Synthesis of superparamagnetic Fe3O4-graphene oxide-based material for the photodegradation of clonazepam.

The global concern over water pollution caused by contaminants of emerging concern has been the subject of several studies due to the complexity of treatment. Here, the synthesis of a graphene oxide-based magnetic material (GO@Fe3O4) produced according to a modified Hummers' method followed by a hydrothermal reaction was proposed; then, its application as a photocatalyst in clonazepam photo-Fenton degradation was investigated. Several characterization analyses were performed to analyze the structure, functionalization and magnetic properties of the composite. A 23 factorial design was used for the optimization procedure to investigate the effect of [H2O2], GO@Fe3O4 dose and pH on clonazepam degradation. Adsorption experiments demonstrated that GO@Fe3O4 could not adsorb clonazepam. Photo-Fenton kinetics showed that total degradation of clonazepam was achieved within 5 min, and the experimental data were better fitted to the PFO model. A comparative study of clonazepam degradation by different processes highlighted that the heterogeneous photo-Fenton process was more efficient than homogeneous processes. The radical scavenging test showed that O 2 · - was the main active free radical in the degradation reaction, followed by hydroxyl radicals (•OH) and holes (h+) in the valence layer; accordingly, a mechanism of degradation was proposed to describe the process.

Adsorption of chloroquine, propranolol, and metformin in aqueous solutions using magnetic graphene oxide nanocomposite.

The work proposes the application of a nanocomposite formed by graphene oxide and magnetite to remove chloroquine, propranolol, and metformin from water. Tests related to adsorption kinetics, equilibrium isotherms and adsorbent reuse were studied, and optimization parameters related to the initial pH of the solution and the adsorbent dosage were defined. For all pharmaceuticals, adsorption tests indicated that removal efficiency was independent of initial pH at adsorbent dosages of 0.4 g L-1 for chloroquine, 1.2 g L-1 for propranolol, and 1.6 g L-1 for metformin. Adsorption equilibrium was reached within the first few minutes, and the pseudo-second-order model represented the experimental data well. While the equilibrium data fit the Sips isotherm model at 298 K, the predicted maximum adsorption capacities for chloroquine, propranolol, and metformin were 44.01, 16.82, and 12.23 mg g-1, respectively. The magnetic nanocomposite can be reused for three consecutive cycles of adsorption-desorption for all pharmaceuticals, being a promising alternative for the removal of different classes of pharmaceuticals in water.

Adsorptive and photocatalytic activity of Fe3O4-functionalized multilayer graphene oxide in the treatment of industrial textile wastewater.

Multilayer graphene oxide (mGO) was synthesized and functionalized via co-precipitation method to produce magnetic Fe3O4-functionalized multilayer graphene oxide nanocomposite (MmGO). Photocatalytic properties of MmGO were investigated in the photodegradation of raw textile wastewater samples. Fourier-transformed infrared spectroscopy revealed Fe-O vibrations, characterized by the band shift from 636.27 to 587.25 cm-1 on MmGO. X-ray diffraction confirmed the successful oxidation of graphite by the (002) peak at 10° and indicated the presence of Fe3O4 on MmGO surface by the peaks at 2θ 35.8° (311), 42.71° (400), 54.09° (511), and 62.8° (440). There was no detection of coercivity field and remnant magnetization, evidencing a material with superparamagnetic properties. Then, the textile effluent was treated by heterogeneous photo-Fenton (HPF) reaction. A 22 factorial design was conducted to evaluate the effects of MmGO dosage and H2O2 concentration on HPF, with color and turbidity removal as response variables. The kinetic behavior of the adsorption and HPF processes was investigated separately, in which, the equilibrium was reached within 60 and 120 min, for adsorption and HPF, respectively. Pseudo-second-order model exhibited the best fit, with COD uptake capacity at equilibrium of 4094.94 mg g-1, for chemical oxygen demand. The modeling of kinetics data showed that the Chan and Chu model was the most representative for HPF, with initial removal rate of 95.52 min-1. The removal of organic matter was 76.36% greater than that reached by conventional treatment at textile mills. The presence of Fe3O4 nanoparticles attached to MmGO surface was responsible for the increase of electron mobility and the enhancement of its photocatalytic properties. Finally, MmGO presented low phytotoxic to Cucumis sativus L. with a RGI of 0.53. These results bring satisfactory perspectives regarding further employment, on large scale, of MmGO as nanocatalyst of textile pollutants.

