The apparent molar heat capacities of LiBO 2 (aq), NaBO 2 (aq), KBO 2 (aq), Na 2 B 4 O 7 (aq) and K 2 B 4 O 7 (aq) solutions at molalities from 0.01 to 2.6 mol·kg −1 , and at temperatures T = (298.12, 313.13 and 328.14) K have been determined using a Picker flow calorimeter built in this work. Further, the standard heat capacities of these solutes were derived from the experimental data by extrapolation to infinite dilution using the Pitzer ion-interaction model. The group contribution method is used to calculate the standard molar heat capacities of tetraborate ion in three equilibria for different assumptions, among which the prediction on the assumption that the standard molar heat capacity of reaction for the association reaction is zero is the most reasonable, and the results are in good agreement with the experimental data.
Herein, B, P co-doped porous carbon (PC BP ) was prepared from K 2 B 4 O 7 and phytic acid-modified cellulose via chemical activation and used as electrode materials for supercapacitors. Of which, K 2 B 4 O 7 not only acts as a source of boron, but also as an activation agent in the process of activation. The electrochemical properties of porous carbon materials were significantly improved by doping P and B. Compared with the porous carbon doped by B, PC BP shows almost higher specific capacitance and better rate performance. When evaluated as supercapacitor electrode materials in 6 M KOH electrolyte under two-electrode test systems, the as-prepared PC BP exhibits an excellent electrochemical performance: a high specific capacitance of 214 F g −1 at 0.05 A g −1 , a good rate capability of 142 F g −1 at 20 A g −1 and 2.7% capacitance loss after 10,000 cycles. Thus, the co-doping of B and P holds great promise for improving the specific capacitance and rate capability, which is attributed to the synergistic effect of B and P co-doped. Graphical abstract
Boron-containing brines are widely distributed in nature, and within the pH range of salt lakes, B4O72– is one of the primary boron forms. To express the brine properties and phase equilibrium behavior of boron-containing brine systems, experiments and thermodynamic research based on the eNRTL framework were carried out. Tetraborate aqueous systems are focused in this study: (1) the phase diagram data of K2B4O7–K2SO4–H2O and K2B4O7–K2SO4–KCl–H2O systems at 298.15 and 323.15 K were experimentally determined; (2) the heat capacity of the B4O72– ion was determined via simultaneously fitting the thermodynamic property and solubility data of Li2B4O7, Na2B4O7 and K2B4O7 aqueous systems; (3) the liquid parameters (interaction parameters between water–ionic pair and ionic pair–ionic pair) and solid parameters (ΔfGk°, ΔfHk°, ΔCp,k°) for three binary systems (Li2B4O7–H2O, Na2B4O7–H2O, K2B4O7–H2O) and two ternary systems (K2B4O7–K2SO4–H2O, K2B4O7–KCl–H2O) were determined by fitting the multitemperature phase diagram data; and (4) the complete structures of the phase diagram for the ternary and quaternary systems were predicted. The results demonstrate that (1) the models can effectively describe the solution properties and solid–liquid phase equilibrium behavior of tetraborate-containing aqueous systems, (2) the parameters exhibit thermodynamic consistency, and (3) the predicted complete phase diagram is reasonable.
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