Novel g-C3N4/g-C3N4 S-scheme isotype heterojunction for improved photocatalytic hydrogen generation

In this research update, we discuss the visible-light photocatalysis. Due to the potential of utilizing freely available solar energy for environmental remediation and fuel generation, this topic has been of increasing interest. Huge amount of work has been done in developing a large variety of photocatalyst materials, and advances have been made in understanding the process. Nevertheless, substantial challenges remain. Some of those challenges could possibly be solved by developing better materials, but in many cases, the biggest problem is whether photocatalysis could be scaled up to an industrial process that would be cost-competitive to existing technologies. Here, we discuss different types of visible-light photocatalysts and their applications and outline various challenges that need to be addressed in the development of practically relevant materials and systems.

Visible-light photocatalysts: Prospects and challenges

The conversion and storage of solar energy to chemical energy via artificial photosynthesis holds significant potential for optimizing the energy situation and mitigating the global warming effect. Photocatalytic water splitting utilizing particulate semiconductors offers great potential for the production of renewable hydrogen, while this cross-road among biology, chemistry, and physics features a topic with fascinating interdisciplinary challenges. Progress in photocatalytic water splitting has been achieved in recent years, ranging from fundamental scientific research to pioneering scalable practical applications. In this review, we focus mainly on the recent advancements in terms of the development of new light-absorption materials, insights and strategies for photogenerated charge separation, and studies towards surface catalytic reactions and mechanisms. In particular, we emphasize several efficient charge separation strategies such as surface-phase junction, spatial charge separation between facets, and polarity-induced charge separation, and also discuss their unique properties including ferroelectric and photo-Dember effects on spatial charge separation. By integrating time- and space-resolved characterization techniques, critical issues in photocatalytic water splitting including photoinduced charge generation, separation and transfer, and catalytic reactions are analyzed and reviewed. In addition, photocatalysts with state-of-art efficiencies in the laboratory stage and pioneering scalable solar water splitting systems for hydrogen production using particulate photocatalysts are presented. Finally, some perspectives and outlooks on the future development of photocatalytic water splitting using particulate photocatalysts are proposed.

Recent advances and perspectives for solar-driven water splitting using particulate photocatalysts.

Narrow band gap semiconductors heterojunction with superior coupling and composition matching can enhance light absorption, reduce carrier recombination and increase redox activity. Here, we report Co9S8/Cd/CdS Z-scheme type heterojunctions with hierarchical tubular heterostructure and inexpensive transition metallic electronic bridge between two distinct semiconductors by a simultaneous immobilization and in-situ reduction strategy. The designed heterostructure greatly promotes the redox activity owing to high-density catalytic sites, excellent visible light capture by small band gap Co9S8/CdS and hollow framework in conjunction with fast charge separation and smooth transfer through intermediary conductive Cd. The optimized photocatalyst exhibits a hydrogen generation rate up to 10.42 μmol h−1 without obvious drop in performance over multiple cycles. The structural design, matching tandem constituent and continuous phase mediator are the pivotal factors to engender an efficient solid-state Z-scheme photocatalysis. The facile synthetic approach and noble metal free tandem structure of this work provide alternative avenues for the development of heterojunction photocatalysts for efficient solar-to-chemical conversion.

Z-scheme transition metal bridge of Co9S8/Cd/CdS tubular heterostructure for enhanced photocatalytic hydrogen evolution

Piezotronic effect boosted photocatalytic performance of heterostructured BaTiO3/TiO2 nanofibers for degradation of organic pollutants

The widespread heterojunction or p–n junction strategies fabricated between different semiconductors are generally used to promote the spatial charge separation in photocatalysis and solar cells, w...

Homophase Junction for Promoting Spatial Charge Separation in Photocatalytic Water Splitting

The anomeric configuration can greatly affect the biological functions and activities of carbohydrates. Herein, we report that N-phenyltrifluoroacetimidoyl (PTFAI), a well-known leaving group for catalytic glycosylation, can act as a stereodirecting group for the challenging 1,2-cis α-glycosylation. Utilizing rapidly accessible 1,6-di-OPTFAI glycosyl donors, TMSOTf-catalyzed glycosylation occurred with excellent α-selectivity and broad substrate scope, and the remaining 6-OPTFAI group can be cleaved chemoselectively. The remote participation of 6-OPTFAI is supported by the first characterization of the crucial 1,6-bridged bicyclic oxazepinium ion intermediates by low-temperature NMR spectroscopy. These cations were found to be relatively stable and mainly responsible for the present stereoselectivities. Further application is highlighted in glycosylation reactions toward trisaccharide heparins as well as the convergent synthesis of chacotriose derivatives using a bulky 2,4-di-O-glycosylated donor.

