MOF基的光解水制氢催化剂研究进展

陈柏瑜; 胡天丁; 陕绍云; 支云飞; 张楚茹; 吴琪

doi:10.13801/j.cnki.fhclxb.20211011.001

MOF基的光解水制氢催化剂研究进展

昆明理工大学化学工程学院，昆明 650500

基金项目: 国家自然科学基金 (21766016)；云南省“万人计划”基金 (YNWR-QNBJ-2018-198)；昆明市科学技术局科技计划基金 (2019-1-G-25318000003480)；倪永浩院士工作站 (2019IC002)；云南省基础研究计划青年项目 (202001AU070023)；昆明市科学技术局科技创新要素聚集计划重点项目 (2019-1-A-24657)；云南省科技厅重大科技专项计划 (202002AB080002)

详细信息

通讯作者:
胡天丁，博士，副教授，硕士生导师，研究方向为金属-有机框架材料（MOFs）的合成与催化反应机理的DFT计算研究　E-mail: teddyhu1991@163.com

陕绍云，博士，教授，博士生导师，研究方向为多孔环保材料 E-mail：shansy411@163.com

中图分类号: TQ032
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出版历程
- 收稿日期: 2021-08-18
- 修回日期: 2021-09-18
- 录用日期: 2021-09-26
- 网络出版日期: 2021-10-17
- 刊出日期: 2022-03-22

Research advances of MOF-based catalyst for photohydrolysis for hydrogen production

Faculty of Chemical Engineering, Kunming University of Science and Technology, Kunming 650500, China

摘要

摘要: 随着能源枯竭和环境污染问题日益严重，人们不得不将目光转向更加清洁环保的氢能源。光解水制氢技术是一种获取氢能源经济且清洁的理想方式，通过光催化手段将太阳能转化为化学能也是一种很有前景的技术手段。然而如何选取高效、经济的光催化剂是制氢最关键的环节。金属-有机框架(Metal-organic frameworks, MOFs)由于比表面积大、孔尺寸可调节、结构易于修饰及活性位点丰富等特点，使其成为光解水制氢理想的光催化剂候选材料。国内外学者就MOFs光解水制氢开展了大量的研究，并且取得了丰硕的成果。本论文综述了MOF基材料作为催化剂在光解水制氢领域的研究进展，总结了MOFs作为催化剂的优点和局限性，并对MOFs及其相关材料在光催化水解制氢领域的发展前景提出展望，以期对未来研究提供参考。
- 金属-有机框架 /
- 光催化 /
- 催化剂 /
- 水解 /
- 制氢
Abstract: The increasingly serious energy exhaustion and environmental pollution accelerates the development of clean hydrogen energy. Water splitting via photocatalysis technology provides an economical and clean way for the hydrogen production, converting solar energy into chemical energy through photocatalytic means is also a promising technical means. The rational selection of photocatalyst is the critical step for obtaining hydrogen energy in an efficient and economical way. Featuring the traits of large specific surface area, adjustable pore size, easy structure modification and abundant active sites, metal-organic frameworks (MOFs) are ideal candidates for photocatalytic hydrogen production scientists from domestic and foreign have carried out numerous researches on the water splitting with MOF-based photocatalysts. Currently, fruitful progresses have been achieved. In this paper, the state-of-the-art advances for the MOF-based materials as catalysts in the field of hydrogen production from splitting water was reviewed, and the advantages and limitations of MOFs as catalysts were summarized. The development prospect of MOFs and related materials in the field of photocatalytic hydrogen production was proposed, providing a valuable guideline for developing future photocatalysts.
- metal-organic frameworks /
- photocatalysis /
- catalyst /
- water splitting /
- hydrogen production

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木材因其优良的力学性能、低廉的成本和独特的美学特性，在建筑和装饰材料领域被广泛应用^[1-3]。然而，木材固有的可燃性限制了其在消防安全要求高的领域的实际应用，尤其是在人口密集的公共区域。因此，对木材进行阻燃处理，是有效提高木材防火安全性和避免潜在的火灾危害的措施之一^[4-5]。

水凝胶具备富水的性质和保水的能力，其中所含有的水分具有较高的摩尔热容量和蒸发焓^[6]。因此，水凝胶作为一道新屏障，在受热时通过水的蒸发可吸收大量的热，降低基体表面温度，稀释可燃气体，延缓材料的热降解，从而抑制火灾^[7-8]。此外，水凝胶在分解过程中不释放有毒挥发物，对人体健康和环境均无危害，是一种极具发展前景的绿色木材阻燃涂料。Zhang等^[9]使用明胶、壳聚糖(CS)和甘油制备出了木材阻燃涂层；结果表明，涂覆涂层的木材的点燃时间(TTI)增加了6倍，峰值热释放速率(pHRR)降低了24.0%，总热释放量(THR)降低了17.2%，与未涂覆涂层的木材相比，具有更长的耐火时间和快速的自熄性。Zhao等^[10]制备出一种聚乙烯醇(PVA)/植酸(PA)水凝胶涂层，并通过冻融循环法来提高木材的阻燃性能；结果表明，与纯PVA水凝胶涂层相比，所获PVA/PA水凝胶涂层具有更好的粘附性能和防火性能。

