Today’s session interprets a review article titled “Leveraging Cross-Cutting Technologies to Unravel Light-Heat-Water Interactions at Solar Evaporation Interfaces: Propelling the Low-Carbon Water-Energy Nexus” published in Advanced Materials, focusing on interfacial evaporation. The link to the original article is provided below.

https://advanced.onlinelibrary.wiley.com/doi/abs/10.1002/adma.202516043

Solar-driven interfacial evaporation (SDIE) systems represent a pivotal technology for clean water production. Through optimized evaporator design and component improvements, these systems have demonstrated high efficiency in small-scale applications such as seawater desalination and steam sterilization, while maintaining stable performance even under extreme environmental conditions. However, challenges remain, including an incomplete understanding of the fundamental mechanisms and limitations in scaling up the technology. This study employs multi-scale analysis and advanced computational modeling to establish a theoretical framework for the optimization of SDIE systems, thereby providing data-driven support for interdisciplinary and sustainable applications.

The development of photothermal interfacial evaporative materials has progressed through multiple stages, centered on the deepening understanding of photothermal conversion mechanisms and the continuous optimization of material performance:

Evaporative Materials: Photothermal Properties and Types

Metallic nanomaterials: Relying on localized surface plasmon resonance (LSPR), noble metal nanoparticles efficiently capture and convert specific wavelengths of light into heat. However, they face limitations such as high cost and narrow spectral absorption.

Carbon-based materials: With blackbody-like characteristics, these materials achieve broad-spectrum absorption from ultraviolet to near-infrared regions. They convert light energy into thermal energy via lattice vibrations (phonons), offering advantages such as low cost and strong chemical stability, making them one of the mainstream choices today.

Semiconductor materials: Through doping or the construction of heterostructures, their band structures can be tuned to extend spectral response into the near-infrared region. This enables a synergistic photothermal–photocatalytic effect, integrating wastewater treatment and freshwater production.

Advanced functional materials: Materials such as MOFs and COFs feature customizable chemical compositions and micro-nano structures, combining high specific surface area, excellent light-harvesting capacity, and efficient water transport. Structural innovations, such as Janus architectures and biomimetic hierarchical porous structures, further enhance performance.

The core strategies in material design focus on optimizing light absorption, enhancing thermal management, and regulating water transport. These efforts have shifted from singular performance improvements to multi-mechanism synergy. In recent years, increasing emphasis has been placed on sustainability and multi-system integration, driving the technology from single-function applications toward systematic solutions.

Evaporation Devices: Design Principles for Surpassing 100% Energy Conversion Efficiency

The core objective of evaporation device design is to achieve highly efficient conversion of solar energy into steam by optimizing photothermal conversion, thermal management, and water transport. Key design strategies include:

Structure–Light Interplay: Theory of Photothermal Conversion

Photothermal conversion efficiency is directly governed by photon–matter interactions, which can be categorized into three fundamental mechanisms:

Metal–Plasmonic Localized Heating: The localized surface plasmon resonance (LSPR) in metal nanoparticles induces collective oscillations of free electrons, facilitating photothermal conversion through near-field enhancement and hot electron excitation.

Semiconductor–Nonradiative Relaxation: Upon photoexcitation, semiconductors generate electron–hole pairs, which release thermal energy via nonradiative recombination. Bandgap engineering—such as doping and heterojunction construction—can extend the spectral response range.

Polymer–Molecular Thermal Vibration: Carbon-based materials and conjugated polymers undergo π–π* electron transitions, converting light energy into lattice thermal vibrations via electron–phonon coupling. Extended conjugated structures can narrow the bandgap and enhance broadband absorption.

In terms of structural optimization, 3D architectural designs enhance light-trapping efficiency by minimizing transmission and reflection losses through multiple light scattering, while simultaneously increasing the effective evaporation area. Coupled with micro-nano structural control—such as inverted pyramids and biomimetic morphologies—these strategies significantly improve overall photon harvesting performance.

