Arsenic Capture Research Articles

Removal of Chromium and Arsenic from Water Using Polyol-Functionalized Porous Aromatic Frameworks.

Chromium and arsenic are two of the most problematic water pollutants due to their high toxicity and prevalence in various water streams. While adsorption and ion-exchange processes have been applied for the efficient removal of numerous toxic contaminants, including heavy metals, from water, these technologies display relatively low overall performances and stabilities for the remediation of chromium and arsenic oxyanions. This work presents the use of polyol-functionalized porous aromatic framework (PAF) adsorbent materials that use chelation, ion-exchange, redox activity, and hydrogen-bonding interactions for the highly selective capture of chromium and arsenic from water. The chromium and arsenic binding mechanisms within these materials are probed using an array of characterization techniques, including X-ray absorption and X-ray photoelectron spectroscopies. Adsorption studies reveal that the functionalized porous aromatic frameworks (PAFs) achieve selective, near-instantaneous (reaching equilibrium capacity within 10 s), and high-capacity (2.5 mmol/g) binding performances owing to their targeted chemistries, high porosities, and high functional group loadings. Cycling tests further demonstrate that the top-performing PAF material can be recycled using mild acid and base washes without any measurable performance loss over at least ten adsorption-desorption cycles. Finally, we establish chemical design principles enabling the selective removal of chromium, arsenic, and boron from water. To achieve this, we show that PAFs appended with analogous binding groups exhibit differences in adsorption behavior, revealing the importance of binding group length and chemical identity.

Immobilization of gaseous As2O3 on γ-Fe2O3 (001) surface by forming monodentate and bidentate complexes: Insight from DFT study

Coal combustion is one primary anthropogenic emission source of atmospheric arsenic. Ferromagnetic γ-Fe2O3 has been regarded as an effective and promising immobilization sorbent for As2O3(g) in flue gas with good magnetic properties. The reported mechanism explorations about gaseous arsenic capture in flue gas by density functional theory (DFT) are mainly based on forming one chemical bond between arsenic and sorbent. Recent studies demonstrated that multidentate arsenic complexes could be formed with iron oxides in solution. However, the possible formation pathway of multidentate complexes between gaseous As2O3 and γ-Fe2O3 was not been reported yet. This is the first study to investigate the thermodynamics and quantum mechanics of bidentate complexes between As2O3(g) and γ-Fe2O3 (001) by DFT. Three kinds of arsenic bidentate complexes were discovered at γ-Fe2O3 (001) surface, including “2 O to 2 Feoct”, “2 O to Fetet & Feoct,” and “As & O to 2 Feoct,” which were named as configuration A, B and C, respectively. Configuration B, “2 O to Fetet & Feoct”, showed the lowest adsorption energy (Eads) among the three kinds of bidentate complexes. The Mulliken population analysis further confirmed the electron transfer between the atoms of newly formed chemical bonds in bidentate configurations. In addition, the projected density of states (PDOS) analysis exhibiting resonance peaks also showed the formation of hybrid orbitals. The criteria for the determination of bidentate complexes were also proposed. The results evidence a convincing conclusion that monodentate and bidentate complexes with stable chemical bonds can be formed when As2O3(g) is immobilized by γ-Fe2O3 (001).

The influence mechanism of SO2 on the capture of gaseous arsenic by pyrolusite

Removal of gaseous arsenic from copper smelting flue gas by solid-phase adsorption effectively reduces the emission of arsenic-containing pollutants into the atmosphere. Nevertheless, the high concentration of SO2 in the flue gas unavoidably impacts the effectiveness of the adsorbent in capturing gaseous arsenic. Currently, there is no research focusing on the adsorption capacity of pyrolusite (PY) for As2O3(g), including the influence of SO2. This study examines the capacities of PY to capture As2O3(g) with and without SO2 under different conditions and delves into the mechanism by which SO2 affects the capture of As2O3(g) by PY. Compared to the states without SO2, the As2O3(g) capture by PY in an atmosphere containing SO2 (2.5 v/v% SO2) decreased to 89.1 % at 400 °C. SO2 can diminish the As2O3(g) capture capacity of PY by competing for active sites, generating sulfate (MnSO4), inhibiting arsenic oxidation, and obstructing the pores of the adsorbent. In addition, SO2 enhances PY's As2O3(g) capture capacity by creating (As2O2)SO4 and forming new active centers. Moreover, the phase transition of PY guided by the high concentration of SO2 during As2O3(g) capture also favors arsenic capture. This research confirms that PY has substantial potential for effectively removing As2O3(g) from high-SO2 flue gas.

