Separation Of Heavy Metal Ions Research Articles

Choline chloride modification of nanofiltration membranes for improving heavy metal ions separation in wastewater

The growing concern over heavy metal ion contamination in industrial wastewater, posing a significant threat to global public health, has led to a heightened interest in devising efficient removal methods. Nanofiltration, while promising, faces a substantial challenge in simultaneously achieving a high rejection of heavy metal cations and maintaining an elevated water permeance. In response, this study utilizes a simple approach by employing choline chloride with a quaternary ammonium group to modify the surface of PEI-TMC membrane, leading to the design of a high-performance PEI-TMC-CC membrane. The choline chloride modification optimized the surface morphology, hydrophilicity, roughness, and combined the Donnan exclusion effect as well as sieving effect, enabling the PEI-TMC-CC membrane to achieve an exceptional rejection of heavy metal ions while retaining a great water permeance. An impressive water permeance 10.0 L·m−2·h−1·bar−1 was performed by the PEI-TMC-CC membrane, nearly three times that of traditional PEI-TMC membranes. Concurrently, the PEI-TMC-CC membrane demonstrated an impressive rejection of heavy metals Cd2+, Pb2+, Ni2+, Zn2+, and Cu2+, reaching rejections of 98.3%, 95.9%, 98.1%, 98.5% and 99.1%, respectively. Moreover, density functional theory (DFT) calculations confirmed the improved hydrophilicity of choline chloride molecules, aligning with experimental results. The modification of traditional nanofiltration membranes using cost-effective, hydrophilic, positively charged chemicals not only leads to significant performance improvements but also holds the potential to advance the development of positively charged nanofiltration membranes tailored for the removing of heavy metals cations from wastewater. This approach demonstrates promising prospects for industrial applications and further development.

Separation of heavy metals from dilute solutions using D2EHPA carrier fixed onto the outer surface of coaxially electrospun core-sheath fibers

In this study, porous membranes based on core-sheath fibers covered with fixed carriers were prepared by coaxial electrospinning for the separation of heavy metal ions from dilute solutions. Cellulose triacetate (CTA) and an extractant di(2-ethylhexyl)phosphoric acid (D2EHPA) were mixed to prepare a sheath-layer solution and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was adopted to prepare a core-layer solution for electrospinning. The morphological and textural properties as well as chemical composition of the fabricated core-sheath fibers were first analyzed to determine the optimal preparation conditions. The ability and selectivity of such fixed D2EHPA carriers were evaluated via the adsorption of Zn2+, Cu2+, and Ni2+ ions from dilute solutions. Dynamic tests revealed that the adsorption of metal ions on the core-sheath fibrous membrane made of 52 wt% PVDF-HFP, 18 wt% D2EHPA, and 30 wt% CTA (on a dry basis) reached equilibrium within 8 h. As expected, all adsorption isotherms at specific equilibrium pH values were well described by the Langmuir equation, ascribed to the chemical reaction nature between metal ions and D2EHPA carrier. The crossflow permeation-adsorption tests of a multi-metal solution in a total recycling mode revealed the adsorption selectivity of Zn2+ over Cu2+ and Ni2+, as observed in conventional liquid–liquid extraction. Four repeated adsorption-regeneration experiments revealed an adsorption efficiency beyond 95 % relative to the first route, demonstrating the satisfactory reusability and stability of the as-prepared core-sheath fibrous membranes for this purpose.

