Effect Of Precursor Composition Research Articles

Effect of precursor composition and heat-treatment on the morphology and physical properties of Ag nanosponges

Nanoporous silver (np-S) was prepared by free corrosion dealloying of a series of Ag–Al thin films containing between 25 and 73 at.% Al. It was found that precursor composition had an important influence on the nanostructures and morphologies of the np-S. In particular the size of the Ag ligaments systematically decreased from 32 to 13 nm as the Al content was increased over the series. In contrast, there was only a weak effect on pore size, which remained in the range 11–15 nm, with the maximum occurring at about 55 at.% Al. There was however a significant increase in the density of the pores as the Al content of the precursor was increased. The electrical resistivity of the np-S increases with the decrease in ligament size, changing from about 3 × 10−8 Ω m for sponges with ligaments of about 32 nm diameter rising to 30 × 10−8 Ω m for the sponge with the 13 nm ligaments. The surface area of the np-S was estimated by the electrochemical capacitance in KNO3 solutions and was estimated to increase by an order of magnitude compared to a smooth Ag surface. There was a systematic change in the optical properties of the sponges, with a trend towards less metallic behaviour as the ligament size decreased and pore density increased. These changes culminated in the sponge prepared from the 73 at.% Al precursor having non-metallic characteristics with regard to visible and near-infrared light. The volume fraction of metal was estimated to be of the order of 40 ± 5%. Prior annealing of the precursor inhibited dealloying.

A Review on the Upgradation of Biomass-derived Hard Carbon Materials

Abstract: Sodium-ion battery is a promising alternative to lithium-ion battery because of its abundant raw material resources, low price, and high specific capacity. Amorphous carbon materials (hard carbon) have micropores and impurities, facilitating the intercalation of sodium ions to form "quasi-metallic sodium," resulting in a high sodium storage capacity and a low sodium storage potential. Consequently, hard carbon is one of the most widely studied negative electrode materials. It can be prepared from biomass by thermochemical conversion and has the advantages of large specific capacity, low cost, good cycling stability, and renewability. This review focuses on the recent advances in biomass-based hard carbon materials. Firstly, the preparation methods of hard carbon, including precursor selection, pretreatment, drying methods, and carbonization processes, are summarized. Secondly, the effects of precursor composition and heteroatom doping structure and properties of hard carbon are examined, and the changes in carbon material pores during the activation process, as well as the selection of optimal drying method, pyrolysis temperature, carbonization temperature, activator dosage, and additive, are discussed. Thirdly, the impact of preparation methods on hard carbon's cost, efficiency, and stability is briefly summarized, and the relevant improvement measures and prospects are proposed. Finally, some insights are provided into preparing highperformance biomass-based anode materials for sodium-ion batteries.

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.

Opening tubular structure polyimide/polyvinyl chloride based carbon nanofibers for supercapacitor

Polyimide (PI) and polyvinyl chloride (PVC) blend electrospun fibers are prepared by electrospinning process. PI/PVC electrospun fibers exhibit a certain degree of phase separation due to the incomplete compatibility of PI and PVC in N, N’-dimethylformamide. PI/PVC based carbon nanofibers with opening tubular structure can be obtained via thermally induced phase separation. The effect of precursor composition on the morphology and pore structure of carbon nanofibers is investigated by theoretical calculation and structural analysis. The relationship between pore structure and electrochemical performance of carbon nanofibers is studied significantly. Opening tubular structure carbon nanofibers derived from PI: PVC (mass ratio = 1: 1) electrospun fibers show suitable average pore diameter (5.12 nm), high BET specific surface area (1127.1 m2∙g−1) and large total pore capacity (0.65 cm3∙g−1). And opening tubular structure carbon fibers as electrodes in ionic liquid electrolyte exhibits a wide electrochemical stability window (3.5 V), high energy density (30.1 Wh∙kg−1), good power density (2685.5 W∙kg−1) and low internal resistance (2.1 Ω).

