Progress in preparation and research of VO2-based composite structure films for smart windows
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摘要:
二氧化钒(VO2)在68℃附近发生绝缘体-金属相转变,同时伴随着近红外光透射率突变,因此在智能节能窗领域具有巨大的应用潜力。近年来,关于 VO2的制备方法、相变机制及改善光学性能方面取得了显著进展。然而,在实际应用中,VO2仍面临一系列挑战,包括本征相变温度较高、可见光透过率(Tlum)较低、太阳能调节效率(∆Tsol)不佳、耐候性差及颜色舒适度较差(呈现棕黄色)。针对这些问题,国内外的研究者进行了大量研究,发现复合结构对改善VO2性能具有显著作用,对推进其实际应用具有重要意义。然而,目前关于VO2基复合结构的综述相对较少。本文概括了VO2基复合结构的制备方法及在智能窗领域的性能研究进展,并对VO2基复合结构薄膜未来发展前景进行了展望。
Abstract:Vanadium dioxide (VO2) exhibits an insulator-metal phase transition near 68℃, coupled with a sudden alteration in near-infrared light transmittance, rendering it highly promising for intelligent energy-saving windows. Despite extensive research in recent years on preparation methods, phase transition mechanisms, and enhancement of dimming capabilities for VO2, practical applications face numerous challenges. These include its high intrinsic phase transition temperature, low visible light transmittance (Tlum), inefficient regulation of solar energy (∆Tsol), poor weather resistance, and limited color comfort (brownish-yellow hue). Addressing these challenges, researchers worldwide have conducted extensive investigations, with composite structures emerging as a promising avenue for enhancing the overall performance of VO2 and advancing its practical applications. However, there remains a paucity of comprehensive reviews on VO2-based composite structures. This paper provides a synthesis and discussion of the preparation methods and performance research progress in the field of smart windows of VO2-based composite structures, while also exploring the future prospects of VO2-based composite structures.
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Keywords:
- vanadium dioxide /
- thermochromism /
- smart windows /
- energy conservation /
- composite structure
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随着印染纺织行业的高速发展,印染废水对环境的危害愈加剧烈,印染废水因此成为目前工业污染最严重的污染源之一[1-2]。印染纺织废水的排量大,且含有大量的有机、有毒的污染物,例如芳香胺和大部分酚类物质具有致癌、致畸性的作用,会对人体造成直接或间接的伤害[3-4]。亚甲基蓝(Methylene blue,MB)作为一种有机氯化物,是印染行业中一类重要的染色剂,可以与无机盐生成复盐,对水体环境和人类健康造成不可逆转的危害[5]。近年来,对MB进行脱色降解的研究较多,处理方法有吸附法、电化学法、超声波脱色法等[6]。但是这些方法存在处理成本高、处理效果不理想等问题,因此如何高效环保地对废水中的MB进行降解和脱色是目前亟待解决的问题。
