Although desalination technologies have been widely adopted as a means to produce freshwater, many of them require large installations and access to advanced infrastructure. Recently, floating structures for solar evaporation have been proposed, employing the concept of interfacial solar heat localization as a high-efficiency approach to desalination. However, the challenge remains to prevent salt accumulation while simultaneously maintaining heat localization. This paper presents an experimental demonstration of a salt-rejecting evaporation structure that can operate continuously under sunlight to generate clean vapor while floating in a saline body of water such as an ocean. The evaporation structure is coupled with a low-cost polymer film condensation cover to produce freshwater at a rate of 2.5 L m−2 day−1, enough to satisfy individual drinking needs. The entire system's material cost is $3 m−2 – over an order of magnitude lower than conventional solar stills, does not require energy infrastructure, and can provide cheap drinking water to water-stressed and disaster-stricken communities.

/pdf/a-salt-rejecting-floating-solar-still-for-low-cost-38jrss8jwp.pdf

A salt-rejecting floating solar still for low-cost desalination

Ultrathin transition metal dichalcogenides (TMDCs) of Mo and W show great potential for digital electronics and optoelectronic applications. Whereas early studies were limited to mechanically exfoliated flakes, the large-area synthesis of 2D TMDCs has now been realized by chemical vapor deposition (CVD) based on a sulfurization reaction. The optoelectronic properties of CVD grown monolayer MoS2 have been intensively investigated, but the influence of stoichiometry on the electrical and optical properties has been largely overlooked. Here we systematically vary the stoichiometry of monolayer MoS2 during CVD via controlled sulfurization and investigate the associated changes in photoluminescence and electrical properties. X-ray photoelectron spectroscopy is employed to measure relative variations in stoichiometry and the persistence of MoOx species. As MoS2-δ is reduced (increasing δ), the field-effect mobility of monolayer transistors increases while the photoluminescence yield becomes nonuniform. Devices fabricated from monolayers with the lowest sulfur content have negligible hysteresis and a threshold voltage of ∼ 0 V. We conclude that the electrical and optical properties of monolayer MoS2 crystals can be tuned via stoichiometry engineering to meet the requirements of various applications.

Influence of Stoichiometry on the Optical and Electrical Properties of Chemical Vapor Deposition Derived MoS2

Effect of using nanofluids and providing vacuum on the yield of corrugated wick solar still.

Direct solar steam generation system for clean water production

Reasonable amounts of fresh water can be produced via inexpensive and sturdy solar stills in places that are exposed to solar radiation and have a brackish water. This work intends to analyze the many studies on factors that affect the performance of solar stills. The results showed that the distillation productivity of solar stills are significantly influenced by ambient conditions (e.g., ambient temperature, insolation, wind velocity, dust and cloud cover), operating conditions (e.g., depth of water, various dyes, salt concentration and inlet temperature of water), and design conditions (e.g., different passive/active designs of solar stills, slope of the cover, materials selection, storing materials, reflectors, insulation, gap distance and sun tracking system). It was also determined that the performance of solar stills was improved through the increase in solar radiation, ambient air temperature, wind speed, and water absorptivity. This also rings through with the decrease in water depth, thickness of cover, gap distance between water surface and condensing cover. It was also determined that both internal and external reflectors are capable of increasing the amount of absorbed solar radiation on the basin liner. The potential output of a basin type still can potentially increase to almost 70–100%. On top of this, the utilization of a sun tracking system was determined to be way more effective in improving the performance of solar still. This translate to the fact that solar stills being able to produce potable water at a very economical cost. Due to the existence of different methods of cost estimation, it is not possible to determine a universal, comparable price per technology; the cost per liter of distilled water obtained from the basin type solar still is ranged from 0.035 to 0.074$/liter. This study proved the fact that distillation productivity of solar still is heavily influenced by climatic, operational, and design parameters. Its output can be further improved via operational and design conditions, as climatic conditions are beyond our control.

Factors affecting basin type solar still productivity: A detailed review

An experimental wick-type solar still system: Design and construction

Solar distillation of water using a V-trough solar concentrator with a wick-type solar still

Molybdenum black solar selective coatings have been produced on cobalt by immersion in a solution of ammonium paramolybdate and nickel sulphate. The cobalt was electroplated on nickel-plated copper prior to immersion in the paramolybdate solution. The maximum solar absorptance of the resulting molybdenum black coating was about 0.91. The minimum emittance was about 0.1 for coatings on cobalt deposited with an addition agent and about 0.23 for coatings on cobalt deposited without addition agent in the 60 °C plating solution. These differences have been related to the coating morphology determined by scanning electron microscopy. The emittance of coatings on cobalt deposited without addition agent decreases (or remains unchanged) during short-term heat treatment while that of coatings deposited on cobalt plated with addition agent increases somewhat. Reduction of the cobalt plating bath temperature to 45 °C can also lead to good initial coating properties but without the requirement for an addition agent in the cobalt plating bath. XPS studies show that the oxidation state of molybdenum in the coatings is approximately + 5 corresponding to Mo4O11. This reduces to + 4 after argon ion bombardment. Some cobalt may be present in the coatings in the form of CoO.

Investigation of solar selective and microstructural properties of molybdenum black immersion coatings on cobalt substrates

Molybdenum black solar selective coatings have been prepared by a simple chemical conversion method on chemically etched zinc substrates. These coatings have been characterized using X-ray diffraction, electron diffraction, XPS and VIS-IR reflectance spectroscopy. Maximum solar absorptance obtained from these coatings was about 0.87 with an emittance of 0.13–0.17. Selectivity of the coatings, mainly attributed to the coating surface morphology, was studied by SEM. Structural studies show that the coating consists of a non-stoichiometric oxide of Mo, namely Mo4O11. XPS depth profiling studies show that the oxidation state of Mo reduces from +5 to +4 after argon ion bombardment.

Characterization of molybdenum black coatings on zinc substrates

Optical and microstructural properties of electrodeposited molybdenum-copper (Mo-Cu) black coatings have been studied with reference to their selectivity in absorption of solar radiation. Such coatings were found to have a solar absorptance, α, about 0.87 and low thermal emittance, ɛ, such that the selectivity, α/ɛ, was 3.6. Electrodeposited molybdenum-black coatings generally have selectivity α/ɛ∼3. The oxidation state of molybdenum in (Mo-Cu) black coatings as determined by X-ray photoelectron spectroscopy is about + 5 (which is fairly close to that of Mo4O11). Large numbers of irregular particles were found on the surface of molybdenum-copper black coatings. There is evidence that the particles contain copper oxide.

B.E. Smith

Papers

An experimental wick-type solar still system: Design and construction

Solar distillation of water using a V-trough solar concentrator with a wick-type solar still

Investigation of solar selective and microstructural properties of molybdenum black immersion coatings on cobalt substrates

Characterization of molybdenum black coatings on zinc substrates

Investigation of microstructure of molybdenum—copper black electrodeposited coatings with reference to solar selectivity