Mechanistic assessment of arsenic capture by aluminum-promoted calcium oxide and its consequences for As2O3 oxidation

Doping techniques have the potential to enhance the adsorption and oxidation of As2O3 by metal oxides for the augmentation of arsenic capture. However, the mechanisms of this facilitating effect, especially concerning the oxidation of As2O3, require further exploration. This study focuses on the effect of Al doping on As2O3 adsorption and oxidation through experimental and density functional theory calculations. The introduction of aluminum increases the specific surface area and stimulates charge transfer, converting Ca atoms into new As2O3 adsorption sites with strong adsorption capacity. The arsenic capture capacity of Al2O3/CaO is almost twice that of CaO when the molar ratio of Al and Ca is 1:6. For arsenic oxidation, Al doping promotes the dissociation of O2 adsorbed on the sorbent surface, making it more prone to react with As2O3. This catalytic effect lowered the activation energy for the conversion of As(III) to As(V), increasing the oxidation efficiency by 2–10%. These results serve as valuable references for the development of efficient arsenic sorbents.

Fe-Ni bimetallic adsorbent for efficient As2O3 removal from coal-fired flue gas under a wide temperature range: Experimental and DFT study

Adding metal oxides in the furnace can effectively control the emission of heavy metal arsenic in the coal-fired flue gas, and α-Fe2O3 has excellent adsorption performance. However, single metal oxides still have defects such as easy sintering or weak oxidation ability during use, which significantly impact the adsorption effect of arsenic. In this work, a new Fe-Ni bimetallic adsorbent was prepared by hydrothermal calcination, and its mechanism of As2O3 adsorption was investigated in depth through the combination of experiment and theory. The experimental results show that the FN8 (Ni-doped molar percentage is 8%) adsorbent exhibits excellent performance, and its arsenic adsorption capacity reaches 405.60 mg/kg, which is more than twice the adsorption capacity of α-Fe2O3. Ni doping can not only regulate the electron transfer between the α-Fe2O3 interface and As, but also promote the conversion of lattice oxygen to chemisorbed oxygen in the system. In the temperature range of 500 °C–900 °C, the prepared FN8 adsorbent can maintain a good microsphere structure, avoid sintering and provide more adsorption sites, and its arsenic capture capacity is stronger than α-Fe2O3. The density functional theory further reveals the microscopic mechanism of improving the oxidation performance of Fe-Ni adsorbent. The results show that Fe-Ni adsorbent has lower adsorption energy than α-Fe2O3. This is due to the synergism of Ni and O, which leads to the redistribution of electrons on the α-Fe2O3 (001) surface, and the Ni atom provides more free electrons for O atoms, which ultimately promotes the oxidation ability of Fe-Ni adsorbent and forms an As-O covalent bond. The Fe-Ni bimetallic composite adsorbent proposed in this work provides a new idea of bimetallic adsorbent for the effective adsorption of arsenic in the flue gas.

Stable and efficient As2O3 removal from simulated flue gas using Al2O3/CaSiO3 prepared by anhydrous grinding and calcination method

CaSiO3 exhibits good arsenic capture performance, but it falls short of meeting the actual needs of power plants due to its susceptibility to acidic gases that inhibit its arsenic capture ability. In this study, an Al2O3/CaSiO3 adsorbent was prepared by combining the anhydrous grinding and calcining methods. Arsenic vapor capture was conducted in flue gas containing or free of SO2 and HCl within the temperature range of 800–1000 ℃. The research indicated that the preparation method used in this study resulted in uniform Al2O3 doping that was less prone to agglomeration, thereby creating a good pore structure. The Al2O3/CaSiO3 adsorbent exhibited the strongest arsenic capture capacity when the atomic molar ratio of Al/Si was 1:5, with an arsenic capture amount of 871.2 mg/kg, which was significantly higher than the capture capacity of the control group calcium silicate. The doping of Al atoms altered the structure and charge distribution of CaSiO3 silica-oxygen chains, resulting in the formation of Al active sites with higher adsorption energy, which is more favorable for the adsorption of arsenic. Although the Al2O3/CaSiO3 adsorbent reacts with acidic gases to form CaSO4 and CaCl2, which can inhibit arsenic capture, it still maintains a high arsenic capture rate. Al2O3/CaSiO3 has excellent arsenic removal, sintering resistance, and acid resistance, making it a promising composite adsorption material for arsenic removal.

