Strong Basicity Research Articles

Removal of copper from aqueous solution using iron-containing adsorbents derived from methane fermentation sludge

Iron-containing adsorbents prepared from methane fermentation sludge (MFS) were characterized by N 2 adsorption, XRD, SEM, EDX, pH determination and elemental analysis. The experiments for copper removal from aqueous solution using the MFS-derived adsorbents were performed, and the effects of iron content, forms of the iron (hydr)oxides, surface basicity and pH of the aqueous solution on copper removal were elucidated respectively. The desorption studies were also performed and the mechanism of Cu(II) adsorption was proposed. The results indicated that the adsorbent obtained at 700 °C for 1 h in a steam atmosphere possessed the highest capability for Cu(II) adsorption. The high copper removal ability of the MFS-derived materials is attributed to their intermediate surface area, strong surface basicity and the presence of iron (hydr)oxides on their surface. The Cu(II) adsorption onto the composite adsorbents is via ion-exchange with H, Ca and K ions, surface precipitation and binding with active sites on the surface of iron (hydr)oxides at various pH values. The desorption of copper in deionized water is quite low. The irreversibility of copper adsorption on the iron-containing adsorbents is attributed to the formation of strong bonds between Cu(II) and the iron (hydr)oxides. The adsorbent can be applied to remove copper from water or soil by fixation onto the surface.

A New Series of Ionic Liquids Based on the Difluorophosphate Anion

A new series of ionic liquids based on the difluorophosphate anion (PO(2)F(2)(-)) has been synthesized by metathesis from the corresponding chloride. Incorporation of the PO(2)F(2)(-) anion with an N-heterocyclic cation (1-ethyl-3-methylimidazolium (EMIm(+)), 1-butyl-3-methylimidazolium, 1-butyl-1-methylpyrrolidinium, or 1-butyl-1-methylpiperidinium (BMPip(+))) produces ionic liquids with low melting points, including some room-temperature ionic liquids. The vibrational frequencies of PO(2)F(2)(-) in the obtained ionic liquids were assigned with the aid of quantum mechanical calculations. The ionic conductivities of the ionic liquids are comparable to those of the corresponding tetrafluoroborate-based ionic liquids (e.g., 12 mS cm(-1) for 1-ethyl-3-methylimidazolium difluorophosphate, [EMIm][PO(2)F(2)]). The stability of ionic liquids against hydrolysis is significantly improved by replacing the hexafluorophosphate anion with the difluorophosphate anion, which suppresses the subsequent liberation of hydrogen fluoride. According to the solvatochromic method, the donor ability of ionic liquids based on PO(2)F(2)(-) is stronger than those of ionic liquids based on BF(4)(-), PF(6)(-), and N(SO(2)CF(3))(2)(-), due to the large negative charge on the oxygen atoms in PO(2)F(2)(-). The electrochemical window of [EMIm][PO(2)F(2)] is around 4.2 V, and the diffusion coefficients of ferrocene in [EMIm][PO(2)F(2)] are 2.83 x 10(-7) cm(2) s(-1) by cyclic voltammetry and 3.03 x 10(-7) cm(2) s(-1) by chronoamperometry, both of which are comparable to those in 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF(4)]). The X-ray structure of [BMPip][PO(2)F(2)] contains two cations and two anions in the asymmetric unit, where one of the two cations is disordered into two positions (chair configurations) even at -173 degrees C. The oxygen atoms in PO(2)F(2)(-) have closer contacts to the hydrogen atoms in BMPip(+) than the fluorine atoms, indicative of their stronger basicity.

