Magnetic carbon-coated palygorskite loaded with cobalt nanoparticles for Congo Red removal from waters

Abstract

Clay-based composites are playing an increasingly important role in dye wastewater treatment. Herein, a modified carbon coated palygorskite (SPal@C) was firstly obtained by etching carbon coated palygorskite (Pal@C) under a small amount of hydrofluoric acid. Then, magnetic Co/SPal@C composites were prepared via impregnation and liquid phase chemical reduction. Adsorption performance of Congo red (CR) was investigated. The maximum adsorption capacity of the Co/SPal@C sample was 458.99 mg/g, which was higher than that of Pal (40.00 mg/g), SPal@C (81.97 mg/g) and Co sample (378.91 mg/g). The adsorption rate constant of the Co/SPal@C sample was up to 26.68 × 10−4 g/min∙mL, which was 3.9 times that of the Co sample (6.90 × 10−4 g/min∙mL). Besides, the magnetic Co/SPal@C adsorbent could allow for efficient magnetic separation from the solution and exhibited excellent regeneration ability. The relative standard deviation of the adsorption capacities for 6 cycles was 1.6%. SPal@C carrier weakened the ferromagnetism of CoNPs and also dispersed CoNPs stably, thus preventing the adsorbent agglomeration during cycling. Enhanced adsorption performance of Co/SPal@C was attributed to the synergistic effect between Co and SPal@C. The chemical interaction and electrostatic attraction between the SO3− group of CR and oxide species (Co3O4 and CoOOH) on the surface of CoNPs dominated the adsorption capacity. SPal@C can effectively disperse and stabilize CoNPs, thus providing more active adsorption sites. The results provided a new path for preparing high-efficiency and easily separable clay mineral-based adsorbents and broadened their application in dye wastewater treatment.