Supplementary Material

Improving the As(III) adsorption on graphene based surfaces: impact of the chemical doping

Diego Cortés-Arriagada* and Alejandro Toro-Labbé

Nucleus Millennium Chemical Processes and Catalysis; Laboratorio de Química Teórica Computacional

(QTC), Departamento de Química-Física, Facultad de Química, Pontificia Universidad Católica de Chile,

Av. Vicuña Mackenna 4860, Macul, Santiago, Chile. (*)E-mail: dcortesr@uc.cl

Adsorption of As(OH)3 onto B and N-doped graphene

Non-covalent interaction analysis (NCI) of As(OH)3 onto Al, Si, P and Fe-doped graphene

As(OH)3 adsorption onto extended and regular functionalized graphene oxide

Propagation of geometry during molecular dynamics trajectories

Geometrical parameters of 2, 3 and 5 systems in a explicit water environment

Molecular electrostatic potential (MEP) of intrinsic and A-doped adsorbents (A=Al, Si, Fe)

Fragmental electron density difference of 2, 3 and 5 systems)(rF

Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics.This journal is © the Owner Societies 2015

Adsorption of As(OH)3 onto B and N-doped graphene

Graphene doping can with these atoms have been widely studied from theory and experiments

because nitrogen and boron have similar outer and inner shell electronic structures as carbon, even with

approximately the same atomic radius but with an open-shell electronic structure[1]. Therefore, B and N

retain the sp2 hybridization and they do not protrude from the graphene surface keeping the surface dihedral

angles in the surface to 180°. However, slightly increase of binding energies toward adsorption are expected

by changing occupation of bonding/anti-bonding orbitals in graphene due to doping with the open-shell,

which decrease stability of adsorbent and improve interaction with adsorbates[1-3]. Considering the isolated

B and N-doped graphene layers, C-B and C-N bond distances were found to be dC-B=1.50 and dC-N=1.41 Å,

respectively, compared to dC-C=1.42 Å found in pristine graphene. These results agree well with previous

DFT-PBE calculations of B/N-doped graphene [1,4].

Both seated (a) and lying-down (b) conformations were analyzed for each system (Fig. S1).

Adsorption on N and B-doped graphene has the same trend as computed on the intrinsic adsorbent, only due

to interactions by dispersion forces. In the case of B-doped graphene (7a, 7b), the intermolecular As-

adsorbent distances are obtained to be 3.35 and 3.99 Å, respectively; adsorption energies of 0.38 (7a) and

0.43 eV (7b) are found, showing increases of until 0.11 eV with respect to intrinsic graphene. Physisorption

on the N-doped adsorbent appear with similar behavior; in the 8a conformation, As is adsorbed to a

intermolecular distance of 3.34 A from the basal plane, while a intermolecular distance of 4.00 Å is found

for 8b. The 8a and 8b conformations have adsorption energies of 0.38 and 0.33 eV, respectively, with a low

improving (up to 0.06 eV) respecting the intrinsic adsorbent. Moreover, in 8b conformation any interaction on

the top of the dopant atom is observed and As takes place at two centers from the dopant with distances at the

basal plane 3.99 Å. Moreover, NCI surfaces (Fig. S2) show same patterns as observed for physisorption on

the intrinsic graphene, even with low charge transfer toward the adsorbent of 110-2e. These results indicate

that B and N-doped graphene are not good candidates to As(III) removal taking into account the low increase

in the adsorption strength with respect to pristine graphene.

Fig. S1 Side and top view of the optimized molecular structures of As(OH)3 adsorbed onto doped graphene

with boron (7) and nitrogen (8); two interaction modes were obtained (a, b). Distances in angstroms (Å).

Fig. S2 NCI surface of weak interactions in the 7-8 systems. NCI plotting: s=0.7, 2=[-0.015; 0.010].

Non-covalent interaction analysis (NCI) of As(OH)3 onto Al, Si, P and Fe-doped graphene

Fig. S3 NCI surface of weak interactions in the 7-8 systems. NCI plotting: s=0.7, 2=[-0.015; 0.010].