Role of CO2 on trace arsenic and selenium separation from coal-fired flue gas by CaO

Coal-fired power plants have been recognized as a major source of arsenic and selenium emissions. Considering that the common temperature window exists, in which both As2O3, SeO2 and CO2 can be effectively captured by CaO-based adsorbents, new principles of CO2 presence affecting arsenic and selenium removal process were investigated by density functional theory (DFT) calculations. The results confirm the suppression role of CO2 on As2O3/SeO2 adsorption by CaO (100) surface. On the basis of single-molecule adsorption on CaO, the adsorption energies of As2O3 and SeO2 are −2.21 eV and −2.05 eV, which are stronger than that of CO2. Three molecules can be chemically adsorbed on CaO with the surface O atom as active sites, leading to the competition for adsorption sites on the CaO surface. Despite the higher preferential adsorption of As2O3 and SeO2 on CaO (100) than CO2, the presence of CO2 weakens the electron transfers from the surface O atoms to As and Se atoms in the co-adsorption configurations. Under the atmosphere of high-concentration CO2, the adsorption of CO2 on CaO surface primarily changes the original electronic field of CaO (100) surface, and abolishes the function of O sites for As2O3/SeO2 adsorption at the final stage of complete carbonation. As2O3 and SeO2 adsorb on the fully carbonated CaO surface by physisorption. The bond population and density of states verify that the presence of CO2 weakens the covalent bonds between the surface O atoms and As/Se atoms, and brings about the intermolecular repulsion in the following As2O3/SeO2 adsorption. In addition, the negative effect of CO2 on arsenic capture by CaO is more pronounced than that on selenium capture. Finally, four mechanisms including isolation mode, competition mode, low-degree carbonation mode and high-degree carbonation mode are determined to gain further insight into the structure-reaction correlation during arsenic and selenium removal from the microscopic aspect.

Capture gaseous arsenic in flue gas by amorphous iron manganese oxides with high SO2 resistance

In non-ferrous metal smelting, the problem of gaseous arsenic in high-sulfur flue gas is difficult to solve. Now we have developed oxygen-enriched amorphous iron manganese oxide (AFMBO) based on the unique superiority of iron-manganese oxide for arsenic capture to realize the effective control of gaseous arsenic in the non-ferrous smelting flue gas. The experimental results show that the arsenic adsorption capacity of AFMBO is up to 102.7 mg/g, which has surpassed most of the current adsorbents. In particular, AFMBO can effectively capture gaseous arsenic even at 12% v/v SO2 concentrations (88.45 mg/g). Moreover, the spent AFMBO possesses pronounced magnetic characteristics that make it easier to separate from dust, which is conducive to reducing the secondary environmental risk of arsenic. In terms of mechanism study, various characterization methods are used to explain the important role of lattice oxygen and adsorbed oxygen in the capture process of gaseous arsenic. Moreover, the reason for the efficient arsenic removal performance of AFMBO is also reasonably explained at the microscopic level. This study provides ideas and implications for gaseous arsenic pollution control research.

