Elsevier

Chemical Physics

Volume 554, 1 February 2022, 111419
Chemical Physics

Cobalt, nickel and copper doped non-stoichiometric cadmium gallate as a prominent magnetic and photocatalytic material

https://doi.org/10.1016/j.chemphys.2021.111419Get rights and content

Abstract

Cobalt, nickel and copper doped non-stoichiometric CdGa2O4 were synthesized via epoxide gel approach. Cubic spinel arrangement of undoped and doped samples was investigated from powder X-ray diffraction pattern and the complete structure analysis was done by using Raman spectroscopy. Additionally, morphology of doped samples was analysed by FESEM images and elemental ratio of these samples have been obtained using Energy Dispersive spectrum (EDS). The oxidation state of doped metal ions was determined by optical and photoluminescence spectroscopy. The magnetic study of the doped samples showed the antiferromagnetic and ferromagnetic behaviour. The variation of band gap in transition metal doped samples has been favourably utilized for the photodegradation studies of aqueous solution of methylene blue and Rhodamine B dye.

Introduction

The most favourable aim of material chemist is the advancements which can be achieved with designing and developing new materials with enhanced applications. The advanced developed materials possess hollow structures which show better and favourable properties such as low density, improved permeation, greater specific surface area, distinctive optical properties that leads to their usefulness in massive fields in sensors, catalysis, photocatalysis, drug distribution, and in various new application areas [1], [2], [3], [4], [5]. Thin film electroluminescence (TFEL) shows intensive applications on sulphide materials. Although, the reported papers on oxide materials are very less in number. The oxide phosphor materials have also been well used in field emission devices and vacuum fluorescent. These materials can be often used as the replacement for sulphide materials due to their larger and better chemical stability [6], [7]. Semiconductor metal oxide-based gas sensor provide a simple, effective and low cost alternative and they are most widely investigated [8], [9]. These metal oxides including transition metal (NiO, CuO, Co2O3) and post transition metal (Ga2O3, In2O3, SnO2), can reversibly react with pre-adsorbed ambient oxygen and target reducing or oxidizing gas, leading to evident variation of their electrical conductivity.

Compared with single metal oxides, mixed metal oxides have displayed significant benefits in the matter of gas sensing performance enhancement [10], [11]. Especially spinel compounds, with a general formula of AB2O4 and very stable crystal structure, providing great flexibility and extensibility to regulate the physical and chemical properties of the materials by tuning the composition, are a promising group of sensor applications [12], [13]. It is already known that Ga2O3 present thermally activated electronic conductivity and high chemical stability, has been investigated to detect reducing gases efficiently at high temperatures around 600–1000 °C.

Therefore, Ga2O3 based spinel compounds exhibit strong potential in sensing applications [14]. ZnGa2O4 serves as a good host material for low voltage cathodoluminescent (CL) phosphor, which has potential applications toward thin film electroluminescent displays, field emission displays (FED), and vacuum fluorescent display (VFD) [15], [16]. Gallate type spinel are effectively used for the degradation of organic pollutant by different available techniques such as photocatalytic, adsorption, catalysis, gas sensing etc [17], [18], [19], [20], [21]. The substitution of transition metal ions in ZnGa2O4 results in remarkable optical, magnetic, photocatalytic and gas sensing properties [22], [23], [24], [25]. Similar trends have also been observed in n-type cadmium based gallate spinel. Both, CdGa2O4 and ZnGa2O4 possess the cubic structures exhibiting normal spinel, about 25% of Cd2+ ion in case of CdGa2O4 sits on octahedral site which denotes to a partially inverse spinel. CdGa2O4 crystallizes in Fd-3 m space group with Cd atoms lying at 8a (1/8, 1/8, 1/8) Wyckoff positions in tetrahedral coordination, Ga atoms lie at the 16d (1/2, 1/2, 1/2) octahedral sites and the 32e (u, u, u) positions were filled with oxygen atoms [26]. The synthesis of CdGa2O4 is the not much explored. Few literatures have been reported on the substitution of monovalent and divalent metal ions in place of Cd2+results in improving the luminescence and gas sensing properties, conductivity and photocatalytic activity [27], [28], [29].

The present work reports the non-stoichiometric CdGa2O4 synthesis by a modified epoxide gel route. In continuation the effect of transition metals doped in non-stoichiometric CdGa2O4 (gallium rich Cd0.90M0.10Ga2O4 (M = Co2+, Ni2+ and Cu2+)) has also been examined. Concurrently, consequences of this doping in term of optical, photoluminescence, magnetic, photocatalytic properties of this system have also been studied in detail.

Section snippets

Synthesis

The epoxide mediated gel route was used for the synthesis of transition metal doped non-stoichiometric cadmium gallate; Cd(NO3)2·4H2O (99%, CDH), HCl (35%, Merck), Ga2O3 (99.5%, Alfa Aesar), and propylene oxide (99%, Alfa Aesar, Massachusetts) were used as the precursors. 0.0748 (2 mmol) of Ga2O3 dissolved in minimum amount of HCl (1:1 by volume) was added to 5 mL absolute ethanol containing 0.0555 g (0.90 mmol) of Cd(NO3)2·4H2O, 0.00475 g (0.10 mmol) of CoCl2·6H2O (98%, CDH), 0.00475 g (0.10 

Structural properties

PXRD patterns of 10% doped samples of Co2+, Ni2+ and Cu2+ on A site in non-stoichiometric CdGa2O4 have been presented in Fig. 1. For the doped samples, peaks pertaining to cubic CdGa2O4 were only observed. No additional reflections were noticed indicating the formation of pure phases. Ionic radii of doped metal ions were presented in Table 1.

A slight shift of the diffraction peaks toward higher 2θ values was noticed. It suggested the inclusion of smaller ionic radii of doped ions. This is

Conclusions

Cobalt, nickel and copper doped non-stoichiometric (gallium rich) samples have been synthesized by modified epoxide gel method and characterized. Cubic spinel arrangement was investigated for transition metal doped non-stoichiometric spinel and structure was determined using powder X-ray diffraction analysis. Energy Dispersive spectrum (EDS) has been carried out to investigate the elemental ratio of the doped samples. Cubic morphology of the doped samples was observed in FESEM images. Normal

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.

Acknowledgement

The authors thanks Nupur Sharad and Harshit Sharma for their help in carrying out the experimental work and Sharda University for facilities.

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