Selenate Adsorption Research Articles

Selenite Adsorption and Reduction via Iron(II) Impregnated Activated Carbon Produced from the Phosphoric Acid Activation of Construction Waste Wood.

Chemical activation of waste materials, to form activated carbon, (AC) is complicated by the large amounts of chemical activating agents required and wastewater produced. To address these problems, we have developed an optimized process for producing AC, by phosphoric acid activation of construction waste. Waste wood from construction sites was ground and treated with an optimized phosphoric acid digestion and activation that resulted in high surface areas (> 2000 m2/g) and a greater recovery of phosphoric acid. Subsequently the phosphoric acid activated carbon (PAC), was functionalized with iron salts and evaluated for its efficacy on the adsorption of selenite and selenate. Total phosphoric acid recovery was 96.7% for waste wood activated with 25% phosphoric acid at a 1:1 ratio, which is a substantially higher phosphoric acid recovery, than previous literature findings. Post activation impregnation of iron salts resulted in iron(II) species adsorbed to the PAC surface. The iron(II) chloride impregnated AC removed up to 11.41 ± 0.502mg selenium per g Iron-PAC. Competitive ions such as sulfate and nitrate had little effect on selenium adsorption, however, phosphate concentration did negatively impact the selenium uptake at high phosphate levels. At 250ppm, approximately 75% of adsorption capacity of both the selenate and the selenite solutions was lost, although selenium was still preferentially adsorbed. Peak adsorption occurred between a pH of 4 and 11, with a complete loss of adsorption at a pH of 13.

Simultaneous removal of selenium and microbial contamination from drinking water using modified ferrihydrite-based adsorbent

The ferrihydrite and modified ferrihydrite-based adsorbents were explored in the present study to remove selenate and bacterial contamination from drinking water. All the zinc-modified absorbents show >80 % bacterial count reduction, contrary to the unmodified adsorbents (30–40 % reduction). Ferrihydrite-based adsorbent modified with zinc (FH2–10) was the most efficient for selenate adsorption and exhibited the highest bactericidal activity. Sorption experiments showed that for Se (VI) concentration of 400 μg L−1, a sorbent dose of 0.5 g L−1 was sufficient to meet drinking water guidelines within the first 10 min. The maximum adsorption capacity of 40.984 mg/ g was obtained for FH2–10. The regeneration and reuse studies show that the selenium removal efficiency retained was >85 % even after three consecutive adsorption-desorption cycles. Column adsorption studies were performed to assess the adsorbent's field applicability, which inferred the adsorption capacity of 1.3 mg/ g. The FH2–10 adsorbent also showed >95 % bacterial growth reduction against E. coli. Hence the present detailed studies infer that FH2–10 is an efficient material for the simultaneous removal of selenium and bacterial contamination from drinking water, with potential for field application if the sulfate co-ions are not present in higher concentrations.

Self-reconstruction of (CoNiFeCuCr)Se high-entropy selenide for efficient oxygen evolution reaction

High-entropy materials (HEMs) have emerged as promising candidates of electrocatalysts owing to their unique structural features. Herein, flower-like high-entropy selenide (CoNiFeCuCr)Se (F-HES) is prepared by a two-step solvothermal method. F-HES demonstrates outstanding oxygen evolution reaction (OER) activity compared to other high-entropy catalysts, characteristic of 252 mV@100 mA·cm−2 along with excellent stability of 50 h, profiting from its specific structure and wide mesoporous distribution. The performance surpasses their quaternary, ternary, binary and unary counterparts can be attributed to the synergistic interaction among multiple metal species. Further investigations reveal the formation of metal (oxy)hydroxide where Co and Ni are more easily activated and the adsorption of selenate during anodization. Density functional theory (DFT) calculations demonstrate high-entropy coordination environment and surface-adsorbed selenate result in the enhanced intrinsic activity of active site and faster reaction kinetics. Meanwhile, the presence of interfacial selenate also improves the wetability of catalyst surface. This work provides a promising platform to design novel, outstanding HEMs for practical water electrolysis.

