Synthesis of Mesoporous Eu3+-Doped Zinc/Silicate Phosphors for Highly Selective and Sensitive Detection of Sulfide Ions.

A mesoporous Eu3+-doped zinc/silicate phosphor with a large surface area (>100 m2g-1) and amorphous structure was prepared in an aqueous solution without using any organic template. The residual concentration of the Zn2+ ion in the filtrate is lower than the standard of effluent 3.5 ppm under a pH 8-11 preparation condition. When a sulfide ion (S2-) is present in aqueous solution, the phosphor can react with the sulfide ion to transform from the amorphous structure to the crystalline ZnS, which causes structural transformation and a subsequent decrease in luminescent intensity. This distinct phosphor with a high surface area and amorphous structure can be applied through the structure transformation mechanism for highly selective and sensitive detection of the sulfide ions at low concentrations. In addition, the luminescent efficiency was obtained from adjustments in the pH value, calcination temperature, and Eu3+ ion concentration. The quenching efficiency, the limit of detection (CLOD), S2- ion selectivity, and phosphor regeneration ability were systematically explored in sulfide ion detection tests. Due to the novel S2- ion-induced structural transformation, we found that the amorphous Eu3+-doped zinc/silicate phosphors demonstrate a CLOD sensitivity as low as 1.8 × 10-7 M and a high Stern-Volmer constant (KSV) of 3.1 × 104 M-1. Furthermore, the phosphors were easily regenerated through simple calcination at 500 °C and showed a KSV value of 1.4 × 104 M-1. Overall, the Eu3+-doped zinc/silicates showed many advantageous properties for detecting sulfide ions, including low toxicity, green synthesis, good selectivity, high sensitivity, and good renewability.

Electrospun Benzimidazole-Based Polyimide Membrane for Supercapacitor Applications.

A benzimidazole-containing diamine monomer was prepared via a simple one-step synthesis process. A two-step procedure involving polycondensation in the presence of aromatic dianhydrides (4,4'-oxydiphthalic anhydride, ODPA) followed by thermal imidization was then performed to prepare a benzimidazole-based polyimide (BI-PI). BI-PI membranes were fabricated using an electrospinning technique and were hot pressed for 30 min at 200 °C under a pressure of 50 kgf /cm2. Finally, the hot-pressed membranes were assembled into supercapacitors, utilizing high-porosity-activated water chestnut shell biochar as the active material. The TGA results showed that the BI-PI polymer produced in the two-step synthesis process had a high thermal stability (Td5% = 527 °C). Moreover, the hot-press process reduced the pore size in the BI-PI membrane and improved the pore-size uniformity. The hot-press procedure additionally improved the mechanical properties of the BI-PI membrane, resulting in a high tensile modulus of 783 MPa and a tensile strength of 34.8 MPa. The cyclic voltammetry test results showed that the membrane had a specific capacitance of 121 F/g and a capacitance retention of 77%. By contrast, a commercial cellulose separator showed a specific capacitance value of 107 F/g and a capacitance retention of 49% under the same scanning conditions. Finally, the membrane showed both a small equivalent series resistance (Rs) and a small interfacial resistance (Rct). Overall, the results showed that the BI-PI membrane has significant potential as a separator for high-performance supercapacitor applications.

Iridescent Colloidal Crystals Composed of SiO2 Porous Hollow Sphere for SERS Application.

In recent years, the application of low-refractive-index materials in the optical field has attracted considerable attention due to it high transmittance and high optical sensitivity. In this study, we synthesized SiO2 porous hollow spheres (SPHS) with an ultralow refractive index (n = 1.05) by using a templating method. Their refractive indices could be easily controlled from 1.05 to 1.08 by tuning the thickness of shell. In addition, a droplet coatings method is proposed for SPHS colloidal crystal (CC) by controlling the temperature and humidity. The SPHS CCs displayed distinct structural colors when the incident angle was adjusted and demonstrated high angular resolution. Moreover, the iridescent color changes could be observed with the naked eye. For surface-enhanced Raman scattering application, more analyte could be absorbed by the porous shells, and metal nanoparticles were coated on the SPHSs surface to increase the hot spot density for improving the SERS intensity.

