Optimization of peroxidase-catalyzed oxidative coupling process for phenol removal from wastewater using response surface methodology

Hydroxylated aromatic compounds (HACs) are considered to be primary pollutants in a wide variety of industrial wastewaters. Horseradish peroxidase (HRP) is suitable for the removal of these toxic substances. However, development of a mathematical model and optimization of the HRP-based treatment considering the economical issues by novel methods is a necessity. In the present study, optimization of phenol removal from wastewater by horseradish peroxidase (HRP) was carried out using response surface methodology (RSM) and central composite design (CCD). As the initial experimental design, 2(4-1) half-fraction factorial design (H-FFD) is accomplished in triplicate at two levels to select the most significant factors and interactions in the phenol removal procedure. Temperature (degrees C), pH, concentration of enzyme (unit mL(-1)), and H202 (mM) were determined as the most effective independent variables. Finally, a fourfactor-five coded level CCD, 30 runs, was performed in order to fit a second-order polynomial function to the results and calculate the economically optimum conditions of the reaction. The goodness of the model was checked by different criteria including the coefficient of determination (R2 = 0.93), the corresponding analysis of variance ((Pmodel > F) < 0.0001) and parity plot (r = 0.96). These analyses indicated that the fitted model is appropriate for this enzymatic system. With the assumption that the minimum enzyme concentration was 0.26 unit mL(-1), the analysis of the response surface contour and surface plots defined the optimum conditions as follows: pH = 7.12, hydrogen peroxide concentration 1.72 mM, and 10 degrees C. This work improves phenol removal operation economically by applying minimum enzyme concentration and highest removal in comparison with previous studies.     

Morphological optimization of electrospun polyacrylamide/MWCNTs nanocomposite nanofibers using Taguchi’s experimental design

The morphological characteristic of electrospun polyacrylamide/multi-walled carbon nanotube (PAAm/MWCNTs) nanocomposite nanofibers is optimized in this work using Taguchi’s experimental design. The optimization is performed considering the effect of PAAm concentration, MWCNTs content, flow rate, and applied voltage on average nanofibers diameter. The reasonable dispersion of MWCNTs in PAAm solution is first ascertained via optical microscopy method. The experimental data required for the optimization process are then provided by statistical calculations on field-emission scanning electron microscopy images of the samples formulated based on a designed L ₉ orthogonal array. PAAm concentration is found to have the most contribution on final fibers morphology according to the results obtained from simultaneous implementation of the analysis of variance and mean effect assessment. Therefore, PAAm concentration, which is in consistence with solution viscosity and surface tension parameter, is found to have the most contribution to forming nanofibers including the finest fiber diameter. On the contrary, the flow rate of solution among the selected parameters shows the least effect on average nanofiber diameter.     

GO nanosheets localization by morphological study on PLA-GO electrospun nanocomposite nanofibers

In this study we prepare a nanocomposite substrate from poly lactic acid (PLA) and graphene oxide (GO) using electrospinning. Determining the possible placement of graphene oxide nano-sheets in the electrospun fiber mats is the main goal of this work. The investigative methods employed include scanning electron microscopy (SEM), atomic force microscopy (AFM) micrographs, tensile modulus and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). It is shown that the localization of nanoparticle by different methods controls different final properties. We performed the study of the mechanical properties, surface chemical structure and topology of obtaining nanofiber mats. Studies showed that the location of GO sheets depends on the lateral size of them and based on this claim we estimated three possible locations for them: (1) small GO sheets (less than 200 nm) fully or partially inside the electrospun fibers, (2) some larger ones rolling around and on the fibers surface under the high applied voltage, and (3) parts of large sheets bridging between the fibers.