Photochemical Transformation of Arsenic in the Presence of Low-Molecular-Weight Organic Acids and Antimony: Volatile Species Formation and Nanoparticle-Mediated Mechanism

Arsenic (As), a well-known toxic element, often coexists with antimony (Sb) due to their similar properties, and elevated As levels are detected near Sb mining sites. Photochemical techniques are important for the treatment of organic and inorganic contaminants, including As and Sb. In this study, the influence of widely distributed low-molecular-weight organic acids (LMWOAs) in the environment or frequently used in heavy-metal remediation techniques on the photochemical reduction of As(III)/As(V) was investigated in the presence of Sb(III)/Sb(V). As was converted into volatile species like As(CH3)3 and AsH3 even with millimolar levels of LMWOAs, and the conversion was significantly affected by the type and concentration of LMWOA. Notably, the coexisting Sb markedly enhanced the formation efficiency of volatile As with an enhancement factor ranging from 6- to 10-fold. Density functional theory (DFT) calculations confirmed that these nanoparticles could adsorb radicals and As, creating a high-concentration reaction zone that promoted the generation of volatile As species. The findings of this study provide valuable insights into the photochemical behavior of As and uncover previously overlooked details regarding the interaction between As and Sb during the photochemical process of pollutant removal.