Halloysite Samples Research Articles

Effect of blunging process on purification of halloysite ore from ferrous impurities by dry magnetic separation

The objective of this research is to study the effects of feed particle size, splitter angle, and washing process on Fe<sub>2</sub>O<sub>3</sub> removal efficiency in the separation of ferrous impurities from halloysite ore by dry magnetic separation in order to increase the purity of halloysite sample after crushing and blunging processes separately. Firstly, after crushing ore in a jaw crusher and sizing to -2+1 mm, -1+0.5 mm, and -0.5+0.212 mm fractions, the sized materials were fed to REMS-type dry magnetic separator at a constant belt speed of 300 rpm with the splitter angles of 0, 15, 30º separately. Maximum Fe<sub>2</sub>O<sub>3</sub> removal efficiency (FRE) (97.1%) was obtained in the nonmagnetic product at -0.5+0.212 mm size fraction and 0º splitter angle. The minimum Fe<sub>2</sub>O<sub>3</sub> content (1.3%) was reached in the nonmagnetic product obtained in the experiment with the feed size of -2+1 mm and a splitter angle of 0º. Secondly, dry magnetic separation was applied to the washed -2+0.212 mm size fraction after drying at room temperature to evaluate the coarse particle-sized halloysite ore that was gained by mechanical dispersion in the aqueous medium towards sodium hexametaphosphate (SHMP), while a significant part of the clay minerals went into fine size after the dispersion process. In the experiment performed with a 0º splitter angle after washing, it was determined that halloysite concentrate of 0.4% Fe<sub>2</sub>O<sub>3</sub> content could be obtained with 98.8% Fe<sub>2</sub>O<sub>3</sub> removal efficiency. As a result of dry magnetic separation experiments, it was seen that Fe<sub>2</sub>O<sub>3</sub> removal efficiency decreased as the splitter angle increased, while Fe<sub>2</sub>O<sub>3</sub> content in magnetic and nonmagnetic products increased. It was determined that washing and cleaning of fine-sized minerals plastered on particle surfaces after mechanical dispersion and particle release of minerals with different magnetic properties increased the dry magnetic separation efficiency, and nonmagnetic products with very low Fe<sub>2</sub>O<sub>3</sub> (0.4%) and high Al<sub>2</sub>O<sub>3</sub> (31.9%) content was obtained. The blunging process in the presence of dispersant caused the dispersion of clay minerals and allowed to liberating of the ferrous minerals from the halloysite ore, hence the increase in the FRE for the magnetic separation.

Adsorption–desorption behavior of halloysite clay for Cu2+ ions and recovery of copper by electrodeposition method

Halloysite sample, obtained from Phu Tho province, Vietnam, was utilized to investigate the adsorption behavior of Cu2+ ions. Several factors influencing Cu2+ adsorption efficiency and capacity were explored, including pH value, contact time, adsorbent dose, and initial Cu2+ concentration. Under optimal conditions (0.8 g of halloysite per 50 mL of solution, an initial Cu2+ concentration of 40 mg/L, pH 6.2, a contact time of 80 min, and a temperature of 25 °C), the study yielded an adsorption efficiency of 85.19% and a capacity of 2.14 mg/g for Cu2+ ions. Adsorption isotherm analysis was conducted using the Langmuir and Freundlich models, while the kinetics of the adsorption process were investigated through the first-order pseudo and second-order pseudo models. Furthermore, the desorption of Cu2+ ions and the recovery of Cu metal were explored, with a recovery efficiency of Cu reaching 94.65% under suitable conditions (0.3 g mass of halloysite, a current of 7.5 mA, and an electrolytic time of 5 h at 60 °C). These findings suggest the potential application of halloysite clay for removing Cu2+ ions from polluted water, recovering Cu metal, and reusing the adsorbent.

