Photoelectrochemical Applications Of Inorganic Semiconductor-microorganism Hybrid Systems

After hundreds of millions of years of natural selection,organisms have evolved specific biological enzymes to achieve highly selective reactions and maintain their own growth,but the energy utilization efficiency in the reaction process is very low.For example,traditional crops have only 1?2%solar-biomass conversion efficiency.In contrast,inorganic semiconductor chemical materials have a wider range of light absorption and higher conversion capacity.Combining the high conversion efficiency of inorganic semiconductor materials with the specific selectivity of microorganisms to construct an inorganic semiconductor-microorganism hybrid system is an effective way to achieve high-efficiency conversion of energy and synthesis of specific chemical substances.Recent studies have shown that inorganic semiconductor-microorganism hybrid system still faces a series of challenges,such as the effective combination of inorganic semiconductor materials and microbial systems,the energy conversion efficiency and reaction mechanism of the inorganic semiconductor materials and microorganisms in the hybrid process.Therefore,a hybrid system of inorganic semiconductor and microorganism was constructed in this paper,which synergized the inorganic semiconductor with the characteristics of efficient light absorption,excellent electrical conductivity and the advantages of specific selection of microorganism,and realized the efficient conversion of solar energy to chemical energy.The main content of this paper includes the following parts:Chapter 1:IntroductionThis chapter first systematically introduces the research background and significance of the inorganic semiconductor-microorganism hybrid system,and then introduces the construction of the inorganic semiconductor-cell hybrid system and the inorganic semiconductor-bacterial hybrid system,the working principle and practical application of the hybrid system.Finally,it expounds the research significance,research content and research innovation of this thesis.Chapter 2:Synergistic bio-recognition/spatial-confinement for effective capture and sensitive photoelectrochemical detection of MCF-7 cellsIn this chapter,we constructed an inorganic semiconductor-cell hybrid system and proposed a synergistic strategy of aptamer biometrics/nanocube space limitation to achieve efficient capture and sensitive detection of MCF-7 cells.Cu₂O@Zn O nanocubes with core/shell structure were designed.The size and spacing of the nanocube were suitable,which could restrict the flow of cancer cells in space and improve the cell capture rate.Au nanoparticles were modified on the surface of the nanocubes by sputtering method,and the aptamers were bonded in the form of Au-S bond.The aptamer biologically specifically recognized the protein on the surface of MCF-7 cancer cells,further improving the cell capture rate.Finally,the hybrid system realized sensitive detection on the photoelectrochemical(PEC)platform.In addition,the Cu₂O@Zn O/Au-aptamer presented the highest cancer cell capture ratio of 47.6%.Based on a signal-to-noise factor of 3(S/N=3),the limit of detection(LOD)of the hybrid system can be calculated to be 2 cells per m L.This study not only offers us an attractive PEC aptasensor for MCF-7 cancer cell detection,but also opens up a new avenue for rational combination of biomolecule recognition units and nanostructures for universal and reliable bio-detections.Chapter 3:Ambient photoelectrochemical N₂ reduction to NH₃ enabled by Cu₂O@TiO₂ NWs/Azotobacter vinelandii hybrid systemIn order to realize the synthesis of specific chemical substances,the inorganic semiconductor-cell hybrid system was expanded to the inorganic semiconductor-bacteria hybrid system.In this chapter,Cu₂O@TiO₂ nanowires(NWs)were prepared by atomic layer deposition(ALD)method,and then combined with Azotobacter vinelandii(A.vinelandii)to construct a hybrid system of inorganic semiconductor and nitrogen-fixing bacteria.Cu₂O@TiO₂ NWs with core/shell structure collect sunlight and generate photoelectrons.A.vinelandii adsorbed on the nanowires is used as biocatalysts to receive photoelectrons.Nitrogenase in bacteria utilizes photoelectrons to achieve efficient catalytic reduction of N₂ to NH₃.In 0.1 M Na₂SO₄ solution,the ammonia yield was as high as 1.5×10^–9 mol s^–1 cm^–2,which is an order of magnitude higher than most inorganic catalysts reported so far.In addition,Cu₂O@TiO₂ NWs/A.vinelandii hybrid system also has self-healing ability,which can maintain long-term photochemical stability and reproducibility.Chapter 4:C₃N₄ QD_S combined with Escherichia coli to achieve efficient hydrogen productionIn extracellular inorganic semiconductor-microorganism hybrid system,inorganic semiconductor absorbs sunlight and generates photogenerated electrons,which are transferred to the bacteria adsorbed on its surface,and the bacteria accept the photoelectrons to accelerate the rate of substance synthesis.However,in the process of photoelectrons transfer to the inside of the bacteria,they need to cross the cell membrane,resulting in partial energy loss,which reduces the efficiency of photoelectrons transfer.In order to further improve the efficiency of photoelectrons transfer,an intracellular inorganic semiconductor-microorganism hybrid system was constructed.Capturing solar energy efficiently and converting it into chemical energy,particularly converting solar energy into and storing it in the chemical bonds of hydrogen,is a global challenge.The urgent need for renewable,sustainable and efficient hydrogen production has driven the rapid development of advanced technologies.Biohydrogen production based on whole-cell microorganisms is one of the most promising strategies to achieve the goal of efficient hydrogen production.The work in this chapter first shows that sunlight enhances the biological hydrogen production of non-photosynthetic bacteria that have not been genetically engineered.This experimental result overturns the conventional conclusion that sunlight has no effect on non-photosynthetic bacteria.In order to further improve the light absorption and transformation ability,an intracellular inorganic and biological hybrid system,C₃N₄ quantum dot(QDs)/Escherichia coli,was proposed.The formation of inorganic semiconductor-biological junction within the bacteria promotes the separation and transfer of photoelectrons,thus obtaining more excellent hydrogen production efficiency.This work reveals the advantages of intracellular inorganic/biological hybrid systems for efficient solar energy conversion and points to a strategy for selectively enhancing solar energy conversion in a more complex and functional manner.