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Overview
Session
E2-02: Photocatalyst
Time:
Monday, 19/Jun/2017:
4:00pm - 6:15pm

Session Chair: Suddhasatwa Basu, Indian Institute of Technology, Delhi
Session Chair: Yi-Jun Xu, Fuzhou University
Location: Rm 328

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Presentations
4:00pm - 4:30pm
Invited

The Discovery of a New Light Absorption Model for Supported Small Platinum Nanoparticles

Yi-Jun XU

State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry, Fuzhou University, China

Recent years have seen a surge of interest in tuning the optical properties of metals for a wide range of applications.[1] In contrast to the well-studied plasmonic metals (mainly Au and Ag), tuning the absorption peak of small (<10 nm) Pt nanoparticles in the visible spectral region, but without increasing their size, has been a major challenge.[1] Here, we report an efficient strategy to identify and tune the absorption peaks of small (<10 nm) Pt nanoparticles in the visible-light region based on a new light absorption model.[1] In this model, the Pt nanoparticles can absorb the scattered light in the near field of the dielectric surface of SiO2 spheres to exhibit distinct absorption peaks, which is conceptually different from the SPR light absorption phenomenon. The absorption peak of Pt nanoparticles can be rationally tuned to the longer wavelength region via controlled nanostructure design, which involves increasing the size of SiO2 spheres, or fine-coating the Pt nanoparticles with a thin layer of TiO2. These results have been corroborated by the joint experimental and theoretical analyses.

The hot electrons generated from the photoexcitation of Pt nanoparticles under visible-light illumination enable the core–shell Pt/SiO2@TiO2 composites to photocatalyze various redox reactions, including selective oxidation of alcohols, hydrogen evolution and selective reduction of aromatic nitro compound. Action spectrum analysis and wavelength-dependent photocurrent enhancement of Pt/SiO2@TiO2 provide robust evidence for the existence of energetic hot electrons derived from the photoexcitation of Pt under visible-light irradiation. It is anticipated that this work,[1] combined with the rational use of nanoscale assembly methods and reactor engineering technology, may enable the wide development of Pt nanoparticle-enhanced semiconductor photocatalysis for solar energy conversion.

Reference:

[1] N. Zhang, C. Han, Y.-J. Xu, J. J. Foley IV, D. Zhang, J. Codrington, S. K. Gray and Y. Sun, Nat. Photonics, 2016, 10, 473-482.


4:30pm - 4:45pm
Oral

Synthesis of CdS-MoS2 and CdS-WS2 Heterostructures for Efficient Photocatalytic Hydrogen Evolution

Junze CHEN, Hua ZHANG

Nanyang Technological University, Singapore

Exploration of low-cost and earth-abundant photocatalysts for highly efficient solar photocatalytic water splitting is of great importance. Although transition metal dichalcogenides (TMDs) showed outstanding performance as cocatalysts for hydrogen evolution reaction (HER), designing TMD-hybridized photocatalysts with abundant active sites for HER still remains challenge. Here, a facile one-pot wet chemical method is developed to prepare MS2–CdS (M = W or Mo) nanohybrids. Surprisedly, in the obtained nanohybrids, single-layer MS2 nanosheets with lateral size of 4–10 nm selectively grow on the Cd-rich (0001) surface of wurtzite CdS nanocrystals. These MS2–CdS nanohybrids possess large number of edge sites in the MS2 layers, which are active sites for HER. The photocatalytic performances of WS2–CdS and MoS2–CdS nanohybrids towards HER under visible light irradiation (>420 nm) are about 16 and 12 times of that of pure CdS, respectively. Importantly, the MS2–CdS nanohybrids showed enhanced stability after long-time test (16 h), and 70% of catalytic activity still remained.

Reference:

[1] J. Z. Chen, X. J. Wu, L. S. Yin, B. Li, X. Hong, Z. X. Fan, B. Chen, C. Xue, H. Zhang, Angew. Chem. Int. Ed., 2015, 54, 1210-1214.


4:45pm - 5:00pm
Oral

Plasmon-controlled Facet-selective Deposition of Palladium on Ag@Au@TiO2 Nanoprisms for Visible-light-driven Hydrogen Generation

Sijia YU, Can XUE

School Of Materials Science & Engineering, Nanyang Technological University, Singapore

The localized surface plasmon resonance (LSPR) of anisotropic metal nanostructures is highly dependent on their size, morphologies and chemical compositions. Previous studies have shown that LSPR excitation of a gold or silver nanoparticle can induce strongly enhanced local electric field, and generate hot electrons for redox reactions. In particular, for the anisotropic structure, plasmon excitation re-distributes local electric field on different crystal facets, as such, the correlation between the electric field enhancement and hot electron distribution becomes critical in order to control the plasmon-driven chemical processes. In this work, we have synthesized triangular Ag@Au@TiO2 core-shell nanoprisms, which have easily identified surface sites with direct correlation to the plasmon mode and electric field intensity, and thereby can serve as an ideal platform to explore the distribution and behaviors of plasmon-induced hot electrons. In the presence of palladium precursors, dipole plasmon excitation of Ag@Au@TiO2 core-shell nanoprisms (at ~700 nm) induces selective deposition of Pd nanoparticles on the prism tips and edges. This observation suggests that the surface sites with stronger electric field can provide more hot electrons, which can diffuse through the thin TiO2 shell and reduce Pd2+ on its surface. Moreover, these hot electrons can induce hydrogen generation on Pd nanoparticle surfaces when the Pd-decorated Ag@Au@TiO2 nanoprisms are excited in the formic acid solution. Our studies provide a new avenue of harvesting low-energy photons for hydrogen production.


