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.

Magnetic nanostructured material as heterogeneous catalyst for degradation of AB210 dye in tannery wastewater by electro-Fenton process.

Degradation of the Acid Black 210 dye (AB210) in synthetic and industrial effluent samples was performed, for the first time, using a heterogeneous electro-Fenton (EF) process with a CoFe2O4/NOM magnetic hybrid catalyst (Hb200). The technique was compared with electrochemical oxidation using electrogenerated hydrogen peroxide (AO-H2O2). The catalyst was synthesized by the sol-gel technique, using water with a high content of natural organic matter (NOM) as an eco-friendly solvent. Analyses using XRD, FTIR, and TEM showed the formation of hybrid nanostructures with average size of 4.85 nm. Electrochemical assays were performed with a GDE/BDD electrode pair, electrogenerated H2O2, and current density of 45.4 mA cm-2. For the synthetic solution of AB210 at pH 3, the EF process presented higher efficiency, compared to AO-H2O2, with the optimum condition achieved using a lower mass of the catalyst (30 mg) and a higher concentration of the dye (55 mg L-1). The EF method also showed superior performance in the treatment of an industrial effluent with high organic load, at pH 6, with almost complete mineralization of AB210 (95%) in 7 h, while the AO-H2O2 process achieved 82% mineralization. The Hb200 hybrid maintained excellent catalytic activity during reuse in 3 cycles, with only 10% lower mineralization efficiency in the last cycle. GC-MS analysis showed that most of the contaminants in the effluent, including bis(2-ethylhexyl) phthalate, one of the most toxic, were eliminated or transformed after the EF treatment with Hb200.

Synthesis of functionalized mesoporous material from rice husk ash and its application in the removal of the polycyclic aromatic hydrocarbons.

The rice husk ash (RHA) was used as an alternative source of silica for the synthesis of the functionalized mesoporous material, which was used in the removal of the PAHs naphthalene (Nap), benzo[b]fluoranthene (B[b]F), benzo[k]fluoranthene (B[k]F), and benzo[a]pyrene (B[a]P) from aqueous media. The PABA-MCM-41 (RHA) was characterized using FTIR, TGA, SAXS, and N2 adsorption-desorption analyses. Removal experiments were performed to determine the initial concentrations, individual adsorption in comparison with the mixture of the PAHs, PABA-MCM-41 (RHA) amount, pH, time, and temperature, and the results obtained were statistically analyzed. The PABA-MCM-41 (RHA) presented the SBET, VT, and DBJH values of 438 m2 g-1, 0.41 cm3 g-1, and 3.59 nm, respectively, and good thermal stability. The qe values found in the kinetic equilibrium for the PAHs mixture followed increasing order: Nap < B[a] P < B[k]F < B[b]F, with removal percentages of 89.08 ± 0.00, 93.85 ± 0.28, 94.54 ± 0.10, and 97.80 ± 0.05%, respectively. Graphical abstract.

Removal of heavy crude oil from water surfaces using a magnetic inorganic-organic hybrid powder and membrane system.

Oil spills are among the most significant threats to aquatic ecosystems. The present work describes the synthesis of different organic-inorganic hybrid matrices with magnetic properties, obtained in the forms of powders and membranes. The powders were synthesized using the following biomass wastes to form the organic phase: coconut mesocarp, sugarcane bagasse, sawdust, and water hyacinth. The resulting powders were denoted HMG-CO, HMG-CN, HMG-SE, and HMG-AP, respectively. Membranes (denoted MHMG-PES) were prepared using polyethersulfone polymer. In both cases, the inorganic phase was cobalt ferrite. The materials were evaluated in terms of their efficiencies in removing crude oil from water surfaces. The presence of organic matter, polyethersulfone, and cobalt ferrite in the structures of the materials was confirmed by XRD and FTIR analyses. The efficiencies of the materials were determined using the Standard Test Method for Sorbent Performance of Adsorbents (ASTM F726-99). Among the hybrids in powder form, the HMG-CN material presented the highest oil removal efficiency (85%, adsorptive capacity of 17 g g-1), which could be attributed to the fibrous nature of the sugarcane bagasse. The MHMG-PES membrane was able to remove 35 times its own mass of oil (adsorptive capacity of 35 g g-1). In addition to this high removal efficiency, an important advantage of MHMG-PES, compared to the HMG-CN hybrid powder, was that the oil could be mechanically removed from the membrane surface, eliminating the need for subsequent time-consuming extraction steps requiring large volumes of organic solvents and additional energy expenditure. When the two materials were used simultaneously, it was possible to remove 45 times their own mass of oil (adsorptive capacity of 45 g g-1), with the adsorptive capacity of HMG-CN increasing by 23%. This high adsorptive capacity was due to the retaining barrier formed by the HMG-CN hybrid powder, which prevented the oil patch from spreading and enabled its homogeneous removal, which was not possible using MHMG-PES alone. It could be concluded that use of the magnetic hybrids synthesized using biomass wastes, together with the hybrid magnetic membrane, provided an effective and inexpensive technological alternative for the removal of oil from water surfaces.

Applications of magnetic hybrid adsorbent derived from waste biomass for the removal of metal ions and reduction of 4-nitrophenol.

