Search

N-doped reduced graphene oxide quantum dots (N-rGQDs) have attracted more and more attention in efficient catalytic degradation of aqueous organic pollutants. However, the synthesis of N-rGQDs is generally a complex and high energy required process for the reduction and N-doping steps. In this study, a facile and green fabrication approach of N-rGQDs is established, based on a metal-free Fenton reaction without additional energy-input. The N structures of N-rGQDs play a significant role in the promotion of their catalytic performance. The N-rGQDs with relatively high percentage of aromatic nitrogen (NAr-rGQDs) perform excellent catalytic activities, with which the degradation efficiency of pollutant is enhanced by 25 times. Density functional theory (DFT) calculation also indicates aromatic nitrogen structures with electron-rich sites are prone to transfer electron, presenting a key role in the catalytic reaction. This metal-free Fenton process provides a green and cost-effective strategy for one-step fabrication of N-rGQDs with controllable features and potential environmental catalytic applications.

Spent lithium-ion battery recycling has attracted significant attention because of its importance in regard to the environment and resource importance. Traditional hydrometallurgical methods usually leach all valuable metals and subsequently extract target meals to prepare corresponding materials. However, Li recovery in these processes requires lengthy operational procedures, and the recovery efficiency is low. In this research, we demonstrate a method to selectively recover lithium before the leaching of other elements by introducing a hydrothermal treatment. Approximately 90% of Li is leached from high-Ni layered oxide cathode powders, while consuming a nearly stoichiometric amount of hydrogen ions. With this selective recovery of Li, the transition metals remain as solid residue hydroxides or oxides. Furthermore, the extraction of Li is found to be highly dependent on the content of transition metals in the cathode materials. A high leaching selectivity of Li (> 98%) and nearly 95% leaching efficiency of Li can be reached with LiNi0.8Co0.1Mn0.1O2. In this case, both the energy and material consumption during the proposed Li recovery is significantly decreased compared to traditional methods; furthermore, the proposed method makes full use of H+ to leach Li+. This research is expected to provide new understanding for selectively recovering metal from secondary resources.

In membrane distillation (MD), complicated feed water with amphiphilic contaminants induces fouling/wetting of the MD membrane and can even lead to process failure. This study reports a facile approach to fabricate robust and self-healing hybrid amphiphobic membranes for anti-surfactant-wetting MD based on the ultra-low surface energy of fluorinated polyhedral oligomeric silsesquioxanes (F-POSS) and its thermal induced motivation and rotation. The thermal treatment makes the membranes achieving amphiphobicity at a very low cost of F-POSS (13.04 wt.%), which is about 1/3 of without thermal treatment. The prepared membrane exhibits excellent amphiphobicity, i.e. ethanol contact angle of 120.3°, without using environmentally toxic fluorinated nanoparticles. Robust MD performance was observed for the amphiphobic membrane in concentrated sodium dodecyl sulfate (SDS) feed solutions. Furthermore, the fabricated membrane exhibited stable amphiphobicity even in extreme environments, including strong acid or alkaline solutions. In the event of a damaged or abraded membrane surface where the F-POSS can be removed, the amphiphobic membrane exhibits self-healing ability with additional thermal treatment. This simple approach without the use of nanoparticles provides an environmentally friendly way for fabrication of amphiphobic membranes for anti-surfactant-wetting membrane distillation.

Cadmium-containing wastewater draws worldwide attention due to its toxicity. In this work, a high-efficiency and eco-friendly MnO2-coated amorphous carbon (AG@MnO2) adsorbent for cadmium (Cd (II)) ...

Traditional technologies for the recycling of spent lithium-ion batteries (LIBs) mainly focus on reductive leaching, which often leads to total leaching rather than selective leaching of metals. As...

Prevention of mechanical and finally electrochemical failures of lithium batteries is a critical aspect to be considered during their design and performance, especially for those with high specific capacities. Internal failure is observed as one of the most serious factors, including loss of electrode materials, structure deformation and dendrite growth. It usually incubates from atomic/molecular level and progressively aggravates along with lithiation. Understanding the internal failure is of great importance for developing solutions of failure prevention and advanced anode materials. In this research, different internal failure processes of anode materials for lithium batteries are discussed. The progress on observation technologies of the anode failure is further summarized in order to understand their mechanisms of internal failure. On top of them, this review aims to summarize innovative methods to investigate the anode failure mechanisms and to gain new insights to develop advanced and stable anodes for lithium batteries. Keywords: Lithium battery, Anode materials, Internal failure

Non-carbon materials in capacitive deionization (CDI) can help to enhance the capacity of removed ions. Here, we report for the first time the removal of chloride ions (Cl−) with a bismuth (Bi) anode when coupled with an activated carbon (AC) cathode in CDI. The effects of carbon black in the Bi electrode, applied voltage, electrode mass loading and initial concentration on Cl− removal are investigated. Moreover, its cycle performance is also tested. Results show that addition of carbon black to a Bi electrode (Bi@CB) significantly improves Cl− removal. The declining trend of Cl− concentration and appearance of peaks assigned to products of bismuth oxychloride (BiOCl) in XRD patterns confirm Cl− storage by the Bi electrode, which is enhanced with an increase in voltage. When coupled with AC in a fixed mass, increasing the Bi mass does not contribute to more Cl− removal. Although the cycle performance is not excellent (the attenuation rate is 74% after 10 cycles), its chloride removal capacity is ∼2–3 times the value of AC (e.g. 0.95 vs. 0.32 mmol gBi−1 at 1.2 V in 500 mg L−1 NaCl solution). Besides, the Bi–AC electrode pair in CDI is more suitable to remove Cl− from a solution with a Cl− concentration of below 600 mg L−1.

With two independent pore systems (intralayer sinusoidal channels and interlayer supercages) and external 12 membered-ring (MR) cups, H-MCM-49 was selected as the acidic support for upgrading palmi...

