Graphene oxide-polyamine preprogrammable nanoreactors with sensing capability for corrosion protection of materials.

Corrosion is one of the major issues for sustainable manufacturing globally. The annual global cost of corrosion is US$2.5 trillion (approximately 3.4% of the world's GDP). The traditional ways of corrosion protection (such as barriers or inhibiting) are either not very effective (in the case of barrier protection) or excessively expensive (inhibiting). Here, we demonstrate a concept of nanoreactors, which are able to controllably release or adsorb protons or hydroxides directly on corrosion sites, hence, selectively regulating the corrosion reactions. A single nanoreactor comprises a nanocompartment wrapped around by a pH-sensing membrane represented, respectively, by a halloysite nanotube and a graphene oxide/polyamine envelope. A nanoreactor response is determined by the change of a signaling pH on a given corrosion site. The nanoreactors are self-assembled and suitable for mass-line production. The concept creates sustainable technology for developing smart anticorrosion coatings, which are nontoxic, selective, and inexpensive.

Recent Advances of Halloysite Nanotubes in Biomedical Applications.

Halloysite nanotubes (HNTs) have emerged as a highly regarded choice in biomedical research due to their exceptional attributes, including superior loading capacity, customizable surface characteristics, and excellent biocompatibility. HNTs feature tubular structures comprising alumina and silica layers, endowing them with a large surface area and versatile surface chemistries that facilitate selective modifications. Moreover, their substantial pore volume and wide range of pore sizes enable efficient entrapment of diverse functional molecules. This comprehensive review highlights the broad biomedical application spectrum of HNTs, shedding light on their potential as innovative and effective therapeutic agents across various diseases. It emphasizes the necessity of optimizing drug delivery techniques, developing targeted delivery systems, rigorously evaluating biocompatibility and safety through preclinical and clinical investigations, exploring combination therapies, and advancing scientific understanding. With further advancements, HNTs hold the promise to revolutionize the pharmaceutical industry, opening new avenues for the development of transformative treatments.

Spherical Assembly of Halloysite Clay Nanotubes as a General Reservoir of Hydrophobic Pesticides for pH-Responsive Management of Pests and Weeds.

The development of smart systems for pesticidal delivery presents a significant advancement in enhancing the utilization efficiency of pesticides and mitigating environmental risks. Here an acid-responsive pesticidal delivery system using microspheres formed by the self-assembly of halloysite clay nanotubes (HNTs) is proposed. Insecticide avermectin (AVM) and herbicide prometryn (PMT) are used as two models of hydrophobic pesticide and encapsulated within the porous microspheres, followed by a coating of tannic acid/iron (TA/FeIII) complex films to generate two controlled-release pesticides, named as HCEAT and HCEPT, resulting in the loading capacity of AVM and PMT being 113.3 and 120.3 mg g-1, respectively. Both HCEAT and HCEPT exhibit responsiveness to weak acid, achieving 24 h-release ratios of 85.8% and 80.5% at a pH of 5.5. The experiment and simulation results indicate that the coordination interaction between EDTA2- and Ca2+ facilitates the spherical aggregation of HNTs. Furthermore, these novel pesticide formulations demonstrate better resistance against ultraviolet (UV) irradiation, higher foliar affinity, and less leaching effect, with negligible impact of the carrier material on plants and terrestrial organisms. This work presents a promising approach toward the development of efficient and eco-friendly pesticide formulations, greatly contributing to the sustainable advancement of agriculture.

Colloidal and Thermal Stability of Three-Component Hybrid Materials Containing Clay Mineral, Polysaccharide and Surfactant.

