Study on Photocatalytic Degradation of Methyl Orange Dye using Metal Complexes Obtained from 4-Chloroisonitrosoacetophenone cyclohexylthiosemicarbazone as a Heterogeneous Catalyst

Abstract

The synthesized 4-chloroisonitrosoacetophenone cyclohexylthiosemicarbazone metal complexes have been employed to study the photocatalytic degradation of azo dye acting as a heterogeneous catalyst. The environmentally friendly catalysts were created with the intention of using them to degrade the organic dye. The photocatalytic activities of complexes were investigated using UV–Vis spectra, with methyl orange serving as a target dye impurity for degradation. Electronic absorbance spectra of methyl orange organic dye showed broad absorption at 480 nm. Using different irradiation periods (30, 60, 90 and 120 min), catalytic dosages (25, 50, 75 and 100 mg), the photocatalytic degradation of methyl orange was examined. Each complex exhibits strong catalytic activity for the degradation of methyl orange. Among the irradiation period, at 120 min catalysts show the highest percentage degradation. Similarly, in large amount of 100 mg of catalysts irradiation exposure of light, maximum degradation occurred. When the catalysts were tested on fresh dye samples (5 trials), the decolorization efficiency dropped effectively, indicating the efficient reusability of all the metal complexes. The possible mechanism for dye degradation has been suggested.

Introduction

This study investigates the photocatalytic degradation of methyl orange (MO), a hazardous azo dye commonly used in textile and industrial applications. Azo dyes are difficult to remove from wastewater because they are highly stable and resistant to heat, light, and oxidation, posing significant environmental and health risks. Conventional treatment methods, such as filtration, precipitation, membrane separation, and biodegradation, are often expensive and inefficient. Photocatalytic degradation using metal-based coordination compounds has emerged as a promising alternative because it can convert toxic dyes into less harmful substances.

The research focuses on 4-chloroisonitrosoacetophenone cyclohexyl thiosemicarbazone and its Co(II), Ni(II), Cu(II), and Zn(II) metal complexes, which were synthesized and characterized using techniques including elemental analysis, FTIR, UV-Visible spectroscopy, NMR, TG-DTA, XRD, cyclic voltammetry, and Chem3D optimization. Since these metal complexes had not previously been studied as photocatalysts, the work evaluates their effectiveness as heterogeneous catalysts for degrading methyl orange dye.

Photocatalytic experiments were conducted using a tungsten filament lamp, with methyl orange solutions exposed to different catalyst amounts (25–100 mg) and irradiation times (30–120 minutes). The degradation efficiency was monitored by measuring the decrease in absorbance at 480 nm using UV-Visible spectroscopy, and the percentage degradation was calculated from the change in absorbance before and after irradiation.

The results show that both irradiation time and catalyst amount significantly influence dye degradation. As exposure time increased, dye absorbance decreased, indicating greater photocatalytic activity. Among the catalysts tested, ZnL? exhibited the highest degradation efficiency (80.58%) after 120 minutes, followed by CuL? (78.64%), NiL? (77.66%), and CoL? (74.75%). Overall, the study demonstrates that thiosemicarbazone metal complexes are effective heterogeneous photocatalysts for the degradation of methyl orange, offering a promising, environmentally friendly approach for treating dye-contaminated wastewater.

Conclusion

In conclusion, the photocatalytic decolorization of industrial textile dye, Methyl orange, under tungsten filament lamp light was investigated employing CoL2, NiL2, CuL2 and ZnL2 as photocatalysts. The solution of methyl orange dye absorbs at the wavelength of 480 nm and initial absorbance (Ao) recorded. The 10 ppm MO dye solution (blank) and MO dye solution with catalysts (test) were used to employed the photocatalytic activity. The observed results show the intensity of the dye colour goes on degraded with increasing time interval of the light exposure and as well as increasing the amount of the catalysts. The absorbance of the samples was noted after every 30 min and after every addition of 25 mg of the catalysts. The absorbance goes on decreasing and degradation rate enhances with increasing time duration. The absorbance also falls down and deterioration increases with increasing the amount of catalyst. These findings clearly demonstrated that the synthesized metal complexes act as a very effective catalyst for the study of degradation of azo dye.

References

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Copyright © 2026 Sayali V. Kadam, Shivani B. Malap, Raju M. Patil. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.