Films composed of white angico gum and chitosan containing chlorhexidine as an antimicrobial agent

Anadenanthera colubrina, popularly known as white angico, is a species extensively cultivated in Brazil, mainly in the cerrado region, including the state of Piauí. This study examines the development of films composed of white angico gum (WAG) and chitosan (CHI) and containing chlorhexidine (CHX), an antimicrobial agent. The solvent casting method was used to prepare films. Different combinations and concentrations of WAG and CHI were used to obtain films with good physicochemical characteristics. Properties such as the in vitro swelling ratio, the disintegration time, folding endurance, and the drug content were determined. The selected formulations were characterised by scanning electron microscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and X-ray diffraction, and the CHX release time and antimicrobial activity were evaluated. CHX showed a homogenous distribution in all CHI/WAG film formulations. The optimised films showed good physicochemical properties with 80% CHX release over 26 h, which is considered promising for local treatment of severe lesions in the mouth. Cytotoxicity tests of the films did not show toxicity. The antimicrobial and antifungal effects were very effective against the tested microorganisms.

Efficient Propylene Carbonate Synthesis from Urea and Propylene Glycol over Calcium Oxide-Magnesium Oxide Catalysts

A series of calcium oxide-magnesium oxide (CaO-MgO) catalysts were prepared under the effects of different precipitating agents and using varied Mg/Ca ratios. The physiochemical characteristics of the prepared catalysts were analyzed using XRD, FE-SEM, BET, FTIR, and TG/DTA techniques. Quantification of basic active sites present on the surface of the CaO-MgO catalysts was carried out using the Hammett indicator method. The as-prepared mixed oxide samples were tested for propylene carbonate (PC) synthesis through the alcoholysis of urea with propylene glycol (PG). The effects of the catalyst composition, catalyst dose, reaction temperature, and contact time on the PC yield and selectivity were investigated. The maximum PC yield of 96%, with high PC selectivity of 99% and a urea conversion rate of 96%, was attained at 160 °C using CaO-MgO catalysts prepared using a Mg/Ca ratio of 1 and Na2CO3 as a precipitating agent. The best-performing catalysts also exhibited good reusability without any significant loss in PC selectivity. It is expected that the present study will provide useful information on the suitability of different precipitating agents with respect to the catalytic properties of the oxides of Ca and Mg and their application in the synthesis of organic carbonates.

Facile extraction and characterization of calcium hydroxide from paper mill waste sludge of Bangladesh

Herein, paper mill waste sludge (PMS) from two different sources has been investigated to extract calcium hydroxide, Ca(OH)₂ by a facile and inexpensive extraction process. PMS samples, collected from local paper mill plants of Bangladesh, were the main precursors wherein HCl and NaOH were used for chemical treatment. The as-synthesized products were analysed by a variety of characterization tools including X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) elemental analyses. Our studies confirm that the extracted product contains Ca(OH)₂ as a major content, albeit it also includes CaCO₃ phase owing to the inescapable carbonation process from the surrounding environment. The particle size of the synthesized products is in the range of 450-500 nm estimated from SEM micrographs. The crystallite domain size of the same estimated from XRD analyses and was found to be approximately 47 and 31 nm respectively for product-A and product-B considering major (101) Bragg peak of Ca(OH)₂. The yield percentage of the isolated products is about 65% for samples collected from both sources.

Phyto-complexation of galactomannan-stabilized calcium hydroxide and selenium-calcium hydroxide nanocomposite to enhance the seed-priming effect in Vigna radiata

