Comprehensive Review on g-C₃N₄-Based Photocatalysts for the Photocatalytic Hydrogen Production under Visible Light

Currently, the synthesis of active photocatalysts for the evolution of hydrogen, including photocatalysts based on graphite-like carbon nitride, is an acute issue. In this review, a comprehensive analysis of the state-of-the-art studies of graphic carbon nitride as a photocatalyst for hydrogen production under visible light is presented. In this review, various approaches to the synthesis of photocatalysts based on g-C3N4 reported in the literature were considered, including various methods for modifying and improving the structural and photocatalytic properties of this material. A thorough analysis of the literature has shown that the most commonly used methods for improving g-C3N4 properties are alterations of textural characteristics by introducing templates, pore formers or pre-treatment method, doping with heteroatoms, modification with metals, and the creation of composite photocatalysts. Next, the authors considered their own detailed study on the synthesis of graphitic carbon nitride with different pre-treatments and respective photocatalysts that demonstrate high efficiency and stability in photocatalytic production of hydrogen. Particular attention was paid to describing the effect of the state of the platinum cocatalyst on the activity of the resulting photocatalyst. The decisive factors leading to the creation of active materials were discussed

Spectroscopic and DFT Study of Rh^III Chloro Complex Transformation in Alkaline Solutions

The hydrolysis of [RhCl₆]^3– in NaOH–water solutions was studied by spectrophotometric methods. The reaction proceeds via successive substitution of chloride with hydroxide to quantitatively form [Rh­(OH)₆]^3–. Ligand substitution kinetics was studied in an aqueous 0.434–1.085 M NaOH matrix in the temperature range 5.5–15.3 °C. Transformation of [RhCl₆]^3– into [RhCl₅(OH)]^3– was found to be the rate-determining step with activation parameters of Δ<i>H</i>^† = 105 ± 4 kJ mol^–1 and Δ<i>S</i>^†= 59 ± 10 J K^–1 mol^–1. The coordinated hydroxo ligand(s) induces rapid ligand substitution to form [Rh­(OH)₆]^3–. By simulating ligand substitution as a dissociative mechanism, using density functional theory (DFT), we can now explain the relatively fast and slow kinetics of chloride substitution in basic and acidic matrices, respectively. Moreover, the DFT calculated activation energies corroborated experimental data that the kinetic stereochemical sequence of [RhCl₆]^3– hydrolysis in an acidic solution proceeds as [RhCl₆]^3– → [RhCl₅(H₂O)]^2– → <i>cis</i>-[RhCl₄(H₂O)₂]⁻. However, DFT calculations predict in a basic solution the trans route of substitution [RhCl₆]^3– → [RhCl₅(OH)]^3– → <i>trans</i>-[RhCl₄(OH)₂]^3– is kinetically favored

Bimetallic Pt-IrO_x/g-C₃N₄ Photocatalysts for the Highly Efficient Overall Water Splitting under Visible Light

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