Applied Clay Science最新文献

Intercalative sorption of isomeric nitrophenolates (NP) was investigated in two different layered hydroxide materials - anionic clay, magnesium aluminium layered double hydroxide (MgAl-LDH) through reconstructive mechanism and the structurally related layered hydroxy salt, Ni₃Zn₂(OH)₈(CH₃COO)₂·mH₂O (NiZn-LHS) through ion-exchange. Intercalation of NP isomers was confirmed by powder X-ray diffraction and infrared spectroscopy. The NP uptake by the layered hydroxide materials was quantified by high performance liquid chromatography. Both the layered hydroxide materials exhibit selective intercalation from the nitrophenolate mixtures. The order of preference is 4-NP > > 2-NP > 3-NP in MgAl-LDH and 4-NP > 2-NP > > 3-NP in NiZn-LHS. The bias in intercalation could be attributed to (1) the concentration of the phenolate ions influenced by the pKa of the isomer and (2) extent of H-bonding of the nitro group of the isomer with the hydroxide slabs. The 4-isomer with lower pKa and better H-bonding with the adjacent hydroxide slabs is preferentially intercalated. The anionic clays can be used to sorb out nitrophenols as well as separate them from their mixtures.

Benzene poses a severe threat to human health due to its prevalence and carcinogenicity. The adsorption behavior of benzene on clay mineral surfaces is significant to its migration and retention in soils. Therefore, it is crucial to understand the mechanism of benzene adsorption behavior under different environmental conditions. In this study, a series of Grand Monte Carlo (GCMC) simulations were performed to obtain benzene isotherms on clay under various temperatures and air humidity. The adsorption mechanisms were investigated via analysis of the distribution of interaction energy, density, and orientation of adsorbed benzene and water. Results show that benzene form multiple layers on mineral surfaces, and surfaces have a great impact on the first layer of adsorbed benzene. The impedance effect of temperature on benzene adsorption is attributed to the temperature-dependent chemical potential of benzene, but not the interaction between benzene and surfaces, which is slightly temperature-reliant. Humidity shows different inhibition effects on benzene adsorption due to different surface hydration behavior and competitive adsorption between water and benzene. Benzene tends to be adsorbed on hollow sites on kaolinite surfaces, which is the same as water. The surface cations on montmorillonite and mica are significant to benzene and water adsorption, and their density distribution causes different competitive adsorption behavior.

Innovative hemodialysis membranes are essential for hemodialysis process, the vital clinical treatment for patients with kidney failure. In the present study, for the first time halloysite nanotubes (Hal) were applied to adsorb creatinine through molecular sieve mechanism. Firstly, calcination process performed to improve the affinity of Hal for creatinine. Afterwards, eight different composite polyacrylonitrile (PAN) nanofibrous membranes containing two types of Hal including raw Hal (RHAL) and calcined Hal (CHAL) were developed via an electrospinning device (10, 20, 30 and 40 wt%). Morphological analysis revealed that, with low contents of Hal (10 and 20 wt%), the structural integrity of nanofibers was  maintained. However, with the high contents of Hal (30 and 40 wt%), structural integrity of nanofibers was affected and conical beads were formed. The mechanical properties and hydrophilicities of the composite PAN based membranes were higher than pure PAN based membrane and improved by increasing Hal contents up to 20 wt% and then reduced. Therefore, among the composite PAN based membranes, the membranes loaded with 10 and 20 wt% of Hal were selected for further evaluations. Adsorption studies showed that the composite PAN based membrane loaded with 20 wt% of CHAL had best performance with >70% of creatinine removal. The MTT assay also presented; the highest cell viability about 90% for the same membrane. Blood compatibility of the membranes for both bovine serum albumin (BSA) surface adsorption and platelet adhesion revealed that the composite PAN membranes were significantly more blood compatible than the polyethersulfone (PES) commercial and pure PAN based membranes. As a result, composite PAN based membrane loaded with 20 wt% of CHAL which combines adsorption and traditional mechanism, seems promising for hemodialysis membranes.

