Journal of Photochemistry and Photobiology A: Chemistry 257 (2013) 44–49 Contents lists available at SciVerse ScienceDirect Journal of Photochemistry and Photobiology A: Chemistry journa l h o me pag e: www.elsevier.com/locate/jphotochem Visible light photocatalytic reduction of 4-Nitrophenol using CdS in the presence of Na 2 SO 3 Agileo Hernández-Gordillo a,∗,1 , Angela G. Romero a,1 , Francisco Tzompantzi a,1 , Socorro Oros-Ruiz b , Ricardo Gómez a,1 a Universidad Autónoma Metropolitana-Iztapalapa, Depto. de Química, Área de Catálisis, Grupo ECOCATAL, Av. San Rafael Atlixco No 189, CP 09340, México, DF, Mexico b Centro de Ciencia Aplicada y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, AP 70-186, CP 04510, México, DF, Mexico a r t i c l e i n f o Article history: Received 20 June 2012 Received in revised form 7 February 2013 Accepted 9 February 2013 Available online 26 February 2013 Keywords: CdS quantum size 4-Nitrophenol Photoreduction Na2SO3 reducing a b s t r a c t The photocatalytic properties of CdS semiconductors were investigated for the photoreduction of 4- Nitrophenol with Na 2 SO 3 under blue light irradiation. The materials were synthesized by co-precipitation method in ethylenediamine–water solution and their structural and optical properties were charac- terized by X-ray diffraction, UV–vis spectroscopy and nitrogen physisorption. The CdS semiconductor prepared at higher EN contents (90 vol.%) presented the highest photocatalytic activity for the reduction of 4-Nitrophenol to 4-Aminophenol. Their photo-efficiency enhancement is attributed to the quantum confinement effect caused by the small particle size (∼15 nm). © 2013 Elsevier B.V. All rights reserved. 1. Introduction Cadmium sulfides are promising semiconductor since the posi- tion of its conduction band is sufficiently negative to carry out the electron transfer process from their surface to the adsorbed molecules, achieving an effective photocatalytic reduction of organic compounds [1–3]. The process rate of the interfacial elec- tronic transference is determined by the over potentials of the conduction band electrons to the acceptor reactant, E e = E ◦ (A/A· - ) - E CB ; and the valence band holes to the donor reactant, E h = E VB - E ◦ (D/D + ) . The efficiency of the semiconductor photoactivity is improved by their optoelectronic properties, high capacity to absorb visible light and the quantum size effect [1]. On the other hand, for aqueous photoreduction reactions, the CdS is always used in the presence of sodium sulfite (Na 2 SO 3 ) as an electron donor to avoid the photo-corrosion process achieving high H 2 produc- tion [4–7]. Particularly, Na 2 SO 3 has also been used as a reducing agent for the methylviologen photoreduction, where the sulfite ions (SO 3 2- ) are oxidized to sulfite radicals (SO 3 *- ), satisfying the electron transfer process [1]. For this case, the photonic energy was supplied from a typical 200–500 W Xe, UV–vis lamp (high power). To the best of our knowledge there are no reports about the ∗ Corresponding author. Tel.: +52 58044668. E-mail address: agileo12@hotmail.com (A. Hernández-Gordillo). 1 Tel.: +52 58044668. 4-NP reduction using photocatalysts semiconductors actives in the visible light region. With the purpose to carry out the photocatalytic reduction of 4-Nitrophenol (4-NP) to 4-Aminophenol (4-AP) using a visible light source, in the present work CdS was used as photoreductor cata- lyst. The CdS semiconductors were synthesized by the precipitation method using ethylenediamine–H 2 O solutions. The photocatalytic reduction of 4-NP was carried out with Na 2 SO 3 under blue light irradiation (450 nm) supplied by a low power LED lamp (3 W). The influence of the power LED lamp in the photoactivity was stud- ied. All the semiconductors were characterized by XRD, DRS-UV-Vis spectroscopies and nitrogen physisorption. 2. Methodology 2.1. Synthesis of CdS semiconductors The CdS semiconductors were synthesized by the precipitation method at low temperature using etilenediamine–H 2 O solutions. In a typical procedure, appropriated amounts of Cd(NO 3 ) 2 H 2 O (Rea- sol) and thiourea (stoichiometry molar ratio 1:3) were dissolved in different ethylenediamine–water solutions with 20, 60 and 90 vol.% of ethylenediamine (EN) at room temperature. Then the solution was heated at 110 ◦ C during 24 h under vigorous magnetic stirring. The precipitated formed was recovered by filtration and washed several times with distilled water and ethanol. The products were dried at 200 ◦ C for 5 h and labeled as CS-20, CS-60 and CS-90 where 1010-6030/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jphotochem.2013.02.016