Direct Solar Absorption Nanoparticle Doped Membranes for a Hybrid Membrane Distillation and Photovoltaic Cell

The growing demand for clean water supplies is driving the need for an innovative approach of water desalination. Developing a method for treating water with high salinities is possible with membrane distillation (MD). Additionally, MD is very attractive for pairing with solar energy due to the low temperature requirements. The integration of a membrane distillation system with a photovoltaic (PV) system will result in the co-production of electricity and clean water, thereby improving the economics of MD. Such a hybrid system will directly absorb thermal energy in the membrane for desalination while taking advantage of the spectrally selective nature of PV to generate electricity. At the top of the system is a PV cell that will filter the visible light wavelengths and transmit the remaining ultraviolet and infrared to a membrane doped with absorbing nanoparticles located at the core of the system. This configuration integrates the system and provides an avenue for increasing the membrane performance by mitigating the temperature polarization effect, which is the gradual decrease of temperature at the thermal boundary layers of the membrane due to the large amount of heat consumed during the phase transition process. A custom multi-step phase inversion process fabricates Polyvinylidene Fluoride (PVDF) membranes through a Diffusion Induced Phase Separation (DIPS) technique. The process allows for the addition and controlled distribution of nanoparticles at different loadings across the membrane structure. The membranes fabricated during this study exhibited a microporous, sponge-like, and hydrophobic nature during the morphological analysis. Scanning Electron Microscopy (SEM) images and contact angle measurements above 100° prove the suitability for MD applications. The membranes doped with a 0.8wt% load of carbon coated copper nanoparticles increased the solar absorptance of the membrane by 80% during the optical analysis. A custom lab-scale direct contact membrane distillation (DCMD) setup characterizes the membranes fabricated off-sun and on-sun. The doped membrane exhibited a 15-32% increase in desalination performance when exposed to solar irradiance while simultaneously producing 0.36W of electrical power. The overall project led to the increased use of renewable energy for desalination while improving the ability to use MD for desalination purposes