No abstract

Textile dyes and microbial contamination of surface water bodies have been recognized as emerging quality concerns around the globe. The simultaneous resolve of such impurities can pave the route for an amicable technological solution. This study reports the photocatalytic performance and the biocidal potential of nitrogen-doped TiO2 against reactive black 5 (RB5), a double azo dye and E. coli. Molecular docking was performed to identify and quantify the interactions of the TiO2 with β-lactamase enzyme and to predict the biocidal mechanism. The sol-gel technique was employed for the synthesis of different mol% nitrogen-doped TiO2. The synthesized photocatalysts were characterized using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET) and diffuse reflectance spectroscopy (DRS). The effects of different synthesis and reaction parameters were studied. RB5 dye degradation was monitored by tracking shifts in the absorption spectrum and percent chemical oxygen demand (COD) removal. The best nanomaterial depicted 5.57 nm crystallite size, 49.54 m2 g−1 specific surface area, 11–40 nm particle size with spherical morphologies, and uniform distribution. The RB5 decolorization data fits well with the pseudo-first-order kinetic model, and the maximum monolayer coverage capacity for the Langmuir adsorption model was found to be 40 mg g−1 with Kads of 0.113 mg−1. The LH model yielded a higher coefficient KC (1.15 mg L−1 h−1) compared to the adsorption constant KLH (0.3084 L mg−1). 90% COD removal was achieved in 60 min of irradiation, confirmed by the disappearance of spectral peaks. The best-optimized photocatalysts showed a noticeable biocidal potential against human pathogenic strain E. coli in 150 min. The biocidal mechanism of best-optimized photocatalyst was predicted by molecular docking simulation against E. coli β-lactamase enzyme. The docking score (−7.6 kcal mol−1) and the binding interaction with the active site residues (Lys315, Thr316, and Glu272) of β-lactamase further confirmed that inhibition of β-lactamase could be a most probable mechanism of biocidal activity.

Bimetallic Cu−Ni/TiO 2 photocatalysts were prepared at different temperatures with varying Cu:Ni mass compositions. The photocatalysts were further calcined at selected temperatures. Characterization procedures were carried out on the photocatalysts to understand the correlation between the photocatalytic activity and the physicochemical and morphological properties. Results from the XRD, FESEM-EDX mapping, and HRTEM analyses were in favor of the metal particles existing in the form of well-dispersed oxides on TiO 2 surface. The surface area of the photocatalysts was almost similar to the bare TiO 2 ∼43 m 2 g −1 except for 1Cu:9Ni-200-b observed with a higher surface area (53.8 m 2 g −1 ) as compared to other photocatalysts. The photocatalyst performance of the bimetallic system is promising as compared to bare TiO 2 and the monometallic photocatalysts. Results for photodegradation studies showed that 1:9 Cu:Ni mass composition was observed with 100% Orange II removal as compared to other Cu:Ni mass compositions. The 1Cu:9Ni-200-a photocatalyst prepared at lower temperature (8−10 °C) displayed 100% Orange II decolorization as compared to 1Cu:9Ni-200-b (prepared at higher temperature of 25 °C) with 65.1% dye removal. Although the results from UV−vis spectra showed the disappearance of the visible band (indicating 100% Orange II removal), TOC analysis indicated the presence of organic compounds derived from the dye degradation process. Therefore, longer irradiation time is required to break the chromophore groups in the degradation intermediates to obtain 100% TOC removal.

A photocatalytic system for decolorization of double azo reactive black 5 (RB5) dye and water disinfection of E. coli was developed. Sol gel method was employed for the synthesis of Fe-TiO2 photocatalysts and were characterized using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS) and Brunauer–Emmett–Teller (BET) analysis. Results showed that photocatalytic efficiency was greatly influenced by 0.1 weight percent iron loading and 300 °C calcination temperature. The optimized reaction parameters were found to be the ambient temperature, working solution pH 6.2 and 1 mg g−1 dose to completely decolorize RB5. The isotherm studies showed that RB5 adsorption by Fe-TiO2 followed the Langmuir isotherm with maximum adsorption capacity of 42.7 mg g−1 and Kads 0.0079 L mg−1. Under illumination, the modified photocatalytic material had higher decolorization efficiency as compared to unmodified photocatalyst. Kinetic studies of the modified material under visible light irradiation indicated the reaction followed the pseudo-first-order kinetics. The illumination reaction followed the Langmuir-Hinshelwood (L-H) model as the rate of dye decolorization increased with an incremental increase in dye concentration. The L-H constant Kc was 1.5542 mg L–1∙h–1 while Kads was found 0.1317 L mg–1. The best photocatalyst showed prominent percent reduction of E. coli in 120 min. Finally, 0.1Fe-TiO2-300 could be an efficient photocatalyst and can provide a composite solution for RB5 decolorization and bacterial strain inhibition.