Unveiling Mechanistic Insight into Accelerating Oxygen Molecule Activation by Oxygen Defects in Co3O4-x/g-C3N4 p-n Heterojunction for Efficient Photo-Assisted Uranium Extraction from Seawater.

Photo-assisted uranium extraction from seawater (UES) is regarded as an efficient technique for uranium resource recovery, yet it currently faces many challenges, such as issues like biofouling resistance, low charge separation efficiency, slow carrier transfer, and a lack of active sites. Based on addressing the above challenges, a novel oxygen-deficient Co3O4-x/g-C3N4 p-n heterojunction is developed for efficient photo-assisted uranium extraction from seawater. Relying on the defect-coupling heterojunction synergistic effect, the redistribution of molecular charge density formed the built-in electric field as revealed by DFT calculations, significantly enhancing the separation efficiency of carriers and accelerating their migration rate. Notably, oxygen vacancies served as capture sites for oxygen, effectively promoting the generation of reactive oxygen species (ROS), thereby significantly improving the photo-assisted uranium extraction performance and antibacterial activity. Thus, under simulated sunlight irradiation with no sacrificial reagent added, Co3O4-x/g-C3N4 extracted a high uranium extraction amount of 1.08 mg g-1 from 25 L of natural seawater after 7 days, which is superior to most reported carbon nitride-based photocatalysts. This study elaborates on the important role of surface defects and inerface engineering strategies in enhancing photocatalytic performance, providing a new approach to the development and design of uranium extraction material from seawater.

Enhancing Commercially Iron Powder Electron Transport by Surface Biosulfuration to Achieve Uranium Extraction from Uranium Ore Wastewater.

The zero-valent iron (ZVI) has attracted increasing attention due to the enhanced reactivity of ZVI to uranium wastewater. However, ZVI practical application is hampered due to its susceptibility to oxidation and the formation of passivation layers during storage and in situ restoration. To address these issues, we used a biosulfuration approach to modify ZVI for application in uranium ore wastewater treatment. A series of physicochemical characterization tools and photoelectronic analyses showed that BS-ZVI considerably increased carrier separation efficiency and visible light absorption capacity, resulting in a significant photoassisted enhancement effect on uranium extraction. Accordingly, the uranium removal efficiency of BS-ZVI reached 91% within 60 min, and its maximum adsorption capacity was 336.3 mg/g. By analyzing the mechanism, the improved U(VI) removal performance was mostly responsible on the dissolution of the passivation layer on the surface of ZVI, the generation of Fe(II) and FeS, and the important role of Shewanella putrefaciens extracellular polymers (EPS). Overall, the BS-ZVI biohybrid merges with the high activity of ZVI, bio-FeS, and self-regeneration ability of bacteria, expanding a promising new approach for sustainable treatment of uranium mine wastewater.

Investigation of Combustion and NO/SO2 Emission Characteristics during the Co-Combustion Process of Torrefied Biomass and Lignite.

This paper investigates the combustion characteristics and pollutant emission patterns of the mixed combustion of lignite (L) and torrefied pine wood (TPW) under different blending ratios. Isothermal combustion experiments were conducted in a fixed bed reaction system at 800 °C, and pollutant emission concentrations were measured using a flue gas analyzer. Using scanning electron microscopy (SEM) and BET (nitrogen adsorption) experiments, it was found that torrefied pine wood (TPW) has a larger specific surface area and a more developed pore structure, which can facilitate more complete combustion of the sample. The results of the non-isothermal thermogravimetric analysis show that with the TPW blending ratio increase, the entire combustion process advances, and the ignition temperature, maximum peak temperature, and burnout temperature all show a decreasing trend. The kinetic equations of the combustion reaction process of mixed gas were calculated by Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) kinetic equations. The results show that the blending of TPW reduces the activation energy of the combustion reaction of the mixed fuel. When the TPW blending ratio is 80%, the activation energy values of the mixed fuel are the lowest at 111.32 kJ/mol and 104.87 kJ/mol. The abundant alkali metal ions and porous structure in TPW reduce the conversion rates of N and S elements in the fuel to NO and SO2, thus reducing the pollutant emissions from the mixed fuel.

