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Electro‐ and photodriven catalysis are emerging as viable alternatives to traditional catalytic methods for producing key global consumer products across various applications. The emergence of this class of catalysis is attributable to increasing need for sustainable and ecofriendly pathways to value‐added chemical synthesis. The roadmap for the highly diverse and multifaceted field of catalysis continues to evolve, highlighting the growing need of understanding their physical and chemical reaction mechanism. Among the many available characterization techniques, in situ and operando investigations stand out for their ability to provide detailed insights into fundamental physicochemical processes under realistic working conditions. In this article, a select group of representative energy material is discussed, where the application of different in situ/operando techniques successfully generates improved understanding. The primary goal is to emphasize the significance of these techniques, particularly those, which have been commonly employed in studying materials relevant to energy and environmental applications. 

Sunlight irradiation is the predominant process for degrading plastics in the environment, but our current understanding of the degradation of smaller, submicron (<1000 nm) particles is limited due to prior analytical constraints. We used infrared photothermal heterodyne imaging (IR-PHI) to simultaneously analyze the chemical and morphological changes of single polystyrene (PS) particles (∼1000 nm) when exposed to ultraviolet (UV) irradiation (λ = 250–400 nm). Within 6 h of irradiation, infrared bands associated with the backbone of PS decreased, accompanied by a reduction in the particle size. Concurrently, the formation of several spectral features due to photooxidation was attributed to ketones, carboxylic acids, aldehydes, esters, and lactones. Spectral outcomes were used to present an updated reaction scheme for the photodegradation of PS. After 36 h, the average particle size was reduced to 478 ± 158 nm. The rates of size decrease and carbonyl band area increase were −24 ± 3.0 nm h–1 and 2.1 ± 0.6 cm–1 h–1, respectively. Using the size-related rate, we estimated that under peak terrestrial sunlight conditions, it would take less than 500 h for a 1000 nm PS particle to degrade to 1 nm.