N,P-dual-doped multilayer graphene as an efficient carbocatalyst for nitroarene reduction: A mechanistic study of metal-free catalysis

Probing the Activity Enhancement of Carbocatalyst with the Anchoring of Atomic Metal

Enhanced catalysis for organic transformation is essential for the synthesis of high-value compounds. Atomic metal species recently emerged as highly effective catalysts for organic reactions with high activity and metal utilization. However, developing efficient atomic catalysts is always an attractive and challenging topic in the modern chemical industry. In this work, we report the preparation and activity enhancement of nitrogen- and sulfur-codoped holey graphene (NSHG) with the anchoring of atomic metal Pd. When employed as the catalyst for nitroarenes reduction reactions, the resultant Pd/NSHG composite exhibits remarkably high catalytic activity due to the co-existence of dual-active components (i.e., catalytically active NSHG support and homogeneous dispersion of atomic metal Pd). In the catalytic 4-nitrophenol (4-NP) reduction reaction, the efficiency (turnover frequency) is 3.99 × 10-2 mmol 4-NP/(mg cat.·min), which is better than that of metal-free nitrogen-doped holey graphene (NHG) (2.3 × 10-3 mmol 4-NP/(mg cat.·min)) and NSHG carbocatalyst (3.8 × 10-3 mmol 4-NP/(mg cat.·min)), the conventional Pd/C and other reported metal-based catalysts. This work provides a rational design strategy for the atomic metal catalysts loaded on active doped graphene support. The resultant Pd/NSHG dual-active component catalyst (DACC) is also anticipated to bring great application potentials for a broad range of organic fields, such as organic synthesis, environment treatment, energy storage and conversion.

Construction and application of carbon aerogels in microwave absorption

Electromagnetic pollution that threatens human health, the ecological environment and electronic equipment has been recognized as a serious environmental issue. In view of this, microwave absorbing materials (MAMs) are urgently required in modern society. Compared with traditional MAMs, carbon aerogels have inherent advantages in microwave absorption because of their high porosity and controllable conductive networks. Moreover, they are self-supporting 3D architectures with tailorable shapes, which satisfy most application scenarios. Therefore, carbon aerogels have aroused great interest in recent years and are being developed as promising absorption materials. In this review, we emphasize recent developments in carbon-aerogel-based MAMs constructed with some typical carbon nanomaterials, including graphene, carbon nanotubes and pyrolytic carbon. Their preparation methods, especially some newly developed strategies, are introduced as well as their influence on the structures and properties of aerogels. With a brief analysis of classic microwave absorption processes, we propose the requirements and strategies for modifying carbon aerogels to achieve ideal microwave absorption performance. Finally, we provide comprehensive comparisons of the MA performances of various carbon aerogels that show application potential and set forth the challenges and prospects of this kind of MAM.

Synthesis of Activated Porous Carbon from Red Dragon Fruit Peel Waste for Highly Active Catalytic Reduction in Toxic Organic Dyes

In this study, an alternative precursor for production of biomass-derived activated carbon was introduced using dragon fruit (Hylocereus costaricensis) peels. Chemical activators such as FeCl3, MgCl2, ZnCl2 were used in the thermal carbonization process to convert carbon into porous carbon (PC). However, heteroatom-doped PC catalysts including N-, B-, and P-doped carbon catalysts in the field of dye removal is highly desirable. Several approaches (XRD, FE-SEM/TEM, XPS, FT-IR, EDS, and elemental mapping) were employed to examine the surface morphology, surface properties, and elemental composition of the PC catalyst. The catalytic activity of metal-free PC catalyst was demonstrated for methylene blue (MB), crystal violet (CV), and Nile blue (NB) in a mild environment The corresponding rate constant (kapp) values were estimated as 0.2473, 0.3248, and 0.3056 min−1, respectively, for MB, CV, and NB, which were significantly greater than those of numerous reports. It exhibited the best catalytic activity and recyclability. Moreover, the approach proposed here could create new opportunities for the remediation of organic dyes in lakes and industrial wastewater.

