Comparative study of arsenic removal efficiency from water by adsorption and photocatalytic oxidation with titanium dioxide

Titanium dioxide, a well-known adsorbent material, has been extensively tested in environmental applications, especially in separation technologies. In the present study, TiO2 nanoparticles were synthesized by using sol-gel method for removing arsenic ions from water. Several water/titanium molar ratios were prepared in order to obtain optimum crystalline structure, morphology, and particle size of titanium dioxide nanoparticles. Two types of TiO2 minerals which were rutile and anatese were mainly synthesized at different calcination temperatures. After characterization of synthesized powders by X-ray diffraction and scanning electron microscopy (SEM), batch adsorption experiments were carried out to analyze removal capacity of the titanium nanoparticles. The maximum % of removal of arsenic was found ~77% at pH 3, respectively when 0.1 g rutile type TiO2 nanoparticles were used at the As0 5 ppm. Anatase type of TiO2 nanoparticles had also closer adsorption capacity which was ~63% at pH 6 with the same initial arsenic concentration. In the light of experimental results, titanium dioxide nanoparticles (TiO2) are found as a promising adsorbent material for arsenic removal from water. However, the effectiveness of TiO2 nanoparticles in removing arsenic species from water have been enhanced by the photocatalytic oxidation by conversion of arsenide ions (As3+) to arsenate ions (As5+), which adsorbs more strongly onto the solid phase of adsorbent than arsenite ions (As3+). Therefore, in the present study the photocatalytic oxidation of As3+ to As5+ is investigated in UV-illuminated and solar irradiated TiO2. Residual arsenic concentrations of the solutions treated with titanium dioxide nanoparticles were measured with a Varian, Vista-Pro CCD simultaneous inductively coupled plasma ICP-OES spectrophotometer. The adsorption isotherms, thermodynamic and kinetic parameters with and without presence of photocatalytic oxidation reaction are obtained to analyze arsenic removal capacity of the TiO2 nanoparticles.