Adsorption of methyl orange and Cr(VI) on mesoporous TiO2 prepared by hydrothermal method.

Mesoporous TiO(2) was synthesized by a hydrothermal method using cetyltrimethyl ammonium bromide (CTAB) as a structure-directing agent, and its adsorption abilities for the removal of methyl orange (MO) and Cr(VI) from waste waters were investigated. Transmission electron micrograph (TEM) observations together with nitrogen adsorption-desorption measurements show the formation of mesoporous TiO(2) with an average pore size of 5.2 nm and a surface area of 161.2 m(2)/g. The adsorption data for both MO and Cr(VI) fit well with either Langmuir or Freundlich adsorption model. The adsorption for MO is slightly influenced by pH of the solutions, while that for Cr(VI) is strongly dependent on solution pH. By an increase in solution pH from 3 to 12, the adsorbed percentage of MO decreases from ca. 87 to 78%; however, the adsorbed percentage of Cr(VI) decreases from ca. 45 to 0%. The maximum adsorption capacities of the mesoporous TiO(2) for MO and Cr(VI) are determined to be 454.5 and 33.9 mg/g, respectively, which suggests that the mesoporous TiO(2) is an excellent adsorbent for MO and Cr(VI).