陈娴等[7]以NaY分子筛为载体,通过离子交换法制备 FeY 催化剂,并对其在非均相光-Fenton 体系中催化降解MB染料废水进行了研究,考察其催化降解性能,降解率可达97%。Nicolas Cheval等[8]提出了一种用原位合成Au NPs对聚酰胺66 (PA66)球晶结构进行湿法金属化的方法,制备PA66/Au NPs杂化材料,该方法制备的PA66微球表面包覆了Au NPs,该材料可有效催化降解MB。目前利用贵金属催化剂、半导体催化剂及生物法催化降解MB染色剂的研究较多,而可再生的生物基材料处理MB染色剂的研究较少,因此寻找一种高效、环保的处理MB染色剂的方法十分必要。
微晶纤维素(Microcrystalline cellulose,MCC)作为一种生物质资源,具有产量高、范围广、可再生、可降解、粉体流动性较好等优点,因此广泛应用于食品、制药工业、化妆品等行业[9]。MCC比表面积大,对其进行化学改性,表面负载化合物或接枝某些基团,可以赋予其特殊的性能。CuO作为一种多功能无机材料,具有较好的电、磁、催化特性,因此被广泛用于催化剂、载体和电极活性材料制备等领域。Wei-Ping Dow等[10]将CuO负载在钇稳定基氧化锆表面,探究了其在不同CuO添加量和不同反应温度下对CO的氧化作用,CuO作为一种催化剂可显著提高氧化锆复合体氧化CO的能力;Hadi Almasi等[11]利用CuO NPs的抗菌性,将其负载于细菌纤维素和甲壳素纤维表面,使其具有抗菌性并增强其释放控制能力。3-氯丙基三甲氧基硅烷(CPTES)作为硅烷偶联剂中的一种,主要用于处理玻璃纤维提高与环氧树脂的黏结力,适用于玻璃纤维表面处理、环氧树脂、聚氨酯、聚酰胺等胶黏剂或复合材料的偶联,并且其中的氯原子易转化为其他官能团[12],因此是一种效果很好的中间体。Mahmoud Nasrollahzadeh等[13]利用CPTES作为中间体,将5-苯基四氮唑磺酸负载在氧化硅包裹的磁性纳米粒子表面制备催化剂,该催化剂在合成1-氨基甲氧基-1-苯基脲类化合物的反应中表现出了良好的催化性能和较高的催化活性。
本研究利用MCC的高结晶度、高聚合度及高比表面积等优势,通过在其表面负载CuO NPs,并添加3-氯丙基三甲氧基硅烷(CPTES)和二乙醇胺(DEA)进行胺基接枝,制备可高效催化降解MB染色剂的CuO NPs@MCC–Si–N(OH)2。探究并分析了制备CuO NPs@MCC–Si–N(OH)2过程中DEA添加量对催化降解MB的影响,研究了不同处理条件下CuO NPs@MCC–Si–N(OH)2对MB的催化降解效果,探讨出催化MB降解的最佳条件,为今后利用环保可再生材料处理MB染色剂奠定了基础。
1. 实验原料及方法
1.1 原材料
桉木浆板(山东恒联纸业集团,产地巴西),MCC(实验室酸水解法自制[13],直径为15~20 μm,长度为150~200 μm),3-氯丙基三甲氧基硅烷(CPTES,分析纯,上海麦克林生化科技有限公司),二乙醇胺(DEA,分析纯,国药集团化学试剂有限公司),NaOH(分析纯,国药集团化学试剂有限公司),无水乙醇(分析纯,国药集团化学试剂有限公司),硼氢化钠(NaBH4,分析纯,天津市永大化学试剂有限公司),MB(分析纯,天津市大茂化学试剂厂)。
1.2 MCC的制备
将桉木浆板置于去离子水中浸泡24 h,然后进行疏解,配置浆浓为2wt%的桉木浆,于瓦利打浆机中打浆至打浆度为48 °SR,于浆袋中洗净脱水后平衡水分备用。
取一定质量的桉木浆置于三颈烧瓶中,加入2.5 mol/L的HCl,固液体积比为1∶15,机械搅拌处理1 h[14]。反应结束后加入去离子水终止反应,离心、洗涤至上清液无氯离子即可(0.1 mol/L AgNO3检验)。将离心产物置于冷冻干燥机中干燥至恒重,即得MCC。
1.3 改性MCC的制备
取适量MCC于三颈烧瓶中,加入一定量体积比为1∶1∶1的NH3·H2O (质量分数为37wt%)、H2O2 (质量分数为30wt%)与去离子水混合液,通风橱中室温搅拌反应1 h。反应结束后加入去离子水终止反应,离心洗涤至上清液为中性为止,取下层沉淀平衡水分,于4℃冷藏室中冷藏备用。
取适量上述多羟基MCC悬浮液于三颈烧瓶中,加入3.0 g CuSO4,水浴中机械搅拌至温度达到75℃,将75 mL 1 mol/L NaOH缓慢滴加至MCC悬浮液中,搅拌反应4 h。反应结束后离心洗涤至上清液为中性为止,下层沉淀即为CuO NPs@MCC,平衡水分,于4℃冷藏室中冷藏备用。
取适量上述CuO NPs@MCC悬浮液于三颈烧瓶中,加入10 wt% CPTES(相对于绝干CuO NPs@MCC),继续加入适量乙醇水溶液(m乙醇∶m水=3∶1),于70℃水浴中搅拌反应6 h。反应结束后离心洗涤四次,下层沉淀即为CuO NPs@MCC–Si,平衡水分,于4℃冷藏室中冷藏备用。
取适量上述CuO NPs@MCC–Si混合液于三颈烧瓶中,分别加入5wt%、10 wt%、15 wt%、20 wt%的二乙醇胺,并持续通入N2,于50℃水浴反应12 h。反应结束后离心洗涤至上清液无氯离子为止(0.1 mol/L AgNO3检验)。将离心产物置于冷冻干燥机中干燥至恒重,即得CuO NPs@MCC–Si–N(OH)2。
1.4 MB溶液的配制
称取适量MB溶于去离子水中,转移至1 000 mL容量瓶中定容。反复摇晃容量瓶并于超声波反应器中超声30 min,转移至棕色瓶中待用。
1.5 性能表征
1.5.1 改性MCC的FTIR测试
