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1. Flux‐mediated synthesis and photocatalytic activity of NaNbO ₃ particles

   https://doi.org/10.1111/jace.16765  

   Hamilton, Adam M. ; O'Donnell, Shaun ; Zoellner, Brandon ; Sullivan, Ian ; Maggard, Paul A. ( September 2019 , Journal of the American Ceramic Society)

   Using molten‐salt synthetic techniques, NaNbO₃(Space groupPbcm; No. 57) was prepared in high purity at a reaction time of 12 hours and a temperature of 900°C. All NaNbO₃products were prepared from stoichiometric ratios of Nb₂O₅and Na₂CO₃together 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 ofa = 5.512(5) Å,b = 5.567(3) Å, andc = 15.516(8) Å from the Na₂SO₄salt 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.more »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 NaNbO₃particles 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 Na₂SO₄flux 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 NaNbO₃prepared using the NaF flux, but this was doubled to 6.8% when prepared using the Na₂SO₄flux. 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.

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2. Cooperative Supramolecular Polymerization of Triphenylamine bis‐Urea Macrocycles

   https://doi.org/10.1002/chem.202300698  

   Prakash, Rahul ; Islam, Md Faizul ; Kothalawala, Rajeen Madawa ; Hossain, Muhammad Saddam ; Smith, Mark D. ; Shimizu, Linda S. ( May 2023 , Chemistry – A European Journal)

   Herein, we probe the hydrogen bond‐driven self‐assembly of a triphenylamine (TPA) bis‐urea macrocycle in the presence and absence of guests. Comprised of methylene urea‐bridged TPAs with exterior tridodecyloxy benzene solubilizing groups, the macrocycle exhibits concentration‐dependent aggregate formation in THF and H₂O/THF mixtures as characterized by¹H NMR and DOSY experiments. Its assembly processes were further probed by temperature‐dependent UV/Vis and fluorescence spectroscopy. Upon heating, UV/Vis spectra exhibit a hypsochromic shift in the λ_max, while fluorescence spectra show an increase in emission intensity. Conversely, the protected macrocycle that lacks hydrogen bond donors demonstrates no significant change. Thermodynamic analysis indicates a cooperative self‐assembly pathway with distinct nucleation and elongation regimes. The morphology and structure of the aggregate were elucidated by dynamic light scattering, atomic force microscopy, scanning and transmission electron microscopy. Variable temperature emission spectra were utilized to monitor the impact of guests, such as diphenylacetylene, that can be bound in the columnar channels. The findings suggest that the elongation of assemblies is influenced by the presence of these guests. In comparison, diphenyl sulfoxide, likely functioning as a chain stopper, limited the assembly size. These studies suggest that judicious selection of (co)monomers may modulate the function and utility of these supramolecular systems.
3. Alpha Lead Oxide (α‐PbO): A New 2D Material with Visible Light Sensitivity

   https://doi.org/10.1002/smll.201703346  

   Kumar, Prashant ; Liu, Jing ; Ranjan, Pranay ; Hu, Yaowu ; Yamijala, Sharma SRKC ; Pati, Swapan K. ; Irudayaraj, Joseph ; Cheng, Gary J. ( February 2018 , Small)

   Even though transition metal dichalcogenides (TMDCs) are deemed to be novel photonic and optoelectronic 2D materials, the visible band gap being often limited to monolayer, hampers their potential in niche applications due to fabrication challenges. Uncontrollable defects and degraded functionalities at elevated temperature and under extreme environments further restrict their prospects. To address such limitations, the discovery of a new 2D material, α‐PbO is reported. Micromechanical as well as sonochemical exfoliation of 2D atomic sheets of α‐PbO are demonstrated and its optical behavior is investigated. Spectroscopic investigations indicate layer dependent band gaps. In particular, even multilayered PbO sheets exhibit visible band gap > 2 eV (direct) which is rare among semiconducting 2D materials. The emission lifetime of multilayer PbO atomic sheets is 7 ns (dim light) as compared to the monolayer which gives 2.5 ns lifetime and an intense light. Density functional theory calculations of layer dependent band structure of α‐PbO matches well with experimental results. Experimental findings suggest that PbO atomic sheets exhibit hydrophobic nature, thermal robustness, microwave stability, anti‐corrosive behaviour and acid resistance. This new low‐cost, abundant and robust 2D material is expected to find many applications in the fields of electronics, optoelectronics, sensors, photocatalysis and energymore »storage.

