Ya-Nan Liu

Enhanced visible-light photocatalytic activity of Z-scheme graphitic carbon nitride/oxygen vacancy-rich zinc oxide hybrid photocatalysts

With the objectives of enhancing the stability, optical properties and visible-light photocatalytic activity of photocatalysts, we modified oxygen vacancy-rich zinc oxide (Vo-ZnO) with graphitic carbon nitride (g-C3N4). The resulting g-C3N4/Vo-ZnO hybrid photocatalysts showed higher visible-light photocatalytic activity than pure Vo-ZnO and g-C3N4. The hybrid photocatalyst with a g-C3N4 content of 1 wt% exhibited the highest photocatalytic degradation activity under visible-light irradiation (λ ≥ 400 nm). In addition, the g-C3N4/Vo-ZnO photocatalyst was not deactivated after five cycles of methyl orange degradation, indicating that it is stable under light irradiation. Finally, a Z-scheme mechanism for the enhanced photocatalytic activity and stability of the g-C3N4/Vo-ZnO hybrid photocatalyst was proposed. The fast charge separation and transport within the g-C3N4/Vo-ZnO hybrid photocatalyst were attributed as the origins of its enhanced photocatalytic performance.

Metallic 1T-LixMoS2 Cocatalyst Significantly Enhanced the Photocatalytic H2 Evolution over Cd0.5Zn0.5S Nanocrystals under Visible Light Irradiation

In the present work, metallic 1T-LixMoS2 is utilized as a novel cocatalyst for Cd0.5Zn0.5S photocatalyst. The obtained LixMoS2/Cd0.5Zn0.5S hybrids show excellent photocatalytic performance for H2 generation from aqueous solution containing Na2S and Na2SO3 under splitting visible light illumination (λ ≥ 420 nm) without precious metal cocatalysts. It turns out that a certain amount of intercalating Li(+) ions ultimately drives the transition of MoS2 crystal from semiconductor triagonal phase (2H phase) to metallic phase (1T phase). The distinct properties of 1T-LixMoS2 promote the efficient separation of photoexcited electrons and holes when used as cocatalyst for Cd0.5Zn0.5S photocatalyst. As compared to 2H-MoS2 nanosheets only having edge active sites, photoinduced electrons not only transfer to the edge sites of 1T-LixMoS2, but also to the plane active sites of 1T-LixMoS2 nanosheets. The content of LixMoS2 in hybrid photocatalysts influences the photocatalytic activity. The optimal 1T-LixMoS2 (1.0 wt %)/Cd0.5Zn0.5S nanojunctions display the best activity for hydrogen production, achieving a hydrogen evolution rate of 769.9 μmol h(-1), with no use of noble metal loading, which is about 3.5 times higher than that of sole Cd0.5Zn0.5S, and 2 times higher than that of 2H-MoS2 (1.0 wt %)/Cd0.5Zn0.5S samples. Our results demonstrate that Li(+)-intercalated MoS2 nanosheets with high conductivity, high densities of active sites, low cost, and environmental friendliness are a prominent H2 evolution cocatalyst that might substitute for noble metal for potential hydrogen energy applications.

Nanoheterostructured photocatalysts for improving photocatalytic hydrogen production

Abstract Rapid industrialization has accordingly increased the demand for energy. This has resulted in the increasingly severe energy and environmental crises. Hydrogen production, based on the photocatalytic water splitting driven by sunlight, is able to directly convert solar energy into a usable or storable energy resource, which is considered to be an ideal alternative energy source to assist in solving the energy crisis and environmental pollution. Unfortunately, the hydrogen production efficiency of single phase photocatalysts is too low to meet the practical requirements. The construction of heterostructured photocatalyst systems, which are comprised of multiple components or multiple phases, is an efficient method to facilitate the separation of electron-hole pairs to minimize the energy-waste, provide more electrons, enhance their redox ability, and hence improve the photocatalytic activity. We summarize the recent progress in the rational design and fabrication of nanoheterostructured photocatalysts. The heterojunction photocatalytic hydrogen generation systems can be divided into type-I, type-II, pn-junction and Z-scheme junction, according to the differences in the transfer of the photogenerated electrons and holes. Finally, a summary and some of the challenges and prospects for the future development of heterojunction photocatalytic systems are discussed.

