Unmodified Halloysite Research Articles

Modified Halloysite as an Adsorbent for the Removal of Cu(II) Ions and Reactive Red 120 Dye from Aqueous Solutions.

The adsorption of copper ions and Reactive Red 120 azo dye (RR-120) as models of water pollutants on unmodified halloysite (H-NM), as well as halloysites modified with sulfuric acid (H-SA) and (3-aminopropyl)triethoxysilane (H-APTES), was investigated. The results showed that adsorption of both the adsorbates was pH-dependent and increased with the increase in halloysite dosage. The adsorption kinetics were evaluated and the results demonstrated that the adsorption followed the pseudo-second-order model. The adsorption isotherms of Cu(II) ions and RR-120 dye on the halloysites were described satisfactorily by the Langmuir model. The maximum adsorption capacities for the Cu(II) ions were 0.169, 0.236, and 0.507 mmol/g, respectively, for H-NM, H-SA, and H-APTES indicating that the NH2-functionalization rather than the surface area of the adsorbents was responsible for the enhanced adsorption. The adsorption capacities for RR-120 dye were found to be 9.64 μmol/g for H-NM, 75.76 μmol/g for H-SA, and 29.33 μmol/g for H-APTES. The results demonstrated that APTES-functionalization and sulfuric acid activation are promising modifications, and both modified halloysites have good application potential for heavy metals as well as for azo dye removal.

Manufacturing and compatibilization of binary blends of polyethylene and poly(bulylene succinate) by injection molding

<p class="JARTEAbstract">In this study was analyzed the effect of three different compatibilizers polyethylene-graft-maleic anhydride (PE-g-MA), unmodified halloysite nanotubes (HNTs), and HNTs treated by silanization with (3-glycidyloxypropyl) trimethoxysilane (GLYMO) (silanized HNTs) in blends of bio-based high-density polyethylene (bioPE) and poly(butylene succinate) (PBS) with a weight ratio of (70/30). Each compatibilizer was added in a proportion of (3 phr regarding PBS). Standard samples were obtained by extrusion and subsequent injection molding. The analyzes of the samples were performed by mechanical tests, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), field emission scanning electron microscopy (FESEM), and wettability (θ<sub>w</sub>). Results suggest that the addition of modified HNTs (silanized HNTs) allowed to obtain better properties than samples compatibilized with unmodified HNTs and PE-g-MA, due to it contributes with the improvement in mechanical properties regarding bioPE/PBS blend, for instance, the tensile modulus and elongation at break increase about 8% and 13%, respectively. In addition, it was determined through FESEM images and that silanized HNTs particles were better dispersed over the matrix, which in fact contribute to the enhance in mechanical properties. TGA showed that silanized HNTs delay the degradation temperature regarding the uncompatibilized blend. While DMTA indicated the reduction in the mobility of the chains in samples with unmodified and modified HNTs. Therefore, it was successfully obtained compatibilized bioPE/PBS blends, which constitutes an interesting option to develop new sustainable polymers.</p>

Performance evaluation and modeling study of PC blended membranes incorporated with SDS-modified and unmodified halloysite nanotubes in the separation of oil from water

Due to the destructive environmental effects of oily wastewaters and the required purification of these effluents, novel polycarbonate (PC) based mixed matrix membranes (MMMs) including two various kinds of halloysite nanotubes (HNTs) were fabricated by phase inversion technique. The additive utilized in the preparation of neat membrane was polyvinyl pyrrolidone (PVP), while sodium dodecyl sulfate (SDS) was used for the modification of HNTs. Both SDS-modified and unmodified HNTs were separately impregnated into the membrane matrix with different nanoparticle loadings and the obtained mixed matrix membranes were utilized in the ultrafiltration process of oil/water emulsion. The effects of additive and nanoparticle loadings were evaluated on some properties of the membranes, namely hydrophilicity, functional groups, surface morphology, and mechanical characteristic via contact angle measurement, Fourier transform infrared spectrophotometry (FTIR), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), and mechanical strength tests, respectively. Based on the obtained results, the membranes containing SDS-modified nanofillers exhibited more hydrophilicity and mechanical strength than the mixed matrix membranes incorporated with unmodified HNTs. Compared to bare polycarbonate membranes, adding SDS-modified HNTs into the membrane casting solution improved the pure water flux of the synthesized membranes and reduced the filtration time for the acquisition of the complete oil removal yield (100%). As an example, the water flux of the PC-0.75MH MMM was enhanced around 319% in comparison with that of the bare polycarbonate membrane. Evaluation of the membranes antifouling characteristic displayed that the optimized PC-0.75MH membrane had a flux recovery of above 95% after 3 regeneration cycles. Furthermore, the water permeability was analyzed using D-Optimal design response surface methodology. The results of the modeling study showed that the experimental data had about 97.37% proximity with the proposed model.

