Vertically Aligned Carbon Nanotube Membranes: Water Purification and Beyond

Lee, Jeong Hoon; Kim, Han Shin; Yun, Eun Tae; Ham, So Young; Park, Jeong Hoon; Ahn, Chang Hoon; Lee, Sang Hyup; Park, Hee Deung

doi:10.3390/membranes10100273

Cited by 17 publications

(11 citation statements)

References 137 publications

(226 reference statements)

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Section: Types Of Carbon Nanotube Membranesmentioning

confidence: 99%

“…[ 46 ] CNT density is one of the most important parameters of VA‐CNT membranes, as it is directly related to the permeability of the membrane. [ 47 ] A higher number of pores per unit area results in higher permeability, therefore many studies have been focused in achieving an increment of CNT density to obtain better permeability rates. Among the different attempts to do so, densification of the VA‐CNTs through capillary‐forces or mechanical densification approaches, providing additional membrane pores, has been the most promising method.…”

Section: Types Of Carbon Nanotube Membranesmentioning

confidence: 99%

“…In fact, permeability depends on several aspects such as pore density, CNT size, and the number of CNT walls. [ 21,47,50 ]…”

Section: Types Of Carbon Nanotube Membranesmentioning

confidence: 99%

“…Even so VA‐CNT membranes could be ideal candidates for their application in membrane processes that require hydrophobicity to operate, these membranes still show limitations mainly related to the complicated fabrication methods associated with the synthesis of highly oriented VA‐CNT arrays with optimal pore microarchitecture (i.e., pore size and porosity). [ 12,47 ] The complex fabrication techniques are a big hurdle of these membranes for large‐scale applications; however, important advances have been made in their application in wastewater regeneration or desalination processes that will be reviewed in the following sections.…”

Section: Types Of Carbon Nanotube Membranesmentioning

confidence: 99%

“…Previous theoretical studies have demonstrated that increasing the diameter of the CNTs results in an adverse effect on the salt rejection efficiency. [ 20–102 ] Appropriate pore diameters act as energy barriers at the channel entries, allowing water to pass through the hollow channels while salt ions are rejected. [ 103 ] Computational studies conducted by Corry et al suggested that the ideal CNT diameter to achieve high water permeability and salt rejection should be <0.6 nm.…”

Section: Water Treatment Applications Of Cnt‐based Membranesmentioning

confidence: 99%

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Carbon Nanotube Membranes in Water Treatment Applications

Barrejón

Prato

2021

Adv Materials Inter

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Carbon nanotube (CNT)‐based membranes combine the promising properties of CNTs with the advantages of membrane separation technologies, offering enhanced membrane performance in terms of permeability and selectivity. This review looks at the existing membrane architectures based on CNTs and their main advantages and disadvantages for water treatment applications. The different types of CNT‐based membranes that are reported in the literature are highlighted, as well as their corresponding fabrication methods. Available methodologies for tailoring the final membrane properties and behavior are thoroughly discussed, making special emphasis in chemical modification of the CNT surface. Finally, the most common applications of CNT‐based membranes in water treatment are reviewed, including seawater or brine desalination, oil–water separation, removal of heavy metals, and organic pollutants. The main limitations and perspectives of CNT‐based membranes are also briefly outlined.

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Section: Types Of Carbon Nanotube Membranesmentioning

confidence: 99%

Section: Types Of Carbon Nanotube Membranesmentioning

confidence: 99%

“…In fact, permeability depends on several aspects such as pore density, CNT size, and the number of CNT walls. [ 21,47,50 ]…”

Section: Types Of Carbon Nanotube Membranesmentioning

confidence: 99%

Section: Types Of Carbon Nanotube Membranesmentioning

confidence: 99%

Section: Water Treatment Applications Of Cnt‐based Membranesmentioning

confidence: 99%

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Carbon Nanotube Membranes in Water Treatment Applications

Barrejón

Prato

2021

Adv Materials Inter

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1.1‐Millimeter Tall Vertically Aligned‐Carbon Nanotubes Grown by Cold Wall CVD Using a Novel Multiple‐Purge Method

Coelho

Machado

2022

Adv Materials Inter

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These processes still have limitation in achieving high yield and quality, and any commercial use of CNTs is limited due to these challenges encountered in large scale synthesis. [17] According to Shi et al. (2017), [18] "The poor reproducibility in CNT synthesis via CVD has been attributed to fluctuations in ambient and reactor-sorbed water vapor, as well as to carbonaceous deposits inside reactors leading to growth hysteresis." The presence of water or oxygen influences the growth gases and contributes to the formation or removal of carbon coated on the catalyst nanoparticles and avoiding this block deposition. The formation of carbon block coated on the catalyst nanoparticles prevents the CNT forests to grow taller, terminating the growth process. Thus, to obtain taller CNT forests, the lifetime of the catalyst should be prolonged. [17] The abrupt saturation point is observed for CNT growth rate controlled by laser with Meshot and Hart ( 2008). [19] The carbon atoms that reach the catalyst nanoparticles contribute to the CNT growth, but they also coat in form of amorphous carbon on the nanoparticle. Xiang et al. ( 2008) [20] refers to the growth limits of CNT carpets, explaining the diffusion mechanism of precursors for several different methods. Xiang et al. ( 2007) [21] refers the catalyst encapsulation occurs and it can be controlled during the growth changing the saturation point, creating a continuous growth mechanism. This deposition can be controlled by continuously supplying an etchant material that etches out the amorphous carbon coated on the catalyst nanoparticles. [17] The etchant materials generally used are CO 2 , H 2 O, and O 2 , however, excess levels of oxygencontaining compounds can result in etching of the CNTs themselves. [18] Sugime et al. ( 2021) [22] using the hot wire filament grew CNT around 14 cm but in this case the industrial growth is far in terms of reproducibility in quantity.Recently, Machado Jr. and Coelho (2021) [23] reported a novel method to obtain 140 µm tall VA-CNT forests, using a coldwall technique based on a two-phase deposition step. The first phase consists of the flow of NH 3 for a short period of time together with the C 2 H 2 flow to ensure catalyst activation. In the second phase, NH 3 flow is replaced by H 2 flow during the remaining growth time, permitting to obtain tall VA-CNT forests. In this work the saturation point was reached before the 40 min on deposition step in order to get 140 µm. Furthermore, the annealing temperature should be lower than the growth temperature to obtain taller forests. [24] Moreover, adding a third phase of H 2 during the deposition step at a temperature 50 °C above the previous phase, including a purge between each phase, allowed to achieve forests as high and uniform as This paper reports a multi-phase deposition for the growth of carbon nanotubes, intercalating phases of effective growth with purges of the reactor, based on the method recently proposed by the author to grow tall vertically aligned carbon nanotubes (VA-CNT) in a c...

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