Research progress in the preparation and application of flame retardant ionic liquids
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摘要:
随着高分子材料科学技术的发展,已被广泛应用的塑料、橡胶等高分子材料因其阻燃性能差,容易引发火灾而受到越来越多的关注。阻燃材料具有耐高温、减少燃烧物产生、降低火焰传播速度和烟雾量的特性,离子液体(Ionic liquids,ILs)由于其高热稳定性和气相阻燃、抑制自由基等反应能力,具有有效抑制火焰蔓延的特性,成为了新型的阻燃材料。因其阴阳离子的结构可调控性、环境友好性等特点,逐渐应用于阻燃领域。简要介绍了离子液体的种类,制备方法以及其阻燃机制,接着围绕离子液体在聚合物、纺织物与电子材料等各种高分子材料中的阻燃应用进行了详细介绍,最后对离子液体在阻燃应用方面的发展做出了展望。
Abstract:With the development of polymer materials science and technology, widely used polymer materials such as plastics and rubber have received increasing attention due to their poor flame retardant performance and susceptibility to fire. Flame retardant materials have the characteristics of high temperature resistance, reduced combustion generation, reduced flame propagation speed and smoke volume. Ionic liquids (ILs) have become a new type of flame retardant material due to their high thermal stability, gas-phase flame retardancy, and ability to suppress free radicals. Due to its controllable structure of anions and cations and environmental friendliness, it has gradually been applied in the field of flame retardancy. This article briefly introduces the types, preparation methods, and flame retardant mechanisms of ionic liquids. Then, a detailed introduction is given on the flame retardant applications of ionic liquids in various polymer materials such as polymers, textiles, and electronic materials. Finally, the development of ionic liquids in flame retardant applications is discussed.
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Keywords:
- ionic liquids /
- flame retardant /
- preparation /
- mechanism /
- polymer materials
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近年来随着工业的快速发展,水污染问题受到越来越多的关注。其中的一部分污染是由抗生素引起的,如阿莫西林、青霉素、四环素等[1-5]。四环素(Tetracycline,TC)作为一种普遍使用的抗生素,因其独特的抗菌作用而被广泛应用于人类疾病的治疗。然而TC长期存在于水环境中难以自然降解,对生态环境和人类健康有很大危害[6-10]。因此,开发一种有效的解决方案来去除水环境中难降解的抗生素是极其重要的。半导体光催化技术因其具有环境友好、无污染、低能耗等优点引起了广泛的研究,成为当今处理有机污染物最有前景的方法之一[11-13]。
在各种光催化剂中,BiOX(X=Cl, Br, I)因其特殊的层状结构、适宜的禁带宽度和较高的稳定性,被广泛用于光降解有机污染物和光催化分解水[14-15]。其中BiOI具有较窄的禁带宽度(1.77~1.92 eV)和较宽的可见光响应范围,但由于光生电子空穴对的高复合率,其光催化性能并不理想。将BiOI与其他半导体材料相结合被认为是增强光催化性能最有前途的策略,2个或2个以上半导体相结合可以形成半导体/半导体异质结,通过提高光生电子空穴对的分离速率从而提高光催化活性。
