A novel layer-by-layer heterogeneous cation exchange membrane for heavy metal ions removal from water

Study of chemical reactivity and molecular interactions of the hydrochlorothiazide-4-aminobenzoic acid cocrystal using spectroscopic and quantum chemical approaches

In this study, the molecular, electronic, and chemical properties of the drug hydrochlorothiazide (HCTZ) are determined after cocrystallization with 4-aminobenzoic acid (4-ABA). Analysis has been performed to understand how those variations lead to alteration of physical properties and chemical reactivity in the cocrystal HCTZ-4ABA. IR and Raman characterizations were performed along with quantum chemical calculations. A theoretical investigation of hydrogen bonding interactions in HCTZ-4ABA has been conducted using two functionals: B3LYP and wB97X-D. The results obtained by B3LYP and wB97X-D are compared which leads to the conclusion that B3LYP is the best applied function (density functional theory) to obtain suitable results for spectroscopy. The chemical reactivity descriptors are used to understand various aspects of pharmaceutical properties. Natural bond orbital (NBO) analysis and quantum theory of atoms (QTAIM) are used to analyze nature and strength of hydrogen bonding in HCTZ-4ABA. QTAIM analyzed moderate role of hydrogen bonding interactions in HCTZ-4ABA. The calculated HOMO-LUMO energy gap shows that HCTZ-4ABA is chemically more active than HCTZ drug. These chemical parameters suggest that HCTZ-4ABA is chemically more reactive and softer than HCTZ. The results of this study suggest that cocrystals can be a good alternative for enhancing physicochemical properties of a drug without altering its therapeutic properties.

Synthesis and characterization of chitosan Schiff base grafted with formaldehyde and aminoethanol: As an effective adsorbent for removal of Pb(II), Hg(II), and Cu(II) ions from aqueous media

Grafted chitosan materials show the characteristics of high stability, easy separation and recovery, and good heavy metal adsorption capacity, and have received much attention in the adsorption process. Therefore, in this work, novel grafted chitosan-based adsorbent CS-EHBSB@F-AE was prepared by a one-pot reaction of chitosan (CS), 3-ethoxy-4-hydroxybenzaldehyde (EHB), formaldehyde (F) and aminoethanol (F). The microstructure and morphology of the as-prepared composite CS-EHBSB@F-AE were characterized by FT-IR, TGA, DSC, FE-SEM, and BET analyses. The adsorption performance of the as-prepared CS-EHBSB@F-AE composite on Pb(II), Hg(II), and Cu(II) ions from aqueous was investigated using batch experiment and the effects of the initial pH of the solution, contact time, and initial metal ions concentration and temperature on the adsorption efficiency were investigated and discussed. At the best conditions, CS-EHBSB@F-AE exhibited remarkable adsorption capacity of 246.7 mg/g, 203.9 mg/g, and 234.4 mg/g in absorbing Pb(II), Hg(II), and Cu(II), respectively. The adsorption equilibrium and the kinetic studies confirmed that the ions adsorption process fits well with the Langmuir isotherm and pseudo-second-order (PSO) models. Additionally, the adsorption efficiency of Pb(II), Hg(II), and Cu(II) metal ions by the composite CS-EHBSB@F-AE was reduced by increasing the temperature from 298 K to 318 K. In addition, after the sixth ads/des cycles, the as-prepared adsorbent still exhibited high removal efficiency with a decrease in adsorption efficiency of Pb(II) (5.53 %), Hg(II) (15.43 %) and Cu(II) (8.27 %). Finally, we proposed that the ions adsorption by CS-EHBSB@F-AE has happened using the coordination of active groups containing nitrogen and oxygen atoms on the surface of the adsorbent with the Pb(II), Hg(II), and Cu(II) metal ions.

Dimercaprol-modified mesoporous silica nanoparticles for efficient removal of toxic mercury ions from aqueous solution

A surface-modified mesoporous silica nanoparticle containing dimercaprol monomers was created utilizing the sol-gel condensation process, using tetraethyl orthosilicate (TEOS) as the silica source and poloxamer as the structure directing agent. To accomplish this synthesis, 3-glycidoxypropyl triethoxysilane (GPTS, 20 mol%) was incorporated into the silica walls during the sol-gel condensation process, along with TEOS. Furthermore, dimercaprol (DM) monomers were incorporated onto silica surfaces by a ring-opening reaction between GPTS epoxy groups, and dimercaprol hydroxyl groups. The prepared dimercaprol-modified silica adsorbent (MSN-DT NPs) material has been studied using a variety of instruments, including XRD, FT-IR, N2 adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric (TG) analysis, and zeta potential analysis. The MSN-DT NPs material selectively adsorbs mercury ions, with a high adsorption amount of 125 mg/g and a removal capability of roughly ~ 90% from the original metal ion mixture comprising other competing metals such as Pb2+, Ni2+, Fe2+, and Zn2+. The MSN-DT NPs adsorbent shows recyclable qualities for up to five cycles when treated with an acidic aqueous solution (0.1 M HCl). As a result, the MSN-DT NPs adsorbent may be regenerated and reused up to five times without losing its adsorption effectiveness. The experimental findings showed that the MSN-DT NPs adsorbent may be employed to selectively remove hazardous Hg2+ ions from an aqueous solution.

Recent advance of nanomaterials modified electrochemical sensors in the detection of heavy metal ions in food and water

As one of the main pollutants, heavy metal ions can accumulate in the human body and cause a cascade of damage. Electrochemical sensors provide great prospects for tracing heavy metal ions because of their properties of high sensitivity, low detection limits and fast response. Electrode surface modification materials play a key role in enhancing the performance of electrochemical sensors. Herein, we summarize in detail the recent work on electrochemical sensors modified by carbon nanomaterials (graphene and its derivatives, carbon nanofibers and carbon nanotubes), metal nanomaterials (gold, silver, bismuth and iron), complexes (MOFs, ZIFs and MXenes) and their composites for the detection of heavy metal ions (mainly include Cd(II), Hg(II), Pb(II), As(III), Cu(II) and Zn(II)) in food and water. The synthetic strategies, mechanisms, innovations, advantages, challenges and prospects of various electrode modification nanomaterials for the detection of heavy metal ions in food and water are discussed.

