Methylene blue removal from aqueous solution using modified Met-SWCNT-Ag nanoparticles: optimization using RSM-CCD

The presence of residual organic dyes in water resources results in a threat for both environment and human health due to their adverse health effects such as mutagenicity, carcinogenicity, and teratogenicity. Thus, they must be removed from industrial wastewater. Among these dyes, methylene blue (MB) is a toxic, carcinogenic, and almost non-biodegradable dye and can pose a significant threat to human health and environmental safety. Thus, it is removed from industrial effluents by a variety of methods, including adsorption, prior to discharge into the environment. This study aims to optimize the adsorption conditions of MB from an aqueous solution with nanocomposite of silver onto single-wall carbon nanotube metronidazole (Met-SWCNTs/Ag). Response Surface Methodology (RSM) based on Central Composite Design (CCD) is used to optimize and model the adsorption of MB dye (as pollutant) on Met-SWCNTs/Ag. The Met-SWCNTs/Ag is synthesized using Met-SWCNT impregnated with silver nitrate. The produced Met-SWCNT/Ag nanocomposite is characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The effect of four independent variables including nanoparticle (NP)/dye ratio, temperature, pH and contact time on MB removal on the specific surface area of SWCNT/Ag and Met-SWCNTs/Ag is evaluated. The accuracy and fit of the model for MB removal using Met-SWCNTs/Ag are estimated by ANOVA with R-2 > 0.99 and P-value < 0.0001. RSM results indicates that the NP/Dye ratio has the most significant influence on the adsorption of MB onto Met-SWCNTs/Ag. The optimal condition of the adsorption process takes place at NP/Dye ratio of 2.21, contact time of 65.57 min, and pH = 6.15 at 25.79 temperature leading into a 98.94 % MB removal. Isotherms and kinetic studies are performed to characterize the adsorption behavior of the adsorbent for MB removal. The adsorption behavior of the MB onto Met-SWCNTs/Ag is best described by the Langmuir isotherm model with regression coefficient R-2 of 0.9935 with the Q(max) of 112.42 mg/g. Adsorption kinetics of Met-SWCNT/Ag is investigated and modelled by means of the pseudo-first-order, pseudo-second-order models which is best fitted to the pseudo-second-order model. The thermodynamic study reveals that the adsorption of MB dye is spontaneous and exothermic. Experimental results suggest that the modified SWCNTs/Ag with Met achieves a higher removal efficiency of (similar to 98 %) when compared to SWCNTs/Ag (similar to 93 %).