Precise Modulation of Carbon Activity Sites in Metal-Free Covalent Organic Frameworks for Enhanced Oxygen Reduction Electrocatalysis.

Metal-free carbon-based materials have gained recognition as potential electrocatalysts for the oxygen reduction reaction (ORR) in new environmentally-friendly electrochemical energy conversion technologies. The presence of effective active centers is crucial for achieving productive ORR. In this study, we present the synthesis of two metal-free dibenzo[a,c]phenazine-based covalent organic frameworks (DBP-COFs), specifically JUC-650 and JUC-651, which serve as ORR electrocatalysts. Among them, JUC-650 demonstrates exceptional catalytic performance for ORR in alkaline electrolytes, exhibiting an onset potential of 0.90 V versus RHE and a half-wave potential of 0.72 V versus RHE. Consequently, JUC-650 stands out as one of the most outstanding metal-free COF-based ORR electrocatalysts report to date. Experimental investigations and density functional theory calculations confirm that modulation of the frameworks' electronic configuration allows for the reduction of adsorption energy at the Schiff-base carbon active sites, leading to more efficient ORR processes. Moreover, the DBP-COFs can be assembled as excellent air cathode catalysts for zinc-air batteries (ZAB), rivaling the performance of commercial Pt/C. This study provides valuable insights for the development of efficient metal-free organoelectrocatalysts through precise regulation of active site strategies.

Red Phosphorus Decorated TiO2 Nanorod Mediated Photodynamic and Photothermal Therapy for Renal Cell Carcinoma.

Clear cell renal cell carcinoma (ccRCC) is a serious and tenacious disease. Photodynamic therapy (PDT) and photothermal therapy (PTT) are effective means of cancer treatment. However, PDT combined with PTT has been rarely reported in ccRCC treatment. In the present study, by developing the core-shell structured TiO2 @red phosphorus nanorods (TiO2 @RP NRs) as a photosensitizer, the feasibility and effectiveness of synchronous PDT and PTT treatments for ccRCC are demonstrated. The core-shell structured TiO2 @RP NRs are synthesized to drive the PDT and PTT for ccRCC, in which the RP shell is the sensitizer even in the near-infrared (NIR) region. The optimized TiO2 @RP NRs can respond to NIR and produce local heat under irradiation. The NRs are estimated in ccRCC treatments via cell counting kit-8 assay, propidium iodide staining, qRT-PCR, and reactive oxygen species (ROS) probes in vitro, while terminal deoxynucleotidyl transferase dUTP nick-end labeling is conducted in vivo. After NIR irradiation, TiO2 @RP NRs can efficiently kill ccRCC cells by producing local heat and ROS and cause low injury to normal kidney cells. Furthermore, treatment with TiO2 @RP NRs and NIR can kill significant numbers of deep-tissue ccRCC cells in vivo. This work highlights a promising photo-driven therapy for kidney cancer.

Controlled Asymmetric Charge Distribution of Active Centers in Conjugated Polymers for Oxygen Reduction.

Active center reconstruction is essential for high performance oxygen reduction reaction (ORR) electrocatalysts. Usually, the ORR activity stems from the electronic environment of active sites by charge redistribution. We introduce an asymmetry strategy to adjust the charge distribution of active centers by designing conjugated polymer (CP) catalysts with different degrees of asymmetry. We synthesized asymmetric backbone CP (asy-PB) by modifying B←N coordination bonds and asymmetric sidechain CP (asy-PB-A) with different alkyl chain lengths. Both CPs with backbone and sidechain asymmetry exhibit superior ORR performance to their symmetric counterparts (sy-P and sy-PB). The asy-PB with greater asymmetry shows higher catalytic activity than asy-PB-A with relatively smaller asymmetry. DFT calculations reveal that the increased dipole moment and non-uniform charge distribution caused by asymmetric structure endows the center carbon atom of bipyridine with efficient catalytic activity.

Metal-Free Thiophene-Sulfur Covalent Organic Frameworks: Precise and Controllable Synthesis of Catalytic Active Sites for Oxygen Reduction.

