Net Thermal Effects Research Articles

Visualization of freezing process in situ upon cooling and warming of aqueous solutions.

The freezing of aqueous solutions and reciprocal distribution of ice and a freeze-concentrated solution (FCS) are poorly understood in spite of their importance in fields ranging from biotechnology and life sciences to geophysics and climate change. Using an optical cryo-miscroscope and differential scanning calorimetry, we demonstrate that upon cooling of citric acid and sucrose solutions a fast freezing process results in a continuous ice framework (IF) and two freeze-concentrated solution regions of different concentrations, FCS1 and FCS2. The FCS1 is maximally freeze-concentrated and interweaves with IF. The less concentrated FCS2 envelops the entire IF/FCS1. We find that upon further cooling, the FCS1 transforms to glass, whereas the slow freezing of FCS2 continues until it is terminated by a FCS2-glass transition. We observe the resumed slow freezing of FCS2 upon subsequent warming. The net thermal effect of the resumed freezing and a reverse glass-FCS1 transition produces the Ttr2-transition which before has only been observed upon warming of frozen hydrocarbon solutions and which nature has remained misunderstood for decades.

Silica gel modified with ethylenediamine and succinic acid-adsorption and calorimetry of cations in aqueous solution

Ethylenediamine molecules were covalently immobilized onto silica gel previously functionalized with 3-chlorosilylpropyltrimethoxysilane (Sil–Cl), producing a Sil–N surface. The Sil–N surface reacted with succinic acid, yielding a Sil–NSuc surface. This new synthesized silica gel surface was used to adsorb divalent cations from aqueous solutions at room temperature. The adsorption isotherms were fit to a modified Langmuir equation using the data obtained by suspending the solid in MCl2 (M=Cu, Ni, and Co) aqueous solutions, yielding the maximum number of moles adsorbed as 1.04±0.01, 1.89±0.02 and 1.85±0.02mmolg−1 for divalent copper, nickel and cobalt, respectively. The metal-basic center ratio for complexes on the surfaces varied with the nature of the metal. The spontaneity of these systems was reflected in the negative values of the Gibbs free energy calculated using calorimetric data. The net thermal effects obtained from the calorimetric titration measurements were adjusted to a modified Langmuir equation, and the calculation of the enthalpies of the interaction for the complexation with Sil–NSuc yielded the following exothermic values: 2.81±0.08, 0.35±0.04±and 0.69±0.05kJmol−1 for Cu2+, Co2+ and Ni2+, respectively. Based on these values, the metals are preferentially adsorbed in the order Cu2+>Co2+>Ni2+. The other thermodynamic data for these systems are favorable at the solid/liquid interface, suggesting the efficacy of this modified silica for cation removal from solution.

Upper atmosphere response to stratosphere sudden warming: Local time and height dependence simulated by GAIA model

AbstractThe whole atmosphere model GAIA is employed to shed light on atmospheric response to the 2009 major stratosphere sudden warming (SSW) from the ground to exobase. Distinct features are revealed about SSW impacts on thermospheric temperature and density above 100 km altitude. (1) The effect is primarily quasi‐semidiurnal in tropical regions, with warming in the noon and pre‐midnight sectors and cooling in the dawn and dusk sectors. (2) This pattern exists at all altitudes above 100 km, with its phase being almost constant above 200 km, but propagates downward in the lower thermosphere between 100 and 200 km. (3) The northern polar region experiences warming in a narrow layer between 100 and 130 km, while the southern polar region experiences cooling throughout 100–400 km altitudes. (4) The global net thermal effect on the atmosphere above 100 km is a cooling of approximately −12 K. These characteristics provide us with an urgently needed global context to better connect and understand the increasing upper atmosphere observations during SSW events.

