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Natural melanin is a ubiquitous material that plays critical biofunctional roles in different living organisms. Scientists have dedicated significant efforts to elucidate the biofunctional roles of melanin since its discovery. It has been confirmed that natural melanin possesses a number of intriguing properties such as broadband light absorption, free-radical scavenging ability, redox activity, metal ion chelating, and electronic-ionic conductivity, enabling it to be a versatile functional material in various applications. Natural eumelanin has been the most investigated type of melanin in the past few decades and is discussed in this Review. Here we have comprehensively discussed the latest advances and associated mechanisms in emerging applications of natural eumelanin in different fields such as functional polymers, energy storage, energy conversion, photocatalysis, photothermal therapy, and wastewater treatment considering its bioinspired properties. Important applications developed based on polydopamine, which is a "eumelanin-like" material, will also be presented to give guidelines to further develop natural-melanin-based applications. Authors' perspectives on the challenges and potentials of developing natural-eumelanin-based applications will also be included. This Review provides a clear picture of the natural-eumelanin-based applications and, in turn, accelerates the expansion of the relevant emerging fields.

The incorporation of carbon nanostructures into Al alloys has the potential to further improve the mechanical and electrical properties of these alloys. We report a novel one-step fabrication method of incorporating carbon in aluminum alloys by the application of a high electric current to molten Al metal containing particles of activated carbon at high temperature and under Ar atmosphere. We propose that the mechanism for carbon incorporation is similar to electromigration where the current facilitates ionization of the carbon atoms followed by polymerization of the carbon structures and the formation of graphitic chains and ribbons along preferred directions of the Al lattice. Furthermore, the current induces transformation from amorphous carbon to crystalline graphitic structures that propagate in the metal matrix. The carbon is identified by the C-K edge in electron energy loss spectra, X-ray photoelectron spectroscopy, Raman and Kelvin probe force microscopy. The stiffness is increased in these samples; hardness, on the other hand, decreases for some samples compared to reference Al alloys with no carbon. The electrical conductivity is superior to that of Al-carbon nanotube composites previously reported. The enhanced properties of Al covetics show potential for naval and aerospace applications and power transmission lines.

Natural melanin is abundant in wide ranges of sources, especially in dark colored animal fibers. Despite the unique features and functionalities, its extensive analyses and applications have greatly been hindered due to its serious self-aggregation. To tackle this issue, this study uses the Stober method to encapsulate the melanin particles extracted from colored alpaca fibers with a thin layer of silica. It was observed that the melanin/silica core-shell particles (MSCPs) with 20 h encapsulation time provided excellent dispersity and optical performance. Different concentrations of MSCPs were then doped in poly (methyl methacrylate) (PMMA) through an in-situ polymerization process to obtain MSCP/PMMA bulk materials. The produced composite materials showed homogeneous appearance, controllable UV absorbance and visible light transmittance. The thermal stability, durability under UV, and mechanical properties of the fabricated composites were examined and the role of melanin on the obtained results was elucidated. It was observed that the PMMA samples with MSCPs showed excellent durability under UV even after 100 h irradiation. Testing the thermal stability and mechanical properties (hardness and elastic modulus) of MSCP/PMMA samples confirmed the positive effect of MSCPs presence in PMMA. These results demonstrated the applicability of natural melanin-based materials and composites in UV-protection related fields.

