Enhancement of the Adsorption Performance of Multiwalled Carbon Nanotubes via APTES Functionalization for Phenol Removal

The nanofluids characterization is of fundamental importance to predict their applicability in a real heat transfer situation. In addition to the transport properties, the nanofluid stability is an important factor to be studied, due to the long pumping, heating, cooling and resting cycles the fluids are usually subjected to. Carbon nanotubes have great potential to be used in nanofluids, due to their high thermal conductivity and low density. However, for aqueous medium, stability requires the use of stabilization methods. This work carried out the study of the transport properties and stability of nanofluids with multiwalled carbon nanotubes (MWCNT), using three stabilization methods: Triton X-100 (TrX–MWCNT) and Arabic gum (AG–MWCNT) as surfactants and functionalized carbon nanotubes with COOH group (COOH–MWCNT). These three nanofluids were compared to investigate the best configuration for heat transfer processes. The thermal conductivity was studied using the hot wire method; rheology was studied through three curves in rotational rheometer of concentric cylinders; specific heat was studied by the differential scanning calorimetry method; density was measured by the Coriolis Effect method; nanoparticles size and zeta potential were measured by the dynamic light scattering method. The COOH–MWCNT nanofluids present the highest thermal conductivity increase reaching 15% at 60 °C and 12% at 30 °C with 1wt% while the A.G–MWCNT and TrX–MWCNT reach 11% and 7.5%, respectively, at 30 °C. A.G–MWCNT nanofluids showed greater stability after long sonication times, while COOH–MWCNT presents best dispersion at 0.125 and 0.25 wt%, from 40 to 160 min of sonication. The specific heat increases with temperature and decreases with MWCNT concentration; however, it presents a peculiar increase in the concentration of 0.25 wt%, increasing about 0.5% and 4.5% for A.G–MWCNT and COOH–MWCNT, respectively at 60 °C. COOH–MWCNT nanofluids showed a thixotropic behavior for 0.5 and 1.0 wt% and large viscosity increase reaching 3.75 and 5.5 times the base fluid viscosity at 5 °C and 60 °C, respectively, with 1 wt%. The nanofluids A.G–MWCNT and COOH–MWCNT present good stability, as well as an increase in transport properties, optimized at a concentration close to 0.25 wt% and the COOH–MWCNT nanofluids can be stabilized simply by changing the water pH.

Carbon Nanotubes (CNT) have emerged and gained great interest for research in many applications because of their unique specific characteristics such as having high porosity, high surface area and the existence of a wide spectrum of surface functional groups through chemical modification. Multiwalled carbon nanotubes (MWCNT) is a type of CNT that comprises of multiple layers of concentric cylinders. The overall study of this research work is to modify MWCNT to become a good adsorbent that can adsorb CO2 at its optimum capacity. In order to make MWCNT as an efficient adsorbent, surface treatment on pristine MWCNT is necessary to overcome the hydrophobicity issue by the introduction of carboxyl group. Upon the surface treatment, functionalization of MWCNT with 3-Aminopropyl triethoxysilane (APTS) was conducted to obtain the attachment of amine group that will assist MWCNT in adsorbing CO2. The surface treatment and functionalization process undergone by MWCNT changed the physical properties of MWCNT such as the surface area, pore volume, and pore size distribution. These properties can be determined using surface area and pore analyzer (SAP). Sample that treated with the mixture of nitric and sulfuric acid (HNO3/H2SO4) and functionalized with APTS gives the lowest surface area (22.07 m2/g) and pore volume (0.06 cm3/g). The pore size distribution also decreases due to the most presence of functional group onto the surface of modified MWCNT. This research paper is focusing on the effect of surface area, pore volume, and pore size distribution on the modified MWCNT.

