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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]

Graphitic carbon nitride g-C3N4 has been modified using platinum and platinum oxide (0.5–5 wt.%) and studied in photocatalytic H2 evolution reactions with ethanol aqueous solution under visible light irradiation (λ = 409 nm). An analysis of the by-products of the reaction (CO2, CH4, C2H6 etc.) was also carried out. The morphology, particle size distribution, and optical properties of the photocatalysts, and the chemical states of platinum cations were examined using various methods. The photocatalysts were investigated using a wide range of methods to clarify the morphology, particle size distribution, optical properties, and the chemical states of platinum cations. Factors affecting not only the activity, but also the selectivity of the photocatalyst in the target process of hydrogen production, have been established. The highest rate of H2 evolution achieved over 0.5 wt.% Pt/g-C3N4 photocatalyst is 0.6 mmol h−1 g−1 (selectivity 98.9%), which exceeds the activity of pristine g-C3N4 by 250 times. Increasing the Pt or PtO content up to 5 wt.% leads to an increase in the rate of formation of by-products (CH4, C2H6, and CO2) and a decrease in the selectivity of H2 evolution. The study also delves into the role of platinum and the mechanism of charge transfer in PtO/g-C3N4 and Pt/g-C3N4 photocatalysts due to light irradiation. [ABSTRACT FROM AUTHOR]

Photocatalysts based on g-C3N4 have been investigated in the CO2 reduction reaction under visible light irradiation (λ = 397, 427, 452 nm). Photocatalysts were prepared by melamine calcination at 500–600 °C with further platinum deposition (0.1–1.0 wt.%). The effect of the preparation conditions of g-C3N4 and the method of platinum deposition on the physicochemical properties and activity of photocatalysts was studied. The photocatalysts were investigated by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, X-ray diffraction, high resolution transmission electron microscopy, UV-Vis spectroscopy, and low temperature nitrogen adsorption techniques. It has been found that the efficiency of CO2 reduction is governed by the surface area of g-C3N4 and the presence of platinum in the metallic state, while the optimal content of platinum is 0.5 wt. %. The highest rate of CO2 reduction achieved over Pt/g-C3N4 photocatalyst is 13.2 µmol h−1 g−1 (397 nm), which exceeds the activity of pristine g-C3N4 by 7 times. The most active photocatalysts was prepared by calcining melamine in air at 600 °C, followed by modification with platinum (0.5 wt.%). [ABSTRACT FROM AUTHOR]

A series of Pt/TiO2 photocatalysts was prepared by impregnation of fresh and thermal-activated titania (commercial Evonik Aeroxide P25 TiO2) with an aqueous solution of H2PtCl6 followed by reduction in an aqueous solution of NaBH4. The thermal activation was performed by annealing in air. The photocatalytic activity of the Pt/TiO2 catalysts was measured for the hydrogen production from a mixture of glycerol under UV radiation. It was found that the activation at 300–600 °C provides an increase in the photoreactivity of resulting Pt/TiO2 photocatalysts in the production of hydrogen while its structural and textural properties do not change. This effect is due to formation of cationic vacancies that limits fast electron–hole recombination. [ABSTRACT FROM AUTHOR]

The work discusses the preparation of multiphase Zn(OH)/CdZnS and Pt/Zn(OH)/CdZnS photocatalysts sensitive to visible light. The synthesized photocatalysts were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and HRTEM techniques. Photocatalytic activity of synthesized samples was investigated in the hydrogen evolution from aqueous solutions of inorganic and organic electron donors, NaS/NaSO and ethanol, respectively, under the influence of visible light with λ = 450 nm. The photocatalytic hydrogen evolution over said multiphase photocatalysts occurs after some induction period needed for the photocatalyst self-activation. The highest apparent quantum efficiencies achieved at 450 nm for hydrogen evolution from NaS/NaSO (over 20 % Zn(OH)/CdZnS) and ethanol (over 1 % Pt/10 % Zn(OH)/CdZnS) aqueous solutions were 39 and 6.1 % respectively, appearing to be quite high values for the photocatalytic hydrogen evolution under visible light. [ABSTRACT FROM AUTHOR]

Multiphase photocatalysts Cd1-xZnxS/TiO2 were synthesized through the deposition of solid solutions of cadmium and zinc sulfides on the surface of titania samples with different porous structures, including a 3D-ordered meso/macroporous structure. The photocatalysts were characterized by a wide range of experimental techniques: X-ray diffraction, high-resolution transmission electron microscopy combined with energy-dispersive X-ray spectroscopy, N2 adsorption at 77 K, X-ray photoelectron spectroscopy, and UV/VIS spectroscopy. The photocatalytic activity was tested in a batch reactor for the H2 evolution reaction from aqueous solutions of Na2S/Na2SO3 under visible-light irradiation (λ=450 nm). The highest achieved photocatalytic activity was 1.8 mmol H2 per gram of photocatalyst per hour. The regular porous structure of titania was demonstrated to enhance the photocatalytic activity and stability of Cd0.4Zn0.6S/TiO2 samples. [ABSTRACT FROM AUTHOR]

