Showing papers in "RSC Advances in 2014"

Size-controlled silver nanoparticles synthesized over the range 5–100 nm using the same protocol and their antibacterial efficacy

Abstract: A systematic and detailed study for size-specific antibacterial efficacy of silver nanoparticles (AgNPs) synthesized using a co-reduction approach is presented here. Nucleation and growth kinetics during the synthesis process was precisely controlled and AgNPs of average size 5, 7, 10, 15, 20, 30, 50, 63, 85, and 100 nm were synthesized with good yield and monodispersity. We found the bacteriostatic/bactericidal effect of AgNPs to be size and dose-dependent as determined by the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of silver nanoparticles against four bacterial strains. Out of the tested strains, Escherichia coli MTCC 443 and Staphylococcus aureus NCIM 5201 were found to be the most and least sensitive strains regardless of AgNP size. For AgNPs with less than 10 nm size, the antibacterial efficacy was significantly enhanced as revealed through delayed bacterial growth kinetics, corresponding MIC/MBC values and disk diffusion tests. AgNPs of the smallest size, i.e., 5 nm demonstrated the best results and mediated the fastest bactericidal activity against all the tested strains compared to AgNPs having 7 nm and 10 nm sizes at similar bacterial concentrations. TEM analysis of AgNP treated bacterial cells showed the presence of AgNPs on the cell membrane, and AgNPs internalized within the cells.

Principles and mechanisms of photocatalytic dye degradation on TiO 2 based photocatalysts: a comparative overview

Abstract: The total annual production of synthetic dye is more than 7 × 105 tons. Annually, through only textile waste effluents, around one thousand tons of non-biodegradable textile dyes are discharged into natural streams and water bodies. Therefore, with growing environmental concerns and environmental awareness there is a need for the removal of dyes from local and industrial water effluents with a cost effective technology. In general, these dyes have been found to be resistant to biological as well as physical treatment technologies. In this regard, heterogeneous advanced oxidation processes (AOPs), involving photo-catalyzed degradation of dyes using semiconductor nanoparticles is considered as an efficient cure for dye pollution. In the last two decades TiO2 has received considerable interest because of its high potential as a photocatalyst to degrade a wide range of organic material including dyes. This review starts with (i) a brief overview on dye pollution, dye classification and dye decolourization/degradation strategies; (ii) focuses on the mechanisms involved in comparatively well understood TiO2 photocatalysts and (iii) discusses recent advancements to enhance TiO2 photocatalytic efficiency by (a) doping with metals, non-metals, transition metals, noble metals and lanthanide ions, (b) structural modifications of TiO2 and (c) immobilization of TiO2 by using various supports to make it a flexible and cost-effective commercial dye treatment technology.

Glutaraldehyde in bio-catalysts design: a useful crosslinker and a versatile tool in enzyme immobilization

Abstract: Glutaraldehyde is one of the most widely used reagents in the design of biocatalysts. It is a powerful crosslinker, able to react with itself, with the advantages that this may bring forth. In this review, we intend to give a general vision of its potential and the precautions that must be taken when using this effective reagent. First, the chemistry of the glutaraldehyde/amino reaction will be commented upon. This reaction is still not fully clarified, but it seems to be based on the formation of 6-membered heterocycles formed by 5 C and one O. Then, we will discuss the production of intra- and inter-molecular enzyme crosslinks (increasing enzyme rigidity or preventing subunit dissociation in multimeric enzymes). Special emphasis will be placed on the preparation of cross-linked enzyme aggregates (CLEAs), mainly in enzymes that have low density of surface reactive groups and, therefore, may be problematic to obtain a final solid catalyst. Next, we will comment on the uses of glutaraldehyde in enzymes previously immobilized on supports. First, the treatment of enzymes immobilized on supports that cannot react with glutaraldehyde (only inter and intramolecular cross-linkings will be possible) to prevent enzyme leakage and obtain some enzyme stabilization via cross-linking. Second, the cross-linking of enzymes adsorbed on aminated supports, where together with other reactions enzyme/support crosslinking is also possible; the enzyme is incorporated into the support. Finally, we will present the use of aminated supports preactivated with glutaraldehyde. Optimal glutaraldehyde modifications will be discussed in each specific case (one or two glutaraldehyde molecules for amino group in the support and/or the protein). Using preactivated supports, the heterofunctional nature of the supports will be highlighted, with the drawbacks and advantages that the heterofunctionality may have. Particular attention will be paid to the control of the first event that causes the immobilization depending on the experimental conditions to alter the enzyme orientation regarding the support surface. Thus, glutaraldehyde, an apparently old fashioned reactive, remains the most widely used and with broadest application possibilities among the compounds used for the design of biocatalyst.

