Acetic acid gas sensors based on Ni^(2+) doped ZnO nanorods prepared by using the solvothermal method

Ni^（2＋）-doped ZnO nanorods with different doping concentrations are prepared via the solvothermal method.The doped ZnO nanorods are characterized by X-ray diffraction（XRD） and scanning electron microscopy （SEM）,respectively.The amount of Ni^（2＋） ions that enter the lattice of ZnO increases with increasing the Ni^（2＋）/Zn^（2＋） molar ratio when the molar ratio of Ni^（2＋）/Zn^（2＋） in the starting solution is lower than 3%and does not change obviously if the mole ratio of Ni^（2＋）/Zn^（2＋） in the starting solution is in the range of 3-10 mol%.The effect of Ni^（2＋） doping on the gas-sensing properties is investigated.The results reveal that the amount of Ni^（2＋） has a great influence on the response（R_a/R_g） and the gas-sensing selectivity.The sensor based on 1 mol%Ni^（2＋） doped ZnO nanorods （120℃,10 h） exhibits a high response to acetic acid vapor,in particular,the responses to 0.001 ppm and 0.01 ppm acetic acid vapor reach 1.6 and 2,respectively.The response time and the recovery time for 0.001 ppm acetic acid are only 4 s and 27 s,respectively.

Core-shell TiO_(2)/ZnO nanorod array films on FTO:Two-step synthesis and improved ethanol sensing performance

In this work,highly regular TiO_(2)nanorod array films were synthesized in situ on FTO by a facile hydrothermal method,and then ZnO shell layers were grown on the surface of the nanorods to form a coreshell structure via an ion-layer adsorption-reaction way.Compared to the TiO_(2)nanorods,the prepared TiO_(2)/ZnO nanocomposites exhibited enhanced ethanol sensing performances,including a low working temperature,higher sensitivity,and faster response capability.The optimum sensor based on 2c-TiO_(2)/ZnO exhibited the maximum response value of 30.85 toward 50×10^(-6)C_(2)H_(5)OH at 340℃,which was almost 4.15 times higher than that of the TiO_(2)sensor.The improved ethanol sensing mechanism was discussed in relation to the unique nanorod array structure and the heterojunctions between TiO_(2)and ZnO.

Urchin-like Na-doped zinc oxide nanoneedles for low-concentration and exclusive VOC detections

In the early-stage diagnosis of lung cancer,the low-concentration(<5 ppm)volatile organic compounds(VOCs)are extensively identified to be the biomarkers for breath analysis.Herein,the urchin-like sodium(Na)-doped zinc oxide(ZnO)nanoneedles were synthesized through a hydrothermal strategy with the addition of different contents of citric acid.The Na-doped ZnO gas sensor with a 3:1 molar ratio of Na^(+)and citric acid showed outstanding sensing properties with an optimal selectivity to various VOCs(formaldehyde(HCOH),isopropanol,acetone,and ammonia)based on working temperature regulation.Specifically,significantly enhanced sensitivity(21.3@5 ppm)compared with pristine ZnO(~7-fold),low limit of detection(LOD)(298 ppb),robust humidity resistance,and long-term stability of formaldehyde sensing performances were obtained,which can be attributed to the formation of a higher concentration of oxygen vacancies(20.98%)and the active electron transitions.Furthermore,the improved sensing mechanism was demonstrated by the exquisite band structure and introduction of the additional acceptor level,which resulted in the narrowed bandgap of ZnO.