Arsenic Adsorption Research Articles

Integrating a high-energy activation method for the sustainable treatment of iron smelting slag, phosphogypsum, and arsenic-contaminated water

Metallurgy is one of the pillar industries in China, but metallurgy inevitably produces a large amount of industrial solid waste and heavy metal pollution. Phosphogypsum (PG) is a by-product of the production of wet-process phosphoric acid, and after the preliminary fieldwork, there is a very small amount of arsenic [As(V)] in some of the phosphorus ores, and there is a risk of heavy metal pollution. In the present study, the preparation of arsenic adsorbent (PG/IS) by doping iron smelting slag (IS) with PG as a base material was proposed and the preparation conditions were optimized by Response Surface Methodology. PG/IS was systematically characterized and its adsorption properties were investigated with respect to a variety of factors. PG/IS exhibits spontaneous endothermic chemical adsorption characteristics for As(V)，its adsorption process is more consistent with the pseudo-second-order kinetic model. Coordination complexation and chemical precipitation are the primary mechanisms by which PG/IS removes As(V). This study provides a new approach for phosphorus chemical enterprises to achieve green development and reduce industrial solid waste and As(V) emissions.

Transforming tire-derived char into powerful arsenic adsorbents by mild modification

A large amount of arsenic-containing wastewater discharged by the non-ferrous metal industry will cause serious environmental problems if it is not properly treated. Pyrolysis char of waste tire is a kind of solid waste. Since the surface properties of tire derived char (TC) are affected by tar/ash adhesion during pyrolysis, it is necessary to modify TC to treat wastewater containing As(V) effectively as an adsorbent. At present, most studies on the modification of TC are prepared into activated carbon by high temperature activation in N2 atmosphere. In this study, TC was modified at room temperature and air atmosphere, and Fe(OH)3-TCNaOH adsorbent with particle size of 61–75 μm was obtained under the premise of the removal rate of As(V) and the settling performance of the adsorbent. When the initial concentration of As(V) was 5 mg/L, the removal rate of As(V) by Fe(OH)3-TCNaOH with a particle size of 61–75 μm could reach 90% within 30 min under a wide pH range (3–9). The adsorption of As(V) by Fe(OH)3-TCNaOH was most affected by the coexistence of PO43-, which resulted in the removal rate of As(V) decreased by about 20%. The adsorption mechanism shows that the significant increase in the number of 3–5 nm mesoporous pores of Fe(OH)3-TCNaOH and the formation of H bonds are beneficial to the adsorption of Fe(OH)3-TCNaOH to As(V), and improve the stability of Fe-As complex.

Prominent differences in the adsorption and substitution characteristics of As(III) and As(V) on gypsum during wet flue gas desulfurization

Arsenic-bearing gypsum (ABG) is a hazardous by-product of wet flue gas desulfurization (FGD) and must be strictly controlled. This study investigated the migration of arsenic species during wet FGD and proposed strategies to reduce the toxicity of FGD gypsum in operation. During gypsum crystallization, the adsorption and substitution characteristics of As(III) and As(V) exhibit significant differences. The amount of As(III) captured by CaSO4·2H2O is greater than that of As(V). The As(III) adsorbed on the growth surface of CaSO4·2H2O can be incorporated into the gypsum by substituting for SO42−, while As(V) tends to remain adsorbed on the surface. Moreover, the arsenic adsorption capacity of the incompletely oxidized product CaSO3·0.5H2O was almost three times that of CaSO4·2H2O, especially for As(III). Based on the differences in the migration characteristics of As(III) and As(V), a strategy was proposed to reduce the arsenic content and biotoxicity in gypsum during operation by enhancing the oxidation of sulfite and highly toxic arsenite, thus ensuring the safe utilization of FGD gypsum.

