Nanostructured TiO 2 is one of the best materials for photocatalysis, thanks to its high surface area and surface reactivity, but its large energy bandgap (3.2 eV) hinders the use of the entire solar spectrum. Here, it is proposed that defect-engineered nanostructured TiO 2 photocatalysts are obtained by hydrogenation strategy to extend its light absorption up to the near-infrared region. It is demonstrated that hydrogenated or colored TiO 2 hollow spheres (THS) composed of hierarchically assembled nanoparticles result in much broader exploitation of the solar spectrum (up to 1200 nm) and the engineered surface enhances the photogeneration of charges for photocatalytic processes. In turn, when applied for photodegradation of a targeted drug (Ciprofloxacin) this results in 82% degradation after 6 h under simulated sunlight. Valence band analysis by photoelectron spectroscopy revealed the presence of oxygen vacancies, whose surface density increases with the hydrogenation rate. Thus, a tight correlation between degree of hydrogenation and photocatalytic activity is directly established. Further insight comes from electron paramagnetic resonance, which evidences bulk Ti 3+ centers only in hydrogenated THS. The results are anticipated to disclose a new path toward highly efficient photocatalytic titania in a series of applications targeting water remediation and solar fuel production.
Composite metal oxide semiconductors are promising candidates for photoelectrochemical water splitting (PEC WS) toward environmentally friendly hydrogen production. Among them, ZnO and α‐Fe2O3 hold great potential thanks to a series of benefits, including fast charge transport in single‐crystalline structures, large surface area and tunable shapes (ZnO), and energy bandgap falling in the visible spectral range (α‐Fe2O3). However, both materials present significant drawbacks, which hinder their successful application in high‐efficiency PEC WS: the wide bandgap of ZnO limits its absorption in the UV range, while the low charge carrier mobility results in heavy recombination losses in α‐Fe2O3 during charge collection. The synthesis of ZnO/hematite composites has recently proven to be an effective approach to improve the overall WS performances. In this review, the recent developments on the application of different morphologies (0D, 1D, 2D, and 3D structures) for PEC WS are illustrated, analyzing the role of the shape and morphology in boosting the functional properties, both in single systems and in composite nanostructures. Complex networks show higher photocatalytic efficiency than the single building blocks and, consequently, composite materials exhibit higher performances. Possible paths for the development of an effective lab‐to‐fab transition based on application of ZnO/α‐Fe2O3 composite structures are also suggested.
Compared to inorganic quantum dot, carbon nanoparticles or carbon quantum dots (C-dots) have gained significant attentions because of their unique optoelectrical properties and less toxicity. Although many review articles summarize...
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