Controllable synthesis of porous silver cyanamide nanocrystals with tunable morphologies for selective photocatalytic CO2 reduction into CH4

Nano-sized aggregate Ti3C2-TiO2 supported on the surface of Ag2NCN as a Z-scheme catalyst with enhanced visible light photocatalytic performance

Exposing the photocatalyst's highly active facets and hybridizing the photocatalyst with suitable cocatalysts in the proper spot have been recognized as strong methods for high-performance photocatalysts. Herein, Ag2NCN/TiO2-Ti3C2 composites were synthesized by applying simple calcination and physically weak interaction deposition processes to obtain an excellent photocatalyst for Rhodamine B (Rh B) degradation when exposed to visible light. The findings from the experiments reveal that the Ag2NCN/TiO2-Ti3C2400 composite exhibited an outstanding photocatalytic rate in 80 min, with the highest Rh B degradation rate (k = 0.03889 min-1), which was 16 times higher than that of pure Ag2NCN (k = 0.00235 min-1) and 2.2 times higher than that of TiO2-Ti3C2400 (k = 0.01761 min-1). The results from the following factors: (i) the powerful interfacial contact created by the in situ formation of TiO2, and the superior electrical conductivity of Ti3C2 that makes carrier separation possible; (ii) TiO2 with electron-rich (101) facets are deposited on the surface of Ag2NCN, significantly reducing charge carrier recombination by trapping photoelectrons; (iii) a Z-type heterojunction is constructed between nanosize aggregate Ti3C2-TiO2 and Ag2NCN with non-metal Ti3C2 as the solid medium, improving the transfer and separation of photogenerated charges and inhibiting the recombination of electrons and holes. Additionally, the redox ability of the composite photocatalyst is enhanced. Furthermore, the analyses of active species showed that photogenerated superoxide radicals and holes were the principal active agents inside the photodegradation of Rh B. Moreover, the composite exhibited outstanding photo-stability.

Visible-light driven boosting electron-hole separation in CsPbBr3 QDs@2D Cu-TCPP heterojunction and the efficient photoreduction of CO2

CsPbBr₃ quantum dots (CPB QDs) have great potential in photoreduction of CO₂ to chemical fuels. However, the low charge transportation efficiency and chemical instability of CPB QDs presents a considerable challenge. Herein, we describe the electrostatic assemblies of negatively charged colloidal two dimensional (2D) Cu-Tetrakis(4-carboxyphenyl) porphyrins (Cu-TCPP) nanosheets and positively CPB QDs to construct the hydride heterojunction. The photogenerated electron migration from CPB QDs to Cu-TCPP nanosheets has been witnessed, providing the supply of long-lived electrons for the reduction of CO₂ molecules adsorbed on Cu-TCPP matrix. As a direct result, The CPB@Cu-TCPP-x (x wt% of CPB QDs) photocatalysts exhibit significantly enhanced photocatalytic conversion of CO₂, compared to the parent Cu-TCPP nanosheets or single CPB QDs. Especially, when with 20% CPB QDs, the heterostruture system achieves an evolution yield of 287.08 µmol g^-1 in 4 h with highly CO selectivity (99%) under visible light irradiation, which is equivalent to a 3.87-fold improvement compared to the pristine CPB QDs. Meanwhile, the CH₄ generation rate can be up to 3.25 µmol g^-1. This optimized construction of heterostructure could provide a platform to funnel photoinduced electrons to the reaction center, which can both act as a crucial capture and the reaction actives of CO₂.

14N, 13C, and 119Sn solid-state NMR characterization of tin(II) carbodiimide Sn(NCN)

We report the first magic-angle spinning (MAS) nuclear magnetic resonance (NMR) study on Sn(NCN). In this compound the spatially elongated (NCN)2− ion is assumed to develop two distinct forms: either cyanamide (N≡C–N2−) or carbodiimide (−N=C=N−). Our 14N MAS NMR results reveal that in Sn(NCN) the (NCN)2− groups exist exclusively in the form of symmetric carbodiimide ions with two equivalent nitrogen sites, which is in agreement with the X-ray diffraction data. The 14N quadrupolar coupling constant | C Q | $\vert {C}_{\text{Q}}\vert $  ≈ 1.1 MHz for the −N=C=N− ion in Sn(NCN) is low when compared to those observed in molecular compounds that comprise cyano-type N≡C– moieties ( | C Q | $\vert {C}_{\text{Q}}\vert $  > 3.5 MHz). This together with the information from 14N and 13C chemical shifts indicates that solid-state NMR is a powerful tool for providing atomic-level insights into anion species present in these compounds. The experimental NMR results are corroborated by high-level calculations with quantum chemistry methods.

