Hierarchical MnO₂ Nanosheets Grown on Cotton Fabric as a Flexible and Washable Solar Evaporator for Seawater Desalination

Abstract

Solar vapor generation is a renewable and hopeful technology for obtaining freshwater from underground water, dyeing wastewater, and seawater. Herein, hierarchical MnO2 nanosheets grown on cotton fabric (Mn-CF) have been developed for solar-driven water evaporation. Black MnO2 nanosheets and nanoflowers are in situ chemically deposited on cotton fabric (CF), which leads to a solar absorption ability as high as 95% from 300 to 2500 nm. Due to the synergistic effect of the super-hydrophilic CF and hierarchical MnO2 nanosheets, Mn-CF results in a water evaporation rate of 1.40 kg m–2 h–1 with the photothermal conversion efficiency of 87.48% under 1 sun illumination (1 kW m–2). During the desalination test, Mn-CF can be renewed by washing off the steamed salts through a simple ultrasonication or hand-washing. Moreover, Mn-CF remains stable after 40 cycles, each lasting 1 h under 1 sun irradiation. A Mn-CF-based solar steam generator (Mn-CF-SSG) enables to effectively purifying simulated dyeing wastewater and seawater using natural sunlight. The cost of preparing 1 m2 Mn-CF is about $1.5. This work provides a simple method to prepare flexible and washable Mn-CF-SSG with low-cost and high efficiency that has huge potential for practical application of seawater desalination.

Bifunctional in situ polymerized nanocomposites for convective solar desalination and enhanced photo-thermoelectric power generation

“…5e represents the comparative evaporation rates and photothermal conversion efficiencies of the four developed evaporating systems, where MnO 2 NWs/polyurethane foam achieved 1.32 kg m −2 h −1 , while the MnO 2 @PPy solar evaporator exhibited an excellent evaporation rate of 1.69 kg m −2 h −1 compared to other MnO 2 /PPy-based solar steam generators. 32–34 The photothermal conversion efficiency of the MnO 2 @PPy solar-driven evaporation system was measured using the following equation: 35 h LV = λ + C Δ T where ṁ v represents the evaporation rate under incident solar energy ( q i ), h LV shows the overall enthalpy change from the liquid to vapor phase together with a practical heat and enthalpy phase change, and λ is the latent heat of phase change, which differs at different temperatures, usually 2430 and 2256 kJ kg −1 at 30 °C and 100 °C, respectively. C denotes the specific heat capacity of water (4.2 kJ kg −1 K −1 ) and Δ T is the steady change in water temperature.…”

“…The MnO 2 @PPy solar steam generator exhibited an efficient mass change (1.69 kg m −2 ) under one sun, which is higher than that of other MnO 2 -based solar evaporators. 32,33 Furthermore, the time-dependent mass change was recorded under different solar irradiances (up to 3 kW m −2 ), as shown in Fig. S8 (ESI †).…”

“…5e represents the comparative evaporation rates and photothermal conversion efficiencies of the four developed evaporating systems, where MnO 2 NWs/polyurethane foam achieved 1.32 kg m −2 h −1 , while the MnO 2 @PPy solar evaporator exhibited an excellent evaporation rate of 1.69 kg m −2 h −1 compared to other MnO 2 / PPy-based solar steam generators. [32][33][34] The photothermal conversion efficiency of the MnO 2 @PPy solar-driven evaporation system was measured using the following equation: 35…”

“…5g demonstrates the comparison of the evaporation performances, e.g., evaporation rate and solar to thermal conversion efficiencies, of our so-fabricated MnO 2 @PPy solar evaporators with other competitive solar evaporators. 29,[32][33][34][36][37][38][39][40][41][42] Li et al 43 reported the average solar irradiation per year in Wuhan using Klein and Theilacker's model, which was estimated to be approximately 2643.15 MJ m −2 . Fig.…”

CuS ‐enhanced light‐absorbing washable solar evaporator based on polydopamine‐cotton fabric for efficient water purification

“…The evaporation rate of PDA‐CF and CuS‐PDA‐CF are compared with previously reported CF‐based solar steam generators as shown in Figure 6A. Such as MWCNTs‐COOH/CF, 31 PPy/CF, 32 Mxene/CNT/CF, 33 TBFF‐PDA‐PPy/CF, 34 Soot/CF, 35 Mn‐CF, 36 RGO/CF, 37 MWCNTs‐COON/BN‐PDA/CF, 18 CsxWO 3 /CF 38 and CNT/CF 19 . Despite CuS‐PDA‐CF acquiring a 1.50 kg m −2 h −1 evaporation rate, it is still in the middle to upper range, and it has a very simple manufacturing procedure with a low cost.…”