Polyaniline@g-C3N4 derived N-rich porous carbon for selective degradation of phenolic pollutants via peroxymonosulfate activation: An electron transfer mechanism.

N-doped carbons have attracted extensive attention as catalysts for peroxymonosulfate (PMS) activation towards environmental remediation. However, synthesis of N-rich carbocatalysts is challenging and PMS activation mechanism is still unclear. Herein, novel N-rich porous carbocatalysts (C-PxCN-T) were synthesized by carbonization of polyaniline nanorods coated g-C3N4. C-P50CN-900 (polyaniline content 50%) calcined at 900 °C had high surface area (358 m2/g), product yield (27.1%) and N content (12.27 at%). It showed superior performance in activating PMS to degrade and mineralize various phenolic pollutants in a wide pH range (2-11) and with the co-existence of water constituents. A positive correlation was observed between phenol oxidation rates and contents of CO, C-C/CC and graphitic N, which served as active sites to facilitate adsorption of pollutants and PMS on C-P50CN-900 and subsequent electron-transfer from pollutants to PMS. Overall, this study provides new insights into rational design of N-doped carbocatalysts and elucidation of electron transfer pathway in PMS activation.

Proton-Conductive Keggin-Type Clusters Decorated by the Complex Moieties of Cu(II) 2,2'-Bipyridine-4,4'-dicarboxylate/Diethyl Analogues.

Three proton-conductive decorated Keggin-type clusters, {[Cu(debpdc)(H2O)3][Cu(debpdc)(H2O)Cl][PMo12O40]} ·2CH3OH ·1.5CH3CN ·3H2O (1), {[Cu(H2bpdc)(H2O)2Cl0.5]2[PW12O40]}·10H2O (2), and {[Cu(H2bpdc)(H2O)2.5]2[SiW12O40]}·10H2O (3) (where debpdc is diethyl 2,2'-bipyridine-4,4'-dicarboxylate and H2bpdc is 2,2'-bipyridine-4,4'-dicarboxylic acid), were synthesized through electrostatic and coordination interactions between Keggin-type anions and Cu(II) H2bpdc/debpdc complex moieties. Interestingly, in the three complexes, both the H2bpdc/debpdc and the Keggin anion are covalently linked to the Cu2+ ions as polydentate organic and inorganic ligands, respectively. Notably, complexes 2 and 3 are the first examples of the functionalization of a Keggin-type cluster with Cu(II)-H2bpdc complex moieties, thereby providing a pathway to design and synthesize multifunctional hybrid materials with cluster structures based on two building units. In them, the free COOH groups of the H2bpdc ligand can act as both hydrogen bond acceptors and proton carriers. 1 has debpdc ligands with ethoxycarbonyl groups, while 2 and 3 have the H2bpdc ligands with free COOH groups; thus, the three complexes help us to understand the influence of the different substituents on the proton conductivity. The measurement results reveal that 2 and 3 have a high conductivity value of over 10-3 S cm-1 at 100 °C under 98% relative humidity, which is 2 orders of magnitude higher than that of 1 under the same conditions.

Proton-Conductive Cocrystals of Twin Isomers of Coordination Polymers in Situ Formed by Keggin Anions and Cu(II)-4,4'-Bis(hydroxymethyl)-2,2'-bipyridine Complex Moieties.

