Modification Of Multi-walled Carbon Nanotubes Research Articles

Designing, modelling, and optimising amido black and Eosin B dyes adsorption on MWCNT/ZrO2/Pb nanocomposites from aqueous solution by response surface methodology

ABSTRACT This research illustrates the modification of multi-walled carbon nanotube (MWCNT) by ZrO2/Pb to construct a nanocomposite (MWCNT/ZrO2/Pb-NC) using a simple precipitation technique, as well as to examine the ability of this NC for the adsorption of two dyes, amido black (AB) and Eosin B (EB), in binary systems. FESEM, XRD, FTIR, and EDX were utilised to investigate the MWCNT/ZrO2/Pb-NC. The results suggested that MWCNT/ZrO2/Pb-NCs possessed as-synthesised crystalline nature with a cubic morphology and the average particle size of 30–50 nm. The nano-adsorbent represented herein showed high adsorption efficiency towards AB and EB. The influence of experimental parameters, i.e. pH, initial concentration of dyes, contact time, and MWCNT/ZrO2/Pb-NCs mass, were analysed by central composite design (CCD). The removal percentages more than 95% for AB and EB dyes were obtained by the adjustment of operational conditions at pH 6.0, 0.05 g of MWCNT/ZrO2/Pb-NCs, 15 min stirring, and 15 mg L−1 of each dye. The binding behaviour of the two dyes on the proposed NC was precisely modelled by the Langmuir isotherm. The adsorption capacities for AB and EB were 15.46 and 16.92 mg g−1, respectively. Pseudo-first order model, owing to its high correlation coefficient and closeness of experimental and theoretical data, well represented the behaviour of the corresponding adsorption system. Mechanism examination strongly affirmed the high contribution of external mass transference as the main rate-controlling step. The successful regeneration of MWCNT/ZrO2/Pb-NC signified the usefulness of the NC in wastewater treatment and its capability of environmental management.

Superior operational stability of immobilized l-asparaginase over surface-modified carbon nanotubes

l-asparaginase (ASNase, EC 3.5.1.1) is an enzyme that catalyzes the l-asparagine hydrolysis into l-aspartic acid and ammonia, being mainly applied in pharmaceutical and food industries. However, some disadvantages are associated with its free form, such as the ASNase short half-life, which may be overcome by enzyme immobilization. In this work, the immobilization of ASNase by adsorption over pristine and modified multi-walled carbon nanotubes (MWCNTs) was investigated, the latter corresponding to functionalized MWCNTs through a hydrothermal oxidation treatment. Different operating conditions, including pH, contact time and ASNase/MWCNT mass ratio, as well as the operational stability of the immobilized ASNase, were evaluated. For comparison purposes, data regarding the ASNase immobilization with pristine MWCNT was detailed. The characterization of the ASNase-MWCNT bioconjugate was addressed using different techniques, namely Transmission Electron Microscopy (TEM), Thermogravimetric Analysis (TGA) and Raman spectroscopy. Functionalized MWCNTs showed promising results, with an immobilization yield and a relative recovered activity of commercial ASNase above 95% under the optimized adsorption conditions (pH 8, 60 min of contact and 1.5 × 10–3 g mL−1 of ASNase). The ASNase-MWCNT bioconjugate also showed improved enzyme operational stability (6 consecutive reaction cycles without activity loss), paving the way for its use in industrial processes.

Multiwall-carbon nanotubes and carbon microbeads hybrid utilized for microwave absorption: A cost effective approach

Materials for stealth application requires efficient microwave absorption ability. Since in real practice they have to be applied on large platforms so the uniform dispersion with proper coating of these materials are of utmost importance. Quantity of material requires is high so altogether the cost of coating material defines their overall usage. In this regard hybrid composite material of micro with nano form had been explored as newer microwave absorber. The hybrid involved low cost carbon microspheres which were porous at their surface. These microbeads were well dispersed in the epoxy matrix with the help of modified Multiwall Carbon nanotubes (MWCNTs). A minimum amount of 2% modified MWCNTs with 7% microbeads showed efficient microwave absorption in X band region. Thus this novel hybrid material paves path for easy, low cost and bulk production of functional material which could be utilized for effective microwave absorption application.

