One-pot synthesis of the direct Z-scheme AgInS2/AgIn5S8 QDs heterojunction for efficient photocatalytic reduction of Cr6+ in neutral condition

We represented one-pot synthesis of direct Z-scheme AgInS2/AgIn5S8 QDs heterojunction, which was employed for photocatalytic reduction of aqueous Cr6+ in this work. With increasing In3+ content of reaction system, the materials have transformed from AgInS2 QDs to AgInS2/AgIn5S8 QDs heterojunction. Comparing to the step-by-step combination, one-pot synthesis of heterojunction could provide tight interface contact and efficient charge separation. The In3+-dependent phase changes, valance states and optical properties were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and UV–vis absorbance spectroscopy, respectively. Besides, energy band alignment and photogenerated charge transport were discussed via investigating its photocurrent, Mott-Schottky plots and time-resolved fluorescence spectroscopy. The photocatalytic activity of AgInS2 QDs and AgInS2/AgIn5S8 QDs heterojunction were tested in the reduction of aqueous Cr6+ under visible-light (λ > 400 nm) irradiation. Under optimal conditions, Z-scheme AgInS2/AgIn5S8 QDs heterojunction showed a superior catalytic activity with ~97.7% of removal efficiency within 20 min. The obtained rate constant (k) for Cr6+ reduction reached up to 2.01 min−1·mol−1, approximately 10-fold higher than that of pristine AgInS2 QDs. Moreover, the obtained heterojunction showed wider pH tolerant, which could be used in acidic and neutral solution.