Fast adsorptive and photocatalytic purification of air from acetone and dimethyl methylphosphonate by TiO2 aerosol

A high concentration (1.5 × 10⁶ cm⁻³) TiO₂ aerosol of the average particle size 0.5 μm was generated by a sonic method inside 0.1 m³ Plexiglas chamber and applied for the adsorptive and adsorptive-photocatalytic purification of air from vapors of acetone and chemical agents’ model dimethyl methylphosphonate (DMMP). The adsorptive capture of acetone over the TiO₂ aerosol results in establishing equilibrium adsorption state and is limited by the rate of the aerosol admission into the chamber. A model derived from the Langmuir isotherm describes well the acetone concentration vs. aerosol mass curve and allows obtaining the adsorption constant and monolayer coverage of acetone in a 10 min experiment. The UV irradiation of TiO₂ aerosol accelerates dramatically the purification from acetone at the high relative humidity (RH) of the air. Increased RH of air decreases the rate of the acetone adsorption but has a little positive effect on the rate of photocatalytic oxidation of acetone over aerosol particles. The DMMP adsorption over TiO₂ aerosol is accompanied by the immediate (τ < 10 s) and irreversible hydrolysis of DMMP with the formation of gas phase methanol and adsorbed methyl methylphosphonic acid. The irreversible reactive adsorption results in the very fast air purification (τ = 20–40 s) due to very small diffusion distances of substrate to the TiO₂ surface in aerosol. The increase of the air RH from 4 to 37% (296 K) decreases the rate of adsorption but accelerates significantly the rate of photocatalytic oxidation. The complete air purification from organic compounds within 10 min is possible only with the photocatalytic oxidation because the adsorption alone does not remove methanol. The time needed for the air purification over the nanosized TiO₂ aerosol is directly determined by the rate of the aerosol generation which allows a further optimization of the TiO₂ aerosol air purification. The obtained results approve experimentally a suggestion that the photocatalytic oxidation over solid atmospheric aerosols actually takes part in the Earth atmosphere and serves as an important sink for airborne organics.     

Factors influencing the hydration of layered double hydroxides (LDHs) and the appearance of an intermediate second staging phase

The hydration of layered double hydroxides (LDHs) was investigated by changing the interlayer anion species, the Mg/Al ratio of the LDH hosts and the relative humidity (RH). The anions were CO₃²⁻, Cl⁻, Br⁻, NO₃⁻, I⁻, SO₄²⁻, and ClO₄⁻ (listed in the order of ion size, small to large) and LDHs with Mg/Al = 1.90 (LDH2) and 2.91 (LDH3) were used. Their XRD profiles were measured by an XRD diffractometer while controlling the RH in the range 0–95% at 25 °C. Only I⁻, SO₄²⁻, and ClO₄⁻ LDH2s and SO₄²⁻ LDH3 showed a large step-wise basal-spacing expansion, 0.24–0.28 nm, under high RH conditions (> ca. 60%) probably due to the insertion of one water layer into the interlayer space. Such hydration occurred more favorably for the LDHs with larger anions and those with a higher layer charge (LDH2). Among them, I⁻ and ClO₄⁻ LDH2s exhibited the second staging – alternate stacking of hydrated (H) and non-hydrated (NH) interlayers – in the intermediate RH region.     

The influence of porosity and surface oxygen groups of peat-based activated carbons on benzene adsorption from dry and humid air

Activated carbons (ACs) prepared from peat were used for benzene adsorption (5 ppmv) from dry and humid (relative humidity (RH) 70%) air streams. Benzene uptake by the ACs was lower in the presence of water vapor due to competition between benzene and water molecules for the adsorption sites. Adsorption of benzene from dry and humid air on the ACs with low content of surface oxygen groups was attributed to the presence of narrow micropores (size <0.7 nm). A linear correlation between the amount of adsorbed benzene and micropore volume calculated from CO₂ adsorption isotherms was found. The coefficients of determination R² were 0.87 for benzene adsorption in the absence of water vapor and 0.83 for adsorption at relative humidity 70%. It was shown that the presence of surface groups in the ACs reduces benzene uptake more profoundly in the presence of moisture than in the dry conditions.     

