Methylviologen ions (MV(2+)) readily adsorb on silica gel surfaces, while the chloride counterions (Cl-) remain in the solution phase. Under aerated conditions, photoirradiation of this system induces an oxidative degradation of MV(2+), which is monitored via emission studies of the products. Under degassed conditions, the photoirradiation produces the monopositive radical cation (MV(.+)), which is confirmed by its characteristic diffuse reflectance, Raman, and electron paramagnetic resonance spectra. The Raman spectrum of MV(.+) on silica gel shows that perturbation due to the adsorbed state is not significant, while EPR studies show common features of the adsorbed radical cation on a surface. The coadsorption of sodium chloride affects the formation and increases yield of MV(.+) in a complex way. The photogenerated MV(.+) reacts with carbon tetrachloride, chloroform, dichloromethane, and 1,2-dichloroethane, which are studied by steady-state and time-resolved methods, and the corresponding rate constants have been determined. Compared to solution, the rigid nature of the silica gel surface stabilizes the initial CT pair (MV(.+)Cl(.)) by several orders of magnitude and increases electron transfer between MV(.+) and CCl4 by an order of magnitude.