Construction of a Robust Radiative Cooling Emitter for Efficient Food Storage and Transportation.

Nowadays, food safety is still facing great challenges. During storage and transportation, perishable goods have to be kept at a low temperature. However, the current logistics still lack enough preservation ability to maintain a low temperature in the whole. Hence, considering the temperature fluctuation in logistics, in this work, the passive radiative cooling (RC) technology was applied to package to enhance the temperature control capability in food storage and transportation. The RC emitter with selective infrared emission property was fabricated by a facile coating method, and Al2O3 was added to improve the wear resistance. The sunlight reflectance and infrared emittance within atmospheric conditions could reach up to 0.92 and 0.84, respectively. After abrasion, the sunlight reflection only decreased by 0.01, and the infrared emission showed a negligible change, revealing excellent wear resistance. During outdoor measurement, the box assembled by RC emitters (RC box) was proved to achieve temperature drops of ∼9 and ∼4 °C compared with the corrugated box and foam box, respectively. Besides, the fruits stored in the RC box exhibited a lower decay rate. Additionally, after printing with patterns to meet the aesthetic requirements, the RC emitter could also maintain the cooling ability. Given the superior optical properties, wear resistance, and cooling capability, the emitter has great potential for obtaining a better temperature control ability in food storage and transportation.

Mechanically Switchable Multifunctional Device for Regulating Passive Radiative Cooling and Solar Heating.

Energy consumption during cooling and heating poses a great threat to the development of society. Thermal regulation, as switchable cooling and heating in a single platform, is therefore urgently demanded. Herein, a switchable multifunctional device integrating heating, cooling, and latent energy storage was proposed for temperature regulation and window energy saving for buildings. A radiative cooling (RC) emitter, a phase-change (PC) membrane, and a solar-heating (SH) film were connected layer by layer to form a sandwich structure. The RC emitter exhibited selective infrared emission (emissivity in the atmospheric window: 0.81, emissivity outside the atmospheric window: 0.39) and a high solar reflectance (0.92). Meanwhile, the SH film had a high solar absorptivity (0.90). More importantly, both the RC emitter and the SH film displayed excellent wear resistance and UV resistance. The PC layer can control the temperature at a steady state under dynamic weather conditions, which could be verified by indoor and outdoor measurements. The thermal regulation performance of the multifunctional device was also verified by outdoor measurements. The temperature difference between the RC and SH models of the multifunctional device could reach up to 25 °C. The as-constructed switchable multifunctional device is a promising candidate for alleviating the cooling and heating energy consumption and realizing energy saving for windows.

Low-Energy Photons Dual Harvest for Photocatalytic Hydrogen Evolution: Bimodal Surface Plasma Resonance Related Synergism of Upconversion and Pyroelectricity.

Utilization of low-energy photons for efficient photocatalysis remains a challenging pursuit. Herein, a strategy is reported to boost the photocatalytic performance, by promoting low-energy photons dual harvest through bimodal surface plasmon resonance (SPR)-enhanced synergistically upconversion and pyroelectricity. It is achieved by introducing triplet-triplet annihilation upconversion (TTA-UC) materials and plasmonic material (Au nanorods, AuNRs) into composite fibers composed of pyroelectric substrate (poly(vinylidene fluoride)) and photocatalyst Cd0.5 Zn0.5 S. Interestingly, the dual combination of TTA-UC and AuNRs SPR in the presence of polyvinylidene fluoride substrate with pyroelectric property promotes the photocatalytic hydrogen evolution performance by 2.88 folds with the highest average apparent quantum yield of 7.0% under the low-energy light (λ > 475 nm), which far outweighs the role of separate application of TTA-UC (34%) and AuNRs SPR (76%). The presence of pyroelectricity plays an important role in the built-in electric field as well as the accordingly photogenerated carrier behavior in the composite photocatalytic materials, and the pyroelectricity can be affected by AuNRs with different morphologies, which is proved by the Kelvin probe force microscopy and photocurrent data. This work provides a new avenue for fully utilizing low-energy photons in the solar spectrum for improving photocatalytic performance.

