Deposition of Nano Tungsten Oxide on Glass Mat Using Hot Filament Chemical Vapor Deposition for High Catalytic Activity

Deposition method

The glass fiber mat was created from E-glass formulation and used in this study. The parameters of the glass mat are presented in Table 1.

The tungsten oxide nanostructures were prepared by an HFCVD system. The CVD apparatus used in the experiments is basically composed of a stainless steel chamber. Schematic of the HFCVD setup is shown in Figure 1. Pure and clean tungsten filament was arrayed as vapor and heating source; the diameter of filament is 0.5 mm. The temperature of the hot tungsten filament was 1,700°C. The distance between the filament and the substrate was 1 cm. The chamber was first pumped to 1×10⁻⁵ torr by a rotary and diffusion vacuum pump and the high-purity argon gas was fed into it. Subsequently, the substrate was heated up to the desired temperature (600°C) and the growth was started in a mixture of gases (85:15 for Ar:O₂) were introduced into the chamber.

Figure 1:

Schematic of an HFCVD setup.

In all series of experiment, the oxygen level and the filament and the substrate temperature were the same. The only variable was the time parameter and HFCVD operation was carried out at 50, 80, 110 and 150 s on glass mats which is shown in Table 2. After reaction time, the chamber was cooled to room temperature, under Ar flow. Tungsten oxide nanostructures were finally produced on the substrate.

Morphological study

The morphology of the fabrics was observed using a scanning electron microscope (SEM) (KYKY EM-3200). All of the samples were gold coated before conducting the SEM examination. The energy dispersive X-ray (EDX) unit connected to the SEM microscope was used to determine the percentage of atomic contents of elements present in the surface-coated fabrics.

Electrical resistance measurement

Samples were all tested on a Hewlett Packard 4145A Semiconductor Parameter Analyzer using two probes at room temperature. This analyzer has movable probes which were positioned at a distance equal to the contact distance on the samples. One sample of each structure type used to determine the resistance. Eight resistance measurements were made on each contact to verify that the probes made good contact with the sample.

Photocatalytic experiments

Methylene blue (MB) was chosen as a colorant that would go through photocatalytic oxidation in this experiment, and its discoloration was observed. Fabric specimens (NO₁, NO₂, NO₅) (1 cm×1 cm) were immersed in 10 mL of 1 mg/L MB solution; then the MB solution was exposed to light for 4 h using the solar cell reliability test system at 20°C, 65% RH. The distance between the sample and the light source was maintained at 10 cm. The experimental setup is illustrated in Figure 2.

Figure 2:

Experimental setup for the photocatalytic decomposition of methylene blue solution.

Many compounds absorb ultraviolet (UV) or visible (VIS) light. According to Beer’s law, the absorbance is proportional to the solution concentration, thus the level of photolysis can be estimated by the decrease in absorbance. The absorbance of solution for each interval was measured using an UV-VIS spectrometer, after which a spectrum was recorded in absorption mode by measuring the absorption peak of MB at 660 nm.

Scanning electron microscopy

Scanning electron microscopy is the best known and most widely used tool for surface analyses. In this research work as it was mentioned, glass mat samples were treated by HFCVD technique for different time periods. The result of SEM is shown in Figure 3. As it can be seen, by increasing the time of HFCVD to 150 s, the surface of glass is covered by tungsten oxide more than other samples. Also by increasing the time of HFCVD, as can be seen in Figure 4, tungsten oxide nanoparticles size increased up to 83 nm.

Figure 3:

SEM image of untreated (no. 1), 50 s treated (no. 2), 80 s treated (no. 3), 150 s treated (no. 5) samples.

Figure 4:

SEM images and particle size of 50 s treated (no. 2), 80 s treated (no. 3) and 150 s treated (no. 5) samples.

EDX analysis results

The X-ray emitted from the sample atoms is characteristic in energy and wavelength to the element of the parent atom, which is used to identify and quantify the elements. EDX analysis was performed on no. 2, no. 3 and no. 5 samples to evaluate the quantity changes of tungsten in the samples.

EDX analysis results of the samples are reproduced in Table 3 and Figure 5. The results reveal that the sample no. 2 contains 53.62 (wt%) tungsten and no. 3 contains 64.22 (wt%) tungsten and no. 5 contains 64.65 (wt%) tungsten. From the EDX analysis data of the coated glass samples, it is clearly shown that the amount of tungsten (wt%) increases with increasing the time of exposure.

Figure 5:

EDX analysis spectrums of glass mat.

Electrical conductivity

Electrical conductivity is the phenomenon that describes the transport of electric charge through materials [17].

Results related to electrical conductivity are listed in Table 4. Results show that the increasing of reaction time led to an increase in the absorption of tungsten oxide and finally led to a decrease in the electrical resistance of glass mat.

Photocatalytic results

The photodegradation properties of the glass fibers were initially examined by testing the decomposition of a blue dye solution under UV lamp irradiation. UV lighting is used because it better resembles indoor lighting conditions and represents the lower level of achievable photocatalytic activity. The UV lamp emission spectrum is shown in Figure 6, along with the absorption spectrum of WO₂ nanoparticles. The UV lamp emits a very low number of photons in the UV range compared to visible range photons. The photocatalytic activities of WO₂-deposited glass mat were assessed by analyzing the decrease in the concentration of the MB as a colorant after exposure to UV irradiation and this difference is shown in Figure 7. The MB concentration decreases continuously, concomitant with the UV irradiation time up to 240 min. The results show that the as-prepared nanocomposite exhibits high photocatalytic activity and provides a good way in the degradation field of dyes wastewater. The photocatalytic activity of sample no. 5 is more when compared with the rest of samples. The absorption amount decreases noticeably. As it is seen in Figure 7, less amount of MB remains in the wastewater after exposure to UV.

Figure 6:

Ultraviolet-visible (UV-VIS) spectra of methylene blue (MB).

Figure 7:

WO₂-deposited glass mat (no. 5) in methylene blue solution (A) after and (B) before 4 h of ultraviolet (UV) irradiation.