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In this study, eco-friendly and magnetic sucrose-derived Fe-containing mesoporous carbon (Fe-MC) composites have been prepared by carbothermal reduction. The Fe-MC3-1000 prepared from sucrose and FeSO 4 with a mass ratio of 1:1 at 1000 °C has a uniform mesoporous structure with a BET surface area of 184 m2/g. The carbothermal reduction of Fe 2 O 3 had dual effects of the pore-forming and the loading. Batch adsorption experiments and electrochemical measurements show that the Fe-MC3-1000 has the optimum performance in both adsorption and supercapacitor applications. For adsorption, the maximum adsorption capacity for Congo red (CR) arrived at 972.1 mg g−1 with a removal percentage of 97.2 %. The adsorption process has good agreement with Langmuir isotherm and Elovich kinetic models. Besides, the Fe-MC3-1000 exhibits good recyclability after five adsorption-desorption cycles. For supercapacitor, the Fe-MC3-1000 electrode has a capacitance value of 179.23 F g−1 and a capacitance retention of 92.8 % at 10 A g−1 after 2000 cycles. The outstanding adsorption and electrochemical performances suggest that the Fe-MC3-1000 is a competitive bi-functional material for adsorption and supercapacitor. [Display omitted] • Magnetic Fe-containing mesoporous carbon was prepared via carbothermal reaction. • Low cost and eco-friendly raw materials promote its economy and sustainablity. • The carbothermal reduction of Fe 2 O 3 had dual effects of pore-forming and loading. • Both high adsorption capacities and removal percentages for CR were achieved. • The Fe-MC3-1000 had good electrochemical performance at a high current density. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pigment adsorption onto iron oxides is mainly due to electrostatic attraction. • The pigment-binding capacity is in the order of ferrihydrite > goethite > hematite. • The affinity of iron oxide towards pigment is in the sequence of AR > TA > BB. • Different mechanisms involved in pigment adsorption vary with pH values. • Pigments and Cu2+ have a mutual promotion effect on their adsorption. The knowledge about the adsorption properties of pigments onto different iron oxide minerals is still limited. The adsorption behaviors of three typical pigments, including amaranth (AR), tartrazine (TA), and brilliant blue (BB), onto three iron oxides (ferrihydrite, goethite, and hematite) were investigated. The primary mechanism of their interactions was the electrostatic attraction. The affinities of iron oxides toward any pigment were generally in the sequence of ferrihydrite > goethite > hematite (e.g., the maximum adsorption amounts (q max) of AR onto the three iron oxides were 35.5 mg/g, 11.6 mg/g, and 4.2 mg/g, respectively), which was related to the differences in physicochemical properties of minerals (e.g., specific surface area, surface hydroxyl density, and crystal structure). Interestingly, for a given iron oxide, the pigment-binding capacity of the mineral was in the order of AR > TA > BB. This effect was attributed to variations in pigment molecular sizes and electrostatic interactions between pigments and minerals. The pigment-binding capabilities of iron oxides changed as the solution pH varied. Hydrogen-bonding and electrostatic interactions were the main mechanisms below and above pH > pH PZC (pH value at zero point charge), respectively. Furthermore, adding Cu2+ facilitated pigment adsorption, mainly stemming from the surface-bridging effect. Pigments also enhanced Cu2+ adsorption onto iron oxides due to the decreasing electrostatic repulsion between Cu2+ and particles as well as the complexion between Cu2+ with pigment molecules adsorbed on mineral surfaces. The insightful information demonstrates that ubiquitous iron oxide minerals can affect the fate of pigments in natural environments. [ABSTRACT FROM AUTHOR]