Mechanisms of selenate adsorption at the imogolite-water interface

Selenium (Se) can be toxic at high concentrations, mainly through exposure to contaminated groundwater and bioaccumulation in plants. Under oxidizing conditions, Se has preferential inorganic forms, Se oxyanions, which are highly soluble and weakly adsorbed on mineral surfaces. Therefore, retarding the release and migration of Se oxyanions is critical for the protection of groundwater quality. Imogolite is a tubular aluminosilicate with a high adsorptive capacity for anions, including IO3-, TcO4-, and PO43-. However, the potential adsorption of selenate on imogolite has not yet been evaluated to determine potential environmental applications including groundwater remediation. In this study, we synthesized and characterized imogolite using solid-state and electrostatic techniques. The synthesized imogolite was used to evaluate the adsorption of selenate under a range of physiochemical conditions using adsorption isotherms combined with various modeling techniques including the Freundlich model and the charge distribution at multi-site surface complexation (CD-MUSIC) model to decipher surface complexation mechanisms of selenate on imogolite. SynopsisAdsorption affinity and mechanisms of selenate on imogolite are mechanistically evaluated to understand potential environmental applications of imogolite for the protection of groundwater quality.

Sulfate availability and soil selenate adsorption alleviate selenium toxicity in rice plants

Selenium (Se) is a micronutrient for humans and other animals; however, it can cause severe toxicity at high concentrations. Selenium and sulfur (S) present a strict relationship in plants and soils, affecting their uptake and accumulations. Thus, addressing selenium-sulfur interaction is important to understand selenium nutrition and toxicity in plants, which could influence crop composition and production, and the toxicity risk to humans and animals. Here, we aimed to evaluate the impact of selenium exposure on rice plants grown under different sulfur supplies at tillering and grain ripening phases. We studied the effects of selenate and sulfate doses on rice plants grown hydroponically or in soils with varying clay contents. In the hydroponic experiment (short-term experiment), rice plants were grown until tillering stage under combinations of two concentrations of Se (0 and 20 µM Se) and S (0.1 and 0.5 mM S) in the nutrient solution. In the long-term, rice plants were grown until the ripening stage in two Oxisols with different clay contents (240 and 620 g kg−1 clay) under combinations of five doses of Se (0; 0.5; 1.0; 2.0 and 4.0 mg dm−3 Se) and three doses of S (0; 45; and 90 mg dm−3 S). We also performed sorption assays to evaluate the influence of soil clay content (240 and 620 g kg−1 clay) and S doses (0; 45; and 90 mg dm−3 S) on selenate adsorption and desorption at exposure to 4.0 mg kg−1 Se. Sulfate supply alleviated selenate toxicity in both short-term and long-term experiments. Selenate treatment up-regulated the expression of sulfate transporters (OsSULTR1;1 and OsSULTR1;2), leading to increased sulfur contents in rice seedlings, which enhanced the antioxidant system (catalase and ascorbate peroxidase activities and glutathione content) and alleviated selenate toxicity. However, this enhanced mechanism is absent in seedlings grown under a low sulfur supply, presenting severe Se toxicity. Moreover, soil clay contents strongly influenced selenate availability. The higher clay content promoted a high selenate adsorption capacity (67% of Se added), resulting in lower selenium contents in shoots and grains and the absence of toxicity symptoms. In contrast, a lower clay content presented a low selenate adsorption capacity (24% of Se added), increasing the Se availability, which can favor the biofortification of crops. However, high selenate doses caused growth and yield impairment in rice cultivated in the soil with lower selenate adsorption, which exhibited higher Se concentrations in shoots and grains, increasing the risk of Se toxicity for humans and animals.

