasibility and effectiveness of the prepared adsorptive nanofiber membranes for the removal of heavy metal ions.

Robust cellulose-based composite adsorption membrane for heavy metal removal

Adsorptive membranes offer an effective mode to remove heavy metal ions from contaminated water, due to the synergies made possible by low-cost, high-affinity adsorbents and highly scalable filtration in one system. However, the development of adsorptive membranes is hampered by their instability in the aqueous phase and low binding affinity with a broad spectrum of heavy metals in a reasonable flux. Herein, a regenerated cellulose support membrane is strongly grafted with stable and covalent-bonded polyelectrolyte active layers synthesized by a reactive layer-by-layer (LBL) assembly method. The LBL assembled layers have been successfully tested by scanning electron microscopy, Fourier-transform infrared spectroscopy and X-ray photo-electron spectroscopy. The covalent bonding provides the membrane with long-term stability and a tunable water flux compared to a membrane assembled by electrostatic bonding. The maximum adsorption capacity of the membrane active layers can reach up to 194 mg/g, showing more efficient adsorption at lower heavy metal concentration and higher pH value of feed solution. The membrane can remove multiple ions, such as Cu, Pb, and Cd, by adsorption and is easy to be regenerated and recovered. The strong covalent bonding can extend the membrane lifetime in water purification to remove multiple heavy metals at high efficiency.

Polyvinylidene fluoride (PVDF)-α-zirconium phosphate (α-ZrP) nanoparticles based mixed matrix membranes for removal of heavy metal ions

The removal of heavy metal ions from industrial wastewater is essential as they pose serious threats to human health and the environment. In this study, novel poly(vinylidene fluoride) (PVDF)-alpha-zirconium phosphate (PVDF-α-ZrP) mixed matrix membranes (MMM) were prepared via the phase inversion method. Membranes with different α-ZrP nanoparticles (NPs) loadings (0.25, 0.50, 0.75, or 1.00 wt%) were fabricated. The impacts of α-ZrP NP loading on the membrane's morphology, functionality, surface charge, and hydrophilicity were evaluated. Fourier-transform infrared and the energy-dispersive X-ray spectroscopy were performed to verify the presence of α-ZrP NPs in the fabricated membranes. The PVDF membranes became more hydrophilic after incorporating the α-ZrP NPs. The thermal and mechanical stability and porosity of the PVDF-α-ZrP MMM were higher than those of the pristine PVDF membrane. The increased hydrophilicity, pore size and porosity and reduced surface roughness of the PVDF-α-ZrP membrane led to significant flux increase and reduced fouling propensity. The PVDF-α-ZrP membrane containing 1.00 wt% α-ZrP was capable of removing 42.8% (Cd²⁺), 93.1% (Cu²⁺), 44.4% (Ni²⁺), 91.2% (Pb²⁺), and 44.2% (Zn²⁺) from an aqueous solution at neutral pH during filtration.