Surface-anchored CdS@Ag3PO4 nanocomposite with efficient visible light photocatalytic activity
Introduction
Semiconductor-assisted photodegradation of organic pollutants receives prime attention as an economic and eco-friendly solution for the remediation of environmental pollution [1], [2]. Recently Ag3PO4 has attracted intense research interest because of its very high photocatalytic activity under visible light irradiation [3]. The composite formation with foreign species provides an effective method to further enhance its photocatalytic activity under visible light illumination [4], [5]. The electrostatically-derived assembly is fairly useful in synthesizing strongly-coupled nanocomposite system, in which the electron transfer between two components remarkably increases the life-times of photoinduced electrons and holes [6], [7]. For the synthesis of Ag3PO4-based nanocomposite, first we try to synthesize anionic Ag3PO4 nanocrystals and apply them for composite formation with positively-charged CdS nanocrystals. Taking into account the fact that CdS has higher band positions than Ag3PO4 [3], [8], an effective charge separation can occur in the nanocomposite consisting of Ag3PO4 and CdS nanoparticles. To the best of our knowledge, we are aware of no reports on the hybridization of CdS with Ag3PO4.
In the present study, surface-anchored CdS@Ag3PO4 nanocomposite is synthesized by the electrostatically-derived assembly between anionic Ag3PO4 nanoparticles and cationic CdS quantum dots (QDs), as illustrated in the left panel of Fig. 1. The CdS@Ag3PO4 nanocomposite is tested as visible light photocatalyst to probe the effect of electronic coupling on the photocatalyst performance of Ag3PO4.
Section snippets
Experimental
Nanocrystalline Ag3PO4 with the particle size of ~30 nm was synthesized by reaction between the aqueous solutions of AgNO3 (Aldrich, ACS reagent, ≥99.0%) and Na2HPO4 (Aldrich, BioXtra, ≥99.0%) in the presence of capping agent poly(vinylpyrrolidone) (PVP; Aldrich, average Mw ~55,000). The secondary particle of Ag3PO4 was formed during the vacuum-drying of primary particles at 40 °C. Also another precursor, positively-charged CdS QD, was obtained by the solution-based synthetic method [9]. The
Results and discussion
As plotted in the right panel of Fig. 1, the as-prepared Ag3PO4 material shows well-developed XRD peaks of body-centered cubic silver orthophosphate structure [3]. According to the particle size calculation with Scherrer equation, the as-prepared Ag3PO4 particle has the particle size of ~30 nm, which corresponds to the size of primary particle.
The FE-SEM image in Fig. 2(a) demonstrates that the Ag3PO4 nanoparticle exhibits spherical morphology with the particle size of ~200–400 nm, which is much
Conclusions
Water-dispersible Ag3PO4 nanoparticle and surface-anchored CdS@Ag3PO4 nanocomposite are synthesized by the crystal growth of silver phosphate with hydrophilic capping agent and the following assembly with positively-charged CdS QD. The CdS@Ag3PO4 nanocomposite shows higher visible light photocatalytic activity than do the precursors Ag3PO4 and CdS nanocrystals, which is attributable to the extended life-time of electrons–holes and to the enhancement of visible light absorption. This study
Supporting information
Zeta potential curves and photograph of the suspensions of Ag3PO4 and CdS precursors. EDS-elemental mapping data, Ag K-edge XANES, band structure model, and time-dependent PL variation of the CdS@Ag3PO4 nanocomposite.
Acknowledgments
This work was supported by Korea Ministry of Environment as “Converging Technology Project” (191-101-001) and by the Core Technology of Materials Research and Development Program of the Korea Ministry of Intelligence and Economy (Grant No. 10041232). The experiments at PAL were supported in part by MOST and POSTECH. The authors thank Prof. T.H. Hyun (SNU, Korea) for helping them collect the TEM data.
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