Adsorption of n-butanol from dilute aqueous solution with grafted calixarenes

Hydrates of adenosine 3′,5′-cyclic monophosphate sodium and their transformation

The difference of crystal water behaviors for cAMPNa hydrates was attributed mainly to the steric effects in lattices. Excessive loss of crystal water would destroy the host structure, and result in the disability of reversible transformation.

Selective Sequestration of Aromatics from Aqueous Mixtures with Sugars by Hydrophobic Molecular Calixarene Cavities Grafted on Silica

The separation of aromatic contaminants from sugar-aromatic aqueous mixtures is required in second-generation biorefineries because aromatic compounds deactivate (bio)catalysts typically involved in upgrading lignocellulosic biomass to fuels and chemicals. This separation remains challenging, however, because of the degree of molecular recognition needed to sequester dilute aromatic impurities from concentrated sugar streams. Herein, we demonstrate that hydrophobic cavities of p- tert-butylcalix[4]arene macrocycles grafted on amorphous silica (calix/SiO₂) perform this separation selectively and efficiently by acting as selective molecular hosts that adsorb aromatic compounds (5-hydroxymethylfurfural, vanillin, and vanillic acid) while excluding monomeric sugar (glucose chosen as a prototypical model) in aqueous mixtures. By comparing calix/SiO₂ to a range of organically modified SiO₂ surfaces and other porous adsorbents, we demonstrate that the organization of hydrophobic functional groups within discrete nests consisting of calixarene cavities is crucial for facilitating the adsorption of aromatics. Density functional theory calculations of the host-guest complex indicate that adsorption is brought about by weak dispersive (van der Waals) interactions between tert-butyl upper-rim substituents in calixarene hosts and aromatic guests. Calix/SiO₂ can be repeatedly reused, demonstrating its viability as an adsorbent within a continuous biorefining process. These calix/SiO₂ adsorbents expand the palette of materials available for selective sugar-aromatic separations, which until now have been limited to pyrene-based sites of metal-organic framework NU-1000, and demonstrate that sites consisting of relatively simple hydrophobic tert-butyl substituents organized around a hemispherical molecular cavity provide a sufficient degree of molecular recognition for performing this separation selectively.

Silica-Calix Hybrid Composite of Allyl Calix[4]arene Covalently Linked to MCM-41 Nanoparticles for Sustained Release of Doxorubicin into Cancer Cells

An inorganic-organic hybrid material, MCM-allylCalix, was synthesized by covalent modification of an MCM-41 surface with a tetra-allyl calixarene conjugate. The synthesized hybrid was characterized by ¹³C and ²⁹Si MAS-NMR, Fourier transform infrared (FT-IR), Brunauer-Emmett-Teller surface area, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) analyses. The application of this MCM-allylCalix hybrid has been demonstrated for loading and in vitro release of doxorubicin (Dox) in phosphate-buffered saline (PBS) buffer as well as in the cancer cells, viz., MCF7, HeLa, and MDA-MB231. The Dox-loaded hybrid, MCM-allylCalix-Dox, was characterized by TEM, FT-IR, TGA, N₂ sorption, diffuse refectance spectroscopy-UV, and fluorescence microscopy to confirm the presence of the drug. The release study of the drug from MCM-allylCalix-Dox was carried out in PBS buffer at pH 5 and 7.4. The results showed ∼140% increase in the release of Dox at pH 5 compared to that at pH 7.4 in 144 h, suggesting a pH-triggered release of the drug. MCM-allylCalix-Dox releases a greater amount of Dox compared to that released from unmodified MCM-Dox. Cytotoxicity studies suggested that MCM-allylCalix-Dox exhibits anticancer activity that is dependent on the nature of the cell. The Dox-loaded hybrid shows more cytotoxicity for MCF7 compared to that for the HeLa and MDA-MB231 cells. This was further supported by ∼120% more internalization of Dox into MCF7 cells compared to that in the other two cell lines. Both fluorescence microscopy and fluorescence-activated cell sorting studies suggested concentration-dependent internalization of Dox into the MCF7 and HeLa cells. The results suggested that the inorganic-organic hybrid can be useful in sustained drug delivery into cancer cells.

Unravelling the influence of carbon dioxide on the adsorptive recovery of butanol from fermentation broth using ITQ-29 and ZIF-8

The presence of CO₂during the vapor phase adsorption of butanol from ABE fermentation at the head space of the fermenter has an important roll on the efficient recovery of biobutanol.

