Proceedings

Solar photocatalytic degradation of organic pollutants using TiO2 functional coatings on glass and steel

Woods, R., Charbonnaeu, C., Khan, K. and Worsley, D., SPECIFIC, Swansea University, UK

(free)

Abstract Titanium dioxide (TiO2) is a promising semiconductor photocatalyst which has led to much research into a number of applications in environmental purification, hydrogen production and next generation solar cell technologies. The development of new technologies to provide safe, clean water has become increasingly important. Industrial effluent from the textile, paper and pulp industries contain residual dyes which are introduced into the natural water courses and are a contributing factor to environmental issues. A TiO2 formulation has been developed which can be coated onto glass and steel using a low cost, scalable process. The photocatalytic properties of the coating containing TiO2 nanoparticles enable the degradation of organic dyes and pollutants present in wastewater. This work describes the development and optimisation of photocatalytic properties of nanoparticles present in a paste which can be used as a water treatment functional coating to facilitate removal of organic pollutants. The high photocatalytic properties of the coating are attributed to the unique formulation containing P25 TiO2 along with 5-6 nm anatase particles, leading to a substantial increase in the surface area compared to formulations containing P25 nanoparticles alone.

Keywords Water Treatment, TiO2, Photocatalysis, Organic dye, Decolorisation, Nanoparticles

Introduction The textile industry constitutes one of the largest producers of pollutants in wastewater. Highly coloured effluent is released into the ecosystem leading to environmental problems such as aesthetic pollution, an increase in BOD and COD and toxicity to living organisms either directly or through absorption or reflection of sunlight. Water pollution from organic compounds such as synthetic dyes can also be generated from paper printing, colour photography and petroleum industries, with 10-15 % of the dye production being lost during processing and released into water streams 1,2. Due to the inexpensiveness, chemical stability and low toxicity, TiO2 powders are commonly used as white pigments in paints, varnishes and the paper industry. Due to TiO2 being active under exposure to UV light, inducing chemical reactions, the application of photocatalysis for water purification has been studied and reported extensively3,4,5. The treatment of wastewater containing dyes is a challenge due to the recalcitrant nature of the organic molecules, their resistance to aerobic digestion and their stability6. Traditional methods such as biological, chemical and physical processes are not effective in treating such waste due to high costs and disposal at such a large scale. Ozonation can be an effective technique for colour removal from wastewater additionally decreasing 7th European Waste Water Management Conference www.ewwmconference.com Organised by Aqua Enviro Technology Transfer Chemical oxygen demand (COD) and toxicity. The production of ozone by cold corona discharge can however be inefficient and the running costs are high7. Another effective process used to treat coloured wastewater is the Fenton process, which can easily be integrated into existing treatment works. Compared to other advanced oxidation processes (AOP) this process requires a relatively short reaction time. A disadvantage of this process is flocculation which transfers impurities from the wastewater to sludge.

Photocatalytic treatment is an attractive alternative for the removal of soluble organic compounds as complete mineralisation can be achieved through photogeneration of •OH radicals originating from the water via the OH groups on the TiO2 surface8. The process does not require expensive oxidants and can also be performed at low temperature and pressure. With the immobilisation of the TiO2 nanoparticles onto a suitable solid inert material, catalyst removal steps are also avoided9. Using solar energy makes photocatalysis a clean, energy efficient and cheap alternative to other technologies. In this study a coating has been developed using a combination of commercially available TiO2 (P25) and synthesised nanocrystaline TiO2 anatase particles. The coating was immobilised on glass and steel panels for applications in decolourising polluted water. After the coating was annealed onto different supports the photoactivity was evaluated by monitoring the degradation of the textile dye indigo carmine under UV light using UV/Vis spectrometry. The nanoparticles were characterised by scanning electron microscopy (SEM) and BET analysis. A comparison of the photoactivity of different formulations was performed by monitoring CO2 evolution from the photodegradation of acetone.

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