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室外空气污染制定的标准和法规,已显著降低了全球许多地区的颗粒物、氮氧化物和二氧化硫的排放量。然而,室内空气污染却未能受到同样关注,且室内空气污染的相关科学研究进展也少于室外空气污染,使政府难以制定有针对性的政策和控制措施,室内空气质量成为影响人类健康的重要因素[1]。挥发性有机物是危害人类健康的“杀手”,而甲醛是一种典型的挥发性有机气体,室内装修甚至烹饪过程都成为甲醛释放的重要来源[2-3]。短时间接触甲醛会产生慢性中毒、皮肤刺激等症状,而长期接触或生活在甲醛超标环境中会严重刺激呼吸系统,导致慢性呼吸道疾病,甚至癌变[4]。因此尤其针对室内低浓度甲醛治理,开发一种安全有效的甲醛净化方法对人类健康至关重要。
目前,物理吸附[5]、光催化降解[6-7]、热催化降解[8-9]等甲醛分解技术已在相关研究领域取得显著效果,其中光催化降解在室温下将甲醛氧化成二氧化碳和水,具有高效、稳定、无二次污染的特点,被认为是一种高级氧化工艺[10]。常见的催化剂主要是氧化物和硫化物半导体。其中,ZnO因无毒、环保、廉价易得[11],同时具有激子结合能高 (60 meV) 等优点而被广泛应用于光电转化、太阳能电池、光催化等领域[12-15]。然而,单一ZnO带隙宽、电子空穴分离程度低等不足制约其在光催化领域的实际应用[16-18],一般而言,ZnO与窄带隙半导体构建异质结有利于解决其光吸收范围窄的弊端[19-20]。CdS作为一种典型的窄带隙半导体因具有强烈的可见光活性及制备成本较低等特点受到广泛关注[21]。半导体ZnO和CdS复合可提高电子-空穴对的分离效率并拓宽光吸收范围,进而提升ZnO的光催化活性[22]。例如LU等[23]通过水热合成簇状CdS/ZnO纳米管S型异质结用于光催化产氢,促进了电子-空穴对的分离,显著提高了单一组分的光催化效率。
然而,半导体表面没有高活性的还原位点,限制了催化剂的催化活性,通常引入助催化剂来解决,助催化剂的功能多样性可有效促进催化活性的提升[24]。贵金属助催化剂因自身良好的光学活性备受瞩目[25-27],其具有的可见光活性可充分利用太阳能,产生表面等离子共振效应 (SPR) ,诱导捕获电子用于光催化反应,具体表现为当光入射到贵金属表面,贵金属内部电子发生均匀、快速、高效的等离子体加热,产生大量热电子,并转移至半导体表面[28],从而提高光学性能。例如,Au纳米颗粒修饰的TiO2纳米棒具有较高的光催化活性,Au纳米颗粒的引入促进热电子向TiO2表面迁移,提高半导体对可见光的利用和电子的捕获能力[29]。YU等[30]研究Au纳米颗粒的表面等离子共振效应提高半导体异质结的光催化活性,结果表明当Au纳米颗粒受到光照射后,表面电子会转移到异质结中用于参与反应,使得用于光催化反应的电子数量大大增加。
因此,本研究首先使用两步水热法在衬底表面制备了一层ZnO/CdS粉末薄膜,然后利用化学浴沉积法,在ZnO/CdS异质结表面修饰一层金纳米颗粒,用于低质量浓度甲醛去除研究,并通过循环稳定性实验验证了催化剂在应用方面的潜力。此外,还探究了催化剂种类、光照波长、甲醛初始质量浓度、相对湿度对甲醛去除效果的影响,为室温下低质量浓度甲醛的实际应用提供参考。
制备ZnO/CdS/Au异质结用于可见光催化降解低浓度甲醛
Synthesis of ZnO/CdS/Au heterojunction for photocatalytic degradation of formaldehyde at room temperature under visible light
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摘要: 采用水热法和化学浴沉积法制备了ZnO/CdS/Au异质结光催化剂,用于可见光下室温去除低浓度甲醛。通过XRD、SEM、TEM、XPS、UV、PL、PEC、EIS等手段对ZnO/CdS/Au异质结光催化剂的光学性能、光电性能进行表征。结果表明,Au负载的ZnO/CdS纳米棒组成的微米花状结构中,异质结和金属等离子体效应能拓宽光谱吸收范围,抑制半导体缺陷发光,促进光吸收以及光生电子空穴的分离和迁移;所制备的ZnO/CdS/Au异质结光催化剂对甲醛的去除具有优异性能,室温下2 h即可将反应舱内低质量浓度甲醛(1.25 mg·m−3)降至0.025 mg·m−3以下,且经过8次重复使用后催化剂活性没有明显下降。此外,影响甲醛去除的因素,如催化剂种类、光照波长、甲醛初始质量浓度、相对湿度也进行了研究和探讨。该研究结果对低浓度甲醛的室温去除具有理论指导意义。Abstract: ZnO/CdS/Au heterojunction photocatalysts were synthesized via hydrothermal and chemical bath deposition methods for the removal of low-concentration formaldehyde under visible light at room temperature. The optical and photoelectronic characteristics of the ZnO/CdS/Au heterojunction photocatalyst were systematically investigated utilizing a suite of analytical techniques, including XRD, SEM, TEM, XPS, UV, PL, PEC, EIS, and other complementary methods. The results revealed that the Au-decorated ZnO/CdS exhibited a micrometer-scale flower-like morphology composed of nanorods. The formation of the heterojunction and the plasmonic effect induced by the metal component led to an expansion of the spectral absorption range, suppression of the defect-related luminescence in the semiconductor, and enhancement of light absorption as well as efficient separation and migration of photogenerated electron-hole pairs. The fabricated ZnO/CdS/Au heterojunction photocatalyst demonstrated exceptional performance in the removal of formaldehyde, achieving