Self-Assembly of Cu2O Monolayer Colloidal Particle Film Allows the

Subscriber access provided by WESTERN SYDNEY U

Functional Inorganic Materials and Devices

Self-assembly of Cu2O Monolayer Colloidal Particle Film Allows the Fabrication of CuO Sensor with Superselectivity for Hydrogen Sulfide Zongke Xu, Yuanyuan Luo, and Guotao Duan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b17251 • Publication Date (Web): 11 Jan 2019 Downloaded from http://pubs.acs.org on January 13, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Self-assembly of Cu2O Monolayer Colloidal Particle Film Allows the Fabrication of CuO Sensor with Superselectivity for Hydrogen Sulfide Zongke Xua, Yuanyuan Luob,c*, and Guotao Duana, b*

a

School of Optical and Electronic Information, Huazhong University of Science and

Technology, Wuhan 430074, P. R. China b

Key Lab of Materials Physics, Anhui Key Lab of Nanomaterials and

Nanotechnology, Institute of Solid State Physics, Chinese Academy of Science, Hefei 230031, P. R. China c

University of Science and Technology of China, Hefei, 230026, P. R. China

* Email: [email protected]; [email protected]

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract CuO monolayer colloidal particle film with controllable thickness and homogeneous microstructure was prepared by self-assembly and subsequent calcination based on Cu2O colloidal particles. Large-scale CuO monolayer colloidal particle film has the particle size of 300-500 nm, and CuO colloidal particles are hollow. It was found that such structure exhibits the excellent room temperature H2S gas sensing properties. It not only has high sensing response and excellent selectivity, but also has a low limit of detection of 100 ppb. The sensors exhibit different sensitive characteristics at low and high concentrations H2S. At low concentration (100~500 ppb), the sensor can be recovered with the increase of gas response, although it takes a longer recovery time at room temperature. At medium concentration (1~100 ppm), although the gas response still increases, the sensor is irreversible at room temperature. When the concentration continues to increase (>100 ppm), the sensor is irreversible at room temperature, and the gas response first increases and then decreases. Two reaction mechanisms are proposed to explain the above-mentioned sensing behavior. More importantly, quasi in-situ XPS spectra confirm the existence of CuS. The CuO sensor with room-temperature response and superselectivity will be found potential applications in industry, environment, or intelligent electronics. Keywords: Self-assembly; Monolayer colloidal particle film; CuO sensor; Hydrogen sulfide; Superselectivity


Page 2 of 43

Page 3 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. Introduction As one highly poisonous and malodorous gas, H2S extensively presents in natural and industrial fields such as petroleum, and coal chemical industry.1-3 According to the safety standards set by American Conference of Government industrial Hygienists, the threshold of H2S is about 10 ppm.4 Therefore, detection or monitoring of H2S is of immense significance to avoid human casualties in case of H2S gas leakage.5 Currently, semiconducting metal oxides have become a research hotspot in the field of gas sensor because of their outstanding characteristics such as good gas response, short response time, inexpensive cost, flexible and simple preparation.6-8 Among the mostly studied H2S gas sensor, SnO29-12 and ZnO13-16, as n-type semiconductor, are the top two materials followed by TiO2,17 WO3,18 In2O319 and Fe2O320-22. In particular, it has been reported that the nanostructured SnO2 and ZnO based sensors have high response to H2S and the selectivity is improved by the doping or modification of a small amount of catalysts i.e. platinum, palladium, and gold, and the other semiconductor materials.5, 12, 23-24 It was noted that one dimensional SnO2 nanostructures modified by p-type CuO show an excellent H2S gas sensing performance at a given operating temperature. However, detection of sub-ppb level H2S at room temperature is imperative in energy consumption and the environmental safety.25 As mentioned above, CuO itself exhibits good gas sensing properties to H2S, besides helping to improve the sensitivity of SnO2 and ZnO to H2S. The gas sensitivity of CuO-based materials to H2S can be explained by the following two



reaction mechanisms:2, 26 (1) The reaction between H2S and negative charge oxygen adsorbed on CuO surface promotes the formation of some electrons. The recombination of these electrons with CuO holes results in the decrease of accumulation layers and ultimately the increase of CuO response. (2) H2S reacts with CuO to generate CuS, which decreases the response of CuO. After H2S gas is pulled out, the atmospheric oxygen can bring to the conversion of CuS into CuO. However, relevant research is relatively limited. In order to obtain a superselective sensor for H2S, it is urgent to further study the reaction mechanisms for the sensitivity of CuO material to H2S. Up to now, some studies on detection of H2S by pure CuO nanostructured thin films have been reported.26,27 Chen et al.27 developed in situ micromanipulation technology in scanning electron microscopy to fabricate CuO nanowire arrays. Copper oxide nanowire arrays can detect hydrogen sulfide gas with lower concentration of 500 ppb at 160 oC. Z. J. Li et al.28 reported the facile hydrothermal preparation and the excellent room temperature sensitivity of porous CuO Nanosheets to 10 ppb H2S. Further researches also indicate all kinds of composites, such as CuO/Pd,29 CuO/SnO2,30 CuO/SWCNT,31 CuO/CuFe2O4,32 and CuO/NiO33 can be used as an alternative means to optimize the sensitivity of CuO-based material to H2S due to the increased hole accumulation layer compared with pure CuO materials. Table 1 lists the work related to the sensitivity of CuO-based material to H2S. The above-mentioned studies indicate the sensing properties based on chemiresistive gas sensor are relative not only to the materials’ chemical composition and phase structure


