Formation Of Inner-sphere Complexes Research Articles

Ferrihydrite-loaded water hyacinth-derived biochar for efficient removal of glyphosate from aqueous solution.

Ferrihydrite-loaded water hyacinth-derived biochar (FH/WHBC) was prepared by in-situ precipitation method to treat glyphosate-containing wastewater. The adsorption properties and mechanism, and actual application potential were deeply studied. Results showed that the adsorption performance of FH/WHBC was closely related with the precipitation pH condition, and the adsorbent prepared at pH 5.0 possessed the highest adsorption capacity of 116.8 mg/g for glyphosate. The isothermal and kinetic experiments showed that the adsorption of glyphosate was consistent with Langmuir model, and the adsorption process was rapid and could be achieved within 30 min. The prepared FH/WHBC was more suitable for application under high acidity environment, and could maintain the great adsorption performances in the presence of most co-existing ions. Besides, it also possessed a good regenerability. Under dynamic condition, the adsorption performance of FH/WHBC was not affected even at high flow rate and high glyphosate concentration. Furthermore, the FH/WHBC can keep excellent removal efficiency for glyphosate in wastewater treatment, and the concentration of glyphosate can be reduced to 0.06 mg·L-1, which was lower than the groundwater quality of class II mandated in China. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) characterization indicated that the adsorption of glyphosate on FH/WHBC was mainly accomplished through electrostatic adsorption and the formation of inner-sphere complexes. In brief, the prepared sorbent FH/WHBC was expected to be used in the treatment of industrial glyphosate wastewater.

Removal of 241Am from Aqueous Solutions by Adsorption on Sponge Gourd Biochar

Luffa cylindrica biomass was converted to biochar and the removal of 241Am by pristine and oxidized biochar fibers was investigated in laboratory and environmental water samples. This species has the added advantage of a unique microsponge structure that is beneficial for the production of porous adsorbents. The main purpose of this study was to valorize this biomass to produce an efficient adsorbent and investigate its performance in radionuclide-contaminated waters. Following the preparation of Am3+ solutions at a concentration of 10-12 mol/L, the adsorption efficiency (Kd) was determined as a function of pH, adsorbent mass, ionic strength, temperature, and type of aqueous solution by batch experiments. At the optimum adsorbent dose of 0.1 g and pH value of 4, a log10Kd value of 4.2 was achieved by the oxidized biochar sample. The effect of temperature and ionic strength indicated that adsorption is an endothermic and entropy-driven process (ΔH° = -512 kJ mol-1 and ΔS° = -1.2 J K-1 mol-1) leading to the formation of inner-sphere complexes. The adsorption kinetics were relatively slow (24 h equilibrium time) due to the slow diffusion of the radionuclide to the biochar surface and fitted well to the pseudo-first-order kinetic model. Oxidized biochar performed better compared to the unmodified sample and overall appears to be an efficient adsorbent for the treatment of 241Am-contaminated waters, even at ultra-trace concentrations.

Remediation of chromium(VI) in contaminated soil by schwertmannite: Leachability, long-term stability, and stabilization mechanism

It has been demonstrated that schwertmannite (Sch) has a strong adsorption ability for hexavalent chromium (Cr(VI)) in wastewater. However, the stabilization of Cr(VI) in soil by Sch has not been studied. In this study, Sch was first applied to the remediation of Cr(VI) contaminated soil. The stabilization effectiveness of Cr(VI) in soils was evaluated by the toxicity leaching tests. A pH-dependent leaching test was used to study the changes in leaching behavior when pH changed on site. The long-term stability of Cr(VI) by Sch was investigated through an up-flow column percolation test. The products of Cr(VI) adsorbed by Sch were characterized, and the stabilization mechanism of Cr(VI) on Sch was discussed. The results showed that in high and low concentrations of Cr-contaminated soil, a 10% addition of Sch reduced the leached- Cr(VI) concentration by 79.96% and 86.59%, respectively. The maximum leachable rate of Cr(VI) was reduced by 20.23% after 10% Sch treatment. The cumulative release rate of Cr(VI) was decreased by 85.79% when the cumulative liquid-solid ratio reached 20. The stabilization of Cr(VI) on Sch was mainly due to the ion exchange of CrO42- with SO42- and the formation of inner-sphere complexes. The results demonstrated that Sch has a significant stabilization effect and long-term stability on soil Cr(VI).

