CdS nanoparticles/CeO2 nanorods composite with high-efficiency visible-light-driven photocatalytic activity

doi:10.1016/j.apsusc.2015.12.021

Applied Surface Science

Volume 363, 15 February 2016, Pages 154-160

https://doi.org/10.1016/j.apsusc.2015.12.021 Get rights and content

Highlights

•
Coupling CdS can effectively improve the light-harvesting ability of wide-band gap CeO₂.
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CdS/CeO₂ composites show high photocatalytic activity under visible light irradiation.
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The mechanism of photocatalytic H₂ evolution over CdS/CeO₂ was proposed.

Abstract

Different mole ratios of CdS nanoparticles (NPs)/CeO₂ nanorods (NRs) composites with effective contacts were synthesized through a two-step hydrothermal method. The crystal phase, microstructure, optical absorption properties, electrochemical properties and photocatalytic H₂ production activity of these composites were investigated. It was concluded that the photogenerated charge carriers in the CdS NPs/CeO₂ NRs composite with a proper mole ratio (1:1) exhibited the longest lifetime and highest separation efficiency, which was responsible for the highest H₂-production rate of 8.4 mmol h⁻¹ g⁻¹ under visible-light irradiation (λ > 420 nm). The superior photocatalytic H₂ evolution properties are attributed to the transfer of visible-excited electrons of CdS NPs to CeO₂ NRs, which can effectively extend the light absorption range of wide-band gap CeO₂ NRs. This work provides feasible routes to develop visible-light responsive CeO₂-based nanomaterial for efficient solar utilization.

Graphical abstract

Coupling CdS with CeO₂ can effectively improve the light-harvesting ability of wide-band gap CeO₂ NRs as the photoinduced electrons on the conduction band of CdS are transfered to the conduction band of CeO₂.

Introduction

The hydrogen produced from water splitting using a catalyst and solar energy is an ideal future energy source, independent of fossil reserves. The search for suitable photocatalysts for hydrogen evolution has led to intensive studies. And a large number of semiconductor materials have been reported exhibiting photocatalytic activities for hydrogen production [1], [2], [3], [4], [5], [6]. Apart from the most commonly used TiO₂, cerium dioxide(CeO₂), a semiconductor with a band gap energy of 3.2 eV, similar to that of TiO₂, also shows promising photocatalytic activity for H₂ production and degradation of various organic dye pollutants under UV illumination [7], [8], [9], [10], [11], [12], [13], [14]. Although photocatalytic activity of CeO₂ has been investigated intensively, the broad band gap energy of this material limits its further application in the visible light region [15], [16], [17]. Hence, efforts have been devoted to improve the light-harvesting capability and photocatalytic activity of CeO₂ photocatalyst either by doping with metal/nonmetal elements or coupling with other narrow band gap semiconductors. As a result, various CeO₂-based composites (Ag₃PO₄/CeO₂ [18], BiVO₄/CeO₂ [19] and Cu₂O/CeO₂ [20]) with enhanced visible light response and photocatalytic activity have been obtained.

Cadmium sulfide (CdS), a typical II–VI semiconductor, has been extensively studied as visible-light photocatalyst for H₂ evolution and a photosensitizer for sensitizing various wide band-gap metal oxides due to its favourable band-edges more negative than 0 V (vs. NHE), and suitable band-gap (2.4 eV) corresponding well with the spectrum of sunlight. More importantly, CdS can couple well with CeO₂ due to their matched band structures [21], [22], [23], [24], [25]. CdS coupled CeO₂ composite materials have been extensively explored in the field of photocatalysis due to its reinforced visible light absorption capacity and microstructure-dependent photocatalytic properties [26]. Tong and co-workers investigated the photocatalytic performance of CdS/CeO_x nanowires and CeO₂/CdS nanospheres prepared by electrochemical process, and found that the both composites exhibited hydrogen evolution rate of 223 and 473.6 μmol h⁻¹ g⁻¹, respectively, higher than that of pure CeO₂ under visible light illumination. Photocatalytic selective reduction of nitroaromatics and water splitting to hydrogen over one-dimensional CdS nanowires-CeO₂ nanoparticles composites under visible light irradiation were also evaluated by Tang et al. [27]. Therein, the optimal photoactivity was obtained when the weight ratio of CeO₂ NPs was 1%. The enhanced photocatalytic activity was believed to be ascribed to the intimate interfacial contact and the matched energy band structures between CdS NWs and CeO₂ NPs. However, the photocatalytic activity of the CdS coupled CeO₂ composite materials is still restricted by low efficiency. Therefore, it is meaningful to explore more efficient methods to further optimize the photocatalytic reactivity of the CdS/CeO₂ composite materials.

