Nitrogen-doped Biochar Research Articles

Competitive adsorption of H2O and CO2 on nitrogen-doped biochar with rich-oxygen functional groups

Competitive adsorption of H2O and CO2 on nitrogen-doped biochar with rich-oxygen functional groups

The effect of carbon supports on the electrocatalytic performance of Ni-N-C catalysts for CO2 reduction to CO

Carbon-supported nickel and nitrogen co-doped (Ni-N-C) catalysts have been extensively studied as selective and active catalysts for CO2 electroreduction to CO. Most studies have focused on adjusting the coordination structure of Ni-Nx active sites, while the impact of the carbon supports has often been overlooked. In this study, a series of Ni-N-C catalysts on different carbon supports, including carbon black (CB), multi-walled carbon nanotubes (CNT), and activated nitrogen-doped biochar (ANBC), were synthesized using a ligand-mediated method. The effect of the carbon support on the electrocatalytic performance for CO2 reduction was investigated at both low current densities, in a H-cell, and high current densities, in a MEA electrolyzer. All of the prepared Ni-N-C catalysts show good faradaic efficiencies (FE) toward CO production (up to ~90%), however, the onset potentials and partial current densities for CO production vary greatly. The textural properties of the carbon support and the distribution of Ni-Nx active sites on the carbon support are demonstrated as the main factors behind the performance differences. In particular, hierarchical porous structures with large specific surface area are helpful to facilitate mass transport and improve the dispersion of active sites, which allows for a better CO2 reduction performance of Ni-N-ANBC compared to Ni-N-CB and Ni-N-CNT. This study demonstrates the importance of the carbon support for Ni-N-C catalysts and provides new insights into the design of efficient Ni-N-C catalysts for the CO2RR.

Comparison between endogenous and exogenous nitrogen of nitrogen-doped carbon catalyst in the process of activating PMS

BackgroundAdvanced oxidation processes (AOPs) based on sulfate radicals (SO4•–) have proven to be highly effective in degrading organics in wastewater. Carbon-based materials have emerged as promising catalysts for activating persulfate, which generates environmentally friendly sulfate radicals (SO4•–), for remediation purposes. The nitrogen doping technique is an effective method for site-specific regulation and can significantly enhance the performance of carbon-based catalysts, which could promote the application of carbon-based catalysts in the future. Endogenous and exogenous nitrogen sources can provide nitrogen sources for N doping. However, there are few reports on the comparison of the structure and catalytic mechanism of these two types of N-doped biochar. It is also of great significance to reveal the mechanisms of constructing catalytic sites using endogenous and exogenous nitrogen. MethodsHerein, the preparation of endogenous nitrogen-doped biochar (BC) was achieved by using soybean as the precursor material, which is rich in natural nitrogen-containing components of proteins. Subsequently, the BC was doped by mixing it with urea and pyrolysis, resulting in the preparation of exogenous nitrogen-doped biochar (NBC). Significant findingsThe characterization of XRD and HRTEM showed that g-C3N4 formed in NBC. The results of catalytic degradation and quenching experiments demonstrate that the exogenous nitrogen-doped catalysts have a better performance than endogenous nitrogen-doped catalysts. The OFL removal rate in BC/PMS was higher than that in the BC/PMS system (71.68% vs. 61.83 %). The kobs in NBC/PMS are also higher than that in BC/PMS (0.00943 min−1vs. 0.01369 min−1). The NBC could be a promising catalyst for PMS activation in practical application. DFT results showed that the g-C3N4 generated from exogenous nitrogen can improve PMS activation performance in the g-C3N4/graphene bilayer structure. The influence on the charge distribution of surrounding carbon materials makes endogenous nitrogen doping a good choice for optimizing the local performance of the material in the absence of natural nitrogen components.

