【作者】 胡文远；

【导师】 董发勤；

【作者基本信息】 西南科技大学 ， 环境科学与工程， 2019， 博士

【摘要】 随着全球工业化进程的高速发展,世界范围内的环境污染与生态破坏日趋严重,环境污染防治的紧迫性日益凸显。各国都在大力探索环境污染治理的新技术与新方法,以实现可持续发展。在众多环境污染治理技术中,半导体矿物多相光催化反应具有可直接利用太阳光、反应条件温和、深度净化污染物等优点,成为一种理想的环境污染治理技术,也是近年来环境科学领域最活跃的研究方向之一。但是,受限于光谱响应范围窄和光生载流子复合率高的瓶颈问题,使其推广应用举步不前。半导体矿物的微结构与其光电转换性能密切相关,众所周知,晶相种类决定了载流子跃迁难易,掺杂与否决定半导体机理,能带结构决定了光谱响应宽窄,表界面形态决定了载流子响应高低及反应活性。只有对上述影响光电转化性能的结构因素进行有效调控才可能实现其性能的优化。现在被广泛研究的氧化物TiO₂和硫化物ZnS半导体矿物由于具有宽带隙可望通过能带调控实现全波段太阳光响应。此外,与之对应的金红石和闪锌矿天然半导体矿物在自然界具有丰富的储量,可望通过从人工合成到天然半导体矿物替代从而极大地降低光电转换的成本。因此,设计合成可有效利用太阳光的半导体矿物、开发利用天然半导体矿物的环境属性进行环境污染治理与修复、探索厘清半导体矿物微结构与光电转换性能之间的构效关系,对充分发挥半导体矿物在环境污染治理领域的作用具有重要的现实意义。基于半导体矿物光电转换在环境污染治理领域巨大的应用价值,为探索低成本的半导体矿物构建方法,并通过微结构的调控来提高其光电转换效能。本文选择在环境污染治理领域具有重要应用前景的氧化物TiO₂和硫化物ZnS两类宽带隙半导体矿物为研究对象,在查明其矿物学信息和半导体特性的基础上,进行了人工合成与天然矿物集成增效结构的构建。通过同质异相结、晶面暴露纳米阵列、电子助剂石墨烯、空位诱导等多因素耦合作用实现光电增效微结构调控,提升其光生载流子分离和传输效率。通过光电化学作用体系研究各因素对光电增效的贡献机制,并将其用于光催化降解甲基橙（MO）及光催化还原Cr（Ⅵ）,研究其光催化性能及动力学特征,探索其光电增效机制。1.锐钛矿/天然金红石（A/NR）同质异相多晶光电增效结构的构建及其增效机制的研究。通过微波水热法,在天然片层金红石矿物上生长锐钛矿纳米颗粒物,得到同质异相多晶光电增效结构的A/NR。研究结果表明,A/NR1:2光电转换性能是天然金红石的20.1倍、是纯TiO₂光电极的3.8倍。A/NR 1:2样品480 min可见光光催化降解MO为55.75%,480 min可见光光催化还原Cr（Ⅵ）为54.70%。机理分析表明,A/NR多晶增效的主要原因是:其一,片层颗粒状的微结构增加了受光面积提高了光吸收比例;其二,锐钛矿和天然金红石构成的同质异相结提升了光生载流子的分离效率;其三,天然金红石中含Fe杂质诱发的晶格畸变产生的电子色心成为捕获中心,进一步降低光生电子-空穴的复合率。2.锐钛矿阵列活性晶面的调控及其增效机制的研究。通过不同溶剂的极性差异,采用低温溶剂热法获得以（001）、（010）和（101）不同晶面暴露比例的锐钛矿TiO₂阵列。结果表明,由溶剂极性不同所导致的液液界面上晶面调控剂浓度的差异是影响生长基元、活性晶面暴露的关键因素。暴露（001）晶面的环己烷体系A001阵列,其光电转换效能为0.25%是纯TiO₂光电极的6.3倍。A001阵列具有较高的光催化降解MO的能力,300min降解率为92.45%,暴露（010）晶面A010阵列具有较高的光催化还原Cr（Ⅵ）性能,300 min还原率为61.92%。机理分析表明,活性晶面暴露产生的不同晶面电荷密度差异引起的内建电场、不同晶面导带和价带电势差驱动的光生电子-空穴的分离改善、阵列的有序结构引起的电子和空穴流动的导向性等因素的协同作用是其光电增效的内在作用机制。3.石墨烯/锐钛矿阵列（RGO_x/A001）构建、晶面调控及其增效机制的研究。采用低温溶剂热法构建了石墨烯/锐钛矿阵列的光电增效结构。结果表明,石墨烯含量为0.80 wt%的RGO_0.8/A001的光电转换效率为0.49%是A001阵列的2.0倍,是纯TiO₂光电极的12.3倍。RGO_0.8/A001光催化降解MO的效能180 min降解率为88.64%,RGO_0.2/A001光催化还原Cr（Ⅵ）的效能180 min还原率为63.68%。其光电增效的机制在于:其一,薄化的生长基元提高了活性晶面（001）暴露的比例,晶面暴露有利于光生电子和空穴在基元空间上的分离;其二,引入的电子助剂GO有利于提高电子输运效率,进一步提高了光生电子和空穴的分离效率。4.活性晶面暴露纤锌矿/天然闪锌矿(W_xS_1-x)的构建及其光电增效机制研究。结果表明,采用水热法制备了在天然闪锌矿片层解理面上生长的纤锌矿ZnS纳米分级球的光电增效结构,该纳米分级球是由活性晶面（002）暴露的纳米柱自组装形成。W_0.4S_0.6的光电转换性能是天然闪锌矿的5.0倍,是纯TiO₂光电极3.8倍。其光催化降解和还原的结果表明,360 min光催化降解MO性能为89.10%,30 min光催化还原Cr（Ⅵ）性能为97.11%。其光电增效的机制在于:其一,纤锌矿/天然闪锌矿构成的同质异相结有利于光生载流子分离效率的提升;其二,活性晶面暴露纳米柱自组装形成的纳米分级球既提高了光的捕获率,又有利于光生电子-空穴在晶面空间上的分离;其三,天然闪锌矿成矿过程中赋存的Zn、S空位作为光生电子和空穴的分离中心,可进一步提升其光电转换效率。5.石墨烯/活性晶面暴露纤锌矿（RGOx/W）的构建及其光电增效机制研究。结果表明,采用光还原法和原位水热法制备了石墨烯/活性晶面暴露纤锌矿,其呈现自组装纳米分级球均匀分布于石墨烯片层上的微结构。石墨烯含量为0.5 wt%的RGO_{G 0.5}/W光电转换效率为0.19%,是纯TiO₂光电极的4.9倍。RGO_{G 0.5 0}/W光催化降解MO的效能为240 min降解率92.18%,光催化还原Cr（Ⅵ）的效能为30 min还原率98.64%。其光电增效的机制在于,其一,活性晶面暴露纳米柱自组装的纳米分级球既提高了光的捕获率,又有利于光生电子-空穴在晶面空间上的分离;其二,引入的电子助剂GO有利于提高电子输运效率,进一步提升了光生电子和空穴的分离效率。更多还原

【Abstract】 With the rapid development of global industrialization,environmental pollution and ecological destruction in the worldwide are becoming more and more serious.So the urgenc y of environmental pollution prevention and control has become increasingl y promine nt.All countries are vigorousl y ex ploring new technologies and new methods of environmental pollution control in order to achieve sustainable development.Among numerous environmentalpollutioncontroltechnologies,theheterogeneous photocatal ytic react i on of semiconductor