Adsorption studies of the hybrid material obtained from the functionalization of silica with alfa and gamma cyclodextrins.

The generation of residues containing dyes by industrial sectors has been mobilizing scientists to develop methodologies capable of treating water containing these contaminants. Adsorption is an option to remove these molecules from the aqueous medium and, for this study, the composites between silica and cyclodextrins alpha (α-CDSI) and gamma (γ-CDSI) were used to capture methylene blue. Adsorption was spontaneous for both composites (ΔG < 0) and characterized as exothermic and of a physical nature, with ΔH of -17.68 and -12.13 kJ mol-1 for α-CDSI and γ-CDSI, respectively. Adsorption took place over a wide pH range, with an efficiency of approximately 96%, reaching equilibrium at 5 minutes. The adsorption kinetics was described by the pseudo-second-order model (R2 > 0.999) and the adsorption isotherms showed that the process must occur mainly by dye complexation in the cyclodextrins cavities. The qm values obtained were 210.8 and 205.2 mg g-1 for α-CDSI and γ-CDSI, respectively; the Sips and Temkin models were the ones that best fit the experimental data. The deposition and interactions of the dye with the adsorbent surface were confirmed by the analysis of the IR spectra. Desorption studies showed that the material maintained its adsorption capacity of around 90% until the fourth adsorption/desorption cycle. Thus, the materials produced showed to efficiently remove methylene blue and that composite reuse is a viable process for application in dye removal.

Effect of the acid treatment conditions of kaolinite on etheramine adsorption: A comparative analysis using chemometric tools.

The present work evaluated the effect of the acid treatment conditions of natural kaolinite (NK) regarding its efficiency in removing etheramine. The treatment was conducted using sulfuric acid at the concentrations of 1 mol L-1 (KA-01), 2 mol L-1 (KA-02) and 5 mol L-1 (KA-05) at 85 °C. The obtained adsorbents were characterized by X-ray fluorescence, X-ray diffraction, N2 adsorption/desorption isotherms, zeta potential analysis and infrared spectroscopy. The Response Surface Method was used to optimize adsorption parameters (initial concentration of etheramine, adsorbent mass and pH of the solution). The results, described by means of a central composite design, were adjusted to the quadratic model. Results revealed that the adsorption was more efficient at the etheramine concentration of 400 mg L-1, pH 10 and adsorbent mass of 0.1 g for NK and 0.2 g for KA-01, KA-02 and KA-05. The sample KA-02 presented a significant increase of etheramine removal compared to the NK sample. The adsorption kinetics conducted under optimized conditions showed that the system reached the equilibrium in approximately 30 min. The kinetic data were better adjusted to the pseudo-second order model. The isotherm data revealed that the Sips model was the most adequate one. The calculation of Eads allowed to infer that the mechanism for etheramine removal in all the evaluated samples was chemisorption. The reuse tests showed that, after four uses, the efficiency of adsorbents in removing etheramine did not suffer significant modifications, which makes the use of kaolinite to treat effluents from the reverse flotation of iron ore feasible.

Kinetic, thermodynamic and physical-chemical study of the removal of copper from cachaça using coconut fibers.

The use of coconut fiber as a copper adsorbent in cachaça was optimised, and changes in the chemical quality of the beverage were observed by analytical techniques. The influence of the adsorbent mass and copper concentration parameters was investigated using the Central Composite Design, and the optimum condition was obtained through the use of Response Surface Methodology. The equilibrium of the adsorption reaction was obtained within 120 min. The kinetic data were better adjusted for the Elovich model (Elovich and Zhabrova 1939) and the isotherm data for the Sips model (Sips 1948). The maximum adsorption capacity was 1.38 mg g-1. Slight changes in the physicochemical quality of the beverage were observed, including a decrease in volatile acidity and alcohol content. Copper levels in cachaça decreased from 8.57 mg L-1 to 4.97 mg L-1 after adsorption. Therefore, the use of biomass as a metal ion adsorbent in beverages can be successfully employed.

Residual determination of anesthetic menthol in fishes by SDME/GC-MS.

The SDME-GC/MS method was applied to residual determination of anesthetic menthol in fish. The extractions took place from the headspace of the sample using 1.8µL of octane as the extraction solvent. To obtain the ideal extraction condition, was used Response Surface Methodology, defining: extraction time 15min, temperature 30°C and salt 3g. The method showed LOD and LOQ of 0.021 and 1.56µgL-1 respectively, recovery of 94% and R2 of 0.9997. The analyzes were performed on tilapia fillets anesthetized in five concentrations between 5 and 15×104µgL-1 and with times of slaughter after anesthesia of 0, 12, 24 and 48h. It was determined that 48h is the required residual period for total metabolization of menthol in the fishes' organisms. This methodology becomes promising regarding the establishment of protocols to regulatory the use of menthol as an anesthetic in aquaculture.