Dual Regulation of Charge Separation and the Oxygen Reduction Pathway by Encapsulating Phosphotungstic Acid into the Cationic Covalent Organic Framework for Efficient Photocatalytic Hydrogen Peroxide Production.

Previous research on covalent organic framework (COF)-based photocatalytic H2O2 synthesis from oxygen reduction focuses more on charge carrier separation but less on the electron utilization efficiency of O2. Herein, we put forward a facile approach to simultaneously promote charge separation and tailor the oxygen reduction pathway by introducing phosphotungstic acid (PTA) into the cationic COF skeleton. Experiments verified that PTA, as an electron transport medium, establishes a fast electron transfer channel from the COF semiconductor conductor band to the substrate O2; meanwhile, the reaction path is optimized by its catalytic cycle for preferable dioxygen capture and reduction in oxygen reduction reaction (ORR) kinetics. The existence of PTA promotes the rate and tendency of converting O2 into •O2- intermediates, which is conducive to boosting the photocatalytic activity and selectivity toward the sequential two-step single-electron ORR. As expected, compared to the pristine TTB-EB, the optimal PTA0.5@TTB-EB achieves a 2.2-fold improvement of visible-light-driven photocatalytic performance with a H2O2 production rate of 897.94 µmol·L-1·h-1 in pure water without using any sacrificial agents. In addition, owing to the robust electrostatic interaction and the confinement effect of porous TTB-EB channels, the PTA@TTB-EB composite possessed favorable stability.

Strengthened Fenton degradation of phenol catalyzed by core/shell Fe-Pd@C nanocomposites derived from mechanochemically synthesized Fe-Metal organic frameworks.

We have prepared core/shell structured hollow Fe-Pd@C nanomaterials derived from Fe-metal organic frameworks which were synthesized via cheap, fast and simple mechanochemical technique. The obtained Fe-Pd@C can steadily and continuously release Fe2+ from the galvanic corrosion of Fe0 anode to trigger H2O2 decomposition into hydroxyl radicals and cause fast (10 min) and efficient (mineralization rate 95%) degradation of phenol. The presence of low level of Pd NPs in Fe-Pd@C (mass ratio of the raw material: Fe/Pd = 100:1) facilitated fast Fe3+/Fe2+ redox cycle and thus improved the catalytic performance and pH endurance of the Fe-Pd@C. After recycled four times, Fe-Pd@C remained high catalytic performance and released low level of iron ions (2.5 mg L-1), which reduced the production of iron sludge after usage. In contrast to zero-valent iron (ZVI) and commercial physically mixed Fe/C materials, the core/shell structure of Fe-Pd@C ensured efficient electron transferring from Fe0 to carbon cathode and targets, and prevented the precipitation of iron ions on Fe0 surface, avoiding the deactivation of Fe0 and termination of Fe-C internal micro-electrolysis (IME) and extending their service life. The reactive species quenching experiments and ESR characterization proved the synergistic effect of electrons and hydroxyl free radicals on degradation of phenol. The carbon-centered DMPO radical detected in reaction solution can be regarded as a proof for the strengthened oxidation ability of the combined IME and Fenton reaction.

Ball milling synthesis of covalent organic framework as a highly active photocatalyst for degradation of organic contaminants.

Facile, environmentally-friendly fabrication of high-yield and stable covalent organic framework (COF) materials has been a limitation to their large-scale production and application. In this work, ball milling was used to synthesize COF by mechanochemical reaction between 1,3,5-triformylphloroglucinol (Tp) and melamine (MA) at ambient temperature. Different routes (liquid-free, solvent-assisted and catalyst-assisted) and proportions of liquids (solvents or catalyst) were investigated. Two morphologies were obtained when various amounts of liquid were added during grinding. The two forms were interwoven thread-shaped and exfoliative thin ribbon-like structures. Further, visible-light photocatalytic (λ > 400 nm) performance and mechanism of the two structures of COFs were investigated. The exfoliative ribbon-like structures exhibited greater rates of photodegradation of phenol and retained 87.6% of initial photodegradation after being used four times. Addition of liquid catalyst not only improved crystallinity of the COF materials, but also enhanced rates of photocatalytic reactions. Photocatalytic activity of the exfoliative structure of TpMA synthesized by ball milling was comparable with that of the photocatalyst prepared by use of the solvothermal method, while time to prepare the catalyst was shortened by 36-fold and the amount of solvent used was reduced by 8-fold at room temperature. Mechanochemical synthesis is a promising potential tool for large-scale production of COFs, which will make greater use of COFs for degradation of pollutants.

