【作者】 吴茂；

【导师】 公衍生；

【作者基本信息】 中国地质大学 ， 材料科学与工程， 2019， 硕士

【摘要】 作为一种能带结构合适、物理化学性质稳定、环境友好型且易制备的聚合物半导体,石墨相g-C₃N₄自2009年首次应用到光催化分解水以来,经过漫长的10年发展和演变,人们对其的兴趣从未消减,认识和改性逐渐深入。但是,光生载流子复合快、比表面积较小、活性位点少依然是g-C₃N₄面临的最棘手的问题,虽然研究者尝试了各种各样物理化学方法,但成效甚微。针对这些缺点,本文通过前驱体改性对g-C₃N₄的形貌和晶体结构进行调控,同时改善其活性位点数量和能带结构;构筑同质/异质结构,促进g-C₃N₄与其他半导体间的电子流动,从而达到载流子分离的目的。具体研究内容如下:（1）采用水热法预处理双氰胺（DCD）,使其形成成分均匀的有机小分子溶液,借助液氮的快速冷冻和热聚合处理,得到一维空心管组成的珊瑚状g-C₃N₄。在此基础上加入植酸（PA）进行磷元素掺杂,产物的可见光吸收显著增强,比表面积和管表面的微观形貌也随着磷掺入量的增加发生了明显改变。与传统方法制备的g-C₃N₄相比,可见光分解水制氢能力较提高了22.4倍,420 nm处的表观量子效率（AQY）为4.32%。这种由一维管壁和二维壳片共同组成的空心管构成了一个同类型不同性质的g-C₃N₄同质结,可以有效地实现电荷的空间分离,大大提高了其光催化性能。（2）在前一个实验的基础上,向水热后的双氰胺溶液中加入稀盐酸来改变有机小分子的官能团,进一步热聚合得到氮缺陷的纳米笼状g-C₃N₄。前驱体官能团的变化,使得产物化学组成、聚合途径和形貌结构都发生了明显改变。该g-C₃N₄大的比表面积、清晰可见且孔径分布广的孔结构有利于反应物的运输和光的反射,且孔边缘氮缺陷的存在提供了光反应的活性位点。同时,不同聚合方式导致的g-C₃N₄同质结使得电荷分离更为有效。在结构和缺陷的双重促进下,其可见光下的分解水制氢能力较传统方法制备的g-C₃N₄提高了20.3倍,420 nm处的表观量子效率（AQY）也达到了3.01%。（3）通过水热法和光沉积技术,制备了g-C₃N₄/TiO₂@Ni_xP三元复合光催化材料。g-C₃N₄和TiO₂以片状形式结合,整体呈现出三维空间结构,增加了可见光的吸收,增强了异质结界面的电荷传递;Ni_xP作为助催化剂,在光沉积作用下定向负载在TiO₂表面,既解决了物理混合引起的界面稳定性差的问题,又避免了界面电荷转移的混乱,大大加快了光反应的快速进行。其在全光谱下表现出良好的催化性能,最高产氢量约为5438.0μmol·g^-1·h^-1。更多还原

【Abstract】 As a kind of polymer semiconductor with suitable band structure,stable physical and chemical properties,friendly environment and easy preparation,graphite g-C₃N₄ has been developed and evolved for a long decade since it was first used for photocatalytic water splitting in 2009.People’s interest in it has never been reduced and researches on it have been gradually deepened.At present,fast recombination of photogenerated carriers,small specific surface area,and the lack of active sites are still the most difficult problems in the field of g-C₃N₄.Although researchers have tried various physical and chemical methods,little effect has been achieved.To solve this problem,we controlled the morphology and crystal structure of g-C₃N₄ by precursor modification method,and the number of active sites and energy band structure were improved.Meanwhile,heterostructure was constructed to facilitate electron flow between g-C₃N₄ and other semiconductors,thus achieving the efficient separation of charges.The specific research content is as follows:（1）Hydrothermal pretreatment of dicyandiamide（DCD）was used to form organic small molecule solutions with uniform composition.Then,Coral-like g-C₃N₄ composed of one-dimensional hollow tubes was obtained by rapid freezing of liquid nitrogen and thermal polymerization.On this basis,phytic acid（PA）was added for phosphorus doping,and the visible light absorption of the product was not only enhanced,but the specific surface area and the microstructure of the tube surface also changed with the increase of doping amount.As a result,its photocatalytic hydrogen production rate in visible light was 22.4 times higher than that of g-C₃N₄ prepared by traditional methods,and its apparent quantum efficiency（AQY）at 420 nm was also excellent,reaching 4.32%.The hollow tube,which is composed of one-dimensional tube wall and two-dimensional shell sheet,constitutes a g-C₃N₄ homogeneous junction with the same type and different properties,which can effectively realize the spatial separation of charges and greatly improve the photocatalytic performance.（2）On the basis of previous experiment,dilute hydrochloric acid was added to the hydrothermal dicyandiamide solution to change the functional groups of small organic molecules,and the nanocage-like g-C₃N₄ with nitrogen-deficient was obtained by further thermal polymerization.Owning to the functional groups of the precursor,the chemical composition,polymerization pathway and morphology of the products were changed.The pore structure of g-C₃N₄ with large specific surface area,clear visibility and wide pore size distribution is conducive to the transportation of reactants and light reflection,and the existence of nitrogen defects at the pore edge provides the active site for light reaction.Meanwhile,g-C₃N₄ homogeneous junction caused by different polymerization modes makes more effective charge separation.With the dual promotion of structure and defect,its photocatalytic ability in visible light was 20.3 times higher than that of g-C₃N₄prepared by traditional methods,and its apparent quantum efficiency（AQY）at 420 nm also reached 3.01%.（3）g-C₃N₄/TiO₂@Ni_x P ternary composite photocatalytic materials were prepared by hydrothermal and photo-deposition methods.g-C₃N₄ and TiO₂ combined in a lamellar form,which present a three-dimensional spatial structure as a whole,increasing the utilization of light and enhancing the charge transfer in the heterogeneous interface.As a cocatalyst,Ni_xP was loaded on TiO₂ under the action of photo-deposition,which not only solved the interface stability caused by physical mixing,but also avoided the confusion of interface charge transfer,greatly accelerating the light reaction.Under the full spectrum,its highest yield of hydrogen is about 5438.0 mol·g^-1·h^-1.更多还原