Chemical Papers最新文献

A two-dimensional simulation was employed to investigate the influence of gas temperature on the collision frequency for both particle–wall and particle–particle collisions. The study examined the collision frequencies within the common temperature range of 0–100 °C. The results demonstrated that the particle–wall collision frequency was proportional to (sqrt T), whereas the particle–particle collision frequency was proportional to (1/sqrt T), where T represents the gas temperature. The particle–wall collision frequency exhibited higher values and less random dispersion around the fitted function compared to the particle–particle collision frequency. A significant deviation from the fitted function (1/sqrt T) was observed at low particle densities. These findings validate the key predictions of kinetic theory and provide deeper insights into the molecular collision dynamics relevant to gaseous and plasma systems, particularly in scenarios involving temperature-dependent interactions.

Indium doped cadmium oxide nanoparticles Cd_1-xIn_xO at x = 0, 0.03, 0.05 and 0.07 were prepared using facile solid-state reaction and studied the role of indium (In) on physical properties of the Cd_1-xIn_xO nanoparticles. The synthesized nanoparticles were subjected to different characterization techniques such as XRD, FESEM, EDAX, FT-IR, UV–Vis-NIR, Raman, PL, and I–V characteristics. The XRD results confirmed that the Cd_1-xIn_xO nanoparticles were in cubic bixbyite structure with crystallite size in the range of 28 nm to 38 nm. Using the optical absorbance and reflectance spectra, the optical band gap of the Cd_1-xIn_xO nanoparticles was calculated, and it decreased from 1.81 to 1.76 eV with an increase in indium concentration. Clear peaks at 480 cm⁻¹ confirmed the metal–oxygen (Cd–O) bonding. The strong Raman modes are observed at 249.94 cm⁻¹, 261.92 cm⁻¹, 260.81 cm⁻¹, 260.53 cm⁻¹ in Raman spectra. The nanoparticle size was further confirmed by FE-SEM micrographs and histogram plots. In the PL spectra, emission peaks were observed at 423 nm, 485 nm, 532 nm, and 606 nm. The electrical properties were studied using two probe methods and the electrical resistance decreased with an increase in indium concentration.

Tin oxide (SnO₂) nanoparticles have been synthesized by Sol–Gel method. Polypyrrole (PPy)–tin oxide (SnO₂) hybrid nanocomposite has synthesized by chemical polymerization of PPy in the presence of SnO₂ nanoparticles. The band gap energy of the hybrid nanocomposite is calculated as 3.39 eV using UV–VIS absorption spectroscopy. The synthesized SnO₂ nanoparticle is tetragonal rutile structure which has been confirmed using X-ray diffraction spectroscopy. Scanning electron microscope is involved in the morphological analysis of the hybrid nanocomposite. Sensing electrodes are fabricated by spin coating of the sensing material on printed circuit board. The electrodes have been investigated for their sensing behaviour towards oxygen (O₂), hydrogen (H₂), ammonia (NH₃), carbon dioxide (CO₂) and liquid petroleum gas at room temperature. The fabricated electrode is selectively sensitive to 1 ppm of NH₃ with improved sensitivity (55%), response time (20 s) and recovery time (8 s). The electrode shows stable sensitivity towards NH₃ at different ranges of relative humidity (% RH) (30%, 50% and 80%). The electrode maintains 85.33% stability for the period of 50 days.

Polyaniline (PANI) and polyaniline-zinc oxide (PANI-ZnO) nanocomposite thin films have been developed to detect NH₃ gas. The physicochemical and optoelectronic properties of developed thin films were explored using X-ray diffraction (XRD), field effect scanning electron microscope (FESEM), ultraviolet-visible spectroscope (UV–Vis.) and Fourier transform infrared spectroscope characterization techniques. Structural and morphological properties were studied via XRD and FESEM characterization, respectively. The developed thin films exhibited an excellent response towards the target NH₃ gas with outstanding sensitivity, selectivity, linearity, and stability which were studied using the chemiresistive modality at room temperature. Compared to PANI thin film, PANI-ZnO thin films exhibit a 9-fold increment in sensing response with an R² value of 0.997. PANI film achieved a response time of ~70 s and a recovery time of ~100 s for 10 ppm NH₃ gas. PANI-ZnO thin films exhibit a response time of ~45 s and a recovery time of ~70 s for the same concentration. All developed films respond to a 5-ppm concentration of NH₃ considered a lower detection limit. The PANI-ZnO thin films show higher stability than PANI films measured in 45 days. Thus, the developed sensors confirmed their potential for the detection of NH₃ gas.

