Oxidative Acid Treatment Research Articles

Chemical and Mineralogical Analysis of Ureteral Stent Encrustation and Associated Risk Factors

To assess the burden and chemical and mineralogical composition of stent coating at both stent ends, with evaluation of associated risk factors. A total of 40 consecutive patients submitted to ureteral-stent removal were considered. Stents were previously positioned for both urolithiasis and during the management of other urologic diseases and/or procedures. Mean indwelling time was 59.2 ± 7.5 days. Encrustations were submitted to chemical-mineralogical analysis as well as to their quantification. Quantification was achieved by measuring the weight of stent fragments before and after oxidative acid treatment to dissolve the deposited (both organic and inorganic) material. The analytical solution obtained by acid attack was used to acquire information on calcium and magnesium content with atomic-absorption spectroscopy. X-ray diffraction was used to determine the mineralogy of encrustations for a group of stent samples characterized by relatively high amounts of deposited material. The composition of encrustations at the proximal coil reflected the composition of stones in patients with urolithiasis. Whewellite was the more common encrustant. In a regression model, the variable mostly related to the burden of proximal encrustation was urolithiasis (P = .04), especially in frequent stone formers. At the distal coil, higher degrees of encrustation were related to urinary tract infection (P = .012) and patient's aging (P = .05), thus suggesting a possible association with a bladder outlet dysfunction. The present study highlighted some variables related to stent encrustation and seems to be the first one analyzing separately the two coils. Our outcomes suggest that the so-obtained risk factors have to be considered when positioning a ureteral stent.

Chemical Surface Modification of CNTs via Three Oxidative Acid Treatments

Carbon nanotubes are commonly used to create polymer-nanotube composite for various applications. To suffice the needs of the emerging interest in utilizing nanotube, a great concern in creating a stable dispersion of the nanotube in solvent emerged. There is a paramount need to enhance the adhesion between the polymer and carbon nanotube to give a homogenous and stable dispersion throughout the polymer matrix. Thus, oxidative acid treatments are often chosen to chemically functionalize carbon nanotube in order to give such dispersing ability to the nanomaterials. In this study, purified multi-walled carbon nanotubes (MWCNTs) is oxidized under the influence of three types of oxidants i) hydrogen peroxide, ii) citric acid monohydrate and iii) mixture of 3:1 sulphuric and nitric acid. All the MWCNTs suspensions ultrasonicated for 8 hours to create opening defects on the MWCNTs to allow the surface modification to occur. In this comparative study of chemically surface modification using oxidative acid treatments, FTIR was used to examine the formation of -OH, -COOH and -C=O groups on the surface of the MWCNTs, TGA and XRD used to determine the thermal behaviour and the crystal structure studies of the modified MWCNTs respectively.

Fractional photo-current dependence of graphene quantum dots prepared from carbon nanotubes.

We report on the photo-conductivity studies of chemically synthesized graphene quantum dots (GQDs) of average size 12 nm obtained by the oxidative acid treatment of MWCNTs. The dependence of photocurrent Iph (Iph = Iill - Idark) on the laser intensity P under a wide range of laser intensities (5 mW ≤ P ≤ 60 mW) shows a fractional power dependence of Iph on light intensity. The temperature dependence (300 K < T < 50 K) of Iph observed in thin films of these GQDs indicates that in the higher temperature region (T > ∼100 K), as the temperature increases, the number of thermally generated carriers increase resulting in increased Iph. At sufficiently low temperatures (T ≤ 100 K), a constant Iph is observed, indicating a constant photo-carrier density. Such a behavior is typically observed in many photoactive disordered semiconductors, which are often used in a variety of applications. We believe that the investigations presented here will enhance our understanding of the photocurrent generation phenomenon in chemically obtained GQDs.

Design real-time reversal of tumor multidrug resistance cleverly with shortened carbon nanotubes.

