Post-polymerization synthesis of a poly(α-naphthylamine)/ninhydrin composite with enhanced surface area for efficient urea adsorption

Abstract

Abstract The presence of urea in aqueous environments and industrial effluents poses significant environmental and health concerns due to its persistence and contribution to nitrogen pollution, necessitating the development of efficient and stable adsorbents. This study reports the successful synthesis of a novel poly(α-naphthylamine)/ninhydrin (P-αNA/Nin) polymeric composite via a post-polymerization modification strategy, aiming to create a high-performance adsorbent for urea removal. The composite formation involved covalent Schiff base (C = N) linkages between the amine groups of poly(α-naphthylamine) and the carbonyl groups of ninhydrin, supported by hydrogen bonding and π–π interactions. Morphological analyses using SEM and TEM revealed a highly porous, nanostructured surface with interconnected micro- and mesopores, confirming a heterogeneous morphology conducive to adsorption. Nitrogen adsorption–desorption measurements indicated a substantial increase in BET surface area from 2090.18 m²/g for pristine P-αNA to 2320.47 m²/g for the P-αNA/Nin composite. FT-IR analysis verified the successful integration of ninhydrin through the formation of imine bonds, while XRD confirmed the predominantly semi-amorphous nature and TGA/DSC analyses demonstrated adequate thermal stability for aqueous-phase applications. Adsorption performance was optimized using Response Surface Methodology (RSM), yielding a maximum urea removal efficiency of 85.3% under optimal operating conditions. Interference studies revealed that while nitrogen-containing compounds like creatinine and ammonia significantly compete for active adsorption sites, the P-αNA/Nin composite demonstrates good reusability with only a slight loss of efficiency over repeated cycles. Overall, the P-αNA/Nin composite exhibits great promise as a stable, selective, and high-capacity adsorbent for effective urea removal in complex aqueous systems, including industrial effluents and potentially medical dialysis applications.