Shuxian Zhong

Engineering on the edge of Pd nanosheet cocatalysts for enhanced photocatalytic reduction of CO2 to fuels

The utilization of a metal cocatalyst is a promising route to improve the solar-to-chemical conversion efficiency of semiconductor-based photocatalysts. The efficiency of the improvement is greatly dependent on the architectural structure of the metal cocatalysts, especially the catalytically active sites on the surface of the cocatalysts. In this article, Pd nanosheets with different sizes have been hybridized with TiO2 nanosheets to disclose how the edge of Pd cocatalysts influences the photocatalytic performance of TiO2–Pd hybrid structures in the reduction of CO2 to fuels. It was found that the highest photocatalytic activity was realized by small Pd nanosheets with the highest edge density on the TiO2 nanosheets. The reason is that the edges of the nanosheets act as the highly active sites for the CO2 reduction reaction. To further verify the edge-dependent photocatalytic performance, Pd nanorings were also deposited on the TiO2 nanosheets, which further improve the photocatalytic activity as compared with original nanosheets resulting from the additional edge sites exposed on the side of the hollow interior in the rings. This work underlines the importance in the edge engineering on the surface of cocatalysts in realizing high-performance photocatalytic applications.

High-index facet engineering of PtCu cocatalysts for superior photocatalytic reduction of CO2 to CH4

Photocatalytic conversion of CO2 to CH4 is beneficial in alleviating global warming and advancing a low-carbon economy. However, it is a challenge to develop semiconductor-based photocatalysts with high CO2 conversion efficiency, resulting from electron–hole recombination in bulk semiconductors as well as the low adsorption and activation ability of stable CO2 molecules on the semiconductor surface. The combination of metal cocatalysts with semiconductors is a promising route to improve the photocatalytic performance in CO2 reduction. Herein, we demonstrate that the photocatalytic performance in the reduction of CO2 to CH4 can be greatly promoted by introducing high-index faceted cocatalysts. In this work, PtCu alloy concave nanocubes with (730) facets were loaded on C3N4 nanosheets, which act as cocatalysts greatly enhancing the photocatalytic activity and selectivity in CH4 production in comparison with (100) facet enclosed PtCu nanocubes. As revealed by experimental characterization combined with density functional theory calculations, the (730) high-index facet has more low-coordinated metal active sites to increase the adsorption and activation of CO2, while the introduction of Cu to Pt leads to synergistic effects between the two metals for high selectivity towards the desired CH4. This work highlights the rational facet design of cocatalysts for enhanced photocatalytic performance in CO2 conversion.

Facet engineered interface design of NaYF4:Yb,Tm upconversion nanocrystals on BiOCl nanoplates for enhanced near-infrared photocatalysis

The combination of upconversion nanocrystals with a wide-bandgap semiconductor is an efficient strategy to develop near-infrared (NIR)-responsive photocatalysts. The photocatalytic activity of the hybrid structures is greatly determined by the efficiency of the energy transfer on the interface between upconversion nanocrystals and the semiconductor. In this work, we demonstrate the interface design of a NaYF4:Yb,Tm-BiOCl hybrid structure based on the choice of suitable BiOCl facets in depositing NaYF4:Yb,Tm upconversion nanocrystals. It was found that the selective deposition of NaYF4:Yb,Tm nanocrystals on the BiOCl(110) facet can greatly enhance the photocatalytic performance in dye degradation compared with the sample with NaYF4:Yb,Tm nanocrystals loaded on the BiOCl(001) facet. Two effects were believed to contribute to this enhancement: (1) a stronger UV emission absorption ability of the BiOCl(110) facet from NaYF4:Yb,Tm in generating more photo-induced charge carriers resulted from the narrower bandgap; (2) a shorter diffusion distance of photogenerated charge carriers to the BiOCl(110) reactive facet for surface catalytic reactions owing to the spatial charge separation between different facets. This work highlights the rational interfacial design of an upconversion nanocrystal-semiconductor hybrid structure for enhanced energy transfer in photocatalysis.