Wet air oxidation (WAO) has an obvious advantage in treating wastewater with high concentration of organics, but harsh reaction conditions are required and the treatment efficiency has not reached a satisfactory level. Herein, we developed a low dosage of persulfate promoted WAO process (PWAO) to remove a model heterocyclic pollutant benzothiazole (BTH). The addition of persulfate remarkably enhanced the elimination of benzothiazole (BTH) and COD from water via degradation and polymerization. Under optimized operation condition (with 11.1 mM K2S2O8 addition into WAO), about 65.0% of BTH converted into microsphere polymers and more than 94.6% COD was eliminated from water after polymers separation. Electron paramagnetic resonance (EPR) analysis and quenching experiments revealed that OH was effectively generated in a wide range of reaction temperature and it played the key role in BTH degradation and polymerization, while SO4 − was detected at low temperature for its fast decomposition at high temperature. Quantum chemical calculation together with ultra-performance liquid chromatography with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS) analysis confirmed that the degradation and polymerization of BTH mainly started from the heterocyclic ring, followed by further oxidation or polymerization. Comparing with normal WAO process, the PWAO technology had an advantage in lower operating cost in removing per unit COD and carbon resource recycle, which indicates a promising prospect in treating wastewater with high concentration of heterocyclic compounds.

Polytetrafluoroethylene (PTFE) is an attractive membrane material due to its superior chemical resistance, thermal stability and strong hydrophobicity. However, PTFE hollow fiber membranes are challenging to produce by conventional technique due to the high solvent resistance and high melt viscosity of PTFE. In this study, novel PTFE hollow fiber membranes composed of pure PTFE nanofibers were firstly fabricated via a scalable and environment-friendly method based on emulsion electrospinning with a non-rotating collector and followed by a high-temperature sintering process. The effects of PTFE/PEO mass ratio and sintering temperature on the morphologies and properties of the resulting membranes were investigated. The prepared PTFE hollow fiber membrane shows the excellent characteristics combining the advantages of both electrospun nanofibers membrane and hollow fiber membrane, such as high porosity (more than 82%), self-supporting and superhydrophobicity. The membrane sintered at 380 °C present the highest mechanical strength, which shows the tensile strength, Young's modulus, strain at break of 30.5 Mpa, 53 Mpa, and 315%, respectively. The permeate flux of the prepared PTFE hollow fiber membrane is about 4.6–8.8 times as that of the commercial PTFE hollow fiber membranes, as well as is approximately 3.2–11.6 times higher than the date of the reported PTFE hollow fiber membranes. Additionally, the prepared membrane shows high and stable flux in long-term and rising salinity experiments, indicating it is very promising for membrane distillation (MD) application and even for the treatment of hyper-saline wastewater.

In this research, a methodology named whole-process pollution control (WPPC) is demonstrated that improves the effectiveness of process optimization. This methodology considers waste/emission treatment as a step of the whole production process with respect to the minimization of cost and environmental impact for the whole process. The following procedures are introduced in a WPPC process optimization: ① a material and energy flow investigation and optimization based on a systematic understanding of the distribution and physiochemical properties of potential pollutants; ② a process optimization to increase the utilization efficiency of different elements and minimize pollutant emissions; and ③ an evaluation to reveal the effectiveness of the optimization strategies. The production of ammonium paratungstate was chosen for the case study. Two factors of the different optimization schemes—namely the cost-effectiveness factor and the environmental impact indicator—were evaluated and compared. This research demonstrates that by considering the nature of potential pollutants, technological innovations, economic viability, environmental impacts, and regulation requirements, WPPC can efficiently optimize a metal production process. Keywords: Whole-process pollution control, Process optimization, Industrial pollution, Tungsten

In the production of lithium-ion batteries (LIBs) and recycling of spent LIBs, a large amount of low-concentration lithium-containing wastewater (LCW) is generated. The recovery of Li from this medium has attracted significant global attention from both the environmental and economic perspectives. To achieve effective Li recycling, the features of impurity removal and the interactions among different ions must be understood. However, it is generally difficult to ensure highly efficient removal of impurity ions while retaining Li in the solution for further recovery. In this study, the removal of typical impurity ions from LCW and the interactions between these species were systematically investigated from the thermodynamic and kinetics aspects. It was found that the main impurities (e.g., Fe3+, Al3+, Ca2+, and Mg2+) could be efficiently removed with high Li recovery by controlling the ionic strength of the solution. The mechanisms of Fe3+, Al3+, Ca2+, and Mg2+ removal were investigated to identify the controlling steps and reaction kinetics. It was found that the precipitates are formed by a zero-order reaction, and the activation energies tend to be low with a sequence of fast chemical reactions that reach equilibrium very quickly. Moreover, this study focused on Li loss during removal of the impurities, and the corresponding removal rates of Fe3+, Al3+, Ca2+, and Mg2+ were found to be 99.8%, 99.5%, 99%, and 99.7%, respectively. Consequently, high-purity Li3PO4 was obtained via one-step precipitation. Thus, this research demonstrates a potential route for the effective recovery of Li from low-concentration LCW and for the appropriate treatment of acidic LCW.

Excessive ammonia nitrogen in wastewater seriously endangers ecological environment, so high-flux and selectivity membrane is urgently needed for ammonia removal using membrane absorption (MA). In this paper, a high-performance electrospun hollow fiber membrane was fabricated and solvent vapor welding treatment was adopted to enhance mechanical strength. The post-treatment membrane showed 103.8% higher in the Young’s modulus than the pristine membrane. High mechanical strength, porosity and hydrophobicity of the membrane make it superior in mass transfer and selectivity. The effects of membrane thickness, pH and temperature of feed solution on experimental overall mass transfer coefficient (KOE) and selectivity coefficient (SNH3/H2O (g)) were intensively investigated to examine the membrane performance in MA application. The results show KOE is 1.35 * 10−5 m s−1 and SNH3/H2O (g) is 7.58 when pH is 11, which are higher than that of commercial membrane. Moreover, the selectivity can be improved greatly from 6.91 to 9.74 by increasing the thickness of the hollow fiber membrane from 55 ± 5 μm to 115 ± 5 μm. The welded electrospun hollow fiber membrane demonstrates great potential for ammonia removal in MA application.

