Super Hydrophilic Activated Carbon Decorated Nanopolymer Foam for Scalable, Energy Efficient Photothermal Steam Generation, as an Effective Desalination System

Abstract

Clean water scarcity is still an intense, prolonged global issue that needs to be resolved urgently. The solar steam generation has shown great potential with a high energy conversion efficiency for clean water production from seawater and wastewater. However, the high evaporation rate of water cannot be preserved due to the inevitable fouling of solar absorbers. Herein, a self-floatable and super hydrophilic solar-driven steam generator composed of activated carbon coated melamine foam (ACM). The deposited ACM photothermal layer exhibits outstanding solar absorption (92%) and an efficient evaporation rate of 1.27 kg m^-2 h^-1, along with excellent photothermal conversion efficiency (80%) as compared to commercially available primitive solar stills. The open porous assembly of melamine foam equipped with 80% flexibility (0.8 MPa) enabled smooth water transport and sustain heat accumulation within the matrix. The thermal insulation of ACM is 10 times greater than pure water. Moreover, open porous assembly of designed solar-powered steam generator rejects salt ions as well as volatile organic compounds efficiently. The low-cost and facile fabrication of photothermal based water production presents a potential solution to single step drinking water supply from various resources of the sea, the lakes and mixtures of emulsified oil and industrial wastewater.

Keywords: activated carbon; melamine nanofoam; nano-desalination; photothermal steam.

Figure 1

Schematic illustration of activated carbon decorated melamine foam-based steam generator.

Figure 2

Surface morphologies and microstructure (a–c) complete fabrication of ACM solar evaporator from activated carbon (a) pure activated carbon (AC); (b) cylindrical shaped melamine foam; (c) activated carbon decorated melamine (ACM) foam-based steam generator. FESEM images labelled (d–f) as (d) homogeneous non-uniform sized particles; (e) porous structure of melamine foam; (f) activated carbon clusters over microchannels of melamine foam.

Figure 3

Crystallographic analysis of pure activated carbon by X-ray diffraction and X-ray photoemission spectroscopies; (a) XRD pattern of pure activated carbon powder; (b) XPS survey of AC; (c) C1s spectra of AC that reveals oxygen presence; (d) wide range of UV–VIS absorption of AC; (e) ultimate tensile stress curve of ACM evaporator; (f) real-time demonstration of ACM evaporator during steam generation.

Figure 4

Solar steam generation investigations; (a) real-time demonstration of activated carbon decorated melamine foam (ACM) based steam generation; (b) mass change profile of three different systems; (c) mass change profile of ACM steam generator under different solar intensity; (d) I.R. image of ACM during functioning; (e) surface temperature of three different systems; (f) thermal conductivity of ACM device under wet state.

Figure 5

Photothermal conversion efficiencies and nano filtering of volatile organic compounds (VOCs): (a) evaporation rate and photothermal conversion efficiencies of three different systems; (b) consecutive solar-driven steam generation cycles; (c) smooth evaporation rate using ACM steam generator against different VOCs emulsions; (d) water purity profile of condensed water from different VOCs emulsions.

Figure 6

Salt rejection and water recovery via ACM solar evaporator: (a) ICP-OES spectroscopy profile of concentration gradient of different salt ions in simulated seawater, and condensed water; (b) real-time water condensing process from muddy wastewater; (c,d) optical morphology of muddy wastewater and ACM treated condensed water.