GO–Polymer Modified Anion Exchange Membranes for Antifouling

Organic fouling was one of key issues limiting the application of electrodialysis in the treatment of industrial wastewater, which results in degradation of membranes and high energy consumption. In this study, a novel graphene oxide (GO)–polymer modified anion exchange membrane (AEM) for antiorganic fouling was first developed by layer-by-layer interfacial polymerization (IP). The surface of AEM was alternately contacted with GO and tannic acid (TA) aqueous as the water phase and an n-hexane solution of trimesoyl chloride (TMC) as the organic phase; thus, a multilayer GO–polymer structure was fabricated on the surface of AEM. Results showed that the aqueous phase was preferred to be the final treatment of layer-by-layer interfacial polymerization, which was more conducive to enhancing hydrophilicity and negative charge density of the membrane surface. Compared with TA-TMC modified AEM, the introduction of GO nanosheets with carboxyl groups into aqueous solution significantly increased the negative charge density of the membrane surface and reduced membrane resistance. The desalination rate of (GOTA-TMC)1.5 was mostly close to that of pristine AEM without fouling, exhibiting significant antifouling performance and good stability. The study provides promising insights into the modification of ion exchange membranes with functional materials and a polymer composite layer

High-Performance Recovery of Vanadium(V) in Leaching/Aqueous Solution by a Reusable Reagent-Primary Amine N1519

Efficient extraction and stripping for recovering vanadium­(V) from the leaching/aqueous solution of chromium-bearing vanadium slag (V–Cr slag) are essential to the reuse of heavy metals. The performance characteristics of a new reagent, primary amine N1519, were first reported for extracting vanadium. With a phase ratio of organic to aqueous up to 1:1, 99.7% of vanadium­(V) can be effectively extracted from the leaching/aqueous solution, and powder of NH₄VO₃ was obtained through the stripping with ammonia. The new reagent can be recyclable in use for sustainable reuse after stripping. Different extraction conditions, e.g., the initial pH of the leaching/aqueous solution and the molar quantity of N1519 were investigated. The powder of vanadium-organic compounds (VOC) with N1519 formed in the process of extraction was obtained and purified through three-steps of solvent-out crystallizations. The hydrogen bond association mechanism of extraction was illustrated with the structure of VOC and the enthalpy change in extraction process. The fast extraction process and slow stripping procedure for recovering vanadium­(V) are suitable for use in annular centrifugal contactors with very short contact/resident times and mixed-settler extractors with very good mass transfer, respectively. The results offer significant advantages over conventional processes

Optimal Design of Solvent Blend and Its Application in Coking Wastewater Treatment Process

One of the key steps of coking wastewater treatment is phenolic and tar removal via extraction. However, the high loss of the extractant, i.e., methyl isobutyl ketone (MIBK), leads to the high cost of the process. The adoption of a novel solvent or solvent blend is considered as an efficient way to address this problem. In this paper, seven solvents (benzene, toluene, m-xylene, ethylbenzene, 1, 3, 5-trimethylbenze, cyclohexane, and octanol), selected as candidate diluters for MIBK according to operating requirements, are studied with a nonlinear programming (NLP) model based on ideal counter-current extraction. The results, verified with experiments, suggest toluene is the most promising candidate. Further investigation of this solvent blend reveals that both <i>D</i>_blend (the distribution coefficient of phenol between solvent blend and water) and <i>m</i>_MIBK (the MIBK concentration in raffinate) increase with <i>x</i>_MIBK (the molar fraction of MIBK in blend). The trade-off between the extraction performance and MIBK loss recommends the blend with <i>x</i>_MIBK = 0.05 as extractant for coking wastewater treatment. An industrial process consisting of extraction, back stripping, distillation, and mixer is presented. A corresponding NLP model is established for its operating optimization. To improve the accuracy, the representatives of typical phenolics and tar in wastewater (2,4 dimethyl phenol, m-xylene, and quinolone) are also considered in addition to phenol. The case study indicates that the blend exhibits economic advantage over pure MIBK with a makeup cost of 11.15 ¥/t, much less than the 185.15 ¥/t in the case of MIBK

Fast Electron Transfer and ^•OH Formation: Key Features for High Activity in Visible-Light-Driven Ozonation with C₃N₄ Catalysts

