@article{hamilton_o'donnell_zoellner_sullivan_maggard_2020, title={Flux‐mediated synthesis and photocatalytic activity of NaNbO
            3
            particles}, volume={103}, ISSN={0002-7820 1551-2916}, url={http://dx.doi.org/10.1111/jace.16765}, DOI={10.1111/jace.16765}, abstractNote={Using molten-salt synthetic techniques, NaNbO3 (Space group Pbcm; No. 57) was prepared in high purity at a reaction time of 12 hours and a temperature of 900°C. All NaNbO3 products were prepared from stoichiometric ratios of Nb2O5 and Na2CO3 together with the addition of a salt flux introduced at a 10:1 molar ratio of salt to NaNbO3, that is, using the Na2SO4, NaF, NaCl, and NaBr salts. A solid-state synthesis was performed in the absence of a molten salt to serve as a control. The reaction products were all found to be phase pure through powder X-ray diffraction, for example, with refined lattice constants of a = 5.512(5) Å, b = 5.567(3) Å, and c = 15.516(8) Å from the Na2SO4 salt reaction. The products were characterized using UV-Vis diffuse reflectance spectroscopy to have a bandgap size of ~3.5 eV. The particles sizes were analyzed by scanning electron microscopy (SEM) and found to be dependent upon the flux type used, from ~<1 μm to >10 μm in length, with overall surface areas that could be varied from 0.66 m2/g (for NaF) to 1.55 m2/g (for NaBr). Cubic-shaped particle morphologies were observed for the metal halide salts with the set of exposed (100)/(010)/(001) crystal facets, while a truncated octahedral morphology formed in the sodium sulfate salt reaction with predominantly the set of (110)/(101)/(011) crystal facets. The products were found to be photocatalytically active for hydrogen production under UV-Vis irradiation, with the aid of a 1 wt% Pt surface cocatalyst. The platinized NaNbO3 particles were suspended in an aqueous 20% methanol solution and irradiated by UV-Vis light (λ > 230 nm). After 6 hours of irradiation, the average total hydrogen production varied with the particle morphologies and sizes, with 753 µmol for Na2SO4, 334 µmol for NaF, 290 µmol for NaCl, 81 µmol for NaBr, and 249 µmol for the solid-state synthesized NaNbO3. These trends show a clear relationship to particle sizes, with smaller particles showing higher photocatalytic activity in the order of NaF > NaCl > NaBr. Furthermore, the particle morphologies obtained from the Na2SO4 flux showed even higher photocatalytic activity, though having a relatively similar overall surface area, owing to the higher activity of the (110) crystal facets. The apparent quantum yield (100 mW/cm2, λ = 230 to 350 nm, pH = 7) was measured to be 3.7% for NaNbO3 prepared using the NaF flux, but this was doubled to 6.8% when prepared using the Na2SO4 flux. Thus, these results demonstrate the powerful utility of flux synthetic techniques to control particle sizes and to expose higher-activity crystal facets to boost their photocatalytic activities for molecular hydrogen production.}, number={1}, journal={Journal of the American Ceramic Society}, publisher={Wiley}, author={Hamilton, Adam M. and O'Donnell, Shaun and Zoellner, Brandon and Sullivan, Ian and Maggard, Paul A.}, year={2020}, month={Jan}, pages={454–464} }
 @misc{sullivan_zoellner_maggard_2016, title={Copper(I)-Based p-Type Oxides for Photoelectrochemical and Photovoltaic Solar Energy Conversion}, volume={28}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.6b00926}, abstractNote={Recent research efforts have been growing into p-type copper(I) based oxides for development of their use in solar energy applications. The oxides of interest include the binary Cu2O and a number of new ternary CuxMyOz oxides. Both the binary and ternary Cu(I)-based oxides have many advantages when compared to other well-known p-type oxides such as NiO, III–V, and II–VI semiconductors. The benefits found within the diverse