Abstract

The hydrophilic and hydrophobic single-walled carbon nanotube membranes were prepared and progressively applied in sorption, filtration, and pertraction experiments with the aim of eliminating three antibiotics—tetracycline, sulfamethoxazole, and trimethoprim—as a single pollutant or as a mixture. The addition of SiO2 to the single-walled carbon nanotubes allowed a transparent study of the influence of porosity on the separation processes. The mild oxidation, increasing hydrophilicity, and reactivity of the single-walled carbon nanotube membranes with the pollutants were suitable for the filtration and sorption process, while non-oxidized materials with a hydrophobic layer were more appropriate for pertraction. The total pore volume increased with an increasing amount of SiO2 (from 743 to 1218 mm3/g) in the hydrophilic membranes. The hydrophobic layer completely covered the carbon nanotubes and SiO2 nanoparticles and provided significantly different membrane surface interactions with the antibiotics. Single-walled carbon nanotubes adsorbed the initial amount of antibiotics in less than 5 h. A time of 2.3 s was sufficient for the filtration of 98.8% of sulfamethoxazole, 95.5% of trimethoprim, and 87.0% of tetracycline. The thicker membranes demonstrate a higher adsorption capacity. However, the pertraction was slower than filtration, leading to total elimination of antibiotics (e.g., 3 days for tetracycline). The diffusion coefficient of the antibiotics varies between 0.7–2.7 × 10−10, depending on the addition of SiO2 in perfect agreement with the findings of the textural analysis and scanning electron microscopy observations. Similar to filtration, tetracycline is retained by the membranes more than sulfamethoxazole and trimethoprim.

Highlights

  • Even though most of this water goes through wastewater treatment plants (WWTP), or sludge treatment plants, a portion of these pharmaceuticals remain in the water effluent of the treatment plants

  • The single-walled carbon nanotubes (SWCNTs) membranes were grafted on a top-layer using the hydrophobic hyper fluorinated monomer HFBM attenuated total reflection (ATR)

  • black phosphorus (BP) slowed down the tests, but the addition of SiO2 allowed a transparent study of how the porosity influences the separation processes

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Summary

Introduction

Emerging contaminants (ECs) have become a major threats to global water quality. A specific subcategory of ECs [3] represents pharmaceuticals. Compounds, such as antibiotics (ATBs), β-blocker hormones, blood lipid regulators, analgesics, and anti-inflammatory or cytostatic drugs, are widely used in daily life [4,5,6]. Even though most of this water goes through wastewater treatment plants (WWTP), or sludge treatment plants, a portion of these pharmaceuticals remain in the water effluent of the treatment plants. The effluent is usually released to environmental surface waters (streams, rivers, lakes, reservoirs, and wetlands) [8,9] where the ATBs can be detected [10,11,12,13]

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