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The rice husk is the outer covering of a rice kernel and protects the inner ingredients from external attack by insects and bacteria. To perform this function while ventilating air and moisture, rice plants have developed unique nanoporous silica layers in their husks through years of natural evolution. Despite the massive amount of annual production near 10 8 tons worldwide, so far rice husks have been recycled only for low-value agricultural items. In an effort to recycle rice husks for high-value applications, we convert the silica to silicon and use it for high-capacity lithium battery anodes. Taking advantage of the interconnected nanoporous structure naturally existing in rice husks, the converted silicon exhibits excellent electrochemical performance as a lithium battery anode, suggesting that rice husks can be a massive resource for use in high-capacity lithium battery negative electrodes.R ice is one of the most widespread food crops for human sustenance (Fig. 1A). It is currently cultivated in about 75 countries, and more than one-third of the global population eats rice as a staple food. Its worldwide annual production amounts to ∼422 million metric tons (1). The cultivation of rice plants generates a waste product, so-called rice husks (RHs), and upon the complete harvest of rice, the content of the RH reaches ∼20 wt% of the entire rice kernel, a very large amount, considering the massive scale of global rice production. The utilization of RHs has been an extensive research topic for decades (2). However, practical applications of RHs have been limited to a narrow range of low-value agricultural items, such as fertilizer additives, stockbreeding rugs, and bed soil, because of their tough and abrasive properties (2). There is a large opportunity for further research targeting more valuable applications.Although RHs contain a variety of components such as lignin, cellulose, and silica, the present study pays attention mainly to recycling of the silica component. It has been known (3, 4) that silica accounts for ∼15-20 wt% of the entire RHs (Fig. 1B, Lower Inset) and originates from monosilicic acid that is first introduced into rice plants through their roots and is then moved to the rigid outer epidermal walls of the plants where it is converted into silica. The silica in RHs plays an important role in protecting rice from external attack by insects and bacteria (3, 5, 6), but simultaneously facilitates ventilation between inside and outside RHs to preserve moisture and nutrients inside the kernels. To perform these critical dual functions, the silica in RHs has developed unique porous nanostructures through years of natural evolution.In an effort to recycle RHs toward high-value applications, in the present investigation, the RH silica possessing unique nanostructures has been applied in high-capacity lithium ion battery (LIB) anodes by reducing the silica to silicon (Si). Si has recently attracted considerable attention as an LIB anode due to its unparalleled theoretical capacity around 4,000 mAh/g ...

Nanostructured silicon electrodes have shown great potential as lithium ion battery anodes because they can address capacity fading mechanisms originating from large volume changes of silicon alloys while delivering extraordinarily large gravimetric capacities. Nonetheless, synthesis of well-defined silicon nanostructures in an industrially adaptable scale still remains as a challenge. Herein, we adopt an industrially established spray drying process to enable scalable synthesis of silicon-carbon composite particles in which silicon nanoparticles are embedded in porous carbon particles. The void space existing in the porous carbon accommodates the volume expansion of silicon and thus addresses the chronic fading mechanisms of silicon anodes. The composite electrodes exhibit excellent electrochemical performance, such as 1956 mAh/g at 0.05C rate and 91% capacity retention after 150 cycles. Moreover, the spray drying method requires only 2 s for the formation of each particle and allows a production capability of ~10 g/h even with an ultrasonic-based lab-scale equipment. This investigation suggests that established industrial processes could be adaptable to the production of battery active materials that require sophisticated nanostructures as well as large quantity syntheses.

tion. A drop of Nylon 6,6±isopropanol suspension was deposited on a carbon-coated TEM grid. The grid was shadowed with a thin layer of platinum. A JEOL (1200 EX II) TEM with an accelerating voltage of 120 kV was used and calibration of the SAED spacing was done using TlCl standards. A Digital Instrument Nanoscope IIIA was used for AFM experiments. A drop of Nylon 6,6 crystal suspension was deposited on a carbon-coated glass slide. The force used by the cantilever was light enough to limit damage to the sample, yet obtain accurate surface features. The scanning rate was 1±3 Hz for the low magnification images (512 512 pixels per image). Arrays of close-packed, equal-sized microspheres have been used as templates for the micro-and nano-fabrication of optical materials. Colloidal suspensions of such monodisperse spheres can be especially useful in making optical materials because they can self-organize into ordered, hexagonally packed crystalline lattices in two or three dimensions. Received[1] These opaline lattices can exhibit optical insulating behavior (i.e., they can have a photonic bandgap (PBG)), similar to semiconductors in electronic devices, and are called photonic crystals. The optical insulating behavior of photonic crystals arises from the cooperative scattering of light from the ordered array of particles.[2] However, these opaline structures do not have a full PBG but only a few narrow stop bands. It is known that inverse opaline structures exhibit wider stop bandgaps, and can possess a full PBG when the refractive index contrast exceeds about 2.8. The inverse opaline structures are formed by infiltrating dielectric material into the interstices between the colloidal spheres and then dissolving the spheres away. [3] This produces an ordered foam of spherical cavities. The stop bands of opals or inverse opals with a face-centered cubic arrangement can be exploited to modify the spontaneous emission of organic dyes and semiconductor nanocrystals embedded in the voids of the colloidal crystals.[4]One of the important issues in the design of photonic crystals is the control of their uniformity in size and shape. This is required for the development of photonic devices, including waveguides and optical components, such as microlenses and beam splitters.[5±7] For other applications, photonic crystals in the form of colloidal clusters could be especially valuable, for example, as light scatterers, light diffusers, and pigments for electronic paper and electronic displays.[8±10] The practical use of these materials, however, requires the production of large quantities of monodisperse colloidal clusters. Here, we report a simple, single-step synthetic route for the generation of uniform colloidal aggregates and their inverse structures by electrospraying an aqueous colloidal suspension. Hereafter, both our opaline balls and their inverse structures COMMUNICATIONS

This paper introduces a facile one-pot method for synthesizing a new structured material, named "ant-cave microball", by continuous ultrasonic spray pyrolysis. The ant-cave-structured microballs are prepared from a colloidal spray solution with polystyrene nanobeads and sucrose. Networking between the nanovoids formed by decomposition of the polystyrene nanobeads results in the formation of nanochannels. The electrochemical properties of these ant-cave-structured MoO3-C microballs, prepared as the first target material for lithium ion batteries, are investigated. The nanochannels are uniformly distributed inside the microballs with MoO3 and carbon components uniformly distributed within the microballs. Further, the microballs have initial discharge and charge capacities of 1212 and 841 mA h g(-1), respectively, at a current density of 2 A g(-1), and the initial discharge and charge capacities based on the weight of MoO3 (disregarding carbon component) are as high as 1814 and 1259 mA h g(-1). The microballs deliver a high discharge capacity of 733 mA h g(-1) even after 300 cycles. This is although microsized MoO3 powders with a filled structure have discharge capacities of 1256 and 345 mA h g(-1) for the first and 300th cycles, respectively.

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Y 2 O 3 : Eu phosphor particles were directly prepared by a spray pyrolysis method. Photoluminescence, morphology, and crystallinity of the as-prepared particles were investigated. The as-prepared particles above 600 ± C had good crystallinity, and the crystallinity increased with increasing reactor temperatures. The particles had spherical morphology and were nonaggregated. The mean size of the particles increased from 0.34 to 1.2 mm when the solution concentration was increased from 0.03 to 1 M. The as-prepared particles had good red emission without annealing at high temperatures when excited with uv light. The main emission peak was 612 nm. The brightness of the as-prepared particles increased with increasing temperatures because of good activation and crystallization at high temperatures.