Removal of sulfanilamide by tailor-made magnetic metal-ceramic nanocomposite adsorbents

Magnetic Chitosan for the Removal of Sulfamethoxazole from Tertiary Wastewaters

Magnetic chitosan nanoparticles, synthesized by in situ precipitation, have been used as adsorbents to remove sulfamethoxazole (SMX), a sulfonamide antibiotic dangerous due to its capacity to enter ecosystems. The adsorption of SMX has been carried out in the presence of tertiary wastewaters from a depuration plant to obtain more realistic results. The effect of pH on the adsorption capacity significantly changed when carrying out the experiments in the presence of wastewater. This change has been explained while taking into account the charge properties of both the antibiotic and the magnetic chitosan. The composition of wastewaters has been characterized and discussed as regards its effect on the adsorption capacity of the magnetic chitosan. The models of Elovich and Freundlich have been selected to describe the adsorption kinetics and the adsorption isotherms, respectively. The analysis of these models has suggested that the adsorption mechanism is based on strong chemical interactions between the SMX and the magnetic chitosan, leading to the formation of an SMX multilayer.

The beneficial role of nano-sized Fe3O4 entrapped in ultra-stable Y zeolite for the complete mineralization of phenol by heterogeneous photo-Fenton under solar light

Highly efficient, separable, and stable magnetic iron-based-photocatalysts produced from ultra-stable Y (USY) zeolite were applied, for the first time, to the photo-Fenton removal of phenol under solar light. USY Zeolite with a Si/Al molar ratio of 385 was impregnated under vacuum with an aqueous solution of Fe2+ ions and thermally treated (500-750 °C) in a reducing atmosphere. Three catalysts, Fe-USY500°C-2h, Fe-USY600°C-2h and Fe-USY750°C-2h, containing different amounts of reduced iron species entrapped in the zeolitic matrix, were obtained. The catalysts were thoroughly characterized by absorption spectrometry, X-ray powder diffraction with synchrotron source, followed by Rietveld analysis, X-ray photoelectron spectroscopy, N2 adsorption/desorption at -196 °C, high-resolution transmission electron microscopy and magnetic measurements at room temperature. The catalytic activity was evaluated in a recirculating batch photoreactor irradiated by solar light with online analysis of evolved CO2. Photo-Fenton results showed that the catalyst obtained by thermal treatment at 500 °C for 2 h under a reducing atmosphere (FeUSY-500°C-2h) was able to completely mineralize phenol in 120 min of irradiation time at pH = 4 owing to the presence of a higher content of entrapped nano-sized magnetite particles. The latter promotes the generation of hydroxyl radicals in a more efficient way than the Fe-USY catalysts prepared at 600 and 750 °C because of the higher Fe3O4 content in ultra-stable Y zeolite treated at 500 °C. The FeUSY-500°C-2h catalyst was recovered from the treated water through magnetic separation and reused five times without any significant worsening of phenol mineralization performances. The characterization of the FeUSY-500°C-2h after the photo-Fenton process demonstrated that it was perfectly stable during the reaction. The optimized catalyst was also effective in the mineralization of phenol in tap water. Finally, a possible photo-Fenton mechanism for phenol mineralization was assessed based on experimental tests carried out in the presence of scavenger molecules, demonstrating that hydroxyl radicals play a major role.

Synthesis of g-C3N4 Derived from Different Precursors for Photodegradation of Sulfamethazine under Visible Light

In this study, a series of g-C3N4 nanosheets were prepared by various thermal oxidative etching times from four different precursors (urea, melamine, dicyandiamide and thiourea). The physicochemical properties of these g-C3N4 nanosheets were analyzed in detail using scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence emission spectra, Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) analysis and ultraviolet-visible diffuse reflectance. The results revealed that the g-C3N4 nanosheets obtained a thinner layer thickness and larger specific surface area, with an extension of thermal oxidative etching time. Meanwhile, sulfamethazine (SMZ), one of the most widely used sulfonamides, was used to evaluate the photocatalyst activity of the g-C3N4 nanosheets prepared in this study. Compared to other g-C3N4 nanosheets, urea-derived g-C3N4 nanosheets under 330 min thermal oxidative etching showed the highest photocatalytic activity for SMZ under visible light. In conclusion, our study provides detailed insights into the synthesis and characterization of g-C3N4 nanosheets prepared from various precursors and highlights the importance of thermal oxidative etching time in determining the photocatalytic activity of these materials.

