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Tunsgten nanostructures

1. WO 3 /WS 2 HYBRID NANOSTRUCTURES -Venugopal Rahul Tuteur référent : Martin Jakoobi et Myrtil Kahn 24/11/2022 19/07/2022

2. 26.04.24 P 2 WHY TUNGSTEN? It is a Lustrous (shining) / silvery white metal and hardness close to diamond It has a very high melting point of 3410 ° C It also has the lowest co-efficient of thermal expansion (material’s potential to expand under the effect of increasing temperature) It is commonly used with steel to increase the hardness and strength of the metal with highest modulus of elasticity (E=400 GPa ). Also has a good Temperature-Strength Characteristics Inert to oxygen at room temperature High thermal and electrical conductivity Atomic Number 74 Atomic Weight 183.85 gmol -1 Melting Point 3410 o C Boiling Point 5660 o C Oxidation States +2, +3, +4, +5, +6

3. 26.04.24 P 3 Tungsten oxide (WO 3 ) is an n-type transition metal oxide with wide ranging applications The phases obtained by corner sharing are monoclinic II (ɛ-WO 3 ), triclinic (δ-WO 3 ), monoclinic I (γ-WO 3 ), orthorhombic (β-WO 3 ), tetragonal (α-WO3), and cubic WO 3 . Experimentally, cubic WO 3 is not commonly observed WO 3 is an Oxygen deficient metal oxide with bandgap between 2.4-2.8 eV Only a partial loss of WO 3 oxygen is needed to affect its electronic band structure and increase its Electrical conductivity TUNGSTEN OXIDE

4. 26.04.24 P 4 HYDROTHERMAL SYNTHESIS OF WO 3 -OXALIC ACID

5. 26.04.24 P 5 HYDROTHERMAL METHOD Formation of yellow precipitate indicating the formation of WO 3 Nanoparticles WO 3 Nanoparticles

6. 26.04.24 P 6 RESULTS: XRD AFTER CALCINATION Compounds WO 3 Crystal system Monoclinic Space group P21/c Lattice Parameters   a=b 7.69092 c 10.53014 Cell volume 423.468 R-Factors   Rp 8.41 Rwp 11.62 GOF 1.55 Rbragg 2.65 All the sharp peaks are in good agreement with the WO 3 structure. All the compounds crystallized in the monoclinic structure with P21/c (No. 14) space group. 002 sharp peak is associated to the formation of WO 3 Lattice constants a=7.69093Å, b= 7.53779Å, c= 10.53014Å The calculated crystallite size was 66.95nm

7. 26.04.24 P 7 RAMAN SPECTRA The observed bands of WO 3 were sharp and well-defined positioned at 806, 717, 326, 269 and 134 cm -1 which are assigned to m-phase of WO 3 The band at 134 cm -1 corresponds to the lattice vibration modes of W-W The peaks at 717 and 806 cm -1 are linked to the stretching modes of W-O-W The strong peak and the weak peak at 269 and 326 cm- 1 respectively were attributed to the bending modes of O-W-O bonds The peak at 945 cm -1 for the precursor could be due to the W=O which later disappears upon calcination.

8. 26.04.24 P 8 FTIR The spectrum of H 2 WO 4 shows five IR bands at 3409, 1637, 1386, 944, 711 cm -1 . A broad band and a sharp intense peak at 3409 and 1624 cm -1 respectively are associated with the ν(O-H) stretching modes The intensity of OH bands are highly reduced in the WO 3 spectra, and they are shifted to 3424 and 1637 cm -1 . The disappearance of 944 cm -1 peak is attributed to the absence of W=O in the WO 3.

9. 26.04.24 P 9 a. ELECTRON DENSITY DISTRIBUTION b. BAND GAP c. DENSITY OF STATES COMPUTATIONAL ANALYSIS

10. 26.04.24 P 10 TUNGSTEN SULFIDE WS 2 is a layer transistion metal disulfide ( Transition metal Dichalcogenides) having bandgap between indirect (1.4 eV) to direct ( 2 eV) when size is decreased. Various Applications include Catalysis, Lubricants, hydrogen storage applications etc. TMD based nanomaterials have interesting electrocatalytic and optical properties Low level toxicity and good substitute for carbon based materials Transition metal dichalcogenides exhibit two main phases: Hexagonal ( Semiconductor) and Octahedral (Metal)

11. 26.04.24 P 11 HYDROTHERMAL SYNTHESIS OF WS2 FLOWCHART

12. 26.04.24 P 12 RESULTS FTIR The formation of WS 2 nanostructures was confirmed using FTIR spectroscopy The band at 571 cm− 1 is attributed to W–S bonds 985 cm− 1 peak corresponds to S–S bonds in WS 2 The bands obtained at 1410 cm− 1 and 1617 cm− 1 are both attributed to stretching deformation of hydroxyl group The small peaks obtained at 2924 cm− 1 and 3534 cm− 1 for WS 2 corresponded to OH vibration

