C6h8o7 h2o

Pure CaTiO₃ (CTO) perovskite nanoparticles were prepared by the sol-gel method. In this synthesis, titanium (IV) isopropoxide Ti(OC₃H₇)₄ (97% Sigma-Aldrich, St. Louis, MO, USA ), calcium (II) nitrate tetrahydrate Ca(NO₃)₂∙4H₂O (99% Sigma-Aldrich, St. Louis, MO, USA), 2-propanol (EMSURE®, Merk, Darmstadt, Germany), and citric acid monohydrate C₆H₈O₇∙H₂O (≥99% Sigma-Aldrich, St. Louis, MO, USA), were used as starting materials. All the chemicals were of analytical grade and no further purification was performed. The synthesis steps are the following (Figure 1): a) Ti(OC₃H₇)₄, Ca(NO₃)₂∙4H₂O and citric acid were weighed accurately according to the stoichiometric composition, and dissolved separately in 2-propanol, under vigorous stirring for 30 min; b) once the solution of Ca(NO₃)₂∙4H₂O was added drop by drop to the solution of Ti(OC₃H₇)₄), the solution of citric acid was likewise added drop by drop to obtain a CTO precursor solution; c) this last solution was stirred vigorously for 30 min at room temperature while deionized water was slowly added until the gel was formed; d) then, the gel was dried at 50 °C for 96 h. The resultant powder (xerogel) was ground in an agate mortar for 5 min and finally calcined at 600 °C over 1 h in air to obtain CTO powder.

As-synthesized NMCP/rGO was prepared using a sol-gel method and a high temperature sintering method (Figure 1). At the beginning, the sieved 5 wt.% GO powder was put into DI-water, and the GO dispersion was formed by shaking it for 1 h in an input shaker. After the temperature of the GO dispersion reached 80 °C, 1 mmol chromium nitrate nonahydrate (Cr(NO₃)₃·9H₂O, 98.5%, Alfa-Aesar, Ward Hill, MA, USA) completely dissolved in 100 mL DI water was added, and the temperature was maintained at 80 °C with continuous stirring. Then, 1 mmol citric acid (C₆H₈O₇·H₂O, 95%, Sigma-Aldrich, Burlington, MA, USA), 1 mmol manganese acetic acid tetrahydrate ((CH₃COO)₂Mn·4H₂O, ≥99%, Acros-Organi, Janssen-Pharmaceuticalaan, Geel, Belgium), 4 mmol anhydrous sodium acetate (CH₃COONa, 98%, Alfa-Aesar, Ward Hill, MA, USA), 1.25 g ascorbic acid (C₆H₈O₆, 99%, Acros-Organi, Janssen-Pharmaceuticalaan, Geel, Belgium), and 1.025 mL phosphoric acid (H₃PO₄, 86%, Echo Chemical Co., Ltd., Miaoli, Taiwan.) were added, and stirred at 80 °C for 1 h, dried in a circulating oven at 120 °C, and finally sintered at 750 °C under argon atmosphere for 9 h. To prepare pristine NMCP, the same procedure described in the previous part was used, only without the step of adding GO in the preparation process of NMCP/rGO.