Kinetic and adsorption isotherm studies of Malachite Green dye onto surfactant-tailored alginate hydrogel beads: An influence of surfactant hydrophobicity

This study details the synthesis and characterization of surfactant-modified sodium alginate hydrogel beads crosslinked with Ba2+ ions through ionotropic gelation. Cationic surfactants such as, dodecyltrimethylammonium bromide (DTAB), didodecyldimethylammonium bromide (DDAB), and butanediyl-α,ω-bis-(dimethyldodecylammonium bromide) (GEM), were employed in the modification process. The surfactant-modified ALG-DTAB, ALG-DDAB, and ALG-GEM beads were investigated for the removal of cationic dye Malachite Green (MG) to elucidate the impact of hydrophobicity of amphiphiles on the adsorption process. The characterizations were carried out using Rheometry, Field Emission Scanning Electron Microscopy (FESEM), Infrared Spectroscopy (IR), and Energy Dispersive X-ray Spectroscopy (EDX). Under optimized conditions, ALG-GEM and ALG-DDAB demonstrated highest maximum adsorption capacity (Qmax > 700 mgg-1). The adsorption data fitted well to pseudo-second order kinetic and Langmuir adsorption models, suggesting the involvement of chemisorption phenomena with notable contributions from pore diffusion. The effects of pH, initial dye concentration, adsorbent dose, temperature, and competing ions on the removal of MG were investigated. Interestingly, ALG-GEM beads exhibited an increase in adsorption capacity with rising pH and a subsequent decrease with increasing temperature, showcasing optimal adsorption at pH 7.0 and 25 °C. The study proposes that ALG beads modified with cationic surfactants with higher hydrophobicity could offer a promising avenue in wastewater treatment processes.

Genetic response analysis of Beauveria bassiana Z1 under high concentration Cd(II) stress

Cadmium (Cd(II)) has carcinogenic and teratogenic toxicity, which can be accumulated in the human body through the food chain, endangering human health and life. In this study, a highly Cd(II)-tolerant fungus named Beauveria bassiana Z1 was studied, and its Cd(Ⅱ) removal efficiency was 71.2% when the Cd(II) concentration was 10 mM. Through bioanalysis and experimental verification of the transcriptome data, it was found that cadmium entered the cells through calcium ion channels, and then complexed with intracellular glutathione (GSH) and stored in vacuoles or excluded extracellular by ABC transporters. Cytochrome P450 was significantly upregulated in many pathways and actively participated in detoxification related reactions. The addition of cytochrome inhibitor taxifolin reduced the removal efficiency of Cd(II) by 45%. In the analysis, it demonstrated that ACOX1 gene and OPR gene of jasmonic acid (JA) synthesis pathway were significantly up-regulated, and were correlated with bZIP family transcription factors cpc-1_0 and pa p1_0. The results showed that exogenous JA could improve the removal efficiency of Cd(II) by strain Z1.

Synthetic of functionalized magnetic titanium-based metal-organic frameworks to efficiently remove Hg(Ⅱ) from wastewater

The rapid development of process technology has led to rapid daily industrial production, which also produced a large amount of waste liquid. At the same time, the existing treatment technology cannot keep up with the demand, resulting in the malicious destruction of the environment by wastewater, especially mercury-containing wastewater was very harmful. Effective means of removing mercury ions need to be found. With magnetic ferric oxide as the core and titanium-based metal-organic frameworks as the shell, a new type of magnetic adsorbent (BTA-MIL-125(Ti)@Fe3O4) was synthesized. Materials were tested by multiple characterization methods and multiple sets of experiments. At optimal pH 6, the removal rate in 100 ppm Hg(Ⅱ) was as high as 95.8%. The theoretical adsorption capacity was 615 mg/L. Isothermal experiments, kinetic experiments and thermodynamic experiments have respectively verified that the material was a kind of adsorption material with self-emission heat based on chemical action and synergistic adsorption with Hill model. By simulating the immunity of a variety of ions (Cu, Zn, Mg, Ni, Cd), the material itself also exhibited a very high affinity for Hg(Ⅱ). The results of five high-cycle stable adsorption proved the repeatable stability of the material itself. Various characterization methods have also shown that nitrogen and sulfur-containing groups chelated with Hg(Ⅱ). All of the above was enough to show that the BTA-MIL-125(Ti)@Fe3O4 was a magnetic adsorption material with excellent performance and great prospects.

Highly effective removal of multi-heavy metals from simulated industrial effluent through an adsorption process employing carboxymethyl-chitosan composites

Monochloroacetic acid precursor-based carboxymethyl chitosan resins were prepared using the chitosan with variant molecular weight. The carboxymethylation assured enhanced active sites on the resin surface, acidic media stability, and henceforth its appropriate constitution to facilitate enhanced multi-heavy metal adsorption-desorption and subsequent regeneration potential. Zn, Pb, and Fe multimetal adsorption properties were investigated. Thereby, kinetic and equilibrium models were sought for their fitness to represent heavy metal sorption data with the preferred complex adsorbate system. The adsorbate system complexity and its constituent co-existing cations significantly influence the sorption characteristics of the mentioned multi-heavy metal ions. The optimal adsorption capabilities for Zn, Pb, and Fe were 238.10 mg g-1, 4.78 mg g-1, and 147.06 mg g-1, respectively. Low-cost acid-base solutions were also considered for the effective regeneration of the resin even after three adsorption-desorption cycles. Prominent findings of the work assured excellent functionality of the carboxymethyl-chitosan resin for the simultaneous lead, iron, and zinc ion elimination from mimicking real-world effluent systems.

