Highly recyclable and stable CdS-alginate hydrogel beads towards prevention of oxidative release of nanoparticles in complete photocatalytic disinfection of multidrug-resistant Escherichia coli

Abstract

The use of nanoparticles for alleviating hazardous pathogenic bacteria in wastewater treatment facilities has been on the rise. However, high mobility, agglomeration, and unwanted oxidation of nanoparticles (NPs) remain as major obstacles for practical usage. Recently, much attention has been paid to the encapsulation of photocatalysts in alginate beads to prevent them from escaping into the environment. In this research, the photocatalyst alginate hydrogel encapsulated cadmium sulphide nanorods (CdS NRs) was verified by SEM analysis and the hydrogel bead material was used for disinfecting high strength multi drug-resistant E. coli and reference strain E. coli (ATCC) under blue LED light irradiation of 10 mW cm⁻² intensity. The highest disinfection efficiency was observed for 20–30% catalyst dosage where a reduction of 6 log CFU mL⁻¹ was observed in 100 min and 80 min for the MDR bacteria and reference bacterial strain, respectively. Exhaustive stability analysis was carried out concerning hydrogel bead weight, shape, distortion factor, and mechanical strength before and after 120 min of photocatalysis. The CdS-alginate beads (CdS-ABs) were found to have very good stability as compared to empty alginate beads (empty ABs). Studies on loss of photocatalyst during disinfection depicted only 1.6 mg L⁻¹ of CdS NPs leaching out into external media from the CdS-alginate beads (CdS-ABs). The recovery and reuse data depicted a high activity level of 97% even after 10 cycles of disinfection. The simple operating protocol of washing and reusing the photocatalytic beads makes this approach ideal for eco-friendly applications of nanotechnology as it alleviates concerns about secondary contamination of the environment due to prevention of oxidative release of nanoparticles.