Melanin/titanium dioxide (TiO2) composite systems are introduced as efficient UV absorbers. Natural melanin particles were extracted from the pigmented alpaca fibers and the spindle-like rutile TiO2 nanoparticles were synthesized through a two-step sol-gel method at room temperature. The composites of melanin/TiO2 were prepared via electrostatic attraction force. In order to understand the UV absorption features of melanin and melanin/TiO2 composite systems, the prepared particles were applied to the surface of wool fabrics. Then, the UV protection and photostability of functionalized fabrics were assessed based on photoinduced chemiluminescence (PICL) emission, UV reflectance spectra, photoyellowing and ultraviolet protection factor (UPF). It was observed that the photostability of treated fabrics enhanced significantly, implying the generation of less free polymeric radicals in the substrate under UV irradiation. Among different synthesized composites, the proportion of melanin/TiO2 1/4 was the most efficient ratio inducing 80% reduction in the PICL emission peak intensity compared with untreated wool samples. The presence of melanin particles significantly enhanced the UPF values of fabrics where 30% increment was observed for wool samples after treating with melanin/TiO2 1/4 compared with pure TiO2. Having some advantages such as nontoxicity, eco-friendly and feasible synthesis approach, the prepared bio-organic/inorganic composite structures can be of some potential applications in photoprotecting and free radical quenching purposes.

Tin (Sn)-based materials are one of most promising candidates for rechargeable (Li+ and Na+ ion) batteries because of their high theoretical capacities (993 mAh/g for Li4.4Sn and 847 mAh/g for Na15Sn4) and reasonable working potentials. However, Sn-based anodes suffer from huge volume changes during cycling that hinder the applications in commercialized rechargeable batteries. Unique particle engineering to fabricate Sncore–carbonshell (Sn@C) particles has been shown to address or circumvent these problems. In this work, a distinct core–shell-structured Sn@C anode material has been successfully developed by using a one-step and template-free process (colloidal spray pyrolysis). A comprehensive analysis of chemical reaction kinetics of core–shell particles assists the product design to control the particle composition and structure by tuning the process variables, such as reaction temperature and cosolvent concentration. The unique Sn@C anode delivers a high capacity of 720 mAh/g after 300 cycles at 0.5C f...

Copper is an inexpensive replacement for silver in electronic applications such as solar cell metallization, electromagnetic interference packaging, and printable electronics. However, copper has a...

Melanin, a ubiquitous natural pigment, has attracted much attention in energy and nanotechnology areas in recent years. With the increasing demand for high-quality melanin materials and sustainable experimental environment, this study was conducted to achieve melanin with intact structure through recyclable extraction method using ionic liquid (IL). Melanin extracted from base dissolution and acid isolation (BA) method and acid hydrolysis (AH) method were also used for comparison. SEM and 13C-NMR characterizations indicated that IL treatment has retained the original structure of melanin while other methods caused particle damage to various degrees. In addition, the recycled IL (up to five times) showed good reproducibility, and the performance of extracted melanin at the 5th cycle was well-maintained.

Spray pyrolysis is a scalable process to fabricate functional particles as cathode/anode materials in rechargeable batteries from precursor solutions. However, one prerequisite of spray pyrolysis to achieve uniform particle-to-particle composition and structure is a stable precursor solution, restricting its usage to highly soluble salts. Otherwise, extremely acidic precursors are necessary to ease the uncontrollable hydrolysis of the salts and the subsequent precipitation. Moreover, strong reducing agents such as H2 are also needed for complete solid-state reactions, introducing potential safety concerns. Herein, for the first time, we develop a novel process, colloidal spray pyrolysis (CSP), which can eliminate all the prerequisites simultaneously. Our process can generate particles directly from a multiphase precursor in mild processing conditions through in-situ solid-state reactions. The product structure and composition can be precisely designed based on aerosol dynamics and reaction kinetics. By applying CSP, Sn@C particles with three distinct interior nanostructures have been synthesized and evaluated as anodes for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). The best performing Sn@C anode delivers 627.9 mAh/g at 2 C with capacity retention of 88.5% after 1500 cycles in LIBs and demonstrates superior rate capability for SIBs. This novel CSP process is promising in preparing electrode materials in LIBs and SIBs for future practical applications.

