Highly Active Visible Light-Promoted Ir/g-C3N4 Photocatalysts for the Water Oxidation Reaction Prepared from a Halogen-Free Iridium Precursor

Cobalt-Loaded Carbon Nitride Demonstrates Enhanced Photocatalytic Production of H2 from Lignocellulosic Biomass Components

Photocatalytic production of hydrogen (H2) from biomass is a promising avenue for advancing sustainable energy generation. We prepared carbon nitride (CN x ) with cobalt (Co) as an oxidation cocatalyst (denoted CN x /Co) to improve photocatalytic H2 production through photoreforming components of lignocellulosic biomass under visual light irradiation. CN x /Co was synthesized by loading Co onto preformed CN x through a straightforward thermal deposition. The thermal loading of Co at 450 °C led to the formation of a mixed valence CoO x , which shifted Co2+ character to Co3+ over the course of the hydrogen evolution reaction (HER). Compared to CN x without Co, our materials with 0.3 and 0.6 wt % Co demonstrate twice the apparent quantum yield (AQY) for H2 production under irradiation at 405 nm using glucose as a sacrificial electron donor (3.0% and 2.8%, respectively, vs 1.4%). Time-resolved spectroscopic investigations indicate that the Co extracts charges in the subnanosecond time scale and promotes the formation of beneficial long-lived charges. Impressively, some photocatalytic activity is observed when using the robust polymers of cellulose and lignin as the oxidation substrates (0.2 and 0.1% AQY, respectively). The ability to oxidize abundant biomass without extensive prepreparation is promising for waste upcycling applications.

Photocatalytic Activity of Ag Nanoparticles Deposited on Thermoexfoliated g-C3N4

The limited access to fresh water and the increased presence of emergent pollutants (EPs) in wastewater has increased the interest in developing strategies for wastewater remediation, including photocatalysis. Graphitic carbon nitride (g-C3N4) is a 2D non-metal material with outstanding properties, such as a 2.7 eV bandgap and physicochemical stability, making it a promising photocatalyst. This work reports the process of obtaining high-surface-area (SA) g-C3N4 using the thermal-exfoliation process and the posterior effect of Ag-nanoparticle loading over the exfoliated g-C3N4 surface. The photocatalytic activity of samples was evaluated through methylene blue (MB) degradation under visible-light radiation and correlated to its physical properties obtained by XRD, TEM, BET, and UV-Vis analyses. Moreover, 74% MB degradation was achieved by exfoliated g-C3N4 compared to its bulk counterpart (55%) in 180 min. Moreover, better photocatalytic performances (94% MB remotion) were registered at low Ag loading, with 5 wt.% as the optimal value. Such an improvement is attributed to the synergetic effect produced by a higher SA and the role of Ag nanoparticles in preventing charge-recombination processes. Based on the results, this work provides a simple and efficient methodology to obtain Ag/g-C3N4 photocatalysts with enhanced photocatalytic performance that is adequate for water remediation under sunlight conditions.

Nanoflower-like graphitic carbon nitride aerogel: Artful cyanuric acid-controlled synthesis and enhanced photocatalytic hydrogen evolution activity

The previously reported studies on cyanuric acid-assembly strategy usually ignores the promoting function of cyanuric acid in the production of g-C3N4, limiting the development of molecular assembly strategies. In this study, a cyanuric acid-controlled synthesis strategy involving the pre-assembly of cyanuric acid with melamine and subsequent one-step calcination was developed to produce a three-dimensional (3D) nanoflower-like graphitic carbon nitride (g-C3N4) aerogel. Some cyanuric acid molecules underwent a polycondensation reaction with melamine during the pre-assembly process and finally polymerized into the g-C3N4 structure during subsequent calcination. Meanwhile, the remaining cyanuric acid molecules assembled with melamine via hydrogen-bond interactions and underwent incomplete decomposition during subsequent calcination, which not only promoted the production of 3D nanoflower-like aerogel structures, but also introduced the carbonyl (CO) and hydroxyl (-OH) groups onto the g-C3N4 surface, resulting in the successful generation of a 3D nanoflower-like oxygen-modified g-C3N4 aerogel. Moreover, the fabricated g-C3N4 aerogel exhibited a greatly enhanced H2 production rate (1573 μmol h-1 g-1), which is ∼ 6.6 times higher than that of bulk g-C3N4 (239 μmol h-1 g-1) owing to the synergistic promotion function of ultrathin nanoflower-like aerogel and oxygen modification structures. This strategy provides a theoretical basis for the development of highly efficient g-C3N4 photocatalysts via molecular assembly.