Preparation and antimicrobial activity of silver nanoparticles impregnated with halloysite clay

In the present work, nanotubular halloysite clay was ultrasonically treated and impregnated with silver nanoparticles. The citrate surface-stabilized silver nanoparticles dispersion was prepared using an effective method of electrochemical synthesis. The elemental and phase composition, and the structure of the obtained AgNPs-impregnated and pristine halloysite were investigated by various methods such as X-ray fluorescence (XRF), powder X-ray diffraction analyses and Fourier-transform infrared spectroscopy. The Ag-loaded halloysite sample with 0.454 wt.% silver content was confirmed by the XRF analysis. The antimicrobial activity of the pristine and the AgNPs-impregnated halloysite clay was tested against Escherichia coli ATCC 25922 (Gram-negative) and Bacillus subtilis ATCC 6633 (Gram-positive) strains. The results show that pure halloysite does not exhibit antibacterial activity. The AgNPs-impregnated halloysite demonstrates antibacterial activity against Escherichia coli and Bacillus subtilis with only bacteriostatic effect.

Mineralogical Characterization of Pegmatites with Occurrences of Halloysite in the Regions of Porciúncula (RJ) and Patrocínio do Muriaé (MG), Southeastern Brazil

Halloysite (Al2Si2O5(OH)4.2H2O) is a polymorphic kaolinite mineral whose predominant morphology is tubular. Due to this characteristic, halloysite is widely used in industrial applications, such as manufacture of silica- luminous catalysts, used for industrial chemical reactions; French porcelain; and the cracking of petroleum fractions into gasoline. Halloysite also has potential as a nanomaterial, particularly as an ingredient in polymer nanocomposites and as active agent for medical, agricultural, and other uses. This clay mineral occurs in a wide variety of geological environments as a product of alteration of rocks rich in sodium and potassium feldspars, such as intrusive acid rocks, granites, anorthosites, and pegmatites. This article characterizes halloysite and describes the treating process of kaolin- halloysite samples from four pegmatites, located in Porciúncula (Rio de Janeiro State) and Patrocínio do Muriaé (Minas Gerais State). The samples of the studied pegmatites were treated for mineralogical characterization and analyzed by X-ray diffractometry and scanning electron microscopy. Density, granulometry, and visual appearance of the grains were also analyzed. The samples were found to be composed of kaolinite/halloysite, feldspar, quartz, biotite, goethite and muscovite. Using X-ray diffractometry, gibbsite were also identified in one sample. With the results presented here, the two regions can be possible targets for researching halloysite deposits in the states of Rio de Janeiro and Minas Gerais.

Comparing the ice nucleation properties of the kaolin minerals kaolinite and halloysite

Abstract. Heterogeneous ice nucleation on dust particles in the atmosphere is a key mechanism for ice formation in clouds. However, the conditions of a particle surface for efficient ice nucleation are poorly understood. In this study, we present results of immersion freezing experiments using differential scanning calorimetry on emulsified mineral dust suspensions, involving the two chemically identical, but morphologically different, kaolin minerals of kaolinite and halloysite. Kaolinite occurs in a platy morphology, while halloysites form predominantly tubular structures. We investigated six different halloysite and two different kaolinite samples. Our results show that, on average, the halloysite samples not only exhibit a higher ice nucleation (IN) activity than the kaolinite samples but also a higher diversity in terms of freezing onset temperatures and heterogeneously frozen fraction. Repeating the freezing experiments after shortly milling the samples led to a decrease in freezing onset temperatures and in the heterogeneously frozen fraction of the halloysite samples, bringing their IN activity closer to that of the kaolinites. To interpret these findings, the freezing experiments were complemented by dynamic vapor sorption (DVS), BET (Brunauer–Emmett–Teller) surface area measurements, pore ice melting experiments with slurries, and transmission electron microscopy (TEM) before and after milling. These measurements demonstrate an increase in surface area and the destruction of tubes by milling and provide evidence for the influence of the tubular structure of the halloysites on their IN activity. We identify the OH–Al–O–Si–OH functionalized edges as being the most likely site for ice nucleation, as the high geometric diversity of the edges best accounts for the high diversity in IN activity of halloysites. We hypothesize that the stacking of layers and the number of stacks in halloysite tubes and kaolinite platelets affect the freezing temperature, with thicker stacks having the potential to freeze water at higher temperatures. The notion that the edges constitute the IN-active part of kaolin minerals is further supported by comparing kaolin minerals with montmorillonites and feldspars, all of which exhibit enhanced IN activity in the presence of ammonia and ammonium-containing solutions. As OH–Al–O–Si–OH functionalized edge surfaces are the only surface type that kaolin particles have in common with montmorillonites and feldspars, the common feature of IN activity enhancement in ammoniated solutions can only be explained by ice nucleation occurring at the edges of kaolin minerals.