Non-destructive measurement of residual adsorption capacity of charcoal filters

A non-destructive method has been developed to measure the residual adsorption capacity (RAC) of charcoal filter beds while in use. A small sample of a weakly adsorbed gas is pulsed as a square wave into the gas stream that passes through the adsorption filter. The effluent pulse is detected by means of an appropriate detector. The RAC of the carbon bed is proportional to the retantion time of the gas. The filter is an adsorption bed that behaves as a gas-solid Chromatograph, and only bare sites, not covered by heavy adsorbate, are available to the pulsed gas. The system chosen was M-11 gas mask canisters containing 2.8 cm × 87 cm² ASC Whetlerite charcoal beds loaded to various degrees with highly polar dimethyl methyl phosphonate (DMMP), which simulated a strongly adsorbed pollutant. 10 cm³ aliquots of non-polar test gases methane and ethane were pulsed into a stream of dry air, at flow velocities of 5.47 l./min (1.05 cm/sec) and bed temperature of 25°C.The retention times of CH₄ dropped from 0.9 min over bare ASC Whetlerite to 0.5 min over carbon 50% saturated with DMMP. Ethane times fell from 24 to 7 min. The accuracy of RAC determination using methane was ± 1.0%. The time required for the test was < l min for methane, < 30 min for ethane.     

Adsorption of toluene onto activated carbons exposed to 100 ppb ozone

The effects of 100 ppb ozone exposure on the adsorption of 1 ppm toluene on activated carbon are presented for dry (less than 5% RH) and humid (55% RH) air. In dry air, the 10% toluene breakthrough times of granular carbon beds exposed to ozone for 208 days are 17% less than those of unexposed carbon beds. At 55% RH, the corresponding reduction in toluene breakthrough time is 78%. For a humid environment with 100 ppb ozone, filter life would be reduced by more than half compared to the expected life based on tests in the absence of ozone. This degradation is attributed to changes in carbon surface chemistry, surface area, and pore volume that occur with relatively brief exposure to the ozone.     

Catalytic combustion of polycyclic aromatic hydrocarbons (PAHs) over zeolite type catalysts: Effect of water and PAHs concentration

The catalytic combustion of 1-methylnaphthalene (1-MN), a PAH representative molecule, was carried out over USHY and 0.8%PtUSHY catalysts in presence of steam. These catalysts are able to transform low concentration of 1-MN into carbon dioxide at 300 °C over USHY catalyst and at 200 °C over PtUSHY, without by-products formation. The presence of platinum on the USHY increases the catalytic activity, hence the reaction rate. The influence of platinum content showed that 0.5% of platinum deposited on the zeolite was sufficient to oxidize 900 ppm of 1-MN at 300 °C.The influence of water content in the feed was investigated and several assumptions were put forth to explain our results. The carbon dioxide yield decreases in the 0–12% range of relative humidity (RH). When RH increases up to 12% the carbon dioxide yield increases. Over USHY catalyst and for low water content (RH < 12%), water could be adsorbed over strong hydrophylic sites of USHY zeolite or via H₂O dimer (neutral complex form) formation. Over PtUSHY catalysts, water adsorption over the PtO phase could be considered. For high water content (RH > 12%), water cluster formation via H₂O dimer (ion-pair complex form) is proposed on both catalysts. This form of H₂O dimer (ion-pair complex) could generate an acidity, which facilitates the formation of oxygenated compounds easily degradable into carbon dioxide.     

Effects of the orientation of smectite particles and ionic strength on diffusion and activation enthalpies of I and Cs ions in compacted smectite