Research on mechanical properties and micro-mechanism of Engineering Geopolymers Composites (EGCs) incorporated with modified MWCNTs

Fly ash-based geopilymers have been considered as a promising alternative for the development of high-ductility and eco-frindly engineered materials. In this study, high ductility EGCs were prepared with the incorporation of polyvinyl alcohol (PVA) fiber and modified multi-wall carbon nanotubes (MWCNTs). The compression, flexural and four-point bending tests were used to evaluate the mechanical behaviors of EGCs. The relationship between the ultimate tensile strain and the mid-span displacement was discussed. Meanwhile, the micro-structure and morphology of EGCs were researched using the field emission scanning electron microscopy(FESEM) analysis. The experimental result showed that the compressive and flexural strength of modified geopolymers containing 0.10% modified MWCNTs and 2.00% PVA fiber at curing age of 28d reached maximal value(38.43 MPa and 7.75 MPa). Meanwhile, the uniaxial tensile strain of EGCs also reached maximal value(8.02%), and the corresponding cracking strain, cracking stress and ultimate tensile stress were 0.08%, 2.00 MPa and 4.70 MPa, respectively. In addition, the computing result of ductility indexes and residual strength indexes were well related with corresponding requirements of the deal elastoplastic material. And the four-point bending test could be employed to evaluate the special mechanical properties of uniaxial tensile test. Most importantly, the mechanism of anti-inferiority of EGCs was explained and analyzed from the point of view of microscopic perspective and mesoscopic perspective, and a new mechanism for the modification of PVA fiber and modified MMWCNTs was revealed.

Thin-film composite polyester nanofiltration membrane with high flux and efficient dye/salts separation fabricated from precise molecular sieving structure of β-cyclodextrin

The treatment of dye pollutant and salts by nanofiltration membrane technology usually has the difficulty of low permeability and higher pressure in the case of maintaining a high rejection. In this study, high flux polyester membranes of β-cyclodextrin/trimesoyl chloride - multiwalled carbon nanotubes (β-CD/TMC-MWCNTs) were fabricated on a modified multiwalled carbon nanotubes (MWCNTs) substrate via interfacial polymerization (IP) process. The modified MWCNTs substrate was not only beneficial to modulating the permeation and distribution of aqueous phase monomer (β-cyclodextrin, β-CD), but also in favor of the formation of an ultrathin loose selective polyester active layer due to the porous network structure. The optimization experiments about the reaction time and monomer concentrations were conducted. The experimental results showed that the pure water flux of the as-prepared β-CD/TMC-MWCNTs membrane was 179.93 L m-2h-1 bar-1 (at the pressure of 0.1 MPa) when the reaction time of IP process was 5 min. The single dye removal efficiency of β-CD/TMC-MWCNTs membrane was 97.41% for Brilliant Green (BG) and 96.39% for Congo red (CR), respectively. The removal efficiency of dye/salt mixture by the membrane was above 84% for BG and over 98% for CR, respectively. The results indicated that the membrane had the efficient selective separation performance for the dye/salt mixture benefiting from the special molecular sieving architectures with the precisely intrinsic inner cavity of β-CD/TMC-MWCNTs membrane. Furthermore, the reusability, chlorine resistance, and antifouling ability of the β-CD/TMC-MWCNTs membrane was relatively excellent, and the membrane could effectively remove BG (>93%) and CR (>98%) simultaneously for mixed BG/CR dyes in real water body. These results suggested that the as-prepared β-CD/TMC-MWCNTs membrane had the potential of practical application in dye wastewater treatment.

