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Transient Cataluminescence on Flowerlike MgO for Discrimination and Detection of Volatile Organic Compounds Honglin Xu, Qiuyan Li, Lichun Zhang, Binrong Zeng, Dongyan Deng, and Yi Lv Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b01881 • Publication Date (Web): 15 Jul 2016 Downloaded from http://pubs.acs.org on July 15, 2016
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Analytical Chemistry
Transient Cataluminescence on Flowerlike MgO for Discrimination and Detection of Volatile Organic Compounds Honglin Xu,† Qiuyan Li, † Lichun Zhang,†,* Binrong Zeng,† Dongyan Deng,† and Yi Lv†,*
†
Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of
Chemistry, Sichuan University, Chengdu, Sichuan 610064, China
*Corresponding Author. Email:
[email protected];
[email protected]; Tel. & Fax: +86-28-8541-2398
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ABSTRACT: Methodologies for simple and rapid identification of gas compounds are pressing needed in the field of environment and security. Here, a new and simple method for the discrimination
of
gas
compounds
was
designed
through
an
interesting
transient
cataluminescence (TRCTL) phenomenon on the highly efficient MgO materials. The flowerlike MgO with high CTL activity was controllable synthesized via a facile and time-saving aqueous precipitation route and characterized by scanning electron microscopy, powder x-ray diffractometer, high-resolution transmission electron microscopy, and N2 adsorption measurements, etc. With flowerlike MgO working as sensing material, the newly developed CTL gas sensor exhibited highly active, ultra-fast, and characteristic responses towards many analytes, the TRCTL curves thus were obtained and ten of VOCs have been successfully identified. Parallel experimental results show that the controllable synthesis of flowerlike MgO can greatly enhance the discrimination capacities to VOCs. Further, the TRCTL of CHCl3 and C2H5OC2H5 were taken as typical examples to illustrate the possible sensing mechanism, which could contribute to explain processes of catalytic oxidations. We expect this novel TRCTL concept will be of practical importance for applications including gas detection, gas discrimination, and researches of chemical kinetic processes.
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Analytical Chemistry
INTRODUCTION SECTION Molecular recognition of organic compounds in the gaseous state is an issue full of challenge, also a hot research subject in chemical workplace and general population nowadays. Exposure to toxic gas, such as volatile organic compounds (VOCs), can cause short- or long-term adverse health effects on human beings, including sensory irritation and chronic diseases.1 In the past decades, a variety of conventional methods for detection and discrimination of gas phase hazardous chemicals were developed, including GC/MS, ICPMS, electronic nose technologies and gas sensor.2-8 Therein, sensor technology, especially cataluminescence (CTL) sensor, is considered to be one of promising sensors for high sensitivity, long-term stability, and simplicity of apparatus.9-13 CTL-based sensing provides a versatile approach
for
VOCs
differentiation.14-15
For
example,
Nakagawa16
developed
a
spectrum-temperature imaging system to discriminate and determine concentrations of organic vapors. Zhang’s group17,18 developed a CTL imaging sensor array to recognize alcohols, amines and thiols, and an extended CTL sensor array with 21 kinds of sensing materials that could successfully discriminate and identify flavors in cigarettes. These pioneering works arose a novel transduction principle for discrimination and detection of gas compounds, we also have to explore sensors with less elements for the stability of the detection system, and improvements in reproducibility are enabled by the reduction in the number of sensing elements. In recent years, Cao19 and Li20 proposed CRC and CCL analysis strategies that allow separately discrimination a variety of analytes, respectively. This may provide a new trend in developing CTL-based single sensor to identify different vapors.
