Absorption Concentration Research Articles

Direct Frequency Comb Cavity Ring-Down Spectroscopy Using Vernier Filtering.

We present direct frequency comb cavity ring-down spectroscopy with Vernier filtering as a straightforward approach to sensitive and multiplexed trace gas detection. The high finesse cavity acts both to extend the interaction length with the sample and as a spectral filter, alleviating the need for dispersive elements or an interferometer. In this demonstration, a free running interband cascade laser was used to generate a comb centered at 3.3 μm covering ∼10 cm-1 (300 GHz), which was coupled into a high-finesse cavity, providing 0.9 km of effective path length. The Vernier configuration transmitted the comb modes in sequence, and ring-down decays could be initiated either with an acousto-optic modulator or by scanning the cavity length beyond the adiabatic limit, with trade-offs between duty cycle and sensitivity. This implementation achieved a figure of merit of 4.3 × 10-8 cm-1 Hz-1/2 per spectral element, and measurements of toluene demonstrated its ability to observe trace concentrations of a continuum absorber. This method does not require anything beyond a conventional single-mode cavity ring-down instrument other than an optical frequency comb, making it readily accessible to a wide range of applications.

Exploring the synergistic effect of NaOH/NaClO absorbent in a novel wet FGD scrubber to control SOx/NOx emissions.

Escalating SOx and NOx emissions from industrial plants necessitates customized scrubbing solutions to improve removal efficiency and tackle cost limitations in existing wet FGD units. This work investigates the real-time intensified removal pathways via an innovative two-stage countercurrent spray tower configuration strategically integrating NaOH (Ma) and NaOH/NaClO (Ma/Mb) to remove SOx and NOx emissions simultaneously from the industrial stack through a comprehensive parametric study of absorbents concentration, reaction temperature, gas flow rate, liquid to gas ratio (FL/FG), and absorbent showering head. Flue gas stream comprising SO2 bearing 4500ppm, SO3 bearing 300ppm, 70ppm NO, and 50ppm NO2 brought into contact with two scrubbing solutions as Ma, and a complex absorbent of Ma/Mb at varying respective ratios. Ninety-two percent SOx emissions were removed using 5% NaOH with double-stage scrubbing, while NOx removal was observed below 50%. Adding NaClO facilitates additional "free radical (ClO-)" chemical pathways for gases to react and decompose into ionic forms for easier solubilization so as to significantly enhance the removal capacities for both SOx and NOx compounds. NaClO oxidizer, along with NaOH, boosted the respective removal efficiencies of SOx to 99.6% and 92% NOx, proving complementary media integration advantages arising from staged exposure and bubbly interphase mass transfer phenomena. The customized synergistic effect of Ma and Mb promoted the development of an additional free radical oxidation route while sustaining the solubilization of SOx/NOx in caustic, driving toward fractional detoxification. A dimensionless emission performance model was developed along with mechanism validation through DFT in context to the successful formation of residual salts by applying the DMol3 tool in Materials Studio by exploring the convergence analysis, geometry optimization, and COSMO sigma profile.

Comparison of Degradation Differences in Typical Urban Wastewater Dissolved Organic Matter

Dissolved organic matter (DOM) is a class of organic mixtures commonly found in natural water bodies with complex structures and diverse sources, which are closely related to the structure and function of the water body environment. Given the declining quality and quantity of lake waters in China, studying the dynamic degradation/change processes of DOM in lakes is essential to understand and manage the ecological health of these water bodies. In this experiment, by conducting photocatalytic experiments of DOM, we analyzed and compared the changes of absorbance and DOC concentration of different kinds of urban wastewater water samples with time, and the results showed that the degradation efficiencies of DOC were in the order of domestic wastewater>farming wastewater>industrial wastewater from the largest to the smallest, and the degradation efficiencies of the light-absorbable substances at the wavelength of 254 nm were farming wastewater>industrial wastewater>domestic wastewater. This study not only explored the photo-degradation process of DOM in urban wastewater, but also provided a scientific basis for wastewater treatment and management, with a view to optimizing the wastewater treatment process, improving the level of water quality management and reducing the impact of harmful pollutants on the environment.

