Controlled Pore Size Distribution Research Articles

3D carbonaceous substrates synthesized from melamine sponges for energy storage: Influence of pyrolysis temperature in physicochemical and electrochemical properties

AbstractHigh-energy global requirements have caused a renewed interest in studying and developing new and improved energy storage devices and, precisely, the electrode materials that compose them, which play a fundamental role in determining the device’s performance. Carbon materials are first-class candidates due to their high electrical conductivity, chemical stability, and surface area. Although several carbon materials and their precursors have been studied, melamine sponges stand out for their nitrogen content, allowing them to act as a template and precursor for N-doped, ultralight carbon materials with good mechanical properties and a controlled pore size distribution. This work reports a simple and quick methodology to form ultralight and flexible carbon foam, along with the influence of the pyrolysis temperature on the physicochemical and electrochemical properties of 3D carbonaceous substrates used for energy storage and synthesized from melamine sponges. The substrates exhibit higher 3D porous structure than previously reported materials, with an average pore diameter of 80–90 µm. This morphology, added to the N content, promotes the remarkable electrochemical behavior (MS–950 °C) and cycling stability (MS–1000 °C) of almost 100% of capacitance retention after 10,000 cycles (≈ 60 F/g @1 A/g).

Hierarchically porous electrospun carbon nanofiber for high-rate capacitive deionization electrodes

Capacitive deionization (CDI) is a promising technology that has gained interest for the desalination of brackish water. Hierarchically porous carbons are commonly used as electrodes for CDI due to their high surface areas and controlled pore size distributions that maximize ion adsorption capacity and rate. Electrospinning is an effective way of generating carbon nanofibers with high inter-fiber macroporosity that can be further modified to improve surface area, total pore volume, and pore size distribution. This work describes the use of sacrificial mesopore formers in tandem with a micropore etching technique to induce hierarchical porosity in electrospun fibers. Mesopores are formed via the dissolution of silica nanoparticles that are introduced into the fibers during the electrospinning step. After mesopore formation, micropores are etched into the resulting surface through KOH impregnation and thermal activation. This sequential technique creates a hierarchical network of pores from the inherent macroporosity of the fiber network, to the mesopores, and finally micropores to simultaneously maximize surface area and accessibility. Micropore formation is optimized to maximize specific surface area while maintaining physical integrity of the fibers. The combination of mesopores and micropores enables fast ion adsorption rates and capacity. Carbon fiber electrodes fabricated in this method achieve specific surface areas exceeding 1400 m2 g−1, with pore volumes exceeding 1.0 cc g−1. The pore size distributions are highly controlled, with 80 % of total pore volume coming from pores <20 nm in radius. In 500 ppm constant voltage CDI tests, these fiber electrodes obtain a salt adsorption capacity of over 14 mg g−1 at a salt adsorption rate of ∼4 mg g−1 min−1, showcasing the high capacity matched with high rate of these easily fabricated, inexpensive materials.

Thermodynamic Window for Size-Controlled Pore Formation in Graphene for Large-Scale Molecular Sieves.

Nanopores in graphene monolayers are a promising option for molecular separation applications, such as desalination and carbon capture. Graphene's atomic thickness allows for an optimal balance between molecular selectivity and permeability, while its chemical stability and robust mechanical properties make it appealing for a wide range of commercial applications. However, scaling to large areas with controlled pore size distribution is an open challenge in ultrathin membranes. Here, using first-principles calculations, we identify a suitable thermodynamic window in a chemical vapor deposition system for directly growing graphene monolayers with a controlled pore size distribution. As an example, our calculations show that a postgrowth annealing step with a supersaturation range of 19.7-25 kJ/mol at 1000 K results in the creation of a controllable pore density at graphene grain boundaries, with pore sizes falling within the range of 5-8 Å. Such pores isolate hydrated Cl ions from water molecules, effectively desalinating seawater. Thus, it allows the design of targeted synthesis of large-scale 2D layers for membrane applications.

Porous Structure and Fractal Dimensions of Activated Carbon Prepared from Waste Coffee Grounds.

