Solid ion transition route to 3D S-N-codoped hollow carbon nanosphere/graphene aerogel as a metal-free handheld nanocatalyst for organic reactions

A novel metal-free bulk nanocatalyst, S--N-codoped hollow carbon nanosphere/ graphene aerogel （SNC-GA-1000）, has been successfully fabricated using a facile and clean solid ion transition route. In this method, ZnS is used as the hard template and S source, while polydopamine acts as a reducing agent and carbon source. At a high annealing temperature, Zn metal is reduced and evaporates, leaving only free S vapor to diffuse into the carbon layer. Interestingly, the as-obtained SNC-GA-1000 exhibits much higher catalytic activity in an organic reduction reaction than unloaded bare S--N-codoped carbon nanospheres. Hydrothermal reduction of the graphene oxide sheets loaded with ZnSC@olydopamine core-shell nanospheres （ZnS@PDA） affords a three-dimensional bulk graphene aerogel. Although nanosized catalysts exhibit high catalytic activities, their subsequent separation is not always satisfactory, making post-treatment difficult. This approach achieves a trade-off between activity and separability. More importantly, due to the 3D structural nature, such bulk and handheld nanocatalysts can be easily separated and recycled.