Design and synthesis of glycopolymers for efficient photocatalytic hydrogen evolution

Abstract

Saccharide-based homopolymers (PMDG and PMDM) and diblock copolymers with 9-vinylcarbazole (PNVK-b-PMDG and PNVK-b-PMDM) were synthesized by deacetylation of RAFT-generated corresponding acetyl-glucopyranoside and acetyl-maltose polymer segments. Synthesized polymers chemical structures were authenticated by spectroscopic methods. SEC investigational values of the polymers’ weight average molecular weights (Mw) were obtained in the orbit of 1849–11166 g/mol with 1.14–1.57 range polydispersity (Ð). The acetylated di-block copolymers exhibited higher thermal stability (Td5%: 265–274 °C) than the corresponding homopolymers (Td5%: 259–261 °C). The acetylated di-block copolymers showed higher Tg values (54–67 °C) than the corresponding deacetylated polymers (52 °C). The glycopolymers with hierarchical porous TiO2 (HPT) semiconductor photocatalyst exhibited relatively long lived charge carriers for efficient photon harvesting and enabling them to efficiently drive sacrificial H2 generation in aqueous NaOH under visible light. The hydrogen production rate gradually increased from 109 μmol g−1 h−1 to 881 μmol g−1 h−1 when the NaOH concentration was boosted from 1 M to 10 M using PNVK-b-PMDG as a sacrificial electron donor with HPT and platinum. The glucose-based PNVK-b-PMDG diblock copolymer exhibited higher hydrogen production of 881 μmol g−1 h−1 with an apparent quantum efficiency (AQY) of ∼ 2.15 % than the di-block from maltose (PNVK-b-PMDM) [730 μmol g−1 h−1, AQY: ∼1.78 %] in the presence of alkaline condition (aqueous NaOH, pH = 10). The pendant carbazole moieties of the diblock copolymers improved the efficiency of photocatalytic H2 production by facilitating interaction of free –OH groups of the glycopolymer segment with the HPT which provide significant increase in the reduction potential and decrease of the charge recombination. This work could lead to a more efficient photoreforming path of novel glycopolymer to harvest renewable H2 energy.