Ferric Salts Research Articles

Comparison of Anion-Exchange Membranes for Diffusion Dialysis of Mixtures of Acids and Their Iron Salts.

This study presents the possibility of using diffusion dialysis for the separation of inorganic acids (hydrochloric, nitric, and hydrofluoric) and their ferric salts whose composition corresponds to that of real spent pickling solutions. At a steady state, the transport properties of three different anion-exchange membranes (Fumasep-FAD, Neosepta-AFN, and Neosepta-AHA) are compared using a continuous counter-current dialyzer. At a constant composition of the solutions (acid concentration 3 mol L-1 and iron concentration 30-40 g L-1), the effects of volumetric liquid flow rates on the transport rate of H+ and Fe3+ ions through the membrane are studied. The dialysis process is characterized by the recovery of acids and the rejection of salts. Furthermore, the values of the dialysis coefficients of acids, iron, and the acid/iron separation factors are calculated and compared. The volumetric flow rates of the inlet streams change in limits from 3 × 10-8 to 6 × 10-8 m3 s-1 (from 3 to 6 L h-1 m-2, relative to the membrane area). A comparison of the tested membranes shows slightly better results for acid recovery, iron rejection, and acid/iron separation factors for the Fumasep-FAD membrane than for the Neosepta-AFN membrane. However, the results obtained show that both of these anion-exchange membranes can be considered good separators for tested mixtures that simulate real spent pickling solutions, and there is a good precondition for using diffusion dialysis for processing these solutions in industrial practice. On the contrary, very low values of acid recovery and the overall dialysis coefficient of acid are found for the Neosepta-AHA membrane in the test range of the volumetric flow rate, and, thus, this membrane is insufficient for the adequate separation of these acids and iron salts.

Biological upcycling of nickel and sulfate as electrocatalyst from electroplating wastewater

Upcycling nickel (Ni) to useful catalyst is an appealing route to realize low-carbon treatment of electroplating wastewater and simultaneously recovering Ni resource, but has been restricted by the needs for costly membranes or consumption of large amount of chemicals in the existing upcycling processes. Herein, a biological upcycling route for synchronous recovery of Ni and sulfate as electrocatalysts, with certain amount of ferric salt (Fe3+) added to tune the product composition, is proposed. Efficient biosynthesis of bio-NiFeS nanoparticles from electroplating wastewater was achieved by harnessing the sulfate reduction and metal detoxification ability of Desulfovibrio vulgaris. The optimal bio-NiFeS, after further annealing at 300 °C, served as an efficient oxygen evolution electrocatalyst, achieving a current density of 10 mA·cm−1 at an overpotential of 247 mV and a Tafel slope of 60.2 mV·dec−1. It exhibited comparable electrocatalytic activity with the chemically-synthesized counterparts and outperformed the commercial RuO2. The feasibility of the biological upcycling approach for treating real Ni-containing electroplating wastewater was also demonstrated, achieving 99.5 % Ni2+removal and 41.0 % SO42− removal and enabling low-cost fabrication of electrocatalyst. Our work paves a new path for sustainable treatment of Ni-containing wastewater and may inspire technology innovations in recycling/ removal of various metal ions.

Coagulation/co-catalytic membrane integrated system for fouling-resistant and efficient water purification

Low-pressure catalytic membranes allow efficient rejection of particulates and simultaneously removing organics pollutant in water, but the accumulation of dissolved organic matters (DOM) on membrane surface, which cover the catalytic sites and cause membrane fouling, challenges their stable operation in practical wastewater treatment. Here we propose a ferric salt-based coagulation/co-catalytic membrane integrated system that can effectively mitigate the detrimental effects of DOM. Ferric salt (Fe3+) serving both as a DOM coagulant to lower the membrane fouling and as a co-catalyst with the membrane-embedded MoS2 nanosheets to drive perxymonosulfate (PMS) activation and pollutant degradation. The membrane functionalized with 2H-phased MoS2 nanosheets showed improved hydrophilicity and fouling resistance relative to the blank polysulfone membrane. Attributed to the DOM coagulation and co-catalytic generation of surface-bound radicals for decontamination at membrane surface, the catalytic membrane/PMS/ Fe3+ system showed much less membrane fouling and 2.6 times higher pollutant degradation rate in wastewater treatment than the catalytic membrane alone. Our work imply a great potential of coagulation/co-catalytic membrane integrated system for water purification application.