The influence of alkaline metals on the strong basicity of Mg–Al mixed oxides: The case of transesterification reactions

Several Mg/Al mixed oxides, prepared by three different co-precipitation procedures, have been tested in different transesterification reactions. The catalytic activity for sunflower oil transesterification correlates with the leachable basicity, and not with the total basicity, measured by titration methods. The presence of residual alkaline ions after crystallization is the main source for the strong basicity in this kind of solids, and the difficulty in the complete elimination of the alkaline traces are probably the origin of the strong discrepancies in basicity detected along the literature data. The effect of these alkaline traces is more evident with a more demanding reaction, such as that of methyl palmitate with isobutanol. In such case the alkaline-free solids did not show any catalytic activity. The nature of these strong basic sites makes the recovery problematic, given that part of the alkaline cation is lost to the reaction medium, a process favored by an increase in the polarity of the medium. This fact is also a general limitation for the application of this kind of solids to liquid phase reactions requiring high basicity.

One-step synthesis of H–β zeolite-enwrapped Co/Al 2O 3 Fischer–Tropsch catalyst with high spatial selectivity

A tailor-made encapsulated catalyst with a H–β zeolite shell has been directly synthesized over Co/Al 2O 3 pellets to form a core–shell structure without pinholes and cracks by a hydrothermal synthesis method. Pretreatment of the Co/Al 2O 3 pellets with reflux of hot TEAOH solution can clean and corrode the pellet surface due to its strong basicity, and can enlarge the mean pore size of the pellets. Impregnation of the Co/Al 2O 3 pellets in EtOH is important to avoid the corrosion of the internal pores, to prevent the introduction of Co species into the zeolite coating, and to realize a pure and uniformed β-zeolite coating. For the catalytic reaction of direct isoparaffin synthesis from syngas, the molar ratio of C isoparaffin/C normal-paraffin of the products obtained from the encapsulated catalyst increased about 64% than that of the products obtained from physical-mixed components. This concept of encapsulated catalyst can be useful to carry out various consecutive or multiple-step catalytic processes, where multiple reactions occur on different active centers.

Altered Activity and Physicochemical Properties of Short Cationic Antimicrobial Peptides by Incorporation of Arginine Analogues

The incorporation of nongenetically encoded amino acids is a well established strategy to alter the behavior of several types of promising cationic antimicrobial peptides. Generally, these elements have been improved mimics of the hydrophobic amino acids yielding peptides with increased stability and potency. In this initial study, the effect of systematic replacement of Arg in a well-defined moderately antimicrobial tripeptide library is described. It is shown that the arginine analogues need to display a strong basicity to produce active peptides. It is further revealed that the hydrophobic units needed for activity in these peptides can be effectively incorporated in the direct vicinity of the cationic charge to produce compounds with improved antibacterial properties. A well-defined facial amphiphilic structure, which remains intact upon introduction of hydrophobic elements in the cationic side chains, is seen for the majority of the tested peptides. Microcalorimetric studies revealed a peptide binding to large anionic unilamellar vesicles (LUVs) mimicking the Gram-positive bacterial membrane as well as a potentially competitive binding to human serum albumin in the low- to mid-micromolar range. No considerable alterations in binding to either albumin or the LUVs were seen for the analogue containing peptides. A neutral LUV mimicking the eukaryotic cell membrane showed no significant binding to any of the peptides. The oral absorption of this class of short lactoferricin based peptides was investigated for the first time and revealed that incorporation of weaker bases than Arg produced peptides with much improved permeability in a recently developed permeation model, the phospholipid vesicle based barrier assay. Collectively, the results presented here show that there is ample room to toggle the activity and physical properties of short cationic antimicrobial peptides by incorporation of arginine analogues.

Models for the sorption of volatile organic compounds by diesel soot and atmospheric aerosols