Copper-Cobalt Nanozyme Mimicking Laccase for Sensitive Colorimetric Determination of Cannabidiol in Food and Cosmetics.

In colorimetric analysis, nanozymes are invaluable tools due to their simple production, long-lasting stability, and adaptable enzymatic activity, which enable them to induce changes in substrate color. In this study, a simple nanozyme-based colorimetric sensor was developed to detect cannabidiol (CBD) by using the laccase activity of the self-made MOF with copper and cobalt loading (Cu/Co@MOF) nanozyme, which was synthesized using a one-pot microwave method. The Cu/Co@MOF has the ability to catalyze the coupling reaction between 4-AP and various phenolic substrates, thereby converting colorless phenolic substrates into red substances. Notably, 16 ng/mL was the limit of detection. Based on Y = 0.137X + 0.003 equation, absorbance and CAN concentrations (0.067 to 10 μg/mL with a correlation value [R2] of 0.993) had a significant correlation. The developed colorimetric method was subsequently employed to determine CBD in facial masks and essential oil samples, resulting in relative standard deviations (RSDs) ranging from 1.4% to 4.3%. Therefore, this sensitive, cost-effective, and rapid method ensures an effective determination of CBD in food and cosmetics.

Direct colorimetric detection of triacetone triperoxide explosive by hydroxylamine-mediated fenton chemistry catalyzed by goethite nanoparticles

Due to the absence of nitro groups or aromatic structures in its structure, spectrophotometric methods that can directly determine triacetone triperoxide (TATP) are absent. In the proposed study, a molecular spectroscopic sensor was developed based on the decomposition of TATP by hydrolysis without the addition of external acid, allowing the direct determination of TATP. The detection principle of the developed sensor is based on the decomposition of TATP by the hydrochloric acid formed as a result of the reaction of TATP with hydroxylamine hydrochloride, taking advantage of the solubility of TATP in acetone, and the hydrogen peroxide formed as a degradation product to form hydroxyl radicals catalyzed by goethite nanoparticles. The formed hydroxyl radicals, thanks to their strong oxidation properties, oxidized N,N-dimethyl-p-phenylenediamine (DMPD) to the pink-colored DMPD•+ radical cation, and the direct determination of TATP was performed by measuring the absorbance of the colored product formed. Thus, a chemo-cybernetic sequence of reactions is proposed for intact TATP assay in a circular self-sustained system, where the reactants at a given step of reactions are supplied by the products of a previous step. By applying the developed method to TATP samples prepared in acetone, absorbances due to DMPD•+ were read at 554 nm to evaluate the results. A calibration curve was created between absorbance versus TATP concentration within a final range of 10 – 33 mg L-1. The limit of detection (LOD) and limit of quantification (LOQ) of the developed TATP method were 3.3 mg L-1 and 10.8 mg L-1, respectively. Five replicate measurements were performed to determine the intra-assay and inter-assay precision of the spectrophotometric determination of TATP, and the relative standard deviations (RSD %) for TATP were found as 2.70 % and 3.76 %, respectively. Interference analysis was carried out to see the effects of ions commonly present in soil/groundwater, and of the substances used as camouflage materials due to their color and appearance similarity to TATP. The selectivity of the method toward TATP was investigated by examining the analyte recovery from explosive mixtures. The developed method was validated against a reference GC–MS method using TATP-contaminated soil samples, and the results were compared statistically.

