As one of the effort to cope with the energy crisis and carbon neutrality, utilization of low-grade energy generated indoors (e.g., light) is imperative because this saves building and house energy, which accounts for ≈40% of total energy consumption. Although photovoltaic devices could contribute to energy savings, it is also necessary to harvest heat from indoor lights to generate electricity because the light absorbed by materials is mostly transformed into heat. For daily life uses, materials should not only have high absorptance and low emittance but also be easily processed into various forms. To this end, this work synthesizes black aqueous suspensions containing winding and bent linear gold nanostructures with diameters of 3-5 nm and length-to-diameter ratios of ≈4-10. Their optical and photo-thermal characteristics are understood through experimental and theoretical investigations. Black gold nanostructures are conveniently processed into metal-dielectric films on metal, glass, and flexible substrates. The film on copper has an absorptance of 0.97 and an emittance of 0.08. Under simulated sunlight and indoor LED light illumination, the film has equivalent photo-thermal and photo-thermoelectric performances to a top-tier sunlight-collecting film. This work attempts to modify the film structure to generate more usable electricity from low-energy indoor light.

Optically left-handed materials refract the propagating light in the opposite direction. Most research has focused on the design of various structures, including split-ring resonators, either on planes or in particle cluster forms to resonate with specific light frequencies. However, for particle-based materials, the circuital structures for optical left-handedness have not been fully understood and the effect of interior structure on the optical handedness have not been investigated. Additionally, scalable methods to deploy the unique characteristics of the materials have not been reported so far and are still urgent. Here, optically left-handed nanopearl beads are synthesized in up to 1.25 L solutions. Nanopearl beads contain assembled Au nanocolloids, a dielectric sphere, and a thin silica layer that fixes the assembled structures to sustainably yield unique inductance-capacitance circuits at specific visible-near-infrared frequencies. The frequencies are tunable by modulating the interior structures. Investigation of the circuit structures and Poynting vectors generated within the nanopearl beads suggest the likelihood of their left-handedness. Moreover, the effects of interior structures on the optical handedness of the nanopearl beads are extensively investigated. The results could help commercialize optically left-handed materials and pioneer fields that have not been realized so far.

Recently developed fabrication methods for inorganic patterns (such as laser printing and optical lithography) can avoid some patterning processes conducted by conventional etching and lithography (such as substrate etching and modulation) and are thereby useful for applications in which the substrates and materials must not be damaged during patterning. Simultaneously, it is also necessary to develop facile and economical methods producing inorganic patterns on various substrates without requiring a special apparatus while attaining the above-mentioned advantages. The present study proposes a reaction-based method for fabricating inorganic patterns by immersing substrates coated with a colloidal nanosheet into an aqueous solution containing inorganic precursors. Silica and TiO₂ patterns spontaneously developed during the conversion of each inorganic precursor. These patterns were successful on rigid and flexible substrates. We fabricated these patterns on a wafer-sized silicon and large flexible poly(ethylene terephthalate) film, suggesting the scalability. We fabricated a biomimetic pattern on both sides of a glass window, as a photovoltaic roof, for minimal optical losses to maximally present photovoltaic effects of a solar cell. The TiO₂ pattern on glass window exhibits sustainable sunlight-driven-cleaning activity for contaminants. The method could provide a platform for economical high-performance inorganic patterns for energy, environmental, electronics, and other areas.