The present work reports the results of a systematic study on the evolution of the morphological properties of porous carbons derived from coffee waste using a one-pot potassium-hydroxide-assisted process at temperatures in the range of 400-900 °C. Raw materials and obtained carbons were studied by TG, DTG, SEM and nitrogen adsorption porosimetry. The decomposition temperature ranges for hemicellulose, cellulose and lignin as the main component of the feedstock have been established. It is shown that the proposed method for the thermochemical treatment of coffee waste makes it possible to obtain activated carbon with a controllable pore size distribution and a high specific surface area (up to 1050 m2/g). A comparative study of the evolution of the distribution of pore size, pore area and pore volume has been carried out based on the BJH and NL-DFT (slit-like pores approximation) methods. The fractal dimension of the obtained carbons has been calculated by Frenkel-Halsey-Hill method for single-layer and multilayer adsorptions.

Exploring potassium trifluoroacetate as a novel electrolyte for enhancing energy density of biomass-derived carbon-based supercapacitors and improving electrolyte-electrode adaptability

Improving the energy density by expanding the operating voltage of electrolytes and enhancing the charge storage capacity of electrode materials is crucial for the development of supercapacitors. This work proposes a potassium trifluoroacetate (CF3COOK, CFK) electrolyte for improving the energy density of supercapacitors without sacrificing the high power density and long-cycle performance while developing honeycomb-like interconnected hierarchical porous carbons (HIHPCs) with controlled pore size distribution, large specific surface area (3028 m2 g−1), interconnected pore structure, and high electrical conductivity (2.01 S cm−1) from waste biomass to match the proposed CFK electrolyte for harvesting high charge storage capability. The prepared HIHPCs exhibit excellent electrochemical performance in the proposed CFK electrolyte, achieving a high specific capacitance of up to 409 F g−1 over a wide operating voltage window of −1.0 to 0.9 V, with high coulomb efficiency, low internal resistance, good rate capability, and perfect electrochemical stability. Symmetric supercapacitors constructed using the obtained HIHPCs and the proposed CFK electrolyte can operate stably at 1.9 V and deliver high specific energy of 24.8 Wh kg−1 at 237.8 W kg−1 with good cycling stability. The effectiveness of the proposed CFK electrolyte as an ideal electrolyte with extended electrochemical stability windows to significantly improve the energy density of aqueous supercapacitors was verified. This work presents a promising approach for developing high-performance aqueous supercapacitors with potential applications in renewable energy systems.

Covalent Organic Frameworks as Emerging Battery Materials

AbstractCovalent organic frameworks (COFs) are emerging as promising energy storage materials due to their unique characteristics, such as adjustable thickness, designable topology, superior stability and controllable pore size distribution. Consequently, COFs can provide diversified high‐rate carrier transport pathways, and the performance of COFs can be easily improved by adjusting conjugated skeleton types, overlapping p‐electron clouds between stacks, and modifying open channels with functional groups. The state‐of‐the‐art COFs electrode materials based on synthetic method and electrochemical performance in recent years are summarized and discussed in this review. The synthesis method, topological structure and application in metal ion (such as Li+, Na+, K+, Zn2+, Mg2+, Al3+, et. al) batteries of COFs electrodes are critically accounted. Finally, we briefly discuss the major challenges in the field that needs to be addressed to pave the way for industrial applications. Although there are still many arduous tasks to be tackled, the burgeoning of COFs‐related technologies and applications in batteries provide a ponderable field for commercial process in the short run.

Facile synthesis of supported CuNi nano-clusters as an electrochemical CO2 reduction catalyst with broad potential range.

A nitrogen-doped carbon-supported CuNi bimetallic nanocluster catalyst (CuNi-NC) was first synthesized via a facile ZIF-derived method. With a synergistic effect between Cu and Ni, the catalyst exhibited a maximum FECO of 96.3%. FECO is higher than 90% in a broad potential range of 600 mV, which was ascribed to the controllable pore size distribution. Density functional theory further demonstrated the preferred formation of *COOH in the catalytic process.

Responsive Optical Materials Based on Ligand-Free Perovskite Quantum Dots Embedded in Mesoporous Scaffolds.

