Photochemistry of Plasmonic Titanium Nitride Nanocrystals | The

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C: Physical Processes in Nanomaterials and Nanostructures

Photochemistry of Plasmonic Titanium Nitride Nanocrystals Alejandro Alvarez Barragan, Sergei Hanukovich, Krassimir N. Bozhilov, Sharma S.R.K.C. Yamijala, Bryan M. Wong, Phillip Christopher, and Lorenzo Mangolini J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b06257 • Publication Date (Web): 12 Aug 2019 Downloaded from pubs.acs.org on August 20, 2019

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The Journal of Physical Chemistry

Photochemistry of Plasmonic Titanium Nitride Nanocrystals Alejandro Alvarez Barragan1, Sergei Hanukovich2,4, Krassimir Bozhilov3, Sharma S.R.K.C. Yamijala4, Bryan M. Wong4,5, Phillip Christopher2, Lorenzo Mangolini1,5*

1. Department of Mechanical Engineering, University of California-Riverside, Riverside, California, 92521, United States 2. Department of Chemical Engineering, University of California-Santa Barbara, Santa Barbara, California, 93106, United States 3. Central Facility for Advanced Microscopy and Microanalysis, University of California-Riverside, Riverside, California, 92521, United States 4. Department of Chemical & Environmental Engineering, University of CaliforniaRiverside, Riverside, California, 92521, United States 5. Materials Science and Engineering Program, University of California-Riverside, Riverside, California, 92521, United States 1 ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

*CORRESPONDING AUTHOR: [email protected]

ABSTRACT

Titanium nitride (TiN) offers advantages compared to standardly used plasmonic materials such as gold and silver in terms of thermal stability, cost and sustainability. While gold and silver nanostructures have played an important role in the rapidly growing field of plasmonic catalysis, the potential of TiN in this application is still underexplored. Here we provide evidence of plasmon-driven chemical activity in TiN by using the photo-reduction of platinum ion under vis-NIR illumination as probe reaction. An aqueous solution of TiN, methanol, and chloroplatinic acid (H2PtCl6) was exposed to visible-near infrared (vis-NIR) radiation (600 to 900 nm). Scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) show nanostructures composed of ~2 nm metallic platinum clusters decorating ~10 nm TiN nanoparticles, 2 ACS Paragon Plus Environment

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confirming the plasmon-driven reduction of the Pt4+ ions to their metallic state. At the same time, the evolution of CO2 resulting from the photo-oxidation of methanol is monitored via gas chromatography. The molar Pt deposition-to-CO2 evolution ratio is in good agreement with the theoretical expectation based on the redox reaction charge balance. We have found that both Pt deposition and CO2 evolution are selflimiting. We attribute this to the increasing plasmon dephasing rate during the photoreduction process, likely due to the high optical losses of Pt in the vis-NIR region. In addition, density functional theory (DFT) simulations of a Pt(111)-TiN(111) junction suggest the existence of an energy barrier limiting electron transfer. This work confirms that plasmonic TiN nanoparticles can use visible light to drive photochemical reactions and highlights the potential of TiN as a cost-effective alternative to gold and silver.

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1. INTRODUCTION The possibility of using plasmonic nanostructures to drive photochemical reactions has generated significant excitement in recent years.1,2 Plasmonic materials provide pathways for converting radiation into chemical energy which are novel and fundamentally different than in semiconductors. The decay of the localized surface-plasmon resonance (LSPR) leads to the formation of hot electrons or holes, which can then drive chemical changes in molecules adsorbed onto the surface of the nanostructure.3,4 A direct charge transfer from the plasmonic structure to the adsorbates can also occur, which has often been called chemical interface damping.5–7 The field enhancement at the surface of plasmonic nanostructures can increase the photo-activity of other structures (such as a catalyst particles) placed in their near-field.6,8– 11 All these approaches leverage the very high extinction cross section of plasmonic structures

and their potential for driving reactions at low temperature and with high selectivity.6,13 This field has been so far dominated by the use of silver and gold as plasmonic materials because they strongly resonate in the visible spectrum. This introduces a number of constraints. First, the thermal stability of gold and silver is limited by their relatively low bulk melting point, further exacerbated by its reduction at the nanoscale.14 Second, silver nanoparticles are chemically unstable in even mild environments.15 Third, the inherent high cost of gold and silver may impact the viability of industrial application of plasmonic catalysis. These considerations motivate the search for alternative plasmonic materials. Metal nitrides are among the proposed materials because they are refractory ceramics with good chemical and thermal stability15–18 and they have a surface plasmon resonance in the vis-NIR region.16,19,20 The work on plasmonic titanium nitride, for example, has already been focused towards the


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development of plasmonic heat transducers,21 photothermal cancer treatment,22,23 and plasmonic waveguides.24 With respect of the photochemistry of TiN, there are to our knowledge only two published reports discussing it. Successful injection of charge carriers generated by LSPR decay in TiN into a TiO2 substrate has been confirmed in a photo-electrochemical cell by correlating photocurrent and optical extinction spectra.25 Also, the photoactivity of TiO2 powders has been enhanced using TiN nanoparticles as additives,26 although no enhancement in the visible-only part of the spectrum was observed. Therefore, a direct demonstration of the capability of TiN to perform useful photochemical reactions under plasmonically-coupled, visible-only radiation is still missing. This work addresses this issue by demonstrating the plasmon-mediated growth of platinum clusters on the surface of TiN nanoparticles. Platinum has been selected because it is ubiquitous in heterogeneous catalysis. Moreover, the reduction of platinum ions and deposition of platinum onto gold plasmonic particles via a light-induced process has been reported by several groups, and it has been used to confirm the capability of plasmonically-generated hot electrons to act as reducing agents.27–29 In this work, platinum clusters have been grown directly onto plasmonic TiN nanoparticles, under visible illumination, by reducing Pt4+ to Pt metal, all while simultaneously oxidizing methanol to balance charge. We synthesized TiN nanoparticles via a non-thermal plasma method previously used in the production of other metal nitrides, semiconductors, and metallic nanoparticles.30–35 To summarize, ammonia (NH3) and titanium tetrachloride (TiCl4) precursors were transported independently into a non-thermal plasma reactor sustained with a 13.56 MHz (RF) power supply. The high reactivity inside the plasma,36 the unipolar charging of particles,37 and the nanoparticle heating due to interactions with plasma-produced 5 ACS Paragon Plus Environment


