Absorption Phenomena Research Articles

A rigorous surface renewal model for transient gas absorption with first-order chemical reaction in a stirred liquid

This work presents a rigorous surface renewal model for unsteady-state gas absorption in a stirred batch cell in which the dissolved gas undergoes a first-order chemical reaction with a liquid-phase reagent for the cases of zero and finite gas-phase mass-transfer resistance, with the concentration of dissolved gas in the bulk liquid being a function of time. For oxygen absorption in water containing a reagent (e.g., sodium sulfite), the model predicts that the rates of absorption and dissolved-gas transfer to the bulk liquid have an inverse behavior during the initial moments of absorption after which they level out as steady state is approached, with the former being higher than the latter due to the consumption of dissolved gas by the reaction occurring in the surface elements. In general, predictions of the dissolved oxygen concentration made with the rigorous model compare quite well with those of a much simpler pseudo steady-state model. However, the rigorous surface renewal model gives a finer grained picture of the phenomenon of absorption, i.e., of the rates of absorption and dissolved-gas transfer, especially during the initial moments of absorption. A hybrid model, which uses both the pseudo steady-state and rigorous surface renewal models, is proposed for performing unsteady-state gas absorption calculations.

MATHEMATICAL MODEL OF DETECTION OF SMALL UNMANNED AERIAL VEHICLES USING PASSIVE OPTICAL SYSTEMS

The work is devoted to the solution of an actual scientific task in the field of civil protection, namely, the development of a new model for the prevention of emergency situations of a terrorist nature at the objects of the critical infrastructure of Ukraine, which are protected, by means of timely detection and identification of small unmanned aerial vehicles by active optoelectronic means. Based on the analysis, it was established that one of the trends in the development of terrorist scenarios at protected critical infrastructure facilities is the use of various small manned and unmanned aerial vehicles to carry out terrorist acts. This work is a continuation of the cycle of previous works on the development of a structural and logical model for managing an emergency situation of a terrorist nature at an object of critical infrastructure of Ukraine, which is protected, caused by the appearance of small-sized aerial targets, intended for the development and constant implementation of procedures of an organizational and technical nature to ensure the safety of the object to the guarded object, when small air targets appear. A mathematical model for the detection of signals reflected from small aerial targets using active optical systems using the phenomena of light absorption and scattering in optically transparent media has been developed, which represents a system of four analytical dependencies. Further research will be directed to conducting field experiments, performed using a specially designed laboratory setup, and theoretical calculations of the value of expected target detection activities as part of numerous experiments that should prove the reliability of the results obtained in the work. Identified directions of further research regarding the presented mathematical model of detecting signals reflected from small unmanned aerial vehicles using active optical systems that use the phenomena of absorption and scattering of light in optically transparent media will be directed to conducting full-scale experiments performed using a specially developed laboratory installation and theoretical calculations of the value of expected target detection activities as part of numerous experiments, with the aim of proving the reliability of the results obtained in the work. Keywords: emergency situation, small unmanned aerial vehicle, violator, model, protected object.

A highly efficient deca-band metasurface absorber for diverse microwave applications

We propose a highly efficient, deca-band, and single-layered metasurface absorber (MA) based on the idea of split-ring resonators (SRRs). The unit cell of the proposed MA is a combination of 2 × 2 symmetrically arranged meta-structured designs, each comprising long and short L-shaped SRRs, two concentric semi-circular rings, and two T-shaped conducting strips. The absorption phenomenon of the proposed structure is successfully demonstrated using the standing wave resonance theory (SWRT), detailed current distribution, and the electric field distribution analysis. The thickness of the proposed MA unit cell is 0.96 mm having 1/56, 1/41, 1/35, 1/21, 1/20, 1/18, 1/17, 1/13, and 1/12 respective free-space wavelengths and has compact unit cell dimensions of 0.018λo×0.018λo, where λo corresponds to the lowest absorption frequency. The proposed structure offers absorption peaks of more than 90% at 10 distinct frequencies to demonstrate its applicability in diverse microwave applications. It is shown in simulations and experimentally that the proposed MA is angularly stable up to 70˚and has polarization insensitivity behavior up to 90˚ for both TE and TM polarized waves. A good agreement between simulation and measurement results demonstrates the efficacy of the proposed MA in a wide range of microwave applications.

