Tailoring of porous and nitrogen-rich carbons derived from hydrochar for high-performance supercapacitor electrodes

The Impact of N/O-Functional Groups on the Sorption Capabilities of Activated Carbons Derived from Furfuryl Alcohol

This work describes the effect of nitrogen and oxygen functional groups on the sorption properties of activated carbons produced from furfuryl alcohol. The poly(furfuryl) alcohol underwent carbonization in nitrogen, ammonia, and ammonia and air (in a 3:2 proportion) atmospheres at 600 °C for 4 h. The resulting materials were subsequently activated in a carbon dioxide atmosphere for 1 h at temperatures of 700 °C, 800 °C, 900 °C, and 1000 °C. The X-ray photoelectron spectroscopy (XPS) findings suggest that ammoxidation is superior to amination in terms of nitrogen doping. The maximum nitrogen concentration achieved after ammoxidation was 25 at.%, which decreased to 4 at.% after activation. Additionally, it was observed that oxygen functional groups have a greater impact on porous structure development compared to nitrogen functional groups. The materials activated through carbonization under an ammonia/air atmosphere attained the highest oxygen concentration of roughly 19 at.% as confirmed by XPS. The materials were evaluated for their sorption capacities for carbon dioxide and ethylene, which were 2.2 mmol/g and 2.9 mmol/g, respectively, at 30 °C.

Mild and Efficient One-Step Synthesis of Nitrogen-Doped Multistage Porous Carbon for High-Performance Supercapacitors

Biomass-derived carbon materials have broad application prospects in energy storage, but still face problems such as complex synthesis paths and the massive use of corrosive activators. In this study, we proposed a mild and efficient pathway to prepare nitrogen-doped porous carbon material (N-YAC) using one-step pyrolysis with solid K2CO3, tobacco straw, and melamine. The optimized material (N-YAC0.5) was not only enriched with nitrogen, but also exhibited a high specific surface area (2367 m2/g) and a reasonable pore size distribution (46.49% mesopores). When utilized in electrodes, N-YAC0.5 exhibited an excellent capacitance performance (338 F/g at 1 A/g) in the three-electrode system, and benefitted from a high mesopore distribution that maintained a capacitance of 85.2% (288 F/g) at high current densities (20 A/g). Furthermore, the composed symmetric capacitor achieved an energy density of 14.78 Wh/kg at a power density of 400 W/kg. In summary, our work provides a novel and eco-friendly approach for converting biomass into high-performance energy-storage materials.

Decoration of sodium carboxymethylcellulose gel microspheres with modified lignin to enhanced methylene blue removal

The introduction of active groups from biomass is currently the most promising alternative method for increasing the adsorption effect of dyes. In this study, modified aminated lignin (MAL) rich in phenolic hydroxyl and amine groups was prepared by amination and catalytic grafting. The factors influencing the modification conditions of the content of amine and phenolic hydroxyl groups were explored. Chemical structural analysis results confirmed that MAL was successfully prepared using a two-step method. The content of phenolic hydroxyl groups in MAL significantly increased to 1.46 mmol/g. MAL/sodium carboxymethylcellulose (NaCMC) gel microspheres (MCGM) with enhanced methylene blue (MB) adsorption capacity owing to the formation of a composite with MAL were synthesized by a sol-gel process followed by freeze-drying and using multivalent cations Al³⁺ as cross-linking agents. In addition, the effects of the MAL to NaCMC mass ratio, time, concentration, and pH on the adsorption of MB were explored. Benefiting from a sufficient number of active sites, MCGM exhibited an ultrahigh adsorption capacity for MB removal, and the maximum adsorption capacity was 118.30 mg/g. These results demonstrated the potential of MCGM for wastewater treatment applications.