Bi2O3的带隙介于2.1~2.8 eV之间,由于其具有较强的可见光区响应、无毒、电化学稳定性高、热稳定性好和低成本等特性[16-18],是一种很有前途的可见光光催化候选材料,可与其他半导体材料形成异质结结构。如CdS/BiOCl/Bi2O3[19]、GO/AgI/Bi2O3[20]、α-Bi2O3/g-C3N4[21]、Bi2O3/ZnS[22]等。
Wei等[23]采用一锅沉淀法在多孔Bi2O3纳米棒上成功沉积了BiOI纳米片。结果表明:与原始Bi2O3和BiOI相比,50% Bi2O3/BiOI复合材料具有更高的光生电子空穴对分离效率和更大的比表面积,在可见光照射下,其光催化还原Cr(VI)的活性显著增强。此外,50% Bi2O3/BiOI复合材料还具有优异的光化学稳定性和可回收性。Li等[24]采用化学刻蚀法制备了BiOI/Bi2O3异质结,在降解苯酚和4-氯苯酚(4-CP)方面表现出良好的光催化活性。其光催化性能的提高是由于BiOI/Bi2O3异质结的形成促进了电子空穴对的有效分离,并提出了光生电荷转移的过程。
目前所制备的同类光催化剂大多数用于去除水环境中的重金属离子和有机染料等,对降解抗生素类药物的研究较少。本文采用简单的溶剂热法制备了Bi2O3/BiOI复合光催化材料,在模拟太阳光照射下通过降解四环素研究了其光催化性能,探究了BiOI与Bi2O3不同摩尔比、反应温度、反应时间、pH等条件对光催化性能的影响。并通过活性物种捕捉实验提出了Bi2O3/BiOI复合光催化材料降解四环素可能的机制。
1. 实验材料和方法
1.1 原材料
五水硝酸铋(上海麦克林生化有限公司,AR)、碘化钾(天津市大茂化学试剂厂,AR)、乙二醇(天津市北辰方正试剂厂,AR)、四环素(上海麦克林生化有限公司,AR)。
1.2 实验仪器
EL104型电子天平(梅特勒-托利多有限公司)、HC-3018型高速离心机(安徽中科中佳科学仪器有限公司)、TGL-5A台式离心机(常州润华电器有限公司)、KSW-4D-I2型马弗炉(北京中兴伟业仪器有限公司)、HJ-1型磁力加热搅拌器(红杉实验设备厂)、101-1A型电热鼓风干燥箱(北京中兴伟业仪器有限公司)、721型可见分光光度计(上海仪电分析仪器有限公司)、KQ5200E型超声波清洗器(昆山市超声仪器有限公司)、250 W金卤灯(上海亚明)。
1.3 实验内容
1.3.1 BiOI光催化材料的制备
称取1 mmol五水硝酸铋置于15 mL乙二醇中,超声处理15 min以获得均匀悬浮液。在不断搅拌下向其中逐滴加入10 mL含1 mmol碘化钾的水溶液,继续搅拌2 h。将产物离心,用水和无水乙醇洗涤数次,在80℃下干燥12 h得到红色的BiOI。
1.3.2 Bi2O3光催化材料的制备
称取一定量的五水硝酸铋,在600℃的马弗炉里煅烧4 h,冷却至室温后,将产物研磨成粉末状,得到淡黄色的Bi2O3。
1.3.3 Bi2O3/BiOI复合光催化材料的制备
将1 mmol五水硝酸铋置于15 mL乙二醇中,超声处理15 min以获得均匀悬浮液。在不断搅拌下向其中逐滴加入10 mL含1 mmol碘化钾的水溶液,继续搅拌2 h。在此期间,用1 mol/L的H2SO4溶液将混合液的pH调至5。然后向上述溶液中加入0.8 mmol已制备好的Bi2O3,继续搅拌1 h。将得到的混合溶液转移至50 mL聚四氟乙烯内衬的不锈钢高压反应釜中,在180℃下反应20 h。自然冷却至室温后,将产物离心,用水和无水乙醇洗涤数次,在80℃下干燥12 h,得到Bi2O3/BiOI复合光催化材料。
1.3.4 光催化性能测试
使用250 W金卤灯模拟太阳光照射,通过降解四环素来评价所制备样品的光催化性能。取50 mg制得的光催化材料放入装有100 mL 25 mg/L TC溶液的烧杯中,黑暗搅拌30 min达到吸附-脱附平衡。然后将混合液置于光反应器中,光照开始计时,每隔20 min取3 mL样,将样品放入离心机中离心取其上层清液并测定吸光度。计算四环素的残余率:
η=C/C0×100%=A/A0×100% 式中:C和C0分别表示t时刻和初始四环素的质量浓度(mg·L−1);A和A0分别表示t时刻和初始四环素的吸光度。
2. 结果与讨论
2.1 Bi2O3/BiOI复合光催化材料的晶相结构
BiOI、Bi2O3和Bi2O3/BiOI的XRD图谱如图1所示。BiOI曲线在9.658°、29.645°、31.657°、37.392°、45.666°、51.345°、55.15°、66.344°和74.09°处出现的衍射峰分别对应BiOI(JCPDS 10-0445)的(001)、(102)、(110)、(112)、(104)、(114)、(212)、(214)和(302)晶面。Bi2O3在21.722°、25.757°、27.377°、33.241°、35.406°、37.595°、42.353°、46.305°、52.373°和58.563°处出现的衍射峰分别对应Bi2O3(JCPDS 41-1449)的(020)、(002)、(120)、(200)、(031)、(112)、(122)、(041)、(−321)和(−331)晶面。Bi2O3/BiOI同时出现了Bi2O3和BiOI的主要衍射峰,说明本实验成功制备了Bi2O3/BiOI复合光催化材料。
