Photochemical Synthesis of Gold and Silver Nanoparticles—A Review

Nanomaterials have supported important technological advances due to their unique properties and their applicability in various fields, such as biomedicine, catalysis, environment, energy, and electronics. This has triggered a tremendous increase in their demand. In turn, materials scientists have sought facile methods to produce nanomaterials of desired features, i.e., morphology, composition, colloidal stability, and surface chemistry, as these determine the targeted application. The advent of photoprocesses has enabled the easy, fast, scalable, and cost- and energy-effective production of metallic nanoparticles of controlled properties without the use of harmful reagents or sophisticated equipment. Herein, we overview the synthesis of gold and silver nanoparticles via photochemical routes. We extensively discuss the effect of varying the experimental parameters, such as the pH, exposure time, and source of irradiation, the use or not of reductants and surfactants, reagents’ nature and concentration, on the outcomes of these noble nanoparticles, namely, their size, shape, and colloidal stability. The hypothetical mechanisms that govern these green processes are discussed whenever available. Finally, we mention their applications and insights for future developments.     

A study of the mechanical, thermal and morphological properties of microcrystalline cellulose particles prepared from cotton slivers using different acid concentrations

Microcrystalline cellulose (MCC) particles are mostly prepared by acid hydrolysis of various agro sources. Acid hydrolysis is usually carried out with high concentration (64 wt%) of sulfuric acid. Here, an attempt has been made to optimize lower acid concentrations which can effectively produce MCC particles. In this work, different concentrations of sulfuric acid (20, 30, 35, 40, 47 and 64 wt%) have been used to prepare MCC particles, which have been characterized by XRD, particle size analysis, scanning electron microscopy, transmission electron microscopy, nanoindentation and thermogravimetric analysis. MCC prepared with 35 and 47% sulfuric acid (MCC 35 and MCC 47) had finest particle size and fibrils were produced in the range of 15–25 nm. MCC 20 showed wide particle size distribution, indicating low breakdown of the cellulose chains. The energy absorption behavior and mechanical properties of the MCC pellets were determined by nanoindentation test for the first time. MCC 35 pellets exhibited lowest modulus and hardness.     

Budding and fission of a multiphase vesicle

We present a model of bi-phasic vesicles in the limit of large surface tension. In this regime, the vesicle is completely stretched and well described by two spherical caps with a fold, which concentrates the membrane stress. The conservation laws and geometric constraints restrict the space of possible shapes to a pair of solutions labeled by a parameter given by line tension/pressure. For a given value of , the two solutions differ by the length of the interface between domains. For a critical value, , the two vesicle shapes become identical and no connected solution exists above this critical value. This model sheds new light on two proposed mechanisms (osmotic shocks and molecule absorption) to explain the budding and the fission in recent experiments.     

Comparison between Conventional and Nonconventional Methods for the Synthesis of Some 2-Oxazolidinone Derivatives and Preliminary Investigation of Their Inhibitory Activity Against Certain Protein Kinases

Russian Journal of Organic Chemistry - A series of propargyl and allyl carbamates were prepared directly from propargyl and allyl alcohols and phenyl or cyclohexyl isocyanate or indirectly by...     

Assessment of Biologically Effective Solar Ultraviolet Exposures for Court Staff and Competitors During a Major Australian Tennis Tournament

Sport is an integral and enduring part of many societies, such as Australia. Participation in outdoor sports, such as tennis, comes with a very real risk of dangerous solar ultraviolet exposure which can result in erythema (sunburn), serious conditions such as skin cancer, including melanoma, and eye conditions such as cataracts and pterygium. This study remotely assesses the effective ultraviolet exposures in response to the increased sun safety awareness at a major summertime tennis tournament in Australia. The assessment only uses publicly accessible data and information. It was found that tournament organizers have effectively adopted sun‐safe protocols into the uniform policy that the court officials (judges and ball kids) are mandated to follow. The combination of sun‐participant geometry and the photoprotection provided by uniforms significantly reduced the ambient ultraviolet exposure, which was recorded to be as high as 9.9 SED h^?1, to just 1.0 and 0.5 SED h^?1 for ball kids and judges, respectively, compared to up to 2.0 SED h^?1 for players. Even though caution is needed against complacency with sun safety, with the need for the court officials and the players to still apply sunscreen, the court officials provided persistent visual role modeling of sun‐safe behaviors.     

