Combined and Hybrid Adsorbents

A consideration has been given to salient features of synthesis of functionalized polysiloxane xerogels using one-, two-, and three-component (in terms of alkoxysilanes) systems. Possibilities have been revealed for potentialities of physical methods for characterizing nature of functional groups, types of structural units that form these xerogels and surface layer structure. Adsorption properties of such hybrid organic-inorganic materials have been described in detail.

Since the first report on the MCM-41 silica in 1992 several thousands of papers have been published on ordered mesoporous materials (OMMs). These novel materials, prepared either by soft- or hard-templating syntheses, become more and more important in many fields of science and technology such as adsorption, catalysis, separations, environmental processes, nanotechnology and biotechnology. The aim of this article is to provide a brief review on the OMMs design and synthesis as well as to show potential of these materials for various environmental applications such as sequestration of carbon dioxide, removal of gaseous organic and inorganic pollutants via adsorption and catalytic degradation, removal of heavy metal ions from contaminated water, and so on. The scope of environmental applications of OMMs is broad and continuously growing. The soft- and hard-templating syntheses create great opportunities for the design of OMMs such as ordered mesoporous silicas, organosilicas and carbons with desired surface and structural properties and for their use in various environmental processes.

The development of ion exchange processes and materials focuses on selective separation. R&D on inorganic materials for selective separation processes has been strong for several years. The superior selectivity of some inorganic ion exchangers compared to other sorption materials presently used in the separation processes has been the major initiative for continuing research. High selectivity is the key to fulfilling the strict regulations concerning waste effluents and to enhancing the energy efficiency of separation processes. Several selective inorganic ion exchange materials have been developed at the Laboratory of Radiochemistry for decontamination of low and intermediate radioactive waste solutions, and some of those materials have found industrial applications.

Polysiloxane xerogels with immobilized calix[4]arenes and covalently bonded calix[4]arene-crown-6 were obtained by sol-gel method. The presence of functional groups introduced in the structure of xerogels was confirmed by FTIR spectroscopy. The synthesized materials are characterized by the developed specific surface area (120-643 m

2

/g) and are able to extract cesium ions in acid medium. It was determined that the quantity of functional groups that take part in this process is 40% maximum.

This report describes the synthesis and some properties of hybrid Poly (acrylonitrile) – silica nanocomposites having potential as chromatography sorbents. The focus is on the fact that the properties of such nanostructures can depend not only on the chemical nature of their components, but also on the synergy of these components. The sol–gel approach involved the hydrolysis and condensation of tetraethoxysilane, with smaller amounts of acrylonitrile polymerized in such a way as to generate polymer dispersed in the continuous silica phase. The resulting polymer–modified silica materials were characterized by infrared spectroscopy, scanning electron microscopy and chromatographic analysis.

The paper deals with fabrication of carbonized and hydrophobized clinoptilolite-rich tuff using organic carbon rich substances, which were pyrolytic combusted and covered the external zeolite surface. Hydrophobization of the zeolite external surface was accomplished by octadecylammonium surfactant. Both surface modified clinoptilolite-rich tuffs were tested and compared to each other in regard to organic (phenol) and inorganic (chromate, arsenate) pollutants removal from aqueous solutions and so far elaborated composites with surface adsorbed pollutant species were analyzed by X-ray photoelectron spectroscopy (XPS).

The changes in sorption properties of products obtained by modification of water insoluble lignins, wood chemical processing wastes, with silicon containing oligomers and bactericide cations: quaternary ammonium and Cu

2+

, were characterized by nitrogen adsorption/desorption, hydrophilic-oleophilic properties, model tests towards different organic contaminants, incl. microorganisms. Goal oriented modification of lignin with Si- and N- containing compounds providing appearance in its structure of novel functional groups, reaction sites and variation in matrix rigity allowed to regulate products porous structure and in prospective to obtain efficient sorbents for terrestrial and water ecosystems able to sequestrate and inhibit action of hazardous contaminants and promote biodegradation. Combination of Si-modified lignin, used as a matrix, with inorganic cation Cu

2+

(a guest phase) results in obtaining of organic-inorganic (OI) hybrid material with an additional dimension to their properties: improved sorption capability towards organic contaminants and high antipathogenic activity. The latter was exemplified by model tests with

E.Coli

and

B.Subtilis

: the vital activity of all bacteria sorbed was suppressed.

