Preparation of lignin surface-functionalized MXene nanosheets and its U(VI)adsorption properties
-
摘要: 为了进一步改善MXene纳米材料对模拟放射性废水中U(VI)的吸附性能,利用天然资源酶水解木质素(EHL)作为生物表面活性剂对MXene进行表面功能化处理,采用SEM-EDS、XRD及FTIR对改性前后的材料进行了表征分析,并在吸附实验中探究了pH、温度、反应时间、干扰离子及不同初始U(VI)浓度等因素对除U(VI)效果的影响。结果表明,EHL阻止了MXene纳米片的聚集堆叠,并且引入了大量活性官能团,提高了EHL功能化MXene纳米片的吸附性能。在MXene与EHL的质量比为1∶5、投加量为0.1 g·L−1、pH为5、温度为303 K时,对U(VI)的最大吸附容量为231.95 mg·g−1。此外,吸附动力学和等温线分析表明,拟二级动力学模型和Freundlich等温线模型能很好地拟合此吸附过程,热力学分析表明其吸附过程是自发吸热的。经历5次循环再生后,对U(VI)的去除率仍在80%以上。表征分析结果表明,MX/EHL与U(VI)之间相互作用机制包括离子交换、静电吸引以及与含氧官能团之间的络合作用。基于此研究,MX/EHL作为一种环境友好型吸附材料,对去除废水中的U(VI)具有巨大潜力。Abstract: In order to further improve the adsorption performance of MXene nanomaterials on U(VI) in simulated radioactive wastewater, the surface functionalization of MXene was carried out by using natural resources of enzymatically hydrolyzed lignin (EHL) as a biosurfactant, and the materials before and after the modification were characterized and analyzed by using SEM-EDS, XRD, and FTIR, and the effects of pH, temperature, and the adsorption experiments were explored, reaction time, interfering ions and different initial U(VI) concentrations on the effect of U(VI) removal. The results show that EHL prevents the re-stacking of MXene nanosheets and introduces a large number of active functional groups, which improves the adsorption performance of EHL-functionalized MXene nanosheets. The maximum adsorption capacity for U(VI) is 231.95 mg·g−1 at the mass ratio of MXene to EHL of 1∶5, the dosage of 0.1 g·L−1, pH=5, and the temperature of 303 K. In addition, the adsorption kinetic and isotherm analyses show that the proposed second-order kinetic model and the Freundlich isotherm model fit this adsorption process well, and the thermodynamic analyses indicate that its adsorption process is spontaneous heat absorption. After five cycles of regeneration, the removal rate of U(VI) is still above 80%. Characterization results reveals that the interaction mechanisms between MX/EHL and U(VI) involve ion exchange, electrostatic attraction, and complexation with oxygen-containing functional groups. Based on this study, MX/EHL has great potential as an environmentally friendly adsorbent material for the removal of U(VI) from wastewater.
-
Keywords:
- MXene /
- lignin /
- nanomaterials /
- U(VI) /
- adsorption performance
-
可再生能源的间隙性和波动性为能量的安全、高效利用带来较大挑战,已经成为经济可持续发展面临的重要议题[1]。钒液流电池(Vanadium liquid flow battery,VRB)可将电能高效储存,具有本征安全、响应速度快和运行寿命长等特点,相对于其他类型储能技术,钒电池技术在大规模、长时储能领域显示出优越的发展前景[1-3]。
作为钒电池的关键部件,质子交换膜(Proton exchange membrane,PEM)需具有如下特性[4-5]:(1)高离子选择性,即高质子传导率和低钒离子渗透率;(2)高拉伸强度和穿刺强度;(3)良好的理化稳定性;(4)较好的经济性。目前,基于全氟磺酸树脂的PEM在VRB中的应用最为广泛,如杜邦公司Nafion系列膜,但其溶胀性和离子选择性等与VRB的严格要求仍存在差距,优化膜的离子渗透性是本领域的研究热点[6-8]。实验表明,向膜中引入具有适宜孔道结构和表面性质的功能材料是改善其离子选择性的有效手段[5],如金属-有机框架(Metal-organic frameworks,MOFs)材料[9-11]。
