Microwave Hydrothermal Synthesis And Properties Of RE（Nd/La）-N-P-TiO₂ Nanocomposite Photocatalyst

To improve the solar utilization ratio and quantum efficiency of nano-TiO2, TiO2 nano-composite photocatalyts with high-performance and visible light response were exploited, which could offer novel high-performance photocatalytic materials for the treatment of environmental pollutants with a photocatalytic technique.A microwave-hydrothermal method without thermal treatment was successfully developed to obtain high-efficiency Nd, N, P-tridoped anatase-TiO2 nano-photocatalyst from TiCl4 hydrolysis in aqueous solution. The samples were characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption- desorption isotherm, X-ray photoelection spectroscopy, Fourier transform infrared spectroscopy, electron paramagnetic resonance, UV-vis absorbance spectroscopy, and photoelectrochemical measurements. Results show that it was very significant that as-synthesized NdNPTO exhibits the highest photocatalytic performance for the degradation of 4-CP among all samples, confirming that a synergistic effect in further increasing the photoactivity occurs due to Nd, N, and P tridoping. As-synthesized NdNPTO is much superior to commercial P25 TiO2. TOC removal rate for 4-CP solution(20 mg/L) in the presence of Nd-N-P-TiO2(0.8 g/L) reaches 83.59% after 120 min irradiation, indicating that 4-CP was mineralized efficiently. The scavenging experiments confirm that it is ?OH rather than ?O2-that directly oxidizes target pollutant 4-CP, and ?O2-can be further protonated to form ?OH and then partake the degradation of 4-CP. The enhanced photoactivity of NdNPTO is attributed to a synergetic effect of reduced recombination of photogenerated electrons and holes, enhanced surface Ti4+–O2-–Ti4+–O-? species, increased surface hydroxyl content, increased UV light absorption, well crystallized anatase structure, as well as increased specific surface area and mesopore structure. NdNPTO exhibits good photochemical stability and can be reused for 5 times with less than 3% decrease in the 4-CP removal efficiency. This research provides a very effective and stable visible light active photocatalyst for environmental application.La, N, and P were first tridoped into TiO2 lattices from the hydrolysis of TiCl4 by the environmentally friendly MAH method to develop a high-performance nano-photocatalyst(LaNPTO). The samples were characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption- desorption isotherm, X-ray photoelection spectroscopy, Fourier transform infrared spectroscopy, electron paramagnetic resonance, UV-vis absorbance spectroscopy, and photoelectrochemical measurements. The effect mechanisms of La-N-P-tridoping on the photoactivity of TiO2 were discussed. Their photocatalytic activities were evaluated by photocatalytic decoloration of 4-CP dye in aqueous solution under simulated sunlight irradiation. The results showed that the presence of La in the LaNPTO is responsible for inhibiting the recombination of the photogenerated electrons and holes. The doped N and oxygen vacancy are responsible for narrowing the band gap. P-doping plays a predominant role in inhibiting both the anatase-to-rutile phase transformation and the crystal growth, in stabilizing the mesoporous textural properties, and in increasing content of surface hydroxyl in LaNPTO. As-synthesized NaNPTO is much superior to commercial P25 TiO2. TOC removal rate for 4-CP solution(20 mg/L) in the presence of Na-N-P-TiO2(0.8 g/L) reaches 79.21% after 120 min irradiation, indicating that 4-CP was mineralized efficiently. The enhanced surface Ti4+–O2-–Ti4+–O-? species by La, N, and P tridoping is in favor of the higher photoactivity. The increased surface hydroxyl groups from La, N, and P tridoping are also very important factor for the improvement of the photoactivity. Additionally, the increased specific surface area, mesopore structure, and well crystallized anatase structure of LaNPTO are also considered as factors for the enhanced photoactivity. Consequently, the enhanced photoactivity of LaNPTO results from a synergetic effect of all above aspects.