Clean water is a vital resource for human survival and social development. With the rapid development of population growth, urbanization, and industrialization in the past decades, the slow process of natural water regeneration can no longer meet the increasing demand for clean water resources (Fig. 1A). However, more than 97 % of natural water resources are seawater and brackish water, which cannot be used directly due to their high salinity. As a result, there is an urgent need for efficient and large-scale desalination technology. Among the traditional desalination technologies, thermal desalination represented by multi-stage flash evaporation and multi-effect distillation has high energy consumption (e.g., every cubic meter of freshwater consumes 10–15 kWh of electricity), while membrane desalination represented by reverse osmosis has energy consumption that can be lowered to 5 kWh m⁻³, but it faces the problem of membrane contamination and requires regular maintenance and replacement, increasing the treatment cost. At the same time, the dependence of these technologies on fossil fuels and electricity has exacerbated the current global energy crisis. Therefore, it is crucial to develop low-energy and renewable methods for water purification production. Solar-driven interfacial evaporation (SIE) technology is a branch of solar thermal energy utilization, which has become a research hotspot in seawater desalination and wastewater purification due to its efficient photothermal conversion efficiency, environmental friendliness, low cost, and simple operation. Photothermal materials are at the core of SIE technology, with current materials including polymers, carbon-based materials, semiconductors, and plasmonic metals. However, evaporators made from these materials typically achieve theoretical evaporation rates of less than 1.47 kg m⁻² h⁻¹ under 1 sun irradiation. Additionally, wastewater often has high salinity, and evaporators may experience salt crystallization on their surfaces and within water transport channels due to insufficient water supply and rapid vapor generation. These salt crystals inevitably increase light reflectance and block water transport channels, leading to reduced evaporation rates and shortened evaporator lifespans.  Moreover, SIE is highly dependent on sunlight, and its performance significantly declines or even ceases under conditions of low light intensity and temperature, such as cloudy days or winter, limiting its large-scale application.

 To overcome these limitations, Prof. Abudukeremu Kadier and Prof. Peng-Cheng Ma’s group at the Xinjiang Technical Institute of Physics and Chemistry (XTIPC) of the Chinese Academy of Sciences (CAS) has successfully developed an innovative basalt fabric-based photothermal interfacial PPY-CNTs-PDA@BF evaporator with SSM 304 electrothermal layer for all-weather efficient brackish water desalination. During the evaporation tests, a xenon lamp was employed to simulate solar radiation, while electrical input was provided by energy converted from solar panels and stored in a battery under low-light or no-light conditions. The evaporator was placed on an electronic balance to monitor changes in mass over time. Under simulated sunlight (1 sun) and 1.5 V in the laboratory, the evaporation rate of actual brackish water can reach 4.43 kg m⁻² h⁻¹; under real sunlight and 1.5 V outdoors, the evaporation rate can reach up to 6.37 kg m⁻² h⁻¹. Additionally, due to the well-designed multilayer structure with Janus hydrophilicity gradient distribution, the evaporator exhibits excellent salt resistance and long-term stability, maintaining a daytime evaporation rate above 2.17 kg m⁻² h⁻¹ during 120-hour continuous operation without any intervention. Purified water meets the drinking water standards set by the WHO, with significant reductions in ion concentrations and chemical oxygen demand. This study provides a promising approach for efficient and sustainable brackish water purification, offering potential applications in water-scarce regions.

 The research results have been recently published in the international journal Separation and Purification Technology. The Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, is the sole corresponding unit. Assistant researcher Ying-Lin He and Zhuo Chen are co-first author, and researchers Abudukeremu Kadier and Peng-Cheng Ma are the corresponding authors. The study was supported by several funding programs, including the Natural Science Foundation of Xinjiang Uygur Autonomous Region, National Foreign Young Talents Program-Department of Foreign Expert Services of the Ministry of Science and Technology, China, and the Western Light Project of the Chinese Academy of Sciences etc.

Figure 1. Illustration of real-world application scheme of the photo-electrothermal interfacial evaporation system with PPY-CNTs-PDA@BF evaporator.

Figure 2. Outdoor evaporation performance of PPY-CNTs-PDA@BF (A: Schematic diagram of the outdoor solar interface evaporation device; B: Solar irradiance and ambient temperature during the daytime; C: Evaporation rates of PPY-CNTs-PDA@BF at different times of the day).