species (radicals and ions)36,38 lead to the nucleation and growth of refractory TiN nanocrystals. The resulting powder was diluted in an aqueous solution with methanol and chloroplatinic acid. Upon vis-NIR light illumination (600 nm to 900 nm) the platinum precursor was reduced. TEM, STEM-EDX, and XPS analyses conclusively show the presence of Pt0 at the TiN surface. Measurements of CO2 evolution as a function of time, which resulted from methanol oxidation by photo-generated holes, show a substantial increase with respect to a sample that was not subjected to light excitation. Moreover, the molar ratio of Pt deposition-to-CO2 production is 1.690.37, in good agreement with the theoretical value of 1.5 which is expected from the charge balance of the redox reaction under consideration. Pt deposition and CO2 production slow significantly after 6 hours because an increasing amount of Pt at the TiN surface induces damping of the plasmon that limits the reaction rate. This is demonstrated through the analysis of experimental spectra and DFT simulations. The work presented here provides evidence of the capabilities of TiN in photochemistry and sets a baseline for the development of more efficient TiN-based plasmonic heterostructures for cost-effective photocatalytic processes. 2. EXPERIMENTAL SECTION 2.1. TiN nanoparticles synthesis. A well-documented non-thermal plasma method was used to synthesize ~10 nm TiN nanoparticles.20 Ammonia (NH3) and titanium tetrachloride (TiCl4) were used as precursor gases and transported independently into the upstream flange of a 25.4-cm long, 2.54-cm diameter quartz reactor, where a plasma discharge was initiated with a 5-cm long, 2.54-cm diameter cylindrical copper electrode wrapped around the reactor and connected to a 13.56 MHz (RF) power supply. The distance between the center of the electrode and the upstream flange was 4 cm. TiCl4 was delivered using a bubbler kept at 6 ACS Paragon Plus Environment

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atmospheric pressure and in a water bath at 22 °C. Argon was used as a carrier gas and maintained at a flow rate of 70 sccm. Based on the vapor pressure of TiCl4, we estimate that the net TiCl4 flow rate is 1 sccm under these conditions. The NH3 flow rate was maintained at 2.0 sccm. The pressure in the reactor was set to 3 Torr. The TiN particles were collected downstream of the reactor on a stainless-steel mesh filter. The samples were subsequently annealed in a tube furnace under an Ar atmosphere at 250 °C to evaporate ammonium salts, which are a by-product of the TiCl4-NH3 reaction. 2.2. Pt-photodeposition. TiN was added to a 90:10 (v/v) water-methanol solution at a concentration of 160 µM. After sonication for 10 minutes, an 8 wt. % H2PtCl6 aqueous solution (Sigma Aldrich) was added at a concentration of 70 µM. The solution was then illuminated with a 500 W Hg-Xe Newport 67005 Arc Lamp Housing and kept under constant stirring. The distance between the reactor and the light source was 23 cm. Two optical filters (600 nm longpass and 900 nm shortpass, Edmund Optics Inc.) were used to limit the incident light in between 600 nm and 900 nm. The spectrum of the incident light was measured with an Avantes SensLine AvaSpec ULS-RS-TEC spectrometer. The light intensity was obtained by placing a Thor Labs PM400 optical power meter in the path of the incident light at precisely the same distance as the illuminated sample. Control samples (under no illumination) were maintained under stirring at 40 °C to match the maximum temperature reached by the illuminated samples due to heating by light absorption of the nanoparticles. Different samples were illuminated for 20 min, 30 min, 1 h, 2 h, 4 h, and 6 h. A pH of 4.0 was measured in the solution throughout all the experiments. 2.3. Characterization of TiN-Pt heterostructure. After illumination, samples were centrifuged and rinsed with water twice to eliminate any additional reactant or Pt precursor. 7 ACS Paragon Plus Environment


TEM samples were prepared by dropcasting a solution of TiN-Pt particles on a lacey carbon copper grid. The dry samples were characterized in a Tecnai T-12 TEM for lower resolution characterization. High resolution TEM (HR TEM) and STEM images were obtained with a FEI Titan Themis 300 instrument with energy dispersive X-ray spectroscopy (EDX) capability for elemental mapping. XPS characterization was performed at the UC Irvine Materials Research Institute (IMRI). Samples were prepared by dropcasting the TiN-Pt solution on a piece of prime-grade silicon previously cleaned with acetone, isopropanol, and DI water. Spectra were acquired with an AXIS Supra by Kratos Analytical tool with a dual anode Al/Ag monochromatic X-ray source. EDX characterization was performed with a FEI Nova NanoSEM450 system equipped with an Oxford Instruments Aztec Synergy software and a X-max 50 mm2 detector with resolution of 127 nm at Mn Kα. The accelerating voltage was kept at 20 kV with a working distance of 5 mm. Extinction measurements were performed on a Varian Cary 500 UV-vis-NIR spectrophotometer. Samples were collected from the reactor and thoroughly washed and centrifuged before obtaining the spectra. Samples were prepared by diluting in DI water and transferred to a 1 cm x 1 cm quartz cuvette. 2.4. DFT calculation. All calculations were performed with Kohn-Sham density functional theory using the PBE exchange-correlation functional as implemented in the FHI-aims software package.39,40 To simulate the Pt-TiN interface, 6-layers of a Pt(111) surface were placed on top of a 6-layer TiN(111) surface, and the combined structure was optimized until the forces were less than 0.01 eV/Å. A vacuum of at least 15 Å was used to avoid any spurious interactions between the periodic images. The Brillouin zone was integrated using a 4x4x1 Monkhrost-Pack k-grid.41 6-layer thick slabs along with 15 Angstroms of vacuum and a 4x4x1 Monkhrost-Pack k-grid were used for the work-function calculations for the 8 ACS Paragon Plus Environment

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(111) surfaces of TiN and Pt. Due to the large system sizes in all these calculations, the FHIaims tier-1 basis was used. 2.5. CO2 evolution. The Pt photodeposition experiment was performed in a three-neck glass reactor with a 35 mm quartz window. Throughout the experiment, the reactor was wrapped in aluminum foil except for the quartz window to focus the incident light onto the reaction solution. The three reactor necks were sealed from the environment with a septa cap, a plastic cap with a thermometer and an O-ring adapter, and a three-way valve adapter connected to an Ar line and a vacuum output. A manometer was also attached to measure the pressure inside the reactor. The valve was opened to vacuum and, after 10 seconds, it was turned towards the Ar line to refill the reactor up to a pressure of 10 psi. This purging cycle was repeated 5 times. 1 mL gas samples were collected with a pressurized syringe injected into the septa cap. The sample was injected into a previously calibrated SRI MG #5 gas chromatograph (SRI Instruments) equipped with a flame ionization detector (FID) with a built-in methanizer for CO2 detection and a thermal conductivity detector (TCD), both downstream of a molecular sieve column (6’ mol sieve 13x). Ar gas was used as the carrier gas. Samples were extracted after 20 min, 40 min, 1 h, 2 h, 4h, and 6 h of visible light illumination. 3. RESULTS AND DISCUSSION Figure 1a shows a schematic of the Pt photodeposition reaction. We used chloroplatinic acid as the metal precursor. Four electrons are necessary to fully reduce platinum to its metallic state, as shown in the reaction below: 𝑃𝑡𝐶𝑙26 ― +4𝑒 ― →𝑃𝑡0 +6𝐶𝑙 ―


