High solar water droplet evaporation rates from Actinocyclus sp. diatom frustules decorated with silver nanoparticles

Abstract

Solar vapour generation technology has emerged as a promising approach for reducing the global problem of water shortage issues via the solar water interfacial evaporation technique utilised for water purification. However, achieving superior light absorption and a high evaporation rate in a solar evaporator remains challenging. Here, we show that high solar interfacial water evaporation rates can be achieved using a natural and sustainable biomaterial, diatom frustules, decorated with silver nanoparticles made using a one-pot synthesis method. The species of diatom selected for this study was Actinocyclus sp. that has complex nano- and micro-structured surfaces and air pores that lead to multiple light scattering. The absorptance before and after silver nanoparticle coating was measured after creating a thin frustule layer on a hydrophobically treated quartz substrate. It was found that the cleaned and uncoated frustules had zero absorptance from 400 nm to 1200 nm. However, silver nanoparticles coated frustules showed a large broadband absorptance up to 90 % from 400 nm to 1200 nm, covering most of the solar spectrum, due to localised surface plasma resonance and multiple light scattering in the air pores. The frustules were floated on the surface of a water droplet for solar water interfacial evaporation rate measurements. A high evaporation rate of 5.4 kg m−2 h−1 under 1 sun irradiation was found for silver nanoparticles decorated frustules and for a droplet volume of 10 mm3. This is significantly larger than that found for frustules without silver nanoparticles or bare water where the evaporation rates were 1.7 kg m−2 h−1 and 1.2 kg m−2 h−1, respectively. Moreover, increasing the number of floating frustules per drop resulted in a factor of 1.67 enhancement. Our results show that research into silver nanoparticle decorated frustules can potentially provide a novel route for fabricating a high-performance solar vapour generator.