Showing papers on "Nitride published in 2022"

Unraveling the Dual Defect Sites in Graphite Carbon Nitride for Ultra-high Photocatalytic H2O2 Evolution

Abstract: Defect engineering modified graphite carbon nitride (g-C3N4) has been widely used in various photocatalytic systems due to the enhanced catalytic activity by multiple defect sites (such as vacancies or functional...

In Situ Growth of Three‐Dimensional MXene/Metal‐Organic Framework Composites for High‐Performance Supercapacitors

Abstract: In this study, we propose a versatile method for synthesizing uniform three-dimensional (3D) metal carbides, nitrides, and carbonitrides (MXenes)/metal–organic frameworks (MOFs) composites (Ti3C2TX/Cu-BTC, Ti3C2TX/Fe,Co-PBA, Ti3C2TX/ZIF-8, and Ti3C2TX/ZIF-67) that combine the advantages of MOFs and MXenes to enhance stability and improve conductivity. Subsequently, 3D hollow Ti3C2TX/ZIF-67/CoV2O6 composites with excellent electron- and ion-transport properties derived from Ti3C2TX/ZIF-67 were synthesized. The specific capacitance of the Ti3C2TX/ZIF-67/CoV2O6 electrode was 285.5 F g−1, which is much higher than that of the ZIF-67 and Ti3C2TX/ZIF-67 electrode. This study opens a new avenue for the design and synthesis of MXene/MOF composites and complex hollow structures with tailorable structures and compositions for various applications.

In Situ Growth of Three‐Dimensional MXene/Metal–Organic Framework Composites for High‐Performance Supercapacitors

Abstract: In this study, we propose a versatile method for synthesizing uniform three-dimensional (3D) metal carbides, nitrides, and carbonitrides (MXenes)/metal-organic frameworks (MOFs) composites (Ti3 C2 TX /Cu-BTC, Ti3 C2 TX /Fe,Co-PBA, Ti3 C2 TX /ZIF-8, and Ti3 C2 TX /ZIF-67) that combine the advantages of MOFs and MXenes to enhance stability and improve conductivity. Subsequently, 3D hollow Ti3 C2 TX /ZIF-67/CoV2 O6 composites with excellent electron- and ion-transport properties derived from Ti3 C2 TX /ZIF-67 were synthesized. The specific capacitance of the Ti3 C2 TX /ZIF-67/CoV2 O6 electrode was 285.5 F g-1 , which is much higher than that of the ZIF-67 and Ti3 C2 TX /ZIF-67 electrode. This study opens a new avenue for the design and synthesis of MXene/MOF composites and complex hollow structures with tailorable structures and compositions for various applications.

Cobalt Single Atoms Anchored on Oxygen-Doped Tubular Carbon Nitride for Efficient Peroxymonosulfate Activation: Simultaneous Coordination Structure and Morphology Modulation.

Abstract: Simultaneous regulation of the coordination environment of single-atom catalysts and engineering architectures with efficient exposed active sites are efficient strategies for boosting peroxymonosulfate (PMS) activation. We isolated cobalt atoms with dual nitrogen and oxygen coordination (Co-N 3 O 1 ) on oxygen-doped tubular carbon nitride (TCN) by pyrolyzing a hydrogen-bonded cyanuric acid melamine-cobalt acetate precursor. The theoretically constructed Co-N 3 O 1 moiety on TCN exhibited an impressive mass activity of 7.61×105 min -1 mol -1 with high 1 O 2 selectivity. Theoretical calculations revealed that the cobalt single atoms occupied a dual nitrogen and oxygen coordination environment, and that PMS adsorption was promoted and energy barriers reduced for the key *O intermediate that produced 1 O 2 . The catalysts were attached to a widely used poly(vinylidene fluoride) microfiltration membrane to deliver an antibiotic wastewater treatment system with 97.5% ciprofloxacin rejection over 10 hours, thereby revealing the suitability of the membrane for industrial applications.

Nonprecious transition metal nitrides as efficient oxygen reduction electrocatalysts for alkaline fuel cells

Abstract: Hydrogen fuel cells have attracted growing attention for high-performance automotive power but are hindered by the scarcity of platinum (and other precious metals) used to catalyze the sluggish oxygen reduction reaction (ORR). We report on a family of nonprecious transition metal nitrides (TMNs) as ORR electrocatalysts in alkaline medium. The air-exposed nitrides spontaneously form a several-nanometer-thick oxide shell on the conductive nitride core, serving as a highly active catalyst architecture. The most active catalyst, carbon-supported cobalt nitride (Co3N/C), exhibited a half-wave potential of 0.862 V and achieved a record-high peak power density among reported nitride cathode catalysts of 700 mW cm−2 in alkaline membrane electrode assemblies. Operando x-ray absorption spectroscopy studies revealed that Co3N/C remains stable below 1.0 V but experiences irreversible oxidation at higher potentials. This work provides a comprehensive analysis of nonprecious TMNs as ORR electrocatalysts and will help inform future design of TMNs for alkaline fuel cells and other energy applications.

Carbon Nitride Photocatalysts with Integrated Oxidation and Reduction Atomic Active Centers for Improved CO2 Conversion.

