| Solar energy,as a renewable and clean energy,is the best choice to improve the sustainable development of energy and environment.Photocatalysis is one of the important means to realize the practical conversion of solar energy,and its core technology is semiconductor photocatalytic.Semiconductor materials using solar energy for redox reaction to degrade phenolic pollutants,antibiotics,dyes and heavy metal ions in water,is regarded as a long-term solution to address the global energy shortage and environmental problems.G-C3N4,owing to its low-cost,environmental friendliness,energy-saving and tunability of band structure,stands out among many photocatalytic materials and has become a hot material in the field of photocatalysis.In recent years,many approaches,such as morphology control,doping,defect introduction and heterojunction construction have been adopted to improve the photocatalytic activity of g-C3N4 materials,which have been applied in many fields such as photocatalytic hydrogen production,CO2 reduction,environmental treatment and so on.Based on the reported modification strategy of g-C3N4,this paper aims to improve the photocatalytic activity of g-C3N4-based photocatalysts fundamentally by promoting photoinduced carrier generation,enhancing driving force of carrier separation and improving carrier migration efficiency,separately,realizing the efficient degradation of pollutants.(1)Construct near-infrared absorption CNS0.6/Au-1 photo-catalyst and its efficient reduction of Cr(Ⅵ):A new idea of increasing the electronic transition types of catalysts to promote carrier generation and improve photocatalystic activity,is proposed.The proposed CNS0.6/Au-1 is established by loading ultrafine Au nanoparticles on the surface of sulfur doped carbon nitride(CNSX).CNSX can not only keep the intrinsic π→π*electronic transition but also awaken the n→π*electronic transition in carbon nitride leading to a slightly widened absorbance to 495 nm.Plasmon-induced hot electron of Au nanoparticles merge with e-excited from n→π*n and π→π*electronic transition in CNSX increasing the amount of catalytically active π electrons,and the efficient carrier separation is also achieved.Benefiting from above unique strategy,CNS0.6/Au-1 possesses the extended absorption region to near 800 nm and exhibits a remarkable photo-reactivity,which can degrade 10 ppm Cr(VI)completely within 40 min.The presence of n-electrons,hot electrons and their catalytic ability are illustrated by electron spin resonance(ESR),ultraviolet spectroscopy,and monochromatic light experiments.The improved carrier separation efficiency of CNS0.6/Au-1 is also confirmed by fluorescence,transient fluorescence and photocurrent measurements.After four cycles of degradation experiments,the photocatalyst still maintains 87.0%reduction rate of Cr(Ⅵ)and has good structural stability.(2)Construction of molecular covalent heterojunction CN-PDA65 to enhance the driving force of carrier separation and realize efficient degradation of BPA:A new idea of constructing molecular covalent heterojunction catalyst to improve the driving force of carrier separation is proposed.The composite photocatalyst CN-PDA65 is created by grafting perylene acid to g-C3N4,which broadens the visible light response range to near 600 nm and improves the utilization efficiency of sunlight.The construction of the molecular-scale heterojunction effectively promotes the separation of photogenerated charges at sufficient heterojunction interface.Furthermore,the strong charge orientation flow between g-C3N4 and perylene acid molecules effectively enhances the driving force for the separation of photogenerated electrons and holes at heterojunction interfaces.The results of PL,transient photocurrent and ESR show that the CN-PDA65 has significantly improved carrier separation efficiency,increased photocurrent response and more active species for degradation.Under the irradiation of 250 W Xenon lamp(λ>420 nm),CN-PDA65 can degrade 10 ppm BPA in 20 min.After 5 cycles of degradation,the degradation rate of composite photocatalyst still remains 87.1%.The molecular-level covalent heterojunction with strong interaction increases the heterojunction interface area and improves the driving force of carrier separation,which provides a reference for the development of metal-free organic photocatalysts.(3)Construction of ultra-thin 2D CN-Br0.12/2%RhOx photo-catalyst with rapid electron and hole migration for efficient bisphenol A degradation:Dual cocatalysts,Br and ultrafine RhOx nanoparticles,are constructed on ultrathin CN for synergetic photocatalysis.Ultrathin CN decreases the migration distances,while cocatalysts Br and RhOx can accelerate electron and hole transfer simultaneously,maximizing carrier transfer performance of CN.X-ray photoelectron spectroscopy(XPS),electron spin resonance(ESR),cyclic voltammetry(CV)and Mott-Schottky plots are used to elucidate the specific mechanism of the co-catalysts of Br and RhOx in the photocatalytic degradation process.The separation efficiency of CN-Br0.12/2%RhOx is also improved with the demonstration of fluorescence,transient fluorescence and transient photocurrent measurements.Therefore,CN-Br0.12/2%RhOx can degrade 10 ppm BPA in 9 min,which is the fastest degradation rate among g-C3N4-based photocatalysts reported so far.The photocatalytic degradation rate of BPA is 89.1%after 6 degradation reactions,and the photocatalyst has good structural stability.This work obtains an enhanced electron-hole separation efficiency and migration efficiency by combining ultrathin CN with dual-channel cocatalysts,leading to the best photocatalytic degradation performance reported for CN. |
