Beyond Mechanical Recycling: Giving New Life to Plastic Waste.

Increasing the stream of recycled plastic necessitates an approach beyond the traditional recycling via melting and re-extrusion. Various chemical recycling processes have great potential to enhance recycling rates. In this Review, a summary of the various chemical recycling routes and assessment via life-cycle analysis is complemented by an extensive list of processes developed by companies active in chemical recycling. We show that each of the currently available processes is applicable for specific plastic waste streams. Thus, only a combination of different technologies can address the plastic waste problem. Research should focus on more realistic, more contaminated and mixed waste streams, while collection and sorting infrastructure will need to be improved, that is, by stricter regulation. This Review aims to inspire both science and innovation for the production of higher value and quality products from plastic recycling suitable for reuse or valorization to create the necessary economic and environmental push for a circular economy.

One pot conversion of glucose to ethyl levulinate over a porous hydrothermal acid catalyst in green solvents.

The one-pot conversion of glucose to ethyl levulinate over an acid-functionalised hydrothermal catalyst (derived from glucose) provides high initial yields up to 37 mol%, comparable to the homogeneous H2SO4 catalyst, whilst catalyst performance is strongly influenced by green solvent choice.

Towards a Sustainable Synthesis of Oxymethylene Dimethyl Ether by Homogeneous Catalysis and Uptake of Molecular Formaldehyde.

Oxymethylene dimethyl ethers (OMEn ; CH3 (-OCH2 -)n O-CH3 , n=3-5) are a novel class of sustainable synthetic fuels, which are of increasing interest due to their soot-free combustion. Herein a novel anhydrous OMEn synthesis route is presented. Catalyzed by trimethyloxonium salts, dimethoxymethane takes up monomeric gaseous formaldehyde instantaneously and forms high purity OMEn at temperatures of 25-30 °C. This new anhydrous approach using molecular formaldehyde and catalytic amounts of highly active trimethyloxonium salts represents a promising new step towards a sustainable formation of OMEn emanating from CO2 and H2 .

An Interesting Class of Porous Polymer--Revisiting the Structure of Mesoporous α-D-Polysaccharide Gels.

The processes involved in the transformation of non-porous, native polysaccharides to their highly porous equivalents introduce significant molecular complexity and are not yet fully understood. In this paper, we propose that distinct changes in polysaccharide local short-range ordering promotes and directs the formation of meso- and micro-pores, which are investigated here using N2 sorption, FTIR, and solid-state (13)C NMR. It is found that an increase in the overall double helical amylose content, and their local association structures, are responsible for formation of the porous polysaccharide gel phase. An exciting consequence of this local ordering change is elegantly revealed using a (19)F NMR experiment, which identifies the stereochemistry-dependent diffusion of a fluorinated chiral probe molecule (1-phenyl-2,2,2-trifluoroethanol) from the meso- to the micro-pore region. This finding opens opportunities in the area of polysaccharide-based chiral stationary phases and asymmetric catalyst preparation.

Sustainable carbon materials.

Carbon-based structures are the most versatile materials used in the modern field of renewable energy (i.e., in both generation and storage) and environmental science (e.g., purification/remediation). However, there is a need and indeed a desire to develop increasingly more sustainable variants of classical carbon materials (e.g., activated carbons, carbon nanotubes, carbon aerogels, etc.), particularly when the whole life cycle is considered (i.e., from precursor "cradle" to "green" manufacturing and the product end-of-life "grave"). In this regard, and perhaps mimicking in some respects the natural carbon cycles/production, utilization of natural, abundant and more renewable precursors, coupled with simpler, lower energy synthetic processes which can contribute in part to the reduction in greenhouse gas emissions or the use of toxic elements, can be considered as crucial parameters in the development of sustainable materials manufacturing. Therefore, the synthesis and application of sustainable carbon materials are receiving increasing levels of interest, particularly as application benefits in the context of future energy/chemical industry are becoming recognized. This review will introduce to the reader the most recent and important progress regarding the production of sustainable carbon materials, whilst also highlighting their application in important environmental and energy related fields.

A sustainable template for mesoporous zeolite synthesis.

A generalized synthesis of high-quality, mesoporous zeolite (e.g., MFI-type) nanocrystals is presented, based on a biomass-derived, monolithic N-doped carbonaceous template. As an example, ZSM-5 single crystals with desirable large-diameter (12-16 nm) intracrystalline mesopores are synthesized. The platform provides scope to optimize template dimensions and chemistry for the synthesis of a range of micro-/mesoporous crystalline zeolites in a cost-effective and highly flexible manner.

Always look on the "light" side of life: sustainable carbon aerogels.

