20 research outputs found
Highly porous photoluminescent diazaborole-linked polymers: synthesis, characterization, and application to selective gas adsorption
The formation of boron–nitrogen (B–N) bonds has been widely explored for the synthesis of small molecules, oligomers, or linear polymers; however, its use in constructing porous organic frameworks remains very scarce. In this study, three highly porous diazaborole-linked polymers (DBLPs) have been synthesized by condensation reactions using 2,3,6,7,14,15-hexaaminotriptycene and aryl boronic acids. DBLPs are microporous and exhibit high Brunauer–Emmett–Teller surface area (730–986 m2 g−1) which enable their use in small gas storage and separation. At ambient pressure, the amorphous polymers show high CO2 (DBLP-4: 4.5 mmol g−1 at 273 K) and H2 (DBLP-3: 2.13 wt% at 77 K) uptake while their physicochemical nature leads to high CO2/N2 (35–42) and moderate CO2/CH4 (4.9–6.2) selectivity. The electronic impact of integrating diazaborole moieties into the backbone of these polymers was investigated for DBLP-4 which exhibits green emission with a broad peak ranging from 350 to 680 nm upon excitation with 340 nm in DMF without photobleaching. This study demonstrates the effectiveness of B–N formation in targeting highly porous frameworks with promising optical properties
Covalent organic frameworks
The first members of covalent organic frameworks (COF) have been designed and successfully synthesized by
condensation reactions of phenyl diboronic acid C6H4[B(OH)2]2 and hexahydroxytriphenylene C18H6(OH)6. The
high crystallinity of the products (C3H2BO)6 (C9H12)1 (COF-1) and C9H4BO2 (COF-5) has allowed definitive
resolution of their structure by powder X-ray diffraction methods which reveal expanded porous graphitic layers that
are either staggered (COF-1, P63/mmc) or eclipsed (COF-5, P6/mmm). They exhibit high thermal stability (to
temperatures up to 500- to 600-C), permanent porosity, and high surface areas (711 and 1590 m2/g, respectively)
surpassing those of related inorganic frameworks. A similar approach has been used for the design of other extended
structures
Metal-organic and covalent organic frameworks (MOFs and COFs) as adsorbents for environmentally significant gases (H2, CO2, and CH4)
A series of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) possessing
various functionalities, pore structures, and surface areas were evaluated for sorption and storage
properties of environmentally significant gases (H_2, CO_2, and CH_4). It was concluded that the gas
sorption behavior follows a general trend that materials with high surface area show enhanced gas
uptake performance. For example, MOF-177 (SA = 5200 m^2/g) captures 7.2 wt% of H_2 at 77 K and 19
wt% of CH_4 at 298 K. In addition, MOF-177 exhibits exceptionally high gravimetric CO_2 uptake up to
120 wt% at 298 K. Similarly, the gas storage capacity for COFs seems to follow the same trend and it is
determined by the apparent surface area. The architectural stability of both COFs and MOFs upon high
pressure H_2 and CH_4 gas sorption measurements were manifested by isotherms which reach saturation
without significant hysteresis
Designed Synthesis of 3D Covalent Organic Frameworks
Three-dimensional covalent organic frameworks (3D COFs) were synthesized by targeting two nets based on triangular and tetrahedral nodes: ctn and bor. The respective 3D COFs were synthesized as crystalline solids by condensation reactions of tetrahedral tetra(4-dihydroxyborylphenyl) methane or tetra(4-dihydroxyborylphenyl)silane and by co-condensation of triangular 2,3,6,7,10,11-hexahydroxytriphenylene. Because these materials are entirely constructed from strong covalent bonds (C-C, C-O, C-B, and B-O), they have high thermal stabilities (400° to 500°C), and they also have high surface areas (3472 and 4210 square meters per gram for COF-102 and COF-103, respectively) and extremely low densities (0.17 grams per cubic centimeter)
Synthesis and Characterization of Porous Benzimidazole-Linked Polymers and Their Performance in Small Gas Storage and Selective Uptake
Porous organic polymers containing nitrogen-rich building
