A Novel Highly Sensitive Humidity Sensor ... - Wiley Online Library

J. Am. Ceram. Soc., 98 [12] 3719–3725 (2015) DOI: 10.1111/jace.13836 © 2015 The American Ceramic Society

Journal

A Novel Highly Sensitive Humidity Sensor Based on ZnO/SBA-15 Hybrid Nanocomposite Vijay K. Tomer,‡ Surender Duhan,‡,† Ritu Malik,§ Satya P. Nehra,¶ and Sunita Devik

‡

Nanomaterials Research Laboratory, Department of Materials Science & Nanotechnology, D.C.R. University of Science & Technology, Murthal (Sonepat), Haryana 131039, India §

Department of Physics, D.C.R. University of Science & Technology, Murthal (Sonepat), Haryana 131039, India ¶

Center of Excellence for Energy and Environmental Studies, D.C.R. University of Science & Technology, Murthal (Sonepat), Haryana 131039, India k

Department of Chemistry, M.K.J.K.M, Rohtak, Haryana 124001, India gap and large exciton binding energy induces exceptional electrical/optoelectronic properties and hence adsorption of water molecules in molecular and hydroxyl form on surface causes it to conduct electrically at room temperature. It has been observed that ZnO nanostructures with high surface/ volume ratio possess more chemically active sites and shows improved performance towards sensing and catalysis applications.8,24–26 Considering the dependability of RH sensing attributes on the surface area of ZnO, novel synthesis procedures were followed to enhance its specific surface area resulting in the presence of more active sites for rapid adsorption/desorption of water molecules which directly contributes in improving its RH sensing properties.24,25 With the mesoporous nanocomposite in view of ZnO/SBA-15, we look for better sensitivity, rapid response/recovery times, wide working %RH range, low operating temperature, and enhanced stability. In this work, we report on synthesis of ZnO loaded SBA15 mesoporous nanocomposite using hydrothermal method and its response towards change in humidity in 11%–98% RH range at room temperature was studied. The ZnO loading in SBA-15 does not destroy the mesoporous structure, however, the hybrid nanocomposite displays enhanced humidity sensitivity and a change of ~5 orders in magnitude was recorded in complete %RH range at 25°C. Moreover, the sensor shows impressive linearity, negligible hysteresis (~1.2%), quick response time (17 s), rapid recovery time (18 s), and outstanding stability (1.8%). These excellent sensing characteristics make the ZnO/SBA-15 nanocomposite a good candidate for the fabrication of high-performance humidity sensors.

This work deals with the study of hydrothermally synthesized zinc oxide (ZnO) loaded mesoporous SBA-15 hybrid nanocomposite for relative humidity sensing (RH) at room temperature. The sensor exhibits an excellent ~5 orders impedance change along with excellent linearity, quick response time (17 s), rapid recovery time (18 s), negligible hysteresis (1.2%), good repeatability, and stability (1.8%) in 11%–98% RH range. In addition, complex impedance spectra of the sensor at different RHs were analyzed to understand the humidity sensing mechanism. Our study can open a new way for realizing ZnO/SBA15 hybrid nanocomposite for fabrication of high-performance RH sensors.

I.

Introduction

R

ELIABLE, versatile, and low-cost relative humidity (RH) sensors play a vital part in numerous detection and control applications, including industry, agribusiness, and ecological fields.1–4 A variety of materials including mesoporous oxides, semiconductor, and polymers has been explored worldwide as a probe for measuring RH.5–9 Mesoporous siliceous oxide materials (SBA-15, acronym for Santa Barbara Amorphous) are specifically gaining worldwide attention as support for sensing materials for their novel physicochemical properties such as large mesoporous surface area, high porosity, tunable and interconnected long pore channels, and well-organized hexagonal pore arrangement.10–12 As an RH sensing material, the high surface area and interconnected pore channels of SBA-15 provide easier adsorption and facile transportation of water molecules across their surfaces.13–15 However, high intrinsic impedance observed in SBA-15 limited its wide practical applications and need for chemical/surface modification by introduction of guest molecules through coating or incorporations and surface or mesopore grafting of metal atoms became necessary to harness full potential of SBA-15. The obtained hybrid nanocomposites based on SBA-15 are suitable for many new applications, such as catalysis, sensors, hydrogen storage, and drug delivery.16–20 Zinc oxide (ZnO) is one of the most promising metal oxide semiconductors for sensing applications.21–23 Its wide band

II.

