Bio-inspired preparation of silver nanoparticles on nanostructured sepiolite clay: Characterization and application as an effective adsorbent for methylene blue removal

The removal of widely used dye, i.e., methylene blue (MB), is very important from an environmental viewpoint. In current work, propolis extract was employed as a green reductant to deposit the silver nanoparticles on the surfaces of sepiolite clay (Sep/Ag). The scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques were used to characterize the morphology, crystal phase, and structure of the fabricated nanocomposite. The effect of experimental factors including Sep/Ag dosage (0.01-0.11 g), solution pH (2.0-8.0), contact time (0-90 min), and initial dye concentration (25-500 mg/L) on the adsorption behavior of MB onto Sep/Ag was examined in details. The equilibrium data was studied using Langmuir, Freundlich and Temkin isotherms. Langmuir adsorption isotherm closely matched the MB adsorption. The maximum adsorption capacity of MB was estimated to be 101.0 mg g-1. The kinetic of removal process was investigated using pseudo-firstorder (PFO) and pseudo-second-order (PSO) equations. In kinetic studies, the PSO provided the best fit (R2 = 0.9897), which illustrated that the MB adsorption is limited by chemisorption. In addition, the spent adsorbent can be regenerated successfully up to four cycles. This research presents that the Sep/Ag nanocomposite can be used as an efficient and environment-friendly sorbent for the environmental cleanup.