Dynamics and characterization of an innovative Raschig rings-TiO2 composite photocatalyst

This study presents a novel supported photocatalyst on Raschig glass rings using polyethylene-graft-maleic anhydride (PEGMA) as a functionalized copolymer to fix TiO2 Degussa P25 on the glass rings. The immobilized photocatalyst presented long-term stability and could be reused during the photodegradation of 4-chlorophenol (4-CP) without a loss in activity. Aqueous solution of 4-CP (0.49 mM or 35 mg C/L) at their natural pH of 5.6 and TiO2 loaded Raschig rings showed complete decomposition of 4-CP within 5 min under irradiation with a medium pressure mercury lamp. The dependence of the 4-CP photodegradation was investigated as a function of: (a) gas atmosphere of the reaction, (b) concentration of the electron acceptor (H2O2), (c) initial concentration of 4-CP (d) intensity of the applied light and (e) pH of the solution. By X-ray photoelectron spectroscopy (XPS), the percentage of the elements and the binding energies (BE) was determined for the main elements on the catalyst surface. Scanning electron microscopy (SEM) determined a coating with variable a thickness of ∼100-300 nm on the glass rings. This is equivalent to a TiO2 Degussa P25 coating of ∼10 layers thick. By atomic force microscopy (AFM) the increase in the roughness radius of TiO2 pores was observed from 37.6 nm before use to 46.4 nm after use. This indicates that the catalyst pore diameter has increased as observed by AFM. The BET area of the sample was observed to increase from 29.4 m2/g for the catalyst before use to 40.7 m2/g for the TiO2 Raschig glass rings samples after use.