Ahmad S. Alshammari

Weaving of organic threads into a crystalline covalent organic framework

Weaving organic threads Woven fabrics are inherently flexible. Liu et al. created a molecular fabric analog using metal-organic frameworks (see the Perspective by Gutierrez-Puebla). Phenanthroline ligands on a copper metal complex directed the addition of organic linkers via imine bonds to create helical organic threads with woven texture. Removing the copper allowed the strands to slide against each other and increased the elasticity of the material 10-fold. Science, this issue p. 365; see also p. 336 A metal-organic framework templates the synthesis of a material made of woven organic polymers. [Also see Perspective by Gutierrez-Puebla] A three-dimensional covalent organic framework (COF-505) constructed from helical organic threads, designed to be mutually weaving at regular intervals, has been synthesized by imine condensation reactions of aldehyde functionalized copper(I)-bisphenanthroline tetrafluoroborate, Cu(PDB)2(BF4), and benzidine (BZ). The copper centers are topologically independent of the weaving within the COF structure and serve as templates for bringing the threads into a woven pattern rather than the more commonly observed parallel arrangement. The copper(I) ions can be reversibly removed and added without loss of the COF structure, for which a tenfold increase in elasticity accompanies its demetalation. The threads in COF-505 have many degrees of freedom for enormous deviations to take place between them, throughout the material, without undoing the weaving of the overall structure.

Room-temperature synthesis of zinc oxide nanoparticles in different media and their application in cyanide photodegradation

Cyanide is an extreme hazard and extensively found in the wastes of refinery, coke plant, and metal plating industries. A simple, fast, cost-effective, room-temperature wet chemical route, based on cyclohexylamine, for synthesizing zinc oxide nanoparticles in aqueous and enthanolic media was established and tested for the photodegradation of cyanide ions. Particles of polyhedra morphology were obtained for zinc oxide, prepared in ethanol (ZnOE), while spherical and some chunky particles were observed for zinc oxide, prepared in water (ZnOW). The morphology was crucial in enhancing the cyanide ion photocatalytic degradation efficiency of ZnOE by a factor of 1.5 in comparison to the efficiency of ZnOW at an equivalent concentration of 0.02 wt.% ZnO. Increasing the concentration wt.% of ZnOE from 0.01 to 0.09 led to an increase in the photocatalytic degradation efficiency from 85% to almost 100% after 180 min and a doubling of the first-order rate constant (k).

MOF-derived cobalt nanoparticles catalyze a general synthesis of amines

A MOF sets the stage to make amines Reductive amination is a common method that chemists use to make carbon-nitrogen bonds. The reaction, which often requires precious metal catalysts, couples ammonia or other amines with carbonyl compounds and then with hydrogen. Jagadeesh et al. report a class of nonprecious cobalt nanoparticles that catalyze this reaction across a very broad range of substrates, including complex molecules of pharmaceutical interest (see the Perspective by Chen and Xu). The cobalt was first embedded in a metal-organic framework (MOF), which, upon heating, transformed into a graphitic shell. The catalyst could be conveniently separated from products and recycled up to six times. Science, this issue p. 326; see also p. 304 Cobalt nanoparticles prepared from a metal-organic framework precursor catalyze a very broad range of reductive aminations. The development of base metal catalysts for the synthesis of pharmaceutically relevant compounds remains an important goal of chemical research. Here, we report that cobalt nanoparticles encapsulated by a graphitic shell are broadly effective reductive amination catalysts. Their convenient and practical preparation entailed template assembly of cobalt-diamine-dicarboxylic acid metal organic frameworks on carbon and subsequent pyrolysis under inert atmosphere. The resulting stable and reusable catalysts were active for synthesis of primary, secondary, tertiary, and N-methylamines (more than 140 examples). The reaction couples easily accessible carbonyl compounds (aldehydes and ketones) with ammonia, amines, or nitro compounds, and molecular hydrogen under industrially viable and scalable conditions, offering cost-effective access to numerous amines, amino acid derivatives, and more complex drug targets.

