Accurate methane quantification by absorption spectroscopy remains challenging in mixed-alkane backgrounds. Broadband alkane absorption induces optical-power attenuation and matrix-dependent wavelength modulation spectroscopy (WMS) harmonic distortion, causing the measured signal to deviate from a simple one-to-one relationship with methane concentration. As a result, conventional direct retrieval based on methane absorbance or harmonic amplitude becomes less reliable without gas separation or effective interference correction. To address this issue, a methane sensor based on a serial-reference physics-guided inference (SRPGI) method is proposed. A serial-reference optical configuration is designed to provide shared reference information within the same scanning cycle, and a physics-guided residual inference framework is developed by integrating reference-assisted features, physics-based priors, and data-driven residual correction. The proposed method enables direct methane quantification without pretreatment or chromatographic separation. Experimental results show that, in the ablation study, the concentration error under interference is reduced from 20.99 ppmv to 0.32 ppmv at 150 ppmv CH4, corresponding to an approximately 65.6-fold reduction in retrieval error. With increasing mixed-gas interference strength, the raw error rises substantially, whereas the SRPGI relative error remains below 0.4%. Across different alkane background gases, the SRPGI relative error remains below 0.25%. The lightweight SRPGI model also preserves the sensor response speed, with the response time (T10%–90%) remaining nearly unchanged from 31.0 s to 31.2 s. These results demonstrate that the proposed sensor provides improved accuracy, stability, and matrix adaptability for direct methane quantification in mixed-alkane background conditions.

Layered double hydroxide (LDH) is a common electrocatalyst for oxygen evolution reaction (OER). However, LDH materials usually undergo a relatively slower reconstruction process, which hinders the efficiency of electrochemical water splitting. Herein we modify pristine NiFe-LDH with Se species-containing FeSe2 to fabricate NiFe-LDH/FeSe2 heterojunction catalyst. At the same time, heterojunction constructing also triggers vacancy formation, which is further proved by electron paramagnetic resonance (EPR) and X-ray absorption spectroscopy (XAS) measurements. In situ Raman spectra and a series of electrochemical experiments have proved the synergistic effect of Se species introduction and vacancy to accelerate the surface reconstruction process of the catalyst, thus greatly enhance OER performance, with a low overpotential of 256 mV under the current density of 10 mA cm-2. This work shed light on ways to design catalysts wither rapid surface reconstruction process and develop catalysts with high efficiency toward electrochemical water splitting.

An active temperature disturbance rejection method was developed to address uncertainties in temperature disturbances and to improve stability for field gas measurements. A symmetric convection heat conduction strategy was used to ensure uniform heating of the multipass cell (MPC). Active disturbance rejection control (ADRC) was adopted to address the nonlinear and uncertain temperature disturbance. The temperature fluctuation is less than 0.01℃ in the stable state during field experiments when controlled at 30℃. The maximum temperature fluctuation during gas sample replacement is less than 0.015 °C. For gas measurement results, CO2 and CH4 concentrations were monitored at 2100-3864 ppmv and 99-104 ppmv, respectively. This temperature control method provides a guarantee for field gas monitoring.

A distributed cavity-enhanced Raman spectroscopy system was developed for the simultaneous detection of H2, O2, N2, and CO2 in confined spaces and complex gas environments. The system adopts an external-host/distributed-detection-cavity configuration, in which laser excitation, cavity-enhanced detection, Raman signal collection, and spectral detection are functionally separated to improve deployment flexibility for remote in situ measurements. Multi-peak fitting was used to extract the spectral band areas of different gas components, and band-area normalization was introduced to reduce the influence of laser power fluctuations, fiber coupling variations, and cavity coupling changes on concentration retrieval. The results show that H2, O2, N2, and CO2 exhibit clearly distinguishable Raman peaks and good linear concentration responses. The fitting correlation coefficients for H2, O2, N2, and CO2 are 0.998, 0.997, 0.996, and 0.998, respectively, with RMSE values of 0.03%, 0.21%, 0.35%, and 0.06%. After normalization, the average relative errors are reduced to 1.6%, 1.5%, 1.4%, and 1.3%, while the maximum relative errors are reduced to 3.2%, 3.1%, 2.9%, and 2.7%, respectively. Continuous measurements yield RSD values of 1.5%, 0.90%, 0.56%, and 1.25%, demonstrating good simultaneous detection capability and quantitative stability. The proposed system provides a feasible approach for online multicomponent gas monitoring in confined and complex environments.