Hydrocracking process of fuel oil using halloysite modified by different methods

The presented article shows the studies of hydrocracking process of fuel oil with the purpose of obtaining light oil products (benzene and diesel fractions) from heavy oil residues (fuel oil), thus, deepening the refining of oil. The hydrocracking of fuel oil was conducted in the presence of halloysite modified with transition metals (Mo, Ni). Toward this end, halloysite was modified by two different methods—absorption and ion-exchange methods. It was shown that, at optimal conditions (430 °C, 4 MPa), 46.6% (wt.), 53.0% (wt.), 63.0% (wt.) and 83.0% (wt.) light oil products are obtained by the hydrocracking process of fuel oil carried out without catalyst, in the presence of unmodified halloysite, halloysite modified by absorption method and halloysite modified by ion-exchange method, respectively. The obtained benzene and diesel fractions after hydrorefining process can be added to fuels as components.

Viscoelastic behavior and constitutive modeling of PP/HNT composites prepared by water‐assisted extrusion

Poly(propylene) (PP) nanocomposites containing 5, 10, and 15 wt% unmodified halloysite nanotubes (HNTs) were prepared using extrusion with and without water injection. Scanning electron microscopy micrographs show that HNT aggregates prepared by water injection are smaller than those prepared by conventional melt extrusion (without water injection). The nanocomposites prepared by water injection exhibit higher storage modulus (G′) and complex viscosity (η*) values than those by conventional melt extrusion. Stress relaxation results indicate that the interaction between HNTs and PP matrix at low concentration (5 wt%) is stronger than its non‐water injection counterpart. Subsequently, for 5 wt% HNT sample, the transient viscosity is simulated numerically using the Kaye–Bernstein–Kearsley–Zapas (K‐BKZ) integral constitutive equation along with experimentally determined damping functions. It is found that the samples prepared by water injection exhibit a more obvious overshoot behavior than conventional samples and the Papanastasiou‐Scriven‐Macosko (PSM) model can predict the transient viscosity of the samples more accurately than Wagner model. Further, the relationship between the dispersion of HNTs and the damping factors in the constitutive models is discussed. The results of this investigation would improve the theoretical understanding of possible polymer–filler interaction during shear flow. POLYM. ENG. SCI., 59:1585–1592 2019. © 2019 Society of Plastics Engineers

Mechanical and Thermal Properties of Ternary System Based on Starch-Grafted-Polyethylene/High Density Polyethylene/Halloysite Nanocomposites

In this paper, the effect of unmodified halloysite nanotubes (HNTs) content on the chemical structure and the thermal and mechanical properties of blends based on starch-grafted-polyethylene (SgP) and high density polyethylene (HDPE) (70/30 w/w) nanocomposites was investigated at various filler content ratios, i.e. 1.5, 3 and 5 wt.%. The study showed the occurrence of chemical interactions between the polymer matrix and HNTs through OH bonding. Further, the addition of HNTs to the polymer blend led to an increase in the crystallization temperature of the nanocomposite samples, in particular at higher filler contents i.e. 3 and 5 wt.%, while the melting temperature remained almost unchanged. Tensile and flexural properties of the nanocomposite samples were however improved compared to the virgin blend with respect to the HNTs content ratio.

