Showing papers in "Journal of Materials Chemistry in 2013"

Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3) PbI3 for solid-state sensitised solar cell applications

Abstract: The hybrid organic–inorganic perovskite (CH3NH3)PbI3 may find application in next generation solid-state sensitised solar cells. Although this material and related perovskites were discovered many decades ago, questions remain concerning their diverse structural chemistry and unusual properties. The article presents a review of previous work and provides a detailed description of the preparation, structural characterisation and physical characteristics of (CH3NH3)PbI3. The phase changes exhibited by (CH3NH3)PbI3 have been probed using variable temperature powder and single crystal X-ray diffraction, combined with differential scanning calorimetry, thermogravimetric analysis and phase contrast transmission electron microscopy. The optical band gap for (CH3NH3)PbI3 determined by UV-Visible spectroscopy was compared to values obtained from density-of-state simulation of the electronic band structure.

Chemical exfoliation of graphitic carbon nitride for efficient heterogeneous photocatalysis

Abstract: Single atomic layer nanosheet materials show great application potential in many fields due to their enhanced intrinsic properties compared to their counterparts and newly born properties. Herein, g-C3N4 nanosheets with a single atomic layer structure are prepared by a simple chemical exfoliation method. The as-prepared nanosheets show a single atomic thickness of 0.4 nm and a lateral size of micrometers. The structure and photocatalytic properties of the as-prepared single layer g-C3N4 are then studied. Compared with the bulk g-C3N4, single layer g-C3N4 nanosheets show great superiority in photogenerated charge carrier transfer and separation. Accordingly, the photocatalytic H2 production and pollutant decomposition activities and photocurrent generation of single layer g-C3N4 nanosheets are much higher than those of the bulk g-C3N4, indicating the great application potential of single layer g-C3N4 nanosheets in photocatalysis and photosynthesis.

Graphene-based gas sensors

Abstract: Graphene materials have been widely explored for the fabrication of gas sensors because of their atom-thick two-dimensional conjugated structures, high conductivity and large specific surface areas. This feature article summarizes the recent advancements on the synthesis of graphene materials for this purpose and the techniques applied for fabricating gas sensors. The effects of the compositions, structural defects and morphologies of graphene-based sensing layers and the configurations of sensing devices on the performances of gas sensors will also be discussed.

From coconut shell to porous graphene-like nanosheets for high-power supercapacitors

Abstract: Sheet-like graphitic carbon with a porous structure can provide low-resistant pathways and short ion-diffusion channels for energy storage, and thus is expected to be an excellent material for high-power supercapacitors. Herein, porous graphene-like nanosheets (PGNSs) with a large surface area were synthesized for the first time via an easy and cost-effective SAG (simultaneous activation–graphitization) route from renewable biomass waste coconut shell. In the synthesis, the graphitic catalyst precursor (FeCl3) and activating agent (ZnCl2) were introduced simultaneously into the skeleton of the coconut shell through coordination of the metal precursor with the functional groups in the coconut shell, thus making simultaneous realization of activation and graphitization of the carbon source under heat treatment. Notably, the iron catalyst in the framework of the coconut shell can generate a carburized phase which plays a key role in the formation of a graphene-like structure during the pyrolytic process. Our results indicated that PGNSs possess good electrical conductivity due to the high graphitic degree, exceptionally high Brunauer–Emmett–Teller surface area (SBET = 1874 m2 g−1) and large pore volume (1.21 cm3 g−1). While being used as a supercapacitor electrode without the use of any conductive additives, PGNSs exhibit a high specific capacitance of 268 F g−1, much higher than that of activated carbon (210 F g−1) fabricated by only activation and graphitic carbon (117 F g−1) by only graphitization at 1 A g−1. Also, PGNSs show superior cycle durability and Coulombic efficiency over 99.5% after 5000 cycles in KOH. Remarkably, in an organic electrolyte, PGNSs also display an outstanding capacitance of 196 F g−1 at 1 A g−1. An energy density of up to 54.7 W h kg−1 could be achieved at a high power density of 10 kW kg−1. The SAG strategy developed here would provide a novel route for low-cost and large-scale production of PGNS electrode materials for high-power supercapacitors.

