Iron encapsulated in 3D N-doped carbon nanotube/porous carbon hybrid from waste biomass for enhanced oxidative activity

Removal of sulfonamide antibiotics by non-free radical dominated peroxymonosulfate oxidation catalyzed by cobalt-doped sulfur-containing biochar from sludge

The reuse of activated sludge as a solid waste is severely underutilized due to the limitations of traditional treatment and disposal methods. Given that, the sulfur-containing activated sludge catalyst doped with cobalt (SK-Co(1.0)) was successfully prepared by one-step pyrolysis and calcinated at 850 ℃. The generation of CoSx was successfully characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), indicating that the sulfur inside the sludge was the anchoring site for the externally doped cobalt. Cobalt (Ⅱ) (Co2+), as the main adsorption site for peroxymonosulfate(PMS), formed a complex (SK-Co(1.0)-PMS* ) and created the conditions for the generation of surface radicals. The SK-Co(1.0)/PMS system showed high degradation efficiency and apparent rate constants for Sulfamethoxazole (SMX) (91.56% and 0.187 min-1) and Sulfadiazine (SDZ) (90.73% and 0.047 min-1) within 10 min and 30 min, respectively. Three sites of generation of 1O2, which played a dominant role in the degradation of SMX and SDZ in the SK-Co(1.0)/PMS system, were summarized as：sulfur vacancies (SVs), the Co3+/Co2+ cycles promoted by sulfur(S) species, oxygen-containing functional groups (C-O). The degradation mechanisms and pathways had been thoroughly investigated using DFT calculations. In view of this, a new idea for the resource utilization of activated sludge solid waste was provided and a new strategy for wastewater remediation was proposed.

Functional Activated Biocarbons Based on Biomass Waste for CO2 Capture and Heavy Metal Sorption

Inexpensive porous activated biocarbons were prepared from biomass and agriculture waste following the method of thermal and hydrothermal carbonization and activation with superheated water vapor. The activated biocarbons were characterized by nitrogen adsorption-desorption at 77 K, SEM, XRD, Raman spectrometry, FTIR spectroscopy, determination of particle size, and elemental composition by XRF. The specific surface area was in the range of 240-709 m2/g, and the total pore volume was from 0.12 to 0.43 cm3/g. The percentage of microporosity in activated biocarbons was 89-92%. These activated biocarbons have been used for CO2 and heavy metal sorption. Activated biocarbons based on pine cones and birch prepared by thermal carbonization and activation with superheated water vapor had the highest ability to capture CO2 and amounted to 6.43 and 6.00 mmol/g at 273 K, as well as 4.57 and 4.22 mmol/g at 298 K, respectively. The best activated biocarbon was characterized by unchanged stability after 30 adsorption and desorption cycles. It was proved that the adsorption of CO2 depends on narrow micropores (<1 nm). Activated biocarbons have also been analyzed as effective adsorbents for removing Cu2+, Zn2+, Fe2+, Ni2+, Co2+, and Pb2+ ions from aqueous solutions. Activated biocarbons are effective adsorbents for the removal of lead and zinc ions from aqueous solutions.

Rapid adsorption of triclosan and p-chloro-m-xylenol by nitrogen-doped magnetic porous carbon

Contamination of water resources with organic substances like phenolic fungicides is undesirable due to the improvement of living standards, the huge production of chemicals, the heavy consumption of daily chemical products, and the growth of the population. In this study, Co-based zeolitic imidazole framework-67 (ZIF-67(Co)) was synthesized using the "one-pot method," and the best Co-based N-doped magnetic porous carbon (Co-NPC) was prepared by ZIF-67(Co) carbonization in an atmosphere of N₂. The materials were tested using an X-ray diffractometer (XRD), scanning electron microscope (SEM), infrared spectroscopy (IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), N₂ adsorption-desorption, and magnetization analysis. These characterizations indicated that the Co-NPC was successfully prepared. With the original morphology of ZIF-67(Co) crystals, the Co-NPC also has good porosity, magnetic properties, and a large specific surface area. In water, Co-NPC-800 has a good adsorption capacity for triclosan (TCS) and p-chloro-m-xylenol (PCMX), which are kinds of aromatic fungicides. The adsorption of Co-NPC-800 on both reached equilibrium within 3 min, which is in accordance with the quasi-second-order kinetic model. At 298 K, the maximum adsorption capacity of Co-NPC-800 for TCS and PCMX was 163 and 39 mg·g^-1, respectively. The adsorption of TCS and PCMX by Co-NPC-800 is a spontaneous endothermic process with reduced entropy. The combination of Co-NPC-800 and phenols come from multiple actions of electrostatic, π-π, and hydrogen bond effects. Moreover, Co-NPC-800 can be regenerated through simple washing and can be reused at least three times by a magnet. The Co-NPC-800 has good porosity, large specific surface area, comparable adsorption capacity, rapid adsorption time, so it could be broadly used in sewage treatments and other environmental fields.