• Fe(OH) 3 and α-FeOOH show highest efficiency for H 2 S/O 2 removal among the 35 samples. • BET surface area and Bronsted acid sites drive adsorption of H 2 S and O 2. • Performance of α-FeOOH was substantiated in a pilot plant with raw biogas. This study deals with the development of iron oxide/hydroxide adsorbents for the alternating removal of H 2 S and O 2 from natural gas and biogas. The considered procedure initially implies the chemisorption of H 2 S. In the second step, O 2 is removed by reaction with the H 2 S-treated substrate accompanied by regeneration of the adsorbent. 35 different iron-based samples were physical-chemically characterized and tested towards H 2 S/O 2 break through behavior and adsorption capacity to evaluate structure-performance correlations. It was derived that high BET surface area, high proportion of meso and micro pores, small average pore diameter, low crystallinity and high number of Bronsted acid sites are crucial properties of the adsorbents. As a consequence, Fe(OH) 3 and α-FeOOH revealed highest efficiency for the successive adsorption of H 2 S and O 2 , while α-Fe 2 O 3 provided rather low performance. Mechanistic investigations were carried out with α -FeOOH and α -Fe 2 O 3 indicating rapid dissociation of H 2 S on α -FeOOH, while slow molecular adsorption prevailed on α -Fe 2 O 3. With proceeding H 2 S exposure, the adsorbents were partially transformed into sulfide and sulfate species with some formation of elemental sulfur. In subsequent reaction with O 2 , the H 2 S-exposed samples were re-oxidized under partial restructuring, whereas elemental sulfur and sulfate entities were additionally produced. Finally, the concept of the alternating adsorption of H 2 S and O 2 on best α -FeOOH substrate was technically evaluated in a biogas pilot plant. The investigations showed efficient conversion of H 2 S for 40–100 h, while subsequent O 2 conversion was achieved for ca. 5.5 h. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel magnetic LLP@Fe 3 O 4 composite was successfully synthesized and characterized. • LLP@Fe 3 O 4 composite possessed a high surface area and good magnetic separation. • The adsorption capacity for MO was 282.3 mg/g by LLP@Fe 3 O 4 at 298 K. • Electrostatic interaction played an important role in the adsorption mechanism. • The removal rate of MO still reached 78.4% after five cycle regenerations. The goal of this work was to prepare a novel magnetic nanocomposite of Lotus leaf powder@iron oxide (LLP@Fe 3 O 4) to remove Methyl Orange (MO) from a liquid medium. The co-precipitation approach was used to successfully synthesize the LLP@Fe 3 O 4 composite, which was then characterized using FT-IR, XRD, pH PZC , SQUID-VSM, BJH/BET, and FE-SEM/EDX analysis. Batch tests were carried out to investigate the adsorption behaviour and mechanisms. The optimal MO removal efficiency of LLP@Fe 3 O 4 reached up to 94.3% under the optimum reaction conditions (LLP@Fe 3 O 4 dosage = 50 mg/30 mL, stirring speed = 200 rpm, contact period = 120 min, MO initial concentration = 20.8 mg/L, temperature = 298 K, and pH = 5.1). Adsorption isotherms and kinetics were analyzed using Temkin, Freundlich, Langmuir, Dubinin-Radushkevich (D-R), pseudo-second-order (PSO), intra-particle diffusion (IPD), pseudo-first-order (PFO), and Elovich models. Adsorption of MO on LLP@Fe 3 O 4 is best matched to the Langmuir isotherm and PSO kinetic models. The data was analyzed utilizing four errors (SSE, ARE, RMSE, and χ2) and regression coefficient functions to estimate the best-fitting kinetic and isotherm models. The maximal monolayer adsorption uptake of MO was estimated to be 282.3 mg/g at 298 K. The thermodynamic variables, namely entropy (Δ So = -98 J/mol K), enthalpy (Δ Ho = -35.6 kJ/mol), and Gibbs free energy (Δ Go = -6.2808 kJ/mol at 298 K), indicated that the adsorption of MO onto LLP@Fe 3 O 4 was spontaneous, exothermic, and feasible. The LLP@Fe 3 O 4 composite may be regenerated and readily separated from the liquid medium without losing any weight. After regeneration, the LLP@Fe 3 O 4 still has good adsorption efficiency for up to five cycles of adsorption and desorption. The experimental findings of this study output could be confirmed that LLP@Fe 3 O 4 is a potential adsorbent to remove dyestuff from wastewater. [ABSTRACT FROM AUTHOR]