Role of graphene/metal oxide composites as photocatalysts, adsorbents and disinfectants in water treatment: a review

Abstract: With a rapidly growing population, development of new materials, techniques and devices which can provide safe potable water continues to be one of the major research emphases of the scientific community. While the development of new metal oxide catalysts is progressing, albeit at a slower pace, the concurrent and rapid development of high surface area catalyst supports such as graphene and its functionalised derivatives has provided unprecedented promise in the development of multifunctional catalysts. Recent works have shown that metal oxide/graphene composites can perform multiple roles including (but not limited to): photocatalysts, adsorbents and antimicrobial agents making them an effective agent against all major water pollutants including organic molecules, heavy metal ions and water borne pathogens, respectively. This article presents a comprehensive review on the application of metal oxide/graphene composites in water treatment and their role as photocatalyst, adsorbent and disinfectant in water remediation. Through this review, we discuss the current state of the art in metal oxide/graphene composites for water purification and also provide a comprehensive analysis of the nature of interaction of these composites with various types of pollutants which dictates their photocatalytic, adsorptive and antimicrobial activities. The review concludes with a summary on the role of graphene based materials in removal of pollutants from water and some proposed strategies for designing of highly efficient multifunctional metal oxide/graphene composites for water remediation. A brief perspective on the challenges and new directions in the area is also provided for researchers interested in designing advanced water treatment strategies using graphene based advanced materials.

Fundamental aspects of property tuning in push-pull molecules†

Abstract: Property tuning in selected examples of D–π–A molecules has been discussed and summarized in this review article. The tuning and structure–property relationships have been demonstrated on the particular A, π and D parts of the push–pull molecule. Special emphasis has been put on the tuning of the FMO levels and optical properties. Further prospective applications of the given chromophore have also been considered.

Thermal-runaway experiments on consumer Li-ion batteries with metal-oxide and olivin-type cathodes

Abstract: Li-ion batteries play an ever-increasing role in our daily life. Therefore, it is important to understand the potential risks involved with these devices. In this work we demonstrate the thermal runaway characteristics of three types of commercially available Li-ion batteries with the format 18650. The Li-ion batteries were deliberately driven into thermal runaway by overheating under controlled conditions. Cell temperatures up to 850 °C and a gas release of up to 0.27 mol were measured. The main gas components were quantified with gas-chromatography. The safety of Li-ion batteries is determined by their composition, size, energy content, design and quality. This work investigated the influence of different cathode-material chemistry on the safety of commercial graphite-based 18650 cells. The active cathode materials of the three tested cell types were (a) LiFePO4, (b) Li(Ni0.45Mn0.45Co0.10)O2 and (c) a blend of LiCoO2 and Li(Ni0.50Mn0.25Co0.25)O2.

Recent development of direct asymmetric functionalization of inert C–H bonds

Abstract: The area of direct asymmetric functionalization of inert C–H bonds has attracted considerable attention in recent years. To realize this type of challenging but promising transformations, a lot of strategies have emerged including asymmetric C–H bond insertion by metal carbenoids or analogs, cross dehydrogenative coupling, [1,5]-hydride transfer, C–H bond functionalization involving a transient metal–carbon species and other miscellaneous methods. This review is intended to summarize and discuss the most recent developments (contributions mainly after 2009) within this area.

