For the first time, octahedral NiGa₂O₄ nanocrystals having reactive pH-dependent {111} facets are synthesized through a facile hydrothermal route without using any template or organic surfactant. The {111} facets of octahedral NiGa₂O₄ display clearly enhanced photocatalytic generation of hydrogen and oxygen from water splitting and good photocatalytic stability. Density functional calculations suggest that mixed statistically occupied Ga/Ni (fourfold- and sixfold-coordinated Ga/Ni) are most likely to be exposed at the (111) surface of NiGa₂O₄, which is very favorable for enhancing the photocatalytic activities, and the photoelectrochemical properties show that the NiGa₂O₄ octahedron displays a better photocurrent than NiGa₂O₄ nanorods with the [100] growth direction. The transient photocurrent decay scan results demonstrate that the NiGa₂O₄ octahedron exposed {111} facet electrode exhibits a transient decay time of 4 s, whereas this time is only 2 s for NiGa₂O₄ nanorod electrodes with the [100] growth direction. This longer transient decay time indicates that the charge-carrier recombination rate is lower in the NiGa₂O₄ octahedron electrode, which will contribute to the enhancement of the photocatalytic activity. The present study also demonstrates that designing nanostructures with the appropriate morphology and surface structures is a feasible approach for enhancing the photoexcited charge-transfer lifetime and developing highly active semiconductor photocatalysts.

Ammonia–borane (AB) is a promising chemical hydrogen-storage material. However, the development of real-time, efficient, controllable, and safe methods for hydrogen release under mild conditions is a challenge in the large-scale use of hydrogen as a long-term solution for future energy security. A new class of low-cost catalytic system is presented that uses nanostructured Ni₂P as catalyst, which exhibits excellent catalytic activity and high sustainability toward hydrolysis of ammonia–borane with the initial turnover frequency of 40.4 mol_(H2) mol_(Ni2P)⁻¹ min⁻¹ under air atmosphere and at ambient temperature. This value is higher than those reported for noble-metal-free catalysts, and the obtained Arrhenius activation energy (E_a=44.6 kJ mol⁻¹) for the hydrolysis reaction is comparable to Ru-based bimetallic catalysts. A clearly mechanistic analysis of the hydrolytic reaction of AB based on experimental results and a density functional theory calculation is presented.

Ammonia–borane (AB) is a promising chemical hydrogen-storage material. However, the development of real-time, efficient, controllable, and safe methods for hydrogen release under mild conditions is a challenge in the large-scale use of hydrogen as a long-term solution for future energy security. A new class of low-cost catalytic system is presented that uses nanostructured Ni₂P as catalyst, which exhibits excellent catalytic activity and high sustainability toward hydrolysis of ammonia–borane with the initial turnover frequency of 40.4 mol_(H2) mol_(Ni2P)⁻¹ min⁻¹ under air atmosphere and at ambient temperature. This value is higher than those reported for noble-metal-free catalysts, and the obtained Arrhenius activation energy (E_a=44.6 kJ mol⁻¹) for the hydrolysis reaction is comparable to Ru-based bimetallic catalysts. A clearly mechanistic analysis of the hydrolytic reaction of AB based on experimental results and a density functional theory calculation is presented.

Crystalline Fe nanoparticles were obtained with fluorescein (Fl) as the photosensitizer in triethylamine (TEA) or triethanolamine (TEOA) aqueous solution with FeCl₃ as the Fe precursor under bright visible-light light-emitting diode (LED) irradiation. Photoinduced electron transfer from excited state Fl* and Fl⁻ to Fe³⁺ produced the Fe nanoparticles, which served as the active catalyst for in situ photocatalytic hydrogen production with Fl and TEA or TEOA as the photosensitizer and electron donors, respectively, in the same system. Robust hydrogen production activities were observed under the Fe nanoparticle photoreduction conditions in basic solution, and tens of milliliters of hydrogen were obtained over prolonged LED irradiation. If inorganic support materials such as NH₂-MCM-41 or reduced graphene oxide were introduced, dispersed nanoparticles with different sizes and shapes were deposited on the supports, which led to variously enhanced hydrogen production activities. The relationships between the morphologies of the Fe/H₂N-MCM-41 or Fe/graphene composites generated in situ and the hydrogen production activities were investigated systematically.

Four new charge-neutral ruthenium(II) complexes containing dianionic Schiff base and isoquinoline or 4-picoline ligands were synthesized and characterized by NMR and ESI-MS spectroscopies, elemental analysis, and X-ray diffraction. The complexes exhibited excellent chemical water oxidation activity and high stability under acidic conditions (pH 1.0) using (NH₄)₂Ce(NO₃)₆ as a sacrificial electron acceptor. The high catalytic activities of these complexes for water oxidation were sustained for more than 10 h at low concentrations. High turnover numbers of up to 3200 were achieved. A water nucleophilic attack mechanism was proposed. A Ru^VO intermediate was detected during the catalytic cycle by high-resolution mass spectrometry.

Two mononuclear ruthenium complexes [Ru(H₂tcbp)(isoq)₂] (1) and [Ru(H₂tcbp)(pic)₂] (2) (H₄tcbp=4,4′,6,6′-tetracarboxy-2,2′-bipyridine, isoq=isoquinoline, pic=4-picoline) are synthesized and fully characterized. Two spare carboxyl groups on the 4,4′-positions are introduced to enhance the solubility of 1 and 2 in water and to simultaneously allow them to tether to the electrode surface by an ester linkage. The photochemical, electrochemical, and photoelectrochemical water oxidation performance of 1 in neutral aqueous solution is investigated. Under electrochemical conditions, water oxidation is conducted on the deposited indium-tin-oxide anode, and a turnover number higher than 15,000 per water oxidation catalyst (WOC) 1 is obtained during 10 h of electrolysis under 1.42 V vs. NHE, corresponding to a turnover frequency of 0.41 s⁻¹. The low overpotential (0.17 V) of electrochemical water oxidation for 1 in the homogeneous solution enables water oxidation under visible light by using [Ru(bpy)₃]²⁺ (P1) (bpy=2,2′-bipyridine) or [Ru(bpy)₂(4,4′-(COOEt)₂-bpy)]²⁺ (P2) as a photosensitizer. In a three-component system containing 1 or 2 as a light-driven WOC, P1 or P2 as a photosensitizer, and Na₂S₂O₈ or [CoCl(NH₃)₅]Cl₂ as a sacrificial electron acceptor, a high turnover frequency of 0.81 s⁻¹ and a turnover number of up to 600 for 1 under different catalytic conditions are achieved. In a photoelectrochemical system, the WOC 1 and photosensitizer are immobilized together on the photoanode. The electrons efficiently transfer from the WOC to the photogenerated oxidizing photosensitizer, and a high photocurrent density of 85 μA cm⁻² is obtained by applying 0.3 V bias vs. NHE.

Four new 1,8-naphthyridine derivatives were synthesized by reacting the parent molecules with aldehydes and characterized. Two of the compounds have completely new and unusual skeletons, and display red-fluorescence emissions and two-photon absorption. Their structures were determined using MS, 1D and 2D NMR, and density functional theory calculations. The structural investigations of 2-methyl-1,8-naphthyridine hydrochloride and hydrobromide showed that abundant hydrogen-bonds and π- π interactions lead to extended networks.