The apparent diffusion coefficients (D_a) for I⁻ and Cs⁺ ions in compacted Na-smectite which is a major constituent clay mineral of bentonite were studied as a function of smectite's dry density (0.9–1.4 Mg/m³), ionic strength ([NaCl] = 0.01, 0.51 M), temperature (22–60 °C) and diffusion direction to the orientated direction of smectite particles. The Na-smectite was prepared by ion-exchanging with Na⁺ ions a Na-bentonite, Kunipia-F®, of which smectite content is over 99 wt.%. The D_a-values for both ions showed a tendency to be higher in the parallel direction than in the perpendicular direction to the orientated direction of smectite particles at a low-ionic strength of [NaCl] = 0.01 M. The D_a-values for I⁻ ions showed different trends depending on diffusion direction and dry density at a high-ionic strength of [NaCl] = 0.51 M. Namely, although the D_a-values for I⁻ ions showed a tendency to be higher in the parallel direction than in the perpendicular direction to the orientated direction of smectite particles at a high-dry density of 1.4 Mg/m³, these showed a reciprocal tendency at dry densities of 0.9–1.0 Mg/m³. The D_a-values for Cs⁺ ions uniformly increased with an increase of ionic strength in both diffusion directions. Considering electrostatic effect from smectite surface and the change in tortuosity on dry density, ionic strength and diffusion direction to the orientated direction of smectite particles, I⁻ ions are considered to mainly diffuse in interstitial pores. While, Cs⁺ ions can diffuse in both interlayer and interstitial pores, and the D_a-values are considered to have elevated by competing with Na⁺ ions. The activation enthalpies (ΔE_a) for I⁻ ions, slightly higher (ΔE_a = 19.8−20.0 kJ/mol) than that of the diffusion coefficient in free water (D^o) for I⁻ ions (ΔE_a = 17.36 kJ/mol) at a low-ionic strength of [NaCl] = 0.01 M, decreased with an increase of ionic strength, became of similar level to that of the D^o at a high-ionic strength of [NaCl] = 0.51 M, increased with an increase of dry density. On the contrary, the ΔE_a-values for Cs⁺ ions, clearly higher (ΔE_a = 25.6−28.4 kJ/mol) than that of the D^o for Cs⁺ ions (ΔE_a = 16.47 kJ/mol) even in low-dry density over the ionic strength, increased with an increase of dry density. The ΔE_a-values for Cs⁺ ions are considered to be due to the decrease in the activity of porewater in addition to the effect of ion exchange enthalpy between Cs⁺ and Na⁺ ions in smectite.     

Adsorption thermodynamics and kinetics study for the self-assembly of 1,8,15,22-tetraaminophthalocyanatocobalt(II) on glassy carbon surface

Spontaneous adsorption of 1,8,15,22-tetraaminophthalocyanatocobalt(II) (4α-Co^IITAPc) on glassy carbon (GC) electrode leads to the formation of a stable self-assembled monolayer (SAM). Since the SAM of 4α-Co^IITAPc is redox active, its adsorption on GC electrode was followed by cyclic voltammetry. SAM of 4α-Co^IITAPc on GC electrode shows two pairs of well-defined redox peaks corresponding to Co^III/Co^II and Co^IIIPc⁻¹/Co^IIIPc⁻². The surface coverage (Γ) value, calculated by integrating the charge under Co^II oxidation, was used to study the adsorption thermodynamics and kinetics of 4α-Co^IITAPc on GC surface. Cyclic voltammetric studies show that the adsorption of 4α-Co^IITAPc on GC electrode has reached the saturation coverage (Γ_s) within 3 h. The Γ_s value for the SAM of 4α-Co^IITAPc on GC electrode was found to be 2.37 × 10⁻¹⁰ mol cm⁻². Gibbs free energy (ΔG_ads) and adsorption rate constant (k_ad) for the adsorption of 4α-Co^IITAPc on GC surface were found to be −16.76 kJ mol⁻¹ and 7.1 M⁻¹ s⁻¹, respectively. The possible mechanism for the self-assembly of 4α-Co^IITAPc on GC surface is through the addition of nucleophilic amines to the olefinic bond on the GC surface in addition to a meager contribution from π stacking. The contribution of π stacking was confirmed from the adsorption of unsubstituted phthalocyanatocobalt(II) (CoPc) on GC electrode. Raman spectra for the SAM of 4α-Co^IITAPc on carbon surface shows strong stretching and breathing bands of Pc macrocycle, pyrrole ring and isoindole ring. Raman and CV studies suggest that 4α-Co^IITAPc is adopting nearly a flat orientation or little bit tilted orientation.     

