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 10². 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 %.