Synthesis and application of hydrogel calcium alginate microparticles as a biomaterial to remove heavy metals from aqueous media

Microfluidic systems are an emerging technology to fabricate uniform spherical microparticles. This study employed a flow-focusing microfluidic device (MFFD) to produce uniform sodium alginate microdroplets by controlling the continuous (soybean oil) and dispersed (sodium alginate solution) flow rates. The resultant hydrogel particles were spherical in shape with diameters ranging from 70 to 100μm, and a size distribution under 10%, depending on the experimental conditions. Observations of dried calcium alginate microparticles using scanning electron microscopy showed a surface characterized by the uniform distribution of regular nodules. The resultant biomaterials were further examined and evaluated in terms of the removal of toxic metals (Cu²⁺ and Ni²⁺ ions); they demonstrated excellent removal performance. The highest adsorption capacities of the prepared calcium alginate microparticles toward Cu²⁺ and Ni²⁺ ions were 0.36 and 0.81 mg/mg alginate microparticles, respectively. Thus, calcium alginate microparticles prepared by MFFD demonstrated the potential for toxic metal treatment at different concentrations with short duration and stability. This approach may also be controlled to prepare microparticles that are narrow in size distribution and exhibit uniform morphology.