Weixin Guan’s research while affiliated with University of Texas at Austin and other places

Solar-driven atmospheric water harvesting (AWH) presents a sustainable approach for freshwater production with sunlight as the sole energy input. To address challenges posed by diurnal moisture variations and diffusive sunlight, we present a system-wide approach that synergistically enhances moisture capture and solar energy utilization in an integrated water harvester. Moisture utilization at the bulk sorbent scale is improved through the hierarchical pore structure of scalable biomass gel sheets enabling rapid regeneration and is further upscaled to system-level performance through a kinetics-matched, continuously multicyclic operation protocol in a multilayered device. Solar energy utilization is enhanced by thermoresponsive hydrogels that lower the energy threshold for water desorption and by efficient thermal and mass flow management that increases energy efficiency. Our system delivers up to 235.09 mL d ⁻¹ of water with an energy efficiency as high as 26.4%, excluding solar panel power. This work offers an insight into developing energy-, material-, and space-efficient AWH systems from a cross-scale understanding of sorbent properties, device engineering, and operation protocol tailoring.

The growing global population, coupled with increasing food demand and water scarcity, has intensified the need for advancements in modern agriculture. As an emerging class of materials featured by intensively tunable properties, smart hydrogels offer innovative solutions to challenges associated with conventional agricultural practices, such as excessive agrochemical and water use and inefficiencies that contribute to environmental degradation. Additionally, hydrogel‐based sensors can monitor environmental conditions and crop health, enabling precise adjustments to optimize growth and resource use. By serving as platforms for the slow and controlled delivery of agrochemicals and smart sensors, hydrogel systems can enhance resource efficiency, reduce labor demands, and improve crop yields in an environmentally sustainable manner. This Perspective article summarizes recent advancements in hydrogel‐based materials, highlights existing challenges, and proposes potential research directions, with a focus on developing advanced hydrogel systems to transform agricultural practices. image

Atmospheric water harvesting (AWH) offers a promising pathway to alleviate global water scarcity, highlighting the need for environmentally responsible sorbent materials. In this context, this research introduces a universal strategy for transforming natural polysaccharides into effective hydrogel sorbents, demonstrated with cellulose, starch, and chitosan. The methodology unites alkylation to graft thermoresponsive groups, thereby enhancing water processability and enabling energy‐efficient water release at lower temperatures, with the integration of zwitterionic groups to ensure stable and effective water sorption. The molecularly functionalized cellulose hydrogel, exemplifying our approach, shows favorable water uptake of 0.86–1.32 g g⁻¹ at 15–30% relative humidity (RH), along with efficient desorption, releasing 95% of captured water at 60 °C. Outdoor tests highlight the water production rate of up to 14.19 kg kg⁻¹ day⁻¹ by electrical heating. The proposed molecular engineering methodology, which expands the range of raw materials by leveraging abundant biomass feedstock, has the potential to advance sorbent production and scalable AWH technologies, contributing to sustainable solutions.

Given the growing emphasis on energy efficiency, environmental sustainability, and agricultural demand, there’s a pressing need for decentralized and scalable ammonia production. Converting nitrate ions electrochemically, which are commonly found in industrial wastewater and polluted groundwater, into ammonia offers a viable approach for both wastewater treatment and ammonia production yet limited by low producibility and scalability. Here we report a versatile and scalable solution-phase synthesis of high-entropy single-atom nanocages (HESA NCs) in which Fe and other five metals-Co, Cu, Zn, Cd, and In-are isolated via cyano-bridges and coordinated with C and N, respectively. Incorporating and isolating the five metals into the matrix of Fe resulted in Fe-C5 active sites with a minimized symmetry of lattice as well as facilitated water dissociation and thus hydrogenation process. As a result, the Fe-HESA NCs exhibited a high selectivity toward NH3 from the electrocatalytic reduction of nitrate with a Faradaic efficiency of 93.4% while maintaining a high yield rate of 81.4 mg h⁻¹ mg⁻¹.

Atmospheric water harvesting (AWH) is recognized as a crucial strategy to address the global challenge of water scarcity by tapping into the vast reserves of atmospheric moisture for potable water supply. Within this domain, sorbents lie in the core of AWH technologies as they possess broad adaptability across a wide spectrum of humidity levels, underpinned by the cyclic sorption and desorption processes of sorbents, necessitating a multi-scale viewpoint regarding the rational material and chemical selection and design. This Invited Review delves into the essential sorption mechanisms observed across various classes of sorbent systems, emphasizing the water-sorbent interactions and the progression of water networks. A special focus is placed on the insights derived from isotherm profiles, which elucidate sorbent structures and sorption dynamics. From these foundational principles, we derive material and chemical design guidelines and identify key tuning factors from a structural-functional perspective across multiple material systems, addressing their fundamental chemistries and unique attributes. The review further navigates through system-level design considerations to optimize water production efficiency. This review aims to equip researchers in the field of AWH with a thorough understanding of the water-sorbent interactions, material design principles, and system-level considerations essential for advancing this technology.

