Preparation And Photocatalytic Properties Of Halloysite-Supported Titanium Dioxide-Based Composite Photocatalyst

In recent years,with the rapid development of global industry and agriculture,environmental pollution has become a major challenge facing mankind in the century.Photocatalytic technology is a kind of green environmental purification technology which uses solar energy to remove environmental pollution.It has the characteristics of high efficiency,low energy consumption,wide application range and no secondary pollution.It can mineralize most organic pollutants into small inorganic molecules,water,CO₂ and so on.Among all kinds of photocatalysts,TiO₂ has attracted wide attention due to its abundant sources,non-toxicity,high stability,low cost and high activity.However,its application in the field of photocatalysis is limited by its shortcomings such as wide bandgap,low quantum efficiency,easy recombination of photogenerated carriers,no response to visible light,easy reunification and difficult separation and recovery.Based on these shortcomings of TiO₂,the supported photocatalyst based on TiO₂ has been successfully prepared by means of designing support,metal ion doping,semiconductor composite and precious metal deposition.Halloysite nanotubes are clay mineral materials with large specific surface area,low cost,high thermal stability,high adsorption,non-toxicity and high mechanical strength.Using halloysite nanotubes as support,the dispersion of TiO₂ can be improved,which is conducive to recovery and reuse.In this paper,we use halloysite nanotubes as carriers and titanium dioxide as main catalyst,and then modify them.Ce-doped TiO₂/HNTs composite photocatalyst was prepared by ion doping modification.The g-C₃N₄/TiO₂/HNTs heterojunction composite photocatalyst was synthesized by semiconductor composite technology,using g-C₃N₄ polymer semiconductor with suitable bandgap coupled with titanium dioxide.The Ag/In₂O₃/TiO₂/HNTs composite photocatalyst with plasma effect was prepared by modifying In₂O₃ and TiO₂ composite semiconductors using the plasma resonance effect of precious metal Ag as surface enhancement technology.The specific contents and results are as follows:?1?Ce doped TiO₂/HNTs composite photocatalyst was prepared by modified sol-gel method.The photocatalyst was characterized by XRD,SEM,TEM,XPS,Raman and UV-vis DRS.The photocatalytic activity and stability of Ce-doped TiO₂/HNTs were investigated with tetracycline and dibenzothiophene as the target degradation products.The results showed that Ce-doped TiO₂ particles were successfully loaded on the surface of HNTs.Compared with TiO₂ monomer,the photocatalytic degradation activity of the composite photocatalyst was significantly improved.When Ce doping amount is 2.0%,the composite photocatalyst has the highest activity.The photocatalytic degradation efficiencies of tetracycline and dibenzothiophene are 77.61%and 72.75%,respectively.After four cycles,Ce-doped titanium dioxide/HNTs still had high activity.?2?Firstly,TiO₂/HNTs was synthesized by sol-gel method,then melamine was used as raw material,and then calcined with TiO₂/HNTs to form a heterojunction.The g-C₃N₄/TiO₂/HNTs heterojunction composite photocatalyst was synthesized.XRD,SEM,TEM,UV-vis DRS,XPS and Raman were used to study g-C₃N₄/TiO₂/HNTs composite.The photocatalytic activity and stability of ciprofloxacin and dibenzothiophene were tested by photodegradation experiments.The results showed that the photocatalytic activity was the best when the amount of melamine was 50%.The degradation rates of ciprofloxacin and dibenzothiophene were 86.13%and76.73%,respectively.Cyclic experiments show that the composite photocatalyst has good photocatalytic activity.?3?Firstly,In₂O₃/TiO₂/HNTs was prepared by sol-gel method,then Ag was deposited on the surface by photoreduction,and Ag/In₂O₃/TiO₂/HNTs composite photocatalyst was prepared.Ag/In₂O₃/TiO₂/HNTs composites were characterized by means of SEM,TEM,XRD,XPS,Raman,UV-vis DRS and PL.The photocatalytic activity and stability of Ag/In₂O₃/TiO₂/HNTs composites were tested by photodegradation of tetracycline and dibenzothiophene.The results show that compared with pure TiO₂,Ag/In₂O₃/TiO₂/HNTs composite absorb more visible light and increase the transport rate of photogenerated carriers.The photocatalytic activity of the composite photocatalyst was the best when the Ag content was 3.0%and the ratio of In₂O₃ to TiO₂ was 0.08:0.92.