Unraveling the capture mechanism of gaseous As2O3 over H-ZSM-5 zeolite from coal-fired flue gas: Experimental and theoretical insights

Gaseous As2O3 discharged from coal-fired power plants results in severe detriments to the ecological environment. It is of great urgency to develop highly efficient As2O3 capture technology for reducing atmospheric arsenic contamination. Utilizing solid sorbents for gaseous As2O3 capture is a promising treatment for As2O3 capture. The zeolite of H-ZSM-5 was applied for As2O3 capture at high temperatures of 500–900 °C. Special attention was paid to clarifying its capture mechanism and identifying the influence of flue gas components via density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. Results revealed that due to high thermal stability with large specific areas, H-ZSM-5 demonstrated excellent arsenic capture at 500–900 °C. The captured arsenic consisted of As3+ and As5+ speciations, ascribed to As2O3 adsorption and oxidation. Moreover, As3+ and As5+ compounds were both through physisorption or chemisorption at 500–600 °C while dominant chemisorption at 700–900 °C. In particular, As3+ compounds were much more steadily fixed in products at all operating temperatures. Combining the characterization analysis and DFT calculations, it further verified that both Si–OH–Al groups and external Al species of H-ZSM-5 could chemisorb As2O3, and the latter exhibited much stronger affinities via orbital hybridization and electron transfer. The introduced O2 could facilitate As2O3 oxidation and fixation in H-ZSM-5, especially at a lower concentration of 2%. Additionally, H-ZSM-5 possessed great acid gas resistance for As2O3 capture under the concentration of NO or SO2 less than 500 ppm. AIMD simulations further identified that compared to NO and SO2, As2O3 was far more competitive and occupied the active sites of the Si–OH–Al groups and external Al species of H-ZSM-5. Overall, it demonstrated that H-ZSM-5 is a promising sorbent for As2O3 capture from coal-fired flue gas.

Crystallization-based upcycling of iron oxyhydroxide for efficient arsenic capture in contaminated soils

Arsenic (As)-contaminated soil inevitably exists in nature and has become a global challenge for a sustainable future. Current processes for As capture using natural and structurally engineered nanomaterials are neither scientifically nor economically viable. Here, we established a feasible strategy to enhance As-capture efficiency and ecosystem health by structurally reorganizing iron oxyhydroxide, a natural As stabilizer. We propose crystallization to reorganize FeOOH-acetate nanoplatelets (r-FAN), which is universal for either scalable chemical synthesis or reproduction from natural iron oxyhydroxide phases. The r-FAN with wide interlayer spacing immobilizes As species through a synergistic mechanism of electrostatic intercalation and surface chemisorption. The r-FAN rehabilitates the ecological fitness of As-contaminated artificial and mine soils, as manifested by the integrated bioassay results of collembolan and plants. Our findings will serve as a cornerstone for crystallization-based material engineering for sustainable environmental applications and for understanding the interactions between soil, nanoparticles, and contaminants.

Metal-Organic Framework with a Redox-Active Bridge Enables Electrochemically Highly Selective Removal of Arsenic from Water.

Selective removal of trace, highly toxic arsenic from water is vital to ensure an adequate and safe drinking water supply for over 230 million people around the globe affected by arsenic contamination. Here, we developed an Fe-based metal-organic framework (MOF) with a ferrocene (Fc) redox-active bridge (termed Fe-MIL-88B-Fc) for the highly selective removal of As(III) from water. At a cell voltage of 1.2 V, Fe-MIL-88B-Fc can selectively separate and oxidize As(III) into the less harmful As(V) state in the presence of a 100- to 1250-fold excess of competing electrolyte, with an uptake capacity of >110 mg-As g-1 adsorbent. The high affinity between the uncharged As(III) and the μ3-O trimer (-36.55 kcal mol-1) in Fe-MIL-88B-Fc and the electron transfer between As(III) and redox-active Fc+ synergistically govern the selective capture and conversion of arsenic. The Fe-based MOF demonstrates high selectivity and capacity to remediate arsenic-contaminated natural water at a low energy cost (0.025 kWh m-3). This study provides valuable guidance for the tailoring of effective and robust electrodes, which can lead to a wider application of electrochemical separation technologies.

Toward a greener approach to detect inorganic arsenic using the Gutzeit method and X-ray fluorescence spectroscopy.

