A Highly Efficient Thermo Responsive Palladium Nanoparticles Incorporated Guar Gum Hydrogel for Effective Catalytic Reactions

Hydrogel, especially stimuli responsive hydrogel, has attracted enormous attention due to its unique properties for many applications. Herein, Pd NPs@ CNCs was firstly attained by in situgeneration of Pd NPs onto CNCs, and subsequently incorporated into guar gum-based hydrogel, so that a thermo responsive Pd NPs@ CNCs/ guar gum hydrogel catalytic system was obtained. The sol-gel transition was achieved viaa simple heating/cooling cycle: a sol state was obtained above 70 °C, allowing the catalytic reaction; a gel state was attained below 20 °C, allowing the reuse/ recycling of the Pd NPs. Pd NPs were formed by in situ reduction of PdCl in the presence of CNCs so that Pd NPs were loaded onto CNCs surfaces. CNCs acted as stabilizers for the Pd NPs. The TEM image showed that the average size of Pd NPs is ˜3 nm. Subsequently, the Pd NPs@ CNCs composites were loaded into the guar gum hydrogel, based on the boron crosslinking chemistry. The hydrogel exhibited rapid sol-gel transition process upon heating (70 °C) and cooling (20 °C) cycles. The Pd NPs loaded sol-gel transition concept was subsequently applied to the Suzuki coupling reactions between aryl bromides and phenyl boronic acids, and a highly efficient catalytic performance (over 85% yield within 2 h) was obtained. The reuse/recycling of the thermo responsive Pd NPs@ CNCs/guar gum hydrogel catalyst system was investigated. This novel Pd NPs loaded thermo-responsive sol-gel transition concept is a promising new catalytic system.