Acid/base treatment of monolithic activated carbon for coating silver with tunable morphology

Abstract

Silver coatings on the exterior surface of monolithic activated carbon (MAC) with different morphology were prepared by directly immersing MAC into [Ag(NH₃)₂]NO₃ solution. Acid and base treatments were employed to modify the surface oxygenic groups of MAC, respectively. The MACs’ Brunauer-Emmett-Teller (BET) surface area, surface groups, and silver coating morphology were characterized by N₂ adsorption, elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM), respectively. The coating morphology was found to be closely related to the surface area and surface functional groups of MAC. For a raw MAC which contained a variety of oxygenic groups, HNO₃ treatment enhanced the relative amount of highly oxidized groups such as carboxyl and carbonates, which disfavored the deposition of silver particles. By contrast, NaOH treatment significantly improved the amount of carbonyl groups, which in turn improved the deposition amount of silver. Importantly, lamella silver was produced on raw MAC while NaOH treatment resulted in granular particles because of the capping effect of carbonyl groups. At appropriate [Ag(NH₃)₂]NO₃ concentrations, silver nanoparticles smaller than 100 nm were homogeneously dispersed on NaOH-treated MAC. The successful tuning of the size and morphology of silver coatings on MAC is promising for novel applications in air purification and for antibacterial or aesthetic purposes.

Keywords

monolithic activated carbon / silver coating / morphology / functional groups / surface modification

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