Removal of Congo red by thermally and chemically modified halloysite: equilibrium, FTIR spectroscopy, and mechanism studies

Unmodified halloysite and its heated and heat-processed/acid-leached forms were utilized for the adsorption of Congo red (CR) from aqueous medium. The samples were analyzed by ICP and nitrogen adsorption prior to the adsorption of the pollutant. We then studied the adsorption equilibrium of CR and the regenerating cycles of the most effective adsorbent. A special attention was paid to Fourier transform infrared analysis to elucidate the mechanism of CR adsorption onto halloysite materials. The thermochemical treatment results in the dehydroxylation of halloysite and an increase in SiO2 content. The modification increases specific surface area up to 503 against 63 m2 g−1 for unmodified halloysite. The Redlich–Peterson isotherm yields the best fit of the Congo red adsorption. The best adsorbent was found to be the heat-treated/acid-leached sample. It interacts with Congo red molecules through an outer-sphere complexation mechanism by implying silanol species and amino and sulfoxide groups. Understanding the interactions between pollutants and halloysite materials is an essential approach to improving the use of these clays in sewage treatment.

Modified halloysite nanoclay as a vehicle for sustained drug delivery

This paper presents the effect of modified halloysite nanotubes on the sustained drug release mechanisms of sodium salicylate. Acid treatment and composite polymer-halloysite modification techniques were adopted in this study. After each modification, sodium salicylate drug was loaded, and in vitro release properties were evaluated and compared with the raw unmodified halloysite nanotubes. The results obtained from SEM, TEM and FTIR analyses indicate that both acid treatment and composite formation have no effect on the tubular structure and morphology of halloysite. However, modification of the halloysite nanotubes did influence the drug release rate. In the acid treatment modification, there was an improved loading of sodium salicylate drug which resulted in the sustain release of large amount of the sodium salicylate. In the polymer/halloysite composite formation, a consistent layer of polymer was formed around the halloysite during the composite formation and thus delayed release providing sustained release of sodium salicylate drug over a longer period of time as compared to the acid treated and unmodified halloysite. The results from the invitro release were best fitted with the Higuchi and the Koresymer-Peppas models.

Effects of surface modification of halloysite nanotubes on the morphology and the thermal and rheological properties of polypropylene/halloysite composites

Abstract Effects of unmodified halloysite nanotubes (HNTs) and hexadecyl trimethyl ammonnium bromide treated halloysite nanotubes (CTAB-HNTs) on the morphology as well as the thermal and rheological properties of the HNT-filled polypropylene (PP) composites were investigated. The composites were melt-blended with a novel vane mixer dominated by extensional deformation. Fourier transform infrared spectroscopy well demonstrated that ammonium molecules were successfully interacted with halloysite groups. Compared with unmodified HNTs, the modified HNTs had a better dispersion in the PP matrix. The degree of crystallinity increased with the introduction of HNTs into the PP matrix. Thermal analyses revealed that CTAB-HNTs can improve the composites’ thermal stability compared with unmodified HNTs. As for dynamic shear rheology, the PP/CTAB-HNT composites showed higher viscoelaticity than neat PP in most frequency regimes, and that the raw HNT/PP composites presented the opposite phenomenon. The relaxation time of PP melt and the availability of heterogeneous PP domains increased with the presence of CTAB-HNTs.

Water-induced structural changes in poly(lactic acid) and PLLA-clay nanocomposites

The influence of nanoclays on the structural changes of hydrated poly(l-lactic acid) (PLLA) was investigated at two temperatures, above and below its Tg. Samples of a commercial PLLA and nanocomposites with 2 wt% of an organically modified montmorillonite and an unmodified halloysite were kept in a phosphate buffered solution for different times at 37 and 58 °C and then characterized. The crystallinity degrees and the nature of the crystalline structures developed were determined by differential scanning calorimetry, X-Ray Diffraction and Fourier Transform infrared spectroscopy. While in the cold crystallization of PLLA in dry conditions the α form is obtained only above 100 °C, different mixtures of α and α′ forms were obtained in water at 58 °C, depending on the clay used. The hydrolytic degradation of PLLA played a main role in the structural transformations found at long immersion times, since the short chains formed allowed greater crystallinity degrees and leaded to more perfect crystals. PLLA structure is changed by clays because of its ability as nucleating agents but also due to its effect on the hydrolytic degradation. The unmodified tubular halloysite inhibited degradation, so that lower degrees of crystallinity were obtained in the halloysite based nanocomposite. On the other hand, the modified montmorillonite acted as catalyst of degradation, which explained the appearance of crystalline structures in the nanocomposite with montmorillonite after 84 days of immersion at 37 °C.