Defective or heteroatom-doped metal-free carbon materials (MFCMs) have been regarded as efficient oxygen reduction reaction (ORR) catalysts in the past decade. However, the active centers for ORR in MFCMs are hard to confirm precisely and synthesize controllably through common methods such as high-temperature pyrolysis or heteroatom doping. To verify the precise structure acting as the active center for the ORR, we first report two crystalline metal-free thiophene-sulfur covalent organic frameworks (MFTS-COFs) as ORR catalysts. The MFTS-COFs show more positive catalytic capability than the thiophene-free COF, indicating that pentacyclic thiophene-sulfur building blocks act as active centers to induce ORR catalytic activity. MFTS-COFs with higher contents of thiophene-sulfur exhibit better ORR performance. The experimental identification is supported by density functional theory calculations. These results thus demonstrate that rational design and precise synthesis of metal-free crystalline organic materials can promote the development of new ORR catalysts.

Three-dimensional Salphen-based Covalent-Organic Frameworks as Catalytic Antioxidants.

The development of three-dimensional (3D) functionalized covalent-organic frameworks (COFs) is of critical importance for expanding their potential applications. However, the introduction of functional groups in 3D COFs remains largely unexplored. Herein, we report the first example of 3D Salphen-based COFs (3D-Salphen-COFs) and their metal-containing counterparts (3D-M-Salphen-COFs). These Salphen-based COFs exhibit high crystallinity and specific surface area in addition to excellent chemical stability. Furthermore, the Cu(II)-Salphen COF displays high activity in the removal of superoxide radicals. This study not only presents a new pathway to construct 3D functionalized COFs but also promotes their applications in biology and medicine.

Three-Dimensional Tetrathiafulvalene-Based Covalent Organic Frameworks for Tunable Electrical Conductivity.

The functionalization of three-dimensional (3D) covalent organic frameworks (COFs) is essential to broaden their applications. However, the introduction of organic groups with electroactive abilities into 3D COFs is still very limited. Herein we report the first case of 3D tetrathiafulvalene-based COFs (3D-TTF-COFs) with non- or 2-fold interpenetrated pts topology and tunable electrochemical activity. The obtained COFs show high crystallinity, permanent porosity, and large specific surface area (up to 3000 m2/g). Furthermore, these TTF-based COFs are redox active to form organic salts that exhibit tunable electric conductivity (as high as 1.4 × 10-2 S cm-1 at 120 °C) by iodine doping. These results open a way toward designing 3D electroactive COF materials and promote their applications in molecular electronics and energy storage.

Heterocyclization Strategy for Construction of Linear Conjugated Polymers: Efficient Metal-Free Electrocatalysts for Oxygen Reduction.

Exploring cost-effective and efficient metal-free electrocatalysts for the oxygen reduction reaction (ORR) is crucial for the development of energy conversion and storage technologies. Reported here is a novel heterocyclization strategy to construct efficient ORR catalysts based on linear conjugated polymers (LCPs), which are composed of N-, S-, or Se-heterocycles. Among these polymers, the covalently linked pyridine and thiophene molecule (P-T) with reduced graphene oxide (rGO) exhibits a remarkable half-wave potential of 0.79 V (vs. RHE) and excellent electrochemical stability, which are among the highest values for metal-free polymers as ORR catalysts. Density-functional theory (DFT) calculations reveal that the molecule with a phenyl unit (P-Ph) is catalytically inactive, and when a thiophene unit is introduced to replace the phenyl unit in the conjugated backbone it features highly efficient electrocatalytic active sites. More importantly, the well-defined molecular structures and controllable active sites in the pyrolysis and metal-free polymers highlight new opportunities for the catalytic metal-free ORR.

Double-Helix Structure in Carrageenan-Metal Hydrogels: A General Approach to Porous Metal Sulfides/Carbon Aerogels with Excellent Sodium-Ion Storage.

