1. CdS/MoS 2 PHOTOCATALYST Elena Bray Dalton Doerr Samantha Wilkerson

2. IDENTITY AND TYPE  P-N heterojunction  3 Types: I, II, and III  CdS/MoS 2 is a type II heterojunction between solid state photocatalysts (1)Marshall, R. Semiconductor Composites: Strategies for Enhancing Charge Carrier Separation to Improve Photocatalytic Activity. Adv. Funct. Mater., 2014, 18, 2421-2440. (2)Liu, Y.; Yu Y.; Zhang, W. MoS 2 /CdS Heterojunction with High Photoelectrochemical Activity for H 2 Evolution Under Visible Light; The Role of MoS 2. J. Phy. Chem. 2013, 117, 12949-12957. Type II is da best!!!!!!!

3. APPLICATIONS  Water splitting  Why does it work so well?  Charge carrier separation  Crystalline structure (1) Liu, Y.; Yu Y.; Zhang, W. MoS 2 /CdS Heterojunction with High Photoelectrochemical Activity for H 2 Evolution Under Visible Light; The Role of MoS 2. J. Phy. Chem. 2013, 117, 12949-12957.

4. PREPARATIONS EElectrodeposition followed by chemical bath 33 steps UUses a high-heat H 2 S atmosphere PPoisonous GGreen, one-step hydrothermal process SSimple and non-poisonous PPreferred (1)Liu, Y.; Yu Y.; Zhang, W. MoS 2 /CdS Heterojunction with High Photoelectrochemical Activity for H 2 Evolution Under Visible Light; The Role of MoS 2. J. Phy. Chem. 2013, 117, 12949-12957. (2)Cao, X.; Xu, J. Characterization and Mechanism of MoS 2 /CdS Composite Photocatalyst Used for Hydrogen Production From Water Splitting Under Visible Light. Chem. Eng. J. 2015, 260, 642-648. (3)Wang, C.; Lin, H.; Xu, Z.; Cheng, H.; Zhang, C. One-Step Hydrothermal Synthesis of Flowerlike MoS 2 /CdS Heterostructures for Enhanced Visible Light Photocatalytic Activities. RSC Adv., 2015, 5, 15621.

5. STRUCTURE: ACTUAL VS. CARTOON Actual Cartoon (1) Liu, Y.; Yu Y.; Zhang, W. MoS 2 /CdS Heterojunction with High Photoelectrochemical Activity for H 2 Evolution Under Visible Light; The Role of MoS 2. J. Phy. Chem. 2013, 117, 12949-12957.

6. FUNCTION  Main function is Hydrogen production  17x faster as a heterojunction than CdS alone  MoS 2 acts to prevent recombination of electrons  This is what makes hydrogen production go faster (1) Liu, Y.; Yu Y.; Zhang, W. MoS 2 /CdS Heterojunction with High Photoelectrochemical Activity for H 2 Evolution Under Visible Light; The Role of MoS 2. J. Phy. Chem. 2013, 117, 12949-12957.

7. CHARACTERIZATION  Scanning Electron Microscope (SEM)  Produces images by scanning a sample with a focused beam of electrons, which interact and produce signals that can be interpreted to show the molecule surface  Image A shows pure CdS  Images B and C show the MoS 2 /CdS structure after differing amounts of CBD.  Image D shows a scan of pure MoS 2 (1) Liu, Y.; Yu Y.; Zhang, W. MoS 2 /CdS Heterojunction with High Photoelectrochemical Activity for H 2 Evolution Under Visible Light; The Role of MoS 2. J. Phy. Chem. 2013, 117, 12949-12957.

8. CHARACTERIZATION  High-Resolution Transmission Electron Microscopy (HRTEM)  Is a technique in which electrons are transmitted through a very thin specimen and a picture is created from analyzing the interactions  This image shows the intimate interfacial contact between CdS and MoS 2, which allows for a better electron transfer (1) Liu, Y.; Yu Y.; Zhang, W. MoS 2 /CdS Heterojunction with High Photoelectrochemical Activity for H 2 Evolution Under Visible Light; The Role of MoS 2. J. Phy. Chem. 2013, 117, 12949-12957.

9. CHARACTERIZATION  X-Ray Diffraction (XRD)  By hitting a sample with an X-Ray, a diffraction pattern is created that is unique to a sample. By using this pattern, an XRD spectrum can be made.  These spectra show both pure MoS 2 and pure CdS, and three different spectra representing different loading amounts for MoS 2. (1) Liu, Y.; Yu Y.; Zhang, W. MoS 2 /CdS Heterojunction with High Photoelectrochemical Activity for H 2 Evolution Under Visible Light; The Role of MoS 2. J. Phy. Chem. 2013, 117, 12949-12957.

10. CHARACTERIZATION XX-Ray Photoelectron Spectroscopy (XPS) TThis technique works by irradiating a sample with X-Rays and then measuring the number of electrons that escape and also the kinetic energy of the sample. TThese two spectra show the binding energies for MoS 2, CdS, and the MoS 2 /CdS. BBy comparing how these change, it becomes possible to see how the heterojunction changes the electron density for MoS 2 and CdS. TThe changes in the electron densities make it possible to see how the production rate of Hydrogen increases with the heterojunction. (1) Liu, Y.; Yu Y.; Zhang, W. MoS 2 /CdS Heterojunction with High Photoelectrochemical Activity for H 2 Evolution Under Visible Light; The Role of MoS 2. J. Phy. Chem. 2013, 117, 12949-12957.

11. SUMMARY  CdS/MoS 2 is a type II solid state heterojunction photocatalyst  Main use is water splitting/hydrogen production  Two preparations  One-step hydrothermal process preferred  Spectra show a heterojunction occurred between CdS and MoS 2  Prove more efficient hydrogen production

12. QUESTIONS??