High-entropy-alloy (HEA) nanoparticles are attractive
for several
applications in catalysis and energy. Great efforts are currently
devoted to establish composition–property relationships to
improve catalytic activity or selectivity. Equally importantly, developing
practical fabrication methods for shaping HEA-based materials into
complex architectures is a key requirement for their utilization in
catalysis. However, shaping nano-HEAs into hierarchical structures
avoiding demixing or collapse remains a great challenge. Herein, we
overcome this issue by introducing a simple soft-chemistry route to
fabricate ordered macro- and mesoporous materials based on HEA nanoparticles,
with high surface area, thermal stability, and catalytic activity
toward CO oxidation. The process is based on spray-drying from an
aqueous solution containing five different noble metal precursors
and polymer latex beads. Upon annealing, the polymer plays a double
role: templating and reducing agent enabling formation of HEA nanoparticle-based
porous networks at only 350 °C. The formation mechanism and the
stability of the macro- and mesoporous materials were investigated
by a set of in situ characterization techniques;
notably, in situ transmission electron microscopy
unveiled that the porous structure is stable up to 800 °C. Importantly,
this process is green, scalable, and versatile and could be potentially
extended to other classes of HEA materials.
Innovating in materials manufacturing processes is a challenge to reduce the environmental impact of the chemical industry in line with sustainable development objectives, such as promote sustainable industrialization, and ensure...
ZnO is an effective photocatalyst applied to the degradation of organic dyes in aqueous media. In this study, the UV-light and sunlight-driven photocatalytic activities of ZnO nanoparticles are evaluated. A handheld Lovibond photometer was purposefully calibrated in order to monitor the dye removal in outdoor conditions. The effect of ZnO defect states, i.e., the presence of zinc and oxygen defects on the photocatalytic activity was probed for two types of dyes: fuchsin and methylene blue. Three morphologies of ZnO nanoparticles were deliberately selected, i.e., spherical, facetted and a mix of spherical and facetted, ascertained via transmission electron microscopy. Aqueous and non-aqueous sol-gel routes were applied to their synthesis in order to tailor their size, morphology and defect states. Raman spectroscopy demonstrated that the spherical nanoparticles contained a high amount of oxygen vacancies and zinc interstitials. Photoluminescence spectroscopy revealed that the facetted nanoparticles harbored zinc vacancies in addition to oxygen vacancies. A mechanism for dye degradation based on the possible surface defects in facetted nanoparticles is proposed in this work. The reusability of these nanoparticles for five cycles of dye degradation was also analyzed. More specifically, facetted ZnO nanoparticles tend to exhibit higher efficiencies and reusability than spherical nanoparticles.
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