Heteroatom-doped carbonaceous materials are the most promising substitutes of noble metals as green catalysts for electrochemical water splitting. In this study, nitrogen and sulfur co-doped graphene ...(N,S-G) is synthesized via a one-pot calcination method. Subsequently, N,S-G is activated by ZnCl2 to enlarge the specific surface areas to construct a porous structure (a-N,S-G) The chemical activation can simultaneously regulate the elemental composition and porous structure of SNG toward enhanced carbocatalysis. As a result, in the OER process, the overpotential of a-N,S-G is only 330 mV vs. RHE at 10 mA cm−2 in 1 M KOH, which surpasses the most reported carbon catalysts. In the HER process, −10 mA cm−2 can be achieved at an overpotential of 0.29 V vs. RHE in 1 M KOH and 0.31 V vs. RHE in 0.5 M H2SO4. By combination with commercial carbon black (CB), the Tafel slopes of a-N,S-G@CB is lower than the metal-based catalysts. A new turnover frequencies (TOF) calculation method is involved to analyze the reactivity of specific active sites of carbocatalyst including both heteroatoms and structural defects. Therefore, the study provides an effective strategy for simultaneous modifications of surface chemistry and porous structure of graphene as high-performance and robust carbocatalysts toward electrochemical water splitting.
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Increased evidence shows that gut microbiota acts as the primary regulator of the liver; however, its role in sepsis-related liver injury (SLI) in the elderly is unclear. This study assessed whether ...metformin could attenuate SLI by modulating gut microbiota in septic-aged rats. Cecal ligation and puncture (CLP) was used to induce SLI in aged rats. Fecal microbiota transplantation (FMT) was used to validate the roles of gut microbiota in these pathologies. The composition of gut microbiota was analysed by 16S rRNA sequencing. Moreover, the liver and colon tissues were analysed by histopathology, immunofluorescence, immunohistochemistry, and reverse transcription polymerase chain reaction (RT-PCR). Metformin improved liver damage, colon barrier dysfunction in aged SLI rats. Moreover, metformin improved sepsis-induced liver inflammation and damage under gut microbiota. Importantly, FMT assay showed that rats gavaged with faeces from metformin-treated SLI rats displayed less severe liver damage and colon barrier dysfunctions than those gavaged with faeces from SLI rats. The gut microbiota composition among the sham-operated, CLP-operated and metformin-treated SLI rats was different. In particular, the proportion of Klebsiella and Escherichia_Shigella was higher in SLI rats than sham-operated and metformin-treated SLI rats; while metformin could increase the proportion of Bifidobacterium, Muribaculaceae, Parabacteroides_distasonis and Alloprevitella in aged SLI rats. Additionally, Klebsiella and Escherichia_Shigella correlated positively with the inflammatory factors in the liver. Our findings suggest that metformin may improve liver injury by regulating the gut microbiota and alleviating colon barrier dysfunction in septic-aged rats, which may be an effective therapy for SLI.
Regulated disposal or re-utilization of dewatered sludge is of economic benefits and can avoid secondary contamination to the environment; however, feasible and effective management strategies are ...still lacking. In this study, a peroxydisulfate/zero-valent iron (PDS-ZVI) system is proposed to destroy proteins in soluble extracellular polymeric substances (S-EPS) and loosely bound EPS (LB-EPS) in anaerobic digested sludge (ADS) to improve the dewaterability. Moreover, ADS derived biochars supported via iron oxides (Fe-ADSBC) were generated by dewatering and thermal annealing. Intriguingly, the iron species was discovered to gradually transform from Fe3O4 to FeO with increased pyrolysis temperatures from 600 to 1000 °C. The manipulated iron species on the biochar can remarkably impact the catalytic activity in PDS activation and degradation of sulfamethazine (SMT). The in situ radical scavenging and capturing tests revealed that the principal reactive oxygen species (ROS) in Fe-ADSBC/PDS system experienced a variation from OH into SO4− at higher annealing temperature (1000 °C). In addition, the carbonaceous ADSBC can promote the catalytic activity of iron oxides by synergistically facilitating the adsorption of reactants and charge transfer through COFe bonds at the interfaces. This study enables the first insights into the properties and catalytic performance of Fe-ADSBC, meanwhile unveils the mechanism, reaction pathways, and environmental impacts of the ultimate transformation products (TPs) from SMT degradation in the Fe-ADSBC/PDS system. The study also contributes to developing value-added green biochar catalysts from bio-wastes towards environmental purification.
