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 °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.