Dielectric properties of organofunctionalized kaolinite clay and application in adsorption mercury cation

Kaolinite clay samples from Amazon region, Pará state, Brazil, were first intercalated with dimethylsulfoxide (DS) followed by immobilization of (3-aminopropyl)triethoxysilane (APS). The samples were characterized by X-ray diffraction, and zero point charge determination. The chemically modified kaolinite samples showed modification of its physical–chemical properties including: specific area of 25.2–421.5 m 2 g −1 for K 1 and K 1-DS/APS, and 24.7–425.9 m 2 g −1 for K 2 and K 2-DS/APS. New d 0 0 1 values of 1.313 and 1.319 nm for the modified kaolinites K 1-DS/APS and K 2-DS/APS, respectively, were obtained. From electrical property investigations an increase in electric permittivity was observed for real ( ɛ |) and imaginary ( ɛ ||) at low frequencies, which are probably related to the interlayer molecules. The energetic effect caused by mercury cation adsorption was determined through calorimetric titration at the solid–liquid interface and gave net thermal effects that enabled the calculation of the exothermic enthalpic values and the equilibrium constant. From these values negative Gibbs free energy and positive entropy were calculated and this set of thermodynamic data is favorable for mercury/basic center interaction at the solid/liquid interface.

Synthesized cellulose/succinic anhydride as an ion exchanger. Calorimetry of divalent cations in aqueous suspension

A synthetic route to a biopolymer/anhydride ion exchanger adds cellulose directly to molten succinic anhydride in a quasi solvent-free procedure. An amount of 3.07 ± 0.05 mmol of pendant groups incorporated onto the polymeric structure, which was characterized by elemental analysis, solid state carbon NMR, infrared, X-ray and thermogravimetry. The new polysaccharide is able to exchange cations from aqueous solution through a batchwise methodology, to obtain 2.46 ± 0.09 mmol g −1 for divalent cobalt and nickel cations. The net thermal effects obtained from calorimetric titrations gave endothermic values of 3.81 ± 0.02 and 2.35 ± 0.01 kJ mol −1. The spontaneity of this ion-exchange process reflected in negative Gibbs energies and also a positive entropic contribution. These thermodynamic data at the solid/liquid interface suggests a favorable ion exchange process for this anchored biopolymer, for cation removal from the environment.

Thermal and bifurcation characteristics of heat-recirculating conversion of gaseous fuels

Thermal and bifurcation characteristics of heat-recirculating conversion of gaseous fuelsThe paper investigates the possibility of utilisation of heat-recirculating systems for fuel conversions having low net thermal effect. The experimental part is conducted with an electrically heated heat exchanger. It is shown that heat-recirculating systems can operate under superadiabatic conditions. Their thermal characteristics are provided by means of the dependencies of heat recirculation ratio on process parameters. Further, the heat-recirculating catalytic combustion system is characterised via combustion bifurcation diagrams. The similarities and differences of both those heat-recirculating systems are qualitatively compared and explained. Bifurcation characteristics proves to be useful tools in concise description of practical complex heat-recirculating fuel conversion systems in energy generation.

Exploring the favorable ion-exchange ability of phthalylated cellulose biopolymer using thermodynamic data

A phthalylated ion-exchange biopolymer was obtained by adding cellulose to molten phthalic anhydride in a quasi solvent-free procedure. Through this route 2.99 ± 0.07 mmol g −1 of pendant groups containing ester and carboxylic acid moieties were incorporated into the polymeric structure that was characterized by elemental analysis, solid-state carbon nuclear magnetic resonance (CP/MAS), infrared spectroscopy, X-ray diffraction, and thermogravimetry. The chemically modified polysaccharide is able to exchange cations from aqueous solution as demonstrated by batchwise methodology. The data were adjusted to a modified Langmuir equation to give 2.43 ± 0.12 and 2.26 ± 0.11 mmol g −1 for divalent cobalt and nickel cations, respectively. The net thermal effects obtained from calorimetric titration measurements were also adjusted to a modified Langmuir equation, and the enthalpy of the interaction was calculated to give endothermic values of 2.11 ± 0.28 and 2.50 ± 0.31 kJ mol −1 for these cations, respectively. The spontaneity of this ion-exchange process is reflected in negative Gibbs energy and with a contribution of positive entropic values. This set of thermodynamic data at the solid–liquid interface suggests a favorable ion-exchange process for this anchored biopolymer for cation exchange from the environment.

