Silver nanoparticles modified ZnO nanocatalysts for effective degradation of ceftiofur sodium under UV-vis light illumination.

Light-induced photocatalytic degradation of ceftiofur sodium (CFS) has been assessed in the presence of plasmonic zinc oxide nanostructures (ZnONSTs), like, ZnO nanoparticles, ZnO nanorods (ZnONRs) and ZnO nanoflowers (ZnONFs). Silver nanoparticles (Ag NPs) loaded ZnO nanostructures (Ag-ZnONSTs) are obtained through seed-assisted chemical reaction followed by chemical reduction of silver. The surface modification of ZnO nanostructures by Ag NPs effectually altered their optical properties. Further, the surface plasmonic effect of Ag NPs facilitates visible light absorption by ZnONSTs and improved the photogenerated electron and hole separation, which makes the ZnONSTs a more active photocatalyst than TiO2 (P25) nanoparticles. Especially, Ag-ZnONRs showed higher CFS oxidation rate constant (k' = 4.6 × 10-4 s-1) when compared to Ag-ZnONFs (k' = 2.8 × 10-4 s-1) and Ag-ZnONPs (k' = 2.5 × 10-4 s-1), owing to their high aspect ratio (60:1). The unidirectional transport of photogenerated charge carriers on the Ag-ZnONRs may be accountable for the observed high photocatalytic oxidation of CFS. The photocatalytic oxidation of CFS mainly proceeds through •OH radicals generated on the Ag-ZnONRs surface under light illumination. In addition, heterogeneous activation of peroxymonosulfate by Ag-ZnONRs accelerates the rate of photocatalytic mineralization of CFS. The quantification of oxidative radicals supports the proposed CFS oxidation mechanism. Stability studies of plasmonic Ag-ZnONSTs strongly suggests that it could be useful to clean large volume of pharmaceutical wastewater under direct solar light irradiation.

Magnetically recyclable CoFe2O4/ZnO nanocatalysts for the efficient catalytic degradation of Acid Blue 113 under ambient conditions.

CoFe2O4/ZnO magnetic nanocatalysts were synthesized using a low-frequency ultrasound-assisted technique to enhance the optical, morphological, magnetic and catalytic properties of ZnO. The as-synthesized nanocatalysts were characterized by XRD, Raman, TEM, DR-UV-Vis and VSM analyses in order to confirm the expected modifications of the resulting nanocatalysts. The Raman spectral analysis revealed substitutional Zn2+ in the CoFe2O4/ZnO nanocatalyst. The as-synthesized material was tested for its catalytic activity in the degradation of Acid Blue (AB113), a known textile pollutant. The CoFe2O4 and CoFe2O4/ZnO nanocatalysts revealed the efficient catalytic degradation of AB113 in ambient conditions. The nanocatalyst dosage and the initial concentration of AB113 were varied by fixing one parameter as constant in order to determine the maximum catalytic efficiency with the minimum catalyst loading for AB113 degradation. The CoFe2O4/ZnO nanocatalyst demonstrated 10-fold enhanced mineralization of AB113 compared to the individual bare nanocatalysts, which could be achieved within 3 hours of catalytic degradation of AB113. The magnetic CoFe2O4/ZnO nanocatalyst was found to be stable for six consecutive recycles of AB113 degradation, which indicates that the catalytic efficiency of the nanocatalyst was retained after various numbers of cycles.

Ultrasmall Plasmonic Nanoparticles Decorated Hierarchical Mesoporous TiO2 as an Efficient Photocatalyst for Photocatalytic Degradation of Textile Dyes.

Hierarchical mesoporous TiO2 was synthesized via a solvothermal technique. The sonochemical method was adopted to decorate plasmonic nanoparticles (NPs) (Ag, Au) on the pores of mesoporous TiO2. The crystallinity, structure, and morphology were determined to understand the physicochemical nature of the nanocomposites. The catalytic efficiency of the plasmonic nanocatalysts was tested for the azo dyes (congo red, methyl orange, acid orange 10, and remazol red) under solar and visible light irradiations. The generation of hydroxyl radicals was also studied using terephthalic acid as a probe molecule. An attempt was made to understand the influence of size, work function and Fermi level of the metal NPs toward the efficiency of the photocatalyst. The efficiency of the nanocomposites was found to be in the order of P25 < mesoporous TiO2 < mesoporous Ag-TiO2 < mesoporous Au-TiO2 nanospheres under both direct solar light and visible light irradiation. The results indicated that the adsorption of dye, anatase phase, and surface plasmon resonance of NPs favored the effective degradation of dyes in aqueous solution. Further, the efficiency of the catalyst was also tested for xanthene (rose bengal), rhodamine (rhodamine B, rhodamine 6G), and thiazine (methylene blue) dyes. Both TiO2 and NPs (Ag & Au) possess a huge potential as an eco-friendly photocatalyst for wastewater treatment.

Sonochemical synthesis of porous NiTiO3 nanorods for photocatalytic degradation of ceftiofur sodium.

Porous NiTiO3 nanorods were synthesized through the sonochemical route followed by calcination at various temperature conditions. Surface morphology of the samples was tuned by varying the heat treatment temperature from 100 to 600°C. The synthesized NiTiO3 nanorods were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, diffused reflectance spectroscopy, photoluminescence spectroscopy and Brunauer-Emmett-Teller (BET) analyses. The characterization studies revealed that the NiTiO3 nanomaterial was tuned to porous and perfectly rod shaped structure during the heat treatment at 600°C. The porous NiTiO3 nanorods showed visible optical response and thus can be utilized in the photocatalytic degradation of ceftiofur sodium (CFS) under direct sunlight. The photoluminescence intensity of the porous NiTiO3 nanorods formed while heating at 600°C was lower than that of the as-synthesized NiTiO3 sample owing to the photogenerated electrons delocalization along the one dimensional nanorods and this delocalization resulted in the reduction of the electron-hole recombination rate. The photocatalytic degradation of ceftiofur sodium (CFS) was carried out using NiTiO3 nanorods under the direct sunlight irradiation and their intermediate products were analysed through HPLC to deduce the possible degradation mechanism. The porous NiTiO3 nanorods exhibited an excellent photocatalytic activity towards the CFS degradation and further, the photocatalytic activity was increased by the addition of peroxomonosulfate owing to the simultaneous generation of both OH and SO4-.

High surface area Ag-TiO2 nanotubes for solar/visible-light photocatalytic degradation of ceftiofur sodium.

Titanium dioxide nanotubes (TiO2 NTs) with very high surface area (469 m(2)/g) have been synthesized through a simple hydrothermal method and their surface has been modified using silver nanoparticles (Ag NPs). The Ag NPs deposited TiO2 NTs (Ag-TiO2 NTs) show an extended optical response from UV to visible region coupled with a surface plasmon resonance band and thus can be utilized as a plasmonic photocatalyst. The photoluminescence intensity of TiO2 NTs is lower than that of TiO2 nanoparticles due to the delocalization of photogenerated electrons along the one dimensional nanotubes which reduces the rate of charge recombination. The Langmuir adsorption constant of Ag-TiO2 NTs (for ceftiofur sodium adsorption) is twice that of P25 TiO2. The Ag-TiO2 NTs exhibit excellent photocatalytic activity toward the degradation of ceftiofur sodium (CFS) due to high surface area and mesoporosity of TiO2 NTs. The addition of peroxomonosulfate in the photocatalytic system greatly amplifies the CFS degradation owing to the simultaneous generation of both OH and SO4(-). The catalyst retains its photocatalytic activity at least up to four consecutive cycles.