The electropolymerization of p-anisidine on graphite electrodes (GE) was investigated in acidic and basic media using cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM), electrochemical impedance spectroscopy (EIS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and scanning electron microscopy (SEM). The results showed significant differences in the polymer formation between the two media. In acidic media, a more electroactive but less stable material is deposited on the electrode surface, whereas the polymer formed in basic media exhibits high resistivity. The CV of the ferricyanide solutions highlighted these differences compared to the unmodified electrode, with an increased current for the acidic polymer and an almost non-existent redox response for the basic polymer. The EIS data corroborated the voltammetry results, revealing significant differences between the resistance values of the two polymers. The charge-transfer resistance increased with increasing pH, indicating slow electron-transfer kinetics. The SEM images show important differences between the graphite electrode and modified electrodes, suggesting the formation of distinct polymer films. ATR-FTIR spectra indicated polymer formation involving nitrogen atoms, with the methoxy group remaining unchanged. Based on electrochemical and spectroscopic evidence, a polymerization mechanism was proposed, involving the formation of tertiary amines in the polymer backbone. The irregular structure of the polymer formed in basic media can explain its resistive behavior. These findings contribute to the understanding of p-anisidine electropolymerization and development of polymer-modified electrodes for potential biosensor applications.

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Commonly used methods for MOF synthesis, such as solvothermal, mechanochemical, and electrochemical syntheses each, have their own disadvantages, such as long reaction times and the need for specialized equipment. The direct mixing method is a simple, fast, and cheap alternative that allows for MOF production at room temperature in times as short as 15 min. The room-temperature synthesis via a direct mixing method of Ni and Mg MOFs based on trimesic acid (BTC) and terephthalic acid (BDC) was studied by evaluating the effect on the product of the synthesis parameters: pH, base, stirring time, and metal–ligand molar ratio. It was found that the base used to adjust the pH was a critical factor to ensure the formation and purity of each MOF, where Na⁺ from NaOH could alter the crystal structure of Mg MOFs by incorporating into it due to its size similarity with Mg²⁺, while the ability of K⁺ from KOH to enter the crystal structure was much lesser due to its larger size and allowed for the proper development of the Mg MOFs crystal structure Similarly, a higher molar ratio of the ligand to the metal resulted in the incorporation of the base’s metal into the MOF as an impurity due to an excess of ligand without enough metal to coordinate with. Pure Ni-BTC and Ni-BDC MOFs could be obtained in ~ 15 min, while the Mg-BTC MOF always contained the base-forming metal as an impurity. All the products had irregular morphologies which resulted in lower surface areas and pore volumes when compared to MOFs obtained by other methods. The improvement of these properties is crucial to make the direct mixing method a viable alternative as higher surface areas and pore volumes are beneficial for many of the applications of MOFs, and it was identified that the choice of metal salt precursor plays an important role over these properties. As such, experimentation with different precursors is an important avenue of future research for the improvement of this method.

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Metal–organic frameworks (MOFs) have emerged as advanced crystalline materials with a periodic network structure made up of metal ions and organic ligands. The tailorable structure, pore size, surface area, and fluorescence of MOFs have led to their applications in diverse fields such as catalysis, sensing, gas storage, and photovoltaic. In the present study, a water-stable and dispersible iron-based MOF, i.e., NH₂-MIL-53(Fe), was hydrothermally synthesized, and demonstrated for the fluorescent detection of tetracycline (TC) antibiotic. The fluorescence of as-prepared NH₂-MIL-53(Fe) was quenched in the presence of TC due to the bonding between OH (of TC) and –NH₂ (of NH₂-MIL-53(Fe). This effective fluorescence quenching of NH₂-MIL-53(Fe) in the presence of TC can be attributed to a combination of the inner filter effect (IFE) and photo-induced electron transfer (PET) process from the ligand of NH₂-MIL-53(Fe) to TC, as described by theoretical and experimental studies. Under the optimum conditions, the ratio of fluorescence intensity and TC concentration showed a good linear range (0.05–1 µM) with a detection limit of 53 nM. Furthermore, the sensing probe was also used to detect TC in the spiked milk and juice samples with good recoveries, i.e., 91.3–98.5% and 95.7–104%, respectively. These results demonstrated the potential of NH₂-MIL-53(Fe) nanosensor to detect TC in real food samples.

