煤气化飞灰合成有序介孔纳米氧化硅及其吸附罗丹明 B 的性能
Ordered mesoporous nanosilica derived from coal gasification fly ash for adsorption of Rhodamine B
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摘要: 煤气化飞灰是煤气化产生的固体废物,其产量逐年增多。 受建材市场需求减弱的影响,煤 气化飞灰制备建工建材的传统利用方式受限,亟待寻求高附加值利用技术。 以煤气化飞灰为硅源 制备硅基材料可实现其高附加值利用,但硅提取效率低及所制备材料性能较差限制了该技术的应 用。 基于此,以 Shell 粉煤气化飞灰为硅源,采用微波加热碱溶(微波法)提取硅-水热合成两步法 制备了有序介孔纳米氧化硅(mSiO2),并对比了微波法和常规水热法在提取 Shell 粉煤气化飞灰中 硅元素,以及以2种方法所得提取液为硅源制备的氧化硅性能上的差异。 采用小角XRD、N2吸附/ 脱附、TEM、FTIR 和 Zeta 电位等方法对所制备纳米氧化硅的结构、形貌、官能团和表面电位进行表 征,并研究了其对废水中染料罗丹明 B(RhB)的吸附性能。 结果表明:微波法能快速、高效、选择性 地提取煤气化飞灰中的硅元素,碱灰比(NaOH 与煤气化飞灰的质量比)为 0.5、反应时间为 30 min 时硅的提取率达 20.2%,且除低浓度的铝元素外,无其他杂质元素溶出,利于高纯度纳米氧化硅的 合成。 碱灰比在0.5~1.5时,相同条件下,微波法提取的Si元素浓度为水热法的2.4~3.3倍。 采用 微波加热碱溶提取硅-水热合成两步法制备的氧化硅为高度有序的介孔材料,比表面积高达 1 069 m2 / g,孔体积高达 1.02 cm3 / g,孔径在 2 ~ 6 nm,Zeta 电位为-63.2 mV。 mSiO2 对废水中 RhB 具有良好的吸附能力,室温下可在 10 min 内将溶液中的 RhB 吸附去除 90%以上,最大去除率达 96%,是以水热法所得提取液制备的介孔氧化硅的 1.9 倍。 mSiO2 良好的吸附性能归因于其多孔结 构和丰富的表面负电荷。 吸附 RhB 后的纳米氧化硅可通过煅烧再生。 良好的吸附能力和易再生 优势,使其在吸附领域具有广阔应用前景。Abstract: Coal gasification fly ash (CGFA) is a kind of solid waste produced by coal gasification, and its output in⁃ creases with the development of coal gasification. The traditional utilization way of coal gasification fly ash for build⁃ ing materials is limited by the weakening demand of building materials market. Therefore, it is urgent to seek for high value⁃added utilization technology. Preparation of silicon⁃based materials using CGFA as silicon source can achieve a high value⁃added utilization of CGFA, but the low extraction efficiency of silicon and the poor properties of the pre⁃ pared materials limit the application of this technology. Based on this, an ordered mesoporous nanosilica was prepared via a two⁃step method⁃microwave assisted alkali⁃dissolution process (microwave method) followed by hydrothermal synthesis, using Shell pulverized coal gasification fly ash as silicon source. The differences between microwave method and conventional hydrothermal method in silicon extraction efficiency and the performance of SiO2 derived from the ex⁃ tracted solution obtained by the two methods were compared. The structure, morphology, functional groups and surface potential of the prepared nanosilica were characterized by small⁃angle XRD, N2 adsorption / desorption, TEM, FTIR, zeta potential, and its adsorption performance for Rhodamine B (RhB) was studied. The results show that the micro⁃ wave method is efficient and can selectively extract silicon from coal gasification fly ash. The extraction efficiency of Si reached up to 20.2% within 30 min when the alkali to ash ratio (the mass ratio of NaOH to coal gasification fly ash) was 0.5, and no other impurity ions dissolved except for a low concentration of Al, which is conducive to the synthesis of high⁃purity nanosilica. When the alkali to ash ratio was in the range of 0. 5 - 1. 5, under the same conditions, the concentration of Si extracted by microwave method is 2.4-3.3 times as high as that of hydrother⁃ mal method. The prepared nanosilica was a highly ordered mesoporous material, with a specific surface area of 1 069 m2 /g, pore volume of 1.02 cm3 /g, pore diameter of 2-6 nm, and zeta potential of -63.2 mV. The material has good adsorption capacity for RhB in wastewater. More than 90% of RhB in the solution was removed by mSiO2 within 10 min at room temperature, and the maximum removal rate was 96%, which was 1.9 times as high as that of SiO2 derived from the conventional hydrothermal extraction solution. The excellent adsorption performance of mSiO2 is attributed to its porous structure and abundant negative surface charges. The used nanosilica could easily be regenerated by calcination. The excellent adsorption capacity and the facile regeneration process would endow the ordered mesoporous nanosilica broad application prospects in the adsorption field.