As(III) removal from aqueous solutions using simultaneous oxidation and adsorption process by hierarchically magnetic flower-like Fe3O4@C-dot@MnO2 nanocomposite

In the present study, a magnetic flower-like Fe3O4@C-dot@MnO2 nanocomposite was synthesized by hydrothermal method and applied for As(III) removal by oxidation and adsorption process. Individual property of the entire material (i.e. magnetic property of Fe3O4, mesoporous surface property of C-dot and oxidation property of MnO2) make the composite efficient with good adsorption capacity for As(III) adsorption. The Fe3O4@C-dot@MnO2 nanocomposite had a saturation magnetization of 26.37 emu/g and it magnetically separated within 40 s. The Fe3O4@C-dot@MnO2 nanocomposite was able to reduce the 0.5 mg/L concentration of As(III) to 0.001 mg/L in just 150 min at pH 3. Pseudo-second-order kinetic and Langmuir isotherm model agreed with experimental data. The uptake capacity of Fe3O4@C-dot@MnO2 nanocomposite was 42.68 mg/g. The anions like chloride, sulphate and nitrate did not show any effect on removal but carbonate and phosphate influenced the As(III) removal rate. Regeneration was studied with NaOH and NaClO solution and the adsorbent was used for repeated five cycles above 80% removal capacity. The XPS studies proposed that As(III) first oxidized to As(V) then adsorb on the composite surface. This study shows the potential applicability of Fe3O4@C-dot@MnO2 nanocomposite to high extent and gives a suitable path for the proficient removal of As(III) from wastewater.

Porous Lanthanum-Zirconium phosphate with superior adsorption capability of fluorine for water treatment

Bimetal oxide is a popular defluorinating material. Hexadecyl trimethyl ammonium bromide (CTAB) as a surfactant successfully synthesizes a novel lanthanum-zirconium phosphate to remove fluorine from groundwater. Lanthanum-zirconium phosphate at a Zr/La molar ratio of 2 exhibited a specific surface area of 455.14 m2/g with a wide pore size, which was achieved by incorporating lanthanum into materials and removing CTAB through calcination. The maximum fluoride adsorption capacity is 109.17 mg/g, which is tenfold that of mesostructured zirconium phosphate. Specifically, analysis revealed that mZrP and LamZrP2-1 were amorphous, which is consistent with HAADF-STEM. The fluoride adsorption fitted well with the pseudo-second-order equation model and Langmuir isotherm mode. LamZrP2-1 had potent anti-interference ability without PO43-. Moreover, LamZrP2-1 was reusable for at least six cycles of adsorption-desorption with little influence. The adsorption mechanism of fluoride was discussed by X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance spectroscopy (NMR) analysis, and Fourier transform infrared (FTIR) spectroscopy. Fluoride was captured by LamZrP2-1 via charge attraction, ligand exchange of different bond strengths, and ion exchange. Lanthanum-zirconium phosphate is important not only in the research and development of bimetal oxides but also in the treatment of groundwater for fluoride removal.

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

The presence of excess fluoride (F^- > 1.5 mg/L) in drinking water affects more than 260 million people globally and leads to dental and skeletal fluorosis among other health problems. This study investigated fluoride removal by graphene oxide-ceria nanohybrid (GO-CeO₂) and elucidated the mechanisms involved. The nanohybrid exhibited ultra-rapid kinetics for fluoride removal and the equilibrium (85% removal, 10 mg F^-/L initial concentration) was achieved within 1 min which is one of the fastest kinetics for fluoride removal reported so far. Fluoride removal by the nanohybrid followed Langmuir isotherm with a maximum adsorption capacity of 8.61 mg/g at pH 6.5 and that increased to 16.07 mg/g when the pH was lowered to 4.0. Based on the experimental results and characterization data, we have postulated that both electrostatic interaction and surface complexation participated in the fluoride removal process. The O^2- ions present in the CeO₂ lattice were replaced by F^- ions to make a coordination compound (complex). While both Ce⁴⁺ and Ce³⁺ were present in ceria nanoparticles (CeO₂ NPs), Ce³⁺ participated in fluoride complexation. During fluoride removal by GO-CeO₂, the GO sheets acted as electron mediators and help to reduce Ce⁴⁺ to Ce³⁺ at the CeO₂ NPs-GO interface, and the additional Ce³⁺ enhanced fluoride removal by the nanohybrid.

Hydrothermal synthesis of a mineral-substituted hydroxyapatite nanocomposite material for fluoride removal from drinking water

Mineral substituted hydroxyapatite (mHAp) nanocomposite was synthesized and it shows high fluoride adsorption capacity.

A new adsorbent of a Ce ion-implanted metal–organic framework (MIL-96) with high-efficiency Ce utilization for removing fluoride from water

Ce ions were implanted into MOFs as an effective adsorbent for removing fluoride from water.

Fluoride adsorption on a cubical ceria nanoadsorbent: function of surface properties

Development of ceria with high fluoride loading capacity at pH 7.0 within 2 h at 1 g L⁻¹ adsorbent dose.