Photocatalysis for Air Treatment Processes: Current Technologies and Future Applications for the Removal of Organic Pollutants and Viruses

Interfacial engineering of a multijunctional In2O3/WO3@Ti4N3Tx S-scheme photocatalyst with enhanced photoelectrochemical properties

Achieving high photoelectrochemical conversion efficiency requires the logical layout of a composite photocatalyst with optimal charge separation and transfer with ideal light harvesting capabilities to enhance the photocatalytic performance and the degradation rate towards organic pollutants. Herein, a novel In2O3/WO3@Ti4N3Tx S-scheme heterojunction was successfully synthesized and confirmed through valence band VB-XPS and Mott Schottky combined analysis. The formed MXene-doped In2O3/WO3@Ti4N3Tx S-scheme significantly enhances the charge flow and spatial separation with an improved oxidation and reduction ability. An in-built interfacial electric field at the WO3-In2O3 boundary enhanced the light-harvesting capacity, whereas Ti4N3Tx MXene offers a unique electron trapping effect which effectively lowers high charge carrier recombination rate-related photocatalytic deficit. It preserves the exceptional redox potency of the photocatalyst by providing a directed acceleration and effective separation of the photogenerated charges. A high carrier density (ND = 7.83 × 1021 cm-3) with a lower negative flat band (VFB = -0.064 V vs. Ag/AgCl) was obtained by Mott-Schottky analysis for 3 wt% In2O3/WO3@Ti4N3Tx, an indicator that a low overpotential is needed to activate photocatalytic reactions. This study, therefore, provides a novel thought for the design and fabrication of an S-scheme heterojunction for photocatalytic reactions for mineralization of organic pollutants in water and clean energy production.

Photocatalysis air purification systems for coronavirus removal: Current technologies and future trends

Air pollution causes extreme toxicological repercussions for human health and ecology. The management of airborne bacteria and viruses has become an essential goal of air quality control. Existing pathogens in the air, including bacteria, archaea, viruses, and fungi, can have severe effects on human health. The photocatalysis process is one of the favorable approaches for eliminating them. The oxidative nature of semiconductor-based photocatalysts can be used to fight viral activation as a green, sustainable, and promising approach with significant promise for environmental clean-up. The photocatalysts show wonderful performance under moderate conditions while generating negligible by-products. Airborne viruses can be inactivated by various photocatalytic processes, such as chemical oxidation, toxicity due to the metal ions released from photocatalysts composed of metals, and morphological damage to viruses. This review paper provides a thorough and evaluative analysis of current information on using photocatalytic oxidation to deactivate viruses.

TiO2-based catalytic systems for the treatment of airborne aromatic hydrocarbons

Among diverse strategies to manage air quality, catalytic oxidation has been a widely used option to mitigate diverse pollutants such as aromatic volatile organic compounds (VOCs), especially benzene, toluene, and xylene (BTX). For such applications, TiO₂-based catalysts have drawn significant research attention for their prominent photo/thermal catalytic activities and photochemical stability. This review has been organized to elaborate on the recent developments achieved in the thermocatalytic, photocatalytic, and photothermal applications of metal/non-metal doped TiO₂ catalysts towards BTX vapors and their reaction mechanisms. The performance of the reported TiO₂-based catalysts has also been analyzed based on multiple computational metrics such as reaction rate (r), quantum yield (QY), space-time yield, and figure of merit (FOM). At last, the research gap and prospects in the catalytic treatment of BTX are also discussed in association with the feasibility and utility of TiO₂-based catalysts in air purification applications.

Application of nanotechnology in air purifiers as a viable approach to protect against Corona virus

The outbreak of COVID-19 disease, the cause of severe acute respiratory syndrome, is considered a worldwide public health concern. Although studies indicated that the virus could spread through respiratory particles or droplets in close contact, current research have revealed that the virus stays viable in aerosols for several hours. Numerous investigations have highlighted the protective role of air purifiers in the management of COVID-19 transmission, however, there are still some doubts regarding the efficiency and safety of these technologies. According to those observations, using a proper ventilation system can extensively decrease the spread of COVID-19. However, most of those strategies are currently in the experimental stages. This review aimed at summarising the safety and effectiveness of the recent approaches in this field including using nanofibres that prevent the spread of airborne viruses like SARS-CoV-2. Here, the efficacy of controlling COVID-19 by means of combining multiple strategies is comprehensively discussed.

РОЗРОБКА ОБЛАДНАННЯ ДЛЯ ЗНЕЗАРАЖЕННЯ ПОВІТРЯ В СИСТЕМАХ ВЕНТИЛЯЦІЇ ТА КОНДИЦІОНУВАННЯ ГРОМАДСЬКИХ БУДІВЕЛЬ МЕТОДАМИ ФОТОКАТАЛІЗУ Й ПЛАЗМОХІМІЇ

