Designable Synthesis And Performance Studies Of Resorcinol-Formaldehyde Resin Based Heterojunction Photocatalysts

Photocatalysis,an advanced solar utilization and conversion technique,is one of the important pathways to solve the energy and environmental crisis,where the design of efficient semiconducting photocatalysts is the key.As a novel class of low-bandgap semiconductor materials,resorcinol-formaldehyde resins（RF）withπ-conjugated benzene-quinone donor-acceptor（D-A）couples have attracted extensive attention due to their strong light absorption capacity and solar to chemical conversion efficiency.However,most of the reported RF-based photocatalysts exhibited single component and simple structure,seriously limiting their active site exposure,mass transfer diffusion and electron-hole pair separation.The photocatalytic properties of RF based materials remain to be improved.To overcome the above challenges,this thesis focuses on the construction of efficient RF-based heterojunctions as high-performance photocatalysts.Through the rational design of heterojunction types and nanostructures,it is expected to simultaneously improve the electron-hole pair separation efficiency,promote reactant adsorption/desorption,enhance redox ability and active site exposure,and thus enhance the photocatalytic performances.The major findings of this thesis are as follows:1.Type Ⅱ RF@layered double hydroxide（ZnCo-LDH）heterojunction has been constructed,using an interfacial growth-transformation strategy for photocatalytic pollutant degradation.The heterojunction exhibits a unique flower-like core-shell structure with ZnCo-LDH nanosheets assembled on the surface of RF nanospheres.The photocatalytic results show that the removal rate of methylene blue（a typical dye pollutant）by RF@LDH reached 95%,significantly higher than that of the single component of RF（71.9%）and ZnCo-LDH（36.3%）.The transient photocurrent response,electrochemical impedance spectroscopy and photoluminescence spectroscopy results indicate that the type Ⅱ heterojunction design significantly enhances the charge separation and transfer efficiency,thus improving the photocatalytic efficiency.2.Compared to type Ⅱ heterojunction,Step-scheme（S-scheme）heterojunction can further promote spatial charge separation and enhance the redox ability.In this thesis,an S-scheme RF@ZnCo-bimetal sulfide（ZCS）heterojunction has been fabricated by growing hollow ZCS nanocages on the surface of RF nanospheres for photocatalytic nitrogen fixation.The S-scheme charge transfer mechanism is confirmed by X-ray photoelectron spectroscopy,ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy.Thanks to the S-scheme heterojunction design,the redox ability of the subunits in RF@ZCS is maximumly preserved with charge separation efficiency,and N₂adsorption and activation ability improved,as evidenced by the results of photoelectrochemical test,linear scanning voltammetry and nitrogen temperature programmed desorption.As a result,the RF@ZCS heterojunction delivers an excellent N₂fixation performance with an ammonia yield of 1.1 mmol·g^-1·h^-1in pure water,significantly higher than that of RF and ZCS.3.Apart from the design of heterojunction types,this thesis further elucidates the crucial role of spatial configuration of heterojunction on regulating the photocatalytic performance.S-scheme TiO₂/RF heterojunction has been prepared by combining hollow RF nanobox with titanium dioxide（TiO₂）nanoparticles for photocatalytic oxygen reduction toward hydrogen peroxide（H₂O₂）production.To study the impact of spatial arrangement,two core-shell-structured TiO₂@RF and RF@TiO₂photocatalysts have been designed,with TiO₂ nanocrystals adhered on the interior and exterior surface of a hollow RF shell,respectively.The photocatalysis results show that TiO₂@RF exhibits a remarkable H₂O₂ yield of 66.6 m M·g^-1·h^-1in pure water,superior to RF@TiO₂ with the same heterojunction but a reversed Janus spatial arrangement and single-component RF and TiO₂.The enhanced performance of TiO₂@RF can be attributed to the following reasons:（a）The S-scheme heterojunction preserves the high redox ability of the TiO₂ and RF pair;（2）the spatial specific Janus design enhances the charge separation,promotes active site exposure,and reduces the H₂O₂ decomposition to a large extent.