Fabrication And Photo-generated Carriers Behaviors Of High Quality Bismuth Vanadate Film

At present,the energy crisis and environmental pollution are common challenges facing mankind.Many countries have put energy security at an important position in the whole national security system,and people's awareness of environmental protection is gradually enhanced.With the acceleration of our country's urbanization process,the consumption of energy in China has increased rapidly,and the environmental problems have become increasingly prominent.Therefore,solving these problems is of great significance for promoting the sustainable development of our society and the environment.Nowadays,the main energy types in China are still dominated by traditional fossil energy such as coal,oil and natural gas.The traditional fossil energy can produce a large amount of carbon dioxide,sulfur oxides and nitrogen oxides,which can cause environmental problems such as acid rain,ozone layer holes and the greenhouse effect.What's more,the traditional fossil energy reserves are limited and will eventually run out.In conclusion,the development and utilization of new renewable energy are very important and urgent.The photocatalysis technology can not only use sunlight to efficiently split water to produce hydrogen energy,but also use sunlight to degrade pollutants.Therefore,photocatalytic technology is deemed as a potential technology to solve both energy crisis and environmental pollution.Titanium dioxide is a photocatalyst that has been studied in depth at present,but it can only absorb the ultraviolet part of sunlight and the utilization rate of sunlight is very low,which greatly limits its application in industry.Therefore,as a visible light-responsive photocatalyst,bismuth vanadate with monoclinic scheelite structure,owning many merits such as low cost,non-toxicity and good stability,has been attracted more and more attention.The research of bismuth vanadate powder has been relatively extensive,but for single crystal bismuth vanadate thin film,especially the conditions for preparing it by pulsed laser deposition technology is still shortage.As the element of bismuth being sensitive to temperature and easy to volatilize at high temperature,the preparation of phase-pure single crystal bismuth vanadate thin film using pulsed laser deposition technology has been a challenge.In this paper,the high quality phase-pure single crystal bismuth vanadate thin films were prepared by pulsed laser deposition technique by control of experimental parameters reasonably.Meanwhile,the behaviors of photogenerated carriers on bismuth vanadate surface were studied by experiments of photodeposition.This paper mainly includes the following contents:?1?High quality phase-pure single crystal epitaxial monoclinic bismuth vanadate thin films were successfully prepared on yttrium-doped zirconia substrate by pulsed laser deposition technology using a stoichiometric target.The effects of the parameters such as substrate temperature,oxygen pressure,deposition time and laser energy on the surface morphology,composition and structure of single crystal bismuth vanadate epitaxial thin films were studied in detail.Furthermore,the optimum experimental conditions for the preparation of high quality phase-pure single crystal bismuth vanadate thin films using a stoichiometric target were determined.?2?The effects of target ratio and oxygen pressure on the surface morphology and optical band gap of single crystal bismuth vanadate thin films were studied.Under the same oxygen pressure,samples with deposition time of 1 min were prepared by different target.Considering the composition of the samples with a deposition time of 1 min could not be determined,the deposition time was extended to 30 min.By adjusting the oxygen pressure,the oxygen pressure values or ranges required for the target with Bi to V of 1,2,4,5,6 and 7 to prepare phase-pure single crystal bismuth vanadate thin films were obtained.The oxygen pressure required by the target with Bi to V of 2 was studied in detail.Finally,the surface morphology and optical band gap of phase-pure single crystal bismuth vanadate films obtained under different oxygen pressures were characterized,and the effect of oxygen pressure on the growth of bismuth vanadate films was studied.?3?The principle of photodeposition and the behaviors of photogenerated carriers of bismuth vanadate were studied.The experiments of photodeposition were carried out on phase-pure bismuth vanadate thin films prepared by target with Bi to V of 6 with Ag⁺,Mn²⁺,Pt⁴⁺ and Pb²⁺.The mechanism of selective photodeposition of Pb²⁺ on the surface of bismuth vanadate was explained in detail.Finally,the in-situ reaction experiments confirmed that the main reason for the rapidly fading of the in-situ system is the photosensitization of nitrate.