Strong nephelauxetic effect on Eu2+ ion in Sr2LiSiO4H: enhancement of Eu 5d centroid shift by hydride ligand coordination.

Transition metal carbides, nitrides, and carbonitrides (MXenes) are emerging two-dimensional (2D) materials, with a variety of applications, such as heterogeneous catalysis, due to their metallic conductivity and resulting charge transport properties. However, the semiconductor photocatalysis of MXene-related materials has not been experimentally demonstrated. Here, we show that stacked MXene sheets of Y 2 CF 2 behave as an n-type semiconductor, with a 1.9 eV band gap and a rather negative conduction band potential of approximately −2.1 V versus Ag/ AgNO 3 . In the presence of triethanolamine as an electron donor, Y 2 CF 2 exhibits the ability to reduce protons into H 2 under visible light. However, Y 2 CF 2 is not very stable during the photoreaction, even in the presence of triethanolamine, undergoing oxidative degradation to form fluorocarbon and carbonate species due primarily to the high-energy valence band formed by C 2p orbitals.

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Monolayer Ta2O5 was fabricated on mesoporous silica (SBA‐15) substrate by the reaction of Ta(OEt)5 with surface hydroxyl groups on silica. The monolayer was defined at the saturation amount of Ta(OEt)5 anchored on SBA‐15 surface in a series of increment of the feed amount the precursor, which was confirmed by elemental (inductively coupled plasma‐atomic emission, ICP‐AE) analysis of the product (Ta2O5/SBA‐15). Ta/Si ratio of Ta2O5/SBA‐15 with saturated amount of Ta was 0.11–0.12. X‐ray photoelectron spectroscopy (XPS) analysis of Ta/Si ratio of a series of samples by using the Ta4 f and Si2p signals met agreement with the gradual increase and the saturation at about 0.11–0.12, as well as the local elemental analysis by energy dispersive X‐ray spectrometry (EDS) using transmission electron microscopy (TEM). The absorption edge of UV‐vis. diffuse reflectance spectra of a series of samples appeared very sharp, decreasing the excitation energy from 5.1 to 4.7 eV by increasing the Ta/Si ratio from 0.01 to 0.11−0.12. X‐ray absorption near edge fine structure (EXAFS) indicated the inhomogeneous (amorphous) feature of Ta2O5 phase on SBA‐15 with Ta octahedral species. The unique surface property of monolayer Ta2O5/SBA‐15 was characterized by infrared (IR) spectroscopy and catalytic reactions.

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