Precursor Composition Research Articles

The flavour of grape colour: anthocyanin content tunes aroma precursor composition by altering the berry microenvironment.

Anthocyanin-less (white) instead of black/red (coloured) fruits develop in grapevine cultivars without functional VviMYBA1 and VviMYBA2 genes, which conditions the colour of wines that can be produced. To evaluate whether this genetic variation has additional consequences on fruit ripening and composition, we performed microenvironment, transcriptomics and metabolomics comparisons of developing grapes between near-isogenic white- and black-berried somatic variants of Garnacha and Tempranillo cultivars. Berry temperature was up to 3.5ºC lower in white- compared to black-berried Tempranillo. An RNA-seq study combined with targeted and untargeted metabolomics revealed that ripening fruits of white-berried variants were characterized by the upregulation of photosynthesis and other light-responsive genes and their higher accumulation of specific terpene aroma precursors, fatty acid-derived aldehyde volatiles and phenylpropanoid precursor amino acids. MYBA1-MYBA2 function proved essential for flavonol trihydroxylation in black-berried somatic variants, which were also characterized by enhanced pathogen defence gene expression in berry skin and increased accumulation of C6-derived alcohol and ester volatiles and GABA. Collectively, our results indicate that anthocyanin depletion entails side effects on grape composition by altering the berry internal microenvironment and the partition of the phenylpropanoid pathway. These findings show how fruit colour can condition other fruit features, such as flavour potential and stress homeostasis.

A Semitransparent Silver–Bismuth Iodide Solar Cell with Voc above 0.8 V for Indoor Photovoltaics

Because the toxicity of lead (Pb) remains a potential threat to the commercialization of perovskite solar cells, silver–bismuth halides such as AgBiI4, AgBi2I7, Ag2BiI5, and Ag3BiI6 with band gaps of 1.8–1.9 eV and strong absorption are considered to be promising alternatives to Pb-based perovskites, not only for outdoor (1 Sun) but also for indoor photovoltaics because their band gap matches best with the indoor artificial light spectrum. To date, almost all studies have focused on improving the power conversion efficiency (PCE) under 1 Sun using thick absorber films made on mesoporous electron-transport layers. However, in this work, we aimed at developing optically semitransparent Ag2BiI5 solar cells that can be used indoor or on windows. We studied the effect of the precursor composition on the phase evolution, energy band levels, film morphology, and, eventually, solar cell performance. Through compositional engineering and thickness optimization, we accomplished the fabrication of a thin (∼100 nm Ag2BiI5) and semitransparent Ag2BiI5 solar cell that works with a power conversion efficiency of ∼2%, which is greater than many reported with thick and opaque films and slightly lower than the best recorded for Ag2BiI5. The cell shows an open-circuit voltage (Voc) of over 800 mV, the highest reported for Ag2BI5. More interestingly, while a thicker/opaque cell was found to work with a PCE of 5.0% under 1000 lx, the semitransparent cell shows a reasonable performance of 3.3% under the same light intensity.

A Two-Step Route to SiO2 Nanofiber-Reinforced Aerogel Composites with Lightweight and High Temperature Resistance for Thermal Insulation

Fiber reinforcement is an effective method to improve the inherent brittleness of conventional aerogels. However, high-density and complex preparation processes plague fiber-reinforced aerogel composites (FACs). For example, they are usually prepared using costly supercritical drying, freeze-drying, and time-consuming atmospheric drying, limiting the further development in applications and technologies of the material. Herein, a straightforward route to FACs is proposed. Namely, electrostatically spun nanofibers are used as reinforcement materials for aerogels. The nanofiber composite silica gel precursors are produced using chemical swelling and sol–gel techniques. Direct calcination is then used to prepare FACs with distinct nanoporous structures. As a result, FACs have a thermal conductivity as low as 0.029 W m–1 K–1 at room temperature, a high porosity of up to 99.55%, and excellent temperature resistance, maintaining a stable porous structure even at 1400 °C. Therefore, FACs have greater potential for thermal insulation applications. The route described in this study will contribute to the opening of a pathway for the simple preparation of FACs with ultralow density and high temperature resistance, thereby promoting the application and development of nanofiber-reinforced aerogel materials.

