Mariusz Barczak

The development and characterisation of novel hybrid sol–gel-derived films for optical pH sensing

This paper focuses on the development and detailed characterisation of a novel hybrid sol–gel material derived from 3-glycidoxypropyltrimethoxysilane (GPTMS) and ethyltriethoxysilane (ETEOS). The material has been doped with a fluorescent pH-sensitive dye, modified 8-hydroxy-1,3,6-pyrene trisulfonic acid (HPTS) and its application as a high-performance optical ratiometric pH sensor has been demonstrated. The optimum sol–gel-based material composition has been characterised using atomic force microscopy (AFM), scanning electron microscopy in combination with energy dispersive X-ray spectroscopy (SEM-EDX), thermal gravimetric-infrared (TGA-IR) analysis, Fourier transform infrared (FT-IR) and Raman spectroscopy, solid state 29Si and 13C nuclear magnetic resonance (NMR). AFM and SEM images demonstrated a high degree of homogeneity of the pH films. FT-IR, Raman and NMR results have shown that hydrolysis and condensation reactions were almost completed and extensive crosslinking occurred in the final material. They also revealed that an opening of the epoxy ring in GPTMS took place which was key to optimum pH response. The pH sensor produced using the hybrid material compares very well with the current state-of-the-art and exhibits very good reversibility, reproducibility, stability, short response time and no leaching. The dynamic range extends from pH 5.0 to 8.0 which is compatible with bioprocessing, environmental and clinical monitoring applications.

Template synthesis of mesoporous silicas containing phosphonic groups

Mesoporous silicas containing the functional group ≡Si(CH2)2P(O)(OC2H5)2 in the surface layer have been obtained using the template method (template—P123). Their treatment by a concentrated hydrochloric acid results in the formation of functional groups of the composition ≡Si(CH2)2P(O)(OH)2 that is in agreement with the IR spectroscopy data. It has been shown that the above treatment causes an increase of the sample specific surface area (up to 605 m2/g), sorption capacity, and pore diameter. As established by means of the CP/MAS NMR spectroscopy on 31P nuclei, the sample drying in vacuum at 110°C results in the formation of fragments ≡Si(CH2)2P(O)(OH)—OSi≡ with the content of 10–15 wt %. However, according to the TEM data, the sample mesoporous structure is retained.

Theoretical determination of the infrared spectra of amorphous polymers.

The simple procedure of calculating the infrared spectra of polymers is presented. It is based on selecting the relevant, medium-size representative fragments of a polymer, for which the vibrational frequencies are computed within the harmonic approximation, in conjunction with the multiparameter scaling techniques. Scaling is necessary to predict the reliable fundamentals, which, along with the calculated intensities and properly chosen band widths, reproduce the observed band shapes with high accuracy. Applications to the three polymers: poly(methyl methacrylate), poly(vinyl acetate), and poly(isopropenyl acetate) are presented. The simulated spectra are in good agreement with the experiment. The assignment of bands is reported. The obtained results indicate strong delocalization of the vibrational modes within polymers, which is in accord with the most recent experimental finding [Macromolecules2008, 41, 2494-2501]. Good agreement between the observed and the calculated spectra of deuterated PMMA confirms the correctness of our approach. The preliminary results obtained for the highly irregular macromolecular compound (vinyl-functionalized silica) are also shown.

Functionalized SBA-15 organosilicas as sorbents of mercury(II), cadmium(II) and copper(II)

Amino- and thiol-functionalized SBA-15 organosilicas have been synthesized by co-condensation of tetraethoxysilane (TEOS) with appropriate trifunctional silanes i. e. aminopropyltriethoxysilane (ATES) and mercaptopropyltriethoxysilane (MTES). The materials were characterized by nitrogen sorption measurements, XRD diffractometry, FTIR/PAS spectroscopy and SEM, TEM and AFM microscopy. The obtained materials exhibit high porosity, good ordering, and high content of functional groups (0.5–1.5 mmol/g). These materials have been tested as sorbents for three bivalent metal ions: Hg(II), Cd(II) and Cu(II) testifying to their usefulness in such sorption applications. The adsorption kinetics was were favour-able-all the metal ions were adsorbed just after several minute and the amounts of adsorbed metals were high and depended on the type and content of surface functionalities.

