Natural Kaolinite Research Articles

Synthesis of Graphene Oxide Enriched Natural Kaolinite Clay and Its Application For Biodiesel Production

A heterogeneous catalyst is one type of catalyst which is very effective for biodiesel production; thus, in this study, a novel heterogeneous bifunctional catalyst was prepared by kaolinite clay obtained from Padang of West Sumatera and impregnated with graphene oxide and potassium hydroxide (KOH) for the simultaneous esterification and transesterification reactions of palm oil into biodiesel. For comparison, two other catalysts were also prepared. The first catalyst was the same clay which was heated at 450ºC for 4 hours, and the second catalyst was the same clay which was impregnated with potassium hydroxide (KOH) only. The three catalysts were characterized using X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), and Fourier Transform Infra-Red (FTIR). XRF analysis showed that the clay sample’s main composition consisted of 54% silica, 35% alumina, and 7% hematite. The XRD analysis results showed that the most dominant crystal composition was quartz, kaolinite, and hematite. The analysis results using FTIR showed a change in intensity and shift in wave numbers indicating a cation exchange. The catalytic activity test was carried out with a ratio of oil and methanol 1:6, catalyst amount 5%, 60ºC reaction temperature, and 4 hours of reaction time.The results showed that the catalytic activity of clays impregnated with graphene oxide and potassium hydroxide was better with a yield of 58% compared to clays without impregnation and other clays that were only impregnated with KOH under the yields of 0.8% and 0.4%, respectively

Efficient and Low-Cost Removal of Methylene Blue using Activated Natural Kaolinite Material

Clays are low-price and very useful material for water treatment purpose. In this work, we reported the application of activated natural kaolinite material which obtained from Wediombo beach, Yogyakarta for methylene blue adsorption. The natural kaolinite material was activated under an acidic condition to obtain the activated kaolinite material. The activated kaolinite material was characterized using Fourier transform infrared, X-ray diffraction, scanning electron microscope, and surface analysis. From the adsorption experiment, the activated kaolinite material gave moderate adsorption percentages for methylene blue. The adsorption kinetics followed the Ho and McKay kinetic model while the adsorption isotherm followed Langmuir model. The qmax value for methylene blue adsorption using activated natural kaolinite material was at a moderate level (3.40 mg g-1). The plausible adsorption mechanism of methylene blue on the surface of activated kaolinite material happened through hydrogen bondings and/or electrostatic interactions. These findings are important for a wastewater treatment using a low-cost adsorbent material.

Effect of dimethyl sulfoxide intercalation into kaolinite on etheramine adsorption: experimental and theoretical investigation

This study evaluated the effect of dimethyl sulfoxide (DMSO) intercalation in natural kaolinite (KN) on etheramine adsorption. The effects of the parameters pH, initial etheramine concentration and adsorbent mass were investigated using central composite design. Optimal conditions were determined using response surface methodology. Theoretical calculations were performed to optimize the geometries of the kaolinite, DMSO, KDMSO, molecular and protonated etheramine structures, as well as the interaction between etheramine and kaolinite. XRD and FTIR results confirm the intercalation of DMSO into kaolinite, the intercalation process caused a significant increase in the isoelectric point. The results show that the adsorption was more efficient in pH 10 and etheramine concentration of 400 mg L-1 for both adsorbents, and 0.1 g of KN and 0.2 g of KDMSO. The kinetic data most accurately fit the pseudo-second-order model. The fitting of the experimental data to the isotherm models indicated that the Sips is the most appropriate model. The calculation of Eads revealed that mechanism of etheramine removal by KN and KDMSO involve chemisorption. The reusability tests determined that after four uses, the etheramine removal efficiency does not change significantly, enabling the use of kaolinite for wastewater treatment. Theoretical studies have enabled a better understanding of the intercalation process. In addition to increasing the interlayer spacing (2.50–8.01 Å), the introduction of the DMSO molecule modifies the charge distribution in the kaolinite structure, which contributes to the increase in the amount of etheramine adsorbed. The protonated etheramine molecule interacts more effectively with the KDMSO.

