Rare earth praseodymium single atoms on g-C3N4 tubes for enhanced in-plane charge transfer towards H2O2 production in pure water

A strong metal-support interaction strategy for enhanced proton-coupled electron transfer and promoted photocatalytic H2O2 production in pure water

Photocatalytic hydrogen peroxide (H2O2) synthesis from water and O2 is an economical, eco-friendly, and sustainable route for H2O2 production. However, single-component photocatalysts are subjected to limited light-harvesting range, fast carrier recombination, and weak redox power. To promote photogenerated carrier separation and enhance redox abilities, an organic/inorganic S-scheme photocatalyst is fabricated by in situ growing In2S3 nanosheets on a covalent organic framwork (COF) substrate for efficient H2O2 production in pure water. Interestingly, compared to unitary COF and In2S3, the COF/In2S3 S-scheme photocatalysts exhibit significantly larger light-harvesting range and stronger visible-light absorption. Partial density of state calculation, X-ray photoelectron spectroscopy, and femtosecond transient absorption spectroscopy reveal that the coordination between In2S3 and COF induces the formation of mid-gap hybrid energy levels, leading to smaller energy gaps and broadened absorption. Combining electron spin resonance spectroscopy, radical-trapping experiments, and isotope labeling experiments, three pathways for H2O2 formation are identified. Benefited from expanded light-absorption range, enhanced carrier separation, strong redox power, and multichannel H2O2 formation, the optimal composite shows an impressive H2O2-production rate of 5713.2µmol g-1 h-1 in pure water. This work exemplifies an effective strategy to ameliorate COF-based photocatalysts by building S-scheme heterojunctions and provides molecular-level insights into their impact on energy level modulation.

A Polyimide-Based Photocatalyst for Continuous Hydrogen Peroxide Production Using Air and Water under Solar Light

Ultrahigh dose-rate radiation (UHDR) produces less hydrogen peroxide (H2O2) in pure water, as suggested by some experimental studies, and is used as an argument for the validity of the theory that FLASH spares the normal tissue due to less reactive oxygen species (ROS) production. In contrast, most Monte Carlo simulation studies suggest the opposite. We aim to unveil the effect of UHDR on H2O2 production in pure water and its underlying mechanism, to serve as a benchmark for Monte Carlo simulation. We hypothesized that the reaction of solvated electrons ( ) removing hydroxyl radicals (•OH), the precursor of H2O2, is the reason why UHDR leads to a lower G-value (molecules/100eV) for H2O2 (G[H2O2]), because: 1, the third-order reaction between and •OH is more sensitive to increased instantaneous ROS concentration by UHDR than a two-order reaction of •OH self-reaction producing H2O2; 2, has two times higher diffusion coefficient and higher reaction rate constant than that of •OH, which means would dominate the competition for •OH and benefit more from the inter-track effect of UHDR. Meanwhile, we also experimentally verify the theory of long-lived radicals causing lower G(H2O2) in conventional irradiation, which is mentioned in some simulation studies. H2O2 was measured by Amplex UltraRed assay. 430.1MeV/u carbon ions (50 and 0.1Gy/s), 9MeV electrons (600 and 0.62Gy/s), and 200kV x-ray tube (10 and 0.1Gy/s) were employed. For three kinds of water (real hypoxic: 1% O2; hypoxic: 1% O2 and 5% CO2; and normoxic: 21% O2), unbubbled and bubbled samples with N2O, the scavenger of , were irradiated by carbon ions and electrons with conventional and UHDR at different absolute dose levels. Normoxic water dissolved with sodium nitrate (NaNO3), another scavenger of , and bubbled with N2O was irradiated by x-ray to verify the results of low-LET electron beam. UHDR leads to a lower G(H2O2) than conventional irradiation. O2 and CO2 can both increase G(H2O2). N2O increases G(H2O2) of both UHDR and conventional irradiation and eliminates the difference between them for carbon ions. However, N2O decreases G(H2O2) in electron conventional irradiation but increases G(H2O2) in the case of UHDR, ending up with no dose-rate dependency of G(H2O2). Three-spilled carbon UHDR does not have a lower G(H2O2) than one-spilled UHDR. However, the electron beam shows a lower G(H2O2) for three-spilled UHDR than for one-spilled UHDR. Normoxic water with N2O or NaNO3 can both eliminate the dose rate dependency of H2O2 production for x-ray. UHDR has a lower G(H2O2) than the conventional irradiation for both high LET carbon and low LET electron and x-ray beams. Both scavengers for , N2O and NaNO3, eliminate the dose-rate dependency of G(H2O2), which suggests is the reason for decreased G(H2O2) for UHDR. Three-spilled UHDR versus one-spilled UHDR indicates that the assumption of residual radicals reducing G(H2O2) of conventional irradiation may only be valid for low LET electron beam.

