Facile preparation of hierarchical porous carbons with tailored pore size obtained using a cationic polyelectrolyte as a soft template

Hierarchical Biobased Macroporous/Mesoporous Carbon: Fabrication, Characterization and Electrochemical/Ion Exchange Properties

With the goal of improving the mechanical properties of porous hierarchical carbon, cellulosic fiber fabric was incorporated into the resorcinol/formaldehyde (RF) precursor resins. The composites were carbonized in an inert atmosphere, and the carbonization process was monitored by TGA/MS. The mechanical properties, evaluated by nanoindentation, show an increase in the elastic modulus due to the reinforcing effect of the carbonized fiber fabric. It was found that the adsorption of the RF resin precursor onto the fabric stabilizes its porosity (micro and mesopores) during drying while incorporating macropores. The textural properties are evaluated by N₂ adsorption isotherm, which shows a surface area (BET) of 558 m²g^-1. The electrochemical properties of the porous carbon are evaluated by cyclic voltammetry (CV), chronocoulometry (CC), and electrochemical impedance spectroscopy (EIS). Specific capacitances (in 1 M H₂SO₄) of up to 182 Fg^-1 (CV) and 160 Fg^-1 (EIS) are measured. The potential-driven ion exchange was evaluated using Probe Bean Deflection techniques. It is observed that ions (protons) are expulsed upon oxidation in acid media by the oxidation of hydroquinone moieties present on the carbon surface. In neutral media, when the potential is varied from values negative to positive of the potential of zero charge, cation release, followed by anion insertion, is found.

Hierarchical porous biochar from plant-based biomass through selectively removing lignin carbon from biochar for enhanced removal of toluene

This study proposed a simple and green air oxidation (AO) method to prepare hierarchical porous biochar by selectively removing lignin carbon from biochar after the pyrolysis of plant-based biomass, based on the fact that the thermal decomposition temperature in air between lignin carbon and cellulose/hemicellulose carbon was different. Three kinds of biomass with different lignocellulose contents were used, including walnut shell, cypress sawdust and rice straw. The results found that AO treatment could effectively improve the pore structure of the three biochar. The specific surface area of WCO-4, CCO-4 and RCO-4 was 555.0 m²/g, 418.7 m²/g and 291.9 m²/g, respectively, which was significantly higher than those of WC (319.5 m²/g), CC (381.7 m²/g) and RC (69.6 m²/g), respectively. Among these, walnut shell biochar with air oxidation (WCO) had higher surface area of 555.0 m²/g and mesopore volume of 0.116 cm³/g, this was related to its high content of lignin, which could facilitate the formation of mesopores by AO treatment with high selectivity. The toluene adsorption capacity of WCO reached 132.9 mg/g, which increased by 223.4% from that without AO treatment. The kinetics study indicated that the diffusion rates of toluene molecule were improved due to the increased mesopores volume of biochar and micropores also play an important role in the adsorption of toluene. The results demonstrate that AO treatment is a promising method to develop hierarchical porous structure for lignocellulose-rich plant-based biomass with low cost and environmental-friendly, which greatly enhanced the toluene adsorption capacity.

Air oxidation coupling NH3 treatment of biomass derived hierarchical porous biochar for enhanced toluene removal

In this study, hierarchical porous biochar was prepared from poplar sawdust by air oxidation coupling with NH₃ treatment for the removal of toluene. The results showed that the mesopore volume of the sample with air oxidation (PS‒O₂) increased significantly to 0.263 cm³/g from the blank sample (PS, 0.053 cm³/g). This could be attributed to the selective removal of the lignin carbon by air oxidation to develop mesopores in biochar. Following further NH₃ treatment (PS‒O₂‒NH₃), the basic surface chemistry on biochar was improved due to increased basic N-containing groups and decreased acidic O-containing groups, together with the micropore volume also increased to 0.231 cm³/g from 0.186 cm³/g of PS‒O₂. The formation mechanism of hierarchical porous structure of biochar was also discussed. The adsorption capacity of PS‒O₂‒NH₃ for toluene reached 218.4 mg/g at the initial concentration of 820 mg/m³, which was 383.2% higher than that of PS. The adsorption isotherm study indicated that the adsorption process of toluene was monolayered and the maximal adsorption capacity of PS‒O₂‒NH₃ for toluene could reach as high as 476.2 mg/g. The results demonstrated that air oxidation coupling NH₃ treatment is a highly effective method for the preparation of hierarchical porous biochar for enhancing toluene adsorption performance.

