Re-evaluation of La0.6Sr0.4Co0.2Fe0.8O3-δ hollow fiber membranes for oxygen separation after long-term storage of five and ten years

Multiplying Oxygen Permeability of a Ruddlesden-Popper Oxide by Orientation Control via Magnets

Ruddlesden-Popper-type oxides exhibit remarkable chemical stability in comparison to perovskite oxides. However, they display lower oxygen permeability. We present an approach to overcome this trade-off by leveraging the anisotropic properties of Nd2 NiO4+δ . Its (a,b)-plane, having oxygen diffusion coefficient and surface exchange coefficient several orders of magnitude higher than its c-axis, can be aligned perpendicular to the gradient of oxygen partial pressure by a magnetic field (0.81 T). A stable and high oxygen flux of 1.40 mL min-1  cm-2 was achieved for at least 120 h at 1223 K by a textured asymmetric disk membrane with 1.0 mm thickness under the pure CO2 sweeping. Its excellent operational stability was also verified even at 1023 K in pure CO2 . These findings highlight the significant enhancement in oxygen permeation membrane performance achievable by adjusting the grain orientation. Consequently, Nd2 NiO4+δ emerges as a promising candidate for industrial applications in air separation, syngas production, and CO2 capture under harsh conditions.

Designing Oxide Catalysts for Oxygen Electrocatalysis: Insights from Mechanism to Application

The electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are fundamental processes in a range of energy conversion devices such as fuel cells and metal-air batteries. ORR and OER both have significant activation barriers, which severely limit the overall performance of energy conversion devices that utilize ORR/OER. Meanwhile, ORR is another very important electrochemical reaction involving oxygen that has been widely investigated. ORR occurs in aqueous solutions via two pathways: the direct 4-electron reduction or 2-electron reduction pathways from O2 to water (H2O) or from O2 to hydrogen peroxide (H2O2). Noble metal electrocatalysts are often used to catalyze OER and ORR, despite the fact that noble metal electrocatalysts have certain intrinsic limitations, such as low storage. Thus, it is urgent to develop more active and stable low-cost electrocatalysts, especially for severe environments (e.g., acidic media). Theoretically, an ideal oxygen electrocatalyst should provide adequate binding to oxygen species. Transition metals not belonging to the platinum group metal-based oxides are a low-cost substance that could give a d orbital for oxygen species binding. As a result, transition metal oxides are regarded as a substitute for typical precious metal oxygen electrocatalysts. However, the development of oxide catalysts for oxygen reduction and oxygen evolution reactions still faces significant challenges, e.g., catalytic activity, stability, cost, and reaction mechanism. We discuss the fundamental principles underlying the design of oxide catalysts, including the influence of crystal structure, and electronic structure on their performance. We also discuss the challenges associated with developing oxide catalysts and the potential strategies to overcome these challenges.

The novel strategy of designing perovskite fiber membrane as reactor for catalytic oxidation

Negative impacts of wastewater contamination include harm to the environment, people, plants, and animals. Metal-based heterogeneous catalysts, particularly transition metal oxide catalysts, are a therapeutic option. However, they have limited reusability and cause secondary contaminations through metal leaching. In this work, a new membrane catalyst made of perovskite-type fiber was created and tested to remove methylene blue from wastewater. These innovative 3D perovskite ceramic catalysts work well in the breakdown of pollutants and dramatically lessen possible secondary contaminations caused by metal leaching from catalysts.

Transition metal oxide-based membranes for oxygen separation

Tonnage oxygen production is still mostly based on the traditional technology of cryogenic distillation, a century-old, capital- and energy-intensive method. It is critical to create a novel low-cost, energy-efficient approach that can meet the growing demand for oxygen in industry from the clean environmental or energy standpoint. Ruddlesden-Popper (RP) perovskite like oxides -based ionic transport membranes for the oxygen transport have recently been developed as a possible replacement for the traditional cryogenic approach. In this work, we detailly reviewed the progress of RP perovskite oxides based membranes for oxygen transport from separation mechanism, material types, synthesis methods to the final separation performance. This work advances the development of RP perovskite membranes for oxygen transport.

