Electron-deficient Carbon Research Articles

Stabilizing In/InN intermediates by electron-deficient carbon for improved CO2 electroreduction to CO

Monitoring and stabilizing the reconstructed active material under operational conditions is crucial for the rational design of electrocatalysts. Herein, we developed a novel hinged structure composited by the electron-deficient carbon and InN nanorods (InN@C) for preserving the high-active In/InN interfaces under electrochemical CO2 reduction process. The electron-deficient carbon, caused by the interfacial rectifying effect, prevents active site annihilation and deep self-reduction of In/InN, leading to synergistic improvements in catalytic activity and long-term stability. Mechanistic studies show that an interfacial dipole between the electron-deficient carbon layer and In/InN promotes CO2 activation and strengthens In−N bonds, inhibiting the deep self-reduction of In/InN. As a result, we achieved remarkable long-term stability of 150 hours, with a Faradaic efficiency of 92 % and a current density of ∼ 40 mA cm−2 at − 0.8 V versus the reversible hydrogen electrode. This study offers a practical approach to preserve the high-active intermediates for synergistically improving the catalytic activity and long-term stability of transition metal compound electrocatalysts.

Nonradical peroxymonosulfate activation via high-level pyrrolic-nitrogen and electron-deficient carbon at 2D ultrathin carbonaceous nanosheets for efficient BPA removal

Activation of persulfate by N-doped carbon is an emerging advanced oxidation process (AOP) for removing organic pollutants from water via singlet oxygen (1O2)-dominated non-radical way, however, the efficient generation of 1O2 is a hot topic worth deep exploration. In this study, glucose was used as an additional carbon and oxygen of prefabricated supramolecular melamine-cyanuric acid precursor, the final co-thermal polymerization products completely changed from conventional graphitic carbon nitride to ultrathin carbonaceous materials when the mass of glucose up to 0.72 g. The simple one-pot strategy can easily generate active electron-deficient carbon sites due to nitrogen and oxygen doping by modulating the electronic structure of the carbon framework, which is critical for the activation of peroxymonosulfate (PMS) to produce 1O2. The glucose content can adjust the degree of disorder of the amorphous carbonaceous nanosheet, and significantly improve the exposure of active pyrrolic nitrogen sites (27.47 %) and doped oxygen through the defective structure, which is another essential factor for the generation of 1O2 in the activation of PMS. The MCAG-0.72/ PMS exhibited excellent performance in BPA degradation, 95 % BPA (20 mg L−1) can be removed in 60 min with 1.0 mM PMS with reaction constant k=0.0209 min−1. Furthermore, MCAG-0.72 also demonstrated excellent BPA degradation in different actual water metrics and performance well in the four consecutive cycles. This study provides a novel convenient strategy to synthesize cost-effective N/O co-doped carbonaceous material for efficient activating PMS to remove refractory organics in water and wastewater, it sheds light on practical large-scale industrial applications in PMS-based AOPs.

Metal-free catalysts with local fluorination regulation for peroxymonosulfate activation: Nearly 100 % singlet oxygen production for selective degradation of aqueous organic pollutants

Generating singlet oxygen (1O2) via activating peroxymonosulfate (PMS) is crucial for the selective removal of organic pollutants in aquatic environments. However, achieving efficient and selective conversion of PMS into 1O2 without consuming energy or metals remains a significant challenge. In this study, graphite phase carbon nitride (g-C3N4) was locally fluorinated via a simple polymerization method. The local fluorinated g-C3N4 (FCN) was used as a metal-free catalyst to activate PMS, enabling highly efficient degradation of 4-chlorophenol (100 %) and detoxification. The FCN/PMS system demonstrates exceptional selectivity for electron-rich pollutants, functions effectively across a broad pH range (2–10), and exhibits remarkable interference resistances to background scavenging ions and natural organic compounds. Furthermore, quenching experiments, probe tests, electron paramagnetic spin resonance measurements, electrochemical characterizations, and theoretical calculations demonstrated that 1O2 was the only reactive species in the catalytic process. Local fluorination regulated the electronic structure of g-C3N4, juxtaposing electron-rich fluorine with electron-deficient carbon dual active sites. This modification alters the electron transfer direction between PMS and g-C3N4, allowing for nearly 100 % selective generation of 1O2via dual electron transfer channels without the need for energy or metals. This study provides a new strategy for designing metal-free heterogeneous catalysts to selectively generate 1O2 in a green way and can facilitate the wider applications of advanced oxidation processes for water purification.

