Separation of Spectroscopically Uniform Nanographenes

Excitation‐dependent photoluminescence (PL) is a well‐known property of graphene quantum dots (GQDs). For the development of carbon‐based photofunctional materials, GQDs possessing uniform PL properties are in high demand. A protocol has been established to separate spectroscopically uniform lipophilic GQD‐ 1 a from a mixture of GQD‐ 1 mainly composed of GQD‐ 1 a and GQD‐ 1 b . The mixture of GQD‐ 1 was synthesized through the reaction of p‐methoxybenzylamine with GQD‐ 2 prepared from graphite by common oxidative exfoliation. Size‐exclusion chromatography gave rise to GQD‐ 1 a and GQD‐ 1 b , with diameters of 19.8 and 4.9 nm, respectively. Large GQD‐ 1 a showed that the PL was fairly independent of the excitation wavelengths, whereas the PL of small GQD‐ 1 b was dependent on excitation. The excitation‐dependent nature is most likely to be associated with the structures of sp² domains on the graphene surfaces. The large sp²‐conjugated surface of GQD‐ 1 a is likely to possess well‐developed and large sp² domains, the band gaps of which do not significantly vary. The small sp²‐conjugated surface of GQD‐ 1 b produces small sp²‐conjugated domains that generate band gaps differing with domain sizes.     

Intrinsic Emission from Nanographenes

Top‐down approaches have been widely used as convenient methods for the production of nanographenes. To understand the photoemission properties of nanographenes, their separation and the optical properties of the individual fractions is important. By using a combination of size‐exclusion and silica‐gel‐adsorption chromatography, we separated lipophilic nanographenes that contained para‐methoxybenzyl groups. The mixture consisted of large (average 19.8 nm) and small (average 4.9 nm) nanographenes, whilst unreacted carboxy groups remained in the latter group. Optical measurements revealed that oxygen‐containing functional groups had little influence on the photoemission of the nanographenes, thus indicating that the intrinsic emission, that is, emission from the sp² surfaces, was responsible for the photoemission. Two photoemission bands were observed for all of the fractions, which likely originated from the edge and inner parts of nanographene.     

Near‐Infrared‐Emitting Nitrogen‐Doped Nanographenes

The quantum‐size effect, which enables nanographenes to emit photoluminescence (PL) in the UV to visible region, has inspired intense research. However, the control of the PL properties of nanographenes through manipulation of their π‐system by post‐modifications is not well developed. By utilizing a ring‐closure reaction between an aromatic 1,2‐dicarboxylic acid and a 1,8‐naphthalenediamine derivative, which produces a perimidine framework, nitrogen‐doped nanographenes were realized. Two nanographenes produced by a one‐pot reaction of edge‐oxidized nanographene (GQD‐ 2 ) with 1,8‐naphthalenediamine derivatives (GQD‐ 1 a and GQD‐ 1 b ) displayed an absorption band extending to >1000 nm; furthermore, the PL wavelength of GQD‐ 1 a was significantly red‐shifted into the near‐infrared (NIR) region in which it can be used for bioimaging. Time‐dependent DFT calculations of model nanographenes showed that the functional groups narrow the HOMO–LUMO gap, realizing the NIR‐emitting nanographenes.     

The Effect of Double Dispersion on Natural Convection Heat and Mass Transfer in a Non-Newtonian Fluid Saturated Non-Darcy Porous Medium

The effect of power law index parameter of the non-Newtonian fluid on free convection heat and mass transfer from a vertical wall is analyzed by considering double dispersion in a non-Darcy porous medium with constant wall temperature and concentration conditions. The Ostwald–de Waele power law model is used to characterize the non-Newtonian fluid behavior. In this case a similarity solution is possible. The variation of heat and mass transfer coefficients with the governing parameters such as power law index, thermal and solutal dispersion parameters, inertia parameter, buoyancy ratio, and the Lewis number is discussed for a wide range of values of these parameters.     