在MOFs材料中,UIO-66 (Zr-MOF)由六核氧化锆簇作为二级构建单元和1, 4-苯二甲酸接头构建[12],具有刚性结构和较强的耐酸性,同时拥有介于水和离子(<0.3 nm)和钒离子(>0.6 nm)的孔道尺寸[13]。UIO-66主要通过水热合成法制备,但在合成过程中,烘箱加热较难提供均匀的受热环境,存在合成时间长、材料结构均一性差等问题[14]。微波加热可促进反应物中分子或离子直接耦合,实现能量的快速传导,具有反应速率快和产率高等优点,已被广泛用于多种纳米材料的合成[14-16]。Zhai等[6]通过在磺化聚醚醚酮(SPEEK)中掺入15wt% 的传统水热法UIO-66-NH2来改善复合膜的质子传导率,在120 mA·cm−2电流密度下,电池的能量效率(Energy efficiency,EE)为77.3%。Lu等[17]制备高质子选择性的聚多巴胺(PDA)@MOF-808,并将其掺入SPEEK中以优化复合膜的性能,在120 mA·cm−2电流密度下,该膜的EE为83.9%。贾儒等[13]和Wan等[14]也分别对UIO-66的合成和应用展开研究,均采用耗时较长的传统水热法。
鉴于此,本文采用不同加热方式制备氨基官能化的UIO-66 (UIO-66-NH2),验证微波加热在UIO-66-NH2材料的合成效率、结构优化方面的优势,并将其与Nafion 掺杂,通过溶液浇筑法制备复合膜,对膜的理化性质和电池性能进行表征,探讨新型膜材料对钒电池性能的影响。
1. 实验部分
1.1 原材料
氯化锆(ZrCl4,98%)、2-氨基对苯二甲酸(BDC-NH2,99%),上海麦克林生化科技有限公司;Nafion溶液(固含量5%),美国杜邦公司;无水乙醇,沈阳试剂二厂;N, N-二甲基甲酰胺(DMF)、MgSO4、硫酸氧钒(VOSO4·5H2O)、浓硫酸(98%)、乙酸(99%),国药集团化学试剂有限公司。
1.2 UIO-66-NH2的制备
UIO-66-NH2合成原料摩尔比:ZrCl4∶BDC-NH2 = 1∶1。首先,将二者分别溶于20 mL DMF,再在配体溶液中加入2.3 mL乙酸,超声波辅助下混合20 min后得均匀的合成液。随后,将适量上述合成液倒入微波合成罐中,在不同温度下合成15 min,离心后获得棕黄色粉末。将上述粉末分散在无水乙醇中,多次更新乙醇下保持48 h,完成产物清洗。最后,在60℃下干燥12 h,获得产物UIO-66-NH2,记为M-U66-NH2。作为对比,采用同样的合成液,利用传统烘箱加热,在120℃条件下反应24 h制备UIO-66-NH2,经过相同的清洗、干燥处理,获得产物UIO-66-NH2,记为T-U66-NH2。具体操作流程和样品编号见图1和表1。
1.3 复合质子交换膜的制备
以溶液浇筑法制备复合膜[18]:称取一定质量的M-U66-NH2,在超声辅助下分散在Nafion树脂溶液(固含量5%)中,在450 r/min下搅拌10 h后获得铸膜液。将适量铸膜液倒入带有凹槽的玻璃板上,在140℃真空烘箱中处理4 h,除去溶剂后得到复合膜,在恒温、恒湿条件下保存、备用。将掺杂M-U66-NH2的复合膜记作M/N-X,X=1、2、3、6和9,X表示Nafion树脂中M-U66-NH2的质量分数。将掺杂T-U66-NH2的复合膜记作T/N-X,X=3。同时,采用相似工艺制备无M-U66-NH2掺杂的纯树脂膜,记作P-N。具体操作流程和样品编号见图1和表1。
图 1 微波合成氨基官能化的UIO-66 (UIO-66-NH2)及Nafion复合膜的制备过程示意图Figure 1. Schematic diagram of the preparation process of UIO-66-NH2 and Nafion composite membraneM-U66-NH2—UIO-66-NH2 prepared by microwave assisted method; UIO-66-NH2—Zr-MOF when the preparation method does not need to be distinguished; BDC-NH2—2-aminoterephthalic Acid; DMF—N, N-dimethylformamide; HAc—Acetic acid表 1 复合质子交换膜的命名Table 1. Naming of composite proton exchange membranesSample name Instruction M-U66-NH2 "M" represents microwave heating; "U66" refers to the metal-organic framework material UIO-66; Overall, it indicates the UIO-66-NH2 sample prepared by microwave heating. T-U66-NH2 "T" represents traditional oven heating; Overall, it indicates the UIO-66-NH2 sample prepared by oven heating. M/N-X "M/N" represents the composite membrane with M-U66-NH2 and Nafion resin; "X" represents the percentage content of M-U66-NH2 in the membrane. T/N-X "T/N" represents the composite membrane with T-U66-NH2 and Nafion resin; "X" represents the percentage content of T-U66-NH2 added to the membrane. P-N A pure, unmodified Nafion membrane N212 Commercial Nafion 212 membrane from DuPont (USA) 1.4 形貌、结构表征和性能测试
采用X射线衍射仪(XRD,Bruker D8)和傅里叶红外光谱(FTIR,Nicolet 380,扫描范围:
4000 ~750 cm−1)评价粉末结构;扫描电子显微镜(SEM,SU8010,Hitachi)和扫描电子能谱(EDS)表征样品的微观形貌和元素分布;万能拉伸试验机(Instron 1186,加载速度为10 mm/min)检测膜的力学性能。膜面积溶胀率的计算公式如下:
SR = (Swet−Sdry)Sdry×100% (1) 式中:Swet为湿膜面积(cm2);Sdry为干膜面积(cm2)。
吸水率的计算公式如下:
WU = (Wwet−Wdry)Wdry×100% (2) 式中:Wwet为湿膜质量(g);Wdry为干膜质量(g)。
应用紫外分光光度计(TU-1810,Beijing Purcell General Instrument Co., Ltd.)测试膜的VO2+渗透性[7],取样间隔12 h,钒离子渗透率计算公式如下:
VBd(CB(t))dt=APL(CA−CB(t)) (3) 式中:CA为VOSO4溶液侧VO2+浓度;CB(t)为t时刻MgSO4溶液侧VO2+浓度;VB为MgSO4溶液体积;P为钒离子渗透率;L为膜厚度;A为膜的有效面积(1.77 cm2)。
应用电化学工作站(CHI660E,上海辰华)测试膜的离子电导率(σ),计算公式如下:
σ=DRb (4) 式中:Rb为膜的面电阻;D为膜厚度。
采用新威电池测试系统表征VRB的电池性能,电流密度范围为100~200 mA·cm−2。循环测试的电流密度为150 mA·cm−2,循环200次。测试膜的放电容量衰减率,计算公式如下:
容量衰减率=Qdis200Qdis1×100% (5) 式中:Qdis200为循环200次后的放电容量;Qdis1为第一次循环前放电容量。
单次衰减=容量衰减率循环次数 (6) 2. 结果分析与讨论
2.1 UIO-66-NH2的形貌与结构
为了优化UIO-66-NH2的合成参数,考察微波合成温度对材料结构的影响。如图2(a)所示,合成时间为15 min,当温度较低时(60℃),晶体结构较规则,颗粒尺寸约为1 μm,但产率仅为60%。随着合成温度的升高,晶体结构特征逐渐增强。如图2(c)所示,100℃下所合成样品具有明显的近八面体的晶体形貌[18]。当温度升至120℃时,晶体结构更加完整,此时粒径约为200 nm (图2(d)),分散性较好,且产率接近90%。由图2(e)可见,通过普通水热法也可以制备出形貌规则的UIO-66-NH2材料,只是所需的合成时间更长[19]。
XRD图谱反映样品的结晶度,如图2(f)所示,样品在2θ=7.40°和8.66°处出现了较明显的衍射峰,对应UIO-66-NH2的(111)和(002)晶面,在2θ=26.22°和31.86°等处出现强度略低的衍射峰,以上峰位置和强度与文献报道结果基本一致[20],证明本实验成功合成出UIO-66-NH2晶体。而且,随着合成温度的升高,晶体的衍射峰强度逐渐增加,即使在60℃下仍能合成出晶体。主要原因在于微波作用下反应釜内晶体前驱体溶液能够快速、均匀受热,微波的折射和反射诱导晶体快速成核、生长[21],合成效率得到显著提高。
2.2 质子交换膜的形貌与结构
为了更清晰地观察复合膜的微观形貌以及膜厚度,本实验对膜样品进行SEM表征。如图3(a)~3(c)所示,不同膜样品均呈现出较均匀、致密的形貌特征,M-U66-NH2的掺杂量对膜形貌的影响较小。图3(d)~3(f)中,不同膜的厚度相近,约为40 μm。P-N膜的截面更加平滑,随着M-U66-NH2掺杂量的增加,复合膜截面的粗糙度逐渐增加,但晶体的掺入未明显改变复合膜的结构。图3(g)~3(j)清晰地展现出M-U66-NH2在M/N-3膜表面的元素分布情况,与M-U66-NH2相关的Zr、N元素及与Nafion树脂相关的F、S元素在膜表面均匀分布,说明复合膜中M-U66-NH2的分散性良好,未发生明显的团聚现象,这为功能材料充分发挥其表面性质和孔道尺寸等优势提供了条件。
图 3 P-N (a)、M/N-1 (b)、M/N-3 (c) 膜的表面SEM图像;P-N (d)、M/N-1 (e)、M/N-3 (f)膜的截面SEM图像;M/N-3膜的表面EDS元素分布图((g) N;(h) Zr;(i) F;(j) S)Figure 3. Surface SEM images of P-N (a), M/N-1 (b) and M/N-3 (c); Cross-section SEM images of P-N (d), M/N-1 (e) and M/N-3 (f); EDS element images of M/N-3 ((g) N; (h) Zr; (i) F; (j) S)为了探究高M-U66-NH2含量对复合膜结构的影响,本实验制备了M/N-6和M/N-9膜。如图4(a)所示,当掺杂量为6wt%时,复合膜截面出现较多尺寸约为2~3 μm的孔洞,这是由于较高掺杂量下,强相互作用促使M-U66-NH2粒子团聚,导致膜内出现缺陷。当掺杂量增至9wt%时,复合膜截面呈现出非对称结构,膜层中可以观察到大尺寸的M-U66-NH2团聚体。产生该现象的原因在于成膜过程中随着溶剂的缓慢挥发,较大尺寸的团聚体会逐渐下沉,并在玻璃板侧富集,形成高M-U66-NH2含量的多孔、疏松区域,此结构不利于UIO-66-NH2功能的充分发挥。同时,产生的缺陷会加速钒离子的跨膜渗透,降低质子交换膜的离子选择性和力学性能[14]。
通过FTIR分析M-U66-NH2、P-N、M/N-3膜样品的结构特征,如图5所示。M-U66-NH2在
3458 、3356 和1436 cm−1处具有明显的特征峰,分别对应N—H的对称和非对称伸缩振动及N—H的剪切伸缩振动,与文献报道一致[22]。P-N膜在1207 、1151 cm−1处为C—F伸缩振动峰,1053 cm−1处为O=S=O振动峰及980 cm−1处为C—F特征峰,此结果与文献中Nafion树脂的特征峰一致[18]。M/N-3膜的FTIR图谱可以近似为M-U66-NH2和P-N图谱的叠加,表明UIO-66-NH2材料在膜中稳定存在,制膜过程并未破坏其微观结构。2.3 复合质子交换膜的理化性质
吸水率和溶胀率是质子交换膜的重要性能指标。如图6(a)所示,基于M-U66-NH2的亲水性和丰富孔道,复合膜的吸水率和溶胀率均随掺入量的提高而增大[23]。同时,M-U66-NH2的刚性结构赋予膜较低的溶胀率(<4%)[24]。膜的吸水率和溶胀率直接影响其离子传导性能,由图6(b)可见,随着UIO-66-NH2掺杂量的提高,膜的质子传导率逐渐增大,而面电阻逐渐变小,如M/N-3的质子传导率达到122.18 mS·cm−1,此改善效果得益于膜中—NH2和—SO3H形成的酸/碱对及存在的氢键网络[25]。当掺杂量超过6wt%时,M-U66-NH2在膜内团聚而缺陷产生,膜的质子传导率较低。比较可见,M/N-3膜的吸水率、溶胀率和质子传导率均高于T/N-3膜,这与UIO-66-NH2的尺寸均一性和完整结构相关。
通过拉伸测试评价膜的机械强度。如图6(c)和图6(d)所示,M-U66-NH2掺杂量低于3wt%时,复合膜的拉伸强度均高于P-N膜,如M/N-3膜的强度达到27 MPa,也高于T/N-3膜(22.3 MPa)。主要原因是UIO-66-NH2具有刚性结构,且—NH2基团与Nafion的—SO3H基团可形成共轭酸碱对,其强相互作用促使Nafion的分子链与UIO-66-NH2发生物理交联,从而提高了复合膜的力学性能[26]。同时,尺寸更小、更规则的M-U66-NH2与Nafion树脂间的分散更充分、交联程度更高,表现出更优的强化作用[1]。当UIO-66-NH2掺杂量超过6wt%时,膜中的孔洞缺陷导致其机械强度显著降低。
2.4 复合膜的钒离子渗透性和离子选择性