Page 4 of 43

Page 5 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


but also to their microstructures, in which the film thickness is an important factor that strongly affects the sensitivity of the sensor to H2S. As we know, in addition to low sensitivity and long response time, the thicker the film thickness, the higher the consistency and stability of the film. On the contrary, the thinner the film thickness, the higher the sensitivity and the faster the response time. Traditional preparation methods of the sensing materials will cause unrepeatable fabrication, imhomogeneous microstructure, and uncontrollable film thickness, which will seriously affect the morphology control and durability of the sensors. Therefore, to prepare the sensing film with the controllable film thickness and the homogeneous microstructure still is a challenge. Recently, thin film made up of monodisperse semiconducting particles presents highly stable structures and properties, which is conducive to the repeatability of thin film preparation.34 Gas sensors based on such assembled semiconducting particles show novel gas performances. In this paper, the CuO monolayer colloidal particle film derived from self-assembly of Cu2O was fabricated. First, the monodisperse Cu2O colloidal particles were synthesized by low temperature solution-phase method. Then, the monolayer Cu2O colloidal particle film was obtained by self-assembly method in air/water interface. Last, CuO sensor was prepared by transferring the Cu2O monolayer colloidal particle film to a sensor’s substrate followed by the annealing. Such CuO films are highly homogeneous in microstructure, controllable in film thickness, and of good reproducibility. The sensitivity of CuO to H2S gas has been detailedly studied. It shows high sensing response and excellent selectivity at



room temperature, which may be found potential applications in industry, environment, or intelligent electronics. 1. Experimental section Materials: Copper acetate monohyreate (Cu(CH3COO)2·H2O A.R.), Sodiuu borohydride (NaBH4, A.R.), Polyvinylpyrrolidone (PVP, G.R. molecular weight = 30 000), and N,N-Dimethylformamide (DMF, anhydrous, A.R.) were bought from Sinopharm Chemical Reagent Co., Ltd. All experiments were conducted with distilled water. Preparation of monodisperse Cu2O colloidal particles: Monodisperse Cu2O colloidal particles were synthesized based on a modified method developed by Li’s group.35 Typically, 0.410 g Cu(CH3COO)2·H2O, 0.222 g PVP and 0.030 g NaBH4 were added in 25 mL DMF under constant stirring for 10 min, respectively. Then 0.05 mL H2O was slowly dropped into the solution during the mixed solution was heated at 90 oC

for 4 min. Finally, the mixture was cooled to room temperature, centrifugally

separated and precipitated, washed with distilled water and absolute ethanol, and dried in an oven at 80 oC. The synthesis of CuO film and sensor: First, glass substrates were ultrasound cleaned according to previously reported methods.36-37 Second, pure Cu2O colloidal particles were dispersed into some alcohol under ultrasound for 10 min and slowly dropped into the glass substrate. Under the action of different surface tensions of water/air interface, the monolayer film was gradually formed. Third, a glass substrate coated with Cu2O film was immersed in water and monolayer film gradually floated on the


Page 6 of 43

Page 7 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


water surface. Fourth, Cu2O film was transferred to ceramic substrate and was heat for several minutes. Finally, after heat treatment (500 oC, 2 hours), the Cu2O film was transformed into CuO and the CuO sensor was finally prepared. Characterization: X-ray diffraction (XRD) spectra were measured using Philips X’Pert diffractometer with CuKα radiation. Field-emission scanning electron microscopy (FESEM) observations were recorded on Sirion200 microscope. Transmission electron microscopy (TEM) measurements were done with H-800 microscope. X-ray photoelectron (XPS) patterns were achieved by ULTRA AXIS DLD spectrometer. Sensor tests: The sensor measurements were done in a home-built testing unit equipped with a source of direct current. By installing two micro fans in the chamber, the uniform H2S or air flow can be achieved. A simple circuit diagram is seen in Figure S1. The total voltage (Vc) of 10 V is applied partly to the load resistance and partly to the sensor, and the sensor is heated by applying other voltage to the Ni-Cr alloy coil. When the voltage of the sensor reaches a constant value, the H2S gas is fed into the chamber and the concentration of H2S is determined according to the injection volume. A signal for gas response was determined by a change in the resistance of the sensor in presence/absence of the H2S gas. The sensor measurements were carried out under the condition of 40 % relative humidity and 25 oC temperature.

2. Results and discussion Nearly monodisperse Cu2O was synthesized by an optimized low temperature



solution-phase method. In this process, DMF is used as the solvent and NaBH4 as the reducing agent. More H2O is used as additive to accelerate the conversion of Cu(CH3COO)2 to Cu2O, and a large amount of H2 is produced. H2 is used as bubble templating, around which Cu2O nucleates, grows and finally assembles into the hollow nanosphere. The morphology of the sample is presented in Figure S2a. One can see that the as-synthesized product is composed of a large number of spherical particles and the diameter of the particles is about 300-500 nm. The corresponding XRD spectra identifies the sample can be indexed as pure cubic phase of Cu2O, which are consistent with the standard values (JCPDS No. 65-3288), as seen in Figure S2b. Based on XRD pattern, the average grain size of Cu2O calculated by Scherrer’s formula38 is about 14.6 nm. The TEM characterizations of Cu2O microsphere are shown in Figure S3. Magnified TEM pattern clearly presents the microspheres’ surface is slightly smooth and the microspheres are hollow, as seen in Figure S3b. Figure S3c reveals the polycrystalline structures of Cu2O microspheres made up of small grain, which is in agreement with that of XRD result. Interface self-assembly has been used to easily prepare 2D or 3D polystyrene or SiO2 colloidal crystals39. However, it is still difficult to prepare 2D or 3D colloidal crystals for other materials due to many factors, such as the substrate wettability, the ink formulation, and so on. Owing to the features of spherical geometry and monodisperse size distribution of the as-prepared Cu2O, it was used for the self-assembling monolayer colloidal particle film at the water/air interface. Cu2O monolayer films have been prepared by a large number of experiments, as seen in


