Evolution of the Electronic Properties and Photocatalytic Activity of z-Type g-C₃N₄@MoS₂ Heterostructures Prepared by a One-Step Calcination Method

Abstract

In the paper, g-C 3 N 4 /MoS 2 materials were prepared by using a one-step calcination method with Na 2 MoO 4 •2H 2 O and thiourea as precursors at different reaction temperatures and reaction rates. With the reaction temperature changing from 500 to 550 °C, the prepared composites were composed with MoS 2 and g-C 3 N 4 nanomaterials, where MoS 2 nanosheets were decorated with g-C 3 N 4 nanoflakes; up to 600 °C, the disappearance of g-C 3 N 4 typical features in FT-IR spectra implies that the composites were mainly consistent with MoS 2 ; further up to 700 °C, XRD patterns and Raman spectra revealed that the composites were composed with MoS 2 nanosheets. All of the prepared samples were used as photocatalysts for hydrogen production, and the highest H 2 production rate of 5.21 mmol•g −1 •h −1 was obtained for sample MC500-2 without a noble metal as a cocatalyst; the sample was prepared at 500 °C with a rate of 2 °C/min. The mechanism behind has been explained with band alignments. UPS and valence spectra revealed that the g-C 3 N 4 /MoS 2 heterostructure in sample MC500-2 is a z-type, which is favorable for the separation of the photogenerated electron−hole pairs. The results will be helpful for the preparation of MoS 2 and g-C 3 N 4 composites and their application in photocatalytic hydrogen production.

Trace Au Induced Growth of Mixed-Phase MoS2 Nanosheets on 2D g-C3N4 to Facilitate the Well-Organized Charge Migration in Photocatalytic H2 Evolution

“…Significant difference in the C 1s and N 1s signals of the samples can be directly observed from Figure b,c. Specifically, the C 1s spectra (Figure b) peaked at 284.8 and 288.4 eV are the standard C–C bond and the N–CN bond hybridized vibration of g-C 3 N 4 , respectively. , The N 1s spectra (Figure c) at 400.3, 399.2, and 398.1 eV are respectively the C–NH x , N–(C) 3 , and C–N–C vibrations . The introduction of Au atoms results in the C 1s and N 1s signal shift toward high energy, indicating the intimate contact of metal Au on g-C 3 N 4 , which effectively reduces the electron density around C and N atoms .…”

“…Raman spectra were further recorded to qualitatively evaluate the introduction of Au on the distribution of MoS 2 . As shown in Figure a, the two Raman bands centered at ∼378 and ∼450 cm –1 can be ascribed to the in-plane (E 2g 1 ) and out-of-plane (A 1g ) vibration modes of MoS 2 , respectively, indicating the successful growth of MoS 2 in the samples. , In addition, we analyzed the distance between E 2g 1 and A 1g signals. CNN/Au 0.12 /MoS 2 displayed a much lower distance (21.1 cm) than CNN/MoS 2 (26.1 cm), clarifying a much decreased stack layer of MoS 2 caused by the Au atoms. , This is in accord with the results obtained from Figure and Figure S2, in which the aggregation of MoS 2 in CNN/MoS 2 results in an increased stack layer.…”