Comparative Analysis of Degradation of Pristine Nafion and Catalyst Coated Membrane Subjected to Ex-Situ Fenton's Test Approach

Polyfluorinated sulfonic –acid ionomer membranes (e.g Nafion) are extensively used today as the benchmark materials for the electrolyte membrane in PEM water electrolysis. It is broadly accepted that the state of the health of PFSA membranes are adversely impacted by the chemical degradation occured during operation of PEMWE. The crossover gases on the catalytic surface generate Hydrogen Peroxide which is homolytically or in the presence of ferrous salts produce reactive oxygen species like hydroperoxyl (HO.) and hydroxyl (HO.) radicals. These radicals attack the ionomer subsequently leading to chain scission, unzipping and loss of functional groups and release of HF in the effluent water.Other than Fe3+, several transition metal ions Cu2+, Ni2+, Ti3+, Cu+, can poison the membrane significantly. The fact that membrane degradation is accelerated owing to introduction of ferrous ions is fervently implemented in ex-situ degradation tests (known as Fentons tests) to evaluate the durability of membrane materials.This work depicts a systematic investigation of degradation of pristine Nafion and catalyst coated Nafion membrane using a Fentons accelerated aging experiment. The durability of Nafion 117 and catalyst coated Nafion membrane with various counter ions against H2O2 was explored as a degradation factor of polymer electrolyte water electrolyser. Two distinct variations of the experiments were compared : (1) Nafion and CCM were dipped in only hydrogen peroxide solution, (2) Nafion and CCM were exposed to a solution containing ferrous ions and peroxide. Accelerated aging experiments were conducted over 3-7 days. The difference in degradation phenomena with and without Fe ions were evaluated in terms of the fluoride ion release. For both cases, to quantify the effect of water activity in Nafion and CCM chemical structure on both water diffusion and interfacial transport, pulse field gradient spin echo nuclear magnetic resonance (PFGSE-NMR) technique has been employed. Furthermore the equivalent weight of the Nafion and CCM can vary in presence of aforementioned chemical stressors which can be accurately quantitatively studied by confocal Raman spectroscopy. Morphological characteristic before and after aging test was also investigated. Role of H2O2 and ferous ion in mechanical behaviour of Nafion and CCM were also analyzed. The same experiment was repeated for different transition metal ions. This work sheds light on decomposition mechanism of Nafion and CCM in more detail.

Effect of ferric salt addition on UV/electro-chlorine advanced oxidation process

ABSTRACT This study discussed the effect of ferric salt addition on UV/electro-chlorine advanced oxidation process using a train of electrolytic and UV flow cells with an ozone-free low-pressure mercury vapour lamp (total irradiance:0.60 W at 254 nm). Ferric salt addition enhanced 1,4-dioxane degradation at an electrolytic current of 0.100 A. By contrast, an inhibitory effect of ferric salt addition was observed at a current of 0.500 A. The enhanced accumulation of free chlorine at a current of 0.500 A directly decreased the 1,4-dioxane degradation rate by scavenging reactive radicals like HO˙ and Cl˙. However, at an electrolytic current of 0.100 A, UV irradiance was relatively excessive for electrochemical chlorine production. The excess UV energy enhanced the photoreduction of FeOH2+, followed by the Fenton-type reaction of Fe2+ and HOCl, which produced HO˙ and consumed free chlorine. As a result, the free chlorine concentration decreased, and the reaction efficiency between the reactive radicals and 1,4-dioxane improved. Thus, the addition of ferric salt to a UV/electro-chlorine system is recommended when the UV irradiance in the system is excessive compared to the electrochemical chlorine supply.

