Lotus-Leaf-Derived Activated-Carbon-Supported Nano-CdS as Energy-Efficient Photocatalysts under Visible Irradiation

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Lotus-leaf-derived activated carbon materials (denoted as LAC-T) were fabricated at different temperatures ( T = 600, 700, and 800 °C), which resulted in carbonaceous materials with various microstructures and porosity. BET surface area of LAC-T increased from 1184 m 2 g –1 to 1807 m 2 g –1 with activation temperatures that varied from 600 °C to 800 °C. These microporous carbonaceous materials were subsequently advanced as ideal platforms for cadmium sulfide (CdS) composite photocatalysts, through the deposition of nano-CdS precursors on LAC-T supports (CdS@LAC-T). It was revealed that the CdS@LAC-T nanocomposites displayed enhanced photocatalytic efficiency, in comparison with the nano-CdS, toward the degradation of various organic dyes under visible light. More specifically, CdS@LAC-800, prepared from a carbonaceous support with the highest BET, gave the best photocatalytic efficiency. Estimated band gap energy for CdS@LAC-800 (2.01 eV) was considerably lower than that of nano-CdS (2.22 eV), which was among the lowest band gap energies observed for CdS photocatalysts. Band-gap narrowing that was observed for nanocomposites indicated noticeable interface interaction between nano-CdS and the carbonaceous supports, and excellent light harvesting ability. Furthermore, the improved photocatalytic activity shown by the best performing CdS@LAC-800 was achieved thanks to the effective production of catalytically active species ( h +, O 2 • –, •OH, and H 2 O 2 ), which were demonstrated by means of extensive mechanism study. Overall, the highly ordered and porous carbonaceous support accounted for the outstanding photocatalytic efficiency of CdS@LAC-800 by synergistically boosting the substrate accessibility, the solar energy harvesting efficiency, and the electron–hole separation in this photocatalytic system.