Hallmarks of a successful catalyst include simplicity of design and low cost of fabrication, high efficiency, facile recovery and extensive reusability, amenability to monitoring between reuses, and ease of scale up. Even though the number of palladium nanoparticle based catalysts reported for the Suzuki–Miyaura reaction has grown exponentially in recent years, the aforesaid criteria are rarely met in a single system. We present a palladium nanoparticle-embedded polymer thin film which functions as a highly efficient and reusable “dip catalyst” for the Suzuki–Miyaura reaction. The multilayer free-standing nanocomposite thin film is fabricated using a simple in situ process through thermal annealing of a spin-coated film of poly(vinyl alcohol) (PVA) containing the palladium precursor. Fabrication parameters of the Pd-PVA film are optimized for enhanced catalyst efficiency. The catalyst is shown to produce very high yield, turn over number and turn over frequency in the prototypical reaction of iodobenzene with phenylboronic acid. The “dip catalyst” film is easily retrieved from the reaction system and reintroduced in successive batches; the high efficiency is retained beyond 30 cycles. The thin film structure enabled convenient catalyst monitoring by spectroscopy and microscopy between reruns. Efficient use of the catalyst up to 5 mmol scale reaction is demonstrated. A simple figure-of-merit is formulated to quantify the catalyst performance, and the present catalyst is evaluated in the context of those reported earlier. Preliminary exploration of the utility of the thin film catalyst in the Suzuki–Miyaura reaction with several substrates as well as in the Heck and Sonogashira coupling reactions is carried out.

Achieving a harmonious combination of the efficiency of homogeneous catalysts with the reusability of heterogeneous catalysts is a fundamental and challenging problem. Metal nanoparticles in a suitable matrix offer a potential solution. However an ideal design is yet to be realized, because the critical requirements of facile access to the catalyst, its durability, and ease of retrieval and reuse are difficult to reconcile. We report herein a multilayer free-standing thin-film catalyst based on silver nanoparticles, generated in situ inside poly(vinyl alcohol) by using a facile protocol, which shows excellent efficiency and extensive reusability in the prototypical reaction, the reduction of 4-nitrophenol by sodium borohydride. The "dip catalyst" film, which can start/stop the reaction instantaneously by mere insertion/removal, is used 30 times leading to a total turnover number (TON) of ≈3390, which is unprecedented for this reaction. The efficiency of the catalyst is reduced only marginally at the end of these runs, promising further extended usage. The unique advantage of convenient catalyst monitoring is illustrated by the periodic spectroscopic and microscopic examinations of the thin film, which revealed the basis of its durability. The demonstrated potential of metal-nanoparticle-embedded polymer thin films, coupled with their versatility and ease of fabrication, promises extensive applications in chemical catalysis.

The utility of polymer-metal nanocomposite thin films with in situ generated silver nanoparticles as substrates for surface-enhanced Raman scattering (SERS) is demonstrated. Thin films of poly(vinyl alcohol) and poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) containing Ag nanoparticles generated in situ through thermal annealing and photoirradiation, respectively (Ag-PVA and Ag-PVVV), are investigated as potential SERS substrates using 4-aminothiophenol and rhodamine 6G as probe molecules. The fabrication protocols are extremely simple and the materials inexpensive. The Ag-PVA substrate is found to produce Raman spectral enhancement factors of ~10(6), whereas Ag-PVVV, a novel nanocomposite thin film developed in the present study, provides enhancement factors of ~10(7). A unique advantage of these nanocomposite films is demonstrated by fabricating them by the in situ process as a thin coating inside glass capillaries and using these disposable SERS substrates for the sensitive detection of the probe molecules. The thin film substrates prepared on glass plates and capillaries facilitate convenient sample preparation for recording the Raman spectra and provide strongly enhanced spectra with high reproducibility, allowing picomols of the analytes to be detected. These aspects combined with the ease of fabrication and low cost of these in situ fabricated nanocomposite thin films make them highly attractive SERS substrates.

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