Page 8 of 43

Page 9 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. First, pure Cu2O colloidal particles were dispersed into some ethanol and slowly dropped into the glass substrate. Under the action of different surface tensions of water/air interface, Cu2O monolayer colloidal particle film was gradually formed, as shown in Figure 1a. Then, a glass substrate coated with Cu2O monolayer film was immersed in water and monolayer film gradually floated on the water surface (Figure 2b,c). Third, this Cu2O monolayer colloidal particle film was transferred into other clean substrates, such as Silicon, quartz, FTO, Al2O3 and so on). In this work, the Cu2O monolayer colloidal particle film was transferred onto the Al2O3 planar substrate used for sensor, which is shown in Figure 1d. Finally, Cu2O was converted into CuO monolayer colloidal particle film after annealing at 500 oC for 2 h, and the gas sensor was thus obtained (Figure 1e). The sketch of the sensor was shown in Figure 1f. CuO monolayer colloidal particle film was fabricated by annealing Cu2O on Au film, strengthening the contact of the CuO film with Au electrode to reduce contact resistance. The heater is mounted on the back of the alumina substrate to heat the sensing layer to the desired operating temperature. Figure 2 presents the corresponding typical photographs illustrating the process of transferring monolayer Cu2O colloidal particle film. After this process and annealing, the Cu2O is converted to CuO to form the CuO gas sensor. The phase and crystallinity of the monolayer colloidal particle film were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM) technologies. Figure 3 shows the XRD patterns of monolayer colloidal particle film. The whole well-defined diffraction peaks can match CuO phase with a



monoclinic structure, which are consistent with the standard diffraction data (JCPDS 45-0937, space group: C2/c). Figure 4a shows the particle size of large-scale CuO monolayer colloidal particle film ranges from 300 to 500 nm, in which the colloidal particles of CuO are hollow. Magnified TEM pattern clearly exhibits that the surfaces of the CuO particles are coarser than those of Cu2O particles, as seen in Figure 4b. Figure 4c shows the local magnification of one CuO colloidal particle in Figure 4b. The spacing between the neighboring fringes is about 0.275 nm, belonging to the (110) crystal plane of CuO. TEM image and HRTEM image confirm that CuO colloidal particles have good crystallinity and are polycrystalline. The microstructures of Cu2O and CuO monolayer colloidal particle array films were investigated by the SEM characterization. Figure 5a,b are the SEM images of Cu2O monolayer microsphere array films on the Al2O3 substrate and Si silicon, respectively. It is obvious that the Cu2O is closely packed and has quasi-hexagonal structure. The monolayer structure is demonstrated by the cross section SEM image in Figure 5b. After annealing at 500 oC for 2 h, the Cu2O is converted to CuO. However, the character of monolayer microsphere array still remains in spite of the change in composition. From Figure 5c,d, it is obvious the close packed quasi-hexagonal arrangement and monolayer structure are still retained. CuO sensor was thus obtained. The response of CuO monolayer colloidal particle film sensor to H2S was investigated in detail. Gas response of the sensor is evaluated as Rg/Rair, where Rair is the resistance of the sensor in air and Rg is the resistance of the sensor in H2S. Figure 6a shows the gas response to 10 parts per million (ppm) H2S in air at various


Page 10 of 43

Page 11 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


temperatures for CuO sensor. One can see the gas response of sensor for 10 ppm H2S decreases as the operating temperature increases. The maximum gas response is 7.4 at room temperature. As is known, response time is determined by the time required for 90% of the maximum resistance change when the sensor output is exposed to H2S. Herein, response time of CuO sensor is very short, 4 s, which is very important in applications (Figure 6b). However, it is worth mentioning that when the temperature is below 100 oC, the sensor cannot recover to its initial state after exposure to 10 ppm H2S, but when the temperature exceeds 150 oC, the sensor can recover quickly. The sensor tests were conducted in a specific mode as shown in Figure 7. Simply, it works with gas-sensing response located at room temperature, while with recovery process located at 300 oC. Figure 7a,b are the change in electrical voltage and the corresponding response curve of CuO sensor for 10 ppm H2S as a function of time, respectively. Taking Figure 7b for a detailed illustration, the sensor has a fast response to 10 ppm H2S. However, it cannot recover when exposed to air. After a complex process with the sensor operated at 300 oC and room temperature for 200 s respectively, the sensor recovers its initial state. Figure 8a shows the sensitivity of CuO sensor for sub-ppm H2S. The concentration of H2S was increased from 100 to 500 parts per billion (ppb), and the continuous test without recoveries was carried out at room temperature to observe the sensor response for different concentrations of H2S. The corresponding sensing signal and response time are about 1.7 and 100 s to 100 ppb H2S, respectively. In the detection of trace or ultra-trace target gases, this low limit of gas sensors is of great