Herein we show that dispersing inorganic cesium lead bromide (CsPbBr3) perovskite quantum dots (QDs) in optical quality films, possessing an accessible and controlled pore size distribution, gives rise to fluorescent materials with a controlled and highly sensitive response to ambient changes. A scaffold-based synthesis approach is employed to obtain ligand-free QDs, whose pristine surface endows them with high sensitivity to the presence of different vapors in their vicinity. At the same time, the void network of the host offers a means to gradually expose the embedded QDs to such vapors. Under these conditions, the luminescent response of the QDs is mediated by the mesostructure of the matrix, which determines the rate at which vapor molecules will adsorb onto the pore walls and, eventually, condensate, filling the void space. With luminescence quantum yields as high as 60%, scaffold-supported ligand-free perovskite nanocrystals display intense photoemission signals over the whole process, as well as high photo- and chemical stability, which allows illuminating them for long periods of time and recovering the original response upon desorption of the condensed phase. The results herein presented open a new route to explore the application of perovskite QD-based materials in sensing.

Microporous Matrimid/PIM-1 Thin Film Composite Membranes with Narrow Pore Size Distribution used for Molecular Separation in Organic Solvents.

Polymers of intrinsic microporosity (PIMs) are a class of microporous organic materials that contain interconnected pores of less than 2nm in diameter. Such materials are of great potential used in membranes for molecular separation, such as drug fractionation in pharmaceutical industry. However, the PIMs membranes are often susceptible to low separation selectivity toward different molecules due to their wide pore size distribution. Herein, a linear polyimide, Matrimid, is incorporated with PIM-1 (a typical member of PIMs) by solution blending, and the blends are dip-coated onto a polyimide P84 support membrane to prepare thin-film composite (TFC) membranes to control pore size distribution while keep high microporosity. The component miscibility, pore characteristics, and molecular separation performances of the Matrimid/PIM-1 TFC membranes are investigated in detail. The Matrimid and PIM-1 are partially miscible due to their similar Hansen solubility parameters. The Matrimid endows the selective layers (coatings) with narrower pore size distribution due to more compact chain packing. The prepared Matrimid/PIM-1 TFC membranes show high selectivity for separation of riboflavin (80% of retention) and isatin (only 5% of retention). The developed membranes exhibit great potential for separating molecules with different molecular weights.

Bimetallic MOFs-Derived Hollow Carbon Spheres Assembled by Sheets for Sodium-Ion Batteries.

Metal-organic frameworks (MOFs) have attracted extensive attention as precursors for the preparation of carbon-based materials due to their highly controllable composition, structure, and pore size distribution. However, there are few reports of MOFs using p-phenylenediamine (pPD) as the organic ligand. In this work, we report the preparation of a bimetallic MOF (CoCu-pPD) with pPD as the organic ligand, and its derived hollow carbon spheres (BMHCS). CoCu-pPD exhibits a hollow spherical structure assembled by nanosheets. BMHCS inherits the unique hollow spherical structure of CoCu-pPD, which also shows a large specific surface area and heteroatom doping. When using as the anode of sodium-ion batteries (SIBs), BMHCS exhibits excellent cycling stability (the capacity of 306 mA h g-1 after 300 cycles at a current density of 1 A g-1 and the capacity retention rate of 90%) and rate capability (the sodium storage capacity of 240 mA h g-1 at 5 A g-1). This work not only provides a strategy for the preparation of pPD-based bimetallic-MOFs, but also enhances the thermal stability of the pPD-based MOFs. In addition, this work also offers a new case for the morphology control of assembled carbon materials and has achieved excellent performance in the field of SIBs.

The porous structure of activated carbon-based on waste coffee grounds

Nanoporous carbon materials (NCM) are used to prepare supercapacitor (SC) electrodes. The high specific energy parameters of SC are closely related to the physical and electrochemical characteristics of NCM. NCM with a highly developed surface area and controlled pore size distribution are obtained by chemical and thermal activation of carbon containing precursors. In our work we propose a thermochemical method of obtaining NCM with a high specific surface area. NCM were obtained by thermochemical activation of potassium hydroxide waste coffee grounds (WCG).

