Preparation and its photocatalysis of Cd1−xZnxS nano-sized solid solution with PAMAM as a template

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Abstract

Cd1−xZnxS solid solution was prepared by coprecipitation method with PAMAM as a template, calcined at 573 K under N2 atmosphere and characterized by BET, XRD, UV–vis, HRTEM and XRF. The size of Cd1−xZnxS solid solution particles was about 5 nm and the bandgap was estimated to be 2.09–3.12 eV. The photocatalytic activities of Cd1−xZnxS solid solutions on degradation of rhodamine B were evaluated under visible-light irradiation. The results indicated that Cd0.59Zn0.22S solid solution exhibited the highest photocatalytic activity among all the as-prepared samples. The mechanism of photocatalysis under visible-light irradiation was also discussed.

Introduction

The utilization of semiconductor for decomposition of chemical contaminants in water and air has attracted much attention in recent years [1], [2], [3], [4], [5]. One of the well-known semiconductors, CdS, has been used due to its narrow bandgap of approximately 2.4 eV. However, CdS is prone to produce photocorrosion in the reaction by the photogenerated holes [6]. Attempts have been made to improve the stability of metal sulfide, for example, incorporating the nanoparticles of metal sulfides into the interlayer photocatalysts, loading the noble metal (Pt) or coupling CdS with another wide-bandgap semiconductor like TiO2 and ZnS [7], [8], [9], [10]. Furthermore, it is known that semiconductor nanoparticles show a higher photocatalytic activity compared with the bulk materials due to changes in the surface area, bandgap, morphology and generation of surface defects [11], [12]. Several techniques such as precipitation, microemulsion, sol–gel, hydrothermal or solvothermal treatment, chemical vapor deposition, spray pyrolysis, and molecular beam epitaxy have been employed in the preparation of nanoscale semiconductors [13].

Poly(amidoamine) (PAMAM) dendrimers are kinds of materials with their characteristic architectural features. These materials consist of a defined core, an interior branch and terminating groups. They can be used as templates or, nanoreactors to synthesize nano-clusters to make dendrimers nanocomposites [14].

Herein, we wish to report the synthesis of nano-sized CdS coupled ZnS nanocrystal (CdS/ZnS) by the templates of PAMAM with coprecipitation and photocatalysis of CdS/ZnS nanoparticles under visible-light irradiation. To the best of our knowledge, there is no report about the synthesis of solid solutions with PAMAM as a template.

Section snippets

Synthesis

A typical procedure was as follows: 0.3549 g G4-PAMAM was dissolved with 0.1 M HCl until the pH was 6 to get solution A. 0.3908 g Cd(NO3)2 · 4H2O and 0.1859 g Zn(NO3)2 · 6H2O were mixed and dissolved in 30 mL of distilled water to get solution B. Then solutions A and B were mixed in a three-neck flask with vigorous agitation for 3 h to get solution C. Meanwhile, 0.6 g Na2S · H2O was dissolved in 20 mL of distilled water and added into the above solution C slowly keeping stirred for 2 h. The precipitate was

XRD analysis

The X-ray diffraction was used to characterize the phase structure of the products. As shown in Fig. 1, CdS exhibits a Greenokite structure and ZnS presents a Wurtzite structure. With the x value of Cd1−xZnxS composition increased, the XRD peaks gradually shift to a higher-angle side. The successive shift of the XRD pattern indicated that the samples were not mixtures of ZnS and CdS phases but Cd1−xZnxS solid solutions [15], [16], [17]. It is considered that the Zn2+ incorporates in the CdS

Conclusion

This paper presents a new method for preparation of the efficient photocatalyst materials, CdS/ZnS nanocomposites, under mild conditions with the templates of PAMAM. XRD, HRTEM results demonstrated that the Cd1−xZnxS solid solution nanoparticles were formed by being calcined at 573 K under N2 atmosphere. PAMAM can not only act as templates for nanoparticles formation but also prevent particles from aggregation. The rational ratio of Cd and Zn in the Cd1−xZnxS solid solution is important for the

Acknowledgements

This work was financially supported by the Natural Science Foundation of Fujian Province, China; Natural Science Foundation of Education Department of Fujian Province, China and Foundation for University Key Teacher by the Ministry of Education.

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