Large improvement of visible-light photocatalytic H2-evolution based on cocatalyst-free Zn0.5Cd0.5S synthesized through a two-step process

Final metal sulfides Zn0.5Cd0.5S (ZnCdS-CH) are synthesized through a coprecipitation process followed by hydrothermal treatment. The morphological, structural and optical properties have been investigated extensively via diverse analytical techniques. The ZnCdS-CH solid solution without noble metal loading is employed in photocatalytic H2 evolution under visible light irradiation (λ ≥ 420 nm) and achieves a superior activity rate of 0.971 mmol h−1, which exceeds those of coprecipitated Zn0.5Cd0.5S (ZnCdS-C) samples by more than 13 times. Moreover, in the recycle test, the ZnCdS-CH photocatalyst shows a stable photocatalytic activity for H2 evolution under long-term visible-light irradiation. Characterization analyses demonstrate that the excellent photocatalytic H2-evolution performance of the ZnCdS-CH sample arises predominantly from the two-step processing procedure of coprecipitation followed by hydrothermal treatment at 200 °C, which makes it possess a hexagonal (wurtzite) structure, good dispersity, enhanced crystallinity, an appropriate band gap, a more negative conduction band, as well as a large number of surface defect states. This finding is of great significance for designing a facile, reproducible and inexpensive method to realise the potential of ZnxCd1−xS ternary metal sulfides in the field of H2 evolution by water splitting.

Supramolecular polymers-derived nonmetal N, S-codoped carbon nanosheets for efficient oxygen reduction reaction

The rational design and fine synthesis of highly efficient and cost-effective electrocatalysts for oxygen reduction reaction (ORR) is crucial for the wide application of fuel cells (FCs). In this work, we select a novel nitrogen and sulfur-rich supramolecular polymer as a precursor for in situ, large scale and controlled synthesis of nitrogen and sulfur dual doped carbon (N, S–C) nanosheets as a catalyst for ORR. The supramolecular polymer MTCA particles are quickly self-assembled via triple-hydrogen-bonding between melamine (M) and trithiocyanuric acid (TCA). The uniform distribution and high content of nitrogen and sulfur in the polymer is beneficial to the high and homogeneous doping in the produced self-supporting catalyst after pyrolysis. When evaluated as an electrocatalyst, the catalyst pyrolyzed at 800 °C (N, S–C/800) shows a superior ORR activity in alkaline solution. Furthermore, the N, S–C/800 catalyst exhibits superb durability and immunity towards methanol crossover. This metal-free, cost-effective and highly efficient ORR catalyst will find wide potential applications in fuel cells.

Synthesis of nanoporous structured iron carbide/Fe–N–carbon composites for efficient oxygen reduction reaction in Zn–air batteries

Large-scale industrial level applications of fuel cells and metal–air batteries have called for the development of highly efficient and low-cost oxygen reduction electrodes. Here we report the effective and simple preparation of iron carbide-embedded Fe–N-doped carbon (Fe3C/Fe–N/C) composites using an iron–phenanthroline (Fe–Phen) complex and dicyandiamide (DCA) as the precursors that are subsequently heat treated. The optimal catalyst pyrolyzed at 800 °C (Fe–Phen–N-800) exhibits superior oxygen reduction activity with onset and half-wave potentials of 0.99 and 0.86 V in 0.1 M KOH, respectively, which are higher than those of Pt/C (onset and half-wave potentials of 0.98 and 0.84 V) at the same catalyst loading. Moreover, the obtained Fe–Phen–N-800 displays comparable activity to Pt/C in 0.1 M HClO4 solution. Notably, the well-developed Fe–Phen–N-800 catalyst shows much higher long-term stability and better methanol tolerance than Pt/C. The results suggest that our catalyst is one of the most promising candidates to replace Pt catalysts toward oxygen reduction. Strikingly, a primary Zn–air battery using Fe–Phen–N-800 as the air cathode catalyst delivers higher voltages and gravimetric energy densities than those of a Pt/C-based system at the discharge current densities of 10 and 25 mA cm−2, thus demonstrating the potential applications of our catalyst for energy conversion devices.

Fe 3 O 4 /g-C 3 N 4 复合催化剂增强芬顿/光-芬顿和类过氧化酶反应的活性及稳定性

Abstract We prepared the Fe3O4/g-C3N4 nanoparticles (NPs) through a simple electrostatic self-assembly method with a 3:97 weight ratio to investigate their Fenton, photo-Fenton and oxidative functionalities besides photocatalytic functionality. We observed an improvement of the Fenton and photo-Fenton activities of the Fe3O4/g-C3N4 nanocomposites. This improvement was attributed to efficient charge transfer between Fe3O4 and g-C3N4 at the heterojunctions, inhibition of electron-hole recombination, a high surface area, and stabilization of Fe3O4 against leaching by the hydrophobic g-C3N4. The obtained NPs showed a higher degradation potential for rhodamine B (RhB) dye than those of Fe3O4 and g-C3N4. As compared to photocatalysis, the efficiency of RhB degradation in the Fenton and photo-Fenton reactions was increased by 20% and 90%, respectively. Additionally, the horseradish peroxidase (HRP) activity of the prepared nanomaterials was studied with 3,3,5,5-tetramethylbenzidinedihydrochloride (TMB) as a substrate. Dopamine oxidation was also examined. Results indicate that Fe3O4/g–C3N4 nanocomposites offers more efficient degradation of RhB dye in a photo-Fenton system compared with regular photocatalytic degradation, which requires a long time. Our study also confirmed that Fe3O4/g-C3N4 nanocomposites can be used as a potential material for mimicking HRP owing to its high affinity for TMB. These findings suggest good potential for applications in biosensing and as a catalyst in oxidation reactions.

