Biomass-derived N, P-codoped Templated Biocarbon@2D-MoS2/Polypyrrole Based Hybrids for U(VI) Electrosorption

Shehzad H., Chen J., Shuang M.T., Liu Z., Farooqi Z.H., Sharif A., Ahmed E., Zhou L., Irfan A., Begum R., Iqbal F., Ouyang J.

In this work, efficient and selective carbonaceous electrode materials based on hierarchical mesoporous functionalized carbon nanotubes, 2D-MoS2 nansheets electrodeposited with variable content of polypyrrole (PPy) were prepared. The simple etching reaction between HNO3 and carbon nanotubes did not only modify the surface but also improved its hydrophilicity. The annealing of carbon nanotubes and electrodeposition of polypyrrole increased the mesopore volume to total volume ratio (Vmeso/Vt) from 0.42 to 0.86. The composite materials were characterized wisely using different characterization techniques and employed for efficient U6+ electro-assisted sorption through capacitive deionization. Electrode material with polypyrrole content (0.3 M) exhibited good specific capacitance Csp (100.2 F/g), improved Vmeso (0.61 cm3/g), superb Vmeso/Vt ratio (0.86) and large specific surface area SBET (149.7 m2/g). The stated electrode showed fast sorption kinetics (teq=30 min), admirable selectivity and exhibited the experimental sorption capacity of 274.50 mg/g at -0.90 V. Electrochemical impendence spectroscopic study revealed that the resulting material exhibited relatively small charge transfer resistance (1.19 Ωcm2), minute electrolytic resistance (0.91 Ωcm2) and large double layer constant phase element (0.0368 S sn/ cm2). These significant characteristics promoted U6+ ions diffusion inside the hierarchical porous electrode surface for better performance of electrosorption process. This new class of hierarchical mesoporous composite electrodes may be used as potential supercapacitor materials not only for removal of uranium but also for other potent desalination applications.

Shehzad H., Chen J., Shuang M.T., Liu Z., Zhou L., Wang Y., Farooqi Z.H., Ahmed E., Sharif A., Irfan A., Ouyang J., Feng Z.

In this work, a templated N/P co-doped hierarchical porous biocarbon was prepared through the carbonization of sugar at high temperature (700 °C). Then, this porous biocarbon was in-situ functionalized with molybdenum disulfide nanosheets through a hydrothermal treatment reaction to get the composite, SC/MoS2. Later, SC/MoS2 on a nickel foam substrate was electrodeposited with different concentrations of polypyrrole, a conducting polymer, at −0.9 V. The prepared composite electrodes (SC/MoS2/PPy) were characterized thoroughly using FTIR, XRD, BET, and SEM. The orderly developed mesoporosity and N, P doping inside the porous carbon network was found to be highly conducive for the U(VI) electrosorption accomplished through capacitive deionization (CDI). The composites had remarkable specific capacitance (95.4 F/g), a large specific surface area (174.4–273.6 m2/g), improved mesopore volume (0.58 cm3/g) and excellent Vm/Vt ratio (0.80). SC/MoS2/PPy-2, among other composites, revealed fast electrosorption kinetics and excellent selectivity with a maximum sorption capacity of 300.66 ± 8.02 mg/g at −0.9 V. The SC/MoS2/PPy-2 retained relatively small charge transfer resistance Rct (1.22 Ω cm2), minute electrolytic resistance Rs (0.77 cm2), and a large double layer constant phase element qdl (0.0369 S sn/cm2) which makes it suitable for U(VI) ion diffusion and fast electron transfer during CDI performance. The composite electrode materials offer novel and potent desalination applications, specifically in uranium extraction from aqueous media.

Tang Z., Zeng H., Zhang K., Li Z., Yan W., Wang H., Yue H.