Molybdenum (Mo) is a naturally-occurring trace element in drinking water. Most commonly, molybdate anions (MoO 4 2-) are in well water and breast milk. In addition, it is used in medical image testing. Recently, the EPA classified Mo as a potential contaminant, as exposure can lead to health effects such as gout, hyperuricemia, and even lung cancer. We have assessed the sorptive removal of aqueous molybdate using Douglas fir biochar (DFBC) and a hybrid DFBC/Fe 3 O 4 composite containing chemically-coprecipitated iron oxide (Fe 3 O 4). Adsorption was studied at various: pH values, equilibrium times (5 min-24 h), initial Mo concentrations (2.5–1000 mg/L), and temperatures (5, 25, and 40 °C) using batch sorption and fixed-bed column equilibrium methods. Langmuir capacities for DFBC and DFBC/Fe 3 O 4 (at pH 3, 2 hrs equilibrium) were within 459.3–487.9 mg/g and 288–572 mg/g, respectively. These adsorbents and their Mo-laden counterparts were characterized by elemental analysis, BET, PZC, SEM, TEM, EDS, XRD, and XPS. MoO 4 2- adsorption on DFBC is thought to be governed primarily via electrostatic attraction. Adsorption by DFBC/Fe 3 O 4 is primarily governed by chemisorption onto magnetite surface hydroxyl groups, while electrostatics prevail in the DFBC-exposed phase. Stoichiometric precipitation of iron molybdates triggered by iron dissolution was also considered. The data suggest that DFBC and DFBC/Fe 3 O 4 are promising candidates for molybdate sorption. [Display omitted] • Douglas fir biochar and its iron oxide analogue removed ∼500 mg/g aqueous molybdate. • Adsorption from anion mixtures and complex natural water was robust. • Fixed-bed column capacity for iron oxide/biochar was ∼19 mg/g. • Uptake was governed by chemisorption, hydrogen bonding and preciptiation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The preparation of multifunctional clay graphene oxide iron oxide nanocomposite was reported. • They prepared nanocomposite showed excellent methyl blue removal efficiency from wastewater. Multifunctional clay graphene oxide iron oxide nanocomposite was prepared for exploring the multiple applications by using single composite. Activated MM clay (local clay "Multani Matti") and graphene oxide (16 and 5%) were mixed gradually to already prepared Fe 2 O 3 nanoparticles followed by annealing at 550 °C to get the fine structured nanocomposite. Clay graphene oxide iron oxide nanocomposite structure was revealed to be face centered cubic with the average particle size of 13.31 nm. The JCPDS data card # (00–013-0458), (00–039-1894) and (00–001-0646) were used to confirm the XRD peaks of synthesized nanocomposite. The prepared nanocomposite showed colorimetric detection of ascorbic acid using paper sensor when treated with uric acid and ascorbic acid respectively. Antibacterial results confirmed the biologically active nature of synthesized material. The photo-luminescence peaks at higher absorption range correlate the minimum efficiency of photocatalytic application than that of adsorption. The adsorption and photocatalytic degradation of organic dyes are main perspectives observed for synthesized Clay/GO/Fe 2 O 3 nanomaterial. BET result shows a higher surface area confirming the capability of Clay/GO/Fe 2 O 3 nanomaterial an improved adsorbent material for removal of toxic dyes even in lower concentration. The nanocomposite showed capability of all the parameters of adsorption studies in terms of effect of contact time, initial dye concentration, adsorbent dosage, pH and temperature by removing methylene blue (MB). Results showed that adsorption of MB followed second order kinetic model. The improved performance of the nanocomposite compared to single phase materials proved to be an appealing contender being used as an efficient adsorbent which could replace conventional and multiple methods for treatment of waste waters as well. [ABSTRACT FROM AUTHOR]

