Reversible Adsorption of Ammonia in the Crystalline Solid of a CO2H-Functionalized Cyclic Oligophenylene

Ammonia (NH3) is a viable candidate for the storage and distribution of hydrogen (H2) due to its exceptional volumetric and gravimetric hydrogen energy density. Therefore, it is desirable to develop NH3 storage materials that exhibit robust stability across numerous adsorption-desorption cycles. While porous materials with polymeric frameworks are often used for NH3 capture, achieving reversible NH3 uptake remains a formidable challenge, primarily due to the high reactivity of NH3. Here, we advocate the use of CO2H-functionalized cyclic oligophenylene 1a with high chemical stability as a novel single-molecule-based adsorbent for NH3. Simple reprecipitation of 1a selectively yielded microporous crystalline solid 1a (N). Crystalline 1a (N) adsorbs up to 8.27 mmol/g of NH3 at 100 kPa and 293 K. Adsorbed NH3 in the pore of 1a (N) has a packing density of 0.533 g/cm3 at 293 K, which is close to the density of liquid NH3 (0.681 g/cm3 at 240 K). Crystalline 1a (N) also exhibits reversible NH3 adsorption over at least nine cycles, sustaining its storage capacity (1st cycle: 8.27 mmol/g; 9th cycle: 8.25 mmol/g at 100 kPa and 293 K) and crystallinity. During each desorption cycle, NH3 was removed from 1a (N) under reduced pressure (∼65 Pa), leaving <3% of the total uptake, and 1a (N) was fully purged under dynamic vacuum conditions (∼5 × 10-4 Pa at 293 K for 1 h) before the subsequent adsorption cycles. Thus, microporous crystalline 1a (N) can reliably adsorb and desorb NH3 repeatedly, which avoids the need for heat-based activation between cycles.

Fluorescent lamp tungsten filament thermionic emission gun as a novel humidity optical sensor

Detecting humidity have been remained a continuing concern within some important areas such as structural health, food processing, industrial as well as agricultural products. In this study, a novel humidity optical sensor is introduced based on the thermionic emission of tungsten filament using the fluorescent lamp set-up. Estimated blue compliant using a charged coupling device camera in optical image of the tungsten filament was confirmed as an appropriate detection system for relative humidity (RH) sensing. The fabricated optical sensor has wide linear range (2.0–98% RH), improved detection limit (< 5.0% RH), acceptable saturated limit (> 99.0% RH), improved percentage of relative standard deviation (4.18%, n = 2), adequate hysteresis (< 4.0% RH) and a shorter rise time (< 5.0 s), respectively. The mechanism behind this detection system is based on the interaction between H₂O and tungsten filament during formation of W\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{O}}_{3}$$\end{document}O3.x \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{H}}_{2}$$\end{document}H2O (x = 1–2) in terms of some spectroscopic obtained evidences as well as Fourier transform infrared and X-ray diffraction spectrometries.

Microporous Zeolite@Vertically Aligned Mg-Al Layered Double Hydroxide Core@Shell Structures with Improved Hydrophobicity and Toluene Adsorption Capacity under Wet Conditions

Zeolites have been recognized as one type of the most promising adsorbents for capturing volatile organic compounds (VOCs, e.g., toluene), but their performance suffers severely from water vapor under wet conditions. In this contribution, we demonstrated that the hydrophobicity of microporous zeolites can be significantly improved by coating vertically aligned LDH nanoplatelets when the contact angle is increased from 16.5-20.1° to 44.4-64.2°. The toluene adsorption capacity of such synthesized zeolite@LDH core@shell composites in wet conditions can thus be largely enhanced when the breakthrough time is increased from 6.4-10.8 to 20.1-27.5 min.

Reversible room temperature ammonia gas absorption in pore water of microporous silica-alumina for sensing applications

Microporous silica and silica-alumina powders exhibit a reversible uptake and release of ammonia gas from water vapor containing gas mixtures at ambient temperature, with capacities of 0.9 and 2.0 mmol g-1 in the presence of 100 ppm and 1000 ppm NH3, respectively. The ammonia trapping mechanism was revealed using a combination of direct excitation 1H MAS, 1H-1H EXSY and 1H DQ-SQ NMR spectroscopy, indicating that the major part of the captured ammonia is blended in the hydrogen bonded water network in the pores of the adsorbent. A small fraction is irreversibly bound as result of protonation and chemisorption. While common ammonia adsorbents need thermal regeneration, microporous silica-alumina can be regenerated by sweeping with dry gas at ambient temperature, desorbing the physisorbed fraction together with occluded water. As carbon dioxide does not interfere with the ammonia absorption process, this reversible absorption process of ammonia gas at ambient temperature is particularly attractive for sensor applications.

Dual role of Cu2O nanocubes as templates and networking catalysts for hollow and microporous Fe-porphyrin networks

Cu₂O nanocubes acted not only as networking catalysts but also as shape controlling templates for the synthesis of hollow and microporous Fe porphyrin networks.

Ammonium removal from high-strength aqueous solutions by Australian zeolite

Removal of ammonium nitrogen (NH4(+)-N) particularly from sources which are highly rich in nitrogen is important for addressing environmental pollution. Zeolites, aluminosilicate minerals, are commonly used as commercial adsorbents and ion-exchange medium in number of commercial applications due to its high adsorption capacity of ammonium (NH4(+)). However, detailed investigations on NH4(+) adsorption and ion exchange capacities of Australian natural zeolites are rare, particularly under higher NH4(+) concentrations in the medium. Therefore, this study was conducted to determine NH4(+) adsorption characteristics of Australian natural zeolites at high NH4(+) concentrations with and without other chemical compounds in an aqueous solution. Results showed that initial NH4(+) concentration, temperature, reaction time, and pH of the solution had significant effects on NH4(+) adsorption capacity of zeolite. Increased retention time and temperature generally had a positive impact on adsorption. Freundlich model fitted well with adsorption process of Australian natural zeolites; however, Langmuir model had best fitted for the adsorption process of sodium (Na(+)) treated zeolites. NaCl treatment increased the NH4(+) adsorption capacity of Australian zeolites by 25% at 1000 mg-N, NH4(+) solution. The maximum adsorption capacity of both natural Australian zeolites and Na(+) treated zeolites were estimated as 9.48 and 11.83 mg-N/g, respectively, which is lower than many zeolites from other sources. Compared to the NH4(+) only medium, presence of other competitive ions and acetic acid in the medium (resembling composition in digested swine manure slurries) reduced NH4(+) removal of natural and Na(+) treated zeolites by 44% and 57%, respectively. This suggests detailed investigations are required to determine practically achievable NH4(+) -N removal potential of zeolites for applications in complex mediums such as animal manure slurries.

Microporous organic network@PET hybrid membranes: removal of minute organic pollutants dissolved in water

Microporous organic networks (MONs) were incorporated into a polyethylene terephthalate (PET) membrane. The resultant MON@PET hybrid membranes showed promising filtration towards aromatic pollutants dissolved in water.