The study on adsorption behavior of 2,4-DCP in solution by biomass carbon modified with CTAB-KOH

Adsorption of bisphenol A and 2,4-dichlorophenol onto cetylpyridinium chloride-modified pine sawdust: a kinetic and thermodynamic study

Using biomass wastes as adsorbents is a promising option for organic waste reclamation, but unfortunately, their adsorption capacity is usually limited, especially for hydrophobic organic pollutants. To address this issue, this work prepared cetylpyridinium chloride (a cationic surfactant)-modified pine sawdust (CPC-PS) and further demonstrated their performance for hydrophobic bisphenol A (BPA) and 2,4-dichlorophenol (DCP) adsorption. Compared to the PS, the CPC-PS improved the maximum adsorption capacity for BPA and DCP by approximately 98% and 122%, respectively. The kinetic and thermodynamic analyses showed that the BPA and DCP adsorption onto the CPC-PS fitted the pseudo-second-order kinetics and the Freundlich model. After regeneration using NaOH, the adsorption capacity of the CPC-PS for BPA still maintained 80.2% of the initial value after five cycles. Based on the experimental results, the CPC-PS was proposed to enhance the BPA and DCP adsorption through the solubilization of hemimicelles for hydrophobic organic pollutants, the π-π stacking between benzene-ring structures, and the hydrogen binding between the adsorbents and the pollutants. This work provides a viable method to use surfactant-modified pine sawdust as effective adsorbents to remove hydrophobic pollutants.

The study of laccase immobilization optimization and stability improvement on CTAB-KOH modified biochar

BACKGROUND

Although laccase has a good catalytic oxidation ability, free laccase shows a poor stability. Enzyme immobilization is a common method to improve enzyme stability and endow the enzyme with reusability. Adsorption is the simplest and common method. Modified biochar has attracted great attention due to its excellent performance.

RESULTS

In this paper, cetyltrimethylammonium bromide (CTAB)-KOH modified biochar (CKMB) was used to immobilize laccase by adsorption method (laccase@CKMB). Based on the results of the single-factor experiments, the optimal loading conditions of laccase@CKMB were studied with the assistance of Design-Expert 12 and response surface methods. The predicted optimal experimental conditions were laccase dosage 1.78 mg/mL, pH 3.1 and 312 K. Under these conditions, the activity recovery of laccase@CKMB was the highest, reaching 61.78%. Then, the CKMB and laccase@CKMB were characterized by TGA, FT-IR, XRD, BET and SEM, and the results showed that laccase could be well immobilized on CKMB, the maximum enzyme loading could reach 57.5 mg/g. Compared to free laccase, the storage and pH stability of laccase@CKMB was improved greatly. The laccase@CKMB retained about 40% of relative activity (4 °C, 30 days) and more than 50% of relative activity at pH 2.0-6.0. In addition, the laccase@CKMB indicated the reusability up to 6 reaction cycles while retaining 45.1% of relative activity. Moreover, the thermal deactivation kinetic studies of laccase@CKMB showed a lower k value (0.00275 min^- 1) and higher t_1/2 values (252.0 min) than the k value (0.00573 min^- 1) and t_1/2 values (121.0 min) of free laccase.

CONCLUSIONS

We explored scientific and reasonable immobilization conditions of laccase@CKMB, and the laccase@CKMB possessed relatively better stabilities, which gave the immobilization of laccase on this cheap and easily available carrier material the possibility of industrial applications.