(660a) Photocatalytic Degradation of Methylene Blue on Multifunctional Titanosilicate ETS-10

Authors: 
Ji, Z., Center for Advanced Microgravity Materials Processing , Northeastern University
Sacco, Jr., A., Northeastern University
Warzywoda, J., Northeastern University
Callahan, Jr., D. M., Center for Advanced Microgravity Materials Processing (CAMMP), Northeastern University
Ismail, M. N., Northeastern University


Semiconductor photocatalysis has attracted increasing attention in recent years as an alternative to traditional physical, chemical, or biological technologies for environmental remediation. The photocatalyst market is expected to reach US $30 billion in the near future [1]. Engelhard titanosilicate ETS-10 is a microporous (4.9 Å x 7.6 Å) zeotype material. The well-defined monatomic -O-Ti-O-Ti-O- chains in ETS-10 with a band gap energy of ~4.03 eV make this semiconductor material a promising candidate for photocatalytic applications. ETS-10 has been reported to exhibit shape selectivity in the photodegradation of phenol, 1,3,5-trihydroxybenzene, and 2,3-dihydroxynaphthalene [2]. The photocatalytic activity of ETS-10 could also be improved by introducing transition metal ions such as Cr (III), Co (II), and Ag (I) into its framework structure [3].

In this investigation, photocatalytic degradation of methylene blue (MB) was used as a model reaction to evaluate the photocatalytic activity of ETS-10 in a stirred batch reactor system under UV irradiation. A 500 mg/L suspension of the photocatalyst was used in all the experiments. The initial concentration of MB was 10 mg/L and the MB concentration change during the photocatalysis process was determined from the absorbance maximum at ~664 nm in its UV-vis spectrum. pH was found to be a key factor in this type of reaction as it affected both the surface charge of the ETS-10 and the ionization of the cationic MB dye. The highest photocatalytic activity of the as-synthesized ETS-10 was achieved in the pH range of 4.0-5.2; for which the pseudo-first-order reaction rate constant was determined to be ~0.043 min-1 m-2. Transition metal ions such as V(IV), Cr (III), Mn (II), Fe (III), Co (II), Cu (II), Ag (I), and Au(I) were introduced into ETS-10 through isomorphous substitution or ion-exchange [3]. Among all these modified ETS-10 crystals, silver exchanged ETS-10 exhibited the highest photocatalytic activity; the reaction rate constant was ~0.191 min-1 m-2, which was 4-5 times higher than that obtained using the as-synthesized EST-10 and two times higher than that obtained using the commercial Degussa P25 TiO2 under the same operating conditions. The enhanced activity may be attributed to the ability of these transition metal ions to scavenge electrons on the ETS-10 particle surface, thereby reducing the undesired electron-hole recombination [4]. The presence of hydrogen peroxide (H2O2) in the ETS-10 photocatalysis system resulted in a synergistic effect. The photocatalytic degradation of MB on the as-synthesized ETS-10 was improved 3-5 times through adjusting the H2O2 concentration. The optimum H2O2 dosage was determined to be ~9 wt.%, at which the pseudo-first-order reaction rate constant was ~0.188 min-1 m-2. Currently, an optical fiber reactor system is being designed and optimized. The photocatalytic activity of the modified ETS-10 crystals will be tested under the optimized operating conditions in this optical fiber reactor and compared with the traditional immobilized photocatalytic reactor systems.

[1] Estimation by the National Institute for Materials Science in Japan, http://www.mext.go.jp/a_menu/shinkou/sangaku/07091398/4_6.pdf.

[2] P. Calza, C. Pazé, E. Pelizzetti, and A. Zecchina, Chem. Commun., (2001) 2130.

[3] S. Uma, S. Rodrigues, I.N. Martyanov, and K.J. Klabunde, Micropor. Mesopor. Mater., 67 (2004) 181.

[4] Marta I. Litter, Appl. Catal. B: Environ., 23 (1999) 89-114.