A new type of carbonized polymer dot was prepared by the one-step hydrothermal method of triethoxylsilane (TEOS) and citric acid (CA). The sensor made from carbonized polymer dots (CPDs) showed superior gas sensing performance toward ammonia at room temperature. The Si, O-codoped CPDs exhibited superior ammonia sensing performance at room temperature, including a low practical limit of detection (pLOD) of 1 ppm (Ra/Rg: 1.10, 1 ppm), short response/recovery time (30/36 s, 1 ppm), high humidity resistance (less than 5% undulation when changing relative humidity to 80 from 30%), high stability (less than 5% initial response undulation after 120 days), reliable repeatability, and high selectivity against other interferential gases. The gas sensing mechanism was investigated through control experiments and in situ FTIR, indicating that Si, O-codoping essentially improves the electron transfer capability of CPDs and synergistically dominates the superior ammonia sensing properties of the CPDs. This work presents a facile strategy for constructing novel high-performance, single-component carbonized polymer dots for gas sensing.@en

A systematic experimental investigation concerning the fretting-induced tribo-chemical state and its effect on the fretting wear behavior of titanium alloys under the vacuum atmospheres (4 × 10^–3 Pa and 4 × 10^–1 Pa) in different fretting regimes is reported. An in situ XPS analysis tester was developed to capture the real tribo-chemical state of worn surface for all test conditions. Results show that samples subjected to different vacuum atmospheres have varied tribo-chemical states depending on the fretting regime, which play significantly different roles in determining the associated damage mechanisms and the resulting fretting wear resistance. Under both vacuum atmospheres, in the partial slip regime (PSR) the worn scars were mainly covered by TiO₂, showing comparable levels of very slight damage, while in the mixed fretting regime (MFR), the tribo-layer is still mainly consisted of TiO₂, but with an evident peak of Ti metal for the high vacuum degree (4 × 10^–3 Pa) in MFR, showing a mild damage. In contrast, in the gross slip regime (GSR), Ti metal was prone to be oxidized to Ti₂O₃ and TiO on the worn scar, especially for the low vacuum degree (4 × 10^–1 Pa) having a highest content of Ti₂O₃. It might be inferred that the tribo-layer containing more Ti₂O₃ formed during fretting wear process is susceptible to be broken, hence showing a highest fretting wear volume in GSR for the low vacuum degree. The results suggest that for the vacuum environments, the Ti6Al4V may be more suitable to be used under the high vacuum atmosphere.

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Synthetic biohybrid systems by coupling artificial system with nature's machinery may offer a disruptive solution to address the global energy crisis. We developed a versatile electroenzymatic pathway for the continuous synthesis of valuable chemicals, facilitated by formate-driven NADH regeneration. Utilizing a bismuth electrocatalyst, we achieved stable CO2 reduction to formate with approximately 90 % Faraday efficiency at a current density of 150 mA cm−2. The generated formate acts as a mediator to regenerate NADH, which is then coupled with immobilized redox enzymes—alcohol dehydrogenase (ADH), L-lactate dehydrogenase (LDH), and L-glutamate dehydrogenase (GDH)—to produce targeted chemicals at significant rates and exceptionally high turnover numbers (1.8×106 to 3.1×106). These achievements not only underscore the efficiency of the system but also its practical applicability in industrial settings. By leveraging in situ generated formate, this innovative approach demonstrates the potential of integrating electrocatalysis with enzymatic reactions for sustainable and efficient chemical production on a practical scale.@en

Transition metal dichalcogenides (TMDCs) garner significant attention for their potential to create high-performance gas sensors. Despite their favorable properties such as tunable bandgap, high carrier mobility, and large surface-to-volume ratio, the performance of TMDCs devices is compromised by sulfur vacancies, which reduce carrier mobility. To mitigate this issue, we propose a simple and universal approach for patching sulfur vacancies, wherein thiol groups are inserted to repair sulfur vacancies. The sulfur vacancy patching (SVP) approach is applied to fabricate a MoS₂-based gas sensor using mechanical exfoliation and all-dry transfer methods, and the resulting 4-nitrothiophenol (4NTP) repaired molybdenum disulfide (4NTP-MoS₂) is prepared via a sample solution process. Our results show that 4NTP-MoS₂ exhibits higher response (increased by 200 %) to ppb-level NO₂ with shorter response/recovery times (61/82 s) and better selectivity at 25 °C compared to pristine MoS₂. Notably, the limit of detection (LOD) toward NO₂ of 4NTP-MoS₂ is 10 ppb. Kelvin probe force microscopy (KPFM) and density functional theory (DFT) reveal that the improved gas sensing performance is mainly attributed to the 4NTP-induced n-doping effect on MoS₂ and the corresponding increment of surface absorption energy to NO₂. Additionally, our 4NTP-induced SVP approach is universal for enhancing gas sensing properties of other TMDCs, such as MoSe₂, WS₂, and WSe₂.

