1. IntroductionThere is currently a growing global need for multifunctional and innovative hybrid materials with strictly controlled chemical composition and defined structure. Such products can be successfully utilized in various fields of science and branches of industry. An important factor is the methodology for synthesis of these products, which should be based on the principles of green chemistry and on low-waste or wasteless technologies. The substrates used in the process should be bioresorbable, easily available, and relatively inexpensive. All of these requirements are satisfied by lignosulfonates (LS), which are derivatives of lignin created as a side product in cellulose production from wood, in the sulfide method or in the sulfate dissolution process called the kraft process, as described in previous work [1–3].
From the chemical point of view, lignosulfonates are alkaline salts (calcium, sodium and magnesium salts, among others) of lignosulfonic acid. The presence of strong acidic sulfonate and hydroxylic groups gives lignosulfonates a hydrophilic character. Conversely the phenylpropane units guaiacyl (G), syringyl (S), and p-hydroxyphenyl (H) are responsible for the hydrophobic character of the LS surface, as described in [4]. The structure of lignosulfonates is extremely complex, and the relative quantities of particular structural units are hard to determine. According to Rencoret et al. [5] the G:S:H molar ratio of the product made from the wood of Paulownia fortunei is 1:59:40.
Lignosulfonates obtained via the sulfide method contain about 6.5% by weight of sulfur (in the form of anionic sulfonate groups). The sulfur content in kraft lignin is as high as 1–2% by weight, as has been shown previously [6,7].
Central European Journal of Chemistry
Silica/lignosulfonate hybrid materials: Preparation and characterization
1Poznan University of Technology, Faculty of Chemical Technology,Institute of Chemical Technology and Engineering, PL-60965 Poznan, Poland
2TU Bergakademie Freiberg, Institute of Experimental Physics, D-09599 Freiberg, Germany
Łukasz Klapiszewski1, Jakub Zdarta1, Tomasz Szatkowski1, Marcin Wysokowski1, Magdalena Nowacka1, Karolina Szwarc-Rzepka1, Przemysław Bartczak1, Katarzyna Siwińska-Stefańska1, Hermann Ehrlich2, Teofil Jesionowski1*
Research Article
The research reported here concerns the synthesis, characterization and potential applications of silica/lignosulfonate hybrid materials. Three types of silica were used (Aerosil®200, Syloid®244 and hydrated silica), along with magnesium lignosulfonate. The effective-ness of the hybrid material synthesis methodology was confirmed indirectly, using Fourier transform infrared spectroscopy, elemental and colorimetric analysis. Dispersive–morphological analysis indicates that the products with the best properties were obtained using 10 parts by weight of magnesium lignosulfonate per 100 parts of Syloid®244 silica. The relatively high thermal stability recorded for the majority of the synthesized products indicates the potential use of this kind of a material as a polymer filler. Results indicating the high electrokinetic stability of the materials are also of great importance. Additionally, the very good porous structure properties indicate the potential use of silica/lignosulfonate systems as biosorbents of hazardous metal ions and harmful organic compounds.
Silica/lignosulfonate hybrid materials: Preparation and characterization
Lignosulfonates might include in their structure a number of contaminations in the form of sugars, sugar acids, terpenes, or sodium and calcium salts. Moreover, due to the low pKa value of sulfonate groups, lignosulfonates are very easily dissolved in water. Their molecular mass is significantly higher than that of kraft lignin, reaching values from 10 000 to 40 000, as confirmed by Ouyang et al. [8] and Brudin and Schoenmakers [9]. Research into lignosulfonates present in solution was begun in 1960 by Rezanowich and Göring [10]. Those authors suggested that lignosulfonate molecules are present in solution in the form of microgels. A model was described by Yean et al. [11], and subsequently improved by Göring [12], Browing [13] and Le Bell [14]. The most recent research by Myrvold [15] shows that the lignosulfate compound is an atactic polyelectrolyte. A similar model has been proposed by Pla and Robert [16]. Myrvold’s research used for the first time a technique called scaling laws. In this method the size of a polymer is controlled in such a way that it is possible to investigate the influence of the molecular mass of polymers on their properties. Lignosulfonates have been found to have a wide range of applications. They have been used, for example, as modifiers in aqueous solutions or gels, stabilizers of colloidal solutions, dispersing agents, plasticizers [8], surfactants [17], adhesives [18], drilling emulsions [19], and cement admixtures [20].
Silica is one of the most abundant natural materials. Its crystallization under natural conditions is a long-term process which requires favorable conditions. These factors are the starting point for the production of synthetic silicon dioxide. It is an amorphous substance, with high chemical resistance, and therefore products of extremely high quality can be manufactured. A number of preparation techniques are used which differ in terms of the type of reagents or properties of the final product. The mechanism of preparation of the compound varies depending on the chemical method used. Of the many methods of silica preparation, the most commonly used are the flame method [21], hydrolysis and condensation of alkoxides developed by Stöber et al. [22] and modified by Ibrahim et al. [23], precipitation from aqueous sodium silicate (water glass) solutions [24], and precipitation from emulsion systems [25,26]. Due to its specific physicochemical properties, silica is used in various everyday applications. However, research is still being carried out to find more applications for this inorganic material, as is evidenced by the vast number of scientific papers published in leading journals.
In the literature only a few publications can be found concerning the synthesis of hybrid materials combining lignin and an inorganic precursor in the form of silica. There are no previous reports on attempts to
interconnect SiO2 and lignosulfonates. In one study by Chinese researchers, it was shown that rice hulls could be a perfect raw material for the manufacture of silica/lignin nanocomposites based on a sol–gel method. The objective was to prepare an advanced biocomposite, and to select the most favorable reaction conditions to obtain a product with optimum properties. It was proved in initial tests that a silica/lignin composite had a much greater surface area than monolithic silica (the BET surface area for the hybrid was 471.7 m2 g-1). This research was carried out by Qu et al. [27]. There are also reports on attempts to prepare a silica/lignin hybrid biomaterial based on synthesis enhanced by electromagnetic radiation. Two experiments were performed by Kajiwara and Chujo [28], one using traditional heating, the other using microwave heating. Interesting conclusions were drawn from the tests: it was stated that the method using microwave radiation was extremely useful and advantageous for the preparation of homogeneous and usable composite materials, compared with conventional heating. In a different report [29], a lignin/silica biocomposite was found to be a good precursor for highly pure silicon carbide. The hypothesis was confirmed by adding lignin to a solution of TEOS, distilled water, and sulfuric acid, which was used as a catalyst. The lignin found in composite fibers was shown to be converted into carbon during initial heating in the thermal reduction of carbon reacted with silica. In another paper [30] it was demonstrated that silica/lignin materials can be successfully applied as polymer fillers, and as selective biosorbents of hazardous metals and of harmful organic compounds.
