Electrostatic Complexation Research Articles

KOH-modified hydrochar produced from Cd/Zn hyperaccumulator Sedum Alfredii Hance for aqueous Cd(Ⅱ) removal: Behavior and mechanism

Hydrothermal carbonization (HTC) has been a promising treatment technology of heavy metal-enriched hyperaccumulator biomass to produce superior hydrochar adsorbent for contamination removal from the wastewater. However, a high amount of heavy metal in derived hydrochar limits its further application. In this study, the effect of reaction temperature (180–270 ℃) and medium pH during HTC on heavy metal contents, speciation and leaching risk of hydrochar from the hyperaccumulator biomass Sedum alfredii Hance was investigated to assess its environmental risk. HTC at a low reaction temperature and acid addition facilitated the removal of Zn/Cd/Pb from the solid phase, meanwhile the addition of acid favored the immobilization of Zn/Cd/Pb and lowered the potential leaching risk of Zn/Cd/Pb. Hydrochar prepared from HTC at 240 °C and pH = 2 had lower heavy metal content and lower releasing risk, followed by KOH modification to obtain high adsorption performance. The modified hydrohcar (KSAB) were characterized by SEM, XRD, BET, Boehm titration and FT-IR, and showed that the surface specific surface area and pore structure were optimized and OFGs of hydrochar were improved significantly after KOH treatment. Adsorption experiments showed that the Cd(II) adsorption process onto KSAB well accorded with pseudo-second-order kinetics and Langmuir isotherms. The maximum Cd(II) adsorption capacity of KSAB was 25.69 mg/g, which was 17 times compared to that of pristine hydrochar. Microstructure characteristics and mechanism analysis further suggested that electrostatic interactions, surface complexation, cation-π and ion exchange were the main Cd(II) removal mechanisms of KOH-modified hydrochar. Therefore, hydrochar derived from hyperaccumulator biomass can be used as a highly efficient absorbent to remove Cd(II) from wastewater after KOH modification.

Natural phosphorus-ferromanganese ore-based composites for the simultaneous remediation of arsenic- and lead-co-contaminated groundwater: synergistic effectiveness, kinetics, and mechanisms.

Natural phosphorus-ferromanganese ore (NPO-NFMO) based composites by mechanical ball milling method, applying for the simultaneous remediation of arsenic (As) and lead (Pb) co-contaminated groundwater. Kinetic behavior adopted pseudo-second-order adsorption mechanism attaining equilibrium in 120min over a wide pH range (2.0-6.0). NPO-NFMO realized higher adsorption capacity for As(III) (6.8mgg-1) and Pb(II) (26.5mgg-1) than those of single NPO (1.7 and 7.8mgg-1) and NFMO (2.9 and 5.1mgg-1), indicating that synergistic effects of NPO and NFMO considerably enhanced the adsorption capacity in mixed adsorption system. Fresh and used NPO-NFMO were characterized, and indicated that NPO-NFMO formed stable minerals of PbAs2O6 and PbFe2(AsO4)2(OH)2. The underlying adsorption mechanism indicated that As(III) and Pb(II) removal was involved with multiple mechanisms, including electrostatic adsorption, oxidation, complexation, and coprecipitation. The effects of key reaction parameters including mass ratios of NPO and NFMO, initial metal ion concentration, dosage, solution pH, and co-existing anions in groundwater were systematically investigated. The novel designed NPO-NFMO-based composites can be deemed as a promising amendment for simultaneous immobilization of As(III) and Pb(II) in co-contaminated soil and groundwater.

Geo-environmental and mechanical behaviors of As(V) and Cd(II) co-contaminated soils stabilized by goethite nanoparticles modified biochar