ТЕРМОДИНАМИЧЕСКИЙ АНАЛИЗ ОКИСЛИТЕЛЬНО – ВОССТАНОВИТЕЛЬНЫХ РЕАКЦИЙ, ПРОТЕКАЮЩИХ ПРИ ГАЛЬВАНОКОАГУЛЯЦИОННОЙ ОЧИСТКЕ СТОКОВ

Abstract. One of the most important environmental problems is the purification of industrial wastewater from heavy metal ions. Various methods are used to solve this problem: chemical, physico-chemical, sorption, but the most promising method for cleaning industrial wastewater containing heavy metal ions, namely copper, nickel and zinc, is the galvanocoagulation method. However, the literature does not sufficiently cover the processes of cementation of heavy metals on cathode loading. A physico-chemical approach to this process is necessary to confirm the process of separation of heavy metal ions from wastewater in the form of sediment and the creation of new industrial wastewater treatment schemes. The composition of the loading is essential in galvanocoagulation neutralization, therefore, in order to determine the effect of the type of active loading, a carbon mineral sorbent (SGN) obtained from ores of cryptocrystalline graphite (Noginsky deposit of the Krasnoyarsk Territory) was used. The studies were carried out in a galvanocoagulation module by passing wastewater through a loading consisting of a mixture of iron shavings and granules of carbon mineral sorbent based on ores of cryptocrystalline graphite (SGN). At the same time, the air dispersed in the lower part of the device was bubbled through the loading. As a result of the operation of the Fe-SGN short-circuited galvanic cell, iron scrap was dissolved and its intensive oxidation to Fe3+ by air oxygen. The article considers the mechanism of galvanocoagulation neutralization of wastewater based on thermodynamic analysis of redox reactions occurring during galvanocoagulation wastewater treatment.
 Subject of the study: both model and real wastewater from the production of electroplating coatings containing copper, zinc and nickel ions with the following concentrations were used: =60 mg/dm3; =15 mg/dm3; =20 mg/dm3
 Materials and methods: galvanocoagulation neutralization using a short-circuited Fe-SGN galvanic cell (carbon mineral sorbent)
 Results: the physico-chemical patterns of the galvanocoagulation process of wastewater treatment have been studied and the thermodynamic parameters of heavy metal ion reduction reactions have been determined
 Conclusions. It has been experimentally established that it is possible to intensify the process of galvanocoagulation of wastewater containing heavy metal ions by using a carbon mineral sorbent as a cathode loading, which reduces the processing time with a high purification effect and a difficult-to-dissolve precipitate is formed.

Investigation of the pH-mediated fabrication process of pure and polyethyleneimine-crosslinked graphene oxide membranes for desalination and heavy metal ion separation

Graphene oxide (GO) membranes have been extensively investigated and employed in separating various ions and molecules due to their superior physicochemical properties. However, the inconsistency in their pore structure, difficulty in the precise tuning of their d-spacing, and instability in aqueous solution – especially at extreme pH values – might hinder their separation efficiency. In this research, we systematically investigated the pH-mediated fabrication process of graphene oxide membranes and evaluated the properties of the resulting membranes. Findings from scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses show that a higher fabrication pH results in a thicker GO layer and an enlarged d-spacing due to the deprotonation of the GO's carboxyl groups. Furthermore, pH-assisted crosslinking between polyethyleneimine (PEI) and GO sheets were facilitated and the chemical analysis results suggest that in acidic environments, the dominant reaction involves C–N bond formation at the basal plane, whereas under alkaline conditions, N–CO (amide) bond formation at the edges is more prevalent. This, in return, accordingly shifted the trend in SEM and XRD, where a thinner GP layer and a decreased d-spacing were observed at a higher fabrication pH due to the deprotonation of the incorporated PEI's amine groups. These findings contributed to the nanofiltration (NF) performance of the membranes against different inorganic salts and heavy metal ions. It was discovered that the GPpH11 membrane formed at pH 11 has the highest Pb2+ rejection of >95%, making it a suitable material for heavy metal ions removal.

Mesoporous Magnetic/Polymer Hybrid Nanoabsorbent for Rapid and Efficient Removal of Heavy Metal Ions from Wastewater.

As an advanced water purification technology, magnetic nanoabsorbents are highly attractive for their sustainability, robustness, and energy efficiency. However, magnetic responsiveness and high adsorptive capacity are irreconcilable during the design and synthesis of a high-performance magnetic nanoabsorbent. Here, we address this issue by designing a kind of mesoporous magnetic polymer hybrid microspheres, where functional polymers such as polyrhodanine and polypyrrole were attached to the pore walls in the interior of mesoporous Fe3O4 microspheres through in situ polymerization. Due to the integrated large saturation magnetic moment, porous structure, and dense polymer layer, the mesoporous magnetic polymer hybrid microspheres demonstrated fast magnetic responsiveness, excellent recycling performance, and high adsorption capacities toward Pb(II) ions (189 mg g-1) for polyrhodanine and Cr(VI) ions (199 mg g-1) for polypyrrole. Furthermore, their potential application in wastewater treatment was verified by a self-made magnetic separation column, where the designed magnetic nanoabsorbent exhibits significant advantages including rapid separation of heavy metal ions and high outflow. This study provided a promising magnetic polymer hybrid nanoabsorbent for realizing efficient removal of heavy metal ions from wastewater.

