Natural Pigments Templated TiO₂-SiO₂ Aerogels For Photocatalytic Reduction Of Hexavalent Chromium And CO₂ By Inorganic Materials Of Plants

Hexavalent chromium is one of the most serious heavy metal ions in water,which is not easy to degrade and has high toxicity.This is a serious threat to human health.Photocatalytic technology is a method that can effectively solve the hexavalent chromium pollution in water,and has the characteristics of economical environmental protection and high stability.TiO2-SiO2 aerogel is a composite material with non-toxic environmentally friendly and stable properties,and its photocatalytic performance is better than pure TiO2 aerogel material.However,TiO2-SiO2 aerogel materials only adsorb UV light,which can not effectively use solar light.In order to improve the photocatalytic activity of TiO2-SiO2 aerogel in the visible range,TiO2-SiO2 aerogel were synthesized by using curcumin and three different types of anthocyanins(scorpion blue,purple sweet potato and grape skin red)as templates.The material was characterized by XRD,SEM,TEM,FT-IR,BET,XPS,UV-Vis,etc.At the same time,their photocatalytic activities for reduction of hexavalent chromium were studied,and the influence of a series of reaction conditions were discussed in detail.Additionly,for the first time,various plant leaves were made into inorganic photocatalysts and used in photocatalytic reduction of CO2.The photocatalytic activity under different reaction conditions was explored.The following main findings were obtained:(1)Compared with TiO2-SiO2 aerogels without pigments,TiO2-SiO2 aerogels perpared by using curcumin as template show good distributive and obvious absorption in the visible region.For photocatalytic reduction of hexavalent chromium,the hexavalent chromium reduction rate is up to 98.0%,far exceeding the TiO2-SiO2 aerogel without pigment.(2)Compared with TiO2-SiO2 aerogels without pigments,it was found by characterization that the materials from anthocyanin have good dispersibility and obvious absorption in the visible region.For photocatalytic reduction of hexavalent chromium,the hexavalent chromium reduction rate is up to 86.1%,far exceeding the TiO2-SiO2 aerogel without pigment.(3)Some plant catalysts still possess the photocatalytic activity after high temperature calcination to break chloroplast,and sugarcane leaves catalyst shows the best reduction efficiency.The activity of the photocatalyst is improved after the addition of the ligand.The sugarcane leaf photocatalyst is a mineral containing potassium and magnesium,which is similar to the magnesium element contained in the core part of the porphyrin ring.This indicates the mechanism for reducing CO2 may resemble with the mechanism of "photosynthesis".