Transparent photochromic Fe-doped W₁₈O₄₉ films with ultrahigh solar energy modulation for smart windows

Abstract

Recently, tungsten oxides have attracted extensive attention in the field of photochromic smart windows due to the naturally ultraviolet response, high luminous transmittance (T_lum), and substantial solar light modulation (ΔT_sol). To promote its applications, limitations such as slow bleaching speed and poor reversibility need to be addressed urgently. Here, we proposed a Fe³⁺-doping mediated rapid electron transfer strategy to improve the overall photochromic performance of W₁₈O₄₉. By increasing the Fe³⁺ doping concentration, the bleaching speed of W₁₈O₄₉ films was significantly improved. Notably, films doped with 6 at% and 8 at% Fe³⁺ could be fully bleached within 5 min, with bleaching rates twice that of undoped films. This improvement is attributed to Fe³⁺ doping, which creates more oxygen vacancies in W₁₈O₄₉, facilitating the reduction of W⁶⁺ to W⁵⁺. Furthermore, the 6 at% Fe³⁺-doped W₁₈O₄₉ bilayer film exhibited excellent photochromic performance, with the ultrahigh T_lum and ΔT_sol of 82.9% and 60.2%, respectively, fast photochromic speed (within 2 min), and nearly complete near-infrared light blocking in the colored state. These findings demonstrate the potential of Fe³⁺-doped W₁₈O₄₉ to significantly improve the performance of photochromic smart windows, offering promising avenues for energy-efficient building technologies.

---

Introduction

The building industry stands out as one of the largest contributors to global energy use, particularly due to the significant role played by building envelopes, such as windows, in energy exchange. Windows, being critical points of heat loss and gain, directly impact the overall thermal performance and energy efficiency of buildings.^1–3 In this context, smart windows, which adapt their optical properties in response to external stimuli such as temperature, light, or voltage, have emerged as a promising solution for minimizing energy consumption in buildings. These technologies offer the potential to enhance indoor comfort while significantly reducing the need for heating, cooling, and artificial lighting.^4,5 Smart windows should exhibit: (1) near-complete blocking of near-infrared (NIR) light during the day (with a transmittance of T_NIR ≈ 0 and a high solar light modulation ΔT_sol > 60%); (2) high visible light transmittance (T_lum > 80%) to maintain natural daylighting.^6,7

One promising approach to developing such windows is through the use of photochromic materials that undergo reversible changes in their optical properties when exposed to light.^8–12 These materials, which transition between different states under specific light conditions, have garnered significant attention in recent years due to their potential to provide dynamic solar control. Photochromic materials can be broadly classified into organic and inorganic types, including transition metal oxides (TMOs), metal halides, and rare earth complexes. Among these, tungsten oxide (WO_3−x) has emerged as one of the most studied and promising candidates for smart window applications, owing to its excellent stability, low cost, and non-toxic nature. Despite these advantages, however, pure WO₃ suffers from limitations such as slow response times and poor reversibility, which hinder its practical application in dynamic window technologies.^13,14

Several strategies have been proposed to enhance the photochromic performance of WO_3−x. Ma et al.¹⁵ investigated the optical properties of Ti⁴⁺-doped W₁₈O₄₉, finding that Ti⁴⁺ doping introduced oxygen-defect structures, increased carrier concentration, and enhanced surface plasmon resonance (LSPR) effects, resulting in improved photochromic properties. Similarly, Zhang et al.¹⁶ developed WO₃@poly(N-isopropylacrylamide) (WO₃@PNIPAM) hybrid spheres, where the amide group in PNIPAM facilitated electron injection during photochromism. Additionally, Zhu and Liu et al.¹⁷ synthesized hypoxic WO₃ quantum dots (WO_3−x QDs) to further boost photochromic performance. While these approaches have shown promising results, the performance of the resulting photochromic films, particularly in terms of ΔT_sol in the near-infrared region, still requires improvement. Compared to thermochromic and electrochromic materials, another drawback of photochromic WO_3−x is its relatively slow bleaching rate, which is mainly controlled by the oxidation kinetics from W⁵⁺ to W⁶⁺. Thus, increasing the bleaching speed is also crucial for the application of photochromic thin films.¹⁸

