Amino-functionalized Nanotubes Research Articles

PH-Responsive TiO2 Nanotube Drug Delivery System Based on Iron Coordination

Nanostructured materials play a fundamental role in orthopedic research owing to their outstanding properties and excellent biocompatibility. Titania nanotube (TNT) arrays engineered by electrochemical anodization process have been extensively explored and used as effective carriers for controlled drug delivery. In this study, we proposed a drug delivery system based on coordination bond. Iron (III), Fe3+, on the nanotube surface can effectively bind to alendronate sodium (NaAL), a drug for the treatment of osteoporosis, through coordination bonds, which can be formed or broken through the change of pH, and thus can be controlled by pH. The pH-responsive system was prepared by three-step procedure: (i) fabrication of TNTs by electrochemical anodization, (ii) modification of amino groups on the surface of nanotubes by hydrothermal method, and (iii) amino-functionalized nanotubes by Fe3+ solution soak. The Fe-modified TNTs not only allowed alendronate-loading content of up to 50.2% by weight, which is significantly higher than most drug delivery systems previously reported, but also delayed and prolonged drug release. Moreover, in vitro drug release experiments demonstrated that coordination bond-based TNT system may have great potential applications in clinical use.

Chemically Grafted Aminated Carbon Nanotubes and l-Lysine in Ultramodified Conditions for Carbon Dioxide Storage.

The study reported CO2 storage properties of single-walled carbon nanotubes (CNTs) modified by introducing amino groups onto CNT surfaces via a chemical process. Two different approaches were used to produce amino-functionalized nanotubes by adding lithium amide and l-lysine amino acid. Lithium amide was introduced on CNT surfaces, and then, it was further modified by adding amino-moiety (l-lysine amino acid) to obtain multiamino sites on the CNT surface for CO2 storage. The aminated CNT were followed by CO2 adsorption experiments, and amino group interactions with CO2 have helped CNT to achieve higher adsorption capacity. The successful modification of CNTs showed ameliorated CO2 storage capacity as compared to pristine CNT. The modified CNT possessed free amine groups on the surface, which led to an enhanced CO2 adsorption capacity. The modified CNT samples were analyzed by X-ray photoelectron spectroscopy, infrared spectroscopy, and X-ray diffraction techniques.

Processing of Functionalized and Pristine Carbon Nanotube Epoxy Composites with Silane-Treated Glass Fiber

In this work, an attempt has been made to study the bonding between the silane coupling agents and the glass fiber (GF) surface. The mechanical properties of the composites so obtained have been specifically analyzed. It has been experimentally found that epoxy silane (ES)-treated GF mat in a neat epoxy matrix showed considerable improvement compared to amino silane (AS)-treated GF. The effect of heat treatment on GF has also been looked into. Moreover, a new processing technique has been explored, which involves the use of amino functionalized nanotube (ACNT) and pristine nanotube (PCNT), homogeneously and uniformly dispersed in an epoxy matrix. Additionally, the effect of ES- and AS-treated GF in the presence of PCNTs and ACNTs has been studied and it has been found that AS shows strong interfacial adhesion in the ACNT matrix, whereas ES shows improved mechanical behavior in the PCNT matrix. The findings from this study have certainly helped us design improved fiber reinforced nanocomposites with enhanced mechanical properties suitable for marine structures.

Synthesis and deposition of ultrafine noble metallic nanoparticles on amino-functionalized halloysite nanotubes and their catalytic application

Using epigallocatechin gallate (EGCG) as both a green reductant and stabilizer, ultrafine noble metal nanoparticles (Rh NPs, Pt NPs, Pd NPs) are synthesized and in situ deposited within amino-functionalized halloysite nanotubes (N-HNTs) via a facile and eco-friendly process. These noble metal nanoparticles with extremely small size (∼1.5nm) are dispersed densely and uniformly on both outside and inside surface of N-HNTs. Rh deposited N-HNTs (Rh–N-HNTs) was investigated as a model composite catalyst and applied in the catalytic reduction of 4-nitrophenol (4-NP), and it exhibited amazing activity and recycle stability. Due to the green and flexibility of the technique described here, noble metal nanoparticles, metal nanoalloy, or metal oxide nanoparticles with ultrafine particle size also can be loaded densely and uniformly on the surface of diverse amino-functionalized nanotubes, nanofibers or nanoporous, and these composites may be applicable in catalysis, photocatalysis, and electrochemical areas.

Physical Aging of Single Wall Carbon Nanotube Polymer Nanocomposites: Effect of Functionalization of the Nanotube on the Enthalpy Relaxation

The glass-transition temperature and enthalpy relaxation of nanocomposites synthesized with low loadings of single wall carbon nanotubes (1 wt %) in poly(methylmethacrylate) (PMMA) have been investigated using differential scanning calorimetry (DSC). The results are compared with pure PMMA, and the effect of carbon nanotubes on the mobility of the polymer chain is discussed. Composites have been synthesized with unmodified nanotubes (SWNT/PMMA) as well as with amino-functionalized nanotubes (a-SWNT/PMMA) to provide a better interaction between the nanotube and the host matrix material. It was found that the glass-transition temperature of the unmodified nanocomposite SWNT/PMMA is the same as the neat PMMA (Tg = 99 °C). A significant increase of 17 °C in the glass-transition temperature of the modified nanocomposite a-SWNT/PMMA is found when compared with the neat PMMA. Glass-transition results indicate that the presence of a-SWNT in PMMA restricts the segmental motion of the polymer chain. No significant change in activation energy of the enthalpy relaxation process or fragility index of PMMA is observed due to the addition of a-SWNT. However, a large broadening of the enthalpy peak is observed with the incorporation of SWNT in PMMA. This broadening leads to difficulty in the calculation of the activation energy and fragility index of SWNT/PMMA. Enthalpy relaxation behavior during isothermal aging is characterized at the same temperature with respect to the respective glass-transition temperatures of the three samples (at Tg and Tg − 2 °C (2 °C lower than the glass-transition temperature of each system)). The equilibrium enthalpy is reached at a shorter aging time in pure PMMA compared with SWNT/PMMA and a-SWNT/PMMA. The results obtained for enthalpy recovery show the signature of the restrictive environment of a-SWNT and SWNT on polymer chain mobility.