High-precision measurement of CH 4 concentration is essential for applications in oil and gas exploration, environmental regulation, and industrial hazard prevention. Although the tunable diode laser absorption spectroscopy (TDLAS) offers high sensitivity and selectivity, its performance is severely limited by laser-induced light intensity noise. Critically, this noise not only multiplies with the absorption signal but also behaves as a multiscale, nonstationary process. In this study, an adaptive light intensity noise suppression (ALINS) method was proposed to enhance the precision of CH 4 detection. To this end, the coaxial perception optical path structure was designed to simultaneously perceive multiscale time-varying light intensity noise. Subsequently, the established dual-time-scale feature extraction strategy provided noise characteristics to the adaptive estimation model. Leveraging these characteristics, the model decoupled noise from the absorption signal in real time. A mid-infrared hollow waveguide methane sensing system was designed, and the performance of the ALINS method was experimentally validated based on this system. Under the conditions of a 5-m optical path and a 0.5-s integration time, a measurement precision of 0.017 ppmv was achieved, improving upon the raw signal performance by a factor of more than 100. The experimental results showed that the long-term stability of ALINS has been improved by 7.4 times compared with the raw data. This study provides a novel method for suppressing the light intensity noise in TDLAS sensors, thereby demonstrating the strong potential for deployment in high-precision critical applications.

The measurement accuracy of quartz-enhanced photoacoustic spectroscopy (QEPAS) gas sensors is affected by the noise from multiple sources. In this study, a cascaded spectral denoising and concentration inversion method (CSDCIM) based on the back propagation neural network (BPNN) was first proposed to improve the measurement accuracy of QEPAS CH4 sensor. The method consisted of a spectral denoising model and a concentration inversion model. The complete original spectral signals were used as input for direct concentration inversion. For the spectral denoising model, noise suppression was achieved by curve fitting with BPNN model, avoiding the requirement for clean signals as reference labels. Experimental results indicated that the proposed model outperformed other denoising algorithms with the signal-to-noise ratio (SNR) improved by 7.2 times. In the concentration inversion model, the cuckoo search (CS) algorithm was employed to optimize the initial weights and biases of BPNN model. The coefficient of determination (R2) reached 0.99986, which was superior to other inversion methods. The measurement uncertainty and stability were further evaluated. The results showed that the CSDCIM reduced measurement deviation to 1.2 ppm at different CH4 concentration levels. In addition, the mean CH4 concentration of 600 repeated measurements was corrected from 904.39 ppm to 900.69 ppm, and the half width at half maximum (HWHM) of concentration distribution became narrower from 7.42 ppm to 6.31 ppm. This method could also be applied to the measurement of dynamic concentrations. The CSDCIM provided an effective noise suppression solution for QEPAS CH4 sensor.

Achieving single-atom catalyst with zero-order approximation or homogeneity necessitates precise control over anchoring sites, which imposes a great challenge as abundance and diversity associated coordination environments. A sound strategy towards such a challenge is to anchor a single atom at a specific localization site on the surface of a twin crystal. Therefore, this article aims to anchor single bismuth (Bi) atom at a specific surface of Zn0.5Cd0.5S twins to maximize charge transfer and achieve redox bifunctional reactions. Such a synergistic mechanism was experimentally and theoretically validated through preparation of Zn0.5Cd0.5S compound as model catalyst with twin phase junction (tetragonal and hexagonal) and Bi atoms doped exclusively in tetragonal form. Bi-anchored (1 mol%) Zn0.5Cd0.5S twins exhibit a peak photocatalytic hydrogen productivity of 5680 mu mol g- 1h- 1 and an oxidative dehydrogenation rate of 4420 mu mol g- 1h- 1 for benzyl alcohol. The presence of biphasic junctions within the sample generates a built-in electric field that accelerates the separation and migration of photogenerated charges from tetragonal to hexagonal. Moreover, following the doping of Bi atoms into the tetragonal phase, 5d electrons of Bi couple with electrons of Zn and Cd, magnifying potential differences between the two conduction bands, which enhanced the transfer rate of photogenerated carriers. Density functional theory (DFT) modelling reveals that Bi atoms served as active center for the oxidation reaction, lowering the reaction potential barrier for intermediates. Consequently, we employ an atomic-level selective doping strategy to optimize photocatalytic activity and establish the relevant structure-activity relationships.

