Preparation And Photocatalytic Performance Of TiO₂/BC Composite Material

Semiconductor photocatalysis technology was considered as one of the most potential strategies to solve the current environmental and energy problems because of its green chemistry,non-toxicity,environmental protection and energy saving.It had a wide application prospect in the fields of electrolytic hydrogen production,pollutant degradation,disinfection and sterilization,but its application was limited by the problems of high band gap energy and easy recombination of photogenerated electron-hole pairs.Photocatalyst supported on carbon-based materials was an effective way to reduce band gap energy and promote carrier separation,but how to improve the light absorption capacity and the separation of photogenerated electron-hole pairs in photocatalysts was still the focus of attention in this field.Aiming at the bottleneck problems of narrow spectral response range,low photocatalytic efficiency and poor degradation performance of TiO₂,this paper prepared TiO₂/biochar（TiO₂/BC）composites with biochar（BC）as the matrix,studied the influence of BC and the preparation process of the composites on the photocatalytic performance of TiO₂/BC composites,and revealed the relationship between material processing,structure and performance.The research contents and results of this paper were as follows:1.The effect of TiO₂/BC composite on photocatalytic degradation of methyl orange（MO）was studied.The results showd that BC can promote light absorption,redshift the band gap,reduce the band gap energy of TiO₂,and prolong the life of photogenerated electron-holes,thus improving the photocatalytic activity of TiO₂.The TiO₂/BC composite showed higher photocatalytic activity than pure TiO₂,BC and TiO₂+BC（physical mixing）.Under the simulated sunlight irradiation,when the irradiation time was 270 min and the dosage was 2g/L,the removal rate of 50 mg/L MO was 76.77%,which was 59.52%higher than that of pure TiO₂.2.The effect of pyrolysis temperature of biochar on photocatalytic degradation of MO in TiO₂/BC composites were studied.The results showed that the specific surface area and pore volume of BC increased with the increase of pyrolysis temperature,and biochar had excellent structural characteristics.At the same time,the specific surface area and pore volume of TiO₂/BC composites also increased with the increase of pyrolysis temperature of BC.The larger specific surface area and pore volume of the composites were beneficial to provide more active sites for the adsorption of reactants.In the certain range of BC pyrolysis temperature,due to the enhanced chemical interaction between BC and TiO₂,TiO₂/BC composites showed enhanced light absorption in the visible region,and excellent separation and transfer efficiency of photogenerated electron-holes.However,excessive pyrolysis temperature reduced the interaction between TiO₂ and BC,hindered the migration of electrons and holes,and was not conducive to photocatalytic performance.The photocatalytic performance of TiO₂/BC composites were higher than that of pure TiO₂（31.08%）at different BC pyrolysis temperatures.When irradiated in simulated sunlight for 270 min,the removal activity of 50 mg/L MO by TiO₂/BC composite（TBC-800）prepared with BC-800 was68.71%.The photocatalytic activity increased with the increase of TiO₂/BC composite dosage.When the dosage of TBC-800 was 7g/L,the removal activity reached 93.02%.3.The effects of TiO₂/BC composites prepared by different processes on photocatalytic degradation of MO were studied.The results showed that composites with different mass ratios of TiO₂/BC mainly existed in anatase phase.When the calcination temperature of the composites were 400～700℃,TiO₂/BC composites all had good anatase structure and good crystallinity,which indicated that the introduction of BC could delay the transformation of TiO₂ from anatase phase to rutile phase.The remarkable enhancement of photocatalytic activity was attributed to the single crystal structure with high electron conductivity and low electron transfer resistance and small grain size,thus effectively separating and transferring photogenerated carriers.Among them,compared with pure TiO₂,TiO₂/BC（10）and TiO₂/BC（650）composites had the highest photocatalytic activity.When the mass ratio of TiO₂ and BC was 10:1,the calcination temperature was 650℃and the dosage of composite was 7g/L,the removal activity of 50 mg/L MO by TiO₂/BC composite reached 97.98%after 270 min of simulated sunlight irradiation.