Oxidative Dehydrogenation on Nanocarbon: Identification and Quantification of Active Sites by Chemical Titration

Selective electrooxidation of 5-hydroxymethylfurfural to 5-formyl-furan-2-formic acid on non-metallic polyaniline catalysts: structure-function relationships

The biomass-derived HMF oxidation reaction (HMFOR) holds great promise for sustainable production of fine chemicals. However, selective electrooxidation of HMF to high value-added intermediate product 5-formyl-furan-2-formic acid (FFCA) is still challenging. Herein, we report the electrocatalytic HMFOR to selectively produce FFCA using carbon paper (CP) supported polyaniline (PANI) as a catalyst. The PANI/CP non-metallic hybrid catalyst with moderate oxidation capacity exhibitsoptimized FFCA selectivity up to 76% in alkaline media, which has reached the best performance in reported literature studies. Identification and quantification of active sites for the HMFOR are further realized via linking the activity to structural compositions of PANI; both polaronic-type nitrogen (N3) and positively charged nitrogen (N4) species are proved responsible for adsorption and activation of HMF, and the intrinsic activity of N4 is higher than that of N3. The present work provides new physical-chemical insights into the mechanism of the HMFOR on non-metallic catalysts, paving the way for the establishment of structure-function relations and further development of novel electrochemical synthesis systems.

Unveiling the Synergistic Role of Frustrated Lewis Pairs in Carbon-Encapsulated Ni/NiOx Photothermal Cocatalyst for Enhanced Photocatalytic Hydrogen Production

The development of high-density and closely spaced frustrated Lewis pairs (FLPs) is crucial for enhancing catalyst activity and accelerating reaction rates. However, constructing efficient FLPs by breaking classical Lewis bonds poses a significant challenge. Here, this work has made a pivotal discovery regarding the Jahn-Teller effect during the formation of grain boundaries in carbon-encapsulated Ni/NiOx (Ni/NiOx@C). This effect facilitates the formation of high-density O (VO) and Ni (VNi) vacancy sites with different charge polarities, specifically FLP-VO-C basic sites and FLP-VNi-C acidic sites. The synergistic interaction between FLP-VO-C and FLP-VNi-C sites not only reduces energy barriers for water adsorption and splitting, but also induces a strong photothermal effect. This mutually reinforcing effect contributes to the exceptional performance of Ni/NiOx@C as a cocatalyst in photothermal-assisted photocatalytic hydrogen production. Notably, the Ni/NiOx@C/g-C3N4 (NOCC) composite photocatalyst exhibits remarkable hydrogen production activity with a rate of 10.7 mmol g-1 h-1, surpassing that of the Pt cocatalyst by 1.76 times. Moreover, the NOCC achieves an impressive apparent quantum yield of 40.78% at a wavelength of 380 nm. This work paves the way for designing novel defect-state multiphase cocatalysts with high-density and adjacent FLP sites, which hold promise for enhancing various catalytic reactions.

Photo-Switchable Peroxidase/Catalase-Like Activity of Carbon Quantum Dots

Nanozymes possess multi-enzyme activities over the natural enzymes, which produce multi-pathway synergistic effects for varies of biomedical applications. Unfortunately, their multi-enzyme activities are in fighting, significantly reducing the synergistic effects. Dynamic regulation of their multi-enzyme activities is the bottleneck for intelligent therapies. Herein, we construct a novel oxygen-nitrogen functionalized carbon quantum dots (O/N-CQDs) with peroxidase-like (Reactive oxygen species (ROS) producer) activity. Interestingly, the peroxidase-like activity can be reversibly converted to catalase-like (ROS scavenger) activity under visible light irradiation. It is found that both the peroxidase/catalase-like activity of O/N-CQDs can be precisely manipulated by the light intensity. The mechanism of switchable enzyme activities is attributed to the polarization of quinoid nitrogen in polyaniline (PANI) precursor retained on O/N-CQDs under visible light, which consumes the ROS to produce O2 and H2O. As a proof-of-concept demonstration, we are able to non-intrusively up and down regulate the ROS level in cells successfully by simply switching off and on the light respectively, potentially facilitating the precise medicine based on the development of the disease. Indeed, the photo-switchable peroxidase/catalase-like activity of O/N-CQDs opens a non-invasive strategy for better manipulations of the multi-activity of nanozymes, promising their wider and more intelligent biomedical applications.

A review on photocatalytic attribution and process of pyrolytic biochar in environment

Biochar has attracted significant attention due to its excellent environmental benefits and extensive applications. Recently, a consensus has been accepted that biochar can act as a photocatalyst and trigger effective photocatalytic reactions in the environment, which is important to energy conversion and the cycle of elements. However, its photocatalytic processes and the corresponding environmental impacts need to receive more and due attention. In this review, we provide a comprehensive summary of the underlying correlations among the pyrolytic evolution of biomass, the structure characteristic of biochar, and the resultant photocatalytic performance. Moreover, the photocatalytic processes and the influence of environmental factors were elaborately investigated on biochar. Finally, future tendencies and challenges in the photocatalysis of biochar have been prospected in the environmental field. This review has offered innovative insights into the photocatalytic essential of biochar and highly enhanced the understanding of its environmental impact.

