Molybdenum Doping Leads to Faster Photo-Dissolution of Commercial Molybdate Red Pigment than Chrome Yellow Pigment Under Sunlight Irradiation

Abstract

The photo-dissolution of lead chromate pigments poses specific environmental hazards. In particular, the presence of molybdenum in lead chromate molybdate pigments, commonly known as molybdate red, might increase the risk of heavy metal leaching when exposed to light. Our study demonstrates that commercial molybdate red pigments can undergo photo-dissolution when exposed to simulated sunlight and exhibit lower photostability compared to lead chromate pigments such as chrome yellow. After 24 hours of irradiation, the leaching rates of toxic lead (Pb) and chromium (Cr)from molybdate red pigments are 2.98 and 3.70 times higher, respectively, than those from chrome yellow pigments under identical conditions. Molybdate red pigment also exhibits a faster initial release rate of heavy metals. The primary factor leading to decreased pigment photostability is the activation of pigment semiconductors facilitated by molybdenum (Mo)doping. Molybdate red pigments, unlike conventional chrome yellow pigments, exhibit a broader light absorption spectrum and more effective separation and transfer of photogenerated charge carriers. This ultimately boosts the photochemical activity of molybdate red pigments in aqueous environments. Overall, this study indicates that Mo doping can reduce the photostability of lead chromate pigments, highlighting the potential for increased environmental risks associated with complex inorganic metal pigments.

Keywords: molybdate red pigment, chrome yellow pigment, photo-dissolution, Mo doping, heavy metal release