Integrated Three-Dimensional Carbon Nanopolyhedron/Metal Sulfides: An Efficient Electrocatalyst Toward Oxygen Reduction Reaction

Carbon-based materials hybridized with metal sulfides have gained growing attention as catalytic materials for oxygen reduction reaction (ORR) due to their synergistic effects in terms of richer structural features and higher electrochemical activities. Here, a series of Zn/Co/Fe-based metal-organic frameworks (MOFs) as the precursors, which can be adopted as efficient ORR catalysts, were synthesized through a sulfuration–calcination treatment. The effects of precursor composition, heteroatom doping, and pyrolysis temperature on the structure and electrochemical performance of the catalysts were discussed in detail. It is found that well-grown carbon nanotubes (CNTs) on the surface of graphitic carbon matrix are formed under the synergy effect of trimetallic-based species during pyrolysis. Benefiting from the three-dimensional unique structure with appropriate dopants and high porosity, the catalyst derived from the optimized Zn/Co/Fe-MOFs achieves a half-wave potential of 0.87 V in an alkaline medium for ORR, which is comparable with commercial electrocatalysts. In addition, an outstanding ORR durability of the proposed catalyst in alkaline media was also demonstrated. This work highlights the potential to rationally design and fabricate high-performance ORR catalysts for commercialization.

Ambient Inkjet‐Printed High‐Efficiency Perovskite Solar Cells: Manipulating the Spreading and Crystallization Behaviors of Picoliter Perovskite Droplets

Drop‐on‐demand inkjet‐printing has the advantages of high cost‐effectiveness and powerful patterning ability, which can be a promising technique for perovskite pattern deposition. However, by far most of the reported works using inkjet‐printing for perovskite films fabrication are printing solvent‐rich wet precursor layers on the high‐temperature meso‐TiO2 substrate, and subsequently require a vacuum‐assisted thermal annealing process to enhance the crystallization of perovskite precursor, which largely elevates fabrication cost and process complexity. Herein, a heat‐assisted inkjet‐printing process is developed to directly print compact and uniform crystalline perovskite films on the planar PEDOT:PSS substrate under ambient condition. The effects of precursor composition, printing temperature, solvent system, and, especially, the printing parameters on the final morphology and microstructure of the printed perovskite films are systematically studied for the first time and the related crystal growth models are revealed, which provide a constructive guidance for the future studies on ambient inkjet‐printed perovskite films and devices. Based on these studies, a champion power conversion efficiency (PCE) of 16.6% for the ambient printed PSC devices is achieved. This work provides a reliable and cost‐effective approach for the scalable fabrication of perovskite films with a low material consumption.

Achievements and prospects for the synthesis of poly(meth)acrylimide foams. Stage of the thermal imidisation of polymer precursors

The review summarises the trends in the development of research on the synthesis of polymethacrylimides (PMIs) and polyacrylimides by the method of intramolecular thermal imidisation of (meth)acrylic polymers. Along with the widely used industry variant of PMI foam of the ‘Rohacell’ series based on bulk copolymers of methacrylonitrile and methacrylic acid, intensive research on alternative variants began after 2005. This review describes the main and side reactions when using polymer precursors of different structures as well as the effect of precursor composition and structure on the properties of the resulting poly(meth)acrylimides. It has been shown that the achievements of the last 15 years provide a basis for reducing the cost of poly(meth)acrylimides which will significantly expand the areas and scale of their application.

Effects of precursor composition on morphology and microstructure of hybrid organic–inorganic perovskite solar cells

The effects of compositions on the crystalline structures, microstructures and optical characteristics of perovskite CH3NH3PbI3 films were investigated via varying the molar ratios of CH3NH3I (MAI) to PbI2 in the precursor solutions. As the amounts of MAI were increased in the precursor solution, the formation of CH3NH3PbI3 was facilitated, and the grain sizes as well as absorbance of the resulting films were increased. The enlarged grain of the prepared films effectively suppressed the carrier recombination at grain boundary and improved the electrical performance of the fabricated solar cells. The analysis of diode parameters also revealed that the additional shunt path was suppressed. On the other hand, once the molar ratio of MAI to PbI2 was further increased, the roughness of film surface was increased and caused the carrier recombination between absorber layers and hole-transport layers, thereby resulting in a dramatic decrease in conversion efficiency. This investigation indicated that controlling the compositions in the precursors of CH3NH3PbI3 films is crucial to improve the photovoltaic properties of perovskite solar cells.

