Ferrioxalate photolysis-assisted green recovery of valuable resources from spent lithium iron phosphate batteries.

Recovering valuable resources from spent cathodes while minimizing secondary waste generation is emerging as an important objective for the future recycling of spent lithium-ion batteries, including lithium iron phosphate (LFP) batteries. This study proposes the use of oxalic acid leaching followed by ferrioxalate photolysis to separate and recover cathode active material elements from spent LFP batteries. The cathode active material can be rapidly dissolved at room temperature using appropriate quantities of oxalic acid and hydrogen peroxide, as determined through thermodynamic calculations. The dissolved ferrioxalate complex ion (Fe(C2O4)33-) is selectively precipitated through subsequent photolysis at room temperature. Depending on the initial concentration, the decomposition ratio can exceed 95 % within 1-4 h. Molecular mechanism analysis reveals that the decomposition of the Fe(C2O4)33- complex ion into water-insoluble FeC2O4·2H2O results in the precipitation of iron and the separation of metal elements. Lithium can be recovered as dihydrogen phosphates through filtration and water evaporation. No additional precipitant is needed and no other side products are generated during the process. Oxalic acid leaching followed by photolysis offers an environmentally friendly and efficient method for metal recovery from spent LFP cathodes. The photochemical process is a promising approach for reducing secondary waste generation in battery recycling.

Effects of ferrous sulfate modification on the fate of phosphorous in sewage sludge biochar and its releasing mechanisms in heavy metal contaminated soils.

Modifications of sludge biochar with metal-based materials can enhance its fertilizing efficiency and improve safety. To elucidate the effects of ferrous sulfate modification on the fate of phosphorus in sludge biochar and its effect on phosphorus fractionation in soil, we investigated the changes in fractionation and bioavailability of phosphorus in modified sludge biochar and studied the changes in soil characteristics, microbial diversity and response, bioavailability, plant uptake of phosphorus, and heavy metals in contaminated soils after treatment with ferrous sulfate modified sludge biochar. The results demonstrated that ferrous sulfate modifications were conducive to the formation of moderately labile phosphorus in sludge biochar, and the concentrations increased by a factor of 2.7 compared to control. The application of ferrous sulfate-modified sludge biochar to alkaline heavy metal-contaminated soils enhanced the bioavailable, labile, and moderately labile phosphorus contents by a factor of 2.9, 3.0, and 1.6, respectively, whereas it obviously reduced the leachability and bioavailability of heavy metals in soils, exhibited great potentials in the fertilization and remediation of actual heavy metal-contaminated soils in mining areas. The biochar-induced reduction in soil pH, enhancement of organic matter, surface oxygen-containing functional groups, the abundance of Gammaproteobacteria, and its phosphonate degradation activity were primarily responsible for the solubilization of phosphorus from modified biochar in heavy metal-contaminated soils.

Unlocking the Interfacial Adsorption-Intercalation Pseudocapacitive Storage Limit to Enabling All-Climate, High Energy/Power Density and Durable Zn-Ion Batteries.

Sluggish storage kinetics and insufficient performance are the major challenges that restrict the transition metal dichalcogenides (TMDs) applied for zinc ion storage, especially at the extreme temperature conditions. Herein, a multiscale interface structure-integrated modulation concept was presented, to unlock the omnidirectional storage kinetics-enhanced porous VSe2-x ⋅n H2 O host. Theory research indicated that the co-modulation of H2 O intercalation and selenium vacancy enables enhancing the interfacial zinc ion capture ability and decreasing the zinc ion diffusion barrier. Moreover, an interfacial adsorption-intercalation pseudocapacitive storage mechanism was uncovered. Such cathode displayed remarkable storage performance at the wide temperature range (-40-60 °C) in aqueous and solid electrolytes. In particular, it can retain a high specific capacity of 173 mAh g-1 after 5000 cycles at 10 A g-1 , as well as a high energy density of 290 Wh kg-1 and a power density of 15.8 kW kg-1 at room temperature. Unexpectedly, a remarkably energy density of 465 Wh kg-1 and power density of 21.26 kW kg-1 at 60 °C also can be achieved, as well as 258 Wh kg-1 and 10.8 kW kg-1 at -20 °C. This work realizes a conceptual breakthrough for extending the interfacial storage limit of layered TMDs to construct all-climate high-performance Zn-ion batteries.

