Breakthroughs in the Design of Novel Carbon-Based Metal Oxides Nanocomposites for VOCs Gas Sensing.

Eleonora Pargoletti,Giuseppe Cappelletti

doi:10.3390/nano10081485

Abstract

Nowadays, the detection of volatile organic compounds (VOCs) at trace levels (down to ppb) is feasible by exploiting ultra-sensitive and highly selective chemoresistors, especially in the field of medical diagnosis. By coupling metal oxide semiconductors (MOS e.g., SnO2, ZnO, WO3, CuO, TiO2 and Fe2O3) with innovative carbon-based materials (graphene, graphene oxide, reduced graphene oxide, single-wall and multi-wall carbon nanotubes), outstanding performances in terms of sensitivity, selectivity, limits of detection, response and recovery times towards specific gaseous targets (such as ethanol, acetone, formaldehyde and aromatic compounds) can be easily achieved. Notably, carbonaceous species, highly interconnected to MOS nanoparticles, enhance the sensor responses by (i) increasing the surface area and the pore content, (ii) favoring the electron migration, the transfer efficiency (spillover effect) and gas diffusion rate, (iii) promoting the active sites concomitantly limiting the nanopowders agglomeration; and (iv) forming nano-heterojunctions. Herein, the aim of the present review is to highlight the above-mentioned hybrid features in order to engineer novel flexible, miniaturized and low working temperature sensors, able to detect specific VOC biomarkers of a human’s disease.

Highlights

Wearable electronics is expected to be one of the most active research areas in the near future
The boosted sensing features are believed to be due to both the presence of reduced graphene oxide (RGO)/zinc oxide (ZnO) hetero-interfaces and the catalytic effect of Au and Pd nanoparticles. These results show that the combination of noble metals, such as Au or Pd NPs, with RGO and ZnO can impart new gas sensing functionalities that are potentially useful for the sensing of either inorganic or organic volatile compounds
The current research attention has been focused on the detection of ppm or even ppb concentrations of several volatile organic compounds, since they are believed to be specific biomarkers of certain human diseases

Summary

Introduction

Wearable electronics is expected to be one of the most active research areas in the near future. Very short response and recovery times within seconds were recorded, resulting in very useful chemoresistors for practical applications The authors ascribed this sensing enhancement to several reasons: (i) the high surface area in a 2D network that may facilitate the diffusion of ethanol molecules, improving the reaction with surface adsorbed oxygen, namely ionosorption model [39,51,54]; (ii) the material porosity of the hybrid compound with respect to the compact pure Fe2O3; (iii) the graphene outstanding electrical conductivity resulting in quick electron spreading in the semiconductor surface, showing faster response and recovery times; (iv) graphene might create a Schottky contact at the interface with MOS nanoparticles, favoring α-Fe2O3 to G electron migration. The so-prepared hybrid sample was revealed as being highly sensitive and selective to aniline molecules, as clearly observable in Figure 3j, thanks to the synergistic effect between metal oxide and graphene materials

Graphene Oxide-MOS Gas Sensors

Reduced Graphene Oxide-Based Chemoresistors

Carbon Nanotubes-Metal Oxides Sensing Materials

Findings

Conclusions and Future Outlooks