Magnetic Fe/Fe3C@C Nanoadsorbents for Efficient Cr (VI) Removal

Magnetic carbon nanocomposites (α-Fe/Fe3C@C) synthesized employing fructose and Fe3O4 magnetite nanoparticles as the carbon and iron precursors, respectively, are analyzed and applied for the removal of Cr (VI). Initial citric acid-coated magnetite nanoparticles, obtained through the co-precipitation method, were mixed with fructose (weight ratio 1:2) and thermally treated at different annealing temperatures (Tann = 400, 600, 800, and 1000 °C). The thermal decomposition of the carbon matrix and the Fe3O4 reduction was followed by thermogravimetry (TGA) and Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, Raman spectroscopy, SQUID magnetometry, and N2 adsorption-desorption isotherms. A high annealing temperature (Tann = 800 °C) leads to optimum magnetic adsorbents (high magnetization enabling the magnetic separation of the adsorbent from the aqueous media and large specific surface area to enhance the pollutant adsorption process). Cr (VI) adsorption tests, performed under weak acid environments (pH = 6) and low pollutant concentrations (1 mg/L), confirm the Cr removal ability and reusability after consecutive adsorption cycles. Physical adsorption (pseudo-first-order kinetics model) and multilayer adsorption (Freundlich isotherm model) characterize the Cr (VI) absorption phenomena and support the enhanced adsorption capability of the synthesized nanostructures.

Study of Photocatalytic Degradation and Simultaneous Removal of a Mixture of Pollutant (MB and MG) Dyes: Kinetic and Adsorption Isotherm

Background: The major challenges faced by developing countries are the issues associated with various pollutants, such as dyes, pesticides, heavy metals, etc. Various materials and methods are available for the removal of these pollutants. Major research works have been performed on single pollutants, and rarely any research literature is available for a mixture of pollutants. This is one of the major reasons to carry out our research work in this field. Objectives: This study aimed to develop an efficient ZnO/GO nanocomposite as a photocatalyst, characterize it by PXRD, FT-IR, and TGA, and evaluate its catalytic activity by degradation of MG, MB and a mixture of both Methods: In this study, GO was synthesized by the modified Hummers method. In this method, graphite powder was mixed with sulphuric acid and NaNO3. Then KMnO4 solution was added under continuous stirring. Excess KMnO4 was removed by H2O2 and the colour of the solution turned to be dark yellow. After proper washing and maintaining pH, the resulting material was dried at 60°C for 12h to obtain GO. GO was dispersed in ethanol, and 0.387g Zn(CH3COO)2.2H2O was added to it. The resulting mixture was sonicated, and a solution of NH3 was added very slowly by maintaining the pH of the solution at ~7. The resulting product was dried at 80°C and then calcined at 500 °C for 2.5 h to get ZnO/GO nanocomposite. Results: The photodegradation of MG, MB and a mixture of MG and MB was found to be 92.23%, 35.96%, and 66.22%, respectively, in 4−5 h. The degradation of the dyes was found to follow Second-order kinetics with a multilayer absorption phenomenon. Conclusion: MB showed less degradation as compared to MG, but its photocatalytic activity enhanced after adding MG. This ZnO/GO nanocomposite seems to be a potential candidate to address the challenges associated with multi-pollutants, such as dyes.

Hybrid fractal acoustic metamaterials for low-frequency sound absorber based on cross mixed micro-perforated panel mounted over the fractals structure cavity

The proposed work enumerates a hybrid thin, deep-subwavelength (2 cm) acoustic metamaterials acting as a completely new type of sound absorber, showing multiple broadband sound absorption effects. Based on the fractal distribution of Helmholtz resonator (HRs) structures, integrated with careful design and construct hybrid cross micro-perforated panel (CMPP) that demonstrate broad banding approximately one-octave low-frequency sound absorption behavior. To determine the sound absorption coefficient of this novel type of metamaterial, the equivalent impedance model for the fractal cavity and the micro-perforated Maa’s model for CMPP are both used. We validate these novel material designs through numerical, theoretical, and experimental data. It is demonstrated that the material design possesses superior sound absorption which is primarily due to the frictional losses of the structure imposed on acoustic wave energy. The peaks of different sound absorption phenomena show tunability by adjusting the geometric parameters of the fractal structures like cavity thickness ‘t’, cross perforation diameter of micro perforated panel, etc. The fractal structures and their perforation panel are optimized dimensionally for maximum broadband sound absorption which is estimated numerically. This new kind of fractals cavity integrated with CMPP acoustic metamaterial has many applications as in multiple functional materials with broad-band absorption behavior etc.

