Readme file for dataset relating to 
Band Gap Engineering of Carbon Nitride Hybrid Photocatalysts for CO2 Reduction in Aqueous Solutions 
Verity L. Piercy[a][b], Gaia Neri[a], Troy Manning[b], Andrea Pugliese[b], Frédéric Blanc[a][b], Alexander J. Cowan[a], Matthew J. Rosseinsky[b]
[a] Stephenson Institute for Renewable Energy, University of Liverpool, L69 7ZF, UK
[b] Department of Chemistry, University of Liverpool, L69 7ZD Liverpool, UK

All data is provided in ASCII format, as .csv, .txt or .xy files. Samples are identified in the file name.

Photocatalytic gas chromatograph data is provide in .prm format as output from the instrument and can be open in any open source GC analysis software such as OpenChrom. It is also provided in ASCII *.xy format

NMR data is provided in standard format that can be opened using any open source NMR analysis software. ASCII files of the NMR spectra are also provided.


Sample Synthesis
CN samples were synthesised by stirring dicyandiamide (3 g) in water with different amounts of barbituric acid; 0, 0.15, 0.3 and 0.6 g, for CN-DCDA, CN-BA(5), CN-BA(10) and CN-BA(20) respectively, where the number in parenthesis refers to the BA% in the precursor mixture. Mixtures were then dried at 60°C and then heated to 550°C in a muffle furnace in covered crucibles for 4 hours in air with a heating and cooling rate of 5 °C/min. Higher surface area carbon nitrides were prepared via thermal oxidation etching of the bulk materials by heating, in open crucibles to 500 °C for 2 hours with a ramp rate of 5 °C/min in a muffle furnace, in air. FeTCPP modified carbon nitrides were prepared by mechanical mixing of 50 mg carbon nitride in 50 mL 90 µM FeTCPP (4 mg) ethanolic solution, left stirring for 24 hours in the dark. After stirring the suspension was then centrifuged, using a Heraeus Megafuge 16R, to remove the FeTCPP solution and then washed twice with 50 mL ethanol. Powders were then dried overnight at 60 °C. Loading of Pt co-catalyst (1 wt%) onto the surface of materials was performed via photodeposition of H2PtCl6 in-situ. For in-situ experiments, the equivalent amount of H2PtCl6 (8 wt% solution) which would provide a maximum of 1 wt% loading (1 mL:0.5 µL, water:H2PtCl6 (8 wt% solution), v:v) was added to the photocatalyst suspension, purged with N2 for 30 minutes and placed under illumination, with gas evolution monitored by gas chromatography (GC). 

Elemental Analysis (CHN) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP OES) were performed by the University of Liverpool analytical services using a ThermoFisher FlashEA 1112 CHN analyser and an Agilent 5110 ICP-OES spectrometer, respecetively. For ICP-OES measurements, samples were prepared by placing 5 mg of the material in 1 mL ~17 M H2SO4 and heating at ~100 °C for 1 hour or until particulates had completely dissolved.

N2 adsorption-desorption isotherms at 77 K were collected on a Micromeritics Tristar instrument. Samples were degassed under vacuum at 130 °C for 20 h before measurement.

Powder X-ray diffraction (PXRD) was carried out using a Bruker D8-Advance X-ray diffractometer operating with Cu Kα1 of λ = 0.15418 nm for carbon nitride samples.

Carbon nitride samples were studied by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) on a Bruker Vertex 70 spectrometer, fitted with a detachable DRIFTS attachment. Discs were prepared by dilution in KBr, specifically, 2 mg of sample in 100 mg KBr, mixed by grinding with a pestle and mortar till reaching homogeneity and then loaded into sample well. Spectra were collected at a resolution of 2 cm-1 over 64 accumulations and were baselined with a KBr powder in air.

All Nuclear Magnetic Resonance (NMR) spectra were recorded under Cross Polarisation (CP) Magic Angle Spinning (MAS) conditions on a Bruker DSX 400 MHz NMR spectrometer equipped with a 4 mm HXY probe tuned to X = 13C at 101 MHz and Y = 15N at 40 MHz. 1H pulses and SPINAL 64 decoupling1 were performed at a radio frequency (rf) field amplitude of 83 kHz.  For the 13C CP step, a 70 – 100 % ramped rf field of 1 ms centred at 35 kHz was applied on 13C, while the 1H rf field was matched to obtain optimum signal at around 66 kHz. For the 15N CP step, a 70 – 100 % ramped rf field of 6 ms centred at 40 kHz was applied on 15N, while the 1H rf field was matched to obtain optimum signal at around 60 kHz. The MAS rates were 10 and 5 kHz for 13C and 15N, respectively. 13C and 15N chemical shift were referenced to CH signal of adamantane at 29.45 ppm2 and the NH3+ signal of glycine at 33.40 ppm