The evaluation of nano-priming effect with galactomannan stabilized Phyto-complexed calcium hydroxide (Ca(OH)₂), selenium oxyanion‑calcium hydroxide SeO-(Ca(OH)₂), and selenium‑calcium hydroxide Se-(Ca(OH)₂) nanocomposites was carried out in Vigna radiata (Green gram) seeds. The green source Cassia angustifolia seed rich in galactomannan and other phytoconstituents was detected experimentally and characterized with GC-MS, UV, FT-IR, NMR, XRD, and SEM studies. The highly active galactomannan and other biomolecules, enable their terminal oxygen and hydroxide groups to bind with calcium and selenium ions through bidentate and monodentate chelation, followed by bio-reduction. On the mild-thermal agitation, bio-stabilized (Ca(OH)₂), SeO-(Ca(OH)₂), and Se-(Ca(OH)₂) nanocomposite coated with seed-derived biomolecules were precipitated under an alkaline condition. The size and morphological parameters of bio-fabricated nanocomposites were characterized to exhibit the spherical and hexagonal shape in nanoscale images of size 17.9 nm for (Ca(OH)₂), 56.2 nm for SeO-(Ca(OH)₂), and 69.3 nm Se-(Ca(OH)₂). The sub-standard seed lot of Vigna radiata (Green gram) seeds (71%) was examined using synthesized nanocomposites at various concentrations, and the obtained physiological parameters in seedlings were compared with hydro-primed seeds. The nano-priming action of all the Phyto-complexed nanocomposites was predicted with a positive response, where the porous Se-(Ca(OH)₂) possess high efficacy interaction on seed embryos and beneficially results at 90% germination.

Facile synthesis of highly tunable monodispersed calcium hydroxide composite particles by using a two-step ion exchange reaction

“Calcium hydroxide [Ca(OH)₂]” is a medicament frequently used for antimicrobial purposes in endodontic procedures, or it is used as a toxic-waste adsorbent in industry. Ca(OH)₂ particles produced through conventional methods are size untunable and have a wide size distribution and polygonal shape. In this paper, a novel and facile approach involving template-mediated synthesis and two-step ion exchange is proposed for uniform size Ca(OH)₂ composite particles generation. “Sodium-alginate (Na-alginate)” was used as a precursor, and monodisperse Na-alginate emulsions were formed through needle droplet or droplet microfluidic technology. After the first ion exchange step with the Ca²⁺ ions, “calcium-alginate (Ca-alginate)” particles were obtained. The Ca-alginate particles were intermediate reaction products and were designed to be the templates for ensuring the spherical shape and size of products. The OH⁻ ions were used for the second ion exchange step to fabricate Ca(OH)₂ composite particles. The results revealed that the Ca(OH)₂ composite particles were size tunable, had a spherical shape, and were monodisperse (with a relative standard deviation of less than 8%). The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay revealed that the Ca(OH)₂ composite particles were potential biocompatible materials.

The synthesized Ca(OH)₂ composite particles were size tunable, had a spherical shape, and were monodisperse.

Effect of Unbleached Rice Straw Cellulose Nanofibers on the Properties of Polysulfone Membranes

In addition to their lower cost and more environmentally friendly nature, cellulose nanofibers isolated from unbleached pulps offer different surface properties and functionality than those isolated from bleached pulps. At the same time, nanofibers isolated from unbleached pulps keep interesting properties such as hydrophilicity and mechanical strength, close to those isolated from bleached pulps. In the current work, rice straw nanofibers (RSNF) isolated from unbleached neutral sulfite pulp (lignin content 14%) were used with polysulfone (PSF) polymer to make membrane via phase inversion. The effect of RSNF on microstructure, porosity, hydrophilicity, mechanical properties, water flux, and fouling of PSF membranes was studied. In addition, the prepared membranes were tested to remove lime nanoparticles, an example of medium-size nanoparticles. The results showed that using RSNF at loadings from 0.5 to 2 wt.% can significantly increase hydrophilicity, porosity, water flux, and antifouling properties of PSF. RSNF also brought about an increase in rejection of lime nanoparticles (up to 98% rejection) from their aqueous suspension, and at the same time, with increasing flux across the membranes. Tensile strength of the membranes improved by ~29% with addition of RSNF and the maximum improvement was obtained on using 0.5% of RSNF, while Young’s modulus improved by ~40% at the same RSNF loading. As compared to previous published results on using cellulose nanofibers isolated from bleached pulps, the obtained results in the current work showed potential application of nanofibers isolated from unbleached pulps for improving important properties of PSF membranes, such as hydrophilicity, water flux, rejection, and antifouling properties.

