@article{700e31e9d8b840969ae25deaa9e4bbae,
title = "Schottky-like photo/electro-catalytic carbon nanotube composite ultrafiltration membrane reactors",
abstract = "Stimuli-responsive membrane reactors offer advanced strategies towards simultaneous separation and degradation of persistent organic contaminants, allowing for triggered response through photo or electro stimuli. However, the scalable fabrication of stimuli-responsive nanoporous membranes with high selectivity and catalytic reactivity is still challenging in practical application. Here, photo-electro responsive membranes were designed by assembling carbon nanotubes (CNT) scaffolds decorated with conformal nanoscale SnO2 coatings. The membranes, built from spinnable CNT materials supported the generation of a unique class of ultrathin and flexible ultrafiltration membranes with thicknesses down to 25 nm and pore size as narrow as ∼20 nm. The CNTs were used as effective conductive photosensitizers to promote charge transfer from the graphitic to the SnO2 layer, supporting synergistic effects arising from generated Schottky-like diodes to improve the photo/electro-catalytic activity of nanocomposite membranes. The SnO2-CNT membranes exhibited high water permeance of 2.24 × 103 L m−2 h−1.bar−1, and faster reaction kinetics of 77.6 × 10−3 for acetaminophen degradation, which was 2–10 times higher than the kinetics achieved by currently available catalytic membrane reactors. The structural stability and outstanding performance of SnO2-CNT membranes were maintained over 8 reuse cycles with ∼99\% degradation efficiency against acetaminophen in 60 min. The unique solid-state fabrication method of uniformly coated catalytic metal oxide on well aligned CNTs provides a scalable feasible approach to produce high-performance ultrafiltration photo/electro-catalytic membrane reactors towards cost-effective water purification at a competent reaction rate.",
keywords = "Carbon nanotube membranes, Carbon nanotube spinning, Catalytic membrane reactor, Photo/electro-catalytic membrane, Schottky-like nanocomposites",
author = "Rashed, \{Ahmed O.\} and Chi Huynh and Andrea Merenda and Si Qin and Usman, \{Ken Aldren S.\} and Abu Sadek and Lingxue Kong and Takeshi Kondo and Dum{\'e}e, \{Ludovic F.\} and Razal, \{Joselito M.\}",
note = "Funding Information: Here, a novel method to fabricate Schottky-like metal oxide-CNT nanocomposite UF membranes was proposed using ALD of Tin (IV) oxide on CNT membranes synthesized by solid-state dry spinning of drawable CNTs on macroporous carbon nanofibre supports for the first time. The simple dry spinning of drawable CNTs enables the generation of continuous matrix of aligned CNT networks, while the deposition of catalytic metal oxides allows the production of Schottky-like metal oxide-CNT barriers across PECMRs. A proposed mechanism was suggested to explain the synergistic effect of UF and PEC degradation of methylene blue and acetaminophen model organic pollutants across Schottky-like SnO2-CNT nanocomposite membranes. Thus, the technology discussed in this work will enable a simple scalable fabrication route of photo/electro-responsive UF membranes for cost-effective water remediation by CNT-based catalytic membrane reactors.Carbon nanofibrous (CNF) support membranes were first synthesized by electrospinning of 12 wt\% PAN solution in DMF, followed by thermal stabilization, carbonization treatment, and plasma oxidation as reported elsewhere [37,38]. CNT-based membranes were fabricated by dry drawing of horizontally aligned CNT sheets from spinnable vertically aligned CNT arrays (CNT forest). The horizontally aligned CNT sheets were collected on CNF supports and fixed on a drum collector using an automated CNT spinning system (Fig. S1a). Thirty CNT layers of drawn CNT sheets were collected by rotating a drum collector using a rotary motor at a fixed speed of 15 revolutions per minute (RPM), while the CNT alignment direction was kept along the CNT sheet length. The horizontally aligned overlapped CNT sheets were stacked well on CNF support, while solvent densification technique was then used to densify the overlapped CNT webs using ethanol spraying and subsequent evaporation [26,28]. Unlike traditional chemical vapor deposition of CNTs on CNF support [39,40], the CNT dry drawing technology provides simple and unique strategy to develop robust, flexible, and self-standing CNT-based membranes directly assembled and well aligned on CNF supports. The automated CNT spinning system used in this work is described in Fig. S1a, while the whole fabrication process of CNT-based membranes is presented in Fig. S1b.A continuous matrix of overlapped CNT webs was developed by CNT drawing technique and ethanol densification to produce dense and well-stacked CNT membranes on CNF supports thus representing an excellent scaffold for the consequent metal oxide deposition step (Fig. 1a and S4). The deposition of SnO2 thin films was then conducted on the electroconductive CNT-based membranes to generate Schottky-like metal oxide-CNT structures, and thus provide the required functionality and catalytic properties. As shown in Fig. 1b–f, the thickness of deposited SnO2 was found to increase linearly between 50 and 400 cycles from 5 to 40 nm corresponding to a growth rate per cycle (GPC) of ∼0.1 nm/cycle. This revealed the consistent deposition of SnO2 on CNT membranes with increasing the number of SnO2 ALD cycles. Interestingly, a coaxial core shell SnO2-CNT structure was observed at higher ALD cycles of 250 as shown in Fig. 1g, while the analyzed SnO2 thickness for the corresponding SnO2-CNT 250 nanocomposite was found to be around 25 nm. This was in line with the measured thickness of SnO2 at 250 cycles by ellipsometry (Fig. S5a). The mean pore size and pore size distribution of CNT-based membranes were also controlled upon SnO2 deposition with varied ALD cycles as presented in Fig. 1h. The mean pore size of pristine CNT membrane (53.9 nm) was gradually reduced after successive introduction of SnO2 ALD cycles to reach 21.2 nm after 400 ALD cycles. Thus, the role of ALD to produce conformal SnO2 thin films on CNT membranes was demonstrated, while SnO2 thickness and the corresponding pore size of SnO2-CNT nanocomposites were precisely controlled by varying the number of ALD cycles.This work was conducted in part at the Melbourne Centre for Nanofabrication (MCN) in the Victorian Node of the Australian National Fabrication Facility (ANFF). The Advanced Characterisation Facility at Deakin University is acknowledged for the use of SEM and TEM instruments. The authors acknowledge the scientific and technical assistance of the RMIT University's Microscopy and Microanalysis Facility, a linked laboratory of the Microscopy Australia. The authors also acknowledge LINTEC OF AMERICA, INC for supplying the drawable CNT forests used in this work. AM acknowledges the Australian Research Council for financial support (DP200100313). LFD acknowledges the support from Khalifa University through project RC2-2019-007. Funding Information: This work was conducted in part at the Melbourne Centre for Nanofabrication (MCN) in the Victorian Node of the Australian National Fabrication Facility (ANFF). The Advanced Characterisation Facility at Deakin University is acknowledged for the use of SEM and TEM instruments. The authors acknowledge the scientific and technical assistance of the RMIT University's Microscopy and Microanalysis Facility, a linked laboratory of the Microscopy Australia. The authors also acknowledge LINTEC OF AMERICA, INC for supplying the drawable CNT forests used in this work. AM acknowledges the Australian Research Council for financial support ( DP200100313 ). LFD acknowledges the support from Khalifa University through project RC2-2019-007 . Publisher Copyright: {\textcopyright} 2022 Elsevier Ltd",
year = "2023",
month = feb,
doi = "10.1016/j.carbon.2022.12.073",
language = "British English",
volume = "204",
pages = "238--253",
journal = "Carbon",
issn = "0008-6223",
publisher = "Elsevier Ltd",
}