Preferential solvation bromophenol blue in water-alcohol binary mixture

A Novel Approach, Based on the Combined Action of Chitosan Hydrogel and Laccases, for the Removal of Dyes from Textile Industry Wastewaters

Dyes are considered as one the most important classes of contaminants that threaten the environment and human life. The synergy between the adsorption capacity of chitosan hydrogels and the catalytic properties of the enzyme laccase was exploited to improve the removal of contaminants from a liquid stream. The adsorption capacity of a chitosan hydrogel was tested on three different textile dyes. The effect of pH on the adsorption efficiency was dependent on the dye tested: the removal of methylene blue (MB), a cationic dye, was more effective at alkaline values of pH, whereas bromophenol blue (BPB) and Coomassie brilliant blue (BB), both anionic dyes, were more effectively removed under acid environments. The use of laccase immobilized onto chitosan has significantly improved the efficiency of dye removal, exploiting the synergy between the adsorption capacity of chitosan and the catalytic properties of the enzyme. The simultaneous processes of adsorption and enzymatic degradation improved the dye removal whatever the pH value adopted, making the removal efficiency less dependent from the pH changes. The chitosan used as a support for the immobilization of laccases showed good stability under repeated cycles, demonstrating the feasibility of the method developed for the application in wastewater remediation.

Efficient photoelectrocatalytic performance of beta-cyclodextrin/graphene composite and effect of Cl− in water: degradation for bromophenol blue as a case study

Photoelectrocatalytic technology has proven to be an efficient way of degrading organic contaminants, including dyes. Graphene (GR) -based catalysts have been frequently used in photoelectrocatalysis, due to their excellent catalytic performances. In this work, the GR/beta-cyclodextrin (GR/β-CD) composite was prepared and used for a widely used triphenylmethane dye (bromophenol blue, BPB) photoelectrocatalytic degradation. The results indicated that the degradation of the prepared GR/β-CD composite for BPB was effective with the combination of external bias voltage and simulated sunlight irradiation. Under optimum conditions, the BPB (10 mg L⁻¹) was completely eliminated by GR/β-CD composite within 120 min. ˙O₂⁻ played a prominent role in the BPB photoelectrocatalytic degradation. The time required for the removal of BPB in water to reach 100% can be reduced to 30 min with the presence of Cl⁻, owing to the generation of ˙Cl. Moreover, the toxicity of the degraded system with Cl⁻, predicted by the QSAR (Quantitative Structure–Activity Relationship) model in ECOSAR (Ecological Structure–Activity Relationships) program, was weaker than that without Cl⁻. The prepared GR/β-CD composite revealed great advantages in photoelectrocatalytic degradation of organic pollutants due to its metal-free, low cost, simplicity, and efficient performance. This work provided new insight into the efficient and safe degradation of organic pollutants in wastewaters.

O₂˙⁻ played a crucial role in the photoelectrocatalytic degradation of BPB by the prepared GR/β-CD. Cl⁻ marginally promoted the degradation of BPB and chlorinated intermediates were generated.