Characterization of magnetic FeCo particles with controlled bimetallic composition

In this study, six bimetallic FeCo particles were synthesized via the hydrothermal method, employing hydrazine hydrate as a reducing agent. These particles were synthesized at specific Fe:Co ratios of 1:0, 3:1, 1:1, 1:3, 1:9 and 0:1. The synthetic feeding of Fe:Co is of fundamental importance as it not only modulates the composition of the particles but also exerts control over their structural, morphological, and performance attributes. X-ray diffraction (XRD) analysis revealed that for particles synthesized from pure ferrous salt and pure cobalt salt, the former exhibited a Fe3O4 spinel structure, while the latter presented an hcp-type metallic Co structure. Conversely, for the remaining four Fe:Co synthetic feedings, the structure of FeCo bimetallic alloys exhibited a gradual transformation from an Fe-based bcc structure to a Co-based bcc structure, eventually culminating in a Co-based hcp structure as the Co content increased. Scanning electron microscopy (SEM) images indicated that particles prepared with a Fe:Co feeding ratio of 1:0 and 3:1 manifested as cube-shaped particles with approximate sizes of 200 nm and 100 nm, respectively. Particles synthesized with a 1:1 Fe:Co ratio exhibited pyramid-like shapes accompanied by small spinel structures. In contrast, those prepared with a 3:1 and 9:1 Fe:Co feeding ratio displayed a flower-like morphology with particle sizes around 10 µm, while particles synthesized using pure cobalt salts assumed a palm frond-like appearance. Moreover, the investigation into thermal stability established that FeCo alloy particles exhibited superior resistance to air oxidation when compared to pure Co particles. The magnetic studies indicated that all the particles were paramagnetic materials, with their magnetic properties being contingent on the composition. Notably, the particles synthesized with synthetic feedings of 1:1 and 3:1 exhibited the highest saturation magnetization of 151.80 emu·g−1 and the lowest saturation magnetization of 62.79 emu·g−1, respectively. These findings hold significant promise for the development of stable and finely-tailored magnetic particles with diverse potential applications in technology.

Empowering municipal wastewater treatment: Enhancing particulate organic carbon removal via chemical advanced primary treatment

The present study aimed to determine the physical and chemical parameters in the primary treatment process of municipal wastewater by flocculation processes using natural and synthetic polymers as chemically advanced primary treatment (CAPT). Flocculants like chitosan-based, starch-based, and polyacrylamide were chosen, and their feasibility for preliminary treated (PSTin) and pre-treated WASTEWATER (PSTout) underwent precise investigations applying the batch test setup. Since TSS concentration varies hourly in wastewater treatment plants (WWTP) and significantly affects the required dosage of the flocculants, various samples with TSS concentrations ranging from extremely low (<100 mg L−1) to incredibly high (> 700 mg L−1) were gathered to account for all TSS ranges. Several tests were then performed on the samples to establish the efficacy, optimum dosage, settleability, and filterability of the flocs generated by the polymers. The flocs' morphological characteristics were also analyzed by two-dimensional image analysis (2D-IA). The results showed that PSTin or PSTout can be purified solely with synthetic and environmentally confirmed natural-based polymers readily and efficiently. This concept introduces one-stage flocculation for the primary treatment of municipal wastewater rather than the conventional two stages of coagulation-flocculation, which has been used so far while applying harmful aluminum or ferric salts. The results also revealed that the CAPT system can be enhanced by coupling with a microstrain (MS) to remove nearly all particulate organic carbon in the form of COD or TSS. Exploring a range of biological treatment options in conjunction with the CAPT system revealed a significant reduction in external energy reliance for municipal WWTPs, transferring from roughly 75 % to complete independence. This evolution also enables the efficient production of valuable byproducts such as Hydrogen, Polyhydroxyalkanoates, and Ammonium chloride fertilizers, ultimately empowering municipal WWTPs from energy-dependent facilities into self-sustaining energy sources.

Green and sustainable synthesis of iron oxide nanoparticles for synergetic removal of melanoidin from ethanol distillery simulated model wastewater

This study investigates a novel approach for removal of melanoidin using Fenton oxidation process. Melanoidins are the biproducts of Maillard’s reaction involving polysaccharides and amino acids. Wastewater generated by ethanol distilleries utilize molasses, a common ingredient containing melanoidin, which is also toxic and imparts a dark color. Various wastewater treatments techniques are present, among which advanced oxidation processes (AOPs), particularly Fenton oxidation, have proven effective in eliminating melanoidins from wastewater. The novelty in this study is that green synthesized iron oxide nanoparticles (FeO NPs) are used in replacement of ferric salts to enhance the Fenton oxidation process for efficient melanoidin removal. The green synthesis provides stability to FeO NPs. FeO NPs were extensively characterized using techniques like FT-IR, XRD, SEM, and EDX analyses. The analyses confirmed that the FeO NPs exhibited a crystalline structure, with an average size of 21.5 nm. The crucial element of this study is to deploy the FeO NPs to power the Fenton oxidation reaction for melanoidin removal.

