PdCu nanoalloy decorated photocatalysts for efficient and selective oxidative coupling of methane in flow reactors.

Methane activation by photocatalysis is one of the promising sustainable technologies for chemical synthesis. However, the current efficiency and stability of the process are moderate. Herein, a PdCu nanoalloy (~2.3 nm) was decorated on TiO2, which works for the efficient, stable, and selective photocatalytic oxidative coupling of methane at room temperature. A high methane conversion rate of 2480 µmol g-1 h-1 to C2 with an apparent quantum efficiency of ~8.4% has been achieved. More importantly, the photocatalyst exhibits the turnover frequency and turnover number of 116 h-1 and 12,642 with respect to PdCu, representing a record among all the photocatalytic processes (λ > 300 nm) operated at room temperature, together with a long stability of over 112 hours. The nanoalloy works as a hole acceptor, in which Pd softens and weakens C-H bond in methane and Cu decreases the adsorption energy of C2 products, leading to the high efficiency and long-time stability.

Nearly 100% selective and visible-light-driven methane conversion to formaldehyde via. single-atom Cu and Wδ.

Direct solar-driven methane (CH4) reforming is highly desirable but challenging, particularly to achieve a value-added product with high selectivity. Here, we identify a synergistic ensemble effect of atomically dispersed copper (Cu) species and partially reduced tungsten (Wδ+), stabilised over an oxygen-vacancy-rich WO3, which enables exceptional photocatalytic CH4 conversion to formaldehyde (HCHO) under visible light, leading to nearly 100% selectivity, a very high yield of 4979.0 µmol·g-1 within 2 h, and the normalised mass activity of 8.5 × 106 µmol·g-1Cu·h-1 of HCHO at ambient temperature. In-situ EPR and XPS analyses indicate that the Cu species serve as the electron acceptor, promoting the photo-induced electron transfer from the conduction band to O2, generating reactive •OOH radicals. In parallel, the adjacent Wδ+ species act as the hole acceptor and the preferred adsorption and activation site of H2O to produce hydroxyl radicals (•OH), and thus activate CH4 to methyl radicals (•CH3). The synergy of the adjacent dual active sites boosts the overall efficiency and selectivity of the conversion process.

Synergy of Pd atoms and oxygen vacancies on In2O3 for methane conversion under visible light.

Methane (CH4) oxidation to high value chemicals under mild conditions through photocatalysis is a sustainable and appealing pathway, nevertheless confronting the critical issues regarding both conversion and selectivity. Herein, under visible irradiation (420 nm), the synergy of palladium (Pd) atom cocatalyst and oxygen vacancies (OVs) on In2O3 nanorods enables superior photocatalytic CH4 activation by O2. The optimized catalyst reaches ca. 100 µmol h-1 of C1 oxygenates, with a selectivity of primary products (CH3OH and CH3OOH) up to 82.5%. Mechanism investigation elucidates that such superior photocatalysis is induced by the dedicated function of Pd single atoms and oxygen vacancies on boosting hole and electron transfer, respectively. O2 is proven to be the only oxygen source for CH3OH production, while H2O acts as the promoter for efficient CH4 activation through ·OH production and facilitates product desorption as indicated by DFT modeling. This work thus provides new understandings on simultaneous regulation of both activity and selectivity by the synergy of single atom cocatalysts and oxygen vacancies.

Binary Au-Cu Reaction Sites Decorated ZnO for Selective Methane Oxidation to C1 Oxygenates with Nearly 100% Selectivity at Room Temperature.

Direct and efficient oxidation of methane to methanol and the related liquid oxygenates provides a promising pathway for sustainable chemical industry, while still remaining an ongoing challenge owing to the dilemma between methane activation and overoxidation. Here, ZnO with highly dispersed dual Au and Cu species as cocatalysts enables efficient and selective photocatalytic conversion of methane to methanol and one-carbon (C1) oxygenates using O2 as the oxidant operated at ambient temperature. The optimized AuCu-ZnO photocatalyst achieves up to 11225 µmol·g-1·h-1 of primary products (CH3OH and CH3OOH) and HCHO with a nearly 100% selectivity, resulting in a 14.1% apparent quantum yield at 365 nm, much higher than the previous best photocatalysts reported for methane conversion to oxygenates. In situ EPR and XPS disclose that Cu species serve as photoinduced electron mediators to promote O2 activation to •OOH, and simultaneously that Au is an efficient hole acceptor to enhance H2O oxidation to •OH, thus synergistically promoting charge separation and methane transformation. This work highlights the significances of co-modification with suitable dual cocatalysts on simultaneous regulation of activity and selectivity.

Thermally Activated Delayed Fluorescence in Commercially Available Materials for Solution-Process Exciplex OLEDs.

Organic light-emitting diodes (OLEDs) have developed rapidly in recent years. Thermally activated delayed fluorescent (TADF) molecules open a path to increase exciton collection efficiency from 25% to 100%, and the solution process provides an alternative technology to achieve lower cost OLEDs more easily. To develop commercial materials as exciplex hosts for high-performance and solution-processed OLEDs, we attempted to use 4,4'-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine (TAPC), poly(9-vinylcarbazole) (PVK), N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPB), and poly(N,N'-bis-4-butylphenyl-N,N'-bisphenyl)benzidine (Poly-TPD) as the donors and 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (POT2T) as the acceptor to obtain the TADF effect. All donors and the acceptor were purchased from chemical suppliers. Our work shows that excellent TADF properties and high-efficiency exciplex OLEDs with low turn-on voltage and high luminance can be achieved with a simple combination of commercial materials.

