Graphitic Biocarbon from Metal-Catalyzed Hydrothermal Carbonization of Lignin

From waste corn straw to graphitic porous carbon: A trade-off between specific surface area and graphitization degree for efficient peroxydisulfate activation

Electron transfer pathways have been verified as overriding regimes when peroxydisulfate (PDS) was activated by porous carbon. The incorporation of graphitic structure into carbon matrix was favorable to the rapid electron transfer, but excessive graphitization would deteriorate the specific surface area (SSA), weakening the catalytic performance. The reasonable trade-off between SSA and graphitization degree was necessary and challenging for the preparation of efficient carbon based PS-activators. Herein, a series of graphitic porous carbon with discrepant SSA and graphitic structure were fabricated. The incorporation of graphitization tracks into ultra-thin edges on porous carbon film was verified by multifarious structural characterization. After trade-off, the optimum catalyst exhibited superior catalytic performance with degradation rate constant (kobs) exceeding that of ungraphitized precursor by up to 16.0 times. Mechanistic investigations substantiated that the sufficient SSA of catalyst provided favorable conditions for its affinity towards PDS and sulfadiazine (SDZ), resulting in the formation of PDS* complexes and SDZ adsorption, while the appropriate graphitization degree ensured the reinforced electron transfer rate, which collectively accelerated SDZ oxidation through electron-transfer pathway. The multivariate linear regression model linking kobs to SSA and graphitization degree was established providing basis to construct efficient catalysts for PDS activation.

Effective Removal of Carcinogenic Azo Dye from Water Using Zea mays-Derived Mesoporous Activated Carbon

Addressing industrial wastewater treatment challenges and removing hazardous organic pollutants, such as carcinogenic methyl orange (MO) and azo dyes, is a pressing concern. This study explores the use of the Zea mays envelope, an agricultural waste product, to produce Z. mays activated carbon (ZMAC) through the chemical activation of maize envelopes with phosphoric acid. Various analytical techniques, including FTIR, XRD, TGA, DSC, and SEM, characterize ZMAC. Results show that ZMAC exhibits an impressive monolayer adsorption capacity of 66.2 mg/g for MO. The Langmuir isotherm model fits the experimental data well, indicating monolayer coverage of the MO on the ZMAC surface. The pH-sensitive adsorption process demonstrates an optimal removal efficiency at pH 4. ZMAC follows the pseudo-second-order kinetic model, and diffusion rate constant analysis identifies three consecutive stages in the adsorption process. Moreover, the uptake of MO ions by ZMAC is identified as an exothermic and spontaneous process. Reusability tests demonstrate efficient regeneration of ZMAC up to five times with 1 mL of 2 M HNO3 in each cycle, without sorbent mass loss. Thermodynamic analysis shows an increase in the uptake capacity from 66.2 to 73.2 mg/g with temperature elevation. This study offers practical solutions for industrial wastewater treatment challenges, providing an environmentally sustainable and effective approach to mitigate the risks associated with hazardous organic pollutants.

Biobased chitosan-derived self-nitrogen-doped porous carbon nanofibers containing nitrogen-doped zeolites for efficient removal of uremic toxins during hemodialysis

Highly efficient adsorbents are needed to remove uremic toxins and reduce the economic and societal burden of the current dialysis treatments in resource-limited environments. In this study, nanostructured porous carbon nanofibers with nitrogen-doped zeolites (NZ-PCNF) were prepared, by electrospinning zeolites with chitosan-poly(ethylene oxide) blends, followed by a one-step carbonization process, without further activation steps or aggressive chemical additives for N-doping. The results showed that N-zeolites were successfully integrated into an ultrafine carbon nanofiber network, with a uniform nanofiber diameter of approximately 25 nm, hierarchical porous structure (micro- and mesopores), and high specific surface area (639.29 m2/g), facilitating uremic toxin diffusion and adsorption. The self-N-doped structure in the NZ-PCNF removed more creatinine (∼1.8 times) than the porous carbon nanofibers when using the same weight of precursor materials. Cytotoxicity and hemolysis tests were performed to verify the safety of NZ-PCNF. This study provides a novel strategy for transforming chitosan-based materials into state-of-the-art porous carbon nanofiber/zeolite self-N-doped composites, affording an efficient bioderived adsorbent for the removal of uremic toxins in patients with chronic kidney disease.

Enhanced Assembling of N-and-K-Riched Macroalgae as Carbon Adsorbent for CO2 Capture with Ni(NO3)2/KOH as Co-Catalysts

Porous-activated carbons have drawn great attention due to their important role in CO2 capture. Ni(NO3)2/KOH, as co-catalysts under different temperatures, were studied to obtain porous graphitized carbon from Sargassum horneri feedstock. The results indicated that the properties of the porous graphitized carbon generated at 850 °C were greatly enhanced, showing a large specific surface area of 1486.38 cm3·g-1 with narrowly distributed micropores (~0.67 nm) and abundant functional groups, which endowed high CO2 uptake; moreover, the high CO2 uptake was mainly attributed to the synergistic effect of Ni(NO3)2 and KOH, both in chemical modification and pore formation. The fitted values of the four kinetic models showed that the double exponential model provided the best description of carbon adsorption, indicating both physical and chemical adsorption. It is worth noting that carbon could be reused four times in the adsorption/desorption procedure in this research with good stability. This work focuses on the high-value-added comprehensive utilization of macroalgae, which not only is important for high-performance adsorbent preparation but also has positive benefits for the development and utilization of macroalgae resources.

