Novelmetal–organic photocatalysts: Synthesis, characterization and decomposition of organic dyes

https://doi.org/10.1016/j.saa.2014.08.045Get rights and content

Highlights

  • The chemical and structural environments of the metal complexes were specified.

  • The interaction of the hydrazone with MCl2⋅nH2O afforded square planar complexes.

  • Transition metal complexes are used as photocatalysts for the degradation of methylene blue dye under UV-light.

  • Ni(II) complex shows higher photodegradation of MB than Co(II) complex at alkaline pH.

  • Tentative mechanism of the photodegradation of dye in the presence of metal complex is described.

Abstract

An efficient method for the photocatalytic degradation of methylene blue in an aqueous medium was developed using metal–organic complexes. Two novel complexes were synthesized using, Schiff base ligand, N′-[(E)-(4-ethylphenyl)methylidene]-4-hydroxybenzohydrazide (HL) and Ni(II) (Complex 1)/Co(II) (Complex 2) chloride respectively. These complexes were characterized using microanalysis, various spectral techniques. Spectral studies reveal that the complexes exhibit square planar geometry with ligand coordination through azomethine nitrogen and enolic oxygen. The effects of catalyst dosage, irradiation time and aqueous pH on the photocatalytic activity were studied systematically. The photocatalytic activity was found to be more efficient in the presence of Ni(II) complexes than the Co(II) complex. Possible mechanistic aspects were discussed.

Graphical abstract

Tentative mechanism of the photodegradation of dye in the presence of metal complex is.

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Introduction

Dyes are applied in textile manufacturing, leather tanning, and paper production and food technology industries as dyeing agents [1]. The release of those colored waste waters in the ecosystem is a dramatic source of esthetical pollution, of eutrophication and of perturbations in the aquatic life. Hence effluents from industries contain a high level of environmentally hazard dyeing agents. Therefore, the effluent water has to be treated before disposal. There are many physicochemical techniques that can remove dyes from its aqueous solution which includes biological techniques- aerobic and anaerobic process, physical techniques-membrane filtration, coagulation/flocculation, precipitation, flotation, adsorption, and chemical techniques chemical oxidation process of chlorination, bleaching, ozonation, Fenton oxidation and photocatalytic oxidation [2]. However, low removal efficiency or high cost of operation often limits their application [3].

In this concern, extensive work has been done recently on the photocatalytic degradation of environmentally hazard pollutants using metal oxides due to their superior photocatalytic performance, non-toxicity, low production cost and high persistence to photocorrosion [4], [5], [6], [7]. The process is based on the generation of the hydroxyl radicals (radical dotOH) that can oxidize a broad range of organic contaminants non-selectively in a short period of time. Interestingly, “advanced oxidation processes” (AOPs) also offer different routes to radical dotOH production, allowing easier tailoring of the process for specific treatment requirements [8], [9], [10], [11], [12]. Since, structurally, dyes are double bonded such as single bondCdouble bondCsingle bond, single bondNdouble bondNsingle bond and heterocyclic compounds, therefore transition metal ions are able to coordinate with most of the organic substances containing this type of bonds. This is because of their lenience in change of the oxidation state and presence of unpaired electrons the metal ions react readily with molecular oxygen, thereby mediating oxygenation of other compounds easily [13]. These properties have made use of transition metal complexes for the chemical, biological, photochemical and photo-biological degradation of the organic ligands. So far a number of metal complexes involving degradation of dyes and other pollutants has been reported from time to time [14].

From the previous reports it is evident that in all the cases hydrogen peroxide plays an important role in generating reactive species such as hydroxyl free radical and is used in the destruction of dispersed dyes. However, higher concentration of H2O2 is hazardous and it is harmful to eyes, lungs and skin. Recently reported degradation of MB in the absence of H2O2 using Co(II), Ni(II) and Cu(II) complexes of (2E)-2-[(2E)-3-phenylprop-2-en-1-ylidene]hydrazinecarbothioamide [15]. In the continuation of our research on MB degradation using metal complexes, herein reporting with Ni(II) and Co(II) complexes of N′-[(E)-(4-ethylphenyl)methylidene]-4-hydroxybenzohydrazide as a catalysts and also investigated the influence of various parameters such as catalyst dosage, irradiation time and aqueous pH on the photocatalytic activity.

Section snippets

Materials

Methylene Blue (C16H18ClN3SCl) was used in this work which was purchased from s.d fine-chem limited, Bombay [99.0% pure]. 4-Hydroxybenzhydrazide [98% pure] and 4-Ethylbenzaldehyde [98% pure] were purchased from Sigma–Aldrich, Bangalore. Nickel chloride hexahydrate and Cobalt chloride hexahydrate [99% pure] were purchased from HiMedia laboratory Pvt. Ltd. Bombay and were used as received to prepare the precursor for the synthesis of photocatalytic complexes. Double-distilled water was used

Characterization of the ligand

The prepared hydrazone, N′-[(E)-(4-ethylphenyl)methylidene]-4-hydroxybenzohydrazide is air stable, readily soluble in common organic solvents. The results of elemental analysis (Table 1) are in good agreement with the proposed formula. IR spectrum (ES Fig. 1) of the ligand spectrum exhibits characteristic absorption bands at 1770, 1562 and 1108 cm−1 due to the ν(Cdouble bondO), ν(Cdouble bondN) and ν(Nsingle bondN) vibrations, respectively [18]. Due to strong intramolecular hydrogen bonding in ligand, the ν(Osingle bondH) groups exhibited

Conclusions

Ni(II) and Co(II) complexes of N′-[(E)-(4-ethylphenyl) methy-lidene]-4-hydroxybenzohydrazide were prepared and characterized using various spectroscopy techniques. The photocatalytic effect of prepared complexes for MB was studied systematically under UV light irradiation. The photocatalytic activity was found to be more efficient in the presence of Ni(II) complexes than the Co(II) complex. Studies revealed that these metal complexes with higher photocatalytic efficiency will be a potential

Acknowledgements

Authors acknowledge financial support from the Visvesvaraya Technological University, Belgaum (VTU/Aca./2010-11/A-9/11341) for financial support and the management of M.S. Ramaiah Institute of Technology, Bangalore.

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