Donor–Acceptor‐Type Heptazine‐Based Polymer Networks for Photocatalytic Hydrogen Evolution

Abstract

A heptazine‐based polymer network (HMP‐3) with a donor–acceptor (D–A) structure was prepared and tested as catalyst for photocatalytic hydrogen evolution from water. Compared to other heptazine‐based materials, which are typically prepared at high temperatures and have recently received much interest as metal‐free photocatalysts, the low‐temperature protocol applied here allows the defined introduction of organic functional groups within the polymer backbone. The structure of HMP‐3 contains alternating heptazine and benzothiadiazole moieties as electron acceptors connected by aminobenzene bridges as electron donors. The resulting material leads to enhanced hydrogen evolution compared to graphitic carbon nitride materials prepared at high temperatures (>500 °C) most probably because of the stabilization of photogenerated charge carriers in the D–A structure.

Bandgap Engineering of Organic Semiconductors for Highly Efficient Photocatalytic Water Splitting

“…[27,28] The total electronic structure of such hybrid polymers consists of CB contributed by O-chains and VB contributed by N-chains, resulting in a narrow bandgap. As reported before, the band position shift originates from the existence of O-linked chains connected to N-linked domains, which have lower (more positively orientated) CB with an electron acceptor nature as illustrated in our recent study.…”

“…[25,26] Very recently, we have theoretically and experimentally proved that the oxygen and nitrogen linker-controlled heptazine-based chains strongly influence the polymer's electronic structure. [28] Also, the selective doping into the linker position instead of heptazine units in the polymer maintains an integrated conjugated framework and avoids additional defect-based recombination centers. More importantly, the electron acceptordonor nature between O-chains and N-chains promotes the physical charge separation for enhanced efficiency.…”

Trends and challenges for microporous polymers

“…The activity of HMPs could be largely increased by connecting the heptazine moieties with a donor-acceptor type structure using benzothiadiazole moieties within the linkers. 148 This approach thus shows that the controlled synthesis of CMPs can indeed be used to tailor their electronic properties and thus photocatalytic performance. In the meantime, Sprick et al reported the application of other CMPs for photocatalytic hydrogen production and thus opened the field to the conventional CMPs prepared by metalcatalyzed coupling reactions.…”

Tailored Band Gaps in Sulfur‐ and Nitrogen‐Containing Porous Donor–Acceptor Polymers

“…More interestingly,a ll networks (with the exception of SNP-TTF) evolve hydrogen from water under visiblel ight (395 nm cut-off filter)w ith and withoutp latinum (Pt) as co-catalyst (Figure 4c). [14] Although there are someb enchmark photocatalystlike heptazine based polymers (1600 mmol h À1 g À1 ), [15] and azine-based COFs (1703 mmol h À1 g À1 ) [16] that outperform (S)NPs, none of the previously reported materials show any photocatalytic activity withoutanoble-metalc o-catalyst. It is noteworthy,t hat no added co-catalystd oes not necessarily equate to at ruly" metal-free" photocatalysis.…”