Anodization is a well-known approach for producing nano-structures on a variety of metallic materials, for example on aluminium (Al), due to the comparatively cost-effectiveness of the process and simple experimental setup (Runge 2018). The nano-structures developed via this technique noticed a wide variety of energy storage applications (Nualsing et al. 2021), and applications of water treatment related to the solar energy (Kaur et al. 2018). Improvements in photo electrochemical, thermal, optical, and mechanical characteristics cab be achieved at low cost by modifying structural parameters of the resultant nanostructures via anodization. These factors include diameter, density of pores, and morphology (for example nanowires (Gillette et al. 2015), nanopores (Pashchanka and Schneider 2016), and nanotubes (Noh et al. 2011)).
Potable water is one of the prominent sources of life for humanity. The demand for the supply of clean water increases day by day because of the industrial development and huge population. Also, only 1% of water is reachable to humans (Ram et al. 2021). Therefore, it is necessary to produce drinkable water to mankind, present and upcoming generations. So, numerous researchers found a way to produce drinkable water from the saline or brine water through various technologies includes reverse osmosis, electrodialysis, membrane, and solar desalination (Akkala Siva Ram and Ajay Kumar Kaviti 2020; Akkala and Kumar Kaviti 2022). The viable method of producing the potable water is solar desalination because of its simplicity and economical in nature.
Thereafter, researchers are focusing on the performance enhancement of solar desalination by employing the various materials such as fins (Kumar et al. 2021b), magnets (Dumka et al. 2019), hydrogels (Zhou et al. 2019), stones (Panchal 2015), nanoparticles (Sahota and Tiwari 2016b), nanofluids (Sahota and Tiwari 2016a), and nanostructures (Fan et al. 2016). Mohiuddin et al. (2022b) significantly elaborated the internal design modifications of recent and past literature reports evaluated by various researchers for the solar desalination. Kaviti et al. (2021b) investigated the double slope solar still performance by utilizing the parabolic and truncated conic fins. The results revealed that truncated fins performed better than parabolic fins. Mary et al. (2021) simulated the fin geometry effect on the solar still performance. Jani and Modi (2019) evaluated the solar still performance by employing the square and circular hollow fins, concluded that circular hollow fins yield higher distillate output when compared to the square hollow fins.
Kaviti et al. (2021a) assessed the stepped solar still performance by utilizing the magnets along with charcoal. The maximum instantaneous efficiency of improved solar still obtained was 75.24% higher, compared with traditional solar still. Kaviti et al. (2022) employed the various sizes of permanent magnets for the enhancement of solar still. The permanent magnets improve the yield by weakening molecular forces of water which caused the disintegration of hydrogen bonds. Mohamed et al. (2019) utilized basalt stones with different sizes in the solar still such as 1 cm, 1.5 cm, and 2 cm. The stones improved productivity of solar still by 19.81% for 1 cm, 27.86% for 1.5 cm, and 33.37% for 2 cm respectively. Kumar et al. (2021a) discussed the different hydrogel materials such as reduced graphene oxide, cellulose based, and biomass derived hydrogels for productivity enhancement of solar desalination. Kumar et al. (2021c) also explored the various high-performance nanomaterials such as carbon cloth, CuO nanoparticles coated plates, and plasmonic metal Au nanoparticles for the performance enhancement of solar desalination.
Kabeel et al. (2019) evaluated the performance of solar still by augmenting TiO2 nanoparticles in black paint, boosted the yield output by 6% in contrast to solar still without nanoparticles. Similarly, Han et al. (2021) utilized silicon nanoparticles with 15wt % concentration and are doped with black paint to improve the absorber plate temperature to as high as 98.5 ℃. Sathyamurthy et al. (2019) developed TiO2 and MgO nanofluids at 0.1% and 0.2% volume fractions to elevated the distillate of solar still. Using TiO2 and MgO nanofluids increased the freshwater yield by 41.05% and 61.89% for 0.2% volume concentration. Similarly, Patel et al. (2020) prepared Al2O3 nanofluid by using the surfactant sodium dodecyl benzene sulphonate (SDBS) in water. The Al2O3 nanoparticles and SDBS was mixed in the ratio of 10:2. The Al2O3 nanofluid improved system performance by 25% in contrast to without nanofluid.
Mohiuddin et al. (2022a) enhanced distillate productivity by 36.4% via nanocoating the SS202 with the aid of Cr-Mn-Fe nanoporous oxide. Arunkumar et al. (2019) improved yield output by 26% with the help of nanocoating of CuO nanoparticles on SS 316 plates and also studied the effect of augmenting nanocoated absorber sheets with PVA (Polyvinyl Alcohol) sponges in solar distillation. Zanganeh et al. (2019) increased 23% condensation rate by nanocoating the silicon nanofluid using dip coating technique on the surface of alumina. Kaviti et al. (Kumar et al. 2021d) developed the micro-nanostructures and improved the evaporation efficiency rates by 60%. Saleh et al. (2017) synthesized ZnO nanostructure via hydro thermal technique for desalination, improved solar still productivity by 30%.
Most of the researchers are focusing on improving yield by using nanotechnology in form of nanoparticles, nanofluids, and nanocoatings. The authors found very few nanostructure literatures available with nanoporous materials. As per authors knowledge, there is no work done by employing nanoporous anodized alumina in solar desalination. Thus, the main objective of this work is to understand the effect of nanoporous structure on the distillate of solar desalination. Moreover, in the present study, anodization technique which is the well-known method is utilized to develop the nanoporous structures because of its simplicity in cost-effectiveness and experimental setup. The anodization was carried out at 0.3 M oxalic acid electrolyte solution with a continuous voltage of 40 V at time t = 40, 80, and 120 mins. Further, SEM with EDAX, XRD, and UV-DRS characterizations were performed to analyze the morphology, optical properties, and phase purity of the nanoporous structure. The developed nanoporous structures were successfully applied to desalination application. Water quality analysis was also reported before and after desalination by considering the ground, lake, and synthetic water.