ZnO-MoS2 nano-composites with excellent light-activated NO2 gas sensitivity and MB photocatalytic degradation efficiency
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摘要: 实现对有毒、有害气体的有效监测和对有机污染物的快速降解，对于减少大气污染和水污染所带来的危害至关重要。本研究采用超声复合方法将溶胶凝胶法制备的ZnO和水热法制备的MoS2复合到一起，成功制备了ZnO-MoS2纳米复合材料。采用XRD、SEM、TEM、XPS等手段对材料结构、形貌和表面化学组分进行表征。结果表明，多层片状MoS2均匀负载到了ZnO纳米颗粒当中，复合材料具有较好的结晶性和丰富的表面缺陷。利用紫外-可见(UV-vis)漫反射光谱、光致发光光谱(PL)和表面光电压(SPV)对材料的光电性能进行了测试。结果表明，ZnO与MoS2的复合在提升光利用率的同时，能够促进光生载流子的更有效分离。以NO2作为目标气体的室温紫外光辅助气敏测试表明，本方法制备的ZnO-MoS2气体传感器具有良好的灵敏度、恢复性、稳定性和选择性，可在室温下实现对低浓度NO2的有效响应，MoS2复合量为5wt%的ZnO-MoS2传感器对0.47 mg/m3 NO2的响应值为19.6%。同时，气敏性能研究还发现空气中O2分子在材料表面的吸附会对传感器的气敏性能产生较大的影响，ZnO-MoS2传感器在无氧条件下对NO2具有更高的气敏响应。此外，在模拟太阳光下进行的光催化降解亚甲基蓝(MB)的实验表明，依靠吸附和光催化降解的共同作用，ZnO-MoS2复合材料能够在40 min内实现水溶液当中较高浓度MB (15 mg/L)的快速清除，MoS2复合量为10wt%的ZnO-MoS2样品的反应速率常数达到了0.032 min−1。对机制的分析表明，MoS2较好的吸附性和复合所导致的光生载流子分离率的提升是ZnO-MoS2复合材料气敏和光催化性能提升的关键。Abstract: Effective monitoring of toxic and harmful gases and rapid degradation of organic pollutants are essential to reduce the hazards of air and water pollution. In this study, the MoS2 nanosheets prepared by hydrothermal method were coupled into the ZnO nanoparticles prepared by sol-gel method to form ZnO-MoS2 nano-composites via a facile ultrasonic chemical route. The structure, morphology and surface chemical component of synthesized materials were characterized by XRD, SEM, TEM and XPS. The characterizations show that multilayer MoS2 nanosheets are well dispersed among ZnO nanoparticles, and ZnO-MoS2 composites have good crystallinity and abundant surface defects. The photoelectric properties were explored by UV-vis diffuse reflectance spectrum, photoluminescence spectra (PL) and surface photovoltage spectra (SPV). The results reveal that the formation of ZnO-MoS2 heterostructure improves the utilization of light and promotes the effective separation of photo-carriers. The UV light-activated gas sensitivity test using NO2 as the target gas preformed at room temperature saw that the prepared ZnO-MoS2 gas sensor exhibited excellent gas sensing properties with good sensitivity, recoverability, stability and selectivity, which could effectively respond to low concentration NO2. The response of the optimized ZnO-MoS2 sensor with 5wt%MoS2 to 0.47 mg/m3 NO2 reached 19.6%. Meanwhile, the gas sensing performance was found to be greatly influenced by the adsorption of O2 molecule on the surface of the materials, and ZnO-MoS2 gas sensor possessed much higher gas sensitivity to NO2 under oxygen free conditions. In addition, the photocatalytic degradation of methylene blue (MB) under simulated sunlight reveal that the ZnO-MoS2 composites can rapidly remove the high concentration of MB (15 mg/L) in aqueous solution within 40 min by combined action of adsorption and photocatalysis, thereinto, the ZnO-MoS2 sample with 10wt%MoS2 shows a reaction rate constant as high as 0.032 min−1. Mechanism analysis shows that the improvement of gas sensing and photocatalytic performance of ZnO-MoS2 composites mainly attribute to the better absorbability of MoS2 and the promotion of photocarrier separation rate caused by combination.
