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An aromatic porous polymer incorporated with carbonyl functionality (APP) was prepared via a facile route of Friedel-Crafts reaction. Subsequent reaction with diethylenetriamine via Schiff-base chemistry produced the amine-functionalized porous polymer (DETA-APP), which was used as a solid backbone to stabilize Pd nanoparticles with sizes of 1–3 nm. The prepared multifunctional Pd/DETA-APP catalyst showed high catalytic activity and selectivity towards the cascade reaction of Knoevenagel condensation-transfer hydrogenation using HCOOH as a hydrogen source. The positive influence of the amine functionality on the Pd/DETA-APP in the hydrogenation step was established after comparing the catalytic performance with that of the Pd/APP. The catalyst could be reused without any loss in reaction efficiency and selectivity for at least 5 times. Finally, a plausible mechanistic pathway for the cascade reaction over Pd/DETA-APP catalyst was proposed.

Direct synthesis of H2O2 from H2 and O2 can avoid the energy and environmental problems of current multi-step anthraquinone oxidation process by enabling high atom utilization and generating only a water by-product. However, the direct process suffers a low H2O2 yield, and it is challenging to suppress the unfavorable side-reactions in the absence of corrosive additives under the restriction of explosion limits. In this study, an efficient new catalyst was prepared by immobilizing Pd nanoparticles (NPs) on an acidic hyper-crosslinked porous polymer (HCPP). The Pd catalyst supported on HCPP functionalized with both carboxylic and sulfonic acids (Pd/c-s-HCPP) achieved as high as 3130 mmol H2O2/g Pd.h with 82% selectivity to H2O2, which corresponded to one of the best catalysts reported so far. Pd/c-s-HCPP showed superior catalytic performance when compared with ones by Pd NPs supported on unfunctionalized HCPP (Pd/HCPP), or sulfonated resin (Pd/SO3H-resin). Extensive characterizations and H2 adsorption measurements indicated that the c-s-HCPP provided (i) selective adsorption sites for Pd precursors, (ii) acted as an efficient H2 reservoir in the proximity of the small Pd NPs formed, and (iii) imparts solid acidity to enhance H2O2 selectivity, which offered a new direction in the catalyst design for the direct synthesis of H2O2.

A new nanoporous N-heterocyclic carbene-based cross-linked aromatic polymer (NHC-CAP-1) incorporated with highly nucleophilic bromide anions and with a large surface area was synthesized by a simple Friedel-Crafts reaction of imidazolium salt, triphenylbenzene, and formaldehyde dimethyl acetal. Subsequently, ZnBr2 was grafted onto the NHC-CAP-1 to obtain NHC-CAP-1(Zn2+) with enhanced Lewis acidity. After systematic evaluation of the structural and chemical properties using different analytical techniques, these were explored for CO2 adsorption and CO2 chemical fixation to cyclic carbonates. Whilst NHC-CAP-1 showed a high CO2 capture capacity (188.2 mg g−1 at 273 K/1 bar) with a moderate CO2/N2 selectivity, NHC-CAP-1(Zn2+) displayed significantly enhanced CO2/N2 selectivity (100/80 at 273/298 K) at the expense of diminished CO2 capture (123.0 mg g−1 at 273 K/1 bar). These values are among the highest reported so far for porous cross-linked organic polymers. As a catalyst, NHC-CAP-1(Zn2+) showed high catalytic activities for CO2 cycloaddition to a series of epoxides to form cyclic carbonates in the absence of co-catalyst and solvent, producing a high turnover frequency (TOF) of 2202 h−1 at 100 °C. The effect of reaction parameters including temperature, reaction time, and catalyst loading was examined. NHC-CAP-1(Zn2+) could be separated readily and reuse for a minimum of 10 runs while maintaining high activity and stability owing to the strong covalent bonding of Lewis acidic Zn2+ to the NHC-CAP-1 backbones. This work demonstrated that NHC-CAP-1 and NHC-CAP-1(Zn2+) are viable porous materials that are highly efficient for both CO2 capture and catalytic conversion of CO2 to cyclic carbonates.

