Synthesis of Boron and Cerium Codoped Titanium Dioxide Photocatalysts For Antibiotic Degradation And Microbial Disinfection Under Solar Light

Abstract

n recent years, antimicrobial resistance has been a global emerging problem due to the emergence of superbugs which poses a major threat to human health and the environment. The presence of antibiotic residues is the primary source of this emerging problem. Photocatalysis, for decades, has been a promising treatment technology in removing recalcitrant organic compounds from the environment. In this study, a systematic series of B and Ce monodoped (0.1 and 1 at.% Ce-TiO2, 1 and 2 at.% B-TiO2) and codoped (BxCe1-xTiO2, x = 0.9, 0.8 and 0.7 at.%) catalysts were synthesized using a facile green EDTA-citrate method. The synthesized catalysts were evaluated for the degradation of ciprofloxacin (CIP, antibiotic) and disinfection of E.coli under sunlight in both suspended and immobilized forms. For immobilization, waste expanded polystyrene (EPS) beads were used as a substrate along with the best performing codoped catalyst. The catalysts were characterized for particle size, BET surface area, surface morphology (SEM and TEM analysis), crystal structure (XRD analysis), surface chemistry (XPS and RAMAN analysis), bandgap (DRS analysis), and recombination (PL analysis). XRD analysis showed anatase rutile and Ce peaks, and no B peaks were detected which is due to the difference in ionic radius of the dopants. From XPS analysis, the elemental compositions of the doped catalysts (suspended form) and the actual amount of photocatalyst added during the film preparation (immobilized form) were in accordance with the selected compositions. Lesser recombination with lower PL intensity was observed for the doped catalysts. The reaction parameters such as catalyst loading, initial concentrations of antibiotic, mineralization (COD/TOC reduction), and reusability were studied, and the degradation pathways were elucidated (LC-MS analysis). The degraded sample was evaluated for the residual antibacterial activity to confirm the degradation of antibiotic. Real water matrices (tap water and river water) were considered in the study. Among the monodoped series, highest degradation of 93.22% was shown by 1 at.% Ce-TiO2 and 93.16% by 1 at.% B-TiO2 after 180 min. Whereas, among the codoped series of catalysts, B0.8Ce0.2TiO2 showed the highest degradation of 97.43% (suspended form) and 81.36% (immobilized form) after 180 min. Immobilized form ii showed 89.17% degradation of CIP at the end of 240 min. In terms of disinfection, the codoped catalyst was found to be 10 times more effective (corresponding to 1 log higher reduction) than the monodoped catalysts. Low molecular weight and less harmful degraded products were observed from LC-MS analysis. Reusability studies up to five consecutive runs proved the stability of these catalysts both in suspended and immobilized forms. The active role of electrons, holes, and OH ̇ species in the degradation was observed from the scavenging studies. The degradation and disinfection efficiencies in the real water samples were slightly lesser than the deionized water, which might be due to the presence of anions and natural organic matter. The performance of the codoped catalysts (in terms of both degradation and disinfection) was better than monodoped catalysts and superior when compared to TiO2. Overall, these boron and cerium (monodoped and codoped) doped catalysts can serve as an efficient solar light active catalysts for both antibiotic degradation and bacterial disinfection.