Bistable electrochromic (EC) materials and systems offer significant potential for building decarbonization through their optical modulation and energy efficiency. However, challenges such as limited design strategies and bottlenecks in cost, fabrication, and color have hindered the full commercialization of energy‐saving EC windows and displays, with few materials achieving true bistability. Herein, a novel strategy for designing bistable electrochromic materials is proposed by leveraging supramolecular interactions. These interactions facilitate reversible color transitions, stabilize the colored structure, and enable spatial confinement to inhibit diffusion, thereby achieving bistable electrochromism. The mechanisms and materials underlying these unconventional electrochromic systems are substantiated through detailed characterization. This strategy enables the preparation of low‐cost and sustainable transparent electrochromic displays with high performance. Notably, the display information remains clearly visible for more than 2 h without consuming energy. Involving biomass materials and removable device structures also enhances the sustainability and scalability of EC technology applications and development. These results demonstrate the crucial role of supramolecular chemistry in the development of cutting‐edge materials for applications such as energy‐saving smart windows.

Electrochromic (EC) displays with electronically regulating the transmittance of solar radiation offer the opportunity to increase the energy efficiency of the building and electronic products and improve the comfort and lifestyle of people. Despite the unique merit and vast application potential of EC technologies, long-awaited EC windows and related visual content displays have not been fully commercialized due to unsatisfactory production cost, durability, color, and complex fabrication processes. Here we develop a unique EC strategy and system based on the natural host and guest interactions to address the above issues. A completely reusable and sustainable EC device has been fabricated with potential advantages of extremely low cost, ideal user-/environment friendly property, and excellent optical modulation, which is benefited from the extracted biomass EC materials and reusable transparent electrodes involved in the system. The as-prepared EC window and nonemissive transparent display also show comprehensively excellent properties: high transmittance change (>85%), broad spectra modulation covering Ultraviolet (UV), Visible (Vis) to Infrared (IR) ranges, high durability (no attenuation under UV radiation for more than 1.5 mo), low open voltage (0.9 V), excellent reusability (>1,200 cycles) of the device’s key components and reversibility (>4,000 cycles) with a large transmittance change, and pleasant multicolor. It is anticipated that unconventional exploration and design principles of dynamic host–guest interactions can provide unique insight into different energy-saving and sustainable optoelectronic applications.

Emerging organic contaminants in water matrices have challenged ecosystems and human health safety. Persulfate‐based advanced oxidation processes (PS‐AOPs) have attracted much attention as they address potential water purification challenges. However, overcoming the mass transfer constraint and the catalyst's inherent site agglomeration in the heterogeneous system remains urgent. Herein, the abundant metal‐anchored loading (≈6–8 g m⁻²) of alginate hydrogel membranes coupled with cross‐flow mode as an efficient strategy for water purification applications is proposed. The organic flux of the confined hydrogel interfaces sharply enlarges with the reduction of the thickness of the boundary layer via the pressure field. The normalized property of the system displays a remarkable organic (sulfonamides) elimination rate of 4.87 × 10⁴ mg min⁻¹ mol⁻¹. Furthermore, due to the fast reaction time (<1 min), cross‐flow mode only reaches a meager energy cost (≈2.21 Wh m⁻³) under the pressure drive field. It is anticipated that this finding provides insight into the novel design with ultrafast organic removal performance and low techno‐economic cost (i.e., energy operation cost, material, and reagent cost) for the field of water purification under various PS‐AOPs challenging scenarios.

Water scarcity is a pressing global issue, requiring innovative solutions such as atmospheric water harvesting (AWH), which captures moisture from the air to provide potable water to many water-stressed areas. Thermoresponsive hydrogels, a class of temperature-sensitive polymers, demonstrate potential for AWH as matrices for hygroscopic components like salts predominantly due to their relatively energy-efficient desorption properties compared to other sorbents. However, challenges such as limited swelling capacity due to the salting-out effect and difficulty in more complete water release hinder the effectiveness of conventional hydrogel sorbents. To overcome these limitations, we introduce molecularly confined hydration in thermoresponsive hydrogels by employing a bifunctional polymeric network composed of hygroscopic zwitterionic moieties and thermoresponsive moieties. Here, we show that this approach ensures stable water uptake, enables water release at relatively low temperatures, and exhibits rapid sorption–desorption kinetics. Furthermore, by incorporating photothermal absorbers, the sorbent can achieve solar-driven AWH with comparable water release performance. This work advances the design of AWH sorbents by introducing molecularly confined hydration in thermoresponsive hydrogels, leading to a more efficient and sustainable approach to water harvesting. Our findings offer a potential solution for advanced sorbent design with comprehensive performance to mitigate the freshwater crisis.