Construction Of Copper-species Coupled With Titanium Dioxide Composites And Enhanced Mechanism Of Photocatalytically Splitting Water To Hydrogen

Photocatalytically splitting water into hydrogen is a hot research spot to solve global energy problems.The semiconductor titanium dioxide（TiO₂）is widely used in photocatalytic water splitting for hydrogen production due to its non-toxic,stable chemical properties and its suitable conduction band（CB）.However,the low solar energy utilization rate of single TiO₂and the easy recombination of photogenerated electron-hole pairs lead to its poor photocatalytic hydrogen production ability.Non-noble metal copper has good charge transport ability and suitable hydrogen adsorption Gibbs free energy and is widely used in photocatalytic water splitting for hydrogen production.In addition,its oxides have matching energy band structures and are widely used to construct heterojunction photocatalytic materials.Based on the above background,this work,titanium dioxide coupled copper-species composites will be constructed by self-reduction under ethylene glycol-water solvothermal system using cuprous oxide as precursor and different titanium sources.On this basis,different copper-species and TiO₂will be used to form multiple heterojunction materials and their photocatalytic hydrogen production performance and enhanced mechanism will be studied.The main research contents are as follows:1.The Cu@TiO₂core-shell structure with TiO₂-wrapped Cu nanoparticles has been successfully prepared by ethylene glycol-water mixed solvothermal treatment,using different morphologies Cu₂O and titanium precursors.The composition and structure has been characterized by powder X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and nitrogen adsorption and desorption.The test results of photocatalytic water splitting for hydrogen production show that the optimal hydrogen production rate of Cu@TiO₂core-shell material reaches 4336.7μmol·g^-1·h^-1,which is about twice the hydrogen production rate of single TiO₂and commercial P25.Photo/electrochemical and photoluminescence spectroscopy results indicate that the Cu@TiO₂core-shell material exhibits enhanced photogenerated charge separation and transfer efficiency.Based on the higher work function of Cu than TiO₂and the good electrical conductivity of Cu,the built-in electric field formed by the Schottky junction of Cu@TiO₂inhibits the rapid recombination of electron-hole pairs.This allows more photogenerated electrons to participate in the photocatalytic process,resulting in enhanced photocatalytic hydrogen production activity.2.Cu@TiO_2-xcomposites containing oxygen vacancies have been obtained by ethylene glycol-water mixed solvothermal treatment.The composition and morphology has been characterized by XRD,XPS,SEM and other tests.Through electron paramagnetic resonance（EPR）studies,both single TiO_2-xand Cu@TiO_2-xcomposites have oxygen vacancy structures.Photocatalytic water splitting for hydrogen production showed that the best hydrogen production rate of the Cu@TiO_2-xcomposite was 7218.8μmol·g^-1·h^-1,which is twice the hydrogen production rate of single TiO_2-xmaterial(3542.7μmol·g^-1·h^-1).The photo/electrochemical test results show that the appropriate oxygen vacancy concentration and the introduction of metallic copper promote the electron-hole separation efficiency of the composite,thereby improving its photocatalytic hydrogen production performance.3.First,the Cu@TiO₂binary composites have been synthesized by ethylene glycol-water solvothermal treatment method,and then Cu₂O particles were deposited on the surface by a simple reduction method at room temperature,and the ternary Cu@TiO₂-Cu₂O composites were successfully prepared.The composition and structure has been characterized by XRD,XPS,SEM.The photocatalytic hydrogen production test results show that the hydrogen production rate of the ternary Cu@TiO₂-Cu₂O composite with the optimal ratio is 12000.6μmol·g^-1·h^-1,which is 4.4 times of single TiO₂material(2728.8μmol·g^-1·h^-1),and it is 2.2 times and 2.1 times of binary composites Cu@TiO₂(5595.5μmol·g^-1·h^-1)and TiO₂-Cu₂O(6076.8μmol·g^-1·h^-1),respectively.The Mott-Schottky test found that p-n junction was formed between TiO₂-Cu₂O,while Cu@TiO₂formed a Schottky contact.Moreover,the photo/electrochemical test results show that both TiO₂-Cu₂O and Cu@TiO₂binary composites can improve the separation efficiency of photogenerated charges,however the charge separation efficiency of Cu@TiO₂-Cu₂O ternary composites is higher than that of binary composite materials and single material.Based on the above results,it is speculated that the formation of p-n junction and Schottky junction in the Cu@TiO₂-Cu₂O ternary composite provides dual channels to facilitate the separation of electron-hole pairs and the transfer of photogenerated carriers,furthermore,which synergistically enhance the activity of photocatalytic water splitting for hydrogen production.