Synthesis of proton conductive membranes based on inorganic–organic hybrid structure bound with phosphonic acid

Proton conductive inorganic–organic hybrid membranes were synthesized from styrene derivatives of alkoxysilane and ethyl 2-[3-(dihydroxyphosphonyl)-2-oxopropyl] acrylate (EPA) through copolymerization followed by sol–gel reaction. Self-standing, homogeneous and transparent hybrid membranes with chemically bound phosphonic acid groups were synthesized. FT-IR analysis exhibited the hybrid membranes included phosphonic acid groups. ¹³C and ²⁹Si NMR studies indicated that alkoxysilyl functionalized styrene derivatives were not only copolymerized with EPA but also condensed yielding Si–O–Si linkages by sol–gel reaction. TG–DTA analysis revealed that these membranes were thermally stable up to 200 °C in dry O₂. The proton conductivities of the hybrid membranes increased with phosphonic acid content and temperature. The P/Si ratio of the membrane was dependent on the number of alkoxy group in the starting alkoxysilane. The hybrid membrane from (dimethylmethoxysilylmethyl)styrene (DMMSMS(M))/EPA = 1/6 revealed proton conductivities of 6.3 × 10⁻³ and 2.4 × 10⁻⁴ S cm⁻¹ at 68.0% relative humidity and 18.8% relative humidity, respectively, at 140 °C.     

Carbon aerogels from gallic acid-resorcinol mixtures as adsorbents of benzene, toluene and xylenes from dry and wet air under dynamic conditions

Carbon aerogels were prepared by carbonization of organic aerogels synthesized by the polycondensation reaction of gallic acid-resorcinol mixtures with formaldehyde. One carbon aerogel was further CO₂-activated. They were characterized by gas adsorption, mercury porosimetry, immersion calorimetry, and temperature programmed desorption. Pore texture of carbon aerogels was constituted by a well-developed, monomodal mesoporous network superimposed over a microporous network with different mean micropore widths according to the degree of activation. In some cases, the BET surface area was lower than that determined by immersion enthalpy into benzene. Dynamic adsorption of benzene, toluene, and xylenes, in dry or wet air flow, was carried out on carbon columns to obtain the breakthrough curves. Adsorption from dry air was governed by the total microporosity of the adsorbent. Amounts adsorbed at the breakthrough point were close to or higher than W₀(CO₂) and lower than W₀(N₂) and increased in the order benzene < toluene < xylenes, in agreement with the variation in relative pressure of the hydrocarbons. Results obtained with wet air were qualitatively similar to those obtained with dry air. However, slightly lower amounts were adsorbed at the breakthrough from the wet versus dry air because of competition between water and hydrocarbon molecules.     

Photocatalytic oxidation of toluene at indoor air levels (ppbv): Towards a better assessment of conversion, reaction intermediates and mineralization

We report here a new analytical methodology for the investigation of toluene photocatalytic removal at indoor-relevant concentration level (ppbv). Experiments were performed using an annular flow-through reactor with TiO₂ as photocatalyst, toluene as a model VOC and under different ranges of relative humidity (RH: 0–70%), inlet concentration (20–400 ppbv) and flow rate (70–350 mL min⁻¹). Analysis of reaction intermediates was conducted using an automated thermal desorption technique coupled to GC–MS instrument (ATD–GC–MS) whereas a GC coupled to pulsed discharge helium ionization detector (GC–PDPID) was used for the first time for on-line measurements of CO and CO₂ at ppbv level.Under these conditions, toluene conversion was up to 90–100% with a slight influence of inlet concentration and RH, whereas flow rate was found to be a prevalent factor. Mineralization (%) varied from 55 to 95% and has shown to be strongly inhibited by the increase of RH whereas flow rate and inlet concentration exhibited a negligible effect. The reaction intermediates were found to be different according to the RH level: in absence of water vapor, traces of low molecular weight carbonyls (formaldehyde, methyl glyoxal, etc.) were detected and quantified in the gas phase whereas at RH 40%, hydroxylated intermediates such as cresols and benzyl alcohol were observed. On the basis of identification results, a reaction mechanism was proposed involving mainly direct hole oxidation at dry conditions and hydroxylation by OH radicals at high RH level.     

