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中国是世界上最主要的产竹国。竹材相比其他生物质材料具有一次成林、储量庞大、生长速度快且经济效益高等优点。然而,竹材利用率低,竹产品附加价值不高[1−3]。竹材砍伐产生的竹梢、竹节、竹枝和竹屑等采伐剩余物以及加工过程中产生的大量竹节隔、竹黄等加工废弃物均未得到合理利用,一般被遗弃在山林或作为普通燃料使用,不仅造成严重的资源浪费,还对环境产生了严重污染[4−6]。因此,高效合理利用竹材加工废弃物,对提高竹材利用率以及经济效益具有一定的价值。竹节隔核心成分为纤维素、半纤维素、木质素,富含碳元素,是制备荧光碳量子点(carbon quantum dots, CQDs)的绿色可持续碳源,无需添加任何化学试剂修饰;竹节隔本身含有的氮、硅元素可通过水热碳化自掺杂到CQDs中,从而提高量子产率和光学性能。竹节隔的高效、绿色利用对竹产业可持续、高质量发展具有重要意义。
CQDs是一种尺寸小于10 nm的新型零维碳纳米材料[7],由于其稳定的光学性能、良好的生物相容性、优异的水溶性、低细胞毒性等诸多特性[8−10],在传感[11]、生物成像[12]、光催化[13]、荧光防伪[14]等领域具有广泛的应用前景。根据工艺条件的不同,CQDs的制备方法通常分为2类:自上而下和自下而上[15]。自上而下制备方法,是通过电弧放电、化学氧化、激光烧蚀等将大尺寸的碳靶剥离或切割成小尺寸的CQDs[16]。但存在设备昂贵、合成条件苛刻等缺陷。自下而上制备方法主要利用微波辅助、水热等将有机小分子前驱体碳化制备得到CQDs[17],在调控CQDs的形状和尺寸等方面具有显著优势。其中,水热法制备CQDs的前驱体来源广泛,但苯二胺、甲酰胺等常用有机化工原料成本昂贵,且部分工艺处理过程繁复,具有一定的毒性,限制了CQDs的应用领域。相比之下,生物质材料具有可再生、成本低廉、环境友好、来源广泛等优点[18−20]。以生物质碳源制备CQDs已成为当前研究热点。AMER等[21]以马齿苋Portulaca oleracea叶为原料,采用一步水热法150 ℃碳化4 h,经过离心、透析等处理后得到绿色荧光碳量子点,并用石英晶体微天平(QCM)检测甲醛等有害气体。近年来,以稻Oryza sativa壳[22]、银杏Ginkgo biloba叶[23]、花生 Arachis hypogaea壳[24]、青稞Hordeum vulgare var. coeleste [25]、枸杞Lycium chinense[26]等生物质材料制备碳量子点,并进一步应用于生物成像、传感器、防伪等诸多领域。目前,以生物质材料为碳源前驱体制备出的CQDs存在荧光颜色单一、荧光量子产率低等问题,仍需进一步探究和优化。
本研究以竹材加工废弃物竹节隔为碳源,采用一步水热法,绿色制备高荧光量子产率的竹节隔CQDs,并探究其在荧光防伪领域应用的可能性,以期提高废弃生物质材料价值,实现竹材加工废弃物的高效利用。
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3~4年生毛竹Phyllostachys edulis竹节隔通过粉碎、过筛得到100目竹节隔粉末;无水乙醇(分析纯);普通定性滤纸、0.22 μm微孔滤膜、500 Da透析袋购于南京化学试剂有限公司;试验中用于合成和透析的水溶液均为去离子水。
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分别称取1.0、1.5、2.0、2.5 g的竹节隔粉末分散于25 mL去离子水中,混合均匀后移入50 mL聚四氟乙烯内衬的反应釜中,180 ℃反应10 h。反应结束,待聚四氟乙烯反应釜冷却至室温后取出内胆,用普通定性滤纸进行过滤,之后将CQDs的滤液放入高速冷冻离心机,10 000 r·min−1离心10 min。离心结束后,用0.22 μm微孔膜过滤上清液,去除聚集颗粒使CQDs纯化。采用500 Da透析袋进行48 h透析,去除未反应的小分子,冷冻后放入真空冷冻干燥机进行干燥备用。竹节隔CQDs制备流程见图1。
取0.4 mg CQDs粉末溶于4 mL乙醇溶液中,配置出质量浓度为0.1 g·L−1的CQDs样品溶液,通过瞬态/稳态荧光光谱仪测定:当竹节隔粉末为2 g时,绝对荧光量子产率最高,因此,表征与分析的对象均为竹节隔粉末2 g、去离子水25 mL制备的CQDs。
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采用透射电子显微镜(JEM-2100F,JEOL公司)和高分辨率透射电子显微镜(JEM-2100UHR, JEOL公司)表征CQDs的形貌与晶格间距;采用X射线衍射(XRD Ultima IV)表征CQDs的晶体性质,测试范围为10°~80°;采用紫外可见光光度计(Lambda950,PE公司)测定CQDs的紫外吸收光谱;采用瞬态/稳态荧光光谱仪(FluoroMax-4,HORIBA公司)测试CQDs最佳激发波长,检测其荧光性能;通过双指数模型计算荧光寿命,并对荧光衰减寿命曲线进行拟合:
$$ {\tau }_{ave}=\frac{{A}_{1}{\tau }_{1}^{2}+{A}_{2}{\tau }_{2}^{2}}{{A}_{1}{\tau }_{1}+{A}_{2}{\tau }_{2}} 。 $$ 其中:$ {\tau }_{\mathrm{a}\mathrm{v}\mathrm{e}} $为平均荧光寿命, $ {A}_{1} $、$ {A}_{2} $为振幅,$ {\tau }_{1} $、$ {\tau }_{2} $为衰减时间。同时,在350 nm激发波长下测试CQDs的绝对荧光量子产率;采用红外光谱仪(VERTEX80V,Bruker公司)表征CQDs的表面官能团状态,波数为500~
4000 cm−1;采用X射线光电子能谱仪(AXIS-Ultra DLD,Shimadzu公司)测定CQDs的元素组成及化学结构。
Preparation of bamboo carbon quantum dots and their application in fluorescence anti-counterfeiting
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摘要:
目的 探究竹节隔碳量子点绿色制备方法,提高废弃生物质材料利用效率和附加值。 方法 以竹材废弃物竹节隔为初始碳源,水为溶剂,采用一步水热法制备荧光碳量子点,通过透射电子显微镜、X射线衍射、红外光谱仪、X射线光电子能谱仪、紫外可见光光度计、荧光光谱等表征手段,对竹节隔碳量子点的微观形貌、化学结构和光学特性进行了表征与分析。 结果 所制备的竹节隔碳量子点形状为近圆形,其粒径分布为0~1.6 nm;绝对荧光量子产率为6.85%;具有优异的荧光特性,在365 nm波长紫外灯下呈现明显的蓝色荧光。 结论 制备的竹节隔碳量子点水溶液绿色环保、性能良好,可通过进一步优化设计,以期应用于家具木制品及人造板等木质材料荧光防伪领域。图7参35 Abstract:Objective The objective is to achieve a green method for the preparation of bamboo carbon quantum dots and to improve the utilization efficiency and added value of waste biomass materials. Method Fluorescent carbon quantum dots were prepared by a one-step hydrothermal method using bamboo waste materials (bamboo septa) as the initial carbon source and water as the solvent. The micro-morphology, chemical structure and optical properties of the carbon quantum dots of bamboo septa were characterized and analyzed by means of transmission electron microscopy, X-ray diffraction, infrared spectrometry, X-ray photoelectron spectroscopy, UV-visible photometry and fluorescence spectroscopy. Result The shape of the prepared carbon quantum dots had a near-circular shape, with a size distribution of 0−1.6 nm. The absolute fluorescence quantum yield was 6.85%, and they had excellent fluorescence properties, with a blue fluorescence under a 365 nm ultraviolet lamp. Conclusion The prepared carbon quantum dots aqueous solution is environmentally friendly and has good performance, which can be further optimized for application in the field of fluorescence anti-counterfeiting of wood materials such as furniture wood products and artificial boards. [Ch. 7 fig. 35 ref.] -
Key words:
- bamboo septum /
- carbon quantum dots /
- fluorescence /
- fluorescent anti-counterfeiting
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https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.20240361