Twin defects engineered Pd cocatalyst on C3N4 nanosheets for enhanced photocatalytic performance in CO2 reduction reaction

Photocatalytic conversion of CO2 to value-added chemicals, a potential route to addressing the depletion of fossil fuels and anthropogenic climate change, is greatly limited by the low-efficient semiconductor photocatalyst. The integration of cocatalyst with light-harvesting semiconductor is a promising approach to enhancing the photocatalytic performance in CO2 reduction reaction. The enhancement is greatly determined by the catalytic active sites on the surface of cocatalyst. Herein, we demonstrate that the photocatalytic performance in the CO2 reduction reaction is greatly promoted by twin defects engineered Pd cocatalyst. In this work, Pd nanoicosahedrons with twin defects were in situ grown on C3N4 nanosheets, which effectively improve the photocatalytic performance in reduction of CO2 to CO and CH4 in comparison with Pd nanotetrahedrons without twin defects. It is proposed that the twin boundary (TB) terminations on the surface of Pd cocatalysts are highly catalytic active sites for CO2 reduction reaction. Based on the proposed mechanism, the photocatalytic activity and selectivity in CO2 reduction were further advanced through reducing the size of Pd icosahedral cocatalyst resulted from the increased surface density of TB terminations. The defect engineering on the surface of cocatalyst represents a novel route in realizing high-performance photocatalytic applications.

Ultrathin nanosheets of palladium in boosting its cocatalyst role and plasmonic effect towards enhanced photocatalytic hydrogen evolution

The combination of a metal with a semiconductor is a promising route to improve the solar-to-chemical conversion efficiency of photocatalysts. In this article, ultrathin Pd nanosheets are integrated with semiconductor TiO2 nanosheets for photocatalytic hydrogen evolution, which acts as a cocatalyst and plasmonic agent in ultraviolet and visible-near-infrared spectral regions, respectively. Owing to the unique two-dimensional (2D) nanostructure, the Pd nanosheet cocatalyst realizes the large TiO2–Pd interfacial area for electron transfer as well as a large Pd exposed area for reduction reactions, while the plasmonic Pd nanosheets offer strong vis-NIR light absorption for “hot” electron production as well as a large interfacial area for “hot” electron injection. As a result, the Pd nanosheets achieve improved photocatalytic activity in comparison with three-dimensional Pd nanotetrahedrons under both light irradiations. This work underlines the importance in choosing a suitable shape of metal in the surface and interface design of semiconductor–metal hybrid photocatalysts as well as the advantages of 2D metal nanostructures in realizing high photocatalytic performance.

Facet Engineered Interface Design of Plasmonic Metal and Cocatalyst on BiOCl Nanoplates for Enhanced Visible Photocatalytic Oxygen Evolution

Integration of plasmonic metal and cocatalyst with semiconductor is a promising approach to simultaneously optimize the generation, transfer, and consumption of photoinduced charge carriers for high-performance photocatalysis. The photocatalytic activities of the designed hybrid structures are greatly determined by the efficiencies of charge transfer across the interfaces between different components. In this paper, interface design of Ag-BiOCl-PdOx hybrid photocatalysts is demonstrated based on the choice of suitable BiOCl facets in depositing plasmonic Ag and PdOx cocatalyst, respectively. It is found that the selective deposition of Ag and PdOx on BiOCl(110) planes realizes the superior photocatalytic activity in O2 evolution compared with the samples with other Ag and PdOx deposition locations. The reason was the superior hole transfer abilities of Ag-(110)BiOCl and BiOCl(110)-PdOx interfaces in comparison with those of Ag-(001)BiOCl and BiOCl(001)-PdOx interfaces. Two effects are proposed to contribute to this enhancement: (1) stronger electronic coupling at the BiOCl(110)-based interfaces resulted from the thinner contact barrier layer and (2) the shortest average hole diffuse distance realized by Ag and PdOx on BiOCl(110) planes. This work represents a step toward the interface design of high-performance photocatalyst through facet engineering.