3D Carbon Microspheres with a Maze-Like Structure and Large Mesopore Tunnels Built From Rapid Aerosol-Confined Coherent Salt/Surfactant Templating

Hierarchically porous carbons with tailor-made properties are essential for applications wherein rich active sites and fast mass transfer are required. Herein, a rapid aerosol-confined salt/surfactant templating approach is proposed for synthesizing hierarchically porous carbon microspheres (HPCMs) with a maze-like structure and large mesopore tunnels for high-performance tri-phase catalytic ozonation. The confined assembly in drying microdroplets is crucial for coherent salt (NaCl) and surfactant (F127) dual templating without macroscopic phase separation. The HPCMs possess tunable sizes, a maze-like structure with highly open macropores (0.3-30 µm) templated from NaCl crystal arrays, large intrawall mesopore tunnels (10-45 nm) templated from F127, and rich micropores (surface area >1000 m2 g-1 ) and oxygen heteroatoms originated from NaCl-confined carbonization of phenolic resin. The structure formation mechanism of the HPCMs and several influencing factors on properties are elaborated. The HPCMs exhibit superior performance in gas-liquid-solid tri-phase catalytic ozonation for oxalate degradation, owing to their hierarchical pore structure for fast mass transfer and rich defects and oxygen-containing groups (especially carbonyl) for efficient O3 activation. The reactive oxygen species responsible for oxalate degradation and the influences of several structure parameters on performance are discussed. This work may provide a platform for producing hierarchically porous materials for various applications.

Specializing Carbon Nanozyme Active Sites for Sensitive Alkaline Phosphatase Activity Metal-Free Detection

As biological enzymes regulate metabolic processes, alkaline phosphatase (ALP) is a critical diagnostic indicator associated with many diseases. To accurately measure the enzyme activity, nanozymactic materials can offer sensitive strategies for ALP detection. However, nanozymes often lack specific target binding sites, and the presence of common co-components, e. g., metal ions, may cause false-positive or false-negative results in enzyme activity determination. Herein, we developed a colorimetric assay for ALP detection using metal-free nanozymatic carbon dots (CDs). The ALP hydrolysis of pyrophosphate ions (PPi) to phosphate ions (Pi) induces a "turn-on" response based on the nanozyme activity. This PPi-induced inhibition mechanism is extensively studied via the Michaelis-Menten model, revealing that PPi acts as a noncompetitive inhibitor for CDs at a binding site distinct from the common nanozyme active site. With superior responses to ALP substrates, a highly sensitive and selective method is established for sensing ALP activity with a linear range of 0.010-0.200 U/L and a detection limit of 0.009 U/L. This finding explores the recognition and binding behavior of nanozymes, allowing for precise and reliable measurements even in complex samples, and represents a significant breakthrough for nanozyme-based assays in biological analysis.

Carboxyl groups on carbon nanodots as co-reactant sites for anodic electrochemiluminescence of tris(2,2-bipyridine)ruthenium(II)

Carbon nanodots (C-dots) with good biocompatibility have been extensively utilized as co-reactants for electrochemiluminescence (ECL) of the tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)32+) system. However, the ECL intensity of this system is still relatively low and the mechanism of C-dots as co-reactants remains unclear, which greatly limits its further application in bio-analysis. In this work, we revealed that the carboxyl groups on C-dots are co-reactant sites for Ru(bpy)32+ ECL by systematically investigating the contribution of carboxyl, hydroxyl and carbonyl groups on the surface of C-dots to the ECL intensity. Further treatment with hydrogen peroxide to increase the carboxyl-group content on C-dots resulted in a 10-fold increase in ECL intensity over the original Ru(bpy)32+/C-dots system. This work provides new insights for the rational design of ECL systems with C-dots as co-reactants and offers new chances for further applications of C-dots in the field of ECL.

Waste leather derived porous carbon boosted Fenton oxidation towards removal of diethyl phthalate: Mechanism and long-lasting performance

The acceleration of Fe(III)/Fe(II) conversion in Fenton systems is the critical route to achieve the long-lasting generation of reactive oxygen species towards the oxidation of refractory contaminants. Here, we found that waste leather derived porous carbon materials (LPC), as a simple and readily available metal-free biochar material, can promote the Fe(III)/H2O2 system to generate hydroxyl radicals (•OH) for oxidizing a broad spectrum of contaminants. Results of characterizations, theoretical calculations, and electrochemical tests show that the surface carbonyl groups of LPC can provide electron for direct Fe(III) reduction. More importantly, the graphitic-N on surface of LPC can enhance the reactivity of Fe(III) for accelerating H2O2 induced Fe(III) reduction. The presence of LPC accelerates the Fe(III)/Fe(II) redox cycle in the Fe(III)/H2O2 system, sustainable Fenton chain reactions is thus initiated for long-lasting generation of hydroxyl radicals without adding Fe(II). The continuous flow mode that couples in-situ Fenton-like oxidation and LPC with excellent adsorption catalytic properties, anti-coexisting substances interference and reusability performance enables efficient, green and sustainable degradation of trace organic pollutants. Therefore, the application of metal-free carbon materials in Fenton-like system can solve its rate-limiting problem, reduce the production of iron sludge, achieve green Fenton chemistry, and facilitate the actual engineering application of economic and ecological methods to efficiently remove trace organic contaminants from actual water sources.