The paper presents the colloidal and thermal stability of the three-component hybrid materials containing halloysite, polysaccharides (alginic acid, cationic cellulose and hydroxyethyl cellulose) and Tritons. TX-100, TX-165 and TX-405 were used as non-ionic surfactants. Stability and other properties of the hybrid materials were tested by the following methods: UV-Vis, TGA (thermogravimetric analysis) and DSC (differential scanning calorimetry), CHN (elemental analysis), SEM-EDX (scanning electron microscopy with energy dispersive X-ray spectroscopy) and tensiometry. According to the results with the increasing polymer concentration the colloidal stability of the tested systems also increases. Moreover, the addition of the surfactants causes the increase of polysaccharide adsorption but the colloidal stability of the tested systems decreases due to large weights of formed aggregates. As follows from the thermal analysis, the comparison of the TG/DTG-DSC curves obtained for the investigated polymers confirms that their thermal decomposition courses have some common features. The obtained results have the application potential in the formation of the materials for the pollutants removal from water and sewages.

TiO2/Loofah-Halloysite Bio-Hybrid Composites as Efficient Systems for VOCs Removal.

Volatile organic compounds (VOCs), recognized as hazardous air contaminants, prompt the exploration of sustainable air purification methods. Solar photocatalytic oxidation emerges as a promising solution, utilizing semiconductor photocatalysts like titanium dioxide (TiO2). However, the raw material crisis necessitates reduced TiO2 usage, leading to investigations into TiO2 modification techniques. The study introduces a novel approach by employing natural fibers, specifically loofah sponge, as a TiO2 support. This method aims to maintain photocatalytic activity while minimizing TiO2 content. The article explores using halloysite, a natural clay mineral, as a supportive material, enhancing mechanical strength and adsorption properties. The resulting TiO2/loofah-halloysite composites are evaluated for their efficacy in gas-phase photocatalytic oxidation of toluene and ethanol, chosen as representative VOCs. The conversion of toluene and ethanol on the composite was 88 % and 39 %, respectively, with high selectivity toward CO2. In addition to its high performance, the bio-composite was stable for several conversion cycles, keeping the conversion activity unchanged. The study contributes to developing green hybrid materials for VOC removal, showcasing potential applications across industries.

A Halloysite Nanotubes-based Probe for Efficient Fluorescence Detection and Adsorption Removal of Pb2+ in Water.

The detection and removal of Pb2+ is of utmost importance for environmental protection and human health due to its toxicity, persistent pollution, and bioaccumulation effects. To address the limitations associated with organic small molecule-based fluorescence probes such as poor water solubility and single functionality in detecting Pb2+, a fluorescence probe based on halloysite nanotubes was developed. This probe not only enables specific, rapid, and reliable detection of Pb2+ but also facilitates efficient removal of it from water. The development of this bifunctional fluorescent probe provides a valuable insight for designing more advanced probes targeting heavy metal ions.

Augmentin loaded functionalized halloysite nanotubes: A sustainable emerging nanocarriers for biomedical applications.

Clay minerals such as Halloysite nanotubes (HNTs), abundantly available green nanomaterial, exhibit a significant advantage in biomedical applications such as drug delivery, antibacterial and antimicrobials, tissue engineering or regeneration, etc. Because of the mesoporous structure and high absorbability, HNTs exhibit great potential as a nanocarrier in drug delivery applications. The sulfuric acid treatment enhances the surface area of the HNTs and thereby improves their drug-loading capacity by enlarging their lumen space/inner diameter. In the present investigation, based on the literature that supports the efficacy of drug loading after acid treatment, a dual treatment was performed to functionalize the HNTs surface. First, the HNTs were etched and functionalized using sulfuric acid. The acid-functionalized HNTs underwent another treatment using (3-aminopropyl) triethoxysilane (APTES) to better interact the drug molecules with the HNTs surfaces for efficient drug loading. Augmentin, a potential drug molecule of the penicillin group, was used for HNTs loading, and their antibacterial properties, cytotoxicity, and cumulative drug release (%) were evaluated. Different characterization techniques, such as X-ray diffractometer (XRD) and Fourier Transform Infra-Red (FT-IR), confirm the loading of Augmentin to the APTES@Acid HNTs. TEM images confirm the effective loading of the drug molecule with the HNTs. The drug encapsulation efficiency shows 40.89%, as confirmed by the Thermogravimetric Analysis (TGA). Also, the Augmentin-loaded APTES@Acid HNTs exhibited good antibacterial properties against E. coli and S. aureus and low cytotoxicity, as confirmed by the MTT assay. The drug release studies confirmed the sustainable release of Augmentin from the APTES@Acid HNTs. Hence, the treated HNTs can be considered as a potential nanocarrier for effectively delivering Augmentin and promoting enhanced therapeutic benefits.

