Eco-friendly fabrication of Au nanoparticles immobilized on tannin-aminopropyltriethoxysilane-coated halloysite nanotubes for thermally tunable catalysis

A facile and eco-friendly approach is developed for the fabrication of highly dispersed gold nanoparticles (Au NPs) immobilized on a thermo-responsive tannin-aminopropyltriethoxysilane (TA-APTES)-coated halloysite nanotubes (HNTs) and the application as a “smart” catalyst in the thermally tunable catalysis. By simply controlling the reaction conditions, the green and versatile TA-APTES coating was assembled onto the HNTs (HTA) with a controllable thickness, and subsequently the thermo-responsive poly(N-isopropylacrylamide) was grafted onto HTA (HTA-P) through a Michael addition reaction. Owing to the adhesive ability, metal ion affinity, and reducibility of TA-APTES coating, Au nanoparticles can be in situ immobilized and homogenously dispersed on both HTA and HTA-P without the assistance of any reducing agent and stabilizing agent. The as-prepared Au/HTA and Au/HTA-P exhibited superior activities in the reduction of 4-nitrophenol, which were comparable to the famous polydopamine-coated counterpart. Notably, Au/HTA-P showed a significant thermo-responsive catalytic performance, where the highest catalytic efficiency was obtained at the lower critical solution temperature of 45 °C, demonstrating the crucial role of the thermo-responsive polymer on the thermally tunable catalysis. Finally, the Au/HTA and Au/HTA-P catalysts prepared in a simple and eco-friendly manner were stable in the successive catalytic cycles, showing great potentials in industrial catalytic applications. Eco-friendly tannin-aminopropyltriethoxysilane-coated halloysite nanotubes were served as multifunctional materials for the fabrication of highly active and thermo-responsive catalysts.