Turning PET bottles into adsorbent material for the removal of antibiotics from water

Turning PET bottles into adsorbent material for the removal of antibiotics from water

Scientists in South Korea have turned old plastic bottles into a material that can remove antibiotics from contaminated water, reducing the spread of multi-drug resistance bacteria while addressing plastic waste at the same time.

Their findings have been published in Composites Part B: Engineering. Excess antibiotics from agricultural run-offs can find their way into the water supply, where they encourage the development of multi-drug resistant bacteria.

As the name suggests, these bacteria can withstand virtually all classes of antibiotics, making them potentially deadly pathogens.

Currently, the most well-known method of effectively removing antibiotics from water uses a porous carbon composite, which is made from metal-organic frameworks (MOFs), crystalline structures bonded in two or three dimensions though a coordination bond between metal ions and organic ligands.

However, since the organic ligands used to synthesize MOFs are expensive, porous carbon composites are too costly for widespread use. Instead of using organic ligands, a team of researchers at the Korea Institute of Science and Technology (KIST) turned to polyethylene terephthalate (PET), a material commonly used to make disposable drink bottles. The team, led by Professor Choi Jae-woo at KIST’s Water Cycle Research Center, extracted high-purity organic ligands from waste PET bottles, using them to synthesize an adsorbent material that could remove antibiotics from water.

To obtain pure terephthalic acid from the waste PET bottles, the team used a process called alkaline hydrolysis, enhancing the efficiency with ultrasound. They then used an iron-based MOF as a precursor to magnetise the terephthalic acid, creating a porous carbon composite that could later be easily separated out using an external magnetic field.

When the resulting porous carbon composite was tested for its ability to remove the antibiotic tetracycline from water, the team showed that it was able to remove all traces of the antibiotic within 90 minutes. The adsorption rate of 671.14 mg/g is superior to that of previously developed adsorbents.

To assess the reusability of the porous carbon composite, the adsorption-desorption process was conducted five times. Even after repeated use, the material maintained 90 percent of its adsorption properties, indicating a high degree of stability and wide applicability for water treatment. “The porous carbon composite developed through this research is applicable to various fields, ranging from eco-materials to energy materials, and I expect that it will soon be highly regarded as a value-added eco-material,” Choi said. 

JOURNAL Abstract

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The widespread overuse of antibiotics has led to the serious risks human life and environmental sustainability. Even though porous carbon composite derived from metal-organic framework (MOF) has been recognized as an efficient adsorbent for sequestering antibiotics owing to its unique properties, the major drawback is the use of the expensive material, such as terephthalic acid (H2BDC), as an organic ligand, thus weakening its cost effectiveness and practical applicability.

Herein, we successfully recovered H2BDC from polyethylene terephthalate (PET) waste bottles via ultrasound-assisted, phase-transfer-catalyzed alkaline hydrolysis under mild conditions. The process conditions were statistically optimized by applying response surface methodology (RSM) based on the Box-Behnken design. As results, 99.91–100% H2BDC recovery was achieved under the following optimized conditions: NaOH concentration = 14.5%; temperature = 83.2 °C; and time = 1.5 h.

High-purity H2BDC was used as an organic ligand in the synthesis of magnetic porous carbon (α-Fe/Fe3C) composite derived from iron-based MOF, and its utilization as an adsorbent for the removal of TCH from aqueous solution was investigated. The as-prepared α-Fe/Fe3C composite comprised α-Fe, Fe3C, and graphitic carbon and exhibited mesoporous structure and superparamagnetic behavior, resulting in an effective adsorption performance and magnetic separation. Its adsorption properties were examined in terms of solution pH, contact time, initial TCH concentration, and temperature. Adsorption kinetics and isotherm data were well-suited to the pseudo-second-order and Langmuir models, respectively. Considering its excellent reusability and magnetic separability, the α-Fe/Fe3C composite showed immense potential for antibiotic-contaminated wastewater remediation.