As promising electrode materials, transition metal selenides show great potential applications in energy storage devices. Here self-supported Ni0.85Se nanowires with Se vacancies (denoted as NiMoSe) on NF were synthesized by a solvothermal route and post-selenization using NiMoO4 as the precursor, which electrochemical performance was optimized by adjusting the Se feeding during the selenization. Whereas, the supercapacitive properties of the optimal NiMoSe need to be further improved for achieving higher rate capability and electrochemical stability. So, an efficient strategy was proposed to improve the electrochemical performance through welding the NiAl hydrotalcite (NiAl-LDH) nanosheets on the NiMoSe surface to construct a novel 1D-2D-3D hierarchical core-shell material (NiMoSe@LDH), which provided more active sites and ensured a high rate-capability and long-term stability. Benefiting from the synergistic effect between NiMoSe nanowires core and NiAl-LDH shell, the NiMoSe@LDH delivered a favorable specific charge of 1381.1 C g−1 at 1 A g−1 with impressive rate capability and cyclic stability (85.2% retention after 5 000 cycles at 5 A g−1). Furthermore, the as-assembled NiMoSe@LDH//AC afforded a high energy density of 50.2 Wh kg–1 at a power density of 800 W kg–1 and good cycling stability (86.5% retention at 5 A g−1 after 10 000 cycles) compared to the NiMoSe//AC (36.3 Wh kg–1 at 800 W kg–1, 77.3% retention). This work provides a new strategy for the design of high-performance transition metal selenides in next-generation energy storage devices.

Yan C., Liao Y., Shen C., Weng X., Lei R., Liao C., Zhou Y., Wang M.

Recently, capacitive deionization has become a promising approach for uranium extraction owing to its energy-efficiency and environmental benign. However, the adsorbed charged uranium (VI) (U(VI)) would repulse the incoming U(VI) ions, and might re-enter into solution, vastly impeding the improvement of electro-adsorption performance. Reducing the adsorbed U(VI) ions into U(IV) precipitation is an ideal way to address above issues. Here, a coupling approach of photocatalytic reduction and electro-adsorption (PEA) was proposed. An asymmetric electrode configuration, composed of phosphate functionalized graphene (GP) cathode and graphene/TiO2 nanocomposite (GT) anode was rationally designed, and originally proved its enhanced U(VI) extraction via the PEA method. The asymmetric electrode device enables the fast transport of photo-electron and the rapidly directed migration of U(VI) ion to the GP cathode. More importantly, it combines three synthetic mechanisms of complexation, electro-adsorption, and photocatalytic reduction to extract U(VI) ions. As a consequence, the as-designed PEA method shows a higher removal rate of 91.3% in comparison with conventional photocatalytic reduction (PA) and electro-adsorption (EA) methods. Meanwhile, its kinetics rate is 225% and 50% faster than PA and EA methods. Furthermore, an enhanced reduction efficiency of U(VI) to U(IV), good selectivity as well as reusability for PEA method were also obtained. The results provide a potential approach to combine multiple mechanisms for efficient U(VI) extraction from aqueous solution by purposeful design of asymmetric electrodes.

Cao R., Zhang J., Wang D., Sun F., Li N., Li J.

It has been proved that capacitive deionization (CDI) technology possesses a significant potential for uranium capture. However, the CDI performance has been limited by the complex preparation process of the electrodes and the poor adhesion between electrode materials and collectors. Here we combine the laser-induced graphene (LIG) and the electrodeposition to develop the LIG/cobalt sulfide (LIG/Co4S3) electrodes with good adsorption performance. The obtained LIG6/Co4S3-15 electrode has both electrical double layers (EDLs) and pseudocapacitance properties, with a specific capacitance of 24.27 F g−1, which is 1.82 times higher than that of LIG6 (13.36 F g−1). The LIG6/Co4S3-15 electrode exhibited a high adsorption capacity of 2702.79 mg g−1. The advantages of this electrode preparation method are mainly attributed to the synergistic effect of the following aspects: (i) simplified graphene preparation by avoiding wet chemistry and post-treatment steps; (ii) simplified tedious electrode preparation such as electrode slurry distribution and sheet coating; (iii) the three-dimensional structure of LIG provides not only the conductive network but also the site for Co4S3 nanosheet growth, thus avoiding nanosheet aggregation. The abundant pore structure of the conductive graphene substrate and the layered structure of the Co4S3 nanosheets enable the LIG6/Co4S3-15 electrode with fast charge/ion transport, high hydrophilicity and superior pseudocapacitance, allowing uranyl (UO22+) to be firstly electrosorbed, then physicochemically adsorbed, and finally electrocatalytically reduced/deposited onto the electrode. This study will offer a simple and environmentally friendly method for the synthesis of electrodes and provide a reference for the design of efficient electroadsorption materials.

