Jakub Matusik

THE EFFECT OF STRUCTURAL ORDER ON NANOTUBES DERIVED FROM KAOLIN-GROUP MINERALS

Kaolin-group clay minerals can be modified to form nanotubular and mesoporous structures with interesting catalytic properties, but knowledge of the best methods for preparing these structures is still incomplete. The objective of this study was to investigate intercalation/deintercalation as a method for the delamination and rolling of kaolinite layers in relation to structural order. To prepare nanotubular material, kaolinites of different crystallinities and halloysite (all from Polish deposits) were chosen. The experimental procedure consisted of four stages: (1) preparation of a dimethyl sulfoxide precursor intercalate; (2) interlayer grafting with 1,3-butanediol; (3) hexylamine intercalation; and (4) deintercalation of amine-intercalated minerals using toluene as the solvent. Structural perturbations and changes in the morphology of the minerals were examined by X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and transmission electron microscopy (TEM). The number of rolled kaolinite layers depended heavily on the efficiency of the intercalation steps. An increase in the structural disorder and extensive delamination of the minerals subjected to chemical treatment were recorded. Kaolinite particles which exhibited tubular morphology or showed rolling effects were observed using TEM. The nanotubes formed were ∼30 nm in diameter, with their length depending on the particle sizes of the minerals.

Immobilization and reduction of hexavalent chromium in the interlayer space of positively charged kaolinites.

This work was designed to investigate the sorption equilibrium and kinetics of modified kaolinites of different structural order toward Cr(VI). The key reaction of modification involved an iodomethane quaternization of the mineral previously interlayer grafted with triethanolamine. This induced positively charged centers (PCNs) associated with nitrogens of ammonium salt molecules formed in the interlayer space. The positive charge was compensated by mobile iodide anions which could be ion-exchanged. Results reveal a significant increase in sorption capacity as compared to raw kaolinites and show that the sorption takes place exclusively in the interlayer space which proved to be accessible for the Cr(VI). The amount of sorbed Cr(VI) depends on the PCN content resulting from the kaolinites reactivity influenced by their structural order. An ion-exchange mechanism followed by Cr(VI) to Cr(III) reduction by iodide is proposed. The amount of initially sorbed Cr(VI) and its anionic form is strongly influenced by the pH. Desorption experiments showed that only the Cr(VI) which was not reduced (~30%) was released to the solution.

INFLUENCE OF SYNTHESIS CONDITIONS ON THE FORMATION OF A KAOLINITE-METHANOL COMPLEX AND SIMULATION OF ITS VIBRATIONAL SPECTRA

Kaolinite is often used as a base for the synthesis of new organo-mineral nanomaterials designed for applications in industry and in environmental protection. To make the mineral structure more likely to interact with organic molecules, a kaolinite-methanol complex (KM) can be used. In the present study, different experimental procedures were tested to investigate the formation of the KM. The kaolinitedimethyl sulfoxide intercalation compound (KDS), either wet or dried, was used as a pre-intercalate. The samples obtained were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, CHNS elemental analysis, 13C CP-magic angle spinning nuclear magnetic resonance (MAS NMR), and 27Al and 29Si MAS NMR techniques. The method of density functional theory with dispersion corrections (DFT-D2) was used to explain the structure and to simulate the vibrational spectra of KM. Theoretical results were compared with experimental data. The most effective formation of the KM (d001 = 11.1 Å — wet; d001 = 8.7 Å — dried) was observed when the dried KDS precursor was used. In such conditions the degree of intercalation reached ~98% after 24 h of reaction time. As indicated by the CHNS elemental analysis, ~1/6 of the inner-surface OH groups were grafted by OCH3 groups. The esterification reaction was less efficient at higher temperatures or when wet KDS was used. In the latter case, the excess of very polar dimethyl sulfoxide molecules prevented intercalation of methanol and further grafting. Detailed analysis of the results of theoretical simulations revealed that the reaction of the KDS with methanol led to the formation of kaolinite with both grafted methoxy groups and intercalated methanol, and water molecules in the interlayer space. The spectra calculated revealed the contribution of individual vibrational modes into the complex bands, i.e. the energy of C-H vibrations was in the order: νasCHmet > νasCHmtx > νsCHmet > νsCHmtx.

