A trickling fibrous-bed bioreactor for biofiltration of benzene in air

A novel trickling fibrous-bed bioreactor was developed for biofiltration to remove pollutants present in contaminated air. Air containing benzene as the sole carbon source was effectively treated with a coculture of Pseudomonas putida and Pseudomonas fluorescens immobilized in the trickling biofilter, which was wetted with a liquid medium containing only inorganic mineral salts. When the inlet benzene concentration (C_gi) was 0·37 g m⁻³, the benzene removal efficiency in the biofilter was greater than 90% at an empty bed retention time (EBRT) of 8 min or a superficial air flow rate of 1·8 m³ m⁻² h⁻¹. In general, the removal efficiency decreased but the elimination capacity of the biofilter increased with increasing the inlet benzene concentration and the air (feed) flow rate. It was also found that the removal efficiency decreased but the elimination capacity increased with an increase in the loading capacity, which is equal to the inlet concentration divided by EBRT. The maximum elimination capacity achieved in this study was ∽11·5 g m⁻³ h⁻¹ when the inlet benzene concentration was 1·7 g m⁻³ and the superficial air flow rate was 3·62 m³ m⁻² h⁻¹. A simple mathematical model based on the first-order reaction kinetics was developed to simulate the biofiltration performance. The apparent first order parameter K_l in this model was found to be linearly related to the inlet benzene concentration (K_l=4·64−1·38 C_gi). The model can be used to predict the benzene removal efficiency and elimination capacity of the biofilter for benzene loading capacity up to ∽30 g m⁻³ h⁻¹. Using this model, the maximum elimination capacity for the biofilter was estimated to be 12·3 g m⁻³ h⁻¹, and the critical loading capacity was found to be 14 g m⁻³ h⁻¹. The biofilter had a fast response to process condition changes and was stable for long-term operation; no degeneration or clogging of the biofilter was encountered during the 3-month period studied. The biofilter also had a relatively low pressure drop of 750 Pa m⁻¹ at a high superficial air flow rate of 7·21 m³ m⁻² h⁻¹, indicating a good potential for further scale up for industrial applications. © 1998 Society of Chemical Industry     

Cationic polymerization of 1,3-pentadiene with (CH3)3SiCl/AlCl3

Summary Cationic polymerizations of 1,3-pentadiene (PD) with AlCl₃ in n-hexane was carried out in the absence and presence of trimethylsilyl chloride (TMSCl). The polymer yield is greatly increased by the addition of TMSCl, indicating that the TMSCl/AlCl₃ combination is an efficient initiating system for PD cationic polymerization. The polymerization rate induced by TMSCl/AlCl₃ is 10 times greater than that by AlCl₃ alone. The introduction of TMSCl does not exert an effect on the crosslinking reaction. The molecular weight of the polymer decreases with the addition of TMSCl to a extent and then remains constant. Structural evidences demonstrate that the polymerization is indeed initiated by AlCl₃ in combination with HCl resulting from hydrolysis of TMSCl by adventitious water.     

Structural,optical, electrical and dielectric properties of Bi1·5Zn0·92Nb1·5−xNixO6·92−3x/2 solid solution

Abstract

The effects of Ni content on the structural, optical, dielectric and electrical properties of Bi_1·5Zn_0·92Nb_1·5O_6·92 pyrochlore ceramics have been investigated. Nickel atoms were inserted into pure samples in accordance to the composition Bi_1·5Zn_0·92Nb_1·5?xNi_xO_6·92?3x/2, with x varying from 0·07 to 0·40. The structural analysis revealed that a single phase of the pyrochlore compound can be obtained for x values of 0·07 and 0·10 only. Further increase in Ni caused the appearance of multiple phases. The optical energy band gaps are determined as 3·30, 3·35 and 3·52 eV for Ni content of 0·00, 0·07 and 0·10 respectively. The temperature dependent electrical resistivity and the frequency dependent capacitance are observed to increase with increasing Ni content. The resonance frequency, which was determined from the capacitance–frequency dependence, was observed to shift from 12·14 to 10·47 kHz as the x values increase from 0·00 to 0·10 respectively.     

