Abstract
Phthalocyanine-based light harvesting nanomaterials are attractive due to their low cost, eco-friendly properties and sensitivity in the red region of the solar spectrum. However, for any practical application, phthalocyanines need to be chemically modified for anchoring groups with wide-band semiconducting nanomaterials. In this paper, zinc phthalocyanine (ZnPc) was functionalized with two carboxyl groups containing a biologically important ligand, tartrate, using a facile wet chemistry route and duly sensitized zinc oxide (ZnO) to form nanohybrids for application in photocatalytic devices. The nanohybrids have been characterized using a high-resolution transmission/scanning electron microscope (HRTEM, FEG-SEM), X-ray diffraction (XRD), steady-state infrared/UV–vis absorption and emission spectroscopy for their structural details and optical properties, whereas the ultrafast dynamical events, which are key for understanding the photocatalytic activities, were monitored using picosecond resolution fluorescence techniques. More specifically, vibrational spectroscopy (FTIR) revealed the covalent connection of ZnPc with the host ZnO nanoparticles via the tartrate ligand. The efficiency of the material for photocatalysis under red light irradiation was found to be significantly enhanced compared to bare ZnO. A mechanistic pathway for the formation of photo-induced reactive oxygen species (ROS) in an aqueous medium for the photocatalytic efficacy was investigated. To make a prototype for a potential application in a flow device for water decontamination, we have sensitized ZnO nanorods (ZnO NR) with tartrate-functionalized ZnPc. The molecular proximity of ZnPc to the ZnO surface has been confirmed by picosecond resolution Förster Resonance Energy Transfer (FRET) from the intrinsic emission of surface defects of ZnO NR to the attached ZnPc. The excited-state electron transfer dynamics, as revealed by a picosecond resolution fluorescence study (TCSPC), is in good agreement with the enhanced charge separation at the interface of the nanohybrid. The enhanced photoresponse, wavelength-dependent photocurrent of the sensitized nanorods and photodegradation of a model water pollutant in a prototype device format confirmed the potential use of the nanohybrids in water purification.
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•Facile synthesis of zinc phthalocyanine (ZnPc)–ZnO nanohybrid via tartrate ligand.•Ultrafast charge transfer dynamics within the nanohybrid upon photoexcitation.•FRET from ZnO Nanorods to the ZnPc confirms molecular proximity.•Enhanced photocatalytic activity of the nanohybrid under red light irradiation.•A prototype flow device for potential application in water purification.