Universal Color Retrofit to Polymer-Based Radiative Cooling Materials.

Polymers with broad infrared emission and negligible solar absorption have been identified as promising radiative cooling materials to offer a sustainable and energy-saving venue. Although practical applications desire color for visual appearance, the current coloration strategies of polymer-based radiative cooling materials are constrained by material, cost, and scalability. Here, we demonstrate a universally applicable coloration strategy for polymer-based radiative cooling materials by nanoimprinting. By modulating light interference with periodic structures on polymer surfaces, specular colors can be induced while maintaining the hemispheric optical responses of radiative cooling polymers. The retrofit strategy is exemplified by four different polymer films with a minimum impact on optical responses compared to the pristine films. Polymer films feature low solar absorption of 1.7-3.7%, and daytime sub-ambient cooling is exemplified in the field test. The durability of radiative cooling and color are further validated by dynamic spectral analysis. Finally, the potential roll-to-roll manufacturing empowers a scalable, low-cost, and easy-retrofitting solution for colored radiative cooling films.

Light-activated photodeformable supramolecular dissipative self-assemblies.

Dissipative self-assembly, one of fundamentally important out-of-equilibrium self-assembly systems, can serve as a controllable platform to exhibit temporal processes for various non-stimulus responsive properties. However, construction of light-fueled dissipative self-assembly structures with transformable morphology to modulate non-photoresponsive properties remains a great challenge. Here, we report a light-activated photodeformable dissipative self-assembly system in aqueous solution as metastable fluorescent palette. Zwitterionic sulfonato-merocyanine is employed as a light-induced amphiphile to co-assemble with polyethyleneimine after light irradiation. The formed spherical nanoparticles spontaneously transform into cuboid ones in the dark with simultaneous variation of the particle sizes. Then the two kinds of nanoparticles can reversibly interconvert to each other by periodical light irradiation and thermal relaxation. Furthermore, after loading different fluorophores exhibiting red, green, blue emissions and their mixtures, all these fluorescent dissipative deformable nanoparticles display time-dependent fluorescence variation with wide range of colors. Owing to the excellent performance of photodeformable dissipative assembly platform, the light-controlled fluorescence has achieved a 358-fold enhancement. Therefore, exposing the nanoparticles loaded with fluorophores to light in a spatially controlled manner allows us to draw multicolored fluorescent images that spontaneously disappeared after a specific period of time.

Light-fueled transient supramolecular assemblies in water as fluorescence modulators.

Dissipative self-assembly, which requires a continuous supply of fuel to maintain the assembled states far from equilibrium, is the foundation of biological systems. Among a variety of fuels, light, the original fuel of natural dissipative self-assembly, is fundamentally important but remains a challenge to introduce into artificial dissipative self-assemblies. Here, we report an artificial dissipative self-assembly system that is constructed from light-induced amphiphiles. Such dissipative supramolecular assembly is easily performed using protonated sulfonato-merocyanine and chitosan based molecular and macromolecular components in water. Light irradiation induces the assembly of supramolecular nanoparticles, which spontaneously disassemble in the dark due to thermal back relaxation of the molecular switch. Owing to the presence of light-induced amphiphiles and the thermal dissociation mechanism, the lifetimes of these transient supramolecular nanoparticles are highly sensitive to temperature and light power and range from several minutes to hours. By incorporating various fluorophores into transient supramolecular nanoparticles, the processes of aggregation-induced emission and aggregation-caused quenching, along with periodic variations in fluorescent color over time, have been demonstrated. Transient supramolecular assemblies, which act as fluorescence modulators, can also function in human hepatocellular cancer cells.

A CoV2O4 precatalyst for the oxygen evolution reaction: highlighting the importance of postmortem electrocatalyst characterization.

Vanadium-doped cobalt oxide materials have emerged as a promising class of catalysts for the oxygen evolution reaction. Previous studies suggest vanadium doping in crystalline Co spinel materials tunes the electronic structure and stabilizes surface intermediates. We report a CoV2O4 material that shows good activity for the oxygen evolution reaction. However, postmortem characterization of the catalyst material shows dissolution of vanadium resulting in an amorphous CoOx material, suggesting that this vanadium-free material, and not CoV2O4, is the active catalyst. This study highlights the importance of postmortem characterization prior to mechanistic and computational analysis for this class of materials.