Rational construction of MoSx via defect engineering for efficient removal of mercury ions from aqueous solution

Mercury ions (Hg2+) are one of the most physiologically toxic heavy metal ions in water. Developing adsorbents for separating and removing mercury ions from aquatic systems has important environmental and social significance. Owing to the hard-soft-acid-base interaction between mercury and sulfur (S) atoms, two-dimensional layered MoS2 holds great promise in capture physiologically toxic Hg2+ from water, but most S atoms are located inside the bulk MoS2, hindering the effective contact with mercury. Defects engineering is considered as an effective way to adjust the structure and achieve superior performance of MoS2. However, reasonable and fine defect modulation to enhance the mercury adsorption performance remains a challenging task. Herein, we reported that molybdenum sulfide with Mo-vacancy structure (MV-MoSx) was fabricated via hydrothermal method and employed to uptake Hg2+. The results showed that this defect type significantly increased the concentration of Mo stripping defects, exposed more active S atoms, and provided MoSx with excellent adsorption performance in adsorption capacity, adsorption kinetics, distribution coefficient, selectivity and so on. In particular, MV-MoSx demonstrates a substantial actual adsorption capacity for mercury, reaching as high as 3723.3 mg/g, which is in close proximity to its theoretical adsorption capacity of 3945.95 mg/g. More importantly, a functionalized composite aerogel system based on MV-MoSx was constructed, which successfully reduced the concentration of Hg2+ solution below the concentration permitted by drinking water standards. Our study not only provide a theoretical basis for the design of novel defect engineering, but also expand the application of transition metal sulfides in the enrichment and separation of heavy metal ions.

High-performance asparagine-modified graphene oxide membranes for organic dyes and heavy metal ion separation

Asparagine-modified GO membranes are prepared to efficiently reject rhodamine B dye up to 99.9%, along with a water permeability of ∼1740 ± 10 L m−2 h−1 bar−1. Further, such membranes are stable in water up to 34 days.

In Situ Fabrication and Characterization of g-C3N4 onto Cellulose Nanofibers and Selective Separation of Heavy Metal Ions.

Graphitic carbon nitride nanosheets were synthesized onto cellulose nanofiber surfaces utilizing an eco-friendly salt melt approach. The fabricated material CNF@C3N4 selectively removes Ni(II) and Cu(II) from electroplating wastewater samples. The immobilization of g-C3N4 on solid substrates eases handling of nanomaterial in a flow-through approach and mitigates sorbent loss during column operations. Characterization techniques such as scanning electron microscopy, tunneling electron microscopy, and X-ray photoelectron microscopy were employed to analyze the surface morphology and chemical bonding within the synthesized material. Selective Cu(II) and Ni(II) sorption predominantly arises from the soft-soft interaction between metal ions and associated nitrogen groups. An inner-sphere surface complexation mechanism effectively elucidated the interaction dynamics between the metal and CNF@C3N4. Experimental findings demonstrated satisfactory separation of Ni(II) and Cu(II) ions, with the extraction of 340.0 and 385.0 mg g-1 of material, respectively. Additionally, the devised technique was executed for the preconcentration and quantification of trace metals ions in water samples with a detection limit and limit of quantification of 0.06 and 0.20 μg L-1, respectively.

