Kaolin Surface Research Articles

Facile fabrication of Cu/kaolin nanocomposite as highly efficient heterogeneous catalyst for 4-nitrophenol reduction in aqueous solution

Hazardous organic pollutants in industrial wastewaters are becoming a major global challenge that threatens life on earth and particularly poses a serious health risk to human beings. 4-Nitrophenol (4-NP) is a highly hazardous organic contaminant that has been extensively utilized across multiple industries, and their wastewater disposal into water streams leads to a higher accumulation of 4-NP. It is therefore important for both academia and industry to make catalysts that are cheap, very effective, good for the environment, easy to recover, and can be used more than once for reducing 4-NP in normal conditions. This paper reports the synthesis, characterization, and application of Cu/kaolin nanocomposite (NC) as an efficient heterogeneous catalyst for decomposing 4-NP, a model organic molecule. The catalyst was synthesized by incorporating a copper precursor into layered kaolin clay and directly reducing the metal precursor using sodium borohydride (NaBH4). The morphology, structure, surface property, and interaction of the resulting Cu/kaolin NC were characterized by ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, scanning electron spectroscopy/energy-dispersive X-ray spectroscopy, selected area electron diffraction, X-ray diffraction, and N2 adsorption/desorption, and the results clearly demonstrated the growth of copper nanoparticles on the kaolin surface. It was discovered that the Cu nanoparticles (NPs) on the kaolin surface had a crystallite size of about 23.6 nm. The significance of Cu NPs and the high catalytic activity of the synthesized Cu/kaolin NC toward 4-NP reduction by NaBH4 were evaluated by the catalytic reduction experiments. Among the different nanocomposites synthesized, 30-Cu/kaolin showed the highest catalytic activity for 4-NP reduction, with a reduction efficiency of over 99 % within 4 min with a pseudo-first-order rate constant, kapp, of 1.23 min−1. Furthermore, the reusability test indicated that Cu/kaolin NC can be reused for up to six runs efficiently without significant decrease in its catalytic performance, indicating the nanocomposite has excellent stability and great potential applications in industrial and agricultural wastewater treatment.

Facilitating the rapid Grotthuss diffusion of OH− in electrolyte for accelerated oxygen evolution reaction

Faster OH− transfer for efficient adsorption on catalysis is key to accelerating the oxygen evolution reaction (OER). The diffusion of OH− in electrolyte mainly involves two mechanism which is dependent on the water coordination number (CN): Grotthuss diffusion (4 CN) and vehicular diffusion (5 CN). The Grotthuss diffusion is much faster but the vehicular diffusion of OH− is predominant in the electrolyte. Herein, negatively charged kaolin, which are simply dispersed in the electrolyte, are utilized to provide surface electrostatic attraction to H2O and repulsion to OH− to reduce the OH− CN from 5 to 4 for rapid Grotthuss diffusion. This contributes to the accelerated OH− adsorption which facilitates the charge transfer, the formation and the deprotonation of *OOH leading to enhanced OER performance. The OH− CN recovery from 4 to 5 is proved quite slow after leaving the kaolin surface, breaking the limitation that kaolin must be on the catalyst surface. This strategy exhibits universality for various electrocatalysts with reduced overpotential by 10–246 mV at 10 mA cm−2. We provide a clean, simple and low-cost way to promote the industrial development of alkaline water electrolysis.

Depth dewatering of kaolinite cake by SDBS/PEI synergy and a mesoscopic mechanism study

