Pt nanoparticles supported on mesoporous graphitic carbon nitride as catalysts for hydrolytic dehydrogenation of ammonia borane

Abstract

Platinum (Pt) nanoparticles (NPs) supported on mesoporous graphitic carbon nitride (mpg-CN/Pt) were synthesized in situ via the reduction of as-prepared mpg-CN/Pt(IV) composites during the catalytic hydrolysis of ammonia-borane (AB) under the white-light irradiation. The yielded mpg-CN/Pt nanocatalysts were characterized by using many advanced analytical techniques including TEM, XRD, ICP-MS, XPS, FTIR, PL, and time-resolved emission spectroscopy (TRES) techniques. Besides the privilege advantageous of the presented in situ synthesis protocol for the synthesis of mpg-CN/Pt nanocatalysts, formation of the heterojunction between in situ generated Pt NPs and visible-light active semiconductor mpg-CN enables an improved charge separation and prolonged lifetime, resulting in 2.25-fold enhanced photocatalytic activity within the hydrolysis of AB under white-light irradiation. The effect of Pt loading on the catalytic activity of mpg-CN/Pt nanocatalysts was examined in the hydrolysis of AB and the highest turnover frequency (TOF) of 274.2 min(-1) was obtained with 5.94 wt % Pt-loaded mpg-CN/Pt nanocatalysts, which is the one of the best TOFs among monometallic Pt-based nanocatalysts and comparable to the ones reported using bimetallic Pt nanocatalysts. Moreover, mpg-CN/Pt nanocatalysts were found to be highly durable in the hydrolysis of AB such that it preserves 78% of its initial catalytic activity after the 10th consecutive runs, which is one of the highest reusability performances among all Pt-based catalysts that have been tested in the hydrolysis of AB so far. Upon the results of the kinetic studies, the rate law and activation parameters for the mpg-CN/Pt-catalyzed AB hydrolysis were also reported. This work demonstrates for the first time that mpg-CN is a proper support material for the in situ synthesis of catalytically active yet stable Pt NPs promoting the photocatalytic hydrogen evolution from the hydrolysis of AB.