Structural Characterization and Antibacterial Activity of Antibiotic Streptomycin Immobilized on Zeolite Synthesized from Natural Kaolinite

This study evaluated the efficacy of antibacterial activities for a zeolite A (ZEO) sample loaded with streptomycin (STR). The ZEO was synthesized from kaolinite (KAO) via the alkaline hydrothermal process and verified with various techniques, such as X-ray Diffraction, Fourier-Transform Infrared spectroscopy, Field Emission Scanning Electron Microscopy with Energy Dispersive X-ray, Transmission Electron Microscopy, and dispersion behavior to confirm the production of ZEO with high purity and reproducibility. The cubic framework of ZEO was maintained after the immobilization of STR, indicating STR molecules' adsorption on the ZEO surface. The STR-loaded ZEO (ZS) samples were prepared in three STR concentrations (50, 100, and 200 mg/L). The samples' antibacterial activity was determined using the disc diffusion technique and minimum inhibition concentration against Gram-negative bacteria (Escherichia coli ATCC 11229) and Gram-positive bacteria (Staphylococcus aureus ATCC 6538). Both bacteria were susceptible to ZS, which showed an antibacterial effect directly proportional to the STR concentration. Thus, the synthesized ZEO synthesized from natural KAO had a good prospect as a carrier system for STR for generating a broad spectrum of antibacterial activity.

Synthesis and Characterization of NaA Zeolite Using Natural Kaolinite Clays from Nigeria by Low Temperature Hydrothermal Method

Zeolites NaA is one of the most valuable synthetic zeolites widely used as ion-exchange material, catalysts, and adsorbents in industry. There is therefore need to adopt a more energy-efficient route for its synthesis from low-cost and sustainable raw materials. In this present work, zeolites Na-A was synthesized from natural kaolinite clays obtained from three selected regions (Ikere, Okpella and Kankara) in Nigeria. The as-received kaolinite clays (IKclay, OKclay and KAclay) were initially beneficiated thoroughly to obtain pure powders (˂75 μm). The processed kaolinite clay powders were then subjected to heating in a muffle furnace at 850oC for 3 h at a heating rate of 10oC/min to convert the kaolinite clays to their respective metakaolins. The obtained metakaolins were then reacted with NaOH solutions at varying concentrations of 3.0 and 4.0M respectively using a low temperature hydrothermal transformation to obtained Zeolites Na-A powders. The obtained zeolites were then analyzed by scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FT-IR). The results showed that zeolite NaA is produced with mixture of hydroxysodalite (HS) while the EDS revealed the presence of Si, Al, O and Na indicating chemical constituents of typical zeolite NaA. All the tested kaolinite clays are therefore suitable for preparation of zeolite NaA as cheaper source of silica and aluminum.

The Effect of Aeration on Mn(II) Sorbed to Clay Minerals and Its Impact on Cd Retention.

Manganese is a redox-sensitive element in soils and sediments that plays an important role in the retention of trace elements. Under anoxic conditions, clay minerals were shown to increase Cd retention by favoring the precipitation of Mn(II) phases. In this study, we investigated the influence of aeration on anoxically formed Mn solid phases and its impact on Cd retention in the presence of two clay minerals with low Fe contents, a natural kaolinite (KGa-1b) and a synthetic montmorillonite (Syn-1). Ca-saturated KGa-1b and Syn-1 were pre-equilibrated with Mn2+ and Cd2+ under anoxic conditions for 1 or 30 days and subsequently exposed to air for 1 or 30 days. The analysis with synchrotron X-ray absorption spectroscopy (XAS) revealed that extended anoxic pre-equilibration (30 days) partially prevented the oxidation of sorbed Mn(II) (MnSiO3 and Mn(II)Al-LDH). Extended exposure to ambient air and short anoxic pre-equilibration favored the formation of feitknechtite (β-MnOOH) and birnessite (δ-MnO2). Aeration resulted in a decrease of pH and a net release of Cd2+ into the solution, indicating that Cd re-sorption by Mn(III/IV)-phases was insufficient to compensate for the release of Cd2+ due to dissolution of Mn(II)-containing phases and the decrease in pH. Our results demonstrate the significance of clay minerals in the (trans)formation of Mn-containing phases and their impact on trace metal retention in environments undergoing fluctuating redox conditions.