(1)


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The other half of the overall process is the oxidation of methanol, shown below: 𝐶𝐻3𝑂𝐻 + 𝐻2𝑂 + 6ℎ + →𝐶𝑂2 + 6𝐻 +

(2)

Organic compounds are commonly used as sacrificial electron donors to overcome the kinetic limitations associated to the oxidation of water.42,43 The oxidation of methanol has been studied previously for the production of hydrogen with platinized TiO2.43–46 In our case, the protons generated via hole injection in reaction 2 likely react with chlorine ions to give HCl. Based on the number of charges needed to fully reduce Pt4+ (4 electrons) and oxidize methanol to CO2 (6 holes), one finds a 3:2 ratio of Pt0: CO2 product formation. Figure 1b shows the extinction spectrum of the TiN nanoparticles before photodeposition. The red rectangle indicates the wavelength range incident on the nanoparticle solution during the experiment. Figure S1 shows the optical spectrum of the lamp after filtering the white light source with 600 nm longpass and 900 nm shortpass filters. By exciting the nanoparticles at these wavelengths, we discard any contribution from interband transitions that take place below 500 nm.25 It is important to note that the experiments were initiated at ambient conditions and that the maximum temperature measured was 38°C. Control experiments on samples not exposed to light and maintained at the same temperature to make up for the thermal contribution of the light source did not show any platinum growth.


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Figure 1. a) Schematic of the intended photocatalytic reaction. Platinum precursor anions adsorb to the surface of the TiN nanoparticles and are reduced by photogenerated electrons. Methanol is oxidized by photogenerated holes to form CO2 and protons. b) Extinction spectrum of the TiN nanoparticles before the reaction. The red rectangle indicates the optical band that is incident on the sample. It coincides with the plasmon peak of the spectrum.

3.1. Photodeposition of Pt nanoparticles. The samples were thoroughly characterized to confirm the deposition of metallic Pt. Figure 2 shows HR-TEM imaging of a sample produced after 6-hour illumination of TiN particles submerged in a 10 % methanol (v/v) aqueous solution containing chloroplatinic acid at a concentration of 70 µM. Well-defined lattice fringes from the TiN and Pt nanostructures are observed in Figure 2a. After FFT postprocessing, we identified signal corresponding to the 111 Pt (yellow square) and 111 TiN (blue square) planes with a d spacing of 0.226 nm and 0.245 nm, respectively. The two signatures can be superimposed and identified upon analysis at the interface of both nanostructures (red square). A high angle annular dark field (HAADF) image and its corresponding EDX map are presented in Figure 2b,c. Since the signal obtained with a 11 ACS Paragon Plus Environment


HAADF detector has a proportional dependence to the atomic number of the sample, the regions with a higher intensity in Figure 2b are attributed to a heavier element. EDX mapping unequivocally confirms the deposition of Pt (green) on the TiN (red) nanoparticles (Figure 2c). To analyze the growth and morphology of the Pt nanoparticles deposited on TiN, we performed HR TEM characterization on samples obtained at different photodeposition times (Figure 3) in the presence of methanol. Immediately at the beginning of the illumination process, a very thin coating appears to cover the TiN particules (Figure 3a). XPS characterization, to be discussed in further details later in the manuscript, confirms that this is a non-reduced, platinum-rich layer. After 30 minutes (Figure 3b) of illumination, clusters decorating the surface of the TiN particles start to become distinguishable. These become more obvious as the process proceeds (Figures 3c and 3d). After 360 minutes, bigger crystalline particles are observed (Figure 3e). The resulting particle size distribution of this sample is shown in Figure 3f. Most particles are within 1 and 3 nm in size. Lower magnification images of the same samples are presented in Figure S2.


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Figure 2. a) High resolution TEM imaging of TiN particles after 6 hour photodeposition of Pt, in presence of methanol. The micrograph shows the lattice fringes of the TiN and the Pt nanostructures. The squares to the left show FFT signal of regions on the image marked with their corresponding colors. Pt 111 and TiN 111 were identified in this analysis. b) HAADFSTEM image of a TiN nanoparticle with Pt clusters. c) EDX mapping of HAADF-STEM image shows a clear signal from Pt atoms.



Figure 3. High resolution TEM micrographs of TiN nanoparticles after a) 0, b) 30, c) 60, d) 120, e) 360 minutes of Pt photodeposition in presence of methanol. f) Size distribution of platinum nanoclusters after 6 hours of photodeposition. To complement the findings from TEM and EDX characterization we also performed XPS on the TiN-Pt samples after 6 hours of irradiation in the presence of methanol (Figure 4). The Pt 4f spectrum in Figure 4a shows a strong signal from Pt0 doublets at 71.0 eV and 74.3 eV.47,48 This sample has been produced under the same conditions that result in the nucleation and growth of the ~2 nm Pt clusters shown in Figures 2 and 3. Figure 4b shows the Pt 4f XPS spectrum of a control sample that remained under constant stirring for 6 hours but was not exposed to visible light. The composition of the solution for this sample is identical to the one for the illuminated samples, i.e. methanol was added to this control sample. The Pt4+ and Pt2+ primary doublets are observed at 75 eV and 72.7 eV.47,48 No signal from Pt0 was 14 ACS Paragon Plus Environment