3D pattern formation from coupled Cahn-Hilliard and Swift-Hohenberg equations: Morphological phases transitions of polymers, bock and diblock copolymers

This work proposes a new mathematical model of a ternary mixture composed of coupled Cahn-Hilliard and Swift-Hohenberg equations solved in three dimensions (3D) through a pseudo-spectral implicit method (a numerical method of the fast Fourier transform). The 3D numerical solutions dynamic is analyzed through its structure factor and growth law to study its behavior and some observed phase transitions. These numerical solutions evolve into glassy and crystalline phases in the form of 3D patterns. The new model has a free energy functional that considers small monomers of polymer (or copolymeric) chains taken into the Edwards free energy, as well as solvent-monomers and solvent-stretch free energies whose dynamic is given by the Cahn-Hilliard and Allen-Cahn equations. Isotropic and anisotropic phases from polymers, block, and diblock copolymers blend such that these phases have a morphological diversity of classical and complex structures. As an application of the dynamics of the new ternary model, it has a diversity of morphologies which allows obtaining porous polymeric materials manufactured by a novel 3D printing technique: the mathematical design process and 3D printing assisted manufacturing (MDP-3DPAM). This method allows the proposal of a new technique for the design and creation of polymeric materials with controlled pore size distribution starting with computational modeling.

Recent progress in template-assisted synthesis of porous carbons for supercapacitors

Porous carbons (PCs) are one of the promising electrode materials for supercapacitors attributed to their low cost, superior electronic conductivity, easy availability, and tailored pore structures. Template methods have been explored as the effective strategies for the fabrication of PCs with desirable morphology and highly controllable pore size distribution. Herein, this review firstly focuses on design and synthetic mechanism of various PCs via hard templates, soft templates, and dual-templates. Secondly, an overview of PCs is presented with a detailed discussion of the structure−activity relationship between electrochemical performances and pore structures. Thirdly, the current challenges and prospects of template-assisted synthesis of PCs for supercapacitors are highlighted regarding further researches. An overview of the synthetic mechanisms, structure-activity relationship between pore structures and capacitance performances, the current challenges, and prospects are provided for porous carbons produced by template strategies.

Additive Manufacturing Assisted Solvent Casting of 3D Free-Standing Carbonaceous Hydrogels and Aerogels As Electrodes for Supercapacitors

In a quest for renewable and highly efficient energy storage devices, carbonaceous hydrogels obtained from biopolymers have received much attention owing to their multifunctional properties [1]. The ability to fine-tune the structures of these hydrogels and the prospects of fabricating 3D hydrogels-based carbon electrodes with highly porous and interconnected nanostructure is believed to provide efficient migration of electrolyte ions and electrons. Even though additive manufacturing (AM) of hydrogels with 3D structures could simplify the fabrication, the printability of each material varies greatly. Furthermore, the mechanical properties of hydrogels are often too weak to withstand the printing of structures with a certain height [2].Herein, we demonstrate a facile and versatile method for the fabrication of novel and highly porous 3D carbon aerogel electrodes from bio-hydrogels based on additive manufacturing assisted solvent casting process followed by freeze drying and pyrolysis. Firstly, the negative templates with the required resolution and geometry were 3D printed using high-resolution stereolithography (SLA) based AM technology to be used as master molds and the pattern were transferred to the biopolymeric hydrogels during ionic crosslinking induced self-assembly, leading to gelation. After completion of the gelling process, the casted hydrogel was removed from the master mold, washed with deionized water, frozen using solid carbon dioxide (dry ice) and lyophilized (freeze-dried) to preserve the structure. The lyophilized free-standing aerogels were then converted to free-standing 3D pyrolytic carbon aerogels in a high-temperature tubular furnace at 900°C under a nitrogen environment. Different characterization techniques such as FTIR, BET, SEM, Raman, XRD and XPS were employed to access the influence of the process parameters on the final microstructure of the 3D carbon aerogels. The as-prepared 3D free-standing carbon aerogel when used as a binder-free electrode showed outstanding charge storage capability and kinetics arising from interconnected 3D porous channels. The versatility of this approach was further verified by the successful preparation of novel multifunctional 3D free-standing carbon aerogel hybrids using GO, CNT and/or metal oxides and its application as a structured binder-free supercapacitor electrode with improved electrochemical performance.With the advantageous features of synergistically regulating the structure and composition, the proposed method combining AM and casting could be used as a versatile tool to develop structured bio-hydrogels, to be used as precursor material for constructing novel architectured free-standing carbon electrode materials with well-defined geometry and controlled pore size distribution. The final shape of carbon electrode depends on the 3D geometry of the additive manufactured negative template used for the replication during solvent casting. This technique would broaden the library of hydrogels materials that could be constructed freely in three-dimensions for the fabrication of structured and free-standing porous bio-carbon based electrodes for high-performance supercapacitor application.

