Functionalized Graphene Nanoballs

A one-pot procedure converts solutions of graphene oxide and precursor ions to crumpled sheets of graphene decorated with nanocrystals, according to a study led by researchers at the University of Wisconsin, Milwaukee (ACS Nano, DOI: 10.1021/nn302818j). The method builds on work reported recently by other scientists that shows graphene sheets can be crumpled into nanosized balls that resist uncrumpling, aggregating, and stacking. The wadded-up form of carbon is endowed with high surface area, making it attractive for energy storage and other applications. But access to those applications typically requires additional chemical processing steps. UW Milwaukee’s Shun Mao and Junhong Chen and coworkers created a general method for making graphene nanoballs and functionalizing them with metals or metal oxides in a single step. The team reports that flowing aerosols of graphene oxide suspensions containing nanoparticle precursors through a furnace causes the aerosol droplets to rapidly evaporate. That process crumples and partially reduces the carbon flakes and triggers spontaneous growth of nanocrystals on the inner and outer surfaces of the balls. The researchers made supercapacitors and lithium-ion batteries from nanoballs coated with Mn₃O₄ and SnO₂, respectively, and report that the devices outperform versions made from flat graphene sheets.