Experimental Investigation of the Absorption Behavior of Date Palm Fiber Reinforced Iso-Polyester Composites: Artificial Neuron Network (ANN) Modeling

ABSTRACT The present article attempts to study absorption properties of bio-composites reinforced with date palm fibers. The effect of fiber loading on water absorption at room temperature 25°C was investigated. The weight gain was measured of bio-composites immersed in distilled water, seawater and rainwater, for more than 670 hours, until reaching the saturation with a measurement interval between 24 and 48 hours. To understand absorption phenomenon, scanning electron microscopy was used. Porosity rate was determined using image J software. It was noted the water absorption rate of the bio composites reached 16.20%, 16.33%, 21.94%, 41.99% for seawater, 16.41%, 16.52%, 20.84%, 30.08% for distilled water, and 14.00%, 14.04%, 19.30%, 36.94% for rainwater, respectively. The absorption increases when increasing fiber content. The diffusion coefficient of bio-composites has minimum and maximum values of about 1.94 × 10−6mm2/s and 3.99 × 10−6mm2/s, respectively. Palm fibers are highly porous. The porosity value was higher than 51%. To predict the absorption rate, artificial neural network method was used. The ANN models obtained are very well correlated with the experimental data where the values of the correlation coefficient of the datasets are all beyond 0.99 and the average error value was estimated at 3 × 10−5.

Triphenylamine-based highly active two-photon absorbing chromophores with push-pull systems

Two triphenylamine-based star-type push-pull chromophores (T1, T2) were designed and synthesized. Triphenylamine serves as the central core and acts as an electron-donating group surrounded by electron-withdrawing pentafluorobenzene or N,N-dimethyl substituted tetrafluorobenzene, which are connected by ethylene bridges. Single-crystal X-ray diffraction confirmed the structures and molecular arrangement of two chromophores. The systematic photophysical research of T1 and T2 absorption characteristics was carried out to gain a better understanding of how structure-property relationships affect the observed nonlinear optical absorption phenomenon. Complementary calculations based on density functional theory (DFT) further confirmed the experimental results. Both chromophores exhibited excellent two-photon absorption (TPA) properties in CH2Cl2. Notably, T2 has more remarkable nonlinear optical absorption effects with the TPA cross-section up to 4.24 × 107 GM. By adjusting the electronic structures of the chromophores through introducing pentafluorobenzene or N,N-dimethyl as functional groups with different electron-donating or withdrawing behaviors, the TPA performance of the small organic molecule could be greatly enhanced. These molecular structures with push-pull systems were excellent candidates for different two-photon applications.

Nonlinear optical properties and photoexcited carrier dynamics of MnPS3 nanosheets.

Here, we systematically report on the preparation of high-quality few-layered MnPS3 nanosheets (NSs) by chemical vapor transport (CVT) and mechanical stripping method, and its carrier dynamics and third-order nonlinear optical properties were studied. Using the classical technique of open aperture Z-scan, a typical phenomenon of saturable absorption (SA) was observed at 475 nm, which indicates that the material is expected to be used as a saturable absorber in ultrafast lasers. The typical phenomenon of reverse saturation absorption (RSA) is observed at 800 and 1550 nm, which shows its potential in the field of broadband optical limiting. Compared with graphene, BP, MXene, MoS2 and other typical two-dimensional materials, MnPS3 NSs has a higher modulation depth. Using the non-degenerate transient absorption spectroscopy technology at room temperature, a slower cooling process of thermal carrier of MnPS3 was observed. Moreover, the carrier lifetime can be tuned according to the wavelength. This work is of great significance to the improvement of MnPS3 based devices, and lays a foundation for the application of MnPS3 in short-wavelength photovoltaic cell, photoelectric detection and other fields.