More than a Leaving Group: N-Phenyltrifluoroacetimidate as a Remote Directing Group for Highly α-Selective 1,2-cis Glycosylation.

Anomeric stereocontrol is usually one of the major issues in the synthesis of complex carbohydrates, particularly those involving β-configured 2,6-dideoxyglycosides and D/L-rhamnoside moieties. Herein, we report that 2-(diphenylphosphinoyl)acetyl is highly effective as a remote stereodirecting group in the direct synthesis of these challenging β-glycosides under mild conditions. A deoxy-trisaccharide as a mimic of the sugar chain of landomycin E was prepared stereospecifically in high yield. The synthetic potential was also highlighted in the synthesis of Citrobacter freundii O-antigens composed of a [→4)-α-D-Man p -(1→3)-β-D-Rha p -(1→4)-β-D-Rha p -(1→] repeating unit, wherein the convergent assembly up to a nonasaccharide was realized with a strongly β-directing trisaccharide donor. Variable-temperature NMR studies indicate the presence of intermolecular H-bonding between the donor and the bulky acceptor as direct spectral evidence in support of the concept of hydrogen-bond-mediated aglycone delivery.

Direct Synthesis of 2,6-Dideoxy-β-glycosides and β-Rhamnosides with a Stereodirecting 2-(Diphenylphosphinoyl)acetyl Group.

Anomeric stereocontrol is usually one of the major issues in the synthesis of complex carbohydrates, particularly those involving β-configured 2,6-dideoxyglycoside and d/l-rhamnoside moieties. Herein, we report that 2-(diphenylphosphinoyl)acetyl is highly effective as a remote stereodirecting group in the direct synthesis of these challenging β-glycosides under mild conditions. A deoxy-trisaccharide as a mimic of the sugar chain of landomycin E was prepared stereospecifically in high yield. The synthetic potential was also highlighted in the synthesis of Citrobacter freundii O-antigens composed of a [→4)-α-d-Manp-(1→3)-β-d-Rhap(1→4)-β-d-Rhap-(1→] repeating unit, wherein the convergent assembly up to a nonasaccharide was realized with a strongly β-directing trisaccharide donor. Variable-temperature NMR studies indicate the presence of intermolecular H-bonding between the donor and the bulky acceptor as direct spectral evidence in support of the concept of hydrogen-bond-mediated aglycone delivery. 

Direct Synthesis of 2,6‐Dideoxy‐β‐glycosides and β‐Rhamnosides with a Stereodirecting 2‐(Diphenylphosphinoyl)acetyl Group

The anomeric configuration can greatly affect the biological functions and activities of carbohydrates. Herein, we report that N-phenyltrifluoroacetimidoyl (PTFAI), a well-known leaving group for catalytic glycosylation, can act as a stereodirecting group for the challenging 1,2-cis α-glycosylation. Utilizing rapidly accessible 1,6-di-OPTFAI glycosyl donors, TMSOTf-catalyzed glycosylation occurred with excellent α-selectivity and broad substrate scope, and the remaining 6-OPTFAI group can be cleaved chemoselectively. The remote participation of 6-OPTFAI is supported by the first characterization of the crucial 1,6-bridged bicyclic oxazepinium ion intermediates by low-temperature NMR spectroscopy. These cations were found to be relatively stable and mainly responsible for the present stereoselectivities. Further application is highlighted in glycosylation reactions toward trisaccharide heparins as well as the convergent synthesis of chacotriose derivatives using a bulky 2,4-di-O-glycosylated donor. 

Yueer Zhou

Papers

Homophase Junction for Promoting Spatial Charge Separation in Photocatalytic Water Splitting

More than a Leaving Group: N-Phenyltrifluoroacetimidate as a Remote Directing Group for Highly α-Selective 1,2-cis Glycosylation.

Direct Synthesis of 2,6-Dideoxy-β-glycosides and β-Rhamnosides with a Stereodirecting 2-(Diphenylphosphinoyl)acetyl Group.

Direct Synthesis of 2,6‐Dideoxy‐β‐glycosides and β‐Rhamnosides with a Stereodirecting 2‐(Diphenylphosphinoyl)acetyl Group

More than a Leaving Group: N‐Phenyltrifluoroacetimidate as a Remote Directing Group for Highly α‐Selective 1,2‐cis Glycosylation