对于阻燃涂层而言，有效的防火时间和基体材料的保护程度是衡量其阻燃性能的重要指标。而将水凝胶作为复合涂层应用于木材上，能延缓木材的点燃时间，从而延长火灾中的逃生时间；但单独使用而不添加其他阻燃剂时，其抑烟性能较差。此外，大多数水凝胶均由有机聚合物聚合而成，在受热水分蒸发后易被烧毁，且高温下只能保持约30 s的完好^[11]。增加水凝胶涂层厚度是一种有效的基体材料保护手段，但其重量会随之大幅度增加，降低其实际应用效果；因此，延长有效的防火时间和增加水凝胶网络的保护程度是优化水凝胶涂层阻燃性能的发展方向^[12]。

添加阻燃剂是一种提高水凝胶阻燃性能的有效手段。次磷酸铝(AHP)是公认的高效无卤阻燃剂之一^[13]，因其优良的阻燃性被广泛应用于聚合物材料的阻燃。Yuan等^[14]以PVA和AHP为原料，采用溶剂共混法制备复合材料，当AHP负载量为15wt%时，复合材料的极限氧指数(LOI)达到28%，阻燃等级达到UL-94中的V-0级。但AHP的高负载量会对涂层的物理性能造成较大的负面影响，通常采用添加协同剂、表面改性和微胶囊等方法解决此问题^[15-17]；其中，添加协同剂是一种简单高效的手段。Zhou等^[18]将AHP与热塑性聚氨酯(PT)共混制备阻燃材料，锥形量热测试结果表明，当AHP为22.5wt%，PT为2.5wt%时，pHRR、THR和总烟释放量(TSR)分别降低了91.2%、70%和63%。Yang等^[19]探究了碳纳米管(m-CNT)和AHP对聚乳酸(PLA)/玄武岩(BF)的阻燃效果的影响；结果表明，含有19wt% AHP和1wt% m-CNT的PLA/BF在UL-94测试中达到了V-0级，LOI为31%，且与纯PLA/BF相比，pHRR和THR分别降低了约64%和27%，说明AHP和m-CNT显著提高了PLA/BF的阻燃性能。

玄武岩岩石在生产过程中会产生纤维和粉末等玄武岩填料^[20]，这是一种天然的、以矿物为基础的无机质硬填料，主要化学成分为43%~48%的SiO₂、11%~12%的Al₂O₃、5%的Fe₂O₃、0%~5%的MgO等^[21]；根据以往的研究，SiO₂和金属氧化物可作为增效剂，来提高聚合物材料的阻燃和抑烟性能。此外，我国玄武岩储量丰富，质量好，作为阻燃填料具有很好的前景^[22]。然而，由于玄武岩表面活性低，分散性能差，作为阻燃填料直接使用时无法实现其高值化利用；故需对玄武岩进行改性处理，以提高其阻燃性能。

本文采用PVA和CS作为水凝胶基质，PVA可增强凝胶网络结构，以提高阻燃涂层与木材的结合强度，CS复配乙酸可形成膨胀型阻燃剂，AHP加入其中以进一步提高其阻燃性，此外，改性玄武岩和植酸金属盐分别作为阻燃填料和促炭剂，起到凝聚相阻燃作用，由此形成了气相/凝聚相阻燃体系，并对该复合阻燃体系对木材阻燃性能的影响进行了研究。通过SEM观察表面改性和沉淀法改性后玄武岩的形貌变化，采用FTIR分析其化学结构变化。利用UL-94阻燃等级标准和锥形量热(CONE)测试水凝胶复合阻燃涂层的阻燃性能；通过TGA测试对涂层的热稳定性进行研究；并测试了具有涂层木材的物理力学性能。

1. 实验部分

1.1 原材料

壳聚糖：粉料，脱乙酰度90%，上海源叶生物科技有限公司；聚乙烯醇：1788型，粉料，醇解度88%，聚合度1700，西陇科学股份有限公司；玄武岩：粉料，粒径 6000目，天津硅酸盐研究所；植酸钠：分析纯，国药集团化学试剂有限公司；乙酸：分析纯，天津市科密欧化学试剂有限公司；乙酸镍(C₄H₆O₄Ni·4H₂O)：分析纯，西陇科学股份有限公司；氢氧化钠(NaOH)：分析纯，西陇科学股份有限公司；乙酸锌(C₄H₆ZnO₄·2H₂O)：分析纯，天津市风船化学试剂科技有限公司；乙酸铝(Al(OH)₂·(CH₃COO))：分析纯，上海麦克林生化科技有限公司；次磷酸铝(Al(H₂PO₂)₃)：分析纯，上海麦克林生化科技有限公司；硅烷偶联剂(KH550)：山东优索化工科技有限公司。

