Koyeli Das, Uttara Sukul, Christian Julius Wijaya, Sarnali Sanfui, Md. Taharia, Gobinda Dey, Raju Kumar Sharma, Cheng-I Lee, Pin-Yun Lin, Chin-Wen Wang, Chien-Yen Chen
Fluoride (F−) contamination in groundwater and surface water seriously threatens environmental and public health, highlighting the need for a sustainable and efficient defluoridation technology. This study presents the synthesis of NaOH-modified lotus seed pericarp biochar (LSPB), prepared under optimized pyrolysis conditions (750 °C, 2 °C min−1, 1 h, nitrogen atmosphere) as a cost-effective adsorbent for F− removal. Synthesized material (LSPB-7) exhibited an amorphous structure, as confirmed by XRD and SAED analyses, and high surface area of 350 m2 g−1 as determined by BET-analysis. The material demonstrated a maximum F− adsorption capacity of 8.6 mg g−1, outperforming several reported biochars such as magnetic corn stover biochar (4.11 mg g−1) and Pine wood biochar (7.66 mg g−1), respectively. Adsorption equilibrium data were best fitted by Freundlich (R2 = 0.937) and BET (R2 = 0.935) isotherm models, indicating multilayer adsorption on a heterogeneous surface, while kinetic behavior followed pseudo-second-order model (R2 = 0.99). Co-existing anions (NO₃−, Cl−, SO₄2−, and CO₃2−) showed minimal impact on F− uptake, indicating selectivity of the adsorbent. Thermodynamic analysis confirmed spontaneous (ΔG° = −6.044 kJ mol−1) and endothermic (ΔH° = +68.669 kJ mol−1) nature of the adsorption process. Regeneration studies revealed the adsorbent retained ∼50 % efficiency after five adsorption-desorption cycles. The preparation cost of LSPB was estimated at 1.26 USD kg−1, substantially lower than commercial activated carbon, supporting its economic viability. Spectroscopic investigations indicated that F− adsorption occurred via electrostatic-attraction, hydrogen bonding, and surface complexation. DFT-analysis confirmed stronger F− binding and enhanced surface reactivity after NaOH-modification. These findings demonstrate LSPB's feasibility for field-scale water defluoridation systems. © 2025
Department of Biomedical Sciences, Graduate Institute of Molecular Biology, National Chung Cheng University, 168 University Road, Min-Hsiung, Chiayi County, 62102, Taiwan; Department of Earth and Environmental Sciences, National Chung Cheng University, 168 University Road, Min-Hsiung, Chiayi County, 62102, Taiwan; Department of Chemical Engineering, Widya Mandala Surabaya Catholic University, Kalijudan 37, Surbaya, 60114, Indonesia; Collaborative Research Center for Zero Waste and Sustainability, Kalijudan 37, Surabaya, 60114, Indonesia; Department of Chemistry, Texas A&M University, College Station, TX-77840, United States; Department of Chemistry and Biochemistry, National Chung Cheng University, 168 University Road, Min-Hsiung, Chiayi County, 62102, Taiwan; Doctoral Progam in Science, Technology, Environment, and Mathematics, Department of Earth and Environmental Sciences, National Chung Cheng University, 168 University Road, Min-Hsiung, Chiayi County, 62102, Taiwan; Center for Nano Bio-Detection, Center for Innovative Research on Aging Society, AIM-HI, National Chung Cheng University, 168, University Road, Min-Hsiung, Chiayi County, 62102, Taiwan; You-Cheng Engineering & Technology Co., Ltd, 168, University Road, Min-Hsiung, Chiayi County, 62102, Taiwan