Ce–Mn@CoOOH nanozyme for constructing a ratiometric colorimetric sensor for rapid and sensitive detection of nitrite in food

In this work, to meet the requirement of nitrite detection, a ratiometric colorimetric sensor was constructed for sensitive and rapid detection of nitrite using Ce–Mn@CoOOH nanozyme. The Ce–Mn@CoOOH nanozyme was prepared by the hydrothermal method, and exhibited excellent oxidase-like activity. Under the catalysis of Ce–Mn@CoOOH nanozyme, colorless TMB can be oxidized to blue TMB complex. Furthermore, the blue TMB complex was further oxidized and diazotized by nitrite, and then respectively produce yellow oxTMB (diimine derivative) and diazonium salt under acidic conditions. There was a good linear correlation between the absorbance (A652/A452) and nitrite concentrations in the range of 0.3–35 μg mL−1 with a low detection of 0.017 μg mL−1. In addition, the developed method was verified using ion chromatography. Importantly, a smartphone-assisted colorimetric sensor was designed for visual detection of nitrite, enabling convenient, low-cost and on-site analysis of nitrite in food.

Corrosion behaviors of electromagnetic wave absorbing coatings with varying absorber content under combined UV and salt spray exposure

Despite extensive research on the impact of environmental weathering on the degradation of electromagnetic wave absorbing (EWA) coatings, the influence of material composition on their service stability remains underexplored. In this study, we prepared EWA coatings with epoxy resin as the matrix and flaky carbonyl iron (FCI) as the absorber, at concentrations of 50 wt%, 60 wt%, and 70 wt%. These coatings underwent a 192-h combined UV irradiation-salt spray accelerated aging test to examine the effects of varying absorber concentrations on their corrosion behavior and mechanisms. Surface morphology, chemical structure evolution, and corrosion diffusion were analyzed using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray spectroscopy (EDX). Corrosion behaviors and their impact on wave absorption performance were further investigated using electrochemical impedance spectroscopy (EIS) and electromagnetic simulations. Our results show that increasing FCI content accelerates the corrosion rate of the composite coating. This acceleration is attributed to the reduced protective effect of the epoxy matrix at higher FCI concentrations and the defects caused by FCI corrosion, which facilitate the penetration of corrosive media. This study elucidates the influence of varying absorber concentrations on the weather resistance of the coatings and their microscopic mechanisms, providing valuable insights for optimizing the service stability of EWA coatings.

Experimental study on the effect of an ionic liquid as anti-crystallization additive in a bi-adiabatic H2O-LiBr absorption chiller prototype

Absorption chillers are attractive because they use natural refrigerants and can be powered by low-grade heat sources. Among the commercially available working fluids, the most common one, H2O-LiBr, has a critical drawback associated with the crystallization of the solution at low temperatures and high absorbent concentrations. This limitation restricts the operating range of these systems, especially when they are air-cooled or used as heat pumps. Additives can be used in H2O-LiBr to reduce the crystallization temperature by improving the solubility of LiBr in the solution. However, they often present disadvantages such as the requirement of a rectifier, and a negative impact on heat and mass transfer. Ionic Liquids (ILs) used as additives represent an alternative to overcome these drawbacks. In the present study, 6 % of [DMIM][Cl] by mass in absorbent (LiBr + [DMIM][Cl]) is added as an anti-crystallization additive to study its effect on the experimental behavior and crystallization limit of a H2O-LiBr single-effect bi-adiabatic absorption chiller prototype. Results of H2O-LiBr and H2O–(LiBr + [DMIM][Cl]) were compared for the individual heat transfer elements and the global system COP. The results show a decrease in the crystallization temperature using H2O–(LiBr + [DMIM][Cl]), which extended the operating range of the prototype. A decrease of 15 °C in crystallization temperature was found for H2O–(LiBr + [DMIM][Cl]) compared to H2O-LiBr at an absorbent mass of 65 %. Crystallization impeded the operation for H2O-LiBr at the highest driving temperature (100 °C) and lowest cold source inlet temperature (9 °C), whereas no crystallization was observed at same operating conditions for the (LiBr + [DMIM][Cl]) solution. Under the tested conditions, the addition of the IL as additive increased the chiller operating range without the requirement of a rectifier and with a negligible impact on the cooling capacity and thermal COP.