Goethite nanoparticles modified biochar (FBC) could address the weak effectiveness of conventional biochar commonly to process heavy metal(loids) (HMs) co-contamination with different charges. However, few studies have focused on the change of soil mechanical properties after stabilization. In this study, FBC was synthesized to stabilize simultaneously arsenic (As (V)) (anions) and cadmium (Cd (II)) (cations) in co-contaminated soils. Batch adsorption, leaching toxicity, geotechnical properties and micro-spectroscopic tests were comprehensively adopted to investigate the stabilization mechanism. The results showed that FBC could immobilize As (V) mainly through redox and surface precipitation while stabilizing Cd (II) by electrostatic attraction and complexation, causing soil agglomeration and ultimately making rougher surface and stronger sliding friction of contaminated soils. The maximum adsorption capacity of FBC for As (V) and Cd (II) was 31.96 mg g−1 and 129.31 mg g−1, respectively. Besides, the dosages of FBC required in contaminated soils generally were approximately 57% higher than those in contaminated water. FBC promoted the formation of small macroaggregates (0.25–2 mm) and the shear strengths of co-contaminated soils by 21.40% and 8.34%, respectively. Furthermore, the soil reutilization level was significantly improved from 0.14–0.46 to 0.76–0.83 after FBC stabilization according to TOPSIS method (i.e., technique for order preference by similarity to an ideal solution). These findings confirm the potential of FBC in immobilizing As (V) and Cd (II) of co-contaminated soils and provide a useful reference for green stabilization and remediation of HMs co-contaminated sites.Graphical

Pseudocapacitive deionization of high concentrations of hexavalent chromium using NiFe-layered double hydroxide/polypyrrole asymmetric electrode

The wastewater polluted by high concentrations of aqueous hexavalent chromium (Cr(VI)) has serious adverse effects on ecological environment and human health. As a burgeoning, environmental-friendly, and promising wastewater treatment technology, capacitive deionization (CDI) process for efficient removal of aqueous Cr(VI) needs to be investigated. In this work, pseudocapacitive NiFe-layered double hydroxide/ polypyrrole (NiFe-LDH/PPy, denoted as NiFe/PPy) electrode was synthesized by the in-situ polymerization of PPy on the NiFe-LDH surface. Results of characterizations manifested that NiFe/PPy had the chain spherical structure of PPy. In particular, excellent PPy provides effective reversible capacitance and ion diffusion and improves the conductivity and pseudocapacitance performance of NiFe-LDH. Then, the NiFe/PPy anode and activated carbon (AC) cathode were assembled into the CDI cell for capacitive removal of high concentrations of aqueous Cr(VI). In 20 mL/min of flow velocity, 1.2 V, and 100 mL 100 mg/L of Cr(VI) solution, the Cr(VI) electrosorption capacity and removal ratio attained to 47.95 mg/g and 95.89%, respectively. The electrosorption of Cr(VI) slightly decreased under the common competing anions of Cl−, NO3−, SO42−, HCO3−, and CO32−. Based on Langmuir isotherm model, the maximum theoretical removal capacity of NiFe/PPy for Cr(VI) was 111 mg/g. The electrostatic attraction, reduction, and surface complexation played primary roles in the CDI system of NiFe/PPy//AC asymmetric electrodes. The outstanding electrosorption performance makes this CDI system have a favorable application prospect in the actual wastewater treatment containing high concentrations of Cr(VI).

ε-Polylysine and soybean protein isolate form nanoscale to microscale electrostatic complexes in solution: properties, interactions and as antimicrobial edible coatings on citrus

A feasible approach to enhance the antimicrobial efficacy of ε-polylysine (PL) in applications is to form delivery complexes with delicate structures and good dispersion properties. This work aims to study the multiscale structures, properties and interactions, and edible coating applications of the electrostatic complex formed by PL and soy protein isolate (SPI). When the mass ratio of SPI to PL (SE) was between 5 and 15, especially 11, microscale solid-liquid phase separation occurred in the system due to the small absolute zeta potential. When the SE was in the range of 15–20, the system formed a stable nanoscale suspension, the average particle size and zeta potential were 191 nm and −20 mV, respectively. The physicochemical properties of the complexes were investigated including the colloidal properties, spectroscopy and interactions analysis, viscosity, contact angle, and antimicrobial activities against Escherichia coli, Staphylococcus aureus, and Penicillium expansum. Finally, the in vivo application on citrus demonstrated that the nanoscale PL/SPI electrostatic complex (SE = 20) as functional coatings has both barrier and antimicrobial activities. The study provides a novel application strategy for PL and nanoscale electrostatic complexes as postharvest coatings.

