The Yin group is interested in the development of functional nanostructured materials for photonic, catalytic, bioanalytical, and energy applications through unique tools including chemical synthesis, surface functionalization, and self-assembly techniques. By producing nanocrystal ensembles with well-controlled overall size, composition, spatial arrangement, porosity, and surface properties, we aim to not only fully utilize the great size-dependent properties of individual nanocrystals, but also overcome many limitations associated with the isolated forms, making it possible to design and fabricate new functional materials for catalytic and biomedical applications as well as novel electronic, magnetic and photonic devices. Our research interests generally include:
- Colloidal inorganic nanostructures: synthesis and surface modification
- Self-assembly approaches to nanoscale electronic and photonic devices
- Smart (responsive) materials
- Functional composite nanomaterials
- Bioanalytical applications of nanostructures
- Nanocatalysts
- Colloidal and interface chemistry
- Nanofabrication using unconventional methods
Highlights of our research activities in the past few years include:
Responsive photonic nanostructures
We have been interested in developing self-assembly approaches for the fabrication of photonic nanostructures that can respond to external stimuli such as magnetic fields, electric fields, mechanical forces, and light illumination. These responsive photonic structures have important applications in areas such as color displays, biological and chemical sensors, smart inks and paints, antifraud devices, and many other active optical components. An interesting example involves highly charged uniform superparamagnetic (SPM) colloids that can be self-assembled into ordered arrays in solvents with reversibly tunable colors across the entire visible spectrum under external magnetic fields. The magnetic assembly strategy can be further extended to nonmagnetic building blocks by using ferrofluids as magnetic media to induce magnetic interaction among nonmagnetic particles and produce the periodicity required for photonic response.
Novel core-shell structured photocatalysts
By collaborating with Prof. Francisco Zaera and Prof. Christopher Bardeen, we aim to develop a novel class of titania-based core-shell composite nanocatalysts for photocatalysis. We have demonstrated how to control the size, morphology, crystallinity, and surface properties of titania-based materials, and further synthesized a series of well-defined metal@TiO2 core-shell photocatalysts which are currently used as model systems for studying fundamental questions encountered in photocatalysts, such as the fast recombination of electron-hole pairs and the recombination of H2 and O2 on the metal surface once they are produced. Our core-shell design affords a high level of structural control and monodispersity, as required to obtain a basic understanding of how the nanoscale morphology affects the function of metal-TiO2 photocatalysts. The core-shell design also allows us to incorporate multiple components into one nanoscale structure in a highly controllable manner to achieve superior catalytic performance.
Metal nanostructures with controllable plasmonic properties
We have been interested in noble metal nanostructures mainly due to the strong dependence of their plasmonic properties on size, shape, and geometric arrangement and consequently their wide applications in photonics, electronics, catalysis, and biomedical sensing. Our primary focus in this field is on the synthesis of anisotropic metal nanostructures as they offer high tunability in plasmonic properties by controlling their shapes. Through systematic studies, we have developed consistently reproducible processes for the synthesis of Ag nanoplates with high efficiency and yields by identifying the critical role of hydrogen peroxide instead of the generally believed citrate in the well-known chemical reduction route. By combining the concepts of selective ligand adhesion and seeded growth, we have further developed processes for the synthesis of silver nanoplates with an extremely high aspect ratio (up to over 400) and a widely tunable surface plasmon resonance band. The principle of controlling the reaction kinetics has been utilized to deposit a uniform thin layer of Au on the surface of Ag nanoplates, producing highly stable Ag@Au nanoplates which were used as an excellent enhancer for constructing a high-performance SPR biosensing system. We have also successfully combined the seeded growth strategy with templating approach for the synthesis of Au, Ag, Pt, and Pd nanorods with well controlled size and morphology in silica nanotubes. The advantage of the templating process is its potential for large scale production.
Dynamic Tuning of Plasmonic Properties
Instantaneous and reversible tuning of the plasmonic property of metal nanostructures holds great promises for developing novel optoelectronic devices and more effective chemical and biomedical sensors by allowing instant selective excitation or quenching of specific plasmon modes. We have demonstrated the dynamic tuning of plasmonic property based on the plasmon coupling between neighboring Au nanoparticles, which can be achieved through the reversible assembly and disassembly of Au nanoparticle chain-like structures by delicately controlling the colloidal interactions using internal or external stimuli, for example, by varying the ionic strength of the aqueous solution. We also demonstrated the thermoresponsive assembly and disassembly of charged Au nanoparticles through the manipulation of the electrostatic interactions by temperature variation, and further showed dynamic and reversible tuning of the surface plasmon coupling by controlling the temperature of the solution. We have created magnetically tunable plasmonic nanostructures by incorporating magnetic actuation into noble metal nanostructures to achieve active tuning of plasmonic properties. The magnetic responsive plasmonic nanostructures can be achieved either by magnetically induced assembly and disassembly of plasmonic nanoparticles or by controlling the orientation of anisotropic noble metal nanostructures such as Au nanorods, using external magnetic fields.
Hierarchically structured electrode materials for energy storage
In the past few years, we have also contributed to the development of hierarchically nanostructured electrode materials for energy storage applications including both lithium ion battery (LIB) and supercapacitors. Our main focus is to introduce porosity at different length scale to the electrode materials to enhance ion diffusion, and to explore methods for improving the overall conductivity of the electrode materials.
Nanocrystal Clusters for Bioseparation.
We have developed a general strategy for the fabrication of novel porous nanostructured materials for efficient separation of biomolecules such as proteins, peptides, and DNA. Nanoparticles of various nanostructured materials with uniform sizes and shapes are firstly synthesized, and then self-assembled into three-dimensional submicrometer clusters containing uniform mesoscale pores. The self-assembly process makes it possible to utilize both the specific material-peptide interactions and size exclusion of the mesoporous structure to enhance the selectivity in bioseparation. It also brings the convenience of incorporation of multiple components into the clusters to further facilitate the separation and detection. As an example, we have demonstrated the use of mesoporous TiO2 nanocrystal clusters for selective enrichment of intact phosphorylated proteins from complex biological systems.
