Uptake of heavy metal ions from aqueous solution using Mg–Al layered double hydroxides intercalated with citrate, malate, and tartrate

Mg–Al layered double hydroxide (Mg–Al LDH) was modified with organic acid anions using a coprecipitation technique, and the uptake of heavy metal ions from aqueous solution by the Mg–Al LDH was studied. Citrate·Mg–Al LDH, malate·Mg–Al LDH, or tartrate·Mg–Al LDH, which had citrate³⁻ (C₆H₅O₇³⁻), malate²⁻ (C₄H₄O₅²⁻), or tartrate²⁻ (C₄H₄O₆²⁻) anions intercalated in the interlayer, was prepared by dropwise addition of a mixed aqueous solution of Mg(NO₃)₂ and Al(NO₃)₃ to a citrate, malate, or tartrate solution at a constant pH of 10.5. These Mg–Al LDHs were found to take up Cu²⁺ and Cd²⁺ rapidly from an aqueous solution at a constant pH of 5.0. This capacity was mainly attributable to the formation of the citrate–metal, malate–metal, and tartrate–metal complexes in the interlayers of the Mg–Al LDHs. The uptake of Cu²⁺ increased in the order malate·Mg–Al LDH < tartrate·Mg–Al LDH < citrate·Mg–Al LDH. The uptake of Cd²⁺ increased in the order malate·Mg–Al LDH < tartrate·Mg–Al LDH = citrate·Mg–Al LDH. These differences in Cu²⁺ and Cd²⁺ uptake were attributable to differences in the stabilities of the citrate–metal, malate–metal, and tartrate–metal complexes. These results indicate that citrate³⁻, malate²⁻, and tartrate²⁻ were adequately active as chelating agents in the interlayers of Mg–Al LDHs.     

Evidence for the trans-influence of axial substituents as a significant factor determining the structure and stability of five-coordinate complexes: molecular structure of the first simple five-coordinate dialkylaluminum O,O′-chelate complex

The addition of 4-methylpyridine to Me₂Al[OC(Me)C₆H₄-2-O] produced the relatively stable five-coordinate Lewis acid–base adduct Me₂Al[OC(Me)C₆H₄-2-O]·(γ-picoline). The resulting compound has been characterized by ¹H and ²⁷Al NMR spectroscopy and cryoscopic molecular weight measurements and the molecular structure has been confirmed by X-ray crystallography. X-ray structure analysis of this simple five-coordinate complex reveals that the trans-influence of axial substituents is a significant factor controlling the structure and stability of five-coordinate aluminum compounds.     

Control of Oxidation State of Eu Ions in Na2O–Al2O3–SiO2 Glasses

Glasses doped with well‐controlled Eu³⁺ and Eu²⁺ ions have attracted considerable interest due to the possibility of tuning the wavelength range of the emitted light from violet to red by using their ⁵D₀→⁷F_j and 5d–4f electron transitions. Glasses were prepared to dope Eu³⁺ ions in a Na₂O–Al₂O₃–SiO₂ system, and the changes in the valence state of Eu³⁺ ions and the glass structure surrounding the Eu atoms during heating under H₂ atmosphere were investigated using fluorescence spectroscopy, X‐ray absorption fine‐structure spectroscopy, and ²⁷Al magic‐angle spinning solid‐state nuclear magnetic resonance spectroscopy. The reduction behavior of Eu³⁺ ions was dependent on the Al/Na molar ratio of the glass. For Al/Na < 1, the Al³⁺ ions formed the AlO₄ network structure accompanied by the Na⁺ ions as charge compensators; the Eu³⁺ ions occupied the interstitial positions in the SiO₄ network structure and were not reduced even under heating in H₂ gas. On the other hand, in the glasses containing Al₂O₃ with the Al/Na ratio exceeding unity, the Eu³⁺ ions commenced to be coordinated by the AlO₄ units in addition to the SiO₄ network structure. When heated in H₂ gas, H₂ gas molecules reacted with the AlO₄ units surrounding Eu³⁺ ions to form AlO₆ units terminated with OH bonds, and reduced Eu³⁺ ions to Eu²⁺ via the extracted electrons.     

