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Article

Metal-Supported TiO2/SiO2 Core-Shell Nanosphere Photocatalyst for Efficient Sunlight-Driven Methanol Degradation

by
M. R. Karimi Estahbanati
1,
Thuy-Dung Vu
1,
Trong-On Do
1,
Zahra Nayernia
2 and
Maria C. Iliuta
1,*
1
Chemical Engineering Department, Université Laval, 1065 Avenue de la Médecine, Québec, QC G1V 0A6, Canada
2
School of Chemical and Petroleum Engineering, Shiraz University, Mollasadra St., Shiraz 7193616511, Iran
*
Author to whom correspondence should be addressed.
Clean Technol. 2023, 5(3), 828-838; https://doi.org/10.3390/cleantechnol5030040
Submission received: 4 November 2022 / Revised: 26 February 2023 / Accepted: 21 June 2023 / Published: 27 June 2023
(This article belongs to the Special Issue Advanced Oxidation Processes for Environmental Remediation)
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Abstract

:
The development of novel and active photocatalysts to industrialize photocatalysis technology is still a challenging task. In this work, a novel method is presented to prepare TiO2/SiO2 NSs by covering SiO2 nanospheres (NSs) with titanate-nanodiscs (TNDs) followed by calcination. In this regard, SiO2 NSs are first synthesized and then TNDs are deposited on the SiO2 NSs using a layer-by-layer deposition technique. The morphology of the prepared samples is analyzed via SEM and TEM analyses before and after the deposition. The analysis of metal (Cu, Pt, and Ni) loading on calcined TNDs/SiO2 NSs reveals the highest specific surface area (109 m2/g), absorption wavelength extension (up to 420 nm), and photocatalytic activity for the Cu-loaded sample. In addition, studying the effect of metal content shows that loading 3% Cu leads to the highest photocatalytic activity. Finally, it is demonstrated that H2S treatment can improve the photocatalytic activity by around 15%. These findings suggest the calcined TNDs/SiO2 NSs are a versatile photocatalyst with potential applications in other processes such as hydrogen production and CO2 valorization.

