Amino Acid-assisted Synthesis Of BiVO 4 And BiOBr Photocatalysts And Their Properties

In this paper,BiVO₄ and BiOBr photocatalysts were prepared with different amino acids as directing agents,and their photocatalytic activities were further modified by a series of methods.The composition,structures,and morphologies of the samples have been studied by means of XRD,UV-Vis-DRS,SEM,FT-IR and BET et.al characterizations.The active species and reaction mechanism in the catalytic process were tested and studied by the addition of trapping agents and electrochemical analysis.The main conclusions are as follows:（1）BiVO₄ crystals with preferentially exposed（040）facets have been hydrothermally synthesized in the presence of different amino acids（glycine,L-glutamate or L-arginine）as morphology-directing agents.The photocatalytic activities of BiVO₄ samples were evaluated by the degradation of methylene blue（MB）under visible-light irradiation（420 nm < λ < 800 nm）.It was confirmed that the photocatalytic activities of BiVO₄ prepared using amino acids as the directing agents were enhanced.The excellent photocatalytic activities of BiVO₄ can be attributed to the prompt charge carrier mobility and the high separation efficiency of photogenerated electron-hole pairs facilitated by the presence of more photogenerated electrons on the larger（040）surface of BiVO₄.（2）BiVO₄ is further modified by changing the synthesis method,ammonia etching and noble metal loading.The m-BiVO₄ photocatalysts with different morphologies have been prepared by one-step or two-step hydrothermal method with different amino acids as templates.Spherical m-BiVO₄ assembled by rod-shaped intercalation with the best adsorption performance was prepared by one-step hydrothermal method in the presence of L-tyrosine as morphology-directing agent.The degradation conversion ratio of Rh B(1×10^-5 M)in the presence of the sample was up to 76 % after adsorption for 1 h in dark.By the two-steps hydrothermal method,the BiVO₄ samples with different morphologies were prepared with different amino acids as morphology-directing agents.And the damaged fish bone sample with glycine as templates showed the best adsorption property towards Rh B.The removal rate of 1×10^-5 M Rh B in the presence of the sample was about 78 % after adsorption for 1h in dark.At the same time,we found that the photocatalytic activity of Bi VO4 can also be improved by further modifying the BiVO₄ sample with ammonia etching and noble metal loading.（3）BiOBr samples with high crystallinity,thinner nanosheets,larger surface area,and high adsorption property have been synthesized by hydrolysis method in the presence of amino acids（L-arginine,glycine,L-glutamate,L-lysine and L-phenylalanine）as morphology-directing agents for the first time.The results revealed that the amino acids as the directing agents in the synthetic process could influence the morphology of BiOBr sample.By changing the pH value of the reaction system and the precipitant,it was found that BiOBr with high photocatalytic activity were prepared by hydrolysis method under the conditions: pH=5,using ethylenediamine as precipitant.