A series of pH-dependent POM-based compounds as photocatalysts and electrochemical sensors. (15th November 2018) - Tian, Ai-Xiang
Graphical abstract: By tuning the pH, we use H2 bdpm ligand to get a series of Keggin- and [Mo8 O26 ] 4− -based compounds. We have studied the electrochemical properties of three compounds and fabricated them into an electrochemical sensors. We have studied five compounds' photocatalytic properties and the possible mechanism of photocatalysis. Abstract: By tuning pH, a Zn complex and five POM-based compounds decorated by a pyrazole derivative 1, 1′-bis(3, 5-dimethyl-1H-pyrazol-4-yl)methane (H2 bdpm), [Ag4 (H2 bdpm)4 (SiW12 O40 )]·4H2 O (1 ), [Ag3 (H2 bdpm)3 (PMo12 O40 )] (2 ), [Cu(H2 bdpm)2 (H2 O)2 (HPMo12 O40 )] (3 ), [Zn(H2 bdpm)2 ( β -Mo8 O26 )0.5 ]·3H2 O (4 ), [(ZnO)2 (H2 O)2 (H2 bdpm)] (5 ) and [( γ -Mo8 O26 )(H2 bdpm)2 ]·2H4 bdpm·4H2 O (6 ), have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction analysis, IR spectra and elemental analyses. In compound1, the infinite wave-like metal–organic chains are linked by POM anions to form a 3D framework. In the compound2, the H2 bdpm ligands are linked by Ag + ions to construct a chain with [PMo12 O40 ] 3− anions suspending up and down this chain by hydrogen bonding interactions. In compound3, there is a mono-supporting [PMo12 O40 ] 3 − anion with one [Cu(H2 bdpm)2 (H2 O)2 ] 2+ subunit. By tuning pH of [Mo7 O24 ] 6− /Zn 2+ /H2 bdpm system with three values, three distinct structures4 –6 were constructed. In compound4, two Zn ions and two H2 bdpm form a bi-nuclear [Zn2 (H2 bdpm)2 ] 4+ cycle. Adjacent cycles connect each other vertically to build a cycle-connecting-cycle chain. The discrete [ β -Mo8 O26 ] 4− anions exist hydrogen bonding interactions with metal–organic chains. In compound5, the cycle-like [(ZnO)4 (H2 O)4 ] subunits are linked by a pair of H2 bdpm alternately to form a 1D chain. Compound6 contains only a [ γ -Mo8 O26 ] 4− anion functionalized by two H2 bdpm through Mo-N bonds. The pH factor is essential for construction of this series. The1 -, 3 - and4 -CPEs not only possess excellent multifunctional electrocatalytic activities but also can be used as electrochemical sensors for the detection of hydrogen peroxide, bromate and nitrite. Photocatalytic investigation indicates that compounds1 –4 and6 are active for the degradation of methylene blue under UV irradiation.