Functionalized nanoporous carbon materials have attracted the colossal interest of the materials science fraternity owing to their intriguing physical and chemical properties including a well-ordered porous structure, exemplary high specific surface areas, electronic and ionic conductivity, excellent accessibility to active sites, and enhanced mass transport and diffusion. These properties make them a special and unique choice for various applications in divergent fields such as energy storage batteries, supercapacitors, energy conversion fuel cells, adsorption/separation of bulky molecules, heterogeneous catalysts, catalyst supports, photocatalysis, carbon capture, gas storage, biomolecule detection, vapour sensing and drug delivery. Because of the anisotropic and synergistic effects arising from the heteroatom doping at the nanoscale, these novel materials show high potential especially in electrochemical applications such as batteries, supercapacitors and electrocatalysts for fuel cell applications and water electrolysis. In order to gain the optimal benefit, it is necessary to implement tailor made functionalities in the porous carbon surfaces as well as in the carbon skeleton through the comprehensive experimentation. These most appealing nanoporous carbon materials can be synthesized through the carbonization of high carbon containing molecular precursors by using soft or hard templating or non-templating pathways. This review encompasses the approaches and the wide range of methodologies that have been employed over the last five years in the preparation and functionalisation of nanoporous carbon materials via incorporation of metals, non-metal heteroatoms, multiple heteroatoms, and various surface functional groups that mostly dictate their place in a wide range of practical applications.

Recent advances in functionalized micro and mesoporous carbon materials: synthesis and applications

The development of nonlinear optical (NLO) materials has been driven by a multitude of important technological applications that can be realized if suitable materials are available 1–15. Future generations of optoelectronic devices for telecommunications, information storage, optical switching, and signal processing are predicted to a large degree on the development of materials with exceptional NLO responses 1–15. A large number of organic π-conjugated molecules have been investigated in the last thirty years for suitability to function as components in hypothetical NLO materials 1–19. Several books and reviews have appeared dealing with theory of nonlinear optics and the structural characteristics and applications of nonlinear optical molecules and materials 1–19. Truly, all-optical NLO effects were not discovered until the discovery of lasers. Second-harmonic generation (SHG) was first observed in a single crystal of quartz by Franken et.al. 20 in 1961. Parametric amplification was observed in lithium niobate (LiNbO3) by two-wave mixing in temperature-tuned single crystals 21. Rentzepis and Pao 22 made the first observation of SHG in an organic material, benzpyrene, in 1964. Heilmeir examined hexamethylenetetramine single crystal SHG in the same year 24. Two other organic materials followed rapidly: hippuric acid and benzil 25. Benzil was the first material that proved relatively easy to grow into large single crystals. Over the last two decades the study of nonlinear optical process in organic and polymer systems has enjoyed rapid and sustained growth 1–19, 25–39. One indication of the growth is the increase in the number of articles published in refereed society journals, as one can find from web of science 25, SCIFINDER 26 and Scopus 27 search. The four years period 1980–1983 saw the publication of 124 such articles. In the next four years period 1984–1987, the production of articles increased to 736 (nearly six times). From 1988–1992, the number of articles increased to more than 4000 25–27. In the last decade, academia, industry and government laboratories have been working in this field to replace electronics by photonics and as a result, the number of publications has reached more than 70,000 25–27.

The rapid growth of the field is mainly due to the technological promise of these materials 1–19, 28–37. Traditionally, the materials used to measure second-order NLO behavior were inorganic crystals, such as lithium niobate (LiNbO3) and potassium dihydrogen phosphate (KDP). The optical nonlinearity in these materials is to a large extent caused by the nuclear displacement in an applied electric field, and to a smaller extent by the movement of the electrons 1–10. This limits the bandwidth of the modulator. Organic materials have a number of advantages over inorganic materials for NLO applications 28–35. The ease of modification of organic molecular structures makes it possible to synthesize tailor-made molecules and to fine-tune the properties for the desired application 28–35. Unfortunately, not all organic materials display second-order NLO properties. At the molecular level, they need to be non-centrosymmetric. A large number of organic π-conjugated molecules have been investigated 1–9, 28–35 in the last twenty years. The outcome of the results has helped to establish certain guidelines for molecular design to get good second order NLO materials. However, roughly more than 80% of all π-conjugated organic molecules crystallize in centro-symmetric space groups 1–19, therefore producing materials with no second order bulk susceptibility. To overcome this limitation, organic NLO material doped or covalently attached in polymers, have been introduced by Dalton et. al 5,6,16,38–39. A few of these chromophores have served as components of functioning polymer-based optoelectronic devices; the physical properties of all these prototype materials possess one or more critical deficiencies that render commercialization of these systems impractical 28–39. These facts suggest that new types of molecular design are necessary if significant advances are to be realized.