High performance of heterogeneous catalytic ozonation for tetracycline removal by a N-doped biochar derived from co-pyrolysis of sludge and water hyacinth

Enhancing the performance of heterogeneous catalytic ozonation (HCO) for contaminant removal using biochar that is both cost-effective and stable is of great significance. In this research, a novel nitrogen-doped biochar (HSBC) was synthesized through the co-pyrolysis of sludge and water hyacinth. The presence of pyrrolic N, pyridinic N and graphitic N in HSBC as well as the high-temperature co-pyrolysis process, conferred a high degree of graphitization to the biochar. The graphitic N species facilitated the generation of free radicals, while the graphitic structure enhanced electron transfer between the catalyst and tetracycline (TC). HSBC demonstrated exceptional efficiency in TC removal via HCO, achieving a 93% removal rate within just 130 minutes. Moreover, the biodegradability of actual printing and dyeing wastewater with a chemical oxygen demand (COD) of (9900 mg/L) was increased sevenfold after HCO treatment. This study offers new perspectives on the preparation of N-doped biochar and its practical application in the treatment of industrial wastewater through HCO processes.

Multicomponent adsorption mechanism of CO2, SO2, NO, and C7H8 from flue gases on nitrogen-doped biochar: Experimental and computational insights

The comprehensive control of CO2 and gaseous pollutants in coal-fired flue gas is urgent and difficult. As a green low-cost adsorbent, nitrogen-doped biochar has potential application in the control technology of flue gas pollutants. Still, its multi-component adsorption characteristics for flue gas are unclear. In this study, the multi-component adsorption characteristics of CO2, SO2, NO, and C7H8 on nitrogen-doped biochar were explored at different temperatures (25–120 °C), and the competitive mechanism of multi-component adsorption was revealed through continuous adsorption experiments and numerical calculation. The adsorption capacities of CO2, SO2, NO, and C7H8 by nitrogen-doped biochar can reach 38.1, 78.9, 3.1, and 245.2 mg/g, among which CO2, SO2, and C7H8 show strong competitive effects. Their adsorption capacities are decreased by 42 % (CO2), 28 % (SO2), and 27 % (C7H8) respectively compared with the single-component adsorption. This is because there are not only more C7H8 adsorption sites on nitrogen-doped carbon, but also C7H8 can partially occupy the adsorption sites of SO2 and CO2 during multi-component adsorption. Combined with the calculation results of density functional theory, the competitive ability of the three gases can be ranked as follows: C7H8 > SO2 > CO2.

Insights into the factors influencing the oxidation of antibiotic pollutants in nitrogen-doped biochar/PMS system: The roles of physicochemical properties and reaction pathways

The advanced oxidation of persulfate catalyzed by nitrogen-doped biochar (NBC) has emerged as a significant area of research, owing to its remarkable efficacy in selectively removing antibiotic organic pollutants from aquatic environments. Despite exhibiting promising results, the comprehension of the selective oxidation mechanisms of NBC remains inadequate, primarily stemming from the intricate complexity of organic pollutants and the vast variety of free radical active species involved. This study aims to elucidate the underlying mechanisms that drive the different oxidation processes promoted by NBC, with a focus on understanding the interactions between the physicochemical properties of various antibiotic contaminants and the resulting oxidation pathways. Regression analysis reveals the significance of adsorption interactions in constructing reaction interfaces, where the molecular polarity, complexity, topological polarity surface area, and molecular weight of pollutants play pivotal roles. However, these parameters do not singularly dictate the oxidation process. Instead, the electrochemical properties of organic pollutants (open-circuit potential, half-wave potential, and molecular orbital energy) primarily determine the selective oxidation. Furthermore, the research highlights that free radicals contribute to the oxidation of pollutants with relatively weak electrochemical properties, such as norfloxacin, but are insufficient to drive the entire oxidation process. Conversely, for pollutants with strong electrochemical properties, such as ofloxacin and oxytetracycline, the influence of free radicals is negligible. Overall, the study seeks to provide insights into the roles of adsorption interactions, electrochemical properties, and free radical dynamics, thereby advancing the development of efficient and targeted strategies for environmental remediation.