The production of carbon aerogels based on the conversion of inexpensive and abundant precursors using environmentally friendly processes is a highly attractive subject in materials chemistry today. This article reviews the latest developments regarding the rapidly developing field of carbonaceous aerogels prepared from biomass and biomass-derived precursors, highlighting exciting and innovative approaches to green, sustainable nanomaterial synthesis. A review of the state-of-the-art technologies will be provided with a specific focus on two complimentary synthetic approaches developed upon the principles of green chemistry. These carbonaceous aerogel synthesis strategies, namely the Starbon and carbogel approaches, can be regarded as "top-down" and "bottom-up" strategies, respectively. The structural properties can be easily tailored by controlling synthetic parameters such as the precursor selection and concentration, the drying technique employed and post-synthesis temperature annealing. In addition to these parameters, the behavior of these sustainable carbon aerogel platforms in a variety of environmental and energy-related applications will also be discussed, including water remediation and fuel cell chemistry (i.e., the oxygen reduction reaction). This Review reveals the fascinating variety of highly porous, versatile, nanostructured, and functional carbon-based aerogels accessible through the highlighted sustainable synthetic platforms.

Molecular-level understanding of the carbonisation of polysaccharides.

Understanding of both the textural and functionality changes occurring during (mesoporous) polysaccharide carbonisation at the molecular level provides a deeper insight into the whole spectrum of material properties, from chemical activity to pore shape and surface energy, which is crucial for the successful application of carbonaceous materials in adsorption, catalysis and chromatography. Obtained information will help to identify the most appropriate applications of the carbonaceous material generated during torrefaction and different types of pyrolysis processes and therefore will be important for the development of cost- and energy-efficient zero-waste biorefineries. The presented approach is informative and semi-quantitative with the potential to be extended to the formation of other biomass-derived carbonaceous materials.

Direct methane oxidation over Pt-modified nitrogen-doped carbons.

Nitrogen-doped carbons derived from biomass precursors were modified with Pt(2+) and successfully tested as solid catalysts in the direct oxidation of methane in fuming sulfuric acid. Remarkably, the catalytic performance was found to be substantially better than the Pt-modified Covalent Triazine Framework (CTF) system previously reported, although deactivation is more pronounced for the biomass derived catalyst supports.

Carbohydrate-derived hydrothermal carbons: a thorough characterization study.

Hydrothermal carbonization (HTC) is an aqueous-phase route to produce carbon materials using biomass or biomass-derived precursors. In this paper, a comprehensive physicochemical and textural characterization of HTC materials obtained using four different precursors, namely, xylose, glucose, sucrose, and starch, is presented. The development of porosity in the prepared HTC materials as a function of thermal treatment (under an inert atmosphere) was specifically monitored using N(2) and CO(2) sorption analysis. The events taking place during the thermal treatment process were studied by a combined thermogravimetric/infrared (TGA-IR) measurement. Interestingly, these inexpensive biomass-derived carbon materials show good selectivity for CO(2) adsorption over N(2) (CO(2)/N(2) selectivity of 20 at 273 K, 1 bar and 1:1 gas composition). Furthermore, the elemental composition, morphologies, degree of structural order, surface charge, and functional groups are also investigated.

Renewable nitrogen-doped hydrothermal carbons derived from microalgae.

Nitrogen-doped carbon materials are synthesized via an effective, sustainable, and green one-step route based on the hydrothermal carbonization of microalgae with high nitrogen content (ca. 11 wt %). The addition of the monosaccharide glucose to the reaction mixture is found to be advantageous, enhancing the fixation of nitrogen in the synthesized carbons, resulting in materials possessing nitrogen content in excess of 7 wt %, and leading to promising reaction yields. Increasing the amount of glucose leads to a higher nitrogen retention in the carbons, which suggests co-condensation of the microalgae and glucose-derived degradation/hydrolysis products via Maillard-type cascade reactions, yielding nitrogen-containing aromatic heterocycles (e.g., pyrroles) as confirmed by several analytical techniques. Increasing the HTC processing temperature leads to a further aromatization of the chemical structure of the HTC carbon and the formation of increasingly more condensed nitrogen-containing functional motifs (i.e., pyridinic and quaternary nitrogen).

Carbon-based ionogels: tuning the properties of the ionic liquid via carbon-ionic liquid interaction.

The behavior of two ionic liquids (ILs), 1-ethyl-3-methylimidazolium dicyanamide [Emim][DCA] and 1-ethyl-3-methylimidazolium triflate [Emim][TfO], in (meso)porous carbonaceous hosts was investigated. Prior to IL incorporation into the host, the carbon matrix was thermally annealed between 180 and 900 °C to control carbon condensation and surface chemistry. The resulting materials have an increasing "graphitic" carbon character with increasing treatment temperature, reflected in a modified behavior of the ILs when impregnated into the carbon host. The two ILs show significant changes in the thermal behavior as measured from differential scanning calorimetry; these changes can be assigned to anion-π interaction between the IL anions and the pore wall surfaces of these flexible carbonaceous support materials.

A sweet killer: mesoporous polysaccharide confined silver nanoparticles for antibacterial applications.