Thermal Air Oxidation-Mediated Synchronous Coordination and Carbonation of Lanthanum on Biochar toward Phosphorus Adsorption from Wastewater.

Biochar has attracted increasing attention as the sustainable and structure-tunable carrier for lanthanum (La) species for diverse applications. Carbonated La species possesses a higher biocompatibility and a lower leaching potential than other commonly used La species, while less attention is paid on the application of carbonated La in phosphorus (P) adsorption. Herein, thermal air oxidation (TAO) was applied as a novel strategy for synchronously tuning the coordination environment and chemical species of La on biochar surface. The results demonstrated that TAO induced the coordination of La with oxidation-generated oxygenated functional groups (OFGs) and carbonation of La species by the oxidation-generated CO2 on the biochar surface. The batch adsorption results showed that the Qm of resultant biochar remarkably increased from 68.92 to 132.49 mg/g at 1 g/L dosage. It also showed a robust adsorption stability in pH 2-6, a strong resistance to the co-existing Cl-, SO42-, NO3-, CO32-, or HCO3-, a stable adsorption recyclability, and an ultralow La leaching potential. The P adsorption was dominated by ligand exchange-induced inner-sphere complexation. In practical swine wastewater, the resultant biochar composite (1 g/L) removed 99.87% of P from 92.3 to 0.12 mg/L at a practical pH of 7.12. The density functional theory calculation further revealed the significant role of the binding of carbonated La by the biochar surface OFGs in reducing the P adsorption energies, indicating the synergism between the oxygenated biochar carrier and the carbonated La in P adsorption. Finally, this study provided a novel route to synchronously tune the coordination environment and chemical species of La on biochar via a facile TAO process for high-efficient P adsorption from wastewater.

Amplified Single-Atom U-O Interfacial Effect Originated from U 5f-O 2p Hybridization over UOx/GO for Enhanced Nitrogen Reduction Reaction.

Uranium-based catalysts have been regarded as promising candidates for N2 fixation owing to the low-valent uranium metal active sites possessing the ability to enhance the electron back-donating to the π* antibonding orbitals of N2 for N≡N dissociation. Herein, we report a directional half-wave rectified alternating current electrochemical method to confine oxygen-rich uranium precursors over ultrathin 2D GO nanosheets. The as-prepared uranium catalysts exhibit a considerable Faradaic efficiency of 12.7% for NH3 and the NH3 yield rate of 18.7 µg h-1 mg-1 for N2 electroreduction. Operando XAS and isotope-labeling FTIR further unravel the preferred nitrogen adsorption reaction intermediate N-(2Oax-1 U-4Oeq) and confirm the key *N2Hy intermediate species derived from the fed N2 gas. Theoretical simulations demonstrate that the U-O atomic interface originated from U 5f-O 2p orbital hybridization can accumulate partial charge from GO, which can facilitate the N≡N dissociation and lower the thermodynamic energy barrier of the first hydrogenation step.

Unveiling the Critical Role of Surface Hydroxyl Groups for Electro-Assisted Uranium Extraction from Wastewater.

The electro-driven extraction of uranium from fluorine-containing uranium wastewater is anticipated to address the challenge of separating fluoro-uranium complexes in conventional technologies. Herein, we developed hydroxy-rich cobalt-based oxides (CoOx) for electro-assisted uranium extraction from fluorine-containing wastewater. Relying on theoretical calculations and other spectral measurements, the hydroxy-rich CoOx nanosheets can enhance the affinity for uranium due to the existence of a substantial quantity of hydroxyl groups. Accordingly, the CoOx nanosheets exhibit outstanding U(VI) removal efficiency in the presence of fluorine ions. Through the utilization of X-ray absorption fine structure (XAFS), we confirm that hydroxy-rich CoOx nanosheets capture free uranyl ions to form a sturdy 2Oax-1U-3Oeq configuration, which can be achieved through electro-driven fluorine-uranium separation. Notably, for the first time, the whole reaction process of uranium species on the CoOx surface from the initial uranium single atom growth to uranium oxide nanosheets is monitored by aberration-corrected transmission electron microscopes (AC-TEM). This work provides a paradigm for the advancement of novel functional materials as electrocatalysts for uranium extraction, as well as a new approach for studying the evolution mechanism of uranium species.

