Elsevier

Chemical Engineering Journal

Volume 255, 1 November 2014, Pages 23-27
Chemical Engineering Journal

Adsorption of antibiotics and iopromide onto single-walled and multi-walled carbon nanotubes

https://doi.org/10.1016/j.cej.2014.06.035Get rights and content

Highlights

  • Lincomycine, sulfamethoxazole, and iopromide adsorbed onto CNT.

  • Freundlich isotherm model well fit adsorption of all target compounds.

  • Adsorption of target compounds more onto single walled CNT than multi-walled CNT.

  • Higher specific surface area of single walled CNT causing it to adsorb more organics.

Abstract

Engineered carbon nanotubes (CNTs) have shown a great promise for many remediation applications. The adsorption of two antibiotics (lincomycine and sulfamethoxazole) and one contrast medium (iopromide) on single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT) was investigated using batch adsorption experiments. These selected pollutants have high detection frequencies in aquatic environments. The adsorption results were compared with those of conventional powdered activated carbon (PAC). Adsorption isotherms for all pollutants on CNTs and PAC were nonlinear and could be described reasonably well with the Freundlich isotherm model. The adsorption generally followed the order SWCNT > PAC > MWCNT. The relatively low adsorption on MWCNT was probably due to its lower specific surface area than other carbon materials. However, correlation of adsorption to the surface area of carbon materials suggests other factors such as properties of adsorbate and type of interaction between pharmaceuticals and CNTs may also contribute to the adsorption processes. Implications of the adsorption results for the removal of pharmaceuticals from aqueous solution using CNTs are briefly discussed.

Introduction

There is an increasing concern on the impact of pharmaceuticals on drinking water supplies, which are usually not easily biodegradable and pose a risk of their deleterious effects to human beings and ecosystems [1], [2], [3], [4]. Among the various pharmaceuticals, antibiotics have raised issues of antibiotic resistant bacteria and genes in the aquatic environment [5], [6], [7], [8], [9]. Besides antibiotics, there is also a concern on X-ray contrast medium, which has been detected in wastewater effluents, surface water, and drinking water at concentrations ranging from 0.5 to 15 μg L−1 [4], [10], [11], [12]. Wastewater treatment plants (WWTPs), which receive waste from hospitals or radiological clinics, have particularly shown high concentrations. Removal of pharmaceuticals and the contrast medium in water is immense important to meet the urgent need to clean water. Effective and sustainable water treatment technologies are critically required to meet the global demand of purified water.

Since the discovery of carbon nanotubes (CNTs) in 1991, engineered CNTs have shown great potential in many medical and environmental remediation applications [13], [14]. CNTs contain cylindrical graphite sheets, which have very high van der Waals index [15]. The benzenoid rings of graphite sheets have sp2-hybridized carbon atoms with high polarizability. These properties of CNTs make them superhydrophobic materials that may also strongly interact with aromatic pollutants through ππ coupling/stacking [16], [17]. Examples include nitroaromatics and amino- and hydroxyl-substituted aromatic compounds [18], [19].

Studies on adsorption of pharmaceuticals onto CNTs are forthcoming [20], [21], [22], [23], [24]. The focus of the present study is on the removal of selected pharmaceuticals and a contrast medium through their adsorption onto CNTs, which have different structural and surface properties. The antibiotics under study were lincomycine (LCN) and sulfamethoxazole (SMX), which have amide and sulfonamide moieties, respectively (Table 1). The contrast medium was iopromide (IPR) that has also amide moieties (Table 1). These pollutants have been detected in water and wastewaters [4]. The tested CNTs for sorption experiments were single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs). The experiments with powdered activated carbon (PAC) were also performed for the comparative purpose. Sorption studies on SMX using CNTs have been carried out [20], but no similar studies with LCN and IPR are known in literature. The objectives were (i) to investigate the sorption behavior of the selected pharmaceuticals onto CNTs, (ii) to understand the influence of particle size and surface area of engineered carbon materials on the interaction between the studied molecules and CNTs, and (iii) to evaluate the potential of CNTs for enhanced removal of micropollutants.

Section snippets

Standards and reagents

SWCNTs (purity > 95%, length 1–5 μm, and outer diameter 1.5 nm) and MWCNTs (purity > 95%, length 1–5 μm, and outer diameter 15 ± 5 nm) were purchased from Nano Lab (Newton, MA, USA) and were used without further purification. Based upon the information provided by the manufacturer, both CNTs have a hollow structure and were produced by a conventional chemical vapor deposition (CVD) method. Coconut-based PAC was obtained from Dongyang Carbon Co., Korea (Cheonan, Korea). Prior to use, the PAC was ground to

Characteristics of adsorbents

The structural properties of carbon materials used in the study are given in Table 2. Both CNTs have similar lengths, but differ in outer diameter and BET surface areas (Table 2). The BET surface area of SWCNT is approximately four times higher than that of MWCNT. Comparatively, the BET surface area of PAC is the highest; a slightly more than that of SWCNT. The size of PAC used in this study is 60–140 mesh (100–250 μm).

Adsorption of LCN

Initially, adsorption kinetics using LCN was performed on all three

Conclusions

CNTs and PAC could effectively adsorb the three pollutants. The adsorption of LCN by different material was almost complete within 100 h and the adsorption kinetics had two phases, rapid step was followed by a relatively slow step. Among the different materials, SWCNT has higher potential to adsorb LCN, SMX, and IPR than MWCNT and PAC. The surface area of the material significantly controlled the adsorption of the pollutants, but other factors including the moieties on the pollutants may also

Acknowledgments

This work was supported by the R&D program of MOTIE/KEIT (R&D program No. 10037331, Development of Core Water Treatment Technologies based on Intelligent BT-NT-IT Fusion Platform). Dr. Huang is partially supported by the Korea Institute of Toxicology, Korea (Project No. KK-1403-02, Environmental Risk Assessment of Manufactured Nanomaterials). Finally, authors wish to thank anonymous reviewers for their comments, which improved the paper greatly.

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