Electrochemical Properties of Nitrogen and Oxygen Doped Reduced Graphene Oxide

Quantum Simulations and Experimental Insights into Glyphosate Adsorption Using Graphene-Based Nanomaterials

The increasing global demand for food and agrarian development brings to light a dual issue concerning the use of substances that are crucial for increasing productivity yet can be harmful to human health and the environment when misused. Herein, we combine insights from high-level quantum simulations and experimental findings to elucidate the fundamental physicochemical mechanisms behind developing graphene-based nanomaterials for the adsorption of emerging contaminants, with a specific focus on pesticide glyphosate (GLY). We conducted a comprehensive theoretical and experimental investigation of graphene-based supports as promising candidates for detecting, sensing, capturing, and removing GLY applications. By combining ab initio molecular dynamics and density functional theory calculations, we explored several chemical environments encountered by GLY during its interaction with graphene-based substrates, including pristine and punctual defect regions. Our results unveiled distinct interaction behaviors: physisorption in pristine and doped graphene regions, chemisorption leading to molecular dissociation in vacancy-type defect regions, and complex transformations involving the capture of N and O atoms from impurity-adsorbed graphene, resulting in the formation of new GLY-derived compounds. The theoretical findings were substantiated by FTIR and Raman spectroscopy, which proposed a mechanism explaining GLY adsorption in graphene-based nanomaterials. The comprehensive evaluation of adsorption energies and associated properties provides valuable insights into the intricate nature of these interactions, shedding light on potential applications and guiding future experimental investigations of graphene-based nanofilters for water decontamination.

The effect of the pyrolysis temperature and biomass type on the biocarbons characteristics

The conversion of biomass and natural wastes into carbon-based materials for various applications such as catalysts and energy-related materials is a fascinating and sustainable approach emerged during recent years. Precursor nature and characteristics are complex, hence, their effect on the properties of resulting materials is still unclear. In this work, we have investigated the effect of different precursors and pyrolysis temperature on the properties of produced carbon materials and their potential application as negative electrode materials in Li-ion batteries. Three biomasses, lignocellulosic brewery spent grain from a local brewery, catechol-rich lignin and tannins, were selected for investigations. We show that such end-product carbon characteristic as functional and elemental composition, porosity, specific surface area, defectiveness level, and morphology strictly depend on the precursor composition, chemical structure, and pyrolysis temperature. The electrochemical characteristics of produced carbon materials correlate with the characteristics of the produced materials. A higher pyrolysis temperature is shown to be favourable for production of carbon material for the Li-ion battery application in terms of both specific capacity and long-term cycling stability.

Morphology, Energy Level Alignment, and Charge Transfer at the Protoporphyrin IX-Semiconductor Interface

The combination of molecular catalysts and semiconductor substrates in hybrid heterogeneous photo- or electrocatalytic devices could yield synergistic effects that result in enhanced activity and long-term stability. The extent of synergy strongly depends on the electronic interactions and energy level alignment between the molecular states and the valence and conduction band of the substrate. These properties of hybrid interfaces are investigated for a model system composed of protoporphyrin IX (PPIX) as a stand-in for molecular catalysts and a variety of semiconductor substrates. Monolayers of PPIX are deposited using Langmuir-Blodgett deposition. Their morphology is studied in dependence of the deposition surface pressure to achieve a high-quality, dense coverage. By making use of ultraviolet-visible spectroscopy and ultraviolet photoelectron spectroscopy, the band alignment is determined by the vacuum level and incorporates an interface dipole of 0.4 eV independent of the substrate. The HOMO, LUMO, and LUMO+1 levels were determined to be at 5.6, 3.7, and 2.7 eV below the vacuum level, respectively. The quenching of PPIX photoluminescence in dependence of the potential gradient between excited state and electron affinity of the semiconductor substrates is overall in good agreement with electron transfer processes occurring at very fast time scales on the order of femtoseconds. Nevertheless, deviations from this model become apparent for narrower band gap semiconductors, which points to an additional relevance of other processes, such as energy transfer. These findings highlight the importance of matching the semiconductor to the molecular catalyst to prevent undesirable deactivation pathways.