Validation of a simple spectrophotometric method for the rapid determination of salicylates in plasma

IntroductionThe determination of salicylate concentrations constitutes a critical aspect of medical diagnostics, particularly in emergency settings. High-performance liquid chromatography (HPLC) and spectrophotometry are efficient methods commonly utilized for this purpose. In emergency laboratories with limited resources, the validation of a cost-effective and reliable spectrophotometric method for salicylates in plasma becomes imperative. The present study aims to validate such a method, ensuring its applicability in toxicological emergencies within resource-constrained laboratories. Materials and methodsThe proposed spectrophotometric analysis relies on detecting salicylic ions amidst the presence of ferric salts, resulting in the formation of a distinct purple chelate complex. To ascertain the method's credibility, the validation guidelines established by the European Medicines Agency (EMA) were employed as a benchmark. A comprehensive validation process was conducted over a three-day period, with three levels of validation standards being considered. ResultsFollowing the EMA protocol, the spectrophotometric method demonstrated commendable fidelity, accuracy, and linearity over a concentration range of 50 to 500 mg/L. The limit of detection and quantification was found to be 10 and 50 mg/L, respectively, and the correlation coefficient was determined to be R2 = 0.998. However, it is essential to acknowledge that interference with phenothiazines occurred at concentrations ranging from 50 to 100 mg/L. Despite this, the method's average sensitivity remains viable for practical use in cases of poisoning. The accuracy per concentration level proved satisfactory, with relative biases remaining below 15%, and the confidence intervals of mean recovery closely approximating the desired target value of 100%. ConclusionIn conclusion, the presented spectrophotometric method stands out as an economical, straightforward, and user-friendly approach, ideally suited for toxicological emergencies when resources are limited. The method delivers satisfying results, establishing its practical utility in critical medical scenarios. This validated method holds immense promise for emergency laboratories facing resource constraints.

Process intensification of chemical phosphorus removal in a microreaction system

Serious problems including excessive ferric salt dose, high effluent phosphorus concentration and long handling time are encountered for chemical phosphorus removal by ferric salt in batch processes due to poor mixing performance. In this work, we develop a microreaction system to intensify phosphorus removal process using ferric chloride by achieving rapid mixing. Phosphorus residual is remarkably reduced by optimizing mixing-related factors, including flow rate, contacting mode, device structures and flow rate ratio which is justified by CFD simulation. The results show that phosphorus removal performance is not sensitive to flow rate ratio. Phosphorus residual can be lower than 0.20 mg/L at [P]0 = 6 mg/L, pH = 6.0, Fe/P = 1.8 and residence time = 42.8 s. Compared with batch processes, the microreaction system has several advantages including much lower phosphorus residual, lower ferric salt dose, shorter processing time and larger handling capacity. Moreover, a machine learning model is established to predict the device performance with high accuracy.

Ligands regulate the application of Fe(Ⅲ)-ligands on Se(Ⅳ) bioreduction: Electron transfer, metabolism activity and EPS secretion