group of Cu(I)-containing oxides include bandgap sizes that can be tuned from ∼1.2 to >3.0 eV, high charge carrier mobility, and favorable band energies relative to fuel-producing redox couples. These properties give them potential utility in a variety of different solar applications, such as in dye-sensitized solar cells and suspended powder photocatalysis. Research efforts into surface modifications and changes in their chemical compositions and structures have allowed for greater stability and greater efficiency in aqueous solutions, both of which have represented two key barriers fo...}, number={17}, journal={CHEMISTRY OF MATERIALS}, author={Sullivan, Ian and Zoellner, Brandon and Maggard, Paul A.}, year={2016}, month={Sep}, pages={5999–6016} }
 @article{boltersdorf_sullivan_shelton_wu_gray_zoellner_osterloh_maggard_2016, title={Flux Synthesis, Optical and Photocatalytic Properties of n-type Sn2TiO4: Hydrogen and Oxygen Evolution under Visible Light}, volume={28}, ISSN={["1520-5002"]}, DOI={10.1021/acs.chemmater.6b02003}, abstractNote={The n-type Sn2TiO4 phase was synthesized using flux methods and found to have one of the smallest visible-light bandgap sizes known that also maintains suitable conduction and valence band energies for driving photocatalytic water-splitting reactions. The Sn2TiO4 phase was synthesized using either a SnCl2 flux or a SnCl2/SnF2 peritectic flux in a 2:1 flux-to-precursor ratio heated at 600 and 400 °C for 24 h, respectively. The two types of salt fluxes resulted in large rod-shaped particles at 600 °C and smaller tetragonal prism-shaped particles at 400 °C. Surface photovoltage spectroscopy measurements produced a negative photovoltage under illumination >1.50 eV, which confirmed electrons as the majority charge carriers and ∼1.50 eV as the effective band gap. Mott–Schottky measurements at pH 9.0 showed the conduction (−0.54 V vs NHE) and valence band (+1.01 V vs NHE) positions meet the critical thermodynamic requirements for total water splitting. The Sn2TiO4 particles were deposited and annealed as polycry...}, number={24}, journal={CHEMISTRY OF MATERIALS}, author={Boltersdorf, Jonathan and Sullivan, Ian and Shelton, Timothy L. and Wu, Zongkai and Gray, Matthew and Zoellner, Brandon and Osterloh, Frank E. and Maggard, Paul A.}, year={2016}, month={Dec}, pages={8876–8889} }
 @article{king_sullivan_watkins-curry_chan_maggard_2016, title={Flux-mediated syntheses, structural characterization and low-temperature polymorphism of the p-type semiconductor Cu2Ta4O11}, volume={236}, ISSN={["1095-726X"]}, DOI={10.1016/j.jssc.2015.08.041}, abstractNote={A new low-temperature polymorph of the copper(I)-tantalate, α-Cu2Ta4O11, has been synthesized in a molten CuCl-flux reaction at 665 °C for 1 h and characterized by powder X-ray diffraction Rietveld refinements (space group Cc (#9), a=10.734(1) Å, b=6.2506(3) Å, c=12.887(1) Å, β=106.070(4)°). The α-Cu2Ta4O11 phase is a lower-symmetry monoclinic polymorph of the rhombohedral Cu2Ta4O11 structure (i.e., β-Cu2Ta4O11 space group R3̅c (#167), a=6.2190(2) Å, c=37.107(1) Å), and related crystallographically by ahex=amono/√3, bhex=bmono, and chex=3cmonosinβmono. Its structure is similar to the rhombohedral β-Cu2Ta4O11 and is composed of single layers of highly-distorted and edge-shared TaO7 and TaO6 polyhedra alternating with layers of nearly linearly-coordinated Cu(I) cations and isolated TaO6 octahedra. Temperature dependent powder X-ray diffraction data show the α-Cu2Ta4O11 phase is relatively stable under vacuum at 223 K and 298 K, but reversibly transforms to β-Cu2Ta4O11 by at least 523 K and higher temperatures. The symmetry-lowering distortions from β-Cu2Ta4O11 to α-Cu2Ta4O11 arise from the out-of-center displacements of the Ta 5d0 cations in the TaO7 pentagonal bipyramids. The UV–vis diffuse reflectance spectrum of the monoclinic α-Cu2Ta4O11 shows an indirect bandgap transition of ∼2.6 eV, with the higher-energy direct transitions starting at ∼2.7 eV. Photoelectrochemical measurements on polycrystalline films of α-Cu2Ta4O11 show strong cathodic photocurrents of ∼1.5 mA/cm2 under AM 1.5 G solar irradiation.}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={King, Nacole and Sullivan, Ian and Watkins-Curry, Pilanda and Chan, Julia Y. and Maggard, Paul A.}, year={2016}, month={Apr}, pages={10–18} }
