Environmental Nanotechnology, Monitoring & Management 16 (2021) 100580
Contents lists available at ScienceDirect
Environmental Nanotechnology, Monitoring & Management
journal homepage: www.elsevier.com/locate/enmm
Adsorption of selenium (iv) oxoanions on calcined layered double
hydroxides of Mg-Al-CO3 from aqueous solution. Effect of calcination and
reconstruction of lamellar structure
B.A. Jiménez-López a, R. Leyva-Ramos a, *, J.J. Salazar-Rábago b, A. Jacobo-Azuara c,
A. Aragón-Piña d
a
Centro de Investigación y Estudios de Posgrado, Facultad de Ciencias Químicas, UASLP, Av. Dr. Manuel Nava No. 6, San Luis Potosí, S.L.P. 78210, México
Facultad de Ciencias Químicas, Universidad Autónoma de Nuevo León, Av. Universidad s/n, Cd. Universitaria, San Nicolás de los Garza, N.L. 66455, México
c
Departamento de Química, División de Ciencias Naturales y Exactas, Universidad de Guanajuato, Noria Alta s/n, Guanajuato, Gto. 36050, México
d
Instituto de Metalurgia, Universidad Autonoma de San Luis Potosi, Av. Sierra Leona 550, Lomas de San Luis, San Luis Potosí, S.L.P. 78210, México
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Adsorption
Calcination
Electrostatic attraction
Layered double hydroxides
Reconstruction
Selenium (IV) oxoanions
The Se(IV) oxoanions adsorption in water solutions onto calcined layered double hydroxide (LDH) was analyzed
detailly. The effects of calcination and reconstruction of the LDH lamellar structure upon the adsorbing capacity
were also argued. The Mg/Al-CO3 LDH was fixed by a co-precipitation method, was calcinated at 550 ◦ C
(LDH550), and was rehydrated in deionized water (LDH550Reh). The characterization revealed that the LDHs
were mesoporous. The XRD analysis confirmed the LDH layered structure and the destruction of the lamellar
structure in the LDH550, as well as the formation of mixed metal oxides. Furthermore, the reconstruction of the
layered structure in LDH550Reh and LDH550 loaded with Se(IV) was corroborated by XRD. The interlaminar
carbonates were removed in the calcination, resulting in a higher positive zeta potential (ZP) on the LDH550
surface and favoring the Se(IV) oxoanions adsorption onto LDH550. At pH = 5 and T = 25 ◦ C, the maximum
adsorption capacity of LDH550 towards Se(IV) was 134.4 mg/g and 5.3-fold bigger than that of uncalcined LDH,
attributed to the increment in basal sites available for adsorbing Se(IV) oxoanions. The adsorbing capacity of
LDH550 towards Se(IV) oxoanions increased by reducing the solution pH from 11 to 5 because of the
enhancement of the electrostatic attraction between the Se(IV) oxoanions in water solutions and the positively
charged surface of LDH550. The temperature effect showed that Se(IV) adsorption on LDH550 was exothermic
for uptakes of Se(IV) adsorbed higher than 90 mg/g. The adsorption of Se(IV) on LDH550 occurred by anion
exchange and electrostatic attractions. The ZP of the LDH was reduced by the Se(IV) adsorption, and the
reduction of ZP was incremented almost linearly with the mass of Se(IV) adsorbed, demonstrating that Se(IV)
was predominantly adsorbed by electrostatic attraction.
1. Introduction
Selenium is a micronutrient essential to sustain the life process of
organisms. It has positive effects on immune functions and thyroid and
fertility activities; however, an excessive selenium intake can be highly
toxic (Plant et al., 2014). A daily intake larger than 0.4 mg may cause
selenosis, characterized by fingernails and hair loss, abnormal func­
tioning of the nervous system, endocrine disruption, as well as paralysis
and diabetes (Plant et al., 2014; Chawla et al., 2020). A maximum se­
lenium limit of 0.04 mg/L in potable water was suggested by World
Health Organization (Plant et al., 2014).
Various physicochemical and biological processes have been applied
for eliminating selenium from aqueous effluents, including adsorption
and ion exchange, oxidation/reduction, phytoremediation and reverse
osmosis (Holmes and Gu, 2016). Ferrihydrite coprecipitation/adsorp­
tion is the U.S. EPA best demonstrated available technology for
removing Se(IV) from industrial wastewater. Usually, the ferric chloride
and sodium hydroxide are added to produce ferrihydrite, and subse­
quently, ferrihydrite precipitates, and the selenium oxoanions are
simultaneously adsorbed on the ferrihydrite surface. However, large
quantities of sludge are produced in this process (Holmes and Gu, 2016).
Adsorption is a simple and easy process to operate and is widely
* Corresponding author.
https://doi.org/10.1016/j.enmm.2021.100580
Received 7 April 2021; Received in revised form 24 August 2021; Accepted 27 September 2021
Available online 30 September 2021
2215-1532/© 2021 Elsevier B.V. All rights reserved.
B.A. Jiménez-López et al.
Environmental Nanotechnology, Monitoring & Management 16 (2021) 100580
applied for eliminating inorganic compounds in aqueous solutions
(Mafu et al., 2014). Different materials have been applied for removing
anions from water solutions, such as bone char (Villela-Martínez et al.,
2020), covalent organic frameworks-based materials (Liu et al., 2021),
hydroxyapatite (Kongsri et al., 2013) and layered double hydroxide
(Isaacs-Paez et al., 2014; Ramírez-Llamas et al., 2015). The selenium
adsorption from water solutions has been studied applying various
traditional materials such as hydroxyapatite, metal oxides, clays, sand
coated with aluminum-oxide and activated alumina (Kuan et al., 1998).
Magnesium oxide, hydroxyapatite and chitosan had the adsorbing ca­
pacities for selenium of 0.82, 1.92, and 0.51 mg/g, respectively, which
are very low (Gonzalez et al., 2011; Kongsri et al., 2013).
The layered double hydroxides (LDHs) are synthetic materials also
called anionic clays because of their layered morphology and anion
exchange capacity (AEC). The LDHs have high chemical and thermal
stability, simple synthesis methods, elevated surface area, excellent
biocompatibility, and significant AEC (Abdolmohammad-Zadeh et al.,
2013; Mosangi et al., 2016; Cai et al., 2016). It is worth mentioning that
the LDHs are very versatile adsorbents because they have been applied
for adsorbing inorganic anions and cations and organic pollutants from
water solutions. Sun et al. (2015) investigated the adsorption of Cu(II),
Ni(II), and Zn(II) cations on calcined LDHs, and Yu et al. (2018) studied
the adsorption of U(VI) cations on calcined ternary oxide nano­
composites. Both works showed that these LDH-based materials
exhibited high adsorption capacity towards these metal cations.
The LDH application for removing anionic species from water solu­
tions such as arsenic, boron, chromium (VI), fluoride, iodine and sele­
nium has previously been studied (Das et al., 2004; Isaacs-Paez et al.,
2014; Ramírez-Llamas et al., 2015; Theiss et al., 2014; You et al., 2001).
The Se(IV) and Se(VI) adsorption on LDH has been analyzed in various
works, and the LDH adsorption capacity depends upon the synthesis
method, the divalent and trivalent metals employed (M2+ and M3+), the
molar ratio M2+/M3+ and the interlaminar anion (Chubar, 2014;
Kameda et al., 2014, Mandal et al., 2009).