Regulation of hierarchically porous structures based on multi-scale nanosheets derived from kaolinite for enhanced adsorption

Hierarchically porous structures were regulated based on the size and surface charge by adjusting the ratios of silica and γ-AlOOH nanosheets (SiNSs and AlNSs). Above multi-scale nanosheets were derived from layered kaolinite via a selective etching-assisted exfoliation and the subsequent hydrothermal approach, respectively. The diverse structures and surface properties of as-prepared hierarchically porous nanosheets (HPNSs) were studied. As a result, the broad-ranged surface areas (217–544 m2/g) and pore volumes (0.49–2.24 cm3/g) of HPNSs are significantly greater than that of as-received kaolinite (23 m2/g and 0.22 cm3/g). The composition, pore structure and Zeta potential analysis reveal the different contributions of SiNSs and AlNSs to the hierarchical micro/meso/macroporous structure based on the steric hindrance effects of multi-scale nanosheets with electrostatic repulsion (pH = 8.5), while the surface charges of as-prepared HPNSs under neutral conditions are originated from the competition between negatively charged Si−OH (SiNSs) and positively charged Al−OH (AlNSs). The adsorption tests toward Congo red anionic dye show larger sorption capacities of the kaolinite-based HPNSs (63–786 mg/g) than that of natural kaolinite, and fast kinetic (within 30 min), further indicating the favorable adsorption characteristics of HPNSs due to the surface Al−OH groups (electrostatic attraction) and the hierarchically porous structures (physisorption and transfer). It exhibits the great potential of diverse kaolinite-based HPNSs as advanced functional materials in the fields of adsorption, separation, catalysis, energy storage and conversion, and biomedicine.

Modification of kaolinite clay using benzyltriethylammonium chloride as a surfactant: Preparation and characterization

Natural kaolinite clay from Perak, Malaysia with cation exchange capacity (CEC) of 2.5 meq/100g was modified using cationic surfactant, benzyltriethylammonium chloride (BTEA-Cl), at 0.5, 1.0, 1.5 and 2.0 times the CEC. A number of techniques, namely energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) nitrogen adsorption-desorption were then used for characterization of the kaolinite and/or organo-modified kaolinite clays. The presence of alkyl groups as a result of successful intercalation of cationic surfactant within the organo-kaolinite layers of the clay was exhibited by the FTIR spectra. The SEM microphotographs exhibited good dispersion of the natural clay particles and slight agglomeration in the organo-modified clay particles. XRD patterns showed that the d001 spacing of the natural kaolinite clay increased from 7.12 Å to between 7.20 - 7.34 Å for the organo-modified clays. Following the BET nitrogen adsorption-desorption technique, all clay samples were of Type IV with narrow hysteresis loops. Surface areas of the clays showed drastic decrease from (25.34 m2/g) for natural kaolinite clay to between 5.90 - 13.11 m2/g for organo-modified clays. The results suggested that modification of natural kaolinite clay using cation surfactant had successfully occurred. The modification can therefore be further applied for alteration and improvement of the properties of natural clays for various industrial applications.

Nanoscale structural and morphological features of kaolinite nanoscrolls

One-dimensional kaolinite nanoscrolls have been arousing great interest due to their applicability in advanced materials for adsorption and slow release of reagents, as well as in nanoscale reactors and carriers. Production of high-quality halloysite-like nanoscrolls with controlled morphology, however, remains challenging as there is a lack of understanding of the curling process of kaolinite layers on the atomic scale. In the present work, the nanoscrolls were efficiently produced from the readily available natural kaolinite using a two-pot solvothermal exfoliation of the kaolinite-dimethyl sulfoxide, kaolinite-urea, and kaolinite-N-methylformamide precursors. The structures, sizes, shapes and crystallographic properties of the produced halloysite-like nanoscrolls were characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and electron tomography in scanning transmission mode (STEM). In order to avoid structural disintegration of the highly electron beam-sensitive nanoscrolls, we used a low imaging current (70–240 e/A2); as a result, the acquisition of structure images was possible. In contrast to the triclinic symmetry of kaolinite, electron diffraction patterns suggest a hexagonal symmetry of exfoliated layers. Both HRTEM and STEM tomography show partially and completely rolled up layers, with the axis of curvature being parallel to either the a or b axes. The methanol-grafted nanoscrolls have a variable but larger basal spacing (from 0.76 to 0.90 nm) than the value in ordered kaolinite (0.72 nm). Their external diameters range from 22 to 75 nm, lengths from 218 to 2287 nm, aspect ratios from 5 to 74, and the scrolls have recognizable chirality. Crystallographic image processing of HRTEM structure images suggest that the tetrahedral sheet can be on either the outer or the inner sides of the nanoscrolls. Molecular simulation results for the curled kaolinite layers are consistent in their details with the experimental observations, suggesting that the layers may roll up either way.