• The adsorption mechanism of monolayer graphene and graphene oxide on the surface of iron oxide was studied by DFT calculations. • The presence of functional groups (hydroxyl and epoxy group) is beneficial for the enhancement of interfacial interaction of GO layer with iron oxide surface. • The enhancement of interfacial interaction has a strong correlation with the adsorption sites of functional groups. Density functional theory (DFT) calculations are performed to explore the effect of functional groups (hydroxyl and epoxy groups) on the interfacial interaction of graphene oxide (GO) with iron oxide (Fe 2 O 3) substrate. The calculation results indicate that the adsorbed functional groups can improve the interaction strength between GO and Fe 2 O 3 substrate, and the magnitude of binding energy enhancement is associate with the adsorption sites of functional groups. For the GO/Fe 2 O 3 -O models with a neighboring C atom of the oxidized atom at the top of a surface O atom, the binding energy is significantly enhanced, which arises from the formation of interfacial C−O covalent bonds. Moreover, the maximum binding energy of GO/Fe 2 O 3 -O model is more than four times that of Gr/Fe 2 O 3 -O model. For the other GO/Fe 2 O 3 -O and GO/Fe 2 O 3 -Fe models studied in this work, the GO layer is physisorption on Fe 2 O 3 surface and the binding energy enhances slightly. This study contributes to a deeper understanding of the protection properties of graphene-based coating materials on iron oxide surface. [Display omitted] [ABSTRACT FROM AUTHOR]

We prepared two-dimensional (2D) stack-structured magnetic iron oxide (Fe 3 O 4) nanoparticle anchored titanium carbide (Ti 3 C 2 T x) MXene material (Ti 3 C 2 T x /Fe 3 O 4). It was used as a potential adsorbent to remove carcinogenic cationic dyes, such as methylene blue (MB) and rhodamine B (Rh B), from aqueous solutions. Ti 3 C 2 T x /Fe 3 O 4 exhibited maximum adsorption capacities of 153 and 86 mg g−1 for MB and Rh B dyes, respectively. Batch adsorption experimental data fits the Langmuir model well, revealing monolayer adsorption of MB and Rh B onto the adsorption sites of Ti 3 C 2 T x /Fe 3 O 4. Additionally, Ti 3 C 2 T x /Fe 3 O 4 showed rapid MB/Rh B adsorption kinetics and attained equilibrium within 45 min. Moreover, Ti 3 C 2 T x /Fe 3 O 4 demonstrated recyclability over four cycles with high stability due to the presence of magnetic Fe 3 O 4 nanoparticles. Furthermore, it exhibited remarkable selectivities of 91% and 88% in the presence of co-existing cationic and anionic dyes, respectively. Given the extraordinary adsorption capacities, Ti 3 C 2 T x /Fe 3 O 4 may be a promising material for the effective removal of cationic dyes from aqueous media. [Display omitted] • Magnetic 2D MXene material towards multiple cationic dye sequestration. • Unprecedented MB and Rh B adsorption capacities of 153 and 86 mg g−1, respectively. • Presence of Fe 3 O 4 provides excellent regeneration capability with high stability. • High selectivities of 91 % and 88 % for MB and Rh B, respectively, with rapid kinetics. • MB and Rh B removal via electrostatic attraction and hydrogen bonding with MXene. [ABSTRACT FROM AUTHOR]