取适量干燥的MCC、CuONPs@MCC、CuO NPs@MCC–Si、CuO NPs@MCC–Si–N(OH)2与烘干至恒重的溴化钾混合均匀并进行压片处理,用IR Prestige-21型傅里叶变换红外光谱仪(日本岛津公司)进行测试,测试条件为:扫描速度32 次/s,分辨率4 cm−1,测试波长4 000~500 cm−1。
1.5.2 改性MCC的晶体结构分析
取适量完全干燥的待测样品于射线衍射槽内(X射线衍射仪,D8-ADVANCE,德国布鲁克AXS公司),采用Cu靶X光管,设置扫描速率为10°/min,在5°~60°衍射角范围内扫描。
1.5.3 改性MCC的热稳定性分析
称取5~10 mg待测样品于坩埚中,置于热重分析仪(TGA-Q50,美国TA仪器公司)中进行测试,测试条件为:N2流速为50 mL/min,升温范围为30~600℃,升温速率为10℃/min。
1.5.4 改性MCC的形貌观察
取适量完全干燥的待测样品于双面导电胶带上,并在金属样品台上固定后进行喷金处理,在扫描电镜(Quanta 200,FRI公司)下观察样品形貌。
1.5.5 MB降解效果测试
MB的降解率:MB的降解过程可通过紫外分光光度计(Agilent Technologies 8453,Palo Alto, California,US)观测(λ=664 nm),可通过配制标样计算标准曲线[15],吸光度A如下式所示:
A=0.0609x−0.0085 (1) 其中:A为MB在不同浓度下的紫外吸光度;x为MB的浓度;R2=0.991。
测定样品吸光度A[16],如表1所示,并代入式(1),计算其浓度,去除率R如下式所示:
R=xt/x0×100% (2) 其中:R为MB在加入CuO NPs@MCC–Si–N(OH)2与还原剂NaBH4后的去除率;xt为MB在加入CuO NPs@MCC–Si–N(OH)2与还原剂NaBH4后反应t时刻下的浓度;x0为添加CuO NPs@MCC–Si–N(OH)2与NaBH4后初始时刻MB的浓度。
表 1 亚甲基蓝 (MB) 标样的浓度与吸光度Table 1. Concentration and absorbance of methylene blue (MB) standardsNo. Concentration/(mg·L−1) Absorbance 1 6.40 0.36672 2 5.12 0.32067 3 3.84 0.22950 4 2.56 0.14548 5 1.28 0.06453 CuO NPs@MCC–Si–N(OH)2中不同DEA添加量对MB催化降解效果的影响:取10 mg上述制备的不同DEA添加量的CuO NPs@MCC–Si–N(OH)2加入至30 mL 2 mmol/L MB溶液中,并加入10 mg NaBH4,磁力搅拌5 min,经滤纸过滤收集滤液,测定其浓度。
CuO NPs@MCC–Si–N(OH)2用量对MB催化降解效果的影响:量取30 mL 2mmol/L的MB溶液,分别加入10 mg、20 mg、30 mg、40 mg、50 mg的CuO NPs@MCC–Si–N(OH)2,加入10 mg NaBH4,磁力搅拌5 min,反应完成后经滤纸过滤收集其滤液,并测量其浓度。
反应时间对MB催化降解效果的影响:量取30 mL 2 mmol/L的MB溶液,加入10 mg的CuO NPs@MCC–Si–N(OH)2和10 mg NaBH4,分别使用磁力搅拌1 min、3 min、5 min、7 min、9 min,反应完成后经滤纸过滤收集其滤液,并测量其浓度。
MB 溶液浓度对催化降解效果的影响:配置1 mmol/L、2 mmol/L、3 mmol/L、4 mmol/L、5 mmol/L的MB溶液,分别量取30 mL上述配置的MB溶液,加入10 mg的CuO NPs@MCC–Si–N(OH)2和10 mg NaBH4,磁力搅拌5 min,经滤纸过滤得其滤液,收集并测量其浓度。
2. 结果与讨论
2.1 MCC基复合材料的官能团结构
图1(a)及图1(b)分别为改性MCC和不同DEA添加量的CuO NPs@MCC–Si–N(OH)2的FTIR图谱。表2为各谱峰功能团归属表。由图1(a)结合表2分析可知,3 500 cm−1处是MCC表面的—OH伸缩振动吸收峰,这是由于MCC表面有大量羟基,并且前期利用NH3·H2O、H2O2与去离子水混合液对MCC进行反应,既可去除MCC表面杂质还可增大其表面羟基含量[17];560 cm−1处是MCC表面CuO的Cu—O伸缩振动吸收峰,相比于MCC,CuO NPs@MCC、CuO NPs@MCC–Si、CuO NPs@MCC–Si–N(OH)2均在560 cm−1处出现了吸收峰,说明CuO已成功负载于MCC表面;1 260 cm−1处是改性MCC表面的Si—C伸缩振动吸收峰[12],CuO NPs@MCC与CuO NPs@MCC–Si–N(OH)2在此处出现了新的吸收峰,说明其已成功接枝硅烷偶联剂中的Si—C。由图1(b)结合表2分析可知,CuO NPs@MCC–Si–N(OH)2在1260 cm−1处的峰强度随DEA添加量的增加而增大,说明硅烷偶联基团接枝程度逐渐增强,同时也更利于接枝胺基[12, 18],进而提高CuO NPs@MCC–Si–N(OH)2的稳定性和电子转移能力[19],增大催化降解MB的能力。