13. 26.04.24 P 13 UV-VIS SPECTRA A tangent is drawn on the graph to get the energy value of bandgap. The estimated bandgap is 1.99 eV for WS 2

14. 26.04.24 P 14 COMPUTATIONAL DETAILS a. ELECTRON DENSITY DISTRIBUTION b. BAND GAP AND DENSITY OF STATES c. DENSITY OF STATES

15. 26.04.24 P 15 The nanocomposite shows wide range of application due to the coupling of two semiconductors with the change of energy band gap. The coexistence of WO 3 and WS 2 in the same particle of the two different energy level shows the enhancement in the luminescence property as well as in many properties. In the present work we synthesized the WO 3 /WS 2 nanocomposite by hydrothermal method using hydroxylamine hydrochloride as additive. The structural, optical and luminescence properties have been investigated. WO 3 /WS 2 HYBRID NANOSTRUCTURES

16. 26.04.24 P 16 The WO 3 and WO 3 /WS 2 nanocomposite is synthesized by hydrothermal method. The stoichiometry amount of sodium tungstate, NH 2 OH.HCl and Surfourea are added into 50 ml of distilled water with continuous string. Hydrochloric acid are added drop wise to the above solution to set the pH value to 6. The solution finally transferred to the Teflon lined stainless steel autoclave which is heated at 180° C for 24 h. The precipitates were washed and centrifuged with ethanol and distilled water many times. The prepared precipitate was finally dried in vacuum oven at 50° C for 10 h. HYDROTHERMAL SYNTHESIS OF WO 3 /WS 2

17. 26.04.24 P 17 The Powder X-ray diffraction were recorded by D8 Advance, Bruker Germany at a scan rate of 10 to 80 degree with the 0.02⁰ step size. FTIR spectrum are investigated by Alpha Bruker Germany in the range of 400-4000 cm -1 . UV-visible spectra were recorded Lamba 365, Perkin Elmer USA in the range of the 200-1000 nm. PL spectra are recorded were recorded on Hitachi FL-2700 fluorescence spectroflurometer CHARACTERIZATION TECHNIQUES

18. 26.04.24 P 18 XRD OF WO 3 /WS 2

19. 26.04.24 P 19 THE XRD DATA CONFIRMS THE PRESENCE OF BOTH WO 3 AND WS 2 IN THE SAMPLE

20. 26.04.24 P 20 COMPOSITION OF THE SAMPLE

21. 26.04.24 P 21 The FTIR spectrum of WO3/WS2 nanostructure are shown in above figure. The band at 746 cm-1 due to W-S bond and 816 cm-1 is due to S-S bond in the spectra. In WO3 the broad absorption peaks at 722 cm-1 and 813 cm-1 are orginated from the stretching vibration of the W-O-W bond . The peak at 954 cm-1 is ascribed due to the streching deformation of hydroxyl group and 950 cm-1 are because of streching vibration of W=O bond. FTIR OF WO 3 /WS 2

22. 26.04.24 P 22 The absorption band is enhanced may improve the WO3/ WS2 nanostructures photocatalytic activity in WS 2 /WO 3 with a band gap of 2.7 eV and 2.9 eV energy band gap for WO 3 . UV-VIS OF WO 3 /WS 2

23. 26.04.24 P 23 PL OF WO 3 /WS 2 Fig shows the PL emission spectra The PL peak of hybrid A is 633.5 nm (1.96 eV), which has the largest energy of PL peak near direct band gap transition. The PL peaks are at 635.4, 638.4, and 640 nm, respectively. The peak shift in hybrids is related to the proportion of natural excitons, trions in PL peak.

24. 26.04.24 P 24 Applications Of WO3/WS2 Hybrid Nanostructures Photoelectro catalytic (PEC) water Oxidation WO3 for waste water treatment Photo-Chromism ( Light induced reversible change of colour ) Gas sensor Photo catalysis for Water splitting Future work: Photocatalytic activity of WO 3 /WS 2 Nanostructures for Waste water treatment

25. 26.04.24 P 25 Some Previous works: Undergraduate Thesis on "Synthesis and Characterization of Titanium Dioxide Nanoparticles for photokilling of Bacteria“ A mini project at Center for Nanoscience and Technology on “Synthesis of TiO 2 nanoparticles by Hydrolysis and Peptization method” at Anna University, Chennai Literature Survey on "Fabrication of Organic - Inorganic Halide Perovskites for LED applications ” Summer Internship on “ ZnO Transparent Conductive oxides” A minor project on " Studies on CdS/Zn(OH) 2 Core Shell Nanostructures" at Amity University, Noida

26. 26.04.24 P 26 THANK YOU