It is challenging to selectively upgrade phenolic compounds to aromatics because of much weaker adsorption of hydroxyl compared to that of phenyl upon Ni catalysts. With 10% Ni loading in theory, three Ni catalysts with different Ni nanoparticle sizes were prepared with the wet impregnation method on SiO2 and Silicalite-1 and with the in situ encapsulation method (Silicalite-1). On the basis of the results, we proposed a general rule concerning temperature-dependent selectivity control on phenol hydroconversion over Ni catalysts. As well as benzene saturation in consecutive mode, hydrogenation of phenyl ring was more dramatically inhibited at elevated temperature via decreased adsorption of benzene rings than that of hydroxyl to selectively favor hydrogenolysis over hydrogenation in parallel mode. Among three Ni catalysts, Ni@Silicalite-1 with 3–5 nm Ni nanoparticle sizes encapsulated imposed the restricted adsorption conformation of phenol via end-up mode within channels of Silicalite-1 zeolite to furthe...

Five negatively charged organic compounds with different structures, sodium methane sulfonate (MS), sodium benzene sulfonate (BS), sodium 6-hydroxynaphthalene-2-sulfonate (NSS), sodium dodecyl sulfate (SDS), and sodium dodecyl benzene sulfonate (SDBS), were used to examine the fouling of an anion exchange membrane (AEM) in electrodialysis (ED), to explore the effect of molecular characteristics on the fouling behavior on the AEM and changes in the surface and electrochemical properties of the AEM. Results indicated that the fouling degree of the AEM by the different organics followed the order: SDBS > SDS > NSS > BS > MS. SDBS and SDS formed a dense fouling layer on the surface of the AEM, which was the main factor in the much more severe membrane fouling, and completely restricted the transmembrane ion migration. The other three organics caused fouling of the AEM by adsorption on the surface and /or accumulation in the interlayer of the AEM, and exhibited almost no influence on the transmembrane ion migration. It was also concluded that the organics with benzene rings caused more severe fouling of the AEM due to the stronger affinity interaction and steric effect between the organics and the AEM compared with organics with aliphatic chains.

Manganese dioxides (MnO2) govern the polymerization of phenolic and anilinic pollutants in nature water body. The studies on the chemistry of different phases of MnO2 was relatively limited. Here we compared two MnO2, layer δ-MnO2 and tunnel γ-MnO2, on their reaction kinetics and removal pathways with acetaminophen (APAP) as model compound. We found the kinetics of acetaminophen transformation by MnO2 were largely influenced by pH values and MnO2 structures. In neutral systems, APAP removal by δ-MnO2 was faster than by γ-MnO2. This was attributed to the higher catalytic potential of δ-MnO2. In acidic systems, APAP removal by γ-MnO2 was faster than by δ-MnO2. This was attributed to the larger surface area and weaker electrostatic repulsion of γ-MnO2 to APAP in acidic conditions. Furthermore, the pathways of acetaminophen transformation were influenced by pH values. Dimerization and hydrolysis-oxidation were the two major APAP transformation pathways by both MnO2 in neutral and acidic systems. Low pH values induced the nucleophilic addition between quinoneimine (the product of hydrolysis-oxidation) and anilines (e.g., APAP and its dimers). Low pH values also promoted the dimerization degrees of APAP. The hydrophilicity of APAP transformation products by MnO2 were significantly reduced by low pH values. This work reconsidered the significances of acidity in the pollutants transformation by MnO2, and provided new perspectives to study the pollutants transformation by different phases of MnO2.

Single-atom electrocatalysts have attracted board interest in the recent years as they combine the advantages of heterogeneous and homogeneous electrocatalysts. Nevertheless, single-atom electrocatalysts with single metal component cannot further satisfy the demand of catalytic properties. This work developed atomic Co/Ni dual sites in N-doped porous carbon Janus-like frameworks through epitaxial growth of cobalt based MOFs on nickel complexes. Structural characterization and atomic-scale transmission electron microscopy revealed the homogeneously dispersed active sites of Co-Ni alloy and single Co/Ni atoms. Electrochemical data strongly demonstrated the advantages of integrating Co-MOF and Ni complex with different topological structures to form a Janus-like structure. The resultant catalysts afforded onset potential of 0.93 V and half-wave potential of 0.84 V for oxygen reduction reaction in alkaline media, and 0.86 V and 0.73 V in acid media, which is better than single noble-metal-free catalysts, even close to commercial Pt/C. Besides, the catalysts also exhibited good oxygen evolution reaction performance (a current density of 10 mA cm−2 at a potential of 1.59 V) and overvoltage between ORR and OER is 0.78 V. Density functional theory calculations indicated the high electrocatalytic activities are originated from the synergetic effect of atomic Co/Ni-N-C bonds and microstructure of the prepared materials. This work paves a new avenue for the development of multiatomic electrocatalysts for energy conversion.

N-doped graphene has demonstrated exceptional activities in versatile metal-free catalytic processes. In this study, reduced graphene oxide (rGO) and N-doped rGO were synthesized by a facile approach via microwave reduction with a low energy input and short reaction time. The activities of the derived carbocatalysts were evaluated by catalytic ozonation of 4-nitrophenol (4-NP). Compared with thermally annealed rGOs in argon atmosphere, microwave treated rGO demonstrated a better performance in catalytic oxidation, and N-doping would further improve the catalytic activity. It is discovered that microwave irradiation not only gave rise to more edging sites and dangling bonds in rGO, making higher catalytic potentials for ozone decomposition than that from thermal annealing, but also resulted in a higher concentration of N dopants. XPS studies revealed that more graphitic N species were incorporated into the carbon basal plane during the microwave reduction processes. The reactive oxygen species (ROS) in 4-NP oxidation were evaluated and identified by liquid-phase electron spin resonance (ESR) and radical scavenging tests, which indicated the generation of O2 −, OH and 1O2 for 4-NP degradation. This study provides a facile protocol for fabricating advanced nanocarbon materials for green oxidation and enables new insights in catalytic ozonation with state-of-the-art carbocatalysis.