The solvation parameter model is used to characterize interactions responsible for the sorption of varied organic compounds by diesel soot and atmospheric aerosols at 15 degrees C and 50% relative humidity. Individual models are obtained for eight aerosol samples characterized as urban, suburban, rural and coastal. Combining the individual aerosol models resulted in a general aerosol model with only a minor loss of modeling power for alkanecarboxylic acids and low-molecular weight alcohols compared with the individual models. A second group of compounds identified as weak nitrogen-containing bases were consistent outliers to all models most likely due to participation in ion-exchange interactions not considered by the models. The diesel soot and atmospheric aerosols exhibit similar characteristics with respect to their sorption interactions although differences in relative magnitude allow the two particle types to be easily distinguished. Sorption interactions are favored by strong dispersion interactions for both particle types. Of note is the strong hydrogen-bond basicity and relatively weak hydrogen-bond acidity of these materials. The particles are quite dipolar/polarizable and slightly electron lone pair repulsive. The sorption properties of the atmospheric aerosols are influenced by the relative humidity, in particular, the aerosols become significantly more hydrogen-bond acidic at high relative humidity most likely due to incorporation of increasing amounts of condensed or film water in the aerosol phase. Dividing the data into training and test sets suggests that the proposed models are capable of estimating distribution constants (log K) to about 0.20 log units for diesel soot (n = 84) and 0.14 log units for the general atmospheric aerosol model (n = 385) where n indicates the number of compounds included in the model.

Formation of ethyl benzene and styrene by side chain methylation of toluene over calcined LDHs

Mg/Al layered double hydroxide (LDH) with various Mg/Al molar ratios 3, 4, 5, 7 and 10 were prepared, calcined and characterized by XRD, FT-IR, ICPES and BET surface area analysis. These LDHs were used for side chain methylation of toluene with methanol between 300 and 450 °C. For comparison, Cu/Al, Ni/Al, Co/Al and Zn/Al LDHs with molar ratio 3 were also prepared. The selectivity of styrene was higher over Mg/Al with low Al content. The selectivity of ethyl benzene was higher at 400 °C. At higher temperature, the side chain alkylation was favored and the selectivity of nuclear alkylation products such as xylene and mesitylene decreased as Mg/Al ratio changes from 3 to 10. The enhanced activity of calcined LDHs is due to the surface sites of low (OH − groups), medium (Mg–O pairs), and strong (O 2− anions) basicity. The surface concentration of low and medium strength basic sites increased with decreasing Al content. On Mg/Al LDHs, nuclear alkylation increased with increasing Al content. Substitution of Co 2+, Ni 2+, Zn 2+ and Cu 2+ for Mg 2+ favored nuclear alkylation. The selectivity of xylene and mesitylene increased with increase in temperature at a maximum 400 °C. Mg/Al LDHs were the most LDHs active than other LDHs for side chain methylation of toluene.

Catalytic performance of porous carbons obtained by chemical activation

Porous carbons were prepared by the pyrolysis of pinewood in nitrogen at 773 K, followed by chemical activation using different concentrations of KOH in nitrogen at 973 K. Both water-washed and acid-washed samples exhibited much higher specific surface areas than unactivated carbon. The water-washed sample showed strong basicity and a high catalytic performance in the decomposition of isopropanol, even higher than superbase 26%KNO 3/γ-Al 2O 3. Moreover, these porous carbons can act as water-resistant solid bases. The formation of the insoluble basic sites is most possibly related to the intercalation of potassium in the carbon during the chemical activation.

Binding Properties of Solvatochromic Indicators [Cu(X)(acac)(tmen)] (X = PF6− and BF4−, acac− = Acetylacetonate, tmen = N,N,N′,N′-Tetramethylethylenediamine) in Solution and the Solid State

The solvatochromic indicator [Cu(acac)(tmen)(H 2O)].PF 6 ( 1.H 2O) has been synthesized and crystallographically characterized. 1.H 2O binds an H 2O molecule at the Cu(II) axial site, while the PF 6 (-) anion is coordination free. The binding properties of [Cu(PF 6)(acac)(tmen)] ( 1) and [Cu(BF 4)(acac)(tmen)] ( 2) have been investigated in solution and the solid state. The donor number of the PF 6 (-) anion (DN PF6) was determined from the UV-vis spectra of 1 in 1,2-dichloroethane. The value of DN PF6 of the PF 6 (-) anion is slightly larger than that of the tetraphenylborate anion (BPh 4 (-)), which is known as a noncoordinating anion. In the solid state, 1 and 2 reversibly bind and release H 2O molecules at the Cu(II) axial sites. The coordinated H 2O molecules in 2 are more easily removed than those in 1 because of the strong Lewis basicity of the BF 4 (-) anion compared to the PF 6 (-) ion. The lower melting point of 1 versus 2 is attributed to the loose binding of the PF 6 (-) anions to the Cu(II) centers, which induces the dynamic nature of the crystal.

