3. Conclusion
In summary, we fabricated a magnetic field induced photothermal
evaporator assembled by carbon-coated
Fe3O4(Fe3O4@C) nanoparticles, which revealed
the adjustable spiny surface structure corresponding to the relative
distance to magnet. At an appropriate relative distance, just 1 mg
mm-2 of Fe3O4@C
nanoparticles was necessary to form a well-distributed spiny surface.
With the optimized surface structure, the solar absorbance of evaporator
could reach up to 94.6% via multiple reflections. The
Fe3O4@C assembled evaporator obviously
improved the water evaporation as high as 1.39 kg m-2h-1 under the 1-sun illumination, about 2.8 times
higher than natural evaporation. Meanwhile, the magnetic evaporator
could also accelerate the seawater evaporation up to 1.31 kg
m-2 h-1 with just a little
performance degradation during long desalination owing to the good
stability of Fe3O4@C. The work can be
considered as a beneficial attempt to optimize the magnetic evaporator
for application. Besides, the facile adjustment of the magnetic
nanoparticles assembled surface via the position in magnetic field has
high potential in not only sustainable solar-driven fresh water
generation but more fields of water treatment.
Experimental Section
Preparation of the carbon-coated nanoparticles : The carbon-coated
nanoparticles were synthesized by a typical hydrothermal method.
Specifically, 0.3 g of Fe3O4nanoparticles, 1 mL of acrylic acid, and 40 mL of H2O
were mixed with a certain amount of glucose in a 100 mL capped glass
bottle. Different amounts of glucose led to different thicknesses of
carbon layers around Fe3O4nanoparticles. The mixture was stirred vigorously at room temperature
for 4 h and transferred to a 100 mL Teflon-lined stainless-steel
autoclave. The autoclave was heated at 200 ℃ for 12 h, then naturally
cooled to room temperature at the end of the reaction. The black
products were washed with DI water and anhydrous ethanol alternately
three times. Subsequently, the products were dried at 60 °C for 6 h. The
obtained samples were named Fe3O4@C, and
Fe3O4@tC respectively according to 1.0
g/2.0 g of glucose.
Fabrication of magnetic photothermal evaporator : A 3D model of
the evaporator was established by SOLIDWORKS software and was converted
into object through 3D printer (raise3D Pro2 Plus) using PLA (polylactic
acid) wire. This evaporator had two parts including an upper holder to
support the magnetic nanoparticles and a lower screw plug equipped with
a NdFeB magnet. The distance between magnet and magnetic nanoparticles
could be adjusted by rotating the screw plug. The air-laid paper was cut
into a specific shape serving as water transfer channels. Magnetic
nanoparticles were deposited at the holder at the density of 1 mg
mm-2, which could self-assemble into a spiny surface
induced by magnetic field.