Preparation Of Calcium Alginate-Encapsulated Sulfur Particles And Their Application In Metal Nanoparticle Capture: A Case Study Of Silver Nanoparticles

Uniform anisotropic sulfur particles of 5.5 +/- 0.4 mu m in length, 3.9 +/- 0.4 mu m 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.