High-Entropy Perovskites Pr1-xSrx(Cr,Mn,Fe,Co,Ni)O3-δ (x = 0-0.5): Synthesis and Oxygen Permeation Properties

High-entropy perovskite oxides have already been studied in various fields owing to their high-entropy-induced properties. Partial substitution of an element by a lower valence element usually improves the oxygen permeability of perovskite oxides, but high substitution amounts may lead to structural instability. In this work, pure high-entropy perovskites Pr1-xSrx(Cr,Mn,Fe,Co,Ni)O3-δ with high amounts Sr up to x = 0.5 were synthesized via a sol-gel method. Several characterization methods prove that the solubility of Sr increases with higher temperatures of the heating treatment. The ceramic with x= 0.5 shows a transition from semi-conductive to metallic behavior when the temperature reaches 873K. Its oxygen flux is comparable to the low-entropy counterpart La0.6Sr0.4Co0.5Fe0.5O3-δ. A stable run of ca. 46.2 h was documented for oxygen permeation under an air/CO2 gradient.

Investigation on the evolution of hydrothermal biochar

The objective of this study was to visualize trends and current research status of hydrothermal biochar research through a bibliometric analysis by using CiteSpace software. The original article data were collected from the Web of Science core database published between 2009 and 2020. A visual analysis network of national co-authored, institutional co-authored and author co-authored articles was created, countries, institutions and authors were classified accordingly. By visualizing the cited literature and journal co-citation networks, the main subject distribution and core journals were identified respectively. By visualizing journal co-citations, the main research content was identified. Further the cluster analysis revealed the key research directions of knowledge structure. Keyword co-occurrence analysis and key occurrence analysis demonstrate current research hotspots and new research frontiers. Through the above analysis, the cooperation and contributions of hydrothermal biochar research at different levels, from researchers to institutions to countries to macro levels, were explored, the disciplinary areas of knowledge and major knowledge sources of hydrothermal biochar were discovered, and the development lineage, current status, hotspots and trends of hydrothermal biochar were clarified. The results obtained from the study can provide a reference for scholars to gain a deeper understanding of hydrothermal biochar.

Rational design of mixed ionic-electronic conducting membranes for oxygen transport

The mixed ionic-electronic conducting (MIEC) oxides have generated significant research efforts in the scientific community during the last 40 years. Since then, many MIEC compounds, most of which are based on perovskite oxides, have been synthesized and characterized. These compounds, when heated to high temperatures, form solid ceramic membranes with high oxygen ionic and electrical conductivity. The driving force for oxygen ion transport is the ionic transfer of oxygen from the air as a result of the differential partial pressure of oxygen across the membrane. Electronic and ionic transport in a range of MIEC materials has been studied using the defect theory, particularly when dopants are introduced to the compound of interest. As a result, many types of ionic oxygen transport limits exist, each with a distinct phase shift depending on the temperature and partial pressure of oxygen in use. In combination with theoretical principles, this work attempts to evaluate the research community's major and meaningful achievements in this subject throughout the preceding four decades.

Heavy metals pollution characteristics and risk assessment in sediments and waters: The case of Tianjin, China