Performance of natural and modified smectite: kinetic and thermodynamics involving arsenic (V) adsorption

A natural smectite sample has been modified by organofunctionalization process using synthetic route involved the reaction of 2-mercaptopyrimidine with 3-chloropropyltriethoxysilane. The resulting material (S MPY) was characterized by SEM, FTIR, textural analysis and 29Si MAS-NMR. The ability of this material to removed As (V) from aqueous solution was followed by series of adsorption isotherms adjusted to the Langmuir equation at room temperature and pH 2.0. The kinetic parameters analyzed by Lagergren and Elovich models gave a good fit for a pseudo-second order reaction with k2 in the 4.9 to 14.0 mmol-1 min-1 range for S MPY. The adsorption process was exothermic (ΔintH = -4.09 to -5.79 kJ.mol-1) accompanied by increase in entropy (ΔintS = 41.29 to 61.80 JK-1.mol-1) and Gibbs energy (ΔintG = -22.34 to -24.19 kJmol-1). The energetic effect caused by arsenic cation adsorption was determined through calorimetric titration at the solid-liquid interface and gave a net thermal effect that enabled the calculation of the exothermic values and the equilibrium constant.

RETRACTED: Modification of magadiite surface by organofunctionalization for application in removing As(V) from aqueous media: Kinetic and thermodynamic

This article has been retracted: please see Elsevier Policy on Article Withdrawal ( http://www.elsevier.com/locate/withdrawalpolicy ). This article has been retracted at the request of the Editors of Applied Surface Science as fraudulent results have been found in this article and other publications in Elsevier journals by the same authors, namely, J. Colloid Interface Sci. , 337 (2009) 122–130, doi: 10.1016/j.jcis.2009.05.013 ; Inorg. Chem. Commun. , 12 (2009) 1145–1149, doi: 10.1016/j.inoche.2009.08.029 ; J. Environ. Radioact. , 101 (2010) 122–133, doi: 10.1016/j.jenvrad.2009.09.005 ; Process Saf. Environ. Prot. , 88 (2010) 53–61, doi: 10.1016/j.psep.2009.10.002 ; J. Phys. Chem. Solids , 70 (2009) 1413–1421, doi: 10.1016/j.jpcs.2009.08.012 ; Appl. Surf. Sci. , 256 (2009) 702–709, doi: 10.1016/j.apsusc.2009.08.045 ; Inorg. Chem. Commun. , 11 (2008) 20–23, doi: 10.1016/j.inoche.2007.09.029 ; Inorg. Chem. Commun , 12 (2009) 1107–1111, doi: 10.1016/j.inoche.2009.08.033 ; J. Hazard. Mat. , 172 (2009) 507–514, doi: 10.1016/j.jhazmat.2009.07.016 ; J. Hazard. Mat. , 171 (2009) 514–523, doi: 10.1016/j.jhazmat.2009.06.032 ; J. Colloid Interface Sci. , 338 (2009) 30–39, doi: 10.1016/j.jcis.2009.06.004 . Publication of an article in a peer-reviewed journal is an important building-block in the development of science. Elsevier has defined policies and ethical guidelines that have to be obeyed by authors and editors and Elsevier takes its duties of guardianship over the scholarly record extremely seriously. The Editors of the Elsevier journals involved found that the allegations of fraud are conclusive and they have decided that these papers should be retracted from the journals.

