(4eh) Materials for Separations: Development of Synthesis Methods for Novel Composite Materials and Their Performance Tuning By Vapor-Phase Processes

My research interests encompass a range of emerging and interdisciplinary subjects across chemical reaction engineering, materials science, and chemistry. The comprehensive objective across these subjects is to design and build reactors for solvent-less vapor phase material deposition and for post-treatment processes to synthesize novel composite materials and tune their physical and chemical properties under a well-controlled system environment, respectively. In addition, fundamental and applied research is performed considering different application fields, ranging from separation processes (e.g., air and water purification and membrane separation for industrially-relevant gases) to electronic devices (e.g., chemical sensors).

My research interests consist of THREE main thrusts:

1) Designing and developing advanced reactors for vapor-solid reaction processes to control material composition, morphology, texture, and density at atomic precision. Given the well-known advantages in separated reactant delivery and self-limiting surface reactions, atomic layer deposition (ALD) is our primary technique to start with for an excellent conformal integration of inorganic components or porous thin films (e.g., metal-organic frameworks (MOFs)), for example, into a wide range of depositing surfaces. Moreover, other complementary reactors for plasma-enhanced ALD, molecular layer deposition, and their hybrid systems can also be built up in parallel to extend the choice of both reactants and materials to be deposited at our discretion. This scheme entails the proper design of the reactors by considering reactant chemistry, thermodynamics, reaction kinetics, and thermal and mass transport in the reactors.

2) Synthesis of multi-functional composite materials using the all-vapor-phase processing techniques developed. I am especially captivated by fabricating diverse composite materials through the vapor-solid reactions with polymeric or electrically conductive fibrous scaffolds to be used as a new class of breathable absorbents and self-detoxifying catalysts to sense and separate toxic chemicals rapidly and efficiently. Other materials of interest as depositing substrates include porous inorganic or organic supports applicable to membrane separation for industrially-important gas and potentially water remediation. Building up in situ characterization tools is also planned to instantaneously monitor and understand the underlying interactions of vapor-phase reactants and supports.

3) Materials modification to manipulate their intrinsic properties on demand, influencing their performance in relevant applications. In particular, I am interested in tuning the material properties, including material phase and defect density, by various post-treatment methods, such as a vapor-phase metal-organic exposure and infiltration as well as external stimuli (e.g., electron beam exposure, X-ray irradiation, or plasma treatment) under controlled processing conditions. Together with fundamental research on systematic changes in the chemistry of the materials and their interactions with, for instance, hazardous micro-pollutants, investigation of how those alterations relate to the corresponding enhancement or deterioration in their performance is an exciting part.

Research Experiences

Postdoctoral Projects:

“Membrane Fabrication and Modification of its Properties for Industrial Gas Separation via Postsynthetic treatment or External Stimuli” Under Prof. Michael Tsapatsis, Johns Hopkins Institute for NanoBioTechnology and Department of Chemical & Biomolecular Engineering, Johns Hopkins University 2019 – present

During my postdoc, I have been involved in multiple projects in part by collaborating not only internally with other lab mates but also externally with Brookhaven National Laboratory (BNL) and Catalysis Center for Energy Innovation (CCEI). My primary role in my own and collaborative work is to synthesize membrane and catalytic materials by vapor-phase reaction methods and to understand their processing-structure-performance relationship.

In the first project, my colleague and I developed a way of permselectivity tuning of membranes (i.e., zeolitic imidazole framework-8 (ZIF-8)) by a facile vapor-phase metal-organic treatment. As a result, we confirmed that the extent of interaction of the reactant vapor with the as-formed membrane surface is controllable by the post-treatment conditions. Furthermore, the modification approach results in a significant increase in selectivity for propylene over propane and hydrogen over other gases at the cost of reduced flux. Similarly, another team-mate and I demonstrated for the first time that electron beam irradiation for ca. 1 min can also modify the gas permeation properties of the membrane with noticeable enhancements in ideal selectivity for carbon dioxide over nitrogen and methane gas. At present, despite a couple of other intriguing projects in progress, I am very excited about my recent finding distinct from other reported strategies, which facilitates the area selective deposition of ZIFs.

Ph.D. Dissertation:

“Chemical Protective Metal-Organic Framework Thin Films on Fiber Systems Driven by Atomic Layer Deposition” Under Prof. Gregory N. Parsons, Department of Chemical & Biomolecular Engineering, North Carolina State University 2014 – 2019

During my time in graduate school, I developed expertise in integrating a class of porous materials (i.e., MOFs) on diverse polymeric fibrous mats and evaluating their performance for toxic chemical removal while taking the lead on multiple projects funded through the US Dept. of Defense. As a complementary technique, I managed and made the best use of the ALD system to diversify routes to integrate different sorts of MOF materials with polymers. During this time, I explored the interaction of vapor-phase reactants with polymeric fibrous scaffolds in the ALD processes, how the ALD-deposited components (e.g., metal oxides) play a role in heterogeneous MOF formation on top, and the possibility of defect engineering on the surface-bound MOF materials to enhance the catalytic performance. Along the way of such rigorous study, I succeeded in quantifying the role of the different metal oxides as nucleation media and the kinetics of extremely hazardous agents (e.g., sarin, soman, and their simulants) detoxification hydrolyzed by the MOF/fiber composites produced. In addition, I established the way of controlling the preferred orientation of the MOF deposits on the fiber surface and enabling, for the first time, growing photo-catalytically active MOF materials on the fibrous scaffolds by the combination of ALD processes and modified wet chemistry approaches. As a result, the multi-functional textile materials with an excellent catalytic performance in degrading sulfur mustard simulant show great promise as field-deployable protective gear.

Publications (selected from 20 Publications):

Teaching Interests:

While I had been served as a research- and teaching assistant under MS and Ph.D. programs in the Chemical Engineering Department, I believe I have developed not only teaching, but also communicating with students to have them effectively learn both in class and out of class. Especially such a research and teaching experience makes me confident of teaching chemical reaction engineering, thermodynamics, and mathematical approach to solving problems in transport phenomena. In addition, I can also teach more advanced or elective courses covering core chemical engineering topics, such as reaction kinetics, separations, and thermodynamics, coupled with sample industrial systems. My teaching goal is to inspire students to actively learn and apply their knowledge to engineering problems that they are facing and intrigued in, thus fostering academia and the industry in the end.