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Carbon and semiconductor nanoparticles are promising photothermal materials for various solar-driven applications. Inevitable recombination of photoinduced charge carriers in a single constituent, however, hinders the realization of a greater photothermal effect. Core–shell heterostructures utilizing the donor–acceptor pair concept with high-quality interfaces can inhibit energy loss from the radiation relaxation of excited species, thereby enhancing the photothermal effect. Here, core–shell structures composed of a covellite (CuS) shell (acceptor) and spherical carbon nanoparticle (CP) core (donor) (abbreviated as CP/CuS) are proposed to augment the photothermal conversion efficiency via the Förster resonance energy transfer (FRET) mechanism. The close proximity and spectral overlap of the donor and acceptor trigger the FRET mechanism, where the electronic excitation relaxation energy of the CP reinforces the plasmonic resonance and near-infrared absorption in CuS, resulting in boosting the overall photothermal conversion efficiency. CP/CuS core–shell coated on polyurethane (PU) foam exhibits a total solar absorption of 97.1%, leading to an elevation in surface temperature of 61.6 °C in dry conditions under simulated solar illumination at a power density of 1 kW m–2 (i.e., 1 sun). Leveraging the enhanced photothermal conversion emanated from the energy transfer effect in the core–shell structure, CP/CuS-coated PU foam achieves an evaporation rate of 1.62 kg m–2 h–1 and an energy efficiency of 93.8%. Thus, amplifying photothermal energy generation in core–shell structures via resonance energy transfer can be promising in solar energy-driven applications and thus merits further exploration.
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Photoexcited charge carrier dynamics and electronic properties of two-dimensional MXene, Nb 2 CT x
Two-dimensional, 2D, niobium carbide MXene, Nb2CTx, has attracted attention due to its extraordinarily high photothermal conversion efficiency that has applications ranging from medicine, for tumor ablation, to solar energy conversion. Here, we characterize its electronic properties and investigate the ultrafast dynamics of its photoexcitations with a goal of shedding light onto the origins of its unique properties. Through density functional theory, DFT, calculations, we find that Nb2CTx is metallic, with a small but finite DOS at the Fermi level for all experimentally relevant terminations that can be achieved using HF or molten salt etching of the parent MAX phase, including –OH, –O, –F, –Cl, –Br, –I. In agreement with this prediction, THz spectroscopy reveals an intrinsic long-range conductivity of ∼60 Ω−1 cm−1, with significant charge carrier localization and a charge carrier density (∼1020 cm−3) comparable to Mo-based MXenes. Excitation with 800 nm pulses results in a rapid enhancement in photoconductivity, which decays to less than 25% of its peak value within several picoseconds, underlying efficient photothermal conversion. At the same time, a small fraction of photoinjected excess carriers persists for hundreds of picoseconds and can potentially be utilized in photocatalysis or other energy conversion applications.
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- Award ID(s):
- 2021871
- PAR ID:
- 10523454
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- 2D Materials
- Volume:
- 11
- Issue:
- 3
- ISSN:
- 2053-1583
- Page Range / eLocation ID:
- 035028
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1088/2053-1583/ad518d