Effects of Ligands in Rare Earth Complex on Properties, Functions, and Intelligent Behaviors of Polyurea-Urethane Composites.

There is a need to create next-generation polymer composites having high property, unique function, and intelligent behaviors, such as shape memory effect (SME) and self-healing (SH) capability. Rare earth complexes can provide luminescence for polymers, and their dispersion is highly affected by ligand structures. Here, we created three different REOCs with different ligands before studying the effects of ligands on REOC dispersion in polyurea-urethane (PUU) with disulfide bonds in main chains. In addition, the effects of different REOCs on mechanical properties, luminescent functions, and intelligent behaviors of PUU composites were studied. The results showed that REOC I (Sm(TTA)3phen: TTA, thenoyltrifluoroacetone; phen, 1,10-phenanthroline) has incompatible ligands with the PUU matrix. REOC I and REOC III (Sm(BUBA)3phen: BUBA, 4-benzylurea-benzoic acid) with amine and urea groups facilitate their dispersion. It was REOC III that helped the maintenance of mechanical properties of PUU composites due to the good dispersion and the needle-like morphologies. Due to more organic ligands of REOC III, the fluorescence intensity of composite materials is reduced. The shape recovery ratio of the composite was not as good as that of pure PUU when a large amount of fillers was added. Besides, REOC I reduced the self-healing efficiency of PUU composites due to poor dispersion, and the other two REOCs increased the self-healing efficiency. The results showed that ligands in REOCs are important for their dispersion in the PUU matrix. The poor dispersion of REOC I is unbeneficial for mechanical properties and intelligent behavior. The high miscibility of REOC II (Sm(PABA)3phen: PABA, 4-aminobenzoic acid) decreases mechanical properties as well but ensures the good shape recovery ratio and self-healing efficiency. The mediate miscibility and needle-like morphology of REOC III are good for mechanical properties. The shape recovery ratio, however, was decreased.

Design of robust superamphiphobic surfaces with enlarged area fractions: the considerable role of Laplace pressure in dynamics of contact lines.

Superamphiphobic surfaces have attracted widespread attention because of their great potential for applications in biotechnology, optoelectronics, water/oil separation, etc. Re-entrant curvatures are widely reported to provide a metastable Cassie state for superamphiphobicity. For high contact angles, re-entrant surfaces with a small area fraction (f) are designed according to the Cassie equation. However, this will make the surfaces take high local pressures under a mechanical force and thus suffer from frangibility. Robustness and high repellency are seemingly mutually exclusive. Herein, contrary to Cassie's equation, we show that high contact angles (>150°) with a large f (69.4%) of water and oleic acid can be achieved by utilizing a large upward Laplace pressure with narrow and parallel channel geometries. We deeply studied the effect of Laplace pressure on superamphiphobicity and suppose that the larger upward Laplace pressure stops the droplet earlier and pins the contact line at a higher position, providing a higher contact angle. The similar effect of viscous force well supports our explanation. These findings enable us to obtain robust and durable superamphiphobic surfaces with an enlarged area fraction and simple re-entrant microstructures. Our work may open up design strategies for robust superamphiphobic surfaces with practical applications.

Efficient photocatalytic H2production realized by MnxCd1-xSeIn situheterojunction.

Fast recombination of photoinduced carriers inhibits the performance of photocatalysts. By constructing heterojunctions, built-in electric fields can be formed to separate electrons and holes and finally enhance the photocatalytic efficiency. Herein, a MnxCd1-xSein situheterojunction was fabricated by a facile solvothermal method to draw upon this advantage. Absorption spectra show that the light absorption of CdSe raises up obviously after the doping of Mn2+. Best performance was achieved when the doping percent of Mn2+was 50%. This Mn0.5Cd0.5Se sample exhibits a 7.2 folds increase in hydrogen evolution against pure CdSe owing to the fast electron transportation. Moreover, it proves well stability in an 18 h cycling test and gains a 6.7% apparent quantum yield under 420 nm light. In summary, this work constructs anin situheterojunction to enhance the photocatalytic hydrogen evolution efficiency and sheds light on a feasible way for the application of photocatalysis.

Crystallinity and ß Phase Fraction of PVDF in Biaxially Stretched PVDF/PMMA Films.