A metal-free carbon catalyst for oxidative dehydrogenation of aryl cyclohexenes to produce biaryl compounds

A metal-free route based on a carbon catalyst to synthesize biphenyls through oxidative dehydrogenation (ODH) of phenyl cyclohexene has been investigated. Among the samples examined, an air-oxidized active carbon exhibits the best activity with a 9.1 × 10-2 h-1 rate constant, yielding 74% biphenyl in 28 h at 140 °C under five bar O2 in anisole. The apparent activation energy is measured as 54.5 kJ⋅mol-1. The extended reaction scope, consisting of 15 differently substituted phenyl cyclohexenes, shows the wide applicability of the proposed method. The catalyst's good recyclability over six runs suggests this ODH method as a promising route to access the biaryl compounds. In addition, the reaction mechanism is investigated with a combination of X-ray photoelectron spectroscopy, functional group blocking, and model compounds of carbon catalysts and is proposed to be based on the redox cycle of the quinoidic groups on the carbon surface. Additional experiments prove that the addition of the catalytic amount of acid (methanesulfonic acid) accelerates the reaction. In addition, Hammett plot examination suggests the formation of a carbonium intermediate, and its possible structure is outlined.

Fabrication of superhydrophilic porous carbon materials through a porogen-free method: Surface and structure modification promoting the two-electron oxygen reduction activity

HYPOTHESIS

Electrochemical manufacture of H₂O₂ through the two-electron oxygen reduction reaction (2e^- ORR), providing prospects of the distributed production of H₂O₂ in remote regions, is considered a promising alternative to the energy-intensive anthraquinone oxidation process.

EXPERIMENTS

In this study, one glucose-derived oxygen-enriched porous carbon material (labeled as HGC₅₀₀) is developed through a porogen-free strategy integrating structural and active site modification.

FINDINGS

The superhydrophilic surface and porous structure together promote the mass transfer of reactants and accessibility of active sites in the aqueous reaction, while the abundant CO species (e.g., aldehyde groups) are taken for the main active site to facilitate the 2e^- ORR catalytic process. Benefiting from the above merits, the obtained HGC₅₀₀ possesses superior performance with a selectivity of 92 % and mass activity of 43.6 A g_cat^-1 at 0.65 V (vs. RHE). Besides, the HGC₅₀₀ can operate steadily for 12 h with the accumulation of H₂O₂ reaching up to 4090±71 ppm and a Faradic efficiency of 95 %. The H₂O₂ generated from the electrocatalytic process in 3 h can degrade a variety of organic pollutants (10 ppm) in 4-20 min, displaying the potential in practical applications.

High-performance photocatalytic peroxymonosulfate activation by carbon quantum dots via precise surface chemistry regulation: Insight into the structure-function relations

Carbon quantum dots (CQDs) are considered promising metal-free green catalysts for the activation of persulfates, but direct experimental evidence to identify the true active sites on the surface of CQDs is still lacking. We prepared CQDs with different oxygen contents by controlling the carbonisation temperature, using a simple pyrolysis method. Photocatalytic activity experiments show that CQDs₂₀₀ exhibits the best PMS activation performance. By investigating the relationship between the oxygen functional groups on CQDs surface and photocatalytic activity, it was postulated that the C=O groups might be the predominant active site, which was confirmed by selective chemical titrations of the C=O, C-OH and COOH groups. Furthermore, limited to the weak photocatalytic properties of the pristine CQDs, ammonia and phenylhydrazine were used to precisely nitrogen-modify the o-CQD surface. We found that phenylhydrazine-modified o-CQDs-PH promoted the absorption of visible light and the separation of photocarriers, thus enhancing the activation of PMS. Theoretical calculations provide more insights from different levels of the pollutant, fine-tuned CQDs, and their interactions.

