​An international group of researchers compared different methods of forming these hybrid materials to test the effect of the synthesis route on the detection capability. They found that making the material in situ led to greater sensitivity in the detection of hydrogen peroxide.

Reduced graphene oxide (RGO) is an important carbon-based nanomaterial (CBNM) used for the development of sensors. It has a number of very interesting properties, including excellent electrical conductivity, high surface area, and good mechanical strength. Hybrid materials of CBNMs and inorganic oxides such as Fe₃O₄ and TiO₂ have been the focus of research interest thanks to their potential in sensing applications.

In these hybrid materials, the distribution of the inorganic oxide phase and the carbon-based material on the surface is important for optimising the chemical performance, and so the synthesis has the potential for influencing this performance. The different methods of synthesis fall into the categories of being ex situ or in situ. 

Ex situ methods involve mixing the CBNM and a previously synthesised nanocrystal of the inorganic oxide. Although this offers more selectivity of the specific nanostructure of the oxide, the coverage can be non-uniform and at lower density. In situ methods usually give better coverage and can give a continuous film of nanoparticles on the surface of the CBNM.

This research tested two methods (in- and ex- situ) for the formation of Co₂TiO₄ (CTO) and RGO hybrids to be used for the development of hydrogen peroxide sensors. The group were able to determine the catalytic effect of these materials for hydrogen peroxide reduction and their application in the electrochemical detection of hydrogen peroxide in real samples.

Fast and accurate determination of hydrogen peroxide concentration has important applications in the electron transfer process of hundreds of enzymes in biological systems, as well as in various industries, such as paper, textiles and pharmaceuticals.

Using the GEM diffractometer at ISIS, along with other characterisation techniques, the group were able to determine the structure of the hybrid materials that they had synthesised, and confirm that there were no contaminants or impurities present. Once they had confirmed their synthesis technique, they were able to test the ability of the materials to detect hydrogen peroxide.

Both of the materials made by the different methods showed electro-catalytic activity towards the electro-reduction of hydrogen peroxide. Crucially the in situ synthesis process led to better coupling between the CTO and RGO. This strong coupling improved the dispersion of the CTO nanoparticles on the RGO surfaces, decreasing the resistance and increasing the electrical conductivity of the final material. The nano-scale structure of the in situ hybrid also enabled easier access of the hydrogen peroxide molecules to the active sites.

These interesting results offer a simple alternative for the quantification of hydrogen peroxide, and open doors for further electrochemical sensor development. Domingo Ruiz, from the Universidad de Santiago de Chile​, one of the paper authors, explains; “this work is important for the development and understanding of new materials for non-enzymatic sensing of peroxides. Thanks to the structural refinement performed with the measurements we did at ISIS, the work also has a secondary impact related to the determination of the cationic distribution of the inorganic-based structure.” ​

Further Information

The full article is available at: Nanomaterials 2019, 9, 1611; doi:10.3390/nano9111611