Thallium adsorption on three iron (hydr)oxides and Tl isotopic fractionation induced by adsorption on ferrihydrite

Thallium (Tl) is an extraordinarily toxic metal, which is usually present with Tl(I) and highly mobile in aquatic environment. Limited knowledge is available on the adsorption and isotopic variations of Tl(I) to Fe-(hydr)oxides. Herein, the adsorption behavior and mechanism of Tl(I) on representative Fe-(hydr)oxides, i.e. goethite, hematite, and ferrihydrite, were comparatively investigated kineticly and isothermally, additional to crystal structure modelling and Tl isotope composition (205Tl/203Tl). The results showed that ferrihydrite exhibited overall higher Tl(I) adsorption capacity (1.11–10.86 mg/kg) than goethite (0.21–1.83 mg/kg) and hematite (0.14–2.35 mg/kg), and adsorption by the three prevalent Fe-minerals presented strong pH and ionic strength dependence. The magnitude of Tl isotopic fractionation during Tl(I) adsorption to ferrihydrite (αsolid-solution ≈ 1.00022–1.00037) was smaller than previously observed fractionation between Mn oxides and aqueous Tl(I) (αsolid-solution ≈ 1.0002–1.0015). The notable difference is likely that whether oxidation of Tl(I) occurred during Tl adsorption to the mineral surfaces. This study found a small but detectable Tl isotopic fractionation during Tl(I) adsorption to ferrihydrite and heavier Tl isotope was slightly preferentially adsorbed on surface of ferrihydrite, which was attributed to the formation of inner-sphere complex between Tl and ≡Fe–OH. The findings offer a new understanding of the migration and fate of 205Tl/203Tl during Tl(I) adsorption to Fe (hydr)oxides.

Uranium Removal from Aqueous Solutions by Aerogel-Based Adsorbents-A Critical Review.

Aerogels are a class of lightweight, nanoporous, and nanostructured materials with diverse chemical compositions and a huge potential for applications in a broad spectrum of fields. This has led the IUPAC to include them in the top ten emerging technologies in chemistry for 2022. This review provides an overview of aerogel-based adsorbents that have been used for the removal and recovery of uranium from aqueous environments, as well as an insight into the physicochemical parameters affecting the adsorption efficiency and mechanism. Uranium removal is of particular interest regarding uranium analysis and recovery, to cover the present and future uranium needs for nuclear power energy production. Among the methods used, such as ion exchange, precipitation, and solvent extraction, adsorption-based technologies are very attractive due to their easy and low-cost implementation, as well as the wide spectrum of adsorbents available. Aerogel-based adsorbents present an extraordinary sorption capacity for hexavalent uranium that can be as high as 8.8 mol kg−1 (2088 g kg−1). The adsorption data generally follow the Langmuir isotherm model, and the kinetic data are in most cases better described by the pseudo-second-order kinetic model. An evaluation of the thermodynamic data reveals that the adsorption is generally an endothermic, entropy-driven process (ΔH0, ΔS0 > 0). Spectroscopic studies (e.g., FTIR and XPS) indicate that the adsorption is based on the formation of inner-sphere complexes between surface active moieties and the uranyl cation. Regeneration and uranium recovery by acidification and complexation using carbonate or chelating ligands (e.g., EDTA) have been found to be successful. The application of aerogel-based adsorbents to uranium removal from industrial processes and uranium-contaminated waste waters was also successful, assuming that these materials could be very attractive as adsorbents in water treatment and uranium recovery technologies. However, the selectivity of the studied materials towards hexavalent uranium is limited, suggesting further developments of aerogel materials that could be modified by surface derivatization with chelating agents (e.g., salophen and iminodiacetate) presenting high selectivity for uranyl moieties.