Summary With the development of modern industries, the sustainability of critical resources has attracted worldwide attention considering the entire supply chain. With a large industrial sector size in China, a safe supply of metal resources is crucial to ensure the effective operation of the whole industry. Although specific criticality analyses have been applied to identify critical resources in some regions, including Europe and the USA, they are not ready to be directly applied in the case of China because the structure of China’s industry is remarkably different from other areas. In this research, a three-dimensional methodology considering supply safety, domestic economy, and environmental risk is demonstrated, where Chinese industrial conditions are specifically considered. In total, 64 materials were introduced to perform the criticality assessment, and 18 metals were classified with a high criticality degree in the three-dimensional criticality space. With the obtained findings decision-makers can formulate strategic deployment to promote resource management., Graphical abstract, Highlights • A systematic evaluation methodology for metal resource criticality was established • Effects of supply risk, economic change, and environmental risk were considered • 64 materials were introduced to perform the criticality assessment • 18 metals were classified with a high criticality degree in China, Environmental science; Materials science; Materials class; Metals

With the undergoing unprecedented development of lithium-ion batteries (LIBs), the recycling of end-of-life batteries has become an urgent task considering the demand for critical materials, environmental pollution, and ecological impacts. Selective recovery of targeted element(s) is becoming a topical field that enables metal recycling in a short path with highly improved material efficiencies. This research demonstrates a process of selective recovery of spent Ni-Co-Mn (NCM)-based lithium-ion battery by systematically understanding the conversion mechanisms and controlling the sulfur behavior during a modified-sulfation roasting. As a result, Li from complex cathode components can be selectively extracted with high efficiency by only using water. Notably, the sulfur driven recovery processes can be divided into two stages: (i) part of the structure of NCM523 was destroyed, and Ni, Co, and Mn were reduced to divalent in different degrees to form sulfate (NiSO

Membrane capacitive deionization (MCDI) usually contains both anion and cation exchange membranes (AEM, CEM) to restrict the ion desorption during charging and re-adsorption during discharging in capacitive deionization (CDI). In this study, different from conventional MCDI, an asymmetric membrane capacitive deionization (AMCDI) device packing an AEM only (AMCDI-AEM) was constructed, where the AEM was lab-synthesized from poly (2, 6-dimethyl-1, 4-phenylene oxide). The effect of the AEM properties, such as ion exchange capacity, water uptake and membrane resistance on the desalination performance of AMCDI-AEM was systematically discussed. The results indicate that an AEM with high ion exchange capacity, low membrane resistance and low water uptake is beneficial for AMCDI-AEM. Furthermore, AMCDI packed with a commercial cation exchange membrane only (AMCDI-CEM) and a conventional MCDI device were also assembled to stress the importance of AEM application. Although the charge efficiency of AMCDI-AEM is lower than a full MCDI cell (54.7 vs 95.0%) due to the unprotected cathode, AMCDI-AEM device shows comparable salt adsorption capacity to MCDI (7.4 vs 7.2 mg g−1), and is much better than that of CDI (2.3 mg g−1) and AMCDI-CEM (1.5 mg g−1), suggesting that AEM plays a stronger role than CEM for membrane-assisted CDI application. By using a single AEM and commercial activated carbon electrode, this work provides an opportunity to reduce membrane cost for the industrialization of MCDI technology.

A novel surface modified anion exchange membrane (AEM) was prepared by electrodeposition of graphene oxide (GO) and polydopamine (PDA) coating, aiming at improving antifouling performance and stability. The AEM was firstly modified by electrodeposition of GO and then immersed into the dopamine solution to form a thin PDA layer. The effects of GO and PDA composite modification were investigated by various analytical techniques and electrodialysis application. The GO@PDA-modified AEM (GO@PDA-M) exhibited highly hydrophilic and negatively charged. In addition, the introduction of PDA coating helped to construct a smoother and denser composite modifying layer composed of GO and PDA, and reduced the roughness of membrane surface. Depending on these properties, the GO@PDA-modified AEM showed significant antifouling ability without compromising the desalination performance. After being fouled by 150 mg/L sodium dodecyl benzene sulfonate (SDBS) for 4 h, the desalination rate of GO@PDA-M increased by 39.3% compared to pristine membrane, while for PDA-modified membrane (PDA-M) and GO-modified membrane (GO-M) were 5.7% and 18.2% respectively. Moreover, it still maintained antifouling ability after 20 h of continuous operation. The stability of GO@PDA-M was immensely improved compared with the GO-M due to the introduction of PDA layer.

Photocatalytic ozonation has great potential in wastewater treatment. However, the role of ozone and the contribution of photogenerated hole in this process have not been fully understood. Here three WO3 materials are synthesized and used as model catalysts in visible-light photocatalytic ozonation for the mineralization of pharmaceutical pollutants. A dual role of ozone in this process has been confirmed: (i) direct oxidation of the pollutant till formation of refractory intermediates, (ii) efficient trapping of photoelectron that cannot be captured by O2. The latter is crucial because it not only induces the O3--mediated pathway for hydroxyl radical (OH) formation but also separates the hole which has proven to be capable of oxidizing water into OH. Evidenced by photoluminescence results, the intrinsic charge separation ability of WO3 in photocatalytic ozonation is no more as important as that in photocatalysis with O2. Finally, this process is more applicable under acidic condition. This work contributes to a better understanding of the significance of ozone in WO3 photocatalytic ozonation and provides us an insight into the mechanism of photocatalytic ozonation.

A novel omniphobic nanofiber membrane for membrane distillation (MD) was successfully fabricated by one-step electrospinning of PVDF-HFP and fluorinated-decyl polyhedraloligomeric silsesquioxane (F-POSS) colloidal suspension solution. The fabricated F-POSS/PVDF-HFP membrane possessed uniform fiber structures and had extreme high F-POSS concentration on the surface. This F-POSS based membrane exhibited excellent omniphobicity, as indicated by its wetting resistance to different low surface tension liquids, including ethanol with a contact angle of 128.2°. Membrane distillation (MD) experiments showed that the water flux and water quality were stably maintained in highly saline feed solutions containing low surface tension substances, which successfully demonstrated its potential application for desalination of challenging industrial wastewater.

