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有机磷酸化TiO2改性阳离子交换膜的制备与性能

周璇, 郑可, 周晓. 有机磷酸化TiO2改性阳离子交换膜的制备与性能[J]. 环境工程学报, 2019, 13(6): 1282-1291. doi: 10.12030/j.cjee.201810116
引用本文: 周璇, 郑可, 周晓. 有机磷酸化TiO2改性阳离子交换膜的制备与性能[J]. 环境工程学报, 2019, 13(6): 1282-1291. doi: 10.12030/j.cjee.201810116
ZHOU Xuan, ZHENG Ke, ZHOU Xiao. Preparation and characterization of organophosphorylated TiO2 modified cation exchange membranes[J]. Chinese Journal of Environmental Engineering, 2019, 13(6): 1282-1291. doi: 10.12030/j.cjee.201810116
Citation: ZHOU Xuan, ZHENG Ke, ZHOU Xiao. Preparation and characterization of organophosphorylated TiO2 modified cation exchange membranes[J]. Chinese Journal of Environmental Engineering, 2019, 13(6): 1282-1291. doi: 10.12030/j.cjee.201810116

有机磷酸化TiO2改性阳离子交换膜的制备与性能

  • 基金项目:

    国家重点研发计划项目2016YFC0400705国家重点研发计划项目(2016YFC0400705)

Preparation and characterization of organophosphorylated TiO2 modified cation exchange membranes

  • Fund Project:
  • 摘要: 通过添加有机磷酸化纳米二氧化钛(organophosphorylated titania nanoparticles,OPTi)的方法提高聚氯乙烯(PVC)阳离子交换膜的性能,先采用氨基三亚甲基膦酸通过磷氧化学键合将纳米二氧化钛有机磷酸化,再将制备好的OPTi与PVC粉末共混制备阳离子交换膜。通过X射线光电子能谱和傅里叶变换红外光谱分析OPTi的元素组成和表面特征官能团,通过扫描电镜研究了异相膜的表面和断面形貌。此外,还考察了不同OPTi的添加量对膜的含水率、离子交换量、机械性能和膜面电阻等性质的影响。结果表明,OPTi的加入使膜的固定电荷浓度、离子选择性和机械性能提高,膜面电阻大大降低并且在电渗析实验中,改性异相膜与原膜比较达到能耗降低26.68%、电流效率提高29.27%的显著效果。
    • 摘要

      通过添加有机磷酸化纳米二氧化钛(organophosphorylated titania nanoparticles,OPTi)的方法提高聚氯乙烯(PVC)阳离子交换膜的性能,先采用氨基三亚甲基膦酸通过磷氧化学键合将纳米二氧化钛有机磷酸化,再将制备好的OPTi与PVC粉末共混制备阳离子交换膜。通过X射线光电子能谱和傅里叶变换红外光谱分析OPTi的元素组成和表面特征官能团,通过扫描电镜研究了异相膜的表面和断面形貌。此外,还考察了不同OPTi的添加量对膜的含水率、离子交换量、机械性能和膜面电阻等性质的影响。结果表明,OPTi的加入使膜的固定电荷浓度、离子选择性和机械性能提高,膜面电阻大大降低并且在电渗析实验中,改性异相膜与原膜比较达到能耗降低26.68%、电流效率提高29.27%的显著效果。

      Abstract

      In this study, the performance of polyvinyl chloride (PVC) cation exchange membrane (CEM) was obviously enhanced by incorporating organophosphorylated titania nanoparticles (OPTi). At first, pristine titania nanoparticles were phosphorylated by amino trimethylene phosphonic acid, then the formed OPTi was mixed with the powder of PVC to fabricate this modified membrane. The element composition and surface function groups of OPTi were determined through XPS and FT-IR. The surface and section morphologies of heterogeneous membrane were recorded by SEM. In addition, the effects of OPTi additive amount in the mixed material on the water uptake of membrane, ion exchange content, mechanical properties and membrane surface resistance were particularly investigated. Results showed that OPTi addition significantly elevated the concentration of fixed charges on the membrane surface, ion selectivity and mechanical properties, while reduced the resistance of membrane surface. Besides, in the electrodialysis test, this composite membrane exhibited a superior electrodialysis performance compared with pristine membrane, such as a reduction of 26.68% on energy consumption and an increase of 29.27% on current efficiency.

      随着世界人口的增长以及工业不断发展,淡水的需求量日益增多。目前,利用脱盐技术从高盐水中获取饮用水,是缓解水资源短缺问题的重要途径之[1,2]。其中,电渗析技术以高效、低成本和低能耗的优点,成为有效处理高盐水问题的一项优势技[3,4,5]。电渗析过程是以电为驱动力的分离过程,通过控制进水中离子在离子交换膜两侧的迁移得到达标出水。离子交换膜一般是在膜基质中固载了可离子交换的基团,从而达到反离子可通过膜而同离子被膜截留的目的。

      离子交换膜作为电渗析过程核心部件,其性能优劣直接影响到电渗析运行费用和工艺效[6,7]。良好的离子交换膜应该具有较高的离子选择性、低膜面电阻、良好的稳定性等特性。为了达到这一目的,已研制出不同的离子交换[8,9]。其中,通过共混制得的异相膜具有相对简单的制作方法和优良的选择分离性能,从而受到水处理领域的重[10,11]

      离子交换膜的制备通常以聚乙烯、聚苯乙烯等材料作为膜基质,本研究采用聚氯乙烯,因其具有更加优良的化学稳定性、热稳定性以及优异的成膜性[12,13]。伴随着纳米领域的不断发展,通过将碳纳米管(CNT)、氧化石墨烯(GO)等纳米材料应用于离子交换膜中,可以使离子交换膜选择性及低电阻等特性得到不断提[14]。SHULIA[15]已经开发出用于水处理的耐高温磷酸化氧化石墨烯/磺化聚酰亚胺复合阳离子交换膜;HOSSEINI[16]采用聚丙烯腈/MWCNT复合纳米粒子修饰PVC基膜制得阴离子交换膜,用于脱盐应用。其中纳米二氧化钛(TiO2-NPs)具有高吸附能力、高亲水性、长期稳定性、低成本、对人体和环境安全等优点,并且其表面的—OH基团可作为有效吸附位点,也可作为活性位[17],是制备离子交换膜的良好材料。AYYARU[18]合成了磺化TiO2-NPs/聚苯乙烯-乙烯丁烯-聚苯乙烯异相膜,具有较高的离子交换能力和良好的燃料电池性能;HOSSEINI[19]采用溶液浇铸工艺制备了具有一、二价选择性的TiO2-NPs改性异相膜,并应用于咸水淡化中。