As(V) adsorption by FeOOH@coal gangue composite from aqueous solution: performance and mechanisms

ABSTRACT Arsenic (As) pollution in water poses a significant threat to the ecological environment and human health. Meanwhile, the resource utilisation of coal gangue is of utmost importance in ecologically sustainable development. Thus, the FeOOH@coal gangue composite (FeOOH@CG) was synthesised for As(V) adsorption in this study. The results showed that α-FeOOH, β-FeOOH and Schwertmannite loaded on the surface of FeOOH@CG. Moreover, the adsorption behaviour of As(V) by FeOOH@CG was investigated under different reaction conditions, such as pH, contact time, initial concentration and co-existing anions. The optimum adsorption conditions were as follows: initial As(V) concentration of 60 mg/L, pH of 3.0 and adsorption time of 180–240 h. The adsorption capacity of FeOOH@CG for As(V) was pH-dependent and the maximum adsorption capacity was 185.94 mg/g. The presence of anions ( H 2 PO 4 − , HCO 3 − and C l − ) decreased the adsorption efficiency of FeOOH@CG for As(V). The adsorption process of FeOOH@CG for As(V) could be well-described by the pseudo-second-order model and Langmuir model, indicating that the adsorption process mainly depended on chemical adsorption. The thermodynamic analysis suggested that the adsorption was a spontaneous and endothermic process. In addition, according to the analyses of XRD, FTIR and XPS, the dominant mechanisms of As(V) adsorption by FeOOH@CG were electrostatic attraction, complexation and precipitation. In conclusion, FeOOH@CG has great potential as an efficient and environmentally friendly adsorbent for As(V) adsorption from aqueous solution.

Fluoride Removal from Water Sources by Adsorption on MOFs

Fluoride is present in several groundwaters due to natural or anthropogenic origins. Although it is necessary for physiological human functions (in small amounts, i.e., 0.5–1.2 mg/L), it could be very harmful when it exceeds the maximum permissible concentration limit of 1.5 mg/L (according to WHO). Among the numerous technologies for removing fluoride from waters, metal–organic framework (MOF) materials are considered to be promising adsorbents due to their advantages of high porosity, high specific surface area, diverse functions and easy modification. In this study, the synthesis of MOFs and the progress of their application to the removal of fluoride from contaminated water, as published in the recent literature mainly over the past five years, are reviewed. The adsorption mechanism(s) and its main characteristics, such as effect of initial fluoride concentration, adsorbent dosage, solution pH, contact time, adsorption capacity, thermodynamic and regeneration studies, etc., for the removal of fluoride with the addition of different MOFs are compared. According to these comparisons, the hydrothermal/solvothermal synthesis method is most commonly used for the preparation of MOFs, whereas higher BET surface areas are shown by specific MOFs based on aluminum metal ions. The main fluoride adsorption mechanisms were found to be electrostatic attraction and/or complexation. The most common pH for conducting experiments was 7.0, but several examined materials were found to be effective over a wide pH range. Four to six regeneration cycles were successfully applied on average, regarding the MOFs under review, whereas in the majority of these cases, the sorption process was found to be endothermic.

Highly efficient adsorption of antibiotic ciprofloxacin hydrochloride from aqueous solution by diatomite-basic zinc chloride composites.

The antibiotic ciprofloxacin (CIP) is used to treat a variety of bacterial infections, yet it poses significant health risks to aquatic environments. While adsorption is a promising technique for CIP removal, current adsorption capacities remain limited. In this study, we introduce a diatomite and basic zinc chloride composite (ZnHC-Dt) prepared using a straightforward deposition method, with the ability to achieve highly efficient ciprofloxacin removal. ZnHC-Dt is characterized using field emission scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), and the Brunauer-Emmett-Teller method (BET). We also assess the zeta potential. The optimized ZnHC-Dt adsorbent, achieved at a mass ratio of 0.45 with ZnHC/(ZnHC+Dt), is adopted with a CIP adsorption capacity of 831.96 mg/g at 25 °C, broad pH adaptability (within 3.0-10.0), rapid adsorption rate (reaching equilibrium in 4 h), and stable performance under Na+ ionic strength. The CIP adsorption process follows pseudo-second-order kinetics and aligns well with the Langmuir adsorption model. The high adsorption capacity of ZnHC-Dt can be attributed to electrostatic attraction, hydrogen bonding, surface complexation, and available adsorption sites. During the desorption process, the CIP removal rate retains 65.33% effectiveness after five cycles. The results suggest that ZnHC-Dt holds significant potential for CIP removal in aqueous solutions.

