Effects Of Surface Phenomena Research Articles

(Invited) Insights into the Electrocatalytic Behavior of Mxenes

The continued rise in global energy consumption, along with the associated environmental hazards, pose a significant risk to our society’s infrastructure unless the main source is changed. Electrocatalysis involving hydrogen evolution reaction (HER), nitrogen reduction reaction (NRR), and oxygen reduction reaction (ORR), provide a pathway for energy storage and conversion due to their enhanced environmental friendliness and efficient energy input compared to their thermocatalytic counterparts. Currently, the state-of-the-art electrocatalysts suffer from scarcity and high cost. MXenes, a novel family of two-dimensional (2D) transition metal carbide and nitride materials, show potential as cost-efficient and highly abundant electrocatalysts with limited knowledge on their electrocatalytic mechanisms. This is especially true when considering the often-overlooked nitride family of MXenes. Herein, we investigate the electrocatalytic performance of a Ti2N nitride MXene under different electrocatalytic conditions. The effect of surface phenomena is investigated through manipulation of the surface passivation layer, as evidenced by Raman and Fourier-transform infrared (FTIR) spectroscopies, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Successful decoupling of the bulk and surface phenomena is achieved through Raman laser power attenuation. Under acidic medium, the surface reactivity towards HER is poor but the bulk reactivity for NRR is favored, making it an optimal NRR catalyst. Under alkaline medium, the surface reactivity of the pristine Ti2N MXene for ORR is high, but also leads to surface passivation and thus hinders the electrocatalytic activity. Overall, these results provide fundamental insights into future optimization strategies of the Ti2N nitride MXene, along with other MXene electrocatalysts, towards electrocatalytic applications.

INTERAÇÕES ENTRE PLUVIOSIDADE E A INTENSIFICAÇÃO DE PROCESSOS GEOMORFOLÓGICOS EM BACIAS HIDROGRÁFICAS URBANAS: UM ESTUDO APLICADO NAS BACIAS DO RIO GRANDE E RIO ANIL NO MUNICÍPIO DO RIO DE JANEIRO

Nas áreas urbanas, eventos pluviais extremos podem desencadear processos erosivos e hidrológicos catastróficos quando associados a formas de uso e ocupação desordenadas. Com o intuito de corroborar essa afirmativa, este trabalho teve como objetivo analisar as condições pluviométricas e o histórico de eventos extremos que causaram movimentos de massa e inundações nas bacias urbanas do Rio Grande e Rio Anil, no município do Rio de Janeiro. Os resultados demostraram que a seletividade espacial das políticas de planejamento urbano aliada a alta pluviosidade regional tem intensificado a magnitude e os efeitos dos fenômenos de superfície nas bacias estudadas, aumentando os riscos de desastres as populações vulneráveis.

Generalized law of multiphase filtration and new effects of surface phenomena at two-phase flows in a porous medium

The generalized law of multiphase filtration, which explicitly takes into account the viscous interaction between fluids, capillary and gravitational effects, is analyzed. A special case is considered – a two-phase filtration flow as the basis of the technology of oil reservoirs flooding. A method for determining new material functions – «coupling» phase permeabilities, and their quantitative contribution to the field development indicators is given. A new effect of the dependence of capillary forces on the direction of flow in anisotropic media has been revealed.

On the Influence of Surface Phenomena Upon Charge Transport in Te‐Based Glassy Semiconductors

