Adsorption and solidification of cadmium by calcium sulfate dihydrate (gypsum) in an aqueous environment: a dispersion-corrected DFT and <i>ab initio</i> molecular dynamics study

Ke, Baolin; Zhang, Qin; Li, Xianhai; Zhang, Shen

doi:10.1039/d1cp03964d

Cited by 7 publications

(9 citation statements)

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“…To investigate the hydrogen bonding structures present on the gypsum surface, we considered results from previously reported simulations. Dispersion-corrected DFT calculations modeled Cd 2+ adsorption on gypsum surfaces containing specific types of vacancies (Ca 2+ , SO 4 2– , and H 2 O) in a unit structure . In this context, the H 2 O molecules are referred to as crystalline or, equivalently, structural water.…”

Section: Resultsmentioning

confidence: 99%

Nonlinear Optical Studies of Water at Gypsum–Air and Gypsum–Aqueous Interfaces

Yiyen,

Sobolewski,

Walker

2024

J. Phys. Chem. C

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Vibrational sum frequency generation (VSFG), Fourier transform infrared (FTIR) absorbance, and Raman scattering were used to investigate the water structure at the gypsum (CaSO 4 •2H 2 O)−air and gypsum−water interfaces under ambient thermal and atmospheric conditions. Results show that water structurally embedded in the gypsum matrix consists of two different populations. One population has decoupled −OH bonds with one bond oriented in-plane, while the second water population has a more traditional, normal mode structure with the molecular C 2 symmetry axis aligned along the surface normal. Based on previously reported molecular dynamics simulations, we propose that surface water molecules having the decoupled −OH bonds (population 1) result from strong hydrogen bond donation to gypsum's sulfate oxygens, whereas water molecules in the second population sample a more symmetric environment that shifts water's vibrational frequencies to ∼3400 cm −1 . Gypsum samples in contact with bulk water show significantly diminished VSFG signals with no observable new features. This result is attributed to loss of VSFG response due to the signal transmission into the bulk water and to an absence of surface-induced structure in the adjacent aqueous phase, consistent with a mineral surface near its point of zero charge. Removal of the bulk aqueous phase results in VSFG spectra that are very similar to those measured prior to water immersion, even when the aqueous phase consisted of D 2 O although relative intensities of individual bands change following exposure to D 2 O. These results imply that some fraction of gypsum's surface structural water remains associated with the substrate and does not readily exchange with an adjacent phase. Furthermore, these findings provide direct molecular-level insight into previous force microscopy studies that proposed the existence of tightly bound surface waters at the gypsum/aqueous interface.

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Section: Resultsmentioning

confidence: 99%

Nonlinear Optical Studies of Water at Gypsum–Air and Gypsum–Aqueous Interfaces

Yiyen,

Sobolewski,

Walker

2024

J. Phys. Chem. C

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“…Thus, the preference along the (020) plane is considered on the basis of the growth of the (040), (021), and (041) planes. The RI for the (020) plane can be computed using eqn (9). 22 The RI of a standard is an essential operator for the exploration of preference growth, which was measured from the ICDD card no.…”

Section: Phase and Crystallographic Analysismentioning

confidence: 99%

“…In eqn (9), the subscript explains the plane of gypsum. The relative intensities of the standard and gypsum samples are 0.521 and 0.505, respectively.…”

Section: Phase and Crystallographic Analysismentioning

confidence: 99%

“…22 The RI of a standard is an essential operator for the exploration of preference growth, which was measured from the ICDD card no. : #00-033-0311 of gypsum using eqn (9).…”

Section: Phase and Crystallographic Analysismentioning

confidence: 99%

“…3 The other applications of gypsum are agriculture waste material-based gypsum walls, which are used as building blocks or wall partitions, and in some cases, fiber-reinforced gypsum composites are also used. 4 The various applications of gypsums are as a source of raw material for cement retarders, 5 in arsenic mitigation by forming gypsum, 6 CO 2 removal by the carbonation process, 7 in biominerals and biomaterials, 8 in the removal of cadmium by solidification, 9 etc.…”

Section: Introductionmentioning

confidence: 99%

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