Preparation of wood functional coatings with carbon dots grafted TiO2 for its photocatalytic degradation of formaldehyde gas
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摘要:目的 为提高二氧化钛（TiO2）光催化剂净化甲醛气体污染物的能力，利用具有优异光吸收性能和电子转移能力的碳量子点（CDs）掺杂改性TiO2，可大幅度提高TiO2光催化性能。方法 采用3-氨丙基三甲氧基硅烷（APTMS）对亲水性纳米TiO2进行表面改性，并将禾本植物柳枝稷合成的CDs负载于TiO2制备了TiO2-CDs复合光催化木材功能涂层。借助高分辨透射电子显微镜、红外光谱、热重分析、紫外可见光光谱、荧光光谱等表征手段对CDs及其负载TiO2复合光催化剂进行表征，并以甲醛气体作为模拟污染物进行光催化降解实验。结果 合成的CDs粒径尺寸为3 ~ 6 nm，表现为较好的石墨相结构，且CDs光致发光具有一定的激发依赖性。CDs功能化TiO2复合材料不仅在紫外光区域有较强的吸收，而且在400 ~ 500 nm波长范围内具有更宽的吸收带，CDs负载TiO2光催化涂层分别在紫外光源与紫外结合可见光源条件下对甲醛气体的净化效率达到68.26%和81.63%，较未改性的TiO2木材涂层提高了35.55%和38.71%，同时TiO2-CDs木材涂层可显著降低木材表面润湿性，其表面水接触角为96.4°，较对照组木材（62.5°）提升了54.24%。表面涂饰对木材表观颜色影响较小，TiO2-CDs净醛功能化木材的表面亮度较对照组木材轻微降低了5.22%，表面色差较对照组为11.03。此外，TiO2-CDs木材涂层具有优良的可重复使用性能，相比第一次循环，7次循环后试样对甲醛气体的降解效率仅分别下降了3.54%和2.56%。结论 CDs掺杂功能化可拓宽TiO2光催化剂在可见光区域净化甲醛气体污染物的能力，同时改善木材表面润湿性，且对木材表观颜色影响较小，对于开发具有净化室内甲醛气体污染物功能的木质材料意义重大。Abstract:Objective In order to broaden the photocatalytic degradation ability of titanium dioxide (TiO2) for formaldehyde gas pollutants, carbon dots (CDs) with excellent light absorption and electron transfer were used to modify the TiO2, which greatly improves the performance of pure TiO2 photocatalyst.Method The surface of TiO2 nanoparticles was modified by (3-aminopropyl) trimethoxysilane (APTMS) and integrated with CDs, which was synthesized from plant biomass of switchgrass. The resulted TiO2-CDs composites were then coated on wood to construct a photocatalytic coating. Multiple characterizations such as high-resolution transmission electron microscopy (HRTEM), infrared spectroscopy (FTIR), thermo-gravimetric analysis (TG), ultraviolet-visible spectroscopy (UV-Vis), fluorescence spectroscopy were applied to characterize the CDs and their loading TiO2 photocatalysts. The photocatalytic experiments were also carried out with formaldehyde gas as a typical pollutant.Result The synthesized fluorescent CDs had a good graphite phase structure with a particle size of 3−6 nm, which also showed strong excitation dependence. TiO2-CDs composites not only had strong absorption under UV light, but also had a wider absorption band in the wavelength range of 400−500 nm. TiO2-CDs wood coatings can achieve 68.26% and 81.63% degradation efficiency of formaldehyde gas under UV light and UV combined with visible light source, which was 35.55% and 38.71% higher than that of unmodified TiO2 coating under the same condition. In addition, TiO2-CDs coating significantly reduced the wettability of wood surface with a water contact angle of 96.4°, which was 54.24% higher than that of the pure wood (62.5°). Moreover, surface coating had little effect on the apparent color of wood. Surface brightness of functional wood was slightly lower than that of the pure wood by 5.22%, and the color difference was only 11.03 compared with the uncoated wood. Furthermore, the TiO2-CDs photocatalytic wood coating showed good recyclability with a degradation efficiency decrease of 2.56% and 3.54%, respectively after 7 cycles.Conclusion The utilization of CDs doping could broaden the degradation ability of formaldehyde gas for TiO2 photocatalyst in the visible light region, reduce the wettability of wood surface and has little effect on the apparent color of wood, which would be useful for the development of wood functional materials for degradation of formaldehyde gas pollutants.
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Keywords:
- carbon dot /
- titanium dioxide /
- formaldehyde /
- photocatalysis
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《北京林业大学学报》（原名《北京林学院学报》）创刊于1979年，由教育部主管、北京林业大学主办，国内外公开发行。历任主编分别为我国6位著名林学家汪振儒、沈国舫、关毓秀、王九龄、贺庆棠、尹伟伦。
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图 1 TiO2-CDs木材光催化功能涂层构建
Figure 1. Preparation of TiO2-CDs photocatalytic coating on wood functional material
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图 2 CDs的形貌结构和荧光发射光谱
a. TEM形貌，插图为CDs的HRTEM图；b. CDs在不同激发波长下的荧光发射光谱，插图为CDs在365 nm紫外灯（右）与日光灯（左）下的光学照片。a, TEM morphology, inset is the HRTEM image of CDs; b, fluorescence emission of CDs solution at varying excitation wavelengths, insets are the photos of CDs solution under 365 nm UV lamp (right) and room light (left).
Figure 2. Morphology, structure and fluorescence emission spectra of CDs
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图 4 改性前后TiO2的结构和成分分析
Figure 4. Structure and composition analysis of TiO2 before and after coated modification
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图 5 木材涂饰TiO2-CDs净醛功能涂层前后形貌
a和c 为对照组木材表面SEM形貌；b和d为TiO2-CDs涂饰后的木材表面SEM形貌。 a and c are SEM of wood surface without coatings; b and d are SEM of TiO2-CDs functional wood.
Figure 5. Morphology of functional TiO2-CDs wood coatings compared with pure wood
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图 6 木材涂饰TiO2-CDs净醛功能涂层的表面能谱分析
a. TiO2-CDs涂饰后的木材面能谱扫描；b. 微区内Si元素的面能谱；c 微区内Ti元素的面能谱。a, EDS scanning of TiO2-CDs functional wood; b, Si element EDS mapping in micro region; c, Ti element EDS mapping in micro region.
Figure 6. EDS analysis of functional TiO2-CDs wood coatings
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图 7 木材净醛功能化前后表面色度及润湿性
Figure 7. Surface chromaticity and wettability of wood before and after net aldehyde functionalization
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图 8 功能化木材降解甲醛气体效率及稳定性测试
a.不同净醛涂层处理木材前后对甲醛的降解效率（λ1 = 365 nm, λ2 ≥ 400 nm）；b. TiO2-CDs木材涂层在不同循环次数下的稳定性。a, degradation rate of formaldehyde in wood treated with different net aldehyde coatings（λ1 = 365 nm, λ2 ≥ 400 nm）; b, stability of TiO2-CDs wood coatings under different cycles.
Figure 8. Degradation and stability test of coated wood for degradation of formaldehyde
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