Heat loss and water transport capacity regulation in hybrid evaporators

Abstract

Solar interface evaporation technology, as a green and low-carbon water treatment solution, faces the core challenge of how to co-optimize photothermal conversion, water transport, and energy management through material design. Hydrogels have attracted significant attention for their hydrophilic networks and unique water molecular states in the field of solar interface evaporation. However, the mechanisms behind their improvement and efficiency enhancement remain unclear. We demonstrated that biochar doping improves the photothermal performance of hydrogels, regulates water absorption and transport, and reduces evaporation enthalpy. The dual photothermal and non-photothermal pathway enhancement mechanisms of functional groups are revealed. It is illustrated that the interaction between biochar and polymer chains changes the pore structure of hybrid hydrogels, promoting light absorption and water transport. Furthermore, the surface functional groups of biochar interact with hydrogen bond networks, increasing IW/FW and effectively enhancing water evaporation capacity. By combining enhanced photothermal performance, hydrophilicity, water transport capabilities, and lowered evaporation enthalpy, the incorporation of biochar comprehensively boosts the evaporation rate of hybrid hydrogels.

Keywords

Hybrid hydrogel / Biochar / Solar evaporation / Synergistic mechanism / Evaporation enthalpy

References

[1] Aleid S, Wu M, Li R, et al.. Salting-in effect of zwitterionic polymer hydrogel facilitates atmospheric water harvesting. ACS Mater Lett, 2022, 4: 511-520

[2] Alex S, Kumar PR, Chattopadhyay K, et al.. Thermally evaporated Cu–Al thin film coated flexible glass mirror for concentrated solar power applications. Mater Chem Phys, 2019, 232: 221-228

[3] Anukunwithaya P, Liu N, Liu S, et al.. Low vaporization enthalpy of modified chitosan hydrogel for high performance solar evaporator. Carbohydr Polym, 2024, 340 Article ID: 122304

[4] Bian Y, Shen Y, Tang K, et al.. Carbonized tree‐like furry magnolia fruit‐based evaporator replicating the feat of plant transpiration (global challenges 10/2019). Glob Chall, 2019, 3(10): Article ID: 1970101

[5] Chen J, Li H, Chen B, et al.. Carbon nanotube-wrapped particles in sodium alginate hydrogels for enhanced solar evaporation and EMI shielding through tortuous channel. Int J Biol Macromol, 2025, 315 Article ID: 144501

[6] Ebrahimi M, Naghali B, Aryanfar M. Thermoeconomic and environmental evaluation of a combined heat, power, and distilled water system of a small residential building with water demand strategy. Energy Convers Manage, 2022, 258 Article ID: 115498

[7] Fan X, Yang Y, Shi X, et al.. A MXene‐based hierarchical design enabling highly efficient and stable solar‐water desalination with good salt resistance. Adv Funct Mater, 2020, 30 Article ID: 2007110

[8] Fan Z, He P, Bai H, et al.. Green recycling of waste poly(ethylene terephthalate) into Ni‐MOF nanorod for simultaneous interfacial solar evaporation and photocatalytic degradation of organic pollutants. Ecomat, 2024, 6 Article ID: e12422

[9] Feng K, Gao N, Zhang W, et al.. Creation of nonspherical microparticles through osmosis‐driven arrested coalescence of microfluidic emulsions. Small, 2020, 16 Article ID: 1903884

[10] Ge Y, Wang L, Su Z, et al.. Efficient solar‐driven interfacial water evaporator using hydrogel modified carbon‐based biomass with abundant microchannels. Small, 2024, 20 Article ID: 2309780

[11] Ghaffar A, Usman M, Khan MU, Hassan M. Simultaneous solar steam and electricity generation from biochar based photothermal membranes. J Cleaner Prod, 2024, 446 Article ID: 141374

[12] Gu J, Zhang Y, Xiao P, et al.. Sunflower-inspired hydrogel evaporator with mutual reinforcement of evaporation and photodegradation for integrated water management. Chem Eng J, 2024, 490 Article ID: 151550

[13] Guo Y, Yu G. Engineering hydrogels for efficient solar desalination and water purification. Acc Mater Res, 2021, 2: 374-384

[14] Guo Y, Bae J, Fang Z, et al.. Hydrogels and hydrogel-derived materials for energy and water sustainability. Chem Rev, 2020, 120: 7642-7707

[15] Guo Y, Fang Z, Yu G. Multifunctional hydrogels for sustainable energy and environment. Polym Int, 2021, 70: 1425-1432

[16] Guo Y, De Vasconcelos LS, Manohar N, et al.. Highly elastic interconnected porous hydrogels through self‐assembled templating for solar water purification. Angew Chem Int Ed, 2022, 61 Article ID: e202114074

[17] He R, Yuan X, Huang Z, et al.. Activated biochar with iron-loading and its application in removing Cr (VI) from aqueous solution. Colloids Surf A Physicochem Eng Asp, 2019, 579 Article ID: 123642

[18] Jiang Y, Gong Y, Guo C, Xiang X. Carbon nanotube-nano-Fe3O4 composite graphene hydrogel with optimized 3D structure for high-performance solar evaporation. Desalination, 2025, 608 Article ID: 118840

[19] Lei W, Khan S, Chen L, et al.. Hierarchical structures hydrogel evaporator and superhydrophilic water collect device for efficient solar steam evaporation. Nano Res, 2021, 14: 1135-1140

[20] Lei C, Guan W, Guo Y, et al.. Polyzwitterionic hydrogels for highly efficient high salinity solar desalination. Angew Chem Int Ed Engl, 2022, 61 Article ID: e202208487

