Investigation of kinetics and adsorption isotherm for fluoride removal from aqueous solutions using mesoporous cerium-aluminum binary oxide nanomaterials

Adsorption removal of fluoride from polluted drinking waters using Mn-Al-La oxide

Trimetal oxides have received high attention in treatment of fluoride-polluted drinking waters. In this study, Mn-Al-La (MAL) oxide with a mole ratio of 2:1:1 was successively prepared and characterized by XRD, FTIR, XPS, and TEM. It exhibited as cotton-like assemblages (500-800 nm of axial lengths), and BET specific surface area was 52 m2/g. It was used to study fluoride adsorptions in aqueous solutions by batch experiments, under different adsorbent/adsorbate levels, times, temperatures, pH and coexisting anions, and treat simulated groundwater (with 2.85 mg/L fluoride and pH 7.0) by batch and column tests. Adsorption data well fitted to pseudo-second-order rate model (R2 = 0.996-0.999), and Langmuir (R2 = 0.962 - 0.997) and Freundlich (R2 = 0.964-0.989) isothermal models. Their maximum adsorption capacities could reach 45-113 mg/g. Only H2PO4- anions had a restrictive impact at pH 7.0, and there was a good removal ability at pH 3-9. Adsorption processes were spontaneous, endothermic, and random. Adsorption mechanisms were electrostatic interaction and ligand exchange at pH 7.0. Adsorption capacity could reach 73% of initial value at pH 7.0, after three cycles. All application data on the polluted groundwater treatments show MAL oxide is a potential adsorbent for fluoride removals.

Functional hBN decorated Ni(OH)2 nanosheets synthesized for remarkable adsorption performance for the elimination of fluoride ions

Occurrence of fluoride in groundwater is a serious concern due to its fatal effects. Functionalized hexagonal boron nitride sheets have been combined with nickel hydroxide nanoparticles by a one step process and a hybrid adsorbent Ni(OH)2@hBN has been developed with an exceptionally high fluoride adsorption capacity of 365 mg g-1, higher than those of Ni(OH)2 and hBN. This maximum adsorption capacity is higher than those of most common adsorbents used for defluoridation including activated alumina, reported nickel oxide and carbon-based 2D material-supported alumina adsorbents. The presence of functionalized boron nitride significantly increased the surface area to 680 m2 g-1 with a pore volume of 0.33687 cm3 g-1 and provided rich hydroxyl group-containing surface sites for the removal of fluoride present in contaminated water. In addition, the adsorption of fluoride onto boron nitride-modified nickel hydroxide followed pseudo-second-order kinetics and the equilibrium data fitted well with the Langmuir adsorption isotherm, suggesting a monolayer adsorption mechanism. Furthermore, the material developed is tested with the water sample collected from a real affected area, from the Dhar district of India, and the material showed promising results in terms of fluoride removal efficacy.

Characterization of modified rice straw biochar in immobilizing Bacillus subtilis 168 and evaluation on its role as a novel agent for zearalenone-removal delivery

Microbial remediation of environmental pollutants can be advanced by carrier based cells immobilization. Whereas the effects of microorganisms immobilized on biochar for removal of zearalenone (ZEN) still remain unknown. Herein, this work presented the characterization of rice straw biochar (RSB) around modification in immobilizing Bacillus subtilis 168 and the role in fighting ZEN in vitro. Specifically, 10% of RSB with pH 5 condition were optimal for bearing cells, where majority of cells loaded inside the pore and minority on surface with agglomeration or scattering status. Octadecyl trimethyl ammonium chloride-inclusion RSB showed better performances including over 93% of ZEN detoxification rate (32.48% in free cells), cells preservation, and stability of detoxification in simulated gastrointestinal environment. RSB treated with sulphuric acid made nutrients adsorption generally less than 6.5%. No residues of α-ZEL and α-ZAL were found in ZEN biotransformation process whether by free cells or composites. Mechanism discussion implied that predominant monolayer chemisorption by RSB and subsequent biodegradation by extracellular enzymes from microorganism involved in ZEN-removal process. Collectively, these findings contribute to provide an applying strategy for coordination of biochar and microorganisms as potentially mycotoxin detoxifying agent in agricultural feed bioremediation and environmental decontamination processes.