[Display omitted] • Alternating H 2 S and O 2 adsorption on Fe oxide/hydroxides was studied. • Bronsted acid sites were shown crucial for H 2 S uptake. • H 2 S adsorption led to strong transformation of the adsorbents into FeS and S 8. • O 2 exposure provided incomplete regeneration of the sulfurized adsorbents. Iron oxides are useful adsorbents for the alternating removal of H 2 S and O 2 from natural gas and biogas. In this context, the present paper aims to elucidate the mechanisms behind the consecutive adsorption of both gases. Three different types of iron oxides/hydroxides were investigated using in-situ infrared and Raman spectroscopy as well as ex-situ X-ray diffraction. The spectroscopic studies confirm that H 2 S is adsorbed on all kinds of surface sites, particularly at Brønsted and Lewis acid sites. However, on the Brønsted acid sites, H 2 S undergoes dissociation, leading to the formation of SH−, S2− and H 2 O. This mechanism substantiates the high H 2 S uptake capacity of the OH-containing adsorbents. Prolonged H 2 S adsorption provokes an increasing consumption of the adsorbent, yielding amorphous FeS and elemental sulfur, with hydrogen sulfate and sulfate species also forming as by-products. Furthermore, the subsequent O 2 adsorption on the sulfidized samples causes some re-formation of the initial adsorbent with the simultaneous production of elemental sulfur and sulfate entities. As a result of the mechanistic understanding gained in this study, it is concluded that the complete regeneration of the iron substrates is almost impossible due to their substantial degradation, associated with partial conversion into sulfates and the deposition of sulfur. [ABSTRACT FROM AUTHOR]

Agricultural processing by-product have been used as the feed stock for effluent treatment to promote the utilization of agricultural waste, the development of green sustainable and construct a green ecological circle nowadays. Based on camellia oleifera shells, attapulgite, and ferric chloride, a novel iron oxide loaded biochar/attapulgite composite (Fe-BC/A) was synthesized via a one-step pyrolysis process and as a low-priced and efficient adsorbent for Cr(VI) removal from aqueous solution. The structure and composition of Fe-BC/A were characterized by SEM-EDS, FT-IR, XRD, and XPS, which confirmed iron oxide (analogous to α-Fe 2 O 3 and β-FeOOH) and attapulgite clay were successfully incorporated with biochar. The maximum adsorption capacity of Cr(VI) by Fe-BC/A was 107 mg/g at pH 2.0, which was much higher than the original biochars (BC: 54.38 mg/g) and biochar/attapulgite composites (BC/A: 81.75 mg/g). The adsorption behavior of Fe-BC/A fitted better with pseudo second-order model and Freundlich model, which indicated that multilayer chemisorption might dominate Cr(VI) adsorption. The thermodynamic analysis of Fe-BC/A represented that removal of Cr(VI) was a spontaneous and endothermic process. Batch experiments results demonstrated that Fe-BC/A had great adsorption capability of Cr(VI) in a broad pH extent of 2.0–10.0, whose most favorable elimination for Cr(VI) at pH of 2.0 and the removal efficiency of Cr(VI) was about 80% at pH = 10 (C 0 = 100 mg/L, 30 °C). Fe-BC/A exhibited a prominent tolerance to the coexisting ions during Cr(VI) removal and only a slight decrease (8.27%) in elimination efficiency after five adsorption-desorption cycles. Mechanism study revealed that electrostatic attraction, reduction, anion exchange, and complexation were involved in the removal of Cr(VI). This study implied the potential practical application of Fe-BC/A in the future Cr(VI) remediation from wastewater. [Display omitted] • Fe-BC/A derived from camellia oleifera shells was synthesized by a simple method. • Efficient removal of Cr(VI) by introducing attapulgite and iron oxide into biochar. • Fe-BC/A showed great adsorption capability of Cr(VI) in a broad pH extent of 2.0–10.0. • Fe-BC/A exhibited a prominent tolerance to the coexisting ions during Cr(VI) removal. [ABSTRACT FROM AUTHOR]

Abstract: The NH3 reactivity was investigated over H-ZSM-5 and iron oxide deposited H-ZSM-5 by temperature-programmed surface interaction (TPSI) of adsorbed NH3 (NH3(ad)) with NO, O2, and “NO+O2”, and by steady-state dynamic reactions consisting of “NH3 +NO”, “NH3 +O2”, and “NH3 +NO+O2” systems. It was found that O2 primarily interacts with NH3(ad) on Brønsted acid sites. NO mainly interacts with NH3(ad) on Lewis acid sites, whereas its interaction with NH3(ad) on Brønsted acid sites results in N2O formation. TPSI provides direct evidence of the “fast” reaction of NO/NO2 with NH3(ad) on Brønsted acid sites in “NO+O2” environment, where O2 concentration plays a critical role. Iron oxide enhances all interactions, particularly those with NH3(ad) on Brønsted acid sites, as witnessed by both TPSI and steady-state reactions. But, iron oxide does not change the activation energy barrier for NH3 conversion, indicating that both acid sites and iron oxide are essential for NH3 SCR of NO x . As a result, a dual mechanism over Lewis and Brønsted acid sites was proposed. [Copyright &y& Elsevier]