Heating and cooling of the thermosphere by internal gravity waves

For the first time, estimates of heating and cooling in the upper thermosphere due to dissipating and breaking gravity waves (GWs) of tropospheric origin have been obtained with a comprehensive general circulation model (GCM). A GW parameterization specifically designed for thermospheric heights has been implemented in the CMAT2 GCM covering altitudes from the tropopause to the F2 region, and simulations for the June solstice have been performed. They reveal that the net thermal effect of GWs above the turbopause is cooling. The largest (up to −170 K d−1 in a zonally and temporally averaged sense) cooling takes place in the high latitudes of both hemispheres near 210 km. The instantaneous values of heating and cooling rates are highly variable, and reach up to 500 and −3000 K d−1 in the F2 region, respectively. Inclusion of the GW thermal effects reduces the simulated model temperatures by up to 200 K over the summer pole and by 100 to 170 K at other latitudes near 210 km.

Maleic anhydride incorporated onto cellulose and thermodynamics of cation-exchange process at the solid/liquid interface

This investigation explores the chemical modification of cellulose by using a quasi solvent-free procedure, in which the biopolymer was added to molten maleic anhydride, producing a mixture of maleated and fumarated celluloses. Using this pathway mainly surface modifications are observed and more than 2.82 ± 0.05 mmol of modifier per gram of synthesized polymer were obtained. These chemically modified materials were characterized by elemental analysis, solid-state 13C NMR CP/MAS, FTIR, XRD, TG and SEM. The chemically modified polysaccharides are able to adsorb cations. The data were adjusted to a modified Langmuir equation to give 1.75 ± 0.09 and 2.40 ± 0.12 mmol/g of Co 2+ and Ni 2+, respectively. The net thermal effects obtained from calorimetric titration measurements were also adjusted to a modified Langmuir equation and the enthalpy of the interaction was calculated to give the endothermic values of 0.29 ± 0.02 and 0.87 ± 0.02 kJ/mol for Co 2+ and Ni 2+, respectively. The thermodynamic data for these systems are favorable for cation adsorption from aqueous solutions at the solid/liquid interface, suggesting the use of this anchored biopolymer for cation removal from the environment.

Chitosan–cyanuric chloride intermediary as a source to incorporate molecules—Thermodynamic data of copper/biopolymer interactions

The reaction of a chitosan–cyanuric chloride (ChC) intermediate with ethylenediamine (d) and diethylenetriamine (t) molecules yielded the new biopolymers ChCd and ChCt, which were characterized by elemental analysis, thermogravimetry, X-ray diffractometry, scanning electron microscopy and infrared and C 13 nuclear magnetic resonance spectroscopies. The precursor chitosan (Ch) and all derivatives adsorb copper from aqueous solution at 298 ± 1 K, determined using a batchwise procedure. The results were fitted to a modified Langmuir equation. The ability to adsorb copper is dependent on the availability of the basic nitrogen atoms attached to the pendant biopolymer chains in the order ChCt > ChCd > ChC > Ch, as given by the values 2.84 ± 0.03, 2.62 ± 0.05, 2.55 ± 0.04 and 2.09 ± 0.03 mol g −1, respectively. The same interactive process was also followed through calorimetric titration at 298.15 ± 0.20 K. The net thermal effects were also adjusted to a modified Langmuir equation to give the thermodynamic data at the solid/liquid interface. The exothermic enthalpic values were −28.98 ± 0.05, −32.77 ± 0.04, −60.60 ± 0.03 and −56.41 ± 0.05 kJ mol −1 for the biopolymers Ch, ChC, ChCd and ChCt, respectively. The spontaneity of the systems is shown by the negative Δ G values, −21.1 ± 0.1, −22.1 ± 0.1, −22.1 ± 0.1 and 23.4 ± 0.1 kJ mol −1 for the same sequence. The negative entropic values −26 ± 1, −36 ± 1, −129 ± 1 and −111 ± 1 J mol −1 K −1 indicate an ordering of solvent as complexation occurred. The thermodynamic data demonstrate the capability of these biopolymers for cation removal from aqueous solutions, being new derivative biomaterials that may act as useful agents to renew an ecosystem.