In the present work an attempt was made to synthesize and characterize silica/magnesium lignosulfonate hybrid materials. The absence of literature reports relating directly to materials of this type provided an additional stimulus to carry out the research. The paper and cellulose industry generates significant amounts of wastes, including lignin and lignosulfonate. Combining these biopolymers with an inorganic matrix is therefore a very interesting solution, and it leads to hybrid materials with extraordinary physicochemical properties. These new parameters open up new areas of application, including in the sorption of hazardous metal ions, or in the future as a novel polymer filler.
2. Experimental procedure
2.1. Silica preparationThe silica matrix was precipitated in a polar medium by direct reaction of a sodium silicate water solution (Vitrosilicon SA, Poland) with 5% sulfuric acid (Chempur,
720
Ł. Klapiszewski et al.
Poland). The reaction mixture was vigorously stirred with a high-speed mixer (Eurostar IKA-Werke GmbH & Co. KG, Germany). The process was carried out at 85°C. A detailed description of the hydrated silica and the specific amounts of reagents used is given by Jesionowski et al. [31]. The types of silica used were a hydrated silica precipitated in a polar medium, Aerosil®200 fumed silica (purchased from Evonik Industries AG, Germany), and Syloid®244 (W.R. Grace & Co., USA).
2.2. Silica/magnesium lignosulfonate hybrid preparationIn order to obtain a silica/lignosulfonate hybrid material, a suitable quantity of magnesium lignosulfonate was first placed in a reactor in the form of a dense liquid of 55% concentration (VIANPLAST 55, BIOTECH Lignosulfonate Handels-GesmbH, Austria), and 100 cm3
of distilled water was added to the reactor. The aqueous solution of lignosulfonate derivative underwent constant stirring (1200 rpm) for about 15 minutes with the use of a high-speed mixer (Eurostar IKA-Werke GmbH & Co. KG, Germany). In the next step, 5 g of inorganic support (hydrated silica or selected commercial silica) was added to the lignosulfonate solution. The resulting system was homogenized for 1.5 h. After this time the product (SiO2/magnesium lignosulfonate hybrid) was placed in a vacuum evaporator (Büchi Labortechnik AG, Switzerland) in order to evaporate the solvent. The final product was dried in a stationary dryer (Memmert, Germany) at 105ºC for about 12 h.
2.3. Physicochemical and dispersive–morphological evaluationThe dispersive properties of the obtained products were evaluated using a Mastersizer 2000 (0.2–2000 μm) apparatus (Malvern Instruments Ltd., UK), employing the laser diffraction method.
The surface morphology and microstructure of the silica/lignosulfonate products were examined on the basis of the SEM images recorded from an EVO40 scanning electron microscope (Zeiss, Germany). Before testing, the samples were coated with Au for a time of 5 seconds using a Balzers PV205P coater.
The elemental composition of the products was established using a Vario EL Cube instrument (Elementar Analysensysteme GmbH, Germany), which is capable of registering the content of carbon, hydrogen, nitrogen and sulfur in samples following high-temperature combustion.
The presence of expected functional groups was examined by means of Fourier transform infrared spectra
(FT-IR), recorded on a Vertex 70 spectrometer (Bruker, Germany). Here the materials were analyzed in the form of tablets, made by pressing a mixture of anhydrous KBr (ca. 0.25 g) and 1 mg of the tested substance in a special steel ring under a pressure of approximately 10 MPa. The investigation was performed at a resolution of 0.5 cm-1.
The zeta potential was measured with a Zetasizer Nano ZS (Malvern Instruments Ltd., UK) equipped with an autotitrator. The measurements were performed in a 0.001M solution of NaCl. This instrument employs a combination of electrophoresis and laser measurement of particle mobility based on the Doppler phenomenon. The speed of particles moving in a liquid in an electric field, known as the electrophoretic mobility, is measured. Then from Henry’s Eq. 1 the value of the zeta potential is obtained:
(1)
where µE – electrophoretic mobility, ε – dielectric constant, ζ – electrokinetic (zeta) potential, η – viscosity, and f(κa) is the Henry function.
A thermogravimetric (TG) analyzer (Jupiter STA 449F3, Netzsch, Germany) was used to investigate the thermal stability of the samples. Measurements were carried out under flowing nitrogen (10 cm3 min-1) at a heating rate of 10°C min-1 over a temperature range of 25–1000°C, with an initial sample weight of approximately 5 mg.
In order to characterize the parameters of the porous structure of the obtained hybrid materials, surface area, pore volume, and average pore size were determined using an ASAP 2020 instrument (Accelerated Surface Area and Porosimetry) from Micromeritics Instrument Co. (USA). The specific surface area was determined by the multipoint BET (Brunauer–Emmett–Teller) method using data for adsorption under relative pressure (p/po). The BJH (Barrett–Joyner–Halenda) algorithm was applied to determine the pore volume and average pore size.
UV-Vis spectroscopy using D65 illumination with 10° standard observer and color measurement according to the CIE L*a*b* colorimetric method, recommended by the Commission Internationale de l’Eclairage (CIE), was carried out on the obtained samples using a Specbos 4000 spectrophotometer (YETI Technische Instrumente GmbH, Germany). L* is the lightness axis [black (0)→white (100)], b* is the blue (-)→yellow (+) axis, and a* is the green (-)→red (+) axis. The total color change is expressed as dE.
Physicochemical and dispersive–morphological evaluation
721
Silica/lignosulfonate hybrid materials: Preparation and characterization
2.4. Adsorption experimentsAn important part of the work was the carrying out of preliminary adsorption tests to confirm the potential for silica/lignosulfonate hybrid materials to be used as biosorbents of hazardous metals. It was investigated how the effectiveness of the removal of cadmium(II) ions from aqueous solution depended on the duration of the process. For this purpose, the process of adsorption of cadmium(II) ions (in a concentration of 50 mg L-1) was carried out over different times (1, 3, 5, 10, 15, 30, 60, 120, 180 minutes), using silica/lignosulfonate hybrids produced from three different types of silica (0.5 g).
The precursor of cadmium(II) ions used was an inorganic salt, tetrahydrated cadmium nitrate (Cd(NO3)2, Sigma Aldrich). Solutions of the cadmium(II) salt (0.1 L) were prepared with a concentration of 50 mg L1, and were placed in conical flasks. To this solution 0.5 g of biosorbent was added, and it was then stirred using a magnetic mixer (Ika Labortechnik Werke GmbH, Germany) for the appropriate time. When that time had elapsed, the mixture was filtered under reduced pressure using specialist equipment. The filtrate obtained from each stage of the adsorption process was subjected to further analysis.
Using AAS analysis it was possible to determine the content of cadmium(II) ions in the filtrate after the adsorption process. This is one of the most precise methods of quantitative analysis. The tests were carried out using a Z-8200 spectrometer (Hitachi, Japan). The results of the AAS analysis were used to perform computations relating to the effectiveness of the process of removing cadmium(II) ions from aqueous solution. The following formula was used:
% removal= % (2)
where Co and Ce are respectively the initial and equilibrium concentrations of cadmium(II) ions (mg L -1).
