Tungsten-oxide frameworks with visible light absorption: An ab initio study

Abstract

Metal-organic frameworks (MOFs) provide a powerful method to develop novel materials for photocatalysis and photovoltaics. To realize efficient visible light absorption for these applications, the metal nodes play the crucial role in determining the bandgap, conduction band position, and thus the light absorption. Tungsten (W) can be an outstanding choice for MOFs owing to their semi-occupied d orbitals, which will reduce the bandgap and shift the light absorption toward the visible-light region. However, there is a lack of pure W-based MOFs (W-MOFs). Here, three W-MOFs, named BOW, BCOW, and BSOW, are constructed by using benzene-based ligands, 1,4-benzene-diol, 1,4-benzenedicarboxylic acid, and 1,4-benzenedisulfonic. Ab initio calculations reveal the energetic stability and the effect of ligands on the modification of the electronic and light absorption properties of these W-MOFs. The benzene-linked BOW has a LUMO–HOMO gap of 1.85 eV and strong absorption in the range of green light owing to the weakened hybridization caused by the nonpolar-benzene-structure, whereas the stronger polarity of –COO– and –SO3– in BCOW and BSOW recovers the high W–O hybridization, enlarges the bandgap, and blueshifts the light absorption.