With over 8 billion tons of plastic produced since 1950, polymers represent one of the most widely usedand most widely discardedmaterials. Ambient-temperature photoreforming offers a simple and low-energy means for transforming plastic waste into fuel and bulk chemicals but has previously only been reported using precious-metal- or Cd-based photocatalysts. Here, an inexpensive and nontoxic carbon nitride/nickel phosphide (CN x |Ni2P) photocatalyst is utilized to successfully reform poly­(ethylene terephthalate) (PET) and poly­(lactic acid) (PLA) to clean H2 fuel and a variety of organic chemicals under alkaline aqueous conditions. Ni2P synthesized on cyanamide-functionalized carbon nitride is shown to promote efficient charge separation and catalysis, with a photostability of at least 5 days. The real-world applicability of photoreforming is further verified by generating H2 and organics from a selection of nonrecyclable wasteincluding microplastics (polyester microfibers) and food-contaminated plasticand upscaling the system from 2 to 120 mL while maintaining its efficiency for plastic conversion.

Solar water-splitting represents an important strategy toward production of the storable and renewable fuel hydrogen. The water oxidation half-reaction typically proceeds with poor efficiency and produces the unprofitable and often damaging product, O2. Herein, we demonstrate an alternative approach and couple solar H2 generation with value-added organic substrate oxidation. Solar irradiation of a cyanamide surface-functionalized melon-type carbon nitride (NCNCNx) and a molecular nickel(II) bis(diphosphine) H2-evolution catalyst (NiP) enabled the production of H2 with concomitant selective oxidation of benzylic alcohols to aldehydes in high yield under purely aqueous conditions, at room temperature and ambient pressure. This one-pot system maintained its activity over 24 h, generating products in 1:1 stoichiometry, separated in the gas and solution phases. The NCNCNx–NiP system showed an activity of 763 μmol (g CNx)−1 h–1 toward H2 and aldehyde production, a Ni-based turnover frequency of 76 h–1, and an external quantum efficiency of 15% (λ = 360 ± 10 nm). This precious metal-free and nontoxic photocatalytic system displays better performance than an analogous system containing platinum instead of NiP. Transient absorption spectroscopy revealed that the photoactivity of NCNCNx is due to efficient substrate oxidation of the material, which outweighs possible charge recombination compared to the nonfunctionalized melon-type carbon nitride. Photoexcited NCNCNx in the presence of an organic substrate can accumulate ultralong-lived “trapped electrons”, which allow for fuel generation in the dark. The artificial photosynthetic system thereby catalyzes a closed redox cycle showing 100% atom economy and generates two value-added products, a solar chemical, and solar fuel.

While natural photosynthesis serves as the model system for efficient charge separation and decoupling of redox reactions, bio-inspired artificial systems typically lack applicability owing to synthetic challenges and structural complexity. We present herein a simple and inexpensive system that, under solar irradiation, forms highly reductive radicals in the presence of an electron donor, with lifetimes exceeding the diurnal cycle. This radical species is formed within a cyanamide-functionalized polymeric network of heptazine units and can give off its trapped electrons in the dark to yield H , triggered by a co-catalyst, thus enabling the temporal decoupling of the light and dark reactions of photocatalytic hydrogen production through the radical's longevity. The system introduced here thus demonstrates a new approach for storing sunlight as long-lived radicals, and provides the structural basis for designing photocatalysts with long-lived photo-induced states.

This study addresses the light intensity dependence of charge accumulation in a photocatalyst suspension, and its impact on both charge recombination kinetics and steady-state H 2 evolution efficiency. Cyanamide surface functionalized melon-type carbon nitride (NCN CN x) has been selected as an example of emerging carbon nitrides photocatalysts because of its excellent charge storage ability. Transient spectroscopic studies (from ps to s) show that the bimolecular recombination of photogenerated electrons and holes in NCN CN x can be well described by a random walk model. Remarkably, the addition of hole scavengers such as 4-methylbenzyl alcohol can lead to ~ 400-fold faster recombination kinetics (lifetime shortening to ~ 10 ps). We show that this acceleration is not the direct result of ultrafast hole extraction by the scavenger, but is rather caused by long-lived electron accumulation in NCN CN x after hole extraction. The dispersive pseudo-first order recombination kinetics become controlled by the density of accumulated electrons. H 2 production and steady-state spectroscopic measurements indicate that the accelerated recombination caused by electron accumulation limits the H 2 generation efficiency. The addition of a reversible electron acceptor and mediator, methyl viologen (MV 2+), accelerates the extraction of electrons from the NCN CN x and increases the H 2 production efficiency under one sun irradiation by more than 30%. These results demonstrate quantitatively that whilst long-lived electrons are essential to drive photoinduced H 2 generation in many photocatalysts, excessive electron accumulation may result in accelerated recombination losses and lower performance, and thus highlight the importance of efficient electron and hole extraction in enabling efficient water splitting photocatalysts.

Photoreforming of lignocellulose is a promising approach toward sustainable H generation, but this kinetically challenging reaction currently requires UV-absorbing or toxic light absorbers under harsh conditions. Here, we report a cyanamide-functionalized carbon nitride, CN, which shows enhanced performance upon ultrasonication. This activated CN allows for the visible-light driven conversion of purified and raw lignocellulose samples into H in the presence of various proton reduction cocatalysts. The reported room-temperature photoreforming process operates under benign aqueous conditions (pH ≈ 2-15) without the need for toxic components.