Wood-Derived Carbon Fibers Embedded with SnO x Nanoparticles as Anode Material for Lithium-Ion Batteries.

Carbon-SnO x composites are obtained by impregnating acetylacetone-treated, delignified wood fibers with tin precursor and successively carbonizing at 1000 °C in 95% argon and 5% oxygen. Scanning electron microscopy and nitrogen sorption studies (Brunauer-Emmett-Teller) show that acetylacetone treatment stabilizes the wood fiber structure during carbonization at 1000 °C and preserves the porous structural features. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy studies show that the small amount of oxygen introduced in inert atmosphere passivates the surface of tin nanoparticles. The passivation process yields thermally and electrochemically stable SnO x particles embedded in carbon matrix. The resultant carbon-SnO x material with 16 wt% SnO x shows excellent electrochemical performance of rate capability from 0.1 to 10 A g-1 and cycling stability for 1000 cycles with Li-ion storage capacity of 280 mAh g-1 at a current density of 10 A g-1. The remarkable electrochemical performance of wood-derived carbon-SnO x composite is attributed to the reproduction of structural featured wood fibers to nanoscale in carbon-SnO x composite and controlled passivation of tin nanoparticles to yield SnO x nanoparticles.

Investigation of In-Situ Carbon Coated LiFePO4 as a Superior Cathode Material for Lithium Ion Batteries.

In the present study, we have developed a simple and cost-effective approach for the synthesis of carbon coated LiFePO4 wherein different carbon precursors were used to find out the suitable precursor for carbon coating. Initially, the appropriate amount of Li, Fe, and P precursors and carbon source (glucose/sucrose/fructose) were dissolved in ethanol solution followed by hydrothermal treatment at 180 °C to obtain carbon coated LiFePO4. The structure and morphological analysis of In-Situ carbon coated LiFePO4 revealed the formation of thin and homogeneous carbon layer on crystalline single-phase LiFePO4 particles with fructose used as carbon precursor. Raman analysis confirms the presence of more ordered graphitic carbon and the ID/IG ratio is 1.01, 0.69 and 0.87 for C-LFP-S, C-LFP-F and C-LFP-G respectively, indicating that fructose assisted In-Situ carbon coating leads to the formation of more ordered carbon coating on LiFePO4 with high graphitization degree in comparison with carbon coating by glucose and sucrose. HR-TEM results revealed the presence of uniform carbon distribution, which encapsulates the crystalline LiFePO4 particles forming a core-shell structure in the presence of fructose as carbon precursor. C-LFP-S delivered a capacity of 125 mAh/g at 0.1 C rate but then due to non-uniform carbon layer distribution, the capacity faded out completely when tested at higher C-rates. Whereas C-LFP-F delivered a discharge capacity of 98 mAh/g at 0.1 C and 48 mAh/g at 1 C, which is promising compared to the LiFePO4 carbon coated using sucrose and glucose. It is concluded that LiFePO4 carbon coated using monosacrides as carbon precursors showed better electro-chemical performance in terms of capacity and cyclic stability when compared to LiFePO4 carbon coated using dissacrides, attributing that uniform, thin layer, and highly ordered graphitic carbon coverage on nano sized LiFePO4 particles greatly reduces the polarization resistance and hence improving the electrochemical performance of C-LFP-F.

Conversion of Solar Energy into Electrical Energy Storage: Supercapacitor as an Ultrafast Energy-Storage Device Made from Biodegradable Agar-Agar as a Novel and Low-Cost Carbon Precursor.

Solar cells hold promise as energy conversion devices but intermittent sunlight limits their continuous applications. The self-powering integrated solar cells and electrical energy storage devices can be an alternative to resolve this problem. This study demonstrates the integration of solar cell with supercapacitor (SC) device and evaluates its performance for energy conversion and storage for practical validity. SC carbon is derived from agar-agar as low-cost carbon precursor and a high-performance SC electrode is utilized for the first time. The fabricated SC shows an excellent specific capacitance of 170 F g-1 and retains 85% of its original value up to 15 000 charge/discharge cycles at 1 A g-1, and it holds a maximum energy density of 17.7 Wh kg-1. The integration of SCs (three cells in series with 5.4 V) with a commercial solar lantern for a self-sustaining power pack is demonstrated. The SC is charged by solar cells in a few seconds and powers a solar lantern with 40 light-emitting diodes without sunlight, demonstrates its potential for efficient conversion of solar energy into electrical energy storage. This result highlights that solar SC can be considered as an ultrafast next-generation energy-storage device that can mitigate the energy demand in the near future.

Development of a novel carbon-coating strategy for producing core-shell structured carbon coated LiFePO4 for an improved Li-ion battery performance.