1.2 实验过程

1.2.1 改性玄武岩的制备

(1) NaOH蚀刻处理：将玄武岩鳞片(30 g)放在1000 mL的锥形瓶中，并加入900 mL的氢氧化钠溶液(4 mol·L⁻¹)，在100℃的水浴锅中磁力搅拌2 h，然后将玄武岩鳞片进行过滤、清洗(直至溶液pH=7.0)和干燥(105℃，24 h)。

(2) KH550接枝处理：将上一步处理后的10 g玄武岩、1 g KH550和800 mL去离子水置于1000 mL锥形瓶中，在80℃水浴锅中磁力搅拌3 h后，将玄武岩鳞片进行过滤、清洗(直至溶液pH=7.0)和干燥(105℃，24 h)。

(3)共沉淀法改性阻燃剂：将上一步改性处理的5 g玄武岩鳞片、9.24 g植酸钠(0.01 mol)和800 mL去离子水置于1000 mL锥形瓶中，并在80℃水浴锅中磁力搅拌1 h，最后加入0.03 mol的乙酸镍、乙酸铝或乙酸锌，继续反应2 h，然后将改性后的玄武岩鳞片进行过滤、清洗(直至溶液pH=7.0)和干燥(105℃，24 h)，得到不同物质改性的阻燃玄武岩鳞片(BS-PA-Ni、BS-PA-Al、BS-PA-Zn)。图1为改性玄武岩的制备工艺流程。

图 1 改性玄武岩(BS)的制备工艺

Figure 1. Preparation process of modified basalt (BS)

PA—Phytic acid

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1.2.2 复合水凝胶阻燃涂层的制备

将4 g CS和4 g PVA溶于92 g醋酸水溶液(3%，v/v)中，在98℃下以200 r/min搅拌直至CS和PVA完全溶解。待CS/PVA溶液冷却至室温(25℃)后，分别加入3wt%的AHP和7wt%的BS (在该比例下，BS与AHP不容易发生团聚，分散效果最佳)，以1500 r/min的转速分散5 min，得到其水凝胶前驱体复合溶液。然后将不同组分的前驱体溶液涂覆于木材表面，制成厚度约为300 μm的水凝胶复合阻燃涂层。最后将所制备的样品在−20℃的冰箱中冷冻12 h。所有样品的组成列于表1中，Control为未添加AHP和BS的复合水凝胶涂层。

表 1 水凝胶阻燃涂料配方

Table 1. Hydrogel flame retardant coating formula

Sample	Hydrogel/wt%	AHP/wt%	Modified BS/wt%
Control	100	0	0
BS-PA-Al	90	3	7
BS-PA-Ni	90	3	7
BS-PA-Zn	90	3	7
Notes: Hydrogel—The amount of hydrogel in the composite coating; AHP—The amount of aluminum hypophosphite in the composite coating; Modified BS—The amount of modified basalt in the composite coating.

下载: 导出CSV

| 显示表格

1.3 测试与表征

采用配备了能量色散X射线分析装置(EDX)的Prisma型扫描电子显微镜(SEM，美国FEI公司)观察样品的微观形貌变化和元素的分布，测试时，对所有样品进行喷铂处理增加导电性，测量电压为20 kV。

采用ALPHA03040404型傅里叶红外光谱仪(FTIR，美国BRUKER公司)测试样品的化学结构变化，样品用溴化钾(KBr)压片法制得，扫描范围为400~4000 cm⁻¹。

在N₂条件下，使用PYris603190148型热重分析仪(TGA，美国PE公司)，在室温到800℃的温度下以10℃/min的线性加热速率对复合材料的热降解行为进行测试，所有样品的质量都保持在5~10 mg以内。

锥形量热(CONE)测试在FTT007型锥形量热计(英国FTT公司)上进行，热通量为50 kW/m²，样品尺寸为100 mm×100 mm×5 mm。

根据GB/T 2408—2008测试标准^[23]，在FTT 0082型仪器(英国FTT公司)上进行UL-94测试来确定复合材料的可燃性试验，试验用试样尺寸为125 mm×13 mm×3 mm。

力学性能粘附试验的样品尺寸根据文献^[24]确定，接触面积为13 mm×20 mm，并对尺寸为125 mm×13 mm×3 mm的涂层样品进行了应力-应变曲线分析。

