Visible-light photocatalysis by carbon-nano-onion-functionalized ZnO tetrapods: degradation of 2,4-dinitrophenol and a plant-model-based ecological assessment

Abstract

The visible-light-induced photocatalytic performance of a three-dimensional (3D) hybrid composite based on carbon nano-onion (CNO)-functionalized zinc-oxide tetrapods (T-ZnO) was investigated to study the photocatalytic degradation of 2,4-dinitrophenol (DNP). The hybrid CNO-functionalized T-ZnO 3D composite was successfully developed via a facile one-step process. The CNOs, synthesized via a green route from flaxseed oil, were decorated on the surface of T-ZnO via chemical mixing. Such a hybrid composite allows for the complete optimization of the T-ZnO/CNO interface to enhance visible-light harvesting, contributing to effective visible-light-induced photocatalysis. The enhanced photocatalytic performance of the T-ZnO-CNO 3D composite is attributed to the strong synergistic effects obtained by the unique cumulative intrinsic properties of CNOs and the 3D architecture of T-ZnO, which lead to exceptional charge transfer and separation. A reaction mechanism for the degradation of DNP is proposed based on a bandgap analysis and trapping experiments. Furthermore, the photocatalyst maintains a favorable reusability during consecutive cycling experiments. The ecological assessment of the photocatalytic process was performed via the germination of common gram seeds (Cicer arietinum) and reveals the low toxicity and environmental safety of the synthesized hybrid 3D composite. The observations confirm that the synthesized hybrid 3D composite facilitates wastewater decontamination using photocatalytic technology and highlights the broad implications of designing multifunctional materials for various advanced applications.Catalysis: Sunlight-powered nano-onions chop up pollutantsA nanomaterial with a unique shape can lower the concentrations of a known carcinogen in wastewater to levels safe enough to sustain plant growth. The industrial chemical 2,4-dinitrophenol (DNP) is hazardous at part-per-million concentrations in water and is exceptionally stable. Kumud Malika Tripathi and TaeYoung Kim from Gachon University in Seongnam, South Korea, and co-workers have developed a hybrid catalyst that traps DNP on its surface and degrades it into smaller by-products using solar energy. The team attached carbon nanomaterials with onion-like structures to the arms of zinc oxide ‘tetrapods’, nanocrystals where four thin rods are connected to one core. When exposed to visible light, catalysts containing carbon nano-onions degraded over 90% more DNP than bare zinc oxide tetrapods. Mechanistic studies suggest the unusual carbon–zinc interface helps draw photogenerated charge to active catalytic sites.3D Hybrid composite of ZnO tetrapods and carbon nano onions is developed to a new direction for the visible-light-induced degradation of 2,4-dinitrophenol without any hazardous by-products.