Photocatalytic hydrogen production from acidic aqueous solution in BODIPY-cobaloxime-ascorbic acid homogeneous system

Diiodo-BODIPY Sensitizing of the [Mo3S13]2- Cluster for Noble-Metal-Free Visible-Light-Driven Hydrogen Evolution within a Polyampholytic Matrix

We report on a photocatalytic setup that utilizes the organic photosensitizer (PS) diiodo-BODIPY and the non-precious-metal-based hydrogen evolution reaction (HER) catalyst (NH₄)₂[Mo₃S₁₃] together with a polyampholytic unimolecular matrix poly(dehydroalanine)-graft-poly(ethylene glycol) (PDha-g-PEG) in aqueous media. The system shows exceptionally high performance with turnover numbers (TON > 7300) and turnover frequencies (TOF > 450 h^-1) that are typical for noble-metal-containing systems. Excited-state absorption spectra reveal the formation of a long-lived triplet state of the PS in both aqueous and organic media. The system is a blueprint for developing noble-metal-free HER in water. Component optimization, e.g., by modification of the meso substituent of the PS and the composition of the HER catalyst, is further possible.

2D Network overtakes 3D for photocatalytic hydrogen evolution

3-Dimensional (3D) cyanide coordination polymers, typically known as Prussian blue Analogues (PBAs), have received great attention in catalysis due to their stability, easily tuned metal sites, and porosity. However, their high crystallinities and relatively low number of surface-active sites significantly hamper their intrinsic catalytic activities. Herein, we report the utilization of a 2-dimensional (2D) layered cobalt tetracyanonickelate, [Co-Ni], for the reduction of protons to H₂. Relying on its exposed facets, layered morphology, and abundant surface-active sites, [Co-Ni] can efficiently convert water and sunlight to H₂ in the presence of a ruthenium photosensitizer (Ru PS) with an optimal evolution rate of 30 029 ± 590 μmol g^-1 h^-1, greatly exceeding that of 3D Co-Fe PBA [Co-Fe] and Co-Co PBA [Co-Co]. Furthermore, [Co-Ni] retains its structural integrity throughout a 6 hour photocatalytic cycle, which is confirmed by XPS, PXRD, and Infrared analysis. This recent work reveals the excellent morphologic properties that promote [Co-Ni] as an attractive catalyst for the hydrogen evolution reaction (HER).

A Time-Resolved Spectroscopic Investigation of a Novel BODIPY Copolymer and Its Potential Use as a Photosensitiser for Hydrogen Evolution

A novel 4,4-difuoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) copolymer with diethynylbenzene has been synthesised, and its ability to act as a photosensitiser for the photocatalytic generation of hydrogen was investigated by time-resolved spectroscopic techniques spanning the ps- to ns-timescales. Both transient absorption and time-resolved infrared spectroscopy were used to probe the excited state dynamics of this photosensitising unit in a variety of solvents. These studies indicated how environmental factors can influence the photophysics of the BODIPY polymer. A homogeneous photocatalytic hydrogen evolution system has been developed using the BODIPY copolymer and cobaloxime which provides hydrogen evolution rates of 319 μmol h⁻¹ g⁻¹ after 24 h of visible irradiation.

The odyssey of cobaloximes for catalytic H2 production and their recent revival with enzyme-inspired design

Cobaloxime complexes gained attention for their intrinsic ability of catalytic H₂ production despite their initial emergence as a vitamin B12 model. The simple, robust, and synthetically manoeuvrable cobaloxime core represents a model catalyst molecule for the investigation of optimal conditions for both photo- and electrocatalytic H₂ production catalytic assemblies. Cobaloxime is one of the rare catalysts that finds equal applications in the analysis of homogeneous and heterogeneous catalytic conditions. However, the poor aqueous solubility and long-term instability of cobaloximes have severely impeded their growth. Lately, interest in the cobaloxime-based catalysts has been resuscitated with the rational use of extended enzymatic features. This unique enzyme-inspired catalyst design strategy has instigated the formation of a new genre of cobaloxime molecules that exhibit enhanced photo- and electrocatalytic H₂ evolution with improved aqueous and air stability.

A three-dimensional self-standing Mo2C/nitrogen-doped graphene aerogel: Enhancement hydrogen production from landfill leachate wastewater in MFCs-AEC coupled system

A hydrothermal-annealing method was adopted to form nitrogen-doped graphene aerogel-supported molybdenum carbide (Mo₂C/NGA) materials by using graphene oxide (GO), poly (propylene glycol) bis(2-aminopropyl ether) (D400 for short) and ammonium molybdate as precursors. The annealing temperature and GO/D400 wt ratio played an important role on the materials structure and electrocatalytic activity. When the annealing temperature reached to 800 °C, the Mo₂C was formed as an active component and improved obviously the hydrogen evolution reaction (HER) activity. After introducing the appropriate amount of D400, the Mo₂C/NGA material not only had a firm porous monolithic framework, but also presented an increasing HER activity. Further, the Mo₂C/NGA-based microbial fuel cells-ammonia electrolysis cell (MFCs-AEC) coupled system was constructed and operated for higher hydrogen production. The coupled system produced hydrogen of 198 mL g^-1_Mo2C/NGA in simulated ammonia-rich wastewater. As using the actual landfill leachate wastewater as substrate, there was 79.2 mL g^-1_Mo2C/NGA of hydrogen production. All of these were attributed to the porous structure with an interconnected network and the nitrogen-doped structure of the NGA.

Development of a "Turn-on" Fluorescent Probe-Based Sensing System for Hydrogen Sulfide in Liquid and Gas Phase

A “turn-on” fluorescence sensing system based on a BODIPY-cobaloxime complex for the detection of H₂S in liquid and gas phase was developed. To that aim, two cobaloxime complexes bearing an axial pyridyl-BODIPY ligand were initially evaluated as sensitive fluorescent HS⁻ indicators in aqueous solution. The sensing mechanism involves the selective substitution of the BODIPY ligand by the HS⁻ anion at the cobalt center, which is accompanied by a strong fluorescence enhancement. The selection of a complex with an ideal stability and reactivity profile toward HS⁻ relied on the optimal interaction between the cobalt metal-center and two different pyridyl BODIPY ligands. Loading the best performing BODIPY-cobaloxime complex onto a polymeric hydrogel membrane allowed us to study the selectivity of the probe for HS⁻ against different anions and cysteine. Successful detection of H₂S by the fluorescent “light-up” membrane was not only accomplished for surface water but could also be demonstrated for relevant H₂S concentrations in gas phase.