Porous Carbon Microspheres Research Articles

MOFs derived magnetic porous carbon microspheres constructed by core-shell Ni@C with high-performance microwave absorption

Lightweight and high-performance are two determining factors for metal-organic-frameworks (MOFs) derived microwave absorbers. However, most of the reported MOFs derived absorbers usually possess high filler loading. Herein, a series of MOFs derived magnetic porous carbon microspheres with tunable diameter and high specific surface area have been synthesized via a pyrolysis process. The synthesized magnetic porous carbon microspheres, constructed by uniformly distributed core-shell Ni@C, exhibit high-performance microwave absorption with a low filler loading of 10 wt%. Considering the mciro-mesoporous structures, matched impedance, strong conductive loss, enhanced dipolar/interfacial polarization as well as strong magnetic coupling network, a minimum reflection loss of -60 dB and an absorption bandwidth of 7.0 GHz can be achieved at 2.6 mm. Moreover, the bandwidth reaches as wide as 10.2 GHz when the thickness is 4 mm. In addition, compared with other MOFs derived absorbers, this work provides us a simple strategy for the synthesis of porous carbon microspheres with lightweight and high-performance microwave absorption for practical applications.

Hierarchically Porous Hydrothermal Carbon Microspheres Supported N-Hydroxyphthalimide as a Green and Recyclable Catalyst for Selective Aerobic Oxidation of Alcohols.

A novel metal-free, reusable, and green catalytic system comprising hydrothermal carbon microspheres (HCMSs) supporting N-hydroxyphthalimide (NHPI) was developed and employed in the aerobic oxidation of alcohol. Hierarchically porous HCMSs with good monodispersity were produced by the hydrothermal carbonization of sucrose and designed NaOH-impregnated calcination under a static air atmosphere. The meso- and macroporous pores on HCMSs make up 71% of the total pore volume. The covalent immobilization of NHPI onto HCMSs was first accomplished by grafting hyperbranched polyquaternary amine via repetitive ring-opening reactions of diglycidyl ether and subsequent amidation with 4-carboxy-NHPI. Owing to the cocatalysis of grafted quaternary ammonium salt, a designed heterogeneous catalyst has superior performance to free NHPI in the oxidation of 2-phenylethanol. The established catalytic system achieved 42% conversion and up to 96% selectivity of acetophenone at 90 °C under 1 atm O2 for 20 h and presented a versatile catalytic effect for diversified alcohols. Immobilized NHPI could be facilely recycled via simple filtration and displayed good stability for six cycles without a discernible decrease of reactivity or damage of catalyst morphology in repeated oxidation test.

Zinc-iron bimetallic-nitrogen doped porous carbon microspheres as efficient oxygen reduction electrocatalyst for zinc-air batteries

Bimetallic-nitrogen doped carbons (bi-MNC) have attracted great attention as oxygen reduction reaction (ORR) catalysts due to their favorable activation of the O-O bond on the dual metal sites. However, zinc based bi-MNC were seldom investigated because the zinc tended to be neglected at elevated temperature owing to its volatile nature. In this work, a zinc-iron–nitrogen doped porous carbon (FeZnNC) was facilely prepared by pyrolysis of PVA-FeCl3-ZnCl2 gel coated commercial melamine foam. It is found that the zinc not only acted as porogen and dopant but also as structural regulator, leading to spherical morphology with more porous defects, larger surface area and more pyridone-N sites. The electrochemical measurements showed that the FeZnNC not only could achieve higher limiting current density of 5.97 mA/cm2, positive onset potential (0.965 V) and half-wave potential (0.873 V), but also display superior electrocatalytic stability than monometallic-nitrogen doped carbons (mono-MNC). Furthermore, the FeZnNC + RuO2 powered rechargeable zinc-air battery could also present longer cycling life than that powered by mono-MNC.