Abstract: Single-atom active site catalysts have attracted significant attention in the field of photocatalytic CO 2 conversion. However, designing active sites for CO 2 reduction and H 2 O oxidation simultaneously on a photocatalyst and combining the corresponding half-reaction in a photocatalytic system is still difficult. Here, we synthesized a bimetallic single-atom active site photocatalyst with two compatible active centers of Mn and Co on carbon nitride (Mn 1 Co 1 /CN). Our experimental results and density functional theory calculations showed that the active center of Mn promotes H 2 O oxidation by accumulating photogenerated holes. In addition, the active center of Co promotes CO 2 activation by increasing the bond length and bond angle of CO 2 molecules. Benefiting from the synergistic effect of the atomic active centers, the synthesized Mn 1 Co 1 /CN exhibited a CO production rate of 47 μmol g -1 h -1 , which is significantly higher than that of the corresponding single-metal active site photocatalyst.

Orthogonal Charge Transfer by Precise Positioning of Silver Single Atoms and Clusters on Carbon Nitride for Efficient Piezocatalytic Pure Water Splitting.

Abstract: Developing efficient piezocatalytic systems for two-electron water splitting (TEWS) with producing H 2 and H 2 O 2 shows great promise to meet the industrial demand. Herein, Ag single atoms (SAs) and clusters are co-anchored on carbon nitride (Ag SA+C -CN) to serve as the multifunctional sites for efficient TEWS. The Ag SAs enhance the in-plane piezoelectric polarization of CN that is intimately modulated by the atomic coordination induced charge redistribution, and Ag clusters afford strong interfacial electric field to remarkably promote the out-of-plane migration of piezoelectrons from CN. Moreover, Ag SA+C -CN yields a larger piezoresistive effect that elevates carrier mobility under strain. Consequently, a superior H 2 and H 2 O 2 evolution rate of 7.90 mmol·g -1 ·h -1 and 5.84 mmol·g -1 ·h -1 is delivered by Ag SA+C -CN, respectively, far exceeding that of the previously reported piezocatalysts. This work not only presents the SAs decoration as an available polarization enhancement strategy, but also sheds light on the superiority of multi-sites engineering in piezocatalysis.

In-Plane Charge Transport Dominates the Overall Charge Separation and Photocatalytic Activity in Crystalline Carbon Nitride

Abstract: Here, taking layered polymeric carbon nitride (CN) as an example, the dominant role of in-plane charge transport is demonstrated both theoretically and experimentally. The in-plane “sewing” and interlayer “cutting” effects of three alkaline potassium salts on the CN polymerization process are enhanced with the increase of alkalinity. The in-plane crystallinity-dependent charge transfer and separation and photocatalytic activity are elucidated through the samples of three alkaline potassium salt series. Our findings provide guidance for improving the photoelectric conversion efficiency by optimizing in-plane charge transfer rather than interlayer charge transfer, targeting layered photoelectric conversion materials.

Silicon nitride passive and active photonic integrated circuits: trends and prospects

Abstract: The use of silicon nitride in integrated photonics has rapidly progressed in recent decades. Ultra-low-loss waveguides based on silicon nitride are a favorable platform for the research of nonlinear and microwave photonics and their application to a wide variety of fields, including precision metrology, communications, sensing, imaging, navigation, computation, and quantum physics. In recent years, the integration of Si and III-V materials has enabled new large-scale, advanced silicon nitride-based photonic integrated circuits with versatile functionality. In this perspective article, we review current trends and the state-of-the-art in silicon nitride-based photonic devices and circuits. We highlight the hybrid and heterogeneous integration of III-V with silicon nitride for electrically pumped soliton microcomb generation and ultra-low-noise lasers with fundamental linewidths in the tens of mHz range. We also discuss several ultimate limits and challenges of silicon nitride-based photonic device performance and provide routes and prospects for future development.

Carbon Nitride Photocatalysts with Integrated Oxidation and Reduction Atomic Active Centers for Improved CO2 Conversion

Abstract: Single-atom active-site catalysts have attracted significant attention in the field of photocatalytic CO2 conversion. However, designing active sites for CO2 reduction and H2 O oxidation simultaneously on a photocatalyst and combining the corresponding half-reaction in a photocatalytic system is still difficult. Here, we synthesized a bimetallic single-atom active-site photocatalyst with two compatible active centers of Mn and Co on carbon nitride (Mn1 Co1 /CN). Our experimental results and density functional theory calculations showed that the active center of Mn promotes H2 O oxidation by accumulating photogenerated holes. In addition, the active center of Co promotes CO2 activation by increasing the bond length and bond angle of CO2 molecules. Benefiting from the synergistic effect of the atomic active centers, the synthesized Mn1 Co1 /CN exhibited a CO production rate of 47 μmol g-1 h-1 , which is significantly higher than that of the corresponding single-metal active-site photocatalyst.

Regulating the *OCCHO intermediate pathway towards highly selective photocatalytic CO₂ reduction to CH₃CHO over locally crystallized carbon nitride

Abstract: Locally crystallized PCN is prone to form *OCCHO groups rather than *CH 2 O groups, regulating the endoergic C–C coupling step to a simultaneous exoergic reaction and changing the reaction pathway towards CH 3 CHO (selectivity of 98.3%) instead of HCHO.