In order to realize CH4 measurement, a vibrating cavity off-axis integrated cavity output spectroscopy (VC-OAICOS) CH4 sensing system was developed in this paper. The inclusion of a vibration module in the system can effectively suppress cavity mode noise. To further eliminate characteristic cavity mode noise and improve system stability, we proposed a new uniform phase empirical mode decomposition (NUPEMD) method. This method enables the selection of the appropriate number of phases and the amplitude of the masking signal, thereby reducing the impacts of mode mixing and residual noise. The self-contained fitting and mutual correlation signal reconstruction technique employed in NUPEMD is particularly effective in eliminating medium- and highfrequency noise. Analysis of the Fourier frequency domain plots of the system noise revealed that the combination of vibration with the NUPEMD method significantly suppresses medium- and high-frequency residual cavity mode noise. Experimental results demonstrated that utilization of this method enabled the VC-OA-ICOS system to achieve a minimum detection limit (MDL) of 0.381 ppmv within 2 s, resulting in a 5.62-fold improvement in measurement accuracy compared to traditional methods. Furthermore, continuous measurements using this enhanced VC-OA-ICOS system on standard CH4 samples over a period of 12 h yielded a longterm detection error of no more than 0.47 %, representing a 1.98-fold improvement in stability. The effectiveness and superiority of both the proposed system and the methodology for CH4 measurement are thoroughly validated through these findings.

Reducing cavity mode noise is crucial for improving the signal-to-noise ratio (SNR) of sensor systems in off-axis integrated cavity output spectroscopy (OA-ICOS). Improving the cavity mode density and smoothness of the cavity mode structure is an effective way to reduce the cavity mode noise. Extensive research has been conducted on ways to reduce the noise of OA-ICOS systems with stable cavities. However, research on the optical noise inside cavities under vibration conditions is limited. Therefore, we propose a novel vibrating cavity (VC) scheme to increase the cavity mode density and reduce cavity mode noise in OA-ICOS systems. Based on existing literature, this is the first theoretical study on the effect of vibration on cavity mode density. Theoretical research results indicated that this method could reduce cavity mode noise by more than twice. We designed a VC-OA-ICOS system and measured the direct absorption (DA) of standard CH4. The ability of the method to suppress cavity mode noise was verified and evaluated using the main technical indicators of the SNR and minimum detection limit (MDL). Moreover, we filtered the sampled spectral signal to reduce the burrs interference generated near the absorption peak. The filter-based VC-OA-ICOS system achieved an SNR of 71 and an MDL of 0.88 ppmv. Compared with the non-vibration (NV) OA-ICOS system, the designed VC-OA-ICOS system provided an improvement in the SNR and MDL by 7.78 times and 3.4 times, respectively. This study provides a new approach for suppressing cavity mode noise in OA-ICOS sensors.

In this paper, the assisted adsorption behavior of O2 molecules on the WO3 (200) crystal plane is studied. Density functional theory simulation results show that there are two adsorption modes of O2 molecules on the crystal plane. The physical adsorption is named mode I and chemical adsorption is named mode II. The adsorption energies are -0.40eV and -6.72eV, respectively. The occurrence of adsorption mode II needs to overcome the crystal plane deformation energy of 0.32eV and it is difficult to occur at room temperature, which is proved by the results of molecular adsorption experiments. Further experiments show that the adsorption mode II of O2 molecules occurs when acetone molecules are present in air at room temperature. Theoretical simulation verifies the experimental result, that is, the adsorbed acetone molecules on crystal plane promote the transformation of O2 molecules from physical adsorption into chemical adsorption. The transformation is demonstrated by gas-sensitive experiments, that is, the assisted chemical adsorption of O2 molecules decreases the gas-sensitive response time for acetone molecules with the increase of the detection concentration (20-100 ppm). In-depth exploration of molecular adsorption behavior is conducive to regulating the properties of the crystal plane and improving gas-sensitive performance.

