High levels of soluble Mn(II) are often detected in groundwater in many countries, including the northeast region of China. It is necessary to remove excess amounts of Mn(II) from groundwater, especially in country sites, outside big cities. Coating manganese oxides onto a stable, cheap granular media provides an attractive alternative for Mn(II) removal from water.
Manganese oxide coated sand (MOCS) was prepared by base activation of sand with 9% NaOH for 24 h, soaking base activated sand with 7% KMnO4 for 24 h and finally calcination at 250 °C for 4 h. The MOCS had a significantly rougher surface and its surface was apparently coated with newly formed clusters of crystalline manganese oxide with a mixed manganese oxidation state of (Mn(III) and Mn(IV)). The manganese oxide effectively oxidized Mn(II) in the water to Mn(III) and Mn(IV). MOCS exhibited good Mn(II) removal performance in the filter bed experiment. The results suggested that a new catalytic flocculent manganese oxide layer was generated on the MOCS surface after filtration.
The new prepared MOCS in this study has potential as a catalytic adsorbent for Mn(II) removal in small waterworks in country sites. © 2014 Society of Chemical Industry
In this study, the characterization and photocatalytic activity of TiO2 nanotube arrays prepared by anodization process with starch addition were investigated in detail. The results suggested that the optimum mass fraction of starch added in anodization process was 0.1%, with which TiO2 nanotube arrays owning good tubular structure were synthesized. The tube length and average inner diameter of nanotubes were approximately 4 μm and 30 nm, respectively. Through the characterization of TiO2 nanotube arrays by energy dispersive spectrometer, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier Transform Infrared (FTIR) spectroscopy, it was found that the as-prepared nanotubes possessed well uniformed and higher photodegradation responsive than the pure TiO2. Moreover, it was expected that the as-prepared nanotubes exhibited good photocatalytic activity for the degradation of RhB under UV-light irradiation, which could be ascribed to their good morphology, enhanced UV-light absorption property and electron transmission ability during the photocatalytic reaction. In addition, the nanotubes were not significantly regenerated during the cycling runs experiment. Overall, this study could provide a principle method to synthesize TiO2 nanotube arrays with enhanced photocatalytic activity by anodization process with starch addition for environmental purification.
In this study, the effect of pH values on the microstructure and photocatalytic activity of Ce-Bi2O3 under visible light irradiation was investigated in detail. In alkaline condition (e.g. pH = 9), the as-prepared Ce-Bi2O3 exhibited an agglomerated status and mesoporous structures without a long-range order. While in weak acid condition (e.g. pH = 5), the Ce-Bi2O3 exhibited a best morphology with irregular nanosheets. Correspondingly, it possessed largest surface area (24.641 m2 g−1) and pore volume (9.825E-02 cm3 g−1). These unique nanosheets can offer an attachment for pollutant molecules and reduce the distance of electron immigration from inner to surface, thus facilitating the separation of photoelectron and hole pairs. Compared with the pure Bi2O3, the band gap of Ce-Bi2O3 prepared at different pH was much lower. Among them, the band gap of Ce-Bi2O3 (pH of 5) was lowest (2.61 eV). Ce-Bi2O3 (pH of 5) exhibited as tetragonal crystal with the bismuth oxide in the form of the composites, which could reduce the band gap width or suppress the charge-carrier recombination, subsequently possessing great photocatalytic activity for acid orange II under visible light irradiation. After 2 h degradation under visible light, the degradation rate of acid Orange II was up to 96.44% by Ce-Bi2O3 prepared at pH 5. Overall, it can be concluded that the pH values had effects on the microstructure and photocatalytic activity of Ce-Bi2O3 catalysts.
In this study, the characterization and photocatalytic activity of Bi2WO6/Bi2O3 under visible-light irradiation was investigated in detail. The results suggested that Bi2WO6/Bi2O3 can be synthesized by a facile one-pot hydrothermal route using a super big 200 mL Teflon-lined autoclave with optimal sodium oleate/Bi molar ratio of 1.25. Through the characterization of Bi2WO6/Bi2O3 by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, UV-vis diffuse reflectance spectra and Photoluminescence spectra, it was found that the as-prepared composite possessed smaller crystallite size and higher visible-light responsive than the pure Bi2WO6. Moreover, it was expected that the as-prepared composites exhibited enhanced photocatalytic activity for the degradation of Rhodamine B under visible-light irradiation, which could be ascribed to their improved light absorption property and the reduced recombination of the photogenerated electrons and holes during the photocatalytic reaction. In general, this study could provide a principle method to synthesize Bi2WO6/Bi2O3 with enhanced photocatalytic activity by one-step hydrothermal synthesis route for environmental purification.