Preparation of Ammonia Dealuminated Metakaolinite and Its Adsorption against Bixin

This study aims to prepare dealuminated metakaolinite which has a high surface area by using NH4OH as an activator. The natural kaolinite sample was treated at 600 °C for 6 h in order to obtain metakaolinite. A dealuminated metakaolinite was then prepared by the repeated activation method using concentrated ammonia (5 M NH4OH) at room temperature. Depending on the nature of each type of material, natural kaolinite, NH4OH treated kaolinite, metakaolinite and NH4OH treated metakaolinite were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and Brunauer-Emmett-Teller (BET-N2) measurements. XRD and FTIR results confirmed that structural transformation from kaolinite to metakaolinite had occurred. According to SEM-EDS data, the activation of metakaolinite by NH4OH allowed the dealumination of metakaolinite. The increase in the Si/Al ratio was almost twice as high as in kaolinite. BET-N2 analysis showed that the specific surface area and the total pore volume increased significantly after activation. Its adsorption properties were tested against bixin. Bixin adsorption on dealuminated metakaolinite followed pseudo-second order kinetic where k2 = 0.20 g/mg min. The adsorption isotherm followed the Langmuir model where qm = 0.72 mg/g.

Chemical, phase and structural change of mullite synthesized during sintering of kaolin

AbstractMullite is of great technological relevance but rarely occurs in nature and as a result different approaches have been adopted in its synthesis from alumina bearing minerals. In this study, chemical, phase and structural change of mullite synthesized from sintering of natural kaolinite clay is investigated. Thoroughly beneficiated kaolinite clay powder was obtained from Nigeria and uniaxially pressed into cylindrical compact of 40 × 30 mm followed by sintering at temperatures of 1200°C and 1300°C, respectively. The chemical composition, microstructure change, phase transformation, and reaction bonding were carried out using EDXRF, SEM, XRD, and FT‐IR, respectively, to assess the synthesized mullite. The results showed that a well‐dispersed primary mullite phase was obtained which was fully developed at increased temperature of 1300°C. Better mullite phase was also obtained with increasing alumina content at more elevated temperature of 1300°C while Si‐O‐Al bonding of mullite crystals was also obtained from the FT‐IR spectra. However, the needle‐shaped mullite structure was not achieved which might be attributed to the sintering temperatures 1200°C‐1300°C utilized.

Thermal behaviors and kinetic analysis of two natural kaolinite samples selected from Qingshuihe region in Inner Mongolia in China

The thermal characteristic behaviors of two kaolinite samples selected from Qingshuihe region in Inner Mongolia in China were studied through thermogravimetry, derivative thermogravimetry, and differential scanning calorimetry (TG–DTG–DSC), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy. The activation energies of dehydroxylation for the two kaolinite samples (determined as Kaol-1 and Kaol-2) were calculated based on KAS and FWO methods. The XRD results indicated that Kaol-1 and Kaol-2 both were determined as kaolinite, and a small amount of quartz, but the Kaol-2 presented many amorphous organic matters. The TG–DSC results displayed the adsorbed water desorption and dehydroxylation with the temperature increased from 200 to 1100 °C. The dehydroxylation is followed as the intensities decrease in the bands at 3690 cm−1, 3620 cm−1 and 914.0 cm−1 attributing to the stretching mode of inner surface hydroxyls, and which disappeared when the temperature reached at 600 °C. The endothermic peak temperature of dehydroxylation for Kaol-2 presented higher than that of Kaol-1, which may be attributed to present of amorphous organic matter and was in agreement with the XRD data. The maximum endothermic temperature of dehydroxylation increased both for Kaol-1 and Kaol-2 with the increase in heating rate, which was attributed to more sufficient decomposition as the decrease in heating rate. The thermal kinetic analysis indicated that the dehydroxylation reaction of Kaol-1 should be a single kinetic mechanism, but the E of Kaol-2 decreased as α increasing from 0.2 to 0.5 and then gradually increased with the increase of α. The average E of dehydroxylation for Kaol-2 both was lower than that of Kaol-1 based on Kissenger–Akahira–Sunose and Flynn–Wall–Ozawa methods, which was attributed to the relatively higher organic carbon content in Kaol-2.