units
are among the most promising materials for selective CO<sub>2</sub> capture and separation which can have a tangible impact on the environment
and clean energy applications. Herein we report on the synthesis and
characterization of four new porous benzimidazole-linked polymers
(BILPs) and evaluate their performance in small gas storage (H<sub>2</sub>, CH<sub>4</sub>, CO<sub>2</sub>) and selective CO<sub>2</sub> binding over N<sub>2</sub> and CH<sub>4</sub>. BILPs were synthesized
in good yields by the condensation reaction between aryl-<i>o</i>-diamine and aryl-aldehyde building blocks. The resulting BILPs exhibit
moderate surface area (SA<sub>BET</sub> = 599–1306 m<sup>2</sup> g<sup>–1</sup>), high chemical and thermal stability, and
remarkable gas uptake and selectivity. The highest selectivity based
on initial slope calculations at 273 K was observed for BILP-2: CO<sub>2</sub>/N<sub>2</sub> (113) and CO<sub>2</sub>/CH<sub>4</sub> (17),
while the highest storage capacity was recorded for BILP-4: CO<sub>2</sub> (24 wt % at 273 K and 1 bar) and H<sub>2</sub> (2.3 wt %
at 77 K and 1 bar). These selectivities and gas uptakes are among
the highest by porous organic polymers known to date which in addition
to the remarkable chemical and physical stability of BILPs make this
class of material very promising for future use in gas storage and
separation applications
Effect of Acid-Catalyzed Formation Rates of Benzimidazole-Linked Polymers on Porosity and Selective CO<sub>2</sub> Capture from Gas Mixtures
Benzimidazole-linked
polymers (BILPs) are emerging candidates for gas storage and separation
applications; however, their current synthetic methods offer limited
control over textural properties which are vital for their multifaceted
use. In this study, we investigate the impact of acid-catalyzed formation
rates of the imidazole units on the porosity levels of BILPs and subsequent
effects on CO<sub>2</sub> and CH<sub>4</sub> binding affinities and
selective uptake of CO<sub>2</sub> over CH<sub>4</sub> and N<sub>2</sub>. Treatment of 3,3′-Diaminobenzidine tetrahydrochloride hydrate
with 1,2,4,5-tetrakisÂ(4-formylphenyl)Âbenzene and 1,3,5-(4-formylphenyl)-benzene
in anhydrous DMF afforded porous BILP-15 (448 m<sup>2</sup> g<sup>–1</sup>) and BILP-16 (435 m<sup>2</sup> g<sup>–1</sup>), respectively. Alternatively, the same polymers were prepared from
the neutral 3,3′-Diaminobenzidine and catalytic amounts of
aqueous HCl. The resulting polymers denoted BILP-15Â(AC) and BILP-16Â(AC)
exhibited optimal surface areas; 862 m<sup>2</sup> g<sup>–1</sup> and 643 m<sup>2</sup> g<sup>–1</sup>, respectively, only
when 2 equiv of HCl (0.22 M) was used. In contrast, the CO<sub>2</sub> binding affinity (<i>Q</i><sub>st</sub>) dropped from
33.0 to 28.9 kJ mol<sup>–1</sup> for BILP-15 and from 32.0
to 31.6 kJ mol<sup>–1</sup> for BILP-16. According to initial
slope calculations at 273 K/298 K, a notable change in CO<sub>2</sub>/N<sub>2</sub> selectivity was observed for BILP-15Â(AC) (61/50) compared
to BILP-15 (83/63). Similarly, ideal adsorbed solution theory (IAST)
calculations also show the higher specific surface area of BILP-15Â(AC)
and BILP-16Â(AC) compromises their CO<sub>2</sub>/N<sub>2</sub> selectivity
Systematic Postsynthetic Modification of Nanoporous Organic Frameworks for Enhanced CO<sub>2</sub> Capture from Flue Gas and Landfill Gas
Controlled postsynthetic nitration
of NPOF-1, a nanoporous organic
framework constructed by nickel(0)-catalyzed Yamamoto coupling of
1,3,5-trisÂ(4-bromophenyl)Âbenzene, has been performed and is proven
to be a promising route to introduce nitro groups and to convert mesopores
to micropores without compromising surface area. Reduction of the
nitro groups yields aniline-like amine-functionalized NPOF-1-NH<sub>2</sub> that has a micropore volume of 0.48 cm<sup>3</sup> g<sup>–1</sup>, which corresponds to 71% of the total pore volume
and a Brunauer–​Emmett–​Teller surface
area of 1535 m<sup>2</sup> g<sup>–1</sup>. Adequate
basicity of the amine functionalities leads to modest isosteric heats
of adsorption for CO<sub>2</sub>, which allow for high regenerability.
