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Background: Biogeochemical processing of metals including the fabrication of novel nanomaterials from metal contaminated waste streams by microbial cells is an area of intense interest in the environmental sciences. Results: Here we focus on the fate of Ce during the microbial reduction of a suite of Ce-bearing ferrihydrites with between 0.2 and 4.2 mol% Ce. Cerium K-edge X-ray absorption near edge structure (XANES) analyses showed that trivalent and tetravalent cerium co-existed, with a higher proportion of tetravalent cerium observed with increasing Ce-bearing of the ferrihydrite. The subsurface metal-reducing bacterium Geobacter sulfurreducens was used to bioreduce Ce-bearing ferrihydrite, and with 0.2 mol% and 0.5 mol% Ce, an Fe(II)-bearing mineral, magnetite (Fe(II)(III)2O4), formed alongside a small amount of goethite (FeOOH). At higher Ce-doping (1.4 mol% and 4.2 mol%) Fe(III) bioreduction was inhibited and goethite dominated the final products. During microbial Fe(III) reduction Ce was not released to solution, suggesting Ce remained associated with the Fe minerals during redox cycling, even at high Ce loadings. In addition, Fe L2,3 X-ray magnetic circular dichroism (XMCD) analyses suggested that Ce partially incorporated into the Fe(III) crystallographic sites in the magnetite. The use of Ce-bearing biomagnetite prepared in this study was tested for hydrogen fuel cell catalyst applications. Platinum/carbon black electrodes were fabricated, containing 10% biomagnetite with 0.2 mol% Ce in the catalyst. The addition of bioreduced Ce-magnetite improved the electrode durability when compared to a normal Pt/CB catalyst. Conclusion: Different concentrations of Ce can inhibit the bioreduction of Fe(III) minerals, resulting in the formation of different bioreduction products. Bioprocessing of Fe-minerals to form Ce-containing magnetite (potentially from waste sources) offers a sustainable route to the production of fuel cell catalysts with improved performance. [ABSTRACT FROM AUTHOR]

The removal of trivalent and divalent heavy metal ions from aqueous solutions by the ion-exchange process was investigated via a theoretical study using two- and three-parameter isotherm models. Fe3+ and Ni2+ ions were chosen as models of trivalent and divalent heavy metal ions in this study. A hybrid zeolite/carbon composite was used to remove these ions from aqueous solutions in a batch test to provide the required data for the theoretical study. This work studied the effect of shaking time (0–24 h), pH solution (2–10), and initial ions concentration (50–500 ppm). The experimental data of ion-exchange of both metal ions were studied using the two-parameter isotherm models including Langmuir isotherm, Freundlich isotherm, and Temkin isotherm. Also, the experimental data of ion-exchange were studied using the three-parameter isotherm models including Hill isotherm, Khan isotherm, Redlich–Peterson isotherm, Radke–Prausnitz isotherm, Sips isotherm, Toth isotherm, Koble–Corrigan isotherm and Liu isotherm. The experimental data of ion-exchange of Fe3+ ions best fitted the Temkin isotherm. Also, they followed the three-parameter isotherm models comparably due to the correlation factor for all studied models ranging from 0.923–0.924 despite the values of some model parameters were away from reality. But, Koble–Corrigan isotherm was not applicable for Fe3+ ion-exchange. While the experimental data of ion-exchange of Ni2+ ions best fitted the Langmuir isotherm with R² = 0.930. Also, they fitted the three-parameter isotherm models indistinguishably despite some model parameters diverted away from reality. For both metal ions, the determined values of exponent of the Toth isotherm confirmed the system heterogeneity. [ABSTRACT FROM AUTHOR]

The pollution by heavy metal ions is a severe risk for aquatic and earthy living creatures. Ionexchange is an easy way to eliminate heavy metal pollution. Different ion-exchangers have been developed and applied for wastewater and other environmental treatments, such as zeolites. The synthesis of zeolites from inexpensive sources is very important in the minerals industry. The recycling of the waste aluminum foil to obtain the alumina source for the preparation of NaY zeolite and NaX zeolite was investigated in this study. Both Faujasite-type zeolites were obtained by a conventional hydrothermal treatment of the gel at 100°C for 24 h. The prepared zeolites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis by X-ray (EDAX), and nitrogen adsorption/desorption isotherms. The synthesized NaY zeolite and NaX zeolite based on aluminum foil had a Si/Al ratio of 2.28 and 1.35, and a specific surface area of 476.248 and 610.256 m²/g, respectively. Also, the treatment of the individual, binary, and ternary metals solutions containing Cd(II), Cu(II) and Hg(II) ions was carried out using ion-exchange by NaY zeolite and NaX zeolite. The affinity of both zeolites to the selected metal ions was in the following order: Cd(II) > Cu(II) > Hg(II). The ion-exchange results highly adapted to the pseudo-second-order kinetic model with high correlation coefficients (R2 > 0.96). Furthermore, stabilization of the removed ions inside the spent zeolites was conducted by geopolymers prepared from ordinary Portland cement and fly ash as cement material. Fly ash showed high potential as a solidifying material for the samples examined in the leaching test by H2SO4 solution. The ratio of 1 cement:3 fly ash gave the least leached metals concentration at all testing conditions. [ABSTRACT FROM AUTHOR]

Perovskite and spinel oxides are promising alternatives to noble metal-based electrocatalysts for oxygen evolution reaction (OER). Herein, a novel perovskite/spinel nanocomposite comprised of SrCo 0.4 Fe 0.6 O 3 and CoFe 2 O 4 (SCF/CF) is prepared through a simple one-step method that incorporates iron doping into a SrCoO 3- δ matrix, circumventing complex fabrication processes typical of these materials. At a Fe dopant content of 60%, the CoFe 2 O 4 spinel phase is directly precipitated from the parent SrCo 0.4 Fe 0.6 O 3 perovskite phase and the number of active B-site metals (Co/Fe) in the parent SCF can be maximized. This nanocomposite exhibits a remarkable OER activity in alkaline media with a small overpotentional of 294 mV at 10 mA cm -2 . According to surface states analysis, the parent SCF perovskite remains in its pristine form under alkaline OER conditions, serving as a stable substrate, while the second spinel CF is covered by 5/8 monolayer (ML) O*, exhibiting considerable affinity toward the oxygen species involved in the OER. Analysis based on advanced OER microkinetic volcano model indicates that a 5/8 ML O* covered-CF is the origin for the remarkable activity of this nanocomposite. The results reported here significantly advance knowledge in OER and can boost application, scale-up and commercialisation of electrocatalytic technologies toward clean energy devices., (© 2023 The Authors. Small published by Wiley‐VCH GmbH.)