Preparation Of Quantum Dot-Sensitized Graphene Mesoporous TiO₂ Coated Composite Nanomaterials QD@MT/GR And Its Visible Light Photocatalytic Properties

TiO₂ photocatalytic technology has the advantages of high efficiency,low energy consumption,simple operation,no toxicity and no secondary pollution.It is a green technology with important application prospects in energy and environment.However,TiO2 photocatalyst can not absorb visible light,and the solar energy utilization rate is low.The unique properties of quantum dots and graphene can expand the visible light absorption range of TiO₂ and increase the quantum yield,which can effectively improve the photocatalytic technology.ZnS,ZnSe and CdS were used as quantum dots（QD）,with sixteen alkyl three methyl ammonium bromide（CTAB）as surfactant,sixteen alkyl three methimidazolium bromide as ionic liquid（Ion liquid,IL）,butyl titanate as titanium source,graphene as carrier,sol-gel method and hydrothermal synthesis method were used to prepare quantum dot sensitive graphene mesoporous QD@MT/GR composite nanomaterials（MT:Mesoporous titanium dioxide,GR:Graphene）.The photocatalytic activity and kinetic mechanism of methylene blue（MB:Methylene Blue）were studied.ZnS@MT and ZnS@MT/GR composite nanomaterials were prepared using ZnS as quantum dots.ZnS quantum dots were successfully deposited into MT mesopores.The samples were calcined at 400^°C for 1 hour in nitrogen.The crystalline size of MT was23-30.65 nm.By GR loading,the size and dispersibility of ZnS@MT particles were more uniform ands better,respectively.And the specific surface area was increased,the absorption range was extended from 400 nm to 600 nm,and the band gap energy was reduced.ZnS@MT/GR-3 has the largest specific surface area of 90.1 m²/g.Under the same photocatalytic conditions,the photocatalytic performance of ZnS@MT/GR-3 is the best.The degradation rate of MB in 200 minutes is 95.9%,and the kinetic constant K_apppp is 0.019 min^-1,which is attributed to its maximum specific surface area and the best combination of MT and quantum dots.ZnSe@MT and ZnSe@MT/GR were synthesized by the same preparation process.It was found that the ZnSe quantum dots were deposited in the MT mesopores.The samples were anatase crystalline.The size distribution of ZnSe@MT/GR particles was uniform with the better dispersibility and the larger surface area.The optical absorption ranged from 400 to 500 nm.The band gap energy of ZnSe@MT/GR-3 was the smallest with the largest surface area of 72.4 m²/g,which results in the best photocatalytic performance under the same conditions.CdS@MT and CdS@MT/GR were synthesized under the same preparation process.The CdS quantum dots were coated in the MT mesopores.The samples were anatase with a grain diameter of about 10 nm.The CdS@MT was loaded with graphene and the particle size distribution was uniform,the dispersion was better,and the surface area was also increased.Compared with CdS@MT,the optical absorption range of CdS@MT/GR was expanded from 400 to 650 nm,and the band gap energy was reduced.Under the same conditions,the degradation rate of MB by CdS@MT/GR-3 reached 96.88%in 200minutes,and the maximum kinetic constant K_app was 0.17 min^-1,which was attributed to the maximum surface area of 200.2 m²/g.