Summary Recent breakthroughs in aqueous electrolytes made highly safe 3.0 V class aqueous Li-ion batteries possible. However, the formed solid-electrolyte interphase therein still cannot effectively support the desired energy-dense anode and cathode materials. In this work, we report a new class of electrolytes, by hybridizing aqueous with non-aqueous solvents, that inherits the non-flammability and non-toxicity characteristics from aqueous and better electrochemical stability from non-aqueous systems. The secondary interphasial ingredient (alkylcarbonate) introduced by non-aqueous component helps to expand the electrochemical window of the hybridized electrolyte to 4.1 V, which supports the operation of a 3.2 V aqueous Li-ion battery based on Li 4 Ti 5 O 12 and LiNi 0.5 Mn 1.5 O 4 to deliver a high energy density of 165 Wh/kg for >1,000 cycles. The understanding of how a better interphase could be tailored by regulating the inner-Helmholtz interfacial structures of the hybridized electrolyte provides important guidelines for designing future electrolytes and interphases for new battery chemistries.

Artificial photosynthesis uses a catalyst to convert CO2 into valuable hydrocarbon products by cleaving the C=O bond. However, this technology is strongly limited by two issues, namely insufficient catalytic efficiency and complicated catalyst-fabrication processes. Herein, we report the development of a novel spray-drying photocatalyst-engineering process that addresses these two issues. Through one-step spray drying, with a residence time of 1.5 s, nanocomposites composed of tin oxide (SnO2) nanoparticles and edge-oxidized graphene oxide (eo-GO) sheets were fabricated without post-treatment. These nanocomposites exhibited 28-fold and five-fold enhancements in photocatalytic efficiency during CO2 reduction compared to SnO2 and commercialized TiO2 (P25), respectively, after irradiation with simulated sunlight for 4 h. This scalable approach, based on short residence times and facile equipment setup, promotes the practical application of artificial photosynthesis through the potential mass production of efficient photocatalysts.

Melanin, the main photoreceptor in living organics, is largely abundant in pigmented hair tissues. Its promising properties have been widely studied in order to fully explore the corresponding applications. However, the photodegradating and aggregating natures of melanin, to some extent, restrict the development of this eco-friendly biomaterial. This study is conducted to overcome both disadvantages by a mature method that coating the original melanin nanoparticles with silica as shells. The results revealed that the aggregation of the melanin/silica nanoparticles (MSNP) was decreased obviously by a 5 h coating and appeared a uniformly mono-dispersed solution. The MSNP that coated for 20 h provided an efficient protection on the photodegradation of the melanin with a 50% maintenance of the melanin content compared with 16% of original melanin and 2% of MSNP-5 h.

Cu–Sn powders are promising alternatives to Ag and Au in applications including printed electronics because of their low cost and high oxidation resistance. Further development requires knowledge of the conductivity of their corresponding one- and two-dimensional structures. Herein, CuSny (y = atom ratio of Sn/Cu) wires and films were produced by direct printing. In situ measurements of structural resistivities with variation of the temperature from 2 to 400 K in oxygen-free conditions revealed that CuSn0.1 wires have resistivities comparable to those of Cu wires. Furthermore, CuSn0.1 films exhibited significantly lower resistivity increases after being heated at 573 K in ambient air, compared with Cu films.

A cost-effective, environmentally friendly and industrialized method of using low-grade sources to prepare high-performance anode material for lithium ion batteries (LIBs) with high energy density and long cycle life is both appealing and challenging. Herein, we present a low-cost, scalable and controllable approach for preparing unique sub-micrometer core-shell structure nanocrystal-FeSi-embedded Si/SiOx (FSO) anode material directly from a low-grade Fe-Si alloy. The sub-micrometer FSO anode materials are controlled by in-situ reaction of the Fe-Si-O in the Fe-Si alloy according to the phase diagram. The XRD and Rietveld refinement results indicate that when the treatment temperature increase, (i) FeSi phase appears together with Si and FeSi2, and then (ii) Fe3Si phase appears together with Si and FeSi. Most importantly, benefited from the formation of the amorphous SiOx as buffer layer and self-conductive nanocrystal-FeSi as a robust skeleton to mechanically support the large volume change of Si during cycling, the sub-micrometer core-shell structure FSO anode exhibits a high capacity (931.3 mA h g−1) at 50 mA g−1 and a prolonged cycle performance with 86% capacity retention over 1000 cycles at 1 A g−1. The full cell with prelithiated FSO as the anode and commercial LiCoO2 as the cathode delivers a high energy density of 467.5 W h kg−1 at the 0.05 C. This work provides a promising route for commercial production of high-performance Si/SiOx-based anode materials in LIBs.

