Near-infrared (NIR) light responsiveness of CuS/S–C3N4 heterojunction photocatalyst with enhanced tetracycline degradation activity

Semiconductor-based photocatalysis represents a promising technology for removing antibiotic given its cost effectiveness and environmental compatibility. However, finding suitable photocatalysts and semiconductors for practical applications can be challenging. This work aims to investigate the photocatalytic performance of as-synthesized photocatalysts under broad-spectrum from visible (Vis) to near-infrared (NIR) sunlight. In this work, a step-scheme (S-scheme) heterojunction photocatalyst, i.e., CuS/S–C3N4, was prepared, employing a single-step hydrothermal route. The synthesized photocatalyst showed excellent crystallinity and high purity content. The CuS loading provided a better NIR light response-ability and improved photocatalytic activity for CuS/S–C3N4. The 2 wt% CuS/S–C3N4 produced the highest tetracycline (TC) photodegradation rate, up to about 95% efficiency under Vis + NIR light irradiation. The result also showed that the 2 wt% CuS/S–C3N4 sample had a first-order kinetic constant (k) that was 6.2-fold higher than the pure S–C3N4 sample under Vis + NIR light irradiation. However, too much CuS content led to the presence of inactive sites on S–C3N4, which hampered the light absorption ability, thus leading to inadequate photocatalytic activity. In addition, the 2 wt% CuS/S–C3N4 sample also showed high photocatalytic stability and insignificant change of the composite structure before and after the experiments. In short, we can enhance the CuS/S–C3N4 photocatalytic activity by increasing the light response range and the separation efficiency of light-induced electrons and holes. Consequently, we have developed a novel strategy and experimental basis for S-scheme heterojunction to be fully utilized under broad-spectrum sunlight.