NiCo2O4-loaded sunflower husk-derived biochar as efficient peroxymonosulfate activator for tetracycline removal in water

In this study, biochar produced from sunflower seeds husk was activated through ZnCl₂ to support the NiCo₂O₄ nanoparticles (NiCo₂O₄@ZSF) in catalytic activation of peroxymonosulfate (PMS) toward tetracycline (TC) removal from aqueous solution. The good dispersion of NiCo₂O₄ NPs on the ZSF surface provided sufficient active sites and abundant functional groups for the adsorption and catalytic reaction. The NiCo₂O₄@ZSF activating PMS showed high removal efficiency up to 99% after 30 min under optimal condition ([NiCo₂O₄@ZSF] = 25 mg L^-1, [PMS] = 0.04 mM, [TC] = 0.02 mM and pH = 7). The catalyst also exhibited good adsorption performance with a maximum adsorption capacity of 322.58 mg g^-1. Sulfate radicals (SO₄^•-), superoxide radical (O₂•-), and singlet oxygen (¹O₂) played a decisive role in the NiCo₂O₄@ZSF/PMS system. In conclusion, our research elucidated the production of highly efficient carbon-based catalysts for environmental remediation, and also emphasized the potential application of NiCo₂O₄ doped biochar.

Recent Advances in Synthesis of Graphite from Agricultural Bio-Waste Material: A Review

Graphitic carbon is a valuable material that can be utilized in many fields, such as electronics, energy storage and wastewater filtration. Due to the high demand for commercial graphite, an alternative raw material with lower costs that is environmentally friendly has been explored. Amongst these, an agricultural bio-waste material has become an option due to its highly bioactive properties, such as bioavailability, antioxidant, antimicrobial, in vitro and anti-inflammatory properties. In addition, biomass wastes usually have high organic carbon content, which has been discovered by many researchers as an alternative carbon material to produce graphite. However, there are several challenges associated with the graphite production process from biomass waste materials, such as impurities, the processing conditions and production costs. Agricultural bio-waste materials typically contain many volatiles and impurities, which can interfere with the synthesis process and reduce the quality of the graphitic carbon produced. Moreover, the processing conditions required for the synthesis of graphitic carbon from agricultural biomass waste materials are quite challenging to optimize. The temperature, pressure, catalyst used and other parameters must be carefully controlled to ensure that the desired product is obtained. Nevertheless, the use of agricultural biomass waste materials as a raw material for graphitic carbon synthesis can reduce the production costs. Improving the overall cost-effectiveness of this approach depends on many factors, including the availability and cost of the feedstock, the processing costs and the market demand for the final product. Therefore, in this review, the importance of biomass waste utilization is discussed. Various methods of synthesizing graphitic carbon are also reviewed. The discussion ranges from the conversion of biomass waste into carbon-rich feedstocks with different recent advances to the method of synthesis of graphitic carbon. The importance of utilizing agricultural biomass waste and the types of potential biomass waste carbon precursors and their pre-treatment methods are also reviewed. Finally, the gaps found in the previous research are proposed as a future research suggestion. Overall, the synthesis of graphite from agricultural bio-waste materials is a promising area of research, but more work is needed to address the challenges associated with this process and to demonstrate its viability at scale.

Highly selective adsorption of Hg (II) from aqueous solution by three-dimensional porous N-doped starch-based carbon

For the first time, N-doped carbon materials with 3D porous-layered skeleton structure was synthesized through a one-step co-pyrolysis method, which was fabricated by co-pyrolysis of natural corn starch and melamine using metal catalysts (Ni (II) and Mn (II)). The 3D-NC possessed a heterogeneously meso-macroporous surface with a hierarchically connected sheet structure inside. Batch adsorption experiments suggested that highly selective adsorption of Hg (II) by the 3D-NC could be completed within 90 min and had maximum adsorption capacities as high as 403.24 mg/g at 293 K, pH = 5. The adsorption mechanism for Hg (II) was carefully evaluated and followed the physical adsorption, electrostatic attraction, chelation, and ion exchange. Besides, thermodynamic study demonstrated that the Hg (II) adsorption procedure was spontaneous, endothermic, and randomness. More importantly, the 3D-NC could be regenerated and recovered well after adsorption-desorption cycles, showing a promising prospect in the remediation of Hg (II)-contaminated wastewater.

Graphite Flows in the U.S.: Insights into a Key Ingredient of Energy Transition

Demand for graphite will grow with expanding use of lithium-ion batteries in the United States. Much graphite is imported, raising supply chain risks. It is therefore imperative to characterize graphite's sources and sinks. Accordingly, we present the first material flow analysis for natural and synthetic graphite in the U.S. The analysis (for 2018) begins with processed graphite trade and includes graphite production, graphite product trade, manufacturing of end products, end product use, and waste management. It considers 11 end-use applications for graphite, two waste management stages, and three recycling pathways. In 2018, 354 thousand tonnes (kt) of processed graphite were consumed in the U.S., including 60 kt natural graphite and 294 kt synthetic graphite. 145 kt of graphite were traded. Refractories and foundries consumed 56% of natural graphite; 42% of synthetic graphite went into making graphite electrodes. Batteries accounted for 10 and 5% of natural and synthetic graphite consumption, respectively; 78% of total graphite used dissipated into the environment; 22% reached the waste disposal stage of which 71% was landfilled and 29% was recycled; and 59 kt of graphite accumulated in in-use stocks. Recycling more graphite and producing graphite from lignin would favorably influence today's supply chain.