Geopolymer mortar with flash-calcined sediments cured under ambient conditions

This paper focuses on the development of a geopolymer (GP) mortar that can be cured under ambient conditions using a combination of flash-calcined dredged sediment (FCS), Metakaolin (MK), granulated blast furnace slag (GBFS), and potassium silicate (K2SiO2) as an alkaline reagent (AR). The goal of this research is to reduce carbon emissions from traditional clinker-based materials by using valorized materials in the formulation of the geopolymer binder. The study investigates the effect of the alkaline reagent-to-binder ratio (AR/Bmm) and precursor composition on the mechanical and durability properties of the GP mortar. The results indicate that the lowest AR/B ratio and formulations with higher GBFS percentages have better performance. Porosity test and microstructural analysis tests such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) was conducted to ensure the stability of the GP formulations exposed to a sulfuric acid attack test, while nuclear magnetic resonance (NMR) tests validate the Q4(1Si, 3Al) network and their assigned Si/Al ratio. The leaching examination concludes that the GP design is not classified as hazardous materials.

Fabrication of Glass‐Ceramic 3D Micro‐Optics by Combining Laser Lithography and Calcination

AbstractThis perspective is an overview of a recent direction in optical 3D printing, where polymerization of crosslinkable materials and nanomaterial fillers can be guided to the final structures and new composites via high temperature annealing (HTA). Defining 3D nano/micro‐structures by ultrafast laser direct writing and tailoring their precursor composition with subsequent tunability of the final properties during 750–1500 °C HTA step takes place at the large surface‐to‐volume ratio conditions favoring efficient pyrolysis and calcination, which are required for exchange of chemical materials/gases between glass/ceramic phase and surrounding. Previously, unexplored inorganic material formation conditions in terms of fast thermal quenching, composition mixing and surface tension guided formation can be harnessed by glass making for creation of new materials endowed with preferable technical properties. An immediate application perspective for a high durability, integrated, and active 3D micro‐optics is foreseen.

Workability, autogenous shrinkage and microstructure of alkali-activated slag/fly ash slurries: Effect of precursor composition and sodium silicate modulus

The alkali-activated slag/fly ash system is used as a cementitious material to instead of ordinary Portland cement and has good application prospects for recycling various solid wastes and low carbonization in the construction field. In this work, we aim to reveal the effects of changes in precursor composition and sodium silicate modulus in alkali-activated slag/fly ash slurry on strength and autogenous shrinkage, and make a comparative study about workability, autogenous shrinkage and microstructure. The test results showed that the engineering performance of alkali-activated cementitious materials mainly depended on the constituent materials and their ratios. With the increase of fly ash content, the slump was enhanced, the setting time was extended, the strength was slightly reduced, and the autogenous shrinkage was significantly mitigated. For the reference slurry (n = 1.2), the 28 d autogenous shrinkage value of S10F0 was 6064.28 μm/m, the 28 d autogenous shrinkage value of S9F1 was 1516.67 μm/m, and the shrinkage value was reduced by 75%. And with the increase of sodium silicate modulus, the slump was enhanced, the setting time was increased, the early strength was reduced, the later strength developed faster, and the influence on the sample autogenous shrinkage was smaller. The reaction products were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). With the increase of fly ash content, the calcite phase was observed in the reacted products, the flocculent components and many unreacted fly ash spheres in diameter were observed, and there were many micro-pores in the hardened solid particles. Combined with autogenous shrinkage and mercury intrusion porosimetry analysis, it could be discovered that when the modulus of sodium silicate increased, the capillary pore volume increased, and the total porosity and pore size decreased significantly, when the modulus of the activator increased from 1.2 to 2.0, the porosity decreased by 44.36%. making the autogenous shrinkage and strength increase. When the activator modulus was 1.2 and the content of fly ash was more than 30%, the content of NaOH in the solution was higher, which accelerated the early reaction rate, resulting in more pores inside the slurry, larger pore size, smaller capillary pore volume, and expansion of alkali-activated material slurry volume. This study may shed valuable insights to the improvement of autogenous shrinkage by adjusting precursor composition and sodium silicate modulus.