A Novel Binding Factor of 14-3-3β Functions as a Transcriptional Repressor and Promotes Anchorage-independent Growth, Tumorigenicity, and Metastasis

The 14-3-3 proteins form a highly conserved family of dimeric proteins that interact with various signal transduction proteins and regulate cell cycle, apoptosis, stress response, and malignant transformation. We previously demonstrated that the beta isoform of 14-3-3 proteins promotes tumorigenicity and angiogenesis of rat hepatoma K2 cells. In this study, to analyze the mechanism of 14-3-3beta-induced malignant transformation, yeast two-hybrid screening was performed, and a novel 14-3-3beta-binding factor, FBI1 (fourteen-three-three beta interactant 1), was identified. In vitro binding and co-immunoprecipitation analyses verified specific interaction of 14-3-3beta with FBI1. The strong expression of FBI1 was observed in several tumor cell lines but not in non-tumor cell lines. Forced expression of antisense FBI1 in K2 cells inhibited anchorage-independent growth but had no significant effect on cell proliferation in monolayer culture. Down-regulation of FBI1 also inhibited tumorigenicity and metastasis accompanying a decrease in MMP-9 (matrix metalloproteinase-9) expression. In addition, the duration of ERK1/2 activation was curtailed in antisense FBI1-expressing K2 cells. A luciferase reporter assay revealed that the FBI1-14-3-3beta complex could act as a transcriptional silencer, and MKP-1 (MAPK phosphatase-1) was one of the target genes of the FBI1-14-3-3beta complex. Moreover, chromatin immunoprecipitation analysis demonstrated that FBI1 and 14-3-3beta were presented on the MKP-1 promoter. These results indicate that FBI1 promotes sustained ERK1/2 activation through repression of MKP-1 transcription, resulting in promotion of tumorigenicity and metastasis.

FT-IR Evidence of Two Distinct Protonic Sites in BEA Zeolite: Consequences on Cationic Exchange and on Acido-Basic Properties in the Presence of Cesium

Two acidic H−BEA zeolites having similar Al content but different structural and textural properties were used to prepare two series of BEA samples containing increasing Cs amounts, added by exchange in solution and then impregnation. Whatever the zeolite, the introduction of Cs up to a Cs/Al ratio close to 1 leads to solely exchanged Cs+ ions, indicating that almost all Al are framework atoms giving cationic exchange capacity. At higher Cs contents, Cs-overloading takes place, giving Cs-oxide-like species with strong basicity on which carbonates are formed upon adsorption of CO2, as followed by Fourier transform infrared (FT-IR) spectroscopy. In spite of such comparable behaviors, the two parent BEAs act in a strongly different manner toward cationic exchange in solution. This is related to the presence, in the most defective sample, of a distinct type of protons able to protonate NH3 but significantly less acidic than protons on regular tetrahedrally coordinated framework sites, as is shown by FT-IR spe...

Adjusting the host–guest interaction to promote KNO 3 decomposition and strong basicity generation on zeolite NaY