Recent advances in lignin-based carbon materials and their applications: A review

As the most abundant natural aromatic polymer, tens of million of tons of lignin produced in paper-making or biorefinery industry are used as fuel annually, which is a low-value utilization. Moreover, burning lignin results in large amounts of carbon dioxide and pollutants in the air. The potential of lignin is far from being fully exploited and the search for high value-added application of lignin is highly pursued. Because of the high carbon content of lignin, converting lignin into advanced carbon-based structural or functional materials is regarded as one of the most promising solutions for both environmental protection and utilization of renewable resources. Significant progresses in lignin-based carbon materials (LCMs) including porous carbon, activated carbon, carbon fiber, carbon aerogel, nanostructured carbon, etc., for various valued applications have been witnessed in recent years. Here, this review summarized the recent advances in LCMs from the perspectives of preparation, structure, and applications. In particular, this review attempts to figure out the intrinsic relationship between the structure and functionalities of LCMs from their recent applications. Hopefully, some thoughts and discussions on the structure-property relationship of LCMs can inspire researchers to stride over the present barriers in the preparation and applications of LCMs.

Sustainable Carbon Derived from Sulfur-Free Lignins for Functional Electrical and Electrochemical Devices

Technical lignins, kraft, soda, lignoboost, and hydrolysis lignins were used for the production of carbon particles at different carbonization temperatures, 1000 °C and 1400 °C. The results showed that the lignin source and carbonization temperature significantly influenced the carbon quality and microstructure of the carbon particles. Soda lignin carbonized up to 1400 °C showed higher degree of graphitization and exhibited the highest electrical conductivity of 335 S·m^-1, which makes it suitable for applications, such as electromagnetic interference shielding and conductive composite based structural energy storage devices. The obtained carbon particles also showed high surface area and hierarchical pore structure. Kraft lignin carbonized up to 1400 °C gives the highest BET surface area of 646 m² g^-1, which makes it a good candidate for electrode materials in energy storage applications. The energy storage application has been validated in a three-electrode set up device, and a specific capacitance of 97.2 F g^-1 was obtained at a current density of 0.1 A g^-1 while an energy density of 1.1 Wh kg^-1 was observed at a power density of 50 W kg^-1. These unique characteristics demonstrated the potential of kraft lignin-based carbon particles for electrochemical energy storage applications.

Upcycling of Plastic Wastes and Biomass for Sustainable Graphitic Carbon Production: A Critical Review

Upcycling of waste plastics diverts plastics from landfill, which helps in reducing greenhouse gas emissions. Graphitic carbon is an interesting material with a wide range of applications in electronics, energy storage, fuel cells, and even as advanced fillers for polymer composites. It is a very strong and highly conductive material consisting of weakly bound graphene layers arranged in a hexagonal structure. There are different ways of synthesizing graphitic carbons, of which the co-pyrolysis of biomass and plastic wastes is a promising approach for large-scale production. Highly graphitized carbon with surface areas in the range of 201 m²/g was produced from the co-pyrolysis of polyethylene and pinewood at 600 °C. Similarly, porous carbon having a superior discharge capacity (290 mAh/g) was developed from the co-pyrolysis of sugar cane and plastic polymers with catalysts. The addition of plastic wastes including polyethylene and high-density polyethylene to the pyrolysis of biomass tends to increase the surface area and improve the discharge capacity of the produced graphitic carbons. Likewise, temperature plays an important role in enhancing the carbon content and thereby the quality of the graphitic carbon during the co-pyrolysis process. The application of metal catalysts can reduce the graphitization temperature while at the same time improve the quality of the graphitic carbon by increasing the carbon contents. This work reports some typical graphitic carbon preparation methods from the co-pyrolysis of biomass and plastic wastes for the first time including thermochemical methods, exfoliation methods, template-based production methods, and salt-based methods. The factors affecting the graphitic char quality during the conversion processes are reviewed critically. Moreover, the current state-of-the-art characterization technologies such as Raman, scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy are discussed in detail, and finally, an overview on the applications, scalability, and future trends of graphitic-like carbons is highlighted.

A Comparison of Functional Fillers—Greenhouse Gas Emissions and Air Pollutants from Lignin-Based Filler, Carbon Black and Silica

The transformation from a fossil-based economy to a sustainable and circular bioeconomy is urgently needed to achieve the climate targets of the Paris Agreement, reduce air pollution and ensure a long-term competitive economy. Due to its carbonaceous and aromatic basic components, lignin has the potential for material valorization within bioeconomy. So far, lignin produced in the pulp and paper industry has mainly been used internally to generate thermal process energy, as it is difficult to extract it from biomass in a pure and unaltered form. The valorization of lignin to improve the economics of pulp mills is a current aim of the industry. Hydrothermal treatment (HTT) of a partial flow from the lignin stream to produce a functional filler for use in polymer blends is one valorization option. The environmental assessment of the lignin-based HTT filler, conducted using life cycle assessment (LCA), shows that substitution of the conventional fillers carbon black and silica could be associated with significant reductions in greenhouse gas emissions and air pollutants. Depending on the allocation methodology and the reference filler considered, approx. 5 kg CO2 eq./kg filler, 80–93% SO2 emissions, 27–79% PM emissions, and 88–98% PAH emissions can be saved.