Fabrication of zero-thermal-expansion ZrSiO4/Y2W3O12 sintered body

We focused on the linear negative thermal expansion of Y₂W₃O₁₂ in a wide-temperature range and on the chemical stability of ZrSiO₄ in the fabrication of the composite material ZrSiO₄/Y₂W₃O₁₂ with a zero-thermal-expansion. The compact composed of Y₂W₃O₁₂ and ZrSiO₄ had a thermal shrinkage rate smaller than that of Y₂W₃O₁₂ and higher than that of ZrSiO₄. SEM–EDX observation clarified that the ZrSiO₄/Y₂W₃O₁₂ sintered body fabricated at 1400 °C for 10 h had a microstructure composed of ZrSiO₄ and Y₂W₃O₁₂ grains, and XRD indicated that only ZrSiO₄ and Y₂W₃O₁₂ phases existed in the sintered body. The relative density of the ZrSiO₄/Y₂W₃O₁₂ sintered body reached 92%, which was larger than that of the ZrSiO₄ sintered body because Y₂W₃O₁₂ grains could be sintered at lower temperatures. The average linear thermal expansion coefficients of the ZrSiO₄/Y₂W₃O₁₂ sintered body were −0.4 × 10⁻⁶ and −0.08 × 10⁻⁶ °C⁻¹ in the temperature ranges from 25 to 500 °C and from 25 to 1000 °C, respectively, which showed an almost zero-thermal-expansion.     

Thermodynamics of hydrogen adsorption on the zeolite Ca-Y

Variable-temperature infrared spectroscopy was used for a thermodynamic study on hydrogen adsorption on the zeolite Ca-Y. Adsorption renders the H–H stretching mode infrared active, at 4078 cm⁻¹; and simultaneous measurement of IR absorbance and hydrogen equilibrium pressure, over a range of temperature, allowed standard adsorption enthalpy and entropy to be determined. They resulted to be ΔH°= −15.0(±1.0) kJ mol⁻¹ and ΔS° = −127(±10) J mol⁻¹ K⁻¹, respectively. These relatively high values of adsorption enthalpy and entropy are discussed in the broader context of corresponding data for other hydrogen adsorbents.     

Diffusion behaviour of selenite and hydroselenide in compacted bentonite

The apparent diffusivities (D_a) for selenium (Se) in compacted bentonite were obtained at a dry density of 1.6 mg/m³ as a function of silica sand content and temperature under reducing conditions, in which the dominant species of Se is predicted to be HSe⁻ (hydroselenide) and were compared with D_a values obtained under anaerobic conditions, in which the dominant species of Se is predicted to be SeO₃²⁻ (selenite). The experiments were carried out by an in-diffusion method and a Na bentonite, Kunigel-V1® with Na smectite content of 46–49 wt.%, was used in a series of diffusion experiments. All diffusion experiments were carried out in a controlled N₂ atmosphere glove box. The effects of silica sand content and temperature on D_a are altogether summarized as follows: (1) The D_a values show a tendency to increase with increasing silica sand content. (2) The D_a values show a tendency to increase with increasing temperature. (3) The increasing rate of D_a with temperature is approximately constant, independent of silica sand content. The D_a values for HSe⁻ are about one order of magnitude smaller than those for SeO₃²⁻. This trend is consistent with that of distribution coefficients obtained by batch method. The D_a values for HSe⁻ were well correlative with smectite partial density for both temperatures. This indicates that Se diffusion, including retardation processes, is predominantly controlled by the properties in part of smectite. The calculated activation energies for diffusion in the porewater [ΔE_a(porewater)] were in the range of 17.6–31.6 kJ/mol and were slightly higher than that of ionic diffusivity in free water [ΔE_{a(free water)}=15.3 kJ/mol] for HS⁻, which takes the same species as HSe⁻ in solution. Furthermore, the relative partial molar activation energies [ _(relative)] calculated from ΔE_{a(free water)} and ΔE_a(porewater) values were in the range of −16.2 to −2.2 kJ/mol. A reason might be that the properties of the porewater of compacted bentonite are different from that of free water.     