      本研究合成了一种新型有机磷酸化二氧化钛(OPTi),并将其嵌入PVC基体中,得到了用于ED的异相阳离子交换膜。采用FT-IR、XPS和SEM等方法对合成的OPTi和OPTi改性异相膜进行了表征。研究了OPTi的加入对膜性能的影响,包括形态、含水率、机械稳定性、膜面电阻和离子选择性。

    • 1 材料与方法

    • 1.1 实验原料

      聚氯乙烯(PVC);Amberlyst®15离子交换树脂(干型);纳米二氧化钛(TiO2);氨基三亚甲基膦酸(ATMP,50%水溶液)、N,N-二甲基乙酰胺(DMAC)、浓盐酸(HCl)、氯化钠(NaCl)、氯化钾(KCl)、无水硫酸钠(Na2SO4)、氢氧化钠(NaOH)、酚酞均为分析纯;商品均相阴离子交换膜,型号HoAM G-1204-05,杭州绿合环保科技公司(参数:IEC 1.8~2.2 mmol∙g-1,面电阻10.0 Ω∙cm2,迁移数0.90);商品异相阳离子交换膜,型号HMED-02315,华膜科技公司(参数:IEC 2 mmol∙g-1,面电阻15 Ω∙cm2,迁移数0.91)。

    • 1.2 实验仪器

      傅里叶红外光谱分析(CCR-1,美国尼高力公司);X射线光电子能谱分析(Escalab 250xi,美国赛默飞公司);超高分辨场发射扫描电镜(Merlin,德国卡尔蔡司公司);动态热机械分析(Q800DE,美国TA公司);接触角测定仪(DSA25,德国克吕士公司);电导率仪(DDS-307A,上海雷磁仪器有限公司);恒温气浴摇床(ZHWY-2102C,上海智城分析仪器制造有限公司);平板刮膜机(BEVS 1811,广州盛华实业有限公司)

    • 1.3 实验方法

      有机磷酸化TiO2制备过程:ATMP为有机磷酸化试剂,首先取100 mL 50%的ATMP水溶液,去离子水稀释至25%;称取1 g TiO2加入200 mL 25%的ATMP水溶液中,室温下剧烈搅拌12 h;离心分离,产物用去离子水反复洗涤,直至洗涤液pH呈中性;最后,将产物80 °C下真空干燥24 h;得到有机磷酸化TiO2,记作OPTi。

      铸膜液的制备过程:将OPTi和树脂粉(过400目筛)溶于DMAC溶液中,超声分散;加入PVC粉末,随后放入气浴摇床60 °C下振荡12 h,得到均匀的铸膜液;取出铸膜液,超声处理1 h脱泡。本研究制备铸膜液的组成成分如表1所示。

      表1 制备阳离子交换膜铸膜液的组成成分

      Table 1 Composition of casting solution for cation exchange membranes preparation

      膜编号DMAC/%PVC/%树脂/%OPTi共混比例
      mem-08510.54.50100
      mem-18510.54.51100
      mem-28510.54.52100
      mem-48510.54.54100
      mem-88510.54.58100

      注:OPTi共混比例由公式m(OPTi)/(m(树脂)+m(PVC))计算得出。

      制膜过程:将铸膜液倾倒于干燥、洁净、平滑的玻璃平板上;以400 μm的不锈钢刮刀刮制成液膜;将液膜60 °C下真空干燥12 h;自然冷却至室温,浸入去离子水中;用1 mol·L-1 HCl 溶液处理12 h后,进行后续膜参数测试。

    • 1.4 分析方法

      采用FT-IR和XPS测试TiO2和OPTi的红外光谱图和表面元素化学形态及含量;采用SEM观察离子交换膜的表面和断面的微观结构;采用DMA方[20]进行拉伸试验测定膜的机械性能;用接触角测定仪测定膜与纯水的接触角。

      离子交换膜的离子交换容量和含水率测试:将待测膜裁成4 cm×4 cm正方形小块,1 mol·L-1 HCl 溶液中浸泡12 h,去离子水冲洗膜表面,然后将膜浸泡于50 mL 2 mol·L-1 NaCl 溶液中,常温慢速振荡24 h。将膜取出精确称量,得湿膜重Ww。而后60 °C真空干燥24 h至恒重,得干膜重Wd。从膜中置换出来的氢离子以酚酞为指示剂,用0.01 mol·L-1 NaOH溶液进行滴定。膜的含水量、离子交换容量及固定电荷浓度根据式(1)~式(3)计算。

      η=Ww-WdWd×100%
      (1)
      QIEC=0.01(Ve-V0)Wd
      (2)
      CFIC=QIECη
      (3)

      式中:η为含水率,%;QIEC为离子交换容量,表示每克干膜所含的活性功能基团的毫摩尔数,mmol·g-1CFIC为固定电荷浓度,表示每单位质量水含活性功能基团的毫摩尔数,mmol·g-1Ve为滴定终点消耗NaOH溶液的体积,mL;V0为空白实验消耗NaOH溶液的体积,mL。

      离子交换膜的面电阻测试采用定制装[21]测定,装置如图1所示。它由2个电极室(I和IV)、2个中间室(II和III)和1个膜固定夹块组成。测试前,待测膜在0.5 mol·L-1 NaCl 溶液中平衡12 h;测量过程中,将0.3 mol·L-1 Na2SO4溶液循环泵入串联的电极室,以0.5 mol·L-1 NaCl 溶液为进料,电流保持在0.05 A不变,用万用表读取Ag/AgCl参比电极间电位U。膜面电阻根据式(4)计算。

      图1
                            电化学测试实验装置示意图

      图1 电化学测试实验装置示意图

      Fig. 1 Schematic diagram of test device for electrochemical measurements

      注:1.电极;2. Ag/AgCl参比电极;3.电压表;4.商品阴离子交换膜;5.自制阳离子交换膜。

      R=(U-U0I)S
      (4)

      式中:R为膜面电阻,Ω∙cm2U0为空白电压即未放置膜时电压读数,V;I为所使用的电流,A;S为膜有效面积,取值7.06 cm2

      离子交换膜的离子迁移数及选择性测试将待测膜浸泡于0.15 mol·L-1 KCl 溶液中平衡12 h,采用膜电阻同样的测试装置,去除2个电极室,其余2室分别循环0.1 mol·L-1和0.2 mol·L-1 KCl溶液,膜电位由Ag/AgCl参比电极及万用电表测定。膜的离子迁移数及选择性根据式(5)和式(6)计算。

      Em=1000RTF(2t-1)lnc1c2
      (5)
      Ps=t-t01-t0
      (6)