The objective of this study was to elucidate the synergistic dewatering mechanism of mixed sodium dodecylbenzene sulfonate (SDBS) and polyethyleneimine (PEI) on kaolinite filter cakes and to test the dewatering effectiveness of a custom-built pressure dewatering device. The dewatering experiments showed that while the reagent dose was reduced by 50%, the dewatering rate decreased to 19.78%, surpassing the optimal dose of a single reagent. During the natural compression stage of the filter cake, the deformation reached its maximum under the same pressure difference. During the transitional period, the closure of the filter cake pores occurred at a slower rate, facilitating better moisture drainage. Under strong compression, the ultimate deformation reached its maximum. PEI acted as a bridging agent for kaolin flocculation and served as a medium for SDBS on the kaolin surface. A small amount of PEI reduced the electrostatic repulsion of SDBS, increasing its adsorption capacity. PEI adsorbed on the kaolin surface through electrostatic and hydrogen bonding, while SDBS could adsorb onto the PEI reagent layer through electrostatic and polar interactions, exposing its alkyl chains on the surface and thereby facilitating flocculation and generating a hydrophobic reagent layer. This study could provide a new method and insights for the efficient pressurized dewatering of kaolin.

Green decorated of gold nanoparticles over kaolin mediated by plant extract and investigation of its anti-bile duct cancer properties in the in vitro condition

In the current research, kaolin-decorated Au nanoparticles were produced by a green medication method by using Strawberry root’s extract as a natural coating and reducing component for capping and stabilizing Au NPs over the kaolin. The Au NPs/kaolin material was thoroughly characterized using XRD, FE-SEM, EDX-elemental mapping, TEM, and ICP. Characterization data confirmed the well-supporting of Au NPs over the kaolin. TEM images displayed the spherical shaped gold nanoparticles averaging 20–40 nm in size over the kaolin surface. The cytotoxicity and anti-bile duct cancer properties of Au NPs/kaolin were investigated through the utilization of MTT assay on three bile duct cancer cell lines, namely OCUCHLM1, EGI1, and GBCSD. Au nanoparticles (Au NPs) combined with kaolin exhibited dose-dependent anti-bile duct cancer properties and significantly reduced cell viability in OCUCHLM1, EGI1, and GBCSD cell lines. Importantly, these effects were observed without causing any cytotoxicity in the normal cell line (HUVECs). The OCUCHLM1 cell line exhibited the most significant anti-bile duct cancer effects when treated with Au NPs/kaolin, surpassing the results observed in other cell lines. Upon the successful validation of the aforementioned findings in the clinical trial investigations, Au NPs/kaolin could potentially serve as an effective chemotherapeutic agent in combating bile duct cancer.

Bio-inspired deposition of gold nanoparticles onto the surface of kaolin for in vitro management of human ovarian cancer and modulation of the inflammatory response in adenomyosis-induced mice in vivo via the MAPK signaling pathway

A mild and eco-friendly protocol has been developed for the preparation of kaolin-decorated Au nanoparticles mediated by Ephedra root extract as a green reducing and stabilizing agents without any toxic substrates. Structural features of the prepared Au NPs/Kaolin were assessed through FE-SEM, TEM, and XRD techniques. TEM images show the good deposition of Au NPs over the surface of extract-modified kaolin without aggregation. Towards the medicinal application, its antioxidant efficacy was assessed by the DPPH method, and the corresponding IC50 value was obtained as 104 μg/mL. Cytotoxicity of the nanoformulated bio-composite was ascertained through MTT analysis against human ovarian carcinoma cells, i.e., PA-1 and SK-OV-3. The IC50 in those studies was 250 and 119 μg/mL against PA-1and SK-OV-3 cells, respectively. In the in vivo design, tamoxifen was used to induce the experimental adenomyosis model in mice. After treatment, the thymus, spleen, uterine, and body weights of all animals were measured. Then, inflammatory factor expression and myometrial infiltration were determined by qRT-PCR, ELISA, and histology examination in the uterus. Western blotting, qRT-PCR, and immune histochemical (IHC) staining were applied to analyze the MAPK/ERK signaling pathway protein expression. Au NPs/Kaolin bio-nanocomposite ameliorated the adenomyosis symptoms by raising the thymus and spleen index and decreasing the myometrial infiltration. The raised levels of TNF-α, IL-6, and IL-1β in adenomyosis model mice uterus and serum were also reduced after Au NPs/Kaolin bio-nanocomposite treatment. The adenomyosis amelioration of Au NPs/Kaolin bio-nanocomposite was gained by preventing the MAPK/ERK signaling pathway, including decreasing the expressions of protein and mRNA of p-p38/p38, p-JNK/JNK, and p-ERK/ERK.

