Rapid microwave-assisted hydrothermal in situ synthesis of nano-ZnS/kaolinite nanocomposite: A non-toxic photocatalyst active under UV and sunlight

Clay mineral kaolinite (K) is suitable for the immobilization of nano-ZnS leading to increase in its photocatalytic activity (PA). Two synthesis methods, conventional hydrothermal (H) and microwave-assisted hydrothermal (M), and various reaction parameters (six reaction times, three n Zn : n S molar ratios) for nano-ZnS/K nanocomposites were compared. In addition to XRPD, FTIR, DRS and SEM analyses, PA was determined on acid orange 7 under UV irradiation (λ = 365 nm), and for selected samples also under natural sunlight. After 360 min of UV irradiation, PA 98 % (H; 210 min; 1:1) and 90 % (M; 30 min; 1:1) were reached. Under the sunlight, PA 97 % (H; 210 min; 2:1) and 93 % (M; 20 min; 2:1) were achieved after 540 min, respectively. Lipid peroxidation tests revealed the inhibition of peroxidation for all nanocomposites. The non-toxicity and hight PA under sunlight suggest the potential for outdoor use of nanocomposites in water purification or construction industry. • Hydrothermal conventional (H) and microwave-assisted (M) syntheses are compared. • Photoactivity (PA) > 90 % reached after 540 min under sunlight for H and M samples. • PA of nano-ZnS/kaolinite (∼ 40 wt% ZnS) comparable to PA of pure nano-ZnS.