High-yield harvest of nanofibers/mesoporous carbon composite by pyrolysis of waste biomass and its application for high durability electrochemical energy storage

Enhancement effect of potassium ferrate on self-activation: Significant improvement in pore structure and adsorption performance of activated carbon

This work developed a method using bamboo shoot shells as raw material to produce Fe-modified ACs combining self-activation and chemical modification. Adding small amounts (0.5-5 %) of K2FeO4 accelerated the pyrolysis process and CO2 release, and reduced the activation energy and temperature of self-activation reaction. This increased the reaction rate and activation efficiency, ultimately significantly improving the pore structure of ACs. The addition of 3 % K2FeO4 resulted in a substantial increase in specific surface area and pore volume of AC, from 1340 m2/g and 0.72 cm3/g to 2184 m2/g and 1.34 cm3/g, respectively. Additionally the introduction of K2FeO4 also enabled iron doping on the surface of the ACs. The improvement of pore structure and iron doping further enhanced the adsorption performance of ACs. The adsorption capacities of ACs for arsenate, ibuprofen, and tetracycline were up to 1.64, 1.50, and 2.38 times higher, respectively, than those of ACs prepared through conventional self-activation.

Ginkgo Leaf-Derived Carbon Supports for the Immobilization of Iron/Iron Phosphide Nanospheres for Electrocatalytic Hydrogen Evolution

Iron/iron phosphide nanospheres supported on ginkgo leaf-derived carbon (Fe&FeP@gl-C) are prepared using a post-phosphidation approach, with varying amounts of iron (Fe). The activity of the catalysts in the hydrogen evolution reaction (HER) outperforms iron/iron carbide nanospheres supported on ginkgo leaf-derived carbon (Fe&FexC@gl-C), due to enhanced work function, electron transfer, and Volmer processes. The d-band centers of Fe&FeP@gl-C-15 move away from the Fermi level, lowering the H2 desorption energy and accelerating the Heyrovsky reaction. Density functional theory (DFT) calculations reveal that the hydrogen-binding free energy |ΔGH*| value is close to zero for the Fe&FeP@gl-C-15 catalyst, showing a good balance between Volmer and Heyrovsky processes. The Fe&FeP@gl-C-15 catalyst shows excellent hydrogen evolution performance in 0.5 m H2SO4, driving a current density of 10 mA cm-2 at an overpotential of 92 mV. Notably, the Fe&FeP@gl-C-15 catalyst outperforms a 20 wt% Pt/C catalyst, with a smaller overpotential required to drive a higher current density above 375 mA cm-2.

Renewable Carbonaceous Materials from Biomass in Catalytic Processes: A Review

This review paper delves into the diverse ways in which carbonaceous resources, sourced from renewable and sustainable origins, can be used in catalytic processes. Renewable carbonaceous materials that come from biomass-derived and waste feedstocks are key to developing more sustainable processes by replacing traditional carbon-based materials. By examining the potential of these renewable carbonaceous materials, this review aims to shed light on their significance in fostering environmentally conscious and sustainable practices within the realm of catalysis. The more important applications identified are biofuel production, tar removal, chemical production, photocatalytic systems, microbial fuel cell electrodes, and oxidation applications. Regarding biofuel production, biochar-supported catalysts have proved to be able to achieve biodiesel production with yields exceeding 70%. Furthermore, hydrochars and activated carbons derived from diverse biomass sources have demonstrated significant tar removal efficiency. For instance, rice husk char exhibited an increased BET surface area from 2.2 m2/g to 141 m2/g after pyrolysis at 600 °C, showcasing its effectiveness in adsorbing phenol and light aromatic hydrocarbons. Concerning chemical production and the oxidation of alcohols, the influence of biochar quantity and pre-calcination temperature on catalytic performance has been proven, achieving selectivity toward benzaldehyde exceeding 70%.

Biomass waste-derived carbon materials for sustainable remediation of polluted environment: A comprehensive review

In response to the growing global concern over environmental pollution, the exploration of sustainable and eco-friendly materials derived from biomass waste has gained significant traction. This comprehensive review seeks to provide a holistic perspective on the utilization of biomass waste as a renewable carbon source, offering insights into the production of environmentally benign and cost-effective carbon-based materials. These materials, including biochar, carbon nanotubes, and graphene, have shown immense promise in the remediation of polluted soils, industrial wastewater, and contaminated groundwater. The review commences by elucidating the intricate processes involved in the synthesis and functionalization of biomass-derived carbon materials, emphasizing their scalability and economic viability. With their distinctive structural attributes, such as high surface areas, porous architectures, and tunable surface functionalities, these materials emerge as versatile tools in addressing environmental challenges. One of the central themes explored in this review is the pivotal role that carbon materials play in adsorption processes, which represent a green and sustainable technology for the removal of a diverse array of pollutants. These encompass noxious organic compounds, heavy metals, and organic matter, encompassing pollutants found in soils, groundwater, and industrial wastewater. The discussion extends to the underlying mechanisms governing adsorption, shedding light on the efficacy and selectivity of carbon-based materials in different environmental contexts. Furthermore, this review delves into multifaceted considerations, spanning the spectrum from biomass and biowaste resources to the properties and applications of carbon materials. This holistic approach aims to equip researchers and practitioners with a comprehensive understanding of the synergistic utilization of these materials, ultimately facilitating effective and affordable strategies for combatting industrial wastewater pollution, soil contamination, and groundwater impurities.

