Facile Fabrication of Seashell-Derived Hydroxyapatite-Graphene Oxide (HAp/GO) Composites for High-Performance Dye Adsorption
Md Sohag Hossain, Md. Sahadat Hossain, Fariha Chowdhury, Md. Saiful Quddus, Umme Sarmeen Akhtar, Nazmul Islam Tanvir, Samina Ahmed, Mashrafi Bin Mobarak
Abstract
High Resolution Image Download MS PowerPoint Slide This work aimed to determine the most effective and facile route for preparing hydroxyapatite-graphene oxide (HAp/GO) composites by comparing three simple methods: in situ (I-HAp/GO), hand grinding (G-HAp/GO), and sonication (S-HAp/GO). The use of seashell-derived HAp made all of the processes cost-effective, and the composites were evaluated through structural and adsorption studies toward Congo red (CR) dye removal performance from aqueous solution. Among the three composites, I-HAp/GO showed distinct advantages by possessing the highest BET surface area (114.65 m 2 /g), greater pore volume, and more homogeneous distribution of HAp nanoparticles (NPs) on GO sheets compared to G-HAp/GO and S-HAp/GO, which exhibited agglomeration and lower surface areas. I-HAp/GO also delivered the best adsorption capacity (68.49 mg/g) and fastest removal efficiency, achieving 94.07% removal of CR (50 mg/L, pH 7, and 50 mg adsorbent) within 10 min with adsorption following the Langmuir isotherm ( R 2 = 0.9806, linear fitting) and pseudo-second-order kinetics ( R 2 = 0.9998). Density functional theory calculations showed a reduced HOMO–LUMO gap (0.0089 eV) for HAp/GO composites, indicating enhanced electronic interactions between HAp and GO. Thermodynamic analysis indicated spontaneous adsorption, and regeneration study confirmed over 88% retention of efficiency using deionized water. These findings demonstrate that the in situ method produces a high-surface-area, fast-acting, and reusable HAp/GO adsorbent, making it the most superior among the tested approaches for dye removal applications.