2.2 Bi2O3/BiOI复合光催化材料的微观形貌
通过SEM分析了所制备光催化材料的微观形貌,结果如图2所示。可以看出,所制备的BiOI是由纳米片自组装形成的花状微球;单一Bi2O3呈现出不同尺寸、不规则的块状结构。从图2(c)可以看出,当BiOI与Bi2O3复合后,块状Bi2O3均匀分散在花状微球的BiOI表面。
2.3 Bi2O3/BiOI复合光催化材料的结构
样品的FTIR图谱如图3所示。499 cm−1和760 cm−1处是BiOI的特征吸收峰,1617 cm−1处的吸收峰对应Bi2O3中Bi—O键的弯曲振动,再次表明BiOI和Bi2O3成功复合在一起。
2.4 Bi2O3/BiOI复合光催化材料的光学性能
利用UV-Vis DRS分析了所制备样品的光学吸收性能,如图4所示。可以看出,纯BiOI的吸收边缘位于681 nm处,纯Bi2O3的吸收边缘位于477 nm,Bi2O3/BiOI复合光催化材料的光吸收边缘位于617 nm。与纯BiOI相比,Bi2O3/BiOI复合光催化材料的光吸收边缘有轻微的蓝移,这是由于与Bi2O3耦合造成的,但其光吸收范围仍然很宽。
不同光催化材料的紫外漫反射(αhv)1/2-hv转换图如图5所示。根据Kubelka-Munk公式,纯BiOI、Bi2O3和Bi2O3/BiOI对应的禁带宽度Eg值分别为1.82 eV、2.60 eV和2.01 eV。
2.5 Bi2O3/BiOI复合光催化材料光生电子空穴对的分离
利用荧光强度来分析光生电子空穴对的复合速率,荧光强度越小,则光生电子复合速率越低,图6为不同光催化材料的荧光光谱。可以看出,在520 nm处,Bi2O3/BiOI的荧光强度低于单一BiOI和Bi2O3,表明复合光催化材料的光生电子空穴对复合速率最低,光催化活性最高。
通过电化学阻抗法研究了不同光催化材料的电荷转移效率,结果如图7所示。Bi2O3/BiOI的圆弧半径小于单一BiOI和Bi2O3,说明其电荷转移电阻较低,电导率增强。电化学阻抗图表明Bi2O3/BiOI能增强光生电子空穴对的电荷转移能力,提高其分离效率,这与荧光分析的结果一致。
2.6 Bi2O3/BiOI复合光催化材料的性能
2.6.1 不同制备条件对光催化性能的影响
通过探究反应物的不同摩尔比、反应温度、反应时间及pH对所制备材料的光催化性能的影响。从图8(a)~8(d)可以看出:当Bi2O3与BiOI的摩尔比为0.8∶1时,在pH=5、180℃下反应20 h得到的Bi2O3/BiOI复合光催化材料对四环素的降解效果最佳,在3 h内对四环素的降解率可达75%。
2.6.2 光催化性能
通过在模拟太阳光照射下降解四环素来评价所制备样品的光催化性能,图9(a)为模拟太阳光照射下降解四环素的曲线图。在3 h内,BiOI、Bi2O3、Bi2O3/BiOI对四环素的降解率分别为55%、57%、75%。图9(b)为模拟太阳光照射下降解四环素的动力学曲线,Bi2O3/BiOI的动力学速率常数(0.007 min−1)分别是BiOI(0.004 min−1)、Bi2O3(0.0045 min−1)的1.75倍、1.56倍。因此,所制备出的Bi2O3/BiOI具有较高的光催化活性。
2.7 Bi2O3/BiOI复合光催化材料降解四环素的机制
使用对苯醌(BQ)、乙二胺四乙酸二钠盐(EDTA-2Na)、异丙醇(IPA)作为·O2−、h+、·OH的捕捉剂,实验结果如图10所示。BiOI对四环素的降解率分别为50%、31%、53%、,由此可以得出h+是BiOI降解四环素的主要活性物质。Bi2O3对四环素的降解率分别为55%、52%、35%,由此可以得出·OH是Bi2O3降解四环素的主要活性物质。
当Bi2O3和BiOI复合后形成Z型异质结时,Bi2O3/BiOI光催化材料对四环素的降解率分别为35%、66%、66%,由此可以得出·O2−是光催化材料降解四环素的主要活性物质。
Bi2O3/BiOI异质结的形成可以提高光生电子空穴对的分离速率,从而提高光催化活性。BiOI 、Bi2O3的导带和价带可以通过下式计算:
ECB=X−Ee−0.5Eg Eg=EVB−ECB 式中:X为半导体的电负性,BiOI和Bi2O3的X值分别为5.94 eV 和6.23 eV;Ee为自由电子在氢标上的能量(约为4.50 eV);Eg为对应的带隙能量,由图3(b)可以得出BiOI和Bi2O3的Eg值分别为1.82 eV和2.60 eV。因此,BiOI和Bi2O3的导带(CB)边缘分别位于0.53 eV和0.43 eV,BiOI和Bi2O3的价带(VB)边缘分别位于2.35 eV和3.03 eV。在可见光照射下所制备的Bi2O3/BiOI异质结被激发并生成光生载流子且BiOI比Bi2O3的CB更正。事实上,在Bi2O3/BiOI异质结中,光子能量会激发BiOI CB上的电子到更高的电位位置(−0.68 eV),因此BiOI CB上的光生电子会转移到Bi2O3的CB上。