Diverse Nanoassemblies of Graphene Quantum Dots and Their Mineralogical Counterparts.

Complex structures from nanoparticles are found in rocks, soils, and sea sediments but the mechanisms of their formation are poorly understood, which causes controversial conclusions about their genesis. Here we show that graphene quantum dots (GQDs) can assemble into complex structures driven by coordination interactions with metal ions commonly present in environment and serve a special role in Earth's history, such as Fe3+ and Al3+ . GQDs self-assemble into mesoscale chains, sheets, supraparticles, nanoshells, and nanostars. Specific assembly patterns are determined by the effective symmetry of the GQDs when forming the coordination assemblies with the metal ions. As such, maximization of the electronic delocalization of π-orbitals of GQDs with Fe3+ leads to GQD-Fe-GQD units with D2 symmetry, dipolar bonding potential, and linear assemblies. Taking advantage of high electron microscopy contrast of carbonaceous nanostructures in respect to ceramic background, the mineralogical counterparts of GQD assemblies are found in mineraloid shungite. These findings provide insight into nanoparticle dynamics during the rock formation that can lead to mineralized structures of unexpectedly high complexity.

Imidazole for Pyridine Substitution Leads to Enhanced Activity Under Milder Conditions in Cobalt Water Oxidation Electrocatalysis.

A previously reported cobalt complex featuring a tetraimidazolyl-substituted pyridine chelate is an active water oxidation electrocatalyst with moderate overpotential at pH 7. While this complex decomposes rapidly to a less-active species under electrocatalytic conditions, detailed electrochemical studies support the agency of an initial molecular catalyst. Cyclic voltammetry measurements confirm that the imidazolyl donors result in a more electron-rich Co center when compared with previous pyridine-based systems. The primary changes in electrocatalytic behavior of the present case are enhanced activity at lower pH and a marked dependence of catalytic activity on pH.

A Polyimide Nanolayer as a Metal-Free and Durable Organic Electrode Toward Highly Efficient Oxygen Evolution.

The exploitation of metal-free organic polymers as electrodes for water splitting reactions is limited by their presumably low activity and poor stability, especially for the oxygen evolution reaction (OER) under more critical conditions. Now, the thickness of a cheap and robust polymer, poly(p-phenylene pyromellitimide) (PPPI) was rationally engineered by an in situ polymerization method to make the metal-free polymer available for the first time as flexible, tailorable, efficient, and ultra-stable electrodes for water oxidation over a wide pH range. The PPPI electrode with an optimized thickness of about 200 nm provided a current density of 32.8 mA cm-2 at an overpotential of 510 mV in 0.1 mol L-1 KOH, which is even higher than that (31.5 mA cm-2 ) of commercial IrO2 OER catalyst. The PPPI electrodes are scalable and stable, maintaining 92 % of its activity after a 48-h chronoamperometric stability test.

Tuning the Adsorption Energy of Methanol Molecules Along Ni-N-Doped Carbon Phase Boundaries by the Mott-Schottky Effect for Gas-Phase Methanol Dehydrogenation.

Engineering the adsorption of molecules on active sites is an integral and challenging part for the design of highly efficient transition-metal-based catalysts for methanol dehydrogenation. A Mott-Schottky catalyst composed of Ni nanoparticles and tailorable nitrogen-doped carbon-foam (Ni/NCF) and thus tunable adsorption energy is presented for highly efficient and selective dehydrogenation of gas-phase methanol to hydrogen and CO even under relatively high weight hourly space velocities (WHSV). Both theoretical and experimental results reveal the key role of the rectifying contact at the Ni/NCF boundaries in tailoring the electron density of Ni species and enhancing the absorption energies of methanol molecules, which leads to a remarkably high turnover frequency (TOF) value (356 mol methanol mol-1 Ni h-1 at 350 °C), outpacing previously reported bench-marked transition-metal catalysts 10-fold.