Preparation of Nano Tio2 Photocatalyst

Supplementary Material

Preparation of nano TiO2 photocatalyst

Titanium dioxide nanosized catalyst was synthesized by the sol-gel method by means of a gradual addition of a solution of titanium isopropoxide (5 ml isopropanol + 5 ml titanium isopropoxide) onto 200 ml of deionized water at pH = 5 with a rate of addition of 2 ml / min. The mixture was kept , after completion of addition, under continuous vigorous mixing at room temperature until the completion of hydrolysis (2 hours).The resulting transparent colloidal solution was left aging for 24 hours then filtered using 0.45 micrometer cellulose membrane, dried at 90 Co for two hours and finally was calcined at 400 Co for 4 hours. Grounding into fine powder, if needed, overcomes the agglomeration.

photocatalytic degradation procedure

Photocatalytic degradation experiments for the synthesized nano anatase TiO2 photocatalyst were carried out in the photolysis cell with 125 milliliter capacity under ultraviolet irradiation. The stock solution of phenol red (100 ppm) was prepared with deionized water and diluted to different concentrations for photocatalytic reaction. For one integral experiment, 75 milliliters of phenol red solutions with certain concentrations, an appropriate amount of hydrogen peroxide and 40 mg photocatalyst were poured into the cell. The pH of the phenol red solution was already adjusted to pH= 4.5 by addition of dilute aqueous solution of HNO3. Oxygen gas was bubbled in the solution to keep all the TiO2 in the suspension. Prior to irradiation, the suspension was magnetically stirred for 20 minutes in the dark to ensure adsorption equilibrium, followed by irradiation for 5 hours with 125W medium pressure UV bulb at 14 centimeter cell-light source distance in the presence of O2 gas. The samples (5 milliliter) were collected every 60 minutes and centrifuged at 3000 rpm for 10 minutes and subsequently to separate the photocatalyst particles from liquid samples. The degradation of phenol red was double beam UV-VIS spectrophotometer, which was set at a wavelength of 432 nm for analysis of phenol red.

Control experiments

Prior to employment of synthesized nano anatase TiO2 for the photodecolorization of phenol red, a series of control experiments were carried out since some phenolic dyes are degradaded by direct UV illumination [22] and further, to check parameters that primarily influence the process. To eliminate the effects of adsorption, the reaction solution was magnetically agitated for 3 hours with samples collected and analyzed by means of a visible spectrophotometer regularly. One set was performed with phenol red solution exposed to TiO2 without UV light irradiation (in dark). The second set was implemented by exposing phenol red to UV light source with absence of TiO2 photocatalyst. The last set was accomplished in the presence of UV light and TiO2 semiconductor, which represents the photocatalysis circumstances. As shown in Fig. 5S, a very small change in the concentration of phenol red was observed when only UV light is present or when only TiO2 is used in dark. However, phenol red could be degraded quickly by UV source illuminated TiO2. Accordingly, these experiments demonstrated that both UV irradiation and the TiO2 photocatalyst are needed for the effective photolysis of phenol red dye. This conclusion was also reported by several researchers for different phenolic pollutants [23-24].