The hazards associated with hexavalent chromium, Cr(VI), have prompted extensive research into treatment technologies for chromium-containing industrial effluents. Selection of an appropriate process depends on wastewater composition, treatment objectives, cost-effectiveness, operational feasibility, and monitoring and maintenance requirements. Mesoporous materials, with pore diameters of 2–50 nm, offer accessible surfaces and pore networks that can support adsorption and photocatalytic reactions. Following the independent discovery of ordered mesoporous materials in the early 1990s by researchers at Mobil and other research groups, their tunable physicochemical properties have supported applications across environmental catalysis. In Cr(VI) photoreduction, accessible surface area, pore connectivity, and surface functionality influence chromium-oxyanion adsorption and reactant transport, while semiconductor composition and interfacial architecture govern light absorption and charge-carrier behaviour. This review examines recent advances in mesoporous photocatalysts for Cr(VI) reduction, focusing on the relationships between pore structure, chemical composition, and reported treatment performance. Metal oxides, carbon-based composites, metal–organic and covalent organic frameworks, and heterostructured systems are discussed alongside strategies involving doping, sensitisation, and interfacial engineering. Particular attention is given to distinguishing adsorption and direct photolysis from photocatalytic reduction and to interpreting performance under different irradiation, pH, and electron-donor conditions. The reviewed literature indicates that mesostructuring can enhance photoreduction when accessible pores are combined with suitable surface chemistry and efficient charge utilisation. However, differences in experimental conditions limit direct comparison between materials. Catalyst recovery, aqueous stability, metal leaching, realistic wastewater matrices, and reactor design remain central considerations in translating laboratory performance into sustainable treatment applications.
Organic hydroperoxy (•QOOH) radicals are key reactive intermediates generated during the oxidation of volatile organic compounds in both combustion systems and the Earth’s atmosphere. Their atmospheric and combustion lifetimes are governed by competition between unimolecular decomposition and bimolecular reactions, with the relative importance of these pathways strongly dependent on molecular structure and temperature. Here, we combine non-adiabatic molecular dynamics simulations with high-level quantum chemical calculations to investigate the excited-state photochemistry of the prototypical •QOOH species, the hydroperoxy-tert-butyl radical, following excitation to electronically excited states accessible in the near-ultraviolet. Our results reveal that photodissociation is the dominant fate of electronically excited •QOOH radicals, primarily forming •OH + epoxide and HO2• + 2-methylpropene (2MP) products. Intramolecular hydrogen-atom transfer leading to organoperoxy radicals is predicted to be a minor photochemical pathway. These findings suggest that solar photolysis may represent a previously overlooked daytime sink for relatively long-lived •QOOH intermediates in the troposphere, with potential implications for atmospheric oxidation chemistry and secondary organic aerosol formation.
The development of multifunctional ceramic materials capable of combining adsorption and photocatalytic activity represents an efficient strategy for the removal of persistent pharmaceutical contaminants from aqueous media. In this work, Al2O3-TiO2 monoliths were synthesized by the ionic encapsulation method and subsequently activated with concentrated nitric acid (HNO3) to enhance surface reactivity. The structural evolution and physicochemical properties of monoliths were analyzed by XRD, FTIR, SEM-EDS, BET, and ζ-potential measurements. XRD results revealed the formation of α-Al2O3 and a mixture of anatase and rutile TiO2 as the dominant crystalline phases after sintering at 1600 °C, while at 800 °C the material consisted of transitional alumina’s and anatase TiO2. FTIR spectra confirmed the presence of Al-O, Ti-O, and oxygen functional groups, which increased upon acid activation. SEM micrographs exhibited a dense polycrystalline morphology with uniform grain distribution, while EDS analysis confirmed the homogeneous dispersion of Al, Ti, and O elements. The activated monoliths displayed a ζ-potential of −23 mV at pH 5, indicating a strong electrostatic affinity toward cationic ciprofloxacin species. Adsorption experiments showed ciprofloxacin removal capacities of 13.03 mg g−1 for Al2O3-TiO2 and 91.2 mg g−1 for acid-activated Al2O3-TiO2, following a mixed adsorption mechanism that combines physical and chemical adsorption, according to Langmuir and Freundlich isotherms (R2 > 0.94). Under a black light bulb, the activated monolith achieved a k1 of 2 × 10−4 min−1 during ciprofloxacin photodegradation, fourfold higher than the untreated monolith (5 × 10−5 min−1) and tenfold higher than photolysis (2 × 10−5 min−1). These findings demonstrate that acid activation enhances adsorption and photocatalytic efficiency of Al2O3-TiO2 monoliths, which is a cost-effective and reusable efficient material for ciprofloxacin removal in real water treatment scenarios.
In this study, we investigated the direct aqueous synthesis of water-soluble ZnTe quantum dots (QDs). To suppress oxidation of the Te precursor, dissolved oxygen was removed from the precursor solution by nitrogen bubbling in a glove box. The hydrothermally synthesized ZnTe QDs exhibited band-edge photoluminescence (PL) with a maximum PL quantum yield of 9.3%. Furthermore, the PL energy was tunable through control of the heating temperature and reaction time. The optimized ZnTe QDs exhibited good crystallinity and a narrow size distribution. These results demonstrate an effective approach for the direct aqueous synthesis of cadmium-free ZnTe QDs and provide useful insights for the development of environmentally friendly luminescent materials.
The requested changes include providing a more explicit version of Equation (1), the inclusion of 11 additional references, and reordering of the other citations [...]