Effect of an alkalized‐modified halloysite on PLA crystallization, morphology, mechanical, and thermal properties of PLA/halloysite nanocomposites

ABSTRACTPoly(lactic acid) (PLA)/alkalized halloysite nanotube (HNTa) nanocomposites were prepared by melt mixing. The morphology, crystallization behavior, mechanical properties, and thermal stability of the nanocomposites were investigated in comparison with those of the pristine PLA. HNTa can nucleate PLA, leading to a lower recrystallization temperature and higher crystallinity. Infrared spectra revealed that the hydroxyl groups of the PLA interacted with the external hydroxyl groups of HNTa nanofillers via hydrogen bonding. The thermal stability of the nanocomposites was improved with the addition of HNTa. The PLA/HNTa nanocomposites exhibited higher modulus and tensile strength than those of the PLA composites containing unmodified halloysite nanotubes (HNTs). The improvement in properties was probably due to a better dispersion of the HNTa in the PLA matrix compared to that of the unmodified HNTs. Therefore, the facile alkali treatment of HNTs offers a low cost nanofiller for the preparation of PLA based nanocomposites with high tensile modulus and tensile strength. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44272.

Enhancing β-phase content and tensile properties in poly(vinylidene fluoride) by adding halloysite nanotubes and injecting water during extrusion

Poly(vinylidene fluoride) (PVDF) nanocomposites containing 5, 7 and 10wt% unmodified halloysite nanotubes (HNTs) are prepared by using extrusion with and without water injection. Scanning electron microscopy micrographs show that a large number of single nanotubes are well dispersed in the PVDF matrix with water injection, which is mainly attributed to formation of hydrogen bonds among the fluorine and/or hydrogen atoms of PVDF molecule, the water molecules and the siloxane groups of HNTs. The crystal structure and crystallization behavior of the PVDF are investigated using wide angle X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry. The results show that the addition of the HNTs especially their better dispersion induced by injected water is beneficial to improving the crystallinities and forming substantially higher fractions of β-phase crystal (F(β)s) in the PVDF/HNTs nanocomposites. The F(β) for the nanocomposite with 10wt% HNTs reaches the maximum of 0.689. Moreover, better HNTs dispersion and higher crystallinities and F(β)s improve the Young's moduli, tensile strengths and elongations at break for the PVDF/HNTs nanocomposites.

Cr(VI) reduction and immobilization by novel carbonaceous modified magnetic Fe3O4/halloysite nanohybrid

In this work, a novel “Dumbbell-like” magnetic Fe3O4/Halloysite nanohybrid (Fe3O4/HNTs@C) with oxygen-containing organic group grafting on the surface of natural halloysite nanotubes (HNTs) and homogeneous Fe3O4 nanospheres selectively aggregating at the tips of modified halloysite nanotubes was successfully synthesized. XRD, TEM, IR spectroscopy, XPS and VSM were used to characterize this newly halloysite nanohybrid and its formation mechanism was discussed. Cr(VI) ions adsorption experiments showed that the Fe3O4/halloysite nanohybrid exhibited higher adsorption ability with a maximum adsorption capacity of 132mg/L at 303K, which is about 100 times higher than that of unmodified halloysite nanotubes. More importantly, with the reduction of Fe3O4 and electron–donor effect of oxygen-containing organic groups, Cr(VI) ions were easily reduced into low toxicity Cr(III) and then adsorbed onto the surface of halloysite nanohybrid. In addition, appreciable magnetization was observed due to the aggregation of magnetite nanoparticles, which make adsorbent facility separated from aqueous solutions after Cr pollution adsorption.