A new C–C bond formation model based on the quantum chemical topology of electron density

Abstract: ELF topological analyses of bonding changes in non-polar, polar and ionic organic reactions involving the participation of CC(X) double bonds make it possible to establish a unified model for C–C bond formation. This model is characterised by a C-to-C coupling of two pseudoradical centers generated at the most significant atoms of the reacting molecules. The global electron density transfer process that takes place along polar and ionic reactions favours the creation of these pseudoradical centers at the most nucleophilic/electrophilic centers of the reacting molecules, decreasing activation energies. The proposed reactivity model based on the topological analysis of the changes in electron density throughout a reaction makes it possible to reject the frontier molecular orbital reactivity model based on the analysis of molecular orbitals.

Photocatalytic degradation of methylene blue in ZIF-8

Abstract: Metal–organic frameworks (MOFs), a new class of porous crystalline materials, have attracted great interest as a promising candidate for sustainable energy and environmental remediation. In this study, ZIF-8, a versatile MOF based on imidazolate ligands, was selected as a photocatalyst to decompose methylene blue (MB) under UV light irradiation. The influence factors, kinetics, and mechanism of photocatalytic MB degradation and stability of ZIF-8, were also studied. The results revealed that the ZIF-8 photocatalyst exhibited efficiently photocatalytic activity for MB degradation under UV irradiation, which was confirmed through the detection of hydroxyl radicals (˙OH) by a fluorescence method. The MB degradation over the ZIF-8 photocatalyst followed a pseudo-first-order kinetics model. ZIF-8 worked effectively over a wide pH range from 4.0 to 12.0, and showed both high adsorption capacity and degradation efficiency for MB in a strong alkaline environment. The enhanced efficiency in a strong alkaline environment resulted from the higher charged ZIF-8 (pH > pHpzc) and the elevated yield of ˙OH facilitated by increased OH− concentration. The possible pathway of photocatalytic degradation of MB in ZIF-8 was proposed. The results indicated that ZIF-8 can be used as a highly efficient photocatalyst to decompose organic pollutants.

Synthesis of ZnO/Au and ZnO/Ag nanoparticles and their photocatalytic application using UV and visible light

Abstract: We report a simple and convenient method for the synthesis of a ZnO/Au and ZnO/Ag heterostructure nanoflower by applying a surfactant mediated route. Initially, pure ZnO nanoflowers have been synthesized followed by Au and Ag deposition on ZnO surface using hydrazine hydrate as reducing agent. Structure, crystallinity, and morphology have been assessed by X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy techniques. The influences of the deposited metal nanoparticles (Au and Ag) on the surface of ZnO have been emphasized by applying the as-synthesized nanostructure in dye degradation under illumination of UV and visible light. The basic motivation behind this work is to find a superior photocatalyst, which can work under UV as well as visible light i.e., to cover the whole range of the solar spectrum. Photocatalytic performances of bare ZnO, ZnO/Au, and ZnO/Ag have been studied thoroughly. Photodegradation results under UV and visible light demonstrated that the incorporation of noble metal nanoparticles significantly (or drastically) increases the catalytic efficiency by promoting the photogenerated charge carrier separation. The main advantage of the proposed ZnO/Au and ZnO/Ag semiconductor is that it delays the recombination process of the electron–hole pairs generated by the photon absorption, which in lieu increases the photocatalytic efficiency. It is a challenging issue to fabricate stable photocatalysts which can work under visible light as it covers 43% of sunlight. To investigate the role of photogenerated electrons and holes in dye degradation, scavenging experiments using different scavengers have also been performed.

Recent advances in the synthesis of quinolines: a review

Abstract: Quinolines have become important compounds because of their variety of applications in medicinal, synthetic organic chemistry as well as in the field of industrial chemistry. In recent years there are greater societal expectations that chemists should produce greener and more sustainable chemical processes. This review article gives information about the green and clean syntheses using alternative reaction methods for the synthesis of quinoline derivatives. The article includes synthesis by microwave, using clay or some other catalyst which could be recycled and reused, one-pot reaction, solvent-free reaction conditions, using ionic liquids, ultrasound promoted synthesis and photocatalytic synthesis (UV radiation).

