GO-CeO₂ nanohybrid for ultra-rapid fluoride removal from drinking water

Double cross-linked chitosan sponge encapsulated with ZrO2/soy protein isolate amyloid fibrils nanoparticles for the fluoride ion removal from water

Fluoride ion pollution in water has become a serious threat to the water environment and human health. Adsorption is a promising means of fluoride removal, but it also faces challenges such as the difficult separation and recovery of powdered particles, the leaching of modified coatings from adsorbents, and the structural disintegration of macroscopic adsorbents. For addressing the above challenges, glutaraldehyde/polyvinyl alcohol co-crosslinked ZrSAF/chitosan spongy composites (ZrS/GPCS) were prepared by utilizing encapsulation strategies and cross-linking. ZrS/GPCS-1, ZrS/GPCS-3 and ZrS/GPCS-4 were prepared due to the different amounts of cross-linking agents. The results showed that their fluoride ion adsorption capacities were 42.02, 44.44 and 39.84 mg/g, respectively. The removal of fluoride ions by ZrS/GPCS was maintained at >80 % in the pH range of 4-10. The addition of glutaraldehyde and polyvinyl alcohol affected the contact efficiency of fluoride ions with chitosan and ZrSAF, influencing the adsorption rate and adsorption effect. Glutaraldehyde, polyvinyl alcohol and ZrSAF improved the thermal stability, mechanical properties and structural integrity of chitosan matrix. Both the chitosan matrix and the internal ZrSAF played an important role in fluoride removal, and the removal mechanisms included electrostatic interaction, hydrogen bonding, and complexation.

Zirconium‑cerium modified polyvinyl alcohol/NaCMC biocomposite film: Synthesis of films through high-speed shear assisted technique and removal fluoride from water

A new zirconium and cerium-modified polyvinyl alcohol (PVA) sodium carboxymethyl cellulose (NaCMC) film (PVA/CMC-Zr-Ce) was synthesized thru a high-speed shear-assisted method and its adsorption for the removal of fluoride was studied, in which the NaCMC provided -COONa for ion exchange between Na and Zr-Ce, thus the loading amount of Zr-Ce on films was accordingly increased. The morphology and structure of PVA/CMC-Zr-Ce were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Besides, the mechanical properties, water contact angle, and swelling ratio of film were also evaluated. The addition of high-speed shear improved the dispersion of the emulsion system, and PVA/CMC-Zr-Ce film with good adsorption performance and film stability was prepared. While, it was found that the adsorption capacity could reach 67.25 mg/g and equilibrium time could reach 20 min. The adsorption mechanism of PVA/CMC-Zr-Ce revealed that ion exchange between hydroxide and fluoride, electrostatic interactions and complexation were the dominating influencing factors. Based on these findings, it can be concluded that PVA/CMC-Zr-Ce film- synthesized with high-speed shear assistance technique is a promising adsorbent for fluoride removal from water.

Humic acid-nanoceria composite as a sustainable adsorbent for simultaneous removal of uranium(VI), chromium(VI), and fluoride ions from aqueous solutions

In this article, the multifunctional behavior of novel, efficient, and cost-effective humic acid-coated nanoceria (HA@CeO2 NPs) was utilized for the sorptive removal of U(VI), Cr(VI), and F- ions at different conditions. The production cost of HA@CeO2 was $19.28/kg and was well characterized by DLS, FESEM, HRTEM, FTIR, XRD, XPS, and TGA. Batch adsorption study for U(VI) (at pH ~ 8), Cr(VI) (at pH ~ 1), and F- (at pH ~ 2) revealed that the maximum percentage of sorption was > 80% for all the cases. From the contact time experiment, it was concluded that pseudo-second-order kinetics followed, and hence, the process should be a chemisorption. The adsorption study revealed that U(VI) and Cr(VI) followed the Freundlich isotherm, whereas F- followed the Langmuir isotherm. Maximum adsorption capacity for F- was 96 mg g-1. Experiments in real water suggest that adsorption is decreased in Kaljani River water (~ 12% for Cr(VI) and ~ 11% for F-) and Kochbihar Lake water (25.04% for Cr(VI) and 20.5% for F-) because of competing ion effect. Mechanism was well established by the kinetic study as well as XPS analysis. Because of high adsorption efficiency, HA@CeO2 NPs can be used for the removal of other harmful water contaminants to make healthy aquatic life as well as purified drinking water.

