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Congo red (CR) dye is a synthetic azo dye expansively used in the textile industry, is discharged to aquatic environments, and is toxic to humans and aquatic flora. The performance of cationic amino-modified banana leaves (CMBL) for CR dye sequestration was evaluated first time in this study. The surface modification of CMBL was analyzed using Scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectrum and compared with raw banana leaves powder (RBL). The optimum condition for CR dye adsorption using CMBL was optimized using Central Composite Design (CCD) by investigating four critical operating parameters: contact time, pH, RBL/CMBL doses, and initial CR dye concentrations. The proposed model (quadratic) was acceptable due to the high values of correlation coefficients R2 (0.96) and adjusted R2 (0.92). The CMBL exhibited maximum removal efficiency of 76.82% towards CR dye at pH 3 compared to RBL, i.e., 19.63%. Electrostatic interaction and hydrogen bonding were the primary removal mechanisms for the CR dye adsorption process using CMBL. Freundlich isotherm and pseudo-second-order kinetic model exhibited a strong correlation for experimental data and reported a correlation coefficient (R2) of more than 0.99. In addition, CMBL showed excellent reusability for the adsorption of CR dye even after three consecutive adsorption-desorption experiments., QC 20231031

Biochar, a promising carbon-rich and carbon-negative material, can control water pollution, harness the synergy of sustainable development goals, and achieve circular economy. This study examined the performance feasibility of treating fluoride-contaminated surface and groundwater using raw and modified biochar synthesized from agricultural waste rice husk as problem-fixing renewable carbon-neutral material. Physicochemical characterizations of raw/modified biochars were investigated using FESEM-EDAX, FTIR, XRD, BET, CHSN, VSM, pHpzc, Zeta potential, and particle size analysis were analyzed to identify the surface morphology, functional groups, structural, and electrokinetic behavior. In fluoride (Fˉ) cycling, performance feasibility was tested at various governing factors, contact time (0–120 min), initial Fˉ levels (10–50 mg L−1), biochar dose (0.1–0.5 g L−1), pH (2–9), salt strengths (0–50 mM), temperatures (301–328 K), and various co-occurring ions. Results revealed that activated magnetic biochar (AMB) possessed higher adsorption capacity than raw biochar (RB) and activated biochar (AB) at pH 7. The results indicated that maximum Fˉ removal (98.13%) was achieved using AMB at pH 7 for 10 mg L−1. Electrostatic attraction, ion exchange, pore fillings, and surface complexation govern Fˉ removal mechanisms. Pseudo-second-order and Freundlich were the best fit kinetic and isotherm for Fˉ sorption, respectively. Increased biochar dose drives an increase in active sites due to Fˉ level gradient and mass transfer between biochar-fluoride interactions, which reported maximum mass transfer for AMB than RB and AB. Fluoride adsorption using AMB could be described through chemisorption processes at room temperature (301 K), though endothermic sorption follows the physisorption process. Fluoride removal efficiency reduced, from 67.70% to 53.23%, with increased salt concentrations from 0 to 50 mM NaCl solutions, respectively, due to increased hydrodynamic diameter. Biochar was, QC 20230706

Fluoride (F-) contamination in water is a global health concern, threatening the well-being of millions. This study investigated the role of ZnCl2/FeCl3-rice husk-modified biochar (Zn-BC and Zn/Fe-BC) in treating F--contaminated surface and groundwater under the influence of varying solution chemistry, co-existing ions, and biochar-amended through column transport experiments. Modified biochar showed maximum F- adsorp-tion, 99.01% and 91.90% using Zn/Fe-BC and Zn-BC, respectively, than 85.87% using raw biochar (R-BC). Raw/modified biochars were characterized with FESEM-EDAX, FTIR, XRD, particle size, surface area, electro-kinetic potential, and point of zero charge analyses. Langmuir and pseudo-second-order kinetic could explain that F--biochar interactions are dominated by chemisorption at ambient temperature while physisorption at higher temperatures. The influence of salt concentrations and co-occurring ions reduced F- sorption using Zn/Fe-BC. Increased salt strengths led to reduced electrophoretic mobility of biochar particles, i.e., biochar-biochar particles attract each other and increase the hydrodynamic diameter, which ultimately reduces the active sites on biochar for F- adsorption. Co-transport and deposition of biochar and F- in saturated porous media revealed lower mobility of biochar, and maximum F- adsorption was observed at 10 mM salt strength. Biochar transport is governed by electrostatic interactions, whereas F- transport mainly occurs through chemisorption. In rural areas, hand pumps and tube wells are generally used as source of potable water for drinking and cooking purposes; thus, biochar-mediated sand columns can be utilized for defluoridation. Thus, Zn/Fe-BC can be utilized as a potential bio-adsorbent for F--contaminated natural surface and groundwater with optimum preparation and treatment costs., QC 20230412