article · Scientific Reports
Industrial release of chemical pollutants such as methylene blue dye poses severe threats to aquatic environments and human health. To address this challenge, nanocomposites combining reduced graphene oxide and zinc oxide were prepared through sustainable synthesis techniques. Graphene oxide components were generated by electrochemically exfoliating graphite rods recovered from discarded dry cell batteries. Additionally, leaf extract from Croton macrostachyus served as a green reducing and capping agent during the synthesis of zinc oxide and the hybrid nanocomposite. When exposed to direct sunlight, the resulting composite achieved a 99.0 percent degradation efficiency against methylene blue dye under optimal conditions, significantly exceeding the performance of its individual components. The degradation followed pseudo-first-order reaction kinetics and demonstrated high efficiency using a low catalyst loading of only 20 milligrams.
Discharging industrial chemical dyes into waterways endangers ecosystems and community water supplies. This research demonstrates an environmentally benign water treatment approach that relies on sunlight and repurposed waste materials, including spent batteries and plant extracts. Reusing electronic waste to neutralise industrial water pollutants presents a sustainable path toward reducing toxic chemical exposure while supporting circular economy practices.
This work could enable sustainable, solar-driven effluent treatment systems for industrial facilities or textile manufacturers discharging dye waste. Utilizing recycled battery materials and plant extracts provides a low-cost production route for water purification catalysts. However, the technology is at an early-stage research level, having been demonstrated only at bench scale on methylene blue dye, and requires further process development and scale-up testing before practical adoption.
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Abstract Industrial chemical pollutants such as methylene blue (MB) dye are released into the water body and potentially cause harm to the human and aquatic biosphere. Therefore, this study aims to synthesize eco-friendly nanocatalysts, i.e., reduced graphene oxide (rGO), zinc oxide (ZnO), and reduced graphene oxide-zinc oxide (rGO@ZnO) nanocomposites, for efficient photocatalytic degradation of MB dye. A graphite rod was obtained from waste dry cell batteries for the electrochemical exfoliation synthesis of graphene oxide (GO) and rGO. For the eco-friendly synthesis of ZnO and rGO@ZnO nanocatalysts, Croton macrostachyus leaf extract was used as a reducing and capping agent. The synthesized nanocatalysts were characterized using a UV–Vis spectrophotometer, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy with energy-dispersive X-ray. The eco-friendly synthesized rGO, ZnO, and rGO@ZnO nanocatalysts were applied for the photocatalytic degradation of MB dye using direct sunlight irradiation. At optimum parameters, photocatalytic degradation of MB dye efficiency reached up to 66%, 96.5%, and 99.0%, respectively. Furthermore, kinetics of the photodegradation reaction based on rGO, ZnO, and rGO@ZnO nanocatalysts follow pseudo-first-order with a rate constant of 2.16 × 10 –3 min −1 , 4.97 × 10 −3 min −1 , and 5.03 × 10 −3 min −1 , respectively. Lastly, this study promotes a low catalyst load (20 mg) for the efficient photodegradation of MB dye.
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DOI: 10.1038/s41598-023-48826-7
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