Biochar-Based Single-Atom Catalyst with Fe-N3O-C Configuration for Efficient Degradation of Organic Dyes by Peroxymonosulfate Activation.

Iron single-atom catalysts (Fe SACs) hold great promise for peroxymonosulfate (PMS) activation and degradation of organic pollutants in wastewater. However, insights into crucial catalytic sites and activation mechanisms of biochar-based Fe SACs for PMS remain a challenge. Herein, cotton stalk-derived biochar-based Fe SACs (Fe SACs-BC) with an asymmetric Fe-N/O-C configuration were prepared, and their PMS activation and acid orange 7 (AO7) degradation mechanisms were investigated. The results showed that the removal efficiency of the Fe SACs-BC catalyst with Fe-N3O-C configuration for AO7 and other five investigated organic dyes reached 95-99% within 15 min. The EPR spectrums, quenching experiments, electrochemical analysis, masking experiments, XPS, and theoretical calculations indicated that degradations of organic dyes were dominated by singlet oxygen, which was generated by direct PMS conversion at the electron-deficient carbon and iron sites in the Fe-N3O-C configuration. The Fe SACs-BC/PMS exhibited high removal efficiency and strong tolerance in different water matrices with a wide pH range, various coexisting anions and interfering substances, showing great potential and applicability for efficient treatment of actual textile wastewaters.

Peroxydisulfate nonradical activation on C[dbnd]C engineered g-C3N4: Electron transfer mechanism for selective degradation of organic contaminants

The activation of peroxydisulfate (PDS) by g-C3N4-based catalysts has captured considerable interest; however, the oxidation prowess falls short of expectations, and the inherent processes remain enigmatic. Herein, a novel CC engineered g-C3N4 (CCN) was successfully developed via a one-step thermal polymerization method for the activation of PDS. Our findings revealed that the CCN/PDS system selectively degraded various organic contaminants, operated effectively across a wide pH range (3−9), and maintained high performance in the presence of common water impurities. Experiments and theoretical calculations indicated that the electron transfer process (ETP) was the primary mechanism for phenol degradation. The introduction of CC led to charge redistribution and improved conductivity in g-C3N4. This enhancement strengthened PDS adsorption at electron-deficient carbon sites and bolstered electron transfer between PDS and organic contaminants. Moreover, a nonradical pathway predicated on ETP emerged when phenol, PDS, and CCN were present, propelled by differences in molecular orbital energies. This study not only deepens our understanding of PDS activation through the ETP but also introduces a novel strategy for the removal of organic contaminants from water.

Efficient electrocatalytic H2O2 activation over nitrogen-doped carbon encapsulated Co3O4 for drinking water disinfection

Waterborne diseases claim a million lives each year in areas without adequate centralized water treatment. Electrocatalytic •OH production presents a promising avenue for decentralized water disinfection. However, existing catalysts are limited by low activity at neutral pH and the risk of metal leaching. We have developed a chainmail catalyst, N-doped carbon (NC) encapsulated Co3O4 (NC@Co3O4), for efficient electrocatalytic H2O2 activation. Co3O4 extracts electrons from NC, thus enhancing the affinity of O atom of H2O2 at the electron deficient carbon sites in NC and promoting the cleavage of O−O bonds. Consequently, the •OH generation rate catalyzed by NC@Co3O4 was 6.5 times of that by NC. Integrating the NC@Co3O4 into a flow-through electrochemical reactor as cathode, a voltage of only 2 V drove the device to achieve more than 6.8 logs (99.99998 %) of Escherichia coli inactivation in tap water. This work provides an energy-efficient, green, and safe solution for decentralized water disinfection.

Mechanism and Origins of Regio- and Stereoselective Alkylboration of Endocyclic Olefins Enabled by Nickel Catalysis.