本实验选取的UIO-66-NH2的有效孔径为0.52 nm,介于水分子(<0.3 nm)和钒离子(>0.6 nm)之间[14],可通过筛分效应提高膜的离子选择性。如图7(a)所示,M/N-X系列复合膜的阻钒性更好,如M/N-3膜的钒离子渗透浓度最低,仅为P-N膜的23%左右,而M/N-9膜的阻钒性能最差。当测试时间大于48 h,T/N-3膜的表现略差于M/N-3膜,主要原因是传统水热法所制备UIO-66-NH2的晶体结构不够完善。
高钒离子渗透性不利于钒电池长期稳定运行,如图7(b)所示,优化条件下所制备的M/N-3膜的钒离子渗透率最低,仅为8.3×10−8 cm2·min−1,且该膜的离子选择性达到15.6×105 S·min·cm−3,约为P-N膜的30倍。当UIO-66-NH2掺入量过低或过高时,膜的离子选择性均较低。另外,与M/N-3膜相比,掺杂T-U66-NH2的复合膜具有接近的离子选择性,这说明两种方法所制备UIO-66-NH2对复合膜离子选择性的影响较小。有研究结果指出增加厚度会提高膜的钒离子渗透率,进而降低膜的离子选择性[7, 27-29]。因此,本实验在充分参考文献数据的基础上,为了平衡氢离子、钒离子的渗透情况,确定膜厚度为40 μm左右。
2.5 复合膜的电池性能
分别将P-N、M/N-X和T/N-3膜组装成模拟电池进行测试,评价不同电池的电压效率(Voltage efficiency,VE)、库伦效率(Coulombic efficiency,CE)和能量效率(EE)。由图8(a)可知,在相同电流密度下,随着M-U66-NH2掺杂量的增加,电池的CE逐渐增大,在100 mA·cm−2电流密度下,M/N-3膜电池的库伦效率达到97.66%,高于P-N膜(95.8%)。因膜内粒子团聚造成了结构缺陷,M/N-6和M/N-9膜电池的CE低于M/N-3膜。图8(b)显示M/N-X复合膜的VE高于P-N膜,且随着电流密度的增加,复合膜所装配电池的VE逐渐减小,该趋势与文献报道相似[5]。能量效率是电池性能的综合体现,由图8(c)可见,在电流密度为100~200 mA·cm−2的范围内,M/N-3膜的电池能量效率均高于P-N膜和N212膜(美国杜邦公司Nafion212商品膜),最高达到83.8%,说明M-U66-NH2的掺入有效提升了Nafion膜的电池性能。图8(d)~8(f)更清晰地显示了P-N膜、M/N-3膜和T/N-3膜的性能。在测试电流密度范围内,M/N-3膜的库伦效率与T/N-3膜相当,而其电压效率和能量效率均高于其他两种类型膜样品。可见,适宜比例M-U66-NH2的引入有利于改善膜性能,进而提升钒电池的充放电效率。
在150 mA·cm−2电流密度下,对不同膜所装配电池充放电200次,比较其循环稳定性。如图9(a)所示,在200次的充放电测试过程中,M/N-3和T/N-3膜的电池CE、VE和EE相对较稳定,无明显降低,说明UIO-66-NH2的引入有效阻碍了钒离子在膜内的渗透,保证了质子在膜中快速、稳定传输。此外,在测试周期内,M/N-3和T/N-3膜的能量效率分别稳定在77.8%和76.5%,无明显衰减,说明复合膜的理化稳定性可以满足钒电池工作环境的需求。但是,测试周期内不同电池的容量衰减情况差异较大。由图9(b)可见,P-N膜的电池容量衰减了81%,而经过同样测试后,掺杂UIO-66-NH2膜的电池容量衰减率仅为45%左右,其中基于M-U66-NH2的复合膜显示出更低的容量衰减率,单次衰减率仅为0.19%,较T/N-3膜(0.24%)提高0.05%,较P-N膜(0.41%)提高0.22%,同时,图9(c)证明了掺杂M-U66-NH2的确会优化VRBs所用质子交换膜的电池性能。
图 9 150 mA·cm−2电流密度下复合膜所装配电池的循环效率(a)、容量保持率(b)以及与报道性能的对比(c)Figure 9. Cycle efficiency (a) and capacity retention (b) of composite membranes at 150 mA·cm−2, and comparisons with reported performance (c)PBI—Polybenzimidazole; PS—Polystyrene; GO—Graphene oxide; SPEEK—Sulfonated poly(ether ether ketone); 2D-ZMs—Two-dimensional zeolite3. 结 论
(1)与传统水热法相比,微波加热合成UIO-66-NH2的效率更高,耗时仅为前者的1/96,且所制备晶体的结构更完整、更均匀,粒径约为200 nm,在Nafion溶液中分散性良好。
(2) UIO-66-NH2可改善复合膜的理化稳定性,且可提高膜的质子传导性和离子选择性,优化条件下复合膜的质子传导率可达122.18 mS·cm−1,离子选择性可达15.6×105 S·min·cm−3。
(3)优化条件下复合膜体现出良好的电池性能。在150 mA·cm−2电流密度下,电池的能量效率大于77%,200次循环周期内单次容量衰减率为0.19%,较纯树脂膜提高0.22%。
(4)基于微波法的UIO-66-NH2与Nafion形成的复合膜具有良好的理化性质和电池性能,为全钒液流电池用高性能质子交换膜的设计和制备提供了新的策略,具有良好的发展前景。
-
图 9 MX/EHL吸附U(VI)的Langmuir (a)、Freundlich (b)和Dubinin-Radushkevich (c)等温吸附模型拟合曲线;(d) lnK0与1/T的线性拟合
Figure 9. Fitting curve of Langmuir (a), Freundlich (b) and Dubinin-Radushkevich (c) isothermal adsorption model of U(VI) adsorption by MX/EHL; (d) Linear fit of lnK0 versus 1/T
Ce—U(VI) concentration at adsorption equilibrium; R—Universal gas constant; T—Temperature (K); K0—Equilibrium constant at different temperatures
表 1 MX和MX/EHL的孔隙结构参数
Table 1 Pore structure parameters of MX and MX/EHL
Material Surface area/
(m2·g−1)Pore volume/
(cm3·g−1)Pore diameter/
nmMX 3.8297 0.0100 10.4628 MX/EHL 8.7751 0.0455 20.7320 表 2 MX/EHL对U(VI)的吸附动力学参数
Table 2 The adsorption kinetic parameters of MX/EHL on U(VI)