Synthesis and characterization of high purity aluminum sec-butoxide from aluminum dross

Aluminum sec-butoxide (ASB) was synthesized to a high purity grade from Al dross through dissolution reaction and vacuum distillation under the condition of 3 mol C₄H₉OH/mol Al as a stoichiometric reactant ratio and 10⁻³ mol HgI₂/mol Al as a catalyst. The dissolution reaction proceeded for 24 hours, then pure ASB was recovered by vacuum distillation from the Al solution obtained after the dissolution. The ASB thus synthesized was quantitatively analyzed by a complexometric method for purity. This reaction gave a 99.2% purity and 28% yield. Characteristics of the synthesized ASB were analyzed by FT-IR, ²⁷Al-NMR, and ¹H-NMR. The result of analysis revealed that the crystalline structure between the synthesized ASB and commercial ASB was identical. Especially, the yield synthesized through this experiment corresponded to the total amount of Al metal existing in Al dross.     

Kinetic study of ethylene polymerization by highly active silica supported TiCL4/MgCl2 catalysts

The kinetics of ethylene polymerization with TiCl₄/MgCl₂/SiO₂ has been investigated in the range of temperatures between 40 and 90°C and in the range of ethylene pressures between 4 and 12.4 kg/cm². The role of MgCl₂ was discussed from the dependence of the Mg/Ti ratio on the catalytic activity. The polymerzation rate was first order with respect to the monomer concentration and the dependence of the polymerization rate on the concentration of Al(C₂H₅)₃ could be described by the Langmuir–Hinshelwood mechanism. The dependence of initial rate and the time to reach the maximum polymerization rate on the concentration of Al(C₂H₅)₃ was also discussed. Polymerization rates as a function of the polymerization temperature showed a maximum and the activation energy was 11.8 kcal/mol between 50 and 80°C. The polymerization rate decreased with the increase of hydrogen partial pressure. The active site concentration (C^*) was 1.9 × 10^?2 mol/mol Ti by the inhibition method with carbon monoxide.     

Synthesis of single-walled carbon nanotubes produced using a three layer Al/Fe/Mo metal catalyst and their field emission properties

Single-walled carbon nanotubes (SWCNTs) were synthesized on SiO₂/Si substrates by thermal chemical vapor deposition using an Al/Fe/Mo triple layer catalyst, methane (CH₄) as the carbon source, and a mixture of Ar/H₂ (10% H₂) as the carrier gas. The effects of volume ratio of CH₄ to Ar/H₂ (10% H₂), pretreatment time, growth temperature, and Al underlayer thickness on SWCNT growth were studied. The pretreatment time in Ar/H₂ and Al underlayer thickness were found to be crucial for a high-yield of high-purity SWCNTs, since they both governed the size of the catalyst nanoparticles. The optimum growth conditions were found to be a pretreatment time of 20 min, growth time of 10 min, growth temperature of 900 °C, and CH₄/Ar/H₂ flow rates of 50/900/100 sccm, with a catalyst composed of Al (2 nm)/Fe (1 nm)/Mo (0.5 nm). The SWCNTs grown under these conditions have excellent field emission characteristics with low turn-on and threshold fields of 2.4 and 4.3 V/μm, respectively, and a current density of 38.5 mA/cm² at 5 V/μm.     

掺杂元素对TiO2/SO2-4固体酸特性的影响

为了进行掺杂元素对超强酸特性的影响研究,采用均匀沉淀法合成了Fe、Si、Al和Zr氧化物掺杂的TiO2/SO2-4的固体酸(TiO2-MrOy),采用XRD、FTIR、NH3-TPD以及H2-FPR等分析方法对催化剂进行表征.以大豆油和甲醇的酯交换反应为活性评价反应,比较了各催化剂的催化活性.研究发现,除了Al外掺杂元...     

