Raquel Cristine Kuhn

Synthesis of zinc aluminate (ZnAl2O4) spinel and its application as photocatalyst

ZnAl2O4 spinel was synthesized by co-precipitation using ammonia as precipitating agent, followed by thermal treatment at 750 oC. The structural properties of particles were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), differential thermal analysis (DTA), and N2 adsorption/desorption isotherms (BET) techniques. The photocatalytic activity was evaluated in the degradation of organic pollutant in aqueous solution under sunlight. The results showed that the ZnAl2O4 particles exhibited a mesoporous structure, and a promising photocatalytic activity for the degradation of pollutant molecules.

Recent advances on biobutanol production

Recent studies have shown that butanol is a potential gasoline replacement that can also be blended in significant quantities with conventional diesel fuel. However, biotechnological production of butanol has some challenges such as low butanol titer, high cost feedstocks and product inhibition. The present work reviewed the technical and economic feasibility of the main technologies available to produce biobutanol. The latest studies integrating continuous fermentation processes with efficient product recovery and the use of mathematical models as tools for process scale-up, optimization and control are presented.

Effects of Solvent Diols on the Synthesis of ZnFe2O4 Particles and Their Use as Heterogeneous Photo-Fenton Catalysts

A solvothermal method was used to prepare zinc ferrite spinel oxide (ZnFe2O4) using ethylene glycol and 1,4 butanediol as solvent diols, and the influence of diols on the physical properties of ZnFe2O4 particles was investigated. The produced particles were characterized by X-ray powder diffraction (XRD), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption isotherms, and the catalytic activity for the organic pollutant decomposition by heterogeneous photo-Fenton reaction was investigated. Both solvents produced particles with cubic spinel structure. Microporous and mesoporous structures were obtained when ethylene glycol and 1,4 butanediol were used as diols, respectively. A higher pore volume and surface area, as well as a higher catalytic activity for the pollutant degradation were found when 1,4 butanediol was used as solvent.

Carbon Nanotubes as Supports for Inulinase Immobilization

The commercial inulinase obtained from Aspergillus niger was non-covalently immobilized on multiwalled carbon nanotubes (MWNT-COOH). The immobilization conditions for the carbon nanotubes were defined by the central composite rotational design (CCRD). The effects of enzyme concentration (0.8%–1.7% v/v) and adsorbent:adsorbate ratio (1:460–1:175) on the enzyme immobilization were studied. The adsorbent:adsorbate ratio variable has positive effect and the enzyme concentration has a negative effect on the inulinase immobilization (U/g) response at the 90% significance level. These results show that the lower the enzyme concentration and the higher the adsorbent:adsorbate ratio, better is the immobilization. According to the results, it is possible to observe that the carbon nanotubes present an effective inulinase adsorption. Fast adsorption in about six minutes and a loading capacity of 51,047 U/g support using a 1.3% (v/v) inulinase concentration and a 1:460 adsorbent:adsorbate ratio was observed. The effects of temperature on the immobilized enzyme activity were evaluated, showing better activity at 50 °C. The immobilized enzyme maintained 100% of its activity during five weeks at room temperature. The immobilization strategy with MWNT-COOH was defined by the experimental design, showing that inulinase immobilization is a promising biotechnological application of carbon nanotubes.

Purification of fructooligosaccharides in an activated charcoal fixed bed column.

Fructooligosaccharides (FOS) are mixtures of oligosaccharides containing mono and disaccharides, therefore, the separation of these sugars results in purer products for human consumption and can be added to various food products (drinks, cookies and yogurt). The aim of this work was the purification of fructooligosaccharides from a mixture of sugars, obtained by enzymatic synthesis, containing fructooligosaccharides, glucose, fructose and sucrose using activated charcoal fixed bed column. Temperature and ethanol concentration effects were analyzed using a 2² central composite design. Good separation conditions were obtained through central composite design. The best separation coefficient between fructooligosaccharides and glucose (ES(fructoolig/gluc)) was 3.99 ± 0.07 and between fructose and fructooligosaccharides (ES(fructoolig/fruct)) was 2.89 ± 0.36 using ethanol 15% (v/v) as eluent, at 50°C. The final FOS purification degree and recovery were about 80% and 97.8%, respectively. The activated charcoal fixed bed columns were shown to be a good alternative for sugar separation, especially for rich mixtures of fructooligosaccharides.