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identified. Additional TEM analysis for the control sample (with methanol added to the solution, but without light exposure) is shown in Figures S3 and S4. TEM images in Figure S3a,c show lower and higher magnification micrographs for samples exposed to light, confirming again the appearance of ~2 nm clusters decorating the TiN particles, consistent with Figures 2 and 3. TEM images for the sample not exposed to light (Figure S3b,d) indicate that a thin coating may be absorbed onto the surface of the TiN particles. A more detailed TEM analysis is shown in Figure S4. HAADF in Figure S4b, which is sensitive to atomic number, confirms that sub-1 nm cluster are absorbed onto the particles’ surface. The EDX scan in Figure S4c confirms the presence of platinum at the particles’ surface, although its atomic fraction is low and equal to ~1.4% with respect of titanium (Pt/Ti atomic fraction). As a comparison, the Pt/Ti atomic fraction for the light-exposed sample is ~12.4%. These combined XPS and TEM data suggest that even without illumination some platinum absorbs onto the surface of the particles, although it is not reduced to its metallic states and metallic clusters do not grow. Moreover significantly more platinum is observed after illumination. The fact that platinum absorbs onto the surface of these particles is not surprising. Due to the low pH of the solution throughout the reaction (4.0), we conclude that this thin platinum coating results from the adsorption of the platinum precursor on the TiN surface. The higher concentration of protons in acidic environments translates into the positive charging of the particles. The negatively charged hexachloroplatinate anions (PtCl6-2) are therefore electrostatically adsorbed onto the TiN.49,50 The presence of Pt2+ doublets in the XPS spectra for the control sample (Figure 4b) suggests that the platinum precursor is partially reduced even without illumination. We attribute this to the presence of methanol, which is a wellknown reducing agent for the growth of platinum particles in solution.51 Methanol may therefore partially reduce the platinum precursor absorbed onto the TiN particle surface, but 15 ACS Paragon Plus Environment


its concentration is not sufficient to drive the full reduction of the platinum salt and the nucleation of platinum particles, as confirmed by the TEM analysis shown in Figures S3 and S4 and by the XPS spectrum in Figure 4b. Illumination is needed to drive the full reduction of the platinum precursor. For completeness, we have also performed XPS and TEM analysis on samples processed with and without illumination, but in the absence of methanol. TEM data (Figure S5) for samples without methanol show small amorphous clusters adsorbed to the particles surface for both the light and the dark samples. No crystalline structure could be detected. XPS data for samples in the dark and after 6 h illumination without methanol show no Pt0 signal (Figure S6). This highlights the importance of methanol as a hole scavenger. While the hole scavenging rate has not been measured for the case of TiN (at least to our knowledge), measurements on TiO2 indicate that the hole lifetime is of the order of few hundreds of picosecond when the material is in contact with methanol.52 The carrier lifetime in metals is well-known to be of the order of few picoseconds, although it has been reported to be significantly longer (tens-to-hundreds of picoseconds) in titanium nitride due to its more complex band structure.53 It is therefore reasonable for the presence of methanol to make such a significant difference in our experiments. By rapidly scavenging holes, methanol increases the electron lifetime so that electrons can effectively reduce the platinum ions. The fact that in the absence of methanol we observe a more significant absorption of a platinum-rich layer onto the TiN surfaces, in combination with the lack of a crystalline structure for platinum, rules out the possibility that the metallic platinum clusters observed in Figures 2 and 3 are formed during exposure to the TEM electron beam. To discard the possibility of direct photodecomposition of H2PtCl6, we acquired the absorbance spectrum of the precursor solution (Figure S7). There is negligible light 16 ACS Paragon Plus Environment

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absorbance of the precursor between 600 nm and 900 nm. Control experiments performed by exposing to light the same solution used for the sample shown in Figure 2 and 3, but without TiN nanoparticles, does not lead to the formation of any solid material. The Ti2p spectra of both illuminated and non-illuminated samples show two pairs of doublets with primary 2p3/2 peaks at ~458.8 eV and ~456.2 eV (Figure 4c,d). We attribute these signals to Ti-O and Ti-N bonds, respectively. These results were expected based on previous work regarding the oxidation mechanism of TiN nanoparticles and thin films.20,54 For this study, we did not observe a substantial difference between the Ti 2p signal of the experiment and control samples. This suggests that the composition of the TiN nanoparticles remains stable during light exposure. Moreover, EDX analysis of the Ti-to-N ratio shown in Figure 5 demonstrates that, over several hours of illumination, the Ti-to-N ratio remains close to 1.0 and relatively unchanged, providing further evidence of the stability of the TiN nanoparticles during the reaction.



Figure 4. Pt 4f spectra of TiN-Pt samples with methanol a) after 6 hours of irradiation and b) after 6 hours in the dark.. Ti 2p spectra of TiN-Pt samples with methanol c) after 6 hours of irradiation and d) after 6 hours in the dark.


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Figure 5. Ti-to-N ratio of TiN samples at different photodeposition times.

3.3. Oxidation of methanol to CO2. As stated in Reaction 2, H+ and CO2 are the products of the methanol oxidation reaction and require 6 photogenerated holes to be formed. In order to ensure that methanol oxidation was coupled to Pt4+ reduction, we measured the CO2 evolution —under illumination and in the dark— as a function of time by gas chromatography. There was a 4-fold increase in CO2 evolution upon illumination (Figure 6a). The evolution of CO2 corresponds solely to the oxidation half of the reaction. It is therefore necessary to investigate the reduction half —determined by the deposition of Pt0— to get a complete perspective of the photodeposition process. To correlate the CO2 evolution with the amount of Pt deposited, we obtained samples after 20 min, 1 h, 4 h, and 6 h of illumination and measured the Pt-to-Ti weight loading by EDX (Figure 6b). The samples were carefully washed and filtered to remove excess Pt precursor. The molar Pt-to-CO2 ratio after 6 hours was 1.690.37. This number is in good agreement with the theoretical 3:2 ratio expected from the charge balance of the redox reaction. An in-depth discussion of these 19 ACS Paragon Plus Environment


calculations is presented in the Supplementary Information file. At longer reaction times, both the CO2 and Pt production rates diminished considerably. We hypothesize that this is a result of the interfacial damping of the plasmon caused by the increasing Pt deposited at the TiN surface. The high optical losses of Pt at the illumination wavelengths, defined by the imaginary part of the dielectric function ε(Im) (Figure S8), cause a decrease of the plasmon dephasing time t, which is inversely proportional to the plasmon bandwidth Γ through the relation t = ħ/πΓ, where ħ is the Planck constant.2,55–57 Quenching of the TiN plasmonic band is observed after Pt photodeposition (Figure 6c). The spectra in Figure 6c are normalized over the concentration of TiN particles in solution to ensure that they are directly comparable. An increase in absorbance in the UV-blue part of the spectrum is expected given the large absorption cross section of platinum in that region. Additional spectra obtained at different reaction times (shown in Figure S9 and normalized to the intensity at 400 nm for clarity) were analyzed by fitting them to a bi-gaussian model to make up for their asymmetric nature (Figure S10). Figure 6d shows the change in peak width of the TiN plasmon peak during the photoplating reaction. An increase of Γ at longer reaction times provides evidence of the shortening of the dephasing time. As more Pt is deposited at the TiN surface, interfacial damping becomes more predominant and impedes the effective reduction of the platinum precursor and the oxidation of methanol. We should also mention that we have performed finite-difference time-domain (FDTD) calculation for TiN nanoparticles using standard and widely utilized software (Lumerical) and have found that, in agreement with previous studies,18 the extinction spectra are dominated by absorption, with negligible contribution from scattering (Figure S11).