Influence of the precursor composition on the resulting absorber properties and defect concentration in Cu2ZnSnSe4 absorbers

In this paper the influence of composition variations during the growth of Cu2ZnSnSe4 (CZTSe) layers on defect concentrations and final absorber properties is analyzed. The samples are prepared from sputtered metallic and alloyed Zn/Cu–Sn/(Sn)/Zn precursors. The variation of sputtered Sn content facilitates different forms for the embedded Sn (Cu3Sn, Cu6Sn5, elemental Sn). The predominating formation reaction during the subsequent annealing is tuned by the ratio of the alloys and the overall chemical composition in the precursor. During the high temperature stage of CZTSe formation the layer undergoes an in-process composition shift (Sn content variation), after which the final absorber composition is reached. As all absorbers are reaching a comparable end composition, in this paper the influence of the different precursor compositions and corresponding reaction pathways on the resulting defects and optoelectronic properties of the absorbers are addressed. Spectroscopic investigations were used to extract the defect configuration of the absorbers. The results are complemented with device performance measurements. Preferable precursor compositions leading to lower defect concentration and improved photoluminescence quantum-yield is identified. The obtained Urbach energy and VOC deficit are among the most promising results measured in our laboratories.

An insight into the role of the metal precursor and its concentration in the Spray Flame Synthesis (SFS) of FexOy@C nanoparticles for Fischer–Tropsch Synthesis (FTS) application

The effect of metal precursor composition on the synthesis of iron oxide nanoparticles in a spray flame reactor was studied. Three compounds, iron nitrate, iron acetylacetonate, and ferrocene, were tested at 0.1 M and 0.2 M concentrations. Variation of the iron precursor showed significant effects in crystallinity, crystallite size, and iron oxides content; the ferrocene produced the highest hematite content, and the nitrate showed the greatest magnetite contribution. Besides, all the particle characteristics changed when the concentration was duplicated, which was found mainly determined by the positive influence of the iron catalytic effect on the flame energy. FTS catalysts were prepared by the FexOy@C samples carburization, obtaining different active phase (χ-Fe5C2) contents from 52% to 92% and depending on the iron precursor employed. Catalysts exhibited good performances for FTS with CO conversions up to 70% and selectivity to C5+ products from 59% to 71%.

Synthesis of Polytitanocarbosilane and Preparation of Si–C–Ti–B Fibers

Continuous SiC fiber is a kind of high–performance ceramic fiber that combines many advantages, such as high strength, high modulus, high hardness and low density. It has excellent mechanical properties, high–temperature and oxidation resistance, which could be applied as essential reinforcement in advanced ceramic matrix composites (CMCs) in the fields of aerospace and advanced weaponry. Melt–spinnable polytitanocarbosilane (PTCS) is an important precursor, which can be used to prepare continuous SiC fibers through a precursor–derived method. In this work, low–softening–point polycarbosilane (LPCS) and tetrabutyl titanate were used to prepare polytitanocarbosilane with a ceramic yield of 67.5 wt% at 1000 °C. FT–IR, TGA, GPC, 1H NMR, 29Si NMR, and elemental analysis were used to analyze the composition and structure of the PTCS precursor. Finally, Si–C–Ti–B fibers with an average tensile strength of 1.93 GPa were successfully prepared by melt spinning, pre–oxidation, pyrolysis, and high–temperature sintering of the PTCS precursor. The strength retention rates were 71.5% and 79.8% after heat treatment at 1900 °C and 2000 °C under an argon atmosphere for 1 h, respectively. The strength retention rates of Si–C–Ti–B fibers are higher than those of commercial Hi–Nicalon fibers, Tyranno ZMI fibers and Hi–Nicalon S fibers. This work can lay a theoretical foundation and technical support for developing high-performance SiC ceramic fibers containing titanium and their ceramic matrix composites.