UV-Vis-NIR diffuse reflectance spectroscopy (DRS) data was obtained with a Shimadzu UV-2550 UV/Vis spectrometer, equipped with an integrating sphere, over the spectral range of 200-1400 nm and BaSO4 was used as a reflectance standard. The diffuse reflectance spectra were then converted from reflectance to absorption according to the Kubelka-Munk function F(R) = k/s = (1-R)^2/(2R), where k and s are absorption and scattering coefficients, respectively and R is the diffuse reflectance based on the Kubelka–Munk theory of diffuse reflectance.  The data can then be plotted using the equation 〖(αhv)〗^(1/n)=A(hv-E_BG) where α is the absorption coefficient, h is Planck's constant, v is the frequency of light A is the proportionality constant and EBG is the band gap. The value of n denotes the nature of the transition, n = ½ for direct transitions or n = 2 for indirect transitions. A Tauc plot of 〖(αhv)〗^(1/n) versus hv can be used to estimate the band gap of the material by linear extrapolation to find the x-intercept.
UV-Vis spectra of solutions were collected on the same piece of equipment with a standard sample compartment, using a 4 mL (path length, 10 mm) or 0.4 mL (path length, 1 mm) quartz cuvette. Determination of concentrations of soaking samples were determined using the Beer-Lambert equation: A= ε l c= 〖log〗_10  I_0/I where, A is the absorbance, ε is molar absorptivity, I is the path length, c is the concentration, I0 is the incident light intensity, and I is the transmitted light intensity.


X-ray photoelectron spectroscopy (XPS) core level spectra were measured using a Mg Kα (1253.6 eV) X-ray source operating at 144 W and a hemispherical PSP Vacuum Technology electron energy analyser, operating with a typical constant pass energy of 20 eV. A sputtered polycrystalline Ag sample was used for calibration, to determine the precision of the analyser. The secondary electron cut-off (SEC) at low kinetic energies was measured with the X-ray source operating at 9 W with an applied bias of 10 V between the sample and analyser, to separate the spectrometer response. All XPS spectra were fitted using CasaXPS software which fits spectra using a Gaussian/Lorentzian product function to approximate a Voigt function after Shirley background removal with a binding energy determination precision of ± 0.1 eV and all spectra were calibrated to an adventitious carbon peak of 284.6 eV.

Steady-State Photoluminescence (PL) and Time-Resolved Emission Lifetime Spectroscopy measurements were recorded on an Edinburgh Instruments FLS980-D2S2-STM spectrophotometer, equipped with a 450 W Ozone free Xe arc lamp, excitation and emission monochromators and a photomultiplier tube detector. Samples were prepared by sandwiching powders in a demountable quartz cuvette (130 µL). Steady-state photoluminescence spectra were collected in air by a single measurement with an excitation wavelength of 390 nm, monitoring between 410 and 700 nm (2 nm step and 0.1 s dwell time). Time-resolved emission lifetime spectra were obtained from time-correlated single photon counting measurements, in which a single wavelength is monitored over a certain time period. Spectra were acquired with a 371 nm pulsed laser diode (pulse period of 2 µs in air) between 0 and 2000 ns and a stop condition of 10,000 counts. The monitored emission wavelength is specified for each sample in the figure heading. As the instrument has a certain electronic response time, the instrument response function (IRF) of the equipment must be determined by measuring the response of the instrument to a purely scattering solution. The IRF of the instrument was determined using a Ludox sample (aqueous dispersion of silica particles) under the same conditions as those used for the actual samples. The emission lifetime data was analysed using DecayFit software5 as this can be used to fit the emission decay to a number of exponential functions, taking the IRF into consideration. The lifetimes were determined by fitting the exponential decay to a multi-component exponential function.


FT-Raman was performed on a Bruker MultiRAM, IRFS27.


Photocatalytic experiments were carried out using 2 mg of photocatalyst dispersed in 2 mL solution in the presence of a range of hole scavengers (EDTA, TEOA) in a 4 mL vial. Vials were purged with N2 or CO2 for 30 minutes prior to being placed under illumination. The tests were carried out using a 300 W Xe lamp (Newport) with a 375 nm long pass filter or a Schott glass KG1 filter (>50% transmission between 375 and 690 nm) at an intensity of ~100 mW cm-2, unless stated otherwise. For the photoresponse experiments a 75 W Xe lamp (OBB Corp.) equipped with a monochromator and was focussed onto the cell at an intensity of ~0.16 mWcm-2. Gases evolved were detected by an Agilent technologies 6890N instrument equipped with a pulsed discharge detector (D-3-I-HP, Valco Vici) and a 5 Å molecular sieve column (ValcoPLOT, 30 m length, 0.53 mm ID) with N6 Helium as the carrier gas (5 mL/min). For isotopic labelling experiments, systems were first purged with N2 for 30 minutes and then purged with 13CO2 for several minutes before being placed under illumination. Gases evolved were collected and injected into a special made pre-purged cell which was then placed in the FTIR equipment. Isotopic labelling experiments were performed using a similar procedure to the typical photocatalytic experiments in which the photocatalyst was placed in a hole scavenger containing solution in a concentration of 1 mg/mL and then illuminated with visible light for 4-24 hours. The only variation from the typical photocatalysis procedure was the way in which the suspensions were purged; samples were first purged with N2 for 30 minutes and then purged with 13CO2 for several minutes before being placed under illumination. The headspace of the experiment was sampled using a gas syringe, the sample was then injected into a special made pre-purged cell and the FTIR spectra was measured at a resolution of 0.5 cm-1 and averaged over 200 accumulations. The cell used for FTIR measurements consisted of a tube with CaF2 windows attached to either end and a septa port for purging and sample injection.