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We have calculated the quantum yield of the reaction by obtaining both the photon flux of the incident light and the photodeposition rate as per the work of Li et. al.:58

𝑞𝑢𝑎𝑛𝑡𝑢𝑚 𝑦𝑖𝑒𝑙𝑑

(

)=

𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝑝ℎ𝑜𝑡𝑜𝑛

(𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 ) 𝑠 𝑝ℎ𝑜𝑡𝑜𝑛𝑠 … (3) 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 𝑝ℎ𝑜𝑡𝑜𝑛 𝑓𝑙𝑢𝑥( 𝑠 )

𝑝ℎ𝑜𝑡𝑜𝑑𝑒𝑝𝑜𝑠𝑖𝑡𝑖𝑜𝑛 𝑟𝑎𝑡𝑒

The intensity of the incident light on the sample was measured (335 mW/cm2) and used to calculate the photon flux absorbed by the particles. The photodeposition rate was obtained by subtracting the initial CO2 evolution rate without illumination to the CO2 rate acquired under illumination (Figure S12). The resulting quantum yield was 0.0024%. A comprehensive discussion of the calculations is presented in the Supplementary Information file. While low quantum yields have also been reported for similar structures, such as in the case of hydrogen evolution from plasmonically excited gold nanorods,59 such low QY underscores the need for a better understanding of plasmon-driven photochemistry in alternative plasmonic materials. The reduction potential of Pt4+ is around 0.75 V with respect of the standard hydrogen electrode (SHE), corresponding to 5.2 V to vacuum. The low efficiency of the photo-reduction process suggests that only a small fraction of the charge carriers generated in TiN may be sufficiently energetic to drive the reaction. Atomistic simulations have been performed to provide additional insights with that respect.



Figure 6. a) CO2 evolution is significantly higher under illumination. The production declines at increasing times. b) The Pt-Ti wt. ratio has a similar behavior to the CO2 evolution rate, demonstrating the interrelation of both processes linked by the electron-hole pair generation from the plasmon decay at the TiN surface. c) Vis-NIR spectra of TiN particles before and after the Pt photodeposition experiment. Increasing deposition of Pt results in the damping of the TiN plasmon. d) Plasmon broadening of the spectra at longer reaction times.

3.4. DFT calculations. DFT calculations have been performed on a 6-layer thick slab of TiN(111) with another 6-layer thick slab of Pt(111) on top of it. Figure 7a shows the atomic structure of the simulated interface. Figure 7b depicts charge-density difference maps 22 ACS Paragon Plus Environment

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between the Pt and the TiN surfaces. Specifically, the purple-colored surfaces denote areas that have gained electrons, and the green-colored surfaces represent areas with depletion of electron density. Upon convergence, we find that electron density is depleted from the Pt interface, which is concomitantly gained by the TiN interface. Thus, we conclude that at the interface there is a charge transfer from the Pt to the TiN. We have also calculated the workfunctions for the 111 faces of the TiN and Pt and found them to be 5.86 and 5.23 eV, respectively. These calculations suggest that electron transfer from TiN to Pt is possible for sufficiently energetic carriers, but an energy barrier of 0.6 eV nevertheless exists. XPS data shown in Figure 4 suggests that oxygen is present at the surface of the TiN particles. To account for the presence of oxygen, we have also repeated the DFT calculations by either fully replacing nitrogen at the surface of the TiN slab with oxygen, or by replacing 25% of the nitrogen sites with oxygen in the first 4 layers of the TiN slab. These two configurations are shown in Figure S13. The work functions of these two configurations are 5.27 eV and 5.37 eV respectively. This suggest that even when accounting for the presence of oxygen, there is still an energy barrier for electron transfer from TiN to Pt. We stress that the calculated work function for Pt(111) is close to experimentally reported values.60,61 There is substantially less experimental data on the work function of TiN(111), with one study on a sputtered sample reporting values between 4.5 eV and 5 eV,62 and another reporting values even lower than 4 eV.63 These are significantly lower than what we find via DFT for the case of stoichiometric TiN, but closer to the values that we obtain when accounting for surface oxidation In our experience, surface oxidation of TiN is unavoidable and likely the work function values reported in the literature were obtained on samples with some degree of oxygen at their surfaces. A more careful investigation of the electronic structure of TiN is



necessary to engineer effective interfaces with other catalysts and fully exploit its potential as a photoactive material. In addition, as the photodeposition proceeds, the enhanced dephasing rate (see Figure 6d) is likely going to result in less energetic carriers. This is consistent with an increasingly reduced rate of electron transfer to Pt and the experimental observation of a self-limiting process.

Figure 7. a) Resulting Ti(111)-Pt(111) interface after DFT simulations. b) Charge transfer from Pt to N (of TiN) at the interface. Green lobes represent a loss in electron density, and purple lobes represent a gain in electron density. An iso-value of 0.01 eÅ-3 was used.