In this work, we significantly enhance the photochromic properties of W₁₈O₄₉ by modifying its electronic structure and light absorption characteristics through Fe³⁺ doping. The effects of Fe³⁺ doping concentrations on the bleaching speed and optical performance were investigated. We found that bleaching speed and ΔT_sol increased as the Fe³⁺ doping concentrations increased, while T_lum remained unchanged. At the optimal doping concentration (6 at%), a visible transparent film with a T_lum of 82.9% and a ΔT_sol of 60.2% was fabricated by tailoring the film thickness. Of note, it can block nearly all NIR light when in the colored state. These performances are in top-tier and are critical for the development of advanced photochromic smart windows, offering substantial potential for energy-efficient building designs.

Experimental section

Materials

Tungsten hexachloride (WCl₆, 99.9%) was purchased from Aladdin Reagent (Shanghai) Co., Ltd. Anhydrous ethanol (EtOH, AR), iron(III) chloride hexahydrate (FeCl₃·6H₂O), and polyvinylpyrrolidone (PVP, K30) were obtained from Sinopharm Group Chemical Reagents Co., Ltd. All chemicals were used without further purification.

Preparation of Fe-doped W₁₈O₄₉ nanoparticles

Fe-doped W₁₈O₄₉ nanoparticles were synthesized using a previously reported solvothermal method (Fig. 1a). In this process, 0.792 g of WCl₆ was dissolved in 40 mL of absolute ethanol and magnetically stirred until a transparent orange-yellow precursor solution (solution A) was obtained, resulting in a concentration of 0.05 mol L⁻¹. Meanwhile, 1.3515 g of FeCl₃·6H₂O was dissolved in 5 mL of ethanol to create solution B, which had a Fe³⁺ concentration of 1 mol L⁻¹. To achieve varying doping concentrations, 0, 40, 80, 120, and 160 μL of solution B were added to solution A, respectively. The resulting solutions were sealed in 100 mL PTFE-lined stainless-steel autoclaves. They were then placed in a drying oven and heated to 180 °C for 12 h. The resulting nanoparticles were separated by centrifugation at 8000 rpm for 5 min. The sediments were subsequently dried and collected. Samples with Fe/W molar ratios of 0%, 2 at%, 4 at%, 6 at%, and 8 at% were designated as Fe/W-0, Fe/W-0.02, Fe/W-0.04, Fe/W-0.06, and Fe/W-0.08, respectively.

Fig. 1 (a) The preparation route to the W₁₈O₄₉ particles. (b) XRD patterns of Fe/W-0.06 and Fe/W-0. (c) high-resolution Fe 2p spectra of Fe/W-0 and Fe/W-0.06 nanoparticles. (d) High-resolution W 4f core level binding energy of Fe/W-0.06 nanoparticles. (e) Photographs of Fe/W-0.06 and Fe/W-0 nanoparticles before and after photochromism. Working mechanism of the photochromic film-based smart windows. HRTEM and SAED patterns of (f) Fe/W-0 and (g) Fe/W-0.06 nanoparticles. (h) The EDS elemental mapping results of the Fe/W-0.06 nanoparticles.

Preparation of W₁₈O₄₉-based photochromic film

The as-obtained nanoparticles were heat-treated in air at 150 °C for 30 min to obtain the bleached W₁₈O₄₉ nanoparticles. Then, they were mixed with PVP (mass ratio was 1 : 3) and ethanol through ball milling to prepare the homogeneous coating slurry. Glass slides (25 × 25 mm²) were used as the substrate, prior to the spin-coating process, the substrates were thoroughly washed with ethanol and water. The W₁₈O₄₉-based photochromic film was fabricated by spin-coating 150 μL of the coating slurry onto the substrate at 500 rpm for 10 s and 1500 rpm for 20 s (Fig. 1a). The as-obtained film was dried at 80 °C for 60 min. Specially, a Fe/W-0.06 bilayer film was fabricated by spin-coating the coating slurry containing Fe/W-0.06 nanoparticles onto both sides of the substrate to increase the film thickness.