Hierarchical Porous Carbon Microfibers Derived from Tamarind Seed Coat for High-Energy Supercapacitor Application

The overwhelming interest in supercapacitors has led to the search for various carbonaceous materials, leading to hierarchical porous carbons. Herein, we report a natural biomass (tamarind seed)-based hierarchical porous carbon without any template and activated by a facile scheme. The tamarind seed coat-based hierarchical porous carbon possessed a unique configuration, making the material exhibit superior supercapacitor properties. A single carbon fiber hosting a distinctive micro- and mesoporous structure formed a connecting thread between the pores. This unique structure enabled high surface area and high capacitance. The highest surface area obtained by this method was 1702 m² g^-1, whereas the capacitance was 157 F g^-1 in 6 M KOH. Further, an ionic liquid-based electrolyte revealed 78 F g^-1 at a current density of 0.5 A g^-1. Outstanding capacity retentions of 96 and 93% were obtained over 1000 cycles at a current density of 2 A g^-1 for aqueous (6 M KOH) and ionic liquid (1-butyl 3-methyl imidazoliumbistrifluorosulfonylimide) electrolytes, respectively. The high charge-storage ability of the porous carbon microfibers (PCMFs) can be ascribed to the coexistence of micro- and mesopores. The power characteristics and the cyclic stability of PCMF materials were appealing in both electrolytes. The synthesis process described is amenable for large-scale applications with less complexity.

Synthesis of garlic skin-derived 3D hierarchical porous carbon for high-performance supercapacitors

A three-dimensional hierarchical porous carbon is synthesized via a facile chemical activation route with garlic skin as the precursor and KOH as the activating agent. The as-obtained carbon presents a high specific surface area of 2818 m² g^-1 and a hierarchical porous architecture containing macroporous frameworks, mesopores (2-4 nm), and micropores (0.6-1.0 nm). As the electrode material for a supercapacitor, due to its unique interconnected porous structure, this garlic skin-derived carbon exhibits excellent electrochemical performance and cycling stability. At a current density of 0.5 A g^-1, the capacitance is up to 427 F g^-1 (162 F cm^-3). Even at a high current density of 50 A g^-1, the capacitance can be maintained to a high value of 315 F g^-1 (120 F cm^-3). After charging-discharging at a current density of 4.5 A g^-1 for 5000 cycles, the capacitance retention is as high as 94%. The results suggest that this garlic skin-derived 3D hierarchical porous carbon is a promising electrode material for high-performance supercapacitors.

Remarkable capacitive enhancement of templated carbon materials by the redox additive electrolyte of p-phenylenediamine

Nanoporous carbon materials with hierarchical porosities have been produced via a template carbonization method, in which potassium citrate (or gelatin) serves as the carbon precursor and Mg(OH)₂ powder as the hard template.

Electrochemical performance of hierarchical porous carbon materials obtained from the infiltration of lignin into zeolite templates

Hierarchical porous carbon materials prepared by the direct carbonization of lignin/zeolite mixtures and the subsequent basic etching of the inorganic template have been electrochemically characterized in acidic media. These lignin-based templated carbons have interesting surface chemistry features, such as a variety of surface oxygen groups and also pyridone and pyridinic groups, which results in a high capacitance enhancement compared to petroleum-pitch-based carbons obtained by the same procedure. Furthermore, they are easily electro-oxidized in a sulfuric acid electrolyte under positive polarization to produce a large amount of surface oxygen groups that boosts the pseudocapacitance. The lignin-based templated carbons showed a specific capacitance as high as 250 F g(-1) at 50 mA g(-1) , with a capacitance retention of 50 % and volumetric capacitance of 75 F cm(-3) at current densities higher than 20 A g(-1) thanks to their suitable porous texture. These results indicate the potential use of inexpensive biomass byproducts, such as lignin, as carbon precursors in the production of hierarchical carbon materials for electrodes in electrochemical capacitors.