| Semiconductor photocatalyst are widely used in energy and the environment.Polymeric graphitic carbon nitride?g-C3N4?was often used as photocatalytic degradation of organic pollutants and photocatalytic hydrogen production,because it belongs to non-metallic semiconductor with high visible light photocatalytic activity,proper electronic band structure,superior physical and chemical stability.However,the bulk g-C3N4 obtained by traditional sintering progress has inherent limitations including:serious recombination of photogenerated electron-hole pairs;limited visible light??<450nm?absorption range;its large size,low specific surface area and poor dispersion in water resulting.In order to effectively solve the above problems,we used nanofibers?NFs?with ultralong one-dimensional structure as the carrier and constructed heterojunctions to promote the separation of photogenerated electron-hole pairs.We prepared the composite NFs photocatalyst with high photocatalytic activity and excellent recyclability by combining the electrospinning technology with impregnation method.?1?g-C3N4 nanostructures were loaded evenly in PVP/TEOS/g-C3N4 NFs by electrospinning technology.Further calcinating the PVP/TEOS/g-C3N4 NFs to obtain SiO2@g-C3N4 NFs and the g-C3N4 nanostructure were highly immobilized on SiO2 NFs.This method can prevent the aggregation of g-C3N4 nanopowder in liquid phase.And then,by changing the calcination temperature,we study the influence of the temperature on load,structure,morphology and catalytic performance.The characterization analyses of structure and morphology showed that SiO2@g-C3N4 NFs have ultra-long one-dimensional nanofiber structure,and the specific surface area(116.3m2.g-1)is higher than that of the g-C3N4nanopowder.The results of photocatalytic test showed that when the calcination temperature is 550?,the SiO2@g-C3N4-550 NFs displayed the best degradation rate.Simultaneously,SiO2@g-C3N4 NFs could prevent the agglomeration of bulk g-C3N4 nanoparticles in liquid phase reaction.SiO2@g-C3N4 NFs could be effectively separated and recycled by natural precipitation,and it still maintained good catalytic performance after five cycles.?2?SiO2@g-C3N4 NFs are used as carriers.BiOI nanosheets were grown on SiO2@g-C3N4 NFs to form the SiO2@g-C3N4/BiOI heterojunction composite NFs via a facile impregnation method at room temperature.This can easily achieve the immobilization of g-C3N4/BiOI heterojunctions.And the degradation rate constant of the SiO2@g-C3N4/BiOI NFs was nearly fourfold that of SiO2@g-C3N4 NFs,SiO2@BiOI-15 NFs and their physical mixture.The enhanced photocurrent densities,decreased photoluminescence intensity,and shortened transient photoluminescence life time of SiO2@g-C3N4/BiOI NFs all confirmed the improved charge separation.Active species trapping and electron spin resonance-trap technique demonstrated that the photogenerated holes,·OH and·O2-are active radicals in the degradation process.And the loaded heterojunctions display a Z-scheme system in photocatalysis.Moreover,the number of g-C3N4/BiOI heterojunction on SiO2@g-C3N4/BiOI NFs can be easily tuned by adjusting the amount of BiOI nanosheets via controllable impregnation times.In addition,with the increase of the number of heterojunctions,the photocatalytic actvity was firstly increased and then decreased,indicating that the morphology,the number of heterojunctions,the specific surface area all would affect the photocatalytic performances.The SiO2@g-C3N4/BiOI NFs with high photocatalytic activity could be easily separated by sedimentation due to the three-dimensional porous network structures of the SiO2 NFs support.Also,the SiO2@g-C3N4/BiOI NFs exhibited high stability and could be reused without much decrease in photocatalytic activity after several recycles. |
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