Carbon–sulfur composites for Li–S batteries: status and prospects

Abstract: We review the development of carbon–sulfur composites and the application for Li–S batteries. Discussions are devoted to the synthesis approach of the various carbon–sulfur composites, the structural transformation of sulfur, the carbon–sulfur interaction and the impacts on electrochemical performances. Perspectives are summarized regarding the synthesis chemistry, electrochemistry and industrial production with particular emphasis on the structural optimization of carbon–sulfur composites.

A new family of carbon materials: synthesis of MOF-derived nanoporous carbons and their promising applications

Abstract: Nanoporous carbons possessing high surface area and narrow pore size distribution are among the most important classes of porous materials that are practically utilized in industries. Recently, several metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) have been demonstrated as promising precursors to create functional nanoporous carbons. In this highlight article, we briefly review the recent progress in preparation of these novel MOF-derived nanoporous carbons. Some promising applications in energy and environment-related areas and future outlook are also discussed.

Nitrogen-containing porous carbons: synthesis and application

Abstract: Nitrogen-containing porous carbon materials are ubiquitous with a wide range of technologically important applications, including separation science, heterogeneous catalyst supports, water purification, electrochemistry, as well as the developing areas of energy generation and storage applications. To date, a variety of approaches has been developed and applied to introduce nitrogen into the carbon matrix. It is important and necessary to design and control a hierarchical porous structure and the surface chemical groups of nitrogen-containing porous carbons for their applications. In this work, we summarize and compare recently reported routes for the preparation of nitrogen-containing porous carbon materials and the effect of nitrogen groups on its applications in adsorption, electrochemistry, catalysis/catalyst supports and hydrogen storage properties.

Graphene oxide–chitosan composite hydrogels as broad-spectrum adsorbents for water purification

Abstract: Water pollution is one of the most pervasive problems afflicting people throughout the world, while adsorption is the most widely used method to remove the contaminants from water. Here, in this paper, we report an eco-friendly graphene oxide–chitosan (GO–CS) hydrogel as a new type of adsorbent for water purification. The GO–CS hydrogels were prepared via self-assembly of GO sheets and CS chains. A three-dimensional network composed of GO sheets crosslinked by CS was found in GO–CS hydrogels. The GO–CS composite hydrogels showed high adsorption capacity towards different contaminants, including cationic and anionic dyes, as well as heavy metal ions. The mechanism of the dye adsorption was investigated with a spectral method, and an electrostatic interaction was found to be the major interaction between ionic dyes and the hydrogel. The influence of the hydrogel composition on the adsorption capacity towards different adsorbates was also studied. Finally, it was demonstrated that the GO–CS hydrogel can be used as column packing, to fabricate a column for water purification by filtration.

Synthesis of a novel and stable g-C3N4–Ag3PO4 hybrid nanocomposite photocatalyst and study of the photocatalytic activity under visible light irradiation

Abstract: A facile and reproducible template free in situ precipitation method has been developed for the synthesis of Ag3PO4 nanoparticles on the surface of a g-C3N4 photocatalyst at room temperature. The g-C3N4–Ag3PO4 organic–inorganic hybrid nanocomposite photocatalysts were characterized by various techniques. TEM results show the in situ growth of finely distributed Ag3PO4 nanoparticles on the surface of the g-C3N4 sheet. The optimum photocatalytic activity of g-C3N4–Ag3PO4 at 25 wt% of g-C3N4 under visible light is almost 5 and 3.5 times higher than pure g-C3N4 and Ag3PO4 respectively. More attractively, the stability of Ag3PO4 was improved due to the in situ deposition of Ag3PO4 nanoparticles on the surface of the g-C3N4 sheet. The improved performance of the g-C3N4–Ag3PO4 hybrid nanocomposite photocatalysts under visible light irradiation was induced by a synergistic effect, including high charge separation efficiency of the photoinduced electron–hole pair, the smaller particle size, relatively high surface area and the energy band structure. Interestingly, the heterostructured g-C3N4–Ag3PO4 nanocomposite significantly reduces the use of the noble metal silver, thereby effectively reducing the cost of the Ag3PO4 based photocatalyst.

