Bifunctional green nanoferrites as catalysts for simultaneous organic pollutants reduction and hydrogen generation: Upcycling strategy.

The upcycling strategy is an approach that includes the conversion of waste into new higher value-added products. This study reports on a new methodology for the environmentally friendly synthesis of MFe2O4 spinel nanoferrites (M = Co, Cu, Fe and Mn) to be used as catalysts applied in the upcycling method. Thus, the reduction of 4-nitrophenol (4-NP), methyl orange, and methyl red to commercially valuable compounds was evaluated, as well as the simultaneous generation of hydrogen in a short time. Therefore, an eco-friendly synthesis was proposed, according to the 12 principles of green chemistry and sustainability. Product were obtained with satisfactory properties in terms of crystallinity, magnetic particle size, and magnetization. The materials exhibited excellent performance in catalytic reduction of 4-NP, whose reduction time decreased in the order MnFe2O4 > Fe3O4 > CoFe2O4 > CuFe2O4. This behavior highlighted the CuFe2O4 nanoferrite, which achieved 4-NP reduction in just 10 s. It proved that it could also be reused for 10 consecutive cycles while maintaining its crystalline structure. The catalyst was also effective in the reduction of azo dyes and subsequent production of substituted aromatic compounds suitable for use in chemical processes. Under the optimized conditions, the green CuFe2O4 catalyst was effective in producing hydrogen by hydrolysis. HGR and activation energy (Ea) values were of the order of 19,600 mL g-1 min-1 and 25.5 kJ mol-1, respectively. The results demonstrated the potential of this simple strategy for the environmental pollutant elimination and power generation.

Chitosan-based magnetic bioadsorbent beads from eucalyptus sawdust waste for the Direct Violet-51 dye remediation: Eco-friendly strategy and statistical optimization.

In the present study, a new application was proposed for the eucalyptus sawdust waste, which is an environmental passive. Three adsorbent materials composed of chitosan (CS), sawdust (CSW), and magnetic beads (CSWF) were developed and used for the Direct Violet-51 remediation. The adsorption testes were optimized based on the variation of the adsorption parameters: (i) pH (2-12), (ii) contact time (5-60 min), (iii) initial dye concentration (10-60 mg L-1), (iv) adsorbent mass (10-100 mg) in 10 mL. The optimized conditions of the adsorption essays showed that the three synthesized adsorbents completely removed the dye from the aqueous medium, but under different experimental conditions. As the main findings in this study, we can highlight the excellent performance of CSW adsorbent material, which promoted maximum removal efficiency of Direct Violet-51 at neutral pH, which is of great importance for the industrial processes. On the other hand, CS and CSWF adsorbent materials exhibited a maximum adsorption efficiency at pH 2. Furthermore, the adsorbent materials were applied in the dye remediation in environmental water samples from the tap water, Marcela dam, and Poxim River, they did not suffer any major matrix interference, whose removal efficiency values varied between 99.8 and 100, 70.7-100, and 98.8-99.5 % for the CS, CSW, and CSWF, respectively. Finally, besides being materials produced from the waste, they can be reused more times, fitting into the concept of circular economy.

Toward efficient electrocatalytic degradation of iohexol using active anodes: A laser-made versus commercial anodes.

The X-ray iodinated contrast medium iohexol is frequently detected in aquatic environments due to its high persistence and the inefficiency of its degradation by conventional wastewater treatments. Hence, the challenge faced in this study is the development of an alternative electrochemical treatment using active anodes. We investigate the oxidation of iohexol (16.42 mg L-1) using different operating conditions, focusing on the role of different mixed metal oxide anodes in the treatment efficiency. The electrocatalytic efficiency of the Ti/RuO2-TiO2 anode prepared using a CO2 laser heating and an ionic liquid is compared with Ti/RuO2-TiO2-IrO2 and Ti/IrO2-Ta2O5 commercial anodes. The hypochlorite ions generated by the anodes are also analyzed. The effect of the electrolyte composition (NaCl, Na2SO4, and NaClO4) and current density (15, 30, and 50 mA cm-2) on the iohexol degradation is also studied. The Ti/RuO2-TiO2 laser-made anode is more efficient than the commercial anodes. After optimizing experimental parameters, this anode removes 95.5% of iohexol in 60 min and displays the highest kinetic rate (0.059 min-1) with the lowest energy consumption per order (0.21 kWh m-3order-1), using NaCl solution as the electrolyte and applying 15 mA cm-2. Additionally, iohexol-intensified groundwater was used to compare the efficiency of anodes. The Ti/RuO2-TiO2 is also more efficient in removing the organic charge from the real water matrix (21.7% TOC) than the commercial anodes. Notably, the iohexol removal achieved is higher than all electrochemical treatments already reported using state-of-the-art non-active anodes in lower electrolysis time. Therefore, data from this study indicate that the electrochemical degradation of iohexol using the Ti/RuO2-TiO2 anode is efficient and has excellent cost-effectiveness; thus, it is a promising approach in the degradation of iohexol from wastewater. Furthermore, the Ti/RuO2-TiO2 active anode is competitive and can be an excellent option for treating effluents contaminated with recalcitrant organic compounds such as iohexol.