Removal of residual nitrate ion from bioactive calcium silicate through soaking

Bioactive calcium silicates prepared by sol–gel routes mainly use calcium nitrate as the calcium precursor. However, the toxic nitrate ions are usually removed by calcination (i.e. 550 °C or over), which poses great challenge for the in situ preparation of inorganic/polymer composites, as polymer moieties could not survive such temperatures. In this study, we prepared 70Si30Ca (70 mol% SiO2 and 30 mol% CaO) bioactive glass at low temperatures where polymer could survive (i.e. 200 °C and 350 °C), and proposed to remove the residual nitrate ions through soaking. Deionized water and simulated body fluid (SBF) were employed as the soaking medium. The results showed that the residual nitrate ions could be removed as quickly as 0.5 h while maintain the bioactivity of the samples. This technique may open the possibility of preparing sol–gel derived bioactive glass/polymer hybrids in situ with reduced potential toxicity.

Graphical abstractThe nitrate ion can be rapidly removed by soaking method for only 0.5 h.Figure optionsDownload full-size imageDownload as PowerPoint slide