Adsorption Behavior of Rhodamine B on UiO-66

The adsorption characteristics of UiO-66 (a Zr-containing metal–organic framework formed by terephthalate) for Rhodamine B (RhB), such as isotherms, kinetics and thermodynamics, were investigated systematically. The batch adsorption data conform well to the Langmuir and Freundlich isotherms. The adsorption kinetics of UiO-66 for RhB can be well described by the pseudo first-order model, and the adsorption thermodynamic parameters ΔG₀, ΔH₀ and ΔS₀ at 273 K are − 6.282 kJ·mol^− 1, 15.096 kJ·mol^− 1 and 78.052 J·mol^− 1·K^− 1, respectively. The thermodynamic analyses show that the adsorption process of RhB on UiO-66 is more favorable at higher temperatures. UiO-66 can be regenerated by desorbing in DMF solution with ultrasonic for 1 h. UiO-66 can keep good performance for at least six cycles of sorption/desorption.     

Kinetic and thermodynamic studies on the removal of Cu(II) ions from aqueous solutions by adsorption on modified sand

Studies on the removal of copper by adsorption on modified sand have been investigated. The adsorbent was characterized by XRD, FTIR and SEM. Removal of Cu was carried out in batch mode. The values of thermodynamic parameters namely ΔG⁰, ΔH⁰ and ΔS⁰ at 25 °C were found to be −0.230 kcal⁻¹ mol⁻¹, +4.73 kcal⁻¹ mol⁻¹ and +16.646 cal K⁻¹ mol⁻¹, respectively. The process of removal was governed by pseudo second order rate equation and value of k₂ was found to be 0.122 g mg⁻¹ min⁻¹ at 25 °C. The resultant data can serve as baseline data for designing treatment plants at industrial scale.     

The effects of the surface oxidation of activated carbon,the solution pH and the temperature on adsorption of ibuprofen

A commercial microporous–mesoporous granular activated carbon was modified by oxidation with either H₂O₂ in the presence or absence of ultrasonic irradiation, or NaOCl or by a thermal treatment under nitrogen flow. Raw and modified materials were characterized by N₂ adsorption–desorption measurements at 77 K, Boehm titrations, pH measurements and X-ray photoelectron spectroscopy. Ibuprofen adsorption kinetic and isotherm studies were carried out at pH 3 and 7 on raw and modified materials. The thermodynamic parameters of adsorption were calculated from the isotherms obtained at 298, 313 and 328 K. The pore size distribution of carbon loaded with ibuprofen brought out that adsorption occurred preferentially into the ultramicropores. The adsorption of ibuprofen on pristine activated carbon was found endothermic, spontaneous (ΔG° = −1.1 kJ mol⁻¹), and promoted at acidic pH through dispersive interactions. All explored oxidative treatments led mainly to the formation of carbonyl groups and in a less extent to lactonic and carboxylic groups. This then helped to enhance the adsorption uptake while decreasing adsorption Gibbs energy (notably −7.3 kJ mol⁻¹ after sonication in H₂O₂). The decrease of the adsorption capacity after bleaching was attributed to the presence of phenolic groups.     

Alcohol ethoxylation kinetics: Proton transfer influence on product distribution in microchannels

The influence of the reactor type on the product distribution of the base catalyzed ethoxylation of fatty alcohols was studied.Commonly, proton exchange equilibrium is assumed when modeling this reaction to calculate the product distribution. The model is applicable for ethoxylates produced in semibatch, but cannot explain the products obtained from a continuous microstructured reactor.In this work, a non-equilibrium model is proposed to explain the observed distributions. The model is better suited to fit the distribution curves, and was used to determine the kinetic parameters of this reaction.For the propagation reaction, an activation energy E_A,P = 74 kJ mol⁻¹ was found, which is in good agreement to literature data. For the proton transfer, activation energies in the range of 56 kJ mol⁻¹ to 68 kJ mol⁻¹ were observed.     

