A recent study published in Advanced Functional Materials presents a new approach to improving both water purification and energy generation. The researchers developed a Janus membrane using advanced materials that aim to address water scarcity and energy needs, especially in areas with limited access to traditional resources.
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Although solar-powered evaporators have improved in recent years, challenges remain. These include low evaporation efficiency, poor long-term performance, and issues with salt buildup.
This study introduces a membrane that uses cellulose nanofibers (CNF) and a modified version of MXene to improve performance in water collection and energy production over longer periods.
Background
Solar-driven evaporation is a promising method for water treatment and energy generation. However, current systems often struggle with problems like membrane fouling and salt buildup. These issues reduce performance over time.
MXenes are materials known for their good water transport and photothermal properties. In this research, the MXene was modified using cetyltrimethylammonium bromide (CTAB). This treatment increased the space between layers and the surface area, which helped improve both water movement and heat conversion.
Cellulose nanofibers were added to strengthen the membrane and improve water transport. The result is a Janus membrane, which has two surfaces with different properties. One side attracts water, and the other repels it. This design is useful for rejecting salt and keeping water moving during evaporation.
The Current Study
To make the CNF@CTAB-MXene/PTFE Janus membrane, the researchers followed several steps. First, they created CNF using the TEMPO oxidation method. This involved treating softwood pulp with chemicals to produce a concentrated suspension of nanofibers.
Next, MXene nanosheets were made by etching the MAX phase Ti₃AlC₂ using a solution of hydrochloric acid and lithium fluoride. This process created a stable MXene dispersion. CTAB was then used to modify the MXene, which improved the internal structure and surface area for better water movement.
The Janus membrane was assembled by layering the CNF@CTAB-MXene composite first. A layer of PTFE was then deposited onto this composite to add superhydrophobic properties. Plasma treatment was applied to improve how well the layers stuck together. This setup allowed water to move through the membrane efficiently and reduced the buildup of salt, which can block the system.
To test the membrane, the researchers built a solar-driven seawater purification system. This system used the membrane to both evaporate water and generate electricity. The tests measured evaporation rate, light absorption, and electrical output from a thermoelectric module built into the setup.
Results and Discussion
The CNF@CTAB-MXene/PTFE Janus membrane performed better than traditional membranes. Under sunlight equal to one sun, the system reached an evaporation rate of 1.51 kg per square meter per hour. It also achieved a photothermal conversion efficiency of 98.56 %. No salt was seen on the membrane surface during a 24-hour test, which shows that the design effectively prevents salt buildup.
The membrane also showed strong mechanical performance, with a tensile strength of 22.19 MPa. It absorbed 94.07 % of light across a broad range of wavelengths. These results are due to the combination of the water-attracting CNF@CTAB-MXene layer and the water-repelling PTFE layer. Together, they keep water moving while reducing problems caused by salt.
When connected to a thermoelectric module, the system also produced electricity. Under stronger sunlight (three suns), it generated 343.8 millivolts. This dual function is useful in remote areas without access to conventional energy, where solar systems can help meet both water and electricity needs.
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Conclusion
This research introduces a Janus membrane made from cellulose-based materials that supports both water purification and electricity generation. The modified MXene, treated with CTAB, improves water transport and light absorption. The PTFE layer helps prevent salt buildup, which keeps the system running over time.
The system remained stable and efficient during extended testing. This suggests that the membrane could be used in real-world applications, including seawater desalination and off-grid energy production.
The study highlights the value of using materials that serve more than one purpose. Systems like this one could play an important role in managing water and energy in sustainable ways. They also support broader environmental and development goals by offering reliable solutions in areas that need them most.
Journal Reference
Li Y., et al. (2025). Advanced nano-fibrillated cellulose modified MXene Janus membrane for continuous 24-h water-power co-generation. Advanced Functional Materials, 2502605. DOI: 10.1002/adfm.202502605, https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202502605