Solubility of Selenium at High Ionic Strength under Anoxic Conditions

Abstract

Solubility experiments for selenium were performed at high ionic strengths (1.0 and 2.0 mol dm À3 NaCl) under anoxic conditions (p O2 < 10 À6 atm) from undersaturation and oversaturation directions. Equilibrium was attained in 40 days. The dominant aqueous selenium species were identified as hydrogen selenide, HSe À , at pH between 5 and 8, and polyselenide, Se 4 2À , at pH between 9 and 13 by UV-Vis absorption spectrometry. A solubility-limiting solid was determined to be amorphous selenium at pH between 5 and 8, and crystalline selenium at pH between 9 and 13. The equilibrium constants oflog K 0 ¼ À16:67 AE 0:03 ð9 < pH < 13Þand ion interaction coefficients for HSe À and Se 4 2À versus Na þ , "(HSe À , Na þ ) = À0:01 AE 0:10 and "(Se 4 2À , Na þ ) = À0:03 AE 0:02, were determined with the specific ion interaction theory. The standard molar free energies of formation of amorphous selenium and polyselenide species were determined to be Á f G m 0 (Se(am)) = 6:0 AE 2:2 kJ mol À1 , Á f G m 0 (Se 2 2À ) = 111:64 AE 1:61 kJ mol À1 , Á f G m 0 (Se 3 2À ) = 98:68 AE 1:02 kJ mol À1 , and Á f G m 0 (Se 4 2À ) = 95:14 AE 0:17 kJ mol À1 .

Copper Selenophosphate, Cu3PSe4, Nanoparticle Synthesis: Octadecane Is the Key to a Simplified, Atom-Economical Reaction

“…221 °C. ,,, However, one can raise the question of whether there is any dissolution or other speciation of (Se 0 ) n under the 221 °C reaction conditions. Literature studies support the claim of dispersed selenium particles, but moderate solubility has only been observed for select solvents, ,,− most notably carbon disulfide, , hydrazine, and ethylenediamine, but with significantly higher solubility (38 wt % gray selenium) recorded in a binary thiol-amine mixture under ambient conditions . In our own hands, some indirect evidence for a dispersion of Se 0 species is observed in an Se/ODA temperature control (Figure S29), where a color transition is noted only after the melting point to a color distinctly different from the clear solution when Cu 3– x P is present.…”

Layered Antimicrobial Selenium Nanoparticle–Calcium Phosphate Coating on 3D Printed Scaffolds Enhanced Bone Formation in Critical Size Defects

“…Se was found to release continuously over the 3-week testing period (c). Extracted medium from PCL-Se-CaP scaffolds showed absorption at 250 nm (d, d1), characteristic of HSe – ions …”

“…It is, therefore, expected that a complete Se release will only occur after about 6 months. Absorption spectra of the extracted medium showed a characteristic absorption of HSe − at around 250 nm 32 (Figure 3d,d1), which was not present in a freshly prepared Se nanoparticle suspension (Figure S1b,b1).…”

“…This result was supported by the ICP results that showed a significant release of Se in the first day and a steady release over 3 weeks. Our group and others have shown that the selenium nanoparticles prepared using the same reduction–precipitation method were amorphous , and thus their relatively high release at physiological pH (−log K 0 ∼ 6) could be attributed to their gradual dissolution. Despite the initial high release of Se, the total release of this ion was only 15% after 3 weeks, suggesting that the antibacterial activity could be sustained for a prolonged time period.…”