Laboratory testing on cracking characteristics and improvement mechanism of coral mud

In recent years, the development and construction of island reefs have been flourishing. Due to the remoteness of island reefs from the mainland, the scarcity of building materials, and the high transportation costs, it is imperative to use local marine resources, and the potential value and status of coral mud on island reefs, which is formed by the remains of corals and other biological entities, is becoming increasingly prominent. Utilization and optimization of natural resources on island reefs have become a brand-new research direction and challenge. This article mainly focuses on the development of a new type of green engineering material, coral mud, for use in building surface layers. Thickness effects, PVA fiber (vinylon staple fiber) modification, and HPMC (Hydroxypropyl Methyl Cellulose) adhesive modification are taken into consideration. Through laboratory tests and image processing technology, fractal theory, and electron microscopy experiments, the macro-meso-microscopic multi-scale cracking rules of the coral mud surface layer and the optimization modification rules of PVA fibers and HPMC adhesives are revealed. The results demonstrate that the performance of the coral mud surface layer is superior to that of the kaolin surface layer, and the 10 mm thickness performs better than the 5 mm and 20 mm thicknesses. As the thickness of the coral mud surface layer increases, the contact between coral mud particles becomes denser, the scale of surface micro-cracks decreases, and the number of micro-pores decreases. PVA fibers can effectively inhibit the further development of macro and micro cracks and play a good bridging role. There is a bonding and adhesion relationship between coral mud and PVA fibers, and they have a good synergistic effect in inhibiting macro and mesoscopic cracks. With the increase in HPMC adhesive content, the number of micro-cracks and the scale of micro-cracks decrease accordingly, and the structure and performance of the coral mud surface layer are further improved. Overall, PVA fibers are more effective than HPMC adhesives in inhibiting the cracking of the coral mud surface layer. This provides valuable guidance for the development and application of coral mud in wall surface materials.

Study Of Effect Adsorption Of E127 Dye By Iraqi Clay From Aqueous Solution

Abstract
 The surface of kaolin was diagnosed by an AFM and the results were shown The height of the highest peak reached by a quantity of Kaolin ‎surface is 2.5 µm, the granules, and their diameter with an average diameter of 666.1nm. Using Kaolin's adsorption properties, erythrosine was removed of its aqueous solution. It was determined that the maximal dye adsorption ranged 36.53–40.61%. ‎‎‎‎The results of using the Freundlich, Langmuir, and Temkin adsorption isotherms revealed that at temperatures of (298,308,318) K, the Freundlich model was followed, the Langmuir model did not match, and the Temkin model could only be partially applied. There is also physical adsorption. One of the three kinetic models of the adsorption process that was examined, the pseudo-second-order model, was found to be applicable significantly based on the result. When the thermodynamic functions were computed using the value of the enthalpy, the process was proven to be exothermic, which was negative and equal to (-16.5582 KJ/mol). The entropy ∆°S value, which equaled (-2.2696 J/mole.K), was also negative. Calculating the Gibbs free energy, it was discovered that the process is exothermic adsorption, non-spontaneous, and happens without randomization. ‎‎‎

Influence of silica-aluminum materials on heavy metals release during paper sludge pyrolysis: Experimental and theoretical studies

It is of great significance to reduce the secondary risk of heavy metals during the pyrolysis of paper sludge. This study used kaolin and alumina-silica-based xerogels to control heavy metals released during sludge pyrolysis. Pyrolyzing a mixture of sludge and 7% kaolin at 400 °C achieved high retention rates for Cu (95.85%), Zn (95.97%), Pb (97.15%), Cd (84.23%), and Cr (84.05%) when the pyrolysis tail gas was treated with 9 g of xerogel. The addition of kaolin facilitated the transformation of Cu, Zn, Pb, and Cr from the unstable fraction to the stable fraction in pyrolysis biochar, reducing their leachability. The xerogels also played a crucial role in adsorbing and stabilizing the heavy metals. The results of thermodynamic equilibrium calculations showed that Pb(g), PbS(g), PbCl2(g), PbCl(g), Zn(g), ZnCl2(g), and Cd(g) were the main gaseous products of Zn, Pb, and Cd during paper sludge pyrolysis. The Pb atoms in PbCl2 and PbS, and the Zn atoms in ZnCl2 bond with the oxygen atoms on the kaolin surface by covalent bonds, while the Cl atoms in PbCl and the Pb atoms of elemental lead form ionic bonds with H and O atoms on the kaolinite surface, respectively. These experimental and simulation results offer new ideas for controlling heavy metals during sludge pyrolysis.

