Theoretical studies on conjugated phenyl-cored thiophene dendrimers for photovoltaic applications

Pi-conjugated dendrimers are an important class of materials for optoelectronic devices, especially for light-harvesting systems. We report here a theoretical investigation of the optical response and of the excited-state properties of three-arm and four-arm phenyl-cored dendrimers for photovoltaic applications. A variety of theoretical methods are used and evaluated against each other to calculate vertical transition energies, absorption and excitation spectra with vibronic structure, charge transport, and excitonic behavior upon photoexcitation and photoemission processes. Photophysical phenomena in these dendrimers are, in general, better explained with ab initio methods rather than with semiempirical techniques. Calculated reorganization energies were found to correlate well with the device photocurrent data where available. The excitons formed during photoexcitation are calculated to be more delocalized than the ones formed after vibrational relaxation in the excited states for fluorescence emission. The localization of excitons in emission processes is a result of geometrical changes in the excited state coupled with vibronic modes. Correlated electron-hole pair diagrams illustrate breaking of pi-conjugation in three-arm dendrimers due to meta linkage of arms with the core, whereas four-arm dendrimers are not affected by such breaking due to presence of ortho and para branching. Yet, ortho branching causes large twist angles between the core and the arms that are detrimental to pi-electron system delocalization over the structure.     

Effect of laser irradiation on thermal and optical properties of selenium–tellurium alloy

The crystallization parameters such as glass transition temperature (T_g), onset crystallization temperature (T_c), peak crystallization temperature (T_p) and enthalpy released (ΔH_C) of the bulk Se–Te chalcogenide glass has been studied by using Differential Scanning Calorimeter (DSC), under non-isothermal condition at a heating rate of 20 K/min. The values of T_g, T_c, T_p and ΔH_C with and without laser irradiation for different exposure time have been studied. The optical absorption of pristine and laser irradiated thermally evaporated Se–Te films has been measured. The films shows indirect allowed interband transition that is influenced by the laser irradiation. The optical energy gap has been found to decrease from 1.61 to 1.38 eV with increasing irradiation time from 5 to 20 min. The results have been analyzed on the basis of laser irradiation-induced defects in the film.     

Synthesis of poly(hydroxamic acid) ligand from polymer grafted corn‐cob cellulose for transition metals extraction

Poly(hydroxamic acid) ligand was synthesized using ester functionalities of cellulose‐graft‐poly(methyl acrylate) copolymer, and products are characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, high‐resolution transmission electron microscopy, and X‐ray photoelectron spectroscopy analysis. The poly(hydroxamic acid) ligand was utilized for the sensing and removal of transition metal ions form aqueous solutions. The solution pH is found a key factor for the optical detection of metal ions, and the reflectance spectra of the [Cu‐ligand]ⁿ⁺ complex were observed to be the highest absorbance 99.5% at pH 6. With the increase of Cu²⁺ ion concentration, the reflectance spectra were increased, and a broad peak at 705 nm indicated that the charge transfer (π‐π transition) complex was formed. The adsorption capacity with copper was found to be superior, 320 mg g^?1, and adsorption capacities for other transition metal ions were also found to be good such as Fe³⁺, Mn²⁺, Co³⁺, Cr³⁺, Ni²⁺, and Zn²⁺ were 255, 260, 300, 280, 233, and 223 mg g^?1, respectively, at pH 6. The experimental data show that all metal ions fitted well with the pseudo‐second‐order rate equation. The sorption results of the transition metal ions onto ligand were well fitted with Langmuir isotherm model (R² > 0.98), which implies the homogenous and monolayer character of poly(hydroxamic acid) ligand surface. Eleven cycles sorption/desorption process were applied to verify the reusability of this adsorbent. The investigation of sorption and extraction efficiency in each cycle indicated that this new type of adsorbent can be recycled in many cycles with no significant loss in its original detection and removal capability. Copyright © 2016 John Wiley & Sons, Ltd.     

Finite presentation of alternating groups

Graham Higman posed the question: How small can the integersp andq be made, while maintaining the property that all but finitly many alternating and symmetric groups are factor groups of Δ(2,p,q)=<x,y:x ²=y ^p =3 (xy) ^q =1>? He proved that for a sufficiently largen, the alternating group is a homomorphic image of the triangle group Δ(2,p,q) wherep=3 andq=7. Later, his result was generalized by proving the result forp=3 andq≥7. Choosingp=4 andq≥17 in this paper we have answered the “Hiqman Question”.     