Removal performance and mechanisms of aqueous Cr (VI) by biochar derived from waste hazelnut shell.

Cr (VI) is still of great concern due to its high toxicity, solubility, and mobility. The transformation of waste biomass to biochar is favorable for sustainable development. Hazelnut shell, an agriculture waste, was utilized as precursor to prepare biochar at 700 °C and firstly conducted for Cr (VI) removal. Nearly all 50 mg L-1 of Cr (VI) was removed from aqueous media in 180 min under the optimal conditions. The best compliance with pseudo-second-order kinetic model (R2 = 0.999)and Langmuir isotherm model (R2 = 0.999) indicated Cr (VI) removal was a monolayer chemisorption process. The hazelnut shell biochar exhibited superior performance on Cr (VI) removal at low pH (2.0) and Cr (VI) concentrations (≤ 50 mg L-1). Various techniques illustrated that the predominant mechanism of Cr (VI) removal by hazelnut shell biochar involved electrostatic attraction, reduction, and complexation. This study provides a promising low-cost alternative for Cr (VI) elimination from acidic wastewater and groundwater after extraction following by pH adjustment to 2.0.

Synthesis of magnesium-modified ceramsite from iron tailings as efficient adsorbent for phosphorus removal

The preparation of ceramsite from iron tailings to remove phosphate can reduce environmental pollution and realize the sustainable development of “treating waste with waste”. This study prepared a modified ceramsite for phosphate removal in water bodies,with iron tailings as the main raw material and magnesium chloride as the modification agent. The optimal preparation conditions for the modified ceramsite were determined as follows: iron tailings: MgCl2 = 50:15, pre-heating at 300 °C for 10 min, and sintering at 800 °C for 60 min. The effects of factors such as adsorbent dosing, contact time, temperature, pH, NH4+ concentration, and coexisting ions were investigated, and the slow-release ability of modified ceramsite after phosphate adsorption was explored. The results show that the adsorption process best fit the pseudo-second-order model and the Sips model at a dose of 1 g/L and an initial phosphorus concentration of 100 mg/L, belonging to multilayer chemical adsorption. The phosphate adsorption was influenced significantly by pH, and the adsorption capacity reached the maximum of 10.24 mg/g at pH 6. The NH4+ concentration of 100 mg/L was favorable for the simultaneous removal of phosphorus and nitrogen. Coexisting anions in water have a minor effect on the adsorption process, while coexisting cations promote adsorption. The XRD, FTIR and XPS characterization results indicate that electrostatic attraction, internal complexation and chemical precipitation are the main mechanisms of action.

High nitrogen content bimolecular co-functionalized graphene nanoflakes for hypertoxic Cr(VI) removal: Insights into adsorption behavior and mechanisms

The proven high carcinogenicity to humans and high destructive force to the environment determine the extreme urgency of eliminating hypertoxic Cr(VI) in water bodies. Herein, a route of room temperature synthesis and secondary grafting was proposed to fabricate graphene oxide-based nanoadsorbent co-functionalized with polydopamine and branched polyethyleneimine (GOPP) to remove Cr(VI). The flexible decoration of polydopamine and polyethyleneimine on GO flakes could gradually enhance the amount of N-containing functional groups and realize selective removal of Cr(VI) with the maximum experimental adsorption capacity of 564.7 mg/g, displaying a significantly high separation factor against alkali metal, alkaline earth metal, and other transition metal ions. Various combination mechanisms, such as electrostatic attraction, reduction, complexation, and hydrogen bonding, were demonstrated to be involved in the adsorption process of Cr(VI) by XPS, ESP, and DFT calculations. And the interaction energies of the five protonated configurations of primary amine, tertiary amine, secondary amine, imine, and secondary amine on the ring with HCrO4− were: −22.66, −12.08, −24.92, −24.26, −27.64 kcal/mol. In the actual industrial wastewater study, a Cr(VI) removal rate of 85.8% was realized. This work provided a viable idea for the elimination of Cr(VI) and was expected to be applied in the field of wastewater treatment.