Characterizations

The crystal structure of the nanoparticles was determined by X-ray diffractometer with Cu-Kα radiation (XRD, D8-ADVANCE, Bruker, Germany). The micro-morphology of the nanoparticles and films was investigated using field emission scanning electron microscopy (FESEM, Zeiss Ultra Plus, Germany). High-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDX) (Talos F200s, USA) were used to characterize the component and structure of the nanoparticles. The compositional information of the nanoparticles was recorded by a Fourier transform infrared spectroscopy (FTIR, Therma Electron, Nicolet 6700, USA). Elemental composition and content changes of the samples before and after photochromism were determined by X-ray photoelectron spectroscopy (XPS, K-Alpha, Thermo Fisher Scientific, USA). The transmittance spectra of the films before and after photochromic were tested by a UV-Vis-NIR spectrophotometer (Shimadzu, UV3600, Japan). To characterize the colouring process of films, transmittance (300–2500 nm) was tested after irradiating by UV light (5 W, 365 nm) for a period of time. To characterize the bleaching process of films, transmittance (300–2500 nm) was tested after heating for a period of time at 80 °C.

To quantitatively evaluate the optical properties of the films used in smart windows, T_lum (380–780 nm) and ΔT_sol (300–2500 nm) were calculated using eqn (1) and (2).

where T(λ) denotes the transmittance at wavelength λ. ϕ_sol(λ) is the solar irradiance spectrum for air mass 1.5 corresponding to the sun standing 37° above the horizon (Fig. 1d), and ϕ_lum(λ) is the sensitivity of human eye for photopic vision.¹⁹

Results and discussions

The Fe-doped nanoparticles were synthesized by a simple solvothermal method (Fig. 1a). XRD results show that the undoped nanoparticles exhibited diffraction peaks consistent with the monoclinic WO₃ phase²⁰ (PDF #83-0950, a = 7.30084 Å, b = 7.53889 Å, c = 7.68962 Å, β = 90.892°). The diffraction peaks at 2θ of 24.36°, 34.16°, and 41.8° correspond to the (200), (220), and (222) crystal planes of WO₃,²¹ respectively. In contrast, the Fe-doped nanoparticles (Fe/W-0.06) predominantly exhibited the monoclinic W₁₈O₄₉ phase (PDF #71-2450, a = 18.334 Å, b = 3.786 Å, c = 14.044 Å, β = 14.044 Å). The diffraction peaks at 2θ of 23.2° and 47.6° were attributed to the (010) and (020) crystal planes of W₁₈O₄₉, respectively.²²

Fe³⁺ doping was found to induce a phase transition in the nanoparticles, even at a low doping concentration of 2 at% (Fig. S1, ESI†). As the doping level increased to 4 at%, the intensity of the diffraction peaks also increased, suggesting an enhancement in crystallinity. However, further doping at 8 at% led to a decrease in peak intensity. This reduction is attributed to the formation of oxygen vacancies and the doping-induced reduction of W⁶⁺ to W⁵⁺, since Fe³⁺ has a lower charge than W⁶⁺. At doping concentrations of 0 to 4 at%, the increased W⁵⁺ content facilitated the formation and improved crystallinity of W₁₈O₄₉. However, when the oxygen vacancy concentration exceeded the stoichiometric limits of W₁₈O₄₉, crystallinity began to deteriorate. The diffraction peak for the (010) crystal plane shifted to a smaller angle (Fig. S2, ESI†), which can be attributed to the larger ionic radius of Fe³⁺ (65 pm) compared to W⁶⁺ (60 pm).²³ These XRD results provide indirect evidence for the partial substitution of W⁶⁺ ions by Fe³⁺ in the crystal lattice.

The survey XPS results confirm that there are no elemental impurities in the Fe/W-0.06 and Fe/W-0 nanoparticles, and the Fe element is only detected in the Fe/W-0.06 nanoparticles (Fig. S3, ESI†). The high-resolution Fe 2p spectra (Fig. 1c) shows two peaks at 710.26 eV and 723.38 eV, corresponding to Fe³⁺ 2p_3/2 and Fe³⁺ 2p_1/2 spin orbits, respectively.²⁴ This confirms that Fe³⁺ has been successfully doped into the crystal lattice of W₁₈O₄₉. Fig. 3d shows the binding energies of W 4f_5/2 and W 4f_7/2 spin orbits peaks for the Fe/W-0.06 nanoparticles. The calculated proportion of W⁵⁺ in Fe/W-0.06 sample is 22.3%, confirming the formation of non-stoichiometric W₁₈O₄₉.

