<i>β</i>-In₂S₃ Quantum dots embedded in cation- exchange membrane for visible light driven photocatalytic microbial disinfection: enhanced ballast water treatment efficiency

Abstract This paper presents the visible-light driven photocatalytic disinfection of microorganisms in seawater using metal chalcogenide organic frame work. The microbial disinfection process which is induced by the photo-generation of reactive oxygen species does not produce any chemical by-products. Tetragonal β -In 2 S 3 quantum dots (5 nm–10 nm) with orientation along [206] plane is embedded in perfluorinated cation exchange membrane (Nafion-117) through Grothuss mechanism. The synthesis conditions were optimized with an In/S ratio of 2/2, a reaction temperature of 70 °C, and a reaction time of 2 h. Nafion preserves the stability, integrity, and reusability of the quantum dots for up to three cycles, as confirmed by the absorption spectra of the films under seawater conditions (pH-8.02; Total Dissolved Solids (TDS) -27680 mg/l). The Raman active modes at E g (ω 3 ), A 1 , A 1g , A 1g (ω 4 ) and F 2 g (ω 5 ) symmetry correspond to the defect-spinel lattice of β -In 2 S 3 . With a wide band gap of 2.73 eV, β -In 2 S 3 quantum dots has intense and broad photoluminescence at 446 nm, 465 nm, 500 nm, 542 nm and 655 nm corresponding to defect bands with energy in the visible region of the electromagnetic spectrum. The presence of sulfur and indium vacancies enhances the efficiency of the photocatalyst, by increasing the kinetics of the disinfection process (100% disinfection within 90 min). The microbiological analysis of the sea water done via spread plate technique confirms complete disinfection from initial count of microbes: 4370 cfu/ ml in Zobell Marine Agar and 1910 cfu/ ml in Nutrient Agar. Further, the UV transmittance at 254 nm (65%) reveals the aggregate of organic matter in untreated seawater which increases to 100% upon treatment.