The era of advanced computer simulations in materials science enables a great potential to design in silico computational experiments for (nano-)material performance. The adsorption efficiency of nanoparticles in various environments can be unveiled by atomistic models and computer simulations. Arsenic (As) is one of the important globally distributed contaminants with a hazardous impact on human health and environment, and it can strongly bind with iron nanocrystals (e.g., hematite (Fe 2 O 3)) depending on their shape and size. Here, we developed a novel Kinetic Monte Carlo (KMC) model capable of exploring and delineating shape-efficiency dependence for Fe 2 O 3 nanocrystals in contact with arsenate-contaminated water. This newly designed model demonstrated the performance of nanocrystals for removal of toxic (As) ions on their surface. The current model opens new avenues for designing further advanced KMC models for nanoparticles-toxic ions interactions, under varying environmentally relevant situations, e.g., groundwater, wetlands, and water treatment systems. In addition to bidentate adsorption complexes, implemented in the model presented, monodentate and outer-sphere adsorption complexes should be incorporated into the KMC model. Detailed environmental controls can be addressed by implementation of pH and background ions. [Display omitted] • Statistical mechanics is applied to reveal adsorption mechanisms of toxic ions. • Arsenate (As(V)) adsorption was modeled on iron oxide (hematite) nanocrystals. • As(V) concentration in water-nanoparticle system is efficiently predicted. • As(V) adsorption depends on shape of iron oxide nanocrystals. [ABSTRACT FROM AUTHOR]

Iron oxide/activated carbon (FeO/AC) composite adsorbent material, which was used to modify the coal-based activated carbon (AC) 12×40, was prepared by the special ferric oxide microcrystal in this study. This composite can be used as the adsorbent to remove arsenic from drinking water, and Langmuir isotherm adsorption equation well describes the experimental adsorption isotherms. Then, the arsenic desorption can subsequently be separated from the medium by using a 1% aqueous NaOH solution. The apparent characters and physical chemistry performances of FeO/AC composite were investigated by X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Batch and column adsorption experiments were carried out to investigate and compare the arsenic removal capability of the prepared FeO/AC composite material and virgin activated carbon. It can be concluded that: (1) the main phase present in this composite are magnetite (Fe3O4), maghemite (γ-Fe2O3), hematite (α-Fe2O3) and goethite (α-FeO(OH)); (2) the presence of iron oxides did not significantly affect the surface area or the pore structure of the activated carbon; (3) the comparisons between the adsorption isotherms of arsenic from aqueous solution onto the composite and virgin activated carbon showed that the FeO/AC composite behave an excellent capacity of adsorption arsenic than the virgin activated carbon; (4) column adsorption experiments with FeO/AC composite adsorbent showed that the arsenic could be removed to below 0.01mg/L within 1250mL empty bed volume when influent concentration was 0.5mg/L. [Copyright &y& Elsevier]

Abstract: A series of hydrous iron oxide samples were prepared by homogeneous precipitation from FeCl3 solution in the presence of SO4 2− ions. Experiments were conducted to study the removal of sulfate ions by varying pH, SO4 2−/Fe3+ molar ratio and the nature of the associated cation. Conventional methods including Infrared Spectroscopy, X-ray Diffraction and Thermal Analyses were used for the characterization of sulfate ions interactions with the hydrous iron surface. The results of macroscopic studies show that the removal of sulfate is highly pH dependent, it is greater at pH range [3–4] and it decreases as the molar ratio enhances. Thermal and IR analyses demonstrate strong interactions of sulfate ions with the hydrous iron oxide. In the pH range studied, the results are consistent with innersphere surface complexes. [Copyright &y& Elsevier]