Graphical Abstract

1. Introduction

Water resource management has become a crucial issue in recent years because of the lack of clean water, population growth, and rapid industrial development. On the other hand, water pollution is constantly increasing because of pollutants discharged in water resources [1]. Therefore, the development of low-cost and high-efficiency methods for water treatment is highly needed. So far, various methods such as adsorption [2,3] and chemical oxidation [4] have been used for removal of contemporary pollutants from water resources. These methods are not effective in some cases because they are slow or non-destructive for some persistent pollutants [5] such as fungicides [6], perfluoroalkyl and polyfluoroalkyl substances (PFAS) [7], and phenolic compounds [8]. Photocatalysis is a sustainable approach that meets most of the requirements of green chemistry. Although the photocatalytic processes have been studied for applications such as hydrogen production [9], wastewater treatment has remained one of the most economically viable applications of photocatalysis [10,11]. The photocatalytic process has been demonstrated to be efficient in the degradation of alcoholic compounds such as methanol [12].
Titanium dioxide (TiO2) is the most commonly used photocatalyst for photocatalytic reactions [12], which shows its high commercialization potential. Various properties of TiO2 such as thermal and chemical stability and resistance to deactivation have introduced it as a promising alternative for wastewater treatment [13]. There is a very bright perspective for TiO2 nanoparticles due to their low cost, high contact surface, ease of production, and good stability under light illumination [14]. However, due to the intrinsic wide bandgap energy of 3.2 eV for the anatase phase, less than 5% of solar light is in the UV range and is absorbed by TiO2 [15]. To overcome this main limitation of using TiO2 in large-scale applications, much research has been conducted to extend the light adsorption wavelength of TiO2 towards the visible region.
The visible light adsorption of TiO2 can be enhanced by its binding to metals such as Cu, Ni, and Pt [16]. As an earth-abundant element, Cu is an efficient dopant with a low cost and good properties [17,18,19]. Shafei and Sheibani [18] showed that doping TiO2-CNT nanocomposite with Cu can increase the degradation rate of methylene blue under visible light irradiation by up to 31%. Ni is another earth-abundant element that can enhance the activity of TiO2 under visible light [20,21,22]. For instance, the degradation of methylene blue under solar irradiation using Ni-doped TiO2 was more than double compared to pure TiO2 [21]. As a noble metal, Pt is one of the most widely used co-catalysts for the enhancement of TiO2 activity [23,24]. Khan et al. [25] showed that methylene blue could be almost completely degraded by loading 0.8 wt% of Pt on TiO2/WO3. Other than increasing the rate of pollution degradation [26], Pt deposition can enhance the photocatalytic activity of TiO2 for various applications such as hydrogen generation [9,16], value-added chemical production [27], and CO2 reduction [23].
TiO2 can be prepared in various shapes such as nanorod, nanosphere, nanosheet, and nanodisc [28]. Tailoring the shape of TiO2 provides the tools to assign it desirable specifications. In a previous work [29], a controlled synthesis method for the preparation of water-soluble titanate nanodiscs (TNDs) as a versatile building block for the design of hybrid nanostructures was proposed. The diameter of these ultrathin TNDs could be tailored in the range of 12–35 nm. These TNDs have uniform size and shape as well as a large surface area and high catalytic activity. In addition, TNDs/CdS composites have shown a very high photocatalytic activity [30]. The use of SiO2 nanospheres (NSs) as a template for TNDs is another alternative to improve its photocatalytic activity by reducing the bandgap and hindering the agglomeration of TND particles. The size of SiO2 nanospheres could be easily controlled using the Stöber method [31].
In this context, in the present work, M/TNDs/SiO2 NSs (M = Cu, Ni, or Pt) are prepared and further calcined (denoted as M/TiO2/SiO2 NSs), and then evaluated as composite photocatalysts. For this purpose, TNDs and SiO2 NSs are first synthesized, and the TNDs are then deposited on the surface of SiO2 NSs. The morphology of the prepared samples is analyzed using SEM and TEM microscopy before and after deposition. In addition, the prepared samples are characterized by BET and UV-Vis analyses. The photocatalytic activity of TiO2/SiO2 NSs under simulated solar radiation is evaluated after loading Cu, Ni, and Pt, through analysis of the degradation capability of methanol, as the model organic pollutant compound. The photocatalytic degradation of methanol in water has been well studied in the prior art, which helps in better understanding the capabilities of the developed photocatalyst by comparing the obtained removal efficiencies with earlier works. The effect of metal content is then assessed for the metal-loaded TiO2/SiO2 NSs with the highest photocatalytic activity. Finally, the influence of H2S treatment on the photocatalytic activity of the selected sample is studied.

2. Materials and Methods

2.1. Chemicals

Titanium butoxide (TB, 97%), benzyl alcohol (BA, 98%), oleylamine (OM, 98%), benzyl ether (BE, 98%), tetraethylammonium (TEA, 98%) hydroxide, tetraethyl orthosilicate (TEOS, 98%), polyethylenimine (PEI, 99%), ammonium hydroxide solution (28%), methanol (99%), and toluene (98%) were provided by Sigma-Aldrich (Milwaukee, WI, USA).

2.2. Material Synthesis

2.2.1. Synthesis of TND

A total of 2 g of TB, 12 g of OM, 12 g of BA (OM:BA weight ratio of 1:1), and 30 g of BE were mixed in a flask to prepare ~22 nm TNDs. The mixture was stirred for 30 min at room temperature followed by transferring into a Teflon-lined stainless-steel autoclave and being heated at 180 °C with a heating rate of 5 °C/min under nitrogen flow. At the end of the reaction after 20 h, the autoclave was left at room temperature to cool down. The obtained sample was washed three times using absolute ethanol and then re-dispersed in toluene and re-precipitated in ethanol to remove the unreacted reagents [29].