Effects of precursor composition used in solution precursor plasma spray on the properties of ZnO coatings for CO2 and UV light sensing

The potential of finely-structured zinc oxide (ZnO) coatings developed via solution precursor plasma spraying (SPPS) as CO2 gas and UV light sensor was explored in this work. The coatings were deposited on stainless steel substrates using aqueous solutions of zinc nitrate and zinc acetate as precursors. The coatings' microstructures were studied in relation to the solution precursors used. Relatively porous coatings were obtained when using acetate as starting precursor compared to the coatings from the nitrate precursor. This was attributed to the different chemical routes of ZnO formation for each precursor droplet upon contact with plasma jet. Phase analysis confirmed the formation of polycrystalline ZnO having wurtzite structure from both precursors. The sprayed ZnO coatings showed good sensitivity and recovery towards UV light. Moreover, the coatings were sensitive towards carbon dioxide (CO2) analyte gas but did not show any good recovery which was attributed to the microstructure of the coatings. These results showed the feasibility of SPPS process for the fabrication of finely-structured ZnO coatings as sensors of CO2 gas and UV light.

Precursor effects on methylamine gas-induced CH3NH3PbI3 films for stable carbon-based perovskite solar cells

Carbon-based perovskite solar cells (PSCs) without hole transport material have attracted much attention due to their high stability. However, their power conversion efficiency (PCE) is still low because of the lack of suitable perovskite deposition methods. In this work, a facile solid-gas reaction method was explored to prepare high quality perovskite and the effects of precursor composition (PbI2, PbI2 + HI, HPbI3 and PbI2 + NH4I) on the CH3NH2 (MA) gas-induced perovskite were systematically investigated. The lack of H+/I− and/or HI suppressed the conversion of PbI2 precursor to MAPbI3, while rapid and complete conversion was achieved for (PbI2 + HI), HPbI3 and (PbI2 + NH4I) precursors. Compared with HPbI3 precursor, the presence of H2O molecules in (PbI2 + HI) precursor lowered the perovskite crystallinity, while the release of NH3 from (PbI2 + NH4I) precursor slower the interaction of MA molecules with MAPbI3 for achieving the highest quality MAPbI3 layer. The application of an anti-solvent treatment during precursor deposition further improved the quality of HPbI3 and (PbI2 + NH4I)-processed perovskite layers, which as a result, significantly promoted the photovoltaic performance of C-PSCs. Both devices exhibited considerably high stability, especially for the (PbI2 + NH4I)-processed C-PSCs, who did not show any PCE degradation after storage in air atmosphere at room temperature for 120 days.

The Effect of Precursor Composition on the Structural Properties of Nanocrystalline Diamond Films.

Nanocrystalline diamond (NCD) films were grown by hot filament CVD and the precursor composition dependence of the structural properties was examined. Films grown at 1 and 2 CH4 Vol% were found to be NCD layers with grain sizes of ~23-25 nm while films grown at 3-5 Vol% were identified as the mixtures of microcrystalline diamond and graphitic phase. The sp2/sp3 bonded carbon ratio in the grown films increased as the CH4 content increased up to 3 Vol% and then decreased beyond 4 Vol%. Microstructure and deposition rate were also found to be affected by the precursor composition and the NCD film grown at 1 CH4 Vol% showed a very dense microstructure and the highest deposition rate of ~3 nm/min.

Synthesis of CIS Quantum Dots in Low-Temperature Regime: Effects of Precursor Composition and Temperature Ramps

Copper Indium Sulfide (CIS) based quantum dots (QDs) have strong potential for future large-scale applications in photovoltaic, display, and optoelectronic sectors, partly due to their minimal toxicity. CIS QDs are usually grown at temperatures over 200 °C. In this work, we present a gram-scale, noninjection synthesis of CIS-based QDs in a low temperature regime and report, through systematic analyses, on the influence of temperature ramping profiles and precursor compositions on the properties of core CIS and core/shell CIS/ZnS QDs. It is established that the temperature ramp method is as important as the peak temperature itself. Nonabrupt temperature ramping results in core CIS QDs with more ligand coverage and fewer defects, and makes ZnS overgrowth possible even with lower Zn:S molar ratios. Precursor level molar ratios of 1:2 for Cu:In and 8:1 for Zn:S resulted in improved efficiency in CIS and CIS/ZnS QDs with strong and long-lived emissions in the 85–245 ns range. Implementing a dropwise addition of the ZnS precursor leads to prolonged QD extraction and shorter emission wavelengths. The different processes showed a wide range of tunability in the visible-to-IR range along with intense photoluminescence. The ZnS shell growth dependence on temperature ramping mode is explained through a mechanism for sulfur consumption, from the core or from the ligands’ thiol groups. The low temperature regime processes, tunability for wide range of emissions, and identified pathways for long-lived emissions make these less-toxic, CIS-based QDs amenable to large area, scaled-up processing for device applications.

