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首页> 外文期刊>RSC Advances >Hematite decorated multi-walled carbon nanotubes (alpha-Fe2O3/MWCNTs) as sorbents for Cu( II) and Cr(VI): comparison of hybrid sorbent performance to its nanomaterial building blocks
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Hematite decorated multi-walled carbon nanotubes (alpha-Fe2O3/MWCNTs) as sorbents for Cu( II) and Cr(VI): comparison of hybrid sorbent performance to its nanomaterial building blocks

机译：赤铁矿装饰的多壁碳纳米管（α-Fe2O3/ MWCNTs）作为Cu（II）和Cr（VI）的吸附剂：混合吸附剂性能与其纳米材料结构单元的比较

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摘要

Major hurdles in the application of engineered nanomaterials for water treatment include loss of reactive surface area arising from particle aggregation and the development of application platforms that limit their potential release into the treated water supply. Here, we develop hybrid nanostructures through the growth of hematite (alpha-Fe2O3) nanoparticles, which are recognized sorbents for various heavy metals, on multi-walled carbon nanotubes (MWCNTs). The hybrid nanostructures were synthesized via hydrolysis of ferric nitrate in the presence of carboxylated MWCNTs, and their activity as sorbents toward Cu(II) and chromate (CrO42-) was examined as a function of pH (i.e., pH-edge experiments) and initial metal concentration (i.e., adsorption isotherms). Characterization of alpha-Fe2O3/MWCNT nanostructures via Raman spectroscopy and transmission electron microscopy (TEM) with selected area electron diffraction (SAED) confirmed the deposited iron phase as alpha-Fe2O3. Further, complementary acid digestions and TEM imaging revealed that the amount (0.1 and 0.5 g g(-1) alpha-Fe2O3/MWCNT) and size [5.9 (+/- 1.1) and 8.9 (+/- 1.5) nm, respectively] of a-Fe2O3 nanoparticles immobilized on MWCNTs were tunable during synthesis. Generally, mass-normalized concentrations of adsorbed Cu(II) and CrO42- were greatest for alpha-Fe2O3/MWCNT hybrids relative to adsorption on either carboxylated MWCNTs or freely suspended alpha-Fe2O3 nanoparticles, with evidence implicating alpha-Fe2O3 as the active sorbent phase in hybrid materials. Indeed, per unit mass of available alpha-Fe2O3, hybrid sorbents exhibited capacities comparable to or exceeding most other iron-based sorbents for Cu(II) and CrO42- (from 220 to 470 mg Cu(II) per g alpha-Fe2O3 and 60 mg CrO42- per g alpha-Fe2O3, respectively, at pH 6 and 20 degrees C). The enhanced sorption capacity of the hybrid nanostructures is due, at least in part, to the greater available surface area of alpha-Fe2O3 nanoparticles immobilized on MWCNTs when compared to their more extensively aggregated state in suspension. Notable differences in the pH-dependent trends of Cu(II) and CrO42- uptake on alpha-Fe2O3/MWCNT hybrids, along with differences in zeta potential measurements across pH, also suggest that the immobilized alpha-Fe2O3 nanoparticles may exhibit unique surface reactivity relative to their freely suspended analogs as a result of their association with the negatively charged MWCNT surface.
机译：工程纳米材料在水处理中的应用中的主要障碍包括颗粒聚集引起的反应表面积的损失以及应用平台的发展，这些应用平台限制了它们潜在地释放到处理后的水源中。在这里，我们通过在多壁碳纳米管（MWCNT）上生长赤铁矿（alpha-Fe2O3）纳米颗粒（公认的各种重金属吸附剂）来开发混合纳米结构。在羧基化的碳纳米管存在下，通过硝酸铁的水解合成了杂化的纳米结构，并考察了它们作为吸附剂对Cu（II）和铬酸盐（CrO42-）的活性随pH的变化（即pH边沿实验）和初始金属浓度（即吸附等温线）。通过拉曼光谱和透射电子显微镜（TEM）以及选定区域电子衍射（SAED）表征α-Fe2O3/ MWCNT纳米结构，证实了沉积的铁相为α-Fe2O3。此外，互补酸消化和TEM成像显示，其量（0.1和0.5 gg（-1）alpha-Fe2O3 / MWCNT）和大小[分别为5.9（+/- 1.1）和8.9（+/- 1.5）nm]。固定在MWCNTs上的α-Fe2O3纳米颗粒在合成过程中是可调的。通常，相对于在羧基化MWCNT或自由悬浮的α-Fe2O3纳米颗粒上的吸附，对于α-Fe2O3/ MWCNT杂化物，吸附的Cu（II）和CrO42-的质量标准化浓度最大，证据表明α-Fe2O3作为活性吸附剂相在混合材料中。确实，每单位质量的可用α-Fe2O3，杂化吸附剂对Cu（II）和CrO42-的吸附能力与其他大多数铁基吸附剂相当或超过（每gα-Fe2O3和60 g含220至470 mg Cu（II））分别在pH 6和20摄氏度下，每克α-Fe2O3含CrO42-。杂化纳米结构的吸附能力的提高至少部分是由于与其悬浮液中更广泛的聚集状态相比，固定在MWCNT上的α-Fe2O3纳米颗粒具有更大的可用表面积。 α-Fe2O3/ MWCNT杂化体对Cu（II）和CrO42-吸收的pH依赖性趋势的显着差异，以及整个pH值的Zeta电位测量值的差异，也表明固定化的α-Fe2O3纳米粒子可能表现出独特的相对表面活性由于它们与带负电荷的MWCNT表面缔合，导致其自由悬浮的类似物的活性降低。

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