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[Display omitted] • The effect of hydroxyl protonation and deprotonation on the adsorption process was discussed in conjunction with density functional theory. • More than 60 % retention of adsorption capacity after five cycles of regeneration test. • Efficient adsorption processes allow for maximum fluoride adsorption capacity of up to 40.5 mg/g. • Complex mechanism of chemisorption process revealed based on XPS and DFT calculations. Due to fluoride pollution in the global water, the development of economical and efficient adsorption materials is urgent. In this study, schwertmannite were successfully synthesized by a low-cost chemical method, and the complex mechanism of fluoride adsorption process was analyzed in depth by combining experiments and theoretical calculations. The fluffy cauliflower-like morphology contributed to increasing the specific surface area of adsorbent (193.4 m2/g) and exposing active sites. The effect of pH on the adsorption process was discussed in conjunction with density functional theory. The experiment found that higher temperature improved fluoride removal, best performance at 318 K with 40.5 mg/g. In addition, fitting results showed that the Langmuir and pseudo-second-order models could better describe the adsorption behavior. Coexisting anions and adsorption regeneration experiments demonstrated the high selectivity and reusability of schwertmannite. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to determine the mechanism of adsorption and fluoride removal. Combined with theoretical calculations, three adsorption configurations and the corresponding binding energies were obtained. The stability of different adsorption modes specifically showed OH-F > SO 4 -HF > OH-HF. Density of states analysis revealed the formation of resonance peaks and stable bonding interactions, further confirming the chemical adsorption mechanism. It provides the foundation for future industrial applications by using schwertmannite to deal with fluoride. [ABSTRACT FROM AUTHOR]

Environmental toxicity of antimony (Sb) is significantly increased through the widespread industrial application. The extended release of Sb above the regulatory level became a risk to humans habituated in the ecosystem. Conventional methods to remediate Sb demand high energy or resource input, which further leads to secondary pollution. The bio-electrochemical system offers a promising bioremediation strategy to remove or reduce toxic heavy metals. Thus, this research explores the possibilities of simultaneous metal sulfide (MeS) precipitation and electricity production using a full biological Microbial fuel cell (MFC). A non-conventional sulfate-reducing bacteria (SRB) Citrobacter freundii SR10 was used for this investigation, where the MFC was operated for lactate utilization in the bio-anode and Sb reduction at the bio-cathode. This study observed 81% of coulombic efficiency (bio-anode) and 97% of sulfate reduction with 99.3% Sb (V) reduction (bio-cathode), and it was concluded that the MeS precipitation entirely depends on sulfide concentration via SR10 sulfate reduction. The MFC-SR10 offers a maximum power density of 1652.9 ± 32.1 mW/m3, and their performance was depicted using cyclic voltammetry and electrochemical impedance spectroscopy. The Sb reduction was evaluated through fluorescence spectroscopy, and the Sb (V) MeS precipitation was confirmed as stibnite (Sb 2 S 3) by Raman spectroscopy and X-ray photoelectron spectroscopy. Furthermore, the matured anodic and cathodic biofilm formation was confirmed by Scanning electron microscopy with Energy-dispersive X-ray spectroscopy. Thus the MFC with SRB bio-cathode can be used as an alternative to simultaneously remove sulfate and Sb from the wastewater with electricity production. [Display omitted] • Full biological Microbial fuel cell (MFC) was developed with the strain of SRB. • Enhanced sulfate reduction (97%) was achieved in dual-chambered MFC. • Power density of 1652.9 ± 32.1 mW/m3 was attained with Antimony (Sb) reduction. • Stibnite is the key compound obtained after 99.3% Sb (V) reduction. [ABSTRACT FROM AUTHOR]