Preparation of calcium alginate-encapsulated sulfur particles and their application in metal nanoparticle capture: A case study of silver nanoparticles

Abstract

Uniform anisotropic sulfur particles of 5.5 ± 0.4 µm in length, 3.9 ± 0.4 µm in width/thickness and an aspect ratio of 1.4 were successfully synthesized for the first time via the reaction of thiosulfate with a weak acid in the presence of sodium alginate which acted as a surfactant to impart water dispersibility and bestow particle size control. The sulfur particles with a zeta potential measured to be −29.5 mV were structurally characterized using PXRD and FESEM. After purification, the alginate-protected sulfur particles were discharged into a calcium chloride solution to produce fibrous calcium alginate-encapsulated sulfur composite (Ca-Alg-S) via ionotropic gelation. Ca-Alg-S was tested as absorbent of silver nanoparticles (Ag NPs) and compared to Ca-Alg gel absorbent. The Ag NPs were produced using sodium alginate as both surfactant and reducing agent under microwave-assisted heating to ensure the effect of surfactant on Ag capture was minimized. The effect of contact time on the removal efficiency of Ag NPs was established by tracking the decreasing absorbance of Ag NPs at 400 nm which was due to the surface plasmon resonance (SPR) band of Ag NPs of 10-20 nm in size. As high as 90% of Ag NP capture efficiency was achieved using Ca-Alg-S within 8 h under ambient conditions. The application of Ca-Alg-S may be extended in the future to other heavy metals including Hg, Cd, Ni and Pd which are known to react readily with sulfur, allowing effective wastewater treatment without the use of toxic sulfide or costly nanofiltration system.

Generation of liquid metal double emulsion droplets using gravity-induced microfluidics

“…Solidication of the shell droplets to stabilize the double emulsion droplets can be subsequently realized by the crosslinking reaction between sodium alginate solution and calcium ions such as the calcium chloride solution. 72,77,79,96 The pH sensitivity of sodium alginate can be used to control the release of its encapsulated content, thus serving as a controlled release system. 58 The carboxyl group in the sodium alginate molecule exists mainly in the form of anions that repel each other when the solution is alkaline, facilitating the entry of water molecules, causing an increase in the swelling rate of the gel.…”

“…Then the solidied spheres were soaked in solutions of different pH values to test the pH sensitivity due to the PH swelling property of calcium alginate hydrogel. [96][97][98] Fig. 7(a) and (b) exhibit the morphologies of coreshell liquid metal hydrogel capsules obtained in 4 wt% CaCl 2 aqueous solution.…”

Green synthesis of silver nanoparticles from Heteropyxis natalensis leaf extract and their potential antibacterial efficacy

“…Over the years, nanotechnology has been introduced into various medical applications; for example, gene therapy, cancer treatment, and drug delivery [3,5]. Metals such as copper, zinc, gold, titanium and silver are used to produce nanoparticles [1,6,7]. The synthesis of metal nanoparticles has gained significant importance due to the particle's unique optical, electronic, magnetic, chemical, and antimicrobial characteristics [8].…”