Cefixime loaded bare and functionalized halloysite nanocarriers and their biomedical applications.

Effective drug delivery for is the foremost requirement for the complete recovery of the disease. Nanomedicine and nanoengineering has provided so many spaces and ideas for the drug delivery design, whether controlled, targeted, or sustained. Different types of nanocarriers or nanoparticles are aggressively designed for the drug delivery applications. Clay minerals are identified as a one of the potential nanocarrier for the drug delivery. Owing to their biocompatibility and very low cytotoxicity, clay minerals showing effective therapeutic applications. In the present investigation, clay mineral, i.e., Halloysite nano tubes are utilized as a nanocarrier for the delivery of antibiotic cefixime (CFX), a third-generation cephalosporin. The HNT was first functionalized with the sulfuric acid and then further treated with the 3-(aminopropyl)triethoxysilane (APTES). The drug is loaded on three different classifications of HNTs, i.e., Bare-CFX-HNT, Acid-CFX-HNT, and APTES-CFX-HNT and their comparative analysis is established. Different characterization techniques such as X-ray diffractometry (XRD), Fourier transform infra-red (FT-IR), Transmission electron microscopy TEM), Brunauer-Emmett-Teller (BET), adsorption studies, and Thermogravimetric analysis (TGA) were performed to evaluate their chemical, structural, morphological, and thermal properties. TGA confirmed the encapsulation efficiency of Bare-CFX-HNT, Acid-CFX-HNT, and APTES-CFX-HNT as 42.65, 52.19, and 53.43%, respectively. Disk diffusion and MTT assay confirmed that the drug loaded HNTs have potential antibacterial activities and less cytotoxicity. The adsorption capacity of CFX with different HNTs are evaluated and Different adsorption and kinetic models have been discussed. Drug release studies shows that APTES-CFX-HNT showing sustained release of cefixime as compared to Bare-CFX-HNT and Acid-CFX-HNT.

Effects of multi-walled carbon nanotubes and halloysite nanotubes on plasma lipid profiles and autophagic lipolysis pathways in mouse aortas and hearts.

Multi-walled carbon nanotubes (MWCNTs) and halloysite nanotubes (HNTs) are widely used tubular-structured nanomaterials (NMs), but their cardiovascular effects are not clear. This study compared the effects of MWCNTs and HNTs on lipid profiles in mouse plasma and gene expression profiles in aortas and hearts. Mice were intravenously injected with 50 µg NMs, once a day, for 5 days. Then, the plasma was collected for lipidomics analysis, and aortas and hearts were collected for RNA-sequencing analysis. While MWCNTs or HNTs did not induce obvious pathological changes in aortas or hearts, the lipid profiles in mouse plasma were altered. Further analysis revealed that MWCNTs more effectively upregulated sphingolipids and sterol lipids, whereas HNTs more effectively upregulated glycerophospholipids and fatty acyls. Consistently, RNA-sequencing data indicated that MWCNTs and HNTs altered signaling pathways related with lipid synthesis and metabolism, as well as those related with endoplasmic reticulum, lysosomes and autophagy, more significantly in aortas than in hearts. We further verified the changes of proteins involved in autophagic lipolysis, that MWCNTs were more effectively to suppress the autophagic biomarker LC3, whereas HNTs were more effectively to affect lipid metabolism proteins. These results may provide novel understanding about the influences of MWCNTs and HNTs on lipid profiles and lipid signaling pathways in cardiovascular systems. Importantly, previous studies considered HNTs as biocompatible materials, but the results from this study suggested that both MWCNTs and HNTs were capable to affect lipid profiles and autophagic lipolysis pathways in cardiovascular systems, although their exact influences were different.

Enhanced antimicrobial efficacy of chlorhexidine-encapsulated halloysite nanotubes incorporated in presurgical orthopedic appliances: an in vitro, controlled study.

