0D, 1D, 2D molybdenum disulfide functionalized by 2D polymeric carbon nitride for photocatalytic water splitting.

Photocatalytic activity of molybdenum disulfide structures with different dimensions (0D, 1D and 2D) functionalized with polymeric carbon nitride (PCN) is presented. MoS2nanotubes (1D), nanoflakes (2D) and quantum dots (0D, QDs) were used, respectively, as co-catalysts of PCN in photocatalytic water splitting reaction to evolve hydrogen. Although, 2D-PCN showed the highest light absorption in visible range and the most enhanced photocurrent response after irradiation with light from 460 to 727 nm, QDs-PCN showed the highest photocatalytic efficiency. The detailed analysis revealed that the superior photocatalytic activity of QDs-PCN in comparison with other structures of MoS2arose from (i) the most effective separation of photoexcited electron-hole pairs, (ii) the most enhanced up-converted photoluminescence (UCPL), (iii) the highest reactivity of electrons in conduction band. Moreover, a narrowed size of QDs affected shorter diffusion path of charge carriers to active reaction sites, higher number of the sites and higher interfacial area between molybdenum disulfide and PCN.

Performance of laterally elongated pillar array columns in capillary electrochromatography mode.

In the present study, cylindrical and laterally elongated pillar array columns were investigated for use in capillary electrochromatography. Minimal theoretical plate heights of H = 1.90 and 1.46 µm (in absence of sidewall effect) were obtained for coumarin C440 under unretained conditions for cylindrical and rectangular (laterally elongated, aspect ratio 4) pillar array columns, respectively. By comparing dispersion at the entire channel width to that at the central zone only, it appears that sidewall related dispersion significantly contributes to overall dispersion. A 40% reduction of the plate height was observed by taking into account only the central channel zone. A kinetic plot analysis was performed to evaluate the potential of the studied geometries by considering a maximum operating voltage of 20 kV as limiting parameter. It was demonstrated that rectangular radially elongated pillars produce a higher efficiency than cylindrical pillars and other microfabricated column structures for microchip capillary electrochromatography previously studied.

Achieving a Peak Capacity of 1800 Using an 8 m Long Pillar Array Column.

In the present study, the peak capacity potential of ultralong porous cylindrical pillar array columns is investigated. Coupling 4 columns of 2 m long allows for working near the minimal separation impedance of small molecules under retained conditions at a maximal pressure load of 250 bar. Minimal plate heights of H = 5.0 µm, H = 6.3 µm, and H = 7.7 µm were obtained for uracil (unretained), butyrophenone (k = 0.85), and valerophenone (k = 1.94), respectively, corresponding to a number of theoretical plates of N = 1.6 × 106, N = 1.2 × 106, and N = 1.0 × 106. The optimal linear velocities were 0.60 mm/s for a retained compound and 0.74 mm/s for an unretained compound. Based on a mixture of 9 compounds, the peak capacity nc was determined as a function of gradient time (tG). Peak capacities (tG-based) of 1103 and 1815 were obtained when applying 650 min and 2050 min gradients (tG/t0 = 4.5 and 14, respectively, with tG as the gradient time and t0 as the void time). These values are much higher than earlier reported peak capacity values for small molecules.

Aqueous size-exclusion chromatographic separations of intact proteins under native conditions: Effect of pressure on selectivity and efficiency.

The selectivity and separation efficiency of aqueous size-exclusion chromatographic separations of intact proteins were assessed for different flow rates, using columns packed with 3 and 5 µm silica particles containing 150 and 290 Å stagnant pores. A mixture of intact proteins with molecular weights ranging between 17 000 and 670 000 Da was used to construct the calibration curves. Both the model fit and the predictive properties, using a leave-one-out strategy, of different polynomial models (up to fifth order) were evaluated for different flow rates. The best compromise between model fit and predictive properties was obtained using a third-order polynomial model. The accuracy of the predictive properties decreased with 10% with an eightfold increase in the flow rate. No changes in retention factors (hence selectivity) were observed in the flow-rate range applied. A strong correlation between molecular weight and plate height was observed. Exclusion of large-molecular-weight proteins led to a significant reduction in the stationary-phase mass-transfer contribution to the total plate-height value, and this effect was also independent of the flow rate applied. The kinetic-performance limits, in terms of plate number and time, and optimal column-length particle-size combinations were determined at the maximum recommended operating pressure of the size-exclusion chromatography columns (20 MPa). Finally, the possibilities of method speed-up using ultra-high-pressure size-exclusion chromatography in combination with columns packed with sub-2 µm particles are discussed.

