TiO2-based strategies for mitigating hexavalent chromium in portland cement: a mechanism-guided mini review

Abstract

Hexavalent chromium, Cr(VI), remains a critical concern in cement and clinker-based materials because of its solubility, mobility, and health-related risks. Recent studies indicate that chromium behavior in cement systems is governed by a combination of raw-material chemistry, oxidation during clinkering, mineral phase partitioning, and hydration-stage stabilization. In parallel, titanium dioxide (TiO2), widely studied for photocatalytic and functional cementitious materials, has been shown to modify hydration kinetics, microstructure, and surface reactivity. These properties make TiO2 a potentially relevant modifier for controlling the formation, retention, or reduction of Cr(VI) in cementitious systems. This mini review examines the mechanistic basis for TiO2-assisted mitigation of Cr(VI) in cement by integrating evidence from four domains: chromium partitioning in clinker phases, stabilization of chromate in hydrated cement, TiO2-modified cement hydration, and TiO2-based Cr(VI) photoreduction literature. The available evidence supports three plausible pathways: suppression of Cr(VI) formation through phase-chemistry control, reduction in Cr(VI) mobility through hydration and pore refinement, and possible photocatalytic or interfacial reduction of Cr(VI) to Cr(III) under exposed conditions. However, direct cement-specific evidence remains limited, and most current support is still indirect. TiO2 should therefore be regarded not as a proven standalone remedy, but as a promising co-strategy within a broader chromium-control framework for cement production and use.