Single and mixture adsorption of clofibric acid, tetracycline and paracetamol onto Activated carbon developed from cotton cloth residue
Graphical abstract
Introduction
Pharmaceuticals drugs are a class of emerging environmental contaminants (Malakootian et al., 2016a) that are extensively and increasingly being used in human and veterinary medicine, agriculture and aquaculture practices. The continuous discharge and occurrence of pharmaceutical drugs in the aquatic ecosystem has become a major problem due to their long persistent period in the environment (Saravanana et al., 2014). These features among others make pharmaceuticals to be evaluated for potential effects on aquatic flora and fauna (Fent et al., 2006).
Low concentrations of pharmaceutical compounds (PhACs) in the environment, which are typically at trace levels (ng L−1 to μg L−1), and the lack of suitable sensitive methods of analysis in the past, have been the main reasons for the recent interest emergence in these compounds (Dordio et al., 2009, Malakootian et al., 2016b, Malakootian et al., 2016c). However, despite low environmental concentrations, PhACs can still induce adverse effects due to cumulative effects and continuous exposure that occurs especially in aquatic ecosystems (Dordio et al., 2009).
These increasing ecotoxicological impacts on organisms in the aquatic and terrestrial environment may include development of antimicrobial resistance, decrease in plankton diversity, and inhibition of growth of human embryonic cells (Zhang et al., 2014, Nawab et al., 2015). In the meantime, the adverse effect caused by chronic aquatic toxicity on Daphnia, algae, higher aquatic plant and bacteria has also been demonstrated.
The most commonly detected pharmaceuticals in the aquatic environment include antibiotics, anti-inflammatory drugs, lipid-lowering agents and anticonvulsants. Various methods have been used to remove these molecules in conventional wastewater treatment plants, including biological processes, filtration, coagulation/flocculation/sedimentation (Malakootian et al., 2015, Malakootian et al., 2016a) and Advanced Oxidation Processes (AOPs). However, the high cost, the requirement for expensive equipment and high reagent or energy requirement limits their use. In addition, AOPs can lead to by-products that are more toxic than the original pollutant. When treating wastewater, adsorption is considered effective because of its simple application and low operational costs (Malakootian et al., 2014). However, the most used adsorbents in this process are activated carbons which are costly. Therefore, there is a high interest in using alternative adsorbents that are inexpensive (Malakootian et al., 2015).
In this sense, the use of largely available residues as precursors of low-cost carbon adsorbents, as is the case of cloth, is an interesting strategy that additionally enables to deal with the problem of waste disposal and recycling. Currently, the major precursors for producing ACCs are composed of synthetic materials such as acrylic, nylon and polyester fibers and natural materials such as wool, flax, viscose and cotton.
The preparation of activated carbon from textile waste by physical or chemical activation is very important from the industrial point of view. Activated carbon can be produced from a variety of carbonaceous materials by either physical or chemical activation processes (Halder et al., 2015). Physical activation involves carbonization of carbonaceous materials followed by activation of the resulting char using gas activating agents (Halder et al., 2014), while in chemical activation, both of carbonization and activation take place at the same stage in the presence of chemical agents. Two important advantages of chemical activation, in comparison to physical, are the lower temperature (usually around 400–600 °C) compared to physical activation (800–1000 °C), in which the process is accomplished and the greatest of the carbon yield is obtained (Sudaryanto et al., 2006).
The nature of activating agent has a great influence on the pore development and surface characteristics of the activated carbon. It also plays a decisive role in affecting the yield and adsorption performance. Although, microporous structure (<2 nm) is generally desired for adsorption, the presence of mesopores (2–50 nm) is also valuable for large molecules or where a faster adsorption rate is required.
Many researchers illustrated the effects of activating agents on yield and pore characteristics of activated carbons. Boudrahem et al. (2011) optimized preparation conditions of activated carbon by H3PO4 chemical activation. Carbon with 1003 m2 g−1 surface area, 0.618 cm3 g−1 total pore volume was obtained at 600 °C, 60 min, and 1 g g−1 Impregnation ratio. The structure was composed of micropores volume of 0.423 cm3 g−1 and microporosity of 68.44%. On the other hand, ZnCl2 chemical activation resulted in a microporous carbon with a surface area of 889 m2 g−1, and average pore diameter of 3.44 nm. It was reported that H3PO4 activation of biomass efficiently produced microporous carbon with greater surface area compared to mesoporous structure with higher pore volumes and diameter by ZnCl2 activation. H3PO4 impregnation agent was preferred since ZnCl2 could give unfriendly environmental impact (Asadullah et al., 2007) and unsuitable activated carbon for food and pharmaceutical industries (Al-Qodah and Shawabkah, 2009). It was also found that the use of H3PO4 provided higher yield (Romero-Anaya et al., 2012) and basically required low activation temperature to produce a higher grade carbon (Al-Swaidan and Ahmad, 2011).
This study presents a simple process for the development of a novel activated carbon from cotton waste with good physico-chemical properties allowing the effective elimination of several types of molecules of pharmaceutical origin. After the preparation and the characterization of the adsorbents prepared, the removal of AC, TC and PC by adsorption from aqueous solution was investigated.
Section snippets
Materials
Cotton cloth waste was used as precursor in the preparation of activated carbons. Nitrogen gas was industrial grade of 99% purity. The reagent grade chemicals used in the study (H3PO4, H2SO4, NaCl, HCl, NaOH, Na2HPO4, KH2PO4, KBr, NaNO3) were purchased from Aldrich and Junsei chemical companies.
Three pharmaceuticals were selected in this research as target compounds: AC (lipid regulator), PC (nonsteroidal anti-inflammatory drugs), TC (antibiotic) all were purchased from Aldrich. These
Textural characteristics of activated carbon
The N2 adsorption–desorption isotherms displayed in Fig. 1 are representative of the results obtained in this study and reveal the essentially microporous nature of the materials. The isotherms of activated carbon produced from cotton using phosphoric acid at 25%, 50% (ACC 25% and ACC 50%) are the type I, according to the IUPAC classification (Gil et al., 1985) since they present a marked knee in the low relative pressure region, and a very low slope in the multilayer, indicating a low external
Conclusion
This study investigated the feasibility of preparation of a new activated carbon form cotton cloth residues, as a low-cost and efficient adsorbent for pharmaceuticals compounds adsorption. The optimum experimental conditions to prepare predominantly microporous activated carbons (ACCs) with high surface area (up to 1175 m2 g−1) and total volume (0.616 cm3 g−1) were an impregnation ratio (mass of H3PO4/mass of precursor) of 50% and a pyrolysis temperature of 600 °C during 1 h. The adsorbents exhibit
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