A method of silica mesoporous mesophase material (

MMM

) of SBA-3 type hydrothermostability (

HTS

) improvement by its post-synthesis hydrothermal treatment (

HTT

) in ammonia solution has been investigated. The effects of treatment duration and ammonia concentration on the structural and textural parameters of

MMM

have been determined. A mechanism of

MMM

transformation under HTT conditions is suggested.

The selectivities of the new sorbents - organozeolites based on natural zeolite (sorbent 1) and magnetized natural zeolite (sorbent 2), modified by polyhexamethyleneguanidine chloride (PGMG), to carbonate complex of uranium from the CO

3

2-

-bearing waste water of special laundry were studied. The equilibrium and kinetic characteristics of the carbonate uranium complex-ions sorption by organozeolites (sorbent 1 and 2) were determined. The high distribution coefficients for the carbonate uranium complex-ions and film-diffusion kinetic mechanism of sorption for sorbent 1 and sorbent 2 were established. The mathematical model describing this process in dynamic conditions was chosen based on obtained equilibrium and kinetic characteristics of sorbents 1 and 2. The calculation of the breakthrough times was carried out for various solution flow rates, degree of waste water decontamination, and other parameters.

An explanation of the template effect of the M

3+

-cations in the course of the sol-gel synthesis of high dispersed titanium and zirconium phosphates is presented. Some ways to vary and to control the porous structure of such phosphates are shown and proposed.

New gel method of synthesis of spherically granulated titanium phosphate materials from technical TiOSO

4

solution has been developed. The influence of additional hydrothermal treatment of synthesized materials in the adsorption properties, crystal structure and chemical stability is studied.

Considering the harmful effects of heavy metals, it is necessary to remove them from liquid wastes at least to a limit accepted by regulatory agencies before their discharge to the environment – i.e. there is a need for a capable, cost-effective treatment method. The application of an innovative, simple and low cost method was tested for the preparation of nanocrystalline iron hydroxides and oxyhydroxides; different iron precursors have been earlier used and combined to different volatile precipitating agents. The examined in the present product, akaganéite [beta- FeO(OH)], had high surface area and definite pore size distribution. Main aim of this study was to evaluate the efficiency of the prepared material in the removal of heavy metal ions, like cadmium cations and arsenate oxyanions, metals that constitute priority pollutants. Batch and column experiments were conducted in current research to investigate metal ions removal.

The adsorption of Astrazon Red (C.I. Basic Red 46) in aqueous solution by a bentonite clay from Benavila, Portugal, was studied. The bentonite sample was mainly composed of montmorillonite, Na-Feldspar and calcite (XRD analysis). The texture characteristics were determined by Hg and He porosimetry and the specific surface area by the methylene blue adsorption method. A kinetic experiment was carried out at 15 °C to determine the time required to reach equilibrium. Experimental data were well described by the pseudo-second order kinetic model. Adsorption equilibrium isotherms were determined at different temperatures and the results fitted to Langmuir and Freundlich models. According to Langmuir model, the adsorption capacities were 141.0, 148.7 and 157.8 mg/g at 15, 25 and 35 °C, respectively.

Microporous activated carbons were prepared from poly(ethyleneterephthalate). This carbon was functionalized to different degrees by cold and hot nitric acid treatment combined with subsequent heating in inert atmosphere to obtain samples with different surface chemistry. According to studies using complementary techniques (e.g., low temperature nitrogen adsorption or small angle X-ray scattering, SAXS) the greatest reduction in the surface area due to the treatment is 75 %, but the pore size distribution in the micropore range is hardly affected. The surface chemistry was characterized in nonaqueous (X-ray photoelectron spectroscopy, XPS) and aqueous medium (pH, pHPZC, Boehm titration). The importance of the surface chemistry is illustrated in standard SAXS combined with contrast variation, as well as in a wide variety of adsorption processes.

