Hydroxypropylmethyl Cellulose Modified with Carbon Dots Exhibits Light-Responsive and Reversible Optical Switching

Hofmeister Effect-Enhanced, Nanoparticle-Shielded, Thermally Stable Hydrogels for Anti-UV, Fast-Response, and All-Day-Modulated Smart Windows

Thermochromic smart windows offer energy-saving potential through temperature-responsive optical transmittance adjustments, yet face challenges in achieving anti-UV radiation, fast response, and high-temperature stability characteristics for long-term use. Herein, the rational design of Hofmeister effect-enhanced, nanoparticle-shielded composite hydrogels, composed of hydroxypropylmethylcellulose (HPMC), poly(N,N-dimethylacrylamide) (PDMAA), sodium sulfate, and polydopamine nanoparticles, for anti-UV, fast-response, and all-day-modulated smart windows is reported. Specifically, a three-dimensional network of PDMAA is created as the supporting skeleton, markedly enhancing the thermal stability of pristine HPMC hydrogels. Sodium sulfate induces a Hofmeister effect, lowering the lower critical solution temperature to 32 °C while accelerating phase transition rates fivefold (30 s vs. 150 s). Intriguingly, small-sized polydopamine nanoparticles simultaneously enable high luminous transmittance of 66.9% and outstanding anti-UV capability. Additionally, the smart window showcases a high solar modulation (51.2%) and maintains a 10.2 °C temperature reduction versus a glass window during all-day modulation applications. The design strategy is effective, opening up new avenues for manufacturing fast-response and durable thermochromic smart windows for energy savings and emission reduction.

Cellulose-based hydrogel simultaneously possessing solar and evaporative cooling performances for energy-saving window and personal thermal management

Thermochromic smart windows have been widely developed for building energy saving. However, most smart windows suffer from limited energy-saving performance, fixed phase transition temperature, and are not suitable for the temperature regulation needs of different application scenarios. Herein, a unique self-adaptive thermochromic hydrogel (HBPEC-PNA) with self-moisture-absorbing performance is reported that assembles solar energy cooling and evaporative heat dissipation. Importantly, the hydrogel shows excellent energy-saving performance by using the synergistic interaction of solar and evaporative cooling. The HBPEC-PNA hydrogel has an adjustable critical transition temperature (21.8-33.9 °C), a high solar modulation (ΔTsol = 78.90 %), and a high light transmittance (Tlum = 90.15 %). Interestingly, the hydrogel harvests water molecules from the surrounding air, enabling it to be directly used in circumstances without losing its ability to dynamically regulate solar energy transmission due to water loss. Furthermore, the indoor simulation experiments confirmed that the dual-cooling system can reduce 14.2 and 2.4 °C, respectively, compared to ordinary glass and conventional smart window. Dramatically, HBPEC-PNA hydrogel can be utilized to personal thermal management due to its superior cooling property. This work provides an attractive strategy that will contribute to the development of thermochromic materials with excellent temperature regulation ability.

Fast-Developing Dynamic Radiative Thermal Management: Full-Scale Fundamentals, Switching Methods, Applications, and Challenges

Rapid population growth in recent decades has intensified both the global energy crisis and the challenges posed by climate change, including global warming. Currently, the increased frequency of extreme weather events and large fluctuations in ambient temperature disrupt thermal comfort and negatively impact health, driving a growing dependence on cooling and heating energy sources. Consequently, efficient thermal management has become a central focus of energy research. Traditional thermal management systems consume substantial energy, further contributing to greenhouse gas emissions. In contrast, emergent radiant thermal management technologies that rely on renewable energy have been proposed as sustainable alternatives. However, achieving year-round thermal management without additional energy input remains a formidable challenge. Recently, dynamic radiative thermal management technologies have emerged as the most promising solution, offering the potential for energy-efficient adaptation across seasonal variations. This review systematically presents recent advancements in dynamic radiative thermal management, covering fundamental principles, switching mechanisms, primary materials, and application areas. Additionally, the key challenges hindering the broader adoption of dynamic radiative thermal management technologies are discussed. By highlighting their transformative potential, this review provides insights into the design and industrial scalability of these innovations, with the ultimate aim of promoting renewable energy integration in thermal management applications.