Highly active nitrogen-doped biochar for catalytic reduction of 4-nitrophenol: Kinetic, thermodynamic and mechanism investigation

Biomass derived metal-free carbon catalysts are urgently needed in wastewater remediation and organic transformation, due to their environmental friendliness, low cost. In this respect, a series of nitrogen-doped hierarchically porous carbons (NHPCs) derived from cheap and abundant eggplant were fabricated via a one-pot strategy under different temperatures from 600 to 900°C, and employed as metal-free catalysts for the reduction of aromatic nitrophenols. Benefiting from the synergistic effects of the hierarchically porous structure, large specific surface area and abundant structural defects, NHPCs obtained from 800 °C has the highest reduction rate of 2.072 min−1 and maximal turnover frequency (TOF) for 4-nitrophenol of 1.23 × 10−2 mM·mg−1·min−1, which is superior to most of the reported metal-free catalysts. In addition, the NHPC-800 also exhibits satisfactory practicality and universality. The kinetic and thermodynamic studies were also conducted, finding that the obtained kinetics data over NHPC-800 fit well to L-H model with a low apparent activation energy (Ea = 18.96 kJ·mol−1). Furthermore, the mechanism was also elucidated by experimental investigation and theoretical calculations, which revealed that the pore creation and doping nitrogen can promote the adsorption of 4-NP and NaBH4 onto NHPC. This study make a significant contribution to the advancement of catalytic reduction of 4-NP by N-doped biochar catalysts.

The biochar derived from Spirulina platensis for the adsorption of Pb and Zn and enhancing the soil physicochemical properties

Microalgae can be collected in large quantities and hold significant potential for environmental remediation, offering a cost-effective solution. This study explores the use of Spirulina platensis (SP) as feedstock for biochar production. SP contains abundant nitrogen-rich components, such as proteins, which can serve as nitrogen sources. We prepared SP-derived biochar through pyrolysis for the adsorption of Pb and Zn from aqueous solutions and used it as an amending agent to remediate heavy metal-contaminated agricultural soil. Pyrolysis of proteins in SP introduces nitrogen-functional groups, resulting in nitrogen-doped biochar. We investigated the surface chemical behavior of thermally treated SP using X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. Surface analysis revealed the presence of pyridine-N and pyrrole-N from protein pyrolysis products. The study also demonstrated that these functional groups affect interactions with heavy metals. Batch experiments examined the effects of pH and initial concentration on the adsorption of Pb and Zn using SP400 and SP600. Both types of biochar showed satisfactory performance in adsorbing Pb and Zn. The effect of SP400 and SP600 on the removal of Pb and Zn through the physicochemical properties and surface functional groups was investigated. Analysis of SP400 and SP600 highlighted that electrostatic interactions, cation exchange, complexation, and mineral precipitation contributed to Pb and Zn adsorption. The study concludes that SP-derived biochar, particularly SP600, is effective for immobilizing Pb and Zn in contaminated agricultural soil, with SP600 showing superior performance.

Assembly of 3D printed N-doped biochar as impeller with CaCO3 as sacrificial pore generator for enhanced dye adsorption

Three-dimensional (3D) printed monolithic catalysts/adsorbents have attracted much attention due to their excellent properties. Herein, the rice husk-derived nitrogen-doped biochar (using urea as the nitrogen dopant) was printed into monolithic adsorbents using direct ink writing technology, and then assembled as agitating paddles for organic dye adsorption. To reduce the over-embedding of active sites in the polymeric matrix, CaCO3 particles in nano-sized or micron-sized were added as sacrificial pore generators to form macropores and expose active sites, leading to an enhanced mass transfer efficiency. Material characterization results confirm the self-sacrificial role of CaCO3. The 3D-printed adsorbents with micron-sized CaCO3 (denoted as 3D-HRSCCm) possessed excellent adsorption performance, as evidenced by a high adsorption capacity and kinetics study. Meanwhile, 3D-HRSCCm adsorbents were mounted as agitating impellers which demonstrated excellent reusability with the adsorption efficiency remaining above 90% after ten cycles. Furthermore, the 3D-HRSCCm exhibited excellent adsorption properties for various dyes such as methylene blue, rhodamine B, crystal violet, and malachite green. Moreover, the numerical simulation confirms that the introduction of CaCO3 as a pore generator improved diffusion by providing wider channels and facilitated the mass transfer that accelerated the adsorption rates.