2. 结果与讨论

2.1 改性玄武岩/水凝胶复合材料微观形貌分析

图2为所制备样品的SEM图像和EDX图像。由于玄武岩鳞片约由50%的SiO₂组成，因此在图2(a)中可以观察到，样品BS的表面较为光滑，这不利于填料与材料之间的结合。在图2(b)中，经NaOH蚀刻后的玄武岩较未改性的具有更粗糙的表面，说明在NaOH蚀刻过程中，溶液中的OH⁻通过微小孔隙进入到玄武岩中，破坏了Si—O—Si键和Si—O—Al键，使得硅铝酸盐网格开始溶解，导致孔隙扩大^[25]。而图2(c)、图2(e)和图2(g)则分别展示了BS-PA-Al、BS-PA-Ni和BS-PA-Zn的微观形貌，可以观察到，被蚀刻后的玄武岩鳞片经KH550接枝和植酸金属盐沉积后，表面变得更加粗糙，且从图2(d)、图2(f)和图2(h)右上角的EDX能谱图中可以看出，Al、Ni和Zn元素均匀分布在玄武岩表面，说明植酸铝、植酸镍和植酸锌的成功沉积，有利于阻燃效果的进一步改善。

图 2 样品的SEM图像：(a) BS；(b) NaOH蚀刻后的BS；(c) BS-PA-Al；(d) BS-PA-Al的EDX能谱图；(e) BS-PA-Ni；(f) BS-PA-Ni的EDX能谱图；(g) BS-PA-Zn；(h) BS-PA-Zn的EDX能谱图

Figure 2. SEM images of samples: (a) Unmodified basalt; (b) NaOH etched basalt; (c) BS-PA-Al; (d) Element distribution of BS-PA-Al; (e) BS-PA-Ni; (f) Element distribution of BS-PA-Ni; (g) BS-PA-Zn; (h) Element distribution of BS-PA-Zn

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2.2 改性玄武岩/水凝胶复合材料化学结构分析

图3为BS、BS-KH550、BS-PA-Al、BS-PA-Ni和BS-PA-Zn的红外吸收光谱图。从图中可知，在850~1284 cm⁻¹出现较强的吸收峰，归属于Si—O—Si的对称与不对称拉伸振动。相比于BS，BS-KH550、BS-PA-Al、BS-PA-Ni和BS-PA-Zn在3554 cm⁻¹处的—OH吸收峰均有所增强，说明经NaOH蚀刻后的玄武岩暴露出更多的—OH，增加了化学反应位点，使得表面更易发生化学修饰；而在1646 cm⁻¹出现的—NH的吸收峰则证明KH550成功接枝到玄武岩表面^[26]。此外，对于BS-PA-Al、BS-PA-Ni和BS-PA-Zn，在1063 cm⁻¹出现了P—O的振动吸收峰，进一步证明了植酸铝、植酸镍、植酸锌成功沉积在玄武岩表面^[27]。此外，在1075~1125 cm⁻¹处出现了较弱的吸收峰，可归属于O=P的伸缩振动峰，但由于该峰与Si—O—Si的吸收峰部分重叠，导致该峰在图谱中不易被观察到。

图 3 改性玄武岩的FTIR图谱

Figure 3. FTIR spectra of modified basalt

KH550—γ-aminopropyl triethoxysilane

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2.3 改性玄武岩/水凝胶复合材料热稳定性分析

利用热重分析(TGA)和热重微分(DTG)曲线来讨论复合涂层的降解过程，相关数据如表2所示。如图4(a)所示，未添加AHP和BS的复合水凝胶涂层(Control)的分解可分为3个阶段：第一阶段(40~170℃)，由于Control组水凝胶复合涂层富含较多的水，因此主要是PVA和CS的脱水过程(释放吸附水)；第二阶段(200~390℃)，由于PVA是多羟基聚合物，且在分子链中保留了大量乙酸基团，在此阶段，残余的乙酸基团分解，CS大分子发生主链断裂和开环反应；第三阶段(400~750℃)，水凝胶阻燃涂层完全降解后无碳残渣的PVA链裂解发生环化反应、CS的主链断裂和开环反应^[28]。对于添加了AHP和改性玄武岩的水凝胶涂层，第一阶段的分解过程与Control组相似，第二阶段的分解主要是PVA、CS和AHP的分解，而在第三阶段中，由于第二阶段AHP的分解催化作用^[14]，使得涂层的热稳定性提高，此阶段最大热失重速率的温度较Control组后移约45~150℃。在分解过程中，玄武岩表面沉积的植酸金属离子可同时作为树脂交联和脱氢反应的催化剂，既能增加膨胀阻燃剂在高温下的交联程度，也能促进炭的形成，提高复合材料的热稳定性，达到更好的阻燃效果^[29]。此外，结合图4(b)和表2的TGA测试数据可得，BS-PA-Al、BS-PA-Ni和BS-PA-Zn涂层的残炭率分别为22.4%、27.3%和20.8%，相较于Control组涂层的3.12%均有所增加，其中BS-PA-Ni组涂层的残炭率达到了27.3%，说明改性玄武岩和添加AHP后能有效防止涂层降解，提高其热稳定性。