Bioimaging based on fluorescent carbon dots

Abstract: Nanosized fluorescent carbon particles, namely, carbon dots (CDs), are a kind of fluorescent material that has drawn increasing attention in recent years. CDs have size-, surface chemistry-, and wavelength-dependent luminescence emission, which is different from traditional semiconductor-based quantum dots. Moreover, with excellent chemical stability, good biocompatibility, low toxicity, up-conversion emission, resistance to photo bleaching, as well as easy chemical modifications, CDs are promising for substantial applications in numerous areas: bioimaging, sensors, and energy-related devices. Herein, three kinds of fluorescent dots are reviewed: graphene quantum dots (GQDs), carbon nanodots (CNDs) and polymer dots (PDs). After the first reported CDs prepared from electrophoretic analysis and purification of fluorescent carbon nanotube fragments, there were hundreds of publications focusing on fluorescent CDs. Bioimaging was one of the most common applications of the CDs; therefore, in this review, most of the chosen reference papers were related to bioimaging based on CDs.

Polymeric micelles as drug delivery vehicles

Abstract: Though much progress has been made in drug delivery systems, the design of a suitable carrier for the delivery of hydrophobic drugs is still a major challenge for researchers. The use of micellar solutions of low molecular weight surfactants has been one of the popular methods for the solubilization of hydrophobic drugs; however, such surfactants suffer from high critical micelle concentration and concomitant low stabilities. In contrast to surfactants of low molecular masses, polymeric micelles are associated with general advantages like higher stability, tailorability, greater cargo capacity, non-toxicity and controlled drug release. Therefore, the current review article is focused on the engineering of the core of polymeric micelles for maximum therapeutic effect. For enhanced drug encapsulation capacity and getting useful insights into the controlled release mechanism we have reviewed the effects of temperature and pH on responsive polymeric micelles. The article also presents important research outcomes about mixed polymeric micelles as better drug carriers in comparison to single polymeric micelles.

Carbon-based quantum dots for fluorescence imaging of cells and tissues

Abstract: Carbon dots (or carbon quantum dots in some literature reports), generally small carbon nanoparticles with various surface passivation effects, have attracted widespread attention in recent years, with a rapidly increasing number of research publications. The reported studies covered many aspects of carbon dots, from the development of many new synthetic methodologies to an improved mechanistic elucidation and to the exploration of application opportunities, especially for those in the fluorescence imaging of cells and tissues. There have also been significant advances in the establishment of a shared mechanistic framework for carbon dots and other carbon-based quantum dots, graphene quantum dots in particular. In this article, representative recent studies for more efficient syntheses of better-performing carbon dots are highlighted along with results from explorations of their various bioimaging applications in vitro and in vivo. Similar fluorescence properties and potential imaging uses of some graphene quantum dots are also discussed, toward a more consistent and uniform understanding of phenomenologically different carbon-based quantum dots.

Metal oxide/hydroxide-based materials for supercapacitors

Abstract: Supercapacitors are promising energy storage and conversion devices with high power densities However, their low energy densities limit their practical application The electrode is a key component that determines the performance of supercapacitors As electrode materials, transition metal oxides/hydroxides usually exhibit high capacitance, leading to high energy densities This review discusses the advantages and disadvantages of different metal oxides/hydroxides, in order to synthesize high-performance electrode materials Two main strategies to enhance the supercapacitive performance are proposed: developing composites and nanostructured materials

Proton-conducting polymer electrolytes and their applications in solid supercapacitors: a review

Abstract: Research on solid supercapacitors over the last few years has aimed to provide high performing and safely operating energy storage solutions for the fast growing application areas of consumer and micro-electronics, providing printable, flexible and wearable devices. Most of the reported research has leveraged proton conducting polymer electrolytes for electrochemical double layer capacitors and pseudo-capacitors. In this paper, we provide an overview of the state-of-the-art solid supercapacitors enabled by proton-conducting polymer electrolytes. After a short overview of the types and configurations of solid supercapacitors, this review introduces proton-conducting polymers electrolytes and the mechanisms of proton conduction in a polymer matrix. Based on their chemistry, synthesizing method, and the nature of proton conduction, proton-conducting polymer electrolytes and the resultant supercapacitors are discussed in two categories: polymeric proton-conducting electrolytes and inorganic/polymer proton-conducting electrolytes. The performance and the technology gaps of the solid supercapacitors enabled by the presented polymer electrolytes are reviewed and compared. The review concludes with an outlook of future advancements required and the key research directions to achieving these.

