Dependence of pH and surfactant effect in the synthesis of magnetite (Fe3O4) nanoparticles and its properties

Nanoparticles of Fe₃O₄ were synthesized by co-precipitation in an aqueous solution containing ferrous and ferric salts (1:2) at varying pH with ammonia as a base. It was found that the value of pH influences the reaction mechanism for the formation of Fe₃O₄. Furthermore, the addition of mercaptoethanol significantly reduced the crystalline size of Fe₃O₄ nanoparticles from 15.03 to 8.02 nm. X-ray diffraction (XRD) spectra revealed that the synthesized nanoparticles were ε-Fe₂O₃ or Fe₃O₄ phase. To further prove the composition of the product, as-prepared Fe₃O₄ were examined by X-ray photoelectron spectroscopy (XPS). Magnetic properties of the obtained particles were determined by vibrating sample magnetometer (VSM). Further analysis of the X-ray studies shows that while maintaining a pH value of 6 and 9 in a solution containing iron salts II and III ions produces ε-Fe₂O₃. Whereas a pH value of 11 produces magnetite (Fe₃O₄) phase. All of these results show that the pH has a major role in the observed phase formation of (Fe₃O₄) nanoparticles.     

Efficient heteronuclear dipolar decoupling in solid-state NMR using frequency-swept SPINAL sequences

Aiming to improve heteronuclear spin decoupling efficiency in NMR spectroscopy of solids and liquid crystals, we have modified the original Small Phase Incremental ALteration (SPINAL) sequence by incorporating a frequency sweep into it. For the resulting sequence, termed SW_f-SPINAL, the decoupling performance of a large number of sweep variants was explored by both numerical simulations and NMR experiments. It is found that introducing a frequency sweep generally increases both the ‘on-resonance’ decoupling performance and the robustness towards parameter offsets compared to the original SPINAL sequence. This validates the concept of extending the range of efficient decoupling by introducing frequency sweeps, which was recently suggested in the context of the frequency-swept SW_f-TPPM method. The sequence found to be best performing among the SW_f-SPINAL variants consists of fully swept 16 pulse pairs and is designated (32)-SPINAL-32. Its good decoupling performance for rigid spin systems is confirmed by numerical simulations and also experimentally, by evaluating the CH₂ resonance of a powder sample of l-tyrosine under MAS. For moderate MAS frequencies, the new sequence matches the decoupling achieved with SW_f-TPPM, and outperforms all other tested sequences, including TPPM and SPINAL-64. (32)-SPINAL-32 also shows excellent decoupling characteristics for liquid crystalline systems, as exemplified by experiments on the 5CB liquid crystal.     

Optimization of components in high-yield synthesis of block copolymer-mediated gold nanoparticles

The optimization to achieve stable and high-yield gold nanoparticles in block copolymer-mediated synthesis has been examined. Gold nanoparticles are synthesized using block copolymer P85 in gold salt HAuCl₄·3H₂O solution. This method usually has a very limited yield which does not simply increase with the increase in the gold salt concentration. We show that the yield can be enhanced by increasing the block copolymer concentration but is limited to the factor by which the concentration is increased. On the other hand, the presence of an additional reductant (trisodium citrate) in 1:1 molar ratio with gold salt enhances the yield by manyfold. In this case (with additional reductant), the stable and high-yield nanoparticles having size about 14 nm can be synthesized at very low block copolymer concentrations. These nanoparticles thus can be efficiently used for their application such as for adsorption of proteins.     

On WDM RoF–EPON link using OSSB transmission with and without DCF + FBG

A system is presented which uses optical SSB transmission on WDM RoF–EPON link to compensate dispersion and FWM with DCF and FBG. Performance of the system is improved by 8.91% with the use of DCF and FBG for equal spacing between the channels and it is further increased by 9.51% by keeping unequal spacing between the channels. Results are compared for equal and unequal spacing with and without DCF and FBG. BER, Q factor and eye diagrams have been analyzed for evaluating the performance of the system.     

Determination of boron concentration in borosilicate glass,boron carbide and graphite samples by conventional wet-chemical and nuclear analytical methods

Boron is an important element in nuclear technology. A comparative study was carried out for the determination of boron in borosilicate glass, boron carbide and graphite samples by wet-chemical and nuclear analytical methods. Wet chemical methods namely titrimetry, Inductively Coupled Plasma Mass Spectrometry and ICP Optical Emission Spectrometry and nuclear analytical methods namely Particle Induced Gamma-Ray Emission and Nuclear Reaction Analysis were used. Boron concentrations were in trace (mg kg^?1) level in graphite and percentage level in borosilicate glass and boron carbide.     

Unilamellar Vesicles from Amphiphilic Graphene Quantum Dots

Graphene quantum dots (GQDs) have attracted considerable interest due to their unique physicochemical properties and various applications. For the first time it is shown that GQDs surface‐functionalized with hydrocarbon chains (i.e., amphiphilic GQDs) self‐assemble into unilamellar spherical vesicles in aqueous solution. The amphiphilic GQD vesicles exhibit multicolor luminescence that can be readily exploited for membrane studies by fluorescence spectroscopy and microscopy. The GQD vesicles were used for microscopic analysis of membrane interactions and disruption by the peptide beta‐amyloid.