CONCLUSIONS


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In summary, we have resonantly coupled visible light into plasmonic TiN nanoparticles to drive the photo-plating of Pt at their surfaces. Extensive characterization conclusively confirms that a light-driven process is responsible for the reduction of platinum to its metallic state. The reaction is accompanied by the evolution of CO2 from the hole-mediated oxidation of methanol upon light excitation. The molar Pt-to-CO2 ratio after 6 hours of illumination is in excellent agreement with the charge balance of both the Pt reduction and methanol oxidation reactions. The Pt0 and CO2 production rates decline at longer reaction times. The high optical losses of Pt at vis-NIR wavelengths cause an interfacial plasmon damping effect. In addition, DFT calculations suggest the presence of a significant energy barrier at the TiNPt interface. This results in an overall low quantum yield and in a self-limiting photoreduction reaction. This work expands the prospects of TiN as viable alternative to gold and silver but also highlights areas that require further consideration for this system. Access to alternative plasmonic materials with higher energy plasmon, such as zirconium nitride,16 and a deeper understanding of the electronic structure of these materials are necessary for advancements in this area. Supporting information: Spectrum of incident light, TEM micrographs of platinized TiN as a function of photodeposition time, TEM micrographs of TiN particles with and without light exposure, HAADF and EDX scan of TiN particles not exposed to light, TEM micrographs of samples without methanol under illumination and in the dark, XPS of samples without methanol under illumination and in the dark, absorbance spectrum of H2PtCl6 in aqueous solution, calculation of Pt-to-CO2 ratio, imaginary part of dielectric function of Pt and TiN, extinction spectra of TiN as a function of Pt photodeposition time, extinction spectra of TiN nanoparticles as a function of Pt photodeposition time, fitting of TiN spectra, 25 ACS Paragon Plus Environment


absorption and scattering cross sections of TiN obtained by FDTD simulations, calculation of quantum yield, initial reaction rates, structures used as input of DFT calculations to account for the role of surface oxidation. Acknowledgement: This work has been primarily supported by the National Science Foundation under Award No. 1351386 (CAREER). A.A.B. acknowledges the support of the “Consejo Nacional de Ciencia y Technologia” (CONACYT, Mexico) and the University of California Institute for Mexico and the United States (UC MEXUS). TEM measurements were performed at the Center for Electron Microscopy and Microanalysis (CFAMM) at UC Riverside. XPS characterization was performed at the UCI Materials Research Institute (IMRI) at UC Irvine. S.S.Y., B.M.W., S.H. and P.C. acknowledge the support of the U.S. Army Research Office under grant number W911NF17-1-0340.

REFERENCES (1)

Linic, S.; Christopher, P.; Ingram, D. B. Plasmonic-Metal Nanostructures for Efficient Conversion of Solar to Chemical Energy. Nat. Mater. 2011, 10 (12), 911– 921.

(2)

Aslam, U.; Rao, V. G.; Chavez, S.; Linic, S. Catalytic Conversion of Solar to Chemical Energy on Plasmonic Metal Nanostructures. Nat. Catal. 2018, 1, 656–665.

(3)

Schlather, A. E.; Manjavacas, A.; Lauchner, A.; Marangoni, V. S.; Desantis, C. J.; Nordlander, P.; Halas, N. J. Hot Hole Photoelectrochemistry on Au@SiO2@Au Nanoparticles. J. Phys. Chem. Lett. 2017, 8, 2060–2067. 26 ACS Paragon Plus Environment

Page 26 of 35

Page 27 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(4)

Christopher, P.; Moskovits, M. Hot Charge Carrier Transmission from Plasmonic Nanostructures. Annu. Rev. Phys. Chem. 2017, 68, 379–398.

(5)

Therrien, A. J.; Kale, M. J.; Yuan, L.; Zhang, C.; Halas, N. J.; Christopher, P. Impact of Chemical Interface Damping on Surface Plasmon Dephasing. Faraday Discuss. 2019, 241, 59–72.

(6)

Li, K.; Hogan, N. J.; Kale, M. J.; Halas, N. J.; Nordlander, P.; Christopher, P. Balancing Near-Field Enhancement, Absorption, and Scattering for E Ff Ective Antenna − Reactor Plasmonic Photocatalysis. Nano Lett. 2017, 17, 3710–3717.

(7)

Boerigter, C.; Campana, R.; Morabito, M.; Linic, S. Evidence and Implications of Direct Charge Excitation as the Dominant Mechanism in Plasmon-Mediated Photocatalysis. Nat. Commun. 2016, 7, 10542.

(8)

Awazu, K.; Fujimaki, M.; Rockstuhl, C.; Tominaga, J.; Murakami, H.; Ohki, Y.; Yoshida, N.; Watanabe, T. A Plasmonic Photocatalyst Consisting of Silver Nanoparticles Embedded in Titanium Dioxide. J. Am. Chem. Soc. 2008, 130, 1676– 1680.

(9)

Christopher, P.; Ingram, D. B.; Linic, S. Enhancing Photochemical Activity of Semiconductor Nanoparticles with Optically Active Ag Nanostructures: Photochemistry Mediated by Ag Surface Plasmons. J. Phys. Chem. C 2010, 114, 9173–9177.

(10)

Liu, Z.; Hou, W.; Pavaskar, P.; Aykol, M.; Cronin, S. B. Plasmon Resonant Enhancement of Photocatalytic Water Splitting Under Visible Illumination. Nano Lett. 2011, 11, 1111–1116. 27 ACS Paragon Plus Environment


(11)

Zhang, C.; Zhao, H.; Zhou, L.; Schlather, A. E.; Dong, L.; Mcclain, M. J.; Swearer, D. F.; Nordlander, P.; Halas, N. J. Al − Pd Nanodisk Heterodimers as Antenna − Reactor Photocatalysts. Nano Lett. 2016, 16, 6677–6682.

(12)

Marimuthu, A.; Zhang, J.; Linic, S. Tuning Selectivity in Propylene. Science (80-. ). 2013, 339 (March), 1590–1593.

(13)

Bonn, M.; Funk, S.; Hess, C.; Denzler, D. N.; Stampfl, C.; Scheffler, M.; Wolf, M.; Ertl, G. Phonon versus Electron-Mediated Desorption and Oxidation of CO on Ru (0001). Science (80-. ). 1999, 285, 1042–1046.

(14)

Kirschner, M. S.; Hannah, D. C.; Diroll, B. T.; Zhang, X.; Wagner, M. J.; Hayes, D.; Chang, A. Y.; Rowland, C. E.; Lethiec, C. M.; Schatz, G. C.; et al. Transient Melting and Recrystallization of Semiconductor Nanocrystals under Multiple Electron-Hole Pair Excitation. Nano Lett. 2017, 17 (9), 5315–5320.

(15)

Naik, G. V.; Shalaev, V. M.; Boltasseva, A. Alternative Plasmonic Materials: Beyond Gold and Silver. Adv. Mater. 2013, 25 (24), 3264–3294.

(16)

Exarhos, S.; Alvarez-Barragan, A.; Aytan, E.; Balandin, A. A.; Mangolini, L. Plasmonic Core-Shell Zirconium Nitride-Silicon Oxynitride Nanoparticles. ACS Energy Lett. 2018, 3 (10), 2349–2356.

(17)

Guler, U.; Ndukaife, J. C.; Naik, G. V.; Nnanna, A. G. A.; Kildishev, A. V.; Shalaev, V. M.; Boltasseva, A. Local Heating with Lithographically Fabricated Plasmonic Titanium Nitride Nanoparticles. Nano Lett. 2013, 13 (12), 6078–6083.

