Heterogeneous Photocatalysis for Indoor Air Purification: Recent Advances in Technology from Material to Reactor Modeling
01 Jan 2020-pp 147-166
TL;DR: In this article, the current status of PCO material technologies, coating methods, performance test methods, and modeling for real-world indoor air-purification application is reviewed and some recommendations for the future research on improving material selection and reactor design to minimize by-product generation and to promote commercialization are also discussed.
Abstract: Heterogeneous photocatalytic oxidation (PCO) has attracted much attention in indoor air-purification applications. Recently, researches focus on developing novel photocatalyst based filters for integrating with the heating, ventilation, and air conditioning (HVAC) systems as well as portable air purifiers. A comprehensive knowledge on factors influencing the indoor volatile organic compounds (VOCs) degradation has been established both in bench-scale and pilot-scale experiments. This paper reviews the current status of PCO material technologies, coating methods, performance test methods, and modeling for real-world indoor air-purification application. Due attention to the basic principle of PCO and the effect of operating parameters is provided, followed by a discussion on the modes of PCO application for buildings. The review also concentrates on the practical limitations in scaling-up PCO air purifiers for large-scale applications. Some recommendations for the future research on improving material selection and reactor design to minimize by-product generation and to promote commercialization are also discussed.
Citations
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TL;DR: In this paper, a review article describes various applications of nanomaterials in removing different types of impurities from polluted water, which carried huge potential to treat polluted water (containing metal toxin substance, different organic and inorganic impurities) very effectively due to their unique properties like greater surface area, able to work at low concentration, etc.
Abstract: Water is an essential part of life and its availability is important for all living creatures. On the other side, the world is suffering from a major problem of drinking water. There are several gases, microorganisms and other toxins (chemicals and heavy metals) added into water during rain, flowing water, etc. which is responsible for water pollution. This review article describes various applications of nanomaterial in removing different types of impurities from polluted water. There are various kinds of nanomaterials, which carried huge potential to treat polluted water (containing metal toxin substance, different organic and inorganic impurities) very effectively due to their unique properties like greater surface area, able to work at low concentration, etc. The nanostructured catalytic membranes, nanosorbents and nanophotocatalyst based approaches to remove pollutants from wastewater are eco-friendly and efficient, but they require more energy, more investment in order to purify the wastewater. There are many challenges and issues of wastewater treatment. Some precautions are also required to keep away from ecological and health issues. New modern equipment for wastewater treatment should be flexible, low cost and efficient for the commercialization purpose.
125 citations
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TL;DR: In this article, the applicability of platinized titanium dioxide (Pt/TiO2) for the removal of gaseous pollutants in light of its numerous advantages (e.g., high removal efficiency, stability, regenerability, and sustainability).
Abstract: Catalytic approaches are regarded as a highly favorable option to treat carcinogenic volatile organic compounds (VOCs: e.g., formaldehyde) released from various sources in indoor and outdoor environment. Among a wide range of engineered materials (e.g., metal oxide-supported noble metals), platinized titanium dioxide (Pt/TiO2) is recognized as a highly effective multi-functional catalyst (e.g., thermocatalyst, photocatalyst, and photothermal-catalyst (as a synergistic combination of the former two)). In this review, an in-depth discussion is offered to describe the applicability of this multi-functional platform towards the removal of gaseous pollutants in light of its numerous advantages (e.g., high removal efficiency, stability, regenerability, and sustainability). Further, the discussion is expanded to address the effects of diverse variables on its performance including inherent material characteristics (e.g., surface chemistry, structure, morphology, and functionalities), process variables (e.g., relative humidity, temperature, and reactant composition), and the underlying mechanisms. To this end, quantitative criteria are established to pursue an evaluation of its performance in a less biased manner for each of all different types of catalytic functions. Finally, the current knowledge gaps and suitable research avenues are discussed for an in-depth exploration of this unique catalytic system.
