Visible-light-driven photocatalysts prepared using renewable resources are crucial but challenging to develop for the efficient degradation of organic pollutants, which is required to solve ever-increasing water deterioration issues. In this study, we report a visible-light-responsive photocatalyst for the efficient degradation of methylene blue (MB) as a model pollutant dye. Green-emissive carbon quantum dots (CQDs) were synthesized from pear juice via a facile, scalable, one-pot solvothermal process. The as-synthesized CQDs exhibit superior photocatalytic activity under visible-light irradiation owing to their efficient light absorption, electron transfer, and separation of photogenerated charge carriers, facilitating ~99.5% degradation of MB within 130 min. A possible mechanism for the photocatalysis is proposed on the basis of comprehensive active species trapping experiments. Furthermore, the CQDs were used in a specific sensitive assay for Fe(III) and ascorbic acid (AA), even with interference from other metal ions. The fluorescence emission of CQDs was “turned off” specifically upon binding of Fe(III) and “turned on” with AA. The prepared CQDs represent efficient photocatalysts and fluorescent probes that are not restricted by toxicity, cost, or lack of scalability.

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.