The exploration of natural agricultural products for the efficient hydrolysis of sodium borohydride (NaBH 4 ) is crucial for environmentally benign hydrogen (H 2 ) generation in water and expanding the industrial use of crop-derived materials. However, the direct use of natural materials to enhance H 2 production has been rarely investigated. This study investigates H 2 production using a commercial lemon juice and freshly squeezed citrus juices from lemons, oranges, limes, and mandarins. It is found that the amount of H 2 is close to theoretical maximum value when the molar ratio of carboxyl groups [COOH] to [NaBH 4 ] is 1 or higher. Since it is known that many citrus fruits contain citric acid as a key chemical, a commercial lemon juice is studied as a catalysis for NaBH 4 hydrolysis. An aqueous solution containing 50 vol% juice and 10 mmol NaBH 4 produces 930.3 ± 23.4 mL of H 2 for 60 min. The amount enables a 200 mL bottle of lemon juice to theoretically generate 18.6 L of H 2 . Additionally, freshly squeezed juices from the four citrus fruits (with or without pulp) also catalyze the reaction. Particularly, lime juice with pulp produced 601.0 ± 8.2 mL of H 2 for 60 min when the aqueous suspension contained 50 wt% juice and 6.5 mmol NaBH 4 , corresponding to an estimated H 2 yield of ∼1.574 L per lime fruit. Overall, these findings demonstrate that citrus fruits can act as natural, effective catalysts for NaBH₄ hydrolysis, offering a promising dual benefit for sustainable energy production and agricultural resource utilization. • Citric acid catalyzes sodium borohydride hydrolysis to produce hydrogen (H 2 ). • Many citrus fruits contain citric acid as a key chemical. • Commercial lemon juice catalyzes the hydrolysis to reach theoretical values of H 2 . • Squeezed citrus fruit juices also catalyze the hydrolysis to produce H 2 . • Citrus fruits can provide a solution for eco-friendly production of H 2 .

Abstract Futuristic and high‐performance windows are required to perform multiple functions, occasionally including photo‐ and electricity‐associated functions. For each function, suitable components must be added, but this might result in complicated window structures that can impede the basic window function: high visibility. Therefore, platform technology is necessary to simplify window structures with minimal components for basic functions while adding specific desirable functions. This study proposes non‐close‐packed indium tin oxide (ITO) photonic crystals coated on both sides of rigid and flexible windows. Their photonic bandgap frequencies (stopbands) are tunable through the modulation of the ITO thickness or lattice constant, thereby manipulating the window light transmittances. When the stopband lies in bluelight (400–500 nm), the window can simultaneously block the bluelight and exhibit high transmittance (antireflection function) at 500–1500 nm. The dual functions are enhanced with double‐sided photonic crystal windows: the optical contrasts in solar irradiance transmittances ( ΔT sol ) between 500–1500 and 280–500 nm are maximally 37.1% and 47.2% for the glass and polyimide windows, respectively. Additionally, the windows can have dual stopbands. Moreover, the window stopbands can enhance the photoluminescence intensities of quantum dot films. This simplistic window is applicable to houses/buildings, automobiles, electronics, displays, and energy industries.

Abstract Smart windows can change their optical characteristics according to environmental conditions or external stimuli (such as heat and electricity). They are manufactured by considering building characteristics, regional climate, energy policies, and indoor air conditions. Their key optical properties have been improved by developing novel materials, fabrication methods, and designs. The optical properties can be further improved by developing multi‐stimuli‐responsive smart window systems. Recently, some smart windows have been integrated with energy storage, solar energy harvesting, self‐cleaning, and air‐purifying functions. The energy consumed by buildings and houses accounts for a considerable portion of the total energy consumed by a country as well as the world; therefore, these state‐of‐the‐art smart windows will greatly contribute to saving energy. Moreover, some multi‐functional smart windows can help in addressing environmental challenges. This mini‐review particularly focuses on discussing the recent advances made in multi‐stimuli‐responsive and multi‐functional smart windows, in addition to summarizing the researches on electrochromic, thermochromic, and other types of smart windows.

