In a paper published in the journal Polymers, novel photocatalysts were synthesized by combining carbon quantum dots (CQDs) with commercial titanium dioxide (TiO2) via sonication. Electrospinning incorporated the resulting TiO2/CQDs composite into polyamide 66 (PA66) nanofibers.
Study: Electrospun Nanofiber Dopped with TiO2 and Carbon Quantum Dots for the Photocatalytic Degradation of Antibiotics. Image Credit: Tayfun Ruzgar/Shutterstock.com
The nanofibers effectively degraded amoxicillin (AMX) and sulfadiazine (SDZ) under simulated solar radiation, significantly reducing their degradation half-lives. The photocatalyst demonstrated consistent efficiency in river water samples over three cycles, suggesting it could be a sustainable solution for antibiotic removal from water.
Related Work
Past work indicated that wastewater treatment plants were ineffective in removing antibiotics like AMX and SDZ, leading to their persistence in aquatic environments and potential antimicrobial resistance. Solar-driven photocatalysis utilizing TiO2 showed promise for efficient antibiotic removal despite rapid electron recombination and recovery issues. Recent research has shown that adding CQDs to TiO2 improves its performance, as does electrospinning photocatalysts into polymer nanofibers to immobilize them.
Synthesis and Characterization of Nanofibers
CQDs were synthesized using a hydrothermal treatment involving citric acid and urea. The mixture was placed in a 70 mL autoclave and heated to 180 °C for five hours after 3.0 g of citric acid and 1.0 g of urea were dissolved in 10 mL of ultrapure water.
Larger particles were then eliminated by centrifugation for 30 minutes at 5000 rpm. The remaining solution underwent purification through 5 to 7 cycles of precipitation using propane-2-ol, followed by centrifugation at the same speed for 10 minutes. Following aggregation, the CQDs were dried at 50 °C after the extra propan-2-ol was eliminated.
The TiO2/CQDs composite was created via a sonication method. First, 1 gram of TiO2 powder was dissolved in 30 millilitres of ethanol in a flask and was ultrasonically treated for five minutes at 70 degrees Celsius. Subsequently, 0.833 mL of a 50 g L−1 aqueous CQD solution was added and allowed to react in the ultrasonic bath for 6 hours at 70 °C, yielding a composite with 4% (w/w) CQDs in TiO2. The final composite was dried at 75 °C.
To prepare PA66 nanofibers incorporating the TiO2/CQDs composite through electrospinning, 0.5 g of PA66 was dissolved in 5 mL of 1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) at room temperature, with stirring at 500 rpm until complete dissolution.
A 0.25 g of TiO2/CQDs was powdered in a mortar, sieved through a 40 µm granulometric sieve, and added to the polymer solution. The mixture underwent ultrasonication for 10 minutes to minimize nanoparticle aggregation, followed by vigorous stirring for uniform dispersion.
At the same time, a 20 kV electric field was applied between the needle and collector positioned 10 cm apart. The fibers were produced at 1:2 TiO2/CQDs to PA66 (w/w), with control fibers made without the TiO2/CQDs composite. The characterization of the nanofibers involved several techniques.
Morphology, size, and composition were analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) with a scanning electron microscope operating at 2 kV. A thin conductive carbon film was applied to the fibers before the SEM analysis.
The average diameter and distribution of fibers were measured from SEM images using ImageJ software. The chemical composition of PA66 and PA66/TiO2/CQDs nanofibers was investigated using Fourier transform infrared (FTIR) spectroscopy, while the crystallinity of the nanofibers was assessed using X-ray diffraction (XRD).
A total organic carbon analyzer was employed to detect pH, salinity, conductivity, total dissolved solids, dissolved oxygen, and organic carbon to determine a range of water matrices utilized in photocatalysis experiments, such as river water and phosphate buffer solution.
Enhanced Antibiotic Degradation Study
The morphological and structural analysis of PA66/TiO2/CQDs nanofibers demonstrated the successful incorporation of the composites. While PA66/TiO2/CQDs fibers showed increased roughness with an average diameter of 300 ± 82 nm, PA66 fibers had a uniform diameter of 253 ± 55 nm, according to SEM pictures.
EDS confirmed the uniform distribution of titanium within the nanofibers. XRD patterns indicated the presence of anatase and rutile phases of TiO2, while FTIR spectroscopy showed retention of polymer peaks and new peaks for Ti-O bonds, confirming effective integration.
Photocatalytic experiments demonstrated enhanced degradation rates of antibiotics with PA66/TiO2/CQDs composites compared to photolysis and bare PA66 fibers. For AMX, the photocatalyst reduced the half-life from 60 ± 1 h without the catalyst to 1.98 ± 0.06 h with PA66/TiO2/CQDs in phosphate-buffered saline (PBS). The study highlighted the effect of organic matter in river water on degradation rates, suggesting that future research should explore photocatalytic degradation mechanisms and byproduct toxicity.
Conclusion
To sum up, the TiO2/CQDs composite was effectively incorporated into PA66 fibers, enhancing the removal of AMX and SDZ under solar irradiation. The half-life of AMX significantly decreased in both PBS and river water with the composite, while SDZ also showed improved degradation rates.
The PA66/TiO2/CQDs demonstrated efficient photocatalytic activity and could be reused for multiple cycles with consistent results. Future studies were recommended to improve wettability and investigate photodegradation mechanisms, byproduct identification, and toxicity.
Journal Reference
Silva, V., et al. (2023). Electrospun Nanofiber Dopped with TiO2 and Carbon Quantum Dots for the Photocatalytic Degradation of Antibiotics. Polymers, 16:21, 2960. DOI: 10.3390/polym16212960, https://www.mdpi.com/2073-4360/16/21/2960
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