Effects of precursor composition and mode of crosslinking on mechanical properties of graphene oxide reinforced composite hydrogels

Graphene oxide (GO) is increasingly investigated as a reinforcing nanofiller for various hydrogels for biomedical applications for its superior mechanical strength. However, the reinforcing mechanism of GO in different hydrogel conditions has not been extensively explored and elucidated to date. Herein, we systematically examine the effects of various types of precursor molecules (monomers vs. macromers) as well as mode of GO incorporation (physical vs. covalent) on the mechanical properties of resulting composite hydrogels. Two hydrogel types, (1) polyacrylamide hydrogels with varying concentrations of acrylamide monomers and (2) poly(ethylene glycol) (PEG) hydrogels with varying molecular weights of PEG macromers, are used as model systems. In addition, incorporation of GO is also controlled by using either unmodified GO or methacrylic GO (MGO) which allows for covalent incorporation. The results in this study demonstrate that the interaction between GO and the surrounding network and its effect on the mechanical properties (i.e. rigidity and toughness) of composite hydrogels are highly dependent on both the type and concentration of precursors and the mode of crosslinking. We expect this study will provide an important guideline for future research efforts on controlling the mechanical properties of GO-based composite hydrogels.

In situ observation on particle formation process via single droplet drying apparatus: Effects of precursor composition on particle morphology

ABSTRACTEudragit® RS 30D/silica composite precursor containing either Rhodamine B or sucrose as model drug was dried in a single droplet drying apparatus. Microparticles with distinct core–shell structure were produced by one-step drying for all compositions, while Rhodamine B showed uneven distribution in core and shell regions. At 5% (w/w) loading, it influenced shell formation process by producing dispersible initial shell and altered particle surface morphology into wrinkling appearance, while similar effects were not observed for sucrose. Decreasing the loading to 0.017% reduced the influence. The observations might be attributed to the properties of Rhodamine B, which affect its migration behavior during drying.

Magnesium-vapor reduction of niobium oxide compounds

The effect of precursor composition and reduction conditions on the characteristics of niobium powders obtained by magnesium reduction were studied. The hypothesis of the possible increase in the specific surface area of the powders by a large factor by using complex oxides as precursors was confirmed. With magnesium niobate Mg4Nb2O9 as the precursor, mesoporous powders, unprecedented in the world, with a specific surface area of up to150 m2 g–1 and an average pore size of 4.6 nm were produced.

Resolving the phase structure of nonstoichiometric Co2FeGa Heusler nanoparticles

Heusler nanocrystals, i.e., Heusler compounds with dimensions in nanometer range are promising materials for next-generation spin-related devices. Recently, we have developed a chemical approach to prepare L21 ordered Heusler nanoparticles and characterized their size-related structure and magnetic properties. In this work, effect of precursor composition is investigated in terms of their importance in controlling the phase structure of Co2FeGa nanoparticles. The formation of the L21 ordered Co2FeGa phase is evidenced by combining X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy and Mössbauer spectroscopy measurements. From XRD, precursor compositions of low Co and high Fe are associated with decreasing amounts and even disappearance of fcc Co and fcc Fe impurities. We also find that, even though the XRD data indicate only pure Co2FeGa phase in sample with excess Fe, EXAFS and Mössbauer spectroscopy data unambiguously reveal the co-existence of bcc Fe with Co2FeGa main phase.

