## 3 Applications
### Catalysis
The initial pH, Cr\({}^{6+}\) concentration, and reaction temperature have been shown to be important factors influencing the efficiency of Cr\({}^{6+}\) removal (Figure 11). Cr\({}^{6+}\) removal efficiency increases with a decrease in the initial pH and an increase in temperature [44]. As can be seen, to maximize the adsorption capacity of CuFe particles, particular attention should be paid to the choice of material for the formation of a heterojunction with CuFe nanoparticles or to modifying its surface, as well as the structure and composition of created nanoparticles and nanocomposites. It would also be worth supplementing the research with the possibility of using CuFe to absorb other toxic metals, such as Pb\({}^{2+}\) and Hg\({}^{2+}\) or Cd\({}^{2+}\). Bimetallic FeCu nanoparticles can be used to eliminate high concentrations of NO\({}^{3-}\)-N [51]. These pollutants are produced by agricultural runoff, landfill leachate, leaky septic tanks, municipal storm sewage, animal feed, and industrial waste [67,68] and pose a threat to human health [69]. The reduction of NO\({}^{3-}\)-N is the most effective while Cu content surrounding nZVI particles is 2.5% (_w/w_) [51]. The textile industry uses dyes that often pollute the water. Dyes are known to be mutagenic, carcinogenic, and toxic to humans and aquatic animals, and therefore adsorbents are needed to remove them [70,71,72]. CuFe and C/CuFe were used as adsorbents to remove indigo blue. Studies have shown that C/CuFe is more effective in removing indigo blue from aqueous solutions than CuFe [41]. CMC-stabilized Fe-Cu bimetal nanoparticles could effectively dechlorinate 1,2,4-trichlorobenzene (1,2,4-TCB) [53]. Cellulose supported Fe-Cu nanoparticles were also applied for reduction of nitroarenes to arylamines [54]. To increase the catalytic activity of the catalysts, porous materials such as mesoporous silica, activated carbon, mesoporous carbon and carbon nanotubes are also used. Compounds such as phenol, benzoic acid, bisphenol A, 2,4,6-trichlorophenol, imidalcoprid, ketoprofen, methylene blue, and methyl orange have been effectively removed from water using CuFe nanoparticles dispersed on mesoporous carbon (CuFe-MC) [60]. The high specific surface area of mesoporous materials increases the absorption of pollutants. [PERSON] et al. [60] indicated the features of a good catalyst:  
* the large surface area, and especially a mesoporous structure, favor the rapid diffusion of reagents and products. * large dispersion of bimetallic iron-copper nanoparticles in the mesoporous carbon matrix significantly increases the number of active centers, which increases absorption and discharge. * the synergistic effect of iron and copper favored the redox cycles Fe\({}^{3+}\)/Fe\({}^{2+}\) and  
Figure 11: The removal of Cr\({}^{6+}\) by GT- nZVI and GT- nZVICu (**a**), effect of pH (**b**), and concentration (**c**) on the removal of Cr\({}^{6+}\). Reprinted from [44], Copyright 2017, with permission from Elsevier. * Cu\({}^{2+}\)/Cu\({}^{+}\), increasing the catalytic activity. * the presence of mesoporous carbon which can also activate H\({}_{2}\)O\({}_{2}\) to produce \(\bullet\)OH. * An additional benefit of using magnetic catalysts is that they can be easily separated by a magnet, which facilitates the removal of contaminants [60].