Speciation of borate in aqueous solutions studied experimentally by potentiometry and Raman spectroscopy and computationally by DFT calculations

Abstract

The speciation of borate has been studied by potential titration in 0.5 M NaClO₄ and Raman spectroscopic titration at 25 °C. Five borate species including B(OH)₄⁻, B₃O₃(OH)₄⁻, B₅O₆(OH)₄⁻, B₃O₃(OH)₅²⁻, and B₄O₅(OH)₄²⁻ along with boric acid, H₃BO₃, are identified, and the corresponding formation constants are determined accordingly in the solutions with initial boron concentrations between 0.01 and 0.7 M. The attributions for the Raman shifts of the spectra at 874 cm⁻¹ to the ν₁ vibrational mode of B(OH)₃, 741 cm⁻¹ to ν₁ of B(OH)₄⁻, 610 cm⁻¹ to ν₁ of B₃O₃(OH)₄⁻, 525 cm⁻¹, 760 cm⁻¹, 915 cm⁻¹, and 994 cm⁻¹ to ν₁, ν₂, ν₄, and ν₃ of B₅O₆(OH)₄⁻, 612 cm⁻¹ to ν₁ of B₃O₃(OH)₅²⁻, and 563 cm⁻¹ (ν_1a) and 938 cm⁻¹ (ν_1b) to B₄O₅(OH)₄²⁻ are made by combining the speciation from potential titrations and deconvolution of Raman spectra with DFT calculations.