Alginate encapsulated fluorescent carbon-core regenerative Azadirachta indica flower-derived nanoparticles for...

Azadirachta indica, a medicinal plant widely grown across the globe, is renowned for its multifaceted bioactivity and environmental compatibility. Its potential as a green adsorbent offers advantages such as biogenic composition, low cost, and sustainability in wastewater treatment. In this study, Azadirachta indica-derived nanoparticles (AzI NPs) were synthesized and evaluated for the adsorption of cationic dyes (malachite green (MG), methylene blue (MB), and crystal violet (CV)). PXRD, SEM, and BET revealed irregular porous morphology of NPs with an average crystallite size of 9 nm, while zeta potential confirmed a negatively charged surface. The carbon-rich core contributed to a strong blue emission at 270 nm excitation, which may be linked to surface defects and conjugated domains. Dye adsorption efficiencies were optimized across various parameters, including dye concentration, pH, adsorbent dosage, contact time, water quality, and temperature. AzI NPs achieved adsorption efficiencies of 95% (MG), 86% (MB), and 85% (CV) within just 3 minutes of contact time. Kinetic studies followed pseudo-second-order (PSO) model, indicating chemisorption, while Elovich model suggests surface heterogeneity and IPD model indicates that pore diffusion may contribute. Furthermore, isotherm analysis aligned with the Langmuir and Temkin models, suggesting monolayer adsorption on a homogeneous surface with moderate adsorbate-adsorbent interactions. Thermodynamic parameters confirmed a spontaneous process and endothermic behavior. At room temperature, ΔG and ΔH were determined to be $-3.695\text{kJ}/\text{mol}$ and $39.17\text{kJ}/\text{mol}$ , respectively. To improve applicability, AzI NPs were encased in eco-friendly biopolymeric alginate matrix to form reusable AzI@SA beads, minimizing NP leaching, secondary pollution, and enabling multiple adsorption cycles. AzI@SA beads demonstrated reusability across eight consecutive cycles with minimal loss in performance. Therefore, AzI@SA has significant potential as an eco-friendly, sustainable, and effective nano-adsorbent for wastewater dye remediation.