(18)

Guler, U.; Suslov, S.; Kildishev, A. V.; Boltasseva, A.; Shalaev, V. M. Colloidal Plasmonic Titanium Nitride Nanoparticles : Properties and Applications. 28 ACS Paragon Plus Environment

Page 28 of 35

Page 29 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Nanophotonics 2015, 4, 269–276. (19)

Naik, G. V; Schroeder, J. L.; Ni, X.; Alexander, V.; Sands, T. D.; Boltasseva, A. Titanium Nitride as a Plasmonic Material for Visible and Near-Infrared Wavelengths. Opt. Mater. Express 2012, 2 (4), 534–537.

(20)

Alvarez Barragan, A.; Ilawe, N. V.; Zhong, L.; Wong, B. M.; Mangolini, L. A NonThermal Plasma Route to Plasmonic TiN Nanoparticles. J. Phys. Chem. C 2017, 121 (4), 2316–2322.

(21)

Ishii, S.; Sugavaneshwar, R. P.; Nagao, T. Titanium Nitride Nanoparticles as Plasmonic Solar Heat Transducers. J. Phys. Chem. C 2016, 120 (4), 2343–2348.

(22)

He, W.; Ai, K.; Jiang, C.; Li, Y.; Song, X.; Lu, L. Plasmonic Titanium Nitride Nanoparticles for in Vivo Photoacoustic Tomography Imaging and Photothermal Cancer Therapy. Biomaterials 2017, 132, 37–47.

(23)

Gschwend, P. M.; Conti, S.; Kaech, A.; Maake, C.; Pratsinis, S. E. Silica-Coated TiN Particles for Killing Cancer Cells. ACS Appl. Mater. Interfaces 2019, 11, 22550– 22560.

(24)

Saha, S.; Dutta, A.; Kinsey, N.; Kildishev, A. V.; Shalaev, V. M.; Boltasseva, A. OnChip Hybrid Photonic-Plasmonic Waveguides with Ultrathin Titanium Nitride Films. ACS Photonics 2018, 5, 4423–4431.

(25)

Naldoni, A.; Guler, U.; Wang, Z.; Marelli, M.; Malara, F.; Meng, X.; Besteiro, L. V.; Govorov, A. O.; Kildishev, A. V.; Boltasseva, A.; et al. Broadband Hot-Electron Collection for Solar Water Splitting with Plasmonic Titanium Nitride. Adv. Opt. Mater. 2017, 5 (15), 1–11. 29 ACS Paragon Plus Environment


(26)

Clatworthy, E. B.; Yick, S.; Murdock, A. T.; Allison, M. C.; Bendavid, A.; Masters, A. F.; Maschmeyer, T. Enhanced Photocatalytic Hydrogen Evolution with TiO 2 – TiN Nanoparticle Composites. J. Phys. Chem. C 2019, 123, 3740–3749.

(27)

Ortiz, N.; Zoellner, B.; Hong, S. J.; Ji, Y.; Wang, T.; Liu, Y.; Maggard, P. A.; Wang, G. Harnessing Hot Electrons from Near IR Light for Hydrogen Production Using PtEnd-Capped-AuNRs. Appl. Mater. Interfaces 2017, 9, 25962–25969.

(28)

Kim, N. H.; Meinhart, C. D.; Moskovits, M. Plasmon-Mediated Reduction of Aqueous Platinum Ions: The Competing Roles of Field Enhancement and Hot Charge Carriers. J. Phys. Chem. C 2016, 120, 6750–6755.

(29)

Forcherio, G. T.; Baker, D. R.; Boltersdorf, J.; Le, A. C.; Mcclure, J. P.; Grew, K. N.; Lundgren, C. A. Targeted Deposition of Platinum onto Gold Nanorods by Plasmonic Hot Electrons. J. Phys. Chem. C 2018, 122, 28901–28909.

(30)

Coleman, D.; Lopez, T.; Yasar-Inceoglu, O.; Mangolini, L. Hollow Silicon Carbide Nanoparticles from a Non-Thermal Plasma Process Hollow Silicon Carbide Nanoparticles from a Non-Thermal Plasma Process. J. Appl. Phys. 2015, 117, 193301.

(31)

Mangolini, L.; Thimsen, E.; Kortshagen, U. High-Yield Plasma Synthesis of Luminescent Silicon Nanocrystals. Nano Lett. 2005, 5, 655–659.

(32)

Yasar-Inceoglu, O.; Mangolini, L. Characterization of Si-Ge Alloy Nanocrystals Produced in a Non-Thermal Plasma Reactor. Mater. Lett. 2013, 101, 76–79.

(33)

Schramke, K. S.; Qin, Y.; Held, J. T.; Mkhoyan, A. K.; Kortshagen, U. R. Nonthermal Plasma Synthesis of Titanium Nitride Nanocrystals with Plasmon 30 ACS Paragon Plus Environment

Page 30 of 35

Page 31 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Resonances at Near-Infrared Wavelengths Relevant to Photothermal Therapy. ACS Appl. Nano Mater. 2018, 1, 2869–2876. (34)

Hunter, K. I.; Held, J. T.; Mkhoyan, K. A.; Kortshagen, U. R. Nonthermal Plasma Synthesis of Core/Shell Quantum Dots: Strained Ge/Si Nanocrystals. ACS Appl. Mater. Interfaces 2017, 9, 8263–8270.

(35)

Kortshagen, U. R.; Sankaran, R. M.; Pereira, R. N.; Girshick, S. L.; Wu, J. J.; Aydil, E. S. Nonthermal Plasma Synthesis of Nanocrystals : Fundamental Principles , Materials , and Applications. Chem. Rev. 2016, 116, 11061–11127.

(36)

Lopez, T.; Mangolini, L. On the Nucleation and Crystallization of Nanoparticles in Continuous-Flow Nonthermal Plasma Reactors. J. Vac. Sci. Technol. B 2014, 32 (6), 061802.

(37)

Kortshagen, U.; Bhandarkar, U. Modeling of Particulate Coagulation in Low Pressure Plasmas. Phys. Rev. E - Stat. Nonlinear, Soft Matter Phys. 1999, 60 (1), 887–898.

(38)

Mangolini, L.; Kortshagen, U. Selective Nanoparticle Heating: Another Form of Nonequilibrium in Dusty Plasmas. Phys. Rev. E - Stat. Nonlinear, Soft Matter Phys. 2009, 79 (December 2008), 026405.