[21] Lei C, Park J, Guan W, et al.. Biomimetically assembled sponge-like hydrogels for efficient solar water purification. Adv Funct Mater, 2023, 33 Article ID: 2303883

[22] Li J, Zhou X, Chen G, et al.. Evaporation efficiency monitoring device based on biomass photothermal material for salt-resistant solar-driven interfacial evaporation. Sol Energy Mater Sol Cells, 2021, 222 Article ID: 110941

[23] Li W, Tian X, Li X, et al.. Ultrahigh solar steam generation rate of a vertically aligned reduced graphene oxide foam realized by dynamic compression. J Mater Chem A, 2021, 9: 14859-14867

[24] Li J, Yan L, Li X, et al.. Porous polyvinyl alcohol/biochar hydrogel induced high yield solar steam generation and sustainable desalination. J Environ Chem Eng, 2022, 10 Article ID: 107690

[25] Li Y-B, Xu L, Han S-J, et al.. Tea waste biochar hydrogel evaporator with high salt − resistance for highly efficient solar interfacial evaporation. Sep Purif Technol, 2025, 361 Article ID: 131276

[26] Liu P, Hu Y, Li X-Y, et al.. Enhanced solar evaporation using a scalable MoS₂-based hydrogel for highly efficient solar desalination. Angew Chem Int Ed, 2022, 61 Article ID: e202208587

[27] Liu G, Zhang B, Zhang X. Fe₃O₄ nanoparticles based dual network microporous hydrogel evaporator for efficient solar water purification. Surf Interfaces, 2025, 56 Article ID: 105659

[28] Long Y, Huang S, Yi H, et al.. Carrot-inspired solar thermal evaporator. J Mater Chem A, 2019, 7: 26911-26916

[29] Peng B, Lyu Q, Li M, et al.. Phase-separated polyzwitterionic hydrogels with tunable sponge-like structures for stable solar steam generation. Adv Funct Mater, 2023, 33 Article ID: 2214045

[30] Shu L, Zhang X-F, Wang Z, et al.. Cellulose-based bi-layer hydrogel evaporator with a low evaporation enthalpy for efficient solar desalination. Carbohydr Polym, 2024, 327 Article ID: 121695

[31] Tarek R, Kospa DA, El-Hakam SA, et al.. Tailoring surface topography of biochar-based hydrogel for hazardous pollutants removal from contaminated seawater through simultaneous steam-electricity generation. Desalination, 2023, 566 Article ID: 116935

[32] Wan H, Fu X, Chen Y, et al.. Biochar-based hydrogel evaporator with vertically arranged channels for efficient solar steam generation, desalination and water purification. Sep Purif Technol, 2025, 359 Article ID: 130795

[33] Wang Z, Wu X, Dong J, et al.. Porifera-inspired cost-effective and scalable “porous hydrogel sponge” for durable and highly efficient solar-driven desalination. Chem Eng J, 2022, 427 Article ID: 130905

[34] Wang P, Cheng J, Luo X, et al.. Composite distillation membranes with highly water-permeable and anti-crystallization polyzwitterionic layers for deep concentration of hypersaline brine. J Membr Sci, 2025, 713 Article ID: 123339

[35] Xu N, Hu X, Xu W, et al.. Mushrooms as efficient solar steam-generation devices. Adv Mater, 2017, 29 Article ID: 1606762

[36] Xu J, Wang G, Zhu L, et al.. Superwetting reduced graphene oxide/alginate hydrogel sponge with low evaporation enthalpy for highly efficient solar-driven water purification. Chem Eng J, 2023, 455 Article ID: 140704

[37] Yang Q, Ma X, Li Y, et al.. One-pot pyrolysis and enhanced efficient solar evaporation of Cu/Cu2O/biochar. Mater Today Sustain, 2023, 22 Article ID: 100363

[38] Yang H, Hu Z, Huang Z, et al.. Three-dimensional zwitterionic hydrogel-based evaporators with simultaneous ultrahigh evaporation rates and anti-fouling performance. Nano Energy, 2024, 127 Article ID: 109784

[39] Yu X, Fang J, Kong X, et al.. Superabsorbent hydrogel evaporator with sandwich SA/CNTs/SA cellular wall for solar-driven water purification. Chem Eng J, 2025, 505 Article ID: 159893

[40] Zhang YS, Khademhosseini A. Advances in engineering hydrogels. Science, 2017, 356 Article ID: eaaf3627

[41] Zhang Q, Zhang Y, Shen Y, et al.. Improving seawater desalination efficiency by solar driven interfacial evaporation based on biochar evaporator of Nannochloropsis oculata residue. J Environ Chem Eng, 2021, 9 Article ID: 105787

[42] Zhang Q, Yang X, Deng H, et al.. Carbonized sugarcane as interfacial photothermal evaporator for vapor generation. Desalination, 2022, 526 Article ID: 115544

[43] Zhang Q, Ye Q, Zhang Y, et al.. High efficiency solar interfacial evaporator for seawater desalination based on high porosity loofah sponge biochar. Sol Energy, 2022, 238: 305-314

[44] Zheng SY, Zhou J, Si M, et al.. A molecularly engineered zwitterionic hydrogel with strengthened anti-polyelectrolyte effect: from high-rate solar desalination to efficient electricity generation. Adv Funct Mater, 2023

[45] Zhu F, Wang L, Demir B, et al.. Accelerating solar desalination in brine through ion activated hierarchically porous polyion complex hydrogels. Mater Horiz, 2020, 7: 3187-3195

Funding

Shenzhen Science and Technology Innovation Program(SYSPG20241211173609007)

RIGHTS & PERMISSIONS

The Author(s)