Cu(PABA) is a Cu-based MOF material assembled from Cu2+ and the organic ligand p-aminobenzoic acid (PABA).Cu(PABA) was synthesized by solvothermal method, characterized and applied to the adsorption of direct red 31 dye(DR-31). The effects of pH, DR-31 concentration and temperature on the adsorption performance of Cu(PABA) were investigated. The adsorption kinetics was analyzed by pseudo-first-order, pseudo-second-order and intra-particle diffusion models, and the adsorption equilibrium data was fitted by Langmuir and Freundlich isotherm models. The pseudo-first -order kinetics and Langmuir model satisfactorily described the adsorption kinetics and adsorption equilibrium, respectively. The maximum adsorption capacity of Cu(PABA) for DR-31dye at room temperature was 1,244.8 mg/g, as calculated using the Langmuir adsorption isotherm model.By response surface methodology (RSM), the optimal adsorption was found at pH value of 10.9, DR-31 dye concentration of 216.6 mg/L, and temperature of 27 °C, and the removal rate was as high as 99.4%.Therefore, Cu(PABA) can be used as an efficient adsorbent for removing DR-31 dye from aqueous solution.

Background: 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. Results: 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 ℃, 30 days) and more than 50 % of relative activity at pH 2-6. 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 t1/2 values (252.0 min) than the k value (0.00573 min-1) and t1/2 values (121.0 min) of free laccase. Conclusions: In summary, 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.