In situ boron-doped cellulose-based biochar for effective removal of neonicotinoids: Adsorption mechanism and safety evaluation

Biochar materials have been widely employed for adsorption of pollutants, which necessitates further consideration of their efficiency and safety in environmental remediation. In this study, a porous biochar (AC) was prepared through the combination of hydrothermal carbonization and in situ boron doping activation to effectively adsorb neonicotinoids. The adsorption process was shown to be a spontaneous endothermic physical adsorption process, where the predominant interaction forces between the acetamiprid and AC were electrostatic and hydrophobic interactions. The maximum adsorption capacity was 227.8 mg g^-1for acetamiprid and the safety of AC was verified by simulating the situation where the aquatic organism (D. magna) was exposed to the combined system (AC & neonicotinoids). Interestingly, AC was observed to reduce the acute toxicity of neonicotinoids owing to the reduced bioavailability of acetamiprid in D. magna and the newly generated expression of cytochrome p450. Thus, it enhanced the metabolism and detoxification response in D. magna, which reducing the biological toxicity of acetamiprid. This study not only demonstrates the potential application of AC from a safety perspective, but also provides insight into the combined toxicity caused by biochar after adsorption of pollutants at the genomic level, which fills the gap in related research.

Effect of Pretreatment with Acids on the N-Functionalization of Carbon Nanofibers Using Melamine

Nowadays, N-functionalized carbon nanomaterials attract a growing interest. The use of melamine as a functionalizing agent looks prospective from environmental and cost points of view. Moreover, the melamine molecule contains a high amount of nitrogen with an atomic ratio C/N of 1/2. In present work, the initial carbon nanofibers (CNFs) were synthesized via catalytic pyrolysis of ethylene over microdispersed Ni-Cu alloy. The CNF materials were pretreated with 12% hydrochloric acid or with a mixture of concentrated nitric and sulfuric acids, which allowed etching of the metals from the fibers and oxidizing of the fibers' surface. Finally, the CNFs were N-functionalized via their impregnation with a melamine solution and thermolysis in an inert atmosphere. According to the microscopic data, the initial structure of the CNFs remained the same after the pretreatment and post-functionalization procedures. At the same time, the surface of the N-functionalized CNFs became more defective. The textural properties of the materials were also affected. In the case of the oxidative treatment with a mixture of acids, the highest content of the surface oxygen of 11.8% was registered by X-ray photoelectron spectroscopy. The amount of nitrogen introduced during the post-functionalization of CNFs with melamine increased from 1.4 to 4.3%. Along with this, the surface oxygen concentration diminished to 6.4%.

Multifunctional Loblolly Pine-Derived Superactivated Hydrochar: Effect of Hydrothermal Carbonization on Hydrogen and Electron Storage with Carbon Dioxide and Dye Removal

Pore modulation via hydrothermal carbonization (HTC) needs investigation due to its crucial effect on surface that influences its multirole utilization of such ultraporous sorbents in applications of energy storage- hydrogen and capacitive- as well as for pollutant abatement- carbon capture and dye removal. Hence, loblolly pine was hydrothermally carbonized followed by KOH activation to synthesize superactivated hydrochars (SAH). The resulting SAHs had specific surface area (SSA) 1462-1703 m²/g, total pore (TPV) and micropore volume (MPV) of 0.62-0.78 cm³/g and 0.33-0.49 cm³/g, respectively. The SAHs exhibit excellent multifunctional performance with remarkably high atmospheric CO₂ capture of 145.2 mg/g and high pressure cryogenic H₂ storage of 54.9 mg/g. The fabricated supercapacitor displayed substantial specific capacitance value of maximum 47.2 Fg^-1 at 1 A g^-1 in 6 M KOH and highest MB dye removal of 719.4 mg/g. Higher HTC temperature resulted in increased surface porosity as higher SSA, TPV benefitted H₂ storage and MB dye removal while superior MPV favored CO₂ capture. Moderate HTC temperature ensured higher mesopore-to-macropore volume ratio favoring electrochemical performance. Isotherm modelling of the adsorbates was compared using models: Langmuir, Freundlich, Langmuir- Freundlich and Temkin.

Nitrogen-doped biochar as peroxymonosulfate activator to degrade 2,4-dichlorophenol: Preparation, properties and structure-activity relationship