Fig. 1e shows significant colour changes during the photochromic process of the Fe/W-0.06 and Fe/W-0 nanoparticles. Due to the higher content of W⁵⁺, the color of Fe/W-0.06 in the colored state is much darker than that of Fe/W-0. The photochromism is reversible, the colouring process can be trigger by UV light (365 nm, 5 W), and the bleaching process occurred when the UV light is removed at ambient temperature. Notably, heating in air can accelerate the bleaching process by promoting the oxidation of W⁵⁺ to W⁶⁺.

In the HRTEM image of the Fe/W-0 sample (Fig. 2a), clear lattice fringes corresponding to the (020) plane with a spacing of 0.372 nm are observed. The SAED patterns (Fig. 2b) show diffraction spots matching the (020), (022), and (002) crystal planes of WO₃, confirming that the Fe/W-0 sample presents a single-crystal WO₃ structure.^25–27 In contrast, the HRTEM image of Fe/W-0.06 nanoparticles (Fig. 2c) reveals lattice fringes corresponding to the (010) plane, with a plane spacing of 0.383 nm. The SAED patterns for Fe/W-0.06 (Fig. 2d) show diffraction rings associated with the (010) and (020) planes of W₁₈O₄₉, indicating that the sample is polycrystalline.^28–30 Additionally, elemental mapping (Fig. 2e) confirms that iron is uniformly distributed throughout the Fe/W-0.06 nanoparticles, suggesting successful incorporation of Fe into the crystal lattice.

Fig. 2 (a) The preparation route to the photochromic W₁₈O₄₉-based films. (b) Working mechanism of the photochromic film-based smart windows, the yellow and blue circle denote the bleached and coloured W₁₈O₄₉ nanoparticles. (c) Surface and cross-section morphologies of the Fe/W-0.06 bilayer film. (d) Fe and (e) W element distribution in the film. (f) Transmittance spectra of the Fe/W-(0-0.08) films in the bleached and coloured states. (g) T_lum and ΔT_sol as a function of doping concentration. (h) Bleaching process of the Fe/W-(0-0.08) films. Note: T₀ = T_{(bleached, λ=1200nm)}−T_{(coloured, λ=1200nm)}, ΔT = T_{(X,λ=1200nm)}−T_{(coloured, λ=1200nm)}, X: the heating time.

To further investigate the impact of doping on the photochromic properties, we fabricated nanocomposite films by spin-coating a slurry containing PVP, ethanol, and W₁₈O₄₉ nanoparticles (Fig. 2a). These films are very uniform and highly transparent and can be colored with UV light and bleached by heating at 80 °C (Fig S4, ESI†). Fig. 2b illustrates the working mechanism of these nanocomposite film-based photochromic smart windows, designed for use in tropical regions. During the day, strong UV light is absorbed by the W₁₈O₄₉ nanoparticles, triggering a photochromic reaction that colors the film. The colored W₁₈O₄₉ nanoparticles then absorb and reflect near-infrared (NIR) light, helping to prevent an increase in indoor temperature. At night, as UV light fades, the film gradually bleaches in ambient air, allowing infrared (IR) light to pass through and enabling normal heat release from the interior.

In the Fe/W-0.06 film, the Fe/W-0.06 nanoparticles (denoted by the white spots) are uniformly dispersed, with the black component being PVP (Fig. 2c). The film has a thickness of 3.26 μm, which is sufficient to accommodate a higher concentration of Fe/W-0.06 nanoparticles. Although the SEM images of the Fe/W-0 and Fe/W-0.06 samples (Fig. S5, ESI†) reveal micro-scale particles, it is likely that the ball milling process used during the preparation of the coating slurry has fractured the initial particles into nanoparticles. The wide bandgap of Fe/W-0 and Fe/W-0.06 ensured the visible light will not be adsorbed by the film (Fig. S6, ESI†). And the small particles evenly distributed in the film will significantly decrease the reflectance and scattering effect. These features explained why the thick film remained almost transparent (Fig. S4, ESI†). Additionally, elemental mapping (Fig. 2d and e) confirms the homogeneous dispersion of Fe/W-0.06 nanoparticles throughout the film.

