Thiocyanate Doping in Gel-Growth Cobalt Oxalate Crystals

Abstract

Abstract The presence of other anions, as impurities and/or doping agents, may alter crystallization and the properties of the crystal. The objective of this research is to examine the effect of thiocyanate doping in the synthesis of cobalt oxalate crystals grown in silica gel. The synthesis was conducted at room temperature for 12 weeks in a U-tube glass filled with silica gel. The gel was prepared from Na2SiO3 at pH 5 using dilute HNO3 with a gelling time of 5 days. Supernatant solutions of (NH4)2C2O4 and Co(NO3)2/KSCN were added on each side of the tube. The Co(NO3)2 and KSCN were firstly mixed before adding onto the gel to increase the possibility of thiocyanate doping in the crystals. Various molar ratio of Co(II):C2O4 −2:SCN− were used (1:1:0, 1:1:1, 1:1:2, 1:1:3, 1:1:4, and 1:1:5). FT-IR and SEM were used to analyse the crystal. The result shows that red block crystals were formed. FTIR analysis for all molar ratios reveals that they all give considerably identical spectra with an absence of thiocyanate peaks around 2200 cm−1, suggesting that all molar ratios give an identical product of cobalt(II) oxalate hydrate. SEM analysis shows that the size of the crystals was significantly bigger than previously reported crystals. The Co(II) centre binds to the oxalate ligand, and not to the thiocyanate, due to chelating effect. However, inconclusive findings were observed regarding the influence of the molar ratio on the crystals yield. The use of a higher concentration of thiocyanate (fivefold molar ratio) did not affect the composition of the product, and the product remains crystallized as cobalt(II) oxalate hydrate.