This
study provides a significant enhancement in CO2 photoconversion
efficiency by the functionalization of a reduced
graphene oxide/cadmium sulfide composite (rGO/CdS) with amine. The
amine-functionalized graphene/CdS composite (AG/CdS) was obtained
in two steps. First, graphene oxide (GO) was selectively deposited
via electrostatic interaction with CdS nanoparticles modified with
3-aminopropyltriethoxysilane. Subsequently, ethylenediamine (NH2C2H4NH2) was grafted by an N,N′-dicyclohexylcarbodiimide coupling
reaction between the amine group of ethylenediamine and the carboxylic
group of GO. As a result, a few layers of amine-functionalized graphene
wrapped CdS uniformly, forming a large interfacial area. Under visible
light, the photocurrent through the AG/CdS significantly increased
because of enhanced charge separation in CdS. The CO2 adsorption
capacity on AG/CdS was 4 times greater than that on rGO/CdS at 1 bar.
These effects resulted in a methane formation rate of 2.84 μmol/(g
h) under visible light and CO2 at 1 bar, corresponding
to 3.5 times that observed for rGO/CdS. Interestingly, a high methane
formation rate (1.62 μmol/(g h)) was observed for AG/CdS under
CO2 at low pressure (0.1 bar), corresponding to a value
20 times greater than that observed for the rGO/CdS. Thus, the enhanced
performance for photocatalytic reduction of CO2 on the
AG/CdS is due to the improved CO2 adsorption related to
the amine groups on amine-functionalized graphene, which sustains
the strong absorption of visible light and superior charge-transfer
properties in comparison with those of graphene.
Incorporating mesoporosity into zeolite catalysts has been regarded as an innovative technology that improves diffusivity and catalytic lifetime. Here, we propose a facile synthesis of the hierarchically structured ZSM-5 with accompanying intracrystalline mesopores, which was achieved by controlling the growth rate of the zeolite nanocrystals without using extra additives. As the crystallization temperature is strongly related to the formation of primary nanocrystals and their further growth, which fills gaps between those nanocrystals, the hierarchically structured ZSM-5 zeolite was synthesized at low crystallization temperatures (<140 °C). 27 Al MAS NMR and UV-vis-DRS analyses revealed that the hierarchically structured ZSM-5 prepared in the present study contained Al located in the straight channel at a higher proportion than the conventional microporous ZSM-5. The substitution of Al was calculated to be more difficult at the channel intersection than at other T-sites, supporting the experimental results. The hierarchically structured ZSM-5 exhibited excellent stability as well as selectivity for a methanol-to-olefin reaction. Reaction free energies calculated along the hydrocarbon pool mechanism pathway revealed that the Al located in the straight channel drives the reaction through the alkene-based cycle, which is responsible for the high olefin selectivity of the hierarchically structured ZSM-5.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.