signification. In addition, the relationship between the sensing signal and the target gas concentration is got, which is shown in Figure 8b. It is found that there is a linear relationship between the signal and the logarithmic value of gas concentration. Figure 8c presents the CuO sensor’s response to the different concentrations of H2S (1 ~ 100 ppm) under the working mode shown in Figure 7. The signal for 1 ppm H2S and response time is 4.6 and 9 s, respectively. Similarly, the signal is linear with the logarithm values of gas concentration. To order to study the response of CuO sensor to large amount of H2S (400 ppm), another gas sensing test was done seen in Figure 9. One can see that at initial injection stage of H2S, the gas response of CuO sensor begins to increase quickly. With the continuous injection of H2S, the gas response of CuO sensor first increases and then sharply decreases. As H2S gas is pumped out, above similar phenomenon that the resistance of CuO sensor cannot be restored under atmosphere condition again appeares, seen in Figure 9. After the sensor is operated at 300 oC, a sudden jump is observed during the corresponding gas sensitive test, indicating the conversion from CuS to CuO. This will be discussed below. Finally, the sensor recovers its initial state with lowering the temperature to room temperature. Up to now, many researchers have reported the sensitivity of pure CuO to H2S gas. For example, Li’s group35 demonstrated similar monodisperse CuO nanospheres with good H2S sensitivity. However, the CuO colloidal particles are so solid that the sensitive film has small specific surface area, leading to higher operating temperature and the sensitivity of the sensor to other flammable gases, such as alcohol and so on.


Page 12 of 43

Page 13 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


N. S. Ramgir et al.26 synthesized good H2S-sensitive CuO thin film by thermal evaporation technique. However, not only the preparation method is expensive, but also gas response of CuO sensor to H2S is poor, which is caused by the larger film thickness and the larger grain size. F. Zhang et al.40 presented very good sensitivity and fast response time with CuO nanosheets to H2S. However, they only studied the sensitivity of CuO to less than 1.2 ppm H2S gases and the working temperature of the sensor is 240 oC. Z. J. Li et al.28 reported the preparation of porous CuO nanosheets and their outstanding H2S sensing behavior at room-temperature. But CuO nanosheets have longer response time to H2S gas as compared with our samples. This may be due to the longer time required to convert CuO to CuS on exposure to H2S. Therefore, it is reasonably believed room temperature H2S sensing behavior of our sensor is excellent. The stability of the sensors is determined by the sensing responses with the multiple repetitions. Figure 10 and Figure 11 show the H2S sensing behavior of CuO sensor with 5 gas-on/off cycles and over 4 weeks, respectively. One can see CuO sensor shows an excellent reproducibility after multiple cycles and 4 weeks, revealing the CuO sensor has a fine stability. Figure 12 shows the selectivity of the CuO sensor to 10 ppm tested gases. One can see, in addition to H2S, CuO sensor responds very little to other toxic gases for example, methanol, nitrogen dioxide, ammonia, acetone, hydrogen, and ethanol. The super-selectivity for H2S at room temperature is critical in applications. As mentioned, the response of CuO sensor to H2S is highest at room temperature,



while it shows no response for H2S at 300 oC. Then, the sensor arrays uniquely identifying H2S can be fabricated consisting of two CuO monolayer colloidal particle film based sensors, which is shown in Figure 13. The working temperature of the CuO sensors changes alternately between room temperature and 300 oC. The time of duration at 300 oC is much shorter than that at room temperature. Both sensors exhibit the same operating mode but the impulse of 300 oC is mutually staggered. Therefore, the H2S uniquely identified once the response is available at any given time. Why is the CuO sensor reversible when the concentration of H2S is below 500 ppb although it takes a long recovery time, but as the concentration of H2S is higher than 1 ppm, it is not reversible? Two different reaction mechanisms were proposed to explain the above sensing behavior, as schematically shown in Figure 14. As we well know, copper vacancies cause CuO to be p-type semiconductor.41 In air, the O2 molecules are adsorbed to form the negative charge oxygen on the CuO surface, which generates the hole-accumulation layer,27 seen in Figure 14 a. When exposed to low concentrated H2S (1 ppm), it might be attributed to H2S reaction with bulk CuO forming CuS besides the H2S oxidation reaction42: H2S(g)+ CuO (s)→CuS(s) +H2O(g)

(2)

Above reaction is determined by thermodynamic favorable conditions, which are estimated by Gibbs’s free energy. The change of Gibbs’s free energy for reaction (2) is negative, about -28.534 Kcal/mol, indicating reaction (2) is feasible43. In addition, from reaction (2), we can know the high concentration of H2S and the high activity of CuO will promote the reaction, which is also in agreement with our experiments. Therefore, it is considered that the sensitive behavior of CuO to 1 ppm~100 ppm H2S is controlled by reaction (1) and reaction (2), as seen in Figure 14b. In other words, the H2S sensitive properties of CuO are still dominated by H2S oxidation reaction (reaction (1)), bringing to the increased response of CuO to H2S, and the irreversibility of recovery mainly results from the CuS formation (reaction (2)). These are the result of the competition between the two reaction mechanisms. The reaction of CuS layer to CuO in sensor recovery is as follows: CuS+3/2O2→CuO+SO2

(3)



The change of Gibbs’s free energy for reaction (3) is about -89.948 Kcal/mol, suggesting reaction (3) is feasible43. However, in our gas sensing experiment, the sensor cannot recover at room temperature, which is attributed to the third reaction being very slow under this condition. When the sensing film is heated to 300 oC, the reaction (3) takes place and the sensor recovers to the initial state, as the results demonstrated. The sensitive behavior of CuO to higher than 100 ppm H2S is different from the previous two cases. A large amount of H2S was injected in tens of seconds. As can be seen from Figure 9, the response of CuO first increases and then decreases with the injection of H2S. At the beginning of H2S injection, the reaction occurs according to equation (1), and the increased response of CuO to H2S mainly results from the H2S oxidation mechanism. After a while, some H2S begins to react with CuO to form CuS, which makes the gas response lower. But the H2S oxidation mechanism is still dominated, which finally cause the increased response of CuO to H2S. With increasing the time, more CuS formation leads to the decreased response of CuO to H2S. Here, the CuS formation plays decisive role in the sensitive mechanisms of CuO to H2S, as seen in Figure 14c. Above analysis reveals the existence of two reaction mechanisms. To further verify the second reaction mechanism, XPS technique was used to distinguish the difference of the valence states and chemical composition of CuO sample before and after exposure in H2S, seen in Figure 15. XPS characterization should be performed within several minutes after CuO exposed in H2S gas. For pure