A Novel Approach, Based on the Combined Action of Chitosan Hydrogel and Laccases, for the Removal of Dyes from Textile Industry Wastewaters

Dyes are considered as one the most important classes of contaminants that threaten the environment and human life. The synergy between the adsorption capacity of chitosan hydrogels and the catalytic properties of the enzyme laccase was exploited to improve the removal of contaminants from a liquid stream. The adsorption capacity of a chitosan hydrogel was tested on three different textile dyes. The effect of pH on the adsorption efficiency was dependent on the dye tested: the removal of methylene blue (MB), a cationic dye, was more effective at alkaline values of pH, whereas bromophenol blue (BPB) and Coomassie brilliant blue (BB), both anionic dyes, were more effectively removed under acid environments. The use of laccase immobilized onto chitosan has significantly improved the efficiency of dye removal, exploiting the synergy between the adsorption capacity of chitosan and the catalytic properties of the enzyme. The simultaneous processes of adsorption and enzymatic degradation improved the dye removal whatever the pH value adopted, making the removal efficiency less dependent from the pH changes. The chitosan used as a support for the immobilization of laccases showed good stability under repeated cycles, demonstrating the feasibility of the method developed for the application in wastewater remediation.

FeS combined ozonation to remove p-aminobenzenesulfonamide from water: Density functional theory insights into the mechanism

The applicability and performance of FeS in ozonation process to remove p-aminobenzenesulfonamide (SN) from water was assessed, and the working mechanism of FeS was comprehensively explored by both experimental means and density functional theory (DFT) simulation. FeS combined ozonation achieved 74% of SN removal in 60 min under the optimal condition, which was 37% higher than by ozonation alone, and 12% higher than FeO combined ozonation. Highly active species of •OH, •SO4-, 1O2 and •O2- were detected in the FeS combined ozonation system, the evolution pathway of the involved species was expounded with the aid of DFT calculation. The results revealed that •O2-, H2O2 and SO42- were originally formed via interface reactions on FeS surface, then gradually transformed into •OH, 1O2 and •SO4- through subsequent chain reactions. Moreover, FeS had a lower energy barrier of 0.16 eV than FeO with a value of 0.83 eV for the transformation of ozone to active atomic oxygen. The presented study provided a significant insight into the role of Fe-based materials in ozonation, and was of great importance to guide the route for ozonation process improvement.

Silica Meets Tannic Acid: Designing Green Nanoplatforms for Environment Preservation

Hybrid tannic acid-silica-based porous nanoparticles, TA-SiO₂ NPs, have been synthesized under mild conditions in the presence of green and renewable tannic acid biopolymer, a glycoside polymer of gallic acid present in a large part of plants. Tannic acid (TA) was exploited as both a structuring directing agent and green chelating site for heavy metal ions recovery from aqueous solutions. Particles morphologies and porosity were easily tuned by varying the TA initial amount. The sample produced with the largest TA amount showed a specific surface area an order of magnitude larger than silica nanoparticles. The adsorption performance was investigated by using TA-SiO₂ NPs as adsorbents for copper (II) ions from an aqueous solution. The effects of the initial Cu²⁺ ions concentration and the pH values on the adsorption capability were also investigated. The resulting TA-SiO₂ NPs exhibited a different adsorption behaviour towards Cu²⁺, which was demonstrated through different tests. The largest adsorption (i.e., ~50 wt% of the initial Cu²⁺ amount) was obtained with the more porous nanoplatforms bearing a higher final TA content. The TA-nanoplatforms, stable in pH value around neutral conditions, can be easily produced and their use would well comply with a green strategy to reduce wastewater pollution.