Fig. 2f presents the photochromic performance of the Fe/W-(0-0.08) films. The initial NIR transmittance increases with the doping content due to the decreased W⁵⁺ content in the bleached state in the samples. W⁵⁺ will generate small polaron to absorb NIR light. These films maintain nearly identical visible transmittance and are highly sensitive to UV irradiation. In their saturated colored state, all films show minimal transmittance in the wavelength range of λ = 1000–1250 nm, which is consistent with the intrinsic W₁₈O₄₉ films, known to exhibit significant localized surface plasmon resonance (LSPR) absorption in the NIR region.³¹ From the calculated optical properties (Fig. 2g and Table S1, ESI†), it is evident that all films demonstrate a luminous transmittance (T_lum) of over 87%, very close to the substrate's transmittance (∼88%), suggesting that the films are nearly transparent. Among the single-layer films, the Fe/W-0.02 film exhibits the highest solar modulation (ΔT_sol) of 48.8%. However, as the Fe³⁺ concentration increases, ΔT_sol gradually decreases, reaching 31.4% for the Fe/W-0.08 film.

Fig. 2h illustrates the bleaching process of the Fe/W films, showing that the bleaching speed increases significantly as the doping concentration rises. The Fe/W-0.06 and Fe/W-0.08 films nearly achieved complete bleaching within 10 min, while the Fe/W-0 film only recovered about 80% of its original transmittance after 30 min (Table S2, ESI†). The bleaching speed of Fe/W-0.06 and Fe/W-0.08 films is approximately twice that of Fe/W-0 film. Combined with the optical properties of the films, Fe/W-0.06 film exhibits the best photochromic performance. Additionally, all films show rapid bleaching within the first 5 min. This is attributed to the fact that a large amount of W⁵⁺ at the surface is in direct contact with oxygen, allowing for quick oxidation to W⁶⁺. Once the oxygen on the surface becomes saturated, a diffusion barrier forms, increasing the potential energy barrier for further oxidation of the inner W⁵⁺ ions. As a result, a higher temperature is required to overcome this barrier, leading to a slower bleaching rate thereafter.³²

In smart window applications, a luminous transmittance (T_lum) over 60% is generally sufficient for indoor lighting. Ideally, the solar modulation (ΔT_sol) should be as high as possible, and the near-infrared (NIR) transmittance in the colored state (T_nir-colored) should be as low as possible to improve energy efficiency. To achieve these goals, the Fe/W-0.06 bilayer film was designed with a slight sacrifice in T_lum to reduce T_NIR-colored and enhance ΔT_sol. As shown in Fig. 3a, in the bleached state, the Fe/W-0.06 bilayer film is transparent and colorless. Upon UV irradiation for 2 min, the film turns deep blue, indicative of the typical color of W⁵⁺ species. After removing the UV light and heating the film at 80 °C for 30 min, the film recovers to its initial transparent state, demonstrating a fully reversible photochromic process.

Fig. 3 (a) Photographs of the Fe/W-0.06 bilayer film from bleached to colored to bleached state. (b) Transmittance spectra of the Fe/W-0.06 bilayer film, the inset illustrates the film structure. (c) Colouring and bleaching process of the Fe/W-0.06 bilayer film. (d) Cyclic stability of the Fe/W-0.06 bilayer film, transmittance at λ = 1200 nm was recorded.