Markedly boosted peroxymonosulfate- and periodate-based Fenton-like activities of iron clusters on sulfur/nitrogen codoped carbon: Key roles of a sulfur dopant and compared activation mechanisms.

Highly dispersed iron nanoclusters on carbon (FeNC@C) hold great promise for wastewater purification in Fenton-like reactions. The microenvironment engineering of central Fe atom is promising to boost the activation capacity of FeNC@C, which is however remains a challenge. This study developed a self-sacrificed templating strategy to S, N-codoped carbon supported Fe nanoclusters (FeNC@SNC) activator and find the key role of sulfur heteroatoms in regulating the electron structure of Fe sites and final activation property. Investigations revealed that the FeNC@SNC composite exhibited unusual bifunctional activity in both peroxymonosulfate (PMS)- and periodate (PI)-based Fenton-like reactions. We also offered insights into the differences between the degradation of organics by the FeNC@SNC/PMS and FeNC@SNC/PI systems. Specifically, under identical conditions, the FeNC@SNC/PMS system delivered a higher oxidation capability and stronger resistance to nontarget matrix constituents, but showed more severe Fe leaching than the FeNC@SNC/PI system. Furthermore, while mediated electron-transfer process was identified as the major route for pollutant decomposition in both systems, the high-valent Fe-oxo species [Fe (IV)] was the auxiliary reactive species found only in the FeNC@SNC/PMS system. Based on these findings, our results provide profound insights into the design of active and durable Fe-based activators toward highly efficient Fenton-like reactions.

Safe disposal of hazardous waste incineration fly ash: Stabilization/solidification of heavy metals and removal of soluble salts.

Hazardous waste incineration fly ash (HFA) is considered a hazardous waste owing to the high associated concentrations of heavy metals and soluble salts. Hence, cost effective methods are urgently needed to properly dispose HFA. In this study, geopolymers were prepared by alkali-activation technology to stabilize and solidify heavy metals in HFA. In addition, the effects of three different aluminosilicates (metakaolin, fly ash, and glass powder) on the heavy metal immobilization efficiency were investigated. Because the soluble salt content of HFA is too high for their direct placement in flexible landfill sites and water washing can lead to heavy metal leaching, water-washing experiments were conducted after alkali-activation treatment to remove soluble salts. The results suggest that the concentrations of heavy metals leached from geopolymers can satisfy the Chinese Standard limits (GB18598-2019) when the addition of aluminosilicates exceeds 20 wt%. More than 77% of Cl- and >64% of SO42- in geopolymers could be removed via water-washing treatment. The Zn leaching concentration was maintained below approximately 0.52 ppm. After alkali-activation treatment, the water-washing process could efficiently remove soluble salts while inhibiting heavy metal leaching. Sodium-aluminosilicate-hydrate (N-A-S-H) gel, a product of the geopolymerization process in this study, was demonstrated to act as a protective shell that inhibited heavy metal leaching. Hence, HFA-based geopolymers are considered suitable for disposal in flexible landfills.

CeO2 Nanoparticle-Loaded MnO2 Nanoflowers for Selective Catalytic Reduction of NOx with NH3 at Low Temperatures.

CeO2 nanoparticle-loaded MnO2 nanoflowers, prepared by a hydrothermal method followed by an adsorption-calcination technique, were utilized for selective catalytic reduction (SCR) of NOx with NH3 at low temperatures. The effects of Ce/Mn ratio and thermal calcination temperature on the NH3-SCR activity of the CeO2-MnO2 nanocomposites were studied comprehensively. The as-prepared CeO2-MnO2 catalysts show high NOx reduction efficiency in the temperature range of 150-300 °C, with a complete NOx conversion at 200 °C for the optimal sample. The excellent NH3-SCR performance could be ascribed to high surface area, intimate contact, and strong synergistic interaction between CeO2 nanoparticles and MnO2 nanoflowers of the well-designed composite catalyst. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) characterizations evidence that the SCR reaction on the surface of the CeO2-MnO2 nanocomposites mainly follows the Langmuir-Hinshelwood (L-H) mechanism. Our work provides useful guidance for the development of composite oxide-based low temperature NH3-SCR catalysts.