A multifunctional activation strategy of ultrathin carbon layers-intertwined carbon microspheres clusters towards markedly enhanced capacitance

Exploiting a facile and effective synthetic strategy integrated with pore-forming and nitrogen doping is highly desirable for developing superior electrode materials. Here, we proposed an ingenious multifunctional activation strategy to synthesize ultra-thin graphite-like carbon layers interwoven N-doped porous carbon microspheres clusters (donated by NCSC) by pyrolyzing self-polymered dopamine nanosphere precursors and g-C3N4, in which g-C3N4 simultaneously served as a pore-foaming agent, nitrogen source and a regulator of nitrogen configuration. The as-prepared NCSC exhibited three-dimensional interwoven porous structures with more favorable hydrophilic interface, high porosity with interconnected open pore structures, and pyrrole-N and pyridine-N dominated high nitrogen doping content (5.70 at.%). In the three-electrode test system, NCSC delivered significantly increased capacitance (235.4F g−1 at 1A g−1) compared to that of dopamine nanospheres derived carbon microspheres clusters(CSC) (124.7F g−1 in 1A g−1), and an excellent cycling durability (97% retention at 20A g−1 after 10,000 cycles). More impressively, the NCSC-based symmetrical supercapacitor with 1.0 M neutral Na2SO4 electrolyte can realize a wide voltage range of 1.8 V, rendering a specific energy density of 14.64 Wh kg−1 at 450 W kg−1. Such kind of integrated multi-functional activation strategy can provide new ideas for developing advanced materials to significantly boost capacitance performance.

One-step fabrication of Pd-embedded hierarchically porous carbon micro-spheres for formaldehyde removal under mild conditions

Using the enclosed space of Pickering emulsion droplets as a template, we adopted a one-step strategy to prepare Pd and N co-doped multi-core layered porous carbon microspheres (Pd@NCMs-T) for room-temperature catalytic oxidation of HCHO.

Rational design of FeCo imbedded 3D porous carbon microspheres as broadband and lightweight microwave absorbers

With the aim to obtain microwave (MW) absorber possessing simultaneous light weight and broad absorption bandwidth, FeCo imbedded 3D porous carbon network microspheres (3DC@FeCo) were synthesized via spray-drying followed by calcination processes. 3DC@FeCo exhibits 3D porous carbon microspheres structure with submicrometer-sized macropores. The FeCo imbedded carbon structure not only restrains the growth and agglomeration of FeCo nanoparticles, but also effectively introduces polarization and suppresses the skin effect from FeCo. In addition, the 3D porous carbon microspheres provide more channels which enhance the multiple reflection for microwave. The microwave absorption performance of 3DC@FeCo can be adjusted through changing the carbonization temperature, and the sample after carbonized at 630 °C (3DC@FeCo-630) shows the best microwave absorption property. It is worth mentioning that there is only 21.8 wt% FeCo in 3DC@FeCo, indicating that the 3DC@FeCo microspheres proposed in this study are one kind of lightweight microwave absorbers. The minimum reflection loss (RL) value of 3DC@FeCo-630 is − 47.4 dB at 6.35 GHz and the effective absorption bandwidth (RL < − 10 dB) can reach up 5.66 GHz (12.08–17.74 GHz) with the matching thickness of only 2.7 mm. The excellent microwave absorption ability can be attributed to favorable impedance matching, strong dielectric loss, magnetic loss, FeCo imbedded carbon and unique 3D porous structure. 3DC@FeCo microspheres as broadband and lightweight microwave absorbers exhibit a promising prospect applied in complex electromagnetic environments.

A clean and industrially applicable approach for the production of copper-doped and core-shell structured porous carbon microspheres as supercapacitor electrode materials