Synthesis and adsorption properties of halloysite/carbon nanocomposites and halloysite-derived carbon nanotubes

Halloysite/carbon nanocomposites are synthesized via a hydrothermal route using halloysite as the template and cellulose as the carbon precursor. Cellulose carbonized as a carbon layer deposited on the surface of halloysite. High-resolution transmission electron microscopy, field-emission scanning electron microscopy, X-ray diffraction, X-ray photo electron spectroscopy, and Fourier-transform infrared spectrometry are employed to study the morphological and structural changes of the halloysite/carbon nanocomposites. The results indicate that the thickness of the carbon layer coated on the halloysite surface ranges from 15nm to 25nm and contains CH2, CH3, CO and other organic groups. Amorphous carbon nanotubes with lengths of 0.5–1μm and diameters of 20–80nm are obtained by removing the halloysite template using hydrofluoric acid. After the activation treatment, the BET surface area of the activated halloysite/carbon and carbon nanotube are obviously enhanced, which values are 1150 and 1288m2/g, respectively. The values are higher than that of the common activated carbon. The adsorption properties of phenol on different materials are compared. In comparison of unmodified halloysite, the phenol removal rate on halloysite/carbon, carbon nanotube, activated halloysite/carbon can be increased by 25-fold, 30-fold and 49-fold, respectively. The phenol removal rate on the activated halloysite/carbon and carbon nanotube are higher than that of common activated carbon. A Freundlich adsorption model well describes the adsorption behavior of phenol onto the halloysite/carbon nanocomposite and carbon nanotube.

Mechanical and Physical Properties of Sago Starch/Halloysite Nanocomposite Film

The incorporation of unmodified halloysite nanotube (HNT) in a thermoplastic sago starch (TPSS) film to form a nanocomposite material was investigated. The TPSS/HNT nanocomposite was fabricated through solvent casting method at varying HNT loading of 0, 0.25, 0.5, 1.0, 3.0, and 5.0 wt.%. Evaluation on mechanical and physical properties (tensile test, water absorption, thickness and density) was made to study the effect of HNT loading on the TPSS properties. Tensile strength achieved an optimum value at 0.25 wt.% of HNT loading and decreased with higher addition of HNT. Meanwhile higher amount of HNT in the nanocomposite film exhibited brittleness with the reduced tensile strain. Water absorption decreased with the addition of HNT due to the difficulty of water molecules to pass through the tortuous path of HNT structure. Thickness and density of the nanocomposite film, however, increased at higher HNT contents. FESEM (field emission scanning electron microscope) which examined the surface morphology of the TPSS/HNT nanocomposite displayed uniformly dispersed HNT in the plasticized starch matrix.

On the use of tris(nonylphenyl) phosphite as a chain extender in melt‐blended poly(hydroxybutyrate‐co‐hydroxyvalerate)/clay nanocomposites: Morphology, thermal stability, and mechanical properties

ABSTRACTThe influence of the incorporation of tris(nonylphenyl) phosphite (TNPP) as a chain extender on the morphology and thermal stability of poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV)/clay nanocomposites obtained by melt mixing has been studied. Two different clays have been used: a laminar organomodified montmorillonite (Cloisite® 30B) and a tubular unmodified halloysite (HNT). The morphology of the so‐obtained nanocomposites has been assessed by transmission electron microscopy, scanning electron microscopy, and wide angle X‐ray diffraction, showing a partially exfoliated structure for PHBV/Cloisite® 30B nanocomposites, as well as a good dispersion of the HNT in the PHBV matrix. The crystallinity of the resulting nanocomposites, determined by DSC, does not change when clays or TNPP are added. An increase in the onset temperature of thermal degradation of PHBV has been obtained with the addition of TNPP, as determined by TGA. With regard to the effect of the nanoclays on the thermal stability of PHBV, the onset temperature of the PHBV/HNT nanocomposites is higher than that of the pure PHBV, while this trend is not observed for the nanocomposites containing Cloisite® 30B. The addition of TNPP to the PHBV/Cloisite® 30B nanocomposites resulted in an improved thermal stability; however, for the HNT nanocomposites, the TNPP does not seem to have a significant effect. For all studied systems, it was shown that the variation of mechanical properties of the nanocomposites is due to the reinforcing effect of the nanoclays on the PHBV matrix. In the case of TNPP, it is due to the increased molecular weight and formation of a long‐chain branching structure. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42390.

Property Relationship in Organosilanes and Nanotubes Filled Polypropylene Hybrid Composites.