Polyvinylidene fluoride (PVDF) and poly(methyl methacrylate) (PMMA) blend films were prepared using biaxial stretching. The effects of PMMA content and stretching ratio on the crystallinity and ß phase fraction of PVDF in blend films were investigated. The distributions of crystallinity and ß phase fraction on variable locations were also studied. The results of FTIR and XRD showed that ß phase appeared in PVDF/PMMA blends after extrusion and casting procedures. Although ß phase fraction decreased after preheating, there was still an increasing trend during following biaxial stretching. More importantly, the increase in PMMA content improved ß phase fraction, and the highest ß phase fraction of 93% was achieved at PMMA content of 30 wt% and stretching ratio of 2×2. Besides, the reduction in PMMA content and the increase in stretching ratio improved the crystallinity of PVDF. The mechanical properties of the stretched films were significantly improved by increasing the stretching ratio as well. The uniform stress distribution on different regions of biaxial stretching films contributed to the uniform distribution of ß phase fraction and crystallinity of PVDF with the aid of simulation. This work confirmed that biaxial stretching can be a candidate method to prepare PVDF/PMMA blend films with uniform distributions of comparable ß phase and crystallinity of PVDF.

Interfacial Design to Enhance Photocatalytic Hydrogen Evolution via Optimizing Energy and Mass Flows.

Energy and mass transfer in photocatalytic systems plays a significant role in photocatalytic water splitting, but relevant research has long been ignored. Here, an interfacial photocatalytic mode for photocatalytic hydrogen production is exploited to optimize the energy and mass flows and mainly includes a heat-insulating layer, a water-channel layer, and a photothermal photocatalytic layer. In this mode, the energy flow is optimized for efficient spreading, conversion, and utilization. A low-loss path (ultrathin water film) and an efficient heat localized zone are constructed, where light energy, especially infrared-light energy, can transfer to the target functional membrane surface with low loss and the thermal energy converted from light can be localized for further use. Meanwhile, the optimization of the mass flow is achieved by improving the desorption capacity of the products. The generated hydrogen bubbles can rapidly leave from the surface of the photocatalyst, along with the active sites being released timely. Consequently, the photocatalytic hydrogen production rate can be increased up to about 6.6 times that in a conventional photocatalytic mode. From the system design aspect, this work provides an efficient strategy to improve the performance of photocatalytic water splitting by optimizing the energy and mass flows.

Sustainable Internal Electric Field for Enhanced Photocatalysis: From Material Design to Energy Utilization.

The intrinsic internal electric field in a ferroelectric photocatalyst is beneficial for improving the photocatalytic properties because of its positive effect on the separation and migration of photogenerated carriers. However, this kind of internal electric field is static and easily saturated by inner and outer shielding effects, seriously restricting its potential in photocatalysis. To overcome this problem, a sustainable internal electric field was introduced into photocatalysis based on piezoelectric and pyroelectric effect, which exhibits good capability in consistently boosting photocatalytic activity, thus becoming a hot research topic. In this Perspective we summarize the recent significant progress in the construction of sustainable internal electric fields for facilitating photocatalysis from material design to energy utilization. Moreover, the fascinating influence of sustainable internal electric fields on carrier behavior is also discussed. Finally, a summary and outlook for building a sustainable internal electric field to further enhance photocatalytic performance are provided.

A Pragmatic Device Based on a Double-Sided Functional Structure for Efficient Water Harvesting.

Water collection from fog has received much attention to meet the challenges of scarcity of clean drinking water in desert and arid regions. Currently, solar-thermal technology is being used as an efficient, sustainable, and low-cost method for water desalination to produce clean water. To collect the clean water, in recent years, most researchers have designed the structure of water collection surfaces. However, the heat released during the liquefaction process of droplets has an adverse effect on the condensation of droplets, and thus affecting the water collection efficiency. Here, in order to improve water collection efficiency, a radiative cooling layer is introduced on the back of the collection surface to dissipate the heat released during droplet liquefaction. The radiative cooling layer, consisting of poly(vinylidene fluoride-co-hexafluoropropene) embedded with SiO2 and CaMoO4 nanoparticles, can theoretically cool 18.1 °C below the ambient temperature in the daytime. With the addition of cooling coating on the back of the water collection surface, the water harvesting efficiency can be increased by 43-52%. The developed water harvesting device may provide a new pathway to the efficient collection of fresh water.