Conventional approaches for the production of copper-doped porous carbon microspheres from biomass involve a multi-step process, including spherical-shape development, carbonization, activation, and thermal treatment in the presence of a copper donor. In this work, a clean and industrially suitable approach is proposed to directly prepare copper-doped porous carbon microspheres from enzymatic hydrolysis lignin by utilizing cupric chloride dihydrate in four aspects: (1) as a microwave absorber to rapidly elevate the heating temperature, achieving an exceedingly short production duration of 8 min and a high carbon yield of 35.1%, (2) as a sphering agent to build a core-shell structure containing disordered carbon in the shell layer and copper-related particles in the core layer, limiting the volume changes of the copper-related particles and restraining their aggregation, (3) as a porogen to obtain a hierarchical porous structure with a high specific surface area of 1083 m2 g−1 and a mesopore ratio of 44.2%, and (4) as a copper donor to grow abundant copper-related particles, bypassing the purification process. The porous structure ensures the rapid ion transport for the copper-related particles which in turn provide a significant pseudo-capacitance. The resultant electrode achieves a remarkably high specific capacitance of 736 F g−1 at 1 A g−1. Moreover, the fabricated supercapacitor delivers an energy density of up to 43.9 W h kg−1 at 0.5 kW kg−1. This work demonstrates a clean and industrially applicable method to utilize biomass waste in high-value-added electrode materials with a low overall production cost.

Encapsulation of Se into Hierarchically Porous Carbon Microspheres with Optimized Pore Structure for Advanced Na-Se and K-Se Batteries.

Sodium-selenium (Na-Se) and potassium-selenium (K-Se) batteries have emerged as promising energy storage systems with high energy density and low cost. However, major issues such as huge Se volume changes, polyselenide shuttling, and low Se loading need to be overcome. Although many strategies have been developed to resolve these issues, the relationship between the carbon host pore structure and electrochemical performance of Se has not been studied extensively. Here, the effect of the carbon host pore structure on the electrochemical performance of Na-Se and K-Se batteries is investigated. N, S-co-doped hierarchically porous carbon microspheres with different pore structures that can incorporate a large amount of amorphous Se (∼60 wt %) are synthesized by spray pyrolysis and subsequent chemical activation at different temperatures. By optimizing the amount of micropore volume and micropore-to-mesopore ratio, high reversible capacity and cycling stability are achieved for the Se cathode. The optimized cathode delivers a reversible capacity of 445 mA h g-1 after 400 cycles at 0.5C for Na-Se batteries and 436 mA h g-1 after 120 cycles at 0.2C for K-Se batteries. This study marks the importance of developing conductive carbon matrices with delicately designed pore structures for advanced alkali metal-chalcogen battery systems.

Rambutan‐like hierarchically porous carbon microsphere as electrode material for high‐performance supercapacitors

AbstractUsed as high‐performance electrodes, both structural and compositional alterations of carbon materials play very important roles in energy conversion/storage devices. Especially in supercapacitors, hierarchical pores and heteroatom doping in carbon materials are indispensable. Here the rambutan‐like hierarchically porous carbon microspheres (PCMs) have been constructed via a hydrothermal treatment, followed by carbonization/activation. The hierarchically porous microstructure is composed of three‐dimensional porous carbon networks, which give rise to a large surface area. Moreover, N and O functional groups are introduced in the as‐prepared samples, which could generate the extra pseudocapacitance. Benefitting from the interconnected hierarchical and open structure, PCM exhibits outstanding capacitive performance, for example, superior specific capacitance and rate capability (397 and 288 F g−1 at 0.5 and 20 A g−1, respectively), as well as long cycling stability (about 95% capacitance retention after 10,000 cycles). These encouraging results may pave an efficient way to fabricate advanced supercapacitors in the future.

Highly Packed Monodisperse Porous Carbon Microspheres for Energy Storage in Supercapacitors and Li−S Batteries

AbstractPorous carbon microspheres and S/microspherical carbon composites with a highly packed hexagonal arrangement have been synthesized by chemical activation of precarbonized resorcinol‐formaldehyde spheres. Sodium thiosulphate is used as a harmless activating agent, S dopant and sulfur precursor. The porous microspheres exhibit large surface areas (2060–2340 m2 g−1) and adequate micro‐mesoporosity. They also have a notable amount of sulfur heteroatoms (5–7 %) and high electronic conductivity (2.3–3.1 S cm−1). The compact organization and suitable porosity of the microspheres allow competitive values of volumetric capacitance to be achieved when used in supercapacitors operating in aqueous and organic electrolytes (130 and 64 F cm−3, respectively), while maintaining good rate capability. In addition, the sulfur/spherical carbon composites with a sulfur content above 80 % are tested as cathode material in lithium‐sulfur batteries, demonstrating high sulfur utilization, large values of volumetric capacity (768 mAh cm−3) and stable long‐term cyclability (0.086 % capacity loss per cycle).

