Ultrasensitive and selective CuAlO2 sensor toward H2S based on surface sulfuration-desulfuration reaction

Firstly, 8 g copper acetate (Cu(CH3COO)2·H2O, Alfa Aesar) was dissolved in 160 mL absolute alcohol with magnetic stirring, 16 mL nitric acid (HNO3, Sinopharm Chemical Reagent), 40 g citric acid (C6H8O7, Sinopharm Chemical Reagent) and 10 g aluminum-sec-butoxide (Al[OCH(CH3)CH2CH3]3, Alfa Aesar) were sequentially added into the above solution. After stirring for about 6 h, 16 mL HNO3 was added to the solution drop by drop to yield a well-mixed deep-blue precursor solution. Dry gels could be obtained by baking the precursor at 100 °C for 12 h. In order to remove the organics, the condensed solution was heated to 300 °C for 6 h. Then the obtained powders were milled in an alumina ceramic vessel at 200 rpm for 10 h by a planetary ball mill(QM-1SP2, Nanjing University Instrument Factory). The zirconia ball(14.5 mm diameter) to powder mass ratio is 10:1. The milled powders were then sintered at 1100 °C for 10 h under air atmosphere. Afterwards, the powders were reground and sintered at 950 °C under flowing N2 atmosphere for 6 h. The heating rate is 10 °C/min for both annealing processes. After natural cooling, the obtained grey products were washed (by 1 M diluted hydrochloric acid, DI water and absolute ethanol) and then dried at 80 °C in an oven 24 h for further usage.X-ray diffraction (XRD) was measured on Rigaku Smartlab by using Cu Kα radiation operated at 40 kV and 40 mA. Scanning electron microscope (SEM, VEGA3 TESCAN) and field emission high resolution transmission electron microscope (HRTEM, Talos F200X) equipped with selected-area electron diffraction (SAED) and energy dispersive spectroscopy (EDS) were used to characterize the morphologies and structural parameters of the samples. The chemical states were analyzed by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS, with He Ⅰ 22.21 eV light source) were performed on Escalab 250Xi (Thermo Fisher). Raman spectra of CuAlO2 sensor before and after H2S gas sensing test were measured on HORIBA(LabRAM HR Evolution) with an excitation wavelength of 532 nm. The fluorescence properties were examined by using photoluminescence(PL, JY Fluorolog-3-Tou) with an excitation wavelength of 250 nm. The total ion chromatograms of tail gas before and after H2S gas sensing tests were performed by gas chromatography-mass spectrometry (GCMS, Thermofisher, TSQ Quantum XLS). Flat band potential measurements were carried out on electrochemical work-station (Zahner Company, Germany) in 1 M NaOH solution (pH = 12.5) with frequencyof 5000 Hz. Platinum sheet, Ag/AgCl electrode and the substrate coated with CuAlO2 samples were used as counter electrode, reference electrode and work electrode, respectively.CuAlO2 powders mixed with appropriate isopropyl alcohol were grounded in a mortar for 15 min to form a paste, which was coated onto commercial thin alumina substrates preprinted with Pt electrodes (HuaChuang Rui Ke Technology Co., Ltd.). After naturally drying, the CuAlO2 sensors were aged at 350 deg;C under flowing air atmosphere for 3h. Supporting information Fig. S1 shows a schematic image of CuAlO2 sensor device. Gas sensing tests were measured by SD101 (Hua Chuang Rui Ke Technology Co., Ltd.) sensing system. The response was defined as Rg/Ra, where Rg and Ra are sensor resistance in the flowing tested gases and reference gas (dry air), respectively. During gas sensing tests, the total flow rate of the dry air and tested gases were fixed to be 500 sccm by mass flow controllers (MFCs). The details of gas sensing measurements can be found in our previous report.