Injectable Antioxidant and Oxygen-Releasing Lignin Composites to Promote Wound Healing

The application of engineered biomaterials for wound healing has been pursued since the beginning of tissue engineering. Here, we attempt to apply functionalized lignin to confer antioxidation to the extracellular microenvironments of wounds and to deliver oxygen from the dissociation of calcium peroxide for enhanced vascularization and healing responses without eliciting inflammatory responses. Elemental analysis showed 17 times higher quantity of calcium in the oxygen-releasing nanoparticles. Lignin composites including the oxygen-generating nanoparticles released around 700 ppm oxygen per day at least for 7 days. By modulating the concentration of the methacrylated gelatin, we were able to maintain the injectability of lignin composite precursors and the stiffness of lignin composites suitable for wound healing after photo-cross-linking. In situ formation of lignin composites with the oxygen-releasing nanoparticles enhanced the rate of tissue granulation, the formation of blood vessels, and the infiltration of α-smooth muscle actin+ fibroblasts into the wounds over 7 days. At 28 days after surgery, the lignin composite with oxygen-generating nanoparticles remodeled the collagen architecture, resembling the basket-weave pattern of unwounded collagen with minimal scar formation. Thus, our study shows the potential of functionalized lignin for wound-healing applications requiring balanced antioxidation and controlled release of oxygen for enhanced tissue granulation, vascularization, and maturation of collagen.

Performance and optimization design of high-strength geopolymer cold-bonded lightweight aggregate: Effect of silica fume

Geopolymer cold-bonded aggregate (GCBA) is a new artificial aggregate manufactured by agglomeration of aluminosilicate precursor powder hardened by alkali activation. This paper presents a multi-objective material design procedure for GCBA based on the simplex centroid design method, using metakaolin (MK), fly ash (FA), and silica fume (SF) as the ternary precursor materials. Based on the test data from 10 groups of GCBAs with designed compositions and response surface models established thereby, the optimal composition domain of the precursors was determined and experimentally validated. The effect of the precursor composition, especially the content of SF, on the performance of GCBA was evaluated. Results showed that in the optimal composition domain of the precursor (36–48 wt% of MK, 33–46 wt% of FA, and 15–24 wt% of SF), the developed GCBA achieved the given high-performance targets of bulk crushing strength higher than 21.0 MPa, the loose bulk density less than 1200 kg/m3, and water absorption less than 10%. SF content (Si/Al ratio) has a great influence on the performance of GCBA: a suitable amount of the incorporated SF (Si/Al<1.7) promoted the formation of K-A-S-H gels in GCBA, leading to an increase in strength and density, and a decrease in water absorption; while excessive SF (Si/Al>1.7) induced a self-foaming reaction, resulting in a porous microstructure and reduced strength and density.

A Novel Hydro-Thermal Synthesis of Nano-Structured Molybdenum-Iron Intermetallic Alloys at Relatively Low Temperatures

Nano-structured Mo/Fe intermetallics were synthesized from precursors that contained 72/28% and 30/70% molar ratios of Mo/Fe, which were given as precursors A and B, respectively. These precursors were prepared from the co-precipitation of aqueous hot solutions of ammonium heptamolybdate tetrahydrate (AHM) and ferrous oxalate. The dry precipitates were thermally treated using TG-DSC to follow up their behavior during roasting, in an Ar atmosphere of up to 700 °C (10° K/min). The TG profile showed that 32.5% and 55.5% weight losses were measured from the thermal treatment of precursors A and B, respectively. The DSC heat flow profile showed the presence of endothermic peaks at 196.9 and 392.5-400 °C during the thermal decomposition of the AHM and ferrous oxalate, respectively. The exothermic peak that was detected at 427.5 °C was due to the production of nano-sized iron molybdate [Fe2(MoO4)3]. An XRD phase analysis indicated that iron molybdate was the only phase that was identified in precursor A, while iron molybdate and Fe2O3 were produced in precursor B. Compacts were made from the pressing of the nano-sized precursors, which were roasted at 500 °C for 3 h. The roasted compacts were isothermally reduced in H2 at 600-850 °C using microbalance, and the O2 weight loss that resulted from the reduction reactions was continuously recorded as a function of time. The influence of the reduction temperature and precursor composition on the reduction behavior of the precursors was studied and discussed. The partially and completely reduced compacts were examined with X-ray powder diffraction (XRD), a reflected light microscope (RLM), and a scanning electron microscope (SEM-EDS). Depending on the precursor composition, the reduction reactions of the [Fe2(MoO4)3] and Fe2O3 proceeded through the formation of intermediate lower oxides, prior to the production of the MO/Fe intermetallic alloys. Based on the intermediate phases that were identified and characterized at the early, intermediate, and final reduction degrees, chemical reaction equations were given to follow up the formation of the MoFe and MoFe3 intermetallic alloys. The mechanism of the reduction reactions was predicted from the apparent activation energy values (Ea) that were computed at the different reduction degrees. Moreover, mathematical formulations that were derived from the gas-solid reaction model were applied to confirm the reduction mechanisms, which were greatly dependent on the precursor composition and reduction temperature. However, it can be reported that nano-structured MoFe and MoFe3 intermetallic alloys can be successfully fabricated via a gas-solid reaction technique at lower temperatures.

