J. Skubiszewska-Zięba

Driving forces of conformational changes in single-layer graphene oxide

The extensive oxygen-group functionality of single-layer graphene oxide proffers useful anchor sites for chemical functionalization in the controlled formation of graphene architecture and composites. However, the physicochemical environment of graphene oxide and its single-atom thickness facilitate its ability to undergo conformational changes due to responses to its environment, whether pH, salinity, or temperature. Here, we report experimental and molecular simulations confirming the conformational changes of single-layer graphene oxide sheets from the wet or dry state. MD, PM6, and ab initio simulations of dry SLG and dry and wetted SLGO and electron microscopy imaging show marked differences in the properties of the materials that can explain variations in previously observed results for the pH dependent behavior of SLGO and electrical conductivity of chemically modified graphene-polymer composites. Understanding the physicochemical responses of graphene and graphene oxide architecture and performing selected chemistry will ultimately facilitate greater tunability of their performance.

pH-driven physicochemical conformational changes of single-layer graphene oxide

Single-layer graphene oxides (SLGOs) undergo morphological changes depending on the pH of the system and may account for restricted chemical reactivity. Herein, SLGO may also capture nanoparticles through layering and enveloping when the pH is changed, demonstrating potential usefulness in drug delivery or waste material capture.

Effect of calcium catalyst loading procedure on the porous structure of active carbon from plum stones modified in the steam gasification process

Abstract The effect of mode of calcium catalyst deposition on the active carbon (produced from plum stones) surface on the formation of micro- and mesoporous structures during gasification of the carbon with steam as well as on the kinetics of this process was investigated. The catalyst (1.44%) was deposited by conventional impregnation or ion exchange. Partial gasification of the modified carbon in the absence of catalyst causes significant increase of micropore volume and small increase of mesopore surface area with the increase of burn-off degree. On the contrary, gasification of the samples in the presence of calcium catalyst causes the decrease of sorption capacity of micropores and the significant increase of mesopore surface. The above changes are more effective for the samples containing the catalyst deposited by ion-exchange. Micropore capacity and surface area of mesopores were determined by means of the αs-method. The adsorption process on the heterogeneous solids was described by means of integral equation including various local isotherms. This equation has been solved by the regularization method. On the basis of this method changes in the structural parameters were estimated. The activation energies of individual reactions were determined. The mechanism of gasification process as well as the selection of proper concentration of steam optimum from the kinetic viewpoint have been discussed.

Structural characteristics of modified activated carbons and adsorption of explosives

Several series of activated carbons prepared by catalytic and noncatalytic gasification and subsequent deposition of pyrocarbon by pyrolysis of methylene chloride or n-amyl alcohol were studied by FTIR, chromatography, and adsorption methods using nitrogen and probe organics (explosives). The relationships between the textural characteristics of carbon samples and the recovery rates (eta) of explosives on solid-phase extraction (SPE) using different solvents for their elution after adsorption were analyzed using experimental and quantum chemical calculation results. The eta values for nitrate esters, cyclic nitroamines, and nitroaromatics only partially correlate with different adsorbent parameters (characterizing microporosity, mesoporosity, pore size distributions, etc.), polarity of eluting solvents, or characteristics of probe molecules, since there are many factors strongly affecting the recovery rates. Some of the synthesized carbons provide higher eta values than those for such commercial adsorbents as Hypercarb and Envicarb.

Structural characteristics of a carbon adsorbent and influence of organic solvents on interfacial water

Different treatments (suspending in water, drying, freezing by liquid nitrogen, de-ashing, oxidation by H2O2, reduction by H2, and some combinations of these methods) of activated carbon Norit R 0.8 Extra lead to changes in micropores to a greater extent than mesopores. Influence of polar (CD3CN, (CD3)2CO and (CD3)2SO) and nonpolar (CCl4, CDCl3 and C6D6) solvents on the structure of interfacial water pre-adsorbed on the carbon adsorbent was studied by 1H NMR spectroscopy with freezing-out of the adsorbed water at 180 K<T<273 K and modelled by using quantum chemistry methods with consideration for the solvation effects. It was found that water interaction with the carbon surfaces depends strongly on the properties of solvents, which can remove a major (by nonpolar solvents insoluble in water) or minor (by polar solvents soluble in water) portion of water from narrow micropores to larger pores.

Carbon–mineral adsorbents from waste materials: case study

Waste bleaching earth from the food industry obtained in the process of fruit juice purification was utilized for preparation of carbon-mineral adsorbents. The waste material, containing 25.8 wt% C, was subjected to three kinds of treatment: (1) direct pyrolysis at 400 degrees C with a suitable temperature program; (2) preliminary hydrothermal modification (200 degrees C, 8 h, 15.3 atm) and then pyrolysis as in method 1; (3) preliminary thermal treatment (400 degrees C) and then chemical treatment (boiling in 3% solution Na(2)CO(3)), followed by heating at 400 degrees C (10 min). Moreover, the materials obtained by these methods were subjected to additional thermal treatment at 700 degrees C with a suitable temperature program. Both the morphology and the topography of carbon deposits and, in consequence, the porous structure of the obtained adsorbents depend on the method of their preparation. The additional thermal treatment of these samples at 700 degrees C makes it possible to obtain adsorbents of more thermally stable carbon deposits possessing better parameters of the porous structure. Carbon-mineral adsorbents of different specific surface areas (S(BET) from 17.6 to 153 m(2)/g) and pore volumes (from 0.035 to 0.093 cm(3)/g) were prepared. The mechanism of phenol and p-nitrophenol adsorption on the obtained adsorbents was discussed and their properties were compared with the suitable literature data.