The film structure is illustrated in Fig. 3b. It has ultra-high transmittance in the bleaching state. In the coloured state, it is visible transparent but is nearly NIR light opaque (Fig. 3b). The calculated T_lum is 82%, while the ΔT_sol reaches 60% (Table S1, ESI†), positioning it as one of the top performers among reported photochromic films. The reversibility of the Fe/W-0.06 bilayer film is essential for its practical use. The film can be fully colored within 2 min under UV irradiation (365 nm, 5 W) and can recover to its transparent state within 30 min upon heating at 80 °C, demonstrating excellent reversibility (Fig. 3c and Table S2, ESI†). At ambient temperature, the film bleaching process will take about 8 h, which means this process can be completed overnight in the real application (Fig. S7 and S8, ESI†). After undergoing 50 full coloring-bleaching cycles, the photochromic performance of the film remains largely unchanged (Fig. 3d), indicating good cyclic stability of the photochromism. However, improving the whole durability of the film is still a challenge because of the polymer matrix we used. To further emphasize the advantages of this bilayer film, a comparison with various WO₃-based photochromic films (Table S3, ESI†) demonstrates that the Fe/W-0.06 bilayer film not only exhibits faster coloring and bleaching speeds but also offers a higher transmittance modulation. This makes it highly promising not only for smart window applications, but also for other applications such as rewritable paper, anti-counterfeiting coatings, and more.

To investigate the photochromic mechanism, we analyzed the change in W⁵⁺ content in both the bleached and colored states using XPS, as the variation in W⁵⁺ concentration significantly influences the observed color change in W₁₈O₄₉. In the Fe/W-0 particles (Fig. 4a), the relative W⁵⁺ content was 14.4% (W⁵⁺/(W⁵⁺ + W⁶⁺)) before UV irradiation and increased to 18.8% after exposure to UV light. This modest increase in W⁵⁺ led to a shift in color from light blue to dark blue. During the bleaching process, W⁵⁺ on the surface was oxidized to W⁶⁺, resulting in the fading of the blue color. To reveal the effect of O₂ during the bleaching process, a controlled experiment under the oxygen-free condition was conducted to observe the bleaching process (Fig. S9, ESI†). The film can’t be bleached in oxygen-free condition (Fig. S10 and S11, ESI†), revealing that O₂ has diffused into the PVP film to react with W⁵⁺. In the Fe/W-0.06 particles (Fig. 4b), the relative W⁵⁺ content showed a more significant increase, rising from 5.4% to 22.3% after UV irradiation. This larger change induced a more pronounced color shift, from white to dark blue. The results suggest that a lower initial W⁵⁺ content corresponds to a lighter color, while a higher W⁵⁺ content results in a more intense color change.

Fig. 4 (a) and (b) High-resolution W 4f core level binding energy of Fe/W-0 and Fe/W-0.06 nanoparticles before and after UV irradiation. (c) Schematic diagram of photochromic mechanism.

The photochromic process is driven by the interaction of UV photons with the W₁₈O₄₉ nanoparticles. When the energy of the ultraviolet photons exceeds or matches the bandgap of the material, electron–hole pairs (e⁻ and h⁺) are generated. During the coloring process, W⁶⁺ ions capture photogenerated electrons and are reduced to W⁵⁺, resulting in the dark blue coloration. Which can be expressed as eqn (3).^33,34 Additionally, Fe³⁺ ions play a key role in accelerating the bleaching process. They act as mediators for electron transfer, facilitating the oxidation of W⁵⁺ to W⁶⁺ by accepting electrons, and promoting the reduction of W⁶⁺ to W⁵⁺ by giving electrons (Fig. 4c). This enhances the overall speed and efficiency of the photochromic transitions.^35,36

W⁶⁺O₃ + xe⁻ + xH⁺ → H_xW⁶⁺_1−xW⁵⁺_xO₃ (3)

Conclusions

In this work, we have synthesized Fe-doped W₁₈O₄₉ nanoparticles for photochromic smart windows. We found that substitute doping of Fe³⁺ can induce a phase transition from WO₃ to W₁₈O₄₉ due to the formation of oxygen vacancy. The presence of Fe³⁺ significantly enhances the bleaching speed of W₁₈O₄₉ films, with a faster bleaching rate corresponding to a higher concentration of Fe³⁺ dopants. Specifically, the bleaching speed of Fe/W-0.06 and Fe/W-0.08 films was twice that of the Fe/W-0 film, highlighting the role of Fe³⁺ as an electron transfer mediator. Fe³⁺ doping also effectively increases ΔT_sol of the films without affecting their T_lum because the Fe³⁺ doped W₁₈O₄₉ nanoparticles contain a higher concentration of activated W⁵⁺, which can be easily oxidized to W⁶⁺ and be restored. During the photochromic process, the transmittance variation is dependent on the content of activated W⁵⁺, the more change of W⁵⁺ content the more pronounced transmittance variation. Fe/W-0.06 bilayer film demonstrated the best overall performance, featuring an ultrahigh T_lum of 82.9%, an excellent ΔT_sol of 60.2%, a fast bleaching and coloring speed. Beside, it has good cycle stability, making it possible to smart windows applications.