表 2 改性MCC的FTIR图谱带分析Table 2. Band characteristics of FTIR spectra related to MCC and grafted MCCWavenumber/cm−1 Peak attribution 3 200-3 600 —OH stretching vibration absorption peak in hydroxyl group and carboxyl group 2 935 Methylene—C—H stretching vibration absorption peak 1 740 —C=O stretching vibration absorption peak 1 260 Si—C stretching vibration absorption peak 800 Si—O—C stretching vibration absorption peak 560 Cu—O stretching vibration absorption peak 2.2 MCC基复合材料的表面形貌
图2为MCC改性前后的SEM图像。可知,未改性的MCC表面无杂质,且较光滑,直径约为20 µm。通过对比发现,CuO NPs@MCC表面有颗粒状或团状物质,团聚现象十分明显,这是由于在溶液体系中反应产生CuO NPs后,其表面有大量羟基,与MCC表面的羟基形成氢键,负载于MCC表面,但是CuO NPs的粒径较小,表面原子占有比较高,具有极高的比表面积和表面活性[20],易团聚在CuO NPs@MCC表面。CuO NPs@MCC–Si–N(OH)2表面也有颗粒状物质,且分布较均匀,团聚现象不明显,由于CPTES通过MCC与CuO NPs表面羟基进行接枝共聚,CPTES中的—S—OCH3在乙醇和水的环境中易水解成硅醇基(—SiOH),然后与MCC表面的羟基(—OH)反应形成氢键,并脱水缩合为—Si—O—M共价键(M:MCC表面),消耗了MCC与CuO NPs表面大量具有亲水性的羟基,使其接触角增大,疏水性增加,有利于纳米粒子团的分散,并且增强了分散体系的热力学稳定性,防止分散粒子再团聚[21]。分析可知,利用硅烷偶联剂的疏水分散性可使CuO NPs更好地分散于MCC表面,增大其比表面积,充分发挥其催化活性,促进CuO NPs@MCC–Si–N(OH)2表面的吸附能力,使电子可迅速高效作用于MB分子,进一步接枝胺基,与MCC表面的Cu2+形成配合物[22],加速体系内电子转移,增强其催化降解活性。
2.3 MCC基复合材料的晶相结构
图3为改性MCC和不同DEA添加量的CuO NPs@MCC–Si–N(OH)2的XRD图谱。由图3(a)可知,MCC在衍射角2θ为15.97°、22.58°处有较强的衍射峰,为结晶区衍射峰101与002;通过对MCC负载CuO NPs得到CuO NPs@MCC、CuO NPs@MCC–Si及不同DEA添加量的CuO NPs@MCC–Si–N(OH)2,可以发现其均具有标准CuO的衍射峰,2θ为35.50°和38.73°处分别为CuO的002、111面,与标准卡片PDF NO.45—0937吻合,为结晶良好的纯相CuO,结合2.2节分析可说明CuO NPs已成功生成并负载于MCC表面。在图2(b)中,相比于CuO NPs@MCC、CuO NPs@MCC–Si、CuO NPs@MCC–Si–N(OH)2在2θ为49.17°、53.51°、57.96°、61.64°、66.45°处出现了衍射峰,衍射角有轻微的弥散。经过对比发现,这些衍射峰为CuO的衍射峰,说明伴随DEA的加入,接枝胺基可以使CuO NPs@MCC–Si–N(OH)2有更好的结晶倾向[19]。由图3(b)可知,随着DEA用量的增加,提高了CuO NPs在CuO NPs@MCC–Si–N(OH)2中的结晶性能,与胺基形成配合物,加快电子转移能力,作用于CuO NPs@MCC–Si–N(OH)2吸附的MB,使其发生降解。
2.4 MCC基复合材料的热稳定性
图4为MCC各改性阶段与不同DEA添加量的CuO NPs@MCC–Si–N(OH)2的TG与TGA曲线。由TG曲线可知,MCC及改性MCC均在30~90℃内有失重现象,且MCC失重较大,主要是样品中游离水的蒸发导致;随着温度升高,MCC及改性MCC的质量趋于平稳,无质量损失。MCC的初始失重温度为256℃,在359℃失重速率达到最高;CuO NPs@MCC初始失重温度为209℃,在350℃失重速率达到最高;CuO NPs@MCC–Si初始失重温度降低至175℃;CuO NPs@MCC–Si–N(OH)2初始失重温度降低至155℃,且不同DEA添加量样品结果相差不大。其中MCC的主要失重阶段在246.47~386.68℃之间,主要是MCC中糖苷键的断裂,使MCC断裂成小分子气体和大分子挥发分造成的[23]。不同DEA添加量的CuO NPs@MCC–Si–N(OH)2在358.91~360.89℃失重速率达到最大,主要是其中接枝的硅烷偶联剂中丙基的降解导致的。改性后产生的新连接键导致初始降解温度降低,并且CuO NPs@MCC–Si–N(OH)2的残余质量相比于CuO NPs@MCC–Si明显降低,说明CuO NPs@MCC–Si–N(OH)2在较高温度下稳定性降低,分析原因可能是由于MCC分子间作用力较强,随着CuO NPs的负载,MCC表面的羟基会与CPTES中硅醇基和CuO NPs表面的羟基形成氢键,胺基与Cu2+形成配合物,使MCC分子间作用力减弱,并且由于CuO NPs粒子均匀负载于MCC表面,会使MCC发生形变[11],使纤维张力变大,强度降低,导致热稳定性降低[24]。
