Small Conjugated Organic Ligand-Modified Polyoxometalate-Based Hybrid Materials for Boosting Photocatalytic CO2 Reduction.

Photocatalytic carbon dioxide (CO2) reduction to value-added chemicals is a multielectron transfer process, and the crucial step is the synthesis of photocatalysts. The introduction of small conjugated organic ligands can make the catalytic active site of the compound easier to be exposed in the reaction system and fully contact with the substrate, accelerating the photocatalytic reaction process. In this paper, we synthesized two isomorphic compounds, namely, {[Co(mtrz)3·(H2O)2]2·[SiW12O40]}·6H2O (1) and {[Ni(mtrz)3·(H2O)2]2·[SiW12O40]}·6H2O (2) (mtrz = 1-methyl-1,2,4-triazole). We found that compound 1 has a great photocatalytic performance through a series of experiments, with a CO reduction yield of 7364.92 µmol g-1 h-1 and a CO selectivity of 82.5%. Furthermore, the high catalytic activity can be maintained over four cycle experiments. The catalytic mechanism of its photocatalytic system is also elucidated, which provides an idea for realizing efficient catalytic reduction of CO2 to CO.

An iron-containing POM-based hybrid compound as a heterogeneous catalyst for one-step hydroxylation of benzene to phenol.

It is a major challenge to perform one-pot hydroxylation of benzene to phenol under mild conditions, which replaces the environmentally harmful cumene method. Thus, finding highly efficient heterogeneous catalysts that can be recycled is extremely significant. Herein, a (POM)-based hybrid compound {[FeII(pyim)2(C2H5O)][FeII(pyim)2(H2O)][PMoV2MoVI9VIV3O42]}·H2O (pyim = 2-(2-pyridyl)benzimidazole) (Fe2-PMo11V3) was successfully prepared by hydrothermal synthesis using typical Keggin POMs, iron ions and pyim ligands. Single-crystal diffraction shows that the Fe-pyim unit in Fe2-PMo11V3 forms a stable double-supported skeleton by Fe-O bonding to the polyacid anion. Remarkably, due to the introduction of vanadium, Fe2-PMo11V3 forms a divanadium-capped conformation. Benzene oxidation experiments indicated that Fe2-PMo11V3 can catalyze the benzene hydroxylation reaction to phenol in a mixed solution of acetonitrile and acetic acid containing H2O2 at 60 °C, affording a phenol yield of about 16.2% and a selectivity of about 94%.

MoO42--templated Ln20Ni21 heterometallic clusters with large low-field magnetic entropy.

The anionic template method is an effective strategy for synthesizing high-nuclearity transition-lanthanide (3d-4f) heterometallic clusters. Herein, two lanthanide clusters with formulas [Gd20Ni21(µ3-OH)21(CO3)6(IDA)21(C2H4NO2)6(C2O4)3(MoO4)1.5(µ2-OH)1.5(H2O)9]Cl10.5·79H2O (1) and [Tb20Ni21(µ3-OH)21(CO3)6(IDA)21(C2H4NO2)6(C2O4)3(MoO4)(µ2-OH)2(H2O)10]Cl11·32H2O (2) were synthesized by introducing MoO42- anions as templates. Structural analysis indicates that compounds 1 and 2 are isomorphic, featuring a fascinating triangular-shaped metal framework. Magnetic property investigations illuminate the fact that compound 1 exhibits a large -ΔSm of 37.83 J kg-1 K-1 at 3 K for ΔH = 7 T. In particular, it is worth mentioning that compound 1 has an excellent low-field magnetic entropy (-ΔSm = 23.85 J kg-1 K-1 at 2 K, 2 T).

Two bimetal-doped (Fe/Co, Mn) polyoxometalate-based hybrid compounds for visible-light-driven CO2 reduction.

Two polyoxometalate (POM)-based hybrid compounds have been successfully designed and constructed by the hydrothermal method with molecular formulas [K(H2O)2FeII0.33Co0.67(H2O)2(DAPSC)]2{[FeII0.33Co0.67(H2O)(DAPSC)]2[FeII0.33Co0.67(H2O)4]2[Na2FeIII4P4W32O120]}·21.5H2O (1), and [Na(H2O)2FeII0.33Mn0.67(H2O)2(DAPSC)]2{[FeII0.33Mn0.67(H2O)(DAPSC)]2[FeII0.33Mn0.67(H2O)4]2[Na2FeIII4P4W32O120(H2O)2]}·24H2O (2) (DAPSC = 2,6-diacetylpyridine bis-(semicarbazone)), respectively. Structural analysis revealed that 1 and 2 consisted of metal-organic complexes containing DAPSC ligands with dumbbell-type inorganic clusters, iron-cobalt (iron-manganese) and some other ions. By utilizing a combination of strongly reducing {P2W12} units and bimetal-doped centres the CO2 photoreduction catalytic capacity of 1 and 2 was improved. Notably, the photocatalytic performance of 1 was much better than that of 2. In CO2 photoreduction, 1 exhibited CO selectivity as high as 90.8%. Furthermore, for 1, the CO generation rate reached 6885.1 µmol g-1 h-1 at 8 h with 3 mg, and its better photocatalytic performance was presumably due to the introduction of cobalt and iron elements to give 1 a more appropriate energy band structure. Further recycling experiments indicated that 1 was a highly efficient CO2 photoreduction catalyst, which could still possess catalytic activity after several cycles.

Layered Co-O Cluster Applied to Photocatalytic CO2 Reduction.

In the field of recycling CO2, the photocatalytic CO2 reduction reaction (CO2RR) is a typical example, and researchers have designed a variety of photocatalysts to improve the conversion rate of CO2 over the years. In this paper, two metal-oxygen clusters are designed and formulated as [Co3Zn(OH)6(SO4)]·4H2O (1) and [Ni3Zn(OH)6(SO4)]·4H2O (2). As for compound 1, the main structure is composed of {CoO6} octahedra connected by edge-sharing to form a two-dimensional layer, on which {ZnO4} and {SO4} tetrahedra are supported. More interestingly, compound 1 has outstanding photocatalytic activity, which is mainly attributed to the open-framework structure and the cobalt ions as active sites. Upon catalysis for eight hours, its maximum CO generation rate is 9982.13 µmol g-1 h-1, with a selectivity of 81.8%. Additionally, compound 1 takes on weak antiferromagnetic coupling due to Co(II) ions.