Synthesis, tailoring and characterization of silica nanoparticles containing a highly stable ruthenium complex

This paper describes the synthesis and characterization of sol-gel silica nanoparticles (NPs) derived from tetraethoxysilane (TEOS) and from tetraethoxysilane and methyltriethoxysilane (TEOS-MTEOS) in which is encapsulated, an in-house synthesized, stable oxygen-sensitive ruthenium complex, ruthenium (II) (bis-2,2-bipyridyl)-2(4-carboxylphenyl) imidazo[4,5-f][1,10]phenanthroline. These NPs were characterized using dynamic light scattering, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and Brunauer-Emmett-Teller analysis. The spherical, stable and monodispersed NPs have been prepared using the Stöber method. It was found that the addition of prehydrolyzed MTEOS-based sol prepared in an acidic environment to the reaction mixture containing TEOS NPs synthesized for 6 h produced material with increased porosity when compared to pure silica NPs. Oxygen sensitivity, stability, photobleaching and leaching have been characterized. The hybrid NPs exhibit enhanced O₂ sensitivity but a high degree of leaching when compared to pure silica NPs, which have minimum O₂ sensitivity and no leaching.

A simple and easy way to enhance sensitivity of Sn(IV) on bismuth film electrodes with the use of a mediator

For the first time an in situ-plated bismuth film electrode prepared with the use of a reversibly deposited mediator (Zn) was applied to anodic stripping voltammetry of the metal ions. This simple and easy way of the electrode surface modification by metal films was suggested to increase the voltammetric signal of Sn(IV) and, consequently, to improve the sensitivity and tin detection limit. The structural and chemical information about the bismuth films plated with and without the use of the mediator were derived from AFM and XPS data analysis.Graphical abstract

Synthesis and structure-related adsorption characteristics of bifunctional polysiloxane xerogels with methyl and 3-mercaptopropyl groups

Polysiloxane xerogels containing 3-mercaptopropyl and methyl groups in the surface layer were synthesized by the sol-gel method with ethanol used as a solvent and fluoride ion used as a catalyst. It is established that an increase in the relative content of methyltriethoxysilane in the initial reaction mixture results in formation of xerogels with a developed porous structure. The tendency for an increase in other characteristics of porous structure, the sorption volume and pore size, is also observed. The analogous effect is found upon increasing relative content of tetraethoxysilane with a constant ratio between two trifunctional silanes. By means of atomic force microscopy, it is shown that the xerogels are composed of aggregated particles with mean sizes of 35–45 nm. These results correlate with the data of scanning electron microscopy. On the basis of the data of IR spectroscopy and 13C CP/MAS NMR spectroscopy, it is concluded that the surface layers contain not only 3-mercaptopropyl and methyl groups but also silanol groups, a part of the unhydrolyzed alkoxy groups, and water molecules involved in the formation of hydrogen bonds. The results obtained by 29Si CP/MAS NMR spectroscopy testify that, in synthesized xerogels, the structural units of T1 type [(≡SiO)Si(OR′)2CH3 and/or (≡SiO)Si(OR′)2(CH2)3SH, R′ = H, OCH3 or OC2H5] are absent and the structural units of T3 type [(≡SiO)3SiCH3 and (≡SiO)3Si(CH2)3SH] dominate compared to the units of T2 type [(≡SiO)2Si(OR′)CH3 and (≡SiO)2Si(OR′)(CH2)3SH]. These results are an indirect indication of enhanced hydrolytic stability of surface layers in such xerogels.