Near-Infrared Light-Induced Sequential Shape Recovery and Separation of Assembled Temperature Memory Polymer Microparticles.

Light-induced, shape-changing polymeric microparticles have many applications. Here, the near-infrared (NIR)-light-triggered sequential recovery and separation of assembled large and small polymer microparticles using cross-linked blends of poly(ethylene-vinyl acetate) and trans-polyisoprene as temperature memory polymers as well as two NaYF4 based up-conversion nanoparticles (UCPs) to provide luminescent and photothermal effects are reported. Under irradiation of NIR light with a low light power density, small particles assembled onto the compressed large one recover first due to the low switching temperature (Tsw ) arising from the temperature-memory effect. The small particles can separate from the underlying large particle in flowing aqueous media. The recovery of the large particle occurs at a high power density. Two UCPs of NaYF4 : 20Yb, 0.2Tm, 5Gd and NaYF4 : 18Yb, 2Er, 5Gd facilitate the detection of small and large microparticles via providing blue and green light emissions, respectively. This work can expand the applications of light-induced shape-changing polymer microparticles in the biomedical field, controlled catalysis, microfluidic devices, and so on.

Construction of Infrared-Light-Responsive Photoinduced Carriers Driver for Enhanced Photocatalytic Hydrogen Evolution.

Infrared light, more than 50% of the solar light energy, is long-termly ignored in the photocatalysis field due to its low photon energy. Herein, infrared-light-responsive photoinduced carriers driver is first constructed taking advantage of pyroelectric effect for enhancing photocatalytic hydrogen evolution. In order to give full play to its role, the photocatalytic reaction is localized on the surface and interface of the composite based on a new semi-immersion type heat collected photocatalytic microfiber system. The system is consisted of distinctive pyroelectric substrate poly(vinylidene fluoride-co-hexafluropropylene (PVDF-HFP), typical photothermal material carbon nanotube (CNT), and representative photocatalyst CdS. The transient photocurrent, electrochemical impedance spectroscopy, time-resolved photoluminescence and pyroelectric potential characterizations indicate that the infrared-light-responsive carriers driver significantly promotes the photogenerated charge separation, accelerates carrier migration, and prolongs carrier lifetime. The photocatalytic hydrogen evolution efficiency is remarkably improved more than five times with the highest average apparent quantum yield of 16.9%. It may open up new horizons to photocatalytic technology for the more efficient use of infrared light.

Effect of Different Aluminum Substitution Rates on the Structure of Tobermorite.

Tobermorite and Al-substituted tobermorite with varying Al/(Si + Al) molar ratios were synthesized via the static hydrothermal method. The effect of different Al substitution ratios on the structure of tobermorite was investigated by XRD, SEM-EDS, TG-DSC, FT-IR, 29Si, and 27Al MAS-NMR. The interplanar crystal spacing of (002) increased with the increment of the Al substitution ratio. The maximum ratio of the Al substitution for Si in the structure of tobermorite was about 15 at %, which was limited by the compositions of tobermorite and the electrostatic repulsive forces caused by Al substitution. The DSC curve of the tobermorite with an Al/(Al + Si) molar ratio of 0.15 showed a larger exothermic peak area at 850 °C, indicating that the Al-O-Si bond was formed in the structure of tobermorite and the Al participated in the recrystallization. The 29Si and 27Al MAS-NMR results confirmed that tetrahedral Al was introduced into the structure of the tobermorite. New silicon sites, Q2(1Al) and Q3(1Al), formed by the Al substitution for Si in bridging and non-bridging sites, were detected. Compared to the tobermorite without Al substitution, the adsorption capacity of Al-substituted tobermorite with Al/(Al + Si) = 0.15 to Na+ was improved by 44%.

A Pragmatic Bilayer Selective Emitter for Efficient Radiative Cooling under Direct Sunlight.