Adsorption of arsenic(III) into modified lamellar Na-magadiite in aqueous medium—Thermodynamic of adsorption process

Synthetic Na-magadiite sample was used for organofunctionalization process with N-propyldiethylenetrimethoxysilane and bis[3-(triethoxysilyl)propyl]tetrasulfide, after expanding the interlayer distance with polar organic solvents such as dimethylsulfoxide (DMSO). The resulted materials were submitted to process of adsorption with arsenic solution at pH 2.0 and 298±1 K. The adsorption isotherms were adjusted using a modified Langmuir equation with regression nonlinear; the net thermal effects obtained from calorimetric titration measurements were adjusted to a modified Langmuir equation. The adsorption process was exothermic (Δ int H=−4.15–5.98 kJ mol −1) accompanied by increase in entropy (Δ int S=41.32–62.20 J k −1 mol −1) and Gibbs energy (Δ int G=−22.44−24.56 kJ mol −1). The favorable values corroborate with the arsenic (III)/basic reactive centers interaction at the solid–liquid interface in the spontaneous process.

Thermodynamics of the nickel and cobalt removal from aqueous solution by layered crystalline organofunctionalized barium phosphate

The available hydroxyl groups inside the lamellar cavity of barium phosphate (BaP) reacted with the silylating agents (RO) 3Si(CH 2) 3L x (L 1 = NH 2, L 2 = NH(CH 2) 2NH 2, and L 3 = NH(CH 2) 2 NH(CH 2) 2NH 2), to yield organofunctionalized BaPSiL 1, BaPSiL 2 and BaPSiL 3 nanomaterials. The amounts of organofunctional groups covalently attached to the inorganic layer were (1.24, 1.46, and 1.23) mmol · g −1, respectively. The basic nitrogen atoms attached to the distinct pendant organic chains adsorb divalent nickel and cobalt from aqueous solutions, as represented by well-established isotherms. The energetic effects caused by metallic cation interactions were determined through calorimetric titration at the solid/liquid interface and gave a net thermal effect that enabled enthalpy and equilibrium constant calculations. Complete thermodynamic results composed of exothermic enthalpy, negative free Gibbs energy and positive entropy result in a set of favourable cation/basic centre interactions, to indicate that these nanomaterials could be useful tools to eliminate undesirable cations from aqueous systems.

Adsorption of arsenic(V) into modified lamellar Kenyaite

The synthetic Kenyaite sample was used for organofunctionalization process with N-propyldiethylenetrimethoxysilane and bis[3-(triethoxysilyl)propyl]tetrasulfide. The resulted materials were submitted to process of adsorption with arsenic solution at pH 2.0 and 298 ± 1 K. The adsorption isotherms were adjusted using a modified Langmuir equation with regression non-linear; the net thermal effects obtained from calorimetric titration measurements were adjusted to a modified Langmuir equation. The adsorption process was exothermic (Δ int H = −4.08 to −5.94 kJ mol −1) accompanied by increase in entropy (Δ int S = 41.29–62.09 J K −1 mol −1) and Gibbs energy (Δ int G = −22.33 to −24.45 kJ mol −1). The energetic effect caused by metal cation adsorption was determined through calorimetric titration at the solid–liquid interface and gave a net thermal effect that enabled the calculation of the exothermic values and the equilibrium constant.

The modified clay performance in adsorption process of Pb2+ ions from aqueous phase—Thermodynamic study

Smectite clay sample from Acre state, Amazon region, Brazil, was used for pillaring and organofunctionalization process in the present study. The pillaring ions were obtained through chemical reaction of AlCl3·6H2O/NaOH, Ti(OC2H5)4/HCl, Cr3(OH)44+/NaOH and ZrOCl2·8H2O solutions. The resulting materials were organofunctionalized with 3-Aminopropyltriethoxysilane (APS). The adsorption capacity was investigated with Pb2+, ions from aqueous solution in pH 5.0 and controlled temperature 298±0.20K. The Langmuir, Freundlich and Temkin adsorption isotherms models have been applied to fit the experimental data, linear regression. The energetic effect caused by metal cation adsorption was determined through calorimetric titration at the solid–liquid interface and gave a net thermal effect that enabled the calculation of the exothermic values and the equilibrium constant.