Hydrothermally assisted synthesis of nano zero-valent iron encapsulated in biomass-derived carbon for peroxymonosulfate activation: The performance and mechanisms for efficient degradation of monochlorobenzene

A facile, green and easily-scalable method of synthesizing stable and effective nano zero-valent iron (nZVI)‑carbon composites for peroxymonosulfate (PMS) activation was highly desirable for in-situ groundwater remediation. This study developed a two-step hydrothermally assisted carbothermal reduction method to prepare nZVI-encapsulated carbon composite (Fe@C) using rice straw and ferric nitrate as precursors. The hydrothermal reactions were conducive to iron loading, and carbothermal temperature was crucial for the aromatization and graphitization of hydrothermal carbonaceous products, the reductive transformation of iron oxides into nZVI and the development of porous structure in composites. At carbothermal temperature of 800 °C following hydrothermal reactions, the stable Fe@C800 with nZVI encapsulated in the spherical carbon shell was obtained and exhibited the best catalytic performance for PMS activation and the degradation of monochlorobenzene (MCB) in a wide range of pH values (3-11) with removal efficiency after 120 min reaction and first-order kinetic rate constant (k₁) of 98.7% and 0.087 min^-1 respectively under the optimum conditions of 10 mM PMS and 0.2 g·L^-1 Fe@C800. The inhibiting effects of common co-existed anions (i.e., Cl^-, HCO₃^- and H₂PO₄^-) and humic acid in groundwater on the removal of MCB in Fe@C800/PMS system was also investigated. Both OH-dominated radical processes and nonradical pathways involving ¹O₂ and surface electron transfers were accounted for PMS activation and MCB removal. The inner nZVI was protected by the carbon shell, endowing Fe@C800 with high reactivity and good reusability. Additionally, 81.2% and 73.5% of MCB removal rates were achieved in tap water and actual contaminated groundwater respectively. This study not only provided a novel strategy to synthesize highly effective and stable nZVI‑carbon composites using the agricultural biomass waste for PMS induced oxidation of organic contaminants in groundwater, but also enhanced the understanding on the activation mechanism of iron‑carbon based catalysts towards PMS.

Carbon nanotube-based materials for persulfate activation to degrade organic contaminants: Properties, mechanisms and modification insights

Removal of harmful organic matters from environment has great environmental significance. Carbon nanotube (CNT) materials and their composites have been demonstrated to possess excellent catalytic activity towards persulfate (PS) activation for the degradation of organic contaminants. Herein, detailed information concerning the function, modification methods and relevant mechanisms of CNT in persulfate-based advanced oxidation processes (PS-AOPs) for organic pollutant elimination has been reviewed. The activation mechanism of PS by CNT might include radical and nonradical pathways and their synergistic effects. The common strategies to improve the stability and catalytic capability of CNT-based materials have also been put forward. Furthermore, their practical application potential compared with other catalysts has been described. Finally, the challenges faced by CNT in practical application are clearly highlighted. This review should be of value in promoting the research of PS activation by CNT-based materials for degradation of organic pollutants and the corresponding practical applications.

