Photocatalytic Decomposition of Formaldehyde by Combination of Ozone and AC Network with UV365nm, UV254nm and UV254+185nm

Synergistic mechanisms of carbon-based materials for VOCs photocatalytic degradation: A critical review

With the rapid expansion of human activities, there has been a significant increase in the release of volatile organic compounds (VOCs) from factories and interior decoration materials, posing a substantial risk to the surrounding ecosystem and human health. Photocatalysis technology based on semiconductors has emerged as a promising solution for mitigating atmospheric pollution and indoor air quality concerns. However, single semiconductors encounter several challenges when it comes to VOC photodegradation, including issues like the weak adsorption capacity for VOC molecules, insufficient surface-active sites, and limited light utilization. In recent decades, carbon-based materials have gained considerable interest in photodegrading VOCs owing to their strong adsorption capacity, electrical conductivity, broad light absorption range, and tunable surface characteristics. The incorporation of carbon materials can enhance the photodegradation efficiency of VOCs by facilitating the transfer of VOCs from the ambient air to the surface of the photocatalysts, increasing the number of active surface sites, expanding the light absorption region, and promoting the separation of charge carriers. This review provides a comprehensive overview of the applications of carbon materials with different dimensions in enhancing the performance of semiconductors for the photocatalytic degradation of VOCs. Based on the fundamental principles of photocatalytic VOC degradation, this review explores the factors influencing the degradation performance of catalysts and elucidates the degradation mechanisms. Moreover, it summarizes a range of synthesis approaches for carbon-based photocatalysts, discussing the multiple roles played by carbon materials in these processes. In conclusion, the review offers insights into the current state of carbon-based photocatalysts and outlines the existing challenges. It also provides a perspective on the future development of these materials, highlighting the need for continued research and innovation in this field.

Ozonation and ozone-enhanced photocatalysis for VOC removal from air streams: Process optimization, synergy and mechanism assessment

The present work evaluates ozone driven processes (O₃, O₃/UVC, O₃/TiO₂/UVA) in the NETmix mili-photoreactor, as a cost-effective alternative for the removal of volatile organic compounds (VOCs) from air streams, using n-decane as a model pollutant. The network of channels and chambers of the mili-photoreactor was coated with a TiO₂-P25 thin film, resulting in a catalyst coated surface per reactor volume of 990 m² m^-3. Ozone and n-decane streams were fed to alternate chambers of the mili-photoreactor, promoting a good contact between O₃/n-decane/catalyst. Initially, direct reaction between n-decane and ozone (ozonation) was assessed for different O₃/n-decane (O₃/dec) feed molar ratios and total feed flow rates. Under the best conditions, ozonation process achieved total n-decane conversion (below the limit of detection), yielding a reaction rate (r_dec) of 6.8 μmol min^-1 or 6.7 mmol m^-3_reactor s^-1. However, the low reactivity of ozone with the degradation by-products resulted in a quite poor mineralization (~10%). For the O₃/UVC system, an increase on relative humidity from 7 to 40% slight improved the n-decane oxidation rate, mainly associated with the generation of HO from the reaction of active oxygen radicals (O) and water molecules. A strong synergistic effect was observed when coupling TiO₂/UVA photocatalysis with ozonation (O₃/TiO₂/UVA), enhancing substantially the mineralization of n-decane molecules up to 100% under O₃/dec feed molar ratio of 15, photonic flux of 2.67 ± 0.03 J s^-1 and a residence time of 2.0 s. Different reaction intermediates were detected for O₃, TiO₂/UVA and O₃/TiO₂/UVA oxidative systems, indicating the participation of different oxidant species (O₃, HO, O, etc.).