Adsorption of diclofenac sodium by composite beads prepared from tannery wastes-derived gelatin and carbon nanotubes

Abstract

Diclofenac is an emerging contaminant belonging to the class of pharmaceutical and personal care products, and its presence in drinking water has been reported in several studies nowadays. The adsorption technique has been highlighted due to its operational simplicity, removal efficiency, and low cost, allowing the use of materials of residual origin. Gelatin has favorable characteristics for the production of adsorbent composites, and it can also be obtained from solid wastes from the tannery industry. Thus, this work aimed to produce composite beads based on gelatin recovered from leather wastes tanned with chromium(III) and the addition of carbon nanotubes, to remove diclofenac sodium. For comparison purposes, a composite based on commercial gelatin and carbon nanotubes was also produced. The composite beads were produced using the drip emulsification method. Equilibrium and kinetic tests were performed, and the materials were characterized by Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), Fourier Transform Infrared (FTIR) Spectroscopy, X-ray diffraction (XRD), Point of zero charge (pHpzc), and Swelling and Water retention capacities. The composite based on gelatin recovered from chromium tanned leather waste and carbon nanotubes showed an adsorption capacity of around 20.57 mg g−1, close to the estimated value for commercial gelatin and carbon nanotubes, that was 26.97 mg g−1. The Freundlich model showed a better fit to the experimental equilibrium data. In adsorption kinetics, the Pseudo-second order model better described the kinetic behavior of removing diclofenac sodium by composite beads.