Highly active ZnO-based biomimetic fern-like microleaves for photocatalytic water decontamination using sunlight

Abstract

Here we present the highly enhanced sunlight photocatalytic efficiency and photocorrosion resistance of biomimetic ZnO-modified micro/nanofern fractal architectures, which are synthesized by using a novel, simple, inexpensive and green electrochemical deposition approach in high stirring conditions. Such fern-like hierarchical structures simultaneously combine enhanced angle independent light trapping and surface/bulk modifications of the ZnO morphology to drastically increase: i) the light trapping and absorption in the visible near-infrared range, and ii) the surface to volume ratio of the architecture. This combination is crucial for boosting the sunlight photocatalytic efficiency. To modulate the electronic properties for extending the operation of the ZnO photocatalysts into the visible domain we have used three different modification approaches: sulfidation (leading to a ZnS shell), Ag decoration, and Ni-doping. The different ZnO-modified bioinspired fern-like fractal structures have been used to demonstrate their efficiency in the photodegradation and photoremediation of three different persistent organic pollutants -methylene blue, 4-nitrophenol, and Rhodamine B - under UV light, simulated and natural UV-filtered sunlight. Remarkably, the ZnO@ZnS core@shell structures exhibited an outstanding photocatalytic activity compared to the pristine ZnO catalyst, with over 6-fold increase in the pollutant degradation rate when using solar light. In fact, the catalytic performance of the ZnO@ZnS micro/nanoferns for the photoremediation of persistent organic pollutants is comparable to or better than the most competitive state-of-the-art ZnO photocatalysts, but showing a negligible photocorrosion. Ag-decorated ZnO, and Ni-doped ZnO exhibited similar excellent visible-sunlight photodegradation efficiency. Although the Ni-doped photocatalysts showed a relatively poor photocorrosion resistance, it was acceptable for Ag-decorated ZnO. Therefore, the easy fabrication and the capacity to drastically enhance the sunlight photocatalytic efficiency of the ZnO@ZnS bioinspired micro/nanoferns, together with their practically negligible photocorrosion and simple recyclability in terms of non-catalyst poisoning, makes them very promising photocatalysts for water remediation.