Removal of Pb2+ from contaminated water using modified multiwalled carbon nanotubes

The effects of ethylene diamine (EDA), poly (amidoamine) (PAMAM) dendrimer and polyvinyl alcohols (PVA) modified multi-walled carbon nanotubes (MWCNTs) were investigated for the adsorption of Pb2+ ions in synthetic water and subsequently, in wastewater samples. The prepared MWCNTs nanocomposites were confirmed by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The concentration of Pb2+ ions were measured by flame-atomic absorption spectroscopy (F-AAS) and inductively coupled plasma-mass spectroscopy (ICP-MS), respectively. Removal of Pb2+ ions from synthetic solutions was carried out by varying parameters such as pH, initial metal ion concentration, contact time and adsorbent dosage. The maximum removal of Pb2+ ions was achievable at a pH of 6.5. The removal efficiency increased (more than 90%) with metal ion concentration; and reached equilibrium at 40 mg/L Pb2+ ions in all nanocomposites. Equilibrium was reached within the first 30 minutes, (at a low adsorbent dosage of 0.03 g) and remained constant in all nanocomposites. The EDA-MWCNTs nanocomposite yielded more than 90% Pb2+ ions removal from synthetic solutions as compared to both PAMAM dendrimers and polyvinyl alcohols. The analysis of wastewater indicated that the concentration of Pb2+ before treatment was ranging from 4.09 to 35.73 µg/L. The nanocomposite was able to remove 99% of Pb2+ from wastewater. Concentrations of Pb2+ varied from 0.200 - 0.234 µg/L after adsorption, which are below acceptable levels recommended by World Health Organisation (WHO), i.e, 10 µg/L Pb2+ .

Multi‐wall carbon nanotubes electrochemically modified with phosphorus and nitrogen functionalities as a basis for bioelectrodes with improved performance

In this study, multi-wall carbon nanotubes (MWCNTs) were electrochemically modified with nitrogen and phosphorus species and employed as platform to immobilize pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) for the fabrication of bioelectrodes for glucose detection. Depending on the upper potential limit used during the electrochemical modification of MWCNTs, the nature and amount of the nitrogen and phosphorus species incorporated in the carbon material surface can be selectively controlled. These species act as anchoring groups for the immobilization of the PQQ-GDH. The value of the upper potential limit used in the electrochemical modification influences the electron-transfer rate between the electrode and the enzyme. The performance of the bioelectrodes for glucose oxidation and detection is improved by the electrochemical modification conditions, leading to an increased sensitivity towards glucose oxidation from 39.2 to 53.6 mA gMWCNT−1 mM−1 in a linear range between 0.1 to 1.2 mM. This electrochemical modification is considered as an alternative for the preparation of highly sensitive glucose bioelectrodes.

Constructing CNTs-based composite membranes for oil/water emulsion separation via radiation-induced “grafting to” strategy

Radiation-induced “grafting to” method was reported for the first time to modify multiwalled carbon nanotubes (MWNTs) with good solution processibility through covalently grafting polyvinyl alcohol (PVA) onto MWNTs’ side walls under γ-ray irradiation at room temperature. FT-IR, 1H NMR, XPS, TEM, Raman and TG results demonstrated that PVA chains were successfully grafted onto MWNTs, which exhibited excellent dispersibility and stability in aqueous solution. Furthermore, CNTs-based composite membranes were facilely constructed by depositing the modified MWNTs on cellulose acetate (CA) microporous membranes with the assistance of vacuum, which showed great hydrophilicity and underwater superoleophobicity. The obtained composite membranes were used to separate dodecane-in-water emulsions through a cross-flow mode, and exhibited high filtration flux (∼1660 L m−2 h−1 bar−1) and oil-rejection (>99.1%). Moreover, high water flux recovery (>86.5%) and almost constant filtration flux were also obtained after five cycles filtration of engine oil-in-water emulsion through the obtained composite membranes, while the bare CA membrane was completely fouled without any flux. This work shows a facile and effective solution process to modify nanocarbon materials and construct functional carbon-based membranes for diverse applications.