The porous structure of activated carbon, the micropores of which are slit-shaped, makes this adsorbent ideal for processes such as gas separation and gas storage. In the first application, the homogeneous and uniform microporosity of carbon molecular sieves is used to separate gases with relatively similar molecular dimensions but different shape, or gases with similar molecular dimensions but different adsorption kinetics. In the second application, the slit-shaped microporosity is responsible for a larger packing density of adsorbed molecules relative to cylindrically-shaped pores of the same dimensions, thus facilitating the adsorption of high amounts of gas adsorbed per unit volume of carbon, with a high packing density of the adsorbate.

Activated carbon-based materials have proven to work efficiently as adsorbents of sulfur containing species such as hydrogen sulfide, sulfur dioxide, methyl mercaptans from gas phase. This is owing to their surface feature such as functional groups, ash constituents, and high volume of small pores. In the pore system, sulfur containing species are oxidized to either elemental sulfur, sulfur dioxide or dimethyldisulfide depending on the chemistry of the species to be removed. Oxygen and nitrogen containing functional groups and catalytic metals such as iron or calcium are involved in this process. Presence of water film ensures sufficient conditions for dissociation providing that the local pH of the surface is greater than pK

a

of the adsorbate. In this brief review the emphasis is placed on the role of activated carbons surfaces, either unmodified or modified in the processes of adsorption and catalytic oxidation of sulfur containing pollutants.

Data on activity of the combined adsorbents

Ultrasorb, Pectopal and Carboxykam

for adsorption of the cations Fe

2+

, Co

2+

, Cd

2+

, Pb

2+

, Zn

2+

, Cu

2+

, Ni

2+

and radioactive isotope

137

Cs from a modeling Ringer salt solution are reported. These adsorbents show high adsorption selectivity for

137

Cs from biological media (distribution factors achieve 30,000), and also high binding ability for the cations Sr

2+

, Pb

2+

, Cd

2+

, etc. The opportunity of combining properties of sorbents of various natures in combined structures, offered for use as medicinal substances in oral adsorption preparations (enterosorbents) for directed action in treatment of the ecologically dependent diseases connected with the accumulation of heavy metals (HM) and radionuclides (RN) in the organism, is investigated. The efficiency of the preparation

Ultrasorb

for removing RN from the human organism by enterosorption is investigated. It is shown that this preparation increases the natural elimination of incorporated RN by 20%. It is established that a 2 week enterosorption treatment lowers 2-3 times the RN blood content of a patient.

New ways of preparation of carbon adsorbents with molecularsieving properties, with low apparent densities, are developed. Highdispersed samples are produced using various types of processing at various stages of manufacturing; their structural-sorptive characteristics are determined.

Since the capacity of an adsorbent is expressed in terms of the surface area or the amount adsorbed per weight unit, high-density adsorbents are required. The dried leftover lignocellulose of furfural production, due to its good self-binding properties, can be granulated or pelletized and used as a potential raw material for production of highdensity activated carbon sorbents with double density, in comparison with activated carbon from charcoal. These high-density microporous sorbents are appropriate for purifying gaseous media. The chemical and mechanical pre-treatment of lignocellulose imparts new properties to the porous structure of the carbon material and to the activated carbon prepared from it.

A novel activated carbon was prepared from spent lubricating oil by chemical activation. Preparation of this material involved the oxidation of lubricating oil with a mixture of sulfuric and nitric acid solutions. FT-IR analysis showed the presence of carboxylic, phenolic and lactonic groups on the surface of this material. Equilibrium sorption isotherms prepared for this carbon demonstrate that it has a significantly high capacity for lead and cadmium sorption. A maximum of 250 mg Pb

2+

and 150 mg Cd

2+

were adsorbed per gram of this carbon.