Tunable polycationic organohalloysite electrocatalyst: Synthesis and characterisation

Methylamine and 1,4-butanediol diglycidyl ether were used as monomers, in a sequential manner, to build from the surface of an aminosilane-grafted halloysite a quaternary ammonium polyelectrocatalyst. The as obtained material was characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption/desorption isotherms (BET method), elemental analysis (EA), Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). XRD analysis showed that the pristine halloysite was in a partial dehydrated state with a d001 value of 0.74 nm. Not only was the success of the grafting process ascertained but also the tubular nature of the used halloysite sample as seen on the SEM micrographs. The significant increase in the d value of the modified clay (H-polyQ22) suggested interlayer grafting. FTIR results showed that grafting was through OH groups, certainly interlayer, lumen and edge aluminol groups as well as defect site silanol groups. The electron transfer enhancing properties of the prepared polyelectrolyte were investigated by electrochemical impedance spectroscopy (EIS). The charge transfer resistance dropped significantly when H-polyQ22 was used as electrode modifier. The electrocatalytic behaviour of the H-polyQ22 modified electrode was further investigated using [Fe (CN)6]3− as anionic target. The halloysite polymer nanocomposite proved to be a good candidate for electrocatalysis.

Cordierite-based refractory ceramics from natural halloysite and peridotite: Insights on technological properties

Cordierite-based ceramics were fabricated from Moroccan natural halloysite clay by using a simple and low-cost manufacturing method. To this end, peridotite and halloysite samples, collected from Beni Bousera and Melilla sites, Morocco, were used as raw materials for ceramics manufacturing. A starting mixture was prepared (76.08 wt% of clay and 23.92 wt% of peridotite), molded and heated to the desired temperature (1250, 1300 and 1350 °C) to fabricate cordierite ceramic specimens. Both raw materials (peridotite and halloysite) and final ceramics were analyzed using routine characterization techniques including chemical analysis by XRF, mineralogical analysis by XRD, thermogravimetric analysis, and morphological characteristics using scanning electron microscopy (SEM). The prepared ceramics were investigated regarding their mineralogical composition, thermal and technological properties, chemical resistance, and microstructural characteristics. Our results indicated that peridotite sample is mainly composed of silica (40.25 wt%) and magnesia (38.05 wt%) while halloysite is consisted essentially of silica (38.00 wt%) and alumina (34.13 wt%). This was confirmed by XRD, TG-DTA and FTIR analyses. The prepared ceramic specimens at different sintering temperatures (i.e., 1250, 1300 and 1350 °C) have regular cylindrical forms, displaying good ceramic properties. This is consolidated with the main technological tests including porosity (4.56–3.11%), bulk density (2.45–2.78 g/cm3), shrinkage (6.51–10.31%), indirect tensile strength (20.35–27.60 MPa), and low linear thermal expansion coefficient (3.05–2.18 × 10−6/°C). Cordierite specimen prepared at 1350 °C provided the best ceramic sample with the highest technological properties, good chemical resistance and thermal properties. Thus, naturally abundant halloysite and peridotite deposits are potential candidates for cordierite-based ceramic manufacture. Therefore, the achieved results have provided cost-effective ceramic bricks with physical, thermal and mechanical properties that are favorable to be used as refractory bricks.

Separation of halloysite/kaolinite mixtures in water controlled by sucrose addition: The influence of the attractive forces on the sedimentation behavior