Low-Toxicity and High-Stability Fluorescence Sensor for the Selective, Rapid, and Visual Detection Tetracycline in Food Samples

With the development and improvement of analysis and detection systems, low-toxicity and harmless detection systems have received much attention, especially in the field of food detection. In this paper, a low-toxicity dual-emission molecularly imprinted fluorescence sensor (CdTe QDs@SiO2/N-CDs@MIPs) was successfully designed for highly selective recognition and visual detection of tetracycline (TC) in food samples. Specifically, the non-toxic blue-emission N-doped carbon dots (N-CDs) with high luminous performance acted as the response signals to contact TC via the covalent bond between amino and carboxyl groups. The red-emission CdTe quantum dots (CdTe QDs) were coated in silica nanospheres as stable reference signals, which effectively avoided the direct contact of CdTe QDs. Under optimum conditions, CdTe QDs@SiO2/N-CDs@MIPs had a rapid response within 1.0 min to TC, and the detection limit of CdTe QDs@SiO2/N-CDs@MIPs was calculated at 0.846 μM in the linear range of 0-140 μM. In complex environments, the CdTe QDs@SiO2/N-CDs@MIPs also exhibited excellent capabilities for the selective, rapid, and visual detection of TC. Furthermore, the accuracy of CdTe QDs@SiO2/N-CDs@MIPs to detect TC was verified by the HPLC method, and satisfactory results were obtained. Moreover, CdTe QDs@SiO2/N-CDs@MIPs showed a satisfactory recovery when measuring TC in milk and egg samples. This work provided an ideal approach for low-toxicity fluorescence sensor design and application.

Toughness and Thermoresponsive Hydrogel for Sandwich Smart Window with Adaptive Solar Modulation and Energy Saving

Thermochromic hydrogels with self-regulating solar transmittance are gaining increasing attention due to their significant potential in the fields of smart windows and energy conservation. Smart windows incorporating viscosity-tough hydrogels as an interlayer exhibit enhanced advantages in resisting external forces. In this study, a tough and thermoresponsive composite hydrogel was developed by incorporating poly(N-isopropylacrylamide) nanoparticles (PNIPAM NPs) and W-doped VO2 into a polyacrylamide-agar (PAM-Agar) double network hydrogel. Upon solar irradiation, thermochromism of PNIPAM NPs could regulate the visible light transmittance of the composite hydrogel and the photothermal effect of W-VO2 contributes to the optical regulation and NIR shielding. The smart window, with the composite hydrogel as an interlayer, demonstrates excellent optical modulation capabilities, with a luminous transmittance (Tum(20 °C)) of 86.81%, high light modulation (ΔTum = 78.89%), a high solar modulation (Tsol) of 83.59%, and a lower critical solution temperature (LCST) of 32.6 °C. The composite hydrogel's superior toughness (0.215 MJ/m3) also enhances the impact resistance of the smart window glass. Additionally, the adhesion between the hydrogel and the glass, with a maximum peeling force of up to 151 N/m (attributed to interactions between the amide groups and the silicon hydroxyl groups), was confirmed through a falling ball experiment. Moreover, the hydrogel exhibits a certain degree of thermal insulation, further promoting its utility in energy-saving applications. In conclusion, this study highlights the significant potential of such composite hydrogels in the development of smart windows for energy-efficient buildings.

Constructing a New Biomass-Based Bistatic Window for Solar Regulation

Smart windows effectively respond to the ever-changing climatic conditions, offering a smart solution for low-carbon buildings. However, current smart windows derived from chromic materials often have inferior solar modulation ability, or showcase high haze that obstructs outdoor views. Here, instead of developing new chromic materials, a new bistatic window is proposed for ultra-high solar modulation and luminous transmission. The new developed window can reduce the indoor surface temperature for ≈11 °C, and reduce the building space cooling and heating energy consumption by 30% to 40%, providing significant energy-related advances over traditional smart windows. In detail, the bistatic window exhibits excellent solar modulation ability (ΔTsol = 61%), high visible transmittance in both bleached (Tlum,bleached = 91%) and colored (Tlum,colored = 56%) states, low haze (< 1%), rapid switching response (switching time < 1 min), high color rendering index (CRI > 80), and long-cyclic stability after 1000 cycles. With the advantages of facile fabrication and scalability, it is foreseen the developed bistatic window holds promising prospect for the next-generation low-carbon buildings, paving a new way for future advancements in the fields of smart windows.