Impact of dispersion conditions and coacervation on fibril formation in gellan gum-potato protein mixtures

The development of plant-based meat analogs as sustainable alternatives to traditional meat products is a major focus of the modern food industry. Meat-like structures and textures can be fabricated from protein-polysaccharide mixtures using soft matter physics approaches. In this study, we investigated the effects of gellan gum dissolution properties on the fiber formation and textural properties of potato protein-gellan gum composites. We hypothesized that the fibrous structures naturally formed by powdered gellan gum when it is dispersed in water may be useful for creating meat analogs. Zeta-potential measurements showed that cationic potato protein and anionic gellan gum formed electrostatic complexes. In the presence of excess protein, complexation of gellan gum and potato protein resulted in the formation of fibrous structures. Fiber formation and thermal gelation of the protein-polysaccharide composites depended on whether salt (100 mM NaCl) was added, and whether it was added before or after the gellan gum. The shear modulus of heat-set composite gels was higher in the presence of salt than in its absence, which was the opposite to what was observed for pure gellan gum gels. Moreover, adding salt before the gellan gum led to stronger heat set gels than adding it after the gellan gum. These effects were mainly attributed to the ability of the mineral ions to screen the electrostatic interactions between the biopolymer molecules, thereby altering their packing behavior. Our findings suggest that controlling the dispersion and coacervation of gellan gum and potato protein can be used to create fibrous structures, which may facilitate the development of plant-based meat products with improved textural attributes.

Interpolymer Complexes Based on Cellulose Ethers: Application.

Interpolymer complexes based on cellulose ethers have gained significant interest in recent years due to their versatile applications. These complexes are formed by combining different polymers through non-covalent interactions, resulting in stable structures. This article provides an overview of the various fields where IPCs based on cellulose ethers find application. IPCs based on cellulose ethers show great potential in drug delivery systems. These complexes can encapsulate drugs and enable controlled release, making them suitable for sustained drug delivery. They offer advantages in terms of precise dosage and enhanced therapeutic efficacy. Coatings and adhesives also benefit from IPCs based on cellulose ethers. These complexes can form films with excellent mechanical strength and enhanced water resistance, providing durability and protection. They have applications in various industries where coatings and adhesives play a crucial role. In food packaging, IPCs based on cellulose ethers are highly relevant. These complexes can form films with effective barrier properties against oxygen and water vapor, making them ideal for packaging perishable foods. They help extend to shelf life of food products by minimizing moisture and oxygen transfer. Various methods, such as solvent casting, coacervation, and electrostatic complexation, are employed to synthesize IPCs based on cellulose ethers.

Synthesis of conch-like layered carbon nanosheets by ball-milling assisted ultrasonic exfoliation for highly selective removal of Cd(II) from multiple water matrices

Development of carbonaceous materials from biomass have attracted tremendous research interest because of their intriguing physicochemical properties and promising applications. However, endowing them with precisely controlled morphologies remains a formidable challenge. Herein, oxygen-functionalized biomass-derived carbon-nanosheets (CNSs) framework was synthesized using ball-milling ultrasonic exfoliation for their application to remove cadmium Cd(II) from water matrices. The obtained CNSs showed remarkably higher surface area (368.9 m2/g), thickness-range (∼6–8 nm) and pore size (10.58 nm) than pristine carbon (PC) (10.126 m2/g, 1–2 µm and 2.13 nm, respectively). CNSs demonstrated higher adsorption capacity (545.76 mg g−1), superior reusability (removal efficiency maintained >91 % after 10 cycles) and excellent selectivity (Kd = 4.7 × 106 mL g−1). The adsorption isotherm and kinetics data were better fitted by Langmuir and pseudo-second order models. High adsorption selectivity of CNSs led to 97.7 % Cd(II) adsorption in presence of Cu(II), Zn(II), Pb(II) and Ni(II) ions. The strong efficiency of CNSs was also evident in complex water matrices including tap water, groundwater (Cd(II) removal of >99 %) and river water (98.97 %). The experimental analyses indicate that electrostatic attraction and surface complexation as the prominent adsorption mechanisms. Overall, this work illustrates an applicable strategy to develop carbon-nanosheets and their successful application to remove toxic metals from water matrices.