Folic Acid-Derived Low-dimensional carbons for efficient oxidative dehydrogenation of ethylbenzene

The oxidative dehydrogenation (ODH) of alkane is one of the most attractive routes in alkane production because of its favourable thermodynamic characteristic. Nitrogen-doped nanocarbons have demonstrated great potential in this reaction due to its cost-effective, high catalytic activity and stability. However, the influence of nitrogen on the catalytic properties of carbon materials is poorly understood due to the complexities of surface oxygen and nitrogen functional groups. Here we derive the performance descriptor that account for the nitrogen-dependent carbocatalysis in ODH reaction. To achieve this, we designed a set of nitrogen-doped nanocarbon materials with tunable nitrogen species by hydrothermal carbonization (HTC) treatment of the biomass folic acid (FA), which are applied in ODH of ethylbenzene. Among them, FA-180-1000 catalyst can achieve high ethylbenzene conversion (up to ∼62 %) and styrene selectivity (∼87 %), outperforming other HTC carbon-based catalysts. Structural characterizations and kinetic analyses revealed that nitrogen doping strongly interferes the charge polarization of CO site via electron transfer between CO, and nitrogen (mainly pyridine nitrogen and graphitic nitrogen) thus enhancing the reactivity of CO. Furthermore, the induction period during reaction process can be shortened by applying of sulfuric acid-assisted HTC method for constructing nitrogen-doped carbon catalyst with low crystallinity. The present work provides new insights into the contribution of nitrogen doping to the ODH reaction of carbon nanocatalysts, as well as guidance for the rational design of carbon catalysts for the conversion of hydrocarbons to high-value chemicals.

Identification of Active Sites over Metal-Free Carbon Catalysts for Flue Gas Desulfurization

Carbon-based catalysts have been extensively used for flue gas desulfurization (FGD) and have exerted great importance in controlling SO₂ emissions over the past decades. However, many fundamental details about the nature of the active sites and desulfurization mechanism still remain unclear. Here, we reported the experimental and theoretical identifications of active sites in FGD on carbon catalysts. Temperature-programmed decomposition allowed us to modulate the number of oxygen functional groups on carbon catalysts and to establish its correlation with desulfurization activity. Selective passivation further demonstrated that the ketonic carbonyl (C═O) groups are the intrinsic active sites for FGD reaction. Combined with transient response experiments, quasi-in situ X-ray photoelectron spectroscopy, and density functional theory simulations, it was revealed that desulfurization reaction on carbon catalysts mainly proceeded via the Langmuir-Hinshelwood mechanism, during which the nucleophilic ketonic C═O groups served as active sites for chemically absorbing SO₂ and their adjacent sp²-hybridized carbon atoms dissociatively activated O₂. It also turned out that the formation of H₂SO₄ is the reaction barrier step. The output of this study should not only advance the understanding of desulfurization at the atomic scale but also provide a general guideline for the rational design of efficient carbon catalysts for FGD.

Potential Risk of NH3 Slip Arisen from Catalytic Inactive Site in Selective Catalytic Reduction of NOx with Metal-Free Carbon Catalysts

Ammonia emissions from industrial processes have rapidly increased in the past years. Recent advances have used carbon-based selective catalytic reduction (SCR) technology combined with a reaction-regeneration process to reduce NO_x from sintering flue gas, while NH₃ slip is seldom accounted for in this process. This study demonstrates that although the electrophilic carboxyl groups (-COOH) on metal-free carbon catalysts exhibit strong adsorption toward NH₃, they do not participate in the SCR reaction. As a result of the competitive adsorption of NH₃ in the reaction step, these catalytic inactive carboxyl groups not only prolong the time to the SCR steady state, but also result in the potential risk of NH₃ slip. A linear relationship with the equimolar ratio between carboxyl groups and slipped NH₃ was established in the regeneration steps. The slip of NH₃ could be alleviated by the decomposition of carboxyl groups, and special attention should be paid to the presence of inactive sites with strong NH₃ adsorption on industrial-employed carbon catalysts. In addition to advancing the understanding of the NH₃-SCR mechanism, this work also provides valuable opportunities for the control of ammonia emissions from industrial processes.

Improvement of Carbonyl Groups and Surface Defects in Carbon Nanotubes to Activate Peroxydisulfate for Tetracycline Degradation

Carbon nanotubes (CNTs) were considered a promising activator for persulfates due to their high electrical conductivity, large specific surface area and low toxicity. The functional groups and surface defects of CNTs could significantly affect their activation performance. In this study, CNTs with high C=O ratio and defect density (CNT-O-H) were prepared through a facile treatment of raw CNTs with HNO₃ oxidation followed by calcination at 800 °C under an argon atmosphere. X-ray photoelectron spectroscopy (XPS) and Raman results showed that the C=O proportion and defect degree (I_D/I_G) rose to 75% and 1.53, respectively. The obtained CNT-O-H possessed a superior performance towards peroxydisulfate (PDS) activation, and the degradation efficiency of tetracycline (TC) in the CNT-O-H/PDS system was increased to 75.2% from 56.2% of the raw CNTs/PDS system within 40 min. Moreover, the activity of CNT-O-H after use could be easily recovered with re-calcination. In addition, the CNT-O-H/PDS system exhibited high adaptabilities towards wide solution pH (2-10), common coexisting substances and diverse organic pollutants. Singlet oxygen (¹O₂) was confirmed to be the dominant reactive oxygen species (ROS) generated in the CNT-O-H/PDS system. It was inferred that surface C=O groups and defects of CNTs were the key site to activate PDS for TC degradation.