A new porphyrinic porous organic polymer (PPOP) with high stability and excellent textural properties (929 m2/g surface area with 0.73 cm3/g pore volume) was made via the Friedel-Crafts reaction and applied for bisphenol A (BPA) adsorption in water. The material was examined by X-ray diffraction, N2 adsorption-desorption isotherms, scanning electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, and solid-state 13C CP-MAS nuclear magnetic resonance spectroscopy. PPOP was proven highly effective for capturing BPA among the many adsorbent materials investigated. The Langmuir model could closely match the adsorption isotherm data with a high adsorption amount of ca. 653 mg/g at 25 °C. Approximately 95% of BPA was adsorbed in 50 min, and the pseudo-second-order kinetic model satisfactorily described the adsorption behavior. This adsorption process was exothermic (ΔH° = −39.10 kJ/mol), and the capacity gradually decreased with increasing pH. Spectroscopic analyses indicated that the BPA adsorption on PPOP was affected by (1) π-π interaction between BPA and the aromatic constituents of PPOP, (2) hydrogen bonding between the N sites of porphyrin units in PPOP and the hydroxyl group of BPA and, and (3) hydrophobic interactions. PPOP was easily regenerated after acetone washing, and >98% efficiency was observed throughout the five repeated adsorption-desorption cycles.

Owing to the environmental and economic problems arising from fly ash (FA), there have been various ongoing efforts over the past decades to find a use for it. Among the various applications of FA, its use as a filler in polymer composites has gained much attention. However, most studies have applied FA as a semi-reinforcing filler, which only marginally improves mechanical properties arising from the poor surface wettability of FA with polymer matrices. To solve this problem and to explore new applications, FA was carbonated by bubbling CO2 in water in this study. The carbonated FA was adopted as a fire-proofing filler in silicone rubber (SR). The surface properties and compositional changes of FA by carbonation were thoroughly examined. Mechanical and thermal properties of carbonated FA-filled SR were evaluated. In particular, the gas torch test confirmed that the carbonation of FA increased the penetration time of SR composites by 11%. In addition, the penetration time of the carbonated FA-filled SR composite was 2–3 times greater than that of the composites filled with commercially available fillers.

Mesoporous silica SBA-15 grafted with benzene-1,3,5-triamido-tetraphosphonic acid (SBA-15-BTATPA) was synthesized. After detailed characterization of the material using various analytical instrumentation, it was applied for the recovery of Nd 3+ as a function of the contact time, ion concentration, and pH, and the adsorption equilibria and kinetics were examined. Under the optimal conditions, adsorption equilibrium was reached within 60 min contact time, and the adsorption capacity of Nd 3+ at room temperature and pH 6 was 129.8 mg g −1 , which was higher than that by other rare earth element (REE) ions tested for comparison (Y 3+ , La 3+ , and Ce 3+ ). The adsorbent showed excellent distribution coefficient for Nd 3+ greater than 1.0 × 10 5 mL/g. The preferential order of adsorption in the ion mixture with equal ion concentrations was Y 3+ >Nd 3+ >Ce 3+ >La 3+ , which followed the sequence of their decreasing atomic size and increasing stability constant. The competing adsorption by transition metal ions, such as Cu 2+ , Ni 2+ , Co 2+ , and Zn 2+ , on the REEs recovery was negligible ( 2 > 0.99), whereas the adsorption kinetics could be described satisfactorily by a pseudo second order kinetic model. The material was reusable for up to 5 consecutive times with only a slight decrease in adsorption capacity.

In order to meet the ever-increasing industrial demand for rare-earth elements (REEs), it is desirable to separate and recycle them at low concentrations from various sources including industrial and urban wastes. Here, we introduced phosphorus binding sites on the hydrophobic surface of a robust and high-surface area porous polymer backbone for environmentally benign and selective recovery of REEs via adsorption. For this purpose, two porous covalent organic polymer (COP) materials incorporated with in-built phosphite functionality (P-COP-1 and P-COP-2) were synthesized and applied for the adsorptive separation of Nd(III) ions from aqueous solution. A strategy to develop a series of P-COPs via a simple Friedel-Crafts reaction was introduced, and their application to the selective adsorption of REEs was explored for the first time. The newly synthesized P-COPs were amorphous and/or weakly crystalline and showed excellent chemical stability and large specific surface area with sufficient mesoporosity for enhanced diffusion of REE ions. P-COP-1 exhibited an exceptionally high Nd(III) adsorption capacity of 321.0 mg/g, corresponding to the stoichiometric ratio of P/Nd(III) = 1:0.7 and high selectivity of >86% over other competing transition and alkaline earth metal ions, whereas P-COP-2 gave a Nd(III) adsorption capacity of 175.6 mg/g at 25 °C and pH 5. Moreover, P-COP-1 showed a distribution coefficient value of 5.45 × 105 mL/g, which is superior to other benchmark adsorbent materials reported so far. Finally, the P-COPs were reusable for a minimum of 10 cycles without deterioration in adsorption capacities.