2.2.2. Synthesis of SiO2 NSs

To prepare SiO2 NSs with a diameter of ~ 220 nm, TEOS (45 mL, as Si precursor) was added to a mixture of ethanol (750 mL, as solvent), H2O (60 mL, as hydrolyzing agent), and ammonium hydroxide solution (40 mL, as the catalyst). Accordingly, TEOS was hydrolyzed to produce Si(OC2H5)4-X (OH)X intermediate. Silanol groups were then produced according to reaction (1), which acts as a substrate for reaction (2), leading to a three-dimensional cross-linked network structure through the formation of siloxane bridges (Si-O-Si).
S i ( O C 2 H 5 ) 4 + 4 H 2 O → s u s p e n s i o n   i n   e t h a n o l S i ( O H ) 4 + 4 C 2 H 5 O H
S i ( O H ) 4 → s u s p e n s i o n   i n   e t h a n o l n a n o − S i O 2 + 2 H 2 O
To reduce the diameter of SiO2 NSs to ~ 120 nm, the amounts of TEOS and ammonia were reduced to 25 mL and 20 mL, respectively, while other volumes were constant. After stirring at room temperature for 4 h, the precipitated SiO2 NSs were centrifuged and washed 3 times with ethanol. The obtained sample was then re-dispersed in 100 mL of H2O [32]. It is worth mentioning that the stability of CdS-based photocatalysts have been already validated in our previous studies, confirming that S atoms do not easily oxidize through photoexcitation [33].

2.2.3. Depositing TNDs on SiO2 NSs

SiO2 NSs were coated with TNDs using a layer-by-layer deposition technique [34]. In this method, 5 g of SiO2 NSs was dispersed in 200 mL of H2O containing 0.2 g of PEI. After stirring the suspension for 30 min to ensure the saturation of PEI adsorption on the SiO2 surface, excess PEI was separated by centrifugation. The saturated SiO2 NS with PEI was then re-dispersed in 200 mL of H2O. Afterward, 10 mL solution of TNDs (containing 0.1 g TNDs) was gradually added to the SiO2 NS suspension while stirring, to attach the TNDs on the surface of SiO2 NS using the PEI as the linking agent. The obtained material was then separated by centrifugation and rinsed with water three times. The dispersion, centrifugation, and washing procedures were repeated three times to obtain TND/SiO2 NSs [32].

2.2.4. Depositing Metal on TNDs/SiO2 NSs

Cu, Ni, or Pt were deposited on the TND/SiO2 NSs using the wet impregnation method. To do so, the obtained TND/SiO2 NSs were re-dispersed in 200 mL of H2O. Afterwards, 10 mL of 15 mM metal (Cu, Ni, or Pt) solution was added to load 3 wt.% metal (for Cu, Ni, or Pt) or 2, 5, and 7 wt% metal (only for Cu). The obtained mixture was kept under stirring for 60 min for equilibrium adsorption of metal on the TND/SiO2 NSs. The resulting precipitate was kept in the oven at 60 °C overnight, followed by calcination at 550 ℃ (heating ramp rate of 2 °C/min) for 4 h to obtain M/TiO2/SiO2 NSs (M = Cu, Ni, or Pt) [32]. The schematic of the TiO2/SiO2 NS preparation is shown in Figure 1.

2.2.5. H2S Treatment

For H2S treatment of the prepared Cu/TiO2/SiO2 NSs, they were heated at 450 °C with a heating rate of 5 °C/min under H2S flow of 4 L/h for 4 h. Through this method, sulfide (S−2) ions could be substituted with oxygen to convert mixed oxide to mixed sulfide [32].