AIMS AND OBJECTIVE: Presurgical infant's orthopedic appliances (PSIOs) play an increasingly crucial role in the interdisciplinary management of neonatal CLP, aiming to improve and maintain adequate nasolabial aesthetics, followed by primary lip/nasal surgery in both unilateral and bilateral CLP cases. The use of PSIOs in cleft lip and palate patients can lead to contamination with oral microflora, acting as a potential reservoir for infectious microorganisms. Acrylic surfaces might provide retention niches for microorganisms to adhere, and inhabit, which is difficult to control in immunocompromised patients, thus predisposing them to increased infection risks. The objective of this multi-assay in vitro study was to investigate the effects of incorporating chlorhexidine-loaded halloysite nanotubes (CHX-HNTs) fillers on the morphological, cytotoxic, release, and antimicrobial characteristics of self-cured acrylic polymethyl methacrylate (PMMA) material used in pre-surgical orthopedic appliances. METHODS: Disk-shaped PMMA specimens were prepared with varying proportions of CHX-HNTs. A control group without any addition served as a reference, and four experimental samples contained a range of different concentrations of CHX-HNTs (1.0, 1.5, 3, and 4.5 wt%). The antimicrobial efficacy was assessed using an agar diffusion test against common reference microorganisms: Candida albicans, Staphylococcus aureus, Streptococcus pneumoniae, and Streptococcus agalactiae. Cytotoxicity was examined using the L929 cell line (mouse fibroblasts) through a (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide, MTT) cell viability assay. The release kinetics of CHX were monitored using UV-spectral measurements. The statistical analysis used a one-way ANOVA followed by Tukey's post hoc test. RESULTS: The integration of CHX-HNTs in PMMA exhibited a substantial dose-dependent antifungal and antibacterial effect against microorganisms at tested mass fractions (1.0 to 4.5 wt%). CHX release was sustained for up to 60 days, supporting prolonged antimicrobial activity. Furthermore, no significant cytotoxicity was determined in the L929 fibroblast cell line (control), indicating the biocompatibility of the CHX-HNTs-enhanced PMMA. CONCLUSION: Incorporating CHX-HNTs in PMMA successfully enhanced its antimicrobial properties, providing sustained CHX release and superior antimicrobial efficacy. These findings demonstrate the potential of antimicrobial nanoparticles in dental therapies to improve therapeutic outcomes. However, rigorous further clinical trials and observational studies are warranted to validate the practical application, safety, and efficacy. CLINICAL RELEVANCE: This study has the potential to make a major impact on the health of infants born with cleft lip and palate by helping to reduce the prevalence of infectious illnesses. The incorporation of CHX-HNTs into PMMA-based appliances is a novel promising preventive approach to reduce microbial infections.

Novel chitosan/citric acid modified pistachio shell/halloysite nanotubes cross-linked by glutaraldehyde biocomposite beads applied to methylene blue removal.

In this study, Cht/PS-CA/HNT biocomposite adsorbent was synthesized using halloysite nanotube as nanomaterial, chitosan which is a biodegradable and biocompatible biopolymer, pistachio shell as biomass source, citric acid as biomass modifier. The removal of methylene blue dyestuff on the synthesized new Cht/PS-CA/HNT from the aqueous medium by adsorption method was investigated. Experimental parameters such as dye concentration, contact time, amount of adsorbent, solution pH and temperature, which affect the adsorption process, were investigated. The adsorption experimental data were analyzed with the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms, which are widely used in aqueous solutions, and it was decided that Langmuir is the most suitable isotherm. The maximum adsorption capacity of the monolayer was calculated to be 111.14 mg/g. Optimum contact time and adsorbent dose were determined as 90 min and 1 g/L. Adsorption experimental data were applied for Pseudo-first-order and Pseudo-second-order kinetic models and it was decided that the most suitable kinetic model was pseudo-second-order. Thermodynamic evaluation of adsorption showed that adsorption is endothermic and adsorption is spontaneous.