The metal sulfide-carbon nanocomposite is a new class of anode material for sodium ion batteries, but its development is restricted by its relative poor rate ability and cyclic stability. Herein, we report the use of double-helix structure of carrageenan-metal hydrogels for the synthesis of 3D metal sulfide (Mx Sy ) nanostructure/carbon aerogels (CAs) for high-performance sodium-ion storage. The method is unique, and can be used to make multiple Mx Sy /CAs (such as FeS/CA, Co9 S8 /CA, Ni3 S4 /CA, CuS/CA, ZnS/CA, and CdS/CA) with ultra-small nanoparticles and hierarchical porous structure by pyrolyzing the carrageenan-metal hydrogels. The as-prepared FeS/CA exhibits a high reversible capacity and excellent cycling stability (280 mA h-1 at 0.5 A g-1 over 200 cycles) and rate performance (222 mA h-1 at 5 A g-1 ) when used as the anode material for sodium-ion batteries. The work shows the value of biomass-derived metal sulfide-carbon heterostuctures in sodium-ion storage.

Preparation of high-strength photochromic alginate fibers based on the study of flame-retardant properties.

Color-changing fibers have attracted much attention for their wide applications in camouflage, security warnings, and anti-counterfeiting. The inorganic color-changing material tungsten trioxide (WO3) has been widely investigated for its good stability, controllability, and ease of synthesis. In this study, photochromic alginate fibers (WO3@Ca-Alg) were prepared by incorporating UV-responsive hybrid tungsten trioxide nanoparticles in the fiber production process. The prepared photochromic alginate fibers changed from white to dark blue after 30 min of UV irradiation and returned to their original color after 64 h. It can be seen that WO3@Ca-Alg has the advantage of long color duration. The strength of this fiber reached 2.61 cN/dtex and the limiting oxygen index (LOI) was 40.9 %, which indicates that the fiber exhibited mechanical resistance and flame-retardant properties. After the cross-linking of WO3@Ca-Alg by sodium tetraborate, a new core-shell structure was generated, which was able to encapsulate tungsten trioxide in it, thus reducing the amount of tungsten trioxide loss, and its salt and washing resistance was greatly improved. This photochromic alginate fiber can be mass produced and spun into yarn.

Mesoporous zinc oxide-based drug delivery system offers an antifungal and immunoregulatory strategy for treating keratitis.

Fungal keratitis is a refractory eye disease that is prone to causing blindness. Fungal virulence and inflammatory responses are two major factors that accelerate the course of fungal keratitis. However, the current antifungal drugs used for treatment usually possess transient residence time on the ocular surface and low bioavailability deficiencies, which limit their therapeutic efficacy. In this work, natamycin (NATA)-loaded mesoporous zinc oxide (Meso-ZnO) was synthesized for treating Aspergillus fumigatus keratitis with excellent drug-loading and sustained drug release capacities. In addition to being a carrier for drug delivery, Meso-ZnO could restrict fungal growth in a concentration-dependent manner, and the transcriptome analysis of fungal hyphae indicated that it inhibited the mycotoxin biosynthesis, oxidoreductase activity and fungal cell wall formation. Meso-ZnO also promoted cell migration and exhibited anti-inflammatory role during fungal infection by promoting the activation of autophagy. In mouse models of fungal keratitis, Meso-ZnO/NATA greatly reduced corneal fungal survival, alleviated tissue inflammatory damage, and reduced neutrophils accumulation and cytokines expression. This study suggests that Meso-ZnO/NATA can be a novel and effective treatment strategy for fungal keratitis.

Facile synthesis of MoS2@red phosphorus heterojunction for synergistically photodynamic and photothermal therapy of renal cell carcinoma.

The therapy of the clear cell renal cell carcinoma (ccRCC) is crucial for the human healthcare due to its easy metastasis and recurrence, as well as resistance to radiotherapy and chemotherapy. In this work, we propose the synthesis of MoS2@red phosphorus (MoS2@RP) heterojunction to induce synergistic photodynamic and photothermal therapy (PDT/PTT) of ccRCC. The MoS2@RP heterojunction exhibits enhanced spectra absorption in the NIR range and produce local heat-increasing under the NIR laser irradiation compared with pure MoS2 and RP. The high photocatalytic activity of the MoS2@RP heterojunction contributes to effective transferring of the photo-excited electrons from the RP to MoS2, which promotes the production of various types of radical oxygen species (ROS) to kill the ccRCC cells. After the NIR irradiation, the MoS2@RP can effectively induce the apoptosis in the ccRCC cells through localized hyperthermia and the generation of ROS, while exhibiting low cytotoxicity towards normal kidney cells. In comparison to MoS2, the MoS2@RP heterojunction shows an approximate increase of 22 % in the lethality rate of the ccRCC cells and no significant change in toxicity towards normal cells. Furthermore, the PDT/PTT treatment using the MoS2@RP heterojunction effectively eradicates a substantial number of deep-tissue ccRCC cells in vivo without causing significant damage to major organs. This study presents promising effect of the MoS2@RP heterojunction-based photo-responsive therapy for effective ccRCC treatment.