A New Metal–Organic ZnII Supramolecular Assembled via Hydrogen Bonds and N···N Interactions as a New Precursor for Preparation Zinc(II) Oxide Nanoparticles, Thermal, Spectroscopic and Structural Studies

A new 1D supramolecular involving two different ligands, {[Zn(GB)₂]·(μ-bpe)₃} _n (ClO₄)_2n ·nH₂O (GB = 2-guanidinobenzimidazole and bpe = 1,2-bis(4-pyridyl)ethylene, has been synthesised, characterized by elemental analysis, IR-, ¹H NMR-, ¹³C NMR spectroscopy. The thermal stability of compound {[Zn(GB)₂]·(μ-bpe)₃} _n (ClO₄)_2n ·nH₂O was studied by thermal gravimetric and differential thermal analyses. The single crystal X-ray analysis shows that the complex is a one-dimensional polymer involving macrocycle rings as a result of non-covalent bridging bpe ligands via N–H···N and N···N interactions, N–H···bpe···bpe···H–N, with the basic repeating {[Zn(GB)₂](μ-bpe)₃}(ClO₄)₂·H₂O units and by connecting [Zn(GB)₂]²⁺ nodes. ZnO nanoparticles were obtained by calcination of compound {[Zn(GB)₂]·(μ-bpe)₃} _n (ClO₄)_2n ·nH₂O at 500 °C in air. The nanoparticles were characterized by X-ray diffraction and scanning electron microscopy.     

Diffraction Studies on Concentrated Aqueous Hydrochloric Acid Solutions

X-ray diffraction and neutron diffraction experiments with H/D isotopically substituted aqueous 21 mol% hydrochloric acid solutions were carried out in order to obtain detailed features concerning the intermolecular hydrogen-bonded structure in highly concentrated aqueous acidic solutions. Structure parameters, namely, intermolecular distance, root-mean-square amplitude, and coordination number, for the nearest neighbor H₃O⁺···H₂O interaction were determined from the least-squares-fitting analysis of the observed X-ray interference term. These were, respectively, r(H₃O⁺···H₂O) = 2.45(1) Å; l(H₃O⁺···H₂O) = 0.11(1) Å; and n(H₃O⁺···H₂O) = 1.8(1). The intermolecular nearest neighbor distances, r(H···H) = 2.02(5) Å and r(O···H) = 1.69(2) Å, were determined from the least-squares fit to partial structure factors, a_ij (Q), derived from the observed neutron intermolecular interference terms for sample solutions with different H/D isotopic ratios. The present values of intermolecular distances are significantly shorter than those for pure liquid water, implying that extremely strong hydrogen bonds exist in concentrated aqueous acidic solutions.     

Synthesis, Structure and DNA Binding Properties of [Cu2(heae)(SCN)2]n?·?nH2O the First One-Dimensional Polymeric Copper(II) Complex Bridged Alternately by Oxamidate and Double End-to-End Thiocyanate Ligands