A methane (CH4) sensor based on off-axis integrated cavity output spectroscopy (OA-ICOS) was developed, equipped with two measurement schemes: direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS). The sensor used an optical resonant cavity composed of two high reflection mirrors (reflectivity > 99%). With a cavity length of 7 cm, an effective optical path length of 10.8 m and a cavity volume of 8.9 mL were achieved. A distributed feedback laser was used to precisely target the CH4 absorption line near 1.6537 µm. Compared with the original system, the cavity mode noise of the CH4 sensor was further reduced by adding white noise perturbations. The white noise perturbations were generated by the broadband random noise from the signal generator. The special customized narrowband RF noise source was not required. The system complexity and cost could be reduced. In DAS mode, the signal-to-noise ratio (SNR) of the OA-ICOS was 16.2 and the minimum detection limit (MDL) was 2.2 ppm at 117 s. In WMS mode, the SNR of the OA-ICOS was 113.9 and the MDL was 1.2 ppm at 106 s. Compared with the results obtained from the WMS mode and DAS mode, the SNR and MDL was improved 7.0 times and 1.8 times, respectively. The proposed sensor system not only enabled high-accuracy trace gas measurement, but also demonstrated strong potential for applications due to its compact design and low cost.

The molecular adsorption behavior of O2, N2, and H2O on the Al3+ modified SnO2(221) crystal plane and its effect on conductivity were simulated using density functional theory (DFT). The results show that the H2O molecule is chemically adsorbed on the crystal plane as characteristic adsorption species (CAS), forming a surface mode named H2O-SnO2-Al (221). The conductivity of H2O-SnO2-Al (221) is reduced by adsorbing O2 and N2 molecules. The simulation results were confirmed by electrochemical impedance spectroscopy (EIS) under various atmospheric conditions. Using the crystal plane as a humidity sensor to test the different humidity of the air. The results show that the conductivity increases with the rising humidity, which contradicts the results of the H2O single molecule adsorption model. Further FTIR data shows that high humidity on the crystal plane led to the formation of aggregated water, which in turn enhanced both conductivity and capacitance.

Spinel oxides still exhibit unsatisfactory electrocatalytic performance toward oxygen evolution reaction (OER) given their low intrinsic activity, poor electronic conductivity, and limited exposure of reaction sites. Defect engineering has garnered intensive attention and become a promising strategy to enhance the reaction kinetics. In this work, spinel NiFe2O4 nanospheres with rich nickel vacancies are prepared via simple one-pot hydrothermal synthesis. Combined electrochemical measurements and in situ Raman characterization prove that a relatively higher degree of electrochemical surface reconstruction is realized after the introduction of nickel vacancies in NiFe2O4, in addition to boosted OER electrocatalytic performance. Further theoretical calculations also reveal that the cation-vacancy-induced effect can reduce the difficulty for surface reconstruction by increasing the octahedral nickel-oxygen covalency in nickel ferrite. Contributed to the great structural flexibility and optimized electronic structure of the pre-catalyst, the reconstructed electrocatalyst presents desirable OER performance, accompanied by long durability in alkaline solution. This work provides a sound strategy to intensify surface reconstruction on spinel oxides and design electrocatalysts with high efficiency toward water oxidation.

Whilst defect engineering is a sound approach to enhance CO2 photoreduction based on metal organic frameworks (MOFs), the underlying mechanisms were not well understood on an atomic scale. This study aims to elucidate the mechanisms at the atomic level, to provide vital insights to enable the design and development of selectively introduced ligand defects to maximize the CO2 photoreduction capability of a classical MOF UiO-66-NH2 without the need for co-catalysts, sacrificial agents and photosensitizers. Defect-containing UiO-66-NH2 (Zr/Ce0.25) demonstrates superior charge separation and CO2 photoreduction than both regular UiO-66-NH2 (Zr/Ce0.25) and UiO-66-NH2. The doped Ce is a key contributor to managing the coordination environment of the linkers, enabling the formation of selectively introduced ligand defects. The selective loss of ligands exposes pyramid-shaped activated clusters and facilitates spatial charge separation. As a result, electrons are transferred through Ce-O-Zr and Ce-Ovacancy-Zr pathways, effectively narrowing the band gap and suppressing photoinduced charge recombination. These findings are expected to provide alternative perspectives on selective defect engineering for the design and manufacture of high-performance MOF photo-catalysts for a variety of value-added engineering applications.