Progress in bio-based plastics and plasticizing modifications

Abstract: Over the coming few decades bioplastic materials are expected to complement and gradually replace some of the fossil oil based materials. Multidisciplinary research efforts have generated a significant level of technical and commercial success towards these bio-based materials. However, extensive application of these bio-based plastics is still challenged by one or more of their possible inherent limitations, such as poor processability, brittleness, hydrophilicity, poor moisture and gas barrier, inferior compatibility, poor electrical, thermal and physical properties. The incorporation of additives such as plasticizers into the biopolymers is a common practice to improve these inherent limitations. Generally, plasticizers are added to both synthetic and bio-based polymeric materials to impart flexibility, improve toughness, and lower the glass transition temperature. This review introduces the most common bio-based plastics and provides an overview of recent advances in the selection and use of plasticizers, and their effect on the performance of these materials. In addition to plasticizers, we also present a perspective of other emerging techniques of improving the overall performance of bio-based plastics. Although a wide variety of bio-based plastics are under development, this review focuses on plasticizers utilized for the most extensively studied bioplastics including poly(lactic acid), polyhydroxyalkanoates, thermoplastic starch, proteinaceous plastics and cellulose acetates. The ongoing challenge and future potentials of plasticizers for bio-based plastics are also discussed.

Challenges and opportunities for mixed-matrix membranes for gas separation

Abstract: Mixed-Matrix Membranes (MMMs) combining the benefits of both polymeric and inorganic materials have become a focus for the next-generation gas separation membranes. In this review, major challenges surrounding MMMs and the strategies to tackle these challenges are given in detail. The selection criteria of polymeric and inorganic materials are discussed in terms of their physical and chemical compatibility as well as large scale fabrication issues. Major models for separation performance prediction of MMMs are reviewed in terms of their interrelations and limitations. A discussion is provided regarding the future direction of MMMs.

Stability and degradation mechanisms of metal–organic frameworks containing the Zr6O4(OH)4 secondary building unit

Abstract: Metal–organic frameworks (MOFs) with the Zr6O4(OH)4 secondary building unit (SBU) have been of particular interest for potential commercial and industrial uses because they can be easily tailored and are reported to be chemically and thermally stable. However, we show that there are significant changes in chemical and thermal stability of Zr6O4(OH)4 MOFs with the incorporation of different organic linkers. As the number of aromatic rings is increased from one to two in 1,4-benzene dicarboxylate (UiO-66, ZrMOF–BDC) and 4,4′-biphenyl dicarboxylate (UiO-67, ZrMOF–BPDC), the Zr6O4(OH)4 SBU becomes more susceptible to chemical degradation by water and hydrochloric acid. Furthermore, as the linker is replaced with 2,2′-bipyridine-5,5′-dicarboxylate (ZrMOF–BIPY) the chemical stability decreases further as the MOF is susceptible to chemical breakdown by protic chemicals such as methanol and isopropanol. The results reported here bring into question the superior structural stability of the UiO-67 analogs as reported by others. Furthermore, the degradation mechanisms proposed here may be applied to other classes of MOFs containing aromatic dicarboxylate organic linkers, in order to predict their structural stability upon exposure to solvents.

