Photocatalytic degradation and transformation of pharmaceuticals using exfoliated metal-free g-C3N4.
Abstract
Pharmaceuticals are micropollutants of global concern that contribute to environmental contamination alongside other anthropogenic and natural chemical compounds. This study addresses the photocatalytic degradation of model pharmaceutical compounds ofloxacin, diclofenac, and caffeine using bulk and thermally exfoliated graphitic carbon nitride (g-C3N4). Bulk g-C3N4 was synthesised from dicyandiamide at 550 °C and exfoliated at 500 °C for 1-3h in ambient atmosphere. The structural, textural, and electronic properties of the prepared materials were evaluated. Graphitic carbon nitride exfoliated for 2h provided the best photocatalytic degradation efficiencies (> 95 %) for both ofloxacin and diclofenac, and approximately 80 % for caffeine, determined for 120 min under irradiation at 420 nm. The pharmaceuticals were degraded, and their intermediate degradation products were investigated using liquid chromatography combined with high-resolution tandem mass spectrometry. The successful identification of the main degradation products allowed us to propose transformation pathways for the studied pharmaceuticals.
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iScience, Volume 28 Supplemental information Photocatalytic degradation and transformation of pharmaceuticals using exfoliated metal-free g-C 3 N 4 Petr Praus, Anna Gavlová, Jan Hrbá� c, Kristina Schmidtová, and Petr Bedná� r
1 Supplemental Information Figure S1. Determination of band gap energies of bulk and exfoliated graphitic carbon nitride according to Tauc´s approach. Figure S2. Photoluminescence decay curves of bulk and exfoliated graphitic carbon nitride. An EPL-375 ps pulsed diode laser (λem = 372 nm) with a pulse width of 66.5 ps, repetition rate of 20 MHz, and average power of 75 μW was used.
2 Figure S3. FTIR spectra of TEX2 treated in 10-30 % hydrogen peroxide solutions for 5 h with a resolution of 2 cm-1. The KBr method was employed. Figure S4. XRD patterns (Co tube) of TEX2 treated with 10-30 % hydrogen peroxide solutions for 5 h. The (002) peaks were shifted from 32.1-32.2 of 2 Theta degrees.
3 Figure S5. XPS spectra of TEX3 treated in 30% hydrogen peroxide using Mg Kα radiation (hν = 1253.6 eV) generated at 12 kV and 10 mA.
4 Figure S6. Set of EPR spectra obtained from the DMPO spin trapping experiment with a bulk graphitic carbon nitride sample. The acquisition time of each spectrum was 30 s with a modulation amplitude of 0.2 mT and a microwave attenuation factor of 10 dB. Figure S7. Set of EPR spectra for the TEX1 sample. The acquisition time of each spectrum was 30 s with a modulation amplitude of 0.2 mT and a microwave attenuation factor of 10 dB.
5 Figure S8. Set of EPR spectra for the TEX3 sample. The acquisition time of each spectrum was 30 s with a modulation amplitude of 0.2 mT and a microwave attenuation factor of 10 dB. Figure S9. Set of EPR spectra from a control experiment involving irradiation of the DMPO spin trap in the absence of graphitic carbon nitride. The acquisition time of each spectrum was 30 s with a modulation amplitude of 0.2 mT and a microwave attenuation factor of 10 dB.
6 Figure S10. Comparison of (A) the maximal PL intensities, (B) specific surface area, and (C) average lifetimes (for two components) of graphitic carbon nitride depending on the exfoliation time. Figure S11. Kinetic curves of the photocatalytic degradation of ofloxacin, diclofenac, and caffeine using TEX3 photocatalysts in the absence of irradiation.
7 Figure S12. X-ray diffraction patterns (Co tube) of TEX3 before and after 3cycles of the photocatalytic degradation of ofloxacin. Figure S13. XPS spectra of TEX3 after 3 cycles of the photocatalytic degradation of ofloxacin using Mg Kα radiation (hν = 1253.6 eV) generated at 12 kV and 10 mA.
8 Table S1. SEM-EDS analysis of bulk and exfoliated g-C3N4 Material C (wt.%) N (wt.%) C/N O (wt.%) Bulk 45.80 51.87 0.883 2.33 TEX1 51.01 46.11 1.11 2.88 TEX2 51.06 46.23 1.10 2.71 TEX3 47.36 50.30 0.942 2.34 Table S2. XPS analysis of bulk and TEX3 g-C3N4 Material C 1s (at. %) O 1s (at. %) N 1s (at. %) C/N Bulk 46.16 3.03 50.81 0.908 TEX3 42.94 1.23 55.83 0.769 TEX3 10% H2O2 42.77 2.10 55.13 0.776 TEX3 30% H2O2 42.22 2.84 54.94 0.768
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