Efficient microbial cellulose/Fe3O4 nanocomposite for photocatalytic degradation by advanced oxidation process of textile dyes.

Fenton-type advanced oxidative processes (AOP) have been employed to treat textile dyes in aqueous solution and industrial effluent. The work focused on assisting the limitations still presented by the Fenton process regarding the use of suspended iron catalysts. Soon, a nanocomposite of bacterial cellulose (BC) and magnetite (Fe3O4) was developed. It has proven to be superior to those available in the literature, exhibiting purely catalytic properties and high reusability. Its successful production was verified through analytical characterization, while its catalytic potential was investigated in the treatment of different textile matrices. In initial tests, the photo-Fenton process irradiated and catalyzed by sunlight and BC/Fe3O4 discolored 92.19% of an aqueous mixture of four textile dyes. To improve the efficiency, the design of experiments technique evaluated the influence of the variables pH, [H2O2], and the number of BC/Fe3O4 membranes. 99.82% of degradation was obtained under optimized conditions using pH 5, 150 mg L-1 of H2O2, and 11 composite membranes. Reaction kinetics followed a pseudo-first-order model, effectively reducing the organic matter (COD = 83.24% and BOD = 88.13%). The composite showed low iron leaching (1.60 ± 0.08 mg L-1) and high stability. It was recovered and reused for 15 consecutive cycles, keeping the treatment efficiency at over 90%. As for the industrial wastewater, the photo-Fenton/sunlight/BC/Fe3O4 system showed better results when combined with the physical-chemical coagulation/flocculation process previously used in the industry's WWTP. Together they reduced COD by 77.77%, also meeting the color standards (DFZ scale) for the wavelengths of 476 nm (<3 m-1), 525 nm (<5 m-1), and 620 nm (<7 m-1). Thus, the results obtained demonstrated that employing the BC/Fe3O4 composite as an iron catalyst is a suitable alternative to materials employed in suspension. This is mainly due to the high catalytic activity and power of reuse, which will reduce treatment costs.

Original nanostructured bacterial cellulose/pyrite composite: Photocatalytic application in advanced oxidation processes.

The development of an original catalytic composite of bacterial cellulose (BC) and pyrite (FeS2) for environmental application was the objective of this study. Nanoparticles of the FeS2 were synthesized from the hydrothermal method and immobilized on the BC structure using ex situ methodology. In the BC, the FTIR and XRD analyzes showed the absorption band associated with the Fe-S bond and crystalline peaks attributed to the pyrite. Thus, the immobilization of the iron particles on the biopolymer was proven, producing the composite BC/FeS2. The use of the SEM technique also ratifies the composite production by identifying the fibrillar structure morphology of the cellulose covered by FeS2 particles. The total iron concentration was 54.76 ± 1.69 mg L-1, determined by flame atomic absorption analysis. TG analysis and degradation tests showed respectively the thermal stability of the new material and its high catalytic potential. A multi-component solution of textile dyes was used as the matrix to be treated via advanced oxidative processes. The composite acted as the catalyst for the Fenton and photo-Fenton processes, with degradations of 52.87 and 96.82%, respectively. The material proved stability by showing low iron leaching (2.02 ± 0.09 and 2.11 ± 0.11 mg L-1 for the respective processes). Thus, its high potential for reuse is presumed, given the remaining concentration of this metal in the BC. The results showed that the BC/FeS2 composite is suitable to solve the problems associated with using catalysts in suspension form.

Treatment of textile matrices using Fenton processes: influence of operational parameters on degradation kinetics, ecotoxicity evaluation and application in real wastewater.

Since conventional processes for treating textile effluents have limitations, this work aimed to investigate the application of advanced oxidation technology in this type of matrix. Initially, for a textile dyes mixture in solution, the photo-Fenton/sunlight process proved to be the most efficient among other systems tested. During the tests it was found that the degradation kinetics depends of the pH and catalyst and oxidant concentrations. After 60 min under optimized conditions, the color was reduced by 98.19%, with 92.52% organic matter conversion. Ecotoxicity tests with the Lactuca Sativa vegetable indicated that the dyes were not totally oxidized to inert compounds, although the treated solution did not cause a significant toxic effect for this species. In the second stage of the research, the photodegradation in real samples of textile wastewater was evaluated. The efficiency of the photo-Fenton/sunlight process was lower than that obtained for the dyes solution, a fact attributed to the greater complexity of the real matrix. However, the data also indicated that the combination of coagulation/flocculation and advanced oxidation processes is the most suitable methodology to reduce the fraction of biodegradable compounds. In summary, research has revealed that photocatalytic degradation of dyes through advanced oxidation is an efficient treatment.