Cold Atmospheric Plasma-Assisted Direct Deposition of Polypyrrole-Ag Nanocomposites for Flexible Electronic Sensors

Conductive polymers and their composite materials have attracted considerable interest due to their potential applications in sensors, actuators, drug delivery systems, and energy storage devices. Despite their wide range of applications, many challenges remain primarily with respect to the complex synthesis and time-consuming manufacturing steps that are often required in the fabrication process of various devices with conductive polymers. Here, we demonstrate the novel use of cold atmospheric plasma (CAP)-assisted deposition technologies as a solvent-free and scalable approach for in situ polymerization and direct deposition of conductive polypyrrole-silver (PPy-Ag) nanocomposites onto the desired substrates under atmospheric conditions. In this study, a systematic approach with different precursor composition mixtures containing pyrrole as the monomer and AgNO3 as the photoinitiator was investigated to assess the effect of precursor composition on the final chemical, electrical, and mechanical properties of the PPy-Ag nanocomposite thin-film coatings which were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and cyclic bending tests. The characterizations indicated the possibility of fabricating PPy-Ag nanocomposite films with tunable degrees of polymerization and Ag nanoparticle loading by simply varying the percentage of AgNO3 in precursor composition mixtures. Finally, as a proof of concept, the potential use of the PPy-Ag nanocomposite films with different Ag nanoparticle loading percentages was assessed for humidity sensing by measuring their level of change in electrical resistance in the relative humidity range of 12-60%. It is envisioned that the developed CAP-assisted deposition technology can provide a new stepping stone toward scalable additive manufacturing of various functional nanocomposite films for different low-cost and flexible electronic applications.

Pure‐Iodide Wide‐Bandgap Perovskites for High‐Efficiency Solar Cells by Crystallization Control

AbstractWide‐bandgap perovskite is a vital part of perovskite‐based tandem solar cells. Currently, wide‐bandgap perovskites are typically based on mixed‐halide (I/Br) materials, but suffer from photoinduced phase separation. The pure‐iodide formamidine/cesium (FA/Cs) based FAxCs1−xPbI3 perovskites with high Cs content are good candidates, whereas the control of crystallization is challenging due to the complex crystallization kinetics. Here, pure‐iodide FA0.5Cs0.5PbI3 wide‐bandgap perovskite solar cells is reported. As an acidic diammonium salt, methylenediaminium dichloride (MDACl2) is applied as an additive to control the whole crystallization process of perovskite films, including both nucleation and crystal growth. Starting from the solution chemistry, the MDACl2 additive with acidity and strong solvation properties can effectively regulate the chemical composition of perovskite precursor, thus inhibiting the growth of undesired 1D intermediates during the nucleation process. Besides, the incorporation of larger‐sized MDA2+ into the lattice compensates for the tolerance factor and accelerates the ion exchange reaction between FA+ and Cs+ in the crystal growth process. As a result, the crystallinity of the perovskite films is significantly improved, benefitting from the dual function of MDACl2. Finally, the efficiency of hole transport layer‐free carbon electrode‐based wide‐bandgap perovskite solar cells reaches 18.52%, which is the highest reported so far.