Sustainable selenium remediation from water using aluminium–iron mixed oxide: Batch and column adsorption studies

Selenium contamination of water resources has become a potential health risk issue. The application of aluminium–iron (AlFe) mixed oxide for the rapid adsorption of both selenite (IV) and selenate (VI) ions from water was studied. The synthesized AlFe mixed oxide was characterized to understand the morphological and structural properties. Batch adsorption experiments were performed to understand the adsorption performance with variable parameters. AlFe mixed oxide was found as efficient for both selenite (IV) and selenate (VI) ion adsorption over a wide pH range up to pH < 9. Adsorption experiments revealed that the dose of 0.1 g L−1 with an initial selenium concentration of 500 μg L−1 is sufficient to meet the WHO guideline value within the first 30 min of contact time. Langmuir, Temkin and Dubinin-Radushkevich (DR) adsorption isotherm and pseudo–second order kinetics presented better fitting for selenite (IV) and selenate (VI) ions with maximum adsorption capacity for Se(VI) and Se(IV) as 33.1 mg g−1 and 6.188 mg g−1 respectively. Column adsorption and regeneration were also studied to understand the practical applicability of the adsorbent. The adsorbent was regenerated using mild alkali and can further be reused without any significant decrease in adsorption efficiency.

Surface water H-bonding network is key controller of selenate adsorption on [0 1 2] α-alumina: An Ab-initio study

Selenate adsorption onto metal oxide surfaces is a cost-effective method to remove the toxin from drinking water systems. However, the low selectivity of metal oxides requires frequent sorbent replacement. The design of selective adsorbents is stymied because the surface factors controlling selenate adsorption remain unknown. We calculate adsorption energies of selenate on the (012) α-Al2O3 surface using density functional theory to unravel the physics that controls adsorption. Our model is validated against experiment by correctly predicting selenate removal efficiency as a function pH. We find that the selenate adsorption energy on the anhydrous α-Al2O3 surface is surprisingly anti-correlated with the fully solvated adsorption energy; therefore, the direct interaction between adsorbate and sorbent is eliminated as the controlling mechanism. Rather, the change in number of surface hydrogen bonds after adsorption is the factor most correlated with the adsorption energy (R2 > 0.8); and is thus determined to be the factor controlling selenate adsorption. We find that pH affects adsorption by controlling the number of surface protons available for H-bonding to selenate. This work demonstrates that adsorption prediction should not be made based on gas phase sorption energies and suggests that surface engineering which increases surface protonation may be an effective strategy for increasing selenate sorption.

Experimental study on migration and transformation of selenium species and DFT calculation in WFGD simulated slurry

Selenium is a harmful trace element emitted during the combustion process of coal-fired power plants. Most of the selenium is enriched in the downstream wet flue gas desulfurization system (WFGD). This study found that S2O82- is the most important factor affecting the oxidation of selenite. In the process of simulating slurry oxidation of selenite to selenate, the presence of S2O82- can increase the oxidation rate of selenate from about 50% to about 80%. At the same time, this study also considered the influence of selenium concentration, initial pH, SO2 concentration and temperature etc. on the transformation of selenium species. It was believed that the application of ORP to the indication of selenite oxidation status needs further demonstration. Energy Dispersive X-Ray Spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) were used to confirm the migration of selenium in the desulfurization slurry to gypsum. In addition, DFT calculation was performed to obtain theoretical parameters for the adsorption of selenite and selenate by gypsum. The results of this study are helpful to understand the transformation and migration of selenium in the desulfurization system, which provide theoretical support for the realization of selenium in-situ control.

