Guava seed activated carbon loaded calcium alginate aerogel for the adsorption of diclofenac sodium: Characterization, isotherm, kinetics, and optimization via Box-Behnken design

Abstract

This study aimed to develop a novel adsorbent designed for the removal of diclofenac sodium (DS) from water. The synthesized adsorbent, a composite sponge known as guava seeds activated carbon loaded calcium alginate (GSAC@CA aerogel), was created through the combination of powdered activated carbon derived from guava seeds and loaded onto a calcium alginate hydrogel. Characterization through SEM, XRD, FT-IR, BET, and XPS revealed a confirmed surface area of 738.82 m2/g. The investigation delved into assessing the influence of pH, initial DS concentration, and adsorbent dose on the adsorption of DS. Isotherm studies on adsorption suggested that a Langmuir model provided a good fit, indicating a monolayer adsorption process. Kinetic studies revealed a well-fitted pseudo-second-order model, shedding light on the dynamics of the reaction. The chemisorption nature was elucidated by the Dubinin-Radushkevich model, demonstrating an adsorption energy of 22.6 kJ/mol. These results affirm the potential of the GSAC@CA aerogel composite sponge as an efficient adsorbent for removing diclofenac sodium from water. Examination of the impact of temperature on the adsorption process revealed an endothermic behavior, indicating an increase in temperature. The positive change in entropy suggested the spontaneous nature of the reaction. Remarkably, the GSAC@CA aerogel composite sponge exhibited strong adsorption capabilities, achieving a maximum adsorption capacity of 489.97 mg/g. Across five consecutive cycles, the composite consistently demonstrated high-level adsorption, maintaining a removal efficiency of 87.77 %. The adsorption mechanism of diclofenac sodium (DS) on the GSAC@CA aerogel composite sponge was determined to encompass various processes, such as hydrogen bonding, π-π interactions, ion exchange, and electrostatic pore filling. Additionally, the adsorbent demonstrated successful regeneration over three cycles when applied to a real-world sample. The incorporation of the Box-Behnken design (BBD) introduced a strategic aspect to enhance adsorption outcomes, offering valuable insights for optimizing the adsorption process in practical applications.