Surface/Interface Structure Control Of ZnO Nanocrystals For Enhancing Photocatalysis

With the rapid process of industrialization,a large amount of fossil energy is consumed,accompanied by increasingly serious environmental problems.Semiconductor-based photocatalysis technology not only can effectively absorb and transform solar energy into hydrogen and other fuels,but also it can also be used in the treatment of environmental pollutants.Therefore,semiconductor-based photocatalysis provides a possible way to solve the problems of energy shortage and environmental pollution.In the past 40 years,great progress has been made in the synthesis and utilization of photocatalytic materials.In fact,the solution of these problems stongly depends on our in-depth understanding of the structure-activity relationship of semiconductor photocatalysts.As a kind of common and important semiconductor material,ZnO not only has high photocatalytic activity,but also has the characteristics of non-toxic,abundant reserves and easy large-scale production.Therefore,ZnO is widely used in the fields of photocatalysis and photoelectric catalysis.In this thesis,choosing ZnO as the research object,we intend to develop facile methods to control the surface of ZnO nanocrystals(NCs)and study their structure-activity relationship in photocatalysis.And on this basis,we hope to improve photocatalytic performances of ZnO photocatalysts by rationally constructing semiconductor heterojunctions with well-defined interfaces.The main research contents are as follows:1)Using olamine as the surface control agent,ZnO nanopyramids with exposed high surface energy surfaces were synthesized.The crystal surfaces of ZnO were determined to be {302 2} by means of the combination of transmission electron microscopy and structural model.Our results show that the ZnO nanopyramids with exposed {3032} facets exhibited better performances in the photodegradation of methyl orange than those with exposed {1010} or {1011} facets.This difference in photocatalytic properties of ZnO nanocrystals is related to the surface structure(oxygen vacancy)of ZnO nanocrystals.2)Hexangonal plate-like ZnO NCs with exposed surfaces of {1010} and {0001?were synthesized.Au nanoparticles were selectively deposited on the surface of {1010} of ZnO nanocrystals in the process of light reduction deposition,while Au nanoparticles were deposited on the surface of {1010} and(0001)simultaneously in the process of chemical reduction(using formaldehyde as reducing agent).Through fluorescence spectra and photocurrent tests,it was found that photo-generated electrons and holes could be separated more effectively by photoreduction-induced selective deposition of Au nanoparticles on specific crystal surfaces.Due to the synergistic effect between specific crystal surface and heterostructure effect,the ZnO/Au heterostructures constructed on specific facets have significantly enhanced performances in the photodegradation of methyl orange.3)The Cu2O cubes were grown on the {1010} crystal surface of ZnO nanorods by a simple wet chemical method to form a semiconductor/semiconductor heterojunetion.The growth mode of Cu2O cubes on ZnO nanords was determined by the comparison between transmission electron microscopy images and structure model.Our results show that this structure not only broadens the visible light absorption of photocatalysts,but also ensures the good interfacial electron transport ability,effectively enhancing the separation ability of photogenerated electrons and holes.Therefore,the photodegradation activity of methyl orange over the as-synthesized ZnO/Cu2O composites was significantly improved compared with pure ZnO and Cu2O.