【作者】 刘悦；

【导师】 陈刚；

【作者基本信息】 哈尔滨工业大学 ， 物理化学， 2017， 硕士

【摘要】 近年来,能源短缺与环境污染早已成为限制经济发展的主要难题。开发环境友好型的新能源可以缓解和解决当前的能源及环境压力。氢能得益于其燃烧值高、产物无污染等优点,成为最具代表性的新能源。在诸多制氢策略中,半导体光催化技术成为最具发展潜力的绿色能源技术之一。该技术以光催化剂为主体,通过光激发形成的光生载流子与环境中的其它物质发生氧化还原反应达到无污染制氢的目的。HCa₂Nb₃O₁₀光催化剂具有类钙钛矿型的特殊结构,表现出优异的载流子传输能力,但较大的禁带宽度,限制了其光催化性能的提高。因此对HCa₂Nb₃O₁₀进行改性研究颇具前景。本论文对HCa₂Nb₃O₁₀进行了复合研究,并利用贵金属负载、元素掺杂等对复合光催化剂进行了改性研究。采用固相-离子交换-剥离法制备了具有三明治结构的HCa₂Nb₃O₁₀/Ca Nb2O6复合纳米片。TEM结果表明在该异质结中,两相通过（001）晶面相结合,在侧面发生了晶格错配,这种结构有助于载流子传输能力的提高。XPS结果表明异质结通过Nb键相互连接,且复合并未影响其他元素的化学环境。PL结果证明复合后样品的荧光强度明显降低,载流子寿命有了显著提高。光电流测试表明负载后的样品的载流子传输能力有了明显的增强。能带表征结果证明HCa₂Nb₃O₁₀和Ca Nb2O6具有相近的禁带宽度和不同的价、导带位置,所以在异质结内能够实现彼此载流子的传输和分离,这也是复合后样品制氢效率提升的主要原因。采用光化学还原沉淀法,制备了Pt负载的HCa₂Nb₃O₁₀/Ca Nb2O6光催化剂,并确定了最佳的反应时间为2 h,最佳的负载比例为0.3%。负载后的样品具有响应太阳光的能力,在模拟太阳光下,分解水制氢性能较负载前有了很大的提升。UV-Vis漫反射光谱的测试结果表明不同反应时间的样品吸光强度一致,不同反应比例的样品随着负载量增加吸光强度逐渐增强,所有光催化剂的吸收边在370 nm左右。光电流测试结果表明负载后样品的光电流强度明显增强,载流子传输能力有了较大提升。但贵金属负载并未对催化剂的物相及形貌等产生影响。采用相同的固相-离子交换-剥离法制备了Ta掺杂HCa₂Nb₃O₁₀/Ca Nb2O6纳米片。TEM照片表明掺杂后的纳米片仍然表现为三明治状的结构,未出现物相及结构的改变。XPS的表征结果表明掺杂后的样品中只有Nb和O元素出现了峰偏移,证明Ta掺杂取代了Nb的位置,影响了Nb与O的结合能。光学性质表征结果表明虽然Ta掺杂并未明显改变纳米片的禁带宽度,但能够提升纳米片的制氢性能。光电流结果证明掺杂能够提升电流强度,有助于载流子迁移及表面氧化还原反应的发生,因此掺杂后样品的制氢性能得到了提升。更多还原

【Abstract】 In recent years,environmental pollution and energy shortage have become main factors limiting development of economic.It is a highly effective measure to relieve the pressure of environment and energy by developing new energy.Photocatalytic water-splitting for hydrogen production utilizing semiconducting materials is essential to answer global environmental pollution and the energy crisis as an economical technique.Photocatalysis technique relies mainly on redox reaction of photogenerated carriers that are produced by semiconductor photocatalyst and substances in the environment.Among the state-of-the-art photocatalysts,HCa₂Nb₃O₁₀ has been suggested as one of high-efficiency photocatalysts for hydrogen production for its special layered perovskite-type structure and high chemical durability.However,the photochemical water splitting capability of HCa₂Nb₃O₁₀ is limited by its rapid carrier recombination.In this work,different measures such as construction of heterojunction,loading noble and doping ion are took to modify hydrogen production performance of HCa₂Nb₃O₁₀.Sandwich-like HCa₂Nb₃O₁₀/Ca Nb2O6 heterostructured nanosheets are successfully fabricated through a facile calcination with sub sequent ion-exchange treatment.The TEM test results indicate interfacial lattice mismatch,which is helpful for the transition of carrier,might occur between（001）planes of layered perovskite-related type HCa₂Nb₃O₁₀ and Ca Nb2O6.It can be speculated that the connection of lattice planes in heterostructure is accomplished by niobium chemical bond from XPS test results.Furthermore,the PL emission intensity of HCa₂Nb₃O₁₀/Ca Nb2O6 reduced significantly compared with HCa₂Nb₃O₁₀ showing charge carrier separation efficiency is greatly improved.The photocurrent density of HCa₂Nb₃O₁₀/Ca Nb2O6 is 2 times higher than HCa₂Nb₃O₁₀.This is attributed to effective carrier separation in the heterostructure.Characterization of band gaps confirms that HCa₂Nb₃O₁₀ and Ca Nb2O6 own similar energy gap but diffierent band position,so there is a separation of carriers in the nanosheets leading to a higher hydrogen production.Pt-loaded HCa₂Nb₃O₁₀/Ca Nb2O6 photocatalyst is prepared by a photochemical reduction precipitation method and optimal conditions are found as,reaction time 2 h,mass ratio 0.3%.The loaded samples exhibit higher activity for hydrogenation than before under simulated sunlight.UV-vis spectra shows that samples with different reaction times and different mass ratios have respectively similar and gradually enhanced intensity of light absorption.The absorption edges of all samples are about 370 nm.The photocurrent density of Pt-loaded samples is higher obviously proving efficient separation of carrier.However,no changes have been made to morphology for the loaded samples.Ta-doped HCa₂Nb₃O₁₀/Ca Nb2O6 nanosheets are obtained by the same method as the first part.TEM indicates that the doped nanosheets exhibit sandwich-like structure without changes in phase composition and construction.XPS characterization proves that Ta replaces location of Nb and affect the binding energy of Nb and O leading to tiny skewing of peaks.The band gap of Ta-doped sample has not changed compared with before but the hydrogen producton is improved.The higher efficiency of carrier transfer is proved by results of photocurrent density.All the results indicate that doping Ta is helpful for separation and transfer of carriers leading to a higher photocatalytic activity.更多还原