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挥发性有机污染物(volatile organic compounds,VOCs)是臭氧和二次气溶胶的重要前体物之一,工业源是VOCs排放源中的最大贡献源[1-2]。以VOCs产品为原料的印刷等工业过程会产生多种VOCs,且这些VOCs的排放条件具有复杂多样的特点[3]。以凹版印刷工艺为例,乙酸乙酯作为有机合成和材料制造中最重要的溶剂和原料之一,是该工艺产生VOCs的主要贡献组分。通过对VOCs废气中诸如此类的主要贡献组分进行检测可达到判断废气中VOCs有效削减量和排放是否达标的目的[4]。目前针对乙酸乙酯的检测方法主要有色谱、质谱、传感器等。与传统的色谱、质谱类检测方法相比,传感器法具有检测成本低、分析速度快、实时响应迅速、易操作的优点[5]。将传感器与VOCs吸附净化相结合,利用传感器检测吸附剂出口乙酸乙酯浓度,可以快速判断吸附剂饱和程度。因此,开发高质量的用于检测乙酸乙酯的传感器在工业检测中至关重要。
金属氧化物半导体(metal oxide semiconductors,MOS)气体传感器由于具有分析速度快、制作简单、成本较低、稳定性良好等优点在VOCs检测领域得到广泛研究与应用[6-7]。通过简单的合成方法构建具有高灵敏度、低检出限和高选择性的半导体传感器对乙酸乙酯的检测具有重要意义。ZnO是一种常见的n型半导体金属氧化物,其具有的宽带隙能、高结合能及热稳定性好、抗氧化性能好、比表面积大、电子迁移率高等优点使其在气体传感器应用方面具有一定优势[8–10]。近年来用于检测乙酸乙酯的ZnO传感材料的设计受到了研究者的关注。AMEEN等[11]采用简单回流法在氟掺杂氧化锡(fluorine doped tin oxide,FTO)衬底上生长出独特的荷叶状ZnO纳米结构,具有139.8 µA∙(mmol∙cm2)−1的高灵敏度、0.26 mmol∙L−1的低检测限和10s的快速响应时间。KAMPARA等[12]通过静电纺丝方法沉积了基于聚乙烯醇(PVA)的 ZnO 纳米纤维。在350 ℃的工作温度下对35.40 mg∙m−3乙酸乙酯的传感响应为99.71 mV,响应恢复时间分别为36 s和25 s。然而,纯ZnO的传感性能还有很大提升的潜力,通过复合掺杂等改性方法可以提升气敏性能。XIE等[13]制造了由晶体纳米线组装的Au修饰的ZnO花状结构,对393.33 mg∙m−3乙酸乙酯的最大响应值约为102,几乎是纯ZnO花状结的传感器的7倍。对393.33 mg∙m−3乙酸乙酯气体的响应和恢复时间分别为10 s和13 s。已有研究[14-15]表明,通过构建p-n异质结可以显著提升材料性能,过渡金属基异质结可以诱导电子重新定位并促进载流子在异质结之间的迁移,通过设计和制造具有优异性能的p-n异质结可以极大地改进催化性能。与贵金属相比,Ni是一种廉价易得的过渡金属,对挥发性有机化合物具有良好的催化作用,NiO是一种典型的p型半导体,具有3.5 eV的良好导电带,已广泛应用于催化挥发性有机化合物,如甲醛、乙醇、苯[16–18]。Ni元素经常以Ni2+和Ni3+的形式存在于金属氧化物中,丰富的价态有助于在掺杂过程中产生氧空位[19]。因此,与NiO构建异质结以增加活性和催化位点有望提升乙酸乙酯传感器的性能。
本研究采用溶胶-凝胶法制备ZnO前驱体,然后采用化学沉淀法制备了NiO纳米颗粒修饰的ZnO纳米棒,并利用SEM、TEM、BET、XRD和XPS对其进行形貌结构和化学组成进行了表征分析,测试了所制备的样品的气敏性能,并对其气敏机理进行了分析。
NiO修饰ZnO气敏材料的制备及其对乙酸乙酯的气敏性能
Preparation of NiO modified ZnO gas sensing material and its gas sensing properties for ethyl acetate
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摘要: 乙酸乙酯是印刷等以VOCs产品为原料的工业生产过程中的主要贡献组分,对乙酸乙酯的便捷检测十分重要。采用化学沉淀法将NiO修饰在制得的ZnO纳米棒上,通过XRD、XPS、SEM、TEM和BET对材料的形貌结构、化学组成、比表面积等进行分析,并以乙酸乙酯为目标气体对其进行了气敏性能测试。结果表明,NiO的微量修饰可以有效改善ZnO的气敏性能,最佳修饰NiO:ZnO摩尔比为3:100,在290 ℃下,NiO:ZnO=3:100对393.33 mg∙m−3乙酸乙酯的响应值达到101(Ra/Rg),同时对乙酸乙酯的响应具有优异的选择性和稳定性。随后探讨了NiO:ZnO=3:100对乙酸乙酯的响应机制,结果表明,NiO与ZnO之间形成p-n异质结,NiO:ZnO=3:100材料表面捕获了更多的电子并产生了更多的氧,从而提高了气敏性能。最后,通过进行气体传感器在吸附净化乙酸乙酯的应用模拟实验得出气体传感器辅助判断吸附剂饱和程度具有应用前景。Abstract: Ethyl acetate is a major contributing component in industrial production processes such as printing, where VOCs products are used as raw materials, and a convenient detection of ethyl acetate is important. In this study, NiO was modified on the fabricated ZnO nanorods by chemical precipitation method, and XRD, XPS, SEM, TEM and BET were used to characterize their morphological structure, chemical composition and specific surface area, and their gas-sensitive properties were tested with ethyl acetate as the target gas. The results showed that the trace NiO modification could effectively improve the gas-sensitive property of ZnO, and the optimal modification ratio of NiO:ZnO was 3:100. The response of NiO:ZnO=3:100 to 393.33 mg∙m−3 ethyl acetate reached 101 (Ra/Rg) at 290 ℃, and the response had an excellent selectivity and stability. Subsequently, the mechanism of NiO:ZnO=(3:100) response to ethyl acetate was explored, and the results showed that a p-n heterojunction occurred between NiO and ZnO, and the surface of NiO:ZnO=3:100 material trapped more electrons and generated more oxygen, which improved the gas-sensitive performance. Finally, simulation experiments for the application of gas sensors in adsorption purification of ethyl acetate were conducted to conclude that gas sensors assisting in determining the degree of adsorbent saturation has a promising application.
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Key words:
- NiO /
- ZnO /
- heterojunction /
- ethyl acetates /
- gas sensing performance
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