Solar-driven seawater desalination via plasmonic hybrid MOF/polymer and its antibacterial activity

Abstract

In recent years, solar seawater desalination has been considered to be a promising and cost-effective technique to produce clean sources for water treatment and water deficiency. In addition, this technique shows high photothermal conversion efficiency by solar collectors to transfer solar energy into heat and the transformation of molecules in the capillaries of solar evaporators. In this study, we report the preparation of graphene-supported MIL-125 with polyurethane foam (MGPU) for solar steam generation. We modified MGPU by using the plasmonic nanoparticles of Ag and a polymer of polyaniline to increase the evaporation rate. Polyurethane foam can float on the surface of water and self-pump water by its hydrophilic porous structure, superior thermal insulation capabilities, and easy fabrication. MIL-125 has a high salt rejection and higher water permeability. It can reduce the affinity between water molecules and the pore surface of membrane, making it simple for water molecules to move through the pores. GO is a great alternative for steam generation applications since it exhibits broad-band light. The strong solar absorption, photothermal conversion efficiency, and photoreaction efficiency are enhanced by the use of silver nanoparticles in the photoreaction. The salt resistance capability is enhanced in saline water in the presence of polyaniline in a composite. Under one solar irradiation, the Ag/PANI/GO@MIL-125 (Ag-PMG) nanocomposite demonstrates an average 1.26 kg m² h^-1 rate of evaporation and an efficiency as high as 90%. The composite exhibits remarkable stability and durability after more than 10 cycles of use without a noticeable decrease in activity. In addition, the composite exhibits excellent organic dye removal from contaminated water and generates pure condensed freshwater. The antibacterial photoactivity of the photocatalysts was examined against B. subtilis and E. coli. The results demonstrate that Ag-PMG shows higher antibacterial activity than MIL-125 and PMG. It was shown that the presence of rGO, PANI, and Ag in the sample enhances the antimicrobial activity.

Fig. 1. (a) XRD patterns and (b) FTIR spectra of pure and modified MIL-125.

Fig. 2. (a) Full survey XPS spectrum of Ag-PMG, (b–f) high-resolution XPS of C 1s, O 1s, N 1s, Ag 3d and Ti 2p, respectively.

Fig. 3. SEM images of (a) PU foam, (b and c) Ag-PMG loaded on PU foam, (d–f) Ag-PMG composite.

Fig. 4. (a) Mass changes for PU, M, MG, PMG, Ag-MG and Ag-PMG. (b) Mass change for Ag-MG, PMG and Ag-PMG of pure and saline water. (c) The evaporation efficiency of fabricated foams. (d) The evaporation rate of Ag-PMG for various concentrations of saline for 60 min, and (e) salt-rejection performance during a daytime salt aggregation time from (I) 5 h to (V) 9 h, and (VI) light-off salt diffusion times.

Fig. 5. Outdoor solar water evaporation system in real sunlight. (a) Evaporation rate during 7 h of outdoor solar desalination recorded over time from 10:00 to 4:00, and temperature of PMG, Ag-MG and Ag-PMG at high intensities. (b) Solar radiation intensities measured over time from 10:00 to 4:00. (c) Evaporation rate and temperature of Ag-PMG recorded over time from 10:00 to 4:00. (d) The mass change of Ag-PMG under the real sun for 60 min, and IR images of Ag-PMG at a high intensity of outdoor solar desalination.

Fig. 6. (a) Temperature change on foam surfaces for different composites in 1 hour, and (b) IR thermal images of (I) PU, (II) M, (III) MG, (IV) PMG, (V) Ag-MG, and (VI) Ag-PMG after 1 h.

Fig. 7. (a) Concentration of metal ions before and after the desalination technique by using Ag-PMG composite, (b) UV-vis absorption spectra of dye-contaminated water before and after desalination, and (c) reusability test of the Ag-PMG sample during 10 cycles.

Fig. 8. Antibacterial activity tests of (1) Ag-PMG, (2) M, (3) PMG composites against both (a) E. coli and (b) B. subtilis bacteria.