Metal nanoparticles (Pt, Au, or Cu) together with multiwalled and single-walled carbon nanotubes (MWCNT and SWCNT) solubilized in Nafion have been used to form nanocomposites for electrochemical detection of trinitrotoluene (TNT) and several other nitroaromatics. Electrochemical and surface characterization by cyclic voltammetry, AFM, TEM, SEM, and Raman spectroscopy confirmed the presence of metal nanoparticles on CNTs. Among various combinations tested, the most synergistic signal effect was observed for the nanocomposite modified glassy carbon electrode (GC) containing Cu nanoparticles and SWCNT solubilized in Nafion. This combination provided the best sensitivity for detecting TNT and other nitroaromatic compounds. Adsorptive stripping voltammetry for TNT resulted in a detection limit of 1 ppb, with linearity up to 3 orders of magnitude. Selectivity toward the number and position of the nitro groups in different nitroaromatics was very reproducible and distinct. Reproducibility of the TNT signal was within 7% (n = 8) from one electrode preparation to another, and the response signal was stable (+/-3.8% at 95% confidence interval) for 40 repeated analyses with 10 min of preconditioning. The Cu-SWCNT-modified GC electrode was demonstrated for analysis of TNT in tap water, river water, and contaminated soil.

A flow analysis electrochemical system has been developed, characterized, and optimized for the determination of arsenite (As(III)). Sensitivity was significantly improved by the electrochemical deposition of gold nanoparticles on a dual glassy carbon electrode, which was inserted into a cross-flow thin-layer electrochemical cell. The electrochemical system was linear up to 15 ppb with a detection limit of 0.25 ppb. Gold deposition was evident from cyclic voltammetry measurements, whereas atomic force microscopy and scanning electron microscopy revealed the size and distribution of deposited gold nanoparticles. The size and density of the nanoparticles were related to the gold salt concentration, deposition time, and potential as well as the electrode position. The response to arsenite was directly related to the frequency, increment, and amplitude of the square wave voltammetry as well as the deposition time and potential. Estimated reproducibility was +/-1.1% at 95% confidence interval for 40 repeated analyses of 8 ppb arsenite during continuous analysis. The reproducibility was far superior if the electrochemical reduction of arsenite was performed in nitric acid instead of hydrochloric or sulfuric acid. The electrochemical system was applicable for analysis of spiked arsenic in mineral water containing a significant amount of various ion elements.

A novel nanocomposite was prepared by deposition of carbonate-stabilized Au nanoparticles (AuNPs) onto the surface of poly(diallyldimethyl ammonium chloride) (PDDA)-coated carboxylated nanocrystalline cellulose (NCC). The hybrid material possessed AuNPs (1.45% by weight) with an average diameter of 2.95 ± 0.06 nm. The catalytic activity of AuNP/PDDA/NCC for reducing 4-nitrophenol to 4-aminophenol was compared to other Au-supported composites. An activation energy of 69.2 kJ mol(-1) was obtained for the reaction. Indeed, the reaction rate constant k of (5.1 ± 0.2) × 10(-3) s(-1) was comparable to the benchmark literature value obtained using AuNPs (<5 nm in diameter) decorated on a network of crystalline cellulose fibers. Our strategy promotes the use of natural resources to prepare reusable hybrid inorganic-organic materials for important reactions with facilitated product isolation/purification.

No abstract

Nafion 117 has been proven as a robust and reusable heterogeneous catalyst for the dehydration of 9.1 % (w/w) xylose in dimethyl sulfoxide (DMSO) to yield 60 % furfural in 2 h at 150 °C. The catalytic high activity promoted shorter reaction times to limit the formation of side‐products which otherwise would lead to decreased yields. Within the allowable operating temperature range of Nafion (125 to 175 °C), the reaction was kinetically controlled. In corroboration with AFM and SEM imaging, ATR–FTIR confirmed that the Nafion catalytic activity remained unchanged after 15 repeated uses. With excellent chemical and thermal stability under the conditions for xylose dehydration compared to existing solid acid catalysts, this reusable Nafion system could be a step towards the more economical production of furfural from renewable biomass, an intermediate chemical for the preparation of value‐added chemicals.

A one-pot green procedure for the treatment of cellulosic biomass with ammonium persulfate (APS) was developed for the synthesis of highly crystalline carboxylated nanocrystalline cellulose (NCC–COOH), an emerging nanomaterial with a plethora of diversified applications. Raman spectroscopy proved applicable for monitoring the fate of APS and its two byproducts during the production of NCC–COOH from microcrystalline cellulose (MCC). The two main byproducts were then identified and quantified as ammonium sulfate (AS) and H2SO4 with the latter accounted for 60% of the total sulfate ions in solution. On the basis of such findings, one-step neutralization of H2SO4 and NCC with NH4OH immediately after reaction was implemented for the formation of additional AS, followed by its quantitative recovery by precipitation. This was a very effective and critical step in waste stream management and cost reduction for the large scale production of NCC. In addition, the process resulted in highly crystalline NCC with COO–NH4 + groups, a nanomaterial with improved dispersion and thermal characteristics over NCC with COOH and COO–Na+ groups.

A CD-modified capillary electrophoretic method has been developed for achiral and chiral analysis of seven bioactive compounds isolated from the fruiting body of Antrodia camphorata. Such important target analytes exhibit similar chemical structures and are known for their diverse properties including antioxidant and anticancer effects. The analytes were separated in 25 min using a pH 9.3, 20 mM sodium borate buffer containing 20 mM methyl-b-CD and 30 mM sulfobutylether-b-CD. With the exception of the optical isomer pairs (antcin B or zhankuic acid A, zhankuic acid C, and antcin A), the remaining bioactive compounds including the chiral pair antcin C were baseline-separated. Analysis time was noticeably longer to baseline separate all of the above chiral pairs ($38 min) by adding 5% DMF to the running buffer. The migration order was reversed compared with the HPLC elution. More hydrophobic compounds complexed favorably with methyl-b-CD and emerged earlier in the electropherogram than their more hydrophilic counterparts which were strongly associated with sulfobutylether-b-CD. The simple capillary electrophoretic method developed was applicable for rapid separation and characterization of several important bioactive compounds isolated from the fruiting body of A. camphorata.

o-Nitrophenol, released from o-nitrophenyl--D-galactopyranose as catalyzed by -galactosidase, a tetramer of Escherichia coli, has been exploited for the detection of E. coli contamination in foodstuffs. This reaction was detected using a boron doped diamond electrode poised at +0.93 V, without any surface modification. The enzyme was effectively induced by isopropyl--D-thiogalacto-pyranoside with the maximum enzyme activity observed with sodium dodecyl sulfate at 50°C. A biphasic calibration plot was observed: 4 × 10 4 to 2 × 10 5 cells/mL and 2 × 10 5 to 6 × 10 6 cells/mL for the first and second region, respectively. The detection limit was 4 × 10 4 cells/mL with a total analysis time of <1.5 h. Electrode fouling was easily overcome by ∼40 rapid CV scans, and the method was applicable for detecting E. coli in artificially spiked samples of beef, pork, chicken, milk, and tap water.