Jianru Liang

Adsorptive removal of As(III) by biogenic schwertmannite from simulated As-contaminated groundwater

This study investigates synthesis of biogenic schwertmannite by Acidithiobacillus ferrooxidans and its role and mechanism in adsorption of As(III) from water. Results indicate that schwertmannite particles formed through oxidation of ferrous sulfate by A. ferrooxidans cells for different times vary greatly in size and in morphology. The hedge-hog like schwertmannite formed after reaction for 72h are aggregative spheroid particles with a diameter of approximately 2.5μm and its chemical formula can be expressed as Fe(8)O(8)(OH)(4.42)(SO(4))(1.79). Batche studies show that both Freundlich and Langmuir model are suitable for describing the adsorption behavior of As(III) on schwertmannite at pH 7.5 and As(III) in simulated groundwater can be effectively removed by biogenic schwertmannite with a maximum adsorption capacity of 113.9mg As(III) g(-1) and the optimal pH is in the range of 7-10. The arsenic removal is hardly affected by the competing anions often observed in groundwater unless the mole concentration of PO(4)(3-) and SO(4)(2-) in groundwater are 75 or 750 times higher than As(III), respectively. The mechanism of As(III) adsorption on biogenic schwertmannite involves ligand exchanges between arsenic species and surface hydroxyl group and sulfate. In addition, experiments show that As(III)-sorbed biogenic schwertmannite aged in deionized water at 25°C exhibits no mineralogy phase changes even after ageing at pH 6.0 and 8.5 for 90d.

Photocatalytic reduction of Cr(VI) by citric and oxalic acids over biogenetic jarosite

In this study, a series of bath experiments were carried out to investigate the photoreduction of Cr(VI) by small molecular weight organic acids (SOAs) over jarosite, a mineral found in acid mine drainage (AMD). The results demonstrated that jarosite or SOAs alone was unable to effectively transform Cr(VI) to Cr(III) even if exposed to an illumination of mimic solar light. However, an addition of jarosite significantly enhanced the reduction of Cr(VI) by SOAs under the same condition. The photocatalytic reduction of Cr(VI) was strongly influenced by pH, the initial concentrations and the structures of SOAs. Of the tested two SOAs, the reaction rates of photocatalytic reduction of Cr(VI) were in the order of oxalic acid>citric acid. The reaction obeyed to zero-order kinetics with respect to Cr(VI) with excess SOAs. A possible mechanism for photoreduction of Cr(VI) by SOAs over jarosite was proposed.

Visible light-degradation of azo dye methyl orange using TiO2/β-FeOOH as a heterogeneous photo-Fenton-like catalyst

In this study, a novel TiO2/β-FeOOH composite photocatalyst was synthesized by a hydrothermal method. X-ray diffraction, Fourier transform infrared spectrum, UV-vis diffuse reflectance spectra and scanning electron microscopy (SEM) were used to characterize the composite photocatalyst. The photocatalytic activity of the prepared composite photocatalyst was evaluated in a heterogeneous photo-Fenton-like process using methyl orange (MO) as target pollutant. The TiO2/β-FeOOH composites exhibited higher photocatalytic activity than pure β-FeOOH and TiO2 under visible-light irradiation. The enhanced photocatalytic activity can be ascribed to the formation of TiO2/β-FeOOH heterostructure, which plays an important role in expanding the photoactivity to the visible light region and in effectively prolonging the lifetime of photoinduced electrons and holes. Further investigation revealed that the 25TiO2/β-FeOOH composite synthesized with the TiO2/Fe(3+) in a mole ratio of 25:75 showed the highest catalytic activity.

Microwave–ultrasound assisted synthesis of β-FeOOH and its catalytic property in a photo-Fenton-like process

In this study, nanoparticles of single-phase akaganeite (β-FeOOH) were synthesized by an ultrasound-microwave assisted method. The synthesis parameters were optimized by means of response surface methodology. X-ray diffractions (XRD), Fourier transform infrared spectrum (FTIR), UV-vis diffused reflection spectra (UV-vis DRS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and specific surface area were used to characterize the as-prepared samples. The catalytic activity of the prepared β-FeOOH was evaluated in a heterogeneous photo-Fenton-like process using methyl orange as target pollutant. It is found that the reaction temperature and interaction between microwave and ultrasound have a significant influence on the catalytic properties of the prepared β-FeOOH samples. The β-FeOOH prepared at microwave power of 400 W, ultrasound power of 200 W, reaction temperature of 70°C and reaction time of 3 h, exhibited considerable catalytic activity in weak alkaline solution and under visible light irradiation, which would be of great promise for the industrial application of this catalyst to oxidize organic pollutants for wastewater treatment.

Potential application of novel TiO2/β-FeOOH composites for photocatalytic reduction of Cr(VI) with an analysis of statistical approach

AbstractnnIn this paper, four TiO2/β-FeOOH photocatalysts were synthesized by a simple deposition–precipitation method and characterized by X-ray diffraction, fourier transform infrared, scanning electron microscope and transmission electron microscope. The characterization showed the presence of nano-sized β-FeOOH particles on the TiO2 support. The photocatalytic efficiency of the catalysts was examined on the Cr(VI) reduction under ultraviolet irradiation in aqueous suspension. The photocatalyst denoted as 25TiO2/β-FeOOH appeared to be most efficient, which is due to effectively inhibiting the recombination of photoinduced electrons and holes. A 24 factorial design methodology was employed to evaluate the statistically important operating conditions (pH of the solution, loading of catalyst, Cr(VI) concentration and reaction time) and their interactions on the photocatalytic reduction efficiency of Cr(VI) over 25TiO2/β-FeOOH.

Removal of Arsenite in Water Using Biogenic Schwertmannite as Adsorbent

Synthesis of schwertmannite through oxidation of ferrous sulfate by Acidithiobacillus ferrooxidans cells and adsorption of arsenite [As(III)] from water were investigated in the present study. Furthermore, the stability of As(III)-sorbed biogenic schwertmannite was studied. Results showed that hedge-hog like schwertmannite formed after reaction for 72 h were spheroid particles with a diameter of approximately 2.5 μm and its chemical formula could be expressed as Fe8O8(OH)4.42(SO4)1.79. As(III) in water could be effectively removed by biogenic schwertmannite with a maximum adsorption capacity of 113.9 mg As(III) per g of adsorbent and the optimum pH for As(III) adsorption was in the range of 7∼10. The As(III) removal was unaffected by the competing monovalent anions such as Cl− and NO3 −, whereas PO4 3− and SO4 2- greatly decreased the As (III) removal efficiency only when the molar ratio of P to As and S to As in solution reached 75∶1 and 750∶1, respectively. Furthermore, As(III)-sorbed biogenic schwertmannite exhibited no mineralogy phase change after ageing at pH 6.0 and 8.5 for 90 d. And As(III) could be effectively immobilized in biogenic schwertmannite, indicating that the transformation of metastable schwertmannite to goethite was significantly inhibited by sorption of As(III). The study shows that synthetic biogenic schwertmannite can be a very efficient innovative adsorbent for removing As(III) from water.