Co/multi-walled carbon nanotubes/polyethylene composites for microwave absorption: Tuning the effectiveness of electromagnetic shielding by varying the components ratio

We present novel polyethylene (PE) composites for electromagnetic interference (EMI) shielding application. They are based on cobalt modified multi-walled carbon nanotubes (MWCNTs) produced via in situ polymerization of ethylene, with the Ti-Ziegler–Natta catalyst preliminarily immobilized on Co/MWCNT hybrids. The electromagnetic properties of the composites were tuned by varying the filler loading and Co:MWCNT ratio. The microstructure of the composites and electromagnetic absorption process were carefully characterized by transmission and scanning electron microscopy, X-ray diffraction, vibrating sample magnetometry, ferromagnetic resonance and vector network analysis. The electromagnetic wave absorbing properties of the nanocomposite were investigated in the 10 MHz−18 GHz frequency range revealing that the EMI absorption properties can be tuned by varying the Co:MWCNT weight ratio in the filler. Interestingly, the Co/MWCNT-PE composite with a total filler and Co loading of only 12 and 1.7 wt%, respectively, showed extremely high reflection loss (RL) of −55 dB. More importantly, an effective bandwidth of 12.8–17.8 GHz (RL below −10 dB) was achieved for a matching thickness of only 1.5 mm. The specific RL value (RL/filler loading) of the composite was superior in comparison with the previously reported nanostructured carbon materials. The highly effective absorbing properties of Co/MWCNT-PE composites are explained primarily by the unprecedented uniform filler distribution in the polyethylene as well as by the synergistic effect of MWCNTs and Co nanoparticles. This approach thus offered an effective strategy to design cost-effective, lightweight and flexible EMI shielding materials with tunable dielectric and magnetic performance.

Functionalized CNTs with DOPO and Silicon Containing Agents: Effective Reinforcer for Thermal and Flame Retardant Properties of Polystyrene Nanocomposites.

DOPO and silicon containing agents modified multiwalled carbon nanotubes (MCNTs) were synthesized through sol-gel process and MCNTs are introduced into polystyrene (PS) through in situ polymerization. TEM observations and FTIR results of MCNTs demonstrated that the MCNT nanofillers were coated with the organic/inorganic flame retardant compound. Moreover, the TEM results of the composites indicate that MCNTs dispersed in polystyrene PS matrix uniformly due to the modification. The PS/MCNTs composites showed improved thermal stability as well as flame retardant properties in comparison with PS/CNTs composites, which are due to the good dispersion of MCNT in the PS matrix. MCNTs in the PS matrix can also reduce the peak heat release rate, total heat release and improve the smoke suppression performance. The improved flame retardant properties are attributed to the char reinforcing effect of CNTs, which can provide enough time for MCNTs and organic/inorganic compound to trap the degradation of polymer chains and catalyze the formation of char. The char layers can not only serve as an efficient insulating barrier to reduce the exposure of PS matrix to heat source but also retard the releasing of combustible gas.

Improvement of the electromechanical properties of thermoplastic polyurethane composite by ionic liquid modified multiwall carbon nanotubes

Abstract Carbon nanotubes (CNTs) were non-covalently modified by two categories of ionic liquids (ILs), including 1-vinyl-3-ethylimidazole bromide (VEIMBr) and 1-vinyl-3-hexylimidazole bromide (VHIMBr) in the ratio of 1:1 and 1:4, respectively. The surface interaction between CNTs and ILs was well-characterized by FTIR, Raman spectra, XPS, etc. Thermoplastic polyurethane (TPU) containing different amounts of CNTs/ILs was fabricated by melting blending method. TPU-CNTs/ILs composites exhibited simultaneously enhanced electromechanical properties with improved dielectric constant and lowered elastic modulus. The electromechanical sensitivity of sample TPU-3CNT/12VHIMBr increased by approximately 45 times in comparison with that of pure TPU at 200 Hz. Besides, improved dispersion of CNTs/ILs in the TPU matrix was also exhibited.

