Molybdenum diselenide/polymeric carbon nitride dual-homojunction photocatalyst with multi-step charge transfer for efficient catalytic carbon dioxide reduction.

Due to the high dissociation energy of carbon dioxide (CO2) and sluggish charge transfer dynamics, photocatalytic CO2 reduction with high performance remains a huge challenge. Herein, we report a novel dual-homojunction photocatalyst comprising of cyano/cyanamide groups co-modified carbon nitride (CN-TH) intramolecular homojunction and 1 T/2H-MoSe2 homojunction (denoted as 1 T/2H-MoSe2/CN-TH) for enhanced photocatalytic CO2 reduction. In this dual-homojunction photocatalyst, the intramolecular CN-TH homojunction could promote the intralayer charge separation and transfer owing to the strong electron-withdrawing capabilities of the two-type cyanamide, while the 1 T/2H-MoSe2 homojunction mainly contributes to a promote interlayer charge transport of CN-TH. This could consequently induce a tandem multi-step charge transfer and accelerate the charge transfer dynamics, resulting in enhanced CO2 reduction activities. Thanks to this tandem multi-step charge transfer, the optimized 1 T/2H-MoSe2/CN-TH dual-homojunction photocatalyst presented a high CO yield of 27.36 µmol·g-1·h-1, which is 3.58 and 2.87 times higher than those of 1 T/2H-MoSe2/CN and 2H-MoSe2/CN-TH single homojunctions, respectively. This work provides a novel strategy for efficient CO2 reduction via achieving a tandem multi-step charge transfer through designing dual-homojunction photocatalyst.

Integrating bimetallic borides with g-C3N4 containing cyanamide defects for efficient photocatalytic nitrogen fixation.

The sustainable generation of ammonia by photocatalytic nitrogen fixation under mild conditions is fascinating compared to conventional industrial processes. Nevertheless, owing to the low charge transfer efficiency, the insufficient light absorption capacity and limited active sites of the photocatalyst cause the difficult adsorption and activation of N2 molecules, thereby resulting in a low photocatalytic conversion efficiency. Herein, a novel bimetallic CoMoB nanosheets (CoMoB) co-catalyst modified carbon nitride with dual moiety defects (CN-TH3/3) Schottky junction photocatalyst is designed for photocatalytic nitrogen reduction reaction (NRR). The photocatalytic nitrogen reduction rate of the optimized CoMoB/CN-TH3/3 photocatalyst is 4.81 mM·g-1·h-1, which is 6.2 and 2.2 times higher than carbon nitride (CN) (0.78 mM·g-1·h-1) and CN-TH3/3 (2.21 mM·g-1·h-1), respectively. The excellent photocatalytic NRR performance is ascribed not only to the introduction of dual moiety defects (cyano and cyanamide groups) that extends the visible light absorption range and promotes exciton polarization dissociation, but also to the formation of interfacial electric field between CoMoB and CN-TH3/3, which effectively facilitates the interfacial charge transfer. Thus, the synergistic interaction between CN-TH3/3 and CoMoB further increases the electron numble of CoMoB active sites, which effectively strengthens the adsorption and activation of N2 and weakens the NN triple bond, thereby enhancing the photocatalytic NRR activity. This work highlights the introduced dual moiety defects and bimetallic CoMoB co-catalyst to synergistically enhance the photocatalytic nitrogen reduction performance.

Bridging engineering of polymeric carbon nitride for boosting photocatalytic CO2 reduction.

The inherent electron localized heptazine structure of carbon nitride (CN) derived from intrinsic tertiary N (N3C) bridging structure makes the photogenerated charge separation rather difficult, which severely limits photocatalytic CO2 activity of CN. Therefore, modulation of N3C bridging structure of CN is highly desirable to enhance the charge separation efficiency of CN. Herein, we reported a novel thiophene-bridged CN (BTCN) with intramolecular donor-π-acceptor (D-π-A) systems synthesized by nucleophilic substitution and Schiff base reaction to improve the photogenerated charge separation efficiency. The experimental and density functional theory (DFT) results indicate that this BTCN exhibits a high π-electron delocalization range and enhanced photogenerated charge transfer efficiency, which mainly account for the enhanced photocatalytic activity. The optimal BTCN photocatalyst exhibits enhanced charge separation efficiency and higher photocatalytic CO2 reduction activity with a CO yield of 23.02 µmol·g-1·h-1, which was higher than those of CN and edge-modified CN (ETCN) counterpart. This work highlights the importance of regulation of π-electron delocalization for the design of highly active CN photocatalysts via the rational substitution of N3C bridging structure with π-spacer molecular linkages for photocatalytic CO2 reduction.

Synergistic Effects of the Ni3B Cocatalyst and N Vacancy on g-C3N4 for Effectively Enhanced Photocatalytic N2 Fixation.

