Preparation Of BiO_2-x-based Composite Photocatalyst And Analysis Of Its Mechanism For Improving The Degradation Performance Of Chlorophenols

Chlorophenols have high biological toxicity and environmental persistence,is a typical case in high-risk environmental pollutants.The existence of stable carbon-chlorine bonds and chlorine atoms in chlorophenols is the main reason why they have such high biological toxicity and are difficult to be degraded.Developing a feasible method to selectively and primarly rupturing the carbon-chlorine bonds is essential for achieving high-efficiency degradation of chlorophenols.Studies have shown that the Bi atoms on the surface of the bismuth-containing oxide photocatalyst interacts with the Cl atoms in the chlorophenols,and it is feasible to apply the bismuth-containing oxide as photocatalyst to achieve photo-generated hole-induced selective dechlorination.Particularly,BiO_2-x has a narrow band gap,special electronic structure,abundant surface active sites and a two-dimensional layered structure.It is expected to be an ideal photocatalyst for photocatalytic efficientcy degradation of chlorophenols.However,traditional synthesis methods are time-consuming and the prepared BiO_2-x have poor crystal phase controllability.In addition,BiO_2-x also has the problem of poor photo-generated charge separation,which seriously affects its photocatalytic activity.Thus,this thesis aims to address the key scientific issues of the poor controllability of the preparation process,the poor utilization of photo-generated electrons,and the mechanism of photocatalytic degradation of chlorophenols is ambiguous.Plan to develop new methods to synthesize ultra-thin BiO_2-x nanosheets and study their composites with transition metal phthalocyanine complexes,combined with in-situ infrared and liquid chromatography-mass spectrometry,in-depth study of its selective dechlorination and degradation of chlorophenols.This article is mainly divided into the following two parts:(1)Preparation of ultra-thin BiO_2-x nanosheets.Using the microwave hydrothermal synthesis method,achieves the rapid preparation of BiO_2-x nanosheets through optimization of reaction conditions.Furthermore,combined with the ultrasonic peeling method,the thickness of the nanosheets was successfully reduced to about 4 nm,and the prepared nanosheets were uniform in size and their crystallinity is high.In the experiment of photocatalytic degradation of chlorophenol,BiO_2-x nanosheets showed excellent adsorption and degradation activity,and its activity was 3 times that of P25Ti O₂.Through the analysis of in-situ infrared test results,it is confirmed that there is a strong interaction between the chlorophenol and the BiO_2-x surface,which enhances the adsorption of the chlorophenol on the catalyst surface,and it is conducive to the occurrence of the photocatalytic reaction.Then,through the free radical capture experiment and liquid chromatography tandem mass spectrometry,which detect and analysis of the reaction intermediate products,the BiO_2-x photogenerated hole-based chlorophenols degradation route was verified.(2)The mechanism analysis of Ni Pc/BiO_2-x composite photocatalytic performance.Different types of metal phthalocyanine complexes were combined with BiO_2-xnanosheets by wet chemical method.It was found that the Ni Pc composited sample showed a significant increase in activity of photocatalytic degradate chlorophenol compared with other metal phthalocyanine complex composited samples.After further optimizing the composite amount of Ni Pc,the 0.5Ni Pc/BiO_2-x composite with the best photocatalytic activity was obtained.By using surface photovoltage and fluorescence lifetime,confirmed the increase of photocatalytic activity,attributed to the charge separation of the 0.5Ni Pc/BiO_2-x composite was improved.When the composite is excited,the holes on the valence band of the spatially separated BiO_2-x directly oxidize the pollutants adsorbed on the catalyst surface.At the same time,the electrons on the LUMO energy level of Ni Pc react with oxygen to generate superoxide radicals,thereby promoting charge separation.The analysis of the results of the free radical capture experiment confirmed that its main active species in the process of photocatalytic degradation of chlorophenols is still photo-generated holes,and the reaction path of its degradation of chlorophenols has not been changed.