Facile Electrospinning Synthesis of Carbonized Polyvinylpyrrolidone (PVP)/g-C3N4Hybrid Films for Photoelectrochemical Applications

Physical regulation of copper catalyst with a hydrophobic promoter for enhancing CO2 hydrogenation to methanol

The hydrogenation of CO₂ to methanol, which is restricted by water products, requires a selective removal of water from the reaction system. Here, we show that physically combining hydrophobic polydivinylbenzene with a copper catalyst supported by silica can increase methanol production and CO₂ conversion. Mechanistic investigation reveals that the hydrophobic promoter could hinder the oxidation of copper surface by water, maintaining a small fraction of metallic copper species on the copper surface with abundant Cu^δ+, resulting in high activity for the hydrogenation. Such a physically mixed catalyst survives the continuous test for 100 h owing to the thermal stability of the polydivinylbenzene promoter.

Recent Progress on Photoelectrochemical Water Splitting of Graphitic Carbon Nitride (g-CN) Electrodes

Graphitic carbon nitride (g-CN), a promising visible-light-responsive semiconductor material, is regarded as a fascinating photocatalyst and heterogeneous catalyst for various reactions due to its non-toxicity, high thermal durability and chemical durability, and "earth-abundant" nature. However, practical applications of g-CN in photoelectrochemical (PEC) and photoelectronic devices are still in the early stages of development due to the difficulties in fabricating high-quality g-CN layers on substrates, wide band gaps, high charge-recombination rates, and low electronic conductivity. Various fabrication and modification strategies of g-CN-based films have been reported. This review summarizes the latest progress related to the growth and modification of high-quality g-CN-based films. Furthermore, (1) the classification of synthetic pathways for the preparation of g-CN films, (2) functionalization of g-CN films at an atomic level (elemental doping) and molecular level (copolymerization), (3) modification of g-CN films with a co-catalyst, and (4) composite films fabricating, will be discussed in detail. Last but not least, this review will conclude with a summary and some invigorating viewpoints on the key challenges and future developments.

Eco-friendly utilization of sawdust: Ionic liquid-modified biochar for enhanced Li+ storage of TiO2

In China, forestry logging and wood processing produce hundreds of thousands of tons of sawdust every year, which is either discarded or burned. These nonecofriendly practices result in some challenges associated with greenhouse gas emissions. Sawdust-based biochar tailored for anodes of lithium-ion batteries (LIBs) can effectively realize value-added utilization of sawdust. The purpose of the current work is to prepare TiO₂/biochar nanocomposites to improve the electrical conductivity and structural stability of the anode. However, poor interfacial interaction between TiO₂ and carbon in the TiO₂/C composites arising from their heterogeneous nature leads to structural deformation of the composites used as anodes of lithium-ion batteries (LIBs). A strategy of constructing ionic liquid-coupled biochar/TiO₂ interfaces is proposed to obtain chemically bonded interfaces between TiO₂ and sawdust-derived biochar. In this study, TiO₂/C-880 composites are prepared by one-step carbonization of TiO₂ nanoparticles (NPs) and sawdust at 880 °C previously dissolved in 1-butyl-3-methyl-imidazolium ([Bmim]H₂PO₄)/dimethyl sulfoxide (DMSO). The morphologies of TiO₂/C-880 demonstrate that the TiO₂ is encapsulated by porous biochar with intimate interfaces, and the X-ray photoelectron spectroscopy (XPS) results indicate the formation of N-Ti-O/N-O-Ti and Ti-O-P bonds that bridge the two components. TiO₂/C-880 electrodes have high reversible specific capacities (404 mAh g^-1 at 0.1 A g^-1) and desirable long-term cyclic stability (100 mAh g^-1 at 2 A g^-1 throughout 2500 cycles). Moreover, large diffusion coefficients (D_Li⁺) ranging from 5.9 × 10^-11 to 1.2 × 10^-9 cm² s^-1 are obtained from galvanostatic intermittent titration (GITT) curves. The N-Ti-O/N-O-Ti and Ti-O-P bonds at the interfaces offer routes for fast Li⁺/electron transport, which account for the high performance of the TiO₂/C-880 electrodes.

