Photocatalytic oxidation of Mn(II) on the surface of Bi2.15WO6via the ligand-to-metal charge transfer (LMCT) pathway.

Biotic and abiotic oxidation of Mn(II) in aqueous environments is an important process for the cycling of many elements. However, the mechanism involved in photocatalytic oxidation of Mn(II) has not been clearly elucidated yet. In this study, the photocatalytic oxidation of Mn(II) on the surface of self-doped Bi2+xWO6 (Bi2.15WO6) under visible light was conducted. Kinetics results show that visible light apparently accelerates the oxidation of Mn(II) to Mn(III, IV) oxides on Bi2.15WO6. The average oxidation states (AOS) of manganese reach 2.18 after 80 min of reaction under visible light at pH 8.50. Characterizations indicate the formation of Bi(III)-O-Mn(II) surface complexes between Mn(II) and surface Bi(III) on Bi2.15WO6, which then decreases the bandgap of [Bi2.15WO6 + Mn(II)]light (2.53 eV) compared with those of [Bi2.15WO6 + Mn(II)]dark (2.72 eV) and pure Bi2.15WO6 (2.86 eV), suggesting the contribution of the ligand-to-metal charge transfer (LMCT) pathway to the photocatalytic oxidation of Mn(II). Moreover, the addition of inorganic oxidants with strong oxidizing capacities (such as Cr2O72-, NO3- or NO2-) significantly increases the oxidation rate of Mn(II), further verifying the contribution of the LMCT pathway to Mn(II) oxidation. We therefore suggest that the LMCT pathway is one of the important oxidation routes for Mn(II) oxidation on Bi2.15WO6 under visible light.

Enhanced permeate flux by air micro-nano bubbles via reducing apparent viscosity during ultrafiltration process.

Micro-nano bubbles (MNBs) play important roles in the reduction of membrane fouling during membrane separation; however, such improvements are always attributed to the reduced concentration polarization on the surface of membranes and little attention has been paid on the variations of physicochemical properties of the feed caused by MNBs. In this study, the separation efficiencies of the feed containing humic acid (HA), bovine serum albumin (BSA), sodium alginate (SA) or dyes can be improved by MNBs during ultrafiltration, and the normalized fluxes can be maximally increased to 139% and 127% in the dead-end and cross-flow modes, respectively in the treatment of HA solution. We further reveal that the decreased apparent viscosity of the feed in the presence of MNBs is the key factor that enhances the normalized flux during ultrafiltration. This study gives new insight on the importance of MNBs in membrane separation and provides valuable clues for other chemical processes.