Iron and molybdenum mixed oxide supported on Al-PILC for the catalytic oxidative desulfurization of dibenzothiophene in simulated diesel fuel.

In this work, three novel catalysts were prepared by 2.5, 5.0, and 10.0 wt.% facile impregnation with an iron and molybdenum mixed oxide (Fe/Mo) on an aluminum pillared clay (Al-PILC) support. These materials were characterized by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), temperature programed reduction (TPR), and nitrogen (N2) physisorption at 77 K. Characterizations indicated that the metal particles were dispersed on the surface of the three catalysts, and the interlayer d001 spacing of the pillared material remained unchanged after the impregnation process. The catalytic tests showed good results for DBT oxidation using the synthesized catalysts, with high turnover frequency (TOF) values, particularly for the material with 5.0 wt.% Fe/Mo. Theoretical calculations were carried out at the density functional theory (DFT) level, to investigate how the DBT molecules were adsorbed onto the surface of the mixed oxide. The lowest energy proposal was obtained when both Fe and Mo were present at the active sites, indicating a possible synergistic effect of the metals on catalyst activity. Reuse tests indicated that the catalysts could be employed effectively for up to 3 cycles in a row, then a decrease in activity occurred and the active sites needed to be regenerated.

Chitosan-iron oxide hybrid composite: mechanism of hexavalent chromium removal by central composite design and theoretical calculations.

In this study, the synthesis of iron oxide stabilized by chitosan was carried out for the application and optimization in the removal process of aqueous Cr(VI) by central composite design (CCD). The calculation of these effects allowed to know, quantitatively, the variables and the interaction between them that could affect the Cr(VI) removal process. It was also verified that the most favorable conditions for chromium removal were the following: pH 5.0, Cr(VI) concentration of 130 mg L-1, adsorbent mass of 5 mg, and Fe(II) content of 45% (w/w) in the CT-Fe beads. The adsorption kinetics performed under these conditions showed that the chitosan/iron hybrid composite is an adsorbent material with high chromium removal capacity (46.12 mg g-1). It was found that all variables were statistically significant. However, it was observed that the variable that most affected Cr(VI) removal was the pH of the solution, followed by the concentration of chromium ions in solution and the interaction between them. Therefore, the studied experimental conditions are efficient in chromium adsorption, besides the operational simplicity coming from statistical design. Theoretical calculations showed that the most stable chitosan was that with Fe(II) in the structure, that is, in the reaction mechanism, there is no competition of Fe(II) with Cr(III, VI) in the available sites of chitosan. Thus, the theoretical calculations show that the proposed Cr(VI) removal is effective.

Combining biochar and sewage sludge for immobilization of heavy metals in mining soils.

Excess heavy metal concentrations in mining areas is a worldwide problem due to their toxicity and persistence. Applying amendments to those areas is a cost-effective remediation technique that would aid revegetation efforts. The aim of this work was to study the ability of sewage sludge-derived biochar (SSB), wood charcoal powder (hereafter named wood biochar - WB), raw sewage sludge (SS), and their blending (WB/SS) to improve soil properties and to immobilize Cd, Pb, and Zn after their addition to heavy-metal contaminated soils from a Zn-mining area. Biochar was prepared from dried sewage sludge and a greenhouse experiment was set using different amendment doses (WB = 30 and 60 g kg-1, SS = 10 and 20 g kg-1). Addition of wood biochar and sewage sludge-derived biochar to soils led to increased leachate and soil pH. Biochar materials were responsible for the greatest reduction of Cd, Pb, and Zn bioavailability. The use of sewage sludge-derived biochar or the combination of sewage sludge with wood biochar in mining areas are potential alternatives for reusing and aggregating value to these locally available wastes, offering an opportunity to solve both soil remediation and waste disposal problems at once.