Surface and interface mediated magnetism in mesoscopic ceria@carbon core–shell structures

CeO2@C submicron core–shell structure was prepared by a two-step synthesis method, and the ceria shell thickness and its microstructure were precisely controlled by the precursor composition and annealing process. The results show that forming the thin ceria shell by aggregating nanoparticles on the surface of the carbon sphere is more favorable for forming ferromagnetism than merely dispersed ceria nanoparticles. The saturation magnetization increases with decreasing shell thickness, indicating the contributions of surfaces and interfaces to the magnetism. Furthermore, high-temperature reduction results in shell densification and the aggregation of defects at the surface. The spectroscopic and microscopic measurements reveal that in such cases, a continuous defect-rich area with a sub-nanometric thickness, doped with electrons extends over the whole surface of the mesostructure. The magnetic strength difference caused by adjusting the thickness of this defective layer from several nanometers to sub-nanometric width can reach 360 times, suggesting that the magnetization of these mesoscopic systems is related to the presence of these quasi-2D electron-rich regions on the surface. This study shows the applicability of giant orbital magnetism to mesoscopic systems, and the results can also provide a reference for the subsequent synthesis of magnetic materials.

Preparation of robust diphenyl silicone elastomers with enhanced mechanical properties and thermal-aging resistances by using phosphazene as catalyst

The properties and applications of silicone elastomers depended on the molecular structure and composition of polysiloxane precursors, which were the most technologically important silicon-based polymers. Preparation of perfect diphenyl silicone elastomers was challenging due to the unexpected branches formed during the ring-opening copolymerization (ROCP) of phenylcyclosiloxane monomer. In this contribution, diphenyl silicone elastomer precursors with controlled structure were successfully prepared by cyclic trimeric phosphazene base (CTPB) catalyzed ROCP of octamethylcyclotetrasiloxane (D4), octaphenylcyclotetrasiloxane (D48Ph), and 2,4,6,8-tetravinyl-2,4,6,8-tetramethylcyclotetrasiloxane (D4Vi) with high molecular weight up to 551.0 kg/mol and dispersity (Đ) ≤ 2.50. 29Si NMR characterization verified the random microstructures of the resulting diphenyl containing polysiloxanes without chain branching. Moreover, the silica-filled elastomer prepared from poly(dimethylsiloxane-co-vinylmethylsiloxane) (PMVS) and poly(dimethylsiloxane-co-diphenylsiloxane-co-vinylmethylsiloxane) (PMPVS) precursors exhibited very high elasticity, which can be stretched to 1043% with a high tensile strength of 7.7 MPa. Thermal oxidation aging test proved the excellent thermal aging resistance of the phenyl-containing silicone elastomers. This work demonstrated facile method to prepare high quality diphenyl containing polysiloxane precursor toward robust silicone elastomers.

Preliminary Reactivity Test for Precursors of Alkali-Activated Materials

Alkali-activated materials (AAMs) result from the dissolution process and polycondensation of precursors in high pH solutions. This material is considered alternative cement with similar properties and lower environmental impact than Portland cement. However, AAMs are subjected to the same standardization applied to cement-based materials since no formal methods exist to characterize this material and/or the precursor reactivity. Therefore, this work aims to develop a method to characterize the reactivity of the main precursors used to produce AAMs. Hence, the precursors were assessed in two steps after chemical, physical, and mineralogical characterization. The first step evaluated the crystallinity change of the material after the acid attack by mixing 1 g of each material in 100 mL of 1% HF solution for 6 h at ambient temperature. The crystallinity change was evaluated by comparing the X-ray diffraction of the materials before and after the acid attack. The second step involved evaluating the formation of geopolymerization products in the pastes of studied precursors through FTIR test. The pastes were produced with Na2SiO3 and NaOH as activators. After 28 days of curing, the pastes were submitted to a FTIR test for structural analysis. This method was tested evaluating the reactivity of traditional precursors for alkali activation (i.e., silica fume (SF), blast furnace slag (BFS), and metakaolin (MK)), in addition sugarcane bagasse ash mechanically treated (SCBAM) and sugarcane bagasse ash mechanically and heat treated (SCBAMH) since SCBA is a promising precursor for alkali activation. Considering the crystallinity change of precursors (step 01), the formation of geopolymerization products (step 02), and the chemical composition of precursors (preliminary characterization), it could be concluded that: (i) surface area is not relevant to materials with small particle size (&lt;23 µm); (ii) amorphous area is only relevant if the material exhibits the optimal chemical composition; and (iii) the chemical composition is a crucial parameter for alkali activation. In addition, the potential precursors for alkali activation should have a significant amorphous halo and a SiO2/Al2O3 ratio of 2 to 5. Also, it could be concluded that SF and SCBAMH do not exhibit adequate reactivity while BFS, MK, and SCBAM can be classified as reactive precursors.

