Effect of pH on the adsorption of Sunset Yellow FCF food dye into a layered double hydroxide (CaAl-LDH-NO 3 ) Fernando Pereira de Sá, Beatriz Nogueira Cunha, Liliane Magalhães Nunes ⇑ Instituto de Química, Universidade Federal de Goiás, 74001-970 Goiânia-GO, Brazil highlights " pH affects the adsorbent surface charge and the degree of anionic dye dissociation. " CaAl-LDH-NO 3 is an effective adsorbent for the removal of Sunset Yellow FCF food dye from aqueous solutions. " Lower pH potentially causes dissolution of the CaAl-LDH-NO 3. graphical abstract article info Article history: Received 8 August 2012 Received in revised form 3 November 2012 Accepted 5 November 2012 Available online 12 November 2012 Keywords: Layered double hydroxides Reactive dye Adsorption Sunset Yellow abstract Effluents that are discarded by food industries are important sources of water pollution because they can contain large concentrations of organic matter and have intense color. The ‘‘batch’’ method for evaluating the adsorption of Sunset Yellow FCF food dye into a CaAl-LDH-NO 3 layered double hydroxide (LDH) system was investigated. The CaAl-LDH-NO 3 was coprecipitated at variable pH and characterized by X-ray diffraction, infrared spectroscopy and scan electron microscopy. Adsorption experiments were car- ried out as a function of pH, contact time and dye concentration. The results showed that pH affects the adsorbent surface charge and the degree of anionic dye dissociation. The effective pH range for dye removal was between 4.0 and 10. Lower pH potentially causes dissolution of CaAl-LDH-NO 3 . The Lang- muir equation adequately describes the equilibrium data. The best-fits showed a maximum adsorption of 398.41 mg/g or 0.88 mmol/g. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Environmental changes due to human action have reached extremely worrisome levels. These actions result in a significant reduction in soil, air and water quality. Over the years, the problem of environmental pollution has become worse, which makes it a matter of public interest. Environmental pollution endangers the health of the community and of future generations. Thus, environ- mental pollution is identified as one of the largest problems of modern society [1,2]. Color is the most obvious water pollution indicator. Synthetic dyes represent a relatively large group of organic chemicals that are found in practically all spheres of our daily life. Annually, approximately 7  10 5 tons of dyes are produced, and approxi- mately 7  10 4 tons/year are discarded by industries, including the textile, rubber, food, paper and plastic industries [1,3,4]. Because of their high organic matter concentrations and their intense colors, the effluents discarded by the food industry are an important source of pollution for water bodies. When dis- charged into streams, these effluents reduce the transmission of sunlight into the depleted dissolved oxygen zone [5–7] and may cause changes in aquatic biota (particularly near the release point). Thus, it becomes necessary to remove these materials before they are mixed with natural and unpolluted water bodies [3]. 1385-8947/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2012.11.024 ⇑ Corresponding author. Tel.: +55 62 81545459; fax: +55 62 35211167. E-mail address: lilianemnunes@gmail.com (L.M. Nunes). Chemical Engineering Journal 215–216 (2013) 122–127 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej