Novel chitosan/polyvinyl alcohol thin membrane adsorbents modified with detonation nanodiamonds: Preparation, characterization, and adsorption performance

Detonation nanodiamonds (DNDs), for the first time, were utilized to modify chitosan/polyvinyl alcohol (CS/PVA) thin membrane adsorbents. For this purpose, different contents of DNDs, from nil to 1.5 wt%, were embedded in the polymer matrix of the membranes to obtain the optimum content. Static adsorption of Pb(II) on the prepared membrane adsorbents was studied. The fabricated membranes were characterized in terms of morphology and performance using scanning electron microscopy (SEM) micrographs and Fourier transform infrared (FTIR) spectrum analyses. Langmuir and Freundlich isotherms were used to model the equilibrium adsorption. The effects of pH, temperature, and initial metal concentration on the adsorption capacity were investigated. Results showed that adsorption of lead ion is more favorable at pH = 6. Thermodynamic parameters including ΔH^o, ΔS^o and ΔG^o revealed endothermic, entropy-driven and spontaneous nature of the adsorption. Adsorption capacity for Pb(II) increased from 29.5 mg g⁻¹ (for the plain membrane) to 121.3 mg g⁻¹ by the addition of 1.5 wt% DNDs; however, the optimal content was 1 wt% DNDs considering both mechanical stability and adsorption capacity. Results revealed that the ultra-thin CS/PVA membrane adsorbents modified with DNDs are very potential candidates for heavy metal adsorption.