Dual functional covalent triazine framework-TiO2 S-scheme heterojunction for efficient sequestration of ciprofloxacin: Mechanism and degradation products
Omoyemen Oyegbeda, Samson O. Akpotu, Brenda Moodley
Abstract
The development of adsorbent and/or photocatalysts based on covalent triazine frameworks (CTF) is fascinating research due to their structural properties, functional groups, and active sites. Herein, a CTF-TiO 2 heterojunction was synthesized by modifying CTF sheets with TiO 2 particles through wet impregnation technique and adsorptive and photocatalytic activities determined for ciprofloxacin (CIP) removal. Comprehensive characterisation of the composites revealed suitable properties of the composites, such as sandwich-like CTF-TiO 2 morphology, improved thermal stability, and better heteroatom effect (HAE). The adsorption capacity of CTF-TiO 2 -1 (CT-1) and CTF-TiO 2 -2 (CT-2) reached 30.30 mg g -1 and 13.61 mg g -1 , respectively. Meanwhile, the CT-2/H 2 O 2 system, compared to all other materials, achieved a better degradation efficiency of 90.7 % within 40 min compared to 77.5 % observed in using only CT-2 for 120 min. In addition, scavenging results suggested that e - and h + was crucial for the effective degradation of CIP. Identification of the degradation product of CIP suggests hydroxylation, decarboxylation, and opening of the quinolone and piperazine ring as possible degradation pathways. The mineralization of CIP was 90.93 % for the CT-2/H 2 O 2 system and its stability maintained for four cycles. The outstanding performance of CT-2 is attributed to its enhanced band gap energy of 2.86 eV, and reduced recombination rate of photogenerated electrons and holes. These results prove these materials are efficient adsorbent/photocatalyst in CIP removal from solution. • TiO 2 nanoparticles sandwiched on CTF sheets through wet impregnation technique. • Adsorption capacity was 30.3 mg g -1 and 13.6 mg g -1 for CT-1 and CT-2, respectively. • CIP degradation reached 90.7 % in the CT-2/H 2 O 2 system. • CIP degradation routes include decarboxylation and ring cleavage. • The S-scheme mechanism preserved the redox potential of CT-2/H 2 O 2 system.