Modified Solvothermal Strategy for Straightforward Synthesis of Cubic NaNbO₃ Nanowires with Enhanced Photocatalytic H₂ Evolution

Abstract

To further improve the photocatalytic H2 evolution activity, NaNbO3 photocatalyts simultaneously possessing cubic crystal structure and 1D morphology have been successfully synthesized via a modified solvothermal strategy. During the process of synthesis employing ethylene glycol as solvent, a temperature fluctuation during the autoclaving period is proposed to regulate the grain growth without any other additives or calcinations. It is demonstrated that the structure-directing effect of the solvent is enhanced in the condition of the temperature fluctuation, contributing to the formation of 1D nanostructure. Otherwise, the irregular NaNbO3 nanoparticles with severe aggregation resulted. Photocatalytic H2 evolution activities of samples under ultraviolet light irradiation with 0.5 wt % of Pt cocatalyst indicate that NaNbO3 nanowires expectedly exhibit an enhanced activity of 699 μmol h–1 g–1, approaching twice that of NaNbO3 nanoparticles. The higher photocatalytic activity of NaNbO3 nanowires is attributed to their large specific surface area, high chemical purity, and powerful reduction ability, which have been confirmed by the further characterizations and analysis based on crystal structure, valence state, elemental composition, and energy band structure. The modified solvothermal strategy provides an alternative pathway to regulate the crystal growth, which can effectively integrate the unique morphology with desired crystalline structure toward increasing photocatalytic activity.

Flux‐mediated synthesis and photocatalytic activity of NaNbO3 particles

“…For the NaNbO 3 sample prepared in the Na 2 SO 4 flux, the average total production of molecular hydrogen over 6 hours was found to be significantly higher at 753 µmol, or 126 µmol/h, plotted in Figure and Table . This hydrogen evolution rate is higher than in several previously reported studies on NaNbO 3 particles, including for preparations under a controlled atmosphere (~20‐40 µmol/h), as nanowires (~70 µmol/h), or as ribbon‐like fibers (~100 µmol/h) . Notably, the latter nanoparticle morphologies all have significantly higher surface areas, that is, >100 m 2 /g, as compared to that obtained from the use of the Na 2 SO 4 flux of only 0.9 m 2 /g, listed in Table .…”

“…The earliest model of this semiconductor‐solution interface was developed by Gerischer, and has been previously investigated in NaNbO 3 and hundreds of other semiconductors . The photocatalytic activity of NaNbO 3 has drawn much recent interest owing to its relatively high rates of hydrogen evolution . The photocatalytic activity of each of the NaNbO 3 products was investigated for their light‐driven production of molecular hydrogen as particle suspensions in aqueous methanol solutions.…”

Isolating the Two Room-Temperature Polymorphs of NaNbO3: Structural Features, Optical Band Gap, and Reactivity

“…[6][7][8] The common elements Na and Nb in these series combined to the occurrence of various polymorphs at room temperature naturally leads to focus specifically on the end member NaNbO3. [9][10][11][12][13] This composition has attracted interest more recently as a photocatalyst for several reactions, namely hydrogen evolution, [14][15][16][17] CO2 reduction 14,15,18,19 and degradation of various organic molecules. [20][21][22][23] In the final catalyst consisting of the niobate alone or combined to other species, the structural variety of NaNbO3 has again been demonstrated to have a strong impact on the catalyst efficiency, especially between the centrosymmetric orthorhombic structure and the cubic one.…”

Fast and scalable synthesis of strontium niobates with controlled stoichiometry

“…Combining features of both techniques, the sol-gel-hydrothermal method has achieved very interesting results in synthesis of metal oxides 6,7 . This technique has become an attractive tool as advantages range from a high degree of crystallinity, good control over the morphology, high purity and a more even particle size distribution, coupled with a reduction of time and temperature needed to obtain such materials 8,9 .…”