A new strategy was utilized to prepare strongly basic zeolite through precoating MgO on the zeolite NaY prior to KNO 3 modification. By controlling the loading amount of the precursor magnesium acetate, MgO could be well dispersed on NaY as long as its content did not exceed 12 wt%. The precoated MgO layer played a significant role in enhancing the basicity of zeolite by adjusting the host–guest interaction to promote the decomposition of KNO 3 on NaY, and at the same time this MgO layer prevented the zeolite framework from corroding by the resulting strongly basic potassium species. As a result, a strong basicity was successfully generated on NaY, and the resulting basic zeolites containing potassium species exhibited good catalytic performance on the vapor phase methylation of cyclopentadiene (CPD) with methanol. The conversion of CPD was 30.1% and 3.5% over parent NaY and Mg 12Y, respectively, accompanied with the methylcyclopentadienes (MCPD) selectivity of 8.3% and 46.1% at the reaction temperature of 500 °C and time of 1 h. However, 38.1% of CPD could be converted over K 10Mg 12Y under the same reaction conditions, and the selectivity of MCPD achieved to 76.7%.

In-situ observation of the dissolution of ZrO2oxide particles in mould fluxes

Dissolution of ZrO2 oxide in synthetic CaO - Al2O3 - SiO2 - Na2O - B2O3 mould fluxes was investigated in situ using a Confocal Scanning Laser Microscope (CSLM). Evolution of particle radius with time is obtained exhibiting strong dependence on temperature and basicity of the mould fluxes. The rate-limiting step of the dissolution process was discussed, and basicity was shown to significantly influence the rate-limiting step.

New Attempt at Directly Generating Superbasicity on Mesoporous Silica SBA-15

Direct generation of superbasicity on mesoporous silica SBA-15 was realized by tailoring the host-guest interaction, and calcium species were selected as the guest in modifying SBA-15. The results show that calcium species could be homogeneously distributed on the surface of SBA-15. Because of the host-guest interaction, the decomposition of the supported calcium nitrate was apparently easier than the bulk one. Surprisingly, the calcium nitrates modified SBA-15 (CaNS) samples exhibited superbasicity with good preservation of the mesostructure after activation, differing from the potassium nitrate loaded SBA-15 samples that displayed weak basicity with collapsed mesostructure. The present superbasic CaNS materials also possess good water resistance and high surface areas, up to 429 m(2) g(-1), which is promising for their potential applications in adsorption and catalysis. Further investigation concerning the roles played by the guest in basicity formation on SBA-15 was conducted. The samples modified by Group 2 metal nitrates showed strong basicity with base strength (H-) of 22.5-27.0 and good preservation of mesostructure. In contrast, loading Group 1 metal nitrates on SBA-15 produced samples with weak basicity ( H-=9.3-15.0) and collapsed mesostructure after activation. Such differences can be related to the interaction between the resulting metal oxide and the silica support, as well as the mobility of the cations in the metal oxide.

Cyclopentadienyl-functionalized mesoporous MCM-41 catalysts for the transesterification of dimethyl oxalate with phenol

Abstract Two kinds of hybrid inorganic–organic catalysts (denoted as Cp′-MCM-41 and Cp″-MCM-41) are prepared by grafting methylcyclopentadienyl (Cp′) or pentamethylcyclopentadienyl (Cp″) group onto the surface of mesoporous MCM-41. Such cyclopentadienyl-functionalized materials are active for the transesterification of dimethyl oxalate (DMO) with phenol. Under test conditions, Cp″-MCM-41 gives higher conversion of DMO and selectivity of diphenyl oxalate (DPO) than Cp′-MCM-41, and this might be assigned to the relatively strong Lewis basicity of Cp″ group.

Preferential CO oxidation in hydrogen-rich stream over Pt catalysts modified with alkali metals

Abstract The addition of alkali metals over Pt/Al 2 O 3 has both promoting and negative effects on the catalytic performance in the preferential CO oxidation in H 2 -rich stream (PROX), therefore there is an optimum amount of alkali metal. The Pt/Al 2 O 3 catalysts modified with Na, K, Rb and Cs were characterized by means of transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), and Fourier transform infrared spectroscopy (FTIR). The results show that the addition of larger amount of alkali metals with stronger basicity causes the aggregation of Pt metal particles. The Pt particles on Pt/Al 2 O 3 modified with alkali metals are more electron-deficient than those on Pt/Al 2 O 3 , and this weakens the strength of CO adsorption on Pt/Al 2 O 3 modified with alkali metals, which is related to the enhancement of turnover frequency of the PROX. In addition, in situ FTIR observation suggests that the coadsorbed species originating from H 2 and O 2 (e.g., the OH species) under the PROX condition, which promote the CO oxidation, can be found on highly active catalysts.