A new one-dimensional polymeric copper(II) complex, [Cu₂(heae)(SCN)₂] _n  · nH₂O [H₂heae is N,N′-bis(N-hydroxyethylaminoethyl)oxamide], has been synthesized and characterized by elemental analysis, molar conductivity measurement, IR and electronic spectra studies, and single-crystal X-ray diffraction. The structure of the complex exhibits a neutral one-dimensional polymeric copper(II) zigzag chain [Cu₂(heae)(SCN)₂] _n constructed by μ-trans-heae and double μ-1,3-thiocyanate ligands. The environment about copper can be described as a square-pyramid. The neighboring second building units (SBUs), [Cu(trans-heae)Cu]²⁺, are unequal with Cu···Cu separations of 5.287 and 5.273 ? for Cu1···Cu1ⁱ and Cu2···Cu2ⁱⁱ, respectively. The double thiocyanate ligands function as μ(1,3)-bridges to link these unequal SBUs thereby forming zigzag chains with a Cu1···Cu2 separation of 5.454 ?. The hydrogen bonds in the crystal structure self-assemble the one-dimensional chains into a three-dimensional supramolecular structure. The interaction of the polymeric copper(II) complex with herring sperm DNA (HS-DNA) has been investigated by using absorption and emission spectra, electrochemical techniques and viscometry. The results reveal that the polymeric copper(II) complex interacts with HS-DNA via a groove binding mode with the intrinsic binding constant of 1.38 × 10⁴ M⁻¹. To the best of our knowledge, this is the first example about the structure and DNA-bonding studies of a one-dimensional polymeric copper(II) complex that is bridged alternately by trans-oxamidate and double-thiocyanate ligands.     

Adsorption of chlorophyll-a from acetone solution on natural and activated bentonite

The adsorption of chlorophyll-a on bentonite desiccated at 110°C, untreated and acid-treated with H₂SO₄ solutions over a concentration range between 0·25 and 2·50 mol dm^?3, from acetone solution at 25°C has been studied. The adsorption isotherms may be classified as using Giles' classification, as type S (untreated sample and 0·25 mol dm^?3 H₂SO₄-treated sample), type H (0·50 mol dm^?3 H₂SO₄-treated sample) and type L (1·00 and 2·50 mol dm^?3 H₂SO₄-treated samples). This fact suggests that the bentonite surfaces (low, high and medium affinity, respectively) behave in differently relation to the adsorption of the chlorophyll-a molecules. The experimental data points have been fitted to the Freundlich equation in order to calculate the adsorption capacities (K_f) of the samples; K_f values range from 0·43 mg kg^?1 for the untreated bentonite up to 108·89 mg kg^?1 for the 0·50 M H₂SO₄-treated bentonite. The removal efficiencies (R) have also been calculated and range from 5·71% for the untreated bentonite up to 85·18% for the 0·50 M H₂SO₄-treated bentonite.     

Synthesis and microwave absorption properties of Ni–Zn–Mn spinel ferrites

A series of Ni_0·5?xZn_0·3?xMn_0·2+2xFe₂O₄ ferrites was successfully prepared by the sol–gel autocombustion method. The structure and electromagnetic properties of the powders were characterised by X-ray diffraction, SEM and vector network analysis. The pure powders were formed by heating at 1200°C for 3 h in air, and grain sizes increased as the amount of substitution ranged from x?=?0·0 to x?=?0·25. For samples with x?=?0·1, a minimum reflection loss of ?27·57 dB was observed at 11·0 GHz with the less than ?10 dB absorption bandwidth at 8·0 GHz with 3·8 mm thickness. The results indicate that substitution with Mn and Zn ions can greatly improve the microwave absorption properties of NiFe₂O₄ ferrites.     

Impinging-Jet Ozone Bubble Column Modeling: Hydrodynamics,Gas Hold-up,Bubble Characteristics,and Ozone Mass Transfer

A transient back flow cell model was used to model the hydrodynamic behaviour of an impinging-jet ozone bubble column. A steady-state back flow cell model was developed to analyze the dissolved ozone concentration profiles measured in the bubble column. The column-average overall mass transfer coefficient, k_La (s^?1), was found to be dependent on the superficial gas and liquid velocities, u_G (m.s^?1) and u_L (m.s^?1), respectively, as follows: k_La?=?55.58 · u_G ^1.26· u_L ^0.08 . The specific interfacial area, a (m^?1), was determined as a = 3.61 × 10³ · u_G ^0.902 · u_L ^?0.038 by measuring the gas hold-up (ε _G?=?4.67 · u_G ^1.11 · u_L ^?0.05 ) and Sauter mean diameter, d_S (mm), of the bubbles (d_S?=?7.78 · u_G ^0.207 · u_L ^{? 0.008} ). The local mass transfer coefficient, k_L (m.s^?1), was then determined to be: k_L?=?15.40 · u_G ^0.354 · u_L ^0.118 .     

