Tuning the Raman Resonance Behavior of Single-Walled Carbon Nanotubes via Covalent Functionalization

Single walled carbon nanotubes covalently functionalized by a ruthenium complex for photocatalytic oxidations

The covalent bonding of a ruthenium bipyridine complex derivative with the aromatic network of single walled carbon nanotubes (SWNT) through a stepwise protocol is presented, thus yielding the sample SWNT-Ru. To do that, an-amino decorated phenanthroline is bonded to the nanotube by means of the diazonium chemistry protocol, providing anchoring points for discrete organometallic units as depicted by the solid characterization techniques employed. The hybrid material, able to emit upon excitation, is active in the visible light-driven photocatalytic oxidation of organic sulfides to sulfoxides. SWNT-Ru presents a wide scope being able to convert more than 10 substrates with different characteristics, including added-value chemicals, with a stable performance over more than 6 cycles without metal leaching and enhanced activity compared to related homogeneous complexes. A versatile character is also demonstrated since this hybrid catalyst follows both possible photooxidation mechanisms.

An Ultrasensitive Norfentanyl Sensor Based on a Carbon Nanotube-Based Field-Effect Transistor for the Detection of Fentanyl Exposure

The opioid crisis is a worldwide public health crisis that has affected millions of people. In recent years, synthetic opioids, primarily illicit fentanyl, have become the primary driver of overdose deaths. There is a great need for a highly sensitive, portable, and inexpensive analytical tool that can quickly indicate the presence and relative threat of fentanyl. In this work, we develop a semiconductor enriched (sc-) single-walled carbon nanotube (SWCNT)-based field-effect transistor (FET) biosensor functionalized with norfentanyl antibodies for the sensitive detection of norfentanyl, the primary inactive metabolite of fentanyl, in urine samples. Different sensor configurations were explored in order to obtain the most optimized sensing results. Moreover, by employing the "reduced" antibody, we achieved orientated immobilization of the norfentanyl antibody and thus brought the antigen-antibody interaction closer to the sensor surface, further improving the sensitivity. The reported norfentanyl biosensors have a limit of detection in the fg/mL region in both calibration samples and synthetic urine samples, showing ultrasensitivity and high reliability.

Tuning of the photoluminescence and up-conversion photoluminescence properties of single-walled carbon nanotubes by chemical functionalization

Single-walled carbon nanotubes (SWNTs) were subjected to alkylation using alkyl bromide and alkyl dibromide, and the photoluminescence (PL) properties of the resulting alkylated SWNTs were characterized. Two new PL peaks were observed along with the intrinsic PL peak at 976 nm when alkyl bromide was used (SWNT-Bu: ∼1095 and 1230 nm, SWNT-Bn: 1104 and 1197 nm). In contrast, the use of α,α'-dibromo-o-xylene as an alkyl dibromide primarily resulted in only one new PL peak, which was observed at 1231 nm. The results revealed that the Stokes shift of the new peaks was strongly influenced by the addition patterns of the substituents. In addition, the time-resolved PL decay profiles of the alkylated SWNTs revealed that the PL peaks possessing a larger Stokes shift had longer exciton lifetimes. The up-conversion PL (UCPL) intensity of the alkylated SWNTs at excitation wavelengths of 1100 and 1250 nm was estimated to be ∼2.38 and ∼2.35 times higher than that of the as-dispersed SWNTs, respectively.

Progress in the Raman spectra analysis of covalently functionalized multiwalled carbon nanotubes: unraveling disorder in graphitic materials

Raman spectroscopy is highly sensitive to the morphology and electronic structures of graphitic materials, but a convenient interpretation model has been lacking for multiwalled carbon nanotubes (MWCNTs), in particular for the discrimination of spectral changes induced by covalent functionalization. The present work describes a systematic investigation of the Raman analysis of covalently functionalized MWCNTs by diazonium chemistry and oxidation methodologies, with typically different mechanisms and reaction sites. A multi-peak deconvolution system and spectral band assignment were proposed based on the chemical and structural modifications identified by X-ray photoelectron spectroscopy, thermogravimetry, X-ray diffraction, specific surface areas and the comparative analysis of the first and second order regions of the Raman spectra. Diazonium functionalization takes place mainly in the π-system of the external sidewall, while oxidation occurs on defects and leads to structure burning. This allowed us to distinguish between spectral features related to aromaticity disruptions within the sidewalls and spectral features related to changes within the inner tubes. The model was validated extending the studies to the functionalization of MWCNTs by the Bingel reaction.