SiC is a newly developed photocatalyst, but it is often used together with a co-catalyst rather than solely for its relatively low activity. Here we reported the high activity of a commercial SiC in a photocatalysis and ozone combined process (photocatalytic ozonation). The commercial SiC showed very weak activity in photocatalysis of oxalic acid (OA) and para-hydroxybenzoic acid (PHBA) degradation, and its performance in catalytic ozonation was also not satisfied. However, the organics degradation and mineralization rates dramatically increased in the SiC photocatalytic ozonation. The different operation parameters were optimized, and the main reactive radicals in this process and its generation pathways were studied. It was found that photo-generated electron reduction of ozone and oxygen are the main pathways to produce hydroxyl radical, which was responsible to the high oxidizing ability of this process.

Novel nanofibers-covered hollow fiber membrane (N-HFM), combining the advantages of both electrospun nanofibers film and hollow fiber membrane was fabricated via electrospinning with non-rotational collectors. The key parameters of electrospinning including positive voltage, negative voltage, polymer concentration and working distance were optimized to examine their effects on the morphology and structure of N-HFM. Meanwhile, a solvent vapor welding post-treatment was firstly applied to enhance the mechanical strength of hollow fiber membranes. The welding can improve the mechanical property and water repellency as well as maintain the high porosity, by fusing the nanofibers just at junctions. After a 40 min welding, the Young's modulus, strain at break and tensile strength of the welded N-HFM increased by 117%, 79% and 90% respectively, compared to the pristine N-HFM. Furthermore, the welded N-HFM was able to present a high flux of 13.2 L m−2 h−1 and a stable salt rejection of over 99.9% during the 5 h of direct contact membrane distillation (DCMD) test, suggesting the competency of the welded N-HFM for MD applications.

In this paper, a sustainable process to recover valuable metals from spent lithium ion batteries (LIBs) in sulfuric acid using ammonium chloride as reductant was proposed and studied. Being easily reused, ammonium chloride is found to be efficient and posing minor environmental impacts during the overall process. By investigating the effects of a wide range of parameters, e.g., H2SO4 concentration, NH4Cl concentration, temperature, leaching time, and solid-to-liquid mass ratio, the leaching behaviour of Li, Ni, Co, and Mn was systematically investigated. And the leaching mechanism and kinetics were determined by mineralogically characterization of residues at various reaction times and by fitting using different kinetic models. With this research, it is possible to provide a win-win solution to improve the recycling effectiveness of spent LIBs by using waste salt that is easily reused as the reductant.

Anode graphite was recovered from a spent lithium ion battery (LIB) and reutilized as a carbon precursor to obtain graphene-based materials. Characterization results revealed that impurities were removed from the obtained graphite powder by cleansing processes. The as-synthesized reduced graphene oxide (rGO) from the purified graphite (LIB-rGO) demonstrated excellent catalytic ozonation activity against organic pollutants removal. To probe potential catalytic active sites, LIB-rGOs with different defective levels but similar oxygen contents were synthesized. Catalytic ozonation tests revealed that a higher defective level resulted in a greater catalytic activity. Density functional theory (DFT) calculation further demonstrated that ozone molecules could spontaneously decompose into active oxygen species on graphene structural vacancies and edges, which consolidated the role of defective structure in catalytic ozonation activity. Meanwhile, we discovered the pollutant-structure-dependent behavior of dominant reactive oxygen species (ROS) with the aid of radical scavenging tests and electron paramagnetic resonance (EPR) spectra. For phenolic pollutants vulnerable to direct ozone attacking, superoxide radicals (O2 −) and singlet oxygen (1O2) were found to be responsible ROS, whereas hydroxyl radicals ( OH) were identified as the principle ROS for aliphatic organic pollutants destruction. This study not only put forward a possible way for reutilization of waste LIB anode, but also stepped further for investigating the catalytic ozonation mechanism towards the graphene-based materials including the active sites and the generation of ROS.

In this work, phenol and oxalic acid (OA) degradation in an ozone and photocatalysis integrated process was intensively conducted with Fe3 +/TiO2 catalyst. The ferrioxalate complex formed between Fe3 + and oxalate accelerated the removal of OA in the ozonation, photolysis and photocatalytic ozonation process, for its high reactivity with ozone and UV. Phenol was degraded in ozonation and photolysis with limited TOC removal rates, but much higher TOC removal was achieved in photocatalytic ozonation due to the generation of OH. The sequence of UV light and ozone in the sequential process also influences the TOC removal, and ozone is very powerful to oxidize intermediates catechol and hydroquinone to maleic acid. Fenton or photo-Fenton reactions only played a small part in Fe3 +/TiO2 catalyzed processes, because Fe3 + was greatly reduced but not regenerated in many cases. The synergetic effect was found to be highly related with the property of the target pollutants. Fe3 +/TiO2 catalyzed system showed the highest ability to destroy organics, but the TiO2 catalyzed system showed little higher synergy.

This study demonstrates the feasibility of layer-by-layer (LbL) assembly of poly(sodium 4-styrene sulfonate) (PSS)/poly(diallyldimethylammonium chloride) (PDADMAC) polyelectrolyte multilayers on an anion exchange membrane (AEM). The electrodeposition of (PSS/PDADMAC)n multilayers on the AEM with a PSS layer as the top surface endows the surface with negative charges and increases the surface hydrophilicity, leading to a significantly improved antifouling performance in electrodialysis (ED) to an organic foulant, i.e., sodium dodecyl sulfate (SDS). The desalination rate during 180 min increased from 24.0% for the pristine AEM to 30.5% for a 5.5 PSS/PDADMAC bilayers modified AEM with 75 mg/L SDS in the initial solution. A SDS fouling layer was formed at the dilute side of the pristine AEM, causing a sharp increase of electrical resistance and restricting the ion transport through the AEM completely. Electrodeposition of 5.5 PSS/PDADMAC bilayers prevented the formation of the SDS fouling layer at the surface of AEM, which reduced the sharp increase of electrical resistance and kept the ion transport through the AEM unaffected. With 100 or 150 mg/L SDS in the initial solution, the desalination rate during 180 min increased from 24.1% or 15.4% for the pristine AEM to 28.4% or 26.8% for the 5.5 PSS/PDADMAC bilayers modified AEM.