Comparison of Fenton-like catalytic activity of biochar by in-situ and ex-situ nitrogen doping: Role of carbon quantum dots

Nitrogen-doped biochar as Fenton-like catalysts has been widely used to remove emerging pollutants in wastewater. However, the effect of in-situ and ex-situ nitrogen doping on the Fenton-like catalytic activity of biochar is unclear. In this study, the nitrogen-doped biochar was prepared by in-situ (NBC) and ex-situ (BC–N) nitrogen doping, and the Fenton-like catalytic activity of NBC and BC-N was compared for activating hydrogen peroxide (H2O2), peroxydisulfate (PDS) and peroxymonosulfate (PMS). The results showed that NBC had higher Fenton-like catalytic activity than BC-N, because the formation of carbon quantum dots (CQDs) significantly increased the adsorption capacity to H2O2, PDS and PMS. NBC could activate H2O2, PDS and PMS for degradation of sulfamethoxazole (SMX), but showed different catalytic activity and degradation mechanism. In the systems of NBC/H2O2 and NBC/PDS, CQDs played a key role in the activation of H2O2 and PDS, and surface-bound reactive species were mainly responsible for SMX degradation. In the system of NBC/PMS, NBC acted as both electron mediator and activator, direct electron transfer between PMS and SMX and surface-bound reactive species contributed to SMX degradation. This study provides an insight into the catalytic activity of NBC for H2O2, PDS and PMS.

Effective amendment of cadmium in water and soil before and after aging of nitrogen-doped biochar: Preparation optimization, removal efficiency and mechanism

Nitrogen-doped biochar (NBC) is a green material for remediating heavy metal pollution, but it undergoes aging under natural conditions, affecting its interaction with heavy metals. The preparation conditions of NBC were optimized using response surface methodology (RSM), and NBC was subjected to five different aging treatments to analyze the removal efficiency of Cd(II) and soil remediation capability before and after aging. The results indicated that NBC achieved optimal performance with a mass ratio of 5:2.43, an immersion time of 10.66 h, and a pyrolysis temperature of 900 °C. Aging diminished NBC's adsorption capacity for Cd(II) but did not change the main removal mechanism of monolayer chemical adsorption. Freeze-thaw cycles (FT), UV aging (L), and composite aging (U) treatments increased the proportion of bioavailable-Cd, and all aging treatments facilitated the conversion of potentially bioavailable-Cd to non-bioavailable-Cd. The application of NBC and five aged NBCs reduced the proportion of bioavailable-Cd in the soil through precipitation and complexation, increasing the proportion of non-bioavailable-Cd. Aging modifies the physicochemical properties of NBC, thus influencing soil characteristics and ultimately diminishing NBC's ability to passivate Cd in the soil. This study provides reference for the long-term application of biochar in heavy metal-contaminated environments.

Nitrogen-doped biochar derived from corn straw for CO2 adsorption: a new vision on nitrogen sources comparison

Biochar as a highly promising CO2 adsorbent is of great significance in addressing global warming and promoting human health. Research has shown that nitrogen doping improves the CO2 adsorption performance of biochar, but selecting chemical nitrogen sources such as urea and melamine to prepare nitrogen-doped biochar is not conducive to green production and environmental protection. Therefore, it is necessary to identify a new nitrogen source to enhance the emission reduction characteristics of this process. This study selected corn straw as the raw material and cow manure as a representative protein-based nitrogen source to explore its potential as a urea substitute and reveal the hydrothermal carbonization doping mechanism of different nitrogen sources. The results indicated that in raw materials with the same C/N ratio, biochar prepared from cow manure as the nitrogen source had a better doping effect and CO2 adsorption performance. Moreover, a moderate amount of cow manure was beneficial for efficient nitrogen doping and the adsorption of CO2 by biochar, with a maximum CO2 adsorption performance improvement of 32.7%. Due to the different carbon-nitrogen bonds of the different nitrogen sources, urea was more likely to retain amino groups, while macromolecular protein nitrogen sources tended to retain structural nitrogen. The results of this study provide new ideas and theoretical support for preparing other nitrogen-doped carbon materials derived from biomass.Graphical

Enhanced CO2 absorption in amine-based carbon capture aided by coconut shell-derived nitrogen-doped biochar