Defects-rich porous carbon microspheres as green electrocatalysts for efficient and stable oxygen-reduction reaction over a wide range of pH values

Carbon materials are promising alternatives to noble metal catalysts for oxygen reduction reactions (ORR) in energy conversion devices. Here we report hierarchically porous carbon microspheres with a trace amount of encapsulated cobalt as highly active and stable electrocatalysts for the ORR under wide pH values ranged from high alkaline to high acidic conditions. We use renewable natural date pulp as the carbon precursor and a facile hydrothermal carbonization method with in situ formed recyclable cobalt as a template for the synthesis. These catalysts yield competitive catalytic activity (a small Tafel slope of 53 mV dec-1) as well as superb durability and methanol tolerance compared to the benchmark Pt/C catalyst in alkaline electrolyte. Even under harsh acidic conditions, the catalysts deliver a satisfactory catalytic performance and good stability, indicating their extensive applicability. This performance is mainly attributed to the rich surface defects and the hierarchically porous structure that provide abundant active sites for the ORR. In situ formed cobalt nanoparticles are critical to the creation of the abundant mesopores, high specific surface area, and catalytically active defect sites over the carbon material. The encapsulated cobalt residual further enhances the ORR activity of the catalysts, while having a negligible effect on the cost due to its trace level (0.2 at.%).

Green Preparation and Environmental Application of Porous Carbon Microspheres

AbstractPorous carbon microspheres (PCM) show bright application prospects in the fields of adsorption, supercapacitors, hydrogen storage, catalysis and sustained release. In this work, PCM were prepared by properly designed hydrothermal and activated processes using waste peanut shell as raw material. PCM maintained the size of hydrothermal carbon microspheres (HCM) with an ultra‐high specific surface area of 3126 m2⋅g−1 and a hierarchical pore structure from micropores to mesopores. X‐ray diffraction pattern and Raman spectrum indicated that the PCM were amorphous and locally graphitized. The adsorption test for methylene blue demonstrated that the PCM had a monolayer adsorption capacity of 1368 mg⋅g−1. The adsorption equilibrium was achieved at 3 h and reached 81.6% of the equilibrium adsorption amount in the initial 0.5 h. The adsorption thermodynamics analysis demonstrated that the adsorption was a spontaneous physicochemical process. In addition, the adsorption performance of PCM displayed satisfactory pH stability.

In-situ growth of core-shell ZnFe2O4 @ porous hollow carbon microspheres as an efficient microwave absorber

The special structure and composition are the important factors that determine the microwave absorption properties. In this study, the porous hollow carbon microsphere (PHCMS) is synthesized by the self-assembly technology, and ZnFe2O4 particles are synthesized inside the carbon sphere by in-situ preparation with taking advantage of the porous and hollow characteristics of the carbon sphere, which prepares ZnFe2O4@PHCMS composite material. The composite shows good performance in terms of minimum reflection loss and absorption bandwidth. The results show that the maximum adsorption capacity of the composite is −51.43 dB at 7.2 GHz. When the thickness is 4.8 mm, the effective absorption bandwidth of RL ≤ 10 dB electromagnetic wave is 3.52 GHz. Such enhanced electromagnetic wave absorption properties of ZnFe2O4@PHCMS are ascribed to the suitable impedance characteristic, the dipole polarization and interfacial polarization, the multiple Debye relaxation process and strong natural resonance, multiple reflection and scattering. This work provides an approach to design effective microwave absorbers having a unique structure to enhance the microwave absorption properties.

