Fabrication of Ag nanoparticles modified TiO2-CNT heterostructures for enhanced visible light photocatalytic degradation of organic pollutants and bacteria

TiO2 synthesized using polymeric template consisting of polyethylene glycol and polyvinyl alcohol (Tev) and loaded with different wt% of Ag (2%, 6%) was exploited to create covalent bonds with carboxylate functionalized SWCNT/MWCNT moieties. The synthesized Ag free Tev-SWCNTs as well as Ag containing Tev-SWCNTs/MWCNTs have been characterized by UV-visible diffuse reflectance, powder XRD, HRTEM, and selected area electron diffraction (SAED), photoluminescence, Raman, FTIR and N2 sorptiometry. The materials containing Ag displayed high photocatalytic activity towards degradation of rhodamine B dye under visible irradiation (λmax > 450 nm). Specifically TevAg6-SWCNT has shown the best performance (0.3 g/l catalyst, 20 ppm RhB conc. and 80 min reaction time) due to the synergistic effects derived from TiO2/Ag°/SWCNT heteroarchitectures. The antibacterial activity of synthesized photocatalysts; under visible light irradiations, towards Escherichia coli and Staphylococcus aureus was tested by performing bacterial DNA and agar well diffusion method. The results revealed that TevAg6-SWCNT was able to effectively kill both gram-positive and gram-negative bacteria. Although TevAg6-SWCNT indicated higher Eg values (1.9 eV) than TevAg2-MWCNT (1.75 cV) and they both exposed not only Ag° nanoparticles but also Ag2O, the former sample confirmed more lethal action against bacterial growth as well as superior photodegradation activity. This was due to delaying the recombination of electrons and holes, increasing the SBET value as well as decreasing the spherical nanoparticles of Ag° to 3 nm diameter. The mechanisms of the dye degradation and destruction of bacterial cell membranes indicate the efficacy of OH and O2− as reactive radical intermediates in both processes.