In the present study, it was determined that chitosan beads prepared using citric acid modified pistachio shells and HNT have strong adsorption properties for dyestuff removal, which is one of the important causes of environmental pollution. The novelty of this work is based on the development of a new composite adsorbent that can be synthesized in a simple and fast method and does not require expensive reagents or complex equipment. Another innovation is that MB dyestuff, which has a highly harmful effect, can be easily removed from polluted water by using simple biowaste-based adsorbents by adopting appropriate procedures.

Micropatterning of biologically derived surfaces with functional clay nanotubes.

Micropatterning of biological surfaces performed via assembly of nano-blocks is an efficient design method for functional materials with complex organic-inorganic architecture. Halloysite clay nanotubes with high aspect ratios and empty lumens have attracted widespread interest for aligned biocompatible composite production. Here, we give our vision of advances in interfacial self-assembly techniques for these natural nanotubes. Highly ordered micropatterns of halloysite, such as coffee rings, regular strips, and concentric circles, can be obtained through high-temperature evaporation-induced self-assembly in a confined space and shear-force brush-induced orientation. Assembly of these clay nanotubes on biological surfaces, including the coating of human or animal hair, wool, and cotton, was generalized with the indication of common features. Halloysite-coated microfibers promise new approaches in cotton and hair dyeing, medical hemostasis, and flame-retardant tissue applications. An interfacial halloysite assembly on oil microdroplets (Pickering emulsion) and its core-shell structure (functionalization with quantum dots) was described in comparison with microfiber nanoclay coatings. In addition to being abundantly available in nature, halloysite is also biosafe, which makes its spontaneous surface micropatterning prospective for high-performance materials, and it is a promising technique with potential for an industrial scale-up.

This international group of authors unites researchers who pioneered halloysite clay nanotubes for biomaterials, and discloses a new strategy for this nanoclay composite design through interfacial architecture. These results confirm Dr. K. Ariga concept of nanoarchitectonics, and demonstrate promising applications. Assembly of the clay nanotubes on biosurfaces, including the coating of human or animal hair, wool, and cotton, was generalized for the process optimization. Halloysite-coated microfibers promise new approaches in cotton and hair dyeing, and medical hemostasis and flame-retardant tissue applications. Related techniques of interfacial halloysite assembly on oil microdroplets (Pickering emulsion) and its quantum dots core­shell structure for cell imaging are also described. Contrary to many other synthetic nanomaterials, described natural halloysite nanotubes are environmentally safe and abundantly available, thus allowing for scale up of the suggested functional biocomposites.

Comparison of Synthetic Pathways for Obtaining Fluorescent Nanomaterials Based on Halloysite and Carbon Dots for Potential Biological Sensing.

Recently, fluorescent sensors have gained considerable attention due to their high sensitivity, low cost and noninvasiveness. Among the different materials that can be used for this purpose, carbon dots (CDs) represent valuable candidates for applications in sensing. These, indeed, are easily synthesized, show high quantum yield and are highly biocompatible. However, it was pointed out that the photoluminescence properties of these nanomaterials are strictly dependent on the synthetic and purification methods adopted. The presence of halloysite nanotubes (HNTs), a natural, low cost and biocompatible clay mineral, has been found to be efficient in obtaining small and highly monodispersed CDs without long and tedious purification techniques. Herein, we report the comparison of synthetic pathways for obtaining halloysite-N-doped CDs (HNTs-NCDs) that could be used in biological sensing. One was based on the synthesis of N-doped CDs by a bottom-up approach on HNTs' surface by a MW pyrolysis process; the other one was based on the post-modification of pristine N-doped CDs with halloysite derivatives. The evaluation of the best synthetic route was performed by different physico-chemical techniques. It was found that the bottom-up approach led to the formation of N-doped CDs with different functional groups onto the HNTs' surface. This evidence was also translated in the different fluorescence quantum yields and the existence of several functional groups in the obtained materials was investigated by potentiometric titrations. Furthermore, the ability of the synthesized nanomaterials as sensors for Fe3+ ions detection was assessed by spectroscopic measurements, and the cellular uptake was verified by confocal/fluorescence microscopies as well.