Mechanisms of Selenate Adsorption at the Imogolite-Water Interface

Mechanisms of Selenate Adsorption at the Imogolite-Water Interface

Selenium desorption in tropical soils by sulfate and phosphate, and selenium biofortification of Mombaça grass under increasing rates of phosphate fertilisation

Selenium (Se) is essential for animals and humans, and studies assessing the influence of sulfur (S) and phosphorus (P) on Se availability and biofortification in tropical soils are required. This study evaluated the adsorption of selenate (SeVI) and selenite (SeIV) in two oxidic soils with contrasting soil texture and assessed effects of phosphate and sulfate as competitive anions on Se desorption. The study also examined Se biofortification of Panicum maximum cv. Mombaça grown in Se-treated clayey soil under increasing rates of P fertilisation. In the laboratory, different Se concentrations were added to soils for adsorption studies (0, 1, 2, 4 mg L–1 for SeVI and 0, 4, 8, 16 mg L–1 for SeIV), with Se desorption performed by adding different concentrations of P (0, 2.18, 4.36, 10.90, 21.90 mg L–1) or S (0, 3.75, 7.5, 15, 30 mg L–1). Mombaça grass was grown in pots for 43 days in the clayey soil fertilised with SeVI and increasing P rates. Selenium adsorption varied depending on Se speciation, Se rate and soil texture, with SeIV showing greater adsorption than SeVI. In general, amounts of SeVI desorbed increased with increasing addition of P and (mainly) S. However, only P had a positive effect for releasing SeIV from soils. At all SeVI rates added in the clayey soil, Se contents in the shoot dry matter of Mombaça grass increased with increasing P fertilisation rate, agreeing with the desorption results. Further studies combining desorption with biofortification data are recommended for assessing the influence of P in sandy clay loam tropical soils.

The adsorption of perchlorate, sulfate, selenate and water on Au(111)-textured electrodes from aqueous solutions: Simultaneous voltammetric, optical and microgravimetric studies

The adsorption of perchlorate, ClO4−(aq), sulfate, SO42−(aq) and selenate, SeO42−(aq) on Au(111)-textured single crystals from aqueous acidic solutions was examined as a function of the applied potential, E, by simultaneous voltammetry, normal incidence differential reflectance spectroscopy, ΔR/R, and electrochemical quartz crystal microbalance, EQCM, techniques. In particular, ΔR/R vs E data collected in pure 0.1 M HClO4 or the same electrolyte containing either 1 mM Na2SO4 or 1 mM Na2SeO4 could be quantitatively accounted for by using a simple model introduced in similar studies reported earlier in this laboratory. This model regards the ΔR/R response as arising from a sum of contributions from bare and adsorbate covered areas of the surface, which are, in each case, linear functions of the applied potential. Adsorption isotherms for ClO4−(aq), and SO42−(aq) on Au(111) from the literature allowed fitting of the model to data obtained in 1 mM Na2SO4 in 0.1 M HClO4 solutions. The two oxyanions were found to co-adsorb over a wide potential range, with SO42−(aq) fully displacing ClO4−(aq) for E > 1.25 V vs RHE. Analogous ΔR/R measurements involving 1 mM Na2SeO4 in 0.1 M HClO4 solutions combined with the model allowed calculation of the coverage of the two oxyanions as a function of E. The experimental isotherms enabled calculation of the mass densities for the adsorbed oxyanions, ρth, yielding values virtually identical to those derived from EQCM experiments, ρexp, for data recorded in the range ca. E < 0.73 V vs RHE in all three solutions. At higher potentials, however, ρexp were significantly larger than those predicted by the optical measurements, a behavior consistent with water co-adsorption.

Selective photocatalytic reduction of selenate over TiO2 in the presence of nitrate and sulfate in mine-impacted water