Synthetic N-containing carbons designed on the basis of copolymer of styrene and divinylbenzene by thermochemical carbonization, impregnation with N-containing compounds (urea and melamine) followed by heat treatment or activation are prepared. The yields of carbons, volumes of sorption pores, specific surface area and content of nitrogen are obtained. The examination of their catalytic properties on the decomposition of hydrogen peroxide test reaction showed that the activity of these carbons is caused by the content of nitrogen atoms introduced into the structure of the prepared sorbent.

Modification of filtration materials and sediments in order to change adsorption and adhesion surface properties are proposed. The structure and sorption characteristics of the resulting materials are discussed. Experimental investigation of their application in water treatment and sewage purification has been carried out. The improvement of the adsorption properties and of the effectiveness of water treatment from highly dispersed insoluble and soluble organic contaminations is observed.

To employ the pulverized zeolites in dynamic conditions it was obtained the composite material - polyacrylonitrile fiber filled by natural zeolite powder - clinoptilolite-bearing tuff according to earlier developed methods. The ion-exchange and adsorption properties of the new combined sorbent, “zeolite in fiber”, on the examples of sorption of Cu

2+

from 0.5 N NaCl and of oil products from the waste water of car-washing stations, were studied. The distribution coefficients and diffusion coefficients of Cu

2+

and the distribution coefficients of oil products on the sorbent were determined. It was shown that the ion-exchange rate of Cu

2+

ions for the new sorbent increased considerably. The filtrating properties are very good. The sorbent is characterized by high selectivity to the oil products.

To avoid emission of volatile hydrocarbons from automotive tank systems, canisters filled with activated carbon (AC) are placed as a buffer to the environment. During the loading of the filter the heat of adsorption released leads to a temperature rise of the AC and hence to an unwanted decrease of storage capacity. By mixing an optimized amount of phase change material (PCM) to the AC the heat effect can be diminished and thus the adsorption capacity of the filter compared with a fixed bed consisting of pure AC increased by more than 15%. Also, the desorption process is enhanced by the PCM, as part of the desorption energy is provided by the latent heat stored in it. The differential and integral heats for n-butane adsorption on activated carbon have been determined by use of a novel sensor gas calorimeter.

1

In knowledge of the data, an optimized amount of PCM to be added to the carbon could be specified. Both, effectiveness of PCM addition as well as the most appropriate melting, i. e. phase changing temperature of the PCM have been investigated in a special testing equipment by systematic experimental work.

It is found that the thermochemical activation of lignins, products of chemical wood processing, leads to the formation of carbon with a developed microporous structure. Active carbons with high adsorption properties and specific area over 2000 m

2

/g were obtained. It has been shown that the decreasing oxygen content in the raw material by thermal pre-treatment is a decisive factor providing a lower consumption of activators, the improvement of sorption properties, and increasing the yield of carbon.

A solution has been proposed for eliminating the diffusion resistance by proper structuring of the activated carbon used as catalyst support or as adsorbent. A structured carbon has been obtained in the form of tubes corked from one side. The fluid flow from the space outside the tubes passes through the pores of the pipe walls, enters the tubes and goes out from their openings in the free cross section. If it contains absorbable components, after passing through the tube wall it goes out purified from them. If the activated carbon holds a catalyst, a chemical reaction between the components of the fluid flow on the surface of the catalyst is carried out. Tubes of activated carbon with different adsorption properties have been obtained, the iodine adsorption capacity achieved by now is up to 1150 mg/g and the surface area achieved is up to 1200 m

2

/g.

Efficiency of active carbon applied in water treatment technologies depends on selection of a proper adsorbent, but also on methods and conditions of its use. These subjects are discussed taking as a model example the sorption of phenol on different, also chemically modified (HNO

3

, ozone) and biological activated carbons. Ozonation of active carbon changes its porous structure and in the case of phenol it reduces its sorptivity. Strong oxidation of the active carbon with HNO

3

, affects also kinetic parameters of the sorption process (the effective diffusion coefficient decreases). The application of biologically active carbon offers wide opportunities. A combination of sorption and biodegradation processes enables advanced removal of phenol from the solution on the one hand, and on the other hand it binds this toxic substance before direct exposure to microorganisms.