Adsorption of cadmium and zinc from aqueous solution on natural and activated bentonite

The adsorption of cadmium and zinc ions on natural bentonite heat-treated at 110°C or at 200°C and on bentonite acid-treated with H₂SO₄ (concentrations: 0·5 mol dm^?3 and 2·5 mol dm^?3), from aqueous solution at 30°C has been studied. The adsorption isotherms corresponding to cadmium and zinc may be classified respectively as H and L types of the Giles classification which suggests the samples have respectively a high and a medium affinity for cadmium and zinc ions. The experimental data points have been fitted to the Langmuir equation in order to calcualte the adsorption capacities (X_m) and the apparent equilibrium constants (K_a) of the samples; X_m and K_a values range respectively for 4·11 mg g^?1 and 1·90 dm³ g^?1 for the sample acid-treated with 2·5 mol dm^?3 H₂SO₄ [(B)-A(2·5)] up to 16·50 mg g^?1 and 30·67 dm³ g^?1 for the natural sample heat-treated at 200°C [B-N-200], for the adsorption process of cadmium, and from 2·39 mg g^?1 and 0·07 dm³ g^?1, also for B-A(2·5), up to 4·54 mg g^?1 and 0·45 dm³ g^?1 [B-N-200], for the adsorption process of zinc. X_m and K_a values for the heat-treated natural samples were higher than those corresponding to the acid-treated ones. The removal efficiency (R) has also been calculated for every sample; R values ranging respectively from 65·9% and 8·2% [B-A(2·5)] up to 100% and 19·9% [B-N-200], for adsorption of cadmium and zinc.     

Non-ionizable Polyacrylic Hydrogels Sensitive to pH for Biomedical Applications

Hydrogels based on ethoxytriethyleneglycol monomethacrylate/methyl methacrylate (T/M) copolymers were prepared by free radical polymerization at 70°C in bulk with azobisisobutyronitrile as initiator. The reactivity ratios were calculated by Fineman–Ross (FR) and Kelen–Tudos (KT) linearization methods and by the non-linear least square method suggested by Tidwell and Mortimer (TM). The reactivity ratios obtained were r_T=0·17±0·03, r_M=0·70±0·01 (FR method); r_T=0·19±0·02, r_M=0·76±0·03 (KT method) and r_T=0·18; r_M= 0·75 (TM method). Microstructure was obtained in terms of the distribution of T- and M-centred triads. The swelling behaviour of the hydrogels was studied by immersion of the films in water and in buffered solutions at various pH values and it was analysed by comparison with that of poly(ethoxytriethyleneglycol monomethacrylate). It was observed that not only the average copolymer composition but also the distribution of monomeric sequences play an important role in the swelling behaviour. © 1997 SCI.     

Phase structure and electrical properties of lead free Na0·5Bi0·5TiO3–CaTiO3 ceramics

Abstract

Abstract

(1?x)Na_0·5Bi_0·5TiO_3?xCaTiO₃ ceramics with x?=?0–0·2 were prepared by solid state sintering method. Structural and morphology studies carried out by X-ray diffraction and scanning electron microscopy indicate the change in crystal structure from rhombohedral to orthorhombic symmetry (R3C to Pnma). The morphotropic phase boundary of this system was found to lie around x?=?0·08–0·14, where the orthorhombic and rhombohedral symmetries coexist. The orthorhombic phase is stabilised for x>0·14, indicating that the rhombohedral phase of Na_0·5Bi_0·5TiO₃ is susceptible to orthorhombic distortion brought about by Ca substitution. Calcium substitution in Na_0·5Bi_0·5TiO₃ caused an obvious decrease in peak temperature and a decrease in relative permittivity. The compositional variation of the fundamental dielectric behaviour is discussed in relation to the crystal chemistry of the system. The highest piezoelectric constant d₃₃ of 85 pC N^?1 is achieved for x?=?0·1, with the coercive field of 18 kV cm^?1 and the dielectric maximum temperature of 148°C.     