Effect of ferrous sulfate modified sludge biochar on the mobility, speciation, fractionation and bioaccumulation of vanadium in contaminated soil from a mining area.

In contaminated soil, pristine biochar has poor applicability for immobilizing vanadium (V), which mainly exists as oxyanions in soil. To elucidate the immobilization potential and biotic/abiotic stabilizing mechanisms of a ferrous sulfate (FS)-modified sludge biochar in a V-contaminated soil from a mining area, we investigated the effects of biochar addition on the soil characteristics, growth of alfalfa, leachability, bioavailability, speciation, and fractionation of V, and changes in the microbial community structure and metabolic response. The results showed that the water extractable, acid-soluble (F1), and pentavalent fractions of V in soil decreased by up to 99 %, 95 %, and 55 %, respectively, whereas the reducible and (F2) oxidizable (F3) fractions increased by up to 45 % and 76 %, respectively. After the soil was treated with the FS-modified biochar for 90 d, the V concentration in the roots and shoots of alfalfa (Medicago sativa L.) decreased by up to 81.5 % and 96 %, respectively. The changes in the speciation, fractionation, and efficient immobilization of V in the studied soil were due to the combined effects of the biochar-induced decrease in soil pH, adsorption and precipitation by elevated iron concentrations, reduction and complexation due to an increase in the organic matter content, and microbial reduction by Proteobacteria.

Harvesting mechanical energy for hydrogen generation by piezoelectric metal-organic frameworks.

Piezocatalysis, the process of directly converting mechanical energy into chemical energy, has emerged as a promising alternative strategy for green H2 production. Nevertheless, conventional inorganic piezoelectric materials suffer from limited structural tailorability and small surface area, which greatly impedes their mechanically driven catalytic efficiency. Herein, we design and fabricate a novel UiO-66(Zr)-F4 metal-organic framework (MOF) nanosheet for piezocatalytic water splitting, with the highest H2 evolution rate reaching 178.5 µmol g-1 within 5 h under ultrasonic vibration excitation (110 W, 40 kHz), far exceeding that of the original UiO-66 host. A reduced bandgap from 2.78 to 2.43 eV is achieved after introducing a fluorinated ligand. Piezoresponse force microscopy measurements demonstrate a much stronger piezoelectric response for UiO-66(Zr)-F4, which may result from the polarity of the introduced fluorinated ligand. This work highlights the potential of MOF-based porous piezoelectric nanomaterials in harvesting mechanical energy to drive chemical reactions such as water splitting.

Decarbonising the iron and steel sector for a 2 °C target using inherent waste streams.

The decarbonisation of the iron and steel industry, contributing approximately 8% of current global anthropogenic CO2 emissions, is challenged by the persistently growing global steel demand and limitations of techno-economically feasible options for low-carbon steelmaking. Here we explore the inherent potential of recovering energy and re-using materials from waste streams, high-temperature slag, and re-investing the revenues for carbon capture and storage. In a pathway based on energy recovery and resource recycling of glassy blast furnace slag and crystalline steel slag, we show that a reduction of 28.5 ± 5.7% CO2 emissions to the sectoral 2 °C target requirements in the iron and steel industry could be realized in 2050 under strong decarbonization policy consistent with low warming targets. The technological schemes applied to engineer this high-potential pathway could generate a revenue of US$35 ± 16 and US$40 ± 18 billion globally in 2035 and 2050, respectively. If this revenue is used for carbon capture and storage implementation, equivalent CO2 emission to the 2 °C sectoral target requirements is expected to be reduced before 2050, without any external investments.