      式中:Em为膜电位,V;t为离子迁移数;Ps为离子选择透过性;R为理想气体常数,取值8.314 J·(mol·K)-1F为法拉第常数,取值96 500 C·mol-1T为热力学温度,K;c1/c2为膜两侧面接触溶液浓度之比;t0为溶液中同离子迁移数,在25 °C下,t0 = 0.49。

      扩散渗析实验采用双室装置进行,由淡化室和浓缩室组成,2室分别以150 r·min-1的速度循环100 mL 1 mol·L-1 NaCl溶液和去离子水,膜有效面积为20 cm2。每5 min记录浓缩室溶液电导率,利用电导率-时间曲线测定扩散离子浓度。

      电渗析采用4室反应装置,由1片阳离子交换膜、2片阴离子交换膜组成,膜有效面积为20 cm2。2片阴离子交换膜把两端极室隔开,中间放置阳离子交换膜,两侧分别为浓缩室和淡化室。电渗析实验在循环条件下进行,200 mL 0.3 mol·L-1 Na2SO4溶液以150 mL·min-1流速泵入串联的2个极室中;200 mL 3 g·L-1 NaCl溶液和200 mL去离子水以150 mL·min-1流速分别泵入淡化室、浓缩室。直流电源提供0.3 A电流,每5 min记录电压及淡化室电导率,当淡化室电导率低于0.1 mS·cm-2时,实验结束。电渗析过程的电流效率及能耗根据式(7)和式(8)计算。

      ηCE=ΔnFZit=0t=tIdt
      (7)
      E=t=0t=tIVdtΔnMw
      (8)

      式中:ηCE为电流效率,%;E为能耗,kWh·kg-1F为法拉第常数,取值96 500 C·mol-1Zi是离子带电荷数;∆n是摩尔变化数;I是电流密度,mA·cm-2V是电压,V;Mw是NaCl摩尔质量;t是时间,h。

    • 2 结果与讨论

    • 2.1 OPTi的合成和表征

      通过采用FT-IR和XPS测试可以确定OPTi纳米粒子的成功合成。图2和图3分别是OPTi的FT-IR和XPS图。由图2可知,谱图中3 440 cm-1和1 640 cm-1处的吸收峰分别是TiO2表面吸附水分子的羟基伸缩振动吸收峰和O—H键的弯曲振动吸收[22];1 143 cm-1是Ti—O的不对称伸缩振动[23];570~660 cm-1段的吸收峰是由Ti—O—Ti伸缩振动引起的强吸收[24]。OPTi新出现的特征峰1 075 cm-1和1 140 cm-1处是P—O—Ti和P̿O伸缩振动引起[25];而1 330 cm-1为P̿O的特征频[26],1 427 cm-1处是P—C伸缩振动引起[27]。由这些结果可以推断,ATMP取代了—OH中H的位置,通过磷酸基团与Ti原子在TiO2表面形成化学键。

      图2
                            TiO2和OPTi的红外光谱图

      图2 TiO2和OPTi的红外光谱图

      Fig. 2 FT-IR spectra of pristine TiO2 and OPTi

      图3
                            TiO2和OPTi的XPS谱图

      图3 TiO2和OPTi的XPS谱图

      Fig. 3 XPS spectra of pristine TiO2 and OPTi

      为了进一步验证磷酸基团成功地引入到TiO2上,实验采用XPS分析了OPTi中O、P元素的光电子能谱。由图3可知,未改性TiO2的全谱图中未发现P2p峰,经有机磷酸化后,OPTi出现了新的P元素峰,且P2p结合能为133.5 eV,表示OPTi中的P为五价[28,29]。如图3所示,TiO2和OPTi的O1s谱都是不对称的,说明其表面不仅仅含有单一的晶格氧。经分峰拟合后,可发现TiO2的O1s分谱由2个峰拟合,分别是529.7 eV处Ti—O键和532.3 eV处—OH[30]。而OPTi中新出现530.7 eV峰为Ti—O—P[31,32]。并且经对比发现,OPTi 532.3 eV处—OH键的峰面积比TiO2相对应的面积要减小许多,这是由于磷酸基团主要与TiO2表面的—OH形成化学键而结合,故经有机磷酸化后的OPTi表面—OH含量会大量减少,谱图对应的峰面积比例也会降低。

    • 2.2 膜结构的表征

      自制离子交换膜由PVC作为基材,树脂和OPTi作为添加剂,采用蒸发溶剂法制成。通过SEM图4观察膜的断面和表面的微观结构,对mem-2和原膜进行对比,可以发现,添加的OPTi纳米颗粒在膜基质中是均匀分布,这样能为反离子的跨膜迁移提供通道,进一步提高膜的选择性。并且树脂和OPTi均匀分布使得膜表面存在较多的导电区域,从而增强膜界面处均匀电场强度,降低浓差极化的现象发[33]

      图4
                            膜表面和断面SEM图

      图4 膜表面和断面SEM图

      Fig. 4 SEM images of surface and cross-section for modified membranes

    • 2.3 OPTi含量对膜的接触角和含水率影响

      由表2可知,随着离子交换膜中OPTi的增加,会使膜的含水量增加。这是由于OPTi的亲水性使得膜基质吸水性增强。通常来说,膜具有高含水率,可以为同离子和反离子跨膜迁移提供更多的通道,但是这样也会一定程度上降低离子交换膜的选择[10]。表2显示了膜的接触角呈现不断减小的趋势,这是由于加入的OPTi含有大量亲水性的羟基和磷酸基,这些羟基和磷酸基被水分子水化,从而增强了表面亲水性。

      表2 不同OPTi含量膜的η和接触角

      Table 2 Water content and contact angle of prepared CEM with various OPTi loading ratios

      膜编号η /%接触角/(°)
      mem-011.7688.89
      mem-112.2377.95
      mem-212.3573.72
      mem-412.5064.61
      mem-814.3055.43
    • 2.4 OPTi含量对膜离子交换量和固定电荷浓度的影响

      由图5所示,随着OPTi含量的增加,膜的离子交换容量(IEC)也逐步增大。这主要归因为加入的OPTi为膜提供了更多的离子官能团,强化了膜的离子交换性能。直至OPTi含量达到2%,膜的IEC达到最大值。此后,随着加入OPTi的量增加,膜的IEC又再次降低。这可能是由于膜基质中树脂颗粒被高浓度的OPTi颗粒所包围,限制了树脂颗粒中磺酸基团的交换性能,从而降低了膜的IEC。