The LDH adsorbing capacity towards anions has been enhanced by
calcination at temperatures ranging from 250 and 600 ◦ C. The calcina­
tion of LDH yielded mixed metal oxides and removed the interlaminar
carbonates. The layered structure of LDH is reconstructed by contacting
the calcined LDH with a water solution, and the original layered struc­
ture is partially recovered. This behavior is known as the “memory ef­
fect” (He et al., 2006). Some authors have suggested that the adsorption
of selenium oxoanions on LDH is due to ion exchange of OH– and CO32–
and electrostatic attractions (Das et al., 2004). Isaacs-Paez et al. (2014)
evaluated the OH– and CO32– milliequivalents released from LDH550
and milliequivalents of borate adsorbed on LDH, demonstrating that the
contribution of ion exchange represented about 30 %.
Usually, the reconstruction and adsorption of anions on calcined
LDH are performed simultaneously. However, no work has been re­
ported in the adsorption capacity if the calcined LDH is reconstructed
first and then the adsorption is performed after reconstruction.
Furthermore, the significance of the electrostatic interaction in the an­
ions adsorption mechanism on LDH has not been studied in detail. The
novelty of this work is to address both issues.
This work’s main objective was to examine the effect of calcination
and reconstruction of LDH upon its capacity for adsorbing Se(IV)
oxoanions from water solutions. The temperature and pH impact upon
the Se(IV) adsorbing capacity of calcined LDH was also evaluated. Be­
sides, the role of the reconstruction in the adsorption mechanism was
elucidated. It was shown that the oxoanions of Se(IV) in solution were
attracted electrostatically to the calcined LDH positive surface and
electrostatic interaction was the predominant adsorption mechanism.
2. Experimental methods
2.1. Materials and chemical substances
Reagent-grade chemicals were utilized in this work for preparing and
characterizing the layered doubled hydroxide (LDH) and carrying out
the adsorption experiments, and all solutions were made utilizing
deionized water. Additionally, a standard solution of Se(IV) (1000 mg/
L) was fixed by weighting a certain mass of Na2SeO3 (2.19 g) and dis­
solving it in deionized water (1 L).
2.2. Synthesis and modification of the LDH
The LDH synthesis was a co-precipitation procedure detailed by
Isaacs-Paez et al. (2014). Briefly, 1 L of 0.5 M Na2CO3 solution was
prepared; while, predetermined amounts of Al(NO3)3 (15 g) and Mg
(NO3)2 (30.8 g) were placed inside a flask and then dissolved using 800
mL of deionized water, maintaining the molar proportion of Mg/Al = 3.
Additionally, a specific volume of deionized water (150 mL) was poured
into a three-neck round-bottom flask and then set on a thermomagnetic
plate to heat up to 70 ◦ C and keep under continuous agitation. Soon
afterward, the Na2CO3 solution and the Al(NO3)3/Mg(NO3)2 solution
were fed into the flask using peristaltic pumps at a volumetric rate of 6
and 5 mL/min, respectively. The solution pH was periodically deter­
mined and maintained alkaline (10–11); if necessary, the pH was
controlled by dispensing drops of 1 M NaOH solution. The suspension in
the flask was continuously agitated for 18 h and keeping T = 70 ◦ C.
Subsequently, the solid was vacuum filtered, rinsed using deionized
water and dried at 110 ◦ C for 24 h. Lastly, an agate mortar was employed
to grind the solid, which was labeled as LDH.
The LDH was modified by calcination heating at 10 ◦ C/min until
reaching a temperature of 550 ◦ C, which was maintained for 8 h more.
The calcined LDH was labeled as LDH550. The memory effect of LDH
was studied by rehydrating the LDH550. The rehydration procedure was
carried out by adding 1 g of LDH550 into a flask (250 mL), pouring 50
mL of deionized water and then continuously agitated for 1 day at room
temperature. Soon afterward, LDH was filtered and dried in an oven t at
110 ◦ C during 24 h and designated as LDH550Reh.
2.3. Chemical composition of the LDH
An atomic absorption (AA) spectrophotometer, Perkin Elmer, model
AAnalyst 200, was used to appraise the Al and Mg concentrations in the
LDHs. Besides, Isaacs-Paez et al. (2014) suggested the procedure for
fixing the LDH sample for AA analysis.
2.4. Methods for characterizing LDH
The N2 adsorption-desorption isotherm measured in a physisorption
apparatus, Micromeritics, model ASAP 2020, was analyzed to calculate
the textural characteristics of the LDH. The surface area calculation was
performed with the BET (Brunauer, Emmett and Teller) technique
(Thommes et al., 2015).
The LDH surface morphology was inspected in a scanning electron
microscope (SEM), JEOL, JSM-6610LV, at a voltage of 8 kV. An X-ray
diffractometer, PANalytical, model EMPYREAN, employing CuKα radi­
ation (λ = 0.15405 nm, 40 mA and 45 kV) was used to recognize the LDH
crystalline species.
A zetameter, Zetasizer, Malvern, Nano series was used to evaluate
the surface zeta potential (ZP) of all LDHs. First, the grinding of LDH and
LDH550 was performed in an agate mortar until the particle sizes passed
through the US mesh size 400. Subsequently, nine suspensions were
fixed by pouring 25 mL of a solution with pH ranging from 4 to 12 and
constant ionic strength (I = 0.01 N) into a plastic vial (50 mL) containing
0.025 g of LDH. The solutions were prepared by combining pre­
determined volumes of 0.01 N HNO3, NaOH and NaNO3 solutions,
2
B.A. Jiménez-López et al.
Environmental Nanotechnology, Monitoring & Management 16 (2021) 100580
covering the pH range 4–12. The nine plastic vials were placed in a
thermostatically controlled bath at 25 ◦ C and were allowed to reach
equilibrium for 10 days. The vials were put on an orbital shaker for 15
min daily to mix the solution, and the solution pH was regularly
determined and regulated by dispensing some small volumes of 0.01 N
HNO3 or NaOH solution, as necessary. After 10 days, the LDH particles
in the suspensions were resuspended by placing the vial in an ultrasonic
bath for 20 min. A portion of the suspension was transferred to a plastic
cell (5 mL), Malvern, model DTS1060, avoiding trapping air inside it.
Soon afterward, the particles ZP in the cell was determined in the
zetameter and graphed against the solution pH. The experimental error
in surface ZP determination was lower than 5 %.
Furthermore, the ZP of LDH550 loaded with Se(IV) (LDH550Se) was
also assessed by a similar procedure. In this case, the solutions with a pH
of 5, 7 and 11 and I = 0.01 N were prepared in 25 mL graduated flasks
and had initial Se(IV) concentrations less than 400 mg/L, corroborated
by AA analysis of a sample (5 mL). Soon afterward, 20 mL of the Se(IV)
solution was poured into a plastic vial (50 mL) containing 0.025 g of
LDH550. During 10 days, the procedure was followed as described
above and then, the ZP of LDH550Se was measured. Additionally, a
solution sample was analyzed by an AA spectroscopic method to quan­
tify the equilibrium concentration of Se(IV), and the amount adsorbed of
Se(IV) onto LDH was computed as described below (section 2.6).