Facile fabrication of Fe/Fe3C embedded in N-doped carbon nanofiber for efficient degradation of tetracycline via peroxymonosulfate activation: Role of superoxide radical and singlet oxygen

The toxic metal ions leaching and metal nanoparticles agglomeration were the critical issues for metal-based carbon materials during the peroxymonosulfate (PMS) activation processes. Herein, a facile strategy was first proposed that zero-dimensional Fe/Fe₃C nanoparticles were embedded in one-dimensional N-doped carbon nanofiber (Fe/Fe₃C@NCNF) to solve the above challenges. The as-obtained Fe/Fe₃C@NCNF-800 possessed a low E_a value (11.7 kJ/mol) and exhibited high activity for activating PMS to degrade tetracycline (TC) in a wide range of pH 3-11. As expected, the iron ions leaching concentration of Fe/Fe₃C@NCNF-800 was very low (0.082 mg/L). Meanwhile, the Fe/Fe₃C@NCNF-800 was easily recovered from the reaction solution due to its magnetic properties. Both superoxide radicals (O₂^∙-) and non-radical of singlet oxygen (¹O₂) were the primary reactive oxygen species (ROS) in the Fe/Fe₃C@NCNF-800/PMS system via quenching tests and electron spin resonance spectroscopy (ESR). The catalytic mechanism suggested that the Fe/Fe₃C and graphitic N were the main active sites in the Fe/Fe₃C@NCNF-800 for PMS activation. This work provided a facile method for the preparation of Fe-based carbon materials with high catalytic ability, low metal leaching and easy recycling, showing a broad prospect for environmental applications.

Fe-doped biochar derived from waste sludge for degradation of rhodamine B via enhancing activation of peroxymonosulfate

The disposal and management of waste sludge is a considerable challenge for environmental protection and resource utilization. Herein, sludge-based biochar material loaded with nano-Fe₃O₄ (xS@Fe-y) was fabricated via hydrothermal carbonization process and employed as catalyst to activate peroxymonosulfate (PMS) for degrading organic dyes in wastewater. Benefiting from the proper iron content, porous structure and the good dispersibility of iron on the catalyst surface, the proposed 5S@Fe-500 catalyst not only exhibited excellent catalytic activity and durability in the activation of PMS to degrade Rhodamine B (RhB), which was almost completely removed in 10 min (50 mL 50 mg L^-1), but also performed broad application prospects in pollutant degradation. More importantly, the free radical quenching test and electron spin-resonance spectroscopy (ESR) detection demonstrated that O₂•^-, SO₄•^-, OH and ¹O₂ were generated during the process of catalyst activation of PMS. Based on this, a possible reaction pathway for degrading RhB with the aid of 5S@Fe-500 was put forward. It is believed that this work offers a promising reuse method of converting the waste sludge to a high efficiency and low-cost nano magnetic catalyst to activate PMS for degrading refractory organic pollutants in aquatic surroundings.

The production and application of carbon nanomaterials from high alkali silicate herbaceous biomass

Herein, value-added materials such as activated carbon and carbon nanotubes were synthesized from low-value Miscanthus × giganteus lignocellulosic biomass. A significant drawback of using Miscanthus in an energy application is the melting during the combustion due to its high alkali silicate content. An application of an alternative approach was proposed herein for synthesis of activated carbon from Miscanthus × giganteus, where the produced activated carbon possessed a high surface area and pore volume of 0.92 cm³.g⁻¹ after two activation steps using phosphoric acid and potassium hydroxide. The S_BET of the raw biomass, after first activation and second activation methods showed 17, 1142 and 1368 m².g⁻¹, respectively. Transforming this otherwise waste material into a useful product where its material properties can be utilized is an example of promoting the circular economy by valorising waste lignocellulosic biomass to widely sought-after high surface area activated carbon and subsequently, unconventional multi-walled carbon nanotubes. This was achieved when the activated carbon produced was mixed with nitrogen-based material and iron precursor, where it produced hydrophilic multi-wall carbon nanotubes with a contact angle of θ = 9.88°, compared to the raw biomass. synthesised materials were tested in heavy metal removal tests using a lead solution, where the maximum lead absorption was observed for sample AC-K, with a 90% removal capacity after the first hour of testing. The synthesis of these up-cycled materials can have potential opportunities in the areas of wastewater treatment or other activated carbon/carbon nanotube end uses with a rapid cycle time.

