Nitrogen and Oxygen-Doped Hierarchical Porous Carbons from Algae Biomass: Direct Carbonization and Excellent Electrochemical Properties

Waste biomass garlic stem-derived porous carbon materials as high-capacity and long-cycling anode for lithium/sodium-ion batteries

Carbon materials are promising anode materials for rechargeable lithium and sodium-ion batteries, due to their low cost, high capacity, and structural designability. In this work, we selected a waste biomass, garlic stem, as the carbon precursor, and we systematically investigated the effect of pyrolysis temperature and time on their battery performance. We find that 800 °C and 2 h are the best pyrolysis conditions, which leads to the optimal carbon material (800C-2H) with a large layer spacing, abundant defect sites, high surface area, and sufficient micro/meso-porous structures. Due to these favorable properties, this carbon anode exhibits an impressive performance for Lithium-ion batteries, with a very high capacity of 480 mAh g-1 and no significant capacity fading after 3000 cycles. Besides, this anode also shows promising performance for Sodium-ion batteries, where a good capacity of 151.9 mAh g-1 and reasonable cycling of 100 cycles are achievable. We also carried out in-situ X-ray diffraction and in-situ Raman spectroscopy experiments to understand the relationship between carbon microstructures and their Li-ion storage.

Electrochemical Performance of Nitrogen Self-Doping Carbon Materials Prepared by Pyrolysis and Activation of Defatted Microalgae

Pyrolysis and activation processes are important pathways to utilize residues after lipid extraction from microalgae in a high-value way. The obtained microalgae-based nitrogen-doped activated carbon has excellent electrochemical performance. It has the advantage of nitrogen self-doping using high elemental nitrogen in microalgae. In this study, two kinds of microalgae, Nanochloropsis and Chlorella, were used as feedstock for lipid extraction. The microalgae residue was firstly pyrolyzed at 500 °C to obtain biochar. Then, nitrogen-doped activated carbons were synthesized at an activation temperature of 700-900 °C with different ratios of biochar and KOH (1:1, 1:2, and 1:4). The obtained carbon materials presented rich nitrogen functional groups, including quaternary-N, pyridine-N-oxide, pyrrolic-N, and pyridinic-N. The nitrogen content of microalgae-based activated carbon material was up to 2.62%. The obtained materials had a specific surface area of up to 3186 m2/g and a pore volume in the range of 0.78-1.54 cm3/g. The microporous pore sizes of these materials were distributed at around 0.4 nm. Through electrochemical testing such as cyclic voltammetry and galvanostatic charge-discharge of materials, the materials exhibited good reversibility and high charge-discharge efficiency. The sample, sourced from microalgae Chlorella residue at activation conditions of 700 °C and biochar/KOH = 1:4, exhibited excellent endurance of 94.1% over 5000 cycles at 2 A/g. Its high specific capacitance was 432 F/g at 1 A/g.

Adsorption performance and mechanism of cationic and anionic dyes by KOH activated biochar derived from medical waste pyrolysis

The massive generation of medical waste (MW) results in a series of environmental, social, and ecological problems. Pyrolysis is one such approach that has attracted more attention because of the production of value-added products with lesser environmental risk. In this study, the activated biochar (ABC600) was obtained from MW pyrolysis and activated with KOH. The adsorption mechanism of activated biochar on cationic (methylene blue) and anionic (reactive yellow) dyes were studied. The physicochemical characterization of biochar showed that increasing pyrolysis temperature and KOH activation resulted in increased surface area, a rough surface with a clear porous structure, and sufficient functional groups. MB and RYD-145 adsorption on ABC600 was more consistent with Langmuir isotherm (R² ≥ 0.996) and pseudo-second-order kinetics (R² ≥ 0.998), indicating chemisorption with monolayer characteristics. The Langmuir model fitting demonstrated that MB and RYD-145 had maximum uptake capacities of 922.2 and 343.4 mg⋅g^-1. The thermodynamics study of both dyes showed a positive change in enthalpy (ΔH°) and entropy (ΔS°), revealing the endothermic adsorption behavior and randomness in dye molecule arrangement on activated-biochar/solution surface. The activated biochar has excellent adsorption potential for cationic and anionic dyes; hence, it can be considered an economical and efficient adsorbent.