5:00pm - 5:30pm
Invited

Nano-structured Fe, Mn and Ag-Ni Based Materials for Efficient Photoelectrochemical Water Splitting

Suddhasatwa BASU

Indian Institute of Technology, Delhi, India

Development of a suitable low cost, efficient, visible-light active photocatalyst for solar hydrogen generation remained a challenge for global researchers. Since the first report by Fujishima and Honda[1] as photoinduced water splitting catalyst on TiO2 semiconductor based electrode, various photocatalysts emerged as efficient catalyst. In spite of significant advancement with TiO2 as photocatalyst, its application is restricted due to wide band gap of 3.2 eV, which hinders visible solar light utilization.

Hematite(α-Fe2O3) has been considered as one of the most promising photo-anode materials due to its lower band gap(~2.2 eV), higher stability, high abundance and low cost. However, the combination effect of low hole mobility, short hole diffusion length and high electron–hole recombination rate has prevented efficient solar energy conversion. In general, loading of oxygen evolution catalysts on the surface of hematite is one of the most popular methods to overcome the oxygen evolution reaction(OER) barrier. Herein, we decorated α-Fe2O3 surface by NiMnOx[2] and CoFeOx[3] co-catalyst to overcome such barriers. The surface modified photo-anodes exhibit enhanced photocurrent density and decreased over potential required driving photoelectrochemical water oxidation compared to pristine α-Fe2O3

Graphitic carbon nitride(g-C3N4) has also attracted much more attention due its suitable band gap of 2.7 eV, which is capable of absorbing sunlight efficiently. Its graphitic carbon-nitrogen network have revealed many visible light driven photocatalytic applications like degradation of organic pollutants in water, solar H2 generation, conversion of CO2 to useful fuel etc. Herein, we report in-situ incorporation of Ag and Ni into g-C3N4 matrix by direct solid state heat treatment method[4]. Photoelectrochemical(PEC) water splitting studied with AgNi/gC3N4 catalyst exhibits excellent activity with respect to higher photocurrent density.

References:

[1] A. Fujishima, K. Honda, Nature, 1972, 238, 37-38.

[2] S. Basu et.al, RSC Adv., 2016, 6, 35239-35247.

[3] S. Basu et.al, ChemPhotoChem, DOI: 10.1002/cptc.201600008

[4] S. Basu et al, ChemSusChem, 2016, 9, 2816-2823


5:30pm - 5:45pm
Oral

Caramelin as an Infra-Red-Light Absorber and Charge-Separation Enhancer for Photocatalytic Hydrogen Production

Mohammad Ziaur RAHMAN, Kenneth DAVEY, Shizhang QIAO

The University of Adelaide, Australia

Increasing visible-light absorption, and efficient separation and transportation of photogenerated electrons to the surface of photocatalysts is essential for high performance. Visible-light absorption can be extended to longer wavelength either by narrowing the bandgap of a semiconductor, or making a tandem structure with another narrow bandgap semiconductor. A tandem structure is more useful as it provides larger overlap in the solar spectrum. Additionally, an efficient separation of charge carrier can be realized by creating a tandem structure.

Here, we introduce caramelin as a new optical material for infra-red light absorption and create a tandem structure with carbon nitride (CN) for photocatalytic hydrogen production via water-splitting. Caramelin is synthesized from table-sugar which is readily available as an inexpensive solid precursor.

When combined with CN, caramelin provides a large overlap in visible-light photon absorption due to its small bandgap (ca. 1 eV). Moreover, it can help to suppress recombination of charge carrier by delocalizing the electron-hole due to band off-set between CN and caramelin. As a result, CN-caramelin tandem structure shows a 25 times greater hydrogen production than that of standalone CN.

The morphology, structure, chemical states and optical properties of the CN-caramelin tandem structure were characterized using SEM, TEM, XRD, FTIR, XPS, UV-VIS and PL. Electrochemical properties were investigated using LSV, Nyquist plot and transient photocurrent methods. The photocatalytic test was performed at 420 nm using 300 W Xe arc lamp as a light source and TEOA as hole-scavenger.

Caramelin might therefore be a future material for a variety of photonics applications. For example, it can be employed as a core semiconductor in optoelectronic devices and solar cells. It can also be used to make tandem structure with wide gap semiconductors for extended visible light absorption.


6:00pm - 6:15pm
Oral

Improved Photocatalytic Activity of the BiFeO3/ZnFe2O4 Nanocomposites under Visible Light Irradiation

Masood HASHEMINIASARI, B. SAFIZADEH, S.M. MASOUDPANAH, A. GHASEMI

Iran University of Science and Technology, Iran

BiFeO3/ZnFe2O4 nanocomposites were synthesized by the glyoxylate precursor method using two step approach. The previously synthesized BiFeO3 nanoparticles were injected to the solution precursor of the zinc ferrite which achieved by redox reaction between ethylene glycol and nitrate anions. The phase evolution, morphology and magnetic and optical properties were investigated by X-ray diffraction, electron microscopy, vibrating sample magnetometry and diffuse reflectance spectroscopy techniques. The composites showed strong absorption in the visible region with the optical band gap calculated from Tauc’s plot in the range of 2.19-2.15 eV. Furthermore, the as-synthesized BiFeO3/ZnFe2O4 nanocomposites exhibited high efficiency for photodegradation of methylene blue (MB) as a typical dye pollutant under visible light irradiation, may be due to the synergic effect between BiFeO3 and ZnFe2O4.



 
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