Valorization of lignocellulosic biomass into sustainable materials for adsorption and photocatalytic applications in water and air remediation

An exponential rise in global pollution and industrialization has led to significant economic and environmental problems due to the insufficient application of green technology for the chemical industry and energy production. Nowadays, the scientific and environmental/industrial communities push to apply new sustainable ways and/or materials for energy/environmental applications through the so-called circular (bio)economy. One of today's hottest topics is primarily valorizing available lignocellulosic biomass wastes into valuable materials for energy or environmentally related applications. This review aims to discuss, from both the chemistry and mechanistic points of view, the recent finding reported on the valorization of biomass wastes into valuable carbon materials. The sorption mechanisms using carbon materials prepared from biomass wastes by emphasizing the relationship between the synthesis route or/and surface modification and the retention performance were discussed towards the removal of organic and heavy metal pollutants from water or air (NO_x, CO₂, VOCs, SO₂, and Hg⁰). Photocatalytic nanoparticle-coated biomass-based carbon materials have proved to be successful composites for water remediation. The review discusses and simplifies the most raised interfacial, photonic, and physical mechanisms that might take place on the surface of these composites under light irradiation. Finally, the review examines the economic benefits and circular bioeconomy and the challenges of transferring this technology to more comprehensive applications.

Removal of Reactive Black Dye in Water by Magnetic Mesoporous Carbon from Macadamia Nutshell

The novel and intriguing role of Fe(NO3)3 as a chemical activator in carbonization of macadamia nutshell is introduced in this work. Magnetic mesoporous carbon was achieved by chemical activation of macadamia nutshell with Fe(NO3)3 under nitrogen atmosphere at 850°C (MMC-850). Porosity of MMC-850 included SBET 317 m2/g with Vmicro 0.0796 cm3/g and considerably high Vmeso 0.4318 cm3/g. Not only did MMC-850 possesses good magnetic properties with saturation magnetization and coercive force of 31.48 emu/g and 506.6 Oe, respectively, but MMC-850 also showed high-removal efficiency of reactive black dye (RB5) with maximum adsorption capacity at 123.51 mg/g. The experimental data fit the Langmuir isotherm and Elovich model. Thermal regeneration was effective in degrading RB5 and removal ability was above 90% after two regeneration cycles. RB5 removal from water by MMC-850 as an adsorbent is considered a facile and inexpensive method since macadamia nutshell is a food by-product which is a green and renewable carbon precursor. MMC-850 is a potential adsorbent because it can be separated from wastewater treatment system using magnetic force. Besides, MMC-850 particle is not brittle compared to other porous biochar/activated carbon with similar size; therefore, it is an excellent candidate for column packing or scaling up for wastewater treatment facilities in the future.

Amine-Modified Biochar for the Efficient Adsorption of Carbon Dioxide in Flue Gas

Biochar-based carbonaceous adsorbents are gaining interest due to their high availability, ease of modification, and low cost; however, they show limited adsorption of CO2 in flue gas due to common textural properties. In this study, TEPA-modified biochar was used to prepare a solid amine adsorbent for the efficient capture of CO2 in flue gas. First, the porous biochar was prepared with FeCl3, Mg(NO3)2, and H2O (g) as activators and walnut shells as carbon sources. Next, the biochar was modified with TEPA to obtain a solid amine adsorbent. Porous texture properties and sample surface functional groups were characterized, and we measured the adsorption CO2 of the amine-modified biochar in a breakthrough adsorption device. Results showed that biochar has a large specific surface area (744.38 m2 g−1), a total pore volume of 1.41 cm3 g−1, and a high mesoporous volume ratio (82.7%). The high pore volume provided a more efficient support space for loading tetraethylenepentamine (TEPA). The adsorbent had an excellent CO2 adsorption capacity, corresponding to 2.82 mmol g−1, which increased to 3.31 mmol g−1 and kept water resistance at 10% H2O (g) simulated flue gas (SFG). The FTIR analysis showed that H2O (g) inhibited urea production after cyclic adsorption. Therefore, solid amine adsorbent created by amine-modified biochar has potential advantages in its application for capturing CO2 in SFG.

Wool-Based Carbon Fiber/MoS2 Composite Prepared by Low-Temperature Catalytic Hydrothermal Method and Its Application in the Field of Gas Sensors

Under the background of the Paris Agreement on reducing greenhouse gases, waste wools were converted into wool carbon fiber (WCF) and WCF-MoS2 composites by low-temperature catalytic hydrothermal carbonization. Their structures and gas-sensing performances were studied for the first time. Due to the existence of heterojunctions, the responses of the WCF-MoS2 composite to the five analytes were 3-400 times those of MoS2 and 2-11 times those of WCF. Interestingly, because of the N, P, and S elements contained in wools, the WCF prepared by the hydrothermal method was realized the doping of N, P, and S, which caused the sensing curves of WCF to have different shapes for different analytes. This characteristic was also well demonstrated by the WCF-MoS2 composite, which inspired us to realize the discriminative detection only by a single WCF-MoS2 sensor and image recognition technology. What's more, the WCF-MoS2 composite also showed a high sensitivity, a high selectivity, and a rapid response to NH3. The response time and the recovery time to 3 ppm NH3 were about 16 and 5 s, respectively. The detection of limit of WCF-MoS2 for NH3 was 19.1 ppb. This work provides a new idea for the development of sensors and the resource utilization of wool waste.

