The Influence of La Doping on Structural, Optical …
365
2.3.2 Photocatalytic Hydrogen Evolution
Photocatalytic hydrogen evolution was studied in cylindrical glass thermostatted
reactors. In a typical experiment, a sample of TiO 2 and La/TiO 2 photocatalyst (0.03 g)
was dispersed in 10.0 ml of aqueous solution containing 2 mol/l ethanol (electron
donor). Co-catalyst Pd/SiO 2 (0.01 g,) was obtained employing PdCl 2 reduction by
hydrogen on the surface of commercial silica in alcohol solution (1 wt% palladium on
SiO 2 ) [21], and was added into the mixture. The reaction mixture was degassed before
irradiation using a forvacuum pump. The suspension was stirred using a magnetic
stirrer and irradiated with a high-pressure mercury lamp (DRSH 1000; 1000 W; λ
max = 365 nm; 50 mW/cm
2 ). The composition of the gas phase above the solution
was determined every 30 min chromatographically.
3 Results and Discussion
3.1 Surface Morphology and Elemental Analysis
Investigation of the obtained powders by means of energy-dispersive spectroscopy
based on energy-dispersive technique proves that these materials include the elements
Ti, O, and La (Figs. 1, 2c) and do not contain other impurities. The EDS elemental
mappings from a selected area show that the La, O. and Ti atoms are distributed
uniformly in the materials (Fig. 1).
Analysis of SEM images of the samples shows that they consist of fragmented
agglomerates (Fig. 2a, b, c).
TEM analysis results are presented in Fig. 3 and prove that agglomerates of pure
TiO 2 consist of ca. 10 nm size crystallites (Fig. 3a) and La/TiO 2 composites—ca.
8–10 nm size crystallites (Fig. 3b).
3.2 XRD Analysis
Crystal structure of the powders was identified using XRD. XRD-pattern of pure
titanium dioxide shows intensive peaks at 2θ = 25.4 (101); 37.8 (004); 48.0 (200);
53.9 (105); 55.1 (211); 62.75 (204); 75.1 (215), which belong to tetragonal modification of TiO 2 anatase and at 2θ = 27.4 (110) being characteristic of rutile (Fig. 4,
curve 1). The content of anatase in pure TiO 2 significantly exceeds the content of
rutile. With the introduction of La in TiO 2 , the anatase content decreases, while that
of rutile increases. The content of rutile in the 2La/TiO 2 composite increases by two
times as compared to pure TiO 2 (Table 2).
Different authors have opposing conclusions about the role of lanthanum in the
anatase—rutile phase transformations. Some authors [15, 22, 23] reported that La
365
2.3.2 Photocatalytic Hydrogen Evolution
Photocatalytic hydrogen evolution was studied in cylindrical glass thermostatted
reactors. In a typical experiment, a sample of TiO 2 and La/TiO 2 photocatalyst (0.03 g)
was dispersed in 10.0 ml of aqueous solution containing 2 mol/l ethanol (electron
donor). Co-catalyst Pd/SiO 2 (0.01 g,) was obtained employing PdCl 2 reduction by
hydrogen on the surface of commercial silica in alcohol solution (1 wt% palladium on
SiO 2 ) [21], and was added into the mixture. The reaction mixture was degassed before
irradiation using a forvacuum pump. The suspension was stirred using a magnetic
stirrer and irradiated with a high-pressure mercury lamp (DRSH 1000; 1000 W; λ
max = 365 nm; 50 mW/cm
2 ). The composition of the gas phase above the solution
was determined every 30 min chromatographically.
3 Results and Discussion
3.1 Surface Morphology and Elemental Analysis
Investigation of the obtained powders by means of energy-dispersive spectroscopy
based on energy-dispersive technique proves that these materials include the elements
Ti, O, and La (Figs. 1, 2c) and do not contain other impurities. The EDS elemental
mappings from a selected area show that the La, O. and Ti atoms are distributed
uniformly in the materials (Fig. 1).
Analysis of SEM images of the samples shows that they consist of fragmented
agglomerates (Fig. 2a, b, c).
TEM analysis results are presented in Fig. 3 and prove that agglomerates of pure
TiO 2 consist of ca. 10 nm size crystallites (Fig. 3a) and La/TiO 2 composites—ca.
8–10 nm size crystallites (Fig. 3b).
3.2 XRD Analysis
Crystal structure of the powders was identified using XRD. XRD-pattern of pure
titanium dioxide shows intensive peaks at 2θ = 25.4 (101); 37.8 (004); 48.0 (200);
53.9 (105); 55.1 (211); 62.75 (204); 75.1 (215), which belong to tetragonal modification of TiO 2 anatase and at 2θ = 27.4 (110) being characteristic of rutile (Fig. 4,
curve 1). The content of anatase in pure TiO 2 significantly exceeds the content of
rutile. With the introduction of La in TiO 2 , the anatase content decreases, while that
of rutile increases. The content of rutile in the 2La/TiO 2 composite increases by two
times as compared to pure TiO 2 (Table 2).
Different authors have opposing conclusions about the role of lanthanum in the
anatase—rutile phase transformations. Some authors [15, 22, 23] reported that La