Transport of double-stranded ribonucleic acids (dsRNA) and deoxyribonucleic acids (DNA) in sand and iron oxide-coated sand columns under varying solution chemistries.

Assessing ecological risks associated with the use of genetically modified RNA interference crops demands an understanding of the fate of crop-released insecticidal double-stranded RNA (dsRNA) molecules in soils. We studied the adsorption of one dsRNA and two double-stranded DNA as model nucleic acids (NAs) during transport through sand- and iron oxide-coated sand (IOCS)-filled columns over a range of solution pH and ionic compositions. Consistent with NA-sand electrostatic repulsion, we observed only slight retention of NAs in sand columns. Conversely, pronounced NA retention in IOCS columns is consistent with strong and irreversible NA adsorption involving electrostatic attraction to and inner-sphere complex formation of NAs with iron oxide coatings. Adsorption of NAs to iron oxides revealed a fast and a slow kinetic adsorption regime, possibly caused by the excluded-area effect. Adsorption of NAs to sand and IOCS increased in the presence of dissolved Mg2+ and with increasing ionic strength, reflecting cation-bridging and screening of repulsive electrostatics, respectively. The co-solute phosphate and a pre-adsorbed dissolved organic matter isolate competitively suppressed dsRNA adsorption to IOCS. Similar adsorption characteristics of dsRNA and similarly sized DNA suggest that existing information on DNA adsorption to soil particles helps in predicting adsorption and fate of dsRNA molecules in soils.

Sulfadiazine oxidation by peroxodisulfate and cobalt loaded graphitic biochar system: The dominant role of graphitic domain

A series of Co and biochar composite catalysts were fabricated by impregnation-pyrolyzation, acid-etching, and second annealing. The peroxodisulfate (PDS) activation capacity of these catalysts were evaluated among which the catalyst with largest surface area and graphitization degree achieved the best sulfadiazine (SDZ) degradation performance. The result of mechanism research excluded the essential contribution of Co species toward PDS activation, and pinpointed the paramount role of a single electron transfer pathway involved the formation of inner sphere complexes between catalyst and PDS (catalyst/PDS*), which could capture electron from SDZ, resulting in SDZ oxidation. The graphitic carbon with excellent electronic conductivity was discerned as the active site and especially the graphite microcrystals along c axis played more significant role in the catalytic degradation than the graphene sheet along a axis. The catalyst/PDS* originated from these catalysts with more graphitization degree possessed higher redox potentials and thereby stronger oxidation capacity. The selective degradation capacity of prepared catalyst and PDS system was demonstrated. Eight degradation intermediates from four proposed degradation pathways were identified and the toxicity of most transformation products was lower than that of SDZ.

Adsorption of Phosphate and Heavy Metals by Lanthanum Modified Zeolite and Its Performance in Sediment Inactivation

Due to the large scale of mining and smelting activities, considerable amounts of heavy metals are discharged into the environment and accumulate in the sediment of rivers and lakes. The combined pollution of heavy metals and the intrinsic phosphorus in sediment calls for novel remediation technologies. In this study, lanthanum-modified zeolite (LMZ) was employed as an inactivation agent for the immobilization of phosphorus, zinc, and lead in sediments. The adsorption capacities as well as the inactivation performance of LMZ for P, Zn, and Pb were investigated, and the adsorption mechanisms were explored via desorption experiments, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The results indicated that the adsorption maximums of LMZ for P, Zn, and Pb were 53.76, 27.70, and 123.45 mg·g-1, respectively. Pre-adsorption of Zn and Pb had a negligible effect on the P adsorption by LMZ, whereas the adsorption of Zn and Pb were inhibited significantly by the pre-adsorption. P, Zn, and Pb in the sediment were transformed to more stable or less bioavailable forms by dosing 0.83% and 1.66% weight percentages of LMZ. It was found that P, Zn, and Pb were adsorbed through the formation of inner-sphere complexes. Further, desorption experiments and XRD patterns suggested that electrostatic attraction and surface precipitation also contributed to the adsorption of Zn and Pb, respectively.