Strain engineering of WS2, WSe2, and WTe2

Abstract: We perform first-principles calculations to investigate the structural, electronic, and vibrational properties of WS2, WSe2, and WTe2 monolayers, taking into account the strong spin orbit coupling. A transition from a direct to an indirect band gap is achieved for compressive strain of 1% for WS2, 1.5% for WSe2, and 2% for WTe2, while the nature of the band gap remains direct in the case of tensile strain. The size of the band gap passes through a maximum under compressive strain and decreases monotonically under tensile strain. A strong spin splitting is found for the valence band in all three compounds, which is further enhanced by tensile strain. The mobility of the electrons grows along the series WS2 < WSe2 < WTe2.

The pros and cons of lignin valorisation in an integrated biorefinery

Abstract: This short critical review outlines possible scenarios for using lignin as a feedstock in a biorefinery environment. We first explain the position of biomass with respect to fossil carbon sources and the possibilities of substituting these in tomorrow's transportation fuels, energy, and chemicals sectors. Of these, the conversion of biomass to chemicals is, in our opinion, the most worthy. Focusing on lignin, we describe the four main processes for its industrial separation (the Sulfite, Soda, Kraft, and Organosolv processes). Then, we detail several short- and long-term perspectives for its valorisation to aromatics, polymers and materials, as well as new products and in-the-pipeline processes. Finally, we examine the limitations in current lignin valorisation and suggest possible ways forward. Combining the chemical aspects with up-to-date data from economic analyses gives a pragmatic and realistic overview of the commercial applications and possibilities for lignin in the coming decades, where biomass will join shale gas and crude oil as a valid and economical carbon source.

Non-covalent functionalization of carbon nanotubes with polymers

Abstract: Carbon nanotubes have emerged as very promising materials in various research fields spanning from biotechnology to energy storage and transformation. Their poor solubility in aqueous and organic solvents and limited compatibility with polymer matrices are major drawbacks, rendering these materials incapable of achieving their full potential. Covalent or non-covalent functionalization with polymers is considered a major key in circumventing this issue. In this feature article, the non-covalent functionalization through various types of interactions between polymers and carbon nanotubes is highlighted and their potential applications are discussed.

Band gap engineering of CeO2 nanostructure using an electrochemically active biofilm for visible light applications

Abstract: Narrowing the optical band gap of cerium oxide (CeO2) nanostructures is essential for visible light applications. This paper reports a green approach to enhance the visible light photocatalytic activity of pure CeO2 nanostructures (p-CeO2) through defect-induced band gap narrowing using an electrochemically active biofilm (EAB). X-ray diffraction, UV-visible diffuse reflectance/absorption spectroscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, Raman spectroscopy, photoluminescence spectroscopy and high resolution transmission electron microscopy confirmed the defect-induced band gap narrowing of the CeO2 nanostructure (m-CeO2). The structural, optical, photocatalytic and photoelectrochemical properties also revealed the presence of structural defects caused by the reduction of Ce4+ to Ce3+ as well as an increase in the number of oxygen vacancies. The as-modified CeO2 (m-CeO2) nanostructure exhibited substantially enhanced, visible light-driven photoactivity for the degradation of 4-nitrophenol (4-NP) and methylene blue (MB) compared to the p-CeO2 nanostructure. The enhancement in visible light performance was attributed to defects (Ce3+ and oxygen vacancy), resulting in band gap narrowing and a high separation efficiency of photogenerated electron–hole pairs. Photoelectrochemical investigations also showed a significantly-enhanced separation efficiency of the photogenerated electron–hole charge carriers in the m-CeO2 nanostructure under visible light irradiation. The DC electrical conductivity of m-CeO2 showed higher electrical conductivity than p-CeO2 under ambient conditions. This study provides a new biogenic method for developing narrow band gap semiconductor nanostructures for efficient visible light driven photocatalysis and photoelectrode applications.

