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This paper reports a systematic study into the effect of nitrogen on iron-catalyzed graphitization of biomass. Chitin, chitosan, N-acetylglucosamine, gelatin and glycine were selected to represent nitrogen-rich saccharides and amino-acid/polypeptide biomass precursors. The materials were pyrolyzed with an iron catalyst to produce carbons with a wide range of chemical and structural features such as mesoporosity and nitrogen-doping. Many authors have reported the synthesis of nitrogen-doped carbons by pyrolysis and these have diverse applications. However, this is the first systematic study of how nitrogen affects pyrolysis of biomass and importantly the catalytic graphitization step. Our data demonstrates that nitrogen inhibits graphitization but that some nitrogen survives the catalytic graphitization process to become incorporated into various chemical environments in the carbon product.

Chemistry experiments are challenging for people with vision impairment (VI) as results often rely on visual observations such as a color change. This puts pupils with VI at a disadvantage both in ...

The sol-gel synthesis of iron carbide (Fe3C) nanoparticles proceeds through multiple intermediate crystalline phases, including iron oxide (FeOx) and iron nitride (Fe3N). The control of particle size is challenging, and most methods produce polydisperse Fe3C nanoparticles of 20-100 nm in diameter. Given the wide range of applications of Fe3C nanoparticles, it is essential that we understand the evolution of the system during the synthesis. Here, we report an in situ synchrotron total scattering study of the formation of Fe3C from gelatin and iron nitrate sol-gel precursors. A pair distribution function analysis reveals a dramatic increase in local ordering between 300 and 350 °C, indicating rapid nucleation and growth of iron oxide nanoparticles. The oxide intermediate remains stable until the emergence of Fe3N at 600 °C. Structural refinement of the high-temperature data revealed local distortion of the NFe6 octahedra, resulting in a change in the twist angle suggestive of a carbonitride intermediate. This work demonstrates the importance of intermediate phases in controlling the particle size of a sol-gel product. It is also, to the best of our knowledge, the first example of in situ total scattering analysis of a sol-gel system.

Iron nitride (Fe3N) and iron carbide (Fe3C) nanoparticles can be prepared via sol–gel synthesis. While sol–gel methods are simple, it can be difficult to control the crystalline composition, i.e., to achieve a Rietveld-pure product. In a previous in situ synchrotron study of the sol–gel synthesis of Fe3N/Fe3C, we showed that the reaction proceeds as follows: Fe3O4 → FeOx → Fe3N → Fe3C. There was considerable overlap between the different phases, but we were unable to ascertain whether this was due to the experimental setup (side-on heating of a quartz capillary which could lead to thermal gradients) or whether individual particle reactions proceed at different rates. In this paper, we use in situ wide- and small-angle X-ray scattering (wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS)) to demonstrate that the overlapping phases are indeed due to variable reaction rates. While the initial oxide nanoparticles have a small range of diameters, the size range expands considerably and very rapidly during the oxide–nitride transition. This has implications for the isolation of Rietveld-pure Fe3N, and in an extensive laboratory study, we were indeed unable to isolate phase-pure Fe3N. However, we made the surprising discovery that Rietveld-pure Fe3C nanoparticles can be produced at 500 °C with a sufficient furnace dwell time. This is considerably lower than the previous reports of the sol–gel synthesis of Fe3C nanoparticles.

This paper reports a simple way to produce porous graphitic carbons from a wide range of lignocellulosic biomass sources, including nut shells, softwood sawdust, seed husks and bamboo. Biomass precursors are milled and sieved to produce fine powders and are then converted to porous graphitic carbons by iron-catalysed graphitization. Graphitizing the raw (unmilled) biomass creates carbons that are diverse in their porosity and adsorption properties. This is due to the inability of the iron catalyst precursor to penetrate the structure of dense biomass material. Milling enables much more efficient impregnation of the biomass and produces carbons with homogeneous properties. Lignocellulosic biomass (particularly waste biomass) is an attractive precursor to technologically important porous graphitic carbons as it is abundant and renewable. This simple method for preparing the biomass enables a wide range of biomass sources to be used to produce carbons with homogeneous properties. This article is part of the theme issue ‘Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 2)’.

