Sponge-templating synthesis of sandwich-like reduced graphene oxide nanoplates with confined gold nanoparticles and thei
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Published online 20 August 2020 | https://doi.org/10.1007/s40843-020-1446-5
Sponge-templating synthesis of sandwich-like reduced graphene oxide nanoplates with confined gold nanoparticles and their enhanced stability for solar evaporation Hong-Wu Zhu, Jin Ge, Hao-Yu Zhao, Lu-An Shi, Jin Huang, Liang Xu and Shu-Hong Yu ABSTRACT Solar evaporation based on plasmonic metal nanoparticles (MNPs) is emerging as a promising technology. However, the fine structure of MNPs is unstable, and both the high temperature generated by intensive light and corrosive ions in water could damage them. The performance will decline after recycling and long-time usage. To address these issues, we adopted a sponge-templating method for preparing sandwich-like nanoplates with the gold nanoparticles (Au NPs) confined in reduced graphene oxide (rGO) nanosheets. Due to the confinement effect, both the surface melting and ion diffusion were suppressed. The solar evaporator based on the sandwich-like nanoplates showed a high solar-vapor conversion efficiency of 85.2% under a high light intensity of 10 kW. After 30 times recycle of seawater desalination, the conversion efficiency scarcely decreased. These sandwich-like nanoplates with enhanced thermal and chemical stability of Au NPs are promising in the practical application of seawater desalination. Keywords: sponge template, confinement effect, surface melting, desalination
INTRODUCTION Solar evaporation is emerging as one of the most promising solar-thermal technologies that can be applied in concentrating solar power [1,2], water desalination [3–7], and sewage treatment [8]. Various solar-thermal materials have been developed, including plasmonic metallic nanoparticles (MNPs) [3,7,9,10], carbon materials [4,11], and metal oxide composites [8,12]. With the localized surface plasmon resonance (LSPR) of MNPs, the tem-
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perature around MNPs will rise drastically, making MNPs ideal solar-thermal conversion materials [3,9]. However, these MNPs are usually unstable under conditions of solar concentrating and sewage dipping [1]. The high temperature generated by intensive light will melt the MNPs [10], and the corrosive media in water like acid, alkali, and salt will etch the MNPs [13], which limit their durability and cycling performance. Therefore, the thermal and chemical stabilities are crucial for the performance of MNPs-based solar evaporators. The nanometer-scale MNPs are quite unstable compared with bulk materials [14,15]. Due to the high surface/volume ratio, surface atoms account for a large proportion of MNPs. The surface atoms are usually far from equilibrium state due to the lack of adjacent atoms. There exist many dangling bonds that tend to combine with other atoms, resulting in the chemically active surface for MNPs [16]. Besides, based on the study of semiinfinite Einstein model crystal [17], the surface atoms become unstable at the melting temperature much lower than bulk lattice, and the so called surface melting effect has been observed [18]. During the surface melting proces
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