Development of Magnetizable, Nickel-Ferrite-Decorated Carbon Nanocomposites as Hydrogenation Catalyst for Aniline Synthesis

Catalysts with magnetic properties can be easily recovered from the reaction medium without loss by using a magnetic field, which highly improves their applicability. To design such systems, we have successfully combined the magnetic properties of nickel ferrite nanoparticles with the positive properties of carbon-based catalyst supports. Amine-functionalized NiFe2O4 nanoparticles were deposited on the surfaces of nitrogen-doped bamboo-like carbon nanotubes (N-BCNT) and carbon nanolayers (CNL) by using a coprecipitation process. The magnetizable catalyst supports were decorated by Pd nanoparticles, and their catalytic activity was tested through the hydrogenation of nitrobenzene (NB). By using the prepared catalysts, high nitrobenzene conversion (100% for 120 min at 333 K) and a high aniline yield (99%) were achieved. The Pd/NiFe2O4-CNL catalyst was remarkable in terms of stability during the reuse tests due to the strong interaction formed between the catalytically active metal and its support (the activity was retained during four cycles of 120 min at 333 K). Furthermore, despite the long-lasting mechanical stress, no significant palladium loss (only 0.08 wt%) was detected.

Cerium Oxide Nanoparticles Confined in Doped Mesoporous Carbons: A Strategy to Produce Catalysts for Imine Synthesis

A group of (doped N or P) carbons were synthesized using soluble starch as a carbon precursor. Further, ceria nanoparticles (NPs) were confined into these (doped) carbon materials. The obtained solids were characterized by various techniques such as N2 physisorption, XRD, TEM, SEM, XPS, and XAS. These materials were used as catalysts for the oxidative coupling between benzyl alcohol and aniline as the model reaction. Ceria immobilized on mesoporous-doped carbon shows higher activity than the other materials, benchmark catalysts, and most of the previously reported catalysts. The control of the ceria NP size, the presence of Ce3+ cations, and an increment in the disorder in the ceria NP structure caused by a support-ceria interaction could increase the number of oxygen vacancies and improve its catalytic performance. CN-meso/CeO2 was also used as the catalyst for a rich scope of substrates, such as substituted aromatic alcohols, linear alcohols, and different types of amines. The influence of various reaction parameters (substrate content, reaction temperature, and catalyst content) on the activity of this catalyst was also checked.

New Insights into N-Doped Porous Carbons as Both Heterogeneous Catalysts and Catalyst Supports: Opportunities for the Catalytic Synthesis of Valuable Compounds

Among the vast class of porous carbon materials, N-doped porous carbons have emerged as promising materials in catalysis due to their unique properties. The introduction of nitrogen into the carbonaceous matrix can lead to the creation of new sites on the carbon surface, often associated with pyridinic or pyrrolic nitrogen functionalities, which can facilitate various catalytic reactions with increased selectivity. Furthermore, the presence of N dopants exerts a significant influence on the properties of the supported metal or metal oxide nanoparticles, including the metal dispersion, interactions between the metal and support, and stability of the metal nanoparticles. These effects play a crucial role in enhancing the catalytic performance of the N-doped carbon-supported catalysts. Thus, N-doped carbons and metals supported on N-doped carbons have been revealed to be interesting heterogeneous catalysts for relevant synthesis processes of valuable compounds. This review presents a concise overview of various methods employed to produce N-doped porous carbons with distinct structures, starting from diverse precursors, and showcases their potential in various catalytic processes, particularly in fine chemical synthesis.

