Correlation between adsorption and photocatalysis in the aqueous system Cr(VI)-TiO2

J.M. MEICHTRY; H.B. RODRÍGUEZ; M.A. GRELA; M.I. LITTER; E. SAN ROMÁN

Photocatalysis: Research and Potential

SCIEPublish

Año: 2025

2958-8774

The photocatalytic removal of Cr(VI) (0.80 mM, pH 2) using various commercially available photocatalysts (P25,UV100, PC50) was revisited, with particular attention given to Cr(VI) adsorption (as a Cr(VI)-TiOsurface complex) and theformation of a Cr(III) hydroxide layer during the photocatalytic reduction. Cr(VI) adsorption followed a quasi-Langmuir-typeisotherm, and the spectra of the Cr(VI)-TiOsurface complex were deconvoluted into two Gaussian peaks, red-shifted when arutile phase was present. Cr(VI) photoreduction exhibited nearly pseudo first-order kinetics, with P25 showing the highestreaction rate. Adsorbed Cr(VI) was reduced by e, and the formed Cr(III) was retained over the TiOsurface under non-equilibrium conditions, acting as a new adsorption site for Cr(VI). At longer reaction times, partial dissolution of the Cr(III)layer was observed. These findings suggest that the photoreduction kinetics are primarily governed by the slow adsorption ofCr(VI) onto the Cr(III) deposition layer. As an important conclusion, three consecutive processes never mentioned before takeplace: (1) reduction of adsorbed Cr(VI), (2) formation of Cr(III) over the photocatalyst and (3) adsorption of Cr(VI) over thedeposited Cr(III) layer, together with partial Cr(III) redissolution. This insight provides a deeper understanding of theunderlying photocatalytic mechanism.