 @article{sullivan_brown_llansola-portoles_gervaldo_kodis_moore_gust_moore_maggard_2015, title={Photoinjection of High Potential Holes into Cu5Ta11O30 Nanoparticles by Porphyrin Dyes}, volume={119}, ISSN={["1932-7447"]}, DOI={10.1021/acs.jpcc.5b02174}, abstractNote={Excited-state hole injection into the valence band of Cu5Ta11O30 nanoparticles (NP-Cu5Ta11O30) was investigated through sensitization with zinc porphyrin dyes using simulated solar irradiance. The Cu5Ta11O30 nanoparticles were prepared by a flux-mediated synthesis and found to have an average particle size of ∼10–15 nm by DLS and TEM. The zinc 4-(10,15,20-tris(4-pyridinyl)-porphin-5-yl)phenylphosphonic acid (D1) and its analogue, in which the pyridine groups are methylated (D2), were synthesized and found to have excited-state reduction potentials appropriate for p-type dye sensitization of the nanoparticles. The dye-sensitized NP-Cu5Ta11O30 exhibited fluorescence quenching consistent with electron transfer from the NP-Cu5Ta11O30 to the dye; forward and recombination rates were obtained by transient absorption measurements. Hole injection times of 8 ps and <100 fs were observed for D1 and D2, respectively. Nanoparticulate films of Cu5Ta11O30 were prepared and evaluated in dye-sensitized solar cells under simulated solar irradiance (AM 1.5 G, 100 mW/cm2). Measurable photocurrents and open-circuit potentials (Voc) of 200 and 110 mV were observed using D1 and D2, respectively.}, number={37}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Sullivan, Ian and Brown, Chelsea L. and Llansola-Portoles, Manuel J. and Gervaldo, Miguel and Kodis, Gerdenis and Moore, Thomas A. and Gust, Devens and Moore, Ana L. and Maggard, Paul A.}, year={2015}, month={Sep}, pages={21294–21303} }
 @article{sullivan_sahoo_fuoco_hewitt_stuart_dougherty_maggard_2014, title={Cu-Deficiency in the p-Type Semiconductor Cu5–xTa11O30: Impact on Its Crystalline Structure, Surfaces, and Photoelectrochemical Properties}, volume={26}, ISSN={0897-4756 1520-5002}, url={http://dx.doi.org/10.1021/CM502891T}, DOI={10.1021/cm502891t}, abstractNote={The p-type semiconductor Cu5Ta11O30 has been investigated for the effect of Cu extrusion on its crystalline structure, surface chemistry, and photoelectrochemical properties. The Cu5Ta11O30 phase was prepared in high purity using a CuCl-mediated flux synthesis route, followed by heating the products in air from 250 to 750 °C in order to investigate the effects of its reported film preparation conditions as a p-type photoelectrode. At 650 °C and higher temperatures, Cu5Ta11O30 is found to decompose into CuTa2O6 and Ta2O5. At lower temperatures of 250 to 550 °C, nanosized CuIIO surface islands and a Cu-deficient Cu5–xTa11O30 crystalline structure (i.e., x ∼ 1.8(1) after 450 °C for 3 h in air) is found by electron microscopy and Rietveld structural refinement results, respectively. Its crystalline structure exhibits a decrease in the unit cell volume with increasing reaction temperature and time, owing to the increasing removal of Cu(I) ions from its structure. The parent structure of Cu5Ta11O30 is conserved...}, number={23}, journal={Chemistry of Materials}, publisher={American Chemical Society (ACS)}, author={Sullivan, Ian and Sahoo, Prangya P. and Fuoco, Lindsay and Hewitt, Andrew S. and Stuart, Sean and Dougherty, Daniel and Maggard, Paul A.}, year={2014}, month={Nov}, pages={6711–6721} }