Simple fabrication of carbon quantum dots and activated carbon from waste wolfberry stems for detection and adsorption of copper ion

Removal of heavy metal pollution is an endless topic, because heavy metals can cause irreversible damage to the human body and environment. It is urgent to develop novel materials for detection and adsorption of heavy metal ions. In this paper, waste wolfberry straw was utilized as a carbon source, and two simple methods were developed to successfully prepare activated carbon (AC) and carbon quantum dots (CQDs). The fabrication conditions were optimized by adjusting the mass ratio of precursor to activator, type of activator and activation times. When sodium hydroxide (NaOH) was selected as an activator (6 : 1, mass ratio of NaOH to AC-precursor), and the activation was performed at 600 °C for 1 h, the highest specific surface area of the obtained AC-NaOH-3 reached 3016 m² g^-1. The adsorption capacity for copper ions (Cu²⁺) reached 68.06 mg g^-1. The preparation conditions for CQDs were also optimized by adjusting the concentration of wolfberry stem, reaction time and temperature. When the wolfberry stem concentration was 7.5 g L^-1, and the activation was performed at 200 °C for 24 h, the obtained CQDs exhibited strong fluorescence emission in the blank and 12 kinds of metal ion solutions, respectively, however, the fluorescence intensity was remarkably decreased after adding Cu²⁺. In the range of 10-80 nM, the linear correlation coefficient between the concentration of Cu²⁺ and fluorescence intensity of CQDs was 0.992, and the limit of detection was 2.83 nmol L^-1. Thus, these two kinds of materials were prepared from wolfberry stem, which opened up a new way for the application in adsorption and detection of copper ions.

Adsorptive performance and mechanism exploration of l-lysine functionalized celluloses for enhanced removal of Pb(II) from aqueous medium

In this study, two novel biosorbents of l-lysine grafted cellulose (L-PCM, L-TCF) were prepared for Pb(II) removal from aqueous solutions. Various adsorption parameters were surveyed, such as adsorbent dosages, initial concentration of Pb(II), temperature and pH, using adsorption techniques. At normal temperature, less adsorbent can achieve better adsorption capacity (89.71 ± 0.27 mg g^-1 with 0.5 g L^-1 of L-PCM, 16.84 ± 0.02 mg g^-1 with 3.0 g L^-1 of L-TCF). The pH range of application for L-PCM was 4-12 and that of L-TCF was 4-13. The adsorption of Pb(II) by biosorbents went through the boundary layer diffusion stage and void diffusion stage. The adsorption mechanism was chemisorption based on multilayer heterogeneous adsorption. The pseudo-second-order model fitted the adsorption kinetics perfectly. The Freundlich isotherm model adequately described Multimolecular equilibrium relationship between Pb(II) and biosorbents; the predicted maximum adsorption capacities of the two adsorbents were 904.12 and 46.74 mg g^-1, respectively. The results showed that the adsorption mechanism was the electrostatic attraction between Pb(II) and -COOH and the complexation between Pb(II) and -NH₂. This work demonstrated that l-lysine modified cellulose-based biosorbents have great potential in the field of Pb(II) removal from aqueous solutions.

Superior Heavy Metal Ion Adsorption Capacity in Aqueous Solution by High-Density Thiol-Functionalized Reduced Graphene Oxides

The preparation of mercapto-reduced graphene oxides (m-RGOs) via a solvothermal reaction using P₄S₁₀ as a thionating agent has demonstrated their potential as an absorbent for scavenging heavy metal ions, particularly Pb²⁺, from aqueous solutions due to the presence of thiol (-SH) functional groups on their surface. The structural and elemental analysis of m-RGOs was conducted using a range of techniques, including X-ray diffraction (XRD), Raman spectroscopy, optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy equipped with energy-dispersive spectroscopy (STEM-EDS), and X-ray photoelectron spectroscopy (XPS). At pH 7 and 25 °C, the maximum adsorption capacity of Pb²⁺ ions on the surface of m-RGOs was determined to be approximately 858 mg/g. The heavy metal-S binding energies were used to determine the percent removal of the tested heavy metal ions, with Pb²⁺ exhibiting the highest percentage removal, followed by Hg²⁺ and Cd²⁺ ions having the lowest percent removal, and the binding energies observed were Pb-S at 346 kJ/mol, Hg-S at 217 kJ/mol, and Cd-S at 208 kJ/mol. The time-dependent removal study of Pb²⁺ ions also yielded promising results, with almost 98% of Pb²⁺ ions being removed within 30 min at pH 7 and 25 °C using a 1 ppm Pb²⁺ solution as the test solution. The findings of this study clearly demonstrate the potential and efficiency of thiol-functionalized carbonaceous material for the removal of environmentally harmful Pb²⁺ from groundwater.

Reprocessed construction and demolition waste as an adsorbent: An appraisal

Construction and Demolition (C&D) waste is solid wastes generated from the construction, demolition, and renovation activities that constitute almost 30-40 % of globally generated solid wastes. Improper disposal and management of these materials can cause negative impacts on the environment, economy, and human health. Most research on C&D waste is limited to reduction, recycling, and reuse of the wastes. However, there is no systematic review dedicated entirely to the applicability of C&D wastes as adsorbent for waste management. This review presents the utilization of C&D wastes-based adsorbents for removing contaminants from environmental matrices covering triple edge benefits in the viewpoints of waste treatment, solid waste management, and disposal. The properties, the capability of C&D waste adsorbents on contaminant removal, and the influence of various factors on the adsorptive removal is detailed. Further, the mechanisms involved in contaminant removal by C&D waste are summarized. The review revealed that, chemisorption is the prominent mechanism of contaminant removal by most C&D wastes. Among the three types of C&D waste reviewed; concrete-based adsorbents were the most efficient for contaminant removal. Limited studies are avaiable in the literature on binary and multiple contaminant systems, reusability studies, and high dependence on solution pH, therefore further studies are warrated. As C&D waste contain trace concentration of heavy metals and contaminants, its leaching potential at different pH levels and adsorbate concentration need to be conducted, which has been hitherto neglected. Finally, the approaches, obstacles, and potential solutions to build an industrially and economically efficient C&D adsorbent are discussed.

Preparation of metal organic frameworks modified chitosan composite with high capacity for Hg(II) adsorption

In this study, a novel modified chitosan composite adsorbent (UNCS) was prepared by crosslinking between chitosan and metal organic frameworks (MOFs) material UiO-66-NH₂ using epichlorohydrin as crosslinker. The influence of the prepared conditions was investigated. The structure and morphology of the composite were characterized by FT-IR, XRD, SEM, TGA, BET and zeta potential analysis. Effects of different variables for adsorption of Hg(II) on this adsorbent were explored. The kinetic studies indicated that the adsorption process followed the pseudo-second-order kinetic model and the adsorption equilibrium could be reached within 2 h. The adsorption was mainly controlled by chemical process. Adsorption isothermal studies illustrated that the adsorption fitted Langmuir isotherm model, implying the homogeneous adsorption on the surface of the adsorbent. The adsorbent exhibited high uptake and the maximum capacity from Langmuir model could reach 896.8 mg g^-1 at pH 6. Thermodynamic studies showed the spontaneous nature and exothermic nature of the adsorption process. Additionally, the removal of Hg(II) on UNCS could achieve over 90 %. The adsorption-desorption cycled experiments indicated the appropriate reusability of the adsorbent. Hence, this adsorbent would be promising for the removal of Hg(II) from wastewater.