首先，将8 g乙酸铜（Cu(CH3COO)2·H2O，Alfa Aesar）置于160 mL无水乙醇中，磁力搅拌至完全溶解；随后依次向上述溶液中加入16 mL硝酸（HNO3，国药集团化学试剂有限公司）、40 g柠檬酸（C6H8O7，国药集团化学试剂有限公司）以及10 g仲丁醇铝（Al[OCH(CH3)CH2CH3]3，Alfa Aesar）。持续搅拌约6 h后，向溶液中逐滴加入16 mL硝酸，得到混合均匀的深蓝色前驱体溶液。将前驱体置于100 ℃下烘烤12 h，即可得到干凝胶。为去除有机组分，将浓缩后的溶液升温至300 ℃并保温6 h。随后采用行星式球磨机（QM-1SP2，南京大学生产仪器厂）将所得粉末置于氧化铝陶瓷罐中，以200 rpm转速球磨10 h，球料比（直径14.5 mm氧化锆球：粉末）为10:1。将球磨后的粉末置于空气气氛中，于1100 ℃下烧结10 h；随后将粉末再次球磨，并置于流动氮气气氛中，于950 ℃下烧结6 h。两次退火过程的升温速率均为10 ℃/min。自然冷却后，将所得灰色产物依次用1 mol/L稀盐酸、去离子水以及无水乙醇洗涤，随后置于80 ℃烘箱中干燥24 h，以备后续实验使用。采用Rigaku Smartlab型X射线衍射仪（X-ray diffraction, XRD）进行物相表征，测试条件为Cu Kα辐射，管电压40 kV，管电流40 mA。采用扫描电子显微镜（Scanning electron microscope, SEM, VEGA3 TESCAN）以及场发射高分辨透射电子显微镜（High Resolution Transmission Electron Microscope, HRTEM, Talos F200X）对样品的形貌与结构参数进行表征，两款设备均配备选区电子衍射（Selected-area electron diffraction, SAED）与能量色散光谱（Energy Dispersive Spectroscopy, EDS）。采用Escalab 250Xi型设备（赛默飞世尔科技，Thermo Fisher）对样品的化学态进行分析，测试手段包括X射线光电子能谱（X-ray photoelectron spectroscopy, XPS）以及紫外光电子能谱（Ultraviolet photoelectron spectroscopy, UPS，采用He Ⅰ 22.21 eV光源）。采用HORIBA LabRAM HR Evolution型拉曼光谱仪，以532 nm为激发波长，测试了CuAlO2气敏传感器在硫化氢（Hydrogen sulfide, H2S）气敏测试前后的拉曼光谱。采用JY Fluorolog-3-Tou型光致发光光谱仪（Photoluminescence, PL），以250 nm为激发波长，对样品的荧光特性进行测试。采用Thermofisher TSQ Quantum XLS型气相色谱-质谱联用仪（Gas Chromatography-Mass Spectrometry, GCMS）测试了硫化氢气敏测试前后的尾气总离子色谱图。采用德国Zahner公司生产的电化学工作站，在1 mol/L氢氧化钠（NaOH，pH=12.5）溶液中，以5000 Hz的频率进行平带电位测试；测试采用铂片作为对电极、Ag/AgCl电极作为参比电极，以及涂覆有CuAlO2样品的基底作为工作电极。将适量异丙醇与CuAlO2粉末混合，在研钵中研磨15 min制成浆料，随后将浆料涂覆在预先印刷有铂电极的商用氧化铝薄基底上（华创瑞科科技有限公司）。自然晾干后，将CuAlO2气敏传感器置于流动空气气氛中，于350 ℃下老化3 h。补充材料图S1给出了CuAlO2气敏传感器器件的结构示意图。气敏测试采用SD101型气敏测试系统（华创瑞科科技有限公司）完成。气敏响应定义为Rg/Ra，其中Rg与Ra分别为传感器在待测流动气体与参比气体（干燥空气）中的电阻值。气敏测试过程中，通过质量流量控制器（Mass Flow Controllers, MFCs）将干燥空气与待测气体的总流量固定为500 sccm。气敏测试的详细步骤可参见我们此前的研究报道。