1. Biofunctionalization of Graphene Oxide Surface for Drug Delivery:

Graphene oxide (GO) exhibits unique 2-D structure and exceptional physical, chemical and optical properties that lead to many potential biomedical applications. In the last few years, GO has attracted increasing interest as a molecular carrier for in vitro and in vivo drug delivery. It is also accepted that functionalization of GO sheets must be conducted to attain high biocompatibility. Results have shown that well-functionalized GO sheets are stable and safe for in vitro drug delivery, and that they can be readily excreted through the renal route and are non- toxic in vivo to mice.From the molecular point of view, the carbonyl, epoxy, hydroxyl and other oxygen functional groups on the basal planes and edges of GO sheets significantly alter their van der Waals and electrostatic interactions compared to those on pristine graphene. This explains why GO can immobilize a large number of substances, including metals, drugs, biomolecules and fluorescent molecules. However, there is still no systematic study on GO functionalization and we do not know the fundamental mechanisms that underlie the design of the GO surface to achieve simultaneously high loading capacity, high sensitivity and high biocompatibility for drug delivery purposes.To aid the integration of GO into clinical drug delivery and other biomedical applications, We are interested in applying and improving multi-scale modeling techniques to address the following challenges:

(1) An efficient method of GO functionalization for high biocompatibility and low toxicity. It is accepted that biofunctionalization can integrate GO with biomolecules, such as nucleic acids, peptides and proteins, and that the GO derivatives bind with the drug molecules through non-covalent interactions;

(2) Smart functionalization to increase targeting efficiency of GO-based drug carrier systems. It is of fundamental advantage to develop delivery systems with a molecular-recognition strategy, in which the therapeutic agents are carried with recognition capacity and optical, fluorescent or electric signals for imaging analysis. It is also important to develop functionalization methods so that the GO–based nano-materials are biodegradable in physiological systems after delivering the drugs.

(3) The interaction mechanisms of GO-drug complexes in physiological systems, for example, the in vivo behaviors of GO-based nanomaterials, the intracellular uptake mechanisms and the intracellular metabolic pathway.

The three challenges require an understanding of covalent interactions between GO and the functionalization polymers or molecules, and of non-covalent interactions between the GO-based nano-materials with the physiological systems, for example, proteins, DNA, peptides, cells, drugs or bacteria.
Our group use theory and multi-scale modeling methods and collaborate with experimental groups for two main goals:

- To understand the behavior and the controlling factors of complex surfaces and interfaces of relevance in energy, environment and biomedical applications;

- To carry out computer-aided discovery and design of structures and materials with targeted properties;
The Huang Group at The University of Oklahoma
2. Mesoporous Titanium Dioxide for Reaction and Mass Transport

The study of heterogeneous catalysis has bred four Nobel Prizes in Chemistry, Fritz Haber in 1918, Carl Bosch and Friedrich Bergius in 1931, Irving Langmuir in 1932, and Gerhard Ertl in 2007. It is of paramount importance in the chemical, biomedical and materials industries, and the field needs a continuous focus and efforts. In the heterogeneous catalysis process, the phase of the catalyst differs from that of the reactants. In general, the reactants diffuse from the bulk to the catalyst surface, adsorb and form new chemical bonds with the catalytic sites, and then desorb and diffuse from the surface after the reactions. We need fundamental understanding of: (a) the diffusion, adsorption, chemical reaction mechanisms and the mass transport phenomena of the reactants; (b) the properties of the catalytic surface and how to select, optimize and design support materials for different catalysts and different applications.

Titanium dioxide material has been widely studied as a heterogeneous photocatalyst for environmental applications, for example the degradation of organic pollutants and the dye- sensitized solar cell. Due to the in vivo biocompatibility, it also finds application in human osteoblasts and other implant materials. We recently examined the TiO2 surface activity by studying water dissociation on different TiO2 facets, and the ReaxFF molecular dynamics simulation results showed that the TiO2-B (100) is the most active but stable facet for water dissociation, and that the activity difference can be explained by the surface density of unsaturated Ti sites and the geometric surface curvature. For this project, we plan to collaborate with experimental groups on this project, to use mesoporous titanium dioxide material and study the simultaneous adsorption, diffusion and reactions of water (H2O), ammonia (NH3) and acetic acid (CH3COOH) for the following objectives:

(1) To develop a ReaxFF force field to describe both the mesoporous TiO2 structure and the reactive interactions between the fluids and TiO2 surfaces;

(2) To develop a coarse- grained model for mesoporous TiO2 structure;

(3) To perform a set of theory and simulation methods, spanning the electronic, atomistic and mesoscale of matter, to treat simultaneous adsorption, diffusion and chemical reaction in mesoporous TiO2 catalysts. The methods will be able to predict the reaction mechanism and rate, the reaction effects on adsorption and diffusion of reactants and the stability of mesoporous TiO2 surface features;

(4) To apply these methods to study ammonia and acetic acid dissociations on the mesoporous TiO2 catalysts;

(5) To study and design mesoporous TiO2 materials, with optimized reaction-diffusion characteristics, controllable surface hydrophobicity and hydrophilicity, and a desirable surface friction property.
@ The Huang Group
On-going Research Projects