Innovative Membrane Technologies for the Treatment of Wastewater Polluted with Heavy Metals: Perspective of the Potential of Electrodialysis, Membrane Distillation, and Forward Osmosis from a Bibliometric Analysis

A bibliometric analysis, using the Scopus database as a source, was carried out in order to study the scientific documents published up to 2021 regarding the use of electrodialysis, membrane distillation, and forward osmosis for the removal of heavy metals from wastewater. A total of 362 documents that fulfilled the search criteria were found, and the results from the corresponding analysis revealed that the number of documents greatly increased after the year 2010, although the first document was published in 1956. The exponential evolution of the scientific production related to these innovative membrane technologies confirmed an increasing interest from the scientific community. The most prolific country was Denmark, which contributed 19.3% of the published documents, followed by the two main current scientific superpowers: China and the USA (with 17.4% and 7.5% contributions, respectively). Environmental Science was the most common subject (55.0% of contributions), followed by Chemical Engineering (37.3% of contributions) and Chemistry (36.5% of contribution). The prevalence of electrodialysis over the other two technologies was clear in terms of relative frequency of the keywords. An analysis of the main hot topics identified the main advantages and drawbacks of each technology, and revealed that examples of their successful implementation beyond the lab scale are still scarce. Therefore, complete techno-economic evaluation of the treatment of wastewater polluted with heavy metals via these innovative membrane technologies must be encouraged.

Preparation and permeation recognition mechanism of Cr(vi) ion-imprinted composite membranes

The Cr(vi) ion-imprinted composite membranes (Cr(vi)-IICMs) were prepared by using the surface imprinting method. The template ion was Cr(vi), the functional monomer was 4-vinylpyridine (4-VP), and the nylon filter membrane (nylon-6) was the support membrane. Non-imprinted composite membranes (NICMs) were prepared under the same conditions as the corresponding Cr(vi)-IICM. The adsorption effect of the imprinted membrane can reach 2.4 times that of the corresponding non-imprinted membrane. Meanwhile, the adsorption quantity of Cr(vi)-IICM was 34.60 μmol·g−1. The physical characteristics of membranes were confirmed by Brunauer–Emmett–Teller and scanning electron microscopy. Inductively coupled plasma emission spectrometry was used to analyze their adsorption properties and permeation selectivity. Cr(vi)-IICM and NICM were both mesoporous materials from the structural characterization and performance test results. Their adsorption behavior conformed to the Langmuir isotherm adsorption model. The permeation recognition mechanism of Cr(vi)-IICM was the Piletsky’s gate model. The IICM still has excellent permeability selectivity to Cr(vi) in the presence of competitive ions. The results provided a reference for the isolation and enrichment of Cr(vi).

Biochar admixture cement mortar fines for adsorptive removal of heavy metals in single and multimetal solution: Insights into the sorption mechanisms and environmental significance

The combined action of biochar and C-S-H (calcium-silicate-hydrate) in the cement mortars as adsorbents was explored for treating heavy metals from water. The biochar admixture cement mortars were ground to fines for use as adsorbents with the rationale that combined action of Ca, Si, Al etc. based industrial waste with conventional adsorbent biochar could enhance the removal efficiency of contaminants and therefore the overarching aim was to study the removal capacity for three selected heavy metals (Pb^2+, Cu²⁺ and Zn²⁺) commonly found in the aqueous waste stream. Batch adsorption was carried out on single and multi-metal systems to determine the removal efficiency under varied conditions such as pH, dosage of adsorbent, the effect of contact time and the initial concentration of the adsorbate. For Pb(II), Cu (II) and Zn(II), pH 5 was optimized for single and multi-metal batch sorption studies. A dosage of 20 mg for single metal and 70 mg for multi-metal of an adsorbent dose was found to be sufficient to remove about 70-90% of the three heavy metals in 25 mL solution. Langmuir model best described the isotherm data with maximum adsorption capacities of 476, 81, 123 mg/g for Pb²⁺, Cu²⁺ and Zn²⁺ for BC-40 during single metal adsorption, which were quite comparable to other C-S-H and cement-based adsorbents. The metal hydroxides precipitation, the ion exchange between the Ca²⁺ and metal ions and metal complexation were explained as plausible mechanisms for the heavy metal removal.

Transition of fouling characteristics after development of membrane wetting in membrane-aerated biofilm reactors (MABRs)

The practical applications of water treatment techniques based on hydrophobic aeration membrane are limited due to membrane pores blocking. Various studies have revealed that both biofilm and microbial secretion can exacerbate membrane fouling. Recently, we constructed a membrane-aerated biofilm reactor (MABR) system for treating micro-polluted surface water in order to identify the primary cause for oxygen transfer rate (OTR) decline. It was found that microbial secretion had a more prominent negative effect than that caused by biofilm, as manifested by the fact the effect of microbial secretion (66.49%) was greater than the resistance of biofilm (38.83%). Fouling decreased the total pore volume of all membrane. The peak location of adsorption capacity was more likely to occur at smaller pore sizes with longer running time. Notably, continuous fluorescence distribution between the separating layer and pores like finger in MABR system exhibited an increasing trend with the operation time, indicating a gradual increase of microbial viability. Core protein structure was revealed by different bond peaks (0-90 d). Specifically, for different organic components of EPS, the hydrophilic HIS was the main content, while the mass transfer resistance caused by the gel increased, which reduced the contact angle and increased the bubble point pressure. Therefore, effects of EPS content and composition should be considered during the application of water treatment techniques based on MABR.