Despite the recent interest in catalytic graphitization to obtain graphite-like materials from hard-carbon sources, many aspects of its mechanism are still poorly unknown. We performed a series of in situ experiments to study phase transformations during graphitization of a hard-carbon precursor using an iron catalyst at temperatures up to 1100 °C and ex situ total scattering experiments up to 2000 °C to study the structural evolution of the resulting graphitized carbon. Our results show that upon heating and cooling, iron undergoes a series of reductions to form hematite, magnetite, and wüstite before forming a carbide that later decomposes into metallic iron and additional graphite and that the graphitization fraction increases with increasing peak temperature. Structural development with temperature results in decreasing sheet curvature and increased stacking, along with a decrease in turbostratic disorder up to 1600 °C. Higher graphitization temperatures result in larger graphitic domains without further ordering of the graphene sheets. Our results have implications for the synthesis of novel biomass-derived carbon materials with enhanced crystallinity. Ministerio de Ciencia, Innovación y Universidades PID2019- 107019R

Contrast-variation small-angle neutron scattering (CV-SANS), small-angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR) measurements of diffusion and isothermal titration calorimetry (ITC) are used to gain insight into the aggregation of an alkyl-C60 derivative, molecule 1, in n-hexane, n-decane and toluene as a function of concentration and temperature. Results point to an associative mechanism of aggregation similar to other commonly associating molecules, including non-ionic surfactants or asphaltenes in non-aqueous solvents. Little aggregation is detected in toluene, but small micelle-like structures form in n-alkane solvents, which have a C60-rich core and alkyl-rich shell. The greatest aggregation extent is found in n-hexane, and at 0.1 M the micelles of 1 comprise around 6 molecules at 25 °C. These micelles become smaller when the concentration is lowered, or if the solvent is changed to n-decane. The solution structure is also affected by temperature, with a slightly larger aggregation extent at 10 °C than at 25 °C. At higher concentrations, for example in solutions of 1 above 0.3 M in n-decane, a bicontinuous network becomes apparent. Overall, these findings aid our understanding of the factors driving the assembly of alkyl-π-conjugated hydrophobic amphiphiles such as 1 in solution and thereby represent a step towards the ultimate goal of exploiting this phenomenon to form materials with well-defined order.

Metal carbides have shown great promise in a wide range of applications due to their unique catalytic, electrocatalytic and magnetic properties. However, the scalable production of dispersible metal carbide nanoparticles remains a challenge. Here, we report a simple and scalable route to dispersible iron carbide (Fe3C) nanoparticles. This uses MgO nanoparticles as a removable ‘cast’ to synthesize Fe3C nanoparticles from Prussian blue (KFeIII[FeII(CN)6]). Electron tomography demonstrates how nanoparticles of the MgO cast encase the Fe3C nanoparticles to prevent sintering and agglomeration during the high-temperature synthesis. The MgO cast is readily removed with ethylenediaminetetraacetic acid (EDTA) to generate Fe3C nanoparticles that can be used to produce a colloidal ferrofluid or dispersed on a support material.

Porous carbons are important for many energy applications. The biopolymer gelatin provides a simple and sustainable route to functional carbon foams with multimodal porosity. In this paper, small angle neutron scattering is applied alongside other techniques to elucidate the mechanism of formation of these foams. Analysis of the data demonstrates that combinations of different metal nitrates can be used to control foam macrostructure. Synergistic interaction of metal ions with the gelatin polypeptide changes the viscoelastic properties and thus controls foam formation.

A fluorescent liquid pyrene derivative with a high fluorescence quantum yield (65%) in the bulk state is reported. With this as the sole oil phase, stable luminescent oil-in-water microemulsions have been prepared. Increasing the loading of liquid pyrene swells the droplets, as detected by small-angle neutron scattering. These larger droplets have a greater proportion of pyrene excimer emission contribution in their photoluminescence spectra, which leads to a red shift in the chromaticity of the emission.

Sol–gel chemistry is a powerful tool for the synthesis of porous or nanocrystalline structures of a wide range of materials. The morphology and composition of the final product can be strongly dependent on the mechanism that operates during the heating step, as has been demonstrated in many investigations of binary, ternary, and quaternary metal oxides. We demonstrate the complex phase transformations occurring in a transition-metal carbide (Fe3C, cementite) synthesis using in situ synchrotron X-ray diffraction. Our new study proves the existence of multiple intermediate phases and elucidates how oxide–nitride and nitride–carbide phase transformations can occur. This is particularly important as many transition-metal nitrides and carbides are metastable, which renders their stability windows sensitive to small changes in sol–gel methodology.

Graphitic carbon nitride (g-CN) is an exciting material – a semiconductor comprised only of carbon and nitrogen. It is very easy to synthesize and there are many papers on the development of this material in key energy applications such as photoelectrochemical (PEC) conversion of solar energy into chemical fuels. As a promising candidate for sustainable photocathodes, g-CN has advantages such as low cost, visible light sensitivity and high chemical stability. However, to date, the performance of g-CN has been limited, partly because standard synthesis methods produce relatively dense materials with low surface area. To combat this, there are now many examples of hard and soft templating to change the structure and morphology of g-CN and introduce porosity. This review will discuss the key advances and challenges in this interesting new field.