A Sustainable Route to Ruthenium Phosphide (RuP)/Ru Heterostructures with Electron-Shuttling of Interfacial Ru for Efficient Hydrogen Evolution.

Ruthenium (Ru) is a promising electrocatalyst for the hydrogen evolution reaction (HER), despite suffering from low activity in non-acidic conditions due to the high kinetic energy barrier of H2O dissociation. Herein, the synthesis of carbon nanosheet-supported RuP/Ru heterostructures (RuP/Ru@CNS) from a natural polysaccharide is reported and demonstrates its behavior as an effective HER electrocatalyst in non-acidic conditions. The RuP/Ru@CNS exhibits low overpotential (106 mV at 200 mA·cm-2) in alkaline electrolyte, exceeding most reported Ru-based electrocatalysts. The electron shuttling between Ru atoms at the RuP/Ru interface results in a lowered energy barrier for H2O dissociation by electron-deficient Ru atoms in the pure Ru phase, as well as optimized H* adsorption of electron-gaining Ru atoms in the neighboring RuP. A low H* spillover energy barrier between Ru atoms at the RuP/Ru interface further boosts HER kinetics. This study demonstrates a sustainable method for the fabrication of efficient Ru-based electrocatalysts and provides a more detailed understanding of interface effects in HER catalysis.

Low temperature-resistant superhydrophobic and elastic cellulose aerogels derived from seaweed solid waste as efficient oil traps for oil/water separation.

Aerogel has excellent application potential in adsorption, heat preservation, and other areas due to its typical advantages of low density and high porosity. However, there are several issues with the use of aerogel in oil/water separation, including weak mechanical qualities and challenges in eliminating organic contaminants at low temperature. Inspired by cellulose Iα, which has excellent performance at low temperature, this study used cellulose Iα nanofibers extracted from seaweed solid waste as the skeleton, through covalent cross-linked with ethylene imine polymer (PEI) and hydrophobic modification of 1, 4-phenyl diisocyanate (MDI), supplemented by freeze-drying technology to form three-dimensional sheet, and successfully obtained cellulose aerogels derived from seaweed solid waste (SWCA). The compression test shows that the maximum compressive stress of SWCA is 61 kPa, and the initial performance still maintains 82% after 40 cryogenic compression cycles. In addition, the contact angles of water and oil on the surface of the SWCA were 153° and 0°, respectively, and the stable hydrophobic time in simulated seawater is more than 3 h. By combining the elasticity and superhydrophobicity/superoleophilicity, the SWCA with an oil absorption capacity of up to 11-30 times its mass, might be utilized repeatedly for the separation of an oil/water mixture.

Theoretical study of local S coordination environment on Fe single atoms for peroxymonosulfate-based advanced oxidation processes.

Tuning the electronic structure of single atom catalysts (SACs) is an effective strategy to promote the catalytic activity in peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs). Herein, a series of Fe-based SACs with S1/2/3/4-coordination numbers on graphene were designed to regulate the electronic structural of SACs at molecular level, and their effects on PMS activation were investigated via density function theory (DFT). The calculation results demonstrate that the electron structure of the active center can be adjusted by coordination environment, which further affects the activation of PMS. Among the studied Fe-SX-C4-X catalysts, with the increase of the S coordination number, the electron density of the Fe-SX-C4-X active center was optimized. The active center of the Fe-S4-C0 catalyst has a largest positive charge density, exhibiting the highest number of electron transfer. It also has a lower kinetic energy barrier (0.28 eV) for PMS dissociation. Organic pollutant such as bisphenol A (BPA) can achieve stable adsorption on Fe-SX-C4-X catalysts, which is conducive to subsequent oxidation by radicals. The dual index ∆f(r) indicates that the para-carbon atom of the hydroxyl group on the benzene ring of BPA is vulnerable to radical attack. This study highlights a theoretical support and a certain guide for designing efficient SACs to activate PMS.