Insight into the molecular interaction of trace As (III) and As(V) onto the hybrid anion exchanger impregnated with Fe/Mn nanoparticles (HA502P-Fe/Mn)

In this study, a hybrid anion exchanger impregnated with Fe/Mn nanoparticles (HA502P-Fe/Mn) was synthesized via two-step mixed metal oxide precipitation using 50:50 % DI: ethanol as solvent. Trace As(III) and As(V) removal efficiency was comprehensively validated in both equilibrium adsorption isotherms and kinetics. The maximum adsorption capacities of HA502P-Fe/Mn toward As(III) and As(V) were 21,590 and 18,930 µg/g, respectively. The kinetics of As(III) removal were best predicted (R2 = 0.986) using a pseudo-second order model (k2 = 0.001 g/µg As(III)·min). Adsorption mechanisms were further characterized using X-ray absorption spectroscopy (XANES and EXAFS), including a comparison with the density functional theory (DFT) data. The XANES results showed complex redox transformation of the adsorbed As(V) on HA502P-Fe/Mn. The EXAFS spectra indicate predominant inner-sphere complex formation of bidentate mononuclear edge-sharing (2E) complexes for Mn-As (bond distance 2.94 Å), and bidentate binuclear corner-sharing (2C) complexes for Fe-As (bond distance 3.34 Å) on HA502P-Fe/Mn surfaces. Based on the DFT simulation, the obtained 3D structures were optimized, and the bond lengths between Fe-As and Mn-As were comparable with the EXAFS. For practical purposes, the fixed-bed column experiments were fully investigated for both As(III) and As(V) removal using NSF standard 53 test water (As(III) 300 ppb, pH 6.5), including the regeneration. The HA502P-Fe/Mn demonstrated 2X treatable bed volumes (4,300 vs 2,000 BVs) more than the commercially available As selective adsorbent. The experiments demonstrated that HA502P-Fe/Mn is a promising novel adsorbent for As(III) removal owing to its relatively high As adsorption capacity and regenerating ability.

Arsenic removal performance and mechanism from water on iron hydroxide nanopetalines

Human health has been seriously endangered by arsenic pollution in drinking water. In this paper, iron hydroxide nanopetalines were synthesized through a precipitation method using KBH4 and their performance and mechanism of As(V) and As(III) removal were investigated. The prepared material was characterized by SEM–EDX, XRD, BET, zeta potential and FTIR analyses. Batch experiments indicated that the iron hydroxide nanopetalines exhibited more excellent performance for As(V) and As(III) removal than ferrihydrite. The adsorption processes were very fast in the first stage, followed a relatively slower adsorption rate and reached equilibria after 24 h, and the reaction could be fitted best by the pseudo-second order model, followed by the Elovich model. The adsorption isotherm data followed to the Freundlich model, and the maximal adsorption capacities of As(V) and As(III) calculated by the Langmuir model were 217.76 and 91.74 mg/g at pH 4.0, respectively, whereas these values were 187.84 and 147.06 mg/g at pH 8.0, respectively. Thermodynamic studies indicated that the adsorption process was endothermic and spontaneous. The removal efficiencies of As(V) and As(III) were significantly affected by the solution pH and presence of PO43– and citrate. The reusability experiments showed that more than 67% of the removal efficiency of As(V) could be easily recovered after four cycles. The SEM and XRD analyses indicated that the surface morphology and crystal structure before and after arsenic removal were stable. Based on the analyses of FTIR, XRD and XPS, the predominant adsorption mechanism was the formation of inner-sphere surface complexes by the surface hydroxyl exchange reactions of Fe–OH groups with arsenic species. This research provides a new strategy for the development of arsenic immobilization materials and the results confirm that iron hydroxide nanopetalines could be considered as a promising material for removing arsenic from As-contaminated water for their highly efficient performance and stability.