Inorganic arsenic is a carcinogen repeatedly found in water and foods threatening global human health. Prior work applied the Gutzeit method and X-ray fluorescence spectroscopy to quantify inorganic arsenic based on a harmful chemical, i.e., mercury bromide, to capture the arsine gas. In this project, we explored silver nitrate as an alternative to mercury bromide for the capture and detection of inorganic arsenic. To compare the performance of mercury bromide and silver nitrate, two standard curves were established in the range from 0 to 33.3 µg/L after optimization of reaction conditions such as the quantity of reagents and reaction time. Our result shows silver nitrate-based standard curve had a lower limit of detection and limit of quantification at 1.02 µg/L and 3.40 µg/L, respectively, as compared to the one built upon mercury bromide that has limit of detection of 4.86 µg/L and limit of quantification of 16.2 µg/L. The relative higher sensitivity when using silver nitrate was contributed by the less interfering elements for X-ray fluorescence analysis and thus lower background signals. A commercial apple juice was studied for matrix inference, and the results show 85%-99% recoveries and 7.4%-24.5% relative standard deviation. In conclusion, we demonstrated silver nitrate is a better choice in terms of safety restrictions and detection capability at lower inorganic arsenic concentrations.

As2O3 capture from incineration flue gas by Fe2O3-modified porous carbon: Experimental and DFT insights

A series of Fe2O3-modified porous carbon sorbents (Fe/PC) were synthesized and used for As2O3 capture from incineration flue gas. The molecular interaction mechanism was investigated by theoretical calculations based on density functional theory (DFT). The results indicate that the flourishing pore structure and high specific surface area of porous carbon are beneficial for Fe2O3 dispersing, which provides affluent active sites for arsenic capture. Fe/PC sorbent with a Fe content of 14.93 wt% exhibited high arsenic removal capacity of 16.09–29.32 mg/g in a wide temperature window (150–400 °C). The pseudo-first-order model best fitted the experimental data of As2O3 removal. The influences of flue gas compositions depend on the adsorption temperature. H2O promoted arsenic removal at lower temperature. HCl and SO2 played facilitation roles in arsenic removal at higher temperature. The states of arsenic in sorbents were As3+ and As5+, both adsorption and oxidation processes are responsible for As2O3 removal by Fe/PC sorbents. DFT calculation results indicate that the O-hollow site on the Fe2O3 surface has the strongest adsorption affinity for As2O3. The deep orbital hybridization and electron sharing between As2O3 and Fe2O3 are responsible for the high adsorption performance of Fe/PC sorbent.

Gaseous Arsenic Capture in Flue Gas by CuCl2-Modified Halloysite Nanotube Composites with High-Temperature NOx and SOx Resistance.

Gaseous arsenic emitted from coal combustion flue gas (CCFG) causes not only severe contamination of the environment but also the failure of selective catalytic reduction (SCR) catalysts in power plants. Development of inexpensive and effective adsorbents or techniques for the removal of arsenic from high-temperature CCFG is crucial. In this study, halloysite nanotubes (HNTs) at low price were modified with CuCl2 (CuCl2-HNTs) through ultrasound assistance and applied for capturing As2O3(g) in simulated flue gas (SFG). Experiments on arsenic adsorption performance, adsorption mechanism, and adsorption energy based on density functional theory were performed. Modification with CuCl2 clearly enhanced the arsenic uptake capacity (approximately 12.3 mg/g) at 600 °C for SFG. The adsorbent exhibited favorable tolerance to high concentrations of NOx and SOx. The As2O3(III) was oxidized and transformed into As2O5(V) on the CuCl2-HNTs. The Al-O bridge had the highest adsorption energy for the O end of the As-O group (-2.986 eV), and the combination formed between arsenic-containing groups and aluminum was stable. In addition, the captured arsenic could be stabilized in the sorbent at high temperature, making it possible to use the sorbent before the SCR system. This demonstrates that CuCl2-HNTs is a promising sorbent for arsenic oxidation and removal from CCFG.