Aggregation behavior and mechanism of kaolin particles suspension in the presence of Xanthan gum and Fe(III)

Aggregation is an economical and widely existing method to in fine particles dewatering, but the mechanism of composite applications of inorganic coagulants/flocculants remains unclear. In this work, the aggregation process of kaolin particles using Fe(III) and xanthan gum (XG) was investigated by settling testing. The results shows that the combination XG and Fe(III) was effective in the flocculation of kaolin, which due to the self-assembly multilayers built onto the surface of kaolin. Further, density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) analyses were performed to detect the flocculation mechanism. It was found that [Fe(Ⅲ)(OH)]2+, [Fe(Ⅲ)(H2O)6]3+ and [Fe(Ⅲ)(OH)2]+ were the dominant species, which could complex with the XG on kaolin surface by the Fe-O adsorption site. However, the precipitate Fe(OH)3(s) covered on the kaolin surface is difficult to combine XG by coordination reaction under alkaline conditions. The research elucidated a new insight into of composite applications of inorganic coagulants and flocculants which could expand our knowledge of aggregation process, further define the relationship between coagulation and flocculation for enhancing colloidal particle settling in practical application.

Preparation, properties and formation mechanism of hydroxyl-silicone oil coating on the surface of kaolin/ TiO2 composites

A simple and effective preparation method of the powder surface coating was found. Namely, spraying hydroxyl-silicone oil (HSO) ethanol solution on the surface of calcined kaolin and nano-TiO2 composite (CKT) powder and formed the HSO layer due to the volatilization of ethanol. Subsequently, the samples were heated at 250 ℃ to form the HSO cure coating. The FT-IR, MAS NMR, XPS and SEM measure results indicate that the surface modification reaction occur between the OH groups in HSO molecules and HO-AlVI in the calcined kaolin. No any chemical reaction carry out on the Si, Ti sites on the surface of CKT composites. The performance testings show the HSO modification reaction dramatically improve the hydrophobicity of the CKT composites. The modification coating has no any negative effect on the whiteness, but the oil absorption values slightly reduce. Interestingly, it increases again after curing because the HSO layer releases a large great of lipophilic groups such as CH3 and CH2 during the curing process. The comparison of performances with nano-TiO2 and calcined kaolin shows that the CKT composites are expected to replace nano-TiO2 in many fields.

Adsorption, Kinetics and Thermodynamics of Reactive Blue 21 Textile Dyestuff Using Copper Doped Zinc Oxide Nanocomposite Decorated on Kaolin Surface

Bu çalışmanın amacı; tekstil endüstrisinde yaygın olarak kullanılan bir boyarmadde olan Reaktif Mavi 21 (RM21)’in atık sulardan adsorpsiyon yöntemiyle uzaklaştırılmasında kaolin yüzeyine dekore edilmiş bakır katkılı çinko oksit nanokompozitinin adsorban olarak kullanılabilirliğinin araştırılmasıdır. Adsorpsiyon üzerine, başlangıç RM21 konsantrasyonu, adsorban miktarı, sıcaklık ve denge süresi gibi çeşitli deneysel parametrelerin etkileri incelenmiştir. Adsorpsiyon hızının ikinci mertebeden hız ifadesine uyduğu ve kaolin yüzeyine dekore edilmiş bakır katkılı çinko oksit nanokompozitinin RM21 üzerine adsorpsiyonunun Redlich-Peterson izoterm modeliyle uyum sağladığı görülmüştür. Bu çalışmanın sonuçları, RM21’nin sulu çözeltilerden uzaklaştırılmasında kaolin yüzeyine dekore edilmiş bakır katkılı çinko oksit nanokompozitinin etkili bir adsorban olarak kullanılabileceğini göstermiştir.