High-temperature oxidation of aluminium in various gases

The oxidation of high-purity aluminium sheet in dry oxygen, moist oxygen, carbon dioxide and carbon monoxide (at total pressure 1.333 × 10³ Nm^?2) was studied in the range 673–923°K, using a vacuum microbalance to follow weight gains. ¹⁴CO₂ and ¹⁴CO were used to elucidate the mechanism of the oxidation in these gases and to estimate the extent of carbon deposition in the oxide layer. The rate of oxidation in moist oxygen was similar to that in dry oxygen, the principle reaction being 2Al + 3H₂O ← Al₂O₃ + 3H₂. It is suggested that there are three steps in the reaction in CO₂, viz. 2Al+3CO₂ ← Al₂O₃ + 3CO, followed by 2Al + 3CO ← Al₂O₃ + 3C, and about 10% of the deposited carbon reacting further by 4Al + 3C ← Al₄C₃. Only the last two reactions are operative in carbon monoxide. The Arrhenius plots show a distinct break in the region 773–823°K for both carbon monoxide and carbon dioxide, but not for dry or moist oxygen. This is tentatively explained by a change in the rate-determining process from diffusion via grain boundaries or cracks in the oxide, to lattice diffusion. It is suggested that carbon may become mobile in the oxide film between 773 and 823°K and may tend to congregate in the grain boundaries and cracks. The oxide film remained protective throughout the duration of the experiments in all the gases.     

Synthesis of aluminum ethoxide from used aluminum cans

Aluminum ethoxide (AE) was synthesized to a high purity grade through dissolution reaction and vacuum distillation from used Al cans (UACs) under the condition of 3 mol C₂H₅OH/mol Al of stoichiometric ratio. 10⁻³ mol Hgl₂/mol Al as a catalyst and 0.5 mol xylene/mol Al as a solvent for the control of reaction temperature were added. The UACs were cut into small pieces and heat-treated at the condition of 600 °C to remove impurities from UACs. Using the pretreated UACs, the high purity AE was synthesized and analyzed quantitatively by a complexometric method. The results of our experiment revealed that the reaction gives a 99.1% purity and 75% yield corresponding to the total amount of Al existing in the pretreated UACs.     

Synthesis of Li/Al LDH using aluminum and LiOH

The synthesis of Li/Al layered double hydroxide (LDH) within the ternary system of LiOH–Al–H₂O was investigated to determine the feasibility of a one-step synthetic process and the optimal yield composition for the process. The dissolution of Al metal in LiOH solutions was spontaneous and resulted in the generation of H₂ gas and heat. Pure Li/Al LDH precipitate was obtained when the Al/Li molar ratio was between 0.1 and 2 and was independent of the LiOH concentration. The yield of Li/Al LDH was correlated with the initial amounts of LiOH and Al in the system and inversely correlated to the quantity of water. However, the Al metal could not be completely dissolved if there was not enough water content due to its consumption in the reaction. The optimal yield of Li/Al LDH, as defined by the efficient conversion from Al and LiOH to Li/Al LDH, was obtained with a LiOH concentration = 3 mol kg^− 1 and an Al/Li molar ratio = 2. The reaction mechanism involves the dissolution of the Al metal in LiOH and the formation of aluminate ions in solution. The aluminate ion and the hydrated Li⁺ ion subsequently form an ion pair, and the polarizing effect of the Li⁺ on the water in its hydration shell leads to the acid hydrolysis of the aluminate ion and the formation of Li/Al LDH. This study demonstrated a synthetic process for Li/Al LDH with a high anion exchange capacity. This synthetic process will have additional economical and environmental benefits if recycled Al metal can be used in the synthesis and the evolved hydrogen gas and heat from the process can be further utilized.     