The Ni-catalyzed alkylboration of endocyclic olefins is a stereo- and regioselective approach for the synthesis of boron-containing compounds. We report a detailed density functional theory (DFT) study to elucidate the mechanism and origins of the stereo-, chemo-, and regioselectivity of alkylboration of endocyclic olefins enabled by nickel catalysis. The alkylboration proceeds via the migratory insertion of alkenes, β-H elimination of the Ni(II) complex, subsequent migratory insertion leading to a new Ni(II) complex, combined with an alkyl radical, and reductive eliminations. The electronic effects of the endocyclic olefins synergistically control the regioselectivity toward the C1- and C2-position boration. In C1-position boration, a more electron-deficient carbon atom tends to combine with an electron-rich -Bpin group and leads to C1-position boration products. The stereoselectivity is influenced by the solvent effect, and the interaction between the substrate and Ni-catalyzed groups, the low-polarity solvent 1,4-dioxane, and a favorable steric hindrance effect result in the cis-alkylboration product. Chemoselectivity toward 1,3-alkylboration results from the steric hindrance effects of the -Bpin group.

Assessing CO2 Adsorption Behavior onto Free-Standing, Flexible Organic Framework-PVDF Composite Membrane: An Empirical Modeling and Validation of an Experimental Data Set.

Covalent organic framework (COF) materials have greatly expanded their range in a variety of applications since the cognitive goal of a highly organized and durable adsorbent is quite rational. The characteristics of a conjugated organic framework are combined with an industrially relevant polymer to produce a composite membrane optimized for selectively adsorbing carbon dioxide (CO2) gas across a wide temperature range. Additionally, treatment of the composite membrane with cold atmospheric plasma (CAP) that specifically enhanced the parent membrane's surface area by 36% is established. Following CAP treatment, the membrane accelerates the CO2 uptake by as much as 66%. This is primarily due to a Lewis acid-base interaction between the electron-deficient carbon atom of CO2 and the newly acquired functionalities on the COFs@PVDF membrane's surface. In particular, the C-N bonds, which appear to be a higher electron density site, play a key role in this interaction. Moreover, the empirical model proposed here has confirmed CO2 adsorption phenomena in the COF@PVDF composite membrane, which closely matches the findings from the experimental data set under designated operating conditions. As a result, the current study may pave the way for future design work as well as refine the covalent framework polymer composite membrane's features, revealing a more sophisticated approach to addressing CO2 capture problems.

Novel strategy for reducing the minimum miscible pressure in a CO2–oil system using nonionic surfactant: Insights from molecular dynamics simulations

Effective CO2-oil miscibility is a vital factor in optimizing oil production during CO2 flooding and enhancing CO2 storage capacity. This research investigates the impact of various surfactants, temperatures, and pressures on CO2-oil interfacial tension (IFT) through experimental measurements. It also evaluates the reduction in minimum miscible pressure (MMP). Subsequently, molecular dynamics (MD) simulations analyze gas-liquid miscibility, focusing on relative concentration, interaction energy, radial distribution function (RDF), and miscibility degree (Dmix). Results indicate that introducing a compound nonionic surfactant SF significantly reduces IFT and MMP, achieving an impressive 19.59% MMP reduction. Moreover, SF inclusion boosts Dmix by 8.57%, reflecting enhanced miscibility. The highest absolute value of average interaction energy (EInter) is observed, primarily driven by van der Waals interactions. SF's augmented CO2 coordination number contributes to improved Dmix and reduced MMP. SF's nonpolar groups react with CO2, reducing asymmetric forces between phases and lowering IFT. Electronegative fluorine atoms in SF interact with electron-deficient carbon atoms in CO2, heightening CO2 solubility. Elevated system pressure or reduced temperature amplifies EInter, the coordination number, and subsequently enhances Dmix. Experimentally measured MMP results closely align with MD simulations, with an average relative error of 4.63%. This study elucidates CO2-oil miscibility mechanisms on experimental and molecular scales, offering a promising avenue for future CO2 flooding research.

Selective adsorption of carbonyl compounds from bio-oil by seaweed-derived carbon: A theoretical study

Bio-oil is a renewable fuel widely used in the chemical industry, but its high oxygen content results in thermal instability and a low heating value. In order to address this issue, the current study aims to use seaweed-derived biochar as a substrate to selectively adsorb carbonyl compounds from the volatile matter during the bio-oil condensation process. The interaction between acetone and different nitrogen-rich seaweed-derived carbon models were analysed using acetone as a model compound and density functional theory. The adsorption structure, energy, and surface electronic properties between acetone and each seaweed-derived carbon model were analysed. Since nitrogen electronegativity is higher than carbon’s, electron-rich nitrogen, and electron-deficient carbon are formed, thereby increasing the adsorption capacity of nitrogen-doped carbon. The results of this study will provide insight into the adsorption mechanism of seaweed biochar and offer a new approach to reducing the oxygen content of bio-oil and improving its quality.

