Adsorption of bisphenol A from aqueous solution onto activated carbons with different modification treatments

Abstract

Two commercial carbons (W20 and F20) had been selectively modified with nitric acid and thermal treatment under a flow of N₂ in present study to adsorb bisphenol A from aqueous solution. The results indicated that the experimental data were well described with pseudo-second-order kinetic model. W20 and its thermal modified sample (W20N) represented a better adsorption capacity, and the equilibrium adsorption amounts reached 382.12 and 432.34 mg/g, respectively. Further, effects of temperature, pH and ionic strength on bisphenol A adsorption onto W20 and W20N had been examined. It was found that the adsorbed amount of bisphenol A decreased with the increase of temperature from 288 to 318 K and changed little with the increase of pH from 5.0 to 9.0. At pH 11.0, the two activated carbons represented the weakest adsorption capacity. The adsorption capacities of bisphenol A onto W20 and W20N first decreased and then increased with the increasing of ionic strength.

Introduction

The problem of phenolic endocrine disrupting chemicals (EDCs) in environmental water has aroused the public concerns as these contaminants were frequently detected in different water sources in recent years [1], [2]. Bisphenol A, as one of the phenolic EDCs, has been widely used in the production of polycarbonate plastics, epoxy resins and flame retardants as an important monomer. The studies have shown that bisphenol A leaches from some of above products under normal conditions of use [3], [4]. The primary sources of bisphenol A released to environmental water are expected to be the discharge of municipal effluent and industrial wastewater [5], [6]. Bisphenol A had been detected in all kinds of environmental water. The maximum concentrations reached up to 17.2 mg/L in hazardous waste landfill leachates [7], 12 μg/L in stream water [8] and 0.1 μg/L in drinking water [9]. Recent finding showed that bisphenol A represented the estrogenic activity at a low dose of 0.23 pg/mL culture medium [10]. Many in vitro and in vivo assays had confirmed that bisphenol A increased the incidence of infertility, genital tract abnormalities and breast cancer [11], [12]. Accordingly, there is an urgent need for developing the effective technology to remove bisphenol A from aquatic environment.

Physical and chemical treatment technologies such as adsorption, ozonation and advanced oxidation processes have been adopted for the removal of bisphenol A [13], [14], [15]. The adsorption by activated carbon is generally considered to be one of the most efficient methods to control organic contaminants in water. Several studies have reported the adsorption efficiency of bisphenol A onto selected activated carbons [16], [17], [18], [19]. According to these reports, the high specific area and low surface polarity of activated carbon was considered the main factor to produce a high adsorption amount of bisphenol A. Particularly, Bautista-Toledo et al. [20] considered that the adsorption of bisphenol A depended fundamentally on the surface nature of activated carbon and the chemical properties of the solution. However, little literature about bisphenol A adsorption onto activated carbons is presently obtained and the main factor that controls the adsorption of bisphenol A onto activated carbon is not clear. Therefore, the further study on the relationship between the adsorption of bisphenol A and the surface chemical properties of activated carbon is required.

The objectives of the present investigation were (1) to compare the surface properties of selected activated carbons and their chemically modified samples, (2) to study the adsorption capacities of bisphenol A onto these activated carbons with various surface properties and adopt two kinetic models to analyze the experimental data, and (3) to examine the effects of operated temperature, solution pH and ionic strength on the adsorption of bisphenol A onto two carbon samples presenting a better adsorption efficiency.