The chemisorption of the labile dimeric platinum nitratocomplex [Pt 2 (μ-OH) 2 (NO 3) 8 ]2- onto graphene oxide doped graphitic C 3 N 4 (g–C 3 N 4 –GO) was performed for the first time to prepare PtO x /g–C 3 N 4 –GO composites with ionic platinum species (Pt(II)) bonded with N-donor groups of the g-C 3 N 4. The thermal treatment of the obtained composites in the hydrogen atmosphere results in a gradual reduction of Pt(II) species with the formation of Pt/g–C 3 N 4 –GO photocatalysts. The Pt/g–C 3 N 4 –GO catalysts paired with TEOA sacrificing agent in an aqueous solution were tested in a photoinduced hydrogen evolution reaction under visible light (λ = 425 nm). The photocatalytic activity of prepared materials strongly influenced by the temperature of the reduction stage so that the maximal rate of H 2 evolution was revealed for the catalyst (0.5 wt% of Pt) reduced at 400 °C with a quantum efficiency of 3.0% and rate of HER of 5.1 mmol h−1 per 1 g of photocatalysts. The photocatalytic activity of this sample was much higher than the activity of 0.5% Pt/g–C 3 N 4 –GO photocatalysts prepared by conventional photoreduction of H 2 PtCl 6 or reduction of this precursor with NaBH 4. The Pt/g–C 3 N 4 –GO photocatalyst with Pt concentration of 0.1 wt% was prepared using the described protocol and shown specific activity of about 1.4 mol h−1 per 1 g of Pt outperforming analogous material reported to date. [Display omitted] • PtO x /g–C 3 N 4 –GO composites were obtained using dimeric platinum(IV) nitratocomplex. • Thermal treatment at 100–400 °C in H 2 results in the formation of Pt/g–C 3 N 4 –GO catalysts. • Activity was tested in H 2 evolution from triethanolamine water solution (λ = 425 nm). • Highest activity (5.1 mmol g−1 h−1) was achieved by photocatalyst reduced at 400 °C. • 0.1% Pt/g–C 3 N 4 –GO (400 °C) achieved specific activity of 1.4 mol h−1 per 1 g of Pt. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C 3 N 4) modified with bromine and iodine was synthesized by a novel two-stage technique that included hydrothermal pre-treatment of melamine and its calcination in a mixture with ammonium halide. Prepared photocatalysts were tested by a set of methods including X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), thermal gravimetric analysis (TGA), low temperature nitrogen adsorption, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CVA), impedance spectroscopy, and the Mott – Schottky method. All the photocatalysts were studied in the photocatalytic hydrogen production from triethanolamine (TEOA) under visible light irradiation (λ = 428 nm). The most active photocatalyst was prepared from a mixture of 50% NH 4 I and 50% melamine. Its catalytic activity (2120 μmol g−1 h−1) was 35 times higher than that of the catalyst synthesized by the simple calcination of melamine. The highest short-circuit current density of 2.7 mA/cm2 was obtained with a sample synthesized from the mixture of 80% NH 4 Br and 20% melamine. [Display omitted] • Halide-modified g-C 3 N 4 was prepared by a novel two-stage technique. • High catalytic activity was assigned to changes in S BET and electronic structure. • I-doped samples were more active in H 2 production than Br-doped ones. • The highest catalytic activity was 2120 μmol Н 2 g−1 h−1. • Br-doped samples demonstrated higher J sc than I-doped samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • 0.01–0.5 % Pt/g-C 3 N 4 was synthesized by thermolysis of melamine cyanurate complex. • Pt/g-C 3 N 4 exhibited the excellent activity in H 2 evolution (λ = 425 nm) • 0.1 % Pt/g-C 3 N 4 achieved outperforming specific activity of 8.5 mol·h−1 per 1 g of Pt. • Large-scale pilot installation for hydrogen production (total volume 1 l) was constructed. • PEMFC with max output 1 W successfully was powered by produced hydrogen. The successive combination including thermolysis of melamine cyanurate complex, chemisorption of platinum from the solution of the labile nitratocomplex and, finally, reductive treatment with hydrogen was implemented to obtain highly active Pt/g-C 3 N 4 photocatalysts (0.01–0.5 wt% of Pt). The prepared in this way materials evinces photocatalytic activity in hydrogen evolution reaction from TEOA/water solutions with the superb rate of H 2 evolution per platinum atom loaded (1560 h−1) and the net rates being among the highest reported to date values (11 mmol·g−1·h−1). Such a remarkable performance correlates with the structure of these materials where the branchy net of the pores provides easy access of reagents to and ejection of products from the nanoparticulated Pt co-catalysts. A crucial contribution to the formation of the noted Pt/g-C 3 N 4 morphology ascribed to the self-catalyzed hydrogenation of the Pt/g-C 3 N 4 composites resulting in "scarifying" of the g-C 3 N 4 particles preferentially at the surface layer where Pt species are located. Taking into account the high productivity of the synthesized Pt/C 3 N 4 materials and robustness of the preparation method this approach can be convenient for the large-scale applications that were successfully demonstrated under pilot installation (total volume 1 l) with the fuel cell (PEMFC with max output 1 W) as a hydrogen consumer. Evaluation of the productivity of the large-scale reactor for hydrogen production with a scaled-up installation was carried out. This study also grants a new vision on developing expandable synthetic approaches to enhance the performance of carbon nitride-based photocatalysts and at the same time mitigate the noble metal co-catalysts usage. [ABSTRACT FROM AUTHOR]