Selection, isolation, and identification of fungi for bioherbicide production

Production of a bioherbicide for biological control of weeds requires a series of steps, from selection of a suitable microbial strain to final formulation. Thus, this study aimed to select fungi for production of secondary metabolites with herbicidal activity using biological resources of the Brazilian Pampa biome. Phytopathogenic fungi were isolated from infected tissues of weeds in the Pampa biome. A liquid synthetic culture medium was used for production of metabolites. The phytotoxicity of fungal metabolites was assessed via biological tests using the plant Cucumis sativus L., and the most promising strain was identified by molecular analysis. Thirty-nine fungi were isolated, and 28 presented some phytotoxic symptoms against the target plant. Fungus VP51 belonging to the genus Diaporthe showed the most pronounced herbicidal activity. The Brazilian Pampa biome is a potential resource for the development of new and sustainable chemical compounds for modern agriculture.

Degradation of Amaranth azo dye in water by heterogeneous photo-Fenton process using FeWO4 catalyst prepared by microwave irradiation.

FeWO4 particles were synthesized by a simple, rapid and facile microwave technique and their catalytic properties in heterogeneous photo-Fenton reaction were evaluated. This material was employed in the degradation of Amaranth azo dye. Individual and interactive effects of operational parameters such as pH, dye concentration and H2O2 dosage on the decolorization efficiency of Amaranth dye were evaluated by 2(3) central composite design. According to characterization techniques, a porous material and a well-crystallized phase of FeWO4 oxide were obtained. Regarding the photo-Fenton reaction assays, up to 97% color and 58% organic carbon removal were achieved in the best experimental conditions. In addition, the photo-Fenton process maintained treatment efficiency over five catalyst reuse cycles to indicate the durability of the FeWO4 catalyst. In summary, the results reveal that the synthesized FeWO4 material is a promising catalyst for wastewater treatment by heterogeneous photo-Fenton process.

Production of Copper and Cobalt Aluminate Spinels and Their Application As Supports for Inulinase Immobilization

Copper and cobalt aluminates were obtained through the use of chitosan as template. In this synthesis route, chitosan is eliminated by heating, and a porous material is produced. These oxides were used as supports for inulinase immobilization by adsorption process. Physical properties of produced particles were analyzed by X-ray diffraction (XRD) and nitrogen adsorption-desorption isotherms. Both oxides presented particles containing mesoporous characteristics and high surface area, which is desirable for applications in enzyme immobilization processes. The results revealed that the copper and cobalt aluminates exhibit high inulinase immobilization efficiencies, which makes them promising supports for enzyme immobilization.

Separation and purification of fructooligosaccharides on a zeolite fixed‐bed column

Fructooligosaccharides (FOS), a well-known prebiotic product, are obtained by enzymatic synthesis and consist of a mixture of mono- and disaccharides. In this work, a methodology for their separation and purification was developed using a zeolite fixed-bed column. The effects of column temperature (40-60°C), eluent flow rate (0.10-0.14 mL/min), injected to bed volume percent ratio (2.6-5.1%), and ethanol concentration in the eluent (40-60%, v/v) were investigated using a fractionary factorial design (2(4-1)), having the separation efficiency and purity as target responses. Additional experiments were performed as well, where the temperature and ethanol concentration were studied in a central composite design (2(2)). In this work, the zeolite fixed-bed column was shown to be a good alternative for FOS purification, allowing a FOS purity of 90% and separation efficiency of 6.86 between FOS and glucose, using an eluent at 45°C with 60% ethanol concentration.

Preparation of Zinc Tungstate (ZnWO4) Particles by Solvo-hydrothermal Technique and their Application as Support for Inulinase Immobilization

ZnWO4 particles were synthesized as a single-phase by a simple and easy solvo-hydrothermal technique using water-ethylene glycol mixture as solvent, without using surfactant. Physical properties of produced particles were analyzed by X-ray diffraction (XRD), infrared spectroscopy (FTIR), surface area (BET), particles size distribution and atomic force microscopy (AFM). This material was used as support for inulinase immobilization by physical adsorption and the influence of temperature (30 and 50 oC) was evaluated. Material with mesoporous characteristic and with a surface area of 35.5 m2.g-1 was obtained. According to the findings, ZnWO4 present a satisfactory inulinase adsorption, and the better result was 605 U.g-1 support at 30 oC. Therefore, ZnWO4 particles prepared by one-step solvo/hydrothermal route provide a new potential support for inulinase immobilization.