We developed two-step solution-phase reactions to form hybrid materials of Mn3O4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn3O4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn3O4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn3O4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn3O4 nanoparticles grown atop. The Mn3O4/RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

Mn3O4-Graphene Hybrid as a High Capacity Anode Material for Lithium Ion Batteries

In pursuit of more sustainable and competitive biorefineries, the effective valorisation of lignin is key. An alluring opportunity is the exploitation of lignin as a resource for chemicals. Three technological biorefinery aspects will determine the realisation of a successful lignin-to-chemicals valorisation chain, namely (i) lignocellulose fractionation, (ii) lignin depolymerisation, and (iii) upgrading towards targeted chemicals. This review provides a summary and perspective of the extensive research that has been devoted to each of these three interconnected biorefinery aspects, ranging from industrially well-established techniques to the latest cutting edge innovations. To navigate the reader through the overwhelming collection of literature on each topic, distinct strategies/topics were delineated and summarised in comprehensive overview figures. Upon closer inspection, conceptual principles arise that rationalise the success of certain methodologies, and more importantly, can guide future research to further expand the portfolio of promising technologies. When targeting chemicals, a key objective during the fractionation and depolymerisation stage is to minimise lignin condensation (i.e. formation of resistive carbon–carbon linkages). During fractionation, this can be achieved by either (i) preserving the (native) lignin structure or (ii) by tolerating depolymerisation of the lignin polymer but preventing condensation through chemical quenching or physical removal of reactive intermediates. The latter strategy is also commonly applied in the lignin depolymerisation stage, while an alternative approach is to augment the relative rate of depolymerisation vs. condensation by enhancing the reactivity of the lignin structure towards depolymerisation. Finally, because depolymerised lignins often consist of a complex mixture of various compounds, upgrading of the raw product mixture through convergent transformations embodies a promising approach to decrease the complexity. This particular upgrading approach is termed funneling, and includes both chemocatalytic and biological strategies.

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Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading

We show that the Raman scattering technique can give complete structural information for one-dimensional systems, such as carbon nanotubes. Resonant confocal micro-Raman spectroscopy of an (n,m) individual single-wall nanotube makes it possible to assign its chirality uniquely by measuring one radial breathing mode frequency omega(RBM) and using the theory of resonant transitions. A unique chirality assignment can be made for both metallic and semiconducting nanotubes of diameter d(t), using the parameters gamma(0) = 2.9 eV and omega(RBM) = 248/d(t). For example, the strong RBM intensity observed at 156 cm(-1) for 785 nm laser excitation is assigned to the (13,10) metallic chiral nanotube on a Si/SiO2 surface.

Structural (n,m) determination of isolated single wall carbon nanotubes by resonant Raman scattering

This review article attempts to provide a comprehensive review of the recent progress in the so-called resistive random access memories (RRAMs) First, a brief introduction is presented to describe the construction and development of RRAMs, their potential for broad applications in the fields of nonvolatile memory, unconventional computing and logic devices, and the focus of research concerning RRAMs over the past decade Second, both inorganic and organic materials used in RRAMs are summarized, and their respective advantages and shortcomings are discussed Third, the important switching mechanisms are discussed in depth and are classified into ion migration, charge trapping/de-trapping, thermochemical reaction, exclusive mechanisms in inorganics, and exclusive mechanisms in organics Fourth, attention is given to the application of RRAMs for data storage, including their current performance, methods for performance enhancement, sneak-path issue and possible solutions, and demonstrations of 2-D and 3-D crossbar arrays Fifth, prospective applications of RRAMs in unconventional computing, as well as logic devices and multi-functionalization of RRAMs, are comprehensively summarized and thoroughly discussed The present review article ends with a short discussion concerning the challenges and future prospects of the RRAMs

Recent progress in resistive random access memories: Materials, switching mechanisms, and performance

Colloidal synthesis offers a route to nanoparticles (NPs) with controlled composition and structural features. This Perspective describes the use of polyvinylpyrrolidone (PVP) to obtain such nanostructures. PVP can serve as a surface stabilizer, growth modifier, nanoparticle dispersant, and reducing agent. As shown with examples, its role depends on the synthetic conditions. This dependence arises from the amphiphilic nature of PVP along with the molecular weight of the selected PVP. These characteristics can affect nanoparticle growth and morphology by providing solubility in diverse solvents, selective surface stabilization, and even access to kinetically controlled growth conditions. This Perspective includes discussions of the properties of PVP-capped NPs for surface enhanced Raman spectroscopy (SERS), assembly, catalysis, and more. The contribution of PVP to these properties as well as its removal is considered. Ultimately, the NPs accessed through the use of PVP in colloidal syntheses are opening new applications, and the concluding guidelines provided herein should enable new nanostructures to be accessed facilely.