Ligands influence the performance of Fe(Ⅲ) on pollutant biotreatment by affecting the properties of Fe(Ⅲ), but few studies focused on the effect and mechanism for Fe(Ⅲ)-ligands on Se(Ⅳ) bioreduction. Results showed that 5 mM Fe(Ⅲ)-ligands (ethylenediaminetetraacetic acid ferric sodium salt (Fe(Ⅲ)EDTA) and ferric citrate (Fe(Ⅲ)Cit)) could accelerate 4–5 times of Se(Ⅳ) bioreduction rate by accelerating electron transfer rate, improving metabolism activity and enhancing extracellular polymeric substances (EPS) secretion, while the performance of Fe(Ⅲ)Cit and Fe(Ⅲ)EDTA to accelerate Se(Ⅳ) bioreduction was influenced by ligands. Cyclic voltammetry (CV) results showed that the specific capacitance in BK + Fe(Ⅲ)EDTA was 64.43% higher than BK + Fe(Ⅲ)Cit. But, the adenosine triphosphate (ATP) in BK + Fe(Ⅲ)Cit was 67.29 ％ higher than BK + Fe(Ⅲ)EDTA. Meanwhile, electron transport system activity (ETSA), reduced coenzyme Ⅰ (NADH) and cytochrome c contents in BK + Fe(Ⅲ)Cit were also higher than those in BK + Fe(Ⅲ)EDTA. EPS analysis showed that Fe(Ⅲ)EDTA led to decreased aromatic protein content in EPS, while Fe(Ⅲ)Cit could enhance aromatic protein content in EPS. This study provided a new insight and valuable mechanism for Fe(Ⅲ)-ligands to regulate Se(Ⅳ) bioreduction.

Turbidity reduction efficacies of seed kernels of Mango (Mangifera indica) genotypes in Uganda

Alum and ferric salts as traditional chemical coagulants for turbidity removal in water and wastewater are expensive, and have known harmful effects. Thus, attempts to replace the chemical coagulants with safe and effective natural solutions are increasingly being made in terms of research studies to investigate the coagulation efficacies of various plants one of which is Mango (Mangifera indica). It is worth noting that M. indica has various genotypes of different origins across the world. In this study, eight (8) common M. indica genotypes in Uganda were identified, protein contents of their seed kernels determined, and coagulating efficacies investigated. Coagulation solution of each selected genotype was obtained by dissolving 5 g powder of the selected Mango seed kernel sample in 100 mL of distilled water. Next, 5 mL of this coagulant (or stock) solution was used to treat 200 mL of turbid water with turbidity ranging from 15 to 120 NTU. Using 0.01 M hydrochloric acid as an extraction solvent, protein contents of selected genotypes including Apple mango, Kate, Kent, Bire, Doodo red, Takataka, Kagoogwa, and Tommy Atkins were 38.02 %, 30.66 %, 15.94 %, 22.11 %, 21.50 %, 16.98 %, 16.36 %, and 17.87 %, respectively. Efficacies of coagulant from Apple mango, Kate, Kent, Bire, Doodo red, Takataka, Kagoogwa, and Tommy Atkins seed kernel samples were 92.2, 89.3, 66.0, 78.7, 76.9, 71.1, 68.9, and 73.1 %, respectively. Apple mango was the best performing genotype as a coagulant and this was followed by Kate. Coagulation efficacy was generally found to increase with increasing turbidity and/or coagulant's concentration. For instance, Apple Mango coagulant removed 16.7 %, 50.3 %, and 92.2 % of initial turbidity 15, 65 and 120 NTU, respectively. Kent removed 57.5, 66, and 69 % of initial turbidity 120 NTU using 5, 20, and 30 mL of stock solution, respectively. This study demonstrated the influence of the choice of a plant genotype on coagulation efficacy.

Acid-leaching mechanism of electroplating sludge: based on a comprehensive analysis of heavy-metal occurrence and the dynamic evolution of coexisting mineral phases.

Electroplating sludge is a typical heavy metal-containing hazardous waste with tens of millions of tons produced annually in China. Acid leaching is the most common method to extract valuable heavy metals for resource recycling and environmental protection. However, the coexisting elements, which are released from electroplating sludge to the leaching solution, will hinder the recycling of valuable heavy metals. In this work, dynamic acid-leaching experiments, X-ray diffraction analysis, and simulation calculations were conducted. It was found that coexisting elements (mainly Ca, Fe, and Al) account for a large proportion, and calcium salts as coexisting mineral phase (especially CaCO3) are ubiquitous in electroplating sludge. Moreover, the evolution of coexisting mineral phase plays an essential role in the acid-leaching process: (1) the dissolution of CaCO3 contributed a strong acid-neutralization capability and released Ca2+; (2) H2SO4 is the optimal extracting reagent, since it triggered the transformation of calcium salts to CaSO4·2H2O, reducing the Ca2+ concentration; (3) the coexisting elements Fe and Al would form ferrous and aluminum salt minerals with the acid-leaching process, which reduces the leaching of low-value elements. This work provides a new perspective on the acid-leaching mechanism of electroplating sludge, where the evolution of the mineral phase effect the release of valuable heavy metals and coexisting elements. This work also provides as comprehensive information as possible on electroplating sludge and inspires the improvement of the acid-leaching method.

