Statistical optimization of amorphous iron phosphate: inorganic sol-gel synthesis-sodium potential insertion

Iron phosphate, Fe₂ (HPO₄)₃*4H₂O, is synthesized at ambient temperature, using the inorganic sol–gel method coupled to the microwave route. The experimental conditions for the gelling of Fe (III)-H₃PO₄ system are previously defined. Potentiometric Time Titration (PTT) and Potentiometric Mass Titration (PMT) investigate the acid–base surface chemistry of obtained phosphate. Variations of surface charge with the contact time, Q a function of T, are examined for time contact varying in the range 0–72 h. The mass suspensions used for this purpose are 0.75, 1.25 and 2.5 g L⁻¹. The point of zero charge (PZC) and isoelectric point (IEP) are defined using the derivative method examining the variations \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\frac{{{\text{dpH}}}}{{{\text{d}}t}} = f\left( {{\text{pH}}} \right)$$\end{document}dpHdt=fpH, at lower contact time. A shift is observed for PZC and IEP towards low values that are found to be 2.2 ± 0.2 and 1.8 ± 0.1, respectively. In acidic conditions, the surface charge behavior of synthesized phosphate is dominated by \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{{ > {\text{POH}}}}$$\end{document}>POH¯ group which pK_a = 2.45 ± 0.15. Q against T titration method is performed for synthesized Fe₂ (HPO₄)₃*4H₂O in NaCl electrolytes. The maximal surface charge (Q) is achieved at the low solid suspension. Hence, for m = 0.75 g L⁻¹, Q value of 50 coulombs is carried at μ = 0.1 and pH around 12, while charge value around 22 coulombs is reached in the pH range: 3–10. The effect of activation time, Q and pH on sodium insertion in iron phosphate, were fully evaluated. To determine the optimal conditions of the studied process, mathematical models are used develop response surfaces in order to characterize the most significant sodium interactions according to the variation of the pH, Q, the contact time and the contents of the synthesized material.

Low-cost composites based on porous titania-apatite surfaces for the removal of patent blue V from water: Effect of chemical structure of dye

Hydroxyapatite/titania nanocomposites (TiHAp) were synthesized from a mixture of a titanium alkoxide solution and dissolution products of a Moroccan natural phosphate. The simultaneous gelation and precipitation processes occurring at room temperature led to the formation of TiHAp nanocomposites. X-ray diffraction results indicated that hydroxyapatite and anatase (TiO2) were the major crystalline phases. The specific surface area of the nanocomposites increased with the TiO2 content. Resulting TiHAp powders were assessed for the removal of the patent blue V dye from water. Kinetic experiments suggested that a sequence of adsorption and photodegradation is responsible for discoloration of dye solutions. These results suggest that such hydroxyapatite/titania nanocomposites constitute attractive low-cost materials for the removal of dyes from industrial textile effluent.

Parameters influencing ciprofloxacin, ofloxacin, amoxicillin and sulfamethoxazole retention by natural and converted calcium phosphates

The retention of four antibiotics, ciprofloxacin, ofloxacin, amoxicillin and sulfamethoxazole by a natural phosphate rock (francolite) was studied and compared with a converted hydroxyapatite powder. The maximum sorption capacities were found to correlate with the molecular weight of the molecules. The mechanisms of sorption depended mostly on the charge of the antibiotic whereas the kinetics of the process was sensitive to their hydrophobic/hydrophilic character. The two materials showed slightly distinct affinities for the various antibiotics but exhibited similar maximum sorption capacities despite different specific surface areas. This was mainly attributed to the more pronounced hydrophobic character of the francolite phase constituting the natural phosphate. These data enlighten that the retention properties of these mineral phases depend on a complex interplay between the inter-molecular and molecule-solid interactions. These findings are relevant to understand better the contribution of calcium phosphates in the fate and retention of antibiotics in soils.

Lead and zinc removal from aqueous solutions by aminotriphosphonate-modified converted natural phosphates

Apatite particles prepared from natural phosphate rock and grafted with nitrilotris(methylene)triphosphonate (NTP) were evaluated for Pb²⁺ and Zn²⁺ sorption from aqueous solutions. Sorption capacities as high as 640 mg.g^-1 and 300 mg.g^-1 could be obtained for the highest organic content (10 wt%). Analysis of the sorption isotherms using Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich models revealed that Pb²⁺ ions have a larger affinity for apatite (sorption energy ≈ 8 kJ.mol^-1) than for NTP so that organo-modified surfaces led to a heterogenous adsorption process. In contrast, Zn²⁺ interacts weakly (sorption energy ≈ 1 kJ.mol^-1) and similarly with the mineral surface and the organic moieties following a homogenous sorption process. Such an association of organic metal ligands with reactive apatite surfaces within porous materials appears as a promising strategy to obtain efficient adsorbents at low cost and limited environmental impact.