Potential health and ecological risks due to heavy metal pollution in surface waters and sediments were evaluated based on a health risk assessment model and a potential ecological risk index method. Combined with the reclamation progress of Tianjin Nangang Industrial Zone, in China, a survey was carried out in the area dealing with heavy metals concentrations in surface waters and sediments, covering from 2008 to 2018. Specifically, concentrations were determined for As, Cd, Hg, Cu, Pb, and Zn. The results show that As、Cd、Hg、Cu 、Pb、Zn average concentrations in surface water were 0.99 μg/L∼1.27 μg/L, 0.13 μg/L∼0.63 μg/L, 0.03 μg/L∼0.13 μg/L, 1.5 μg/L∼4.65 μg/L, 1.25 μg/L∼4.7 μg/L, 13.5 μg/L∼20.99 μg/L and which average concentrations in sediment were 5.12 mg/kg∼12.34 mg/kg, 0.12 mg/kg∼0.18 mg/kg, 0.04 mg/kg ∼0.087 mg/kg, 13.45 mg/kg∼31.92 mg/kg, 13.2 mg/kg ∼21.26 mg/kg, 21.58 mg/kg ∼77.21 mg/kg, respectively. The background values of the Hailuan River basin near the study area were taken as the reference and compared with the national sediment quality standards a tell us the quality of the sediments in Tianjin Nangang coastal area being good. As regards the characteristics of pollution, heavy metals showed a high concentration in 2008 and then decreased significantly, which related to the dredging of large amounts of contaminated surface sediment during port construction. According to the phase equilibrium partition coefficient (Kp) and temporal and spatial distribution characteristics of heavy metals, sediments can be seen as an obvious sink for lead, with this element being mainly affected by exogenous input in coastal seawater. Zn, As, Cd, and Hg contents in surface water were greatly affected by the endogenous release from sediments. The results of the environmental risk assessment showed that the main environmental health risk of Tianjin coastal waters was carcinogenic, and specifically due to As. The potential heavy metals ecological risk assessment results of surface sediments were mild for the affected areas.

Zirconium and Yttrium Co-Doped BaCo0.8Zr0.1Y0.1O3-δ: A New Mixed-Conducting Perovskite Oxide-Based Membrane for Efficient and Stable Oxygen Permeation

Oxygen permeation membranes (OPMs) are regarded as promising technology for pure oxygen production. Among various materials for OPMs, perovskite oxides with mixed electron and oxygen-ion (e^-/O^2-) conducting capability have attracted particular interest because of the high O^2- conductivity and structural/compositional flexibility. However, BaCoO_3-δ-based perovskites as one of the most investigated OPMs suffer from low oxygen permeation rate and inferior structural stability in CO₂-containing atmospheres. Herein, zirconium and yttrium co-doped BaCoO_3-δ (BaCo_1-2xZr_xY_xO_3-δ, x = 0, 0.05, 0.1 and 0.15) are designed and developed for efficient and stable OPMs by stabilizing the crystal structure of BaCoO_3-δ. With the increased Zr/Y co-doping content, the crystal structural stability of doped BaCoO_3-δ is much improved although the oxygen permeation flux is slightly reduced. After optimizing the co-doping amount, BaCo_0.8Zr_0.1Y_0.1O_3-δ displays both a high rate and superior durability for oxygen permeation due to the well-balanced grain size, oxygen-ion mobility, crystal structural stability, oxygen vacancy concentration and surface exchange/bulk diffusion capability. Consequently, the BaCo_0.8Zr_0.1Y_0.1O_3-δ membrane delivers a high oxygen permeation rate of 1.3 mL min^-1 cm^-2 and relatively stable operation at 800 ∘C for 100 h. This work presents a promising co-doping strategy to boost the performance of perovskite-based OPMs, which can promote the industrial application of OPM technology.

State-of-the-Art Organic- and Inorganic-Based Hollow Fiber Membranes in Liquid and Gas Applications: Looking Back and Beyond

The aggravation of environmental problems such as water scarcity and air pollution has called upon the need for a sustainable solution globally. Membrane technology, owing to its simplicity, sustainability, and cost-effectiveness, has emerged as one of the favorable technologies for water and air purification. Among all of the membrane configurations, hollow fiber membranes hold promise due to their outstanding packing density and ease of module assembly. Herein, this review systematically outlines the fundamentals of hollow fiber membranes, which comprise the structural analyses and phase inversion mechanism. Furthermore, illustrations of the latest advances in the fabrication of organic, inorganic, and composite hollow fiber membranes are presented. Key findings on the utilization of hollow fiber membranes in microfiltration (MF), nanofiltration (NF), reverse osmosis (RO), forward osmosis (FO), pervaporation, gas and vapor separation, membrane distillation, and membrane contactor are also reported. Moreover, the applications in nuclear waste treatment and biomedical fields such as hemodialysis and drug delivery are emphasized. Subsequently, the emerging R&D areas, precisely on green fabrication and modification techniques as well as sustainable materials for hollow fiber membranes, are highlighted. Last but not least, this review offers invigorating perspectives on the future directions for the design of next-generation hollow fiber membranes for various applications. As such, the comprehensive and critical insights gained in this review are anticipated to provide a new research doorway to stimulate the future development and optimization of hollow fiber membranes.

