Stochastic detection and characterisation of individual ferrocene derivative tagged graphene nanoplatelets

Abstract

Graphene nanoplatelets (GNPs) are 'tagged' with 1-(biphen-4-yl)ferrocene. Chronoamperometry is then utilised to observe single particle impacts when GNPs suspended in solution collide with a carbon fibre micro wire electrode held at an oxidising potential, resulting in current/time transient "spikes". The impacts are associated with two types of charge transfer: Faradaic due to oxidation of the 'tag' and capacitative due to disruption of the double layer. Analysis of the spikes suggests approximate monolayer coverage of 1-(biphen-4-yl)ferrocene on the GNP surfaces, with a surface coverage of (2.2 ± 0.3) × 10(-10) mol cm(-2). In contrast non-derivatised ferrocene does not exhibit any significant adsorption on the GNP material.

Nanoimpacts Reveal the Electron‐Transfer Kinetics of the Ferrocene/Ferrocenium Couple Immobilised on Graphene Nanoplatelets

“…Figure shows that the reductive back peak is less defined than the oxidative forward peak at EPPG electrodes modified with both PVFc (black line) and PVFc–GNPs (red line). This could be attributed to the co‐ordination of the ferrocenium and the anion from the supporting electrolyte, which stabilises the former sufficiently that its reduction becomes thermodynamically unfavourable. However, this influence of ion pairing has been minimised by the choice of NaClO 4 , as compared to KCl, for example (see the Supporting Information for further details on the choice of supporting electrolyte).…”

“…The preparation of GNP suspensions follows a method reported earlier . For the unmodified GNP suspension, the GNPs (5.6 mg) were mixed with aqueous solution supported with 0.1 m NaClO 4 (100 mL).…”

“…To estimate the weight of a single GNP, its density was assumed to be the same as graphite, 2.26×10 6 g m −3 . By taking the volume of the single GNP, the weight of the GNPs could be determined as 1.68×10 12 g mol −1 , and the concentration of the GNPs in use was determined to be approximately 3×10 −14 m …”

“…For nanoimpacts chronoamperometry, an aqueous solution with 0.1 m NaClO 4 (5 mL) was added to the vial. Such a supporting electrolyte was chosen to minimise ion pairing between the ferrocenium and the anion, as elaborated on in the following section. The mixture was shaken vigorously and sonicated to ensure that the PVFc–GNPs were well suspended in the solution.…”

“…As compared to modification with single ferrocene molecules, modification with polymers such as poly(vinylferrocene) (PVFc) introduces a higher number of electroactive centres in the nanoparticles, leading to greater nanoimpacts signals and facilitating electron‐transfer kinetics studies. Nanoimpacts can be used to study the size, concentration and catalytic properties of nanoparticles, as well as surface coverage of redox moieties on the nanoparticulate surface. However, the quantitative measurement of electron‐transfer kinetics at individual nanoparticles is very limited …”