Impact of pH on Regulating Ion Encapsulation of Graphene Oxide Nanoscroll for Pressure Sensing

Recently, graphene oxide nanoscroll (GONS) has attracted much attention due to its excellent properties. Encapsulation of nanomaterials in GONS can greatly enhance its performance while ion encapsulation is still unexplored. Herein, various ions including hydronium ion (H₃O⁺), Fe³⁺, Au³⁺, and Zn²⁺ were encapsulated in GONSs by molecular combing acidic graphene oxide (GO) solution. No GONS was obtained when the pH of the GO solution was greater than 9. A few GONSs without encapsulated ion were obtained at the pH of 5-8. When the pH decreased from 5 to 0.15, high-density GONSs with encapsulated ions were formed and the average height of GONS was increased from ~50 to ~190 nm. These results could be attributed to the varied repulsion between carboxylic acid groups located at the edges of GO nanosheets. Encapsulated metal ions were converted to nanoparticles in GONS after high-temperature annealing. The resistance-type device based on reduced GONS (rGONS) mesh with encapsulated H₃O⁺ showed good response for applied pressure from 600 to 8700 Pa, which manifested much better performance compared with that of a device based on rGONS mesh without H₃O⁺.