Statistical Simulation, a Tool for the Process Optimization of Oily Wastewater by Crossflow Ultrafiltration

This work aims to determine the optimized ultrafiltration conditions for industrial wastewater treatment loaded with oil and heavy metals generated from an electroplating industry for water reuse in the industrial process. A ceramic multitubular membrane was used for the almost total retention of oil and turbidity, and the high removal of heavy metals such as Pb, Zn, and Cu (>95%) was also applied. The interactive effects of the initial oil concentration (19−117 g/L), feed temperature (20−60 °C), and applied transmembrane pressure (2−5 bar) on the chemical oxygen demand removal (RCOD) and permeate flux (Jw) were investigated. A Box−Behnken experimental design (BBD) for response surface methodology (RSM) was used for the statistical analysis, modelling, and optimization of operating conditions. The analysis of variance (ANOVA) results showed that the COD removal and permeate flux were significant since they showed good correlation coefficients of 0.985 and 0.901, respectively. Mathematical modelling revealed that the best conditions were an initial oil concentration of 117 g/L and a feed temperature of 60 °C, under a transmembrane pressure of 3.5 bar. In addition, the effect of the concentration under the optimized conditions was studied. It was found that the maximum volume concentrating factor (VCF) value was equal to five and that the pollutant retention was independent of the VCF. The fouling mechanism was estimated by applying Hermia’s model. The results indicated that the membrane fouling given by the decline in the permeate flux over time could be described by the cake filtration model. Finally, the efficiency of the membrane regeneration was proved by determining the water permeability after the chemical cleaning process.

Sulfhydryl Functionalized Magnetic Chitosan as an Efficient Adsorbent for High-Performance Removal of Cd(II) from Water: Adsorption Isotherms, Kinetic, and Reusability Studies

In this study, dimercaptosuccinic acid-functionalized magnetic chitosan (Fe3O4@CS@DMSA) was synthesized via in situ coprecipitation process and amidation reaction, aiming to eliminate cadmium (Cd(II)) ions from an aqueous environment. The structure, morphology, and particle size of the Fe3O4@CS@DMSA adsorbent were investigated using FTIR, TEM, EDX, TGA, zeta potential, and XRD techniques, and the obtained results approved the successful synthesis of the Fe3O4@CS@DMSA nanocomposite. The influence of external adsorption conditions such as pH solution, adsorbent mass, initial Cd(II) concentration, temperature, and contact time on the adsorption process was successfully achieved. Accordingly, pH: 7.6, contact time: 210 min, and adsorbent mass:10 mg were found to be the optimal conditions for best removal. The adsorption was analyzed using nonlinear isotherm and kinetic models. The outcomes revealed that the adsorption process obeyed the Langmuir and the pseudo-first-order models. The maximum adsorption capacity of Fe3O4@CS@DMSA toward Cd(II) ion was 314.12 mg/g. The adsorption mechanism of Cd(II) on Fe3O4@CS@DMSA nanocomposite is the electrostatic interaction. The reusability test of Fe3O4@CS@DMSA nanocomposite exhibited that the adsorption efficiency was 72% after the 5th cycle. Finally, this research indicates that the Fe3O4@CS@DMSA exhibited excellent characteristics such as high adsorption capacity, effective adsorption-desorption results, and easy magnetic separation and thus could be an effective adsorbent for removing Cd(II) ions from aqueous solutions.

Tuning phase compositions of MoS2 nanomaterials for enhanced heavy metal removal: performance and mechanism

Two-dimensional MoS₂ nanosheets have shown great potential in heavy metal remediation due to their unique properties. MoS₂ has two primary phases: 1T and 2H. Each has different physiochemical properties, but the impact of these differences on the overall material's heavy metal removal performance and associated mechanisms is rarely reported. In this study, we synthesized morphologically similar but phase-distinct MoS₂ samples via hydrothermal synthesis, which comprised dominantly either a metallic 1T phase or a semiconducting 2H phase. 1T-MoS₂ samples exhibited higher removal capacities for Ag⁺ and Pb²⁺ cations relative to 2H-MoS₂. In particular, an eight-fold increase in the Pb²⁺ adsorption capacity was observed in the 1T-MoS₂ samples (i.e. ∼632.9 mg g^-1) compared to the 2H-MoS₂ samples (∼81.6 mg g^-1). The mechanisms driving the enhanced performance of 1T-MoS₂ were investigated through detailed characterization of metal-laden MoS₂ samples and DFT modelling. We found that 1T-MoS₂ intrinsically had a larger interlayer spacing than 2H-MoS₂ because water molecules were retained between the hydrophilic 1T nanosheets during hydrothermal synthesis. The widened interlayer spacing in 1T-MoS₂ allowed the diffusion of heavy metal ions into the nanochannels, increasing the number of adsorption sites and total removal capacities. On the other hand, DFT modelling revealed the energy-favorable adsorption complex of Ag⁺ and Pb²⁺ for 1T-MoS₂, in which each metal atom was bonded with three S atoms leading to much higher adsorption energies relative to 2H-MoS₂ for Ag⁺ and Pb²⁺. This study unravels the underlying mechanisms of phase-dependent heavy metal remediation by MoS₂ nanosheets, providing an important guide for the use of 2D nanomaterials in environmental applications which include heavy metal removal, contaminant sensing, and membrane separation.

Synthesis of hybrid biosorbent based on 1,2-cyclohexylenedinitrilotetraacetic acid modified crosslinked chitosan and organo-functionalized calcium alginate for adsorptive removal of Cu(II)

The present study is based on the synthesis of a novel hybrid biosorbent using 1,2-cyclohexylenedinitrilotetraacetic acid modified crosslinked chitosan and amino-thiocarbamate moiety functionalized sodium alginate (CDTA-CS/TSC-CA). The fabricated sorbent was employed to investigate the efficient recovery of Cu(II) from aqueous media. CDTA-CS/TSC-CA was characterized using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Analysis confirmed the successful modification of both biopolymers and subsequent loading of Cu(II) ions. CDTA-CS/TSC-CA was casted in the form of hydrogel beads having different CDTA-CS to TSC-CA mass ratios i.e., 10.0-40.0% by mass. The hydrogel beads 4CDTA-CS/TSC-CA with CDTA-CS/TSC-CA mass ratio of 40.0% was found most effective for copper sorption. Equilibrium sorption results showed that initial concentration of copper, medium pH, contact time, sorbent dosage and temperature influenced the sorption capacity (q_e). Rate of sorption data was interpreted using different kinetic models and found best fitted with pseudo second order rate expression (R² ≈ 0.99), illustrating that the rate determining step includes the electron density transfer from sorbent coordination sites to central copper ions. Crank's RIDE equation and Elovich chemisorption model (ECM) revealed the presence of two sorption phases, initially rapid sorption followed by comparatively a slow uptake. Equilibrium sorption data was well depicted by Langmuir model and maximum monolayer adsorption capacity (q_m) was computed as 276.53 mg·g^-1 at 298 K. Standard Gibbs free energy change, ∆G° (-19.99, -20.18 and -20.36 kJ/ mol), standard enthalpy change, ∆H° (-8.95 kJmol) and standard entropy change, ∆S° (0.04 kJ/mol K^-1) values suggested that the adsorption process is spontaneous and exothermic. Hence, 4CDTA-CS/TSC-CA was found efficient biosorbent for copper removal from its dilute effluents.

