Abstract
In this work, the photocatalytic hydrogen evolution from ammonia borane under near-infrared laser irradiation at ambient temperature was demonstrated by using the novel core-shell upconversion-semiconductor hybrid nanostructures (NaGdF4:Yb3+/Er3+@NaGdF4@Cu2O). The particles were successfully synthesized in a final concentration of 10 mg/mL. The particles were characterized via high resolution transmission electron microscopy (HRTEM), photoluminescence, energy dispersive X-ray analysis (EDAX), and powder X-ray diffraction. The near-infrared-driven photocatalytic activities of such hybrid nanoparticles are remarkably higher than that with bare upconversion nanoparticles (UCNPs) under the same irradiation. The upconverted photoluminescence of UCNPs efficiently reabsorbed by Cu2O promotes the charge separation in the semiconducting shell, and facilitates the formation of photoinduced electrons and hydroxyl radicals generated via the reaction between H2O and holes. Both serve as reactive species on the dissociation of the weak B-N bond in an aqueous medium, to produce hydrogen under near-infrared excitation, resulting in enhanced photocatalytic activities. The photocatalyst of NaGdF4:Yb3+/Er3+@NaGdF4@Cu2O (UCNPs@Cu2O) suffered no loss of efficacy after several cycles. This work sheds light on the rational design of near-infrared-activated photocatalysts, and can be used as a proof-of-concept for on-board hydrogen generation from ammonia borane under near-infrared illumination, with the aim of green energy suppliers.
Highlights
Due to the extensive production of air-based pollution and the limited supply of fossil fuels, a search for a suitable fuel replacement is a priority
For the first time, we report the synthesis and characterization of core-shell upconversion nanoparticles (UCNPs)-semiconductor (NaGdF4 : Yb3+ /Er3+ @ NaGdF4 @Cuprous oxide (Cu2 O)) hybrid nanostructures, and demonstrate the NIR-driven photocatalytic activities for H2 evolution from ammonia borane (AB) molecules
Cuprous oxide (Cu2 O), a p-type semiconductor with high optical absorption coefficients, has a bulk band gap of ~2.2 eV [89–91]. This interesting exitonic feature ensures the spectral overlapping between absorption of Cu2 O and emission bands of UCNPs, which results in efficient energy transfer from UCNPs to Cu2 O through the reabsorbing of upconverted light photons
Summary
Due to the extensive production of air-based pollution and the limited supply of fossil fuels, a search for a suitable fuel replacement is a priority. Non-semiconductor catalysts based on metals including platinium [57], rhenium [58], ruthenium [59,60], and iridium [61] have been used in the catalytic generation of H2 [62,63] For these photocatalysts with their light absorption threshold confined in either ultraviolet (UV, 300–400 nm) or visible (VIS, 400–700 nm) region [64], the major limitation is that only UV and/or visible light photons can be utilized, which accounts for 5% and 43% of the full solar spectrum, respectively. Cuprous oxide (Cu2 O), a p-type semiconductor with high optical absorption coefficients, has a bulk band gap of ~2.2 eV [89–91] This interesting exitonic feature ensures the spectral overlapping between absorption of Cu2 O and emission bands of UCNPs, which results in efficient energy transfer from UCNPs to Cu2 O through the reabsorbing of upconverted light photons. We can envision that this paradigm will provide new insights for the rational design of NIR-responsive photocatalysts, and reveal a new way for exploitation of sustainable energy sources
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