The effect of montmorillonite modification by Cr(III)-compounds on its microcrystalline structure and electrosurface properties

Modification of clay minerals by nanoclusters of hydroxycations Cr(ІІІ) opens the perspectives for development of a new materials (catalysts, adsorbents, pigment concentrates, leather fillings) and nanocomposites. In order to examine the effect of montmorillonite modification by Cr(III)-compounds with different basicity on its electrosurface properties the dependences of ζ -potential and the stability of MMT dispersions on pH medium and concentration of chromium nitrate have been studied. For pH 2-12, three zones of stability are observed, which alternate with three zones of coagulation. The triple change of MMT charge sign in Cr(NO₃)₃ solutions and alternation of stability and coagulation zones of dispersions are explained by hydrolysis, complex formation of Cr³⁺-ions and ionization of hard phase groups. Charge reversal of MMT surface and appearance of the second zone of stability of positively charged sol are conditioned by excess adsorption) of polymerized cationic species of chromium. The adsorption of polymeric hydroxychromium cations depends upon the basicity of Cr(NO₃)₃ solution exceeds the CEC of MMT by 2-5 times. Hydroxychromiummontmorillonite (Hydroxy-Cr-MMT) has high positive charge (tens or hundreds μC/cm²) and highly developed accessible specific surface area (95-260 m²/g). Modification of MMT by hydroxychromium cations was accompanied by increase of the interlayer space along c-axis up to d001 = 1.68 nm and appearance of highly developed micro- and mesoporous turbostratified (disordered) structure.