Dispersibility and chemical bonds between multi-walled carbon nanotubes and poly(ether ether ketone) in nanocomposite fibers

Electrical conductivity and thermal stability of polypropylene containing well-dispersed multi-walled carbon nanotubes disentangled with exfoliated nanoplatelets

The adsorption performance of multi-walled carbon nanotubes (MWCNTs) towards CO2 gas was enhanced by covalently grafting of phenylenediamine (PDA) via an activation-grafting process. Different loading amounts were achieved by changing the activation time and the dosage of activating agent. The so-synthesized adsorbents were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, Thermogravimetry analysis, Transmission electron microscope, Raman spectroscopy and Nitrogen adsorption–desorption analysis. The CO2 adsorption properties were studied via static volumetric method. The results indicated that the modification process did not alter the crystal structure, whilst the quantity of defect sites and amorphous structures increased greatly. Moreover, the average pore size after functionalization increased from 9.68 to 23.80 nm. 0.59 mmol·g−1 of CO2 were captured by aminated MWCNTs at 303.15 K and 200 kPa, while the adsorption capacity of the raw materials was only 0.17 mmol·g−1 under the same conditions. Adsorption–regeneration cycles exhibited the stability of the PDA modified MWCNTs during the prolonged cyclic operations. We found that the adsorption of CO2 on MWCNTs belonged to physical adsorption and the adsorption behavior of CO2 on PDA modified MWCNTs was a chemical adsorption. The effective enhancement of the CO2 capture ability was attributed to the increased number of active sites, which offered stronger interactions with CO2 after PDA grafting.

A facile and novel approach towards carboxylic acid functionalization of multiwalled carbon nanotubes and efficient water dispersion

In this paper, synthesis and characterization of polymer intercalated carbon nanotube buckypaper for improved structural, morphological, electrical, and thermal properties have been discussed. Resin-infiltration technique was opted for the preparation of polyvinylchloride intercalated poly(ethylene glycol) -modified-multi-walled carbon nanotube buckypaper. The effect of increasing purified nanotube (purified multi-walled carbon nanotube) and functional nanotube (functional multi-walled carbon nanotube) content on the properties of BP-polyvinylchloride/poly(ethylene glycol)/purified multi-walled carbon nanotube and BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube buckypaper composites was investigated, while using same amount of polymer. Results indicated better interaction between polyvinylchloride and functional multi-walled carbon nanotube due to hydrogen bonding relative to polyvinylchloride and purified multi-walled carbon nanotube where no chemical link was present between the two. Fourier transform infrared spectroscopy results confirmed the modification of functional multi-walled carbon nanotube, and formation of buckypaper composite. Scanning electron microscopy micrographs showed better network formation in BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube samples and intercalation of polymer can be seen forming polymer-coated functional multi-walled carbon nanotube network. Thermal stability was found to be improved by the increment of multi-walled carbon nanotube and the difference between the thermal stability of functional multi-walled carbon nanotube and purified multi-walled carbon nanotube buckypaper was also prominent. The maximum degradation temperature (Tmax) of functional composite BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube 0.05 (469℃) was higher relative to non-functional BP-polyvinylchloride/poly(ethylene glycol)/purified multi-walled carbon nanotube 0.05 (461℃). The glass transition temperature of BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube 0.05 was found as 249℃, while BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube 0.05 depicted higher Tg of 271℃. Amorphous character of polymer/carbon nanotube -buckypaper composite showed a trend towards crystallinity according to X-ray diffraction results. Purified multi-walled carbon nanotube-based buckypaper presented conductivity up to 1.91 × 10−1 S cm−1, while BP-polyvinylchloride/poly(ethylene glycol)/functional multi-walled carbon nanotube 0.01–0.08 had increased conductivity up to 9.88 × 10−1 S cm−1.