表 2 复合涂料的主要TGA数据

Table 2. Main TGA data of composite coatings

Sample	T_10%/℃	T_50%/℃	Residue/%
Control	164.36	327.91	3.12
BS-PA-Al	129.07	339.87	22.4
BS-PA-Ni	123.64	382.43	27.3
BS-PA-Zn	116.88	351.55	20.8
Notes: T_10%—Temperature at 10% mass loss; T_50%—Temperature at 50% mass loss; Residue—Residual carbon content.

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图 4 水凝胶阻燃涂料热重曲线：(a)热重曲线；(b)热重微分曲线

Figure 4. Thermogravimetric curves of hydrogel flame retardant coating: (a) TG; (b) DTG

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2.4 复合涂层/木材的阻燃性能

(1)锥形量热测试

为了更好地了解涂层的阻燃效果，将水凝胶涂层涂覆于木材表面，对样品进行阻燃效果测试，CONE的主要燃烧参数如表3所示，未涂覆涂层的木材(Pure wood)的点燃时间(TTI)为12 s，而水凝胶涂层木材(Control、BS-PA-Al、BS-PA-Ni、BS-PA-Zn)较Pure wood的TTI分别增加了292%、83%、125%和75%，这表明水凝胶阻燃复合涂层能有效提高木材的消防安全，TTI的延长对火灾救援具有重要意义。此外，从表3中可以观察到，BS-PA-Ni(dry)水凝胶涂层木材的TTI仍比未涂覆涂层的木材的长，表明失水后的水凝胶涂层仍具有阻燃性能。图5(a)和图5(b)为样品的HRR和THR变化曲线，水凝胶阻燃涂层木材的HRR和THR较未涂覆涂层木材明显降低；HRR曲线出现两个峰值：第一个峰值是由于水凝胶阻燃涂层降解释放可燃气体；第二个峰值是由于木材的涂层烧焦后，表面炭层裂解，可燃气体从裂缝中挥发，使得木材燃烧加剧，而涂覆水凝胶涂层的木材则延缓了第二峰值的出现。此外，从表3可得，Control、BS-PA-Al、BS-PA-Ni和BS-PA-Zn水凝胶涂层木材的pHRR较未涂覆涂层的木材分别降低48.6%、63.6%、64.2%和58.0%，THR分别降低18.9%、24.1%、32.7%和19.8%，说明改性玄武岩/水凝胶复合涂层对木材阻燃的改善效果较为显著。结合图5(c)、图5(d)和表3可知，BS-PA-Al、BS-PA-Ni和BS-PA-Zn水凝胶涂层木材的TSR较未涂覆涂层木材分别降低55.3%、51.3%和31.2%，而Control水凝胶涂层在燃烧时的TSR较未涂覆涂层的木材有所增加，这是由于该水凝胶阻燃涂层在物理和化学方面共同起到阻燃作用：首先水凝胶的高含水量能够吸收部分热量和稀释可燃气体，随着温度的升高，AHP分解产生的PO•和HPO•与燃烧过程中产生的自由基进行反应、终端燃烧链支化反应，达到阻燃效果；除此之外，玄武岩表面沉积的植酸金属离子亦能同时作为树脂交联和脱氢反应的催化剂，提高膨胀阻燃剂在高温下的交联程度以及促进炭的形成，而BS的存在也增加了炭层的致密性，使得热稳定性有了明显的提升，从而达到了更好的阻燃效果。其中BS-PA-Ni阻燃涂层的效果最佳，这可能是由于Ni⁺的催化性能最佳，在催化成炭，提高炭层的质量方面优于Al³⁺和Zn^2+[30]。

表 3 水凝胶阻燃涂料锥形量热主要数据

Table 3. Hydrogel flame retardant CONE main data

Sample	TTI/s	pHRR/ (kW·m⁻²)	THR/ (MJ·m⁻²)	TSR/ m²
Pure wood	12	572.90	44.17	1.99
Control	47	294.50	35.80	2.91
BS-PA-Al	22	210.51	33.51	0.89
BS-PA-Ni	27	205.38	29.74	0.97
BS-PA-Zn	21	240.68	35.44	1.37
BS-PA-Ni(dry)	17	397.90	39.14	3.16
Notes: TTI—Time to ignition of wood; pHRR—Peak heat release rate; THR—Total heat release; TSR—Total smoke release.