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.

Construction of 3D-Printed Sodium Alginate/Chitosan/Halloysite Nanotube Composites as Adsorbents of Methylene Blue.

In this study, sodium alginate/chitosan/halloysite nanotube composites were prepared by three-dimensional printing and characterized in terms of morphology, viscosity, thermal properties, and methylene blue (MB) adsorption performance. The high specific surface area and extensively microporous structure of these composites allowed for effective MB removal from wastewater; specifically, a removal efficiency of 80% was obtained after a 60 min treatment at an adsorbent loading of 1 g L-1 and an MB concentration of 80 mg L-1, while the maximum MB adsorption capacity equaled 376.3 mg g-1. Adsorption kinetics and isotherms were well described by quasi-second-order and Langmuir models, respectively. The composites largely retained their adsorption performance after five adsorption-desorption cycles and were concluded to hold great promise for MB removal from wastewater.

Modification of polymethylmethacrylate bone cement with halloysite clay nanotubes.

BACKGROUND: Polymethylmethacrylate (PMMA) bone cement is used in orthopedics and dentistry to get primary fixation to bone but doesn't provide a mechanically and biologically stable bone interface. Therefore, there was a great demand to improve the properties of the PMMA bone cement to reduce its clinical usage limitations and enhance its success rate. Recent studies demonstrated that the addition of halloysite nanotubes (HNTs) to a polymeric-based material can improve its mechanical and thermal characteristics. OBJECTIVES: The purpose of the study is to assess the compressive strength, flexural strength, maximum temperature, and setting time of traditional PMMA bone cements that have been manually blended with 7 wt% HNT fillers. METHODS: PMMA powder and monomer liquid were combined to create the control group, the reinforced group was made by mixing the PMMA powder with 7 wt% HNT fillers before liquid mixing. Chemical characterization of the HNT fillers was employed by X-ray fluorescence (XRF). The morphological examination of the cements was done using a scanning electron microscope (SEM). Analytical measurements were made for the compressive strength, flexural strength, maximum temperature, and setting time. Utilizing independent sample t-tests, the data was statistically assessed to compare mean values (p < 0.05). RESULTS: The findings demonstrated that the novel reinforced PMMA-based bone cement with 7 wt% HNT fillers showed higher mean compressive strength values (93 MPa) and higher flexural strength (72 MPa). and lower maximum temperature values (34.8 °C) than the conventional PMMA bone cement control group, which was (76 MPa), (51 MPa), and (40 °C), respectively (P < 0.05). While there was no significant difference in the setting time between the control and the modified groups. CONCLUSION: The novel PMMA-based bone cement with the addition of 7 wt% HNTs can effectively be used in orthopedic and dental applications, as they have the potential to enhance the compressive and flexural strength and reduce the maximum temperatures.

Fabrication of 2D/1D Bi2WO6/halloysite nanotubes photocatalyst towards water purification: a support effect onin situconstruction and electron-hole separation.

In this research work, a reusable and efficient 2D/1D heterogeneous structured photocatalyst based on amine-functionalized halloysite nanotubes (MHNTs) and Bi2WO6nanosheet (BWO) was prepared using a facile hydrothermal method for decomposing PPCPs under simulated sunlight. On the degradation of tetracycline hydrochloride (TCH), the effects of composite catalysts prepared under various conditions were discussed. The results showed that over BWO/MHNTs with a mass ratio was 3:1, the synthesizing temperature was 120 °C and the precursor pH value was 1, the TCH (10 mg l-1) degradation efficiency reached 100% after 1 h irradiation of simulated sunlight. Moreover, BWO/MHNTs composites kept good recovery and stable photocatalytic activity after 5 cycles. The excellent dispersion of Bi2WO6on the surface of clay minerals and the oxygen vacancy enhanced electron-hole separation may be responsible for the its high activity and stability. Futhermore, the radical capture test demonstrated that ·O-2was primarily responsible for the photodegradation of TCH. Thus, BWO/MHNTs composites exhibit a good application prospect in the field of sunlight-driven photocatalytic degradation towards PPCPs pollutants in water.