Fabrication and comparison of mechanical and EMI shielding properties of various fibre reinforced multi-layered epoxy composites

The present work deals with the comparison of the various Fibre Reinforced Epoxy Composites (FRECs) for EMI shielding applications. The fabrication of the FRECs was done by simple hand-lay-up method. The composites consisting of silk fibre, glass fibre, carbon fibre with single and double layer and the hybrid of these three fibres. The collation of different FRECs revealed that the properties of the neat epoxy could be improved by the reinforcement of fibres. The double layered composites showed high tensile strength and flexural strength than the single layered composites whereas the EMI shielding property of the both single and double layered composites remain unchanged. Among FRECs, the CFRP-2 composite showed excellent mechanical properties with 24.9 N/mm2 tensile strength and 140.5 N/mm2 flexural strength. Also, the CFRP and hybrid composites exhibited nearly same EMI shielding Effectiveness (SE) value of around −27dB to −29.7 dB in the X-band frequency range. The work imparted the dominance of absorption phenomenon over the reflection in the prepared FRECs. Being insulators, Glass fibre, silk fibre and epoxy, GFRP and SFRP composites showed low EMI SE value. However, the EMI shielding property of these composites can be increased by incorporating conducting and magnetic fillers to the composites. Hence, the FRECs due to its light weight, corrosion resistance and high mechanical properties became the potential candidate for developing EMI shielding material over conventional metals.

A three-band perfect absorber based on a parallelogram metamaterial slab with monolayer MoS2

As a two-dimensional (2D) material, monolayer MoS2 which limits its optical applications has a low absorption efficiency. In this paper, we propose a three-band perfect metamaterial absorber in the visible light range based on monolayer MoS2. The peak absorptivity of the structure at each resonance wavelength is nearly perfect, moreover, the light absorption of monolayer MoS2 is obviously enhanced at the three resonant wavelengths. The dielectric–dielectric–metal structure we designed produces the coupling of Fabry–Perot resonance and high-order diffraction guided-mode resonance at different absorption peaks, which has been proved by the slab waveguide theory. In addition, the multi-modal absorption phenomenon is explained by extracting the equivalent impedance. The results show that we can adjust the absorption peak wavelength by regulating the parameters of the structure. This structure not only provides an idea for enhancing the interaction between light and two-dimensional materials but also has potential applications for optical detection devices.

Fabrication of hydrophilic and hydrophobic membranes inspired by the phenomenon of water absorption and storage of cactus

Water shortage has become one of the most severe practical problems facing humans. Thus, an efficient and economic water-harvesting technology is urgent to develop. In this work, to prepare samples of hydrophilic and hydrophobic bilayer structures, three kinds of hydrophobic polyethylene terephthalate (PET) fibers with different pore diameters were dip coated to fabricate hydrophobic surfaces, which showed different hydrophobic effects. TiO2 was then sprayed onto the hydrophobic surface to form irregular protrusions and to increase surface roughness and surface energy. The distribution amount of TiO2 was controlled by adjusting the spraying distance of TiO2. Finally, ultraviolet irradiation was performed. The light response made the protrusions super hydrophilic and improved the capture of mist and moisture by increasing the surface wettability and Laplace pressure. Water-collection test was performed for samples with different spraying distances irradiated by ultraviolet rays. The spraying distance with the best water-collection efficiency was achieved. The hydrophilic surface (particles) was attached to a hydrophobic membrane, which quickly and effectively captured the mist and converted it to water, thereby easily discharging a large amount of water. This study is expected to promote the development of fogging drainage and alleviate the problem of water shortage.

Influence of LiBr concentration in the generation of superheated vapor for a Hygroscopic Cycle

The novel proprietary Hygroscopic Cycle Technology (HCT) is a power cycle distinguished for using hygroscopic compoundswater mixtures as the working fluid to optimize the condensation process of the turbine exhaust steam by absorption phenomena. Previous works focused on the performance of the condensation/cooling section of the cycle as well as in the main improvements achieved by HCT in comparison to traditional thermal power generation cycles in terms of efficiency and profitability. Nevertheless, the thermodynamic characteristics of the steam generated from hygroscopic-water mixtures in the HCT boiler are yet to be studied. In this article, a theoretical analysis of temperature and pressure conditions of pure water steam generated from different concentrations of LiBr-water mixtures is carried out by using the Engineering Equation Solver (EES) software. Results show that LiBr-H2O mixtures display higher saturation temperatures than pure water, which enables the cycle to directly generate superheated vapor with no need for superheating equipment inside the boiler. This fact further improves the economic advantages previously shown by HCT, since erection, operation and maintenance costs related to the superheating process are avoided.