Modified active carbons were used for removal of hydrogen sulfide, ammonia and nitrite ions from water solutions. Obtained results demonstrate that active carbon oxidized with H

2

O

2

following impregnation with Co(II) possesses higher adsorption capacity for NH

4

+

compared with unimpregnated samples. It was established that active carbon obtained from nut shells has better oxidation properties compared with active carbons obtained from plum stones. The optimal conditions for adsorption and oxidation of sulfide and hydro-sulfide ions were established. Active carbons impregnated with Fe

+3

and Cu

+2

ions possess higher oxidation capacity demonstrating that these catalysts more effectively catalyze the oxidation of sulfide ions to S

IV

and S

VI

species.

A novel activated carbo-aluminosilicate material prepared from oil shale was used as an adsorbent for chromium ions from aqueous solutions. The maximum sorption capacity was found to be 92 mg/g. This value was obtained at pH 4 which is bellow the zero point of charge (pH

ZPC

) for this material. The pH

ZPC

was estimated at different mass to solution ratios and ranged from 7.9 to 8.3.

The opportunity of utilizing solid cellulose-containing wastes of food and processing industry for manufacturing sorption materials is considered.

We report a method for selective detecting viruses of plants using porous silicon at room temperature. The sizes of pores in porous silicon are larger than those of the researched viruses of plants. The samples of porous silicon have characteristic heterogeneity of porosity and chemical structure along its surface and depth. Adsorbed viruses of plants on the surface of porous silicon induce changes in the measured voltage-current and voltagefarad characteristics. Adsorption of viruses results in the growth of the parameter

c

(U)

in the field of voltage greater than 2 V. The characteristic

c

(U)

depends on type of the adsorbed viruses.

A factorial design methodology was used to evaluate the effects of temperature, pH and initial concentration of Pb(II) in sorption process onto the marine macro-algae

Ascophyllum nodosum

. The Box-Behnken factorial design method gives a mathematical model that shows the influence of each variable and their interactions on the process efficiency. Study ranges were 10-40 °C for temperature, 3.00-5.00 for pH and 50-200 mg/L for initial Pb(II) concentration. Within these ranges, the adsorption capacity is slightly dependent on temperature and pH but markedly increases with initial concentration. Maximum adsorption capacity of Pb(II) by

Ascophyllum nodosum

was 180 mg/g, which corresponds to the following values of those variables: temperature = 40 °C, pH = 5.00 and initial concentration = 200 mg/L.

The objective of this work was to study the sorption properties of chitin containing sorbents (ShCS) which were prepared from fungus mycelium of

Aspergillus niger

– waste of biotechnological production of citric acid. These sorbents were used for removing heavy metals (Cu(II), Zn(II), Cr(VI), Cd(II), Pb(II)) from water solutions. For comparison chitosan containing sorbents (ChaCS) from

Aspergillus niger

, which are prepared according to the Muzzarelli method, were used. The influence of the degree of deacetylation (DD) and size of particles on the sorption properties of ChCS and ChaCS was shown. Molecular modeling of chelating complex Pb(II) – chitin was realized by the method of molecular mechanics MM+.

Raw seaweed Gelidium sesquipedale and a composite material prepared from an industrial algal waste have been converted into inexpensive biosorbents, which were used for removal of Pb

2+

/Cd

2+

from aqueous solutions. The equilibrium data follow a multi-component discrete model and indicate a good adsorption capacity. The biosorption behavior of both materials during one sorption-desorption cycle of Pb

2+

/Cd

2+

has been investigated in a packed-bed flow-through column. In the sorption process, Cd breaks through the column faster than Pb due to its low affinity. An overshoot in the outlet Cd concentration was observed and explained by ion exchange between Pb and Cd, whereby the higher affinity of the Pb ion displaces the Cd ion bounded to the biosorbent. A 0.1 M HNO

3

solution was used as eluant for the desorption process. Desorption was 100% effective for Cd and Pb. A mass transfer model for the adsorption and desorption processes was used to simulate the column performance.

