Use of phosphorus-doped microporous carbon from olive mill wastewater for effective removal of Crystal violet and Methylene blue

Abstract

In this study, a Phosphorus-doped microporous carbon was prepared from olive mill wastewater and successfully applied to the removal of Methylene blue (MB) and Crystal violet (CV) from an aqueous solution. The development of doped carbon was performed by an original method based on direct pyrolysis with thermal shock/impregnation in H3PO4 at 25 °C, representing a clean and sustainable process. The optimal Phosphorus-doped carbon was obtained at 950 °C with a yield of about 17%. The optimized Phosphorus-doped carbon is microporous, has a high specific surface (1939 m2 g−1) and rich in anionic active sites. Adsorption tests showed a high adsorption capacity, up to 1123 mg g−1 for Crystal violet and 1010 mg g−1 for Methylene blue. The removal rates reached up to 97% and the application in real wastewater treatment showed an efficiency of 69%. The equilibrium data were better fitted to the Langmuir isotherm and the kinetics were better described by the pseudo second order model. The initial adsorption kinetics can reach up to 51 mg g−1.min−1 for Methylene blue and 283 mg g−1.min−1 for Crystal violet. The thermodynamic study showed a physical, spontaneous and endothermic adsorption. The substrates were adsorbed by electrostatic and π- π interactions. Reuse tests showed that this Phosphorus-doped carbon can be used repeatedly. The present work proposes a successful example of conversion of olive mill wastewater to phosphorus-doped microporous carbon for removal of Methylene blue and Crystal violet in an aqueous medium.