Lithium–sulfur battery (LSB) as one of the most promising energy storage devices suffers from poor conductivity of sulfur and fast capacity decay triggered by the dissolution of polysulfides. In this work, functionalized carbonized mesoporous wood fiber (f-CMWF) is employed as a host to accommodate sulfur for the first time. Natural wood microfiber has unique hierarchical and mesoporous structure, which is well-maintained after carbonization. With such a hierarchical mesoporous structure, a high sulfur loading of 76 wt % is achieved in CMWF electrodes. The pore size of CMWF is tunable by atomic layer deposition (ALD) of a 5 nm Al2O3 coating to form the f-CMWF. Such a thin layer slightly decreases the sulfur loading to 70%, but it remarkably promotes the cyclic stability of sulfur cathode, which delivers an initial capacity of 1115 mAh g–1, and maintains a reversible capacity of 859 mAh g–1 for 450 cycles, corresponding to a slow capacity decay rate of 0.046% per cycle. More importantly, natural wood micro...

Solid-state lithium batteries (SSLBs) have been regarded as one of the next-generation energy storage systems. With the adoption of solid-state electrolytes (SSEs) and lithium metal anodes, SSLBs enable higher energy density and more reliable safety than the state-of-the-art lithium-ion batteries. Among potential SSEs, the cation-doped Li7La3Zr2O12 (LLZO) is promising for its high ionic conductivity (~10 −3 S cm−2) at room temperature and high stability with Li metal anode. However, the storage of doped LLZO in the ambient condition suffers the aging effect, including the structural transition (i.e. low-temperature cubic form) and the stoichiometric changes (i.e. Li2CO3). These changes are detrimental to LLZO ionic conductivity and interfacial stability in SSLBs. To this end, we are motivated to investigate the structural and stoichiometric reversibility of aged LLZO during thermal treatment. With the help of an in-situ synchrotron-based high-energy X-ray diffraction technique, our experiments revealed that the LLZO powders became a low-temperature cubic phase when exposed to the ambient condition for an extended period of time. A high temperature cubic form can be restored after a thermal treatment of the aged LLZO powder, regardless of the type of dopant . However, the restoration of the stoichiometry remained a challenge, and the degree of the restoration showed a clear dependence on the dopant chemistry.

The particle pulverization induced by volume change and the disproportionation reaction of Mn3+ to Mn4+ and electrolyte-soluble Mn2+ are two major challenges for Na0.67MnO2 cathodes in Na-ion batteries. Herein, Ni and/or Fe doped Na0.67MnO2 was synthesized to suppress the particle pulverization and disproportionation reaction. The replacement of 33% Mn ions by Ni in Na0.67MnO2 can effectively reduce the particle pulverization and disproportionation of Mn3+, resulting in improved cycling stability at the cost of reduced capacity. To develop a high capacity and long cycle life cathode material, Ni in Na0.67Ni0.33Mn0.67O2 is further partially substituted by Fe to generate Na0.67Fe0.20Ni0.15Mn0.65O2, which retains ∼70% of its initial capacity after 900 cycles, corresponding to a very low capacity decay rate of 0.033% per cycle. To the best of our knowledge, the Na0.67Fe0.20Ni0.15Mn0.65O2 synthesized by ultrasonic spray pyrolysis (USP) represents one of the best cathode materials for Na-ion batteries to date. In addition, a thin layer (5 nm) of Al2O3 is deposited on the Na0.67MnO2 electrode by atomic layer deposition (ALD) to further reduce the dissolution of Mn ions and accommodate the volume change, which further extend the cycling stability of Na0.67MnO2 electrodes.