2.3. Material Characterization

Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images of the prepared samples were obtained using a JOEL JEM 1230 instrument operated at 120 kV, and a JEOL 6360 instrument operated at 15 kV, respectively. The UV-vis spectra were recorded using a Cary 300 Bio UV-visible spectrophotometer. BET measurements were performed using a Micrometrics TRISTAR 3000 instrument. The samples were dried for 4 h at 120 °C to remove the adsorbed water before BET measurements [32]. More information about BET analysis and the obtained BET surface area of the prepared samples in this work are presented in the Supplementary Materials.

2.4. Photocatalytic Experiments

The photocatalytic activity of the prepared composite photocatalysts was investigated in a top-down-type photoreactor connected to a closed-gas circulation system. A total of 0.1 g of the photocatalyst was dispersed in a 5000-ppm solution of methanol (as the representative pollution) in water. The reactor was then filled with Praxair and stirred for 1 h to obtain a steady-state condition. Afterwards, a solar simulator (150 W Xe lamp AM 1.5 G, 100 mW·cm−2) was used to illuminate the reactor for 3 h to decompose the methanol. An amount equal to 500 μL of the solution was sampled and analyzed using a gas chromatograph (GC) to evaluate the amount of remaining methanol after the photocatalytic reaction. The analysis was performed using a GC (Agilent 7820A) equipped with a TCD and HP-PLOT U column, and helium as the carrier gas. The confidence interval for the degradation values was estimated to be between 1 and 1.5% [32].

3. Results

3.1. Microscopic Analysis of Prepared Samples

3.1.1. TNDs

Figure 2a shows the TEM image of the prepared TNDs with a mean diameter of 20 nm that was prepared using the TB:OM mass ratio of 1:6. It can be seen that these TNDs are similar to the ones synthesized in the previous work [29]. To estimate the thickness of TNDs, they were dispersed in ethanol to self-assemble and then analyzed using TEM after drying. Figure 2b depicts the layers of TNDs which were obtained by HRTEM. As seen, the TNDs are ultra-thin, and the distance between the layers is around 0.75 nm. Since no cavity is being observed between these layers, the thickness of TNDs is expected to be close to 0.75 nm. This analysis confirmed the nanodisc morphology of the prepared TNDs, implying a very high surface area. Further characterization results of these TND nanocomposites including HRTEM images, SAED of a single TND, and XRD patterns can be found in previously published works [29,30].

3.1.2. SiO2

Figure 3 illustrates the SEM images of SiO2 NSs with 120 and 220 nm diameters. The size of these NSs, which were prepared using 25 and 45 mL TEOS, illustrates that, by increasing the concentration of TEOS, the size of SiO2 increased, which is in good agreement with previous works [35]. It could be attributed to the fact that as the TEOS concentration increased, the rate of hydrolysis became faster, resulting in more intermediate [Si(OC2H5)4-X (OH)X] ion generation. However, when it reached the supersaturation region, the condensation rate of the [Si(OC2H5)4-X (OH)X] ions was relatively fast, which shortened the nucleation period. Thus, they had more chances to collide and form the gel network, resulting in large particles. As the diameter of TNDs was as small as 20 nm, the SiO2 NSs with 120 nm diameters were found to be more suitable for the preparation of TND/SiO2 composites with high surface areas.

3.1.3. TND/SiO2

Figure 4 compares the TEM images of SiO2 NS before and after TND coating on its surface. Figure 4a clearly shows that the prepared SiO2 NSs have a diameter of around 120 nm. Figure 4b shows the surface morphology of TNDs/SiO2 composites prepared with 120-nm-diameter SiO2 particles after 10 times of layer-by-layer coating. As seen, the particle diameter increased by 10 nm (from 120 nm to 130 nm). On the other hand, this figure illustrates the surface roughness increased meaningfully, which suggests the increase in the specific surface area of the sample. To evaluate that, its specific surface area was analyzed, and it was found to be 20 m2/g for SiO2 NS, an increase of around 5.5 times after TND coating.

