**1. Introduction**

POMs is one of the most outstanding materials in modern chemistry, as the metal-oxide clusters with abundant structures and interesting properties [1–6], which render them to potential applications in electrochemistry [7, 8], photochemistry [9, 10], catalytic fields [11, 12], and so on (**Figure 1**). Chalkley reported the photoredox conversion of H3[PW12O40] into a reduced POM by photoirradiation with UV light in the presence of 2-propanol as a reducing reagent in 1952 [13]. Hill et al. started systematic investigation of photoredox catalysis using POMs in the 1980s [14]. Accordingly, POMs photocatalysis has been applied to a wide range of reactions, including H2 evolution, O2 evolution, CO2 reduction, metal reduction, and the degradation of organic pollutants and dyes [15–20].

POMs are subdivided into isopolyoxometalates, which feature addenda metal and oxygen atoms, and heteropolyoxometalates, where a central heteroatom provides added structural stabilization and enables reactivity tuning [21]. In recent years, the research of POMs is mainly focused on heteropolyoxometalates. The arsenomolybdates are essential member of the heteropolymolybdates family [22], because of the redox properties of Mo and As atoms. The discoveries of many excellent articles on arsenomolybdates for ferromagnetic, antitumor activity, electrocatalysis properties, and lithium-ion battery performance have been reported in the last years [23–26]. However, there is no stress and discuss on the progress of arsenomolybdates for degradation of organic dyes. Arsenomolybdates possess

**Figure 1.** *The potential application field of arsenomolybdates.*

high-efficient proton delivery, fast multi-electron transfer, strong solid acidity and excellent reversible redox activity [27], which may result to prominent photocatalytic activities. In particular, the integration of metal-organic frameworks (MOFs) into arsenomolybdates for photocatalysis has attracted widespread attention over the past decade, since MOFs combine porous structural and ultrahigh internal surface areas.

arsenomolybdates crystals. Therefore, further exploration of synthetic conditions is necessary, which can provide more experimental data for arsenomolybdates.

Up to now, various structures of arsenomolybdates were reported and discussed in detail. The following types are classical arsenomolybdates clusters: (i) {As2Mo6} type, Pope's group reported the first {As2Mo6} cluster [28], in which the Mo6O6 ring is constructed from six MoO6 octahedra connected via an edge-sharing mode, the opposing faces have two capped AsO4 tetrahedra. Then Zubieta's group and Ma's

octahedron is coordinated with six {MoO6} octahedra hexagonally arranged by sharing their edges in a plane. The cyclic As3O6 trimers are capped on opposite faces of Anderson-type anion plane. Each As3O6 group consists of three AsO3 pyramids linked in a triangular arrangement by sharing corners and bonded to the central MO6 octahedron and two MoO6 octahedra via μ3-oxo groups. Wang and co-workers reported the compound (C5H5NH)2(H3O)2[(CuO6)Mo6O18(As3O3)2] [31], Zhao groups synthesized the compound [Cu(arg)2]2[(CuO6)Mo6O18(As3O3)2]�4H2O [32]. (iii) {AsMo12} type, has a AsO4 tetrahedron at the center and 12 surrounding MoO6 octahedra, such as [NBu4]6[Fe(C5H5)2][HAsMo12O40]2 [33]. {As2Mo9}) type, is derived from the trivacant Keggin moiety, which is capped by a triangular pyramidal {AsO3} group, e.g., [Cu(en)2H2O]2{[Cu(en)2][Cu(en)2AsIIIAsVMo9O34]}

<sup>n</sup>� (RAsO3 = organoarsenic acid) and

9O34]2} [34, 35]. (iv) {As2Mo18} type, as a classical Wells–Dawson

5MMo22O85 (H2O)]<sup>n</sup>� (M = Fe3+, n = 14; M = Ni2+ and Mn2+, n = 15) [39],


<sup>4</sup>�(Ph = PhAsO3H2) clusters [29, 30]. (ii) {As6Mo6} type, which

<sup>10</sup>�, the central {MO6}

<sup>9</sup>� units derived from an Keggin anion

**2.2 Structure of classical arsenomolybdates**

*Arsenomolybdates for Photocatalytic Degradation of Organic Dyes*

*DOI: http://dx.doi.org/10.5772/intechopen.92878*

*The synthesis chart of arsenomolybdates crystal.*

is derived from the A-type Anderson anion [(MO6)Mo6O18]

2�4H2O and [Cu(en)2 (H2O)]4[Cu(en)2(H2O)2]{[Cu(phen)(en)]

by the removal of a set of three corner-sharing MoO6 octahedra, e.g.,

In comparison with the classical arsenomolybdates, many nonclassical arsenomolybdates have also been prepared in the past of years, such as Ag12.4Na1.6Mo18As4O71 [37], (NH4)11[AgAs2Mo15O54]3�6H2O�2CH3CN [38],

The novel arsenomolybdate structure is gaining more and more attention.

cluster, can be described as two [AsMo9O34]

[Himi]6[As2Mo18O62]�11H2O [36].

group reported [MoxOyRAsO3]

[Mo6O18(O3AsPh)2]

**Figure 2.**

[AsIIIAsVMoVI

2FeIII

[AsIII

**119**

{Cu(2,2<sup>0</sup>

Based on these results, we provide a summary of recent works in the synthesis, structure, the photocatalytic activity, reaction kinetics and mechanism mechanisms of arsenomolybdates, which aim at finding the direction followed with the opportunities and challenges for the arsenomolybdates photocatalysis to accelerate the step to realize its practical application in degradation of organic dyes.