The effect of MWCNT modification on structural and morphological properties of Li4Ti5O12

Lithium titanium oxide (Li4Ti5O12) particles were surface-modified with 1–5% wt. of multi-walled carbon nanotubes (MWCNT) using a new low temperature method (LTM). Subsequent techniques have been applied to characterize all materials: X-ray powder diffraction (XRD), Raman and X-ray photoelectron (XPS) spectroscopy, scanning electron (SEM), transmission (STEM), and atomic force (AFM) microscopy. The selected materials have been subjected to preliminary electrochemical analysis. The effect of the synthesis conditions on the obtained series of LTO/1–5% wt. MWCNT nanocomposites was analyzed. X-ray diffraction showed that the crystal structure of LTO is not affected by the multi-walled carbon nanotubes (MWCNT) modification. Raman spectroscopy confirms the XRD results that the MWCNTs do not affect the LTO structure and all nanocomposites show similar levels of defects and/or degree of graphitization. The XPS measurements showed the most intense line at the binding energy of 284.5 eV, which corresponds to the C=C/C-C bonding in carbon atoms in the graphitic structure on the surface of the LTO material. Additionally, the peak at 285.3 eV was attributed to aliphatic structures, edges, and defects in the graphitic nanotube structure, whereas the peaks at 286.1, 287.6, 289.0 and 290.1 eV, correspond to CO, CO, HO-C=O, and OCOO, carbon atoms attached to different oxygen-containing moieties, respectively. CNTs were well distributed between LTO particles, as revealed by STEM observations. Single CNTs or agglomerates by joining LTO particles created cross-links for electron transfer. The relationship and effect between the structural and morphological analysis of spinel Li4Ti5O12 structure modified with carbon nanotubes was examined for the first time in this work. The performed preliminary electrochemical measurements revealed that the best electrochemical properties was obtained for LTO powder modified with 1%wt. of MWCNT. After 50 cycles of charge/discharge processes at the current rate of 1 C, the LTO/1%wt. MWCNT powder retained more than 98% of its specific capacity.

Development of Cobalt coated MWCNTs/Polyurethane composite for microwave absorption

This research work describes the design and method of development of microwave absorber and was conducted for analysis of reflection loss performance with the magnetic modifications of Multi-Walled Carbon Nanotubes (MWCNTs). Cobalt coated Multi-Walled Carbon Nanotubes composites were prepared by three step methods. Composites were developed with varying weight percentage of Cobalt (II) Chloride Hexahydrate and Multi-Walled Carbon Nanotubes. The morphology, elementary analysis and absorbing properties of Cobalt coated Multi-Walled Carbon Nanotubes composites were studied by FESEM, EDX and Vector Network Analyzer. The obtained Co coated MWCNTs/PU composite demonstrated the maximum reflection loss of -21.06 dB at 12.63 GHz and the maximum absorption bandwidth of 3.7 GHz, in the frequency range of 8-13 GHz with 3 mm thickness. These microwave absorption parameters can be credited to synergistic effect of improved matched impedance and greater microwave attenuation properties of the absorber. The combined usage of dielectric loss and magnetic loss absorber design shows great diversity and can be a promising candidate for designing high performance microwave absorbing materials.

Microwave-absorption characteristics of polyaniline-coated multi-walled carbon nanotube composites

ABSTRACT In this study, the microwave-absorption characteristics of multi-layered radar-absorbing structures (RASs) were investigated. Electrical-grade glass (e-glass)/epoxy composites containing modified multi-walled carbon nanotubes (MWCNTs) were fabricated. The poly aniline (PANI) coated MWCNTs was obtained by in-situ polymerisation of aniline in the presence of MWCNTs. The PANI-coated MWCNTs (PCNTs) were then used as reinforcements in the polymer matrix, and their morphologies, microstructures, thermal stabilities, and microwave-absorbing properties were investigated. The complex permittivity and permeability of the composites were measured and found to have increased with increasing filler concentration. Microwave absorbing properties were analysed via waveguide measurement. The three-layered RASs reinforced with PCNTs having a thickness of 4 mm exhibited a RL of –5 dB over the entire X-band and a reflection peak of –24.53 dB at 10.0 GHz. Hence, the epoxy/PCNTs composites are suitable for use in microwave-absorption applications.

Convenient CNT-Paper Gas Sensors Prepared by a Household Inkjet Printer.

