The effect of sunlight induced surface defects on the photocatalytic activity of nanosized CeO sub(2) for the degradation of phenol and its derivatives

• Published in: Applied catalysis. B, Environmental Vol. 180; pp. 391 - 402
• Main Authors: Aslama, M, Qamara, M T, Soomroa, MTahir, Ismaila, Iqbal MI, Salahc, Numan, Almeelbia, Talal, Gondale, MA, Hameeda, A
• Format: Journal Article
• Language: English
• Published: 01.01.2016
• Subjects: Catalytic activity; Degradation; Electrochemical impedance spectroscopy; Exposure; Phenol; Photocatalysis; Photons; Sunlight
• ISSN: 0926-3373
• DOI: 10.1016/j.apcatb.2015.06.050

The photocatalytic activity of nanostructured CeO sub(2) was investigated for the degradation of phenol and its derivatives (2-chlorophenol, 2-bromophenol and 2-nitrophenol) in the exposure of complete spectrum and visible region (420-800 nm) of sunlight. The adopted experimental parameters imparted high crystallinity, phase purity, controlled morphology and uniform particle size of similar to 11 nm to the synthesized CeO sub(2). During the evaluation of the photocatalytic activity, the initial low degradation of the substrates till the 90 min of complete spectrum sunlight exposure followed by a piercing increase predicted the favorable photon induced surface changes in CeO sub(2). The careful examination of the exposed and unexposed CeO sub(2) by spectroscopic techniques (diffuse reflectance (DR), photoluminescence (PL), ATR-FTIR and Raman spectroscopy) and electrochemical tools (cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry (CP)) revealed the vital role of photon induced surface phases for the improved spectral response and suppressed charge carries recombination process. Based on the appearance of additional weak reflection at 2[thetas] = 28.15 degree in the X-ray diffraction (XRD) pattern and inhalation of O sub(2) in the thermogravimetric analysis (TGA) of sunlight exposed samples revealed the prevalence of photon induced defects generated by the departure of surface oxygen from CeO sub(2). The induction of defects composed of CeO sub(2-x) states resulted in the improved activity of the exposed compared to unexposed CeO sub(2) in the visible spectrum (420-800 nm) of sunlight. The efficient degradation of 2-CP, 2-BP and 2-NP compared to a mild degradation for phenol, in the complete spectrum sunlight exposure, indicated the facilitating role of substituents attached to the aromatic system in the degradation process. The monitoring of the photocatalytic degradation process by HPLC and identification of intermediates by GC-MS analysis revealed the formation of aromatic intermediates in the degradation of phenol and 2-BP while no aromatic intermediate was identified in the degradation of 2-NP and 2-CP. The rapid disappearance of the total carbon and further oxidation of released anions supported the major role of superoxide anion radicals in the oxidation process. Both pure and sunlight exposed CeO sub(2) exhibited sustained photocatalytic activity in the repeated exposures.