Synergistic ultra-high adsorption and oxidation of arsenic in groundwater by iron-modified biochar: Mechanisms and potential application

This study explores the potential of low-cost biochar modified with ferrihydrite and goethite for the remediation of heavily As-polluted groundwater. Combining batch experiments and synchrotron radiation-based characterization, we investigated the mechanisms of As(III) adsorption and oxidation. The modified biochars exhibited significant adsorption capacities, achieving fitted qmax of 45.7 ± 3.9 mg/g for ferrihydrite-modified biochar (FhGM) and 20.2 ± 1.5 mg/g for goethite-modified biochar (GtGM) at a dosage of 1.0 g/L and an initial concentration of 10 mg/L As(III) over 24 h. Biochar facilitated approximately 30 % As(V) generation from As(III) due to enhanced electron transfer. Moreover, over 90 % of As(III) was oxidized to As(V) following the addition of H2O2, with scanning transmission X-ray microscopy revealing the distribution of As(III), and As(V) on the solid phase. In the GtGM-H2O2 system, reactive oxidation species, primarily O2•–, served as the main oxidant. In the FhGM-H2O2 system, Fe(IV) likely acted as the primary oxidizing agent. Column experiments with 0.64 g of FhGM demonstrated that, when treating 50 mg/L As-contaminated groundwater, the effluent total As concentration remained below the maximum allowable limit of 10 μg/L after 21 h. Furthermore, in the presence of H2O2, the system managed to treat 200 mg/L As-contaminated groundwater, and the effluent total As concentration exceeded 10 μg/L after 11 h. This study provides valuable insights and practical results for the remediation of high-concentration arsenic-contaminated groundwater, highlighting the effectiveness of iron-modified biochar in this application.

Investigation of Toxicity of the Combined Exposure of Microplastics and Arsenic (III) on Clams

Introduction: Microplastics is a new type of global pollutant that can absorb pollutants in the environment and enter the food chain. Arsenic (As) is a kind of heavy metal element, and its pollution to the environment has been concerned. Nowadays, the threat of both to Marine ecology is gradually increasing, and people are paying more attention to the harm of microplastics and heavy metal pollution to human health. Method: The aim of this paper is to study the adsorption of arsenic by microplastics and the toxic effects of the combination of the two on clams. The toxicity effects of microplastics and As (III) on clams were determined by joint toxicity test. The fatality rates caused by microplastics polypropylene (PP), polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) with concentrations between 10 mg/L and 500 mg/L adsorbed with As (III) in first 48 h were 0-30.0%, 0-10.0%, 0-30.0%, 0-15.0% and 0-50.0% (larval clams); 0-35.0%, 0-25.0%, 0-30.0%, 0-50.0% and 0-15.0% (adult clams), respectively. Results: Compared with the group of As (III) alone, the fatality rates caused by PP, PE, PS, PVC and PMMA after 48 h increased dramatically to 80%, 62%, 40%, 60% and 70% (larval clams); 85%, 72%, 40%, 72% and 65% (adult clams), respectively. Conclusion: The death rate of clams was proportional to the input of microplastic particles containing As (III), that is, the higher the concentration used, the higher the fatality rates and the faster the death rates of clams.

Fabrication of Fe-Ti heteroatom-based metal-organic framework with vantage defects for high-efficient arsenic removal from water

Arsenic (As) contamination in water remains a formidable concern due to its high toxicity and detrimental impacts on human health and the environment. Selective adsorption utilizing solid adsorbents has emerged as a promising method for the removal of arsenate (As(V)) from drinking water. However, current adsorbents encounter limitations in effectively reducing relatively low-concentration As(V) from water. Here, we designed a Fe-Ti heteroatom-based metal–organic framework (MOF) MIL-125(Ti,Fe) with vantage defects for efficient As(V) removal. In the batch adsorption experiments, MIL-125(Ti,Fe) exhibited an exceptional removal efficiency of 99.3 % from the 10 ppm As(V)-containing water, which clearly overperformed counterpart MOF adsorbents of MIL-125(Ti) and MIL-101(Fe). Kinetic analysis indicated that the adsorption behavior of all three adsorbents followed pseudo-second-order kinetics. Importantly, dynamic breakthrough experiments demonstrated that MIL-125(Ti,Fe) could effectively reduce the As(V) concentration from 1 ppm to 3 ppb, well below the safety limit of 10 ppb set by WHO. Mechanistic analysis revealed that the arsenic adsorption mechanism of MIL-125(Ti,Fe) involved chemical adsorption between As(V) and the incorporated Fe as well as formed oxygen vacancies in MIL-125(Ti,Fe), which acted as essential adsorption sites and interacted with As(V) through the formation of Fe-O-As groups. The novel MIL-125(Ti,Fe) adsorbent demonstrated its great potential for arsenic removal, particularly in treating relatively low-concentration As-contaminated water.