Evaluation of phase transformation behaviors of zeolite and antibacterial properties against Gram‐positive and ‐negative bacteria

AbstractThis study deals with the synthesis of zeolite from natural kaolinite using hydrothermal treatment and evaluation of its phase transformation behaviors. The synthesized zeolites were modified with silver ion by using the ion exchange method for the enhancement of antibacterial properties. The characterizations were performed by using X‐ray diffraction spectroscopy, Fourier‐transform infrared spectroscopy, field emission scanning electron microscopy, and energy‐dispersive X‐ray. Disk diffusion technique (DDT) was used for the evaluation of the antibacterial property of the modified zeolites. This study observed the transformation of kaolinite into amorphous metakaolin after calcination treatment at 900°C and the successful reconstruction of amorphous metakaolin into synthesized crystal zeolite in the presence of sodium hydroxide as an activating agent. It was also found that the zeolite type A was produced at 100°C, while sodalites were produced at 120 and 140°C. DDT analysis revealed that the modified zeolites showed significant antibacterial capability against Escherichia coli ATCC 11229 and Staphylococcus aureus ATCC 6538. In general, the present study has proven that the zeolites can be synthesized from natural material and can be modified with silver ion to enhance their antibacterial activity.

Solar-active clay-TiO2 nanocomposites prepared via biomass assisted synthesis: Efficient removal of ampicillin, sulfamethoxazole and artemether from water

New solar-active nanocomposites free from toxic reagents or precious metals were developed. They were prepared from natural kaolinite clay, Na2WO4, titania, and biomass. The photocatalytic activity of the nanocomposites against two antibiotics [Ampicillin (AMP) and Sulfamethoxazole (SMX)] and an antimalarial drug [Artemether (ART)] under sunlight suggests an unusually fast photodegradation that is >90% complete in 30 min especially with the photocatalytic nanocomposite prepared from Musa paradisiaca peels (plantain peels) @ 500 °C (TZPP5). The presence of both biomass and TiO2 is essential for the effective function of the photocatalytic nanocomposites. With TZPP5, ca. 80% and ca. 50% mineralisation of AMP and SMX, respectively, was observed after 60 min. The photocatalytic reaction releases inorganic by-products (SO42-, NO3- and NH4+) at levels below WHO permissible limits for drinking water. The presence of anions reduces the efficiency of TZPP5, indicating that it releases electrons and reactive oxygen species that are also responsible for photodegradation of the drugs. However, changing concentrations of electrolyte (NaCl) do not influence its efficiency, suggesting that adsorption may not precede photocatalysis, contrary to common models. Reuse studies suggest a slight loss in photodegradation efficiency (≈6%) of the nanocomposite for AMP in the first two cycles followed by subsequent stability at 70% for subsequent cycles. This is different for SMX, which maintained ≈58% removal for all cycles after the 1st cycle. With efficient treatment of raw wastewater from an abattoir, a river, and a hand-dug well for drinking water, the photocatalytic nanocomposite shows potential for treating drinking water especially in point-of-use water treatment devices.

Rational design of efficient visible-light driven photocatalyst through 0D/2D structural assembly: Natural kaolinite supported monodispersed TiO2 with carbon regulation