Green preparation of hierarchical porous carbon with tunable pore size for supercapacitors

It is attractive to use green activators to prepare hierarchical porous carbon with controllable pore size distribution. Herein, we attempted plant ash as the activator to prepare hierarchical porous carbon through high-temperature carbonization and activation. The pore size of the obtained porous carbon varies from 1 to 7 nm with temperature. It has a high specific capacitance (387.8 F/g at 1 A/g) in 6 M KOH, showing high rate performance (capacitance retention rate of 73.2%, from 1 to 10 A/g). Then, it also exhibits excellent cycle stability after 10,000 cycles. The assembled symmetrical supercapacitor (PC-6/PC-6) has a high energy density of 23.25 Wh/kg in 1 M Na2SO4 solution when the power is 450 W/kg. In short, biomass as the green activator achieves high specific capacitance and excellent rate performance for the first time in supercapacitors. This work provides ideas for the green preparation of porous carbon with controlled pore size distribution.

Carbon Nanomaterials With Hollow Structures: A Mini-Review.

Carbon nanomaterials with high electrical conductivity, good chemical, and mechanical stability have attracted increasing attentions and shown wide applications in recent years. In particularly, hollow carbon nanomaterials, which possess ultrahigh specific surface area, large surface-to-volume ratios, and controllable pore size distribution, will benefit to provide abundant active sites, and mass loading vacancy, accelerate electron/ion transfer as well as contribute to the specific density of energy storage systems. In this mini-review, we summarize the recent progresses of hollow carbon nanomaterials by focusing on the synthesis approaches and corresponding nanostructures, including template-free and hard-template carbon hollow structures, metal organic framework-based hollow carbon structures, bowl-like and cage-like structures, as well as hollow fibers. The design and synthesis strategies of these hollow carbon nanomaterials have been systematically discussed. Finally, the emerging challenges and future prospective for developing advanced hollow carbon structures were outlined.

Control of pore-size distribution on CO2 adsorption volume and kinetics in Gondwana coals: Implications for shallow-depth CO2 sequestration potential

We report experimental CO2 adsorption isotherms and diffusion-related parameters of fresh coal samples from Jharia (350–360 m) and South Karanpura (50–60 m) coalfields, India at three different temperatures (28, 35 and 45 °C) and up to 4 MPa CO2 pressures. The results confirm that temperature possesses an inverse relationship with the excess adsorption volume. Data modelling with the Langmuir and Dubinin-Radushkevich (D-R) equations show the D-R equation better predicts the experimental excess adsorption data. A conversion of the excess adsorbed volume to absolute adsorption further reveals that the modified D-R equation is even a better model to estimate absolute adsorption than the conventional D-R equation. Adsorption kinetics data indicate that temperature has a positive influence on the adsorption rate. We determined the diffusion coefficients of CO2 in these coals using the unipore model, which suggest that it increases with pressure and temperature. Effective diffusivity and diffusion-time maintain a direct and inverse relationship, respectively, with the elevation of temperature. The experimental adsorbed volume and kinetics data are correlated with the corresponding pore-size distribution of the samples. Shallow depth South Karanpura samples have lower average pore diameter, higher volumetric proportion of micropores and surface area compared to those of higher depth Jharia coal samples. Lower adsorption volume and sluggish adsorption kinetics in Jharia coals result from a small surface area and relatively sparse distribution of semi open-ended micropores with poor interconnection. Based on our experimental observations, we discuss and suggest the potential and possible conditions for CO2 sequestration in the Permian Gondwana coalfields, India.

