Facile fabrication of mesoporous In2O3/LaNaTaO3 nanocomposites for photocatalytic H2 evolution
Graphical abstract
Introduction
To solve the progressively energy and environment issue, photocatalysis applications have drawn huge attention in the last four decades as a promising approach. Many efforts are being made to investigate the effective photocatalysts for H2 evolution from H2O splitting, air purification and degradation of toxic organic compounds [[1], [2], [3], [4], [5], [6]]. The first report for H2O splitting to generate H2 evolution was performed by TiO2 photocatalyst in the electrochemical cell in 1972 [7]. After that, other oxides, mixed oxides and perovskite, such as tantalates and niobates, have also been employed as effective photocatalysts. One of the best perovskite photocatalysts, NaTaO3 has been extensively employed for H2O splitting under UV illumination owing to its outstanding photocatalytic efficiency [8,9]. In comparison with TiO2, NaTaO3 has a minimum conduction band owing to the existence of Ta 5d orbit, which exhibits that Ti 3d orbit has lesser negative potential than Ta 5d orbit; which is responsible for the reduction driving force [10,11]. However, the narrow light adsorption and low charge separation are extremely restricted the photocatalytic activity of perovskite NaTaO3 photocatalyst. To promote the photocatalytic performance of perovskite NaTaO3 photocatalyst, it is essential to address some parameters such as the charge carriers separation and the light harvest region. To date, there are different approaches to address and promote the photocatalytic performance of NaTaO3 photocatalysts, such as oxygen vacancies, loading of noble metal, and heterojunction fabricated by incorporating two semiconductors with the rational design of band alignment [[12], [13], [14], [15]]. The two semiconductors heterojunction construction can not only decrease the photogenerated charge carriers recombination but also enhance the capability of photoabsorption, which is advantageous for enhancing the photocatalytic efficiency. Electrocatalytic water splitting offers a solution to both challenges, in which it converts electrical energy into O2 and hydrogen H2, which serves as fuel and feedstock for the chemical industry [[16], [17], [18]]. Also, there are several materials such as CoAl2O4, NiAl2O4/NiO, Zn2GeO4/graphene and Zn2SnO4 nanocomposites were employed for electrochemical hydrogen storage and photocatalytic H2 production [[19], [20], [21], [22]].
In the last four decades, scientists have been worked to promote the photonic efficiency of NaTaO3 photocatalyst. For example, p-n heterojunction Ag2O/NaTaO3 and Ag/AgCl/NaTaO3 photocatalysts were synthesized, which exhibited a superb photocatalytic performance for the Rhodamine B photodegradation [23,24]. Heterostructure NaTaO3/Ta2O5 nanofibers have been prepared by the modified system of synchronous etching-epitaxial growth, which exhibited an improvement photocatalytic H2 evolution under simulant solar light [25]. Photophysical properties and electronic structure of LaFeO3–NaTaO3 and Fe-doped NaTaO3 employing solid solution approach have been studied for H2 evolution through visible light illumination [26]. Construction of In2S3/NaTaO3 nanocomposites has been conducted for promoting the photocatalytic efficiency for photodegradation of tetracycline [27]. These above photocatalysts reveal that the heterojunction construction of photocatalysts is significant to the improvement of photonic efficiency of NaTaO3 perovskite. Therefore, the rational design of the photocatalyst structure is of considerable significance to construct the NaTaO3-based photocatalysts.
Indium oxide (In2O3), the semiconductor has stable physicochemical, wide absorption visible-light and low toxicity with bandgap energy (Eg) around 2.8 eV. It has drawn considerable attention in H2O photosplitting to generate H2 and photocatalytic oxidation of toxic organic pollutants [28,29]. In addition, In2O3 nano-/microspheres and mesoporous structure with hollow inner could provide understandable geometrical construction for potential photocatalysis, which is owing to the presence of void space between mesostructure and hollow particles, which they can be employed to increase active area, shorten ion diffusion path, modify the refractive index, as well as lower density [30,31]. The use of wide bandgap photocatalysts is extremely restricted owing to its slighter optical absorption region. It is supposed that the effective separation photoinduced electron-hole pairs could be performed after fabricating the heterojunction with appropriate nanostructures.