Hydrogenation/oxidation induced efficient reversible color switching between methylene blue and leuco-methylene blue

In this paper, we present the use of graphitic carbon nitride (g-C3N4) supported palladium nanoparticles (Pd/g-C3N4) for reversible color switching of methylene blue (MB). g-C3N4 with a high polymeric degree could improve the dispersity of Pd nanoparticles, contributing to fast color switching of MB as the agglomeration of metal nanoparticles is significantly prevented. Moreover, strong metal-support interaction (SMSI) between Pd nanoparticles and g-C3N4 support promotes the adsorption and subsequent dissociation of molecular hydrogen and oxygen, thus leading to efficient reversible conversion between MB and leuco-methylene blue (LMB). Our obtained Pd/g-C3N4 nanocatalyst exhibits outstanding hydrogenation activity of blue MB to colorless LMB with a turnover frequency as high as 165 h−1 at room temperature, moreover, colorless LMB can quickly switch back to MB upon exposing the same reaction system to oxygen for oxidation. It is noted that our color switching system exhibits remarkable reversibility and stability without obvious fatigue even after 10 consecutive cycles. This novel redox-driven reversible color switching system could find potential in food packaging, sensing and organic transformations.

Hydrogenation/oxidation triggered highly efficient reversible color switching of organic molecules

Catalytic hydrogenation and oxidative dehydrogenation reactions are fundamental and significant processes in organic transformation, and reversible color switching of organic redox dyes finds potential applications in rewritable paper, sensing devices, data recording and security feature technologies. In this study, we report an interesting result of reversible hydrogenation and oxidative dehydrogenation of a redox dye over a Pd–ZnO1−x hybrid nanocatalyst under ambient conditions. Thionine (TH+) is used as a model compound to evaluate the catalytic performance. The reversible color switching between purple thionine (TH+) and colorless leuco-thionine (LTH) depends on the reducing or oxidizing environments. Our newly developed Pd–ZnO1−x nanocatalyst exhibits high catalytic activity for the hydrogenation of TH+ with a turnover frequency (TOF) as high as 397 h−1 under H2 (1 bar). The oxidative dehydrogenation of LTH is performed under 1 bar O2 flow in the same reaction system. The Pd–ZnO1−x nanocatalyst readily adsorbs and subsequently dissociates O2 to oxidize LTH to the original purple colored TH+ with higher efficiency. The abundant oxygen vacancies on ZnO1−x nanorods and strong metal–support interaction (SMSI) promote the adsorption and subsequent dissociation of molecular hydrogen and oxygen leading to high catalytic activity. This novel reversible color switching of organic dyes can be performed successively for more than 10 cycles in a one pot-fashion using a Pd–ZnO1−x nanocatalyst with a small loss in performance. The highly efficient reversible color switching of TH+/LTH over the Pd–ZnO1−x nanocatalyst provides a state-of-the-art protocol to find practical applications as printing inks for rewritable paper and in sensing and security feature devices.

Oxygen deficient Pr6O11 nanorod supported palladium nanoparticles: highly active nanocatalysts for styrene and 4-nitrophenol hydrogenation reactions

The design and development of highly efficient and long lifetime Pd-based catalysts for hydrogenation reactions have attracted significant research interest over the past few decades. Rational selection of supports for Pd loadings with strong metal-support interaction (SMSI) is beneficial for boosting catalytic activity and stability. In this context, we have developed a facile approach for uniformly immobilizing ultra-small Pd nanoparticles (NPs) with a clean surface on a Pr6O11 support by a hydrogen thermal reduction method. The hydrogenations of p-nitrophenol and styrene are used as model reactions to evaluate the catalytic efficiency. The results show highly efficient styrene hydrogenation performance under 1 atm H2 at room temperature with a TOF value as high as 8957.7 h−1, and the rate constant value of p-nitrophenol reduction is 0.0191 s−1. Strong metal-support interaction and good dispersion of Pd nanoparticles, as demonstrated by XPS and HRTEM results, contribute to the excellent hydrogenation performance. Electron paramagnetic resonance (EPR) results suggest the presence of oxygen vacancies in the support, which serve as electron donors and enhance the adsorption and activation of reactants and subsequent conversion into products. Moreover, the catalyst can be recovered and reused up to 10 consecutive cycles without marked loss of activity. Overall, our results indicate that oxygen-deficient Pr6O11 nanorods (NRs) not only play a role as support but also work as the promoter to substantially boost the catalytic activities for organic transformations, therefore, providing a novel strategy to develop other high-performance nanostructured catalysts for environmental sustainability.