Triethylamine, a crucial industrial raw material, poses significant threats to both the ecosystem and human health. However, detecting lower concentrations of TEA remains an arduous task. In this study, we report the facile hydrothermal and ultrasonic treatment synthesis of 2D SnSe2 micro-flower modified with 0D In2O3 nanoparticles to form SnSe2/In2O3 heterojunctions for the first time. The SnSe2/In2O3 sensor has a response value of 4.86 for 10 ​ppm TEA gas at 120 ​°C, with response and recovery times of 18 ​s and 79 ​s respectively, and detection limits as low as 100 ​ppb. In addition, the SnSe2/In2O3 sensor is essentially unaffected by humidity in the 30% RH to 60% RH range, and the SnSe2/In2O3 sensor response value decreases slightly in the 70% RH to 97% RH range, demonstrating excellent humidity tolerance. More importantly, the sensor maintained excellent cyclic-stability performance during a four-month cyclic stability test. The improved gas-sensitive performance can be attributed to the large number of n-n heterojunctions in the SnSe2/In2O3 material, which enhances the interfacial charge transfer, as well as the active-sites on the material surface. This work serves as a valuable complement to the TEA gas sensor and holds significant potential for detecting low concentrations of TEA at low temperatures in environmental sensing applications.

A series of UiO-66 samples with various amino functional group ratios were prepared by modulating the proportion of terephthalic acid (H2BDC) and aminoterephthalic acid (H2BDC-NH2) ligands, and the microstructure of the samples and dependence of methyl orange (MO) adsorption properties on the amino group content were investigated by X-ray diffraction, scanning electron microscopy, FTIR spectra, nitrogen adsorption, positron annihilation lifetime spectroscopy, and UV-vis spectra. The results showed that as the ratio of amino groups increased, the specific surface area and total porosity of the samples decreased, primarily due to decrement in the crystallinity as well as the bulky effect of amino groups in inherent pores. Interestingly, the amino-functionalized samples possessed considerable adsorption capacity of MO even in alkaline conditions due to the hydrogen bonding between the MO and -NH2 groups. The adsorption kinetics, isotherms, and thermodynamics revealed that MOs' adsorption process in amino-functionalized UiO-66s was exothermic, obeying a Langmuir-type adsorption dominated by chemisorption. UiO-66-NH2-0.4 (H2BDC:H2BDC-NH2 = 2:3) exhibited the best adsorption performance, with a maximum adsorption capacity of 336.7 mg/g, and the adsorption capacity was slightly decreased with increasing salt concentration in solution. UiO-66-NH2-0.4 could be easily regenerated by washing with a mixed solution of ethanol and water. The results demonstrated that although amino groups led to relatively less crystallinity and lower micropore volumes, the strong electrostatic attraction and hydrogen bonding between amino groups and MOs enhanced the adsorption capacity of MOs in amino-functionalized UiO-66s, in which MOs were adsorbed in two types of inherent pores, as shown by a significant decrement in positronium annihilation in them upon MO adsorption.

High-performance proton exchange membranes are of great importance for fuel cells. Here, we have synthesized polycarboxylate plasticizer modified MIL-101-Cr-NH2 (PCP-MCN), a kind of hybrid metal organic framework, which exhibits a superior proton conductivity. PCP-MCN nanoparticles are used as additives to fabricate PCP-MCN/Nafion composite membranes. Microstructures and characteristics of PCP-MCN and these membranes have been extensively investigated. Significant enhancement in proton conduction for PCP-MCN around 55 degrees C is interestingly found due to the thermal motion of the PCP molecular chains. Robust mechanical properties and higher thermal decomposition temperature of the composite membranes are directly ascribed to strong intermolecular interactions between PCP-MCN and Nafion side chains, i.e., the formation of substantial acid-base pairs (-SO3 ...H+-NH-), which further improves compatibility between additive and Nafion matrix. At the same humidity and temperature condition, the water uptake of composite membranes significantly increases due to the incorporation of porous additives with abundant functional groups and thus less crystallinity degree in comparison to pristine Nafion. Proton conductivity (sigma) over wide ranges of humidities (30 100% RH at 25 degrees C) and temperatures (30 98 degrees C at 100% RH) for prepared membranes is measured. The sigma in PCPMCN/Nafion composite membranes is remarkably enhanced, i.e. 0.245 S/cm for PCP-MCN-3wt.%/Nafion is twice that of Nafion membrane at 98 degrees C and 100% RH, because of the establishment of well-interconnected proton transport ionic water channels and perhaps faster protonation- deprotonation processes. The composite membranes possess weak humidity-dependence of proton transport and higher water uptake due to excellent water retention ability of PCP-MCN. In particular, when 3 wt.% PCP-MCN was added to Nafion, the power density of a single-cell fabricated with this composite membrane reaches impressively 0.480, 1.098 W/cm2 under 40% RH, 100% RH at 60 degrees C, respectively, guaranteeing it to be a promising proton exchange membrane.

