Adsorptive removal of Cr(VI) from aqueous solution with green synthesized silver nanoparticle using Justicia schimperiana leaf extract

Abstract

Abstract The pollution of heavy metals in the environment is a critical problem due to their toxicity. Cr(VI) is a toxic substance of widespread use in many industries and mixing with the environment. Silver nanoparticles (AgNPs) were synthesized using aqueous leaf extracts of Justicia schimperiana and trisodium citrate for Cr(VI) adsorption. The nature of bio- and chemo-synthesized AgNPs were characterized and showed the presence of multiple functional groups namely hydroxyl, carbonyl, nitriles, amines, and amides indicating the surface-bound phenolic groups and proteins from Justicia schimperiana leaf and played a crucial role in the biosynthesis, capping, and stabilizing agent of AgNPs. The X-ray diffraction studies confirmed the face-centered cubic structure and indicated the presence of pure crystalline shapes of AgNPs. The silver nanoparticles-Justicia schimperiana leaf extract (AgNPs-GSLE) had a size range of 34.42–37.85 nm with an average size of 36.81 nm and silver nanoparticles-citrate (AgNPs-citrate) had a size range of 11–16 nm with an average size of 14.00 nm with irregular shape and spherical shape in the sample, respectively, similar to the results obtained from the scanning electron microscope. AgNPs-GSLE and AgNPs-citrate were able to perform the maximum adsorption capacity of 128.70 and 34.38 mg/g for the removal of Cr(VI), respectively. The equilibrium results were fitted better to the Langmuir adsorption isotherm model. Cr(VI) adsorption on AgNPs-GSLE followed pseudo-first-order kinetics while AgNPs-citrate followed pseudo-second-order kinetics. The synthesized nanoparticle using Justicia schimperiana extract is promising for Cr(VI) removal from an aqueous solution with a high surface area and green method.

Keywords

• Silver nanoparticles
• Cr(VI)
• Adsorption
• Isotherm
• Justicia schimperiana