Adsorption kinetics of an organic dye by wet hybrid gel monoliths

Wet hybrid gel monoliths are prepared with bis(trimethoxysilylpropyl)amine (TSPA) or the mixture of TSPA with n-propyltriethoxysilane (PTES) or bis(trimethoxysilyl)hexane (TSH) or tetraethoxysilane (TEOS) as precursors. The adsorption kinetics of an organic dye (erioglaucine disodium salt, EDS) by the gel monoliths in aqueous solutions is studied comprehensively. The effects of temperature, pH, and ionic strength on the adsorption kinetics are investigated. Kinetic studies show that in general the kinetic data are well described by the pseudo second-order kinetic model. Initial adsorption rate increases with the increase in temperature, but decreases with the increase in solution pH and ionic strength. The adsorption activation energy is found to be 17–51 kJ mol⁻¹ under our experimental conditions. The internal diffusion of the dye into the hybrid gels appears to be the rate-limiting step of the overall adsorption process. The adsorption is promoted by hydrogen bonding, hydrophobic and electrostatic attractions in acidic or neutral solutions, suppressed by the electrostatic repulsion in basic solutions and by the ionic exchange competition of Cl⁻ with the dye anions in solutions with a high NaCl concentration. After adsorption for 165 h, all the gel monoliths present a linear shrinkage less than 10%.     

Research progress on hybrid organic-inorganic perovskites for photo-applications

Hybrid organic-inorganic perovskite materials have attracted significant attention of most researchers in recently years, which is ascribed to the superior photoelectric properties, such as the suitable band gaps for harvesting sunlight, and exhibit high optical adsorption, high charge-carrier lifetimes and long diffusion lengths. The photodetectors, light-emitting diodes, solar cells and photocatalysts represent the remarkable applications for the hybrid organic-inorganic perovskite materials. Herein, we review the recent progress of hybrid organic-inorganic perovskite-based photodetectors, light-emitting diodes, solar cells and photocatalysts. The challenges and outlook for the hybrid organic-inorganic perovskite-based photodetectors, light-emitting diodes, solar cells and photocatalysts are considered.     

One-step separation and purification of hydrolysable tannins from Geranium wilfordii Maxim by adsorption chromatography on cross-linked 12% agarose gel

The hydrolysable tannins corilagin and geraniin, the major active components of the traditional Chinese medicine Geranium wilfordii Maxim, have been separated and purified from crude extracts in one step by adsorption chromatography on cross‐linked 12% agarose gel (Superose 12 10/300 GL). The separation was achieved by gradient elution using mobile phase A composed of 5% ethanol and 5% acetic acid and mobile phase B composed of 30% ethanol and 30% acetic acid. The gradients were composed as follows: 0–240 mL, 0–25% B; 240–480 mL, 25–40% B; after 480 mL, 100% B. The purities of the collected corilagin and geraniin were 92.4 and 87.2%, and the corresponding yields were 88.0 and 76.8%, respectively.     

Hierarchically imprinted organic-inorganic hybrid sorbent for selective separation of mercury ion from aqueous solution

A new type of hierarchically organic-inorganic hybrid sorbent was prepared by a double-imprinting approach for the selective separation of Hg(II) from aqueous solution. In the imprinting process, both mercury ions and surfactant micelles (cetyltrimethylammonium bromide, CTAB) were used as templates, N-[3-(trimethoxy-silyl)propyl]ethylenediamine (TPED) as functional monomer, and tetraethoxysilane (TEOS) as cross-linking agent. The mercury ions and surfactant were removed from sorbent via acid leaching and ethanol extraction, respectively. The adsorption property and selective recognition ability of the sorbents were studied by equilibrium-adsorption method. Results showed that in the presence of Cu(II) or Cd(II) the biggest selectivity coefficient of the imprinted sorbents for Hg(II) was over 100, which is much higher than those of non-imprinted sorbents. The largest relative selectivity coefficient (k′) of the ion-imprinted functionalized sorbent between Hg(II) and Cu(II) was over 300, and between Hg(II) and Cd(II) over 200. The uptake capacities and the selectivity coefficients of the hierarchically imprinted sorbent were much higher than those of the sorbent prepared without CTAB template. Furthermore, the new imprinted sorbent possessed a fast kinetics for the removal of Hg(II) from aqueous solution with the saturation time less than 5 min, and could be used repeatedly. This sorbent has been successfully applied to the separation and determination of the trace Hg(II) in real water samples and those spiked with standards. This new sorbent can be used as an effective solid-phase extraction material for the selective preconcentration and separation of Hg(II) in environmental samples.     

