Iridium doped ZnO nanocomposites: Synergistic effect induced photocatalytic degradation of methylene blue and crystal violet

Highlights

• A novel Ir doped ZnO photocatalysts were successfully constructed via one-pot hydrothermal method.

• Ir doped ZnO nanocomposites exhibited superior photocatalytic activity endowed by synergistic effect.

• Ir nanoparticles were played a major role in charge carrier separations.

Abstract

A series of novel iridium (Ir) nanoparticles doped ZnO nanocomposites were constructed via one-pot simple hydrothermal strategy and used as a visible light driven photocatalyst for the degradation of Methylene Blue (MB) and Crystal Violet (CV). The synthesized pure ZnO and Ir loaded ZnO nanocomposites were systematically characterized by crystal structure, structural morphology, elemental and optical properties. The photocatalytic performance of Ir doped ZnO (2%) nanocomposite is much higher than that of pure ZnO and other Ir doped ZnO nanocomposites and more encouragingly, 10 mg/L of MB can be completely removed within 50 min of irradiation. The Ir doped in the lattice of ZnO can act as the electron trapping sites, which effectively improve the charge carrier separation. The enhanced photocatalytic activity of Ir doped ZnO (2%) composite is mainly attributed to the synergistic interaction between ZnO and Ir NPs, which could not only enhance the light absorption range, but also accelerate photo-induced interfacial charge transfer during the photocatalytic processes. Influence factors such as initial dye concentrations and catalyst doses were investigated. The generation of reactive oxidative species (ROS) such as OH, h⁺ and O₂⁻ was also been demonstrated. Moreover, this study also paves a new vista for promising applications in environmental water purity and energy harvesting.

Introduction

In this year water pollution is one of most worldwide problem of our society because many of the industry are ejecting the wastewater into rivers. Industry wastewater containing large amount of organic dye compounds such as methyl orange, rhodamine B, congo red, crystal violet and methyl blue and inorganic compounds, and these dyes are comes from textile industry, food industry, leather industry and etc., [1], [2]. Most of these organic dyes are present in water at low concentration, causes many problem to human and animals due to their mistrusted carcinogenic and mutagenic [3], [4], [5]. The complex structures and chemical stability of organic dyes were affecting the degradation process [6], [7]. The organic dye pollutants were removed from water by using several techniques, they are biological degradation [8], [9], chemical oxidation [10], ultrasound degradation, advanced oxidation processes (AOPs), reverse osmosis, coagulation and flocculation [11], [12]. AOPs are one of the cost effective and highly recommendable techniques for completely degradation of the dye hazardous to simpler and non-toxic inorganic compound [13], [14].

In recent years, heterogeneous photocatalyst has been widely studied for the environment remediation. ZnO is one of the mostly used semiconductor photocatalyst which has the advantages of high efficiency, low cost, non-toxicity, photochemical stability and high luminescence property [15], [16], [17]. It has wide band gap semiconductor with the band gap value is 3.4 eV and the large excitation energy of ~60 meV [18]. Different kinds of nanostructured ZnO photocatalyst used to degradation of organic pollutants, such as nanorods, nanobelts, nanoplate and hollow sphere [19], [20], [21], [22]. The drawback of ZnO photocatalyst was activated only UV light irradiation because of its large band gap energy value. Another drawback of this photocatalyst is its photo instability in aqueous solution due to the photocorrosion with UV light irradiation, which leads to decrease the photocatalyst activity, rapid recombination rate of photogenerated charge carriers and very poor responsible for visible light [23].

The enhancement in the photocatalytic activity of ZnO can be adequately done by doping or coupling with metals/non metals and forming heterojuctions with semiconductor metal oxides. The doping of noble metals (such as Ag, Au, Pd and Pt, etc.) with semiconductor has been receiving considerable attention due to improve the charge transfer by trapping the photo induced charge carriers and enhance the photocatalytic activity [24], [25]. Besides, among the noble metals, Pt-group metals (i.e., Pt, Pd, Rh, Ru, and Ir), Iridium is having some unique properties like low surface coverage, sintering resistance, charge injection properties and non-toxic effects to the environmental [26]. In this work, we report a series of Ir loaded ZnO nanoparticles were prepared with facile one-pot hydrothermal method. The structural, morphology, optical properties and photocatalytic activity of as prepared ZnO and Ir loaded/doped ZnO nanocomposites were systematically investigated and evaluated by multi-technologies. The effect of catalyst weight, concentration and catalyst stability were also been discussed. Meanwhile, the photocatalytic mechanism were discussed by radical trapping experiments and proposed in detail.