2.5 MCC基复合材料在不同反应条件下催化MB降解的性能
图5为DEA添加量、CuO NPs@MCC–Si–N(OH)2用量、反应时间和MB浓度对 MB 催化降解性能的影响。通过在制备改性MCC过程中改变DEA添加量,得到不同DEA添加量的CuO NPs@MCC–Si–N(OH)2,固定CuO NPs@MCC–Si–N(OH)2与NaBH4用量、反应时间、MB含量及浓度,考察制备CuO NPs@MCC–Si–N(OH)2过程中不同DEA添加量对催化降解MB性能的影响。由图5(a)与表3可知,当加入DEA添加量为5wt%的CuO NPs@MCC–Si–N(OH)2,反应结束溶液中MB浓度为48.00 mg/L,去除率达到92.5%。随着CuO NPs@MCC–Si–N(OH)2中DEA添加量的增加,反应结束后MB浓度逐渐降低,去除率逐渐提高。DEA添加量为20wt%的CuO NPs@MCC–Si–N(OH)2处理MB染色剂的效果最佳,反应结束后MB浓度为18.25 g/L,去除率达到97.15%。这是由于在改性过程中,随着DEA用量的增加,CuO NPs@MCC–Si–N(OH)2表面的胺基增多,亲水性降低,可与CuO NPs形成配合物,结合性增强,避免CuO NPs的脱落,即增强了溶液体系的吸附能力和电子转移能力,使溶液中的BH4−提供的电子可以更高效地作用于MB分子[25]。
表 3 不同DEA添加量、CuO NPs@MCC–Si–N(OH)2用量、反应时间和MB浓度时催化MB的去除率和去除量Table 3. Removal rate and amount of MB catalyted by CuO NPs@MCC–Si–N(OH)2 with different DEA addition amounts, dosage of CuO NPs@MCC–Si–N(OH)2, reaction time and concentration of MBFixed factor Research factor (variable) Range of variable Removal rate
of MB/%Removal amount
of MB/mgDosage of CuO NPs@MCC–Si–N(OH)2 10 mg
Dosage of NaBH4 10 mg
Reaction time 5 min
MB 30 mL 2 mmol/LDEA addition amount 5wt% 92.50±0.21 17.76±0.04 10wt% 95.16±0.15 18.27±0.03 15wt% 95.70±0.15 18.37±0.03 20wt% 97.15±0.10 18.65±0.02 DEA addition amount 20wt%
Dosage of NaBH4 10 mg
Reaction time 5 min
MB 30 mL 2 mmol/LDosage of CuO NPs@MCC–Si–N(OH)2 10 mg 97.15±0.10 18.65±0.02 20 mg 98.23±0.12 18.86±0.02 30 mg 99.71±0.10 19.14±0.02 40 mg 99.84±0.09 19.17±0.02 50 mg 99.87±0.08 19.18±0.02 DEA addition amount 20wt%
Dosage of CuO NPs@MCC–Si–N(OH)2 30 mg
Dosage of NaBH4 10 mg
MB 30 mL 2 mmol/LReaction time 1 min 92.50±0.41 17.76±0.08 3 min 95.76±0.29 18.39±0.06 5 min 99.71±0.10 19.14±0.02 7 min 99.80±0.07 19.16±0.01 9 min 99.80±0.09 19.16±0.02 Dosage of CuO NPs@MCC–Si–N(OH)2 30 mg
DEA addition amount 20wt%
Dosage of NaBH4 10 mg
Reaction time 5 minConcentration of MB 1 mmol/L 99.78±0.07 9.58±0.01 2 mmol/L 99.71±0.10 19.14±0.02 3 mmol/L 99.18±0.16 28.56±0.03 4 mmol/L 40.53±5.76 15.56±1.11 5 mmol/L 31.37±6.81 15.02±1.31 当固定CuO NPs@MCC–Si–N(OH)2与NaBH4用量和反应时间,DEA添加量为20 wt%时的CuO NPs@MCC–Si–N(OH)2处理MB 效果最佳。固定最佳DEA添加量、NaBH4用量、反应时间、MB含量及浓度,考察CuO NPs@MCC–Si–N(OH)2用量对催化降解MB性能的影响。