Dual-functionalized porous organic polymer as reusable catalyst for one-pot cascade C C bond-forming reactions

Urea-rich porous organic polymer as a hydrogen bond catalyst for Knoevenagel condensation reaction and synthesis of 2,3-dihydroquinazolin-4(1H)-ones

In this research, a new urea-rich porous organic polymer (urea-rich POP) as a hydrogen bond catalyst was synthesized via a solvothermal method. The physiochemical properties of the synthesized urea-rich POP were investigated by using different analyses like Fourier transform infrared (FT-IR) spectroscopy, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), energy-dispersive X-ray spectroscopy (EDS), elemental mapping analysis, X-ray diffraction analysis (XRD) and Brunauer-Emmett-Teller (BET) techniques. The preparation of urea-rich POP provides an efficacious platform for designing unique hydrogen bond catalytic systems. Accordingly, urea-rich POP, due to the existence of several urea moieties as hydrogen bond sites, has excellent performance as a catalyst for the Knoevenagel condensation reaction and multi-component synthesis of 2,3-dihydroquinazolin-4(1H)-ones.

Preparation of a Dual-Functionalized Acid-Base Macroporous Polymer via High Internal Phase Emulsion Templating as a Reusable Catalyst for One-Pot Deacetalization-Henry Reaction

A macroporous dual-functional acid-base covalent organic polymer catalyst poly(St-VBC)-NH₂-SO₃H was prepared using high internal phase emulsion polymerization using vinylbenzyl chloride (VBC), styrene (St), and divinylbenzene (DVB) as substrates toluene as a porogenic solvent, and subsequent modification with ethylenediamine and 1,3-propane sultone. The role of various amounts of toluene as the porogenic solvent as well as the amount of 1,3-propane sultone (different ratio of acid/base sites) on the structure of the prepared materials have been carefully investigated. The prepared materials were characterized by Fourier transform infrared (FT-IR), CHNS elemental analysis, energy-dispersive X-ray (EDX), elemental mapping, field emission scanning electron microscopy (FE-SEM), and thermalgravimetric analysis (TGA). The catalytic activity of the poly(St-VBC)-NH₂-SO₃H series with different acid/base densities was assessed for one-pot cascade C-C bond-forming reactions involving deacetylation-Henry reactions. The poly(St-VBC)-NH₂-SO₃H(20) sample bearing 1.82 mmol/g of N (base site) and 1.16 mmol/g (acid site) showed the best catalytic activity. The catalyst demonstrated superior activity compared to the homogeneous catalysts, poly(St-DVB)-SO₃H+EDA, poly(St-VBC)-NH₂+chlorosulfonic acid, and poly(St-DVB)-SO₃H+poly(St-VBC)-NH₂ as the catalyst system. The optimized catalyst showed excellent catalytic performance with 100% substrate conversion and 100% yield of the final product in the one-pot production of β-nitrostyrene from benzaldehyde dimethyl acetal under cascade reactions comprising acid-catalyzed deacetalization and base-catalyzed Henry reactions. It was shown that these catalysts were reusable for up to four consecutive runs with a very slight loss of activity. The excellent performance of the catalyst was attributed to the excellent chemical and physical properties of the developed support since it provides an elegant route for preparing site-isolated acid-base dual heterogenized functional groups and preventing their deactivation via chemical neutralization.

The effects of continuous- and stop-flow gas streams on adsorptive removal of benzene vapor using type - II covalent organic polymers

Various materials have been investigated for the adsorptive removal of volatile organic compounds (VOCs, such as benzene). However, most materials proposed for the adsorptive removal of gaseous benzene (and other VOCs) perform relatively poorly (e.g., an impractically low-service 10% breakthrough volume [BTV10] at < 100 ppm). The adsorbent uptake rate (mg g^-1 min^-1) can also be assessed as a function of the gas-stream flow rate (or space velocity). The main aim of this study is to explore the effect of two different gas-stream supply modes - stopped flow (at a fixed stream flow rate of 330 mL atm min^-1) vs. continuous flow (a variable-stream flow rate of 100, 200, or 330 mL atm min^-1) on the adsorption metrics of gaseous benzene on 5 mg of two types of - II covalent organic polymers (COPs: CBAP-1 [DETA], CD; or CBAP-1 [EDA], CE). The sorbent tube outlet stream was sampled by two respective sampling methods (i.e., a large-volume injector [LVI] for stopped flow vs. syringe injection [SI] for continuous flow) for sample quantitation by gas chromatography flame-ionization detection (GC-FID). The observed BTV10 values in the two sampling modes were similar when tested using 10 ppm benzene, irrespective of sorbents: 56/60 (CD) vs. 620/624 L atm g^-1 (CE). BTV10 values increased systematically with decreasing stream-flow rates to reflect the importance of space velocity in adsorptive removal of benzene. The overall assessment of adsorption performance between stopped flow (LVI) and continuous flow (SI) revealed that the performance of the adsorbent is independent of flow mode (e.g., when performance was compared at flow rate of 330 mL min^-1).

Magnetic core–shell dendritic mesoporous silica nanospheres anchored with diamine as an efficient and recyclable base catalyst

In the present study, diamine-functionalized magnetic core–shell dendritic mesoporous silica nanospheres have been successfully synthesized by an oil–water biphasic stratification-coating strategy.