A critical review on the development of lanthanum-engineered biochar for environmental applications.

Biochar and lanthanum (La) have been widely used in environment. However, there is a lack of knowledge and perspective on the development of La-engineered biochar (LEB) for environmental applications. This review shows that LEBs with a variety of La species via pre-/post-doping routes are developed for environmental applications. Specifically, precipitation, gelation, and calcination are the common sub-processes involved in the pre-/post-doping of La on the resultant LEB. The dominant La species for LEBs is La(OH)3, which is formed through precipitation of La ions with various bases. Various La carbonates, e.g., LaOHCO3, La2(CO3)3, La2CO5, and NaLa(CO3)2, are also involved in the preparation of LEBs. The LEBs are high-efficient in the adsorption of phosphate, arsenic, antimonate and fluoride ions, attributed to the strong affinity of La to oxyanions and Lewis hard base. Lanthanum is also favorable for co-doping with transition metal species to further enhance the performances in adsorption or catalysis. This review also analyzes the prospects and future challenges for the preparation and application of LEBs in environment. Finally, this review is beneficial to inspire new breakthroughs on the preparation and environmental application of LEBs.

Effects of Torrefaction Pretreatment on the Structural Features and Combustion Characteristics of Biomass-Based Fuel.

Wheat straw, a typical agricultural solid waste, was employed to clarify the effects of torrefaction on the structural features and combustion reactivity of biomass. Two typical torrefaction temperatures (543 K and 573 K), four atmospheres (argon, 6 vol.% O2, dry flue gas and raw flue gas) were selected. The elemental distribution, compositional variation, surface physicochemical structure and combustion reactivity of each sample were identified using elemental analysis, XPS, N2 adsorption, TGA and FOW methods. Oxidative torrefaction tended to optimize the fuel quality of biomass effectively, and the enhancement of torrefaction severity improved the fuel quality of wheat straw. The O2, CO2 and H2O in flue gas could synergistically enhance the desorption of hydrophilic structures during oxidative torrefaction process, especially at high temperatures. Meanwhile, the variations in microstructure of wheat straw promoted the conversion of N-A into edge nitrogen structures (N-5 and N-6), especially N-5, which is a precursor of HCN. Additionally, mild surface oxidation tended to promote the generation of some new oxygen-containing functionalities with high reactivity on the surface of wheat straw particles after undergoing oxidative torrefaction pretreatment. Due to the removal of hemicellulose and cellulose from wheat straw particles and the generation of new functional groups on the particle surfaces, the ignition temperature of each torrefied sample expressed an increasing tendency, while the Ea clearly decreased. According to the results obtained from this research, it could be concluded that torrefaction conducted in a raw flue gas atmosphere at 573 K would improve the fuel quality and reactivity of wheat straw most significantly.

Synthesis of Uranium Single Atom from Radioactive Wastewater for Enhanced Water Dissociation and Hydrogen Evolution.

As a common nuclide in radioactive wastewater, uranium (U) is generally treated by landfill, which induces the massive abandonment of uranium resources. In this work, a pulse voltammetry method for the synthesis of U single atoms on MoS2 (U/MoS2 ) nanosheets from radioactive wastewater for the electrocatalytic alkaline hydrogen evolution reaction (HER) is reported. The mass loading of U single atoms is facilely controlled with high selectivity for coexisting ions in radioactive wastewater. In the electrolyte of 1 m of KOH, U/MoS2 nanosheets with 5.2% of U single atoms exhibit relatively low overpotentials of 72 mV at 10 mA cm-2 . The mechanistic study reveals that the HER on U/MoS2 includes the water dissociation on U single atoms to form OH* and H transfer from OH* to adjacent S-edge atoms. This procedure exhibits decreased activation energy for transition state in water dissociation and optimized Gibbs free energy for H* adsorption.

MXene-Derived 3D Defect-Rich TiO2@Reduced Graphene Oxide Aerogel with Ultrafast Carrier Separation for Photo-Assisted Uranium Extraction: A Combined Batch, X-ray Absorption Spectroscopy, and Density Functional Theory Calculations.

