Oussama M. El-Kadri

Semiconducting Metal Oxide Based Sensors for Selective Gas Pollutant Detection

A review of some papers published in the last fifty years that focus on the semiconducting metal oxide (SMO) based sensors for the selective and sensitive detection of various environmental pollutants is presented.

Pyrene-directed growth of nanoporous benzimidazole-linked nanofibers and their application to selective CO2 capture and separation

A pyrene-based benzimidazole-linked polymer (BILP-10) has been synthesized by the co-condensation of 1,3,6,8-tetrakis(4-formylphenyl)pyrene and 1,2,4,5-benzenetetramine tetrahydrochloride in dimethylformamide. The use of pyrene as a molecular building unit leads to the formation of self-assembled nanofibers that have moderate surface area (SABET = 787 m2 g−1) and very high CO2/N2 (128) and CO2/CH4 (18) selectivities at 273 K. Furthermore, results from gas uptake measurements indicate that BILP-10 can store significant amounts of CO2 (4.0 mmol at 273 K/1.0 bar) and H2 (1.6 wt% at 77 K/1.0 bar) with respective isosteric heats of adsorption of 38.2 and 9.3 kJ mol−1 which exceed all of the previously reported values for BILPs and are among the highest values reported to date for unmodified porous organic polymers. Under high pressure settings, BILP-10 displays moderate uptakes of H2 (27.3 g L−1, 77 K/40 bar), CH4 (72 L L−1, 298 K/40 bar), and CO2 (13.3 mmol g−1, 298 K/40 bar). The unusually high CO2 and H2 binding affinities of BILP-10 are presumably facilitated by the amphoteric pore walls of the polymer that contain imidazole moieties and the predominant microporous nature.

Preparation and characterization of molybdenum and tungsten nitride nanoparticles obtained by thermolysis of molecular precursors

Treatment of Mo(NtBu)2Cl2 with [K(Ph2pz)(THF)]6 (pz = pyrazolyl) in tetrahydrofuran afforded Mo(NtBu)2(Ph2pz)2 (85%), while treatment of W(NtBu)2(NHtBu)2 with 3,5-diphenylpyrazole afforded W(NtBu)2(Ph2pz)2 (97%). The complexes M(NtBu)2(Ph2pz)2 were characterized completely by spectral and analytical data, and by an X-ray crystal structure determination for Mo(NtBu)2(Ph2pz)2. Thermolysis of M(NtBu)2(Ph2pz)2 at 800 °C under nitrogen afforded 2–3 nm metal nitride nanoparticles that were embedded in an amorphous carbon–oxygen matrix, as determined by X-ray powder diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. X-Ray photoelectron spectroscopy also revealed the presence of metal oxide phases, which were amorphous by X-ray powder diffraction. The nanoparticles prepared at 800 °C were insoluble. Thermolysis of M(NtBu)2(Ph2pz)2 at 425 °C afforded amorphous 2–3 nm nanoparticles, as determined by X-ray powder diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. X-Ray photoelectron spectroscopy suggested a molybdenum(IV) nitride and W2N/WN, as well as MoO3 and an oxidized tungsten nitride. Materials prepared at 425 °C were not embedded in a matrix, and were soluble in tetrahydrofuran. Infrared and NMR spectroscopy suggested the presence of surface organic fragments that contain alkyl-substituted phenyl groups. Such surface groups are most likely derived from decomposition of the heterocyclic ligands. Simultaneous differential thermal analysis/thermogravimetric analysis indicated that the amorphous nitride materials convert to crystalline nanoparticles consistent with M2N phases between 600–700 °C, along with a weight loss that may correspond to dinitrogen evolution. The amorphous carbon–oxygen matrix also forms upon heating from 425 to 800 °C. This work provides the first description of tungsten nitride nanoparticles, as well as the first description of soluble group 4–6 nanoparticles.