7 citations
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TL;DR: In this paper, a comprehensive review of the photoreactors for gas-phase reaction focusing on process intensification and recent computer simulations is provided, in which the state-of-the-art of photocatalytic air treatment providing examples such as the VOCs oxidation and NOx degradation.
Abstract: This article provides a comprehensive review of the photoreactors for gas-phase reaction focusing on process intensification and recent computer simulations. This review selected two photocatalytic gas-phase reactions, namely the oxidation of volatile organic compounds (VOCs) and the degradation of nitrogen oxides (NOx). It was also discussed two photocatalytic gas-phase reactions’ importance from a scientific and social perspective. Therefore, heterogeneous photocatalysis was applied, and it excelled itself as a promising technology for gas-phase reaction applications. However, despite the numerous advances in photocatalytic processes in recent times, there are still several challenges in their development for this technology to achieve high performance. Mass transfer and low quantum efficiency (photon transfer) are some of these challenges becoming a significant concern for the design of new photoreactors or the improvement of existing ones. Different types of photocatalytic reactors have already been designed, examined, and simulated, seeking to maximize the pollutant-catalyst contact (enhancing mass transfer) and to maximize the lighting efficiency throughout the catalyst surface (enhancing photon transfer). The process intensification has been highlighted in the development of photoreactors to ensure the improvement in mass and photons transfer. Here, we will address the monolithic photoreactors, photocatalytic membrane reactors, and photo-microreactors, in which each photoreactor has its advantages and drawbacks. CFD-based models, combined with the design of the photoreactors, are essential since they can successfully predict the performance of various geometric configurations and identify the limitations to the photon and the mass transfer with only validated virtual prototypes. From this perspective, this review presents the state-of-art of photocatalytic air treatment providing examples such as the VOCs oxidation and NOx degradation. Furthermore, this review also reports a literature exam of three different types of photoreactor designs presenting their advantages and limitations regarding the mass and the photons transfer focusing on photocatalytic process intensification. Also, it is presented a discussion of the recent applications of photocatalytic reactor modeling using computational fluid dynamics (CFD) for the gaseous pollutant degradation.
2 citations
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TL;DR: In this paper, 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.
Abstract: 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.
References
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TL;DR: In this paper, the authors showed that the anatase and rutile particles separately form their agglomerates and the average sizes of anatase particles are 85 and 25 nm, respectively.
Abstract: The TiO2 powder (Degussa, P-25), which is a standard material in the field of photocatalytic reactions, contains anatase and rutile phases in a ratio of about 3 : 1 Transmission electron microscopy showed that the anatase and rutile particles separately form their agglomerates The average sizes of the anatase and rutile elementary particles are 85 and 25 nm, respectively Diffuse reflectance spectra of the TiO2 powder were successfully traced by physically mixing pure anatase and rutile particles in a ratio of 3 : 1 By the HF treatment of the TiO2 powder, pure rutile particles were isolated All these results indicate that the rutile phase does not exist as an overlayer on the surface of anatase particles, but it exists separately from anatase particles We also found that photocatalytic oxidation of naphthalene is inefficient on pure anatase and rutile powders However, the reaction is very efficient on the P-25 powder, as well as on a mixture of pure anatase and rutile particles Under the conditions of the photocatalytic reactions, the anatase and rutile agglomerates are considered to be decomposed, and the anatase and rutile particles are in contact, leading to a synergy effect
996 citations
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TL;DR: In this paper, a carbon-doped TiO2 photocatalyst was obtained by using glucose as a carbon source and was characterized by XRD, XPS, TEM, nitrogen adsorption, and UV-vis diffuse reflectance spectroscopy.