Medium-range order and physicochemical properties of (100 ? x)(0.5PbO · 0.5P2O5) · xTeO2 glasses in terms of the constant stoichiometry grouping concept

Glasses in the (100 − x)(0.5PbO · 0.5P₂O₅) · xTeO₂ section of the PbO-P₂O₅-TeO₂ system have been synthesized over the entire composition range for the first time and their properties (Raman spectra, refractive index n, density d, glass transition temperature T _g , and light scattering losses) have been investigated. It has been demonstrated that the Raman spectra can be represented as a superposition of constant spectral forms corresponding to constant stoichiometry groupings PbO · P₂O₅, TeO₂ · 2PbO · 2P₂O₅, TeO₂ · PbO · P₂O₅, 2TeO₂ · PbO · P₂O₅, and TeO₂. The existence of crystals of the corresponding stoichiometry has been predicted using the constant stoichiometry grouping concept. The diagram of the constant stoichiometry grouping contents (determined from the Raman spectra) in glasses of the system under investigation has made it possible to determine the partial properties of constant stoichiometry groupings, to calculate the dependences of the refractive index and density on the composition, and to refine the values of n and d for vitreous tellurium dioxide and lead metaphosphate. The practical importance of glasses in the system under consideration for the use in photonic devices has been discussed.     

Photoinduced Charge-Transfer Dissociation in van der Waals Complexes. III. Na···FCH3

Complexes Na···FCH₃)_n, n = 1–6, in beams were identified by photoionization time-of-flight (TOF) mass spectrometry. Dissociation of Na···FCH₃ was studied by photodepletion. The depletion spectrum (450–750 nm) suggested excitation of Na in the complex followed by charge-transfer to yield Na⁺···FCH₃⁻ → NaF + CH₃. The depletion cross section was substantial, peaking at 1.1 Ų.     

Ferroelectric,dielectric and pyroelectric properties of Sr and Sn codoped BCZT lead free ceramics

The 1?mol.-%Sr and 1?mol.-%Sn codoped (Ba_0·84Ca_0·15Sr_0·01)(Ti_0·90Zr_0·09Sn_0·01)O₃ (BCSTZS) ceramics were synthesised by the normal solid state sintering method. The electric field and temperature dependence of the ferroelectric properties of the BCSTZS ceramics were investigated. Their energy storage density depending on electric field and temperature was determined from the polarisation–electric field (P–E?) hysteresis loops. According to the dielectric analysis, the BCSTZS ceramics experience three-phase transitions upon cooling. At room temperature, the pyroelectric coefficient p calculated from the remnant polarisation–temperature (P_r–T?) curve is 1116·7?μC?K^??1?m^??2, and the figures of merit F_d is 18·1?μPa^??1/2, F_v is 0·013?m²?C^??1 and F_i is 479·3?pm?V^??1 respectively. The pyroelectric figures of merit exhibit high frequency stability over a wide range from 100 to 2000?Hz, whereas these values vary gradually with the increase in temperature, which deserves further research to improve their stability. The excellent pyroelectric property of the BCSTZS ceramics is considered as correlating with a polymorphic phase transition occurring around room temperature. The present study demonstrates that the lead free BCSTZS ceramics are promising candidate for replacing the lead zirconate titanate based ceramics.     