Use of Interfacial Interactions and Complexation of Carbon Dots to Construct Ultra-Robust and Efficient Photothermal Film From Micro-Carbonized Polysaccharides

Solar energy conversion technologies, particularly solar-driven photothermal conversion, are both clean and manageable. Although much progress has been made in designing solar-driven photothermal materials, significant challenges remain, not least the photobleaching of organic dyes. To tackle these issues, micro-carbonized polysaccharide chains, with carbon dots (CDs) suspended from the chains, are conceived, just like grapes or tomatoes hanging from a vine. Carbonization of sodium carboxymethyl cellulose (CMC) produces just such a structure (termed CMC-g-CDs), which is used to produce an ultra-stable, robust, and efficient solar-thermal film by interfacial interactions within the CMC-g-CDs. The introduction of the CDs into the matrix of the photothermal material effectively avoided the problem of photobleaching. Manipulating the interfacial interactions (such as electrostatic interactions, van der Waals interactions, π-π stacking, and hydrogen bonding) between the CDs and the polymer chains markedly enhances the mechanical properties of the photothermal film. The CMC-g-CDs are complexed with Fe3+ to eliminate leakage of the photothermal reagent from the matrix and to solve the problem of poor water resistance. The resulting film (CMC-g-CDs-Fe) has excellent prospects for practical application as a photothermal film.

Energy-Efficient Smart Window Based on a Thermochromic Hydrogel with Adjustable Critical Response Temperature and High Solar Modulation Ability

Thermochromic smart windows realize an intelligent response to changes in environmental temperature through reversible physical phase transitions. They complete a real-time adjustment of solar transmittance, create a livable indoor temperature for humans, and reduce the energy consumption of buildings. Nevertheless, conventional materials that are used to prepare thermochromic smart windows face challenges, including fixed transition temperatures, limited solar modulation capabilities, and inadequate mechanical properties. In this study, a novel thermochromic hydrogel was synthesized from 2-hydroxy-3-butoxypropyl hydroxyethyl celluloses (HBPEC) and poly(N-isopropylacrylamide) (PNIPAM) by using a simple one-step low-temperature polymerization method. The HBPEC/PNIPAM hydrogel demonstrates a wide response temperature (24.1-33.2 °C), high light transmittance (Tlum = 87.5%), excellent solar modulation (ΔTsol = 71.2%), and robust mechanical properties. HBPEC is a functional material that can be used to adjust the lower critical solution temperature (LCST) of the smart window over a wide range by changing the degree of substitution (DS) of the butoxy group in its structure. In addition, the use of HBPEC effectively improves the light transmittance and mechanical properties of the hydrogels. After 100 heating and cooling cycles, the hydrogel still has excellent stability. Furthermore, indoor simulation experiments show that HBPEC/PNIPAM hydrogel smart windows have better indoor temperature regulation capabilities than traditional windows, making these smart windows potential candidates for energy-saving building materials.

Enhanced Photothermal Effect Assisted by Resonance Energy Transfer in Carbon/Covellite Core-Shell Nanoparticles toward a High-Performance Interfacial Water Evaporation Process

Carbon and semiconductor nanoparticles are promising photothermal materials for various solar-driven applications. Inevitable recombination of photoinduced charge carriers in a single constituent, however, hinders the realization of a greater photothermal effect. Core-shell heterostructures utilizing the donor-acceptor pair concept with high-quality interfaces can inhibit energy loss from the radiation relaxation of excited species, thereby enhancing the photothermal effect. Here, core-shell structures composed of a covellite (CuS) shell (acceptor) and spherical carbon nanoparticle (CP) core (donor) (abbreviated as CP/CuS) are proposed to augment the photothermal conversion efficiency via the Förster resonance energy transfer (FRET) mechanism. The close proximity and spectral overlap of the donor and acceptor trigger the FRET mechanism, where the electronic excitation relaxation energy of the CP reinforces the plasmonic resonance and near-infrared absorption in CuS, resulting in boosting the overall photothermal conversion efficiency. CP/CuS core-shell coated on polyurethane (PU) foam exhibits a total solar absorption of 97.1%, leading to an elevation in surface temperature of 61.6 °C in dry conditions under simulated solar illumination at a power density of 1 kW m-2 (i.e., 1 sun). Leveraging the enhanced photothermal conversion emanated from the energy transfer effect in the core-shell structure, CP/CuS-coated PU foam achieves an evaporation rate of 1.62 kg m-2 h-1 and an energy efficiency of 93.8%. Thus, amplifying photothermal energy generation in core-shell structures via resonance energy transfer can be promising in solar energy-driven applications and thus merits further exploration.