Nitrogen-doped biochar (NCMs) has shown great potential as metal-free catalysts for persulfates. To understand the evolution law of properties of NCMs with preparation conditions, eleven NCMs were prepared and characterized by EA, BET, Raman, XPS, and conductivity. Surface area and conductivity can be improved by higher pyrolysis temperature and longer retention time. Distribution of nitrogen species of NCMs was greatly influenced by pyrolysis temperature. Subsequently, these NCMs were applied to activate peroxymonosulfate to degrade 2,4-dichlorophenol. A linear correlation of the initial apparent degradation rate constant (k_obs) of 2,4-dichlorophenol with conductivity and ratio of graphitic N was newly established, revealing that conductivity and graphitic N of NCMs would be the key property deciding degradation efficiency of 2,4-dichlorophenol. Positive effect of conductivity can be ascribed to the mediated electron-transfer mechanism. Electron-transfer mechanism is also proved by quenching experiments and solvent deuterium isotope effect experiment. Graphitic N would be the main active site for PMS activation. Understanding the evolvement rule of properties of NCMs with preparation conditions combined with the correlations between reactivity and properties of NCMs is meaningful for preparation of nitrogen-doped biochar as well as the development of carbonaceous materials with high performance in persulfates-based advanced oxidation processes.

High-efficiency N-doped activated carbon-based defluoridation adsorbent prepared from itaconic acid fermentation waste liquid

Excessive amounts of fluoride in water cause irreversible harm to people and seriously threaten human health.

A Short Review on the Electrochemical Performance of Hierarchical and Nitrogen-Doped Activated Biocarbon-Based Electrodes for Supercapacitors

Cheap and efficient carbon electrodes (CEs) for energy storage systems (ESS) such as supercapacitors (SCs) and batteries are an increasing priority issue, among other things, due to a globally increasing share of intermittent electricity production (solar and wind) and electrification of transport. The increasing consumption of portable and non-portable electronic devices justifies research that enables environmentally and economically sustainable production (materials, processing techniques, and product design) of products with a high electrochemical performance at an acceptable cost. Among all the currently explored CEs materials, biomass-based activated carbons (AC) present enormous potential due to their availability and low-cost, easy processing methods, physicochemical stability, and methods for self-doping. Nitrogen doping methods in CEs for SCs have been demonstrated to enhance its conductivities, surface wettability, and induced pseudocapacitance effect, thereby delivering improved energy/power densities with versatile properties. Herein, a short review is presented, focusing on the different types of natural carbon sources for preparing CEs towards the fabrication of SCs with high electrochemical performance. The influences of ACs' pore characteristics (micro and mesoporosity) and nitrogen doping on the overall electrochemical performance (EP) are addressed.

An all-lignin-based flexible supercapacitor based on a nitrogen-doped carbon dot functionalized graphene hydrogel

In this manuscript, the synthesis of a nitrogen-doped carbon dot functionalized graphene hydrogel and its application as a supercapacitor electrode have been reported.

Challenges and opportunities of hydrothermal carbonisation in the UK; case study in Chirnside

The latest research and development in hydrothermal carbonisation (HTC) processes are reviewed and the feasibility of application to small towns in the UK is assessed. The HTC process designed in this report is theoretically evaluated for the biodegradable municipal waste and sewage waste produced by the small town of Chirnside, in the Scottish Borders. Calculation of mass and energy balances of the process are carried out alongside the evaluation of challenges and environmental, social and economic opportunities presented. The hypothetical HTC plant is capable of processing 267.14 t per year of food waste and 105.12 t per year of faecal sludge produced by Chirnsides estimated 2250 residents in 2041. The plant would be capable of producing 99.08 t per year of hydrochar with an estimated total energy content of 540.26 MWh per year. When used in a Biomass Combined Heat and Power Plant, the hydrochar would be capable of supplying Chirnsides residents with 0.71% and 3.43% of its domestic thermal energy demand and domestic electrical energy demand in 2041, respectively. Both the expected opportunities and challenges for the application of HTC are discussed, shedding light on the associated research in regards to this sustainable technology.

The latest research and development in hydrothermal carbonisation (HTC) processes are reviewed and the feasibility of application to small towns in the UK is assessed.

Bamboo derived hydrochar microspheres fabricated by acid-assisted hydrothermal carbonization

In this study, bamboo residues derived functional hydrochar microspheres have been fabricated by different acids-assisted hydrothermal carbonization including hydrochloric aicd, sulfuric acid or nitric acid.The energy-dispersive X-ray fluorescence spectroscopy and Fourier Transform Infrared spectroscopy analyses showed that sulfur- and nitrogen-containing functional groups were grafted on the surface of hydrochar microspheres, respectively. Elemental analysis indicates that the addition of acids has a significant influence on the hydrothermal reaction pathway and promotes the hydrolysis process. When the hydrothermal carbonization temperature is 220 °C, hydrochloric acid and nitric acid can effectively overcome the agglomeration of hydrochar microspheres and form single micron carbon sphere. Irregularly shaped hydrochar particles groups were formed during sulfuric acid-assisted hydrothermal treatment. The results indicate the viability of acid assisted hydrothermal carbonization to produce the functional hydrochar microsphere using bamboo residues.

