**3.3. Ag3PO4-based heterostructure photocatalysts**

Many narrow-band-gap metal oxides or chalcogenides have been coupled with Ag3PO4 photocatalyst to enhance its photocatalytic activity and/or improve its stability. In Yao's work, Ag3PO4/TiO2 has been synthesized via the in situ deposition of Ag3PO4 nanoparticles onto the TiO2 surface, which facilitates electron–hole separation, thereby leading to enhanced photo‐ catalytic activity [128].

In our work, the phenomenon of "self-corrosion" was first observed in the simple physical mixed Ag3PO4/TiO2 compounds (Fig. 8). It is found that both self-corrosion and photocorrosion in Ag3PO4/TiO2 compounds alter the chemical environment of Ag. The corrosion degree, however, is different due to a slight difference in the chemical environment of Ag. Further‐ more, it is the strong adsorption capacity that determines the photocatalytic activities of

**Figure 7.** (a) TEM image of pure Ag3PO4 nanoparticles; (b and c) TEM images of Ag3PO4/2.1 wt% RGO nanocomposite; (d) HRTEM image of a single Ag3PO4 nanoparticle in the Ag3PO4/2.1 wt% RGO nanocomposite; (e) scheme of synthetic procedure for the Ag3PO4/RGO nanocomposite; (f) variation of MO and MB concentration against irradiation time us‐ ing Ag3PO4/RGO nanocomposites with various RGO contents under visible-light irradiation and plots of ln(C0/C) ver‐ sus irradiation time representing the fit using a pseudo-first-order reaction rate; (g) repeated photocatalytic degradation of MB solution under visible-light irradiation. Reproduced with permission from ref. 134 © 2013 Elsevier B.V.

can be used as protective coatings that inhibit the photocorrosion of Ag3PO4. Thus, the Ag3PO4/RGO nanocomposites with excellent photocatalytic performance and enhanced stability can find promising applications in addressing environmental protection issues.

**Figure 6.** SEM images of (a) branched, (b) tetrapod, (c) nanorod-shaped, and (d) triangular-prism-shaped Ag3PO4 crys‐ tals; (e) schematic illustration of the possible formation mechanism of Ag3PO4 crystals with four typical morphologies prepared under static and ultrasonic conditions; (f) variation of MB solution concentration against illumination time in the presence of branched, tetrapod, nanorod-shaped, triangular-prism-shaped, and irregular spherical Ag3PO4 prod‐

Many narrow-band-gap metal oxides or chalcogenides have been coupled with Ag3PO4 photocatalyst to enhance its photocatalytic activity and/or improve its stability. In Yao's work, Ag3PO4/TiO2 has been synthesized via the in situ deposition of Ag3PO4 nanoparticles onto the TiO2 surface, which facilitates electron–hole separation, thereby leading to enhanced photo‐

In our work, the phenomenon of "self-corrosion" was first observed in the simple physical mixed Ag3PO4/TiO2 compounds (Fig. 8). It is found that both self-corrosion and photocorrosion in Ag3PO4/TiO2 compounds alter the chemical environment of Ag. The corrosion degree, however, is different due to a slight difference in the chemical environment of Ag. Further‐ more, it is the strong adsorption capacity that determines the photocatalytic activities of

**3.3. Ag3PO4-based heterostructure photocatalysts**

ucts. Reproduced with permission from ref. 143 © 2013 RSC.

346 Advanced Catalytic Materials - Photocatalysis and Other Current Trends

catalytic activity [128].

Ag3PO4/TiO2compounds under UV light irradiation, which is almost independent of selfcorrosion. In contrast, it is the amount of visible-light response of Ag3PO4 in Ag3PO4/TiO2 compounds that mainly determines the photocatalytic activities under visible-light irradiation, which is highly relevant to self-corrosion [146].

Besides Ag3PO4/TiO2 composite heterostructures, AgX/Ag3PO4 (*X* = Cl, Br, I) heterocrystals have also attracted much attention due to their excellent photocatalytic activity [129]. Bi and coworkers have reported that the AgX/Ag3PO4 (*X* = Cl, Br, I) heterocrystals embodied some advantages compared to the single Ag3PO4, and it is a more promising and fascinating visible-

**Figure 8.** Images of fresh samples of (a1 and a3) P25 TiO2, bare Ag3PO4, and Ag3PO4/TiO2 compounds and their coun‐ terparts (b1 and b3) kept in dark for 5 days; (c) XPS spectra of Ag 3d; (d) UV–Vis absorption spectra for related sam‐ ples; (e1) effects of "self-corrosion" on the photocatalytic activity under UV light irradiation, (e2) maintained time, (e3) decreased degradation percentage, (e4) adsorption capacity. Reproduced with permission from ref. 146 © 2014 Elsevier B.V.

light-driven photocatalyst than pure Ag3PO4 [129]. In their work, the AgBr/Ag3PO4 hybrid displayed much higher photocatalytic activity than single AgBr or Ag3PO4, as well as high stability under visible-light irradiation.
