Silver-coated activated carbon nanocomposite by Moringa oleifera for dye removal by multivariate optimization approach

Industrial waste effluent is harmful and hazardous for living organism, environment, and mankind through food web and food chain. This study focused on the degradative removal of organic dyes by novel green method–synthesized silver nanoparticles (AgNPs), where these synthesized nanoparticles were further coated on activated carbon which was prepared by Moringa oleifera seed pods by green approach to modify the surface and enhance its photocatalytic capacity and dye removal efficiency. These AgNPs were characterized through X-ray diffraction (XRD), ultraviolet-visible (UV-Vis) spectrophotometry, scanning electron microscopy (SEM-EDX), and Fourier transform infrared spectroscopy (FTIR). The nanoparticles were used for the photodegradation of methyl blue (MB) and methyl orange (MO) from waste effluent and showed excellent degradation efficiency. Detailed characterization of UV spectrophotometry and XRD techniques confirmed that the AgNP particle size synthesized through green approach is found in the ranges of 200 to 305 nm. Experimental results reveal that silver nanoparticles (AgNPs/AC) had the highest dye degradation removal efficiency for methyl blue and methyl orange and achieved 405 mg/g and 346 mg/g removal capacities accountable to 90% and 77% photodegradation, respectively, in a short period of time of 30 min as compared to previous reported catalysts. The mechanism of adsorption was finest to be defined by the Langmuir isotherm tailed by pseudo-second-order kinetic. The t/q_t versus t plot for pseudo-second-order kinetics yielded a high-regression coefficient (R² = 0.96) that expressed the adsorbate sorption tailed by the pseudo-second-order kinetic. Residual plots for response, interaction plot for response, and contour plots were used to find the optimum point. Moreover, based on the experimental findings, a degradation mechanism was proposed for the photocatalytic degradation of organic dyes with AgNPs/AC catalyst.