Functional Materials Letters

Solid-state polymer lithium-ion batteries with better safety and higher energy density are one of the most promising batteries, which are expected to power future electric vehicles and smart grids. However, the low ionic conductivity at room temperature of solid polymer electrolytes (SPEs) decelerates the entry of such batteries into the market. Creating polymer-in-salt solid electrolytes (PISSEs) where the lithium salt contents exceed 50wt.% is a viable technology to enhance ionic conductivity at room temperature of SPEs, which is also suitable for scalable production. In this review, we first clarify the structure and ionic conductivity mechanism of PISSEs by analyzing the interactions between lithium salt and polymer matrix. Then, the recent advances on polyacrylonitrile (PAN)-based PISSEs and polycarbonate derivative-based PISSEs will be reviewed. Finally, we propose possible directions and opportunities to accelerate the commercializing of PISSEs for solid polymer Li-ion batteries.

Corrole compounds with the 18-$\pi$ electron marcrocycle display unique electrochemical properties and show potential value in sensor fields. In this paper, a novel 10-(4-Chlorophenyl)-5,15-di(4-methylphenyl)-Corrole (Cl-Cor 1) and its metal complex 10-(4-Chlorophenyl)-5,15-di(4-methylphenyl)-Corrole-Co (Cl-Cor-Co 2) were synthesized. Then corrole compounds were introduced onto graphene oxide (GO). UV-Vis spectroscopy, fourier-transform infrared spectroscopy (FTIR), and mass spectrometry were used to determine synthesized compounds. Capacity gas sensing analysis system was also examined to evaluate the gas sensitivity toward NO₂ of Cl-Cor 1, Cl-Cor-Co 2, Cl-Cor+GO 3, Cl-Cor-Co+GO 4 and GO 5 at room temperature. It can be found that Cl-Cor-Co 2 has gas-sensing property for nitrogen dioxide (NO)₂, but recovery performance is low. It is interesting that the gas sensitivity and recovery performance could be evidently improved when the GO is grafted onto Cl-Corrole-Co, which is ascribed to the $\pi$-$\pi$ interaction between Corrole and GO. The gas respond at room temperature enormously indicating that covalently Cl-Cor-Co+GO 4 can be used as gas sensors candidate.

With the progress of microelectronic devices, more attention has been paid to carbon nanotube (CNTs) because of their excellent mechanical and electrical properties. A microfluidic-based method for fabricating oriented CNT strain-sensitive fibers is proposed in this work. By manipulating CNTs, NaAlg and CaCl₂ solutions in a three-coaxial laminar flow glass capillary device, CNTs can be arranged in an oriented manner and solidified into microfibers with a hydrogel shell through a chemical polymerization reaction. The diameter of the fiber could be controlled by the microfluidic device. Scanning electron microscopy and Raman spectroscopy show that the CNTs are perfectly aligned along the fiber axis under the influence of the viscous drag force of the fluid, and the electrical and mechanical properties of the CNT fibers are obviously strengthened. Experiments suggest that the devices based on the oriented CNT–alginate microfibers are able to achieve simple motion monitoring function. The proposed microfluidic method is simple, cost effective and can be applied to produce functional nanomaterial fibers for application in flexible devices.

Three-dimensional (3D) ZnO nanostructures, hierarchical nanorods with trunks and branches, were synthesized via a multi-step growth method. The ZnO trunk-branch nanorods are immobilized on glass substrates and their fabrication technologies include the deposition of ZnO seed crystals by magnetron sputtering and the hydrothermal growth of ZnO nanorods without any directing agents. The sputtering pressure for the deposition of ZnO seed crystals was varied and the corresponding effect on the morphology and microstructure of 3D ZnO nanostructures was characterized by various spectroscopic and microscopic techniques. The growth mechanism of ZnO trunk-branch nanorods was discussed and their optical property was also explored. The multi-level constructions of ZnO nanorods would benefit their photo-related functional applications.