the reduction of low-mass concentration formaldehyde (1.25 mg·m−3) in a reaction chamber to below 0.025 mg·m−3 within 2 h at room temperature. Moreover, the catalyst retained its activity with negligible degradation after 8 consecutive cycles. Furthermore, this study elucidated the influence of various factors on the removal of formaldehyde, such as the type of catalyst, light wavelength, initial mass concentration of formaldehyde, and relative humidity. A comprehensive discussion of these factors is presented herein. The findings of this research hold significant theoretical implications for the effective abatement of low-concentration formaldehyde at room temperature.
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Key words:
- photocatalysis /
- heterojunction /
- metal /
- low concentration /
- formaldehyde
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表 1 ZCAu中元素的绝对含量
Table 1. Absolute content for the elements of ZCAu
元素 元素含量/(mg·kg−1) 元素的质量分数/% Au 8 125.7 0.8 Cd 472 584.7 47.3 S 123 247.2 12.3 Zn 307 689.6 30.8 O — — 表 2 重复使用次数对ZCAu的HCHO去除效果及催化剂脱落的影响
Table 2. Effect of regeneration on HCHO removal and catalyst shedding for ZCAu
循环次数 反应后甲醛
质量浓度/ (mg·m−3)衬底和催化剂
质量/g1 0.018 16.75 2 0.029 16.74 3 0.039 16.71 4 0.046 16.66 5 0.049 16.62 6 0.041 16.58 7 0.051 16.55 8 0.065 16.48 -
[1] LEWIS A C, JENKINS D, WHITTY C J M. Hidden harms of indoor air pollution-five steps to expose them[J]. Nature, 2023, 614(7947): 220-223. doi: 10.1038/d41586-023-00287-8 [2] 王学川, 宋云云, 韩庆鑫. TiO2及其复合材料光催化降解室内甲醛的研究进展[J]. 功能材料, 2021, 52(5): 5076. doi: 10.3969/j.issn.1001-9731.2021.05.011 [3] 惠世恩, 朱新伟, 王登辉, 等. 活性炭负载TiO2吸附与光催化降解甲醛研究进展[J]. 洁净煤技术, 2022, 28(2): 1-12. [4] 杨振洲, 蔡同建. 室内甲醛的危害及其预防[J]. 中国公共卫生, 2003, 19(6): 765-768. doi: 10.3321/j.issn:1001-0580.2003.06.063 [5] CHEN X, GAO P, GUO L, et al. High-efficient physical adsorption and detection of formaldehyde using Sc-and Ti-decorated graphdiyne[J]. Physics Letters A, 2017, 381(9): 879-885. doi: 10.1016/j.physleta.2017.01.009 [6] ZHU X, JIN C, LI X S, et al. Photocatalytic formaldehyde oxidation over plasmonic Au/TiO2 under visible light: moisture indispensability and light enhancement[J]. ACS Catalysis, 2017, 7(10): 6514-6524. doi: 10.1021/acscatal.7b01658 [7] RAN M, CUI W, LI K, et al. Light-induced dynamic stability of oxygen vacancies in BiSbO4 for efficient photocatalytic formaldehyde degradation[J]. Energy & Environmental Materials, 2022, 5(1): 305-312. [8] 田景晨, 吴功德, 刘雁军, 等. 负载型廉价金属催化剂在低温催化氧化甲醛中的应用[J]. 化学进展, 2021, 33(11): 2069. [9] YE J, WANG L, ZHU B, et al. Light-enhanced metal-support interaction for synergetic photo/thermal catalytic formaldehyde oxidation[J]. Journal of Materials Science & Technology, 2023, 167: 74-81. [10] TASBIHI M, BENDYNA J K, NOTTEN P H L. A short review on photocatalytic degradation of formaldehyde[J]. Journal of nanoscience and nanotechnology, 2015, 15(9): 6386-6396. doi: 10.1166/jnn.2015.10872 [11] NEMIWAL M, ZHANG T C, KUMAR D. Recent progress in g-C3N4, TiO2 and ZnO based photocatalysts for dye degradation: Strategies