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Polyvinylpyrrolidone (PVP) in nanoparticle synthesis

Synthesis and characterization of boron doped graphene nanosheets for supercapacitor applications

HPWA/MCM-41 mesoporous molecular sieves of appropriate ratios were prepared by loading HPWA on siliceous MCM-41 by the wet impregnation method. The prepared HPWA/MCM-41 materials were characterized by X-ray diffraction analysis (XRD) and BET surface area and FT-IR measurements. The morphology of mesoporous materials was studied by TEM observation. The catalytic activity of the above materials was tested for the condensation of dimedone (active methylene carbonyl compound) and various aromatic aldehyes under liquid phase conditions at 90 °C. The products were confirmed by FT-IR, 1H NMR and 13C NMR studies. HPWA supported MCM-41 catalysts catalyses efficiently the condensation of dimedone and aromatic aldehydes in ethanol and other solvents under liquid phase conditions to afford the corresponding xanthenedione derivatives. Activities of the catalysts follow the order: HPWA/MCM-41(20 wt.%) > HPWA/MCM-41(30 wt.%) > H3PW12O40·nH2O > HPWA/MCM-41(10 wt.%) > HPWA/SiO2 (20 wt.%) > HM (12) > Hβ (8) > Al-MCM-41 (50). Various advantages associated with these protocols include simple workup procedure, short reaction times, high product yields and easy recovery and reusability of the catalyst.

Heteropolyacid (H3PW12O40) supported MCM-41: An efficient solid acid catalyst for the green synthesis of xanthenedione derivatives

Mesoporous silica molecular sieves MCM-41 containing zinc and aluminum ions (Zn-Al-MCM-41) with Si/(Zn + Al) ratio equal to 340 and 380 and only aluminum ions with Si/Al ratio equal to 93 and 104, respectively, were synthesized under hydrothermal conditions using cetyltrimethylammonium (CTMA + ) surfactants as template in the absence of auxiliary organics. The mesoporous materials, viz. Zn-Al-MCM-41 and Al-MCM-41 were characterized using several techniques, e.g. powder X-ray diffraction (XRD), nitrogen adsorption measurements, Fourier transform-infra red spectroscopy (FT-IR) and thermogravimetric–differential thermal analyzer (TG–DTA). XRD studies indicated that the calcined materials had the standard MCM-41 structure. Nitrogen adsorption was used to determine specific surface area, pore volume, and pore size distribution in the Zn-Al-MCM-41(340), Zn-Al-MCM-41(380), Al-MCM-41(93) and Al-MCM-41(104) mesoporous molecular sieves. FT-IR studies showed that Zn and Al ions were incorporated into the hexagonal mesoporous structures of Zn-Al-MCM-41 and Al-MCM-41. The thermal stability of the as-synthesized materials was studied using TG–DTA. The effect of reaction temperature, WHSV and isopropanol:toluene ratios on the selectivity of p-cymene were studied. The Zn-Al-MCM-41(340) catalyst containing larger pore size and higher number of Bronsted acid sites was found to be more effective in the alkylation of alkyl aromatics, for example, in the production of p-cymene from toluene, using 2-propanol as the alkylating reagent. The selectivity of p-cymene under varying experimental condition, viz. effect of reaction temperature, WHSV and ratio of isopropanol:toluene for the various catalysts follows the sequence Zn-Al-MCM-41(340 )> Al-MCM-41(93 )> Zn-Al-MCM-41(380 )> Al-MCM-41(104). © 2002 Elsevier Science B.V. All rights reserved.

Synthesis, characterization and catalytic application of MCM-41 mesoporous molecular sieves containing Zn and Al

Mesoporous Al-MCM-41 molecular sieves in the Si/Al ratios 33, 52, 72 and 114 were synthesized under hydrothermal condition. They were characterized using powder X-ray diffraction (XRD), FT-IR, BET and thermogravimetric-differential thermal analyser (TGA-DTA). The XRD spectra showed that the materials were of hexagonal mesoporous structure. The FT-IR spectra revealed the order of hydrophobic character of the catalyst materials by comparing the broad envelope due to the O H stretching of water in the higher energy region. The acidity of the catalyst was measured by FT-IR using pyridine as the diagnostic base. The BET surface area measurements indicated the surface areas between 900 and 1000 m2/g and pore diameter around 26 A units. The catalytic activity of the materials was tested for the vapour phase esterification of acetic acid and n-butanol under autogenous condition. The effect of reaction temperature, mole ratio of the reactant, time and catalyst loading on n-butanol conversion and selectivity of n-butyl acetate was studied and the results are discussed. Al-MCM-41 (33) was found to be more active than the other catalysts owing to its high density of Bronsted acid sites. The reaction was also influenced by the hydrophobic property of the catalyst, as the conversion over Al-MCM-41 (114) is nearly equal to Al-MCM-41 (33). The requirement of Bronsted acid sites for the reaction was clearly established by running the reaction in the absence of catalyst. Occurrence of the reaction mainly within the pores was confirmed by running the reaction over the as-prepared catalyst that provides 60% less conversion than the calcined material. The reaction was also studied over H-Mordenite, H-beta, H-ZSM-5 and HY zeolites, and the results are compared.

Arumugam Pandurangan

Papers

Synthesis and characterization of boron doped graphene nanosheets for supercapacitor applications

Heteropolyacid (H3PW12O40) supported MCM-41: An efficient solid acid catalyst for the green synthesis of xanthenedione derivatives

Synthesis, characterization and catalytic application of MCM-41 mesoporous molecular sieves containing Zn and Al

A highly efficient catalyst for the esterification of acetic acid using n-butyl alcohol

Synthesis and characterization of Mn–MCM-41and Zr–Mn-MCM-41