Photocatalytic Reduction of Aromatic Nitro Compounds with Ag/AgxS Composites under Visible Light Irradiation

A series of silver sulfide composites were prepared via the hydrothermal method with l-cysteine and AgNO3 in water at a range of l-cysteine/AgNO3 molar ratio of 0.5–8. The prepared Ag/AgxS materials were consisted of Ag, Ag2S, Ag2S2, and Ag2Sn species as confirmed by XRD, TEM, and XPS. The Ag/AgxS composites are active for the photocatalytic reduction of aromatic nitro compounds under the visible light irradiation. The composition of the stoichiometric Ag2S, the nonstoichiometric Ag2S2 and Ag2Sn, and metallic Ag species affected the photocatalytic performances largely. When more nonstoichiometric Ag2S2 and Ag2Sn presented on the surface, the absorption in the visible (vis) light region was enhanced remarkably and presented a blue shift, leading to a bigger band gap energy value (Eg) and higher cathodic conduction band edge potential (ECB), which promoted the formation of photogenerated electrons and inhibited the combination of photoelectrons and holes. When the more Ag0 presented on the surface, the more photogenerated electrons were transferred from the conduction band of AgxS to Ag0, preventing the combination of photoelectrons and holes. Thus, the photocatalytic performances of the Ag/AgxS composites could be controlled by varying the surface composition.