The kinetics of the cadmium(II) ion absorption process was also investigated. The biosorbents used for this purpose were silica/lignosulfonate hybrids made from the commercial silica Syloid®244 and different quantities of lignosulfonate (3, 10, 30 and 50 parts by weight per 100 parts SiO2). Syloid®244 was selected for investigation of the kinetics of the adsorption process because it had the best porous structure parameters, and these undoubtedly have a significant effect on the process of removal of cadmium(II) ions.
The value qt was calculated, this being necessary for the determination of different kinetic models, including pseudo-first-order [32] and pseudo-second-order equations [33]. The concentration of cadmium(II) ions in the filtrate after the adsorption process was found
using the AAS method. The quantity of cadmium(II) ions adsorbed in unit time was calculated from the equation:
(3)
where C0 and Ct are the concentrations of cadmium(II) ions in the solution before and after sorption respectively (mg L-1), V is the volume of the solution (L), and m is the mass of the silica/lignosulfonate biosorbent (g).
3. Results and discussion
3.1. Dispersive–morphological characteristicsThree types of silica were used, differing in synthesis methodology and in basic physicochemical and dispersive–morphological properties. Hydrated silica was precipitated in the laboratory in a polar medium, while the remaining two silicas are commercial products sold under the names Aerosil®200 and Syloid®244. As the SEM microphotographs show, silica can have diverse morphological and microstructural properties. However, in each of the three cases (Figs. 1a–c), the presence of single primary particles of nanometric size, which tend to create aggregates (<1 µm), as well as agglomerates (>1 µm), can be noticed.
The results of the dispersive–morphological analysis of the silica/lignosulfonate hybrid materials obtained based on the three different types of silica are presented in Table 1 and in the microphotographs in Fig. 2. The data acquired from the Mastersizer 2000 show that the products with the best dispersive properties were hybrids based on Syloid®244. In the sample labeled S3, containing 3 parts by weight of lignosulfonate per 100 parts of silica, 10% of the volume is occupied by particles smaller than 4.3 µm, while 50% and 90% of the sample volume are attributed to the presence of particles smaller than 18.3 and 38.9 µm respectively. The addition of lignosulfonate increases the values of the parameters d(0.1), d(0.5) and d(0.9) for these products. A similar tendency was observed for the remaining hybrid materials, based on Aerosil®200 and the hydrated silica. The values of the analyzed parameters are relatively high in the case of the hybrid materials, which indicates the increased tendency of these systems to form agglomerated structures.
These conclusions are fully confirmed by the SEM microphotographs (Fig. 2). From the SEM images it can be clearly seen that the systems exhibit a tendency to aggregate and agglomerate. The higher the lignosulfonate content relative to the silica support, the more marked is the tendency. As was also demonstrated in previous work [6,30] in which the main precursor
722
Ł. Klapiszewski et al.
was kraft lignin, the product with optimal dispersive–morphological properties was that obtained using 10 parts by weight of biopolymer per 100 parts of silica.
3.2. Elemental analysisBased on the results of elemental analysis, the content of nitrogen, carbon, hydrogen and sulfur in the analyzed samples was determined. The results, given in Table 2, indirectly confirm the effectiveness of the methodology for silica/lignosulfonate hybrid synthesis. Magnesium lignosulfonate contains in its structure approximately 4% by mass of sulfur, present in the form of sulfonate groups. The increase in the quantity of this element with increasing lignosulfonate content in the hybrid materials
serves as evidence of successful interconnection of the biopolymer with the silica surface. In the analyzed samples trace amounts of nitrogen were found, which most likely result from plausible impurities originating from the process of isolation of lignin from wood. As the weight contribution of magnesium lignosulfonate in proportion to silica increases, there is also observed an increase in carbon and hydrogen content, these being the main building elements of the lignosulfonate structure. The results given in Table 2 support the conclusion that, based on all of the silicas used, expected and desirable hybrid systems have been obtained. Hydrated silica is considered to be the best support, since it shows the highest increase in the content of individual elements
Figure 1. SEM images of: Aerosil®200 (a), Syloid®244 (b), hydrated silica (c), and magnesium lignosulfonate (d).
Table 1. Dispersive characteristics of silica/magnesium lignosulfonate materials.
Sample name Type of silica
Content of lignosulfonate in relation to the silica
matrix (wt./wt.)
Particle diameter from Mastersizer 2000 (μm)
d(0.1) d(0.5) d(0.9) D[4.3]
A3
Aerosil®
200
3 4.8 20.3 38.9 21.8
A10 10 5.0 22.6 43.5 24.0
A30 30 5.0 22.9 44.2 24.3
A50 50 5.2 25.4 49.5 28.3
S3
Syloid®
244
3 4.4 19.8 40.2 22.8
S10 10 4.9 20.1 40.9 23.1
S30 30 5.1 22.4 46.2 24.4
S50 50 5.3 24.8 49.8 28.1
H3
Hydrated
3 5.0 23.5 46.3 26.1
H10 10 5.2 25.1 48.3 28.4
H30 30 5.1 25.2 50.3 29.1
H50 50 5.4 28.8 53.3 30.9
723
Silica/lignosulfonate hybrid materials: Preparation and characterization
as the lignosulfonate contribution rises in proportion to the silica support. For a sample containing 50 parts by weight of magnesium lignosulfonate per 100 parts of hydrated silica, a carbon contribution of 8.35% was recorded, which is far greater than the value for product H3 (C=1.34%). Moreover, attention should be paid to the results of elemental analysis obtained for the pure silicas. In this case there is a clear similarity in the results for carbon and hydrogen content. The low content of these elements indicates above all the high purity of the silicas used in the research. The results of this analysis indirectly confirm the effective interconnection of each type of silica with magnesium lignosulfonate, which supports the correctness of the methodology used in the experiments.
3.3. FT-IR analysisInfrared spectroscopy with Fourier transformation, carried out for the precursors used in the research (Fig. 3a), indicates the presence of series of characteristic functional groups on their surface. In the FT-IR spectra of the utilized silicas (Aerosil®200, Syloid®244 and hydrated silica) a strong wide band between 3600–3200 cm-1 is visible, generated by the stretching vibrations of –OH groups. The increased intensity of the band in the case of hydrated silica is caused by the presence of a greater number of hydroxyl groups in this compound compared with the commercial products. The characteristic signals originating from
≡Si–O–Si≡ groups at wavenumbers of 1120 cm-1 and 860 cm-1 are generated by asymmetric and symmetric bending vibrations respectively, as previously described by Szwarc-Rzepka et al. [34]. The presence of a band at wavenumber 960 cm-1 is associated with out-of-plane deformation vibrations of ≡Si–OH groups, whereas the signal at 469 cm-1 can be attributed to asymmetric in-plane vibrations of those groups [31]. The distinct signal at a wavenumber of 1647 cm-1 is associated with in-plane deformation vibrations of –OH groups, and with the presence of physically adsorbed water molecules on the silica surface.
