Comparative Study on Adsorption of Crystal Violet and Chromium (VI) by Activated Carbon Derived from Spent Coffee Grounds

In the context of the circular economy, used coffee grounds were transformed into powdered activated carbon by chemical activation using potassium hydroxide. Its characterisation was conducted in comparison with that of a commercial activated carbon by scanning electron microscopy (SEM) coupled with energy dispersive X-ray microanalysis (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Boehm titration, and point zero charge (pH(PZC)) and by determination of the methylene blue number (MBN) and the iodine number (IN). Performance of the prepared activated carbon was tested in the adsorption of the cationic dye crystal violet (CV) and hexavalent chromium. Batch adsorption tests were carried out and the effects of operating parameters were studied. The results collected on the adsorption kinetics show that the adsorption followed pseudo-second order kinetics and that the Langmuir isotherm best fits the equilibrium data for crystal violet and hexavalent chromium. The thermodynamic study showed that the adsorption of both adsorbates is spontaneous and exothermic and leads to a decrease in disorder at the solid-liquid interfaces. These results indicate that this activated carbon can be used as an alternative adsorbent to remove cationic dyes and heavy metals from aqueous solutions.

Automated summary

In this study, used coffee grounds were chemically activated to produce powdered activated carbon, which was compared with commercial activated carbon. The activated carbon was characterized using various techniques and its performance in adsorbing crystal violet and hexavalent chromium was tested. The results showed that the adsorption followed pseudo-second order kinetics and the Langmuir isotherm best described the equilibrium data. Thermodynamic analysis revealed that the adsorption process was spontaneous, exothermic, and resulted in a decrease in disorder at the solid-liquid interfaces. This study suggests that the prepared activated carbon can be utilized as an alternative adsorbent for removing cationic dyes and heavy metals from aqueous solutions.