Page 16 of 43

Page 17 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


CuO sample, the peak at binding energy 934.3 eV comes from the Cu 2p3/2 state, as seen in Figure 15 (a). For CuO sample exposed in H2S gas, the peaks centered at 933.2 and 931.5 eV separately are related to Cu 2p3/2 spectra of CuO and CuS26, as shown in Figure 15 (a), revealing the presence of CuS. Figure 15 (b) shows high resolution XPS spectra and the corresponding Gaussian fitting curves of S 2p. The binding energy at 162.8 eV comes from S 2p from S2-. This result is in agreement with the binding energy of S 2p in CuS materials reported previously. Above results demonstrate that CuS indeed appears in the CuO sample after exposure to H2S.

3. Conclusion We fabricated CuO monolayer colloidal particle film derived from the synthesis and self-assembly of Cu2O colloidal particles. It was found that large-scale CuO monolayer colloidal particle film is made up of a large quantity of nearly homogeneous spherical particles with the size of 300-500 nm and CuO colloidal particle has hollow structure. CuO sensor has the excellent room temperature H2S sensing properties. Such sensor shows the response time of 4 s and gas response of 7.4 to 10 ppm H2S at room temperature. The sensor can detect sub-ppm H2S as low as 100 ppb at room temperature, indicating the detection limit is low. The excellent room temperature H2S gas sensing properties of CuO sensor also demonstrated which can be used to fabricate sensor arrays uniquely identifying H2S. Furthermore, it was found that at a low concentration H2S (100~500 ppb), the sensor can be recovered with the increase of gas response, although it takes a longer recovery time at room temperature.



In this case, the oxidation of H2S by the negative charge oxygen on the CuO surface is the main reaction mechanism. At medium concentration (1~100 ppm), although the gas response still increases, the sensor is irreversible at room temperature. When the concentration continues to increase (>100 ppm), the sensor is irreversible at room temperature and the gas response first increases and then decreases. It is thought that H2S reacts with bulk CuO to form CuS beside the H2S oxidation mechanism. Two different reaction mechanisms compete with each other to explain the sensing behavior. More importantly, the quasi in-situ XPS spectra confirm the existence of CuS. The as-fabricated CuO sensor with room-temperature response and superselectivity will found potential applications in industry, environment, or intelligent electronics.


Page 18 of 43

Page 19 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ASSOCIATED CONTENT Supporting Information Simple circuit diagram of CuO sensor and the morphology, phase characterization of Cu2O colloidal particles. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Authors *(Y. L.) E-mail: [email protected] *(G. D.) E-mail: [email protected]

Notes The authors declare no competing financial interest.

Acknowledgements The authors acknowledge the financial support from the National Key R&D Program of China (2016YFC0201103), the Natural Science Foundation of China (Grant Nos. 51471161, 11674320 and 51471163), Anhui Provincial Natural Science Foundation for Distinguished Young Scholar (1408085J10), and Youth Innovation Promotion Association CAS and Key Research Projects of the Frontier Science CAS (QYZDB-SSW-JSC017).



Figure captions

Figure 1. The fabrication process of the CuO sensor. (a) Preparation of Cu2O monolayer film (b) Cu2O monolayer colloidal particle array film prepared under the action of different surface tensions of water/air interface. (c) The Cu2O film is separated from glass substrate and appeared on the water surface. (d) Cu2O thin film is transferred into Al2O3 substrate. (e) The CuO film is formed after annealing Cu2O film on Al2O3 substrate at 500 oC. (f) The sketch of CuO sensor.


Page 20 of 43

Page 21 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. The photographs of the self-assembling process of Cu2O monolayer colloidal particle array film. (a) Cu2O film prepared by self-assembly. (b) Cu2O film is separated from glass substrate and (c) appears on the water surface. (d) Cu2O film is picked up by Al2O3 planar electrode.



Figure 3. The XRD spectra of CuO monolayer colloidal particle array film.


Page 22 of 43

Page 23 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. (a, b) The TEM images of CuO colloidal particles. (c) HRTEM image of CuO colloidal particle.



Figure 5. The SEM of (a) Cu2O and (c) CuO monolayer colloidal particle array film on the Al2O3 planar substrate. (b) and (d) is the corresponding cross section SEM images for of Cu2O and CuO monolayer colloidal particle array film, respectively.


Page 24 of 43

Page 25 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. (a) Dependence of CuO sensor’s response on the operating temperature on exposure of 10 ppm H2S. (b) The magnification of (a) to show room temperature H2S gas sensitive properties of CuO sensor.



Figure 7. Dependence of CuO sensor’s key parameters on time in the present of 10 ppm H2S: (a) output voltage, (b) gas response.


Page 26 of 43

Page 27 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8. H2S sensing behavior of CuO sensor: (a) Dynamic response to H2S with increasing the gas concentration from 100 ppb to 500 ppb. (b) The sensing response vs. H2S concentration increasing from 100 ppb to 500 ppb. (c) Dynamic response to H2S with increasing the gas concentration from 1 ppm to 100 ppm. (d) The sensing response vs. H2S concentration ranging from 1 ppm to 100 ppm.



