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van der Waals Heterostructures for Innovative PhotoCATalysts

Periodic Reporting for period 1 - WHIPCAT (van der Waals Heterostructures for Innovative PhotoCATalysts)

Reporting period: 2017-09-01 to 2019-08-31

1. WHIPCAT focuses on the fabrication and characterization of two-dimensional (2D) van der Waals
(vdW) solids, particularly semiconducting transition metal dichalcogenide (STMD) vdW alloys and heterostructures for exploitation in visible light photo(electro)catalysis [PEC]. A new class of 2D materials, such as MoS2, WS2 & their alloys with ‘Se’ (MoS2(1-x)Se2x, WS2(1-x) Se2x) were synthesized by physical vapor transport deposition (PVT) technique. Further, WS2-Pt147 hetersostructure was fabricated using cluster beam deposition on a free standing WS2 sheet. In-particular, HAADF-STEM was performed on several batches of samples in-order to address the alloy formation as well as cluster seeding on a two dimensional (2D) atomic layer. Most of the time of the WHIPCAT project was spent on the sample preparation and HAADF imaging of 2D alloys and WS2-Pt147 system. At the same time, a custom made photoelectrocatalytic (PEC) was designed and developed for the photocatalysis studies. WHIPCAT is an interdisciplinary research project targeting applications in clean energy and environmental pollution, which are both serious challenges being faced globally today. In particular, the effective removal of organic pollutants from water is essential to providing better and safer living conditions to a large part of the world’s population. This calls for the development of new materials and new methods, which can provide clean water and a sustainable environment, and enable the universal adoption of renewable energy sources. The degradation of organic pollutants using solar irradiation is the most attractive approach to wastewater treatment. A wide variety of semiconductor photocatalysts have been developed in the last few decades for practical and commercial applications. However, semiconducting transition metal dichalcogenides (STMD) and their new class of van der Waals (vdW) solids offer a radically new perspective for visible light PEC, water purification and hydrogen fuel production via water splitting, i.e electrochemical hydrogen evolution reaction (HER).
2. The overall objectives of the project are shown below, which are proposed during proposal writing stage, in the form of work packages of WHIPCAT research proposal.
Work Package (WP):
WP1 Optimization and Growth of the STMD vdW crystals.
WP2 Characterization of combinatorially stacked STMD vdW crystals.
WP3 The visible light photocatalytic and PEC characteristics of the as-grown and post-processed
samples of the STMD vdW clusters will be measured.
WP4 Training and Dissemination activities
In WHIPCAT program, we have achieved controlled growth of MoS2, WS2, MoSe2 and WSe2 STMD based atomic layers and their alloyed versions with ‘Se’ (MoS2(1-x)Se2x, WS2(1- x)Se2x) were achieved using physical vapor transport (PVT) technique. I have investigated catalytic properties of MoS2(1-x)Se2x, WS2(1- x)Se2x by performing electrochemical measurements and supported with theoretical evidences. At end of the period of the project, I fabricated size selected platinum 147 (Pt147) nanoclusters on top of tungsten di sulphide (WS2) STMD atomic layers using CBD. A preferential seeding of Pt147 atomic clusters were deposited at 0.1 eV per atom kinetic energy with and without Ar ion defects on WS2 atomic layers.
Expected impact of research and training on career prospects of fellow
I explored the PEC properties of STMD vdW solids such as pristine and alloyed versions of MoS2 and WS2 with non-metal ‘Se’ doping. Further motivated to fabricate WS2-Pt147 clusters in-order to explore the preferential nucleation of Pt atoms to clusters on the 2D basal plane, which may increase the catalytic activity of WS2 as compared to pristine due to most of the TMDs catalytic activity will be either from the edges or defects/functional groups present on the 2D material. However, we have not performed full measurements, yet to be done. I have strengthen my technical and scientific competencies (e.g. HAADF-STEM imaging, PEC, spectroscopy, etc.) and also hone transferable skills such as project management with regular project meetings and reporting on the progress of the work with Dr. Wolfgang Theis. I have communicated WHIPCAT project outcomes in several international conferences in UK (UK-China Conference on 2D materials, 2019) and Europe (Nanospain -2019) and public outreach activities (Think –Tank program at Birmingham city museum) in-order to familiarize about 2D materials such as STMD combinatorial stacks for clean energy and environment applications, particularly photocatalysis. During secondment program, I have visited Prof. Dryfe’s laboratory for Raman and photoluminescence (PL) measurements on STMD vdW stacks including Raman imaging on those samples. Importantly, I have collaborated with with my old groups at the IIT Guwahati and TIFR- Center for Interdisciplinary Sciences (TCIS) Hyderabad and achieved interesting results on the alloyed version of the STMD based 2D materials. Perticularly, HAADF-STEM imaging to interpret the site specific physical property of the 2D STMD crystals. On the other hand, immediately I joined at TIFR- TCIS further controlled experiments on the PEC of STMD vdW solids.
Quality of the proposed measures to exploit and disseminate the action results
Some of the results of WHIPCAT proposal findings are published in international peer reviewed journals as mentioned above (section 1.2). The final accepted manuscript have been deposited to UBIRA (University of Birmingham Research Archive), the University repository, according to publisher compliances with Open Access license. I published 4 research articles as a co-author in high impact journals (Journal of Materials Chemistry A, Small (Wiley Publishers), Applied Materials Today, PSS- Rapid Research Letters), few of them with equal contribution. Note that several manuscripts are under preparation (see above) on 1) Fabrication and characterization of STMD combinational vdW solids using physical vapor transport (PVT) and cluster beam deposition (CBD), 2) Efficient hydrogen revolution reaction activity (HER) from the combinational STMD vdW solids. All papers are published with Open Access and/or self-archiving in the UoB Research Archive (UBIRA), indexed by search engines such as Google Scholar. I gave several talks at leading international conferences (Nanospain 2019, CTMSE-2019) which are mix of specialist conferences including International Symposium on 2D materials (UK-China 2019 Conference 2D materials) and Graphene meetings with a multidisciplinary attendance National Graphene Institute, University of Manchester, UK.