Capacitive Removal of Heavy Metal Ions from Wastewater via an Electro-Adsorption and Electro-Reaction Coupling Process

Heavy metals widely exist in wastewater, which is a serious threat to human health or water environment. Highly efficient removal of heavy metal ions from wastewater is a major challenge to wastewater treatment. In this work, capacitive removal of heavy metal ions from wastewater via an electro-adsorption and electro-reaction coupling process was originally demonstrated. The removal efficiency of heavy metal ions in the binary-component solutions containing metal nitrate (10 mg/L) and NaCl (100 mg/L) can reach 99%. Even the removal efficiency of heavy metal ions can be close to 99% in the multi-component solution containing all the seven metal nitrates (10 mg/L for each) and 100 mg/L NaCl. Meanwhile, the electro-adsorption and electro-reaction coupling process maintained excellent regeneration ability even after 20 cycles. Furthermore, the heavy metal ions removal mechanism was proven to be the pseudocapacitive intercalation of heavy metal ions into the layered structure of the employed W18O49/graphene in the electro-adsorption and electro-reaction coupling process. This work demonstrates great potential for general applicability to wastewater treatment. </p

Capacitive Deionization of Saline Water by Using MoS₂-Graphene Hybrid Electrodes with High Volumetric Adsorption Capacity

Capacitive deionization (CDI) has received wide attention as an emerging water treatment technology because of its low energy consumption, low cost, and high efficiency. However, the conventional carbon electrode materials for CDI have low densities, which occupy large volumes and are disadvantageous for use in limited space (e.g., in household or on offshore platforms). In order to miniaturize the CDI device, it is quite urgent to develop high volumetric adsorption capacity (VAC) electrode materials. To overcome this issue, we rationally designed and originally developed high VAC MoS2-graphene hybrid electrodes for CDI. It is interesting that MoS2-graphene hybrid electrode has a much higher NaCl VAC of 14.3 mg/cm3 with a gravimetric adsorption capacity of 19.4 mg/g. It has been demonstrated that the adsorption capacity is significantly enhanced because of the rapid ion transport of MoS2 and high electrical conductivity of graphene. In situ Raman spectra and high-angle annular dark-field scanning transmission electron microscopy tests demonstrated a favorable Faradaic reaction, which was crucial to enhancing the NaCl VAC of the MoS2-graphene hybrid electrode. This work opens a new avenue for miniaturizing future CDI devices.</p

Beneficial synergy of adsorption-intercalation-conversion mechanisms in Nb₂O₅@nitrogen-doped carbon frameworks for promoted removal of metal ionsviahybrid capacitive deionization

Capacitive deionization (CDI) is an emerging water purification technology, but the ion adsorption capacity of traditional carbon-based CDI electrodes is still unsatisfactory. Herein, a novel faradaic electrode by anchoring Nb2O5nanoparticles on nitrogen-doped carbon frameworks as anodes and activated carbon (AC) as cathodes in a hybrid capacitive deionization (HCDI) system was originally developed to capture Na+ionsviaadsorption-intercalation-conversion mechanisms. The synergistic effects of the nanostructure and carbon coating were beneficial to enhancing electrical conductivity and offering fast Na+ion diffusion pathways. Impressively, the HCDI system demonstrated an excellent ion adsorption capacity of 35.4 mg g−1in a 500 mg L−1NaCl solution at 1.2 V as well as stable regeneration ability.In situRaman andex situXPS measurements unraveled that the mechanism of ion removal from water was the reversible redox reaction of Nb2O5. The new overall understanding of the synergistic effects opens opportunities for the design of HCDI systems for efficient removal of metal ions from saline water.</p

Efficient removal of metal ions by capacitive deionization with straw waste derived graphitic porous carbon nanosheets

Capacitive deionization (CDI) is considered to be an energy-efficient and cost-effective technology for ion removal from saline or waste water. However, its implementation remains challenging due to low ion adsorption capacity of the commonly used electrode materials. It is thus desirable to develop highly efficient CDI electrode materials for ion removal. Herein, graphitic porous carbon nanosheets (GPCSs) were originally prepared from straw waste via a combined activation and graphitization process. Being composed of graphitic carbon sheets with abundant pores in the framework, the obtained GPCSs had a large specific surface area and good conductivity and wettability, which can provide sufficient adsorption sites and promote efficient ion transport. The GPCS electrodes presented a higher specific capacitance, good stability and low inner resistance in electrochemical tests. Moreover, the GPCSs showed a high deionization capacity of 19.3 mg g-1 at 1.2 V in a 500 mg L-1 NaCl solution. Repeated adsorption-desorption experiments demonstrated the good regeneration performance of the GPCS electrodes. Furthermore, the removal efficiency towards Cd2+, Ni2+ and Cu2+ of the GPCS electrodes is 91.5%, 97.0% and 100% at 1.2 V in a 100 mg L-1 CdCl2, NiCl2 or CuCl2 solution, respectively. This work offers a promising solution to efficient removal of ions from saline or waste water and a new route to the utilization of straw waste.</p

Enhanced capacitive deionization of saline water using N-doped rod-like porous carbon derived from dual-ligand metal-organic frameworks