Removal of 1,1′-Dimethyl-4,4′bipyridyl Dichloride from Aqueous Solution by Natural and Activated Bentonite

The sorption of 1,1′-dimethyl-4,4′bipyridilium dichloride (paraquat) on bentonite desiccated at 110°C untreated, and acid-treated with H₂SO₄ solutions over a concentration range between 0·25 M and 1·00 M , from aqueous solution at 30°C has been studied by using batch experiments. In addition, column experiments were carried out with the bentonite sample treated with the 1·00 M H₂SO₄ solution [B-A(1·00)] by using two aqueous solutions of paraquat of different concentrations (C = 29·40 mg dm⁻³ and C = 65·38 mg dm⁻³). The experimental data points have been fitted to the Langmuir equation in order to calculate the sorption capacities (X_m) of the samples; X_m values range from 1·35×10⁵ mg kg⁻¹ for the sample acid-treated with 0·375 M H₂SO₄ [B-A(0·375)] up to 1·96×10⁵ mg kg⁻¹ for the untreated bentonite [B-N]. The removal efficiency (R) has also been calculated; R values ranging from 44·61% for the [B-A(0·375)] sample up to 67·23% for B-N. The batch experiments show that the natural bentonite is more effective than the acid-treated bentonite in relation to sorption of paraquat. The column experiments show that the B-A(1·00) sample might be reasonably used in removing paraquat, the column efficiency increasing from 37·55% for the C = 65·38 mg dm⁻³ aqueous solution of paraquat up to 66·58% for the C = 29·40 mg dm⁻³ one. © 1997 SCI.     

Influence of aluminium hydroxide and lime on the hydration of tricalcium silicate

Experiments by isothermal calorimetry, indicate that the hydration of 3CaO·SiO₂ (C₃S) is influenced very little by gibbsite; it is influenced by bayerite to a somewhat larger extent. In the presence of amorphous Al(OH)₃ the reaction of C₃S with water shows a very complicated course and gives four heat peaks. If CaO is added in addition to this Al(OH)₃, the third and the fourth heat peaks are more pronounced. From qualitative d.t.a., infra-red, electron-microscope and X-ray investigations, as well as from quantitative X-ray analysis, a reaction mechanism is proposed. The quantity of C₃S reacted, determined by means of quantitative X-ray analysis, is greater during the reaction of 2·00 g C₃S with 0·40 g amorphous Al(OH)₃, 0·08 g CaO and 2·00 ml water, than during the reaction of 2·00 g C₃S with 2·00 ml water.     

Surface Praseodymium Species on MgO: Characterization and Activity for Oxidative Coupling of Methane

On pulsing CH₄ over MgO containing various amounts of praseodymium oxide (PrO_x) at 1023 K, the CH₄ conversion decreased with increasing pulse number, and both the initial activity and selectivity to C₂ products (corresponding to the first pulse) decreased with increasing PrO_x content. Characterization by XRD, SEM-EDX and XPS showed calcined materials to contain well-dispersed PrO_x (x = 1·83–2) at low Pr concentrations, but only crystalline PrO_1·83 at high (10 wt%) Pr concentration. A PrO_1·83 phase was present at all Pr concentrations after the He treatment at 1023 K, and PrO_1·83, PrO_1·75 and PrO_1·5 after reaction. © 1997 SCI     

Syntheses, Structures and Properties of Two Metal–Iodide Polymers Based on a Flexile N-Donor Ligand

Two novel metal–organic frameworks based on 1,3-bis(imidazol-1-ylmethyl)-benzene (m-bix), namely [(Cu₄I₄)(bix)₂] _n (1) and [HgI₂(bix)] _n (2) have been synthesized and characterized by IR, elemental analysis, thermogravimetry, luminescent properties and X-ray crystallography. The structure of compound 1 exhibits a 1D metal–organic chain composed of Cu₄I₄ clusters and m-bix ligands, and such chains are further united together to generate a 3D supramolecular structure through inter-chain π···π interactions. In compound 2, the HgI₂-bix chains interact each other to form a layer structure through π···π interactions, then the layers are extended to 3D supramolecular architecture through intermolecular C–H···π interactions.