Abstract Development of a convenient method for complex nanostructures on substrates is essential in fabricating economically viable functional nanosurfaces for electronics, bioengineering, optoelectronics, and energy systems. Colloids can be introduced to make complex patterns, but substrate modification/modulation, more than two types of colloids, and specially designed colloids are required. Herein, it is discovered that colloidal nanomazes are created from a metamorphosis of colloidal bilayer sheets when the sheets are immersed in a salt aqueous solution. Closely and regularly packed colloids in the bilayer spontaneously rearrange their arrays (separation, settling, and insertion) in the solution: This mechanism, suggested from the experimental results, enables the straightforward production of nanostructures without experiencing complex procedures. Additionally, it is demonstrated that the colloidal nanomazes are successfully transformed into functional inorganic nanomazes, Si and Au nanomazes. The anti‐reflective functions of colloidal and Si nanomazes lower the light reflectance or increase the light transmittance: The transmittance of a transparent substrate can be further increased by fabricating the colloidal nanomazes on its both sides. Au nanomazes can also lower the light reflectance, which are discussed with theoretical calculations. The calculation further suggests the Au nanomazes can extensively manipulate the visible–near infrared light, irrespective of polarization modes, from fine tuning the nanomaze geometries.

Dynamic\nmetamolecules (DMMs) are composed of a hydrogel dielectric\ncore surrounded by randomly packed plasmonic nanobeads. The optical\nproperties of DMMs can be tuned by controlling their core diameter\nusing temperature variations. We have recently shown that DMMs display\nstrong optical magnetism, including magnetic dipole and magnetic quadrupole\nresonances, offering significant potential for novel applications.\nHere, we use a T-matrix approach to characterize the magnetic multipole\nresonance modes of model metamolecules and explore their presence\nin experimental data. We show that high-order multipole resonances\nbecome prominent as the nanobead or the overall structure size is\nincreased and when the interbead gap is decreased. In this limit,\nmode mixing among high-order magnetic multipole modes also becomes\nsignificant, particularly in the directional scattering spectra. We\ndiscuss trends in magnetic scattering observed in both experiments\nand simulations and provide suggestions for the experimental design\nand verification of high-order optical magnetic resonances using forward\nand backward scattering measurements. In addition, we show that the\nangular scattering of higher-order magnetic modes can display Fano-like\ninterference patterns, which should also be experimentally detectable.

As one of the effort to cope with the energy crisis and carbon neutrality, utilization of low-grade energy generated indoors (e.g., light) is imperative because this saves building and house energy, which accounts for ≈40% of total energy consumption. Although photovoltaic devices could contribute to energy savings, it is also necessary to harvest heat from indoor lights to generate electricity because the light absorbed by materials is mostly transformed into heat. For daily life uses, materials should not only have high absorptance and low emittance but also be easily processed into various forms. To this end, this work synthesizes black aqueous suspensions containing winding and bent linear gold nanostructures with diameters of 3-5 nm and length-to-diameter ratios of ≈4-10. Their optical and photo-thermal characteristics are understood through experimental and theoretical investigations. Black gold nanostructures are conveniently processed into metal-dielectric films on metal, glass, and flexible substrates. The film on copper has an absorptance of 0.97 and an emittance of 0.08. Under simulated sunlight and indoor LED light illumination, the film has equivalent photo-thermal and photo-thermoelectric performances to a top-tier sunlight-collecting film. This work attempts to modify the film structure to generate more usable electricity from low-energy indoor light.

Optically left-handed materials refract the propagating light in the opposite direction. Most research has focused on the design of various structures, including split-ring resonators, either on planes or in particle cluster forms to resonate with specific light frequencies. However, for particle-based materials, the circuital structures for optical left-handedness have not been fully understood and the effect of interior structure on the optical handedness have not been investigated. Additionally, scalable methods to deploy the unique characteristics of the materials have not been reported so far and are still urgent. Here, optically left-handed nanopearl beads are synthesized in up to 1.25 L solutions. Nanopearl beads contain assembled Au nanocolloids, a dielectric sphere, and a thin silica layer that fixes the assembled structures to sustainably yield unique inductance-capacitance circuits at specific visible-near-infrared frequencies. The frequencies are tunable by modulating the interior structures. Investigation of the circuit structures and Poynting vectors generated within the nanopearl beads suggest the likelihood of their left-handedness. Moreover, the effects of interior structures on the optical handedness of the nanopearl beads are extensively investigated. The results could help commercialize optically left-handed materials and pioneer fields that have not been realized so far.