Name of
samplePseudo-first-order Pseudo-second-order Intraparticle diffusion qe,exp/
(mg·g−1)k1/
min−1qe,cal/
(mg·g−1)R2 k2/
min−1qe,cal/
(mg·g−1)R2 kp1/
(mg·(g·
min0.5)−1)C1 R21 kp2/
(mg·(g·
min0.5)−1)C2 R22 kp3/
(mg·(g·
min0.5)−1)C3 R23 MX 35.22 0.017 3.487 0.882 0.021 35.51 0.999 0.688 29.782 0.973 0.406 31.266 0.989 0.015 35.029 0.804 MX/EHL (1:4) 46.92 0.017 2.737 0.949 0.027 47.13 0.999 0.282 43.819 0.958 0.324 43.568 0.986 0.058 46.175 0.653 MX/EHL (1:5) 48.24 0.018 2.502 0.930 0.030 48.43 0.999 0.338 45.002 0.981 0.303 45.243 0.994 0.035 47.794 0.615 Notes: qe,exp—Actual adsorption capacity at adsorption equilibrium; qe,cal—Calculated adsorption capacity at adsorption equilibrium; k1 and k2—Adsorption rate constants of the pseudo-first and pseudo-second, respectively; R2—Correlation coefficient; kp1, kp2, kp3—Adsorption rate constants of intraparticle diffusion; C1, C2, C3—Adsorption constants of intraparticle diffusion. 表 3 Langmuir、Freundlich和Dubinin‒Radushkevich吸附等温线模型的相关参数
Table 3 Parameters associated with Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherm models
T/K Langmuir Freundlich Dubinin‒Radushkevich qmax/(mg·g−1) KL/(L∙mg−1) R2 KF 1/n R2 qDR E/(kJ·mol−1) R2 293 205.493 0.164 0.890 48.175 0.399 0.982 115.99 1.879 0.554 298 217.057 0.221 0.925 58.802 0.378 0.989 129.09 2.077 0.607 303 231.947 0.251 0.924 65.565 0.379 0.997 138.33 2.337 0.627 Notes: qmax—Maximum adsorption capacity; KL—Langmuir adsorption equilibrium constant; KF and n—Constants that are related to the adsorption capacity and the adsorption intensity, respectively; qDR—Theoretical isotherm saturation capacity; E—Average free energy of adsorption. 表 4 不同吸附剂对U(VI)的吸附去除效果对比
Table 4 Comparison of adsorption and removal effects of different adsorbents on U(VI)
Adsorbent pH T/K qmax/(mg·g−1) Ref. C-TC 5 308 165.43 [20] MXene/SA 4 298 126.82 [34] C-TC-CS 6 313 141.96 [36] PANI/Ti3C2Tx 5 298 102.80 [37] PAO/Ti3C2Tx 4 298 98.04 [38] Ti3C2-AO-PA 8.3 298 81.10 [41] MX/EHL 5 303 231.95 This work Notes: C-TC—Chloroacetic acid modified-Ti3C2Tx; MXene/SA—MXene composite sodium alginate gel microsphere; C-TC-CS—Chloroacetic acid-modified MXene-CS gel microspheres; PANI/Ti3C2Tx—Polyaniline modified MXene composites; PAO/Ti3C2Tx—Polyamidoxime functionalized MXene composite; Ti3C2-AO-PA—Polyamide enhanced amidoxime-functionalized Ti3C2 nanosheet. 表 5 MX/EHL吸附U(VI)的热力学参数
Table 5 Thermodynamic parameters of MX/EHL adsorption of U(VI)
T/K lnK0 ΔG0/(kJ·mol−1) ΔH0/(kJ·mol−1) ΔS0/(J·(mol·K)−1) 293 4.69 −11.43 38.89 175.26 298 5.00 −12.39 303 5.23 −13.18 Notes: ΔH0—Standard enthalpy change; ΔG0—Standard free energy change; ΔS0—Standard entropy change. -
[1] YUAN D, ZHANG S, XIANG Z, et al. Highly efficient removal of uranium from aqueous solution using a magnetic adsorbent bearing phosphine oxide ligand: A combined experimental and density functional theory study[J]. ACS Sustainable Chemistry & Engineering, 2018, 6(8): 9619-9627.
