Synthesis Of Titanium-based MOFs And Its Derivatives Photocatalyst And Study On Photocatalytic Degradation Of Organic Pollutants

In recent years,as the fast development of economy,modernization and city,quantity of toxic and harmful organic substances have been widely applied to various fields and industries,leading to increasingly serious environmental pollution,especially organic pollution in water.Because of the serious harmfulness and long latency,the human health,sustainable development of the environment and ecological balance may be affected.At present,photocatalytic technology is regarded as one of the most promising water pollution treatment technologies due to its high efficiency,stability and green.The drawbacks of conventional semiconductor photocatalysts such as small surface area,low light utilization and photocarriers limit the application of photocatalytic oxidation in the removal of organic pollutants.Owing to the large surface areas,high porosity,adjustable pore sizes and structure and semiconductor-like properties,metal organic frameworks（MOFs）have the potential to be a photocatalytic material for remediate contamination.Therefore,in this paper,the synthesis method and technology of MIL-125（Ti）derived in-situ carbon-doped titanium dioxide photocatalyst and histidine（His）doped titanium-based metal organic framework NH₂-MIL-125（Ti）photocatalyst were developed by calcination of MOFs precursor and post-synthetic modification,respectively.The MOFs-based photocatalytic materials with high photocatalytic activity and stable structure were synthesized and used in the degradation of bisphenol A（BPA）and phenol in water to evaluate their photocatalytic activity.At the same time,the internal relationship among the morphology,structure and the improved photocatalytic performance was investigated in detail,and the possible reaction sequence of the generation and transformation of free radicals in the photocatalytic reaction process was systematically explored to achieve the purpose of effective photocatalytic degradation.The main research contents and results are summarized as follows:（1）A series of in-situ carbon-doped（substituent carbon and carbonate）Ti O₂（C_x/Ti O₂）composites with a porous structure were successfully synthesized via one-step and low-temperature calcination of titanium metal-organic framework（MOF）,MIL-125（Ti）.The resultant materials C_x/Ti O₂shows 9.6 times higher photocatalytic BPA degradation rate than the benchmark Ti O₂photocatalyst（P25）under visible light irradiation.This excellent photocatalytic performance is closely related to the morphology,crystallinity and structure of the catalysts.The unique porous structure from MOFs can enhance the light collection through the reflection effect.In addition,the co-doping of carbonate and substituted carbon can accelerate the separation of photogenerated charges and reduce the band gap.Furthermore,the reaction sequence of free radical generation and transformation in the process of photocatalytic reaction was speculated by means of electron paramagnetic resonance,motshottky and quantitative detection of reactive oxygen species.The results show that holes（h⁺）and superoxide radicals（·O₂^-）were the main reactive species,which are responsible for the BPA photocatalytic degradation.（2）The histidine（His）doped titanium-based metal organic framework（His-NH₂-MIL）was synthesized by post-synthetic modification method.The photodegradation of bisphenol A（BPA）and phenol under visible light irradiation was studied.Compared with undoped NH₂-MIL-125（Ti）,His-NH₂-MIL showed significantly improved photocatalytic activity.When the histidine content was 0.78 wt%,the prepared material showed the highest photocatalytic activity.The removal rate and mineralization rate of BPA were as high as 94.5%and 72.9%respectively.And the removal rate and mineralization rate of phenol were 60.0%and 46.4%respectively.In addition,further research showed that holes（h⁺）and superoxide radicals（·O₂^-）are the main active oxygen species in the degradation process.