Iron and copper fluorides are of interest as conversion cathode materials in lithium batteries but they suffer from high hysteresis and low cyclability, respectively. To overcome these limitations and take advantage of the electrochemical properties of each of the fluorides, fluoride mixtures that combine the two redox centers Fe³⁺ and Cu²⁺ are synthesized using Layered Double Hydroxides (LDH) as a 2D multi-metallic template. Hydrotalcite-type phases substituted with Cu²⁺ and Fe³⁺ ions are prepared by coprecipitation then fluorinated with fluorine gas in static mode at temperatures chosen according to their thermal evolution monitored by mass spectrometry. After each fluorination treatment, the materials are characterized by X-ray diffraction and most LDH materials are found stable up to 200 °C, treatment above leads to the formation of fluorides of each of the cations. The initial dispersion of the cations in the LDH sheets nevertheless allows, after fluorination, a composite of fluorides making them totally accessible to the phenomenon of electrochemical conversion shown here in a metallic lithium battery assembly with a Solid Polymer Electrolyte (SPE). In such All-Solid-State Battery (ASSB) configuration often limiting in terms of columbic efficiency, 76% the first discharge capacity is recovered in charge for an optimized composition (up to 560 mAh.g⁻¹). This good reversibility positions these LDH templates very well for future investigations in the field of electrochemical storage.

Uncertainties associated with durability and sustainability of geopolymer due to formation of efflorescence, shrinkage and activator cost are setbacks for its real-life applications. Therefore, the aim of this study was to produce geopolymers with improved durability and sustainability using local kaolin clay as precursor, cocoa-pods-ash (CPA) as alternative alkali hydroxide activator, periwinkle-shells-ash (PSA) as hardener and quarry-dust (QD) as filler. Local kaolin clay calcined at 700 °C (M7C), was replaced with some fractions of CPA and activated with only Na₂SiO₃ to produce binders (CPAG). The PSA was added to the best fit of M7C/CPA as fast-setting-agent, while QD was added to the best fit of M7C/CPA/PSA to produce mortars. 100% kaolin clay activated with 8MNaOH/Na₂SiO₃ was used as reference geopolymer. The geopolymers were cured at R.T for 7 and 28 days and characterised for physical, mechanical and durability properties. Clay, CPA, PSA, QD and geopolymers were characterised using XRF, ATR-FTIR and XRD. Reactivity was studied using isothermal conduction calorimetry. The ATR-FTIR and XRD results indicated transformation of kaolinite to metakaolinite in the clay, presence of K-C-O bond in CPA and O-C-O bond in PSA. Reference geopolymers set at 4 h while CPAG ranged from 14 to 19 h. With the addition of PSA, setting time reduced to values between 4 and 11 h. The compressive strength of reference geopolymer was 18.1 ± 0.3 MPa at 28 days, while CPAGs values ranged from 23.5 ± 0.3 to 35.6 ± 0.3 MPa. Best compressive strength was achieved with 2% PSA addition. No shrinkage in CPA-containing geopolymers while reference geopolymer had value of 0.03%. Efflorescence tendencies of the CPA-containing geopolymers reduced by 25–75% when compared with reference. Application of CPA as alternative activator improved the mechanical property, durability and sustainability of geopolymers.

This study investigates the conversion of biotite, a subgroup of clay minerals, into photocatalysts through heat treatment with CaCl₂. The resulting reaction products were analyzed in terms of their composition, structure, optical properties, and photocatalytic activity against Cr^VI and salicylic acid (SA). Biotite and CaCl₂ mixtures could be heated to 600 °C while retaining the biotite crystal structure, whereas heating to 700 °C resulted in transformation to octahedral wadalite crystals. The band gap of the wadalite obtained after heat treatment was approximately 3.10 eV. The photocatalytic reduction rate per unit surface area increased markedly with increasing heat-treatment temperature, and the Cr^VI reduction and SA degradation rates of the sample calcined at 800 °C were approximately 18 and 9 times greater, respectively, than those of the sample calcined at 500 °C. Leaching tests of the reaction products revealed that the elution of Ca²⁺ and Cl⁻ was particularly significant. Even the samples that retained the biotite structure after heat treatment displayed some photocatalytic activity, indicating that this method may be applicable to preparing photocatalysts from mica and related minerals with similar structures.

