Search

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]

• 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]

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]

[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]

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: 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]

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]

• 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]