A new molecularly imprinted polymer electrochemical sensor based on CuCo2 O4 /N-doped CNTs/P-doped GO nanocomposite for detection of 25-hydroxyvitamin D3 in serum samples

25-Hydroxyvitamin D₃ as a main circulating metabolite of vitamin D is usually measured in serum to evaluate the vitamin D status of humans. So, developing an accessible, fast response, sensitive, and selective detection method for 25-hydroxyvitamin D₃ is highly important. In this study, we designed a sensitive and selective electrochemical sensor based on the modification of glassy carbon electrode by nanocomposite of CuCo₂ O₄ /nitrogen-doped carbon nanotubes and phosphorus-doped graphene oxide. Then 25-hydroxyvitamin D₃ -imprinted polypyrrole was coated on the electrode surface through electropolymerization. Moreover, ferricyanide was used as a mediator for the creation of a readable signal, which was considerably decreased after rebinding of 25-hydroxyvitamin D₃ on the electrode. The proposed sensor successfully detected 25-hydroxyvitamin D₃ in the range of 0.002-10 μM, with a detection limit of 0.38 nM, which was highly lower than deficiency concentration (20 ng/ml; 49.92 nM). Finally, the proposed sensor was checked for detection of 25-hydroxyvitamin D3 in serum samples with recovery in the range of 80%-106.42%. The results demonstrated the applicability of the designed sensor for the detection of 25-hydroxyvitamin D₃ in biological samples.

Photocatalytic H2 production and degradation of aqueous 2-chlorophenol over B/N-graphene-coated Cu0/TiO2: A DFT, experimental and mechanistic investigation

Energy and environmental challenges are global concerns that scientists are interested in alleviating. It is on this premise that we prepared boron/nitrogen graphene-coated Cu0/TiO2 (B/N-graphene-coated Cu/TiO2) photocatalyst of varying B:N ratios with dual functionality of H2 production and 2-Chlorophenol (2-CP) degradation. In-situ coating of Cu0 with B/N-graphene is achieved via solvothermal synthesis and calcination under an inert atmosphere. All B/N-graphene-coated Cu/TiO2 exhibit higher photonic efficiencies (5.68%-7.06% at 300 < λ < 400 nm) towards H2 production than bare TiO2 (0.25% at 300 < λ < 400 nm). Varying the B:N ratio in graphene influences the efficiency of H2 generation. A B:N ratio of 0.08 yields the most active composite exhibiting a photonic efficiency of 7.06% towards H2 evolution and a degradation rate of 4.07 × 10-2 min-1 towards 2-chlorophenol (2-CP). Density functional theory (DFT) investigations determine that B-doping (p-type) enhances graphene stability on Cu0 while N-doping (n-type) increases the reduction potential of Cu0 relative to H+ reduction potential. X-ray photoelectron spectroscopy reveals that increasing the B:N ratio increases p-type BC2O while decreasing n-type pyridinic-N in graphene thus altering the interlayer electron density. Isotopic labelling experiments determine water reduction as the main mechanism by which H2 is produced over B/N-graphene-coated Cu/TiO2. The reactive species involved in the degradation of 2-CP are holes (h+), hydroxyl radical (OH•), and O2•-, of which superoxide (O2•-) plays the major role. This work displays B/N -graphene-coated Cu/TiO2 as a potential photocatalyst for large-scale H2 production and 2-CP degradation.

A Defective Nanotube Molecule of C552 H496 N24 with Pyridinic and Pyrrolic Nitrogen Atoms

A 3-nm molecule comprising a cylindrical core and cross-shaped rims was designed and synthesized by developing a modular synthetic route. By using a cyclic precursor from previous studies as a starting material, multiple carbazole units were installed at the rims of the defective cylinder. The defective cylinder was synthetically doped with two types of nitrogen atoms, that is, pyridinic and pyrrolic nitrogen atoms, which resulted in solvatochromic shifts in fluorescence by charge-transfer interactions. The structure of the large, C₅₅₂ H₄₉₆ N₂₄ molecule was fully disclosed by crystallographic analyses, and the unique helical arrangement of nitrogen-doped cylinders in the crystal was revealed.

