Electrochimica Acta 55 (2010) 4942–4951 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Specific adsorption of arsenic and humic acid on Pt and PtO films Hebert A. Menezes, Gilberto Maia ∗,1 Department of Chemistry, Universidade Federal de Mato Grosso do Sul, Av. Filinto Muller, 1555, Cidade Universitária s/n, C.P. 549, Campo Grande, MS 79070-900, Brazil article info Article history: Received 20 November 2009 Received in revised form 29 March 2010 Accepted 30 March 2010 Available online 8 April 2010 Keywords: Cyclic voltammetry Cyclic massogram As Humic acid Specific adsorption abstract A study of specific adsorption of arsenic (As) and humic acid (HM) onto Pt and PtO films using cyclic voltammetry and cyclic massogram in 0.5-M H 2 SO 4 is presented, which may serve as an alternative to studies involving specific adsorption of these species on soil minerals. Adsorption of As is normally evalu- ated by conducting batch adsorption experiments, followed by analysis using hydride-generation atomic absorption spectrophotometry (HGAA) or inductively coupled plasma-optical emission spectrometry (ICP-OES). We found that specific adsorption of As and HM depends both on the surface and on these species present in the adsorption solution. HM does not desorb previously adsorbed As at the HM concen- trations used in the present study, but it does co-adsorb with As from a 1 × 10 -6 -M aqueous solution of As 2 O 3 containing 1 mg of carbon L -1 HM. Arsenic adsorbs strongly on Pt in the presence of HM or during sequential specific adsorption with HM. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction Arsenic, a common element in nature, is a naturally occurring contaminant of drinking water and can be found in the Earth’s crust in soil and seawater, as well as in the organic world [1]. Occurring in natural waters in a variety of manners, including soluble, partic- ulate, and organic-bound forms, but mainly in inorganic trivalent As(III) and pentavalent As(V) oxidation states [2], arsenic is a toxic element with detrimental effects on humans, plants and animals [1]. Diseases such as gastroenteritis and lung, skin, and bladder can- cer can be caused by contact with As in aqueous or other media [3]. Wastewaters from activities such as metallurgy, mining, chemical pharmacy, chemical and pesticide production, and leather tanning are often polluted with As. Despite its four stable oxidation states (+3, +5, -3, and 0), it occurs in aqueous solutions as As(III) and As(V) in the form of arsenites (AsO 3 3- ) and arsenates (AsO 4 3- ), respec- tively [3]. In near-neutral pH waters, arsenite is present primarily as uncharged arsenous acid (As(OH) 3 ), whereas arsenate occurs predominantly in anionic form [4]. Humic substances (HS), which are major components of natural organic matter (NOM), are some of the most abundant materials on Earth. They are formed during the decomposition of plant and animal biomass in natural systems and usually comprise a skele- ton of alkyl and aromatic units with functional groups such as carboxylic acid, phenolic hydroxyl, and quinone groups attached ∗ Corresponding author. Tel.: +55 67 3345 3551; fax: +55 67 3345 3552. E-mail address: gmaia@nin.ufms.br (G. Maia). 1 ISE member. [5,6]. The presence of HS in natural waters may compete with tar- get pollutants (including As) and diminish their removal efficiency by reducing their adsorption rates and equilibrium capacities [5]. In natural waters, HS occur in the range of a few mg of carbon L -1 to a few hundred mg of carbon L -1 [6]. Dissolved humic substances (DHS) are composed of a mixture of humic and fulvic acids (HM and FV) of different molecular weights [7]. HM can complex metals and metalloids by its oxygen-containing functional groups, and further may adsorb onto mineral particle surfaces. These modified surface sites often control the fate and transport of trace contaminants in both aquatic and terrestrial environments [8]. Many studies have reported the adsorption of As on different oxides in the presence or absence of HM. Bauer and Blodau [9], for instance, found that sorption of dissolved organic matter (DOM) has the potential to mobilize As from iron oxides, soils and sediments. Liu et al. [10], investigating the effect of NOM on As adsorption onto commercial TiO 2 in a range of simulated As(III)-contaminated raw waters, reported that NOM decreased As adsorption within the tested pH range of 4.0–9.4 and suggested that NOM is an important factor controlling As speciation and adsorption onto TiO 2 surfaces. Ko et al. [8], in studies evaluating the influence of contact order on speciation during As adsorption in equilibrated ternary systems consisting of As, HM, and hematite, found that overall As adsorp- tion decreased in the presence of soil HM, unlike the behavior noted for cationic metal adsorption. The low affinity of HM for complex- ation with As leads to decreased adsorption [8]. Habuda-Stani ´ c et al. [11] investigated As removal from drinking water using pre- pared adsorbents to coat the surface of two polymeric materials (natural alum silicate exchanger zeolite–clinoptilolite and an ionic exchanger resin modified with hydrous ferric oxide). They found 0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2010.03.099