The Performance And Mechanism Of Photocatalytic Degradation Of Phenolic Pollutants By Graphene/TiO₂-based Composite Membranes

With the rapid development of economy and society,the water pollution has become more and more serious,threatening the human health and ecological safety.Some physical,chemical,biological technologies have been used for sewage treatment,however,most of these methods exhibit low degradation efficiency,high cost and time consuming,especially for the toxic and harmful substances that are difficult to biodegrade,restricting the wastewater pollution control.In recent years,the photocatalytic oxidation technology has attracted extensive attention owing to the advantages,such as direct use of sunlight,economy,mild reaction conditions,and no secondary pollution.The preparation of photocatalysts with efficient and stable pollutant degradation efficiency is still a hotspot in the field of photocatalysis.At the same time,the research and theoretical prediction of photocatalytic performance towards the same series of organic pollutants has also become a new research focus.In this paper,a series of composite membranes photocatalyst graphene?GR?/Ti O2,phosphotungstic acid?HPW?/GR/Ti O2 and black phosphorus?BP?/GR/Ti O2 were prepared,respectively.Transmission electron microscopy?TEM?,scanning electron microscope?SEM?,X-ray photoelectron spectroscopy?XPS?,X-ray diffraction analysis?XRD?,Raman spectroscopy?Raman?,X-ray energy spectrum?EDS?,ultraviolet visible diffuse?UV-VIS/DRS?,Fourier infrared spectrum?FTIR?,fluorescence spectroscopy?PL?,photoelectric chemical experiment and electron spin resonance?ESR?were used to study the properities of prepared membranes.The photocatalytic performance,degradation conditions and photocatalytic mechanism of composite membranes were investigated by using o-chlorophenol?o-CP?as target pollutant.The photocatalytic degradation of eight phenolic compounds?chlorophenols and bisphenols?by HPW/GR/Ti O2 were analyzed,and the QSAR model of phenolic compounds structural parameters and photocatalytic degradation rate constant?k?were established,finally realizing the theoretical prediction of the k of phenolic pollutants.The main research results of this paper are as follows:?1?The vascular plant?tall fescue?was used as a carbon source for GR preparation.The obtained GR was combined with Ti O2 by a sol-gel method,getting the GR/Ti O2 composite membrane.The results indicated that the doping of GR not only increased the visible light absorption range of the catalyst,but also improved the separation rate of Ti O2 photogenerated e^-and h⁺.When the doping amount of GR was 0.3%,the layer-structure of GR could be maintained and the double-layer composite membrane?DL-GR/Ti O2?displayed the highest photocatalytic degradation performance towards o-CP.Compared with pure Ti O2,the photocatalytic degradation efficiency of GR/Ti O2 composite was increased by 30.98%.The photocatalytic mechanism research revealed that the ROS responsible for o-CP decomposition using GR/Ti O2composite were·OH and·O₂^-.This study provides basic data for the application of bio-derived GR in the field of photocatalysis,and also reduces the cost of photocatalyst preparation.?2?The phosphotungstic acid?HPW?/GR/Ti O2 composite membrane was prepared by the sol-gel method.The characterization results proved that the introduction of HPW increased the separation rate of Ti O2 photogenerated e^-and h⁺.And the interaction among HPW,GR and Ti O2was stronger than that of GR/Ti O2.These significantly improved the photocatalytic activity of HPW/GR/Ti O2 composite membrane,and also enhanced the stability and recyclability.When the HPW doping amount was 1.0%,initial concentration of o-CP solution was 5 mg L^-1 and p H value was 6.3,the HPW/GR/Ti O2 composite membrane presented the highest o-CP removal efficiency?97.02%?,much higher than that of GR/Ti O2.After 10 cycles,the photocatalytic degradation efficiency of HPW/GR/Ti O2 composite membrane was still reach 94.33%.In the process of photocatalytic degradation,the HPW/GR/Ti O2 composite membrane produced more·O₂^-than GR/Ti O₂.?3?The photocatalytic activity of HPW/GR/Ti O2 composite membrane was comprehensively evaluated using 8 phenolic compounds as target pollutants.The photocatalytic mechanism research revealed that·OH and·O₂^-were the main ROS for the most phenolic compounds degradation.Under the same conditions,HPW/GR/Ti O2 composite membrane photocatalytic degradation removal rates of chlorophenol and bisphenol were as follows:O-CP?97.02%?>2,4,6-Trichlorophenol?96.95%?>Pentachlorophenol?92.88%?>2,4-Dichlorophenol?82.71%?;Bisphenol S?93.28%?>Bisphenol A?91.39%?>Bisphenol AP?74.71%?>Bisphenol AF?68.63%?.The different results was mainly caused by the structural difference of phenolic compounds.A QSAR model was constructed by using the structural parameters of phenolic compounds and the photocatalytic degradation rate constant?k??log k=–1.960–0.007 RDF060s–0.441 MATS5m,n=8,R²adj=0.970?.Based on this model,the k values of other phenolic compounds photocatalytic degradation using HPW/GR/Ti O2 composite membrane could be predicted successfully.This study could supply guidence for the practical application of HPW/GR/Ti O2 composite membrane photocatalytic degradation of phenol wastewater.?4?The new material black phosphorene?BP?was synthesized,and the BP/Ti O2 and BP/GR/Ti O2 composite membranes photocatalyst were prepared successfully by the sol-gel method.The doping of BP increased the specific surface area and the visible light absorption range of the composite membrane,more importantly,the new ROS-¹O2 were generate.When the BP doping amount was 0.3%,the photocatalytic degradation efficiency,stability and reusability of BP/GR/Ti O2?10 cycles,the removal rate of o-CP was 98.16%?96.49%?composite membrane were much higher than HPW/GR/Ti O2?10 cycles,the removal rate of o-CP was97.02%?94.33%?.After 10 h simulated sunlight irradiation,the o-CP mineralization degree by BP/GR/Ti O2 composite membrane?60.12%?was higher than that of HPW/GR/Ti O2?42.23%?.This study provides basic data for the further application of BP in the field of photocatalytic degradation of organic pollutants.