Kinetics and modified clay thermodynamic from the Brazilian amazon region for lead removal

Modified Brazilian smectite-bearing clay samples displayed ability for lead adsorption. The structure modification of smectite were obtained through pillaring process and functionalization with [3-(2-aminoethylamino)propyl]trimethoxysilane. The chemical modification process increases the basal spacing of the natural smectite from 1.354 to 2.364 nm. The Langmuir model was fitted to experimental data in linear regression. Kinetic studies showed an equilibrium adsorption time of 700 min on the modified clay. The experimental data were correlated with two distinct kinetic models were used: (i) external mass transfer diffusion and (ii) intraparticular mass transfer diffusion. However, the intraparticle mass transfer diffusion model gave a better fit to these experimental data. The energetic effects caused by lead interactions were determined through calorimetric titration at the solid–liquid interface and gave a net thermal effect that enabled the calculation of the exothermic values and the equilibrium constant.

Adsorption and thermodynamic studies of Cu(II) and Zn(II) on organofunctionalized-kaolinite

Kaolinite-bearing clay samples from Perus, São Paulo state, Brazil, were used for chemical modification process with dimethyl sulfoxide and organofunctionalized with the silyating agent (RO) 3Si(CH 2) 3NH(CH 2) 2NH 2 in the present study. The resulting material and natural kaolinite were subjected adsorpion process with Cu(II) and Zn(II) from aqueous solution at pH 6.0 and controlated temperature of 298 K. The Langmuir adsorption isotherm model has been applied to fit the experimental data. The results showed that the chemical modification process increases the basal spacing of the natural kaolinite from 0.711 to 0.955 nm. The energetic effects caused by Cu(II) and Zn(II) interactions were determined through calorimetric titration at the solid–liquid interface and gave a net thermal effect that enabled the calculation of the exothermic values and the equilibrium constant.

Adsorption of uranyl(II) into modified lamellar Na-Kanemite

The Na-Kanemite sample was used for organofunctionalization process with N-propyldiethylenetrimethoxysilane and 3-aminopropyltriethoxysilane, after expanding the interlayer distance with polar organic solvents such as dimethyl sulfoxide (DMSO). The new organofunctionalized matrix was characterized by carbon nuclear magnetic resonance in the solid state SEM and chemical analysis. The resulted material was submitted to the process of adsorption with uranyl(II) at pH 2.0 and 298±1K. The Langmuir adsorption isotherm model has been to fit the experimental data with regression non-linear; the net thermal effects obtained from calorimetric titration measurements were adjusted to a modified Langmuir equation. The adsorption process was exothermic (ΔH=−7.14 to −5.98kJmol−1) accompanied by an increase in entropy (ΔS=52.28–62.12JK−1mol−1) and Gibbs energy (ΔG=−22.62 to −24.44kJmol−1). The favorable values corroborate with the uranyl(II)/basic reactive centres interaction at the solid/liquid interface in the spontaneous process for the new nanomaterials.

Aplicação de Zr/Ti-PILC no processo de adsorção de Cu(II), Co(II) e Ni(II) utilizando modelos físico-químicos de adsorção e termodinâmica do processo

The aim of this investigation is to study how Zr/Ti-PILC adsorbs metals. The physico-chemical proprieties of Zr/Ti-PILC have been optimized with pillarization processes and Cu(II), Ni(II) and Co(II) adsorption from aqueous solution has been carried out, with maximum adsorption values of 8.85, 8.30 and 7.78 x10-1 mmol g-1, respectively. The Langmuir, Freundlich and Temkin adsorption isotherm models have been applied to fit the experimental data with a linear regression process. The energetic effect caused by metal interaction was determined through calorimetric titration at the solid-liquid interface and gave a net thermal effect that enabled the calculation of the exothermic values and the equilibrium constant.