Fabrication of tannin-based hydroxyl-rich, uniform and size-controllable nanospheres as carriers for silver nanoparticles

High loading of Ag nanoparticles (Ag NPs) with small sizes on catalyst carriers/support is crucial to achieve efficient catalysis, such as catalytic degradation of organic dyes in wastewater; however, it is still challenging to develop Ag NPs catalyst carriers/support with excellent Ag NPs loading. In this work, we developed bio-based (tannin and lignin-derived catechol) nanospheres (TCR) that are hydroxyl-rich, highly uniform, size-controllable, and the resultant TCR nanospheres were subsequently used as catalyst carriers/support for Ag NPs (TCR@Ag), achieving a high loading of Ag NPs yet with the ultrafine nanoparticles. The size of as-prepared TCR nanospheres can be adjusted from 737 nm to 403 nm by regulating the amount of tannin added, and the polydispersity index (PDI) of TCR nanospheres is as low as 0.042, indicating remarkable nanosphere uniformity. As catalyst carriers of Ag NPs, the use of tannin makes TCR nanospheres rich in phenolic-OH groups, which is responsible for the well-dispersed and high-density loading of Ag NPs, and the highest loading is 48.4 wt%; meanwhile, the size of Ag NPs is only 16.8 nm. The as-prepared TCR@Ag catalysts show superior catalytic performance for the typical organic dye-containing wastewater samples, and the reaction rate constants are 2.44 min-1 and 4.87 min-1 for methylene blue (MB) and methyl orange (MO), respectively, outperforming those of the most reported Ag-based catalysts. In addition, TCR@Ag catalysts also possess good environmental adapt-ability, dispersion stability, reusability, antioxidation activity, and negligible biological toxicity, so the novel TCR@Ag catalysts have great potential as effective catalysts for environmental remedy purpose.