Original Paper: Sol–gel, hybrids and solution chemistries
Mesoporous transition metal oxides (MTMO) with large surface area, nanocrystalline framework, and controlled porosity have brilliant prospects in fields such as energy, environment, catalysis, or nanomedicine. However, the green, reproducible, and scalable production of MTMO are still a bottleneck for their industrial applications. Although spray-drying methods permit to obtain MTMO in a potentially scalable fashion, the use of highly acidic alcoholic precursor solutions presents two main limitations: corrosion and flammability, which hinder their production in large quantities and lower cost. In this work, we present a general, reproducible, simple, and environment-friendly aerosol method for the synthesis of spherical MTMO particles from mildly acidic aqueous solutions. Acetylacetonate and acetate are used as condensation-controlling agents. Mixed oxides of high valence cations (M(IV) such as Ti, Zr, Ce, and their mixed oxides) were prepared with a yield over 95%, virtually without changing the formulation of the precursor mixture, which can be extended potentially to M(III) or M(V) oxides. The replacement of organic solvents by water allows working in air atmosphere, making this approach much safer, cheaper and environmentally friendly than the current aerosol-based routes. We also present the beneficial effect of mesoporous titania spheres as an additive to nickel electrodes used in the hydrogen evolution reaction, as a demonstrator to potential applications. A threefold increase in the electrocatalytic hydrogen production is observed in mesoporous titania-modified nickel electrodes with respect to a pure nickel catalyst. This performance can be further improved ~25% upon UVA-visible irradiation, due to the photoelectrocatalytic effect of the mesoporous TiO2.
A green spray-pyrolysis method to produce spherical mesoporous oxides with high surface area and nanocrystalline walls from aqueous solutions is reported.
The method can be extended to several oxides such as TiO2, ZrO2, CeO2, and mixed oxides with high yield (95%) and minor precursor changes.
A nickel catalyst combined with mesoporous titania presents a threefold increase in the electrocatalytic hydrogen production, and improves further with UVA-visible irradiation.
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The authors thank financial support from Agencia Nacional de Promoción Científica y Tecnológica (PICT 2015-3625, PICT Start Up 2017 –4651, PICT 2017-0250, FSNANO 2010-007, Mincyt-UOttawa OT-17/02) and CONICET. MVL acknowledges a postdoctoral fellowship from CONICET. AZ, EAF, and GJAAS-I are permanent research fellows of CONICET.
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Conflict of interest
The authors declare that they have no conflict of interest.