Abstract: The oxidative removal of natural organic matter (NOM) from waters using hydrogen peroxide and iron-coated pumice particles as heterogeneous catalysts was investigated. Two NOM sources were tested: humic acid solution and a natural source water. Iron coated pumice removed about half of the dissolved organic carbon (DOC) concentration at a dose of 3000mgl−1 in 24h by adsorption only. Original pumice and peroxide dosed together provided UV absorbance reductions as high as 49%, mainly due to the presence of metal oxides including Al2O3, Fe2O3 and TiO2 in the natural pumice, which are known to catalyze the decomposition of peroxide forming strong oxidants. Coating the original pumice particles with iron oxides significantly enhanced the removal of NOM with peroxide. A strong linear correlation was found between iron contents of coated pumices and UV absorbance reductions. Peroxide consumption also correlated with UV absorbance reduction. Control experiments proved the effective coating and the stability of iron oxide species bound on pumice surfaces. Results overall indicated that in addition to adsorptive removal of NOM by metal oxides on pumice surfaces, surface reactions between iron oxides and peroxide result in the formation of strong oxidants, probably like hydroxyl radicals, which further oxidize both adsorbed NOM and remaining NOM in solution, similar to those in Fenton-like reactions. [Copyright &y& Elsevier]

This study investigates low-cost sorbents as replacements for current costly methods of removing heavy metals from solution. This investigation explores the waste iron oxide material (F1), which is a by-product of the fluidized-bed reactor (FBR)–Fenton reaction, for use in the treatment of the wastewater in Taiwan. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the F1. In this investigation, F1 are tested as adsorbents for removing copper (Cu2+) from aqueous solutions. The highest Cu2+ adsorption capacity of F1 adsorbent was determined as 0.21mmolg−1 for 0.8mmoldm−3 initial Cu2+ concentration at pH 6.0 and 300K. Adsorption data were well described by the Freundlich model and the thermodynamic constants of the adsorption process, ΔG°, ΔH° and ΔS° were evaluated as −6.12kJmol−1 (at 318K), 9.2kJmol−1 and 48.19Jmol−1 K−1 (at 318K), respectively. Additionally, a pseudo-second-order rate model was adopted to describe the kinetics of adsorption. [Copyright &y& Elsevier]

Abstract: Photocatalytic oxidation of arsenite and simultaneous removal of the generated arsenate from aqueous solution were investigated. The whole process was performed using an adsorbent developed by loading iron oxide and TiO2 on municipal solid waste melted slag. The loading was carried out through chemical reactions and high-temperature process. In the removal process, arsenite was first oxidized to arsenate, and then was removed by adsorption. The oxidation of arsenite was rapid, but the adsorption of the generated arsenate was slow. A concentration of 100mgl−1 arsenite could be entirely oxidized to arsenate within 3h in the presence of the adsorbent and under UV-light irradiation, but the equilibrium adsorption of the generated arsenate needed 10h. Arsenite could also be oxidized to arsenate only by UV-light, but the reaction rate was approximately 1/3 of that of the photocatalyzed reaction. Both acidic and alkaline conditions were favorable for the oxidation reaction, and the optimum pH value for the oxidation and adsorption was proposed to be around 3. To oxidize and remove original 20mgl−1 or 50mgl−1 arsenite from aqueous solution, the necessary adsorbent amount was 2gl−1 or 5gl−1, respectively. Furthermore, the surface properties of the adsorbent were examined and the oxidation mechanism of arsenite was discussed. It is believed that the adsorbent developed in this study is efficient, cost-effective and environment-friendly for application in arsenic-contaminated wastewater treatment. [Copyright &y& Elsevier]

