A Sillenite-Type Bi₁₂MnO₂₀ And Its UV-VIS-NIR Induced Photocatalytic Properties For Degradation Of Contaminants

With the rapid development of economy and the improvement of people's consumption level,the environmental pollution and energy shortages have become the top issue for us today.So,it is imperative to find a novel contamination treatment technology of energy conservation and environmental protection.Photocatalysis technology has gained much attention to solve the global environmental pollution and energy crisis because of its many advantages,such as recyclability,superior contaminant degrading ability,non-secondary-pollution,economizing energy and so on.It is well known that the core of photocatalysis technology is Photocatalytic materials.sillenite,as a new type of photocatalyst with photorefractive,photoluminescence and photoconductive properties due to its unique electronic structure,has been studied intensively.In this work,Bi₁₂MnO₂₀ was synthesized by a facile and mild Sol-Gel method with different calcine temperature and time.The photoreduction properties of Bi₁₂MnO₂₀ are assessed by decomposition of potassium dichromate under UV,visible and near infrared light,and the photooxidation properties are assessed by decomposition of acid red solution under visible light.In the present study,we discussed the relationship between the light response range and the internal structure of prepared photocatalyst,and the photocatalytic degradation mechanism.The main research work is as follows:?1?Bi₁₂MnO₂₀ was prepared by Sol-Gel method using Bi?NO₃?₃·5H₂O as inorganic metal raw material and C₄H₆MnO₄·4H₂O as organic metal raw material,citric acid monohydrate and EDTA as complexing agent.All chemicals were of analytical grade and used as received without further purification.First 0.072 mol citric acid monohydrate and 18 mmol Bi?NO₃?₃·5H₂O were added into 30 mL distilled water under stirring.Second,14 g EDTA was dissolved completely in 20 mL of ammonia under vigorous stirring,which was transferred into above-mentioned solution under thermostatic water-bath?80 ^oC?stirring until the formation of colorless transparent bismuth acid solution.Third,1.5 mmol C₄H₆MnO₄·4H₂O was completely dissolved in 50 mL of ammonia under vigorous stirring,which was transferred into aforesaid solution under thermostatic water-bath?80 ^oC?stirring until the formation of white sticky sol.Fourth,The sol was transferred into a 300 mL of ceramic crucible,which was heated on a electric furnace until the sol was carbonized to black bituminous material.Fifth,The black bituminous material was further scorched about 2 hours at400 ^oC to remove organic substances.Sixth,After above-mentioned substances cools,grind it,and then calcine it with different calcine temperature and time.Finally,we analyzed the as-samples by XRD,SEM and TEM and a series of characterization.The analysis results indicate that the atrovirens photocatalyst which grain size are micron grade is synthesized successfully by the Sol-Gel method,and the calcination temperature and calcination time have a certain effects on the purity of Bi₁₂MnO₂₀photocatalyst.?2?The photocatalytic performance of Bi₁₂MnO₂₀ material was evaluated by the degradation rate of hexavalent chromium ions and the removal rate of acid red?ARG?in the sewage.The calcination temperature,the calcination time,the dosage of the catalyst and the initial concentration of pollutant have a certain effect on the degradation of Cr?VI?and the removal of ARG.A series of experimental results show that the degradation efficiency of the Bi₁₂MnO₂₀0 photocatalytic material to hexavalent chromium solution can reach 98%under visible light,and the efficiency can reach50%under near infrared light,which indicates that the photocatalyst has UV-VIS-NIR wide spectral response.In addition,the photocatalytic material on ARG removal rate can reach about 55%under the visible light irradiation for 2 h.?3?By analyzing the results of UV-visible-near infrared spectrophotometer,we know that the new-produced Bi₁₂MnO₂₀ crystal presents peculiar and strong absorption capability,covering the spectrum of UV,visible and NIR lights in the range of 200-1300 nm.The main reason is that by incorporating the Mn⁴⁺ions into tetrahedra sites of metastable cubic?-Bi₂O₃,the 3d orbits of Mn⁴⁺was split.As a result,the as-prepared Bi₁₂MnO₂₀ semiconductor would provide a new potential to fulfill the full spectrum responsive photocatalysis.What's more,the DFT calculation further confirms the existence of intermediate band state in the band gap of Bi₁₂MnO₂₀,which was formed by the hybrid of O 2p and Mn 3d orbits.More importantly,under the irradiation of UV,visible and NIR lights,Bi₁₂MnO₂₀ exhibits excellent photo-reduction activity of Cr?VI?,which is mainly due to the relatively good charge separation enhanced by unique electronic structure of the Bi³⁺6s² lone pair,the suitable band positions and the introduction of intermediate band state.In addition,Bi₁₂MnO₂₀0 specimen also displays good visible light driven photo-oxidation property for ARG,which is mainly caused by h⁺and·O^2-species.The as-prepared Bi₁₂MnO₂₀ semiconductor would provide a new potential to fulfill the full spectrum responsive photocatalysis.