A sustainable one-step strategy for highly graphitized capacitive carbons with hierarchical micro-meso-macro porosity

Large micropore surface area, superior electrical conductivity and suitable pore size are simultaneously desired characteristics for high-performance capacitive carbons. However, these desired features tend to be mutually competing, and are generally difficult to integrate into a single carbon. Considering this challenge, we developed a sustainable, less time-demanding, pollution-free strategy to construct highly graphitized porous carbon (GPC) by one-step heat-treatment. This approach achieves the need of the abovementioned characteristics for capacitive carbons, wherein potassium ferrate works as both an activating agent and graphitization catalyst to achieve synchronous hierarchical porosity and graphitization of wasted natural wood, and the resultant carbon materials possess a large micropore surface area of 870.4 m2 g-1, a highly graphitic carbon skeleton and a well-interconnected micro-meso-macropore structure. The assembled GPC-based symmetrical capacitors exhibited a satisfactory capacitive performance in different aqueous electrolytes (H2SO4, KOH and Na2SO4), including high specific capacitance, prominent rate capability, satisfactory energy density and good cycle stability. Meanwhile, we compared the contributions of porosity and the graphitized structure to capacitive performance, and porosity was dominant in determining capacitance and the graphitized skeleton had a positive effect in enhancing the capacitive performance. In addition, we established the relationship between the structure of GPC and electrochemical capacitive performance in different aqueous electrolytes, providing a valuable reference for GPC-based supercapacitors in different practical applications. More importantly, this strategy holds great promise to sustainably convert biowaste to high-added-value capacitive carbons for advanced energy storage applications in the future.

Facile and green preparation of solid carbon nanoonions via catalytic co-pyrolysis of lignin and polyethylene and their adsorption capability towards Cu(ii)

Carbon nanomaterials, such as carbon nanoonions (CNOs), possess promising applications in various fields. There are urgent demands to synthesize carbon nanomaterials from a green and renewable carbon source. In this study, solid CNOs with relatively uniform size distribution (with diameters of about 30-50 nm), abundant structure defects and oxygen-containing surface functional groups (such as -OH and -COOH) are developed from co-pyrolysis of lignin (LG) and polyethylene (PE) in the presence of Ni-based catalysts. The type of catalyst, the concentration of catalyst and catalytic co-pyrolysis temperature play important roles in the morphologies and properties of CNOs as confirmed by TEM and SEM. Furthermore, the produced CNOs can act as a low-cost and highly-efficient adsorbent to remove Cu(ii) from aqueous solution according to a homogeneous monolayer, chemical action-dominated, endothermic and spontaneous process. The theoretical maximum adsorption capacity of CNOs calculated from the Langmuir model is 100.00 mg g-1. Surface deposition, complexation, π electron-cation interaction and electrostatic interaction are responsible for the adsorption of Cu(ii) using the prepared CNOs.

Heavy metal removal by biomass-derived carbon nanotubes as a greener environmental remediation: A comprehensive review

The concentrations of heavy metal ions found in waterways near industrial zones are often exceed the prescribed limits, posing a continued danger to the environment and public health. Therefore, greater attention has been devoted into finding the efficient solutions for adsorbing heavy metal ions. This review paper focuses on the synthesis of carbon nanotubes (CNTs) from biomass and their application in the removal of heavy metals from aqueous solutions. Techniques to produce CNTs, benefits of modification with various functional groups to enhance sorption uptake, effects of operating parameters, and adsorption mechanisms are reviewed. Adsorption occurs via physical adsorption, electrostatic interaction, surface complexation, and interaction between functional groups and heavy metal ions. Moreover, factors such as pH level, CNTs dosage, duration, temperature, ionic strength, and surface property of adsorbents have been identified as the common factors influencing the adsorption of heavy metals. The oxygenated functional groups initially present on the surface of the modified CNTs are responsible towards the adsorption enhancement of commonly-encountered heavy metals such as Pb²⁺, Cu²⁺, Cd²⁺, Co²⁺, Zn²⁺, Ni²⁺, Hg²⁺, and Cr⁶⁺. Despite the recent advances in the application of CNTs in environmental clean-up and pollution treatment have been demonstrated, major obstacles of CNTs such as high synthesis cost, the agglomeration in the post-treated solutions and the secondary pollution from chemicals in the surface modification, should be critically addressed in the future studies for successful large-scale applications of CNTs.

Rice Hull-Derived Carbon for Supercapacitors: Towards Sustainable Silicon-Carbon Supercapacitors

A simple and effective mixing carbonization-activation process was developed to prepare rice hull-derived porous Si-carbon materials. The morphologies and pore structures of the materials were controlled effectively without any loading or additions at various carbonization temperatures. The structures of the samples changed from large pores and thick walls after 800 ∘C carbonization to small pores and thin walls after 1000 ∘C carbonization. An additional alkali activation-carbonization process led to coral reef-like structures surrounded by squama in the sample that underwent 900 ∘C carbonization (Act-RH-900). This optimal material (Act-RH-900) had a large specific surface area (768 m² g^-1), relatively stable specific capacitance (150.8 F g^-1), high energy density (31.9 Wh kg^-1), and high-power density (309.2 w kg^-1) at a current density of 0.5 A g^-1 in 1 M KOH electrolyte, as well as a good rate performance and high stability (capacitance retention > 87.88% after 5000 cycles). The results indicated that Act-RH-900 is a promising candidate for capacitive applications. This work overcomes the restrictions imposed by the complex internal structure of biomass, implements a simple reaction environment, and broadens the potential applicability of biomass waste in the field of supercapacitors.