In the present study, LiFePO4 (LFP) has been synthesized using a flame spray pyrolysis unit followed by carbon coating on LFP using a novel strategy of dehydration assisted polymerization process (DAP) in order to improve its electronic conductivity. Characterization studies revealed the presence of a pure LFP structure and the formation of a thin, uniform and graphitic carbon layer with a thickness of 6-8 nm on the surface of the LFP. A carbon coated LFP with 3 wt% of carbon, using a DAP process, delivered a specific capacity of 167 mA h g-1 at a 0.1C rate, whereas LFP carbon coated by a carbothermal process (CLFP-C) delivered a capacity of 145 mA h g-1 at 0.1C. Further carbon coated LFP by the DAP exhibited a good rate capability and cyclic stability. The enhanced electrochemical performance of C-LFP by DAP is attributed to the presence of a uniform, thin and ordered graphitic carbon layer with a core-shell structure, which greatly increased the electronic conductivity of LFP and thereby showed an improved electro-chemical performance. Interestingly, the developed carbon coating process has been extended to synthesize a bulk quantity (0.5 kg) of carbon coated LFP under optimized experimental conditions as a part of up-scaling and the resulting material electro-chemical performance has been evaluated and compared with commercial electrode materials. Bulk C-LFP showed a capacity of 131 mA h g-1 and 87 mA h g-1 at a rate of 1C and at 10C, respectively, illustrating that the developed DAP process greatly improved the electrochemical performance of LFP in terms of rate capability and cyclic stability, not only during the lab scale synthesis but also during the large scale synthesis. Benchmark studies concluded that the electro-chemical performance of C-LFP by DAP is comparable with that of TODA LFP and better than that of UNTPL LFP. The DAP process developed in the present study can be extended to other electrode materials as well.

Facile One-Step Route for the Development of in Situ Cocatalyst-Modified Ti3+ Self-Doped TiO2 for Improved Visible-Light Photocatalytic Activity.

Development of visible-light-driven photocatalysts by employing a relatively simple, efficient, and cost-effective one-step process is essential for commercial applications. Herein, we report for the first time the synthesis of in situ Cu-ion modified Ti3+ self-doped rutile TiO2 by such a facile one-step solution precursor plasma spray (SPPS) process using a water-soluble titanium precursor. In the SPPS process, Ti3+ self-doping on Ti4+ of rutile TiO2 is found to take place because of electron transfer from the created oxygen vacancies to Ti4+-ions. In situ Cu modification of the above Ti3+ self-doped rutile TiO2 by additionally introducing a Cu solution into plasma plume is also demonstrated. While the Ti3+ self-doping induces broad absorption in the visible-light region, the addition of Cu ion leads to even broader absorption in the visible region owing to resulting synergistic properties. The above materials were evaluated for various self-cleaning photocatalytic applications under visible-light illumination. Cu-ion modified Ti3+ self-doped rutile TiO2 is noted to exhibit a remarkably enhanced visible-light activity in comparison with Ti3+ self-doped rutile TiO2, with the latter itself outperforming commercial TiO2 photocatalysts, thereby suggesting the suitability of the material for indoor applications. The broad visible-light absorption by Ti3+ self-doping, the holes with strong oxidation power generated in the valence band, and electrons in Ti3+ isolated states that are effectively separated into the high reductive sites of Cu ions upon visible-light irradiation, accounts for improved photocatalytic activity. Moreover, the synthesis process (SPPS) provides a valuable alternative to orthodox multistep processes for the preparation of such visible-light-driven photocatalysts.

Size-controlled SnO2 hollow spheres via a template free approach as anodes for lithium ion batteries.

Tin oxide hollow spheres (SnO2 HS) with high structural integrity were synthesized by using a one pot hydrothermal approach with organic moieties as structure controlling agents. By adjusting the proportion of acetylacetone (AcAc) in the precursor formulation, SnO2 HS of 200 and 350 nm dimensions, with a uniform shell thickness of about 50 nm, were prepared. Using the optimized solution composition with a Sn precursor, heating duration dependent structural evolution of SnO2 was performed at a fixed temperature of 160 °C, which revealed a transition from solid spheres (1 h) to aggregated spheres (4 h) to porous spheres (10 h) to optimized HS (13 h) and finally to broken enlarged HS (24 h). A heating temperature dependent study carried out with a constant heating span of 13 h showed a metamorphosis from spheres with solid cores (140 °C) to ones with hollow cores (160 °C), culminating with fragmented HS, expanded in dimensions (180 °C). A growth mechanism was proposed for the optimized SnO2 HS (2.5 or 5.0 mL of AcAc, 160 °C, 13 h) and the performance of these HS as anodes for Li ions batteries was evaluated by electrochemical studies. The 200 nm SnO2 HS demonstrated an initial lithium storage capacity of 1055 mA h g(-1) at a current density of 100 mA g(-1), and they retained a capacity of 540 mA h g(-1) after 50 charge-discharge cycles. The SnO2 HS also showed excellent rate capability as the electrode exhibited a capacity of 422 mA h g(-1) even at a high current density of 2000 mA g(-1). The notable capacity of SnO2 HS is a manifestation of the mono-disperse quality of the SnO2 HS coupled with the high number of electrochemically addressable sites, afforded by the large surface area of the HS and the striking cyclability is also attributed to the unique structure of HS, which is resistant to degradation upon repeated ion insertion/extraction. The SnO2 HS were also found to be luminescent, thus indicating their usefulness for not only energy storage but also for energy harvesting applications.