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•Persulfate/zero-valent iron was used for dewatering of anaerobic digested sludge (ADS).•The treated ADS was pyrolyzed for synthesis of iron oxides@biochar (Fe-ADSBCs).•Fe-ADSBCs were effective in persulfate activation for sulfamethazine degradation.•The activation and degradation mechanisms were comprehensively investigated.
Iron nanoparticles encapsulated within boron and nitrogen co-doped carbon nanoshell (B/N-C@Fe) were synthesized through a novel and green pyrolysis process using melamine, boric acid, and ferric ...nitrate as the precursors. The surface morphology, structure, and composition of the B/N-C@Fe materials were thoroughly investigated. The materials were employed as novel catalysts for the activation of potassium monopersulfate triple salt (PMS) for the degradation of levofloxacin (LFX). Linear sweep voltammograms and quenching experiments were used to identify the mechanisms of PMS activation and LFX oxidation by B/N-C@Fe, where SO4− as well as HO were proved to be the main radicals for the reaction processes. This study also discussed how the fluvic acid and inorganic anions in the aqueous solutions affected the degradation of LFX and use this method to simulate the degradation in the real wastewater. The synthesized materials showed a high efficiency (85.5% of LFX was degraded), outstanding stability, and excellent reusability (77.7% of LFX was degraded in the 5th run) in the Fenton-like reaction of LFX. In view of these advantages, B/N-C@Fe have great potentials as novel strategic materials for environmental catalysis.
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•Iron nanomaterials were encapsulated in boron/nitrogen co-doped carbon nanoshell.•The B/N-C@Fe4 700 catalysts were synthesized through a green pyrolysis process.•The role of anions in advanced oxidation processes of PPCPs was emphasized.•The B/N-C@Fe4 700 catalysts exhibited an excellent stability and reusability.•The catalysts showed better reusability than N-doped graphene and carbon nanotubes.
Accelerating the rate-limiting Fe3+/Fe2+ circulation in Fenton reactions through the addition of reducing agents (or co-catalysts) stands out as one of the most promising technologies for rapid water ...decontamination. However, conventional reducing agents such as hydroxylamine and metal sulfides are greatly restricted by three intractable challenges: (1) self-quenching effects, (2) heavy metal dissolution, and (3) irreversible capacity decline. To this end, we, for the first time, introduced redox-active polymers as electron shuttles to expedite the Fe3+/Fe2+ cycle and promote H2O2 activation. The reduction of Fe3+ mainly took place at active N–H or O–H bonds through a proton-coupled electron transfer process. As electron carriers, H atoms at the solid phase could effectively inhibit radical quenching, avoid metal dissolution, and maintain long-term reducing capacity via facile regeneration. Experimental and density functional theory (DFT) calculation results indicated that the activity of different polymers shows a volcano curve trend as a function of the energy barrier, highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap, and vertical ionization potential. Thanks to the appropriate redox ability, polyaniline outperforms other redox-active polymers (e.g., poypyrrole, hydroquinone resin, poly(2,6-diaminopyridine), and hexaazatrinaphthalene framework) with a highest iron reduction capacity up to 5.5 mmol/g, which corresponds to the state transformation from leucoemeraldine to emeraldine. Moreover, the proposed system exhibited high pollutant removal efficiency in a flow-through reactor for 8000 bed volumes without an obvious decline in performance. Overall, this work established a green and sustainable oxidation system, which offers great potential for practical organic wastewater remediation.
Oxygen reduction reaction (ORR) is the cornerstone for clean and sustainable energy conversion/storage technologies, depending on effective and robust catalysts. In the rational design of efficient ...and renewable carbon-based ORR electrocatalysts, the effect of intrinsic carbon edge sites on ORR remains elusive. In this study, nano-cutting is applied to multi-walled carbon nanotubes (MWCNTs) to synthesize a series of edge-engineered nanoribbon/nanotube hybrids with variable edge contents to probe the role of carbon edges. The previously overlooked but certainly emerged difference in conductivity in the edge creation process among the dopant-free carbocatalysts is taken into account towards the ORR activity, aiming to distinguish the function of edges. The carbocatalyst with a higher edge content is proven to be more reactive for ORR, with the premise of catalyst conductivity higher than ~70 S m−1. Further, with heteroatoms (N and S) introduced into the carbocatalysts, a positive correlation between the accommodated heteroatom content and the edging degree is revealed, indicating that edge sites afford anchoring sites for heteroatoms into the carbon framework, which further accelerates the ORR kinetics. This study provides new insights to the intrinsic role of the edge sites in nanocarbons as well as the synergy with heteroatom doping for promoted activity of carbocatalysts in ORR.