Electrodeposited ultra-thin FeCo2O4 nanosheets on nickel foam as binder-free electrodes for high-performance supercapacitors

The cobalt-based spinel oxides MCo2O4(M = Ni, Mn, Cu, Fe, etc.) have garnered significant attention due to their potential applications in energy storage. In this study, ultra-thin FeCo2O4 nanosheets have been synthesized through a facile electrodeposition method and used as binder-free electrodes for high-performance supercapacitors. The results indicate that the FeCo2O4 nanosheet (FCS) electrode obtained through 5 min of electrodeposition using ferrous salt (FeSO4) as the precursor has a more abundant pore structure and exhibits the best electrochemical performance. The specific capacitance of the FeCo2O4 nanosheets electrode reaches 679 F g−1 at a current density of 1 A g−1, and it retains 92.9 % of its initial capacitance after undergoing 5000 cycles. In addition, the assembled FeCo2O4 nanosheet (FCS)//activated carbon (AC) asymmetric supercapacitor shows a high energy density of 62.5 Wh kg−1 at 750 W kg−1 and with a capacitance retention of 91.3 % after 5000 cycles. Furthermore, the electrodeposition method utilized in the synthesis of the FeCo2O4 nanosheets is cost-effective, environmentally friendly, and can be employed to fabricate other MCo2O4 materials with superior electrochemical properties.

Integrating the Fe2+/H2O2-strengite method in airlift reactor for phosphorus removal and recovery from organic phosphorus wastewater

Organic phosphorus (OP) pollution control and phosphorus resource recycling are essential for promoting ecological health and sustainable development. The development of an efficient strategy to remove and recover phosphorus from OP contaminations has garnered significant interest. In this study, we propose the integration of the Fe2+/H2O2-Strengite method in an airlift reactor (ALR) to enhance recovery product particle sizes and accelerate the settling process while achieving excellent phosphorus removal efficiency. In ALR, phosphorus is removed and recovered through the reaction with ferric salts, adsorption of hydrous ferric oxide, and flocculation of ferric salts. The unique liquid circulation within the ALR ensures a regular cyclic motion of product particles along the draft tube, promoting the agglomeration of microparticle into larger ones and reducing suspended microparticles. This internal circulation, combined with the presence of quartz as carriers, contributes to the production of recovery products with uniform particle sizes and enables a faster settling process. The resulting phosphorus recovery products consist of amorphous strengite analogue and goethite (FeOOH) mixed with phosphorus. Upon calcination, these products undergo transformation into crystalline FePO4 and Fe3PO7, thus facilitating phosphorus resource recycling. Notably, this high-performance phosphorus removal and recovery strategy for OP pollution yields valuable recovery products without causing secondary pollution, contribution to sustainable phosphorus resource management. This work offers valuable insights into addressing potentially competing challenges of resource depletion and environmental quality.

Unveiling the formation mechanism of polydisperse iron oxide nanoparticles in coprecipitation route

Coprecipitation is the simplest, fastest, and most inexpensive method for preparing metal oxide nanoparticles (NPs). It is considered one of the most convenient methods for simultaneously precipitating two or more aqueous metal salt precursors (such as chlorides, nitrates, oxychloride, etc.) into NPs in a basic solvent, yielding uniform composition. However, the main drawback of this route is the production of NPs with a broad size distribution (polydispersed particle formation), which limits their use in various applications. The present work addresses the experiments and formation mechanism of polydispersed iron oxide magnetite (Fe3O4) NPs using this route. Experiments involving the drop-wise addition of mixed ferric (Fe3+) and ferrous (Fe2+) chloride salt solutions to NaOH base solution at room temperature resulted in a polydispersed Fe3O4 NP system containing both large and small particles at the end of 30 min of the reaction. A mechanism is proposed to explain the formation of these polydispersed Fe3O4 NPs based on the time scales of different individual particle formation events and the experimental aging time. The mechanism elucidates that the time scales of events such as Fe3O4 nucleation, diffusional-limited and Ostwald ripening growth of small and large particles, and the coagulation of two small particles or a small particle with a large particle are smaller, and completed within the experimentally allowed aging time. Conversely, the coagulation time for two large particles exceeds the experimental time, preventing complete coagulation. As a result, incomplete coagulation of large particles and the completion of all other events lead to the formation of a polydispersed Fe3O4 NP system at the end of the synthesis. The combined experiments and time scale-based mechanism explain the polydispersed NP formation in the coprecipitation route, and the insights gained from this understanding can be beneficial for optimizing synthesis conditions to achieve a controlled size distribution of Fe3O4 and other NP systems.

