Synthesis of novel BiVO₄/Cu₂O heterojunctions for improving BiVO₄ towards NO₂ sensing properties

To develop a high sensitive and low temperature NO₂ gas sensor, the novel BiVO₄/Cu₂O heterojunctions were synthesized by a modified metal organic decomposition method to decorate BiVO₄ nanoplates using Cu₂O nanoparticles for enhancement of BiVO₄ sensing performance to NO_2. The structure and morphology of BiVO₄, Cu₂O and BiVO₄/Cu₂O composites were characterized by XRD, SEM and TEM spectra. The results indicate that the BiVO₄/Cu₂O heterojunctions are composed of monoclinic BiVO₄ nanoplates with the thickness about 1.0-1.2 μm and 30-40 nm diameters of cubic Cu₂O nanoparticles. The gas-sensing tests display that the composite exhibits rapid and linear responses to low concentration NO₂ (from 100 ppb to 8.0 ppm), the highest response reaches 4.2 towards 4 ppm NO₂ at 60 °C and relative humidity of 28.3%, which is more than 2 times of pure BiVO₄ at the same condition. The enhanced sensing properties benefit from the novel p-n heterojunction between BiVO₄ and Cu₂O, which forms a depletion layer at the interface, leading to resistance increase of composites in NO₂. The work demonstrates the as-synthesized BiVO₄/Cu₂O is a promising sensing material to detect NO₂ gas.