Near-infrared photoactive Yb-MOF functionalized with a large conjugate ionic liquid: synthesis and application for photoelectrochemical immunosensing of carcinoma embryonic antigen

A novel near-infrared (NIR)-excited photoelectrochemical (PEC) immunosensor based on an ionic liquid functionalized metal organic framework (Yb-MOF) and gold nanoparticles (Au-NPs) was designed for the high-performance determination of carcinoembryonic antigen (CEA). The Yb-MOF was synthesized from the coordination of the Yb3+ metal ion with the 1,1'-(1,5-dihydropyrene-2,7-diyl)bis(3-(4-carboxybenzyl)-1H-imidazol-3-ium) bromide [DDPDBCBIm(Br)2] ionic liquid by a hydrothermal method. To improve the photoelectric conversion efficiency of the Yb-MOF in the NIR region, the surface of the Yb-MOF was integrated with gold nanoparticles (AuNPs) to fabricate a Yb-MOF@AuNP nanocomposite through an in situ reduction of chloroauric acid with sodium borohydride. The NIR photoelectrochemical response of the Yb-MOF@AuNPs at 808 nm was enhanced 4-fold over the pristine Yb-MOF. Subsequently, a photoelectrochemical platform based on the Yb-MOF@AuNPs was constructed for loading the CEA antibody (anti-CEA). After cross-linking with glutaraldehyde followed by blocking with bovine serum albumin, a photoelectrochemical sensor for assaying CEA was fabricated. Upon specifically interacting with CEA, CEA can block the photogenerated electron-hole pair transfer and the mass transfer of ascorbic acid to the sensing interface, thus leading to a decrease in photocurrent response. The photocurrent variation can be used for determining CEA quantitatively. After optimizing the experimental conditions, the photocurrent variations before and after incubation with CEA were linearly correlated with the CEA concentration over the range of 0.005-15 ng mL-1. The detection limit of CEA was calculated to be 0.25 pg mL-1 (S/N = 3). The immunosensor was employed for the measurement of free CEA in clinical serum samples, and the results were very consistent with the values obtained by clinical tests. The NIR PEC immunosensor also demonstrated excellent accuracy and recovery, which corroborates its potential as a practical technique in clinical diagnosis.

Dry Formulation of Virus-Like Particles in Electrospun Nanofibers

Biologics can be combined with liquid polymer materials and electrospun to produce a dry nanofibrous scaffold. Unlike spray-drying and freeze-drying, electrospinning minimizes the physiological stress on sensitive materials, and nanofiber mat properties such as hydrophobicity, solubility, and melting temperature can be tuned based on the polymer composition. In this study, we explored the dry formulation of a virus-like particle (VLP) vaccine by electrospinning VLP derived from rabbit hemorrhagic disease virus modified to carry the MHC-I gp100 tumor-associated antigen epitope. VLP were added to a polyvinylpyrrolidone (PVP) solution (15% w/v) followed by electrospinning at 24 kV. Formation of a nanofibrous mat was confirmed by scanning electron microscopy, and the presence of VLP was confirmed by transmission electron microscopy and Western blot. VLP from the nanofibers induced T-cell activation and interferon- (IFN-) γ production in vitro. To confirm in vivo cytotoxicity, Pmel mice treated by injection with gp100 VLP from nanofibers induced a gp100 specific immune response, lysing approximately 65% of gp100-pulsed target cells, comparable to mice vaccinated with gp100 VLP in PBS. VLP from nanofibers also induced an antibody response. This work shows that electrospinning can be used to dry-formulate VLP, preserving both humoral and cell-mediated immunity.

Engineering Kinetics-Favorable Carbon Sheets with an Intrinsic Network for a Superior Supercapacitor Containing a Dual Cross-linked Hydrogel Electrolyte