Functional and unmodified MWNTs for delivery of the water-insoluble drug Carvedilol – A drug-loading mechanism

Preparation, characterization and properties of polycaprolactone diol-functionalized multi-walled carbon nanotube/thermoplastic polyurethane composite

Background: Multiwall Carbon Nanotubes (MWCNTs) have innovative characteristic features strongly associated with nanotechnology and drug delivery applications. Objectives: The current work was performed with an objective to assess the inhalation toxicity of multi-walled carbon nanotubes. Methods: Functionalization of multi-walled carbon nanotubes was carried out by the initial basic treatment with hydrochloric acid and nearly assessed by Infrared (IR) spectroscopy, mass spectroscopy, and Transmission electron microscopy (TEM) in comparison with pure multi-walled carbon nanotubes. The acute inhalation toxicity of these functionalized and pure multi-walled carbon nanotubes was assessed in Wistar rats. The parameters: hematology, liver function test, kidney function test, and histopathology observed, evaluated and interpreted for the toxicity study. Results: The functionalized multi-walled carbon nanotubes and pure multi-walled carbon nanotubes were nearly assessed by IR spectroscopy, mass spectroscopy, and TEM. The assessments affirmed and anticipated that the pure multi-walled carbon nanotube undergoes successful functionalization. Results obtained showed a remarkable difference in the ranges of hemoglobin and platelet. The acute inhalation toxicity study did not show any toxicity of functionalized multi-walled carbon nanotubes when compared to pure multi-walled carbon nanotubes. The results of acute inhalation toxicity studies did not show any significant changes also not demonstrated hazard potential in rats following acute exposures to the functionalized multi-walled carbon nanotubes and there is no significant toxicity. Because of basic treatment during functionalization all impurity gets removed. During functionalization addition of oxygen containing group and removal of carbon dioxide group occurs. Conclusion: Functionalized multi-walled carbon nanotubes can prove to be a novel, safe, and non-toxic carrier for the delivery of drugs by inhalation route.

Multi-walled carbon nanotubes (MWCNTs) were fabricated and oxidized by different concentrations of sodium hypochlorite (NaOCl) solutions. The untreated MWCNTs and modified MWCNTs were employed as adsorbents to study their characterizations and adsorption performance of toluene, ethylbenzene and xylene isomers (TEX) in an aqueous solution. The physicochemical properties of MWCNTs were greatly affected after oxidation, which influences TEX adsorption capacity. The 3% NaOCl-oxidized MWCNTs shows the greatest enhancement in TEX adsorption, followed by the 30% NaOCl. More interestingly, the 15% NaOCl-oxidized MWCNTs has lower adsorption capacities than untreated MWCNTs. The adsorption mechanism of TEX on treated MWCNTs is attributed to the combined action of hydrophobic interaction, π-π bonding interaction between the aromatic ring of TEX and the oxygen-containing functional groups of MWCNTs and electrostatic interaction. 3% NaOCl solution could not only introduce much oxygen-containing functional groups on MWCNTs, but also lead to less damage for the pore structure. This suggests that the CNTs-3% NaOCl is efficient adsorbent for TEX and that they may possess good potential for TEX removal in wastewater treatment.

Multi-walled carbon nanotubes (MWCNTs) are known as efficient drug carriers. To improve their interaction with other materials, surface modification of MWCNTs is necessary. In this work, MWCNTs were functionalized with acid and polysaccharides (chitosan and gelatin). The functionalization process was done via modification with acid solutions of nitric acid, sulfuric acid, and a mixture of nitric acid-sulfuric acid first, followed by functionalization with chitosan and gelatin. To achieve the optimum condition of MWCNTs functionalization, the reaction time, temperature, and acid ratio were varied. Furthermore, the effect of chitosan and gelatin addition into MWCNTs was studied at various mass ratios. The synthesized materials were characterized by Fourier transform infrared spectrophotometer, Boehm titration, and dispersion test. The Boehm titration results showed that the acid functional groups had been attached successfully to MWCNTs surface. The amount of acid functional groups increased along with reaction time. The highest amount of acidic group obtained from the data was 2.33 mmol/g. It was achieved when MWCNTs reacted with nitric acid for 24 hours. Temperature and acid ratio variations on the MWCNTs functionalization did not provide significant results. From the FTIR data, sharp peaks at 3480 cm-1 and 1040 cm-1 indicates a -CONH bond, which shows that chitosan and gelatin have been successfully grafted onto MWCNTs surface via an amide linkage. Moreover, the dispersion test showed that the functionalized materials were stable for 48 hours.