Understanding SiOC atomic structures via synchrotron X-ray and reactive force field potential studies

Silicon oxycarbide (SiOC) is a unique system that can generate various compositions and microstructures via different polymeric precursors and pyrolysis conditions. However, understanding of the atomic structure evolution, such as cluster formation, phase evolution, and atomic coordination, is lacking. In this study, cluster evolution and atomic coordination for different SiOC ceramics pyrolyzed at 1200 °C and 1500 °C were investigated by high energy X-ray diffraction (HE-XRD) and radial distribution function (RDF) analysis. A new Reactive Force Field (ReaxFF) molecular dynamics modeling approach was developed to understand nanocluster separation and early-stage atomic radial coordination. For the first time, we demonstrate that orthorhombic SiO2 forms and converts to growth resistant amorphous SiO2. Cubic β-SiC also forms at lower temperatures than reported, along with a minor amount of hexagonal SiC that has never been reported. The RDF data support such phase evolution understanding. ReaxFF simulation provides direct data on atomic mixing, elemental separation, and effects of precursor molecular structures and compositions, especially in the early stage of the pyrolysis. The simulated RDF data complement the experimental data, revealing the significant presence of C–H bonds along with Si–O and C–C bonds.

AQUEOUS-PHASE HYDROGENATION OF FURFURAL IN THE PRESENCE OF SUPPORTED METALLIC CATALYSTS OF DIFFERENT TYPES. A REVIEW

Hydrogenation of furfural in the presence of heterogeneous catalysts has recently attracted increased interest as a method for the synthesis of oxygen-containing compounds of various classes based on renewable raw materials. The composition of the catalyst and the conditions of its preparation essentially determine which of the routes of reductive conversions during the hydrogenation of furfural will be predominant. The present review summarizes and analyzes methods for controlling the physicochemical and functional properties of various metal catalysts with an emphasis on Pd-, Ni-, Co, and Cu-containing catalytic compositions, as the most common and practically significant in the hydrogenation of furfural. Many examples show the influence of the nature of the support, the composition of the active metal precursor, and the conditions for the formation of metal nanoparticles on the activity and selectivity of supported catalysts in the reductive conversions of furfural under aqueous-phase hydrogenation conditions. Promising directions of research on the development of methods for the synthesis of efficient catalysts with controlled functional properties in the hydrogenation of furfural are considered. The bibliography includes 127 references.

Design of Multicationic Copper‐Bearing Layered Double Hydroxides for Catalytic Application in Biorefinery

AbstractEthanol has been used as a renewable hydrogen‐donor in the conversion of a lignin model molecule in subcritical conditions. Noble metal‐free porous mixed oxides, obtained by activation of Cu−Ni−Al and Cu−Ni−Fe layered double hydroxide (LDH) precursors, have been used as heterogeneous catalysts for Meerwein‐Ponndorf‐Verley (MPV) hydrogen transfer and further hydrogenation by ethanol dehydrogenation products. Both the Cu/(Cu+Ni) ratio and the nature of the trivalent cation (Al or Fe) affect the activity of the catalysts, as well as the selectivity towards the different steps of the hydrogenation reactions and the cleavage of lignin‐like phenylether bonds. Accounting for the peculiar behaviour of Cu2+ and M(III) cations in the synthesis of LDHs, the coprecipitation of the precursors has been monitored by titration experiments. Structural and textural properties of the catalysts are closely related to the composition of the LDH precursors.