Preparation and characterization of surface modified boron nitride epoxy composites with enhanced thermal conductivity

Abstract: Hexagonal boron nitride (h-BN) microparticles, modified by surface coupling agent 3-aminopropyl triethoxy silane (APTES), were used to fabricate thermally conductive epoxy/BN composites, and the effects of modified-BN content on the thermal and insulating properties were investigated. It was found that incorporation of h-BN particles in the epoxy matrix significantly enhanced the thermal conductivity of the composites. With 30 wt% modified-BN loading, the thermal conductivity of the composites was 1.178 W m−1 K−1, 6.14 times higher than that of the neat epoxy. Fabricated epoxy/BN composites exhibited improved thermal stability, storage modulus, and glass transition temperature with increased BN content. The composites also possessed excellent electrical insulation properties. These results revealed that epoxy/BN composites are promising as efficient heat-releasing materials for thermal management and microelectronic encapsulation.

Recent developments in palladium catalysed carbonylation reactions

Abstract: Recently, carbonylation reactions have gained considerable interest as they are becoming a versatile tool in the synthesis of pharmaceuticals, agrochemicals and their intermediates. Nowadays, a plethora of transition metal catalysts are available for the synthesis of various functional groups like ureas, carbamates, oxamates, oxamides, α-keto amides, ketones, esters, etc. using carbonylation methodology. Several carbonylation reactions such as aminocarbonylation, alkoxycarbonylation, double carbonylation and oxidative carbonylation, provide efficient and attractive alternatives to the conventional synthetic routes on a laboratory or industrial scale. Oxidative carbonylation is an important reaction as it allows direct carbonylative C–H bond activation. A double carbonylation reaction provides a one step alternative route for the synthesis of α-keto amides, oxamides, and oxamates. It also eliminates the use of conventional thermally unstable and toxic reagents like oxalyl chloride. Several recent studies have focused on the various aspects of these reactions, including catalyst–product separation, and catalyst recoverability and reusability. In view of this, developments in anchoring homogeneous catalysts using various techniques like biphasic catalysis and supported liquid phase catalysis are gaining importance. Carbonylation routes using these techniques are simple, efficient, economical, avoid the use of ligands, and give the desired products in excellent yields. The use of phosphine ligands is disadvantageous as it leads to air/moisture sensitivity, tedious work-up procedures and high work-up costs. Several phosphine-free carbonylation routes eliminate the use of phosphine ligands, and provide economical and simple methods for these transformations. In this review we have summarized the recent trends in carbonylative transformations, which have undergone a rapid development.

Graphene and its nanocomposite material based electrochemical sensor platform for dopamine

Abstract: Dopamine (DA) is an important catecholamine neurotransmitter in the mammalian central nervous system that influences several physiological functions. The impact of DA levels within the human body significantly affects the body functions. Maintaining DA level is essential and the electrochemical detection methods are often used to detect the DA level to regulate the body function. In this review, graphene (functionalized graphene and N-doped graphene) and its composites (metal, metal oxide, polymer, carbonaceous materials, clay, zeolite, and metal–organic framework based graphene composites) modified electrodes with their improved sensing performance towards DA along with several interfering species are described. Further, recent developments on the fabrication of various graphene based composite modified electrodes are also presented. Some important strategies to improve the selectivity and sensitivity towards DA with graphene based composite modified electrodes are also described.