Mitigation of lead (Pb) toxicity in rice cultivated with either ground water or wastewater by application of acidified carbon

Toxicity induced by a high concentration of lead (Pb) can significantly decrease plant's growth, gas exchange, and yield attributes. It can also causes cancer in humans. The use of organic amendments, especially biochar, can alleviate Pb toxicity in different crops. The application of biochar can decrease the uptake of Pb by plant roots. However, the high pH of thermo-pyrolyzed biochar makes it an unfit amendment for high pH soils. As Pb is an acute toxin and its uptake in rice is a major issue, the current experiment was conducted to explore the efficacy of chemically produced acidified carbon (AC) to mitigate Pb toxicity in rice. Lead was introduced in concentrations of 0, 15, and 30 mg kg^-1 soil in combination with 0, 0.5, and 1% AC, underground water (GW) and wastewater (WW) in rice plants. The addition of 1% AC significantly improved the plant height (52 and 7%), spike length (66 and 50%), 1000 grains weight (144 and 71%) compared to 0% AC under GW and WW irrigation, respectively at 30 mg Pb kg^-1 soil (30 Pb) toxicity. Similar improvements in the photosynthetic rate, transpiration rate and stomatal conductance also validated the effectiveness of 1% AC over 0% AC. A significant decrease in electrolyte leakage and plant Pb concentration by application of 0.5 and 1% AC validates the effectiveness of these treatments for mitigating 30 Pb toxicity in rice compared to 0% AC under GW or WW irrigation. In conclusion, 1% AC is an effective amendment in alleviating Pb toxicity in rice irrigated with GW or WW at 30 Pb.

Ultra low-cost and bio-sustainable carbonized green algae for wastewater purification in gold smelting industry

As a promising solar energy conversion technology, solar water evaporation has been regarded as an energy-efficient approach to alleviate the freshwater shortage caused by industrial water pollution. In this paper, we developed a straightforward method with a solar-driven steam generator (SSG) based on the carbonized green algae (CGA) as a light-to-heat conversion material (LHCM) to deal with the industrial wastewater of gold smelting. CGA SSG exhibited excellent light absorption, hydrophilicity, and water evaporation rate (1.66 kg·m^-2·h^-1). It accomplished the non-selective removal of heavy metal ions (Cu²⁺, Pb²⁺, Zn²⁺, Hg²⁺) and CN^- in the treatment of gold smelting wastewater, and the ion removal rate was 99%. Compared with traditional and complex wastewater treatment technologies, the solar-driven CGA SSG presented many advantages (low cost, simple preparation, and high performance) in water purification, which could be employed in backward areas to obtain clean water.

One-pot synthesis of stable and functional hydrophilic CsPbBr3 perovskite quantum dots for "turn-on" fluorescence detection of Mycobacterium tuberculosis

All-inorganic CsPbBr3 perovskite quantum dots (QDs) are widely studied owing to their excellent optoelectronic properties; however, they are usually hydrophobic and unstable in water and thus their biomedical applications are seriously limited. In this study, stable and hydrophilic CsPbBr3 QDs functionalized with carboxyl groups (CsPbBr3-COOH QDs) were prepared in one-pot with the aid of new ligands amino-poly(ethylene glycol)-carboxyl and perfluorooctyltriethoxylsilane. The aqueous solution of CsPbBr3-COOH QDs maintained the initial fluorescence intensity after 8 days of storage; the free carboxyl groups on the surface of CsPbBr3-COOH QDs were covalently conjugated with amino-terminal DNA to construct CsPbBr3 QDs-DNA probes for subsequent application. Then, a biosensing platform utilizing fluorescence resonance energy transfer between hydrophilic CsPbBr3 QDs-DNA and MoS2 nanosheets was developed for the sensitive and selective detection of the Mycobacterium tuberculosis DNA with a low limit of detection of 51.9 pM and the identification of drug-resistant clinical strains. This study advances the preparation of hydrophilic carboxyl-functionalized CsPbBr3 QDs with enhanced stability and extends their application in biomolecule detection.

Chitosan-assisted MOFs dispersion via covalent bonding interaction toward highly efficient removal of heavy metal ions from wastewater

Metal organic frameworks (MOFs) have been considered to be robust adsorbent for the removing heavy metal ions from wastewater due to their unique properties such as large active sites, high specific surface area and high porosity, etc., however, their practical engineering application faces the problem of serious agglomeration. In this work, a new strategy of chitosan (CS) assisting MOF dispersion was proposed to develop the new generation of MOF-based adsorbents, namely, CS grafted UiO-66-NH₂ composite materials (CGUNCM). The UiO-66-NH₂ was selected and it was grafted onto the main chains of CS through covalent bonding interaction with the aid of glutaraldehyde, which was totally different from the common method that grafting molecular chains on the surface of MOFs resulting in the dramatic reduction of active adsorption sites. The results show that grafting MOFs onto CS main chains not only greatly improves the dispersion of MOFs but also reserves the morphology of MOFs as much as possible. The adsorption performances toward Cu(II) and Pb(II) were intensively studied by varying adsorbate concentration, ionic strength, the contact time, adsorption temperature and pH value of solution. The results show that the composite adsorbent exhibits high adsorption efficiency and the adsorption equilibrium can be reached within 45 min, and the maximum adsorption capacity toward Cu(II) and Pb(II) achieve 364.96 mg/g and 555.56 mg/g, respectively. Furthermore, the composite adsorbent shows good reusability. This work provides a new method of fabricating the MOF-based adsorbent and paves the way for the practical application of such adsorbents in wastewater treatment.

