Incorporated chromate in MgAlTi hydrotalcite-like compound nanosheets as high-performance visible-light NOx removal photocatalysts

Abstract

Visible-light activation of photocatalysts for NOX depollution remains challenging. In this study, we propose a strategy based on the intercalation of chromate ions (CrO₄2−) into a hydrotalcite-like MgAlTi compound to impart visible-light activity for the photo-oxidation of gaseous NOX. Chromate-containing hydrotalcites were synthesized by mixing chromate solutions (0.002, 0.02, and 0.2 M, pH = 4.5, 8) with MgAlTi-CO3 hydrotalcite. The pH and concentration of the chromate solution determined the successful preparation of the samples. Hydrotalcite structure is preserved when ≤0.02 M solutions are employed. The chromate-containing MgAlTi samples exhibit flower-like morphology formed by very thin nanosheets (10–12 nm). The incorporation and homogeneous distribution of chromate ions into the hydrotalcite structure were confirmed, which allows visible-light absorption. The chromate-containing photocatalysts exhibit good efficiency for removing NOx gas under visible light (NOx removal = 45 %), preventing the release of NO2 during the photochemical DeNOx process. Moreover, chromate-containing photocatalysts outperform TiO2 P25 benchmark at operating conditions under simulated sunlight irradiation (NOx removal = 77.5 % and 61.6 %, respectively). Repetitive efficiency in air purification activity aligns with the ability of these photocatalysts to produce ROS radicals when illuminated with visible light.