Příprava a charakterizace fotokatalyticky aktivních nanočástic ZnS a nanokompozitů ZnS/kaolinit

Abstract

Environmental pollution by organic substances is one of the burning problems of today. Photocatalytic active materials are able to degrade organic impurities into smaller molecules and, ideally, to water and carbon dioxide. This dissertation focuses on the preparation and characterization of photoactive nanostructured ZnS (nano-ZnS) and composite nano ZnS/kaolinite. Clay mineral kaolinite (K) is used for the immobilization of the photoactive nano-ZnS, while increasing the photocatalytic activity (FA) of the resulting nanocomposite. Influence of reaction conditions on properties of nano-ZnS and composite nano-ZnS/K was investigated. Considering preparation time and energy consumption, the nano-ZnS and composite nano-ZnS/K was synthesized from ZnCl2 and Na2S via conventional hydrothermal (H) and microwave-assisted hydrothermal (M) method with reaction times 90, 150, 210 min and 10, 20, 30 min, respectively. For all reaction times, three nZn:nS molar ratios (1:1; 1.5:1; 2:1) were tested. In the composite nano-ZnS/K precursors (ZnCl2 and Na2S) : K mass ratio was 1:1 for all samples. The same reaction times and nZn:nS molar ratios as in the case of nano-ZnS were tested. Samples were characterized by XRPD, FTIR, Raman microspectroscopy, UV-VIS and SEM. FA was determined on Acid orange 7 under UV radiation (λ = 365 nm), and for selected samples also under the sunlight (SL). After 360 min of UV radiation, FA 96 % (nano-ZnS; H; 210 min; 1:1, 1.5:1 or 2:1) and 92 % (nano-ZnS; M; 30 min; 1.5:1 or 2:1) was reached. Under the SL, FA 96 % (nano-ZnS; H; 210 min; 2:1) and 92 % (nano-ZnS; M; 20 min; 2:1) was achieved after 120 and 540 min, respectively. In comparison, nano-ZnS/K composites were able to achieve similar FA despite having a much lower ZnS content (~40 wt%). After 360 min of UV irradiation, FA 98 % (nano-ZnS/K; H; 210 min; 1:1) and 90 % (nano-ZnS/K; M; 30 min; 1:1) were reached. Under the SL, FA 97 % (nano-ZnS/K; H; 210 min; 2:1) and 93 % (nano-ZnS/K; M; 20 min; 2:1) were achieved after 540 min, respectively. Lipid peroxidation tests revealed the ability to inhibit the peroxidation for all nanocomposites compared to the blank negative control (i.e. solution without sample). The non-toxicity and hight FA under natural SL suggest the potential for outdoor use in water purification or construction industry. In addition, the nanocomposites show similar antibacterial effects against S. aureus and E. coli bacteria, which predicts their possible use as antibacterial agents without using external irradiation to activate the photocatalyst.