Surface implantation of ionically conductive polyhydroxyethylaniline on cation exchange membrane for efficient heavy metal ions separation

Extraction of heavy metal ions from aqueous could enable recycling of wastewater and reusing of high-value ion resources. Recently, electrodialysis (ED) technology has been applied in the removal of heavy metal ions from wastewater, however, developing high-efficient and stable heavy metal ions selective cation exchange membrane (CEM) remains an elusive challenge. Herein, we demonstrate the fabrication of high-efficient cations selective CEM with the surface implantation of ionically conductive polyhydroxyethylaniline (PANI-OH) on a commercial CEM membrane (CTG) containing sulfonic acid groups via the electrostatic attraction. Implanted hydrophilic and positively charged PANI-OH facilitates fast and selective transfer of Cu2+ over Zn2+ cations through the membrane. Meanwhile, the synergistic effect of rigid conjugate structure and hydrogen-bond interaction of PANI-OH renders the resultant membrane CTG-PANI-OH with stable structure and separation performance. As such, the Cu2+/Zn2+ permselectivity of CTG-PANI-OH membrane is ~1.70, which is about 190 % of that of the pristine CTG membrane. This work provides a facile design and strategy for the construction of high-efficient cations selective CEMs with great application prospects in the purification and extraction of heavy metal ions from wastewater.

UiO-66-NH2 modified thin film nanocomposite (TFN) membranes for selective separation of Li+/Co2+ in a flow electrode capacitive deionization system

As key metal elements in lithium-ion batteries (LIBs), the recovery of lithium (Li) and cobalt (Co) showed both economic and environmental benefits. In this study, a thin-film nanocomposite (TFN) membrane with high selectivity was fabricated based on nanoscale UiO-66-NH2 particles, and the modified membranes were applied in the flow-electrode capacitive deionization device (FCDI) for the separation of monovalent and divalent cations. UiO-66-NH2 provided hydrophilic water channels and increased the permeability of Li+. TFN exhibited a rejection rate of Co2+ over 95%, and the separation factor of Li+/Co2+ was 27.44 during the operation of 150 min in FCDI with the addition of 10 mg UiO-66-NH2, which was about 1.52 times greater than that of the commercial cation-selective membrane (CSO). The size repulsion effect caused by size difference between hydrated ions and membrane pores and Donnan electrostatic repulsion force generated by positively charged membranes were evaluated to be the main basis for the ion separation of prepared membranes. The novel system using TFN membrane in FCDI had a better ability to resist Co2+ fouling and a good Li+/Co2+ separation effect. We believe these modified membranes have promising potential for the selective separation of heavy metal ions and the recycling of metal resources.

Titanium-embedded nanocomposite material stimulates ion-exchange characteristics to deal with toxic heavy metal pollutants in aquatic environment

ABSTRACT Nano-sized composite ion-exchanger can be applied as an electrochemically switchable ion-exchanger for waste water treatment, especially in the separation of heavy metal ions from the polluted aquatic system. Advanced polyaniline/Ti(IV) iodomolybdate nanocomposite ion-exchanger have been synthesized by in-situ chemical oxidation polymerization shows better ion-exchange capacity than individual inorganic counterpart. The physico-chemical characterization was done by FT-IR, XRD, simultaneous TGA-DTA, SEM, HR-TEM and electrochemical impedance studies. According to impedance/dielectrical study, it has high resistivity in the low-frequency region. The distribution studies and binary separation revealed that the ion-exchange material is highly selective for Pb2+, which is a most important environmental pollutant. Thus, PANI/TIM nanocomposite ion-exchanger can be used for Pb(II) ion-selective membrane for the treatment of aquatic pollutants in future.

Application of chitosan-based materials in wastewater treatment

Chitosan, as a natural polysaccharide material, plays a great role in the field of wastewater treatment due to its good biodegradability, antimicrobial activity, and other properties. However, it may have some differences in the processes of adsorption, flocculation, and membrane separation. We comprehensively describe the application effect and mechanism of action of chitosan-based materials on the above three major water treatment processes. In the adsorption process, chitosan-based adsorbents such as hydrogels and chitosan beads are prepared by cross-linking, impregnation, and the introduction of functional groups. These chitosan-based materials exerted efficient removal performance in the adsorption of heavy metals, organic dyes, anionic pollutants, etc., which was attributed to their large specific surface area and abundant functional groups. In the flocculation process, the chitosan-based materials were modified by grafting and modifying their shape, while heavy metal ions, organic dyes, and algae were removed using processes such as chelation and charge neutralization. In the membrane separation process, a number of nanofiltration and microfiltration membranes were created by coating chitosan ions, and physicochemical modification was done for the separation of heavy metal ions and emulsified oil droplets in water to improve the fouling resistance and retention rate of the membrane materials. This paper reviews the application of chitosan-based materials in wastewater treatment and proposes that in-depth studies on their toxicity and reusability should be conducted in the future, with a view to playing a role in areas such as the removal of malodorous water odors.