      图5
                            不同OPTi含量膜的IEC和FIC

      图5 不同OPTi含量膜的IEC和FIC

      Fig. 5 IEC and FIC of prepared CEM with various OPTi loading ratios

      膜的IEC与η之间存在着一定的关系,共同影响着膜的性能。膜的固定电荷浓度(FIC)为膜的IEC与η的比值。如图5所示,随着膜中OPTi含量的不同,IEC和η的变化,FIC也呈现着一种特殊趋势。高固定电荷浓度可以有效控制膜基质中同离子的迁移通道,从而提高膜的离子选择性。

    • 2.5 OPTi含量对膜的离子迁移数及选择性的影响

      当离子交换膜两侧界面与浓度不同的溶液接触时,跨膜电位差就此形成。而此电位差主要取决该膜的电化学特性以及电解质溶液的性质和浓度。如图6所示,OPTi含量增加至2%时,膜的离子迁移数和离子选择性都呈现上升的趋势。这可能是膜的固定电荷浓度和膜电荷密度升高所致,并且增强了唐南排斥效应。膜表面和膜基质中导电区域的增加使膜周围电场强度得以增强,从而缓和了界面浓差极化的现象。

      图6
                            不同OPTi含量膜的离子迁移数和选择透过性

      图6 不同OPTi含量膜的离子迁移数和选择透过性

      Fig. 6 Transport number and permselectivity of prepared CEM with various OPTi loading ratios

    • 2.6 OPTi含量对膜的面电阻的影响

      在电渗析过程中,离子交换膜的膜电阻对能耗有着重要影响。制备低膜面电阻的离子交换膜对电渗析技术是非常必要的。如图7所示,通过添加OPTi之后,所有改性异相膜的面电阻相较于原膜都有明显的下降,并在OPTi添加量为2%时达到最小值,与原膜相比,下降了71%。这是由于,OPTi的加入使得膜的含水率和IEC都有所升高,在膜基质中形成了更多的反离子通道,从而降低了膜电阻。

      图7
                            不同OPTi含量膜的面电阻

      图7 不同OPTi含量膜的面电阻

      Fig. 7 Surface resistance of prepared CEM with various OPTi loading ratios

    • 2.7 膜的机械性能

      由表3可以看出,膜的拉伸强度随OPTi含量增加变化不是很大,直至含量达到4%后开始下降。当膜受到施加的压力时,膜基质中的孔隙和吸附的水相当于增塑剂使膜能承受一定形变,故含水量高的膜弹性更好。

      表3 不同OPTi含量膜的机械性能

      Table 3 Mechanical properties of prepared CEM with various OPTi loading ratios

      膜编号拉伸强度/MPa断裂伸长率/%
      mem-017.656.45
      mem-116.5910.63
      mem-216.2815.31
      mem-417.3917.92
      mem-815.3211.58
    • 2.8 扩散渗析实验

      如图8所示,溶液中NaCl离子浓度变化由电导率表示。膜的扩散渗析过程属于电渗析过程的反效应,若过多的同离子扩散会使进料液经过电渗析处理效果不理[34]。离子扩散率主要取决于膜中反离子的传输速度,在一定程度上反映了离子交换膜的选择透过[35]。结果显示,随着OPTi的加入,膜对离子扩散出现了明显的阻碍作用,这是由于OPTi的加入提高了膜的离子交换官能团的浓度,使得膜的离子选择透过性得到改善,抑制了同离子扩散。当OPTi含量为2%时,膜的扩散速率较原膜明显降低。之后,由于OPTi含量持续增加,使得膜的含水率和膜面粗糙度也不断升高,这就导致膜对离子的选择截留作用降低,扩散现象明显。

      图8
                            膜的扩散渗析实验中浓缩室电导率与实验时间的关系

      图8 膜的扩散渗析实验中浓缩室电导率与实验时间的关系

      Fig. 8 Curves of conductivity in concentration chamber-experiment time during membrane diffusion progress

    • 2.9 电渗析实验

      为了评价膜对高盐水脱盐性能,在ED实验验中使用了简化的四室电渗析装置,并在实验中使用了一种商用阳离子膜作为参考。

      淡化室中NaCl溶液电导率的变化如图9所示,当电导率低于0.1 mS·cm-1实验结束。同时,本实验考察了各膜脱盐过程中通量、能耗和电流效率,如图10所示。由实验结果可以看出,改性异相膜较商品膜表现出高的脱盐效率,效果最优的为OPTi添加量为2%,这主要归因于其低膜面电阻和高的离子选择性。同时,改性异相膜较商品膜表现出高通量、高电流效率及低能耗的特点,表明其在ED技术处理高盐水的潜在应用。

      图9
                            膜的电渗析实验中淡化室电导率与实验时间的关系

      图9 膜的电渗析实验中淡化室电导率与实验时间的关系

      Fig. 9 Curves of conductivity in desalination chamber-ED experiment time during membrane electrodialysis progress

      图10
                            膜的电渗析实验中能耗与电流效率

      图10 膜的电渗析实验中能耗与电流效率

      Fig. 10 Curves of energy consumption and current efficiency during membrane electrodialysis progress

    • 3 结论

      1) 氨基三亚甲基膦酸为有机磷酸化试剂,使得磷酸基团以P—O键结合的方式成功接枝于TiO2表面。

      2) OPTi的加入提高了膜的离子交换容量,改善膜的离子选择性并且大大降低了膜面电阻,综合膜的各项性能,OPTi含量为2%时为最优选择膜。

      3) OPTi粒子的加入明显改善了膜的电渗析性能,在本实验条件下,改性异相膜能耗较原膜降低了26.68%,电流效率提高了29.27%,且远高于商品异相膜。表明此膜在ED处理高盐水脱盐领域具有应用潜力。