Recent nanobiotechnological advancements in lignocellulosic biomass valorization: A review

Increase in human population, rapid industrialization, excessive utilization of fossil fuel utilization and anthropogenic activities have caused serious threats to the environment in terms of greenhouse gas emissions (GHGs), global warming, air pollution, acid rain, etc. This destruction in sustainability can be averted by a paradigm shift in the fuel production from fossil resources to bioenergy. Amongst different forms of bioenergy, lignocellulosic biomass can be utilized as an attractive substrate for the production of several high-value products owing to its renewability, easy availability, and abundance. Additionally, utilization of these waste biomasses reduces the environmental hazards associated with its disposal. Impedance of lignin and crystalline nature of cellulose pose major bottlenecks in biomass based energy. Though, several physio-chemicals processes are recommended as mitigation route but none of them seems to be promising for large scale application. In recent years, a right fusion of biological treatment combined with nanotechnology for efficient pretreatment and subsequent hydrolysis of biomass by ubiquitous enzymes seems to be promising alternative. In addition, to overcome these difficulties, nanotechnology-based methods have been recently adopted in catalytic valorization of lignocellulosic biomass. The present review has critically discussed the application of nano-biotechnology in lignocellulosic biomass valorization in terms of pretreatment and hydrolysis. A detailed discussion on the application of various nanoparticles in these processes, enzyme immobilization and end-production utilization is presented in this review. Finally, the review emphasizes the major challenges of this process along with different routes and recommendations to address the issues.

Pd–Au Bimetallic Catalysts for the Hydrogenation of Muconic Acid to Bio-Adipic Acid

The hydrogenation reaction of muconic acid, produced from biomass using fermentative processes, to bio-adipic acid is one of the most appealing green emerging chemical process. This reaction can be promoted by catalysts based on a metal belonging to the platinum group, and the use of a second metal can preserve and increase their activity. Pd–Au bimetallic nanoparticle samples supported on high-temperature, heat-treated carbon nanofibers were prepared using the sol immobilization method, changing the Pd–Au molar ratio. These catalysts were characterized by TEM, STEM, and XPS analysis and tested in a batch reactor pressurized with hydrogen, where muconic acid dissolved in water was converted to adipic acid. The synthesized Pd–Au bimetallic catalysts showed higher activity than monometallic Au and Pd material and better stability during the recycling tests. Moreover, the selectivity toward the mono-unsaturated changed by decreasing the Pd/Au molar ratio: the higher the amount of gold, the higher the selectivity toward the intermediates.

The Production of Carbon Nanofiber on Rubber Fruit Shell-Derived Activated Carbon by Chemical Activation and Hydrothermal Process with Low Temperature

Recently, the conversion of biomass into carbon nanofibers has been extensively studied. In this study, carbon nanofibers (CNFs) were prepared from rubber fruit shell (RFS) by chemical activation with H₃PO₄, followed by a simple hydrothermal process at low temperature and without a vacuum and gas catalyst. XRD and Raman studies show that the structure formed is an amorphous graphite formation. From the thermal analysis, it is shown that CNFs have a high thermal stability. Furthermore, an SEM/TEM analysis showed that CNFs’ morphology varied in size and thickness. The obtained results reveal that by converting RFS into an amorphous carbon through chemical activation and hydrothermal processes, RFS is considered a potential biomass source material to produce carbon nanofibers.

A Modification of Palm Waste Lignocellulosic Materials into Biographite Using Iron and Nickel Catalyst

This paper presents an alternative way to maximize the utilization of palm waste by implementing a green approach to modify lignocellulosic materials into a highly crystalline biographite. A bio-graphite structure was successfully synthesized by converting lignocellulosic materials via a simple method using palm kernel shell (PKS) as a carbon precursor. This involved the direct impregnation of a catalyst into raw material followed by a thermal treatment. The structural transformation of the carbon was observed to be significantly altered by employing different types of catalysts and varying thermal treatment temperatures. Both XRD and Raman spectroscopy confirmed that the microstructural alteration occurred in the carbon structure of the sample prepared at 800 and 1000 °C using iron, nickel or the hybrid of iron-nickel catalysts. The XRD pattern revealed a high degree of graphitization for the sample prepared at 1000 °C, and it was evident that iron was the most active graphitization catalyst. The presence of an intensified peak was observed at 2θ = 26.5°, reflecting the formation of a highly ordered graphitic structure as a result of the interaction between the iron catalyst and the thermal treatment process at 1000 °C. The XRD observation was further supported by the Raman spectrum in which PKS-Fe1000 showed a lower defect structure associated with the presence of a significant amount of graphitic structure, as a low value of (Id/Ig) ratio was reported. An HRTEM image showed a well-defined lattice fringe seen on the structure for PKS-Fe1000; meanwhile, a disordered microstructure was observed for the control sample, indicating that successful structural modification was achieved with the aid of the catalyst. Further analysis from BET found that the PKS-Fe1000 developed a surface area of 202.932 m2/g with a pore volume of 0.208 cm3/g. An overall successful modification from palm waste into graphitic material was achieved. Thus, this study will help those involved in waste management to evaluate the possibility of a sustainable process for the generation of graphite material from palm waste. It can be concluded that palm waste is a potential source of production for graphite material through the adoption of the proposed waste management process.