Bowknot-like Zr/La bimetallic organic frameworks for enhanced arsenate and phosphate removal: Combined experimental and DFT studies.

Hazardous oxyanions in water bodies are potentially toxic to aquatic life, and the coexistence of multiple anions aggravates the toxicity. Herein, bowknot-like Zr/La bimetallic organic frameworks (Zr/La-BTC) were developed with superior hazardous oxyanion adsorption capacities, i.e., approximately 102 mg/g for arsenate and 159 mg/g for phosphate, respectively. The molar ratio of Zr to La in Zr/La-BTC plays a significant role in the structure and the adsorption efficiencies. Notably, the experiment-derived adsorption capacities of various Zr/La-BTC samples were consistent with their adsorption energies calculated by density-function theory (DFT). Further mechanism analysis revealed that coordination of Zr/La atoms with the target anion groups occurred during adsorption. The positive shift of binding energies in La 3d and Zr 3d XPS spectra and Bader charge analysis unveiled that back-donation interactions dominated the adsorption process. The reliable adsorption selectivity and reusability of 0.1Zr/La-BTC were verified with anion competition experiments and four adsorption-desorption cycles. Overall, this study provides significant insight into the design of high-performance bimetallic organic frameworks for the enhanced removal of hazardous oxyanions from water.

The effect of soil amendment derived from P-enhanced sludge pyrochar on ryegrass growth and soil microbial diversity.

The application of pyrolyzed sewage sludge for land remediation is increasingly being considered as a technical solution to reuse nutrients in the sludge and mitigate the burden of sludge treatment. In this study, the enhancement effect of Ca-based additives, via phosphorus pyrolysis transformation promotion, was systematically investigated for the growth of ryegrass and soil microbial diversity. In the pot experiment, pyrochar-modified methods mainly changed the content of available phosphorus and organic matter in the soil and then affected ryegrass growth. Soils treated with pyrochar prepared with CaO and Ca(OH)2 addition were dominated by phosphorus precipitation-capable Ramlibacter, while metal uptake-accelerating Massilia showed a high prevalence in the group treated with pristine sludge pyrochar. The results showed that the species composition of CaO and Ca(OH)2 treated groups were similar, while the groups treated with Ca3(PO4)2 and pristine sludge pyrochar exhibited similar compositional structures of microbial species. Furthermore, less than 3% of Pb accumulated in the shoots of the Ca-based additive-treated groups, but more than 35% of Pb was distributed in shoots treated with pristine sludge pyrochar. Therefore, the application of P-enhanced pyrochar adjusted by Ca-based additives to soil was beneficial to the growth of ryegrass and preventing metal transfer from soil to ryegrass. Based on both macroscopic and microscopic information, we summarized the promotion effect of P-enhanced pyrochar on ryegrass growth and soil physicochemical properties with the aim of designing a smart pyrochar for waste-to-resource applications.

Metal-organic framework-derived magnetic carbon for efficient decontamination of organic pollutants via periodate activation: Surface atomic structure and mechanistic considerations.

Practical implementation of periodate-based advanced oxidation processes for environmental remediation largely relies on the development of cost-effective and high-performance activators. Surface atomic engineering toward these activators is desirable but it remains challenging to realize improved activation properties. Here, a surface atomic engineering strategy used to obtain a novel hybrid activator, namely cobalt-coordinated nitrogen-doped graphitic carbon nanosheet-enwrapped cobalt nanoparticles (denoted as Co@NC-rGO), from a sandwich-architectured metal-organic framework/graphene oxide composite is reported. This activator exhibits prominent periodate activation properties toward pollutant degradation, surpassing previously reported transition-metal-based activators. Importantly, the activator shows good stability, magnetic reusability, and the potential for application in a complex water matrix. Density functional theory modeling implies that the strong activation capability of Co@NC-rGO is related to its surface atomic structure for which the embedded cobalt nanoparticles with abundant interfacial Co-N coordinations display modified electronic configurations on the active centers and benefit periodate adsorption. Quenching experiments and electrochemical measurements showed that the system could oxidize organics through a dominant nonradical pathway. Additionally, a lower concentration of cobalt leaching was observed for the Co@NC-rGO/periodate system than for its Co@NC-rGO/persulfate counterpart. Our work provides a pathway toward engineering surface atomic structures in hybrid activators for efficient periodate activation.