Ni-Pd-Incorporated Fe3O4 Yolk-Shelled Nanospheres as Efficient Magnetically Recyclable Catalysts for Reduction of N-Containing Unsaturated Compounds

The use of metal-based heterogeneous catalysts for the degradation of N-containing organic dyes has attracted much attention due to their excellent treatment efficiency and capability. Here, we report the synthesis of heterometals (Ni and Pd)-incorporated Fe3O4 (Ni-Pd/Fe3O4) yolk-shelled nanospheres for the catalytic reduction of N-containing organic dyes using a facile combination of solvothermal treatment and high-temperature annealing steps. Benefiting from the magnetic properties and the yolk-shelled structure of the Fe3O4 support, as well as the uniformly dispersed active heterometals incorporated in the shell and yolk of spherical Fe3O4 nanoparticles, the as-prepared Ni-Pd/Fe3O4 composite shows excellent recyclability and enhanced catalytic activity for three N-containing organic dyes (e.g., 4-nitrophenol, Congo red, and methyl orange) compared with its mono metal counterparts (e.g., Ni/Fe3O4 and Pd/Fe3O4). In the 4-nitrophenol reduction reaction, the catalytic activity of Ni-Pd/Fe3O4 was superior to many Fe3O4-supported nanocatalysts reported within the last five years. This work provides an effective strategy to boost the activity of iron oxide-based catalytic materials via dual or even multiple heterometallic incorporation strategy and sheds new light on environmental catalysis.

Catalytic Properties of High Nitrogen Content Carbonaceous Materials

The influence of structural modifications on the catalytic activity of carbon materials is poorly understood. A collection of carbonaceous materials with different pore networks and high nitrogen content was characterized and used to catalyze four reactions to deduce structure-activity relationships. The CO₂ cycloaddition and Knoevenagel reaction depend on Lewis basic sites (electron-rich nitrogen species). The absence of large conjugated carbon domains resulting from the introduction of large amounts of nitrogen in the carbon network is responsible for poor redox activity, as observed through the catalytic reduction of nitrobenzene with hydrazine and the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine using hydroperoxide. The material with the highest activity towards Lewis acid catalysis (in the hydrolysis of (dimethoxymethyl)benzene to benzaldehyde) is the most effective for small molecule activation and presents the highest concentration of electron-poor nitrogen species.

Heteroatom Codoped Graphene: The Importance of Nitrogen

Although graphene has exceptional properties, they are not enough to solve the extensive list of pressing world problems. The substitutional doping of graphene using heteroatoms is one of the preferred methods to adjust the physicochemical properties of graphene. Much effort has been made to dope graphene using a single dopant. However, in recent years, substantial efforts have been made to dope graphene using two or more dopants. This review summarizes all the hard work done to synthesize, characterize, and develop new technologies using codoped, tridoped, and quaternary doped graphene. First, I discuss a simple question that has a complicated answer: When can an atom be considered a dopant? Then, I briefly discuss the single atom doped graphene as a starting point for this review's primary objective: codoped or dual-doped graphene. I extend the discussion to include tridoped and quaternary doped graphene. I review most of the systems that have been synthesized or studied theoretically and the areas in which they have been used to develop new technologies. Finally, I discuss the challenges and prospects that will shape the future of this fascinating field. It will be shown that most of the graphene systems that have been reported involve the use of nitrogen, and much effort is needed to develop codoped graphene systems that do not rely on the stabilizing effects of nitrogen. I expect that this review will contribute to introducing more researchers to this fascinating field and enlarge the list of codoped graphene systems that have been synthesized.

Mechanism and efficiency research of P- and N-codoped graphene for enhanced paracetamol electrocatalytic degradation

Electrocatalytic oxidation is an effective technology for treatment of refractory organic pollutants, and its performance strongly depends on anode materials. Among all anode materials, graphene (GN) owns the advantages of high stability and lack of secondary pollution. The catalytic performance of GN can be further improved through heteroatom doping. Here, P/N-codoped graphene (PN-GN) materials were optimized and used as an anode material for 4-acetamidophenol (APAP) electrocatalytic degradation. Result indicated that PN-GN had lower internal resistance, larger specific surface area, and higher electrochemical activity than single-doped graphene materials. The catalytic activity of GN was greatly improved by P/N codoping. When PN-GN (P8.4%-N7.6%-500 °C) was used as catalyst (current of 20 mA, initial pH of 7, reaction time of 60 min), the degradation efficiency of APAP reached 98.2% ± 1.8%, which was 17.9% ± 3.6% higher than P-codoped graphene (P-GN), 14.7% ± 4.6% higher than N-codoped graphene (N-GN), and 54.0% ± 5.2% higher than GN. After 180 min of reaction, the degradation efficiency of total organic carbon (TOC) was 78.5%. The reaction conditions were optimized and the degradation pathway of APAP was estimated to elucidate the catalytic mechanism. The main active substances generated in the system were identified as active chlorine and O₂^•-.