A review of extractive desulfurization of fuel oils using ionic liquids

Abstract: Hydrodesulfurization (HDS), a widely employed method in industries for the desulfurization of fuel oils, such as gasoline and diesel fuel is faced with the challenge of producing lower-sulfur or sulfur-free fuel oils, which are required by more and more countries. However, HDS is not very effective for the removal of thiophenic sulfur compounds due to sterically-hindered adsorption on the catalyst surface, unless operated under harsh conditions, such as high temperature, high pressure, and requirement of a noble catalyst and hydrogen. Extractive desulfurization (EDS) of fuel oils using ionic liquids (ILs) has been intensively studied in recent decades and has a good future as an alternative or complementary method to HDS. In this review, we reviewed the research results of EDS using ILs and provided comprehensive discussions on diverse factors, which influence desulfurization, such as the IL species, IL–oil mass ratio, initial sulfur content, temperature, time, mutual solubility, multiple extractions and regeneration. Potential problems or shortcomings were also stated. Some other desulfurization methods currently under study, such as extraction, oxidation, adsorption and biodesulfurization were also briefly outlined. It can be inferred that ILs remain a class of ideal solvents to realize clean fuel oil in the near future because of their desirable physiochemical properties, which are lacking in molecular organic solvents, while there are possible challenges, such as relatively high viscosity and low efficiency.

Studies on the transformation process of PVDF from α to β phase by stretching

Abstract: Poly(vinylidene fluoride) (PVDF) has excellent pyro- and piezoelectric properties which are related to the β-crystal of PVDF. Most of the β-crystal of PVDF can be transformed from the α-crystal by mechanical stretching. The effects of stretching conditions on the transformation from α to β phase of PVDF were studied in this paper. In addition, changes of crystalline structure of PVDF during the stretching process were observed in situ under an optical tensile stress microscopy tester, and the samples after being stretched were investigated using a 3D digital microscope and an infrared microscope. The results show that stretching temperature (Ts) and drawing ratio (λ) are critical to the transformation from α-crystal to β-crystal of PVDF. The Ts around 100 °C and λ above 3 is recommended. The in situ observation indicates that the deformation of crystalline structure began from the middle of α-spherulite and extended to another spherulite, and caused the large-scale transformation. Scanning results of infrared microspectroscopic and 3D digital microscopy revealed that α phase of PVDF would change into β phase with the deformation of the spherulite, and the distribution of the different crystalline phase in PVDF after being stretched was also given. It is believed that this work is instructive and meaningful to studies on phase transformation and production of the piezoelectric film of PVDF.

Van der Waals density functional study of the energetics of alkali metal intercalation in graphite

Abstract: We report on the energetics of intercalation of lithium, sodium and potassium in graphite by density functional theory using recently developed van der Waals (vdW) density functionals. First stage intercalation compounds are well described by conventional functionals like GGA, but van der Waals functionals are crucial for higher stage intercalation compounds and graphite, where van der Waals interactions are important. The vdW-optPBE functional gave the best agreement with reported structure and energetics for graphite and LiC6 and was further applied for intercalation of Na and K. The enthalpy of formation of LiC6 and KC8 were found to be −16.4 and −27.5 kJ mol−1 respectively. NaC6 and NaC8 were unstable with positive enthalpies of formation (+20.8 and +19.9 kJ mol−1). The energetics of stacking of graphene and intercalant layers was investigated from first to fifth stage intercalation compounds. Higher stage compounds of Li and K were stable, but with less negative enthalpy of formation with increasing stage order. The higher stage Na compounds possessed positive enthalpy of formation, but lower in magnitude than the energy difference of 0.6 kJ mol−1 between graphite with AB and AA stacking. The abnormal behaviour of the lower stage Na intercalation compounds was rationalized by the lower energy involved in the formation of the chemical bond between carbon Na relative to the corresponding bond with Li or K. The chemical bond between alkali metal and carbon is characterized by charge transfer from the alkali-metal to carbon resulting in ionized alkali-metals. The intercalation induces only a subtle increase in the in-plane C–C bond lengths, with longer C–C bonds in the vicinity of the alkali metals but without breaking the hexagonal symmetry.

NiO nanostructures: synthesis, characterization and photocatalyst application in dye wastewater treatment

Abstract: Nickel oxide (NiO) nanostructures have been prepared via a thermal decomposition method. Nanostructures were prepared by calcining β-Ni(OH)2 at various temperatures. H2(pnAA2), 1,3-propylenediamine, nickel nitrate, NaOH and acetyl acetonate were applied as starting reagents to fabricate the NiO nanostructures. The band gap was 2.83 eV, confirming the semi-conductive nature of the prepared NiO nanostructures and indicating its potential as a photocatalyst in effluent treatment. UV irradiation times, quantity of catalyst, pH and dye concentration were investigated by degrading Rhodamine B (RB, C28H31N2O3Cl) dye. These crucial factors indicated that the NiO nanostructures are an effective photocatalyst. Kinetic investigations of photodegradation revealed that the reactions followed the improved Langmuir–Hinshelwood model. The as-produced nanostructures were characterized using XRD, FESEM, FT-IR, UV-vis, VSM and BET.