High-performance nanostructured bio-based carbon electrodes for energy storage applications

Polyacrylonitrile (PAN)-based carbon precursor is a well-established and researched material for electrodes in energy storage applications due to its good physical properties and excellent electrochemical performance. However, in the fight of preserving the environment and pioneering renewable energy sources, environmentally sustainable carbon precursors with superior electrochemical performance are needed. Therefore, bio-based materials are excellent candidates to replace PAN as a carbon precursor. Depending on the design requirement (e.g. carbon morphology, doping level, specific surface area, pore size and volume, and electrochemical performance), the appropriate selection of carbon precursors can be made from a variety of biomass and biowaste materials. This review provides a summary and discussion on the preparation and characterization of the emerging and recent bio-based carbon precursors that can be used as electrodes in energy storage applications. The review is outlined based on the morphology of nanostructures and the precursor's type. Furthermore, the review discusses and summarizes the excellent electrochemical performance of these recent carbon precursors in storage energy applications. Finally, a summary and outlook are also given. All this together portrays the promising role of bio-based carbon electrodes in energy storage applications.

Insight into activated carbon from different kinds of chemical activating agents: A review

Activated carbon (AC) is an important material in various fields owing to its low cost, well-developed porosity, and favorable chemical stability. Key factors for the optimal synthesis of AC are the carbon precursors, activation pathways, activating agents, and design of the procedure parameters. So far, no case studies have reviewed the activating agents used during the chemical activation process. Accordingly, the present review provides a summary of recent research, highlighting the development of activating agents during the process of AC. Detailed lists of pore-forming mechanisms by various activating agents, including alkaline, acidic, neutral, and self-activating agents, have been systematically summarized. Furthermore, the effects of activating agents on the experimental procedures have also been established. Finally, a comprehensive discussion about the influences of activating agents on the physical and chemical properties of the resultant AC is included. The objective of this study is to reveal and distinguish the individual roles of different activating agents during AC synthesis.

Pyrolysis of heavy metal contaminated biomass pre-treated with ferric salts: Product characterisation and heavy metal deportment

The metal(loid)-enriched Avicennia marina biomass obtained from phytoremediation was impregnated with two ferric salts (FeCl₃ and Fe(NO₃)₃) prior to pyrolysis at 300-700 °C, aiming to study the influence on pyrolytic product properties and heavy metal(loid) deportment. Results showed that the impregnated ferric salts increased the fixed carbon content of biochars, hydrocarbon fractions in bio-oils, and the evolution of CO and H₂ in gases. Cd in biomass could be effectively removed from the biomass by FeCl₃ impregnation. During pyrolysis, the ferric salts enhanced the elemental recovery of As, Cr, Ni and Pb in the biochars and decreased their distribution in gases. Notably, the ferric salt pre-treatment inhibited the mobility and bio-availability of most elements in the biochars. This study indicated that ferric salt impregnation catalysed the pyrolysis process of metal(loid) contaminated biomass, enabled the operation temperature at 500-700 °C with minimal environmental risks, providing a safe and value-added way to the phytoremediation-pyrolysis scheme.

Hierarchical Porous Carbon with Interconnected Ordered Pores from Biowaste for High-Performance Supercapacitor Electrodes

Using biowastes as precursors for the preparation of value-added nanomaterials is critical to the sustainable development of devices. Lignosulphonates are the by-products of pulp and paper-making industries and usually discarded as wastes. In the present study, lignosulphonate is used as the precursor to prepare hierarchical ordered porous carbon with interconnected pores for the electrochemical energy storage application. The unique molecular structure and properties of lignosulphonate ensure the acquisition of high-quality porous carbon with a controllable pore structure and improved physical properties. As a result, the as-prepared hierarchical order porous carbon show excellent energy storage performance when used to assemble the symmetric supercapacitor, which exhibits high-specific capacitance of 289 F g-1 at a current density of 0.5 A g-1, with the energy density of 40 Wh kg-1 at the power density of 900 W kg-1. The present study provides a promising strategy for the fabrication of high-performance energy storage devices at low cost.

Review on Activated Carbons by Chemical Activation with FeCl3

This study reviews the most relevant results on the synthesis, characterization, and applications of activated carbons obtained by novel chemical activation with FeCl3. The text includes a description of the activation mechanism, which compromises three different stages: (1) intense de-polymerization of the carbon precursor (up to 300 °C), (2) devolatilization and formation of the inner porosity (between 300 and 700 °C), and (3) dehydrogenation of the fixed carbon structure (>700 °C). Among the different synthesis conditions, the activation temperature, and, to a lesser extent, the impregnation ratio (i.e., mass ratio of FeCl3 to carbon precursor), are the most relevant parameters controlling the final properties of the resulting activated carbons. The characteristics of the carbons in terms of porosity, surface chemistry, and magnetic properties are analyzed in detail. These carbons showed a well-developed porous texture mainly in the micropore size range, an acidic surface with an abundance of oxygen surface groups, and a superparamagnetic character due to the presence of well-distributed iron species. These properties convert these carbons into promising candidates for different applications. They are widely analyzed as adsorbents in aqueous phase applications due to their porosity, surface acidity, and ease of separation. The presence of stable and well-distributed iron species on the carbons’ surface makes them promising catalysts for different applications. Finally, the presence of iron compounds has been shown to improve the graphitization degree and conductivity of the carbons; these are consequently being analyzed in energy storage applications.