Adsorption properties of advanced functional materials against gaseous formaldehyde

Intense efforts have been made to eliminate toxic volatile organic compounds (VOCs) in indoor environments, especially formaldehyde (FA). In this study, the removal performances of gaseous FA using two metal-organic frameworks, MOF-5 and UiO-66-NH₂, and two covalent-organic polymers, CBAP-1 (EDA) and CBAP-1 (DETA), along with activated carbon as a conventional reference material, were evaluated. To assess the removal capacity of FA under near-ambient conditions, a series of adsorption experiments were conducted at its concentrations/partial pressures of both low (0.1-0.5 ppm/0.01-0.05 Pa) and high ranges (5-25 ppm/0.5-2.5 Pa). Among all tested materials at the high-pressure region ㅐ (e.g., at 2.5 ppm FA), a maximum adsorption capacity of 69.7 mg g^-1 was recorded by UiO-66-NH₂. Moreover, UiO-66-NH₂ also displayed the best 10% breakthrough volume (BTV10) of 534 L g^-1 (0.5 ppm FA) to 2963 L g^-1 (0.1 ppm FA). In contrast, at the high concentration test (at 5, 10, and 25 ppm FA), the maximum BTV10 values were observed as: 137 (UiO-66-NH₂), 144 (CBAP-1 (DETA)), and 36.8 L g^-1 (CBAP-1 (EDA)), respectively. The Langmuir isotherm model was observed to be a better fit of the adsorption data than the Freundlich model under most of the tested conditions. The superiority of UiO-66-NH₂ was attributed to the van der Waals interactions between the linkers (framework) and the hydrocarbon "tail" (FA) coupled with interactions between its open metal sites and the FA carbonyl groups. This study demonstrated the good potential of these advanced functional materials toward the practical removal of gaseous FA in indoor environments.

Competitive adsorption of gaseous aromatic hydrocarbons in a binary mixture on nanoporous covalent organic polymers at various partial pressures

Covalent-organic polymers (COPs) are recognized for their great potential for treating diverse pollutants via adsorption. In this study, the sorption behavior of benzene and toluene was investigated both individually and in a binary mixture against two types of COPs possessing different -NH₂ functionalities. Namely, the potential of COPs was tested against benzene and toluene in a low inlet partial pressure range (0.5-20 Pa) using carbonyl-incorporated aromatic polymer (CBAP)-1-based diethylenediamine (EDA) [CD] and ethylenetriamine (DETA) [CE]. The maximum adsorption capacity and breakthrough values of both COPs showed dynamic changes with increases in the partial pressures of benzene and toluene. The maximum adsorption capacities (A_max) of benzene (as the sole component in N₂ under atmospheric conditions) on CD and CE were in the range of 24-36 and 33-75 mg g^-1, respectively. In contrast, with benzene and toluene in a binary mixture, the benzene A_max decreased more than two-fold (range of 2.7-15 and 6-39 mg g^-1, respectively) due to competition with toluene for sorption sites. In contrast, the toluene A_max values remained consistent, reflecting its competitive dominance over benzene. The adsorption behavior of the targeted compounds (i.e., benzene and toluene) was explained by fitting the adsorption data by diverse isotherm models (e.g., Langmuir, Freundlich, Elovich, and Dubinin-Radushkevich). The current research would be helpful for acquiring a better understanding of the factors affecting competitive adsorption between different VOCs in relation to a given sorbent and across varying partial pressures.

Amine-Functionalized Metal-Organic Frameworks and Covalent Organic Polymers as Potential Sorbents for Removal of Formaldehyde in Aqueous Phase: Experimental Versus Theoretical Study

Porous materials have been identified as efficient sorbent media to remove volatile organic compounds. To evaluate their potential as adsorbents, the adsorptive removal of formaldehyde (FA) in aqueous environments was investigated using four materials, two water-stable metal-organic frameworks (MOFs) of UiO-66 (U6) and U6-NH₂ (U6N) and two covalent organic polymers (COPs) with amine-functionality, CBAP-1-EDA (CE) and CBAP-1-DETA (CD). U6N exhibited the highest removal capacity of 93% (0.56 mg g^-1) of the tested materials [e.g., CE (81.1%, 0.53 mg g^-1) > CD (67.2%, 0.43 mg g^-1) > U6 (66.9%, 0.42 mg g^-1)], which was 2 times higher than that of the reference sorbent, activated carbon (AC: 50%, 0.30 mg g^-1). The results of Fourier transform infrared and powder X-ray diffraction analyses confirmed the interactions between FA molecules and the amine components of the materials (U6N, CD, and CE). According to density functional theory calculations, the formation of hydrogen bonds between FA molecules and amine components was apparent and was further verified by FA/amine distance (CD: 2.83, CE: 2.88, and U6N: 2.66 Å) along with enthalpy values (CD: -32.4, CE: -45.5, and U6N: -272 kJ mol^-1). In case of U6, the major interactions occurred in the metal-clusters (-19.3 kJ mol^-1) via electrostatic interactions (distance: 5.49 Å). Furthermore, the sorption by amine-functionalized materials such as U6N is suggested to be dominated by hydrogen bonding which ultimately led to the formation of imine. If the performance of the tested materials is evaluated in terms of partition coefficient, U6N (1153 mg g^-1 mM^-1) is found as the outperformer in all tested subjects. Regeneration of spent MOFs/COPs was also plausible in the presence of ethanol to maintain their structural integrity even after 10 adsorption-desorption cycles. Overall, the selected MOFs/COPs were seen to have very high removal capacity for hazardous FA molecules in aqueous phase.