Multidrug resistance (MDR) in tumors renders many currently available chemotherapeutic drugs ineffective. Research in nanobiotechnology-based therapeutic alternatives has provided innovative and promising strategies to overcome MDR. The aim of this study was to investigate whether the new strategy of a co-loaded reversal agent and chemotherapeutic drug with shortened carbon nanotubes (CNTs) would show useful effects on the real-time reversal of tumor MDR. CNTs were cut and purified via ultrasonication and oxidative acid treatment to optimize their length for drug-delivery vehicles, then verapamil (Ver) and doxorubicin (Dox) were co-loaded on shortened CNTs (denoted as Ver/Dox/shortened CNTs), which acted as a drug delivery system. The multidrug resistant leukemia K562/A02 cells were treated with the denoted Ver/Dox/shortened CNTs. The real-time reversal of tumor MDR were evaluated by flow cytometer, 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays, acridine orange/ethidium bromide staining, and Western blot analysis. In the same MDR tumor cells the new strategy of a co-loaded reversal agent and chemotherapeutic drug with CNTs could inhibit the function of P-glycoprotein in real-time by Ver as reversal agent, significantly increase the uptake of Dox, enhance the sensitivity of the MDR cancer cells to the chemotherapeutic agent, and induce apoptosis. It was therefore concluded that a co-loaded reversal agent and chemotherapeutic drug with shortened CNTs could have real-time reversal ability of MDR in tumors, which could represent a promising approach in cancer therapy.

Oxidative stress reduces the expression of neuronal NOS in cardiac tissue and cell (545.3)

Obesity is a major global health concern and greatly increases the risk of developing insulin resistance and type 2 diabetes. Diabetic patients are also predisposed to various cardiovascular diseases; however, the underlying mechanism of the effects of diabetes on cardiomyocyte viability and thus, overall heart function remains to be established. Increased fatty acid oxidation during diabetes results in increased oxidative stress, which likely contributes to the adverse changes in the myocardium. Nitric oxide (NO) is involved in the regulation of cardiovascular homeostasis in experimental animal models and humans. Neuronal nitric oxide synthase (nNOS) knockout in mice resulted in increased oxidative stress in heart. In cardiac myocytes. nNOS was shown to coimmunoprecipitate with xanthine oxidoreductase, a critical enzyme for superoxide production, and to inhibit its production by the formation of peroxynitrite, all of which suggest a critical role of nNOS‐derived NO in regulating oxidative stress in heart. To investigate the effect of oxidative stress or fatty acids on nNOS expression in cardiomyocytes, we treated HL‐1 cardiomyocyte cells with hydrogen peroxide(H2O2) or palmitate. We show here for the first time that H2O2 or palmitate decreases the expression of nNOS in the cardiomyocytes, as assessed by immunoblot analysis. Furthermore, nNOS expression is also reduced in the heart lysates from thioredoxin 2 (TRX 2) knockout mice, which are prone to oxidative stress. The effect of such a decrease in nNOS expression by oxidative stress or saturated fatty acid treatment on cardiomyocyte viability, overall cardiac hypertrophy and cardiac function is under investigation.Grant Funding Source: Supported by NIH #HL07446 and #GM052419

The hemocompatibility of oxidized diamond nanocrystals for biomedical applications.

Low-dimensional carbon-based nanomaterials have recently received enormous attention for biomedical applications. However, increasing evidence indicates that they are cytotoxic and can cause inflammatory responses in the body. Here, we show that monocrystalline nanodiamonds (NDs) synthesized by high-pressure-high-temperature (HPHT) methods and purified by air oxidation and strong oxidative acid treatments have excellent hemocompatibility with negligible hemolytic and thrombogenic activities. Cell viability assays with human primary endothelial cells suggested that the oxidized HPHT-NDs (dimensions of 35–500 nm) are non-cytotoxic. No significant elevation of the inflammatory cytokine levels of IL-1β and IL-6 was detected in mice after intravenous injection of the nanocrystals in vivo. Using a hindlimb-ischemia mouse model, we demonstrated that 35-nm NDs after covalent conjugation with polyarginine are useful as a drug delivery vehicle of heparin for prolonged anticoagulation treatment. The present study lays a solid foundation for further therapeutic applications of NDs in biomedicine.

Optical absorption response of chemically modified single-walled carbon nanotubes upon ultracentrifugation in various dispersants

Arc discharge single-walled carbon nanotubes (SWCNTs) were modified through different oxidative treatments and functionalization reactions. The modified SWCNT powders were dispersed in four different aqueous media and purified by ultracentrifugation. Extinction coefficients of the modified SWCNTs depended on the SWCNT type but did not depend on the dispersion medium. According to visible/near infrared spectroscopy, the purity of all the modified SWCNT dispersions substantially improved after ultracentrifugation; however, the spectrum profile, the degree of purity and the centrifugation yield were influenced by the SWCNT type, the surface functional groups and the dispersion medium. Semi-quantitative purity indexes calculated from optical absorption spectra were supported by transmission electron microscopy observations. Contents in metal impurities were analyzed by energy dispersive X-ray spectroscopy. SWCNT samples processed by oxidative acid treatments and ultracentrifugation showed metal contents of lower than 0.5wt%.

