B. Charmas

High resolution argon and nitrogen adsorption assessment of the surface heterogeneity of carbosils

Abstract Carbon mineral adsorbents are promising materials for a wide range of applications due to the dual polar–apolar properties of their surfaces. The changes in surface properties of a mineral support depend on the way in which carbon is organized on that mineral surface. In the present work, a set of carbosils has been synthesized, by increasing exposition duration to dichloromethane at 550°C. The corresponding variations in surface properties were studied using high resolution quasi-equilibrium adsorption of nitrogen and argon. For a given gas, the derivative of adsorption isotherm, taken with respect to the logarithm of relative pressure, can be considered as a finger print of surface heterogeneity. Quantitative information on adsorption energy distribution was also obtained by applying the derivative isotherm summation method. The combined qualitative and quantitative information makes it possible to draw conclusions about the topography and adsorption energy distribution of pyrocarbon deposit on the mineral surface.

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.

Structural and energetic heterogeneities of hybrid carbon-mineral adsorbents

Abstract A variety of pyrocarbon-mineral adsorbents (carbosils) were synthesised on the basis of mesoporous silica gel (Si-60, Si-40) and studied by means of the nitrogen adsorption and 1 H NMR methods. Structural and energetic parameters were determined using overall adsorption isotherm approximation with consideration for structural heterogeneity described in the terms of different components in the integral equation. Changes in structural parameters as functions of deposit concentration were compared with changes in the free surface energy estimated by using the 1 H NMR method with freezing-out of bulk water in aqueous suspension of carbosils. To test proposed integral adsorption isotherm equation, the pore size distributions (PSDs) were determined for mechanical mixtures of four adsorbents (silica gel, fumed silica, activated carbon and carbon black) characterised by different types of the porosity.

Effect of biochar activation by different methods on toxicity of soil contaminated by industrial activity

The objective of the study was to determine the effect of various methods of biochar activation on the ecotoxicity of soils with various properties and with various content and origin of contaminants. The biochar produced from willow (at 700°C) was activated by 1) microwaves (in a microwave reactor under an atmosphere of water vapour), 2) carbon dioxide (in the quartz fluidized bed reactor) and 3) superheated steam (in the quartz fluidized bed reactor). Three different soils were collected from industrial areas. The soils were mixed with biochar and activated biochars at the dose of 5% and ecotoxicological parameters of mixture was evaluated using two solid phase test - Phytotoxkit F (Lepidium sativum) and Collembolan test (Folsomia candida) and one liquid phase test - Microtox® (Vibrio fischeri). Biochar activation had both positive and negative impacts, depending on the activation method, kind of bioassay and kind of soil. Generally, biochar activated by microwaves increased the effectiveness of ecotoxicity reduction relative to non-activated biochars. Whereas, biochar activated with CO2 most often cause a negative effect manifested by deterioration or as a lack of improvement in relation to non-activated biochar or to non-amended soil. It was also demonstrated that the increase of biochar specific surface area caused a significant reduction of toxicity of water leachates from the studied soils. Effectiveness of the reduction of leachate toxicity was weakened in the presence of dissolved organic carbon in the soil.

Characterization of spatial and energetic structures of carbon–silica gels

Carbon/silica (carbosil) samples prepared with mesoporous silica gel (Si-60) modified due to methylene chloride pyrolysis at 550°C were studied by means of nitrogen adsorption over a broad pressure range of 10−8<p/p0<1 analyzed using a constrained regularization procedure with several adsorption equations giving detail distributions of the pore size f(Rp), adsorption energy f(E) and fractal dimension f(DFRDA). The structural characteristics of carbosils depend markedly on the amount of carbon deposit and the changes in f(Rp) with increasing carbon concentration suggest its grafting mainly into pores resulting in diminution of the pore volume, specific surface area and average mesopore radius. An increase in the concentration of the carbon deposit also causes a slight displacement of the f(E) peaks towards the high energy, as narrower micropores appear in samples due to carbon grafting.

