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

Adsorption of cadmium (II) on organic xerogel microspheres: effect of adding sepiolite or vermiculite and operating conditions on the adsorption capacity

The organic xerogel (OX) was synthesized through sol-gel polymerization of formaldehyde and resorcinol in inverse emulsion using Na2CO3 as a catalyst. Meanwhile, OX containing sepiolite (OX-Sep) and vermiculite (OX-Ver) were prepared similarly to OX but adding clays during synthesis. All materials were mesoporous and presented spherical morphology, and the surface of these materials exhibited an acidic character because the concentration of acidic sites was higher than those of basic sites. Cd(II) adsorption from aqueous solutions onto OX, OX-Sep, and OX-Ver was examined, and the OX-Sep showed the highest adsorption capacity towards Cd(II) of 189.7 mg/g, being 1.5, 2, and 36 times higher than that of OX-Ver, OX, and Sep. The OX-Sep capacity for adsorbing Cd(II) was significantly lessened by decreasing the pH from 7 to 4 and raising the ionic strength from 0.01 N to 0.1 N. This trend was ascribed to electrostatic attraction between the Cd+2 in water and the negatively charged surface of OX-Sep. Besides, desorption studies at pH 4 showed that the average desorption percentage of Cd(II) adsorbed on OX-Sep was 80%. The characterization results and the effect of the operating conditions on the adsorption capacity proved that electrostatic attraction and cation exchange play a crucial role in the adsorption mechanism.

Adsorption of Cd (II) ions and methyl violet dye by using an agar-graphene oxide nano-biocomposite

In this work, an agar-graphene oxide hydrogel was prepared to adsorb Cd (II) and Methyl Violet (MV) from water. The hydrogel was synthesised and characterised through SEM and EDS. Kinetic, equilibrium and regeneration studies were carried out, in which Langmuir, Freundlich and Sips isotherm models were fitted to the equilibrium experimental data; and regarding the kinetics, studies were conducted by modelling experimental data considering both empirical and phenomenological models. SEM and EDS have shown the composite present a 3D-disordered porous microstructure and that it is mainly constituted of C and O. Sips model fitted well to Cd (II) (R2 = 0.968 and χ2 =  0.176) and MV (R2 = 0.993 and χ2 =  0.783). The qmax values for MV and Cd (II) were 76.65 and 11.70 mg.g-1, respectively. Pseudo-order models satisfactorily described Cd (II) and MV adsorption kinetics with R2 > 0.90. Regeneration experiments revealed an outstanding reuse capacity of the adsorbent after three cycles of adsorption-desorption for both Cd (II) and MV. This study evidences the possibility of a feasible adsorbent for Cd (II) and MV removal from water for successive cycles of use.

Investigation of adsorption potential of acid violet 90 dye with chitosan/halloysite/boron nitride composite materials

In this study, composite adsorbents consisting of a mixture of chitosan (CTS), boron nitride (h-BN) and halloysite (HNT) were used for the adsorption of Acid Violet 90 (AV90) dye in a batch system. Adsorbents CTS, CTS/HNT, CTS/h-BN and CTS/h-BN/HNT beads were prepared by simple dropping method and dried in a freeze dryer. The beads were characterized by FT-IR, SEM and zeta potential analysis. The effects of pH (2-8) and dye concentration (50-250 mg/L) on AV90 adsorption properties of beads were investigated. In addition, Langmuir, Freunlich, Temkin and Henry adsorption isotherm models were used to examine the dye adsorption mechanism. It was observed that the Langmuir and Freundlich adsorption isotherm models were in good agreement with the experimental data. In the dye concentration range studied, the qm values of CTS, CTS/h-BN1, CTS/h-BN3, CTS/HNT/h-BN1, CTS/HNT/h-BN3, CTS/HNT obtained from the Langmuir isotherm model was 27.62, 17.80, 10.11, 8.71, 32.57, 19.96 mg/g, respectively. Pseudo-first order, pseudo-second order and intra-particle diffusion kinetic models were used to examine the adsorption kinetics of adsorbents. As a result, it is thought that the use of this study in the field of dye adsorption can be an innovative and important study.