In the spectrum of magnesium lignosulfonate (Fig. 3a) a greater number of signals are present, which is a consequence of the complex structure of the compound and the presence of multiple functional groups. A strong and characteristic band between 3600 and 3200 cm-1 is associated with –OH stretching vibrations. The significant intensity of the peak is due not only to the presence of hydroxyl groups, but also to adsorbed water on the polar surface of the precursor. The signal at wavenumber 2850 cm-1 is generated by stretching vibrations of ≡C–H, =CH2 and –CH3 groups, as described by Moubarik et al. [35]. Additional confirmation of the presence of those groups is a signal generated by in-plane deformation vibrations, occurring at wavenumber 1460 cm-1. Moreover, in the dactyloscopic range, at wavenumber 675 cm-1, there is a signal originating from vibrations of =CH2 groups. An intensive band
Figure 2. SEM images of silica/lignosulfonate hybrid materials labeled as samples: A3 (a), A10 (b), A30 (c), A50 (d), S3 (e), S10 (f), S30 (g), S50 (h), H3 (i), H10 (j), H30 (k), and H50 (l).
724
Ł. Klapiszewski et al.
at wavenumber 1720 cm-1 is attributed to stretching vibrations of aldehyde and ketone groups. Three clearly visible signals at wavenumbers 1490 cm-1, 1430 cm-1 and 1380 cm-1 are related to vibrations of carbon-carbon bonds in aromatic rings. Characteristic bands for Ar–H bonds are visible in the spectrum around wavenumber 3030 cm-1, but overlap with the strong band of hydroxyl groups. A medium band noticeable at wavenumber 900 cm-1 is associated with out-of-plane deformation vibrations of Ar–H bonds. Also visible in the spectrum are signals at wavenumber 1600 cm-1. These bands, according to Mohammed-Ziegler et al. [36], are characteristic of aromatic hydrocarbons, and originate from stretching vibrations of =C=C= bonds in aromatic rings. Signals at wavenumber 1250 cm-1 and 1030 cm-1 are generated respectively by asymmetric and symmetric stretching vibrations of Ar–O–C≡, as has been confirmed in [37].
FT-IR analysis of the silica/lignosulfonate hybrid materials based on the commercial silica Syloid®244 (Fig. 3c) indicates the presence of characteristic signals for magnesium lignosulfonate which are not visible in the spectrum of the silica precursor. These bands include those visible at wavenumber 2850 cm-1, attributed to ≡C–H, =CH2 and –CH3 groups, signals characteristic
of aromatic compounds in a range from 1550 cm-1 to 1380 cm-1, and small bands at wavenumber 675 cm-1 related to vibrations of =CH2 groups. The spectrum of the hybrid material also contains a more intensive characteristic band for hydroxyl groups, whereas signals between 1250 cm-1 and 1030 cm-1, generated by ether bonds, are overlapped by an intensive band attributed to ≡Si–O–Si≡ bonds originating from the Syloid®244. It is noteworthy that the intensity of the bands generated by the obtained hybrid material increases with an increase in the quantity of magnesium lignosulfonate used.
When the commercial product Aerosil®200 is used (Fig. 3b), the intensity of signals characteristic of lignosulfonate increases as its weight contribution to the hybrid rises. In the FT-IR spectrum of the hybrid, the signals are analogous to those for the material in which Syloid®244 was used as the support. Attention should be drawn to the increase in their intensity, particularly visible for the bands generated by vibrations of ≡C–H, =CH2 and –CH3 groups at wavenumber 2850 cm-1, and by aromatic groups in the spectrum range between 1550 cm-1 and 1380 cm-1.
The FT-IR spectra of the silica/lignosulfonate hybrid materials obtained using hydrated silica (Fig. 3d) show the highest intensity of signals originating from the
Figure 3. FT-IR spectra of silicas and magnesium lignosulfonate (a), and of silica/lignosulfonate hybrid materials based on Aerosil®200 (b), Syloid®244 (c), and hydrated silica (d).
725
Silica/lignosulfonate hybrid materials: Preparation and characterization
magnesium lignosulfonate, among all the silica supports used. Strong signals associated with the vibrations of aromatic groups, and bands generated by carbon-carbon bonds of aromatic groups, serve as confirmation of the success of the process of hybrid preparation. Similarly as in the case of the previous silica matrices, the intensity of functional groups originating from the magnesium lignosulfonate increases with increasing quantity of precursor used.
Based on the FT-IR spectra for the obtained silica/lignosulfonate systems, it can be noted that desirable hybrid materials can be obtained with the use of any of
the three types of silica studied. The weight contribution of magnesium lignosulfonate has a clearly noticeable impact on the effectiveness of support surface functionalization. Based on the analysis, a scheme of reaction between silica and lignosulfonate is proposed, presented in Fig. 4. The proposed reaction scheme of synthesis of the silica/lignosulfonate hybrid material is based on the formation of stable, covalent oxygen bridges between silicon atoms of the inorganic support and oxygen atoms of magnesium lignosulfonate. The process of the formation of these bonds is based on a condensation reaction between hydroxyl groups of
Figure 4. Proposed reaction scheme for the preparation of silica/lignosulfonate hybrid material.
726
Ł. Klapiszewski et al.
both precursors, in which the product is water. The presented reaction scheme is based on the assumption that in the silica, silicon atoms possess partial positive charge. This charge results from the direct connection of the silicon atoms with the more electronegative oxygen atoms. Magnesium lignosulfonate contains in its structure terminal hydroxyl groups with oxygen atoms with partial negative charge, and therefore nucleophilic attack by an oxygen atom of a hydroxyl group on a silicon atom is possible. As a result, the hydrogen atom can be transferred to a neighboring hydroxyl group, and a molecule of water is formed and detached. Oxygen bridges formed in this way between the magnesium lignosulfonate and silica are stable and enable the effective synthesis of silica/lignosulfonate hybrid materials [38].
Additional confirmation of the proposed mechanism of covalent bond formation between silica and magnesium lignosulfonate is provided by the results of the FT-IR analysis. In the spectra of the products an intensive signal is visible, with a maximum around 3400 cm-1, which originates from stretching vibrations of hydroxyl groups. However, the peak is narrower than in the case of the precursors. This effect most likely results from the formation of hydrogen bonds between the precursors.
3.4. Electrokinetic characteristicFrom the results given in Table 3 it can be seen that silica (commercial as well as synthetic) exhibits almost identical values of zeta potential over the analyzed pH range. This has already been described in detail in our previous publications [7,30].
