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Metal and pH Effects on Adsorption of Poly(vinyl alcohol) by Silicon Oxide

Dep. of Plant Science, U-67, Univ. of Connecticut, Storrs, CT 06269

S. Tokunaga

National Inst. of Materials and Chemical Research, Higashi, Tsukuba Science City, Ibaraki 305, Japan

*Corresponding author (cschulth{at}canrl.cag.uconn.edu).

ABSTRACT

The adsorption of pentanol onto a smectite shows an adsorption edge at pH 10. Because adsorption similarities between smectites and Si oxides have been noted in the literature, we anticipated that poly(vinyl alcohol) (PVA) would also display an adsorption edge near pH 10 on a Si oxide (SiO₂). Adsorption edges between pH 9 and 10 on Si oxide were confirmed when using two PVA polymers of 98 and 88% hydrolysis (MW = 11 000 and 10 000 g mol^-1, respectively). The decrease in adsorption at high pH is attributed to the interference of Na⁺ adsorption on the Si oxide. The addition of aqueous metals (Al³⁺, Pb²⁺, Cu²⁺, Mg²⁺, and Ba²⁺) significantly modified the adsorption envelope of PVA on the Si oxide in various ways. Three mechanisms are proposed: metals may modify the Si surface, interact with the PVA while in the aqueous phase, or form an additional independent surface that can adsorb the PVA polymer. New PVA adsorption envelopes were observed at high pH in the presence of Mg, Cu, and (adsorbed) Pb. The presence of metals also increased the amount of PVA (98% hydrolysis) adsorbed at low pH, but caused no change in, or decreased, the amount of PVA (88% hydrolysis) adsorbed on a mass per area basis. Because of this, we suggest that the metals can modify the effective thickness of the polymers on the surface. The adsorption of Pb and Al on the Si oxide modified the solubility of Si, suggesting a chemisorption reaction with the surface.

Storrs Agric. Exp. Stn. Scientific Contribution no. 1540.

Received for publication May 23, 1994.

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