High surface area thermally stabilized porous iron oxide/silica nanocomposites via a formamide modified sol-gel process

Iron oxide/silica (Fe:Si as 1:10 atomic ratio) composite materials have been prepared by calcination for 3 h at different temperatures (400-900 °C) of xerogel precursor obtained via a formamide modified sol-gel process. The process involved TEOS and iron(III) nitrate, nitric acid and formamide. Genesis of the composite materials from the xerogel precursor has been investigated by TGA, DSC, FTIR, XRD, SEM and EDX. Results indicated that all the calcined composites are mainly composed of amorphous iron oxide dispersed as finely divided particles in amorphous silica matrixes. Nitrogen adsorption/desorption isotherms revealed a reversible type I of isotherms indicative of microporosity. However, high S_BET surface area and microsporosity were observed for the calcined composite materials (e.g. S_BET = 625 m² g⁻¹, and S_αs = 556 m² g⁻¹ for the composite calcined at 400 °C). Formation of the porous texture was discussed in terms of the action of formamide, which enhanced strengthening of the silica gel network during evaporation of the more volatile components within the composite body during the drying process.     

Vacancy formation and strain in low-temperature Cu/Cu(100) growth

The development of compressive strain in metal thin films grown at low temperature has recently been revealed via x-ray diffraction and explained by the assumption that a large number of vacancies were incorporated into the growing films. The results of our molecular dynamics and parallel temperature-accelerated dynamics simulations suggest that the experimentally observed strain arises from an increased nanoscale surface roughness caused by the suppression of thermally activated events at low temperature combined with the effects of shadowing due to off-normal deposition.     

Two classes of alongside charge-transfer interactions defined in one [2]catenane

A [2]catenane, which incorporates hydroquinone (HQ) and a sterically bulky tetrathiafulvalene (TTF) into a bismacrocycle, has been designed to probe the alongside charge-transfer (CT) interactions taking place between a TTF unit and one of the bipyridinium moieties in the tetracationic cyclophane cyclobis(paraquat-p-phenylene) (CBPQT4+). A template-directed strategy employs the HQ unit as the primary template for formation of the tetracationic cyclophane CBPQT4+, affording the desired [2]catenane structure but as an uncharacteristic green solid. The X-ray crystal structure and detailed 13C NMR assignments have identified a stereoselective preference for catenation about the cis isomer. The 1H NMR spectroscopy, electrochemistry, and X-ray crystallography all confirm that the CBPQT4+ cyclophane encircles the HQ unit, thereby defining a structure which would normally determine a red color. The visible-NIR region of the absorption spectrum displays a band at approximately 740 nm that is unambiguously assigned to a TTF --> CBPQT4+ CT transition on the basis of resonance Raman spectroscopy using 785 nm excitation. The profile of the CT band changes depending on the ratio of the cis- to trans-TTF isomers in the [2]catenane for which the molar absorptivity of each isomer is estimated to be significantly different at epsilon max = 380 and 3690 M-1 cm-1, respectively. Molecular modeling studies confirmed that the observed difference in the absorption spectroscopic profile can be accounted for by both a better overlap of the HOMO(TTF) and LUMO+1(CBPQT4+) as well as a more stable face-to-face (pi...pi) conformation in the trans isomer compared to the edge-to-face cis isomer of the [2]catenane. The latter is arranged for pi-orbital overlap through the sulfur atoms of the TTF unit, thereby defining an [Spi...pi] interaction.     

Use of an Internal Keto-Imino Compound as the Photoinitiator in the Polymerization of Methyl Methacrylate

Photopolymerization of MMA in visible light was studied at 40°C using acridone as the photoinitiator. The polymerization was found to proceed via a free radical mechanism and the radical generation process was considered to follow an initial complexation reaction between monomer and acridone. Kinetic data indicated a lower order dependence of R_p on the initiator concentration (initiator exponent < 0.5). Initiator-dependent chain termination was significant along with the usual bimolecular mode of chain termination. The monomer exponent varied from about 1.0 to 1.5, depending on the nature of the solvent used. The nonidealities in this case were also analyzed.