The synthesis of metal-organic frameworks (MOFs) with in-built porphyrin units remains challenging. It takes long synthesis time under carefully controlled reaction conditions, and a mixed-phase with different crystal morphologies is still frequently observed. In this work, Zr-based porphyrinic MOF-525 and MOF-545 in high purity and uniform size were produced through a sonochemical route in 2.5 and 0.5 h, respectively, using zirconyl chloride octahydrate and tetrakis (4-carboxyphenyl) porphyrin. Benzoic acid was used as a modulator for MOF-525, and trifluoroacetic acid for MOF-545. The physicochemical properties of the MOF products were examined by X-ray diffraction, scanning electron microscopy, and N2 adsorption-desorption isotherms. Additionally, the defect sites in the MOF samples were analyzed by UV–vis spectrometry, thermogravimetric analysis, and inductively coupled plasma mass spectrometer. The sonochemically synthesized MOF samples had more defect sites than the conventionally prepared ones and exhibited improved textural properties. In particular, the MOF-545 had a significantly smaller (ca. 1.0 μm) particle size than the conventionally prepared sample (ca. 4.8 μm). The MOF-525 and MOF-545 prepared by the sonochemical route exhibited enhanced hydrolysis of the chemical warfare simulant dimethyl-4-nitrophenyl phosphate (DMNP) and a faster and higher bisphenol-A adsorption than the conventionally prepared MOF samples.

Aluminum fumarate was tested as a catalyst for CO2 cycloaddition to epichlorohydrin under solvent-free reaction conditions. This material was synthesized hydrothermally via a sonochemical route (Al fumarate-(S)), which exhibited a higher catalytic activity than Al fumarate synthesized by a conventional method owing to the higher number of Lewis acid sites formed in Al fumarate-(S). The CO2 uptake of Al fumarate-(S) was high: approximately 269 mg g−1 at 25 °C and 10 bar. High conversion (96%) of epichlorohydrin with excellent selectivity (97%) to cyclic carbonate was obtained at 50 °C and 10 bar CO2 after 6 h of reaction. The kinetic analysis of the reaction confirmed an approximately 1st order dependence on the epichlorohydrin concentration and CO2 pressure with an activation energy of approximately 39 kJ mol−1. The recovered Al fumarate-(S) catalyst, however, showed a steady decline in catalytic activity during the recycling runs, as reported for other metal-organic framework catalysts. The deactivation was monitored by N2 adsorption-desorption isotherms and spectroscopic analyses.

A metal-free microporous triazine polymer (MCTP) was applied as a heterogeneous catalyst for the oxidative desulfurization (ODS) of thiophenic sulfur compounds in decane as a model fuel. Using a molecular oxygen (O2)/aldehyde system as the oxidant, complete removal of dibenzothiophene (DBT) from a 400 ppm DBT solution (10 mL) was achieved at room temperature in 15 min with 2 mmol of isobutyraldehyde (IBA). The highly efficient conversion of the DBT was explained by the formation of an acyl radical from IBA aided by the MCTP catalyst, which was converted to a peroxyacid that oxidized the DBT to DBT sulfone. The conversion efficiency of thiophenic compounds followed the sequence of electron densities in the individual S atoms: DBT > benzothiophene > thiophene. The MCTP catalyst could be reused for ODS for at least five consecutive runs without any reduction in the catalytic performance after a simple acetone wash.

A zeolite-like metal-organic framework with a rho topology was synthesized via a sonochemical route (rho-ZMOF(S)), and its physicochemical properties were compared with the one prepared via a conventional solvothermal route (rho-ZMOF(C)). The physicochemical properties of the samples were examined using various instrumentation. High-quality rho-ZMOF(S) was obtained only after 2 h with uniform particles of ca. 600 nm in size, whereas rho-ZMOF(C) produced after 72 h was of ca. 60 µm in size. According to the temperature-programmed desorption of ammonia, rho-ZMOF(S) showed ca. 20% higher acid amount than rho-ZMOF(C). The beneficial effect of the higher acidity with the smaller particles in rho-ZMOF(S) was demonstrated by a significant enhancement in catalytic activity for the CO2 cycloaddition reaction to epichlorohydrin.

The direct synthesis of cyclic carbonates from olefins involves epoxidation and CO2 cycloaddition reactions in series. It is, however, a challenging task to devise single catalyst with the multiple functions for one-pot reaction. Herein, an imidazolium bromide ionic liquid-functionalized metalloporphyrin ImBr-MOF-545(Mn) was proposed as an effective catalyst for the reaction. The effects of temperature, pressure, catalyst loading, and time were examined for individual reactions and finally for one-pot reaction. ImBr-MOF-545(Mn) was efficient under solvent-free condition of 60 °C, 5/5 bar (O2/CO2), and 10 h. The Mn(III) ions with the dual functions of oxidation and acting as Lewis acid catalyst with strong nucleophilic/leaving bromide anion in an adjacent position of mesoporous MOF-545 resulted in high efficiency and selectivity to the cyclic carbonates. The catalyst also showed sufficient stability for up to 5 runs with little decline in catalytic activity. A radical mechanism for the epoxidation step and a plausible reaction pathway was proposed.