Pd Catalysts Supported on Bamboo-Like Nitrogen-Doped Carbon Nanotubes for Hydrogen Production

Bamboo-like nitrogen-doped carbon nanotubes (N-CNTs) were used to synthesize supported palladium catalysts (0.2–2 wt.%) for hydrogen production via gas phase formic acid decomposition. The beneficial role of nitrogen centers of N-CNTs in the formation of active isolated palladium ions and dispersed palladium nanoparticles was demonstrated. It was shown that although the surface layers of N-CNTs are enriched with graphitic nitrogen, palladium first interacts with accessible pyridinic centers of N-CNTs to form stable isolated palladium ions. The activity of Pd/N-CNTs catalysts is determined by the ionic capacity of N-CNTs and dispersion of metallic nanoparticles stabilized on the nitrogen centers. The maximum activity was observed for the 0.2% Pd/N-CNTs catalyst consisting of isolated palladium ions. A ten-fold increase in the concentration of supported palladium increased the contribution of metallic nanoparticles with a mean size of 1.3 nm and decreased the reaction rate by only a factor of 1.4.

Nitrogen/Carbon-Coated Zero-Valent Copper as Highly Efficient Co-catalysts for TiO2 Applied in Photocatalytic and Photoelectrocatalytic Hydrogen Production

Zero-valent copper (Cu⁰) is a promising co-catalyst in semiconductor-based photocatalysis as it is inexpensive and exhibits electronic properties similar to those of Ag and Au. However, its practical application in photocatalytic hydrogen production is limited by its susceptibility to oxidation, forming less active Cu species. Herein, we have carried out in situ encapsulation of Cu⁰ nanoparticles with N-graphitic carbon layers (14.4% N) to stabilize Cu⁰ nanoparticles (N/C-coated Cu) and improve the electronic communication with a TiO₂ photocatalyst. A facile solvothermal procedure is used to coat the Cu⁰ nanoparticles at 200 °C, while graphitization is achieved by calcination at 550 °C under an inert atmosphere. The resultant N/C-coated Cu/TiO₂ composites outperform the uncoated Cu counterparts, exhibiting a 27-fold enhancement of the hydrogen evolution rate compared to TiO₂ and achieving a rate of 19.03 mmol g^-1 h^-1 under UV-vis irradiation. Likewise, the N/C-coated Cu co-catalyst exhibits a less negative onset potential of -0.05 V toward hydrogen evolution compared to uncoated Cu (ca. -0.30 V). This superior activity is attributed to coating Cu⁰ with N/C, which enhances the stability, electronic communication with TiO₂, conductivity, and interfacial charge transfer processes. The reported synthetic approach is simple and scalable, yielding an efficient and affordable Cu⁰ co-catalyst for TiO₂.

Göndör Z, Pekker P, Kristály F, Szőri M, Rágyanszki A, Viskolcz B, Fiser B, Vanyorek L. Fine-tuning the catalytic activity by applying nitrogen-doped carbon nanotubes as catalyst supports for the hydrogenation of olefins

Nitrogen-free multi-wall carbon nanotubes (MWCNTs) and N-doped bamboo-like carbon nanotubes (BCNTs) were synthesized by using catalytic vapor deposition (CVD) and used as catalyst support materials. Pd, Rh, Ru, and Ir have been deposited onto the nanotubes to achieve metal/nanotube catalysts. The catalytic activity of the samples was fine-tuned by changing the type of support. BCNT supported Pd and Rh (Pd/BCNT, Rh/MWCNT) catalysts were found to be the most active for liquid phase hydrogenation of octadecene amongst these samples. The initial olefin hydrogenation rate of the Pd/BCNT sample was slightly higher than the corresponding MWCNT-supported catalyst. Based on the hydrogenation reaction, the performance of these catalyst had been ranked as follows: Pd/BCNT ≈ Rh/MWCNT > Pd/MWCNT > Rh/BCNT >  > Ir/MWCNT > Ru/BCNT > Ir/BCNT > Ru/MWCNT. The structural properties of chemisorbed Pd on MWCNT and N- BCNT were also characterized by means of computational chemical methods in order to shed some light on the nature of metal binding properties of N-doped and undoped surfaces. The calculations shown preference towards the edges of the surfaces which is in good agreement with the experimental findings.

