Modification And Photocatalytic Performance Study Based On G-C₃N₄

Using solar photocatalytic reaction can realize either photocatalytic water splitting to produce hydrogen and oxygen,or photocatalytic decomposition of pollutants in water,and so it become a kind of green,efficient,effective way to solve the problem of energy and the environment.Exploring high performance and low cost semiconductor photocatalyst becomes the key issue in the photocatalytic reaction.Graphite carbon nitride?g-C₃N₄?,as a new metal free polymeric visible-light catalyst,because of its unique electronic,band structure and excellent chemical stability,is considered to be one of the photocatalytic materials that is most worth exploring.This thesis mainly designed and prepared various of g-C₃N₄ and g-C₃N₄ composite photocatalytic materials with excellent photocatalytic performance by employing the different modification strategies through a simple thermal condensation method.We also further investigated the regulation rules and effects of its crystal structure regulation,band gap regulation,construction heterojunction,and photoelectrical properties on g-C₃N₄ photocatalytic activity.Sulfur-mediated uniform porous g-C₃N₄ and sucrose-mediated mesoporous g-C₃N₄ were obtained by using a simple bubble templates method,and the obtained porous g-C₃N₄ shows increased specific surface area.The possible formation mechanism of porous g-C₃N₄ was investigated by TG-DSC analysis.The obtained porous g-C₃N₄ displays improved light absorption due to the multiple reflection and scattering of incident light from the porous structure.PL and EIS measurements reveals that the sulfur-mediated uniform porous g-C₃N₄ and sucrose-mediated mesoporous g-C₃N₄ exhibits enhanced charge carrier separation efficiency,which suggests that the porous structures can shorten the distance and time for charge carrier transfer from bulk to surface,and thus improve the phtocatalytic performance of g-C₃N₄.Graphitized polyacrylonitrile?g-PAN?/g-C₃N₄ composite nanosheets were synthesized through a simple one-step thermal condensation approach,and hollow tapered carbonized polyacrylonitrile?C-PAN?/g-C₃N₄ composite nanotubes were successfully constructed by sulfur-mediated self-templating method.The formation mechanism of the composite nanotubes was thoroughly discussed by FESEM,TEM and EDS-mapping measurements.Uv-vis DRS measurement shows that by compositing C-PAN enhanced light absorption.PL and electrochemical measurements reveal that C-PAN acts as an effective charge carrier transfer channel to promote the interface charge transfer,and the lifetimes of charge carriers are effectively prolonged.Both of the g-PAN/g-C₃N₄ composite nanosheets and hollow tapered C-PAN/g-C₃N₄ composite nanotubes show superior photocatalytic H2 evolution activities compared with pure g-C₃N₄ under visible light irradiation.And the photocatalytic H2 evolution activity of C-PAN/g-C₃N₄ composite nanotubes is higher than that of g-PAN/g-C₃N₄ composite nanosheets.Carbonized polydopamine?C-PDA?/g-C₃N₄ composites were synthesized by combining in situ polymerization,and thermal condensation methods with carbonation.XRD and HRTEM measurements indicate that the C-PDA/g-C₃N₄ composites display enhanced crystallinity compared with pure g-C₃N₄.It suggests that C-PDA can act as a microreactor keeping the precursor of melamine and intermediates from evaporation and decomposition,to promote the completely condensation of g-C₃N₄.And PL and EIS measurements indicate that C-PDA can also function as a charge carrier transfer channel facilitating the charge separation and transfer.C-PDA/g-C₃N₄ composites show superior photocatalytic H2 evolution activities under visible light irradiation,and also display superior photocatalytic O2 evolution performance as well as the photocatalytic performance for degradation of Rh B.Zeolitic imidazolate framework?ZIF-8?derived carbon?C-ZIF?/g-C₃N₄ composites were prepared via a simple thermal condensation method.The obtained C-ZIF/g-C₃N₄ composites exhibit superior H2 evolution activities in the absence of Pt under visible light irradiation,which is even 2.8 times higher than that of Pt/g-C₃N₄.PL,LSV and EIS measurements reveal that the C-ZIF/g-C₃N₄ composites show enhanced charge carrier separation efficiency,and the C-ZIF/g-C₃N₄ composites also display superior electrochemical H2 evolution performance,which suggests that the C-ZIF not only acts as an electron acceptor to improve charge carrier separation,and functions as a cocatalyst to promote the photocatalytic H2 evolution.This work constructs a metal-free,all carbon-based photocatalytic system for efcient hydrogen evolution for the first time.