Confined space effects driving to heterogenization of solutions at the interfaces

Water and concentrated solutions of acids (HCl, H3PO4, and H3PO3) or H2O2 are clustered at the interfaces of nanosilicas and multi-layer graphene oxide (MLGO) as shown by low-temperature 1H NMR spectroscopy. The acid solutions in contact with silica or MLGO powders placed in nonpolar (CCl4) or weakly polar (CDCl3) media form nanodomains and clusters of several types and sizes with different contents of water and solutes. This differentiation of the solutions is stronger at a surface of more compacted nanosilicas because of enhanced confinement effects in narrower pores (voids) between adjacent nanoparticles. For MLGO, the confined space effects are relatively weak but the formation of ice crystallites during freezing of the suspension changes the material texture. Obtained results are of importance for deeper insight into the mechanism of the interfacial behavior of complex solutions under different confined space effects and due to the influence of organic co-solvents.

Evaluation of surface area of carbon component of model carbon-silica adsorbents from adsorption data of p-nitrophenol from aqueous solutions

Abstract Complex carbon-mineral adsorbents have become very attractive materials owing to their wide applicability. Determination of carbon deposit morphology and topography is one of the most essential tasks. The paper presents the results of studies on texture and structure of a series of carbon-silica adsorbents (carbosils) differing in the carbon deposit content (0.8–35.0% w/w) based on the data of gas and liquid adsorption as well as electron microscopy. The theoretical approach was also used to describe the complex adsorbent texture models.

Complex investigations of structural and thermal properties of silica-titania adsorbents

Mesoporous titanium-containing silicas with different Titania contents were investigated. The structural parameters of the materials were characterized by low-temperature adsorption/desorption of nitrogen and X-ray diffraction analysis. The thermodesorption of water using the quasi-isothermal thermogravimetry as well as the differential scanning calorimetry were used to characterize thermal and surface properties of these materials. The adsorbed water layers and the concentration of weakly and strongly bound water as well as the surface free energy on the adsorbent/water interfaces were calculated. It was stated that the increase of Titania content causes a gradual decrease of specific surface area and formation of biporous structure inside the tested materials. The water thermodesorption from the surface proceeds in two or three stages, which is connected mainly with pore distribution and TiO2 content. One can observe the increase of the total surface free energy (ΔGΣ) with the increasing TiO2 content, but the largest ΔGΣ value at the adsorbent/strongly bound water interface is exhibited by the adsorbent of intermediate content (30%) of TiO2. Freezing temperature of water contained in the pores of the studied materials is connected largely with their porous structure. Due to the well developed porous structure, the water freezing process is a multi-stage one.

Physicochemical and technological aspects of the hydrothermal modification of complex sorbents and catalysts. Part I. Modification of porous and crystalline structures

This paper deals with the hydrothermal modification of the physicochemical properties of complex mineral sorbents and catalysts. The hydrothermal modification of alumina, magnesia, ferric oxide and zirconia/silica hydro- and xero-gels as well as other complex adsorbents obtained by the coprecipitation and mechanical stirring of suitable components is discussed. The paper deals with the following topics: (a) the physicochemical bases of the hydrothermal method; (b) methodological and technological problems of the hydrothermal treatment of adsorbents; (c) hydrothermal modification of porous structure parameters (specific surface area, pore volume and size); and (d) characteristics of the hydrothermal modification of the porous structure of multicomponent adsorbents and catalysts. In addition, the mechanism of the hydrothermal modification of the porous structure of composite materials is discussed.

Effect of hydrothermal modification on the porous structure and thermal properties of carbon–silica adsorbents (carbosils)

Abstract Characterisation of porous structure and thermal properties of unmodified and hydrothermally modified (using H2O2, under high pressure conditions) carbon–silica adsorbents (carbosils) prepared by dichloromethane pyrolysis (under dynamic conditions) on the surface of narrow pore silica were discussed. The analysis was made based on the data of low-temperature nitrogen adsorption/desorption isotherms, transmission electron microscopy (TEM) and the results of differential thermal analysis. It was stated that both porous structure and thermal properties of tested samples are in correlation with the morphology and topography of the carbon deposit. This deposit forms globules and aggregates whose size and position on the inner and outer surface of silica depends on the time of its carbonisation. It was stated that hydrothermal treatment (HTT) of the carbosils changes both the porous structure and thermal properties of the tested samples. As a result of HTT of silica, decondensation and recondensation of orthosilic acid on large particles of silica takes place. Then a decrease in the specific surface area and increase in the radius of pores are observed. In the case of carbosils these changes are smaller and depend on the accessibility of the silica surface, which is connected with topography of carbon deposit.