Developing high-performance triethylamine (TEA) gas sensors are vital for human health. Defect engineering is a common method to enhance sensor performance. In this work, Cu-doped MoO3 nanobelts with different Cu/Mo molar ratios were synthesized by a low-cost solvothermal method. The 7.5CM sensor (molar ratio of Cu/ Mo=7.5%) exhibited a response value of 135 to 10 ppm TEA at 240 C-degrees. The sensor also showed excellent selectivity and sub-ppm detection limit (12.5 ppb). Based on X-ray photoelectron spectroscopy (XPS) and positron annihilation lifetime spectroscopy (PALS) analysis, the enhanced gas sensing performance and mechanism of Cu-doped MoO3 were discussed. PALS results indicated that higher V ' MoVo & sdot;& sdot;Vo & sdot;& sdot; vacancy defect clusters content on the surface of Cu-doped MoO3. The enhanced gas sensing performance was attributed to the increased concentration of vacancies/vacancy clusters on the surface of MoO3 nanobelts due to Cu doping, which facilitated the formation of surface chemisorbed oxygen and provided more active sites for the reaction of TEA. Additionally, CuMoO4 nanocrystals formed in MoO3 nanobelts can provide p-n heterojunctions on the surface, which generates potential barrier, enabling a wide variation range for the resistance of the sensor. This work provided a simple and effective method for the application of defect engineering in gas sensing materials.

Improving the proton conductivity (sigma) of proton exchange membranes at low temperatures is very important for expanding their application areas. Here, sulfonated poly ether ether ketone (SPEEK) membranes were prepared with different sulfonation degrees, and its maximum ion exchange capacity is 3.15 mmol/g for 10 h at 60 degrees C. Highly sulfonated SPEEK membrane exhibits ultra-high water uptake and excellent proton conductivity of 0.074 S/cm at -25 degrees C due to its abundant -SO3H. Nevertheless, its high swelling ratio and low mechanical strength are not conducive to the practical application of the membrane. Luckily, by employing the chelation of Cu2+ with -SO3- on the SPEEK chain, Cu2+-coordinated SPEEK membranes were prepared, and they not only retain high -SO3H content but also possess robust mechanical properties and good dimensional stability compared to pristine SPEEK membrane. Meanwhile, the sigma of the SPEEK-Cu membrane reaches 0.054 S/cm at -25 degrees C, and its fuel cell maximum power (W-max) reaches 0.42 W/cm(2) at -10 degrees C, demonstrating superior low-temperature performance in comparison to other reported materials. Particularly, water states in the prepared membranes are quantified by low-temperature differential scanning calorimetry. Because much more water bound to the plentiful SO3H and Cu2+ inside the membrane endows it with anti-freezing performance, the decay of the sigma and the W-max for the SPEEK-Cu membrane is retarded at sub-zero temperatures. It is envisioned that composite membranes comprising metal ions such as Cu2+-SPEEK have a high potential for sub-zero fuel cell applications.

Big crystals of HKUST-1 were synthesized under solvothermal conditions, and HKUST-1 fine powders were also ground from them and directly synthesized. The specific surface areas of the powders were found to be much smaller than that of the big crystals, indicative of micropore collapse in the powders. Interestingly, positron annihilation lifetime spectroscopy (PALS) showed two long ortho-positronium (o-Ps) lifetimes for the powders representing o-Ps annihilation in two types of inherent pores of HKUST-1, whereas only one long lifetime in the relatively larger pores could be derived for the big crystals. Meanwhile, continuous positron lifetime analysis showed two well-decomposed o-Ps lifetime distributions accompanied by relatively higher total o-Ps intensities in the powders. Due to the nature of o-Ps atoms in porous materials, they may diffuse in well-interconnected pores, and preferentially be localized and merely annihilate in larger pores in the big crystals of HKUST-1 with intact frameworks, resulting in only one o-Ps lifetime in them. The abnormal PALS results can be well explained for the collapse of large surface pores and the formation of a dense layer on the surfaces of fine powders of HKUST-1, demonstrating PALS is a useful method for studying the pore structures of metal-organic frameworks (MOFs).

In this work, MOF-5, consisted of [Zn4O]6+ clusters connected with organic linkers terephthalic acid (H2BDC) to form a cubic network, was synthesized at different temperatures. Various measurement methods including powder X-ray diffraction patterns, scanning electron microscopy, thermos-gravimetric analysis, nitrogen adsorption-desorption isotherms at 77 K, and positron annihilation lifetime spectroscopy (PALS) were applied to investigate the properties of MOF-5. It was found that the crystallinity sizes, and porosity strongly depended on the synthesis temperature. Results showed that higher synthesis temperature was favorable to improve the porosity of MOFs because of the removal of residual ligand molecules. Remarkably, significant differences in pore radius distributions derived from nitrogen adsorption and PALS was obtained from MOF-5 synthesized at 110 °C, suggesting that there exist closed pores due to the presence of ligand molecules in the inherent pores and/or pore entrances, where nitrogen molecules could not get in.

Buffer layers of TiO2 nanoparticles are introduced on the surface of the MIL-101-Cr, a kind of metal-organic frameworks (MOFs), to improve performances of MOFs/Nafion proton exchanging membranes. A series of Nafion composite membranes are fabricated by doping TiO2-wrapped MIL-101-Cr (TiO2@MIL-101-Cr). The water uptakes of composite membranes reasonably increase while their swelling ratios unexpectedly reduce in comparison to pristine Nafion. Nevertheless, the swelling ratios of composite membranes gradually increase with the increment of TiO2@MIL-101-Cr due to their enlarged free volumes and more amorphous phases. The introduction of additive facilitates water molecules diffusion as well as overall hydration of the composite membranes, resulting in a significant increment in the proton conductivity. As a result of the formation of extra proton conducting highways both around/in TiO2@MIL-101-Crs and the Nafion matrix, a composite membrane in single-cell possesses a maximum power density of 0.946 W/cm2. Furthermore, higher thermal and oxidative stabilities are observed for the composite membranes. This work demonstrates that the addition of encapsulated structural TiO2@MIL-101-Crs in Nafion is promising for fabricating proton exchanging membranes with superior electrochemical performance and high thermal, oxidative stabilities.