Figure 9. Gas response of CuO sensor for 400 ppm H2S.


Page 28 of 43

Page 29 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 10. Gas responses of CuO sensor to periodic variation of gas composition.



Figure 11. The sensing response of CuO sensor for 10 ppm H2S over 4 weeks.


Page 30 of 43

Page 31 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 12. The room temperature selectivity of CuO sensor.



Figure 13. Measuring mode of CuO sensor.


Page 32 of 43

Page 33 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 14. Different sensing mechanism of CuO film exposed to different concentrations of H2S. (a) In the air, the O2 molecules are adsorbed to form the negative charge oxygen on the CuO surface, which generates the hole-accumulation layer. (b) When low concentration hydrogen sulfide is injected, the electrons released from the reaction of H2S with O2− adsorbed on the CuO surface decrease the accumulation of holes, thus improving the gas response of CuO film to H2S. (c) When high concentration H2S is injected, besides the H2S oxidation reaction, a CuS layer appears on the CuO surface due to the reaction of H2S with CuO, which decreases the gas response of the CuO film to H2S.



Figure 15. (a) Cu 2p3/2 and (b) S 2p XPS patterns of (1) pure CuO and (2) 400 ppm H2S exposed CuO.


Page 34 of 43

Page 35 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1 CuO gas sensors to detect H2S Structures

Nanowire Pore Nanosheets

Gas concentratio n (ppm)

Respons e time (s)

Recovery time (s)

Respons e

Ref

1-100

Operatin g temp.(oC ) 160

-

-

27

60-0.01

RT

234 (10ppb)

unrecoverabl e 76 (10ppb)

28

336 (200ppb)

543 (200ppb)

1.25 (10ppb) Ra/Rg 5 (200ppb) Ra/Rg 31243 (100 ppm) ΔR/Ra 500 at 170 oC ΔR/Ra -

Pd doped nanorod

20-100

300

670 (100 ppm)

80 (100 ppm)

CuO/SnO2

25-300

100-250

-

CuO/SWCN T CuO/CuFeO2

50 -0.1

130-150

1-75

120, 240

60 (100 ppm) 7 (1 ppm) 31 (10 ppm, 240 oC)

CuO/NiO

10-100

220, 260, 300

18 (100 ppm, 260 oC)

Nanobelt

0.1-10

135

Nanosheet

0.03-1.2

240

0.1-50

RT

> 0.01

325

12 (0.1 ppm) 4 (1 ppm) 60 (0.1 ppm) -

CuO films

thin

Nanowire

28 (1 ppm) 40 44.8 at (10 ppm, 240 120 oC oC) (10 ppm) Rg/Ra 29 47.6 at 260 oC (100 ppm, 260 oC) (100 ppm) Rg/Ra 17 1.2 (0.1 ppm) (0.1 ppm) Rg/Ra 9 320 (1 ppm) ΔR/Ra 90 2.1 (0.1 ppm) (0.1 ppm) ΔR/Ra 1.2 (0.01 ppm) Rg/Ra


.

29

30

31

32

33

44

40

26

45


References (1) Kim, J.; Yong, K., Mechanism Study of ZnO Nanorod-Bundle Sensors for H2S Gas Sensing, J. Phys. Chem. C 2011, 115, 7218-7224. (2) Mirzaei, A.; Kim, S. S.; Kim, H. W., Resistance-based H2S Gas Sensors Using Metal Oxide Nanostructures: A Review of Recent Advances, J. Hazard. Mater. 2018, 357, 314-331. (3) Kumar, A.; Samanta, S.; Singh, A.; Roy, M.; Singh, S.; Basu, S.; Chehimi, M. M.; Roy, K.; Ramgir, N.; Navaneethan, M.; Hayakawa, Y.; Debnath, A. K.; Aswal, D. K.; Gupta, S. K., Fast Response and High Sensitivity of ZnO Nanowires-Cobalt Phthalocyanine Heterojunction Based H2S Sensor, ACS Appl. Mater. Interfaces 2015, 7, 17713-17724. (4) Shao, F.; Hoffmann, M. W. G.; Prades, J. D.; Zamani, R.; Arbiol, J.; Morante, J. R.; Varechkina, E.; Rumyantseva, M.; Gaskov, A.; Giebelhaus, I.; Fischer, T.; Mathur, S.; Hernández-Ramírez, F., Heterostructured p-CuO (Nanoparticle)/n-SnO2 (Nanowire) Devices for Selective H2S Detection, Sensors and Actuators B: Chemical 2013, 181, 130-135. (5) Pandey, S. K.; Kim, K.-H.; Tang, K.-T., A Review of Sensor-based Methods for Monitoring Hydrogen Sulfide, TrAC, Trends Anal. Chem. 2012, 32, 87-99. (6) Zhou, X.; Lee, S.; Xu, Z.; Yoon, J., Recent Progress on the Development of Chemosensors for Gases, Chem. Rev. 2015, 115, 7944-8000. (7) Yamazoe, N.; Sakai, G.; Shimanoe, K., Oxide Semiconductor Gas Sensor, Catalysis Surveys from Asia 2003, 7(1), 63-75.