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This study aimed to develop various CaO/zeolite adsorbents tailored for mid-temperature CO₂ adsorption. It investigated the CO₂ uptake efficiency of these adsorbents during carbonation–decarbonation cycles, highlighting the effect of CaO loading on the adsorption efficiency of adsorbents produced by different synthesis methods. CO₂ temperature-programmed desorption (CO₂-TPD) confirmed the CO₂ uptake capacity of CaO/USY at medium temperatures (300 °C). Among the CaO/zeolite adsorbents synthesized, the 10% CaO/USY exhibited the highest adsorption capacity at 300 °C, with a CO₂ uptake of 34.94 mmol·kg⁻¹ during the first cycle. The adsorbent also maintained its CO₂ capacity at 21 mmol·kg⁻¹ over the next nine cycles. Physicochemical analysis revealed that the porous volume of the 10% CaO/USY adsorbent was 0.28 cm³·g⁻¹, and its substantial surface area was 506.20 m²·g⁻¹, as determined through N₂ adsorption measurements. Characterization using FTIR and FESEM confirmed the successful loading and uniform dispersion of CaO on USY, respectively. X-ray diffraction (XRD) analysis revealed that 10% CaO/USY exhibited a smaller CaO crystallite size (29 nm) compared to bulk CaO (65 nm) and 15% CaO/USY (32 nm). Additionally, XRD identified the presence of calcium silicate salts (CaSiO₃ and Ca₂SiO₄) and calcium aluminate salts (Ca₁₂Al₁₄O₃₃), which reduce the CO₂ capture capacity but enhance cyclic stability. This finding suggests a potential approach to enhancing the effectiveness of adsorbents by optimizing the conversion of CaO into these salts. The results provide valuable insights for advancing and scaling up CaO/zeolite adsorbents for CO₂ capture.

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Mg–Ni alloys have high hydrogen storage capacity, easy activation, high discharge capacity but poor corrosion resistance. In order to further improve the hydrogen storage performance and corrosion resistance of Mg–Ni alloys, Ce metal was introduced into Mg–Ni alloys by electrodeposition. The hydrogen storage performance, corrosion resistance and electrochemical behavior of Mg–Ni–Ce hydrogen storage alloy coatings were investigated by electrochemical method. The first charging capacity of the Mg–Ni–Ce hydrogen storage alloy coatings is 797 mA h g⁻¹, and the first discharging capacity is 716.5 mA h g⁻¹. Compared with Mg–Ni alloy coatings, the addition of Ce element is beneficial to the positive shift of the corrosion voltage of the alloy and the improvement of corrosion resistance. Through cyclic voltammetry testing, the results show that the reduction mechanism of Ce³⁺ on the copper electrode is Ce³⁺ + 3e⁻ → Ce, and the reduction process is irreversible and controlled by diffusion, with a diffusion coefficient of 7.310 × 10⁻¹¹ cm² s⁻¹.

The anaerobic dehydrogenation of dodecanol to dodecanal has been investigated in a continuous fixed bed reactor over a series of Cu-based catalysts with different supports (SiO₂, Al₂O₃, ZnO and MgO). These catalysts have been systematically characterized by XRD, H₂-TPR, NH₃-TPD, CO₂-TPD, XPS and N₂ adsorption/desorption measurements. And the results indicate that the support has significant effect on the physicochemical properties of the catalysts and their catalytic performances, and Cu/SiO₂ exhibited the highest catalytic activity in the dehydrogenation. Synergistic effect between Cu⁺ and Cu⁰ species has been observed, and proper ratio of Cu⁺/Cu⁰ is believed to be able to improve the catalytic performance of Cu-based catalysts. The surface acidity and basicity demonstrate significant effect on the distribution of the products and the selectivity to aldehyde. Under the optimized conditions, an 82.3% conversion of dodecanol with an excellent 98.9% selectivity toward dodecanal could be obtained. Moreover, the catalytic performance of Cu/SiO₂ kept almost steady in 200 h, indicating its good stability and application potential in the dehydrogenation process.