Enhanced Photocatalysis And Photothermalcatalysis Of Semiconductor Oxides By Modulating Surface Electronic States

Semiconductor oxide photocatalytic materials have shown great application potential in the field of environmental pollution and renewable energy,but the low efficiency of photocatalysis has always been the bottleneck of semiconductor oxide.Compared with single photocatalysis,photothermalcatalysis can significantly enhance the surface reaction rate of semiconductor oxides,activate lattice oxygen and improve product selectivity,which has attracted much attention.However,the introduction of heat energy in photocatalysis is difficult to avoid the thermal recombination of photogenerated carriers,and how to improve the utilization of photogenerated carriers is the key to the highly efficient photothermalcatalysis of semiconductor oxides.The results show that the modulation of surface electronic states,such as the distribution of energy level,the density of states and the composition of states,is an effective way to improve the photocatalytic reaction efficiency of semiconductor oxides.This paper focuses on the enhancement of photothermalcatalysis of semiconductor oxides by modulating the surface electronic states.The efficiency and selectivity of photothermalcatalysis can be improved by modulating the distribution of electronic states on the oxide surface and cooperating with noble metal co-catalyst.By adjusting the density of surface electronic states,the response of spectral range is broadened and the utilization of solar spactrum is increased.Through regulating the composition of surface electronic states and coupling with photothermal effect,the transition probability between the deep bound electron subband gap is increased,and the reduction ability of electron is improved.Specific research results are as follows:1.TiO2 treated by ultrasonic method constructs surface disorder,which reduced the size of photodeposited Pt nanoparticles and significantly improved the selectivity of CH4 in photothermal CO2 reduction.A disordered layer was introduced on the surface of TiO2 by ultrasonic method and loaded Pt nanoparticles by photodeposition.The double-beam photoacoustic spectroscopy showed that the disordered layer could reduce the electrons trapped in the deep level,which resulted in the size of the photodeposited Pt nanoparticles shrinking from 4.06 nm to 2.33 nm.When the temperature of reaction is 393 K,the rate of CO2 conversion over Pt(2.33 nm)/TiO2 is 155 times that of the original TiO2,and the selectivity of CH4 is 87.5%.Thermally assisted photocatalysis is more conducive to the splitting of H2 over Pt(2.33nm)/TiO2,thus promoting the generation of CH4.Introducing disordered layer on the surface to control the size of Pt nanoparticles provides a new idea for the design of efficient photothermalcatalysts.2.Solution plasma process(SPP)modulates the surface electronic states of self-doped TiO2to enhance the photo-and photothermal-catalytic activities under solar light.The photocatalytic activity of self-doped wideband gap semiconductor oxides with visible light response is limited by the existence of deep defect electron traps.To solve this problem,we propose a new strategy of constructing shallow defect level as electron transfer bridge between deep defect level and conduction band.TiO2 with rich oxygen vacancies was taken as the model and treated by SPP.The analysis of solid ~1H NMR and the double-beam photoacoustic spectroscopy shows that hydrogen atoms can be introduced into the TiO2 lattice and form a shallow defect level above the oxygen vacancy level.Under solar light,TiO2 treated by SPP was increased by 300 times in photothermalcatalytic CO2 reduction.Under UV light,the rate of photothermal acetaldehyde degradation was increased by 7.5 times.The visible light activity of the sample can be extended to the region of green light.The strategy is also applicable to WO3,Zn O,Ta2O5 and other semiconductor oxides.This strategy solves the problem of the deep-level electron trap in self-doped wideband gap semiconductor oxides which is of great value for the development of visible light responsive photocatalysts.3.Solution plasma process(SPP)improved the photo-and photothermal-catalytic activities of N-TiO2.The surface defects in the anionic doping,as the recombination center,seriously limit the catalytic activity.N-doped TiO2 with stable visible light absorption was used as the research model,and the samples were treated by SPP with different atmosphere.O2 SPP has the best ability to remove surface defects.The double beam photoacoustic spectrum test shows that O2-SPP is more beneficial to the construction of shallow defect level.Among them,N-TiO2treated by pure O2-SPP has the highest catalytic activity.Under UV light,the mineralization rate of acetaldehyde degradation is close to 100%in 1 hour;and under visible light,the rate of acetaldehyde degradation is increased by 3.2 times.Under UV light,the photocatalytic and photothermal catalytic rate of acetaldehyde degradation were 1.7 and 1.5 times that of P25,respectively.This method provides a new way for the application of anion-doped oxides in visible light catalysis.