Catalytic applications of graphene oxide towards the synthesis of bioactive scaffolds through the formation of carbon–carbon and carbon–heteroatom bonds

During the past several decades, metal-based catalysis is one of the major and direct approaches for the synthesis of organic molecules. Nowadays, materials containing predominantly carbon element which are termed as carbocatalysts, become the most promising area of research to replace transition metal catalysts. In this context of carbocatalysis, the use of graphene oxide (GO) and GO-based materials are under spotlight due to their sustainability, environmental benignity and large scale-availability. The presence of oxygen containing functional groups in GO makes it benign oxidant and slightly acidic catalyst. This chapter provides a broad discussion on graphene oxide (GO) as well as its preparation, properties and vast area of application. The catalytic activity of GO has been explored in different organic transformations and it has been recognized as an oxidation catalyst for various organic reactions.

Metal-Free Chemoselective Reduction of Nitroarenes Catalyzed by Covalent Triazine Frameworks: The Role of Embedded Heteroatoms

Chemoselective reduction of nitroarenes to arylamines is a core technology for the synthesis of numerous chemicals. The technology, however, relies on applying precious noble metal catalysts. We present our findings on the development of robust nanoporous covalent triazine frameworks (CTFs) as metal-free catalysts for the green chemoselective reduction of nitroarenes. The turnover frequency is found to be 43.03 h^-1, exceeding activities of the heteroatom-doped carbon nanomaterials by a factor of 30. The X-ray photoelectron spectroscopy and control experiments provide further insights into the nature of active species for prompt catalysis. This report confirms the importance of quaternary 'N' and 'F' atom functionalities to create active hydrogen species via charge delocalization as a critical step in improving the catalytic activity.

Facile and template-free synthesis of porous carbon modified with FeOx for transfer hydrogenation of nitroarenes

Porous carbon modified with FeOx was developed using an in situ activation method for transfer hydrogenation of nitroarenes.

Carbon-based metal-free electrocatalysts: from oxygen reduction to multifunctional electrocatalysis

Since the discovery of N-doped carbon nanotubes as the first carbon-based metal-free electrocatalyst (C-MFEC) for oxygen reduction reaction (ORR) in 2009, C-MFECs have shown multifunctional electrocatalytic activities for many reactions beyond ORR, such as oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO₂RR), nitrogen reduction reaction (NRR), and hydrogen peroxide production reaction (H₂O₂PR). Consequently, C-MFECs have attracted a great deal of interest for various applications, including metal-air batteries, water splitting devices, regenerative fuel cells, solar cells, fuel and chemical production, water purification, to mention a few. By altering the electronic configuration and/or modulating their spin angular momentum, both heteroatom(s) doping and structural defects (e.g., atomic vacancy, edge) have been demonstrated to create catalytic active sites in the skeleton of graphitic carbon materials. Although certain C-MFECs have been made to be comparable to or even better than their counterparts based on noble metals, transition metals and/or their hybrids, further research and development are necessary in order to translate C-MFECs for practical applications. In this article, we present a timely and comprehensive, but critical, review on recent advancements in the field of C-MFECs within the past five years or so by discussing various types of electrocatalytic reactions catalyzed by C-MFECs. An emphasis is given to potential applications of C-MFECs for energy conversion and storage. The structure-property relationship for and mechanistic understanding of C-MFECs will also be discussed, along with the current challenges and future perspectives.