The removal of Se(IV), Se(VI), Sb(III) and Sb(V) from aqueous solutions by ion exchange using the commercially available weakly basic anion exchanger Duolite A7 with secondary amino groups has been investigated. This work comprises investigations of the equilibria of the sorption of Se and Sb and of the kinetics of uptake. The efficiency of sorption of selenium and antimony species depend strong on the pH. Se(IV) is well sorbed in a narrow range between pH 2.5 and 5.5 whereas Se(VI) is well sorbed between pH = 1 and 6. Sb(III) shows a maximum sorption between pH = 1 and 7, and for Sb(V) optimum sorption is obtained for pH < 5. The kinetic studies show that Se(VI) was removed almost completely in 20 min while sorption of the other species developed slowlier. Studies on sorption equilibria from pure solutions revealed the highest exchanger loadings for Se(VI) and smaller ones for the other species.

The opportunities of pulsed NMR methods for studying the mobility of adsorbed molecules and porous structure of microporous rigid and non-rigid adsorbents of different nature are considered. The distribution of nuclear magnetic relaxation times were used to determine the distribution of water and benzene molecules adsorbed in active carbons and in polymer sorbents. The dimensions of the areas corresponding to different porosities have been estimated from the self-diffusion data of water and benzene in AC. The self-diffusion study of water and benzene in the synthetic opals indicate the existence of ultramicropores. The obtained data of nuclear magnetic relaxation and self-diffusion of the adsorbed water and benzene in the different adsorbents are in accordance with the adsorption investigations and complement them.

Porous structure of tissue scaffolds is essential to ensure normal cell functioning providing them with nutrients, oxygen and optimal growth conditions and removing waste products. Characterization of the porous structure of hard implants is less of a problem compared to soft polymer hydrogels. In this work the results of the evaluation of the porous structure of two polymers widely used as implants or scaffolds, polycaprolactone as a hard material and collagen based hydrogel as a soft material are presented. The characterization was carried out using electron, fluorescence and confocal microscopy, quartz crystal microbalance technique and diffusion of macro-molecules.

This paper deals with the current state of modeling the breakthrough behavior of activated carbon beds. Different models are discussed as well as the differences between dealing with industrial dangers and with military/terrorist threats. Finally some of the problems are highlighted. These are mainly the result of the real-life, i.e. non-ideal, conditions of use of the protective mask-activated carbon canister combination.

A brief introduction to chemical engineering modeling is given. It is then applied to several systems, showing that the introduction of dimensionless variables in the model equations enable the identification of the parameters that control the systems behavior. These parameters can generally be determined by independent experiments for a given system and the behavior of the system can be reasonably predicted through simulation. The systems here considered are the removal of color from liquid streams using natural waste materials from the Portuguese seafood industry, carbon filters for individuals protection in toxic environments, a class of polyacrilic gel beads reinforced by a polyamide membrane for metals extraction from aqueous media and the use of exhausted resins from an industrial demineralizing plant in the recovery of gold. The eventual weaknesses of the materials used in those processes are evidenced by simulation, showing the limiting parameters and in what sense should they be changed in order to improve the system behavior.

Theoretical calculation of rate constant of adsorption of polyatomic particles on the surface of amorphous solid is carried out in this work. Calculation is conducted within the frames of quantum theory. The question of the characteristics (geometric parameters and frequencies of intramolecular vibrations) of polyatomic polarizable adsorbing particles in polar medium is considered. Calculations are carried out taking into account the interaction of intramolecular vibrations of the particle with polarization fluctuations of the medium. The proposed scheme of calculations allows taking into account the effects of frequency and spatial dispersion of amorphous solid. Events of physical and chemical adsorption are considered.

The dynamic behavior of water vapor adsorption on activated carbon filters is studied by simulation. A model, that includes axial dispersion and where the adsorption equilibrium is represented by the Dubinin-Serpinski equation, is developed. The influence of the axial Peclet number on the breakthrough curve is evaluated.