Hydrothermal stabilization of ZSM-5 catalytic-cracking additives by phosphorus addition

ZSM-5 zeolites with different Si/Al ratios (15, 25, 40) were impregnated with phosphorus (0.5–3 wt%) in form of H₃PO₄ or NH₄H₂PO₄. The samples were characterized before and after severe hydrothermal treatment by XRD, IR, ²⁷Al, ²⁹Si, ³¹P MAS NMR, and their activity for the cracking of n-decane was measured. It was found that phosphorus impregnation increases the hydrothermal stability of framework aluminum whatever the source of phosphorus used. The acidity and cracking activity of steamed samples reached an optimum for a P/Al molar ratio of ca. 0.5–0.7. A chemical model for the phosphorus–zeolite interaction is proposed in which the framework aluminum pairs are stabilized by extra-framework cationic species formed by protonation of orthophosphoric acid. The influence of isolated versus pairs of aluminum on activity and selectivity after steaming is discussed. When P-impregnated ZSM-5 sample is used as an additive for cracking industrial feeds, selectivity to propylene and butenes increases.     

Characterization of the acid properties of [Al]-, [Ga]- and [Fe]-HZSM-5 by low-temperature FTIR spectroscopy of adsorbed dihydrogen and ethylbenzene disproportionation

[Al]-, [Ga]- and [Fe]-HZSM-5 having closely similar Brønsted acid site densities were prepared. The low-temperature adsorption of H₂ and D₂ was studied by FTIR spectroscopy and the frequency shifts Δν_OH and Δν_HH (Δν_DD) were measured and compared with corresponding frequency shifts observed for CO and N₂ probes. A linear correlation between |Δν_OH|^1/2 which is proportional to the heat of formation &;/Delta;H_B of the H-bonded complex O-H···B (B representing the H-bond acceptor), and the proton affinities of the three probe molecules was found for [Al]-HZSM-5. The ΔνOH-values measured for CO and H2 (D2) on the three isomorphously substituted zeolites suggested the following acid strength ranking: [Al]-HZSM-5 > [Ga]-HZSM-5 ≈ [Fe]-HZSM-5. This sequence is clearly reflected in the relative activities of the materials for the acid-catalyzed disproportionation of ethylbenzene.     

Electropolymerization of aniline in acid media on the bare and chemically pre-treated aluminum electrodes: A comparative characterization of the polyaniline deposited electrodes

The electrosynthesis of polyaniline on the bare aluminum and pre-treated aluminum surface achieved in aqueous H₂PtCl₆ solution saturated with NaF for few seconds is described. The effect of some factors such as pre-treatment time, aniline and sulfuric acid concentrations on the electropolymerization process was investigated and optimum conditions were obtained. The stability of polyaniline film on the pre-treated aluminum electrode (Al-Pt) was studied as function of the potential imposed on the electrode. For applied electrode potentials of 0.1-0.7 V, the first-order degradation rate constant, k, of polyaniline film varies between 1 × 10⁻⁶ and 2 × 10⁻⁵ s⁻¹, and a relatively low slope (i.e. 2.1) was obtained for the plot of log k versus E. The coatings were characterized by scanning electron microscopy (SEM), and cyclic voltammetric behavior of the polyaniline-deposited Al electrode (Al/PANI) and polyaniline-deposited Al-Pt electrode (Al-Pt/PANI) in 0.1 H₂SO₄ solutions is described. The electrocatalytic activity of the Al-Pt/PANI electrode against para-benzoquinone/hydroquinone (Q/H₂Q) and Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ redox systems was investigated and the obtained results are compared with those obtained on Al/PANI and bulk Pt electrodes.     