SURFACE AREA AND POROSITY OF NANOTUBES OBTAINED FROM KAOLIN MINERALS OF DIFFERENT STRUCTURAL ORDER

Mesoporous materials with pore diameters in the range 2–50 nm forming tubular or fibrous structures are of great interest due to their unique properties. Because they are commonly used as sorbents and catalyst carriers, knowledge of their surface area and porosity is critical. A modified intercalation/deintercalation method was used to increase the efficiency of nanotube formation from kaolin-group minerals which differ in terms of their degree of structural order. Unlike previous experiments, in the procedure adopted in the present study, methanol was used instead of 1,3-butanediol for grafting reactions and octadecylamine intercalation was also performed. The samples were examined using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The specific surface area and porosity of previously described and newly formed materials were investigated by N2 adsorption/desorption. Compared to results described earlier, the percent yield of nanotubes obtained in the present study was significantly greater only in the case of ‘Maria III’ kaolinite, which has high structural order. This increase was obtained mainly by the grafting reaction with methanol. Highly ordered stacking of kaolinite-methanol intercalates was noticed and, thus, the amine intercalation was more efficient. In particular, the use of long-chain octadecylamine significantly increased the nanotube yield. The grafting reaction with methanol procedure yielded fewer nanotubes, however, when applied to poorly ordered samples (‘Jaroszów’ kaolinite and ‘Dunino’ halloysite). In the case of the ‘Maria III’ kaolinite, the diameter of the rolled layers observed by TEM was ~30 nm and corresponded to average diameters of newly formed pores (DmN) determined using N2 adsorption/desorption, confirming that nanotubes contributed to an increase in surface area and total pore volume. In the case of ‘Jaroszów’ kaolinite and ‘Dunino’ halloysite mainly macropores (DmN > 100 nm) and mesopores (20 nm > DmN > 40 nm) were formed. The pores were attributed to interparticle and interaggregate spaces in the stacks of platy particles and to the small relative number of nanotubes.

Di- and triethanolamine grafted kaolinites of different structural order as adsorbents of heavy metals.

Efficient sorbents based on widely available clay minerals are of particular value in the field of pollution control. The research shows mineral-based sorbents formed through organic modification of two kaolinites differing in structural order. Their structure and texture was characterized by XRD, FTIR, DTA/TG, CHN, XPS and N2 adsorption/desorption methods. The obtained materials were tested as adsorbents of Cd(II), Zn(II), Pb(II) and Cu(II) in equilibrium and kinetic experiments. Moreover, the sorption mechanisms were subjected to investigation. The synthesis procedure involved interlayer grafting of kaolinites with diethanolamine (DEA) and triethanolamine (TEA). The organo-kaolinites showed resistance to hydrolysis and temperature up to ∼300 °C. The adsorption improvement was observed for the modified materials, particular the DEA derivatives and materials based on the poorly ordered kaolinite. The XPS analyses of elements local environment coupled with binding strength tests enabled to confirm the immobilization mechanisms. The pure kaolinites removed metal ions through either the ion-exchange or the surface complexation, exclusively on the external surfaces. In turn, the grafted materials additionally immobilized ions in the interlayer space which was expanded. The ions were attracted by the grafted DEA or TEA, which are N and O-donors and readily form complexes with metals, particularly with the Cu(II).

The effect of acid activation and calcination of halloysite on the efficiency and selectivity of Pb(II), Cd(II), Zn(II) and As(V) uptake

Abstract The present study investigated the efficiency and mechanisms of aqueous Pb(II), Cd(II), Zn(II) and As(V) adsorption on natural (H), calcined (HC), and acid-activated halloysite (HA). The XRD and FTIR measurements indicated that the aluminosilicate framework was not affected by high-temperature treatment, in contrast to acid activation, which led to structural changes mainly in the tetrahedral sheet. The sorption of cations on H sample was low, though it was most effective for As(V). The X-ray photoelectron spectroscopy results suggested that removal of As(V) might be related to its reduction to As(III) involving oxidation of Fe(II) present in the mineral structure and/or iron minerals. The calcination enhanced halloysite sorption capacity for cations, while the As(V) sorption decreased. This was due to partial dehydroxylation and the subsequent formation of additional active sites. The acid treatment induced selective adsorption of Pb(II).