[2] HUANG S, JIANG S, PANG H, et al. Dual functional nanocomposites of magnetic MnFe2O4 and fluorescent carbon dots for efficient U(VI) removal[J]. Chemical Engineering Journal, 2019, 368: 941-950. DOI: 10.1016/j.cej.2019.03.015
[3] HE Z, HUANG D, YUE G, et al. Ca2+ induced 3D porous MXene gel for continuous removal of phosphate and uranium[J]. Applied Surface Science, 2021, 570: 150804. DOI: 10.1016/j.apsusc.2021.150804
[4] ZHANG S, YUAN D, ZHANG Q, et al. Highly efficient removal of uranium from highly acidic media achieved using a phosphine oxide and amino functionalized superparamagnetic composite polymer adsorbent[J]. Journal of Materials Chemistry A, 2020, 8(21): 10925-10934. DOI: 10.1039/D0TA01633K
[5] ZAHERI P, DAVARKHAH R. Selective separation of uranium from sulfuric acid media using a polymer inclusion membrane containing alamine 336[J]. Chemical Papers, 2020, 74(8): 2573-2581. DOI: 10.1007/s11696-019-01029-9
[6] ORREGO P, HERNÁNDEZ J, REYES A. Uranium and molybdenum recovery from copper leaching solutions using ion exchange[J]. Hydrometallurgy, 2019, 184: 116-122. DOI: 10.1016/j.hydromet.2018.12.021
[7] CHEN J, HUANG Q, HUANG H, et al. Recent progress and advances in the environmental applications of MXene related materials[J]. Nanoscale, 2020, 12(6): 3574-3592. DOI: 10.1039/C9NR08542D
[8] YU H, WANG Y, JING Y, et al. Surface modified MXene-based nanocomposites for electrochemical energy conversion and storage[J]. Small, 2019, 15(25): 1901503. DOI: 10.1002/smll.201901503
[9] ZHOU Z, LIU J, ZHANG X, et al. Ultrathin MXene/calcium alginate aerogel film for high performance electromagnetic interference shielding[J]. Advanced Materials Interfaces, 2019, 6(6): 1802040. DOI: 10.1002/admi.201802040
[10] SINHA A, DHANJAI, ZHAO H, et al. MXene: An emerging material for sensing and biosensing[J]. TrAC Trends in Analytical Chemistry, 2018, 105: 424-435. DOI: 10.1016/j.trac.2018.05.021
[11] ZHANG Y, WANG L, ZHANG N, et al. Adsorptive environmental applications of MXene nanomaterials: A review[J]. RSC Advances, 2018, 8(36): 19895-19905. DOI: 10.1039/C8RA03077D
[12] YING Y, LIU Y, WANG X, et al. Two-dimensional titanium carbide for efficiently reductive removal of highly toxic chromium(VI) from water[J]. ACS Applied Materials & Interfaces, 2015, 7(3): 1795-1803. DOI: 10.1021/am5074722
[13] SHAHZAD A, RASOOL K, MIRAN W, et al. Two-dimensional Ti3C2T x MXene nanosheets for efficient copper removal from water[J]. ACS Sustainable Chemistry & Engineering, 2017, 5(12): 11481-11488.
[14] ZHANG P, WANG L, DU K, et al. Effective removal of U(VI) and Eu(III) by carboxyl functionalized MXene nanosheets[J]. Journal of Hazardous Materials, 2020, 396: 122731. DOI: 10.1016/j.jhazmat.2020.122731
[15] ZHANG F, LI S, ZHANG Q, et al. Adsorption of different types of surfactants on graphene oxide[J]. Journal of Molecular Liquids, 2019, 276: 338-346. DOI: 10.1016/j.molliq.2018.12.009
[16] MENG Y, LU J, CHENG Y, et al. Lignin-based hydrogels: A review of preparation, properties, and application[J]. International Journal of Biological Macromolecules, 2019, 135: 1006-1019. DOI: 10.1016/j.ijbiomac.2019.05.198
[17] LUO R, ZHANG W, HU X, et al. Preparation of sodium ligninsulfonate functionalized MXene using hexach-lorocyclotriphosphazene as linkage and its adsorption applications[J]. Applied Surface Science, 2022, 602: 154197. DOI: 10.1016/j.apsusc.2022.154197
[18] WANG S, LIU Y, LYU Q F, et al. Facile preparation of biosurfactant-functionalized Ti2CT x MXene nanosheets with an enhanced adsorption performance for Pb(II) ions[J]. Journal of Molecular Liquids, 2020, 297: 111810. DOI: 10.1016/j.molliq.2019.111810
[19] ZHANG K N, WANG C Z, LU Q F, et al. Enzymatic hydrolysis lignin functionalized Ti3C2Tx nanosheets for effective removal of MB and Cu2+ ions[J]. International Journal of Biological Macromolecules, 2022, 209: 680-691.
[20] XIE L, YAN J, LIU Z, et al. Synthesis of a two-dimensional MXene modified by chloroacetic acid and its adsorption of uranium[J]. ChemistrySelect, 2022, 7(1): e202103583. DOI: 10.1002/slct.202103583
[21] LYU Q F, LUO J J, LIN T T, et al. Novel lignin-poly(n-methylaniline) composite sorbent for silver ion removal and recovery[J]. ACS Sustainable Chemistry & Engineering, 2013, 2(3): 465-471.
[22] HU Y, ZHUO H, LUO Q, et al. Biomass polymerassisted fabrication of aerogels from MXenes with ultrahigh com-pression elasticity and pressure sensitivity[J]. Journal of Materials Chemistry A, 2019, 7(17): 10273-10281. DOI: 10.1039/C9TA01448A
[23] SALEH T A. Carbon nanotube-incorporated alumina as a support for MoNi catalysts for the efficient hydrode-sulfurization of thiophenes[J]. Chemical Engineering Journal, 2021, 404: 126987. DOI: 10.1016/j.cej.2020.126987
[24] WANG Q M, LIU Z H, LYU Q F. Lignin modified Ti3C2T x assisted construction of functionalized interface for separation of oil/water mixture and dye wastewater[J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2023, 656: 130371.
