Green-Mediated Co-Precipitation Synthesis of CoWO?/gCN Nanocomposites for Rose Bengal Photocatalytic Degradation

Abstract

In the present study, high-performance cobalt tungstate/graphitic carbon nitride (CoWO?/gCN) binary nanocomposites were successfully synthesized through a low-cost, green co-precipitation route assisted by Phoenix dactylifera L. fruit extract. The plant extract acted as an eco-friendly reducing and fuel agent, eliminating the need for toxic chemicals while promoting controlled nucleation, particle growth and effective interfacial coupling between CoWO? and gCN. Structural and compositional analyses using XRD, FE-SEM, TEM, XPS, EDAX and elemental mapping confirmed the formation of phase-pure monoclinic CoWO? uniformly anchored onto gCN sheets. UV–Vis diffuse reflectance spectroscopy revealed enhanced visible-light absorption with a narrowed band-gap energy in the range of 2.3–2.55 eV, attributed to heterojunction formation and improved charge separation. Photocatalytic evaluation using Rose Bengal dye under visible-light irradiation demonstrated outstanding activity, achieving ~81.01 % degradation within 75 min and maintaining ~78 % efficiency after three consecutive cycles, indicating excellent stability and reusability. Compared with conventional CoWO?-based photocatalysts, the present system exhibits superior efficiency through sustainable synthesis and effective charge-transfer pathways, underscoring its potential for visible-light-driven wastewater remediation.

Introduction

Nanotechnology plays a crucial role in modern materials science because materials at the nanoscale exhibit unique physicochemical properties influenced by particle size, morphology, and interfacial interactions. Among nanomaterials, nanocomposites are particularly attractive due to synergistic effects such as enhanced charge transport, improved surface activity, and superior optical performance. These features make them highly suitable for environmental and energy applications.

Material Background

Metal tungstates (AWO?) are widely studied semiconductors due to their chemical stability and multifunctional properties. Cobalt tungstate (CoWO?), a p-type semiconductor with a wolframite structure, has applications in photocatalysis, electrochemical devices, pigments, and dielectrics. However, pristine CoWO? suffers from:

• Rapid electron–hole recombination

• Limited visible-light absorption

Similarly, graphitic carbon nitride (g-C?N? or gCN) is a metal-free, visible-light-active semiconductor known for its stability and low cost. Yet, pristine gCN has limitations such as low surface area and inefficient charge separation.

To overcome these issues, the study develops a CoWO?–gCN binary nanocomposite, forming a heterojunction that:

• Enhances interfacial charge transfer

• Suppresses electron–hole recombination

• Broadens visible-light absorption

• Improves photocatalytic efficiency

Green Synthesis Approach

The nanocomposite is synthesized via a microwave-assisted co-precipitation method, using date palm extract (Phoenix dactylifera L.) as a natural reducing and stabilizing agent. The extract contains bioactive compounds (polyphenols, flavonoids) that:

• Control nucleation

• Stabilize particles

• Promote surface functionalization

• Enhance light absorption and charge transfer

This eco-friendly method is simple, cost-effective, scalable, and promotes strong interfacial contact between CoWO? and gCN.

Environmental Application: Rose Bengal Dye Degradation

The photocatalytic performance of the synthesized nanocomposite was tested for degradation of Rose Bengal, a persistent and toxic xanthene dye widely used in textile, pharmaceutical, and laboratory applications. Due to its stability and aromatic structure, Rose Bengal contaminates water bodies, reducing dissolved oxygen and harming aquatic life.

Under visible-light irradiation:

• The CoWO?/gCN nanocomposite effectively degrades Rose Bengal.

• The heterojunction facilitates rapid charge separation.

• Reactive oxygen species (•OH and •O?? radicals) are generated.

• These radicals oxidatively decompose dye molecules.

• The catalyst shows high recyclability and structural stability.

Materials and Methods Overview

Synthesis Steps:

1. Preparation of aqueous date palm extract.

2. Thermal polymerization of urea and citric acid to form bulk gCN.

3. Co-precipitation of CoWO? with varying gCN ratios.

4. Microwave treatment and calcination to improve crystallinity.

Characterization Techniques

The nanocomposite was characterized using:

• XRD (X-ray diffraction): Confirmed monoclinic wolframite CoWO? phase and successful integration with gCN. Average crystallite size ≈ 25.12 nm.

• XPS (X-ray photoelectron spectroscopy): Confirmed chemical states (Co²?, W??) and strong interfacial coupling.

• FE-SEM: Revealed homogeneous distribution of CoWO? nanoparticles on layered gCN sheets.

• EDX: Verified elemental purity and correct stoichiometric ratios.

• UV–Vis DRS: Demonstrated improved visible-light absorption and bandgap modulation.

Key Findings

1. Successful heterojunction formation between CoWO? and gCN.

2. Enhanced visible-light photocatalytic activity compared to pristine materials.

3. Efficient charge carrier separation and migration.

4. High recyclability and structural stability.

5. Green, sustainable synthesis route.

Conclusion

Overall, a visible-light-responsive CoWO?/gCN nanocomposite was successfully prepared through a microwave-assisted co-precipitation route. Structural characterization confirmed the formation of monoclinic CoWO? and its intimate integration with the gCN framework. The nanocomposite exhibited enhanced optical absorption with a narrowed band gap, promoting improved charge utilization under irradiation. As a result, efficient photocatalytic degradation of Rose Bengal was achieved within a short irradiation time, following pseudo-first-order kinetics. Radical trapping experiments indicated that superoxide radicals played the dominant role in the degradation pathway. Moreover, the photocatalyst demonstrated good recyclability over multiple cycles, highlighting its stability. Collectively, the CoWO?/gCN heterostructure represents a promising and reusable photocatalytic platform for sustainable wastewater remediation under visible light.

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Copyright © 2026 Priyanka ., Dr. Heena Dahiya. 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.