Selenium contamination is a critical global issue across numerous industries. Industrial waters such as mine-impacted water (MIW) can contain toxic levels of selenate, in addition to varying concentrations of many different dissolved species from the underlying strata, such as sulfate, carbonate, nitrate, organic matter, and many dissolved metals. The removal of selenate from MIW is desired, due to selenate's acute and chronic toxicity in aquatic ecosystems at elevated concentrations. However, due to the complexity of the water matrix and the presence of many other dissolved constituents, this is often very challenging. In this study, we present for the first time the reduction of selenate in a real industrial wastewater, namely MIW, and reveal a significant advantage of photocatalytic reduction; the ability to selectively reduce selenate from >500 μg L−1 to <2 μg L−1 in the presence of the more energetically favourable electron acceptor, nitrate (250× molar concentration of selenate) and high concentrations of sulfate (1,940× molar concentration of selenate). The presence and impacts of sulfate, chloride, carbonate, and nitrate on the competitive adsorption and reduction of selenate on TiO2 are thoroughly investigated for the first time, using formic acid as an electron hole scavenger. The electron transfer mechanism proposed follows TiO2 conduction band electrons are responsible for the reduction of selenate to elemental Se (Se0) and both carbon dioxide radicals (CO2·−) and Se conduction band electrons are responsible for the further reduction of Se0 to hydrogen selenide (H2Se).

Selenite and Selenate Adsorption on Low-Crystalline Magnesium Oxide Under Alkaline Conditions

Natural geochemical processes and anthropogenic activities produce selenium (Se)-containing wastewater, in which selenium is present as selenous acid (Se(IV)) and selenic acid (Se(VI)). Herein, we evaluated the Se removal performances of magnesium oxide (MgO) with different crystallinities at pH 10.5. Normal MgO and low-crystalline (LC-MgO) were reacted in 1, 2, and 5 mg dm−3 Se(IV) or Se(VI) solution for 120 min. The Se concentrations of both the species did not apparently decrease in the normal MgO systems. However, >90% of Se(IV) was successfully removed by LC-MgO within 5 min under all conditions. X-ray diffraction (XRD) analysis indicated that Se(IV) was removed via surface complexation on Mg(OH)2 formed by the rapid hydration of LC-MgO. The enhancement of Se removability of the LC-MgO system was explained by the rapid hydration of the higher surface area of LC-MgO when compared with that of normal MgO. Majority of the Se(VI) (60–80%) was removed by LC-MgO during the first 20 min; however, it was gradually released back into the solution over time. During hydration, the changing XRD peak patterns and zeta potential of LC-MgO indicated that the increased charge density obtained by the accumulation of Mg2+ released via MgO dissolution would cause the temporal uptake of Se(VI) in the interlayer of Mg(OH)2. Subsequently, the charge density decreased with the hydration of Mg2+, indicating that Se(VI) was redissolved. Therefore, LC-MgO is a promising material for treating Se-containing alkaline wastewater. However, short-time operation and low concentration (<1 mg dm−3) must be ensured for successful Se(VI) removal.

Conversion of cattle manure into functional material to remove selenate from wastewater

Herein, pyrolysis of cattle manure was conducted to synthesize an effective material for removing heavy metals (e.g., selenium) from water environments. To remove selenate from aqueous solution, iron-impregnated cattle manure biochar (Fe/CM–biochar) was synthesized. The Fe-impregnation was performed by pre-treating cattle manure before its pyrolysis. The pretreatment increased the biochar yield. Influence of various factors such as contacting time, initial selenate concentration, reaction temperature, pH, and presence of coexisting anions were explored by performing batch adsorption experiments. The selenate adsorption reached equilibrium within 15 min. The Langmuir model was better fitted to equilibrium adsorption data than the Freundlich model. The maximum adsorption capacity of Fe/CM–biochar was calculated to be 52.56 mg-Se/g, which is superior to other adsorbents reported in the literature. As the reaction temperature increased in the range (15–35) °C, selenate adsorption on Fe/CM–biochar showed an endothermic and nonspontaneous reaction. The enthalpy change during selenate adsorption was 18.44 kJ/mol, which ranges in physical adsorption. The increase of solution pH (3–11) reduced the selenate adsorption (46.4–37.7 mg-Se/g). The extent of co-existing anion impact on selenate adsorption followed an order of HPO42− > HCO3− > SO42− > NO3−. These results indicate that Fe/CM–biochar is an effective functional material for the removal of selenate from wastewater.