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图 5 水凝胶阻燃涂料的热释放速率(HRR) (a)、总热释放量(THR) (b)、产烟速率(SPR) (c)以及总烟释放量(TSR)(d)

Figure 5. Heat releaserate (HRR) (a), THR (b), smoke production rate (SPR) (c) and TSR (d) of hydrogel flame retardant coating

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(2)垂直燃烧测试

采用UL-94进一步验证水凝胶涂层木材的阻燃性能，相关数据列于表4。由表可知，未涂覆涂层的木材在被点燃后完全燃烧，而BS-PA-Al和BS-PA-Ni水凝胶涂层木材的UL-94等级达到V-0级，Control和BS-PA-Zn水凝胶涂层木材达到V-1级。其中BS-PA-Al和BS-PA-Ni水凝胶涂层木材在第一个和第二个10 s均未被点燃，且Control和BS-PA-Zn水凝胶涂层木材在点燃后也会在较短时间内熄灭，说明水凝胶阻燃涂层可赋予木材优异自熄性能和阻燃性能，其中BS-PA-Al和BS-PA-Ni水凝胶涂层木材的性能最佳。

表 4 水凝胶阻燃涂料的垂直燃烧数据

Table 4. Vertical combustion data of hydrogel flame retardant coating

Sample	T₁/s	T₂/s	UL-94	Dripping or not
Pure wood	—	—	NR	Yes
Control	2	21	V-1	No
BS-PA-Al	0	0	V-0	No
BS-PA-Ni	0	0	V-0	No
BS-PA-Zn	3	13	V-1	No
Notes: T₁—The first fire of wood; T₂—The second fire of wood; UL-94—UL-94 combustion rating of wood; Dripping or not—Whether the coating drips during wood burning.

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2.5 复合涂层/木材的力学性能

为了研究水凝胶阻燃涂层对木材力学性能的影响，对涂覆水凝胶阻燃涂层和未涂覆的木材进行拉伸实验对比，由图6(a)可知，未涂覆涂层的木材、Control、BS-PA-Al、BS-PA-Ni和BS-PA-Zn水凝胶阻燃涂层木材的抗拉强度分别为64.7、56.0、53.2、80.4和62.2 MPa，说明经过涂覆水凝胶阻燃涂层的木材与未涂覆涂层的木材的抗拉强度变化不大，对木材的力学性能影响较小。此外，涂层与基体材料的附着力是衡量涂层阻燃效果有否优异的一个重要指标，按照图6(b)所示的方案进行拉伸附着力测试，结果表明，Control、BS-PA-Al、BS-PA-Ni和BS-PA-Zn水凝胶阻燃涂层与木材之间的粘附力分别为5.0、1.4、3.4和2.0 MPa，说明AHP和改性BS的添加降低了水凝胶涂层与木材间的附着力，这是由于木材表面具有管孔结构，水凝胶涂层可渗透到木材表面，固化后在木材内部形成了凝胶网络互锁结构；此外，由于水凝胶涂层的成膜物质PVA和CS富含羟基，因此也能通过氢键与木材表面的羟基结合，来增加木材与水凝胶阻燃涂层间的附着力。

图 6 水凝胶阻燃涂料的力学性能：未涂覆和涂覆木材的抗拉强度(a)、涂层附着力测试图(b)

Figure 6. Mechanical properties of hydrogel flame retardant coating: Tensile strength (a) and coating adhesion test diagram (b) of uncoated and coated wood

F—Force

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2.6 改性玄武岩/水凝胶复合涂层的阻燃机制

图7解释了水凝胶阻燃涂层的阻燃机制，该涂层由气相和凝聚相阻燃共同作用。当涂覆该涂层的木材受热时，由于CS中含有—NH₂，可在高温下热分解生成NH₃等不可燃气体，降低燃烧气体浓度。CS与乙酸进行复配后，构成的膨胀型阻燃体系能够初步起到催化成炭的作用，在木材表面形成炭层，保护木材内部不被燃烧。此外，由于水凝胶丰富的含水量，涂层内部的水首先被加热蒸发，吸收大部分热量，降低了木材表面温度，同时蒸发的水蒸气稀释样品周围的空气。当温度达到约290℃时，其含有的AHP开始分解，在该过程中会产生化学稳定性高的HPO和PO•自由基，以及化学性质活泼的H•和HO•自由基，PO•可以捕获H•和HO•自由基，减缓或终止自由基氧化反应的发生，达到良好的阻燃效果。此外，AHP会分解生成不可燃的磷酸盐固体物质如AlPO₄、Al(H₂PO₄)₃等，这些物质可以隔绝可燃气体和助燃气体的进入，起到保护木材的作用，且生成的H₃PO₄也能够起到催化成炭作用，使得聚乙烯醇和壳聚糖的脱氢交联反应，进一步生成更加紧密的炭层。化学反应过程如方程式(1)~(3)所示。