to improve photocatalytic activity[J]. Science of the total environment, 2021, 767: 144896. doi: 10.1016/j.scitotenv.2020.144896 [12] ZHANG Y, QIU J, ZHU B, ET AL. ZnO/COF S-scheme heterojunction for improved photocatalytic H2O2 production performance[J]. Chemical Engineering Journal, 2022, 444: 136584. doi: 10.1016/j.cej.2022.136584 [13] GOKTAS S, GOKTAS A. A comparative study on recent progress in efficient ZnO based nanocomposite and heterojunction photocatalysts: A review[J]. Journal of Alloys and Compounds, 2021, 863: 158734. doi: 10.1016/j.jallcom.2021.158734 [14] WIBOWO A, MARSUDI M A, AMAL M I, et al. ZnO nanostructured materials for emerging solar cell applications[J]. RSC advances, 2020, 10(70): 42838-42859. doi: 10.1039/D0RA07689A [15] WANG Y, ZHENG Z, WANG J, et al. New Method for Preparing ZnO Layer for Efficient and Stable Organic Solar Cells[J]. Advanced Materials, 2023, 35(5): 2208305. doi: 10.1002/adma.202208305 [16] SIVASAKTHI S, GURUNATHAN K. Graphitic carbon nitride bedecked with CuO/ZnO hetero-interface microflower towards high photocatalytic performance[J]. Renewable Energy, 2020, 159: 786-800. doi: 10.1016/j.renene.2020.06.027 [17] LAHMAR H, BENAMIRA M, DOUAFER S, et al. Photocatalytic degradation of methyl orange on the novel hetero-system La2NiO4/ZnO under solar light[J]. Chemical Physics Letters, 2020, 742: 137132. doi: 10.1016/j.cplett.2020.137132 [18] HADDAD M, BELHADI A, BOUDJELLAL L, et al. Photocatalytic hydrogen production on the hetero-junction CuO/ZnO[J]. International Journal of Hydrogen Energy, 2021, 46(75): 37556-37563. doi: 10.1016/j.ijhydene.2020.11.053 [19] ZAMAN F, XIE B, ZHANG J, et al. MOFs derived hetero-ZnO/Fe2O3 nanoflowers with enhanced photocatalytic performance towards efficient degradation of organic dyes[J]. Nanomaterials, 2021, 11(12): 3239. doi: 10.3390/nano11123239 [20] NEENA D, HUMAYUN M, ZUO W, et al. Hierarchical hetero-architectures of in-situ g-C3N4-coupled Fe-doped ZnO micro-flowers with enhanced visible-light photocatalytic activities[J]. Applied Surface Science, 2020, 506: 145017. doi: 10.1016/j.apsusc.2019.145017 [21] SHEN R, REN D, DING Y, et al. Nanostructured CdS for efficient photocatalytic H2 evolution: A review[J]. Science China Materials, 2020, 63(11): 2153-2188. doi: 10.1007/s40843-020-1456-x [22] SUN G, XIAO B, ZHENG H, et al. Ascorbic acid functionalized CdS-ZnO core-shell nanorods with hydrogen spillover for greatly enhanced photocatalytic H2 evolution and outstanding photostability[J]. Journal of Materials Chemistry A, 2021, 9(15): 9735-9744. doi: 10.1039/D1TA01089A [23] LU H, LIU Y, ZHANG S, et al. Clustered tubular S-scheme ZnO/CdS heterojunctions for enhanced photocatalytic hydrogen production[J]. Materials Science and Engineering:B, 2023, 289: 116282. doi: 10.1016/j.mseb.2023.116282 [24] 郭俊兰, 梁英华, 王欢, 等. 光催化制氢的助催化剂[J]. 