Determination of Hafnium in Zirconium by Spectrophotometry

Zirconium and hafnium have opposite nuclear properties and are used very differently in the nuclear industry. However, hafnium is a common metal impurity in zirconium, and the chemical properties of the two are very similar except for nuclear properties, and it is difficult to separate and detect them. At present, the detection of hafnium content in zirconium is usually achieved by using an inductively coupled plasma (ICP) spectrometer, but ICP equipment is expensive, and the detection cost is high. Therefore, it is necessary to develop a simple and low-cost method for the determination of hafnium content in zirconium. Based on this, this paper takes the spectrophotometric method as a starting point. Through a series of experiments on the influence of pH and concentrations of the color-developing agent xylenol orange sodium salt on the absorbance of zirconium and hafnium ions, the appropriate variables are selected to detect the content of hafnium in zirconium. Finally, according to the measured absorbance and total ion concentration, by comparing the working curve of zirconium and hafnium ions, the content of hafnium in zirconium is calculated based on the lever principle.

SEMI-BATCH EXPERIMENTAL STUDY ON MULTIPLE CARBON DIOXIDE BUBBLES ABSORPTION IN SWEETENER SOLUTION UNDER VARYING PRESSURES

Increasing the absorbed carbon dioxide amount in sweetener solution is a new trend to modify soft drinks. This research investigated the optimum increase in absorbed carbon dioxide within the limits of permissible food specifications in the bubble column. Response surface methodology (RSM) utilizing the Box Behnken design (BBD) was used to conduct experiments operating conditions for achieving desired responses within specified ranges of pressure (2-4 bar), temperature (5-25°C), gas flow rate (0.2–0.4 L/min), and absorbent concentration (0–150 g/L). The experimentally obtained results were fitted to a second-order polynomial model—the increase in pressure and gas flow rate results in an increase in absorption yield (YCO2). Also, increasing the gas flow rate and temperature will increase the volumetric mass transfer coefficient (KLa), while, at high pressure and pore size KLa will be reduced. According to the obtained results at optimum conditions, 4 bar, 5°C, gas flow rate 0.4 L/min, sucrose concentration of 0 g/L, and pore diffuser 0.5 μm; The CO2 content (YCO2) was 8.34 g/L. The optimum conditions for combining the effect of high CO2 content (6.125 g/L) and best KLa value (0.1043 L/min) were: 2.83 bar, 5 °C, a gas flow rate of 0.4 L/min, a sucrose concentration of 65.15 g/L, and pore diffuser of 0.5 μm.

Copper Single-Atom Nanozyme Mimicking Galactose Oxidase with Superior Catalytic Activity and Selectivity.

Due to the low stability and high cost of some natural enzymes, nanozymes have been developed as enzyme-imitating nanomaterials. Single-atom nanozymes are a class of nanozymes with metal centers that mimic the structure of metal-based natural enzymes. Herein, Cu-N-C single-atom nanozyme (SAN) is synthesized with excellent peroxidase- and enhanced oxidase-like activities to mimic the action of natural galactose oxidase. Cu-SAN demonstrates stereospecific activity akin to that of natural galactose oxidase by oxidizing D-galactose and primary alcohol but not L-Galactose or other carbohydrates. The SAN can catalyze the oxidation of galactose in the presence of oxygen, producing hydrogen peroxide as a sub-product. The produced hydrogen peroxide then oxidizes 3,3',5,5'-tetramethylbenzidine catalyzed by the SAN, yielding the typical blue product. The relationship between absorbance and galactose concentration is linear in the 1-60µm range with a detection limit as low as 0.23µm. This strategy can be utilized in the diagnosis of galactosemia disorder and detection of galactose in some dairy and other commercial products. DFT calculations clarify the high activity of the Cu sites in the POD-like reaction and explain the selectivity of the Cu-SAN oxidase-like reaction toward D-galactose.

