Adsorptive behavior of multi-walled carbon nanotubes functionalized with iron nanoparticles for bisphenol A removal

Bisphenol A (BPA) is a persistent organic pollutant with toxic effects on human health and ecosystems. In this study, the performance of MWCNT-OH functionalized with iron nanoparticles (MWCNT-OH@Fe) using sugarcane bagasse extract as a reducing agent (green synthesis) was evaluated for BPA adsorption. The kinetics are fast, between 10 and 20 min in the range of concentrations evaluated and the resistance to external film diffusion (external film mass transfer) identified as the rate-limiting step of the process. The q_max was 0.301 mmol/g, determined by the Langmuir model, at 40 °C. The adsorption process was spontaneous and exhibited a transition in thermodynamic behavior: endothermic from 12 to 40 °C and exothermic from 40 to 55 °C. Among these methods, thermal regeneration showed the highest regeneration efficiency. The material was characterized before and after BPA adsorption using SEM/EDS, BET, FTIR, TGA, XRD, and ELS techniques. The main properties include a specific surface area of 100.3 m²/g, thermal stability up to 500 °C, and a pH_ZPC of 8.69. FTIR and XRD analyses confirmed iron functionalization and the presence of reduced iron species in the synthesized material. Regeneration of the adsorbent used was evaluated over three adsorption-desorption cycles using different eluent solutions, including NaCl, CaCl₂, NaOH, HNO₂, and ethanol, as well as thermal regeneration. Among these methods, thermal regeneration showed the highest efficiency, preserving the adsorption capacity of the material throughout the three adsorption/desorption cycles.