The promotion of the photocatalytic activity of the Cd 0.3 Zn 0.7 S nanoparticles via deposition of some copper species, such as Cu x S and Cu 0 , as a co-catalyst, in the hydrogen production under visible light irradiation from aqueous solutions of a sacrificial Na 2 S/Na 2 SO 3 system was studied. The state of the samples was characterized with a wide range of physical methods both in the initial state as well as after their photocatalytic operation. An evolution of both photocatalytic activity and the state of the photocatalyst particles was registered by a set of the physical methods. The highest apparent quantum efficiency and photocatalytic activity which were achieved at illumination by light with λ = 450 nm over the 0.1 wt% Cu x S/Cd 0.3 Zn 0.7 S sample for the photocatalytic hydrogen evolution from Na 2 S/Na 2 SO 3 aqueous solutions were 23.1% and 6.4 mmol g −1 h −1 , respectively. It was shown that the deposited Cu species undergo the transformation to Cu x S during the photocatalytic production of hydrogen, and these are the copper sulfide nanoparticles that increase the activity of the Cd 1-x Zn x S solid solutions. This statement agrees well with the principle of a constancy of the state of heterogeneous catalysts under their operation in the same reaction media established by G.K. Boreskov in the 1950s. [ABSTRACT FROM AUTHOR]

The transformations of single-phase Pt/Cd 1− x Zn x S and multiphase Pt/Cd 1− x Zn x S/ZnO/Zn(OH) 2 and Pt/Cd 1− x Zn x S/Zn(OH) 2 during photocatalytic hydrogen evolution from aqueous solutions of ethanol under visible light ( λ = 450 nm) were investigated. Cyclic tests including long-term experiments were conducted for all photocatalysts. The photocatalysts were investigated before and after the photocatalytic reaction by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–vis spectroscopy techniques. Activation during photocatalytic hydrogen evolution was observed for all multiphase photocatalysts, whereas single phase Pt/Cd 1− x Zn x S was shown to exhibit a strong deactivation. The activation is likely caused by the formation of the ϵ-Zn(OH) 2 phase in a basic medium. The highest exhibited rate of hydrogen evolution on the composite photocatalyst was 3400 μmol g −1 h −1 , and stability during ten 5-hour photocatalytic runs was observed. [ABSTRACT FROM AUTHOR]

Multiphase photocatalysts Pt/Cd 1− x Zn x S/ZnO/Zn(OH) 2 , Pt/Cd 1− x Zn x S/ZnO, and Pt/Cd 1− x Zn x S/Zn(OH) 2 were synthesized by a new two-step technique. The photocatalysts were characterized by a wide range of experimental techniques: X-ray diffraction, high-resolution transmission electron microscopy combined with energy-dispersive X-ray spectroscopy, low-temperature N 2 adsorption/desorption, and UV/VIS spectroscopy. The photocatalytic activity was tested in a batch reactor in the reaction of H 2 evolution from aqueous solutions of ethanol under visible light irradiation ( λ > 420 nm). The highest achieved photocatalytic activity was 2256 μmol H 2 per gram of photocatalyst per hour; the highest quantum efficiency was 10.4%. The activity of Pt/Cd 1− x Zn x S/Zn(OH) 2 was higher than that of Pt/Cd 1− x Zn x S/ZnO/Zn(OH) 2 and Pt/Cd 1− x Zn x S/ZnO. The explanation of enhanced activity of zinc–cadmium sulfide/ε-zinc hydroxide based on quantum calculations was suggested. [ABSTRACT FROM AUTHOR]

• Pt/TiO 2 and CuO x /TiO 2 photocatalysts were synthesized. • Hydrogen evolution from glycerol aqueous solutions was performed (λ = 380 nm). • Pt/TiO 2 photocatalyst was found to be more active and stable. • Wider variety of glycerol oxidation products was obtained over CuO x /TiO 2. Pt/TiO 2 and CuO 0.68 /TiO 2 were synthesized and tested in the photoreforming of glycerol. The photocatalysts were characterized by UV–vis spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy. It was found that the Pt/TiO 2 photocatalyst was more active and stable, but the use of the CuO x /TiO 2 photocatalyst made it possible to obtain a wider variety of products and a higher percentage of formation of organic products from glycerol. The highest rate of hydrogen evolution was equal to 0.55 mmol h−1 g−1 and to 1.35 mmol h−1 g−1 for CuO x /TiO 2 and Pt/TiO 2 , respectively. [ABSTRACT FROM AUTHOR]