Date Published: April 15, 2019
Publisher: Public Library of Science
Author(s): Xiuying Huang, Meng Zhang, Runze Sun, Gaoyuan Long, Yifan Liu, Weirong Zhao, Satya Pal Nehra.
Titanium dioxide nanoparticles co-modified with CuOx (0≤x≤2) and carbonaceous materials were prepared with a simple hydrolysis and photo-reduction method for photocatalytic hydrogen generation. SEM/TEM and XPS analysis indicated that the carbonaceous materials were mostly coated on the TiO2 surface and clearly revealed that the Cu species exhibited multivalence states, existing as CuOx (0≤x≤2). The optimal catalyst showed a 56-fold enhanced hydrogen evolution rate compared with that of the pure C/TiO2 catalyst. Further, an intensive multiple electron transfer effect originating from CuOx and the carbonaceous materials is proposed to be responsible for the elevated photoactivity. CuOx species serve as electron donors facilitating charge carrier transfer and proton reduction sites. The carbonaceous materials function as the “bridge” that transfers the electrons of TiO2 to the CuOx species, which provides a new route for electron transfer and reinforces the effect of CuOx as a co-catalyst. In this study, the CuOx and C co-modified TiO2 catalyst was prepared with multiple electron transport pathways and enhanced hydrogen production evolution, which provides a deep understanding for the design of co-catalyst-based photocatalysts.
Hydrogen, as an efficient, renewable and clean energy source, is considered to be one of the best fuels for the future [1, 2]. Hence, photocatalytic hydrogen production with semiconductors has been regarded as a promising strategy for its mild reaction conditions, and cost-effectiveness [3, 4]. Among the various studied photocatalysts, titanium dioxide (TiO2) has received tremendous attention for photocatalytic hydrogen evolution owing to its suitable conduction and valence bands edge position, as well as its characteristics of nontoxicity, low cost, and photocorrosion resistance [5, 6]. However, the undesirable charge carrier recombination and the inferior solar light utilization efficiency of TiO2, which leads to the low photocatalytic hydrogen generation efficiency, restrict their photochemical applications . It is a hot issue to develop an effective method to overcome the intrinsic limitation.
Carbon coated on a TiO2 surface modified with CuOx has been prepared via a simple hydrolysis and photo-reduction method. With systematic structure characterization, carbonaceous materials were observed to be absorbed onto the surface of TiO2 nanoparticles. The Cu species existed as CuOx with multivalence states grafted both on the TiO2 surface and the carbonaceous materials. With CuOx functioning as a cocatalyst, the CuOx-CTR exhibited high activities in photocatalytic hydrogen evolution. The photocatalytic hydrogen generation rate of the CuOx-CT400 catalyst (433.3 μmol/h) is 56 times as high as that of CT400 (7.7 μmol/h). This significant increase is attributed to the synergistic effect between CuOx and the carbon species. CuOx grafted on the surface of the catalyst accepts photoexcited electrons inhibiting electron-hole recombination and serving as proton reduction sites. Meanwhile, carbonaceous materials function as good conductors by transferring electrons to the CuOx, which significantly enhances the CuOx co-catalyst effect. This work demonstrates a simple method to prepare a Cu and C co-modified TiO2 catalyst with high photocatalytic performance and proposes the synergistic effect between copper and carbon, which presents a significant step in determining the photoexcited electron transfer mechanism.