Retention behavior of anionic radionuclides using metal hydroxide sludge

With the speedy growth of nuclear power production, the removal and disposal of radioactive nuclides such as 129I, 99Tc, 79Se, 36Cl, 93Mo, and 137Cs become major environmental security issues. Retention of these radionuclides, especially anionic species such as 129I (t1/2 1.7 × 107 years), 93Mo (t1/2 4 × 103 years) and 79Se (t1/2 3.27 × 105 years) has been challenging. 129I, 93Mo and 79Se bind very weakly to most sorbents and deposits. This study has examined the sorption potential of Metal hydroxide sludge (MHS) for 125I (t1/2 60.2 days), 99Mo (t1/2 2.75 days) and 75Se (t1/2 120 days) as a surrogate for 129I, 93Mo and 79Se, respectively. MHS has been characterized by different techniques and the factors affecting the sorption processes were investigated. The experimental data were analyzed using kinetic models and thermodynamic parameters. The results showed that the kinetics of sorption of 125I and 99Mo on MHS proceeds according to the pseudo-first-order, on the contrary of 75Se sorption follows pseudo second-order kinetic model. The maximum sorption capacity of MHS was found to be 51.2 mg/g, 46.5 mg/g and 40.2 mg/g for 125I, 99Mo and 75Se, respectively. It can be concluded that, in the case of release of anionic radionuclide species to the surroundings the MHS could act as a succeeded and economical sorbent material for retention of different anionic radionuclides such as 133, 129I, 79Se, 36Cl, 93, 99Mo, and 99Tc. To avoid the release of such anionic species from the stored nuclear wastes to the environment.

Inorganic Nanomaterials for Restoration of Cultural Heritage: Synthesis Approaches towards Nanoconsolidants for Stone and Wall Paintings

The synthesis of inorganic nanostructured materials for the consolidation of stone and wall paintings is reviewed. To begin, a description of the methods most commonly used to prepare nanoconsolidants is provided, particularly in the frame of colloid chemistry. Some concepts of the carbonation mechanism as well as the transport properties of some of these materials are addressed. An overview of the synthesis methods together with some of the application particularities of the distinct consolidants are presented thereafter. Furthermore, the requisites for efficient consolidants and some drawbacks of the nanoconsolidants are discussed.

Characterization of Chlorhexidine-Loaded Calcium-Hydroxide Microparticles as a Potential Dental Pulp-Capping Material

This study explores the delivery of novel calcium hydroxide [Ca(OH)₂] microparticles loaded with chlorhexidine (CHX) for potential dental therapeutic and preventive applications. Herein, we introduce a new approach for drug-delivery to deep dentin-surfaces in the form of drug-loaded microparticles. Unloaded Ca(OH)₂ [Ca(OH)₂/Blank] and CHX-loaded/Ca(OH)₂ microparticles were fabricated by aqueous chemical-precipitation technique. The synthesized-microparticles were characterized in vitro for determination of surface-morphology, crystalline-features and thermal-properties examined by energy-dispersive X-ray scanning and transmission electron-microscopy (EDX-SEM/TEM), Fourier-transform infrared-spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential scanning-calorimetry (DSC). Time-related pH changes, initial antibacterial/biofilm-abilities and cytotoxicity of CHX-loaded/Ca(OH)₂ microparticles were evaluated. Microparticles were delivered to dentin-surfaces with subsequent SEM examination of treated dentin-substrates. The in vitro and ex vivo CHX-release profiles were characterized. Ca(OH)₂/Blank were hexagonal-shaped with highest z-average diameter whereas CHX-inclusion evidenced micro-metric spheres with distinguishable surface “rounded deposits” and a negative-shift in diameter. CHX:Ca(OH)₂/50 mg exhibited maximum encapsulation-efficiency with good antibacterial and cytocompatible properties. SEM examination revealed an intact layer of microparticles on exposed dentin-surfaces with retention of spherical shape and smooth texture. Microparticles loaded on dentin-surfaces showed prolonged release of CHX indicating substantial retention on dentin-substrates. This study validated the inherent-applicability of this novel drug-delivery approach to dentin-surfaces using micro-metric CHX-loaded/Ca(OH)₂ microparticles.

Effects of reduced dimensionality on the properties of magnesium hydroxide and calcium hydroxide nanostructures

DFT and SCC-DFTB calculations shed light on the size and dimensionality dependence of the properties of metal hydroxides.