The effect of solution pH was investigated by carrying out experi­
ments at pH values of 5, 7, 9 and 11, at T = 25 ◦ C and I = 0.01 N. The
effect of temperature was examined by obtaining experimental adsorp­
tion data at 15, 25, and 35 ◦ C while keeping the solution pH constant at 5
and I = 0.01 N. At pH = 5 and T = 25 ◦ C, the effect of ionic strength was
examined by performing experiments at the ionic strength of 0.01, 0.05
and 0.1 N, for this purpose, the Se(IV) solutions were prepared by mixing
predetermined volumes of 0.01, 0.05 and 0.1 N NaOH and HNO3
solutions.
3. Results and discussion
3.1. LDHs chemical composition
Aluminum and magnesium hydroxides, water sorbed and interlam­
inar carbonates are the main constituents of the LDH synthesized in this
work. The LDH is usually characterized by the following formula
[ 2+ 3+
]x+ n−
M1− x Mx (OH)2
[A ]x/n mH2 O. In this formula, An− indicates the
interlaminar anionic species, M3+ and M2+ designate the trivalent and
divalent metallic cations, and × represents the molar ratio M3+/(M2+ +
M3+). The weight percentages of Al and Mg in LDH were quantified to be
17.43 and 38.77 %, correspondingly. Ramírez-Llamas et al. (2015) re­
ported similar weight percentages for an LDH synthesized using the
same Al and Mg salts. Furthermore, the molar ratio Mg/Al and × for
LDH were estimated to be 2.81 and 0.26. These results are within those
in the LDH technical literature. A pure phase of LDH was synthesized in
this work because Mg/Al was in the range 2 ≤ Mg/Al ≤ 4 or × was in the
range 0.2 ≤ x ≤ 0.33 (Evans and Slade, 2005; Santamaría et al., 2020).
2.5. Quantification of Se(IV) concentrations in aqueous solutions
In a water sample, the Se(IV) concentration was quantified in an AA
spectrophotometer, Varian, AAnalyst 200. The Se(IV) concentration was
evaluated using a calibration curve obtained at the sample pH.
3.2. XRD characterization
2.6. Technique for procuring the adsorption data
Fig. 1 displays the LDH, LDH550, LDHReh and LDH550Se XRD
patterns. The reflections of (003), (006), (012), (015), (018), (110) and
(113) are at the angles 2θ of 11.7◦ , 34.7◦ and 23.5◦ 39.3◦ , 46.7◦ , 60.4◦
and 61.6◦ , and are characteristic of LDH and correspond to a hydro­
talcite phase (JCPDS 14-191) (Sharma et al., 2008). The typical XRD
pattern of LDHs is generally characterized by sharp and symmetrical
reflections for basal (003), (006), (110) and (113) planes (Sun et al.,
2015), and asymmetrical and comparatively slight non-basal reflections
for (012), (015) and (018) planes (Lin et al., 2014). This result indicated
that LDH fixed in this work consisted of a single crystalline phase. The
reflections for (012), (015), (018) and (110) planes confirmed the
presence of hexagonal lattice with rhombohedral 3R symmetry (Sun
et al., 2015).
The LDH550 XRD pattern depicts the disappearance of the LDH
Several Se(IV) solutions having different initial concentrations were
made by pipetting different volumes of the Se(IV) stock solution into
graduated flasks (50 mL) and adding a solution having and an ionic
strength of I = 0.01 N and a preset pH. The latter solution was fixed by
mixing predefined volumes of 0.01 N NaOH and HNO3 solutions. The
initial Se(IV) concentrations changed in the range 100–450 mg/L, and
were verified by AA analysis of a sample (5 mL).
The Se(IV) adsorption data on LDH, LDH550, and LDHReh were
obtained in batch adsorbers (50 mL vial) set in a thermostatically
controlled bath. An LDH mass (0.1 g) and a volume of a Se(IV) solution
(45 mL) were mixed in the batch adsorber and were allowed to attain
equilibrium. Three times daily, the adsorber solutions were mechani­
cally shaken for 15 min in an Orbital Shaker TS-100. In all the adsorp­
tion runs, the pH was determined regularly and constantly maintained
by supplementing 0.01, 0.05 and 0.1 N HNO3 or NaOH solutions, as
needed. The supplemented volume was invariably smaller than 1 mL
and was supposed irrelevant compared to the initial volume of the
adsorber solution. Previous experiments have shown that contacting the
solution and the adsorbent for 10 days is sufficient for reaching
adsorption equilibrium. The adsorber solution was analyzed by AA
spectroscopy to determine the Se(IV) concentration after approaching
equilibrium. The amount adsorbed of Se(IV) was ascertained by the
subsequent relationship:
q =
V
(C0 -C)
m
(1)
Where C0 denotes the Se(IV) concentration at the beginning, mg/L; C
represents the equilibrium Se(IV) concentration, mg/L; q designates the
amount adsorbed of Se(IV) on LDH, mg/g; V represents the Se(IV) so­
lution volume in the adsorber, L. The error associated with Se(IV)
determination was found to be minor than 1.5 %, ensuring that the
deviations in the estimation of the uptake were lower than 4 % in all
cases.
Fig. 1. XRD patterns of LDH, LDH550, LDHReh, and LDH550Se.
3
B.A. Jiménez-López et al.
Environmental Nanotechnology, Monitoring & Management 16 (2021) 100580
characteristic reflections, corroborating that the hydrotalcite structure
was destroyed. The layered structure was converted to a mixture of
metal oxides because of the loss of water and interlaminar CO32– during
calcination (Isaacs-Paez et al., 2014). The reflections of (111), (200) and
(220) correspond to mixed cubic MgO-like oxide (Kuśtrowski et al.,
2005). The mixed metal oxides of LDH550 were rehydrated in deionized
water, and the original lamellar structure of the LDH was partially
reconstructed in the rehydration. Thus, the basal reflections (003) and
(006) associated with the hydrotalcite disappeared in the calcination but
reappeared in LDH550Reh after rehydration. This LDH reconstruction
feature is known as the memory effect. Nevertheless, the reflections
close to 2θ = 60◦ were not symmetrical as in the LDH XRD pattern since
the interchangeable CO32– were removed during the calcination.
The XRD pattern of LDH550Se presented in Fig. 1 shows that the
hydrotalcite structure was partially reconstructed due to the rehydration
and adsorption of oxyanions of Se(IV) from the solution. The low in­
tensity and asymmetry of the reflections indicated that the LDH550Se
has low crystallinity and disordered lamellar structure.
The strong basal reflections of (003) and (006) at low angles can be
related to consecutive stacking of LDH or brucite-like sheets. The cell
parameter c can be ascertained from these reflections and the subse­
quent relationship: c = (3d003 + 6d006)/2 (Braterman et al., 2004;
Kuśtrowski et al., 2005). The interlayer spacing d or the distance be­
tween adjoining LDH sheets is one-third of parameter c, d = c/3. In the
LDH sheets, the mean cation–cation distance is designated as the cell
parameter a, which can be calculated from the reflection of (110) as
follows a = 2d110 (Braterman et al., 2004). The LDH sheet thickness is
0.48 nm (Braterman et al., 2004) and was subtracted from d to calculate
the gallery height. Table 1 records the basal reflections, the cell pa­
rameters, interlayer spacing d and gallery heights. Alike values have
been found by Isaacs-Páez et al. (2014) and Ramírez-Llamas et al.
