A High-Energy Density Li-Ion Hybrid Capacitor Fabricated from Bio-Waste Derived Carbon Nanosheets Cathode and Graphite Anode.

The Li-ion hybrid capacitor (LIHC) system explores the possibility of achieving both high energy and power density in a single energy storage system with an intercalation anode and capacitive cathode. However, to achieve a high power and energy-based system, the properties of the cathode electrode material are vital. Here, bio-waste plant stem-derived activated porous carbon is explored as a cathode for LIHC application. A specific surface area of 1826 m2 g-1, enhanced degree of crystallinity, and graphitization results for porous carbon from activation by potassium hydroxide. When employed as supercapacitor material, the device exhibits good rate capability, energy, and power attributes with a specific capacitance of 116 F g-1 (1 A g-1). Simultaneously when tested for LIHC application the formulated device shows good capacity retention for 2500 cycles with a high energy density of 125 Wh kg-1 at a power density of 69 W kg-1. The work demonstrates unique, cost-effective strategy to develop a crystalline high surface area carbon from any such bio-waste sources to be employed as potential electrodes for energy storage applications.

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.

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.

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.

Improved photocatalytic efficiency of a WO3 system by an efficient visible-light induced hole transfer.

Amorphous Cu(II) nanoclusters grafted WO(3) particles were coated on a smooth TiO(2) film, and site selective depositions of PbO(2) and metal Ag particles by photocatalytic processes were observed on TiO(2) and WO(3) due to transfer of holes to TiO(2), and accumulation of electrons in WO(3) respectively. As a result, the photocatalytic activity of TiO(2) modified Cu(II)-WO(3) increased ~3.5 fold higher than that of Cu(II)-WO(3).

Ce-doped ZnO (Ce(x)Zn(1-x)O) becomes an efficient visible-light-sensitive photocatalyst by co-catalyst (Cu2+) grafting.

We have fabricated an efficient visible-light-sensitive Cu(2+)-grafted Ce-doped ZnO photocatalyst (Cu(2+)-Ce(x)Zn(1-x)O) by adopting a metal ion doping and co-catalyst modification. Impurity states were formed below the conduction band (CB) edge in Ce(x)Zn(1-x)O, and these impurity states induce the visible-light absorption. Ce(x)Zn(1-x)O without a Cu(2+)-co-catalyst showed negligible visible-light activity due to the low reduction power of electrons in impurity levels. Surprisingly, Cu(2+)-modification over Ce(x)Zn(1-x)O drastically increased its visible-light activity. Excited electrons in impurity states can transfer to the Cu(2+)-ions on the surface and form Cu(2+)/Cu(+) redox couples, which cause the efficient oxygen reduction through a multi-electron reduction process. One of the striking features of the present study is that the metal doped semiconductors which were inactive due to their impurity states become efficient visible-light photocatalysts upon co-catalyst modification. The successful strategy used here for designing a highly active visible-light photocatalyst would provide numerous opportunities to develop an efficient metal-ion based visible-light photocatalyst.

Single crystalline zinc stannate nanoparticles for efficient photo-electrochemical devices.

Single crystalline zinc stannate (Zn(2)SnO(4) and ZnSnO(3)) nanoparticles were synthesized by a simple one-step hydrothermal reaction with a high production yield. Zn(2)SnO(4) is a (111) face-exposed octahedron, whereas ZnSnO(3) is a (100) face-exposed hexahedron structure. In particular, Zn(2)SnO(4) exhibits an efficient performance for applications in dye-sensitized solar cells.

Visible-light-driven superhydrophilicity by interfacial charge transfer between metal ions and metal oxide nanostructures.

Single-crystalline rutile nanorods were synthesized by a facile acid treatment on titanate nanotubes. These rutile nanorods could be highly dispersed in water to form a stable colloidal solution. Cu(2+) ions were grafted onto these rutile nanorods, and the Cu(2+)-grafted nanorods could absorb visible light by the interfacial charge transfer between the valence band of rutile TiO(2) and surface-modified Cu(2+) ions. Transparent thin films of Cu(2+)-grafted nanorods were coated on substrates by a facile spin-coating method. These films exhibited superhydrophilic conversion under visible light irradiation.

Novel microporous carbon material with flower like structure templated by MCM-22.

Novel flower like microporous carbons with very high surface area have been synthesized for the first time using MCM-22 zeolite as a template and sucrose as a carbon source. The textural parameters of the materials can easily be tuned by the simple adjustment of the sucrose to MCM-22 weight ratio. It has been also found that the specific surface area of the microporous carbon materials is much higher as compared with that of its parent zeolite template.

RETRACTED: Photocatalytic activity of Bi-doped TiO(2) in the degradation of monocrotophos in aqueous solution.

This article has been retracted consistent with Elsevier Policy on Article Withdrawal. Please see . The Publisher apologizes for any inconvenience this may cause.