The Preparation Of TiO₂-based Photocatalysts And Their Ultrafast Interfacial Carrier Dynamics

As a kind of clean energy,solar energy is considered to be the most potential energy.Utilizing the solar energy can effectively help human to solve the increasingly serious energy crisis and environmental pollution.Photocatalytic technology and solar cell technique are mainly two kinds of photoelectric conversion technology.Traditional photovoltaic is based on silicon or polycrystalline silicon as a raw material which is very expensive,and the preparation process makesmuch pollution.The newly developed metal oxide nano materialswith non-toxic,high stability,low-cost and other advantages have been widely employed in photocatalytic hydrogen production and the thin film solar cell.Nevertheless,the single metal oxide often exhibit poor light trapping ability,low photogenerated carrier concentration,and low photo quantum efficiency,thus retard the large-scale industrialization.This paper takes TiO₂-based heterojunction nanocomposites as research topic,which is expected to point the direction for preparing the high performance photocatalysis.Firstly,making use of the feature of n-type TiO₂,together with the p-type Cu₂ O narrow band gap semiconductor,we prepared the Cu₂O/TiO₂ p-n heterojunction nanohybrids.Cu₂O/TiO₂ nanohybrids have a built-in electric field which can enhance the separation of photo-generated electron-hole pairs and accelerate the free carriers transfer across the interface,meanwhile,they have enhanced visible light absorption,thus exhibit strong photocatalytic hydrogen production activity.One pot hydrothermal method synthesis of Cu₂O/TiO₂ show well-dispersed and high surface area.Employing the time-resolved spectroscopy,we study the carrier dynamics across the Cu₂O/TiO₂ interfaces.It's well identified that the electron transfer rate is higher than TiO₂ as a result of the built-in electric field at the interface of Cu₂O/TiO₂.We also estimate the electron-hole recombination rate,and elucidate the electron transfer mechanism.Next,we synthesized plasmonic Cu nanoparticles modified TiO₂ nanohybrids in ethanol and ethylene glycol system via a pot solvothermal method.Under visible light irradiation,Cu/TiO₂ nanohybrids exhibit enhanced photocatalytic hydrogen production versus pure TiO₂.Employing the picosecond photoluminescence spectroscopy and femtosecond transient absorption spectroscopy,we study the carrier dynamics across the Cu/TiO₂ interfaces.In contrast to the noble metal Au and Ag,Cu nanoparticles also exhibit the strong surface plasmon resonance absorption in the visible region.Based on design concept of Schottky junction,Cu/TiO₂ nanohybrids is relative low cost and ideal photoelectrical conversion materials.Lastly,on the basis of preparation of Cu₂O/TiO₂ and Cu/TiO₂ nanohybrids,we proposed a solvothermal method for synthesizing the multi-component Cu/Cu₂O/TiO₂ nanojunction.In the ethanol,ethylene glycol and water system,we can obtain the well-dispersed Cu/Cu₂O/TiO₂ nanohybrids by controlling the proportion of ethanol and ethylene glycol.Because of the reducibility of ethylene glycol,Cu²⁺ can be firstly reduced to Cu⁺,and then be reduced to elemental Cu.Using the time-resolved spectroscopy,we found the multi-component Cu/Cu₂O/TiO₂ nanohybrids have shortest fluorescence lifetime,and the fluorescence quenching can be observed.It indicates the multi-component photocatalysis can accelerate the electron transfer,thereby show high photocatalytic activity.