Design And Preparation Of High Efficient BiVO₄-based Photocatalysts And The Mechanism Of Enhanced Photocatalytic Performance

Semiconductor photocatalysis technology is considered to be one of the most promising environmental treatment methods.The development of high-efficiency new photocatalysts with visible light activity has been hot research topics in this field.Monoclinic BiVO₄ has attracted wide attentions because of its narrow band gap,easy preparation,low cost,and non-polluting advantages.However,its weak adsorption performance and high electron-hole recombination rate largely limit the improvement of its photocatalytic efficiency.In this thesis,on the bases of the current research status and the problems that influence the photocatalytic performance of BiVO₄,and proposes the construction of p-n heterostructures and exposed high-activity crystal faces to improve photocatalysis.The works on design and preparation of high efficient BiVO₄-based photocatalysts and the mechanism of enhanced photocatalytic performance were systematically summarized,in which the research contents and achievements are as the following two aspects:1)A new strategy of selecting n-type NiS to construct NiS/BiVO₄p-n heterostructures is proposed to improve the photocatalytic performance of BiVO₄.NiS/BiVO₄p-n heterostructured photocatalysts were synthesized by a two-step hydrothermal method,and the photocatalytic degradation performance of various organic dyes was investigated.It was found that the effective compounding of the n-type semiconductor NiS with the p-type BiVO₄,although it might not significantly increase the specific surface area,the optimal photocatalytic efficiencies of methyl orange（MO）and rhodamine B（Rh B）within 90 min could also reach 95.6% and 99.0%.Its degradation rates for MO and Rh B are 1.7971 h^-1 and 2.7870 h^-1,respectively,being increased nearly 16 and 19 times compared with those of bare BiVO₄(MO 0.1134 h^-1 and Rh B 0.1476 h^-1),respectively.Moreover,NiS/BiVO₄ has better catalytic stability.The analysis shows that the better light harvesting,higher photocurrent response,and effective charge separation and transfer characteristics of the NiS/BiVO₄ composite structures are the main factors for the substantial improvement of its photocatalytic efficiency.The mechanism of photocatalytic performance enhancement is analyzed.2)Based on the above research,the monoclinic BiVO₄ with exposed（040）crystal planes was designed and fabricated,and the NiS/（040）-BiVO₄p-n heterostructured photocatalyst was constructed by compounding with n-type NiS.Under the synergistic effect of the homojunction formed by the crystal planes and the p-n heterojunction,the best degradation rates of 98.4%,99.0% and 98.3% for MO,RhB and tetracycline（TC）were obtained within 30 minutes.Compared with the degradation rate of（040）-BiVO₄,it increased by nearly 12,12.1 and 8 times.The photocatalytic mechanism of the significantly enhanced photocatalytic performance was analyzed in detail.