This paper reports the direct transformation of raw lignocellulosic biomass into nanostructured graphitic carbon in a single step. Catalytic iron carbide nanoparticles are generated in situ by thermal decomposition of absorbed iron nitrate followed by carbothermal reduction. The Fe3C particles then etch through the biomass to generate intertwined graphitic tubules through catalytic graphitization. The materials are mesoporous with the pore size dependant on the iron content. Conversion of raw biomass into stable graphitic carbon at relatively low temperatures (800 °C) offers a promising route to large-scale and sustainable synthesis of carbons for electrode or filtration applications. This facile method can also be used to produce nanocomposites of Fe3C/graphite combined with nanoparticles of metal oxides such as CaO or MgO, again from a one-pot precursor, giving potential for a wide range of applications.

Contrast-variation small-angle neutron scattering (CV-SANS), small-angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR) measurements of diffusion and isothermal titration calorimetry (ITC) are used to gain insight into the aggregation of an alkyl-C

From its initial use to describe hydrolysis and condensation processes, the term ‘sol–gel’ is now used for a diverse range of chemistries. In fact, it is perhaps better defined more broadly as covering the synthesis of solid materials such as metal oxides from solution-state precursors. These can include metal alkoxides that crosslink to form metal–oxane gels, but also metal ion–chelate complexes or organic polymer gels containing metal species. What is important across all of these examples is how the choice of precursor can have a significant impact on the structure and composition of the solid product. In this review, we will attempt to classify different types of sol–gel precursor and how these can influence a sol–gel process, from self-assembly and ordering in the initial solution, to phase separation during the gelation process and finally to crystallographic transformations at high temperature.

Biologisches Material ist eine ergiebige Quelle fur chemisch vielfaltige Makromolekule wie Polysaccharide, Polypeptide und polyaromatische Verbindungen. Viele dieser biologischen Polymere (Biopolymere) sind auf spezifische Funktionen hin evolutionar optimiert, z. B. uber die Molekulkettenlange, die Funktionalisierung und die Monomersequenz. Gegenwartig werden zahlreiche Anstrengungen unternommen, die sich auf den chemischen Aufschluss von Biopolymeren fur die Verwendung als Treibstoff oder als Ausgangsverbindungen fur die Synthese richten. Daruber hinaus gibt es ein steigendes Interesse an der unmittelbaren Verwendung von Biopolymeren fur die Herstellung funktioneller Materialien. Dieser Kurzaufsatz zieht Beispiele aus der jungeren Vergangenheit heran, um aufzuzeigen, wie Biopolymere neue Wege fur die Synthese nanostrukturierter Materialien eroffnen konnen.

Biomass is an abundant source of chemically diverse macromolecules, including polysaccharides, polypeptides, and polyaromatics. Many of these biological polymers (biopolymers) are highly evolved for specific functions through optimized chain length, functionalization, and monomer sequence. As biopolymers are a chemical resource, much current effort is focused on the breakdown of these molecules into fuels or platform chemicals. However there is growing interest in using biopolymers directly to create functional materials. This Minireview uses recent examples to show how biopolymers are providing new directions in the synthesis of nanostructured materials.

In this article, we report a facile, one-pot route to phase-pure Fe3C nanoparticles (mean diameter = 20 nm) that show a remarkably high saturation magnetization (∼130 emu/g), higher than iron oxide (Fe3O4) and comparable to that of bulk Fe3C (∼140 emu/g). A readily available biopolymer (gelatin) is used as a matrix to disperse an aqueous iron acetate precursor. On heating, the biopolymer induces nucleation of magnetite (Fe3O4) nanoparticles before decomposing to form a carbon-rich matrix. This then acts as a reactive template for carbothermal reduction of the magnetite nanoparticles to Fe3C at a moderate temperature of 650 °C. This method represents a considerable advance over previous reports that often use high-energy procedures or costly and hazardous precursors. These homogeneous, highly magnetic nanoparticles have many potential applications in biomedicine and catalysis.

In this paper we focus on the synthesis and use of superacids, in particular 1,1,2,2-tetrafluoroethanesulfonic acid(TFESA), and describe how these can be optimized for reactions of key industrial importance. One area of considerable interest is the field of superacid catalysis and, specifically, the development of safer and more cost-effective acid catalysts. We report a new simplified route for preparation of these acids, making these more readily available and opening up a large number of opportunities. Partially fluorinated superacids offer several advantages over the acids commonly used in catalysis (sulfuric, hydrofluoric acid and aluminium chloride): lower loadings, lower reaction temperatures (leading to increased selectivity), fewer by-products, shorter reaction times and higher throughput. TFESA and its longer chain analogs are much less volatile than triflic acid (CF3SO3H). We tested these superacids in several processes (aromatic alkylation, acylation of arenes, isomerization, oligomerization and the Fries rearrangement). These materials are excellent acid catalysts, comparable to triflic acid, and yet easier to handle. We have also prepared supported versions of these catalysts and introduced the ability to recycle.