Open Tubular Column Immobilized with Covalent Organic Frameworks for Rapid Separation of Small Molecular Compounds by Capillary Electrochromatography

Preparation of a novel TpBD (synthesized from phloroglucinol and benzidine) covalent organic framework (COF) immobilized open-tubular (OT) capillary is described by in situ growth strategy. The stationary phase in the column was characterized by Fourier transform infrared (FTIR) spectra, X-ray diffraction (XRD), thermogravimetric analysis (TGA), nitrogen adsorption–desorption isotherms, scanning electron microscope (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectrum (EDS). Several families of compounds with different properties (alkylbenzenes, parabens, sulfonamides and benzoic acids) were selected to evaluate the performance of the TpBD COF immobilized capillary. The results showed that the stationary phase was uniform with about 6.0 μm thickness under the optimal preparation conditions, and the relative standard deviations (RSDs) were no more than 3.13% of alkylbenzenes on the TpBD COF immobilized capillary for 11 consecutive runs, which exhibited its excellent reproducibility and stability. A rapid baseline separation of each family of the analytes (neutral parabens, amphoteric sulfonamides and acidic benzoic acids) was obtained in less than 6 min with a resolution (Rs) of 2.79~9.30, which sufficiently verified the rapid separation, high resolution and wide application range of the TpBD COF immobilized capillary, and further revealed this strategy of fabricating COF to capillary column to show great promise in capillary electrochromatography.

Perovskite oxide for emerging photo(electro)catalysis in energy and environment

Using solar energy to catalyse photo-driven processes to address the energy crisis and environmental pollution plays a role in the path to a sustainable society. Many oxide-based materials, especially perovskite oxides, have been widely investigated as catalysts for photocatalysis in energy and environment because of the low-cost and earth-abundant and good performance. At this stage, there is a need to present a scientific-based evaluation of the technologies developed so far and identify the most sustainable technologies and the existing limitations and opportunities for their commercialisation. This work comprehensively investigated the outcomes using various scientometric indices on perovskite oxide-based photo(electro)catalysts for water splitting, nitrogen fixation, carbon dioxide conversion, organic pollutant degradation, current trends and advances in the field. According to the results achieved, efforts in both energy and environment based on perovskite oxides have been initiated in the 1990s and accelerated since the 2010s. China and the United States were identified as the most contributing countries. Based on the results achieved in this study, the main milestones and current trends in the development of this field have been identified. The aim of this research is to provide useful guidelines for the further investigation of perovskite oxide-based catalysts for photoelectrocatalysis and photocatalysis both in energy and environment on the applications such as water splitting, nitrogen fixation, carbon dioxide conversion, and wastewater treatment.

On Thermodynamic Aspects of Oxide Crystal Growth

Several metal oxide compounds, especially those containing metals possessing several valence states, are able to absorb or release oxygen under suitable thermodynamic conditions. Such behavior is found often in systems containing oxides of transition metals. It is important to note that the equilibrium oxidation level of those metal oxides can depend on the aggregation state, which may significantly impede crystal growth processes from the melt. If during the melt growth of such oxide crystals, the average valence state of the oxides is different in the molten and solid state, then crystallization is connected with the absorption of free oxygen from the ambient gas, or with the release of free oxygen into it. This phenomenon can be detected by simultaneous DTA/TG measurements and can deteriorate the stability of crystal growth. This holds especially if the average valence in the solid is smaller than in the melt, because oxygen release can lead to bubble formation at the crystallization front.

