RSC Advances

Bagherzadeh, M.; Amrollahi, M. A.; Makizadeh, S.

doi: 10.1039/c5ra22315fpmid: N/A

This study focuses on covalent grafting of Fe3O4 magnetic nanoparticles (MNPs) to graphene oxide nanosheets (GNOS) via three different chemical routes. To this purpose, firstly, dopamine-functionalized Fe3O4 (Fe3O4/DA) nanoparticles were firmly attached onto the surface of GONS by activation of carboxylic groups of GONS via thionyl chloride (SOCl2), anhydride formation by using trifluoro acetic acid (TFAA) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-hydroxysuccinimide (EDC/NHS) to form Fe3O4/DA/GONS. The attachment of Fe3O4 MNPs on the GONS surface was evaluated and compared by using FT-IR, XRD, TEM, TGA, VSM, TEM and SAED techniques. The results showed that, depending on the route used, the density and immobilization site of Fe3O4 MNPs can be different.

Kharisov, Boris I.; Kharissova, Oxana V.; García, Beatriz Ortega; Méndez, Yolanda Peña; de la Fuente, Idalia Gómez

doi: 10.1039/c5ra22738kpmid: N/A

Forest-like nanostructures, their syntheses, properties, and applications are reviewed. Nanoforests are mainly represented by carbon nanotubes, zinc and titanium oxides, and gold, and much less frequently by other metals, metal oxides, arsenides and phosphides. These nanostructures generally consist of more simple 1D objects, such as nanowires, nanopillars, nanorods, nanotrees, nanofibers or nanotubes. Synthesis methods for nanoforests vary from catalytic pyrolysis or thermal decomposition of hydrocarbons to electrophoretic deposition, hydrothermal routes, electron beam lithography, focused-ion-beam techniques, vapor phase transport, facet-selective etching and pulsed deep reactive etching technologies, among others. A number of applications for the forest-like nanostructures are generalized, for instance as sensors/detectors, photoanodes in solar and fuel cells, supercapacitors and energy storage devices, in SERS applications, optical and MEMs switching devices, water splitting processes, CO2 fixation, and as supports or targets for biomolecules. In general, it is expected that more varieties of compounds and materials with exciting properties can be obtained in this form in the near future, thus expanding numerous applications of forest-like nanostructures.

Barman, Jitesh; Nagarajan, Arun Kumar; Khare, Krishnacharya

doi: 10.1039/c5ra21936apmid: N/A

Aqueous drops on silicone oil infused lubricating surfaces are cloaked with a thin layer of oil to minimize their surface energy. These oil cloaked aqueous drops exhibit pseudo-stable coalescence or spontaneous coalescence depending upon the lubricating oil thickness which controls the interaction point of the drops. For thick oil films, drops interact with each other through the surrounding oil menisci resulting in pseudo-stable non-coalescence due to a thin oil layer between the drops. This stabilizing oil layer drains itself out due to the Laplace pressure of the aqueous drops. An external electric field applied between the drops forces the oil to drain faster, due to additional electrostatic pressure, resulting in faster coalescence. This happens in two steps: bulk drainage of the oil and final rupture due to the electric field induced hydrodynamic instability of the thin oil layer. For thin lubricating films, the contact point of aqueous drops is in the vicinity of the water–air interface resulting in spontaneous coalescence. By applying an external electric field between the drops and substrate (to decrease the apparent contact angle by electrowetting), the interaction point is brought close to the oil meniscus resulting in pseudo-stable aqueous drops against coalescence.