TiO₂ is a promising photocatalyst in the reaction of water splitting for hydrogen. Here, we used NaBH₄ reduction reaction to introduce ${\text{Ti}}^{3+}$/V_O defect states into Si-doped TiO₂ nanotubes and investigated the photoelectrochemical water splitting properties. It was found that the photocatalytic activity was improved through NaBH₄ reduction because of the existence of ${\text{Ti}}^{3+}$/V_O. The defect states (${\text{Ti}}^{3+}$/V_O) could play a role of capture trap and accelerate the separation of photogenerated electrons and holes. The photocurrent density of the Si-doped TiO₂ nanotubes reduced for 3h was 1.5mA/cm² compared to 0.7mA/cm² of the unreduced nanotubes. The conversion efficiency was 0.7%, which was almost 4 times than that of pure TiO₂. On the other hand, reduction for a long time would generate excess defect states and thus cause the decrease of photocurrent density. Excess defect states could act as the recombination centers of photogenerated electrons and holes.

In this research, the adsorption properties of biomass tube clusters (dandelion pappi) and carbonized biomass tube clusters toward dyes were investigated, respectively. The results showed that both biomass tube clusters and carbonized biomass tube clusters exhibited excellent adsorption properties for cationic dyes (alkaline orange and methyl violet). The adsorption properties of biomass tube clusters are better than that of carbonized biomass tube clusters. The adsorption capacity of biomass tube clusters to alkaline orange and methyl violet are 162.25mg${\text{g}}^{-1}$ and 258.34mg${\text{g}}^{-1}$, respectively, and carbonized biomass tube clusters are 158.50mg${\text{g}}^{-1}$ and 136.95mg${\text{g}}^{-1}$, respectively. Moreover, these materials display the excellent performance in terms of adsorption kinetics, and can reach adsorption equilibrium within 40min due to the characteristic of tubular structure. Simulation results demonstrated that the adsorption isotherm and the adsorption kinetics of the two materials were well matched with the Langmuir model and the pseudo first-order kinetic model, respectively. Besides the excellent adsorption property, many other advantages such as wide sources, environmental friendliness and low-cost make the present tube clusters potential application value in the field of dye wastewater treatment.

Mesoporous titanium dioxide (TiO₂) hollow nanofibers (HNFs) were successfully prepared by a facile electrospinning and calcination method. Techniques such as X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to characterize TiO₂ fibers. It was revealed that TiO₂ crystals with an appropriate anatase fraction (71.58%) were grown and a tubular mesoporous structure was formed with a high specific surface area. Photodecomposition of methyl orange (MO) solution showed that TiO₂ HNFs exhibited much higher photocatalytic activity than corresponding TiO₂ nanofibers (NFs) and loose-structured nanofibers (LNFs). The significant enhancement of photocatalytic activity was attributed to both the sufficient growth of active anatase phase primarily and a tubular mesoporous nature of TiO₂ HNFs.

As a novel strategy for improving the photocatalytic activity through hybrid with small molecule photosensitizer, $\alpha$-Fe₂O₃ has been successfully functionalized with protoporphyrin IX (PPIX) in order to enhance sunlight-driven photocatalytic degradation of dyes and antimicrobial activity due to the staggered energy band structures which promote a charge transfer between $\alpha$-Fe₂O₃ and PPIX and generate free holes and electrons. The results show that $\alpha$-Fe₂O₃ could absorb more sunlight and generate more free electrons and holes after being decorated with PPIX. As a result, PPIX-functionalized $\alpha$-Fe₂O₃ has an enhanced photocatalytic degradation of dyes ability against rhodamine B and methyl orange and antimicrobial activity against Escherichia coli. The present strategy gives a promising way to prepare photocatalytic agent hybrid with small molecule photosensitizer.