同时,Bi2O3 VB上的空穴将转移到BiOI的VB上。而Bi2O3 CB上的电子不能与O2反应生成·O2−(O2/·O2−=−0.33 eV),·O2−是降解四环素的主要活性物质,这与捕获实验的结果不一致。结合以上结果,提出了一种更可能的光催化机制,如图11所示。BiOI和Bi2O3在可见光照射下都能产生光生电子空穴对,Bi2O3 CB上的光生电子和BiOI VB上的空穴在库仑力的作用下会重新组合。此外,BiOI的CB上的光生电子可以与O2反应生成·O2−,然后·O2−与TC反应,有效地实现了Bi2O3/BiOI异质结的光催化降解过程。综上所述,Bi2O3/BiOI异质结能够有效提高光生电子空穴对的分离效率,从而显著提高光催化性能。
3. 结 论
(1) 以五水硝酸铋为原料,采用溶剂热法制备了Bi2O3/BiOI复合光催化材料,在制备过程中加入Bi2O3可以提高单一BiOI的光催化性能,在3 h内对四环素的降解率为75%,是单一BiOI降解速率的1.75倍。
(2) BiOI、Bi2O3成功复合在一起并形成了异质结结构,Bi2O3/BiOI复合光催化材料通过提高光生电子空穴对的分离速率从而提高光催化活性。
(3) 降解机制研究表明,·O2−在降解四环素中起主要作用,且所制得的复合材料可应用于对四环素的降解,并有望进一步用于对其他抗生素的降解处理以解决实际问题。
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图 8 EP和EP/1-甲基-3-((6-氧化二苯并[c,e][1,2]氧代磷化氢-6-基)甲基)-1H-咪唑-3-铉-4-甲基苯磺酸盐([Dmim]Tos)的热释放速率(HRR) (a)、总热释放量(THR) (b)、烟雾释放率(SPR) (c)和总烟释放量(TSR) (d)曲线[40]
Figure 8. Heat release rate (HRR) (a), total heat release (THR) (b), smoke production rate (SPR) (c) and total smoke release (TSR) (d) curves of EP and EP/1-methyl-3-((6-oxodibenzo [c,e] [1,2] phosphine-6-yl) methyl)-1H-imidazole-3-xuan-4-methylbenzenesulfonate ([Dmim]Tos)[40]
图 9 棉花(a1)、Cot/环氧氯丙烷修饰芳纶纳米纤维(AEP)/IL (b1)和Cot/AEP/IL/Cu (c1)的数码照片;棉花((a2), (a3))、Cot/AEP/IL ((b2), (b3))和Cot/AEP/IL/Cu ((c2), (c3))的SEM图像;(d) Cot/AEP/IL/Cu的元素映射谱[44]
Figure 9. Digital photos of cotton (a1), Cot/epichlorohydrin-modified aramid nanofibers (AEP)/IL (b1), and Cot/AEP/IL/Cu (c1); SEM images of cotton ((a2), (a3)), surface modified cotton fabric (Cot)/AEP/IL ((b2), (b3)), and Cot/AEP/IL/Cu ((c2), (c3)); (d) Element mapping spectra of Surface modified cotton fabric Cot/AEP/IL/Cu[44]
图 10 (a)不阻燃聚氨酯(R-PU)膜热分解后气体产物的三维红外光谱;(b) 含磷阻燃离子液体聚氨酯(FR-ILPU)膜热分解后气体产物的三维红外光谱;(c) 膜在热降解过程中释放的总气体;(d) FR-ILPU分解后碳层表面位置A的SEM-EDX结果;(e) FR-ILPU分解后内碳层B位的SEM-EDX结果;(f) FR-ILPU膜阻燃机制示意图[47]
Figure 10. (a) 3D-infrared spectra of gas products after the thermal decomposition of non-flame retardant polyurethane (R-PU) membrane; (b) 3D-infrared spectra of gas products after the thermal decomposition of phosphorus-containing flame retardant ionic liquid polyurethane (FR-ILPU) membrane; (c) Total gas release of membranes during the thermal degradation; (d) SEM-EDX result for position A in the surface of carbon layer after the decomposition of FR-ILPU; (e) SEM-EDX result for position B of the inner carbon layer after the decomposition of FR-ILPU; (f) Schematic diagram of the flame retardant mechanism of FR-ILPU membrane[47]