Silver nanoparticles (AgNP) confined within porous starch have been prepared in a simple, green and efficient manner, utilising the nanoporous structure of predominantly mesoporous starch (MS) to act as nanoparticle stabiliser, support and reducing surface. MS/AgNP materials present high surface areas (S(BET) > 150 m(2) g(-1)) and mesopore volumes (V(meso) > 0.45 cm(3) g(-1)). The interaction of the AgNP precursor and forming nanoparticle nuclei with the mesoporous domains of the porous polysaccharide, direct porosity to increasingly narrower and more defined pore size distributions, indicative of a degree of cooperative assembly. Transmission electron microscopy images indicated the presence of spherical AgNP of a size reflective of the porous polysaccharide mesopore diameter (e.g., 5-25 nm), whilst XPS analysis confirmed the metallic Ag(0) state. Materials were prepared at relatively low Ag loadings (<0.18 mmol g(-1)), demonstrating excellent antimicrobial activity in solid and liquid phase testing against Gram negative (E. coli) and positive (S. aureus) model bacteria. The resulting materials are biocompatible and present a useful solid porous carbohydrate-based polymer vehicle to control the AgNP size regime and facilitate transference to a biological environment.

Functional hollow carbon nanospheres by latex templating.

A facile and sustainable synthesis of hollow carbonaceous nanospheres is presented, offering a scalable and multifunctional route to the generation of useful nanocontainers, which critically possess the stability not offered by polymeric equivalents and functionality not afforded by other nanocarbons. Carbonization temperature provides a subtle but elegant mechanism to control structure and thereby hydrophobicity, nanopartitioning, and permeation between the inner and outer space.

Porous carbohydrate-based materials via hard templating.

Among various techniques, the hydrothermal carbonization (HTC) of biomass (either isolated carbohydrates or crude plants) is a promising candidate for the synthesis of novel carbon-based materials with a wide variety of potential applications. In this Minireview, we discuss various synthetic routes towards such porous carbon-based materials or composites through the HTC process, using the nanocasting procedure. We focus on the synthesis of carbon materials with different pore systems and morphologies directed by the presence of various nanostructured inorganic sacrificial templates. This method allows tailoring of the final structure via the tools of colloid and polymer science, leading to selectable material morphology for a wide range of applications.

Pectin-derived porous materials.

Porous forms of pectin, a major industrial waste biomass polysaccharide, have been prepared by aqueous phase expansion routes (S(BET)>200 m(2) g(-1); V(pore)>0.80 cm(3) g(-1)). It was demonstrated that the aqueous phase acidity crucially influenced the properties of the porous pectin form. Preparation route selection allows direction of material textural and morphological properties, thought to be the result of polysaccharide configuration, and methyl ester group hydrolysis, believed to alter the lowest energy accessible metastable polysaccharide state during gel recrystallisation. The resulting low density amorphous powders or mouldable monoliths (rho(powder) approximately 0.20 g cm(-3)/rho(monolith) approximately 0.07 g cm(-3)) can be directly transformed by thermal carbonisation into low density mesoporous carbonaceous materials (e.g. rho approximately 0.27 g cm(-3) (T(p)=550 degrees C)), which possess textural and nanoscale material morphology reflective of the porous pectin precursor employed. Acidic gelation promotes methyl ester groups hydrolysis of the polysaccharide structure, generating carbons with unusual interdigitated rod-like nanoscale morphology. Importantly, the materials presented herein are produced directly from the parent porous pectin material, without the need for additive catalyst (or template) to yield highly mesoporous products (e.g. V(meso) > or = 0.45 cm(3) g(-1); polydispersity (PD)>10 nm), with accessible tuneable functionally rich surfaces. Due to the high mesoporosity (>85%), materials have potential application in chromatography, heterogeneous catalysis and large molecule adsorption strategies.

Supported metal nanoparticles on porous materials. Methods and applications.

Nanoparticles are regarded as a major step forward to achieving the miniaturisation and nanoscaling effects and properties that have been utilised by nature for millions of years. The chemist is no longer observing and describing the behaviour of matter but is now able to manipulate and produce new types of materials with specific desired physicochemical characteristics. Such materials are receiving extensive attention across a broad range of research disciplines. The fusion between nanoparticle and nanoporous materials technology represents one of the most interesting of these rapidly expanding areas. The harnessing of nanoscale activity and selectivity, potentially provides extremely efficient catalytic materials for the production of commodity chemicals, and energy needed for a future sustainable society. In this tutorial review, we present an introduction to the field of supported metal nanoparticles (SMNPs) on porous materials, focusing on their preparation and applications in different areas.

Tuneable porous carbonaceous materials from renewable resources.

Porous carbon materials are ubiquitous with a wide range of technologically important applications, including separation science, heterogeneous catalyst supports, water purification filters, stationary phase materials, as well as the developing future areas of energy generation and storage applications. Hard template routes to ordered mesoporous carbons are well established, but whilst offering different mesoscopic textural phases, the surface of the material is difficult to chemically post-modify and processing is energy, resource and step intensive. The production of carbon materials from biomass (i.e. sugars or polysaccharides) is a relatively new but rapidly expanding research area. In this tutorial review, we compare and contrast recently reported routes to the preparation of porous carbon materials derived from renewable resources, with examples of our previously reported mesoporous polysaccharide-derived "Starbon" carbonaceous material technology.