Structure–Thermal Energy Interrelationship: Heat Transfer Processes and Thermal Management

The essence of thermal management lies in thermal localization and the suppression of energy dissipation, which requires a delicate balance between heat input and heat loss:

Solid–Liquid Interfacial Heat Transfer: Heat transfer efficiency is enhanced by modulating material wettability—such as using hydrophilic surfaces to reduce interfacial thermal resistance—and optimizing surface roughness to expand the contact area. In boiling heat transfer, bubble dynamics, including nucleation density and growth rate, significantly influence thermal performance.

Thermal Loss Mitigation: Thermal losses primarily arise from conduction, convection, and radiation. These can be suppressed through strategies such as employing thermal insulation materials with low thermal conductivity, confined domain evaporation designs, and selective radiative surfaces. Additionally, latent heat recovery via phase change can improve overall energy utilization efficiency.

Energy balance analysis reveals that enhancing broadband light absorption, reducing the thermal conductivity of materials, and lowering surface emissivity collectively contribute to the suppression of various thermal losses, thereby improving evaporation efficiency.

Structure–Hydraulic Energy Interrelationship: Water Supply and Activation

Water transport and activation are critical to enhancing evaporation efficiency, centered on hydrophilic effects and capillary action:

Water Transport Regulation: Through capillary-driven flow in micro-nano porous structures, enhanced hydrophilicity (e.g., via cellulose or hydrogel materials), and Janus structure design, efficient and directional water transport can be achieved. This balances the water supply rate with evaporation demand while inhibiting salt deposition.

Water Activation Strategies: Water molecules exist in three states: free water, bound water, and intermediate water. Intermediate water exhibits a lower evaporation enthalpy due to weakened hydrogen bonding. Material molecular engineering can increase the proportion of intermediate water and disrupt the hydrogen-bonding network of water clusters, thereby reducing the energy barrier for evaporation.

Mechanisms for water activation include dissociation of hydrogen-bond networks, interfacial polarization effects, and multi-field coupling regulation. These approaches can reduce the evaporation enthalpy by 30%–40%, leading to a significant increase in evaporation rate.

Evaporation Applications: Small-Scale Scenarios and Interdisciplinary Fields

Leveraging its high efficiency and low-carbon characteristics, SDIE technology demonstrates significant application value in small-scale distributed resource scenarios, primarily spanning four key areas:

Freshwater Production (Seawater Desalination): Photothermal materials concentrate solar energy at the water surface to drive evaporation, with vapor condensed into freshwater while salts are retained. By optimizing porous media permeability based on Darcy’s law, a daily water production rate of 5–10 L/m² can be achieved, with energy consumption only one-tenth that of conventional reverse osmosis.

Water–Electricity Cogeneration: High-temperature and high-pressure steam generated via photothermal conversion drives turbines for power generation, while condensed steam yields freshwater. By integrating Rankine and Carnot cycles, the overall system efficiency can exceed 20%.

Pollution Remediation: Combining photocatalytic degradation (for organic pollutants), sterilization (disrupting microbial structures), oil–water separation (via wettability control), and dye treatment (through concentration and degradation), this approach enables synergistic pollutant removal and water resource recovery.

Agricultural and Food Technologies: Seawater desalination irrigation uses localized heating to separate salts, producing water that meets agricultural standards. Food drying employs directed heating to rapidly remove moisture while preserving heat-sensitive nutrients such as vitamins, reducing drying time by 30%–50% compared to conventional methods.

Additionally, the technology shows potential in medical sterilization, industrial heat dissipation, and water supply in extreme environments.

