188宝金博页面版

95This chapter explores the feasibility of g-C 3 N 4 as a photocatalyst for hydrogen production from water. Graphitic carbon nitride was synthesised via thermal decomposition, using 4 different precursors, at various calcination temperatures, calcination ramp rates, cleaning techniques, and cocatalyst element/weighting. A novel strategy was found to make highly eff i cient g-C 3 N 4 for H 2 production from urea, resulting in an internal quantum yield for hydrogen production of 26.5 % at 400 nm, over an order of magnitude larger than previously reported values [1]. In order to determine the reason for the high reactivity, in comparison to previously documented examples, a series of characterisation methods were employed. TGA-DSC-MS was used to monitor the formation mechanism of g-C 3 N 4 derived from both urea and thiourea—which was found to be drastically different during the pri-mordial stages of synthesis. In the case of urea derived g-C 3 N 4 , it is shown that the high surface area and porosity is created by the continuous loss of CO 2 , a result not seen before. Formaldehyde (CH 2 O) is also continually produced throughout the decomposition of urea to g-C 3 N 4 , a process which is proposed to reduce the percentage of hydrogen/protons in carbon nitride.Using the N1 s core level data from XPS, it is shown that from sample to sam-ple, there is a correlation between surface hydrogen/proton content and hydrogen production rate. A larger surface hydrogen/proton content leads to a lower hydro-gen production rate. This trend is further conf i rmed by bulk hydrogen analysis carried out by elemental analysis. It has been shown in previous studies that a less polymeric carbon nitride intrinsically has more hydrogen/protons due to break-ages, but it was unclear as to why this leads to a less effective photocatalyst. XRD analysis conf i rms that a greater level of condensation, and thus a less polymerised g-C 3 N 4 leads to a less active photocatalyst.In collaboration with Dr. Stephen Shevlin and Prof. Z. Xiao Guo, using DFT calculations, we demonstrate that increasing the hydrogen/proton content causes a positive shift in the conduction band edge (with respect to NHE), therefore reducing the driving force for reduction reactions. As shown by TDDFT excess protonation localizes photoelectrons at non-active redox sites, which is further detrimental to the photocatalytic ability.Chapter 4Hydrogen Evolving Photocatalyst Development© Springer International Publishing Switzerland 2015 D.J. Martin, Investigation into High Eff i ciency Visible Light Photocatalysts for Water Reduction and Oxidation, Springer Theses, DOI 10.1007/978-3-319-18488-3_4