Adsorption of phenanthrene from aqueous solutions by biochar derived from an ammoniation-hydrothermal method

An innovative ammoniation-hydrothermal method of biochar production was developed for the adsorption of phenanthrene (PHE) from aqueous solutions in this paper. Phragmites australis (PA) was used to produce biochar in a hydrothermal kettle at 280 °C in muffle furnace using urea as an ammoniation reagent. Characterizations were executed by scanning electron microscope (SEM), N₂ adsorption/desorption isotherms, X-ray diffraction (XRD), elemental analysis, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) to explore its morphological, physical, and chemical properties. Batch experiments of PHE adsorption were carried out to study the adsorption isotherms and kinetics. Quantum chemistry computational simulations were employed based on density functional theory (DFT) to establish and optimize adsorption configurations and analyze the biochar's structural effects on adsorption performance. Results showed that the ammoniation-hydrothermal method produced biochar with a higher surface area and a maximum equilibrium adsorption capacity of 1.97 mg/g. The adsorption fitted well with Freundlich isotherm model (R² > 0.96) and Pseudo-second-order kinetic model (R² > 0.82). Adsorption energy calculation revealed that the N functionalities, especially pyridine N in the N-doped biochar structure, exhibited stronger binding ability with PHE, which contributed most to the favorable adsorption ability of the ammoniation-hydrothermal biochar.

Porous Carbon Materials Obtained by the Hydrothermal Carbonization of Orange Juice

Porous carbon materials are currently subjected to strong research efforts mainly due to their excellent performances in energy storage devices. A sustainable process to obtain them is hydrothermal carbonization (HTC), in which the decomposition of biomass precursors generates solid products called hydrochars, together with liquid and gaseous products. Hydrochars have a high C content and are rich with oxygen-containing functional groups, which is important for subsequent activation. Orange pomace and orange peels are considered wastes and then have been investigated as possible feedstocks for hydrochars production. On the contrary, orange juice was treated by HTC only to obtain carbon quantum dots. In the present study, pure orange juice was hydrothermally carbonized and the resulting hydrochar was filtered and washed, and graphitized/activated by KOH in nitrogen atmosphere at 800 °C. The resulting material was studied by transmission and scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and nitrogen sorption isotherms. We found porous microspheres with some degree of graphitization and high nitrogen content, a specific surface of 1725 m²/g, and a pore size distribution that make them good candidates for supercapacitor electrodes.

Facile Synthesis of Bio-Template Tubular MCo2O4 (M = Cr, Mn, Ni) Microstructure and Its Electrochemical Performance in Aqueous Electrolyte

In this project, we present a comparative study of the electrochemical performance for tubular MCo2O4 (M = Cr, Mn, Ni) microstructures prepared using cotton fiber as a bio-template. Crystal structure, surface properties, morphology, and electrochemical properties of MCo2O4 are characterized using X-ray diffraction (XRD), gas adsorption, scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), cyclic voltammetry (CV), and galvanostatic charge-discharge cycling (GCD). The electrochemical performance of the electrode made up of tubular MCo2O4 structures was evaluated in aqueous 3M KOH electrolytes. The as-obtained templated MCo2O4 microstructures inherit the tubular morphology. The large-surface-area of tubular microstructures leads to a noticeable pseudocapacitive property with the excellent electrochemical performance of NiCo2O4 with specific capacitance value exceeding 407.2 F/g at 2 mV/s scan rate. In addition, a Coulombic efficiency ~100%, and excellent cycling stability with 100% capacitance retention for MCo2O4 was noted even after 5000 cycles. These tubular MCo2O4 microstructure display peak power density is exceeding 7000 W/Kg. The superior performance of the tubular MCo2O4 microstructure electrode is attributed to their high surface area, adequate pore volume distribution, and active carbon matrix, which allows effective redox reaction and diffusion of hydrated ions.

