An understanding of local surface pH and binding of peptides to membranes is of interest for a number of biological processes. Ionic dispersion forces that give rise to Hofmeister effects have not previously been taken into account by theories. It is demonstrated that pH-changes near surfaces (e.g. membrane and mica) and binding of peptides to membranes depend on the specific ionic species. Near mica surfaces, the effect can be especially large: some anions, for example, Br-, experience large attractive dispersion forces that can give rise to strong co-ion adsorption and enhanced pH-gradients. The concentration of hydronium ions at a model membrane surface is obtained from a modified nonlinear Poisson-Boltzmann equation that includes ionic dispersion potentials consistently. The fraction of ionizable surface groups is treated as a self-consistent functional of the electrostatic potential. We finally demonstrate that good agreement between theoretical and experimental binding energies of peptides to membranes requires ionic dispersion potentials that are consistent with our previous estimates based on surface tension of salt solutions.