3.2. Analysis of the Effect of the Loaded Metal Type

The effect of metal loading on the surface of the prepared TNDs/SiO2 NSs was investigated using Cu, Ni, and Pt as the representative metals. Analysis of the color of the Cu-deposited sample showed it turned from white to moss green, which indicates the oxidation of Cu to CuO. The BET tests showed that the Cu-loaded sample had a larger specific surface area (109 m2/g) compared to Ni/TiO2/SiO2 NSs (98 m2/g) and Pt/TiO2/SiO2 NSs (67 m2/g). It suggests the Cu-loaded sample would have higher photocatalytic activity.
Figure 5 compares the UV-Vis absorption spectra of Cu, Ni, and Pt-loaded TiO2/SiO2 NSs with a bare photocatalyst. The absorption bands of all the samples illustrate a slight redshift in comparison to the bare photocatalyst, which would be because of the incorporation of Cu, Ni, or Pt in the TND matrix. The absorption increased in the range of 220–330 nm, which could be due to the presence of metals [36,37]. As seen, the light absorption capacity of Cu/TiO2/SiO2 NSs is better than the other two metals, in both UV and visible light. In addition, Cu-, Ni-, and Pt-loaded TNDs /SiO2 after calcination absorb visible light with a wavelength higher than 420, 400, and 390 nm, respectively. The greater adsorption band shift of the Cu-loaded sample towards the visible range suggests a higher photocatalytic activity of the Cu/TNDs/SiO2 NSs under visible radiation. It is worth emphasizing that the experiments were conducted using a solar simulator consisting of 46% visible and 3% UV light.
To analyze the photocatalytic activity of the samples loaded with Cu, Ni, and Pt, their performance in methanol decomposition in an aqueous solution was tested under solar light irradiation (Figure 6). As illustrated, the average decomposition efficiency was 50.8%, 48.9%, and 31.2% for Cu-, Pt-, and Ni-loaded samples, respectively. It means that the Cu-deposited sample had 4% and 63% higher photocatalytic activity than the Pt- and Ni-deposited samples, respectively. The higher performance of the Cu-loaded sample is attributed to its higher surface area as well as the extension of the adsorption band toward visible light. In previous studies, nanosphere composites such as Pt/TiO2/CxNy-triazine and C/Pt/TiO2 were capable of degrading methanol by 10% [38,39]. In a similar study, methanol degradation in 11 and 24 h cycles demonstrated efficiencies lower than 20% using TiO2-SiO2-Pt [40].

3.3. Analysis of the Effect of the Loaded Metal Content

As the most effective metal, Cu was selected to analyze the effect of the amount of the loaded metal (2–7 wt%) on the properties of TNDs/SiO2 NSs. The UV-Vis absorption spectra of different concentrations of Cu loading on TNDs/SiO2 NSs followed by calcination is depicted in Figure 7. In this figure, the shift of optical absorption was attributed to the presence of CuO. The adsorption edges of Cu-containing samples had a slighter redshift than those of blank TiO2 (no Cu loading), which is most likely due to the presence of CuO in the TiO2 matrix. The significant absorption enhancement at around 400 nm could be attributed to the existence of Cu species [41]. It can also be seen that the larger the redshift of the absorption edge, the higher the absorption in the visible light region [42]. In addition, the analysis of the extension of light adsorption by Cu-loading concentrations showed that the wavelength adsorption edge increased from 390 nm (for blank TiO2) up to 420 nm.
The photocatalytic activity of the prepared Cu/TiO2/SiO2 NSs with different Cu contents was investigated as shown in Figure 8. Accordingly, the photocatalytic activity generally increased with Cu loading, and the highest decomposition of 50.8% was obtained at 3% Cu concentration. Loading 3% Cu compared to 2% and 5% increased the decomposition percentage by 57% and 19%, respectively. Although the UV-Vis absorption spectra of this sample were similar to the ones with higher Cu concentrations (Figure 7), the photocatalytic activity reduced at higher Cu concentrations. This observation could be attributed to the hindering of the effective adsorption of the light by the semiconductor because of the shading effect of Cu.

