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Photocatalytic oxidation of NOx on TiO2 immobilized on recycled rubber tiles under simulated solar light

Solar photocatalysis has been widely researched during the last five decades as a promising technology for water and air purification for a real scale applications [1]. In urban areas, increased emissions of nitrogen oxides (NOx) caused by industrial and traffic activities, have been impacting on environmental and health issues, such as production of tropospheric ozone, acid rains, global warming and human diseases relevant to respiratory and immune systems [2]. A significant proportion of the world population lives in urban areas, where violation nitrogen dioxide (NO2) is now generally recognized as one of air pollutants that most significantly affect human health. Around 90% of city dwellers in Europe are exposed to pollutants at concentrations higher than the air quality levels deemed harmful to health [1]. In an advanced oxidation process, reactive species formed in synergy of solar irradiation, photocatalyst (semiconductor) and moisture could be applied to degrade air contaminants to less harmful and contribute to improvement of air quality. Preliminary experiments were performed in Compound Parabolic Collector reactor (CPC) under simulated solar irradiation with different portions of UV light. As a photocatalyst, titanium dioxide (TiO2) was used and immobilized on recycled rubber tiles by modified sol-gel method [3]. Rubber tiles were obtained from industry which incorporates recycled rubber granulates mixed with polyurethane and catalyst pressed under high temperature. For sol- gel solution commercially available material TiO2 P25 supplied by Evonik, deionized water and ethanol, acetic acid and tetraethoxysilane (TEOS) was used. The CPC-based configuration assumes closed tubular reactors whereby immobilized TiO2 is fully exposed to incident irradiation [4]. The CPC reactor consists of quartz tube (L = 500 mm, Douter = 30 mm, Dinner = 27 mm) placed in the middle of a compound parabolic mirror made of highly reflective alumina (JBL Solar Reflect 50) [4]. The irradiation source was a custom-made panel composed of three pairs of full- spectra lamps. The aim of the experiments was to remove NOx from the air stream which were represented by nitrogen dioxide (NO2), nitric oxide (NO) and nitrous oxide (N2O). First set of experiments were done on referent rubber tiles without photocatalyst in dark or under irradiation to obtain the baseline of NOx in the outlet and respective residence time. Second set of experiments were done with the rubber tiles with immobilized TiO2 in dark to research adsorption influence on recycled polymere material. In the end, last set of experiments consist rubber tiles with immobilized TiO2 under irradiation which represents photocatalytic oxidation of NOx. Continuous monitoring of gases CO, CO2, NOx, NO, NO2, HC and H2S was conducted using a gas analyzer Testo 350. Reactor was upgraded with a simple Arduino-based analytical platform for continuous monitoring of the temperature and humidity. The kinetic study resulted with intrinsic reaction rate constants calculated using axial dispersion model and zero order reaction rate kinetics with photon absorption effects. The results confirmed photocatalytic oxidation of nitrogen oxides towards molecular nitrogen with different reactor’s aspects, a photocatalyst’s surface, mass transfer and irradiation usage. Solar photocatalysis as a promising technology of air purification for real scale applications can be represent with results in this work for sizing reactors on semi-pilot and pilot level to prevent further environmental pollution.

photocatalysis, titanium dioxide, recycled rubber tiles, nitrogen oxides, Compound Parabolic Collector reactor.

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