Kinetics and thermodynamics of bromophenol blue adsorption by a mesoporous hybrid gel derived from tetraethoxysilane and bis(trimethoxysilyl)hexane

A mesoporous hybrid gel is prepared with tetraethoxysilane (TEOS) and bis(trimethoxysilyl)hexane (TSH) as precursors without using any templating agent. Nitrogen sorption, TG-DTA, FTIR, and point of zero charge (PZC) measurement are used to characterize the gel. The gel has a specific surface area of 695 m(2) g(-1) with a pore size of 3.5 nm, a pore volume of 0.564 cm(3) g(-1), and a point of zero charge (PZC) of 6.2. The kinetics and thermodynamics of bromophenol blue (BPB) adsorption by the gel in aqueous solution are investigated comprehensively. The effects of initial BPB concentration, pH, ionic strength, and temperature on the adsorption are investigated. Kinetic studies show that the kinetic data are well described by the pseudo-second-order kinetic model. Initial adsorption rate increases with the increase in initial BPB concentration and temperature. Adsorption activation energy is found to be 62.5-67.5 kJ mol(-1) depending on the initial BPB concentration. Internal diffusion appears to be the rate-limiting step for the adsorption process. The equilibrium adsorption amount increases with the increase in the initial BPB concentration, solution acidity, and ionic strength, but decreases with the increase in temperature. The thermodynamic analysis indicates that the adsorption is spontaneous and exothermic. The adsorption isotherms can be well described with Freundlich equation indicating the heterogeneity of the hybrid gel surface. Electrostatic and hydrophobic interactions are suggested to be the dominant mechanism for adsorption.     

Amine-rich polymers for water purification applications

Water pollution induced by biological, agricultural, and industrial activities has risen to prominence as a scientific issue as it poses a direct threat to life or water scarcity. Thus, it has become critical to design and develop nanomaterials and understand their properties to combat water pollution. Herein, a survey of amine-rich polymers (ARPs) was conducted. They were classified based on the source of their raw materials, whether natural or synthetic. The chemical structure and essential synthesis routes were shown casually. Ammonium-based polymers, a subclass of these polymers, were also demonstrated. It is beneficial to consolidate the rules for the surface group behavior through the chemical interaction of their containing polymers. The exploitation of ARP in pollutant adsorption, flocculation/coagulation, photocatalysis, and membrane purification was highlighted. Amine groups determine these materials' approaches and their performance in the selected applications. Moreover, ARPs differ among themselves in their internal structure, which helps to determine the impact of the polymer backbones and forms on the performance of amine and ammonium groups. Hence, the crucial roles of amine/ammonium groups have been analyzed, indexed, and explained. Perspectives and indicators are introduced that help design nanomaterials based on these groups to serve environmental purposes. In light of this review, potential directions for the future with ARPs have been proposed.     

Application of a new hybrid organic-inorganic monolithic column for efficient deoxyribonucleic acid purification

A new hybrid organic-inorganic monolithic column for efficient deoxyribonucleic acid (DNA) extraction was prepared in situ by polymerization of N-(β-aminoethyl)-γ-aminopropyltriethoxysilane (AEAPTES) and tetraethoxysilane (TEOS). The main extraction mechanism was based on the Coulombic force between DNA and the amino silica hybrid monolithic column. DNA extraction conditions, such as pH, ion concentration and type, and loading capacity, were optimized online by capillary electrophoresis with laser-induced fluorescence detection. Under optimal condition, a 6.0-cm monolithic column provided a capacity of 48 ng DNA with an extraction efficiency of 74 ± 6.3% (X ± RSD). The DNA extraction process on this monolithic column was carried out in a totally aqueous system for the successful purification of DNA and removal of proteins. The PBE2 plasmid could be extracted from Bacillus subtilis (B. subtilis) crude lysate within 25 min, and the purified DNA was suitable for the amplification of a target fragment by polymerase chain reaction. This study demonstrates a new attractive solid-phase support for DNA extraction to meet the increasingly miniaturized and automated trends of genetic analyses.     