Uranium Isotope (U-232) Removal from Waters by Biochar Fibers: An Adsorption Study in the Sub-Picomolar Concentration Range.

The adsorption of the U-232 radionuclide by biochar fibers in the sub-picomolar concentration range has been investigated in laboratory aqueous solutions and seawater samples. The adsorption efficiency (Kd values and % relative removal) of untreated and oxidized biochar samples towards U-232 has been investigated as a function of pH, adsorbent mass, ionic strength and temperature by means of batch-type experiments. According to the experimental data, the solution pH determines to a large degree the adsorption efficiency, and adsorbent mass and surface oxidation lead to significantly higher Kd values. The ionic strength and temperature effect indicate that the adsorption is based on the formation of inner-sphere complexes, and is an endothermic and entropy-driven process (ΔH° and ΔS° > 0), respectively. Regarding the sorption kinetics, the diffusion of U-232 from the solution to the biochar surface seems to be the rate-determining step. The application of biochar-based adsorbents to treat radioactively (U-232) contaminated waters reveals that these materials are very effective adsorbents, even in the sub-picomolar concentration range.

Complexation modelling and oxidation mechanism of organic pollutants in cotton pulp black liquor during iron salt precipitation and electrochemical treatment

Removal behavior of organic pollutants such as lignin in cotton pulp black liquor (CPBL) was investigated in precipitation followed by electrochemical oxidation (EO) using FeCl3, Fe2(SO4)3, FeCl2 and FeSO4 as precipitants, electrolyte and catalysts. Based on comparison of precipitation efficacy of iron salts, spectroscopic techniques, thermodynamic equilibrium calculations and molecular dynamics (MD) simulations were used to provide insight into the interaction between iron cations and lignin. The results showed that FeCl3 achieved the highest removal of chemical oxygen demand (COD, 76.05%), UV254 (69.21%) and lignin (78.28%). Iron cationic complexation with lignin was identified as the key mechanism in precipitation. Fe3+ was more active in binding to organic ligands mainly due to charge effect compared to Fe2+. The strong Fe−sulphate coordination affected the complexation with lignin. MD simulations showed the formation of inner sphere complexes of iron cations with deprotonated carboxyl and hydroxyl groups via bidentate and monodentate coordination. The removal efficiency of electrochemical oxidation (EO) as a post−treatment of the precipitation was dependent on iron salts. Removals of COD, UV254 and color can achieve 98.88%, 98.9% and 99.97% by FeCl3 precipitation and EO processes. The effluent reached the primary discharge standard specified in Integrated Wastewater Discharge Standard of China (GB8978−1996). FeCl3 demonstrated significant advantages in the removal of organic pollutants from cotton pulp black liquor in the combined process of precipitation and electrochemical treatment and may have practical application potential.

Efficient Removal of Polyvalent Metal Ions (Eu(III) and Th(IV)) from Aqueous Solutions by Polyurea-Crosslinked Alginate Aerogels.

The removal of polyvalent metal ions Eu(III) and Th(IV) from aqueous solutions using polyurea-crosslinked calcium alginate (X-alginate) aerogels has been investigated by batch-type experiments under ambient conditions and pH 3. The material presents relatively high sorption capacity for Eu(III) (550 g kg−1) and Th(IV) (211 g kg−1). The lower sorption capacity for Th(IV) compared to Eu(III) is attributed to the net charge of the dominant species in solution under the given experimental conditions, which is Eu3+ for Eu(III), and Th(OH)22+ and Th(OH)3+ for Th(IV). Generally, the sorption is an endothermic and entropy-driven process, and it follows the Langmuir isotherm model. According to the FTIR spectra, sorption occurs via formation of inner-sphere complexes between the surface functional groups and the f-metal cationic species. The presence of europium and thorium in the adsorbent material was confirmed and quantified with EDS analysis. To the best of our knowledge, this is the first report of an aerogel material used as an adsorbent for Eu(III). Compared to other materials used for the sorption of the specific ions, which are mostly carbon-based, X-alginate aerogels show by far the highest sorption capacity. Regarding Th(IV) uptake, X-alginate aerogels show the highest capacity per volume (27.9 g L−1) among the aerogels reported in the literature. Both Eu(III) and Th(IV) could be recovered from the beads by 65% and 70%, respectively. Furthermore, Th(VI) could also be quantitatively removed from wastewater, while Eu(III) could be removed by 20%. The above, along with their stability in aqueous environments, make X-alginate aerogels attractive candidates for water treatment and metal recovery applications.