Substrate-dependent strategies to mitigate sulfate inhibition on microbial reductive dechlorination of polychlorinated biphenyls

Sulfate widely co-exists with polychlorinated biphenyls (PCBs) at various concentrations in the subsurface environment. Previous studies have suggested that sulfate often hampers microbial degradation of aliphatic chlorinated solvents such as chloroethenes. However, the impact of sulfate on microbial reductive dechlorination of aromatic PCBs and the underlying mechanisms have received limited attention. Likewise, strategies to mitigate such inhibition remain scarce. Here we found that the mechanisms and mitigation strategies of sulfate inhibition on PCB dechlorination were substrate-dependent. Under electron donor-limiting conditions, even a low concentration of sulfate (2 mM) resulted in a decreased PCB dechlorination rate by 88.7% in a co-culture comprising Dehalococcoides mccartyi CG1 and the sulfate-reducing bacterium Desulfovibrio desulfuricans F1, an inhibition which was attributed to the competition for electron donor between sulfate reduction and PCB dechlorination. As expected, re-amendment of 5 mM lactate effectively re-initiated PCB dechlorination. However, in the presence of a higher concentration of sulfate (5 mM), the PCB dechlorination rate in the co-culture was 77.7% lower than in the control, even with excessive electron donor supply. This inhibition was linked to high concentration of sulfide (∼5 mM) produced from sulfate reduction, as suggested by high availability of electron donor, recovery of dechlorination activity after removal of sulfide, and negligible influence of sulfate on PCB dechlorination in the axenic culture of D. mccartyi CG1. Indeed, sulfide (>5 mM) was found to directly suppress expression of PCB-dechlorinating reductive dehalogenase gene. The highest transcriptional level of pcbA1 was 2.9 ± 0.3 transcripts·cell−1 in the presence of ∼5 mM sulfide, which was increased to 37.4 ± 5.0 transcripts·cell−1 when sulfide was removed. Under this scenario, introduction of ferrous salts (5 mM) efficiently alleviated sulfide inhibition on PCB dechlorination. Interestingly, the augmentation of methanogens in the co-culture was also effective in mitigating sulfide inhibition on PCB dechlorination, offering a new approach to protect Dehalococcoides under sulfide stress. Collectively, these findings deepen our understanding of the influence of sulfate on microbial reductive dechlorination of PCBs and contribute to developing appropriate strategies based on geochemical conditions to alleviate sulfate inhibition during bioremediation of PCB-contaminated sites.

Sustainable catalytic graphitization of biomass to graphitic porous carbon by constructing permeation network with organic ligands

Common strategies for catalytic graphitization of biochar into graphitic porous carbon (GPC) still face great challenges, such as the realization of simple procedures, energy conservation, and green processes. Controlling over the graphitization degree and pore structure of biochar is the key to its structural diversification. Herein, a clean and energy-efficient method is developed to synthesize adjustable graphitic degree and structure porosity GPC from rice husk-based carbon (RHC) at a relatively low temperature of 800–1000 °C with environment-benign organometallic catalyst ethylenediaminetetraacetic acid ferric sodium salt (EDTA-iron) and the recovery ratio of catalyst is as high as 97%. The formed by the organic ligands of EDTA-iron facilitates the etching of RHC surface and pore by iron, resulting in highly graphitized and developed porous GPCs. The pore structure and graphitization degree of GPCs can be adjusted by altering the catalyst loading, temperature, and holding time. The catalyst EDTA-iron with a lower concentration mainly plays the role of etching, which promotes the formation of porous carbon with larger surface area (SBET = 1187.2 m2·g−1). The catalyst with higher concentration mainly plays the role of catalyzing graphitization and promotes the obtaining of graphitic carbon with high graphitization degree (ID/IG = 0.19). The mechanism of EDTA-iron catalyzed graphitization of RHC is explored by the comprehensive analysis of BET, XRD, Raman, TEM and TGA. This research not only provides an efficient method for the preparation of high-quality biomass-based graphite carbon, but also provides a feasible method for the preparation of biomass-based porous carbon.