Covalent Organic Frameworks (COFs) are promising in the field of photonic energy conversion. However, most efforts have been concentrated on the design of ligand geometric structures and chemical bonding relationships, while understanding the impact of stacking methods on photonic energy conversion remains a significant challenge. In this work, four COFs (1D-COF, 1D-MeCOF, 1D-tBuCOF and 2D-COF) with the same main-chain structure but different stacking methods are designed and synthesized, using photocatalytic hydrogen evolution as a model reaction. Mortise-tenon stacked 1D-MeCOF exhibits far superior photocatalytic hydrogen evolution performance to other stacking methods, and it maintains high efficiency and stability in natural seawater systems. Extensive characterization demonstrates that such a unique mortise-tenon stacking structure of 1D-MeCOF inhibits interchain slippage, enhances π-stacking, and maximizing light absorption capabilities. Furthermore, unidirectional carrier transport characteristics of one-dimensional structure can generate a strong photo-induced self-built electric field, which acts as "self-catalysis" to accelerate carrier transport. This work provides an effective design strategy and mechanistic insights on the stacking engineering of photonic energy conversion materials.

The development of catalytic materials suitable for room-temperature or near infrared regions is of great significance for the degradation of organic pollutants in natural water bodies. In this paper, the influence laws of g-C3N4 2D material and N defects on its optical and molecular adsorption properties were simulated by density functional theory (DFT). The results show that with the expansion of the material area and the increase of N defects, the absorbed light moves towards the long-wave direction. The N defects make the material prone to form subband gap state energy levels with excitation energy lower than 1.63 eV. This means that under near infrared light excitation, the material has degrade organic pollutants relatively well. The hexagonal prism assembly prepared by the chemical assembly method can form 2D g-C3N4 with N defects under different temperatures and atmospheres. The results of photocatalysis and room-temperature degradation of RhB experiments on it confirmed the theoretical simulation results. The contribution rate of near infrared light degradation reached 97.1 %, which was much higher than 57.6 % of the hexagonal prism C3N4 obtained by the solid-phase sintering method. The results of XRD, absorption spectra, FTIR spectra and XPS spectra show that the materials obtained by the chemical assembly method have better 2D characteristics and more N defects than those by the solid-phase sintering method. Solid-phase sintering makes the material layers bond closely with each other, so that more 3D material characteristics are retained inside the prism. By adjusting the heat treatment temperature and oxygen concentration, the 2D polymerization expansion and N defects of g-C3N4 material can be further regulated, thereby controlling its optical, photoelectric, molecular adsorption and photocatalytic degradation properties.

The Fe–Co–Se–O-300 has a low η 10 of 280 mV. EPR results show that the catalyst has numerous oxygen vacancies. In situ Raman results indicate that Se species are oxidized to SeO 3 2− , which is beneficial for OER performance through additional experiments.

The limited active site density and narrow ion transport channels of covalent organic frameworks (COFs) lead to unsatisfying capacity. The lack of performance evaluation under high mass loading conditions (> 4.0 mg cm(-2)) significantly hinders the practical application of COF-based materials. Here, a mesoporous COF with multiple redox active sites (TP-COF) is designed as anode material for aqueous calcium ion batteries (CIBs). Featuring nitrogen-rich, multiple carbonyls active sites and a large mesoporous pore size (2.0 nm), TP-COF shows a high capacity of 229 mAh g(-1) at 1.0 A g(-1), with 82 % capacity retention after 3000 cycles at 5 A g(-1). Remarkably, under high mass loading conditions (10.0 mg cm(-2)), TP-COF still achieve a high specific capacity of 166 mAh g(-1) at 1 A g(-1) due to large ion transport channels and abundant active sites. This work offers a new avenue for COF materials design for practical high performance aqueous CIBs.