Photocatalytic ozonation of wastewater pollutants by sunlight is a highly attractive technology close to real application. Understanding this process on the atomic scale and under realistic working conditions is challenging but vital for the rational design of catalysts and photocatalytic decontamination systems. Here we study two highly active C₃N₄ photocatalysts (bulk C₃N₄ and a nanosheet-structured C₃N₄) under simultaneous visible-light irradiation and O₃ bubbling in water by in situ EPR spectroscopy coupled with an online spin-trapping technique. The photoexcitation of electrons to the conduction band (CB-e^–), their further trapping by dissolved O₂ and O₃, and the evolution of reactive oxygen species (ROS) have been semiquantitatively visualized. A dual role of O₃ in boosting the CB-e^– to ^•OH conversion is confirmed: (i) an inlet 2.1 mol % O₃/O₂ gas mixture can trap about 2–3 times more CB-e^– upon aqueous C₃N₄ suspension than pure O₂ and further produce ^•OH by a robust ^•O₃^–-mediated one-electron-reduction pathway (O₃ → ^•O₃^– → HO₃^• → ^•OH); (ii) O₃ can readily take CB-e^– back from ^•O₂^– to form ^•O₃^–, thus blocking the inefficient H₂O₂-mediated three-electron-reduction route (O₂ → ^•O₂^– → HO₂^• → H₂O₂ → ^•OH) but further strengthening the ^•O₃^–-mediated pathway. In the presence of 2.1 mol % O₃/O₂, the ^•OH yield increases by 17 and 5 times, and consequently, the mineralization rate constant of oxalic acid increases by 84 and 41 times over bulk C₃N₄ and NS C₃N₄, respectively. This work presents an attractive opportunity to boost the yield of ROS species (^•OH) for water purification by visible-light-driven photocatalysis and provides a powerful tool to monitor complex photocatalytic reactions under practical conditions

Efficient Catalytic Ozonation over Reduced Graphene Oxide for <i>p</i>‑Hydroxylbenzoic Acid (PHBA) Destruction: Active Site and Mechanism

Nanocarbons have been demonstrated as promising environmentally benign catalysts for advanced oxidation processes (AOPs) upgrading metal-based materials. In this study, reduced graphene oxide (rGO) with a low level of structural defects was synthesized via a scalable method for catalytic ozonation of <i>p</i>-hydroxylbenzoic acid (PHBA). Metal-free rGO materials were found to exhibit a superior activity in activating ozone for catalytic oxidation of organic phenolics. The electron-rich carbonyl groups were identified as the active sites for the catalytic reaction. Electron spin resonance (ESR) and radical competition tests revealed that superoxide radical (^•O₂^–) and singlet oxygen (¹O₂) were the reactive oxygen species (ROS) for PHBA degradation. The intermediates and the degradation pathways were illustrated from mass spectroscopy. It was interesting to observe that addition of NaCl could enhance both ozonation and catalytic ozonation efficiencies and make ·O₂^– as the dominant ROS. Stability of the catalysts was also evaluated by the successive tests. Loss of specific surface area and changes in the surface chemistry were suggested to be responsible for catalyst deactivation

Determination of the Heavy Metal Levels in <i>Panax notoginseng</i> and the Implications for Human Health Risk Assessment

<div><p>ABSTRACT</p><p>High levels of heavy metals in <i>Panax notoginseng</i> (Sanchi), a valued traditional Chinese medicine, have drawn increasing concern regarding the safe usage of Sanchi preparations. Here, we measured the concentrations of six heavy metals in Sanchi samples from 20 major plantations, investigated the pharmaceutical processes and usages of Sanchi preparations, and assessed the associated potential health risks to consumers. The average concentrations of chromium (Cr), copper (Cu), nickel (Ni), zinc (Zn), lead (Pb), and arsenic (As) in the Sanchi samples were 2.7, 3.7, 6.2, 22.1, 2.0, and 1.4 mg/kg, respectively. The hazard quotients (HQs) for these six single metals and the hazard index (HI) of these metals’ combination were all far less than 1, indicating the absence of a non-carcinogenic health hazard to consumers. The carcinogenic risk of As was 2.1 × 10⁻⁶, which is higher than the allowable level suggested by the U.S. Environmental Protection Agency but less than the level suggested by the World Health Organization (WHO). The probabilities of consumers’ exposure due to daily medicine consumption exceeding the allowable daily intakes from medicine (ADIs_drug, 1% of the ADI) suggested by the WHO were 0.0%, 0.1%, 0.1%, 0.0%, 1.6%, and 27.3% for Cr, Ni, Cu, Zn, Pb, and As, respectively.</p></div

Sustainable Preparation of LiNi_1/3Co_1/3Mn_1/3O₂–V₂O₅ Cathode Materials by Recycling Waste Materials of Spent Lithium-Ion Battery and Vanadium-Bearing Slag