图 7 水凝胶阻燃涂料的阻燃机制

Figure 7. Hydrogel flame retardant coating flame retardant mechanism diagram

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$\mathrm{Al}\left(\mathrm{H}_2 \mathrm{PO}_2\right)_3 \rightarrow \mathrm{AlPO}_4+2 \mathrm{PH}_3 \uparrow+\mathrm{O}_2 \uparrow$

(1)

$\mathrm{Al}\left(\mathrm{H}_2 \mathrm{PO}_2\right)_3 \rightarrow \mathrm{Al}\left(\mathrm{H}_2 \mathrm{PO}_4\right)_3+6 \mathrm{PH}_3 \uparrow+3 \mathrm{H}_2 \mathrm{O} \uparrow$

(2)

$\mathrm{PH}_3 \uparrow+2 \mathrm{O}_2 \uparrow \rightarrow \mathrm{H}_3 \mathrm{PO}_4$

(3)

除此之外，BS表面沉积的植酸金属络合物作为树脂交联和脱氢反应的催化剂，有助于提高复合材料的热稳定性、成膜物质在高温下的交联程度和热稳定性，以及促进炭的形成，并且其含有的磷酸基团可催化PVA的前期降解，改善PVA的阻燃性。而BS由于具有较好的力学性能，能够使得可连接残炭以保持凝聚相完整，增加炭层的致密性，而紧密的炭层在阻燃中可以起到物理屏障作用，减缓热量的传递，延缓基体材料的燃烧。因此该炭层可更好地保护火焰下的基体材料，从而减慢热和氧气的传递，两者协同作用共同改善了抑烟性能，同时提高了水凝胶的膨胀型阻燃体系的阻燃效率。

3. 结论

以添加次磷酸铝阻燃剂的聚乙烯醇和壳聚糖作为水凝胶基质，经氢氧化钠预处理、硅烷偶联剂KH550接枝和植酸金属化合物改性后的玄武岩作为阻燃填料，两者复合后形成水凝胶阻燃涂层。

(1) SEM和FTIR结果表明，植酸铝、植酸镍和植酸锌在改性后的玄武岩表面成功沉积；

(2) TGA、CONE和垂直燃烧表明，经植酸镍改性的玄武岩与水凝胶基质复合得到的阻燃涂层具有最佳的阻燃性能，其UL-94测试达到V-0级，相较于未处理的木材，其残炭率增至27.3%，pHRR、THR和TSR降低64.2%、32.7%和51.3%。当涂层的厚度为300 µm时，抗拉强度较小，且其附着强度能达到3.4 MPa；

(3)改性玄武岩和次磷酸铝的添加能够提高水凝胶涂层的热稳定性，并提高涂层的阻燃抑烟性能，使木材具有良好的防火阻燃性能。

图 1 金属-有机框架(MOFs)适用于催化的结构特征^[19]

Figure 1. Structural characteristics of metal-organic frameworks (MOFs) apply to catalytic^[19]

PSM—Post-synthetic modification

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图 2 MOFs应用于光催化的种类

Figure 2. Types of MOFs used in photocatalysis

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图 3 Al₃(OH)₃(HTCS)₂(AlTCS-1)在水和三乙醇胺(TEOA)混合溶剂中光催化裂解水的机制^[24]

Figure 3. Mechanism of the photocatalytic water splitting process of Al₃(OH)₃(HTCS)₂(AlTCS-1) in mixed solvents of H₂O and triethanolamine (TEOA)^[24]

NHE—Normal hydrogen electrode; TCS—Tetrakis (4-oxycarbonylphenyl) silane; CB—Conduction band; VB—Valence band; E_g—Energy gap

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图 4 (a) 金属有机框架-808-乙二胺四乙酸 (MOF-808-EDTA) 模型图；(b) 封装单原子Pt的MOF-808-EDTA模型图^[32]

Figure 4. (a) Metal-organic frameworks-808-ethylenediaminetetraacetic acid (MOF-808-EDTA) model diagram; (b) Model diagram of MOF-808-EDTA encapsulating a single atomic Pt^[32]

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图 5 Al-TCPP-Pt光催化制氢机制图^[31]

Figure 5. Schematic illustration showing the synthesis of Al-TCPP-Pt for photocatalytic hydrogen production^[31]

Al-TCPP—(AlOH)₂H₂TCPP (H₂TCPP = 4, 4′, 4″, 4″-(Porphyrin-5, 10, 15, 20-tetrayl)tetrabenzoate)

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图 6 MOFs复合材料种类

Figure 6. Types of MOFs composites

COFs—Covalent organic frameworks; POMs—Polyoxometalates; QDs—Quantum dots

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图 7 [Ru(cod)(cot)]_3.5@MOF-5模型^[47]

