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The occurrence of antibiotics in water systems is now a global problem and has raised concerns about the effects on the natural ecosystem, especially surrounding fish egg production inhibition, sex reversal of males and even human health.
A team of Chinese researchers have now developed a hybrid aerogel material, composed of cellulose nanofibrils and graphene oxide, that can remove up to 21 different kinds of antibiotics through adsorptive mechanisms.
The increasing presence of antibiotics in aquatic ecosystems has not only caused concern, but has driven researchers to find feasible solutions for antibiotic pollution control. Many different types of removal methods have been trialed, but adsorption removal methods have by far been the most effective.
Many materials have been trialed as pollutant adsorbents, but suffer from low removal capacities, difficult separations, secondary environmental pollution and unsatisfactory recycling abilities. The need for a new and efficient material prompted the researchers to create a cellulose nanofibril/graphene oxide hybrid aerogel.
Aerogels are porous nanostructured materials which possess low density, high specific surface area and excellent adsorption properties. However, purely inorganic aerogels have a tendency to be a bit fragile and may collapse. Hybrid aerogels can provide the extra flexibility and stability required for real-world applications.
Hybrid aerogel materials based around cellulose nanofibers (CNF) have gathered particular interest of late, especially as 3-dimensional (3D) absorption structures. This is due to the excellent physical properties that they possess. CNFs as absorbent materials are known to show a high aspect ratio, high surface-to-volume area, flexibility, ductility and a hierarchically porous structure.
Graphene oxide (GO) is a material that has previously been used as an antibiotic absorption material, although not for the absorption of multiple antibiotics. As such, it is an obvious hybrid material to test the potential of CNFs for antibiotic absorption applications.
Aside from previously proving itself, graphene oxide possesses an extreme hydrophilicity, ultrahigh surface area and abundant surface oxygen-containing groups. It is not only ideal for structural benefits, but can also enhance the absorption properties of a hybrid material.
The researchers produced the CNF-GO hybrid material through a one-step ultrasonication method. The interconnected 3D network is composed of 2D graphene oxide nanosheets, grown alongside the CNFs through hydrogen bonding interactions.
The researchers extensively characterized and tested the structures through scanning electron microscopy (FEI Quanta 200), transmission electron microscopy (FEI Tecnai G20), Fourier transform infrared spectroscopy (Nicolet 5700), X-ray diffraction (Rigaku D/MAX 2200), confocal Raman microscopy (WiTec ALPHA 300), X-ray photoelectron spectroscopy (Thermo Fisher Scientific-K-Alpha 1063), thermal analysis (TA Instruments SDT Q600), high performance liquid chromatography (Aglient-1200) and UV-Vis spectroscopy (ERSEE TU-1900).
The hybrid material showed an excellent absorption ability for 21 antibiotics, with the removal rate being a minimum of 69%.
The researchers tested 6 different classes of antibiotics and the absorption efficiencies towards each class was found to be: tetracyclines > quinolones > sulphonamides > chloramphenicols > β-lactams > macrolides.
The absorption mechanism was found to utilize a number of intermolecular interactions including electrostatic attractions, p-π interactions, π-π stacking and hydrogen bonds. Specifically, the absorption capacities for the various antibiotic classes are 454.6 mg g-1 for tetracyclines, 128.3 mg g-1 for quinolines, 227.3 mg g-1 for sulphonamides, 418.7 mg g-1 for chloramphenicols, 230.7 mg g-1 for β-lactams and 291.8 mg g-1 for macrolides.
The researchers also found that the aerogels showed good ease of separation and could be used repeatedly without any obvious degradation in the absorption performance.
The researchers have produced a material that has the potential to solve the issue of antibiotic pollution and could be used in the future as an efficient, economical adsorbent for the removal of antibiotics from wastewater and aqueous ecosystems.
Sources and Further Reading
Yao Q., Fan B., Xiong Y., Jin C., Sun Q., Sheng C., 3D assembly based on 2D structure of Cellulose Nanofibril/Graphene Oxide Hybrid Aerogel for Adsorptive Removal of Antibiotics in Water, Scientific Reports, 7, 45914