Pezhumkattil Palakkal, Jasnamol; Lekshmi, P. Neenu; Thomas, Senoy; Suresh, K. G.; Varma, Manoj Raama

doi: 10.1039/c5ra24092apmid: N/A

We present the observation of a high-temperature magnetic transition along with ferromagnetic short-range correlations (FSCs) in La2FeMnO6 perovskite system. XPS analysis confirmed the presence of Fe3+ and Mn3+ cations. Magnetization vs. temperature curves show two distinct transitions at TC1 ∼ 60 K and TC ∼ 425 K. Coercivity values of ∼1140 Oe and ∼35 Oe are observed at 2 K and 300 K respectively. Thermomagnetic analysis reveals the presence of FSCs in La2FeMnO6 up to T* = 570 K, well above the transition point, similar to a Griffiths-like phase (GP). The presence of ferromagnetic clusters in the paramagnetic region might be due to the intrinsic inhomogeneities associated with the structure, the quenched disorder related to the B-site cations and the antisite boundaries. The coefficient of lower temperature electronic specific heat is as high as 59.5 mJ mol−1 K−2. The electron spin resonance spectra show ferromagnetic resonance signals that point to the possibility of the presence of FSCs at room temperature. The material seems to be quite a promising candidate for some room temperature applications due to the possibility of the coexistence of functionalities like ferromagnetism, ferrimagnetism, GP, magnetotransport coupling, etc. in a single material.

Tanimura, Shinobu; Park, Yensil; Amaya, Andrew; Modak, Viraj; Wyslouzil, Barbara E.

doi: 10.1039/c5ra19782apmid: N/A

Heterogeneous nucleation of CO2 onto H2O ice particles may play an important role in proposed innovative CO2 capture technologies, as well as in the formation of Martian clouds. In this work we follow the nucleation/condensation of CO2/H2O gas mixtures with microsecond resolution in supersonic Laval nozzles using pressure trace measurement (PTM) and small angle X-ray scattering (SAXS). The latent heat release detected by the PTM reveals that the first phase transition in the expanding CO2/H2O mixture is the formation of H2O ice particles by the homogeneous nucleation/condensation and freezing of H2O. This is followed by the heterogeneous nucleation and growth of CO2 on the H2O ice particles. The onset conditions for heterogeneous nucleation, i.e. the partial pressure of CO2 and temperature from PTM and the radius of gyration of the H2O ice particles from SAXS, were determined in the temperature range 124 to 146 K and for particles with radii of gyration in the range of 2.1 to 4.3 nm. The onset conditions suggest that the heterogeneous nucleation of CO2 may start from the supercooled liquid phase under our conditions. Downstream of the onset point, the partial pressure of CO2 and temperature rapidly approach the vapor–solid equilibrium line of CO2, demonstrating that even if CO2 condensation is initiated by heterogeneous nucleation of the liquid phase, it proceeds via growth of the solid.

Giri, Karuna; Rivas Yepes, Laura; Duncan, Bradley; Kolumam Parameswaran, Praveen; Yan, Bo; Jiang, Ying; Bilska, Marcela; Moyano, Daniel F.; Thompson, Michael A.; Rotello, Vincent M.; Prakash, Y. S.

doi: 10.1039/c5ra16305fpmid: 26877871

Bacterial biofilms are associated with persistent infections that are resistant to conventional antibiotics and substantially complicate patient care. Surface engineered nanoparticles represent a novel, unconventional approach for disruption of biofilms and targeting of bacterial pathogens. Herein, we describe the role of surface charge of gold nanoparticles (AuNPs) on biofilm disruption and bactericidal activity towards Staphylococcus aureus and Pseudomonas aeruginosa which are important ventilator associated pneumonia (VAP) pathogens. In addition, we study the toxicity of charged AuNPs on human bronchial epithelial cells. While 100% positively charged AuNP surface was uniformly toxic to both bacteria and epithelial cells, reducing the extent of positive charge on the AuNP surface at moderate concentrations prevented epithelial cell toxicity. Reducing surface charge was however also less effective in killing bacteria. Conversely, increasing AuNP concentration while maintaining a low level of positivity continued to be bactericidal and disrupt the bacterial biofilm and was less cytotoxic to epithelial cells. These initial in vitro studies suggest that modulation of AuNP surface charge could be used to balance effects on bacteria vs. airway cells in the context of VAP, but the therapeutic window in terms of concentration vs. surface positive charge may be limited. Additional factors such as hydrophobicity may need to be considered in order to design AuNPs with specific, beneficial effects on bacterial pathogens and their biofilms.

