Study Of Hydrothermal Synthesis Of Nano β-MnO₂

One-dimensionβ-MnO₂ nano-powders were hydrothermally synthesized by the reaction of potassium permanganate with different anions bivalence manganese salts(MnSO₄,Mn(NO₃)₂ and MnCl₂)at 150～240℃.The effect of processing parameters on crystal structure,morphology and particle diameter of the powders were systemically researched.When MnSO₄ reacted with KMnO₄ without addition of acid or alkali(initiative pH of the reaction was about 0.34)at 160℃,one-dimensional nanoβ-MnO₂ powders were obtained, which have particles diameter of 18～45nm,the ratio of length and diameter of 5.3～59,and specific surface aeras of～61m²/g.When reactants had different bivalence anions,one-dimensional nanopowdersβ-MnO₂ could be attained at 160～240℃.With the increase of reactive temperature the diameters of the powders became wider and the lengths became shorter.In addition different anions had obvious effect on the powders morphology.More regularer and larger ratio of length and diameter of the powers had been prepared when SO₄^2-existed other than NO₃^- or Cl^-keeping same conditions.The diameters of the powders were 18～45nm and the ratio of length and diameter reached 5.3～59.At the same time when NO₃^-existed the diameters were 70～700nm and the ratio of length and diameter was 5.7～10 and when Cl^- existed the diameters of 24.5～212nm and the ratio of length and diameter of 5.1～19.pH had very important effect on both the crystal sturcture and morphology of the powders.When an acid was added,β-MnO₂ was still obtained at 160℃,but the particles obviously became wider, and the ratio of length and diameter became smaller.The diameters were 29～166nm and the ratio of length and diameter was 15.0～27.6.On the contrary,the increase of pH of the reaction,β-MnO₂ couldn't be attained. When adding PVP,nothing can be gained,perhaps due to high viscosity of the dispersant to restrict the contact of MnO₄^- and Mn²⁺.When CTAB or PEG was added,β-MnO₂ cannot be producted directly,and the product wasγ-MnOOH, which can be calcined to transform into finalβ-MnO₂ at 400℃.