This study introduces a doughnut-like, highly porous g-C3N4 photocatalyst fabricated using a double bubble templating method which employs two synergistic gas-generating agents (H2O2 and NH4Cl). The concurrent thermolysis of H2O2 and NH4Cl synergistically enhances g-C3N4 exfoliation and nanopore production, as the released O2 and NH3 undergo violent exothermic reactions during g-C3N4 growth. The resultant g-C3N4 (H2O2-NH4Cl-g-C3N4) exhibited 8.9 times higher specific surface area compared to bulk g-C3N4, and 3.2–6.4 times as large as those synthesized using individual NH4Cl or H2O2. The photocatalytic activities of these g-C3N4 samples were found to linearly correlate with their valance band (VB) maximum potentials; for example, H2O2-NH4Cl-g-C3N4 possessed a VB maximum down-shifted by 0.34 eV, and consequently exhibited 7.1 times larger photocatalytic hydroquinone degradation rate than the bulk g-C3N4. Electrochemical analysis and trapping experiments collectively suggested that the VB downshift caused more efficient separation of charge carriers, and subsequent enhancement in positive hole-dominated photocatalytic oxidation of hydroquinone.

The rapid growth of lithium ion batteries (LIBs) for portable electronic devices and electric vehicles has resulted in an increased number of spent LIBs. Spent LIBs contain not only dangerous heavy metals but also toxic chemicals that pose a serious threat to ecosystems and human health. Therefore, a great deal of attention has been paid to the development of an efficient process to recycle spent LIBs for both economic aspects and environmental protection. In this paper, we review the state-of-the-art processes for metal recycling from spent LIBs, introduce the structure of a LIB, and summarize all available technologies that are used in different recovery processes. It is notable that metal extraction and pretreatment play important roles in the whole recovery process, based on one or more of the principles of pyrometallurgy, hydrometallurgy, biometallurgy, and so forth. By further comparing different recycling methods, existing challenges are identified and suggestions for improving the recycling effectiveness can be proposed. Keywords: Spent lithium ion batteries, Valuable metals, Pretreatment, Metal extraction, Product preparation, Recycling

The heterogeneous anion exchange membranes (AEMs) were modified by electrodeposition of graphene oxide (GO) under different conditions. The physicochemical properties of GO-modified membranes were characterized systemically to obtain the optimized conditions for the electrodeposition of GO on the surface of AEMs. The results indicated that the contact angle and zeta potential of the modified AEMs decreased when increasing the concentration of GO from 0.05 g/L to 0.1 g/L. The higher concentration of NaCl, as the supporting electrolyte, could hinder the electrodeposition of GO on the AEMs for the competitive migration between the GO and Cl− ions. The increase of current density had a positive effect on properties of GO-modified membranes in the range of 1–5 mA/cm2. Compared with the pristine AEM, all the GO-modified AEMs exhibited smoother surface, higher hydrophilicity and negative zeta potential. It was also found that the GO modifying layer did not increase electrical resistance and had only a negligible effect on the desalination performance of AEMs. In the fouling experiments with sodium dodecyl benzene sulfonate (SDBS) as the model foulant, the GO-modified AEMs exhibited improved fouling resistance to SDBS.

Three kinds of graphitic carbon nitride materials (bulk, porous and nanosheet g-C3N4) were composited with a multiwall carbon nanotube (MWCNT) by a hydrothermal method, and the obtained b-C3N4/CNT, p-C3N4/CNT and n-C3N4/CNT materials were used in the electrodes for electro-peroxone process. It was found that the n-C3N4/CNT composite exhibited the highest efficiency in oxalate degradation, though it performed the worst in the oxygen-reduction reaction for H2O2 production. The n-C3N4/CNT composite exhibited higher activity than CNT and other composites in catalytic ozonation experiments, due to the higher pyrrolic-N content modified on the CNT surface and higher surface area. It also has higher electron transfer ability, which benefited to the electro-reduction of both O2 and O3. The result confirmed that catalytic ozonation process was an important means to enhance the degradation efficiency in the electro-peroxone process, besides peroxone process and O3-electrolysis.

The nitrogen heterocyclic compounds (NHCs) are very toxic and widely used in many industries, while the treatment of NHCs in wastewater has not attracted enough concern till now. Here we studied the complete degradation of a typical NHCs, benzopyrazole (BP), in wet oxidation. The effects of different operation parameters, such as stirring speed, temperature, reaction time and initial pH, on BP degradation and chemical oxygen demand (COD) removal were studied. BP was totally degraded and the COD removal efficiency achieved 76.7%, after 120 min reaction at 220 °C with initial pH 6.5. Meanwhile, 81.7% of the nitrogen from BP was removed from the solution. The toxicity of the BP solution was reduced by 95.2% after wet oxidation at 240 °C for 180 min. The influences of coexisted NO3−, CO32−, SO42− and PO43− ions were also investigated. With quantum chemical calculation and intermediates analysis by electrospray ionization mass spectrometry, a very detailed degradation pathway of BP in wet oxidation was proposed.

Ion exchange process is an alternative technique for removal of heavy metal ions from industrial wastewater. The main aim of this paper is to evaluate the performance of different ion exchange resins in removing Cr(VI) from wastewater. The effects of resin types and dosage, initial pH were examined systemically. The results showed that the performance of different resins had obvious difference for the removal of the Cr(VI) ions, in which the type of functional groups of the resin was the main factor. The SEM images indicated that the micro-morphology of resins before and after adsorption of the Cr(VI) presented a little difference. The EDS analysis showed that the adsorbed Cr(VI) was uniformly distributed at the surface of the resins with formation of oxygen-containing groups. The adsorption isotherms and kinetics of Cr(VI) by the different resins are also discussed.