Recent advances in metal-free heteroatom-doped carbon heterogonous catalysts

The development of cost-effective, efficient, and novel catalytic systems is always an important topic for heterogeneous catalysis from academia and industrial points of view. Heteroatom-doped carbon materials have gained more and more attention as effective heterogeneous catalysts to replace metal-based catalysts, because of their excellent physicochemical properties, outstanding structure characteristics, environmental compatibility, low cost, inexhaustible resources, and low energy consumption. Doping of heteroatoms can tailor the properties of carbons for different utilizations of interest. In comparison to pure carbon catalysts, these catalysts demonstrate superior catalytic activity in many organic reactions. This review highlights the most recent progress in synthetic strategies to fabricate metal-free heteroatom-doped carbon catalysts including single and multiple heteroatom-doped carbons and the catalytic applications of these fascinating materials in various organic transformations such as oxidation, hydrogenation, hydrochlorination, dehydrogenation, etc.

Photochemical Transformation and Catalytic Activity of Dissolved Black Nitrogen Released from Environmental Black Carbon

Biomass combustion results in the formation and wide distribution of black carbon (BC) in soils, wherein the dissolved fractions are among the most active components. Although the presence of dissolved black nitrogen (DBN) in BC has been identified, its environmental behavior and implication are not understood. This study investigated the photochemical transformation and catalytic activity of DBN under simulated solar irradiation. DBN is more easily transformed than dissolved BC due to its photoactive heteroaromatic N structure, and the half-life of DBN produced at 500 °C (8.6 h) is two times shorter than that of the dissolved BC counterpart (23 h). Meanwhile, solar irradiation is favorable for the homoaggregation of DBN. During irradiation, DBN generates not only reactive oxygen species (e.g., ¹O₂, O₂^-, and ^•OH) but also reactive nitrogen species (mainly ^•ON), which account for its higher photocatalytic degradation of bisphenol A than dissolved BC. These findings shed new light on the impact of heteroatoms on the phototransformation and activity of BC as well as cycling of N in terrestrial systems.

Probing Activity Enhancement of Photothermal Catalyst under Near-Infrared Irradiation

Exploring highly efficient catalysts with excellent photothermal conversion and further unveiling their catalytic mechanism are of significant importance for photothermal catalysis technologies, but there remain grand challenges to these activities. Herein, we fabricate a nest-like photothermal nanocatalyst with Pd decorated on a N-doped carbon functionalized Bi₂S₃ nanosphere (Bi₂S₃@NC@Pd). Given its well-dispersed ultrafine Pd nanoparticles and the excellent photothermal heating ability of support material, the Bi₂S₃@NC@Pd composite exhibits a superior activity and photothermal conversion property to commercial Pd/C catalyst for hydrogenation of organic dyes upon exposure to near-infrared (NIR) light irradiation. In addition, the photothermal effect (temperature rise) and activity enhancement of the heterogeneous catalysis system are further probed by comparing the reaction rate with and without the NIR light irradiation. Furthermore, the catalytic behaviors of the Bi₂S₃@NC@Pd catalyst under conventional and photothermal heating are investigated at the same reaction temperature. This work not only improves our fundamental understanding of the catalytic behavior in heterogeneous liquid-solid reaction systems under near-infrared irradiation but also may promote the design of catalysts with photothermally promoted activity.

Diyne-linked and fully π-conjugated polymetalloporphyrin nanosheets for outstanding heterogeneous catalysis

Two-dimensional, ultrathin, robust, and fully π-conjugated organic nanomaterials are highly desirable for application in various fields due to their unique photoelectric characteristics and great number of exposed active sites. However, such matters combining excellent stability, full π-conjugation and adjustability are rare, which has become a bottleneck for their practical application. Herein, we present a novel kind of diyne-linked polymetalloporphyrin nanosheet featuring permanent porosity and full π-conjugation, which exhibits a high-aspect-ratio, outstanding stability and convenient tailoring for electronic structures. Importantly, the novel nanosheets with monodisperse nickel atoms were found to be outstanding heterogeneous catalyst with unprecedented catalytic activity and selectivity for 4-nitrophenol reduction to 4-aminophenol under mild conditions. The findings recommend that diyne-linked polymetalloporphyrin nanosheets may offer new platforms for the conversion of photoelectricity and energy in the future.

