Preliminary study of the use of β-SiC foam as a photocatalytic support for water treatment
Introduction
Photocatalytic oxidation using semi-conductors is one of the advanced oxidation processes (AOPs) utilised for the rapid degradation of organic pollutants in water and air. However the future of photocatalysis as an efficient method for water treatment in the context of a policy of sustainable development requires that the scientific community and companies involved in this area must resolve a number of challenges. One of the most significant of these challenges is to develop photocatalytic materials that can be integrated into industrial processes for large-scale water treatment.
TiO2 is an excellent photocatalyst that can mineralise a large range of organic pollutants including some of the most refractory ones such as pesticides, herbicides and dyes [1], [2], [3]. The basic process of photocatalysis consists in ejecting an electron from the valence band (VB) to the conduction band (CB) of the TiO2 semi-conductor thus creating a h+ hole in the valence band. This in turn induces the formation of extremely reactive radicals such as °OH at the semiconductor surface or by direct oxidation of the polluting species by h+. The ejected electrons will react with electron acceptors such as adsorbed oxygen.
To achieve an industrial-scale application of this process, it is necessary to deposit the photocatalyst (titanium dioxide) on a suitable medium. The original element of this study is its use of medium surface area β-SiC foam (20–30 m2 g−1), a three-dimensional photocatalytic medium for the preparation of photocatalytic materials [4]. This β-SiC foam is a tridimensional medium with an alveolar, adaptable and flexible geometry permitting both good performance in light transmission and in optimum fluid flow thus promoting increased contact between the photocatalytic active coating and the polluted water. This support was synthesized using the shape-memory synthesis developed by Ledoux et al. which is a gas–solid reaction between SiO and Carbon [5].
In the relevant literature, very few studies refer to TiO2/β-SiC composite in an environmental application and, to our knowledge none to the TiO2 deposited on β-SiC foam by the sol–gel method. Currently, Rodriguez et al. [6] have used a process of TiO2 coating on SiC by dip-coating and using TiO2–P25 suspensions with different formulations. The photocatalytic performance of the resulting material was evaluated by studying the photooxidation of aqueous ammonia. The authors conclude that TiO2 anchored on β-SiC foam is a promising material for photocatalytic applications and could be exploited as an internal structuration in classical reactors. Yamashita et al. [7] studied the TiO2–SiC composite prepared by calcination of nano-particles of TiC–SiC precursor obtained by a carbothermic reduction of SiO2–TiO2 which showed high photocatalytic reactivity for the degradation of 2-propanol diluted in water. The formation of well-crystallized TiO2 on SiC and the hydrophobic surface of SiC were found to be related to the photocatalytic efficiency.
The objective of this study is to optimize the process of deposition of TiO2 photocatalyst on the β-SiC Foam. The performances of the materials prepared as the basis of the study are evaluated against their ability to degrade an aqueous solution of Diuron (herbicide) under UV irradiation.
Section snippets
Products
All the reagents used in this work were of analytical grade and were used without any further purification: tetraisopropylorthotitanate Ti(OC3H7)4 (Aldrich, 97%), ethanol (SdS-France, 99.9%) and acetic acid (Prolabo, 99.5%). Diuron (98% purity, (N-(3,4-dichlorophenyl)-N,N-dimethylurea) was purchases from Aldrich Company. Titanium dioxide P25 from Degussa Corporation (70% anatase and 30% rutile, 99.8% purity, average particle size 30 nm and specific surface of 50 m2/g) was used as supplied.
The
Optimization and evaluation of photocatalytic activity of TiO2 powder
The photodegradation kinetics of the Diuron in TiO2 dispersions under UV irradiation have often been modelled on the Langmuir–Hinshelwood equation. When the solution is highly diluted, the reaction is essentially an apparent first order reaction and after integration, the L.H. equation can be reduced to the following equation: ln(C0/C) = kapt where kap is the apparent rate constant of a pseudo first-order reaction. By plotting ln(C0/C) versus t, the apparent rate constant (kap) can be determined
Conclusion
Titanium dioxide nanoparticles and TiO2 supported on β-SiC foam were prepared via sol–gel methods. Several parameters (CH3COOH/Ti ratio, temperature of calcination) were used to optimize the efficiency of the prepared materials. In correlation with the increase of the CH3COOH concentration in the sol–gel solution, the photocatalytic oxidation of Diuron also increases. The optimized TiO2/β-SiC foam material was very stable. TiO2 remains strongly attached to the surface of the foam. The
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