Efficient synthesis of a new heterogeneous gold nanocatalyst stabilized by di-alkyne ligand and its applications for photocatalytic dye degradation and transfer hydrogenation reaction

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A new form of carbon-based ligand supported robust heterogeneous gold nanocatalyst was synthesized and its potential catalytic applications are demonstrated. The high yield (> 90%) synthesis procedure involves ligand exchange between hydrophilic polyvinylpyrrolidone polymer stabilized gold nanoparticles (Au:PVP) with a di-alkyne ligand (1,4-Diethynylbenzene). The ultrasmall stabilized gold nanoparticles (1.8 ± 0.3 nm) are bonded to di-alkyne ligand through acetylenic carbon atom (≡C-Au) with an electronically conjugated 3D network. The synthesized material (Au-P1) was meticulously characterized using several spectroscopic and microscopic techniques, e.g., Fourier transform infrared spectroscopy (FTIR), optical absorption spectroscopy (UV-Vis), powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscope (TEM) and thermogravimetric analysis (TGA). The Au nanocatalyst showed good photocatalytic activity for degradation of several organic dye molecules in aqueous phase under visible light irradiation in presence of oxidizing agent (H2O2). The proposed mechanism involves dye absorption on ligand surface through π-π interaction followed by transfer of electron from excited dye molecules to gold core through electronically conjugated ligand for generation of reactive oxygen species (·OH). The catalyst has also been demonstrated for transfer hydrogenation of organic carbonyl and nitro functional groups (>C=O, -NO2) with potassium formate (HCOOK) as hydrogen source in water. The catalyst could be recovered by simple filtration, and it was reused up to five cycles for both of these catalytic transformations with complete retention of its catalytic activity.