Fabrication of a lamellar alginate-based aerogel decorated with carbon quantum dots for controlled fluorescence behaviors.

This study aimed to construct an alginate aerogel doped with carbon quantum dots and investigate the fluorescence properties of the composites. The carbon quantum dots with the highest fluorescence intensity were obtained using a methanol-water ratio of 1 : 1, a reaction time of 90 minutes, and a reaction temperature of 160 °C. The fluorescent carbon quantum dot sodium alginate-based aerogel (FCSA) obtained by compounding alginate and carbon quantum dots exhibited excellent fluorescence properties when the concentration of nano-carbon quantum dot solution was 10.0 vol%. By incorporating nano-carbon quantum dots, the fluorescence properties of the lamellar alginate aerogel can be easily and efficiently adjusted. The alginate aerogel decorated with nano-carbon quantum dots exhibits promising potential in biomedical applications due to its biodegradable, biocompatible, and sustainable properties.

Quasi-Three-Dimensional Cyclotriphosphazene-Based Covalent Organic Framework Nanosheet for Efficient Oxygen Reduction.

Metal-free carbon-based materials are considered as promising oxygen reduction reaction (ORR) electrocatalysts for clean energy conversion, and their highly dense and exposed carbon active sites are crucial for efficient ORR. In this work, two unique quasi-three-dimensional cyclotriphosphazene-based covalent organic frameworks (Q3CTP-COFs) and their nanosheets were successfully synthesized and applied as ORR electrocatalysts. The abundant electrophilic structure in Q3CTP-COFs induces a high density of carbon active sites, and the unique bilayer stacking of [6 + 3] imine-linked backbone facilitates the exposure of active carbon sites and accelerates mass diffusion during ORR. In particular, bulk Q3CTP-COFs can be easily exfoliated into thin COF nanosheets (NSs) due to the weak interlayer π-π interactions. Q3CTP-COF NSs exhibit highly efficient ORR catalytic activity (half-wave potential of 0.72 V vs. RHE in alkaline electrolyte), which is one of the best COF-based ORR electrocatalysts reported so far. Furthermore, Q3CTP-COF NSs can serve as a promising cathode for Zn-air batteries (delivered power density of 156 mW cm-2 at 300 mA cm-2). This judicious design and accurate synthesis of such COFs with highly dense and exposed active sites and their nanosheets will promote the development of metal-free carbon-based electrocatalysts.

Alginate Fiber-Grafted Polyetheramine-Driven High Ion-Conductive and Flame-Retardant Separator and Solid Polymer Electrolyte for Lithium Metal Batteries.

Traditional polymer-based separators and solid polymer electrolytes (SPEs) often suffer from inherent poor flame retardancy and unsatisfied ionic conductivity, which seriously affect the safety and energy storage performance of lithium metal batteries (LMBs). Inspired by the mechanism of Li+ conductivity, an alginate fiber (AF)-grafted polyetheramine (AF-PEA) separator with efficient Li+ transport and excellent flame retardancy is dedicatedly designed, which also can act as the backbone for PEO-based SPEs (PEO@AF-PEA). Based on the intrinsic flame retardancy of the AF, the AF-PEA shows self-extinguishing ability, and its Li+ transport ability (1.8 mS cm-1 at 25 °C) is enhanced by grafting the ion-conductive PEA chain segment. By simulating the transport and distribution of Li+ in the AF-PEA, the PEA with 7-segment chain lengths can uniformly fill the Li+ transport space between the alginate backbone to promote the Li+ adsorption and the utilization of Li+ anchoring points in PEA side chains, increasing the Li+ transport rate and migration capacity. The LiFePO4/Li solid-state battery assembled using PEO@AF-PEA SPEs exhibits high safety and excellent cycling performance (exceeding 100 mAh g-1 after 1500 cycles at 2 C current density and 80 °C with less than 0.016% capacity decay for each cycle).