In this work, we propose an easy strategy for the separation of halloysite/kaolinite mixtures in sucrose aqueous solution. Preliminarily, we investigated the influence of the sucrose addition on the colloidal stability of kaolinite nanoplates and halloysite nanotubes (HNTs) dispersed in water. Dynamic Light Scattering (DLS) measurements revealed that the HNTs aqueous mobility is dependent on the sucrose concentration, while the ζ-potential is negligibly affected by the addition of the carbohydrate in the aqueous solvent. On the other hand, any variations on the surface charge and dynamic behavior of kaolinite were detected in the presence of sucrose. The obtained ζ-potential and DLS results were useful to interpret the sedimentation kinetics of kaolinite and halloysite dispersions. In particular, the peculiar sedimentation behavior of halloysite were discussed by considering the screening effect of sucrose on the attractive interactions between the nanotubes. The latter was evaluated by the calculation of the corresponding Hamaker constants. On this basis, we estimated that the optimization of the separation between kaolinite and halloysite might be achieved in 10 wt% sucrose aqueous solution. This hypothesis was confirmed by the separation experiments, which exploited the different sedimentation behavior of halloysite and kaolinite. Thermogravimetric experiments on the separated material and kaolinite/halloysite composites with variable composition allowed us to determine the efficiency of the separation protocol. To this purpose, the differential thermogravimetric curves were accurately analysed by using split Gaussian functions. In conclusion, this paper represents a further step in the purification of natural halloysite samples exploiting the ability of sucrose to control the attractive forces of the clay nanotubes as well as the colloidal stability of kaolinite nanoplates in aqueous solvent.

Compositional, structural, and surface characterization of heat-treated halloysite samples: Influence of surface treatment on photochemical activity

Quasi-homogeneous nanoparticulate halloysite clay with layered scroll morphology is an ideal material for photochemical activity due to the lack of interference from Fe contaminants and mixed mineral phases. In this work, halloysite was used as a model system for studying the influence of compositional defect sites on the structure and photochemical activity as a result of thermal modifications in the range of 400–480 °C and with 30–180 min exposure. The change in the Al-coordination environment was studied by 27Al, 1H magic-angle spinning (MAS) and cross-polarization (CP)/MAS nuclear magnetic resonance (NMR), and infrared (IR) spectroscopic techniques. The structural and morphological changes were followed by powder X-ray diffraction (XRD) and transmission electron microscope (TEM) techniques. Pore structure description was obtained from nitrogen gas adsorption measurements. The amount of residual hydroxide groups was determined by thermogravimetric analysis (TGA). Temperature-controlled desorption (TPD) and 1H MAS NMR techniques were used for the characterization of acid-base properties of thermally created defect sites. These defect sites showed a decrease in Al-coordination number and an increase in the number of acidic sites. However, evidence for the formation of basic sites during long exposure experiments can be seen, which emphasises the impact of the duration of the heat treatment. The emergence of acidic sites was correlated with the increase in photochemical activity. A significantly different photochemical activity was found for thermally treated halloysite than expected from the semiconductor-type photocatalysis model on the basis of the number of hydroxyl radicals generated as a function of the irradiation time.

Adsorption of Lysozyme on Silica and Aluminosilicate Adsorbents

A study is performed of the adsorption of lysozyme on biporous silica, silicalite-1 (silica with the structure of MFI zeolite), ZSM-5 zeolite, and two halloysite samples (natural aluminosilicate nanotubes). Adsorption isotherms are obtained, and the limiting values of adsorption and the areas on surfaces of the adsorbent per enzyme molecule are found. The maximum adsorption per unit of adsorbent mass (350 mg/g) is obtained for biporous silica along with the one per unit of surface area (0.962 mg/m2) on halloysite.

Ca treated Palygorskite and Halloysite clay minerals for Ferrous Iron (Fe+2) removal from water systems

Abstract Palygorskite fibers and halloysite nanotubes (HNT) were used for the Fe (II) uptake from aqueous solutions under various experimental conditions. Palygorskite and halloysite samples were characterized using XRD, FTIR, SEM, BET and CEC and then were saturated by exchanging Ca + 2 cations. The Ca-Palygorskite (Ca-Pal) and Ca-Halloysite (Ca-Hall) were characterized as well, and applied in batch kinetic experiments series. It was shown that both Ca-treated clay minerals were more efficient adsorbents for the lowest ferrous concentrations removal (5 mg/L), especially when the highest solid: liquid ratio (20 g/L) have been applied, reaching 99.8% and 91.2% removal with Ca-Pal and Ca-Hall respectively, within 10 min at the optimal room temperature (20 ± 1 °C). The pH value affected the adsorption’s efficiency, as Ca-Pal was more efficient adsorbent at acidic values (4–6), while Ca-Hall efficiency is positively correlated with pH increase (7 ). Moreover, the competitive ions found to prohibit Ca-Hall capacity for Fe (II), following the order Mn K Cu Zn Ba Mg Na, but Ca-Pal is slightly affected by K Na=Mn Zn Cu Mg Ba, highlighting its preference to a Fe cations. According to the thermodynamic analysis the Fe (II) uptake is a physical and spontaneous process, while both Ca-Pal and Ca-Hall fit in Langmuir isotherm instead of Freundlich, indicating monolayer sorption. The exact mechanism of Ca-Pal efficient adsorption was verified and further explained with molecular simulation optimization by Material Studio 4.3.