Polypropylene composites with different filler contents were prepared by creating a masterbatch containing 3 wt%. filler. A variety of silanol groups were used to synthetized three compounds in different media trough a sol-gel process with acetic acid, formic acid and ammonium hydroxide as catalysts. Besides, four different nanotubular fillers were also used to analyze their behavior and compare it with the effect caused by the silanol groups. These tubular structures comprise: unmodified halloysite, carbon nanotubes and functionalized halloysite and carbon nanotubes. Morphological characterization in SEM and STEM/TEM showed dispersion in the polypropylene matrix. According to TGA and DSC measurements thermal behavior remain similar for all the composites. Mechanical test in tension demonstrate that modulus of the composites increases for all samples with a major impact for materials containing silanol groups synthetized in formic acid. Rheological measurements show a significantly increment in viscosity for samples containing unmodified and modified carbon nanotubes. No difference was found for samples containing silanol groups and halloysite when compared to neat polypropylene. Finally, the oxygen transmission rate increased for all samples showing high barrier properties only for samples containing natural and functionalized halloysite nanotubes.

Adsorption of chloroanilines from aqueous solutions on the modified halloysite

Batch removal of 3-, 4-chloroaniline and 3,4-dichloroaniline from an aqueous solution using unmodified and acid-activated halloysite was investigated in this study. The influence of acid concentration used for digesting the halloysite, contact time as well as the concentration of chloroaniline solutions was reported.The results show that the adsorption of 4-chloroaniline was greatly enhanced by using a sulfuric acid-treated halloysite, as compared to the unmodified halloysite. A comparison of kinetic models applied to the adsorption of chloroanilines on an acid-treated halloysite was evaluated for pseudo first-order, pseudo second-order, and intraparticle diffusion kinetic models. The chemisorption pseudo-second order kinetic model was found to correlate the experimental data well. The adsorption mechanism of acid-treated halloysite -chloroaniline system complied well with the Langmuir model in the case of 4-chloroaniline and 3,4-dichloroaniline and with the Freundlich model for 3-chloroaniline.

Loading and in vitro release of ibuprofen in tubular halloysite

Halloysite (Hal) and 3-aminopropyltriethoxysilane (APTES)-modified Hal were used as drug carriers for the loading and release of ibuprofen (IBU). IBU exhibited a low loading capacity and a fast release in unmodified Hal because of the weak interaction (hydrogen bonds) between IBU and the unmodified halloysite. APTES modification increased the loading capacity of IBU and slowed the release of IBU by introducing a strong affinity through electrostatic attraction, which was generated between the carboxyl groups of IBU and the introduced aminopropyl groups of the grafted APTES. The release profiles of IBU were well fitted with the modified Korsmeyer–Peppas model. The release mechanism of IBU from unmodified and APTES-modified Hal, indicated by the exponent of the modified Korsmeyer–Peppas model, was Fickian diffusion and non-Fickian diffusion, respectively.

Natural halloysite nanotubes as mesoporous carriers for the loading of ibuprofen

Natural halloysite with a mesoporous lumen was used as a carrier for the loading of ibuprofen (IBU) for the first time. The halloysite products were characterized by elemental analysis, nitrogen adsorption, X-ray diffraction, diffuse reflectance infrared Fourier transform spectrometry, thermogravimetric analysis, differential scanning calorimetry, solid-state nuclear magnetic resonance, scanning electron microscopy, and transmission electron microscopy. IBU was loaded mainly into the lumen and partially on the external surface of the halloysite. The loaded IBU was present as nanocrystal and amorphous state. In unmodified halloysite, initially the IBU were anchored to the surface hydroxyl groups by hydrogen bonding, and then the added IBU molecules formed aggregates via hydrogen-bonds to the anchored IBU. The surface functionalization of halloysite by 3-aminopropyltriethoxysilane (APTES) promoted the loading of IBU in halloysite. APTES induced a strong affinity through electrostatic attraction, between the carboxyl groups of IBU and the aminopropyl groups of the grafted APTES. In grafted halloysite, a thermal pretreatment at 400°C reduced the water content leading to a restriction of the APTES oligomerization in the lumen. Consequently, the free lumen space was preserved and resulted in a further increase in IBU loading. The modified halloysite, pretreated by heating and grafted by APTES, had the largest IBU loading, which was 25.4% greater than that in unmodified halloysite.