Using Thermally Crosslinkable Hole Transporting Layer to Improve Interface Characteristics for Perovskite CsPbBr3 Quantum-Dot Light-Emitting Diodes.

In this paper, a thermally crosslinkable 9,9-Bis[4-[(4-ethenylphenyl)methoxy]phenyl]-N2,N7-di-1-naphthalenyl-N2,N7-diphenyl-9H-fluorene-2,7-diamine (VB-FNPD) film served as the hole transporting layer (HTL) of perovskite CsPbBr3 quantum-dot light-emitting diodes (QD-LEDs) was investigated and reported. The VB-FNPD film crosslinked at various temperatures in the range of 100~230 °C followed by a spin-coating process to improve their chemical bonds in an attempt to resist the erosion from the organic solvent in the remaining fabrication process. It is shown that the device with VB-FNPD HTL crosslinking at 170 °C has the highest luminance of 7702 cd/m2, the maximum current density (J) of 41.98 mA/cm2, the maximum current efficiency (CE) of 5.45 Cd/A, and the maximum external quantum efficiency (EQE) of 1.64%. Our results confirm that the proposed thermally crosslinkable VB-FNPD is a candidate for the HTL of QD-LEDs.

Surface defect passivation of Ta3N5 photoanode via pyridine grafting for enhanced photoelectrochemical performance.

Tantalum nitride (Ta3N5) is a promising photoanode material for photoelectrochemical (PEC) water splitting, while the Ta3N5/Ta photoanode synthesized via general thermal oxidation and nitridation on a Ta foil method usually has serious carrier recombination at the surface, which usually reduces the PEC activities. Herein, we demonstrate an efficient strategy of decorating pyridine, a small organic molecule at the surface of the Ta3N5/Ta photoanode, to alleviate the surface recombination. Such decoration yields a stable photocurrent density of 4.4 mA cm-2 at 1.23 VRHE under AM 1.5G (air mass 1.5 global, 100 mW cm-2) simulated sunlight, which is about 1.4 times higher than that of Ta3N5/Ta without modification, and the photocurrent density still remained ∼100% of its original value after a 5 h stability test. Further characterization of the incident photon-to-current conversion efficiency and absorbed photon-to-current efficiency of the pyridine/Ta3N5/Ta photoanode showed a significant increase to 62% and 72% at 500 nm, respectively. The enhanced pyridine/Ta3N5/Ta PEC performance can be attributed to minimizing the density of nitrogen vacancies due to the passivation of pyridine grafting, which results in the decreased recombination centers and improved charge separation efficiency at the surface. We thus believe that our study of surface passivation by using small organic molecules provides an alternative to address the surface recombination of Ta3N5 based photoelectrodes.

Laser-generated BiVO4 colloidal particles with tailoring size and native oxygen defect for highly efficient gas sensing.

To alleviate the poor sensing performance of BiVO4, developing new strategies for the fabrication of unique device with improved sensing properties is very necessary and has great practical significance. In this work, size-tailored and uniform black BiVO4 colloids with abundant oxygen vacancy were synthesized by a unique method of pulsed laser irradiation of colloidal nanoparticles (PLICN). The corresponding laser irradiation effects on the sensing properties are comparatively investigated. The results indicate that the BiVO4 nanospheres with average size of 50 nm shows best sensing properties with high sensitivity, superior selectivity, low detection limit (44 ppb) to H2S at low working temperature (75 °C). Its sensing response is over 4 times higher when comparing with that of the raw material. Further investigation manifests that laser irradiation could induce quantity of the oxygen vacancy and decrease the resistance of the sensing device, which is mainly responsible for the enhanced sensing performance. Moreover, the density functional theories (DFT) calculations suggest that the oxygen vacancies can greatly decrease the surface absorption energy with enhanced H2S absorption capability on BiVO4 surface and lower the bader charger transfer from the absorbed H2S molecules to the BiVO4, thus enabling the implementation for the enhanced gas-sensing properties.

Embedding laser generated nanocrystals in BiVO4 photoanode for efficient photoelectrochemical water splitting.

Addressing the intrinsic charge transport limitation of metal oxides has been of significance for pursuing viable PEC water splitting photoelectrodes. Growing a photoelectrode with conductive nanoobjects embedded in the matrix is promising for enhanced charge transport but remains a challenge technically. We herein show a strategy of embedding laser generated nanocrystals in BiVO4 photoanode matrix, which achieves photocurrent densities of up to 5.15 mA cm-2 at 1.23 VRHE (from original 4.01 mA cm-2) for a single photoanode configuration, and 6.22 mA cm-2 at 1.23 VRHE for a dual configuration. The enhanced performance by such embedding is found universal owing to the typical features of laser synthesis and processing of colloids (LSPC) for producing ligand free nanocrystals in desired solvents. This study provides an alternative to address the slow bulk charge transport that bothers most metal oxides, and thus is significant for boosting their PEC water splitting performance.