A comprehensive predictive model for selenate adsorption on oxide minerals

A comprehensive predictive model for selenate adsorption on oxide minerals

Selenate Adsorption from Water Using the Hydrous Iron Oxide-Impregnated Hybrid Polymer

Hybrid adsorbent, based on the cross-linked copolymer impregnated with hydrous iron oxide, was applied for the first time for Se(VI) adsorption from water. The influence of the initial solution pH, selenate concentration and contact time to adsorption capacity was investigated. Adsorbent regeneration was explored using a full factorial experimental design in order to optimize the volume, initial pH value and concentration of the applied NaCl solution as a reagent. Equilibrium state was described using the Langmuir model, while kinetics fitted the pseudo-first order. The maximum adsorption capacity was found to be 28.8 mg/g. Desorption efficiency increased up to 70%, and became statistically significant with the reagent concentration and pH increase, while the applied solution volume was found to be insignificant in the investigated range. Based on the results obtained, pH influence to the adsorption capacity, desorption efficiency, Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analysis of loaded adsorbent, it was concluded that the outer- and inner-sphere complexation are mechanisms responsible for Se(VI) separation from water. In addition to the experiments with synthetic solutions, the adsorbent performances in drinking water samples were explored, showing the purification efficiency up to 25%, depending on the initial Se(VI) concentration and water pH. Determined sorption capacity of the cross-linked copolymer impregnated with hydrous iron oxide and its ability for regeneration, candidate this material for further research, as a promising anionic species sorbent.

Enhanced Selenate Removal in Aqueous Phase by Copper-Coated Activated Carbon.

In this study, we prepared a novel sorbent derived from precipitating copper ion onto the surfaces of activated carbon (Cu-AC). The sorbents were comprehensively characterized by Brunauer–Emmett–Teller (BET), zeta potential analysis, SEM, XRD, and FTIR. Batch experiments were conducted to evaluate selenate removal by Cu-AC under different conditions. The results showed that Cu was uniformly coated on the AC surface. Copper pretreatment markedly decreased the specific surface area and total pore volume of AC, and changed its surface zeta potential from highly negative to low negative and even positive. The Cu-AC substantially improved selenate adsorption capacity from the 1.36 mg Se/g AC of raw AC to 3.32, 3.56, 4.23, and 4.48 mg Se/g AC after loading of 0.1, 0.5, 1.0, and 5 mmol Cu/g AC, respectively. The results of toxicity leaching test showed AC coated with ≤1.0 mmol Cu/g was acceptable for potential application. Selenate adsorption was significantly inhibited by high ionic strength (>50 mM NaCl) and pH (>10). The electrostatic attraction between positive surface charge of Cu-AC and selenate ions and hydrogen bonding between CuO and HSeO4− might contribute to selenate sorption. Evidence showed that the selenate adsorption might involve outer-sphere surface complexation. The adsorption data appeared to be better described by Langmuir than Freundlich isotherm. The spent adsorbent could be effectively regenerated by hydroxide for reuse. Only a little decrease of removal efficiency was observed in the second and third run. This study implies that Cu-coated AC is a potential adsorbent for sustainable removal selenate from relative low salinity water/wastewater.

Simultaneous removal of selenite and selenate from drinking water using mesoporous activated alumina

The present study reports detailed evaluation of mesoporous activated alumina (MAA) for simultaneous removal of two hazardous inorganic species of selenium, namely selenite and selanate, from drinking water. MAA was used after washing with deionized water followed by drying at 110 °C for 8 h. The material was characterized using pXRD, FTIR, zeta potential, SEM and BET surface area measurements. Batch adsorption studies were performed, and various adsorption isotherms and kinetic parameters were computed to delineate the mechanism of adsorption. It was observed that Freundlich adsorption isotherm was the best-fit model for both the species of selenium. The adsorption capacity obtained from Freundlich isotherm for selenite and selenate was found to be 9.02 µg g−1 and 5.38 µg g−1, respectively. Kinetics studies revealed that adsorption of selenite follows pseudo-second-order model, whereas selenate adsorption follows pseudo-first-order model. The efficiency of the material was also evaluated at different pH and in the presence of different competitive co-ions, which confirms efficacy of MAA at near-neutral pH and lower concentrations of competitive co-ions. Negligible changes in the pH were observed during the course of adsorption. Further, the saturated adsorbent was subjected to regeneration and reuse studies up to ten cycles, showing insignificant reduction in adsorption efficiency of the adsorbent during few initial cycles. The study infers the effectiveness of MAA as a potential adsorbent for drinking water treatment contaminated with selenium.

