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This paper addresses the multiple level warehouse layout problem, which involves assigning items to cells and levels with the objective of minimizing transportation costs. A monthly demand and an inventory requirement are associated with every item type along with vertical and horizontal unit transportation costs. The warehouse has one port to transport items vertically from ground floor to the other levels, where each item must be assigned to exactly one cell on the assigned level. An ant colony optimization (ACO) algorithm is adapted to this NP-complete problem and its performance is evaluated by comparing its solutions to the ones obtained using genetic algorithms (GA) as well as the optimal solutions for small problems. The computational results reflected the superiority of ACO in large-size problem instances, with a marginally better performance than GA in smaller ones, while solving the tested instances within a reasonable computational time. Furthermore, ACO was able to attain most of the known optimal solutions for small-size problem instances. Publisher's Version

The efficient storage of energy combined with a minimum carbon footprint is still considered one of the major challenges towards the transition to a progressive, sustainable and environmental friendly society on a global scale. The energy storage in pure chemical form using gas carriers with high heating values, including H-2 and CH4, as well as via electrochemical means using state-of-the-art devices, such as batteries or supercapacitors, are two of the most attractive alternatives for the combustion of finite, carbon-rich and environmentally harmful fossil fuels, such as diesel and gasoline. A few-step, reproducible and scalable method is presented in this study for the preparation of an ultra-microporous (average pore size around 0.6 nm) activated carbon cloth (ACC) with large specific area ( GT 1200 m(2)/g) and pore volume (similar to 0.5 cm(3)/g) upon combining chemical impregnation, carbonization and CO2 activation of a low-cost cellulose-based polymeric fabric. The ACC material shows a versatile character towards three different applications, including H2 storage via cryo-adsorption, separation of energy-dense CO2/CH4 mixtures via selective adsorption and electrochemical energy storage using super-capacitor technology. Fully reversible H-2 uptake capacities in excess of 3.1 wt% at 77 K and similar to 72 bar along with a significant heat of adsorption value of up to 8.4 kJ/mol for low surface coverage have been found. Upon incorporation of low-pressure sorption data in the ideal adsorbed solution theory model, the ACC is predicted to selectively adsorb about 4.5 times more CO2 than CH4 in ambient conditions and thus represents an appealing adsorbent for the purification of such gaseous mixtures. Finally, an electric double-layer capacitor device was assembled and tested for its electrochemical performance, constructed of binder-free and flexible ACC electrodes and aqueous CsCl electrolyte. The full-cell exhibits a gravimetric capacitance of similar to 121 F/g for a specific current of 0.02 A/g, which relative to the ACCs specific area, is superior to commercially available activated carbons. A capacitance retention of more than 97% was observed after 10,000 charging/discharging cycles, thus indicating the ACCs suitability for demanding and high-performance energy storage on a commercial scale. The enhanced performance in all tested applications seems to be attributed to the mean ultra-micropore size of the ACC material instead of the available specific area and/or pore volume.

Structured porous materials have provided several breakthroughs that have facilitated high rate capability, better capacity retention and material stability in Li-ion batteries. However, most advances have been limited to half cells or lithium batteries, and with a single mode of charge storage (intercalation, conversion, or alloying etc.). The use of dual-mode charge storage with non-traditional material pairings, while maintaining the numerous benefits of nanoscale materials, could significantly improve the capacity, energy density, stability and overall battery safety considerably. Here, we demonstrate an efficient, high capacity full inverse opal Li-ion battery with excellent cycle life, where both the cathode and anode binder-free electrodes are composed of 3D nanocrystal assemblies as inverse opal (IO) structures of intercalation-mode V2O5 IO cathodes and conversion-mode Co3O4 IO anodes. Electrochemically charged Co3O4 IOs function as Li-ion anodes and the full V2O5/Co3O4 cell exhibits superior performance compared to lithium batteries or half cells of either IO material, with voltage window compatibility for high capacity and energy density. Through asymmetric charge–discharge tests, the V2O5 IO/Co3O4 IO full Li-ion cell can be quickly charged, and discharged both quickly and slowly without any capacity decay. We demonstrate that issues due to the decomposition of the electrolyte with increased cycling can be overcome by complete electrolyte infiltration to remove capacity fading from long term cycling at high capacity and rate. Lastly, we show that the V2O5 IO/Co3O4 IO full Li-ion cells cycled in 2 and 3-electrode flooded cells maintain 150 mA h g−1 and remarkably, show no capacity fade at any stage during cycling for at least 175 cycles. The realization of an all-3D structured anode and cathode geometry with new mutually co-operative dual-mode charge storage mechanisms and efficient electrolyte penetration to the nanocrystalline network of material provides a testbed for advancing high rate, high capacity, stable Li-ion batteries using a wide range of materials pairings.

Core-shell structured nanohybrids are currently of significant interest due to their synergetic properties and enhanced performances. However, the restriction of lattice mismatch remains a severe obstacle for heterogrowth of various core-shells with two distinct crystal structures. Herein, a controlled synthesis of lattice-mismatched core-shell TiO2@MoS2 nano-onion heterostructures is successfully developed, using unilamellar Ti0.87O2 nanosheets as the starting material and the subsequent epitaxial growth of MoS2 on TiO2. The formation of these core-shell nano-onions is attributed to an amorphous layer-induced heterogrowth mechanism. The number of MoS2 layers can be well tuned from few to over ten layers, enabling layer-dependent synergistic effects. The core-shell TiO2@MoS2 nano-onion heterostructures exhibit significantly enhanced energy storage performance as lithium-ion battery anodes. The approach has also been extended to other lattice-mismatched systems such as TiO2@MoSe2, thus suggesting a new strategy for the growth of well-designed lattice-mismatched core-shell structures. A controlled synthesis of lattice-mismatched core-shell TiO2@MoS2 nano-onion heterostructures is developed, using unilamellar Ti0.87O2 nanosheets as the starting material and the subsequent epitaxial growth of MoS2 on TiO2. The formation of these core-shell nano-onions is attributed to an amorphous layer-induced heterogrowth mechanism. The core-shell TiO2@MoS2 nano-onion heterostructures exhibit significantly enhanced energy storage performance as lithium-ion battery anodes. 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Scopus

