Selective adsorption of various phosphorus species coexistence in water-soluble ammonium polyphosphate on goethite: Experimental investigation and molecular dynamics simulation.

The geochemical processes of polyphosphates (poly-Ps) are important for phosphorus (P) management and environmental protection. Water-soluble ammonium polyphosphate (APP) containing various P species has been increasingly used as an alternative P-fertilizer. The various P species coexistence and the chelation of poly-Ps with mental would trigger the P's competitive adsorption and affect the APP's adsorption intensity on goethite, compared to single orthophosphate (P1). P adsorption behaviors of APP1 with two P species and APP2 with seven P species on goethite were investigated via batch experiments in comparison to the traditional P-fertilizer of mono-ammonium phosphate (MAP). Coadsorption of P1 and pyrophosphate (P2) on goethite was investigated by molecular dynamics (MD) simulation. The more Fe3+ dissolved from goethite as a bridge due to the chelation of poly-Ps in APP and contributed to the stronger APP adsorption on goethite compared with MAP. Ion chromatography and spectral analysis showed P1 and P2 in APP were mainly adsorbed by goethite via mainly forming bidentate complexes. The goethite preferentially adsorbed P1 at lower APP concentration but increased the poly-Ps' adsorption at higher APP concentration. MD simulation showed that electrostatic interaction and hydrogen bonds played a key role in water-phosphates-goethite systems. The P1 pre-adsorbed on goethite could be replaced by P2 at high P2 concentration. The results develop new insights regarding the selective adsorption of various P species coexistence in goethite-rich environments.

Fe3O4@C Nanoparticles Synthesized by In Situ Solid-Phase Method for Removal of Methylene Blue.

Fe3O4@C nanoparticles were prepared by an in situ, solid-phase reaction, without any precursor, using FeSO4, FeS2, and PVP K30 as raw materials. The nanoparticles were utilized to decolorize high concentrations methylene blue (MB). The results indicated that the maximum adsorption capacity of the Fe3O4@C nanoparticles was 18.52 mg/g, and that the adsorption process was exothermic. Additionally, by employing H2O2 as the initiator of a Fenton-like reaction, the removal efficiency of 100 mg/L MB reached ~99% with Fe3O4@C nanoparticles, while that of MB was only ~34% using pure Fe3O4 nanoparticles. The mechanism of H2O2 activated on the Fe3O4@C nanoparticles and the possible degradation pathways of MB are discussed. The Fe3O4@C nanoparticles retained high catalytic activity after five usage cycles. This work describes a facile method for producing Fe3O4@C nanoparticles with excellent catalytic reactivity, and therefore, represents a promising approach for the industrial production of Fe3O4@C nanoparticles for the treatment of high concentrations of dyes in wastewater.

A low-cost solvent-free method to synthesize α-Fe2O3 nanoparticles with applications to degrade methyl orange in photo-fenton system.

Hematite nanoparticles (α-Fe2O3 NPs) were successfully synthesized by a low-cost solvent-free reaction using Ferrous sulfate waste (FeSO4·7H2O) and pyrite (FeS2) as raw materials and employed for the decolorization of Methyl Orange by the photo-Fenton system. The properties of α-Fe2O3 NPs before and after photo-Fenton reaction were characterized by X-ray powder diffraction (XRD), Field emission scanning electron microscopy (FESEM), Fourier transform infrared (FT-IR) spectrum and X-ray photoelectron spectroscopy (XPS), and the optical properties of α-Fe2O3 NPs were analyzed by UV-vis diffuse reflectance spectra (UV-vis DRS) and Photoluminescence (PL) spectra. The analytic results showed that the as-formed samples having an average diameter of ~50 nm exhibit pure phase hematite with sphere structure. Besides, little differences were found by comparing the characterization data of the particles before and after the photo-Fenton reaction, indicating that the photo-Fenton reaction was carried out in solution rather than on the surface of α-Fe2O3 NPs. A 24 central composite design (CCD) coupled with response surface methodology (RSM) was applied to evaluate and optimize the important variables. A significant quadratic model (P-value<0.0001, R2 = 0.9664) was derived using an analysis of variance (ANOVA), which was adequate to perform the process variables optimization. The optimal process conditions were performed to be 395 nm of the light wavelength, pH 3.0, 5 mmol/L H2O2 and 1 g/L α-Fe2O3, and the decolorization efficiency of methyl orange was 99.55% at 4 min.

Heterogeneous activation of persulfate by ZnCo x Fe2-x O4 loaded on rice hull carbon for degrading bisphenol A.

A new low-cost composite of ZnCo x Fe2-x O4 loaded on rice hull carbon (ZnCo x Fe2-x O4-RHC) was synthesized via waste ferrous sulfate (the industrial waste produced in the process of producing titanium dioxide) and rice hull as raw materials, which was applied for the degradation of bisphenol A (BPA) by heterogeneous activated peroxodisulfate (PS). A series of characterizations including XRD, SEM, FTIR, and BET analysis were carried out to analyze the structure and morphology of the materials. It is confirmed that the ZnCo x Fe2-x O4-RHC composites show better catalytic activity and performance than other control samples, which can be attributed to the synergistic effect of Fe and Co, ZnCo x Fe2-x O4 and RHC based on these analyses. The degradation rate of BPA by ZnCo1.3Fe0.7O4-50%RHC reached 100% within 15 min, and it can still maintain good catalytic efficiency after 5 cycles. ESR test and XPS results showed that free radical and non-free radical processes were involved in BPA degradation. These findings offer a novel, low cost and simple strategy for rational design and modulation of catalysts for the industrial degradation of organic pollutants, and provide a new idea for the utilization of waste ferrous sulphate in titanium dioxide industry.

Chromium (VI) adsorption from wastewater using porous magnetite nanoparticles prepared from titanium residue by a novel solid-phase reduction method.

Porous magnetite nanoparticles were successfully synthesized by reduction of titanium residue with pyrite under nitrogen protection, and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, vibrating sample magnetometer, X-ray photoelectron spectroscope, zeta potential and Brunauer-Emmett-Teller method. The XRD analysis confirmed the formation of porous magnetite nanoparticles with single spinel structure. The SEM image demonstrated that porous magnetite nanoparticles displayed spherical shape with the average diameter of ~51nm. The surface area of porous magnetite nanoparticles with high magnetic moment (78emu·g-1) was 11.1m2g-1. The experimental results revealed that equilibrium adsorption behavior of Cr(VI) was well described by Langmuir isotherm model with the maximum adsorption capacity of 14.49mgg-1 at 298.15K, and kinetic data was found to fit well with pseudo-second-order model. The adsorption rate for Cr(VI) was controlled by both boundary layer diffusion and intraparticle diffusion. Thermodynamics analysis showed that the adsorption processes of Cr(VI) were endothermic and spontaneous. In addition, the adsorption of Cr(VI) on porous magnetite nanoparticles was classified as chemisorption adsorption, which depended on electrostatic attraction accompanied with reduction of Cr(VI) to Cr(III). Porous magnetite nanoparticles were readily regenerated and used repeatedly for Cr(VI) adsorption at least five cycles. Furthermore, the experimental results indicate that porous magnetite nanoparticles have a promising application for Cr(VI) adsorption from wastewater.