Ultrasonically aided selective stabilization of pyrrolic type nitrogen by one pot nitrogen doped and hydrothermally reduced Graphene oxide/Titania nanocomposite (N-TiO2/N-RGO) for H2 production

Herein, we report the simultaneous doping of nitrogen on TiO₂ and reduced graphene oxide (N-TiO₂/N-RGO) with exclusive stabilization of pyrrolic type nitrogen on RGO network by ultrasonic conditions followed by hydrothermal method for efficient photocatalytic H₂ production. Interestingly, during synthesis of N-TiO₂/N-RGO composite, pyrrolic type nitrogen in RGO has been exclusively stabilized as confirmed by XPS analysis. The exclusive stabilization of pyrrolic nitrogen changed the optical and electronic properties of N-TiO₂/N-RGO nanocomposites by giving two π-electrons to the system for extended conjugation, which enhanced the optical absorption and charge carrier separation efficiency as confirmed by UV-Vis DRS and PL studies. Notably, N-TiO₂/N-RGO nanocomposite demonstrated. This enhanced photocatalytic activity can be ascribed to synergetic action of N-TiO₂ and N-RGO in optical and photogenerated charge carrier separation. Moreover, the plausible mechanism for exclusive stabilization of pyrrolic type nitrogen and enhanced photocatalytic activity were also proposed.

Multiple nitrogen functionalized magnetic nanoparticles as an efficient adsorbent: synthesis, kinetics, isotherm and thermodynamic studies for the removal of rhodamine B from aqueous solution

The continuous demand for clean and affordable water needed for the survival of man is now a major challenge globally. Therefore, the treatment of wastewater generated from printing, textile and dyeing industries containing soluble dyes like rhodamine B (Rh-B) is of utmost important. This study investigates the efficiency of new multifunctionalized superparamagnetic nanoparticles (MNP-Tppy) for the removal of cationic Rh-B from aqueous solution. To afford MNP-Tppy, the surface of MNP was covalently functionalized with terpyridine ligand to enable an anionic charge on the adsorbent. The results of characterization including Brunauer-Emmett-Teller (BET) analysis, thermal gravimetric analysis (TGA), vibrating sample magnetometer (VSM), scanning electron microscope (SEM) and fourier transform infra–red spectroscopy (FTIR) indicate that this superparamagnetic nanoparticle functionalized with multiple nitrogen atoms was successfully synthesized. Adsorption experiments involving the effect of pH, time, temperature, adsorbent dose and adsorbate concentration show that the maximum adsorption of Rh-B using MNP-Tppy was observed at pH 9 and removal was observed to increase as solution pH increases. Similarly, time variation shows that adsorbate removal increases as adsorption time increases until the removal attained equilibrium at 15 min. Kinetic studies conducted among four kinetic models using the data obtained from effect of time indicate that the adsorption process can best be described by the pseudo-second order model. Isotherm studies conducted at three different temperatures revealed that Langmuir isotherm model fitted well for the equilibrium data with q_m value of 113.64 mg g⁻¹ and thermodynamic studies showed that the adsorption process involving the removal of Rh-B from aqueous solution by MNP-Tppy is spontaneous, endothermic and realistic in nature. Lastly, Reusability experiments indicate that MNP-Tppy can be regenerated and re-used.