Preparation and Characterization of Cu(In,Ga)Se2Thin Films by Selenization of Cu0.8Ga0.2and In2Se3Precursor Films

Se-containing precursor films with two different compositions were prepared by magnetron sputtering from and targets, and then were selenized using Se vapor. The effects of precursor composition and selenization temperature on the film properties were investigated. The results show that Se phase plays a critical role in film growth and electrical properties of CIGS films. The Cu-rich films exhibit different surface morphology and better crystallinity, as compared to the Cu-poor films. All the CIGS films exhibit p-type conductivity. The resistivity of the Cu-rich films is about three orders of magnitude lower than that of the Cu-poor films, which is attributed to the presence of p-type highly conductive Se phase.

Assembly of magnetic microcomposites from low pH precursors using a novel micro-fluidic-jet-spray-dryer

Spray drying is a convenient method to produce particles in high yields within a short period of time. The benefits of this technique include efficient uses of energy and solvent, and being a virtually waste-free process that allows for scale-up. A major drawback in conventional spray drying is the polydispersity of the produced particles. Herein, a specially designed spray dryer called micro-fluidic-jet-spray-drier (MFJSD) coupled with a micro-fluidic-aerosol-nozzle (MFAN) could generate droplets in a single trajectory pattern, to produce monodisperse particles. The drying temperature could vary from <90 °C to 300 °C to accommodate heat sensitive materials if necessary. For the first time we investigated the use of MFJSD to generate uniform magnetic microcomposites, specifically focusing on the effects of precursor composition, droplet size, and secondary heat treatment on the final properties of the particles. The presence of silica nanoparticles in the precursor was demonstrated to directly affect the morphology of the particles. Precursor containing silica nanoparticles generated particles with bowl-like shapes due to slower redistribution of solutes to support the particle skeleton during drying. In the absence of silica nanoparticles, the particles were almost perfectly spherical albeit with dimpled surfaces. After being subjected to calcination after drying, iron oxide crystals were found on the particle surfaces accounting for the overall magnetic property of the microcomposites, with lower magnetisation observed for particles containing higher amount of silica.

Fabrication of composite microcapsules by drop-on-demand inkjet: Effect of precursor composition on the process limits

The feasibility of using drop-on-demand inkjet technology for the fabrication of calcium alginate hydrogel microcapsules containing dispersed sub-micron solid particles (TiO 2 photocatalyst) was demonstrated. The influence of the printed solution viscosity on the micro-droplet size has been investigated and a study of the effect of solids fraction in the suspension on its printability was carried out. It was found that solutions with viscosities of up to 28 mPa s and solids content of up to 7.8 vol% can be reproducibly printed, resulting in droplets ranging from 45 to 105 μm depending on the inkjet operating conditions. In order to ensure stable and reproducible droplet formation, a pressure difference ranging from −200 to −1800 Pa had to be maintained in the nozzle. A uniform distribution of dispersed solids in the resulting microcapsules was achieved by adjusting pH and viscosity. The relationship between the printhead operating pressure, the fluid viscosity, the solids loading and the final size of the obtained microcapsules was established, allowing rapid prototyping of artificial cell-like structures with internal solid inclusions by the inkjet method.

The effect of precursor composition and sintering additives on the formation of β-sialon from Al, Si and Al 2O 3 powders

A study was performed to investigate the effect of increasing the Al or Al 2O 3 precursor content, above the stoichiometric amount, on the formation of β-sialon by pressureless sintering of Al, Si and Al 2O 3 powders in flowing nitrogen gas. The effect of adding Y 2O 3 or Fe to the precursor mixture, on the β-sialon formation, was also studied. The phase morphology and yield produced by the various compositions were examined using X-ray diffraction (XRD). Additional Al 2O 3 decreases the β-sialon phase yield and results in a greater amount of Al 2O 3 in the final sintered material. Additional Al improved the conversion to β-sialon up to a maximum of 4 wt% Al beyond which the β-sialon:15R sialon ratio in the sintered material decreases. 1 wt% Y 2O 3 was determined to be the optimum sintering additive content, as yttrium aluminium garnet (YAG) was found to be present in materials formed from higher Y 2O 3 containing precursors. The presence of Fe in the precursor powder retards the formation of β-sialon by preferentially forming Fe silicides at low temperatures, thus depleting the reaction system of elemental Si, favouring the formation of 15R sialon.