Synthesis of char-based adsorbents from cotton textile waste assisted by iron salts at low pyrolysis temperature for Cr(VI) removal

Char-based adsorbents (char-FeCl₃, char-FeCl₂, and char-FeCit) derived from cotton textile waste (CTW) were synthesized by one-step low-temperature pyrolysis approach with different iron salts. The properties of the samples were conducted by BET, SEM, EDS, XRD, XPS, TEM, and FTIR. The results suggested that the surface areas of char-FeCl₃ and char-FeCl₂ were higher than those of char-FeCit. The presence of Fe₂O₃ as well as pyrolysis gas (HCl (g) and H₂O (g)) could catalyze the formation of porosity. Meanwhile, FeCl₃ showed the strongest catalysis effect to decompose cellulose to produce char. The pyrolysis process analysis was investigated by means of thermogravimetry-DSC. FeCl₃ and FeCl₂ could accelerate the breakage of cellulose structure whereas FeC₆H₅O₇ was not beneficial to form char at low temperature as the incomplete decomposition of citrate. The adsorption property of Cr(VI) for the chars was evaluated. Adsorption processes were fitted well with the Freundlich model, and char-FeCl₃ presented the best adsorptive capacity (70.39 mg/g). Thus, this low-temperature pyrolysis method was economical and technologically simplified as well as efficient adsorption capacity of Cr(VI) removal. Graphical abstract.

Understanding reactions and pore-forming mechanisms between waste cotton woven and FeCl3 during the synthesis of magnetic activated carbon

FeCl₃ is a valuable iron salt used in the synthesis of magnetic waste cotton woven-based activated carbon. Although it has received extensive research attention, more information is required regarding its interactions with the carbon matrix. This systematic study describes the potential reactions of FeCl₃ and waste cotton woven. First, the textural properties of waste cotton woven-based activated carbon synthesized under various conditions were investigated via element analysis, N₂ sorption/desorption isotherms, and scanning electron microscopy. Then, the possible reaction mechanisms were deduced through various characterization methods. The results demonstrate that FeCl₃ can lower the initial decomposition temperature of WCW to 135 °C and catalyze decarboxylation and decarbonylation at 100-330 °C to elevate the formation of microporous structures. Moreover, FeCl₃ can also form Lewis acid sites at 330-700 °C and promote the cross-linking reaction to develop intricate microporous structures and carbonaceous materials with the synergistic effect of Fe³⁺ and Cl^-. FeCl₃ could be used as a template-like agent to form mesoporous structures. Meanwhile, it can also act as a magnetizer that Fe₃O₄ derived from the decomposition of FeCl₃ would insert into the carbon matrix and combine with C-Cl to tailor the magnetic controllable activated carbon. Finally, we confirmed that extending the activation time could convert the structure of waste cotton woven-based activated carbon and increase the number of active sites, thereby further improving the catalytic properties of FeCl₃ in pore formation.

Biochar-supported magnetic noble metallic nanoparticles for the fast recovery of excessive reductant during pollutant reduction

The catalytic reduction of diverse pollutants by noble metal catalysts in the presence of reductants is a highly effective and widely used method. However, the considerable cost of noble metal catalysts impedes the practical application of this method, and the recovery of excessive reductants has not been reported previously. In this work, we prepared inexpensive biochar-supported magnetic noble metallic nanoparticles (NPs) and efficiently recovered the excessive reductants in the form of H₂. The as-synthesized biochar-supported noble metallic NPs exhibited high H₂ recovery during the 4-nitrophenol reduction reaction. Results showed that the catalysts with low noble metallic content have higher H₂ recovery rate than commercial Pd/C, Ag/C, and Pt/C. The catalytic mechanism of magnetic biochar-supported noble metallic NPs was demonstrated to be a "synergetic effect", where biochar and Fe₃O₄ acted as accelerants that enable noble metallic NPs to produce active hydrogen for the reduction reaction, and the excess active hydrogen atoms combined to form H₂.

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.

Accelerated Microbial Reduction of Azo Dye by Using Biochar from Iron-Rich-Biomass Pyrolysis

Biochar is widely used in the environmental-protection field. This study presents the first investigation of the mechanism of biochar prepared using iron (Fe)-rich biomass and its impact on the reductive removals of Orange G dye by Shewanella oneidensis MR-1. The results show that biochars significantly accelerated electron transfer from cells to Orange G and thus stimulated reductive removal rate to 72–97%. Both the conductive domains and the charging and discharging of surface functional groups in biochars played crucial roles in the microbial reduction of Orange G to aniline. A high Fe content of the precursor significantly enhanced the conductor performance of the produced biochar and thus enabled the biochar to have a higher reductive removal rate of Orange G (97%) compared to the biochar prepared using low-Fe precursor (75%), but did not promote the charging and discharging capacity of the produced biochar. This study can prompt the search for natural biomass with high Fe content to confer the produced biochar with wide-ranging applications in stimulating the microbial reduction of redox-active pollutants.

