促进电荷分离一维结构顶端和侧面上结的构筑及光催化性能

Photocatalytic materials and technologies have gained rapid progresses in the past decades and photogenerated charge process is essential. Charge separation decisively influences functions of materials and devices, also has become an interdisciplinary research frontier of energy and environment, nanomaterials, and surface and interface. But charge separation still faces severe challenges of extremely high probability of charge recombination and low transport rates. So, a crucial question is raised to develop strategies and novel materials for precisely tuning built-in electric field and electric transport, because built-in electric field and charge transport are within micro-nano meter scale and strongly controlled by band gap, geometric structure, and defect of materials. This proposal introduces a strategy and materials of building up junctions on one dimensional crystals with well-defined regular locations and combinations. In details, we construct junctions with symmetric and asymmetric structures and side-junctions with intimate contact, materializing synergistic control of electric field and charge transport. We realize control of transport rate and distance by crystallinity and geometric structure of one dimension material. So, our strategy features two advantages, i.e. synergistic control of both built-in electric field and charge transport and clearly-defined structure-property relation. Our proposal would provide possible new understanding for charge separation at micro-nano meter scale, and also scientific basis for designing and precisely synthesizing customized photocatalysts.

光催化材料与技术近十多年重新得到了快速发展，其本质是光生电荷分离。电荷分离决定着材料和器件的功效，成为能源与环境、纳米材料、表界面交叉学科前沿研究方向。电荷分离面临着复合几率极高、传输速率低的挑战，关键科学问题是精准构筑内建电场和大力提高对内建电场和电荷传输的协同调控，因为内建电场和电荷传输在微纳米尺度且受材料制备等多因素控制。本申请提出高精度化学调控一维纳米晶体上的结(Junction)的规则分布和组合作为解决此问题的突破口，即在一维晶体的顶端上形成对称和不对称型的结或在侧面上形成单一结（多结），径向和横向上分别协同调控电荷分离和传输, 通过一维结构的结晶度和尺寸调控电荷迁移速度、距离，最终实现光催化性能的大幅度提高。该方法具有协同调控内建电场和电荷传输、清晰构效关系的双重优势。该申请为提高微纳米尺度电荷分离提供新的认识和策略，为可定制光催化剂的设计和精准制备提供科学基础。

光催化的本质是光生电荷过程，即吸收光子产生电子和空穴对，电子和空穴对需要克服静电引力才能分离并参与化学反应。因此，如何精准设计和制备光催化材料促进电荷分离是关键的科学问题。主要的研究内容包括：（1）一维材料顶端对称异质结的可控制备与表征、光催化性能测试及光催化机理的推导；（2）一维材料不对称异质结的可控制备与结构表征、光催化性能增强及光催化机理; (3)一维材料侧面异质结的构筑与光催化性能。创新之处在于一维材料上对称和不对称异质结的精准构筑和电荷分离增强。采用高温溶剂热解法和种子生长法成功地制备了CdSe@CdS纳米棒，采用光辅助沉积法，实现了纳米棒顶端对称沉积金属Pd、Fe及半导体PdS，沉积位置的选择性大于８5%。通过详细的表征，发现金属为顶端的对称异质结光生电子迁移到顶端，而半导体为顶端的对称异质结光生空穴迁移到顶端，因此实现了光生电荷分离在一维方向上的调控。在对称异质结的基础上，成功地利用光沉积法和阳离子交换法可控制备了纳米棒上不对称型异质结，即纳米棒两端分别沉积金属和半导体，沉积位置选择性超过65%。不对称异质结用于光催化制氢，比对照催化剂制氢量提高约３个数量级，且光稳定性得到显著地提高。通过系列表征，发现不对称异质结中的光生电子迁移到金属端而空穴迁移到半导体端，极大地增强了电荷分离效率和光催化制氢量。在TiO2纳米线的侧面沉积量子点Cu2O形成侧面异质结，显著地增强了对氯苯酚的光催化降解，经过表征发现光催化机理为S机制。该项目通过一维材料异质结的可控制备，成功地实现了电荷分离在一维方向上的调控和光催化性能的显著增强，为进一步提高低维材料内建电场调控和电荷分离方向调控提供新的认识和策略，为可定制光催化剂的设计和精准制备提供科学基础。