Layered double hydroxides pillared by macropolyoxometalates

Pillared derivatives of Mg_1−xAl_x layered double hydroxides (LDHs) were prepared by anion exchange reaction of a synthetic meixnerite precursor, [Mg₃Al(OH)₂](OH), with macromolecular polyoxometalate ions. The intercalated polyoxometalates included the lacunary Dawson ion (α-P₂W₁₇O₆₁)¹⁰⁻, the Finke (Zn₄(H₂O)₂(AsW₉O₃₄)₂)¹⁰⁻ and (WZn₃(H₂O)₂(ZnW₉O₃₄)₂)¹²⁻ ions, the doubled Dawson (P₄W₃₀Zn₄(H₂O)₂O₁₁₂)¹⁶⁻ and the polyoxocryptates (NaSb₉W₂₁O₈₆)¹⁸⁻ and (NaP₅W₃₀O₁₁₀)¹⁴⁻. Anion exchange reaction of [Zn₂Al(OH)₂](NO₃⁻) with (NaP₅W₃₀O₁₁₀)¹⁴⁻ also resulted in a crystalline pillared product. The intercalates exhibited gallery heights up to 16.6 Å and thermal stabilities to 200°C. Nitrogen adsorption/desorption studies for the LDH intercalates showed that access to the gallery micropores was achieved upon POM intercalation. All of the intercalates contained a salt-like impurity phase, as indicated by XRD. The Zn₂Al–(NaP₅W₃₀O₁₁₀)¹⁴⁻ LDH was investigated as a catalyst for the peroxide oxidation of cyclohexene. A comparison of the reactivities of three samples containing different fractions of the salt-like impurity suggested that the impurity phase contributes significantly to the observed activity.     

Direct oxidation of sodium borohydride on Pt, Ag and alloyed Pt–Ag electrodes in basic media. Part I: Bulk electrodes

We studied the borohydride oxidation reaction (BOR) by voltammetry for BH₄⁻ concentrations between 10⁻³ M and 0.1 M NaBH₄ in 0.1–1 M NaOH for bulk polycrystalline Pt, Ag and alloyed Pt–Ag electrocatalysts. In order to compare the different electrocatalysts, we measured the kinetic parameters and the number of electrons exchanged (faradic efficiency). BOR on bulk Pt is more efficient when the concentration of NaBH₄ increases (3e⁻ in 1 mM and 6e⁻ in 10 mM BH₄⁻/0.1 M NaOH). BOR on Pt can occur both in a direct pathway and in an indirect pathway including hydrogen generation via heterogeneous hydrolysis of BH₄⁻ and subsequent oxidation of its by-products (e.g. BH₃OH⁻ and H₂). BOR on Ag strongly depends on the pH: improved faradic efficiency is monitored for high pH (2e⁻ at pH 12.6 and 6e⁻ at pH 13.9 at 25 °C). The BOR kinetics is faster for Pt than for Ag (i_Pt=0.02 A cm⁻², i_Ag=1.4 10⁻⁷ A cm⁻² at E=−0.65 V vs. NHE in 1 mM NaBH₄/0.1 M NaOH, 25 °C) both as a result from Pt high activity regarding the BH₄⁻ heterogeneous hydrolysis and subsequent HOR, above −0.83 V vs. NHE and following direct oxidation of BH₄⁻ or BH₃OH⁻ below −0.83 V vs. NHE. Both Pt–Ag bulk alloys show unique behaviour: the number of electrons exchanged is rather high whatever the BH₄⁻ concentration and pH, while the kinetic parameters are quite similar to that of platinum, showing possible synergistic alloying effect.     

Synthesis, electrorheology and creep behavior of polyindole/polyethylene composites

In this study, polyindole (PIN) and polyindole/polyethylene (PIN/PE) conducting composites, having various amounts of PIN, were synthesized by chemical polymerization using FeCl₃ as an oxidizing agent and taking the ratio of salt:monomer as 3:1. The samples of PIN and PIN/PE composites were characterized by FTIR, UV–vis, TGA, SEM, Gouy scale magnetic susceptibility, conductivity (1.2 × 10⁻³ S cm⁻¹ > σ > 1.96 × 10⁻⁶ S cm⁻¹, at T = 25 °C) and density measurements. FTIR analysis suggested a 2,3-propagation mechanism for PIN formation. The ground milled samples were subjected to particle size analysis by dynamic light scattering (DLS) and a micron-sized particle distribution was obtained. A series of volume fractions ( = 10–25%) were prepared from the materials in silicone oil (SO) and their sedimentation stabilities determined. The most stable composite [PIN(89%)/PE(11%)] against gravitational sedimentation was subjected to flow-rate measurements under externally applied electric field strength (E) and an electrorheological (ER) activity was observed; threshold energies (E_t) were calculated. The effects of volume fraction, shear rate, external E, frequency and temperature onto ER activities of the suspensions were investigated. Enhancement in the electric field viscosities and shear thinning viscoelastic behaviors were observed for all the samples studied. Recoverable viscoelastic deformations were determined from the creep tests under external E.     