Robust superhydrophobic polyurethane sponge as a highly reusable oil-absorption material

Abstract: The fabrication of robust superhydrophobic 3D porous materials is of great importance for both academic research and industrial applications. The main challenge is the poor adhesion between porous substrates and superhydrophobic coatings. In this study, a robust superhydrophobic polysiloxane layer was coated onto the surface of 3D porous polyurethane sponges through a one-step solution immersion method. The durability of the resulting sponges was investigated by repeated mechanical compressions, ultrasonication in polar solvents, and strong acid/alkali attacks. Results revealed that the superhydrophobic sponges showed excellent elasticity, high mechanical durability and good chemical stability. By combining the special wettability and high porosity, the sponges exhibited high oil-absorption capacity and high selectivity when they were employed as absorptive materials for cleaning oils on the water surface. More importantly, the superhydrophobic sponges could be reused for oil–water separation for more than 300 cycles without losing their superhydrophobicity, exhibiting the highest reusability and durability among the reported counterparts. Therefore, the present study offers a simple and low-cost strategy for large-scale fabrication of robust superhydrophobic 3D porous materials that might be applied to the cleanup of oil spills on the water surface.

Reduced TiO2 nanotube arrays for photoelectrochemical water splitting

Abstract: We report a facile one-step chemical method to synthesize partially reduced TiO2 nanotube arrays (NTAs). The NaBH4 treatment introduces oxygen vacancies on the surface and interior of TiO2. Oxygen vacancy extends the photocatalytic activity of TiO2 NTAs from the UV to visible light region, and enhances the electrical conductivity as well as charge transportation. Surface oxygen vacancies serve as charge carrier traps as well as adsorption sites where the charge transfer to adsorbed species inhibits the surface charge recombination, whereas bulk oxygen vacancies tend to act as charge carrier traps where e–h recombination occurs. The optimally reduced TiO2 NTAs yield a photocurrent density of 0.73 mA cm−2 at 1.23 VRHE and a highest photoconversion efficiency of 1.31% at a rather low bias of 0.40 VRHE under a standard AM 1.5G solar illumination. Not only does the incident photon to current conversion efficiency (IPCE) spectrum increase in the UV region, but photoactivity in visible light also emerged. Surface oxygen vacancies, serving as electron donors, cause a noticeable negative flatband shift and increase the donor density of TiO2 NTAs 2-fold. Electron paramagnetic resonance (EPR) spectra confirm the presence of oxygen vacancies on the surface and interior of TiO2. Benefitting from the oxygen vacancy, a narrowed band gap of 2.46 eV and suitable localized states for hydrogen production are observed.

One-pot synthesis of a mesoporous NiCo2O4 nanoplatelet and graphene hybrid and its oxygen reduction and evolution activities as an efficient bi-functional electrocatalyst

Abstract: Mesoporous NiCo2O4 nanoplatelets and graphene sheets (NiCo2O4–G) are combined as a hybrid material via a one-pot synthesis process to demonstrate excellent bi-functional catalytic activity towards both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Physical characterizations have confirmed the formation of NiCo2O4 nanoplatelets created by selective adsorption of PVP onto specific crystal orientations, which provides spatial confinement for an anisotropic growth into 2-dimensional nanostructures. In addition, the decomposition of surface adsorbed PVP during the calcination process creates uniformly distributed meso-sized pores in the NiCo2O4 nanoplatelets. The beneficial hybrid and PVP effects are investigated via half-cell testing with NiCo2O4–G in comparison to graphene-free NiCo2O4 and PVP-free NiCo2O4–G, respectively, where much lower activation energy and higher current densities are observed with the mesoporous NiCo2O4–G hybrid for both ORR and OER. Furthermore, the positive impact of Ni incorporation was exclusively demonstrated, whereby NiCo2O4–G outperformed Co3O4–G in terms of onset potential and current densities for both ORR and OER. This is attributed to the increased electrical conductivity and the creation of new active sites with much lower activation energy due to the incorporation of Ni cations into the octahedral sites of the spinel crystal structure. This cost effective and highly efficient bi-functional catalyst is highly suitable for rechargeable metal–air battery technologies.