Preparation and characterization of three-dimensional hierarchical porous carbon from low-rank coal by hydrothermal carbonization for efficient iodine removal

Low-rank coal, such as Shengli lignite (SL) and Datong bitumite (DT), has abundant reserves and is low in cost. Due to its high moisture content, abundant oxygen-containing groups, high ash content and low calorific value, low-rank coal is mainly used in a low-cost method of direct combustion. For better value-added utilization of SL and DT, a novel strategy has been developed for the preparation of oxygen-rich hierarchical porous carbons (HPCs) by hydrothermal carbonization (HTC), followed by steam activation. In this paper, firstly, the physical and chemical properties of SL and DT were improved by HTC pretreatment, bringing them closer to high rank coal. Then, the effects of HTC pretreatment and activation temperature on the properties of the HPCs were investigated in detail. The results show that the HPCs have mainly microporous structures (the microporosity of 200-SLHPC-900 is 79.58%) based on the N2 adsorption-desorption isotherm analysis and exhibit a higher specific surface area (SSA) and larger pore volume (25.02% and 2.69% improvement for 200-SLHPC-900; 4.93% and 14.25% increase for 200-DTHPC-900, respectively) after HTC pretreatment. The two types of HPCs also present good adsorption performance. The iodine adsorption value of lignite-based HPC presents an increase of 13.72% from 503 mg g-1 to 572 mg g-1, while the value of bitumite-based HPC increases up to 924 mg g-1. A preliminary additional HTC step is therefore an effective method by which to promote the performance of low-rank coal based porous carbon. The process of hydrothermal carbonization and steam activation is a cost-effective and environmentally-friendly preparation method, which omits the use of a chemical activator and reduces the step of alkaline waste liquid discharge compared with the route of carbonization and chemical activation.

The effect of black carbon on the chemical degradability of PCB1 via TENAX desorption technology from the perspective of adsorption states

Chemical degradation is one of the crucial methods for the remediation of hydrophobic organic compounds (HOCs) in soil/sediment. The sequestration effect of black carbon (BC) can affect the adsorption state of HOCs, thereby affecting their chemical degradability. Our study focused on the chemical degradability of 2-Chlorobiphenyl (PCB1) sequestrated on the typical BC (fly ash (FC), soot (SC), low-temperature biochar (BC400) and high-temperature biochar (BC900)) by iron-nickel bimetallic nanomaterials (nZVI/Ni) based on TENAX desorption technology. The results showed that PCB1 adsorbed in various states were simultaneously dechlorinated by nZVI/Ni. Specifically, rapid-desorption-state PCB1 tended to degrade more easily than resistant-desorption-state PCB1. Moreover, the degradation mechanism varied according to the type of BC. In the case of FC and SC, the degradation rate was lower than the desorption rate for the PCB1 in rapid and slow desorption states, and the degradation rate of PCB1 in the resistant desorption state was negligible. The PCB1 on FC and SC was first desorbed from BC and then degraded. However, in terms of BC400 and BC900, the degradation rate was higher than the desorption rate, and the degradation rate of the resistant-desorption-state PCB1 was 1.4 × 10^-2 h^-1 and 4.1 × 10^-2 h^-1, respectively. The graphitized structure of BC900 can directly transfer electrons, so more than 90% of the resistant-desorption-state PCB1 could be degraded. In addition, BC may affect the longevity of nZVI/Ni, thereby affecting its degradability. Therefore, the chemical degradability of BC-adsorbed HOCs should be comprehensively evaluated based on the adsorption state and the properties of BC.

Hydrothermal Synthesis of Biomass-Derived Magnetic Carbon Composites for Adsorption and Catalysis

The synthesis of magnetic iron-carbon composites (Fe/C) from waste avocado seeds via hydrothermal carbonization (HTC) has been demonstrated for the first time. These materials are shown to be effective in adsorption and catalytic applications, with performances comparable to or higher than materials produced through conventional processing routes. Avocado seeds have been processed in high-temperature water (230 °C) at elevated pressure (30 bar at room temperature) in the presence of iron nitrate and iron sulfate, in a process mimicking natural coalification. Characterization of the synthesized material has been carried out by X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectrometry (ICP-OES), Fourier-transform infrared spectroscopy (FT-IR), magnetometry, and through surface area measurements. The supported iron particles are observed to be predominately magnetite, with an oxidized hematite surface region. The presence of iron catalyzes the formation of an extended, ordered polymeric structure in the avocado seed-derived carbon. The magnetic Fe/C has been demonstrated as an adsorbent for environmental wastewater treatment using methylene blue and indigo carmine. Kinetic analysis suggests that the adsorbates are chemisorbed, with the positive surface charge of Fe/C being preferential for indigo carmine adsorption (49 mg g-1). Additionally, Fe/C has been evaluated as a heterogeneous catalyst for the hydroalkoxylation of phenylacetylene with ethylene glycol to 2-benzyl-1,3-dioxolane. Product yields of 45% are obtained, with 100% regioselectivity to the formed isomer. The solid catalyst has the advantages of being prepared from a waste material and of easy removal after reaction via magnetic separation. These developments provide opportunities to produce carbon-based materials for a variety of high-value applications, potentially also including energy storage and biopharmaceuticals, from a wide range of lignocellulosic biomass feedstocks.

Mechanical Properties of Pack Carburized SCM 420 Steel Processed Using Natural Shell Powders and Extended Carburization Time

The feasibility of using coconut shell powder (CSP) and dog conch shell powder (DCSP) as carburizing media in the pack carburization of SCM 420 steel was investigated. The carbon content and surface hardness of the carburized specimens prepared with different CSP:DCSP ratios and carburizing durations were examined and compared. A CSP:DCSP ratio of 60%:40% and an extended carburizing time of 12 h were found to increase the carbon content of the carburized specimens to 1.14 ± 0.007 wt%. Furthermore, the surface hardness was significantly improved to 961.3 ± 4.918 HV following water quenching. Finally, the thickness of the carburized layer of the quenched specimens increased by around 2.5 times as the carburizing duration was increased from 3 to 12 h.