From 1998 onwards, researchers started effort on developing various nanomaterials, with high second order NLO properties and seeking for their applications in photonics as well as chemical and biological detection 40–106. The surface-enhanced phenomenon is predicted to have a particularly important impact in nonlinear optical NLO applications, since the generally weak nonlinear effects can be significantly increased via strong electromagnetic fields at the surfaces of metallic nanostructures 60–129. NLO based sensing have provided great potentials and opportunities for detecting different environmental toxins that exhibit some specific advantages, compared to other conventional and nanomaterial based techniques. Aim of this review is mainly to summarize and evaluate the achievements in development of nanoparticle based second order NLO materials with different sizes and shapes and it will focus on the following three major issues: (i) design of novel NLO active materials using nanoparticles (ii) nonlinear optical properties of single nanoparticle, nanoparticle aggregates and self assembly, and (iii) applications in chemical and biological sensing.

/pdf/size-and-shape-dependent-second-order-nonlinear-optical-33i51r20vh.pdf

Size and shape dependent second order nonlinear optical properties of nanomaterials and their application in biological and chemical sensing.

High-surface-area, nanostructured carbon is widely used for encapsulating sulfur and improving the cyclic stability of Li–S batteries, but the high carbon content and low packing density limit the specific energy that can be achieved. Here we report an approach that does not rely on sulfur encapsulation. We used a low-surface-area, open carbon fibre architecture to control the nucleation and growth of the sulfur species by manipulating the carbon surface chemistry and the solvent properties, such as donor number and Li+ diffusivity. Our approach facilitates the formation of large open spheres and prevents the production of an undesired insulating sulfur-containing film on the carbon surface. This mechanism leads to ~100% sulfur utilization, almost no capacity fading, over 99% coulombic efficiency and high energy density (1,835 Wh kg−1 and 2,317 Wh l−1). This finding offers an alternative approach for designing high-energy and low-cost Li–S batteries through controlling sulfur reaction on low-surface-area carbon. Sulfur encapsulation with nanoporous carbon is a widely adopted approach for Li–S batteries, but this often results in low sulfur utilization and low volumetric energy density. Here the authors report a non-encapsulation approach for the growth of S-containing species with low-surface-area carbon and high energy.

Non-encapsulation approach for high-performance Li–S batteries through controlled nucleation and growth

Nanoparticles in sustainable agriculture: An emerging opportunity

Transparent glass-ceramics functionalized by dispersed crystals

Nitrogen-doped mesoporous carbons for high performance supercapacitors

Copper nanoparticles (NPs) with a tunable shape (cube, hemisphere and agglomerate), size (42–146 nm) and density were synthesized on the ITO substrate by electrochemical deposition. SEM, TEM, SAED, XRD, XAES and UV-vis spectrophotometry were employed to characterize these nanoparticles. The important parameters including the capping agent, Cu2+ concentration, applied potential and deposition time were chosen to determine the final morphology and composition of the nanoparticles. Sodium citrate, served as the capping agent and reducing agent, absorbed selectively on Cu {111} faces instead of {100} faces, which affected the thermodynamic equilibrium in crystal growth, reduced aggregation and contributed to the synthesis of pure Cu NPs. The copper source, applied potential and deposition time affected the dynamic process, thereby controlling the nuclei number and growth rate. The optical properties of copper nanoparticles were studied by UV-visible absorption spectroscopy, and it was found that the intensity and position of the LSPR peak was strongly related to the shape, size and density of Cu NPs. Cu NPs with a tunable LSPR peak may be conducive to designing biosensors, catalysis, optoelectronic devices, etc.

Shape-, size-, and density-tunable synthesis and optical properties of copper nanoparticles

In this work layered copper films with smooth surface were successfully fabricated onto ITO substrate by electrochemical deposition (ECD) and the thickness of the films was nearly 60 nm. The resulting films were characterized by SEM, TEM, AFM, XPS, and XRD. We have investigated the effects of potential and the concentration of additives and found that 2D dendritic-like growth process leaded the formation of films. A suitable growth mechanism based on diffusion limited aggregation (DLA) mechanism for the copper films formation is presented, which are meaningful for further designing homogeneous and functional films.

/pdf/electrochemical-deposition-of-layered-copper-thin-films-3nkqx5j2ak.pdf

Electrochemical deposition of layered copper thin films based on the diffusion limited aggregation.

Hollow spheres of solid solution Fe7Ni3S11/CN as advanced anode materials for sodium ion batteries

Enhanced hetero-elements doping content in biomass waste-derived carbon for high performance supercapacitor

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