Biosynthesis Of Hexagonal CdS Quantum Dots For Photocatalytic Hydrogen Production And Organic Dyes Degradation

With the rapid development of human society and economy,the problems of energy shortage and environmental pollution have become increasingly prominent,and the development of cleaner and more efficient new energy and new economic and eco-friendly pollutant treatment technologies is urgently needed.Semiconductor photocatalysis technology has received widespread attention because of its ability to convert solar energy into electrical/chemical energy and efficiently treat environmental pollutants.Currently,one of the research focuses of photocatalysis technology is to develop green and efficient semiconductor photocatalysts.Because of its suitable visible light absorption band gap（E_g≈2.4 e V）and sufficiently negative proton reduction potential,CdS has been widely used in the photocatalytic decomposition of water to produce hydrogen and the treatment of environmental pollutants.Traditional chemical synthesis processes of CdS（such as hydrothermal,solvothermal,electrochemical synthesis,etc.）have problems such as high temperature,high pressure,high energy consumption,and the use of toxic and harmful chemical reagents,which are difficult to meet the needs of green and sustainable development.Therefore,biosynthesis technology has emerged as a method for the synthesis of semiconductor materials with mild synthesis conditions,simple operation and environment-friendly.However,due to the complex biological metabolism of nanomaterial of the synthesizer has not been fully clarified,etc.,the current biosynthetic method has problems such as poor product controllability and poor catalytic performance.Therefore,it is still a challenging task to prepare semiconductor photocatalysts with high catalytic activity through biosynthesis.In this thesis,an aerobic biosynthesis method of CdS quantum dots was established by Shewanella oneidensis MR-1,and a hexagonal crystal CdS quantum dot with high catalytic activity was successfully prepared through the regulation of metabolic process.Studies have shown that the hexagonal CdS quantum dots have excellent photocatalytic hydrogen production activity,and the photocatalytic degradation of organic dyes has been further studied.The main research conclusions are as follows:（1）Established a method for aerobic biosynthesis of hexagonal CdS quantum dots.Using L-Cysteine as a sulfur source,under aerobic conditions,H₂S produced by S.oneidensis MR-1 metabolism combines with Cd²⁺to generate CdS quantum dots.Furthermore,the synthesis conditions of biological CdS QDs were optimized.X-ray diffraction analysis shows that when the YP concentration increases from 2%to 6%,the synthesized CdS QDs.The crystal form changed from tetragonal sphalerite to hexagonal wurtzite.The size statistics of high-resolution transmission electron microscopy（HRTEM）showed that the size of the synthesized hexagonal crystal CdS QDs was about 5 nm.（2）Analyzed the photocatalytic hydrogen production performance of CdS QDs and explored the mechanism of its high-efficiency hydrogen production.When the YP concentration is 6%,the hexagonal crystal CdS QDs synthesized by S.oneidensis MR-1 have the highest hydrogen production activity.On this basis,the photocatalytic hydrogen production conditions of hexagonal crystal CdS quantum dots were optimized,and the hydrogen production rate can reach 22.1±0.6 mmol/g/h,which is about 2 times higher than that before optimization.Further research found that,compared with biological CdS QDs synthesized under other conditions,hexagonal CdS QDs has the largest band gap（with a larger redox potential while ensuring sufficient visible light absorption）and the fastest electron transfer rate and the smallest transfer resistance.（3）Analyzed the photocatalytic degradation performance of hexagonal CdS QDs on organic dyes.Under visible light irradiation,the hexagonal crystal CdS QDs reached the maximum degradation efficiency of rhodamine B（Rh B）and methylene blue（MB）at an initial concentration of 5 mg/L at 40 min,which were 44.6%and 36.7%,respectively.The degradation kinetic analysis showed that the degradation kinetic constants of Rh B and MB were 0.01584 min^-1 and 0.01260 min^-1,respectively.Monitoring the active species in the degradation process found that the main active species for the photocatalytic degradation of Rh B and MB in the hexagonal crystal form of CdS QDs were·OH and·O₂^-,and the hole h⁺had little effect in the degradation.In summary,this study synthesized hexagonal CdS quantum dots with high photocatalytic hydrogen production activity and good photocatalytic degradation of organic pollutants,which have certain application potential in clean energy production and pollutant degradation.