PEG-modified halloysite as a hydrophilic interaction and cation exchange mixed-mode sorbent for solid-phase extraction of biogenic amines in fish samples.

A novel type of PEG-modified halloysite was prepared and used as a hydrophilic interaction and cation exchange mixed-mode sorbent for solid-phase extraction of biogenic amines in fish samples. The eluates were analyzed by high-performance liquid chromatography-ultraviolet detection after the derivatization with benzoyl chloride. The developed sorbent was characterized by scanning electron microscopy, infrared spectroscopy, X-ray diffraction, zeta potential analyzer, and thermo-gravimetric analysis. After the optimization of various parameters influencing the extraction efficiency, the PEG-modified halloysite-based SPE method was evaluated. The adsorption capacities of putrescine, spermine, phenethylamine, and histamine were as high as 9.3, 8.5, 5.7, and 5.6 mg g-1, respectively. Satisfactory reproducibility of sorbent preparation was obtained with within-batch and batch-to-batch relative standard deviations (RSDs) lower than 3.9% and 8.6%, respectively. The biogenic amine spiking recoveries in fish samples ranged from 84.3 to 105.5% with good RSDs lower than 7.8%. Intra-day and inter-day precision, expressed as RSDs, were better than 8.8%. The limits of detection of histamine, putrescine, phenethylamine, and spermine were 9.4, 1.9, 0.5, and 0.9 µg L-1, respectively. This work provides a new hydrophilic interaction and cation exchange mixed-mode sorbent and is successfully applied to the extraction of trace biogenic amines from fish samples.

Contribution of halloysite as nanotubular clay mineral on mechanism and adsorption rate of Cd(II) onto nanocomposites alginate-halloysite.

In this work nanocomposites based on alginate (Alg) and halloysite as a nanotubular clay (Hy) were developed. Characterization techniques reveal that Hy/Alg nanocomposites are cation exchangers with predominantly negative charge density and good thermal stability. The adsorption equilibrium of Cd(II) in aqueous solution onto Hy/Alg nanocomposites revealed that by increasing the mass of halloysite in the nanocomposite, the adsorption capacity diminished significantly due to the halloysite-alginate interactions. Maximum adsorption capacities of 8, 65, 88, and 132 mg/g of Cd(II) were obtained for samples Hy, Hy/Alg 50%, Hy/Alg 95%, and Alg, respectively. In addition, the adsorption equilibrium of Cd(II) on the Hy/Alg bionanocomposites was affected by the pH and temperature of the solution, demonstrating the presence of electrostatic interactions during adsorption and that this is an exothermic process. The controlling mechanism of adsorption was cation exchange influenced by electrostatic forces. The Cd(II) adsorption rate studies were interpreted by the diffusion-permeation model and reveal that the presence of Hy in the structure of the nanocomposites enhances the permeation coefficient, that is, the adsorption rate was increased. The values of the permeation coefficient varied from 1.95 × 10-7 to 8.50 × 10-7 cm2/s for Hy/Alg 50% and from 1.70 × 10-7 to 3.55 × 10-7 cm2/s for Hy/Alg 95%.

Natural halloysite nanotubes as an efficient catalyst in strecker reaction: the synthesis of α-amino nitriles under solvent-free conditions.

In this work, a green and cost-effective method based on halloysite as natural catalyst for the synthesis of α-amino nitriles via Strecker three-component reaction is introduced. The chemical and physical structure of natural halloysite has characterized thoroughly, and then the effect of different parameters such as the amount of catalyst, solvent, and temperature was optimized in the synthesis of 2-phenyl-2-(phenylamino)acetonitrile as the model reaction. Then, various substituted benzaldehydes and anilines were converted to the desired α-amino nitriles under the optimized conditions. Electronic properties of substituents on aldehydes and aromatic amines have been affected the reaction efficiency. For all substrates, good to excellent yields of the corresponding α-amino nitriles were obtained under solvent-free conditions at room temperature. The catalyst has been recovered and reused five times in successive Strecker reaction.