Self-supported nitrogen doped and electrochemically active nanofibrous carbon for the efficient removal of aqueous lead ions by adsorption

Self-supported carbon nanofiber (CNF) was synthesized using Cu-tartrate as a precursor through H₂-reduction and catalytic chemical vapour deposition (CVD). The synthesis involved two key steps: reduction of Cu-tartrate to Cu nanoparticles (NPs) at 300 °C, followed by CVD of acetylene at 350 °C, with Cu NPs serving as catalyst for CNF growth. Temperature-programmed reduction (TPR) guided the choice of reduction conditions. The resulting material (Cu-CNF) was further functionalized with tetraethylenepentamine (TEPA) at varying loadings (10–40%) to introduce nitrogen functionalities. The amine treated materials are termed as x-TEPA-Cu-CNF (x = loading of TEPA). Characterization by SEM/TEM confirmed the tubular morphology of CNFs and the presence of Cu NPs (avg. size: 24 nm, by XRD analysis) at the tips of CNFs. The materials were tested for Pb²⁺ removal from aqueous solutions. The best performance was observed for 30 %-TEPA-Cu-CNF, with a maximum Pb²⁺ adsorption capacity of 179 ± 4 mg/g at pH 6 by Liu's isotherm model. Adsorption followed pseudo-second-order kinetics and Liu isotherm, indicating chemisorption and multilayer behaviour. The removal mechanism involved electrostatic attraction, surface complexation between oxygen containing surface functional groups (–OH, -COOH) and Pb²⁺ ions, pore filling, and NH₂–Pb²⁺ complexation. Electrochemical analysis showed that 30 %-TEPA-Cu-CNF electrochemically active, with electrochemically accessible area was approximately 73.68 times greater than the flat projected geometric surface area of the electrode, due to surface roughness and porosity. Low R_s and R_ct values confirmed good ionic conductivity and fast charge transfer, highlighting the material's potential for practical water treatment applications.