Broadband 1T-polytype tantalum disulfide saturable absorber for solid-state bulk lasers

1T-polytype tantalum disulfide ( 1 T-TaS 2 ), an emerging strongly correlated material, features a narrow bandgap of 0.2 eV, bridging the gap between zero-bandgap graphene and large-bandgap 2D nonlinear optical (NLO) materials. Combined with its intense light absorption, high carrier concentration, and high mobility, 1 T-TaS 2 shows considerable potential for applications in broadband optoelectronic devices. However, its NLO characteristics and related applications have rarely been explored. Here, 1 T-TaS 2 nanosheets are prepared by chemical vapor deposition. The ultrafast carrier dynamics in the 400–1100 nm range and broadband NLO performance in the 515–2500 nm range are systematically studied using femtosecond lasers. An obvious saturable absorption phenomenon is observed in the visible to IR range. The nonlinear absorption coefficient is measured to be − 22.60 ± 0.52 cm MW − 1 under 1030 nm, which is larger than that of other typical 2D saturable absorber (SA) materials (graphene, black phosphorus, and MoS 2 ) under similar experimental conditions. Based on these findings, using 1 T-TaS 2 as a new SA, passively Q-switched laser operations are successfully performed at 1.06, 1.34, and 1.94 μm. The results highlight the promise of 1 T-TaS 2 for broadband optical modulators and provide a potential candidate material system for mid-IR nonlinear optical applications.

Formation of zircon‐type (Zr,Ti)1−x(Dy)x(SiO4)1−x(PO4)x solid solution and their optical and magnetic characteristics

AbstractThe present study is aimed to tailor the structure of zircon (ZrSiO4) for potential application in hard tissue replacements. In this context, zircon (Zr,Ti)1−x(Dy)x(SiO4)1−x(PO4)x type solid solution has been formed through a simple sol–gel technique. Zircon formation is induced by the Ti4+ substitution, whereas the progressive addition of Dy3+/PO43− led to their accommodation at the resultant lattice sites. The maximum occupancy limit of Dy3+/PO43− is determined as 20 wt.% beyond, in which the ZrSiO4 structure is destabilized to enable the exclusion of Ti4+ and Zr4+ and subsequently yields ZrTiO4 trace alongside the crystallization of DyPO4. Dy3+ accommodation facilitated the improved absorption and emission (blue [483 nm] and yellow [576 nm]) phenomena and further the paramagnetic features are also induced in the resultant ZrSiO4.

Optical Spectrum Analyzer Integrated Fiber optic Modified nanocrystalline annealed Al[formula omitted]O[formula omitted] cladding for improved evanescent-wave toxic gas detection

To detect toxic gases, a clad modified fiber optic sensor with nanocrystalline Al2O3 is proposed. The cladding of the fiber in the gas sensing region is made of as-prepared and annealed Al2O3 (500 °C & 1200 °C) samples. The sensitivity to poisonous gases such as acetone, isopropyl alcohol, and benzene at ambient temperature is studied using the phenomenon of the evanescent wave absorption. For various gas concentrations (0-50-100––500 ppm), the spectrum characteristics of the fiber optic gas sensor are investigated. The spectral peak intensity of the sensor varies linearly with the acetone concentration. For gas selectivity, the sensor’s properties with isopropyl alcohol and benzene gases are also investigated. Acetone (1200 °C) had a higher sensitivity than isopropyl alcohol and benzene among the three gas vapors. The sensor’s time response characteristics are also presented.

