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合成染料在诸多行业中被广泛应用,如纺织、皮革、印染、化妆品、造纸等[1-2]。但是,大多数染料及其降解产物具有毒性[3],在进入环境后对生态系统产生威胁。孔雀石绿(MG)是一种常见的阳离子染料[4],极易溶于水,在水环境中不易被降解,具有高毒素,致畸、致癌、致突变等危害[5-6]。目前,常见的处理含染料废水的方法包括吸附、膜处理、絮凝和高级氧化等[7]。但是,传统的吸附和絮凝等方法只能将水溶液中的染料转移到吸附剂中,容易造成二次污染问题[8-9]。而高级氧化法对反应条件要求相对严格,一般在酸性条件下进行,反应后需要对废水进行二次处理[10-11]。膜分离技术成本相对较高,一般在实际应用中很少使用[12]。
近年来,纳米零价铁(nZVI)作为一种新型材料在污染物去除中得到了广泛的应用[13]。nZVI具有高还原性,易制得且价格低廉,对持久性有机污染物以及重金属等污染物都有较好的处理效果。但是nZVI易团聚,且极易被氧化,导致反应活性降低[14-16]。近年来的研究发现,将nZVI负载在多孔吸附介质,如生物炭(BC)、活性炭(AC)和膨润土等成为一种有效的将nZVI分散并保持其反应活性的方法[17-20]。有研究表明,nZVI-AC在吸附染料方面有较好的作用,使用0.5 g·L−1的吸附剂可去除99.41%的MG;通过玉米秸秆在500 ℃的高温下热解制备生物炭,然后制备nZVI-BC磁性复合材料在20 min后对MG染料的去除效率高达99.9%;一种新型复合材料可循环多壁碳纳米管/凹凸棒石负载纳米级零价铁(nZVI/MWCNTs/APT),用于去除阳离子染料MG,在反应90 min时对MG的去除率可达98.9%[21-23],由此可见纳米铁与炭的结合对染料去除效果较好。但是,目前使用的大部分负载介质的颗粒都较小,一部分容易进入环境中,不利于回收利用,且容易产生二次污染问题。此外,在实际水处理过程中,常见的去除工艺包括人工湿地、生物滤池以及反应器技术等,需要使用的材料具备一定的承压能力。因此,需要开发一种具备一定颗粒大小以及强度的材料,以方便应用于实际处理过程。
为了提高nZVI的处理效率,避免其快速氧化、团聚和二次污染等不足,本研究通过液相还原法,将nZVI负载于活性炭粉末(PAC)后,添加高岭土并在高温下烧制,对负载后的材料进行硬化,制备了具有一定强度的硬质纳米零价铁/炭颗粒(nZVI/PAC)。利用单因素实验优化了制备条件,对比了与纯nZVI造粒和纯活性炭造粒对MG的去除差异,探究了初始pH、MG初始浓度、nZVI/PAC投加量以及反应温度对去除结果的影响,并研究了MG的反应动力学以及反应机理,为开发粒状nZVI/PAC材料作为填充材料应用于实际水处理提供了参考。
粒状纳米零价铁/炭的制备及对孔雀绿的降解机理
Removal of malachite green from wastewater by zero-valent iron nanoparticles supported on activated carbon powder
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摘要: 以活性炭粉末(PAC)为载体,在负载纳米零价铁(nZVI)后,利用高岭土作为黏合剂,制备了1 cm大小的粒状纳米零价铁/炭颗粒(nZVI/PAC),对制备条件进行了优化,并采用X射线衍射(XRD)、透射电子显微镜(TEM)、氮吸附/脱附、热重法(TG)对合成对材料进行了表征,, 模拟了其对典型染料孔雀石绿(MG)的去除研究。结果表明,制备的nZVI/PAC材料对nZVI具有较好的分散性,且提高了nZVI的抗氧化能力。在投加10 g·L−1的nZVI/PAC反应体系中,对含有0.1 g·L−1的MG废水的去除率达到99.5%。MG的去除率随着pH的降低而升高,而升温也有利于MG的去除。MG的去除符合准二级反应动力学模型,nZVI/PAC对MG的去除机理主要是破坏了MG的发色基团和共轭结构,使MG染料脱色并从溶液中去除。且该材料浸水后抗压强度可达1.241 MPa,适用于实际工程应用。Abstract: Powder activated carbon (PAC) supported nanoscale zero valent iron composites (nZVI/PAC) were synthesized. Subsequently, granular nZVI/PAC (1 cm) materials were prepared using kaolin clay for sintering and granulation. The optimized conditions for synthesis of granular nZVI/PAC were tested. The resultant materials using X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption/desorption, thermogravimetry (TG). In addition, experiments were carried to investigate removal of malachite green (MG) by the materials. The results showed that the prepared granular nZVI/PAC materials had better dispersion of nZVI and improved the antioxidant capacity of nZVI. The removal rate of MG at concentration of 0.1 g·L−1 reached 99.5% with nZVI/PAC of 10 g·L−1. It also found that the removal rate of MG increased with the decrease of pH, in contrast, the removal rate of MG was enhanced as the temperature increased. MG removal was consistent with a quasi-secondary reaction kinetic model. The mechanism of MG removal by nZVI/PAC is mainly the destruction of MG chromophores and conjugate structures, resulting in MG dye decolorization and removal from the solution. The material has a compressive strength of 1.241 MPa after immersion in water and is suitable for practical engineering applications.
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Key words:
- zero-valent iron nanoparticles /
- pelletized /
- malachite green /
- removal mechanism
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表 1 颗粒nZVI/PAC材料在不同温度下的抗压能力
Table 1. Compressive resistance of granular nZVI/PAC materials at different temperatures
煅烧温度/℃
Calcination
temperature浸水前抗压能力
Resistance to pressure before immersion浸水后抗压能力
Resistance to pressure after immersion in water峰值负荷/N
Peak load峰值应力/Mpa
Peak stress峰值负荷/N
Peak load峰值应力/Mpa
Peak stress400 68.60 0.889 31.89 0.418 600 92.82 1.208 67.24 0.876 800 154.65 2.013 95.34 1.241 1000 297.91 3.865 207.20 2.684 表 2 nZVI/PAC去除孔雀石绿的准一级动力学模型和准二级动力学模型的动力学参数
Table 2. Kinetic parameters of the quasi-first-order kinetic model and quasi-second-order kinetic model for removal of malachite green by nZVI/PAC
MG浓度/
(mg·L−1)准一级动力学
Quasi-first order dynamics准二级动力学
Quasi-second order dynamicsk1/min–1 qe/(mg·g−1) R2 k2/(g·mg−1·min−1) qe/(mg·g−1) R2 50 0.2222 49.656 0.9938 0.0890 49.656 0.9965 100 0.0099 99.932 0.9922 0.0543 99.932 0.9784 150 0.0079 149.806 0.9816 0.0536 149.806 0.9958 200 0.0064 199.404 0.9336 0.0918 199.404 0.9933 -
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