Efficient Synthesis of Pt Nanoparticles Supported on Hydrophobic Graphitized Carbon Nanofibers for Electrocatalysts Using Noncovalent Functionalization

AbstractAs an alternative to the oxidative acid treatment, a noncovalent π–π interaction method is employed to deposit Pt electrocatalysts on highly hydrophobic carbon nanofibers (CNFs) for the application of polymer electrolyte membrane (PEM) fuel cells. Three different functionalization agents, namely benzyl mercaptan (BM), 1‐aminopyrene (AP), and 1‐pyrenecarboxylic acid (PCA), are used to functionalize CNFs and the effect of these groups on the electrochemical properties is examined. While the BM and AP act as a poison to Pt catalyst, the functionalization of CNF with PCA improves the distribution and loading of Pt as well as reducing the sintering of Pt particles. From the carbon corrosion test, unlike the oxidative acid treatment, the PCA treatment sustains the corrosion resistance of CNFs because it preserves the intrinsic properties of CNFs without damaging their surface structure. Therefore, the PCA treatment is a very effective way to prepare catalysts for PEM fuel cells and also extended to the fabrication of graphitized‐carbon‐supported catalysts of other precious metal for various applications.

Polypyrrole-modified hydrophobic carbon nanotubes as promising electrocatalyst supports in polymer electrolyte membrane fuel cells

As an alternative to oxidative acid treatment, a hydrophobic graphitized carbon nanotube (CNT) was functionalized with 1–4 nm thick polypyrrole (PPy) prior to application as catalyst supports in polymer electrolyte membrane (PEM) fuel cells. Unlike oxidative acid treatment, the PPy coating method converts the hydrophobic surface of a CNT to a hydrophilic one without creating defects on the surface of the CNT. As a result, Pt nanoparticles deposited on the PPy-coated CNTs showed an improved distribution, which significantly enhanced the fuel cell performance while preserving the intrinsic properties of the CNTs, i.e., resistance to electrochemical carbon corrosion. An additional advantage of PPy coating is that it prevents Pt nanoparticles from agglomerating on the CNT surface. These results indicated that PPy-coated CNTs are a promising catalyst support to improve both the performance and durability of PEM fuel cells.

Effective Purification of Single-Walled Carbon Nanotubes with Reversible Noncovalent Functionalization

An effective purification method for single-walled carbon nanotubes (SWNTs) based on a combination of oxidative acid treatment and reversible noncovalent functionalization with 1-pyreneacetic acid is reported. The functionalization was selective toward the nanotubes, allowing a nearly complete removal of residual metal catalysts and carbonaceous impurities. The resulting highly pure SWNTs remained solvent-dispersible, a valuable feature to potential applications that require solvent-based processing. The functionalization agent could be recovered quantitatively and reused. Effects of the purification process on the composition and properties of the nanotube sample were evaluated.

Noncovalent Functionalization as an Alternative to Oxidative Acid Treatment of Single Wall Carbon Nanotubes with Applications for Polymer Composites

We have created stable dispersions of single wall carbon nanotubes (SWNTs) in water by employing a noncovalent functionalization scheme that allows carboxylic acid moieties to be attached to the SWNT surface by a pi-pi stacking interaction. Pyrenecarboxylic acid (PCA) is noncovalently attached to the surface of SWNTs and affords highly uniform and stable aqueous dispersions. This method was developed to provide a noncovalent alternative to the commonly used oxidative acid treatment functionalization of carbon nanotubes. This alternative strategy avoids the damage to the carbon nanotube structure inherent to oxidative acid treatments. Carbon nanotubes are commonly functionalized with oxidative acid treatment schemes to create polymer-nanotube composites and improve the adhesion between the polymer and carbon nanotubes. Composites of SWNTs and polycarbonate were prepared and tested to determine the effect of PCA on the adhesion of the SWNTs to the polymer matrix. These tests confirmed that PCA improved the SWNT-polycarbonate adhesion and improved the dispersion of the SWNTs throughout the matrix. This study demonstrates that stable dispersions of SWNTs can be achieved without substantial cutting, introduction of defects, or covalent modification, by employing a simple and effective noncovalent functionalization with PCA.

