Zinc content (x) induced impact on crystallographic, optoelectronic, and photocatalytic parameters of Cd1-xZnxO (0 ≤ x ≤ 1) ternary nanopowder

https://doi.org/10.1016/j.mseb.2020.115001Get rights and content

Highlights

  • Cd1-xZnxO (0 ≤ x ≤ 1) nanopowder is formed by noble co-precipitate technique.

  • Structural analysis emphasized the modification of cubic CdO due to hexagonal ZnO.

  • Uv–vis spectra revealed red shift and Eg is calculated in the range 2.5 ≤ Eg ≤ 3.5 eV.

  • PL results showed emission peaks positioned at 387, 422, 448, 486, and 520 nm.

  • Cd0.2Zn0.8O has highest photocatalytic efficiency for decomposition of Methyl blue.

Abstract

We have synthesized Cd1-xZnxO (0 ≤ x ≤ 1) nanopowder by co-precipitation method for its comprehensive study. The Crystalline phase is changed from rocksalt CdO to wurtzite ZnO with an increase in ‘x’. The existence of H2O, COO, CdO, and ZnO group are confirmed by FTIR. SEM analysis investigated the spherical structure for x = 0.0 & 0.2 and flakes morphology for x = 0.4 & 0.6 and hexagonal block structure for x = 0.8 & 1.0. UV–Vis spectroscopy insured the increasing trend in bandgap energy within the range 2.5 ≤ Eg ≤ 3.5 eV. PL results revealed a blue shift in excitonic and band edge emission. Methyl blue dye is being selected for decomposition using different samples of Cd1-xZnxO (0 ≤ x ≤ 1) nanopowder. It is found that sample with x = 0.8 has the highest catalytic efficiency under UV light. Moreover, higher efficiency of the ternary system is managed by its highly crystalline structure, less microstrain, large surface/volume ratio, and optical bandgap.

Introduction

Nowadays formation of composite nanostructures is the stimulating field and the evolution of ternary alloy nanocrystals by incorporating different components from the II-VI series is a futuristic area in the field of nanoscience and technology. Oxides of both cadmium or zinc are excellent II-VI semiconductors applicable as buffer layer or window in solar cells and thin films because of high transparency in the visible region [1], [2]. Cadmium oxide is non-stoichiometric binary which is successfully employed for large application in the devices like phototransistors, gas sensors, and solar cells [3], [4]. The bandgap of CdO nanoparticles varied as 2.29–2.73 eV which depends upon the different synthesis methods and growth conditions while ZnO has a high impedance and a wide energy gap around 3.35–3.55 eV [5]. The large intrinsic durability of cadmium/zinc oxides along with enhanced mobility revealed high conductivity devoted to the existence of prime promoters like oxygen vacancies, interstitial and intrinsic atoms. The homogeneous composition of these two oxides leads intermediate structural and optical parameters to that of pristine CdO/ZnO which would make such materials attractive for various applications like photocatalyst, antibacterial and thin films in the photovoltaic industry [6], [7].

In our best knowledge, there is majority of research work exists on cadmium (Cd) doped ZnO [8], CdO-ZnO binary [9], ZnxCd1-xO films [10], but relatively less attention has been paid on ternary formation of Cd1-xZnxO nanopowder for entire compositional range i.e. 0 ≤ x ≤ 1. Such ternary system is evolved by optimum composition of Zn into CdO lattice due to similarities in the characteristics of zinc and cadmium ions and therefore considered as topic of investigation. In this study, the aim of choosing Zn as dopant is to enlarge the band gap of cadmium oxide, because Zn ion has a small dimension (rion ~ 0.74 Å) to the host cadmium ion (Cd2+) ~0.95 Å and consequently the band gap energies can be significantly tailored as bandgap energy of CdO is smaller (2.45 eV) than ZnO (3.37 eV) [5], [6].