(2015).
The LDH interlayer spacing with interlaminar carbonates varies from
0.749 to 0.875 nm (Isaacs-Páez et al., 2014; Theiss et al., 2014; Wang
et al., 2012). It is a well-known fact that the type of interlaminar anion
can modify the values of the cell parameters. The hydrated ion radius of
the CO32– is 2.66 Å (Lin et al., 2014), while the selenite (SeO32− ) pre­
sents an effective ionic radius of 3.18 Å (Cowan et al., 1990). After
adsorbing Se(IV), the interlayer spacing and gallery height increased
from 0.78 to 0.85 nm and from 0.30 to 0.37 nm, respectively, demon­
strating the intercalation of Se(IV) anions during the structural recon­
struction of the LDH550.
Fig. 2. Adsorption-desorption isotherms of N2 on a) LDH, b) LDH550 and
c) LDH550Reh.
Table 2
Textural properties of different LDHs.
The nitrogen adsorption–desorption isotherms for LDH, LDH550 and
LDH550Reh are depicted in Fig. 2. The isotherm shapes are type IIb, and
the hysteresis loops can be classified as type H3 (Rouquerol et al., 2014),
typical of aggregates of platy particles.
Table 2 shows the values of the principal textural properties of LDH,
LDH550 and LDH550Reh, and these values are within the values re­
ported previously (Isaacs-Paez et al., 2014; Mandal et al., 2009; Yang
et al., 2020; Yun et al., 2002). The mean pore diameters showed that
both LDH and LDH-550 were mesoporous. The LDH calcination at
LDH
LDHReh
LDH550Se
0.78
0.39
0.15
2.34
0.30
0.78
0.30
0.79
0.40
0.15
2.38
0.30
0.79
0.31
0.85
0.45
0.15
2.62
0.30
0.87
0.39
Pore volume
(cm3/g)
Average pore diameter
(nm)
LDH
LDH550
LDHReh
101
210
100
0.4
1.2
0.6
8.8
15.3
17.8
3.4. Physicochemical characterization
Table 1
Basal reflections, cell parameters, interlayer spacing d and gallery heights of
LDH, LDHReh, and LDH550Se.
d003 (nm)
d006 (nm)
d110 (nm)
c (nm)
a (nm)
interlayer spacing d (nm)
gallery height (nm)
Surface area (BET)
(m2/g)
550 ◦ C increased the average pore diameter, pore volume and surface
area from 8.8 to 15.3 nm, 0.4 to 1.2 cm3/g and 101 to 210 m2/g,
respectively. This tendency confirms that the calcination collapsed the
LDH lamellar structure due to the interlayer CO32– anions elimination
and caused disordering of the layered structure. On the other hand, after
rehydration, the LDH550Reh recovered almost the pore volume and
surface area of the starting LDH, as explained by the memory effect (Tian
et al., 2017). The increase in the average pore diameter may be associ­
ated with the loss of impurities and the layer disordering after the
calcination process.
The examination of LDH surface morphology was performed by
scanning electron microscopy (SEM). The SEM photomicrographs of
LDH, LDH550 and LDHReh are shown in Fig. A1, and the typical
lamellar structure of LDH can be noticed. The spherical and semi­
spherical particles are formed by the aggregation of plate-like sheets
(Brucite) or flakes. Other authors have described similar particle
morphology (Wang et al., 2012). Fig. A1b exhibits the LDH550 particles,
and it can be observed that the layered structure is more disordered and
the flake thickness is smaller than in the LDH. The SEM image for the
LDHReh is presented in Fig. A1c, exhibiting larger aggregates formed by
flakes and more disordering than in the LDH.
3.3. Textural and morphological characterization
Parameters
Adsorbent
In the pH range from 4 to 12, the ZP distributions of the LDH and
LDH550 are presented in Fig. 3. The isoelectric point (pHIEP) is an
important physicochemical property for characterizing the surface of
adsorbing materials containing oxides and hydroxides. The pHIEP cor­
responds to the pH at which the ZP is neutral. In other words, the net
surface ZP is positive when the solution pH < pHIEP; however, the sur­
face ZP is negative for pH > pHIEP.
The isomorphic substitution of Mg+2 by Al+3 in the basal sites of LDH
layers induced the LDH positive charge, resulting in an imbalance in the
4
B.A. Jiménez-López et al.
Environmental Nanotechnology, Monitoring & Management 16 (2021) 100580
constants by interpreting the experimental data using each isotherm
model. Additionally, the average percentage deviation (%D) was
selected as the goodness of fitting test for each isotherm, and %D was
appraised by the succeeding relationship:
(
⃒)
N ⃒
⃒qexp − qpred ⃒
1 ∑
⃒
⃒ × 100 %
(8)
%D =
⃒
N i=1 ⃒ qexp
where qexp (mg/g) denotes the equilibrium uptake of Se(IV) adsorbed
determined experimentally, qpred (mg/g) represents the equilibrium
uptake of Se(IV) adsorbed estimated using the isotherm model, and N
represents the number of adsorption data.
Table 4 registers the parameters and %D for the Prausnitz-Radke,
Langmuir and Freundlich isotherms. The P-R model better represented
the adsorption data since its %D was less than those of the Langmuir and
Freundlich isotherms in 6 out of 10 experimental conditions shown in
Table 3. This finding can probably be explained considering that the P-R
isotherm is a three-constant model, although the Freunlich and Lang­
muir isotherms have two constants. Hence, the P-R isotherm was
selected to correlate the Se(IV) adsorption data on the different LDHs.
Fig. 3. Zeta potential distribution of LDH and LDH550 concerning the solu­
tion pH.
3.6. Effects of calcination and reconstruction upon the LDH adsorption
capacity
surface charge. The substitution in the basal sites is expressed as ≡Al+,
and the balancing of the basal sites positive charge by the interlayer
CO32– is represented subsequently:
2( ≡ Al+ ) + CO2−3 →( ≡ AL+ )2 CO2−3
The Se(IV) adsorption isotherm on LDH550 was compared to that on
LDH to evaluate the calcination effect on the LDH adsorbing capacity.
The Se(IV) adsorption isotherms on the various LDHs are presented in
Fig. 4 at pH of 5 and 25 ◦ C, and the LDH calcination considerably
enhanced the adsorbing capacity towards Se(IV). For an equilibrium Se
(IV) concentration of 100 mg/L, the Se(IV) uptakes on LDH and LDH550
were 20.3 and 107.2 mg/g, evidencing that the capacity was augmented
5.3 times by the calcination.
Several studies have shown that eliminating interlayer carbonates in
the LDH calcination (350–550 ◦ C) promotes the LDH adsorption ca­
pacity (Dos Santos et al., 2017; Das et al., 2007; Kuśtrowski et al., 2005).
Ramírez-Llamas et al. (2015) found that the Mg-Al-CO3 LDH capacity for
adsorbing fluoride depended highly on the levels of interlayer CO32–,
and reported that the adsorption capacity towards fluoride improved by
augmenting the calcination temperature from 350 to 550 ◦ C. The
enhancement of the LDH550 capacity for adsorbing Se(IV) is associated
with the elimination of the CO32– in the interlayer spacing. The reduc­
tion of the level of CO32– in the LDH550 was confirmed by FTIR analysis.