Optimizing the Micro/Mesoporous Structure of Hierarchical Porous Carbon Synthesized from Petroleum Pitch Using the Solvent-Free Method for Ultra-Fast Capacitive Deionization.

In this work, a solvent-free ZnO-template method is used to synthesize hierarchical porous carbons (denoted as HPC-X; X = 1, 1.5, 2, and 4 g of ZnO) via the pyrolysis of petroleum industrial-residual pitch with ZnO. The proposed method allows precise control of the micro/meso/macroporous structure of the HPC by adjusting the amount of ZnO. The results show that the average pore size of HPCs prominently increases from 2.4 to 3.7 nm with the increase in the ZnO/pitch ratio. In addition, it is shown that HPCs have a high surface area between 1141 and 1469 m2 g-1, a wide-range pore size distribution (micro-, meso-, and macropores), and a tap density ranging from 0.2 to 0.57 g cm-3. The capacitive deionization performances of HPCs for sodium and chloride ions are investigated. The results show that HPC-2 exhibits the highest electrosorption capacity of 9.94 mg g-1 within 10.0 min and a maximum electrosorption capacity of 10.62 mg g-1 at 1.2 V in a 5.0 mM NaCl solution. Hence, HPC-2 is a highly promising candidate as an electrode material for rapid deionization.

Fabrication and Characterization of Nylon 66/PAN Nanofibrous Film Used as Separator of Lithium-Ion Battery.

In recent years, portable electronic devices have flourished, and the safety of lithium batteries has received increasing attention. In this study, nanofibers were prepared by electrospinning using different ratios of nylon 66/polyacrylonitrile (PAN), and their properties were studied and compared with commercial PP separators. The experimental results show that the addition of PAN in nylon 66/PAN nanofibrous film used as separator of lithium-ion battery can enhance the porosity up to 85%. There is also no significant shrinkage in the shrinkage test, and the thermal dimensional stability is good. When the Li/LiFePO4 lithium battery is prepared by nylon 66/PAN nanofibrous film used as separator, the capacitor can be maintained at 140 mAhg-1 after 20 cycles at 0.1 C, and the coulombic efficiency is still maintained at 99%, which has excellent electrochemical performance.

Effects of morphology and pore size of mesoporous silicas on the efficiency of an immobilized enzyme.

An investigation is performed into the efficiency of the Streptomyces griseus HUT 6037 enzyme immobilized in three different mesoporous silicas, namely mesoporous silica film, mesocellular foam, and rod-like SBA-15. It is shown that for all three supports, the pH value changes the surface charge and charge density and hence determines the maximum loading capacity of the enzyme. The products of the enzyme hydrolytic reaction are analyzed by 1H-NMR. The results show that among the three silica supports, the mesoporous silica film (with a channel length in the range of 60-100 nm) maximizes the accessibility of the immobilized enzyme. The loading capacity of the enzyme is up to 95% at pH 7 and the activity of the immobilized enzyme is maintained for more than 15 days when using a silica film support. The order of the activity of the enzyme immobilized in different mesoporous silica supports is: mesoporous silica film > mesocellular foam > rod-like SBA-15. Furthermore, the immobilized enzyme can be easily separated from the reaction solution via simple filtration or centrifugation methods and re-used for hydrolytic reaction as required.

Green and Highly-Efficient Microwave Synthesis Route for Sulfur/Carbon Composite for Li-S Battery.

