Effects of Mixed Carriers on Diatomite-Assisted Nano-TiO2 – Scientific Reports

Production of DE/nano-TiO2

XRD analysis

It is generally believed that the anatase phase in nano-TiO2 Particle has high photocatalytic activity22. The energy gap of anatase nano-TiO2 particle (3.2 eV) was slightly larger than that of rutile (3.0 eV). Yu et al.23 showed that after calcination of DE/TiO2 at 300–800 °C for 2 h with increasing calcination temperature the characteristic diffraction peaks of the sharp TiO2 Phase (2θ = 25.2°) gradually increased and the crystal form was gradually intact (Fig. 1). When the temperature was raised to 700°C, the optimum state of anatase crystal phase appeared. However, when the temperature exceeded 700°C, the crystal form was significantly affected. The high temperature can also crack the nano titanium dioxide layer grown on the surface of DE. Wang et al.24 also showed that grain growth was accelerated significantly when the calcination temperature exceeded 650°C. Therefore, a calcination temperature of 700°C for 2 h was assumed in this experiment. The XRD results are in Fig. 2. Figure 2 shows that the corresponding characteristic peaks appear in the XRD of all samples, proving that the produced nano-TiO2 is a mixed crystal form of anatase type and rutile type. The characteristic peaks of the anatase phase appeared at 2θ = 37.18° and 47.16°, and the rutile phase appeared at 2θ = 27.14°, 36.10° and 54.13°.

illustration 1
illustration 1

XRD pattern of DE-assisted nano-TiO2 prepared by precipitation method (TiOSO4urea) and calcined at 300–800 °C for 2 h23.

figure 2
picture 2

XRD pattern of the prepared DE/nano-TiO2 after calcination at 700 °C for 2 h (open circle: anatase; cross symbol: rutile).

The particle size of nano-TiO2 was with Eq. (1), and the results are shown in Table 2. The particle size of nano-TiO2 was between 20 and 24 nm for all samples. When the concentration of titanyl sulfate and urea was 0.01 mol/L and 0.1 mol/L, respectively, the particle size of nano-TiO2 was the smallest (20.4 nm). When the urea concentration was fixed, the particle size did not change significantly with increasing titanyl sulfate concentration. However, when the concentration of titanyl sulfate was constant with increasing urea concentration, the anatase phase peak and particle size decreased and increased, respectively. These changes can be attributed to the use of urea as a precipitating agent, leading to agglomeration of the particles.

Table 2 Particle size of nano-TiO2 (nm).

SEM observation

SEM images of DE and DE/nano-TiO2 are in Fig. 3. By observing the left SEM image, it can be seen that the nano-TiO2 Particles were loaded onto the surface and cavities of the DE, proving that the nano-TiO2 was successfully attached. In the right SEM image, the overall damage of DE during nano-TiO loading2 can be watched.

figure 3
picture 3

SEM image of DE/nano-TiO2.

Effect of mixed carriers on nano-TiO support2

After confirming that DE has been successfully loaded onto Nano-TiO2 particles, we investigated the effect of mixed carriers on nano-TiO loading2. From the above experiments, the urea concentration has a great influence on the particle size of nano-TiO2. In this experiment we used a concentration of 0.01 mol/L titanyl sulfate to study the effect of urea concentration.

The particle size of nano-TiO2 was calculated using the XRD detection results of nano-TiO2 supported by a mixed carrier as shown in Table 3. The experimental results show that almost all mixed carriers tend to increase the particle size of nano-TiO2. When the mixture (calcium carbonate + DE) was used as a carrier with a urea concentration of 0.1 mol/L, the particle size was nano-TiO2 became the smallest (33.3 nm). On the other hand, when (sepiolite + DE) was used as the carrier, the particle size was of nano-TiO2 was the smallest at 15.2 nm when the urea concentration was 0.05 mol/l. However, when the urea concentration was 0.2 mol/L, the particle size was nano-TiO2 was the largest at 56.5 nm. The results showed that the agglomeration of sepiolite was more severe than that of calcium carbonate, which could also be observed in the SEM.

Table 3 Particle size of nano-TiO2 (nm).

In the SEM image observation, it was observed that the agglomeration phenomenon of nano-TiO2 raised on the surface of the mixing carrier (Fig. 4). The analysis of the explosives detection system (EDS) is shown in Fig. 5a and b showed that the content of Si and Al in DE/nano-TiO2 decreased more than that of meta-DE, while the Ti content increased significantly. When the carrier/nano-TiO2 was mixed (Fig. 5c,d), the Si and Al content decreased to some extent, while the Ti content increased. This variation showed that the mixed supported nano-TiO2 was doable. Furthermore, in the case of (calcium carbonate + DE)/nano-TiO2the Ti content increased significantly, suggesting that the mixture of calcium carbonate improves the growth of nano-TiO2 on the surface of DE. This phenomenon can be attributed to the fact that calcium carbonate enters the DE voids during the high temperature of the roasting process, which promotes the conversion of DE from macropores to mesopores17. Therefore, this phenomenon will be further studied in the future.

figure 4
figure 4

SEM image of DE mixed with calcium carbonate or sepiolite/nano-TiO2. (Has) calcium carbonate + DE + titanyl sulfate 0.01 mol/L + urea 0.1 mol/L; (b) sepiolite + DE + titanyl sulfate 0.01 mol/L + urea 0.1 mol/L.

Figure 5
Figure 5

SEM image of the sample and its EDS pattern. (Has) FROM; (b) DE/nano-TiO2; (vs) (calcium carbonate + DE)/nano-TiO2; () (sepiolite + diatomite)/nano-TiO2.

DE and calcium carbonate are commonly used fillers in papermaking. The DE of the vegetation in this experiment or (calcium carbonate + DE) loaded with nano-TiO2 as a composite filler, can be used to make paper with photocatalytic performance using a papermaking process. The experimental results provide a theoretical basis for paper-based photocatalytic materials.

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