3.4. Analysis of the Effect of H2S Treatment

Cu/TiO2/SiO2 NSs with 3% Cu concentration were heated under H2S flow to form CuS- and S-doped TiO2. This treatment changed the color of the sample from moss green to very dark green. It was reported that the H2S treatment at low temperatures (lower than 300 °C) leads to the formation of very strong Ti-SH bonds [43]. At temperatures higher than 300 ℃, the S-H bond becomes weak and breaks. The released H• atom then moves to a neighboring O, forming an OH• group. Finally, H2O is formed at the surface by the combination of the OH• group with another H• atom. On the other hand, CuS could be formed after the H2S treatment [43]. The formed CuS can act as a co-catalyst for the TiO2/SiO2 NSs.
The BET analysis of the H2S-treated sample showed around 25% decrease in the specific surface area after the treatment (82 m2/g for the H2S treated sample compared to 109 m2/g for the non-treated one). This observation could be explained by the sintering occurring at 450 °C during the H2S treatment. The UV-Vis spectrum of the H2S-treated sample was compared with the non-treated one in Figure 9. A wide absorption edge shift in the H2S treated sample at wavelengths higher than 370 nm is clearly observed, which implies higher photocatalytic activity.
The effect of H2S treatment on the photocatalytic activity of Cu/TiO2/SiO2 NSs with 3% Cu concentration is depicted in Figure 10. As seen, the H2S treatment enhanced the photocatalytic activity by around 15% (58.5% for the H2S-treated sample compared to 50.8% for the non-treated one). This improvement could be attributed to the simultaneous occurrence of (i) doping TiO2 with S and [43] the presence of dual CuS/Cu co-catalysts.

4. Conclusions

In this work, C/TNDs/SiO2 NSs (C = Cu, Ni, or Pt) were prepared and analyzed as composite photocatalysts for the degradation of methanol (model organic pollutant compound). In this regard, uniform TNDs with an average diameter of 22 nm were synthesized and used as photocatalysts. SiO2 NSs with 120 nm diameters were also prepared and then covered with TNDs in the presence of PEI to make TNDs/SiO2 NS composites. TEM and SEM analyses confirmed the nanodisc and nanosphere shape of the prepared samples as well as the coverage of SiO2 NSs with TNDs. In addition, it was found that the surface area of SiO2 NSs increased around 5.5 times by depositing TNDs on their surface. Analysis of Cu, Pt, and Ni loading on the prepared TNDs/SiO2 NSs illustrated the following:
  • The Cu-loaded TiO2/SiO2 NSs had the highest surface area of 109 m2/g, while it was 98 and 67 m2/g for the Ni- and Pt-loaded samples, respectively;
  • Loading Cu, Ni, and Pt extended the absorption wavelength to 420, 400, and 390 nm, respectively;
  • The photocatalytic activity of the Cu-deposited sample was 4% and 63% higher than the Pt- and Ni-deposited samples, respectively.
Furthermore, studying the metal-loading content on the TiO2/SiO2 NSs revealed the following:
  • The deposition of 3, 5, and 7% Cu fairly similarly extended the absorption wavelength from 390 nm (for blank TiO2) up to 420 nm;
  • The highest photocatalytic activity was obtained for 3% Cu deposition content.
In addition, it was revealed that the H2S treatment of the Cu/TiO2/SiO2 NSs improved photocatalytic activity by around 15%.
This work suggests that the TiO2/SiO2 NSs could represent a versatile photocatalyst for other potential applications such as hydrogen production and CO2 valorization.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/cleantechnol5030040/s1, Table S1. BET surface area of the prepared samples in this work.

Author Contributions

M.R.K.E.: writing—original draft preparation; visualization; T.-D.V.: investigation; T.-O.D.: conceptualization, methodology, validation, resources, supervision, funding acquisition, review; Z.N.: literature review; visualization; M.C.I.: conceptualization, methodology, validation, resources, supervision, project administration, funding acquisition, writing—review, and editing. All authors have read and agreed to the published version of the manuscript..