The effect of heat, adsorption and mechanochemical treatments on stuck structure and adsorption properties of fumed silicas

Abstract The structural characteristics of fumed silicas synthesised under varied conditions and standard fumed silicas subjected to different types of pre-treatment, such as heating, suspending–ball-milling–drying, ball-milling of dry powder, and immobilisation of polymers, were studied using adsorption–desorption methods. Variations of preparation conditions and applied treatments influence the structure of finished samples in respect of both micropores and mesopores in primary particle swarms (aggregates, agglomerates) dependent on the treatment time nonlinearly. However, pre-treatments change the mesopore parameters of final adsorbents to a greater extent than those of micropores due to significant rearrangement of the primary particle agglomerates and gaps between aggregates. Application of the regularisation procedure to compute the pore size distributions using overall adsorption equation based on the combination of the Kelvin equation and the statistical adsorbed film thickness allows us to study the dependence of the structural characteristics of fumed silicas on treatment conditions in details.

Synthesis and characterization of Fe2O3/SiO2 nanocomposites

Fe2O3/SiO2 nanocomposites based on fumed silica A-300 (S(BET)=337 m2/g) with iron oxide deposits at different content were synthesized using Fe(III) acetylacetonate (Fe(acac)3) dissolved in isopropyl alcohol or carbon tetrachloride for impregnation of the nanosilica powder at different amounts of Fe(acac)3 then oxidized in air at 400-900 degrees C. Samples with Fe(acac)3 adsorbed onto nanosilica and samples with Fe2O3/SiO2 including 6-17 wt% of Fe2O3 were investigated using XRD, XPS, TG/DTA, TPD MS, FTIR, AFM, nitrogen adsorption, Mössbauer spectroscopy, and quantum chemistry methods. The structural characteristics and phase composition of Fe2O3 deposits depend on reaction conditions, solvent type, content of grafted iron oxide, and post-reaction treatments. The iron oxide deposits on A-300 (impregnated by the Fe(acac)3 solution in isopropanol) treated at 500-600 degrees C include several phases characterized by different nanoparticle size distributions; however, in the case of impregnation of A-300 by the Fe(acac)3 solution in carbon tetrachloride only alpha-Fe2O3 phase is formed in addition to amorphous Fe2O3. The Fe2O3/SiO2 materials remain loose (similar to the A-300 matrix) at the bulk density of 0.12-0.15 g/cm3 and S(BET)=265-310 m2/g.

Structural, textural and adsorption characteristics of nanosilica mechanochemically activated in different media

The structural, textural, and adsorption characteristics of mechanochemically activated (MCA) fumed silica A-300 as dry or water, ethanol, or water/ethanol-wetted powders (0.5 g of a solvent per gram of silica) in a ball mill for 1-6 h were studied in comparison with those of the initial powder. The MCA treatment enhances bulk density (ρ(b)) of the powder (from 0.045 g/cm(3) for the initial silica to 0.4 g/cm(3) for 6 h-MCA-treated water-wetted silica) depending on medium type and MCA time (t(MCA)). Stronger effects are observed for the MCA treatment of water-wetted silica than of dry or ethanol- or water/ethanol-wetted samples. The MCA treatment weakly affects the specific surface area (S(BET)). However, void (pore) size distribution, porosity, particle aggregation and size distribution in aqueous suspension, behavior of interfacial water, properties of poly(vinyl alcohol)/silica composites and adsorption of gelatin depend more strongly on the t(MCA) and ρ(b) values. Some of the observed changes in the characteristics (e.g., gelatin adsorption) depend on the ρ(b) value but are independent of the medium type used on the MCA. Other characteristics are nonlinear functions of both t(MCA) and ρ(b) values.

Adsorption and migration of poly(vinyl pyrrolidone) at a fumed silica surface

A series of poly(vinyl pyrrolidone) (PVP)/fumed silica powder samples were studied using adsorption, FT-IR and AFM methods. Mild treatment (293 K for several hours) of PVP/A-300 powder with an added additional portion of A-300 in a glass reactor (2 dm3) using a mixer (> 500 rpm which provided the powder as a pseudo-liquid state, PLS) led to the redistribution (migration) of the PVP molecules between silica particles previously covered by PVP and free of PVP. This time-dependent rearrangement of the adsorbed PVP molecules caused the formation of a denser polymer layer at the silica surface. The aggregate size of the primary silica particles with adsorbed PVP molecules decreased after treatment. The volume of macropores with a pore radius Rp > 25 nm increased due to the decrease in the distances between aggregates in agglomerates because of the adhesive effect of the PVP molecules. However, the volume of micropores at Rp < 1 nm decreased because of the penetration of the PVP molecules into the primary silica particle aggregates and the filling of gaps between adjacent particles. A decrease occurred in the amount of adsorbed water in the PVP layer exhibiting a maximum density.