Investigation of Rheological Behavior of Untreated and Microwave-Assisted Alkaline Pretreated Sugarcane Straw for Biofuel Production

This research article published by Springer Nature Switzerland AG., 2020Purpose Biomass slurries, such as those subjected to microwave-assisted alkaline (MAA) pretreatment, will become common substrates for the production of biofuels in the future. While the rheology of acid and ionic liquid pretreated biomass is known, the rheology of alkaline pretreated biomass is not yet reported; hence, the goal of this study was to establish the rheological characteristics of untreated and MAA pretreated sugarcane straw (SC). Methods Using rotational rheometry and rheological models, the rheology of SC slurries was assessed as a function of particle size and insoluble solids concentration. Results In the range of 5–17% insoluble solids concentration, the slurries were consistently pseudo-plastic (n = 0.33 ± 0.02), possessed yield stress with their flow accurately described by the Casson rheological model (R2 = 0.98–0.99). The apparent viscosity and yield stress increased by two orders of magnitude with an increase in insoluble solids concentration. Essentially, MAA pretreated slurries exhibited significantly higher values of apparent viscosity and yield stress than the untreated ones, in the range of 55–80% and 21–63% for particle sizes of < 63 µm (P63) and 90–180 µm (P90), respectively. Pretreated P63 samples exhibited higher apparent viscosity and yield stress than the P90. On the other hand, for untreated samples, P63 samples had a reduced apparent viscosity than P90 samples. Conclusion The results of this study definitively reveal that MAA significantly increases the shear rate dependent shear viscosity values along with the yield stress of biomass slurries. This will, therefore, serve as a benchmark for characterizing other MAA pretreated biomass slurries to guide the design of industrial-scale production equipment

Gaseous complex hydrides NaMH and NaMH (M = B, Al) as hydrogen storage materials: a quantum chemical study.

This research article published by Springer Nature Switzerland AG., 2020Metal hydrides are feasible for energy storage applications as they are able to decompose with hydrogen gas release. In this work, gaseous complex sodium hydrides, NaMH and NaMH (M = B or Al), have been investigated using DFT/B3P86 and MP2 methods with 6-311++G(d,p) basis set; the optimized geometry, vibrational spectra and thermodynamic (TD) properties have been determined. Based on TD approach, a stability of the hydrides to different dissociation channels is analysed; the enthalpies of formation ∆H°(0) of gaseous species have been obtained: - 1 ± 17 kJ mol (NaBH), 91 ± 14 kJ mol (NaAlH), - 13 ± 16 kJ mol (NaBH), and 71 ± 16 kJ mol (NaAlH). The complex hydrides are confirmed to produce gaseous products with hydrogen gas release at elevated temperature, whereas heterophase reactions, with NaH and B/Al products in condensed state, are predicted to occur spontaneously at lower temperature. Graphical abstract

Optimization of microwave-assisted alkali pretreatment followed by acid hydrolysis of sugarcane straw for production of acetone-butanol-ethanol

This research article published by Taylor & Francis Online, 2020The production of acetone-butanol-ethanol (ABE) calls for effective pretreatment and hydrolysis techniques to maximize reducing sugar yields. In this study, optimized microwave-assisted alkali (MAA) pretreatment followed by acid hydrolysis was assessed for the production of reducing sugars from sugarcane straw (SCS). To evaluate effects of MAA pretreatment on SCS composition, response surface methodology (RSM) was employed upon subjecting SCS to 320, 640, and 960 W microwave power, using 1–3% (w/v) NaOH, and residence time of 5, 15, and 25 min. The pretreated SCS was made to undergo acid hydrolysis at 121 °C temperature and reaction time of 10–60 min to release reducing sugars. ABE was produced by anaerobic fermentation of reducing sugars using Clostridium beijerinkii. After pretreatment, maximum responses of 76.3% lignin removal, 21.1% hemicellulose, and 71.9% cellulose were achieved at 640 W microwave power, 2.8% NaOH concentration, and 19 min. The maximum reducing sugar concentration was 46.2 g/L while 18.7 g/L of ABE was produced. The results revealed that optimized MAA pretreatment followed by acid hydrolysis can enhance the yield of reducing sugars for ABE production with no need for costly enzymes

High energy density materials based on fluorinated bridged trinitromethyl azo triazole derivatives: a quantum chemical study of thermodynamic and energetic properties

