Coconut shell-based activated carbon for wastewater treatment

Abstract

Introduction: Adsorption is an emerging technique for wastewater treatment utilizing abundantly available biomass (especially agricultural wastes) (1-2). Coconut-based agricultural wastes have gained wide attention as effective adsorbents due to low-cost and significant adsorption potential for the removal of various aquatic pollutants. The activation of adsorbent carbon using chemical activating agents (phosphoric acid and sulphuric acid) which can be very well utilized for wastewater treatment. Methods: The coconut shells were carbonized in a slow pyrolytic unit and activated by impregnating in sulphuric acid (SAC) and phosphoric acid (PAC). Later, kept in hot air oven at 110°C for 12 hours followed by soaking in 2% Na₂CO₃ overnight. After activation, the samples were stored in air tight containers for further characterization. The SAC and PAC were evaluated for the adsorptive potential of malachite green dye through batch study. Results & Discussions: Carbonization resulted in the production of adsorbent carbon with a yield of 30 percent. The porosity of the activated carbon ranged from 19.19 to 49.02%. The pH_zpc of the SAC and PAC were 5.2, and 4.6 respectively. The SEM micrograph showed micro and nano-pores ranging from 2-6 μm and 200-900 nm respectively. The BET surface area of the SAC and PAC were between 464.43 m² g^-1 and 544.66 m² g^-1 with stability of -27.4 and -29.4 mV, respectively. Isotherm and kinetic studies were investigated to understand the mechanism of adsorption. The acidic functional groups (carboxylic acid, phenolic and alcohol) present on surface of activated carbon were responsible for asorption. The best-suited model were in accordance with Freundlich isotherm for SAC (R²=0.979) and PAC (R²=0.972). The intraparticle diffusion is rate-limiting process for SAC (0.948) and PAC (0.923). Conclusions: The results of the study proved the effectiveness of utilizing chemicals in activating the carbon produced from coconut shells. Cocos nucifera shells are economical alternative and productive adsorbent due to low-cost. Further studies can be performed on the production of activated carbon from different ligno-cellulosic biomass by varying the activation techniques for the scale up. Keywords: Coconut shells, Chemical activation, Malachite green dye adsorption, Kinetics and Isotherm Acknowledgment We thank, Department of Science and Technology - Science and Engineering Research Board (DST-SERB), New Delhi for providing financial support to carry out the project work under sanction number EEQ/000807/2016 is greatly acknowledged. We also thank the Department of Environmental Sciences, TNAU, Coimbatore who facilitated and supported the smooth conduct of the experiments. References 1. M. Alipour, M. Vosoughi, S.A. Mokhtari, H. Sadeghi, Y. Rashtbari, M. Shirmardi and R. Azad, Int. J. Environ. Anal. Chem, 2019; 20. 2. R. Ruiz-Rosas, F.J. García-Mateos, M. del, C. Gutiérrez, J. Rodríguez-Mirasol and T. Cordero, Front. Mater. 2019; 6: 134.