Pd Nanoparticle-Decorated 3D-Printed Hierarchically Porous TiO2 Scaffolds for the Efficient Reduction of a Highly Concentrated 4-Nitrophenol Solution

The large amount of 4-nitrophenol (4-NP) wastewater produced by the chemical industry has received increased concern over the growing risk of environmental pollution. The ability to catalyze the reduction of highly concentrated 4-NP wastewater is highly desirable for the practical treatment of industrial wastewater, yet it remains a significant challenge. Herein, we report Pd nanoparticle-decorated 3D-printed hierarchically porous TiO₂ scaffolds (Pd/TiO₂ scaffolds) for the efficient reduction of highly concentrated 4-NP wastewater (2 g·L^-1, ∼14.38 mM). The millimeter-sized interconnected channels in the scaffolds are conducive to rapid mass and ion transportation; meanwhile, the abundant micrometer- and nanometer-sized pores on the surface of the scaffolds offer adequate anchoring sites for Pd nanoparticles. The turnover frequency of the hierarchically porous Pd/TiO₂ scaffold (16 layers) is up to 2.69 min^-1, which is 1063 times higher than that of the Pd/TiO₂-bulk material with the same size (0.00253 min^-1). Importantly, no obvious deactivation of the catalytic activity is observed even after 20 cycles of catalytic reduction of 4-NP, showing excellent catalytic stability and reusability. Our strategy of loading the nanostructured catalyst on 3D-printable hierarchically porous structures put forward a flexible and versatile approach for boosting the catalytic performance of the catalysts, including catalytic activity, stability, and reusability, which can help promote their practical application in industry.

Graphene-based carbocatalysts for carbon-carbon bond formation

Organic transformations are usually catalyzed by metal-based catalysts. In contrast, metal-free catalysts have attracted considerable attention from the viewpoint of sustainability and safety. Among the studies in metal-free catalysis, graphene-based materials have been introduced in the reactions that are usually catalyzed by transition metal catalysts. This review covers the literature (up to the beginning of April 2020) on the use of graphene and its derivatives as carbocatalysts for C-C bond-forming reactions, which are one of the fundamental reactions in organic syntheses. Besides, mechanistic studies are included for the rational understanding of the catalysis. Graphene has significant potential in the field of metal-free catalysis because of the fine-tunable potential of the structure, high stability and durability, and no metal contamination, making it a next-generation candidate material in catalysis.

Photochemically Synthesized Ruthenium Nanoparticle-Decorated Carbon-Dot Nanochains: An Efficient Catalyst for Synergistic Redox Reactions

Ruthenium nanoparticle (NP)-decorated carbon dots (Ru/C-dots) were fabricated as a potential catalyst in the application of both oxidation and reduction. The photochemical method was used to synthesize Ru/C-dot nanohybrids. The as-prepared Ru/C-dots exhibited a core-shell-based nanochain structure, in which the spherical nature of C-dots further evolved to a layer structure to homogeneously encapsulate Ru NPs. Such Ru/C-dots have excellent catalytic properties, which were demonstrated in the oxidation of flavonoids and concomitantly reduction of inorganic complex and organic dyes, each yielding a high catalytic rate constant. We also proposed an appropriate catalytic mechanism for each reaction. Higher catalytic activity was achieved by the synergistic effect of the encapsulated Ru NPs and the C-dots layer. Further, this nanohybrid was successfully applied to inspect a real aqueous sample. We anticipated that Ru/C-dots nanohybrid may open up a broad platform for the design of efficient multifunctional catalysts.

The duet of surface and radical-based carbocatalysis for oxidative destructions of aqueous contaminants over built-in nanotubes of graphite

