Gunjan Sharma

Photocatalysis stands at the forefront of efforts to address global challenges in sustainable energy and environmental remediation. In this review, we critically examine the two major classes of heterogeneous photocatalysts-plasmonic materials and semiconductors-highlighting their fundamental distinctions, catalytic mechanisms, and potential for driving light-induced chemical transformations. We first explore the fundamentals of plasmonic materials and semiconductors, highlighting key distinctions and overlaps in their photophysical properties, elucidating how these differences govern their photocatalytic performance and reaction pathways. This review further explores practical examples of photocatalytic reactions, including CO₂ reduction, N₂ reduction, and dry reforming of methane (DRM), illustrating the versatility, catalytic efficiency, and inherent limitations of each class of materials. Additionally, we explore the excited-state dynamics of both plasmonic and semiconductor materials, with a focus on the underlying mechanisms that govern charge carrier behavior under light excitation. This review provides an overview of the present state of plasmonic and semiconductor photocatalysis, while also highlighting promising directions for future advancements. By exploring synergistic strategies that bridge these two classes of materials, it aims to unlock new pathways for light-driven chemical transformations, ultimately advancing catalytic performance for sustainable energy and environmental applications.

Sustainable plastic waste upcycling using plasmonic black gold achieves >80% conversion and >75% alkane selectivity in 1 hour. Driven by sunlight, this sacrificial-agent-free method uses photothermal heating and hot electrons to create fuels.

Catalytic CO ₂ reduction into value-added products is an energy-intensive process and typically relies on molecular hydrogen as reductant. Coupling CO ₂ reduction with propane dehydrogenation for in situ hydrogen generation presents a sustainable alternative but conventionally demands high temperatures, causing undesirable side reactions such as cracking and coke formation. Here, we demonstrate a nonthermal catalytic pathway driven by hot electrons generated via localized surface plasmon resonance. Using a plasmonic catalyst comprising Ga–Ni–Mn active sites anchored on broadband plasmonic “black gold,” we achieve tandem CO ₂ reduction and propane dehydrogenation under visible-light irradiation. The catalyst consistently produces equimolar amounts (~1,600 µmol g ⁻¹ h ⁻¹ ) of CO and propene under flow conditions, maintaining exceptional stability even after 500 h. Notably, light illumination suppresses undesired side reactions, such as dry reforming of propane, cracking, and coking, preserving a stable stoichiometric ratio of CO and propene. Mechanistic studies, including controlled thermal experiments, Arrhenius analysis, and finite-difference time-domain simulations, confirm that catalytic selectivity and stability originate specifically from plasmon-induced hot electrons rather than photothermal effects. Comprehensive structural characterization using X-ray absorption near-edge structure and extended X-ray absorption fine structure, in situ diffuse reflectance infrared Fourier transform spectroscopy, ultrafast transient absorption spectroscopy, and density functional theory calculations elucidate that plasmonic excitation promotes advantageous charge-transfer states within Ga–Ni–Mn ensembles, facilitating selective activation of CO ₂ and propane. This study establishes hot electron–driven plasmonic catalysis as a distinctive strategy for tandem propane dehydrogenation and circular CO ₂ utilization under mild conditions.

Synergistic coupling of Cu LSPR, charge carrier separation via SMSI at the Cu–TiO₂ interface, and O-vacancy defects stabilized by SMSI collectively enhance the photocatalytic CO₂ reduction performance of the DFNS-supported hybrid catalyst.

Heterogeneous catalysts have emerged as a potential key for closing the carbon cycle by converting carbon dioxide (CO ₂ ) into value-added chemicals. In this work, we report a highly active and stable ceria (CeO ₂ )-based electronically tuned trimetallic catalyst for CO ₂ to CO conversion. A unique distribution of electron density between the defective ceria support and the trimetallic nanoparticles (of Ni, Cu, Zn) was established by creating the strong metal support interaction (SMSI) between them. The catalyst showed CO productivity of 49,279 mmol g ⁻¹ h ⁻¹ at 650 °C. CO selectivity up to 99% and excellent stability (rate remained unchanged even after 100 h) stemmed from the synergistic interactions among Ni-Cu-Zn sites and their SMSI with the defective ceria support. High-energy-resolution fluorescence-detection X-ray absorption spectroscopy (HERFD-XAS) confirmed this SMSI, further corroborated by in situ electron energy loss spectroscopy (EELS) and density functional theory (DFT) simulations. The in situ studies (HERFD-XAS & EELS) indicated the key role of oxygen vacancies of defective CeO ₂ during catalysis. The in situ transmission electron microscopy (TEM) imaging under catalytic conditions visualized the movement and growth of active trimetallic sites, which completely stopped once SMSI was established. In situ FTIR (supported by DFT) provided a molecular-level understanding of the formation of various reaction intermediates and their conversion into products, which followed a complex coupling of direct dissociation and redox pathway assisted by hydrogen, simultaneously on different active sites. Thus, sophisticated manipulation of electronic properties of trimetallic sites and defect dynamics significantly enhanced catalytic performance during CO ₂ to CO conversion.

The debate surrounding the roles of thermal and non-thermal pathways in plasmonic catalysis has captured the attention of researchers and sparked vibrant discussions within the scientific community. In this review, we embark on a thorough exploration of this intriguing discourse, starting from fundamental principles and culminating in a detailed understanding of the divergent viewpoints. We probe into the core of the debate by elucidating the behavior of excited charge carriers in illuminated plasmonic nanostructures, which serves as the foundation for the two opposing schools of thought. We present the key arguments and evidence put forth by proponents of both the non-thermal and thermal pathways, providing a perspective on their respective positions. Beyond the theoretical divide, we discussed the evolving methodologies used to unravel these mechanisms. We discuss the use of Arrhenius equations and their variations, shedding light on the ensuing debates about their applicability. Our review emphasizes the significance of localized surface plasmon resonance (LSPR), investigating its role in collective charge oscillations and the decay dynamics that influence catalytic processes. We also talked about the nuances of activation energy, exploring its relationship with the nonlinearity of temperature and light intensity dependence on reaction rates. Additionally, we address the intricacies of catalyst surface temperature measurements and their implications in understanding light-triggered reaction dynamics. The review further discusses wavelength-dependent reaction rates, kinetic isotope effects, and competitive electron transfer reactions, offering an all-inclusive view of the field. This review not only maps the current landscape of plasmonic photocatalysis but also facilitates future explorations and innovations to unlock the full potential of plasmon-mediated catalysis, where synergistic approaches could lead to different vistas in chemical transformations.