Activation of persulfate on fluorinated carbon: Role of semi-ionic C-F in inducing mechanism transition from radical to electron-transfer nonradical pathway

Carbon-driven nonradical persulfate activation exhibits compelling advantages due to its good reactivity in complex aquatic surroundings. However, uncertainties still exist in the construction of nonradical-oriented activation systems and the role of positively charged carbon is ambiguous because of intricate carbon structure. In this regard, this study found that F-doping strategy not only improved the catalytic activity of carbon material, but also switched free radical persulfate (PS)-activated process into the electron-transfer-based nonradical process. The CF-1.0 achieved the promising performance in degrading bisphenol A (BPA) with a removal rate of 99.5% within 60 min, where the percentage of electron transfer contribution was up to 73.27%. Based on the Bader charge analysis in density functional theory (DFT) calculation, the “electron-loss” induced catalytic mechanism was proposed. Stimulated by the incorporation of F atom that can create the electron-deficient carbon layer, the electron-rich BPA tended to transfer electrons to carbon-activated persulfate complex (C-S2O82-*), in an effort to balance the electron loss in the carbonaceous matrix, thereby realizing the oxidative degradation of pollutant. Quantitative structure-activity relationships (QSARs) indicated that semi-ionic C-F, C-OH, and structural defects could function as electron transfer channel, SO4•−/• OH, and 1O2 formation sites, respectively. In addition, the catalytic behaviors towards periodate (PI) were also investigated in detail. Overall, this research develops nonradical reaction-targeted fluorinated carbocatalyst for persulfate activation and deepens the understanding of positively charged carbon in electron-transfer regime.

Correction to “New Insights into the Generation of Singlet Oxygen in the Metal-Free Peroxymonosulfate Activation Process: Important Role of Electron-Deficient Carbon Atoms”

Correction to “New Insights into the Generation of Singlet Oxygen in the Metal-Free Peroxymonosulfate Activation Process: Important Role of Electron-Deficient Carbon Atoms”

Terminal methylene phosphonium ions: precursors for transient monosubstituted phosphinocarbenes.

Isolable singlet carbenes are among the most important tools in chemistry, but generally require the interaction of two substituents with the electron deficient carbon atom. We herein report a synthetic approach to monosubstituted phosphinocarbenes via deprotonation of hitherto unknown diprotic terminal methylene phosphonium ions. Two methylene phosphonium salts bearing bulky N-heterocyclic imine substituents at the phosphorus atom were isolated and fully characterized. Deprotonation studies indicate the formation of transient monosubstituted carbenes that undergo intermolecular cycloadditions or intramolecular Buchner ring expansion to afford a cycloheptatriene derivative. The reaction mechanism of the latter transformation was elucidated using DFT calculations, which reveal the ambiphilic nature of the phosphinocarbene enabling the insertion into the aromatic C-C bond. Additional computational studies on the role of substituent effects are presented.

Water Enables Lattice Oxygen Activation of Transition Metal Oxides for Volatile Organic Compound Oxidation

A small amount of water can enhance the catalytic combustion activity of volatile organic compounds (VOCs) on transition metal oxides (TMOs), but its intrinsic mechanism is still controversial. Herein, we systematically demonstrate that water molecules can constantly activate lattice oxygen of transition metal oxides to form hydroxyl species theoretically and experimentally. The oxygen atoms of the generated hydroxyl species possess a weak bonding strength with circumjacent metal atoms to easily escape from the surface and attack electron-deficient carbon atoms of VOCs due to their comparatively stronger nucleophilicity, leaving abundant oxygen vacancies as the active sites for subsequent molecular oxygen activation. This work helps us deeply understand the role of water in lattice oxygen activation of transition metal oxides and provides direction for water-related catalysis, such as catalytic VOC combustion, water splitting, water–gas shift reactions, and corrosion.

