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Two-dimensional (2D) semiconductor colloidal nanoplatelets (NPLs) have shown great potential as light-harvesting materials due to their advanced optical properties. Here, we designed hybrid nanostructures of 2D CdSe nanoplatelets with phenothiazine (PTZ) for high-performance photodetector with varying thickness of CdSe NPLs by controlling the charge transfer process. Significant photoluminescence quenching and the shortening of the average decay time of CdSe NPLs in the presence of PTZ reveal the charge transfer process. Transient absorption spectroscopic analysis reveals the hot carrier cooling dynamics varies with changing the thickness of monolayers (ML) of CdSe NPLs. Furthermore, the slow exciton recombination of CdSe NPLs in the presence of PTZ indicates the efficient charge separation. The optimized CdSe NPLs-PTZ hybrid exhibits a significant enhancement of photocurrent (∼(4.7 × 103)-fold photo-to-dark current ratio) as compared to pure 3 ML CdSe NPLs (∼10 fold) at the applied voltage of 1.5 V. The measured external quantum efficiency, maximum detectivity, and response time for the optimized hybrid are found to be ∼40%, 4 × 1011 Jones, and 107 ms, with the responsivity value of 160 mA/W. These highly efficient measured parameters clearly suggest that CdSe NPLs-PTZ hybrid systems are a promising alternate for ultrasensitive photodetector.

The present work reports green route-waste recycled carbon nanolights, i.e., carbon dots (GCDs), synthesized via a facile one-step pyrolysis method from Citrus limetta waste pulp. The size of these obtained pristine GCDs is ∼4−7 nm (HR-TEM), with high optical and structural quality as revealed by FT-IR and Raman spectroscopic analysis. They exhibit the highest quantum yield of 63.3% over other similar green synthesized GCDs, favorable for many applications. Further, we demonstrate the multifunctional aspects of these synthesized GCDs for photoelectrochemical water splitting, photocatalytic methylene blue degradation, Fe(III) ions sensing, bactericidal activity (against E. coli and S. aureus), and bioimaging with excellent performance. The visible light active characteristic of GCDs is observed to achieve an efficient current density of ∼6 mA/cm 2 toward water splitting. This study demonstrates the waste to wealth potential of recycled waste derived GCDs in a wide range of application domains.

Photoelectrochemical water-splitting offers unique opportunity in the utilization of abundant solar light energy and water resources to produce hydrogen (renewable energy) and oxygen (clean environment) in the presence of a semiconductor photoanode. Zinc oxide (ZnO), a wide bandgap semiconductor is found to crystallize predominantly in the hexagonal wurtzite phase. Herein, we first report a new crystalline triclinic phase of ZnO by using N-rich antidiabetic drug metformin as a template via hydrothermal synthesis with self-assembled nanorod-like particle morphology. We have fabricated a heterojunction nanocomposite charge carrier photoanode by coupling this porous ZnO with a covalent organic framework, which displayed highly enhanced photocurrent density of 0.62 mA/ cm 2 at 0.2 V vs. RHE in photoelectrochemical water oxidation and excellent photon-to-current conversion efficiency at nearneutral pH vis-à-vis bulk ZnO. This enhancement of the photocurrent for the porous ZnO/COF nanocomposite material over the corresponding bulk ZnO could be attributed to the visible light energy absorption by COF and subsequent efficient charge-carrier mobility via porous ZnO surface.

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