Mechanism for the simultaneous removal of Sb(III) and Sb(V) from mining wastewater by phytosynthesized iron nanoparticles

Since antimony (Sb) is a toxic metalloid cost-effective method for the simultaneous removal of the two major Sb species from mining wastewater has attracted much attention. In this study, phytosynthesized iron nanoparticles (nFe) prepared using a eucalyptus leaf extract were successfully used to simultaneously remove Sb(III) and Sb(V) via an adsorption and oxidation mechanism with removal efficiencies of 100 and 97.7% for Sb(III) and Sb(V), respectively. Advanced analysis using X-ray photoelectron spectroscopy (XPS), ion chromatography-atomic fluorescence spectroscopy (IC-AFS), and electrochemical analysis confirmed that Sb(III) was oxidized to Sb(V) by Fe(III) on the nFe surface while Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) indicated that both Sb(III) and Sb(V) were adsorbed onto nFe. Adsorption of both Sb(III) and Sb(V) best fit the Langmuir adsorption model with R2 of 0.999 and 0.989, respectively and both followed pseudo-second-order kinetics with R2 of 0.999 and 0.981, respectively. Furthermore, the adsorption rate of Sb(III) was faster than that of Sb(V) due to inner-sphere complex formation, and the Fe–O bonds in the asymmetric tetrahedron structure of Sb(III) were easier to break due to a lower energy barrier (0.863 eV). Consequently, a simultaneous removal mechanism of Sb(III) and Sb(V) was proposed. Finally, nFe was used practically to remove Sb in mining wastewater with a removal efficiency of 93.5%, demonstrating that nFe have significant potential to remove Sb in contaminated mining wastewaters.

Co-precipitation synthesis of non-cytotoxic and magnetic cobalt ferrite nanoparticles for purging heavy metal from the aqueous medium: Pb(II) adsorption isotherms and kinetics study

ABSTRACT Owing to unique physical and chemical properties, nanostructured magnetic materials have proved their efficacy in treating heavy metals from the aqueous system. In this study, oleic acid-coated cobalt ferrite is synthesised by the co-precipitation method for the remediation of Pb(II) ions from an aqueous solution. The synthesised CoFe2O4@OA was characterised by various analytical techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), Fourier transform infrared spectroscopy (FT-IR) and dynamic light scattering (DLS). The non-cytotoxic behaviour of CoFe2O4@OA suggests it a risk-free adsorbent for the aquatic environment. The mechanism of adsorption reveals that electrostatic interaction, inner-sphere complex formation within Pb(II) ions and CoFe2O4@OA are responsible for the removal. The kinetics experiment followed the pseudo-second-order model with a regression coefficient (R 2) of 0.999. In the isothermal study, equilibrium data were well tuned with the Langmuir isotherm model with a maximum adsorption capacity of 16.7 mg g−1. The desorption experiment with a series of acid (HCl, HNO3) and alkali (NaOH, KOH) solvents informs the high dependency of desorption efficiency on the solvent type and concentration. Pb(II) ions removal efficiency using 0.5M HCL and 0.6M NaOH was attainted 98% and 82%, respectively, after three cycles. Thus, CoFe2O4@OA maintains sustainable development by reusing and saving the aquatic ecosystem by eliminating Pb(II) ions.