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  • [1] ELIMELECH M, PHILLIP W A. The future of seawater desalination: Energy, technology, and the environment[J]. Science, 2011, 333(6043): 712-717.
    [2] ZHENG X, CHEN D, WANG Q, et al. Seawater desalination in China: Retrospect and prospect[J]. Chemical Engineering Journal, 2014, 242(15): 404-413.
    [3] LOPEZ A M, WILLIAMS M, PAIVA M, et al. Potential of electrodialytic techniques in brackish desalination and recovery of industrial process water for reuse[J]. Desalination, 2017, 409: 108-114.
    [4] CAMPIONE A, GURRERI L, CIOFALO M, et al. Electrodialysis for water desalination: A critical assessment of recent developments on process fundamentals, models and applications[J]. Desalination, 2018, 434(SI): 121-160.
    [5] STRATHMANN H, KEDEM O, WILF M. Electrodialysis, a mature technology with a multitude of new applications[J]. Desalination, 2010, 264(3): 268-288.
    [6] XU T. Ion exchange membranes: State of their development and perspective[J]. Journal of Membrane Science, 2005, 263(1/2): 1-29.
    [7] RAN J, WU L, HE Y, et al. Ion exchange membranes: New developments and applications[J]. Journal of Membrane Science, 2017, 522: 267-291.
    [8] LUO T, ABDU S, WESSLING M. Selectivity of ion exchange membranes: A review[J]. Journal of Membrane Science, 2018, 555: 429-454.
    [9] RAN J, WU L, HE Y, et al. Ion exchange membranes: New developments and applications[J]. Journal of Membrane Science, 2017, 522: 267-291.
    [10] HOSSEINI S M, ANDANI S M J M, JAFARI M R. Tailoring the ionic transfer characteristics of polyvinyl chloride-based heterogeneous ion exchange membranes by embedding carboxy methyl cellulose in membrane channels[J]. Journal of Polymer Research, 2016, 23(8): 160.
    [11] HOSSEINI S M, JASHNI E, HABIBI M, et al. Evaluating the ion transport characteristics of novel graphene oxide nanoplates entrapped mixed matrix cation exchange membranes in water deionization[J]. Journal of Membrane Science, 2017, 541:641-652.
    [12] VOGEL C, MEIER-HAACK J. Preparation of ion-exchange materials and membranes[J]. Desalination, 2014, 342(5): 156-174.
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  • 刊出日期:  2019-06-18
周璇, 郑可, 周晓. 有机磷酸化TiO2改性阳离子交换膜的制备与性能[J]. 环境工程学报, 2019, 13(6): 1282-1291. doi: 10.12030/j.cjee.201810116
引用本文: 周璇, 郑可, 周晓. 有机磷酸化TiO2改性阳离子交换膜的制备与性能[J]. 环境工程学报, 2019, 13(6): 1282-1291. doi: 10.12030/j.cjee.201810116
ZHOU Xuan, ZHENG Ke, ZHOU Xiao. Preparation and characterization of organophosphorylated TiO2 modified cation exchange membranes[J]. Chinese Journal of Environmental Engineering, 2019, 13(6): 1282-1291. doi: 10.12030/j.cjee.201810116
Citation: ZHOU Xuan, ZHENG Ke, ZHOU Xiao. Preparation and characterization of organophosphorylated TiO2 modified cation exchange membranes[J]. Chinese Journal of Environmental Engineering, 2019, 13(6): 1282-1291. doi: 10.12030/j.cjee.201810116

有机磷酸化TiO2改性阳离子交换膜的制备与性能

  • 1. 华南理工大学环境与能源学院,广州 510006
  • 2. 贵州科学院,贵阳 550001
基金项目:

国家重点研发计划项目2016YFC0400705国家重点研发计划项目(2016YFC0400705)

摘要: 通过添加有机磷酸化纳米二氧化钛(organophosphorylated titania nanoparticles,OPTi)的方法提高聚氯乙烯(PVC)阳离子交换膜的性能,先采用氨基三亚甲基膦酸通过磷氧化学键合将纳米二氧化钛有机磷酸化,再将制备好的OPTi与PVC粉末共混制备阳离子交换膜。通过X射线光电子能谱和傅里叶变换红外光谱分析OPTi的元素组成和表面特征官能团,通过扫描电镜研究了异相膜的表面和断面形貌。此外,还考察了不同OPTi的添加量对膜的含水率、离子交换量、机械性能和膜面电阻等性质的影响。结果表明,OPTi的加入使膜的固定电荷浓度、离子选择性和机械性能提高,膜面电阻大大降低并且在电渗析实验中,改性异相膜与原膜比较达到能耗降低26.68%、电流效率提高29.27%的显著效果。

English Abstract

      摘要

      通过添加有机磷酸化纳米二氧化钛(organophosphorylated titania nanoparticles,OPTi)的方法提高聚氯乙烯(PVC)阳离子交换膜的性能,先采用氨基三亚甲基膦酸通过磷氧化学键合将纳米二氧化钛有机磷酸化,再将制备好的OPTi与PVC粉末共混制备阳离子交换膜。通过X射线光电子能谱和傅里叶变换红外光谱分析OPTi的元素组成和表面特征官能团,通过扫描电镜研究了异相膜的表面和断面形貌。此外,还考察了不同OPTi的添加量对膜的含水率、离子交换量、机械性能和膜面电阻等性质的影响。结果表明,OPTi的加入使膜的固定电荷浓度、离子选择性和机械性能提高,膜面电阻大大降低并且在电渗析实验中,改性异相膜与原膜比较达到能耗降低26.68%、电流效率提高29.27%的显著效果。

      Abstract

      In this study, the performance of polyvinyl chloride (PVC) cation exchange membrane (CEM) was obviously enhanced by incorporating organophosphorylated titania nanoparticles (OPTi). At first, pristine titania nanoparticles were phosphorylated by amino trimethylene phosphonic acid, then the formed OPTi was mixed with the powder of PVC to fabricate this modified membrane. The element composition and surface function groups of OPTi were determined through XPS and FT-IR. The surface and section morphologies of heterogeneous membrane were recorded by SEM. In addition, the effects of OPTi additive amount in the mixed material on the water uptake of membrane, ion exchange content, mechanical properties and membrane surface resistance were particularly investigated. Results showed that OPTi addition significantly elevated the concentration of fixed charges on the membrane surface, ion selectivity and mechanical properties, while reduced the resistance of membrane surface. Besides, in the electrodialysis test, this composite membrane exhibited a superior electrodialysis performance compared with pristine membrane, such as a reduction of 26.68% on energy consumption and an increase of 29.27% on current efficiency.

      随着世界人口的增长以及工业不断发展,淡水的需求量日益增多。目前,利用脱盐技术从高盐水中获取饮用水,是缓解水资源短缺问题的重要途径之[1,2]。其中,电渗析技术以高效、低成本和低能耗的优点,成为有效处理高盐水问题的一项优势技[3,4,5]。电渗析过程是以电为驱动力的分离过程,通过控制进水中离子在离子交换膜两侧的迁移得到达标出水。离子交换膜一般是在膜基质中固载了可离子交换的基团,从而达到反离子可通过膜而同离子被膜截留的目的。

      离子交换膜作为电渗析过程核心部件,其性能优劣直接影响到电渗析运行费用和工艺效[6,7]。良好的离子交换膜应该具有较高的离子选择性、低膜面电阻、良好的稳定性等特性。为了达到这一目的,已研制出不同的离子交换[8,9]。其中,通过共混制得的异相膜具有相对简单的制作方法和优良的选择分离性能,从而受到水处理领域的重[10,11]

