Preparation And Photocatalysis Properties Of Sargassum Horneri Based Activated Carbon Modified Titanium Dioxide

Polycyclic aromatic hydrocarbons(PAHs)are one of the priority pollutants listed in US EPA and environmental monitoring and controlling work in China,due to their strong carcinogenic,teratogenic and mutagenic properties.TiO₂photocatalytic degradation technology has been proved to be applicable to the field of photocatalytic degradation of PAHs,however,the application of this technology is still limited by some inherent deficiencies.For example,TiO₂only responds to ultraviolet light,but ultraviolet light only accounts for about 5%of sunlight,which greatly reduces to improve the utilization of sunlight resources,and the TiO₂in the water phase has the problem of difficult recovery.In order to solve these problems,this paper explored the preparation of Sargassum Horneri-based biomass activated carbon(SAC)using polytetrafluoroethylene(PTFE)as the activator and Sargassum Horneri as the raw material.SAC-TiO₂(TiO₂modified SAC)was successfully synthesized by attaching sol-gel prepared nano-titanium dioxide(Nano-TiO₂)on the referred activated carbon.Further more,a kind of precious metal,silver(Ag)modified SAC-TiO₂was synthesized,defined as SAC-(TiO₂-Ag),to increase the visible-light response.Under simulated sunlight conditions,the typical PAHs of naphthalene were photocatalyzed.The results show that:(1)Compared with the Sargassum Horneri activated carbon prepared by the traditional chemical activation method,the activated carbon prepared in this work had a decreased pore volume and specific surface area,but its pore diameter increased to6.1489 nm,and its adsorption effect on naphthalene was significantly enhanced.TiO₂was modified with activated carbon,which showed that the response of titanium dioxide to sunlight was redshifted,and the band gap width decreased significantly,from 3.26 eV to 2.58 eV.With the addition of precious metal Ag,the bandgap width of the composite continued to decrease to 2.41 eV.According to the TEM characterization of the sample,the Ag nanoparticles with a particle size of 0.23 nm were well distributed on the surface of titanium dioxide.(2)In the experiment of photocatalytic degradation of naphthalene,it was found that the addition of SAC and Ag could significantly improve the photocatalytic performance of titanium dioxide for the following two reasons:1)The presence of activated carbon in the aqueous phase can enrich naphthalene via adsorption,thus forming a high concentration environment around titanium dioxide and effectively improving the processing efficiency of naphthalene;2)Precious metal Ag can interact with titanium dioxide to form schottky barrier,which can effectively inhibit the synthesis of photogenerated carriers.Meanwhile,the modified titanium dioxide can also broaden the absorption spectrum bandwidth,thus improving the efficiency of photocatalysis.(3)Pure phase titanium dioxide has limited catalytic effect on naphthalene,especially under neutral and alkaline conditions,which greatly restricts photocatalytic application.In this work,the composite materials SAC-TiO₂and SAC-(TiO₂-Ag)showed excellent degradation properties for naphthalene in a wide pH range(pH=3-8).Under the condition of 0.6 g·L^-1and 120 min of light,the degradation rate of naphthalene remained above 80%and 88%,respectively.This indicated that this material is beneficial to the prevention and control of PAHs pollution in both fresh and marine aquatic environment.(4)GC-MS analysis showed two possible degradation pathways of naphthalene,and the intermediate products were 2,4-2-tert-butylphenol,2,5-2-tert-butylphenol and the benzene series formed by subsequent carbon chain growth,respectively,the final products are H₂O and CO₂.