The filtration efficiency of all groups was measured using the method described on the measurement page. A microplastic suspension was prepared for standardizing the filtration efficiency test by diluting PS microspheres with diameters of 100nm, 1μm, 5μm, and 10μm. As evident from the previous description, the unchanging substrate is the BC membrane, while OP (oat protein), CBM3-CBM3, CBM3-OP-CBM3, APT, tannic acid, and tea polyphenols serve as optional additive materials.

First, the experimental groups with varying concentrations of oat protein were tested for their microplastic filtration ability. Based on measurements, the it was determined that the optimal ratio for oat protein was 15wt%.

When using oat protein alone, the filtration efficiency was measured at 75.51%. However, the sponge's structure(just like in the literature) limited its practical application. In the experimental group where bacterial cellulose and oat protein were combined through the Maillard reaction, a noticeable increase in removal efficiency was observed, improving from 77.36% to 85.57%. This demonstrates that oat protein indeed has the effect of increasing microplastic adsorption sites. Through testing different ratios, it was determined that the optimal oat protein concentration is 15wt% (concentration 2).

The experimental group that only contains CBM3-CBM3 and BC achieved a removal efficiency of 79.77% for the microplastic mixture. In the group containing OP (CBM3-OP-CBM3), the removal efficiency increased to 91.70%. This result aligns with the outcomes of computer simulations, suggesting that specific functional groups on the target protein's side chains, as well as its isoelectric characteristics, may facilitate electrostatic and hydrophobic interactions with microplastics, enhancing the adsorption of composites to microplastics. The increase in adsorption efficiency proves the effectiveness of our system.

The measured removal efficiency of BAM for the MP mixture was 96.17%, while Jiang et al. reported an efficiency of 99.81%. The discrepancy between these results may stem from slight human errors, or it could also be attributed to the use of a broader range of PS microspheres in our MP suspension (Jiang et al. employed 100nm, 0.5μm, and 1μm PS microspheres, whereas we used microspheres with diameters of 100nm, 1μm, 5μm, and 10μm). However, overall, the observed filtration effectiveness of BAM for microplastics is excellent. This suggests that APT, as the sole additive on the BC membrane, plays a primary role in enhancing filtration performance.

Due to the exceptional enhancement of adsorption efficiency by APT, we decided to test its combination with CBM3-OP-CBM3, which resulted in the best removal efficiency among all experimental groups, achieving 98.15%. One possible reason for this improvement is the addition of composite proteins enhances the strength and fiber structure of bacterial cellulose. Additionally, due to the properties of oat protein, it improves the membrane's porosity and enhances the interaction between the experimental membrane and microplastics. Consequently, it strengthens the filtration efficiency for larger and a wider range of microplastic sizes.

Considering the high cost of synthesizing and purifying composite proteins (CBM3-OP-CBM3), we explored the use of tannic acid, as mentioned in a recent publication, which also has microplastic adsorption capabilities. We also tested a similar substance, tea polyphenols. Tannic acid, due to its low cost and excellent performance, was combined with oat protein, resulting in a filtration efficiency of 92.35%. On the other hand, tea polyphenols achieved a filtration efficiency of 80.10%. This provides more options for our product's future industrial applications, increasing the versatility of membrane components.

Results