The effect of surface phenomena caused by adsorption of NO2, CO2, and H2O vapor on the charge transport in thin films of chalcogenide glassy semiconductors (ChGS) of the As2S3Ge8–Te system has been studied. The investigations have been carried out by measuring the dynamic conductivity of these films in a large (5 to 107 Hz) frequency range, in both dry air and its mixture with controlled concentrations of the above mentioned gases at different temperatures. In addition to this, the temperature dependence of DC conductivity has also been measured for an unambiguous interpretation of the results. It is shown that depending on material's composition, the AC conductivity in dry air can either be frequency independent across the full range or be frequency independent until ≈104 Hz, with increasing σ(ω) ≈ ωn (n ≈ 0.7) at higher frequencies. This behavior demonstrates that for these glassy films there is a competition of several transport mechanisms, so that depending on frequency at normal temperatures the charge is carried: by free holes or by tunneling between localized states at either valence band edge or those near the Fermi level. An estimation has been made for the density of states at the Fermi level of As2S3Ge8Te13 that appears to be N(EF) ≈ 1.3 × 1021 eV−1 cm−3. Changes of environmental conditions either in air humidification or application of even very small (ppm) concentration of NO2 dramatically influence the spectra of dynamic conductivity that, on the other hand, remain nearly unaffected upon CO2 vapor application. This is evidence that for some chalcogenide materials the surface phenomena disturb the energetic distribution of states adjacent to surface, changing the transport mechanisms.

Effect of Surface Phenomena on Evaporation and Condensation of Water Systems

Experimental results for the dynamic surface tension, surface electrization, and for the rate of evaporation (condensation) of water systems are presented.

Effect of surface phenomena on target destruction by a multiple impact of solids

An explanation is offered for elevated effectiveness of penetration of a group of solids into solid targets with a moderate velocity of a multiple impact.

SURFACE PHENOMENA IN THE HYDRODYNAMICS OF AN INCOMPRESSIBLE FLUID

By taking as an example the outflow of an incompressible fluid through a hole with small geometric parameters under the conditions of supersmall pressures, we attempted to evaluate the effect of surface phenomena on its flow by the similarity method. The Navier–Stokes differential equation was supplemented by parameters allowing for the effect of surface forces. The modified Navier–Stokes equation was subjected to similarity conversion. This yielded a dimensionless group that includes the whole range of variable parameters affecting the fluid flow, namely, the generalized criterion Pv. The graphic dependence of the coefficient of the fluid flow rate on the generalized criterion Pv is presented on the basis of experimental data.

On the chaotic behaviour induced by surface phenomena in some general relativistic stellar models

The effects of surface phenomena on the evolution of the boundary of some general relativistic compact objects are analyzed. In particular it is shown that for a subfamily of these objects which expand permanently in the absence of surface phenomena, the presence of arbitrarily small surface tension leads to bounded configurations.

Surface Effects in Ecotoxicology

One of the basic approaches to the disposal of pollutants is to dilute and disperse them. Frequently, however, biological systems concentrate and confine these same materials especially if they are non-metabolizable. Studying the processes whereby this occurs ought to be one of the components of ecotoxicology. I shall consider three aspects of these processes. These are: 1 The considerable value of radioisotopes as tools for tracing ecological events. 2 The effects of surface phenomena in dictating the distribution of toxicants in the environment. 3 The way that the properties of toxic substances can be used to reveal new features of biological systems.

Effect of surface phenomena in solids on surface acoustic waves

A review of the modern status of the theory of surface acoustic waves in solids with accounting the surface effects is presented. The main approaches are discussed to the determination of surface parameters: surface tension, surface elasticity, and surface mass density. The careful derivation of non-classical boundary conditions describing the influence of surface phenomena is given. One of the topics for discussion is the specification in boundary conditions, which is due to the modes of description of the prestressed subsurface layer. The effect of surface phenomena on the properties of Rayleigh surface waves is analyzed in comparison with the results of classical approaches to the waves in layered media. Shear surface acoustic waves caused by surface effects are also considered. One of the problems to discuss is the comparison of the phenomenological or semiphenomenological results with the results followed from lattice dynamics theories. The analysis is presented on the influence of surface phenomena on the reflection of bulk acoustic waves. Some special cases are described, in which the role of surface phenomena seems to be the most significant.

The effect of surface phenomena on a solvent extraction process

The effect of surface phenomena on a solvent extraction process