Sunlight-assisted photocatalytic degradation of azithromycin using cellulose nanocrystals–TiO₂ composites

Antibiotics are life-saving drugs that fight bacterial infections by killing or inhibiting their reproduction. However, the overuse and misuse of this drug can contaminate water as it can reach the water surface very quickly through various pathways. The consumption of contaminated water may lead to the development of antibiotic resistance, which has been proliferating across the world recently. Azithromycin (AZM), an essential antibiotic drug, has been identified in wastewater and surface water, prompting apprehension regarding its potential environmental and public health consequences. The present investigation assessed the efficacy of photocatalytic degradation of AZM in water samples under sunlight. Exploiting the surface chemistry and high surface area of cellulose nanocrystals (CNC), nanocomposites with high loading (80 wt%) of titanium dioxide (TiO₂) nanoparticles on a minimal amount of scaffold (20 wt% CNC) were synthesized and used as catalysts. Maximum removal efficiency of 98.8% was achieved in 5 h at a catalyst dose of 175 mg/L for an AZM solution with 10 mg/L concentration. Synthesized CNC–TiO₂ nanocomposites demonstrated superior performance both in terms of high degradation efficiency and lowest catalyst loading per the g of AZM compared the material reported in the literature for the degradation of AZM. In conclusion, CNC–TiO₂ nanocomposites are highly effective catalysts for the photocatalytic degradation of AZM. The developed method further ensures the hygiene of water sources and prevents the spread of antibiotic resistance.