An appropriate co-catalyst can significantly promote the photocatalytic efficacy, but this has been seldom studied in the visible-light photocatalysis combined with ozone, namely photocatalytic ozonation. In this work, a dendritic bismuth vanadium tetraoxide (BiVO4) material composited with highly dispersed MnOx nanoparticles was synthesized, and its catalytic activity is 86.6% higher than bare BiVO4 in a visible light and ozone combined process. Catalytic ozonation experiments, ultraviolet- visible (UV-Vis) diffuse reflectance spectra and photoluminescence spectra jointly indicate that MnOx plays a triple role in this process. MnOx strengthens the light adsorption and promotes the charge separation on the composite material, and it also shows good activity in catalytic ozonation. The key reactive species in this process is $OH, and various pathways for its generation in this process is proposed. This work provides a new direction of catalyst preparation and pushes forward the application of photocatalytic ozonation in water treatment.

The recovery of high-purity vanadium has attracted significant attention regarding both sustainability and environmental protection necessities. However, insufficient understanding of vanadium species in aqueous solution constrains further optimization of the vanadium recovery process. Here, a closed-loop technical route (extraction and stripping) was realized to recover high-purity vanadium products by in situ monitoring/controlling vanadium species. The evolution of vanadium species in the extraction reaction was semiquantitatively visualized by the system combined with annular centrifugal contactors (ACCs) and electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), while the active (V4 and V10 species) and nonactive (H2VO4–) vanadium species were identified. In the stripping process, the behaviors of vanadium species have been described, which affected the morphology of recycled NH4VO3 products. As a result, the transformation pathway of vanadium species in the whole recovery process was...

Computer-aided molecular design (CAMD) has attracted much attention in the past 30 years. The generation of a candidate molecular structure satisfying a set of structural constraints is an important part of such a problem. However, the commonly used structural constraints proposed by Odele and Macchietto [Odele, O.; Macchietto, S. Computer Aided Molecular Design: A Novel Method for Optimal Solvent Selection. Fluid Phase Equilib. 1993, 82, 47], cannot provide sufficient and necessary conditions for generating cyclic molecules. In this paper, the sufficient and necessary conditions for molecular generation were presented. According to these conditions, some modifications of the conventional constraints were made, and mathematical proofs demonstrated that the modified constraints can perfectly generate structurally feasible molecules with no more than two rings. Moreover, some new constraints were proposed to help generate feasible aromatic molecules with less than two rings. Finally, several cases were pres...

This paper deals with a systematic thermodynamic study on the liquid–liquid extraction of vanadium from aqueous solution (0.001–0.1 mol/kg) using primary amine N1923 (0.004–0.3 mol/kg). Suitable and practical thermodynamic models (Pitzer–Pitzer and Pitzer–Margules) were improved and verified for the first time. Firstly, the Pitzer parameters were correlated based on solid–liquid equilibrium data, and then employed as the initial values in regression progress. Finally, all the interaction parameters (βaq0, βaq1, βRV,RVorg, βR,RVorg, βR,Rorg, ARV,Rorg, Atol,RVorg and Atol,Rorg) were regressed. Liquid–liquid equilibrium data were predicted using those parameters and compared to the experimental results, which confirmed the reliability and suitability of these models for the present system. Furthermore, these models provided excellent predictions of the effect of the initial amine molality and pH value on the extraction, showing great promise for industrial applications.

The annular centrifugal contactors (ACCs) have been used for liquid-liquid extraction in bench scale/pilot-plant tests. In view of good hydraulic properties and high mass-transfer efficiency, the state-of-the-art of extraction process using ACC/ACCs can satisfy the mass transfer enhancement, cascade and operational security liquid-liquid extraction processes. The many investigations of ACCs have been focused on the flow instabilities, multiphase flows, axial mixing, etc. The published literatures on these aspects have been critically analyzed and presented in a coherent manner. But in this review, the summaries of the application of ACCs in many specific extraction processes were presented, and how to optimize the operation conditions to reach good hydraulic properties were summarized using the designed equipments of ACCs. The good hydraulic properties were significant to the quick and excellent separation of the immiscible phase, and the high mass-transfer efficiency for liquid-liquid extraction were performed by cascade of ACCs. The advantages and disadvantages of the ACCs were discussed in detail. Recommendations have been made for future work with aim of more information for the application of the hydrometallurgical process.

Effective recycling of spent graphite from lithium-ion batteries (LIBs) has a strong application potential. In this research, anode scrap of spent LIBs is efficiently recovered and reused as high-performance cathode in electro-Fenton system. Role of different recovery processes in the reuse of anode scrap powder in electro-Fenton system is focused, including Anode raw powder (RP), acid leaching (AL), acid and alkali leaching (AAL) residual powder. The results indicate functional groups of anode powder are changed by different leaching processes, which can significantly affect the subsequent reuse in electro-Fenton system. According to evaluation by electrochemical characterization, the AAL has a higher hydrogen peroxide (H2O2) selectivity and yield than RP and AL due to highly active two-electron reduction of oxygen (O2). Interestingly, when anode powder is reused in electro-Fenton system, the AL electrode achieves 100% bisphenol A (BPA) removal in 70 min and 87.4% COD removal in 240 min, showing the best degradation efficiency. The reason can be attributed to higher carboxylic group content (35.83%) of AL powder than that of AAL (7%). Thus, part of iron ion in solution can be adsorbed on the surface of AL cathode, forming a partial heterogeneous iron oxidation-reduction. Furthermore, the reusability of AL electrode is evaluated. Compared with other carbon cathode, the AL cathode with a low current density still maintains 100% BPA removal after 10 reuse cycles. Since it is inherent with high reusability and environmental friendliness comparing with traditional cathode materials, this research demonstrates a potentially new approach to cooperatively treat pollutants from solid waste and waste water.

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 LiNi1/3Co1/3Mn1/3O2 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...

Recovery of valuable metals from spent lithium-ion battery (LIB) is of both environmental and economic importance. Acidic leaching usually encounters issues of low selectivity or slow kinetics with considerable secondary waste generation during further purification. In this research, a closed-loop process with improved leaching selectivity for recycling of spent LiNixCoyMn1-x-yO2 battery using weak acidic leachant was demonstrated. To obtain optimal conditions of the leaching process, the effects of acid concentration, solid to liquid (S/L) ratio, temperature and reductant content were systematically investigated. Almost all Co, Li, Mn and Ni could be effectively recovered into the solution while Al remained in the residue as metallic form, after one-step leaching. The role of reductant during leaching was further evaluated which was found to be critical for the leaching kinetics. It is clear that the addition of reductant could alter the rate-controlling step of leaching from the ion diffusion in the residue layer to the surface chemical reactions. With high selectivity against impurities, this research proposed and verified a process to recover high purity Li2CO3 from the cathode scrap of LIBs, and more than 90% of the global recovery rate of valuable metals can be achieved.