[25] DING L, WEI Y, WANG Y, et al. A two-dimensional lamellar membrane: MXene nanosheet stacks[J]. Angewandte Chemie International Edition, 2017, 56(7): 1825-1829. DOI: 10.1002/anie.201609306
[26] HAN R, MA X, XIE Y, et al. Preparation of a new 2D MXene/PES composite membrane with excellent hydrophilicity and high flux[J]. RSC Advances, 2017, 7(89): 56204-56210. DOI: 10.1039/C7RA10318B
[27] LI S, WANG L, PENG J, et al. Efficient thorium(IV) removal by two-dimensional Ti2CT x MXene from aqueous solution[J]. Chemical Engineering Journal, 2019, 366: 192-199. DOI: 10.1016/j.cej.2019.02.056
[28] GUO Y, GONG Z, LI C, et al. Efficient removal of uranium (VI) by 3D hierarchical Mg/Fe-LDH supported nanoscale hydroxyapatite: A synthetic experimental and mechanism studies[J]. Chemical Engineering Journal, 2020, 392: 123682. DOI: 10.1016/j.cej.2019.123682
[29] DONG X, WANG Y, JIA M, et al. Sustainable and scalable insitu synthesis of hydrochar-wrapped Ti3AlC2-derived nanofibers as adsorbents to remove heavy metals[J]. Bioresource Technology, 2019, 282: 222-227. DOI: 10.1016/j.biortech.2019.03.010
[30] LEVITT A S, ALHABEB M, HATTER C B, et al. Electrospun MXene/carbon nanofibers as supercapacitor electrodes[J]. Journal of Materials Chemistry A, 2019, 7(1): 269-277. DOI: 10.1039/C8TA09810G
[31] MA Z, LI S, FANG G, et al. Modification of chemical reactivity of enzymatic hydrolysis lignin by ultrasound treatment in dilute alkaline solutions[J]. International Journal of Biological Macromolecules, 2016, 93: 1279-1284.
[32] AN L, WANG G, JIA H, et al. Fractionation of enzymatic hydrolysis lignin by sequential extraction for enhancing antioxidant performance[J]. International Journal of Biological Macromolecules, 2017, 99: 674-681. DOI: 10.1016/j.ijbiomac.2017.03.015
[33] KONG L, RUAN Y, ZHENG Q, et al. Uranium extraction using hydroxyapatite recovered from phosphorus containing wastewater[J]. Journal of Hazardous Materials, 2020, 382: 120784. DOI: 10.1016/j.jhazmat.2019.120784
[34] 李仕友, 胡俊毅, 贺俊钦, 等. MXene/SA凝胶微球的制备及对U(VI)的吸附性能[J]. 复合材料学报, 2022, 39(10): 4868-4878. LI Shiyou, HU Junyi, HE Junqin, et al. Preparation of MXene/SA gel microspheres and its adsorption performance for U(VI)[J]. Acta Materiae Compositae Sinica, 2022, 39(10): 4868-4878(in Chinese).
[35] REN X, WANG S, YANG S, et al. Influence of contact time, pH, soil humic/fulvic acids, ionic strength and temperature on sorption of U(VI) onto MX-80 bentonite[J]. Journal of Radioanalytical and Nuclear Chemistry, 2009, 283(1): 253-259.
[36] LI S, HE J, WANG Y, et al. Adsorption characteristics of U(VI) in aqueous solution by chloroacetic acid-modified MXene-CS gel microspheres[J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2023, 674: 131983. DOI: 10.1016/j.colsurfa.2023.131983
[37] 顾鹏程, 宋爽, 张塞, 等. 聚苯胺改性Mxene复合材料对U(VI)的高效富集及机理研究[J]. 化学学报, 2018, 76(9): 701-708. GU Pengcheng, SONG Shuang, ZHANG Sai, et al. Enrichment of U(VI) on polyaniline modified mxene composites studied by batch experiment and mechanism investigation[J]. Acta Chimica Sinica, 2018, 76(9): 701-708(in Chinese).
[38] ZHOU Y, HAO H X, DONG T H, et al. Efficient enrichment of U(VI) by two-dimensional layered transition metal carbide composite[J]. Radiochimica Acta, 2022, 110(5): 311-322. DOI: 10.1515/ract-2021-1130
[39] SHAHZAD A, NAWAZ M, MOZTAHIDA M, et al. Ti3C2T x MXene core-shell spheres for ultrahigh removal of mercuric ions[J]. Chemical Engineering Journal, 2019, 368: 400-408. DOI: 10.1016/j.cej.2019.02.160
[40] FENG X, YU Z, LONG R, et al. Self-assembling 2D/2D (MXene/LDH) materials achieve ultra-high adsorption of heavy metals Ni2+ through terminal group modification[J]. Separation and Purification Technology, 2020, 253: 117525. DOI: 10.1016/j.seppur.2020.117525
[41] ZHANG D, LIU L, ZHAO B, et al. Highly efficient extraction of uranium from seawater by polyamide and amidoxime cofunctionalized MXene[J]. Environmental Pollution, 2023, 317: 120826. DOI: 10.1016/j.envpol.2022.120826
[42] ZAHAKIFAR F, KESHTKAR A R, TALEBI M. Performance evaluation of sodium alginate/polyvinyl alcohol/polyethylene oxide/ZSM5 zeolite hybrid adsorbent for ion uptake from aqueous solutions: A case study of thorium(IV)[J]. Journal of Radioanalytical and Nuclear Chemistry, 2020, 327(1): 65-72.