The use of industrial waste to synthesize materials of technological interest is a rational way to minimize or solve environmental pollution problems. This work investigates the adsorption of cadmium and lead ions by magnetic hybrid adsorbents synthesized using the in natura biomasses coconut mesocarp (CCFe), sawdust (SAFe), and termite nest (TEFe) for the organic phases and magnetic cobalt ferrite as the inorganic phase. The formation of a cobalt ferrite phase was confirmed by XRD. The use of XRD and FTIR analyses revealed the presence of organic matter in the structure of the material. Removal assays performed at different pH values (2.0-8.0) showed the effectiveness of the adsorbent for the removal of Pb2+ at pH 3.0 and Cd2+ at pH 4.0. The adsorption processes showed fast kinetics, with removal of 79-86% of Pb2+ and 49% of Cd2+ within only 5 min, and removal of 92-96% of the metal species at equilibrium. In the case of cadmium, the hybrid sorbents (CCFe, SAFe, and TEFe) showed high removal capacity after three reuse cycles, while the removal of lead decreased from 99% to 40%. The adsorbent matrices saturated with the recovered cadmium and lead ions showed excellent catalytic performance in the reduction of 4-nitrophenol, with 99.9% conversion within 43-56 s. The materials showed high capacities for reuse in three successive reduction cycles. The findings highlight the effectiveness of an industrial symbiosis approach to the development of new technologically important materials.

Biodegradation of anthracene and several PAHs by the marine-derived fungus Cladosporium sp. CBMAI 1237.

The biodegradation of polycyclic aromatic hydrocarbons (PAHs) by marine-derived fungi was reported in this work. Marine-derived fungi (Trichoderma harzianum CBMAI 1677, Cladosporium sp. CBMAI 1237, Aspergillus sydowii CBMAI 935, Penicillium citrinum CBMAI 1186 and Mucor racemosus CBMAI 847) biodegraded anthracene (14days, 130rpm, 50mgmL-1 initial concentration in malt 2% medium). Cladosporium sp. CBMAI 1237 was the most efficient strain and biodegraded more anthracene in the presence (42% biodegradation) than in the absence (26%) of artificial seawater, suggesting that the biodegradation of PAHs may be faster in seawater than in non-saline environment. After 21days, Cladosporium sp. CBMAI 1237 biodegraded anthracene (71% biodegradation), anthrone (100%), anthraquinone (32%), acenaphthene (78%), fluorene (70%), phenanthrene (47%), fluoranthene (52%), pyrene (62%) and nitropyrene (64%). Previous undocumented metabolites were identified and, anthraquinone was a common product of different PAHs biodegradation. The marine-derived fungus Cladosporium sp. CBMAI 1237 showed potential for bioremediation of PAHs.

Green synthesis of a magnetic hybrid adsorbent (CoFe2O4/NOM): Removal of chromium from industrial effluent and evaluation of the catalytic potential of recovered chromium ions.

This work describes the removal of chromium ions from industrial effluent using a hybrid magnetic adsorbent, CoFe2O4/NOM, synthesized using water rich in natural organic matter. The hybrid obtained at ambient temperature (HbAmb) was calcined at 200, 400, and 800°C for 2h, and formation of the cobalt ferrite phase was confirmed by XRD, which indicated the presence of NOM in the structure of the material. Removal tests showed that HbAmb provided efficient removal of chromium at the natural pH of the effluent, while the other materials were effective at pH 6. Evaluation of the kinetics showed excellent performance of the process, with 70-87% removal in 20min, which provided a high degree of flexibility. The hybrid showed high removal during five reuse cycles, ranging from 96% in the first cycle to 82% in the final. The matrices containing the saturated adsorbent (HbAmb_Sat) and recovered chromium ions (CrD) showed high performance in the catalytic reduction of 4-nitrophenol, with conversion rates of 99.9% in short periods of time, as well as excellent potential for reuse in three cycles. The results demonstrated that the production of a technological material and its use for remediation could be achieved in an ecologically sustainable manner.

Evaluation of the interactions between chitosan and humics in media for the controlled release of nitrogen fertilizer.

The aim of this study was to evaluate the interactions of peat, humic acids, and humin with urea dispersed in chitosan, in systems intended for the controlled release of urea. Spheres of chitosan with humic material and urea intentionally added to the media were prepared and characterized by means of elemental analysis (CHN), electron paramagnetic resonance (EPR), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The spheres possessed functional groups related to humic substances that interacted with the chitosan, and the presence of urea in the media was also confirmed after it has been added. Release experiments demonstrated that the samples released urea in a controlled manner that was dependent on pH, increasing in the order: pH 2.5 < pH 4.0 < pH 9.0. In soil experiments, the degree of release of urea (α) increased over time, with values of 0.44 for chitosan-humic acids-urea (CHAU), 0.48 for chitosan-peat-urea (CPTU), and 0.67 for chitosan-humin-urea (CHMU) obtained in the first day of the experiment. The release of urea did not exceed 70% after 7 days. The results demonstrated the potential of using peat, humic acids, and humin, in combination with chitosan, in order to manufacture controlled release urea fertilizers and contribute to reducing adverse environmental and economic impacts.