Impact of Bacillus species on Fe reduction of kaolin in bioleaching: surface, structural, and chemical studies.

Conventional techniques to remove Fe impurities in kaolin typically involve high environmental impact and cost. Alternative methods have been focused on the use of bioleaching where Fe in kaolin is reduced with microorganisms. Early results established a noticeable effect of the bacteria on the redox state of Fe, but knowledge gaps persist such as details on the bacterial-kaolin interactions during attachment of bacteria onto kaolin surface, the metabolites produced by bacteria, and changes in Fe(II)/Fe(III) ion equilibria in solution. To bridge these gaps, this study was conducted to determine the detailed physicochemical changes in bacteria and kaolin during bioleaching through surface, structural, and chemical analysis. Bioleaching experiments were conducted for 10days where each of the three Bacillus sp. was put in contact (at 9 × 108CFU) with 20g of kaolin powder using 200mL of 10g/L glucose solution. All samples treated with bacteria showed increasing trends in Fe(III) reduction up until day 6 or 8 followed by a slight decrease towards the end of the ten-day period. Examination of scanning electron microscope (SEM) images suggests that bacterial activity damaged the edges of kaolin particles during bioleaching. Ion chromatography (IC) results showed that during bioleaching, Bacillus sp. produced organic acids such as lactic acid, formic acid, malic acid, acetic acid, and succinic acid. EDS analysis of kaolin before and after bioleaching showed Fe removal efficiencies of up to 65.3%. Analyses of color properties of kaolin before and after bioleaching showed an improvement in whiteness index of up to 13.6%. KEY POINTS: • Dissolution of iron oxides by Bacillus species proven with phenanthroline analysis. • Organic acid type and concentration unique to species detected during bioleaching. • Whiteness index of kaolin is improved after bioleaching.

Kaolin-Supported Silver Nanoparticles as an Effective Catalyst for the Removal of Methylene Blue Dye from Aqueous Solutions.

Water contamination by organic dyes has become a reason for severe environmental pollution and has been threatening the aquatic ecosystem. In this study, kaolin-supported silver nanoparticle (Ag-NP) composites were synthesized by a facile two-step adsorption-reduction method through the reduction of silver ions adsorbed onto locally available, inexpensive, and easily pretreated kaolin surfaces by using sodium borohydride (NaBH4) for the catalytic degradation of methylene blue (MB) dye in aqueous solution. The morphology, structure, surface area, and interaction of the synthesized materials were investigated by scanning electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller, and Fourier transform infrared spectroscopy, respectively. Characterization results showed the successful growth of Ag-NPs on the kaolin surface. To understand the catalytic degradation performance of the catalyst, batch experiments were carried out using MB dye as a model dye. The catalytic reduction tests confirmed the importance of Ag-NPs and the high catalytic activities of the synthesized Ag-NPs/kaolin composite toward MB dye reduction. The degradation results indicated that the increased Ag-NP content on the kaolin surface through repeating cycles could effectively enhance the removal of MB dye from an aqueous solution. The kinetic analysis of the MB dye degradation of the catalyst has fitted the pseudo-first-order kinetic model. More than 97% removal efficiency was still present after five reuse cycles, demonstrating exceptional stability and reusability of the composite. In conclusion, the Ag-NPs supported kaolin (Ag-NPs/kaolin) composite was found to be a promising catalyst for the excellent catalytic activity to reduce a model dye MB from the aqueous solution in the presence of NaBH4 with catalytic efficiency higher than 97% and a reduction rate constant, k red, higher than 0.86 min-1.

