Synthesis and characterization of mupirocin-LDH/PVA nanofibrous composite as a dual-carrier drug release system

Nowadays, nanofibrous structures based on organic and inorganic materials are considered a drug delivery system for the controlled release of antibiotics and other antibacterial agents. The main goal of this research is a combination of the special properties of nanofibrous structure and Mupirocin-loaded Layered double hydroxide (LDH) to obtain a dual-carrier drug release system to provide long term antibacterial properties in wound healing process. Regards, unloaded layered double hydroxide (LDH) and Mupirocin-loaded LDH, which were synthesized by co-precipitation method, were added to Polyvinyl alcohol (PVA) solution in different mass ratio and electrospun using different processing conditions. The physico-chemical characterizations were performed using SEM, FTIR and tensile strength tests. The biological properties of the fabricated nanocomposites were evaluated using antibacterial test and in vitro cell culturing followed by MTT assay. The SEM results showed a bead-less and uniform morphology of nanofibrous composite containing Mupirocin(2.3 wt%)-LDH(15 wt%)/PVA with an average fiber diameter of about 270 ± 58 nm. According to the release study, the maximum release of the mupirocin drug was about 54 % in the first 6 h. The antibiogram analysis exhibited good antibacterial activity of mupirocin-loaded nanocomposite against both bacteria, especially gram-positive one. Finally, MTT assay approved the biocompatibility of the mupirocin-loaded nanocomposite. Overall, the produced nanofibrous composites would be a promising dual-carrier system for controlled release of antibiotic.

Regulation of Structure and Anion-Exchange Performance of Layered Double Hydroxide: Function of the Metal Cation Composition of a Brucite-like Layer

As anion-exchange materials, layered double hydroxides (LDHs) have attracted increasing attention in the fields of selective adsorption and separation, controlled drug release, and environmental remediation. The metal cation composition of the laminate is the essential factor that determines the anion-exchange performance of LDHs. Herein, we review the regulating effects of the metal cation composition on the anion-exchange properties and LDH structure. Specifically, the internal factors affecting the anion-exchange performance of LDHs were analyzed and summarized. These include the intercalation driving force, interlayer domain environment, and LDH morphology, which significantly affect the anion selectivity, anion-exchange capacity, and anion arrangement. By changing the species, valence state, size, and mole ratio of the metal cations, the structural characteristics, charge density, and interlayer spacing of LDHs can be adjusted, which affect the anion-exchange performance of LDHs. The present challenges and future prospects of LDHs are also discussed. To the best of our knowledge, this is the first review to summarize the essential relationship between the metal ion composition and anion-exchange performance of laminates, providing important insights for regulating the anion-exchange performance of LDHs.

LDH-TiO2 Composite for Selenocyanate (SeCN-) Photocatalytic Degradation: Characterization, Treatment Efficiency, Reaction Intermediates and Modeling

Selenium as a nutrient has a narrow margin between safe and toxic limits. Hence, wastewater discharges from selenium-containing sources require appropriate treatment that considers health concerns and stringent selenium-related water treatment standards. This work examined the use of a photocatalysis-cum-adsorption system based on a layered double hydroxide coupled with TiO2 (LDH-TiO2) to remove aqueous phase selenocyanate (SeCN−), which is difficult to treat and requires specific treatment procedures. The synthesized LDH and LDH-TiO2 composite samples were characterized using the X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and thermogravimetry analysis (TGA) methods. The XRD results for the uncalcined LDH indicated a hydrotalcite mass with a rhombohedral structure, whereas increasing the calcination temperature indicated transition to an amorphous state. FESEM results for the LDH-TiO2 matrix indicated round titanium dioxide particles and LDH hexagonal layers. The TGA findings for uncalcined LDH showed a gradual decrease in weight up to 250 °C, followed by a short plateau and then a sharp decrease in LDH weight from 320 °C, with a net weight loss around 47%. Based on the characterization and initial selenocyanate adsorption results, the 250 °C calcined LDH-TiO2 matrix was used for the selenocyanate photocatalysis. A ~100% selenium removal was observed using LDH:TiO2 at a 1.5:1 w/w ratio with a 2 g/L dose, whereas up to 80% selenium removal was noted for LDH:TiO2 at a 0.5:1 w/w ratio. The respective difference in the efficiency of selenium treatment was attributed to enhanced LDH-based adsorption sites in the enhanced LDH:TiO2 w/w ratio. Furthermore, the selenite and selenate that occurred during SeCN− photocatalytic degradation (PCD) were also nearly completely removed via adsorption. An optimization exercise using response surface methodology (RSM) for total selenium removal showed R2 values of more than 0.95, with a prediction accuracy of more than 90%. In summary, the present findings show that the use of a photocatalysis-cum-adsorption system based on LDH-TiO2 is a promising technique to treat industrial wastewater discharges for selenocyanate and also remove the resulting intermediates.