Kinetic modelling of the liquid-phase dimerization of isoamylenes on Amberlyst 35

Selectivity, conversion, yield and kinetics of the liquid-phase dimerization of 2-methyl-1-butene and 2-methyl-2-butene mixture have been studied in a batch stirred tank reactor in the temperature range 60–100 °C catalysed by the acid resin Amberlyst 35 and using ethanol as a selectivity enhancer. Selectivity to dimers showed a maximum at R_IA/EtOH = 20. Obtained diisoamylenes consisted mainly of 3,4,4,5-tetramethyl-2-hexene, 2,3,4,4-tetramethyl-1-hexene and 3,4,5,5-tetramethyl-2-hexene. LHHW type kinetic model was derived for the dimerization reaction as a whole. The kinetic model assumes that three active sites take part in the rate-limiting step of dimerization; the apparent activation energy for the dimerization reaction being 65 kJ mol⁻¹. A pseudohomogeneous kinetic model was used to describe the dimerization reaction network. The apparent activation energy for each dimerization reaction was found to be in the range 61–81 kJ mol⁻¹.     

Template-free synthesis of N-doped porous carbons and their gas sorption properties

Nitrogen-rich carbon precursors are prepared and subsequently used for the preparation of N-doped porous carbons (NPCs). Two carbon precursors (CPs), CP-60 and CP-40, are prepared at different temperatures, 60 °C and 40 °C, respectively. The obtained CP materials are almost nonporous based on the N₂ adsorption/desorption analysis. These nonporous CP materials are converted into NPC materials through a carbonization at 800 °C. Porous NPC-60-800 and NPC-40-800 are prepared from CP-60 and CP-40, respectively. In contrast to the CP materials, the NPC materials exhibit higher surface areas. The surface areas of NPC-60-800 and NPC-40-800 are 422.9 m² g⁻¹ and 520.8 m² g⁻¹, respectively. The respective N-contents of NPC-60-800 and NPC-40-800 materials are 4.30 and 3.54 wt.% based on the elemental analysis. The types of N-containing groups of NPC materials are investigated by X-ray photoelectron spectroscopy (XPS) analysis. The NPC materials are good sorbents for CO₂ storage. The heats of CO₂ adsorption (Q_st) are 48.4 kJ mol⁻¹ for NPC-60-800 and 47.0 kJ mol⁻¹ for NPC-40-800. Both materials are also good H₂ sorbents at 77 K: 1.23 wt.% (NPC-60-800) and 1.22 wt.% (NPC-40-800).     

Thermochemistry of onion-like carbons

The standard enthalpies of formation at 25 °C of onion-like carbons (OLC) with different structural ordering have been investigated by high-temperature oxidation calorimetry. In terms of enthalpy and depending on the degree of structural ordering, OLC can be up to 16 kJ mol⁻¹ less stable than graphite but up to 27 kJ mol⁻¹ more stable than their fullerene allotropes. Furthermore, OLC are approximately 5–9 kJ mol⁻¹ less stable than single-wall carbon nanotubes (SWCNTs). The samples prepared at 1800 °C are energetically less stable than samples made at 1300 and 1500 °C. These changes in energetics may stem from oxygen-containing functional groups bonded to the structure or from the creation of topological defects (polygonization and pentagon formation) whose concentration increases with increasing temperature and whose higher energy is balanced by configurational entropy.     

Characterization of catalysts in their active state by adsorption microcalorimetry: Experimental design and application to sulfated zirconia

A method to characterize the surface sites of catalysts in their active state by adsorption microcalorimetry was developed. A calorimeter cell was used as a flow-type reactor, and the skeletal isomerization of n-butane (1 kPa) at 378 K and atmospheric pressure proceeded at comparable rates and with the same states of induction period, maximum and deactivation phase as in a tubular reactor. The reaction was run for selected times on stream and after the removal of weakly adsorbed species, n-butane or isobutane were adsorbed at 313 K. The surface of activated sulfated zirconia was characterized by at least two different sites for n-butane adsorption, a small group of sites (about 20 μmol g^?1) that yielded heats of 50–60 kJ mol^?1 and sites that were populated at higher pressures (above about 5 hPa n-butane) and yielded heats of about 40 kJ mol^?1. The strongly interacting sites disappear during the induction period and are proposed to be the sites where the isomerization reaction is initiated.     