Fabrication of size-controlled hierarchical ZnS@ZnIn2S4 heterostructured cages for enhanced gas-phase CO2 photoreduction

Designing and constructing advanced heterojunction architectures are desirable for boosting CO₂ photoreduction performance of semiconductor photocatalysts. Herein, we have prepared hierarchical ZnS@ZnIn₂S₄ core-shell cages with controlled particle sizes using sequential synthesis of Zeolitic imidazolate (ZIF-8) polyhedrons, ZnS cages, and ZnIn₂S₄ nanosheets on the ZnS polyhedron cages. ZIF-8 polyhedrons are firstly synthesized by a liquid-phase approach. The subsequent sulfidation of the ZIF-8 polyhedrons results in the formation of ZnS polyhedron cages, which act as substrates for fabricating ZnS@ZnIn₂S₄ core-shell cages by growing ZnIn₂S₄ nanosheets. The size of ZnS cages can be tuned to optimize CO₂ photoreduction performance of hierarchical ZnS@ZnIn₂S₄ core-shell cages. The synergy of the unique hierarchical core-shell cage-like structure and heterojunction composition endows the hybrid catalyst high incident light utilization, abundant active sites, and effective separation of photoexcited charge carriers. Benefiting from these advantages, the optimized hierarchical ZnS@ZnIn₂S₄ core-shell cages exhibit enhanced performance for CO₂ photoreduction with the CO yield of 87.43 μmol h^-1g^-1 and 84.3% selectivity, which are much superior to those of single ZnIn₂S₄ or ZnS. Upon Au decoration, the CO₂ photoreduction performance of ZnS@ZnIn₂S₄ core-shell cages is further enhanced because of the Schottky junctions and surface plasmon resonance effect.

The fabrication of two-dimensional g-C3N4/NaBiO3·2H2O heterojunction for improved photocatalytic CO2 reduction: DFT study and mechanism unveiling

Photocatalytic CO₂ reduction is typically limited by the separation efficiency of photogenerated carriers for a single semiconductor. Thus, fabricating a two-dimensional/two-dimensional (2D/2D) heterojunction photocatalyst with high separation efficiency of photogenerated carriers has become a research priority. Here, a 2D/2D g-C₃N₄/NaBiO₃·2H₂O (CN/NBO) heterojunction photocatalyst was successfully synthesized for CO₂ photoreduction. With the assistance of the nature of CN, the 10CN/NBO composite showed the best performance with the production yield rates of 110.2 and 43.8 µmol g^-1 for CO and CH₄, respectively. Our experiments showed that the introduction of CN in CN/NBO composites, which is under the step-scheme (S-step) transfer direction of photogenerated carriers, could greatly inhibit the recombination of photogenerated e^--h⁺ pairs to prolong the carriers' lifetime, which was further confirmed by analysis of photoluminescence and photochemical characterization. As we expected, the CN/NBO composites show improved photocatalytic CO₂ reduction activity. The in situ infrared spectroscopy was also performed to study the intermediate products of the photocatalytic CO₂ reduction process. This study provides a way to design CN-based heterojunction photocatalysts for CO₂ photoreduction.

Line defects in plasmatic hollow copper ball boost excellent photocatalytic reaction with pure water under ultra-low CO2 concentration

By using a low CO₂ concentration as a C1 source, the design of a plasmonic catalyst that can effectively photocatalytic CO₂ reduction is of great significance for sustainable and ecological development. Herein, the space confinement effect and liquid environment of the molten salt result in uniform hollow structure, while the strong aggressive force furnished via using molten salt enhances the formation of line defects. This special structure can not only provide a large number of active sites but also greatly accelerate the transport of photoinduced charge carriers. The hollow copper ball with line defects (CCu) shows excellent photocatalytic activity with pure water (1028.57 μmol g^-1), and it also shows good catalytic activity even under ultra-low CO₂ content, which far exceeds the catalytic activity of most semiconductor-based catalysts. This work is designed to simultaneously construct line defect and hollow structure in plasmatic metal nanoparticles for efficient photocatalytic CO₂ reduction.

Rational construction of Ni(OH)2 nanoparticles on covalent triazine-based framework for artificial CO2 reduction

Artificial photoreduction of CO₂ to chemical fuel is an intriguing and reliable strategy to tackle the issues of energy crisis and climate change simultaneously. In the present study, we rationally constructed a Ni(OH)₂-modified covalent triazine-based framework (CTF-1) composites to serve as cocatalyst ensemble for superior photoreduction of CO₂. In particular, the optimal Ni(OH)₂-CTF-1 composites (loading ratio at 0.5 wt%) exhibited superior photocatalytic activity, which surpassed the bare CTF-1 by 33 times when irradiated by visible light. The mechanism for the enhancement was systematically investigated based on various instrumental analyses. The origin of the superior activity was attributable to the enhanced CO₂ capture, more robust visible-light response, and improved charge carrier separation/transfer. This study offers an innovative pathway for the fabrication of noble-metal-free cocatalysts on CTF semiconductors and deepens the understanding of photocatalytic CO₂ reduction.