Titanium dioxide (TiO2) has been extensively investigated in photocatalysis due to its high stability, low toxicity, and biocompatibility. However, its application in hydrogen peroxide (H2O2) production is hindered by the rapid recombination of photogenerated charge carriers and the poor selectivity of the two-electron oxygen reduction reaction (2e- ORR). Here, a CuO/TiO2 photocatalyst is reported, in which CuO nanoparticles are anchored on the TiO2 surface as cocatalysts to provide additional active sites and promote efficient separation of photogenerated electrons and holes. The optimized CuO/TiO2 exhibits a remarkable photocatalytic H2O2 production rate of 19.48mmol g-1 h-1, which is 162 times higher than that of pristine TiO2, with excellent stability sustained over 7 h' continuous irradiation. The apparent quantum yield (AQY) of CuO/TiO2 reaches 7.30% at 365nm. Notably, the CuO/TiO2 demonstrated the promising H2O2 production in pure water (182.31 µmol g-1 h-1). Femtosecond transient absorption spectra (Fs-TAS) reveal that the average lifetime of photogenerated electrons in CuO/TiO2 is 5.8 times longer than in TiO2, confirming the enhanced charge separation and transfer. In situ spectroscopic analyses further demonstrate that CuO/TiO2 facilitates both oxygen reduction and water oxidation pathways. These results highlight CuO/TiO2 as a cost-effective and efficient photocatalyst for sustainable H2O2 production.

The direct production of hydrogen peroxide (H2O2) through photocatalytic reaction via H2O and O2 is considered as an ideal approach. However, the efficiency of H2O2 generation is generally limited by insufficient charge and mass transfer. Covalent organic framework (COFs) offer a promising platform as metal‐free photocatalyst for H2O2 production due to their potential for rational design at the molecular level. Herein, we integrated the multipolar structures and carboxyl groups into COFs to enhance the efficiency of photocatalytic H2O2 production in pure water without any sacrificial agents. The introduction of octupolar and quadrupolar structures, along with an increase of molecular planarity, created efficient oxygen reduction reaction (ORR) sites. Meanwhile, carboxyl groups could not only boost O2 and H2O2 movement via enhancement of pore hydrophilicity, but also promote proton conduction, enabling the conversion to H2O2 from ⋅O2−, which is the crucial intermediate product in H2O2 photocatalysis. Overall, we demonstrate that TACOF‐1‐COOH, consisting of optimal octupolar and quadrupolar structures, along with enrichment sites (carboxyl groups), exhibited a H2O2 yield rate of 3542 μmol h− 1 g−1 and a solar‐to‐chemical (SCC) efficiency of 0.55 %. This work provides valuable insights for designing metal‐free photocatalysts for efficient H2O2 production.