Experimental Procedure

(1) Materials Pluronic P123 [Ethylene Oxide-Propylene Oxide-Ethylene Oxide, (EO20PO70EO20), Mw = 5800; Sigma Aldrich, Bengaluru, India], Tetraethoxy orthosilicate [(C2H5O)4Si, TEOS, Sigma Aldrich] Zinc acetate [Zn(CH3COO)2; Merck, Mumbai, India], and HCl (35%; Fisher Scientific, Mumbai, India) were of analytical grade and used as received. Double-distilled water was used throughout the experiments. (2) Sample Preparation In a typical recipe, 2.5 g P123 was dissolved in 100 mL distilled water at 45°C under vigorous stirring (1000 rpm) followed by addition of 12.5 mL HCl (2M). After 3 h of continuous stirring, a clear transparent solution was obtained. Thereafter, 6 mL of TEOS was added to the above

P. Gouma—contributing editor

Manuscript No. 36795. Received April 27, 2015; approved July 15, 2015. † Author to whom correspondence should be addressed. e-mail: surender6561@ yahoo.co.in

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solution and kept under stirring for 24 h at 45°C. The gel product thus obtained was put for hydrothermal treatment in a 250 mL capacity Teflon-lined stainless steel autoclave and treated at 100°C for 24 h. After cooling down to room temperature, the solid products were filtered, washed, and dried at 70°C and were calcined at 550°C (heating rate of 2°C/min) for 6 h in air to remove organic templates and thus mesoporous white powder of mesoporous silica was obtained. For the synthesis of ZnO/SBA-15 nanocomposite, required amount of zinc acetate aqueous salt solution was added in miceller solution of P123 under stirring before the addition of TEOS. The mixture was vigorously stirred and allowed for homogeneous collation of zinc species with polymeric micelles through stirring for 3 h. TEOS was then added to the solution and the reaction mixture was kept under stirring for 24 h and further following the same route as used for pure SBA-15. Effect of systematic loading of zinc oxide nanoparticles in SBA-15 mesoporous framework on humidity sensing response was determined by varying the concentrations of ZnO in SBA-15. The nanocomposite products were designated as ZnO/SBA-15(Z), where Z was the content of zinc oxide in wt%. The values of Z in our experiments were 1, 5, 10, and 15 for four different ZnO/SBA-15 samples.

(3) Fabrication of Humidity Sensors For the fabrication, the as-synthesized samples were coated on the top of a ceramic substrate (13.4 mm 9 7 mm 9 0.5 mm) with two Ag-Pd interdigital electrodes (IDE). The IDE consists of five pairs of Ag-Pd tracks having thickness and separation distance of 0.2 mm. Prior to use, the IDE substrates were cleaned by an ultrasonic treatment in acetone, then rinsed thoroughly with double-distilled water and dried under vacuum. The as-synthesized samples were ground and mixed with ethanol in a weight ratio of 5:100 to form a dilute paste and coated on IDE using a 100 lL pipette to deposit a film of thickness ~50 lm. The coated substrates were dried at 80°C for 12 h and used as sensing elements to evaluate the humidity sensing characteristics. The schematic diagram of fabricated sensor is shown in Fig. 1.

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bands were acquired by exposing the sensor in the closed chambers with distinctive %RH environment for the uptake of water molecules until the impedance of the sensing material arrived at a stable value. The introduction of sensing substrate to laboratory climate amid exchanging of sensor material between diverse chambers makes it practically difficult to quantify the response transients precisely. However, amid the tests, we have attempted to finish the chamber change process as speedy as could reasonably be expected, which might be possible short of what 1 s.

(5) Characterization The crystal structure of pure SBA-15 and ZnO/SBA-15(Z) nanocomposites were determined by both small angle (2h = 0.5°–4°) and wide-angle (2h = 15°–70°) XRD. The diffraction patterns were obtained on a Bruker D8 advance diffractometer (Karlsruhe, Germany) using CuKa monochro as X-ray source. The mormatic radiation (k = 1.5418 A) phology of the samples was characterized by scanning electron microscope equipped with an energy-dispersive X-ray spectroscope (SEM-EDX; FEI QUANTA 200F, Hillsboro, OR). The samples for SEM analysis were prepared by spreading the powder samples on a double-sided conducting adhesive tape. Information concerning nanosized ZnO particles dispersion inside SBA-15 was obtained by EDX spectroscopy on the same instrument. N2 adsorption–desorption measurements were conducted to calculate specific surface area, pore size distribution, and pore volume by N2 physiosorption (Micrometrics Tristar 3000, Norcross, GA) at 196°C. A known mass of sample (~120 mg) was first degassed overnight at