A versatile EDTA and chitosan bi-functionalized magnetic bamboo biochar for simultaneous removal of methyl orange and heavy metals from complex wastewater

At present, the simultaneous removal of organic dyes and heavy metals in complex wastewater has raised considerable concern, owing to their striking differences in physicochemical properties. Adsorption, as one of the few removal methods, has attracted extensive attention and gained popularity. Herein, a versatile EDTA and chitosan bi-functionalized magnetic bamboo biochar adsorbent (ECMBB) was synthesized for coinstantaneous adsorption of methyl orange (MO) and heavy metals (Cd(II) and Zn(II)). In this case, the as-synthesized ECMBB composites inherited favorable anionic MO removal performance from bamboo biochar (BB) obtained at 700 °C through electrostatic attraction, hydrogen bonding and π-π interaction, also enhanced the binding of cationic metals by introducing amino groups of chitosan and carboxyl groups of EDTA. In the unitary system, the removal of MO, Cd(II) and Zn(II) by three as-prepared adsorbents can be well illuminated by pseudo-second-order kinetic model and Langmuir isotherm theory. The saturated capture amounts of ECMBB at 25 °C are 305.4 mg g^-1 for MO, 63.2 mg g^-1 for Cd(II) and 50.8 mg g^-1 for Zn(II), which, under the same conditions, are 1.3, 2.6 and 2.5 times those of chitosan-modified magnetic bamboo biochar (CMBB) and 1.9, 6.1 and 5.4 times those of magnetic bamboo biochar (MBB), respectively. Remarkably, in MO-metal binary system, coexisting MO visibly enhanced the adsorption of Cd(II) and Zn(II), while coexisting heavy metals had no significant impact on MO adsorption. Furthermore, ECMBB exhibited no significant loss in adsorption efficiency even after eight adsorption-desorption experiments. This study lays the foundation for fabricating desired integrative biochar adsorbents in the simultaneous purification of organic and metallic pollutants from complex wastewater.

Novel application of ion exchange membranes for preparing effective silver and copper based antibacterial membranes

Ion exchange membranes (IEMs) are widely used in water treatment applications such as electrodialysis. However, the exploration of IEMs as effective antibacterial food contact materials (e.g., food packaging membranes) against pathogenic bacteria to ensure food safety has not been reported. Here, we report a simple but effective method to prepare high performance antibacterial membranes via ion exchange coupled with in-situ reduction. The general membrane properties are characterized using SEM, EDS, FTIR, XPS, XRD, DSC, TGA, water uptake, etc. The distribution of silver and copper in the membranes are generally in line with the distribution of sulfur, indicating that the antibacterial ions are introduced into the membranes via ion exchange and are bonded with the sulfonate groups in the membranes. The antibacterial performance is investigated using zone of inhibition tests and continuous bacteria growth inhibition tests. All of the prepared membranes show obvious antibacterial activities compared to the bare cation exchange membranes. The diameters of inhibition zone against Staphylococcus aureus (S. aureus) are all larger than those of Escherichia coli (E. coli), indicating that the prepared membranes are more efficient in inhibiting S. aureus compared to E. coli. Furthermore, the silver-based membrane shows more sustainable antibacterial activities compared to the copper-based membrane. Especially, the results clearly reveal that the silver-based membrane is capable of killing bacteria instead of just inhibiting the growth of bacteria. We have shown for the first time that membranes derived from IEMs have the potential as food contact materials to inhibit the growth of pathogenic bacteria so as to eliminate the risk of bacterial infections and meanwhile delay food spoilage due to bacteria growth.

Sequestration of free and chelated Ni(II) by structural Fe(II): Performance and mechanisms

Ni(II) and chelated Ni(II) in wastewater are of environmental concern. This study explores the sequestration potential of structural Fe(II) in solid phase (≡Fe(II)) on Ni(II) and EDTA-Ni(II) using freshly prepared ferrous hydroxyl complex (FHC) as the Fe(II)-bearing mineral. The 1 mM Ni(II) could be completely sequestrated in 20 min by 3 mM FHC, although the sequestrated Ni(II) was partially released after 20 min. It is calculated that up to 156 mg Ni(II)/g Fe(II) can be sequestrated by ≡Fe(II) under neutral pH and anaerobic condition. According to the characterizations of the solid products, the large surface area for Ni(II) adsorption and the high ≡Fe(II) reduction capacity for Ni(II) reduction are the main contributors to the Ni(II) sequestration. After the reaction, the FHC is transformed to stable Fe-Ni layered double hydroxides. The concomitant ions can be either promotional or inhibitory to the sequestration performance depending on the ion type. The combination of FHC and Fe(III) can effectively sequestrate EDTA-Ni(II), whereas FHC alone has a low efficiency. Fe(III) substitutes Ni(II) from the EDTA-Ni(II), benefiting the subsequent Ni(II) sequestration by ≡Fe(II). This study demonstrates that ≡Fe(II) suspension is an cost-effective option for remediating Ni(II)-containing wastewater.

Layer-by-Layer Encapsulation of Herbicide-Degrading Bacteria for Improved Surface Properties and Compatibility in Soils

E. coli cells overexpressing the enzyme atrazine chlorohydrolase were coated using layer-by-layer self-assembly. The polymeric coating was designed to improve the surface properties of the cells and create positively charged, ecologically safe, bio-hybrid capsules that can efficiently degrade the herbicide atrazine in soils. The physio-chemical properties of the bacteria/polymer interface were studied as a function of the polymeric composition of the shell and its thickness. Characterization of cell viability, enzyme activity, morphology, and size of the bio-capsules was done using fluorescence spectroscopy, BET and zeta potential measurements and electron microscopy imaging. Out of several polyelectrolytes, the combination of polydiallyldimethylammonium chloride and polysodium 4-styrenesulfonate improved the surface properties and activity of the cells to the greatest extent. The resulting bio-hybrid capsules were stable, well-dispersed, with a net positive charge and a large surface area compared to the uncoated bacteria. These non-viable, bio-hybrid capsules also exhibited a kinetic advantage in comparison with uncoated cells. When added to soils, they exhibited continuous activity over a six-week period and atrazine concentrations declined by 84%. Thus, the concept of layer-by-layer coated bacteria is a promising avenue for the design of new and sustainable bioremediation and biocatalytic platforms.

