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Journal of Environmental Science and Technology
  Year: 2009 | Volume: 2 | Issue: 1 | Page No.: 22-30
DOI: 10.3923/jest.2009.22.30
 
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Water Adsorption and Surface Acidity of Nano-Ball Allophane as Affected by Heat Treatment

Hamayoon Khan, Rozina Khan, Naoto Matsue and Teruo Henmi

Abstract:
Effect of heat treatment on the water adsorption and surface acidity of two nano-ball allophane samples with varying Si/Al ratio under different relative humidities (RHs) was studied. The water vapor adsorption of two allophane samples under various relative humidities, decreased with preheating treatment up to 400 °C for 2 h. The decrease in water adsorption at monolayer level (RH≤0.45) was greater for KnP sample than for KyP sample, whereas the decrease in water adsorption due to capillary condensation between allophane unit particles (RH≥0.6) was greater for KyP sample. These indicate that allophane hollow spherical particles in KyP sample were directly connected each other with the preheating, but those in KnP sample were not. Heat treatment caused the enhancement in the surface acidity of nano-ball allophane samples. The enhancement in the surface acidity after heat treatment is attributed to the inductive effect on the Si-OH groups present at the pore region of the hollow sphere. The results showed that surface acidity of the allophane with higher Si/Al ratio (KnP) was stronger than the (KyP) sample having lower Si/Al ratio. This trend was observed under RH between 0 and 75%; then the acid strength for the two samples was the same at RH of 98%. After the heat treatment at lower level of RH, the surface acidity of KnP was higher than KyP. The presence of polymerized silicate tails exposed outside of hollow spherical allophane particles (KnP), causes the enhancement of the BrØnsted acidity and also prevent direct connection between the particles after heating.
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How to cite this article:

Hamayoon Khan, Rozina Khan, Naoto Matsue and Teruo Henmi, 2009. Water Adsorption and Surface Acidity of Nano-Ball Allophane as Affected by Heat Treatment. Journal of Environmental Science and Technology, 2: 22-30.

DOI: 10.3923/jest.2009.22.30

URL: https://scialert.net/abstract/?doi=jest.2009.22.30

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