Synthesis And Gas Sensing Performance Of Nickel Doped Tin Oxide Flower-like Microstructures

As an n-type semiconductor with wide band gap,tin oxide?SnO₂?exhibits good performance in electrical characteristics.Moreover,the sensors based on SnO₂ possess the characteristic of low cost and long life,which also has good gas sensitivity and response/recovery for various gases.For those reason,it is not only one of the earliest to appliance in the field of gas sensors,but also universally applied up to now.Nevertheless,the bulk SnO₂-based gas sensors have some shortcomings,such as poor stability and selectivity.It is still necessary to solve those problems to further improve the gas sensing performances.Element doping and heterojunction have been demonstrated as efficient methods to improve the gas-sensing performance of SnO₂ materials.In this paper,the flower-like SnO₂ hierarchical structures have been prepared via a simple hydrothermal method.On this basis,it was modified by 4mol%and high Ni-doped concentration?corresponding doping amount is 20mol%,25 mol%,33.3 mol%?.The synthesized samples were systematically studied by various characterization methods.What's more,the gas sensing properties of 4 mol%Ni doped SnO₂ for methanol and high doped concentration for acetone were studied respectively,and the mechanisms of the enhanced gas-sensing properties were expounded.The results of experiments were showed as follows:?1?Ni-doped flower-like SnO₂ microstructures with different concentrations were prepared by hydrothermal method.When with low concentration of 4mol%,the Ni atoms entered into the lattice of SnO₂,and no new crystalline phase existed in the modified samples.When the doping amount is increased,Ni atoms dissolve from the solid solution of SnO₂ and form NiO by oxidation.So the synthesized of NiO-Sn O₂ composite is synthesized.Moreover,the introduction of Ni elements not only changes the morphology of Sn O₂significantly,but also decreases its size.?2?Gas sensing properties of 4 mol%Ni-doped SnO₂ for methanol were investigated.The obtained results demonstrated that response of Ni-doped Sn O₂toward 100 ppm methanol can reach to 13.0 at the optimum operating temperature of 280°C,which is about 2.4 times higher than that of pristine SnO₂.Meanwhile,the gas sensor based on Ni-doped SnO₂ also exhibits fast response/recovery time?⁶ s/5 s?and better selectivity to methanol.?3?Moreover,gas-sensing properties of the as-fabricated pristine SnO₂ and high Ni-doped concentration sensor devices were investigated systematically toward acetone detection.Compared with the pure SnO₂,the sensors based on Ni-doped SnO₂ showed enhanced gas sensor properties:the response was improved,the recovery time was shortened,and the stability and selectivity were better.In particular,the Ni₁Sn₃ gas sensor can reach a response of 20.18toward 50 ppm acetone under optimum operating temperature?300°C?,which is about 3.3 times higher than that of pristine sensor.Moreover,the sensor based on Ni₁Sn₃ also possess short response/recovery time?2 s/9 s?and low detection limit?10 ppb?.?4?The gas sensing mechanisms were discussed respectively as follow:For the sample of 4 mol%Ni-doped SnO₂,the substitutional doping make Ni ions enter into the lattice of SnO₂ and produce oxygen vacancies,which are more conducive to the adsorption of oxygen molecules.One the other hand,which also leads to the introduction of additional energy levels,making the electrons more easily excited,thus improving the gas sensitivity.The high concentration of Ni was doped to form Ni O-SnO₂ composite structure.The gas sensitivity of the sensor was greatly improved due to the p-n heterojunction formed between NiO and SnO₂.Due to the Fermi energy effect,the depletion layer was widened and the gas sensitivity of the sensor to acetone was greatly improved.