      离子交换膜的制备通常以聚乙烯、聚苯乙烯等材料作为膜基质,本研究采用聚氯乙烯,因其具有更加优良的化学稳定性、热稳定性以及优异的成膜性[12,13]。伴随着纳米领域的不断发展,通过将碳纳米管(CNT)、氧化石墨烯(GO)等纳米材料应用于离子交换膜中,可以使离子交换膜选择性及低电阻等特性得到不断提[14]。SHULIA[15]已经开发出用于水处理的耐高温磷酸化氧化石墨烯/磺化聚酰亚胺复合阳离子交换膜;HOSSEINI[16]采用聚丙烯腈/MWCNT复合纳米粒子修饰PVC基膜制得阴离子交换膜,用于脱盐应用。其中纳米二氧化钛(TiO2-NPs)具有高吸附能力、高亲水性、长期稳定性、低成本、对人体和环境安全等优点,并且其表面的—OH基团可作为有效吸附位点,也可作为活性位[17],是制备离子交换膜的良好材料。AYYARU[18]合成了磺化TiO2-NPs/聚苯乙烯-乙烯丁烯-聚苯乙烯异相膜,具有较高的离子交换能力和良好的燃料电池性能;HOSSEINI[19]采用溶液浇铸工艺制备了具有一、二价选择性的TiO2-NPs改性异相膜,并应用于咸水淡化中。

      本研究合成了一种新型有机磷酸化二氧化钛(OPTi),并将其嵌入PVC基体中,得到了用于ED的异相阳离子交换膜。采用FT-IR、XPS和SEM等方法对合成的OPTi和OPTi改性异相膜进行了表征。研究了OPTi的加入对膜性能的影响,包括形态、含水率、机械稳定性、膜面电阻和离子选择性。

    • 1 材料与方法

    • 1.1 实验原料

      聚氯乙烯(PVC);Amberlyst®15离子交换树脂(干型);纳米二氧化钛(TiO2);氨基三亚甲基膦酸(ATMP,50%水溶液)、N,N-二甲基乙酰胺(DMAC)、浓盐酸(HCl)、氯化钠(NaCl)、氯化钾(KCl)、无水硫酸钠(Na2SO4)、氢氧化钠(NaOH)、酚酞均为分析纯;商品均相阴离子交换膜,型号HoAM G-1204-05,杭州绿合环保科技公司(参数:IEC 1.8~2.2 mmol∙g-1,面电阻10.0 Ω∙cm2,迁移数0.90);商品异相阳离子交换膜,型号HMED-02315,华膜科技公司(参数:IEC 2 mmol∙g-1,面电阻15 Ω∙cm2,迁移数0.91)。

    • 1.2 实验仪器

      傅里叶红外光谱分析(CCR-1,美国尼高力公司);X射线光电子能谱分析(Escalab 250xi,美国赛默飞公司);超高分辨场发射扫描电镜(Merlin,德国卡尔蔡司公司);动态热机械分析(Q800DE,美国TA公司);接触角测定仪(DSA25,德国克吕士公司);电导率仪(DDS-307A,上海雷磁仪器有限公司);恒温气浴摇床(ZHWY-2102C,上海智城分析仪器制造有限公司);平板刮膜机(BEVS 1811,广州盛华实业有限公司)

    • 1.3 实验方法

      有机磷酸化TiO2制备过程:ATMP为有机磷酸化试剂,首先取100 mL 50%的ATMP水溶液,去离子水稀释至25%;称取1 g TiO2加入200 mL 25%的ATMP水溶液中,室温下剧烈搅拌12 h;离心分离,产物用去离子水反复洗涤,直至洗涤液pH呈中性;最后,将产物80 °C下真空干燥24 h;得到有机磷酸化TiO2,记作OPTi。

      铸膜液的制备过程:将OPTi和树脂粉(过400目筛)溶于DMAC溶液中,超声分散;加入PVC粉末,随后放入气浴摇床60 °C下振荡12 h,得到均匀的铸膜液;取出铸膜液,超声处理1 h脱泡。本研究制备铸膜液的组成成分如表1所示。

      表1 制备阳离子交换膜铸膜液的组成成分

      Table 1 Composition of casting solution for cation exchange membranes preparation

      膜编号DMAC/%PVC/%树脂/%OPTi共混比例
      mem-08510.54.50100
      mem-18510.54.51100
      mem-28510.54.52100
      mem-48510.54.54100
      mem-88510.54.58100

      注:OPTi共混比例由公式m(OPTi)/(m(树脂)+m(PVC))计算得出。

      制膜过程:将铸膜液倾倒于干燥、洁净、平滑的玻璃平板上;以400 μm的不锈钢刮刀刮制成液膜;将液膜60 °C下真空干燥12 h;自然冷却至室温,浸入去离子水中;用1 mol·L-1 HCl 溶液处理12 h后,进行后续膜参数测试。

    • 1.4 分析方法

      采用FT-IR和XPS测试TiO2和OPTi的红外光谱图和表面元素化学形态及含量;采用SEM观察离子交换膜的表面和断面的微观结构;采用DMA方[20]进行拉伸试验测定膜的机械性能;用接触角测定仪测定膜与纯水的接触角。

      离子交换膜的离子交换容量和含水率测试:将待测膜裁成4 cm×4 cm正方形小块,1 mol·L-1 HCl 溶液中浸泡12 h,去离子水冲洗膜表面,然后将膜浸泡于50 mL 2 mol·L-1 NaCl 溶液中,常温慢速振荡24 h。将膜取出精确称量,得湿膜重Ww。而后60 °C真空干燥24 h至恒重,得干膜重Wd。从膜中置换出来的氢离子以酚酞为指示剂,用0.01 mol·L-1 NaOH溶液进行滴定。膜的含水量、离子交换容量及固定电荷浓度根据式(1)~式(3)计算。

      η=Ww-WdWd×100%
      (1)
      QIEC=0.01(Ve-V0)Wd
      (2)
      CFIC=QIECη
      (3)

      式中:η为含水率,%;QIEC为离子交换容量,表示每克干膜所含的活性功能基团的毫摩尔数,mmol·g-1CFIC为固定电荷浓度,表示每单位质量水含活性功能基团的毫摩尔数,mmol·g-1Ve为滴定终点消耗NaOH溶液的体积,mL;V0为空白实验消耗NaOH溶液的体积,mL。

      离子交换膜的面电阻测试采用定制装[21]测定,装置如图1所示。它由2个电极室(I和IV)、2个中间室(II和III)和1个膜固定夹块组成。测试前,待测膜在0.5 mol·L-1 NaCl 溶液中平衡12 h;测量过程中,将0.3 mol·L-1 Na2SO4溶液循环泵入串联的电极室,以0.5 mol·L-1 NaCl 溶液为进料,电流保持在0.05 A不变,用万用表读取Ag/AgCl参比电极间电位U。膜面电阻根据式(4)计算。