The adsorption of methylene blue (MB) from an aqueous solution by polyacrylic acid-bound iron oxide magnetic nanoparticles was studied. It was shown that the novel magnetic nano-adsorbent was quite efficient for the adsorption/desorption of MB. In the aqueous solution of MB at 25 °C, the adsorption data could be fitted by the Langmuir equation with a maximum adsorption amount of 0.199 mg/mg and a Langmuir adsorption equilibrium constant of 10.1 ml/mg. The adsorption capacity increased with the increase in solution pH (2–10) and the adsorption process was endothermic in nature with an enthalpy change (ΔH) of 30.9 kJ/mol at 10–40 °C. By using the methanol solution of acetic acid, the adsorbed MB could be desorbed. In addition, it was notable that both the adsorption and desorption of MB were quite fast and could be completed within 2 min due to the absence of internal diffusion resistance. [Copyright &y& Elsevier]

• Selective flocculation is one of the plausible solid-solid separation methods. • Xanthan gum can be prudently used for selective flocculation of Fe 2 O 3 -SiO 2 mixture. • Xanthan gum interacts with Fe 2 O 3 through electrostatic forces and hydrogen bonding. The changes in the surface chemical properties of iron oxide and silica suspensions consequent to the addition of xanthan gum were studied. The adsorption density of xanthan gum for iron oxide was found to be maximum at pH ~ 2, whereas almost nil adsorption was found for silica throughout the pH range investigated. The isoelectric points (i.e.p.) of iron oxide and silica were found to be located at pH ~ 8.4 and presumably less than pH 2 respectively. The addition of xanthan gum shifted the i.e.p. of iron oxide towards more acidic pH values, in proportion with the concentration of xanthan gum added, with a concomitant change in the zeta potentials to more electronegative or less electropositive values. The maximum flocculation of iron oxide (98%) was observed in the wide pH regime of 2–9 with the optimum dosage of xanthan gum (20–50 ppm). The electrokinetic and flocculation characteristics of the silica were not altered much by the addition of xanthan gum, akin to the adsorption result. FTIR spectral investigations provide evidence in support of hydrogen bonding and chemical interaction forces between iron oxide and xanthan gum. Maximum separation efficiency of 65% for iron oxide-silica mixture was observed in selective flocculation tests. [ABSTRACT FROM AUTHOR]

• Pure hematite crystal mainly exposes {101}, {12}, {110} and {104} facets. • Al substitution for Fe decreases Cr(VI) adsorption density on hematite. • Cr(VI) forms more monodentate mononuclear complexes on Al-doped hematite surfaces. • Involvement of Fe2+ promotes Cr(VI) reduction and fixation on hematite. Aluminum substitution is common in iron (hydr)oxides in subsurface environments, and can significantly modify mineral interactions with contaminants. However, few studies investigate Cr(VI) adsorption and its subsequent mobility on Al-substituted iron (hydr)oxide surfaces. Here shows that Al substitution gradually modifies hematite crystals from {101}, {112}, {110} and {104} faceted rhombohedra to {001} faceted plates, resulting in a general decrease in Cr(VI) adsorption density and favoring of monodentate mononuclear over bidentate binuclear Cr(VI) adsorption complexes. Consequently, the mobility of Cr(VI) might be increased in environments with an abundance of Al-containing iron (hydr)oxides. However, pre-adsorption of Fe2+ on hematite promotes Cr(VI) adsorption, reduction and fixation, and Al-substituted hematite removes more Cr(VI) than pure hematite. Similarly, although addition of Fe2+ to Cr(VI)-adsorbed hematite remobilizes a small proportion of Cr, it greatly increases the proportion of Cr fixed. As the coexistence of Fe2+ and iron (hydr)oxides is common in subsurface environments, Al-containing iron (hydr)oxides will promote Cr(VI) uptake and retention, with a significant proportion fixed as Cr(III), limiting Cr mobility and toxicity. These results offer new insights into how iron (hydr)oxides might control the behaviors of other high-valence redox-sensitive contaminants, and provide a platform for modeling such processes in complex soil and sediment systems. [ABSTRACT FROM AUTHOR]