Adsorption of organic and inorganic arsenic from aqueous solution: Optimization, characterization and performance of Fe-Mn-Zr ternary magnetic sorbent

3D-printing of Fe-Ni bimetallic particles and their application in removal of arsenic from water

Arsenic is a hazardous element found in water sources, and removing it is crucial for ensuring a safe environment and water quality. Iron-based metal oxides efficiently remove arsenic; however, their small particle sizes make separation from water difficult after arsenic removal. Furthermore, the growing global issue of polymer waste further complicates environmental concerns. Combining three-dimensional (3D) printing and adsorption technology by incorporating nanosized functional materials into supporting polymers offers a potential solution to address both challenges. In this study, we developed a 3D-printed adsorption material through the incorporation of synthesized Fe-Ni bimetallic particles into a supporting polymer using selective laser sintering (SLS) technology. This adsorbent's properties were examined through scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and zeta potential. Furthermore, its performance in removing As(III) and As(V), even at trace levels, was assessed under varied conditions. The 3D-printed adsorbent demonstrated excellent removal of As(III) at pH 6, and As(V) at pH 4, lowering their concentration below 10 μg/L, thereby adhering to the limit established by the World Health Organization (WHO). Both As(III) and As(V) fitted the Freundlich isotherm and pseudo-second-order model, suggesting potential heterogeneous and chemisorption processes. FT-IR indicated that the exchange of the -OH group of Fe-OH with oxyanions of As(III) and As(V) could be the adsorption mechanism. Additionally, thermodynamic evaluation unveiled an endothermic and non-spontaneous adsorption reaction. The 3D-printed adsorbent exhibited excellent reusability across recurring adsorption cycles. The combination of SLS 3D printing with Fe-Ni bimetallic particles produces structures that retain their functionality in removing both arsenic species present in water. This indicates the potential of the 3D-printed adsorbent for effective treatment of arsenic-contaminated water, offering remedies to challenges like handling small particle sizes, mitigating polymer waste, and addressing environmental concerns.

Arsenate removal using chitosan-coated bentonite via fixed-bed system: a process integration by fuzzy optimization

Groundwater contamination is a global concern that has detrimental effect on public health and the environment. Sustainable groundwater treatment technologies such as adsorption require attaining a high removal efficiency at a minimal cost. This study investigated the adsorption of arsenate from groundwater utilizing chitosan-coated bentonite (CCB) under a fixed-bed column setup. Fuzzy multi-objective optimization was applied to identify the most favorable conditions for process variables, including volumetric flow rate, initial arsenate concentration, and CCB dosage. Empirical models were employed to examine how initial concentration, flow rate, and adsorbent dosage affect adsorption capacity at breakthrough, energy consumption, and total operational cost during optimization. The ε-constraint process was used in identifying the Pareto frontier, effectively illustrating the trade-off between adsorption capacity at breakthrough and the cost of the fixed-bed system. The integration of fuzzy optimization for adsorption capacity and its total operating cost utilized the global solver function in LINGO 20 software. A crucial equation derived from the Box-Behnken design and a cost equation based on energy and material usage in the fixed-bed system was employed. The results from identifying the Pareto front determined boundary limits for adsorption capacity at breakthrough (ranging from 12.96 ± 0.19 to 12.34 ± 0.42 μg/g) and total operating cost (ranging from 955.83 to 1106.32 USD/kg). An overall satisfaction level of 35.46% was achieved in the fuzzy optimization process. This results in a compromise solution of 12.90 μg/g for adsorption capacity at breakthrough and 1052.96 USD/kg for total operating cost. Henceforth, this can allow a suitable strategic decision-making approach for key stakeholders in future applications of the adsorption fixed-bed system.

