Portlandite crystal: Bulk, bilayer, and monolayer structures

Abstract

Ca(OH) 2 crystals, well known as portlandite, are grown in layered form, and we found that they can be exfoliated on different substrates. We performed first principles calculations to investigate the structural, electronic, vibrational, and mechanical properties of bulk, bilayer, and monolayer structures of this material. Different from other lamellar structures such as graphite and transition-metal dichalcogenides, intralayer bonding in Ca(OH) 2 is mainly ionic, while the interlayer interaction remains a weak dispersion-type force. Unlike well-known transition-metal dichalcogenides that exhibit an indirect-to-direct band gap crossover when going from bulk to a single layer, Ca(OH) 2 is a direct band gap semiconductor independent of the number layers. The in-plane Young's modulus and the in-plane shear modulus of monolayer Ca(OH) 2 are predicted to be quite low while the in-plane Poisson ratio is larger in comparison to those in the monolayer of ionic crystal BN. We measured the Raman spectrum of bulk Ca(OH) 2 and identified the high-frequency OH stretching mode A 1g at 3620 cm −1 . In this study, bilayer and monolayer portlandite [Ca(OH) 2 ] are predicted to be stable and their characteristics are analyzed in detail. Our results can guide further research on ultrathin hydroxites.

Arsenene/Ca(OH)2 van der Waals heterostructure: strain tunable electronic and photocatalytic properties

“…8,9 However, the studies on single layer alkaline-earth-metal hydroxides (AEMHs) (i.e., Ca(OH) 2 and Mg(OH) 2 ) are sparse and have only started very recently. 11,12 Aierken et al investigated the structural, electronic, magnetic, vibrational, and mechanical properties of monolayer Ca(OH) 2 by rst-principles calculations. The results show that Ca(OH) 2 can be isolated in monolayer form and it is a direct bandgap semiconductor independent of the number of layers.…”

“…The results show that Ca(OH) 2 can be isolated in monolayer form and it is a direct bandgap semiconductor independent of the number of layers. 12 Besides, monolayer gray arsenic (arsenene), a new elemental 2D semiconducting material with buckled honeycomb lattice, has been recently proposed and was predicted to be kinetically very stable based on the theoretical calculations. [13][14][15][16] It is also found that the arsenene is an indirect-band-gap semiconductor and undergoes an indirect-to-direct band-gap and semiconducting-to-metallic transitions under external electric elds or strains.…”

Single layer PbI2: hydrogenation-driven reconstructions

“…Aer a decade of research which was triggered by the synthesis of graphene, 1 the theoretical prediction and synthesis of many 2D ultrathin materials such as silicene, 2,3 germanene, 2,4,5 stanene, 6,7 transition metal dichalcogenides (TMDs), [8][9][10][11][12][13][14][15] hexagonal III-V binary compounds (h-BN, h-AlN) [16][17][18][19] and metal hydroxides (Ca(OH) 2 , Mg(OH) 2 ) 20,21 have been achieved. However, recent research efforts have been directed towards not only the synthesis of graphene-like materials, but also towards the functionalization of existing ultra-thin crystal structures.…”

Highly Surface-Active Ca(OH)2Monolayer as a CO2Capture Material

“…Structure and Stability of Portlandene Few-layered Ca(OH) 2 crystals have already been successfully synthesized at ambient conditions. 23 Here, we start our analyses by showing that monolayer portlandene corresponds to a local energy minimum on the Born-Oppenheimer surface using various stringent stability tests. The optimized geometrical parameters of the monolayer structure are presented in Figure 1(a).…”