Modeling of visible light photocatalysis for indoor air purification

MARÍA DE LOS MILAGROS BALLARI; ROMINA MINEN; JOAQUÍN CARBALLADA; ORLANDO M. ALFANO; ALBERTO E. CASSANO

San Diego

Conferencia; The 18th International Conference on Semiconductor Photocatalysis and Solar Energy Conversion (SPASEC-18); 2013

Redox Technologies, Inc.

The indoor air quality has a significant impact over the human health due to the fact that people spend most of the time in these environments. A wide range of inorganic and organic pollutants, like nitrogen oxides (NO and NO2), sulfur dioxide (SO2) and volatile organic compounds (VOCs), are emitted continuously to indoor atmosphere or transferred from outside of the buildings causing drowsiness, headache, sore throat, and mental fatigue. Accordingly, it is of vital importance to remove these contaminants in order to improve the wellness of indoor habitants. Acetaldehyde is one of toxic, irritant, and probable carcinogen VOC contaminant in indoor and outdoor environments. It is a result of combustion processes, such as vehicle exhaust, tobacco smoke, and wood burning. Its main sources in homes include building materials, like laminate, linoleum, wooden varnished, and cork/pine flooring; plastic water based and matt emulsions paints as well as wooden, particleboard, plywood and chipboard furniture. It is also created by thermal degradation of polymers in the plastics processing industry. An alternative method for air quality control is the Heterogeneous Photocatalytic Oxidation (PCO) employing titanium dioxide (TiO2) as catalyst. However, normal TiO2 can only be activated by UV radiation (280-400 nm) which represents 4% of the total energy of the sun; whereas the visible light constitutes 45% of the solar radiation. On the other hand, the UV radiation is scanty in indoor lighting. To extend the use of PCO to visible light region, it is necessary to prolong TiO2 radiation absorption to wavelengths corresponding to visible spectrum (400-700 nm). So far, several modification methods of photocatalysts to extend the absorption spectrum to visible radiation have been investigated and therefore, the applicability of heterogeneous photocatalysis has been expanded. Moreover, several commercial types of modified TiO2 can be already found in the market for indoor visible light applications. In the present work, a visible light TiO2 type commercially available (Kronos vlp 7000), doped with carbon, is studied for the photocatalytic degradation of a representative VOC under visible light. The TiO2 powder was immobilized on borosilicate glass plates according to a dip coating method. Then, the photocatalytic performance of these plates under visible light was evaluated in a continuous gas flat plate photoreactor using acetaldehyde as a simple-structured organic contaminant of indoor air environments. The photocatalytic reaction was studied varying the main parameters of the system, such as the flow rate, relative humidity, pollutant level, and irradiance. Additionally, the optical properties of the photocatalytic films were measured under visible light, validating the photocatalytic activity under the used wavelengths. Complementarily, the modeling of the studied system was carried out, including the kinetic expression for the acetaldehyde degradation and main intermediates generation, the mass balance in the continuous reactor and the lamps emission model for the radiation distribution in the system. Under the operating conditions employed in this work a significant mineralization of acetaldehyde in gas phase was observed with a small amount of formaldehyde formation, as the main stable intermediate of the photocatalytic reaction. The good photocatalytic performance of carbon doped TiO2 under visible light shows promising results for a concrete and practical scale air treatment under typical indoor illuminating conditions.