由图5(b)与表3可知,当加入10 mg的CuO NPs@MCC–Si–N(OH)2,反应结束时溶液中MB浓度为18.25 mg/L,去除率为97.15%;随着CuO NPs@MCC–Si–N(OH)2用量的增加,反应速率增大,溶液中MB浓度呈现出先迅速下降后缓慢下降的趋势;当CuO NPs@MCC–Si–N(OH)2用量为30 mg时,MB的去除率增幅最大,达到99.71%;继续增大CuO NPs@MCC–Si–N(OH)2用量至50 mg,去除率则达到99.87%,增幅不明显。分析可知,BH4−是亲核离子,可以提供电子供体,MB为接受电子的受体;由于供体和受体之间存在电位差,CuO NPs@MCC–Si–N(OH)2可以接收来自供体提供的电子,将其转移给受体[26]。CuO NPs@MCC–Si–N(OH)2具有比表面积大的优点,因此具有一定的吸附性,可以将MB吸附于CuO NPs@MCC–Si–N(OH)2表面,此时BH4−反应生成的电子会迅速作用于CuO NPs@MCC–Si–N(OH)2表面的MB上[11],使MB分子发生降解。随着CuO NPs@MCC–Si–N(OH)2用量的增大,溶液体系中的吸附性能和电子转移的能力更高效,催化降解MB的效果更佳。
对上述实验结果中MB催化降解率与实际成本分析可知,最佳DEA添加量和CuO NPs@MCC–Si–N(OH)2用量分别为20 wt%、20 mg。固定最佳DEA添加量与CuO NPs@MCC–Si–N(OH)2用量、NaBH4用量、MB含量及浓度,考察反应时间对催化降解MB性能的影响。由图5(c)与表3可看出,当反应时间由1 min增加至5 min时,溶液中MB浓度由47.99 mg/L下降至1.86 mg/L,去除率由92.50% 增加至99.71%,增幅为7.21%。继续增加反应时间至7 min,MB去除率为99.80%,继续增大反应时间,MB去除率无变化。分析可知,单位时间内,CuO NPs@MCC–Si–N(OH)2的吸附能力和BH4−提供给MB分子的电子数量有限,增大反应时间,CuO NPs@MCC–Si–N(OH)2吸附的MB分子的量会增加,同时其接受的由BH4−提供的电子数量也会增多[16],导致更多MB分子被降解,溶液中MB含量下降,去除率上升。
对上述实验分析可知,最佳DEA添加量、CuO NPs@MCC–Si–N(OH)2用量及反应时间分别为20 wt%、20 mg、5 min,此时改变MB浓度考察其对催化降解MB性能的影响。由图5(d)与表3可知,MB浓度由1 mmol/L增加至3 mmol/L时,反应结束后溶液中MB含量由0.70 mg增加至7.87 mg,去除率则由99.78%下降至99.18%,去除率略微下降,但是催化降解的MB绝对含量则由9.58 mg增加至28.56 mg;继续增大MB浓度至4 mmol/L与5 mmol/L时,MB去除率则分别骤降至40.53%、31.37%,催化降解的MB绝对含量分别为15.56 mg、15.05 mg。分析原因可能是CuO NPs@MCC–Si–N(OH)2比表面积较大,可在其表面吸附大量MB分子,使电子由电子供体快速转移至电子受体,从而将MB降解为毒性较小的无色亚甲蓝(Leucomethylene blue)。当MB浓度较小时,CuO NPs@MCC–Si–N(OH)2在一定时间内吸附MB分子效率较高,但是由于MB分子在溶液体系中较分散,CuO NPs无法将所有MB分子吸附至其表面进行催化降解;当溶液中MB浓度增大,MB分子在溶液体系中分布广泛,CuO NPs@MCC–Si–N(OH)2可吸附大量MB分子并进行降解,但是当CuO NPs@MCC–Si–N(OH)2吸附MB分子数量达到饱和后,其吸附能力将下降,从而导致BH4−提供的电子不能迅速传递至MB分子使其降解,从而导致MB的催化降解效率降低,去除率下降。
综上可知,当还原剂NaBH4用量为10 mg,使用30 mg DEA用量为20wt%的CuO NPs@MCC–Si–N(OH)2催化30 mL 3mmol/L MB,反应时间为5 min时效果最佳,MB去除率达到99.71%。此时过滤取出CuO NPs@MCC–Si–N(OH)2,并用1 mol/L NaBH4对其反复冲洗5 min,冷冻干燥后得到样品,并将其在最佳实验条件下进行循环性测试,五次循环后,溶液中MB含量为 43.24 mg/L,去除率为93.24%。
3. 结 论
(1)通过在微晶纤维素(MCC)表面成功负载纳米CuO颗粒(CuO NPs),并利用硅烷偶联剂提高其分散性并接枝胺基,制备具有高催化活性的CuO NPs@MCC–Si–N(OH)2。
(2)改变制备CuO NPs@MCC–Si–N(OH)2过程中二乙醇胺(DEA)的添加量,分析接枝胺基含量对MCC的催化性能的影响,发现增加DEA添加量,亚甲基蓝(MB)的去除率呈逐渐增加趋势,说明接枝胺基有助于提高MCC的催化性能,接枝上的胺基可提高CuO NPs在MCC上的分散性和稳定性,并与Cu2+形成金属配合物,增加催化活性。
(3)通过优化发现DEA用量为20wt%时制得的CuO NPs@MCC–Si–N(OH)2催化效果最好,CuO NPs@MCC–Si–N(OH)2用量为30 mg,NaBH4用量为10 mg,处理30 mL 3 mmol/L MB溶液5 min后,MB去除率可达99.71%,五次循环性测试后,MB去除率为93.24%。
