The photoluminescence quenching of CdTe QDs in the presence of three different Co (III)-complexes is studied to elucidate the role of interactions between functional groups of positively charged cysteamine capped CdTe QDs and negatively charged Co (III) complexes bearing carboxylic groups. The steady state and time resolved spectroscopy has been used to investigate the mechanism of quenching. After detailed analysis, it is concluded that quenching is contributed by both static as well as dynamic processes. The static contribution has been assigned to the electrostatic assembly formation via ionic interactions between the amine functional groups of positively charged cysteamine capped CdTe QDs and carboxylic acid groups of negatively charged complexes. The electrostatic interactions were confirmed by zeta potential measurement as well as from effect of salt addition. These studies have implications in designing donor/acceptor pairs having complementary functional groups for efficient optoelectronic devices or photocatalytic systems.

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Herein, we report the photo-electrochemical water splitting of CdSe quantum dots sensitized PbTiO3 perovskite in a sacrificial electrolyte. TheCdSe quantum dots are synthesized via hot injection method and perovskite. The PbTiO3 is synthesized via hydrothermal synthesis procedure. The CdSe quantum dots are sensitized to PbTiO3 using mercaptopropionic acid as linker to form hetero-structure.The phase purity and crystallinity of CdSe quantum dots and PbTiO3 are examined using X-ray diffraction analysis and the morphologies are studied using field emission scanning electron microscopy (FESEM) and transition electron microscopy (TEM) techniques. The optical properties are examined using UV-visible spectroscopy and the band gap of quantum dots and perovskite are derived. The XRD analysis of CdSe quantum dots revealed the high crystallinity with a cubic phase and tetragonal phase for PbTiO3. The surface morphological observations demonstrate that PbTiO3 size in the range of 80-120 nm in size. The TEM analysis revealed the single crystalline nature for PbTiO3 nanoparticles. The optical band gap of PbTiO3 is found to be 3.7 and 2.25 eV for CdSe quantum dots. The CdSe quantum dots sensitized PbTiO3 hetero-structure's photo-electrochemical water splitting behaviour is examined in 1 M Na2S electrolyte under 100 mW/cm 2 light illumination. As photoanode, CdSe quantum dots sensitized PbTiO3 heterostructure demonstrated 63 mA/cm 2 under illumination and 51 mA/cm 2 dark at 0.8 V (vs. Ag/AgCl), which implies that photocurrent density of 12 mA/cm 2 at 0.8 V (vs. Ag/AgCl) and also showed 1.2 mmol/g of H2 evolution during the period of 4 h in chrono-amperometry studies at 0.8 V (vs. Ag/AgCl). This work discusses the significance and novelty of the usage of CdSe quantum dots sensitized PbTiO3 heterostructureas photo-electrocatalyst and paves pathway for newer materials development for enhanced photo-electrochemical water splitting.

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