The Photocatalytic Properties Of Nd-doped Heteroiunction Ms/tz-BiVO₄ Under Visible Light

The problem of energy and environment is becoming more and more serious.As a kind of green environmental protection,semiconductor photocatalysis has provided a feasible way to solve these two problems because of the use of solar energy.BiVO₄ has three kinds of phases:tetragonal zircon,tetragonal scheelite and monoclinic scheelite,and monoclinic scheelite BiVO₄ shows a better photocatalytic activity under visible light irradiation.However,there are still some problems such as the recombination of the photogenerated electron-hole pairs,the weak surface absorption and the low quantum yield of monoclinic scheelite BiVO₄.In this paper,the photocatalytic activity of BiVO₄ was enhanced by Nd³⁺ doping,and the effect of Nd³⁺ doping ratio on the photocatalytic performance of BiVO₄ was investigated.With the increase of the Nd³⁺ doping ratio,the tetragonal structure of BiVO₄ was stabilized and the conversion of BiVO₄ tetragonal to monoclinic structure was slowed down.In the process of doping,part of Nd³⁺ are placed interstitially and some of them replace Bi³⁺ in the crystal lattice.When the Nd³⁺ doping ratio is low,the sample is rod-like morphology with good dispersion,which is favorable to the photocatalytic reaction.With the increase of doping ratio,the size of rod-shaped structure becomes smaller,and more and more irregular particles and agglomeration phenomena appear,which is not conducive to the photocatalytic reaction of samples.The low doping ratio of Nd³⁺ reduces the band gap of BiVO₄,which is beneficial to improve the visible absorption properties of BiVO₄.With the increase of the proportion of Nd³⁺ doping,the band gap of BiVO₄ increases.The sample with 1 at%Nd³⁺ doping have the best photocatalytic activity,which is due to the decrease of the band gap of BiVO₄ and the upconversion phenomenon caused by Nd³⁺ doping,which improves the optical absorption of BiVO₄ and increases the number of photons involved in the photocatalytic reaction.In this paper,ms/tz-BiVO₄ photocatalysts with different reaction time have been synthesized by hydrothermal method.With the increase of hydrothermal time,the tetragonal zircon BiVO₄ was gradually transformed into the monoclinic scheelite phases,and the irregular morphology gradually became a rod-like structure.DRS can prove the existence of two phases and upconversion luminescence induced by Nd³⁺doping.After doping with Nd³⁺,the photocatalytic activity of the samples was improved obviously.The samples with two kinds of crystal structure have better photocatalytic activity than the sample containing monoclinic phase,which shows the formation of the double crystal heterojunction can effectively promote the separation of photogenerated electron-hole pairs and improve the photocatalytic activity of BiVO₄.In this paper,by changing the pH value of the precursor solution,the BiVO₄ photocatalysts with different morphologies and structures were prepared by hydrothermal synthesis without additives.With the increase of the pH value of the precursor solution,the proportion of the tetragonal form of the sample increased,which hindered the process of the conversion of BiVO₄ tetragonal to monoclinic phases.As ms-BVO,the pH=7 sample has the best crystallinity and exposure of the?040?crystal plane.The pH value of precursor solution has a great influence on the morphology of BiVO₄.When the flooding solution is acidic,the morphology of the sample is irregular granular,and the dispersion of the sample is not good.When the current solution is neutral or alkaline,the morphology of the sample is rod-shaped structure.The photocatalytic activity of BiVO₄ is affected by morphology.Rod-shaped BiVO₄ with good dispersion has a larger surface area,which provides more active adsorption site to improve the photocatalytic activity of BiVO₄.