Regulation of electronic structures of MOF-derived carbon via ligand adjustment for enhanced Fenton-like reactions.

Peroxymonosulfate (PMS)-based Fenton-like reactions are widely used for wastewater remediation. Metal-free carbonaceous activators can avoid the secondary pollution caused by metal leaching but often suffer from insufficient activity due to limited active centers and mass transfer barriers. Here, we prepared a series of heteroatom (N, S, F)-doped, highly porous carbonaceous materials (UC-X, X = N, S, F) by pyrolyzing UiO-66 precursors assembled by various organic ligands. Density functional theory calculations showed that the heteroatoms modulated the electronic structures of the carbon plane. UC-X exhibited significantly enhanced PMS activation capability compared with the undoped counterpart, in the efficiency order of UC-N > UC-S > UC-F > UC. UC-N (calcined at 1000°C) showed the best PMS activation, exceeding that of commonly used carbocatalysts. The prominent performance of UC-N originated from its unique porous structure and homogeneously dispersed graphitic N moieties. Trapping experiments and electron spin resonance showed a nonradical degradation pathway in the UC-N/PMS system, through which organics were oxidized by donating electrons to UC-N/PMS* metastable complexes. This work not only reports a universal way to access high-performance, metal-free PMS activators but also provides insight into the underlying mechanism of the carbon-activated PMS process.

Enhancement of Scattering and Near Field of TiO2-Au Nanohybrids Using a Silver Resonator for Efficient Plasmonic Photocatalysis.

Recently, localized surface plasmon resonances (SPRs) of metallic nanoparticles (NPs) have been widely used to construct plasmonic nanohybrids for heterogeneous photocatalysis. For example, the combination of plasmonic Au NPs and TiO2 provides pure TiO2 visible-light activity. The SPR effect induces an electric field and consequently enhances light scattering and absorption, favoring the transfer of photon energy to hot carriers for catalytic reactions. Numerous approaches have been dedicated to the improvement of SPR absorption in photocatalysts. Here, we have designed a core@shell-satellite nanohybrid catalyst whereby an Ag NP core, as a plasmonic resonator featuring unique dual functions of strong scattering and near-field enhancement, is encapsulated by SiO2 and TiO2 layers in sequence, with Au NPs on the outer surface, Ag@SiO2@TiO2-Au, for efficient plasmonic photocatalysis. By varying the size and number of Ag NP cores, the Au SPR can be tailored over the visible and near-infrared spectral region to reabsorb the scattered photons. In the presence of the Ag core, the incident light is efficiently confined in the reaction suspension by undergoing multiple scattering, thus leading to an increase of the optical path to the photocatalysis. Moreover, using numerical analysis and experimental verifications, we demonstrate that the Ag core also induces a strong near-field enhancement at the Au-TiO2 interface via SPR coupling with Au. Consequently, the activity of the TiO2-Au plasmonic photocatalyst is significantly enhanced, resulting in a high H2 production rate under visible light. Thus, the design of a single structural unit with strong scattering and field enhancement, induced by a plasmonic resonator, is a highly effective strategy to boost photocatalytic activity.

Cobalt-Enhanced Mass Transfer and Catalytic Production of Sulfate Radicals in MOF-Derived CeO2 • Co3 O4 Nanoflowers for Efficient Degradation of Antibiotics.

