Synthesis using natural functionalization of activated carbon from pumpkin peels for decolourization of aqueous methylene blue

Abstract

In this study, a novel approach was applied for modification and functionalization of pumpkin peels (PP) derived carbon using natural beetroot extract. PP waste biomass was carbonized at 250 (AC250), 350 (AC350), 450 (AC450) and 550 °C (AC550) and used as adsorbent for the scavenging of methylene blue (MB). The adsorption results revealed that AC250 was the most efficient material. Thereafter, AC250 was further modified with different acids and natural beetroot extract to enhance the adsorption efficiency for MB removal. Modified and functionalized carbon materials were characterized to determine the functional groups, crystalline nature and surface morphology of adsorbents using Fourier Transformed Infra-Red spectroscopy, X-ray Diffraction and Scanning Electron Microscopy. The pore size distribution measurements by non-local density functional theory (NLDFT) revealed the presence of large number of mesopores in the beetroot activated carbon (BAC) with the BET specific surface area of 3.6 m2.g−1. The adsorption studies exhibited the highest adsorption (198.15 mg.g−1) for MB using 0.5 g.L−1 of adsorbent mass at 200 mg.L−1 MB concentration and 50 °C within 180 min. Reaction kinetics analysis of the experimental data revealed that adsorption followed pseudo second order kinetic model where BAC250 showed highest reaction rate constant value of 0.0095 and correlation coefficient value of 0.9992. The equilibrium data were tested by using Freundlich and Langmuir isotherm models. For both isotherms, the characteristic parameters were determined and the adsorption behaviour was found to fit well with the Langmuir isotherm model indicating monolayer adsorption of MB.