# Application of Spinel and Hexagonal Ferrites in Heterogeneous Photocatalysis
## 5 Other Magnetic-Photocatalytic Composites
### Spinel Ferrite Composites  
The summary of selected materials containing spinel ferrites is presented in Table 5. Despite the semiconductor and ferrite types, all composites (presented in the Table 5) have \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Photocatalyst**} & **Pollutants** & \multicolumn{1}{c}{**Experimental Conditions**} & **Findings** & **Ref.** \\ \hline BaFe\({}_{12}\)O\({}_{19}\)/TiO\({}_{2}\) & & & 75\% deg. (BaFe\({}_{12}\)O\({}_{19}\)); & \\  & & & 96\% deg. & [105] \\ (10-30\% TiO\({}_{2}\)) & & 4 \(\times\) 8 W UV bulbs (\(\lambda_{\text{max 365 nm}}\)); & (BaFe\({}_{12}\)O\({}_{19}\)/30\% TiO\({}_{2}\)) & \\  & & 10 ppm; 300 min & 60\% deg. & \\ BaFe\({}_{12}\)O\({}_{19}\)/TiO\({}_{2}\) & & & 500 \% C heat treatment); 70\% & \\  & & & deg. (BaFe\({}_{12}\)O\({}_{19}\)/30\% TiO\({}_{2}\) & \\  & & & without heat treatment); & \\ \hline SrFe\({}_{12}\)O\({}_{19}\)/TiO\({}_{2}\) & & UV light (\(\lambda_{\text{max 254 nm}}\)) & 95\% deg. (UV) and & \\ (70-85\% TiO\({}_{2}\) content) & & or vis light (\(\lambda>\) 420 nm); pH 7; & 99\% deg. (vis) & [107] \\  & & 2 g\(\cdot\)L\({}^{-1}\); 10 ppm; 300 min & for SrFe\({}_{12}\)O\({}_{19}\)/80\% TiO\({}_{2}\) & \\ \hline SrFe\({}_{12}\)O\({}_{19}\)/SiO\({}_{2}\)/TiO\({}_{2}\) & MB & 20 W UV light; 50 ppm; 180 min & 80\% deg. & [108] \\ \hline PbFe\({}_{12}\)O\({}_{19}\)/TiO\({}_{2}\) & ABI; AV; ABk & 10 W UV light; & \\  & & 20 g\(\cdot\)L\({}^{-1}\); 10 ppm; 60 min & \(\sim\)100\% dec. of all dyes & [109] \\ \hline \hline \end{tabular} ABk—Acid Black 1; ABI—Acid Blue 29; AV—Acid Violet 7; dec—decolorization; deg—degradation; MB—Methylene Blue.  
\end{table} 
Table 4: Summary of TiO\({}_{2}\)-hexaferrite photocatalysts. revealed high photocatalytic activity, in the range of 96% (ZnS-WO\({}_{3}\)-CoFe\({}_{2}\)O\({}_{4}\)[114] and Ag\({}_{3}\)PO\({}_{4}\)/MnFe\({}_{2}\)O\({}_{4}\)[115]) to even 100% (rGO-based spinel ferrite composites [116, 117]). It has also been proven by [PERSON] et al. [115] that MB degradation for single-phase manganese spinel ferrites and trisilver phosphates is much lower than that for the composite (58%, 80%, and 96%, respectively), probably due to the formation of a heterojunction between the phases, allowing the effective charge separation. Additionally, in a large number of research works, the recovery/recycling of the magnetic composites was investigated. The use of external magnetic field allows the genuine separation, and thus the reuse, of the photoactive material in at least three cycles of pollutant degradation. As a prominent example, in the work of [PERSON] et al. [118], during eight cycles of carbamazepine photodegradation on the Fe\({}_{3}\)O\({}_{4}\)-based Pt-modified composite, 100% efficiency was preserved. Carbon-based materials, i.e., containing graphene, reduced graphene oxide (rGO), carbon nanotubes (CNT) or graphitic carbon nitride, have recently been widely used for photocatalytic reactions. After coupling them with spinel ferrite NPs, an efficient composite with both photocatalytic activity and magnetic separability can be obtained. What is more important, the photogenerated electrons can migrate only from ferrite to carbon material. In this regard, the main shortcoming of a ferrite-based photocatalyst, i.e., photobleaching, is inhibited [63]. The schematic mechanism of heterojunction for non-carbon-based ferrites is shown in Figure 7, where ZnFe\({}_{2}\)O\({}_{4}\) NPs and BiFeO\({}_{3}\) represent the group of p-type and n-type materials, respectively. It has been proposed that during visible-light irradiation, the excited electron from CB of ZnFe\({}_{2}\)O\({}_{4}\) could migrate to CB of BiFeO\({}_{3}\). At the same time, the created holes are transferred between the valence bands, in the opposite direction, due striving for the equilibrium state. Accordingly, this separation of charge carriers might effectively improve the photoactivity of the composite [119].