In-depth investigation of Sodium percarbonate as oxidant of PAHs from soil contaminated with diesel oil.

Sodium percarbonate (SPC, 2Na2CO3∙3H2O2), is a compound that can be used under multiple environmental applications. In this work, SPC was employed as oxidant in the treatment of soil contaminated with diesel oil. The soil samples were collected during the earthmoving stage of RNEST Oil Refinery (Petrobras), Brazil. Then, the samples were air-dried, mixed and characterized. Subsequently, raw soil was contaminated with diesel and treated by photo-Fenton reaction (H2O2/Fe2+/UV). SPC played a significant role in the generation of hydroxyl radicals under the catalytic effect of ferrous ions (Fe2+), hydrogen peroxide (H2O2) and radiation. These radicals provoked the photodegradation of polycyclic aromatic hydrocarbons (PAHs), in the soil remediation. A factorial design 33 was carried out to assess the variables which most influenced the decrease in total organic carbon (TOC). The study was performed with the following variables: initial concentration of [H2O2] and [Fe2+], between 190.0 and 950.0 mmol L-1 and 0.0-14.4 mmol L-1, respectively. UV radiation was supplied from sunlight, blacklight lamps, and system without radiation. All experiments were performed with 5.0 g of contaminated soil in 50.0 mL of solution. The initial concentration of Fe2+ showed the statistically most significant effect. The oxidation efficiency evaluated in the best condition showed a decrease from 34,765 mg kg-1 to 15,801 mg kg-1 in TOC and from 85.750 mg kg-1 to 20.770 mg kg-1 in PAHs content. Moreover, the sums of low and high molecular weight polycyclic aromatic hydrocarbons (LMW-PAHs and HMW-PAHs) were 19.537 mg kg-1 and 1.233 mg kg-1, respectively. Both values are within the limits recommended by the United Sates Environmental Protection Agency (USEPA) and evidenced the satisfactory removal of PAHs from contaminated soil, being an alternative to classic oxidation protocols.

Fructo-oligosaccharides production by an Aspergillus aculeatus commercial enzyme preparation with fructosyltransferase activity covalently immobilized on Fe3O4-chitosan-magnetic nanoparticles.

Pectinex Ultra SP-L, a commercial enzyme preparation with fructosyltransferase activity, was successfully immobilized by covalent binding to Fe3O4-chitosan- magnetic nanoparticles. Immobilization carried out according to a 23-full factorial design where glutaraldehyde concentration, activation time and time of contact between enzyme and support were selected as the independent variables and immobilization yield as the response. The highest immobilization yield (94.84%) was obtained using 3.0% (v/v) glutaraldehyde and activation and contact times of 180 and 30 min, respectively. The immobilized biocatalyst, which showed for both hydrolytic and transfructosylating activities optimum pH and temperature of 7.0 and 60 °C, respectively, retained 70 and 86% of them after 6 cycles of reuse. A kinetic/thermodynamic study focused on thermal inactivation of the immobilized construct indicated high thermostability at temperatures commonly used for fructo-oligosaccharides (FOS) production. Maximum FOS concentration obtained in lab-scale experiments was 101.56 g L-1, with predominant presence of 1-kestose in the reaction mixture. The results obtained in this study suggest that the immobilized-enzyme preparation may be effectively exploited for FOS production and easily recovered from the reaction mixture by action of a magnetic field.