The Effect of Functional Group Polarity in Palladium Immobilized Multiwalled Carbon Nanotube Catalysis: Application in Carbon-Carbon Coupling Reaction.

Carbon nanotubes (CNTs) are effective supports for nanometals and together they represent hybrids that combine the unique properties of both. A microwave-induced reaction was used to deposit nanopalladium on carboxylated and octadecylamine functionalized multiwall CNTs, which were used to carry out C-C coupling reactions in dimethylformamide (DMF) and toluene. These hybrids showed excellent catalytic activity with yield as high as 99.8%, while its enhancement with respect to commercially available Pd/C catalyst reached as high as 109%, and the reaction times were significantly lower. The polarity of the functionalized form was found to be a significant factor with the polar carboxylated CNT showing better activity in DMF while the relatively nonpolar octadecyl amine was better in toluene. The results suggest the possibility of tailor making functionalized CNTs when used as catalyst supports.

The Effects of Varying Degree of MWCNT Carboxylation on Bioactivity in Various In Vivo and In Vitro Exposure Models.

Functionalization has been shown to alter toxicity of multi-walled carbon nanotube (MWCNT) in several studies. This study varied the degree of functionalization (viz., amount of MWCNT surface carboxylation) to define the relationship between the extent of carboxylation and effects in a variety of in vitro cell models and short-term ex vivo/in vivo particle exposures. Studies with vitamin D3 plus phorbol ester transformed THP-1 macrophages demonstrated that functionalization, regardless of amount, corresponded with profoundly decreased NLRP3 inflammasome activation. However, all MWCNT variants were slightly toxic in this model. Alternatively, studies with A549 epithelial cells showed some varied effects. For example, IL-33 and TNF-α release were related to varying amounts of functionalization. For in vivo particle exposures, autophagy of alveolar macrophages, measured using green fluorescent protein (GFP)- fused-LC3 transgenic mice, increased for all MWCNT tested three days after exposure, but, by Day 7, autophagy was clearly dependent on the amount of carboxylation. The instilled source MWCNT continued to produce cellular injury in alveolar macrophages over seven days. In contrast, the more functionalized MWCNT initially showed similar effects, but reduced over time. Dark-field imaging showed the more functionalized MWCNTs were distributed more uniformly throughout the lung and not isolated to macrophages. Taken together, the results indicated that in vitro and in vivo bioactivity of MWCNT decreased with increased carboxylation. Functionalization by carboxylation eliminated the bioactive potential of the MWCNT in the exposure models tested. The observation that maximally functionalized MWCNT distribute more freely throughout the lung with the absence of cellular damage, and extended deposition, may establish a practical use for these particles as a safer alternative for unmodified MWCNT.

Modification of nano-silver bioactivity by adsorption on carbon nanotubes and graphene oxide.

OBJECTIVE: The toxicity of silver nanomaterials in various forms has been extensively evaluated, but the toxicity of silver nanocarbon composites is less well understood. Therefore, silver-carbon nanotube composites (Ag-MWCNT-COOH) and silver-graphene oxide composites (Ag-GO) were synthesized by microwave irradiation and evaluated in two in vitro cell models. MATERIALS/METHODS: Toxicity of silver nanosphere (Ag), Ag-MWCNT-COOH and Ag-GO were analyzed by MTS assay and LDH assay in primary C57BL/6 murine alveolar macrophages and human THP-1 cells. Activation of NLRP3 inflammasome by particle variants in these models was done by proxy using LPS co-culture and IL-1ß release. RESULTS: The results depended on the model, as the amount of Ag on the modified carbon resulted in slightly increased toxicity for the murine cells, but did not appear to affect toxicity in the human cell model. IL-1ß release from carbon particle-exposures was decreased by the presence of Ag in both cell models. Suspensions of Ag-MWCNT-COOH, Ag-GO and Ag in artificial lysosomal fluid were prepared and ICP-MS was used to detect Ag ions concentration in three silver suspension/solutions. The amount of Ag ions released from Ag-MWCNT-COOH and Ag-GO were similar, which were both lower than that of Ag nanospheres. CONCLUSIONS: The results suggest the bioactivity of silver composites may be related to the amount of Ag ions released, which can be dependent on the cell model under investigation.

Variation in chemical, colloidal and electrochemical properties of carbon nanotubes with the degree of carboxylation.

Multiwalled carbon nanotubes (CNTs) were carboxylated via microwave irradiation where the treatment time was varied to alter the degree of functionalization, and as many as one in 15 carbons in the CNT could be oxidized. Chemical, physical, electrochemical, and colloidal behavior of the carboxylated CNTs was studied. All properties changed with the degree of functionalization to a point beyond which they appeared to remain constant. The surface area increased from 173.9 to 270.9 m2/g while the critical coagulation concentration (CCC) values increased from 142.14 to 168.69 mM in the presence of NaCl, and the corresponding increase was from 0.97 to 5.32 mM in the presence of MgCl2. As seen from cyclic voltammetry curves, the functionalized CNTs showed mainly non-Faradic interactions with Na2SO4, but showed Faradic behaviors in alkaline KOH.