Reduction mechanism of Au(III) species adsorbed on δ-MnO2

Au(III)-chloride complex and its hydrolysis products, [AuCl4−n(OH)n]-, are typical Au species in the hydrosphere, and are known to be adsorbed and then reduced to Au(0) on some metal oxides. However, the process from adsorption to reduction has not been made clear. In this paper, adsorption of [AuCl4−n(OH)n]- was performed using two different metal oxides, Al2O3 and δ-MnO2. The experiments were performed for 72 h at pH 4.0, with Au(III) initial concentration of 0.10 mmol/dm3 and 1.0 g/dm3 of δ-MnO2 or Al2O3. The adsorption behavior of [AuCl4−n(OH)n]- differed greatly between the solids. On Al2O3, Au(III) complex ions formed outer sphere complexes and maintained their coordination structure even after adsorption. On the other hand, Au(III) complex ions formed inner sphere complexes on δ-MnO2 and the adsorption ratio reached 100% within 30 min. And then, the adsorbed Au(III) complex ions spontaneously reduced to Au(0). Detailed analysis of both the solid and liquid phases proved that the Au(III) complex ion, [AuCl1.67(OH)2.33]-, first adsorbed onto δ-MnO2 by exchanging its OH- with surface OH groups. After that, Cl-, which was originally coordinated to Au(III) complex ions, was gradually changed to OH- in water to form pseudo [Au(OH)4]- on the surface, and Au(III) was reduced. Our experimental results suggested that ligand exchange caused by the formation of inner sphere complexes is the key to inducing redox reactions after adsorption.

Efficient Sorption of Arsenic on Nanostructured Fe-Cu Binary Oxides: Influence of Structure and Crystallinity.

To study the structure-performance relationship, a series of nanostructured Fe-Cu binary oxides (FCBOs) were prepared by varying synthesis conditions. The obtained binary oxides were well characterized using X-ray diffraction (XRD), transmission electron microscope (TEM), Brunner-Emmet-Teller (BET), magnetic and Zeta potential measurement techniques. Both As(V) and As(III) sorption on the FCBOs were evaluated by batch tests. Results show that the surface structure and crystallinity of FCBOs are greatly dependent on preparation conditions. The crystallinity of FCBOs gradually increases as the synthesis pH value increasing from 9.0 to 13.0, from amorphous phase to well-crystalline one. Simultaneously, the morphology change of FCBOs from irregular agglomerate to relatively uniform polyhedron has been observed. The sorption of arsenic is greatly influenced by the crystallinity and structure of FCBOs, decreasing with increasing degree of crystallinity. The amorphous FCBO has higher surface hydroxyl density than well-crystalline one, which might be the reason of higher sorption performance. As(V) is sorbed by the FCBOs via formation of inner-sphere surface complexes and As(III) is sorbed through formation of both inner- and outer-sphere surface complexes. This investigation provides new insights into structure-performance relationship of the FCBO system, which are beneficial to develop new and efficient sorbents.

A Universal Synergistic Rule of Cd(II)-Sb(V) Coadsorption to Typical Soil Mineral and Organic Components

Heavy metals and metalloids are common cooccurrence in contaminated soils, making their behaviors more complex than their individual presences. Adsorption to soil minerals and organic components determines the solubility and mobility of heavy metals. However, little information is available regarding coadsorbing metals (e.g., Cd) and metalloids (e.g., Sb) to soil components, and whether there is a universal coadsorption rule needs to be illuminated. This study investigated the coadsorption behaviors of Cd(II) and Sb(V) to goethite, kaolinite, and bacteria ( Bacillus cereus) at both acidic (pH 4.5) and alkaline pH (pH 8.5). Equilibrium adsorption experiments, coupled with scanning electron microscopy- (SEM-) energy-dispersive X-ray spectrum (EDS) and X-ray photoelectron spectroscopy (XPS), were applied to determine the batch adsorption phenomena and possible mechanisms. Batch results showed that Cd(II) adsorption was greater at pH 8.5 whereas Sb(V) adsorption was greater at pH 4.5. The presence of Cd or Sb promoted each other’s adsorption to goethite, kaolinite, and bacteria, but slight differences were that Sb(V) preferred to enhance Cd(II) adsorption at acidic pH, whereas Cd(II) was more able to increase Sb(V) adsorption at alkaline pH. SEM-EDS analyses further showed that the distribution of Cd and Sb was colocalized. The surface FeOH, AlOH, and COOH groups participated in the binding of Cd(II) and Sb(V), probably through the formation of inner-sphere complexes. Two possible ternary complexes, i.e., sorbent-Cd2+-Sb(OH)6 – and sorbent-Sb(OH)6 –-Cd2+, were possibly formed. Both the charge effect and the formation of ternary complexes were responsible for the collaborative coadsorbing of Cd-Sb. The universal synergistic rule obtained suggests that current models for predicting Cd(II) or Sb(V) sequestration based on single systems may underestimate their solid-to-liquid distribution ratio in a coexistence situation. The results obtained have important implications for understanding the chemical behavior of Sb and Cd in contaminated soils.