Rapid, Solventless, Bulk Preparation of Metal Nanoparticle-Decorated Carbon Nanotubes

A rapid, solventless method is described for the decoration of carbon nanotubes with metal nanoparticles. The straightforward two-step process utilizes neither reducing agents nor electric current and involves the dry mixing of a precursor metal salt (e.g., a metal acetate) with carbon nanotubes (single- or multi-walled) followed by heating in an inert atmosphere. The procedure is scalable to multigram quantities and generally applicable to various other carbon substrates (e.g., carbon nanofiber, expanded graphite, and carbon black) and many metal salts (e.g., Ag, Au, Co, Ni, and Pd acetates). As a model system, Ag nanoparticle-decorated carbon nanotube samples were prepared under various mixing techniques, metal loading levels, thermal treatment temperatures, and nanotube oxidative acid treatments. These nanohybrids were characterized by a variety of microscopic and spectroscopic techniques. For example, X-ray diffraction and scanning electron microscopy indicated that the average size of the Ag nanoparticles has little to do with the thermal treatment temperature but can be easily controlled by varying the Ag loading. Raman spectroscopy illustrated both the metal-nanotube electronic interactions and the surface enhancement effect from the Ag nanoparticle attachment. High-resolution transmission electron microscopy captured the in situ salt-to-metal conversion events on the nanotube surface. The mechanistic implications from the characterization results are discussed.

Effects of vacancy-carboxyl pair functionalization on electronic properties of carbon nanotubes

Density functional calculations are performed to investigate the functionalization of carbon nanotubes with the vacancy and carboxyl group that always appear in pairs after chemical oxidation (such as oxidative acid treatment). It is found that the geometrical structures and electronic properties of the nanotubes are changed significantly, with the formation of a strong covalent bond between the carboxyl and the defected tube. The electrical conductivity of the system could be considerably enhanced, which sensitively depends upon the axial density of vacancy-carboxyl pairs. A promising approach, controllable oxidative acid treatment, is designed to make carbon nanotube-based chemical and nanoelectronic devices.

Control of the Properties of Carbon Nanotubes Synthesized by CVD for Application in Electrochemical Biosensors

Interest in carbon nanotubes (CNT) has grown at a very rapid rate in the last decade. Their interesting physical and chemical properties open attractive possibilities in many application areas. These properties depend on the process conditions during synthesis and on subsequent purification steps. Recent studies have demonstrated that CNT can promote the electron transfer of biomolecules. These exceptional properties make them attractive for use in electrochemical biosensors. Multi walled nanotubes have been synthesized by the Chemical Vapor Deposition (CVD) method using methane as a carbon source and Ni–Al2O3–SiO2 as the catalyst. The influence of the variation of certain reaction parameters such as feed gas composition, catalyst mass, temperature and reaction time in the yield of the CVD process has been established. In addition, the structural and chemical characteristics of the CNTs have been studied and a purification process to eliminate the catalyst and amorphous carbon has been developed that involves a gaseous oxidative process and acid treatment. The efficiency of the purification step has been determined by analytical techniques. Atomic force microscopy, Raman scattering, thermogravimetric analysis, inductively coupled plasma atomic spectroscopy are the characterization techniques employed in this work.

Synthesis and characterization of water-soluble carbon nanotubes from mustard soot

Carbon nanotubes (CNT) has been synthesized by pyrolysing mustard oil using an oil lamp. It was made water-soluble (wsCNT) through oxidative treatment by dilute nitric acid and was characterized by SEM, AFM, XRD, Raman and FTIR spectroscopy. The synthesized wsCNT showed the presence of several junctions and defects in it. The presence of curved graphene structure (sp2) with frequent sp3 hybridized carbon is found to be responsible for the observed defects. These defects along with the presence of di- and tri-podal junctions showed interesting magnetic properties of carbon radicals formed by spin frustration. This trapped carbon radical showed ESR signal in aqueous solution and was very stable even under drastic treatment by strong oxidizing or reducing agents. Oxidative acid treatment of CNT introduced several carboxylic acid group functionalities in wsCNT along with the nicking of the CNT at different lengths with varied molecular weight. To evaluate molecular weights of these wsCNTs, an innovative method like gel electrophoresis using high molecular weight DNA as marker was introduced.

