Kappa carrageenan reduced-stabilized colloidal silver nanoparticles for the degradation of toxic azo compounds

Abstract

Silver nanoparticles (AgNPs) possess unique electrical, optical, and thermal properties, making them viable in versatile applications from photovoltaics to biological/chemical sensors, antimicrobial coatings, to conductive materials production. However, these versatile applications are severely hampered by their agglomeration/aggregation behavior. Therefore, highly stable AgNPs were successfully synthesized using the silver nitrate and Kappa carrageenan (κ-car), which functions as a reducing and simultaneously stabilizing agent. No other hazardous or toxic reagents were used to maintain the green chemistry protocol. Variable synthesis parameters such as time, temperature, solution pH, and κ-car concentration (hereafter referred to as ‘process parameters’) were systematically studied using factorial design experiments (FED) to control the ultimate features of AgNPs (shape, size, and crystallinity) and optimize the reduction/stabilization performances. The characterizations revealed that the particles synthesized at optimum condition are mostly spherical, highly crystalline (d-spacing = 0.234 nm), and nano-range size (5.69 ± 1.26 nm) with a narrow distribution. The particles are well capped by a thin layer of κ-car carbohydrate that significantly stabilized (zeta potential =−27.0 mV) them. The as-synthesized AgNPs can serve as an excellent catalyst for the catalytic degradation of model azo compounds: reactive red 195 and reactive yellow 145. This approach is simple but effective, economical, nontoxic, and rapid, which could be extended to the industrial application for azo contained wastewater treatment.