Context: 

In a significant breakthrough to tackle global freshwater scarcity, researchers from the Indian Institute of Technology (IIT) Bombay have developed a Dual-Sided Superhydrophobic Laser-Induced Graphene (DSLIG) evaporator that can facilitate water desalination.  

Current Limitations in Solar Desalination

Only about 3% of Earth's water is freshwater, and in that less than 0.05% is easily accessible. 

Removing salt (desalination) from seawater and brackish water is seen as one of the solutions to address this problem, with researchers working towards developing more efficient and faster desalination techniques. 

However, brine (concentrated salt solution) from desalination is a big problem in landlocked places, and industries are looking for zero liquid discharge. 

Solar energy-based desalination is desirable due to its low carbon footprint. But, fluctuations in sunlight intensity and availability limit the efficiency and consistency of current methods.

One of the solar energy-based desalination methods is Interfacial evaporation systems. It has an evaporator made from materials that can absorb solar energy and heat up. 

• The evaporator, placed on the surface of the water, focuses solar heat on a thin layer of water at the evaporator’s surface rather than heating the entire volume. 
• This localized heating minimizes heat loss and enhances the efficiency of the desalination process.

These systems minimize heat loss and improve efficiency. However, they are also susceptible to:

• Reduced performance during cloudy conditions or inconsistent solar radiation.
• Salt crystal buildup on evaporator surfaces hinders water contact and lowers efficiency. 

The DSLIG evaporators aims to address both of these issues.

About the Dual-Sided Superhydrophobic Laser-Induced Graphene (DSLIG) 

It incorporates two innovations:

• Dual Heating Modes: It can be heated using both solar energy and electricity (Joule heating). This ensures consistent performance even with fluctuating sunlight.
• Superhydrophobic Surface: This surface repels water, like lotus leaves, reducing contact area so droplets roll off instead of sticking. This prevents salt accumulation on the evaporator and ensures long-term efficiency.

Material Design and Fabrication:  DSLIG is fabricated using:

• A base of poly (ether sulfone) (PES), which provides mechanical strength. 
• Polyethersulfone (PES) is a thermoplastic polymer known for its high thermal stability, good chemical resistance, and biocompatibility.
• A coating of polyvinylidene fluoride (PVDF) on one side, enabling hydrophobicity. 
• Piezoelectric polymers like PVDF are polymers that can generate electric charges on the surface under pressure/strain thus convert mechanical energy into electrical energy.
• Graphene engraving via laser technology on the PVDF side.
• The name DSLIG reflects its dual-sided structure—PES for stability and PVDF for superhydrophobicity (water repellent nature).

Performance and Applications:

• Resists salt deposition: Exhibits lotus leaf-like behavior to prevent salt buildup on the surface.
• Operates under dual heating: Performs efficiently with both solar and electric heating.
• Treats high-salinity water: Effective for desalinating brine from existing plants and treating industrial wastewater.
• Scalable performance: Performance improves when multiple evaporators are stacked.
• Sustainable potential: With a low carbon footprint, low toxicity, and cost-effectiveness, DSLIG is a promising solution for large-scale sustainable desalination and wastewater treatment.