Extent of As(III) versus As(V) adsorption on iron (oxyhydr) oxides depends on the presence of vacancy cluster-like micropore sites: Insights into a seesaw effect

Iron (oxyhydr)oxides are ubiquitous in terrestrial environments and play a crucial role in controling the fate of arsenic in sediments and groundwater. Although there is evidence that different iron (oxyhydr)oxides have different affinities towards As(III) and As(V), it is still unclear why As(V) adsorption on some iron (oxyhydr)oxides is larger than As(III) adsorption, while it is opposite for other ones. In this study, six typical iron (oxyhydr)oxides are selected to evaluate their adsorption capacities for As(III) and As(V). The characteristics of these iron minerals such as morphology, arsenic adsorption species, and pore size distribution are carefully examined using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), positron annihilation lifetime (PAL) spectroscopy, and X-ray absorption spectroscopy (XAS). We confirm a seesaw effect occurred in different iron minerals for As(III) and As(V) immobilization, i.e., at pH 6.0, adsorption of As(V) on hematite (0.73 μmol m−2) and magnetite (0.33 μmol m−2) is higher than for As(III) (0.61 μmol m−2 and 0.27 μmol m−2, respectively), for goethite and lepidocrocite it is almost equal, while As(III) sorption on ferrihydrite (5.77 μmol m−2) and schwertmannite (28.41 μmol m−2) showed higher sorption than As(V) (1.53 μmol m−2 and 12.99 μmol m−2, respectively). PAL analysis demonstrates that ferrihydrite and schwertmannite have a large concentration of vacancy cluster-like micropores, significantly more than goethite and lepidocrocite, followed by hematite and magnetite. The difference of adsorption of As(III) and As(V) to different iron (oxyhydr)oxides is due to differences in the abundance of vacancy cluster-like micropore sites, which are conducive for smaller size As(III) immobilization but not for larger size of As(V). The findings of this study provide novel insights into a seesaw effect for As(III) and As(V) immobilization on naturally occurring iron mineral.

​Statistical-based optimization and mechanism assessments of Arsenic (III)​ adsorption by ZnO-Halloysite nanocomposite​

Arsenic contamination in aqueous media is a serious environmental problem, especially in developing countries. In this research, the Box-Behnken response surface methodology was used to optimize the most relevant variables affecting arsenic adsorption on the ZnO-halloysite surface, including temperature, adsorbent dosage, pH, contact time, and As (III) initial concentration. The regression analysis indicated that the experimental data were appropriately fitted to a quadratic model with the adjusted R-squared value (R2) of 0.982 for As(III) adsorption capacity and a linear model with R2 of 0.931 for As(III) removal. The p-values for both adsorption capacity and removal efficiency were below 0.05, with F-values of 116.91 and 115.58, respectively, supporting the model’s validity. The optimum conditions for maximum removal of As(III) were determined through numerical and graphical optimization using the desirability function. It was found that the optimum conditions for adsorption were pH = 7.99, contact time of 3.99 h, As(III) initial concentration of 49.96 mg/L, and adsorbent dosage of 0.135 g/40 ml. The accuracy of the optimization procedure was confirmed by a confirmatory experiment, which showed a maximum arsenic removal of 91.31% and an adsorption capacity of 12.63 mg/g under optimized conditions. Moreover, XPS analysis was performed at different pH levels to investigate the As (III) adsorption mechanism. The results demonstrated that As(III) adsorption occurs at acidic and neutral pH levels. On the other hand, when pH is increased to 8, As (III) oxidizes to As (V), and then adsorption occurs.

Insight into the adsorption mechanism of arsenic and selenium by different mineral adsorbents

The adsorption characteristics of arsenic and selenium by CaO, CaCO3, MgO and Fe2O3 at different temperatures and the influence of steam are investigated using simulated flue gas by a vertical furnace. Experiments show that the adsorption capacity of CaCO3 for arsenic and selenium reached the maximum at 900 °C. Steam addition exerts a notable inhibitory impact on the adsorptive efficacy of CaO, MgO, and Fe2O3. Low-concentration steam has a certain improvement on adsorption of arsenic by CaCO3, while excessive steam will have an inhibitory effect. Based on CaCO3, the adsorption effect of composite minerals is investigated. When the mass ratio of CaCO3 and Fe2O3 is 3:1, the best adsorption is achieved, attributing to the generated Ca2Fe2O5 at high temperature. It is verified in the drop tube furnace. The relative enrichment factor of As and Se are 88.24 % and 75.11 %, respectively, which achieved efficient removal.