Adsorption of iodate on nanosized tubular halloysite

Naturally occurring porous minerals as adsorbents for the remediation of environmental pollution has been one of the hot topics in environmental science and material science. In this study, the adsorption of iodate (IO3−) on two nanosized tubular halloysite samples (HBHal and SCHal, from Hubei and Sichuan Province, China, respectively) were investigated for the first time. To evaluate the impact of nanopore of halloysite on the adsorption of IO3−, chemically similar platy kaolinite was used for comparative studies in the batch experiments. The adsorption of IO3− on HBHal reached equilibrium within 36 h, and the adsorption kinetics and isotherm fitted the pseudo-second-order and Langmuir equation well, respectively. Both HBHal and SCHal exhibited high adsorption capability to IO3−, with distribution coefficients (Kd's) of 131.6 ± 14.6 and 126.6 ± 3.1 mL/g, respectively, which were >30 times higher than that for kaolinite (4.2 ± 2.3 mL/g). The specific surface area normalized Kd values on halloysite samples were >13.5-fold higher than that on kaolinite. In addition, halloysite had high selectivity to IO3−, and the adsorption capacities on the two halloysite samples were slightly affected by the concurrent anions, such as SO42−, NO3−, or ClO3−. It was proposed that the curved octahedral sheet caused geometry match between three oxygen atoms in the iodate and three OH above the vacant site of the octahedral sheet. This work also gave insight into the potential application of halloysite on the adsorption of radioactive iodate in natural and engineering environments.

Dispersion and diffusivity of halloysite and bentonite nanoclays in aqueous Pb (II): Effect of particle concentration, temperature, and pH

This study investigates the influence of particle concentration, temperature, and pH to the dispersion properties and diffusivity of nanoparticles – halloysite and bentonite nanoclays in water, with and without the presence of lead (II) ions. Light scattering analyses were conducted to observe the changes on hydrodynamic radius, zeta potential, and diffusion coefficient of the nanoparticles. Results showed that with the increase of particle concentration and as pH increases, the average hydrodynamic radii for the two nanoclays seems to decrease, and were much smaller in the presence of Pb (II) ions. Conversely, the size of the nanoparticles appears to increase as temperature increases for the halloysite sample while the opposite was found for the bentonite dispersion. Sizes increase and decrease even more upon Pb (II) additions for the halloysite and bentonite dispersions respectively. In terms of zeta potential, both lead-free nanoparticles showed a more negative surface net charge as concentration and pH increases indicating an improvement in suspension stability. This was not the case with respect to temperature changes where halloysite dispersions become more unstable. Pb (II)–bentonite samples on the other hand exhibit a rather unpredictable trend in the zeta potential as the temperature increases but were both more stable than pure bentonite. Lastly, the diffusion coefficients were obtained and data suggest that temperature has the highest influence among all parameters while the addition of Pb (II) ions increases the overall diffusivities except for low-zeta potential dispersions.

Silanization of heat-treated halloysite nanotubes using γ-aminopropyltriethoxysilane