Co-remediation of Ni-contaminated soil by halloysite and Indian mustard (Brassica juncea L.)

Abstract The effects of increasing nickel contamination of soil on the update of selected microelements by Brassica juncea L. in the presence of raw halloysite (RH) and halloysite modified by thermal treatment (calcination) at 650°C (MH) were investigated experimentally. Such treatment causes partial dehydroxylation and enhances mineral-adsorption properties towards cations. In a vegetative-pot experiment, four different levels of Ni contamination, i.e. 0 (control), 80, 160, 240 and 320 mg kg-1 were applied in the form of an analytical-grade NiSO4·7H2O solution mixed thoroughly with the soil. Among the minerals which were added to soil to alleviate the negative impact of Ni on plant biomass, MH had a particularly beneficial effect on the growth of B. juncea L. The amount of Ni, Zn, Cu, Mn, Pb and Cr in Indian mustard depended on the Ni dose and type of accompanying mineral structure. The average accumulation of trace elements in B. juncea L. grown in Ni-contaminated soil follow the decreasing order Mn > Zn > Cu > Ni > Pb > Cr.

Halloysite for Adsorption and Pollution Remediation

Abstract The disordered aluminium silicate structure, with numerous adsorption centres and a unique nanotubular morphology, makes halloysite a promising adsorbent. The continuous increase of interest in halloysite use for remediation results from a constant development of nanotechnology and research into naturally occurring nanomaterials. This clay mineral is especially attractive due to its low cost of production compared to other mineral and nonmineral adsorbents. Moreover, its chemical properties make it inert for the environment. The halloysite structure is susceptible for modification involving multistep intercalation, interlayer grafting reactions or both. The appropriate selection of introduced organic molecules enables to design and synthesize halloysite-based hybrids with adsorption functionalities targeted towards individual contaminants (eg, polar/apolar or positively/negatively charged). This chapter summarizes the studies showing the use of pure and modified halloysite for the removal of selected inorganic and organic pollutants.

Halloysite Composites with Fe3O4Particles: The Effect of Impregnation on the Removal of Aqueous Cd(II) And Pb(II)

Abstract In this study, halloysite-Fe3O4composites were synthesized by a chemical-precipitation method to facilitate magnetic separation of the sorbents from aqueous solution. The research focused on the effect of Fe3O4phase on the halloysite sorption properties. The X-ray diffraction (XRD) results confirmed successful deposition of Fe3O4particles on a halloysite surface. They showed that the coating with Fe3O4particles enhanced the halloysite adsorption affinity toward Cd(II) and Pb(II). The highest adsorption capacity was determined for the composites having 10% of the surface deposited with Fe3O4. In this case, the adsorption capacity for Cd(II) and Pb(II) was 33 and 112 mmol·kg-1, respectively. The point of zero charge (pHPZC) and desorption results indicated that the removal mechanism of metals is mainly related to chemisorption involving reaction with hydroxyls of either halloysite or Fe3O4phase. The ion exchange is of limited importance due to the low cation exchange capacity (CEC) of halloysite - Fe3O4composites.

Halloysite-like Structure via Delamination of Kaolinite

Abstract A nanotubular morphology of particles with accessible and functionalised lumen is of high demand in several applications, including catalysis, selective adsorption and drug delivery. However, the natural deposits of tubular halloysite are rather unique and the resources are relatively low. In turn, the deposits of kaolinite, which exhibits platy morphology, are widespread and commonly exploited. New methods are being developed in order to synthesise different nanotubes starting from various materials, including kaolinite. The theoretical and experimental research that has been conducted shows the possibility of 1:1 layer rolling, which could be induced by weakening interlayer hydrogen bonds through grafting, intercalation and deintercalation processes. This chapter summarises the current state of knowledge of synthetic routes that lead to transformation of platy kaolinite to halloysite-like nanotubes without destroying the initial aluminium silicate structure. The described techniques include one-step and two-step intercalation and deintercalation procedures, as well as polymer-induced exfoliation/delamination and subsequent layer rolling.