Activated carbons for the adsorption of ibuprofen
Introduction
Pharmaceuticals and personal care products (PPCPs) are important and indispensable elements of modern life. This group of substances describes a large class of chemical contaminants that can arise from human usage and excretions and also veterinary applications of a variety of products, such as over-the-counter and prescription medicines, fungicides and disinfectants used for industrial, domestic and agricultural practices [1].
PPCPs are an environmental emerging concern since this class of products comprises not only new compounds commercially available, but also many substances that were recently detected, due to the development of powerful analytical strategies that decrease the detection limits at the sub-ppt (ng dm−3) level [2]. The maximum concentration admissible for PPCPs in the environment are, in most cases, still unregulated, most probably because there is a lack of knowledge about the long-term effects of continuous exposure to these compounds and their metabolites, even if they are present in the environment at trace level [1], [3]. On the other hand, these contaminants do not need to persist long time in the environment to cause negative effects. In fact, even if they could have high transformation/removal rates, the levels in the environment must remain almost constant due to a continuous release [3].
Ibuprofen is one of the most consumed medicines all over the world. For instance, in the United Kingdom it is one of the top five most consumed drugs, having an estimated annual production of several kilotons [4]. It is a nonsteroidal anti-inflammatory (NSAID), analgesic and antipyretic drug widely used in the treatment of rheumatic disorders, pain and fever. Being slightly soluble in water it is readily soluble in organic solvents, and so it has high mobility in the aquatic environment. Measurements made on wastewaters and rivers of Germany showed that ibuprofen is present in concentrations in the order of ppb (μg dm−3) [5].
Recent studies concerning drinking or wastewater treatments for PPCPs removal revealed that conventional processes (coagulation, flocculation and sedimentation) are not totally effective [6]. On the contrary, for instance, oxidation with chlorine and ozone, and activated carbon based processes show to be more efficient for the abatement of PPCPs [6], [7]. Then the use of activated carbons based technologies is a possible option to eliminate PPCPs from aqueous medium, or act as concentrators of those pollutants for analysis purposes. In fact, activated carbons may, virtually, remove any PPCP since the existence of benzene rings or amine groups in the structure of the majority of these compounds enhance their ability to be adsorbed by the activated carbon.
In the literature there is a considerable number of works concerning the use of activated carbons in the treatment of liquid effluents. These studies are mainly focused on the adsorption of metals [8], [9], dyes [10], [11], [12], phenolic compounds [10], [12], [13], [14] and endocrine-disrupting compounds [15], [16]. To our knowledge, in what concerns the removal of PPCPs by activated carbons there are only few studies, and in all the cases commercially available carbons were employed [6], [7], [15], [16]. It should be stressed also that these studies are usually made in an analytical chemistry point of view, so there is no detailed textural or surface chemistry characterization of the activated carbons, what is essential to optimize the removal performance.
Concerning the quantities of wastewaters that have to be treated in industrialized societies, and the fact that environmental regulations are becoming more stringent, it is important to develop low cost technologies for decontamination processes, keeping high removal efficiencies. Activated carbons obtained from agricultural or industrial sub-products, i.e. wastes, are good alternatives to be used in adsorption based technologies. In Portugal, cork processing is an important industrial sector giving rise to large amounts of cork waste powder. In the last years, we have used this environmental friendly and low cost material as precursor to prepare activated carbons that presented high apparent specific surface areas and good performance when tested as adsorbents for noxious volatile organic compounds [17], [18], [19]. These results justify the evaluation of the potentialities of cork based activated carbons in the removal of pollutants from solution and, in the case of the present study, a PPCP was selected, namely, the ibuprofen. In this way, kinetic and equilibrium adsorption data were obtained and the effect of several experimental parameters (temperature, pH and initial ibuprofen concentration) in the adsorption process was evaluated. Textural and surface chemistry characterization of the adsorbents was also considered and its influence on the liquid phase adsorption performance of the materials is discussed.
Section snippets
Materials
Two activated carbon samples – CAC and CPAC – were prepared using as raw material cork powder waste, as supplied. The CAC sample was obtained by chemical activation of cork with K2CO3, according with the procedure previously optimized [19]. Briefly, cork powder (fraction < 0.297 mm) was mixed with ground K2CO3, in a 1:1 weight proportion, and calcined in a horizontal furnace (Thermolyne, model 21100) under nitrogen flow (5 cm3 s−1). Temperature was raised (10 °C min−1) up to 700 °C and kept for 1 h.
Ash content
Ash content is one characteristic of the activated carbon that can influence its adsorption performance. To reduce the ash content an acid treatment of the raw material is usually the first step in the methodology of the preparation of activated carbons. Besides being time-consuming this step is not an environmental friendly procedure, since it uses large quantities of, usually, 10% solution of H2SO4, what implies the consumption of large volumes of water to leach all the acid.
To check the
Conclusions
In this study, the potentialities of activated carbons prepared from cork waste for ibuprofen removal from liquid phase were evaluated. Two samples of carbon were used: CAC prepared by chemical activation with K2CO3 and CPAC prepared by a two-step activation methodology (chemical activation with K2CO3 followed by steam activation). The preparation procedures led to samples with only small textural differences, but with distinct surface chemistry properties.
The adsorption of ibuprofen onto these
Acknowledgments
This work was supported by FCT (Portugal) through the pluriannual programme of CQB. A.S. Mestre thanks FCT for a Ph.D. grant (SFRH/BD/17942/2004). The authors thank N.R. Neng and F.C.M. Portugal for technical assistance in HPLC measurements, M.L. Pinto for the assistance in the molecular dimensions determination, and Generis Farmacêutica S.A. (Portugal) for the ibuprofen supply.
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