Our research program aims to expand our understanding of materials, surfaces, and interfaces and to apply this knowledge to make advances in a number of technologically emerging and societally critical areas. Currently, at the fundamental level, we are interested in low-dimensional materials, hybrid organic/inorganic materials, metal oxides and silicates. In these materials systems, we aim to establish synthesis-structure-property relationships, and to understand and control their surfaces and interfaces. These insights are helping to guide our interest in impacting areas such as environment, health, sustainability and energy as detailed below.
Chemical Sensing
Starting from the days of the canary in the coal mine, technologies have been developed to assist with the detection of chemicals in the environment, whether they be toxic, combustible, or simply contain an unpleasant odor. At the core of gas sensor development is the exploitation of some chemical or physical property of the target chemical to detect its presence. There are several broad classes of techniques, each with its own advantages and limitations, including electrochemical sensors, conductometric sensors, calorimetric sensors, optical sensors, acoustic sensors, and more. Below some of our current activities in this area are detailed.
Fundamental understanding of MOX-based sensors:
Chemiresistive sensors, which transduce target gas concentrations based on the change in resistance of a sensing material, provide sensitive, low-cost detection of gaseous analytes in applications such as environmental monitoring, quality control, and clinical diagnostics. Semiconducting metal oxides (MOX) such as SnO2 are an industry-standard material system for chemiresistive sensing. We aim to develop MOX-based sensors with stable long-term characteristics by investigating how the structural and electronic properties of MOX respond to different operating temperatures, durations, and environments. To enhance the stability, sensitivity, and selectivity of our sensors, we are also investigating catalytically active noble metals, such as Pt, Au, and Pd, loaded onto MOX materials to form noble metal-loaded MOX nanocomposites. These nanocomposites are integrated with interdigited electrodes to form fully functioning sensors. To understand the sensing mechanisms of pristine MOX and metal-loaded MOX nanocomposites, we are correlating charge transport processes elucidated by impedance spectroscopy with structural and chemical information conveyed by X-ray photoelectron spectroscopy. Mature sensors will leverage energy-efficient (~15 mW to reach 500 °C) poly-Si and SiC microheater platforms previously developed by our group to enable robust, low-power gas microsensors for a variety of applications.Materials innovations:
Atomically dispersed supported metal catalysts (also referred to as single atom catalysts) constitute a new class of materials that contains isolated individual atoms or synergistically coupled few-atom ensembles dispersed on, and/or coordinated with the surface atoms of appropriate solid supports. Examples include noble metals such as Pd and Pt on metal oxides, graphene, graphene oxide and various other two-dimensional materials. These materials have emerged as a rapidly developing class of catalysts offering the advantage of the most efficient use of noble metals combined with unique properties considerably different from their conventional nanoparticle equivalents. These include excellent selectivity for gas adsorption, electron transport and improved resistance to poisoning and coke formation. Herein, we aim to develop atomically dispersed Pd catalysts supported on two different support materials, namely graphene oxide and tin (IV) oxide for the fabrication of robust gas sensors for in-door air quality monitoring. Sensitivity, selectivity and response of the fabricated sensors towards the target gases, and recovery time, detection limit, stability, and working temperature of the sensors at different humidity levels are being investigated. We strive to elucidate their gas sensing mechanisms relevant to target gases (e.g., H2, CO and CH4) through their detailed structural, chemical, electrical and optical characterization. A classic challenge in gas sensing is the tunability of the sensing material for the selective absorption of target gases without interference from unwanted species. Metal-organic frameworks (MOFs), made up of metal-cluster nodes connected by organic linkers, can achieve selective adsorption owing to their high chemical and structural tunability. Their selectivity and flexibility make MOFs attractive for gas sensing, as realized in novel low-power, low-footprint, on-chip devices such as the chemical-sensitive field-effect transistor, previously demonstrated by our group. In this project, we aim to explore the large library of MOFs (consisting of different metal nodes and organic linkers) towards novel electronic sensor arrays. This effort includes investigating the underlying electronic transduction mechanisms of MOFs through resistance measurement, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and infrared and Raman spectroscopies, targeting important polluting and toxic gases such as CO2, CH4, CO, CH2O.Materials Synthesis in Microgravity
International Space Station National Laboratory provides the opportunity to synthesize materials under microgravity conditions. From the fundamental point of view, this capability allows us to understand the effect of gravity on materials synthesis (such as crystal growth). For the applied point of view, it may allow the fabrication of materials with properties superior to those on Earth. In collaboration with ISS and Professor Debbie Senesky at Stanford University, we are exploring the effect of microgravity on the synthesis and properties of graphene hydrogel where one would expect a depression in the effects of sedimentation that is seen here on Earth. We are also exploring the growth of metal-organic frameworks (MOF) under microgravity where one would expect a suppression in buoyancy-driven convection and a purely a diffusion-controlled growth environment.
Sustainable Construction
Global usage of concrete has tripled in the last 40 years, and continues to grow rapidly, placing immense pressure on the environment while requiring its use for safe and effective infrastructure. Concrete accounts for roughly 10% of worldwide CO2 emissions annually. A promising method for directly reducing the CO2 emissions associated with concrete is through replacement of cement, the primary binding material in concrete, with a percentage of carbon, creating so called carbon-incorporated cement composites (CCC). Carbon may be sourced from the waste product of methane pyrolysis, a process that is being explored to produce hydrogen fuel at large with lower CO2 footprint, making CCCs a method for carbon sequestration. Along with the environmental benefits, CCCs have displayed beneficial mechanical properties in the form of tensile strength and allow for opportunities with in-situ structural health monitoring arising from the electrical conductivity differences of solid carbon in concrete. Previous work has demonstrated the capability for CCCs to monitor compressive, tensile, and flexural stresses in concrete members at carbon replacements of 0.6% (wt.). This work looks to increase the carbon replacement to levels up to 10% while maintaining (or improving) the sensing, mechanical, and workability properties of concrete. To achieve this, surface modification of carbon materials, namely carbon fibers, via various methods will be used to increase dispersion of fibers in concrete necessary for mechanical and electrical effects and as an enabler towards low-carbon intensity hydrogen fuel.
RECENT NEWS
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- August 2023 – Maboudian lab goes to space! Our graphene aerogel produced aboard ISS in collaboration with Stanford (article)
- April 2023 – Anthony receives the SURF Rose Hill Fellowship!
- April 2023 – Stuart receives the NSF Graduate Fellowship!
- February 2023 – Xiaohong Zhu receives the EBI-Shell Postdoctoral Fellowship!
- May 2022 – Veronica receives the SURF Rose Hill Fellowship!
- May 2022 – Jeffrey graduates with the highest honors and heads to Stanford for graduate studies!
- March 2022 – Zhou successfully completes his PhD and joins Stanford as a postdoc!