The degradation of an azo dye, acid orange 7 (AO7), caused by different high voltage pulsed electrical discharge modes (spark, streamer and corona discharge) induced by the various initial conductivities was investigated. A new type of pulsed high voltage source with thyratron switch and Blumlein pulse forming net (BPFN) was used. The typical discharge waveforms of voltage, current, power, pulse en-ergy and the pictures of spark, streamer and corona discharge modes were presented. The results in-dicated that pulsed electrical discharges led to complete decolorization and substantial decrease of the chemical oxygen demand (COD) of the dye solution. The main intermediate products were monitored by GC-MS. The discharge modes changed from spark to streamer and to corona discharge, and the streamer length decreased with the liquid conductivity increasing. At a constant input power, the peak voltage, peak current, peak power and energy per pulse of the three discharge modes ranked in the following order: spark > streamer > corona. The effective energy transfer efficiency of AO7 removal was higher for spark discharge (57.2%) than for streamer discharge (40.4%) and corona discharge (27.6%). Moreover, the energy utilization efficiency of AO7 removal for spark discharge was 1.035×10^(-9) mol/J, and for streamer and corona discharge they were 0.646×10^(-9) and 0.589×10^(-9) mol/J. Both the energy transfer efficiency and the energy utilization efficiency of spark discharge were the highest.
In order to realize hydrogen generation under visible light, novel CdS/TiO_2 nanotubes arrays are de- veloped by electrochemical anodization of Ti in 0.15 mol/L NH_4F + 0.08mol/L H_2C_2O_4 electrolyte. The diameter of the nanotube is 80―100nm and the length is approximately 550 nm. The CdS nano-particles are deposited on the TiO_2 nanotubes arrays by chemical bath deposition (CBD) in the ammonia-thiourea system. A 300W Xe lamp is used as the light source, CdS/TiO_2 nanotube arrays are used as the photoanode with the application of 1.0V bath voltage, and 0.1 mol/L Na_2S + 0.04 mol/L Na_2SO_3 solution is used as the electrolyte, then the rate of photoelectrocatalytic hydrogen generation is 245.4 μL/(h·cm^2). This opens new perspectives for photoelectrocatalytic hydrogen generation by using CdS/TiO_2 nanotubes arrays.
Fabrication and S-F-codoping of TiO2 nanotubes were carried out by a one-step electrochemical ano-dization process to extend the photoresponse of TiO2 to the visible-light region. The prepared samples were annealed in air and detected by SEM,XRD,XPS and UV-vis DRS spectrophotometer. The results showed that the average tube diameter of the nanotubes was 150 nm and the average tube length was 400 nm. The doped TiO2 nanotubes exhibited strong absorption in visible-light region. Photoelectro-catalytic degradation efficiency of 4-CP over S-F-codoped TiO2 nanotubes was 39.7% higher than that of only-F-doped sample. Moreover,sulfur and fluorine codoped into substitutional sites of TiO2 had been proven to be indispensable for strong response and high photocatalytic activity under visible light,as assessed by XPS.
In this study, supported nonmetal (boron) doping TiO2 coating photocatalysts were prepared by chemical vapor deposition (CVD) to enhance the activity under visible light irradiation and avoid the recovering of TiO2. Boron atoms were successfully doped into the lattice of TiO2 through CVD, as evidenced from XPS analysis. B-doped TiO2 coating catalysts showed drastic and strong absorption in the visible light range with a red shift in the band gap transition. This novel B-TiO2 coating photocatalyst showed higher photocatalytic activity in methyl orange degradation under visible light irradiation than that of the pure TiO2 photocatalyst.
