Jindui Hong

Mesoporous carbon nitride with in situ sulfur doping for enhanced photocatalytic hydrogen evolution from water under visible light

In situ sulfur-doped mesoporous g-C3N4 (mpgCNS) was synthesized from a simple organosulfur compound, thiourea, using SiO2 nanoparticles as the hard template. The resultant product has a high surface area of 128 m2 g−1 and mesopores in the range of 10–20 nm. Based on X-ray photoelectron spectroscopy analysis, the doped sulfur was proposed to substitute carbon in mpgCNS and a downshift of 0.25 eV was resulted in its conduction band. Optical studies indicated that mpgCNS exhibits enhanced and extended light absorbance in the visible light region and a much lower density of defects compared to the native g-C3N4. As a result, mpgCNS has been found to be 30 times more active than the native g-C3N4 for hydrogen evolution from photocatalytic water splitting. A high quantum efficiency of 5.8% at 440 nm was obtained which is among the highest for carbon nitride photocatalysts.

Nickel–Thiolate Complex Catalyst Assembled in One Step in Water for Solar H2 Production

We report the use of a simple complex assembled from Ni(II) salt and 2-mecaptoethanol in one step in water as the efficient catalyst in a molecular hydrogen system which can be sensitized by a low-cost xanthene dye, Erythrosin B. An excellent quantum efficiency of 24.5% is attained at 460 nm. This simple system is expected to contribute toward the development of economical and environmentally benign solar hydrogen production systems.

Noble‐Metal‐Free NiS/C3N4 for Efficient Photocatalytic Hydrogen Evolution from Water

A NiS/C3 N4 photocatalyst containing earth-abundant elements only was constructed by means of a simple hydrothermal method. This photocatalyst shows efficient hydrogen evolution (48.2 μmol h(-1) ) under visible light when using triethanolamine as a sacrificial reagent. The optimal loading of 1.1 wt % NiS on C3 N4 as a cocatalyst can enhance the H2 production by about 250 times compared with the native C3 N4 . The highest apparent quantum efficiency of 1.9 % was recorded at 440 nm.

Noble-Metal-Free NiS/C3N4for Efficient Photocatalytic Hydrogen Evolution from Water

A NiS/C3 N4 photocatalyst containing earth-abundant elements only was constructed by means of a simple hydrothermal method. This photocatalyst shows efficient hydrogen evolution (48.2 μmol h(-1) ) under visible light when using triethanolamine as a sacrificial reagent. The optimal loading of 1.1 wt % NiS on C3 N4 as a cocatalyst can enhance the H2 production by about 250 times compared with the native C3 N4 . The highest apparent quantum efficiency of 1.9 % was recorded at 440 nm.

Post-synthesis modification of a metal–organic framework to construct a bifunctional photocatalyst for hydrogen production

To construct photocatalytically active MOFs, various strategies have recently been developed. We have synthesized and characterized a new metal–organic framework (MOF-253-Pt) material through immobilizing a platinum complex in 2,2′-bipyridine-based microporous MOF (MOF-253) using a post-synthesis modification strategy. The functionalized MOF-253-Pt serves both as a photosensitizer and a photocatalyst for hydrogen evolution under visible-light irradiation. The photocatalytic activity of MOF-253-Pt is approximately five times higher than that of the corresponding complex. The presence of the short Pt⋯Pt interactions in the framework was revealed with extended X-ray absorption fine structure (EXAFS) spectroscopy and low temperature luminescence. These interactions play an important role in improving the photocatalytic activity of the resulting MOF.

Carbon nitride nanosheets for photocatalytic hydrogen evolution: remarkably enhanced activity by dye sensitization

Carbon nitride (CN) nanosheets with a thickness of around 3 nm were prepared by pyrolysis of urea. Well-dispersed Pt nanoparticles of about 3 nm were pre-loaded on CN nanosheets as the co-catalyst by chemical reduction in ethylene glycol. The Pt/CN sample showed a H2 evolution rate of 45.1 μmol h−1 from an aqueous solution of triethanolamine (TEOA) under visible light irradiation (λ > 420 nm). By simply adding a low-cost dye Erythrosin B (ErB) in the photoreaction suspension, a remarkably enhanced H2 evolution rate of 652.5 μmol h−1 was observed. Efficient electron transfer from excited ErB to the conduction band of CN is expected due to the energy difference between the LUMO level of excited ErB (−3.59 eV vs. vacuum level) and the conduction band potential of CN (−3.71 eV vs. vacuum level). A dye sensitization mechanism between ErB and CN is proposed. Upon irradiation with light of long wavelength (λ > 550 nm), the Pt/CN–ErB photocatalyst system still exhibited a high H2 evolution rate of 162.5 μmol h−1. The highest quantum efficiency of 33.4% was obtained at 460 nm. Moreover, the Pt/CN photocatalyst could be easily recycled by simple filtration and 90% of the activity was still kept after five consecutive runs.

