| With the development of society,the problem of fossil energy shortage and worsening environment is increasingly serious.The inexhaustible solar-driven semiconductor photocatalysis technology has shown unique advantages in solving problems such as environmental pollution and energy shortage.Graphite carbon nitride(g-C3N4)has been widely used in the field of photocatalysis for its unique properties.In this paper,we mainly focus on its large particle size,small surface area,high recombination rate of photogenerated carriers,modified g-C3N4 by morphology control and semiconductor coupling.Cr(?)and diclofenac sodium(DCF)were chosen as the representative of the heavy metals and refractory organics in water,respectively.And photocatalytic and photoelectrocatalytic oxidation technologies were used to remove the pollutants.The main research contents and results are as follows:(1)Firstly,a simple,effective and environmental-friendly method was developed for enhancing the photocatalytic activity of g-C3N4 in the reduction of aqueous Cr(?)(organic acid addition)under visible-light irradiation.The enhancement was achieved via treatment of g-C3N4 in organic solvent with addition of NaOH particles by ultrasonic process for two hours.The results demonstrated that the treated g-C3N4 exhibited much higher photocatalytic activity than pristine g-C3N4 in the reduction of Cr(?)under visible-light(X>400 nm)irradiation.Under visible light irradiation for 120 min,the reduced ratios of Cr(?)in the presence of the treated g-C3N4 and pristine g-C3N4 were 100%and 37.1%,respectively.With the addition of fulvic acid,Cr(?)was efficiently removed at 40 min.Based on the characterization results of the structures and other physiochemical properties of the treated g-C3N4 and pristine g-C3N4 by X-ray diffraction,scanning electron microscopy,transmission electron microscopy and UV Vis diffuse reflectance(UV-vis),the possible reasons responsible for the enhanced photocatalytic activity of the treated g-C3N4 were proposed.The yield and mechanism of different exfoliation methods were compared by semi-quantitative method.Nanostructured g-C3N4/BiVO4 composite films with enhanced photoelectrochemical performance have been fabricated via the facile electrospinning technique.The g-C3N4 nanosheets could not only form the heterojunctions with BiVO4,but also could prevent the agglomeration of BiVO4,helping to form the nanostructures.The as-prepared g-C3N4/BiVO4 films are with good coverage and well stability.The photoelectrochemical(PEC)performance of the g-C3N4/BiVO4 films are much enhanced compared with that for individual BiVO4 films due to the enhanced electron-hole separation.The photocurrent density is 0.44 mA/cm2 for g-C3N4/BiVO4 films at 0.56 V in the linear sweep current-voltage(LSV)test,over 10 times higher than that of individual BiVO4 films(0.18 mA/cm2).The effects of preparation conditions including g-C3N4 content,collector temperature,calcination temperature and electrospinning time on the PEC performance were investigated;and the reasons for the effects were proposed.The optimal preparation condition was with 3.9 wt%g-C3N4 content in the electrospinning precursor,185? collector temperature,450 ?calcination temperature and 40 min electrospinning time.g-C3N4/BiVO4 composite was used as photoanode for photoelectrocatalytic degradation of diclofenac sodium.The photoelectrocatalytic degradation efficiency of DCF by the g-C3N4/BiVO4 photoanode is much higher than that by the individual g-C3N4 and BiVO4 photoanodes.The first order kinetic constants are estimated to be 3.2 × 10-3 min-1 for g-C3N4/BiVO4 photoanode,while the kinetic constants are 1 ×10-4 min-1 and 1.1 × 10-3 min-1 for g-C3N4 and BiV04 photoanode.To further increase the degradation of DCF in PEC process,H2O2 was added into the system,and the results indicated that DCF degradation was largely increased.The kinetic rate constant was 5.6 × 10-3 min-1 for H2O2 assisted PEC process and it was estimated to be 3.2 ×10-3 min-1 and 1 × 10-5 min-1 for the individual PEC process and H2O2 oxidation process,respectively.Effect of initial pH,H2O2 dosage and applied bias on DCF degradation was investigated in detail.The highest DCF degradation efficiency was achieved at initial pH of 3.17 and applied bias potential of 1.0 V(vs.SCE)with 10 mM H2O2 addition.Involved reactive active species were studied using electron spin resonance;a proposed reaction pathway was proposed.The excellent PEC performance and the facile preparation method suggest the g-C3N4/BiVO4 films are good candidates in energy and environmental remediation area. |
PDF Full Text Request