The direct production of hydrogen peroxide (H2O2) through photocatalytic reaction via H2O and O2 is considered as an ideal approach. However, the efficiency of H2O2 generation is generally limited by insufficient charge and mass transfer. Covalent organic framework (COFs) offer a promising platform as metal-free photocatalyst for H2O2 production due to their potential for rational design at the molecular level. Herein, we integrated the multipolar structures and carboxyl groups into COFs to enhance the efficiency of photocatalytic H2O2 production in pure water without any sacrificial agents. The introduction of octupolar and quadrupolar structures, along with an increase of molecular planarity, created efficient oxygen reduction reaction (ORR) sites. Meanwhile, carboxyl groups could not only boost O2 and H2O2 movement via enhancement of pore hydrophilicity, but also promote proton conduction, enabling the conversion to H2O2 from ⋅O2 -, which is the crucial intermediate product in H2O2 photocatalysis. Overall, we demonstrate that TACOF-1-COOH, consisting of optimal octupolar and quadrupolar structures, along with enrichment sites (carboxyl groups), exhibited a H2O2 yield rate of 3542 μmol h- 1 g-1 and a solar-to-chemical (SCC) efficiency of 0.55 %. This work provides valuable insights for designing metal-free photocatalysts for efficient H2O2 production.

Sonochemical hydrogen production in a 300kHz sonoreactor: Comparative effects of short‑chain carboxylic acids, pH, and dissolved gas.

3D ordered macroporous sulfur-doped g-C3N4/TiO2 S-scheme photocatalysts for efficient H2O2 production in pure water

Semiconductor photocatalysis is deemed as a novel and promising process that can produce H2O2 from earth-abundant water and gaseous dioxygen using sunlight as the energy supply. The searching of novel catalysts for photocatalytic H2O2 production has received increasing attention in the last few years. Herein, size-controlled growth of ZnSe nanocrystals was realized via a solvothermal method by varying the amount of Se and KBH4. The performance of the as-obtained ZnSe nanocrystals towards photocatalytic H2O2 production depends on the mean size of the synthesized nanocrystals. Under O2-bubbling, the optimal ZnSe sample presented an excellent H2O2 production efficiency (8.596 mmol g-1 h-1), and the apparent quantum efficiency for H2O2 production reaches as high as 2.84% at λ = 420 nm. Under air-bubbling, the accumulation of H2O2 was as high as 1.758 mmol L-1 after 3 h irradiation at the ZnSe dosage of 0.4 g L-1. The photocatalytic H2O2 production performance is far superior to the most investigated semiconductors such as TiO2, g-C3N4, and ZnS.

Heterostructure engineering of resorcinol-formaldehyde resins and sulfur-vacancy-containing Zn3In2S6 for high-efficiency photocatalytic H2O2 production

Cu-doped hollow tubular ZnIn2S4 using MIL-68-NH2 as templates for efficient photocatalytic synthesis of H2O2 in ambient air and pure water.

Polyimide/ZnIn2S4 heterostructures toward outstanding photocatalytic H2O2 production from pure water and air

Reasonably utilizing solar energy to synthesize hydrogen peroxide (H2O2) from oxygen and water is a promising and sustainable solution. In this work, we constructed an S-scheme photocatalyst ZnIn2S4/PDA (ZIS/PDA) by loading polydopamine (PDA) on the surface of ZnIn2S4, which significantly enhanced the separation and transfer of photogenerated charge carriers while retaining excellent oxidation and reduction abilities and exhibited outstanding H2O2 production performance (1747 μmol·g–1·h–1) under visible light in pure water, which is 39 times the yield of pure ZnIn2S4. The presence of PDA coating enhanced the adsorption capacity of catalysts for oxygen and improved the selectivity of the direct two-electron oxygen reduction reaction (2e–ORR) and formation rate by effectively reducing the Gibbs free energy (ΔG) of *OOH. In addition, ZIS/PDA significantly inhibited the decomposition of H2O2 by promoting the rapid desorption of H2O2, which is conducive to the stable accumulation of H2O2. In summary, the innovative ZIS/PDA photocatalyst demonstrates remarkable efficiency in H2O2 production, offering a potential solution for the sustainable energy synthesis.

Piezocatalytic degradation of organic dyes and production of H2O2 with hydroxyapatite