Covalent organic frameworks-derived hierarchically porous N-doped carbon for 2,4-dichlorophenol degradation by activated persulfate: The dual role of graphitic N

A series of hierarchically porous carbon catalysts with high N content and large surface area were prepared via self-templated carbonization of covalent organic frameworks (COFs). The catalyst was used to activate persulfate (PS) for degrading 2,4-dichlorophenol (2,4-DCP). Experimental results demonstrated that the prepared catalyst treated at 700 °C (PNC-700) showed both strong adsorption ability and enhanced PS activity for 2,4-DCP degradation. A variety of characterization techniques were used to investigate the properties of prepared catalysts. We found that the graphitic N functional groups acted as both activity sites and electron transfer access. The activity of the catalyst was also closely related to the hierarchical pore structure and good electrical conductivity. The influencing factors of PNC-700/PS system in 2,4-DCP degradation were discussed. In addition, PNC-700 displayed excellent recyclability. The activation process especially non-radical pathway was promoted by increasing graphitic N contents. The possible reaction mechanism and degradation pathways were also proposed.

Mesoporous Weaved Turbostratic Nanodomains Enable Stable Na+ Ion Storage and Micropore Filling is Revealed to be More Unsafe than Adsorption and Deintercalation

Advanced wave-shape non-graphitizable carbon sheets are derived, comprising mesoporous weaved turbostratic micropore enabled stable Na⁺ ion storage. The non-graphitizable amorphous characteristics are determined from the obtained two broad diffraction peaks at 22.7° and 43.8°. The observed D-band at 1325 cm^-1 and G-band at 1586 cm^-1 confirm the disordered graphitic structure, attributed to the measured specific surface area of 54 m² g^-1. Mesoporous weaved wave-shape carbon sheet architecture is confirmed by surface morphological studies, showing lattice fringes of disordered graphitic structures and dispersed ring patterns for the non-crystalline characteristics. The predominant stable redox peak at 0.014 V/0.185 V and the broader rectangular shape between 0.9 and 0.15 V depict the adsorption-micropore filling mechanism. The mesoporous hard carbon sheet delivers discharge-charge capacities of 450/311 mAh g^-1 (1st cycle) and 263/267 mAh g^-1 (250th cycle) at 25 mA g^-1, exhibiting a superior anode for sodium-ion batteries. Besides, in situ multimode calorimetry results disclose that the micropore filling Na⁺ ion storage shows a higher released total heat energy of 721 J g^-1 than the adsorption (471 J g^-1). Ultimately, differential scanning calorimetry analysis of micropore filling Na⁺ ion storage (discharged state at 0.01 V) has revealed a predominant exothermic peak at 156 °C with the highest released total heat energy of 2183 J g^-1 compared to adsorption (553 J g^-1) and deintercalation (85 J g^-1), indicating that micropore filling status is more unsafe than the adsorption and deintercalation for SIBs.

Facile preparation of multi-porous biochar from lotus biomass for methyl orange removal: Kinetics, isotherms, and regeneration studies

Biomass is a promising carbon source because of its low-cost and rich carbon component. Here, lotus root as self N-source was used to produce N-doped biochar via a simple carbonization after freeze-drying, showing surface areas up to 694 m²/g with partial mesopores. Applicability of biochar as adsorbent for dyes removal was explored using methyl orange (MO) as model pollutant dye. LBC-800 sample obtained at 800 °C had the largest capacity of 320 mg/g in 300 mg/L solution at 25 °C with fast equilibrium time of 60 min, and pseudo-second order model expressed better for kinetics. LBC-800 also had an unprecedented maximum capacity of 449 mg/g with superior conformity to Langmuir model. The biochar was efficient for MO removal with high capacity and fast kinetic, and significantly the sustainable feature of lotus root would allow a large-scale production of biochar as well as promising use in wastewater treatment fields.

