Fabrication Of Copper-based Materials-meso Porous Titanium Dioxide Composites And Their Photocatalytic Hydrogen Evolution Performance

In recent years,the photocatalytic technology of hydrogen evolution from water splitting driven by solar energy has attracted wide attention.Porous TiO₂ has been widely applied to photocatalytic water decomposition for hydrogen production due to its suitable valence band and conduction band position and large specific surface area.However,there are some shortages in the photocatalytic reaction of single TiO₂ ,such as fast recombination of photogenerated carriers,narrow spectrum utilization and low efficiency of solar energy utilization,which limit its practicle application in the photocatalytic hydrogen evolution.At the same time,it was found that the introduction of cocatalyst can effectively promote the separation of photogenerated electron-holes,reduce reaction overpotential and provide active sites for hydrogen production,thereby improving the efficiency of semiconductor photocatalytic hydrogen production system.Nowadays,noble metal and non-noble metal cocatalysts are the main types of cocatalysts,but noble metal could not be widely used because of its rarity,which makes the search for efficient and earth-abundant non-noble metal cocatalysts attracted much attention.Among them,non-noble copper-based cocatalysts have good charge transfer ability and suitable Gibbs free energy for hydrogen adsorption,so they have potential applications in photocatalytic splitting of water for hydrogen production.Based on the above background,porous TiO₂ with stable chemical properties,easy preparation,non-toxicity and low cost was used as the host-catalyst,and the simplest non-precious copper was selected as the cocatalyst to construct binary and ternary composite materials by appropriate preparation methods,and their catalytic activity in photocatalytic hydrogen production were also studied.The possible catalytic and synergistic mechanism were discussed.The main works are summarized as follows:1.The rod-like porous TiO₂ material was obtained by hydrolysis of titanium glycolate precursor.By adding TiO₂ into the reaction system containing copper source and dual ligand agents for solvothermal reduction,the copper particles were successfully loaded onto the surface of porous TiO₂ to form TiO₂-Cu composite.The composition and structure of the TiO₂-Cu hybrid were analyzed by powder X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,and nitrogen adsorption.The results of photocurrent and electrochemical impedance analysis show that Schottky contact is formed at the interface between copper and n-type TiO₂ ,which showed significant photocurrent enhancement.The results of photocatalytic water splitting for hydrogen showed that pure TiO₂ had lower hydrogen production activity (260?mol?g^-1?h^-1).However,the introduction of appropriate amount of copper nanoparticles can improve the photocatalytic hydrogen production efficiency of TiO₂ .When the content of Cu reached 2.5 wt%,the TiO₂-Cu hybrid exhibits superior hydrogen evolution capability with rate of 6046?mol?g^-1?h^-1,which is 23 times higher than that of pure TiO₂ .Transient photocurrent results demonstrated that due to the rectification effect of Schottky junction,the maximum photocurrent density of TiO₂-Cu hybrid was almost 28 times that of pure TiO₂ ,which further indicates the TiO₂-Cu composite could effectively separate and transfer photogenerated electron-hole pairs to improve the photocatalytic efficiency of water decomposition for hydrogen production.In addition,because the work function of copper metal is larger than that of TiO₂ ,metallic copper can be used as the electron capture center to accumulate electrons and eefctively reduce protons or water,thus further promoting the rate of hydrogen evolution.This work not only provides a method for fabricating copper-semiconductor composites,but also further verifies that the reasonable design and construction of metal-semiconductor with Schottky contacts in can significantly improve their photocatalytic activity.2.Choosing the binary TiO₂-Cu hybrid with positive charge from the first part.Ternary TiO₂-Cu@C composite was successfully prepared by mixing TiO₂-Cu hybrid with negatively charged amorphous carbon dots?CDs?solution by electrostatic self-assembly method.The ternary TiO₂-Cu@C was characterized by XRD,XPS and Fourier transform infrared spectroscopy?FT-IR?.The results showed that metallic copper and CDs were dispersed on porous TiO₂ .In the experiment of photocatalytic hydrogen evolution,there was almost no hydrogen production in the catalysis materials of TiO₂ and TiO₂ @C.The results indicated that CDs could not provide the active sites for hydrogen production.The optimum TiO₂-Cu@C exhibited remarkable hydrogen evolution rate of 3911?mol h^-1g^-1and excellent cyclic catalytic activity,which is 1.6 times higher than that of binary TiO₂-Cu hybrid.Photoelectrochemical measurements and time-resolved fluorescence analysis indicated that both metallic Cu and CDs have good conductivity which was beneficial to promote the charge transfer and separation in TiO₂-Cu@C composite.Thus,CDs act as an electronic medium in ternary TiO₂-Cu@C composite to create another electron transfer pathway to further enhance the activity of binary TiO₂-Cu,where the photogenerated electrons on TiO₂ could pass through the CDs to the copper cocatalyst and reduce water to hydrogen.This work provides a reference for the construction of ternary composite materials for high-efficiency photcatalytic hydrogen production.