Efficient arsenic removal from water using iron-impregnated low-temperature biochar derived from henequen fibers: performance, mechanism, and LCA analysis

The present study aims to investigate the low-energy consumption and high-efficiency removal of arsenic from aqueous solutions. The designed adsorbent Fe/TBC was synthesized by impregnating iron on torrefaction henequen fibers. Isothermal adsorption experiments indicated maximum adsorption capacities of 7.30 mg/g and 8.98 mg/g for arsenic(V) at 25.0 °C and 40.0 °C, respectively. The interference testing showed that elevated levels of pH, HCO3− concentration, and humic acid content in the solution could inhibit the adsorption of arsenic by Fe/TBC. Characterization of the adsorbent before and after adsorption using FTIR and SEM–EDS techniques confirmed arsenic adsorption mechanisms, including pore filling, electrostatic interaction, surface complexation, and H-bond adhesion. Column experiments were conducted to treat arsenic-spiked water and natural groundwater, with effective treatment volumes of 550 mL and 8792 mL, respectively. Lastly, the life cycle assessment (LCA) using OpenLCA 2.0.3 software was performed to treat 1 m3 of natural groundwater as the functional unit. The results indicated relatively significant environmental impacts during the Fe/TBC synthesis stage. The global warming potential resulting from the entire life cycle process was determined to be 0.8 kg CO2-eq. The results from batch and column experiments, regeneration studies, and LCA analysis indicate that Fe/TBC could be a promising adsorbent for arsenic(V).

Arsenic Adsorption in Subunits of Metal‐Organic Frameworks—A DFT Approach to Assist Water Treatment

AbstractThe removal of arsenic compounds from water is classified as an urgent concern by the World Health Organization, since many of these species are hazardous to human health. However, the conventional water treatments are not able to extract them, which makes the development of new methodologies of arsenic removal noteworthy. The application of metal‐organic frameworks (MOFs) as adsorbents to attend this purpose is very promising, because these materials can be intelligently built for the desired application. In this work, the performance of common subunits usually found in MOFs were individually evaluated for the adsorption of some arsenic species through computer simulations based on density functional theory (DFT). Thus, important information at molecular level was obtained, which can assist the design of an optimized adsorbent. Three factors were identified to strengthen the adsorption: ionic coordinate bond, hydrogen bonds, and cycle formation. Furthermore, the evaluated subunits showed to be proper for the removal of HAsO2, once the change in the Gibbs free energy was up to −30.8 kcal mol−1. The comparison with possible coexistent species showed that Cl−, , and can interfere with adsorptive process depending on the MOF composition and on the arsenic species to be removed from water.

Remediation of Arsenic and Heavy Metals and Soil Stabilization by Waste Chitosan based Biochar

Objectives : This study aims to evaluate the feasibility of converting waste chitosan adsorbents, laden with microalgae, into biochar for application as a stabilizing agent to remediate heavy metal-contaminated soil and improve soil quality.Methods : Waste chitosan adsorbents were converted into biochar through two processes: dry thermal carbonization at 400°C to produce pyrochar and hydrothermal carbonization at 200°C to produce hydrochar. The elemental compositions, surface functional groups, morphologies of the biochars were evaluated by elemental analyzer, FT-IR spectrometer, and SEM analysis. The arsenic and heavy metal adsorption characteristics of the produced biochars were assessed. Additionally, the produced biochars were applied as stabilizing agents to arsenic and heavy metal-contaminated soil with varying mixing ratios of 2, 5 and 10 wt%. After a one-week soil stabilization experiment, soil properties and TCLP(Toxicity Characteristic Leaching Procedure) leaching tests were conducted.Results and Discussion : The pyrochar produced from waste chitosan exhibited a porous structure with high pH (pH 10) and minimal surface functional groups. The hydrochar consisted of spherical particles with functional groups such as hydroxyl and amine groups on the surface, exhibiting a slightly acidic pH of 5.8. Pyrochar has a higher adsorption capacity for cationic heavy metals compared to hydrochar due to its porous structure and high pH. On the other hand, when applied to soil, hydrochar demonstrated superior stabilization efficiency for arsenic and heavy metals. This is attributed to the diverse surface functional groups containing oxygen on the hydrochar. The stabilization efficiency was influenced by the biochar mixing ratio, with a 5% hydrochar application resulting in 10-64% stabilization efficiency for all elements.Conclusion : This study confirmed that biochar produced from waste chitosan effectively stabilizes arsenic and heavy metals in soils. Additionally, the quantity of biochar used can impact its effectiveness in stabilization.

