TAP/GMA@CN metal-chelating membrane for enhanced and efficient capture of Cu(II)

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.

Highly efficient removal of Cr(VI) from wastewater using electronegative SA/EGCG@Ti/SA/PVDF sandwich membrane

The use of green, non-toxic raw materials is of great significance to the sustainable development of the environment, among which epigallocatechin gallate (EGCG) is a renewable carbon source from plants. At present, there is a lack of research on the metal-polyphenol nanomaterials their use in water decontamination. In this study, a novel SA/EGCG@Ti/SA/PVDF (SESP) sandwich membrane was prepared to effectively solve the problems of difficult recovery of nanomaterials and the leaching of metal ions. The membrane was made by scraping SA on the surface of the PVDF substrate as the bottom protective layer, depositing EGCG@Ti NPs as the functional layer, then coating SA as the surface isolation layer, and finally cross-linking with anhydrous calcium chloride. Results showed that EGCG@Ti NPs dispersed well on the surface of the SA/PVDF basement membrane. SESP sandwich membrane had good hydrothermal and acid-base stability, and it can be applied to wastewater with multiple co-existing heavy metals (e.g., Cu, Pb, Cd, and Ni). The contact angle and pure water flux of the SESP sandwich membrane with a negatively charged surface were 14.0-15.6° and 171.40 L/m2 h, respectively. The pure water flux of the regenerated membrane after BSA pollution recovered to 98.68 L/m2 h, and the interception efficiency and the interception flux of Cr(VI) were 100 % and 72.92 L/m2 h at 40 min of interception, respectively. Additionally, the removal efficiency of Cr(VI) by SESP sandwich membrane was maintained above 83 % for simulated wastewater and 100 % for actual wastewater after five adsorption-desorption cycles. Cr(VI) and Cr(III) can be removed simultaneously with the negatively charged SESP sandwich membrane. EDS and XPS analysis showed that the removal of Cr(VI) was controlled by the Donnan effect, anion exchange, chelation/complexation, and reduction mechanism. In contrast, Cr(III) was mainly influenced by electrostatic attraction and chelation/complexation mechanisms. In conclusion, the newly prepared sandwich membrane has good application potential in treating Cr(VI) wastewater.

Amidoxime functionalized PVDF-based chelating membranes enable synchronous elimination of heavy metals and organic contaminants from wastewater

Aiming at the synchronous elimination of heavy metals and organic contaminants from wastewater, the amidoxime functionalized PVDF-based chelating membrane was fabricated in this study. The structure and morphology of the chelating membrane were characterized using infrared spectroscopy (FT-IR), nuclear magnetic resonance spectrometer (NMR) and scanning electron microscopy (SEM). The SEM results show that the chemical modification with amidoxime groups did not damage the structure of the PVDF-based membrane. The chelating membrane has a high removal efficiency for Cu²⁺ (77.33%) and Pb²⁺ (79.23%) owing to the chemisorption through coordination bonds. However, the chelating membrane exhibits a low removal efficiency for Cd²⁺ (29.88%) due to the physical adsorption. The chelating membrane has a high rejection efficiency of BSA (95.17%) and lysozyme (70.09%), which is attributed to the sieving effect and increased hydrophobicity. Furthermore, the membrane performance for simultaneously removing metals and proteins from simulated wastewater was examined. The interaction of metal ions with proteins (BSA and lysozyme) can enhance the ion removal efficiency of the chelated membrane, but decrease the protein rejection efficiency due to the destructive effect. The amidoxime functionalized PVDF-based chelating membrane has a high potential for application in wastewater treatment.

Molecularly Imprinted Affinity Membrane: A Review

A molecularly imprinted affinity membrane (MIAM) can perform separation with high selectivity due to its unique molecular recognition introduced from the molecular-printing technique. In this way, a MIAM is able to separate a specific or targeted molecule from a mixture. In addition, it is possible to achieve high selectivity while maintaining membrane permeability. Various methods have been developed to produce a MIAM with high selectivity and productivity, with their respective advantages and disadvantages. In this paper, the MIAM is reviewed comprehensively, from the fundamentals of the affinity membrane to its applications. First, the development of a MIAM and various preparation methods are presented. Then, applications of MIAMs in sensor, metal ion separation, and organic compound separation are discussed. The last part of the review discusses the outlook of MIAMs for future development.

Ongoing progress on novel nanocomposite membranes for the separation of heavy metals from contaminated water

Membranes, as the primary separation element of membrane-based processes, have greatly attracted the attention of researchers in several water treatment applications, including wastewater treatment, water purification, water disinfection, toxic and non-toxic chemical molecules, heavy metals, among others. Today, the removal of heavy metals from water has become challenging, in which chemical engineers are approaching new materials in membrane technologies. Therefore, the current review elucidates the progress of using different concepts of membranes and potential novel materials for such separations, identifying that polymeric membranes can exhibit a removal efficiency from 77 up to 99%; while novel nanocomposite membranes are able to offer complete removal of heavy metals (up to 100%), together with unprecedented permeation rates (from 80 up to 1, 300 L m^-2 h^-1). Thereby, the review also addresses the highlighted literature survey of using polymeric and nanocomposite membranes for heavy metal removal, highlighting the relevant insights and denoted metal uptake mechanisms. Moreover, it gives up-to-date information related to those novel nanocomposite materials and their contribution to heavy metals separation. Finally, the concluding remarks, future perspectives, and strategies for new researchers in the field are given according to the recent findings of this comprehensive review.