Despite the physicochemical advantages of two-dimensional (2D) carbons for supercapacitors, the inappropriate texture within 2D carbon materials suppresses the charge storage capability. Reported here are heteroatom-rich carbon sheets with the overall network engineered by molecular structure modulation and subsequent chemical activation of a three-dimensional (3D) cross-linked polymer. The 3D-to-2D reconstruction mechanism is unveiled. The architecture with a large active surface, fully interpenetrating and conductive network, and rich surface heteroatoms relieves well the ionic diffusion restriction within thick sheets and reduces the overall resistance, exhibiting fast transport kinetics and excellent stability. Indeed, high gravimetric capacitance (281.1 F g^-1 at 0.5 A g^-1), ultrahigh retention rate (92.5% at 100 A g^-1), and impressive cyclability (89.7% retention after 20 000 cycles) are achieved by this material. It also possesses a high areal capacitance of 3.56 F cm^-2 at 0.5 A g^-1 under a high loading of 25 mg cm^-2. When coupled with the developed dual cross-linked hydrogel electrolyte (Al-alginate/poly(acrylamide)/sodium sulfate), a quasi-solid-state supercapacitor delivers an energy density of 28.3 Wh kg^-1 at 250.1 W kg^-1, which is significantly higher than those of some reported aqueous carbon-based symmetric devices. Moreover, the device displays excellent durability over 10 000 charge/discharge cycles. The proposed cross-linked polymer strategy provides an efficient platform for constructing dynamics-favorable carbon architectures and attractive hydrogel electrolytes toward improved energy supply devices.

Synthesis of metallic copper modified g-C3N4 by molecular self-assembly structure and its combined catalytic performance with activated sludge

Copper modified carbon nitride (CuCN) was prepared by a hydrothermal self-assembly reaction and following high temperature thermal polymerization process. Finally, the sample exhibits uniform one-dimensional tubular structure. Interestingly, the separation efficiency of electron-hole pair is improved, and more catalytic active sites are exposed due to the special hollow structure. Meanwhile, the presence of copper element narrows its band gap, leading to the enhancement of photocatalytic degradation performance under simulated sunlight. In addition, the effect of CuCN on dehydrogenase activity of activated sludge was determined by TTC reduction method. After adding CuCN-2, the activity of activated sludge reached 0.134 μmol g^-1 min^-1, which indicated that the prepared CuCN-2 had good biocompatibility. It is suitable for both photocatalytic process and activated sludge treatment process. Therefore, the combination of photocatalytic technology and activated sludge process can further completely degrade organic pollutants. We found that CuCN could protect the survival and growth of microorganisms in activated sludge, so that the degradation efficiency of CuCN to nitrobenzene could reach 94.4 %. Therefore, CuCN has broad application prospects in photocatalytic-activated sludge combined treatment.

Current-induced restructuring in bent silver nanowires

A number of metallic one-dimensional nanostructures have been proposed as interconnects for next-generation electronic devices. Generally, reports on charge transport properties consider low current density regimes in nanowires (or nanotubes) with intrinsically straight configurations. In these circumstances, direct observations of the interconnecting nanofilament electrical failure are scarce, particularly for initially crooked structures. Here, the electrical and structural responses of suspended silver nanowires exposed to increasing current densities were analysed using in situ transmission electron microscopy. At low rates of bias application, initially straight nanowires showed trivial behaviour up to their breakdown, with electromigration and gradual necking taking place. By contrast, these nanowires with an initially crooked configuration exhibit a mixed set of responses which included string-like resonance and structural rearrangements. Remarkably, it was observed that restructuring does not necessarily compromise the transport function of these interconnectors. Hence, initially crooked nanowires could import higher resilience to future nanoelectronic devices by delaying catastrophic breakdown of interconnectors subjected to unexpected current surges.

Carbon Nitride Materials for Water Splitting Photoelectrochemical Cells

Graphitic carbon nitride materials (CNs) have emerged as suitable photocatalysts and heterogeneous catalysts for various reactions thanks to their tunable band gap, suitable energy-band position, high stability under harsh chemical conditions, and low cost. However, the utilization of CN in photoelectrochemical (PEC) and photoelectronic devices is still at an early stage owing to the difficulties in depositing high-quality and homogenous CN layer on substrates, its wide band gap, poor charge-separation efficiency, and low electronic conductivity. In this Minireview, we discuss the synthetic pathways for the preparation of various structures of CN on substrates and their underlying photophysical properties and current photoelectrochemical performance. The main challenges for CN incorporation into PEC cell are described, together with possible routes to overcome the standing limitations toward the integration of CN materials in PEC and other photoelectronic devices.