Hydrolysis of aluminium on weakly acidic organic exchangers: Implications for phosphate adsorption

In contrast to its behaviour on soil clays and in aqueous solution, aluminium is more extensively hydrolysed between pH3 and 4.5 on organic exchangers because the weakly acidic carboxyl groups appear to act as sinks for the protons released by hydrolysis and polymerization of the Al(H₂O) ₆ ³⁺ ions. In consequence, the basicity (measured by the OH/Al mole ratio) of Al adsorbed on samples of acid peat, humic acid and Amberlite IRC-50 resin was closely correlated with the apparent pK_a of the acid groups. The amount of phosphate adsorbed depended not only on the amount of Al adsorbed but also on the basicity of the adsorbed Al. Phosphate and OH^– ions competed for Al on the exchange sites with the result that the P/Al mole ratio on the exchanger was inversely related to the basicity of the adsorbed Al. Once adsorbed, the Al was quite stable and P adsorption on the Al-exchanger was unaffected by a rise in pH from 4.5 to 6.4.     

Novel Au/TiO2/Al2O3 · xH2O catalysts for CO oxidation

Au/Al₂O₃ · xH₂O and Au/TiO₂/Al₂O₃ · xH₂O (x = 0–3) catalysts were prepared by assembling gold nanoparticles on neat and TiO₂-modified Al₂O₃, AlOOH, and Al(OH)₃ supports, and their catalytic activity in CO oxidation was tested either as synthesized or after on-line pretreatment in O₂–He at 500 °C. A promotional effect of TiO₂ on the activity of gold catalysts was observed upon 500 °C-pretreatment. The catalyst stability as a function of time on stream was tested in the absence or presence of H₂, and physiochemical characterization applying BET, ICP-OES, XRD, TEM, and ²⁷Al MAS NMR was conducted.     

Synthesis of AlPO4-34 and its large single crystal by partially substituting framework fluorine with oxygen species

AlPO₄-34 is a fluorine containing aluminophosphate with two fluorine atoms located in the bridge of two octahedrally coordinated Al atoms of a 4-ring. It has a unit cell composition (C₄H₁₀NO⁺)₂ (AlPO₄)₆F₂ ^? with the stoichiometric value of Al:P:F being 3:3:1 (F/Al?=?0.33) and to be named as AlPO₄-34F. The presence of fluorine in the reacting gels favors the formation of AlPO₄-34 structure, but hinders the growth of its large crystals. In present work, a seesaw effect between organic template and hydrofluoric acid on the crystallization of AlPO₄-34 has been found and used to synthesize AlPO₄-34 with F/Al in the framework lower than 0.33. Large single crystal of AlPO₄-34 has been prepared from a gel having the molar ratio of HF/Al₂O₃?=?0.125. Single crystals refinement has shown that the unit cell formula of the AlPO₄-34 is (C₄H₁₀NO⁺)₂(AlPO₄)₆F _1.18 ^? (OH) _0.82 ^? (H₂O)_0.5. The molar ratio of Al:P:F:O_b is 3:3:0.59:0.41 with 40% fluoride ions being substituted by oxygen species (O_b: oxygen atoms in the bridges of Al?CO?CAl). Ion chromatography analysis has confirmed the partial substitution of fluorine by oxygen. It was named as AlPO₄-34P. Thermal analyses have shown that oxygen species in the bridge position of two octahedrally coordinated Al atoms are more instable than fluoride ions. Under heating, the AlPO₄-34P will transform to chabazite structure at a temperature lower than AlPO₄-34F.     

