Research

Our research interests fall within four thematic areas:

(i) Carbon materials

(ii) Nanotoxicology and material safety by design

(iii) Graphene-based materials and technologies

(iv) Environmental nanotechnology

The problems we select often require multidisciplinary approaches, and we enjoy bringing our core skills in materials chemistry and chemical/biochemical engineering to collaborations with a variety of academic and industrial researchers.  Our research interests are described in more detail below:

Carbon materials

We are interested in the broad class of solid materials composed primarily of elemental carbon, ranging from graphene to artist's charcoal.  Carbon materials are of both natural and synthetic origin; they can form incidentally in flames or in the earth’s crust, or can be highly engineered functional materials.  Our group works studies the fundamental structure, surface chemistry, properties, and behaviors of carbon materials.  We are particularly interested in the conceptual model of carbons as quasi-physical assemblies of graphene layers whose stacking, curving, and orientation in 3D determine the properties of the material and its anisotropy.  This conceptual model allows carbon structures to be understood in detail through high-resolution TEM methods.  It also guides the synthesis of highly engineered carbons through directed assembly of disk-like or sheet-like precursors or building blocks. In the topic of supramolecular carbon synthesis, we work with planar polyaromatic molecules as building blocks that are assembled with the aid of surfaces or flows, and often involve liquid crystalline phases (below).  The analogous use of pre-isolated graphene sheets as building blocks has developed into the separate theme of 3D graphene architectures (see below).   We are also interested in porous carbon forms as advanced sorbents and catalyst supports and collaborate with Prof. Tayhas Palmore and members of the C4 Center at Brown to develop carbon supports for new homogeneous and heterogeneous catalysts that reduce CO2 into useful chemical products.

 

 

 
  
    

Nanotoxicology and material safety by design

The development of new nano-enabled technologies is being accompanied by a major international effort to assess and manage their potential risks to human health and the environment.  We collaborate extensively with the pathobiology research group of Prof. Agnes Kane at Brown to understand the complex ways in which nanomaterials interact with living systems.   A long-term goal of this work is to understand the material features that initiate toxicity pathways, and to reformulate or reengineer them to achieve the goals of “safety by design.”   As a materials chemistry group, our particular interest is how specific material features initiate toxicity pathways within cells or organisms.   The features include surface chemistry that can lead to hydrophobic interactions with biomolecules, surface redox activity leading to oxidative damage pathways, or nanometal oxidation by dioxygen leading to dissolution and release of soluble toxic ions (below left).  We have also worked on identifying artifacts in in vitro test methods associated with the ability of high-surface-area nanocarbons to adsorb molecular probe dyes or micronutrients (below).  We are also now collaborating with the Haujian Gao group in engineering to study the role of nanomechanics in the interaction of high-aspect ratio nanomaterials (HARNs, such as CNTs and graphene), with soft biological structures to determine cellular uptake and the subsequent toxicity pathways (right).

 

 

 

 

   

Graphene-based materials and technologies

The discovery of graphene led to intense interest in its device applications, but in addition the carbon field was given a new type of precursor for design and fabrication of 3D carbon materials.  Our interest in supramolecular routes to carbon is easily extended to these atomically thin, 2D giant “molecules”, and we are actively engaged in discovering ways to align, stack, wrap, fold, crumple, or gel graphene sheets into new 3D carbon-based carbon forms.  Most of this work uses water-processable graphene oxide as a precursor, and like its smaller molecular cousins forms liquid crystal phases, but can also bend and fold due to large lateral dimension.  We have been using graphene oxide to make cargo-filled nanosacks (right-hand image), exploded porous forms (below left), folding/unfolding actuators, or can be tiled at the oil-water interface on the surfaces of dispersed droplets make new types of liquid-liquid emulsions (below).  

Carbons formed through graphene oxide assembly have fundamentally different structures than those from molecular precursors, and have applications that range from barriers and membranes, to electrocatalysts, to biomedical imaging proves with high-contrast agents encapsulated in folded graphene.

 

 

 

Environmental nanotechnology

More than two decades of nanoscience research has produced an enormous variety of new materials that now form a “toolkit” for developing the next generation of environmental technologies for the protection or clean-up of air, land, and water.  On the other hand, large-scale nanomanufacturing will generate products and effluents containing nanomaterials that may become the pollutants of the future, and whose risks must be characterized and managed.  Environmental nanotechnology embodies both the “applications and implications” for the environment – the two faces of Janus.

In the implications area, we are interested in how nanomaterials transform when released into the natural environment.  Can they biodegrade, or oxidize (right), or undergo reaction with sulfides (below right) to form new materials that pose a greater or lesser risk to humans or environmental organisms.  In the applications area we are interested in high-surface-area nanosorbents and catalysts for capture or oxidative destruction of pollutants.  We are also developing graphene materials as barriers and selective membranes (below) that prevent the transport of toxicants to limit human exposure.  This work is enabled by our participation with Superfund Research Program center grant at Brown University.