(4) Humidity Sensor Measurement The different RH levels were generated by using standard saturated salt solutions in airtight closed glass chambers at room temperature (25°C). Self made six different standard saturated aqueous salt solutions of LiCl, MgCl2 6H2O, MgNO3 4H2O, NaCl, KCl, and K2SO4 which yielded 11%, 33%, 54%, 75%, 84%, and 98% relative humidity, respectively, were used to act as humidity source.27 The soaked saturated salt arrangements were put overnight in the chambers at room temperature to ensure that the air in the chamber arrived at balance states. These RH levels were observed by a standard hygrometer. The nanocomposite coated substrate was put progressively into the chambers with distinctive RH levels at room temperature and the impedance of the sensor was measured as a function of RH at 25°C (1°C) utilizing a basic two-probe arrangement with a LCR Meter. The voltage connected was AC 1 V and the frequency was varied from 50 Hz to 10 kHz. The characteristics RH response

Fig. 1.

Schematic drawing of humidity sensor.

Fig. 2. Low-angle XRD patterns (a), and Wide-angle XRD patterns (b), of SBA-15 and ZnO/SBA-15(Z) nanocomposites.

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Table I. Structural and Textural properties of Mesoporous SBA-15 and ZnO/SBA-15(Z) Nanocomposites Determined from XRD, N2 Adsorption–Desorption, and EDX Analysis

Sample

SBA15 Z=1 Z=5 Z = 10 Z = 15

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ZnO/SBA-15 Based Humidity Sensor

d100spacing (nm)†

ao (nm)‡

DP (nm)§

VP (cm3/ g)¶

DW (nm)k

SBET (m2/ g)††

10.27

11.86 8.98

1.23

2.88

881

10.16 9.91 9.41 8.83

11.73 11.44 10.86 10.19

1.14 1.06 0.94 0.89

3.44 3.73 3.95 4.02

799 727 688 609

8.29 7.71 6.91 6.17

Effective ZnO wt %‡‡

— 0.79 3.7 6.81 9.76

†

d100: d-spacing. a0: Unit cell parameter [a0 = 2 9 d100/√3]. § DP: Pore size. – VP: Pore volume. k DW: Pore wall thickness [DW = a0DP]. †† SBET: Total surface area. ‡‡ Calculated from EDX studies. ‡

400°C under vacuum. The specific surface area, SBET, was calculated from the linear part of the BET plot.28 The mesopore size distribution was determined from the desorption branch of the isotherms using the Barrett–Joyner–Halenda (BJH) model.29 The total pore volume was calculated as the amount of nitrogen adsorbed at the relative pressure until 0.99. The HRTEM of the samples (dispersed in acetone, deposited on 300 mesh Cu grid with holey carbon film and dried) were recorded on a TECNAI G20 (FEI) electron microscope at an accelerating voltage of 220 kV.

III.

Results and Discussion

(1) Characterization Figure 2(a) shows the small angle XRD patterns for pure mesoporous silica and zinc oxide loaded mesoporous silica

nanocomposites in the 2h (0.5°–4°) range. For pure SBA-15, three well resolved peaks appear at 2h = 0.86°, 1.53°, and 1.61° which could, respectively, be indexed to (100), (110), (200) and the corresponding d-spacing for these planes are respectively. These reflections 102.72, 57.74, and 54.87 A, belong to highly ordered, hexagonal p6mm space group for mesoporous silica material.30 A lowering of peak intensities of ZnO/SBA-15(Z) was observed with increasing in the concentration of zinc species in the mesoporous framework. This could be possibly due to weakening in the scattering contrast caused by pore filling effect. A decrease in d-spacing along (100) direction was also observed with the gradual increasing concentration of zinc oxide nanoparticles in SBA-15, thus causing framework shrinkage and the peaks gets shifted toward higher angles. The physicochemical data as obtained from LAXRD results for SBA-15 and ZnO/SBA-15(Z) nanocomposites is given in Table I. Figure 2(b) shows wide-angle XRD patterns (2h = 15°– 70°) of SBA-15 and ZnO/SBA-15(Z) nanocomposites. As can be seen, all sample shows a broad peak centered at 2h = 22° corresponding to amorphous silica walls of the pristine material.31 In the lower concentration region (1–5 wt%) of ZnO, the corresponding peaks of zinc species were almost invisible. This depicts the amorphous nature of the nanocomposite at low loadings. However, when the content of ZnO in SBA-15 raises to 10 wt%, small diffraction peaks were observed at 2h = 31.6°, 34.2°, 36.5°, 47.4°, 56.2°, and 62.0° corresponding to (100), (002), (101), (102), (110), and (103) planes of zinc oxide (JCPDS card no. 36-1451). This strengthening of zinc oxide crystalline peaks from lowest (1 wt%) to highest concentration (15 wt%) results from the increase in loading of zinc oxide nanoparticles in mesoporous silica framework. The SEM images of SBA-15 and ZnO/SBA-15(10) are shown in Figs. 3(a) and (c). Both samples exhibit almost similar morphologies consisting of twisted clusters of short-sized rods with relatively uniform size of ~0.5 lm. This type of morphology is generally exhibited by materials having longrange parallel channels with the 2-D hexagonal mesostruc-