Herein, we synthesize and design a mesoporous In2O3/La0.02Na0.98TaO3 nanocomposite by coupling In2O3 nanoparticles and La0.02Na0.98TaO3 for significantly facilitating the H2 evolution. Mesoporous La0.02Na0.98TaO3 nanocomposites were synthesized in presence of F127 template. An amorphous inorganic solid was calcined at low temperature at 700 °C for 8 h. However, it required elevated temperature at 1300 °C for the solid-state approach in the previous literature. The produced mesoporous In2O3/La0.02Na0.98TaO3 nanocomposites showed high surface area (200 m2/g) for the first time and large pore volume, which is playing an essential role in the promotion photocatalytic activity. The maximum yield of H2 ~ 2350 μmol g−1 was obtained over mesoporous 1%In2O3/La0.02Na0.98TaO3 nanocomposite. The synthesized mesoporous 1%In2O3/ La0.02Na0.98TaO3 nanocomposite exhibited further enhancement H2 production, in which the rate of H2 evolution can be as high as 235 μmol g−1 h−1, 435 times higher than those of mesoporous La0.02Na0.98TaO3. And mesoporous In2O3/La0.02Na0.98TaO3 nanocomposites exhibit high stability for photocatalytic H2 evolution, indicated that photocatalytic performance could be well sustained for 45 h through illumination. The measurement of photoluminescence spectroscopy, transient photocurrent spectra and UV- diffuse reflectance spectra indicated that the distinctive structure of mesoporous In2O3/La0.02Na0.98TaO3 nanocomposites is considered the key in participating to the promoted photocatalysis.
Section snippets
Materials
Indium (III) nitrate hydrate In(NO3)3.xH2O, lanthanum (III) nitrate hexahydrate La(NO3)3. 6H2O, tantalum(V) chloride, TaCl5, sodium acetate CH3COONa, C2H5OH, HCl, CH3COOH, and F-127 surfactant (EO106-PO70EO106, MW 12600 g/mol) were purchased from Sigma-Aldrich.
Synthesis of mesoporous In2O3/La0.02Na0.98TaO3 photocatalysts
First, mesoporous La0.02Na0.98TaO3 nanocomposites were synthesized by Pluronic F-127 assisted sol-gel approach as previously reported [2]. 1.6 g of F-127 was added in C2H5OH of 30 mL through stirring for 1 h. Then, 2.3 mL of CH3COOH and
Structural characterization
The XRD patterns of the synthesized mesoporous La0.02Na0.98TaO3 and In2O3/La0.02Na0.98TaO3 nanocomposites at diverse In2O3 nanoparticles (0.1–2 wt%) were demonstrated in Fig. 1. The results indicated that the diffraction planes of (100), (101), (111), (200), (102), and (112) were corresponded to 2Ө values at 22.8°, 32.5°, 40.1°, 46.6°, 52.4°, and 57.9° respectively, which are listed as the monoclinic structure of NaTaO3 crystalline (JCPDS No.74–2478). It can be indicated that all the
Conclusions
A new class of mesoporous In2O3/La0.02Na0.98TaO3 nanocomposites was achieved for the H2 evolution under UV illumination in the presence of [10%] glycerol as a hole scavenger. As a result, the rate of H2 evolution of the optimized mesoporous 1%In2O3/La0.02Na0.98TaO3 photocatalyst was calculated to be around 235 μmol g−1 h−1, 435 times greater than that of mesoporous La0.02Na0.98TaO3 (0.54 μmol g−1 h−1), indicating the highly promoted photocatalytic H2 evolution of 1%In2O3/La0.02Na0.98TaO3
Acknowledgement
This project was funded by the Deanship of Scientific Research (DSR) at King Abdulaziz University, Jeddah, Saudi Arabia under grant no. KEP-PhD-27-130-38. The authors, therefore, acknowledge with thanks DSR for technical and financial support.
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