化学进展, 2020, 33(7): 1100. doi: 10.7536/PC200803 [25] AHMAD M, REHMAN W, KHAN M M, et al. Phytogenic fabrication of ZnO and gold decorated ZnO nanoparticles for photocatalytic degradation of Rhodamine B[J]. Journal of Environmental Chemical Engineering, 2021, 9(1): 104725. doi: 10.1016/j.jece.2020.104725 [26] SANAKOUSAR F M, VIDYASAGAR C C, JIMÉNEZ-PÉREZ V M, et al. Recent progress on visible-light-driven metal and non-metal doped ZnO nanostructures for photocatalytic degradation of organic pollutants[J]. Materials science in semiconductor processing, 2022, 140: 106390. doi: 10.1016/j.mssp.2021.106390 [27] KARTHIK K V, RAGHU A V, REDDY K R, et al. Green synthesis of Cu-doped ZnO nanoparticles and its application for the photocatalytic degradation of hazardous organic pollutants[J]. Chemosphere, 2022, 287: 132081. doi: 10.1016/j.chemosphere.2021.132081 [28] LI X S, MA X Y, LIU J L, et al. Plasma-promoted Au/TiO2 nanocatalysts for photocatalytic formaldehyde oxidation under visible-light irradiation[J]. Catalysis Today, 2019, 337: 132-138. doi: 10.1016/j.cattod.2019.03.033 [29] VEZIROGLU S, OBERMANN A L, ULLRICH M, et al. Photodeposition of Au nanoclusters for enhanced photocatalytic dye degradation over TiO2 thin film[J]. ACS Applied Materials & Interfaces, 2020, 12(13): 14983-14992. [30] YU Z B, XIE Y P, LIU G, et al. Self-assembled CdS/Au/ZnO heterostructure induced by surface polar charges for efficient photocatalytic hydrogen evolution[J]. Journal of Materials Chemistry A, 2013, 1(8): 2773-2776. doi: 10.1039/c3ta01476b [31] ZHAO X, WU Y, HAO X. Electrodeposition synthesis of Au-ZnO hybrid nanowires and their photocatalytic properties[J]. International Journal of Electrochemical Science, 2013, 8(3): 3349-3356. doi: 10.1016/S1452-3981(23)14395-1 [32] ZHANG N, XIE S, WENG B, et al. Vertically aligned ZnO-Au@CdS core-shell nanorod arrays as an all-solid-state vectorial Z-scheme system for photocatalytic application[J]. Journal of Materials Chemistry A, 2016, 4(48): 18804-18814. doi: 10.1039/C6TA07845A [33] JIMENEZ-SALCEDO M, MONGE M, TERESA TENA M. An organometallic approach for the preparation of Au-TiO2 and Au-g-C3N4 nanohybrids: Improving the depletion of paracetamol under visible light[J]. Photochemical & Photobiological Sciences, 2022, 21(3): 337-347. [34] WEI R B, KUANG P Y, CHENG H, et al. Plasmon-enhanced photoelectrochemical water splitting on gold nanoparticle decorated ZnO/CdS nanotube arrays[J]. ACS Sustainable Chemistry & Engineering, 2017, 5(5): 4249-4257. [35] SHAFIQ F, TAHIR M B, HUSSAIN A, et al. The construction of a highly efficient p-n heterojunction Bi2O3/BiVO4 for hydrogen evolution through solar water splitting[J]. International Journal of Hydrogen Energy, 2022, 47(7): 4594-4600. doi: 10.1016/j.ijhydene.2021.11.075 [36] FU H, MA Y, YANG Z, et al. Construction of MnFe2O4/Bi5O7I composite heterojunction and its visible light-driven photocatalytic degradation of RhB[J]. Ionics, 2022, 28(8): 3893-3905. doi: 10.1007/s11581-022-04626-z [37] JIANG T, WANG X, CHEN J, et al. Hierarchical Ni/Co-LDHs catalyst for catalytic oxidation of indoor formaldehyde at ambient temperature[J]. Journal of Materials Science:Materials in Electronics, 2020, 31: 3500-3509. doi: 10.1007/s10854-020-02898-7