A mini review of multifunctional ultrafiltration membranes for wastewater decontamination: Additional functions of adsorption and catalytic oxidation

Multifunctional ultrafiltration membranes, which achieve ultrafiltration and additional functions in one unit, are a new strategy developed in recent years for wastewater treatment. In this mini review, we summarized and commented on the development of adsorptive and catalytically oxidative multifunctional ultrafiltration membranes, as well as pointed out possible further trends. The main methods for membrane preparation, i.e., blending, surface coating, reverse filtration, etc., were summarized, and the advantages and disadvantages of each method were discussed. In addition, the key criteria which influence the performance of membranes, including the efficiency of additional functions, original ultrafiltration, permeance, and stability, were analyzed. Furthermore, we introduced the applications of different classes of multifunctional ultrafiltration membranes, and tried to further analyzed some examples of multifunctional ultrafiltration membranes used for adsorption and catalytic oxidation. The most significant advantage of this technology is the high efficiency for the simultaneous removal of different kinds of pollutants or for the removal of one kind of pollutant during the deep treatment of multicomponent wastewater. However, some challenges still oppose the practical application of multifunctional ultrafiltration. We believe that breaking the trade-off between the high efficiency of additional functions and high flux, strengthening the stability of the membranes, achieving synergistic effects between multi-effect functions, and investigating the interaction mechanisms between active materials and the membrane are key points for further research.

Low pressure operated ultrafiltration membrane with integration of hollow mesoporous carbon nanospheres for effective removal of micropollutants

An effective way to remove micropollutants is desirable for water purification. In this work, a dual-functional ultrafiltration (DFUF) membrane was fabricated by loading hollow mesoporous carbon nanospheres (HMCNs) into the finger-like support layer pores of the polymeric ultrafiltration (UF) membrane. The designed DFUF membrane combines the high selectivity of ultrafiltration that removes macromolecules based on size exclusion mechanism, and excellent adsorption capacity of HMCNs towards micropollutants in water. When tetracycline (TCN) and 17β-Estradiol (E2) were selected as model micropollutants, corresponding 97 % and 94 % removal were achieved at a low pressure less than 0.15 bar and a flux of 50 and 64 L h^-1 m^-2 (estimated residence time less than 6 s), respectively. Moreover, simultaneous removal of multiple pollutants was demonstrated by filtering a mixture containing TCN and polyethylene glycols (PEG) 600 kDa macromolecules. Over a long filtration period (more than 60 h) that produced 3180 L/m² of permeate, the TCN concentration reduced from 100 μg/L in the feed to less than 10 μg/L in the permeate. The above results indicate that the DFUF membrane is capable of removing the small molecular and macromolecular pollutants simultaneously at low pressure, and hence offers remarkable potential in water treatment applications.

The hierarchical flower-like MoS2 nanosheets incorporated into PES mixed matrix membranes for enhanced separation performance

Membrane fouling is an issue of concern due to the hydrophobic properties of polyethersulfone (PES) membrane when applied in water treatment. In this work, a facile hydrothermal method was utilized to synthesize hierarchical flower-like structured molybdenum disulfide nanosheets (HF-MoS2 NSs) that then incorporated into PES membranes as composite membranes. We characterized their permeability, the separation performance, the antifouling performance, and the antibacterial activity systematically. Results showed that composite membranes exhibited a better pure water flux (286 LMH/bar) at the HF-MoS₂ NSs content of 0.4 wt%, which was 1.8 times higher than the control membrane. Also, composite PES membranes achieved 98.2% and 96.9% rejection of BSA and HA in comparison with the control PES membrane (87.3%, and 84.5%, respectively). Compare to the control PES membrane, the flux recovery ratio of the composite membrane increased from 69% to 88% for BSA fouling and increased from 84% to 93% for HA fouling. The retention rate for the organic dyes also improved slightly after HF-MoS2 NSs incorporation into the membrane. Additionally, the composite membranes exhibited a relatively high antibacterial activity against E. coli and B. subtilis with antibacterial rates of 67.8% and 82.5%, respectively. In conclusion, HF-MoS2 NSs incorporated composite membranes were shown to have outstanding filtration performance and could be a promising candidate for practical application in water filtration.

A high-flux and anti-interference dual-functional membrane for effective removal of Pb(II) from natural water

The development of high efficiency filter membranes, particularly those capable of removing trace heavy metals from drinking water sources, is a global challenge. In this study, a dual-functional membrane (P_mG_n@PVDF) was successfully developed by doping graphene oxide (GO) and then depositing polydopamine (PDA). The pure water flux (Jw) was 188 LMH/bar and Pb(II) could be effectively removed in the water volume of 2106.36 L m^-2. Both PDA and GO performed positive functions. PDA layer exhibited a high affinity toward Pb(II) by chelating with amino groups. And doping GO maintained a high pure water flux, which had been decreased by the extra PDA layer. In addition, the effective treatment volume of Pb(II) was elevated to 5029.06 L/m² by the co-existence of citric acid, since neutral PbHL coordinated with neutral NH₂ and cationic PbL- interacted with NH₃⁺ through electrostatic attraction. Furthermore, P_mG_n@PVDF showed the excellent anti-interference performance in high salt and nature organic matters solutions. Thus, this novel dual-functional membrane could be considered as a competitive alternative of NF/RO for the efficient and advanced removal towards heavy metals from natural water.