Research progress of sensing materials for VOCs detection
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摘要: 挥发性有机化合物(Volatile organic compounds,VOCs)检测是环境治理的重要环节,而开发快速、灵敏的检测系统仍然面临挑战。基于智能系统的VOCs传感器能够实时监测空气中污染物浓度,从而严格把控排放标准,减小VOCs对环境和健康的影响。通过调控材料及构筑方法能够制成适用于识别和快速捕获VOCs的敏感元件,从而获得传感性能优越、安全可靠的气敏传感器。本文以敏感机制为出发点,介绍了聚合物、金属氧化物、复合材料及新材料作为敏感膜的研究进展,重点讨论了VOCs与敏感膜的相互作用机制。基于此,分析了提高VOCs检出浓度和响应速度的构筑方法。最后,展望了基于光学效应的光致发光型和手性向列型敏感膜材料在VOCs智能检测领域的前景和面临的挑战。Abstract: Monitoring the volatile organic compounds (VOCs) is an important part in the environmental governance. However, it is still a great challenge to develop rapid and high-sensitive detecting system for VOCs detection. The VOCs sensor based on sensing materials can achieve the real-time monitoring of the concentration of pollutants in the air. Therefore, the emission standard of VOCs can be adjusted to reduce the harm of VOCs to human body and environment. Sensitive elements with the performance of repaid identification and capture of VOCs, can be accomplished by controlling materials and methods. And hence the gas sensor with superior sensitivity, safety and reliability can be obtained. This paper extensively reviewed the research progress of VOCs-sensing films prepared with the materials of polymers, metallic oxides, composites and novel materials, focusing the attention on the mechanisms of interaction between VOCs and sensing membranes. Furthermore, the construction strategies of sensing materials for improving the sensitivity and detection limit for VOCs detection were discussed. Finally, the prospects and challenges of sensing films with optical effect (e.g. photoluminescent and chiral nematic sensitive films) on the VOCs detection were indicated.
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Key words:
- volatile organic compounds /
- gas sensors /
- gas sensitive materials /
- sensing technology /
- composite
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图 2 吸附挥发性有机化合物(VOCs)分子作用示意图:(a) 甲醛分子与干凝胶之间席夫碱吸附和氢键吸附[15];(b) 官能化的碳纳米管表面上芳族VOCs的相互作用[20]
Figure 2. Schematic diagram of adsorption of volatile organic compounds (VOCs) molecule: (a) Adsorption of Schiff base and hydrogen bond between formaldehyde molecule and xerogel[15]; (b) Interaction of aromatic VOCs on functionalized carbon nanotube[20]
△H—Adsorption enthalpy change values
图 5 电负载效应材料敏感机制示意图:(a) 电子导电型材料对还原性气氛的反应机制[5];(b) 空穴导电型材料对氧化性气氛的反应机制[50]
Figure 5. Schematic diagram of sensing mechanism of materials with electric load effect: (a) Reaction mechanism of electronic conductive materials in reducing atmosphere[5]; (b) Reaction mechanism of hole conducting materials in oxidizing atmosphere[50]
Ev—Valence band; Ec—Conduction band; Ef—Fermi level; VBM—Valence band maximum; CBM—Conduction band maximum; Eg—Band gap; F—Work function
图 6 纳米晶纤维素(CNC)的湿度和甲醛响应机机制示意图[63] (a)、柱状近晶噬菌体纳米结构合成的示意图[66] (b)、蒸发法[63] (c) 和推拉法[64] (d) 制CNC彩虹膜
Figure 6. Schematic diagram of humidity response mechanism and formaldehyde response mechanism of crystalline nanocellulose (CNC) periodic spiral structure[63] (a), schematic diagram of synthesis of columnar smectic phage nanostructure[66] (b), evaporation method[63] (c) and push-pull method[64] (d) to prepare CNC rainbow film
MCC—Microcrystalline cellulose
表 1 基于吸附效应VOCs传感器的性能
Table 1. Performance of VOCs sensor based on adsorption effect
Sensitive membrane
materialsSensitive
gasGas concentration/
(mg·m−3)Sensitivity/
(Hz·mg−1)Detection
limit/mgResponse
time/sRef. Graphene oxide (rGO) Formaldehyde 0-4.29 11.6 0.07 60 [25] Polyethylene acetate Benzene 1597.3-9584.0 0.006 98.39 225 [26] Chitosan Ethanol 1.88-69.72 0.21 5.38 15 [27] rGO/CuO Trimethylamine 0-12.09 1.96 0.23 20 [23] ZnO/acetaldehyde molecularly
imprinted polymerHexanal 8.19-450.61 1.73 1.73 — [24] rGO/chitosan Dimethylamine 24.98-749.50 1.25 4.06 16 [28] Co/Zn- Zeolite imidazolium salt framework Benzene 319.47-3194.66 8.01 1.63 — [29] MIL-101(Cr) Formaldehyde 2.47-61.41 1.36 2.18 25 [30] Note: "—"—No specific values are given in the references. 表 2 改性金属基VOCs传感器的敏感性能
Table 2. Performance of modified metals-based VOCs sensor
Sensitive membrane
materialsSensitive
gasMicrocrystalline
size/mmOptimum working
temperature/℃Response value
(Ra/Rg)Gas concentration/
(mg·m−3)Response
time/sRef. Pd/SnO2 nanoclusters loaded Toluene 5 300 1720 188.42 — [37] Pt/ZnO/g-C3N4 Ethanol 90 250 23 92.41 9 [38] Mpg-CN loaded with pt-MoO3 Acetone — 175 34.1 90.04 8.6 [39] CdS doped SnO2 Toluene 51.53 200 51 18842.41 — [40] Ag doped ZnO N-butanol 6-12 250 156 303.15 — [41] SiO2@ZnO core-shell structure Ethanol 136 400 22.6 565.27 16.2 [42] SiO2@ZnO core-shell structure Isopropanol 30 300 99.03 1 686.08 14 [43] ZnO@ZIF–8 core-shell heterostructures Formaldehyde 400 300 — 6.87 16 [44] Note: Ra and Rg—Resistance of the gas sensor in air and in the detected gases. -
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