Вступ. Сезонні хвилі спалаху ГРВІ, зокрема й COVID-19, спричиняють потребу розробки комплексу заходів щодостворення безпечних для здоров’я умов перебування в місцях скупчення людей.Проблематика. Наявні припливно-витяжні системи централізованого опалення, вентиляції і кондиціювання повітря (ОВіК) не лише не захищають від зараження, а й слугують джерелом накопичення та поширення патогенних мікроорганізмів. Пошук ефективних способів очищення повітря у місцях масового скупчення людей як складової протиепідемічних заходів є актуальним завданням.Мета. Розробка та створення обладнання для очищення і знезаражування повітря від аеродисперсної патогенноїмікрофлори в системах ОВіК, яке може вмонтовуватися в централізовані системи вентиляції будівель без їхньої реконструкції та зміни технологічних параметрів.Матеріали й методи. Комплекс фізико-хімічних методів, які охоплюють аналітичне та експериментальне дослідження з використанням теорії електрогазодинаміки дисперсних систем та залученням методів растрової скануючої мікроскопії, методів порівняння однотипних якісних показників проб і вихідних зразків.Результати. Для дослідження ефективності як окремих плазмохімічних і фотокаталітичних модулів, так і установки вцілому при режимах роботи, що моделюють умови експлуатації систем централізованої вентиляції, створено експериментальний стенд. Визначено оптимальні технологічні параметри процесів для підвищення ефективності знезараження й очищення повітря в ОВіК системах методами плазмофотокаталізу. Запропоновано технічні рішення для підвищення енергоефективності дослідно-експериментальної установки комплексного очищення і знезараження повітря від широкого класу забруднювачів повітря в системах припливно-витяжної вентиляції будівель.Висновки. Знезаражування повітря методом комбінованого плазмофотокаталітичного впливу на повітряний потік із системою каталітично-термічного розкладання надлишкового озону забезпечує ефективне очищення від забруднювачів та дозволяє знизити ступінь мікробіологічної контамінації повітря до безпечного рівня.

Ultraviolet photocatalytic oxidation technology for indoor volatile organic compound removal: A critical review with particular focus on byproduct formation and modeling

Photocatalytic oxidation (PCO)-based air filters are gaining attention owing to their capacity for indoor pollutant removal. This review summarized the application of ultraviolet-photocatalytic oxidation (UV-PCO) in heating, ventilation, and air conditioning (HVAC) systems, including the modeling studies, reactor designs, the influence of operational conditions, with emphasis on the common issue of byproduct generation, and the resulting indoor byproduct exposure levels. As a result, the concentrations of the typical byproducts for the most challenging pollutants were relatively low, except for the PCO of ethanol. Hence, UV-PCO is not recommended for buildings with high ethanol concentrations. Based on the formation of the formaldehyde, a new exposure-based evaluation standard for UV-PCO was developed to evaluate the feasibility of integrating UV-PCO reactors into an HVAC system. Then, applying the newly developed evaluation standard on a developed database (data size: 174) from the literature, 32.5% of the cases were identified as suitable for HVAC system applications in residential and commercial buildings, and all cases could be used for industrial buildings. Finally, a case study was conducted to develop a support vector machine (SVM) classification model with good accuracy, and challenging compound types, inlet concentrations, and air velocity were found to be the main parameters affecting the applicability of UV-PCO.

Synthesis and Performance of Photocatalysts for Photocatalytic Hydrogen Production: Future Perspectives

Photocatalysis for “green” hydrogen production is a technology of increasing importance that has been studied using both TiO2–based and heterojunction composite-based semiconductors. Different irradiation sources and reactor units can be considered for the enhancement of photocatalysis. Current approaches also consider the use of electron/hole scavengers, organic species, such as ethanol, that are “available” in agricultural waste, in communities around the world. Alternatively, organic pollutants present in wastewaters can be used as organic scavengers, reducing health and environmental concerns for plants, animals, and humans. Thus, photocatalysis may help reduce the carbon footprint of energy production by generating H2, a friendly energy carrier, and by minimizing water contamination. This review discusses the most up-to-date and important information on photocatalysis for hydrogen production, providing a critical evaluation of: (1) The synthesis and characterization of semiconductor materials; (2) The design of photocatalytic reactors; (3) The reaction engineering of photocatalysis; (4) Photocatalysis energy efficiencies; and (5) The future opportunities for photocatalysis using artificial intelligence. Overall, this review describes the state-of-the-art of TiO2–based and heterojunction composite-based semiconductors that produce H2 from aqueous systems, demonstrating the viability of photocatalysis for “green” hydrogen production.

Toward Scaling-Up Photocatalytic Process for Multiphase Environmental Applications

Recently, we have witnessed a booming development of composites and multi-dopant metal oxides to be employed as novel photocatalysts. Yet the practical application of photocatalysis for environmental purposes is still elusive. Concerns about the unknown fate and toxicity of nanoparticles, unsatisfactory performance in real conditions, mass transfer limitations and durability issues have so far discouraged investments in full-scale applications of photocatalysis. Herein, we provide a critical overview of the main challenges that are limiting large-scale application of photocatalysis in air and water/wastewater purification. We then discuss the main approaches reported in the literature to tackle these shortcomings, such as the design of photocatalytic reactors that retain the photocatalyst, the study of degradation of micropollutants in different water matrices, and the development of gas-phase reactors with optimized contact time and irradiation. Furthermore, we provide a critical analysis of research–practice gaps such as treatment of real water and air samples, degradation of pollutants with actual environmental concentrations, photocatalyst deactivation, and cost and environmental life-cycle assessment.

Photocatalytic Conversion of Organic Pollutants in Air: Quantum Yields Using a Silver/Nitrogen/TiO2 Mesoporous Semiconductor under Visible Light

This research studies the photocatalytic conversion of methanol (25–90 µmol/L range) as a volatile organic compound (VOC) surrogate into CO2, using a N/Ag/TiO2 photocatalyst under visible light irradiation in a Photo-CREC Air unit. The N/Ag/TiO2 mesh supported photocatalyst is prepared via the solvothermal method. While the bare-TiO2 is inactive under visible light, the N/Ag/TiO2 2 wt.% loaded stainless-steel woven mesh displays 35% quantum yields, with 80% absorbed photons and 60% methanol conversion in a 110 min irradiation period. Results obtained are assigned to silver surface plasmon resonance, silver and nitrogen species synergistic impacts on band gap, and their influence on particle agglomerate size and semiconductor acidity. The determined quantum yields under visible light in a Photo-CREC Air unit, are the highest reported in the technical literature, that these authors are aware of, with this opening unique opportunity for the use of visible light for the purification of air from VOC contaminants.