Yan W., Zeng H., Zhang K., Long Y., Wang M.

Ternary transition metal sulfides have attracted much attention due to their superior electrochemical properties. Nevertheless, it is difficult to commercialize sulfides due to their intrinsic properties such as dull reaction kinetics and an insufficient number of active sites. Herein, a self-supporting porous NiCoMnS sulfide (NiCoMnS/NF) arrayed on nickel foam (NF) with 3D honeycomb-like structure was designed and prepared via a hydrothermal and post-sulfidation process. It was found that the 3D hierarchically network architecture, constructed by nanosheets with abundant cavities, endowed NiCoMnS/NF with a high specific area and rich ion/electron-transport channels, which facilitated ion/electron transfer and Faradaic reaction kinetic. The optimal NiCoMnS/NF exhibited a markedly improved electrochemical performance due to the merits of complementary multi-composition and unique 3D network structure with multi-level "superhighways". Furthermore, the NiCoMnS//AC device fabricated with NiCoMnS/NF cathode and activated carbon (AC) anode delivered an excellent specific charge and exceptional energy density. This work offers a reference for designing the structure of electrode materials.

Zhu K., Xian H., Peng L., Wang S., Chen C., Liu J.

A molybdenum disulfide/biochar (MoS2/BC) composite was synthesised by a facile hydrothermal process and used for the adsorption of U(VI) from aqueous solution through batch experiments. Results showed that MoS2/BC exhibit a saturated adsorption capacity of 451.3 mg/g at pH = 5, t = 60 min, T = 298 K, M/V = 0.02 g/L, CU(VI) = 10 mg/L, which was higher than that of MoS2 and biochar. The process of MoS2/BC for U(VI) adsorption was better simulated via the pseudo-second-order kinetic model (R2 = 0.999) and Langmuir isotherm model (R2 = 0.999). The adsorption mechanism of U(VI) includes chemical adsorption, electrostatic attraction, surface complexation of oxygen-containing functional groups, cation-π bond and coordination of S group. After five adsorption–desorption experiments, the elimination rate remained above 80%.

Liu Q., Wang N., Xie B., Xiao D.

As an indispensable element in the field of nuclear energy, uranium (U(VI)) is widely concerned because it is abundant and easy to obtain from seawater. Herein, we report a promising dual-template strategy to prepare heteroatom-doped carbon materials with hierarchical micro−/meso−/macroporous from low-cost biomass precursors. The carbon materials with hierarchical porosity nitrogen/oxygen are synthesized through freeze-drying, high-temperature thermal treatment and subsequent HF etching treatment by in-situ growth of SiO2 on the precursor with ethyl silicate as silicon source and introduction of ZnCl2 as hard template and starch/ammonia as carbon and nitrogen source. Based on the advantages of three-dimensional interconnected hierarchical porous heteroatom doping, the electrosorption capacity reaches 67.25 mg/g, and the removal efficiency is as high as 98.45%, when the initial UO2(NO3)2 concentration is 80 mg/L in capacitive deionization. The isothermal adsorption of nitrogen doped hierarchical porous carbon (NHPC) is consistent with the Langmuir model, with a maximum electrosorption capacity of 152.43 mg/g, good cycle stability and high charge efficiency (energy consumption is only 0.77 kg-U kWh−1). Fascinatingly, the initial UO2(NO3)2 concentration is 80 mg/L and it also has a high adsorption capacity in 3.5 wt% NaCl solution, and the U(VI) removal efficiency could reach 42.5% after 8 h of continuous adsorption, with high selectivity. The prepared adsorbent NHPC shows good selectivity for U(VI) in the solution of 11 metal ions co-existing, and the effective selectivity Kd value of U(VI) is 1620.84 mL/g. Finally, X-ray photoelectron spectroscopy analysis reveals that in addition to Coulomb interaction and chelation during the adsorption process, there is also a synergistic effect of the conversion of U(VI) to UO2 under electric drive to improve the adsorption capacity of U(VI).