Page 36 of 43

Page 37 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(8) Korotcenkov, G.; Cho, B. K., Porous Semiconductors: Advanced Material for Gas Sensor Applications, Crit. Rev. Solid State Mater. Sci. 2010, 35, 1-37. (9) Verma, M. K.; Gupta, V., A Highly Sensitive SnO2-CuO Multilayered Sensor Structure for Detection of H2S Gas, Sensors and Actuators B: Chemical 2012, 166-167, 378-385. (10) Zhao, Y.; He, X.; Li, J.; Gao, X.; Jia, J., Porous CuO/SnO2 Composite Nanofibers Fabricated by Electrospinning and Their H2S Sensing Properties, Sensors and Actuators B-Chemical 2012, 165, 82-87. (11) Verma, M.; Chowdhuri, A.; Sreenivas, K.; Gupta, V., Comparison of H2S Sensing Response of Hetero-Structure Sensor (CuO-SnO2) Prepared by rf Sputtering and Pulsed Laser Deposition, Thin Solid Films 2010, 518, E181-E182. (12)Wagh, M. S.; Patil, L. A.; Seth, T.; Amalnerkar, D. P., Surface Cupricated SnO2-ZnO Thick Films as a H2S Gas Sensor, Mater. Chem. Phys. 2004, 84, 228-233. (13) Yu, H.-L.; Li, L.; Gao, X.-M.; Zhang, Y.; Meng, F.; Wang, T.-S.; Xiao, G.; Chen, Y.-J.; Zhu, C.-L., Synthesis and H2S Gas Sensing Properties of Cage-like α-MoO3/ZnO Composite, Sensors and Actuators B: Chemical 2012, 171-172, 679-685. (14) Wang, L.; Kang, Y.; Wang, Y.; Zhu, B.; Zhang, S.; Huang, W.; Wang, S., CuO Nanoparticle Decorated ZnO Nanorod Sensor for Low-Temperature H2S Detection, Materials Science and Engineering: C 2012, 32, 2079-2085. (15)Bodade, A. B.; Bende, A. M.; Chaudhari, G. N., Synthesis and Characterization of CdO-doped Nanocrystalline ZnO:TiO2-based H2S Gas Sensor, Vacuum 2008, 82,



588-593. (16)Badadhe, S. S.; Mulla, I. S., H2S Gas Sensitive Indium-doped ZnO Thin Films: Preparation and Characterization, Sensors and Actuators B: Chemical 2009, 143, 164-170. (17) Chen, D.; Caruso, R. A., Recent Progress in the Synthesis of Spherical Titania Nanostructures and Their Applications, Adv. Funct. Mater. 2013, 23, 1356-1374. (18) Tao, W. H.; Tsai, C. H., H2S Sensing Properties of Noble Metal doped WO3 Thin Film Sensor Fabricated by Micromachining, Sensors and Actuators B-chemical 2002, 81, 237-247. (19) Wang, Y.; Duan, G.; Zhu, Y.; Zhang, H.; Xu, Z.; Dai, Z.; Cai, W., Room Temperature H2S Gas Sensing Properties of In2O3 Micro/Nanostructured Porous Thin Film and Hydrolyzation-induced Enhanced Sensing Mechanism, Sensors and Actuators B: Chemical 2016, 228, 74-84. (20)Jiang, Z. X.; Li, J.; Aslan, H.; Li, Q.; Li, Y.; Chen, M. L.; Huang, Y. D.; Froning, J. P.; Otyepka, M.; Zboril, R.; Besenbacher, F.; Dong, M. D., A High Efficiency H2S Gas Sensor Material: Paper like Fe2O3/graphene Nanosheets and Structural Alignment Dependency of Device Efficiency, Journal of Materials Chemistry A 2014, 2, 6714-6717. (21) Balouria, V.; Kumar, A.; Samanta, S.; Singh, A.; Debnath, A. K.; Mahajan, A.; Bedi, R. K.; Aswal, D. K.; Gupta, S. K., Nano-crystalline Fe2O3 Thin Films for ppm Level Detection of H2S, Sensors and Actuators B: Chemical 2013, 181, 471-478. (22) Deng, J.; Ma, J.; Mei, L.; Tang, Y.; Chen, Y.; Lv, T.; Xu, Z.; Wang, T., Porous


Page 38 of 43

Page 39 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


α-Fe2O3 Nanosphere-based H2S Sensor with Fast Response, High Selectivity and Enhanced Sensitivity, Journal of Materials Chemistry A 2013, 1, 12400. (23) Wang, S.; Xiao, Y.; Shi, D.; Liu, H. K.; Dou, S. X., Fast Response Detection of H2S by CuO-doped SnO2 Films Prepared by Electrodeposition and Oxidization at Low Temperature, Mater. Chem. Phys. 2011, 130, 1325-1328. (24) Chowdhuri, A.; Gupta, V.; Sreenivas, K.; Kumar, R.; Mozumdar, S.; Patanjali, P. K., Response Speed of SnO2-based H2S Gas Sensors with CuO Nanoparticles, Appl. Phys. Lett. 2004, 84, 1180. (25)Toda, K.; Ohira, S.; Tanaka, T.; Nishimura, T.; Dasgupta, P. K., Field Instrument for Simultaneous Large Dynamic Range Measurement of Atmospheric Hydrogen Sulfide, Methanethiol, and Sulfur Dioxide, Environ. Sci. Technol. 2004, 38, 1529-1536. (26)Ramgir, N. S. G., S. K.; Kaur, M.; Datta, N.; Muthe, K. P.; Aswal, D. K.; Gupta, S. K.; Yakhmi, J. V., Sub-ppm H2S Sensing at Room Temperature Using CuO Thin Films. Sensors and Actuators B 2010, 151 (1), 90-96. (27) Chen, J. J.; Wang, K.; Hartman, L.; Zhou, W. L., H2S Detection by Vertically Aligned CuO Nanowire Array Sensors, Journal of Physical Chemistry C 2008, 112, 16017-16021. (28) Li, Z.; Wang, N.; Lin, Z.; Wang, J.; Liu, W.; Sun, K.; Fu, Y. Q.; Wang, Z., Room-Temperature High-Performance H2S Sensor Based on Porous CuO Nanosheets Prepared by Hydrothermal Method, ACS Appl. Mater. Interfaces 2016, 8, 20962-20968.