This research article published by Springer Nature Switzerland AG., 2020High energy density materials (HEDM) have gained extensive attention due to their energetic properties and safety issues. Nitro and fluoro groups, among others, have become viable substituents on the triazole framework because of their particular contribution to detonation properties and moderate sensitivity. In this study, Density Function Theory (DFT) approach was employed to design fluorinated bis(trinitromethyl) azo triazoles. The molecular structures, thermodynamic properties of gaseous species (e.g., enthalpies of detonation and enthalpies of formation) and energetic properties of solid materials (detonation heat Q, pressure PD and velocity VD) have been investigated. The best characteristics attained for the designed azo fluorinated solid compounds are as follows: Q 1650–1690 cal g−1, PD 44–46 GPa and VD 9.8 km s−1. These characteristics are superior to those of conventional explosives, indicating that fluorinated bis(trinitromethyl) azo triazoles are promising HEDM

Betanidin isomerisation and decarboxylation, thermodynamic and charge transfer dye properties towards dye sensitised solar cells application

This research article published by John Wiley & Sons, Inc., 2021Along with attractiveness of natural dyes for solar technologies, the instability is a well‐known drawback of the dyes, which impedes their usage for dye sensitised solar cells (DSSCs) application. The planar isomer appeared to be predominant in equilibrium vapour despite its less energetic stability. Both betanidins belong to red–purple pigments betacyanins, which experimentally demonstrated good adsorption in a visible range. In this study, the structural, thermodynamic, and optoelectronic properties of betanidins have been determined from density functional theory (DFT) and time‐dependent DFT (TD–DFT) computations. On the basis of the thermodynamic approach, isomerisation reaction between two structural conformers of betanidin, bent and planar, and also decarboxylation reactions have been analysed. The planar isomer appeared to be predominant in equilibrium vapour despite its less energetic stability; both betanidin molecules exhibit an inclination to decay into decarboxylated betanidin and CO2. As for worthy optoelectronic properties and applicability in DSSCs, the dyes considered satisfy most requirements to sensitise the semiconductor TiO2 and be regenerated by electrolytes. Adsorption of the dyes at the TiO2 surface has been simulated; for the dye@TiO2 complexes, the binding energies, electronic spectra, and relevant molecular orbital (MO) isosurfaces have been computed and discussed

Guanidinium tin halide perovskites: structural, electronic, and thermodynamic properties by quantum chemical study

This research article published by Springer Nature Switzerland AG., 2021The orthorhombic phase of guanidinium tin halide perovskites C(NH2)3SnX3, X = Cl, Br, I has been studied by quantum chemical method. The lattice parameters are optimized to obtain the minimum energy using the density functional theory with the generalized gradient approximation, GGA-PBE. The Kohn–Sham electronic band structures have been computed; the materials have direct bandgaps of 3.00, 2.47, and 1.78 eV for the C(NH2)3SnCl3, C(NH2)3SnBr3, and C(NH2)3SnI3, respectively, situated at the gamma symmetry points. The projected densities of states are analyzed and the contribution of the p- and s-states of the tin and halogen atoms evaluated. For the GUASnX3 compounds, thermodynamic stability to different decomposition routes has been assessed and standard enthalpies of formation obtained

Complex Hydrides Li2MH5 (M = B, Al) for Hydrogen Storage Application: Theoretical Study of Structure, Vibrational Spectra and Thermodynamic Properties

This research article published by Science Publishing Group, 2015Gaseous lithium complex hydrides Li2MH5 (M = B, Al) have been studied using DFT/B3P86 and MP2 methods with 6-311++G(d,p) basis set. High content of hydrogen by these materials accord them with good candidacy as a class of hydrogen storage materials. The optimized geometrical parameters, vibrational spectra and thermodynamic properties of the hydrides and the subunits LiH, Li2H+, Li2H2, MH3, MH4−, and LiMH4 have been determined. For the LiBH4 the equilibrium configuration was tridentate of C3v symmetry. For LiAlH4 two isomeric forms, bidentate (C2v) and tridentate (C3v), were confirmed to exist, and C2v isomer was shown to dominate in saturated vapor. For complex hydrides Li2MH5, different structural forms were considered but only one asymmetric form (C1) appeared to be equilibrium. Several possible channels of dissociation of Li2MH5 were considered; the enthalpies and Gibbs free energies of the reactions were computed. The enthalpies of formation ∆fH(0) of the complex hydrides in gaseous phase were determined: 60 ± 10 kJmol1 (Li2BH5) and 33 ± 10 kJmol1 (Li2AlH5). Heterophase decomposition of the gaseous Li2MH5 with solid products LiH and B/Al and hydrogen gas release was shown to be spontaneous at ambient temperature. Production of hydrogen gas via gaseous decomposition is highly endothermic and achievable at elevated temperatures. The complexes Li2MH5 are therefore proposed to be useful hydrogen storage materials under appropriate conditions