Enriched nitrogen-doped carbon derived from expired drug with dual active sites as effective peroxymonosulfate activator: Ultra-fast sulfamethoxazole degradation and mechanism insight

It’s a win–win strategy to treat organic wastewater by activating peroxymonosulfate (PMS) with nitrogen-doped carbocatalysts derived from solid waste. However, the preparation of carbocatalysts with a high nitrogen content is still tricky. Herein, enriched nitrogen-doped carbon (NDC20) with dual active sites derived from expired drugs (999 cold medicine) was developed to improve PMS activation and ultra-fast sulfamethoxazole (SMX) degradation. NDC20 with high N-doping level (23.26 at %) adjusted the charge distribution of the catalyst surface, resulting in an excellent catalytic activation of PMS. Remarkably, the NDC20/PMS system fully eliminated SMX within 2 min (kobs = 4.912 min−1), which was higher than all previously reported N-doped carbon catalysts. Quenching and electron paramagnetic resonance (EPR) experiments verified that the main mechanism involved a dual nonradical pathway involving singlet oxygen (1O2) and direct electron transfer (DET). Combined with theoretical calculations and in situ FTIR spectra, the exclusive role of dual active sites (pyridinic N/pyrrolic N and electron-deficient carbon atoms) was identified. An unanticipated generation pathway of 1O2 involving electrons acquisition by dissolved oxygen to form a superoxide radical (O2·-) and PMS oxidation over electron-deficient carbon atoms was revealed. Moreover, the possible pathways of SMX degradation were proposed, and the toxicity of the intermediates was anticipated. Finally, the practical application experiments demonstrated the sustainability of the catalytic activity of NDC20, which completely removed SMX after 100 h. This work provides a neoteric idea for synthesizing high-level N-doped carbocatalysts and solid waste treatment, and deepens the mechanistic understanding of PMS activation over high-level N-doped carbocatalysts.

Electron-rich ketone-based covalent organic frameworks supported nickel oxyhydroxide for highly efficient peroxymonosulfate activation and sulfadiazine removal: Performance and multi-path reaction mechanisms

NiOOH/PMS system suffers from relative lower catalytic performance of PMS activation on the degradation of extremely recalcitrant organic pollutants and potential high risk of leaching Ni(II) ions. To address these, ketone-based covalent organic frameworks (COFs) with electron-deficient and electron-rich areas and large surface area was employed as a novel 2D carbon supporter to synthesize NiOOH@COFs composite. It turned out that the reaction rate constant of sulfadiazine in the NiOOH@COFs/PMS (0.1221 min−1) was 2.06 and 2.39 times than that in the NiOOH/PMS (0.0594 min−1) and COFs/PMS system (0.0509 min−1), respectively. This was attributed from the efficient synergic effect of NiOOH and COFs on the PMS activation, resulting in faster and more production of multiple reactive oxygen species (ROS) (SO4−, OH, O2− and 1O2). Specifically, the PMS could be reduced around the electron-rich oxygen atom of the ketone for radical (SO4−, OH) generation, and could be oxidized over the electron-deficient carbon atom of the ketone for the non-radical (1O2) generation. Moreover, NiOOH can active PMS to simultaneously generate non-radical (1O2) and radicals (SO4−, OH, and O2−). 1O2 is distinguished as the dominant ROS contributing to the degradation of sulfadiazine. Furthermore, the leaching of total Ni ions is reduced by 72% than counterparts from NiOOH, demonstrating improved stability and reusability. Hence, this study provides new insights into the multi-path mechanism of the synergistic PMS activation by NiOOH and ketone-COFs, and sheds new light on the development of efficient metal-free catalysts with rich-electronic structure for peroxymonosulfate-mediated environmental remediation.

Ce(III)/Photoassisted Synthesis of Amides from Carboxylic Acids and Isocyanates

The Ce(III)-photocatalyzed synthesis of amides from carboxylic acids and aryl isocyanates was developed. The reaction includes the formation of alkyl radicals from carboxylic acids followed by radical addition to the electron-deficient carbon of isocyanate.

Dangling Carboxylic Group That Participates in O-O Bond Formation Reaction to Promote Water Oxidation Catalyzed by a Ruthenium Complex: Experimental Evidence of an Oxide Relay Pathway.