Harnessing wood bottom ash for efficient arsenic removal from wastewater: Adsorption mechanisms and process optimisation

This study explored the innovative application of wood bottom ash (WBA) as an adsorbent for arsenic (As) removal from wastewater, focusing on the adsorption mechanism and optimisation of the operational conditions. Comprehensive spectroscopic analyses, including FE-SEM/EDS, BET, XRF, XRD, FT-IR, and XPS, were performed to examine the elemental and mineralogical changes in WBA before and after As adsorption. The study assessed the adsorption kinetics and isotherms, revealing that As adsorption reached equilibrium within 48 h, with a maximum capacity of 121.13 mg/g. The adsorption process followed a pseudo-second-order kinetic model and aligned well with the Langmuir isotherm, indicating that the process is governed by chemisorption and occurs as monolayer adsorption. The primary removal mechanism was the surface precipitation of amorphous calcium arsenate. Response surface methodology was employed to analyse and optimise the factors influencing As removal, including solution pH, ionic strength, adsorbent dose and reaction time. The optimal conditions for maximum As removal were pH 7.11, 8.37 mM ionic strength, 9.08 g/L WBA dose, and 2.58 h reaction time. This study offers novel insights into the efficient and cost-effective use of WBA for As removal, highlighting its potential as a sustainable solution for wastewater treatment in developing countries.

Study on the nanocomposites of polyaniline and Zn doped Fe3O4 using for arsenic absorption in water

The polyaniline/Fe2.9Zn0.1O4 (PANI/Fe2.9Zn0.1O4) nanoparticles with different mass ratios were synthesized by both co-precipitation and in situ polymerization methods. The FT-IR spectra and DTA analyses showed the involvement of PANI in the nanocomposite samples. The grain size of samples measured by SEM ranges from 25 to 40 nm. The magnetization of samples at 300 K, H = 11000 Oe decreased from 65 to 43 emu g−1 as PANI/Fe2.9Zn0.1O4 mass ratio increased from 9% to 40%. At pH 7 and 300 K, the maximum arsenic (III) adsorption capacities of sample S1 (mass ratio of 9%) qmax = 43.48 mg g−1 was higher than that of others and Fe3O4. Additionally, the substitution of Fe2+ ions by Zn2+ ions and the presence of PANI in samples contributed to improving the magnetic and chemical stability of samples over time. Furthermore, these materials could be reused after desorption in a solution at pH 14.

A Route to Selective Arsenate Adsorption in Phosphate Solutions via Ternary Metal Biopolymer Composites

With the increased need for improved adsorbents for efficient water treatment, sodium alginate (NaAlg) and chitosan (Chi) represent promising platform biopolymers for the preparation of biocomposite adsorbents for the effective removal of waterborne oxyanion (arsenate (Asi) and orthophosphate (Pi)) contaminants. The TMCs were characterized by spectroscopy (infrared (IR), SEM with an energy dispersive X-ray (SEM-EDX)), point-of-zero-charge (PZC) measurements, and dye adsorption by employing p-nitrophenol at variable pH. Based on dye adsorption results, the adsorbent surface area (SA) was 271 m2/g for Al-TMC, 286 m2/g for Fe-TMC, and 311 m2/g for Cu-TMC. This indicates the role of adsorbent pore structure and swelling in water. Further, the role of either aluminum (Al), copper (Cu), or iron (Fe) for the preparation of TMCs for the selective Asi removal in the presence of Pi as a competitor anion was evaluated. While Al, Fe, and Cu coordinate to the biopolymer framework at C=O sites, only Fe coordinates to –NH2 sites. While Al coordinated via Al-O and interfacial hydroxy groups, Cu showed the formation of Cu2(OH)3NO3 in contrast to Fe, which observed FeOOH formation. Adsorption of Asi was highest for Al-TMC (80 mg/g), followed by Fe-TMC (77 mg/g) and Cu-TMC (31 mg/g). Adsorption of Pi was highest for Al-TMC (93 mg/g), followed by Fe-TMC (66 mg/g) and Cu-TMC (17 mg/g). While Al-TMC showed the highest adsorption capacity overall, only Fe-TMC (followed by Cu-TMC) showed strong arsenate selectivity over orthophosphate. The selectivity toward Asi in presence of Pi was determined and the binary separation factor (αt/c) and the selectivity coefficient (βt) were calculated, where Cu-TMC (αt/c = 6.1; βt = 4.4) and Fe-TMC (αt/c = 8.3; βt = 5.0) exceeded Al-TMC (αt/c = 1.5; βt = 1.2). This work contributes to the field of oxyanion-selective adsorbents via judicious selection of the metal salt precursor during the synthetic design of the ternary biocomposite systems, as demonstrated herein.