minerals has attracted wide attention due to direct use of sunlight,mild reaction conditions and deep purification of pollutants.Thus,it has become an ideal environmental pollution control technology,and is also one of the most acti ve research directions in the field of Environmental Science in recent years.However,the application of this technology is not advanced due to two crucial deficiencies,one is its wide band gap,which limits its response range in sunlight.And the other is a high recombination rate of photogenerated carriers that limits the utilization rate for them.The photoelectric conversion properties of semiconductor minerals are closel y related to their microstructures.As everyone knows,the t ype of crystal phase determines the difficult y of carrier transition;doping or not determines the semiconductor mechanism;the band structure determines the range of the spectral response;the surface morphology determines the carrier response and reactive activit y.It is possible to optimize the photoelectric conversion performance onl y b y effectivel y adjusting and controlling the structural factors as described above.Semiconductor minerals of the ox ide（TiO ₂）and sulfide（ZnS）with the wide band gap,which have been widel y studied,are ex pected to achieve full-band solar response through the band regulation.In ad dition,natural semiconductor minerals of rutile and sphalerite with abundant reserves in nature are ex pected to greatl y reduce the cost of photoelectric conversion materials through replacing the artificial s ynthesis with the natural semiconductor mineral.Therefore,it is of great practical significance to utilize semiconductor minerals to control environmental pollution through designing and s ynthesizing them to u tilize full range sunlight,developing and utilizing their environmental attributes and exploring and clarifyin g the relationship between the microstructure and the photoelectric conversion propert y of semiconductor minerals.Based on the potential application value of photoelectric conversion of semiconductor mineral in the field of environmental pollution control,in order to explore methods of low-cost semiconductor mineral construction and improve its photoelectric conversi on efficiency through the regulation of micro-structure,two kinds of semiconductor minerals with broad band gap,titanium dioxide and zinc sulfide,which are important application prospects in the field of environmental pollution control,are selected as the research objects in this paper.On the basis of identifyin g the mineral propert y and semiconductor characteristics,compounds of s ynthetic and natural minerals wereprepared.Theirmicrostructuresarecontrolledusingthe heterophase junction with the same chemical composition,active crystal-facet nanoarrays,electronic promoter of graphene and vacancy to improve the separation and transmission efficiency of photogenerated carriers.The contribution mechanism of various factors to photoelectric efficiency was studied b y photoelectrochemical s ystem.The photocatal ytic degradation of meth yl orange（MO）and the photocatal ytic reduction of chromium（Ⅵ）using semiconductor minerals,the photocatal ytic performance and kinetic characteristics and the