The influence of carbon nanotubes on enzyme activity and structure: investigation ofdifferent immobilization procedures through enzyme kinetics and circular dichroismstudies

In the last decade, many environmental organizations have devoted their efforts toidentifying renewable biosystems, which could provide sustainable fuels and thus enhanceenergy security. Amidst the myriad of possibilities, some biofuels make use ofdifferent types of waste biomasses, and enzymes are often employed to hydrolyzethese biomasses and produce sugars that will be subsequently converted intoethanol. In this project, we aimed to bridge nanotechnology and biofuel production:here we report on the activity and structure of the enzyme amyloglucosidase(AMG), physically adsorbed or covalently immobilized onto single-walled carbonnanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). In fact, carbonnanotubes (CNTs) present several properties that render them ideal supportsystems, without the diffusion limitations displayed by porous material and with theadvantage of being further functionalizable at their surface. Chemical ligationwas achieved both on oxidized nanotubes (via carbodiimide chemistry), as wellas on amino-functionalized nanotubes (via periodate-oxidized AMG). Resultsshowed that AMG retained a certain percentage of its specific activity for allenzyme–carbon nanotubes complexes prepared, with the physically adsorbedsamples displaying better catalytic efficiency than the covalently immobilizedsamples. Analysis of the enzyme’s structure through circular dichroism (CD)spectroscopy revealed significant structural changes in all samples, the degree of changebeing consistent with the activity profiles. This study proves that AMG interactsdifferently with carbon nanotubes depending on the method employed. Due to thehigher activity reported by the enzyme physically adsorbed onto CNTs, thesesamples demonstrated a vast potential for further development. At the same time,the possibility of inducing magnetic properties into CNTs offers the opportunityto easily separate them from the original solution. Hence, substances to whichthey have been attached can be separated from a reaction medium, or directedby an external magnetic field to achieve efficient biofuel production. This pavesthe way for future design of efficient CNT–enzyme nanostructure bioreactors.

Controlled Amine Functionalization on Conducting Polypyrrole Nanotubes as Effective Transducers for Volatile Acetic Acid

Pristine (carboxylated) and aminated polypyrrole nanotubes were successfully fabricated using vapor deposition polymerization with a template. In particular, aminated polypyrrole nanotubes were readily synthesized by modifying the nanotube surface with open polyamine chains. Pristine and aminated polymer nanotubes were used as the transducer to acetic acid vapor. Amino-functionalized nanotubes revealed more enhanced sensitivity than the pristine carboxylated nanotubes with the increasing number of amine spacers due to the increased polymer/analyte partition coefficient and mass uptake of the analyte. Moreover, polyamine-functionalized nanotubes presented a reversible and reproducible response to acetic acid up to 40% sensitivity. The aminated polypyrrole nanotubes demonstrated the potential capability to be excellent transducers for volatile fatty acids in disposable sensors.

Amino-Functionalized Carbon Nanotubes for Binding to Polymers and Biological Systems

Single-walled carbon nanotubes (SWCNT) functionalized with amino groups were prepared via chemical modification of carboxyl groups introduced on the carbon nanotube surface. Two different approaches (amide and amine-moieties) were used to produce the amino-functionalized nanotubes. The amino-termination allows further chemistry of the functionalized SWCNTs and makes possible covalent bonding to polymers and biological systems such as DNA and carbohydrates. The functionalization of the SWCNTs was characterized in detail using FTIR and XPS.

Sidewall functionalization of single-walled carbon nanotubes through CF 4 plasma treatment and subsequent reaction with aliphatic amines

Single-walled carbon nanotubes (SWNTs) with aliphatic amines covalently attached to their side walls have been prepared starting from fluorinated SWNTs (F-SWNTs) obtained by CF 4 plasma treatment. TEM images showed the practical use of sidewall fluorination of SWNTs to achieve unroping of them while infrared and thermogravimetric measurements demonstrated the obtained sidewall fluorination of the tubes. Amino-sidewall functionalization of SWNTs have been then obtained at room temperature by fluorine displacement reactions of F-SWNTs with amines. This work demonstrates the practical use of plasma fluorination to achieve functionalization and unroping of SWNTs as well as yields sidewall amino-functionalized nanotube precursors for the preparation of thermosettings-SWNTs polymer materials.

Sidewall Amino-Functionalization of Single-Walled Carbon Nanotubes through Fluorination and Subsequent Reactions with Terminal Diamines

Single-walled carbon nanotubes (SWNTs) with the N-alkylidene amino groups covalently attached to their side walls have been prepared starting from colloidal solutions of fluorinated SWNTs (fluoronanotubes) in terminal alkylidene diamines followed by heating at 70−170 °C. On the basis of data from thermal gravimetric and energy-dispersive X-ray analyses, the degree of SWNT functionalization achieved was estimated to be as high as 1 in 8 to 12 sidewall carbons. The demonstrated new C−N functionalization method provides a synthetic tool for binding amino acids, DNA, and polymer matrices to the side walls of the SWNTs as well as yields sidewall amino-functionalized nanotube precursors for the preparation of nylon−SWNT polymer materials.