Design of hydrotalcite and biopolymers entrapped tunable cerium organic cubic hybrid material for superior fluoride adsorption

The excess fluoride in drinking water is serious risk which leads to fluorosis. The adsorption method is facile route for defluoridation studies. Hybrid adsorbent possesses unique advantages like high surface area and high stability has been employed for water treatment. In the present work, hydrotalcite (HT) fabricated Ce-metal organic frameworks (MOFs) bridged with biopolymers (alginate and chitosan) namely HT-CeMOFs@Alg-CS cubic hybrid beads was developed and employed towards fluoride removal in batch mode. The fabricated HT-CeMOFs@Alg-CS beads were analyzed by DTA, FTIR, SEM, EDAX, TGA and XRD studies. Besides, FTIR and EDAX proved the affinity of HT-CeMOFs@Alg-CS cubic hybrid beads on fluoride was majorly attributed by electrostatic interaction, ion-exchange and complexation mechanism. To include detail insight into adsorption route; the kinetics, thermodynamic and isotherm studies were investigated for fluoride adsorption. The equilibrium data of HT-CeMOFs@Alg-CS cubic hybrid beads for fluoride adsorption was fitted with Langmuir isotherm model. Thermodynamic investigation results demonstrated that the fluoride adsorption was spontaneous with endothermic nature. The regeneration and field investigation results revealed that the developed HT-CeMOFs@Alg-CS cubic hybrid beads are reusable and more apt at field environment.

Simultaneous and efficient removal of fluoride and phosphate in phosphogypsum leachate by acid-modified sulfoaluminate cement

The high concentration of fluoride and phosphate in phosphogypsum leachate is harmful to the environment and ecosystem. Thus, there is a need to develop feasible materials or technologies to remove both fluoride and phosphate in acidic phosphogypsum leachate. In this study, sulfoaluminate cement (SC) was used to simultaneously remove fluoride and phosphate in wastewater based on its moderate alkalinity and rich content of metal elements (Ca, Al and Fe, etc). The acidized sulfoaluminate cement (ASC) composite was prepared through modifying SC with hydrochloric acid, which can increase the specific surface areas of the raw SC, as well as the activity of the metal elements in SC. Compared with other coagulants, ASC showed excellent removal performance for fluoride and phosphate, such as higher removal efficiency, better effluent quality, and accelerated settling rate. The fluoride and phosphate removal performances of ASC herein were investigated at different dosages, pH values, coexisting substances, and initial concentrations. As a result, ASC exhibited wide pH adaptability and satisfactory selectivity for fluoride and phosphate. The possible removal mechanisms of fluoride and phosphate by ASC included chemisorption, ion exchange, and precipitation. The main end products associated with fluoride were fluorite (CaF₂), aluminum fluoride (AlF₃), and iron trifluoride (FeF₃). The main final products amid phosphate removal, on the other hand, were brushite (CaHPO₄·2H₂O), aluminophosphate ((H₃O)·AlP₂O₆(OH)₂), silicocarnotite (Ca₂SiO₄·Ca₃(PO₄)₂) and iron phosphate (Fe(H₂PO₄)₃). More importantly, ASC can effectively treat the phosphogypsum leachate at a wide range of concentrations, and the concentrations of phosphate and fluoride in the effluents were lower than 0.5 mg P L^-1 and 4 mg L^-1, respectively. To sum up, ASC is a competitive candidate to treat wastewater with high fluoride and phosphate content, such as phosphogypsum leachate.

Carbon dots capped cerium oxide nanoparticles for highly efficient removal and sensitive detection of fluoride

Since the excess exposure to F^- may induce serious issues to human health, the effective adsorption and sensitive detection of F^- is essential. Therefore, carbon dots (CDs) capped CeO₂ (CeO₂@CDs) was synthesized via hydrothermal treatment of tannic acid and CeCl₃. Due to abundant phenolic hydroxyl are reserved and excellent hydrophilicity, CeO₂@CDs possess high F^- adsorption capacity. The partition coefficient parameters (PC) are determined to be 2.65 L/g, which is comparable with previous work. The kinetics results and adsorption isotherm are consistent with pseudo-second-order model and Freundlich model, respectively, indicating the chemisorption dominate the adsorption, mainly via the ion exchange between hydroxyl and F^-. Since phenolic hydroxyl existed on the CeO₂@CDs, synergetic effect of CDs and CeO₂ contribute to superior ROS eliminating capacity, even at acidic conditions. Moreover, due to the ROS scavenging of CeO₂ @CDs abilities can be potentiated by F^-, colorimetric detection of F^- can be realized via horseradish peroxidase as an indicator. The linear range is 0.3-2.1 mM with limit of detection is 0.13 mg/L. The current results imply that CeO₂@CDs possess potential in both efficient removal and sensitive detection of F^- related contamination issues and elucidation of development to address other anions related issues.