Bio-butanol sorption performance on novel porous-carbon adsorbents from corncob prepared via hydrothermal carbonization and post-pyrolysis method

A series of porous-carbon adsorbents termed as HDPC (hydrochar-derived pyrolysis char) were prepared from corncob and used for the 1-butanol recovery from aqueous solution. The influences of pyrolysis temperature on properties of the adsorbents were systematically investigated. The results showed that hydrophobicity, surface area, and pore volume of HDPC samples increased with an increase in pyrolysis temperature. Furthermore, the adsorption mechanism of 1-butanol on the adsorbents was explored based on correlation of the samples properties with adsorption parameters extracted from the 1-butanol adsorption isotherms (K_F and Q_e12). Overall, the 1-butanol adsorption capacity increased with a decrease in polarity and an increase in aromaticity, surface area and pore volume of HDPC samples. However, at different pyrolysis temperature, the factors causing the increase of 1-butanol adsorption on the adsorbents are variable. The kinetic experiments revealed that the pores played a vital role in the 1-butonal adsorption process. The intraparticle diffusion model was used to predict the adsorption kinetic process. The simulation results showed that intraparticle diffusion was the main rate-controlling step in the 1-butanol adsorption process.

In situ biobutanol recovery from clostridial fermentations: a critical review

Butanol is a precursor of many industrial chemicals, and a fuel that is more energetic, safer and easier to handle than ethanol. Fermentative biobutanol can be produced using renewable carbon sources such as agro-industrial residues and lignocellulosic biomass. Solventogenic clostridia are known as the most preeminent biobutanol producers. However, until now, solvent production through the fermentative routes is still not economically competitive compared to the petrochemical approaches, because the butanol is toxic to their own producer bacteria, and thus, the production capability is limited by the butanol tolerance of producing cells. In order to relieve butanol toxicity to the cells and improve the butanol production, many recovery strategies (either in situ or downstream of the fermentation) have been attempted by many researchers and varied success has been achieved. In this article, we summarize in situ recovery techniques that have been applied to butanol production through Clostridium fermentation, including liquid-liquid extraction, perstraction, reactive extraction, adsorption, pervaporation, vacuum fermentation, flash fermentation and gas stripping. We offer a prospective and an opinion about the past, present and the future of these techniques, such as the application of advanced membrane technology and use of recent extractants, including polymer solutions and ionic liquids, as well as the application of these techniques to assist the in situ synthesis of butanol derivatives.

Comparative Study of the Effect of Defects on Selective Adsorption of Butanol from Butanol/Water Binary Vapor Mixtures in Silicalite-1 Films

A promising route for sustainable 1-butanol (butanol) production is ABE (acetone, butanol, ethanol) fermentation. However, recovery of the products is challenging because of the low concentrations obtained in the aqueous solution, thus hampering large-scale production of biobutanol. Membrane and adsorbent-based technologies using hydrophobic zeolites are interesting alternatives to traditional separation techniques (e.g., distillation) for energy-efficient separation of butanol from aqueous mixtures. To maximize the butanol over water selectivity of the material, it is important to reduce the number of hydrophilic adsorption sites. This can, for instance, be achieved by reducing the density of lattice defect sites where polar silanol groups are found. The density of silanol defects can be reduced by preparing the zeolite at neutral pH instead of using traditional synthesis solutions with high pH. In this work, binary adsorption of butanol and water in two silicalite-1 films was studied using in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy under equal experimental conditions. One of the films was prepared in fluoride medium, whereas the other one was prepared at high pH using traditional synthesis conditions. The amounts of water and butanol adsorbed from binary vapor mixtures of varying composition were determined at 35 and 50 °C, and the corresponding adsorption selectivities were also obtained. Both samples showed very high selectivities (100-23 000) toward butanol under the conditions studied. The sample having low density of defects, in general, showed ca. a factor 10 times higher butanol selectivity than the sample having a higher density of defects at the same experimental conditions. This difference was due to a much lower adsorption of water in the sample with low density of internal defects. Analysis of molecular simulation trajectories provides insights on the local selectivities in the zeolite channel network and at the film surface.

