Adsorption of formaldehyde from aqueous solution using activated carbon prepared from Hibiscus rosa-sinensis

Abstract

ABSTRACTFormaldehyde is one of the most dangerous organic components in industrial wastewaters, which pollutes the environment as a result of human activities and various industrial operations. In the present work, the adsorption of formaldehyde from the synthetic wastewater using the activated carbon prepared from Hibiscus rosa-sinensis leaves was investigated in batch mode. The effects of operating parameters such as pH (3–10), adsorbent dosage (0.1–0.7 g/L), initial formaldehyde concentration (10–60 mg/L), temperature (298–348 K) and contact time (10–80 min) on the adsorption efficiency of formaldehyde were studied. The porous structure and characteristics of the adsorbent surface were studied using BET, SEM, FTIR, XRD, XRF, EDS and MAP techniques. Additionally, the maximum adsorption efficiency which was 95.49% was achieved in optimum experimental conditions (pH = 5), adsorbent dosage of 0.4 g/L, Initial formaldehyde concentrations of 50 mg/L, temperature of 25°C and contact time of 50 min. Moreover, based on BET results, the adsorbent’s specific surface area was 12.110 m2/g. Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms were used for describing the adsorption equilibrium, among them Langmuir isotherm showed the best performance. In addition, the maximum adsorption capacity (qmax) of the prepared activated carbon was 14.903 mg/g. Kinetic studies showed that pseudo second-order kinetic model (R2 = 0.9941) was more capable than pseudo first-order kinetic model (R2 = 0.8702) for description of formaldehyde removal kinetics. Additionally, thermodynamic investigations showed that the current adsorption process was exothermic (∆H° = −11.89 KJ/mol). Regeneration studies also revealed that there was a gradual decline in the adsorption efficiency of the recovered activated carbon after six cycles. The results of this work suggested that the activated carbon prepared from H. rosa-sinensis leaves is a suitable adsorbent for adsorption of formaldehyde from the synthetic wastewater.