Abstract:

Objective A sustainable supply of clean water is essential for the development of modern society, and using solar energy for desalination and sewage treatment has been considered as a promising solution to produce clean water. However, solar vapor generation technology often requires large installations and advanced infrastructure, leading to poor efficiency and high cost. In view of the above problems, this paper intends to design and develop a solar-interface water evaporator with simple structure and high efficiency, in order to capture and convert sunlight into heat and distil water from various sources into steam.

Method A solar-interface water evaporator, with titanium carbonitride (MXene) as photo thermal conversion layer and viscose fiber bundles as water transport channels was designed to achieve efficient solar driven water evaporation based on the principle of solar-driven interfacial water evaporation. The thermal local performance of the solar-interface water evaporator, the effects of the number of MXene coatings and light intensity on its water evaporation performance, and the stability of the solar-interface water evaporator were investigated using the simulated solar system. A viscose fiber bundle assembly with a length of 3 cm and a diameter of 0.9 cm was used as a water transport channel, and the self-made MXene dispersion was uniformly coated on the surface of the fiber bundle assembly as a photothermal conversion layer. Moisture absorption performance and photothermal conversion performance of solar interface water evaporators were characterized by testing the core absorption performance of adhesive fiber bundle assemblies and the interface temperature of the photothermal conversion layer. The evaporation performance of solar interface water evaporators was characterized by testing water evaporation capacity, evaporation rate, and evaporation efficiency.

Results Under the light intensity of 1 kW/m², the temperature of the central point of the fiber bundle containing the MXene coating increased from room temperature (about 22.3 ℃) to 44.7 ℃ within 5 min(Fig. 3), and the temperature of the central point of the coating surface was higher than that of the surrounding area. Increasing the number of MXene coatings and light intensity was beneficial to improve the evaporation performance of the solar-interface water evaporator. When the number of MXene coatings was increased from 1 to 5, the evaporation rate and evaporation efficiency increased from 0.78 kg/(m²·h) and 39.4% to 1.47 kg/(m²·h) and 74.4% at 1 kW/m², respectively (Fig. 4). During the test, the temperature of the water body remained basically unchanged, but the temperature of the water vapor increased rapidly within 0-5 min and became stable after 10 min, and the greater the light intensity, the higher the temperature of the water vapor, indicating that the system was in the heating state, the system basically reached thermal equilibrium after 10 min(Fig. 5(a)).When the light intensity increased from 1 kW/m² to 5 kW/m², the evaporation rate increased from 1.47 kg/(m²·h) increased to 6.45 kg/(m²·h), and the evaporation efficiency increased from 70.6% to 82.4% (Fig. 5(b)). However, with the increase of light intensity, the evaporation efficiency of the system did not show a continuous increasing trend, and reached the maximum when the light intensity was 2 kW/m², and then decreased slightly. After 144 hours of evaporation test at 2 kW/m², the evaporation rate and evaporation efficiency of the solar-interface water evaporator were still as high as 3.31 kg/(m²·h) and 82.1%, respectively, and decreased by only 4.1% and 3.5% compared with the initial value (Fig. 6). The data fitting results show that the evaporation rate and evaporation efficiency of the solar-interface water evaporator were 2.09 kg/(m²·h) and 56.9%, respectively, which remained above 60% of the initial value after 500 h.

Conclusion The viscose fiber bundles have good hygroscopic properties, and the grooves and vertical arrangement on the surface of viscose fibers provide channels for water transmission. As a photo thermal conversion layer, MXene exhibits excellent photo thermal conversion efficiency and high solar energy utilization efficiency. The solar-interface water evaporator prepared in this experiment demonstrates good evaporation performance and stability, and the MXene/viscose fiber bundle shows a good application prospect in the field of solar water evaporation.

Key words: viscose fiber bundle, titanium carbonitride, solar interface water evaporator, photothermal conversion layer, water evaporation performance