Determination of Penicillins in Milk by a Dual-Optrode Biosensor

Penicillins are the most frequently found antibiotic residues in milk, as they are commonly used for the treatment of bacterial infections in cows. In the present study, we introduce a method for the rapid detection of penicillin residues in raw milk based on the determination of glucose concentration in milk with a dual flow-through biosensor. The molar concentration of glucose in milk is typically over 500 times lower than the concentration of lactose and is highly dependent on the rate of lactose hydrolysis, which is catalyzed by β-galactosidase. Glucose concentrations in milk change with variation in the β-galactosidase activity. β-Galactosidase is an enzyme produced in the microbiota in milk and its activity is inhibited by benzylpenicillin. Spiking milk with benzylpenicillin lowers glucose concentrations in comparison to high-quality milk after short storage intervals. The presence of penicillin in the milk of treated animals resulted in decreased glucose concentrations in comparison with high-quality milk that contained no antibiotics. The glucose concentration in milk samples was followed by the system enabling the elimination of the effects of bacterial respiration in the output with reliable results in less than 1?min.     

A Supramolecular Polymer Network of Graphene Quantum Dots

Graphene quantum dot (GQD)–organic hybrid compounds (GQD‐ 2 b – e ) were prepared by introducing 3,4,5‐tri(hexadecyloxy)benzyl groups (C16) and linear chains terminated with a 2‐ureido‐4‐[1H]‐pyrimidinone (UPy) moiety onto the periphery of GQD‐ 1 . GQD‐ 2 b – e formed supramolecular assemblies through hydrogen bonding between the UPy units. GPC analysis showed that GQDs with high loadings of the UPy group formed larger assemblies, and this trend was confirmed by DOSY and viscosity measurements. AFM images showed the polymeric network structures of GQD‐ 2 e on mica with flat structures (ca. 1.1 nm in height), but no such structures were observed in GQD‐ 2 a , which only carries the C16 group. GQD‐ 2 c and GQD‐ 2 d formed organogels in n‐decanol, and the gelation properties can be altered by replacing the alkyl chains in the UPy group with ethylene glycol chains (GQD‐ 3 ). GQD can thus be used as a platform for supramolecular polymers and organogelators by suitable chemical functionalization.     

Structure and evolved gas analyses (TG/DTA-MS and TG-FTIR) of <Emphasis Type="Italic">mer</Emphasis>-trichlorotris(thiourea)-indium(III), a precursor for indium sulfide thin films

The indium complex, mer-trichlorotris(thiourea)-indium(III) (In(tu)₃Cl₃, 1), crystallized from aqueous solution of InCl₃ and SC(NH₂)₂ (tu) with molar ratio of 1:3, is a single-source precursor for In₂S₃ films by chemical spray pyrolysis. The structural model of the triclinic crystal 1 (space group P-1 with a = 8.4842(2) Å, b = 10.5174(2) Å, c = 13.1767(2) Å, α = 111.1870(10)°, β = 98.0870(10)°, γ = 97.889(2)°) has been improved by single crystal X-ray diffraction analysis through successful separation of the disordered positions of the asymmetric complex molecule situated on the inversion centre into two spatial arrangements. Thermal decomposition of 1 occurs with very similar mass loss courses till 400 °C in both nitrogen and air, anyhow the DTA curve indicates a gas-phase oxidation with an additional exothermic heat effect at 255 °C in air. Partial or more advanced oxidation of the initially evolved CS₂ has taken place in both atmospheres, as its oxidation products, SO₂, COS, CO₂ are accompanied by the release of NH₃, HCl in temperature range of 205–275 °C, while H₂NCN and HCN evolve in air. In the third mass loss step, in the temperature interval of 405–750 °C in nitrogen and 405–700 °C in air, two processes, evaporation and oxidation of the solid residues are competing with each other, resulting in final decomposition product of 1 in air In₂O₃, while also some In₂O₃ in inert atmosphere beyond the main phase of In₂S₃ where, in addition considerable extent of loss of indium occurs, probably through volatile dimeric indium chloride species, which could not be detected either by EGA-MS or EGA-FTIR systems of ours. Nevertheless, evolution of HNCS is confirmed by EGA-FTIR, and release of CO₂, H₂NCN, SO₂, and a little HCl is detected at temperatures above 450 °C in both atmospheres.