Porous Doped Carbons from Anthracite for High-Performance Supercapacitors

Carbon-based materials, as some of the most important electrode materials for supercapacitors (SC), have spurred enormous attentions. Now, it is highly desirable but remains an open challenge to design stable and high-capacity carbons for further enhancing supercapacitive function. Here, a facile chemical activation recipe is introduced to develop biomass-derived functional carbons using cheap and abundant natural resources, anthracite, as the heteroatom-rich carbon sources, and potassium hydroxide (KOH) as activator. These porous carbons have high BET surface areas of roughly 2814 m2 g−1, large pore volumes of up to 1.531 cm3 g−1, and a high porosity that combines micro- and small-sized mesopores. The optimal nanocarbon features two additional outstanding virtues: an appropriate N-doping level (2.77%) and a uniform pore size distribution in the narrow range of 1–4 nm. Synergy of the above unique structural traits and desirable chemical composition endows resultant samples with the much boosted supercapacitive property with remarkable specific capacitance at varied current densities (e.g., 325 F g−1 at 0.5 A/g), impressive energy/power density, and long cycling stability over 5000 cycles at 10 A g−1 (92% capacity retention). When constructing the symmetric supercapacitor utilizing a common neutral Na2SO4 electrolyte that can strongly circumvent the corrosion effect occurring in the strong acid/alkaline solutions, both an elevated operation voltage at 1.8 V and a fascinating energy density of 23.5 Wh kg−1 are attained. The current study paves the way to explore the stable, efficient, and high-voltage SC assembled by the anthracite-derived porous doped nanocarbons for a wide spectrum of applications like automobiles, vehicle devices, and so on.

N-Doped 3D hierarchical carbon from resorcinol–formaldehyde–melamine resin for high-performance supercapacitors

N-Doped hierarchical porous carbons were fabricated by foaming and carbonizing resorcinol–formaldehyde–melamine resin and used as electrodes for flexible solid-state supercapacitors.

Hydrothermal carbonization of various lignocellulosics: Fuel characteristics of hydrochars and surface characteristics of activated hydrochars

In the present study, various lignocellulosic biowastes (wood sawdust, olive pomace, walnut shell, apricot seed, tea stalk, hazelnut husk) were hydrothermally carbonized at 220 °C for 90 min. Since the hydrochars have several end-uses, this study particularly investigates their end-use as solid fuels and precursors of activated carbon after chemical activation. Activated hydrochars were obtained from the hydrochars of wood sawdust, olive pomace, walnut shell, apricot seed, tea stalk, hazelnut husk by chemical activation with KOH at 600 °C. As fuels, all hydrochars had higher fixed carbon content, lower volatile matter content and higher ignition temperatures compared to their original biomass samples. Olive pomace hydrochar, which has high heating value (25.56 MJ/kg) and low ash content (5.5%), has the best fuel properties among hydrochars investigated. Activated hydrochars demonstrated BET surface areas of 308.9-666.7 m²/g (activated hydrochar of wood sawdust and tea stalk), and total pore volumes of 0.25-0.73 cm³/g (activated hydrochar of olive pomace and wood sawdust). The average pore size distribution of the activated hydrochars ranged between 1.05 nm (olive pomace)- 4.74 nm (wood sawdust). All agricultural-based activated hydrochars had similar average pore size distribution of 1.05-1.25 nm, which fell in the range of super-microporous structure. With the average pore size of 4.74 nm, activated hydrochar of wood sawdust could be classified under mesoporous structure. This study clearly points out that biomass type definitely affected fuel properties of hydrochars and the porous structure of the activated hydrochars.

Hierarchical porous carbons from polysaccharides carboxymethyl cellulose, bacterial cellulose, and citric acid for supercapacitor

This study reports excellent supercapacitor performance of hierarchical composite porous carbon (HPC) materials successfully fabricated by one-step carbonization and activation process derived from polysaccharides carboxymethyl cellulose, bacterial cellulose, and citric acid. The resultant HPC displayed unique porous nanosheet morphology with high specific surface area (2490 m² g^-1) and rich oxygen content (7.3%). The developed structures with macropores, mesopore walls, micropores, and high oxygen content led to excellent electrochemical performance for electrode of electric double-layer capacitors (EDLCs). In a three-electrode system, the HPC electrode showed a high specific capacitance of 350 F g^-1, good rate performance, and excellent cycling stability. The energy density of supercapacitor based on HPC was comparable to or higher than that of commercially supercapacitors. More importantly, two series-wound devices were easy to light light-emitting diode (LED, 3.0 V). These results suggest that the current material is a promising candidate for low-cost and eco-friendly energy storage devices.

