Removal of Ponceau Red and Carmoisine Red from water using NaOH-activated olive stone carbon: kinetic, isotherm, thermodynamic, and mechanistic studies

Olive Stone Activated Carbon (OSAC) sustained the removal of Ponceau Red (PR) and Carmoisine Red (CR) from water; OSAC was developed from chemical activation using sodium hydroxide (NaOH). The properties of OSAC were studied using several analytical techniques (BET, XRD, FTIR, SEM), all confirming that OSAC has a very porous structure with lots of functional groups that interacted with PR and CR, facilitating their removal. Studies were designed to assess the interactions between various factors (e.g., contact time; amount of OSAC used; initial concentration of dye; temperature) on dye removal. Results showed that dye removal followed the pseudo-second order kinetics model while equilibrium data were best-fitted to the Langmuir isotherm with an acceptable fit to the Temkin and Sips models as well. The maximum capacity for dye removal was 425.6 mg/g (PR) and 398.4 mg/g (CR). Adsorption was spontaneous and exothermic based on the thermodynamic data. There were a number of contributing mechanisms for dye removal including: electrostatic attraction (ion charges), π–π interactions; hydrogen bonding and intraparticle diffusion. Regeneration studies demonstrated that ~ 80% of dye removal efficiency was maintained after 5 cycles of dye removal using OSAC. There are low costs to produce 1 kg of OSAC (~ $4), making it an efficient and cost-effective adsorbent for treating dye contaminated wastewater.