Construction of a superior visible-light-driven photocatalyst based on a C3N4 active centre-photoelectron shift platform-electron withdrawing unit triadic structure covalent organic framework.

Herein, three functional factors inducing photocatalytic ability were artfully integrated into a covalent organic framework (COF), where triazine units served as photoactive centers, cyclic ketone units served as electron-withdrawing moieties, and the conjugated structure served as a photoelectron shift platform. This COF with segregated donor-acceptor alignments exhibits an excellent visible-light photocatalytic capacity for the decomposition of organic pollutants.

Facile Synthesis of Magnetic Covalent Organic Framework with Three-Dimensional Bouquet-Like Structure for Enhanced Extraction of Organic Targets.

A facile strategy for the fabrication of novel bouquet-shaped magnetic porous nanocomposite via grafting a covalent organic framework (COF, TpPa-1) onto the surface-modified Fe3O4 nanoparticles (Fe3O4 NPs) was reported. The magnetic TpPa-1 (a COF synthesized from 1,3,5-triformylphloroglucinol (Tp) and p-phenylenediamine (Pa-1)) contains clusters of core-shell magnetic nanoparticles and interconnected porous TpPa-1 nanofibers. Thus, it possesses larger specific surface area, higher porosity, and supermagnetism, making it an ideal sorbent for enrichment of trace analytes. Its performance was evaluated by the magnetic solid-phase extraction (MSPE) of trace polycyclic aromatic hydrocarbons (PAHs) from environmental samples prior to high-performance liquid chromatographic analysis. The results indicated that the magnetic TpPa-1 possessed superior enrichment capacity of such organic compounds.

One-step synthesis of potassium ferricyanide-doped polyaniline nanoparticles for label-free immunosensor.

A novel, label-free and inherent electroactive redox immunosensor for ultrasensitive detection of carcinoembryonic antigen (CEA) was proposed based on gold nanoparticles (AuNPs) and potassium ferricyanide-doped polyaniline (FC-PANI) nanoparticles. FC-PANI composite was synthesized via oxidative polymerization of aniline, using potassium ferricyanide (K3[Fe(CN)6]) as both oxidant and dopant. FC-PANI acting as the signal indicator was first fixed on a gold electrode (GE) to be the signal layer. Subsequently, the negatively charged AuNPs could be adsorbed on the positively charged FC-PANI modified GE surface by electrostatic adsorption, and then to immobilize CEA antibody (anti-CEA) for the assay of CEA. The CEA concentration was measured through the decrease of amperometric signals in the corresponding specific binding of antigen and antibody. The wide linear range of the immunosensor was from 1.0 pg mL(-1) to 500.0 ng mL(-1) with a low detection limit of 0.1 pg mL(-1) (S/N=3). The proposed method would have a potential application in clinical immunoassays with the properties of facile procedure, stability, high sensitivity and selectivity.

Direct electron transfer of glucose oxidase and biosensing for glucose based on PDDA-capped gold nanoparticle modified graphene/multi-walled carbon nanotubes electrode.

In this work, poly (diallyldimethylammonium chloride) (PDDA)-capped gold nanoparticles (AuNPs) functionalized graphene (G)/multi-walled carbon nanotubes (MWCNTs) nanocomposites were fabricated. Based on the electrostatic attraction, the G/MWCNTs hybrid material can be decorated with AuNPs uniformly and densely. The new hierarchical nanostructure can provide a larger surface area and a more favorable microenvironment for electron transfer. The AuNPs/G/MWCNTs nanocomposite was used as a novel immobilization platform for glucose oxidase (GOD). Direct electron transfer (DET) was achieved between GOD and the electrode. Field emission scanning electron microscopy (FESEM), UV-vis spectroscopy and cyclic voltammetry (CV) were used to characterize the electrochemical biosensor. The glucose biosensor fabricated based on GOD electrode modified with AuNPs/G/MWCNTs demonstrated satisfactory analytical performance with high sensitivity (29.72mAM(-1)cm(-2)) and low limit of detection (4.8 µM). The heterogeneous electron transfer rate constant (ΚS) and the apparent Michaelis-Menten constant (Km) of GOD were calculated to be 11.18s(-1) and 2.09 mM, respectively. With satisfactory selectivity, reproducibility, and stability, the nanostructure we proposed offered an alternative for electrode fabricating and glucose biosensing.