The doping of foreign cations and anions is one of the effective strategies for engineering defects and modulating the optical, electronic, and surface properties that directly govern the photocatalytic O 2 and H 2 evolution reactions. BaTaO 2 N (BTON) is a promising 600 nm-class photocatalyst because of its absorption of visible light up to 660 nm, small band gap (E g = 1.9 eV), appropriate valence band-edge position for oxygen evolution, good stability under light irradiation in concentrated alkaline solutions, and nontoxicity. Although the photocatalytic and photoelectrochemical water-splitting efficiencies of BaTaO 2 N have been progressively improved, it is still far from the requirements set for practical applications. Here, we employ a 5% B site-selective doping of aliovalent metal cations (Al 3+ , Ga 3+ , Mg 2+ , Sc 3+ , and Zr 4+ ) to enhance sacrificial visible light-induced photocatalytic H 2 and O 2 evolution over BaTaO 2 N. The results of physicochemical characterizations reveal that no significant change in crystal structure, crystal morphology, and optical absorption edge is observed upon cation doping. Therefore, the difference observed in O 2 and H 2 evolution during the photocatalytic reactions over pristine and doped BaTaO 2 N photocatalysts is explained by examining optical, electronic, and surface properties. Also, molecular dynamics (MD) is used to gain insights into the respective effect of cation doping on adsorption energy of water molecules and formed intermediates (H* for H 2 evolution and HO*, O*, and HOO* for O 2 evolution) on the BaTaO 2 N surfaces terminated with TaO 6 , TaN 6 , and TaO 4 N 2 octahedra. Finally, the experimental reaction rates for H 2 and O 2 evolution are correlated well using a linear energy−performance relationship, elucidating the doping and surface-termination trends observed in the BaTaO 2 N photocatalysts.

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In this communication, a remote experimental activity in chemical kinetics is described, taking into account the quantification based on the optical sensor of a smartphone. The objective pursued herein is to equip students with the appropriate tools and strategies required to empirically determine the parameters of the rate law including reaction orders, rate constant (k), frequency factor (A), and activation energy (E a ). Typical results of the proposed protocol are shown and discussed in the framework of the bleaching reaction of food dye allura red (RD40) and hypochlorite, as a representative example. A graphical approach of the concentration vs time data measured under the experimental condition where [RD40] ≪ [ClO − ] (isolation method) suggests a first-order kinetics with respect to the dye. In addition, the analysis of the pseudo-first-order constant (k obs ) shows a firstorder relationship with respect to ClO − . In addition, using the two-point form of the Arrhenius equation, values of 3.22 × 10 7 s/M and 44.55 kJ/mol were obtained for A and E a , respectively. Interestingly, all the kinetic parameters (reaction orders, k, A, and E a ) are on the same order of magnitude as those previously reported in the literature and acquired with more sophisticated and accurate equipment. This experience provides evidence that it is possible to proceed with remote experimental activities to deepen the collection and analysis of kinetic data during a pandemic.

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Among 600 nm class transition-metal oxynitrides, BaTaO2N with a cubic Pm3̅m perovskite-type structure is promising for solar water oxidation due to its absorption of visible light up to 660 nm, narrower band gap (E g = 1.9 eV), appropriate valence band edge position for oxygen evolution, good stability in concentrated alkaline solutions, and nontoxicity. However, high defect density stemmed from long high-temperature ammonolysis limits the separation and transfer efficiency of photogenerated charge carriers in BaTaO2N. Here, a NH3 delivery system is specifically localized just above the synthesis mixture to reduce the synthesis time and defect density of BaTaO2N by a fresh supply of more active nitriding species and minimizing the generation of N2 and H2. Particularly, the effects of synthesis temperature (700–950 °C), synthesis time (1–8 h), and gas composition are systematically investigated to gain insights into the formation of single-phase BaTaO2N by solid-state reaction and flux method. Time-dependent experiments conducted at 950 °C show that single-phase BaTaO2N can be synthesized ≥6 and ≥4 h by solid-state reaction and flux method, respectively, revealing the advantage of the flux method over solid-state reaction in a localized NH3 delivery system. Subsequently, the separation and transfer efficiency and kinetics of photogenerated charge carriers are studied in BaTaO2N samples. Photoelectrochemical studies made it possible to resolve trends during visible-light-induced water oxidation, evidencing the inverse relationship between recombination and charge transfer phenomena. Transient absorption spectroscopy reveals that the dynamics of the photogenerated charge carriers in both types of BaTaO2N samples are different: (i) BaTaO2N synthesized by flux method has a greater number of holes despite the similar number of deeply trapped charge carriers and (ii) solid-state reaction led to the formation of a higher number of free electrons in BaTaO2N. The findings demonstrate the advantage of reducing the transfer distance of active nitriding species to the surface of the synthesis mixture for enhancing the photoelectrochemical water oxidation of BaTaO2N at neutral pH.

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Trigonal ZnIn2S4 layered crystals were grown by a binary flux method using ZnS-containing industrial waste.