Investigation Of Configuring Active Sites On Graphitic Carbon Nitride For Photocatalytic Hydrogen Evolution

The over-reliance for fossil energy has lead to severe energy and environment problem in human society.Hydrogen(H2)energy is a promising and iedal energy carrier,which possesses high energy density(142 MJ kg-1)and has no carbon emission during usage.Since TiO2 was reported to produce H2 from water splitting under ultraviolet incidence,it has been considered as an effective and continuable approach to convert renewable solar energy to storable hydrogen energy through photo/electrocatalytic water splitting over semiconductor.The theory for such energy conversion is that under incident light,the photo-excited electrons and holes of semiconductor are separated and migrate to the surface and subsequently undergo reduction and oxidation reaction to produce H2 and O2 respectively.Till today,numerous semiconductor photocatalysts has been reported to exhibit excellent performance towards photocatalytic hydrogen evolution,such as metal-based oxide,sulfide,and nitride etc.In recent years,organic non-metal graphitic carbon nitride(g-C3N4)has been discovered as a superstar photocatalyst for its advantages in cost,non-toxicity,easy preparation and stability.Even though,the inherent recombination of excited electron-hole pairs in g-C3N4 tremendously restricts the photocatalytic H2 evolution performance.Besides,the relatively wide gap of g-C3N4(?2.7 eV)seriously limits the absorbance capacity for most visible light in sunlight.These photoelectric properties astrict the photocatalytic performance and commercial application of g-C3N4.Aimed at the demerits of g-C3N4 as photocatalyst and combined with recent photocatalytic research status,we have designed a series surface-modified co-catalytic sites on g-C3N4 to improve the separation of photo-excited carriers and expand the absorbance for visible even near-infrared(Vis-NIR)region in sunlight.The prepared g-C3N4-based nano-hybrid photocatalysts exhibit significantly enhanced photocatalytic H2 evolution performance.Here comes the specific details:1.In the first work,we have firstly prepared g-C3N4(CN)ultrathin nanosheets powder by a two-step calcination method,which was respectively decorated with MoS2 nanodots with high-purely metallic phase(1T-MNDs)and metallic MoS2 nanosheets(1T-MNSs),forming CN/ND and CN/NS heterogeneous photocatalysts.It was revealed that both of the composites showed higher photocatalytic performance than pure g-C3N4,while CN/ND exhibited the highest performance up to 5.6 mmol g-1 h-1,even comparable to hybrid CN/Pt with the same weight percentage of co-catalyst.Because of the high electron conductivity and low-Fermi energy,1T-MNDs as co-catalyst could effectively trap photo-excited electrons of g-C3N4 and notably enhance the photo-excited carries separation efficiency;moreover,1T-MNDs with more exposed active sites compared to 1T-MNSs endows CN/ND exhibit higher photocatalytic performance than CN/NS.2.In the second work,we have designed metal nickle nanoparticles(NNPs)uniformly laden on the surface of g-C3N4 forming CN/NNPs nano-heterogeneous photocatalyst and investigated the photo-thermal effect for photocatalytic hydrogen evolution induced by plasmonic NNPs.The result showed that under AM 1.5 irradiation,CN/NNPs composite enables the reaction solution to rise to nearly 80? within 2 hour and the H2 evolution manifests a significant increasing rate up to 12.23 mmol g-1h-1.The superior photocatalytic performance is attributed to:(1)NNPs anchored on g-C3N4 provide co-catalytic site and effectively trap the photo-excited electron of CN,eventually boosting the charge carrier separation,transportation and infection towards proton for HER.(2)NNPs with surface plasmon resonance(SPR)supplement the absorbance for visible and near-infrared(Vis-NIR)light,simultaneously enhance the local electromagnetic field at the heterogenous interface and promote the photo-excited carrier excitation and transmission in result.(3)The thermal relaxation of plasmonic NNPs is verified to make contribution to photocatalytic performance,providing an innovative method for developing versatile co-catalysts.