Waste streams containing heavy metals are always of concern from both environmental and resource-depleting points of view. The challenges are in most cases related to the effectiveness for high-value-added materials recovery from such waste, with which the environmental impacts during recycling shall be low. In this research, two typical heavy-metal-containing waste streams, i.e., spent lithium-ion batteries and vanadium-bearing slag, were simultaneously treated, and this enables regeneration of the LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials which was considered difficult because of the dislocation of nickel and lithium ions during electrochemical performance. By using the intermediate product during vanadium-bearing slag treatment, the vanadium-embedded cathode material can be prepared which delivers excellent electrochemical performances with a specific capacity of 156.3 mA h g^–1 after 100 cycles at 0.1C with the capacity retention of 90.6%; even the additive amount is only 5%. A thin layer of vanadium oxide is found to be effective to promote electrochemical performance of the cathode material. Using the principles of green chemistry, this process enables high-performance cathode material regeneration without introducing extraction chemicals and with much lower environmental impacts as compared to traditional metallurgical technologies

Macropore- and Micropore-Dominated Carbon Derived from Poly(vinyl alcohol) and Polyvinylpyrrolidone for Supercapacitor and Capacitive Deionization

We developed a kind of macropore- and micropore-dominated carbon (HPAC) derived from poly­(vinyl alcohol) and polyvinylpyrrolidone for electric double-layer capacitive (EDLC) applications, e.g., supercapacitors and capacitive deionization (CDI). By comparing the EDLC performance of HPAC with those of ordered mesoporous carbon (OMC) and commercial activated carbon (AC), we evaluated the pore size effects. Cyclic voltammetry (CV) was employed for static and flowing CDI processes to identify the disparities between supercapacitors and CDI. HPAC exhibits a specific capacitance of 309 F g^–1 at a specific current of 0.5 A g^–1 (6 M KOH) in a three-electrode half-cell and has a salt removal capacity of 16.3 mg g^–1 (1.2 V, 500 mg L^–1 NaCl), which is better than those of AC and OMC. Cycling tests of HPAC in supercapacitors and CDI show excellent stability. The properties of HPAC, fine, hydrophilic, macroporous, and microporous, endow HPAC with the promising possibility of use in supercapacitors and capacitive deionization. The disparities of supercapacitors and CDI include ionic species and concentrations and solution hydromechanics. CV analysis of static and flowing CDI equipped with HPAC electrodes suggests that increasing the salt concentration in CDI is beneficial for the carbon electrode to show high capacitance and to reduce the pumping energy during the CDI process

Lithium Carbonate Recovery from Cathode Scrap of Spent Lithium-Ion Battery: A Closed-Loop Process

A closed-loop process to recover lithium carbonate from cathode scrap of lithium-ion battery (LIB) is developed. Lithium could be selectively leached into solution using formic acid while aluminum remained as the metallic form, and most of the other metals from the cathode scrap could be precipitated out. This phenomenon clearly demonstrates that formic acid can be used for lithium recovery from cathode scrap, as both leaching and separation reagent. By investigating the effects of different parameters including temperature, formic acid concentration, H₂O₂ amount, and solid to liquid ratio, the leaching rate of Li can reach 99.93% with minor Al loss into the solution. Subsequently, the leaching kinetics was evaluated and the controlling step as well as the apparent activation energy could be determined. After further separation of the remaining Ni, Co, and Mn from the leachate, Li₂CO₃ with the purity of 99.90% could be obtained. The final solution after lithium carbonate extraction can be further processed for sodium formate preparation, and Ni, Co, and Mn precipitates are ready for precursor preparation for cathode materials. As a result, the global recovery rates of Al, Li, Ni, Co, and Mn in this process were found to be 95.46%, 98.22%, 99.96%, 99.96%, and 99.95% respectively, achieving effective resources recycling from cathode scrap of spent LIB

A Closed-Loop Process for Selective Metal Recovery from Spent Lithium Iron Phosphate Batteries through Mechanochemical Activation

With the increasing consumption of lithium ion batteries (LIBs) in electric and electronic products, the recycling of spent LIBs has drawn significant attention due to their high potential of environmental impacts and waste of valuable resources. Among different types of spent LIBs, the difficulties for recycling spent LiFePO₄ batteries rest on their relatively low extraction efficiency and recycling selectivity in which secondary waste is frequently generated. In this research, mechanochemical activation was developed to selectively recycle Fe and Li from cathode scrap of spent LiFePO₄ batteries. By mechanochemical activation pretreatment and the diluted H₃PO₄ leaching solution, the leaching efficiency of Fe and Li can be significantly improved to be 97.67% and 94.29%, respectively. To understand the Fe and Li extraction process and the mechanochemical activation mechanisms, the effects of various parameters during Fe and Li recovery were comprehensively investigated, including activation time, cathode powder to additive mass ratio, acid concentration, the liquid-to-solid ratio, and leaching time. Subsequently, the metal ions after leaching can be recovered by selective precipitation. In the whole process, about 93.05% Fe and 82.55% Li could be recovered as FePO₄·2H₂O and Li₃PO₄, achieving selective recycling of metals for efficient use of resources from spent lithium ion batteries