Production and characterisation of activated carbon and carbon nanotubes from potato peel waste and their application in heavy metal removal

Herein, activated carbon (AC) and carbon nanotubes (CNTs) were synthesised from potato peel waste (PPW). Different ACs were synthesised via two activation steps: firstly, with phosphoric acid (designated PP) and then using potassium hydroxide (designated PK). The AC produced after the two activation steps showed a surface area as high as 833 m2 g-1 with a pore volume of 0.44 cm3 g-1, where the raw material of PPW showed a surface area < 4 m2 g-1. This can help aid and facilitate the concept of the circular economy by effectively up-cycling and valorising waste lignocellulosic biomass such as potato peel waste to high surface area AC and subsequently, multi-walled carbon nanotubes (MWCNTs). Consequently, MWCNTs were prepared from the produced AC by mixing it with the nitrogen-based material melamine and iron precursor, iron (III) oxalate hexahydrate. This produced hydrophilic multi-wall carbon nanotubes (MWCNTs) with a water contact angle of θ = 14.97 °. Both AC and CNT materials were used in heavy metal removal (HMR) where the maximum lead absorption was observed for sample PK with a 84% removal capacity after the first hour of testing. This result signifies that the synthesis of these up-cycled materials can have applications in areas such as wastewater treatment or other conventional AC/CNT end uses with a rapid cycle time in a two-fold approach to improve the eco-friendly synthesis of such value-added products and the circular economy from a significant waste stream, i.e., PPW. Graphical abstract .

Efficient degradation of drug ibuprofen through catalytic activation of peroxymonosulfate by Fe3C embedded on carbon

Ibuprofen (IBU), a nonsteroidal anti-inflammatory drug, is becoming an important member of pharmaceuticals and personal care products (PPCPs) as emerging pollutants. To degrade IBU, magnetic Fe₃C nanoparticles embedded on N-doped carbon (Fe₃C/NC) were prepared as a catalyst by a sol-gel combustion method. As characterized, the Fe₃C/NC nanoparticles were composed of a NC nano-sheet and capsulated Fe₃C particles on the sheet. The Fe₃C/NC nanoparticles were confirmed an efficient catalyst for peroxymonosulfate (PMS) activation to generate sulfate radicals (SO₄^•-), single oxygen (¹O₂) and hydroxyl radicals (•OH) toward the degradation of IBU. The added IBU (10 mg/L) was almost completely removed in 30 min by using 0.1 g/L Fe₃C/NC and 2 g/L PMS. The catalyst was confirmed to have good ability and excellent reusability through leaching measurements and cycle experiments. A catalytic mechanism was proposed for the catalytic activation of PMS on Fe₃C/NC, which involves both Fe₃C reactive sites and N-doped carbon matrix as reactive sites in Fe₃C/NC. Moreover, the degradation pathway of IBU in the Fe₃C/NC-PMS system was proposed according to the detections of degradation intermediates.

Synthesis of 3D N-doped graphene/carbon nanotube hybrids with encapsulated Ni NPs and their catalytic application in the hydrogenation of nitroarenes

A Ni@N-CNTs-GS catalyst prepared via pyrolysis is shown to be active and stable for the hydrogenation of nitroarenes to anilines via a direct route.

ZIF-8 derived nitrogen-doped porous carbon as metal-free catalyst of peroxymonosulfate activation

Nitrogen-doped porous carbon (NPC) is synthesized through a direct pyrolysis of zeolitic imidazolate framework (ZIF)-8 under N₂ flow followed by acid washing process. It is found that NPC-800 pyrolyzed at 800 °C can inherit the perfect rhombic dodecahedron morphology of ZIF-8 crystals and achieve the considerable nitrogen-doping content of 15.20%. When NPC-800 is applied as the heterogeneous catalyst in peroxymonosulfate (PMS) activation for the degradation of Rhodamine B (RhB) and phenol, NPC-800 will exhibit its better performance than some conventional transition metal-based oxides and common carbon materials. The active sites can be primarily ascribed to nitrogen modification and sp ²-hybridized carbon frameworks. Besides, the influence of several parameters such as the dosage of catalyst, the concentration of oxidant, and reaction temperature is conducted systematically. More importantly, NPC-800 can maintain its considerable degradation in the presence of some anions and natural organic matters, even under some actual water background conditions. Although NPC-800 displays mild deactivation in repeated experiments, its catalytic performance can be easily recovered through heat treatment at 350 °C in air. Radical quenching tests reveal that both sulfate and hydroxyl radicals are responsible for the removal of organic pollutants. This research may provide a new way for the application of novel metal-free carbocatalysts in terms of PMS activation.