Effects of multiwalled carbon nanotube surface modification and purification on bovine serum albumin binding and biological responses.

The potential diagnostic and therapeutic applications such as drug delivery of multi-walled carbon nanotubes (MWCNTs) are being increasingly explored due to their unique mechanical, chemical and biological properties. Carboxylation of MWCNTs has been widely used to improve the solubility in aqueous systems, and for further functionalization with biologically active moieties. Purity of carboxylated MWCNTs is of great importance in nanomedicine. An important consideration is that oxidation debris is generated during the process of carboxylation, which can be removed by base washing. We hypothesized that surface modification as well as further purification by debris removal may alter physicochemical properties of MWCNTs and their ability to bind proteins. In this study, we utilized pristine MWCNT carboxylated MWCNTs (F-MWCNTs) and base-washed carboxylated MWCNTs (BW-F-MWCNTs) to examine formation of a bovine serum albumin (BSA) protein corona and impact on biological responses. We found that carboxylation increased the capability of F-MWCNTs to bind BSA, and base washing further increased this binding by 41% implying that purification of F-MWCNTs is an important consideration in biological applications. The BSA protein corona decreased the hydrodynamic size of MWCNTs by nearly 50% because the coating improved colloidal behavior. The effect was significantly less pronounced for F-MWCNTs and BW-F-MWCNTs because they were highly dispersible to begin with. Functionalization increased cellular uptake by both rat aortic endothelial cells (RAEC) and macrophage-like murine cells (RAW264.7), while base washing showed results similar to the functionalized analog. Interestingly, BSA binding downregulated mRNA levels of interleukin-6 (IL-6) and heme oxygenase 1 (Hmox1) in RAEC cells but upregulated the expression of IL-6 and Hmox1 in RAW264.7 cells, indicating the dependence of cell types in biological responses to MWCNTs. Overall, our study demonstrated that surface modification as well as further purification impacted the interaction of MWCNTs with proteins and subsequent cellular responses. Interestingly, while the corona associated with the F-MWCNTs and BW-F-MWCNTs were significantly different, their respective cellular uptake and biological responses were similar. This implied that surface functionalization played a more important role than surface corona.

Water defluoridation using a nanostructured diatom-ZrO2 composite synthesized from algal biomass.

Frustules or the rigid amorphous silica cell wall of unicellular, photosynthetic microalgae with unique porous architecture has been used to synthesize a composite by immobilizing ZrO2 on its surface and in the pores. This was effective in water defluoridation. The average diameter of the composite was 80±2 nm and surface area was 140 m(2)/g. The adsorption isotherms followed both Langmuir and Freundlich models, and the composite was regenerable. Adsorption kinetics followed second order model and the adsorption capacity was as high as 11.32 mg/g, while the Langmuir maximum adsorption capacity (q(m)) reached 15.53 mg/g. The research findings highlight the potential of diatoms as hosts for nanomaterials for use in water treatment.

Microwave Induced Reactive Base Wash for the Removal of Oxidation Debris from Carboxylated Carbon Nanotubes.

Removal of oxidation debris for generating high purity functionalized carbon nanotubes (CNTs) has been a challenge, where base washing has been found to be an effective purification treatment. In this paper we report microwave induced reactive base wash (MRW) as a fast, green alternate to conventional filtrate washing. Carboxylated CNTs of three different dimensions were subjected to MRW and the results were compared to conventional base-wash. The results showed that MRW was an effective method for the removal of oxidation debris which reduced the reaction time from 4 hours to 20 min and alkali consumption by 75%. The CNTs from MRW were similar to those from conventional base wash in terms of dimensions, elemental composition, BET surface area and colloidal stability in aqueous media.

Instillation versus inhalation of multiwalled carbon nanotubes: exposure-related health effects, clearance, and the role of particle characteristics.