Encapsulation of nano-semiconductor materials in three-dimensional (3D) adsorbents to build a typical semiconductor-adsorbent heterostructure is a forward-looking strategy for photo-assisted uranium extraction. Here, we develop 3D MXene-derived TiO2(M)@reduced graphene oxide (RGO) aerogel for photo-assisted uranium extraction. Theoretical simulations demonstrate that oxygen vacancies on TiO2(M) tailor the energy level structure and enhance the electron accumulation at gap states of TiO2(M), thereby further realizing the spatial separation efficiency of electron-hole pairs by the Schottky junction. By virtue of the in situ X-ray photoelectron spectroscopy spectrum, we identify that photogenerated electrons generated over TiO2(M) were transferred to graphene oxide aerogel by the Schottky junction. Accordingly, TiO2 (M)@RGO aerogel presents a considerable removal efficiency for U(VI) with a removal ratio of 95.7%. Relying on the X-ray absorption spectroscopy technique, we distinguish the evolution of 2H2O-2Oax-U-5Oeq into H2O-2Oax-U-3Oeq from dark to light conditions, further confirming the reduction of high-valent uranium. This strategy may open a paradigm for developing novel heterojunctions as photocatalysts for selective U(VI) extraction.

Connection of Ru nanoparticles with rich defects enables the enhanced electrochemical reduction of nitrogen.

The electrochemical reduction of N2 into NH3 under ambient conditions is an attractive topic in the chemical industry, but the chemical inertness of N2 and the competing hydrogen evolution reaction hamper the activity and selectivity of this reaction. Herein, we connected Ru nanocrystals through a facile annealing process, which constructed intraparticle grain boundaries and stacking faults in the connection regions to enhance the N2 reduction reaction. The connected Ru nanoparticles exhibited an enhanced yield rate and faradaic efficiency for NH3 production. At -0.1 V versus RHE, the connected Ru nanoparticles exhibited a maximum yield rate of 29.3 µg cm-2 h-1 (148.0 µg mgcat-1 h-1) for NH3 production with a faradaic efficiency of 7.0%. Mechanistic study revealed that the promotion of the electrochemical reduction of N2 over connected Ru nanoparticles could be attributed to the decreased work function and facilitated electron transfer, which originated from the abundant defects in the connection region.

Preparation of novel porous Al2O3-SiO2nanocomposites via solution-freeze-drying-calcination method for the efficient removal of uranium in solution.

In this work, the efficient extraction of uranium in solution using Al2O3-SiO2-T was reported. Kinetics and isotherm models indicated that the removal process of uranium on Al2O3-SiO2-T accorded with pseudo-second-order kinetic model and Langmuir isotherm model, which showed that the adsorption process was a uniform mono-layer chemical behavior. The maximum adsorption capacity of Al2O3-SiO2-T reached 738.7 mg g-1, which was higher than AlNaO6Si2(349.8 mg g-1) and Al2O3-SiO2-NT (453.1 mg g-1), indicating that the addition of template could effectively improve the adsorption performance of Al2O3-SiO2to uranium. Even after five cycles of adsorption-desorption, the removal percentage of uranium on Al2O3-SiO2-T remained 96%. Besides, the extraction efficiency of uranium on Al2O3-SiO2-T was 72.5% in simulated seawater, which suggested that the Al2O3-SiO2-T was expected to be used for uranium extraction from seawater. Further, the interaction mechanism between Al2O3-SiO2-T and uranium species was studied. The results showed that the electrostatic interaction and complexation played key roles in the adsorption process of Al2O3-SiO2-T to uranium.

Boosting the Loading of Metal Single Atoms via a Bioconcentration Strategy.

