Fabrication of bulk, nanosheets and quantum dots of graphitic carbon nitride on electrodes: Morphology dependent electrocatalytic activity

Abstract

The present work aims to find a suitable morphology of graphitic carbon nitride (g-CN) for electrocatalytic applications which includes bulk g-CN (g-CNB), g-CN nanosheets (g-CNNS) and g-CN quantum dots (g-CND). The different morphologies of g-CN were synthesized by solid-phase thermal method using urea, citric acid and trisodium citrate as precursors. The X-ray diffraction (XRD) pattern of g-CNs showed characteristic 2θ values due to (0 0 2) interlayer diffraction and (1 0 0) in-plane structural packing. The g-CN with the morphology of bulk, sheets and dots were then attached directly on GC electrode by immersing it into the respective g-CN solution. The scanning electron microscopy (SEM) images showed that the g-CNB coated on GC plate displays layer like structure whereas g-CNNS exhibits crumpled and enfolded thin sheets like graphene. The SEM image of g-CND coated GC plate shows that they were uniformly covered the whole area as dots with the size of 30 nm. Under optimized conditions, the electrochemical impedance studies showed that the order of the charge transfer resistance was as follows: g-CNNS < g-CND < g-CNB < GC. The impact of g-CN morphology on the oxidation of ascorbic acid (AA) and dopamine (DA) and the reduction of hydrogen peroxide (HP) was studied at pH 7.2 phosphate buffer (PB) solution. The g-CNs modified electrodes irrespective of the morphology enhanced the electrocatalytic activity in contrast to bare GC electrode. Among the three g-CNs, GC/g-CNNS electrode exhibited higher electrocatalytic activity towards all the three analytes. The cause for the higher electrocatalytic activity was attributed to its higher electroactive surface area and faster electron transfer rate in contrast to GC/g-CNB and GC/g-CND electrodes. Further, GC/g-CNNS electrode was effectively used for the sensitive determination of HP. While increasing its concentration from 100 nM to 1 mM, HP reduction current increases linearly with R2 value of 0.9905 and LOD was 11 nM (S/N = 3). Finally, GC/g-CNNS electrode was successfully used to quantify HP in blood serum samples.