Simultaneous Removal of As(iii) and As(v) from Aqueous Solution by Using Iron-Functionalized Polythiophene: A Novel Approach toward Water Treatment.

Arsenic contamination in groundwater poses a significant threat to human health, affecting millions worldwide. This study presents a novel approach for simultaneous remediation of both As(III) and As(V) by using iron-functionalized polythiophene (PTh@Fe) composites. The PTh@Fe composite was synthesized by a reduction process involving FeCl2/FeCl3 byproducts of polymerization, resulting in a highly efficient adsorbent for both As(III) and As(V) species. The investigation systematically examined key parameters influencing arsenic removal, including adsorbent dosage, pH, initial arsenic concentration, and contact time. The composite exhibited exceptional adsorption capacities, with maximum removal percentages of 98.7% for As(III) and 98.8% for As(V) under the optimized conditions. Thermodynamic and kinetic analyses suggested endothermic and spontaneous adsorption processes following a pseudo 2nd-order mechanism. Furthermore, the Langmuir isotherm model provided an excellent fit to the experimental data, with maximum adsorption capacities of 8.62 mg/g for As(V) and 7.57 mg/g for As(III). Density functional theory (DFT) calculations confirmed the feasibility of arsenic adsorption onto iron species in various oxidation states, offering valuable theoretical insights into the process. Furthermore, the composite demonstrated good reusability over multiple adsorption-desorption cycles and tolerance to coexisting anions, highlighting its practical applicability for water purification. This research demonstrates the potential of iron-functionalized polythiophene composites as a promising solution for addressing arsenic contamination in water sources, bridging the gap between innovative materials and theoretical understanding in environmental science and water treatment technologies.

Hierarchical Anion Exchange and Reverse Electron Transfer in Layered Double Hydroxides/Peroxymonosulfate System for Roxarsone Elimination.

Roxarsone (ROX) is the main form of arsenic pollution in the world, and developing effective methods for its elimination is beneficial to human health and the ecological environment. Herein, we report glutaraldehyde cross-linked chitosan-encapsulated CoCe-LDH (layered double hydroxides) as an outstanding catalyst for the advanced oxidation of ROX and the efficient adsorption of inorganic arsenic. 100% of ROX and more than 98.5% of As(III)/As(V) were eliminated, and over 99.3% of remaining inorganic arsenic was oxidized to low-toxicity As(V) in the peroxymonosulfate (PMS) activation system, and some specific properties of LDH are considered the main reasons. The hierarchical anion exchange has been confirmed to be beneficial for constructing a high-concentration PMS interlayer microenvironment. The unique reverse electron transfer process induced 100% selective production of singlet oxygen. This work not only develops an advanced ROX removal method but also provides a new understanding of the LDH-based advanced oxidation process.