Effect of surface modification on carbon nanotubes (CNTs) catalyzed nitrobenzene reduction by sulfide

Carbon nanotubes (CNTs) could be directly used as metal-free catalysts for the reduction of nitroaromatics by sulfide in water, but their catalytic ability need a further improvement. This study evaluated the feasibility of surface modification through thermal and radiation pretreatments to enhance catalytic activity of CNTs on nitrobenzene reduction by sulfide. The results show that thermal treatment could effectively improve the catalytic behaviors of CNTs for the reduction of nitrobenzene by sulfide, where the optimum annealing temperature was 400 °C. However, plasma radiation pretreatment didn't result in an obvious improvement of the CNTs catalytic activity. Moreover, the possible reasons have been explored and discussed in the study. Additionally, the impacts of various operational parameters on nitrobenzene reduction catalyzed by the CNTs after an optimized surface modification were also evaluated. It was found that the rate of nitrobenzene removal by sulfide was positively correlated with CNTs doses in a range of 0.3-300 mg L^-1; the optimum pH was around 8.0; higher temperature and sulfide concentration facilitated the reaction; and the presence of humic acid exhibited a negative effect on nitrobenzene reduction.

Templating Synthesis of Mesoporous Fe3C-Encapsulated Fe-N-Doped Carbon Hollow Nanospindles for Electrocatalysis

Developing cost-efficient alternatives to the noble metal catalysts toward oxygen reduction reaction (ORR) has attracted much attention. Herein, a kind of mesoporous hollow spindlelike Fe-N-C electrocatalysts with iron carbide nanoparticles encased in the N-doped graphitic layers has been synthesized by a novel "reactive hard template" strategy through the Fe³⁺-assisted polymerization of dopamine on the Fe₂O₃ cores and the following calcinations. The Fe₂O₃ nanospindles not only as the hard template guide the formation of well-defined shape and structure of the catalyst but also as the reactive template provide Fe reservoir to generate Fe₃C nanoparticles in the catalyst during the thermochemical process. The superiority in accessible active sites of Fe-N _x species, Fe₃C nanoparticles in graphenelike layers, and highly mesoporous hollow structure enables the catalysts to exhibit excellent ORR performances including high catalytic activity, outstanding long-term cycling stability, and good tolerance to methanol.

Thermal Transition of Bimetallic Metal-Phenolic Networks to Biomass-Derived Hierarchically Porous Nanofibers

The development and utilization of biomass resources could contribute to new materials for long-term sustainable energy storage and environmental applications, reduce environmental impacts, and meet the urgent need for green and sustainable development strategies. Herein, a bimetallic metal-phenolic network (MPN) was applied to incorporate different metallic element species into cattle skin and fabricate collagen-fiber-derived complex oxide nanofibers using natural polyphenols (Myrica tannins). Direct thermal transition of these biomass-MPN composites generates hierarchically porous nanofibers possessing micro- and mesoporous architectures along with a well-preserved macroscopic structure. The pore system and complex oxide composition provide excellent photocatalytic performance. This low-cost, simple, and readily scalable MPN-based approach provides a straightforward route to synthesize nanostructured materials directly from biomass, which could play important roles in a wide range of potential applications.

Enhanced lead and cadmium removal using biochar-supported hydrated manganese oxide (HMO) nanoparticles: Behavior and mechanism

Hydrated manganese oxide (HMO) nanoparticles were impregnated into a peanut shell-derived biochar (BC) to obtain a remarkable nanocomposite adsorbent, HMO-BC, which overcomes the technical barriers of singly applying either HMO or BC in practical heavy metal-containing wastewater treatment. HMO-BC can effectively sequestrate Pb(II) and Cd(II) in a wide pH range of 3-7 and exhibited more preferable sorption than bare BC in the presence of high-level competing cations. BC also significantly lowered the Mn leaching at acidic pH. Fixed-bed column adsorption tests showed that the effective treatment volume of HMO-BC for a simulated Pb(II)- or Cd(II)-laden wastewater is about 4-6 times higher than that of the BC host. In addition, HMO-BC was effective in removing Pb(II) from a real Pb-containing electroplating wastewater to discharge limit (0.2mgL^-1) with treatable volume of 525BV, much higher than that of the bare BC (60BV). More importantly, the saturated HMO-BC can be thoroughly regenerated for repeated uses without any observable capacity loss. Such attractive results of HMO-BC were attributed to the complementary effect of its two components. The embedded HMO nanoparticles provide preferable capture of target cations through specific inner-sphere complexation, as illustrated by XPS spectra of Pb 4f_7/2 and O1s, while the non-diffusive negatively charged oxygen-containing groups bound to BC facilitate the pre-enrichment and permeation of Pb(II) and Cd(II) cations into the pore channels prior to their preferable sorption through the Donnan membrane effect.

