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Herein, two mixed-valence Mn16-containing polyanions, (Mn16) [MnIII10MnII6O6(OH)6(PO4)4(A-a-SiW9O34)4]28- (Mn16-Cs) and [MnIII4MnII12(OH)12(PO4)4(A-a-SiW9O34)4]28- (Mn16-Rb), were successfully fabricated on an indium tin oxide (ITO)-coated glass electrode and a glass carbon electrode (GCE) by a layer-by-layer assembly method. Moreover, four composite films, i.e. [PDDA/Mn16-Cs]n, [PDDA/Mn16-Rb]n, [Mn16-Cs/Rubpy]n, and [Mn16-Rb/Rubpy]n (PDDA: poly(diallyldimethylammonium chloride); Rubpy: tris(2,2'-bipyridyl)ruthenium(ii) chloride; n = 1-10), were constructed for comparison and characterized by UV-visible spectroscopy, cyclic voltammetry (CV), and X-ray photoelectron spectroscopy (XPS). Their electrocatalytic activities towards water oxidation were studied under the same experimental conditions. The results of the controlled experiments indicate that (1) all the four films exhibit expected electrocatalytic activities towards water oxidation; (2) the electrocatalytic activity of Mn16-Cs is better than that of Mn16-Rb in solution and composite films; and (3) the electrocatalytic activities of the composite film [Mn16/Rubpy]n are better than those of the composite film [PDDA/Mn16]n.

With the increase in gas population, the demand for clean and renewable energy is increasing. Hydrogen energy has a high combustion conversion energy while water is its combustion product. In recent years, a way to convert water into hydrogen and oxygen has been found by human beings inspired by plant photosynthesis. However, water decomposition consumes a significant amount of energy and is expensive. People expect to obtain a water decomposition catalyst with low cost and high efficiency. This work selected a six-manganese containing polyoxometalate with a similar structure characteristic to photosynthesizing PSII to fabricate with graphite C3N4 nanosheets for the construction of composite film (Mn6SiW/g-C3N4NSs) electrode via layer by layer self-assembly technology, which was used for the photo-electrochemical decomposition of water under visible light conditions. The binary composite film electrode displayed good catalytic efficiency. The photoelectric density of the composite electrode is 46 μA/cm2 (at 1.23 V vs. Ag/AgCl) and 239 μA/cm2 (at 1.5 V vs. Ag/AgCl). Compared with the g-C3N4NSs electrode alone, the photoelectric density of the composite electrode increased by 1 time. The reason is attributed to the fact that Mn6SiW has a similar structure characteristic to photosynthesizing PSII and high electron transferability. The construction of the composite film containing low-cost Mn6SiW to modify g-C3N4NSs can effectively improve the photocatalytic decomposition of water, thus this study provides valuable reference information for the development of low-cost and high-performance photo-electrocatalytic materials.

A composite film containing g-C3N4NS and SiMoW was constructed by LBL assembly to realize fluorescence switch regulation.

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The discharge of emerging pollutants in the industrial process poses a severe threat to the ecological environment and human health. Photocatalytic self-Fenton technology combines the advantages of photocatalysis and Fenton oxidation technology through the in situ generation of hydrogen peroxide (H2O2) and interaction with iron (Fe) ions to generate a large number of strong reactive oxygen species (ROS) to effectively degrade pollutants in the environment. Graphite carbon nitride (g-C3N4) is considered as the most potential photocatalytic oxygen reduction reaction (ORR) photocatalyst for H2O2 production due to its excellent chemical/thermal stability, unique electronic structure, easy manufacturing, and moderate band gap (2.70 eV). Hence, in this review, we briefly introduce the advantages of the photocatalytic self-Fenton and its degradation mechanisms. In addition, the modification strategy of the g-C3N4-based photocatalytic self-Fenton system and related applications in environmental remediation are fully discussed and summarized in detail. Finally, the prospects and challenges of the g-C3N4-based photocatalytic self-Fenton system are discussed. We believe that this review can promote the construction of novel and efficient photocatalytic self-Fenton systems as well as further application in environmental remediation and other research fields.

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