Facile synthesis of nitrogen-doped carbon dots as sensitive fluorescence probes for selective recognition of cinnamaldehyde and l-Arginine/l-Lysine in living cells

The disorder of amino acid metabolism and the abuse of small molecule drugs pose serious threats to public health. However, due to the limitations of existing detection technologies in sensing cinnamaldehyde (CAL) and l-Arginine/l-Lysine (l-Arg/l-Lys), there is an urgent need to develop new sensing strategies to meet the severe challenges currently facing. Herein, nitrogen-doped carbon dots (N-CDs) were developed using a simple one-pot hydrothermal carbonization method. These N-CDs exhibited numerous distinctive characteristics such as excellent photoluminescence, high water dispersibility, favorable biocompatibility, and superior chemical inertness. Strikingly, the as-prepared CDs as a highly efficient fluorescent probe possessed significant sensitivity and selectivity toward CAL and l-Arg/l-Lys over other analytes with a low detection limit of 58 nM and 16 nM/18 nM, respectively. The fluorescence of N-CDs could be quenched by CAL through an electron transfer process. Then, the strong electrostatic interaction between l-Arg/l-Lys and N-CDs induced the efficient fluorescence recovery. More importantly, the outstanding biosafety and excellent analyte-responsive fluorescence characteristics of N-CDs have also been verified in living cells as well as in serum and urine. Overall, the N-CDs had a wide application prospect in the diagnosis of amino acid metabolic diseases and small molecule drug sensing.

Thermo-Responsive Poly(N-isopropylacrylamide)/Hydroxypropylmethyl Cellulose Hydrogel with High Luminous Transmittance and Solar Modulation for Smart Windows

Thermochromic smart windows are considered to be promising energy-saving devices for reducing energy consumption in buildings. The ideal materials for thermochromic smart windows should have high transmittance, high solar modulation, low phase-transition temperature, and excellent high-temperature thermal stability, which are difficult to achieve simultaneously. This work reports a simple one-step low-temperature polymerization method to prepare a thermo-responsive poly(N-isopropylacrylamide)/hydroxypropylmethyl cellulose (PNIPAM/HPMC) hydrogel achieving the above performances simultaneously. The low-temperature polymerization environment endowed the hydrogel with a high luminous transmittance (T_lum) of 90.82%. HPMC as a functional material effectively enhanced the mechanical properties and thermal stability of the hydrogel. Meanwhile, the PNIPAM/HPMC hydrogel showed a low phase-transition temperature (∼32 °C) and high solar modulation (ΔT_sol = 81.52%), which proved that it is an ideal material for thermochromic smart windows. Moreover, a PNIPAM/HPMC smart window exhibited high light transmittance (T_380-760 = 86.27%), excellent light modulation (ΔT₃₆₅ = 74.27%, ΔT_380-760 = 86.17%, and ΔT₉₄₀ = 63.93%), good indoor temperature regulation ability and stability, which indicated that it was an attractive candidate for application in reducing energy consumption in buildings. This work also provides an option and direction for modifying PNIPAM-based thermochromic smart windows.

Thermochromic Smart Windows Assisted by Photothermal Nanomaterials

Thermochromic smart windows are optical devices that can regulate their optical properties actively in response to external temperature changes. Due to their simple structures and as they do not require other additional energy supply devices, they have great potential in building energy-saving. However, conventional thermochromic smart windows generally have problems with high response temperatures and low response rates. Owing to their great effect in photothermal conversion, photothermal materials are often used in smart windows to assist phase transition so that they can quickly achieve the dual regulation of light and heat at room temperature. Based on this, research progress on the phase transition of photothermal material-assisted thermochromic smart windows is summarized. In this paper, the phase transition mechanisms of several thermochromic materials (VO₂, liquid crystals, and hydrogels) commonly used in the field of smart windows are introduced. Additionally, the applications of carbon-based nanomaterials, noble metal nanoparticles, and semiconductor (metal oxygen/sulfide) nanomaterials in thermochromic smart windows are summarized. The current challenges and solutions are further indicated and future research directions are also proposed.