Nitrogen-Rich Porous Polymers for Carbon Dioxide and Iodine Sequestration for Environmental Remediation

The use of fossil fuels for energy production is accompanied by carbon dioxide release into the environment causing catastrophic climate changes. Meanwhile, replacing fossil fuels with carbon-free nuclear energy has the potential to release radioactive iodine during nuclear waste processing and in case of a nuclear accident. Therefore, developing efficient adsorbents for carbon dioxide and iodine capture is of great importance. Two nitrogen-rich porous polymers (NRPPs) derived from 4-bis-(2,4-diamino-1,3,5-triazine)-benzene building block were prepared and tested for use in CO2 and I2 capture. Copolymerization of 1,4-bis-(2,4-diamino-1,3,5-triazine)-benzene with terephthalaldehyde and 1,3,5-tris(4-formylphenyl)benzene in dimethyl sulfoxide at 180 °C afforded highly porous NRPP-1 (SABET = 1579 m2 g-1) and NRPP-2 (SABET = 1028 m2 g-1), respectively. The combination of high nitrogen content, π-electron conjugated structure, and microporosity makes NRPPs very effective in CO2 uptake and I2 capture. NRPPs exhibit high CO2 uptakes (NRPP-1, 6.1 mmol g-1 and NRPP-2, 7.06 mmol g-1) at 273 K and 1.0 bar. The 7.06 mmol g-1 CO2 uptake by NRPP-2 is the second highest value reported to date for porous organic polymers. According to vapor iodine uptake studies, the polymers display high capacity and rapid reversible uptake release for I2 (NRPP-1, 192 wt % and NRPP-2, 222 wt %). Our studies show that the green nature (metal-free) of NRPPs and their effective capture of CO2 and I2 make this class of porous materials promising for environmental remediation.

Effective Approach for Increasing the Heteroatom Doping Levels of Porous Carbons for Superior CO2 Capture and Separation Performance

Development of efficient sorbents for carbon dioxide (CO2) capture from flue gas or its removal from natural gas and landfill gas is very important for environmental protection. A new series of heteroatom-doped porous carbon was synthesized directly from pyrazole/KOH by thermolysis. The resulting pyrazole-derived carbons (PYDCs) are highly doped with nitrogen (14.9-15.5 wt %) as a result of the high nitrogen-to-carbon ratio in pyrazole (43 wt %) and also have a high oxygen content (16.4-18.4 wt %). PYDCs have a high surface area (SABET = 1266-2013 m2 g-1), high CO2 Qst (33.2-37.1 kJ mol-1), and a combination of mesoporous and microporous pores. PYDCs exhibit significantly high CO2 uptakes that reach 2.15 and 6.06 mmol g-1 at 0.15 and 1 bar, respectively, at 298 K. At 273 K, the CO2 uptake improves to 3.7 and 8.59 mmol g-1 at 0.15 and 1 bar, respectively. The reported porous carbons also show significantly high adsorption selectivity for CO2/N2 (128) and CO2/CH4 (13.4) according to ideal adsorbed solution theory calculations at 298 K. Gas breakthrough studies of CO2/N2 (10:90) at 298 K showed that PYDCs display excellent separation properties. The ability to tailor the physical properties of PYDCs as well as their chemical composition provides an effective strategy for designing efficient CO2 sorbents.

Chapter 11:Designing Functional Porous Organic Frameworks for Gas Storage and Separation

Over the past decade, considerable progress has been made in the targeted synthesis of porous organic polymers (POPs) and their use in gas storage and separation. POPs are prepared by versatile synthetic avenues from purely organic building blocks and can be tailored to possess specific textural and chemical properties to enhance their performance. This chapter provides an overview of the synthesis strategies for preparing highly porous POPs with special emphasis on the design and functionalization of the frameworks at the molecular level for improved gas storage like hydrogen, methane, and carbon dioxide. In addition, the performance of POPs in carbon dioxide separation from nitrogen and methane is discussed. The chemical composition and physical properties of POPs can be controlled by both pre-synthesis and post-synthesis modification steps. The resultant functionalized networks enable effective gas separation which is very important for natural gas purification and mitigating CO2 release to the atmosphere. Finally, we present the current challenges and opportunities in the development and use of POPs.