<i>Sesbania grandiflora</i> activated carbon as a high-efficiency stable and reusable adsorbent for sustainable fluoride removal

Abstract

BACKGROUND AND OBJECTIVE: Excess fluoride in groundwater poses environmental and public health risks, causing skeletal and dental fluorosis. Conventional defluoridation methods struggle with cost, efficiency, and reusability. This study evaluates Sesbania grandiflora activated carbon as a stable, reusable fluoride adsorbent, focusing on its characterization, optimal adsorption conditions, and reusability.METHODS: Sesbania grandiflora activated carbon was synthesized and characterized using fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction to assess structural integrity and surface interactions. Batch adsorption experiments were conducted by varying particle size (up to 2.360 millimeter), dosage (2–10 grams), agitation speed (100–500 revolution per minutes), and contact time (up to 140 minutes) to determine the optimal conditions for fluoride removal. Adsorption isotherms and kinetics were analyzed using Freundlich and Langmuir models, while reusability was evaluated over five regeneration cycles with 0.1 mole sodium hydroxide.RESULTS: Fourier transform infrared spectroscopy revealed interactions between fluoride ions and surface functional groups. Scanning electron microscopy showed a porous structure (pore size 0.5–5 microns) that smoothed post-adsorption, confirming fluoride uptake. Energy dispersive x-ray spectroscopy showed before treatment, Sesbania grandiflora activated carbon had 78.3 percent carbon and 16.5 percent oxygen, while after treatment, carbon increased to 78.8 percent, oxygen to 17.1 percent, and sodium rose to 2.1 percent, with phosphorus and sulphur undetected. X-ray diffraction confirmed that activated carbon from Sesbania grandiflora remained mostly amorphous, with crystallinity increasing from 17.2 percent to 17.4 percent. The study identified optimal adsorption conditions as 2.360 millimeter particle size, 8 gram dosage, 300 revolution per minute agitation speed, and 120 minute contact time, achieving a maximum fluoride removal of 89.3 percent. Adsorption followed the Freundlich isotherm (coefficient of determination is 0.9976), suggesting a multilayer heterogeneous adsorption process. Pseudo second order kinetics (coefficnet of determination is 0.9988) confirmed chemisorption as the dominant mechanism. Sesbania grandiflora activated carbon maintained 78.3 percent efficiency after five regeneration cycles, demonstrating good reusability.CONCLUSION: Sesbania grandiflora activated carbon is a highly efficient, stable, and reusable adsorbent for groundwater fluoride removal, maintaining structural integrity and high efficiency. Its potential for scalable, sustainable water treatment warrants further study on scale-up, hybrid integration, and enhanced regeneration techniques.