Nguyen, Lan Thi Mai; Park, Hunmin; Banu, Marimuthu; Kim, Jae Yul; Youn, Duck Hyun; Magesh, Ganesan; Kim, Won Yong; Lee, Jae Sung

doi: 10.1039/c5ra21017hpmid: N/A

Pure formic acid was successfully produced via CO2 hydrogenation for the first time over a heterogeneous catalyst of PdNi alloy on a carbon nanotube-graphene (CNT-GR) support in water as an eco-friendly solvent without a base additive. The highest formic acid yield obtained was 1.92 mmol with a turnover number of 6.4 and a turnover frequency of 1.2 × 10−4 s−1 under mild reaction conditions of 40 °C and 50 bar. Alloying Pd with Ni brought a significant enhancement in catalytic activity compared to the monometallic Pd catalyst. In addition, the CNT-GR composite as a catalytic support improved the dispersion of Pd–Ni alloy particles, which exhibited good stability under the reaction conditions.

Palanisamy, Selvakumar; Lee, Hsin Fang; Chen, Shen-Ming; Thirumalraj, Balamurugan

doi: 10.1039/c5ra20512cpmid: N/A

In the present work, we report a single step electrochemical fabrication of a platinum nanoparticle decorated reduced graphene oxide (RGO–PtNPs) composite for enhanced electrochemical sensing of hydrogen peroxide (H2O2). The RGO–PtNPs composite was fabricated by the reduction of graphene oxide modified electrode in an electrolyte solution containing a 0.5 mM K2PtCl6 solution with 1 mM KCl at a constant applied potential of −1.4 V for 300 s. The fabricated composite modified electrode was further characterized by scanning electron microscopy, elemental analysis and cyclic voltammetry. Compared with GO–PtNPs and PtNPs modified electrodes, the RGO–PtNPs composite modified electrode showed an enhanced electrocatalytic activity toward the reduction of H2O2. The amperometric response of the RGO–PtNPs composite modified electrode for the reduction of H2O2 was linear over the concentration ranging from 0.05 to 750.6 μM with the limit of detection of 16 nM. The sensor reached its steady state current response within 2 s. The sensitivity of the sensor was calculated as 0.686 + 0.072 μA μM−1 cm−2. The proposed sensor showed a satisfactory selectivity in the presence of biologically coactive compounds. In addition, the sensor also showed a good practicability toward the detection of H2O2 in commercial contact lens solutions and human urine samples.

Shil, Suranjan; Roy, Moumita; Misra, Anirban

doi: 10.1039/c5ra16670epmid: N/A

We have designed seven organic diradicals with polyacene couplers to show the effect of the configuration, aromaticity [estimated with the help of Nucleus Independent Chemical Shift (NICS(0) and NICS(I)), and Harmonic Oscillator Model of Aromaticity (HOMA)] and HOMO–LUMO gap of the couplers on the exchange coupling constant of the diradicals. It has been observed that the linear polyacenes are less aromatic compared to the corresponding angular ones. We have correlated aromaticity indexes NICS and HOMA to explain the change of aromaticity for structures having the same number of carbon and hydrogen atoms and rings. The diradicals with linear couplers manifest stronger exchange coupling constants compared to those with angular couplers. It has been found that the NICS value cannot adequately address the aromaticity of the polyacenes, whereas the HOMA value can reliably account for the observations. Here, we have found the HOMO–LUMO gap is the determining factor for the extent of the magnetic exchange coupling constant in the diradicals. It has been found that not only the energy value of the LUMO, but also its occupation number and spatial position, play an important role in magnetic exchange in diradicals. Thus, the role of the LUMO in magnetic exchange has been firmly established through this work. The magneto-structural correlation has also been studied to establish the mechanism of magnetic interaction.

Saikia, Bishwajit; Borah, Parinita

doi: 10.1039/c5ra20133kpmid: N/A

We have developed a novel protocol to realize the Dakin reaction in a more greener way. In fact, by the use of H2O2–WERSA, we can oxidize aromatic arylaldehydes to phenols at room temperature. It is remarkable that the catalytic system does not require activation or any toxic ligand, additive/promoter, transition metal catalyst, base, organic solvent and so on. A range of substituted hydroxylated benzaldehydes were screened to investigate the scope of this protocol.