A hydrosoluble light-sensitive polymer named PSAG (poly-styrenesulfonate acrylic acid glycidyl methacrylate) was synthesized by acrylic acid (AA), sodium 4-styrenesulfonate (SS), and glycidyl methacrylate (GMA). PSAG is used to modify multiwall carbon nanotubes (MWCNTs) with a length diameter between 0.004 and 0.016. An inkjet conductive ink was formed by well-dispersed MWCNTs in aqueous and organic solvents, which could adjust the surface tension and viscosity of the ink. Gas sensors were then fabricated using this conductive ink on a household inkjet printer. The sensors demonstrated good reproducibility and acceptable recovery time (<200 s) to ammonia, methanol, and acetone. The resistance of the inkjet-printed sensor electrodes remained stable in the process of bending the sensors to different angles because of ultraviolet curing.

Silicon Phthalocyanine Modified Multi-Walled Carbon Nanotubes As a Novel Metal-Free Catalyst for the Oxygen Electroreduction

Finding an alternative catalysts for the oxygen reduction reaction (ORR) has been a key issue in modern electrocatalysis. Traditional platinum-based catalysts are not viable in the long term and thus much effort has been focused on non-precious metal catalysts. Heteroatom doped and metal-heteroatom co-doped carbon materials have emerged as the main candidate for replacing the platinum-based catalysts. Different MN4 macrocycles, such as metal phthalocyanines and porphyrins, have been studied as promising materials to prepare electrocatalysts for ORR in alkaline media [1]. While the development of non-precious metal and non-metal carbon catalysts has gained a lot of attention recently, non-metal phthalocyanines are a less studied topic [2].In this work a novel catalyst material including multi-walled carbon nanotubes (MWCNT) and silicon phthalocyanine dichloride (SiPcCl2) was synthesised and the electrochemical activity towards the oxygen reduction reaction (ORR) in alkaline media was studied. Different ratios of phthalocyanine-to-nanotubes were pyrolysed at 800 °C. After optimising the ratio of phthalocyanine-to-nanotubes, the pyrolysis process was also carried out at different temperatures, but the results showed that the best temperature for pyrolysis is still 800 °C. ORR activity on SiPc/MWCNT catalyst was studied in 0.1 M KOH by employing rotating disc electrode method. Physical characterisation was carried out with X-ray photoelectron spectroscopy and transmission electron microscopy. The results showed successful incorporation of silicon and nitrogen into the carbon framework. We show that doping MWCNTs with a non-metal phthalocyanine creates a highly active ORR catalyst rivaling the activity of metal-based catalysts in alkaline conditions. This work clearly demonstrates that non-metal macrocyclic compound modified carbons, similar to the the SiPc/MWCNT can be used as alternative cathode catalysts for the metal-air batteries and alkaline membrane fuel cells.[1] Y. Liu, X. Yue, K. Li, J. Qiao, D.P. Wilkinson, J. Zhang, PEM fuel cell electrocatalysts based on transition metal macrocyclic compounds, Coord Chem Rev. 315 (2016) 153-177.[2] K.-K. Türk, K. Kaare, I. Kruusenberg, M. Merisalu, U. Joost, L. Matisen, V. Sammelselg, J.H. Zagal, K. Tammeveski, Oxygen electroreduction on zinc and dilithium phthalocyanine modified multiwalled carbon nanotubes in alkaline media, J. Electrochem. Soc. 164 (2017) H338-H344.

Fabrication of cobalt filled multi-walled carbon nanotubes/polyurethane composite for microwave absorption

This research work describes the design and method of development of microwave absorber. This study was conducted for analysis of reflection loss performance with the magnetic modifications of Multi-Walled Carbon Nanotubes (MWCNTs). Cobalt filled Multi-Walled Carbon Nanotubes composites were prepared by three step method. Composites were developed with varying weight percentage of Cobalt Sulphate and Multi-Walled Carbon Nanotubes. The morphology, elementary analysis and absorbing properties of Cobalt filled Multi-Walled Carbon Nanotubes composites were studied by FESEM, EDX and Vector Network Analyzer. The maximum reflection loss is observed for (50% MWCNT and 50% Cobalt Sulphate) is −30.22 dB at 11.8 GHz and the maximum bandwidth window is available for (40% MWCNT and 60% Cobalt Sulphate) is 3.9 GHz in the frequency range of 8–13 GHz with 3 mm thickness, which can be credited to synergistic effect of improved matched impedance and greater microwave attenuation properties of the absorber. The combined usage of dielectric loss and magnetic loss absorber design shows great diversity and can be a promising candidate for designing high performance microwave absorbing materials.