The photocatalytic fixation of N2 is a promising technology for sustainable production of ammonia, while the unsatisfactory efficiency resulting from the low electron-transfer rate, narrow light absorption range, and limited active sites of the photocatalyst seriously hinder its application. Herein, we designed a noble metal-free Schottky junction photocatalyst constructed by g-C3N4 nanosheets with N vacancies (VN-CN) and metallic Ni3B nanoparticles (Ni3B/VN-CN) for N2 reduction to ammonia. The ammonia yield rate over the optimized Ni3B/VN-CN is 7.68 mM g-1 h-1, which is 6.7 times higher than that of pristine CN (1.15 mM g-1 h-1). The superior photocatalytic N2 fixation performance of Ni3B/VN-CN can be attributed not only to the formation of Schottky junctions between Ni3B and VN-CN, which facilitates the migration and separation of photogenerated electrons, but also to the incorporation of VN into g-C3N4, which enhances visible light absorption and improves electrical conductivity. More importantly, Ni3B nanoparticles can act as the cocatalyst, which provide more active sites for the adsorption and activation of N2, thereby improving the N2 reduction activity. This work provides an effective strategy of designing noble metal-free-based cocatalyst photocatalyst for sustainable and economic N2 fixation.

Bismuth nanoparticles and oxygen vacancies synergistically modified HNb3O8 nanosheets for enhanced photocatalytic N2 reduction towards NH3.

Due to the high stability of the N2 molecule and the low charge separation efficiency, the photocatalytic reduction of N2 to high-value chemicals (NH3) under mild conditions remains a great challenge. Herein, a composite photocatalyst (Bi/HNb3O8-Vo nanosheets) with Bi nanoparticles modified the HNb3O8-Vo nanosheets are designed for the conversion of N2 into NH3. In this design, the introduction of oxygen vacancies on the catalyst surface facilitates the formation of defective energy levels within the band gap of HNb3O8-Vo NS, which promotes the absorption of visible light, and enhances the charge carrier transport and separation. Bi nanoparticles co-catalyst not only facilitates the separation and migration of photogenerated charges, but also acts as reaction sites to adsorb and activate N2 molecule. Consequently, the optimized 5 % Bi/HNb3O8-Vo photocatalysts show a NH3 yield of 372.7 µmol/L g-1h-1 under full spectral irradiation without sacrificial agent, which is much higher than that of HNb3O8 NS (92.2 µmol/L g-1h-1). This work provides a new way for the design of efficient N2 reduction photocatalysts through the synergistic effect of surface vacancies and metal co-catalysts.

Ni3B as p-Block Element-Modulated Cocatalyst for Efficient Photocatalytic CO2 Reduction.

Due to the multiple electron and proton transfer processes involved, the photogenerated charges are easily recombined during the photocatalytic reduction of CO2, making the generation of the eight-electron product CH4 kinetically more difficult. Herein, Ni3B nanoparticles modulated by p-block element were combined with TiO2 nanosheets to construct a novel Schottky junction photocatalyst (Ni3B/TiO2) for the selective photocatalytic conversion of CO2 to CH4. The formed Ni3B/TiO2 photocatalyst with Schottky junction ensures a transfer pathway of photogenerated electrons from TiO2 to Ni3B, which facilitates the accumulation of electrons on the surface of Ni3B and subsequently improves the activity of photocatalytic CO2 reduction to CH4. The optimized Ni3B/TiO2 Schottky junction shows an improved CH4 yield of 30.03 µmol g-1 h-1, which was much higher than those of TiO2 (1.62 µmol g-1 h-1), NiO/TiO2 (2.44 µmol g-1 h-1), and Ni/TiO2 (4.3 µmol g-1 h-1). This work demonstrated that the introduction of p-block elements can alleviate the scaling relationship effect of pure metal cocatalysts to a certain extent, and the modified Ni3B can be used as a promising new cocatalyst to effectively improve the selective photocatalytic of CO2 to CH4.

Carbon vacancy-mediated exciton dissociation in Ti3C2Tx/g-C3N4 Schottky junctions for efficient photoreduction of CO2.

Earth-abundant g-C3N4 is a promising photocatalyst for CO2 reduction, but its practical application is severely limited by the excitonic effect of g-C3N4 derived from strong binding energy and lack of electron-enriched active sites. Herein, we design a novel 2D/2D Schottky junction photocatalysts comprising of Ti3C2Tx-modified defective g-C3N4 nanosheets with carbon vacancy (denoted as Ti3C2Tx/Vc-CN) by a self-assembly method. The carbon vacancies in g-C3N4 promote exciton dissociation into free charge, while the formed Schottky junctions between Ti3C2Tx and Vc-CN further enables a directional charge transfer, thus providing an electron-rich catalytic surface for the CO2 reduction. Thanks to the synergy of promoted exciton dissociation and directional electron transfer, the optimal 20% Ti3C2Tx/Vc-CN display a high CO evolution rate of 20.54 µmol·g-1·h-1 under visible light irradiation, which is 7.4 times higher than that of bare CN. This work highlights the synergy of the promoted exciton dissociation and directional electron transfer in the activity enhancement of photocatalytic CO2 reduction.