Edge engineering is successfully implemented by controllably nano-cutting multi-walled carbon nanotubes to regulate edge contents and probe the edge activity. The critical conductivity of 70 S m−1 is essential for carbon edges to perform their catalytic activity effectively. Edge-promoted doping, featuring a doping level positively correlated to the edging degree, further accelerates oxygen reduction reaction. Display omitted
•Edge engineering is successfully executed to regulate edge contents in nanocarbons.•Conductivity is for the first time evaluated in the probing of edge activity.•70 S m−1 in this model is proposed as the critical conductivity for effective edges.•Dopants are anchored by edges in a quantity positively correlated to edging degree.
Photocatalysis is a green technology and has received increasing attention owing to its potential in solving environmental problems in a sustainable manner. Among the candidates of semiconductor ...photocatalysts, graphitic carbon nitride (g-C3N4) stands out for environmental purification because of its elemental abundances, structure robustness, and high performances. In this paper, we present a mini review of sustainable photocatalytic remediation of micropollutants over morphology-engineered g-C3N4. The methods for advanced morphology control of g-C3N4 are discussed and insights into morphology-dependent photocatalysis over g-C3N4 are unveiled. The review also provides perspectives of challenges and solutions to sustainable water purification over the metal-free polymer materials.
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•Photocatalytic remediation over morphology-engineered g-C3N4 are reviewed.•The methods for advanced morphology control of g-C3N4 are discussed.•The morphology-dependent photocatalysis over g-C3N4 are unveiled.•Future challenges and solutions to sustainable water purification using polymer materials are provided.
Abstract
Stability and reusability are important characteristics of advanced catalysts for wastewater treatment. In this work, for the first time, sulfate radicals (SO
4
∙
−
) with a high oxidative ...potential (E
o
= 2.5–3.1 V) were successfully activated from persulfate by a Fe
78
Si
9
B
13
metallic glass. This alloy exhibited a superior surface stability and reusability while activating persulfate as indicated by it being used for 30 times while maintaining an acceptable methylene blue (MB) degradation rate. The produced SiO
2
layer on the ribbon surface expanded strongly from the fresh use to the 20
th
use, providing stable protection of the buried Fe. MB degradation and kinetic study revealed 100% of the dye degradation with a kinetic rate
k
= 0.640 within 20 min under rational parameter control. The dominant reactive species for dye molecule decomposition in the first 10 min of the reaction was hydroxyl radicals (∙OH, E
o
= 2.7 V) and in the last 10 min was sulfate radicals (SO
4
∙
−
), respectively. Empirical operating variables for dye degradation in this work were under catalyst dosage 0.5 g/L, light irradiation 7.7 μW/cm
2
, and persulfate concentration 1.0 mmol/L. The amorphous Fe
78
Si
9
B
13
alloy in this work will open a new gate for wastewater remediation.
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•Band matching induces faster electron transfer and less electron-hole recombination.•The synergic photoelectrocatalytic effect obtained between PC and EC-CO2RR.•The mechanism of CO2 ...reduction on ZnPc/carbon nitride was proposed.
Zinc phthalocyanine/carbon nitride nanosheets photoelectrocatalysts were obtained by evaporation and calcination of the mixture of ZnPc and carbon nitride. It exhibits highly efficient synergistic function between PC-CO2RR and EC-CO2RR. The energy band matching between the ZnPc and carbon nitride results in the faster electrons transfer and less electron-hole pairs recombination. The optimized ZnPc/carbon nitride at a ratio of 0.1 wt% demonstrates high efficiency in photoelectrocalytic reduction of CO2 under visible light, generating a major product of methanol at a yield of 13 μmol·cm−2 after 8 h. The efficiency of photoelectrocalytic reduction of CO2 to methanol is 2.6 times as high as that of electrocatalytic CO2 reduction reaction, and 5.9 times as high as that of photocatalytic CO2 reduction reaction. The mechanism of the photoelectrocatalytic CO2 reduction reaction to methanol was discussed in detail.
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