Determination of selected protoporphyrins in parma ham with use of 5,10,15,20-tetra(4-hydroxyphenyl)porphyrin as a surrogate standard in the recovery study.

A high-performance liquid chromatographic method for the determination of hemin, protoporphyrin IX (PPIX), and zinc(II)protoporphyrin IX (Zn(II)PPIX) in Parma ham was developed. The detection was done by means of a universal DAD-detector, whereby quantification of the three naturally occurring protoporphyrins was carried out at lambda = 414 nm, i.e., very close to the respective maxima of their Soret bands. The extraction thereof from the meat matrix was done by a mixture of acetone and chloroacetic acid (100 mL + 0.2 g). Usage of 5,10,15,20-tetra(4-hydroxyphenyl)porphyrin (THPP) as a surrogate standard and its detection fixed at lambda = 444 nm, allowed to obtain accurate (ca. 96%) recovery results. Established concentrations of hemin, Zn(II)PPIX, and PPIX in the Parma ham samples were 15.97, 19.96 and 1.52 µg g(-1), respectively.

Boosting of photocatalytic hydrogen evolution via chlorine doping of polymeric carbon nitride.

Chlorine is found to be a suitable element for the modification of polymeric carbon nitride properties towards an efficient visible-light photocatalytic activity. In this study, chlorine-doped polymeric carbon nitride (Cl-PCN) has been examined as a photocatalyst in the hydrogen evolution reaction. The following aspects were found to enhance the photocatalytic efficiency of Cl-PCN: (i) unique location of Cl atoms at the interlayers of PCN instead of on its π-conjugated planes, (ii) slight bandgap narrowing, (iii) lower recombination rate of the electron-hole pairs, (iv) improved photogenerated charge transport and separation, and (v) higher reducing ability of the photogenerated electrons. The above factors affected the 4.4-fold enhancement of the photocatalytic efficiency in hydrogen evolution in comparison to the pristine catalyst.

Simultaneous enantioseparation of nonsteroidal anti-inflammatory drugs by a one-dimensional liquid chromatography technique using a dynamically coated chiral porous silicon pillar array column.

The preparation of a highly efficient chiral liquid chromatography (LC) column is explored by dynamically coating a reversed-phase porous silicon pillar array column with hydroxypropyl-ß-cyclodextrin (Hp-ß-CD) as the chiral selector. Analyte mixtures composed of non-steroidal anti-inflammatory drugs were tested to reveal the enantioseparation potential of the column. The mechanism of chiral discrimination was investigated. The adsorbed Hp-ß-CDs on the column surface experience different interaction with enantiomers. The chiral stationary phase showed satisfying stability and could be easily restored by recovering the selector with sufficient flushing and repeating the loading procedure. The peak capacity of the column was evaluated, and it was found high enough to separate three enantiomer couples using a one-dimensional LC technique.

Graphitic Carbon Nitride and Titanium Dioxide Modified with 1 D and 2 D Carbon Structures for Photocatalysis.

Enhancing the photocatalytic performance of graphitic carbon nitride (g-C3 N4 , GCN) and titanium dioxide (TiO2 ) has played a key role in the energy and environmental protection research community. Therefore, it is necessary to explore the synergy of both materials with carbon nanostructures for photocatalysis. Among the variety of carbon materials, graphene flakes and nanotubes, as nanoadditives to improve electron charge transfer and the optical absorption behavior in the visible-light region, have been widely explored. Thus, flake-like (2 D) and tubular (1 D) carbon structures in composition with GCN and/or TiO2 are reviewed, as are their photocatalytic response. Current trends clearly indicate that this type of molecular hybrids can be efficiently exploited in this field. This Minireview covers state-of-the-art research over the period of 2015 to 2018.