Increasing the mass loading of transition metal single atoms coordinated with nitrogen in carbon-based materials (M-N-C) is still challenging. Herein, inspired by the bioconcentration effect in the living body, a biochemistry strategy for the synthesis of Fe-N-C single atoms is demonstrated. Through introducing ferrous glycinate into the growth of fungus, the Fe atoms are bioconcentrated in hyphae. The highly dispersed Fe-N-C single atoms in hyphae-derived carbon fibers (labeled as Fe-N-C SA/HCF) are prepared by the pyrolysis of Fe-riched hyphae. In the bioconcentration process, the uptake of Fe ions by hyphae promotes the secretion of glutathione and ferritin, which provides additional coordination sites for Fe ions. Accordingly, the mass content of Fe in bioconcentrated Fe-N-C SA/HCF reaches 4.8%, which is 5.3 times larger than that of the sample prepared by the conventional pyrolysis process. The present bioconcentration strategy is further extended to the preparation of Co, Ni, and Mn single atoms. Owing to the high content of Fe-N-C single atoms, Fe-N-C SA/HCF shows the onset potential (Eonset ) of 0.931 V versus reversible hydrogen electrode (RHE) and half-wave potential (E1/2 ) of 0.802 V versus RHE in oxygen reduction reaction measurements, which is comparable to the commercial Pt/C catalysts.

Manganese dioxide-loaded mesoporous SBA-15 silica composites for effective removal of strontium from aqueous solution.

Manganese dioxide-loaded mesoporous SBA-15 silica (MnO2/SBA-15) composites with short pore length were aprepared for the first time by simply immersing SBA-15 into a KMnO4 and MnCl2 mixed solution. Adsorption of Sr2+ from aqueous solution by using the MnO2/SBA-15 was investigated by varying the pH, contact time, initial Sr2+ concentration, MnO2 content and temperature. The adsorption process was rapid during the first 40 min and reached equilibrium in 120 min. The Sr2+ adsorption capacity increased with increasing pH, MnO2 content and temperature, and the adsorption capacity of SBA-15 was significantly improved by the loading of MnO2. Moreover, the experimental adsorption data were analyzed using different equilibrium isotherm, kinetic and thermodynamic models. The results showed that the isotherm data were well-described by the Langmuir model. The maximum Sr2+ adsorption capacity was determined to be 75.1 mg g-1 at 283 K based on the Langmuir model. The analyzed kinetic data indicated that the Sr2+ adsorption process was well fitted by the pseudo-second order model. Furthermore, the thermodynamic parameters of adsorption were also determined from the equilibrium constant values obtained at different temperatures. The results suggested that the adsorption process was spontaneous and endothermic, and the overall mechanism of Sr2+ adsorption was a combination of physical and chemical processes.

Hybridization of Defective Tin Disulfide Nanosheets and Silver Nanowires Enables Efficient Electrochemical Reduction of CO2 into Formate and Syngas.

Integrating the defect engineering and conductivity promotion represents a promising way to improve the performance of CO2 electrochemical reduction. Herein, the hybridized composite of defective SnS2 nanosheets and Ag nanowires is developed as an efficient catalyst for the production of formate and syngas toward CO2 electrochemical reduction. The Schottky barrier in Ag-SnS2 hybrid nanosheets is negligible due to the similar Fermi level of SnS2 nanosheets and Ag nanowires. Accordingly, the free electrons of Ag nanowires participate in the electronic transport of SnS2 nanosheets, and thus give rise to a 5.5-fold larger carrier density of Ag-SnS2 hybrid nanosheets than that of SnS2 nanosheets. In CO2 electrochemical reduction, the Ag-SnS2 hybrid nanosheets display 38.8 mA cm-2 of geometrical current density at -1.0 V vs reversible hydrogen electrode, including 23.3 mA cm-2 for formate and 15.5 mA cm-2 for syngas with the CO/H2 ratio of 1:1. A mechanistic study reveals that the abundant defect sites and carrier density not only promote the conductivity of the electrocatalyst, but also increase the binding strength for CO2 , which account for the efficient CO2 reduction.

Biomass-derived composite aerogels with novel structure for removal/recovery of uranium from simulated radioactive wastewater.