Comparative Study of the Structural Features and Electrochemical Properties of Nitrogen-Containing Multi-Walled Carbon Nanotubes after Ion-Beam Irradiation and Hydrochloric Acid Treatment

Using a set of microscopic, spectroscopic, and electrochemical methods, a detailed study of the interrelation between the structural and electrochemical properties of the as-prepared nitrogen-containing multi-walled carbon nanotubes (N-MWCNTs) and their modified derivatives is carried out. It was found that after treatment of nanotubes with hydrochloric acid, their structure is improved by removing amorphous carbon from the outer layers of N-MWCNTs. On the contrary, ion bombardment leads to the formation of vacancy-type structural defects both on the surface and in the bulk of N-MWCNTs. It is shown that the treated nanotubes have an increased specific capacitance (up to 27 F·g-1) compared to the as-prepared nanotubes (13 F·g-1). This is due to an increase in the redox capacitance. It is associated with the reversible Faraday reactions with the participation of electrochemically active pyridinic and pyrrolic nitrogen inclusions and oxygen-containing functional groups (OCFG). Based on the comparison between cyclic voltammograms of N-MWCNTs treated in HCl and with an ion beam, the peaks on these curves were separated and assigned to specific nitrogen inclusions and OCFGs. It is shown that the rate of redox reactions with the participation of OCFGs is significantly higher than that of reactions with nitrogen inclusions in the pyridinic and pyrrolic forms. Moreover, it was established that treatment of N-MWCNTs in HCl is accompanied by a significant increase in the activity of nitrogen centers, which, in turn, leads to an increase in the rate of redox reactions involving OCFGs. Due to the significant contribution of redox capacitance, the obtained results can be used to develop supercapacitors with increased total specific capacitance.

Recent Progress of Two-Dimensional Materials for Ultrafast Photonics

Owing to their extraordinary physical and chemical properties, two-dimensional (2D) materials have aroused extensive attention and have been widely used in photonic and optoelectronic devices, catalytic reactions, and biomedicine. In particular, 2D materials possess a unique bandgap structure and nonlinear optical properties, which can be used as saturable absorbers in ultrafast lasers. Here, we mainly review the top-down and bottom-up methods for preparing 2D materials, such as graphene, topological insulators, transition metal dichalcogenides, black phosphorus, and MXenes. Then, we focus on the ultrafast applications of 2D materials at the typical operating wavelengths of 1, 1.5, 2, and 3 μm. The key parameters and output performance of ultrafast pulsed lasers based on 2D materials are discussed. Furthermore, an outlook regarding the fabrication methods and the development of 2D materials in ultrafast photonics is also presented.

Nanocomposite Materials Based on Electrochemically Synthesized Graphene Polymers: Molecular Architecture Strategies for Sensor Applications

The use of graphene and its derivatives in the development of electrochemical sensors has been growing in recent decades. Part of this success is due to the excellent characteristics of such materials, such as good electrical and mechanical properties and a large specific surface area. The formation of composites and nanocomposites with these two materials leads to better sensing performance compared to pure graphene and conductive polymers. The increased large specific surface area of the nanocomposites and the synergistic effect between graphene and conducting polymers is responsible for this interesting result. The most widely used methodologies for the synthesis of these materials are still based on chemical routes. However, electrochemical routes have emerged and are gaining space, affording advantages such as low cost and the promising possibility of modulation of the structural characteristics of composites. As a result, application in sensor devices can lead to increased sensitivity and decreased analysis cost. Thus, this review presents the main aspects for the construction of nanomaterials based on graphene oxide and conducting polymers, as well as the recent efforts made to apply this methodology in the development of sensors and biosensors.

Influence of Graphene Oxide on Rheological Parameters of Cement Slurries

In recent years, graphene-based nanomaterials have been increasingly and widely used in numerous industrial sectors. In the drilling industry, graphene oxide in cement slurry has significantly improved the mechanical parameters of cement composites and is a future-proof solution. However, prior to placing it in a borehole ring space, cement slurry must feature appropriate fluidity. Graphene oxide has a significant influence on rheological parameters. Therefore, it is necessary to study graphene oxide’s influence on the rheological parameters of cement slurries. Thus, this paper presents rheological models and the results of studies on rheological parameters. A basic cement slurry and a slurry with a latex addition were used. The latex admixture was applied at concentrations of 0.1%, 0.03%, and 0.06%. In total, studies were carried out for six slurries with graphene oxide and two basic slurries. The obtained results of studies on the slurries with graphene oxide were compared with the control slurry. It was found that the smallest graphene oxide concentration increased slurry value, some rheological parameter values, plastic viscosity, and the flow limit. Surprisingly, a concentration up to 0.03% was an acceptable value, since the increase in plastic viscosity was not excessively high, which allowed the use of cement slurry to seal the hole. Once this value was exceeded, the slurry caused problems at its injection to the borehole.