Preparation of CeO2/CaO with Anti-sintering for Efficient Capture of As2O3 from Flue Gas at a High Temperature

Arsenic emissions from coal-fired power plants are highly toxic and volatile, posing a serious threat to human health and the natural environment. The removal of arsenic from coal-fired flue gases has attracted widespread attention worldwide. Calcium-based sorbents can capture arsenic, thus solving the environmental problem of heavy metal arsenic pollution from coal-fired power plants, but its sintering and low capture efficiency impede its application. Doping CaO with CeO2 is an efficient technique to improve resistance to sintering and facilitate capture efficiency. In this study, the CeO2/CaO sorbent was synthesized by the sol–gel method and then carried out in the flue gas at high temperatures from 600 to 900 °C to capture gaseous arsenic. The introduction of CeO2 not only reduces the grain size of CaO, but uniformly dispersed CeO2 forms a barrier layer that effectively prevents the growth and sintering of CaO grains. As a result, the sintering resistance of the sorbent is enhanced, and the sorbent exhibits excellent thermal stability. On the basis of characterization analysis, lattice oxygen provided by cerium oxide greatly promotes the reaction process of As(III) oxidation to As(V). The experimental results demonstrate that CeO2/CaO possesses the highest arsenic capture capacity compared to untreated CaO and CeO2. With the increase of the temperature, the capture efficiency of CeO2/CaO increases and reaches a maximum of 1.90 mg/g at 900 °C. Additionally, the density functional theory (DFT) was further used to study the adsorption energy of untreated CaO and CeO2/CaO. The results exhibited that CeO2/CaO has stronger adsorption capacity for As2O3. Finally, the adsorption mechanism of As2O3 on CeO2/CaO was proposed. As a result of the excellent anti-sintering property and high capture capacity, CeO2/CaO is expected to be an excellent sorbent for arsenic removal from coal combustion flue gas.

Microscopic Spherical α-Fe2O3 for Highly Efficient Gaseous Arsenic Capture in Simulated Flue Gas Under a Wide Temperature Range

Arsenic emitted from coal-fired flue gas poses a threat to human health and the ecological environment due to its high toxicity and bioaccumulation. In this work, the microscopic spherical α-Fe2O3 sorbent was prepared by a one-step hydrothermal method to effectively capture arsenic in the flue gas. The effects of reaction temperature, sulfur dioxide (SO2), nitric oxide (NO), oxygen (O2), and inlet arsenic concentration on its adsorption performance were investigated. The results showed that the most suitable adsorption temperature was 600 °C, and As2O3(g) was finally fixed in the product in the form of FeAsO4. SO2 and O2 played a positive role in the adsorption of arsenic, while NO displayed a slight effect on the adsorption of arsenic. In addition, the arsenic adsorption capacity improved with the increase of the inlet arsenic concentration. Based on its excellent arsenic removal performance and SO2 resistance performance, the α-Fe2O3 sorbent can be considered a promising material for arsenic removal.

Comprehensive insight into the role of HCl on arsenic capture by CaO during coal combustion: A combined experimental and theoretical study

Influence of HCl on As capture capability of CaO during coal combustion was studied in this work. Experimental results have confirmed the dramatic suppression role of HCl on As capture by CaO, and demonstrated the potential contributions of CaO chlorination to the inhibition role of HCl on As capture. Meanwhile, the clogging impact of HCl on CaO was omitted. For comprehensive understanding of inhibition mechanism of HCl, theoretical adsorption behaviors of As2O3(g) and AsCl3(g) on CaO (001) slab and CaCl2 (001) slab were investigated. It was concluded that chlorination of As2O3(g) and CaO both contributed to the inhibition effect of HCl, and the inhibition role of As2O3(g) chlorination was stronger than that of CaO chlorination. Comparing with the excellent activity of Ca and O sites in CaO (001) surface for As2O3(g) adsorption, CaO chlorination abolished the function of surface O, while As2O3 chlorination limited the activity of surface Ca. Moreover, interactions between AsCl3(g) and CaCl2 induced the offsetting effect of HCl on As capture capability of CaO. Correspondingly, the validity of As2O3(g) chlorination during coal combustion was verified. Moreover, it was also clarified that the suppression role of HCl on arsenic capture by CaO was better than that of SO2.