With the development of nuclear energy, the removal/recovery of radionuclides has attracted increasing attention. Here, an ultra-light, super-elastic, konjac glucomannan/graphene oxide composite aerogel (KGCA) as a high performance adsorbent for radionuclide removal/recovery was fabricated by a three-step process of freeze-casting, freeze-drying, and carbonization. The as-prepared bionic structured KGCA showed ultralow density, high specific surface area, desirable super-elasticity, and abundant oxygen-containing functional groups. Batch adsorption results demonstrated the maximum adsorption capacity of uranium (U(VI)) on KGCA is as high as 513.4 mg g-1, far exceeding other biomass carbon aerogels. Furthermore, KGCA showed good radiation stability, selective adsorption of U(VI), and high recycling performance. The KGCA also showed good adsorption properties even under simulated seawater or high salt concentration. Thus, these ultra-light and super-elastic biomass-derived composite aerogels could have a wide range of applications for nuclear wastewater treatment in the future.

Bio-inspired and assembled fungal hyphae/carbon nanotubes aerogel for water-oil separation.

Carbon nanotube (CNT)-based materials have attracted tremendous interest for their high performance in oil separation. However, the preparation of CNT based materials always require harmful and expensive chemicals. Here, a biological assembly route was applied to assemble CNTs onto a fungal hyphae (FH) to produce FH/CNTs composites, followed by pyrolysis to obtain a hydrophobic CNT based aerogel for oil separation, which is a more environmentally friendly process. The as-prepared FH/CNTs-800 aerogel (pyrolyzed at 800 °C) showed hydrophobicity with a water contact angle of 143° and high specific surface area (1041.2 m2 g-1). The oil absorption results showed that the as-prepared FH/CNTs aerogels could absorb a wide range of oils with high absorption capacities ranging from 48 to 138 times their own weight. Furthermore, the oil-loaded aerogel was recycled through burning with little reduction in the oil absorption capacity. In addition, FH/CNTs-800 provided a high specific capacitance of 232 F g-1 at 1 A g-1 and maintained a capacity retention of 70.62% at 20 A g-1. Therefore, this study offers a simple, low-cost and environmentally friendly bioassembly route for large-scale assembly of CNTs into macroscopic 3D hydrophobic aerogels for highly efficient water-oil separation.

One step hydrothermal synthesis of 3D CoS2@MoS2-NG for high performance supercapacitors.

A three-dimensional (3D) MoS2 coated CoS2-nitrogen doped graphene (NG) (CoS2@MoS2-NG) hybrid has been synthesized by a one step hydrothermal method as supercapacitor (SC) electrode material for the first time. Such a composite consists of NG embedded with stacked CoS2@MoS2 sheets. With a 3D skeleton, it prevents the agglomeration of CoS2@MoS2 nanoparticles, resulting in sound conductivity, rich porous structures and a large surface area. The results indicate that CoS2@MoS2-NG has higher specific capacitance (198 F g-1 at 1 A g-1), better rate performance (with about 56.57% from 1 to 16 A g-1) and an improved cycle stability (with about 96.97% after 1000 cycles). It is an ideal candidate for SC electrode materials.

Rheological Properties of Graphene Oxide/Konjac Glucomannan Sol.

We have demonstrated there is a significant intermolecular interaction between GO and KGM that results from hydrogen bonding and physical cross-linking by studying the rheological properties of a graphene oxide/konjac glucomannan (GO/KGM) solution. When the addition of GO was 5%, the storage modulus (G') and loss modulus (G″) were only improved by 0.25%. However, G' and G″ were improved by approximately 90% and 73.4%, respectively, when the GO content was increased to 7.5%. The moduli also displayed a relationship between the power function and concentration. Furthermore, the formation mechanism of GO/KGM was investigated by Raman, FT-IR, XPS and SEM. The results suggested that hydrogen bonding and physical crosslinking are generated from the abundant carboxy and hydroxyl groups of graphene oxide and the hydroxyl groups of konjac glucomannan.

Bioinspired, Ultrastrong, Highly Biocompatible, and Bioactive Natural Polymer/Graphene Oxide Nanocomposite Films.

Tough and biocompatible nanocomposite films: A new type of bioinspired ultrastrong, highly biocompatible, and bioactive konjac glucomannan (KGM)/graphene oxide (GO) nanocomposite film is fabricated on a large scale by a simple solution-casting method. Such KGM-GO composite films exhibit much enhanced mechanical properties under the strong hydrogen-bonding interactions, showing great potential in the fields of tissue engineering and food package.