Calcium-chloride-assisted approach towards green and sustainable synthesis of hierarchical porous carbon microspheres for high-performance supercapacitive energy storage

Spherical carbon materials exhibit great competence as electrode materials for electrochemical energy storage, owing to the high packing density, low surface to volume ratio, and excellent structure stability. How to utilize renewable biomass precursor by green and efficient strategy to fabricate porous carbon microspheres remains a great challenge. Herein, we report a KOH-free and sustainable strategy to fabricate porous carbon microspheres derived from cassava starch with high specific surface area, high yield, and hierarchical structure, in which potassium oxalate monohydrate (K2C2O4·H2O) and calcium chloride (CaCl2) are employed as novel activator. The green CaCl2 activator is crucial to regulate the graphitization degree, specific surface area, and porosity of the carbon microspheres for improving the electrochemical performance. The as-prepared carbon microspheres exhibit high specific surface area (1668 m2 g−1), wide pore size distribution (0.5–60 nm), high carbon content (95%), and exfoliated surface layer. The hierarchical porous carbon microspheres show high specific and areal capacitance (17.1 μF cm−2), superior rate performance, and impressive cycling stability. Moreover, the carbon microspheres based symmetric supercapacitor exhibits high capacitance and excellent cycling performance (100% after 20 000 cycles at a current density of 5 A g−1). This green and novel approach holds great promise to realize low-cost, high-efficient and scalable of renewable cassava starch-derived carbon materials for advanced supercapacitive energy storage applications.

Honeycomb-like structure-tunable chitosan-based porous carbon microspheres for methylene blue efficient removal

Chitosan (CS) can be used for the preparation of carbon materials with different morphologies due to its excellent properties, but there are no reports on its spherical morphology. In this study, a feasible step-by-step strategy was proposed to fabricate nitrogen-containing chitosan-based porous carbon microspheres (CPCM) in HCl and KOH. The unique spherical morphology and honeycomb-like porous structure of CPCM were accurately regulated. A great quantity of micro/mesopores endowed CPCM an ultra-high specific surface area up to 2463.9 m2 g−1. Moreover, CPCM exhibited an ultra-high maximum adsorption capacity up to 1599.03 mg g−1 for methylene blue (MB), meanwhile the adsorption process was in well agreement with the Langmuir isotherm and pseudo-second-order kinetic models. It was simultaneously a favorable reusable adsorbent with high regenerative capacity. The high dye adsorption properties suggest that chitosan can be a promising candidate for sewage treatment in the form of carbon microspheres.

Hierarchical porous nitrogen-doped carbon microspheres after thermal rearrangement as high performance electrode materials for supercapacitors

Polyimides have been used as the precursor of carbon materials. Thermal rearrangement polymers with porous structure can be prepared by thermal treatment of hydroxyl-containing polyimides in the solid state. Herein, hydroxyl-containing polyimides with hierarchical microspheres were firstly prepared by solvothermal method. After thermal rearrangement at 450 °C and further carbonization, the hierarchical porous nitrogen-doped carbon microspheres were obtained, which showed good electrochemical characteristics. The effects of the concentration of polymer solution, thermal rearrangement time and final carbonization temperature on the structure and properties of final carbon materials were investigated. The hierarchical porous carbon materials were tested as an electrode for supercapacitors, and HPI-45–2-800 with high specific surface area of 877 m2 g−1 exhibited excellent electrochemical properties. The specific capacitance of HPI-45–2-800 was 211.3 F g−1 at the current density of 0.5 A g−1. When the current density was increased to 10 A g−1, the retention rate of specific capacitance was as high as 55%. After 10,000 cycles of charging and discharging, the specific capacitance of HPI-45–2-800 electrode was still retained 99.94% of the initial capacitance, showing excellent long-term charge–discharge cycling stability. The hierarchical porous nitrogen-doped carbon microspheres after thermal rearrangement are expected to be high performance electrode materials for supercapacitors.

