Preparation and Photocatalytic Performance of ZnO/Sepiolite Composite Materials

Table 2

Characteristics of the ZnO/sepiolite composites obtained by the five different methods.

Method	SEM	Infrared spectroscopy	XRD	Conclusion
Sol-gel	The sepiolite is coated by a layer of a gelatinous material with a large load and even distribution.	In the 400–600 cm^−1 region, the variation range of the characteristic absorption peaks is small.	The diffraction peak of zinc oxide is strong and exhibits a good shape.	Zinc oxide is successfully supported on sepiolite in the gel state with a large load, uniform particle distribution, and high degree of crystallinity.
Hydrothermal reduction	The sepiolite is coated by a layer of a crystalline material with a large load and uneven distribution.	In the 400–600 cm^–1 region, the variation range of the characteristic absorption peaks is high.	The diffraction peak of zinc oxide is strong and exhibits a good shape.	Zinc oxide is successfully supported on sepiolite in the crystal form with a large load, uneven distribution, and high degree of crystallinity.
Hydrolytic precipitation	The sepiolite is coated by a layer of fine particles with a large load and uneven distribution.	In the 400−600 cm^−1 region, the variation range of the characteristic absorption peaks between the two groups is small.	The diffraction peak of zinc oxide is weak and exhibits a poor shape.	Zinc oxide is successfully supported on sepiolite in the form of fine particles with a large load, uneven distribution, and low degree of crystallinity.
Powder sintering	The sepiolite is coated by a layer of fine, evenly distributed particles with a moderate load.	In the 400−600 cm^−1 region, the variation range of the characteristic absorption peaks is large.	The diffraction peak of zinc oxide is strong and exhibits a good shape.	Zinc oxide is successfully supported on sepiolite with a moderate load, uniform distribution, and high degree of crystallinity.
Impregnation-reduction	The sepiolite is coated by a layer of small loose particles with a large load and uniform distribution that undergo partial agglomeration.	In the 400–600 cm^−1 region, the variation range of the characteristic absorption peaks between the two groups is average.	The diffraction peak of zinc oxide is strong and exhibits a good shape. A part of the peak indicates the occurrence of a passivation process.	Zinc oxide is successfully supported on sepiolite in the form of loose particles with a large load, uniform distribution, high degree of crystallinity, and high degree of agglomeration.