As(OH)3 adsorption onto extended and regular functionalized graphene oxide

In order to gain insights about the effect on the adsorption strength due to multiple functional groups

onto the graphene oxide surface, the As(OH)3 adsorption on extended and regular functionalized adsorbent

was studied and its effect on the physisorption strength. The models of oxidized graphene on the bulk were

based in those proposed from DFT and Monte-Carlo simulations[5], while functionalization at the edges was

done considering the most stable structures and low distortions. The O:C ratio of GO models was retained

below 0.4. Several conformations were computed to account for different interaction modes. The 6e, 6f, 6g

and 6h systems were selected as representatives.

Table S1 Adsorption energies (Eads) in gas phase and percentage of contribution of van der Waals interactions

(%EvdW) for As(OH)3 adsorption on extended and regular functionalized graphene oxide. All values are

counterpoise corrected.

Conformation Eads (eV) %EvdW (%)

GOmulti-epoxide

A 0.50 69B 0.44 95C 0.74 40D 0.47 88E 0.46 60F 0.65 57G 0.72 62H 0.73 52

I (6e) 0.72 63

GOmulti-hydroxyl

A (6f) 0.59 65C 0.50 63D 0.47 95

GOmulti-carboxyl

A 0.69 31B (6g) 0.83 26

GOmulti-carbonyl

A (6h) 0.55 30B 0.55 30

Fig. S4. Optimized molecular structures of As(OH)3 adsorbed onto oxidized graphene containing multiple

epoxide (6e), hydroxyl (6f), carboxyl (6g) and carbonyl (6h) groups. Distances in angstroms (Å).

Propagation of geometry during molecular dynamics trajectories

(continue)

Fig. S5 Geometry of 2, 3 and 5 systems during molecular dynamics calculations at 300 K..

Geometrical parameters of 2, 3 and 5 systems in a explicit water environment

In order to gain insights about the effect of solvent molecules on the “seated” and “lying-down”

conformations for the As(OH)3 molecule on the adsorbent, an explicit/implicit methodology was adopted by

surrounding the adsorbate with explicit 15 H2O molecules and re-optimizing the whole system with the

implicit SMD method model to create the “water environment”. It was observed that although H2O molecules

form a cluster surrounding the adsorbate, the adsorbate retains its stables conformations as determined in the

gas phase. Naturally, geometrical parameters are modified for the effect of the charge environment generated

by surrounding water molecules.

Table S2. Geometrical parameters of 2, 3 and 5 systems in a explicit water environment (15H2O molecules).

Distances d in angstrom (Å) and angles in degree (°).

SystemParameter 2a 2b 3a 3b 5a 5b

dA-O1 1.89 1.86 1.73 1.73 1.99 2.05dO1-As 1.86 1.73 1.84 1.85 1.84 1.84dO2-As 1.83 1.92 1.83 1.93 1.83 1.86dO3-As 1.83 1.89 1.87 1.86 1.83 1.92dO1-H 1.06 - 1.78 1.52 1.04 1.04

A-O1-As120.3

7140.5

9110.7

0129.0

3120.2

2135.6

5O1-As-

O2 96.10 98.92 89.86 93.84 94.90 91.47O2-As-

O3 88.48 94.24 95.42 94.85 96.31 95.09O3-As-

O1 92.63 98.32 92.37 94.08 90.60 91.67

Fig. S6. Minimum energy geometry of the “seated” and “lying-down” conformations of As(OH)3 adsorbed

onto Al, Si and Fe-doped graphene in a solvent environment; As(OH)3 is surrounded by 15 H2O molecules

depicted in white with pointed hydrogen bonds.

Molecular electrostatic potential (MEP) of intrinsic and A-doped adsorbents (A=Al, Si, Fe)

Fig. S7. Molecular electrostatic potential (MEP) of As(OH)3, intrinsic and Al, Si and Fe-doped graphene.

Fragmental electron density difference of 2, 3 and 5 systems)(rF

Fig. S8. Fragmental electron density difference ( ) of 2a and 2b systems, obtained as )(rF

, where stand for the electron density of the A-B system )()()()( rrrr BAABF )(rAB

(adsorbate-adsorbent), and and are the electron density of each fragment ( adsorbate and )(rA )(rB

adsorbent). The figure shows the electron density decreasing (blue color) and electron density increasing

(yellow color).

References

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