EMPEP—Ethylene glycol methyl phosphonate ethylene glycol propionate; H-NMIm—N-methylimidazole tetrafluoroborate diethylene glycol ether; HDI—Hexamethylene diisocyanate
图 12 (a) 阻燃聚氨酯/碳复合泡沫的制造;(b) IL催化聚氨酯泡沫(PUF)在水存在下形成的合理机制[51]
Figure 12. (a) Fabrication of flame retardant polyurethane/carbon composite foam; (b) Plausible mechanism of IL-catalyzed polyurethane foam (PUF) formation in the presence of water[51]
CB—Carbon black; EGFs—Expandable graphite flakes; FRs—Flame retardant fillers; MDI—Methylene diphenyl diisocyanate; [Bmim]DBP—1-butyl-3-methylimidazolium dibutylphosphate
表 1 阻燃离子液体类型
Table 1 Types of flame retardant ionic liquids
Type Chemical name Structural formula Application Phosphates L-aspartic acid phosphate Polyvinyl alcohol[8] 1, 3-dimethylimidazolium methyl phosphate Cellulose[9] Silicon salts 1-methylimidazole chloropropyl triethoxysilane Cellulose fabric[10] 1-pyridine chloropropyl triethoxysilane salt Cellulose fabric[10] Borates Tetrabutyl tetrafluoroborate phosphate salt Polylactic acid[11] Octyltriphenylphosphine chelated orthoborate Epoxy resin[12] Imidazole salts 1-butyl-3-methylimidazole chloride salt Cellulose[13] 1-ethyl-3-methylimidazole chloride Polyurethane[14] Sulfonates 1-butyl-3-methylimidazolium methanesulfonate Polyamide 6[15] 1-butyl-3-methylimidazolium methanesulfonate Polyamide 6[15] 表 2 不同类型阻燃离子液体参数
Table 2 Parameters of different types of flame retardant ionic liquids
Type Melting point Boiling point Feature Disadvantage Phosphates >150℃ <200℃ High thermal stability, strong solubility, and wide liquid phase range May contain highly toxic phosphorus elements, resulting in higher preparation costs Silicon salts >200℃ <300℃ Low melting point, good electrochemical stability Has high viscosity, which is not conducive to fluidity and mixing Borates >200℃ <250℃ Strong acidity or alkalinity, good solubility May be too acidic or alkaline Imidazole salts <25℃ Around 200℃ High thermal stability and good solubility May have certain toxicity to organisms and high preparation cost Sulfonates >200℃ <300℃ High conductivity and good solubility The high solubility in water may lead to some electrolyte loss issues 表 3 阻燃离子液体在聚合物上的应用