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Along with a series of CTL-based sensor systems developed, the CTL behaviors of VOCs on different catalytic nanomaterials have been continually investigated, even the same nanomaterial exhibits different CTL properties upon exposure to different analytes.21 For instance,22-24 it is reported that different MgO-based CTL sensors were developed to identify ethylene glycol ethers, vinyl acetate, etc. Based on the above, we would hazard a guess that highly CTL efficient MgO catalysts can be utilized as a diverse sensing material in VOCs detection. Hypothetically, MgO with high CTL activity was controllable synthesized, which could trigger rapid catalytic chemical reactions in the sensor, thus TRCTL curves characteristic to various VOCs could be obtained due to their different catalytic reaction dynamic processes and less interference, we would be able to differentiate compounds by comparing their TRCTL curves obtained from a single MgO-based sensor. However, to confirm this hypothesis, highly efficient MgO catalyst that enables a fast interfacial catalytic reaction to trigger TRCTL emission is firstly required. As is well-known, controllable synthesis of micro- or nanoscale materials is demonstrated to be an efficient way to promote the catalytic activities of catalysts.25-28 For instance, Zhang et al.29-30 had demonstrated that the controllable synthesized α-Fe2O3 nanotubes showed more superiorities than non-uniform α-Fe2O3 nanoparticles with stronger CL intensity towards H2S. Similarly, the identical view that the CTL activities of materials are correlated with their morphological and structural features has also been verified on the controllable synthesis of Mn3O4 and Y2O3 microstructures in our laboratory.31-32 In the past decades, various MgO microstructures (nanofibers, fishbones, nanoflowers, nanowires)
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Analytical Chemistry
have been synthesized in diverse ways,33-37 all the methods share their own strengths, here we proposed a facile and environmentally friendly method to synthesize highly efficient MgO. As a proof-of-principle work, being of special performance on structural and chemical properties, the controllable synthesized flowerlike MgO showed high and ultra-fast CTL responses to multiple VOCs, therefore the original MgO-based sensor with transient luminescence was established, and the identification of ten kinds of VOCs was successfully realized on a single CTL sensor. Further, to understand TRCTL curves, we have characterized flowerlike MgO in details and investigated the CTL behavior of CHCl3 and C2H5OC2H5 on flowerlike MgO catalysts, in some cases it will contribute to explaining the possible sensing mechanisms on catalytic oxidation.
EXPERIMENTAL SECTION Materials. All the reagents were of analytical grade and used as received without further purification. MgCl2·6H2O, Na2CO3, Na2SO4, and sodium citrate were obtained from Chengdu Kelong
Chemical
Reagent
Company
(China).
Dimethyl
formamide
(DMF)
and
Polyethyleneglycols (PEGs) with tunable degrees of polymerization (of 200, 400 and 1500) were purchased from Aladdin Chemistry Co. Ltd. Deionized water was obtained from a Milli-Q water purification system (ULUPURE Co. Ltd, Chengdu, China). Synthesis of flowerlike MgO. Here we take a simple, time-saving and environmentally friendly aqueous precipitation strategy for the synthesis of highly dispersed flowerlike MgO. In a typical synthesis, firstly, 0.1 g PEG200 was added into 1.0 mol·L-1 Na2CO3 solution and kept stirring for 30 min; and then the mixed solution was gradually added into a 0.5 mol·L-1 MgCl2
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solution (30 °C) drop by drop. Secondly, the reaction mixture was stirred for 30 min and then kept standing for another 30 min to fully precipitate the product. After the precipitate was filtered, washed, and dried at 70 °C for 24 h, the obtained product was calcined at 550 °C for 3 h as resulting materials. It’s known that surfactant can seriously influence the morphology and structure of reaction products,38-39 a series of parallel experiments were conducted by altering PEG200 with different degrees of polymerization (400 and 1500) and sodium citrate, etc. In addition, the influences of reaction time and calcination temperature on the synthesis were also studied. For brevity, abbreviations PEG200-MgO, PEG400-MgO, PEG1500-MgO and S-MgO stand for MgO products assisted with PEG200, PEG400, PEG1500, and sodium citrate, respectively. Characterization. The structures of the products and precursors were characterized via an X’Pert pro x-ray diffractometer (XRD, Philips) with Cu Kα1 radiation (λ=1.5406Å), the diffraction patterns were obtained in the range of 10°< 2θ