photocatal ytic s ynergistic mechanism were studied.1.Anatase/natural rutile（A/NR）het erophase junction was prepared,and its s ynergistic mechanism was studied.A/NR with the photoelectric s ynergistic-structure of homogeneous pol ycr ystalline was obtained,which was anatase nanoparticles gr owing on natural rutile sheets b y microwave h ydrothermal method.The results show that the photoelectric conversion performance of A/NR1:2 is 20.1 times as that of natural rutile and 3.8 times as that of pure titanium dioxide photoelectrode.The photocatal ytic degradation（MO）performance of A/NR 1:2 under visible light is 55.75%at480 min,and the photocatal ytic reduction of Cr（Ⅵ）is 54.70%at 480 min under visible light.The mechanism analysis shows that the main s ynergism reasons of the pol ycrystalline A/NR are as follows:firstly,the lamellar granular microstructures increase the light-absorbing area and increase the light absorption ratio;secondl y,the homogeneous heterophase junctions composed of anatase and natural rutile improve the separation efficiency of photogenerated carriers;thirdl y,the el ectron color centers produced b y lattice distortion due to Fe-containing impurities in the natural rutile become capture centers,further reducing the photogenerated electron-hole recombination rate.2.Anatase arrays with the active crystal facet were s ynthesized,and their s ynergistic mechanism was studied.Anatase arrays with different exposure ratios of（001）,（010）and（101）crystal planes were obtained in d ifferent polarit y solvents using low-temperature solvothermal method.The results show that the different concentration of crystal surface regulators at liquid-liquid interface caused b y the polarit y of solvents is the key factor,which affects the growth units and the ratio of active cryst al facets.The photoelectric conversion efficiency of A001 array prepared in cyclohex ane with（001）crystal facet exposed is 0.25%,which is 6.3 times as that of pure titanium dioxide photocathode.A001 arrays have high photocatal ytic abilit y to photocatal ytic degrade of MO,which is 92.45%in 300 minutes,and A010arrays with exposed（010）crystal facet prepared in toluene have high photocatal ytic performance to photocatal ytic reduce of Cr（Ⅵ）,which is 61.92%in 300 min utes.The s ynerg y mechanism involves the following aspects:the s ynergistic effects of the built-in electric field caused b y the different charge densit y on different crystal facets,the improvement of photogenerated electron-hole separation driven b y diff erent conduction-band and valence-band potentials in the different crystal facets and the orientation of electron and hole flow induced b y the ordered structure of the array are the intrinsic mechanisms of the improvement of photoelectric efficiency.3.Reduced graphene oxide/anatase arrays（RGOx/A001）were prepared,and the crystal facet regulation and the syn ergistic mechanism were studied.The photoelectric syn ergistic structure of reduced graphene oxide/anatase arrays was constructed using low temperature solvothermal method in cyclohex ane.The results show that the photoelectric conversion efficiency of RGO_0.8/A001 with reduced graphene oxide content of 0.8 wt%is 2.0 times as that of A001 arrays