The physicochemical and structural properties of the AMX (homogeneous AEM), AMA (semi-homogeneous AEM) and HAEM (heterogeneous AEM) were characterized systematically to examine their effects on membrane fouling from sodium dodecyl sulfate (SDS) in electrodialysis. Results demonstrated that the fouling of three AEMs was closely related to their membrane structure, and the denser membrane structure caused more SDS accumulated on the membrane surface to make the severer membrane fouling. The existence of SDS in the dilute solution caused the desalination rate of AMX, AMA and HAEM decreased by 42.3%, 15.3% and 9.2%, respectively. Different fouling layer was formed on the surface of AMX and AMA except HAEM, which was demonstrated firstly by element mapping of membrane cross-section. Electrochemical impedance spectroscopy (EIS) suggested the ionic migration through the fouled AMX was restricted completely, different from the transmembrane migration of partial ions through the fouled AMA and HAEM. Compared with the fouled AMA and HAEM, the performance of the fouled AMX caused by SDS was more difficult to be recovered due to its denser membrane structure.

Recycling of spent lithium-ion batteries (LIBs) has attracted significant attention in recent years due to the increasing demand for corresponding critical metals/materials and growing pressure on the environmental impact of solid waste disposal. A range of investigations have been carried out for recycling spent LIBs to obtain either battery materials or individual compounds. For the effective recovery of materials to be enhanced, physical pretreatment is usually applied to obtain different streams of waste materials ensuring efficient separation for further processing. Subsequently, a metallurgical process is used to extract metals or separate impurities from a specific waste stream so that the recycled materials or compounds can be further prepared by incorporating principles of materials engineering. In this review, the current status of spent LIB recycling is summarized in light of the whole recycling process, especially focusing on the hydrometallurgy. In addition to understanding different hydromet...

The electro-peroxone (E-P) process normally exhibits low efficiency in organic degradation in acid solution due to the limited rate constant of the reaction between O3 and H2O2 (peroxone reaction). In this paper, a C3N4–Mn/CNT composite material was synthetized and characterized with XRD, FTIR, SEM and XPS. With the function of the C3N4–Mn/CNT catalyst, the substrate oxalic acid (OA) was completely degraded in the E-P process within 30 min at pH 3, while only 15% degradation could be achieved after 60 min without the catalyst. The comparison of different reaction systems using the C3N4–Mn/CNT catalyst confirmed that the catalyst promoted the peroxone reaction, rather than the catalytic ozonation or electro-Fenton like reaction. Correlating the XRD and XPS analysis with the degradation data using the C3N4–Mn/CNT catalyst, we deduced that Mn coordinated with nitrogen was the active site for the peroxone reaction. Furthermore, the catalyst showed good chemical and catalytic stability in five cycles of the E-P process for OA degradation.

The identification of active sites and the establishment of structure-reactivity relationship at atomic scale is important for designing efficient catalysts and understanding the reaction mechanism. Here, single atom catalysts (SACs) of Fe anchored on g-C3N4 were synthesized. The catalysts have larger surface area, more photo-generated electrons with stronger reduction ability and faster charge carrier migration than g-C3N4, thereby exhibited dramatically enhanced activity and stability in electron reduction of ozone (O3) under visible light. However, lower catalytic performance was observed when Fe nanoparticles coexisted, which regulated more photoelectrons to reduce O2 to OH via two or three-electron reduction pathways rather than one-electron reduction of O3. Mossbauer spectrum and X-ray adsorption spectroscopy indicated that the presence of Fe nanoparticles led to higher proportion of Fe(II)Nx, which played more significant role in the adsorption and reduction of O2. The insight on the contribution of different Fe sites with well-defined local coordination structure is beneficial for rational design of efficient catalysts in photocatalytic ozonation.

Flow electrode capacitive deionization (FCDI) has attracted growing attention for the treatment of high-concentration saline water and continuous operation, but the mechanism responsible for the separation of ions has so far received minimal attention. In this study, an asymmetric FCDI (AFCDI) was assembled with nickel hexacyanoferrate (NiHCF) as cathode and activated carbon (AC) as anode. Its desalination performance and distribution of the removed ions were investigated and compared with FCDI using AC as both cathode and anode. Results showed better desalination performance for AFCDI than FCDI at high applied voltages of 2.4 and 2.8 V. The removed ions were adsorbed by active materials (capacitance contribution) and existed in the electrode electrolyte (charge neutralization contribution). However, the contribution of capacitance and charge neutralization was significantly different between NiHCF electrode and AC electrode. When NiHCF was used as electrode, capacitance contribution dominated the removal of sodium and more than 80% sodium was adsorbed by NiHCF at applied voltages of 1.2–2.8 V. On the contrary, the removed ions mainly existed in electrode solution when AC was used as electrode and charge neutralization contributed to about 80% of removed ions at 2.8 V. These results clarify the mechanism of ions removal in FCDI.

Rechargeable aqueous zinc ion batteries have attracted significant attention for potential applications in large-scale energy storage. However, developing suitable cathode materials with both high capacity and rate performance remains a great challenge. Herein, we report an efficient method for functional materials via controlling the stage of hydrogen bond association extraction to fabricate well-structured vanadium oxynitride without adding extra templates, turning the waste to advanced materials towards high-performance zinc ion storage. Primary amines as highly efficient selective extractant are used in this work. They result in two different structures, from hollow microsphere to novel 0D-in-2D pillared lamellar structure, for the vanadium oxynitrides. Impressively, based on structural merits of abundant electrolyte-accessible sites and transfer pathways, the resulting products are found to be excellent cathode materials with a high reversible specific capacity and rate capability for rechargeable zinc ion batteries (ZIBs). Hence, this work introduces a new clue for designing unique nanostructure vanadium oxynitride to boost the electrochemical properties of aqueous ZIBs.