Electrostatic Interaction in Amino Protonated Chitosan-Metal Complex Anion Hydrogels: A Simple Approach to Porous Metal Carbides/N-Doped Carbon Aerogels for Energy Conversion.

In the face of the increasingly serious rapid depletion of fossil fuels, exploring alternative energy conversion technologies may be a promising choice to alleviate this crisis. Transition metal carbides (TMCs)/carbon composites are considered as prospective electrocatalysts due to their high catalytic activities and structural stability. In this work, we report the simple synthesis of TMCs/N-doping carbon aerogels (TMCs/NCAs, including Fe3C/NCA, Mo3C2/NCA, and Fe3C-Mo2C/NCA) for the oxygen reduction reaction (ORR) using protonated chitosan/metal complex anion-chelated aerogels. Among them, the Fe3C/NCA composite possesses efficient ORR activity (similar to Pt/C), and the Fe3C/NCA-assembled Zn-air battery exhibits high power densities of about 250 mW cm-2. The density functional theory calculation reveals that the presence of graphite-N, pyridine-N, and carbon defects in the carbon framework effectively reduces the free energy of ORR occurring in Fe3C. This work provides a simple and extensible strategy for the preparation of TMCs from chitosan, which is expected to be extended to other metal carbides.

Drug-loaded mesoporous carbon with sustained drug release capacity and enhanced antifungal activity to treat fungal keratitis.

Fungal keratitis is a severe infectious corneal disease with a high rate of incidence and blindness. Since traditional treatments natamycin (NATA) eye drops, exhibit poor dissolution and bioavailability, and the efficacy of current therapeutic approaches remains limited. In this study, we innovatively utilized mesoporous carbon (Meso-C) and microporous carbon (Micro-C) as nanocarriers loaded with the antifungal drug NATA and silver nanoparticles (Ag-NPs). Porous carbon loaded with NATA and Ag-NPs has not previously been studied in fungal keratitis. Due to the mesoporous structure, high surface area and larger pore volume of Meso-C, it displayed greater superiority in sustained drug release and drug dispersity than Micro-C. Moreover, Meso-C could adsorb inflammatory cytokines during fungal infection. In vitro, Meso-C/NATA/Ag showed excellent antifungal effects. In vivo, compared with pure NATA treatment, Meso-C/NATA/Ag exhibited significantly improved therapeutic effects and reduced dosing frequency when treating fungal keratitis. Our study is the first to report the sustained drug release and improved drug dispersity of Meso-C/NATA and demonstrates that NATA and Ag-NPs-loaded Meso-C has therapeutic effects against fungal keratitis.

Hydrogen Bond Interpenetrated Agarose/PVA Network: A Highly Ionic Conductive and Flame-Retardant Gel Polymer Electrolyte.

The gel polymer electrolyte (GPE) is the key to assembling high-performance solid-state supercapacitors (SSCs). The commercial poly(vinyl alcohol) (PVA) GPE has developed a reputation due to low ionic conductivity endowed by its high crystallinity and poor water retention capacity. In this work, density functional theory (DFT) calculations first revealed that the high crystallinity of PVA can be greatly disrupted by forming hydrogen bonds with natural agarose macromolecules. The hydrogen bond interpenetrated three-dimensional agarose/PVA network offers high water retention and large amounts of channels for movement of Li+ on hydroxyl oxygen atoms. So, an optimized formation of the Li-O coordinate bond (gLi-O(r) = 8.78) and improved diffusion coefficient of Li+ (DLi+) (71 × 10-6 cm2 s-1) were obtained in the agarose/PVA model. When assembled into SSCs, agarose/PVA-GPE with 2 M LiOAc (AP-GPE) exhibits an outstanding specific capacitance (697.22 mF cm-2 at 5 mA cm-2). The high water retention of agarose and large amounts of -OH groups in the agarose macromolecular can generate H2O by dehydration reaction, reducing the flammability of PVA and greatly enhancing the safety of SSCs.