Experimental Study On The Photocatalytic Depolymerization Of Corn Stover By TiO₂-based Photocatalyst

Currently,biomass is a proven renewable energy source that can be used to generate heat,electricity and liquid fuels.Corn stover,as the main representative of biomass,has the main characteristics of biomass energy:complex composition,large volume,low density,storage and transportation difficulties,and difficult to use directly.However,its hydrolysis can be decomposed into glucose,xylose and other kinds of reducing sugars,and then utilization such as microbial hydrogen production will be more efficient and convenient.Degradation technology is one of the bottlenecks that restrict the conversion and deep utilization of biomass energy,and it is also an indispensable link in the process of biomass energy conversion.In response to the problems of low light utilization efficiency and low availability of photocatalyst in the photocatalytic depolymerization of corn stover,and the difficulty of separation of photocatalyst and raw material after the reaction,relevant research was carried out.The effects of six photocatalysts,including TiO2,CdS,ZnO,ZrO2,SnO2 and SiC,on the degradation effect of corn stover under white light irradiation were investigated,and the 6-h time profile of each catalyst on the degradation of corn stover into reducing sugar was obtained experimentally under white light to determine the optimal irradiation time.Subsequently,the catalytic efficiency of the six catalysts was investigated under the irradiation of eight light sources,including 365,385,420,450,485,535,595 and 630 nm,in the reactor under the most significant irradiation time with the light source wavelength as the only variable.Finally,the expected reducing sugar yield of each catalyst under simulated sunlight was calculated based on the spectral energy distribution,and the effect of each photocatalyst on the depolymerization of corn stover was evaluated in combination with the electron microscopy scan of corn stover after photocatalytic degradation,and it was concluded that TiO2,CdS,and ZnO had significant photocatalytic activity on corn stover degradation.Based on the experimental results in the first part,TiO2 thin films with both anatase and rutile phases were prepared by hydrothermal method,and CdS was selected to be compounded with them using the modification method of semiconductor coupling,and the CdS/TiO2 bicrystal thin film photocatalysts were successfully prepared.SEM,EDS,RAMAN and UV-Vis were used to characterize the surface morphology,material composition and optical properties of the CdS/TiO2 bicrystal thin films.The effect of photocatalytic degradation of corn straw by CdS/TiO2 bicrystal thin film was studied,and the key technical mechanism analysis and experimental research were carried out.The CdS/TiO2 bicrystal thin film broadened the absorption spectrum to 420 nm under the combined effect of semiconductor coupling effect and mixing crystal effect,and showed high efficiency in the degradation of corn straw.The process conditions for the photocatalytic degradation of corn stover by CdS/TiO2 bicrystal thin film were optimized.The optimal levels of feedstock concentration,irradiation time and stirring intensity were determined by single-factor experiments using the increase in reducing sugar yield of corn stover after photocatalytic degradation as the response value.The process conditions were further optimized using response surface methodology.The results of the single-factor experiments showed that the maximum reducing sugar yield improvement was 231 mg/L at a raw material concentration of 1200 mg/L,The maximum reducing sugar improvement was 223.4 mg/L at an optimum irradiation time of 4 h.The maximum reducing sugar improvement was 209.4 mg/L at a stirring speed of 60 r/min.In the response surface experiments,the effects on reducing sugar yield improvement were in the following order:raw material concentration>stirring intensity>irradiation time,where the interaction between raw material concentration and irradiation time was significant,and the interaction between raw material concentration and stirring intensity was the least significant.After response surface optimization,the model predicted that the optimal conditions were 1503.15 mg/L raw material concentration,4.4 h irradiation time and 64.29 r/min stirring intensity,and the predicted reducing sugar enhancement was 247.354 mg/L.In the validation experiments,the reducing sugar enhancement was 237.9 mg/L.The final results were in good agreement with the simulations.The final results were in good agreement with the simulated results,indicating that the process is feasible.