Sodium carbonate monohydrate

Yttrium (III) nitrate hexahydrate (Y(NO₃)₃·6H₂O, 99.9%), ruthenium (III) nitrosyl nitrate solution (Ru(NO)(NO₃)_x(OH)_y, x + y = 3), Nafion^® 117 solution (~ 5%), ruthenium (IV) oxide (RuO₂, 99.9%), and sodium carbonate monohydrate (Na₂CO₃·H₂O, 99.5%) were purchased from Sigma-Aldrich. Iridium (IV) oxide (IrO₂, 99.9%), manganese (II) nitrate tetrahydrate (Mn(NO₃)₂·4H₂O, 99.9%), iridium(III) chloride hydrate (IrCl₃·xH₂O, 99%), and manganese(IV) oxide (MnO₂, 99.9%) were purchased from Alfa Aesar. Citric acid monohydrate (C₆H₈O₇·H₂O, 99%) and sodium hydroxide (NaOH, 99.4%) were from Fisher Chemical. Veritas^® double distilled perchloric acid (HClO₄, 70%) was obtained from GFS Chemicals. Yttrium(III) chloride hexahydrate (YCl₃·6H₂O, 99.9%) was purchased from Stream Chemicals. Tetrahydrofuran (THF) was obtained from Macron Fine Chemicals. Vulcan carbon XC-72 was purchased from Cabot Corporation. Hydrogen (H₂, 99.999%) and oxygen (O₂, 99.999%) were supplied by Airgas, Inc. All these chemicals and gases were used without further purification.

Sodium citrate tribasic dihydrate (Na₃(cit)·2H₂O, cit = citrate = C₆H₅O₇, ACS reagent, ≥99,0% pure), terbium (III) chloride anhydrous (TbCl₃, 99.9% pure, trace metals), calcium chloride dihydrate (CaCl₂·2H₂O, Bioxtra, ≥99.0% pure), and sodium phosphate dibasic (Na₂HPO₄, ACS reagent, ≥99.0% pure) were provided by Sigma-Aldrich (St. Louis, MO, USA). Sodium carbonate monohydrate (Na₂CO₃·H₂O, ACS reagent, 99.5% pure) was supplied by Merck (Darmstadt, Germany) and hydrochloric acid (HCl, ACS reagent, 37 wt% in H₂O) by Panreac (Barcelona, Spain). Solutions were prepared with ultrapure deionized Milli-Q water (0.22 μS, 25 °C, Millipore, Burlington, MA, USA). The precipitation experiments were carried out by thermal decomplexing of M^(2+/3+)/Ca²⁺/cit/phosphate/carbonate solutions at 80 °C [30 (link),31 (link)], using Tb³⁺ as doping lanthanide ion (x = 0, 0.001, 0.005, 0.010, 0.015, and 0.020 M) and decreasing concentrations of Ca²⁺ in the precipitating solution (y = 0.100, 0.099, 0.095, 0.090, 0.085, and 0.080) to set x + y = 0.100 M. The experiments lasted 4 h, 24 h, 96 h, and 7 days. The precipitates were subjected to washing by centrifugation with ultrapure water (6 cycles, 9000 rpm, 9 min each) and freeze-dried overnight at −50 °C under vacuum (3 mbar).

For the experiments the following reagents were purchased from Sigma-Aldrich (St Louis, MO, USA): Terbium (III) chloride anhydrous (TbCl₃, 99.9% pure, trace metals), sodium citrate tribasic dihydrate (Na₃(cit)·2H₂O, where cit = citrate = C₆H₅O₇, ACS reagent, ≥99.0% pure), calcium chloride dihydrate (CaCl₂·2H₂O, Bioxtra, ≥99.0% pure), and sodium phosphate dibasic (Na₂HPO₄, ACS reagent, ≥99.0% pure). Sodium carbonate monohydrate (Na₂CO₃·H₂O, ACS reagent, 99.5% pure) and hydrochloric acid (HCl, ACS reagent, 37 wt % in H₂O) were provided by Merck (Darmstadt, Germany) and Panreac (Barcelona, Spain), respectively. Solutions were prepared with ultrapure deionized water (0.22 µS, 25 °C, Milli-Q, Millipore, Burlington, MA, USA).
The synthesis of nanocrystals was carried out by the already established method of thermal decomplexing of M^(2+/3+)/Ca²⁺/cit/phosphate/carbonate solutions [29 (link)], using Tb³⁺ as lanthanide ion (y = 0.09, 0.07, 0.05 and 0.03 M) and increasing concentrations of doping Ca²⁺ in the solution (x = 0.01 M, 0.03, 0.05, and 0.07 M) to set x + y = 0.1 M. The experiments lasted 4 h, 24 h, and 96 h. Some of them were matured for 7 days. The precipitates were subjected to washing by centrifugation with ultrapure water (6 cycles, 9000 rpm, 9 min each) and freeze-dried overnight at −50 °C under vacuum (3 mbar).