Perovskite oxides for oxygen transport: Chemistry and material horizons

Oxygen permeable membrane, which has the advantages of high separation selectivity, low energy consumption and simple process in oxygen separation, can be used in the fields of environment and energy, such as pure oxygen preparation, fuel cell, oxygen-enriched combustion and chemical reactor for methane catalytic conversion (e.g. partial oxidation of methane, carbon dioxide reforming with methane). New materials and technological development are needed to achieve this target for GHG reformation. In this direction, mixed ionic-electronic conducting (MIEC) oxides based on perovskite oxides are one of the prominent materials for oxygen transport at high temperatures. These compounds were created into solid ceramic membranes with considerable electronic and oxygen ionic conductivity. As a result of the differential partial pressure of oxygen across the membrane, this process enables the ionic transfer of oxygen from the air, providing the driving force for oxygen ion transport. Notably, over the last 40 years, the defect theory has been applied to a wide range of MIEC materials, providing insight into electronic and ionic transport, widely applied to designing catalysts for wastewater treatment and gas purification. However, a critical review by in-depth analysis from the material side on perovskite oxides for oxygen transport is needed. This work evaluates the research community's significant and relevant contributions in the perovskite oxides for gas separation domain over the previous four decades in conjunction with theoretical concepts, which would give rise to the fundamental understanding of the impact of various transitional metal elements on oxygen transport performance and stability in a different atmosphere.

Hydrogen Purification through a Highly Stable Dual-Phase Oxygen-Permeable Membrane

Using oxygen permeable membranes (OPMs) to upgrade low‐purity hydrogen is a promising concept for high‐purity H₂ production. At high temperatures, water dissociates into hydrogen and oxygen. The oxygen permeates through OPM and oxidizes hydrogen in a waste stream on the other side of the membrane. Pure hydrogen can be obtained on the water‐splitting side after condensation. However, the existing Co‐ and Fe‐based OPMs are chemically instable as a result of the over‐reduction of Co and Fe ions under reducing atmospheres. Herein, a dual‐phase membrane Ce_0.9Pr_0.1O_2−δ‐Pr_0.1Sr_0.9Mg_0.1Ti_0.9O_3−δ (CPO‐PSM‐Ti) with excellent chemical stability and mixed oxygen ionic‐electronic conductivity under reducing atmospheres was developed for H₂ purification. An acceptable H₂ production rate of 0.52 mL min⁻¹ cm⁻² is achieved at 940 °C. No obvious degradation during 180 h of operation indicates the robust stability of CPO‐PSM‐Ti membrane. The proven mixed conductivity and excellent stability of CPO‐PSM‐Ti give prospective advantages over existing OPMs for upgrading low‐purity hydrogen.

Insight into Steam Permeation through Perovskite Membrane via Transient Modeling

A dynamic model based on BaCe_0.9Y_0.1O_3−δ (BCY10) perovskite membrane for steam permeation process is presented here to essentially investigate the internal mechanism. The transient concentration distribution and flux of the charged species and the electric potential distribution within the membrane on the steam permeation process are analyzed in detail via simulation based on this model. The results indicate that the flux of steam can be improved via elevating operating temperatures, enlarging the difference of the partial steam pressure between two sides of the membrane, increasing the membrane density, and reducing the membrane thickness. Moreover, it was found that the polarization electric potential between both sides of the membrane occurs during the steam permeation process, especially at the steady state of the steam permeation process. The polarization electric potential reaches the maximum value at about 1050 K in this membrane. The evolution of electric potential can explain the influence of the above-mentioned factors on the steam permeation process. This study advances the mechanism of steam permeation through perovskite membrane, which provides a new strategy for the fundamental investigation of related species permeation (oxygen, carbon dioxide, hydrogen, etc.) on inorganic membranes via transient modeling.

Catalytic mixed conducting ceramic membrane reactors for methane conversion

Schematic of catalytic mixed conducting ceramic membrane reactors for various reactions: (a) O₂ permeable ceramic membrane reactor; (b) H₂ permeable ceramic membrane reactor; (c) CO₂ permeable ceramic membrane reactor.