Traditional techniques can be problematic due to secondary pollution while natural clay aroused great concern. For example, halloysite has high structural activity and excellent potential in toxic metals removal. The polymerization of halloysite to form Ca-zeolite with better metal-binding performance is of great significance for the immobilization of toxic metals. However, halloysite lacks exchangeable cations, which may restrict its polymerization conversion. Thus, it is efficacious to induce halloysite's structural recombination and speciation when calcium is introduced into the polymerization. The curly multilayer halloysite tubes in-situ unfolded and formed kelp-like Ca-zeolite by using calcium as a structure-directing agent. When the calcium content increased, the cubic zeolite was broken into pieces. The pore size distribution showed that micropores and mesoporous structure of halloysite disappeared and converted zeolite hierarchical shape. The characterization analysis indicated that new toxic metal compound groups were generated, confirming the lattice exchange of Ca and toxic metal ions in the Ca-zeolite. Otherwise, the lattice fringe showed that Pb was mainly immobilized on the 001 plane via ion exchange, while Cd formed inner complexes on the 110 plane. Above all, the halloysite-zeolite polymerization technology provides a new method for zeolite synthesis, which is significant for the control of toxic metal pollution in water.

Herein montmorillonite and halloysite have been exploited to prepare advanced lactoferrin-loaded nanohybrid biomaterials for potential biomedical applications. Nanohybrids were prepared following two methodologies: a traditional procedure which induces spontaneous drug-clay interactions to take place in aqueous environment and by spray drying, as alternative and preferred industrial technique for protein processing. Structural assembly of the obtained nanohybrids was assessed by solid state characterization techniques and determination of their surface charge properties. Full microscopy studies, including scanning electron microscopy and ultra-high resolution transmission electron microscopy coupled with EDS were also carried out. Cytotoxicity assays were performed to assess biocompatibility of nanohybrids towards human fibroblast cell cultures. Results showed that both intercalation-solution and spray drying procedures led to the effective formation of nanohybrids structures, with greater extent of peptide-clay mineral interactions in those obtained by spray drying. All the samples exhibited cell viability % higher than 80%, with best results for halloysite coupled with spray drying technique.

This study investigated the surface treatment of halloysite nanotubes (HNTs) with zinc oxide (ZnO) and used to enhance the mechanical properties of butyl rubber (SBR) composites. The prepared ZnO-modified HNTs (ZnO/HNTs) was characterized by X-ray diffraction (XRD), Fourier infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). The results indicated that ZnO particles were successfully loaded on the surface of HNTs and interacted with hydroxyl groups. The outer surface of HNTs became rough due to the loading of ZnO. The effects of ZnO/HNTs on the processing and mechanical properties of filled SBR composites were evaluated. The results showed that the ZnO/HNTs particles displayed a fine dispersion in the matrix system and have a strong interaction compatibility with rubber matrix chains. The tensile strength reached at the maximum of 9.35 MPa at a filler content of 60 phr, which was 405% and 31.69% higher than those of pure SBR and the HNTs/SBR composites, respectively. The enhancement of the mechanical properties of filled SBR composites is attributed to the fine dispersion of the ZnO/HNTs particles in the SBR matrix and the improved incorporation between the rubber molecules and the filler particles due to the loading of ZnO on the surface of HNTs, which restricts the movement of the rubber chains by entrapping molecules when the composites is subjected to stress loading.