An evaluation of subcritical hydrothermal treatment of end-of-pipe palm oil mill effluent

This study evaluates the effects of subcritical hydrothermal treatment on palm oil mill effluent (POME) and its concomitant formations of solid hydrochar, liquid product and gaseous product. The reactions were carried out at temperatures ranged 493 K–533 K for 2 h. The highest reduction of chemical oxygen demand (COD) and biochemical oxygen demand (BOD) were 58.8% and 62.5%, respectively, at 533 K. In addition, the removal of total suspended solids (TSS) achieved up to 99%, with the pH of POME reaching 6 from the initial pH 4. The gas chromatography coupled with mass spectroscopy (GC-MS) analysis showed that the fresh POME contained n-Hexadecanoic acid as the dominant component, which gradually reduced in the liquid product in the reaction with increased temperature, in addition to the attenuation of carboxyl compounds and elevation of phenolic components. The gaseous products contained CO₂, CO, H₂, and C₃ – C₆ hydrocarbons. Traces of CH₄ were only found at 533 K. CO₂ is the dominant species, where the highest of 3.99 vol% per 500 mL working volume of POME recorded at 533 K. The solid hydrochars showed negligible morphological changes across the reaction temperature. The O/C atomic ratio of the hydrochar range from 0.157 to 0.379, while the H/C atomic ratio was in the range from 0.930 to 1.506. With the increase of treatment temperature, the higher heating value (HHV) of the hydrochar improved from 24.624 to 27.513 MJ kg^-1. The characteristics of hydrochar make it a fuel source with immense potential. POME decomposed into water-soluble compounds, followed by deoxygenation (dehydration and decarboxylation) in producing hydrochar with lower oxygen content and higher aromatic compounds in the liquid product. Little gaseous hydrocarbons were produced due to subcritical hydrothermal gasification at low temperature.

A higher efficiency removal of neonicotinoid insecticides by modified cellulose-based complex particle

Cellulose as an eco-friendly material is extensive in the nature. In this study, modified cellulose-based complex particle (MCCP) was produced through hydrothermal carbonization with methacrylic acid in the stirring and sand bath circumstance. The activated modified carbon-based porous particle (AMCCP) was prepared by treating with potassium hydroxide at high temperature, showing higher efficiency in removing neonicotinoids than MCCP. The AMCCP was fully characterized via scanning electron microscopy, X-ray photoelectron spectroscopy and Brunauer-Emmett-Teller analysis. The Brunauer-Emmett-Teller analysis showed the prepared AMCCP has smaller aggregated particles with higher surface area than MCCP. The adsorption kinetic and the adsorption isotherm of AMCCP were studied, revealing that the pseudo-second-order kinetic model and the Langmuir model correlated with the experimental data better. The maximum adsorption capacity of AMCCP is 142.36 mg/g for acetamiprid. The adsorption process is spontaneous, favorable, and endothermic in nature. After five regeneration time, the adsorption efficiency of the AMCCP is still over 95%.

Hydrothermal carbonization of arecanut husk biomass: fuel properties and sorption of metals

In this study, hydrothermal carbonization of arecanut husk and its potential application as an alternate solid fuel and heavy metal sorption (adsorbent) was attempted. Arecanut husk (AH) treated with citric acid for 9 h resulted in the hydrochar yield of 58.7% with increased fixed carbon from 17 to 39.7% and HHV from 16.98 to 21.14 MJ kg^-1 compared to the parent biomass. The arecanut husk hydrochar (AHH) had H/C of 1.27, O/C ratio of 0.59 with an energy yield of 72.81%, and energy densification ratio of 1.24, and the values have the similar fuel characteristics of lignite. The pH, zeta potential, and surface of the hydrochar were 5.56, - 22.60 mV, and 0.98 m² g^-1 respectively. Hydrochar with a dosage of 0.1% showed a maximum rate of adsorption for Pb²⁺ (79.86 mg g^-1) at the initial concentration of 100 mg L^-1 in the aqueous solution compared to Zn²⁺, Cr⁶⁺, and Ni²⁺. SEM with EDAX and FT-IR spectroscopy results confirmed the presence of Pb²⁺ and changes in functional groups in arecanut husk hydrochar after adsorption of heavy metals in the aqueous solution.

