Enhancing Charge Separation in Metallic Photocatalysts: A Case Study of the Conducting Molybdenum Dioxide

Abstract

A new visible‐light responsive metallic photocatalyst, nanostructured MoO2, has been discovered. The metallic nature of MoO2 is confirmed by valance X‐ray photoelectron spectroscopy spectrum and theoretical calculations. However, MoO2 itself shows only moderate activity due to the serious charge recombination, a general disadvantage of metallic photocatalysts. The findings suggest that its effective charge diffusion length Lp is smaller than 1.0 nm while the separation efficiency ηsep is less than 10%. Therefore, only the periphery of the metallic MoO2 can effectively contribute to photocatalysis. This limitation is overcome by integrating MoO2 in a hydrothermal carbonation carbon (HTCC) matrix (mainly contains semiconductive polyfuran). This simple chemical modification brings two advantages: (i) an internal electric field is formed at the interface between MoO2 and HTCC due to their appropriate band alignment; (ii) the nanostructured MoO2 and the HTCC matrix are intertwined with each other intimately. Their small size and large contact area promote charge transfer, especially under the internal electric field. Therefore, the separation rate of photoexcited charge carrier in MoO2 is greatly enhanced. The activity increases by 2.4, 16.8, and 4.0 times in photocatalytic oxygen evolution, dyes degradation, and photoelectrochemicl cell, respectively. The new approach is helpful for further development of metallic photocatalysts.

Hydrothermal Carbonation Carbon-Coated CdS Nanocomposite with Enhanced Photocatalytic Activity and Stability

“…Thus, we can conclude the existence of HTCC in the composite. polyfuran in the HTCC [19]. Therefore, we can infer that the HTCC is mainly composed of polyfuran components, which is in good agreement with previous studies [18,19].…”

“…The band 1702 cm −1 is ascribed to the C=O stretching, suggesting that some furan rings are open in the polymer, which is common for the polyfuran. Moreover, 13 C solid-state CP-MAS NMR spectroscopy was also performed ( Figure S1), and further confirmed the existence of polyfuran in the HTCC [19]. Therefore, we can infer that the HTCC is mainly composed of polyfuran components, which is in good agreement with previous studies [18,19].…”

“…polyfuran in the HTCC [19]. Therefore, we can infer that the HTCC is mainly composed of polyfuran components, which is in good agreement with previous studies [18,19]. The morphology and microstructure are investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis in Figure 3.…”

“…Moreover, 13 C solid-state CP-MAS NMR spectroscopy was also performed ( Figure S1), and further confirmed the existence of polyfuran in the HTCC [19]. Therefore, we can infer that the HTCC is mainly composed of polyfuran components, which is in good agreement with previous studies [18,19]. Comparing the FT-IR spectra of HTCC and 0.1C/CdS-PVP, we can find some characteristic peaks of HTCC in the 0.1C/CdS-PVP sample, such as 861 cm −1 , 1020 cm −1 , 1200 cm −1 , and 1365 cm −1 .…”

“…Recently, our group found that the HTCC derived from glucose is a polyfuran-based n-type semiconductor, containing plenty of sp 2 -hybridization structures [19,25]. Under solar light illumination, HTCC generates photoexcited electrons, holes, and hydroxyl radicals.…”