Self-Assembling Peptide-Based Magnetogels for the Removal of Heavy Metals from Water.

In this study, we present the synthesis of a novel peptide-based magnetogel obtained through the encapsulation of γ-Fe2O3-polyacrylic acid (PAA) nanoparticles (γ-Fe2O3NPs) into a hydrogel matrix, used for enhancing the ability of the hydrogel to remove Cr(III), Co(II), and Ni(II) pollutants from water. Fmoc-Phe (Fluorenylmethoxycarbonyl-Phenylalanine) and diphenylalanine (Phe2) were used as starting reagents for the hydrogelator (Fmoc-Phe3) synthesis via an enzymatic method. The PAA-coated magnetic nanoparticles were synthesized in a separate step, using the co-precipitation method, and encapsulated into the peptide-based hydrogel. The resulting organic/inorganic hybrid system (γ-Fe2O3NPs-peptide) was characterized with different techniques, including FT-IR, Raman, UV-Vis, DLS, ζ-potential, XPS, FESEM-EDS, swelling ability tests, and rheology. Regarding the application in heavy metals removal from aqueous solutions, the behavior of the obtained magnetogel was compared to its precursors and the effect of the magnetic field was assessed. Four different systems were studied for the separation of heavy metal ions from aqueous solutions, including (1) γ-Fe2O3NPs stabilized with PAA, (γ-Fe2O3NPs); (2) Fmoc-Phe3 hydrogel (HG); (3) γ-Fe2O3NPs embedded in peptide magnetogel (γ-Fe2O3NPs@HG); and (4) γ-Fe2O3NPs@HG in the presence of an external magnetic field. To quantify the removal efficiency of these four model systems, the UV-Vis technique was employed as a fast, cheap, and versatile method. The results demonstrate that both Fmoc-Phe3 hydrogel and γ-Fe2O3NPs peptide magnetogel can efficiently remove all the tested pollutants from water. Interestingly, due to the presence of magnetic γ-Fe2O3NPs inside the hydrogel, the removal efficiency can be enhanced by applying an external magnetic field. The proposed magnetogel represents a smart multifunctional nanosystem with improved absorption efficiency and synergic effect upon applying an external magnetic field. These results are promising for potential environmental applications of γ-Fe2O3NPs-peptide magnetogels to the removal of pollutants from aqueous media.

Molecular dynamics simulation of hexagonal boron nitride slit membranes for wastewater treatment

Nanoporous boron nitride (BN) nanosheets are promising reverse-osmosis membrane materials, suitable for the removal of hazardous heavy metals, with advantages such as separation energy efficiency, eco-friendliness, heat resistance, acid resistance, and good antifouling properties. BN slit membranes (BNSMs) are a special class of nanoporous BN membranes that have not yet been extensively explored for heavy metal ion separation. To address the existing knowledge gap regarding these membranes, molecular dynamics (MD) simulations were performed herein to investigate the performance of BNSMs in purifying water from arsenic (As3+) and mercuric (Hg2+) cations, as well as chloride (Cl-) anions. For this purpose, the effects of slit width in monolayer, bilayer, and trilayer BN, interlayer distance, and membrane flexibility were evaluated. Based on the results obtained in this work, water flow rate increases, while ion rejection decreases, with increasing slit width. For rigid monolayer BNSMs having slit widths of 8–10 Å, the ion rejection percentage was in the order of As3+ > Cl- > Hg2+. The highest rejection percentage of As3+ cations in these membranes is attributed to their largest repulsive interaction energies of 27 kcal/mol with the membrane surface and the largest hydration radii of these cations (3.8 Å). For a rigid monolayer BNSM with the slit width of 7 Å, the rejection percentages of all ions were approximately equal to 100 % due to the dominant effect of slit geometric constraints against ion transport. For a rigid bilayer BNSM, both the number of filtered water molecules and water flow rate decreased with a decrease in the interlayer distance. In terms of ion rejection performance, the geometric constraints (size exclusion mechanism) were again responsible for the high (above 98 %) ion rejection percentages in these membranes with interlayer distances of 7–9 Å. Finally, flexible monolayer BNSMs were found to provide higher water flow rates and lower ion rejection percentages when compared to the rigid membranes. This behavior can be attributed to the larger slit cavity that results from membrane flexibility, thereby facilitating water flow and ion transport through the membrane. The use of molecular dynamics simulations in this study demonstrates the potential of computational methods in the design and screening of novel membrane materials, paving the way for further computational and experimental investigations in this field.