      图1
                            电化学测试实验装置示意图

      图1 电化学测试实验装置示意图

      Fig. 1 Schematic diagram of test device for electrochemical measurements

      注:1.电极;2. Ag/AgCl参比电极;3.电压表;4.商品阴离子交换膜;5.自制阳离子交换膜。

      R=(U-U0I)S
      (4)

      式中:R为膜面电阻,Ω∙cm2U0为空白电压即未放置膜时电压读数,V;I为所使用的电流,A;S为膜有效面积,取值7.06 cm2

      离子交换膜的离子迁移数及选择性测试将待测膜浸泡于0.15 mol·L-1 KCl 溶液中平衡12 h,采用膜电阻同样的测试装置,去除2个电极室,其余2室分别循环0.1 mol·L-1和0.2 mol·L-1 KCl溶液,膜电位由Ag/AgCl参比电极及万用电表测定。膜的离子迁移数及选择性根据式(5)和式(6)计算。

      Em=1000RTF(2t-1)lnc1c2
      (5)
      Ps=t-t01-t0
      (6)

      式中:Em为膜电位,V;t为离子迁移数;Ps为离子选择透过性;R为理想气体常数,取值8.314 J·(mol·K)-1F为法拉第常数,取值96 500 C·mol-1T为热力学温度,K;c1/c2为膜两侧面接触溶液浓度之比;t0为溶液中同离子迁移数,在25 °C下,t0 = 0.49。

      扩散渗析实验采用双室装置进行,由淡化室和浓缩室组成,2室分别以150 r·min-1的速度循环100 mL 1 mol·L-1 NaCl溶液和去离子水,膜有效面积为20 cm2。每5 min记录浓缩室溶液电导率,利用电导率-时间曲线测定扩散离子浓度。

      电渗析采用4室反应装置,由1片阳离子交换膜、2片阴离子交换膜组成,膜有效面积为20 cm2。2片阴离子交换膜把两端极室隔开,中间放置阳离子交换膜,两侧分别为浓缩室和淡化室。电渗析实验在循环条件下进行,200 mL 0.3 mol·L-1 Na2SO4溶液以150 mL·min-1流速泵入串联的2个极室中;200 mL 3 g·L-1 NaCl溶液和200 mL去离子水以150 mL·min-1流速分别泵入淡化室、浓缩室。直流电源提供0.3 A电流,每5 min记录电压及淡化室电导率,当淡化室电导率低于0.1 mS·cm-2时,实验结束。电渗析过程的电流效率及能耗根据式(7)和式(8)计算。

      ηCE=ΔnFZit=0t=tIdt
      (7)
      E=t=0t=tIVdtΔnMw
      (8)

      式中:ηCE为电流效率,%;E为能耗,kWh·kg-1F为法拉第常数,取值96 500 C·mol-1Zi是离子带电荷数;∆n是摩尔变化数;I是电流密度,mA·cm-2V是电压,V;Mw是NaCl摩尔质量;t是时间,h。

    • 2 结果与讨论

    • 2.1 OPTi的合成和表征

      通过采用FT-IR和XPS测试可以确定OPTi纳米粒子的成功合成。图2和图3分别是OPTi的FT-IR和XPS图。由图2可知,谱图中3 440 cm-1和1 640 cm-1处的吸收峰分别是TiO2表面吸附水分子的羟基伸缩振动吸收峰和O—H键的弯曲振动吸收[22];1 143 cm-1是Ti—O的不对称伸缩振动[23];570~660 cm-1段的吸收峰是由Ti—O—Ti伸缩振动引起的强吸收[24]。OPTi新出现的特征峰1 075 cm-1和1 140 cm-1处是P—O—Ti和P̿O伸缩振动引起[25];而1 330 cm-1为P̿O的特征频[26],1 427 cm-1处是P—C伸缩振动引起[27]。由这些结果可以推断,ATMP取代了—OH中H的位置,通过磷酸基团与Ti原子在TiO2表面形成化学键。

      图2
                            TiO2和OPTi的红外光谱图

      图2 TiO2和OPTi的红外光谱图

      Fig. 2 FT-IR spectra of pristine TiO2 and OPTi

      图3
                            TiO2和OPTi的XPS谱图

      图3 TiO2和OPTi的XPS谱图

      Fig. 3 XPS spectra of pristine TiO2 and OPTi

      为了进一步验证磷酸基团成功地引入到TiO2上,实验采用XPS分析了OPTi中O、P元素的光电子能谱。由图3可知,未改性TiO2的全谱图中未发现P2p峰,经有机磷酸化后,OPTi出现了新的P元素峰,且P2p结合能为133.5 eV,表示OPTi中的P为五价[28,29]。如图3所示,TiO2和OPTi的O1s谱都是不对称的,说明其表面不仅仅含有单一的晶格氧。经分峰拟合后,可发现TiO2的O1s分谱由2个峰拟合,分别是529.7 eV处Ti—O键和532.3 eV处—OH[30]。而OPTi中新出现530.7 eV峰为Ti—O—P[31,32]。并且经对比发现,OPTi 532.3 eV处—OH键的峰面积比TiO2相对应的面积要减小许多,这是由于磷酸基团主要与TiO2表面的—OH形成化学键而结合,故经有机磷酸化后的OPTi表面—OH含量会大量减少,谱图对应的峰面积比例也会降低。

    • 2.2 膜结构的表征

      自制离子交换膜由PVC作为基材,树脂和OPTi作为添加剂,采用蒸发溶剂法制成。通过SEM图4观察膜的断面和表面的微观结构,对mem-2和原膜进行对比,可以发现,添加的OPTi纳米颗粒在膜基质中是均匀分布,这样能为反离子的跨膜迁移提供通道,进一步提高膜的选择性。并且树脂和OPTi均匀分布使得膜表面存在较多的导电区域,从而增强膜界面处均匀电场强度,降低浓差极化的现象发[33]

      图4
                            膜表面和断面SEM图

      图4 膜表面和断面SEM图

      Fig. 4 SEM images of surface and cross-section for modified membranes

    • 2.3 OPTi含量对膜的接触角和含水率影响

      由表2可知,随着离子交换膜中OPTi的增加,会使膜的含水量增加。这是由于OPTi的亲水性使得膜基质吸水性增强。通常来说,膜具有高含水率,可以为同离子和反离子跨膜迁移提供更多的通道,但是这样也会一定程度上降低离子交换膜的选择[10]。表2显示了膜的接触角呈现不断减小的趋势,这是由于加入的OPTi含有大量亲水性的羟基和磷酸基,这些羟基和磷酸基被水分子水化,从而增强了表面亲水性。