Aged layered double hydroxide nanosheet-polyvinyl alcohol dispersions for enhanced gas barrier coating performance

Whilst applying a coating layer to a polymer film is a routine approach to enhance the gas barrier properties of the film, it is counter-intuitive to consider that the gas barrier performance of the film would improve by ageing the coating dispersion for weeks before application. Herein, we report that the oxygen barrier performance of a 12 μm PET film coated with a dispersion of inorganic nanosheets in polyvinyl alcohol can be significantly enhanced by ageing this coating dispersion for up to 8 weeks before application. We found up to a 37-fold decrease in the oxygen transmission rate (OTR) of the PET coated film using aged dispersions of [Mg_0.66Al_0.33(OH)₂](NO₃)_0.33 layered double hydroxide nanosheets (Mg₂Al-LDH NS) in polyvinyl alcohol (PVA) compared to the film coated with an equivalent freshly prepared LDH/PVA dispersion. A limiting OTR value of 0.31 cc m^-2 day^-1 was achieved using the PET film coated with a 3 week aged LDH NS/PVA dispersion. X-ray diffraction experiments show that the degree of in plane alignment of LDH NS on the PET film surface increased significantly from 70.6 ± 0.6 to 86.7 ± 0.6 (%) (100% represents complete alignment of LDH NS platelets on the film surface) for the 4 week aged dispersion compared to the freshly prepared layer. We postulate that when the Mg₂Al-LDH NS are aged in PVA the coiled PVA aggregates start to unwrap and attach onto the Mg₂Al-LDH NS through hydrogen bonding and eventually form a hydrogen bonded ordered network that facilitates the alignment of nanosheet dispersions during the coating process. Our results suggest that the ageing of inorganic nanosheet dispersions in PVA or other potential hydrogen bonding adhesive systems could be a general approach to improve the alignment of the nanosheets on the polymer film surface once applied and thus improve their performance characteristics for barrier coating applications.

Mg-Al/Biochar Composite with Stable Structure for Malachite Green Adsorption from Aqueous Solutions

Mg-Al-layered double hydroxide (LDH) was fabricated using a coprecipitation method at pH 10. Thereafter, Mg-Al-LDH was impregnated with biochar to manufacture a Mg-Al/Biochar composite. The composite was characterized using powder X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, N2 adsorption—desorption, thermogravimetry-differential thermal analysis (TG-DTA), and scanning electron microscopy (SEM) experiments, and was subsequently used for malachite green (MG) adsorption. MG adsorption experiments were performed in a batch system, and the effects of temperature and adsorption kinetic and isotherm parameters on the adsorption process were analyzed. The stability of Mg-Al/Biochar was evaluated using regeneration experiments over three cycles. The peaks at 11.47° (003), 22.86° (002), 34.69° (012), and 61.62° (116), in the XRD profile of Mg-Al/Biochar suggested that Mg-Al/Biochar was successfully fabricated. The surface area of Mg-Al/Biochar was up to five times larger than that of pristine Mg-Al-LDH. The adsorption of MG on Mg-Al/Biochar was dominated by interactions at the surface of the adsorbent and was classified as physical adsorption; moreover the maximum adsorption capacity ofMg-Al/Biochar was 70.922 mg/g. Furthermore, the MG removal of Mg-Al/Biochar during three successive adsorption cycles (i.e. 66.73%, 65.57%, and 65.77% for the first, second, and third adsorption cycle) did not change significantly, which indicated the stable structure of the adsorbent. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

CuAl LDH/Rice Husk Biochar Composite for Enhanced Adsorptive Removal of Cationic Dye from Aqueous Solution

The preparation of CuAl LDH and biochar (BC) composite derived from rice husk and its application as a low-cost adsorbent for enhanced adsorptive removal of malachite green has been studied. The composite was prepared by a one-step coprecipitation method and characterized by X-ray Diffraction (XRD), Fourier Transform Infra Red (FTIR), Brunauer-Emmett-Teller (BET), and Scanning Electron Microscopy - Energy Dispersive X-ray (SEM−EDX). The result indicated that CuAl LDH was successfully incorporated with the biochar that evidenced by the broadening of XRD peak at 2θ = 24° and the appearance of a new peak at 1095 cm−1 on the FTIR spectra. The BET surface area analysis revealed that CuAl/BC composite exhibited a larger surface area (200.9 m2/g) that the original CuAl LDH (46.2 m2/g). Surface morphological changes also confirmed by SEM image, which showed more aggregated particles. The result of the adsorption study indicated the composite material was efficient in removing malachite green with Langmuir maximum adsorption capacity of CuAl/BC reaching 470.96 mg/g, which is higher than the original CuAl LDH 59.523 mg/g. The thermodynamic analysis suggested that the adsorption of malachite green occurs spontaneously (ΔG < 0 at all tested temperature) and endothermic nature. Moreover, the CuAl/BC composite showed strong potential as a low-cost adsorbent for cationic dye removal since it showed not only a high adsorption capacity but also good reusability. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Hydrodynamic assembly of two-dimensional layered double hydroxide nanostructures

Formation mechanisms of two-dimensional nanostructures in wet syntheses are poorly understood. Even more enigmatic is the influence of hydrodynamic forces. Here we use liquid flow cell transmission electron microscopy to show that layered double hydroxide, as a model material, may form via the oriented attachment of hexagonal nanoparticles; under hydrodynamic shear, oriented attachment is accelerated. To hydrodynamically manipulate the kinetics of particle growth and oriented attachment, we develop a microreactor with high and tunable shear rates, enabling control over particle size, crystallinity and aspect ratio. This work offers new insights in the formation of two-dimensional materials, provides a scalable yet precise synthesis method, and proposes new avenues for the rational engineering and scalable production of highly anisotropic nanostructures.

While liquid-phase synthesis of 2D materials presents opportunities for large-scale production, achieving precise control over product quality, size and morphology remains challenging. Here, the authors show that hydrodynamic manipulation of nanoparticle assembly enables control over crystallinity, size and aspect ratio.