Peng H., Wang L., Zheng X.

To extend the adsorption-photocatalytic application of biochar in wastewater purification, S-defected MoS2 coupling with S,N-codoped porous biochar (MoS2/SN-BC) was prepared from chitosan via the in-situ sulfurization. Compared with S-doped biochar (S-BC) and S,N-codoped biochar (SN-BC), MoS2/SN-BC has better adsorption and photocatalytic activities for tetracycline hydrochloride (TCH). The removal efficiency of TCH over optimal 3-MoS2/SN-BC with a Mo content of 12.69 % is 97.99 % for 180 mg L−1 within 120 min, and the tested adsorption capacity is 382.43 mg g−1. The adsorption-photocatalytic activity of 3-MoS2/SN-BC slightly declines after five cycles. The adsorption isotherm and kinetics of 3-MoS2/SN-BC follow the Langmuir and second order models, respectively. The abundant edge-sites favor TCH molecules adsorption and photons capture, and the tight junction interface between S-defected MoS2 and S,N-codoped porous biochar promotes the photo-excited electrons transfer and mobility.

Yin L., Hu P., Liang C., Wang J., Li M., Qu W.

Lignin is a renewable biomacromolecule that can be used as precursors for carbon materials. In this work, highly flexible lignin-based carbon nanofibers with abundant ultra-micropores are constructed via electrospinning, oxidative stabilization and carbonization. The results indicate that replacing PAN with 80 % lignin is feasible in regulating ultra-micropores. The synthesized L4P1-CNFs possess many attractive properties (e.g., pore size distribution, electrochemical and deionization property) compared with that produced from other non-renewable precursors or more-complexed processes. It shows excellent electrochemical double-layer capacitance in 6 M KOH (233 to 162 F g-1 at 0.5 to 5 A g-1) and 1 M NaCl (158 to 82 F g-1 at 0.5 to 5 A g-1) electrolytes. Upon assembling into CDI cells, the average salt adsorption rate could reach 1.79 mg g-1 min-1 at 1.2 V and 3.32 mg g-1 min-1 at 2 V in 500 mg L-1. Benefiting from the excellent flexibility, we innovatively stack four layers of L4P1-CNFs to improve the areal electrosorption capacity to 0.0817 mg cm-2 at 500 mg L-1, significantly higher than that of traditional carbon-based electrodes. The good desalination property makes lignin-based carbon nanofibers ideal for practical, low-cost capacitive deionization applications.

Ye H., Li T., Huang Y., Jin J., Fei J., Wu M., Yao J.

• Amyloid-like coatings provide electrodes with binding sites to uranium and anti-fouling properties. • The modified electrodes achieved equilibrium adsorption capacity as high as 2850 mg/g. • Unfolded BSA coatings enable the electrodes with superior reusability and long-term stability. • Both adsorption capacity and adsorption rates are better than most of other adsorbents. Electro-adsorption has been regarded as one of the most effective methods for uranium extraction from seawater since this method could gather ultralow-concentration uranyl ions at the adsorbent surfaces for higher adsorption capacity and adsorption rates. However, the marine microorganisms and pollutants would also migrate to the adsorbent surfaces, causing serious inhibiting effects. Herein, the pristine electrodes were modified by the convenient amyloid-like assembly to solve the above problem. The unfolded bovine serum albumin (BSA) coatings not only offer adsorption sites toward uranium but also enable the electrodes with excellent anti-fouling and anti-adhesion properties. The modified electrodes achieved superior reusability and long-term stability even with the interferences of various pollutants and microorganisms. To the best of our knowledge, the overlooked but pernicious influences of the fouling phenomenon are firstly investigated in electro-adsorption. This finding not only removes the barriers in the practical applications of electro-adsorption, but also guides the design strategy of adsorbents for uranium extraction.