To generate light in the visible spectra, a modification in the energy gap is essential which is achieved in this study by incorporating appropriate Zn content in CdO lattice. Only a few reports on Zn doped CdO nanopowder have been mentioned in literature owing to their specific applications. For example, Pratheepa et al. [11] has incorporated Zn in CdO nanoparticles to be used as supercapacitor. However, some other metals have also been alloyed to CdO to examine their antibacterial properties as reported by Gupta et al. [12]. Nanofluid alloys have significant heat transfer properties that were studied by Nesaraj et al. [13]. In 21st century, Cd1-xZnxO type ternary supper lattices would be useful as main component in II-VI semiconductor based laser diodes (LDs), light emitting diodes and detectors appliances [14], [15]. For these application areas, detailed investigation of excitonic optoelectronic behavior of Cd1-xZnxO nanopowder is essential. In recent years, these II-VI oxide semiconductors are also used as environment purifier because of their large applications as a water disinfectant, in purifying the air and waste management [16]. Because of the chemical stability of the pollutants released from different factories futile the traditional water waste treatment strategies. Numerous reports on semiconductor photocatalysts are available devoted to depose of organic dyes due to their ability to mineralize the selected pollutant. In this way, many metal oxides such as TiO2, CeO2, CdS, SnO2, MgO, and their coupled binaries are studies as the most active photocatalyst which utilize UV–Visible light to remove recalcitrant objects from aqueous medium [17], [18]. The major issue for single form of oxide semiconductor is the fast electron-hole recombination which significantly affects the photocatalytic efficiency. Moreover, the admixing or coupling can modify the energy gap and shift the band edge towards the visible portion of the spectra. As a result, separation in electron-hole pair increases in presence of light and accordingly photocatalytic behavior is pronounced [19], [20]. Keeping this in view, the synthesis of Cd1-xZnxO heterogeneous photocatalysis has been proposed to decompose synthetic dyestuffs excreted by textile industries. Particular methyl blue (MB) has been chosen as the representative organic dye to examine the photocatalytic performance of Cd1-xZnxO nanopowder in full composition range.

To explore the possibility of generating the unique properties of nano-scaled ternary optical material, Cd1-xZnxO is prepared by the co-precipitation method, and the effect of Zn content (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) has been studied on structure, optical and photocatalytic behavior. We have used the wet chemical co-precipitation method, which is straightforward, low temperature, multilateral, and frugally practicable for the synthesis of nanocrystallites [21]. In this method, control over the lifetime of the charge carriers, surface morphology, particle size, and chemical stability can be attained by carefully monitoring the preparation parameters resulting in enhanced structural, optical and photocatalytic performance.

Section snippets

Preparation of samples

In this study, all chemical precursors were purchased from Sigma Aldrich Pvt Ltd with analytic grade standards. Cd{(CH)3COO}2·2H2O (cadmium acetate dihydrate) and C4H6O4Zn·2H2O (zinc acetate dihydrate) were employed according to the optimal molar ratio in a conical flask. Both precursors were mixed thoroughly and magnetically stirred approximately for sixty minutes at room temperature. Then, about 0.5 M sodium hydroxide (NaOH) added dropwise to the solution with the help of the burette. It was

Crystallographic analysis

Crystallographic analysis of synthesized samples has been performed to evaluate crystal structure and phase purity of Cd1-xZnxO (0 ≤ x ≤ 1) nanopowder as denoted by B0, B1, B2, B3, B4, and B5, respectively.

The X-ray diffraction (XRD) pattern of various samples is shown in Fig. 2 which represents the variation in the intensity of many peaks observed at different 2θ values. These signature diffractograms indicate the formation of various phases composed of CdO, CdZnO, and ZnO. Each sample has a

Conclusions

We have synthesized and characterized the Cd1-xZnxO (0 ≤ x ≤ 1) ternary nanopowder across the full composition range. The crystalline structure is changed from rocksalt CdO to wurtzite ZnO with increasing Zn composition. From the UV–Visible spectra, it is concluded that prepared samples of ternary nanopowder are transparent in the entire visible region. However, band edge is shifted towards longer wavelength i.e. redshift occurred with increasing ‘x’ and corresponding bandgap energy is

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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