Novel porous carbon microtubes and microspheres produced from poly(CL-b-VbC) triarm block copolymer as high performance adsorbent for dye adsorption and separation

Dandelion-like and microtube-containing novel porous carbons were synthetized from brush type poly (ε-caprolactone-b-4-vinyl benzyl chloride) (poly(CL-b-VbC)) triarm block copolymer with KOH (PCLVbK) and ZnCl2 (PCLVbZn) through optimized chemical activation at low temperature. These porous carbons were used for the adsorption and separation of cationic Malachite green (MG) and anionic Congo red (CR) and Methyl orange (MO) dyes. The synthetized porous carbons were characterized by SEM, N2 adsorption-desorption isotherms, FTIR, Raman and XRD. PCLVbK and Zn porous carbons were quite effective in cationic (MG) dye adsorption from aqueous solution thanks to different functional groups, surface areas and pore volumes. The MG adsorption capacities of PCLVbZn and PCLVbK were found to be 1684 mg/g and 869.5 mg/g, and these results are considerably higher than the other adsorbents studied in the literature. Also, it was determined that while PCLVbZn could adsorb both cationic and anionic dyes, PCLVbK could only perform the adsorption of cationic dyes. The kinetic studies conducted with MG showed that both PCLVbK and Zn porous carbons fitted better with the pseudo-second-order model. At the end of the adsorption equilibrium studies, it was observed that PCLVbZn fitted with both the Langmuir and Freundlich adsorption models while PCLVbK fitted better with the Langmuir model. In conclusion, it was observed that PCLVbK could perform high and fast adsorption and separation owing to its oxygen functional groups, while PCLVbZn turned out to be effective in the adsorption of both anionic and cationic dyes thanks to its large surface area (1006 m2/g) and empty microtubes. Based on these results, it can be argued that PCLVbK and Zn porous carbons are promising adsorbents for both high adsorption and effective separation from aqueous solution.

Hierarchically Porous Carbon Microsphere Doped with Phosphorus as a High Conductive Electrocatalyst for Oxidase-like Sensors and Supercapacitors

A hierarchically porous carbon microsphere (PCM) with phosphorus doping (A-PCM) for an oxidase-like sensor and supercapacitor was prepared by the hydrothermal reaction using d-(+)-xylose as a carbo...

Preparation and adsorption property of novel inverse-opal hierarchical porous N-doped carbon microspheres

The design of pore structure is the key factor for the performance of porous carbon spheres. In this work, novel micron-sized colloidal crystal microspheres consisting of fibrous silica (F-SiO2) nanoparticles are firstly prepared by water-evaporation-induced self-assembly of F-SiO2 nanoparticles in the droplets of an inverse emulsion system to be used as sacrificial templates. Acrylonitrile (AN) was infiltrated in the voids of the F-SiO2 colloidal crystal microspheres, and in-situ induced by 60Co γ-ray to polymerize into polyacrylonitrile (PAN). After the PAN-infiltrated F-SiO2 colloidal crystal microspheres were carbonized and etched with HF solution, novel micron-sized inverse-opal N-doped carbon (IO-NC) microspheres consisting of hollow carbon nanoparticles with a hierarchical macro/meso-porous inner surface were obtained. The IO-NC microspheres have a specific surface area as high as 266.4 m2/g and a molar ratio of C/N of 5. They have a good dispersibility in water, and show a high adsorption capacity towards rhodamine B (RhB) up to 137.28 mg/(g microsphere). This work offers a way to obtain novel micron-sized hierarchical macro/meso-porous N-doped carbon microspheres, which opens a new idea to prepare high-performance hierarchical porous carbon materials.

Porous carbon microspheres with highly graphitized structure for potassium-ion storage

Porous carbon materials are promising candidates for anode materials in rechargeable potassium-ion batteries. However, their high surface area and low crystallinity usually cause side reactions with electrolytes and slanted charge/discharge profiles. Herein, we report the synthesis of porous carbon microspheres with highly graphitized structure and enhanced potassium-ion storage properties. The prepared carbon microspheres exhibit a low working potential of ~0.2 V, high Coulombic efficiency, and a stable reversible capacity of 292.0 mAh/g after 100 cycles, which is significantly higher than that of commercial graphite (137.5 mAh/g after 100 cycles). These desirable performances are attributed to the high crystallinity of carbon and its porous structure, which provide active sites for potassium-ion storage and alleviate the stress caused by the large volume change during the insertion and extraction of potassium ions.