Construction And Photocatalytic Performance Study Of Halloysite-Based Semiconductor Materials

Halloysite nanotubes,a natural clay mineral with fine texture and low impurities,are distributed widely in China and all over the world.Due to large specific surface area and good biocompatibility,it has been widely used in biomedicine,waste water treatment and other related fields.This article aims to use the tubular morphology and unique surface structure of HNTs to construct a variety of semiconductor materials,and apply to the photocatalytic degradation of pollutants,water splitting to produce hydrogen and hydrogeneration reactions,in order to explore the important applications of HNTs in the pollutant removal and energy conversion.A series of mesoporous tubular g-C₃N₄ semiconductor catalysts were prepared by a simple calcination-leaching method using natural halloysite as hard template.The tetracycline hydrochloride（TC）was used as the target pollutant to explore the effect of the catalyst dosage,pollutant concentration and initial p H value on the performance of photocatalytic degradation of TC.The microstructure of the catalysts was tested through a series of characterizations containing X-ray powder diffraction（XRD）,Fourier infrared spectroscopy（FT-IR）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscope（SEM）,transmission electron microscope（TEM）and electron paramagnetic resonance（EPR）.The intermediate products of photocatalytic degradation of TC and possible degradation paths were analyzed.And the photocatalytic degradation mechanism was proposed based on the capture experiment and ESR test results.The results showed that the unique one-dimensional（1D）mesoporous tubular structure of TCN and a small amount of associated carbon in halloysite played important roles in improving the catalytic performance of TCN.In addition,superoxide radicals and singlet oxygen were the active species.Composite catalysts xZIS-HNTs and zZIS-HNTs/Ay with sulfur vacancies were synthesized by a one-step solvothermal method using natural halloysite/modified halloysite as the carriers,and XRD,FTIR,XPS,SEM,TEM,EPR,UV-vis diffuse reflectance spectra（DRS）,Valence band XPS（VB-XPS）and Mott-Schottky（MS）curve were employed to explore the microstructure of the catalysts.The performance of the catalysts was tested by photocatalytic water splitting to produce hydrogen and in-situ hydrogenation reactions,and the influences of the type and proportion of modifier,the amount of sacrificial agent,the type and loading of co-catalyst on the catalytic ability were explored.The possible photocatalytic mechanism was proposed.The results showed that halloysite/modified halloysite not only formed a stable Schottky junction with ZnIn₂S₄,but also the surface groups contributed the generation of more defect sites.This eventually caused the conduction band of the catalyst to move upward,which improved the separation and transfer efficiency of photo-generated charges while enhancing the reduction ability,thus validly enhancing the photocatalytic activity of the composite catalyst.