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Two series of bimetallic photocatalysts (0.5% Pt/0.01–0.5% IrOx/g-C3N4 and 0.1% Pt/0.01–0.1% IrOx/g-C3N4) were synthesized by the thermolysis of melamine cyanurate and a successive deposition of platinum and iridium labile complexes (Me4N)2[Pt2(μ-OH)2(NO3)8] and fac-[Ir(H2O)3(NO2)3. The synthesized photocatalysts were studied by a set of physicochemical analysis techniques. Platinum exists in two states, with up to 60% in metallic form and the rest in the Pt2+ state, while iridium is primarily oxidized to the Ir3+ state, which was determined by X-ray photoelectron spectroscopy (XPS). The specific surface area (SBET), which is determined by low-temperature nitrogen adsorption, ranges from 80 to 100 m2 g−1 and the band gap energy (Eg) value is in the range of 2.75–2.80 eV as found by diffuse reflectance spectroscopy (DRS). The activity of the photocatalysts was tested in the photocatalytic production of hydrogen from ultrapure water under visible light (λ = 400 nm). It was found that the splitting of water occurs with the formation of the stochiometric amount of H2O2 as an oxidation product. Two photocatalysts 0.5% Pt/0.01% IrOx/g-C3N4 and 0.1% Pt/0.01% IrOx/g-C3N4 showed the highest activity at 100 μmol h−1 gcat−1, which is among the highest in H2 production published for such systems. [ABSTRACT FROM AUTHOR]

The first fully inorganic Pt(IV) carbonato-complex trans -[Pt(CO 3 ) 2 (OH) 2 ] 2- with a {PtO 6 } coordination sphere was isolated as the (Me 4 N) 2 [Pt(CO 3 ) 2 (OH) 2 ] ( 1 ) salt. The compound 1 was characterized using single-crystal and powder X-ray diffraction, Raman spectroscopy, infrared spectroscopy (FTIR), electrospray ionization mass spectrometry (ESI-MS), nuclear magnetic resonance spectroscopy (NMR), and thermogravimetric analysis (TG). Density functional theory (DFT) calculations were also performed to analyze the spectral features of the complex. 1 crystallizes in the triclinic system (P-1) with a Z of 1. The trans -[Pt(CO 3 ) 2 (OH) 2 ] 2- anion has axial hydroxo ligands and κ 2 -CO 3 ligands, which form an equatorial plane. This anionic complex exhibits notable stability in aqueous solutions, while the axial hydroxo ligand can be readily modified, as exemplified by the acylation of the trans -[Pt(CO 3 ) 2 (OH) 2 ] 2- into trans -[Pt(CO 3 ) 2 (OAc) 2 ] 2- anion. Furthermore, it has been shown that rigid and glittering platinum coatings can be electrochemically deposited from an aqueous solution of 1 without the addition of surfactants.

A combination of the exceptional stability of fac -[Ir(H 2 O) 3 (NO 2 ) 3 ] together with thermolability of nitro and aqua ligands and high solubility in various solvents makes it promising as a brand-new chlorine-free precursor of iridium for the preparation of heterogeneous catalysts. In the current work, a new technique of fac -[Ir(H 2 O) 3 (NO 2 ) 3 ] preparation based on hydrothermal treatment of (NH 4 ) 3 [Ir(NO 2 ) 6 ] was developed. For this purpose, the influence of reaction parameters such as the reaction time, temperature, and pH of the solution on the process of hexanitroiridate salt hydrolysis was investigated. The synthesized fac -[Ir(H 2 O) 3 (NO 2 ) 3 ] solution in this optimized way was used for the preparation of the series of Ir/g-C 3 N 4 catalysts, which were evaluated in the water oxidation reaction with NaIO 4 utilized as a sacrificial reagent. A 20-fold enhancement of the oxygen evolution reaction (OER) activity was found to take place under visible light (λ = 411 nm) illumination of the systems. The highest rate of the photoinduced OER per iridium center was achieved by the Ir 0.005 /g-C 3 N 4 (air, 400°C) catalyst with an exceptional turnover frequency value of 967 min -1 approaching the activity of known homogeneous iridium OER catalysts. The leaching experiments have shown that aquated Ir species are generated in a solution after prolonged functioning of the catalysts. Despite this, in the closed system the photodriven OER activity persists at a steady-state level evidencing an equilibrium achieved between dissolved and anchored Ir species forming catalytic tandem with the g-C 3 N 4 .

An efficient method for the deposition of ionic platinum species PtO x onto a TiO 2 surface was developed on the basis of light-induced activation of the [Pt(NO 3 ) 6 ] 2- anion. The deposited PtO x species with an effective Pt oxidation state between +4 and +2 have an oxygen-made environment and include single ion centers {PtO n } and polyatomic ensembles {Pt n O m } connected to a TiO 2 surface with Pt-O-Ti bonds. The resulting PtO x /TiO 2 materials were tested as photocatalysts for the hydrogen evolution reaction (HER) from a water ethanol mixture and have shown uniquely high activity with the rate of H 2 evolution achieving 11 mol h -1 per gram of Pt, which is the highest result for such materials reported to date. A combination of spectral methods shows that, under HER conditions, reduction of the supported PtO x species leads to the formation of well-dispersed nanoparticles of metallic platinum attached on the surface of TiO 2 by Ti-O-Pt bonds. The high activity of the PtO x /TiO 2 materials is believed to result from a combination of uniform distribution of small platinum nanoparticles over the titania surface and their close interaction with TiO 2 .

A series of tetraalkylammonium salts with anionic platinum nitrato complexes (Me 4 N) 2 [Pt 2 (μ-OH) 2 (NO 3 ) 8 ] (1), (Et 4 N) 2 [Pt 2 (μ-OH) 2 (NO 3 ) 8 ] (2), ( n-Pr 4 N) 2 [Pt 2 (μ-OH) 2 (NO 3 ) 8 ] (3b), ( n-Pr 4 N) 2 [Pt(NO 3 ) 6 ] (3a), and ( n-Bu 4 N) 2 [Pt(NO 3 ) 6 ] (4) were isolated from nitric acid solutions of [Pt(H 2 O) 2 (OH) 4 ] in high yield. The structures of salts 2, 3a, 3b, and 4, prepared for the first time, were characterized by X-ray diffraction. The sorption of [Pt(NO 3 ) 6 ] 2- and [Pt 2 (μ-OH) 2 (NO 3 ) 8 ] 2- complexes onto the ceria surface from acetone solutions of salts 4 and 1 was examined. The dimeric anion was shown to quickly and irreversibly chemisorb onto the CeO 2 carrier, selectively transforming into Pt(II) centers after thermal treatment, becoming active in the low-temperature CO oxidation reaction ( T 50% = 110 °C at a space velocity of 240 000 h -1 ). By contrast, the homoleptic complex [Pt(NO 3 ) 6 ] 2- did not interact with the ceria, which may be attributed to the substitutional inertness of the [Pt(NO 3 ) 6 ] 2- anion. We believe that the strategy based on the sorption of polynuclear platinum nitrato complexes is an effective route to prepare ionic platinum species uniformly distributed on an oxide carrier for various catalytic applications.