[43] WU J, ZHENG Z, ZHU K, et al. Adsorption performance and mechanism of g-C3N4/UiO-66 composite for U(VI) from aqueous solution[J]. Journal of Radioanalytical and Nuclear Chemistry, 2022, 331(1): 469-481. DOI: 10.1007/s10967-021-08116-w
[44] WU L, LIN X, ZHOU X, et al. Removal of uranium and fluorine from wastewater by double-functional microsphere adsorbent of SA/CMC loaded with calcium and aluminum[J]. Applied Surface Science, 2016, 384: 466-479. DOI: 10.1016/j.apsusc.2016.05.056
[45] 张鹏丽, 武莉娅, 杨宗政, 等. MXene改性材料的制备及其吸附除Sr2+性能[J]. 复合材料学报, 2023, 40(10): 5678-5691. ZHANG Pengli, WU Liya, YANG Zongzheng, et al. Preparation of modified MXene material and its adsorption performance for Sr2+[J]. Acta Materiae Compositae Sinica, 2023, 40(10): 5678-5691(in Chinese).
[46] WANG L, SONG H, YUAN L, et al. Efficient U(VI) reduction and sequestration by Ti2CT x MXene[J]. Environmental Science & Technology, 2018, 52(18): 10748-10756. DOI: 10.1021/acs.est.8b03711
[47] ZHANG P, WANG L, HUANG Z, et al. Aryl diazonium-assisted amidoximation of MXene for boosting water stability and uranyl sequestration via electrochemical sorption[J]. ACS Applied Materials & Interfaces, 2020, 12(13): 15579-15587.
[48] HALIM J, COOK K M, NAGUIB M, et al. X-ray photoelectron spectroscopy of select multilayered tra-nsition metal carbides (MXenes)[J]. Applied Surface Science, 2016, 362: 406-417. DOI: 10.1016/j.apsusc.2015.11.089
[49] RETHINASABAPATHY M, HWANG S K, KANG S M, et al. Amino-functionalized POSS nanocage-intercalated titanium carbide (Ti3C2T x) MXene stacks for efficient cesium and strontium radionuclide sequestration[J]. Journal of Hazardous Materials, 2021, 418: 126315. DOI: 10.1016/j.jhazmat.2021.126315
[50] MISHRA V, SURESHKUMAR M K, GUPTA N, et al. Study on sorption characteristics of uranium onto biochar derived from eucalyptus wood[J]. Water, Air, & Soil Pollution, 2017, 228: 1-14.
-
目的
新型纳米材料MXene在吸附重金属离子过程中存在稳定性较弱,容易被氧化等不足,此外,在范德华力的影响下,MXene纳米片往往会发生严重的聚集堆叠现象,导致其表面大量的活性位点无法得到有效利用,严重限制了其吸附性能。为了进一步改善MXene纳米材料对模拟放射性废水中U(Ⅵ)的吸附性能,利用天然资源酶水解木质素(EHL)作为生物表面活性剂对MXene进行表面功能化处理,探究酶水解木质素的引入对于MXene纳米材料的作用以及改性前后材料对U(Ⅵ)的吸附性能和作用机制。
方法通过溶液共混法将具有抗氧化性和生物活性的工业副产物酶水解木质素(EHL)引入到MXene纳米材料的表面和层间,制备一种有机-无机杂化复合材料(MX/EHL)。采用现代表征分析技术SEM-EDS、XRD及FTIR等对改性前后的材料进行了表征分析,探究改性前后MXene材料微观结构发生的变化。通过批量静态吸附实验探究pH、温度、反应时间、干扰离子、吸附剂投加量及不同初始U(Ⅵ)浓度等影响因素对吸附剂除U(Ⅵ)效果的影响。通过吸附解吸实验探究吸附剂的循环再生能力。根据吸附实验结果以及表征分析结果探究吸附剂对U(Ⅵ)的作用机制。
结果(1)SEM-EDS、XRD、FTIR等表征分析结果表明酶水解木质素(EHL)成功引入到MXene纳米材料上,并且EHL的引入不仅没有破坏MXene材料的多层结构,而且附着在MXene纳米片层间的EHL颗粒还阻止了纳米片的聚集堆叠,增大了层间距,使得更多的活性吸附位点能够得到利用。此外,EHL表面丰富的含氧基团赋予了其极佳的亲水性和化学反应活性,使其能够与MXene表面的-OH和-F基团产生良好的相互作用,极大地克服了MXene材料在吸附过程中易于氧化的缺点。(2)批量静态吸附实验结果表明,MX/EHL在弱酸性条件下能够有效吸附铀酰离子。在MXene与EHL的质量比为1:5、投加量为0.1 g·L、pH为5、温度为303 K、反应时间为2 h时,对U(VI)的最大吸附容量达到231.95 mg·g,去除率达到96.6%,具有超快的吸附动力学(5 min,去除率>90%),优于同类型的其他吸附剂。吸附动力学和等温线分析表明,吸附过程符合拟二级动力学模型(=0.999),表明化学吸附占主导作用,吸附等温线符合Freundlich模型,说明MX/EHL对U(VI)的吸附以多层吸附为主,U(VI)在MX/EHL非均相表面发生吸附过程。(3)经历5次循环再生后,对U(VI)的去除率仍在80%以上,表明该吸附材料具有良好的循环再生性能。
结论将酶水解木质素(EHL)引入到MXene纳米材料中可以改善纯MXene纳米材料在吸附重金属离子过程中所出现的易聚集堆叠和易氧化的缺点,所合成的MX/EHL复合材料对U(VI)的吸附性能显著提高,在多种干扰离子存在的情况下仍能实现对U(VI)的选择性吸附,并且具有良好的循环再生性能。