Adsorption of Metal Ions onto Hydrophilic Silicon Surfaces from Aqueous Solution: Effect of pH

Abstract

This work examines the pH and time dependence of metal deposition onto hydrophilic silicon surfaces. We find that the surface concentration of metal species is proportional to the pH. Time dependence is seen for only a few metals, notably Cr and Fe in this study, especially at high pH. Si surfaces with wet chemical oxides were exposed to a dilute solution of ten metals: Al, Ba, Ca, Cr, Cu, Fe, K, Ni, Sr, and Zn, in dilute nitric acid solution, from pH 3 to 5.6, for different periods of time, from about 1 to 1000 s. At equilibrium the surface concentration of metals is approximately proportional to the ratio of ionic charge to ionic radius of the metal ions for many of the metal ions which exist as hydrated cations at that particular pH. We observe this proportionality over the pH range under study, although the surface concentration varies over several orders of magnitude. Cations which form amphoteric species, such as A13+ which forms A1,0, and Al(0H); at high pH, and several other cations that do not exist as simple cations at some pHs (e.g., Fe3', Zn2+, and Ni2' at high pH), do not show this dependence on ionic charge and radius.

Competitive Adsorption of Metal Ions onto Hydrophilic Silicon Surfaces from Aqueous Solution

“…Discussion Relationship between model and theoretical coefficients.-Equation 12 is a generalized form of Eq. 9 log SiOM ϭ Const ϩ m(pH) ϩ n(pM) ϩ p log [12] We can obviously relate the theoretical coefficients, m, n, and p, in Eq. 12 to the empirical, model coefficients, a 1 , a 2 , and a 3 of Eq.…”

“…Loewenstein and Mertens, on the other hand, found that cations are the adsorbing species in acidic solution. 12 All of these studies lack a comprehensive model relating the concentrations of adsorbing species in solution to the resulting metal concentrations on the wafer surface. While we know that materials in solution somehow end up on the silicon surface, we do not know the relationship between solution and surface concentration.…”

“…In earlier work, 12 we examined the role of pH on metal adsorption and provided an understanding of the attraction between some metals and the wet chemical oxide surface. The current work examines the relationship between solution concentration and surface concentrations.…”

Detection of pH variation using modified microcantilever sensors

“…On a silicon surface, since there are no SiNH 2 sites, only interactions described by Eqs. (2) and (3) take place [15,16]. The de¯ection of the cantilever should be due to the sum of all the interactions happening at the surface and the effect of the electrolyte layer on the silicon surface [16].…”

Avaliação da técnica de eletroosmose na remoção de contaminante orgânico em meios particulados.

“…4.22 Uma característica importante nos óxidos de silício é que estes compostos em meio aquoso estabelecem espontaneamente cargas negativas em sua superfície [20,36,62]. …”