Isotherms, kinetics and thermodynamic sorption of paranitroaniline on Cocos nucifera shell activated carbon@TiO₂ composite

Abstract

A comparative study was conducted on the adsorption capacity of Cocos nucifera shell‐activated carbon (CNSA) and Cocos nucifera shell‐activated carbon@TiO2 composite (CNSA‐TiO2) for para‐nitroaniline in an aqueous medium. The CNSA was carbonized at 500 °C and activated with 1 M HNO3 while the CNSA‐TiO2 composite was prepared by wet impregnation method. The prepared adsorbents were characterized through Brunauer–Emmett–Teller (BET), energy dispersive X‐ray (EDX) spectroscopy, Fourier‐transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). The BET‐surface area of CNSA‐TiO2 (748.96 m2/g) was established to be larger than CNSA (574.21 m2/g), however both materials are mesoporous. The effects of initial p‐NA concentration, pH, adsorbent dosage, contact time, and temperature, were explored for both adsorbents. The results showed that the adsorption operating parameters influenced the adsorption process except for temperature, with maximum adsorption of 38.26 and 38.36 mg/g for CNSA and CNSA‐TiO2, respectively. Freundlich, Langmuir, Temkin, and Dubinin‐Radushkevich isotherms were tested on the adsorption data, and the adsorption process of both adsorbents followed the Freundlich isotherm model (R2 > 0.988). Among the kinetic models studied, the pseudo‐second‐order model (R2 = 1) best described both processes. The thermodynamic parameters such as ∆G °, ∆H ° and ∆S ° were calculated. The process was exothermic, spontaneous and feasible.