Author contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Data availability

The data that support the findings of this study are available on request from the corresponding author upon reasonable request.

Conflicts of interest

The authors declare no conflict of interest.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant No. 51772229), the 111 project (No. B18038), the National Key R&D Program of China (No. 2017YFE0192600), Key R&D Project of Hubei Province (No. 2020BAB061), Open Foundation of the State Key Laboratory of Silicate Materials for Architectures at WUT (No. SYSJJ2020-04 and No. SYSJJ2021-05), Open Research Fund Program of Science and Technology on Aerospace Chemical Power Laboratory (No. STACPL220191B02), and State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology (No. P2021-010). We thank the Analytical and Testing Center of WUT for the help with carrying out XRD, FESEM, TEM, and FTIR analyses.

References

1. Y.-H. Wang, K. H. Rahman, C.-C. Wu and K.-C. Chen, Catalysts, 2020, 10, 598.
2. V. Hariharan, B. Gnanavel, R. Sathiyapriya and V. Aroulmoji, Int. J. Adv. Sci. Eng., 2019, 5, 1163–1168.
3. X. Dong, Y. Lu, X. Liu, X. Liu and Y. Tong, J. Photochem. Photobiol., C, 2022, 53, 100555.
4. J.-L. Wang, J.-W. Liu, S.-Z. Sheng, Z. He, J. Gao and S.-H. Yu, Nano Lett., 2021, 21, 9203–9209.
5. S.-Z. Sheng, J.-L. Wang, B. Zhao, Z. He, X.-F. Feng, Q.-G. Shang, C. Chen, G. Pei, J. Zhou, J.-W. Liu and S.-H. Yu, Nat. Commun., 2023, 14, 1–9.
6. Z. Yu, Y. Ma, L. Mao, Y. Lian, Y. Xiao, Z. Chen and Y. Zhang, Mater. Horiz., 2024, 11, 207–216.
7. S. Liu, Y. Du, R. Zhang, H. He, A. Pan, T. C. Ho, Y. Zhu, Y. Li, H. Yip, A. K. Y. Jen and C. Y. Tso, Adv. Mater., 2024, 36, 2306423.
8. H. Wang, L. Sun, Z. Zeng and W. Xue, Ind. Eng. Chem. Res., 2023, 62, 10163–10174.
9. S. Wang, W. Fan, Z. Liu, A. Yu and X. Jiang, J. Mater. Chem. C, 2018, 6, 191–212.
10. D. K. Hwang, H. J. Kim, H. S. Han and Y. G. Shul, J. Sol-Gel Sci. Technol., 2004, 32, 137–141.
11. M. Chen, X. Zhang, W. Sun, Y. Xiao, H. Zhang, J. Deng, Z. Li, D. Yan, J. Zhao and Y. Li, Nano Energy, 2024, 123, 109352.
12. Y. Badour, S. Danto, S. Albakour, S. Mornet, N. Penin, L. Hirsch and M. Gaudon, Sol. Energy Mater. Sol. Cells, 2023, 255, 112291.
13. X. Dong, Y. Dang, Z. Wu, Y. Tong, X. Liu and Y. Lu, Mater. Today Energy, 2024, 44, 101632.
14. J. Y. Kwak, Y. H. Jung and Y. I. Kim, J. Korean Chem. Soc., 2023, 67, 33–41.
15. T. Ma, B. Li, S. Tian, J. Qian, L. Zhou, Q. Liu, B. Liu, X. Zhao and G. Sankar, Chem. Eng. J., 2023, 468, 143587.