Lamellar Graphene Oxide-Based Composite Membranes for Efficient Separation of Heavy Metal Ions and Desalination of Water.

Sufficient efforts have been carried out to fabricate highly efficient graphene oxide (GO) lamellar membranes for heavy metal ion separation and desalination of water. However, selectivity for small ions remains a major problem. Herein, GO was modified by using onion extractive (OE) and a bioactive phenolic compound, i.e., quercetin. The as-prepared modified materials were fabricated into membranes and used for separation of heavy metal ions and water desalination. The GO/onion extract (GO/OE) composite membrane with a thickness of 350 nm shows an excellent rejection efficiency for several heavy metal ions such as Cr6+ (∼87.5%), As3+ (∼89.5%), Cd2+ (∼93.0%), and Pb2+ (∼99.5%) and a good water permeance of ∼460 ± 20 L m-2 h-1 bar-1. In addition, a GO/quercetin (GO/Q) composite membrane is also fabricated from quercetin for comparative studies. Quercetin is an active ingredient of onion extractives (2.1% w/w). The GO/Q composite membranes show good rejection up to ∼78.0, ∼80.5, ∼88.0, and 95.2% for Cr6+, As3+, Cd2+, and Pb2+, respectively, with a DI water permeance of ∼150 ± 10 L m-2 h-1 bar-1. Further, both membranes are used for water desalination by measuring rejection of small ions such as NaCl, Na2SO4, MgCl2, and MgSO4. The resulting membranes show >70% rejection for small ions. In addition, both membranes are used for filtration of Indus River water and the GO/Q membrane shows remarkably high separation efficiency and makes river water suitable for drinking purpose. Furthermore, the GO/QE composite membrane is highly stable up to ∼25 days under acidic, basic, and neutral environments as compared to GO/Q composite and pristine GO-based membranes.

Extraction and enrichment of zinc from chloride media using emulsion liquid membrane: Emulsion stability and demulsification via heating-ultrasonic method

Emulsion liquid membrane (ELM) is highly efficient in heavy metal ion separation from wastewater. However, substantial effort is required to overcome the instability in the process. Hence, this research demonstrates the stability of water-in-oil-in-water (W/O/W) emulsion and demulsification for zinc recovery from chloride media. Iron (III) oxide (Fe2O3) nanoparticles were used as a solid stabilizer in the formation of water-in-oil (W/O) emulsion. Several operating parameters affecting the stability of W/O/W emulsion by means of breakage/swelling and globule size diameter were studied, such as organic-to-internal phase (O/I) ratio, agitation speed, time, and treatment ratio. The most stable formulated W/O/W emulsion was used in the demulsification process using heating-ultrasonic method. The study was conducted by manipulating the temperature, frequency, and time. Meanwhile, experiments on the effect of modifier type, carrier, and stripping agent concentration were carried out for zinc recovery. The most stable W/O/W emulsion was obtained at 1.35:1O/I ratio, 300 rpm agitation speed, 3 min agitation time, and 1:5 treatment ratio. Complete demulsification was achieved at a temperature of 50 °C, 40 kHz frequency, and 210 min contact time. At the best condition of 3% (w/v) 1-octanol, 0.03 M carrier concentration (D2EHPA/Cyanex 302), and 1.375 M acidic thiourea, approximately 93.14% zinc was extracted, and 4.65 times enrichment was obtained in the recovery phase. Hence, it can be concluded that enhancing the stability of emulsion could potentially make ELM applicable in the industry.

