Study On The Surface Defect Regulation Of Mesoporous TiO₂ Nanotubes And The Preparation And Photocatalytic Performance Of The Assembly

Mesoporous TiO₂ nanotubes have been widely used in photocatalytic field due to their unique tubular morphology,mesoporous structure,high stability and non-toxicity.However,it is well known that traditional TiO₂ can only absorb 5%of the ultraviolet light in the sunlight because of its bandgap limitation,which greatly limits the utilization of sunlight.And the single component of TiO₂ is also facing the defect of low electron-hole separation efficiency,which has become another factor in the current low photocatalytic efficiency.How to improve charge separation efficiency and solar photocatalytic performance is still facing this serious challenge at present.Based on the consideration above,we synthesized Ti³⁺self-doped mesoporous black TiO₂ nanotubes by one-step solvothermal and surface hydrogenation.The mesoporous channels are maintained by the protective effect of ethylenediamine on molecules,and at the same time,the crystalline phase has not changed.The band gap of the black TiO₂ material after hydrogenation is reduced,which causes the absorption range of light to extend from the ultraviolet to the visible light region.At the same time,we use it as a substrate,composite cocatalyst such as NiS and Pt nanoparticles,and further improve the visible light catalytic performance by utilizing the good electron transfer characteristics of NiS and the surface plasmon resonance effect of noble metal Pt.In this paper,the preparation of mesoporous black TiO₂ nanotubes and their complexes and the relationship between their photocatalytic properties are discussed,which are mainly divided into the following parts:1.Mesoporous black TiO₂ nanotubes?BTNs?were prepared by solvothermal method,which have good performance in simulating solar photocatalytic water splitting to produce hydrogen.It is worth mentioning that the uniform growth of the nanosheets on the surface of the black TiO₂ nanotubes will increase the specific surface area of the materials and expose more reactive sites.The optical band gap is about 2.87 eV,and the decrease of the band gap means that the light response range can be extended from ultraviolet to visible light region.The photocatalytic hydrogen production performance of black TiO₂ nanotubes driven by sunlight is about 3.95 mmol h^-1 g^-1,which is about four times higher than that of the original white TiO₂ nanotubes?TNs?(⁰.94 mmol h^-1g^-1).This improvement is attributed to the reduction of band gap which increases the utilization of solar energy,the formation of Ti³⁺which improves the separation efficiency of photogenerated charge carriers,and the special 1D mesoporous structure which provides more surface reactive sites.2.Using mesoporous black TiO₂ nanotubes as host materials,NiS nanoparticles/mesoporous black TiO₂ nanotubes?N-BTNs?with high photocatalytic activity and excellent stability were prepared by secondary solvothermal strategy.The specific surface area of N-BTNs is relatively high,with pore diameters of⁸9 m² g^-1and⁹.8 nm,respectively.The catalyst of N-BTNs has good photocatalytic hydrogen production rate(3.17 mmol h^-1 g^-1)under solar irradiation,which is almost as high as that of samples loaded by Pt nanoparticles.The apparent quantum yield of N-BTNs is5.4%at 420 nm,which is much higher than that of pristine TiO₂ nanotubes.In addition,its photocatalytic performance remains almost unchanged after repeated recycling,confirming that it has good stability.This is attributed to the fact that the composite structure of NiS nanoparticles and mesoporous black TiO₂ nanotubes can efficiently separate the electron-hole pairs of TiO₂,while TiO₂ absorbs most of the ultraviolet light,effectively suppressing the photocorrosion phenomenon commonly faced by sulfides.3.Using NiS nanoparticles/mesoporous black TiO₂ nanotubes as host materials,Pt nanoparticles/NiS nanoparticles/mesoporous black TiO₂ nanotube composites?P-N-BTNs?ternary assembly composite were prepared by ultrasonic impregnation-photoreduction strategy.The absorption efficiency of visible light was further improved by using the surface plasmon resonance effect of noble metal Pt.Under AM 1.5 irradiation,the photocatalytic hydrogen production rate of solar energy reached 5.32 mmol h^-1 g^-1,and the photocatalytic performance was better than the binary assembly of Pt-BTNs and N-BTNs,which was due to the synergistic effect of Pt and NiS nanoparticles further promoting the separation of photogenerated carriers.This novel multi-component material has potential applications in fields of energy.