Kaolin supported heteropoly acid catalysts for methacrolein oxidation: Insights into the carrier acidity effect on active components

The application of heteropoly acid catalyst in methacrolein (MAL) oxidation reaction is limited for its poor thermal stability and few active centers. Here, the supported catalyst of P-Mo-V heteropoly acid (CsNH4KPMoV) active components supported on kaolin were prepared, and were characterized by FT-IR, TG/DTA, XRD, N2-adsorption and desorption, NH3-TPD, TPO-MS and XPS. The results show that kaolin was weak acidity and the negative charge on the surface of kaolin promoted the reduction of V5+ species to V4+(VO2+) active species. There was a strong electron interaction between kaolin and HPVA, and chemical adsorption occurred by DFT calculations. Under optimal conditions, higher MAL conversion (81.8%) and Methacrylic acid (MAA) selectivity (88.2%) were obtained by 50CsNH4KPMoV/kaolin catalyst. The Keggin structure was maintained and the acid strength and acidity did not decrease after the catalyst was used continuously for 100 h. There was no carbon deposition in the reaction process.

Adsorption of Fe metal in groundwater by magnetite-kaolinite

The magnetite-kaolin was synthesized via coprecipitation method with variation kaolin-magnetite = 1:1, 2:1, 3:1 and the material used to remove Fe metal in groundwater. The kaolin clay, magnetite, and kaolin-magnetite composite was characterized by X-ray diffraction, Fourier transform infra red, and adsorption efficiency test for Fe metal ion. The results indicated magnetite particle adhering to the surface of kaolin by lewis interaction. The results for adsorption kaolin:magnetite = 1:1, 2:1, 3:1 in groundwater showed better results compares to kaolin and magnetite. The optimum kaolin-magnetite adsorb Fe metal in 2:1 ratio with a stirring time of 60 minutes and the eficiency adsorption values is 73.35%. Based on this results, kaolin-magnetite composite can be relied in water treatment with the advantages of high adsorption capacity and the presence of magnetic properties to facilities the procces of transferring adsorbent and adsorbat.

Interaction of cyanidin with a hydroxylated surface (kaolin), modeling the effect of pН

The development of interest in anthocyanins in recent years is associated with an increase in the range of applications of these natural glycosides, contained in plants and berries, the color changes from red to blue with increasing pH. In addition to coloring properties (clay, fabric, hair), the use of anthocyanins – components of red and blue berries (including blueberries) – helps to reduce the risk of cardiovascular disease, Parkinson's disease and more.Most practical studies concern the interaction of anthocyanins with surfaces (clay, tissue, gastrointestinal mucosa, etc.) that have many hydroxyl groups. Therefore, the question of determining the approximate pH range is relevant, in which such an interaction is most likely. The aim of the work was to determine the priority form of the dye (according to the pH of the medium), which can be better fixed on the surface of kaolinSimulation of the interaction of cyanidin with the surface of white clay was performed by the Hartree-Fock-Rutaan method, using the GAMESS software package.The paper presents the results of modeling the interaction of different forms of the anthocyanin model – cyanidin (the content of cyanidin in plants is 50 % of the mass of all types of anthocyanins) in solutions with pH<3 (red – forms of cyanidin), 3<pH<7 (violet) and pH>7 (blue) with a hydroxylated surface of white clay – kaolin, having different types of hydroxyl groups.
 The aglycone part of the cyanidin molecule artificially was approached at a distance of approximately 2.5 Å to the surface of kaolin.
 It was shown, that the quinoid form of cyanidin (violet) was the most active of the three forms, mainly in interaction with the silanol groups of the kaolin surface. The form of cyanidin at pH<3 (red) have the lowest energies of interaction with the surface of kaolin

