Humidity sensor based on solution processible microporous silica nanoparticles

doi:10.1016/j.snb.2018.03.052

Sensors and Actuators B: Chemical

Volume 266, 1 August 2018, Pages 131-138

https://doi.org/10.1016/j.snb.2018.03.052 Get rights and content

Highlights

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The organic-inorganic hybrid materials MSNs-DMCs were prepared and applied for humidity monitoring.
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The small size and the modification of polyelectrolyte endow the solution processibility for sensitive film preparation.
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The channels formed by particle stacking in the sensitive film leads to a rapid response and recovery.

Abstract

Composites fabricated by mesoporous silica loading hydrophilic elements have been widely investigated as humidity sensitive materials. The physical mixing process for loading hydrophilic elements is difficult to guarantee the uniformity and structural stability of the composites. Furthermore, the poor dispersibility of the silica skeleton restricts its solution processability. Herein, solution processible organic-inorganic hybrid materials were synthesized via a thiol-ene click reaction between sulfhydryl functionalized microporous silica nanoparticles (MSNs) and hydrophilic alkenyl monomer. The optimal hybrid material could disperse in water stably with a concentration of 50 mg/mL owing to the small particle size (about 105 nm) and the hydrophilic characteristic. Humidity sensors were fabricated by solution process and the humidity sensing properties were investigated. The sensor exhibits high sensitivity (about three orders impedance modulus change), small hysteresis (∼2% RH) and rapid response (the response and recovery time are 5 and 40 s, respectively) in the humidity range of 11%–95% RH.

Introduction

Humidity is a mutable parameter among our peripheral environment and has significant effects on many fields, such as agriculture, electronic industry, storage and medical, etc [[1], [2]]. In recent years, various kinds of materials, such as electrolytes [3], metal oxides [4] and polymers [5] have been applied to fabricate humidity sensors. In addition, composites based humidity sensors are also attractive [[6], [7]]. In the last decade, mesoporous silica-based composites by loading hydrophilic electrolytes, metal oxides or polymers have been widely investigated [[8], [9], [10]]. The order pore structure and large pore volume could avoid the agglomeration of hydrophilic elements and enhance the contact area with targeted molecules. However, composites fabricated by a physical mixing process always suffer from the poor adherence between host and guest materials, and the poor solubility of silica is not beneficial to the uniform dispersion of hydrophilic materials.

In our previous work, organic-inorganic hybrid materials synthesized by anchoring hydrophilic organic units onto the sites of functionalized mesoporous silica were developed [11]. Through the chemical modification, stable bonds were formed between host and guest materials. But the mesoporous silica-based sensitive materials were bulk like with the particle size of several micrometers which is difficult to disperse well in solutions. In this work, the sulfhydryl functionalized microporous silica nanoparticles (MSNs-SH) were synthesized and modified with hydrophilic methacrylatoethyl trimethyl ammonium chloride (DMC) via click chemistry. By controlling the particle size and modifying hydrophilic organic group, the resultant hybrid materials exhibited good dispersibility in water. Thus, sensitive film could be prepared via the solution-process. Meanwhile, channels formed by particle stacking are available for water molecules transport in the sensitive film which could accelerate the response and recovery process. Moreover, the modification of the hydrophilic units inside the hybrid particles are expected to lead high sensitivity and wide sensing range of the humidity sensors.

Section snippets

Chemicals

Benzoin dimethyl ether (DMPA) and (3-mercaptopropyl) trimethoxysilane (MPTMS) were purchased from Aladdin. DMC was purchased from Tokyo Chemical Industry. Cetyltrimethylammonium chloride (CTAC), tetraethoxysilane (TEOS), Diethanolamine (DEA), tetrahydrofuran (THF), hydrochloric acid (HCl), methanol and ethanol were purchased from Beijing Chemical Corp (Beijing, China). All chemicals were used as received without further purification. The water used throughout all experiments was purified

Results and discussions

MSNs-DMCs were designed and synthesized as the humidity sensitive material, as shown in Fig. 1. The MSNs-SH was obtained by a simultaneous condensation of TEOS and MPTMS. Different contents of hydrophilic DMC were then modified on the MSNs skeleton. The resultant products were washed with deionized water to remove the unreacted DMC monomer.

The FT-IR spectroscopy and EA were carried on to determine the chemical structure of resultant materials. From the FT-IR spectroscopy (shown in Fig. 2), a

Conclusion

In summary, the DMC modified MSNs hybrid materials have been synthesized as the humidity sensitive materials. The small particle size (about 105 nm) and the modification of the hydrophilic organic units lead the hybrid materials could disperse in water stably with a concentration up to 50 mg/mL, which is beneficial for preparing film via the solution process. The modification of the electrolytes in MSNs enhances the adsorption ability to moisture. Meanwhile, channels formed by particle stacking

Acknowledgements

This work was supported by the Natural Science Foundation Committee (NSFC, No. 61773178), Projects of Science and Technology Development Plan of Jilin Province (No. 20160520093JH).

Hongran Zhao received his B.S. degree from the College of Electronic Science and Engineering, Jilin University, China in 2013. As a Ph.D. student, his research interest is functional sensing materials and devices.

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Tong Zhang completed her M.S. degree in semiconductor materials in 1992 and her Ph.D. in the field of microelectronics and solid-state electronics in 2001 from Jilin University. She was appointed as a full-time professor in the College of Electronics Science and Engineering, Jilin University in 2001. Her research interests are sensing functional materials, gas sensors, and humidity sensors.

Rongrong Qi received her B.S. degree from the College of Electronic Science and Engineering, Jilin University, China in 2016. As a M.S. student, her research interest is functional sensing materials.

Jianxun Dai received his B.S. degree from the College of Electronic Science and Engineering, Jilin University, China in 2015. As a M.S. student, his research interest is humidity sensors based on organic polymers.

Sen Liu received his B.S. degree in 2005 in Chemistry and Ph.D. degree in 2010 in Inorganic Chemistry from Jilin University. Now he is an associate professor in Jilin University and his current research is focused on the carbon-based functional materials and chemical sensors.

Teng Fei received his B.S. degree in 2005 in chemical engineering and technology and Ph.D. degree in 2010 in polymer chemistry and physics from Jilin University, China. He is currently an associate professor in the College of Electronics Science and Engineering, Jilin University. His research interests include sensing functional materials and devices.

Geyu Lu received the B.Sci. degree in electronic sciences in 1985 and the M.S. degree in 1988 from Jilin University in China and the Dr. Eng. degree in 1998 from Kyushu University in Japan. Now he is a professor of Jilin University, China. His current research interests include the development of chemical sensors and the application of the function materials.

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Humidity sensor based on solution processible microporous silica nanoparticles

Highlights

Abstract

Introduction

Section snippets

Chemicals

Results and discussions

Conclusion

Acknowledgements

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Microporous Mesoporous Mater.