Kinetic model of CaO/fly ash sorbent for flue gas desulphurization at moderate temperatures

Characteristics of the sulphation reaction between SO₂ and CaO/fly ash sorbent were analyzed based on TGA results to develop a kinetic model for a dry moderate temperature (400–800 °C) FGD process. It was found that SO₂ diffusion within sorbent particles involved three sub-processes: inter-particle diffusion, inter-grain diffusion and diffusion through product layers and the diffusion dominated the whole sulphation reaction process. The activation energy for product layer diffusion E_diff of 49.3 kJ mol⁻¹ being greater than the chemical reaction activation energy E_a of 13.9 kJ mol⁻¹ verified the importance of the diffusion. Predictions using the kinetic model in which k₀ varies with temperature agree well with the experimental data.     

Comparative study on the curing kinetics and mechanism of a lignin-based-epoxy/anhydride resin system

Curing kinetics and mechanism of liquid lignin based epoxy resin (LEPL)–maleic anhydride (MA) system accelerated with benzyldimethylamine (BDMA) were studied by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). In order to investigate the difference in the curing process, heating FTIR was used to study the change of the functional group. Complete consumption of the epoxides has been observed after the heating temperature was higher than 110 °C. E constant method and E variable method, to study the dynamic DSC curves, were deduced by assuming a constant and a variable activation energy, respectively. With E constant method, the cure reaction activation energy E, the frequency factor A and overall order of reaction n + m are calculated to be 59.68 kJ mol⁻¹, e^20.6 and 1.462, respectively. With E variable method, E is proved to decrease initially, and then increases as the cure reaction proceeds. The value of E spans from 60.16 to 87.80 kJ mol⁻¹. With the E constant method, E variable method and heating FTIR spectra used together, we can have a comprehensive and profound understanding of the cure reactions of the LEPL–MA system.     

Bomb calorimetry as a bulk characterization tool for carbon nanostructures

Multiwalled carbon nanotubes (MWCNTs) consisting of coaxial graphene cylinders (cylindrical MWCNTs), cones (herringbone MWCNTs) or carbon fibers were combusted in an isothermal bomb calorimeter. Their standard enthalpies of formation were determined to be 16.56 ± 2.76 kJ mol⁻¹(C – per carbon mol) for carbon fibers, 21.70 ± 1.32 kJ mol⁻¹(C) for herringbone MWCNTs and 8.60 ± 0.52 kJ mol⁻¹(C) for cylindrical ones. All materials were characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, thermogravimetry, and elemental analysis. A linear correlation between the standard enthalpies of formation and D/G and G′/G Raman bands ratio (D – band is centered at 1350 cm⁻¹, G – 1585 cm⁻¹, G′ – 2700 cm⁻¹) demonstrates the applicability of bomb calorimetry for characterization of the “defectiveness” of the bulk carbon material in the sense Raman spectroscopy is widely used nowadays. Also, we show that the calorimetry may be used to estimate the oxygen content in the bulk carbon nanomaterials, as there is a linear correlation between the oxygen content (both total content and in carboxyl groups separately) and the standard enthalpies of formation for herringbone nanotubes oxidized by nitric acid.     

Diphasic aluminosilicate gels with two stage mullitization in temperature range of 1200–1300 °C

The crystallization of mullite in amorphous diphasic gel aged for 6 months has been studied using non-isothermal differential scanning calorimetry (DSC) and powder X-ray diffraction with Rietveld structure refinement analysis. The diphasic premullite gels undergo structural changes by aging even when they are calcined at 700 °C. These changes imply segregation of the sample to Al₂O₃-rich and SiO₂-rich regions. From the Al₂O₃-rich region crystallizes poorly defined AlSi spinel at 977 °C followed by two-step mullite crystallization in the temperature interval of 1200–1300 °C. Two overlapped exothermic peaks on DSC scan of aged gel were observed; the first at 1233 °C and the second at 1261 °C. The former is attributed to mullite crystallization by transformation of AlSi spinel, by which excess alumina occurs, which in the second step of mullitization reacts with amorphous SiO₂-rich phase. The activation energy for mullite crystallization in the first step was E_a=935±14 kJ mol⁻¹ and the Avrami exponent n=2.5. The values E_a=1119±25 kJ mol⁻¹ and n=1.2 were obtained for mullite formation in the second step. If amorphous SiO₂-rich phase is extracted from the sample, the value E_a=805±26 kJ mol⁻¹ is obtained. Mullite crystallizing from AlSi spinel (when SiO₂-rich phase has been extracted) differentiates compositionally from that formed by both reactions. Smaller unit cell parameters and higher amount of oxygen vacancies are incorporated into tetrahedral positions of mullite structure, as was determined by Rietveld structure refinement method.     

