Hydrogen peroxide is the most stable and abundant reactive oxygen species in an organism and present in many biological processes [1]. It is a general enzymatic product of oxidases and a substrate of peroxidases, which are important in biological processes and biosensors. H2O2 is also an essential mediator in food, pharmaceutical, clinical, industrial, and environmental analysis [2]. Quantitative detection of H2O2 has important scientific significance for understanding intracellular signal transduction and realizing the normal function of cells. The development of low cost, high-speed, uncomplicated, highly selective, and sensitive H2O2 sensors are essential.
After discovering the existence of graphene by A. Geim and K. Novoselov, this new material is one of the most celebrated discoveries presently in the field of material science [3]. Several unique properties of graphene make it a capable contender to be used as a sensor. The conjugated structure of graphene can facilitate the electron transfer between the bioreceptor and transducer, which can generate high signal sensitivity for electrochemical sensors. The incorporation of graphene and its related nanomaterials in (bio)sensor technologies have shown great promise due to its high surface area (2630 m2 g-1), electron mobility at room temperature ( up to 200000 cm2 V-1 s-1), chemical stability and its capacity to immobilize a variety of different biomolecules. Moreover, chemical doping of graphene-based materials is an easy and effective method to modify materials intrinsically, tailor electronic properties, manipulate surface chemistry, and produce local changes to the elemental composition of host materials [3].
The aim of this work was to produce N-doped reduced graphene oxide (rGO) and to investigate its sensitivity in the non-enzymatic detection of hydrogen peroxide.
GO was prepared from natural graphite using the synthesis protocol reported by Yan et al. [4]. In a typical experiment, graphite powder was treated with concentrated H2SO4, K2S2O8, and P2O5. The obtained pre-oxidized graphite was subjected to oxidation by Hummers' method using NaNO3, H2SO4, and KMnO4 [5]. The thermally rGO was produced from GO using a thermal shock method. The dried GO powder was quickly inserted into a preheated tubular furnace at a temperature of about 800 °C in Ar atmosphere. To introduce N-functionalities, the rGO surface was modified with gaseous ammonia at 950 °C for 8 h or with melamine at 700 °C for 1 h [6, 7]. The obtained materials were characterized by different methods (elemental analysis, BET measurement, SEM investigations, Raman spectroscopy). Electrochemical measurements, in particular, cyclic voltammetry and electrochemical impedance spectroscopy were used to evaluate the obtained samples sensitivity toward hydrogen peroxide detection.
The results demonstrated that after the reduction of GO, a characteristic morphology of rGO and N-doped rGO occurs independent on the functionalization protocol. Moreover, it was observed, that various nitrogen species including pyridinic-N, pyrrolic-N and quaternary-N were detected in the N-doped rGO. BET measurement results prove that all prepared samples were meso- and macroporous in nature. In addition, after the ammonia-treatment at high temperatures, both BET surface area and pore volume of the samples increased compared to the pristine GO and rGO. Finally, the conducted electrochemical measurements highlighted that N-doped rGO could be a promising electrode material for the detection of hydrogen peroxide.