Micron-sized solid Cu–Sn particles have been considered as a replacement for more expensive materials (e.g., Ag, Pd, and Au) in conductive pastes used in printed electronics, solar cell metallization, and interference packaging. With the formation of a tin oxide layer, Cu–Sn particles could combine relatively low electrical resistivity with high oxidation resistance. However the oxidation behavior of this system is not well understood. Here, the oxidation of CuSny solid particles, fabricated by spray pyrolysis without direct addition of H2, was investigated. Our experimental results and theoretical analysis suggest that at a low oxidation temperature (300 °C), the migration of O2− through the oxide layer controls the oxidation. At high temperature (500 °C), the grain growth of the oxide layer is believed to be the rate-limiting step. Among the CuSny particles tested, CuSn0.1 powders exhibited the best particle structure (solid and spherical) and highest oxidation resistance.

Cu-Sn binary particles were generated via spray pyrolysis from metal salt precursors with ethylene glycol as the co-solvent and reducing agent. The morphology, crystallinity, and elemental distribution of particles were tunable by changing the reaction temperature, residence time, and quench gas flow rate. Hollow porous particles were fabricated with a higher Sn concentration on the particle surface when the furnace set point was 500°C, while solid particles with a lower surface Sn concentration were generated when the furnace set point was 1000°C. Particles with spherical morphologies were obtained at long residence time conditions (4.5 s). Cu-Sn binary particles with irregular structures (e.g., pores on the particle surface, fragmented spherical particles, and lamellar fragments) were formed at short residence time conditions (0.92 s). A possible spray pyrolysis mechanism was proposed that incorporates chemical reaction steps and structural progression. By this mechanism, the metal salts are believed to sequentially undergo hydrolysis to metal hydroxides, decomposition to metal oxides, reduction to metals, and finally diffusion of Sn into the Cu matrix to generate the Cu-Sn solid solution. Copyright © 2017 American Association for Aerosol Research

Silver nanoparticles (AgNPs) are in situ synthesized for the first time on microfibrillated silk (MFS) exfoliated from domesticated Philosamia cynthia ricini (eri) and Bombyx mori (mulberry) silkworm silk fibers. The process is rapid (hours time), does not rely on harmful chemicals, and produces robust and flexible AgNPs coated MFS (MFS-AgNPs) protein papers with excellent handling properties. None of these can be achieved by approaches used in the past to fabricate AgNPs silk systems. MFS bonds the AgNPs strongly, providing good support and stabilization for the NPs, leading to strong wash fastness. The mechanical properties of the MFS-AgNPs papers largely do not change compared to the MFS papers without nanoparticles, except for some higher concentration of AgNPs in the case of mulberry silk. The improved tensile properties of eri silk papers with or without AgNPs compared to mulberry silk papers can be attributed to the higher degree of fibrillation achieved in eri silk and its inherent higher ductility. MFS-AgNPs from eri silk also exhibit strong antibacterial activity. This study provides the basis for the development of smart protein papers based on silk fiber and functional nanomaterials.

Melanin has attracted researchers’ attention in recent years due to its intriguing properties and various applications in different fields. Here, we fabricated a highly efficient photocatalytic material through utilizing the natural melanin (NM) isolated from textile scraps like yak hair wastes. A simple one-step process was employed to synthesize titanium dioxide (TiO2) nanoparticles on the surface of NM. The synthesized NM/TiO2 hybrids exhibited prominent photocatalytic activity for the simultaneous removal of methyl orange (MO) and hexavalent chromium ions (Cr (VI)) under visible light irradiations, which constitute ∼45 % of the solar light. Our results revealed that NM served as a base material with abundant catechol groups to form C-O-Ti bonds with TiO2 nanoparticles, which narrowed the band gap and broadened the light response of the hybrids. The working mechanism of NM/TiO2 hybrids for the simultaneous removal of dyes (MO) and heavy metal ions (Cr (VI)) was thoroughly explored and proposed. This work highlighted the potential of the NM/TiO2 hybrids for textile dyeing effluent treatment with more efficient utilization of solar spectrum. Our work also opens a pathway for the design of advanced NM-based functional materials from various NM-enriched wastes such as human hair wastes, squid ink, etc.

