**5. Challenges and perspectives**

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

**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

Long afterglow phosphor-assisted novel photocatalysts become promising functional mate‐ rials due to their effective utilization of solar light in practical applications of environmental purification. In this section, the recent development on TiO2-based and Ag3PO4-based fluo‐ rescence photocatalyst composites with full-time active photocatalytic properties is reviewed. The long afterglow phosphor (CaAl2O4:(Eu, Nd)) has a high luminescent brightness around 440 nm of wavelength, long afterglow time, good chemical stability, and low toxicity. The luminescent brightness around 440 nm can excite the visible-light-responsive nitrogen-doped titania (TiO2–xNy). Therefore, TiO2–xNy photocatalyst was expected to possess a novel photo‐

stability under visible-light irradiation.

348 Advanced Catalytic Materials - Photocatalysis and Other Current Trends

B.V.

**4. Long afterglow phosphor-assisted photocatalysts**

catalytic property after coupling with CaAl2O4:(Eu, Nd).

Photocatalysis appears to be a promising avenue to solve environmental and energy issues in the future. A variety of strategies, such as doping, coupling with graphene, precipitating with metal particles, crystal growth design, heterostructuring, were explored to enhance the efficiencies of photocatalytic activities. Besides modified TiO2 and Ag3PO4, other visible-lightdriven photocatalysts, including CdS, BiVO4, Bi2WO6, and g-C3N4, even fluorescence-assisted photocatalyst composites, have attracted increased attention [147–156].

Although great progresses have been achieved, some challenges still exist to design high efficiency of photocatalytic systems. First, fundamental studies are essential to tackle the bottleneck problems in the field, including improved charge separation and transfer, promoted optical absorption, optimized band-gap position, lowered cost, and toxicity. Second, faceted photocatalysts remain a challenge and the development of surfactant-free synthesis routes is highly desirable, since most synthesis strategies involve the use of morphology-controlling agents that must be eventually removed in order to obtain clean facets. Finally, photostability of photocatalyst is and will continue to be a main challenge for practical applications. There‐ fore, new material design and innovative strategies for improving the efficiency and increasing the visible-light absorption of photocatalysts will be the key challenge and opportunity in this field.