      表2 不同OPTi含量膜的η和接触角

      Table 2 Water content and contact angle of prepared CEM with various OPTi loading ratios

      膜编号η /%接触角/(°)
      mem-011.7688.89
      mem-112.2377.95
      mem-212.3573.72
      mem-412.5064.61
      mem-814.3055.43
    • 2.4 OPTi含量对膜离子交换量和固定电荷浓度的影响

      由图5所示,随着OPTi含量的增加,膜的离子交换容量(IEC)也逐步增大。这主要归因为加入的OPTi为膜提供了更多的离子官能团,强化了膜的离子交换性能。直至OPTi含量达到2%,膜的IEC达到最大值。此后,随着加入OPTi的量增加,膜的IEC又再次降低。这可能是由于膜基质中树脂颗粒被高浓度的OPTi颗粒所包围,限制了树脂颗粒中磺酸基团的交换性能,从而降低了膜的IEC。

      图5
                            不同OPTi含量膜的IEC和FIC

      图5 不同OPTi含量膜的IEC和FIC

      Fig. 5 IEC and FIC of prepared CEM with various OPTi loading ratios

      膜的IEC与η之间存在着一定的关系,共同影响着膜的性能。膜的固定电荷浓度(FIC)为膜的IEC与η的比值。如图5所示,随着膜中OPTi含量的不同,IEC和η的变化,FIC也呈现着一种特殊趋势。高固定电荷浓度可以有效控制膜基质中同离子的迁移通道,从而提高膜的离子选择性。

    • 2.5 OPTi含量对膜的离子迁移数及选择性的影响

      当离子交换膜两侧界面与浓度不同的溶液接触时,跨膜电位差就此形成。而此电位差主要取决该膜的电化学特性以及电解质溶液的性质和浓度。如图6所示,OPTi含量增加至2%时,膜的离子迁移数和离子选择性都呈现上升的趋势。这可能是膜的固定电荷浓度和膜电荷密度升高所致,并且增强了唐南排斥效应。膜表面和膜基质中导电区域的增加使膜周围电场强度得以增强,从而缓和了界面浓差极化的现象。

      图6
                            不同OPTi含量膜的离子迁移数和选择透过性

      图6 不同OPTi含量膜的离子迁移数和选择透过性

      Fig. 6 Transport number and permselectivity of prepared CEM with various OPTi loading ratios

    • 2.6 OPTi含量对膜的面电阻的影响

      在电渗析过程中,离子交换膜的膜电阻对能耗有着重要影响。制备低膜面电阻的离子交换膜对电渗析技术是非常必要的。如图7所示,通过添加OPTi之后,所有改性异相膜的面电阻相较于原膜都有明显的下降,并在OPTi添加量为2%时达到最小值,与原膜相比,下降了71%。这是由于,OPTi的加入使得膜的含水率和IEC都有所升高,在膜基质中形成了更多的反离子通道,从而降低了膜电阻。

      图7
                            不同OPTi含量膜的面电阻

      图7 不同OPTi含量膜的面电阻

      Fig. 7 Surface resistance of prepared CEM with various OPTi loading ratios

    • 2.7 膜的机械性能

      由表3可以看出,膜的拉伸强度随OPTi含量增加变化不是很大,直至含量达到4%后开始下降。当膜受到施加的压力时,膜基质中的孔隙和吸附的水相当于增塑剂使膜能承受一定形变,故含水量高的膜弹性更好。

      表3 不同OPTi含量膜的机械性能

      Table 3 Mechanical properties of prepared CEM with various OPTi loading ratios

      膜编号拉伸强度/MPa断裂伸长率/%
      mem-017.656.45
      mem-116.5910.63
      mem-216.2815.31
      mem-417.3917.92
      mem-815.3211.58
    • 2.8 扩散渗析实验

      如图8所示,溶液中NaCl离子浓度变化由电导率表示。膜的扩散渗析过程属于电渗析过程的反效应,若过多的同离子扩散会使进料液经过电渗析处理效果不理[34]。离子扩散率主要取决于膜中反离子的传输速度,在一定程度上反映了离子交换膜的选择透过[35]。结果显示,随着OPTi的加入,膜对离子扩散出现了明显的阻碍作用,这是由于OPTi的加入提高了膜的离子交换官能团的浓度,使得膜的离子选择透过性得到改善,抑制了同离子扩散。当OPTi含量为2%时,膜的扩散速率较原膜明显降低。之后,由于OPTi含量持续增加,使得膜的含水率和膜面粗糙度也不断升高,这就导致膜对离子的选择截留作用降低,扩散现象明显。

      图8
                            膜的扩散渗析实验中浓缩室电导率与实验时间的关系

      图8 膜的扩散渗析实验中浓缩室电导率与实验时间的关系

      Fig. 8 Curves of conductivity in concentration chamber-experiment time during membrane diffusion progress

    • 2.9 电渗析实验

      为了评价膜对高盐水脱盐性能,在ED实验验中使用了简化的四室电渗析装置,并在实验中使用了一种商用阳离子膜作为参考。

      淡化室中NaCl溶液电导率的变化如图9所示,当电导率低于0.1 mS·cm-1实验结束。同时,本实验考察了各膜脱盐过程中通量、能耗和电流效率,如图10所示。由实验结果可以看出,改性异相膜较商品膜表现出高的脱盐效率,效果最优的为OPTi添加量为2%,这主要归因于其低膜面电阻和高的离子选择性。同时,改性异相膜较商品膜表现出高通量、高电流效率及低能耗的特点,表明其在ED技术处理高盐水的潜在应用。

      图9
                            膜的电渗析实验中淡化室电导率与实验时间的关系

      图9 膜的电渗析实验中淡化室电导率与实验时间的关系

      Fig. 9 Curves of conductivity in desalination chamber-ED experiment time during membrane electrodialysis progress

      图10
                            膜的电渗析实验中能耗与电流效率

      图10 膜的电渗析实验中能耗与电流效率

      Fig. 10 Curves of energy consumption and current efficiency during membrane electrodialysis progress

    • 3 结论

      1) 氨基三亚甲基膦酸为有机磷酸化试剂,使得磷酸基团以P—O键结合的方式成功接枝于TiO2表面。

      2) OPTi的加入提高了膜的离子交换容量,改善膜的离子选择性并且大大降低了膜面电阻,综合膜的各项性能,OPTi含量为2%时为最优选择膜。

      3) OPTi粒子的加入明显改善了膜的电渗析性能,在本实验条件下,改性异相膜能耗较原膜降低了26.68%,电流效率提高了29.27%,且远高于商品异相膜。表明此膜在ED处理高盐水脱盐领域具有应用潜力。

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