Inhaled multiwalled carbon nanotubes (MWCNTs) may cause adverse pulmonary responses due to their nanoscale, fibrous morphology and/or biopersistance. This study tested multiple factors (dose, time, physicochemical characteristics, and administration method) shown to affect MWCNT toxicity with the hypothesis that these factors will influence significantly different responses upon MWCNT exposure. The study is unique in that (1) multiple administration methods were tested using particles from the same stock; (2) bulk MWCNT formulations had few differences (metal content, surface area/functionalization); and (3) MWCNT retention was quantified using a specialized approach for measuring unlabeled MWCNTs in rodent lungs. Male Sprague-Dawley rats were exposed to original (O), purified (P), and carboxylic acid functionalized (F) MWCNTs via intratracheal instillation and inhalation. Blood, bronchoalveolar lavage fluid (BALF), and lung tissues were collected at postexposure days 1 and 21 for quantifying biological responses and MWCNTs in lung tissues by programmed thermal analysis. At day 1, MWCNT instillation produced significant BALF neutrophilia and MWCNT-positive macrophages. Instilled O- and P-MWCNTs produced significant inflammation in lung tissues, which resolved by day 21 despite MWCNT retention. MWCNT inhalation produced no BALF neutrophilia and no significant histopathology past day 1. However, on days 1 and 21 postinhalation of nebulized MWCNTs, significantly increased numbers of MWCNT-positive macrophages were observed in BALF. Results suggest (1) MWCNTs produce transient inflammation if any despite persistence in the lungs; (2) instilled O-MWCNTs cause more inflammation than P- or F-MWCNTs; and (3) MWCNT suspension media produce strikingly different effects on physicochemical particle characteristics and pulmonary responses.

Fractionation of carboxylated carbon nanotubes and the corresponding variation in their colloidal behavior.

Length dependent dispersibility of carboxylated multi-walled carbon nanotubes is presented using a novel approach where a batch of carboxylated nanotubes was size sorted via ultracentrifugation into different fractions with lengths ranging from 150 to 950 nm. The different fractions had the same tube diameter and degree of oxidation. The dispersibility of the nanotube fractions showed dependence on the length where the longer tubes showed more aggregation in terms of larger particle size, zeta potential and lower critical coagulation concentrations (CCC) in the presence of electrolytes. It is hypothesized that the longer tubes formed a more complex electrostatic double layer that increased their entanglement and aggregation.

Fabrication of high-performance flexible alkaline batteries by implementing multiwalled carbon nanotubes and copolymer separator.

A flexible alkaline battery with multiwalled carbon nanotube (MWCNT) enhanced composite electrodes and polyvinyl alcohol (PVA)-poly (acrylic acid) (PAA) copolymer separator has been developed. Purified MWCNTs appear to be the most effective conductive additive, while the flexible copolymer separator not only enhances flexibility but also serves as electrolyte storage.

Enhanced charge-carrier transport through shorter carbon nanotubes in organic photovoltaics.

We demonstrate for the first time the efficiency improvement of organic photovoltaics by the addition of shorter multiwalled carbon nanotubes (MWNTs) generated by size sorting. The different size MWNTs were generated by size sorting a batch of carboxylated MWNTs and were introduced as charge carriers in poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction photovoltaic cells. As compared to a control with only PCBM, the addition of the long and short MWNT resulted in 12 and 34% improvement in short circuit current density (Jsc) respectively. The results indicate that length of carbon nanotubes is an important consideration in photovoltaic and possibly other nanoelectronic devices.

Effect of MWCNT size, carboxylation, and purification on in vitro and in vivo toxicity, inflammation and lung pathology.

BACKGROUND: Several properties of multi-walled carbon nanotubes (MWCNT) have the potential to affect their bioactivity. This study examined the in vitro and in vivo outcomes of the influence of diameter, length, purification and carboxylation (in vitro testing only) of MWCNT. METHODS: Three original 'as received' MWCNT that varied in size (diameter and length) were purified and functionalized by carboxylation. The resulting MWCNT were characterized and examined for cytotoxicity and inflammasome activation in vitro using THP-1 cells and primary alveolar macrophages from C57BL/6 mice. Oropharyngeal aspiration administration was used to deliver original MWCNT and in vivo bioactivity and lung retention was examined at 1 and 7 days. RESULTS: Studies with THP-1 macrophages demonstrated that increased length or diameter corresponded with increased bioactivity as measured by inflammasome activation. Purification had little effect on the original MWCNT, and functionalization completely eliminated bioactivity. Similar results were obtained using alveolar macrophages isolated from C57BL/6 mice. The in vivo studies demonstrated that all three original MWCNT caused similar neutrophil influx at one day, but increasing length or diameter resulted in the lavaged cells to release more inflammatory cytokines (IL-6, TNF-α, and IL-1ß) ex vivo. Seven-day histology revealed that, consistent with the in vitro results, increasing width or length of MWCNT caused more severe pathology with the longest MWCNT causing the most severe inflammation. In addition, the same two larger MWCNT were retained more in the lung at 7 days. CONCLUSIONS: Taken together, the results indicated that in vitro and in vivo bioactivity of MWCNT increased with diameter and length. Purification had no significant modifying effect from the original MWCNT. Functionalization by carboxylation completely eliminated the bioactive potential of the MWCNT regardless of size in in vitro testing.