Full Length ArticleModification of Ag nanoparticles on the surface of SrTiO3 particles and resultant influence on photoreduction of CO2
Graphical abstract
A series of cubic and all-edge-truncated SrTiO3 with and without thermal pretreatment in air are modified by Ag nanoparticles via photodeposition method, which can photoreduce CO2 into CO under visible-light illumination.
Introduction
SrTiO3 (STO), an n-type semiconductor with a simple perovskite structure, has been regarded as one of the most promising photocatalysts because of its relatively high catalytic activity, photochemical stability and optical property [1]. However, STO only responds to the UV light due to its wide bandgap (3.2 eV) in nature. It is necessary to expand the spectral response of STO so as to efficiently use the visible light. One popular approach to achieve this is being doped with nonmetals and metals [2], [3], while sometimes this may lead to a decrease in the redox potential [4]. Recently noble metal nanoparticles like Ag and Au loaded semiconductor have drawn great attention as a new type of visible-light photocatalyst [5], [6], [7], [8]. Among all the noble metals, Ag is one of the most suitable candidates because its low cost, nontoxicity and easy preparation [9]. In addition, Ag NPs exhibit light absorption and scattering in the visible-light region owing to localized surface plasmon resonance [10]. It is generally agreed that in most plasmonic metal/semiconductor hybrid nanostructures [8], [11], [12], [13], the plasmon resonance can excite electrons in the noble metal that can then transfer to the conduction band of a semiconductor when they are in direct contact.
It is noted that the physicochemical properties of the semiconductor in such a hybrid nanostructure also plays an important role. It is reported that the photocurrent density is much higher if the Ag nanoparticles are loaded in the TiO2 nanotubes with specific hierarchical structure instead of the conventional TiO2 nanotubes due to the unique pore-wall structure in the nanotube array [14]. The selective deposition of noble metal and oxide co-catalysts onto different facet of STO can greatly improve the photocatalytic efficiency of water splitting [15]. In addition, the surface defects like oxygen vacancy (VO) can act as both the electron trap and adsorption site, while the bulk defects only serve as the trap of charge carriers where the photogenerated electron-hole pairs can recombine therein [16], [17], [18], [19]. Thus, it is critical to modulate the distribution of VO in a photocatalyst so as to improve its activity. Tan et al. have prepared a series of SrTiO3@SrTiO3–x crystal-core@amorphous-shell nanostructures with different concentrations of surface VO via controllable solid-state reaction [19]. The highest photocatalytic activity is observed in the obtained catalyst with an optimal value of VO concentration. Li et al. have deposited Au nanoparticles onto the BiOCl containing VO, which exhibits selective benzyl alcohol oxidation under visible-light irradiation, as the surface VO in BiOCl can facilitate the trapping and transfer of plasmonic hot electrons to adsorbed O2 [20]. Furthermore, the presence of VO in a catalyst can facilitate the adsorption of CO2 [21] and, thereby, enhance the photocatalytic activity [16].
Herein, we demonstrated that the Ag nanoparticles can be loaded on the surface of the VO-rich all-edge-truncated SrTiO3 via photodeposition route, which is a mild technique for the in-situ synthesis of nanoparticles. Specifically, the size and amount of Ag nanoparticles can be readily controlled by adjusting the deposition time. The obtained systems can be utilized as the catalysts for the photoreduction of CO2 to CO under visible-light irradiation.
Section snippets
Chemicals
All chemicals employed in this work were analytical grade and used without further purification. The TiCl4 (99.5%), 1,3-propanediol (98%), LiOH (98%), SrCl2·6H2O (99.5%), and AgNO3 (99.8%) were purchased from Aladdin Holding Group. Milli-Q water was used throughout the experiments.
Synthesis of SrTiO3 samples
The SrTiO3 (STO) was prepared via a solvothermal method as previously reported [22], [23]. In a typical synthesis, 0.133 mL of TiCl4 was added into 13 mL of pure water containing 1 mL of 1,3-propanediol (or without),
Photodeposition of Ag nanoparticles on SrTiO3
The crystal structure of the STO and Ag-STO samples prepared under different conditions was studied by using XRD. As shown in Fig. 1a, the main peaks can be assigned to the cubic perovskite SrTiO3 (JCPDS 35-0734) for all of the samples, indicating that pure phase of STO is always maintained regardless of annealing. Compared with STO-T sample, it is found that the position of the diffraction peaks slightly shifts to a larger value of 2θ for STO-T-Air and STO-C-Air, indicating decrease in cell
Conclusions
In summary, the SrTiO3 particles with different morphology have been successfully synthesized via a facile route. The distribution of Ag nanoparticles photodeposited onto the SrTiO3 surface for the truncated particles is different from the cubic ones. In addition, Ag nanoparticles locate mainly on the {001} facets for the samples without annealing pretreatment in air like Ag-STO-T-180, while they are primarily present on the {110} facets for the samples with annealing pretreatment. This is
Acknowledgements
This work was financially supported by the Ministry of Science and Technology of China (2015DFG62610) and the National Natural Science Foundation of China (21673052).
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