Fig. A2 presents the FTIR spectrum of LDH, and the band shown at 1359
cm− 1 is associated with the asymmetric stretching mode of CO32– (Goh
et al., 2008). The LDH550 FTIR spectrum did not display this charac­
teristic band of CO32–, corroborating the significant reduction of the
concentration of CO32– in LDH550.
The subsequent reaction represents the elimination of CO32– from the
basal sites:
(2)
Besides, the layer hydroxyls (≡M− OH) affect the LDH surface charge
by the subsequent reaction schemes (Isaacs-Paez et al., 2014):
Protonation reaction :≡ M − OH + H + → ≡ M − OH2+
(3)
Deprotonation reaction :≡ M − OH→ ≡ M − O− + H +
(4)
The pHIEP of the LDH is 9.8 (see Fig. 3, which is similar to that
determined by Chubar et al. (2013) for a Mg-Al-CO3 LDH prepared by
three different synthesis methods. On the other hand, the pHIEP of the
LDH550 was at 11.4, which is higher than the 9.6 evaluated by IsaacsPaez et al. (2014). These results corroborate that pHIEP was raised during
the calcination of the LDH. This finding can be justified by recognizing
that the thermal decomposition of interlayer carbonates occurs during
calcination, and the carbonates balance the positive charges in the
lamella of LDH. Thus, the higher number of unbalanced positive sites
leads to the displacement of the pHIEP to higher pH values (Isaacs-Paez
et al., 2014).
3.5. Adsorption isotherms of Se(IV)
The isotherm models of Prausnitz-Radke, Freundlich and Langmuir
interpreted the adsorption equilibrium data of Se(IV) on the different
LDHs, and these models are outlined subsequently:
1
n
q = kC
( ≡ Al+ )2 CO23 - →2( ≡ Al+ ) + CO23 -
(5)
q =
qm KC
1 + KC
(6)
q =
aC
1 + bCβ
(7)
(9)
In this way, the oxoanions of Se(IV) are attracted to the extra positive
charges in the basal sites (≡Al+), and the oxoanions of Se(IV) counter­
balance the positive charge of ≡Al+.
The adsorption isotherm of Se(IV) on LDH550Reh is also graphed in
Fig. 4. For an equilibrium concentration of 100 mg/L, the uptake
adsorbed of Se(IV) on LDH550 and LDH550Reh were 107.2 to 25.8 mg/
g, correspondingly; consequently, the LDH550Reh adsorbing capacity
was significantly lower than that of LDH550. The layered structure
reconstruction and the adsorption of Se(IV) on LDH550 took place
simultaneously, whereas, in the LDH550Reh, the reconstruction of
LDH550Reh was carried out first by placing the LDH550 in water so­
lution without Se(IV). This significant difference in adsorption capacity
can be justified by arguing that the basal sites are more accessible to the
Se(IV) oxoanions during the reconstruction of the lamellar structure of
LDH550 and the disordering of the layers facilitates the adsorption and
Where a (L/g), b (Lβ/mgβ) and β are the Redlich-Peterson model con­
stants, C (mg/L) denotes the equilibrium Se(IV) concentration, k
(mg1− 1/nL1/n/g) and n designate the Freundlich model constants, K (L/
mg) and qm (mg/g) are the Langmuir isotherm parameters associated
with the adsorption heat and the maximum mass adsorbed of Se(IV) on
LDHs, respectively, and q (mg/g) represents the equilibrium amount
adsorbed of Se(IV).
A least-squares method was employed to evaluate the isotherm
5
B.A. Jiménez-López et al.
Environmental Nanotechnology, Monitoring & Management 16 (2021) 100580
Table 3
Isotherm parameters of the Freundlich, Langmuir and Prausnitz-Radke adsorption isotherms and %D for the adsorption of Se(IV) from aqueous solution on LDH,
LDH550, and LDHReh.
Material
LDH
LDH550
LDHReh
T (◦ C)
25
25
pH
15
35
25
5
5
7
9
11
5
5
5
25
5
I (N)
0.01
0.01
0.05
0.10
0.01
Freundlich
Langmuir
Prausnitz-Radke
k (mg(1− 1/n) L(1/n)/g)
n
%D
qm (mg/g)
K (L/mg)
%D
a (L/g)
b (Lβ/mgβ)
β
%D
4.40
40.3
39.4
36.3
8.91
22.3
28.0
30.2
19.2
14.8
3.06
4.71
6.29
9.00
3.18
2.77
4.12
4.54
3.23
9.00
13.8
9.85
15.9
9.03
6.37
9.73
9.01
5.49
2.92
8.01
24.5
98.6
84.1
60.7
44.7
145
102
87.5
102
24.6
0.05
0.73
0.78
0.64
0.06
0.04
0.07
0.29
0.05
0.53
5.92
19.2
16.4
5.39
10.8
4.85
9.16
13.7
11.8
3.93
1.89
229
140
50.9
9.22
6.47
11.8
24.3
4.39
12.6
0.14
5.60
2.65
0.98
0.57
0.045
0.20
0.56
0.07
0.50
0.87
0.79
0.90
0.97
0.82
0.99
0.89
0.85
0.90
0.99
1.73
8.33
15.6
5.95
5.46
4.80
8.04
11.8
10.9
5.47
Fig. 4. Adsorption isotherms of Se(IV) on LDH, LDH550 and LDHReh in
aqueous solution at pH = 5, I = 0.01 N and T = 25 ◦ C. The lines represent the
Prausnitz-Radke isotherm.
Fig. 5. Effect of pH on the adsorption isotherms of Se(IV) in aqueous solution
on LDH550 at T = 25 ◦ C and I = 0.01 N. The lines represent the PrausnitzRadke isotherm.
intercalation of the Se(IV) oxyanions.
because the ZP of LDH550 was positive at pH below pHIEP of 11.4, fa­
voring the adsorption of oxoanions. Furthermore, the electrostatic
attraction intensity between the oxoanions and the LDH550 surface
decreased by incrementing the pH from 5 to 11 because the ZP of
LDH550 was also reduced (See Fig. 3. Therefore, the decrease in the
LDH550 adsorbing capacity was related to reducing the electrostatic
attraction intensity.
3.7. Influence of pH upon the LDH550 capacity for adsorbing Se(IV)
At 25 ◦ C and I = 0.01 N, the Se(IV) adsorption isotherms on LDH550
were determined at pH of 11, 9, 7 and 5 to ascertain the variation of the
LHD550 adsorption capacity with solution pH. This pH range was cho­
sen based upon the fact that the LDH layered structure of the LDH is
slightly affected at a pH less than 4 since the LDH layers start dissolving
in water solutions (Abdolmohammad-Zadeh et al., 2013; RamírezLlamas et al., 2015). Fig. 5 illustrates the Se(IV) adsorption isotherms on
LDH550 at different pH values, revealing that the adsorbing capacity
decreases by incrementing the pH. Several authors have reported the
same trend for adsorbing other anions from water solution on LDH (Das
et al., 2004; Mandal et al., 2009; Isaacs-Paez et al., 2014).