Synthesis, characterization and photoinduced charge separation of carbon nanohorn–oligothienylenevinylene hybrids

Two new nanohybrids combining carbon nanohorns (CNHs) and oligothienylenevinylenes (nTVs) have been prepared. Light excitation of these nanohybrids induces charge-separated states.

Carbon nanotubides: an alternative for dispersion, functionalization and composites fabrication

In this review, we systematically describe the state-of-knowledge in the area of carbon nanotubides (CNTDs). CNTDs can be used for achieving highly concentrated dispersions of SWCNTs and can also be used as an important intermediate for covalent chemical modification. In recent years, researchers have used SWCNTDs as starting materials for the functionalization of SWCNTs with functionalities such as alkyl chains, carboxylic acids, sulfide, amino, hydroxyl, silyl, bromide, ethers, ketones and polymers. Also, we discussed the observed selectivity on the covalent functionalization towards certain classes of CNTs. Finally, we describe the use of SWCNTDs in the manufacture of fibers, films and other functional materials.

Design of antimicrobial membrane based on polymer colloids/multiwall carbon nanotubes hybrid material with silver nanoparticles

The aim of this study was to obtain membranes with antimicrobial activity presenting a complex sandwich-type structure. The outer layers are comprised of poly(methyl methacrylate) membranes, whereas the inner active layer consists of a modified commercial membrane to achieve antimicrobial properties. This activity arises due to the presence of silver nanoparticles in a material with a hybrid composition deposited on a commercial membrane. This hybrid material consists of polymer colloids and multiwall carbon nanotubes used for both the stabilization of the active layer by the interconnections of the polymer particles and as active component. The filtration tests revealed a good stability of the materials and an increased hydrophilicity of the hybrid membranes. The antimicrobial properties have been evaluated using Staphylococcus aureus and Escherichia coli, and have been correlated with the content and migration rate of silver ions.

Facile synthesis and enhanced nonlinear optical properties of porphyrin-functionalized multi-walled carbon nanotubes

Two multi-walled carbon nanotube (MWCNT)-based nanohybrids, MWCNT-ZnTPP and MWCNT-TPP (TPP=5-[4-{2-(4-formylphenoxy)- ethyloxy}phenyl]-10,15,20-triphenylporphyrin, ZnTPP=5-[4-{(4-formylphenyl)ethynyl}phenyl]-10,15,20-triphenylporphinatozinc(II)), were prepared directly from pristine MWCNTs through 1,3-dipolar cycloaddition reactions. Covalent attachment of the porphyrins to the surfaces of the MWCNTs was confirmed by Fourier transform infrared spectroscopy, ultraviolet/visible absorption, fluorescence, Raman, and X-ray photoelectron spectroscopy, elemental analysis, transmission electron microscopy, and thermogravimetric analysis. Attachment of the porphyrin moieties to the surface of the MWCNTs significantly improves the solubility and ease of processing of these MWCNT-porphyrin composite materials. Z-scan studies reveal that these MWCNT-porphyrin nanohybrids exhibit enhanced nonlinear optical properties under both nanosecond and picosecond laser pulses at λ=532 nm in comparison with free MWCNTs and the free porphyrin chromophores, whereas superior optical limiting performance was displayed by MWCNT-porphyrin composite materials rather than MWCNTs/ZnTPP and MWCNTs/TPP blends, which is consistent with a remarkable accumulation effect as a result of the covalent linkage between the porphyrin and the MWCNTs.