The continuous increase in manufacturing coupled with the difficulty of recycling of plastic products has generated huge amounts of waste plastics. Most of the existing chemical recycling and upcycling methods suffer from harsh conditions and poor product selectivity. Here we demonstrate a photocatalytic method to oxidize polystyrene to aromatic oxygenates under visible light irradiation using heterogeneous graphitic carbon nitride catalysts. Benzoic acid, acetophenone, and benzaldehyde are the dominant products in the liquid phase when the conversion of polystyrene reaches >90% at 150 °C. For the transformation of 0.5 g polystyrene plastic waste, 0.36 g of the aromatic oxygenates is obtained. The reaction mechanism is also investigated with various characterization methods and procedes via polystyrene activation to form hydroxyl and carbonyl groups over its backbone via C–H bond oxidation which is followed by oxidative bond breakage via C–C activation and further oxidation processes to aromatic oxygenates.
The construction
of C–N bonds by the direct incorporation
of dinitrogen (N2) instead of ammonia (NH3)
into active species is particularly desirable but has been rarely
reported. Herein, a ditantalum carbide cluster anion (Ta2C4
–) capable of cleaving the NN
bond and constructing a C–N bond under mild conditions has
been identified using mass spectrometry, photoelectron imaging spectroscopy,
and quantum-chemical calculations. The photoelectron spectrum of Ta2C4N2
– is remarkably
different from that of Ta2C4
– and matches the simulated spectrum of the Ta2C4N2
– species with an end-on-bonded CN
unit. The formation of the C–N bond has also been supported
by the CN– fragment observed in the collision-induced
dissociation of Ta2C4N2
–. The exceptional reactivity of Ta2C4
– is ascribed to the low-valent metal center serving as an electron
reservoir. This study provides a non-NH3 route to construct
C–N bonds by incorporating N2 into carbide compounds
to produce nitrogenous species.
Two
novel small molecule acceptors (DTNIC6 and DTNIC8) based on
a ladder-type dithienonaphthalene (DTN) building block with linear
(hexyl) or branched (2-ethylhexyl) alkyl substituents are designed
and synthesized. Both acceptors exhibit strong and broad absorption
in the range from 500 to 720 nm as well as appropriate highest occupied
molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)
levels. Replacing the linear hexyl chains with the branched 2-ethylhexyl
chains has a large impact on the film morphology of photoactive layers.
In the blend film based on DTNIC8 bearing the branched alkyl chains,
morphology with well-defined phase separation was observed. This optimal
phase morphology yields efficient exciton dissociation, reduced bimolecular
recombination, and enhanced and balanced charge carrier mobilities.
Benefited from these factors, organic solar cells (OSCs) based on
PBDB-T:DTNIC8 deliver a highest power conversion efficiency (PCE)
of 9.03% with a high fill factor (FF) of 72.84%. This unprecedented
high FF of 72.84% is one of the highest FF values reported for nonfullerene
OSCs. Our work not only affords a promising electron acceptor for
nonfullerene solar cells but also provides a side-chain engineering
strategy toward high performance OSCs.
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