Robust ultrafine ruthenium nanoparticles enabled by covalent organic gel precursor for selective reduction of nitrobenzene in water

Metal nanoparticles (NPs) supported on nitrogen-doped porous carbon (NPC) are one type of promising heterogeneous catalysts. The tuning and understanding of metal-support interactions are crucial for the design and synthesis of highly durable and efficient heterogeneous catalytic systems. Here, we present an effective strategy to integrate ultrafine metal NPs into NPC via utilizing a covalent organic gel (COG) as the precursor for the first time. The ruthenium (Ru) NPs were uniformly dispersed in NPCs with the average size as low as 1.90 ± 0.4 nm. Irrespective of their ultrafine size, Ru NPs showed unprecedented stability and recyclability in Ru-catalyzed reduction of nitrobenzene and were greatly superior to commercial Ru/C and NPC-supported Ru NPs synthesized by the traditional post-loading method. This synthetic strategy can be extended to the synthesis of other metal or alloy NPs for a variety of advanced applications.

Surface-Group-Oriented, Condensation Cyclization-Driven, Nitrogen-Doping Strategy for the Preparation of a Nitrogen-Species-Tunable, Carbon-Material-Supported Pd Catalyst

A nitrogen-carbon framework with the thickness of several molecules was fabricated through a straightforward nitrogen-doping strategy, in which specially designed surface-oxygen-containing groups (SOGs) first introduced onto the porous carbon support were used to guide the generation of a surface-nitrogen-containing structure through condensation reactions between SOGs and the amidogen group of organic amines under hydrothermal conditions. The results indicate that different kinds of SOGs generate different types and abundances of N species. The CO-releasing groups are apt to form a high proportion of amino groups, whereas the CO2-releasing groups, especially carboxyl and lactones, are mainly transformed into pyrrolic-type nitrogen. In the framework with dominant pyrrolic-type nitrogen, an electron-rich Pd activated site composed of Pd, pyrrolic-type N and C is built, in which electron transfer occurs from N to C and Pd atoms. This activated site contributes to the formation of electron-rich activated hydrogen and desorption of p-chloroaniline, which work together to achieve the superior selectivity about 99.90 % of p-chloroaniline and the excellent reusable performance. This strategy not only provides low-cost, nitrogen-doped carbon materials, but also develops a new method for the fabrication of different kinds of nitrogen species structures.

Generation of radical species in CVD grown pristine and N-doped solid carbon spheres using H2 and Ar as carrier gases

A mechanism showing the role of carrier gas on the N-configuration of the post-N-doped CSs synthesized in the presence of (a) H₂ and (b) Ar, respectively.

Stable and Inert Cobalt Catalysts for Highly Selective and Practical Hydrogenation of C≡N and C═O Bonds

Novel heterogeneous cobalt-based catalysts have been prepared by pyrolysis of cobalt complexes with nitrogen ligands on different inorganic supports. The activity and selectivity of the resulting materials in the hydrogenation of nitriles and carbonyl compounds is strongly influenced by the modification of the support and the nitrogen-containing ligand. The optimal catalyst system ([Co(OAc)2/Phen@α-Al2O3]-800 = Cat. E) allows for efficient reduction of both aromatic and aliphatic nitriles including industrially relevant dinitriles to primary amines under mild conditions. The generality and practicability of this system is further demonstrated in the hydrogenation of diverse aliphatic, aromatic, and heterocyclic ketones as well as aldehydes, which are readily reduced to the corresponding alcohols.

Probing oxygen reduction and oxygen evolution reactions on bifunctional non-precious metal catalysts for metal–air batteries

Increase in surface coverage by oxygen reduction reaction intermediates with increase in overpotential impeding diffusion of oxygen to the electrode surface.

Nitrogen-functionalised carbon nanotubes as a novel adsorbent for the removal of Cu(ii) from aqueous solution

Nitrogen-functionalized multiwalled carbon nanotubes synthesized were effective and efficient for the removal of Cu²⁺ from aqueous solutions.

Metal-supported carbon-based materials: opportunities and challenges in the synthesis of valuable products

We summarize relevant applications and limitations of metal-supported carbons and nanocarbons in the synthesis of valuable products and the recent advances in this field.