Ethylene glycol-induced metal alkoxides via phase-transfer catalyst as multi-talented adsorbents for boosted adsorption performance of toxic anions/oxyanions from waters

An outstanding multi-talented complex material for the removal of several toxic anions is of greater interest than that used for single-pollutant adsorption. Here, we report the synthesis of highly stable lanthanum- and zirconium-alkoxides (La-Alk and Zr-Alk) using a strong‐field ligand and the electron-donating nature of ethylene glycol (EG) through a phase-transfer catalyst, dodecyltrimethylammonium bromide (DTAB), was employed to boost the adsorption densities of various toxic anions, such as arsenate (AsO43−), arsenite (AsO33−), dichromate (Cr2O72−), phosphate (PO43−), fluoride (F−), and selenate (SeO42−) in water by the application of the basic concept of the HSAB principle. The adsorbents had been characterized before and after adsorption of highly concentrated toxic anions (each of 1 mM) using XPS, PXRD, FTIR, BET, and SEM, and the possible adsorption mechanism was elucidated. The coordination of EG over La(OH)3 and ZrO2 was confirmed by the FTIR and PXRD patterns. The SEM images of La-Alk revealed a regular flower-like structure, whereas the structure of Zr-Alk was spherical, which differs from their precursors or pristine forms. The selectivity and stability of the materials were confirmed by a study on the coexisting anions in a binary mixture solution and reusability studies by repeated use, respectively. We found that La-Alk was more selective for the adsorption of arsenate, dichromate, phosphate, fluoride, and selenate, whereas Zr-Alk was highly selective for arsenite at a concentration of 1 mM. We are certain that the multifunctional La- and Zr-Alk nanocomplexes developed in this study will be useful for practical applications in water and wastewater streams.

Preferential adsorption of selenium oxyanions onto {1 1 0} and {0 1 2} nano-hematite facets

As the commercial use of nano metal oxides, including iron oxides, becomes more prevalent, there is a need to understand functionality as it relates to the inherent properties of the nanomaterial. Many applications of nanomaterials rely on adsorption, ranging from catalysis to aqueous remediation. In this paper, adsorption of selenium (Se), an aqueous contaminant, is used as a model sorbate to elucidate the relationships of structure, property, and (adsorptive) function of nano-hematite (nα-Fe2O3). As such, six nα-Fe2O3 particles were synthesized controlling for size, shape and surface area without capping agents. Sorbent characteristics of the six particles were then assessed for their impact on selenite (HSeO3−) and selenate (SeO42−) adsorption capacity and mechanism. Mechanism was assessed using in-situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and extended X-ray absorption fine edge spectroscopy (EXAFS). Regression analyses were then performed to determine which characteristics best describe adsorption capacity and binding mechanisms of Se on nα-Fe2O3. The results demonstrate that crystal surface structure, specifically presence of the {0 1 2} facet promotes adsorption of Se and the presence of {0 1 2} facets promotes SeO42− sorption to a greater extent than HSeO3−. The data further indicates that {1 1 0} facets bind HSeO3− with binuclear complexes while {0 1 2} facets bind HSeO3− via mononuclear inner-sphere complexes. Specific nα-Fe2O3 facets also likely direct the ratio of inner to outer-sphere complexes in SeO42− adsorption.