Antibiotics discharge has been a critical issue as the abuse in clinical disease treatment and aquaculture industry. Advanced oxidation process (AOPs) is regarded as a promising approach to degrade organic pollutants from wastewater, however, the catalysts for AOPs always present low activities, and uncontrollable porosities, thus hindering their further wider applications. In this work, an aliovalent-substitution strategy is employed in metal-organic framework (MOF) precursors assembly, aiming to introduce Co(II/III) into Ce-O clusters which could modify the structure of the clusters, then change the crystallization, enlarge the surface area, and regulate the morphology. The introduction of Co(II/III) also enlarges the pore size for mass transfer and enriches the active sites for the production of sulfate radicals (SO4• - ) in MOF-derived catalysts, leading to excellent performance in antibiotics removal. Significantly, the CeO2 •Co3 O4 nanoflowers could efficiently enhance the generation of sulfate radical SO4• - and promote the norfloxacin removal efficiency to 99% within 20 min. The CeO2 •Co3 O4 nanoflowers also present remarkable universality toward various antibiotics and organic pollutants. The aliovalent-substitution strategy is anticipated to find wide use in the exploration of high-performance MOF-derived catalysts for various applications.

Ce-based heterogeneous catalysts by partial thermal decomposition of Ce-MOFs in activation of peroxymonosulfate for the removal of organic pollutants under visible light.

Metal-organic framework (MOF) derivatives have drawn considerable attention for applications in various fields. In this work, spindle-shaped Ce-TCPPs were assembled by a rapid microwave-assisted hydrothermal method. After thermal treatment at low temperature under a N2 atmosphere, the Ce-TCPPs were partially pyrolyzed and converted to a novel CeO2/N-doped carbon/Ce-TCPP nanocomposite. Compared to completely decomposed materials, these partially decomposed heterogeneous catalysts exhibited significantly higher photocatalytic activation ability toward PMS for the removal of organic pollutants (e.g., rhodamine B, methylene blue, methyl orange, tetracycline and oxytetracycline). For the optimized sample thermal treated at 450 °C, a 100 mL RhB solution (10 mg/L) can be removed within 20 min with the assistance of PMS under visible light. The significantly enhanced activity can be attributed to the effective spatial separation of photogenerated electrons and holes in the formed Z-scheme CeO2/N-doped carbon/Ce-TCPP system. This work may provide useful guidance for the design and fabrication of MOF-derived photocatalytic systems for environmental remediation.

Performance and mechanism of mold-pressing alkali-activated material from MSWI fly ash for its heavy metals solidification.

The safe disposal of municipal solid waste incineration fly ash (MSWIFA) has become the weakest link of the circular economy of MSW due to its hazardous nature. In this study, we focused on the heavy metals solidification of MSWIFA by using alkali-activation technology and introducing a mold-pressing method. The influence of alkaline activator (AA) including alkali concentration and dosage of sodium silicate solution were well designed and studied. MSWIFA before and after alkali-activation, as well as the sample treated by commercial chelating agent (CA), were contrastively studied the performance of heavy metals solidification. The results show that the alkali-activated MSWIFA exhibits superior solidification for heavy metals than the blank control and the CA treated ones. With mold-pressing technology, the alkali-activated MSWIFA shows a core-shell structure, in which a thin layer that is composed of mainly N-A-S-H gel is as the shell and acts as a protective layer to inhibit the leaching of heavy metals. Besides, the introduced mold-pressing technology is beneficial for the improvement of materials strength and the reduction of AA dosage. The optimal AA composition is that the net concentration of NaOH is ∼4 M and sodium silicate dosage is ∼65 wt% in alkaline activator, and the total alkaline activator requirement is only 32 wt% of MSWIFA, yielding 7.9 MPa compressive strength at 10.2 MPa molding pressure. In summary, this work paves a potential new way for safe and recycling use of hazardous MSWIFA, which will be of great significance to environmental sustainability.

Atomically Dispersed Cobalt Sites on Graphene as Efficient Periodate Activators for Selective Organic Pollutant Degradation.

