Pt-loaded N-doped Carbon Derived From Different Precursors And Its Promoted Photocatalytic Hydrogen Production

Hydrogen energy is regarded as one of the best green energy sources to solve the two major problems of energy scarcity and environmental pollution because of its high calorific value and clean combustion products.Using renewable solar energy to decompose water into hydrogen under the action of catalyst is an ideal way to obtain hydrogen energy,so the photocatalyst becomes an indispensable part of the development of photocatalysis technology.Among all kinds of photocatalysts,Ti O₂ and CdS semiconductor photocatalysts have gained wide attention because they are cheap and easy to obtain and can be easily prepared by various methods.However,both of them have the shortcomings of the easy recombination of electron-hole pairs generated by photoexcitation,few reactive sites and low surface reactivity,which seriously limit their practical application.Therefore,in view of the above problems,the main research content of this study is as follows.（1）The Pt metal-organic framework（Pt MOF）was firstly supported on the surface of Ti O₂ nanosheet by a simple hydrothermal reaction,and then annealed at high temperature in inert atmosphere,obtaining the NC@Pt/Ti O₂ composite catalyst.The morphology,structure,and photoelectric properties of the catalyst were characterized by Raman,XRD,SEM,TEM,XPS,BET,ICP-MS,UV-Vis,PL,EIS,and so on.During the annealing process,the metal-organic framework is transformed into N-doped carbon skeleton（NC）,while the Pt precursor bonded to the metal-organic framework is reduced in situ to Pt nanoparticles and dispersedly loaded onto the Ti O₂ surface by means of the NC skeleton,thus exposing more Pt reaction sites and accelerating charge transfer and surface reaction.Finally,NC@Pt/Ti O₂exhibited remarkable hydrogen production activity under UV light.The effects of the annealing temperature and the air/N₂ ratios on the photocatalytic performance of NC@Pt/Ti O₂-y were investigated.The results exhibited that the hydrogen production activity of NC@Pt/Ti O₂-700 was the best,and the hydrogen production capacity was 11.83mmol·h^-1·g^-1,which was 78.1 times that of pure Ti O₂(0.15 mmol·h^-1·g^-1).Moreover,after long cycle testing,it showed good repeatability and can maintain stable hydrogen production performance under 40 h photocatalytic testing.（2）The Pt precursors coordinated by chitosan（CS）were coated on SiO₂ nanoparticles as hard templates so as to make Pt nanoparticles dispersed at molecular level,following by its annealing at high temperature in an inert atmosphere to get the N-doped carbon（NC）layer embedded with Pt on the SiO₂ outer surface（SiO₂@Pt-NC）.Then,CdS was coated on the SiO₂@Pt-NC surface through the hydrothermal reaction,during which the SiO₂ is etched off synchronously,so as to obtain the hollow composite material Pt-NC@CdS-HS.Finally,the hollow multi-shell photocatalyst Pt-NC@CdS@Ni Co-LDH-HS was formed by coatingfurther Ni Co-LDH on Pt-NC@CdS-HS outer surface by hydrothermal reaction.The structure and morphology were characterized by XRD,TEM and XPS.The photoelectric properties were also tested and analyzed by UV-Vis,PL,EIS,and so on.The prepared photocatalyst Pt-NC@CdS@Ni Co-LDH-HS has good photoelectric properties.Under the conditions of visible light and lactic acid as sacrificial agent,the photocatalytic hydrogen production capacity of Pt-NC@CdS@Ni Co-LDH-HS was as high as 64.51 mmol·h^-1·g^-1,which was 1.8and 215 times those of Pt-NC@CdS-HS and CdS-HS,respectively.The strong photocatalytic activity is mainly attributed to the high dispersion and strong loading of Pt nanoparticles in the NC layer,which provides more reactive sites for hydrogen evolution reaction and effectively separates photoelectrons-hole pairs,promoting the photocatalytic performance of CdS.In addition,CdS/Ni Co-LDH heterojunction is constructed,which reduces the band gap width of CdS and broadens its visible light absorption range.More importantly,S-type heterojunction between CdS and Ni Co-LDH can transfer photogenerated electrons and holes in a directional way,forming a"production-transport-utilization"mode of photogenerated charge carriers to realize its effective separation.