Methylammonium tin iodide perovskite: structural, electronic and thermodynamic properties by a DFT study with different exchange–correlation functionals

This research article published by Springer Nature Switzerland AG., 2020Lead-free perovskites have drawn much attention of researchers in the field of electronics and photovoltaics due to the toxicity issue of the lead halide perovskites. The methylammonium tin iodide CH3NH3SnI3 amongst others has become a viable alternative due to its eco-friendliness, as well as narrower bandgap and its wider visible absorption spectrum. In this study different theoretical approaches were employed in investigating the structural, electronic and thermodynamic properties of the orthorhombic phase (O-phase) of the CH3NH3SnI3 perovskite. By using the first-principle calculations with the density functional theory, a direct bandgap was determined at gamma symmetry points with three exchange–correlation functionals: PBE 1.12 eV, PBEsol 0.98 eV, and LDA 0.46 eV. Based on the comparison of lattice constants and bandgaps with the experimental values, the best performance resulted from PBE. The decomposition of the CH3NH3SnI3 perovskite into solid state products, CH3NH3I and SnI2, was considered; the enthalpy of the reaction ΔrH° (0 K) = 37 kJ mol−1 and enthalpy of formation of the O-phase perovskite ΔfH° (CH3NH3SnI3, 0 K) =  − 390 kJ mol−1 were evaluated, indicating the stability of the O-phase CH3NH3SnI3 at low temperature, in agreement with experimental findings

Biogas-slurry derived mesoporous carbon for supercapacitor applications

This research article published by Elsevier Ltd., 2017This study reports on the transformation of biogas slurry into mesoporous carbon for supercapacitor electrodes. Pore structures have been modified by altering activation time, temperature and KOH/carbon mass ratio. The mesoporous carbons are successively developed as evidenced by type IV isotherms obtained in nitrogen sorption studies. BET, micropore and mesopore surface area of 515, 350, and 165 m2 g−1, respectively as well as a narrow pore width distribution of 3–4.5 nm are obtained. X-ray photoelectron results have confirmed the presence of functional groups of oxygen and nitrogen in the samples which facilitates the pseudocapacitance. The electrochemical measurements in 6 M KOH using a three electrode cell with Ag/AgCl as reference electrode and platinum as counter electrode has been performed. The materials activated at 700 °C, 3:1 KOH to carbon mass ratio, and for 120 min exhibit high specific capacitance of 289 F g−1 at a scan rate of 5 mV s−1. Shortening activation time to 30 and 60 min reduces specific capacitance to 163 and 182 F g−1, in that order. Additionally, at 3:1 KOH to carbon mass ratio and 60 min activation time, specific capacitances of 170 and 210 F g−1 at 600 and 800 °C, respectively are obtained. Moreover, specific capacitance increases with increasing the KOH to carbon mass ratio from 148 F g−1 for 1:1–163 F g−1 for 3:1 at 700 °C. Electrochemical impedance spectroscopy studies demonstrate that material has high conductivity. In addition; capacity retention of 96% after 20,000 cycles is shown at scan rate of 30 mV s−1. The study shows that high performance electrodes can be designed from biogas slurry derived porous carbon

Investigation of optoelectronic properties of triphenylamine-based dyes featuring heterocyclic anchoring groups for DSSCs’ applications: a theoretical study

This research article published by Springer Nature Switzerland AG., 2020Design and synthesis of new potent sensitizers are of interest for realization of high-efficiency Dye Sensitized Solar Cells (DSSCs). Modification of the triphenylamine-based dyes by introducing suitable anchoring groups aimed at improvement of optoelectronic properties is attempted in our work. The molecular structure, molecular orbitals and energies, electronic absorption spectra, free energies of electron injection and dye regeneration, chemical reactivity parameters and adsorption to TiO2 semiconductor have been reported. Density functional theory (DFT) and time-dependent DFT (TD-DFT) were used to obtain the reported properties. The results reveal superior optical, electronic properties, chemical reactivity parameters and adsorption energies for the investigated dyes. The findings evince that the dyes featuring heterocyclic anchoring groups could be potential candidates for DSSCs’ applications; the new materials are worthy of being investigated experimentally