This paper describes a powerful and versatile approach that combines the benefits of sol-gel processing with controlled phase separation to yield oxide-carbide-carbon or oxide-nitride-carbon nanocomposites.

Nanowire Growth Observed In the hypothetical microcrucible growth mechanism for nanowires, a molten catalytic particle located in a pore on a substrate continually feeds the outward growth of the wire. To observe such a mechanism requires the ability to examine nanowire growth in situ. Boston et al. (p. 623 ) studied various stages of Y 2 BaCuO 5 nanowire growth using transmission electron microscopy and were able to observe a microcrucible growth mechanism directly.

Photoelectrochemical (PEC) conversion of solar light into chemical fuels is one of the most promising solutions to the challenge of sustainable energy. Graphitic carbon (IV) nitride polymer (g-CN) is an interesting sustainable photocathode material due to low-cost, visible-light sensitivity, and chemical stability up to 500 °C in air. However, grain boundary effects and limited active sites greatly hamper g-CN activity. Here, we demonstrate biopolymer-activation of g-CN through simultaneous soft-templating of a sponge-like structure and incorporation of active carbon-dopant sites. This facile approach results in an almost 300% increase in the cathodic PEC activity of g-CN under simulated solar-irradiation.

Biomass is an abundant source of chemically diverse macromolecules, including polysaccharides, polypeptides, and polyaromatics. Many of these biological polymers (biopolymers) are highly evolved for specific functions through optimized chain length, functionalization, and monomer sequence. As biopolymers are a chemical resource, much current effort is focused on the breakdown of these molecules into fuels or platform chemicals. However there is growing interest in using biopolymers directly to create functional materials. This Minireview uses recent examples to show how biopolymers are providing new directions in the synthesis of nanostructured materials.

Metal oxide/nitride nanocomposites have many existing and potential applications, e.g. in energy conversion or ammonia synthesis. Here, a hybrid oxide/nitride nanocomposite (anatase/TixW1−xN) was synthesized by an ammonia-free sol–gel route. Synchrotron x-ray diffraction, complemented with electron microscopy and thermogravimetric analysis, was used to study the structure, composition and mechanism of formation of the nanocomposite. The nanocomposite contained nanoparticles (

We report a one-pot route to Au/CeO2 nanocomposites. A readily-available biopolymer, sodium alginate, is exploited for controlled formation and stabilisation of gold nanoparticles followed by in situ growth of a sponge-like network of CeO2 nanoparticles. The flexible nature of this method as a general route to mixed metal/metal oxide nanocomposites is also demonstrated.

Here it is shown that the chemical nature of outer organic surfactant layers, used to stabilize inorganic nanoparticles (NPs), is a key factor controlling solubility in a mixed liquid CO(2)-heptane (10% vol) solvent.

Graphitic carbon nitride materials show some promising properties for applications such as photocatalytic water splitting. However, the conversion efficiency is still low due to factors such as a low surface area and limited light absorption. In this paper, we describe a “triple templating” approach to generating porous graphitic carbon nitride. The introduction of pores on several length-scales results in enhanced photocatalytic properties.

One of the biggest challenges for materials science is to design facile routes to structurally complex materials, which is particularly important for global applications such as fuel cells. Doped nanostructured carbons are targeted as noble metal-free electrocatalysts for this purpose. Their intended widespread use, however, necessitates simple and robust preparation methods that do not compromise on material performance. Here, we demonstrate a versatile one-pot synthesis of nitrogen-doped carbons that exploits the templating ability of biological polymers. Starting with just metal nitrates and gelatin, multiphase C/Fe3C/MgO nanomaterials are formed, which are then etched to produce active carbon electrocatalysts with accessible trimodal porosity. These show remarkable performance in the oxygen reduction reaction – a key process in proton exchange membrane fuel cells. The activity is comparable to commercial platinum catalysts and shows improved stability with reduced crossover effects. This simple method offers a new route to widely applicable porous multicomponent nanocomposites.

Carbon fibers were obtained using hydrothermal carbonization of rice husk followed by further heat treatment at 1000 °C to increase the conductivity and removal of the silica fraction to increase the porosity. These carbon fibers show superior capacity retention and rate performance as anode in lithium ion batteries.

Iron nitride (Fe3N) is a promising material to replace scarce and costly noble metals in many catalytic applications. Here, we report the synthesis of Fe3N nanostructures by a simple sol–gel based route. This aqueous, one-pot method based on a self-expanding polypeptide foam represents a breakthrough in Fe3N nanostructure synthesis, which previously has only been achieved through ammonolysis. Through extensive X-ray diffraction and compositional analysis, a formation mechanism is proposed, based on in-situ nitridation by the decomposing gel matrix. The Fe3N nanoparticle sponge is shown to be a promising catalyst for ammonia decomposition, an easy process for CO2-free hydrogen supply and off-gas treatment.