Degradation mechanism of hydrogen-terminated porous silicon in the presence and in the absence of light

Si is well-known semiconductor that has a fundamental bandgap energy of 1.12 eV. Its photogenerated electrons in the conduction band can react with the ubiquitous oxygen molecules to yield ⋅O2− radicals, but the photogenerated holes in the valance band can’t interact with OH− to produce ⋅OH radicals. In this paper, we study the degradation of methyl orange (MO) by hydrogen-terminated porous Si (H-PSi) in the presence and in the absence of light. The absorption spectra of the degraded MO solutions indicated that the H-PSi had superior degradation ability. In the dark, the reduction of dye occurs simply by hydrogen transfer. Under room light, however, some of the dye molecules can be reduced by hydrogen transfer first and then decomposed in the conduction and valance bands. This result should be ascribed to its wide band gap energies centered at 1.79-1.94 eV.