Synthesis and characterization of hybrid borosiloxane gels as precursors for Si–B–O–C fibers

The sol–gel method has been used for the synthesis of borosilicate gels from mixtures of methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES) and boric acid. The use of boric acid, B(OH)₃ allows the hydrolysis and condensation of hybrid silicon alkoxides without further addition of water or catalyst. The use of difunctional silicon units, –(CH₃)₂SiO– promote the formation, during the sol–gel process, of linear oligomers which facilitate fiber drawing before gelation. Gel characterization performed by FT-IR, XRD, TG-DTA and DCS analysis indicates the formation of a mixed network with incorporation of the boron units via =B-O-Si≡ bridges. The formation of borosiloxane bonds seems favored by the presence of DMDES. SiBOC glasses were obtained after pyrolysis of the borosilicate gels in argon atmosphere at 1000 °C. TG-DTA study indicates that the ceramic yield decreases by increasing the amount of DMDES. Gel fibers were successfully prepared from convenient partially-aged solutions by hand drawing. Pyrolysis of the obtained gel fibers under argon atmosphere at 1000 °C open the possibility to produce SiBOC homogeneous glass fibers with diameter as low as 10 μm.     

New hybrid bidentate ligands as precursors for smart catalysts

1-Phosphanorbornadiene derivatives were grafted onto various periodically organized mesoporous powders, including a new zirconia/silica mixed oxide synthesized by aerosol techniques. After complexation with the [Rh(CO)2]+ fragment, these materials were revealed to be more active in olefin hydrogenation than their homogeneous counterparts. The reasons for this higher activity are discussed in the light of theoretical modeling. Various surface treatments, such as esterification, drying, and functionalization with PhSi(OEt)3, provided insights into the nature and mechanism of formation of the active species. Zirconia-based materials were found to be active in internal olefin hydroformylation. Investigation of the mechanism of this reaction shows that the isomerization step is catalyzed by the Lewis acidic support, whereas the hydroformylation step is driven by the rhodium catalyst. Dissociation of these two steps leads to enhancement of activity.     

Selective chemisorption of carbon monoxide by organic-inorganic hybrid materials incorporating cobalt(III) corroles as sensing components

Twenty-one hybrid materials incorporating cobalt(III) corrole complexes were synthesized by a sol-gel process or by grafting the metallocorrole onto a mesostructured silica of the SBA-15 type. All the materials show an almost infinite selectivity for carbon monoxide with respect to dinitrogen and dioxygen in the low-pressure domain where the chemisorption phenomenon is predominant. This peculiar property is of prime importance for an application as a CO sensor. The selectivity slightly decreases at high pressures where nonselective physisorption phenomena mainly occur. The percentage of active sites for CO chemisorption ranges from 22 to 64 %. This low percentage may be attributable to interactions between the cobalt(III) corroles with silanol or siloxane groups remaining at the surface of the materials which prevent further coordination of the CO molecule. Notably, the most efficient materials are those prepared in the presence of a protecting ligand (pyridine) during the gelation or the grafting process. The removal of this ligand after the gelation process releases a cavity around the cobalt ion that favors the coordination of a carbon monoxide molecule. The CO adsorption properties of the SBA-15 hybrid were not affected over a period of several months thus indicating a high stability of the material. Conversely, the xerogel capacities slowly decrease owing to the evolution of the material structure.     

Silica gel ethyleneimine and its adsorption capacity for divalent Pb, Cd, and Hg

Activated silica gel was directly modified with a cyclic molecule, ethyleneimine, yielding a surface with various nitrogen basic centers, ≡Sil–O(CH₂CH₂NH)_nCH₂CH₂NH₂. Infrared spectroscopy, ¹³C NMR, thermal, and elemental analyses confirmed the covalent attachment of the organic species onto the silica matrix. The purpose of this paper is to describe the interaction involving the grafted species on silica surface with the divalent heavy cations, Pb(II), Cd(II), and Hg(II), from aqueous solutions at room temperature. The process of metal extraction was followed by the batch method and the order of the maximum extraction capacities found was: 1.27 ± 0.04, 1.02 ± 0.02, and 0.98 ± 0.01 mmol g⁻¹ for Pb(II), Cd(II), and Hg(II) chlorides, respectively. These interactions were followed by calorimetric titration. The enthalpies of these processes are: −3.05 ± 0.02, −1.09 ± 0.01, and −9.88 ± 0.03 kJ mol⁻¹ for Pb(II), Cd(II), and Hg(II), respectively. The standard molar Gibbs free energies are in agreement with the spontaneity of the proposed reactions between cation and basic center.     