The sluggish CO2 absorption kinetics and constrained CO2 absorption capacity diminish the practicality of using amine-based absorption for CO2 capture, impeding progress toward carbon neutrality goals. This study aims to develop a catalytic CO2 absorption process to promote CO2 absorption by introducing a solid base catalyst, namely, coconut shell-derived nitrogen-doped biochar (NBC), into an amine-based solution. The coconut shells were modified with urea and activated with KOH to prepare an NBC catalyst with improved basic characteristics. The findings showed that compared to non-catalytic absorption, the NBC catalyst increased the CO2 absorption amount, CO2 absorption rate, and absorption efficiency of the monoethanolamine (MEA) solution by 16.9 %, 43.4 %, and 13.1 %, respectively. The basic sites on the NBC surface provided extra electrons to motivate the formation of MEACOO- and HCO3-. NBC’s large surface area and porous structure also advanced the gas–liquid mass transfer, accelerating the CO2 absorption rate. Furthermore, the NBC exhibited excellent cyclic stability and facilitated the subsequent CO2 desorption process. This work develops a promising and practical approach to significantly improve the amine-based absorption and reuse of waste biomass resources for efficient CO2 capture.

Nitrogen-functionalized catalyst synthesized using spent coffee ground biochar-cobalt hybrid for oxygen reduction reaction via pyrolysis and ball-milling

In this work, oxygen reduction reaction (ORR) catalysts were developed from a precursor of spent coffee ground-based biochar. Nitrogen doping was achieved via urea addition preceding a pyrolysis synthesis process, yielding nitrogen-doped biochar (NDB). Cobalt was deposited onto the NDB surface using a non-conventional ball-milling procedure. The microstructure of the synthesized samples was studied through Scanning Electron Microscopy (SEM), where a rather distorted surface, highlighted by prominent wrinkles (which doubled the surface area at 50.58 m2/g), was shown for nitrogen-doped samples. Moreover, the high energy ball-milling technique shows an almost perfect coverage of cobalt nanoparticles on the biochar surface through SEM/EDS and Raman results. Additionally, electrochemical testing was conducted using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Cyclic voltammetry measurements conducted under nitrogen (inert) and oxygen-saturated alkaline solution (0.1 M KOH) conditions showed that nitrogen doping enhances the oxygen reduction reaction current (-1 vs -0.59 mA.cm−1 at -0.3 V vs Hg/HgO) and slightly reduces the onset potential compared to pristine biochar. Depositing cobalt onto the NDB surface had a minor adverse effect on the onset potential, but significantly increased the oxygen reduction reaction current, reaching a value of -2.09 mA.cm−2 at -0.3 V vs Hg/HgO. All catalysts were compared to a commercial carbon supported platinum catalyst (Pt10%C) to showcase the potential room of improvement for the developed catalysts.

Molecular simulation of different VOCs adsorption on nitrogen-doped biochar

Nitrogen-doped biochar has potential application in the removal of volatile organic compounds (VOCs) from coal-fired flue gas. To explore the adsorption characteristics of different VOCs on nitrogen-doped biochar by molecular simulation, in this study, six typical aromatic VOCs (benzene, toluene, phenol, naphthalene, p-xylene, and chlorobenzene), and an amorphous carbon model with nitrogen/oxygen groups were selected and constructed. Grand Canonical Monte Carlo (GCMC) simulations were performed to evaluate the adsorption capacities of VOCs on nitrogen-doped biochar. The results showed that the optimized carbon model was in good agreement with the pore structure parameters of nitrogen-doped biochar, and the agreement of toluene adsorption capacities was more than 80 % at room temperature. The adsorption capacity of nitrogen-doped biochar for different VOCs was 184 − 317 mg/g with the order of phenol > naphthalene > p-xylene > toluene ≈ benzene ≈ chlorobenzene (single-component adsorption). Among them, the phenol molecule is more easily adsorbed due to its strong polarity, resulting in stronger electrostatic interaction with the adsorbent. The decrease rate of benzene adsorption capacity is the lowest with increasing adsorption temperature because of its low molecular weight. As gas concentration increases, van der Waals interactions between molecules and between molecules and porous carbon also increase, leading to an increase in VOCs adsorption capacity. Nitrogen-doped biochar not only has the highest VOCs/N2 selective adsorption coefficient for phenol (up to 36) but also has the highest adsorption capacity of 63 mg/g when 6 kinds of VOCs are multi-component adsorption at 25 °C. This study can provide references for the practical application of adsorption method in the removal of VOCs from coal-fired flue gas.

