Phase-Dependent Photocatalytic Activity of Bulk and Exfoliated Defect-Controlled Flakes of Layered Copper Sulfides under Simulated Solar Light

Sunlight-driven photocatalysis is an environmentally friendly approach to solve ecological issues. The development of simple yet sufficiently stable photocatalytic materials capable of responding to the full-spectrum light remains challenging. Here, we demonstrate the phase transformations of bulk copper sulfides from digenite (Cu9S5) to djurleite (Cu1.97S) and low chalcocite (Cu2S) by the reactive thermal annealing during ambient pressure chemical vapor deposition, followed by their top-down exfoliation. Using multiple techniques, we confirm that monoclinic Cu2S is primarily formed at higher temperatures or greater reaction times and using a reducing atmosphere. We measured the average thickness to be approximately 4 nm for the exfoliated flakes with relatively large lateral sizes of up to 10 μm. We tested the three phases of bulk copper sulfides and their exfoliated forms as photocatalysts for dye degradation under simulated solar light irradiation. Exfoliated Cu2S flakes exhibited superior photocatalytic activity (0.007 min-1), roughly twice higher than that of bulk chalcocite, which could be predominantly attributed to their 2D structure and also 2D planar defects, which could serve as active centers for dye photodegradation. Our study paves the way for developing next-generation full-spectrum-responsive 2D copper sulfide photocatalysts for environmental decontamination.