Extrusion Based 3D Printing of Sustainable Biocomposites from Biocarbon and Poly(trimethylene terephthalate)

Three-dimensional (3D) printing manufactures intricate computer aided designs without time and resource spent for mold creation. The rapid growth of this industry has led to its extensive use in the automotive, biomedical, and electrical industries. In this work, biobased poly(trimethylene terephthalate) (PTT) blends were combined with pyrolyzed biomass to create sustainable and novel printing materials. The Miscanthus biocarbon (BC), generated from pyrolysis at 650 °C, was combined with an optimized PTT blend at 5 and 10 wt % to generate filaments for extrusion 3D printing. Samples were printed and analyzed according to their thermal, mechanical, and morphological properties. Although there were no significant differences seen in the mechanical properties between the two BC composites, the optimal quantity of BC was 5 wt % based upon dimensional stability, ease of printing, and surface finish. These printable materials show great promise for implementation into customizable, non-structural components in the electrical and automotive industries.

Physiochemical Properties of Biochar and Activated Carbon from Biomass Residue: Influence of Process Conditions to Adsorbent Properties

This study evaluates the influence of hydrothermal carbonization (HTC) or slow pyrolysis (SP) process conditions on the physicochemical properties of precursor biochars and activated carbon (AC). The AC is achieved through a direct or a two-step method with subsequent chemical activation using KOH. A theory is developed on the biochar propensity to be chemically activated based on the lignocellulosic structure composition. X-ray photoelectron spectroscopy elemental analysis shows that the O/C ratio decreases after chemical activation for HTC biochar but remains the same for SP biochar. X-ray powder diffraction indicates that the SP biochar and all ACs have broad amorphous carbon peaks, whereas corn stover and the HTC biochar have distinct cellulosic crystalline peaks. Vanillin adsorbent experiments were performed on various ACs with up to 98% reduction shown. The best adsorbent for vanillin was the AC produced directly from corn stover, followed by AC HTC and then AC SP.

Characterization of Chemically and Physically Activated Carbons from Lignocellulosic Ethanol Lignin-Rich Stream via Hydrothermal Carbonization and Slow Pyrolysis Pretreatment

The aim of the present work is to investigate the possibility of producing activated carbons from the residual lignin stream of lignocellulosic ethanol biorefineries, as this represents an optimal opportunity to exploit a residual and renewable material in the perspective of sustainable bioeconomy, increasing biorefinery incomes by producing value-added bioproducts in conjunction with biofuels. Activated carbons (ACs) were produced via chemical (KOH) and physical (CO2) activation. Char samples were obtained by slow pyrolysis (SP) and hydrothermal carbonization (HTC). Several HTC experiments were carried out by varying residence time (0.5–3 h) and reaction temperature (200–270 °C), in order to evaluate their influence on the product yield and on the morphological characteristics of the hydrochar (specific surface area, total pore volume and pore size distribution). ACs from hydrochars were compared with those obtained from pyrochar (via physical activation) and from the raw lignin-rich stream (via chemical activation). In both cases, by increasing the HTC temperature, the specific surface of the resulting activated carbons decreased from 630 to 77 m2 g−1 for physical activation and from 675 to 81 m2 g−1 for chemical activation, indicating that an increase in the severity of the hydrothermal pretreatment is deleterious for the activated carbons quality. In addition, the HTC aqueous samples were analyzed, with GC-MS and GC-FID. The results suggest that at low temperatures the reaction mechanisms are dominated by hydrolysis, instead when the temperature is increased to 270 °C, a more complex network of reactions takes place among which decarboxylation.

Application of metallic nanoparticle-biochars with ionic liquids for thermal transfer fluids

Ionic liquids (ILs (1-butyl-3-methylimidazolium chloride ([C₄mim][Cl]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([C₄mim][BF₄]))) were used as heat transfer fluids for solar thermal collectors. The additive of ILs was biochar containing copper and silver nanoparticles (Cu-Ag/biochar) to improve the adsorption of solar irradiation and thermal conductivities. After impregnation and reduction processes, nanoparticles such as Cu, CuO, Cu(OH)₂, Ag, and Ag₂O were found in the biochar by X-ray powder diffraction (XRD) spectroscopy. With adding 2% Cu-Ag/biochar into the ILs, the thermal conductivities of [C₄mim][Cl] and [C₄mim][BF₄] containing 10% Cu-1% Ag/biochar were individually increased 9.2 and 6.6 times compared to the base ILs due to the high graphitization of biochar and metallic nanoparticles. The ¹H NMR (nuclear magnetic resonance) features of the imidazole ring and methyl group in the ILs were highly disturbed due to the formation of weak or strong hydrogen bonds between the cations in ILs and Cu-Ag/biochar. The high hydrogen bond acceptance of anions in ILs also affected the thermal properties. The thermal properties of the metals/biochar [C₄mim][Cl] were better than those of metals/biochar [C₄mim][BF₄] due to high hydrogen bond acceptance of [Cl]^-. The strong hydrogen bonds between the Cu-Ag/biochar and the cations and anions in ILs result in thermal properties of heat transfer fluids. Under simulated sunlight, the temperatures of [C₄mim][Cl] and [C₄mim][BF₄] containing 10% Cu-1% Ag/biochar rose from 304 to 345 and 340 K within 24 min, respectively. A novel heat transfer fluid was developed for high adsorption of irradiation, high thermal conductivities, and speedy transfer of heat.