Room temperature synthesis of Ce based UiO-66 and UiO-66-NH2 metal organic frameworks for arsenic adsorption from aqueous solution

The exploration of a suitable adsorbent for removal of toxic elements is a challenging task and in this context we have employed UiO-66 (Ce) based Metal Organic Frameworks (MOFs) synthesized by a room temperature method for the remediation of arsenic from aqueous solutions. The synthesized UiO-66 (Ce) and UiO-66 (Ce)-NH2 MOFs were well characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), Thermogravimetry (TG), Brunauer–Emmett–Teller (B.E.T.), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Octahedral morphology was observed for UiO-66 (Ce) whereas the morphology of UiO-66 (Ce)-NH2 synthesized by this method was non-uniform. Bare MOF exhibited higher surface area and higher thermal stability in contrast to the amine functionalized MOF. We have studied the arsenic adsorption on both these MOFs in varying pH conditions. The adsorption isotherm studies revealed that bare MOF is much superior for adsorption of arsenic with adsorption capacity of ∼308 mg/g whereas the adsorption capacity of amine functionalized MOF was mere 70 mg/g. Adsorption kinetic studies demonstrated that MOFs follow Pseudo Second Order (PSO) model and elucidated that the adsorption process is predominantly chemisorption in nature. UiO-66 (Ce) could be successively used multiple times without much penalty in the adsorption capacity and the thermodynamics of adsorption suggested it to be spontaneous and favorable. Finally, an overview of the probable mechanism of adsorption is discussed by employing different experimental techniques like XRD, FT-IR and XPS.

How Fe-La-CS microspheres have selective adsorption capacity for As(V) over a wide pH range: Coupling molecular scale interpretation with experiments

In this study, an Fe-La-CS adsorbent with a reticulated structure was prepared by an in situ method, which was able to adsorb arsenate efficiently over a wide pH range of 3–11. The incorporation of iron and lanthanum ions broadened the tolerant pH range of the adsorbent compared with chitosan beads (CS). Arsenic was mainly present in the pH range of 3–9 as two forms, H2AsO4− and HAsO42−. Calculations using the density-functional theory (DFT) showed that in the Ligand interactions and electrostatic interactions dominate in the pH range, with surface precipitation, and hydrogen bonding interactions playing a facilitating role. The background ions mainly compete with arsenic adsorption for electrostatic interaction sites. However, due to the different valence states of the background ions, the competition intensity is different. Such as low valence state representative ions Na+, K+ competitiveness is weak, and arsenic competition adsorption first occupy different adsorption sites, therefore, from the quantum chemistry and molecular dynamics point of view of Na+, K+ on arsenic adsorption almost no effect. Cl−, SO42− will have some influence on arsenic adsorption because of the same charge with arsenic, but the charged amount is smaller than arsenic and the molecular structure is different from that of arsenic, so the influence is not very big. In summary, the material design of Fe-La-CS adsorbent has great potential and theoretical significance for selective purification of heavy metal wastewater at wide pH.

Construction of magnetic bimetallic oxide‐decorated attapulgite‐based adsorbents for arsenic ion adsorption

AbstractBACKGROUNDArsenic contamination can exert severe detrimental effects on the ecological environment and human health. It can cause acute or chronic poisoning, resulting in cell distortion or cancer when humans come into contact with or consume arsenic‐containing water. Adsorption technology is one of the effective methods for arsenic removal. In this study, using attapulgite (ATP) as a support for bimetallic iron–manganese oxides, a series of adsorbents (Fe‐Mn/ATP) with different manganese‐to‐iron molar ratios were prepared via the coprecipitation method. Scanning electron microscopy coupled with energy‐dispersive X‐ray spectroscopy mapping, X‐ray diffraction and zeta potential measurements were used to analyze the structure and properties of Fe‐Mn/ATP. In addition, the adsorption performance of the material for arsenic ions was investigated by static adsorption and dynamic adsorption experiments.RESULTSA novel Fe‐Mn/ATP adsorbent was prepared using ATP as the raw material and manganese‐to‐iron molar ratio was 1:3 by coprecipitation at 60 °C for 1 h. The adsorption efficiency of arsenic ions was optimal at an Fe‐Mn/ATP dosage of 2 g L−1, pH 4 and a contact time of 10 min, reaching a maximum adsorption capacity of 38.27 mg g−1 at room temperature. The adsorption process followed the pseudo‐second‐order kinetic model and the Langmuir isotherm adsorption model, indicating that arsenic ion adsorption by Fe‐Mn/ATP was mainly monolayer chemical adsorption. Furthermore, Fe‐Mn/ATP showed a removal rate for arsenic ions of over 80% after four cycles of regeneration, revealing a great potential for practical application.CONCLUSIONThis study offers a promising Fe‐Mn/ATP adsorbent for removal of arsenic ions from wastewater. © 2024 Society of Chemical Industry (SCI).