Multiporous carbons (MPCs) are prepared using ZnO as a hard template and biomass pyrolysis oil as the carbon source. It is shown that the surface area, pore volume, and mesopore/micropore ratio of the as-prepared MPCs can be easily controlled by adjusting the ZnO/oil ratio. Sulfur/MPC (S/MPC) composite is prepared by blending sulfur powder with the as-prepared MPCs followed by microwave heating at three different powers (100 W/200 W/300 W) for 60 s. The unique micro/mesostructure characteristics of the resulting porous carbons not only endow the S/MPC composite with sufficient available space for sulfur storage, but also provide favorable and efficient channels for Li-ions/electrons transportation. When applied as the electrode material in a lithium-ion battery (LIB), the S/MPC composite shows a reversible capacity (about 500 mAh g-1) and a high columbic efficiency (>95%) after 70 cycles. Overall, the method proposed in this study provides a simple and green approach for the rapid production of MPCs and S/MPC composite for high-performance LIBs.

Green synthesis of nitrogen-doped multiporous carbons for oxygen reduction reaction using water-caltrop shells and eggshell waste.

A green synthesis method is proposed for the preparation of nitrogen-doped multiporous carbons (denoted as N-MPCs) from water-caltrop shell (WCS) using eggshell waste as both a nitrogen-dopant and an activating agent. It is shown that the surface area, porosity, yield and nitrogen content of the as-prepared N-MPCs can be easily controlled by adjusting the activation temperature. Moreover, in oxygen reduction reaction (ORR) tests performed in O2-saturated 0.1 M KOH(aq) electrolyte containing 1.0 M methanol, the N-MPC catalysts show a high ORR stability and good resistance to methanol corrosion. In addition, as a cathode material in Al-air battery tests, the N-MPCs achieve a power density of 16 mW g-1 in a saturated NaCl(aq) electrolyte. Overall, the results show that the N-MPCs have a promising potential as a green and sustainable material for ORR catalysis applications.

Correction: Green synthesis of nitrogen-doped multiporous carbons for oxygen reduction reaction using water-caltrop shells and eggshell waste.

[This corrects the article DOI: 10.1039/D1RA02100A.].

Synthesis of Multiporous Carbons from the Water Caltrop Shell for High-Performance Supercapacitors.

In this study, an economic, sustainable, and green synthesis method of multiporous carbons from agricultural waste, water caltrop shell (denoted as WCS), was presented. To prepare the WCS biochar, the dried WCS was first carbonized to a microporous carbon with a surface area of around 230 m2 g-1 by using a top-lit-updraft method. Then, the microporous WCS biochar was directly mixed with an appropriate amount of ZnO nanoparticles and KOH as activating agents via a solvent-free physical blending route. After further activation at 900 °C, the resulted carbons possess both micropores and mesopores that were named as WCS multiporous carbons. The carbon yield of the prepared WCS multiporous carbons with high surface area in the range of 1175-1537 m2 g-1 is up to 50%. Furthermore, the micropore/mesopore surface area ratio can be simply tuned by controlling the ZnO content. For supercapacitor applications, the as-prepared WCS multiporous carbon electrodes showed high specific capacitance (128 F g-1 at 5 mV s-1) with a good retention rate at 500 mV s-1 scan rate (>60% compared to the capacitance at 5 mV s-1) and low Ohmic resistance in a 1.0 M LiClO4/PC electrolyte. In addition to the ZnO nanoparticles, CaCO3 nanoparticles with low environmental impact were also used to prepare the WCS multiporous carbons. The assembled supercapacitors also demonstrate high specific capacitance (102 F g-1 at 5 mV s-1) and good retention rate (∼70%).

Electrochemical fabrication and evaluation of a self-standing carbon nanotube/carbon fiber composite electrode for lithium-ion batteries.