Development and applications of quaternary ammonium (QA) membrane electrodes in pharmaceutical preparation and in bioavailability of Prostaglandin E1 and Deoxycholate

The two novel ion-pairs (PB-TPB and NB-TPB) of quaternary ammonium drugs; propantheline bromide (PB), N,N-Diisopropyl-N-methyl-N-[2-(xanthen-9ylcarbonyloxy)ethyl] ammonium bromide and neostigmine bromide (NB), 3-(dimethylcarbamoyloxy) phenyl]-trimethylazanium have been synthesized, respectively and incorporated in poly (vinyl chloride)-based membrane electrodes for the quantification of propantheline bromide and neostigmine bromide in different pharmaceutical preparations. The influences of membrane compositions on the potentiometric responses of membrane electrodes have been found to substantially improve the performance characteristics. The best performance was reported with membranes having composition (w/w) of PB-TPB or NB-TPB (6%): PVC (34%): o-NPOE (60%). The proposed electrodes exhibit nernstian response in the concentration ranges of 2.1 × 10⁻⁷ M to 1.0 × 10⁻² M and 4.4 × 10⁻⁷ M to 1.0 × 10⁻² M with detection limit of 1.5 × 10⁻⁷ M and 3.3 × 10⁻⁷ M, respectively. Both the membrane electrodes perform satisfactorily over pH ranges of (3.5–7.5 and 4.0–7.0) with fast response times (11 s and 13 s), respectively. These drugs (PB and NB) were further utilized as different ion-pairs of Prostaglandin E₁ (PGE₁) and Deoxycholate (DOC) in poly (vinyl chloride)-based membrane electrodes for the determination of bioavailability of Prostaglandin E₁ and Deoxycholate in plasma of different patients.     

Adsorption of cationic dye from aqueous solutions by activated carbon

Batch sorption experiments were carried out to remove a cationic dye, methylene blue (MB), from its aqueous solutions using a commercial activated carbon as an adsorbent. Operating variables studied were pH, stirring speed, initial methylene blue concentration and temperature. Adsorption process was attained to the equilibrium within 5 min. The adsorbed amount MB dye on activated carbon slightly changed with increasing pH, and temperature, indicating an endothermic process. The adsorption capacity of methylene blue did not significantly change with increasing stirring speed. The experimental data were analyzed by various isotherm models, and found that the isotherm data were reasonably well correlated by Langmuir isotherm. Adsorption measurements showed that the process was very fast and physical in nature. Thermodynamic parameters such as the adsorption entropy (ΔS^o) and adsorption enthalpy (ΔH^o) were also calculated as 0.165 kJ mol⁻¹ K⁻¹ and 49.195 kJ mol⁻¹, respectively. The ΔG^o values varied in range with the mean values showing a gradual increase from −0.256 to −0.780 to −2.764 and −7.914 kJ mol⁻¹ for 293, 313, 323 and 333 K, respectively, in accordance with the positive adsorption entropy value of the adsorption process.     

Prediction of breakthrough curves for adsorption on activated carbon fibers in a fixed bed

A new model is proposed to describe the removal of volatile organic compounds (VOC) from a gas stream passing through a bed packed with activated carbon fibers (ACFs). Toluene was used as the test compound. Both pore diffusion and surface diffusion are considered in the model. The equilibrium behavior is shown to fit the Dubinin–Radushkevich isotherm with the values of parameters K and W₀ of 1.101 × 10⁻⁹ and 57.73 kg/m³, respectively. The experimental results show that this model can predict VOC breakthrough curve very well.