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Constructing near-infrared light (NIR) light-enhanced room temperature gas sensors is becoming more promising for practical application. In this study, learning from the structure and photosynthetic process of chlorophyll thylakoid membranes in plants, the first “Thylakoid membrane” structural formaldehyde (HCHO) sensor is constructed by matching the upconversion emission of the lanthanide-doped upconversion nanoparticles (UCNPs) and the UV–vis adsorption of the as-prepared nanocomposites. The NIR-mediated sensor exhibits excellent performances, including ultra-high response (R_a / R_g = 2.22, 1 ppm), low practical limit of detection (50 ppb), reliable repeatability, high selectivity, and broadband spectral response. The practicality of the NIR-mediated gas sensor is confirmed through the remote and external stimulation test. A study of sensing mechanism demonstrates that it is the UCNPs-based light transducer produces more light-induced oxygen species for gas response in the process of non-radiative/radiative energy transfer, playing a key role in significantly improving the sensing properties of the sensor. The universality of NIR-mediated gas sensors based on UCNPs is verified using ZnO, In₂O_3, and SnO₂ systems. This work paves a way for fabricating high-performance NIR-mediated gas sensors and will expand the application fields of NIR light.

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Achieving convenient and accurate detection of indoor ppb-level formaldehyde is an urgent requirement to ensure a healthy working and living environment for people. Herein, ultrasmall In₂O₃ nanorods and supramolecularly functionalized reduced graphene oxide are selected as hybrid components of visible-light-driven (VLD) heterojunctions to fabricate ppb-level formaldehyde (HCHO) gas sensors (named InAG sensors). Under 405 nm visible light illumination, the sensor exhibits an outstanding response toward ppb-level HCHO at room temperature, including the ultralow practical limit of detection (pLOD) of 5 ppb, high response (R_a/R_g = 2.4, 500 ppb), relatively short response/recovery time (119 s/179 s, 500 ppb), high selectivity, and long-term stability. The ultrasensitive room temperature HCHO-sensing property is derived from visible-light-driven and large-area heterojunctions between ultrasmall In₂O₃ nanorods and supramolecularly functionalized graphene nanosheets. The performance of the actual detection toward HCHO is evaluated in a 3 m³ test chamber, confirming the practicability and reliability of the InAG sensor. This work provides an effective strategy for the development of low-power-consumption ppb-level gas sensors.

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Inspired by the CO₂-induced reversible activation mechanism of the slow anion channel 1 (SLAC1) in plant stomatal guard cells during plant photosynthesis, we designed and prepared a CO₂- switchable H⁺/OH⁻ ion channel (CSPH ion channel). A high-performance chemiresistive room temperature CO₂ sensor has been prepared based on this CSPH ion channel. The obtained CO₂ room temperature sensor γ-CD-MOF@RhB exhibits high sensitivity (R_g/R₀ = 1.50, 100 ppm), excellent selectivity, good stability (less than 5% reduction in 30 days response value), and 99.96% consistency with commercial infrared CO₂ meter. The practical limit of detection (pLOD) of the γ-CD-MOF@RhB sensor reaches 10 ppm at room temperature toward CO₂, which is the lowest for reported MOF-derived chemiresistive room temperature CO₂ sensors so far. Ion conduction mechanism studies have shown that the CSPH ion channel behaves as a CO₂-switchable H⁺/OH⁻ ion channel with a switching point of approximately 60 000 ppm CO₂. As an application attempt, the fabricated low pLOD CO₂ sensor has been used for human exhaled CO₂ detection to compare CO₂ concentration in the breath of individuals before and after exercise and COVID-19. It was also logically indicated that the average concentration of human exhaled CO₂ after COVID-19 recovery is different for undiseased subjects.

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Implementing parts per billion-level nitric oxide (NO) sensing at room temperature (RT) is still in extreme demand for monitoring inflammatory respiratory diseases. Herein, we have prepared a kind of core-shell structural Hemin-based nanospheres (Abbr.: Hemin-nanospheres, defined as HNSs) with the core of amorphous Hemin and the shell of acetone-derived carbonized polymer, whose core-shell structure was verified by XPS with argon-ion etching. Then, the HNS-assembled reduced graphene oxide composite (defined as HNS-rGO) was prepared for RT NO sensing. The acetone-derived carbonized polymer shell not only assists the formation of amorphous Hemin core by disrupting their crystallization to release more Fe-N4 active sites, but provides protection to the core. Owing to the unique core-shell structure, the obtained HNS-rGO based sensor exhibited superior RT gas sensing properties toward NO, including a relatively higher response (Ra/Rg = 5.8, 20 ppm), a lower practical limit of detection (100 ppb), relatively reliable repeatability (over 6 cycles), excellent selectivity, and much higher long-term stability (less than a 5% decrease over 120 days). The sensing mechanism has also been proposed based on charge transfer theory. The superior gas sensing properties of HNS-rGO are ascribed to the more Fe-N4 active sites available under the amorphous state of the Hemin core and to the physical protection by the shell of acetone-derived carbonized polymer. This work presents a facile strategy of constructing a high-performance carbon-based core-shell nanostructure for gas sensing.

