Stability and Crystallinity of Sodium Poly(Heptazine Imide) in Photocatalysis.

Poly(heptazine imide) (PHI) salts, as crystalline carbon nitrides, exhibit high photocatalytic activity and are being extensively researched, but its photochemical instability has not drawn researchers' attention yet. Herein, sodium PHI (PHI-Na) ultrathin nanosheets with increased crystallinity, synthesized by enhancing contact of melamine with NaCl functioning as a structure-induction agent and hard template, exhibits improved photocatalytic hydrogen evolution activity, but low photochemical stability, owing to Na+ loss in the photocatalytic process, which, interestingly, can be enhanced by the common ion effect, e.g., addition of NaCl that is also able to remarkably increase the photoactivity with the apparent quantum yield at 420 nm reaching 41.5 %. This work aims at attracting research peers' attention to photochemical instability of PHI salts and provides a way to enhance their crystallinity.

Interfacial Affinity Determined Photocatalytic Activity: A Comparison between Defective and Bulk Polymeric Carbon Nitride.

The photoexcited charge separation efficiency of photocatalysts is generally considered as the key factor for enhancement of their photocatalytic activity, and sometimes, their photoabsorption capability and interfacial reaction kinetics play a key part, but the role of interfacial affinity of photocatalysts with substrates was rarely researched systematically. Herein, nitrogen vacancy-modified polymeric carbon nitride porous nanotubes (PCNpts) were simply synthesized, using tartaric acid as a crosslinking and corrosion agent, and exhibit a remarkable increment in surface area, wettability, photoabsorption and charge separation capability, and photocatalytic activity in water splitting to produce H2, but, interestingly, exhibit substrate-dependent variation of photoactivity in contaminant degradation, compared with bulk PCN. More interestingly, the interfacial affinity of PCNpts and PCN with contaminants and H2O, rather than photoabsorption and charge separation capability, is confirmed to dominate their photoactivity.

Ion-Induced Synthesis of Crystalline Carbon Nitride Ultrathin Nanosheets from Mesoporous Melon for Efficient Photocatalytic Hydrogen Evolution with Synchronous Highly Selective Oxidation of Benzyl Alcohol.

Crystalline carbon nitride (CCN) with a poly(heptazine imide) structure is efficient in photocatalytic hydrogen evolution (PHE), but synthesis of CCN ultrathin nanosheets (CCNuns) and their use in PHE with selective organic oxidation are still rare. Herein, CCNuns with Na+ doping are prepared using NaCl as the ion-induction and templating agent and mesoporous melon as the feedstock, exhibiting efficient synchronous PHE and benzyl alcohol oxidation to benzaldehyde, with an apparent quantum yield of 10.5% at 420 nm and a visible light PHE rate that is 94.3 times that of bulk polymeric carbon nitride (PCN). The selectivity of benzaldehyde formation (90.5%) is also much higher than that of PCN (40.7%). Interestingly, this selectivity increases gradually with increasing light wavelengths. The high photoactivity of CCNuns originates from their ultrathinness and Na+ doping, which considerably enhance the photogenerated charge separation. This work opens up an avenue for the synthesis of CCNuns and extends their application.

Single-atom cobalt-hydroxyl modification of polymeric carbon nitride for highly enhanced photocatalytic water oxidation: ball milling increased single atom loading.

Expediting the oxygen evolution reaction (OER) is the key to achieving efficient photocatalytic overall water splitting. Herein, single-atom Co-OH modified polymeric carbon nitride (Co-PCN) was synthesized with single-atom loading increased by ∼37 times with the assistance of ball milling that formed ultrathin nanosheets. The single-atom Co-N4OH structure was confirmed experimentally and theoretically and was verified to enhance optical absorption and charge separation and work as the active site for the OER. Co-PCN exhibits the highest OER rate of 37.3 µmol h-1 under visible light irradiation, ∼28-fold higher than that of common PCN/CoO x , with the highest apparent quantum yields reaching 4.69, 2.06, and 0.46% at 400, 420, and 500 nm, respectively, and is among the best OER photocatalysts reported so far. This work provides an effective way to synthesize efficient OER photocatalysts.

Supramolecular Self-Assembly of Atomically Precise Silver Nanoclusters with Chiral Peptide for Temperature Sensing and Detection of Arginine.

Metal nanoclusters (NCs) as a new type of fluorescent material have attracted great interest due to their good biocompatibilities and outstanding optical properties. However, most of the studies on metal NCs focus on the synthesis, atomic or molecular assembly, whereas metal NCs ability to self-assemble to higher-level hierarchical nanomaterials through supramolecular interactions has rarely been reported. Herein, we investigate atomic precise silver NCs (Ag9-NCs, [Ag9(mba)9], where H2mba = 2-mercaptobenzoic acid) and peptide DD-5 were used to induce self-assembly, which can trigger an aggregation-induced luminescence (AIE) effect of Ag9-NCs through non-covalent forces (H-bond, π-π stacking) and argentophilic interactions [Ag(I)-Ag(I)]. The large Stokes shift (~140 nm) and the microsecond fluorescence lifetime (6.1 µs) indicate that Ag9-NCs/DD-5 hydrogel is phosphor. At the same time, the chirality of the peptide was successfully transferred to the achiral Ag9-NCs because of the supramolecular self-assembly, and the Ag9-NCs/DD-5 hydrogel also has good circularly polarized luminescence (CPL) properties. In addition, Ag9-NCs/DD-5 luminescent hydrogel is selective and sensitive to the detection of small biological molecule arginine. This work shows that DD-5 successfully induces the self-assembly of Ag9-NCs to obtain high luminescent gel, which maybe become a candidate material in the fields of sensors and biological sciences.