Insights into the mechanism of carbocatalysis for peracetic acid activation: Kinetic discernment and active site identification

Peracetic-acid-based advanced oxidation processes (PAA-AOPs) on metal-free catalysts have emerged as charming strategies for water contaminant removal. However, the involved reactive species and their corresponding active sites are ambiguous. Herein, using carbon nanotube (CNT) as a model carbocatalyst, we demonstrated that, under neutral conditions, the CNT-PAA* complex was the dominant reactive species to oxidize phenolic compounds via electron-transfer process (ETP), whereas the surface-bound hydroxyl radicals (^·OH_surface) played a minor role on the basis of quenching and electrochemical tests as well as Raman spectroscopy. More importantly, the experimental and density functional theory (DFT) calculation results collaboratively proved that the active site for ETP was the sp²-hybridized carbon on the CNT bulk, while that for radical generation was the edge-located hydroxyl group (C-OH), which lowered the energy barrier for cleaving the O-O bond in CNT-PAA* complex. We further discerned the oxidation kinetic constants (k_oxid) of different pollutants from the apparent kinetic constants in CNT/PAA system. The significant negative linear correlation between lnk_oxid and half-wave potential of phenolic compounds suggests that the pollutants with a lower one-electron oxidation potential (i.e., stronger electron-donating ability) are more easily oxidized. Overall, this study scrutinizes the hybrid radical and non-radical mechanism and the corresponding active sites of the CNT/PAA system, providing insights into the application of PAA-AOPs and the development of ETP in the remediation of emerging organic pollutants.

Carbon Surface Chemistry: New Insight into the Old Story

The enormous complexity of the carbon material family has provoked a phenomenological approach to develop its potential in different applications. Although the electronic, chemical, mechanical, and magnetic properties of carbon materials have been widely discussed based on defect control engineering, there is still a lack of fundamental understanding of the carbon surface chemistry, which leads to many controversial conclusions. Here, by analyzing various defects on carbon surface, some commonly neglected aspects and misunderstandings in this field are pointed out, clarifying how surface chemistry affects the chemical behaviors of carbon in some specific chemical reactions. With this full-scale consideration of the carbon surface chemistry, the behaviors of carbon materials with various functions can be well defined, which is indispensable for their scalable applications. Perspectives on future developments of carbon surface chemistry are also provided to enable practically accessible design of advanced carbon in those applications.

Treated activated carbon as a metal-free catalyst for effectively catalytic reduction of toxic hexavalent chromium

In this work, activated carbon treated in N₂ atmosphere, as a non-metallic catalyst, exhibits excellent catalytic performance in reduction of Cr (VI) to Cr (III) using HCOOH as the reducing agent at room temperature. A series of characterizations and control experiments were carried out to deduce the possible reaction mechanism. The results showed that the improved catalytic performance can be attributed to the enhanced graphitization degree and basic sites such as pyrone-like, which favor electron transferring and activation of reactant. The reaction rate constant observed herein for the C-800 was 22 and 6 times more than that for C-0 and Pd/C catalyst, respectively. In addition, C-800 showed good recycle performance, and no loss of activity was observed after 5 cycles. This study broadens the application of nonmetallic catalyst and provides an easy-available and cost-effective catalytic material for removing toxic Cr (VI).

Plastering Sponge with Nanocarbon-Containing Slurry to Construct Mechanically Robust Macroporous Monolithic Catalysts for Direct Dehydrogenation of Ethylbenzene

Nanocarbons have shown great potential as a sustainable alternative to metal catalysts, but their powder form limits their industrial applications. The preparation of nanocarbon-based monolithic catalysts is a practical approach for overcoming the resulting pressure drop associated with their powder form. In our previous work, a ploycation-mediated approach was used to successfully prepare nanocarbon-containing monoliths. Unfortunately, because there are no macropores in the monolith, it needs to be crashed into millimeter-sized particles before application. Therefore, developing a facile method for preparing mechanically robust nanocarbon-based macroporous monolithic catalysts is vital but still challenging. Herein, evoked by swallows building their nests, we report an approach for successfully preparing a mechanically robust nanodiamond-based macroporous monolith catalyst by plastering melamine sponge (MS) with a slurry composed of nanodiamonds (NDs) and poly(imidazolium-methylene) chloride (PImM) followed by an annealing process. The macroporous monolith catalyst (ND/NC_MS-NC_PImM) containing NDs well dispersed in N-doped carbon is mechanically robust with enriched macroscopic pores. It exhibits outstanding catalysis toward ethylbenzene to styrene through a direct dehydrogenation reaction with a high styrene rate in a steady state (5.50 mmol g^-1 h^-1) and high styrene selectivity (99.5%). ND/NC_MS-NC_PImM shows much higher activity than powder ND by 1.9 fold. In addition, this work solves the significant problem of large pressure drop encountered with conventional powdered nanocarbon catalysts in the flow reactor. This work not only creates an excellent nanodiamond-based macroporous monolithic ethylbenzene direct dehydrogenation catalyst but also presents a promising avenue for preparing other macroporous monolithic catalysts for diverse transformations.