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4. UV/Peracetic Acid for Degradation of Pharmaceuticals and Reactive Species Evaluation

   https://doi.org/https://doi.org/10.1021/acs.est.7b04694  

   Cai, M. ; Sun, P. ; Zhang, L. ; Huang, C.-H. ( January 2017 , Environmental science & technology)

   Peracetic acid (PAA) is a widely used disinfectant, and combined UV light with PAA (i.e. UV/PAA) can be a novel advanced oxidation process for elimination of water contaminants. This study is among the first to evaluate the photolysis of PAA under UV irradiation (254 nm) and degradation of pharmaceuticals by UV/PAA. PAA exhibited high quantum yields (Φ254nm = 1.20 and 2.09 mol·Einstein−1 for the neutral (PAA0) and anionic (PAA-) species, respectively) and also showed scavenging effects on hydroxyl radicals (k•OH/PAA0 = (9.33±0.3)×108 M−1·s−1 and k•OH/PAA- = (9.97±2.3)×109 M−1·s−1). The pharmaceuticals were persistent with PAA alone but degraded rapidly by UV/PAA. The contributions of direct photolysis, hydroxyl radicals, and other radicals to pharmaceutical degradation under UV/PAA were systematically evaluated. Results revealed that •OH was the primary radical responsible for the degradation of carbamazepine and ibuprofen by UV/PAA, whereas CH3C(=O)O• and/or CH3C(=O)O2• contributed significantly to the degradation of naproxen and 2-naphthoxyacetic acid by UV/PAA in addition to •OH. The carbon-centered radicals generated from UV/PAA showed strong reactivity to oxidize certain naphthyl compounds. The new knowledge obtained in this study will facilitate further research and development of UV/PAA as a new degradation strategy for water contaminants.
5. Thermally Stimulated Depolarization Current Measurements on Degraded Lead Zirconate Titanate Films

   https://doi.org/10.1039/d1tc02668  

   Akkopru-Akgun, Betul ; Marincel, Daniel M. ; Tsuji, Kosuke ; Bayer, Thorsten J.M. ; Randall, Clive A. ; Lanagan, Michael T. ; and Trolier-McKinstry, Susan ( October 2021 , Journal of the American Ceramic Society)

   Charge transport mechanisms governing DC resistance degradation in ferroelectric films are influenced by defects, particularly oxygen vacancies. This paper demonstrates that oxygen vacancies migrate in lead zirconate titanate (PZT) films under a DC bias field and contribute to resistance degradation. Model PZT thin films were developed in which the concentration and distribution of oxygen vacancies were controlled via (a) changing the dopant type and concentration from 1%–4% Mn (acceptor) to 1%–4% Nb (donor) or (b) annealing undoped PZT films at varying partial pressures of PbO. The presence of associated (immobile) and dissociated (mobile) oxygen vacancies was distinguished by thermally stimulated depolarization current (TSDC) measurements. The impact of mobile oxygen vacancies on local defect chemistry and associated charge transport mechanisms was explored by electron energy loss spectroscopy (EELS). For Mn-doped PZT films, following resistance degradation, TSDC studies revealed only one depolarization peak with an activation energy of 0.6–0.8 eV; this peak was associated with ionic space charge presumably due to migration of oxygen vacancies. The magnitude of the depolarization current peak increased with increasing degradation times. A similar depolarization current peak attributed to the existence of mobile oxygen vacancies was also observed for undoped and Nb-doped PZT films; the magnitude ofmore »this peak decreased as the Nb or PbO contents in PZT films increased. An additional TSDC peak associated with polaron hopping between Ti3+ and Ti4+ was found in both Nb-doped PZT films and undoped PZT films annealed under low PbO partial pressure. Degraded Nb-doped samples exhibited a chemical shift in the TiL2,3 peak to lower energy losses and the appearance of shoulders on the t2g and eg peaks, implying a reduction of Ti cations in regions near the cathode.« less