Adsorption Characteristics of Heavy Metals onto Functionalized Microplastics

Area of Science:

• Environmental Science
• Materials Science
• Analytical Chemistry

Background:

• Microplastics are persistent environmental pollutants, posing risks amplified by co-occurring heavy metals.
• Research on conventional microplastics is extensive, but functionalized microplastics and their interactions with heavy metals are understudied.
• Functionalized microplastics exhibit complex behaviors due to richer functional groups, necessitating further investigation.

Purpose of the Study:

• To investigate the adsorption behavior of cadmium (Cd2+), copper (Cu2+), and lead (Pb2+) onto functionalized microplastics: polyacrylate (PAT), biobased polyurethane (BPU), and petroleum-based polyurethane (PPU).
• To evaluate the influence of microplastic particle size and UV aging on heavy metal adsorption.
• To determine the adsorption mechanisms and kinetics using isotherm and kinetic models.

Main Methods:

• Adsorption experiments were conducted using Cd2+, Cu2+, and Pb2+ with PAT, BPU, and PPU microplastics of different sizes (150 μm and 1-2 mm).
• Langmuir and Freundlich isotherm models were applied to analyze adsorption capacities.
• Pseudo-second-order kinetic model was used to assess adsorption kinetics, with and without UV aging treatment.
• Analysis of variance (ANOVA) was used to determine statistical significance.

Main Results:

• Microplastics with a particle size of 150 μm demonstrated significantly enhanced adsorption capacities for Cd2+, Cu2+, and Pb2+ compared to larger particles (1-2 mm).
• Polyacrylate (PAT) exhibited the highest adsorption affinity for Pb2+ (34.68 mg/g), Cu2+ (29.85 mg/g), and Cd2+ (12.31 mg/g).
• UV aging increased PAT's adsorption capacity for Cd2+ but decreased the adsorption rate constant, indicating slower kinetics.

Conclusions:

• Functionalized microplastics, particularly smaller ones and polyacrylate, are effective adsorbents for heavy metals like lead, copper, and cadmium.
• Microplastic particle size significantly influences heavy metal adsorption efficiency.
• UV aging alters the adsorption kinetics of functionalized microplastics, highlighting the dynamic nature of microplastic-pollutant interactions in aquatic environments.