Super-enrichment of ultra-low concentration rhenium via synergistic co-flocculation precipitation using CTAB and ferric salt hydrolysis micelles

Super-enrichment and recovery of associated Rhenium (Re) in sandstone-type uranium deposits is challenging due to its sparse distribution and ultra-low contents in raw ores. Conventional industrial processes are extremely difficult to achieve economic recovery of Re with a concentration below 0.1 mg/L from in-situ leaching solutions of sandstone-type uranium deposits. This study proposes a novel approach for achieving super-enrichment ultra-low concentration of Re using a synergistic co-flocculation precipitation system composed of cetyltrimethylammonium-bromide (CTAB) and ferric salt (FeCl3) hydrolysis micelles. Experimental results reveal that the enriched content of Re in the co-flocculation precipitates is as high as 503 g/t, nearly 3353 times higher than that in the in-situ leaching solutions. The synergistic precipitation percentage of Re can reach more than 60%, which is larger than the sum of using CTAB micellar flocculation (30.16%) and FeCl3 hydrolysis micellar flocculation (5.43%) separately. Furthermore, the synergistic co-flocculation and precipitation mechanism of Re is examined by SEM, turbidity, Fourier transform infrared spectroscopy, Zeta potential analysis, and DTF calculations. Results demonstrate that the ReO4- anions first form ion associations with CTA+ cations through electrostatic force, which are subsequently captured to forms insoluble co-flocculating precipitate via weak intermolecular hydrogen bond force between Fe(OH)3 and ReO4-, which promotes the super-enrichment of the ultra-low concentration Re. In summary, this process presents great potential for the efficient recovery Re from a large amounts of sandstone-type uranium deposits leaching solution, and provides new insights into the enhancement mechanism of synergistic co-flocculation precipitation.

Fe-Based Nanomaterials and Plant Growth Promoting Rhizobacteria Synergistically Degrade Polychlorinated Biphenyls by Producing Extracellular Reactive Oxygen Species.

Plant growth promoting rhizobacteria (PGPR) produce extracellular reactive oxygen species (ROS) to protect plants from external stresses. Fe-based nanomaterials can potentially interact with PGPR and synergistically degrade organic pollutants, yet they have received no study. Here, we studied how the interaction between a typical PGPR (Pseudomonas chlororaphis, JD37) and Fe-based nanomaterials facilitated the degradation of 2,4,4'-trichlorobiphenyl (PCB28), by comparing the zerovalent iron of 20 nm (nZVI20), 100 nm (nZVI100), and 5 μm; iron oxide nanomaterials (α-Fe2O3, γ-Fe2O3, and Fe3O4) of ca. 20 nm; and ferrous and ferric salts. Although all Fe materials (0.1 g L-1) alone could not degrade aqueous PCB28 (0.1 mg L-1) under dark or aerobic conditions, nZVI20, nZVI100, α-Fe2O3, and Fe2+ promoted PCB28 degradation by JD37, with the half-life of PCB28 shortened from 16.5 h by JD37 alone to 8.1 h with nZVI100 cotreatment. Mechanistically, the nanomaterials stimulated JD37 to secrete phenazine-1-carboxylic acid and accelerated the NADH/NAD+ conversion, promoting O2*- generation; JD37 increased Fe(II) dissolution from the nanomaterials, facilitating *OH generation; and the ROS gradually degraded PCB28 into benzoic acid through dihydroxy substitution, oxidation to quinone, and Michael addition. These findings provide a new strategy of nanoenabled biodegradation of organic pollutants by applying Fe-based nanomaterials and PGPR.