A study published in Polymers presents a new photocatalyst synthesized by combining carbon quantum dots (CQDs) with titanium dioxide (TiO2) and integrating it into polyamide 66 (PA66) nanofibers. These PA66/TiO2/CQD nanofibers efficiently degraded antibiotics like amoxicillin and sulfadiazine under simulated sunlight, showing potential for sustainable water treatment.
Study: Electrospun Nanofiber Dopped with TiO2 and Carbon Quantum Dots for the Photocatalytic Degradation of Antibiotics. Image Credit: Tayfun Ruzgar/Shutterstock.com
Conventional wastewater treatment plants often struggle to eliminate antibiotics like AMX and SDZ, which allows these compounds to remain in aquatic environments, thereby contributing to antimicrobial resistance.
To address this, solar-driven photocatalysis using TiO2 has emerged as a promising approach for antibiotic degradation. However, this method faces challenges, including rapid electron recombination and issues with catalyst recovery. Recent advancements indicate that combining TiO2 with CQDs could significantly enhance photocatalytic performance. Moreover, embedding these materials in polymer nanofibers through electrospinning could improve their stability and effectiveness by effectively immobilizing the photocatalysts.
Synthesis and Characterization of Nanofibers
For the study, CQDs were synthesized via hydrothermal treatment using citric acid and urea. A solution of 3.0 g citric acid and 1.0 g urea dissolved in 10 mL of ultrapure water was placed in a 70 mL autoclave and heated at 180 °C for five hours. Larger particles were removed by centrifugation at 5000 rpm for 30 minutes. The remaining solution was purified through 5-7 precipitation cycles with propane-2-ol, followed by 10-minute centrifugation at the same speed. The CQDs were then dried at 50 °C after removing excess propane-2-ol.
The TiO2 /CQDs composite was created using a sonication method. A solution of 1 g TiO2 powder in 30 mL ethanol was ultrasonically treated at 70 °C for five minutes. Next, 0.833 mL of a 50 g/L aqueous CQD solution was added and reacted in an ultrasonic bath at 70 °C for six hours, yielding a composite containing 4 % (w/w) CQDs in TiO2. The final product was dried at 75 °C.
For the preparation of PA66 nanofibers with TiO2 /CQDs, 0.5 g of PA66 was dissolved in 5 mL of 1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) at room temperature, stirred at 500 rpm until fully dissolved. A 0.25 g portion of the TiO2/CQDs composite, ground and sieved to a 40 µm particle size, was added to the polymer solution. This mixture was ultrasonicated for 10 minutes to reduce nanoparticle aggregation and then stirred vigorously for uniform dispersion.
Electrospinning was performed with a 20 kV electric field between the needle and collector, set 10 cm apart. The fibers were produced at a TiO2/CQDs to PA66 ratio of 1:2 (w/w), and control fibers were prepared without the composite.
Characterization involved SEM and EDS at 2 kV to analyze morphology, size, and composition, with a conductive carbon film coating applied to the fibers before SEM analysis. Average fiber diameter and distribution were assessed using ImageJ software. FTIR spectroscopy examined the chemical composition of PA66 and PA66/TiO2/CQDs nanofibers, while XRD determined their crystallinity.
Photocatalytic water matrix characteristics, including pH, salinity, conductivity, total dissolved solids, dissolved oxygen, and organic carbon, were measured using a total organic carbon analyzer, examining matrices such as river water and phosphate buffer solutions.
Enhanced Antibiotic Degradation Study
The analysis confirmed the successful incorporation of TiO2/CQDs within PA66 nanofibers. SEM images showed that PA66/TiO2/CQDs fibers had an increased roughness, with an average diameter of 300 ± 82 nm, compared to the uniform 253 ± 55 nm diameter observed in PA66-only fibers.
EDS analysis verified the even distribution of titanium within the nanofibers, while XRD patterns revealed the characteristic anatase and rutile phases of TiO2. FTIR spectroscopy further confirmed effective integration, displaying both preserved polymer peaks and new peaks associated with Ti-O bonds.
Photocatalytic experiments indicated that PA66/TiO2/CQDs composites significantly improved antibiotic degradation rates over photolysis and PA66-only fibers. For example, with AMX, the composite photocatalyst reduced the antibiotic’s half-life from 60 ± 1 hour (without catalyst) to 1.98 ± 0.06 hours in phosphate-buffered saline (PBS). The study also noted the effect of organic matter in river water on degradation rates, emphasizing the need for future research to explore photocatalytic degradation mechanisms and the toxicity of byproducts.
Conclusion
In summary, the TiO2/CQDs composite was successfully integrated into PA66 fibers, resulting in enhanced degradation of antibiotics AMX and SDZ under solar irradiation. With the composite, the half-life of AMX was significantly reduced in both PBS and river water, while SDZ also experienced improved degradation rates.
The PA66/TiO2/CQDs fibers exhibited strong photocatalytic activity and maintained effectiveness over multiple reuse cycles. Future research should focus on enhancing fiber wettability, exploring detailed photodegradation mechanisms, and identifying byproducts and their potential 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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