CdS/MoS2 Photocatalyst Elena Bray Dalton Doerr Samantha Wilkerson

Identity and Type Type II is da best!!!!!!! P-N heterojunction 3 Types: I, II, and III CdS/MoS2 is a type II heterojunction between solid state photocatalysts Marshall, R. Semiconductor Composites: Strategies for Enhancing Charge Carrier Separation to Improve Photocatalytic Activity. Adv. Funct. Mater., 2014, 18, 2421-2440. Liu, Y.; Yu Y.; Zhang, W. MoS2/CdS Heterojunction with High Photoelectrochemical Activity for H2 Evolution Under Visible Light; The Role of MoS2. J. Phy. Chem. 2013, 117, 12949-12957.

Applications Water splitting Why does it work so well? Charge carrier separation Crystalline structure (1) Liu, Y.; Yu Y.; Zhang, W. MoS2/CdS Heterojunction with High Photoelectrochemical Activity for H2 Evolution Under Visible Light; The Role of MoS2. J. Phy. Chem. 2013, 117, 12949-12957.

Preparations Electrodeposition followed by chemical bath 3 steps Uses a high-heat H2S atmosphere Poisonous Green, one-step hydrothermal process Simple and non-poisonous Preferred Liu, Y.; Yu Y.; Zhang, W. MoS2/CdS Heterojunction with High Photoelectrochemical Activity for H2 Evolution Under Visible Light; The Role of MoS2. J. Phy. Chem. 2013, 117, 12949-12957. Cao, X.; Xu, J. Characterization and Mechanism of MoS2/CdS Composite Photocatalyst Used for Hydrogen Production From Water Splitting Under Visible Light. Chem. Eng. J. 2015, 260, 642-648. Wang, C.; Lin, H.; Xu, Z.; Cheng, H.; Zhang, C. One-Step Hydrothermal Synthesis of Flowerlike MoS2/CdS Heterostructures for Enhanced Visible Light Photocatalytic Activities. RSC Adv., 2015, 5, 15621.

Structure: Actual vs. Cartoon (1) Liu, Y.; Yu Y.; Zhang, W. MoS2/CdS Heterojunction with High Photoelectrochemical Activity for H2 Evolution Under Visible Light; The Role of MoS2. J. Phy. Chem. 2013, 117, 12949-12957.

Function Main function is Hydrogen production 17x faster as a heterojunction than CdS alone MoS2 acts to prevent recombination of electrons This is what makes hydrogen production go faster (1) Liu, Y.; Yu Y.; Zhang, W. MoS2/CdS Heterojunction with High Photoelectrochemical Activity for H2 Evolution Under Visible Light; The Role of MoS2. J. Phy. Chem. 2013, 117, 12949-12957.

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 MoS2/CdS structure after differing amounts of CBD. Image D shows a scan of pure MoS2 (1) Liu, Y.; Yu Y.; Zhang, W. MoS2/CdS Heterojunction with High Photoelectrochemical Activity for H2 Evolution Under Visible Light; The Role of MoS2. J. Phy. Chem. 2013, 117, 12949-12957.

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 MoS2, which allows for a better electron transfer (1) Liu, Y.; Yu Y.; Zhang, W. MoS2/CdS Heterojunction with High Photoelectrochemical Activity for H2 Evolution Under Visible Light; The Role of MoS2. J. Phy. Chem. 2013, 117, 12949-12957.

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 MoS2 and pure CdS, and three different spectra representing different loading amounts for MoS2. (1) Liu, Y.; Yu Y.; Zhang, W. MoS2/CdS Heterojunction with High Photoelectrochemical Activity for H2 Evolution Under Visible Light; The Role of MoS2. J. Phy. Chem. 2013, 117, 12949-12957.

CHARACTERIZATION X-Ray Photoelectron Spectroscopy (XPS) 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. These two spectra show the binding energies for MoS2, CdS, and the MoS2/CdS. By comparing how these change, it becomes possible to see how the heterojunction changes the electron density for MoS2 and CdS. 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. MoS2/CdS Heterojunction with High Photoelectrochemical Activity for H2 Evolution Under Visible Light; The Role of MoS2. J. Phy. Chem. 2013, 117, 12949-12957.

Summary CdS/MoS2 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 MoS2 Prove more efficient hydrogen production

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