Novel C3N4–CdS composite photocatalysts with organic–inorganic heterojunctions: in situ synthesis, exceptional activity, high stability and photocatalytic mechanism

Abstract: Novel organic–inorganic composites composed of two visible light responsive semiconductors of graphitic carbon nitride (C3N4) and CdS were successfully synthesized via an “in situ” precipitation–deposition method. The C3N4–CdS heterostructures were fabricated by depositing CdS nanoparticles onto the surface of C3N4. The morphology and optical property of compsoites can be tuned by adjusting the mass ratio of C3N4–CdS, which determines the enhanced level of photocatalytic activity. The optimum activity of 0.7C3N4–0.3CdS photocatalyst is almost 20.5 and 3.1 times higher than those of individual C3N4 and CdS for the degradation of methyl orange, and 41.6 and 2.7 fold higher for the degradation of 4-aminobenzoic acid, respectively. Moreover, its activity is also much higher than those of C3N4–TiO2 and CdS–TiO2 composites, as well as N-modified TiO2. Of special significance is that the present C3N4–CdS composites exhibit high stabilities under illumination, in contrast with CdS. The enhancement in both performance and stability should be assigned to the effective separation and transfer of photogenerated charges originating from the well-matched overlapping band-structures and closely contacted interfaces. Our work highlights that coupling semiconductors with well-matched band energies provides a flexible route to improve the activity and stability of photocatalysts, and gives ideas for the design and synthesis of other highly active and stable materials.

Improved hydrophilicity, permeability, antifouling and mechanical performance of PVDF composite ultrafiltration membranes tailored by oxidized low-dimensional carbon nanomaterials

Abstract: Polyvinylidene fluoride (PVDF)–oxidized carbon nanotubes (OMWCNTs), PVDF–graphene oxide (GO) and PVDF–OMWCNTs–GO composite ultrafiltration membranes were prepared by solution-blending the ternary mixture of PVDF–oxidized low-dimensional carbon nanomaterials–dimethylacetamide in combination with the phase inversion method. The microscope images of the PVDF matrix microstructure showed that the composite membranes exhibited a bigger mean pore size and higher roughness parameters than pristine membranes. The contact angle of the membranes decreased from 78.5° (PVDF) to 66.8° (PVDF–OMWCNTs), 66.4° (PVDF–GO) and 48.5° (PVDF–OMWCNTs–GO). For the PVDF–OMWCNTs, PVDF–GO and PVDF–OMWCNTs–GO composite membranes, there was a 99.33%, 173.03% and 240.03% increase in permeation flux and a 21.71%, 17.23% and 14.29% increase in bovine serum albumin (BSA) rejection, respectively, compared with those of the pristine membranes. The newly developed composite ultrafiltration membranes demonstrate an impressive prospect for the anti-irreversible fouling performance in multi-cycle operations from BSA treatment. Additionally, the addition of OMWCNTs and GO increased the tensile strength of composite membranes from 1.866 MPa to 2.106 MPa and 2.686 MPa, respectively. Conspicuously, the PVDF composite ultrafiltration membranes endowed with oxidized low-dimensional carbon nanomaterials demonstrated fascinating hydrophilicity, permeability, antifouling and mechanical performance and promising application prospects owing to the rich oxygen-containing functional groups, high specific surface and synergistic effect of inorganic additive.