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Key words:
- ZnO-MoS2 /
- photocatalysis /
- NO2 gas sensing /
- heterojunction /
- nanocomposite /
- degradation /
- methylene blue
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图 1 气敏测试示意图
Figure 1. Schematic diagram of gas sensitivity test
LED—Light emitting diode; UV—Ultra violet
图 3 ZnO (a)、MoS2 (b)、ZnO-5MoS2 ((c), (d))、ZnO-10MoS2 ((e), (f)) 和ZnO-20MoS2 ((g), (h)) 的SEM图像
Figure 3. SEM images of ZnO (a), MoS2 (b), ZnO-5MoS2 ((c), (d)), ZnO-10MoS2 ((e), (f)) and ZnO-20MoS2 ((g), (h))
图 5 ZnO-20MoS2样品的XPS图谱：(a) Zn2p；(b) O1s；(c) S2p；(d) Mo3d
Figure 5. XPS spectra of ZnO-20MoS2 sample: (a) Zn2p; (b) O1s; (c) S2p; (d) Mo3d
OL—Lattice oxygen; OV—Vacant oxygen; OC—Chemisorbed oxygen
图 6 ZnO和ZnO-MoS2样品的UV-vis吸收图谱
Figure 6. UV-vis absorption spectra of ZnO and ZnO-MoS2 samples
图 7 ZnO和ZnO-MoS2样品的光致发光图谱
Figure 7. Photoluminescence spectra of ZnO and ZnO-MoS2 samples
图 8 ZnO和ZnO-MoS2样品的表面光电压图谱
Figure 8. Surface photovoltage spectra of ZnO and ZnO-MoS2 samples
图 9 (a) 室温紫外光照射下，ZnO和ZnO-MoS2传感器对0.47~2.35 mg/m3浓度NO2的动态响应曲线(干燥空气作为背景气体)；(b) 4组传感器的响应-浓度曲线；(c) 4组传感器恢复率与浓度之间的关系
Figure 9. (a) Time-dependent response curves of ZnO, and ZnO-MoS2 sensors to 0.47-2.35 mg/m3 NO2 at room temperature with the irradiation of UV light (Dry air as background gas); (b) Response-concentration curves of four sensors; (c) Recovery rate-concentration plots of four sensors
Rg—Measuring the resistance; R0—Initial resistance; Rec—Percentage of recovery rate; Response—Response intensity; C—Concentration
图 10 (a) 室温紫外光照射下，ZnO和ZnO-MoS2传感器对2.35 mg/m3浓度NO2的5次重复动态响应曲线(干燥空气作为背景气体)；(b) ZnO-5MoS2气体传感器对不同气体的选择性测试
Figure 10. (a) Repeated time-dependent response curves of ZnO and ZnO-MoS2 sensors to 2.35 mg/m3 NO2 in five cycles at room temperature with the irradiation of UV light (Dry air as background gas); (b) Selectivity test of ZnO-5MoS2 gas sensor for different gases
图 12 (a) 氮气作为背景气体四种传感器对0.47~2.35mg/m3 NO2的动态响应曲线；(b) ZnO-5MoS2气体传感器分别在空气与氮气作为背景气体时对0.47~2.35mg/m3的动态响应曲线
Figure 12. (a) Time-dependent response curves of the four sensors to 0.47~2.35 mg/m3 NO2 with nitrogen as background gas; (b) Time-dependent response curves of ZnO-5MoS2 gas sensor to 0.47~2.35 mg/m3 NO2 with air and nitrogen as background gas respectively
图 13 (a) ZnO及ZnO-MoS2样品在暗环境中吸附和在模拟太阳光照射下光催化降解亚甲基蓝(MB)的曲线；(b) 光照20 min时4种样品对于MB的清除效率；(c) 光照前20 min 4种样品降解MB的反应速率常数；(d) 模拟太阳光照射下添加不同牺牲剂后ZnO-10MoS2样品降解MB的反应速率常数
Figure 13. (a) Dark adsorption and photocatalytic degradation of methylene blue (MB) with the ZnO and ZnO-MoS2 samples under simulated sunlight irradiation; (b) MB removal efficiency for four samples after 20 min irradiation; (c) Reaction rate constants of four samples for the first 20 min of irradiation; (d) Reaction rate constants of ZnO-10MoS2 for photodegradation of MB with different sacrificial agents under the simulated sunlight irradiation
IPA—Isopropyl alcohol; EDTA-2Na—Edetate disodium; BQ—Benzoquinone; K—Reaction rate constant (min−1); C0—Initial concentration; Ct—Concentration at time t
表 1 ZnO-MoS2 样品成分配比
Table 1. Composition proportion of ZnO-MoS2 samples
Samples Mass of ZnO/g Mass of MoS2/g ZnO-5MoS2 0.95 0.05 ZnO-10MoS2 0.90 0.10 ZnO-20MoS2 0.80 0.20 
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表 3 不同ZnO基材料光催化降解MB对比
Table 3. Comparison of photocatalytic efficiency of ZnO based composites for the degradation of MB
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