Third-generation solar cells: a review and comparison of polymer:fullerene, hybrid polymer and perovskite solar cells

Abstract: The need for large scale low carbon solar electricity production has become increasingly urgent for reasons of energy security and climate change mitigation. Third-generation solar cells (SCs) are solution processed SCs based on semiconducting organic macromolecules, inorganic nanoparticles or hybrids. This review considers and compares three types of promising 3rd-generation SCs: polymer:fullerene, hybrid polymer and perovskite SCs. The review considers work reported since an earlier review (Saunders et al., Adv. Colloid Interface Sci., 2008, 138, 1) and highlights the great progress that has been made in each area. We consider the operation principles for each SC type and also review the state-of-the-art devices. The polymer:fullerene and hybrid polymer SC open circuit voltages are compared to values predicted from the well-known Scharber equation and similarities and differences discussed. The perovskite SCs are also considered and their remarkable rate of power conversion efficiency performance increase is discussed. The review considers the requirements for large-scale deployment in the contexts of semiconducting polymer and hole transport matrix synthesis and materials selection. It is concluded that the 3rd-generation SC technologies discussed here are well placed for major contribution to large scale energy production. (This has already been partially demonstrated for polymer:fullerene SCs.) Looking further ahead we propose that several of the 3rd-generation SCs considered here have excellent potential to provide the low cost large-scale deployment needed to meet the terawatt challenge for solar electricity generation.

Advancement of sorption-based heat transformation by a metal coating of highly-stable, hydrophilic aluminium fumarate MOF

Abstract: The distinctive water sorption properties of microporous aluminium fumarate (s-shaped isotherm, narrow hysteresis, loading >0.3 g g−1 at a relative pressure as low as p/p0 = 0.3 under realistic working conditions) permit a large advancement of MOF-based sorption heat transformation processes, especially as we demonstrate that the favourable sorption properties are accompanied by an unprecedented cyclic hydrothermal stability. With regard to the application of heat transformation, where unhindered heat and mass transfer are crucial for fast ad-/desorption cycles and a high power density, the question of proper shaping was also addressed. A 300 μm thick, polycrystalline, thermally well coupled and highly accessible coating of microporous aluminium fumarate was deposited on a metal substrate via the thermal gradient approach, and found to be stable for the first 4500 ad-/desorption cycles with water vapour.

Naturally occurring phenolic sources: monomers and polymers

Abstract: Exploration of sustainable alternatives to chemicals derived from petro-based industries is the current challenge for maintaining the balance between the needs of a changing world while preserving nature. The major source for sustainable chemicals is either the natural existing plant sources or waste generated from agro-based industries. The utility of such resources will supplement new processed materials with different sets of properties and environmental friendliness due to their biodegradability and low toxicity during preparation, usage and disposal. Amongst other polymers used on a day-to-day basis, phenolic resins account for vast usage. Replacement of petro-based monomers such as phenol and its derivatives either partly or completely utilized for the synthesis of such resins is ongoing. Extraction of natural phenolic components from cashew nut shell liquid, lignin, tannin, palm oil, coconut shell tar or from agricultural and industrial waste, and their utilization as synthons for the preparation of bio-based polymers and properties obtained are reviewed in this paper. This review article is designed to acknowledge efforts of researchers towards the “3C” motto – not only trying to create but also adapting the principles to conserve and care for a sustainable environment. This review paper describes how extraction, separation and recovery of desired phenolic compounds have occurred recently; how substituted phenol compounds, unmodified and modified, act as monomers for polymerization; and how the presence of sustainable phenolic material affects the properties of polymers. There are about 600 references cited and still there is a lot to uncover in this research area.