Preparation Of Graphene Oxide Based Photocatalysts And Degradation Performance Towards Tetracycline

The potential risks of new antibiotic-like contaminants to the environment and humans have attracted considerable attention.Tetracycline,a typical broad-spectrum antibiotic,is heavily used in health care,aquaculture,and animal husbandry.The ensuing potential water environmental pollution problems have posed higher requirements for our urban water purification and treatment processes.In this study,copper oxide modified bismuth chloride oxide(BOC/Cu2O)photocatalytic materials were prepared,and GO@BOC/Cu2O composites were synthesized using graphene oxide(GO)as the matrix.The influence of the doping modification on the photocatalytic performance of the materials was explored,and the potential of the "adsorption+photocatalytic" system for the removal of tetracycline in an aqueous environment was confirmed.The surface morphology,chemical composition and functional group characteristics of the materials were analyzed by field emission scanning electron microscopy(FESEM),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),Raman spectroscopy,X-ray electron spectroscopy(XPS),ultraviolet-visible absorption spectroscopy(UV-Vis DRS)and Zeta potential.The main conclusions are as follows:(1)GO,BOC,BOC/Cu2O and GO@BOC/Cu2O materials were synthesized in this work.The presence of unevenly distributed folds and stacking structures on the GO surface was observed under field emission scanning electron microscopy(FESEM),and the materials exhibited a lamellar structure,which provided active sites for the adsorption of tetracycline.In addition,the BOC materials exhibited lamellar morphological features,and the size of the lamellae ranged from 0.2 to 2 μm.Cu2O microspheres and BOC flakes were observed on the surface of GO@BOC/Cu2O,which were bound to GO by intercalation and stacking.Most of the folds as well as the surface structural features of GO were preserved in the composites,but the transparency of the edge regions was increased.This indicates that the repulsive force between the layers is enhanced and GO may be reduced during the grafting process of Cu2O and BOC.The Raman spectroscopy results show that the degree of carbon defects in the composites appears to be increased to some extent,which is related to the introduction of heteroatoms.Satellite peaks corresponding to Cu2+ were observed in the composites’ highresolution Cu 2P spectrograms,indicating that a partial conversion of Cu1+ to Cu2+ occurred during the loading process.The photo absorption sidebands of BOC/Cu2O showed a significant red shift as Cu2O doping increased,and the material’s photocatalytic performance was improved due to the combined effect of Cu1+ and Cu2+.The banding gap of GO@BOC/Cu2O-25%is 2.84 eV,the addition of GO suppressed the composite of photogenerated carriers,and the photocatalytic activity of the composites was improved further.(2)The doping of Cu2O did not significantly enhance the adsorption of the material.GO@BOC/Cu2O showed the best adsorption of tetracycline at 25%GO addition and the adsorption process could reach equilibrium within 120 min.The correlation coefficient of the proposed primary kinetic model(R2=0.9851)was higher than the proposed secondary kinetic(R2=0.9827),indicating that the adsorption process was dominated by physical adsorption.According to the internal diffusion model and Boyd’s model,the adsorption rate of tetracycline by GO@BOC/Cu2O was influenced by both internal and external diffusion steps,but external diffusion played a more important role.The Langmuir model can better describe the adsorption process.The adsorption of tetracycline by GO@BOC/Cu2O is more in favor of monomolecular layer adsorption,with a maximum calculated adsorption capacity of 23.14 mg/g.The enthalpy change of the adsorption reaction ΔH0>0 and the Gibbs energy change ΔG0<0.The adsorption process is a heat absorption reaction that can proceed spontaneously.Increasing the temperature will facilitate the adsorption process,which is consistent with the result that increasing the temperature increases the adsorption efficiency.(3)The removal of tetracycline by photocatalysis for 120 min reached 80%under the conditions of Cu2O doping ratio of 25%,GO doping of 25%,catalyst injection of 0.5 mg/L,ambient pH=5,temperature of 15℃ and initial concentration of tetracycline of 10 mg/L.The addition of anions has a weak inhibitory effect on the photocatalytic process.This is because NO3-reduces the contact of tetracycline on the GO@BOC/Cu2O surface through competitive adsorption,while Cl-,HCO3-and CO32-in water can combine with ·OH to generate the weaker oxidizing ability of ClOH-,·Cl2,·Cl-,-Cl2,·CO32-and other free radicals,which have a scavenging effect on ·OH.The presence of tert-butanol(TBA),p-benzoquinone(PBQ),and ethylenediaminetetraacetic acid(EDTA)slowed the reaction rate significantly(kcontrol=0.0076 min-1,kEDTA=0.0022 min-1,kTBA=0.0054 min-1,kPBQ=0.0025 min-1).Tetracycline’s degradation is dominated by the oxidation of superoxide radicals and cavities.The GO@BOC/Cu2O was regenerated by centrifugation,alkaline washing and drying.After five recycling trials,the regenerated GO@BOC/Cu2O was found to have good catalytic stability and recycling performance,and the removal rate of tetracycline from water could be maintained above 70%.