CoPP coating for limited oxygen diffusion and reduced electron scavenging in light-activated room temperature TiO2 nanoparticle gas sensing films

TiO2 is an important metal oxide semiconductor gas sensor material. It has many benefits, such as high response, natural abundance and low toxicity. TiO2 gas sensor material can be activated by light and operated at room temperature, thus reducing the energy consumption of the sensor and improving its safety. The electric resistance of light-activated TiO2 is altered in the presence of an analyte due to photo-induced hole scavenging by gas and electron accumulation in the conduction band. However, the response is limited due to competing processes - electron consumption by ambient oxygen - thus hindering their practical applicability. Here, we demonstrate the light-activated TiO2 gas sensor based on ultra-small nanoparticle (<5 nm) films modified with 5,10,15,20-tetraphenyl-21H,23H-porphyrin Cobalt (II) (CoPP). Coating the TiO2 film surface with CoPP increases the room temperature gas response towards 5 ppm EtOH 12.58 times from S = 46.72 +/- 1.77 to S = (5.88 +/- 0.39) x 10(2). The sensors show selectivity towards alcohols, such as ethanol, and exhibit response S = 1.086 +/- 0.049-100 ppm EtOH even in the presence of relative humidity as high as 50 %.