Preparation Of Organic （g-C₃N₄）-Inorganic （BiOI） Photocatalyst And Their Application In Degradation Of Endocrine Disrupting Chemicals-Bisphenol A （BPA） Under Simulated Solar Irradiation

Bisphenol A (BPA,2,2-bis(4-hydroxyphenyl)propane) is an important building block material and used extensively as the monomer to manufacture polycarbonate plastic and epoxy resins. Due to its large production and wide application, a large amount of BPA has been released into the aquatic environment. Unfortunately, it could cause adverse effects to human beings, such as the occurrence of breast cancer for female and prostatitis for male and so on. It could also result in the sexual precocity of infants. Thus, a great concern has been raised to remove BPA from water by different techniques, such as physical absorption, chemical remediation, and microbial degradation. Among these methods, photocatalytic degradation with TiO2is attracting widespread attention due to its simplicity, low energy consumption, mild reactive conditions, effective activity and low toxicity. However, TiO2could only use <5%solar energy for photodegradation due to its large bandgap energy, and this restricts its application. It is of significance to develop new photocatalysts to utilize solar energy efficiently.Firstly, palladium modified mesoporous graphitic carbon nitride polymer (Pd/mpg-C3N4) was fabricated by thermal condensation coupled with liquid phase reduction and used for the degradation of bisphenol A (BPA) in water. Doping Pd on the surface of mpg-C3N4enhanced the light absorbance in the range of UV-Vis region. Most of the embedded Pd was present as Pd0and could act as electron traps and reduce the recombination of photogenerated holes and electron pairs. As a result, the photocatalytic performance was improved significantly. The reaction rate constant (Kobs) increased with the Pd loading on the surface of mpg-C3N4and the maximum was achieved with1.50%Pd. Almost100%of BPA (20mg·L-1) was photodegraded by the solids of0.5g·L-1Pd/mpg-C3N4after irradiation with simulated solar light for360min, meanwhile, the photocurrent intensity generated by1.5%-Pd/mpg-C3N4electrode was also enhanced and was about2.0times of that induced by mpg-C3N4under visible light irradiation. The Pd/mpg-C3N4exhibited very stable and high efficient photocatalytic activity to BPA in a wide range of pH (3.08-11.00). It also displayed high photocatalytic activity without photocorrosion after reuse for many times. Hydroxyl radicals, photogenerated holes, and superoxide radical species were responsible for the photodegradation while the superoxide radical species were more predominant in the Pd/mpg-C3N4reaction system.Secondly, a novel3D Bi/BiOI composite was synthesized by a facile one-step solvothermal method. The resultant catalysts were comprehensively characterized by means of XRD、FE-SEM、HR-TEM、FT-IR、UV-vis DRS、XPS、and N2adsorption/desorption. The solvothermal temperature and reaction time affected the chemical compositions, crystallinity and morphology of the prepared materials. The photocatalyst prepared at180℃for24h (BOI-180-24) contained approximate12.5%metallic Bi and displayed the best photocatalytic performance to BPA under simulated solar light irradiation. About92.8%of40mg L-1BPA was degraded after90min reaction using1g L-1BOI-180-24as catalyst under simulated solar irradiation, while79.0%of TOC was removed at the same time. The photocatalytic efficiency was affected by many factors, such as the amount of photocatalyst, the initial concentration of BPA and pH and so on. Photogenerated holes, superoxide radical species and singlet oxygen were responsible for the photodegradation while the superoxide radical species were more predominant in the Bi/BiOI photocatalytic reaction system. Only one intermediate (m/z133) was observed by LC-MS/MS and a simple degradation pathway of BPA was proposed:BPA was first oxidized to4-isopropenyphenol and hydroquinone or phenol which was further transfer to CO2and H2O.Finally, a novel organic-inorganic3D mesoporous graphite carbon nitrogen/BiOI (MCN/BiOI) heterojunction photocatalyst was synthesized by a facile solvothermal method. The crystal phase, morphology, constituent and light absorbance of the resultant was characterized by XRD, FE-SEM, HR-TEM, FT-IR, UV-vis DRS, XPS, and N2adsorption/desorption. After hybridization with MCN, a heterojunction would be formed and then photogenerated carriers could be effectively separated by the internal electric field built at the heterojunction interface. The photocatalytic and photoelectrochemical performance of BiOI was improved and was much higher than pure BiOI and MCN. The composite with10%MCN displayed the highest photocatalytic performance, and about90%of BPA (20mg-L-1) was photodegraded by the solids of1.0g·L-110%-MCN/BiOI after irradiation with visible light for240min. The photocurrent intensity generated by10%-MCN/BiOI electrode was about1.5and2.0times of those induced by BiOI and MCN under visible light irradiation, respectively. The superoxide radical species were predominant in the reaction system.