Capacitive deionization (CDI) removes ions from brine, and is forward-looking technology due to its low energy consumption, low cost and prevention of secondary pollution. Removal capacity is still an issue for CDI technology. It is quite urgent to design a high-performance CDI electrode material with a reasonable porous structure, excellent conductivity and hydrophilic surface. Herein, we originally designed nitrogen-doped rod-like porous carbon derived from dual-ligand metal-organic frameworks (MOFs), in which two ligands, namely 1,4-benzenedicarbocylic acid and triethylenediamine, coordinate with zinc (Zn). 1,4-Benzenedicarbocylic acid can be used as a pore-forming agent to increase the specific surface area of the carbon material, and triethylenediamine is used as a nitrogen doping source to increase the hydrophilicity and conductivity of the carbon material. By adjusting the ratio of the two ligands, the optimal specific surface area and nitrogen doping for the carbon material is obtained, thereby achieving the highest removal capacity for capacitive deionization of brine. The obtained carbon materials possess a hierarchical porous structure with moderate nitrogen doping. The large specific surface area of the electrode materials delivers many adsorption sites for adsorption of salt ions. The hierarchically porous structure provides rapid transport channels for salt ions, and high-level N doping enhances the conductivity and hydrophilicity of the carbon materials to some extent. More importantly, the salt removal capacity of the electrodes is as high as 24.17 mg g-1 at 1.2 V in 500 mg L-1 NaCl aqueous solution. Hence, the moderate nitrogen-doping porous carbon material derived from dual-ligand MOFs is a potential electrode material for CDI application. Such results provide a new method for the preparation of high-performance electrodes to remove ions from saline water.</p

Self-passivated freestanding superconducting oxide film for flexible electronics

The integration of high-temperature superconducting YBa2Cu3O6+x (YBCO) into flexible electronic devices has the potential to revolutionize the technology industry. The effective preparation of high-quality flexible YBCO films therefore plays a key role in this development. We present a novel approach for transferring water-sensitive YBCO films onto flexible substrates without any buffer layer. Freestanding YBCO film on a polydimethylsiloxane substrate is extracted by etching the Sr3Al2O6 sacrificial layer from the LaAlO3 substrate. In addition to the obtained freestanding YBCO thin film having a Tc of 89.1 K, the freestanding YBCO thin films under inward and outward bending conditions have Tc of 89.6 K and 88.9 K, respectively. A comprehensive characterization involving multiple experimental techniques including high-resolution transmission electron microscopy, scanning electron microscopy, Raman and X-ray Absorption Spectroscopy is conducted to investigate the morphology, structural and electronic properties of the YBCO film before and after the extraction process where it shows the preservation of the structural and superconductive properties of the freestanding YBCO virtually in its pristine state. Further investigation reveals the formation of a YBCO passivated layer serves as a protective layer which effectively preserves the inner section of the freestanding YBCO during the etching process. This work plays a key role in actualizing the fabrication of flexible oxide thin films and opens up new possibilities for a diverse range of device applications involving thin-films and low-dimensional materials.Comment: 22 pages,4 figures,references adde

Defect-induced efficient dry reforming of methane over two-dimensional Ni/h-boron nitride nanosheet catalysts

Efficient enhancement of catalytic stability and coke-resistance is a crucial aspect for dry reforming of methane. Here, we report Ni nanoparticles embedded on vacancy defects of hexagonal boron nitride nanosheets (Ni/h-BNNS) can optimize catalytic performance by taming two-dimensional (2D) interfacial electronic effects. Experimental results and density functional theory calculations indicate that surface engineering on defects of Ni/h-BNNS catalyst can strongly influence metal-support interaction via electron donor/acceptor mechanisms and favor the adsorption and catalytic activation of CH4 and CO2. The Ni/h-BNNS catalyst exhibits superior catalytic performance during a 120 h durability test. Furthermore, in situ techniques further reveal possible recovery mechanism of the active Ni sites, identifying the enhanced catalytic activities of the Ni/h-BNNS catalyst. This work highlights promotional mechanism of defect-modified interface and should be equally applicable for design of thermochemically stable catalysts

Rational design of 3D hierarchical foam-like Fe2O3@CuOxmonolith catalysts for selective catalytic reduction of NO with NH3

Herein, we have rationally designed and originally fabricated a high-performance monolith catalyst based on 3D hierarchical foam-like Fe2O3@CuOx for selective catalytic reduction (SCR) of NO with NH3. The Fe2O3@CuOx foam catalyst was synthesized by calcining the Cu foam in air first to form CuOx foam with CuOx nanowire arrays on the surface and then the Fe2O3 could be in situ formed on the surface of CuOx through the reaction in the interfacial region between the aqueous solution of Fe2+ and CuO via a hydrothermal method. This catalyst was mainly characterized by the techniques of X-ray diffraction, transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, NH3/NO + O2 temperature-programmed desorption and in situ diffuse reflectance infrared Fourier transform spectroscopy. Both the atomic concentration of Cu+ and chemisorbed oxygen species are enhanced by the coating of Fe2O3, which facilitates NO attack on active sites, resulting in the in situ formation of NO2 and promoting the “fast SCR” reaction. Moreover, there is a strong interaction between CuOx and Fe2O3, which could not only lead to better reduction ability but also raise the acid amount and enhance the acid strength as well as NOx adsorption ability. Based on these favourable properties, the Fe2O3@CuOx catalyst exhibits a higher activity and more extensive operating temperature window than the catalyst without Fe2O3. More importantly, the Fe2O3 not only prevents the generation of ammonium sulfates from blocking the active sites but also inhibits the formation of copper sulfates, resulting in a high SO2-tolerance. In addition, the catalyst also displays favourable stability and H2O resistance. The rational design of 3D hierarchical foam-like Fe2O3@CuOx paves a new way for the development of environmentally-friendly and high-performance monolith deNOx catalysts