(29)Kim, H.; Jin, C.; Park, S.; Kim, S.; Lee, C., H2S Gas Sensing Properties of Bare and Pd-functionalized CuO Nanorods, Sensors and Actuators B: Chemical 2012, 161, 594-599. (30)Vasiliev, R. B.; Rumyantseva, M. N.; Yakovlev, N. V.; Gaskov, A. M., CuO/SnO2 Thin Film Heterostructures as Chemical Sensors to H2S, Sensors and Actuators B-Chemical 1998, 50, 186-193. (31) Asad, M.; Sheikhi, M. H., Highly Sensitive Wireless H2S Gas Sensors at Room Temperature based on CuO-SWCNT Hybrid Nanomaterials, Sensors Actuators B: Chem. 2016, 231, 474-483. (32)Hu, X. B.; Zhu, Z. G.; Li, Z. H.; Xie, L. L.; Wu, Y. H.; Zheng, L. Y., Heterostructure of CuO Microspheres Modified with CuFe2O4 Nanoparticles for Highly Sensitive H2S Gas Sensor, Sensors and Actuators B 2018, 264, 139-149. (33)Wang, Y. F.; Qu, F. D.; Liu, J.; Wang, Y.; Zhou, J. R.; Ruan, S. P., Enhanced H2S Sensing Characteristics of CuO-NiO Core-shell Microspheres Sensors, Sensors and Actuators B 2015, 209, 515-523. (34)Dai, Z.; Dai, H.; Zhou, Y.; Liu, D.; Duan, G.; Cai, W.; Li, Y., Monodispersed Nb2O5 Microspheres: Facile Synthesis, Air/Water Interfacial Self-Assembly, Nb2O5-Based Composite Films, and Their Selective NO2 Sensing, Advanced Materials Interfaces 2015, 2, 1500167. (35)Zhang, J. T.; Liu, J. F.; Peng, Q.; Wang, X.; Li, Y. D., Nearly Monodisperse Cu2O and CuO Nanospheres: Preparation and Applications for Sensitive Gas Sensors, Chem. Mater. 2006, 18, 867-871.


Page 40 of 43

Page 41 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(36)Xu, Z.; Duan, G.; Zhang, H.; Wang, Y.; Xu, L.; Cai, W., In situ Synthesis of Porous Array Films on a Filament Induced Micro-gap Electrode Pair and Their Use as Resistance-type Gas Sensors with Enhanced Performances, Nanoscale 2015, 7, 14264-14271. (37)Dai, Z.; Jia, L.; Duan, G.; Li, Y.; Zhang, H.; Wang, J.; Hu, J.; Cai, W., Crack-Free Periodic Porous Thin Films Assisted by Plasma Irradiation at Low Temperature and Their Enhanced Gas-Sensing Performance, Chemistry-a European Journal 2013, 19, 13387-13395. (38)Luo, Y. Y.; Pan, S. S.; Xu, S. C.; Zhong, L.; Wang, H.; Li, G. H., Influence of Sputtering Power on the Phase Transition Performance of VO2 Thin Films Grown by Magnetron Sputtering. J. Alloys Compd. 2016, 664, 626-631. (39)Xu, Z. W. W., L. Y.;

Fang, F. Z.;

Fu, Y. Q.;

Yin, Z.;, A Review on

Colloidal Self-Assembly and their Applications. Current Nanoscience 2016, 12, 725-746. (40)Zhang, F. Z., A. W.;

Luo, Y. P.;

Tian, Y.; Yang, J. H.;

Qin, Y.;, CuO

Nanosheets for Sensitive and Selective Determination of H2S with High Recovery Ability. J. Phys. Chem. C 2010, 114, 19214-19219. (41)Barsan, N.; Weimar, U., Conduction Model of Metal Oxide Gas Sensors, J. Electroceram. 2001, 7, 143-167. (42)Hennemann, J.; Kohl, C.-D.; Smarsly, B. M.; Sauerwald, T.; Teissier, J.-M.; Russ, S.; Wagner, T., CuO Thin Films for the Detection of H2S Doses: Investigation and Application, physica status solidi (a) 2015, 212, 1281-1288.



(43)Dean, J. A., Handbook of Lanshi Chemistry. Science Press 1991, 9-1~9-66. (44)Chen, Y.-J.; Meng, F.-n.; Yu, H.-l.; Zhu, C.-l.; Wang, T.-s.; Gao, P.; Ouyang, Q.-y., Sonochemical Synthesis and ppb H2S Sensing Performances of CuO Nanobelts, Sensors and Actuators B: Chemical 2013, 176, 15-21. (45)Steinhauer, S.; Brunet, E.; Maier, T.; Mutinati, G. C.; Köck, A., Suspended CuO Nanowires for ppb Level H2S Sensing in Dry and Humid Atmosphere, Sensors and Actuators B: Chemical 2013, 186, 550-556.


Page 42 of 43

Page 43 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC graphic CuO monolayer colloidal particle film was synthesized and such structure has the excellent room temperature H2S sensing properties. The sensor exhibits different sensitive characteristics at low and high concentrations H2S. Two reaction mechanisms are proposed to explain the above-mentioned sensing behavior.


Self-Assembly of Cu2O Monolayer Colloidal Particle Film Allows the

Recommend Documents