For an equilibrium Se(IV) concentration of 100 mg/L, the Se(IV)
uptakes on LDH550 predicted with the P-R isotherm were 35, 60, 83 and
107 mg/g at pH of 11, 9, 7 and 5, correspondingly. Therefore, the
adsorbing capacity was lessened 3-fold while the pH was incremented
from 5 to 11. This result can be mainly attributed to the electrostatic
interactions between the Se(IV) oxoanions in water and the LDH550
surface charge. The Se(IV) oxoanions present in water solutions are
selenite (SeO32− ) and hydrogen selenite (HSeO3− ), and the speciation
diagram of Se(IV) is illustrated in Fig. A3. Accordingly to this figure, the
HSeO3− species is predominant at pH = 5, the HSeO3− (67%) and
SeO32− (33%) are present at pH = 7, and SeO32− is predominant at pH
higher than 9. The LDH550 surface attracted the Se(IV) oxoanions
3.8. Effect of ionic strength on LDH550 adsorption capacity towards Se
(IV)
This effect was studied at pH = 5 because the maximum adsorption
of LDH550 towards Se(VI) was attained at this pH. Fig. A4 shows the
dependence of the adsorption capacity of LDH550 upon de ionic
strength, and the adsorption capacity was reduced by increasing the
ionic strength from 0.01 N to 0.1 N for concentrations of Se(IV) at
equilibrium less than 100 mg/L. The Se(IV) uptake at a Se(IV) equilib­
rium concentration of 25 mg/L was estimated to be 79.3, 63.4 and 49.1
mg/g for I of 0.01, 0.05 and 0.1 N, respectively. In other words, the
adsorption capacity was decreased 1.6 times by increasing the I from
0.01 to 0.1 N. For Se(IV) concentrations at equilibrium higher than 100
mg/L, the adsorption capacity of LDH550 diminished when the I was
increased from 0.01 N from 0.05 N, but remained essentially constant
while raising the I from 0.05 to 0.1 N. The adsorption capacity of
LDH500 was diminished on the average 1.3 times.
At pH = 5, the LDH550 surface was positively charged, and HSeO3was the predominant species, so the HSeO3− was attracted to the
6
B.A. Jiménez-López et al.
Environmental Nanotechnology, Monitoring & Management 16 (2021) 100580
LDH550 surface. The ionic strength was varied by changing the Na+ and
Cl− concentrations in the solution, and the Cl- ions were attracted and
adsorbed on the LDH550 positive surface, balancing the positive charge
of the LDH550 and decreasing the attraction between HSeO3− and the
LDH550 surface, diminishing the uptake of Se(IV) adsorbed. Hence, the
decrease of the LDH550 adsorption capacity by increasing the ionic
strength corroborated that the electrostatic interactions affected the
adsorption capacity of LDH550 towards Se(IV).
mol.
For an uptake of Se(IV) adsorbed of 90 mg/g, the Se(IV) concentra­
tions at equilibrium were Ce2 = 33.3 mg/L and Ce1 = 90.6 mg/L at T2 =
288.15 K and T1 = 308.15 K, correspondingly. The (ΔHads )q evaluated
with equation (7) was − 36.94 KJ/mol, demonstrating that the Se(IV)
adsorption on LDH550 is an exothermic process. The value of (ΔHads )q is
less than 40 KJ/mol confirming that the Se(IV) oxoanions were being
physically adsorbed. It is important to point out that this value of
(ΔHads )q can only be applied for uptakes of Se(IV) adsorbed higher than
90 mg/g.
3.9. Temperature effect on LDH550 adsorption capacity towards Se(IV)
3.10. Se(IV) adsorbing mechanism on LDH550
At pH = 5, the influence of temperature upon the adsorption
isotherm was assessed by procuring the Se(IV) equilibrium data DH550
at 15, 25 and 35 ◦ C. The pH of 5 was chosen because the maximum
capacity was achieved at this pH value.
Fig. 6 depicts the influence of temperature upon the Se(IV) adsorp­
tion isotherm on LDH550. At concentrations of Se(IV) at equilibrium
below 20 mg/g, the LDH550 adsorption capacity exhibits an unusual
behavior because the adsorption capacity is decreased by either raising
temperature from 25 to 35 ◦ C or diminishing temperature from 25 to
15 ◦ C. However, for equilibrium concentrations higher than 30 mg/L,
the adsorption capacity of LDH550 diminished when the temperature
was elevated from 15 to 35 ◦ C. The boron adsorption on Mg-Al-CO3 LDH
calcined at 550 ◦ C displayed the same tendency in the temperature range
from 15 to 35 ◦ C (Isaacs-Paez et al., 2014). Although, Das et al. (2007)
found that the capacity of Mg-Fe-CO3 LDH for adsorbing Se(IV)
increased by augmenting temperature from 30 to 60 ◦ C.
For an equilibrium Se(IV) concentration of 100 mg/L, the LDH 550
adsorbing capacity was 88.1, 107 and 118 mg/g at 35, 25 and 15 ◦ C,
correspondingly. These results show that the LDH550 adsorbing ca­
pacity was diminished 1.3-fold by elevating temperature from 15 to
35 ◦ C.
The subsequent equation was applied to estimate the isosteric heat of
adsorption (Do, 1998):
( )
RLn CCe1e2
(10)
(ΔHads )q = 1
− T12
T1
The anions adsorption mechanism on LDHs includes mainly ion ex­
change of carbonates and electrostatic attractions (Das et al., 2004; Das
et al., 2007; Isaacs-Paez et al., 2014; Li et al., 2018; Li et al., 2020;
Mandal et al., 2009). Likewise, Chen and An (2012) pointed out that the
adsorbing capacity of these materials diminishes by increasing the pH
due to competition for the active sites between the OH– ions and the
anions of selenium present in the solution.
The following reactions represent the ion exchange of CO32– and OH–
from LDH550 by hydrogen selenite:
≡ (Al+ )2 − CO23 + 2HSeO−3 ↔ 2 ≡ (Al+ ) − HSeO3 + CO2−3
(11)
≡ M − OH + HSeO−3 → ≡ M − HSeO3 + OH −
(12)
Isaacs-Paez et al. (2014) proposed these reactions for the adsorption
of boron anions on LDH calcined. The subsequent reactions illustrate the
mechanism of electrostatic attraction between the LDH550 surface and
the hydrogen selenite in solution:
≡ Al+ + SeO−3 ↔ ≡ Al+ HSeO−3
(13)
≡ Al − OH + + HSeO−3 ↔ ≡ Al − OH + HSeO−3
(14)
As reported previously, the behavior of the adsorption capacity of
LDH550 towards Se(IV) anions regarding the effect of the solution pH
and ionic strength (See sections 3.7 and 3.8), corroborated that the
adsorption capacity was dependent upon electrostatic attraction.
The adsorption of the Se(IV) oxoanions by electrostatic attraction
can cause a reduction of the ZP of LDH550 surface since the Se(IV)
oxoanions balance the positive charge of the LDH550 surface. The
importance of electrostatic attraction in the overall Se(IV) adsorption
was evaluated by determining the variation of the ZP of LDH550 with
different loadings of Se(IV) adsorbed (LDH550Se).