Visible-light photocatalysis on C-doped ZnO derived from polymer-assisted pyrolysis†

C-doped ZnO with a large surface area was prepared via F127-assisted pyrolysis at 500 °C and used for visible-light-responsive photocatalytic water purification. The band structure of the C-doped ZnO was investigated using valance band XPS and DFT simulation. The C-doped ZnO possessed enhanced absorption of UV and visible light, though it showed lower visible-light-responsive photocatalytic activity than ZnO because of significant recombination of photogenerated charge carriers arising from overloaded C-dopant and oxygen vacancies.

Significant Formation of Adipic Acid by Direct Oxidation of Cyclohexane Using Supported Nano‐Gold Catalysts

Adipic acid (AA) is one of the highest volume chemicals in world use with a wide range of commercial applications. This paper demonstrates the possibility of producing significant proportions of AA by the selective oxidation of cyclohexane (CH) in one step using various supported gold‐nanoparticle (AuNP) catalysts. The catalysts were characterized by ICP, BET, XRD, X‐ray photoelectron microscopy, and TEM. The catalytic activity tests were carried out in the liquid phase using autoclaves in the temperature range of 100–170 °C at 10 bar. A CH conversion of over 25 %, with 26% selectivity of AA and 70% selectivity of KA oil (cyclohexanone+cyclohexanol), was achieved over a nano‐gold/TiO2 (anatase) catalyst. The superior performance of this catalyst is attributed to the smaller size of AuNPs, which has an average particle size of 2 nm. Good correlation between activity and Au particle size could be achieved. Overall, the particle size of the AuNPs showed a strong influence on catalytic performance.

Catalytic alcoholysis of urea to diethyl carbonate over calcined Mg–Zn–Al hydrotalcite

The synthesis of diethyl carbonate (DEC) from urea and ethanol was carried out over Mg–Zn–Al composite oxide catalysts derived from hydrotalcites (HTs). The catalytic results showed that the ternary hydrotalcites calcined at 450 °C with Mg : Zn : Al = 1 : 1.7 : 1 exhibited superior catalytic activity, and the highest DEC yield was 67.8%. Similar to ethanol, other alcohols such as methanol and butanol can also be transformed to corresponding dialkyl carbonates. Catalysts were characterized by XRD, BET, SEM and TPD with the aim of establishing a relationship between performance and structure. The results indicated that MgZn1.7Al-450 with nanoplate morphology and more accessible active medium basic sites were favourable for obtaining much superior catalytic activity. Recycling experiments demonstrated that the catalyst could be successfully reused.

Molecular Retrofitting Adapts a Metal–Organic Framework to Extreme Pressure

Despite numerous studies on chemical and thermal stability of metal–organic frameworks (MOFs), mechanical stability remains largely undeveloped. To date, no strategy exists to control the mechanical deformation of MOFs under ultrahigh pressure. Here, we show that the mechanically unstable MOF-520 can be retrofitted by precise placement of a rigid 4,4′-biphenyldicarboxylate (BPDC) linker as a “girder” to afford a mechanically robust framework: MOF-520-BPDC. This retrofitting alters how the structure deforms under ultrahigh pressure and thus leads to a drastic enhancement of its mechanical robustness. While in the parent MOF-520 the pressure transmitting medium molecules diffuse into the pore and expand the structure from the inside upon compression, the girder in the new retrofitted MOF-520-BPDC prevents the framework from expansion by linking two adjacent secondary building units together. As a result, the modified MOF is stable under hydrostatic compression in a diamond-anvil cell up to 5.5 gigapascal. The increased mechanical stability of MOF-520-BPDC prohibits the typical amorphization observed for MOFs in this pressure range. Direct correlation between the orientation of these girders within the framework and its linear strain was estimated, providing new insights for the design of MOFs with optimized mechanical properties.