Surface modification of multiwall carbon nanotubes by electrochemical anodic oxidation

Surface modification of multiwall carbon nanotubes by electrochemical anodic oxidation

Influence of preparation methods on the activity of macro-structured ball-milled MWCNT catalysts in the ozonation of organic pollutants

A series of macro-structured catalysts consisting of nanostructured layers of mechanically processed multiwalled carbon nanotubes (MWCNT) coated onto cordierite monoliths were prepared using a novel methodology and assessed as catalysts in the ozonation of a model organic pollutant. The often used chemical vapor deposition method for formation of nanostructured layers of carbon materials is, by nature, incompatible with ball-milling or other methods for mechanical or mechano-chemical modification of MWCNT. The preparation method here described was designed to translate the positive effect observed in the performance of ball-milled MWCNT as ozonation catalysts when compared with unmodified MWCNT to macro-structured catalytic systems. The performance of such macro-structured catalysts in the ozonation of organic pollutants is reported and analyzed for the first time. The effect of the preparation methodology, which includes physical functionalization of the MWCNT with a non-ionic surfactant (Triton X-100®), in the performance of the powder catalysts was evaluated. It was found that, for the coated nanostructured layers, the decrease in the expected activity is related to the packing of the materials. Nevertheless, the catalytic nanostructured coated layers were found to compare favorably with a reference sample. Thus, the beneficial effect of ball-milling MWCNT is still retained upon coating, even with a decrease in the intrinsic activity of the powder material. The increase in MWCNT mass in the coated samples introduces diffusion limitations, suggesting that creating a macroporous system in the MWCNT layers might be desirable. The introduction of oxygen-containing surface functionalities improved the long-term stability of the nanostructured catalytic layers.

Influence of modified multi-walled carbon nanotubes on the mechanical behavior and toughening mechanism of an environmentally friendly granulated blast furnace slag-based geopolymer matrix

This study aimed to investigate the mechanical behavior of an environmentally friendly granulated blast furnace slag-based geopolymer matrix reinforced with modified multi-walled carbon nanotubes (MWCNTs). The modified MWCNTs were obtained using a modification method combining nitric acid and sulfuric acid and were then dispersed using sodium dodecylsulfate (SDS) as a dispersant. Two types and three concentrations of MWCNTs were mixed directly into the aqueous solution, sonicated, and then mechanically mixed with waste granulated blast furnace slag to form the geopolymer matrix. Raman and Fourier transform infrared (FT-IR) spectroscopy were used to evaluate the ordered structure and crystallization degree of the modified MWCNTs. Then, the dispersity of the modified MWCNTs was characterized using transmission electron microscopy (TEM). The compressive and bending strengths were measured to evaluate the mechanical behavior of specimens. Moreover, the polycondensation products, polycondensation degree, pore structure, and microscopic morphology of the geopolymer matrix were analyzed using X-ray diffraction (XRD), FT-IR spectroscopy, nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), and field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDS). The experimental results showed that the incorporation of 0.1% functionalized MWCNTs had an optimal influence on the fluidity and mechanical behavior. The slump diameters of geopolymers with 0.1% functionalized MWCNTs with and without SDS were increased by 16.3% and 23.5%, respectively, compared with the reference geopolymer matrix. For geopolymer matrix samples at a curing age of 28 d, the compressive strength of geopolymers with 0.1% functionalized MWCNTs with and without SDS were increased by 16.3% and 17.6%, respectively. For the bending strength, the corresponding increases were 17.6% and 18.7%, respectively. It was found that functionalized MWCNTs could increase the degree of polycondensation, leading to a more traditional amorphous N-A-S-H phase, a finer C–S–H phase, more Q4 (2Al) and Q4 (3Al), and lower porosity. In addition, the propagation of micro-cracks in the geopolymers was inhibited by the incorporation of functionalized MWCNTs.