Carbon oxidation characteristics of yttrium manganate catalyst prepared via urea decomposition

YMnO₃ is a hexagonal crystal characterized by high carbon oxidation activity. In this study, carbon black powder has been directly oxidized at temperatures as low as 250 °C with the active oxygen species generated by YMnO₃ catalyst. The activation energies measured for the non-catalyzed and YMnO₃-catalyzed carbon oxidation reactions were 160 kJ mol⁻¹ and 131 kJ mol⁻¹, respectively. During combustion testing of particulate matter in a ceramic form coated with YMnO₃, the captured soot was continuously purified at a temperature of 350 °C.     

Diffusion of niobium in yttria-stabilized zirconia and in titania-doped yttria-stabilized zirconia polycrystalline materials

Bulk and grain boundary diffusion of Nb⁵⁺ cations in yttria-stabilized zirconia (YSZ, 8 mol% Y₂O₃–92 mol% ZrO₂) and in titania-doped yttria-stabilized zirconia (Ti–YSZ, 5 mol% TiO₂–8 mol% Y₂O₃–87 mol% ZrO₂) was studied in air in the temperature range from 900 to 1300 °C. Experiments were performed in the B-type kinetic region. Diffusion profiles were determined using the secondary ion mass spectrometry (SIMS). The temperature dependencies of the bulk diffusion coefficient D and the grain boundary diffusion parameter D′δs for both the materials were calculated. The activation energies of these transport processes in YSZ amounts to 258 and 226 kJ mol⁻¹, respectively, and 232 and 114 kJ mol⁻¹ in Ti–YSZ. The results were compared to the diffusion data of other cations previously obtained for the same material.     

Kinetics,equilibrium and thermodynamic studies on biosorption of hexavalent chromium by dead fungal biomass of marine Aspergillus niger

Quite a number of reports are available on metal binding capacity of different groups of microorganisms. However, reports on the equilibrium studies on biosorption by marine fungi are quite inadequate. The present study was carried out in a batch system using dead biomass of marine Aspergillus niger for the sorption of Cr(VI). The removal rate of Cr(VI) was increased with a decrease in pH and an increase in Cr(VI) and biomass concentration. A. niger exhibited the highest Cr(VI) uptake of 117.33 mg g^?1 of biomass at pH 1.0 in the presence of 400 mg l^?1 Cr at 50 °C. Kinetics studies based on fractional power, zero order, first order, pseudo-first order, Elovich, second order and pseudo-second order rate expressions have also been carried out. The experimental data were analyzed using five, two-parameter isotherms (Langmuir, Freundlich, Dubinin–Radushkevich, Temkin and Halsey). It was observed that Langmuir model exhibited the best fit to experimental data. Thermodynamic parameters of the biosorption (ΔG°, ΔH° and ΔS°) were also determined.     

On the stepwise change of activation energies in the hydrodechlorination of chlorobenzene over supported nickel

Kinetics of chlorobenzene hydrodechlorination have been measured over Ni on SiO₂, Al₂O₃, MgO, activated carbon and graphite. A stepwise variation of E_a is analysed using the selective energy transfer model where E_a is identified as the vibrational energy associated with an excitation of the chlorobenzene out-of-plane C–H bending mode. Variation of E_a with vibrational quantum number yields a vibrational frequency of 749 cm⁻¹ and a value (−1.1 cm⁻¹) for the anharmonicity term, which is characteristic of bending vibrational modes. Our analysis suggests that the reacting species are weakly adsorbed on the catalyst: heat of adsorption = −0.31 kJ mol⁻¹.     

Selectively combusting CO in the presence of propylene

Acrylic acid plant capacity can be increased by 30% by substituting propane for nitrogen (in air) thereby increasing the overall gas heat capacity. To minimize propane purge rates, the effluent is recycled but the CO in the recycle stream must be oxidized to avoid poisoning the catalyst. We studied the kinetics of CO combustion in a micro-fluidized bed with a catalyst inventory of 1 g and a 4 cm ID reactor charged with 5 g of catalyst – Pd/zeolite – and 145 g of inert. Experiments were run at temperatures between 90 and 240 °C and at 1 and 3.2 bara. At temperatures below 140 °C propylene conversion was less than 30% while CO conversion approached 90% at gas hourly space velocities near 10,000 h⁻¹. A first order kinetic model characterized the data over the whole range of conditions in which conversion was varied between 2% and 99+%. The rate constant for CO conversion was equal to 0.75 s⁻¹ whereas it equaled 0.04 s⁻¹ for propylene oxidation; the activation energy for CO oxidation was 95 kJ mol⁻¹ K⁻¹ whereas it was 140 kJ mol⁻¹ K⁻¹ for propylene.     

