Photocatalytic overall water splitting under visible light enabled by a particulate conjugated polymer loaded with iridium

The production of hydrogen from water via solar water splitting is a potential method to overcome the intermittency of the Sun’s energy by storing it as a chemical fuel. Inorganic semiconductors have been studied extensively as photocatalysts for overall water splitting, but polymer photocatalysts are also receiving growing attention. So far, most studies involving organic polymers report hydrogen production with sacrificial electron donors, which is unsuitable for large-scale hydrogen energy production. Here we show that a linear conjugated polymer photocatalyst can be used for overall water splitting to produce stoichiometric amounts of H2 and O2. We studied a range of different metal co-catalysts in conjunction with the linear polymer photocatalyst, the homopolymer of dibenzo[b,d]thiophene sulfone (P10). Photocatalytic activity was observed for palladium/iridium oxide-loaded P10, while other co-catalysts resulted in materials that showed no activity for overall water splitting. The reaction conditions were further optimized and the overall water splitting using the IrO2-loaded P10 was found to proceed steadily for an extended period (>60 hours) after the system stabilized. These results demonstrate that conjugated polymers can act as single component photocatalytic systems for overall water splitting when loaded with suitable co-catalysts, albeit currently with low activities. Significantly, though, organic polymers can be designed to absorb a large fraction of the visible spectrum, which can be challenging with inorganic catalysts. Transient spectroscopy shows that the IrO2 co-catalyst plays an important role in the generation of the charge separated state required for water splitting, with evidence for fast hole transfer to the co-catalyst. This solid-state approach should be transferable to other polymer photocatalysts, allowing this field to move away from sacrificial hydrogen production towards overall water splitting.

Photocatalytic Degradation of Fluoroquinolone Antibiotics in Solution

The photocatalytic degradation of two quinolone-type antibiotics (ciprofloxacin and levofloxacin) in aqueous solution was studied, using catalysts based on ZnO nanoparticles, which were synthesized by a thermal procedure. The efficiency of ZnO was subsequently optimized by incorporating different co-catalysts of gC3N4, reduced graphene oxide and nanoparticles of gold. The catalysts were fully characterized by electron microscopy (TEM and SEM), XPS, XRD, Raman, and BET surface area. The most efficient catalyst was 10%Au@ZnONPs-3%rGO-3%gC3N4, allowing to obtain degradations of both pollutants above 96%. This catalyst has the largest specific area, and its activity has been related to a synergistic effect, involving factors as relevant as the surface of the material and the ability to absorb radiation in the visible region, mainly produced by the incorporation of rGO and gC3N4 to the semiconductor. The use of different scavengers during the catalytic process, was used to establish the possible photodegradation mechanism of both antibiotics.

Robust MOF-derived carbon-supported bimetallic Ni-Co catalysts for aqueous phase hydrodeoxygenation of vanillin

Currently, rapidly increasing consumption of fossil resources has propelled the upgrading of biomass as an alternative and sustainable technology to produce important chemicals and bio-oils. In this regard, rational design...

Multiscale porous single-atom Co catalysts for epoxidation by O2

Epoxides are versatile intermediates in the production of a diverse set of chemical products. Direct epoxidation of alkene using O2 represents an environmentally friendly and economical process to replace the...

Review: chemical approaches toward catalytic lignin degradation

Lignin is a potentially high natural source of biological aromatic substances. However, decomposition of the polymer has proven to be quite challenging, as the complex bonds are fairly difficult to break down chemically. This article is intended to provide an overview of various recent methods for the catalytic chemical depolymerization of the biopolymer lignin into chemical products. For this purpose, nickel-, zeolite- and palladium-supported catalysts were examined in detail. In order to achieve this, various experiments of the last years were collected, and the efficiency of the individual catalysts was examined. This included evaluating the reaction conditions under which the catalysts work most efficiently. The influence of co-catalysts and Lewis acidity was also investigated. The results show that it is possible to control the obtained product selectivity very well by the choice of the respective catalysts combined with the proper reaction conditions.

Exploration of the Photocatalytic Cycle for Sacrificial Hydrogen Evolution by Conjugated Polymers Containing Heteroatoms

We analyze the photocatalytic activity of heteroatom containing linear conjugated polymers for sacrificial hydrogen evolution using a recently proposed photocatalytic cycle. We find that the thermodynamic barrier to electron transfer, relevant both in the presence and absence of noble metal co-catalysts, changes with polymer composition, reducing upon going from electron-rich to electron-poor polymers, and disappearing completely for the most electron-poor polymers in a water rich environment. We discuss how the latter is probably the reason why electron-poor polymers are generally more active for sacrificial hydrogen evolution than their electron-rich counterparts. We also study the barrier to hydrogen-hydrogen bond formation on the polymer rather than the co-catalyst and find that it too changes with composition but is always, at least for the polymer studied here, much larger than that experimentally reported for platinum. Therefore, it is expected that in the presence of any noble metal particles these will act as the site of hydrogen evolution.

Construction of UiO-66/Bi4O5Br2 Type-II Heterojunction to Boost Charge Transfer for Promoting Photocatalytic CO2 Reduction Performance

One of the basic challenges of CO2 photoreduction is to develop efficient photocatalysts, and the construction of heterostructure photocatalysts with intimate interfaces is an effective strategy to enhance interfacial charge transfer for realizing high photocatalytic activity. Herein, a novel UiO-66/Bi4O5Br2 heterostructure photocatalyst was constructed by depositing UiO-66 nanoparticles with octahedral morphology over the Bi4O5Br2 nanoflowers assembled from the Bi4O5Br2 nanosheets via an electrostatic self-assembly method. A tight contact interface and a built-in electric field were formed between the UiO-66 and the Bi4O5Br2, which was conducive to the photo-electrons transfer from the Bi4O5Br2 to the UiO-66 and the formation of a type-II heterojunction with highly efficient charge separation. As a result, the UiO-66/Bi4O5Br2 exhibited improved photocatalytic CO2 reduction performance with a CO generation rate of 8.35 μmol h−1 g−1 without using any sacrificial agents or noble co-catalysts. This work illustrates an applicable tactic to develop potent photocatalysts for clean energy conversion.

The potential scarcity, or not, of polymeric overall water splitting photocatalysts

We perform a high-throughput computational screening of a set of 3240 conjugated alternating binary co-polymers and homo-polymers, in which we predict their ability to drive sacrificial hydrogen evolution and overall water splitting when illuminated with visible light. We use the outcome of this screening to analyse how common the ability to drive either reaction is for conjugated polymers loaded with suitable co-catalysts, and to suggest promising (co-)monomers for polymeric overall water splitting catalysts.