Two mononuclear ruthenium(II) complexes of the types [Ru(trpy)(HL1)(OH2)]2+ (1Aq) and [Ru(trpy)(L2-κ-N2O)] (2) [where trpy = 2,2':6',2″-terpyridine, HL1 = 2-(2-pyridyl)benzimidazole, H2L2 = 2-(pyridin-2-yl)-1H-benzo[d]imidazole-4-carboxylic acid] have been synthesized and thoroughly characterized by analytical and spectroscopic [UV-vis, NMR, high-resolution mass spectrometry, and IR] techniques. Complex 1Aq has been further characterized by X-ray crystallography. In an acidic aqueous medium (pH 1), complex 2 undergoes carboxylate/water exchange readily to form an aqua-ligated complex, [Ru(trpy)(H2L2-κ-N2)(OH2)]2+ (2Aq), having a dangling carboxylic group. This exchange phenomenon has been followed by IR, 1H NMR, and UV-vis spectroscopic techniques. Electrochemical analyses of 1Aq and 2Aq (Pourbaix diagram) suggest the generation of a formal RuV═O species that can potentially promote the oxidation of water. A comparative study of the water oxidation activity catalyzed by 1Aq and 2Aq is reported here to see the effect of a dangling carboxylic group in the catalytic performance. Complex 2Aq shows an enormously higher rate of reaction than 1Aq. The pendant carboxylic group in 2Aq participates in an intramolecular O-O bond formation reaction with the reactive formal RuV═O unit to form a percarboxylate intermediate and provides an electron-deficient carbon center where water nucleophilic attack takes place. The isotope labeling experiment using 18O-labeled water verifies the attack of water at the carbon center of the carboxylic group rather than a direct attack at the oxo of the formal RuV═O unit. The present work provides experimental evidence of the uncommon functionality of the carboxylic group, the oxide relay, in molecular water oxidation chemistry.

Quantification of σ-Acceptor and π-Donor Stabilization in O, S and Hal Analogues of N-Heterocyclic Carbenes (NHCs) on the Magnetic Criterion.

The spatial magnetic properties, through-space NMR shieldings (TSNMRSs), of stable O, S and Hal analogues of N-heterocyclic carbenes (NHCs) have been calculated using the GIAO perturbation method employing the nucleus-independent chemical shift (NICS) concept and the results visualized as iso-chemical-shielding surfaces (ICSSs) of various sizes and directions. The TSNMRS values (actually the anisotropy effects measurable in 1H NMR spectroscopy) are employed to qualify and quantify the position of the present mesomeric equilibria (carbenes ↔ ylides). The results are confirmed by geometry (bond angles and bond lengths), IR spectra, UV spectra, and 13C chemical shifts of the electron-deficient carbon centers.

N-doped graphitic C3N4 nanosheets decorated with CoP nanoparticles: A highly efficient activator in singlet oxygen dominated visible-light-driven peroxymonosulfate activation for degradation of pharmaceuticals and personal care products

CoP nanoparticle-loaded N-doped graphitic C3N4 nanosheets (CoP/N-g-C3N4) were fabricated via a facile three-step method to degrade pharmaceuticals and personal care products (PPCPs) via a visible-light-driven (VLD) peroxymonosulfate (PMS) activation system. 2 ppm carbamazepine (CBZ) can be removed completely within 10 min by the VLD-PMS system with a kinetic constant of k = 0.29128 min−1, as 25.8 times compared to that under dark conditions (k = 0.01128 min−1). The experimental and theoretical results showed that the doped graphitic N atoms could modulate the electronic properties of the g-C3N4 nanosheets. Subsequently, the Density Functional Theory (DFT) explained that CoP showed preference to bonding with the nitrogen atoms involved in the newly formed N˭N bond, and the Co‒N bond dramatically enhanced the transfer of photo-generated electrons from the N-g-C3N4 nanosheets. Electron paramagnetic resonance (EPR) tests show that singlet oxygen (1O2) plays a leading role in this case. Moreover, PMS molecules are also tended to be absorbed onto the electron-deficient carbon atoms near the newly formed N˭N bonds for PMS reduction, synergistically enhancing the degradation efficiency for CBZ and benzophenone-3 (BZP). The newly established VLD-PMS activation system was shown to treat the actual sewage in Hong Kong sewage treatment plants (STPs) very well. This work supplements the fundamental theory of radical and non-radical pathways in the sulfate radical (SO4•-)-based advanced oxidation process (SR-AOP) for environmental cleanup purposes.