Calcium l-Lactate Frameworks as Naturally Degradable Carriers for Pesticides

Two porous, chiral metal-organic frameworks (MOFs), Ca14(l-lactate)20(acetate)8(C2H5OH)(H2O) (MOF-1201) and Ca6(l-lactate)3(acetate)9(H2O) (MOF-1203), are constructed from Ca2+ ions and l-lactate [CH3CH(OH)COO-], where Ca2+ ions are bridged by the carboxylate and hydroxyl groups of lactate and the carboxylate group of acetate to give a three-dimensional arrangement of Ca(-COO, -OH) polyhedra supporting one-dimensional pores with apertures and internal diameters of 7.8 and 9.6 Å (MOF-1201) and 4.6 and 5.6 Å (MOF-1203), respectively. These MOFs represent the first examples of extended porous structures based on Ca2+ and lactate. They show permanent porosity of 430 and 160 m2 g-1, respectively, and can encapsulate an agriculturally important fumigant, cis-1,3-dichloropropene. MOF-1201 shows a 100 times lower release rate compared with liquid cis-1,3-dichloropropene under the same test conditions (25 °C, air flow rate of 1 cm3 min-1). The hydrolysis of MOF-1201 in water makes it the first example of a degradable porous solid carrier for such fumigants.

Interaction between CO2 and ionic liquids confined in the nanopores of SAPO-11

A series of ionic liquids (P4,4,4,6BF4, APMIMBF4, P4,4,4,6Triz, as well as the newly prepared anion dual-functionalized amino-triz IL P4,4,4,6ATriz, etc.) supported on glass powder and SAPO-11 were prepared, and their interaction with CO2 was investigated by “limited” temperature-programmed desorption. The results showed that the strength of the interaction of CO2 with IL/glass powder (11 wt%) followed the order P4,4,4,6BF4 < APMIMBF4 < P4,4,4,6Triz < P4,4,4,6ATriz. Two desorption peaks were observed for P4,4,4,6Triz, probably attributed to the two sites of interaction between Triz and CO2, and the Gaussian 03 program was employed to obtain the optimized structures, revealing the interaction between P4,4,4,6Triz and CO2. When ILs were confined in the nanopores of SAPO-11, the desorption capacity and interaction strength increased because of the nano-confinement effect. Meanwhile, the loading, as well as the structure of ILs and Na2CO3-modified SAPO-11, significantly affected the interaction between CO2 and ILs. Besides, P4,4,4,6ATriz/SAPO-11 (modified with Na2CO3, 30 wt%) with a maximum CO2 desorption capacity of 1.55 moleCO2/moleILs could reversibly adsorb CO2 15 times without any apparent reduction in the desorption capacity.

Binary Mg–Fe oxide as a highly active and magnetically separable catalyst for the synthesis of ethyl methyl carbonate

Magnetic binary Mg–Fe oxides were prepared by a co-precipitation method, characterized and tested in the synthesis of ethyl methyl carbonate (EMC) from di methyl carbonate (DMC) and diethyl carbonate (DEC). The obtained results showed that the Mg/Fe oxide catalyst with a 1 : 1 molar ratio and calcined at 400 °C exhibited superior catalytic activity. The yield of EMC could reach 66% (at 100 °C for 1.5 h) with a TOF of 220 mmol h−1 gcat−1. The prepared catalysts could be magnetically separated, and reused for ten runs without noticeable deactivation. XRD and Mossbauer spectra revealed that there was a synergistic effect between Mg and Fe oxides in the catalysts, which was consistent with the results of TPR, i.e. the introduction of the Mg component favored the reduction of the Fe2O3. XPS and IR characterizations indicated that there were a large number of accessible Fe-OHs on the surface of MgFe-400, and combining the Fe-OHs with the basic MgO may be related to the highly catalytic performance.