Metal-free mesoporous graphitic frameworks with built-in nanotubes (CPGs) were synthesized via facile co-pyrolysis of cyclodextrin and a cobalt salt with subsequent acid pickling to remove the embedded metal species. Due to the high graphitic degree and built-in few-layer nanotubes, the as-synthesized carbonaceous materials possess a higher catalytic ozonation activity than that of the state-of-the-art carbon nanotubes (CNTs) and LaMnO₃ perovskite catalysts for the destruction of different aqueous contaminants. For recalcitrant oxalic acid removal, 50 mg L^-1 oxalic acid was completely degraded in 20 min. Compared with other nanocarbons, the as-synthesized materials also demonstrated robust structural stability and reusability. The electron paramagnetic resonance (EPR) and selective radical quenching tests revealed that the destruction of the aqueous organics predominantly relied on surface-adsorbed complexes (O*_ad and O₂*) from activated ozone molecules. Owing to the occurrence of this surface oxidation pathway, the compatibility of the CPGs/O₃ system was significantly enhanced for treatment of real wastewater, where the inorganic anions and organic natural organic matter would inhibit radical oxidation as radical scavengers. Furthermore, by employing organics with different ionization potentials (IPs) as the target pollutants, the CPGs/O₃ system was discovered to obtain a high oxidation potential.

Exfoliation and stabilization mechanism of graphene in carbon dioxide expanded organic solvents: molecular dynamics simulations

CO₂ expanded organic solvents possess significant advantages in liquid-phase exfoliation to obtain monolayer/few-layer graphene from graphite. Further insights into the mechanism of graphene exfoliation in such solvents are essential to explore liquid-phase dispersion of graphene as a more potent alternative to chemical vapor deposition. In this study, dynamic processes of exfoliation and stabilization of graphene in CO₂-N,N-dimethylformamide (DMF), CO₂-N-methylpyrrolidone (NMP), CO₂-dimethyl sulfoxide (DMSO), and CO₂-ethanol (EtOH) were investigated using molecular dynamics simulations. The origin of the effect of each solvent on graphene exfoliation was analyzed quantitatively through potential mean force simulations. It has been found that the organic solvent in a CO₂ expanded solvent should be chosen with proper surface tension, and there exist two different graphene exfoliation processes in the effective solvents, which can be described as "burger dissociation" and "extrusion-taking away" processes, respectively. In the former process, a characteristic "super-burger-like" conformation with a semi-exfoliated structure was formed, which was the deciding factor to obtain high ratio of monolayer/few-layer graphene in dispersion product. A theoretical explanation has also been provided at the molecular level to the earlier experimental phenomena. A predicted simulation of the CO₂-3,3'-iminobis(N,N-dimethylpropylamine) (DMPA) system is also calculated. This investigation helps to avoid incompatible CO₂ expanded organic solvents employed in the experimental studies and provides theoretical clues to understand the mechanism of exfoliation and stabilization of graphene in such solvents.

Recent Advances in Carbon-Based Metal-Free Electrocatalysts

Precious noble metals (such as Pt, Ir) and nonprecious transition metals (e.g., Fe, Co), including their compounds (e.g., oxides, nitrides), have been widely investigated as efficient catalysts for energy conversion, energy storage, important chemical productions, and many industrial processes. However, they often suffer from high cost, low selectivity, poor durability, and susceptibility to gas poisoning with adverse environmental issues. As a low-cost alternative, the first carbon-based metal-free catalyst (C-MFC based on N-doped carbon nanotubes) was discovered in 2009. Since then, various C-MFCs have been demonstrated to show similar or even better catalytic performance than their metal-based counterparts, attractive energy conversion and storage (e.g., fuel cells, metal-air batteries, water splitting), environmental remediation, and chemical production. Enormous progress has been achieved while the number of publications still rapidly increases every year. Herein, a critical overview of the very recent advances in this rapidly developing field during the last couple of years is presented.

Calixarene-Assisted Pd Nanoparticles in Organic Transformations: Synthesis, Characterization, and Catalytic Applications in Water for C-C Coupling and for the Reduction of Nitroaromatics and Organic Dyes

