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

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.

Applications of Ceramic/Graphene Composites and Hybrids

“…This section focuses on nanocomposites and hybrids of the last two systems, providing a summary of recent developments on this matter. Metal oxide (MO x )/GO nanomaterials are predominantly used as gas sensors for different harmful gases, since the hybridization of both types of materials generate beneficial synergic effects [ 153 , 154 ]. The remainder ceramic-graphene nanocomposites are mostly used as electrochemical sensors and biosensors.…”

VOCs Sensing by Metal Oxides, Conductive Polymers, and Carbon-Based Materials

“…Overall, the gas sensing properties of CbMs are strongly connected with the presence of defects and residual contaminants at the surface. Hence, for practical applications, the sensitivity of CbMs is usually enhanced by modifying or functionalizing them with metals [ 54 , 55 ], MOXs [ 56 ], or POMs [ 57 , 58 ], as can be seen in Figure 1 a.…”

Monitoring Lipolysis by Sensing Breath Acetone down to Parts‐per‐Billion

“…Compact, [ 22 ] low‐cost, and highly sensitive [ 23 ] acetone sensors already exist even commercially (e.g., LEVL, Ketonix, Keyto, Lexico Health Keto Breath Analyzer, ACE KETOSCAN mini). They are usually based on solid‐state [ 24 ] chemoresistive [ 25 ] (metal oxides [ 26 ] or carbon‐based hybrids [ 27 ] ), electrochemical [ 28 ] or optical [ 18 ] sensors, or arrays. [ 29 ] Despite extensive research [ 24 ] since 1984, such acetone sensors still have not been established for routine healthcare monitoring, [ 30 ] as they usually fall short on accuracy, [ 31 ] mostly due to lack of acetone selectivity.…”