A binder-free self-standing carbon nanotube (CNT)/carbon fiber (CF) composite electrode, which has been developed using an electrophoretic deposition approach, was utilized as a lithium-ion battery anode. The morphology of the CNT/CF composite has been examined using scanning electron microscopy, and the results indicated that a CNT layer uniformly deposited on the CFs. The thickness and density of the CNT layer increased as the electrodeposition time increased, while overdeposition caused the CNT layer to exfoliate. Electrochemical evaluation revealed that the specific capacity, cycling stability, and rate capability of the CNT/CF anode were superior to those of the CF anode. The electrochemical impedance analysis results further revealed that the solid/electrolyte interface resistance and interface resistance induced by the oxygen-containing surface functional groups of CFs dominated the impedance of the anode. However, these resistance values could be potentially reduced via CNT surface modification, which could lead to the enhanced electrochemical performance of the CNT/CF anode. Our findings should open new avenues for the potential use of the CNT/CF composite as a self-standing anode for lithium-ion battery applications.

Hierarchical Micro/Mesoporous Carbons Synthesized with a ZnO Template and Petroleum Pitch via a Solvent-Free Process for a High-Performance Supercapacitor.

Hierarchical micro/mesoporous carbons were prepared using ZnO nanoparticles as hard templates and a petroleum industrial-residual pitch as the carbon source via a solvent-free process. The ZnO templates can be easily removed using HCl(aq), thereby avoiding limitations present in conventional porous silica templating approaches that require highly corrosive HF(aq) for template removal. Notably, the proposed solvent-free synthetic method from low-cost pitch to high-value porous carbons is a friendly process with respect to our overexploited environment. With the combination of ZnO nanoparticles and pitch, the surface area (76-548 m2 g-1) of the resultant mesoporous carbons increases with an increase in the weight ratios of ZnO to pitch. Furthermore, the hierarchical micro/mesoporous carbons with a large surface area (854-1979 m2 g-1) can be feasibly fabricated by only adding an appropriate amount of an activating agent. Meanwhile, N-doped hierarchical porous carbons can be achieved by carbonizing the blend of these materials with melamine. For supercapacitor application, the resultant carbons exhibit a high capacitance up to 200.5 F g-1 at 5 mV s-1 using LiClO4/PC as the electrolyte in a symmetrical two-electrode cell. More importantly, the coin-cell supercapacitor based on porous carbons achieved a capacitance of 94 F g-1 at 5 mV s-1 and 63% capacitance retention at 500 mV s-1, thereby holding the potential for commercialization.

Stable Lithium Deposition Generated from Ceramic-Cross-Linked Gel Polymer Electrolytes for Lithium Anode.

In this work, a composite gel electrolyte comprising ceramic cross-linker and poly(ethylene oxide) (PEO) matrix is shown to have superior resistance to lithium dendrite growth and be applicable to gel polymer lithium batteries. In contrast to pristine gel electrolyte, these nanocomposite gel electrolytes show good compatibility with liquid electrolytes, wider electrochemical window, and a superior rate and cycling performance. These silica cross-linkers allow the PEO to form the lithium ion pathway and reduce anion mobility. Therefore, the gel not only features lower polarization and interfacial resistance, but also suppresses electrolyte decomposition and lithium corrosion. Further, these nanocomposite gel electrolytes increase the lithium transference number to 0.5, and exhibit superior electrochemical stability up to 5.0 V. Moreover, the lithium cells feature long-term stability and a Coulombic efficiency that can reach 97% after 100 cycles. The SEM image of the lithium metal surface after the cycling test shows that the composite gel electrolyte with 20% silica cross-linker forms a uniform passivation layer on the lithium surface. Accordingly, these features allow this gel polymer electrolyte with ceramic cross-linker to function as a high-performance lithium-ionic conductor and reliable separator for lithium metal batteries.

High performance of transferring lithium ion for polyacrylonitrile-interpenetrating crosslinked polyoxyethylene network as gel polymer electrolyte.