and 12.3 times as that of pure titanium dioxide photoelectrode.The photocatal ytic degradation efficiency o f MO b y RGO_0.8/A001 is 88.64%in 180 min,and the photocatal ytic reduction efficiency of Cr（Ⅵ）is 63.68%in 180 min.The s yn ergism mechanism of photoelectric efficiency is as follows:firstl y,t hinning growth units increase the proportion of active crystal facet（001）exposure,and the ex posure of active crystal facets is beneficial to the separation of photogenerated electrons and holes in the cell space;secondl y,the introduction of GO,electr onic assistant,is conducive to improving the electron transport efficiency and further improving the separation efficiency of photogenerated electrons and holes.4.Active crystal-facet wurtzite/natural sphalerite(W _x S_1-x)was prepared,and its photoelect ric s yn ergistic mechanism was studied.The photoelectric s ynergistic structure of wurtzite/natural sphalerite was prepared b y h ydrothermal method,which is nano hierarchical sphere grown on lamellar cleavage surface.The nano hierarchical-spheres were fo rmed b y self-assembl y of nano columns with active crystal facet（002）exposed.The photoelectric conversion performance of W _0.4S_0.6 is 5.0 times as that of natural sphalerite,and 3.8 times as that of pure titanium diox ide.The photocatal ytic degradation p erformance of MO and photocatal ytic reduction performance of Cr（Ⅵ）using W _0.4S_0.6 are 89.10%in 360 min and 97.11%in30 min under UV light,respectivel y.The enhancement mechanism of photoelectric efficiency is as follows:firstl y,the homogeneous hetero geneous junction of wurtzite/natural sphalerite is beneficial to the enhancement of the separation efficiency of photogenerat ed carriers;secondl y,the nano hierarchical-sphere with active crystal facet ex posed not onl y improves the light capture rate,bu t also facilitates the separation of photogenerated electrons and holes in crystal plane space;thirdl y,the vacancies of Zn and S occurring in the mineralization process of natural sphalerite act as the separation center of photogenerated carriers,which can further improve the photoelectric conversion efficiency.5.Reduced graphene ox ide/wurtzite（RGOx/W）with active crystal facet ex posed was prepared,and its photoelectric s ynergistic mechanism was studied.Reduced g raphene oxide/active surface exposed wurtzite was obtained b y photoreduction and in situ h ydrothermal method,whose micromorphology was the self-assembled nano hierarchical-spheres uniforml y distributed on the graphene lamellar structure.The photoelectric conversion efficiency of RGO _{G 0.5}/W is 0.19%,which is 4.9 times as that of pure titanium dioxide photocathode.The photocatal ytic degradation of MO using RGO_G0.50/W is 92.18%in 240 min,and the photocatal ytic reduction of Cr（Ⅵ）is 98.64%in 30 min.The mechanism of the photoelectric efficiency is as follows:firstl y,self-assembled nanospheres can not onl y improve the light capture rate,but also facilitate the separation of photogenerated electrons and holes in the crystal plane space;secondl y,the introduction of electronic assistant GO can improve the electron transport efficiency and further enhance the separation efficiency of photogenerated electrons and holes.更多还原