Boosting peroxymonosulfate activation with a composite of highly dispersed FeS2 nanoparticles anchored on N-doped biochar for efficient tetracycline degradation

The rational design of inexpensive peroxymonosulfate (PMS) activators with high efficiencies is still in high demand. Herein, a composite with highly dispersed FeS2 anchored on nitrogen-doped biochar (FeS2@NBC) was prepared via a hydrothermal process and used for PMS activation to degrade the pollutant tetracycline (TC). Benefiting from in situ growth of FeS2 on the NBC surface, FeS2@NBC alleviated the side effects caused by FeS2 agglomeration, and the synergistic catalytic effect of the FeS2 nanoparticles and N-doped biochar resulted in excellent performance. The optimal FeS2@NBC/PMS system could degrade 87.6 % of TC within 10 min, and it exhibited adaptability to pH changes and the presence of common inorganic anions. A comprehensive study involving radical scavenging experiments, electron paramagnetic resonance (EPR) spectroscopy, electrochemical tests and XPS analyses revealed that the singlet oxygen (1O2) and hydroxyl radical (•OH) were the dominant reactive oxygen species (ROS), the sulfate radical (SO4•−) and electron transfer were involved in the TC degradation process. Moreover, three degradation pathways were indicated by LC−MS detection, and the toxicities of the degradation intermediates were predicted and evaluated. Finally, FeS2@NBC showed excellent reusability and stability after five cycles of TC degradation. This work provides a reference for designing efficient catalysts that can be combined with metal sulfides and biochar for efficient PMS activation.

Activation of peroxymonosulfate by Fe,N co-doped walnut shell biochar for the degradation of sulfamethoxazole: Performance and mechanisms

Fe and N co-doped walnut shell biochar (Fe,N-BC) was prepared through a one-pot pyrolysis procedure by using walnut shells as feedstocks, melamine as the N source, and iron (III) chloride as the Fe source. Moreover, pristine biochar (BC), nitrogen-doped biochar (N-BC), and α-Fe2O3-BC were synthesized as controls. All the prepared materials were characterized by different techniques and were used for the activation of peroxymonosulfate (PMS) for the degradation of sulfamethoxazole (SMX). A very high degradation rate for SMX (10 mg/L) was achieved with Fe,N-BC/PMS (0.5 min−1), which was higher than those for BC/PMS (0.026 min−1), N-BC/PMS (0.038 min−1), and α-Fe2O3-BC/PMS (0.33 min−1) under the same conditions. This is mainly due to the formation of Fe3C and iron oxides, which are very reactive for the activation of PMS. In the next step, Fe,N-BC was employed for the formation of a composite membrane structure by a liquid-induced phase inversion process. The synthesized ultrafiltration membrane not only exhibited high separation performance for humic acid sodium salt (HA, 98%) but also exhibited improved self-cleaning properties when applied for rhodamine B (RhB) filtration combined with a PMS solution cleaning procedure. Scavenging experiments revealed that 1O2 was the predominant species responsible for the degradation of SMX. The transformation products of SMX and possible degradation pathways were also identified. Furthermore, the toxicity assessment revealed that the overall toxicity of the intermediate was lower than that of SMX.

Simultaneous elimination of antibiotic-resistant bacteria and antibiotic resistance genes by different Fe-N co-doped biochars activating peroxymonosulfate: The key role of pyridine-N and Fe-N sites