Mechanism of biochar functional groups in the catalytic reduction of tetrachloroethylene by sulfides

In recent years, biochar has become of considerable interest for environmental applications, it can be used as a catalyst for sulfides reduction of perchloroethylene, but the crucial role of biochar properties played in catalyzing dechlorination remained ambiguous investigation. To pinpoint the critical functional groups, the modified biochars were respectively produced by HNO₃, KOH and H₂O₂ with similar dimensional structures but different functional groups. Combined with the adsorption and catalytic results of different biochars, the acid-modified biochar had the best catalytic performance (99.9% removal) due to the outstanding specific surface area and ample functional groups. According to characterization and DFT results, carboxyl and pyridine nitrogen exhibited a positive correlation with the catalytic rate, indicating that their contribution to catalytic performance. Customizing biochar with specific functional groups removed depth demonstrated that the carboxyl was essential component. Further, alkaline condition was conducive to catalytic reduction, while tetrachloroethylene cannot be reduced under acidic conditions, because HS^- and S^2- mainly existed in alkaline environment and the sulfur-containing nucleophilic structure formed with biochar was more stable under this condition. Overall, this study opens new perspectives for in situ remediation by biochar in chlorinated olefin polluted anoxic environment and promotes our insight of modifying for biochar catalyst design.

Tailoring surface carboxyl groups of mesoporous carbon boosts electrochemical H2O2 production

Oxygen-doped porous carbon materials have been shown promising performance for electrochemical two-electron oxygen reduction reaction (2e^- ORR), an efficient approach for the safe and continuous on-site generation of H₂O₂. The regulation and mechanism understanding of active oxygen-containing functional groups (OFGs) remain great challenges. Here, OFGs modified porous carbon were prepared by thermal oxidation (MC-12-Air), HNO₃ oxidation (MC-12-HNO₃) and H₂O₂ solution hydrothermal treatment (MC-12-H₂O₂), respectively. Structural characterization showed that the oxygen doping content of three catalysts reached about 20%, with the almost completely maintained specific surface area (exception of MC-12- HNO₃). Spectroscopic characterization further revealed that hydroxyl groups are mainly introduced into MC-12-Air, while carboxyl groups are mainly introduced into MC-12- HNO₃ and MC-12- H₂O₂. Compared with the pristine catalyst, three oxygen-functionalized catalysts showed enhanced activity and H₂O₂ selectivity in 2e^- ORR. Among them, MC-12-H₂O₂ exhibited the highest catalytic activity and selectivity of 94 %, as well as a considerable HO₂^- accumulation of 46.2 mmol L^-1 and excellent stability in an extended test over 36 h in a H-cell. Electrochemical characterization demonstrated the promotion of OFGs on ORR kinetics and the greater contribution of carboxyl groups to the intrinsically catalytic activity. DFT calculations confirmed that the electrons are transferred from carboxyl groups to adjacent carbon and the enhanced adsorption strength toward *OOH intermediate, leading to a lower energy barrier for forming *OOH on carboxyl terminated carbon atoms.

Calcium-Mobilizing Properties of Salvia miltiorrhiza-Derived Carbon Dots Confer Enhanced Environmental Adaptability in Plants

Biomass-derived carbon dots (CDs) are promising nanotools for agricultural applications and function as a reactive oxygen species (ROS) scavenger to alleviate plant oxidative stress under adverse environments. Nevertheless, plants need ROS burst to fully activate Ca²⁺-regulated defensive signaling pathway. The underlying mechanism of CDs to improve plant environmental adaptability without ROS is largely unknown. Here, Salvia miltiorrhiza-derived CDs triggered ROS-independent Ca²⁺ mobilization in plant roots. Mechanistic investigation attributed this function mainly to the hydroxyl and carboxyl groups on CDs. CDs-triggered Ca²⁺ mobilization was found to be dependent on the production of cyclic nucleotides and cyclic nucleotide-gated ion channels. Lectin receptor kinases were verified as essential for this Ca²⁺ mobilization. CDs hydroponic application promoted Ca²⁺ signaling and plant environmental adaptability under salinity and nutrient-deficient conditions. All these findings uncover that CDs have a Ca²⁺-mobilizing property and thus can be used as a simultaneous Ca²⁺ signaling amplifier and ROS scavenger for crop improvement.