Covalent Organic Framework as a Metal-Free Photocatalyst for Dye Degradation and Radioactive Iodine Adsorption

Exploring a covalent organic framework (COF) material as an efficient metal-free photocatalyst and as an adsorbent for the removal of pollutants from contaminated water is very challenging in the context of sustainable chemistry. Herein, we report a new porous crystalline COF, C₆-TRZ-TPA COF, via segregation of donor-acceptor moieties through the extended Schiff base condensation between tris(4-formylphenyl)amine and 4,4',4″-(1,3,5-triazine-2,4,6-triyl)trianiline. This COF displayed a Brunauer-Emmett-Teller (BET) surface area of 1058 m² g^-1 with a pore volume of 0.73 cc g^-1. Again, extended π-conjugation, the presence of heteroatoms throughout the framework, and a narrow band gap of 2.2 eV, all these features collectively work for the environmental remediation in two different perspectives: it could harness solar energy for environmental clean-up, where the COF has been explored as a robust metal-free photocatalyst for wastewater treatment and as an adsorbent for iodine capture. In our endeavor of wastewater treatment, we have conducted the photodegradation of rose bengal (RB) and methylene blue (MB) as model pollutants since these are extremely toxic, are health hazard, and bioaccumulative in nature. The catalyst C₆-TRZ-TPA COF showed a very high catalytic efficiency of 99% towards the degradation of 250 parts per million (ppm) of RB solution in 80 min under visible light irradiation with the rate constant of 0.05 min^-1. Further, C₆-TRZ-TPA COF is found to be an excellent adsorbent as it efficiently adsorbed radioactive iodine from its solution as well as from the vapor phase. The material exhibits a very rapid iodine capturing tendency with an outstanding iodine vapor uptake capacity of 4832 mg g^-1.

Template-Free Synthesis of Magnetic La-Mn-Fe Tri-Metal Oxide Nanofibers for Efficient Fluoride Remediation: Kinetics, Isotherms, Thermodynamics and Reusability

The occurrence of fluoride contamination in drinking water has gained substantial concern owing to its serious threat to human health. Traditional adsorbents have shortcomings such as low adsorption capacity and poor selectivity, so it is urgent to develop new adsorbents with high adsorption capacity, renewable and no secondary pollution. In this work, magnetic electrospun La-Mn-Fe tri-metal oxide nanofibers (LMF NFs) for fluoride recovery were developed via electrospinning and heat treatment, and its defluoridation property was evaluated in batch trials. Modern analytical tools (SEM, BET, XRD, FTIR) were adopted to characterize the properties of the optimized adsorbent, i.e., LMF11 NFs with a La:Mn molar ratio of 1:1. The surface area calculated via BET method and pH_pzc assessed using pH drift method of LMF11 NFs were 55.81 m² g^-1 and 6.47, respectively. The results indicated that the adsorption amount was highly dependent on the pH of the solution, and reached the highest value at pH = 3. The kinetic behavior of defluoridation on LMF11 NFs was dominated by the PSO model with the highest fitted determination coefficients of 0.9999. Compared with the other three isotherm models, the Langmuir model described defluoridation characteristics well with larger correlation coefficients of 0.9997, 0.9990, 0.9987 and 0.9976 at 15 °C, 25 °C, 35 °C and 45 °C, respectively. The optimized LMF11 NFs exhibited superior monolayer defluoridation capacities for 173.30-199.60 mg F^-/g at pH 3 at 15-45 °C according to the Langmuir isotherm model. A thermodynamic study proved that the defluoridation by LMF11 NFs is a spontaneous, endothermic along with entropy increase process. In addition, the LMF11 NFs still showed high defluoridation performance after three reused cycles. These findings unveil that the synthesized LMF11 NFs adsorbent is a good adsorbent for fluoride remediation from wastewater owing to its low cost, high defluoridation performance and easy operation.

Synthesis of stable flowerlike MgAl-LDH@MIL-88A and its adsorption performance for fluoride

MgAl-LDH@MIL-88A as an effective adsorbent was successfully prepared by a simple stirring method in water bath through loading MIL-88A onto the surface of flowerlike MgAl-LDH, which was synthesized via solvothermal method. Interestingly, the results of characterizations showed that the MIL-88A could still grow, but extrude the brucite-like layers of MgAl-LDH. The influences of initial solution pH, contact time, temperature, and co-existing ions on the adsorption performance of MgAl-LDH@MIL-88A were studied systematically by batch static adsorption experiments. It was found that MgAl-LDH@MIL-88A represented the highest adsorption loading of fluoride (14.00 mg g−1) at initial pH 7.0 in 420 min. The uptake process was described appropriately by the pseudo-second-order, the Temkin and the Freundlich isotherm models. The thermodynamic parameters confirmed the endothermic and spontaneous nature of adsorption. MgAl-LDH@MIL-88A was the green adsorbent as the residual mental contents ([Mg2+] = 1.095 mg L−1, [Fe3+] = 0.007 mg L−1, [Al3+] = 0.076 mg L−1) after adsorption met the Chinese sanitary standard for drinking water (GB 5749-2006). The mechanism of fluoride removal by MgAl-LDH@MIL-88A involved the electrostatic interactions between Fe3+ of MIL-88A and fluoride, and ligand exchange among hydroxyl groups of MgAl-LDH, carboxylate groups of the C4H4O4 and fluoride.