Calcium alginate gel as encapsulation matrix for coimmobilized enzyme systems

Encapsulation within calcium alginate gel capsules was used to produce acoimmobilized enzyme system. Glucose oxidase (GOD) and catalase (CAT) were chosen as model enzymes. The same values of V _max and K _mapp for the GOD encapsulated system and for the GOD-CAT coencapsulated system were calculated. When gel beads and capsules were compared, the same catalyst deactivation sequence for the two enzymes was observed. However, when capsules were employed as immobilization support, GOD efficiencies were higher than for the gel beads. These results were explained in terms of the structure of the capsules.     

Membrane affinity chromatography for analysis and purification of biopolymers

Summary Affinity columns suitable for HPLC were prepared by immobilization of various ligands of protein A, human IgG, human IgM and pectinase on GMA modified cellulose membrane. The adsorption capacity, affinity efficiency and activity recovery of various IgGs on these affinity columns were measured. It was observed that the length of the coupling arm plays a very important role in affinity efficiency, and the effect of eluent flow-rate on adsorption capacity was very small. The protein A column was exploited for the process monitoring of dog IgG in clinical experiments on immuno-adsorption therapy. A pectinase column was used for the determination of polygalacturonase inhibiting proteins first purified on a hydroxyapatite column. It took only about 2.5 min for analysis at a flow-rate of 1.0 mL min⁻¹. The high speed analysis of biopolymers could be performed at a flow rate of 6.0 mL min⁻¹ within 15 s. Membrane affinity chromatography gives good reproducibility, high efficiency, low column-pressure and is rapid. It can also be used for micro-scale purification of biopolymers.     

Preparation of a novel hybrid organic-inorganic monolith for the separation of lysozyme by high performance liquid chromatography

A novel hybrid organic-inorganic monolith for high performance liquid chromatography (HPLC) was firstly developed by atom transfer radical polymerization (ATRP) by a simple and rapid method, in which vinyl ester resin was used as the monomer, natrium bisulfurosum was used both as organic adjunct and coadunate initiator to alter the activity of the free radical in the process of polymerization and then to control the molecular mass. The conditions of polymerization were optimized. The chemical group of the monolith was assayed by infrared spectra method, the morphology of monolithic material was studied by scanning electron microscopy (SEM) and the pore size distribution was determined by a mercury porosimeter. Finally, the monolith was used to separate lysozyme (Lys) from chicken egg white with good resolution and reproducibility that were obtained in a short time (10 min) by HPLC. In addition, the influences of buffer concentration and pH value on elution have been investigated and the hybrid monolith was used to separate benzene and its homologs from the mixture.     

Molecularly imprinted polymers for chemical agent detection in multiple water matrices

In the past few years concerns over the possibility of terrorist actions against domestic and military water supplies has become paramount. Antibodies, peptides, and enzymes have been used as molecular recognition elements in chemical sensors; however, such devices often have storage and operational stability issues that limits their success. Molecularly imprinted polymers (MIPs), have been successfully demonstrated an alternative in pesticide applications [A.L. Jenkins, R. Yin, J.J. Jensen, Analyst 126 (2001) 798-802]. The MIP materials possess selective molecular recognition properties that are complementary to the analyte in the shape and positioning of functional groups. These polymers have high selectivity and affinity constants while maintaining excellent thermal and mechanical stability. In this study, direct imprinting of chemical agents EA2192, VX, sarin, and soman (the “G” agents), was performed and the limits of detection calculated. The ability of these sensors to work in various water matrices including tap, deionized and reverse osmosis water with residual chlorine was also evaluated. Typical detection limits for these MIP sensors are approximately 50 ppt with wide linear dynamic ranges (ppt-ppm). Sensor response time is approximately 15 min.     

Synthesis of Gd-DTPA-cholesterol: a new lipophilic gadolinium complex as a potential MRI contrast agent

A straightforward and efficient synthesis of Gd-DTPA-cholesterol is reported. This new lipophilic gadolinium complex can be easily incorporated into mixed micelles in order to achieve MRI contrast agents with increased relaxivity. These supramolecular systems can find potential application in magnetic resonance angiography (MRA).     