Fig. 7 shows the ZP distribution of LDH550 and LDH550Se with
Where Ce2 and Ce1 are the Se(IV) equilibrium concentrations at the
temperatures T2 and T1 , correspondingly, and for the same q, mg/L; R
denotes the universal constant of ideal gases, 8.314 J/mol K; (ΔHads )q
represents the isosteric heat for the Se(IV) adsorption on LDH550, J/
Fig. 6. Effect of temperature on the adsorption isotherm of Se(IV) on LDH550
in aqueous solution at pH = 5 and I = 0.01 N. The lines were predicted with the
Prausnitz-Radke isotherm.
Fig. 7. Zeta potential distribution of LDH550Se at different initial concentra­
tions of Se(IV) at T = 25 ◦ C, I = 0.01 N and pH of 5, 7 and 11.
7
B.A. Jiménez-López et al.
Environmental Nanotechnology, Monitoring & Management 16 (2021) 100580
different loadings of Se(IV) adsorbed at pH of 5, 7 and 11. At a specific
pH, the positive ZP of the LDH550Se lessened by incrementing the initial
Se(IV) concentration. It is essential to mention that the mass adsorbed of
Se(IV) on LDH550Se, QSe(IV), increased with the initial Se(IV) concen­
tration. In other words, LDH550 positive charge decreased by raising QSe
(IV), confirming that the positive charge of LDH550 surface is balanced
by the adsorption of Se(IV) anions from the water solution. Se(IV)
adsorption on LDH550 diminished the ZP of LDH550Se up to zero, and
then ZP was not further reduced. Therefore, the electrostatic attraction
favored the adsorption of selenite and hydrogen selenite on the posi­
tively charged surface of the LDH550.
The difference between the ZP of the LDH550Se and the ZP of the
LDH550 was estimated with the following equation:
Δ(Zeta Potential) = ZPLDH550Se − ZPLDH550
Table 4
Comparison of Se(IV) adsorption capacities of several materials.
Adsorbent
Experimental
conditions
Maximum
adsorption
capacity (mg/g)
Reference
Bismuth-based MOF
Without
controlling pH,
room temperature
pH = 6, T = 25 ◦ C
255.3
Ouyang et al.
(2018)
179.59
pH = 3, T = 25 ◦ C
161.4
pH = 5, T = 25 C
134.4
Tian et al.
(2017)
Abukhadra
et al. (2020)
This study
pH = 9, T = 25 ◦ C
120
Citrus peel treated with
HNO3
Ferrihydrite-loaded
magnetic sugar cane
bagasse charcoal
Fe-MOF modified with
Al3+
Zr MOF UiO-66
pH = 6.5, T = 25 ◦ C
116.2
pH = 3, T = 45 C
95.15
Without pH
control, T = 25 ◦ C
pH = 6, T = 25 ◦ C
75.33
Calcined Mg-(Al-Zr)–
CO3 LDH
Calcined Mg-Fe-CO3
LDH
Hematite coated with
Fe3O4 nanoparticles
Calcined Mg-Al-CO3
LDH
pH = 6, T = 30 C
41.9
pH = 6, T = 30 ◦ C
32.05
pH = 7, T = 25 ◦ C
25
T = 65 ◦ C
1.5
Calcined Mg-Al-CO3
LDH
Kaolinite/cellulose
nanocomposite
Calcined Mg-Al-CO3
LDH
Mg-Al LDH
(15)
Fig. 8 depicts QSe(IV) vs. –(ΔZeta Potential) for pH of 5 and 7, and as
expected, QSe(IV) was incremented by increasing –Δ(Zeta Potential).
Besides, the increase of QSe(IV) is proportional to –Δ(Zeta Potential) and
the variation of QSe(IV) concerning –Δ(Zeta Potential) is nearly linear.
This behavior indicated that the Se(IV) oxoanions adsorption on
LDH550 is chiefly ascribed to electrostatic attraction. At pH = 5, the
maximum adsorbing capacity of LDH550, QMax = 134.4 mg/g, was
attained when the ZP of LDH550Se was reduced to almost zero, or the
–(ΔZeta Potential) reached its maximum value as seen in Figs. 7 and 8.
This result further corroborates the importance of electrostatic
attraction.
3.11. Comparison of adsorption capacities towards Se(IV)
Several traditional adsorbents and novel nanomaterials have been
tested for removing Se(IV) oxoanions in an aqueous solution. Table 4
lists the maximum capacities of several materials for adsorbing Se(IV).
Several MOFs and LDHs have been studied. The Bismuth-based MOF
presented a very high Se(IV) adsorbing capacity of 255.3 mg/g; how­
ever, lesser capacities were displayed by other MOFs, such as Fe-MOF
modified with Al3+ (Wang et al., 2019) and Zr-MOF UiO-66 (Wei
et al., 2018). Kaolinite/cellulose nanocomposite (Abukhadra et al.,
2020), citrus peel treated with HNO3 (Dev et al., 2020) and a magnetic
sugar cane bagasse charcoal loaded with ferrihydrite (Xin et al., 2021)
displayed a reasonably high capacity for adsorbing Se(IV).
In previous studies, LDHs modified by calcination have been applied
for adsorbing Se(IV), and the adsorbing capacities varied considerably
from 1.5 to 41.9 mg/g (Das et al., 2004; Das et al., 2007; Yang et al.,
2005). You et al. (2001) found that the adsorption capacity of
◦
◦
◦
59.9
You et al.
(2001)
Dev et al.
(2020)
Xin et al.
(2021)
Wang et al.
(2019)
Wei et al.
(2018)
Das et al.
(2004)
Das et al.
(2007)
Ma et al.
(2018)
Yang et al.
(2005)
uncalcined Mg-Al LDH towards Se(IV) was 120 mg/g. Chubar (2014)
utilized the alkoxide-free sol-gel technique for synthesizing Mg-Al LDH
and reported that its adsorption capacity towards Se(IV) was 160 mg/g
at pH = 5. An Mg-Al-CO3 LDH synthesized using Mg and Al sulfate salts
and calcined it at 500 ◦ C, exhibited an adsorbing capacity of 179.6 mg/g
at pH = 6 and T = 25 ◦ C (Tian et al., 2017), which is the highest
adsorption capacity of all LDHs synthesized previously. The calcined
Mg-Al-CO3 LDH synthesized in this work presented a very high
adsorption capacity towards Se(IV) of 134.4 mg/g but was 25 % less
than that of the LDH synthesized by Tian et al. (2017). The LDH550
presented a very high adsorption capacity because the interlayer anion
was removed during the calcination at 550 ◦ C and the reconstruction of
the layered structure during adsorption facilitated the access of the Se
(IV) oxoanions to the adsorption sites.
4. Conclusions
The synthesis conditions and calcination of LDH significantly
affected its adsorption capacity towards the Se(IV) oxoanions from
water solutions. The calcination of LDH at 550 ◦ C eliminated the
interlaminar carbonates of LDH and destroyed the LDH550 lamellar
structure. The lamellar structure of LDH550 was partially reconstructed
by hydrating in water solutions with or without Se(IV).