Synthesis of adsorption materials based on volcanic glass and kaolin

Obtaining adsorbent materials based on cheap and available raw materials for water purification from toxic cadmium ions is an important environmental task. It is economically feasible and promising to use natural clays and silicates modified with iron-containing compounds, for example, zero-valent iron.
 Adsorbents based on kaolin, volcanic glass (perlite), and nanoscale zero-valent iron (Fe0) were studied using the methods of scanning electron microscopy, IR-spectroscopy, X-ray phase analysis, and the method of low-temperature nitrogen adsorption-desorption. Adsorption experiments were performed to evaluate the efficiency of Cd2+ removal from water. The equilibrium metal concentration was determined by inductively coupled plasma atomic emission spectroscopy. The successful completion of modifying the surface of kaolin and perlite with nanoscale zero-valent iron is confirmed by the obtained IR-spectra of the samples, which show characteristic bands at 447 and 682 cm-1, which correspond to Fe-O valence vibrations. On morphology photos of the pure perlite show many artificially formed open and closed pores of different diameters. A typical layered structure is observed for kaolin. After modification of silicates with zero-valent Fe0, clusters of nanosized iron particles appear in the images. The diffractograms of the modified adsorbents show the formation of a crystalline phase of zero-valent iron (α-Fe0), its oxides (FeO), and oxyhydroxides (FeOOH). After applying a layer of iron-containing compounds, the specific surface of the obtained samples increases by 20 - 25%. For modified kaolin and perlite, it reaches values ​​of 12 cm2/g and 10 cm2/g, respectively. At the same time, the total volume of pores increases by 1.5-3 times, but their radius decreases. Thus, the pore radius of the modified kaolin is 2.36 nm, and that of the pure one is 4.3 nm. Coincident, for the modified samples of perlite, there is an insignificant decrease in the size of the pores compared to the unmodified sample - 2.05 nm and 2.36 nm, respectively. This is because, in the modification process, a porous reaction layer of nanosized iron is formed on the surface of silicates, which by its properties differs from the inorganic matrix. The main physicochemical features of removing cadmium ions from water were determined to determine the effectiveness of the obtained adsorbents. During research of the optimal conditions were studied the influence of the concentration of adsorbents, the pH of the aqueous medium, the kinetics of the cadmium removal process and the construct of adsorption isotherms. Under the given research conditions, the optimal dose of adsorbents for the maximum removal of cadmium ions from water is 2 g/l. The study of the dependence of the contact time of modified materials and model solutions on the efficiency of cadmium removal showed that its removal from water occurs relatively quickly. In 20 minutes of interaction, the samples adsorbed about 96% of Cd2+. Experiments to study the effect of pH on adsorption processes established that the degree of Cd2+ removal does not depend on the pH of the aqueous medium in the range of 3.2 - 7.5. The maximum value of cadmium adsorption is 7.8 mg/g for the perlite-based composite and 8.0 mg/g for the kaolin-based material, which is significantly higher than that for the natural silicates - 0.16 mg/g and 0.35 mg/ g respectively. Adsorption isotherms were calculated using the empirical Freundlich and Langmuir equations. The calculated parameters of the equations indicate that the Langmuir equation better describes the adsorption isotherms on the pure kaolin and perlite (correlation coefficients R2 are 0.978 and 0.946, respectively). In order, the Freundlich equation better describes the isotherms for the modified samples of kaolin and perlite (R2 is 0.990 and 0.980, respectively).
 Applying a layer of nanosized zero-valent iron on the surface of natural silicates significantly increases their adsorption capacity to cadmium ions. The resulting composite materials are promising for deep purifying polluted waters with heavy metals in concentrations close to the maximum permissible.

Deposition kinetics of bacteriophage MS2 on Microcystis aeruginosa and kaolin surface

Waterborne virus contamination might easily adsorb on the organic or inorganic surface in the complex aquatic environment. A quartz crystal microbalance coupled with dissipation monitoring was used to investigate the effects of the ionic strength of monovalent cation and divalent cation and pH on the deposition kinetics of bacteriophage MS2 on silica surface coated with Microcystis aeruginosa or kaolin, which represents organic or inorganic particle, respectively. Derjaguin–Landau–Verwey–Overbeek theory was used to illustrate the deposition mechanisms of MS2. The increased concentration of Na+ significantly enhanced the deposition rates of MS2 on both coated silica surfaces due to the reduction of repulsive electrostatic interactions. However, the MS2 deposition rates decreased at higher ionic strength of Ca2+, which accounted for the steric and hydrophobic interactions. And the higher MS2 deposition rates on both surfaces occurred at pH 3. In addition, the deposition rates of MS2 on kaolin-coated silica surfaces were higher than on the Microcystis-coated surface under all studied conditions. Furthermore, the Derjaguin–Landau–Verwey–Overbeek theory could elucidate the deposition mechanism in Na+ solution, whereas the steric and hydrophobic interactions should be considered for the presence of high concentration of Ca2+.