A comprehensive review on the synthesis and applications of ion exchange membranes

Ion exchange membranes (IEMs) are undergoing prosperous development in recent years. More than 30,000 papers which are indexed by Science Citation Index Expanded (SCIE) have been published on IEMs during the past twenty years (2001-2020). Especially, more than 3000 papers are published in the year of 2020, revealing researchers' great interest in this area. This paper firstly reviews the different types (e.g., cation exchange membrane, anion exchange membrane, proton exchange membrane, bipolar membrane) and electrochemical properties (e.g., permselectivity, electrical resistance/ionic conductivity) of IEMs and the corresponding working principles, followed by membrane synthesis methods, including the common solution casting method. Especially, as a promising future direction, green synthesis is critically discussed. IEMs are extensively applied in various applications, which can be generalized into two big categories, where the water-based category mainly includes electrodialysis, diffusion dialysis and membrane capacitive deionization, while the energy-based category mainly includes reverse electrodialysis, fuel cells, redox flow battery and electrolysis for hydrogen production. These applications are comprehensively discussed in this paper. This review may open new possibilities for the future development of IEMs.

Evaluation of zinc adsorption through batch and continuous scale applying Bayesian technique for estimate parameters and select model

This work aims to study the efficiency of zinc adsorption onto granular-activated carbon, predicting the mathematical models that best describe the adsorption behavior in a fixed bed column. First, batch scale experiments were performed to evaluate the influence of pH (3 to 6), contact time (5 to 60 min), and absorbent concentration (5 to 25 g L^-1) using synthetic effluent. Fixed bed column experiments were performed by varying the adsorbent concentration (10, 13, 20, and 40 g L^-1) and the effluent flow rate (15 and 20 mL min^-1). Markov Chain Monte Carlo and Bayesian criteria information were applied to describe the phenomena using Langmuir, Freundlich, Temkin, Redlich-Peterson, Sips, Toth, Khan, Radke-Prausnitz, for isotherm models, and Thomas; Yoon-Nelson; Yan; Clark models for breakthrough curve. Adsorption operating best conditions were pH 5, 20 g L^-1 of solid, and 50 min of contact time. These parameters allowed 80% of Zn removal, being better described by the Tempki model. In tests on a pilot plant, the Yan model was able to predict the second-order kinetic model, with an increase in the effluent flow and a 50% increase in the bed saturation time with a greater amount of adsorbent solid.

Effective water/wastewater treatment methodologies for toxic pollutants removal: Processes and applications towards sustainable development

Release of pollutants due to inflating anthropogenic activities has a conspicuous effect on the environment. As water is uniquely vulnerable to pollution, water pollution control has received a considerable attention among the most critical environmental challenges. Diverse sources such as heavy metals, dyes, pathogenic and organic compounds lead to deterioration in water quality. Demand for the pollutant free water has created a greater concern in water treatment technologies. The pollutants can be mitigated through physical, chemical and biological methodologies thereby alleviating the health and environmental effects caused. Diverse technologies for wastewater treatment with an accentuation on pre-treatment of feedstock and post treatment are concisely summed up. Pollutants present in the water can be removed by processes some of which include filtration, reverse osmosis, degasification, sedimentation, flocculation, precipitation and adsorption. Membrane separation and adsorption methodologies utilized to control water pollution and are found to be more effective than conventional methods and established recovery processes. This audit relatively features different methodologies that show remarkable power of eliminating pollutants from wastewater. This review describes recent research development on wastewater treatment and its respective benefits/applications in field scale were discussed. Finally, the difficulties in the enhancement of treatment methodologies for pragmatic commercial application are recognized and the future viewpoints are introduced.

Biorenewable, transparent, and oxygen/moisture barrier nanocellulose/nanochitin-based coating on polypropylene for food packaging applications

Aluminum-coated polypropylene films are commonly used in food packaging because aluminum is a great gas barrier. However, recycling these films is not economically feasible. In addition, their end-of-life incineration generates harmful alumina-based particulate matter. In this study, coating layers with excellent gas-barrier properties are assembled on polypropylene films through layer-by-layer (LbL) deposition of biorenewable nanocellulose and nanochitin. The coating layers significantly reduce the transmission of oxygen and water vapors, two unfavorable gases for food packaging, through polypropylene films. The oxygen transmission rate of a 60 μm-thick, 20 LbL-coated polypropylene film decreases by approximately a hundredfold, from 1118 to 13.10 cc m^-2 day^-1 owing to the high crystallinity of nanocellulose and nanochitin. Its water vapor transmission rate slightly reduces from 2.43 to 2.13 g m^-2 day^-1. Furthermore, the coated film is highly transparent, unfavorable to bacterial adhesion and thermally recyclable, thus promising for advanced food packaging applications.

Fabrication of zinc doped aluminium oxide/polysulfone mixed matrix membranes for enhanced antifouling property and heavy metal removal

Heavy metal removal from water resources is essential for environmental protection and the production of safe drinking water. In this direction, Zinc doped Aluminium Oxide (Zn:Al₂O₃) nanoparticles were incorporated into Polysulfone (PSf) to prepare mixed matrix membranes for the efficient removal of heavy metals from water. These Zn:Al₂O₃ nanoparticles prepared by the solution combustion method have a very high surface area (261.44 m²/g) with an approximate size of 50 nm. X-ray Photoelectron Spectroscopy analysis showed that the Al and Zn were in +3 and + 2 oxidation states, respectively. Cross-sectional Scanning Electron Microscopy images revealed the finger-like morphology and porous nature of the membranes. In this study, the optimum loading amount of Zn:Al₂O₃ nanoparticles was determined. Synthesized membranes showed enhanced hydrophilicity, surface charge, and porosity, which enabled the removal of arsenic and lead with efficiencies of 87% and 98%, respectively. A study of the antifouling properties carried out at various pressures with a feed solution containing Bovine Serum Albumin (BSA) showed 98.4% of flux recovery ratio and reusability up to three continuous cycles. Moreover, this work demonstrates a rational design of novel mixed matrix membranes exhibiting characteristics of hydrophilicity, surface charge, and porosity adequate to realize the efficient removal of heavy metals.