Efficient ZnO-based visible-light-driven photocatalyst for antibacterial applications.

Herein, we report the development of a ZnO-based visible-light-driven photocatalyst by interfacial charge transfer process for the inactivation of pathogens under visible-light illumination. Surface modification by a cocatalyst on ZnO, prepared by flame spray pyrolysis process is carried out to induce the visible-light absorption in ZnO. Optical studies showed that surface modification of Cu(2+) induces the visible-light absorption in ZnO by interfacial charge transfer between ZnO and surface Cu(2+) ions upon light irradiation. The photocatalytic efficiency of pure and modified ZnO is evaluated for the inactivation of pathogens and the decomposition of methylene blue under visible-light illumination. The antibacterial activity of Cu(2+)-ZnO is several orders higher than pure ZnO and commercial Degussa-P25 and comparable with Cu(2+)-TiO2. Cu(2+)-ZnO nanorods show better photocatalytic activity than Cu(2+)-ZnO nanosphere, which is attributed to high surface area to volume ratio of former than later. The holes generated in the valence band and the Cu(1+) species generated during the interfacial charge transfer process may attribute for the inactivation of bacteria, whereas the strong oxidation power of hole is responsible for the decomposition of methylene blue. Besides the advantage of Cu(2+)-modified ZnO for visible-light-assisted photocatalytic applications, the method (FSP) used for the synthesis of ZnO in the present study is attractive for commercial application because the process has potential for the production of large quantities (2-3 kg/h) of semiconductors.

Efficient reduced graphene oxide grafted porous Fe3O4 composite as a high performance anode material for Li-ion batteries.

Here, we report facile fabrication of Fe3O4-reduced graphene oxide (Fe3O4-RGO) composite by a novel approach, i.e., microwave assisted combustion synthesis of porous Fe3O4 particles followed by decoration of Fe3O4 by RGO. The characterization studies of Fe3O4-RGO composite demonstrate formation of face centered cubic hexagonal crystalline Fe3O4, and homogeneous grafting of Fe3O4 particles by RGO. The nitrogen adsorption-desorption isotherm shows presence of a porous structure with a surface area and a pore volume of 81.67 m(2) g(-1), and 0.106 cm(3) g(-1) respectively. Raman spectroscopic studies of Fe3O4-RGO composite confirm the existence of graphitic carbon. Electrochemical studies reveal that the composite exhibits high reversible Li-ion storage capacity with enhanced cycle life and high coulombic efficiency. The Fe3O4-RGO composite showed a reversible capacity ∼612, 543, and ∼446 mA h g(-1) at current rates of 1 C, 3 C and 5 C, respectively, with a coulombic efficiency of 98% after 50 cycles, which is higher than graphite, and Fe3O4-carbon composite. The cyclic voltammetry experiment reveals the irreversible and reversible Li-ion storage in Fe3O4-RGO composite during the starting and subsequent cycles. The results emphasize the importance of our strategy which exhibited promising electrochemical performance in terms of high capacity retention and good cycling stability. The synergistic properties, (i) improved ionic diffusion by porous Fe3O4 particles with a high surface area and pore volume, and (ii) increased electronic conductivity by RGO grafting attributed to the excellent electrochemical performance of Fe3O4, which make this material attractive to use as anode materials for lithium ion storage.

Superhydrophilic graphene-loaded TiO2 thin film for self-cleaning applications.

We develop a simple approach to fabricate graphene-loaded TiO(2) thin films on glass substrates by the spin-coating technique. Our graphene-loaded TiO(2) films were highly conductive and transparent and showed enhanced photocatalytic activities. More significantly, graphene/TiO(2) films displayed superhydrophilicity within a short time even under a white fluorescent light bulb, as compared to a pure TiO(2) film. The enhanced photocatalytic activity of graphene/TiO(2) films is attributed to its efficient charge separation, owing to electrons injection from the conduction band of TiO(2) to graphene. The electroconductivity of the graphene-loaded TiO(2) thin film also contributes to the self-cleaning function by its antifouling effect against particulate contaminants. The present study reveals the ability of graphene as a low cost cocatalyst instead of expensive noble metals (Pt, Pd), and further shows its capability for the application of self-cleaning coatings with transparency. The promising characteristics of (inexpensive, transparent, conductive, superhydrophilic, and highly photocatalytically active) graphene-loaded TiO(2) films may have the potential use in various indoor applications.