By X-ray diffraction, thermal analysis, diffuse reflectance infrared spectrometry, solid state nuclear magnetic resonance (1H and 29Si), and transmission/high-resolution transmission electron microscopy, silanization of heat-treated halloysite samples (300–1200 °C calcination) using γ-aminopropyltriethoxysilane through condensation reaction was investigated. Driven by calcining at higher temperatures, the crystalline structure of halloysite transformed to metahalloysite (500–900 °C), mixed phases of γ-alumina, silica, and primary mullite (~1000 °C, accompanied by an exothermic reaction), and secondary mullite (1200 °C), sequentially; while the lower calcination temperature 300 °C failed to change the crystalline structure except for dehydrating surface moisture. In the calcining processes, the tubular morphology of halloysite remained largely unchanged in the range 300–900 °C with additional surface mottling at temperatures ≥600 °C, but got damaged at higher temperatures ≥1000 °C. For the still tubular-shaped calcined samples, the hydroxyl distribution of the 300 °C-calcined sample was similar to that of raw halloysite; while for other samples from 600 to 900 °C calcination, the inner-surface Al-OH groups gradually decreased until completely diminished, and the external surface Si-OH groups reached maximum at 700 °C with decreasing trends as the temperature deviated from 700 °C. The 700 °C-calcined sample with maximum Si-OH groups acting as reactive sites was thus optimal for silanization, giving the highest silane loading of 5.87 mass %, which would depend on the main modification sites at the tube external surface without strict space limitation, and the unignorable oligomerization reaction of silane species besides their grafting reaction in this case. These results would be very helpful for surface properties optimization of halloysite nanotubes by heat-activation followed by silane modification, and hence for the development of halloysite-based advanced materials.

Adsorption of diastase over natural halloysite nanotubes (HNTs)

Adsorption of diastase over natural halloysite nanotubes is studied in order to evaluate the adsorption capacity of diastase. The halloysite surface characteristics were assessed using nitrogen adsorption, x-ray diffraction (XRD), thermal gravimetric analysis (TGA) and Fourier transformed infrared (FTIR). The surface area of the natural halloysite is found to be 51 m2·g-1, with total pore volume of 0.106 cm3·g-1. The natural halloysite has a basal spacing (d001) of 10 Å confirming the structure of the natural halloysite material. TGA results indicated that halloysite loses its interlayer water in the range of 30 to 105 °C and the dehydration in the structural layer above 150 °C. The dehydroxylation of halloysite has occurred at approximately 460 °C. The FTIR result of the thermally treated halloysite sample indicated that the bands observed are assigned to Si-O and Al-O bonds. The effects of solution pH and temperature were studied on the adsorption capacity and percent removal of diastase from the solution. The adsorption kinetic found to fit well with both the Pseudo first-order and Pseudo second-order models, and the values of the kinetic constant were found to be 0.173 min-1 and 0.00018 g·mg-1·min-1 respectively. The Langmuir isotherm model is found to fit well to the adsorption data and a kinetic value is found to be 0.00059 m3·g-1. The maximum adsorption capacity was found to be 370 mg·g-1, indicating the potential for applications of the natural nanostructured halloysite material as an effective adsorbent for diastase.

Thermal behavior analysis of halloysite selected from Inner Mongolia Autonomous Region in China

Thermal behavior of halloysite selected from Erdos, Inner Mongolia Autonomous Region in China, was investigated by thermogravimetry and differential thermal gravity (TG–DTG), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscope (SEM). The XRD results indicated that the mineralogical composition of halloysite sample was determined as 7 A halloysite with the d (001) value of 0.734 nm, a small amount of 10 A halloysite with the d (001) value of 0.998 nm, quartz, calcite, anhydrite, siderite, and analcite. The crystal chemical formula of halloysite specimen is (Ca0.007Na0.039K0.048)(Al1.935Fe 0.032 3+ Mn 0.003 2+ Ti 0.002 4+ Mg 0.015 2+ Ca 0.021 2+ )2 [(Si1.935Al 0.065 3+ )2](OH)4·2H2O according to the oxygen atom method. The TG–DTG–DSC data showed that a small amount of water molecule layer in the interlayer and the dehydroxylation was observed at 493.6 °C. The XRD, FT-IR, and SEM data clearly show that the structure changes and dehydroxylation of the halloysite with the temperature increased from 200 to 1200 °C. The dehydration of the halloysite is followed by the loss of intensity and evolution of the OH vibration bands and the change in microstructure. Dehydroxylation is followed by the decrease in the intensity of the bands at 3696 and 3620 cm−1, which is completely disappeared at 700 °C. The thermal behavior of halloysite was influenced by the mineralogy composition and impurities.

