Novel carbon nanohair with activated carbon as a 1D–3D composite from olive leaves for antibiotics removal: experimental and DFT investigation

Abstract

The carbon nanohair/activated carbon (CNH/OAC) composite derived from olive leaves was fully characterized using surface chemistry, morphology, and thermal analysis techniques. The synthesized composite exhibits nanohairs featuring an average diameter of 6 nm and a d-spacing of 0.33 nm, indicative of microporosity with an average pore size of ∼2.0 nm. In this study, a CNH/OAC composite was synthesized and applied as an adsorbent for doxycycline hyclate (DOX) and oxytetracycline-HCl (OTC). Evaluation of the initial pH conditions showed the optimal removal efficiency of DOX and OTC at pH 2. FTIR spectra analysis pre and post-adsorption indicated surface oxidation of CNH/OAC, with noticeable changes in functional groups. XPS analysis confirmed the adsorption process, showing the appearance of CO peaks at 286.76 eV (DOX) and 287.04 eV (OTC). Adsorption kinetics revealed rapid chemisorption, thoroughly characterized by the pseudo-second-order model. Isotherm studies demonstrated Langmuir model suitability, with 100 mg g⁻¹ for DOX and 357.14 mg g⁻¹ for OTC adsorption capacity. The Elovich isotherm model showed higher adsorption capacity (107.527 mg g⁻¹) and affinity for DOX adsorption. Thermodynamic calculations confirmed the spontaneous, exothermic nature of adsorption with increased orderliness. The CNH/OAC composite demonstrated superior reusability, with pyrolysis (300 °C) and 1 N HNO₃ activation restoring up to 99.99% and ∼93.32% of the adsorption capacity for DOX and OTC, respectively. DFT analysis confirmed stable structures of DOX and OTC on CNH/OAC, with stronger non-covalent bonds observed for OTC due to increased oxygen content. Adsorption annealing simulations showed DOX's highly stable adsorption (−482.606 kcal mol⁻¹) primarily through H-bond interactions, contrasting with OTC's adsorption (−91.415 kcal mol⁻¹) via electrostatic interactions. FMO and DOS spectra analyses indicated greater stability for DOX-CNH/OAC compared to OTC-CNH/OAC. This study contributes to multiple SDGs, including SDG 6 (Clean Water and Sanitation), SDG 13 (Climate Action), and SDG 15 (Life on Land), by offering a sustainable solution to reduce water footprint and potentially accrue carbon credits through carbon dioxide sequestration. The findings underscore the composite's environmental sustainability, economic viability, and role in achieving various SDGs.