Herein, CdS NPs/CeO₂ NRs composites with effective contacts were synthesized through a two-step hydrothermal method. The photocatalytic activity for H₂ evolution was measured under visible light irradiation from lactic acid aqueous solution. An attempt was made to delineate the factors responsible for the photocatalytic activity of these CdS NPs/CeO₂ NRs nanocomposits. This work provides feasible routes to synthesize CeO₂-based photocatalysts for efficient solar utilization, and in-depth understanding of the microstructure-dependent photocatalytic activity of CdS/CeO₂ composits.

Section snippets

Materials

Cerium(III) nitrate hexahydrate (Ce(NO₃)₃·6H₂O), sodium hydroxide (NaOH), sodium sulfide nonahydrate (Na₂S·9H₂O) and cadmium acetate dihydrate (Cd(CH₃COO)₂·2H₂O) were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Commercial cerium oxide (CeO₂) powder was purchased from Alfa Aesar China Co., Ltd (Tianjin, China). All materials were used as received without further purification. Deionized water that was used in the synthesis was obtained from local sources.

Catalyst preparation

The CdS

XRD analysis and Raman spectra measurement of samples

Fig. 1 presents the typical XRD patterns of the as-prepared CeO₂, CdS and CdS/CeO₂ (n:m) composites. Diffraction peaks of the bare CeO₂ at 28.8°, 33.3°, 47.6° and 56.4° can be indexed as the (1 1 1), (2 0 0), (2 2 0) and (3 1 1) planes of the face-centered cubic structure of CeO₂ (JCPDS No. 34-0394), respectively. And the peaks of the bare CdS at 26.5°, 44.0° and 52° can be characterized as the (1 1 1), (2 2 0) and (3 1 1) planes of the cubic structure of CdS (JCPDS No.42-1411), respectively. The XRD

Conclusions

The CdS NPs/CeO₂ NRs hybrid nanostructures were successfully synthesized via a facile two-step hydrothermal method. The as-obtained composites show greatly enhanced photocatalytic activity for H₂ production, and the CdS/CeO₂(1:1) shows the highest H₂ production rate of 8.4 mmol h⁻¹ g⁻¹ under visible-light (λ > 420 nm) irradiation, with a high AQY up to 11.2%. The superior photocatalytic H₂ evolution properties are attributed to the transfer of visible-excited electrons of CdS NPs to CeO₂ NRs, which

Acknowledgments

This work was financially supported by the NSFC (Grants Nos. U1305242, 21373050), the National Key Basic Research Program of China (973 Program: 2013CB632405, 2014CB239303, 2014CB260410 and 2014BAC13B03).

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CdS nanoparticles/CeO2 nanorods composite with high-efficiency visible-light-driven photocatalytic activity

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Catalyst preparation

XRD analysis and Raman spectra measurement of samples

Conclusions

Acknowledgments

Nano Energy

J. Catal.

Int. J. Hydrogen Energy

Mater. Res. Bull.

Ceram. Int.

Appl. Catal., B: Environ.

Catal. Commun.

Appl. Surf. Sci.

J. Photochem. Photobiol., A: Chem.

Mater. Res. Bull.

Mater. Chem. Phys.

Int. J. Hydrogen Energy

Appl. Surf. Sci.

Electrochemical photolysis of water at a semiconductor electrode

Nature

Advanced nanoarchitectures for solar photocatalytic applications

Chem. Rev.

Synthesis and photocatalytic hydrogen production of a novel photocatalyst LaCO3OH

J. Mater. Chem. A

Enhanced catalytic performance of F-doped CeO2–TiO2 catalysts in selective catalytic reduction of NO with NH3 at low temperatures

Indian J. Chem. A

Morphology-controllable synthesis of mesoporous CeO2 nano and microstructures

Chem. Mater.

Redox cycles promoting photocatalytic hydrogen evolution of CeO2 nanorods

J. Mater. Chem.

Defect-induced band gap narrowed CeO2 nanostructures for visible light activities

Ind. Eng. Chem. Res.

Photocatalytic degradation of methyl orange by CeO2 and Fe-doped CeO2 films under visible light

Sci. Rep.

CdS nanoparticles/CeO₂ nanorods composite with high-efficiency visible-light-driven photocatalytic activity

Synthesis and photocatalytic hydrogen production of a novel photocatalyst LaCO₃OH

Morphology-controllable synthesis of mesoporous CeO₂ nano and microstructures

Defect-induced band gap narrowed CeO₂ nanostructures for visible light activities

Photocatalytic degradation of methyl orange by CeO₂ and Fe-doped CeO₂ films under visible light