Xie Yongbing

Double layered, one-pot hydrothermal synthesis of M-TiO2 (M = Fe3+, Ni2+, Cu2+ and Co2+) and their application in photocatalysis

A double layered, one-pot hydrothermal method was adopted in this work to prepare transition metal ions (Fe3+, Ni2+, Cu2+ and Co2+) doped TiO2. The morphology and chemical properties of TiO2 and the status of metal ions were characterized with XRD, TEM, BET, UV-Vis and XPS analysis. TEM images show that the obtained TiO2 was very uniform with an average particle size of 10.4 nm. XPS, TEM and XRD results show that transitional metals were doped onto TiO2 in the form of ions. Photocatalytic decomposition of oxalic acid under UV illumination and methylene blue degradation under visible light on these materials were conducted, respectively. The results reveal that Cu2+-TiO2 and Co2+-TiO2 showed a highest activity under UV and visible light illumination, respectively, and they were both more active than commercial P25 TiO2. With this special design of double layers, the hydrolysis of titanium precursor in the system with water can be easily controlled and metal ions are simply doped. This strategy can be further applied to synthesize metal ion doped TiO2 using various metal precursors with controllable amounts, and thus lead to better optimization of highly active photocatalyst.

Coagulation behaviors and in-situ flocs characteristics of composite coagulants in cyanide-containing wastewater: Role of cationic polyelectrolyte

In this paper, composite coagulants (PFS, PFSC05, PFSC1 and PFSC5), prepared by mixing polyferric sulfate (PFS) and cationic polyelectrolyte (CP) coagulants with different weight percent (Wp) of CP (Wp = 0%, 0.5%, 1% and 5%, respectively), were adopted to treat cyanide-containing wastewater. PFSC5 exhibited superior coagulation performances at optimal conditions: the removal of total cyanide (TCN) and chemical oxygen demand (COD) was 95%–97% and 50%–55%, respectively. The effects of CP on the properties and structure of flocs were investigated by laser diffraction instrument and small-angle laser light scattering (SALLS), respectively. The results show that the flocs of PFSC5 have higher growth rate, higher strength factor and lower recovery factor than other flocs. They are also much denser and more uniform owing to the higher fractal dimension (Df) and less microflocs (10–100 μm). Furthermore, the dense structure of the PFSC5 flocs can be restored after shear and is more resistant to hydraulic conditions. Particularly, detailed morphology evolution of the flocs was in-situ detected by on-line particle imaging. Due to strong ionic strength in wastewater, the CP in PFSC5 plays a significant role of adsorption, while the main mechanism of CP is electrostatic patch aggregation during the PFSC05 systems.