Surface and Interface Engineering in Ag2S@MoS2 Core-Shell Nanowire Heterojunctions for Enhanced Visible Photocatalytic Hydrogen Production

An Ag2S@MoS2 core–shell nanowire heterojunction, facilely synthesized by simultaneous sulfuration of Ag nanowires (NMs) and growth of MoS2, is used as a model system to disclose how the surface and interface structures influence the photocatalytic activity. The Ag2S@MoS2 NWs with different loading amounts of MoS2 are used as photocatalysts for H2 production. It is found that the highest photocatalytic activity is realized by a moderate loading amount of MoS2. A lower loading amount of MoS2 not only reduces the interfacial contact for insufficient electron–hole separation but also decreases the number of catalytic active sites for H2 production, while a higher loading amount of MoS2 increases the light‐shielding effect of Ag2S and extends the distance of electron transfer to the catalytic active sites for H2 production. Furthermore, with the same loading amount of MoS2, Ag2S@MoS2 NWs also exhibit superior H2 production activity in comparison with pre‐Ag2S@MoS2 NWs with MoS2 grown on pre‐synthesized Ag2S nanowires. The proposed reason is that the simultaneous sulfuration of Ag nanowires and growth of MoS2 results in an intimate contact between Ag2S and MoS2 for smooth interfacial charge transfer, while the two‐step synthetic method leads to a lower quality of the MoS2‐Ag2S interface and thus poor interelectron transfer. This work highlights the importance of a rational surface and interface design of semiconductor heterojunctions for realizing high‐performance photocatalytic applications.

Chemical etching of graphene-supported PdPt alloy nanocubes into concave nanostructures for enhanced catalytic hydrogen production from alkaline formaldehyde aqueous solution

Catalytic hydrogen production from alkaline formaldehyde aqueous solution is a promising route to supply hydrogen on a large scale for practical applications. Producing highly efficient and low-cost catalysts is the main challenge for future development of the hydrogen economy through this route. In this paper, PdPt concave nanostructures supported on reduced graphene oxide (rGO) nanosheets are facilely obtained through chemical etching of PdPt nanocubes with nitric acid. By adjusting the Pd : Pt ratio of the nanocubes, PdPt alloy nanostructures with different degrees of concavity are obtained as a result of different etching kinetics. The as-obtained rGO supported concave nanostructures serve as highly efficient catalysts in H2 production from alkaline formaldehyde aqueous solution. On one hand, through adjusting the Pd : Pt molar ratio, a synergistic effect between Pd and Pt is realized to enhance the catalytic activity. On the other hand, the surface concave structures of the PdPt nanocrystals offer a high density of low-coordinated atoms, serving as highly active sites for the catalytic H2 production reaction. Furthermore, rGO nanosheets as a support are found to prevent the aggregation of metal nanocrystals and to improve the catalytic activity and stability. Based on the surface composition and structure optimization, the as-obtained rGO supported Pd90Pt10 octapods achieved the highest average hydrogen production rate of 0.85 mmol gcat−1 min−1, about 9 times higher than that of pure Pt nanoparticles. Also, the advantages of the rGO-Pd90Pt10 COPs are highlighted by the minimal Pt content and excellent catalytic stability during successive cyclic processes. This work not only highlights the shape-controlled synthesis of concave metal nanocrystals through adjustment of the etching kinetics, but also underlines the importance of the collaborative design of the surface structure and composition as well as the catalyst support in realizing highly efficient hydrogen generation.

Order engineering on the lattice of intermetallic PdCu co-catalysts for boosting the photocatalytic conversion of CO2 into CH4

Photocatalytic conversion of CO2 to CH4, a promising approach to reduce the depletion of fossil fuels and concomitant global warming, is greatly limited by the production of CO and H2 by side reactions. Rational design of co-catalysts holds promise to address this grand challenge. In this paper, via the transformation from a random A1 alloy phase to an ordered B2 intermetallic phase, order engineering is performed on PdCu co-catalysts to realize enhanced photocatalytic activity and selectivity in reduction of CO2 with H2O to CH4. Based on the experimental results of PdCu co-catalysts with different ordered degrees of atomic arrangement obtained through tuning the annealing temperatures and Pd/Cu molar ratios, two effects are proposed to contribute to this enhancement: (1) the strong electronic interaction between Pd and Cu atoms in the periodic structure increases the electron trapping ability of ordered PdCu co-catalysts; (2) the periodic structure increases the number of isolated Cu atoms in the ordered PdCu co-catalysts, which act as highly active catalytic sites in the reduction of CO2 to CH4. This work represents a step toward the design of high-performance photocatalysts through lattice engineering of the co-catalysts with atomic precision.