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图 2 ((a), (b)) VO2纳米颗粒[18-19];((c), (d))无机壳层结构[24];((e), (f))有机壳层结构[32];((g), (h))无机-有机壳层结构[33]
DA—Dopamine; PDA—Polydopamine; PET—Polyethylene terephthalate; PVB—Polyvinyl butyral
Figure 2. ((a), (b)) Nanocomposite particle[18-19]; ((c), (d)) Inorganic shell structure[24]; ((e), (f)) Organic shell structure[32]; ((g), (h)) Inorganic-organic shell structure[33]
图 4 (a) SiO2@TiO2@VO2三层空心纳米球结构[48];(b) VO2@SiO2双层空心核壳结构[49];(c) VO2-Mg1.5VO4多孔结构[50]
VS1-VS4—VO2@SiO2 bivalve particles prepared by reaction of vanadium dioxide precursor solution at 60℃ for 1-4 h
Figure 4. (a) SiO2@TiO2@VO2 three-layer hollow nanospheres[48]; (b) VO2@SiO2 double layer hollow core-shell structure[49]; (c) VO2-Mg1.5VO4 porous structure[50]
图 5 (a) Cr2O3-VO2缓冲层结构[70];(b) VO2-TiO2减反射结构[74];(c) 空心SiO2-VO2-FSiO2-聚合物多功能结构[80];(d) VO2-HfO2多功能结构[81]
Figure 5. (a) Cr2O3-VO2 buffer layer structure[70]; (b) VO2-TiO2 antireflection structure[74]; (c) Hollow SiO2-VO2-FSiO2-polymer multi-function structure[80]; (d) VO2-HfO2 multi-function structure[81]
表 1 VO2核壳结构复合薄膜的光学性能
Table 1 Optical properties of VO2 core-shell composite thin films
Structure Tlum/% ∆Tsol/% Tc/℃ Ref. VO2@SiO2 38.0 18.9 — Du et al[30] VO2@ZnO 51.0 19.1 — Chen et al[27] VO2@SiO2 50.6 14.7 25.2 Zhu et al[34] VO2@TiO2 59.3 6.2 — Li et al[28] VO2@PDA 56.3 14.5 33.8 Guo et al[32] VO2@PMMA — 17.5 57 Hu et al[35] VO2@Polymer — 20.34 — Zhao et al[36] VO2@MgF2@PDA — 25.0 — Zhao et al[33] Notes:Tlum—Luminous transmittance; ∆Tsol—Modulation of solar energy; Tc—Transition temperature; A@B—Core(A)@shell(B) structure; PMMA—Polymethyl methacrylate. 表 2 不同基质材料VO2基复合薄膜的光学性能
Table 2 Optical properties of VO2-based composite films of different matrix materials
Structure Tlum/% ∆Tsol/% Ref. VO2-hydrogel 62.6 34.7 Zhou et al[40] VO2-Ni-Cl-IL 66.85 23.77 Zhu et al[41] VO2-{[(C2H5)2NH2]2NiBr4@SiO2} 52.9 25.7 Zhao et al[51] VO2-spiropyran 48.58 23.58 Zhao et al[45] VO2@SiO2 61.8 12.6 Qu et al[49] SiO2@TiO2@VO2 73.9 12.0 Yao et al[48] VO2-[1, 4-bis (benzoxazol-2-yl) naphthalene] 73.0 9.0 Qin et al[52] VO2-PDA 56.23 7.64 Wang et al[53] Notes: A-B is the mixture of A and B; Ni-Cl-IL is the ionic liquid-nickel-chlorine complexes. 表 3 VO2多层结构复合薄膜的光学性能
Table 3 Optical properties of VO2 multilayer composite films