Enhanced treatment performance of phenol wastewater and membrane antifouling by biochar-assisted EMBR

Biochar-assisted EMBR (BC-assisted EMBR) was built to enhance treatment performance of phenol wastewater and membrane antifouling. BC-assisted EMBR significantly increased phenol degradation efficiency, owing to combined effects of biodegradation, adsorption and electro-catalytic degradation. Meanwhile, BC-assisted EMBR obviously mitigated membrane fouling. The coupling effect of BC and voltage led to the lower N-acyl-homoserine lactones (AHLs) and bound extracellular polymeric substances (bound EPS) contents around and on membrane surface. Protein (PN)/polysaccharide (PS) in bound EPS was decreased, led to the increase of negative charge and decrease of hydrophobicity of sludge, which abated bound EPS adsorption on membrane surface. Microbial community analyses revealed that the coupling effect of BC and voltage could enrich phenol-degraders (e.g., Comamonas), electron transfer genus (Phaselicystis), and biopolymer-degraders (Phaselicystis and Tepidisphaera) in BC-assisted EMBR and on its membrane surface, while decrease biofilm-former (e.g., Acinetobacter) and bound EPS-producer (Devosia), which was beneficial to promote phenol treatment and mitigate membrane fouling.

Effect of Solvents on Fe-Lignin Precursors for Production Graphene-Based Nanostructures

Kraft lignin was catalytically graphitized to graphene-based nanostructures at high temperature under non-oxidative atmospheres. To obtain the best catalytic performance, a uniform catalyst–lignin mixture must be made by bonding transitional metal (M) ions to oxygen (O), sulfur (S) or nitrogen (N)-containing functional groups in kraft lignin. One of the strategies is to dissolve or disperse kraft lignin in a suitable solvent, whereby the polymer chains in the condensed lignin molecules will be detangled and stretched out while the functional groups are solvated, and when mixing lignin solution with catalyst metal solution, the solvated metal ions in an aqueous solution can diffuse and migrate onto lignin chains to form M-O, M-S, or M-N bonds during the mixing process. Therefore, solvent effects are important in preparing M–lignin mixture for production of graphene-based nanostructures. Fe–lignin precursors were prepared by dissolving lignin with different solvents, including water, methanol, acetone, and tetrahydrofuran (THF). Solvent effects on the catalytic performance, size and morphology of graphene-based nanostructures were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HRTEM), and nitrogen sorption measurements. The sizes, morphologies, and catalytic properties of the products obtained from Fe–lignin precursors are greatly influenced by the solvents used. It was found that Fe–lignin (THF) had the highest iron dispersion and the smallest iron particle size. Furthermore, Fe–lignin (THF) exhibited the best catalytic performance for graphitization of kraft lignin while the graphitization degree decreased in the order: Fe–lignin(THF) > Fe–lignin(Acetone) > Fe–lignin(methanol) > Fe–lignin(water).

Molten salt induced nitrogen-doped biochar nanosheets as highly efficient peroxymonosulfate catalyst for organic pollutant degradation

Advanced oxidation processes based on carbon catalysis is a promising strategy possessing great potential for environmental pollution degradation. Herein, nitrogen-doped biochar nanosheets (NCS-x) were synthesized using a nitrogen-rich biomass (Candida utilis) as sole precursor. The involvement of environmental-friendly molten salt (NaCl and KCl) in pyrolysis process not only facilitated the exfoliation of biochar, but also favored the retention of N element in biochar. When applying as catalyst for peroxymonosulfate activation, the as-obtained NCS-6 exhibited outstanding performance in catalytic degradation of bisphenol A (BPA). A 100% removal efficiency was observed in 6 min with fast reaction kinetic (k = 1.36 min^-1). Based on quenching test and in-situ electron paramagnetic resonance analysis, both radical pathway and non-radical pathway were suggested to be involved in BPA degradation, while singlet oxygen was identified as the dominant reactive oxygen species. Furthermore, the ecotoxicity evaluation using Chlorella vulgaris as ecological indicator indicated that BPA solution after degradation was less toxic than the original solution. It is expected that this green and facile strategy holds great promise for value-added conversion of nitrogen-rich biomass to highly efficient biochar nanosheets for environment remediation.

Synthesis of Porous Biochar Containing Graphitic Carbon Derived From Lignin Content of Forestry Biomass and Its Application for the Removal of Diclofenac Sodium From Aqueous Solution

Porous biochar containing graphitic carbon materials have received great attention from various disciplines, especially for environmental pollutant treatment, due to their cost-effective and specific textural properties. This study exhibited a two-step strategy to compose lignin-porous biochar containing graphitic carbon (LPGC) from pitch pine sawdust and investigated its adsorptive removal for diclofenac sodium (DCF) from an aqueous solution. Sulfuric acid (H2SO4) was utilized to obtain lignin content from biomass and potassium ferrate (K2FeO4) and was adopted to fulfill the synchronous carbonization and graphitization of LPGC. Through slow pyrolysis in atmospheric N2 (900°C - 2 h), the structure of the as-prepared sample was successfully modified. Using SEM images, a stripped layer structure was observed on the H2SO4-treated sample for both one-step and two-step activated samples, indicating the pronounced effect of H2SO4 in the layering of materials. K2FeO4 acted as an activator and catalyst to convert biomass into the porous graphitic structure. The BET surface area, XRD and Raman spectra analyses demonstrated that LPGC possessed a micro/mesoporous structure with a relatively large surface area (457.4 m2 g-1) as well as the presence of a graphitic structure. Further adsorption experiments revealed that LPGC exhibited a high DCF adsorption capacity (qmax = 159.7 mg g-1 at 298 K, pH = 6.5). The effects of ambient conditions such as contact time, solution pH, temperature, ionic strength, electrolyte background on the uptake of DCF were investigated by a batch adsorption experiment. Results indicated that the experimental data were best fitted with the pseudo second-order model and Langmuir isotherm model. Furthermore, the adsorption of DCF onto the LPGC process was spontaneous and endothermic. Electrostatic interaction, H-bonding interaction, and π-π interaction are the possible adsorption mechanisms. The porous biochar containing graphitic carbon obtained from the lignin content of pitch pine sawdust may be a potential material for eliminating organic pollutants from water bodies.