16. Q. Zhang, R. Wang, Y. Lu, Y. Wu, J. Yuan and J. Liu, ACS Appl. Mater. Interfaces, 2021, 13, 4220–4229.
17. Y. Zhu, Y. Yao, Z. Chen, Z. Zhang, P. Zhang, Z. Cheng and Y. Gao, Sol. Energy Mater. Sol. Cells, 2022, 239, 111664.
18. W. Meng, A. J. J. Kragt, Y. Gao, E. Brembilla, X. Hu, J. S. van der Burgt, A. P. H. J. Schenning, T. Klein, G. Zhou, E. R. van der Ham, L. Tan, L. Li, J. Wang and L. Jiang, Adv, Mater., 2023, 2304910.
19. Z. Zhao, Y. Liu, D. Wang, C. Ling, Q. Chang, J. Li, Y. Zhao and H. Jin, Sol. Energy Mater. Sol. Cells, 2020, 209, 110443.
20. C. Cantalini, M. Z. Atashbar, Y. Li, M. K. Ghantasala, S. Santucci, W. Wlodarski and M. Passacantando, J. Vac. Sci. Technol., A, 1999, 17, 1873–1879.
21. D. Susanti, N. Stefanus Haryo, H. Nisfu, E. P. Nugroho, H. Purwaningsih, G. E. Kusuma and S.-J. Shih, Front. Chem. Sci. Eng., 2012, 6, 371–380.
22. G. Xi, S. Ouyang, P. Li, J. Ye, Q. Ma, N. Su, H. Bai and C. Wang, Angew. Chem., Int. Ed., 2012, 51, 2395–2399.
23. M.-H. Vu, C.-C. Nguyen and T.-O. Do, ACS Sustainable Chem. Eng., 2020, 8, 12321–12330.
24. S. Bai, N. Yang, X. Wang, F. Gong, Z. Dong, Y. Gong, Z. Liu and L. Cheng, ACS Nano, 2020, 14, 15119–15130.
25. C. Santato, M. Odziemkowski, M. Ulmann and J. Augustynski, J. Am. Chem. Soc., 2001, 123, 10639–10649.
26. Y. Chai, F. Y. Ha, F. K. Yam and Z. Hassan, Procedia Chem., 2016, 19, 113–118.
27. S. Ramanavičius, M. Petrulevičienė, J. Juodkazytė, A. Grigucevičienė and A. Ramanavičius, Materials, 2020, 13, 523.
28. D. Zhou, X. Guo, Y. Chen, X. Yuan and J. Liu, Nano Res., 2022, 15, 3575–3586.
29. B. Bhuyan, B. Paul, S. S. Dhar and S. Vadivel, Mater. Chem. Phys., 2017, 188, 1–7.
30. Y. Wang, X. Wang, Y. Xu, T. Chen, M. Liu, F. Niu, S. Wei and J. Liu, Small, 2017, 13, 1603689.
31. C. Feng, L. Tang, Y. Deng, J. Wang, Y. Liu, X. Ouyang, Z. Chen, H. Yang, J. Yu and J. Wang, Appl. Catal., B, 2020, 276, 119167.
32. R. Li, Y. Zhou, Z. Shao, S. Zhao, T. Chang, A. Huang, N. Li, S. Ji and P. Jin, ChemistrySelect, 2019, 4, 9817–9821.
33. Y. Badour, M. Pedros, M. Gaudon and S. Danto, Adv. Opt. Mater., 2024, 12, 2301717.
34. M. Bourdin, G. Salek, A. Fargues, S. Messaddeq, Y. Messaddeq, T. Cardinal and M. Gaudon, J. Mater. Chem. C, 2020, 8, 9410–9421.
35. W. Meng, A. J. J. Kragt, X. Hu, J. S. Van Der Burgt, A. P. H. J. Schenning, Y. Yue, G. Zhou, L. Li, P. Wei, W. Zhao, Y. Li, J. Wang and L. Jiang, Adv. Funct. Mater., 2024, 34, 2402494.
36. B. Cui, C. Guo, G. Fu and Z. Zhang, J. Photochem. Photobiol., A, 2023, 435, 114320.

---

Footnotes

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4tc05269b

‡ Yongkang Zhu and Bin Li contributed equally.

---