Pollutant degradation via periodate (IO4-)-based advanced oxidation processes (AOPs) provides an economical, energy-efficient way for sustainable pollution control. Although single-atomic metal activation (SMA) can be exploited to optimize the pollution degradation process and understand the associated mechanisms governing IO4--based AOPs, studies on this topic are rare. Herein, we demonstrated the first instance of using SMA for IO4- analysis by employing atomically dispersed Co active sites supported by N-doped graphene (N-rGO-CoSA) activators. N-rGO-CoSA efficiently activated IO4- for organic pollutant degradation over a wide pH range without producing radical species. The IO4- species underwent stoichiometric decomposition to generate the iodate (IO3-) species. Whereas Co2+ and Co3O4 could not drive IO4- activation; the Co-N coordination sites exhibited high activation efficiency. The conductive graphene matrix reduced the contaminants/electron transport distance/resistance for these oxidation reactions and boosted the activation capacity by working in conjunction with metal centers. The N-rGO-CoSA/IO4- system exhibited a substrate-dependent reactivity that was not caused by iodyl (IO3·) radicals. Electrochemical experiments demonstrated that the N-rGO-CoSA/IO4- system decomposed organic pollutants via electron-transfer-mediated nonradical processes, where N-rGO-CoSA/periodate* metastable complexes were the predominant oxidants, thereby opening a new avenue for designing efficient IO4- activators for the selective oxidation of organic pollutants.

Biogas Upgrading via Cyclic CO2 Adsorption: Application of Highly Regenerable PEI@nano-Al2O3 Adsorbents with Anti-Urea Properties.

Solid amine adsorbents are among the most promising CO2 adsorption technologies for biogas upgrading due to their high selectivity toward CO2, low energy consumption, and easy regeneration. However, in most cases, these adsorbents undergo severe chemical inactivation due to urea formation when regenerated under a realistic CO2 atmosphere. Herein, we demonstrated a facile and efficient synthesis route, involving the synthesis of nano-Al2O3 support derived from coal fly ash with a CO2 flow as the precipitant and the preparation of polyethylenimine (PEI)-impregnated Al2O3-supported adsorbent. The optimal 55%PEI@2%Al2O3 adsorbent showed a high CO2 uptake of 139 mg·g-1 owing to the superior pore structure of synthesized nano-Al2O3 support and exhibited stable cyclic stability with a mere 0.29% decay per cycle even under the realistic regenerated CO2 atmosphere. The stabilizing mechanism of PEI@nano-Al2O3 adsorbent was systematically demonstrated, namely, the cross-linking reaction between the amidogen of a PEI molecule and nano-Al2O3 support, owing to the abundant Lewis acid sites of nano-Al2O3. This cross-linking process promoted the conversion of primary amines into secondary amines in the PEI molecule and thus significantly enhanced the cyclic stability of PEI@nano-Al2O3 adsorbents by markedly inhibiting the formation of urea compounds. Therefore, this facile and efficient strategy for PEI@nano-Al2O3 adsorbents with anti-urea properties, which can avoid active amine content dilution from PEI chemical modification, is promising for practical biogas upgrading and various CO2 separation processes.

Enhanced Piezocatalytic Activity of Sr0.5Ba0.5Nb2O6 Nanostructures by Engineering Surface Oxygen Vacancies and Self-Generated Heterojunctions.

Piezocatalysis provides a promising strategy for directly converting weak mechanical energy into chemical energy. In this work, we report a simple one-step hydrogen reduction route for the simultaneous generation of surface defects and heterojunctions in Sr0.5Ba0.5Nb2O6 nanorods fabricated by a molten salt synthesis method. The as-fabricated Sr0.5Ba0.5Nb2O6/Sr2Nb2O7 nanocomposites with controllable oxygen vacancies exhibited excellent piezocatalytic activity under ultrasonic vibration, with an about 7 times enhancement of the rate constant (k = 0.0395 min-1) for rhodamine B degradation and an about 10 times enhancement of the water-splitting efficiency for hydrogen generation (109.4 µmol g-1 h-1) for the optimized sample (H2 annealed at 500 °C) compared to pristine Sr0.5Ba0.5Nb2O6 nanorods. This work demonstrates the essential role of a well-modulated oxygen vacancy concentration in the piezocatalytic activity and provides an inspiring guide for designing self-generated heterojunction piezocatalysts.