PVA:GA polymer hydrogel/activated carbon (AC) nanocomposite as solar photothermal materials: study of structural, optical absorption and water purification properties

In this study, a solar evaporation hybrid material including a hydrogel as water transmitter and activated carbon (AC) as solar strong absorber material were prepared for fast evaporation and purification of seawater. We used the polyvinyl alcohol (PVA) polymer as hydrophilic agent and glutaraldehyde (GA) as chemical cross linker for preparation of PVA:GA/AC hydrogel nanocomposite by physical crosslinked freezing/thawing (F-T) process. Structural properties of hydrogel/activated carbon (AC) nanocomposite were characterized by X-ray diffraction (XRD) analysis, surface morphology by field emission scanning electron microscope (FESEM), optical absorption and band gap of components by UV–Vis spectroscopy and chemical bonding by Fourier transform infrared spectroscopy (FTIR). The FESEM images show the capillary and porous structure of the hydrogel for light absorption and hydrophilicity. The results show that solar water evaporation system of the Hydrogel:polyvinyl alcohol (PVA):GA/AC nanocomposite under solar radiation can work continuously to produce clean water with high efficiency, good stability, and high salt removal for water purification applications. The evaporation rate can be up to 2.49 kg h⁻¹m⁻² and achieves ultra high purification of seawater and produces clean water. For PVA:GA/AC(NH₃) hydrogel, the hardness of seawater decreased from 2580 to 12 ppm and ion conductance from 5489 (μs) to 25 (μs) with evaporation rate = 2.49 (kgm⁻²h⁻¹). The optical band gap was measured in the range of 1.60 eV–3.10 eV, which indicates the absorption of more wavelengths in the solar spectrum.