A polyacrylonitrile (PAN)-interpenetrating cross-linked polyoxyethylene (PEO) network (named XANE) was synthesized acting as separator and as gel polymer electrolytes simultaneously. SEM images show that the surface of the XANE membrane is nonporous, comparing to the surface of the commercial separator to be porous. This property results in excellent electrolyte uptake amount (425 wt %), and electrolyte retention for XANE membrane, significantly higher than that of commercial separator (200 wt %). The DSC result indicates that the PEO crystallinity is deteriorated by the cross-linked process and was further degraded by the interpenetration of the PAN. The XANE membrane shows significantly higher ionic conductivity (1.06-8.21 mS cm(-1)) than that of the commercial Celgard M824 separator (0.45-0.90 mS cm(-1)) ascribed to the high electrolyte retention ability of XANE (from TGA), the deteriorated PEO crystallinity (from DSC) and the good compatibility between XANE and electrode (from measuring the interfacial-resistance). For battery application, under all charge/discharge rates (from 0.1 to 3 C), the specific half-cell capacities of the cell composed of the XANE membrane are all higher than those of the aforementioned commercial separator. More specifically, the cell composed of the XANE membrane has excellent cycling stability, that is, the half-cell composed of the XANE membrane still exhibited more than 97% columbic efficiency after 100 cycles at 1 C. The above-mentioned advantageous properties and performances of the XANE membrane allow it to act as both an ionic conductor as well as a separator, so as to work as separator-free gel polymer electrolytes.

Benzylamine-assisted noncovalent exfoliation of graphite-protecting Pt nanoparticles applied as catalyst for methanol oxidation.

A novel method has been developed to physically exfoliate graphite and uniformly disperse Pt nanoparticles on graphite nanoplates without damaging the graphene structures. A stable aqueous suspension of graphite nanoplates was achieved by benzylamine-assisted noncovalent fuctionalization to graphite and characterized by transmission electron microscopy, X-ray diffraction and Raman spectroscopy. A uniform dispersion of Pt nanoparticles was then prepared on the graphite nanoplates, where the benzylamine acts as a stabilizer. These Pt loaded graphite nanoplates were then prepared as an electrode, which significantly increased catalytic activity toward the methanol oxidation reaction, resulting in a 60% increment in mass activity compared to that of E-TEK.

Stabilization of embedded Pt nanoparticles in the novel nanostructure carbon materials.

An extremely durable and highly active Pt catalyst has been successfully prepared by embedding Pt(0) nanoparticles inside the pores of the nitrogen-dotted porous carbon layer surrounding carbon nanotubes (Pt@NC-CNT). The Pt@NC-CNT catalyst has a high BET surface area of 271 m(2) g(-1) (62 m(2) g(-1) for Pt/XC-72) and comparably high electrochemically active surface area of 64.3 m(2) g(-1) (68.2 m(2) g(-1) for Pt/XC-72). The prepared Pt nanoparticles are small in size (2.8 ± 1.3 nm) and have a strong interaction of nitrogen to platinum, as evidenced by the binding energy observed at 399.5 eV. The maximum current densities (I(f)) during methanol oxidation observed for Pt@NC-CNT (13.2 mA cm(-1)) is 1.2 times higher than that of Pt/XC-72 (10.8 mA cm(-1)) catalysts. Remarkably, in the long term durability test, the I(f) after 1000 cycles for Pt@NC-CNT decreased to 10.6 mA cm(-1) compared with Pt/XC-72, which decreased to 2.6 mA cm(-2). This means that the Pt@NC-CNT catalyst has a tremendously stable electrocatalytic activity for MOR because of the unique structure of Pt@NC-CNT formed in this novel synthesis technique.

Excellent performance of Pt0 on high nitrogen-containing carbon nanotubes using aniline as nitrogen/carbon source, dispersant and stabilizer.

Novel high nitrogen-containing carbon nanotubes (NC-CNT) (14% N) as catalyst support have been successfully prepared using aniline as a dispersant to CNT and as a source for both carbon and nitrogen coated on the surface of the CNT.