Recent advances in the application of clay-containing hydrogels for hemostasis and wound healing

INTRODUCTION

Immediate control of bleeding and anti-infection play important roles in wound management. Multiple organ dysfunction syndrome and death may occur if persistent bleeding, hemodynamic instability, and hypoxemia are not addressed. The combination of clay and hydrogel provides a new outlet for wound hemostasis. In this review, the current research progress of hydrogel/clay composite hemostatic agents was reviewed.

AREAS COVERED

This paper summarizes the characteristics of several kinds of clay including kaolinite, montmorillonite, laponite, sepiolite, and palygorskite. The advantages and disadvantages of its application in hemostasis were also summarized. Future directions for the application of hydrogel/clay composite hemostatic agents are presented.

EXPERT OPINION

Clay can activate the endogenous hemostatic pathway by increasing blood cell concentration and promoting plasma absorption to accelerate the hemostasis. Clay is antimicrobial due to the slow release of metal ions and has a rich surface charge with a high affinity for proteins and cells to promote tissue repair. Hydrogels have some properties such as good biocompatibility, strong adhesion, high stretchability, and good self-healing. Despite promising advances, hydrogel/clay composite hemostasis remains a limitation. Therefore, more evidence is needed to further elucidate the risk factors and therapeutic effects of hydrogel/clay in hemostasis and wound healing.

Role of Clay Substrate Molecular Interactions in Some Dairy Technology Applications

The use of clay materials in dairy technology requires a multidisciplinary approach that allows correlating clay efficiency in the targeted application to its interactions with milk components. For profitability reasons, natural clays and clay minerals can be used as low-cost and harmless food-compatible materials for improving key processes such as fermentation and coagulation. Under chemical stability conditions, clay materials can act as adsorbents, since anionic clay minerals such as hydrotalcite already showed effectiveness in the continuous removal of lactic acid via in situ anion exchange during fermentation and ex situ regeneration by ozone. Raw and modified bentonites and smectites have also been used as adsorbents in aflatoxin retention and as acidic species in milk acidification and coagulation. Aflatoxins and organophilic milk components, particularly non-charged caseins around their isoelectric points, are expected to display high affinity towards high silica regions on the clay surface. Here, clay interactions with milk components are key factors that govern adsorption and surface physicochemical processes. Knowledge about these interactions and changes in clay behavior according to the pH and chemical composition of the liquid media and, more importantly, clay chemical stability is an essential requirement for understanding process improvements in dairy technology, both upstream and downstream of milk production. The present paper provides a comprehensive review with deep analysis and synthesis of the main findings of studies in this area. This may be greatly useful for mastering milk processing efficiency and envisaging new prospects in dairy technology.

Facile synthesis and characterization of Fe3O4/analcime nanocomposite for the efficient removal of Cu(II) and Cd(II) ions from aqueous media

In the water purification field, heavy metal pollution is a problem that causes severe risk aversion. This study aimed to examine the disposal of cadmium and copper ions from aqueous solutions by a novel Fe3O4/analcime nanocomposite. A field emission scanning electron microscope (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction were used to characterize the synthesized products. The FE-SEM images showed that the analcime and Fe3O4 samples consist of polyhedral and quasi-spherical shapes with average diameters of 923.28 and 28.57 nm, respectively. Besides, the Fe3O4/analcime nanocomposite consists of polyhedral and quasi-spherical shapes with average diameters of 1100.00 nm. The greatest uptake capability of the Fe3O4/analcime nanocomposite toward the copper and cadmium ions is 176.68 and 203.67 mg/g, respectively. The pseudo-second-order kinetic model and Langmuir equilibrium isotherm best describe the uptake of copper and cadmium ions using the Fe3O4/analcime nanocomposite. The uptake of copper and cadmium ions using the Fe3O4/analcime nanocomposite is exothermic and chemical in nature.