2012 Chinese Journal of Catalysis Vol. 33 No. 8 文章编号: 0253-9837(2012)08-1347-07 国际版 DOI: 10.1016/S1872-2067(11)60422-1 研究论文: 1347~1353 Photocatalytic Synthesis of Phenol by Direct Hydroxylation of Benzene by a Modified Nanoporous Silica (LUS-1) under Sunlight Ghasem SHIRAVAND 1 , Alireza BADIEI 1,* , Ghodsi Mohammadi ZIARANI 2 , Morteza JAFARABADI 1 , Majid HAMZEHLOO 1 1 School of Chemistry, College of Science, University of Tehran, Tehran, Iran 2 Department of Chemistry, Faculty of Science, Alzahra University, Tehran, Iran Abstract: Fe-g-C 3 N 4 -LUS-1 was prepared by the thermal decomposition of dicyandiamide inside the pores of LUS-1 under an inert atmos- phere. It was used as a photocatalyst for the hydroxylation of benzene to phenol in sunlight. The catalysts were characterized by Fourier transform infrared spectroscopy, N 2 adsorption-desorption, X-ray diffraction, and scanning electron microscopy. In Fe-g-C 3 N 4 -LUS-1, a single layer of graphitic carbon nitride (g-C 3 N 4 ) was formed on the surface of LUS-1. The photocatalytic activity of the iron containing g-C 3 N 4 based catalysts was investigated, and the catalytic activity was remarkably enhanced when the reaction condition was changed from dark to sunlight. The best result was obtained with 20%Fe-g-C 3 N 4 -LUS-1 in sunlight. Key words: mesoporous silica; photocatalyst; phenol; benzene hydroxylation; sunlight; nanoporous silica; carbon nitride CLC number: O643 Document code: A Received 21 January 2012. Accepted 30 May 2012. *Corresponding author. Tel: +98-2161112614; Fax: +98-2161113301; E-mail: abadiei@khayam.ut.ac.ir This work was supported by University of Tehran. English edition available online at Elsevier ScienceDirect (http://www.sciencedirect.com/science/journal/18722067). There is increasing interest in the photocatalytic technol- ogy in catalytic processes for hydrogen production from splitting water, self-cleaning coatings, high efficiency solar cells, and dye degradation [1–8]. These processes need con- siderable energy, and providing the energy is one of the most important issues. Many attempts have been made to find photocatalytic processes that utilize a renewable low cost irradiation source, such as sunlight, instead of expen- sive artificial irradiation sources [8–12]. Since visible light comprises a large portion of the solar energy reaching the surface of the earth, the utilization of visible light will give a more efficient solar energy usage. To achieve this, a mate- rial with a suitable band gap for absorbing visible light and that acts as an oxidative material is needed. Several materi- als, e.g., Bi 38 ZnO 58 [13], CuO [14], Au/TiO 2 [15], NiO/InTaO 4 [16], BiVO 4 [17], and g-C 3 N 4 [3,18], have a suitable band gap for use in photocatalytic processes under visible light irradiation and in sunlight. The band gap of graphitic carbon nitride (g-C 3 N 4 ) was estimated to be 2.7 eV from its UV-Vis diffuse reflectance spectrum [19], which is equal to 460 nm wavelength. As a result, g-C 3 N 4 can be used as a photocatalyst in the visible light region. There are several models for the structure of these compounds. The tri-s-triazine based model is the predicted most stable struc- ture of g-C 3 N 4 [20,21]. Several methods have been used to synthesize g-C 3 N 4 , e.g., by solid state reaction [21,22], solvothermal reaction [23,24], thermal decomposition [25], ionothermal reaction [26], and other methods [27–29]. Several precursors such as cyanamide, dicyandiamide, melamine, and cyanuric chlo- ride have been used to get the g-C 3 N 4 solid [28–31]. The easy sublimation of melamine is a serious issue in thermo- lysis. Dicyandiamide is recommended as a precursor to suppress this sublimation [20]. g-C 3 N 4 has been used as a photocatalyst in several reac- tions [18,32,33]. Chen et al. [18] investigated the catalytic performance of graphitic carbon nitride for the direct hy- droxylation of benzene to phenol. They reported that ben- zene is adsorbed and activated on g-C 3 N 4 , and therefore, this catalyst is a promising catalyst for the hydroxylation of benzene to phenol. In this work, graphitic carbon nitride was prepared and loaded on the surface of mesoporous Type LUS-1 silica. Due to its high surface area (800 cm 2 /g), long range ordered pores (average pore diameter 3 nm) and hydrothermal stability, LUS-1 is a good support for catalytic reactions such as the hydroxylation of benzene [34]. The hydroxylation of benzene to phenol over Fe-loaded mesoporous silica, such as SBA-15 or MCM-41, with dif- ferent iron contents had been investigated previously [35,36]. In this study, the properties and applications of xFe-g-C 3 N 4 and xFe-g-C 3 N 4 -LUS-1 in the direct hydroxyla- tion of benzene were studied. These reactions were carried