The unique combination of high surface area, microporous structure,
and amine-functionalized pore walls enables NPOF-1-NH<sub>2</sub> to
have remarkable CO<sub>2</sub> working capacity values for removal
from landfill gas and flue gas. The performance of NPOF-1-NH<sub>2</sub> in CO<sub>2</sub> removal ranks among the best by porous organic
materials
Exceptional Gas Adsorption Properties by Nitrogen-Doped Porous Carbons Derived from Benzimidazole-Linked Polymers
Heteroatom-doped
porous carbons are emerging as platforms for use in a wide range of
applications including catalysis, energy storage, and gas separation
or storage, among others. The use of high activation temperatures
and heteroatom multiple-source precursors remain great challenges,
and this study aims to addresses both issues. A series of highly porous
N-doped carbon (CPC) materials was successfully synthesized by chemical
activation of benzimidazole-linked polymers (BILPs) followed by thermolysis
under argon. The high temperature synthesized CPC-700 reaches surface
area and pore volume as high as 3240 m<sup>2</sup> g<sup>–1</sup> and 1.51 cm<sup>3</sup> g<sup>–1</sup>, respectively, while
low temperature activated CPC-550 exhibits the highest ultramicropore
volume of 0.35 cm<sup>3</sup> g<sup>–1</sup>. The controlled
activation process endows CPCs with diverse textural properties, adjustable
nitrogen content (1–8 wt %), and remarkable gas sorption properties.
In particular, exceptionally high CO<sub>2</sub> uptake capacities
of 5.8 mmol g<sup>–1</sup> (1.0 bar) and 2.1 mmol g<sup>–1</sup> (0.15 bar) at ambient temperature were obtained for materials prepared
at 550 °C due to a combination of a high level of N-doping and
ultramicroporosity. Furthermore, CPCs prepared at higher temperatures
exhibit remarkable total uptake for CO<sub>2</sub> (25.7 mmol g<sup>–1</sup> at 298 K and 30 bar) and CH<sub>4</sub> (20.5 mmol
g<sup>–1</sup> at 298 K and 65 bar) as a result of higher total
micropores and small mesopores volume. Interestingly, the N sites
within the imidazole rings of BILPs are intrinsically located in pyrrolic/pyridinic
positions typically found in N-doped carbons. Therefore, the chemical
and physical transformation of BILPs into CPCs is thermodynamically
favored and saves significant amounts of energy that would otherwise
be consumed during carbonization processes
Pyrene Bearing Azo-Functionalized Porous Nanofibers for CO2 Separation and Toxic Metal Cation Sensing
This article describes the construction of a novel luminescent azo-linked polymer from 1,3,6,8-tetra(4--aminophenyl)pyrene using a copper(I)-catalyzed oxidative homocoupling reaction
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 CO<sub>2</sub> and
I<sub>2</sub> capture. Copolymerization of 1,4-bis-(2,4-diamino-1,3,5-triazine)-benzene
with terephthalaldehyde and 1,3,5-trisÂ(4-formylphenyl)Âbenzene in dimethyl
sulfoxide at 180 °C afforded highly porous NRPP-1 (SA<sub>BET</sub> = 1579 m<sup>2</sup> g<sup>–1</sup>) and NRPP-2 (SA<sub>BET</sub> = 1028 m<sup>2</sup> g<sup>–1</sup>), respectively. The combination
of high nitrogen content, π-electron conjugated structure, and
microporosity makes NRPPs very effective in CO<sub>2</sub> uptake
and I<sub>2</sub> capture. NRPPs exhibit high CO<sub>2</sub> uptakes
(NRPP-1, 6.1 mmol g<sup>–1</sup> and NRPP-2, 7.06 mmol g<sup>–1</sup>) at 273 K and 1.0 bar. The 7.06 mmol g<sup>–1</sup> CO<sub>2</sub> 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 I<sub>2</sub> (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 CO<sub>2</sub> and I<sub>2</sub> make this class
of porous materials promising for environmental remediation