Establishing a Chemical Toolbox for Programmed Assembly of Metal Chalcogenide Nanoparticles into "Wired" Architectures

我们周围到处都是能量，但其中大部分并不是很有用。科学家们对如何把浪费的能源转化为有用的能源很感兴趣。斯蒂芬妮·布洛克博士正在研究如何将大量的太阳能转化为电能或化学燃料。她对如何收获“光”这个具有挑战性的问题特别感兴趣。量子点是一种非常小的粒子，其尺寸约为红细胞的千分之一，在吸收太阳辐射和产生带电粒子方面非常出色。因此，布洛克博士正在开发技术，使这些亚微观量子点粒子能够组装成薄膜和毫米到厘米尺寸的三维多孔结构。布洛克博士正在开发一种方法，使具有不同化学势的量子点能够相互连接，从而产生电压差，从而在结构内移动电流。她还致力于了解粒子间键合的化学性质如何影响电荷快速移动的能力，以及这些电荷有时如何被“困住”并抵抗提取。这些基础知识有助于设计高效太阳能电池和光化学水分解（氢燃料生成）系统。布洛克博士的研究对研究生和本科生都很有吸引力，他们通过参与她的实验室接触到前沿科学。布洛克博士还在开发针对初高中学生的科学模块，让他们在实验室中获得实践经验。她正在通过韦恩州立大学的GO-GIRLs外展计划实施这些计划。在这个研究项目中，韦恩州立大学的Stephanie Brock博士得到了大分子、超分子和纳米化学（MSN）项目的支持，开发了一个化学工具箱，以(1)使不同金属硫族纳米粒子组分的组装速度能够改变。这种能力可以决定多组分体系中相偏析的程度；(2)在装配后和装配前对界面进行化学修饰，以促进电子传递。研究了决定纳米颗粒（由MQ制成，其中M =镉、铅、锌；Q =硫、硒、碲）氧化组装的动力学参数与Q的氧化还原性质、M的溶解度、MQ的晶体结构、表面能量学和表面配基的关系。与此同时，通过凝胶化后的氧化加成反应或（预凝胶化）通过金属阳离子组装硫化物或卤化物覆盖的纳米颗粒，评估了用金属离子交联取代氧化界面的方法。能够控制金属硫族化物纳米颗粒的溶液相组装速率，从而使不同的纳米颗粒组件可编程组装成具有特定程度非均质性的2- 3-D“有线”架构，使设计多组件组件的应用受益于短距离快速注入电荷(例如：光催化剂由光敏剂+催化剂的均相组装而成)或需要远距离提取（例如，包含p + n半导体的大块纳米异质结太阳能电池）。化学原理也被用来调整粒子间界面的性质，从而增加粒子间的传递和组装的整体稳定性。Brock博士让研究生和本科生参与跨学科合作研究和现代表征技术。她通过GO-GIRLs外展项目向底特律地区的青春期女孩（其中许多是少数族裔）介绍化学知识。

Energy is all around us, but much of it is not very useful. Scientists are interested in ways to take wasted energy, and convert it into useful energy supplies. Dr. Stephanie Brock is investigating how to convert plentiful solar energy into electricity or chemical fuels. She is particularly interested in the challenging problem of how to harvest "light". Quantum dots are very small particles that have dimensions on the order of 1/1000th of a red blood cell and are great at absorbing solar radiation and producing charged particles. Accordingly, Dr. Brock is developing techniques that enable these sub-microscopic quantum dot particles to be assembled into films and 3 dimensional porous structures with millimeter to centimeter dimensions. Dr. Brock is developing methods that enable quantum dots with different chemical potentials to attach to each other, thereby creating a voltage difference that can move an electrical current within the structure. She is also working to understand how the chemical nature of the inter-particle bonding affects the ability to rapidly move the charges, and how these charges can sometimes get "trapped" and resist extraction. This fundamental knowledge helps in the design of efficient solar cells and photochemical water-splitting (hydrogen fuel generation) systems. Dr. Brock's research is attractive to graduate and undergraduate students alike, who are exposed to cutting-edge science through participation in her lab. Dr. Brock is also developing science modules aimed at middle-to-high school students to give them hands-on experiences in the lab. She is implementing these through the Wayne State University's GO-GIRLs outreach program. In this research program, Dr. Stephanie Brock of Wayne State University is supported by the Macromolecular, Supramolecular and Nanochemistry (MSN) Program to develop a chemical toolbox to (1) enable the rate of assembly of different metal chalcogenide nanoparticle components to be varied. This ability may dictate the degree of phase-segregation in multicomponent systems; (2) provide post- and pre-assembly chemical modifications of the interfaces to facilitate electron transport. The kinetic parameters dictating oxidative assembly of nanoparticles (made of MQ where M = cadmium, lead, zinc; Q = sulfur, selenium, tellurium) are studied as a function of the redox properties of Q, the solubility of M, the crystal structure of MQ, the facet energetics and the surface ligand group. In parallel, methods for replacement of oxidized interfaces with metal-ion crosslinks by post-gelation oxidative addition reactions or (pre-gelation) assembly of sulfide or halide-capped nanoparticles via metal cations, are evaluated. The ability to control the rate of solution-phase assembly of metal chalcogenide nanoparticles, thereby enabling programmable assembly of disparate nanoparticle components into 2- and 3-D "wired" architectures with specified degrees of heterogeneity, enable design of multicomponent assemblies for applications that benefit from rapid injection of charges over short distances (e.g., photocatalysts prepared from homogeneous assembly of photosensitizer + catalyst) or require extraction over large distances (e.g., bulk nanoheterojunction solar cells comprising p + n semiconductors). Chemical principles are also employed to tune the nature of the interparticle interfaces, thereby augmenting interparticle transport and the overall stability of the assembly. Dr. Brock involves graduate and undergraduate students in interdisciplinary collaborative research and modern characterization techniques. She introduces Detroit-area adolescent girls, many of whom are minorities, to chemistry through the GO-GIRLs outreach program.