Abstract: A visible-light-active TiO2 photocatalyst was prepared through carbon doping by using glucose as carbon source. Different from the previous carbon-doped TiO2 prepared at high temperature, our preparation was performed by a hydrothermal method at temperature as low as 160 °C. The resulting photocatalyst was characterized by XRD, XPS, TEM, nitrogen adsorption, and UV–vis diffuse reflectance spectroscopy. The characterizations found that the photocatalyst possessed a homogeneous pore diameter about 8 nm and a high surface area of 126 m2/g. Comparing to undoped TiO2, the carbon-doped TiO2 showed obvious absorption in the 400–450 nm range with a red shift in the band gap transition. It was found that the resulting carbon-doped TiO2 exhibits significantly higher photocatalytic activity than the undoped counterpart and Degussa P25 on the degradation of rhodamine B (RhB) in water under visible light irradiation (λ > 420 nm). This method can be easily scaled up for industrial production of visible-light driven photocatalyst for pollutants removal because of its convenience and energy-saving.
824 citations
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TL;DR: A review of the status of research on photocatalytic oxidation (PCO) purification of VOCs in indoor air can be found in this paper, where some recommendations are made for future work to evaluate the performance of PCO catalysts, to reduce the generation of harmful intermediates and to design new PCO reactors with integrated UV source and reaction surface.
Abstract: Volatile organic compounds (VOCs) are prevalent components of indoor air pollution. Among the approaches to remove VOCs from indoor air, photocatalytic oxidation (PCO) is regarded as a promising method. This paper is a review of the status of research on PCO purification of VOCs in indoor air. The review and discussion concentrate on the preparation and coating of various photocatalytic catalysts; different kinetic experiments and models; novel methods for measuring kinetic parameters; reaction pathways; intermediates generated by PCO; and an overview of various PCO reactors and their models described in the literature. Some recommendations are made for future work to evaluate the performance of photocatalytic catalysts, to reduce the generation of harmful intermediates and to design new PCO reactors with integrated UV source and reaction surface.
660 citations
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TL;DR: In this article, the basic reaction mechanisms on photocatalyst surface under the irradiation of ultraviolet and their corresponding applications in building and construction materials are reviewed and the problems faced in practical applications and the trends for future development are also discussed.
Abstract: Heterogeneous photocatalysis has been intensively studied in recent decades because it only requires photonic energy to activate the chemical conversion contrasting with conventional catalysis which needs heat for thermo-activation. Over the years, the theories for photochemical activity of photocatalyst including photo-induced redox reaction and super-hydrophilic conversion of TiO 2 itself have been established. The progress in academic research significantly promotes its practical applications, including the field of photocatalytic construction and building materials. TiO 2 modified building materials are most popular because TiO 2 has been traditionally used as a white pigment. The major applications of TiO 2 based photocatalytic building materials include environmental pollution remediation, self-cleaning and self-disinfecting. The advantage of using solar light and rainwater as driving force has opened a new domain for environmentally friendly building materials. In this paper, the basic reaction mechanisms on photocatalyst surface under the irradiation of ultraviolet and their corresponding applications in building and construction materials are reviewed. The problems faced in practical applications and the trends for future development are also discussed.
553 citations
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TL;DR: The concentrations and emission rates of commonly occurring VOCs in indoor air are presented, the effective catalyst systems, under UV and visible light, are discussed and the kinetics of photocatalytic oxidation is also presented.
Abstract: Volatile organic compounds (VOCs) are the major pollutants in indoor air, which significantly impact indoor air quality and thus influencing human health. A long-term exposure to VOCs will be detrimental to human health causing sick building syndrome (SBS). Photocatalytic oxidation of VOCs is a cost-effective technology for VOCs removal compared with adsorption, biofiltration, or thermal catalysis. In this paper, we review the current exposure level of VOCs in various indoor environment and state of the art technology for photocatalytic oxidation of VOCs from indoor air. The concentrations and emission rates of commonly occurring VOCs in indoor air are presented. The effective catalyst systems, under UV and visible light, are discussed and the kinetics of photocatalytic oxidation is also presented.
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