Biomass, strain engineering, and fermentation processes for butanol production by solventogenic clostridia

Butanol is considered an attractive biofuel and a commercially important bulk chemical. However, economical production of butanol by solventogenic clostridia, e.g., via fermentative production of acetone-butanol-ethanol (ABE), is hampered by low fermentation performance, mainly as a result of toxicity of butanol to microorganisms and high substrate costs. Recently, sugars from marine macroalgae and syngas were recognized as potent carbon sources in biomass feedstocks that are abundant and do not compete for arable land with edible crops. With the aid of systems metabolic engineering, many researchers have developed clostridial strains with improved performance on fermentation of these substrates. Alternatively, fermentation strategies integrated with butanol recovery processes such as adsorption, gas stripping, liquid-liquid extraction, and pervaporation have been designed to increase the overall titer of butanol and volumetric productivity. Nevertheless, for economically feasible production of butanol, innovative strategies based on recent research should be implemented. This review describes and discusses recent advances in the development of biomass feedstocks, microbial strains, and fermentation processes for butanol production.

Organically-modified magnesium silicate nanocomposites for high-performance heavy metal removal

A disulfide-grafted polyethyleneimine (PES)@Mg₂SiO₄composite was synthesized, characterized, and used successfully to remove heavy metals from wastewater.

Insight into a direct solid–solid transformation: a potential approach for the removal of residual solvents

A simple humidity process allows a direct solid–solid transformation from the solvate (methanol trihydrate of cAMPNa) to its hydrate form (pentahydrate).

Pillar[5,6]arene-functionalized silicon dioxide: synthesis, characterization, and adsorption of herbicide

A layer of synthetic supramolecular macrocycles, that is, perhydroxyl-pillar[5]arene and perhydroxyl-pillar[6]arene, has been covalently attached to hydrophilic silica supports through Si-O-Si linkages with a coverage of up to 250 μmol pillar[5,6]arenes/g to form novel absorbent hybrid materials. Their adsorption toward a typical herbicide, namely, paraquat, from its aqueous solution has been investigated. Kinetic studies disclosed that paraquat adsorption fits a first-order kinetic model. Equilibrium adsorption data could be explained very well by the Langmuir equation. The pillar[6]arene-modified materials showed more obvious adsorption as compared with pillar[5]arene-modified ones and the saturation adsorption quantity reached about 0.20 mmol of paraquat per gram of materials. The entire process of adsorption was endothermic, and significantly an elevated temperature led to an increase in the adsorption quantity. This new type of pillarene-based adsorbent materials can be considered as a potential adsorbent for harmful substances removal from wastewaters.

Desorption of 1-butanol from polymeric resin: experimental studies and mathematical modeling

Modeling of desorption kinetics and dynamic desorption process of 1-butanol from a polymeric resin.

Efficient synthesis of lower rim α-hydrazino tetrazolocalix[4]arenes via an Ugi-azide multicomponent reaction

Herein, we developed an efficient synthesis of α-hydrazino tetrazolocalix[4]arene derivatives, suitable for metal ion complexation as investigated, via an Ugi-azide multicomponent reaction.

Immobilization of cryptophane derivatives onto SiO2/Au and Au substrates

The synthesis of a cryptophane molecule bearing five methoxy substituents and an alkanethiol chain, 4, as well as its subsequent grafting onto a gold surface, is reported. Immobilization of cryptophane derivatives onto silica (SiO2/Au) surfaces was also performed by reacting a cryptophane molecule bearing one or six acid functions, 5 or 6, respectively, with an amino-terminated self-assembled monolayer (SAM). Polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) was used to characterize the two types of cryptophane monolayers. Surface coverage of cryptophane monolayers was estimated by comparing the PM-IRRAS intensity of cryptophane bands with that calculated from the optical constants of pentamethoxy-cryptophane for a compact monolayer. A very efficient grafting of 4 onto a gold surface was found, with a surface coverage close to 100%. On the other hand, the reaction of mono-acid, 5, or hexa-acid, 6, cryptophanes with amino-terminated SAM was less efficient, since the surface coverage did not exceed 15%. Finally, a good surface coverage (75%) was also obtained by using a cysteamine coupling agent to modify 5 before its grafting onto a gold surface.

