Synthesis And Performance Of Oxygen Vacancy Zinc Oxide Based Materials

The constitutions,structures and performances of materials have been a hot rese-arch area for a long time.The synthesis of regulated materials that are satisfied with practical needs is always an important goal pursued by researchers.Comparing to ideal crystals,crystals with structural deficiencies have different physical and chemistry pro-perties.Therefore,how to obtain materials needed by using deficiencies has attracted wide attention.We can generate deficiencies with different methods and the deficien-cies obtained also belong to various categories.We can obtain materials with altered properties or composite materials that can be applied in wider areas by designing de-ficiencies and controlling the concentration of vacancy.In this thesis,we focus on introducing a few Oxygen Vacancy Zinc Oxide based materials obtained by different synthesis methods,which have high performance in visible light photocatalytic.After forming composite materials,they can be applied in photocatalyst for hydrogen evolu-tion?hydrolysis of ammonia borane and hydrogenation of styrene to ethylbenzene.Fist,we studied Oxygen deficient ZnO1-x nanosheets with high visible light pho-tocatalytic activity.Zinc oxide is one of the most important wide-band-gap(3.2 eV)materials with versatile properties,however,it can not be excited by visible light.In this work,we have developed an exquisite and simple way to prepare oxygen-deficient ZnO1x nanosheets with a gray-colored appearance and excellent visible light photoca-talytic activity.Detailed analysis based on UV-Vis absorption spectra,X-band electron paramagnetic resonance spectra,and photoluminescence spectra confirms the existence of oxygen vacancies in ZnO1-x.The incorporation of oxygen defects could effectively extend the light absorption of ZnO1-x into the visible-light region due to the fact that the energy of the localized state is located in the forbidden gap.Thus,our obtained ZnO1-x shows a higher photodegradation of methyl orange compared to defect-free ZnO under visible light illumination.Additionally,the high content of OH radicals with a strong photo-oxidation capability over the ZnO1-x nanosheets significantly contributes to the improvement in the photocatalytic performance.Our oxygen deficient ZnO1-x sample shows a very high photocatalytic activity for the degradation of MO even after 5 cy-cles without any obvious decline.The results demonstrate that defect engineering is a powerful tool to enhance the optoelectronic and photocatalytic performances of nano-materials.Second,we studied artificial photosynthetic Z-scheme photocatalyst for hydrogen evolution with high quantum efficiency.As global energy consumption continues to rise,it is imperative to develop clean and renewable sources of energy as alternatives to the fossil fuel energy sources.Photocatalytic hydrogen generation or photochemi-cal water splitting is a promising carbon-free technology producing H2 and O2 from water.Here,we report an exciting advance in the photocatalytic hydrogen evolution from water under visible light,using a new developed direct Z-scheme heterostructures constructed by oxygen deficient ZnO1-x nanorods and Zn0.2Cd0.8S nanoparticles by calcination.The highest rate for hydrogen production reaches 2518 ?maol · h-1 over optimal ZnO1-x/Zn0.2Cd0.8S Z-scheme photocatalyst with a high apparent quantum efficiency of 49.5%at 420 nm,which is 20 times higher than bare Zn0.2Cd0.8S,and 25 times higher than ZnO1-x sample.From the results of photocurrent response,electro-chemical impedance spectroscopy and time-resolved PL spectra,we demonstrate that the high increase in the photocatalytic hydrogen generation arises from the formation of artificial photosynthetic Z-scheme system and oxygen vacancy abundant ZnO1x in the heterojunction.Direct Z-scheme ZnO1-x/Zn0.2Cd0.8S nanoheterostructures result in an efficient charge carrier separation and strong reduction ability for enhanced H2 production,additionally,the presence of oxygen vacancies in the sample significantly enhances visible light absorption,these synergistic effects lead to highly efficient photo-catalytic hydrogen production with an exceptional high quantum efficiency under visi-ble light irradiation.Our findings provide possibilities for creating other high-efficiency photocatalysts mimicking natural photosynthetic Z-scheme system.Third,we applied air-stable Pd-ZnO1-x nanoparticles as Catalysts for the Hyd-rolytic Dehydrogenation of BH3NH3.We report on Pd-ZnO1-x nanoparticles as catalysts for hydrogen generation from hydrolysis of ammonia borane(BH3NH3,AB).The Pd-ZnO1-x nanoparticles were prepared through a certain amount of K2PdCl4 was slowly dripped to the dried oxygen vacancy ZnO nanoparticles at room temperature and then calcined at 250? for 2 h at H2/Ar(5%)atmosphere.The oxygen vacancy ZnO nanoparticles were synthesized using hydrothermal method at 200?.Compared with oxygen vacancy ZnO nanoparticles and commercial ZnO,as prepared Pd-ZnO1-x shows higher hydrogen generation from hydrolysis of ammonia borane.By using the catalyst containing 1.0 wt%Pd,the catalyst performs highest activity.The TOF is 538.3 h-1 at room temperature and when temperature comes to 333 K,the catalyst achieve high efficiency with TOF of 5400h-1.These results indicate that the Pd-ZnO1-x nanoparticles are a promising low-cost catalyst for on-board hydrogen generation from hydrolysis of borohydride.Last,we applied Pd nanoparticles supported on Oxygen Vacancy Zinc Oxide as highly stable catalyst enhanced catalytic activity for reduction reactions.Zinc oxide,a wide-band-gap semiconductor with versatile properties which has many applications.In this work,a novel strategy has been developed for Pd nanoparticles supported on oxygen-vacancy-rich ZnO,our obtained oxygen vacancy ZnO shows a higher photo-degradation of methyl orange compared to defect-free ZnO under visible light illumi-nation.The high concentration of OH radicals contributes to the large improvement during the photocatalytic progress.Afterwards,we demonstrate that Pd doped oxy-gen vacancy ZnO with exposed(100)facets exhibit a highly efficient catalytic activity for catalytic reduction of 4-nitrophenol,a variety of other reaction about aromatic ni-tro compounds to aromatic amine products and selective hydrogenation of styrene at room temperature,which is much higher than that of traditional Pd doped ZnO wit-hout vacancies,commercial ZnO and pure Pd nanoparticles.By further optimizing the reaction parameters,the optimized catalytic activity of the reduction of 4-nitrophenol to 4-aminophenol is a constant of k=16.98 min 1 while the noble doping content is as low as 0.05 wt%.Forthemore,the Pd-ZnO1-x(0.05 wt%Pd)catalyst makes a series of tandem reaction for reduction of substituted aromatic nitro compounds using only 1 minute under ambient conditions.When using Pd-ZnO1-x(1.0 wt%Pd)na-nocomposite as catalyst in the hydrogenation of styrene to ethylbenzene,the hydrogen generation rates could reach up to 5237 h-1.By the strong metal-support interaction,the Pd Schottky contacts fabricated on oxygen vacancy ZnO nanorods has standed out as an excellent catalyst with high efficiency and stability.