One-step preparation of N,O co-doped 3D hierarchically porous carbon derived from soybean dregs for high-performance supercapacitors

Hierarchically porous carbon (HPC) material based on environmental friendliness biomass has spurred much attention, due to its high surface area and porous structure. Herein, three-dimensional (3D) N,O co-doped HPC (N–O-HPC) was prepared by using a one-step fabrication process of simultaneously carbonizing and activating soybean dregs and used as an electrode for supercapacitors (SCs). The obtained N–O-HPC with 4.8 at% N and 6.1 at% O exhibits a pretty small charge transfer resistance (0.05 Ω) and a large specific capacitance (408 F g⁻¹ at 1 A g⁻¹), due to its 3D hierarchically porous framework structure with extremely large specific surface area (1688 m² g⁻¹). Moreover, a symmetrical SC assembled with the HPC electrode exhibits an amazingly high energy density (22 W h kg⁻¹ at 450 W kg⁻¹) and a stable long cycling life with only 6% capacitance loss after 5000 cycles in 1 M Na₂SO₄ solution. This work provides a facile, green, and low-cost way to prepare electrode materials for SCs.

N,O co-doped 3D HPC derived from soybean dregs was prepared by a one-step method and displays an amazingly high energy density of 22 W h kg⁻¹ (450 W kg⁻¹) using 1 M Na₂SO₄ solution.

Distinctive Construction of Chitin-Derived Hierarchically Porous Carbon Microspheres/Polyaniline for High-Rate Supercapacitors

Recently, nanostructured porous carbons are attracting significant interest in various important applications. However, a green and innovative method to fabricate hierarchically porous-structured carbon is still a challenge. In the present work, hierarchically porous carbon microspheres (HCMs) were prepared by pyrolyzing the chitin microspheres fabricated from a chitin/chitosan blend solution, in which chitosan was used as a forming agent of nanopores/nanochannels to construct the microspheres. The HCM displayed hierarchical porous structure and improved specific surface area of 1450 m²/g. For the application of HCM in hybrid electrode materials as supercapacitors, polyaniline (PANI) nanoclusters were further deposited on the surface of HCM. A symmetric supercapacitor based on HCM-PANI exhibited high rate capability with retaining over 64% of the capacitance as the scan rate increased from 2 to 500 mV/s. This work introduced a distinctive and green method to fabricate hierarchically porous carbon materials, having considerable application prospect for energy storage.

Hierarchical Nanostructures of Nitrogen-Doped Porous Carbon Polyhedrons Confined in Carbon Nanosheets for High-Performance Supercapacitors

Interconnected close-packed nitrogen-doped porous carbon polyhedrons (NCPs) confined in two-dimensional carbon nanosheets (CNSs) have been prepared through a sustainable one-pot pyrolysis of a simple solid mixture of zeolitic imidazolate framework-8 (ZIF-8) crystals and with organic potassium as the precursors. The hierarchically organized framework of the NCP-CNS composites enables NCPs and CNSs to act as well-defined electrolyte reservoirs and mechanical buffers accommodating large volume expansions of NCPs, respectively. Among the unique composite nanostructures, the NCPs with vast micropores provide electric double-layer capacitances, while the CNSs bridge the individual NCPs to form a conductive pathway with a hierarchical porosity. As a result, the NCP-CNS composites with high electrical integrity and structural stability are used as electrode materials for high-performance supercapacitors, which exhibit excellent electrochemical capacitive characteristics in terms of an outstanding capacitance of 300 F g^-1 at 1 A g^-1, large energy density of 20.9 W h kg^-1, and great cycling performance of 100% retention after 6000 cycles. This work therefore presents a one-pot and efficient strategy to prepare an ordered arrangement of ZIF-8-derived porous carbons toward new electrode materials in promising energy storage systems.

