Nitrogen Dioxide Sensing Using Multilayer Structure of Reduced Graphene Oxide and α-Fe2O3

Abstract

Multilayers consisting of graphene oxide (GO) and α-Fe2O3 thin layers were deposited on the ceramic substrates by the spray LbL (layer by layer) coating technique. Graphene oxide was prepared from graphite using the modified Hummers method. Obtained GO flakes reached up to 6 nanometers in thickness and 10 micrometers in lateral size. Iron oxide Fe2O3 was obtained by the wet chemical method from FeCl3 and NH4OH solution. Manufactured samples were deposited as 3 LbL (GO and Fe2O3 layers deposited sequentially) and 6 LbL structures with GO as a bottom layer. Electrical measurements show the decrease of multilayer resistance after the introduction of the oxidizing NO2 gas to the ambient air atmosphere. The concentration of NO2 was changed from 1 ppm to 20 ppm. The samples changed their resistance even at temperatures close to room temperature, however, the sensitivity increased with temperature. Fe2O3 is known as an n-type semiconductor, but the rGO/Fe2O3 hybrid structure behaved similarly to rGO, which is p-type. Both chemisorbed O2 and NO2 act as electron traps decreasing the concentration of electrons and increasing the effective multilayer conductivity. An explanation of the observed variations of multilayer structure resistance also the possibility of heterojunctions formation was taken into account.

The Synergistic Properties and Gas Sensing Performance of Functionalized Graphene-Based Sensors

“…A technique used by Tadeusz Pisarkiewicz and co-workers [145] demonstrates Fe 2 O 3 as an n-type semiconductor, but in the rGO/Fe 2 O 3 hybrid structure it behaves similarly to ptype rGO. Both chemisorbed O 2 and NO 2 act as electron traps, decreasing the concentration of electrons, with a decrease of resistance (hole density increases).…”

Mechanisms of NO2 Detection in Hybrid Structures Containing Reduced Graphene Oxide: A Review

“…It exhibits poor sensitivity to NO 2 detection at room temperatures. The combination of rGO nanoflakes and Fe 2 O 3 nanoparticles allows a material similar to a p-type semiconductor to be obtained, which is more sensitive for NO 2 than both materials separately [ 67 ]. The SEM image of GO/Fe 2 O 3 is shown in Figure 14 .…”

“…Combination of Fe 2 O 3 grains and rGO causes a formation of a heterojunction [ 67 ] ( Figure 15 ) in which electrons are transferred from rGO to Fe 2 O 3 [ 67 ]. rGo/Fe 2 O 3 exhibits additional active sites (defects and/or oxygen functional groups) which improve the sensitivity [ 68 ].…”

“…When the structure is exposed in air, oxygen is adsorbed on the surface of rGO/Fe 2 O 3 in the forms of , and ions [ 48 ]. These ions react with NO 2 molecules in the surrounding atmosphere (10) [ 67 ] ( Figure 16 ) and, as a result, an unbalanced negative charge is formed on the Fe 2 O 3 surface. To neutralize this charge, electrons from the rGO are transferred.…”

The Heterostructures of CuO and SnOx for NO2 Detection

“…Various metal oxides are used as gas sensors; for example, barium titanate, strontium titanate and barium strontium titanate doped with various elements depending on the doped materials; they behave as p-type or n-type [ 31 , 32 ], n-type including zinc oxide (ZnO) [ 33 , 34 ], tin dioxide (SnO 2 ) [ 35 ], tungsten trioxide (WO 3 ) [ 36 ], indium oxide (In 2 O 3 ), gallium oxide (Ga 2 O 3 ), vanadium oxide (V 2 O 5 ) and iron oxide (Fe 2 O 3 ) and p-type metal oxides such as nickel oxide (NiO), copper oxide (CuO) [ 37 ], cobalt oxide (Co 3 O 4 ), manganese oxide (Mn 3 O 4 ) and chromium oxide (Cr 2 O 3 ) [ 38 , 39 ]. As gas-sensitive materials in gas sensors, heterostructures are also used, such as tin sulfide/tin oxide (SnS 2 /SnO 2 ), tungsten disulfide/titanium dioxide (WS 2 /TiO 2 ), molybdenum disulfide/tin oxide (MoS 2 /SnO 2 ), molybdenum disulfide/zinc oxide (MoS 2 /ZnO), reduced graphene oxide/tin oxide (rGO/SnO 2 ), reduced graphene oxide/carbon dot (rGO/CD), reduced graphene oxide/molybdenum disulfide (rGO/MoS 2 ) [ 40 ], reduced graphene oxide/iron oxide (rGO/F 2 O 3 ) [ 41 ], cobalt tetroxide/titanium dioxide (Co 3 O 4 /TiO 2 ) [ 42 ], zinc oxide/indium oxide (ZnO/In 2 O 3 ), tin oxide/cupric oxide (SnO 2 /CuO), titanium dioxide/vanadium pentoxide (TiO 2 /V 2 O 5 ) [ 30 ], graphene in combination with metal oxides [ 43 ] and many others.…”