Hydrogen Storage in High Surface Area Carbon Nanotubes Produced by Catalytic Chemical Vapor Deposition

Carbon nanotubes, mostly single- and double-walled, are prepared by a catalytic chemical vapor deposition method using H2−CH4 atmospheres with different CH4 contents. The maximum hydrogen storage at room temperatures and 10 MPa is 0.5 wt %. Contrary to expectations, purification of the carbon nanotube specimens by oxidative acid treatments or by heating in inert gas decreases the hydrogen storage. Decreasing the residual catalyst content does not necessarily lead to an increase in ASH. Moreover, increasing the specific surface area does not necessarily increase the hydrogen storage capacity. There seems to be a correlation between the pore volume at low pore diameters (<3 nm) and the hydrogen storage capacity. Contribution from nanoscale disordered carbon to the hydrogen storage cannot be ruled out.

Importance of activated carbon's oxygen surface functional groups on elemental mercury adsorption ☆

The effect of varying physical and chemical properties of activated carbons on adsorption of elemental mercury (Hg 0) was studied by treating two activated carbons to modify their surface functional groups and pore structures. Heat treatment (1200 K) in nitrogen (N 2), air oxidation (693 K), and nitric acid (6N HNO 3) treatment of two activated carbons (BPL, WPL) were conducted to vary their surface oxygen functional groups. Adsorption experiments of Hg 0 by the activated carbons were conducted using a fixed-bed reactor at a temperature of 398 K and under N 2 atmosphere. The pore structures of the samples were characterized by N 2 and carbon dioxide (CO 2) adsorption. Temperature-programmed desorption (TPD) and base–acid titration experiments were conducted to determine the chemical characteristics of the carbon samples. Characterization of the physical and chemical properties of activated carbons in relation to their Hg 0 adsorption capacity provides important mechanistic information on Hg 0 adsorption. Results suggest that oxygen surface complexes, possibly lactone and carbonyl groups, are the active sites for Hg 0 capture. The carbons that have a lower carbon monoxide (CO)/CO 2 ratio and a low phenol group concentration tend to have a higher Hg 0 adsorption capacity, suggesting that phenol groups may inhibit Hg 0 adsorption. The high Hg 0 adsorption capacity of a carbon sample is also found to be associated with a low ratio of the phenol/carbonyl groups. A possible Hg 0 adsorption mechanism, which is likely to involve an electron transfer process during Hg 0 adsorption in which the carbon surfaces may act as an electrode for Hg 0 oxidation, is also discussed.

Enrichment of Large-Diameter Single-Walled Carbon Nanotubes by Oxidative Acid Treatment

Herein we reported a simple way to enrich the large-diameter single-walled carbon nanotubes (SWNTs) by using a mixed concentrated H2SO4/HNO3 treatment. The proportion of the SWNTs with diameter larger than 2 nm measured from transmission electron microscopy was only ca. 3% in the original sample prepared by chemical vapor deposition method. It is found that this proportion becomes remarkably increased with treatment time and reached ca. 20% after 96 h of acid treatment.

Production of monoclonal antibodies against target schistosomal antigen secreted in the urine of Schistosoma mansoni-infected patients

This study was undertaken to develop an immunodiagnostic test of active human schistosomiasis mansoni using a monoclonal antibody which targets urinary schistosomal antigen. Polyclonal antisera raised in rabbits against the processed urine of Schistosoma mansoni-infected patients showed very high and significant reactivity with ES product of ova compared with other different S. mansoni antigens. The monoclonal antibody (4.23) was reactive with repetitive epitopes of S. mansoni soluble egg antigen and ES product of ova with molecular mass range of 65–23 kDa and 80–23 kDa, respectively. It recognised different stages of the parasite life-cycle, with no cross reaction with Fasciola or hydatid antigen. MAbs were characterised by isotyping, immunoelectrophoresis, SDS–PAGE and the enzyme-linked immunoelectrotransfer blot technique, ELISA, and their recognition of carbohydrate or protein antigenic epitopes by periodate oxidation and trichloroacetic acid treatment of the antigen. It was used for detection of circulating schistosomal antigen in an antigen capture antibody sandwich ELISA on sera and urines of 58 S. mansoni-infected patients, 17 S. haematobium-infected patients, 15 parasite-free negative healthy controls and sera from 13 schistosomiasis-free patients harbouring Fasciola or hydatid infections. The percentage sensitivity of the assay in the serum of S. mansoni-infected patients was 98.4% and in urine 94.8%. A positive correlation was found between the number of faecal S. mansoni eggs and the circulating antigen, both in serum and in urine. Antigen circulating in urine correlated with that in the sera of S. mansoni patients. These data provide a sensitive and non-invasive method almost comparable with the use of sera for immunodiagnosis of schistosomiasis and an indirect way to reflect the intensity of infection. Australian Society for Parasitology.