Structure and optical properties have been successfully determined for a series of niobium- and tantalum-containing layered alkaline-earth silicate compounds, Ba3(Nb6−xTax)Si4O26 (x = 0.6, 1.8, 3.0, 4.2, 5.4). The structure of this solid solution was found to be hexagonal P-62m (No. 189), with Z = 1. With x increases from 0.6 to 5.4, the lattice parameter a increases from 8.98804(8) to 9.00565(9) Å and c decreases from 7.83721(10) to 7.75212(12) Å. As a result, the volume decreases from 548.304(11) to 544.479(14) Å3. The (Nb/Ta)O6 distorted octahedra form continuous chains along the c-axis. These (Nb/Ta)O6 chains are in turn linked with the Si2O7 groups to form distorted pentagonal channels in which Ba ions were found. These Ba2+ ions have full occupancy and a 13-fold coordination environment with neighboring oxygen sites. Another salient feature of the structure is the linear Si–O–Si chains. When x in Ba3(Nb6−xTax)Si4O26 increases, the bond valence sum (BVS) values of the Ba sites increase slightly (2.09–2.20), indicating the size of the cage becoming progressively smaller (over-bonding). While SiO cages are also slightly smaller than ideal (BVS range from 4.16 to 4.19), the (Nb/Ta)O6 octahedral cages are slightly larger than ideal (BVS range from 4.87 to 4.90), giving rise to an under-bonding situation. The bandgaps of the solid solution members were measured between 3.39 and 3.59 eV, and the x = 3.0 member was modeled by density functional theory techniques to be 3.07 eV. The bandgaps of these materials indicate that they are potential candidates for ultraviolet photocatalyst.

Heterogeneous photocatalytic oxidation technology is currently a technology with the potential to solve environmental pollution and energy shortages. The key to this technology is to find and design efficient photocatalysts. Here, a series of inorganic coordination polymer quantum sheets (ICPQS)@graphene oxide (GO) composite photocatalysts are synthesized by adding GO to the synthesis process of ICPQS: {[CuII(H2O)4][CuI4(CN)6]}n. These composite photocatalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, cyclic voltammetry, scanning electron microscopy, transmission electron microscopy, Zeta potential, and N2 adsorption/desorption isotherms. The photocatalytic degradation of methylene blue showed that the activity of ICPQS@GO composite photocatalysts is better than that of ICPQS. Among ICPQS@GO composite photocatalysts, the 10.6% ICPQS@GO composite photocatalyst has the best activity, which can reach 3.3 mg/(L min) at pH 3. This method of loading low–specific surface area photocatalysts onto GO to improve photocatalytic performance indicates the direction for the synthesis of highly efficient photocatalysts.

Two novel porphyrins (5,10,15,20-tetra(3-(carboethoxymethyleneoxy)phenyl)porphyrin, H2TEPp and 5,10,15,20-tetra(3-(carboxymethyleneoxy)phenyl)porphyrin, H2TCPp) and their copper(II) porphyrins (CuTEPp, CuTCPp) were synthesized. With these porphyrins, four new porphyrin-sensitized TiO2 nanorod composites (H2TEPp/TiO2, H2TCPp/TiO2, CuTEPp/TiO2, and CuTCPp/TiO2) were prepared and characterized by methods of XRD, SEM, TEM, FT-IR, UV-vis DRS, nitrogen adsorption–desorption and fluorescence spectra. Besides, the photocatalytic activity and stability of the composites were assessed in the degradation of 4-nitrophenol (4-NP). The results indicate that the morphologies and structures of these composites are less influenced by the loaded porphyrins or copper porphyrins compared with the nanorods TiO2 (anatase). The porphyrin or copper porphyrin molecules are confirmed to bond on the surface of TiO2 through carboxyl group, which is beneficial to the electron transfer between porphyrin and TiO2. All composites exhibit enhanced photoactivities compared with the bare TiO2 nanorods. The possible reason is that the recombination of photoproduced electron–hole has been controlled effectively in these composites, which can be seen from their decreased fluorescence emission. The stability results of composites show that they still hold considerable photocatalytic activities after six cycling experiments.