Considerable progress has been made recently in the use of nanoporous materials for hydrogen storage. In this article, the current status of the field and future challenges are discussed, ranging from important open fundamental questions, such as the density and volume of the adsorbed phase and its relationship to overall storage capacity, to the development of new functional materials and complete storage system design. With regard to fundamentals, the use of neutron scattering to study adsorbed H2, suitable adsorption isotherm equations, and the accurate computational modelling and simulation of H2 adsorption are discussed. The new materials covered include flexible metal-organic frameworks, core-shell materials, and porous organic cage compounds. The article concludes with a discussion of the experimental investigation of real adsorptive hydrogen storage tanks, the improvement in the thermal conductivity of storage beds, and new storage system concepts and designs. Scopus

A novel, one-step, wet-free, environmental friendly and high-yield method for producing few-layer graphene powders with large surface areas (up to 800 m2/g) and narrow nanopore sizes (0.7-0.8 nm) using plasma-induced exfoliation of natural graphite is presented. Advanced characterization techniques were employed, including scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction and N2 gas adsorption/desorption measurements at 77 K, to investigate the morphological, elemental, structural and textural/porosity properties of these nanomaterials. Fully reversible H2 gas adsorption/desorption isotherms with maximum gravimetric capacities of up to ∼2 wt.% at 77 K and ∼60 bar are reported here. The H2 storage performance at 77 K is well correlated with certain textural features such as specific surface area and microporosity. The results of this work provide a valuable feedback for further research on plasma-processed graphene-based materials towards efficient H2 storage via cryo-adsorption. © 2016 Elsevier Inc. All rights reserved. 225 482 487 482-487

RGO/Sb2S3 nanocomposite has been investigated in this study as a dual anode material for Li- and Na-ion battery applications. The stibnite phase of Sb2S3, and its rGO composite have been obtained from a molecular complex, Sb(SCOPh)3 or its rGO mixture by solid state decomposition or hydrothermal treatment. The pristine sample consists of micron sized particles with rod-like morphology while the rGO composite is made of nanoparticles of Sb2S3 embedded in rGO sheets. Electrochemical lithium and sodium storage properties of the prepared materials have been investigated using galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy studies. The rGO composite demonstrates better lithium storage capacity than the pristine sample owing to enhanced conductivity. In addition, the rGO sheets act as a buffer for volume change during lithium/sodium cycling resulting in a better energy storage. 2016 American Chemical Society. J.J.V. thanks the Ministry of Education, Singapore, through NUS Tier 1 FRC grant (No. R143-000-562-112). M.V.R. would like to thank the National Research Foundation (NRF), Singapore, for the research Grant no. WBS:R-284-000-115-281. Scopus

cited By 3; International audience; Adsorption properties of gram-scale samples of different kind of arc discharge nanotubes were studied, namely: (A) raw collaret collected on the cathode, (B) raw soots collected on the lateral reactor wall, (C) thermally treated soot, and (D) thermally then chemically treated soot. The morphology, structure, and composition of these materials were characterized by SEM, TEM, TGA, and BET. In addition, hydrogen adsorption isotherms were recorded experimentally for A, B, and D samples over the pressure range of 0 to 55 bar at ambient temperature. Our experiments indicated a maximum - yet weak - hydrogen storage at room temperature of ∼0.13 H 2 wt% for the purified product (D). Copyright © 2007 American Scientific Publishers All rights reserved.

Fe promoted NOx storage materials were synthesized in the form of FeOx/BaO/Al2O3 ternary oxides with varying BaO (8 and 20 wt %) and Fe (5 and 10 wt %) contents. Synthesized NOx storage materials were investigated via TEM, EELS, BET, FTIR, TPD, XRD, XPS, and Raman spectroscopy, and the results were compared with the conventional BaO/Al2O3 NOx storage system. Our results suggest that the introduction of Fe in the BaO/Al2O3 system leads to the formation of additional NOx storage sites which store NOx mostly in the form of bidentate nitrates. NO2 adsorption experiments at 323 K via FTIR indicate that, particularly in the early stages of the NOx uptake, the NOx storage mechanism is significantly altered in the presence of Fe sites where a set of new surface nitrosyl and nitrite groups were detected on the Fe sites and the surface oxidation of nitrites to nitrates is significantly hindered with respect to the BaO/Al2O3 system. Evidence for the existence of both Fe3+ as well as reduced Fe2+/(3-x)+ sites on the freshly pretreated materials was detected via EELS, FTIR, Raman, and XRD experiments. The influence of the Fe sites on the structural properties of the synthesized materials was also studied by performing ex situ annealing protocols within 323-1273 K followed by XRD and Raman experiments where the temperature dependent changes in the morphology and the composition of the surface domains were analyzed in detail. On the basis of the TPD data, it was found that the relative stability of the stored NOx species is influenced by the morphology of the Ba and Fe containing NOx-storage domains. The relative stabilities of the investigated NOx species were found to increase in the following order: N2O3/NO+ < nitrates on γ-Al2O3 < surface nitrates on BaO < bidentate nitrates on FeOx sites < bulk nitrates on BaO.