The effect of water adsorption on the structure of the carboxylate containing metal–organic frameworks Cu-BTC, Mg-MOF-74, and UiO-66

Abstract: Metal–organic frameworks (MOFs) with metal–carboxylate bonds, including Cu-BTC (HKUST-1), Mg-MOF-74 (Mg/DOBDC), and UiO-66, have been shown to have varying degrees of water stability. The three MOFs in this study are three of the most highly studied MOFs in the literature. We investigate here how each MOF degrades at several temperature and humidity conditions over the course of 28 days. At conditions of 90% relative humidity (RH) and 25 °C, water uptake for Cu-BTC is shown to be higher than at 90% RH and 40 °C, causing the degradation of the inner structure of Cu-BTC to occur more readily at the lower temperature. However the external surfaces of Cu-BTC degrade more readily, as shown through SEM images, at conditions of 90% RH and 40 °C. Mg-MOF-74 has a nearly complete loss of surface area after just one day of exposure to each of the conditions studied, however the PXRD patterns show only a change in the [100] peak. We offer here a novel mechanism for the degradation of Mg-MOF-74, involving a 6-coordinate Mg intermediate, which leaves the 1-dimensional channels of Mg-MOF-74 intact. Furthermore, we conclude that UiO-66 is stable to each of the aging conditions for the full 28 days of this study.

Ionic liquid polymer electrolytes

Abstract: Ionic liquids (ILs) are room-temperature molten salts that possess unique properties, such as negligible vapour pressure, good thermal stability and non-flammability, together with high ionic conductivity and a wide window of electrochemical stability. Combining ILs with polymer electrolytes offers the prospect of new applications e.g. in batteries and fuel cells, where they surpass the performance of conventional media such as organic solvents (in batteries) or water (in polymer electrolyte membrane fuel cells), giving advantages in terms of improved safety and a higher operating temperature range. However, the most important challenge is how to immobilize ILs in polymer matrices while retaining their sought-after properties. Our goal in this review is to survey the recent developments and issues within IL research in polymer electrolytes.

Graphene for supercapacitor applications

Abstract: Graphene has attracted extensive interest in the field of supercapacitor research due to its 2D structure which grants it exceptional properties such as superior electrical conductivity and mechanical properties as well as an extensive surface area better than that of carbon nanotubes (CNTs). Furthermore, unlike other carbon materials, graphene is particularly optimal for supercapacitor applications as its surface area does not vary with pore size distribution and grants electrolyte access to both its surfaces. This article aims to review the advances in recent research and development of the use of graphene for supercapacitor use. The focus would mainly be on the areas of graphene synthesis, graphene modification, graphene–nanoporous carbon composites, graphene–polymer composites and graphene–metal oxides and their potential use in both asymmetric and symmetric supercapacitors. Lastly, the article aims to identify optimal testing methods for electrode performance and choice of electrolytes. It will then stress the increasing need to standardise electrode testing to ensure that test results are as relevant to real life applications as possible.

Mechanically strong graphene oxide/sodium alginate/polyacrylamide nanocomposite hydrogel with improved dye adsorption capacity

Abstract: In this paper, a novel graphene oxide (GO)/sodium alginate (SA)/polyacrylamide (PAM) ternary nanocomposite hydrogel with excellent mechanical performance has been fabricated through free-radical polymerization of acrylamide (AAm) and SA in the presence of GO in an aqueous system followed with ionically crosslinking of calcium ions As-prepared GO/SA/PAM (weight ratio SA : AAm = 1 : 2) ternary nanocomposite hydrogel with 5 wt% of GO displays a compressive stress as high as 1543 MPa at the compressive deformation of 70% The tensile strength and modulus of the hydrogel achieved ∼2017 and ∼308 kPa, respectively In the meantime, the ternary nanocomposite hydrogels can recover a large proportion of elongation at breakage and exhibits good elasticity Additionally, the GO/SA/PAM ternary nanocomposite hydrogel exhibited good adsorption properties for water-soluble dyes After introducing GO, the dye adsorption capacities of the hydrogel were significantly improved

CTAB-assisted synthesis of single-layer MoS2–graphene composites as anode materials of Li-ion batteries

