Fabrication of Low-Cost Porous Carbon Polypropylene Composite Sheets with High Photothermal Conversion Performance for Solar Steam Generation

Abstract

The development of absorber materials with strong light absorption properties and low-cost fabrication processes is highly significant for the application of photothermal conversion technology. In this work, a mixed powder consisting of NaCl, polypropylene (PP), and scale-like carbon flakes was ultrasonically pressed into sheets, and the NaCl was then removed by salt dissolution to obtain porous carbon polypropylene composite sheets (P-CPCS). This process is simple, green, and suitable for the low-cost, large-area fabrication of P-CPCS. P-CPCS has a well-distributed porous structure containing internal and external connected water paths. Under the dual effects of the carbon flakes and porous structure, P-CPCS shows excellent photothermal conversion performance in a broad wavelength range. P-CPCS-40 achieves a high temperature of 128 °C and a rapid heating rate of 12.4 °C/s under laser irradiation (808 nm wavelength, 1.2 W/cm² power). When utilized for solar steam generation under 1 sun irradiation, P-CPCS-40 achieves 98.2% evaporation efficiency and a 1.81 kg m^-2 h^-1 evaporation rate. This performance means that P-CPCS-40 outperforms most other previously reported absorbers in terms of evaporation efficiency. The combination of carbon flakes, which provide a photothermal effect, and a porous polymer structure, which provides light-capturing properties, opens up a new strategy for desalination, sewage treatment, and other related fields.

Keywords: desalination; photothermal conversion; porous structure; solar steam generation; ultrasonic pressing.

Figure 1

Schematic illustration for the preparation of P-CPCS.

Figure 2

Formability and structural characteristics of P-CPCS. (a) Photographs of P-CPCS-30, P-CPCS-40, and P-CPCS-50. (b) P-CPCS-40 in bending state and after bending multiple times. (c) Variation in thickness of P-CPCS with ultrasonic duration time. Cross-section SEM images and magnified views of (d) CPCS, (e) P-CPCS-30, and (f) P-CPCS-40.

Figure 3

(a) Pore size distributions of CPCS, P-CPCS-30, and P-CPCS-40 and (b) XRD patterns.

Figure 4

FTIR spectra of raw materials, CPCS, P-CPCS-30, and P-CPCS-40.

Figure 5

(a) Experimental reflectance spectra of CPCS, P-CPCS-30, and P-CPCS-40. (b) Schematic illustration showing light trapping by the porous structure of P-CPCS.

Figure 6

P-CPCS photothermal conversion evaluation. (a) Schematic diagram showing the photothermal conversion experiment. Temperature curves of samples under (b) 405 nm, (c) 532 nm, (d) 655 nm, (e) 808 nm, and (f) 1064 nm laser irradiation at a power density of 0.25 W/cm². (g) Heating rates of the samples irradiated by 405, 532, 655, 808, and 1064 nm lasers at a power density of 0.25 W/cm². (h) Temperature curves of P-CPCS-40 irradiated by 808 nm laser at power densities of 0.4, 0.6, 0.8, 1.0, and 1.2 W/cm². (i) Heating rates of samples irradiated under 808 nm laser at different power densities. (j) IR images of CPCS, P-CPCS-30, and P-CPCS-40 irradiated by 405, 532, 655, 808, and 1064 nm lasers at a power density of 0.25 W/cm².

Figure 7

Evaluation of P-CPCS for solar steam generation. (a) Temperature curves of CPCS, P-CPCS-30, and P-CPCS-40 in water and air obtained under 1 sun irradiation. (b) IR images of CPCS, P-CPCS-30, and P-CPCS-40 in air and P-CPCS-40 in water under 1 sun irradiation from 0 to 900 s. (c) WCAs of CPCS, P-CPCS-30, and P-CPCS-40.

Figure 8

Evaporation performance of P-CPCS. (a) Physical image of the experimental setup for the solar-driven water evaporation experiment. (b) Changes in water mass achieved by CPCS, P-CPCS-30, and P-CPCS-40 under 1 sun irradiation. (c) Evaporation rates of P-CPCS-40 under 1 sun irradiation for 10 cycles.

Figure 9

Comparison of evaporation rates and evaporation efficiencies reported for other absorber materials in previous studies.

Figure 10

Desalination and sewage treatment performance of P-CPCS. (a) Schematic illustration of experimental setup utilized for evaporation and steam collection. (b) Na⁺, Mg²⁺, K⁺, and Ca²⁺ concentrations in simulated seawater before irradiation and in the water collected during evaporation by P-CPCS-40 (WHO standard: dashed line). (c) UV–Vis–NIR absorbance spectra of MB solution before irradiation and the water collected during evaporation by P-CPCS-40.