Jiang M., Wang B., Huang J., Yang G., Wang H., Peng F., Cao Y., Yu H.

The remediation of industrial wastewater still faces challenges, which is of great practical significance for the industrial and academic communities. Electrosorption is considered an attractive and efficient technology to treat wastewater with the advantages of energy-saving and low-cost. Using carbon monolith as electrode materials to remove pollutants from wastewater has not been well summarized and discussed. Also, the difference between the two perform models, such as Flow-by and Flow-through models, used in the electrosorption is discussed, which is an overlooked issue. The role of carbon monoliths in the removal of pollutants under the assistance of an electric field is entirely elaborated. The possibility of metal extraction under the assistance of the electric field is discussed as well. • Remediation of industrial wastewater is the ongoing challenge. • Carbon monolith as the adsorbent with the electric field is the promising strategy. • Texture and surface chemistry of carbon monolith affect the removal performance. • Flow-by and Flow-through models greatly influence the removal performance. • Organic and inorganic contaminants are treated efficiently by this method.

Li Y., Dai Y., Tao Q., Gao Z., Xu L.

Exploiting eco-friendly, highly controlled preparation and convenient solid-liquid separation adsorbent to separate uranium from aquatic medium is of importance and in demand. In this study, magnetic ferroferric oxide nanoparticles synthesized through a facile hydrothermal reaction was cross-linked with chitosan. The intermediate product was subsequently chemically grafting with four amino acids such as alanine, serine, glycine or L-cysteine to produce Ala-MCS, Ser-MCS, Gly-MCS and Cys-MCS. The resultants were verified by SEM, EDS, XRD, VSM, FT-IR and XPS. Adsorption of uranium with amino acids-modified magnetic chitosans were carried out. The parameters that affected the adsorption ability, selectivity toward uranium, and reusability have been illustrated. pH 6.5 was the most beneficial for the adsorption. The saturation adsorption capacity of Ala-MCS, Ser-MCS, Gly-MCS, Cys-MCS were found as 658.88 mg/g ± 1.0 %, 616.10 ± 0.3 % mg/g, 646.38 ± 1.8 % mg/g, 653.96 ± 3.4 % mg/g and 409.15 ± 4.6 % mg/g, respectively. The adsorption process was analyzed using kinetics (pseudo-first-order, pseudo-second-order and intraparticle diffusion models) and isotherms models (Langmuir and Freundlich models). The adsorption of uranium on Ala-MCS, Ser-MCS, Gly-MCS and Cys-MCS happened on monolayer and were controlled by chemisorption. The certified high adsorption amount and efficient solid-liquid separation proved amino acids-modified magnetic chitosan are promising adsorbents for removal of uranium from wastewater.

Luo Q., Jin T., huang J., Liu Z., Huang D., Qian Y.

A novel phytic acid-doped sodium alginate aerogel (Alg-PA) was prepared via a simple doping and freeze-drying method and was used as a self-supporting electrode material to remove uranium ions from aqueous solutions. The effects of chemical composition, UO22+ concentration, solution pH, and applied voltage on the adsorption of UO22+ were investigated. Chemical adsorption was found to be the main mechanism of uranium adsorption and the application of voltage can effectively improve the adsorption capacity and adsorption rate in this removal system. The experimental maximum capacity of the Alg-PA electrode was 430.8 mg/g, while the theoretical maximum capacity of Alg-PA was found to be 563.8 mg/g. Moreover, Alg-PA also has a good reusability and selectivity to uranium ions. These advantages make Alg-PA a promising material for extracting of uranium from uranium-containing solutions.

Gayathiri M., Pulingam T., Lee K.T., Sudesh K.