The coexistence of antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB) in the environment poses a potential threat to public health. In our study, we have developed a novel advanced oxidation process for simultaneously removing ARGs and ARB by two types of iron and nitrogen-doped biochar derived from rice straw (FeN-RBC) and sludge (FeN-SBC). All viable ARB (approximately 108 CFU mL−1) was inactivated in the FeN-RBC/ peroxymonosulfate (PMS) system within 40 min and did not regrow after 48 h even in real water samples. Flow cytometry identified 96.7 % of dead cells in the FeN-RBC/PMS system, which verified the complete inactivation of ARB. Thorough disinfection of ARB was associated with the disruption of cell membranes and intracellular enzymes related to the antioxidant system. Whereas live bacteria (approximately 200 CFU mL−1) remained after FeN-SBC/PMS treatment. Intracellular and extracellular ARGs (tetA and tetB) were efficiently degraded in the FeN-RBC/PMS system. The production of active species, primarily •OH, SO4•- and Fe (IV), as well as electron transfer, were essential to the effective disinfection of FeN-RBC/PMS. In comparison with FeN-SBC, the better catalytic performance of FeN-RBC was mainly ascribed to its higher amount of pyridine-N and Fe0, and more reactive active sites (such as CO group and Fe-N sites). Density functional theory calculations indicated the greater adsorption energy and Bader charge, more stable Fe-O bond, more easily broken OO bond in FeN-RBC/PMS, which demonstrated the stronger electron transfer capacity between FeN-RBC and PMS. To encapsulate, our study provided an efficient and dependable method for the simultaneous elimination of ARGs and ARB in water.

Activating peroxymonosulfate by high nitrogen-doped biochar from lotus pollen for efficient degradation of organic pollutants from water: Performance, kinetics and mechanism investigation

Nitrogen-doped biochars are promising metal-free catalysts for peroxymonosulafe (PMS) activation due to their low-cost, high chemical stability and metal-free leaching. However, the nitrogen content in the biochar is usually low with unsatisfactory performance, and the in-depth analysis on the kinetic of pollutant degradation is still insufficient. Herein, high nitrogen doped biochars were prepared by one-step pyrolysis of lotus pollen (LP) and melamine, which were used to trigger PMS for degrading organic pollutants in water. The optimized nitrogen-doped LP biochar (N-LPC-5) possessed ultrahigh nitrogen content (up to 15.75 at%) and abundant oxygen-containing functional groups, which exhibited the optimal performance in activating PMS to degrade reactive black 5, atrazine, ketoprofen and p-nitrophenol. The removal efficiency for all the organic pollutants in the N-LPC-5/PMS system can reach above 90 % in 20 min, and the degradation performance was outstanding in a wide pH range from 2.0 to 10.5. The pollutant degradation followed a two-stage process including a fast stage of initial oxidation and a slow stage. An appropriate mathematic kinetic model was proposed to describe the two-stage reaction. Fitting the experimental data with the proposed kinetic model, the initial removal rate and the maximal oxidation capacity can be obtained accordingly, and the correlation coefficients were very close to 1.0, indicative of the excellent fitness of the proposed model. In addition, the catalytic mechanisms such as the reactive oxygen species, electron-transfer pathway and active sites were also investigated by various techniques. The present study highlights the tremendous potential of N-biochar for wastewater remediation, and helps to understand the dynamic kinetics and catalytic mechanism of metal-free carbon activating PMS.

Nitrogen-Doped Biochar for Enhanced Peroxymonosulfate Activation to Degrade Phenol through Both Free Radical and Direct Oxidation Based on Electron Transfer Pathways.

Nowadays, super nitrogen-doped biochar (SNBC) material has become one of the most promising metal-free catalysts for activating peroxymonosulfate (PMS) to degrade organic pollutants. To understand the evolution of SNBC properties with fabrication conditions, a variety of SNBC materials were prepared and characterized by elemental analysis, N2 adsorption-desorption, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. We systematically investigated the activation potential of these SNBC materials for PMS to degrade phenol. SN1BC-800 with the best catalytic performance was obtained by changing the activation temperatures and the ratio of biochar to melamine. The effects of catalyst dosage, the PMS concentration, pH, and reaction temperature on phenol degradation were studied in detail. In the presence of 0.3 g/L SN1BC-800 and 1 g/L PMS, the removal rate of 20 mg/L phenol could reach 100% within 5 min. According to electron paramagnetic resonance spectra and free radical quenching experiments, a nonfree radical pathway of phenol degradation dominated by 1O2 and electron transfer was proposed. More interestingly, the excellent catalytic performance of the SN1BC-800/PMS system is universally applicable in the degradation of other typical organic pollutants. In addition, the degradation rate of phenol is still over 80% after five reuses, which shows that the SN1BC-800 catalyst has high stability and good application prospects in environmental remediation.