Organic electrode materials are promising for green and sustainable lithium-ion batteries. However, the high solubility of organic materials in the liquid electrolyte results in the shuttle reaction and fast capacity decay. Herein, azo compounds are firstly applied in all-solid-state lithium batteries (ASSLB) to suppress the dissolution challenge. Due to the high compatibility of azobenzene (AB) based compounds to Li3 PS4 (LPS) solid electrolyte, the LPS solid electrolyte is used to prevent the dissolution and shuttle reaction of AB. To maintain the low interface resistance during the large volume change upon cycling, a carboxylate group is added into AB to provide 4-(phenylazo) benzoic acid lithium salt (PBALS), which could bond with LPS solid electrolyte via the ionic bonding between oxygen in PBALS and lithium ion in LPS. The ionic bonding between the active material and solid electrolyte stabilizes the contact interface and enables the stable cycle life of PBALS in ASSLB.

Organic compounds are desirable alternatives for sustainable lithium-ion battery electrodes. However, the electrochemical properties of state-of-the-art organic electrodes are still worse than commercial inorganic counterparts. Here, a new chemistry is reported based on the electrochemical conversion of nitro compounds to azo compounds for high performance lithium-ion batteries. 4-Nitrobenzoic acid lithium salt (NBALS) is selected as a model nitro compound to systemically investigate the structure, lithiation/delithiation mechanism, and electrochemical performance of nitro compounds. NBALS delivers an initial capacity of 153 mAh g-1 at 0.5 C and retains a capacity of 131 mAh g-1 after 100 cycles. Detailed characterizations demonstrate that during initial electrochemical lithiation, the nitro group in crystalline NBALS is irreversibly reduced into an amorphous azo compound. Subsequently, the azo compound is reversibly lithiated/delithiated in the following charge/discharge cycles with high electrochemical performance. The lithiation/delithiation mechanism of azo compounds is also validated by directly using azo compounds as electrode materials, which exhibit similar electrochemical performance to nitro compounds, while having a much higher initial Coulombic efficiency. Therefore, this work proves that nitro compounds can be electrochemically converted to azo compounds for high performance lithium-ion batteries.

Nanoparticle self-assembly promises scalable fabrication of composite materials with unique properties, but symmetry control of assembled structures remains a challenge. By introducing a governing force in the assembly process, we develop a strategy to control assembly symmetry. As a demonstration, we realize the tetragonal superlattice of octagonal gold nanorods, breaking through the only hexagonal symmetry of the superlattice so far. Surprisingly, such sparse tetragonal superstructure exhibits much higher thermostability than its close-packed hexagonal counterpart. Multiscale modeling reveals that the governing force arises from hierarchical molecular and colloidal interactions. This force dominates the interactions involved in the assembly process and determines the superlattice symmetry, leading to the tetragonal superlattice that becomes energetically favorable over its hexagonal counterpart. This strategy might be instructive for designing assembly of various nanoparticles and may open up a new avenue for realizing diverse assembly structures with pre-engineered properties., Shape complementarity is the primary way to control the symmetry of nanoparticle assemblies. Here, the authors introduce a governing force that dominates symmetry control of nanorod superlattices, using it to obtain an unexpected and highly thermostable tetragonal lattice.

Real-time observations on gold nanorods evolving into spiral or lamellar superlattices are demonstrated. 2D critical nuclei and screw dislocations initiate the crystallization process. Kinetics of the superlattice growth is determined to be similar to that of classical crystal growth, where three basic modes are involved: spiral, layer-by-layer and dendritic.