The Removal of Reactive Red 141 From Wastewater: A Study of Dye Adsorption Capability of Water-Stable Electrospun Polyvinyl Alcohol Nanofibers

Abstract The dye production and its use in textile and related industries resulted in discharge of dye to wastewater. Adsorption for color removal is known as equilibrium separation process, and the resultant decolorization is influenced by physicochemical factors such as adsorbent surface area. The nanofiber membranes prepared by the electrospinning method have controllable nanofiber diameter and pore size distribution (PSD) with a high surface area to volume or mass ratio. In this study, polyvinyl alcohol (PVA) nanofibrous membranes were prepared by the electrospinning method at different collection times such as 3, 5 and 10 h and heat fixated at 130, 150 and 170°C for 10 min, and then, the adsorption capability of PVA nanofiber membranes for Reactive Red 141 from aqueous solution was investigated. In order to make PVA nanofibers stable to water, the nanofibrous membranes were chemically cross-linked by a polycarboxylic acid (1,2,3,4 butanetetracarboxylic acid (BTCA)). PVA nanofibrous membranes were characterized by scanning electron microscopy, thermogravimetric analysis, swelling tests and pore size analysis. The results indicated that BTCA crosslinking improved the thermal and water stability of the nanofibrous structure but has no significant effect on the pore sizes of the membranes. Adsorption of Reactive Red 141 was studied by the batch technique, and it was observed that PVA nanofibers removed approximately &gt;80% of the dye.

Remarkably improving the specific energy of supercapacitor based on a biomass-derived interconnected hierarchical porous carbon by using a newly-developed mixed alkaline aqueous electrolyte with widened operation voltage

Improving the energy density of supercapacitors without sacrificing their large charge storage capacity, high power density, and excellent cycle stability is extremely attractive for researchers. Herein, we develop a mixed alkaline aqueous (MAA) electrolyte with widened operation voltage. Meanwhile, a biomass-derived interconnected hierarchical porous carbon (IHPC) with controlled pore size distribution, ultra-large specific surface area (up to 3463 m2 g−1), and high conductivity (up to 8.7 S cm−1) is prepared to match this electrolyte. The obtained IHPC can stably charge-discharge within 1.3 V and exhibit a high specific capacitance of up to 462 F g−1 in the MAA electrolyte. The symmetrical supercapacitors based on the prepared IHPC and the MAA electrolyte deliver a high specific energy of up to 19.7 Wh kg−1 at a specific power of 203 W kg−1, while a specific energy of 14.5 Wh kg−1 is recorded at a large specific power of 12.2 kW kg−1. Meanwhile, the assembled devices based on the MAA electrolyte exhibit good rate capability and excellent cycle stability, up to 89% of initial specific capacitance is retained even at a large current density of 20 A g−1, and more than 91.4% of initial specific capacitance is retained after 30,000 cycles.

Ordered reticulated-structured carbon foams via surfactant-addition into the polymerization medium of bio-based polyols

In the solvolytic liquefaction reaction of biomass, biopolymers are produced by bond-breakage in the complex lignocellulosic composition using the appropriate solvent and functionalizing the related fragments under mild conditions. The utilization of these bio-polyols as carbon sources has enhanced the conspicuous relevance in the handling of agroforestry by-products as an alternative to fossil fuel-based sources, taking into account the terms sustainability and environmental impact. In this study, a green and inexpensive method based on the resinification and subsequent foaming of bio-polyols produced by solvolytic liquefaction of the tree bark was adopted to synthesize carbon foams with a well-developed hierarchical porous structure. The novelty of this study to brighten the studies in the literature was to examine the characteristics of biomass-based carbon foams produced by adding two types of non-ionic surfactants (P123 and PEG3000) into the synthesis medium at different surfactant/biomass ratios (0.15 and 0.20 w/w). This study comprises a promising technique that promotes self-foaming in the existence of non-ionic surfactants to produce reticulated carbon foams from forest industry wastes with porous graphitic structure, high surface area (up to 758 m2/g), and controlled pore size distribution in the micro-pore region (dp<2 nm).