Cooperative adsorption of bisphenol-A and chromium(III) ions from water on activated carbons prepared from olive-mill waste

The aim of this study was to investigate the simultaneous adsorption of bisphenol A (BPA) and chromium ions from aqueous solution on activated carbons (both commercial and prepared from olive-mill waste), analyzing both kinetic and equilibrium adsorption data. The effects of solution pH and ionic strength on the adsorption processes were also studied, as well as the chemical interactions between the carbon surface and the pollutants. The activated carbon prepared from olive-mill waste showed: a large surface area (up to 1641 m² g⁻¹), a highly heterogeneous micropore distribution, and a basic chemical nature. The pore volume diffusion model was used to predict the adsorption kinetics of both pollutants. The effective diffusion coefficients ranged between 1.15 × 10⁻⁶ and 9.18 × 10⁻⁷ cm² s⁻¹ for the BPA–Cr(III) system and between 1.65 × 10⁻⁶ and 2.8 × 10⁻⁶ cm² s⁻¹ for the Cr(III)–BPA system. The presence of both Cr(III) and BPA in the binary systems increases the adsorption effective diffusion coefficients and therefore the overall adsorption rate of each pollutant. The increased adsorption of each adsorbate when both pollutants are present is due to the in situ formation of complex compounds between Cr(III), acting as central metallic cation, and BPA, acting as ligand, during adsorption of both adsorbates on activated carbon.     

Studies on formation and siliconization of carbon template of coir fibreboard precursor to SiC ceramics

Formation reaction of carbon template of coir fibreboard samples via pyrolytic decomposition was studied by methods of thermogravimetric, derivative thermogravimetric and differential thermal analysis using different heating rates (5–20 K min⁻¹). The major decomposition reaction at 250–500 °C had activation energy and frequency parameter of 121.84 ± 8.78 kJ mol⁻¹ and 3.2 × 10⁹–2.1 × 10¹¹ min⁻¹, respectively, supporting a free radical mechanism. Siliconization reaction of the carbon template was also studied by non-isothermal DTA technique using varying heating rates (5–20 K min⁻¹); exothermic C-Si reaction was preceded by endothermic melting of Si and it had activation energy of 2793.09 ± 187.65 kJ mol⁻¹; diffusion through solid reaction product was found to control the heterogeneous chemical reaction process. On the basis of these experimental results separate experiments were conducted for preparation of carbon templates and their subsequent siliconization. The correlations between the properties of the coir fibreboard precursor, the carbon template and the siliconized product (SiC) were explained.     

Selective boron extraction by polymer supported 2-hydroxylethylamino propylene glycol functions

Boron sorption ability of polymer supported 2-hydroxyethylamino propylene glycol functions was investigated. 2-hydroxyethylamino propylene glycol was prepared by reaction of glycidol with excess ethanolamine in N-methyl, 2-pyrrolidone (NMP). This was reacted with terpolymer of glycidyl metacrylate (0.4 mol) with methyl metacrylate (0.5 mol) and divinylbenzene (0.1 mol) which was prepared in spherical beads form (210–422 μm) by suspension polymerization.The resulting terpolymer having hydroxyethylamino propylene glycol functions (1.82 mmol g⁻¹) was found to be as efficient as previously reported iminodipropylene glycol functional resins in removal of trace boron from water. The resin showed a boron loading capacity of 1.6 mmol g⁻¹. Nearly second-order kinetics, with respect to the boric acid (k = 1.65 mol l⁻¹ s⁻¹, with a correlation factor of 0.99129) was determined in non-buffered conditions.It was observed that, more than 95% of boron is extracted by this resin from very dilute H₃BO₃ solution (100 ppm initial concentration) in less than 30 min of contact time. Splitting of sorbed boron can be achieved by simple acid leaching (4 M HCl) and regenerated by NaOH (0.1 M) solution.