Comparative study of tributyltin adsorption onto mesoporous silica functionalized with calix[4]arene, p-tert-butylcalix[4]arene and p-sulfonatocalix[4]arene

The adsorption of tributyltin (TBT), onto three mesoporous silica adsorbents functionalized with calix[4]arene, p-tert-butylcalix[4]arene and p-sulfonatocalix[4]arene (MCM-TDI-C4, MCM-TDI-PC4 and MCM-TDI-C4S, respectively) has been compared. Batch adsorption experiments were carried out and the effect of contact time, initial TBT concentration, pH and temperature were studied. The Koble–Corrigan isotherm was the most suitable for data fitting. Based on a Langmuir isotherm model, the maximum adsorption capacities were 12.1212, 16.4204 and 7.5757 mg/g for MCM-TDI-C4, MCM-TDI-PC4 and MCM-TDI-C4S, respectively. The larger uptake and stronger affinity of MCM-TDI-PC4 than MCM-TDI-C4 and MCM-TDI-C4S probably results from van der Waals interactions and the pore size distribution of MCM-TDI-PC4. Gibbs free energies for the three adsorption processes of TBT presented a negative value, reflecting that TBT/surface interactions are thermodynamic favorable and spontaneous. The interaction processes were accompanied by an increase of entropy value for MCM-TDI-C4 and MCM-TDI-C4S (43.7192 and 120.7609 J/mol K, respectively) and a decrease for MCM-TDI-PC4 (−37.4704 J/mol K). It is obviously observed that MCM-TDI-PC4 spontaneously adsorbs TBT driven mainly by enthalpy change, while MCM-TDI-C4 and MCM-TDI-C4S do so driven mainly by entropy changes.

Recovery of dilute aqueous acetone, butanol, and ethanol with immobilized calixarene cavities

Macrocyclic calixarene molecules were modified with functional groups of different polarities at the upper rim and subsequently grafted to mesoporous silica supports through a single Si atom linker. The resulting materials were characterized by thermogravimetric analysis, UV-visible spectroscopy, nitrogen physisorption, and solid-state NMR spectroscopy. Materials were then used to separate acetone, n-butanol, and ethanol from dilute aqueous solution, as may be useful in the recovery of fermentation-based biofuels. For the purpose of modeling batch adsorption isotherms, the materials were considered to have one strong adsorption site per calixarene molecule and a larger number of weak adsorption sites on the silica surface and external to the calixarene cavity. The magnitude of the net free energy change of adsorption varied from approximately 15 to 20 kJ/mol and was found to decrease as upper-rim calixarene functional groups became more electron-withdrawing. Adsorption appears to be driven by weak van der Waals interactions with the calixarene cavity and, particularly for butanol, minimizing contacts with solvent water. In addition to demonstrating potentially useful new sorbents, these materials provide some of the first experimental estimates of the energy of interaction between aqueous solutes and hydrophobic calixarenes, which have previously been inaccessible because of the insolubility of most nonionic calixarene species in water.

Electrospinning of calixarene-functionalized polyacrylonitrile nanofiber membranes and application as an adsorbent and catalyst support

Polyacrylonitrile (PAN) nanofiber membranes functionalized with calix[8]arenes (C[8]) were successfully prepared by electrospinning of PAN solutions with addition of various calixarenes. Uniform electrospun C[8]/PAN nanofibers were obtained by incorporating three types of calix[8]arenes into the PAN matrix and characterized by scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared (ATR-FTIR), thermal gravimetric analysis (TGA), and X-ray powder diffraction (XRD). The SEM results showed that the addition of calix[8]arenes resulted in a decrease in the diameter of PAN nanofibers. Static adsorption behavior was studied by using C[8]/PAN nanofibers as an adsorbent and Congo red and Neutral red as model dye molecules. The adsorption of Congo red onto Amide-Cal[8]-15/PAN nanofibers fitted the second-order kinetic model, and the apparent adsorption rate constant was 1.1 × 10(-3) g·mg(-1)·min(-1) at 25 °C. Then, by virtue of electrostatic attraction, as-prepared Au nanoparticles were immobilized on Amide-Cal[8]/PAN nanofibers to form Au/Amide-Cal[8]/PAN composite nanofibers. The catalytic activity of the as-prepared Au/Amide-Cal[8]/PAN composite nanofibers was investigated by monitoring the reduction of Congo red in the presence of NaBH4. The reduction kinetics was explained by the assumption of a pseudo-first-order reaction with regard to Congo red. Au/Amide-Cal[8]/PAN composite nanofibers exhibited high catalytic activity, excellent stability, and convenient recycling.

The future of butyric acid in industry

In this paper, the different applications of butyric acid and its current and future production status are highlighted, with a particular emphasis on the biofuels industry. As such, this paper discusses different issues regarding butyric acid fermentations and provides suggestions for future improvements and their approaches.