Preparation Of Supported G-C₃N₄ Photocatalyst And Study On Degradation Of Rhodamine B

In the new era of rapid development of industry and technology,printing and dyeing wastewater accounts for about 10%of the total industrial wastewater.Due to the complex composition and poor biodegradability of printing and dyeing wastewater,it cannot be completely removed by traditional sewage treatment methods.Photocatalytic technology,a kind of green,highly oxidative wastewater treatment technology that can completely mineralize refractory,toxical and harmful organic pollutants into CO₂,H₂O or smaller inorganic molecular substances.The abundance and universality of solar energy makes it can be used on site without additional operating costs.However,due to the difficulty in recovering the powdery catalyst and the high cost of separation after the photocatalytic reaction,the photocatalytic technology is limited in practical applications to some extent.Therefore,this study carried out the on photocatalyst loading and its degradation performance of rhodamine B?RhB?,which mainly includes the following three parts:A photocatalytic membrane was formed on the stainless steel mesh by a phase inversion method after the powdery g-C₃N₄ photocatalyst and the binder polyvinylidene fluoride?PVDF?were supported on a stainless steel mesh,and 50 mg g-C₃N₄ and 80 mg g-C₃N₄ and 110 mg g-C₃N₄ contained photocatalytic membrane were prepared.SEM,XRD,FI-IR,Raman,and XPS analysis of the photocatalytic membrane showed that PVDF and g-C₃N₄ only physically mixed,and no interaction occurred between them.The crystal structure,surface functional group,skeleton structure and chemical valence of g-C₃N₄ in the photocatalytic membrane were not changed.According to UV-vis spectra,the light absorption wavelength range of the photocatalytic membrane is basically the same as that of the powdery g-C₃N₄,which is about 460 nm.The porosity of the photocatalytic membrane containing 80 mg g-C₃N₄ was the largest among the three samples,which was 47.93%.The maximum photocurrent response value was 6.8?A/cm² and the radius of the Nyquist curve arc was the smallest,demonstrating the efficient separation of phorogenerated electrons and holes.The performance of the photocatalytic membrane for degrading rhodamine B was investigated,the photocatalytic membrane containing 80mg g-C₃N₄ had the best degradation effect,which was 58.76%,20,76%and 3.93%higher than that of photocatalytic membranes containing 50 mg g-C₃N₄ and 110 mg g-C₃N₄,respectively.The photocatalytic membrane prepared above was modified via hydrophilicity,and part of PVDF was replaced by amphiphilic block binder F-127,and 1wt%F-127,3wt%F-127 and 5wt%F-127 photocatalytic membrane were prepared.From the contact angle test it can be known that the modified photocatalytic membrane changed from hydrophobic to hydrophilic,and the porosities of the three photocatalytic membranes were 49.23%,53.92%,and 54.05%,respectively,about 6%higher than unmodified photocatalytic membrane.Similarly,the structural characterization analysis of the modified photocatalytic membrane showed that there was no significant changes in the phase,crystal structure,surface functional group,and skeleton structure.After testing,the light absorption wavelength of the photocatalytic membrane containing 3wt%F-127 was the largest at about 482 nm.The photocurrent response value also increased,and the photocatalytic membrane containing 3wt%F-127 was the largest,about 8.7?A/cm².Under visible light irradiation,the removal rates for RhB of photocatalytic membranes containing 1wt%F-127,3wt%F-127,and 5wt%F-127 were 66.55%,79.90%,and 72.16%,respectively.Among them,the photocatalytic membrane containing 3wt%F-127 had the best degradation effect,which was 21.70%higher than the removal rate of the photocatalytic membrane before modification?containing 80mg g-C₃N₄?.Through active factor trapping experiments,it was proved that superoxide radical?·O₂^-?was the active group that played a major role in the photocatalytic degradation of rhodamine B.The effects of three factors:hydraulic retention time,initial concentration of rhodamine B,and light intensity on the degradation of rhodamine B were investigated.Response surface methodology was used to optimize the optimal process parameters and the extent of the effects.The order of the effect of RhB removal rate was:hydraulic retention time>initial concentration of RhB>light intensity.The best process conditions were:163.45 min of hydraulic retention time,13.34 mg/L of initial concentration of RhB,and 39844.81 Lux of light intensity.By this,the theoretical removal rate of RhB was 92.94%,and the vale was 91.37%by the experiment,indicating that the sub-model was very reliable.After 5 repeated experiment,the degradation rate of RhB in the photocatalytic membrane decreased from 91.37%to76.22%,and it still had the good photocatalytic performance.