CuO And Cu Nanoparticle Modified Mesoporous TiO₂ Spheres-preparation And Hydrogen Evolution Application

The environment and energy crisis are the two major problems troubling every country in the world,meanwhile,human development will be hindered without enough energy.Considering the serious environmental problems caused by the use of fossil fuels,hydrogen is seen as a potential alternative clean energy due to the high calorific value and clean property.Photocatalytic H₂ production by water splitting is a promising alternative to conventional fossil fuels,which is of great potential to relieve the energy and environmental issues and bring an energy revolution in a clean and sustainable manner.Photocatalysts play a key role in the photocatalytic hydrogen production,TiO₂with excellent resistance ability to photo corrosion and chemical corrosion,environmental friendness and good photocatalytic activity is one of the most popular catalytic materials and has been widely studied in photocatalytic hydrogen production.However,due to the wide band gap and the fast recombination rate of photogenerated electrons and holes,it is difficult for TiO₂ to achieve efficient catalysis and move towards practical application.Recently,several strategies have been proposed to improve the photocatalytic performance of TiO₂,including metal co-catalyst coupling,non-metal doping,photosensitizer modification and defect introduction.Hierarchically mesoporous TiO₂ has extremely high specific surface area,large pore volume,adjustable pore structure and morphology,and nanoscale effect.These characteristics make hierarchically mesoporous TiO₂ become a material with good performance in many fields.Cu-based materials have attracted much attention due to their abundant reserves,low price,controllable valence state and controllable catalytic performance of their different oxidation states.This paper focuses on the synthesis,modification,characterization and photocatalytic performance of hierarchically mesoporous TiO₂ to improve the photocatalytic hydrogen production activity,committed to achieve the green industrial application of TiO₂-based photocatalyst.The research content of this paper mainly involves the following aspects:（1）Photocatalytic hydrogen evolution reaction is one of the most promising solution to the rapid increasing environmental and energy issues.In this part,a highly efficient photocatalyst-small CuO nanoparticles decorated TiO₂ mesoporous spheres（CuO/TiO₂）was prepared through the introducton of the copper（II）ions into the layered titanate nanosheets before thermal phase transformation into CuO/TiO₂ composites.The small CuO nanoparticles greatly improve charge separation efficiency and enable a significant enhancement on the photocatalytic hydrogen evolution reaction（HER）efficiency to 12.45 mmol/g/h.Cyclic HER measurement of 20 h demonstrated excellent stability of photoactivity for the obtained sample.（2）Mesoporous TiO₂ modified by metal Cu nanoparticles with controllable particle size.In this work the confinement of“copper ions”within the mesoporous TiO₂precursor-layered titanate nanosheets enabled preparation of copper modified TiO₂mesoporous spheres（Cu/TiO₂）,which contain well dispersed small copper nanoparticles with a diameter of approximately 3-5 nm over the TiO₂ mesoporous spheres.Without cocatalyst（e.g.Pt）,the obtained samples exhibited superior photocatalytic hydrogen evolution reaction（HER）activity（13.45 mmol/g/h）and excellent durability during a cyclic HER testing for 120 h,compared against 2.41mmol/g/h of the Cu-modified P25 TiO₂.Computational simulations suggest that the Fermi level of small copper nanoparticles is located between the conduction band of TiO₂ and the H⁺/H₂ reduction potential and if extrapolated to nanoparticles,this holds for particles up to approximately 9 nm.This would efficiently facilitate electron trapping and then transfer from the TiO₂ to the copper followed by the reduction reaction,leading to excellent photocatalytic H₂ evolution reaction.