During synthesis of the studied systems, the main influence on the obtained zeta potentials (and therefore on the electrokinetic stability) came not from the silica, but from the magnesium lignosulfonate. This can be characterized as a complex polymer, possessing various functional groups, such as sulfonate, methoxy, carboxylic and phenolic groups. Particularly the sulfonate and carboxylic groups present in the structure of the analyzed magnesium lignosulfonate have a major influence on its dispersive properties, as has been observed by Zhou et al. [39]. Thus these groups can variously influence the physicochemical and electrokinetic properties of the resulting SiO2/magnesium lignosulfonate systems. This influence is also reflected in the values of electrokinetic (zeta) potential obtained. It is also of crucial significance when estimating the electrokinetic stability of the synthesized products. Zeta potential values obtained for the SiO2/magnesium lignosulfonate hybrid make it possible to confirm indirectly the effectiveness of the suggested method of synthesis. Moreover, the analyzed
Table 2. Elemental content of nitrogen, carbon, hydrogen, and sulfur in silicas, magnesium lignosulfonate, and silica/lignosulfonate hybrid materials.
Sample name Elemental content (%)N C H S
Aerosil®200 - 0.10 0.11 -
Syloid®244 - 0.19 0.13 -
Hydrated silica - 0.19 0.10 -
Magnesium lignosulfonate 0.15 37.19 4.94 4.00
A3 0.07 1.23 0.59 0.17
A10 0.09 2.43 0.76 0.41
A30 0.10 5.58 1.20 1.01
A50 0.13 8.08 1.57 1.54
S3 0.05 1.03 0.81 0.23
S10 0.06 2.04 1.00 0.49
S30 0.10 5.20 1.39 1.17
S50 0,11 7.32 1.76 1.65
H3 0.04 1.34 0.97 1.43
H10 0.05 2.49 1.23 1.77
H30 0.07 5.98 1.81 2.27
H50 0.11 8.35 2.11 2.37
727
Silica/lignosulfonate hybrid materials: Preparation and characterization
systems exhibit highly negative values of zeta potential (regardless of pH value), which indicates their good electrokinetic stability. This is of great significance in the evaluation of the applicability of such compounds, including in the polymer and paper industries, in agriculture and in the production of dyes and pigments. Similar electrokinetic properties have been observed for SiO2/kraft lignin, described in detail by Klapiszewski et al. [7].
3.5. Thermal stabilityThe wide range of physicochemical analysis carried out included investigation of the thermal stability of the hybrid materials and precursors, including both hydrated silica and commercial silicas (Aerosil®200 and Syloid®244). The magnesium lignosulfonate also underwent thermal analysis. The resulting graphs show the relationship between mass loss and temperature. Change in sample mass during heating occurs due to physical changes (evaporation, sublimation, desorption) and chemical reactions (reduction, decomposition, or oxidation). Fig. 5a shows TG curves for the precursors, while Figs. 5b–5d show the temperature-dependent mass changes for hybrid materials based on Aerosil®200, Syloid®244 and hydrated silica respectively.
The results obtained for the silicas show decreased resistance of the inorganic material to high temperature. The TG curve for hydrated silica shows a mass loss as high as 8%, whereas for the commercial silicas the mass loss is smaller (~3%). The TG curves for the commercial silicas indicate that both samples exhibit high thermal stability over practically the whole range of analyzed temperatures. The thermogravimetric curve recorded for magnesium lignosulfate exhibits two characteristic stages. The first, below 200°C, results from endothermic water desorption from the sample. The second, more severe mass loss (~40%), starting at a temperature of about 200°C, reflects the gradual degradation and
consequent fragmentation of the compound. The results are in agreement with data given by Brebu et al. [40] and Lemes et al. [41].
The thermal stability of selected silica/magnesium lignosulfonate hybrid materials was also investigated. Fig. 5b shows thermogravimetric curves for hybrid materials containing 3, 10, 30 and 50 parts by weight of magnesium lignosulfonate to 100 parts of Aerosil®200 silica. Among the four analyzed samples, the sample with the highest content of magnesium lignosulfonate (A50) exhibits the lowest thermal stability. In this specimen a 17% mass loss was observed relative to the initial sample mass. Somewhat better thermal properties are demonstrated by the other three hybrid materials (A3, A10 and A30), for which the mass loss values are similar, at 6% (sample A3), 8% (sample A10) and 13% (sample A30). The results confirm the assumption that the addition of magnesium lignosulfonate causes a slight lowering of the thermal stability of the synthesized hybrid materials.
Fig. 5c shows the mass change of samples S3, S10, S30 and S50 as a function of temperature (20–1000 oC), these being hybrid materials based on Syloid®244 and magnesium lignosulfonate. The TG curves for these samples exhibit a similar tendency as in the case of products based on Aerosil®200 and magnesium lignosulfonate: with an increase in the quantity of alkaline salt of lignosulfonate acid, the thermal stability of the synthesized hybrid materials decreases. For sample S3 the mass loss is equal to 7% of the initial sample mass. In the case of hybrid materials containing 10, 30 and 50 parts by weight of magnesium lignosulfonate the mass losses are respectively 10% (S10), 14% (S30) and 18% (S50) of the initial sample mass.
The thermogravimetric analysis of hybrid materials prepared based on hydrated silica is shown in Fig. 5d. For the sample containing 3 parts by weight of magnesium lignosulfonate per 100 parts of hydrated
Table 3. Results for zeta potential, depending on pH, for the precursors and silica/lignosulfonate hybrid materials.
silica, greater thermal stability can be observed (mass loss 14%). For the sample with the highest content of magnesium lignosulfonate (H50) the mass loss is 26%.
The thermal analysis of the silica/lignosulfonate hybrid materials leads to the following conclusion: in all three analyzed series the addition of magnesium lignosulfonate causes a slight lowering of the hybrid materials’ thermal stability, compared with the initial silicas. A similar tendency has previously been reported [6,30] in experiments where kraft lignin was used. Moreover, the most thermally stable systems are those based on the commercial silicas (Aerosil®200 and Syloid®244). The hybrid materials synthesized from hydrated silica have slightly poorer thermal stability. These thermal analysis results indicate that hybrid materials based on silica and lignosulfonate may be successfully used as novel polymer fillers.
3.6. Porous structure analysisA determination was also made of the BET surface area, total pore volume and pore size of the obtained hybrid materials. The analysis was carried out on products made with the addition of 3, 10, 30, 50 parts by weight of magnesium lignosulfonate. The main aim was to evaluate the possibility of using SiO2/magnesium lignosulfonate hybrid material as a potential biosorbent
for hazardous metal ions and harmful organic compounds. Porous structure properties of the silicas, magnesium lignosulfonate and resulting hybrids are shown in Table 4. The commercial silica Aerosil®200 has a large BET surface area, equal to 198 m2 g-1. The addition of magnesium lignosulfonate was found to reduce the surface area to 121 m2 g-1 (for the sample containing 3 parts by weight of biopolymer). Further increasing the content of magnesium lignosulfonate reduces the surface area to 93 m2 g-1 (for sample A50 containing 50 parts by weight of magnesium lignosulfonate per 100 parts of Aerosil®200 silica). The total pore volume decreases gradually. For the hybrid material with the lowest content of lignosulfonate (A3), the pore volume is 0.09 cm3 g-1, while for samples A10, A30 and A50 the total pore volume is 0.08, 0.07 and 0.06 cm3 g-1 respectively. However, the pore size of the analyzed samples remained at virtually the same level, being equal to 2.9 nm in all cases except for sample A3, for which it was 3.0 nm.