Novel monomers with N‐methyl‐D‐glucamine segments and their application in structured porous materials for arsenic capture

AbstractThe N‐methyl‐D‐glucamine moieties exhibit high ability and selectivity toward arsenate ions in water by a complexation mechanism that involves their hydroxyl groups. In this work, the syntheses of two monomers containing N‐methyl‐D‐glucamine, namely 4‐vinylbenzyl‐N‐methyl‐D‐glucamine (VbNMDG), and N‐methyl‐D‐glucamine methacrylamide (MNMDG) were studied. Different synthetic routes were considered in order to obtain liquid monomers able to polymerize and selectively capture arsenic. Furthermore, the incorporation of protective groups like trimethylsilyl moieties in the molecular structure was assessed to prevent transfer reactions during further polymerization. After polymerization, hydroxyl groups were deprotected using hydrofluoric acid. Following this methodology, structured microporous polymeric films based on colloidal crystal templates were prepared. NMR and FTIR techniques were used to follow the reactions and to determine the chemical structure of the obtained products. The morphology of materials was characterized by SEM. The performances of the developed polymeric films to selectively capture arsenic were determined. Films showed an improved and reproducible sensitivity to arsenic detection exhibiting high values of arsenic capturing capability (around 90%).

Determination on the activity of formed CaSO4 for arsenic adsorption during arsenic capture by CaO with the presence of SO2: Experimental and density functional theory study

Impact of SO2 on arsenic capture by CaO during oxy-coal combustion was investigated. The key question was to reveal the role of formed CaSO4 for arsenic capture. Drop tube furnace experiments verified that SO2 largely inhibited arsenic capture by CaO, and the adverse effect was assigned to the plugging and sulfation of CaO. Density functional theory study was further conducted to determine the impact of CaO transition to CaSO4 on arsenic adsorption. While, the feeble gap of adsorption energy between hexahedral As2O3 on CaO (001) surface and hexahedral As2O3 on CaSO4 (001) surface was incongruous with the apparently weakened arsenic capture capability of CaO by SO2. Then deformation of hexahedral As2O3 to chain As2O3 was firstly proposed to improve theoretical calculations, since the high combustion temperature and low deformation energy. Finally, huge adsorption energy gap between chain As2O3 on CaO (001) surface and chain As2O3 on CaSO4 (001) surface was observed. It not only demonstrated the much weaker activity of CaSO4 as opposed to CaO for As2O3 adsorption, but also confirmed the validity of As2O3 deformation. The widely applied hexahedral As2O3 structure was not the factual structure in flue gas during coal combustion, and the deformation should be concerned. Additionally, it was identified that Ca and O sites in CaO (001) surface were active for As2O3 adsorption. While, sulfur atoms in CaSO4 (001) surface were idle for As2O3 adsorption, and restricted the activity of surface O sites for As2O3 adsorption. Meanwhile, the activity of surface Ca sites was not affected by sulfur atoms.

Structure-tunable trivalent Fe-Al-based bimetallic organic frameworks for arsenic removal from contaminated water

Arsenic pollution of groundwater and surface water has come to the attention of the public. To explore economically affordable and efficient adsorbents for the treatment of arsenic, bimetallic MOFs based on trivalent iron and aluminum were synthesized and used to capture arsenic from wastewater. Characterization methods including SEM, EDX, XRD, and N2 adsorption–desorption were applied to analyze the morphology and element content, crystal structure, porosity and specific surface area of the Fe/Al-BDC-NH2 materials. The microstructures of bimetallic MOFs were tuned through changing the ratio of Al and Fe in the precursor material. Adsorption results show that introducing aluminum into the iron-based material formed bimetallic Fe/Al-BDC-NH2 MOFs that had much better adsorption performance for arsenic than the monometallic Fe-BDC-NH2 or Al-BDC-NH2 MOF. The adsorption isotherm of bimetallic MOF materials for arsenic is in accordance with the Langmuir isotherm model, and the maximum adsorption capability of Fe/Al-BDC-NH2 (1:1) at 298 K was 146.8 mg g−1. The kinetics of arsenic adsorption follow the pseudo-second-order model. Also, the thermodynamics indicate that arsenic adsorption is endothermic. Fe/Al-BDC-NH2 (1:1) is suitable for removal of arsenic from wastewater in a relatively wide pH range (5.0–9.0). Within this pH range, Fe and Al are hardly dissolved in water after arsenic capture, and this indicates that Fe/Al-BDC-NH2 (1:1) is very stable and suitable for arsenic capture from water without generating secondary pollution. Furthermore, through FTIR and XPS analysis, ligand exchange was identified as the main adsorption mechanism of Fe/Al-BDC-NH2 (1:1) for arsenic.