Heterogeneous Catalyst Design Principles for the Conversion of Lignin into High-Value Commodity Fuels and Chemicals

Lignin valorization has risen as a promising pathway to supplant the use of petrochemicals for chemical commodities and fuels. However, the challenges of separating and breaking down lignin from lignocellulosic biomass are the primary barriers to success. Integrated biorefinery systems that incorporate both homo- and heterogeneous catalysis for the upgrading of lignin intermediates have emerged as a viable solution. Homogeneous catalysis can perform selected chemistries, such as the hydrolysis and dehydration of ester or ether bonds, that are more suitable for the pretreatment and fractionation of biomass. Heterogeneous catalysis, however, offers a tunable platform for the conversion of extracted lignin into chemicals, fuels, and materials. Tremendous effort has been invested in elucidating the necessary factors for the valorization of lignin by using heterogeneous catalysts, with efforts to explore more robust methods to drive down costs. Current progress in lignin conversion has fostered numerous advances, but understanding the key catalyst design principles is important for advancing the field. This Minireview aims to provide a summary on the fundamental design principles for the selective conversion of lignin by using heterogeneous catalysts, including the pairing of catalyst metals, supports, and solvents. The review puts a particular focus on the use of bimetallic catalysts on porous supports as a strategy for the selective conversion of lignin. Finally, future research on the valorization of lignin is proposed on the basis of recent progress.

Three-dimensional hierarchical porous carbon structure derived from pinecone as a potential catalyst support in catalytic remediation of antibiotics

In this study, pinecone was converted via two stage pyrolysis to produce low cost activated carbon. Furnace pyrolysis was used in the first step to convert pinecone to carbonized material, followed by microwave pyrolysis of the carbonized material activated with KOH to obtain activated carbon (ACK) materials as a suitable catalyst support. The ACK samples were characterized by their morphology, structural, adsorption and electrochemical properties. The optimized ACK 2.24-16 prepared from the pinecone had a complex three-dimensional (3D)-hierarchical porous structure, with an abundance of micropores and mesopores compared to other ACK samples judging from the high iodine number (1900 mg g^-1) and the methylene blue number (4000 mg g^-1) capacity. The optimized ACK 2.24-16 had the highest current response and least charge transfer resistance, along with moderate surface area (427 m² g^-1) as a promising photocatalyst support. The 3D hierarchical porous ACK significantly assisted catalyst dispersion, and enhanced visible light absorption and fast interfacial charge transfer. This work shows the promising aspect of utilizing pinecone to produce a low-cost photocatalyst support for environmental remediation.

Ultrathin 2D Metal-Organic Framework Nanosheets In situ Interpenetrated by Functional CNTs for Hybrid Energy Storage Device

The ultrathin nickel metal–organic framework (MOF) nanosheets in situ interpenetrated by functional carboxylated carbon nanotubes (C-CNTs) were successfully constructed. The incorporated C-CNTs effectively adjust the layer thickness of Ni-MOF nanosheets. The integrated hybrid MOF nanosheets delivered the boosted electrochemical performances and exhibited superior specific capacity of 680 C g−1 at 1 A g−1.

The controllable construction of two-dimensional (2D) metal–organic framework (MOF) nanosheets with favorable electrochemical performances is greatly challenging for energy storage. Here, we design an in situ induced growth strategy to construct the ultrathin carboxylated carbon nanotubes (C-CNTs) interpenetrated nickel MOF (Ni-MOF/C-CNTs) nanosheets. The deliberate thickness and specific surface area of novel 2D hybrid nanosheets can be effectively tuned via finely controlling C-CNTs involvement. Due to the unique microstructure, the integrated 2D hybrid nanosheets are endowed with plentiful electroactive sites to promote the electrochemical performances greatly. The prepared Ni-MOF/C-CNTs nanosheets exhibit superior specific capacity of 680 C g−1 at 1 A g−1 and good capacity retention. The assembled hybrid device demonstrated the maximum energy density of 44.4 Wh kg−1 at a power density of 440 W kg−1. Our novel strategy to construct ultrathin 2D MOF with unique properties can be extended to synthesize various MOF-based functional materials for diverse applications.

Preparation of a Hierarchically Porous Lead/Carbon Composite and Its Application in Lead-Carbon Batteries

A novel and scalable lead-modified phenolic resin-based carbon material (Pb/PRC) has been successfully prepared by using lead-modified phenolic resin (Pb/PR) as a precursor, toluene as a pore-forming agent, and KOH as an activating agent. The Pb/PRC composite presents a hierarchically porous nanosphere structure, and this structure contributes to prolong its cycling life under high-rate partial state-of-charge (HRPSoC) operation. Pb/PRC with nano-lead can effectively inhibit hydrogen evolution and provide pseudocapacitance. Compared with a blank negative plate, a lead-carbon battery with Pb/PRC displays 18 000 cycles under HRPSoC operation and exhibits a capacity of 100 mA h g^-1 at 2 C discharge rate.