The results obtained for the porous structure of hybrid materials prepared based on Syloid®244 silica show similar patterns as in the case of the products based on Aerosil®200, discussed above. Namely, increasing the quantity of magnesium lignosulfonate gradually reduces the surface area
Figure 5. Thermal analysis of precursors (a), and of silica/magnesium lignosulfonate hybrid materials based on Aerosil®200 (b), Syloid®244 (c), and hydrated silica (d).
729
Silica/lignosulfonate hybrid materials: Preparation and characterization
of the product, from 212 m2 g-1 (sample S3) down to 132 m2 g-1 (sample S50). The total pore volume is slightly greater than for hybrids based on Aerosil®200 and magnesium lignosulfonate, but still the value drops from 0.14 cm3 g-1 (sample S3) down to 0.10 cm3 g-1 for sample S50. Pore size is the same for all samples and is equal to 2.6 nm.
The smallest BET surface area was recorded for products based on hydrated silica and magnesium lignosulfonate. The surface area of the pure silica was found to differ from the values obtained for the commercial silicas. This confirms the assumption that the method of synthesis has a significant influence on the porous structure parameters. As regards the porous properties for hybrids based on hydrated silica, it was noted that the sample with the smallest amount of magnesium lignosulfonate (H3) had a BET surface area of 31 m2 g-1, while for the sample with the highest magnesium lignosulfate content (H50) the value was 9 m2 g-1. The total pore volume in the obtained hybrids also decreases with increasing content of magnesium lignosulfate. The pore sizes of the products based on hydrated silica range between 2.5 and 3.0 nm.
The relatively high surface areas obtained for the products, especially those based on commercial silicas (Aerosil®200 and Syloid®244), imply that it will be possible to apply these hybrids as selective biosorbents of hazardous metal ions, harmful organic compounds
and others. Research is currently being carried out in which the obtained hybrid materials are utilized for adsorbing hazardous metal ions (Ni, Cd) from aqueous solutions. It is noteworthy that the relatively small BET specific area (as found in the case of products based on hydrated silica) does not eliminate those systems as potential biosorbents. Of much greater importance in this case is the presence of multiple functional groups in the structure of lignin and its derivatives, including lignosulfonates, which provide an opportunity to bond hazardous metal ions and/or harmful organic compounds chemically to the hybrid’s surface, as has previously been demonstrated in [42–45].
3.7. Colorimetric propertiesThe obtained hybrid materials were also subjected to color intensity analysis. Colorimetric analysis using the CIE L*a*b* color space was performed to determine color lightness, contribution of individual colors, saturation and shades of colors. Analysis of this type is of practical importance in evaluating possible applications in which color plays a meaningful role. In the analysis, the three types of silica were used as reference samples (Aerosil®200, Syloid®244 and hydrated silica). These have high values for the lightness parameter L*, respectively 93.78, 93.63 and 92.93. The value of this parameter for magnesium lignosulfonate is 36.26.
Table 4. Porous structure parameters of silicas, magnesium lignosulfonate, and silica/lignosulfonate materials.
Sample name BET surface area(m2 g-1)
Total volume of pores(cm3 g-1)
Mean size of pores(nm)
Aerosil®200 198 0.11 2.8
Syloid®244 262 0.17 2.6
Hydrated silica 89 0.02 3.0
Magnesium lignosulfonate 1 0.01 11.4
A3 121 0.09 3.0
A10 113 0.08 2.9
A30 101 0.07 2.9
A50 93 0.06 2.9
S3 212 0.14 2.6
S10 183 0.12 2.6
S30 156 0.10 2.5
S50 132 0.10 2.6
H3 31 0.02 3.0
H10 20 0.01 2.6
H30 13 0.01 2.5
H50 9 0.01 2.9
730
Ł. Klapiszewski et al.
Table 5 contains the results of colorimetric analysis for Aerosil®200/magnesium lignosulfonate, Syloid®244/magnesium lignosulfonate, and hydrated silica/magnesium lignosulfonate. These hybrid materials exhibit a decrease in lightness (parameter L*) as the content of magnesium lignosulfonate increases. In the case of hybrid materials based on Aerosil®200 silica, the lightness parameter decreases from L*=85.74 for sample A3 down to L*=46.27 for sample A50. For the sample containing 3 parts by weight of magnesium lignosulfonate per 100 parts of Syloid®244 silica the value is L*=88.19, while sample S50, in which the lignosulfonate content is significantly higher, has L*=48.13. The greatest decrease in the L* value was observed for the hydrated silica/magnesium lignosulfonate system. Here the initial value was L*=83.91, whereas the addition of 50 parts by weight of the lignosulfonate derivative per 100 parts of hydrated silica caused the value to fall to 45.19.
The values of the parameters a* and b* (which determine the contribution of individual colors – red and yellow respectively) are clearly seen to increase with increasing content of magnesium lignosulfate. The greatest increase in yellow color contribution was recorded for the hydrated silica/magnesium lignosulfate hybrid, from an initial value of b*=13.98 (sample H3) to b*=20.01 for the sample containing the largest amount of magnesium lignosulfate (H50). Based on analysis of
the data, an increase in the parameters characterizing total color change (dE) for each series of products was obtained. The limit for the human eye to recognize color change is about dE = 2–3 [46]. The total color change for the studied products was much greater, which means that the changes can be noticed with the naked eye. The samples become more brown as the content of lignin increases. This may be of significant importance in some applications, including in the filling of polymers. This phenomenon may be a serious limitation for the preparation of colorless polymers or polymers with low color saturation.
In summary, colorimetric analysis leads to satisfactory results for each type of hybrid material studied. This indirectly confirms the effectiveness of the research methodology. Similar conclusions have been noted in earlier publications, in which the main precursor was kraft lignin [6,30]. The results obtained will certainly be of practical significance with regard to applications of the hybrid materials in various branches of industry.
3.8. Results adsorption testThe silica/lignosulfonate hybrid materials obtained in the present work demonstrated unique physicochemical and electrokinetic properties, which imply that they can be used as effective sorbents of hazardous metal ions. For this reason, preliminary tests were carried
Table 5. Colorimetric data for silicas, magnesium lignosulfonate and silica/lignosulfonate products.