(39)

Blum, V.; Gehrke, R.; Hanke, F.; Havu, P.; Havu, V.; Ren, X.; Reuter, K.; Scheffler, M. Ab Initio Molecular Simulations with Numeric Atom-Centered Orbitals. Comput. Phys. Commun. 2009, 180 (11), 2175–2196.

(40)

Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865–3868. 31 ACS Paragon Plus Environment


(41)

Monkhorst, H. J.; Pack, J. D. Special Points for Brillouin-Zone Integrations. Phys. Rev. B 1976, 13 (12), 5188–5192.

(42)

Ni, M.; Leung, M. K. H.; Leung, D. Y. C.; Sumathy, K. A Review and Recent Developments in Photocatalytic Water-Splitting Using TiO2for Hydrogen Production. Renew. Sustain. Energy Rev. 2007, 11 (3), 401–425.

(43)

Schneider, J.; Bahnemann, D. W. Undesired Role of Sacrificial Reagents in Photocatalysis. J. Chem. Lett. 2013, 4, 3479–3483.

(44)

Ran, J.; Gao, G.; Li, F.; Ma, T.; Du, A.; Qiao, S. Photocatalytic Hydrogen Production from Liquid Methanol and Water. Chem. Commun. 1980, No. 384, 695.

(45)

Kandiel, T. A.; Dillert, R.; Bahnemann, D. W. Enhanced Photocatalytic Production of Molecular Hydrogen on TiO2 Modified with Pt-Polypyrrole Nanocomposites. Photochem. Photobiol. Sci. 2009, 8, 683–690.

(46)

Kandiel, T. A.; Dillert, R.; Robben, L.; Bahnemann, D. W. Photonic Efficiency and Mechanism of Photocatalytic Molecular Hydrogen Production over Platinized Titanium Dioxide from Aqueous Methanol Solutions. Catal. Today 2011, 161 (1), 196–201.

(47)

Sungbom, C.; Kawai, M.; Tanaka, K. XPS Studies of the Platinum Species Photodeposited on Titania from Aqueous Chloroplatinic Acid. Chem. Soc. Japan 1984, 57, 871–872.

(48)

Lee, J.; Choi, W. Photocatalytic Reactivity of Surface Platinized TiO 2 : Substrate Specificity and the Effect of Pt Oxidation State. J. Phys. Chem. B 2005, 109, 7399– 7406. 32 ACS Paragon Plus Environment

Page 32 of 35

Page 33 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(49)

Schreier, M.; Regalbuto, J. R. A Fundamental Study of Pt Tetraammine Impregnation of Silica: 1. The Electrostatic Nature of Platinum Adsorption. J. Catal. 2004, 225 (1), 190–202.

(50)

Jiao, L.; Regalbuto, J. R. The Synthesis of Highly Dispersed Noble and Base Metals on Silica via Strong Electrostatic Adsorption: II. Mesoporous Silica SBA-15. J. Catal. 2008, 260 (2), 342–350.

(51)

Lin, C.-S.; Khan, M. R.; Lin, S. D. The Preparation of Pt Nanoparticles by Methanol and Citrate. J. Colloid Interface Sci. 2006, 299, 678–685.

(52)

Tamaki, Y.; Furube, A.; Murai, M.; Hara, K.; Katoh, R.; Tachiya, M. Direct Observation of Reactive Trapped Holes in TiO2 Undergoing Photocatalytic Oxidation of Adsorbed Alcohols: Evaluation of the Reaction Rates and Yields. J. Am. Chem. Soc. 2006, 128, 416–417.

(53)

Ferguson, H.; Guler, U.; Kinsey, N.; Shalaev, V. M.; Norris, T.; Boltasseva, A. Interband Effects on Hot Carrier Relaxation in Titanium Nitride Films. In Conference on Lasers and Electro-Optics; 2017.

(54)

Saha, N. C.; Tompkins, H. G. Titanium Nitride Oxidation Chemistry : An x-Ray Photoelectron Spectroscopy Study. J. Appl. Phys. 1992, 72, 3072–3079.

(55)

Aslam, U.; Chavez, S.; Linic, S. Controlling Energy Flow in Multimetallic Nanostructures for Plasmonic Catalysis. Nat. Nanotechnol. 2017, 12, 1000–1005.

(56)

Habteyes, T. G.; Dhuey, S.; Wood, E.; Gargas, D.; Cabrini, S.; Schuck, P. J.; Alivisatos, A. P.; Leone, S. R. Metallic Adhesion Layer Induced Plasmon Damping and Molecular Linker as a Nondamping Alternative. ACS Nano 2012, 6 (6), 5702– 33 ACS Paragon Plus Environment


5709. (57)

Heilweil, E. J.; Hochstrasser, R. M. Nonlinear Spectroscopy and Picosecond Transient Grating Study of Colloidal Gold. J. Chem. Phys. 1985, 82, 4762–4770.

(58)

Li, K.; Hogan, N. J.; Kale, M. J.; Halas, N. J.; Nordlander, P.; Christopher, P. Balancing Near-Field Enhancement, Absorption, and Scattering for Effective Antenna-Reactor Plasmonic Photocatalysis. Nano Lett. 2017, 17 (6), 3710–3717.

(59)

Stucky, G. D.; Moskovits, M.; Mubeen, S.; Lee, J.; Singh, N.; Kra, S. An Autonomous Photosynthetic Device in Which All Charge Carriers Derive from Surface Plasmons. Nat. Nanotechnol. 2013, 8 (April), 247–251.

(60)

Kiskinova, M.; Pirug, G.; Bonzel, H. P. Coadsorption of Potassium and CO on Pt(111). Surf. Sci. 1983, 133, 321–343.

(61)

Alnot, M.; Ehrhardt, J. J.; Barnard, J. A. A Characterization of Heterogenous Pt Surfaces by Work Function Measurements and Photoemission of Adsorbed Xenon. Surf. Sci. 1989, 208, 285–305.

(62)

Sjöblom, G.; Westlinder, J.; Olsson, J. Investigation of the Thermal Stability of Reactively Sputter-Deposited TiN MOS Gate Electrodes. IEEE Trans. Electron Devices 2005, 52 (10), 2349–2352.

(63)

Matenoglou, G. M.; Koutsokeras, L. E.; Patsalas, P. Plasma Energy and Work Function of Conducting Transition Metal Nitrides for Electronic Applications. Appl. Phys. Lett. 2009, 94, 152108.


Page 34 of 35

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