Glass frit plays an important role in the silver paste for silicon solar cells. In this work, we prepare glass frit doped with different rare-earth elements (Y, La, Sm, Er) and study how the doping element affects the performance of the solar cells. Solar cells with La-doped and Sm-doped glass frits show average conversion efficiencies higher than 17.5%, while solar cells with Y-doped or Er-doped frit show lower efficiencies. By analyzing the Raman spectra of the rare-earth doped glass frits, we find that the average coordination number of Te–O (${\text{N}}_{\mathrm{\text{Te-O}}}$) in the glass can be tuned by the rare-earth dopant. La or Sm doping leads to a moderate value of ${\text{N}}_{\mathrm{\text{Te-O}}}$, which is believed to achieve a glass formation ability that optimizes the structure of the Ag–Si interface of the cell for the best performance.

Co-doped ZnO/C composites derived from Co-doped MOF-5 were applied as the anode materials for Li-ion batteries (LIBs), which showed advanced capacity and rate performance. Their good electrochemical properties were attributed to the Co-doping and C complex which greatly enhance ZnO electrical conductivity, and the microporous and macroporous structure which augments the contact area between electrolyte and electrode shortening the diffusion path of Li ions as well as releasing the intense heat caused by Li alloying.

Grain boundary engineering is considered an effective approach to improve the performance of thermoelectric materials. Herein, by introducing KOH into the grain boundary of Bi₂${\text{Te}}_{2.7}$${\text{Se}}_{0.3}$ (BTS) via liquid phase sintering strategy, the thermoelectric performances are improved significantly. The melting KOH spreads over the grain boundaries during the high temperature sintering process, which could be used to optimize the carrier/phonon transport behavior. The maximum ZT reaches up to 0.97 for the sample incorporated with 0.5%Wt of KOH at 425K, which achieves 30% improvement over the pure BTS. The homogeneous distribution of KOH layer on the grain boundaries forms efficient potential barrier scattering, which increases power factor and reduces thermal conductivity simultaneously. Particularly, it is found that the maximum ZT can be tuned gradually in the temperature range from 450K to 375K by tuning the weight percent of KOH, demonstrating a possibility in adjusting the thermoelectric properties of BTS using a relatively simple method.

The advanced oxidation processes (AOPs) based on sulfate radicals have triggered tremendous research efforts in environmental remediation field. In this study, we proposed a facile silver ferrite (${\text{AgFeO}}_2)$ nanocatalyst via a simple co-precipitation at room temperature. The as-prepared AgFeO₂ was characterized by XRD, SEM, TEM, XPS, FTIR and N₂ adsorption–desorption techniques and was used for persulfate (PDS) activation for the first time. The result showed that AgFeO₂ as a PDS activator exhibited superior degradation efficiency of Rhodamine B (RhB) as compared to bare Ag₂O, FeOOH and CuFeO₂. Moreover, the AgFeO₂ catalyst also demonstrated high degradation efficiency for 4-nitrophenol and Methyl Orange in the presence of PDS. The catalytic performance of AgFeO₂ was further evaluated in terms of various parameters, including solution pH, PDS concentration and catalyst dosage. The degradation pathway was proposed based on Liquid Chromatography Mass Spectrometer (LC-MS) result and the degradation mechanism was elucidated through radical scavenger experiments. These findings will extend the scope of novel catalysts for PDS activation and promote the use of AgFeO₂ in more practical applications.

Using ionic liquids (ILs) as electrolytes in developing electrochemical sensors for SO₂ detection is of much interest. We compared the electrochemical behaviors of SO₂ in choline chloride–ethylene glycol-based deep eutectic solvent (ChCl–EG-based DES), 1-(3-hydroxypropyl)-3-methylimidazolium tetrafluoroboride ([C₃OHmim]BF₄), and [C₃OHmim]${\text{BF}}_4+$monoethanolamine (MEA) (6.2:1 in molar ratio). Addition of MEA into [C₃OHmim]BF₄ can significantly increase the SO₂ absorption capacity and enhance the electrochemical response of SO₂. However, as we use ChCl–EG-based DES, the reduction current is 10 times larger than in [C₃OHmim]BF₄ and 4 times larger than in [C₃OHmim]${\text{BF}}_4+$MEA (6.2:1 in molar ratio). And SO₂ gas shows high diffusion coefficient value as in the ChCl–EG-based DES. A good linear relationship between the reduction current and the SO₂ content was obtained in the tested SO₂ gas content range from 200ppm to 1500ppm. Our findings provide new route for DESs as electrolytes for SO₂ sensor designing with high sensitivity.

