| Steadily deteriorating environmental pollution and energy shortages have become the arduous challenges to the sustainable development of modern human society.Recently,as one of the most attractive technologies,photocatalysis has been extensively studied due to its potential applications in solar energy,storage conversion and environmental pollution control.Up to now,a diversity of conventional semiconductors has been broadly investigated for photocatalytic degradation of organic pollutants.Nevertheless,application of conventional photo-catalysts was practically limited by absorption of the ultraviolet component in the solar spectrum and their rapid e--h+recombination.Although the research of conventional semiconductor photocatalysts has been obtained great progress,there were still many deficiencies.This has promoted a great deal of research on pursuing efficient,stable,low-cost,and eco-friendly photocatalysts.Among many semiconductor photocatalysts,polymeric graphitic carbon nitride(g-C3N4)has attracted considerable research interest owing to its extraordinary chemical stability,metal-free composition,visible light response and 2D structure.However,due to small specific surface area,the active site is insufficient in the photocatalytic reaction and the rapid recombination rate of charge carriers of original g-C3N4 result in low photocatalytic efficiency.In this paper,g-C3N4 semiconductor materials were prepared by direct pyrolysis and hydrothermal method.The samples were investigated in preparation,characterization,modification and catalytic performance,and the following results were obtained:(1)Pure phase g-C3N4 powder was synthesized by thermal condensation.The effect of the heat treatment time on the structure and photocatalytic properties of the g-C3N4 powder sample was investigated.The X-ray diffraction pattern results show that the prepared g-C3N4 powder samples have two peaks,which can be indexed as(100)and(002)diffraction planes,respectively.At the same time,its microscopic morphology gradually transited from a thick lamellar layer to a lamellar layer.The experimental results of photocatalytic degradation of rhodamine B showed that after 60 minutes of visible light irradiation,the samples sintered for 4 h had the highest degradation efficiency,and the degradation efficiency reached 63%.This sample was defined as the original g-C3N4,and its modification was investigated.(2)Using ammonium hydrogen carbonate(NH4HCO3)as a gas template,g-C3N4 with a porous structure was synthesized by adjusting its mass ratio to precursor urea.It was found from the X-ray diffraction pattern that the graphite-like structure of g-C3N4 was not destroyed by using the NH4HCO3 gas template,and the microscopic morphology thereof exhibited a transition from a few pore structures to a porous structure.In particular,the specific surface area and pore volume(59 m2/g and 0.35 cm3/g)of the sample synthesized from urea:NH4HCO3(10:3)were significantly improved compared to the original g-C3N4(31 m2/g and 0.16 cm3/g),its degradation efficiency at visible light irradiation of 60 min could reach 97%,which was greatly improved compared with the degradation efficiency of 63%of the original g-C3N4.This was attributed to the larger specific surface area of the porous sample,thus providing more reaction site.(3)The desired sample was prepared by protonation treatment with concentrated hydrochloric acid for the original g-C3N4 sample followed by sonication.The(002)diffraction peak of g-C3N4 showed a slight red shift after treatment by the protonated ultrasonic process based on the X-ray diffraction pattern,which indicated that the interlayer spacing of g-C3N4 was decreased.At the same time,according to the UV-visible absorption spectrum,it could be seen that the light absorption edge of the modified sample showed a slight blue shift,and the photocatalytic degradation efficiency is 60%at 60 min of visible light radiation,which was not improved compared with the photocatalytic efficiency of the original g-C3N4.(4)The g-C3N4/MWCNT composite photocatalyst was successfully prepared by solvothermal method.According to the X-ray diffraction pattern,a small amount of MWCNT was found,which not affected the structure of g-C3N4.At the same time,according to the UV-visible absorption spectrum,it was seen that the light absorption edge of the composite material showed a slight blue shift,and it had a certain degree of absorption in the visible light range.The peak strength of the composite was much lower than that of the pure sample by photoluminescence spectrum could be found that the MWCNT was beneficial to the electron transfer and reduced the electron hole recombination rate due to the formation of heterojunction.In particular,the photocatalytic degradation efficiency of g-C3N4/MWCNT after protonated sonication was 86%at 60 min of visible light irradiation. |
PDF Full Text Request