Pyridinic Nitrogen-Doped Graphene Nanoshells Boost the Catalytic Efficiency of Palladium Nanoparticles for the N-Allylation Reaction

Nitrogen-Doped Graphene: The Influence of Doping Level on the Charge-Transfer Resistance and Apparent Heterogeneous Electron Transfer Rate

Three nitrogen-doped graphene samples were synthesized by the hydrothermal method using urea as doping/reducing agent for graphene oxide (GO), previously dispersed in water. The mixture was poured into an autoclave and placed in the oven at 160 °C for 3, 8 and 12 h. The samples were correspondingly denoted NGr-1, NGr-2 and NGr-3. The effect of the reaction time on the morphology, structure and electrochemical properties of the resulting materials was thoroughly investigated using scanning electron microscopy (SEM) Raman spectroscopy, X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), elemental analysis, Cyclic Voltammetry (CV) and electrochemical impedance spectroscopy (EIS). For NGr-1 and NGr-2, the nitrogen concentration obtained from elemental analysis was around 6.36 wt%. In the case of NGr-3, a slightly higher concentration of 6.85 wt% was obtained. The electrochemical studies performed with NGr modified electrodes proved that the charge-transfer resistance (Rct) and the apparent heterogeneous electron transfer rate constant (Kapp) depend not only on the nitrogen doping level but also on the type of nitrogen atoms found at the surface (pyrrolic-N, pyridinic-N or graphitic-N). In our case, the NGr-1 sample which has the lowest doping level and the highest concentration of pyrrolic-N among all nitrogen-doped samples exhibits the best electrochemical parameters: a very small Rct (38.3 Ω), a large Kapp (13.9 × 10-2 cm/s) and the best electrochemical response towards 8-hydroxy-2'-deoxyguanosine detection (8-OHdG).

Application of Biochar Derived From Pyrolysis of Waste Fiberboard on Tetracycline Adsorption in Aqueous Solution

In this study, biochars derived from waste fiberboard biomass were applied in tetracycline (TC) removal in aqueous solution. Biochar samples were prepared by slow pyrolysis at 300, 500, and 800°C, and were characterized by ultimate analysis, Fourier transform infrared (FTIR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), etc. The effects of ionic strength (0–1.0 mol/L of NaCl), initial TC concentration (2.5–60 ppm), biochar dosage (1.5–2.5 g/L), and initial pH (2–10) were systemically determined. The results present that biochar prepared at 800°C (BC800) generally possesses the highest aromatization degree and surface area with abundant pyridinic N (N-6) and accordingly shows a better removal efficiency (68.6%) than the other two biochar samples. Adsorption isotherm data were better fitted by the Freundlich model (R² is 0.94) than the Langmuir model (R² is 0.85). Thermodynamic study showed that the adsorption process is endothermic and mainly physical in nature with the values of ΔH⁰ being 48.0 kJ/mol, ΔS⁰ being 157.1 J/mol/K, and ΔG⁰ varying from 1.02 to −2.14 kJ/mol. The graphite-like structure in biochar enables the π-π interactions with a ring structure in the TC molecule, which, together with the N-6 acting as electron donor, is the main driving force of the adsorption process.

Capacitive Sodium-Ion Storage Based on Double-Layered Mesoporous Graphene with High Capacity and Charging/Discharging Rate

Sodium-ion batteries (SIBs) are regarded as an ideal alternative to lithium-ion batteries, but the larger radius of Na⁺ compared with Li⁺ results in lower energy density, shorter cycle life, and sluggish kinetics of SIBs. Therefore, it is of significant importance to explore appropriate Na⁺ storage materials with high capacity and fast Na⁺ transport kinetics. Herein, doublelayered mesoporous graphene nanosheets codoped with oxygen and nitrogen (O,N-MGNSs) were developed as a new cathode material with high Na⁺ storage capacity and fast ion-transport kinetics for SIBs. The codoping of MGNSs with oxygen and nitrogen by in situ chemical vapor deposition endowed them with a hierarchical porous network, robust structures, good conductivity, and abundant functional groups. The O,N-MGNSs could host Na⁺ in two ways: surface adsorption and surface redox reaction, and this endowed them with high Na⁺ storage capacity and fast charging/discharging rates in SIBs. Electrochemical results revealed that the O,N-MGNSs delivered a reversible capacity of 156 mAh g^-1 at a current density of 0.5 A g^-1 (corresponding to a rate of 3 C) between 1.5 and 4.2 V and exhibited a high cycling stability (95 % capacity retention at 1 A g^-1 for more than 1000 cycles).

Palladium decorated on a new dendritic complex with nitrogen ligation grafted to graphene oxide: fabrication, characterization, and catalytic application

Immobilized Pd nanoparticles on a new ligand, namely, tris(pentaethylene-pentamine)triazine supported on graphene oxide (Pd_np-TPEPTA_(L)-GO) was introduced as a novel and robust heterogeneous catalyst for use in C–C bond formation reaction. The Pd_np-TPEPTA_(L)-GO catalyst was synthesized by complexation of Pd with TPEPTA as a ligand with high N-ligation sites that were supported on graphene oxide through 3-chloropropyltrimethoxysilane. The prepared catalyst was characterized using some microscopic and spectroscopic techniques. The TPEPTA_(L)-GO substrate is a 2D heterogeneous catalyst with a high specific surface area and a large amount of N-ligation sites. The Pd_np-TPEPTA_(L)-GO catalyst used in the C–C bond formation reaction between aryl or heteroaryl and phenylboronic acid derivatives was applied towards the synthesis of biaryl units in high isolated yields. Notably, a series of competing experiments were performed to establish the selectivity trends of the presented method. Also, this catalyst system was reusable at least six times without a significant decrease in its catalytic activity.

Immobilized Pd nanoparticles on a new ligand, namely, tris(pentaethylene-pentamine)triazine supported on graphene oxide (Pd_np-TPEPTA_(L)-GO) was introduced as a novel and robust heterogeneous catalyst for use in C–C bond formation reaction.