Photocatalytic oxidation technology for indoor environment air purification: The state-of-the-art (original) (raw)
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Building and Environment, 2018
Ultraviolet photocatalytic oxidation (UV-PCO) is regarded as one of the promising technologies for indoor air remediation. The present study examines the photocatalytic activity of four commercialized titanium dioxide photocatalysts (P25, PC500, UV100, and S5-300A) in a smallscale single-pass continuous flow reactor. Challenge compounds have been chosen from two prevalent VOC families in indoor environment: toluene (aromatics) and methyl ethyl ketone (ketones). The influence of key experimental conditions including concentration (100-1000 ppb), relative humidity (0-50% at 23 ˚C), light intensity (1.25-5 W•m-2), and residence time (0.02-0.1 sec) on removal efficiency are evaluated. Due to the fact that one of the main shortcomings of PCO air purifiers is by-products generation, a special emphasis is put on identification and quantification of gaseous by-products using HPLC and GC-MS methods. The obtained efficiencies on various photocatalysts are explained considering crystalinity, crystalline phase, crystal size, surface area, and population of surface hydroxyl groups. Despite possessing lower crystalinity, PC500, UV100 and S5-300A outperformed P25 in toluene and MEK removal efficiency, primarily owed to their larger surface area, smaller crystal size, and higher
TiO2 photocatalyst for removal of volatile organic compounds in gas phase – A review
Chemical Engineering Journal, 2017
Heterogeneous photocatalytic oxidation process (PCO) is a promising technology for removing indoor volatile organic compounds (VOCs) contaminants. Titanium dioxide (TiO 2) has been regarded as the most suitable photocatalyst for its cost effectiveness, high stability and great capability to degrade various VOCs. However, no TiO 2-based photocatalysts completely satisfy all practical requirements given photoexcited charge carriers' short lifetime and a wide band gap requiring ultraviolet (UV) radiation. Strategies for improving TiO 2 photocatalyst activities by doping with different metal and/or non-metal ions and by coupling with other semiconductors have been examined and reported. These techniques can improve PCO performance through the following mechanisms: i) by introducing an electron capturing level in the band gap that would generate some defects in the TiO 2 lattice and help capture charge carriers; ii) by slowing down the charge carrier recombination rate and increasing VOCs degradation. This paper reports the outcomes of a comprehensive literature review of TiO 2 modification techniques that include approaches for overcoming the inherent TiO 2 limitations and improving the photocatalytic degradation of VOCs. Accordingly, it focuses on the recent development of modified-TiO 2 used for degrading gas phase pollutants in ambient conditions. Modification techniques, such as metal and non-metal doping, co-doping, and the heterojunction of TiO 2 with other semiconductors, are reviewed. A brief introduction on the basics of photocatalysis and the effects of controlling parameters is presented, followed by a discussion about TiO 2 photocatalyst modification for gas phase applications. The reported experimental results obtained with PCO for eliminating VOCs are also compiled and evaluated.
Materials
Indoor air quality has become a significant public health concern. The low cost and high efficiency of photocatalytic technology make it a natural choice for achieving deep air purification. Photocatalysis procedures have been widely investigated for environmental remediation, particularly for air treatment. Several semiconductors, such as TiO2, have been used for photocatalytic purposes as catalysts, and they have earned a lot of interest in the last few years owing to their outstanding features. In this context, this review has collected and discussed recent studies on advances in improving the photocatalytic activity of TiO2-based materials for indoor air treatment and bacterial inactivation. In addition, it has elucidated the properties of some widely used TiO2-based catalysts and their advantages in the photocatalytic process as well as improved photocatalytic activity using doping and heterojunction techniques. Current publications about various combined catalysts have been su...
Considerations to improve adsorption and photocatalysis of low concentration air pollutants on TiO2
Catalysis Today, 2014
Rapid development of nanoscience and nanotechnology has greatly supported the industrialization of titanium dioxide for environmental pollution control during the past decade. Nowadays, low concentration air purification seems to be one of the most promising directions of environmental TiO 2 applications. However, much more effort is needed to perfect this technology and make it broadly applicable. Understanding the nature of the adsorption and photooxidation under realistic and practical conditions would give clear guidance for the development of novel catalytic materials and technologies. This paper describes the significant effects of the adsorption of low concentration gas-phase pollutants in practical conditions on the photocatalytic oxidation efficiency and mechanism. We also review the influences of several important conditions, such as pollutant concentration, contact time, co-existing pollutants, water vapor, and light exposure, on the nature of the adsorption process and thereby the photooxidation. Finally, catalytic materials which might enhance the adsorption of low-concentration pollutants are summarized.
2004
A fixed bed photocatalytic reactor has been designed and built with a UV radiation source. Ti02 pellets were placed on the three fixed beds within the reactor. Acetone was used as an indicator of volatile organic compounds (VOCs) during the experiment. Under the flow rate of 12.75 l/min, the oxidation efficiencies were obtained at four different concentrations of acetone laden gas streams ranged from 40ppm to 250ppm. It was found that the lower the acetone concentration of the untreated inlet gas, the higher the oxidation efficiency; the obtained oxidation efficiency was in the range of 40-70% for various concentrations of untreated gases.
Photocatalytic Treatment of Air: How to dealwith the problem of TiO2 deactivation
Chemical and Biochemical Engineering Quarterly, 2011
In this study photocatalytic oxidation of toluene, used as model VOCs in the gas phase on different types of Ti-based catalytic materials was investigated. The objective of this work was to find out additional information regarding activity and stability of catalyst during photocatalytic treatment of the polluted air. Two designs of the photoreactor were used: classical type of an annular reactor and annular reactor with recirculation. All measurements were performed at room temperature, atmospheric pressure and at constant initial toluene concentration, relative humidity and total flow rate of the reaction mixture. Some experiments were carried out with catalysts thermally treated on different temperatures (350–450 °C). It was found out that thermal treatment of deactivated photocatalyst at higher temperature is efficient method of TiO2 reactivation. According to results presented in this paper problem of catalyst deactivation can be partially solved by using annular reactor with r...
Heterogeneous Photocatalysts Based on TiO 2 for Abatement of Hazardous Air Pollutants
Research & Development in Material science, 2021
A mixture of suspended solid particles and gases coming from car emissions, chemicals from factories, dust, and pollen in the air is called air pollution. Human exposure to common hazardous air pollutants such as NOx, SOx, CO, H2S, NH3, and VOCs is associated with chronic respiratory diseases and cancer. Moreover, exposure to one of the most dangerous forms of air pollution very fine particulates PM2.5 can cause such deadly illnesses as lung cancer, stroke, and heart disease. Given all these facts, this paper discusses newly developed advanced smart building materials based on TiO2 with self-cleaning and pollutant removal capability from the environment.
Evaluation Of Titanium Dioxide As An Air Pollutant Removing Photocatalyst
2007
This report was prepared as the result of work sponsored by the California Energy Commission. It does not necessarily represent the views of the Energy Commission, its employees or the State of California. The Energy Commission, the State of California, its employees, contractors and subcontractors make no warrant, express or implied, and assume no legal liability for the information in this report; nor does any party represent that the uses of this information will not infringe upon privately owned rights. This report has not been approved or disapproved by the California Energy Commission nor has the California Energy Commission passed upon the accuracy or adequacy of the information in this report. i ii Acknowledgments Many individuals generously shared their expertise during this technology evaluation exercise.