Enhanced peroxidase‐like activity of MnFe2O4 nanoparticles on halloysite nanotubes for uric acid detection

AbstractNanozymes have significantly advanced sensing assays by replicating native enzyme functions. However, designing nanozymes with high catalytic activity and easy recyclability remains challenging. The study presented here has resulted in the development of a highly efficient and sensitive colorimetric system for the detection of uric acid, utilizing MnFe2O4@HNTs—a novel composite material consisting of MnFe2O4 loaded onto halloysite nanotubes. These nanocomposites exhibited outstanding peroxidase‐like activity and attractive magnetic properties. The catalytic efficiency of the MnFe2O4@HNTs in the oxidation of 3,3′,5,5′‐tetramethylbenzidine, in the presence of H2O2, was remarkable, leading to a distinct color change from colorless to blue. A linear relationship was observed between absorbance and UA concentration in the range of 1–20 μM, with a detection limit as low as 52 nM. Mechanistic investigations revealed that reactive oxygen species (ROS), specifically singlet oxygen (1O2), were generated through the decomposition of H2O2, which is responsible for the peroxidase‐like activity demonstrated by the MnFe2O4@HNTs. The method showed minimal interference from serum substances and high selectivity. Magnetic MnFe2O4 allowed easy separation and maintained over 95% activity after seven reuse cycles. The developed assay was successfully applied to the detection of uric acid in human serum, achieving recoveries greater than 98.60%. This research significantly advances the design of recyclable high‐performance nanozymes and establishes an effective colorimetric sensing platform for UA detection in clinical samples, potentially improving diagnostic tools for healthcare applications.

Optimising corn (Zea mays) cob powder as an effective sorbent for diverse gel matrices: exploring particle size and powder concentration effects

SummaryThis study aims to valorise a plant waste, corn cobs (Zea mays) enriched with fibres (cellulose of 19.09–19.18% and hemicellulose of 34.04–60.13%), to create gel‐like sorbents. Corn cobs (CB) were dried, grounded and sieved to obtain 500, 250 and 125 μm powder size fractions. Various CB powder concentrations (10–40% w/w) were mixed with distilled water and rice bran oil for 2 min at ambient temperature to form hydrogel‐like and oleogel‐like sorbents, respectively. Visual appearance indicated that selected gels formed by 250 and 125 μm CB powders were self‐sustained right after mixing, while the largest particles (500 μm) could not fabricate gels at the CB concentrations studied. FTIR results suggested that the gelation process was primarily attributed to physical absorption rather than chemical binding. Comprehensive analyses of microstructure, physicochemical properties and rheological behaviour indicated that gelation was due to fibre–fibre interaction (125 μm) and oil/water–fibre interaction (250 μm). An increase in CB powder concentration enhanced the microstructural density and hardness of gels. Thus, 250 μm particles and higher absorbent concentrations resulted in brittle sorbents characterised by high hardness but low cohesiveness. The 250 μm particles also exhibit a superior antioxidant profile and lower oil/water loss than the 125 μm CB particles due to effective intra‐particle trapping mechanisms.

Micro-Milli Scale for the Removal of Iron and Copper by a Positively Charged Foam before Nickel Colorimetric Detection using Handy Spectrometer

Introduction: Simple alternative detection of nickel with iron and copper as interferences was proposed. The procedure was based on sampling a milligram sample and a micro-milliliter operation. Methods: The method has been applied to jewelry items. A 50 mg sample was digested by 5 mL of nitric acid with heating. The obtained solution was added with KSCN before passing through polyurethane foam (PUF) (1 cm i.d. × 8 cm length). Some metal ions-SCN complexed (e.g., Fe(III) and Cu(II)) were retained in the column while Ni(II) ions were in the eluate. A 200-500 µL aliquot was added with 4-(2-pyridylazo)-resorcinol (PAR) as the color reagent. At least 30 µL of a portion was measured for the absorbance of the color product using a handy spectrometer. Results: The positively charged foam could remove iron and copper altogether before determining nickel. A standard calibration was a plot of absorbance versus Ni(II) concentration for 1-30 mg/L: absorbance = 0.0123[Ni(II), mg/L] + 0.0435 (R2=0.9945) with a limit of detection (LOD) and limit of quantitation (LOQ) of 0.24 mg/L and 0.81 mg/L, respectively. Two bracelet samples showed the presence of nickel at 0.97 ± 0.25 and 0.27 ± 0.04 mg/g, respectively, and agreed with the reference FlameAAS method. Conclusion: The proposed method could be used to assay nickel in samples containing high levels of iron and copper, such as jewelry. This will benefit general wearers with health concerns associated with nickel, particularly in case of inexpensive accessories. The handy spectrometer used in the study might make be helpful to carry out these studies with a limited tight budget.