Efficient As(III) removal from water by ZrO2 modified covalent organic framework under visible light irradiation

Adsorption-oxidation is a promising technique to decontaminate As(III) polluted water. In present study, ZrO2-modified covalent organic framework (ZrO2-COF) was fabricated and used to remove arsenic from water under visible light irradiation. The results showed that ZrO2-COF (0.2 g/L) could efficiently capture As(III) (5 mg/L) from water and then oxidize the adsorbed As(III) into less toxic As(V) under visible light irradiation (60 min), achieving the complete decontamination of As(III) polluted water. Based on characterization results and theoretical calculations, we found that in ZrO2-COF composite, ZrO2 served as sites for adsorption of As(III)/the latter transformed As(V), while COF worked as photocatalytic center for As(III) oxidation. Effective As(III) removal could also be achieved by ZrO2-COF under visible light irradiation in complex water chemistry conditions including wide solution pH range (3-11), broad solution ion strength range (1-100 mM), the copresence of natural organic matter (0.1-1 mg/L humic acid) and various coexisting ions in solutions, as well as in real water samples. In addition, we found that ZrO2-COF had excellent reuse performance in 4 consecutive cycles. Our results showed that under visible light irradiation, ZrO2-COF composites could be a promising technique for efficient As(III) removal from water.

Exploring the interference mechanisms of surface and aqueous complexes with groundwater arsenate and arsenite adsorption

Ca2+, Mg2+, and HCO3- are extremely common coexisting ions with arsenic (As) in geogenic As-polluted groundwaters. Although extensive research has improved our knowledge of groundwater As removal techniques and mechanisms, there is still a lack of a definite explanation of the distinct influences of Ca2+ and Mg2+ on As immobilization. Furthermore, the question of whether the occurrence of metal-As aqueous complexes has positive or detrimental effects on As adsorption is still open, which hinders our ability to predict the effectiveness of groundwater As removal. The goal of our present work was to investigate the molecular-level interference mechanisms of Ca2+, Mg2+, and HCO3- on arsenic adsorption with batch/column filtration experiments and spectroscopic techniques. The results showed that the co-presence of Ca2+ and As significantly increased As(V) and As(III) adsorption by 22.1 and 12.2% in batch studies and by 20.1 and 16.7% in column adsorptive filtrations, which could be explained by forming a ternary Ca-As-TiO2 complex. Without the surface complex, Mg2+ only had a slightly positive effect on As removal. Co-existence of Ca2+ and HCO3- prevented the generation this surface complex, which significantly decreased the elimination of As(III). Inversely, the As(V) ternary complex and adsorption were not interfered by HCO3-. Moreover, an aqueous Ca-As(V) complex was detected without surface, which facilitated generation of the surface complex and As(V) adsorption. The results of this work clarified the distinct effects of Ca2+ and Mg2+ and As(V) and As(III) adsorption, which was critical in predicting the As adsorption efficiency in column filtration processes.

Filamin A facilitates NLRP3 inflammasome activation during arsenic-induced nonalcoholic steatohepatitis

Prolonged exposure to arsenic can cause nonalcoholic steatohepatitis (NASH). The NOD-like receptor protein 3 (NLRP3) inflammasome plays an essential role in the process of NASH. However, the mechanism by which arsenic promotes NLRP3 expression remains unclear. Three-month NaAsO2 gavage led to the nuclear factor-κB (NF-κB) signaling pathway activation and NASH. Additionally, NaAsO2 upregulated the level of Filamin A (FLNA) and pyroptosis, thereby activating the NLRP3 inflammasome in SD rat liver. Using FLNA siRNA, NASH-associated inflammation and pyroptosis were clearly mitigated by reducing activation of the NLRP3 inflammasome. Furthermore, arsenic treatment facilitated activation of the NF-κB signaling pathway and promoted p-p65 translocation into the nucleus. Chromatin immunoprecipitation (Ch-IP) assay indicated that FLNA promoted p65 binding to the NLRP3 gene and upregulated the transcription of NLRP3, ultimately leading to pyroptosis and NASH. Our findings indicate that FLNA and pyroptosis are strongly associated with NASH induced by NaAsO2. Collectively, the findings of this study indicated that FLNA mediates NF-κB signaling pathway-induced activation of the NLRP3 inflammasome and ultimately activates pyroptosis and NASH upon NaAsO2 exposure. This information may be useful for improving therapeutic strategies against arsenic-induced NASH.