Mesoporous Calcium-Silicate Nanoparticles Loaded with Prussian Blue Promotes Enterococcus Faecalis Ferroptosis-Like Death by Regulating Bacterial Redox Pathway ROS/GSH

Background

Mesoporous calcium-silicate nanoparticles (MCSNs) are advanced biomaterials that have been used to control drug delivery for many years. Ultrasmall Prussian blue nanoparticles (UPBNPs) showed high peroxidase and catalase-like activities. This study evaluated the antibacterial and antibiofilm properties, mechanism and cytotoxicity of UPBNPs-MCSNs composites synthesized by both as precursors.

Methods

UPBNPs-MCSNs were prepared and characterized. The antibacterial effect of UPBNPs-MCSNs was evaluated by the MTT assay and CFU counting method, and their biosafety was tested by CCK8. Then explore the antibacterial mechanism, including TEM observation of bacterial morphology, and detection of bacterial ROS, LPO and GSH levels. The antibiofilm activity of UPBNPs-MCSNs was tested by E. faecalis biofilm model in human roots. The roots were pretreated with materials and cultured with E. faecalis, and the survival of E. faecalis on the root canal wall was observed by SEM and CLSM.

Results

The results showed that UPBNPs-MCSNs had potent antibacterial and antibiofilm activities. They can aggregate on the dentin surface and significantly inhibit E. faecalis adhesion and colonization. Their antibacterial activity is as effective as NaClO and calcium hydroxide (CH), can significantly prolong the time of bacterial colonization than CH, but have lower cytotoxicity to normal cells. We found that UPBNPs-MCSNs trigger a like classic ferroptosis pathway in bacteria. UPBNPs-MCSNs can induce bacteria to produce ROS and LPO, and reduce GSH level. Moreover, we observed that the metal ions chelator and the antioxidant could block their antibacterial activity.

Conclusion

These results reveal that UPBNPS-MCSNs have high antibacterial and antibiofilm, and can mediate the bacterial redox pathway ROS/GSH like the classical pathway of ferroptosis, providing a theoretical basis for them to develop into a safe and effective novel root canal disinfectant.

Probing the effect of Ni, Co and Fe doping concentrations on the antibacterial behaviors of MgO nanoparticles

The divalent transition metal ions (Ni, Co, and Fe)-doped MgO nanoparticles were synthesized via the sol–gel method. X-ray diffraction showed the MgO pure, single cubic phase of samples at 600 °C. Field emission electron microscope showed the uniform spherical shape of samples. The magnetic behavior of Ni, Co, Fe-doped MgO system were varied with Ni, Co, Fe content (0.00, 0.01, 0.03, 0.05, 0.07). The magnetic nature of pure had changed from paramagnetic to ferromagnetic. The number of oxygen vacancies increases with increasing amounts of dopant ions that lead to an ionic charge imbalance between Ni²⁺/Co²⁺/Fe²⁺ and Mg²⁺, leading to increase magnetic properties of the samples. The magnetic nature of prepared samples makes them suitable for biomedical applications. A comparative study of the antibacterial activity of nanoparticles against the Gram-negative (E. coli) and Gram-positive bacteria (S. aureus) was performed by disc diffusion, pour plate techniques, and study surface morphology of untreated and treated bacterial cell wall. An investigation of the antibacterial activity of doped MgO nanoparticles reveals that the doped MgO nanoparticles show effective antibacterial activity against the Gram-negative (E. coli) and Gram-positive (S. aureus) bacterium. The minimum inhibitory concentration of the synthesized nanoparticles against microorganisms was recorded with 40 μg/ml, while the maximum inhibitory concentration was observed with 80 μg/ml. At a concentration of 80 μg/ml, the complete growth inhibition of the E. coli was achieved with 7% Co-doped MgO and 7% Fe-doped MgO, while bacterial growth of S. aureus was inhibited by 100% in the presence of 7% Fe-doped MgO. The present work is promising for using nanomaterials as a novel antibiotic instead of the conventional antibiotics for the treatment of infectious diseases which are caused by tested bacteria.