Interface engineering for improved performance of perovskite solar cells using CdTe buffer layer

In order to achieve high power conversion efficiency, interface engineering of the charge transport layers in perovskite solar cells (PSCs) has significantly reduced the energy band mismatching and charge accumulation. This simulation study investigated the effect of cadmium telluride (CdTe) buffer layer (BL) on the performance of PSC through SCAPS-1D modeling program. The device configuration with BL consisted of metal electrode/CuI/CdTe/CH3NH3SnI3/TiO2/TCO/glass substrate. The insertion of BL between absorber and HTM improved the energy band alignment by increasing the power conversion efficiency (PCE) from 11.09 % to 14.76 %. The important parameters including thicknesses of the buffer and absorber layers, the doping concentrations of absorber, electron transport material (ETM), and hole transport material (HTM) were investigated. Moreover, the effect of the electron affinity of the ETM, HTM and the hole mobility of HTM were optimized to further enhance the performance of the proposed structure. The optimized results showed the noticeable increase in efficiency of 23.56 %.

Improving the activity of CO2 capturing from flue gas by membrane gas – solvent absorption process

This work is focused on increasing the capturing efficiency of carbon dioxide (CO2) through flue gas purification systems. To maximize the CO2 capture process, many process variables such as temperature, flow rates, absorbent concentrations, and nanoparticles were investigated. This study describes the use of a polypropylene hollow fiber membrane contactor to separate CO2 from nitrogen using different solvents, including Potassium carbonate (K2CO3), N-methyl diethanolamine (MDEA), and monoethanolamine (MEA). Also, the presence of silica nanoparticles and piperazine (PZ) enhances the process performance. On the other hand, the amine and mixed amino absorbents MDEA-PZ and MDEA-MEA were prepared and compared based on the absorption capacity. The optimal order of amine absorbent performance when applied to CO2 membrane absorption is MDEA-MEA followed by MDEA-PZ. At a solute concentration of 9%, MDEA-MEA exhibits the highest CO2 removal efficiency, which is 74.12%. However, at a concentration of 11%, MEA, MDEA-PZ, and MDEA have the highest CO2 removal efficiencies of 80.15%, 75.13%, and 63.12%, respectively.

Insight in NO synthesis in a gliding arc plasma via gas temperature and density mapping by laser-induced fluorescence

A gliding arc (GA) plasma, operating at atmospheric pressure in a gas mixture of 50% N2 and 50% O2, is studied using laser-induced fluorescence spectroscopy. The main goal is to determine the two-dimensional distribution of both the gas temperature and the NO ground state density in the afterglow. As GA plasma discharges at atmospheric pressure normally produce rather high NO x densities, the high concentration of relevant absorbers, such as NO, may impose essential restrictions for the use of ‘classical’ laser-induced fluorescence methods (dealing with excitation in the bandhead vicinity), as the laser beam would be strongly absorbed along its propagation in the afterglow. Since this was indeed the case for the studied discharge, an approach dealing with laser-based excitation of separate rotational lines is proposed. In this case, due to a non-saturated absorption regime, simultaneous and reliable measurements of both the NO density and the gas temperature (using a reference fitting spectrum) are possible. The proposed method is applied to provide a two-dimensional map for both the NO density and the gas temperature at different plasma conditions. The results show that the input gas flow rate strongly alters the plasma shape, which appears as an elongated column at low input gas flow rate and spreads laterally as the flow rate increases. Finally, based on temperature map analysis, a clear correlation between the gas temperature and NO concentration is found. The proposed method may be interesting for the plasma-chemical analysis of discharges with high molecular production yields, where knowledge of both molecular concentration and gas temperature is required.