Sample name Colorimetric dataL* a* b* dE
Aerosil®200 93.78 0.24 2.55 -
Syloid®244 93.63 0.22 2.13 -
Hydrated silica 92.93 0.18 2.01 -
Magnesium lignosulfonate 36.26 12.16 26.92 48.24
A3 85.74 3.38 15.33 15.31
A10 74.30 6.90 17.13 24.13
A30 59.73 10.01 18.88 40.72
A50 46.27 14.15 19.64 47.18
S3 88.19 3.33 14.99 14.32
S10 76.48 6.98 17.18 19.15
S30 55.13 9.97 17.98 38.53
S50 48.13 13.69 18.83 45.93
H3 83.91 3.53 13.98 15.15
H10 73.19 5.01 15.53 26.93
H30 58.66 8.93 18.03 42.17
H50 45.19 13.33 20.01 49.13
731
Silica/lignosulfonate hybrid materials: Preparation and characterization
out involving the use of these sorbents to remove cadmium(II) ions from aqueous solutions. The tests also aimed to determine how the sorption properties are influenced by the type of silica used to produce the silica/lignosulfonate hybrid. The experimental data obtained are shown in Fig. 6. Analysis of the results indicates that a state of adsorption equilibrium was being reached after 30 minutes, but the process was most effective after the elapse of 60 minutes. Satisfactory results were obtained for each type of silica: the effectiveness of the process of removal of cadmium(II) ions from aqueous solution was in the range 82–87% for all three types. The differences between the results obtained for the different types of inorganic precursor were not very significant.
The results indicate unambiguously the effectiveness of the process of adsorption of cadmium(II) ions from model aqueous solutions using silica/lignosulfonate materials. It should be remembered that these are preliminary tests, which imply enormous possibilities for using these hybrid systems as sorbents of hazardous metal ions. It is planned to use the tested sorbent for removing ions of lead, nickel, mercury and uranium, as well as organic compounds.
3.9. Adsorption kineticTo obtain more detailed information about the effectiveness of the process of removing cadmium(II) ions from aqueous systems, the adsorption kinetics were investigated for a silica/lignosulfonate system where the inorganic precursor was the commercial silica Syloid®244. Tests were performed for materials with differing content of magnesium lignosulfonate per 100 parts by weight of SiO2.
The kinetics of the process of adsorption of cadmium(II) ions on a biosorbent can be described using
kinetic models of Lagergren’s pseudo-first-order type [32] and Ho’s pseudo-second-order type [33]. These models describe the changes in the concentration of the adsorbate as a function of time during the adsorption process until equilibrium is attained.
For a Lagergren pseudo-first-order kinetic model, the rate of reaction is directly proportional to the difference between the equilibrium concentration of adsorbate in the solid phase of the adsorbent and the instantaneous concentration in the solid phase. The Lagergren pseudo-first-order model can be expressed by Eq. 4 [32]:
(4)
where qe and qt (mg g-1) are the amounts of the cadmium(II) ions adsorbed at equilibrium and at time t (min) respectively, and k1 (min-1) is the rate constant for the pseudo-first-order rate equation.
Following integration with application of the boundary conditions (qt = 0 at t = 0 and qt = qt at t = t), Eq. 4 can be rearranged to give Eq. 5, enabling linear data plotting:
(5)
The equilibrium adsorption capacity (qe) and adsorption rate constant (k1) (Table 6) were computed experimentally by determining the relationship log(qe — qt) versus t. Fig. 7 shows the plot of log(qe — qt) versus t.
The correlation coefficient (r2) obtained using the Lagergren pseudo-first-order kinetic model, for all of the initial cadmium(II) ion concentrations investigated, lay within the range 0.826–0.939 (Table 6). This indicates that the pseudo-first-order kinetic model fits poorly to the experimental data. The results for adsorption capacity (qe,cal) obtained on the basis of the pseudo-first-order kinetic calculations deviated significantly from the values of the experimental capacities (qe,exp). A much better fit was obtained using the pseudo-second-order kinetic model.
In the case of Ho’s pseudo-second-order kinetic model, we assume the proportionality of the rate of the adsorption process to the square of the difference between the equilibrium concentration of adsorbate in the solid phase of the adsorbent and the instantaneous concentration in the solid phase of the adsorbent. This model is represented by Eq. 6 [33]:
(6)
where (g mg-1 min-1) is the rate constant for the pseudo-second-order rate equation, and
Figure 6. Effect of contact time on cadmium(II) removal by silica/ lignosulfonate biosorbent.
732
Ł. Klapiszewski et al.
qe and qt are the quantities (mg g-1) of cadmium ions adsorbed at equilibrium and at time t (min).
Incorporating the boundary conditions, Eq. 6 takes the following form:
(7)
The initial adsorption rate, h (mg g-1 min-1), is defined as follows:
(8)
To calculate the model second-order rate constant (k2) and the equilibrium adsorption capacity (qe), a linear plot of t/qt versus t was constructed (Fig. 8).
When Ho’s pseudo-second-order model was used, the values obtained for the correlation coefficient (r2) lay within the range 0.998–0.999. This indicates the very good fit of the pseudo-second-order model to the values obtained experimentally. The adsorption capacity (qe,cal) calculated from the pseudo-second-order model corresponded very closely to the values of the experimental capacities (qe,exp). The kinetic parameters obtained clearly show that, with an increase in the content of magnesium lignosulfonate per 100 parts by weight of SiO2, the material’s sorption capacity with respect to cadmium(II) ions improves. This is confirmed by the rise in the value of the initial adsorption rate (h), the rate constant in the pseudo-second-order model (k2) and adsorption capacity (qe,cal) as the content of magnesium lignosulfonate increases.
4. ConclusionsThis paper has described the preparation of multifunctional silica/magnesium lignosulfonate hybrid materials. The effectiveness of interconnection of the precursors was confirmed by Fourier transform infrared spectroscopy and by elemental analysis. Based on those results, a plausible reaction mechanism has been suggested. The resulting systems exhibit highly negative values of zeta potential (regardless of pH),
Table 6. Pseudo-first-order and pseudo-second-order kinetic parameters and coefficient of determination for adsorption of cadmium(II) ions onto silica/lignosulfonate biosorbents.
Type of kinetic Parameters Syloid®244/magnesium lignosulfonate biosorbentssymbols units S3 S10 S30 S50
Pseudo- first order
qe.exp mg g-1 8.092 8.202 8.478 8.758
qe.cal mg g-1 0.720 0.851 1.114 0.749
k1 1 min-1 0.149 0.155 0.258 0.143
r2 — 0.827 0.939 0.826 0.877
Pseudo-second order
qe.cal mg g-1 8.087 8.185 8.461 8.732
k1 1 min-1 0.836 0.908 1.213 1.290
r2 — 0.999 0.999 0.999 0.998
h mg g-1 min-1 54.721 60.863 86.912 98.441
Figure 7. Pseudo-first-order kinetic fit for adsorption of cadmium(II) ions onto SiO2/lignosulfonate biosorbents.