Abstract: A facile and scalable process was developed for the synthesis of single-layer MoS2–graphene nanosheet (SL-MoS2–GNS) composites based on the concurrent reduction of (NH4)2MoS4 and graphene oxide sheets by hydrazine in the presence of cetyltrimethylammonium bromide (CTAB), followed by annealing in a N2 atmosphere. The morphology and microstructure of the composites were examined by X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. The formation process for the SL-MoS2–GNS composites was also investigated. The SL-MoS2–GNS composites delivered a large reversible capacity and good cycle stability as a Li-ion battery anode. In particular, the composites easily surpassed MoS2 in terms of rate performance and cycle stability at high current densities. Electrochemical impedance spectroscopy revealed that the GNS in the composite not only reduced the contact resistance in the electrode but also significantly facilitated the electron transfer in lithiation and delithiation reactions. The good electrochemical performance of the composites for reversible Li+ storage could be attributed to the synergy between the functions of SL-MoS2 and GNS.

Facile synthesis of highly active g-C3N4 for efficient hydrogen production under visible light

Abstract: A highly active graphitic C3N4 photocatalyst prepared from a mixture of urea and melamine with advanced structural, optical and electronic properties and enhanced photocatalytic activity for the production of hydrogen gas is explored. The prepared photocatalyst is able to generate a high rate of hydrogen gas production (135 μmol h−1) by loading with 1 wt% Pt as a co-catalyst. The good separation of C3N4 sheets, lower recombination rate of excitons and the high amount of generated photocurrent have significantly contributed towards the photocatalytic activity of graphitic carbon nitride prepared from a mixture of urea and melamine.

B, N- and P, N-doped graphene as highly active catalysts for oxygen reduction reactions in acidic media

Abstract: Graphene has been highlighted recently as a promising material for energy conversion due to its unique properties deriving from a two-dimensional layered structure of sp2-hybridized carbon. Herein, N-doped graphene (NGr) is developed for its application in oxygen reduction reactions (ORRs) in acidic media, and additional doping of B or P into the NGr is attempted to enhance the ORR performance. The NGr exhibits an onset potential of 0.84 V and a mass activity of 0.45 mA mg−1 at 0.75 V. However, the B, N- (BNGr) and P, N-doped graphene (PNGr) show onset potentials of 0.86 and 0.87 V, and mass activities of 0.53 and 0.80 mA mg−1, respectively, which are correspondingly 1.2 and 1.8 times higher than those of the NGr. Moreover, an additional doping of B or P effectively reduces the production of H2O2 in the ORRs, and shows much higher stability than that of Pt/C in acidic media. It is proposed that the improvement in the ORR activity results from the enhanced asymmetry of the spin density or electron transfer on the basal plane of the graphene, and the decrease in the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the graphene through additional doping of B or P.

LiMnPO4 - A next generation cathode material for lithium-ion batteries

Abstract: Development of an eco-friendly, low cost and high energy density (∼700 W h kg−1) LiMnPO4 cathode material became attractive due to its high operating voltage ∼4.1 V vs. Li falling within the electrochemical stability window of conventional electrolyte solutions and offers more safety features due to the presence of a strong P–O covalent bond. The vacancy formation energy for LiMnPO4 was 0.19 eV higher than that for LiFePO4, resulting in a 10−3 times-diluted complex concentration, which represents the main difference between the kinetics in the initial stage of charging of two olivine materials. This review highlights the overview of current research activities on LiMnPO4 cathodes in both native and substituted forms along with carbon coating synthesized by various synthetic techniques. Further, carbon coated LiMnPO4 was also prepared by a solid-state approach and the obtained results are compared with previous literature values. The challenges and the need for further research to realize the full performance of LiMnPO4 cathodes are described in detail.