In this work, kaolinite supported monodispersed TiO2 with carbon regulation was prepared through rational design and different dimensions’ assembly, leading to generation of TiIII species in carbon doped TiO2/kaolinite (C-TiO2/kaolinite) composite. The C-TiO2/kaolinite composite exhibited improved degradation performance towards ciprofloxacin under visible light, with a reaction rate constant of 0.00597 min−1, which is about 3.24 and 24.88 times higher than that of 2.0C-T (2.0% carbon-doped TiO2) and pure TiO2, respectively. Based on various materials characterization methods and DFT calculations, it was indicated that the electronic structure was correlated with the changes in light absorption, charge carrier lifetime, and reactive oxygen species (ROS). The enhanced visible light responding ability could be attributed to the synergistic effect between natural kaolinite and nanosized TiO2, the formation of localized occupied states in the gap, and the formation of TiIII defects consisted of surface oxygen vacancies. All of them effectively increase the separation efficiency, migration velocity, and lifetime of the photoinduced charge carriers under visible-light irradiation. Overall, our study provides a promising candidate for effective degradation of trace amounts of pharmaceutical and personal care products and other highly toxic contaminants with the assistance of solar light.

Plasma spraying of natural kaolinite and metakaolinite

Metakaolinite was obtained by thermal treatment of natural kaolinite. Both of them, kaolinite with structurally bonded water and metakaolinite without it, were, after sieving to acceptable size fraction, plasma sprayed. The coatings were rather lightweight and composed predominantly of amorphous material. Stainless steel was used for producing self standing deposits, whereas other materials like carbon steel or ceramic tiles formed a permanent substrate-coating system. Metakaolinite coating was less porous, harder and its thermal behavior was simpler compared to kaolinite. Crystallization and formation of secondary phases was monitored after annealing with and without dust particles known in the barrier coatings field as CMAS.

Cancrinite synthesis from natural kaolinite by high pressure hydrothermal method: Application to the removal of Cd2+ and Pb2+ from water

Abstract Zeolites were synthesized from natural Tunisian clay by hydrothermal treatment under high pressure (100 MPa H2O pressure) at different gradients of temperature in high pressure autoclaves. The natural clay was first heated at 650 °C (HC-heated clay) and then transformed to an amorphous phase at 650 °C by adding different amount of NaOH. By increasing temperature and NaOH content, low-density frameworks zeolites like faujasite are transformed into more stable zeolites having higher density frameworks like cancrinite due to dissolution and recrystallisation steps. Cancrinite (Na8(H20)2CO3[Al6Si6O24]) (IZA-code: CAN) was successfully synthesized with a good purity. The synthesized CAN was characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The removal performance of heavy metal ions (Cd2+, Pb2+) from solution by pure CAN and clays has been studied. The kinetics of adsorption of Cd2+ and Pb2+ are very fast: equilibrium is reached within 2 min at 298 K. The capacity of adsorption of CAN is higher for Pb2+ (192 mg g−1) than for Cd2+ (68 mg g−1). Adsorption equilibrium of Cd2+ and Pb2+ on CAN were well represented by Langmuir equation although the thermodynamic study reveals a more complex mechanism: thermodynamic parameters, such as equilibrium constant, free energy, entropy and enthalpy for adsorption were obtained from the experimental data, including adsorption microcalorimetry.

Immobilization of l-alanine into natural kaolinite via amidation catalyzed by boric acid for the development of biohybrid materials

