Activated carbon as a photothermal absorber in PVDF membranes for solar driven air-gap membrane distillation

Abstract

Renewable energy-enabled desalination systems are crucial for solving the global water scarcity challenges in an environmentally friendly manner. In this work, we report an air gap membrane distillation (AGMD) process that utilizes polyvinylidene fluoride (PVDF) membranes blended with a photothermally active and relatively inexpensive activated carbon (AC). The composite membrane absorbed the solar radiation and generated local heat at the membrane surface, providing the driving force required in the AGMD process. This strategy overcame one of the key limitations of traditional MD—temperature polarization, and increased the energy efficiency significantly. We show that the blending of 5 to 9 %AC into the PVDF matrix can significantly boost the solar-energy-driven flux of AGMD by 281–1400 %, compared to the pristine membrane. PVDF membrane blended with 9 %AC exhibited an average AGMD permeate flux of 0.31 kg.m−2.h−1, with a GOR of 0.29 and a photothermal efficiency of 17.64 %. All PVDF-AC membranes showed excellent salt rejection, reaching 99.9 % for PVDF-9%AC. Finally, the AGMD performance of the fabricated membranes was compared by estimating their normalized MD coefficients (B/δ). PVDF-9%AC exhibited a B/δ value of 18.8E-5 kg s−1 m−3 Pa−1, as opposed to a meager 0.89E-5 kg s−1 m−3 Pa−1 exhibited by its pristine counterpart.

Keywords: Membrane distillation, Solar desalination, Photothermal membrane, Activated carbon, Temperature polarization