Tryptophan photooxidation promoted by new hybrid materials prepared by condensation of naphthalene imides with silicate by the sol–gel process

Three novel hybrid organic/inorganic materials were synthesized from 4-substituted (NO₂, Br, H) 1,8-naphthalene imide-N-propyltriethoxysilane by the sol–gel process. These materials were obtained as a xerogel and partially characterized. The ability to photosensitize the oxidation and degradation of tryptophan indole ring by these materials was studied through photophysical and photochemical techniques. Although the derivatives containing Br and NO₂ as substituent do not cause efficient tryptophan photodamage, the hybrid material obtained from 1,8-naphthalic anhydride is very efficient to promote tryptophan photooxidation. By using laser flash photolysis it was possible to verify the presence of naphthalene imide transient radical species. The presence of oxygen causes an increase of the yield of radical formation. These results suggest that the mechanism of photodegradation of tryptophan occurs by type I, i.e. the transient radical (TrpH⁺) formed by the direct reaction of the triplet state of the naphthalene imide moiety with tryptophan. Thus a inorganic–organic hybrid material that can be used to promote the oxidation of biomolecules was obtained.     

Sol-gel approach to in situ creation of high pH-resistant surface-bonded organic-inorganic hybrid zirconia coating for capillary microextraction (in-tube SPME)

A novel zirconia-based hybrid organic-inorganic sol-gel coating was developed for capillary microextraction (CME) (in-tube SPME). High degree of chemical inertness inherent in zirconia makes it very difficult to covalently bind a suitable organic ligand to its surface. In the present work, this problem was addressed from a sol-gel chemistry point of view. Principles of sol-gel chemistry were employed to chemically bind a hydroxy-terminated silicone polymer (polydimethyldiphenylsiloxane, PDMDPS) to a sol-gel zirconia network in the course of its evolution from a highly reactive alkoxide precursor undergoing controlled hydrolytic polycondensation reactions. A fused silica capillary was filled with a properly designed sol solution to allow for the sol-gel reactions to take place within the capillary for a predetermined period of time (typically 15-30 min). In the course of this process, a layer of the evolving hybrid organic-inorganic sol-gel polymer got chemically anchored to the silanol groups on the capillary inner walls via condensation reaction. At the end of this in-capillary residence time, the unbonded part of the sol solution was expelled from the capillary under helium pressure, leaving behind a chemically bonded sol-gel zirconia-PDMDPS coating on the inner walls. Polycyclic aromatic hydrocarbons, ketones, and aldehydes were efficiently extracted and preconcentrated from dilute aqueous samples using sol-gel zirconia-PDMDPS coated capillaries followed by thermal desorption and GC analysis of the extracted solutes. The newly developed sol-gel hybrid zirconia coatings demonstrated excellent pH stability, and retained the extraction characteristics intact even after continuous rinsing with a 0.1 M NaOH solution for 24 h. To our knowledge, this is the first report on the use of a sol-gel zirconia-based hybrid organic-inorganic coating as an extraction medium in solid phase microextraction (SPME).     

Polypyrrole/copper hexacyanoferrate hybrid as redox mediator for glucose biosensors

A copper containing Prussian Blue analogue was incorporated into a conducting polypyrrole film. The modified electrode was synthesized through an electrochemical two-step methodology leading to very stable and homogeneous hybrid films. These electrodes were proved to show excellent catalytic properties towards H₂O₂ detection, with a performance higher than those observed for Prussian Blue and other analogues. Electrochemical impedance spectroscopy experiments demonstrated that the excellent performance of these hybrid films is strongly related to the electronic conductivity of the polymeric matrix that is wiring the copper hexacyanoferrate sites. A glucose biosensor was built-up by the immobilization of glucose oxidase; the sensitivity obtained being higher than other biosensors reported in the literature even in Na⁺ containing electrolytes.     

A hybrid genetic algorithm for estimating the equilibrium potential of an ion-selective electrode

Non-linear equations can be used to model the measured potential of ion-selective electrodes (ISEs) as a function of time. This can be done by using non-linear least squares regression to fit parameters of non-linear equations to an ISE response curve. In iterative non-linear least squares regression (which can be considered as local optimisers), the determination of starting parameter estimates that yield convergence to the global optimum can be difficult. Starting values away from the global optimum can lead to either abortive divergence or convergence to a local optimum. To address this issue, a global optimisation technique was used to find initial parameter estimates near the global optimum for subsequent further refinement to the absolute optimum. A genetic algorithm has been applied to two non-linear equations relating the measured potential from selected ISEs to time. The parameter estimates found from the genetic algorithm were used as starting values for non-linear least squares regression, and subsequent refinement to the absolute optimum. This approach was successfully used for both expressions with measured data from three different ISEs; namely, calcium, chloride and lead ISEs.