Photocatalytic Reduction of Carbon Dioxide over Self- Assembled Carbon Nitride and Layered Double Hydroxide: The Role of Carbon Dioxide Enrichment

A self‐assembly of carbon nitride (C3N4) and layered double hydroxide (LDH) was constructed by electrostatic interaction. The pristine nitrate‐intercalated Mg‐Al‐LDH is turned to carbonate LDH through anion exchange during the photoreduction of CO2 in aqueous solution. The carbonate anions enriched in the interlayer of LDH exhibit a remarkably high reduction efficiency to CH4 in the presence of a C3N4 photoabsorber and Pd cocatalyst.

Photocatalytic reduction of CO2: a brief review on product analysis and systematic methods

Photocatalytic reduction of CO2 for fuels production by using solar energy is an attractive process to address both energy and environmental issues. Currently, it is still a great challenge to control the CO2 reduction pathways. As a result, many possible chemicals could be present in the reaction products, ranging from CO, CH4 to higher alkanes in the gas phase, and oxygenates in the liquid phase such as alcohols, aldehydes and carboxylic acids. A thorough and accurate determination of products is of critical importance for the evaluation of photocatalyst performance. However to date, only very few studies have paid attention to the screening of reduction products, and more comprehensive and standard analysis methods are not yet reported in the literature. In this review, different analysis methods reported so far are summarized. At the same time, we also developed one set of techniques involving (1) the design of a two-channel-three-detector gas chromatography system for gaseous product analysis in the presence of a high concentration of CO2 and alcohols analysis in the liquid phase, and (2) a high performance liquid chromatography system for the analysis of aldehydes and carboxylic acids in the liquid phase. The effect of commonly used organic additives as well as alkaline conditions on liquid phase analysis was also investigated for the first time.

Effect of depositing silver nanoparticles on BiVO4 in enhancing visible light photocatalytic inactivation of bacteria in water

Recently, photocatalytic processes have been shown to be a promising low-cost and sustainable alternative for water and wastewater treatment. In this study Ag/BiVO4 composites were fabricated and their photocatalytic disinfection activity was tested against Escherichia coli under visible light (λ > 420 nm). Deposition of silver nanoparticles on the surface of BiVO4 led to a significant improvement of the photocatalytic activity. Irradiation of the suspension of Escherichia coli (107 CFU mL−1) in the presence of Ag/BiVO4 resulted in the total disinfection of the cells within 3 h. The photocatalytic activity of the composite was stable in repeated runs. The disinfection study was also conducted under the tropical afternoon sun in Singapore. The significant enhancement in the photocatalytic activity of Ag/BiVO4 can be ascribed to the effect of metallic silver nanoparticles, which act as an electron trap on the surface of BiVO4 and promote the separation of photo-induced electron/hole pairs for the generation of reactive oxygen species.

Bio-inspired organic cobalt(II) phosphonates toward water oxidation

The development of artificial photosynthesis systems that can efficiently catalyze water oxidation to generate oxygen remains one of the most important challenges in solar energy conversion to chemical energy. In photosystem II (PSII), the Mn4CaO5 cluster adopts a distorted coordination geometry and every two octahedra are linked by di-μ-oxo (edge-shared) or mono-μ-oxo (corner-shared) bridges, which is recognized as a critical structure motif for catalytic water oxidation. These structural features provide guidance on the design and synthesis of new water oxidation catalysts. Herein we synthesized a new layered organic cobalt phosphonate crystal, Co3(O3PCH2–NC4H7–CO2)2·4H2O (1) and demonstrate it as a heterogeneous catalyst for water oxidation. Its catalytic activity was compared to those of cobalt phosphonates with different structures (2–4) in terms of O2 evolution rate and O2 yield under the same reaction conditions. The compound with both mono- and di-μ-oxo bridged octahedral cobalt displays superior catalytic activity. In contrast, the presence of only mono-μ-oxo bridged cobalt in the structure results in lower O2 yield and O2 evolution rate. Further structural analysis reveals that the presence of a longer Co–N bond induces a distorted dissymmetry coordination geometry, and consequently facilitates water oxidation. These results provide important insight into the design of water oxidation catalysts.