Rheological behaviour and spectroscopic investigations of cerium-modified AlO(OH)colloidal suspensions

The rheological behaviour of aqueous suspensions of boehmite (AlO(OH)) modified with different Ce-salts (Ce(NO3)3, CeCl3, Ce(CH3COO)3 and Ce2(SO4)3) was investigated at a fixed Ce/Al molar ratio (0.05). Freshly prepared boehmite suspensions were near-Newtonian and time-independent. A shear-sensitive thixotropic network developed when Ce-salts with monovalent anions were introduced in the nanoparticle sols. The extent of particle aggregation dramatically increased with ageing for Ce(NO3)3 and CeCl3 whereas an equilibrium value was reached with Ce(CH3COO)3. The addition of Ce2(SO4)3 with divalent anions involved no thixotropy but rather a sudden phase separation. The combined data set of IRTF and DRIFT spectra indicated that free View the MathML source anions of peptized boehmite adsorb on the nanoparticle surface by H-bond. The introduction of Ce-salts in the boehmite sol led to the coordination between Ce3+ ions and View the MathML source anions adsorbed on boehmite i.e. to [Ce(NO3)4(H2O)x]− complex. Such coordination led to a thixotropic behaviour which was lower with Ce(NO3)3 compared to CeCl3 and Ce(CH3COO)3. In contrast, Ce2(SO4)3 formed insoluble complexes with dissolved aluminium species. The formation of H-bonded surface nitrate complexes was found to play a decisive role on the particle–particle interactions and consequently on the rheological behaviour of the sols