Nitrogen-doped carbon nanotubes enhanced Fenton chemistry: Role of near-free iron(III) for sustainable iron(III)/iron(II) cycles

The sluggish kinetics of Fe(II) recovery strongly impedes the scientific progress of Fenton reaction (Fe(II)/H₂O₂) towards practical application. Here, we propose a novel mechanism that metal-free nitrogen-doped carbon nanotubes (NCNT) can enhance Fenton chemistry with H₂O₂ as electron donors by elevating the oxidation potential of Fe(III). NCNT remarkably promotes the circulation of Fe(III)/Fe(II) to produce hydroxyl radical (^•OH) with excellent stability for multiple usages (more than 10 cycles) in the NCNT/Fe(III)/H₂O₂ system. Although carbonyl on NCNT can act as the electron supplier for Fe(III) reduction, the behavior of NCNT is distinct from common reductants such as hydroxylamine and boron. Electrochemical analysis and density functional theory calculation unveil that nitrogen sites of NCNT can weakly bind with Fe(III) to elevate the oxidation potential of Fe(III) (named near-free Fe(III), primarily FeOH²⁺) at pH ranging from 2.0 to 4.0. Without inputs of external stimulations or electron sacrificers, near-free Fe(III) can promote H₂O₂ induced reduction of Fe(III) to initiate Fenton chain reactions for long-lasting generation of ^•OH. To our delight, it is a common property of N-doped carbon materials (e.g., graphene, carbon nanofibers, and acetylene black), our research thus provides a novel, sustainable, and green strategy for promoting Fenton chemistry.

Identification of active sites of B/N co-doped nanocarbons in selective oxidation of benzyl alcohol

Developing highly active and stable nanocarbon catalysts for selective oxidation reactions has attracted much attention due to their potential as an alternative to traditional metal-based or noble metal catalysts. However, the nature of active sites and the reaction mechanism of nanocarbon catalysts for oxidation reactions still remains largely unknown, which hinders the rational design and development of highly efficient carbon-based catalysts. Here we report a facile strategy for the synthesis of boron and nitrogen co-doped carbon nanosheet material (BNC), which exhibits excellent catalytic activity with 91% conversion and 99% selectivity in selective oxidation of benzyl alcohol into benzaldehyde, superior to those of traditional carbon materials (oxidized carbon nanotubes, graphites and commercial nanocarbons). Structural characterizations and kinetic measurements are studied to clarify the active site, in which phenolic hydroxyl on BNC is responsible for the production of benzaldehyde. Meanwhile, we put forward a possible reaction mechanism and point out the key factors in determining the reactivity for this reaction. Therefore, the present work provides new insight into structure-function relationships, paving the way for the development of highly efficient nanocarbon catalysts.

The highly efficient electrocatalytic oxidation of 5-hydroxymethylfurfural on copper nanocrystalline/carbon hybrid catalysts: structure–function relations

The Cu species in Cu(NSD)/CP exhibit a high electrochemical specific surface area, which allows efficient transformation from Cu0 and Cu1+ species to Cu2+ with high catalytic capacity, resulting in excellent catalytic performance (96% yield of FDCA).

Controllable Synthesis of Polyphenol Spheres via Amine-Catalyzed Polymerization-Induced Self-Assembly

A facile and general strategy for preparing uniform and multifunctional polyphenol-based colloidal particles through amine-catalyzed polymerization-induced self-assembly is described. The size and interfacial adhesion of polyphenol spheres can be easily controlled over a wide range via adjusting the concentration of the cosolvent and monomer. Moreover, the polyphenol spheres showed excellent thermal and chemical stability and highly active properties and could efficiently deplete the reactive oxygen species (ROS), which are helpful for in vivo ROS regulation for inflammatory therapeutic. The accessible and versatile method provides a feasible way for the rational engineering of multifunctional polyphenol spheres, which have great potential in many fields.

Reduced Graphene Oxides as Carbocatalysts in Acceptorless Dehydrogenation of N-Heterocycles

The catalytic properties of graphene-derived materials are evaluated in acceptorless dehydrogenation of N-heterocycles. Among them, reduced graphene oxides (rGOs) are active (quantitative yields in 23 h) under mild conditions (130 °C) and act as efficient heterogeneous carbocatalysts. rGO exhibits reusability and stability at least during eight consecutive runs. Mechanistic investigations supported by experimental evidence (i.e., organic molecules as model compounds, purposely addition of metal impurities and selective functional group masking experiments) suggest a preferential contribution of ketone carbonyl groups as active sites for this transformation.

Photo-fluorination of nanodiamonds catalyzing oxidative dehydrogenation reaction of ethylbenzene

Styrene is one of the most important industrial monomers and is traditionally synthesized via the dehydrogenation of ethylbenzene. Here, we report a photo-induced fluorination technique to generate an oxidative dehydrogenation catalyst through the controlled grafting of fluorine atoms on nanodiamonds. The obtained catalyst has a fabulous performance with ethylbenzene conversion reaching 70% as well as styrene yields of 63% and selectivity over 90% on a stream of 400 °C, which outperforms other equivalent benchmarks as well as the industrial K-Fe catalysts (with a styrene yield of 50% even at a much higher temperature of ca. 600 °C). Moreover, the yield of styrene remains above 50% after a 500 h test. Experimental characterizations and density functional theory calculations reveal that the fluorine functionalization not only promotes the conversion of sp3 to sp2 carbon to generate graphitic layers but also stimulates and increases the active sites (ketonic C=O). This photo-induced surface fluorination strategy facilitates innovative breakthroughs on the carbocatalysis for the oxidative dehydrogenation of other arenes.