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It is a great challenge to develop efficient room-temperature sensing materials and sensors for nitric oxide (NO) gas, which is a biomarker molecule used in the monitoring of inflammatory respiratory diseases. Herein, Hemin (Fe (III)-protoporphyrin IX) is introduced into the nitrogen-doped reduced graphene oxide (N-rGO) to obtain a novel sensing material HNG-ethanol. Detailed XPS spectra and DFT calculations confirm the formation of carbon–iron bonds in HNG-ethanol during synthesis process, which act as electron transport channels from graphene to Hemin. Owing to this unique chemical structure, HNG-ethanol exhibits superior gas sensing properties toward NO gas (R_a/R_g = 3.05, 20 ppm) with a practical limit of detection (LOD) of 500 ppb and reliable repeatability (over 5 cycles). The HNG-ethanol sensor also possesses high selectivity against other exhaled gases, high humidity resistance, and stability (less than 3% decrease over 30 days). In addition, a deep understanding of the gas sensing mechanisms is proposed for the first time in this work, which is instructive to the community for fabricating sensing materials based on graphene-iron derivatives in the future.

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In this work, an in-situ XPS analysis test combined self-designed high precision fretting wear tester was carried out to study the fretting wear behavior and the resulting tribo-oxidation of thermal-oxidation film on Ti6Al4V titanium alloy under the varied working atmosphere. The fretting-induced tribo-oxidation under the air and vacuum (4 × 10-3 Pa) environment was analyzed and its response on the resulting fretting wear resistance and damage mechanism was discussed. Results show that the working environment plays a significant role in the formation of tribo-oxidation and then determining the fretting wear resistance. Thermal-oxidation film in the vacuum atmosphere shows a better fretting wear resistance than that in the air atmosphere for all fretting regimes, except for partial slip regime (PSR) where there is an equivalent fretting wear resistance. Compared with the substrate Ti6Al4V titanium alloy, the thermal-oxidation film in the vacuum atmosphere performs a good protection for titanium alloy, especially for slip regime (SR), but not applied for air atmosphere.

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An experimental investigation was conducted to study the fretting wear behavior of low alloyed construction steel in the tempered fully martensitic state. The resulting damage mechanism and the resistance to fretting wear of martensitic steels subjected to different tempering temperature was evaluated and compared with the virgin (un-tempered) martensitic steel under the different loading conditions. The results show that the friction coefficient increases with the increase of the tempering temperature for all the applied loads. The fretting wear resistance mainly depends on the tempering temperature. Compared to the virgin (un-tempered) full martensite, most of the tempered martensites have better fretting wear resistance, in which the tempered martensitic (TM) steel of 200° due to a good balance of strength and ductility has a super fretting wear resistance for all loading conditions. In addition, the correlation of fretting wear resistance with the initial hardness was discussed.

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Tree-level information can be estimated based on light detection and ranging (LiDAR) point clouds. We propose to develop a quantitative structural model based on terrestrial laser scanning (TLS) point clouds to automatically and accurately estimate tree attributes and to detect real trees for the first time. This model is suitable for forest research where branches are involved in the calculation. First, the Adtree method was used to approximate the geometry of the tree stem and branches by fitting a series of cylinders. Trees were represented as a broad set of cylinders. Then, the end of the stem or all branches were closed. The tree model changed from a cylinder to a closed convex hull polyhedron, which was to reconstruct a 3D model of the tree. Finally, to extract effective tree attributes from the reconstructed 3D model, a convex hull polyhedron calculation method based on the tree model was defined. This calculation method can be used to extract wood (including tree stem and branches) volume, diameter at breast height (DBH) and tree height. To verify the accuracy of tree attributes extracted from the model, the tree models of 153 Chinese scholartrees from TLS data were reconstructed and the tree volume, DBH and tree height were extracted from the model. The experimental results show that the DBH and tree height extracted based on this model are in better consistency with the reference value based on field survey data. The bias, RMSE and R² of DBH were 0.38 cm, 1.28 cm and 0.92, respectively. The bias, RMSE and R² of tree height were-0.76 m, 1.21 m and 0.93, respectively. The tree volume extracted from the model is in better consistency with the reference value. The bias, root mean square error (RMSE) and determination coefficient (R²) of tree volume were-0.01236 m³, 0.03498 m³ and 0.96, respectively. This study provides a new model for nondestructive estimation of tree volume, above-ground biomass (AGB) or carbon stock based on LiDAR data.

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