Separation of heavy metal ions from multi-component solutions using ultrafiltration enhanced with complexing polymer

Separation of heavy metal ions from multi-component solutions using ultrafiltration enhanced with complexing polymer

Recent Advances in Graphene Oxide‐Based Membranes for Heavy Metal Ions Separation

AbstractGraphene oxide (GO)‐based membranes have been widely investigated for separation of dyes, salt ions, heavy metal ions, and biomolecules due to their high mechanical strength, single‐layered structure, large surface area, and high affinity. However, due to irregular pore structure, nanochannels, interlayer distance, easy functionalization, swelling effect, and chemical stability under aqueous environment limited their separation efficiency. In this review, different fabrication methods of GO membranes are summarized. The role of functionalization and cross‐linking on membrane's structural properties, separation performance, and practical applications are discussed. Further, the GO‐based membranes (GOMs) for separation and removal of heavy metal ions are discussed in detail. The factors which influence the separation performance are also highlighted. Finally, recommendations and future directions are suggested.

Cu(II) ions removal from wastewater using starch nanoparticles (SNPs): An eco‐sustainable approach

AbstractThe complex structured starch particles were reduced to the nanoscale size range through hydrolysis utilizing low concentration acid assisted by ultrasound irradiation. The synthesized starch nanoparticles (SNPs) were characterized by transmission electron microscopy (TEM), Fourier‐transform infrared (FTIR), and X‐ray diffraction (XRD) techniques. The synthesized SNPs possessed surface activated entities, as many cationic functional groups were confirmed through the FTIR spectrum. Also, these SNPs were effectively utilized to separate heavy Cu metal ions from the synthetic ion solution. The SNPs were characterized using field emission scanning electron microscope (FESEM), X‐ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) analysis for the surface modification after the adsorption process. The weak electrostatic interaction between the SNP surface and Cu ion was confirmed by the XPS spectrum and energy‐dispersive X‐ray spectroscopy. The maximum efficiency of Cu ions removal was about 93% at an optimal pH 5 and 25 mg/ml dosage. The adsorption equilibrium was obtained in 60 min. The nitrogen isotherm BET analysis of SNPs after adsorption shows a higher specific surface area of 18.552 m2/g, attributed to the interaction and presence of Cu ions on the SNP surface. The process feasibility was validated by the Langmuir isotherm model. The process exhibits pseudo‐second‐order adsorption kinetics and follows the Langmuir isotherm. The RL predicted by the Langmuir isotherm mechanism is 0.017, implying favourable adsorption. The process is reproducible and allows for the separation of heavy metal ions from the wastewater through biosorption effectively.

ZIF-67 modified MXene/sepiolite composite membrane for oil–water separation and heavy metal removal

In this study, polyvinylpyrrolidone (PVP) was used as a cross-linking agent leading to ZIF-67 in-situ grow on the surface of sepiolite (Sep) to increase the specific surface area and space volume of Sep. Subsequently, a hydrothermal synthesis method was used to form a stable super-hydrophilic composite membrane from the composite MXene by polydopamine. Compared to the MXene/PDA/Sep (MPS) composite membrane, the composite membrane with ZIF-67 exhibited improved hydrophilicity and heavy metal separation. In addition, the introduction of negatively charged Sep@ZIF-67–24 (SZ-24) increased the number of adsorption active sites and negative potential for the surface of the membrane, and this was conducive to the demulsification and adsorption of oil–water emulsions. The MXene/PDA/Sep@ZIF-67–1 (MSZ-1) composite membrane had excellent separation effects on surfactant-stabilized emulsions (SSEs) and surfactant-free emulsions (SFEs) oil–water emulsions which were above 99.4 %. Furthermore, the separation effect on oil–water, under extreme water conditions, was greater than 99 %. The MSZ-1 composite membrane can achieve excellent separation of heavy metal ions, especially Cu2+ that the rejection was 79.9 %, under high flux and extreme conditions. Therefore, the MSZ-1 composite membrane has broad application prospects in oil–water treatment and heavy metal separation.