Funding

This research received no external funding.

Acknowledgments

The authors thank the Natural Sciences and Engineering Research Council of Canada (NSERC) for funding support.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Schematic illustration of the synthesis of metal-loaded TiO2 NSs.
Figure 1. Schematic illustration of the synthesis of metal-loaded TiO2 NSs.
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Figure 2. TEM image of TNDs: (a) front view showing the shape and diameter, and (b) lateral view showing the thickness.
Figure 2. TEM image of TNDs: (a) front view showing the shape and diameter, and (b) lateral view showing the thickness.
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Figure 3. SEM image of the prepared SiO2 NSs with different diameters: (a) d ~120 nm; (b) d ~220 nm.
Figure 3. SEM image of the prepared SiO2 NSs with different diameters: (a) d ~120 nm; (b) d ~220 nm.
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Figure 4. TEM images of SiO2 NSs before and after TND deposition.
Figure 4. TEM images of SiO2 NSs before and after TND deposition.
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Figure 5. UV-Vis absorption spectra of TNDs/SiO2 NSs loaded with Cu, Pt, and Ni followed by calcination.
Figure 5. UV-Vis absorption spectra of TNDs/SiO2 NSs loaded with Cu, Pt, and Ni followed by calcination.
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Figure 6. Comparison of the photocatalytic activity of the calcined samples of Cu-, Pt-, and Ni-loaded TNDs/SiO2 NSs.
Figure 6. Comparison of the photocatalytic activity of the calcined samples of Cu-, Pt-, and Ni-loaded TNDs/SiO2 NSs.
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Figure 7. UV-Vis absorption spectra of the calcined samples of different concentrations of Cu loading on TNDs/SiO2 NSs.
Figure 7. UV-Vis absorption spectra of the calcined samples of different concentrations of Cu loading on TNDs/SiO2 NSs.
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Figure 8. Comparison of the photocatalytic activity of the calcined Cu/TNDs/SiO2 NSs with different Cu concentrations.
Figure 8. Comparison of the photocatalytic activity of the calcined Cu/TNDs/SiO2 NSs with different Cu concentrations.
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Figure 9. UV-Vis absorption spectra of the H2S-treated and non-treated Cu/TiO2/SiO2 NSs with 3% Cu concentration.
Figure 9. UV-Vis absorption spectra of the H2S-treated and non-treated Cu/TiO2/SiO2 NSs with 3% Cu concentration.
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Figure 10. The effect of H2S treatment on the photocatalytic activity of Cu/TiO2/SiO2 NSs with 3% Cu concentration.
Figure 10. The effect of H2S treatment on the photocatalytic activity of Cu/TiO2/SiO2 NSs with 3% Cu concentration.
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MDPI and ACS Style

Karimi Estahbanati, M.R.; Vu, T.-D.; Do, T.-O.; Nayernia, Z.; Iliuta, M.C. Metal-Supported TiO2/SiO2 Core-Shell Nanosphere Photocatalyst for Efficient Sunlight-Driven Methanol Degradation. Clean Technol. 2023, 5, 828-838. https://doi.org/10.3390/cleantechnol5030040

AMA Style

Karimi Estahbanati MR, Vu T-D, Do T-O, Nayernia Z, Iliuta MC. Metal-Supported TiO2/SiO2 Core-Shell Nanosphere Photocatalyst for Efficient Sunlight-Driven Methanol Degradation. Clean Technologies. 2023; 5(3):828-838. https://doi.org/10.3390/cleantechnol5030040

Chicago/Turabian Style

Karimi Estahbanati, M. R., Thuy-Dung Vu, Trong-On Do, Zahra Nayernia, and Maria C. Iliuta. 2023. "Metal-Supported TiO2/SiO2 Core-Shell Nanosphere Photocatalyst for Efficient Sunlight-Driven Methanol Degradation" Clean Technologies 5, no. 3: 828-838. https://doi.org/10.3390/cleantechnol5030040

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