Engineered Geomedia Kaolin Clay-Reduced Graphene Oxide-Polymer Composite for the Remediation of Olaquindox from Water.

Globally, there is an upsurge in the use of unregulated veterinary pharmaceuticals with enhanced release into the environment, resulting in water pollution, which is difficult to remediate. To address this issue, we synthesized and characterized highly hydrophobic three-dimensional ordered engineered geomedia with multiple channels. Kaolin clay (K) was functionalized with either graphene oxide (GO) synthesized via Tour’s method or reduced GO in situ with covalently linked methoxyether polyethylene glycol (GO-PEG) using a simple and easily scalable amidation reaction. This was done to enhance the adsorption of olaquindox, a veterinary antibiotic. The X-ray diffraction profile confirmed the grafting of GO and GO-PEG to kaolin. Morphological analysis revealed the architecture of thin films of GO/GO-PEG grafted on the kaolin surface with extensive porosity. Energy-dispersive X-ray mapping, infra-red spectra, and elemental analysis confirmed the successful synthesis of the engineered geomedia composite of K, GO/rGO, and PEG (KrGO-PEG). Due to multiple surface functional groups of polyamide and amido-carbonic groups on the KrGO-PEG composite, it was suitable for olaquindox adsorption. In batch sorption studies of 0.5XKrO-PEG, the effect of pH (2–10) was negligible but with fast equilibrium time (2–1440 min) at 30 min, while the kinetics and equilibrium data suited the pseudo-second order and Langmuir models, respectively. The maximum adsorption value obtained for the composite was 59.5 mg/g; the higher the GO content, the higher the adsorption. The sorption mechanism was majorly through hydrophobic and π–π interactions. Regenerated/reused adsorbents after 4 cycles had the same efficacy in remediating olaquindox from simulated/real water.

Experimental and theoretical studies on the adsorption performance of lead by thermal pre-activation and phosphate modified kaolin sorbent

Lead removal from flue gas continues to be an important environmental issue. Adding sorbents in the furnace is a reliable method to control lead emission. Modified kaolin sorbent developed by a combined method of thermal pre-activation and phosphate impregnation was first applied to capture lead from flue gas. Modified kaolin exhibited higher PbCl2 removal performance than raw kaolin at 800–1100 ℃. The best adsorption performance of raw and modified kaolin was obtained at 1000 ℃ with adsorption efficiencies of 76.72 % and 85.87 %, respectively. The adsorption capacity of modified kaolin was about 283.51 mg/g at 1000 ℃. Lead aluminosilicate and lead phosphate were produced in the adsorption reaction. O2 was conducive to the conversion of PbCl2 to PbO, and directly participated in the formation of lead aluminosilicate· H2O was in favor of the adsorption reaction, and reduced the energy barrier for dechlorination of PbCl2, and promoted the eutectic melting process. SO2 and NO inhibited PbCl2 removal due to the competitive adsorption between SO2/NO and PbCl2 at the active sites. High concentration of HCl can obviously suppress the reaction of PbCl2 and modified kaolin. Quantum chemistry calculations were conducted to identify the active sites, and to uncover the molecular-level interaction of PbCl2 and modified kaolin. Theoretical results manifested that PbCl2 adsorption was chemisorbed on kaolin (001) surface. The adsorption energies of PbCl2 on raw kaolin and modified kaolin were − 124.60 and − 205.90 kJ/mol, respectively. Al, O and P atoms of modified kaolin were identified as the active sites for PbCl2 adsorption.