Characterization and environmental application of polypropylene coated nano-TiO2 in wastewater depuration

Ground water contamination causes degradation of water quality and is likely to be the primary contact of human with toxic chemicals. Organic dyes, coming from different sources such as textile industries, paper and pulp industries, pharmaceutical industries, tannery, etc, undesirable in water even in very small amounts, can affect the ecosystems integrity [1]. Residual dyes from these sources are considered as a wide variety of organic pollutants introduced into the natural water resources that represent an environmental danger. The discharge of dyes into the water environment is unpleasant, not only for their color, but also because many released dyes and their breakdown products are toxic, carcinogenic or mutagenic to life forms [2]. In addition, since the dyes are intentionally chosen to resist to light and to aerobic oxidation by microorganisms, only partial degradation of dyes is possible [3]. Alizarin Red S (sodium salt of 1,2-dihydroxyanthraquinone-3-sulfoacid, ARS) represents a durable dyes because cannot be completely degraded by general chemical, physical and biological processes. In recent years it has been observed a great progress in the field of photocatalytic studies [4] and heterogeneous photocatalysis has gained the attention as promising technique that can be used as alternative or as a complementary to conventional wastewaters treatment using UV or visible light. The most used photocatalyst is TiO2 and its applications show advantages such as chemical and biological resistance, low price, non-toxicity, expensive recycling and its recovery [5]. In this study Polypropylene coated nano-TiO2 photocatalyst (PP@TiO2) were successfully prepared. The optimization of TiO2 pastes preparation using two commercial TiO2 (Degussa P-25 and Anatasio) has been performed and green, low-cost dip-coating procedure was developed. The study is been conducted in four steps. In the first, Electron Diffraction, Scanning Electron Microscopy and Atomic Force Microscopy were used in order to obtain crystallographic and morphological informations of TiO2 on support material. In the second, ARS has been spectrophotometrically characterized at different pH conditions showing that at acid pH, the dyes favorably bind on TiO2 surface through the sulfo group. In the third, equilibrium and kinetic data of ARS adsorption process were obtained showing difference in absorption capacity, isotherm model and kinetic constants between two types of TiO2. Finally, in the fourth step, adsorption/photodegradation process of ARS were studied simultaneously and as separated process under the action of visible light, obtaining for the two types of TiO2 kinetic data. According to all obtained results the kinetic model for adsorption/photodegradation process has been proposed confirming that the use of PP@TiO2 in the Visible light photodegradation of ARS permits to obtain efficiently dye degradation suggesting an application for environmental treatment of wastewaters.