From Hollow to Solid Carbon Spheres: Time-Dependent Facile Synthesis.

Here, we report a facile route for obtaining carbon spheres with fully tunable shell thickness. Using a hard template in chemical vapor deposition (CVD), hollow carbon spheres, solid carbon spheres, and intermediate structures can be obtained with optimized process time. The resulting carbon spheres with particle diameters of ~400 nm, as well as a controllable shell thickness from 0 to 70 nm, had high Brunauer⁻Emmett⁻Teller (BET) specific surface area (up to 344.8 m²·g-1) and pore volume (up to 0.248 cm³·g-1). The sphere formation mechanism is also proposed. This simple and reproducible technique can deliver carbon materials for various applications, e.g., energy storage and conversion, adsorption, catalytic, biomedical, and environmental applications.

A Comparison of Hydrogen Storage in Pt, Pd and Pt/Pd Alloys Loaded Disordered Mesoporous Hollow Carbon Spheres.

Comprehensive study to evaluate the ability of hydrogen uptake by disordered mesoporous hollow carbon spheres doped witch metal such as Pt, Pd or Pt/Pd was conducted. They were synthesized facilely using sonication and then calcination process under vacuum at the temperature of 550 °C. The effect on hydrogen sorption at neat-ambient conditions (40 °C, up to 45 bar) was thoroughly analyzed. The results clearly revealed that metal functionalization has a significant impact on the hydrogen storage capacity as the mechanism of gas uptake depends on two factors: metal type and certain size of particles. Thus, functionalized spheres adsorb hydrogen by physisorption forming metal hydrides or metal hydrides combined with hydrogen spillover effect. As a result, a sample with narrower distribution of nanoparticles and smaller specific size exhibited enhanced hydrogen uptake.

A comprehensive study to protein retention in hydrophobic interaction chromatography.

The effect of different kosmotropic/chaotropic salt systems on retention characteristics of intact proteins has been examined in hydrophobic interaction chromatography (HIC). The performance was assessed using different column chemistries, i.e., polyalkylamide, alkylamine incorporating hydrophobic moieties, and a butyl chemistry. Selectivity in HIC is mainly governed by the salt concentration and by the molal surface tension increment of the salt. Typically, a linear relationship between the natural logarithm of the retention factor and the salt concentration is obtained. Using a 250mm long column packed with 5µm polyalkylamide functionalized silica particles and applying a 30min linear salt gradient, a peak capacity of 78 was achieved, allowing the baseline separation of seven intact proteins. The hydrophobicity index appeared to be a good indicator to predict the elution order of intact proteins in HIC mode. Furthermore, the effect of adding additives in the mobile phase, such as calcium chloride (stabilizing the 3D conformation of α-lactalbumin) and isopropanol, on retention properties has been assessed. Results indicate that HIC retention is also governed by conformational in the proteins which affect the number of accessible hydrophobic moieties.

Phenothiazinium photoantimicrobials with basic side chains.

Derivatives of the standard cationic photosensitiser, methylene blue, were synthesised, having extra amino (basic) functionality in the auxochromic side-chain. The resulting analogues were profiled for photodynamic activity in vitro, and screened against standard Gram-positive and Gram-negative bacteria for photobactericidal activity. The substitution pattern of the derivatives was such that ionisation of the amino groups in situ, via protonation, provided a range of charge distribution and degree of charge across the molecular framework. While most examples exhibited greater activity than the lead compound, in addition to similar activity to the known, but more powerful, phenothiazinium photoantimicrobial, dimethyl methylene blue, this was also associated with relatively high dark toxicity, inferring that these compounds were targeting crucial structures before illumination. One derivative having an asymmetrical structure, with separation between a lipophilic and a hydrophilic region exhibited a combination of very high phototoxicity coupled with very low dark effects, against both the standard screen and an additional one containing further, relevant pathogen species, including Candida albicans. It is suggested that the great activity of this analogue is due to efficient membrane targeting.