Visible-light-responsive Photocatalysts
Graphitic carbon nitride has emerged as a novel visible light responsive photocatalyst in water splitting, carbon dioxide reduction, selective aerobic oxidation, and environmental remediation. Graphitic carbon nitride is synthesized from low-cost earth-abundant materials, it is chemically stable and non-soluble in water, and it shows promising results for photocatalytic oxidation of persistent organic contaminants and microbial inactivation under visible light irradiation, from both a xenon lamp source and light emitting diodes (LEDs). We are currently working on the development of graphitic carbon nitride with enhanced performance for persistent contaminant removal, pathogen inactivation, and exploring the mechanisms of photocatalytic oxidation.
Ongoing Projects
Integrated Experimental and Computational Studies for Understanding the Interplay of Photoreactive Materials and Persistent Contaminants (Funded by NSF Environmental Chemical Sciences Program, 2018-2022)
Persistent organic micropollutants are detected in natural aquatic environment, and their fate and transformation raise concerns because of their resistance to natural degradation and adverse impacts to human beings and ecological systems at very low concentrations. Photoreactions can degrade these contaminants under sunlight. However, most studies have been focused on contaminant photolysis. The ubiquitous presence of mineral photocatalysts in nature, and ever-increasing release of anthropogenic photocatalysts to the natural environment can promote the phototransformation of the contaminants on these photoreactive materials. The mechanism of contaminant transformation by photocatalysis is unique compared to photolysis, because it involves surface-mediated oxidation on the photocatalysts. Hence, current knowledge of photolysis cannot be translated into photocatalysis. Though photocatalysis was extensively studied in engineered systems, most studies paid attention to radical induced contaminant transformation, and the mechanistic exploration of surface mediated oxidation is still at its nascent stage. The complexity of natural aquatic environment and reactions of an extended time scale was also not well-recognized in previous research. Photocatalytic performance for contaminant transformation could be impacted by co-existing natural water constituents, and photocatalyst ageing in complex water matrices could tailor the photocatalyst properties and hence influence contaminant transformation.
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Undoped graphitic carbon nitride interacting with phenol
Undoped graphitic carbon nitride interacting with atrazine
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We are collaborating with Profs. Hanning Chen (American University) and Nan Jiang (University of Illinois at Chicago), and we aim to understand the transformation of persistent organic micropollutants on mineral and released anthropogenic photocatalysts in complex natural aquatic environment, through a highly integrated and sophisticated computational and experimental approach. Sphalerite (ZnS) and graphitic carbon nitride (g-C3N4) will be selected as the photocatalysts in our study, because of their ubiquitous presence in nature or (potentially) extensive applications, and distinct properties and corresponding photoreactivity. Molecular simulations, advanced spectroscopic and microscopic characterizations, and the evaluation of reaction kinetics and pathways will shed light on mechanistic understanding of the interaction of photocatalysts and contaminants at a(n) atomic/molecular scale, and also elucidate the impact of intrinsic complexity and heterogeneity of environmental systems for contaminant transformation.
Interactions between Photoreactive 2D Nanomaterials and Biofilms (Funded by NSF-Nanoscale Interactions Program, 2019-2022)
With extensive engineering applications of nanomaterials, their fate, transport, transformation, and environmental and ecological impact attract great attention in recent years. Incidental release and inappropriate disposal of these nanomaterials could pose adverse impacts to nature through a broad range of mechanisms. Specifically, photoreactive 2D nanomaterials, as an important group of the nanomaterial family, could interfere biological systems via posing physical, chemical, and thermal stresses under light exposure. Graphitic carbon nitride (g-C3N4) and black phosphorus (BP) nanosheets will be selected as two emerging photoreactive 2D nanomaterials because they hold promise in practical applications and they have unique and different photoreactivity. g-C3N4 nanosheets comprises single or stacked layers of tri-s-triazines interconnected via tertiary amines while BP nanosheets contains single or multiple layers of phosphorene, and these 2D nanomaterials can harvest and utilize visible to mid-infrared light to produce oxidative species such as O2-⋅/HO2⋅, 1O2, H2O2, ⋅OH, and holes. Specifically, BP nanosheets have a strong photothermal effect that can convert light energy into localized heat. Biofilms will be selected as a representative biological system in nature, because the biofilms play a critical role in the natural environment and ecological systems for degrading contaminants, participating in biogeochemical cycles, and acting as primary producers in the food chain. In addition, pathogenic bacteria in biofilms are also important for investigation because they pose health risks to humans. However, it is still largely unknown how photoreactive 2D nanomaterials influence biofilms in nature through different types of stresses, how biofilms respond to and evolve under the stresses, and how nanomaterial ageing in complex water matrices change nanomaterial behavior towards biofilms.
We are collaborating with Profs. Yun Shen (University of California, Riverside) and Na Wei (University of Illinois at Urbana-Champaign), and we aim to understand the interplay between emerging photoreactive 2D nanomaterials, i.e., g-C3N4 and BP nanosheets, and biofilms in natural environment through a highly integrated and sophisticated approach of nanomaterial, biomaterial, and bioinformatics characterizations. The research outcomes will provide insights on environmental and ecological impact of reactive nanomaterials on the most abundant biological system of biofilms, which can guide safe nanomaterial design and implementation. In addition, the outcomes can also be translated into related engineering and biomedical fields, e.g., antimicrobial development, self-cleaning surfaces, photodynamic and photothermal therapy.
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(a) Electron microscopy of bulk g-C3N4 synthesized from urea and melamine. Atomic force microscopy of (b) g-C3N4 nanosheets and (c) BP nanosheets.
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