Structure Tlum/% ∆Tsol/% Ref. Double-layer ZnO-VO2 46.4 6.0 Gagaoudakis et al[82] VO2-TiO2 61.5 15.1 Chen et al[61] TiO2-VO2 50.49 20.11 Wu et al[74] TiO2-VO2 47.3 8.8 Ji et al[83] VO2-HfO2 55.8 15.9 Chang et al[81] VO2-C₈H20O₄Si 52.7 16.4 Liu et al[84] TiO2-VO2 49.0 7.0 Jin et al[72] Three-layer SiNx-VO2-SiNx 40.4 14.5 Long et al[85] Cr2O3-VO2-SiO2 50.0 16.1 Chang et al[86] TiO2-VO2-TiO2 57.6 2.9 Jin et al[69] Multi-layer VO2-fluorescent brightener-organic polymer 78.87 7.34 Gao et al[87] SiNx-NiCrOx-SiNx-VOx-SiNx-NiCrOx-SiNx 40.5 18.4 Zhan et al[88] TiO2-VO2-TiO2-VO2-TiO2 45 12.1 Mlyuka et al[89] HSi-VO2-FSi-P 54.0 16.4 Yao et al[80] Notes: A-B is the multi-layer structure of the lower layer (A) and the upper layer (B); HSi is the antireflective hollow SiO2 layer; FSi is the protective fluorosilane SiO2 layer; P is the antifogging cross-linked poly(vinyl alcohol) and poly(acrylic acid)layer. -
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目的
近年来,关于VO的制备方法、相变机制以及改善热致变色性能的研究取得了显著进展。然而,在实际应用中,VO仍面临一系列挑战,包括较高的本征相变温度()、较低的可见光透过率()、不尽人意的太阳能调制能力()、较差的耐候性以及不美观的棕黄色外观。针对这些问题,国内外研究者开展了大量研究,发现复合结构能够显著改善VO的性能。然而,目前关于VO基复合结构薄膜的综述相对较少。因此,迫切需要对这一领域的最新研究进展进行全面综述。
方法本文综述了VO基复合结构薄膜的制备方法及性能提升策略的研究进展,并最后对智能窗用VO基复合结构薄膜未来的发展方向进行了展望。①本文阐述了VO基智能窗的性能评价指标;②总结了VO纳米颗粒基复合结构的制备方法及其性能提升策略,包括核壳结构和基质材料,核壳结构涵盖无机、有机及无机-有机外壳材料,基质材料则包括变色基质及具有不同微纳结构的基质;③总结了多层结构的制备方法及其性能提升策略,包括缓冲层、减反射层和多功能层;④展望了智能窗用VO基复合结构薄膜的发展前景。
结果通过调节壳层结构、改变VO纳米颗粒的分散基质以及设计多层结构等方式,可以制备具有优异热致变色性能的VO基复合薄膜。①通过将VO纳米颗粒与无机或有机材料形成核壳结构,复合薄膜可获得卓越的热致变色性能和稳定性;②选择有机热致变色材料作为基质的复合薄膜展现了丰富的颜色,而以多孔材料作为基质的复合薄膜则具备减反射效果和高度分散性的VO纳米颗粒,表现出优异的光学性能;③多层结构的设计不仅有助于改善复合薄膜的光学性能,还能赋予其自清洁和防雾等附加功能。
结论随着能源日益枯竭和环境污染问题的日益严峻,迫切需求采取节能减排措施。热致变色智能窗可根据环境温度的变化自动调整太阳光透过率,无能源消耗,因此成为当前研究的焦点。VO基热致变色智能窗的主要研究方向是光学性能和环境耐久性。然而,为了满足实际应用的需求,需要确保各项指标达到应用标准。复合结构在同时改善VO光学性能和稳定性方面优势显著,但现有的VO复合结构较为简单,限制了其综合性能的提升。因此,有必要探索新的制备方法以丰富复合结构,进一步改善VO的综合性能,促进其在智能窗等节能领域的实际应用。
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近年来,关于VO2 制备方法、相变机制以及改善热致变色性能的研究取得了显著进展。然而,在实际应用中,VO2仍面临一系列挑战,包括本征相变温度较高、可见光透过率(Tlum)较低、太阳能调节效率(∆Tsol)不够高、耐候性不佳,以及呈现棕黄色的颜色舒适度较差。针对这些问题,国内外的研究者进行了大量研究,发现复合结构可以显著改善VO2的性能,因此迫切需要对这一领域的最新研究进展进行综述。围绕“智能窗用二氧化钒基复合结构薄膜的制备及研究进展”这一主题,本文涵盖四部分内容:(1)阐述了二氧化钒基智能窗的性能评价指标;(2)总结了二氧化钒纳米颗粒基复合结构的制备方法及其性能提升策略,其中包括核壳结构和二氧化钒纳米颗粒基质材料;(3)总结了多层结构的制备方法及其性能提升策略,其中包括缓冲层,减反射层和多功能层;(4)对智能窗用二氧化钒基复合结构薄膜的发展前景进行了展望。