Combination of interfacial reduction of hexavalent chromium and trivalent chromium immobilization on tin-functionalized hydroxyapatite materials

Abstract

We present an ecofriendly hydroxyapatite (HAP) material functionalized with tin (Sn/HAP) for an efficient interfacial reduction of Cr(VI) to Cr(III).Tin was deposited on HAP at different concentrations (from 0.2 to 1.2 mmol/g) using colloidal or clear acid solutions of SnCl 2 . The morphological and structural properties of fresh and used Sn/HAP samples were determined (N 2 adsorption-desorption, transmission electron microscopy techniques, XRPD, XPS). Tests were performed under various conditions: at different pH 3-7, inert or oxidant atmosphere, sample aging (up to 15 days).Sn/HAP samples prepared using colloidal acid solutions revealed the best performances in the reduction of Cr (VI) to Cr(III), carried out under mild conditions (40 • C in acidified solution) with initial concentration of Cr(VI) in the range from 25 to 50 ppm. Best removal of Cr(VI) (10 mg/g) was obtained by using a Sn-concentration of 0.65 mmol/g with complete adsorption of the formed Cr(III) at HAP surface. This finding was associated with higher Sn-dispersion (surface Sn, 9.4 at.%) compared to samples prepared from clear solutions (surface, Sn 7.7 at. %), as evidenced by HAADF-STEM/EDX and XPS analyses. Remarkably, tin was tightly retained on the HAP surface under reaction conditions (0.7% leaching), confirming the occurrence of Cr(VI) reduction at solid-liquid interphase.

Phosphate Cements Based on Calcined Dolomite: Influence of Calcination Temperature and Silica Addition

“…The reduced efficiency in immobilization of Cr in this type of cement can be due to the inhibition of K-struvite formation (suggested by XRD data— Figure 6 ). Nevertheless, the presence of hydroxyapatite (HAp) in this composition could contribute to the immobilization of Cr [ 33 , 34 ], explaining the low amount of chromium levigated in the CMPC with a lower chromium waste content (0.5 wt. %).…”

Preparation, characterization of mixed-valence antimony-tin phosphomolybdic polyoxometalates and application in the cyclohexanone oxidation in the presence of hydrogen peroxide

“…6c) shows two photo peaks in the range 496-488 eV, characteristic of Sn 3d 5/2 and Sn 3d 3/2 . Based on literature data, the binding energy value of 487.2 eV, does not permit to distinguish between both oxidation states II and IV of tin [26,29]. However, the detection of both Mo(V) 3d 5/2 and Mo(V) 3d 3/2 with binding energies of 232.0 and 235.2 eV, respectively, in addition to those of Mo(VI) 3d 5/2 and Mo(VI) 3d 3/2 with binding energies of 233.2 and 236.3 eV, respectively [51], indicates that tin may be present also as Sn(IV), results in agreement with those observed in UV-Vis that have evidenced the presence of Mo(V).…”

“…as a counter-ion using the precipitation method from the parent heteropolyacid (HPA) in the presence of ammonium chloride or cesium chloride [19][20][21][22][23][24][25]. The introduction of antimony or tin in the POM-framework has already been the subject of several studies [22,[26][27][28][29][30][31] (A n+ = Sb 3+ , Bi 3+ or Sn 2+ ) were also prepared. In the case of Sn II based POMs, the Sn IV state is formed in situ, a presence that is demonstrated by XPS or UV-Visible (UV-Vis).…”

Innovative Magnetite Based Polymeric Nanocomposite for Simultaneous Removal of Methyl Orange and Hexavalent Chromium from Water

“…Furthermore, as a conventional toxic heavy metal, chromium not only causes significant damage to human health, but also generates extreme environmental contamination that is hard to remediate [6]. Trivalent chromium Cr (III) and hexavalent chromium Cr (VI) are the two oxidation states of chromium [7]. Cr (VI) is carcinogenic and known to be a very 2 of 15 dangerous contaminant, while Cr (III) is less toxic to humans and other organisms and is less movable in environmental systems [8].…”