Role of TiO2 Anatase Surface Morphology on Organophosphorus Interfacial Chemistry

Optimization of physicochemical properties of TiO2 anatase for organophosphorus remediation remains challenging. One approach is to use anatase nanofibers, prepared from hydrothermally synthesized titanates. Charge densities and potentials of anatase nanofibers were determined from atomic force microscopy force-curve measurements using the modified Derjaguin, Landau, Verwey, Overbeek theory, which includes roughness and hydration forces, in the pH range 4-9. Calculated values were -0.007 to -0.03 C m(-2) and -70 to -150 mV, respectively. In contrast, at neutral pH, the magnitudes of diffuse layer surface charge densities and potentials have a minimum in anatase nanoparticles. These observations and zeta-potential results suggest that nanofiber surfaces are more acidic compared with nanoparticles. This is consistent with nanofibers having similar to 3-fold higher adsorption for organophosphorus methyl parathion (pH approximate to 7). The resulting adsorption includes contributions from (1) charge accumulation at local coordination sites caused by the morphological roughness; (2) greater crystallographic nanoscale variations; and (3) active site competition between parent and daughter species. The structural features of nanofibers have potential applications in catalysis and sequestration of organophosphorus compounds.