(a)

(b)

(c)

(d)

Fig. 3. (a and c) SEM image of SBA-15 and ZnO/SBA-15(10) nanocomposite; and Fig 3(b and d) Corresponding EDX spectra of SBA-15 and ZnO/SBA-15(10) nanocomposite.

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Fig. 4.

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(a) N2 adsorption–desorption isotherms curves and (b) pore size distributions curves for SBA-15 and ZnO/SBA-15(Z) nanocomposites.

(a)

(b)

Fig. 5. HRTEM image (a) showing uniform channels with long-range order of SBA-15 and (b) image showing the hexagonal pore arrangement ZnO/SBA-15(10) nanocomposite.

ture.32 The EDX spectra of SBA-15 and ZnO/SBA-15(10) are shown in Figs. 3(b) and (d), respectively. As observed, the samples are free from any impurities and no other elements were detected except Si and O, which confirms the purity of the obtained sample. Figure 3(d) shows spectrum for ZnO/SBA-15(10) nanocomposite. For 10 wt% ZnO loaded in SBA-15, approximately 6.8% of ZnO gets loaded in the channels of SBA-15. The summarized result in Table I reveals that the efficiency of ZnO loading in SBA-15 decreases continuously with successive loading of ZnO nanoparticles in the SBA-15 matrix. This inversely proportional relation between experimental and theoretical loading concentration of ZnO nanoparticles could be due to constant pore blockage of SBA-15 leading to the depreciation of effective Si–OH bonding sites for ZnO nanoparticles. The N2 adsorption/desorption curves of pure mesoporous silica and ZnO/SBA-15(Z) are shown in Fig. 4(a). As can be seen, all the samples exhibit type IV characteristics curves which firmly matches with the IUPAC classification of mesoporous materials and H1 type broad hysteresis loop, implying a uniform cylindrical geometry.31 In addition, the shape of type IV curves was retained with loading of ZnO nanoparticles, confirming the mesoporous structure of ZnO/SBA-15 (Z) nanocomposites. The other physicochemical parameters obtained from surface area analysis are listed in Table I. A decrease in specific surface area was observed with loading of ZnO nanoparticles in SBA-15 without affecting the mesoporous structural integrity of the nanocomposites. These results were quite consistent with the results of low-angle XRD. The information related to pore diameter, pore volume, and wall thickness was determined from pore size distribution curves [Fig. 4(b)]. A systematic decrease in pore diameter and pore volume of nanocomposite was observed with increasing ZnO wt% in SBA-15 because of the hinder-

Fig. 6. Humidity sensing curves showing decrease in impedance with increase in %RH for ZnO/SBA-15(Z) nanocomposites.

ing caused by partially filled pores in the path of forthcoming ZnO nanoparticles. This continuous blockage of pores causes the broadening of the walls of nanocomposite suggesting that zinc oxide has been confined inside the pore channels of mesoporous silica. The HRTEM images for pure SBA-15 and ZnO/SBA-15 (10) are shown in Fig. 5. As can be seen, long-range order of uniform channels can be located which confirms the 2D p6mm regular hexagonal mesostructure of samples.31 The zinc oxide nanoparticles were found to be homogeneously dispersed in the mesoporous framework due to the fact that zinc and silica were simultaneously introduced into the reaction system during the initial phase of prolonged stirring. The average distance between the adjacent centers of hexago-

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Fig. 7. Relationship of impedance and relative humidity based on nanocomposite ZnO/SBA-15(10) at various frequencies.