Fabrication of N-doped carbons from waste bamboo shoot shell with high removal efficiency of organic dyes from water

N-doped carbons were obtained from bamboo shoot shell via hydrothermal pretreatment under salt assistance followed by carbonization, using melamine as nitrogen source. The carbons with tubular morphology and surface areas in 406-489 m²/g range were used as adsorbents for the removal of methyl orange (MO) and rhodamine B (RhB). Adsorption isotherms and kinetic fitting showed much better accordance with Freundlich model and pseudo-second-order, showing balanced capacity (q_e) of 50 mg/g for MO and 42 mg/g for RhB on the pristine carbons (BHC-800) at 25 °C. After N-doping treatment, carbons (BSC-M20) had q_e of MO and RhB up to 140 and 100 mg/g, respectively, confirming a positive effect of N-doping on the enhancement of dyes removal. The findings indicated that hydrothermal treatment followed by carbonization was efficient to obtain N-doped carbons from biomass materials, and the present BSS-derived carbons were promising adsorbents for organic dyes removal from water.

Structure Engineering in Biomass-Derived Carbon Materials for Electrochemical Energy Storage

Biomass-derived carbon materials (B-d-CMs) are considered as a group of very promising electrode materials for electrochemical energy storage (EES) by virtue of their naturally diverse and intricate microarchitectures, extensive and low-cost source, environmental friendliness, and feasibility to be produced in a large scale. However, the practical application of raw B-d-CMs in EES is limited by their relatively rare storage sites and low diffusion kinetics. In recent years, various strategies from structural design to material composite manipulation have been explored to overcome these problems. In this review, a controllable design of B-d-CM structures boosting their storage sites and diffusion kinetics for EES devices including SIBs, Li-S batteries, and supercapacitors is systematically summarized from the aspects of effects of pseudographic structure, hierarchical pore structure, surface functional groups, and heteroatom doping of B-d-CMs, as well as the composite structure of B-d-CMs, aiming to provide guidance for further rational design of the B-d-CMs for high-performance EES devices. Besides, the contemporary challenges and perspectives on B-d-CMs and their composites are also proposed for further practical application of B-d-CMs for EES devices.

Effective Adsorption of Diesel Oil by Crab-Shell-Derived Biochar Nanomaterials

This study, for the first time, rendered crab shell activated biochar modified by potassium hydroxide (KOH) impregnation (CSAB), revealing a new potential application in the removal of diesel oil from oily wastewater. The structural characteristics of crab shell biochar (CSB) and CSAB were investigated by SEM, and the crystal structure and optical properties of as-prepared samples were analyzed using XRD and FTIR. Results showed that CSAB had stratified surface structure morphology, abundant functional groups, and that its high specific surface area could reach up to 2441 m²/g, which was about eight times larger than that of untreated CSB (307 m²/g). An adsorption isotherm study indicated that the actual adsorption process both of CSAB and CSB were found to fit better with the Freundlich equation. Moreover, chemical interaction controlled the adsorption kinetics efficiency while the adsorption equilibrium capacity was 93.9 mg/g. Due to its highly developed pore structure, unique surface characteristics, and effective adsorption performance, this low-cost activated carbon had the potential to serve as an efficient adsorbent for water pollution purification.

In6S7 nanoparticle-embedded and sulfur and nitrogen co-doped microporous carbons derived from In(tdc)2 metal-organic framework

Indium sulfide nanoparticle (NP)-embedded microporous carbons co-doped with S- and N-dopants are easily prepared by a direct carbonization of the as-prepared In(iii)-based metal-organic framework (In-MOF), [Et₂NH₂][In(tdc)₂]·DEF, containing ditopic S-containing 2,5-thiophenedicarboxylate (tdc^2-) bridging linkers as a potential source of S-dopant. The charge on the anionic framework of [In(tdc)₂]^- is balanced by Et₂NH₂⁺, which is also a potential N-dopant. Simultaneous embedding of In-based NPs, S-, and N-co-doping is achieved in a simple single step carbonization of In-MOF. Three porous carbon materials (PCMs), PCM-700, PCM-800, and PCM-900, are obtained from the carbonization of In-MOF at 700, 800, and 900 °C, respectively. The gas sorption analysis indicates them as good CO₂ sorbents. The photocatalytic degradation of methyl orange by PCMs under visible light irradiation is also effectively operable owing to the photocatalytically active semiconducting indium sulfide NP with a small bandgap. The main component of indium sulfide NPs is revealed as In₆S₇ based on the powder X-ray diffraction pattern. Small amounts of metallic In and In₂S₃ are also observed. The specific capacitances of PCMs are also estimated from the galvanostatic charge/discharge curves. PCM-900 exhibits the highest gravimetric specific capacitance of 99.0 F g^-1 at a current density of 0.05 A g^-1.

