Bismuth oxide/carbon nanodots/indium oxide heterojunctions with enhanced visible light photocatalytic performance

Carbon nanodots (CDs) were introduced into the Bi 2 O 3 /In 2 O 3 heterojunctions to form bismuth oxide/carbon nanodots/indium oxide (Bi 2 O 3 /CDs/In 2 O 3 ) heterojunctions via the water curing treatment and high-temperature sintering process. The structure, composition, micro-morphology, and optical performance of the Bi 2 O 3 /CDs/In 2 O 3 heterojunctions were characterized via X-ray diffraction, Fourier infrared spectrum , X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM (HRTEM), solid Ultraviolet–Visible (UV−Vis) diffuse reflectance spectrum, and electrochemical impedance spectroscopy. The optimum content of the CDs is 10 mg when the amount of the heterojunctions is 400 mg. The band gap of the Bi 2 O 3 /CDs/In 2 O 3 heterojunctions is 1.70 eV. The photocatalytic performance of the heterojunctions for the degradation of methylene blue (MB) under natural solar light irradiation was analyzed. CDs in the heterojunctions decrease the band gap and increase the absorption ability of the visible light. The reaction rate value is 12.04, 22.23, and 4.45 times than that of Bi 2 O 3 (0.0024 min −1 ), In 2 O 3 (0.0013 min −1 ), and Bi 2 O 3 /In 2 O 3 (0.0065 min −1 ), respectively. 10 mg L −1 MB solution can be fully degraded within 100-min solar light irradiation using the heterojunctions. Superoxide radicals (·O 2 − ), hydroxyl radicals (·OH), and holes (h + ) are the main active species for MB degradation. The Bi 2 O 3 /CDs/In 2 O 3 heterojunctions possess excellent photocatalytic cycle stability and usability.