Figure 8. Pseudo-second-order kinetic fit for adsorption of cadmium(II) ions onto silica/lignosulfonate biosorbents.
733
Silica/lignosulfonate hybrid materials: Preparation and characterization
which indicates their very high electrokinetic stability. This property is crucial for the evaluation of applications of substances of this type in the polymer industry, in agriculture and in the production of dyes and pigments. Moreover, the investigated systems demonstrate good thermal stability, which in combination with their electrokinetic stability enables them to be considered as potential polymer fillers. Most of the prepared silica/magnesium lignosulfonate hybrid materials have a high BET surface area, which in combination with the large number of functional groups means that these materials may serve as biosorbents of hazardous metal ions and
other substances. Research currently being carried out on possible applications of the hybrid materials is very promising, and the conclusions presented here are expected to be confirmed in a further publication which is currently in preparation.
AcknowledgementsThe study was financed within the Polish National Centre of Science funds according to decision no. DEC-2013/09/B/ST8/00159.
S.A. Gundersen, J. Sjöblom, Colloid Polym. Sci. 277, 462 (1999)N.E.E. Mansouri, J. Salvado, Ind. Crop. Prod. 24, 8 (2006)A. Aoyama, R. Kurane, K. Nagai, J. Biosci. Bioeng. 115, 279 (2013)W.O.S. Doherty, P. Mousavioun, C.M. Fellows, Ind. Crop. Prod. 33, 259 (2011)J. Rencoret, G. Marques, A. Gutiérrez, L. Nieto, J. Jiménez−Barbero, A.T. Martínez, J.C. del Río, Ind. Crop. Prod. 30, 137 (2009)Ł. Klapiszewski, M. Mądrawska, T. Jesionowski, Physicochem. Probl. Miner. Process. 48, 463 (2012)Ł. Klapiszewski, M. Nowacka, G. Milczarek, T. Jesionowski, Carbohydrate Polym. 94, 345 (2013)X. Ouyang, X. Qiu, P. Chen, Colloids Surf. A 282–283, 489 (2006)S. Brudin, P. Schoenmakers, J. Sep. Sci. 33, 439 (2010)A. Rezanowich, D.A.I. Göring, J. Colloid Sci. 15, 452 (1960)W.Q. Yean, A. Rezanowich, D.A.I. Göring, Actes du Symposium International de Grenoble, pp. 327-343 (1964) (in French)D.A.I. Göring, in: K.V. Sarkanen, C.H. Ludwig (Eds.), Polymer properties of lignin and lignin derivatives (Wiley Interscience, New York, 1971)W.C. Browning, Appl. Polym. Symp. 28, 109 (1975)J.C. Le Bell, Colloids Surf. 9, 237 (1984)B.O. Myrvold, Ind. Crop. Prod. 27, 214 (2008)F. Pla, A. Robert, J. Biol. Chem. Phys. Technol. Wood 38, 37 (1984)G. Telysheva, T. Dizhbite, E. Paegle, A. Shapatin, I. Demidov, J. Appl. Polym. Sci. 82, 1013 (2001)M.V. Alonso, M. Oliet, F. Rodriguez, G. Astarloa, J.M. Echeverria, J. Appl. Polym. Sci. 94, 643 (2004)
C.I. Chiwetelu, V. Hornof, G.H. Neale, A.E. George, Can. J. Chem. Eng. 72, 534 (1994)A. Ansari, M. Pawlik, Miner. Eng. 20, 600 (2007)G. Wypych, Handbook of Fillers (ChemTec Publishing, Toronto, 2010)W. Stöber, A. Fink, E. Bohn, J. Colloid Interface Sci. 26, 62 (1968)I.A.M. Ibrahim, A.A.F. Zikry, M.A. Sharaf, J. Am. Sci. 6, 985 (2010)J. Żurawska, A. Krysztafkiewicz, T. Jesionowski, J. Chem. Technol. Biotechnol. 78, 534 (2003)T. Jesionowski, Colloids Surf. A 190, 153 (2001)T. Jesionowski, J. Mater. Process. Technol. 203, 121 (2008)Y. Qu, Y. Tian, B. Zou, J. Zhang, Y. Zheng, L. Wang, Y. Li, C. Rong, Z. Wang, Bioresource Technol. 101, 8402 (2010)Y. Kajiwara, Y. Chujo, Polym. Bull. 66, 1039 (2011)I. Hasegawa, Y.S. Fujii, K. Yamada, C. Kariya, T. Takayama, J. Appl. Polym. Sci. 73, 1321 (1999)Ł. Klapiszewski, M. Nowacka, K. Szwarc–Rzepka, T. Jesionowski, Physicochem. Probl. Miner. Process. 49, 497 (2013)T. Jesionowski, J. Żurawska, A. Krysztafkiewicz, M. Pokora, D. Waszak, W. Tylus, Appl. Surf. Sci. 205, 212 (2003)S. Lagergren, K. Sven, Vetenskapsakad. Handl. 24, 1 (1898) (in German)Y.S. Ho, G. McKay, Process Biochem. 34, 451 (1999)K. Szwarc–Rzepka, B. Marciniec, T. Jesionowski, Adsorption 19, 483 (2013)A. Moubarik, N. Grimi, N. Boussetta, A. Pizzi, Ind. Crop. Prod. 45, 296 (2013)I. Mohammed-Ziegler, A. Holmgren, W. Forsling, M. Lindberg, M. Ranheimer, Vib. Spectrosc. 36, 65 (2004)D.Z. Ye, M.H. Zhang, L. Gan, Q. Li, X. Zhang, Int. J.
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13][14][15][16]
[17]
[18]
[19]
[20][21]
[22]
[23]
[24]
[25][26]
[27]
[28][29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
734
Ł. Klapiszewski et al.
Biol. Macromol. 60, 77 (2013)R. Zhang, X. Xiao, Q. Tai, H. Huang, J. Yang, Y. Hu, High Perform. Polym. 24, 738 (2012)M. Zhou, X. Qiu, D. Yang, H. Lou, J. Dispersion Sci. Technol. 27, 851 (2006)M. Brebu, G. Cazacu, O. Chirila, Cellul. Chem. Technol. 45, 43 (2011)A. Lemes, M. Soto-Oviedo, W. Waldman, L. Innocentini-Mei, N. Durán, J. Polym. Environ. 18, 250 (2012)
S.K. Srivastava, A.K. Singh, A. Sharma, Environ. Technol. 15, 353 (1994)S. Babel, T.A. Kurniwan, J. Hazard. Mater. 97, 219 (2003)D. Mohan, C.U. Pittman, P.H. Steele, J. Colloid Interface Sci. 297, 489 (2006)X. Guo, S. Zhang, X.Q. Shan, J. Hazard. Mater. 151, 134 (2008)I. Mohammed-Ziegler, I. Tánczos, Z. Hórvölgyi, B. Agoston, Colloids Surf. A 319, 204 (2008)