Template-assisted in situ confinement synthesis of nitrogen and oxygen co-doped 3D porous carbon network for high-performance sodium-ion battery anode

Nitrogen and oxygen co-doped porous carbon network is synthesized by NaCl template-assisted in situ confinement method and used for a high-performance sodium-ion battery anode.

Hierarchical porous activated biochar derived from marine macroalgae wastes (Enteromorpha prolifera): facile synthesis and its application on Methylene Blue removal

Biochar is one of the most promising candidates of the cost-effective adsorbent for wastewater treatment. Herein, a novel hierarchical porous activated biochar derived from Enteromorpha prolifera (EPAC) was synthesized via an oily sludge-assisted “one-step” carbonization and activation approach. The results proved that the oily sludge additive acts as a natural structure directing agent during the EPAC preparation. The resultant EPAC possesses favorable properties such as high surface area and hierarchical pore distribution, which bring about its outstanding adsorption capability (910 mg g⁻¹) for Methylene Blue dyes from wastewater. The adsorption kinetics, isotherms, thermodynamics and the effect of pH and the background ionic species on the adsorption process were investigated. The adsorption data could be well illustrated by Langmuir models and pseudo-second-order models. Furthermore, thermodynamic parameters revealed that the adsorption reaction was an endothermic and spontaneous process. The adsorption process was influenced by the solution pH and background ionic species because of the competitive adsorption. Moreover, the regeneration analysis demonstrates a presentable recyclability of the EPAC. In view of its good adsorption performance, the EPAC prepared in this study has the potential of treating dye wastewater in practical applications.

Enteromorpha prolifera-based activated biochar was synthesized by an oily sludge-assisted “one-step” carbonization and activation method for Methylene Blue removal.

Symmetric Supercapacitor Electrodes from KOH Activation of Pristine, Carbonized, and Hydrothermally Treated Melia azedarach Stones

Waste biomass-derived activated carbons (ACs) are promising materials for supercapacitor electrodes due to their abundance and low cost. In this study, we investigated the potential use of Melia azedarach (MA) stones to prepare ACs for supercapacitors. The ash content was considerably lower in MA stones (0.7% ash) than that found in other lignocellulosic wastes. ACs were prepared by KOH activation of pristine, carbonized, and hydrothermally-treated MA stones. The morphology, composition, surface area, porosity, and surface chemistry of the ACs were determined. Electrochemical measurements were carried out in three- and two-electrode cells, 3EC and 2EC, respectively, using 1 M H₂SO₄ as the electrolyte. The highest capacitance from galvanostatic charge-discharge (GCD) in 2EC ranged between 232 and 240 F·g⁻¹ at 1 A·g⁻¹. The maximum energy density reached was 27.4 Wh·kg⁻¹ at a power density of 110 W·kg⁻¹. Electrochemical impedance spectroscopy (EIS) revealed an increase in equivalent series resistance (ESR) and charge transfer resistance (R_CT) with greater ash content. Electrochemical performance of MA stone-derived ACs was compared with that of other ACs described in the recent literature that were prepared from different biomass wastes and results showed that they are among the best ACs for supercapacitor applications.

Macroalgae-derived nitrogen-doped hierarchical porous carbons with high performance for H2 storage and supercapacitors

Enteromorpha prolifera was converted into hierarchical carbons through the carbonization and activation with surface area and pore volume up to 3345 m² g⁻¹ and 1.94 cm³ g⁻¹, showing excellent performance for H₂ storage and supercapacitors.