p-n heterojunction Ag₂CO₃/Ag₃PO₄/Ni thin films were prepared by electrochemical co-deposition. The surface morphology and structural properties of the thin films were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). The photocatalytic (PC) properties of the Ag₂CO₃/Ag₃PO₄/Ni composite thin films were investigated by their ability to degrade rhodamine B (RhB) and Congo red (CR) under visible light irradiation. The results showed that the photodegradation efficiency of RhB by an Ag₂CO₃/Ag₃PO₄/Ni thin film under visible-light irradiation for 30min (98.84%) was 2.64 times higher than that of an Ag₃PO₄/Ni thin film and 3.44 times higher than of an Ag₂CO₃/Ni thin film. The presence of a $p$-$n$ heterojunction greatly increased the charge conductivity of the film and its ability to photocatalytically reduce dissolved oxygen, which are the main reasons for the improved PC performance of the Ag₂CO₃/Ag₃PO₄/Ni films.

Mesoporous g-C₃N₄ is prepared by a hard template method and is then decorated by carbon quantum dots (CQDs) and TiO₂ nanoparticles through an impregnation route followed by a hydrothermal method. The synthesized hybrids possess higher specific surface area up to 131cm²/g and show effective absorption of visible light range and improved instantaneous photocurrent response, which reveals the enhanced photo-generated carrier separation efficiency. The first-order kinetic reaction rate constant of photocatalytic degradation of gaseous benzene by TCPCN-2 is 5.5 times of the bulk g-C₃N₄. Its degradation rate is up to 96.08% with good photocatalytic stability. Thus, the TiO₂ nanoparticles and CQDs co-decorated g-C₃N₄ hybrids are promising photocatalysts.

Nano Pd-Ni/$\gamma$-Al₂O₃ bimetallic catalyst was prepared by chemical precipitation method enhanced with ultrasonic wave. The influence of dosage of dispersant, ultrasonic intensity and mass ratio of Pd to Ni on the dechlorination property of the catalyst obtained was investigated in detail. The appearance morphology, composition and structure of the catalysts prepared were characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption, while the specific surface area was determined using the Brunauer–Emmett–Teller (BET) isotherm and the chemical composition of active gradients was tested with inductively coupled plasma-atomic emission spectrometry (ICP-AES). Results indicate that the nano Pd-Ni/$\gamma$-Al₂O₃ bimetallic catalyst prepared has uniform distribution of active ingredients with an average particle size of 4.91nm, and the chlorine content of shellac dechlorinated with the catalyst obtained is 0.34wt.% which is lower than that reported in the literature, meaning the perfect dechlorination property of the catalyst.

In this work, we proposed an effective strategy to prepare nitrogen-doped popcorn-like porous carbons (NPPCs) via ultra-fast carbonization of zeolitic immidazolate frameworks (ZIFs-8), where the ZIFs-8 acted as carbon precursor as well as the template. The obtained NPPCs possess popcorn-like morphology with large specific surface area of 1243m²/g, total pore volume of 1.48cm³/g and high nitrogen content. Remarkably, the average pore diameter of NPPCs was 4.72nm, indicating the presence of amount substantial mesopores. As the electrode of supercapacitor, the NPPCs revealed a relatively high specific capacitance of 610.4F/g in KOH (6mol/L) at 5mV/s. Even the scan rate was increased to 50mV/s, an impressive capacity of 424.8F/g can be achieved, suggesting good rate capability. Besides, it exhibited outstanding cycling stability with 93% of specific capacitance retention after 10,000 GCD cycles. Moreover, the NPPCs electrode demonstrated high electrochemical performance and stability by designing the coin-type and flexible supercapacitor. The large specific surface area, abundant accessible mesoporosity and novel nanostructure are account for the superior performance.