The proximity effect on semiconducting mineral surfaces: A new aspect of mineral surface reactivity and surface complexation theory?

The observation and description of surface proximity effects, whereby the c hemical reaction of one surface site influences the electronic structure an d reactivity of neighboring or nearby sites, is presented in this study for the semiconducting minerals galena (PbS) and pyrite (FeS2). The methods us ed to study this effect include ab initio molecular orbital calculations an d scanning tunneling microscopy and spectroscopy. The surface proximity eff ect can be manifested in different ways, although the principle is the same . For example, we predict that electron transfer in redox reactions on gale na surfaces can involve separated sites with specific and special locations . Another example is seen for pyrite where the oxidation of one site on a t errace influences next-nearest neighbor sites, making them far more suscept ible to oxidative attack relative to sites further away. The range of poten tial applications of the surface proximity effect model is also outlined fo r a number of environmentally and industrially important examples. These fi ndings, in combination with surface complexation theory, an important model for attachment/detachment reactions at mineral-water interfaces, may event ually lead to an extended model that will include the specific influence of semiconductor-type proximity effects. Copyright (C) 2001 Elsevier Science Ltd.