Fluoride exposure induces lysosomal dysfunction unveiled by an integrated transcriptomic and metabolomic study in bone marrow mesenchymal stem cells

Fluoride has received much attention for its predominant bone toxicity in the human body. However, the toxic mechanism of bone injury caused by fluoride exposure remains largely unclear. Bone marrow mesenchymal stem cells (BMSCs) are widely used as model cells for evaluating bone toxicity after environmental toxicant exposure. In this study, BMSCs were exposed to fluoride at 1, 2, and 4 mM for 24 h, and fluoride significantly inhibited cell viability at 2 and 4 mM. A multiomics analysis combining transcriptomics with metabolomics was employed to detect alterations in genes and metabolites in BMSCs treated with 2 mM fluoride. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of transcriptomics profiles identified "lysosomes" as the top enriched pathway, which was severely damaged by fluoride exposure. Lysosomal damage was indicated by decreases in the expression of lysosomal associated membrane protein 2 (LAMP 2) and cathepsin B (CTSB) as well as an increase in pH. Upregulation of the lysosome-related genes Atp6v0b and Gla was observed, which may be attributed to a compensatory lysosomal biogenesis transcriptional response. Interestingly, inhibition of glutathione metabolism was observed in fluoride-treated BMSCs at the metabolomic level. Moreover, an integrative analysis between altered genes, metabolites and lysosome signaling pathways was conducted. Palmitic acid, prostaglandin C2, and prostaglandin B2 metabolites were positively associated with Atp6v0b, a lysosome-related gene. Overall, our results provide novel insights into the mechanism responsible for fluoride-induced bone toxicity.

Synergistic removal of fluoride from groundwater by seed crystals and bacteria based on microbially induced calcium precipitation

A new hypothesis that seed crystals (SC) and bacteria based on microbially induced calcium precipitation (MICP) synergistically remove fluoride (F^-) from groundwater was proposed, with a focus on evaluating the defluoridation potential of this method and revealing its F^- removal mechanism. The crucial conditions were optimized to reduce preparation and operation costs. SC furnished more available binding sites due to the existence of bacteria, and the reuse experiments showed that the defluoridation efficiency of SC still remained a high level after 14 cycles (70.10%), with a residual F^- concentration of 0.96 mg L^-1. The SEM-EDS, FTIR and XRD analyses indicated the predominant F^- removal mechanism of SC could be ascribed to the chemisorption, ion exchange, and co-precipitation. Moreover, ion exchange and co-precipitation (PO₄^3- involvement) were validated more contributive than chemisorption (CaCO₃ and CaSO₄ involvement). As a feasible, reusable, and eco-friendly technique, SC suggests promising applications in the treatment of fluoride-contaminated groundwater.

Defluoridation using hydroxyapatite implanted lanthanum organic framework-based bio-hybrid beads

The present study reports on biopolymer based material namely HAp–La-BTC MOFs@Alg–CS hybrid beads were developed and it was potentially employed for fluoride removal.

Nanocomposite of Ceria and Trititanate Nanotubes as an Efficient Defluoridating Material for Real-Time Groundwater: Synthesis, Regeneration, and Leached Metal Risk Assessment

Ceria-incorporated trititanate nanotube composite (CTNC) was synthesized via a simple two-step wet chemical route for efficient fluoride removal not only from synthetic water but also from groundwater. The synthesized nanomaterial was systematically characterized for its physical and chemical properties. CTNC was shown to be highly porous with a surface area of 267 m²/g. The high surface area exposed majority of its adsorption sites, that is, surface hydroxyl groups, for fluoride removal. The plausible adsorption mechanism deduced based on FTIR and XPS data showed that ion exchange between the surface hydroxyl groups and the fluoride ions in water played a vital role in defluoridation by CTNC. A novel approach was used to quantify the adsorption sites with the use of BET and thermogravimetric analysis. TEM images confirmed the morphology of CTNC to be nanotubes decorated with ceria particles. The analysis of treated water samples for the metal ion content was carried out by an ICP-MS technique. CTNC exhibited characteristics of an ideal adsorbent such as high adsorption capacity, faster kinetics, pH independent adsorption, good regeneration, and negligible leaching of metal ions into the effluent. These attractive characteristics enabled the applicability of CTNC for real-time use.