Wavelength-Dependent Nonlinear Absorption in Platinum Nanoparticles at Off-Resonant Wavelength

In order to obtain optical nonlinear materials with high transparency and low propagation loss in the visible and infrared range, noble metal materials in the off-resonant band have become a hot spot in the optical field in recent years. Therefore, the nonlinear absorption characteristics of platinum nanoparticles (PtNPs) with the surface plasmon resonance (SPR) in the ultraviolet band were investigated with multi-wavelength (500–700 nm) nanosecond Z-scan technology. The measurement results showed that the SPR wavelength of PtNPs was far away from the excitation wavelength, but there were still the saturated absorption (SA) and the reverse saturated absorption (RSA) phenomena, and the size of nonlinear absorption was related to the excitation wavelength and the excitation energy. When the excitation wavelength was constant, with the increase in excitation energy, PtNPs converted from SA to RSA. When the excitation energy was constant, with the excitation wavelength approaching SPR, PtNPs also converted from SA to RSA. The SA and RSA phenomena in the off-resonant region were complementary to the systematic study of the nonlinearity of PtNPs.

Strong third-and higher-order nonlinear optical studies on femtosecond laser ablated Germanium metalloid nanoparticle colloid in the wide spectral domain (450–1500 nm)

Wide spectral region higher-order optical nonlinearities are hereby reported for ultrashort pulsed laser ablated germanium nanoparticle (Ge NPs) colloidal solutions. The Ge NPs colloids are studied for optical nonlinearities under a wide spectral domain (∼450–1550 nm) utilizing the femtosecond laser (120 fs, 1 kHz) pulses. The results of the nonlinear absorption indicate a strong dominance of multi-photon absorption phenomena (two-, three- and four-photon absorptions), involving band-to-band and defect induced energies of the quantum confined Ge NPs. The intensity-dependent [(4–8) × 1015 W m−2] nonlinear absorption exhibits a monotonically decremental trend with the increase in excitation intensity, suggesting the involvement of higher-order nonlinear optical effects. Moreover, the obtained presented results also depict strong nonlinear contribution evidenced by two orders of higher magnitude nonlinear refraction in the infrared (IR) region, 1000–1550 nm. The enhanced optical nonlinearities in the IR region propound the capabilities of these Ge NPs as a potential substitute for silicon in IR photonics-related applications.

Dual-band and broadband tunable absorber based on Weyl semimetals

The density of the electric and the magnetic fields reveal the physical mechanisms of the absorption phenomenon. This paper presents perfect dual-band and broadband absorbers formed by Weyl semimetals (WSMs) and dielectric layers above the metallic ground plane. The tunability of absorption frequencies is achieved by changing the chemical potential of WSMs. The influence of structure parameters on dual-band absorption is also investigated. The dual-band absorbers shows absorptivity over 99% and are insensitive to the polarization angle of electromagnetic waves. The broadband absorbers show absorptivity over 80% in the wideband range of 2.49–4.96 THz. This proposed absorber has significant potential in terahertz detection, radar stealth, and biological monitoring.

Analytical and Numerical Models for TE-Wave Absorption in a Graded-Index GNP-Treated Cell Substrate Inserted in a Waveguide

In this paper, absorption phenomena in a hollow waveguide with an inserted graded dielectric layer are studied, for the case of transverse electric (TE) wave propagation. The waveguide model aims to be applicable to a study of a potential cancer treatment by heating of gold nanoparticles (GNPs) inside the cancer cells. In our previous work, general exact analytical fomulas for transmission, reflection, and absorption coefficients were derived. These fomulas are further developed here to be readily applicable to the calculation of the absorption coefficient within the inserted lossy layer only, quantifying the absorption in the GNP-fed cancer tissue. To this end, we define new exact analytic scale factors that eliminate unessential absorption in the surrounding lossy medium. In addition, a numerical model was developed using finite element method software. We compare the numerical results for power transmission, reflection and absorption coefficients to the corresponding results obtained from the new modified exact analytic fomulas. The study includes both a simple example of constant complex permittivities, and a more realistic example where a dispersive model of permittivity is used to describe human tissue and the electrophoretic motion of charged GNPs. The results of the numerical study with both non-dispersive and dispersive permittivities indicate an excellent agreement with the corresponding analytical results. Thus, the model provides a valuable analytical and numerical tool for future research on absorption phenomena in GNP-fed cancer tissue.