A High-Performance Asymmetric Supercapacitor Based on Tungsten Oxide Nanoplates and Highly Reduced Graphene Oxide Electrodes

Tungsten oxide/graphene hybrid materials are attractive semiconductors for energy-related applications. Herein, we report an asymmetric supercapacitor (ASC, HRG//m-WO₃ ASC), fabricated from monoclinic tungsten oxide (m-WO₃) nanoplates as a negative electrode and highly reduced graphene oxide (HRG) as a positive electrode material. The supercapacitor performance of the prepared electrodes was evaluated in an aqueous electrolyte (1 m H₂SO₄) using three- and two-electrode systems. The HRG//m-WO₃ ASC exhibits a maximum specific capacitance of 389 F g⁻¹ at a current density of 0.5 A g⁻¹, with an associated high energy density of 93 Wh kg⁻¹ at a power density of 500 W kg⁻¹ in a wide 1.6 V operating potential window. In addition, the HRG//m-WO₃ ASC displays long-term cycling stability, maintaining 92 % of the original specific capacitance after 5000 galvanostatic charge–discharge cycles. The m-WO₃ nanoplates were prepared hydrothermally while HRG was synthesized by a modified Hummers method.     

Synthesis and Electrochemical Performance of Urea Assisted Pristine LiMn2O4 Cathode for Li Ion Batteries

We report the synthesis of electrochemically active LiMn₂O₄ nanoparticles at varied temperature and pH values by sol–gel method using urea as a chelating and combusting agent. The effect of pH and annealing temperature on the structure, morphology and electrochemical performance was evaluated. The results obtained by XRD, SEM, TEM, and FTIR show that LiMn₂O₄ has uniform porous morphology and highly crystalline particles that can be obtained at pH 7.0 and 8.0 and at a relatively lower temperature of 600°C. Cyclic voltammetry measurements showed reversible redox reactions with fast kinetics corresponding to Li ions intercalation/deintercalation at 600°C at neutral pH 7.0. Charge/discharge studies carried out at a current rate of 40 mA g^–1 reveal that LiMn₂O₄ synthesized at 600°C and pH 7.0 has the best structural stability and excellent cycling performance.

     

Analysis of chemically reactive species with mixed convection and Darcy–Forchheimer flow under activation energy: a novel application for geothermal reservoirs

Journal of Thermal Analysis and Calorimetry - In the present article, an analysis has been performed to discuss the impact of steady mixed convection with Darcy–Forchheimer flow towards...     

Preparation and Utilization of Jute‐Derived Carbon: A Short Review

This article summarizes the preparation and applications of carbon derived from jute sticks and fibers that are low‐cost, widely available, renewable, and environmentally friendly. Both the fibers and sticks are considered ideal candidates of carbon preparation because they are composed of cellulose, hemicelluloses, and lignin, and contain negligible ash content. Various carbon preparation methods including simple pyrolysis, pyrolysis with chemical and physical activations are discussed. The impacts of several parameters including types of activating agents, impregnation ratio, and temperature on their morphology, surface area, pore size, crystallinity, and surface functional groups are also emphasized. Various treatments to endow functionalization for increasing the practical applicability, such as chemical, physical, and physico‐chemical methods, are discussed. In addition, applications of jute‐derived carbon in various practical areas, including energy storage, water treatment, and sensors, are also highlighted in this report. Due to the porous fine structure and a large specific surface area, the jute‐derived carbon could be considered as a powerful candidate material for various industrial applications. Finally, possible future prospects of jute‐derived carbon for various applications are pointed out.     

Simplified Synthesis of Biomass-Derived Si/C Composites as Stable Anode Materials for Lithium-Ion Batteries

Synthesis of silicon/carbon (Si/C) composites from biomass resources could enable the effective utilization of agricultural products in the battery industry with economical as well as environmental benefits. Herein, a simplified process was developed to synthesize Si/C from biomass, by using a low-cost agricultural byproduct “rice husk (RH)” as a model. This process includes the calcination of RH for SiO₂/C and the reduction of SiO₂/C by Al in molten salts at a moderate temperature. This process does not need the removal of carbon before thermal reduction of SiO₂, which is thought to be necessary to avoid the formation of SiC at elevated temperatures. Thus, carbon derived from biomass can be directly used for Si/C composites for anode materials. The resultant Si/C shows a high reversible capacity of 1309 mAh g⁻¹ and long cycle life (300 cycles). This research advocates a new and simplified strategy for the synthesis of RH-based biomass-derived Si/C, which is beneficial for low-cost, environmentally friendly, and green energy storage applications.