Fig. 8. Humidity response (humidification from 11%–98%RH) and recovery (desiccation from 98%–11%RH) curves.

nal pores for pure mesoporous silica as estimated from The average thickness of the wall HRTEM image is 123 A. and the pore diameter acquired from the images are around respectively, which is quite consistent with the 35 and 89 A, results obtained from N2 adsorption/desorption analysis and XRD results.

Table II. S. No.

1 2 3 4 5 6 7 8 9 10 11 12 [13 14 15 16 17

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(2) Humidity Sensing Properties Figure 6 shows RH-dependent impedance response of the samples measured at 1 V and 100 Hz at room temperature in 11%–98% RH range. As can be seen, at low %RH, all samples exhibit very high impedance, but a dramatic decrease in impedance was observed with increasing %RH. Pure SBA-15 shows poor response in the 11%–55% RH range with a change in only 2.5 orders of impedance in complete %RH range, however, ZnO/SBA-15(Z) nanocomposites shows much larger measurement range (11%–98%RH) and a 5 orders change in impedance was achieved. As observed, the presence of ZnO nanoparticles directly contributes to the increase in conductivity and improving the linearity in response for hybrid nanocomposites. As can be seen, when the ZnO content was 1–10 wt%, the curves shows a ~5 order of magnitude change toward change in %RH but as soon as the ZnO content increases to 15 wt%, the response decreases and only 3 orders change was observed. Possibly, the blockage of SBA-15 channels with ZnO nanoparticles could be the reason for this response behavior. The pore blockage leaves little possibility for the flow of charge carriers across the mesoporous channels of SBA-15. Overall, the nanocomposite having 10 wt% of ZnO loaded in SBA-15 shows highest change in impedance and also exhibits best linearity, therefore this nanocomposite was selected for evaluation of further RH sensing characteristics. To determine the effect of frequency variation on change in response of ZnO/SBA-15(10) nanocomposite, tests were conducted at 0.5 V by varying the frequency from 50 Hz to 10 kHz and impedance was measured in 11%–98% RH range. As observed in Fig. 7, the impedance decreases with increase in RH and almost flat impedance response was observed at higher frequencies due to the fact that water cannot be polarized at higher frequencies. Considering the high response with good linearity, a lower frequency was preferred. Hence, we choose to perform experiments at 100 Hz in the following experiments. The response and recovery time are necessary variables to judge the actual performance of humidity sensing materials. The time taken by a sensor to obtain ~90% of overall impedance change is defined as the response time and recovery time in case of adsorption and desorption, respectively.9 Figure 8 demonstrates that ZnO/SBA-15(10) nanocomposite possesses quick response time (17 s) for humidification from 11% to 98%RH and rapid recovery time (18 s) for dehumidification from 98% to 11%RH. In contrast to the results

A Comparison of Humidity Sensing Performance of Hybrid SBA-15 and ZnO-Based Materials

Material

Order of impedance change in complete %RH range

Response time (s)

Recovery time (s)

SnO2/SBA-15 ZnO nanosheets Feather like ZnO TiO2/SBA-15 Fe2O3/SBA-15 Mn/SBA-15 ZnO-SiO2 WO3/SBA-15 Ag/SBA-15 ZnO cauliflowers ZnO nanotetrapods NiO-PPY/SBA-15 Fe/SBA-15 Li/A-SBA-15 MgO-KCl/SBA-15 Li/SBA-15 ZnO/SBA-15

5.5 2 2 5 4 5 4 4.5 5 — — 3.5 3.5 3.5 4 3 5

15 600 40 14 20 110 50 18 100 20 36 45 20 60 6 21 15

21 3 80 19 40 170 100 25 125 3 17 90 50 180 26 51 16

Hysteresis (%)

1.5 5 – 1.4 3 Negligible 2 2.6 Negligible 4.16 — — — 3 4 6 1.2

Reference

[3] [4] [8] [9] [11] [14] [15] [17] [20] [22] [23] [33] [34] [35] [36] [37] This work

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obtained in previous work (Table II), our results demonstrates that sensor possess rapid response and recovery time. Hysteresis is a vital characteristic among the most paramount qualities of a humidity sensor, which is utilized to gage the reliability of a sensor by measuring the time slack in adsorption and desorption processes. For the most part, a sensing material experiences hysteresis impact at increasing and decreasing %RH. The hysteresis was measured by exchanging the sensor between closed chambers with 11%, 33%, 43%, 75%, 85%, and 98% RH and afterward trans-

Fig. 9. Hysteresis curve showing adsorption–desorption responses measured in the 11%–98%RH range of ZnO/SBA-15(10).