Radiative cooling can make the selective emitter cool below ambient temperature without any external energy. Recent advances in photonic crystal and metamaterial technology made a high-efficiency selective emitter achievable by precisely controlling the emitter's Infrared emission spectrum. However, the high cost of the photonic crystals and meta-materials limit their application. Herein, an efficient bilayer selective emitter is prepared based on the molecular vibrations of functional nanoparticles. By optimizing the volume fraction of the functional nanoparticles, the bilayer selective emitter can theoretically cool 36.7 °C and 25.5 °C below the ambient temperature in the nighttime and daytime, respectively. Such an efficient cooling performance is comparable with the published photonic crystal and metamaterial selective emitters. The rooftop measurements show that the bilayer selective emitter is effective in the ambient air even under direct sunlight. The relatively low cost and excellent cooling performance enable the bilayer selective emitter to have great potential for a practical purpose.

Microstructural Properties of Cement Paste and Mortar Modified by Low Cost Nanoplatelets Sourced from Natural Materials.

Nanomaterials have been widely used in cement-based materials. Graphene has excellent properties for improving the durability of cement-based materials. Given its high production budget, it has limited its wide potential for application in the field of engineering. Hence, it is very meaningful to obtain low cost nanoplatelets from natural materials that can replace graphene nanoplatelets (GNPs) The purpose of this paper is to improve the resistance to chloride ion penetration by optimizing the pore structure of cement-based materials, and another point is to reduce investment costs. The results illustrated that low cost CaCO3 nanoplatelets (CCNPs) were successfully obtained under alkali treatment of seashell powder, and the chloride ion permeability of cement-based materials significantly decreased by 15.7% compared to that of the control samples when CCNPs were incorporated. Furthermore, the compressive strength of cement pastes at the age of 28 days increased by 37.9% than that of the plain sample. Improvement of performance of cement-based materials can be partly attributed to the refinement of the pore structure. In addition, AFM was employed to characterize the nanoplatelet thickness of CCNPs and the pore structures of the cement-based composites were analyzed by MIP, respectively. CCNPs composite cement best performance could lay the foundation for further study of the durability of cement-based materials and the application of decontaminated seashells.

Near-Infrared Light and Solar Light Activated Self-Healing Epoxy Coating having Enhanced Properties Using MXene Flakes as Multifunctional Fillers.

Two issues are required to be solved to bring intrinsically self-healing polymer coatings into real applications: remote activation and satisfied practical properties. Here, we used MXene, a newly reported two-dimensional material, to provide an epoxy coating with light-induced self-healing capabilities and we worked to enhance the properties of that coating. The self-healing coatings had a reversible crosslinking network based on the Diels-Alder reaction among maleimide groups from bis(4-maleimidopheny)methane and dangling furan groups in oligomers that were prepared through the condensation polymerization of diglycidylether of bisphenol A and furfurylamine. The results showed that the delaminated MXene flakes were small in size, around 900 nm, and dispersed well in self-healing coatings. The MXene flakes of only 2.80 wt % improved greatly the pencil hardness of the coating hardness from HB to 5H and the polarization resistance from 4.3 to 428.3 MΩ cm-2. The self-healing behavior, however, was retarded by MXene flakes. Leveling agent acted a key part here to facilitate the gap closure driven by reverse plasticity to compensate for the limitation of macromolecular mobility resulting from the MXene flakes. The self-healing of coatings was achieved in 30 s by thermal treatment at 150 °C. The efficient self-healing was also demonstrated based on the recovery of the anti-corrosion capability. MXene flakes also played an evident photothermal role in generating heat via irradiation of near-infrared light at 808 nm and focused sunlight. The healing can be quickly obtained in 10 s under irradiation of near-infrared light at 808 nm having a power density of 6.28 W cm-2 or in 10 min under irradiation of focused sunlight having a power density of 4.0 W cm-2.

Enhancement of fluorescent emission in photonic crystal film and application in photocatalysis.