Figure 7. Model of [Ru(cod)(cot)]_3.5@MOF-5^[47]

cod—1, 5-Cyclochloro ethane; cot—1, 3, 5-Cyclochlorine ethane

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图 8 基于连接簇电荷转移 (LCCT) 机制的Pt负载Ti-MOF-NH₂光催化制氢反应机制图^[55]

Figure 8. A schematic illustration of photocatalytic hydrogen production reaction over Pt-supported Ti-MOF-NH₂ on the basis of the ligand-to-cluster charge transfer (LCCT) mechanism^[55]

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图 9 结晶多氧钛簇/CdS/MIL-101 (PTC/CdS/MIL-101) 催化水裂解制氢示意图^[63]

Figure 9. Schematic diagram of polyoxo-titanium clusters/CdS/MIL-101 (PTC/CdS/MIL-101) catalytic water cracking for hydrogen production^[63]

MIL-101—Materials of institute lavoisier-101

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图 10 NH₂-UiO-66/TpPa-1-共价有机框架 (NH₂-UiO-66/TpPa-1-COF) (4:6)杂化材料制氢机制示意图^[66]

Figure 10. Mechanism schematic of hybrid material NH₂-UiO-66/TpPa-1-covalent organic framework (NH₂-UiO-66/TpPa-1-COF) (4:6) for photocatalytic hydrogen production^[66]

SA—Sodium ascorbate; E—Electrode potential

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图 11 掺Fe的TiO₂用于可见光下催化产氢^[70]

Figure 11. Fe-loaded TiO₂ catalyzes hydrogen production under visible light^[70]

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图 12 ZnIn₂S₄-In₂O₃异质结构用于产生H₂的电荷分离和转移的示意图^[74]

Figure 12. Schematic illustration of the charge separation and transfer in the ZnIn₂S₄-In₂O₃heterostructure for H₂ evolution^[74]

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图 13 Cu₃P@CoP的曙红Y (EY) 敏化剂p-n异质结在可见光照射下水分解制氢过程机制图^[78]

Figure 13. Mechanism diagram of the hydrogen production process by water decomposition of Eosin Y (EY) sensitizer p-n heterojunction of Cu₃P@CoP under visible light irradiation^[78]

SCE—Saturated calomel electrode; E_f—Fermi level; ISC—Inter system crossing

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表 1 有关MOF/纳米颗粒复合材料作为可见光照射下的光催化析氢反应的催化剂

Table 1 MOF/nanoparticle composites as catalysts for photocatalytic hydrogen evolution under visible light irradiation

Photocatalyst	Bandgap E_g/eV	Sacrificial agents	Co-catalysts	H₂ Production rate/(mmol·h⁻¹ ·g⁻¹)	Recycled times	Solution stability/h	Ref.
TiO₂@ZIF-8	3.28	Methanol	—	0.25	4	24	[56]
MOF-199/Ni	—	Triethanolamine	Pt	24.40	3	9	[57]
Ru-Pt-UiO-67	—	N, N-Dimethylacetamide	—	34.00	3	30	[58]
Pt@MIL-125/Au	—	Triethanolamine	—	1.74	3	6	[59]
Calix-3/Pt@UiO-66-NH₂	—	Methanol	—	1.53	3	9	[60]
Ni-MOF-74-CdS/Co₃O₄	1.97	Lactic acid	—	0.58	4	20	[61]
ZIF-9/Zn_0.8Cd_0.2S	—	Triethanolamine	—	6.42	—	—	[62]

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表 2 部分用于可见光催化析氢反应的MOFs衍生物

Table 2 Some MOFs derivatives used in visible light catalytic hydrogen evolution reaction

Photocatalyst	MOF precursors	Bandgap E_g/eV	Sacrificial agents	Co-catalysts	H₂ Production rate/(mmol·h⁻¹·g⁻¹)	Recycled times	Solution stability/h
Cu_0.9Co_2.1S₄@MoS₂	ZIF-67(Cu/Co)	—	Triethanolamine	—	40.16	3	30
FeO_3.3C_0.2H_1.0	MIL-101(Fe)	1.61	—	—	125.00	4	24
Pt-Zn₃P₂-CoP	ZnCoZIF-8	—	Methanol	—	9.15	4	24
Co-Zn_0.5Cd_0.5S	ZnCoZIF-8	—	${\mathrm{S}\mathrm{O}}_{3}^{2-}$ / ${\mathrm{S}}^{2-}$	—	17.36	6	30
Hollow Cu-TiO₂/C	SiO₂@HKUST-1	—	Methanol	Pt	14.05	3	18
Hollow CdS nanoboxes	Cd-MOF-74	2.30	Lactic acid	Pt	21.65	4	16
Co/NGC@ZnIn₂S₄	ZIF-8@ZIF-67	2.10	Triethanolamine	—	11.27	5	20
Notes: NGC—N-Doped graphitic carbon; HKUST-1—Hong Kong University of Science and Technology-1.

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