The use of activated carbon is evidenced by the increased scope of carbon-based applications in various industrial applications including pharmaceutical antidotes, wastewater remediation, aquaculture and toxin removal. Activated carbon produced from biomass waste by various processing methods and conditions is emerging as a promising adsorbent for remediation of the ecosystem due to extensive discharge of pollutants. Methods of producing activated carbon, nature of lignocellulosic biomass waste, and interaction of adsorbent-adsorbate are some of the crucial factors that need to be scrutinized to produce an effective adsorbent. However, these factors have not been thoroughly discussed in the literature. Activated carbon needs to go through continuous and rigorous research and development through optimization of key parameters such as type of activation (physical/chemical) and processing conditions, especially for large-scale production. It is imperative to have a detailed understanding of the preeminent characteristics of the activated carbon such as pore size distribution, total pore volume, surface area, and yield of activated carbon that control the extents of adsorptions and production of activated carbon. To further clarify the involved mechanism, studies should focus on all the possible variables that influence the system. Therefore, this review provides a better understanding of factors that affect the production of an efficient activated carbon, important properties to be used as an adsorbent, and the involved mechanisms during the adsorption process followed by increasing demand for activated carbon in various fields. • Method of activation affects the surface area of the activated carbon. • Chemical composition varies for different biomass wastes. • Characteristics of activated carbon influence the adsorption capacity. • Adsorption mechanism depends on various application of activated carbon. • Activated carbon has high future demand for its adsorption capability.

Yang B., Zhao J., Zhang C., Guo S., Chen Y., Wang Y., Huang X., Zeng Q.

Wei G., Bai Z., Pang H., Wang X., Yu S., Fu D., Wang X.

核能作为清洁能源,可以很好地解决传统化石能源所带来的高污染问题,因而在近些年来得以快速发展.但核燃料在开采、运输、利用等过程中,放射性核素U(VI)会由于操作不当等原因进入水体环境中,对环境以及生物的健康产生威胁.本研究以厨余垃圾之一的柚子皮为原材料制备生物炭(BC),再加以聚苯胺改性,制成聚苯胺/生物炭复合材料(BC-PANI),将其应用于水体中U(VI)的去除.通过SEM、EDS、XRD、BET、FT-IR等一系列表征,证实了富氨基官能团的BC-PANI材料的成功制备.通过宏观批次实验,探究了反应时间、温度、pH、离子强度等因素对材料吸附U(VI)的影响.结果表明,BC-PANI在328 K下对U(VI)的最大吸附量可达80.6 mg·g-1,在15 min就可达到吸附平衡.宏观实验和XPS分析说明BC-PANI高效去除U(VI)是氨类官能团的化学吸附与还原反应的协同作用.此外,BC-PANI的循环实验表明其具有良好重复利用性,经济效益较高.综上,BC-PANI是一种高效、低成本、可循环使用的材料,具有很大应用前景,本研究也对放射性核素的去除治理提供了一定的参考价值.

Yang Y., Zhang X., Peng Y., Wu X., Cai T., Hua Y., Li M., Tang D.

Uranium (U) pollution in soil resulted by human activities is a critical environmental issue. Goethite and humic acid (HA), as predominant soil constituents, significantly influence the migration and transformation of uranium in soil, but effects of combining them together on the sequestration and immobilization of U at different mineralization condition are still rare. To simulate the ability of different combinations of HA and goethite to limit the migration of uranium (VI) in the soil environment, the humic acid-modified goethite (OPHG, TSHG) were synthesized by one-pot and two steps synthesis methods in this study. After modified by HA, the specific surface area of materials increased from 29.67 m2/g to 121.53 m2/g and 39.89 m2/g respectively. The effects of dosage, contact time, pH, initial concentration and temperature on the removal of U(VI) by goethite and modified goethite were investigated. The results showed the maximum difference of them reached 41.59% and 15.69 mg/g for reaction 60 min at pH=4.5. The equilibrium adsorption data fit to the pseudo-second-order kinetics and Langmuir models, and the maximum adsorption capacities increased from 64.63 mg/g to 92.04 mg/g. The analyses results indicated that OPHG remove U(VI) mainly through the formation of ≡FeOUO2OH between Fe−O and uranyl ions, as well as the complexation of carboxyl and hydroxyl groups on HA molecules with uranium to form the HA-Goethite-U(VI) ternary complexes FeOHAUO2. These results are benefited for understanding the effects of HA and goethite on immobilization uranium in soil and would be used to predict and remediate the polluted soil.