Carbonaceous aerogel and CoNiAl-LDH@CA nanocomposites derived from biomass for high performance pseudo-supercapacitor

Conversion of waste biomass to valuable carbonaceous material is a sustainable and environmental benign method for energy and reduction of greenhouse gas emission. Herein, a two-step hydrothermal method was developed to fabricate high performance electrode material from pomelo peels. In the first step, the pomelo peels were transformed to carbonaceous aerogel (CA), which constructed of three-dimensional, sponge-like brown monolith with hierarchical pores, low-density (0.032g/cm³) and excellent mechanical flexibility. Then, the cobalt nickel aluminum layered double hydroxide (CoNiAl-LDH) was in situ loaded on the surface of CA to form exquisite core-shell structure (CoNiAl-LDH@CA) through the second hydrothermal step. When used as an electrode material for supercapacitor, CoNiAl-LDH@CA exhibited high specific capacitances of 1,134F/g at 1A/g and 902F/g at 10A/g, respectively. Furthermore, they displayed an excellent cycling stability without an obvious capacitance decrease after 4,000 cycles.

Surface-rough Fe-N/C composite wrapped on carbon nanotubes as efficient electrocatalyst for oxygen reduction reaction

Fe-N/C composites are considered one of the most promising non-precious-metal electrocatalysts for oxygen reduction reaction (ORR). In this paper, we fabricate a novel and efficient carbon nanotube (CNT)-supported Fe-N/C composite catalyst, via the surface-self-polymerization of polydopamine and then the incorporation with Fe species on CNTs, followed by the pyrolysis process. The obtained catalyst demonstrates excellent electrocatalytic performance towards ORR in alkaline media. The modification of Fe-incorporated nitrogen-rich-carbons (Fe-CN_x) on CNTs lowers the ORR half-wave-potential by ∼190 mV, giving this catalyst with an onset ORR potential of 0.95 V (versus reversible hydrogen electrode (RHE)), a half-wave potential of 0.82 V (versus RHE), and the limiting current density of 5.39 mA cm^-2 in 0.1 M KOH. The performance of the as-prepared catalyst is comparatively better than the commercially available Pt/C in terms of positive half-wave potential and larger limiting current, superior durability, and higher tolerance to the methanol.

MnO2 Nanowire/Biomass-Derived Carbon from Hemp Stem for High-Performance Supercapacitors

Hierarchical 3D nanostructures based on waste biomass are being offered as promising materials for energy storage due to their processabilities, multifunctionalities, environmental benignities, and low cost. Here we report a facile, inexpensive, and scalable strategy for the fabrication of hierarchical porous 3D structure as electrode materials for supercapacitors based on MnO₂ nanowires and hemp-derived activated carbon (HC). Vertical MnO₂ wires are uniformly deposited onto the surface of HC using a one-step hydrothermal method to produce hierarchical porous structures with conductive interconnected 3D networks. HC acts as a near-ideal 3D current collector and anchors electroactive materials, and this confers a specific capacitance of 340 F g^-1 at 1 A g^-1 with a high rate capability (88% retention) of the 3D MnO₂/HC composite because of its open-pore system, which facilitates ion and electron transports and synergistic contribution of two energy-storage materials. Moreover, asymmetric supercapacitors fabricated using 3D HC as the anode and 3D MnO₂/HC as the cathode are able to store 33.3 Wh kg^-1 of energy and have a power delivery of 14.8 kW kg^-1.

Reduction of Bromate by Cobalt-Impregnated Biochar Fabricated via Pyrolysis of Lignin Using CO2 as a Reaction Medium

In this study, pyrolysis of lignin impregnated with cobalt (Co) was conducted to fabricate a Co-biochar (i.e., Co/lignin biochar) for use as a catalyst for bromate (BrO₃^-) reduction. Carbon dioxide (CO₂) was employed as a reaction medium in the pyrolysis to induce desired effects associated with CO₂; (1) the enhanced thermal cracking of volatile organic compounds (VOCs) evolved from the thermal degradation of biomass, and (2) the direct reaction between CO₂ and VOCs, which resulted in the enhanced generation of syngas (i.e., H₂ and CO). This study placed main emphases on three parts: (1) the role of impregnated Co in pyrolysis of lignin in the presence of CO₂, (2) the characterization of Co/lignin biochar, and (3) evaluation of catalytic capability of Co-lignin biochar in BrO₃^- reduction. The findings from the pyrolysis experiments strongly evidenced that the desired CO₂ effects were strengthened due to catalytic effect of impregnated Co in lignin. For example, the enhanced generation of syngas from pyrolysis of Coimpregnated lignin in CO₂ was more significant than the case without Co impregnation. Moreover, pyrolysis of Coimpregnated lignin in CO₂ led to production of biochar of which surface area (599 m² g^-1) is nearly 100 times greater than the biochar produced in N₂ (6.6 m² g^-1). Co/lignin biochar produced in CO₂ also showed a great performance in catalyzing BrO₃^- reduction as compared to the biochar produced in N₂.

Carbon-Based Functional Materials Derived from Waste for Water Remediation and Energy Storage

Carbon-based functional materials hold the key for solving global challenges in the areas of water scarcity and the energy crisis. Although carbon nanotubes (CNTs) and graphene have shown promising results in various fields of application, their high preparation cost and low production yield still dramatically hinder their wide practical applications. Therefore, there is an urgent call for preparing carbon-based functional materials from low-cost, abundant, and sustainable sources. Recent innovative strategies have been developed to convert various waste materials into valuable carbon-based functional materials. These waste-derived carbon-based functional materials have shown great potential in many applications, especially as sorbents for water remediation and electrodes for energy storage. Here, the research progress in the preparation of waste-derived carbon-based functional materials is summarized, along with their applications in water remediation and energy storage; challenges and future research directions in this emerging research field are also discussed.