Removal of hexavalent chromium from aqueous by Chitosan-stabilized FeS

In this study, FeS and chitosan (CTS) were compounded to form a new Cr (Ⅵ) treatment material FeS/CTS. FeS/CTS was characterized by SEM, FTIR, XRD, XPS, BET, etc, and the removal performance and mechanism of FeS/CTS for Cr (Ⅵ) were also discussed. The removal of Cr (Ⅵ) by the composite was the result of electrostatic force, redox reaction, complexation and precipitation. When the initial concentration of Cr (Ⅵ) was 50 mg∙L−1, the removal of Cr (Ⅵ) was attributed to 87.14% reduction and 12.86% adsorption. The fitting results of the kinetic and isothermal models proved that chemical adsorption playsed a dominant role in the removal process. At pH 5 and the initial Cr (Ⅵ) concentration of 40 mg∙L−1, the removal rate of Cr (Ⅵ) by the composite could reach 99.90%. All results showed that FeS/CTS composite can be used as a potential Cr (Ⅵ) removal material in water.

Enhanced removal of Cr(VI) by polyethyleneimine-modified bamboo hydrochar.

Hydrochar is an environmentally friendly and cheap adsorbent, but its adsorption amounts for anions is very limited. The functionalized hydrochar can overcome this shortcoming. Herein, polyethyleneimine-modified hydrochar (PEI-HC) was synthesized from hydrothermal carbonization (HTC) of methyl acrylate and bamboo after addition of initiator ammonium persulfate, and then modified by polyethyleneimine (PEI), which was used to treat Cr(VI). PEI-HC was tested by XANES, EXAFS, SEM-EDS, XPS, FTIR, N2 sorption isotherms, zeta potential, and elemental analyses. The characterizations showed that PEI was successfully grafted onto hydrochar, and the PEI-HC was rich in N and O functional groups, which presented high Cr(VI) sorption ability (528.41 mg·g-1 at pH 2). The bath experiments found the pseudo-second-order kinetic and Freundlich equations can well describe the adsorption kinetics and isotherm of the Cr(VI) adsorption onto PEI-HC, respectively. Electrostatic interaction, reduction, complexation, and H-bonding are the main removal mechanisms as supported by XANES, EXAFS, XPS, and FTIR. This study provides a strategy of combining HTC and free radical graft polymerization to convert agricultural and forestry wastes into functionalized hydrochar, showing highly efficient removal of Cr(VI).

Adsorption of MB and Pb(II) before and after magnetic modification: Performance and mechanism

This study described the simple fabrication process of manganese dioxide decorated composites(Mn@RS) and magnetic-functional modified composites (MC-Mn@RS) that can effectively adsorb MB and Pb(II) in the aqueous medium. The structural and physicochemical characteristics of the as-prepared composites were evaluated by BET, XRD, SEM, FTIR, XPS, point of zero charge (pHPZC), TGA and VSM techniques. The effect of the contact time, pH value, and initial concentration on the adsorption capacity of MB and Pb(II) onto Mn@RS and MC-Mn@RS were investigated by using batch equilibrium experiments. The results exhibited that in single system, the adsorption capacity of Mn@RS against MB and Pb(II) were obtained 128.5 mg g−1 and 196.04 mg g−1, respectively. The adsorption capacity of MC-Mn@RS against MB and Pb(II) were obtained 325.8 mg g−1 and 98.07 mg g−1, respectively. Till now, the mutual effects and competitive adsorption of MB and Pb(II) onto biochars have never been reported. In the binary systems, the Pb (II) adsorption on Mn@RS was severely inhibited, while the uptake of MB was not affected significantly, clearly demonstrating the adsorption affinity was in the order of MB > Pb(II) in the coexisting solution. The electrostatic attraction, complexation, surface precipitation and physical adsorption were the main adsorption mechanism of Pb (II) on Mn@RS and MC-Mn@RS. The adsorption mechanism of MB on Mn@RS mainly contained electrostatic attraction, π-π interaction, n–π interaction and electrostatic attraction, while that on MC-Mn@RS mainly were determined by pore filling and n–π interactions. In addition, the MC-Mn@RS exhibited excellent reusability (retained 90.76% removal efficiency after five cycles) and solid–liquid separation efficiency due to strong magnetism(24.78 emu g−1). The gained results were powerful proof for removing MB and Pb(II) from wastewater, economically and effectively, and for paving the way to the preservation of cleaner fresh water resources and a greener society.