The metal-organic frameworks MOF-525 and MOF-545 comprised of Zr-oxide clusters and porphyrin moieties in different geometries were synthesized solvothermally and applied for the adsorptive removal of the broadly used organic contaminant sulfamethoxazole (SMX) from water. Both MOFs were found highly efficient for the adsorption of SMX with the maximum adsorption capacities of 585 and 690 mg/g for MOF-525 and MOF-545, respectively. The latter value is the highest adsorption capacity reported so far for the adsorption of SMX molecules on any adsorbent. The adsorption equilibrium could be modeled successfully by the Langmuir model, which showed close to matching with the experimental data. Their adsorption equilibriums were attained within 120 and 30 min for MOF-525 and MOF-545, respectively. MOF-545 with mesopores demonstrated superior adsorption kinetics to MOF-525 with micropores, and the simulation by the pseudo-second-order kinetic model indicated ca. 20 times faster adsorption by MOF-545 than MOF-525. Both showed pH-dependent adsorption of SMX with a gradual reduction at high pH due to the repulsion between negatively charged adsorbent and SMX. The adsorption of SMX conducted over a group of representative MOFs with different physicochemical properties and detailed characterization confirmed that the high adsorption capacity of the porphyrin MOFs is achieved by H-bonding between the SMX molecule and the N-sites of the porphyrin units in the MOFs, π-π interaction, and the high surface area. The adsorbents were easily regenerated by simple washing with acetone and reusable with >95% efficiency during 4 repeated adsorption-desorption cycles.

Widespread use of pharmaceuticals, especially antibiotics is causing serious contamination of both surface and underground water. In this study, four different microporous organic polymers (MOP): microporous triazine polymer (MCTP), carbonyl-incorporated aromatic polymer (CBAP), CBAP-functionalized with ethylenediamine (CBAP-EDA), and CBAP-functionalized with sulfonic acid (CBAP-SO3H) were synthesized and tested for adsorptive removal of the common antibiotic sulfamethoxazole (SMX) from aqueous solutions. MCTP with the largest BET surface area (1406 m2/g) attained equilibrium in 1 h and showed the highest SMX adsorption capacities (ca. 483 mg/g), significantly better than that of a commercial activated carbon (AC, 259 mg/g) with the sequence of AC

Efficient rare earth elements (REEs) separation and recovery are crucial to meet the ever-increasing demand for REEs extensively used in various high technology devices. Herein, we synthesized a highly stable chromium-based metal–organic framework (MOF) structure, Cr-MIL-101, and its derivatives with different organic functional groups (MIL-101-NH2, MIL-101-ED (ED: ethylenediamine), MIL-101-DETA (DETA: diethylenetriamine), and MIL-101-PMIDA (PMIDA: N-(phosphonomethyl)iminodiacetic acid)) and explored their effectiveness in the separation and recovery of La3+, Ce3+, Nd3+, Sm3+, and Gd3+ in aqueous solutions. The prepared materials were characterized using various analytical instrumentation. These MOFs showed increasing REE adsorption capacities in the sequence MIL-101 < MIL-101-NH2 < MIL-101-ED < MIL-101-DETA < MIL-101-PMIDA. MIL-101-PMIDA showed superior REE adsorption capacities compared to other MOFs, with Gd3+ being the element most efficiently adsorbed by the material. The adsorption of Gd3+ onto MIL-...

A porous covalent organic framework incorporated with both imine and triazine functionalities (TPA-TCIF) was synthesized by Schiff-base condensation of 2,4,6-tris(4-aminophenyl)triazine and tris(4-formylphenyl)amine under the solvothermal condition of a 1-butanol:1,2-dichlorobenzene mixture. The resulting TPA-TCIF was a highly ordered crystalline network with surface area of 2938 m2 g−1, which was among the highest reported imine-based porous covalent organic frameworks. TPA-TCIF was also stable in water and other organic solvents. Pd(II) was immobilized into TPA-TCIF network and the resultant Pd/TPA-TCIF was tested as a catalyst for the additive-free cyanation of haloarenes with non-toxic K4[Fe(CN)6]. The catalyst showed excellent catalytic activity, and both electron-donating / -withdrawing groups attached to the para- and meta-positions of bromoarenes produced the respective nitriles with good to excellent yields. The catalyst could be reused up to five times without noticeable loss of activity or catalyst poisoning by cyanide ions during the reaction.