Fluorescent photonic crystal films composed of monodisperse NaYF4:15Yb,0.5Tm@SiO2 (where 15 and 0.5 represent the mole percentage of reactants) core-shell spheres were successfully fabricated and applied in photocatalysis. The core-shell spheres were prepared using a modified Stober method, and fluorescent photonic crystal films were fabricated via a simple self-assembly method. The morphologies, structures and upconversion fluorescent properties of the fluorescent photonic crystal films with different photonic band gaps were characterized. Moreover, their photocatalytic capability in decomposing rhodamine B using near-infrared light was studied. Results indicate that the band edge effect plays a critical role in the enhancement of short wave emission intensity of fluorescent photonic crystal films. Specifically, in comparison to the reference sample without a band edge effect, the 363 nm emission intensity was enhanced by 5.97 times, while the percentage of UV upconversion emission was improved by 6.23%. In addition, the 451 nm emission intensity was enhanced by 5.81 times, and the percentage of visible upconversion emission was improved by 8.88%. Furthermore, fluorescent photonic crystal films with enhanced short wave emission exhibited great photocatalytic performance in the degradation of rhodamine B aqueous solutions under near-infrared light.

Oriented Built-in Electric Field Introduced by Surface Gradient Diffusion Doping for Enhanced Photocatalytic H2 Evolution in CdS Nanorods.

Element doping has been extensively attempted to develop visible-light-driven photocatalysts, which introduces impurity levels and enhances light absorption. However, the dopants can also become recombination centers for photogenerated electrons and holes. To address the recombination challenge, we report a gradient phosphorus-doped CdS (CdS-P) homojunction nanostructure, creating an oriented built-in electric-field for efficient extraction of carriers from inside to surface of the photocatalyst. The apparent quantum efficiency (AQY) based on the cocatalyst-free photocatalyst is up to 8.2% at 420 nm while the H2 evolution rate boosts to 194.3 µmol·h-1·mg-1, which is 58.3 times higher than that of pristine CdS. This concept of oriented built-in electric field introduced by surface gradient diffusion doping should provide a new approach to design other types of semiconductor photocatalysts for efficient solar-to-chemical conversion.

Selectivity Enhancement in Heterogeneous Photocatalytic Transformations.

Photocatalysis has been invariably considered as an unselective process (especially in water) for a fairly long period of time, and the investigation on selective photocatalysis has been largely neglected. In recent years, the field of selective photocatalysis is developing rapidly and now extended to several newer applications. This review focuses on the overall strategies which can improve the selectivity of photocatalysis encompassing a wide variety of photocatalysts, and modifications thereof, as well as the related vital processes of industrial significance such as reduction and oxidation of organics, inorganics, and CO2 transformation. Comprehensive and successful strategies for enhancing the selectivity in photocatalysis are abridged to reinvigorate and stimulate future investigations. In addition, nonsemiconductor type photocatalysts, such as Ti-Si molecular sieves and carbon quantum dots (CQDs), are also briefly appraised in view of their special role in special selective photocatalysis, namely epoxidation reactions, among others. In the end, a summary and outlook on the challenges and future directions in the research field are included in the comprehensive review.

Synthesis and Study of Shape-Memory Polymers Selectively Induced by Near-Infrared Lights via In Situ Copolymerization.

Shape-memory polymers (SMPs) selectively induced by near-infrared lights of 980 or 808 nm were synthesized via free radical copolymerization. Methyl methacrylate (MMA) monomer, ethylene glycol dimethylacrylate (EGDMA) as a cross-linker, and organic complexes of Yb(TTA)2AAPhen or Nd(TTA)2AAPhen containing a reactive ligand of acrylic acid (AA) were copolymerized in situ. The dispersion of the organic complexes in the copolymer matrix was highly improved, while the transparency of the copolymers was negligibly influenced in comparison with the pristine cross-linked PMMA. In addition, the thermal resistance of the copolymers was enhanced with the complex loading, while their glass transition temperature, cross-linking level, and mechanical properties were to some extent reduced. Yb(TTA)2AAPhen and Nd(TTA)2AAPhen provided the prepared copolymers with selective photothermal effects and shape-memory functions for 980 and 808 nm NIR lights, respectively. Finally, smart optical devices which exhibited localized transparency or diffraction evolution procedures were demonstrated based on the prepared copolymers, owing to the combination of good transparency and selective light wavelength responsivity.