Adsorption of L-Histidine onto Functionalized Mesoporous SBA-15 Organosilicas

Adsorption of L-histidine (LH) over mesoporous SBA-15 silicas functionalized by amine-, thiol- and cyano-functional groups has been studied. These organosilicas have been synthesized by co-condensation of proper monomers in the presence of a template (Pluronic P-123), and characterized by elemental analysis, nitrogen adsorption, X-ray diffraction and transmission electron microscopy. The highest LH static adsorption capacity was observed for the cyano-functionalized sample [approximately 70 mg g−1 (450 mol g−1)]; by contrast, pristine SBA-15 had a lowest adsorption capacity of approximately 25 mg g−1 (170 mol g−1).

Bridged polysilsequioxane adsorption materials containing phosphonic acid residues

Reactions of hydrolytic polycondensation of bis(triethoxysilane) [(C2H5O)3Si]2C2H4 (or [(C2H5O)3Si]2C6H4) and functional agent (C2H5O)3Si(CH2)2P(O)(OC2H5)2 (alkoxysilanes molar ratio of 2: 1 and 4: 1, fluoride ion catalyst and ethanol solvent) yielded powder-like xerogels that contained phosphonic acid residues in the surface layer. Their treatment with boiling concentrated hydrochloric acid resulted in transformation of functional groups ≡Si(CH2)2P(O)(OC2H5)2 into acid groups ≡Si(CH2)2P(O)(OH)2. The methods of IR, 1H MAS NMRm and 13C, 29Si, 31P MAS NMR spectroscopy showed the following (1) The surface layer in the initial xerogels contains not only phosphorus functional groups, but also some non-hydrolyzed ethoxysilyl groups as well as silanol groups. (2) The hydrochloric acid treatment of the initial xerogels causes the hydrolysis of not only ethoxy groups in the phosphonic acid residues, but also most residual ethoxysilyl groups. (3) Vacuum drying of xerogels after acid treatment forms ≡Si(CH2)2P(O)(OH)-OSi≡ links in their surface layer (not more than 20% of phosphorus-containing groups). (4) According to 29Si CP MAS NMR spectroscopic data, boiling acid treatment relatively enriches the xerogel structure T2 and T3 units and accounts for the higher rigidity of the hybrid framework. These units also account for retention of the porous structure in these xerogels over time, while most initial xerogels have porous structures that collapse in 12–18 months of storage. The acid-treated xerogels were attributed to microporous adsorbents (having specific surface area of 620 to 760 m2/g). According to the AFM data, both initial and acid-treated xerogels contain almost spherical aggregates of the primary particles (globules).

Bridge polysilsesquioxane xerogels with a bifunctional surface layer of the ≡Si(CH2)3NH2/≡Si(CH2)3SH composition

Xerogels with a bifunctional surface layer of the ≡Si(CH2)3NH2/≡Si(CH2)3SH composition are synthesized by hydrolytic co-polycondensation of bis(triethoxy)silane (C2H5O)3Si(CH2)2Si(OC2H5)3 and two trifunctional silanes, namely, 3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane. Using IR, 1H MAS NMR, and 13C CP/MAS NMR spectroscopic techniques, it is shown that in addition to complexing groups, the surface layer also contains water, silanol groups that are involved in the hydrogen bond formation and also residual ethoxysilyl groups. According to 29SiCP/MAS NMR spectroscopic data, the degree of polycondensation of synthesized xerogels exceeds 80%. It is found that the use of 1,2-bis(triethoxysilyl)ethane as the structuring agent in place of tetraethoxysilane allows one to synthesize bifunctional xerogels with the highly developed biporous structure (Ssp = 607–680 m2/g, Vc = 1.38–1.47 cm3/g, d = 2.9–3.1 and 18.3 nm). Changing the ratio structuring-silane/functionalizing-silane-mixture from 2: 1 to 4: 1 in the reaction system has virtually no effect on the porous structure parameters of final xerogels.