An optimized and general synthetic strategy based on in-situ iodine modifying of polymeric graphitic carbon nitride is discussed. The as-prepared iodine functionalized g-CN shows enhanced electronic and optical properties, as well as increased photocatalytic activities in an assay of hydrogen evolution.

Direct splitting of pure water into H2 and O2 in a stoichiometric molar ratio of 2 : 1 by conjugated polymers via a 4-electron pathway was established for the first time, as demonstrated here using a g-C3N4 polymer and redox co-catalysts of Pt and Co species.

The development of stable systems to generate chemical fuels through water splitting by sunlight is a key challenge of modern materials chemistry, one that is driven by increasing energy demands and climate change. The central problems are to design chemically stable light-harvesting antenna molecules and co-factors, and then to assemble these active components into an integrated photosystem. Various substances have been examined as visible-light converters, including metal-organic dyes, [1] inorganic semiconductors, [2] and conjugated polymers. [3] The last are of particular interest, as they are much closer to biological systems in composition and are potentially sustainable, as well as cheap and easily processable. Principally, properties such as the HOMO and LUMO position and the resulting band gap can be precisely chemically engineered by synthesizing the constituents. To date, in spite of the wide availability of conducting polymers developed for photovoltaics, [4] the impact of these polymers on water splitting technology remains minor, because ordinary conducting polymers are usually unstable to visible light irradiation in conjunction with exposure to oxygen and water.A recent study has explored metal-free, polymeric graphitic carbon nitride (g-C 3 N 4 ) for the generation of hydrogen from a protic solution with visible light. [5] This carbon nitride (CN) polymer was not only found to be a stable semiconductor, but also to be capable of achieving both half reactions of water splitting, meaning that the band-gap covers both the water reduction and water oxidation potentials. This is indeed a rare and lucky case. However, the activity of pristine g-C 3 N 4 remains moderate. [5] Several strategies, such as nanostructuring, [6] doping, [7] cocatalyzing, [5,8] and copolymerization, [9] have been exploited to improve the photocatalytic activity and selectivity of carbon nitride. Indeed, it was shown that by copolymerizing simple barbituric acid with the carbon nitride precursor through a Schiff base reaction, the performance of g-C 3 N 4 could be enhanced, which is an effect resulting from extension of the optical absorption of the polymer to cover more of the visible light range. [9] However, in this case the HOMO was decreased in energy, thus lowering the oxidation potential, which is presumably the most difficult step in achieving overall water splitting with organic semiconductors. This is why the design of appropriate comonomers with diverse chemical composition and structure to allow for modification of the band structure and optoelectronic properties of carbon nitride is still a relevant and promising task.Herein, we advance this strategy by employing a variety of new monomer building blocks with the desired compositions and electronic structures for chemical incorporation into the conjugated polymeric network of g-C 3 N 4 . Most precursors of carbon nitride polymers contain cyano groups, amino groups, or both, with the simplest case being cyanamide, which can undergo multiple thermal condensations to ...

The generation of sustainable and stable semiconductors for solar energy conversion by photoredox catalysis, for example, light-induced water splitting and carbon dioxide reduction, is a key challenge of modern materials chemistry. Here we present a simple synthesis of a ternary semiconductor, boron carbon nitride, and show that it can catalyse hydrogen or oxygen evolution from water as well as carbon dioxide reduction under visible light illumination. The ternary B–C–N alloy features a delocalized two-dimensional electron system with sp2 carbon incorporated in the h-BN lattice where the bandgap can be adjusted by the amount of incorporated carbon to produce unique functions. Such sustainable photocatalysts made of lightweight elements facilitate the innovative construction of photoredox cascades to utilize solar energy for chemical conversion.

Catalysis by single isolated atoms of precious metals has attracted much recent interest, as it promises the ultimate in atom efficiency. Most previous reports are on reducible oxide supports. Here we show that isolated palladium atoms can be catalytically active on industrially relevant g-alumina supports. The addition of lanthanum oxide to the alumina, long known for its ability to improve alumina stability, is found to also help in the stabilization of isolated palladium atoms. Aberration-corrected scanning transmission electron microscopy and operando X-ray absorption spectroscopy confirm the presence of intermingled palladium and lanthanum on the g-alumina surface. Carbon monoxide oxidation reactivity measurements show onset of catalytic activity at 40°C. The catalyst activity can be regenerated by oxidation at 700°C in air. The high-temperature stability and regenerability of these ionic palladium species make this catalyst system of potential interest for low-temperature exhaust treatment catalysts.

Single-atom catalysts have attracted attention because of improved atom efficiency, higher reactivity, and better selectivity. A major challenge is to achieve high surface concentrations while preventing these atoms from agglomeration at elevated temperatures. Here we investigate the formation of Pt single atoms on an industrial catalyst support. Using a combination of surface sensitive techniques such as XPS and LEIS, X-ray absorption spectroscopy, electron microscopy, as well as density functional theory, we demonstrate that cerium oxide can support Pt single atoms at high metal loading (3 wt % Pt), without forming any clusters or 3D aggregates when heated in air at 800 °C. The mechanism of trapping involves a reaction of the mobile PtO2 with under-coordinated cerium cations present at CeO2(111) step edges, allowing Pt to achieve a stable square planar configuration. The strong interaction of mobile single-atom species with the support, present during catalyst sintering and regeneration, helps explain the sinter resistance of ceria-supported metal catalysts.

The search for metal-free organic photocatalysts for H2 production from water using visible light remains a key challenge. Reported herein is a molecular structural design of pure organic photocatalysts, derived from conjugated polybenzothiadiazoles, for photocatalytic H2 evolution using visible light. By alternating the substitution position of the electron-withdrawing benzothiadizole unit on the phenyl unit as a comonomer, various polymers with either one- or three-dimensional structures were synthesized and the effect of the molecular structure on their catalytic activity was investigated. Photocatalytic H2 evolution efficiencies up to 116 μmol h(-1) were observed by employing the linear polymer based on a phenyl-benzothiadiazole alternating main chain, with an apparent quantum yield (AQY) of 4.01 % at 420 nm using triethanolamine as the sacrificial agent.

In semiconductor-mediated photocatalysis, the optical property of semiconductors is a key parameter and closely related to the conversion efficiency of solar energy. However, endeavors in achieving a wide spectral response of semiconductors are still limited in impurity incorporation or using other assistants. Here, we report on a structuredistortion-induced extension in the optical absorption of conjugated polymer semiconductors without relying on any extra species, by taking a typical example of twodimensional graphitic carbon nitride (g-C 3 N 4 ) nanosheets. Experimental and theoretical calculation results both identified the close relationship between the band structure and the structural distortion and the amount of the layers, while keeping in-plane fundamental units intact and the connecting mode invariable during the peeling process. Photocatalytic activity was evaluated toward hydrogen evolution over different samples with visible light. The results showed that distorted g-C 3 N 4 exhibited higher activity and its wavelength-dependence activity can be extended to 550 nm with desirable H 2 production. This finding offers a new channel for researchers to design a polymer with photocatalytic activity under its extending visible spectrum.