Fig. 10. The response of ZnO/SBA-15(10) monitored at different humidity conditions for 30 d.

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ferred back. The process of adsorption (low %RH to high % RH) and desorption (high %RH to low %RH) for ZnO/ SBA-15(10) is shown in Fig. 9. The sensor shows profoundly reversible sensing properties and the sensing curves for the adsorption and desorption process very nearly cover over another, indicating just about immaterial hysteresis. The humidity hysteresis error (cH) was calculated using the max expression, cH ¼ DH 2FFS , where, ΔHmax is the difference in output of adsorption and desorption processes and FFS is the full scale output. The maximum absolute value of humidity hysteresis error (cH) is found to be ~1.2%, lower than earlier reported results (Table II), indicating a good reliability of the sensor. To determine the stability of the synthesized sensor, ZnO/SBA-15 response toward %RH was tested every 5th day was tested over a span of 30 d. As seen in Fig. 10, the sensor shows consistency and a satisfactory variation in impedance (~1.8%) is measured at each humidity level.

(3) Humidity Sensing Mechanism Mesoporous materials due to their high intrinsic surface range, pore volume, and wider pore channels helps in the creation of active surface sites for easier adsorption of water molecules and smoother engendering of charge carriers across the surface of the material. To understand the sorption mechanism of ZnO/SBA-15(10) nanocomposite at different RH%, complex impedance spectra were plotted at different RH values (Fig. 11) and measured over a frequency range to expose the polarization and conductivity processes taking place in a nanocomposite material. A small portion of semicircle is observed at low %RH (11%, 33%, and 55%) which corresponds to the intrinsic impedance of the nanocomposite [Fig. 11(a)]. At low %RH, water molecules glued with the surface of material due to hydrogen bonding. Extra layer of water atoms is encouraged by the H-holding between oxygen atom of water molecule and base hydroxyl layer. The H3O+ ions bouncing over these chemisorbed layers of water atoms are the real wellspring of conduction at low %RH.38 As %RH increases (75%, 84% and 98%), a line is observed at lower frequency prompting the formation of smaller semicircle and this line get increases with the increase in %RH [Fig. 11(b)]. The line represents Warburg impedance due to the diffusion of the electroactive species at the electrode.39 At such higher %RH, water layers get physically adsorbed leading to a continuous layer on the nanocomposite surface. This ceaseless chemisorption of water molecules layers looks like bulk fluid phase of water in which proton generation happens from the hydration of H3O+ (H3O+?H2O + H+). These protons effectively tuned in control transportation and thus a noteworthy abatement in impedance is observed. On the other hand, the presence of Zn2+ particles gives dynamic locales to the adsorption of

Fig. 11. The measured and simulated complex impedance spectra (Nyquist plot) based on ZnO/SBA-15(10), RH varying from 11% to 98%.

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water molecules because of their high charge density and enables the regular ionization of physisorbed water molecules at the surface and pores of the nanocomposite which results in the generation of H+ ions for electrical conduction. The procedure of ionization of water molecules increments from 11% to 98% RH resulted in growth of effective charge transporters on the surface of nanocomposite and we get a ~5 order change in impedance magnitude. In general, our ZnO/ SBA-15 material displays higher order of methodical change in impedance, negligible hysteresis, rapid response/recovery time and impressive stability. Consequently, it can be considered as a potential RH sensor material.

IV.

Conclusion

In summary, ZnO/SBA-15 nanocomposites were synthesized using facile hydrothermal process. A study of their sensing properties uncovers that the sensor shows excellent response towards change in humidity exhibiting a change of 5 orders of impedance magnitude with quick response (17 s) and recovery time (18 s), marginal hysteresis (1.2%), and outstanding stability (1.8%) over a span of 30 d in complete 11%–98% RH range. It is expected that RH sensor utilizing mesoporous nanocomposite materials will be effective in outlining materials for novel RH sensing applications.

Acknowledgments Authors are grateful to UGC, New Delhi (grant no. 41-997/2012(SR)) for providing financial assistance. Authors are also thankful to Dr. I.S. Mulla (Emeritus scientist, CSIR, India) for his thoughtful and valuable suggestions.

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