The purpose of this paper is studying the effect of incorporation of Multiwall Carbon Nanotubes (MWCNT) into two different nanocomposites in poly vinyl alcohol (PVA)/polyvinylpyrrolidone (PVP), and PVA/Polyethylene glycol (PEG). MWCNT were synthesized by chemical vapor deposition (CVD) method using acetylene and Fe/Co/Al2O3 as carbon precursor and catalyst, respectively. Nitric acid and sulfuric acid were used for purification and functionalization of MWCNT. Afterward, highly pure and functionalized MWCNT (0, 0.02, and 0.05% w/w) were incorporated in PVA/PVP and PVA/PEG to synthesize PVA/PVP/MWCNT and PVA/PEG/MWCNT nanocomposites hydrogel membranes that cross-linked by freezing–thawing. PEG and PVP were selected in these nanocomposites as dispersion matrix for MWCNT as well as for increasing the elasticity of the nanocomposites membranes. The morphology of the hydrogels was characterized by SEM, FTIR, XRD, TGA, and the mechanical properties of the hydrogel membranes were investigated. The swelling behavior in different pH-buffer solutions was studied as well as studying weight loss percentage and swelling kinetic. The drug releasing process of the hydrogel membranes was investigated using salicylic acid as a model drug. It was found that MWCNT are dispersed well into the polymers and crystallinity, mechanical properties and thermal stability of the hydrogels contain MWCNT are better than that without MWCNT. Maximum degree of swelling was observed at pH 7 and swelling degree increases with increasing the ratio of MWCNT in the hydrogels from 0.02 to 0.05%. All hydrogel membranes followed non-Fickian mechanism and drug releasing were controlled by varying the pH and amount of MWCNT.

Understanding the characteristics of nanomaterials in the context of electrode designs for bio-electrocatalysis is an emerging research direction. Applications for fuel cells, batteries, and biosensors are directly benefited. The objective of this study is to understand the influence of unfunctionalized multiwalled carbon nanotubes (MWNT) in comparison to carboxylated nanotubes (MWNT–COOH) for pi-pi stacking with 1-pyrenebutyric acid (Py) and covalent immobilization of bilirubin oxidase (BOD) enzyme toward the resulting oxygen reduction currents. We designed pyrolytic graphite-edge electrodes modified with MWNT/Py, MWNT–COOH/Py, or only MWNT–COOH for carbodiimide activation and BOD immobilization. The relative increase in surface –COOH groups as we move from MWNT to MWNT/Py to MWNT–COOH/Py modification is voltammetrically estimated. Although the MWNT–COOH/Py displayed the highest relative amount of surface −COOH groups, the oxygen reduction current was the largest for the BOD-immobilized MWNT/Py electrode than others. Results indicate that unfunctionalized MWNT is the optimal choice for pi-pi stacking with pyrene linkers and covalent BOD immobilization as biocathode for direct electrocatalysis with high current densities. Favorable hydrophobic MWNT surface to interact more closely with the electron-receiving T1 Cu site of BOD, as opposed to the relatively polar and more defective MWNT–COOH material due to functionalization, is suggested to be one of the underlying factors for the observed electrocatalytic trend.

Ladderlike polysilsesquioxanes (LPSs) containing chloromethylphenyl groups were synthesized from (p‐chloromethyl)phenyltrimethoxysilane under basic conditions. Functionalized multiwalled carbon nanotubes (MWNT–COOH) were prepared by the acid treatment of pristine multiwalled carbon nanotubes (MWNTs). MWNT–COOH was reacted with LPS to prepare LPS‐grafted MWNTs via ester linkages. The functionalization of MWNTs with LPS significantly altered the surface roughness of the MWNTs; there was a significant increase in the diameter of the MWNTs. The LPS‐grafted MWNTs had a 10–20 nm thickness along the outer walls according to the functionalization of the MWNTs with LPS. An advantage of the hybrid LPS‐grafted MWNTs was shown as improved thermal behavior. The composition, thermal properties, and surface morphology of the LPS‐grafted MWNTs were studied by Fourier transform infrared spectroscopy, thermogravimetric analysis, energy‐dispersive spectroscopy, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012