Probing the pore structure and dehumidifying characteristics of chemically modified zeolite Y

This study was aimed at modifying the pore structure and surface chemistry of a zeolite to achieve an ideal material for gas-fired dehumidifying and cooling system application. Zeolite Y was chemically modified with various amounts of ethylenediaminetetraacetic acid (H₄EDTA) corresponding to H₄EDTA/Al (zeolite) molar ratio, X=0.5, 0.6, 0.75, 0.9 and 1.0 under reflux condition to achieve various degrees of dealumination. Sample treated with X=0.5 remained highly crystalline, but crystallinity of the samples decreased as the X increased. Although the sample treated with X=0.9 was x-ray amorphous, SEM micrographs indicated that the original crystal morphology was largely preserved. Chemical analysis and ²⁹Si showed a progressive extraction of Al and Na with increased X. ²⁷Al MASNMR indicated that Al^IV was the only Al species up to X=0.75, whereas the x-ray amorphous phase (X=0.9) exhibited three peaks at 60, 52 and 38 ppm indicating the distortion of and change in Al^IV coordination. Adsorption analyses using H₂O, N₂ or Ar as probe molecules indicated that the X-ray amorphous product remained essentially microporous having a broad micropore size distribution and a reduced hydrophilicity. Consequently, water adsorption isotherm changed from an extreme Type I to a moderate Type I. The moderate Type I isotherm with water is the key for its suitability as a desiccant in gas-fired dehumidifying and cooling system. These materials are also potentially useful in solar heating and cooling applications.     

Efficient ring-opening polymerization of -caprolactone using anilido-imine–aluminum complexes in the presence of benzyl alcohol

A number of new anilido-imine–Al complexes ortho-C₆H₄(CHNAr¹)(NAr²)AlMe₂ [Ar¹ = C₆H₅, Ar² = C₆H₅ (2a); Ar¹ = 2,6-Me₂C₆H₃, Ar² = 2,6-Me₂C₆H₃ (2b); Ar¹ = 2,6-Et₂C₆H₃, Ar² = 2,6-Et₂C₆H₃ (2c); Ar¹ = 2,6-ⁱPr₂C₆H₃, Ar² = 2,6-Me₂C₆H₃ (2d); Ar¹ = 2,6-ⁱPr₂C₆H₃, Ar² = 2,6-Et₂C₆H₃ (2e)] were synthesized, characterized and used as initiators for the ring-opening polymerization of -caprolactone in the presence of benzyl alcohol. The effect of initiator structure and reaction conditions, such as benzyl alcohol/Al molar ratio and reaction temperature on the reactivity, and polymer molecular weight were investigated. The polymerization of -caprolactone initiated by these complexes was found to take place in an immortal fashion.     

The mechanism of electrodeposition of acrylic resin on aluminium

A mechanism for the electrodeposition of acrylic resin on aluminium is proposed, based on experimental studies of acid value, anodic gas evaluation and anodic film resistance. The mechanism can be expressed as Alf Al³⁺ + 3e 2Al³⁺ + 3H₂Of Al₂O₃ + 6H⁺ 2Al³⁺ + 6H₂Of 2Al(OH)₃ + 6H⁺ H⁺ + RCOC^– f RCOOH. This is different from the mechanism for zinc and steel, where it is metal ions from anodic dissolution which neutralize the macro-ions and cause a deposit on the anode surface.     

Effects of Fe addition on the structure and catalytic performance of mesoporous Mn/Al–SBA-15 catalysts for the reduction of NO with ammonia

Mesoporous Al–SBA-15 has been synthesized by a hydrothermal method and used as a support for Mn/Al–SBA-15, Fe/Al–SBA-15, and Mn–Fe/Al–SBA-15 catalysts. XRD, N₂ sorption, XPS, H₂-TPR and activity tests have been used to assess the properties of catalysts. The Mn–Fe/Al–SBA-15 catalyst exhibited a higher SCR activity than Mn/Al–SBA-15 or Fe/Al–SBA-15 due to a synergistic effect between Mn and Fe. After the addition of Fe, the binding energy of Mn 2p_3/2 on Mn–Fe/Al–SBA-15(573) decreased by about 0.4 eV and the Mn^4 +/Mn^3 + ratio decreased to 1.10. The appropriate Mn^4 +/Mn^3 + ratio may have a great effect on the reduction of NO over Mn–Fe/Al–SBA-15(573) catalyst.