Novel coagulation waste-based Fe-containing carbonaceous catalyst as peroxymonosulfate activator for pollutants degradation: Role of ROS and electron transfer pathway

A facile one-step pyrolysis method was employed to prepare an iron containing carbonaceous catalyst using coagulation waste (CW) from paper mill. The catalyst (noted as PMCW) was used to activate peroxymonosulfate (PMS) for decomposition of Reactive Red 2 (RR2). The degradation mechanism was analyzed by reactive oxygen species (ROS) scavenging experiments, electron spin resonance spectroscopy, electrochemical measurements, selective deactivation of the functional groups on the catalyst surface, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Results showed that, besides ROS (^•OH, SO₄^•- and ¹O₂), electron transfer pathways induced by -OH functional groups and the π-π* system are involved in the degradation mechanism of RR2. Concerning different decomposition pathways, seven intermediates were identified, and three important steps, including attack on the azo group, cleaving the N9-C10 bond, and opening the naphthalene ring, were deduced via application and analysis of quadrupole time-of-flight liquid chromatography/mass spectrometry (QTOF LC/MS) and density functional theory (DFT) calculations based on Fukui indices and electrostatic potential (ESP) distributions. This work not only provides a novel facile recycling strategy of industrial waste from paper manufacturing to good carbonaceous catalysts but also deepens the understanding of the mechanisms of PMS activation with carbonaceous materials.

A CuNi Alloy-Carbon Layer Core-Shell Catalyst for Highly Efficient Conversion of Aqueous Formaldehyde to Hydrogen at Room Temperature

A copper (Cu) material is catalytically active for formaldehyde (HCHO) dehydrogenation to produce H₂, but the unsatisfactory efficiency and easy corrosion hinder its practical application. Alloying with other metals and coating a carbon layer outside are recognized as effective strategies to improve the catalytic activity and the long-term durability of nonprecious metal catalysts. Here, highly dispersed CuNi alloy-carbon layer core-shell nanoparticles (CuNi@C) have been developed as a robust catalyst for efficient H₂ generation from HCHO aqueous solution at room temperature. Under the optimized reaction conditions, the CuNi@C catalyst exhibits a H₂ evolution rate of 110.98 mmol·h^-1·g^-1, which is 1.5 and 4.9 times higher than those of Cu@C and Ni@C, respectively, which ranks top among the reported nonprecious metal catalysts for catalytic HCHO reforming at room temperature to date. Furthermore, CuNi@C also displays excellent stability toward the catalytic HCHO reforming into H₂ in tap water owing to the well-constructed carbon sheath protecting CuNi nanocrystals from oxidation in an alkaline medium. Combined with density functional theory calculations, the superior catalytic efficiency of CuNi@C for H₂ generation results from the synergistic contribution between the massive active species from HCHO decomposition on the Cu sites and the remarkable H₂ evolution activity on Ni sites. The improved performance of CuNi@C highlights the enormous potential of advancing noble-metal-free nanoalloys as cost-effective and recyclable catalysts for energy recovery from industrial HCHO wastewater.

Chemical Identification of Catalytically Active Sites on Oxygen-doped Carbon Nanosheet to Decipher the High Activity for Electro-synthesis Hydrogen Peroxide

Electrochemical production of hydrogen peroxide (H₂ O₂ ) through two-electron (2 e^- ) oxygen reduction reaction (ORR) is an on-site and clean route. Oxygen-doped carbon materials with high ORR activity and H₂ O₂ selectivity have been considered as the promising catalysts, however, there is still a lack of direct experimental evidence to identify true active sites at the complex carbon surface. Herein, we propose a chemical titration strategy to decipher the oxygen-doped carbon nanosheet (OCNS₉₀₀ ) catalyst for 2 e^- ORR. The OCNS₉₀₀ exhibits outstanding 2 e^- ORR performances with onset potential of 0.825 V (vs. RHE), mass activity of 14.5 A g^-1 at 0.75 V (vs. RHE) and H₂ O₂ production rate of 770 mmol g^-1  h^-1 in flow cell, surpassing most reported carbon catalysts. Through selective chemical titration of C=O, C-OH, and COOH groups, we found that C=O species contributed to the most electrocatalytic activity and were the most active sites for 2 e^- ORR, which were corroborated by theoretical calculations.

Enhancing selectivity through decrypting the uncoordinated zirconium sites in MOF electrocatalysts

Zirconium (Zr)-based porphyrinic metal-organic frameworks (PCN-223-M) were employed as the electrocatalysts to explore the effect of uncoordinated Zr sites on the performance of the CO₂ reduction reaction (CO₂RR). PCN-223-AA with the lowest uncoordinated number of 0.79 exhibited the highest FE(CO) of 90.7%. It was demonstrated that the catalytic performance of PCN-223-M showed negative correlation to the uncoordinated Zr sites. This research provided a rational strategy to design efficient MOF electrocatalysts with few uncoordinated metal sites for highly selective CO₂RR.