Visible-Light-Driven Hydrogen Evolution of PtNP/[Ru(bpy)₃]²⁺/Polyampholyte Hybrid Hydrogels

Abstract

The integration of catalysts and photosensitizers into a soft matter matrix is an important step for technological deployment and potential repair strategies. Here we present a polyelectrolyte hydrogel platform as a flexible and reusable heterogeneous catalyst for hydrogen evolution reaction (HER), combining polydehydroalanine (PDha) hydrogels with Pt nanoparticles (PtNPs). We demonstrate that the PDha hydrogel can readily adsorb the precursor salt at pH 7, allowing for an in situ capping agent-free synthesis of PtNPs upon UV irradiation. When combined with [Ru(bpy)3]2+ via electrostatic attachment and irradiated under visible light, PtNPs@PDha hybrid hydrogels with 6000 ppm of Pt could evolve 6 μmol H2 after 32 h, which leads to a TON of 60 based on the Pt weight fraction, by adding triethylamine as a sacrificial e– donor in 1:1 MeOH/H2O. If the amount of Pt is reduced to 60 ppm, the obtained TON increased to 350, although the evolved H2 amount was reduced to 0.35 μmol. The water uptake of the hydrogel significantly decreased after the attachment of PtNPs and Ru dye. After photocatalytic HER, the characteristic bands of [Ru(bpy)3]2+ (MC at 352 nm and MLCT at 454 nm) in the absorption spectrum of [Ru]@PtNPs@PDha hybrid hydrogels were shifted, presumably due to the degradation of dyes leading to a broad absorption band stretching toward 600 nm with a shoulder visible at 507 nm. Those degraded dyes were investigated by UV–Vis spectroscopy and could be released at low pH values due to the polyampholytic nature of the surrounding PDha hydrogel. Besides the high activity toward HER, the flexible nature of the herein presented hybrid hydrogels renders these materials interesting and promising systems for heterogeneous light-driven catalysis.

Noble Metal-Free Light-Driven Hydrogen Evolution Catalysis in Polyampholytic Hydrogel Networks

“…The chemical cross-linking of poly­(dehydroalanine) allows us to obtain pH-responsive, transparent, and self-supporting hydrogels featuring a high density of pH-dependent charges, and these hydrogels were already successfully utilized as scaffold matrix for immobilizing [Ru­(bpy) 3 ] 2+ photosensitizers and H 2 or O 2 evolution catalysts. , In this work, we integrate an organic photosensitizer derived from PMI into PDha-based hydrogels bearing quaternary ammonium side chains to obtain a fully organic light-harvesting hybrid hydrogel. To this end, we used a PMI derivative with a negatively charged anchoring group for attachment and modified PDha before cross-linking to increase the adsorption capability.…”

“…1,7,9,10-Tetraselenophenoxy perylene monoimide (PMI) was synthesized according to a reported protocol . (NH 4 ) 2 [Mo 3 S 13 ]·2H 2 O was prepared as reported earlier …”

“…24 (NH 4 ) 2 [Mo 3 S 13 ]•2H 2 O was prepared as reported earlier. 40 Synthesis of PDha-g-GTMAC Hydrogels. P(Dha-co-AMA) was synthesized by cleavage of Boc and methyl ester groups on PtBAMA (M n of 18.000 g/mol) synthesized by nitroxide-mediated polymerization of tBAMA as described in an earlier report.…”

“…P(Dha-co-AMA) was synthesized by cleavage of Boc and methyl ester groups on PtBAMA (M n of 18.000 g/mol) synthesized by nitroxide-mediated polymerization of tBAMA as described in an earlier report. 40 Synthesis of PDha-g-GTMAC. P(Dha 0.9 -co-AMA 0.1 ) (200 mg) and glycidyltrimethylammonium chloride (GTMAC) (1 equiv per monomer unit) were dissolved in 0.1 M KOH solution (20 mL each, pH 13).…”

“…Another prime example described by Okeyoshi et al involves a H 2 -evolving gel obtained by incorporating a HER catalyst into a cross-linked network comprising comonomers derived from [Ru­(bpy) 3 ] 2+ (bpy = 2,2′-bipyridine) and viologen. , While this gel system offers flexibility in usage and potential adaptation to catalytic systems for O 2 production, the demanding preparation of monomers involved in the catalytic process (e.g., light-harvesting, electron relay) poses a significant challenge. Inspired by this, we have reported a polyampholyte hydrogel designed for immobilizing a PS and CAT only via electrostatic attachment, demonstrating the capability for both visible light-driven HER and water oxidation. , These networks, based on polydehydroalanine (PDha), form hydrogels with dynamic charges arising from ionizable groups (−NH 2 and −COOH). Therefore, they can accommodate both positively and negatively charged guest molecules, making them suitable matrices for various PS/catalyst combinations through attractive electrostatic interactions.…”