One‐Step Synthesis of Hydrogen‐Bonded Microcapsules for pH‐Triggered Protein Release

One‐step microfluidic approach in which interfacial complexation of hydrogen bonding polymers is utilized to prepare pH‐responsive microcapsules is presented. Using water‐in‐oil‐in‐oil‐in‐water (W1/O1/O2/W2) triple‐emulsion droplets as templates, it is shown that polymeric microcapsules with an aqueous core and a shell that consists of two complementary hydrogen bonding polymers, poly(propylene oxide)(PPO) and poly(methacrylic acid)(PMAA), can be prepared in a robust manner. The presence of a buffer layer enables controlled interfacial complexation of PMAA and PPO at the water/oil interface, followed by spontaneous dewetting of the oil droplet to result in hydrogen‐bonded microcapsules dispersed in aqueous media. In addition, it is demonstrated that the permeability of the PPO/PMAA membrane can be readily tuned by varying the molecular weight of PMAA. Furthermore, it is shown that the resulting PPO/PMAA microcapsules are stable at a high salt concentration (>1 m NaCl) unlike analogous capsules prepared through electrostatic complexation while they release the encapsulated protein above the critical pH of which the PMAA ionizes and results in disassembly of the shell membrane.

Enhanced recovery of germanium(IV) from zinc residue leachate by tartaric acid functionalized chitosan: Experiments and DFT calculation

The recovery of germanium (Ge) from zinc residue leachate has attracted increasing attention. Herein, this study report on the development of a tartaric acid functionalized chitosan (TA-CS) material serving as an efficient adsorbent for Ge(IV). The introduction of TA resulted in abundant protonatable hydroxyl and carboxyl groups, which endows materials with excellent buffering capacity under acidic conditions. Adsorption kinetics and isotherms showed a fast and efficient adsorption capacity of 57.28 mg/g for Ge(IV). In binary systems, Ge(IV) was preferentially adsorbed over Zn(II), a major coexisting ion, with a separation factor of 3.22. The SEM–EDS FT-IR, XPS and DFT results revealed that mechanisms in combination, including electrostatic adsorption, complexation, hydrogen bonding, and ion exchange, promoted the immobilization of Ge(IV) on TA. The TA-CS material also exhibited great reusability with an adsorption efficiency of 70% after 3 recycles. For the recovery of Ge(IV) in practical zinc residue leachate, the TA-CS material showed superior affinity toward Ge(IV) and a 10-fold higher of adsorption capacity compared to that of pristine chitosan. Together, TA-CS demonstrates that it is a viable and economical material for the separation and preconcentration of Ge(IV) from zinc residue leachate.

Clean water production from plastic and heavy metal contaminated waters using redox-sensitive iron nanoparticle-loaded biochar

The unceasing release of tiny plastics (microplastics and nanoplastics) and their additives, like metal ions, into the aquatic systems from industries and other sources is a globally escalating problem. Their combined toxic effects and human health hazard are already proven; hence, their remediation is requisite. This study utilised the nano-zerovalent iron-loaded sugarcane bagasse-derived biochar (nZVI-SBC) for simultaneous removal of Nanoplastics (NPs) of different functionality and size along with metal ions (Ni2+, Cd2+, AsO43−, and CrO42−). Batch and column experiments were conducted, and the results showed an efficient removal of contaminants with maximum sorption of carboxylate-modified NPs of size 500 nm (qmax = 90.3 mg/g) among all three NPs types. Significant removal was observed in Cd2+ in case of cations and CrO42− in case of anions with qmax = 44.0 and 87.8 mg/g, respectively. Kinetics and the isotherm modelling better fitted the pseudo-second-order kinetic model and Sips isotherm model, respectively for both NPs and metal ions. The designed material worked well in pH range of 4–8, ionic strength 1–20 mM and in complex aqueous matrices, with >90% removal. FTIR, zeta potential and the imaging analysis of the reaction precipitates confirmed the electrostatic attraction, pore retention and complexation as the potential mechanisms for removing NPs, whereas, XPS studies confirmed the reduction co-precipitation and surface complexation as the possible mechanism for removing metal ions. High values of attachment efficiency factor calculated from colloidal filtration theory (CFT) validated the experimental results and justified the high sorption of carboxylate modified 500 nm NPs particles. The synthesized material successfully removed both NPs of varying size and functionality and metal ions simultaneously with significant efficacy in complex environmental samples proving the broad applicability of material in realistic environmental conditions and different types of water treatment processes.