Evaporation Simulation: Macro/Micro-Scale Numerical Analysis

Numerical simulation serves as a key tool for unraveling the complex coupled heat and mass transfer mechanisms within evaporators, operating across macro- and micro-scale dimensions:

Macroscopic Simulation: Based on continuum theory and implemented using platforms such as COMSOL and ANSYS, this approach dynamically tracks gas–liquid interface evolution, temperature and salinity distribution, and salt transport pathways. It supports structural optimization and thermal management strategy design, making it suitable for system-level energy efficiency evaluation.

Microscopic Simulation: Employing methods such as FDTD (for nano-optical response), DFT (for electronic structure and photothermal properties), and MD (for atomic-scale energy transport and evaporation dynamics), this dimension reveals non-equilibrium evaporation mechanisms at solid–liquid interfaces, guiding atomistic design of photothermal materials.

Cross-scale simulation, combined with experimental validation—such as synchrotron radiation characterization—enables deeper understanding of key issues including the limits of photothermal conversion and salt crystallization suppression.

Evaporation Limitations: From Computational Errors to Discrepancy Sources

Practical SDIE systems are subject to three main types of energy loss (bulk water heating, container heat dissipation, and environmental losses). Key sources of error and their characteristics include:

Material Intrinsic Property Errors: Light absorption rate fluctuations of 5%–20%, thermal conductivity gradient errors of ±10%–30%, and contact angle variations of ±10° due to surface heterogeneity.

Light–Environment Dynamic Coupling Disturbances: Light source intensity fluctuations of 5%–10%, wavelength deviations of ±5 nm, and ambient temperature, humidity, and wind speed variations causing evaporation rate deviations of 5%–25%.

Heat Transfer and Thermodynamic Modeling Errors: System thermal losses of 5%–15%, and simplified thermodynamic models leading to evaporation rate prediction errors of ±10%–30%.

Other Errors: Measurement instrument accuracy, liquid layer thickness uniformity, and data processing methods also introduce deviations of varying degrees.

When multiple error sources couple, the total deviation in evaporation rate can reach ±58%–70%. Mitigation requires improved material homogeneity, controlled experimental conditions, and refined modeling approaches.

Conclusion

Technological Innovation: Thermodynamics and System Design

Advancing Thermodynamic Limit Optimization: Thermal localization is enhanced through interfacial micro/nano-structuring, while phase change materials and nanofluids are utilized to mitigate heat loss. Entropy generation during evaporation is controlled via optimized temperature and pressure conditions.

Integrated Multiphysics System Design: Synergistic transport of water, heat, electricity, and mass is achieved across scales—from nanoscale capillary action to meter-level fluid distribution networks.

Application Dimension: Sustainable Development and Regional Adaptation

Addressing Global Sustainability Needs: Integration with wind and biomass energy facilitates the establishment of low-carbon industrial chains, enhancing both freshwater production efficiency and energy cogeneration capacity.

Complementing Infrastructure in Specific Regions: Modular water-electricity cogeneration systems are deployed for off-grid areas, supporting closed-loop Water-Energy-Food (WEF) cycles—such as agricultural wastewater reuse and PV-powered farms on saline-alkali land.

Challenge Dimension: Bridging Basic Science and Engineering Gaps

Thermodynamic Constraints: Evaporation rate under AM 1.5G irradiation faces a theoretical upper limit imposed by phase change entropy and the energy barrier of hydrogen bond dissociation in water molecules.

Material Service Reliability: Photothermal absorption degrades under high-salinity and extreme pH conditions, while porous structures are prone to failure when treating high-viscosity wastewater.

Adaptability to Extreme Environments: Evaporation driving force and optical penetration depth are significantly reduced under high humidity or low temperature, necessitating dew point regulation and light-guiding technologies.

Future Directions

Future efforts will focus on optimizing the structure and outdoor durability of photothermal micro/nano materials, enhancing cross-scale mass transfer in extreme environments, and enabling multi-objective optimization of regional WEF systems. These advances are expected to accelerate the large-scale application of SDIE in distributed desalination farms and industrial zero-liquid-discharge water recovery scenarios.