Polyethylene and poly (butyleneadipate-co-terephthalate)-based biodegradable microplastics modulate the bioavailability and speciation of Cd and As in soil: Insights into transformation mechanisms

Microplastics (MPs) that enter the soil can alter the physicochemical and biochemical properties of soil and affect speciation of heavy metals (HMs), thereby perturbing the bioavailability of HMs. However, the mechanisms underlying these effects are not understood. Therefore, we investigated the effects of MPs from poly (butyleneadipate-co-terephthalate)-based biodegradable mulch (BM) and polyethylene mulch (PM) in Cd- or As-contaminated soil on soil properties and speciation of HMs. MPs were characterised using Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The addition of MPs reduced the bioavailability of HMs in soil and promoted the transformation of HMs into inert fractions. The mechanisms underlying the reduction of the bioavailability of HMs in soils could be as follows: (1) the entry of MPs into the soil changed its properties, which reduced the bioavailability of HMs; (2) FTIR and XPS analyses revealed that the hydroxyl and carboxyl groups and benzene ring present on the surface of aged MPs stabilized complexes (As(V)-O) with As(V) may have directly reduced the bioavailability of As(V) in soil; (3) aged BM exposed more amounts and types of reactive functional groups and was more effective in stabilising soil HMs than PM. Overall, this study provides new insights regarding the complexation mechanisms of soil HMs by MPs from different plastic mulch sources.

Synthesis and Application of Ion-Exchange Magnetic Microspheres for Deep Removal of Trace Acetic Acid from DMAC Waste Liquid

In order to develop a deep method for removing trace acetic acid from industrial solvents, a type of quaternary ammonium-salt-modified magnetic microspheres was developed as a potential nanoadsorbent for low-concentration acetic-acid-enhanced removal from DMAC aqueous solution. The ion-exchange magnetic microspheres (Fe₃O₄@SiO₂@N(CH₃)₃⁺) have been prepared by a two-step sol-gel method with N-trimethoxysilylpropyl-N, N, N-trimethylammonium chloride as functional monomer, tetraethyl orthosilicate as a cross-linking agent, Fe₃O₄@SiO₂ as a matrix. The nanocomposite is characterized by SEM, FI-IR, XRD, VSM, and XPS. Moreover, the optimization of adsorption experiments shows that the maximum adsorption capacity of nanoadsorbent is 7.25 mg/g at a concentration = 30 mg/L, adsorbent dosage = 10 mg, V = 10 mL, and room temperature. Furthermore, the saturated Fe₃O₄@SiO₂@N(CH₃)₃⁺ achieved an efficient regeneration using a simple desorption method and demonstrated a good regeneration performance after five adsorption/desorption cycles. In addition, Fe₃O₄@SiO₂@N(CH₃)₃⁺ was used to remove acetic acid in DMAC waste liquid; the adsorption effect is consistent with that of a nanoadsorbent of acetic acid in an aqueous solution. These results indicate that Fe₃O₄@SiO₂@N(CH₃)₃⁺ can efficiently treat acetic acid that is difficult to remove from DMAC waste liquid.

Design and optimization of an innovative lanthanum/chitosan bead for efficient phosphate removal and study of process performance and mechanisms

Presence of excessive phosphorus in surface waters is the main cause for eutrophication. In this study, a lanthanum/chitosan (La/CS) bead was prepared so as to provide a cost-effective solution to the problem. The optimization of bead for the treatment was conducted, leading to the optimal condition: 30 wt% La/CS bead at a dosage of 30 g L^-1 (wet weight). A higher phosphate removal around 90% was obtained in pH 4.0-10.0. Most of uptake occurred in the first 2 h and the equilibrium was reached in about 6 h. Coexisting ions of Cl^-, [Formula: see text] , [Formula: see text] , and [Formula: see text] had negligible effects on the treatment, while the presence of F^- reduced the uptake by 10.39%. The maximum adsorption capacity of 261.1 mg-PO₄·g^-1 (dried weight) at pH 5.0 was achieved, which is much better than many reported La-based adsorbents. The adsorbed phosphate can be effectively recovered with an alkaline solution. A multi-cycle regeneration-reuse study illustrated that the treated water still met the phosphorus discharge standard. The characterization results demonstrated the disappearance of La(OH)₃ and La₂(CO₃)₃ on the bead and the formation of NH₃⁺ … P and La-P groups after the adsorption, indicating the significant roles of ion exchange and electrostatic attraction on the uptake. The excellent performance found in this study clearly indicates that the optimized La/CS bead is promising in the treatment of phosphate and perhaps its recovery for industrial use.