Photocatalytic water treatment with different TiO2 nanoparticles and hydrophilic/hydrophobic layer silicate adsorbents

The degradation of 2-chlorophenol (2-CP) was investigated by a combination of TiO2-based photocatalysis and adsorption. Three combined systems were compared: (i) TiO2 was intercalated into the interlamellar space of a hydrophilic montmorillonite by means of a heterocoagulation process (TiO2 pillared montmorillonite, TPM); (ii) TiO2 was hydrothermally crystallized on hexadecylpyridinium chloride-treated montmorillonite (HDPM-T); (iii) hexadecylpyridinium chloride-treated montmorillonite (HDPM) was used as adsorbent and Degussa P25 TiO2 as photocatalyst (HDPM/TiO2). The process of mineralization of the organic substrate was characterized by measuring the total organic carbon (TOC) and total inorganic chloride contents, while the degradation of 2-CP and the formation of intermediates were followed by HPLC. The adsorbent-photocatalyst systems were characterized by X-ray diffraction measurements. In all the investigated systems, the degradation of 2-CP was accompanied by a continuous decrease in TOC content. The most advantageous situation was found with HDPM/TiO2, for which the highest rate of oxidation of 2-CP was observed. In this case the photocatalytically recovered adsorbent may be re-used without further regeneration. A significantly lower 2-CP degradation rate was observed when TiO2 was fixed on layer silicates. When TPM was applied, only a rather low decrease in TOC content was observed during 10 h of irradiation, i.e. only slight mineralization of the organic pollutant occurred, which is probably due to the low crystallinity and small size of the TiO2 particles. In the case of HDPM-T, the observed quite high reduction in TOC content shows that the hydrothermally processed TiO2 sample may compete with the Degussa P25, but the degradation of the organic pollutant is accompanied by a continuous destruction of the adsorbent. (C) 2003 Elsevier B.V. All rights reserved.