Table 3 Application of flame retardant ionic liquids on polymers
Ionic liquid Polymer matrix Ionic liquid
composite
methodIonic liquid
addition
amount/wt%Flame retardant
effect parameters
(LOI)/%Flame retardant
mechanismRef. L-aspartic acid phosphate PVA Graft 20 30.1 The main
consumption effect[8] 1-(3-triethoxysilylpropyl)-3-
methylimidazolium chlorideHigh density
polyethylene (HDPE)Blending 1 27.6 The main
carbonization effect[38] 1-ethyl-3-(diethoxyphosphoryl)-
propylimidazolium bromidePolyurethane
elastomer (IFR/TPU)Blending 10 30.1 The main
carbonization effect[39] 1-methyl-3-((6-
oxidodibenzo[c,e][1,2]oxaphosphinin-
6-yl)methyl)-1H-imidazol-3-ium 4-
methylbenzenesulfonateEP Blending 4 32.5 The main
consumption effect[40] 1-methylimidazole-3-
bromopropylamine hydrobromideEP Blending 3 29.8 The main
consumption effect[41] Note: LOI—Limiting oxygen index. 表 4 阻燃离子液体在纺织品上的应用
Table 4 Application of flame retardant ionic liquids in textiles
Ionic liquid Polymer matrix Ionic liquid
composite
methodIonic liquid
addition
amount/wt%Flame retardant
effect parameters
(LOI)/%Flame retardant
mechanismRef. Hexafluorophosphate
N-hexylpyridiniumPolyacrylate (PA),
polyurethane (PU),
and latexBlending 2 29.3 The main
carbonization effect[43] 1-aminopropyl-3-
methylimidazolium
hexafluorophosphateCotton fabric Graft 5 28.5 The main
carbonization effect[44] 1, 3-dimethylimidazolium
methylphosphonate
1-ethyl-3-methylimidazolium
methylphosphonateCellulose Graft 5 32.5 The main
carbonization effect[9] 表 5 阻燃离子液体在电子材料上的应用
Table 5 Application of flame retardant ionic liquids in electronic materials
Ionic liquid Polymer matrix Ionic liquid composite method Ionic liquid addition amount/wt% Flame retardant effect parameters (LOI)/% Flame retardant mechanism Ref. N-methylimidazole tetrafluoroborate diethylene glycol ether PU Graft 15 32.3 The main consumption effect [47] 1-butyl-3-menthylimidazolium-hexafluorophosphate Commercial organic electrolytes Blending 5 30.2 The main consumption effect [48] POSS-imidazoli ionic liquids Polyionic liquid Copolymerization 2 33.5 The main consumption effect [49] Note: POSS—Polyhedral oligomeric silsesquioxanes. 表 6 阻燃离子液体在其他材料上的应用