Na2Ti3O7: an intercalation based anode for sodium-ion battery applications

Abstract: We report here the electrochemical properties of Na2Ti3O7, a potential non-carbon based, low-voltage anode material for room temperature sodium ion battery applications. A solid-state route was used to prepare Na2Ti3O7. Further, XRD, SEM, TEM, HRTEM, SAED, XPS and EDX techniques were used to characterize the material. The Na/Na2Ti3O7 cell displayed a charge capacity of 177 mA h g−1 at 0.1 C rate. High rate and long term cyclic performance at different rates showed relatively stable storage capacities. Surprisingly, if the lower cut-off voltage is altered, the appearance of a new charge plateau is seen, with no apparent change in the discharge behaviour. The kinetics of sodium insertion and extraction are discussed utilizing CV and EIS techniques. We also report the sodium chemical diffusion coefficient of the Na2Ti3O7/CB electrode estimated using GITT.

Facile extraction of thermally stable cellulose nanocrystals with a high yield of 93% through hydrochloric acid hydrolysis under hydrothermal conditions

Abstract: A facile approach for extracting cellulose nanocrystals (CNCs) was presented through hydrochloric acid hydrolysis of cellulose raw materials under hydrothermal conditions. The influences of preparation parameters, such as reaction time, reaction temperature, and acid-to-cellulose raw material ratio, and different neutralization methods on the yield, microstructure and properties were studied. A high yield of up to 93.7%, crystallinity of 88.6%, and a maximum degradation temperature (Tmax) of 363.9 °C can be achieved by combining hydrochloric acid hydrolysis under hydrothermal conditions and neutralization with ammonia, compared with only 30.2%, 84.3% and 253.2 °C for sulfuric acid hydrolysis, respectively. More importantly, good stability of aqueous CNC suspensions can also be obtained due to the existence of ammonium groups, which can easily be removed through simple heat treatment before using the CNCs.

Importance of small micropores in CO2 capture by phenolic resin-based activated carbon spheres

Abstract: Phenolic resin-based carbon spheres obtained by a slightly modified Stober method are shown to be superior CO2 adsorbents. A direct KOH activation of polymeric spheres gave carbons with small micropores (<0.8 nm) and large specific surface area (2400 m2 g−1), which are able to adsorb an unprecedented amount of CO2 (up to 8.9 mmol g−1) at 0 °C and ambient pressure.

A novel magnetic recyclable photocatalyst based on a core–shell metal–organic framework Fe3O4@MIL-100(Fe) for the decolorization of methylene blue dye

Abstract: We describe a novel type of magnetic recyclable Fe3O4@MIL-100(Fe) photocatalyst on the basis of a porous metal–organic framework (MOF) and its photocatalytic activities in the photodegradation of methylene blue (MB) dye. It was found that Fe3O4@MIL-100(Fe) exhibited photocatalytic activity for MB dye degradation under both UV-vis and visible light irradiation, and the MB decolorization over the Fe3O4@MIL-100(Fe) photocatalyst followed first-order kinetics. Moreover, it can be easily separated and recycled without significant loss of photocatalytic activity after being used many times. Therefore, compared to the conventional photocatalysts of TiO2 and C3N4 used in the photocatalytic degradation of dye, this magnetic core–shell photocatalyst is green, cheap and more suitable for large scale industrial applications.

Activation of graphitic carbon nitride (g-C3N4) by alkaline hydrothermal treatment for photocatalytic NO oxidation in gas phase

Abstract: Photocatalytic activity of graphitic carbon nitride (g-C3N4) was significantly improved by an alkaline hydrothermal treatment. The specific surface area of g-C3N4 obtained by heating melamine at 550 °C was only 7.7 m2 g−1, which was too small for it to be utilized as a catalyst for air purification. By the hydrothermal treatment with NaOH solution at 90–150 °C, the surface area was increased up to 65 m2 g−1, and the oxidation rate of nitrogen oxide (NO) under visible light (380 < λ < 480 nm) was increased by 8.6 times. XRD, ESR, elemental analysis and electron microscopy showed that unstable domains of not-well-ordered carbon nitride were removed by hydrolysis to form a mesoporous structure with a higher surface area. Deactivation of g-C3N4 was not observed during the experimental period, although a small part of carbon nitride was decomposed by self-oxidation.