Digested sludge-derived three-dimensional hierarchical porous carbon for high-performance supercapacitor electrode

Digested sludge, as the main by-product of the sewage sludge anaerobic digestion process, still contains considerable organic compounds. In this protocol, we report a facile method for preparing digested sludge-derived self-doped porous carbon material for high-performance supercapacitor electrodes via a sustainable pyrolysis/activation process. The obtained digested sludge-derived carbon material (HPDSC) exhibits versatile O-, N-doped hierarchical porous framework, high specific surface area (2103.6 m² g^-1) and partial graphitization phase, which can facilitate ion transport, provide more storage sites for electrolyte ions and enhance the conductivity of active electrode materials. The HPDSC-based supercapacitor electrodes show favourable energy storage performance, with a specific capacitance of 245 F g^-1 at 1.0 A g^-1 in 0.5 M Na₂SO₄; outstanding cycling stability, with 98.4% capacitance retention after 2000 cycles; and good rate performance (211 F g^-1 at 11 A g^-1). This work provides a unique self-doped three-dimensional hierarchical porous carbon material with a favourable charge storage capacity and at the same time finds a high value-added and environment-friendly strategy for disposal and recycling of digested sludge.

A novel and facile synthesis approach for a porous carbon/graphene composite for high-performance supercapacitors

We propose a novel and facile synthesis approach to a porous carbon/graphene composite. Graphene is obtained from room-temperature expanded graphite (RTEG), not involving the use of graphite oxide (GO). Porous carbon is acquired by carbonization and KOH-activation of polyvinylpyrrolidone (PVP), which is used to exfoliate RTEG into graphene and inhibit the restacking of the resultant graphene in the present work. The prepared porous carbon/graphene composite has a high specific surface area (SSA) (3008 m² g^-1) and a hierarchical micro- and meso- pore structure (dominant pores in the range of 1-5 nm). Electrochemical measurement demonstrates that the as-prepared porous carbon/graphene composite can deliver an outstanding specific capacitance of up to 340 F g^-1 at 5 mV s^-1 in 6 M KOH electrolyte. This specific capacitance is among the highest reported so far for porous carbon/graphene materials. Moreover, the prepared composite as an electrode material also exhibits excellent cycling stability (94.4% capacitance retention over 10 000 cycles). The as-fabricated symmetrical supercapacitor exhibits a high energy density of 10.9 W h kg^-1 (based on total mass of electrode materials) and an outstanding energy density retention, even at high power density. Compared with conventional preparation routes for porous carbon/graphene composites, the present approach is significantly simple, convenient and cost-effective, which will make it more competent in the development of electrode materials for high-performance supercapacitors.

A carbonised sieve-like corn straw cellulose–graphene oxide composite for organophosphorus pesticide removal

The development of efficient adsorbents for the removal of organophosphorus pesticides from water is a major challenge. In this work, we prepared an activated carbon derived from sieve-like cellulose/graphene oxide composites (ACCE/G) for the removal of several organophosphorus pesticides. We employed corn straw to produce a sieve-like cellulose–graphene oxide composite (CCE/G); then, by treating CCE/G with potassium hydroxide at high temperatures, the efficient adsorbent ACCE/G was prepared. The adsorption capacity of ACCE/G is higher than those of other sorbents, including a multi-wall carbon nanotube, graphitised carbon black, activated carbon, C18, and primary secondary amine adsorbent. The ACCE/G structure has been fully characterised via scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and Brunauer–Emmett–Teller analysis. The maximum adsorption capacity of ACCE/G is 152.5 mg g⁻¹ for chlorpyrifos. The mechanism, the thermodynamic properties, and the kinetics of the adsorption process have been investigated as well. Our findings demonstrate that the adsorption mechanism depends on the electron-donating abilities of the S and P atoms. Moreover, the Langmuir model gives the best fit for the isotherm data, and the adsorption efficiency of the ACCE/G is still over 80% after eight times of recycling, making ACCE/G a valuable candidate for the removal of OPPs.

Synthesizing a reusable adsorbent from waste corn straw is a sustainable way to utilize secondary resources and purify water.

Facile fabrication of hierarchical porous carbon based on extract separated from coal with outstanding electrochemical performance

Herein, a novel kind of hierarchical porous carbons were directly synthesized from low-cost extracts of coal by coupling nano MgO template with in situ KOH activation strategy.