CO2 desorption and mass transfer characteristic study in micropacked bed reactors

The chemical desorption method with amine-based solvent have been widely applied in CO2 capture and storage (CCS) industrial. However, there is still exist mass transfer limitation and difficult to achieve packing/catalyst immobilization in conventional reactors for CO2 desorption process. In this work, micropacked bed reactors (μPBRs) with glass beads are adopted to investigate CO2 desorption performance. Effects of absorbent type, temperature, initial concentration of absorbent, liquid superficial velocity, initial loading of absorbent, particle size, and N2 superficial velocity on the desorption efficiency and desorption rate are discussed. The desorption efficiency of μPBR is 36 ∼ 81 % based on the MDEA absorbent. The value of desorption rate in μPBR is from 0.38 to 3.37 mmol/min, which is bigger than microchannel reactor. Liquid phase mass transfer coefficient of μPBR is 0.06 ∼ 1.38 s−1 for CO2 desorption process, which is 1–3 orders higher than that of packed column. Then, an empirical correlation of mass transfer coefficient is developed in μPBR. μPBR has a high mass transfer rate with an advantage of fixed packing/catalyst compared with other CO2 desorption equipment.

Dual-Channel Mapping–Gas Column Concentration Inversion Method Based on Multispectral Imaging

Infrared multispectral imaging technology can achieve the long-distance, wide-ranging and fast detection of target gas, and has been widely used in the fields of dangerous-gas detection and environmental monitoring. However, due to the difficulty in acquiring background radiation as well as atmospheric disturbance and noise interference in the detection process, the quantitative detection of gas concentration has become a difficult problem to solve. Therefore, this paper proposes an inversion method for gas column concentration based on infrared multispectral imaging technology. Firstly, infrared background radiation images of the non-target gas absorption spectrum band were collected and converted into background radiation images of the target gas absorption spectrum band according to the dual-channel mapping relationship. Then, combined with the gas radiation images of the target gas absorption spectrum band, the column concentration distribution of the gas was obtained by using the measured calibration relationship between absorbance and column concentration. Experiments of gas detection in different environments were carried out, and the column concentration distribution of the target gas was inverted using this method; the results showed that the average relative error of the inversion of the gas column concentration was 4.84%, which enables the quantitative detection of gas column concentration in a complex environment.

Topological Flexible 3D Microwave Perfect Absorber

AbstractIn this work, an approach to achieve perfect absorption and microwave absorption enhancement is proposed by combining traditional wave‐absorbing materials with metamaterials. Specifically, an absorbing basement membrane (BM) is integrated with 3D woodpile (WP) photonic crystals, both of which are composed of flexible silicon materials as matrix and carbonyl iron powder (CIP) as absorbent. Direct ink writing (DIW) is used to fabricate the 3D photonic crystals with either single or coupled concentrations of absorbent. Experiments show that the 10‐dB bandwidth of the integrated absorber can reach 10 GHz with a wide elevation angle of incidence. The absorber composed of BM and WP with coupled concentrations of absorbent leads to perfect absorption with a maximum absorption of over 100 dB at an elevation angle of 30°. By changing the concentration of absorbent in BM, the frequency of perfect absorption can be engineered in the range of 6–16 GHz. Such absorption singularity reveals an experimentally observable topological charge that confirms the robustness of the singularity of perfect absorption. The topologically protected flexible 3D microwave absorber offers exceptional performance for versatile scenarios and enriches the studies on topology arising from scattering singularity.