CTAB-functionalized δ-FeOOH for the simultaneous removal of arsenate and phenylarsonic acid in phenylarsenic chemical warfare

This study prepared a cetyltrimethylammonium bromide (CTAB) functionalized δ-FeOOH using the coprecipitation method to remove arsenate and phenylarsonic acid in water polluted by phenylarsonic chemical warfare agents. Under neutral conditions, the adsorption capacity for arsenate and phenylarsonic acid was 45.7 and 85.3 mg g−1, respectively. The adsorption process conformed to the pseudo-second-order kinetics and Freundlich isothermal adsorption model, and the adsorption was spontaneous and endothermic. The CTAB-functionalized δ-FeOOH could effectively resist the interference of coexisting anions except for CO32−, SiO32− and PO43−. Furthermore, the adsorption mechanism was proposed by combining the adsorption experimental results, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and density functional theory analyses. The results showed that the adsorption of arsenate by the CTAB-functionalized δ-FeOOH was mainly through the formation of bidentate-dinuclear inner-sphere complexes and electrostatic interactions. While for phenylarsonic acid, the formation of monodentate-mononuclear inner-sphere complexes on (100) and (110) crystal facets, and the formation of bidentate-dinuclear inner-sphere complexes on the (002) crystal facet, as well as hydrogen bonding, electrostatic interaction, and π-hydrophobic interaction between organic compounds were the primary mechanism. Moreover, the CTAB-functionalized δ-FeOOH could maintain about 60% of the adsorption capacity for the two pollutants after five cycles. Overall, CTAB-functionalized δ-FeOOH has good potential for the remediation of inorganic and organic arsenic-contaminated water bodies.

Enhanced phosphate removal from solution using Al-doped aragonite nanoparticles

Attempts have been dealt to stabilize the aragonite (CaCO3) and improve its environmental applications for high concentration of phosphate removal by the introduction of aluminum (Al) species. The nano-pellets of aragonite doped with Al (Al/aragonite) was therefore manufactured in this study. With a combination of XRD, FTIR, zeta potential, SEM-EDX and XPS analysis, the synthesized Al/aragonite materials before/after phosphate sorption were characterized. The incorporation of Al species in aragonite lattice significantly increased the high phosphate scavenging from solution. Compared with the Langmuir monolayer coverage of phosphate on aragonite and calcite, the multi-layer sorption onto Al/aragonite could be described well by Freundlich model. Thus, the phosphate removal of Al/aragonite was 6 time stronger than aragonite, and 15 times than calcite at alkaline pH. The likely reason was that the Al species doped in Al/aragonite nanoparticles increased the surface area and reduced the negative surface charges, especially, provided the more adsorption sites for the formation of irreversible inner-sphere phosphate complexes which induced the vastly unlimited growth of CaHPO4 in the pH range of 5.0–12.0. Overall, the Al/aragonite nanoparticles (Al/Ca molar ratio = 0.205) was found to be the optimal material to efficiently remove the high-level phosphate from wastewater within the wide pH ranges.