Lignin-Supported Heterogeneous Photocatalyst for the Direct Generation of H2O2 from Seawater.

The development of smart and sustainable photocatalysts is in high priority for the synthesis of H2O2 because the global demand for H2O2 is sharply rising. Currently, the global market share for H2O2 is around 4 billion US$ and is expected to grow by about 5.2 billion US$ by 2026. Traditional synthesis of H2O2 via the anthraquinone method is associated with the generation of substantial chemical waste as well as the requirement of a high energy input. In this respect, the oxidative transformation of pure water is a sustainable solution to meet the global demand. In fact, several photocatalysts have been developed to achieve this chemistry. However, 97% of the water on our planet is seawater, and it contains 3.0-5.0% of salts. The presence of salts in water deactivates the existing photocatalysts, and therefore, the existing photocatalysts have rarely shown reactivity toward seawater. Considering this, a sustainable heterogeneous photocatalyst, derived from hydrolysis lignin, has been developed, showing an excellent reactivity toward generating H2O2 directly from seawater under air. In fact, in the presence of this catalyst, we have been able to achieve 4085 µM of H2O2. Expediently, the catalyst has shown longer durability and can be recycled more than five times to generate H2O2 from seawater. Finally, full characterizations of this smart photocatalyst and a detailed mechanism have been proposed on the basis of the experimental evidence and multiscale/level calculations.

Nanometric distance measurements between Mn(ii)DOTA centers.

Pulse electron-electron double resonance (PELDOR) is a versatile technique for probing the structures and functions of complex biological systems. Despite the recent interest in high-spin metal-ions for high field/frequency applications, PELDOR measurements of Mn(ii) remain relatively underexplored. Here we present Mn(ii)-Mn(ii) PELDOR distance measurements at 94 GHz on polyproline II (PPII) helices doubly spin-labeled with Mn(ii)DOTA, which are distinguished by their small zero-field interaction. The measured Mn-Mn distances and distribution profiles were in good agreement with the expected values from molecular models. Additional features in the frequency-domain spectra became apparent at certain combinations of detect and pump frequencies. Spin-Hamiltonian calculations showed that they likely arose from contributions from the pseudo-secular component of the dipolar interaction that were found to be non-negligible for Mn(ii)DOTA. However, the influence of the pseudo-secular component on the distance distribution profiles apparently was limited. The results show the potential of Mn(ii)DOTA spin labels for high-field PELDOR distance measurements in proteins and other biological systems.