The natural amino acid l-alanine was immobilized on the interlayer space and surface of the natural Brazilian São Simão’s kaolinite using two different routes. In the first 3-aminopropyltriethoxysilane was previously grafted into kaolinite interlayer space resulting into aminofunctionlized kaolinite that was further employed as reactive sites on kaolinite surfaces to bond l-alanine via amidation reaction. In the second route 3-aminopropyltriethoxysilane was first modified by l-alanine via amidation reaction catalyzed by boric acid and the modified alkoxide grafted into kaolinite using kaolinite-dimethylsulfoxide resulting on the biohybrid. In both strategies the amino acid was covalently bounded using the carboxylic acid from the amino acids and amine groups present on the kaolinite surfaces resulting in amide bonds. In both routes, the reaction was catalyzed by boric acid. Results confirms that the nature and loading of immobilized l-alanine changes depending of the route employed. X-ray diffraction confirmed the expansion of the interlayer spaces of the grafted solids resulting in 8.3 ​Å and 10.8 ​Å respectively for grafted materials routes one and two respectively. Reaction effectivity was kinetically evaluated by infrared vibrational spectroscopy that confirms the presence of amide bonds in both products due to the bands at 1560 ​cm−1, due to carbonyl (N–CO) stretching, and 1490 ​cm−1, ascribed to N–H plane vibrations and C–N stretching. The typical vibration of inner surface aluminol groups at 938 ​cm−1 (for purified kaolinite) is absent for both routes employed after grafting reactions confirming the attachment of the modified alkoxide into aluminol groups via covalent bonds resulting in bonds type Al–O–Si. Thermal analysis showed the typical reduction of dehydroxylation temperature from 510 ​°C on pure kaolinite to 480 and 450 ​°C, respectively, on the biohybrid materials and confirmed the functionalization in both routes, the amount of organic content was quantified and was 0.193 and 0.298 ​mol of organic unit per 1 ​mol of kaolinite minimal formulae using route of previous grafting of kaolinite with amine groups and direct grafting of modified alkoxide into kaolinite dimethyl sulfoxide respectively. Specific surface area analysis by N2 adsorption-desorption isotherms (BET method), cationic exchange capacity, and total specific surface area by the methylene blue method also confirmed the reduction of specific surface area from kaolinite grafted derivatives induced by amidation reaction. The solids obtained was tested as matrix to incorporate acetyl salicylic acid and ibuprofen and reveal that grafted clays incorporate a higher amount of both drugs (qt ​= ​210 ​mg/g) The model that explain the adsorption kinetic mechanism was the pseudo-second order that reveal the higher affinity between adsorbent and acetyl salicilSalicylic acid and ibuprofen using the grafted kaolinite with alanine.

Understanding Powder X-ray Diffraction Profiles from Layered Minerals: The Case of Kaolinite Nanocrystals.

Powder X-ray diffraction (PXRD) techniques are widely used to characterize the nature of stacking of submicrometer-wide nanometer-thick layers that form layered mineral nanocrystals, but application of these methods to infer the in-plane configuration of the layers is difficult. Line-profile-analysis algorithms based on the Bragg equation cannot describe the broken periodicity in the stacking direction. The Debye scattering equation is an alternative approach, but it is limited by the large-scale atomistic models required to capture the multiscale nature of the layered systems. Here, we solve the Debye scattering equation for kaolinite nanocrystals to understand the contribution of different layer-stacking defects to PXRD profiles. We chose kaolinite as a case study because its approximately constant composition and lack of interlayer expansion ensure that interstitial cations and/or molecules and substitutional ions can be ignored. We investigated the structure factor change as a function of crystal structural and microstructural features such as layer structure in-plane misorientation and shift (in or out of the 2D plane) and the diameter, number, and lateral indentation of the layers. Perfect and turbostratic stacking configurations bounded the range of intensity variation for hkl and 00l reflections, as well as for any scattering angle. A unique degree of disorder was computed by the average deviation from such limiting cases, and multivariate analysis was used to interpret the observed diffraction profiles. Analysis of the data for KGa-1, KGa-2, and API-9 standard kaolinites demonstrated that the estimated densities of different stacking defects are highly correlated. In addition, analysis of API-9 particle-size fractions revealed a dispersion of four or more components in the standard sample. The results illustrate that the use of a distribution of sizes, defects, and even individual kaolinite components is necessary to accurately characterize any sample of natural kaolinite.

Interfacial Chemical-Bond-Modulated Charge Transfer of Heterostructures for Improving Photocatalytic Performance.

Interface engineering of heterostructured photocatalysts plays a very important role in the transfer and separation process of interfacial charge carriers, but how to regulate the transfer and separation of photogenerated charge carriers still is a huge challenge at the nanometric interface of heterostructures (HCs). Herein, we demonstrate that interfacial chemical bonds can effectively modulate photogenerated charge transfer in nanoclay-based HCs constructed by natural Kaolinite (Kaol) nanosheets and P25-TiO2. Experimental results and density functional theory (DFT) calculations confirm that stable Al-O-Ti bonds form at the interfaces by interactions of the Al-OH groups of Kaol and (101) surfaces of anatase TiO2. The Al-O-Ti bond strengthens the energy band bending of the space charge region near the interfacial bond and thus provides a fast transfer channel for interfacial photogenerated charge, resulting in the boosted charge transfer and separation ability of Kaol/P25 HCs. The findings reported here provide a deeper insight into modulating interfacial charge transfer by chemical bonds and shed new light on interface engineering of efficient heterostructured photocatalysts for environmental applications.