Attempt to Generate Strong Basicity on Silica and Titania

Modification and control of surface function on porous materials have been a very promising and appealing area of chemistry. In this paper, the reason as to why it is impossible to generate a strong basicity on silica and titania is explored in detail, and consequently, a new strategy was adopted to overcome this obstacle, not only to obtain a solid strong base derived from silica and titania for the first time but also in a new environmentally benign way. Base precursor KNO3 was loaded on silica and titania along with alumina and zirconia for comparison. Varied dispersion and thermal decomposition behavior of KNO3 on these supports as well as the different resulting basicity of the composites were delineated, and the surface vacant sites and electronegativity of cations in supports were proven to be responsible for such differences. Further, a redox strategy was employed to convert the supported KNO3 to basic sites at relatively mild conditions, through which a strong basicity was finally generated on silica and titania, while superbasicity was formed on alumina and zirconia. Moreover, the present redox strategy could significantly reduce the release of harmful gases such as nitrogen oxides, which is beneficial to the protection of the environment. The different mechanisms for the thermal activation and redox approach on the preparation of solid strong basic materials were determined.

Biodiesel synthesis using calcined layered double hydroxide catalysts

The catalytic properties of calcined Li–Al, Mg–Al and Mg–Fe layered double hydroxides (LDHs) were examined in two transesterification reactions, namely, the reaction of glyceryl tributyrate with methanol and the reaction of soybean oil with methanol. While the Li–Al catalysts showed high activity in these reactions at the reflux temperature of methanol, the Mg–Fe and Mg–Al catalysts exhibited much lower methyl ester yields. CO2 TPD measurements revealed the presence of sites of weak, medium and strong basicity on both Mg–Al and Li–Al catalysts, the latter showing higher concentrations of medium and strong base sites; by implication, these are the main sites active in transesterification catalyzed by calcined Li–Al LDHs. Maximum activity was observed for the Li–Al catalysts when a calcination temperature of 450–500°C was applied, corresponding to decomposition of the layered double hydroxide to the mixed oxide without formation of crystalline lithium aluminate phases.

Calcium methoxide as a solid base catalyst for the transesterification of soybean oil to biodiesel with methanol

In this study, physical and chemical characterizations of calcium methoxide were investigated to assess its performance as an excellent solid base catalyst using some instrumental methods, such as BET surface area measurement, scanning electron micrographs and particle size distribution. Then, it was used to catalyze transesterification of soybean oil to biodiesel with methanol. The effects of various factors such as mass ratio of catalyst to oil, reaction temperature and volume ratio of methanol to oil were studied to optimize the reaction conditions. The results showed that calcium methoxide has strong basicity and high catalytic activity as a heterogeneous solid base catalyst and it was obtained a 98% biodiesel yield within 2 h in this reaction. Besides, the recycling experiment results showed it had a long catalyst lifetime and could maintain activity even after being reused for 20 cycles.

Low-temperature adsorption of hydrogen on ion-exchanged Y zeolites

Ion-exchanged Y zeolites with several alkali metal cations and proton have been used to analyze the effect of electrostatic field or basicity on the hydrogen adsorption at low temperature and low pressure. The adsorption capacity per surface area, isosteric heat of adsorption ( - Δ H ads ) , surface coverage and micropore occupancy increase with the decreasing electronegativity of the metals that are introduced in the zeolite. Ion-exchanged zeolites also favorably adsorb hydrogen at relatively low pressures when the electronegativity of the metal is low. This work demonstrates that zeolites with strong electrostatic fields or high basicity are beneficial for high hydrogen uptake especially at low pressure and low temperature.