A new type of ternary hybrid, Pd@MCM-Calix_ox, based on mesoporous silica, calixarene conjugate, and Pd(0) nanoparticles (NPs) was synthesized by sacrificial oxidation of allylic calixarene conjugate eventually functionalized with mesoporous silica without using any external reducing agent. The role of the calix conjugate in the formation of Pd@MCM-Calix_ox has been established. The hybrid, Pd@MCM-Calix_ox, was characterized by different techniques to support the formation of well-dispersed Pd(0) NPs of 12 ± 2 nm size. The catalyst, Pd@MCM-Calix_ox, has been proven to be a resourceful one in water in three different types of reactions, namely, Suzuki C-C cross coupling, reduction of both hydrophilic and hydrophobic nitroaromatic compounds, and reduction and degradation of cationic, anionic, and neutral organic dyes. The catalyst exhibited higher turnover frequencies for all these transformations even when a very low concentration of Pd-based catalyst was used. The Pd@MCM-Calix_ox hybrid catalyst can be recycled several times without experiencing any significant loss in the activity. Also, the regenerated catalyst showed retention of well-spread Pd(0) species even after several catalytic cycles. The tetraallyl calixarene, allylCalix, conjugate acts as a reducing agent, also controls the size, and yields the well-dispersed Pd(0) NPs. The calix conjugate further provides a hydrophobic core in assisting the diffusion of hydrophobic substrates toward catalytic sites.

Mesoporous Carbon and Ceria Nanoparticles Composite Modified Electrode for the Simultaneous Determination of Hydroquinone and Catechol

In this work, a novel material that was based on mesoporous carbon and ceria nanoparticles composite (MC–CeNPs) was synthesized, and a modified electrode was fabricated. When compared with a bare glass electrode, the modified electrode exhibited enhanced electrocatalytic activity towards the simultaneous determination of hydroquinone (HQ) and catechol (CC), which is attributed to the large specific area and fast electron transfer ability of MC–CeNPs. Additionally, it exhibited linear response ranges in the concentrations of 0.5–500 µM and 0.4–320 µM for HQ and CC, with detection limits (S/N = 3) of 0.24 µM and 0.13 µM, respectively. This method also displayed good stability and reproducibility. Furthermore, the modified electrode was applied to the simultaneous determination of HQ and CC in tap and lake water samples, and it exhibited satisfactory recovery levels of 98.5–103.2% and 98–103.4% for HQ and CC, respectively. All of these results indicate that a MC–CeNPs modified electrode could be a candidate for the determination of HQ and CC.

A comparative study of nitrobenzene reduction using model catalysts

A zigzag-type quinone plays an important role in the reduction of nitrobenzene even in the co-existence of other functional groups.

Simple Preparation of Porous Carbon-Supported Ruthenium: Propitious Catalytic Activity in the Reduction of Ferrocyanate(III) and a Cationic Dye

The present study involves the synthesis, characterization, and catalytic application of ruthenium nanoparticles (Ru NPs) supported on plastic-derived carbons (PDCs) synthesized from plastic wastes (soft drink bottles) as an alternative carbon source. PDCs have been further activated with CO₂ and characterized by various analytical techniques. The catalytic activity of Ru@PDC for the reduction of potassium hexacyanoferrate(III), (K₃[Fe(CN)₆]), and new fuchsin (NF) dye by NaBH₄ was performed under mild conditions. The PDCs had spherical morphology with an average size of 0.5 μm, and the Ru NP (5 ± 0.2 nm) loading (4.01 wt %) into the PDC provided high catalytic performance for catalytic reduction of ferrocyanate(III) and NF dye. This catalyst can be recycled more than six times with only a minor loss of its catalytic activity. In addition, the stability and reusability of the Ru@PDC catalyst are also discussed.

Novel perovskite-based composites, La1−xNdxFeO3@activated carbon, as efficient catalysts for the degradation of organic pollutants by heterogeneous electro-Fenton reactions

Perovskites, which have excellent electrocatalytic properties, are promising for use in heterogeneous catalysis. However, the design and development of green and effective electrocatalysts for environmental water treatment remains an arduous challenge. To overcome such difficulties, we present a facile sol–gel method for the design and preparation of a series of perovskite-activated carbon (AC) composites (La_1−xNd_xFeO₃@AC) for the degradation of methyl orange (MO) by heterogeneous electro-Fenton reactions. Furthermore, the as-made La_0.6Nd_0.4FeO₃@AC composite anode had the strongest oxidation ability and stability, with MO wastewater and COD removal rates reaching 99.81% and 96.66% within 10 minutes, respectively. As far as we know, the La_1−xNd_xFeO₃@AC composites can be regarded as a series of the most effective catalysts for the degradation of MO to date.

We present a facile sol–gel method for the design and preparation of a series of perovskite-activated carbon composites (La_1−xNd_xFeO₃@AC) for the degradation of methyl orange.