Halloysite nanotubes as carriers of vancomycin in alginate-based wound dressing

The influence of an inorganic support – halloysite nanotubes – on the release rate and biological activity of the antibiotic encapsulated in alginate-based dressings was studied. The halloysite samples were loaded with approx. 10wt.% of the antibiotic and then encapsulated in Alginate and Gelatin/Alginate gels. The material functionalized with aliphatic amine significantly extended the release of vancomycin from alginate-based gels as compared to that achieved when silica was used. After 24h, the released amounts of the antibiotic immobilized at silica reached 70%, while for the drug immobilized at halloysite the released amount of vancomycin reached 44% for Alginate discs. The addition of gelatin resulted in even more prolonged sustained release of the drug. The antibiotic was released from the system with a double barrier with Higuchi kinetic model and Fickian diffusion mechanism. Only the immobilized drug encapsulated in Alginate gel demonstrated very good antimicrobial activity against various bacteria. The inhibition zones were greater than those of the standard discs for the staphylococci and enterococci bacteria tested. The addition of gelatin adversely affected the biological activity of the system. The inhibition zones were smaller than those of the reference samples. A reduction in the drug dose by half had no significant effect on changing the release rate and microbiological activity. The in vivo toxicity studies of the material with immobilized drug were carried out with Acutodesmus acuminatus and Daphnia magna. The material studied had no effect on the living organisms used in the bioassays. The proposed system with a double barrier demonstrated high storage stability.

Effect of pH on the cation exchange capacity of some halloysite nanotubes

AbstractThe cation exchange capacity (CEC) of seven well characterized halloysite nanotubes (HNTs) in the dehydrated 7 Å form has been measured using a method based on cobalt hexammine exchange. In addition to unbuffered measurements, which varied between 2.9 and 9.3 cmol(+)kg−1, CECs were also determined over a wide pH range and proton titration measurements were conducted on two samples. The data were fitted using a constant capacitance model based on the presence of two sites: permanently charged sites and pH-dependent variable charged sites. Normalization of CEC to the average specific surface area (BET) of the halloysite samples reduces considerably the variation of CEC values for the different samples particularly over the intermediate pH range (5–9) with the average value at pH 7 equal to 8.5 cmol(+)kg−1and a standard deviation of 1.17. Overall the CEC behaviour of the seven samples appears reasonably consistent throughout the set. Calculations based on proton titrations suggest a ratio of variable charge to basal sites for the dehydrated halloysite nanotubes of ∼3:1.

Carbon dioxide sorption on EDTA modified halloysite

In this paper the sorption study of CO2 on EDTA surface modified halloysite was conducted. In the paper chemical modification of halloysite from the Dunino deposit (Poland) and its influence on sorption of CO2 are presented. A halloysite samples were washed with water-EDTA 1% solution, centrifuged to separate liquid and impurities and dried. The samples were tested for the sorption capacity using a manometric method with pressure up to 3 MPa. A Langmuir adsorption model was fitted to the data. The results showed that EDTA had a limited effect on the increase of sorption potential at low pressure and the samples exhibited similar results to that ones treated solely with the water solution.

Trichlorophenol removal from aqueous solutions by modified halloysite: kinetic and equilibrium studies

To obtain new materials, we modified Algerian halloysite by thermal activation (HalC), acid activation (HalA), combined thermal-acid activation (HalCA) and acid-thermal activation. X-ray diffraction, Fourier Transform infrared and BET textural analysis were used to characterize changes. After the HalC of halloysite at 600°C, no XRD peaks were shown and a total disappearance of the absorption bands ranging from 3,700 to 3,600 cm−1. The treatment of halloysite by sulphuric acid increases the surface area from 185.4 to 321.0 m2/g. Halloysite is first calcined and then activated by acid, its surface area increases from 74.3 to 538.6 m2/g. The effect of initial pH, adsorbent dose, contact time and temperature on the removal of 2,4,5-trichlorophenol (TCP) by modified halloysite samples was investigated. Equilibrium data were fitted to the Langmuir, Freundlich and Toth models. The best fit of the cited models was the Freundlich model, which suggested infinite adsorption onto heterogeneous surface. The pseudo-first-order, pseudo-second-order and intraparticle diffusion models were applied to the experimental kinetic data. The results showed that the pseudo-second-order is the best model to describe the process. The study of thermodynamic parameters shows that the process of adsorption of TCP onto the prepared samples was spontaneous, endothermic and physical in nature.