Perparation And Performance Characterization Of Bismuth Base Semiconductors Visible-light Photocatalysts

Nowadays,environmental pollution and energy crisis are holding back human's sustainable development.Semiconductors using solar energy as photocatalysts provide a novel way to solve the both problems mentioned before.Titanium dioxide?TiO₂?is one of the most important photocatalysts among them.However,as a photocatalyst,there are two defects in TiO₂ including the large gap and the high charges recombination rate,which are obstacles to its widespread use.Bismuth base semiconductors,a new visible light photocatalyst,is attracting more and more attention.In this paper,we use 3 different ways to prepare 3 different bismuth base semiconductors,which all realize the high visible photocatalytic activity.?1?Single-crystalline bismuth ferric?BiFeO₃?nanosheets with rectangular shape and exposed{101}facets were successfully synthesized via a facile hydrothermal method.The average side lengths of BiFeO₃ nanosheets are around 140 and 230 nm,and thickness is about30 nm.As a result,the BiFeO₃ nanosheets photocatalyst reaches as high as 89%of photodegradation efficiency of rhodamine B?RhB??10 mg/L?under 180 min visible light irradiation,which is about 10.47 and 4.77 times that of BiFeO₃ powders prepared by solid-state reaction and sol-gel process respectively.The internal electric fields produced due to the ferroelectric nature are perpendicular to the surfaces of BiFeO₃ nanosheets,which can promote the separation efficiency of photoinduced charges along[101]direction.?2?Single-crystalline bismuth titanate(Bi₄Ti₃O₁₂)nanosheets with rectangular shape and exposed?001?facets were successfully synthesized via a facile molten salt method.The average side lengths of Bi₄Ti₃O₁₂2 nanosheets are around 500⁸00 nm,and thickness is about 50⁸0nm.The best Bi₄Ti₃O₁₂ nanosheets?50-800?-2h?reaches as high as 98.0%of photodegradation efficiency of Rh B?10 mg/L?under 120 min visible light irradiation,which is more than 8 times that of Bi₄Ti₃O₁₂ powders prepared by solid-state reaction.There are several reasons that Bi₄Ti₃O₁₂ nanosheets show such high photocatalytic performance,including thin sheets shape and the internal electric fields perpendicular to exposed?001?facets.As the result,photoinduced charges can transfer to Bi₄Ti₃O₁₂ nanosheets'surface fast and then participate in reactions.?3?Based on the results obtained before,we use molten salt method to prepare lanthanum?La?doped Bi₄Ti₃O₁₂ nanosheets.Bi_3.25La_0.75Ti₃O₁₂ nanosheets with rectangular shape were successfully synthesized.The average side lengths of Bi_3.25La_0.75Ti₃O₁₂ nanosheets are around200⁵50 nm,and thickness is about 40 nm,which is smaller and thinner than Bi₄Ti₃O₁₂nanosheets.The best sample is Bi_3.25La_0.75Ti₃O₁₂?1.5h?,which reaches as high as 97.9%of photodegradation efficiency of RhB?10 mg/L?under 120 min visible light irradiation.Compared to Bi₄Ti₃O₁₂ nanosheets prepared by the same preparation condition,the photocatalytic performance of the best Bi_3.25La_0.75Ti₃O₁₂ nanosheets is enhanced by 57%,that's because Bi_3.25La_0.75Ti₃O₁₂ nanosheets possess the stronger internal electric fields and the thinner thickness.?4?We prepare bismuth oxychloride/titanium dioxide?BiOCl/TiO₂?heterojunction using single-crystalline Bi₄Ti₃O₁₂ nanosheets and hydrochloric acid as raw material.We obtain the BiOCl/TiO₂ heterojunction innovatively by using Bi₄Ti₃O₁₂ without the complex process,which enhances the photocatalytic performance of Bi₄Ti₃O₁₂ efficiently.In order to further improve the the photocatalytic performance of Bi OCl/TiO₂ heterojunction,niobium pentoxide?Nb₂O₅?was added into it,and then BiOCl/TiO₂/Nb₂O₅ heterojunction was obtained.BiOCl/TiO₂/Nb₂O₅ heterojunction shows extremely high photocatalytic performance.The best sample reaches nearly 100%of photodegradation efficiency of RhB?10 mg/L?under 12 min visible light irradiation.