Reduced graphene oxide/BiFeO3 nanohybrids-based signal-on photoelectrochemical sensing system for prostate-specific antigen detection coupling with magnetic microfluidic device

A novel magnetic controlled photoelectrochemical (PEC) sensing system was designed for sensitive detection of prostate-specific antigen (PSA) using reduced graphene oxide-functionalized BiFeO₃ (rGO-BiFeO₃) as the photoactive material and target-triggered hybridization chain reaction (HCR) for signal amplification. Remarkably enhanced PEC performance could be obtained by using rGO-BiFeO₃ as the photoelectrode material due to its accelerated charge transfer and improved the visible light absorption. Additionally, efficient and simple operation could be achieved by introducing magnetic controlled flow-through device. The assay mainly involved in anchor DNA-conjugated magnetic bead (MB-aDNA), PSA aptamer/trigger DNA (Apt-tDNA) and two glucose oxidase-labeled hairpins (H1-GOx and H2-GOx). Upon addition of target PSA, the analyte initially reacted with the aptamer to release the trigger DNA, which partially hybridized with the anchor DNA on the MB. Thereafter, the unpaired trigger DNA on the MB opened the hairpin DNA structures in sequence and propagated a chain reaction of hybridization events between two alternating hairpins to form a long nicked double-helix with numerous GOx enzymes on it. Subsequently, the enzymatic product (H₂O₂) generated and consumed the photo-excited electrons from rGO-BiFeO₃ under visible light irradiation to enhance the photocurrent. Under optimal conditions, the magnetic controlled PEC sensing system exhibited good photocurrent responses toward target PSA within the linear range of 0.001 - 100ng/mL with a detection limit of 0.31pg/mL. Moreover, favorable selectivity, good stability and satisfactory accuracy were obtained. The excellent analytical performance suggested that the rGO-BiFeO₃-based PEC sensing platform could be a promising tool for sensitive, efficient and low cost detection of PSA in disease diagnostics.

Electrospinning Preparation of Nanostructured g-C3N4/BiVO4 Composite Films with an Enhanced Photoelectrochemical Performance

Nanostructured g-C₃N₄/BiVO₄ composite films with an enhanced photoelectrochemical (PEC) performance have been fabricated via the facile electrospinning technique. The g-C₃N₄ nanosheets can not only form heterojunctions with BiVO₄ but also prevent the agglomeration of BiVO₄, helping the formation of nanostructures. The as-prepared g-C₃N₄/BiVO₄ films exhibit good coverage and stability. The PEC performance of the g-C₃N₄/BiVO₄ films is much more enhanced compared with that for individual BiVO₄ films because of the enhanced electron-hole separation. The photocurrent density is 0.44 mA/cm² for g-C₃N₄/BiVO₄ films at 0.56 V in the linear sweep current-voltage test, over 10 times higher than that of individual BiVO₄ films (0.18 mA/cm²). The effects of the preparation conditions including the g-C₃N₄ content, collector temperature, calcination temperature, and electrospinning time on the PEC performance were investigated, and the reasons for the effects were proposed. The optimal preparation condition was with 3.9 wt % g-C₃N₄ content in the electrospinning precursor, 185 °C collector temperature, 450 °C calcination temperature, and 40 min electrospinning time. The excellent PEC performance and the facile preparation method suggest that the g-C₃N₄/BiVO₄ films are good candidates in energy and environmental remediation area.

WO3/g-C3N4 composites: one-pot preparation and enhanced photocatalytic H2 production under visible-light irradiation

A series of WO₃/g-C₃N₄ composites with different WO₃ contents were prepared via a facile one-pot pyrolysis method, and showed notably enhanced visible-light-driven photocatalytic H₂-evolution activities, with the highest rate of 400 μmol h^-1 g_cat^-1 that was 15.0 times of that for pristine g-C₃N₄. Contents and sizes of WO₃ crystallites in the composites were easily adjusted by changing the molar ratios of (NH₄)₂WS₄ to C₃H₆N₆ in the feed reagents, thereby successfully optimizing the Z-scheme system constructed by WO₃ and g-C₃N₄ and thus effectively reducing the recombination of photogenerated charge carriers in g-C₃N₄. Moreover, pore volumes and surface areas of the composites were gradually enlarged by introducing WO₃ into g-C₃N₄ via the one-pot preparation strategy, therefore promoting the redox reactions to evolve H₂. This work presented an effective route to simultaneously optimize the phase compositions and textural structures of photocatalysts for enhanced H₂ evolution.