The pivotal role of defects in fabrication of polymeric carbon nitride homojunctions with enhanced photocatalytic hydrogen evolution.

Fabrication of homojunctions is a cost-effective efficient way to enhance the photocatalytic performance of polymeric carbon nitride (CN), but the generation of defects upon synthesizing CN homojunctions and their roles in the homojunction fabrication were hardly reported. Herein, nitrogen-deficient CN homojunctions were simply synthesized by calcining dicyandiamide-loaded CN (prepared from urea and denoted as UCN) with dicyandiamide polymerizing into CN (denoted as DCN) and simultaneous formation of nitrogen vacancies in the surface of UCN. Fabrication of the nitrogen-deficient UCN (dUCN)/DCN homojunction depends on the nitrogen vacancy content in dUCN which can tune the energy band structure of dUCN from not matching to matching with that of DCN. The dUCN/DCN homojunction exhibits extended optical absorption and remarkably enhanced charge separation and photocatalytic H2 evolution, compared with UCN and DCN. This work illustrates the pivotal role of defects in fabricating CN homojunctions and supplies a new facile way to synthesize nitrogen-deficient CN.

Band structure engineering of polymeric carbon nitride with oxygen/carbon codoping for efficient charge separation and photocatalytic performance.

The high charge recombination efficiency and weak visible-light absorption of polymeric carbon nitride (CN) severely suppress its photocatalytic performance. To overcome these defects, oxygen/carbon codoped CN (OCN) was prepared firstly using acrylamide as the additive. OCN exhibits much enhanced visible light absorption, charge separation and transfer, and thus photoactivity in hydrogen production and environmental remediation. OCN exhibits a ~6-fold higher photocatalytic hydrogen production rate (~2626 µmol h-1 g-1) than CN, comparable to most of nonmetal-doped CN, and an apparent quantum yield of ~16.3% (420 nm). OCN is also much better at producing singlet oxygen than CN. The significantly enhanced charge separation for OCN arises from the O/C codoping structure which forms an impurity level above the valence band edge in the bandgap, i.e., works as a hole-capture center. This work affords a simple and effective strategy to synthesize modified CN for photoactivity enhancement, clarifies the doping mechanism, and may guide research on other nonmetal doped organic semiconductor photocatalysts.

Construction of direct all-solid-state Z-scheme p-n copper indium disulfide/tungsten oxide heterojunction photocatalysts: Function of interfacial electric field.

Construction of Z-scheme heterojunction (ZCH) is one of the most effective ways to enhance photocatalytic performance of photocatalysts. The direct all-solid-state p-n ZCH shows the best prospect, but its fabrication mechanism, especially function of the interfacial electric field (IEF) was rarely expounded explicitly. Herein, a direct all-solid-state p-n copper indium disulfide/tungsten oxide (CIS/WO) ZCH was prepared through a facile hydrothermal process for the first time. The CIS/WO ZCH exhibits enhanced photocatalytic activity because of significantly accelerated photogenerated charge separation via a Z-scheme charge migration process. The Z-scheme charge transfer pathway is inferred from matched energy band levels of CIS and WO and the IEF is confirmed to play a key role. The CIS/WO ZCH can fast produce singlet oxygen via hole oxidation of superoxide radicals under visible light irradiation, while pure CIS and WO cannot, effectively verifying the Z-scheme charge transfer process. This work illustrates the principle for fabrication of the direct all-solid-state p-n ZCH and function of the IEF, as well as provides a new ZCH.

Hyperbranched exopolysaccharide-enhanced foam properties of sodium fatty alcohol polyoxyethylene ether sulfate.

The foam properties, such as the foamability, foam stability, drainage, coalescence and bulk rheology, of aqueous solutions containing an eco-friendly exopolysaccharide (EPS) secreted by a deep-sea mesophilic bacterium, Wangia profunda SM-A87, and an anionic surfactant, sodium fatty alcohol polyoxyethylene ether sulfate (AES), were studied. Both the foamability and foam stability of the EPS/AES solutions are considerably higher than those of single AES solutions, even at very low AES concentrations, although pure EPS solutions cannot foam. The improved foamability and foam stability arise from the formation of the EPS/AES complex via hydrogen bonds at the interfaces. The synergism between the EPS and AES decreases the surface tension, increases the interfacial elasticity and water-carrying capacity, and suppresses the coalescence and collapse of the foams. The EPS/AES foams are more salt-resistant than the AES foams. This work provides not only a new eco-friendly foam with great potential for use in enhanced oil recovery and health-care products but also useful guidance for designing other environmentally friendly foam systems that exhibit high performance.