Table 6 Application of flame retardant ionic liquids on other materials
Ionic liquid Polymer matrix Ionic liquid composite
methodIonic liquid addition
amount/wt%Flame retardant effect parameters (LOI)/% Flame retardant mechanism Ref. 1-butyl-3-methylimidazole hexasodium fluorophosphate EP Graft 15 37 The main carbonization effect [50] 1-butyl-3-methylimidazolium dibutylphosphate PUF Blending 4.9 30.4 The main carbonization effect [51] Tetrabutylphosphonium tetrafluoroborate Raw lacquer Blending 10 28.6 The main consumption effect [52] -
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研究背景
大多数高分子材料容易燃烧,可能引发火灾,从而导致人员伤亡和经济损失。早期使用的卤系阻燃剂等在防火过程中会释放大量烟雾以及腐蚀性、有毒有害的卤化氢气体,不再满足发展需求。离子液体具有不可燃性、非挥发性、良好的化学稳定性和热稳定性、可循环利用及对环境友好的特性,有望成为新型高效阻燃剂或协效剂。
种类离子液体种类很多,但并非所有离子液体都具有阻燃性能。目前常用的阻燃离子液体按照所含盐种类划分,主要有磷酸盐类、硅盐类、硼酸盐类、咪唑盐类和磺酸盐类。
制备(1)直接合成法:包括了常规离子液体的一步、两步合成法,通过控制材料的配比、反应条件、设备及反应辅助装置,利用加成反应、酸碱中和反应等原理,制备出具有阻燃性能的新型离子液体。(2)改性法:对离子液体进行结构或性质上的调整,通过引入特定的功能基团、改变其离子组成等方式,使得阻燃分子结构嵌入到离子液体中,以改善其阻燃性能或满足特定的阻燃需求。(3)插层法:使阻燃剂与离子液体分子以层状分布,形成阻燃离子液体复合物,阻燃剂与离子液体之间的配合有利于阻燃效果的提升,可以实现阻燃性能的调控。(4)计算机辅助设计: 通过计算机辅助设计来预测离子液体性质,进而确定所需的阻燃离子液体。
机制(1)消耗作用:阻燃离子液体中的分子在高温下与材料或燃烧产物中的自由基等活性物质反应,消耗这些物质同时放出不燃性气体使得火焰衰竭,减缓火焰传播速度。(2)炭化作用:阻燃离子液体中的分子在高温下单独或与材料分子协同反应生成炭质物,这些炭质物可以在材料表面形成一层炭化层,隔绝空气,从而阻止火焰的进一步传播。
应用(1) 阻燃离子液体在聚合物中的应用:聚合物分子具有相对较低的熔点和燃点,当受到热源的作用时容易软化或燃烧。阻燃离子液体在聚合物材料中的研究发展趋势主要集中在提高阻燃效果、改善材料性能和实现绿色发展上。然而,其在工程应用中存在成本较高、加工难度大以及长期耐久性等方面的问题。(2)离子液体在纺织品阻燃中的应用:离子液体凭借高热稳定性、不挥发性,不易燃性等独特理化性质以及高温下排放降解产物的吸热效应,减少有害化学物质的排放的同时,提高了纺织品的阻燃性,可以有效减少消防事故,更好地保障医疗、餐饮工作的安全。目前,耐久性和成本较高的问题阻碍了阻燃离子液体应用。(3)离子液体在电子材料阻燃中的应用:电池遇到安全隐患着火时,会释放出大量的热量和有毒的烟雾,可以在短时间内导致死亡。而离子液体具有电化学稳定性强、阻燃和离子电导率高等优点。其研究发展趋势朝着提高其安全性和稳定性的方向不断深入。然而,其导电性、充放电性能等方面仍存在短板,需要进一步研究和解决。 (4) 离子液体在其他材料阻燃中的应用:离子液体作为一种新型阻燃剂,在其他材料如纳米材料、生漆等中的应用不断增多。但大多数研究仍集中在实验室规模,缺乏工程应用中的实际验证,需要针对工程应用的性能评价和应用推广研究。
结语通过引入阻燃离子液体,高分子材料的化学稳定性及防火性能等得到有效提升,对现阶段研究发现的问题及未来研究方向分析如下:目前所用离子液体自身成本较高,合成方法复杂,生产工艺尚不成熟,还可能改变材料的透明度,不易成型,使其应用受到影响。存在着工程应用验证不足、长期稳定性欠佳等短板还难以运用到实际的工业生产中。因此,探究以绿色、可循环、无毒害原材料为基础的阻燃离子液体高效制备;推进阻燃离子液体与其他材料复合改性的研究;研发多功能阻燃离子液体。