One-step synthesis of layered double hydroxide-intercalated gluconate for removal of borate

Abstract

The sorption of borate by ion exchange using a traditional layered double hydroxide (LDH) is affected by external conditions such as coexisting anions. Hydrotalcite intercalated with d-gluconate (G–LDH) was synthesized through a one-step microwave-assisted treatment and characterized by XRD, TEM, FTIR, TG/DTA and two-dimensional 11B NMR. Several factors that influence sorption of borate were investigated: gluconate content in the LDH, G–LDH dosage, coexisting anions, initial pH of borate solution and sorption temperature. The synthesized adsorbent exhibited a greater borate sorption rate than the traditional hydrotalcite (NO3–LDH) or a boron-specific resin. The maximum sorption capacity was 1.27mmol/g (obtained by fitting to the Langmuir model). The G–LDH sorption density increased with increasing initial borate concentration and adsorbent dosage. In the presence of 50mM sulfate, sorption of borate by NO3–LDH significantly decreased and no obvious sorption could be observed, whereas the sorption of borate by G–LDH was maintained at ∼0.57mmol/g. 11B NMR indicated that the sorption mechanism of borate by G–LDH is mainly through bischelate and monodentate types of complexation with borate. This mechanism is similar to that of CRB05, and fundamentally different from that of NO3–LDH.