Evaluation of Tellurium Optimal Setting and Its Stability in Thermal Desalination

Water scarcity has been a major challenge. It is estimated that approximately 4 billion people still face water shortage problem.[1] Although more than 70 percent of the earth is covered by water, only 2.5 percent of it is drinkable.[2] The condition worsens as the overall global usage of water keeps increasing by roughly 1 percent annually.[3] Currently, there are mainstream water processing technologies such as reverse osmosis, ion-exchange, and membrane bioreactor to cater to water demand. However, they are energy-intensive and involve high setup cost, thus making them difficult to be implemented in less affluent countries. Solar thermal desalination appears to be a viable solution because it employs free renewable source: sunlight.

In conventional solar stills, the freshwater production rate is not comparable to existing water processing technology. To enhance freshwater yield, materials that have high thermal conductivity and high solar intensity absorption can be added into the saline water. [4] The resulting mixture will be a better absorbent of solar energy which in that promote water evaporation. To minimize the obstruction of sunlight by the material added, researchers start to look for nanoparticles solution. Scientists found that carbonaceous, plasmonic and some metal oxide nanoparticles have high solar absorptivity and able to convert solar energy to heat effectively.[5] These include graphene, silicon carbide (SiC), and aluminum oxide (Al2O3) respectively.[6] They were utilized to mix with saline water to form nanofluid. After the suspended nanoparticles in the mixture absorb solar energy, they form multiple localized hotspot to heat the surrounding water. The enhancement of freshwater yield depends on the desired properties of nanoparticles. [7]

Recently, it was found that tellurium nanoparticles drastically improved distilled water evaporation rate under sunlight by three folds [8]. Tellurium nanoparticles are the first material that exhibits both plasmonic-like (≤120nm) and all-dielectric properties (≥120nm) in the solar electromagnetic radiation region. Its solar absorption ability covers the entire spectrum of solar radiation making it a promising nanomaterial to bring another breakthrough in solar thermal desalination. [9] However, due to its recent discovery, tellurium nanoparticles are not directly compared to the performance of existing nanomaterials under similar solar thermal desalination setting. Moreover, there is no relevant research about the stability of tellurium nanoparticles under the action of saline water. There is a possibility where nanoparticles start to agglomerate when salinity of nanofluid exceeds certain threshold. [10]

The main objective is to find out the experimental freshwater yield of tellurium, graphene, SiC and Al2O3 nanofluid in similar passive single slope solar still. The secondary objective is to investigate the stability of tellurium nanoparticles under the action of saline water. This paper covers the effect of nanofluid depth and weight fraction of nanoparticles in nanofluid to the performance of solar thermal distillation as well as the effect of salt concentration on the stability of tellurium nanoparticles. The rest of the variables are not covered. The experimental result is crucial to conduct an economic feasibility study and to evaluate the optimal setting of nanofluid for solar thermal desalination.