Unveiling the Role of Heteroatom Gradient-Distributed Carbon Fibers for Vanadium Redox Flow Batteries with Long Service Life

The fundamental understanding of electrocatalytic reaction process is anticipated to guide electrode upgradation and acquirement of high-performance vanadium redox flow batteries (VRFBs). Herein, a carbon fiber prototype system with a heteroatom gradient distribution has been developed with enlarged interlayer spacing and a high graphitization that improve the electronic conductivity and accelerate the electrocatalytic reaction, and the mechanism by which gradient-distributed heteroatoms enhance vanadium redox reactions was elucidated with the assistance of density functional theory calculations. All these contributions endow the obtained electrode prominent redox reversibility and durability with only 1.7% decay in energy efficiency over 1000 cycles at 150 mA cm^-2 in the VRFBs. Our work sheds light on the significance of elaborated electrode design and impels the in-depth investigation of VRFBs with long service life.

Preparation of Microporous Carbon from Sargassum horneri by Hydrothermal Carbonization and KOH Activation for CO2 Capture

High-performance microporous activated carbon (AHC) for CO2 capture was prepared from an emerging marine pollutant, Sargassum horneri, via hydrothermal carbonization (HTC) and KOH activation. The as-synthesized carbon material was characterized by N2 sorption-desorption measurement, TGA, SEM, XRD, FTIR, and elemental analysis. Impressively, the activated carbon exhibited high specific surface area (1221 m2/g), narrow distributed micropores (∼0.50 nm), and a relatively high nitrogen content (3.56 wt.%), which endowed this carbon material high CO2 uptake of 101.7 mg/g at 30°C and 1 bar. Moreover, the carbon material showed highly stable CO2 adsorption capacity and easy regeneration over four adsorption-desorption cycles. Two kinetic models were employed in this work and found that the pseudo-first-order kinetic model (R2 = 0.99) provided the best description. In addition, the high CO2 uptake is mainly attributed to the presence of abundant narrow microporous. The macroporous structure of hydrochar (HC) played an important role in the production of microporous carbon with high adsorption properties. This work provides an efficient strategy for preparing microporous activated carbon from Sargassum horneri, and AHC is a promising candidate acting as an efficient CO2 adsorbent for further industrial application.

Synthetic Bio-Graphene Based Nanomaterials through Different Iron Catalysts

Kraft lignin was catalytically graphitized to graphene-based nanostructures at 1000 °C under argon atmosphere with four iron catalysts, iron(III) nitrate (Fe-N); iron(II) chloride (Fe-Cl₂); iron(III) chloride (Fe-Cl₃); and iron(II) sulfate (Fe-S). The catalytic decomposition process of iron-promoted lignin materials was examined using thermalgravimetric analysis and temperature-programmed decomposition methods. The crystal structure, morphology and surface area of produced materials were characterized by means of X-ray diffraction, Raman, scanning electron microscopy, high resolution transmission electron microscopy and N₂ adsorption-desorption techniques. Experimental results indicated that iron nitrate catalyst had better iron dispersion three other iron salts. Iron nitrate was the most active catalyst among four iron salts. The low activity of iron in iron chloride-promoted samples was because the residual chlorine over iron surfaces prevent iron interaction with lignin functional groups.

Iron nanoparticles in situ encapsulated in lignin-derived hydrochar as an effective catalyst for phenol removal

In this work, we have developed a low-cost and green strategy for nanoscale zero-valent iron (ZVI) in situ encapsulated in lignin-derived hydrochar (Fe@HC) by a facile one-pot synthesis route. The as-synthesized Fe@HC was characterized for physicochemical properties by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscope (TEM), thermal gravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FT-IR). Further catalytic experiment revealed that phenol could be completely degraded by Fe@HC-800 within 20 min with peroxymonosulfate (PMS) at mild temperatures. Fe@HC-800 catalyst also exhibited stable performance after three runs of regeneration. The XPS and XRD results proved the key role of Fe⁰ in the degradation of phenol. This approach is of great potential to the development of green materials biomass-derived carbon materials for wastewater treatment applications.

Rapid transformation of heterocyclic building blocks into nanoporous carbons for high-performance supercapacitors

The ever-increasing global energy consumption necessitates the development of efficient energy conversion and storage devices. Nitrogen-doped porous carbons as electrode materials for supercapacitors feature superior electrochemical performances compared to pristine activated carbons. Herein, a facile synthetic strategy including solid-state mixing of benzimidazole as an inexpensive single-source precursor of nitrogen and carbon and zinc chloride as a high temperature solvent/activator followed by pyrolysis of the mixture (T = 700–1000 °C under Ar) is introduced. The addition of ZnCl₂ prevents early sublimation of benzimidazole and promotes carbonization and pore generation. The sample obtained under the optimal carbonization temperature of 900 °C and ZnCl₂/benzimidazole weight ratio of 2/1 (ZBIDC-2-900) features a moderate specific surface area of 855 m² g⁻¹, high N-doping level (10 wt%), and a wide micropore size distribution (∼1 nm). ZBIDC-2-900 as a supercapacitor electrode exhibits a large gravimetric capacitance of 332 F g⁻¹ (at 1 A g⁻¹ in 1 M H₂SO₄) thanks to the cooperative advantages of the electrochemical activity of the nitrogen functional groups and the accessible porosity. The excellent capacitance performance coupled with robust cyclic stability, high yield and straightforward synthesis of the proposed carbons holds great potential for large-scale energy storage applications.

Zinc chloride activated benzimidazole derived carbons (ZBIDCs) with optimal textural and chemical properties exhibit remarkable and stable performance in supercapacitor applications.