Cocrystals and isomers, two well-known unique concepts in supramolecular chemistry, are rarely put together until now. For the first time, we report three unprecedented and interesting cocrystals of twin isomers of coordination polymers (CPs) in situ formed by typical Keggin anions and Cu(II)-4,4'-bis(hydroxymethyl)-2,2'-bipyridine (Cu(II)-H2L) complex moieties. In cocrystals 1-3, the Cu(II)-H2L complex moieties are quadrisupported on Keggin-type anions through W(Mo)-Ot-Cu-Ot-W(Mo) (Ot is the terminal O atom) links in the crystal to form two twin ionic/neutral CPs with a fixed chemical stoichiometry. Cocrystals 1-2 contain ionic isomers as {[Cu1(H2L)(H2O)2]2[P1W12O40]} n n+/{[Cu2(HL)(H2O)2]2[P2W12O40]} n n- for 1 and {[Cu1(H2L)(H2O)2]2[P1Mo12O40]} n n+/{[Cu2(HL)(H2O)2]2[P2Mo12O40]} n n- for 2. Cocrystal 3 contains neutral isomers as {[Cu1(H2L)(H2O)2]2[Si1W12O40]} n and {[Cu2(H2L)(H2O)2]2[Si2W12O40]} n. Cooperation of conformation and hydrogen bond network isomerism of Cu(II)-H2L fragments and tetracoordinated mode isomerism of Keggin anion is perfectly embodied in twin isomers. Moreover, based on hydrogen-bonding interactions, twin isomers are alternately arranged in a 1:1 stoichiometric ratio to give a cocrystal. Complicated accumulation of three types of hydrogen-bonding assemblies in the same crystal may be the reason that they give conductivity values over 10-4 S·cm-1 at 100 °C under 98% relative humidity.

Crystal structures and proton conductivities of a MOF and two POM-MOF composites based on Cu(II) ions and 2,2'-bipyridyl-3,3'-dicarboxylic acid.

We have succeeded in constructing a metal-organic framework (MOF), [Cu(bpdc)(H(2)O)(2)](n) (H(2) bpdc=2,2'-bipyridyl-3,3'-dicarboxylic acid, 1), and two poly-POM-MOFs (POM=polyoxometalate), {H[Cu(Hbpdc)(H(2)O)(2)](2) [PM(12)O(40)]·nH(2)O}(n) (M=Mo for 2, W for 3), by the controllable self-assembly of H(2) bpdc, Keggin-anions, and Cu(2+) ions based on electrostatic and coordination interactions. Notably, these three compounds all crystallized in the monoclinic space group P2(1)/n, and the Hbpdc(-) and bpdc(2-) ions have the same coordination mode. Interestingly, in compounds 2 and 3, Hbpdc(-) and the Keggin-anion are covalently linked to the transition metal copper at the same time as polydentate organic ligand and as polydentate inorganic ligand, respectively. Complexes 2 and 3 represent new and rare examples of introducing the metal N-heterocyclic multi-carboxylic acid frameworks into POMs, thereby, opening a pathway for the design and the synthesis of multifunctional hybrid materials based on two building units. The Keggin-anions being immobilized as part of the metal N-heterocyclic multi-carboxylic acid frameworks not only enhance the thermal stability of compounds 2 and 3, but also introduce functionality inside their structures, thereby, realizing four approaches in the 1D hydrophilic channel used to engender proton conductivity in MOFs for the first time. Complexes 2 and 3 exhibit good proton conductivity (10(-4) to ca. 10(-3) S cm(-1)) at 100 °C in the relative humidity range 35 to about 98%.

Multifunctional polythreading coordination polymers: spontaneous resolution, nonlinear-optic, and ferroelectric properties.

The reactions of methylenediisophthalic acid (H4L) and N-auxiliary ligands (1,2-bis(4-pyridyl)ethylene, 1,2-bis(4-pyridyl)ethane) with transition-metal centers (Co2+/Mn2+) have given rise to four unprecedented polythreading coordination polymers. Single-crystal X-ray diffraction analyses revealed that the compounds can be described as 3D2− ⊂2[1D2+] + 2D6− for 1, 3D4− ⊂1D2+ + 1D6− for 2, and 2D4− ⊂0D2+ + 2[1D3−] for 3 and 4. All the polymers are formed through the assembly of two kinds of motifs with opposite charges. Noncentrosymmetric structures and multifunctionality in 2­4 are established by varying ligands and metal centers. Spontaneous resolution upon crystallization occurred in compounds 3 and 4 in the absence of any chiral source. The enantiomers of 3 and 4 consist of three chiral building blocks of L4−/HL3− and Mn2+ centers. In the solid state, polar compounds 2­4 exhibit nonlinear-optic (NLO) and ferroelectric properties at room temperature. The assembly of two kinds of motifs with opposite charges provides a useful method for the preparation of multifunctional compounds.