The Se(IV) adsorption and the reconstruction of the layered structure
of LDH550 occurred simultaneously. The elimination of carbonates and
the layered structure reconstruction enhanced the LDH capacity for
adsorbing Se(IV), facilitating the accessibility to the basal or adsorption
sites of LDH550. The capacity of LDH550 for adsorbing Se(IV) increased
5.3 times by calcination, and its maximum value was 134.4 mg/g at pH
= 5 and 25 ◦ C. The LDH550 adsorbing capacity for Se(IV) decreased
considerably by reducing the pH because the electrostatic attraction
between the Se(IV) oxoanions and LDH550 surface positive charge
diminished due to the reduction of the ZP of LDH550. The adsorption
capacity of the LDH550 also depends on the temperature, and the
temperature influence on the adsorption capacity exhibited an anoma­
lous behavior.
Fig. 8. Dependence of the uptake of Se(IV) adsorbed on the -Δ(Zeta Potential)
at T = 25 ◦ C, I = 0.01 N and pH of 5 and 7.
8
Environmental Nanotechnology, Monitoring & Management 16 (2021) 100580
B.A. Jiménez-López et al.
Both electrostatic attraction and anion exchange are essential
mechanisms for adsorbing Se(IV) on LDH550. The LDH550 surface
positive charge decreased with the amount of Se(IV) adsorbed, and the
uptake of Se(IV) adsorbed augmented almost linearly by increasing the
decrease of the ZP of the LDH550Se. Thus, the Se(IV) oxoanions are
attracted electrostatically to the LDH550 positive surface, and this
mechanism contributes significantly to Se(IV) adsorption on LDH550.
Das, J., Sairam Patra, B., Baliarsingh, N., Parida, K.M., 2007. Calcined Mg-Fe-CO3 LDH as
an adsorbent for the removal of selenite. J. Colloid Interface Sci. 316 (2), 216–223.
https://doi.org/10.1016/j.jcis.2007.07.082.
Dev, S., Khamkhash, A., Ghosh, T., Aggarwal, S., 2020. Adsorptive removal of Se(IV) by
citrus peels: effect of adsorbent entrapment in calcium alginate beads. ACS Omega. 5
(28), 17215–17222. https://doi.org/10.1021/acsomega.0c0134710.1021/
acsomega.0c01347.s001.
Do, D.D., 1998. Adsorption Analysis: Equilibria and Kinetics. Imperial college press,
London.
Dos Santos, R.M.M., Gonҫalves, R.G.L., Constantino, V.R.L., Santilli, C.V., Borges, P.D.,
Tronto, J., Pinto, F.G., 2017. Adsorption of acid yellow 42 dye on calcined layered
double hydroxide: effect of time, concentration, pH and temperature. Appl. Clay Sci.
140, 132–139. https://doi.org/10.1016/j.clay.2017.02.005.
Evans, D.G., Slade, R.C.T., 2005. Structural aspects of layered double hydroxides. In:
Duan, X., Evans, D.G. (Eds.), Layered Double Hydroxides. Springer, Berlin, pp. 1–87.
Goh, K.-H., Lim, T.-T., Dong, Z., 2008. Application of layered double hydroxides for
removal of oxyanions: a review. Water Res. 42 (6-7), 1343–1368. https://doi.org/
10.1016/j.watres.2007.10.043.
Gonzalez, C.M., Hernandez, J., Parsons, J.G., Gardea-Torresdey, J.L., 2011. Adsorption
of selenite and selenate by a high- and low-pressure aged manganese oxide
nanomaterial. Instrum. Sci. Technol. 39 (1), 1–19. https://doi.org/10.1080/
10739149.2010.537721.
He, J., Wei, M., Li, B.o., Kang, Y.u., Evans, D.G., Duan, X., 2006. In: Structure and
BondingLayered Double Hydroxides. Springer-Verlag, Berlin/Heidelberg,
pp. 89–119.
Holmes, A.B., Gu, F.X., 2016. Emerging nanomaterials for the application of selenium
removal for wastewater treatment. Environ. Sci. Nano. 3 (5), 982–996. https://doi.
org/10.1039/C6EN00144K.
Isaacs-Paez, E.D., Leyva-Ramos, R., Jacobo-Azuara, A., Martínez-Rosales, J.M., FloresCano, J.V., 2014. Adsorption of boron on calcined AlMg layered double hydroxide
from aqueous solutions. Mechanism and effect of operating conditions. Chem. Eng. J.
245, 248–257. https://doi.org/10.1016/j.cej.2014.02.031.
Kameda, T., Kondo, E., Yoshioka, T., 2014. Equilibrium and kinetic studies of Se(VI)
removal by Mg-Al layered double hydroxide doped with Fe2+. RSC Adv. 4,
61817–61822. https://doi.org/10.1039/C4RA11645C.
Kongsri, S., Janpradit, K., Buapa, K., Techawongstien, S., Chanthai, S., 2013.
Nanocrystalline hydroxyapatite from fish scale waste: Preparation, characterization
and application for selenium adsorption in aqueous solution. Chem. Eng. J. 215,
522–532. https://doi.org/10.1016/j.cej.2012.11.054.
Kuan, W.-H., Lo, S.-L., Wang, M.K., Lin, C.-F., 1998. Removal of Se(IV) and Se(VI) from
water by aluminum-oxide-coated sand. Water Res. 32 (3), 915–923. https://doi.org/
10.1016/S0043-1354(97)00228-5.
Kuśtrowski, P., Sułkowska, D., Chmielarz, L., Rafalska-Łasocha, A., Dudek, B.,
Dziembaj, R., 2005. Influence of thermal treatment conditions on the activity of
hydrotalcite-derived Mg–Al oxides in the aldol condensation of acetone. Micropor.
Mesopor. Mater. 78 (1), 11–22. https://doi.org/10.1016/j.micromeso.2004.09.011.
Li, E., Liao, L., Lv, G., Li, Z., Yang, C., Lu, Y., 2018. The interactions between three typical
PPCPs and LDH. Front. Chem. 6 (16), 1–9. https://doi.org/10.3389/
fchem.2018.00016.
Li, S., Dong, L., Wei, Z., Sheng, G., Du, K., Hu, B., 2020. Adsorption and mechanistic
study of the invasive plant-derived biochar functionalized with CaAl-LDH for Eu(III)
in water. J. Environ. Sci. 96, 127–137. https://doi.org/10.1016/j.jes.2020.05.001.
Lin, Y., Fang, Q., Chen, B., 2014. Metal composition of layered double hydroxides (LDHs)
regulating ClO4− adsorption to calcined LDHs via the memory effect and hydrogen
bonding. J. Environ. Sci. 26 (3), 493–501. https://doi.org/10.1016/S1001-0742(13)
60462-3.
Liu, X., Pang, H., Liu, X., Li, Q., Zhang, N., Mao, L., Qiu, M., Hu, B., Yang, H., Wang, X.,
2021. Orderly porous covalent organic frameworks-based materials: superior
adsorbents for pollutants removal from aqueous solutions. The Innovation. 2
(100076), 1–28. https://doi.org/10.1016/j.xinn.2021.100076.
Ma, Z., Shan, C., Liang, J., Tong, M., 2018. Efficient adsorption of Selenium (IV) from
water by hematite modified magnetic nanoparticles. Chemosphere. 193, 134–141.
https://doi.org/10.1016/j.chemosphere.2017.11.005.
Mafu, L.D., Msagati, T.A.M., Mamba, B.B., 2014. Adsorption studies for the simultaneous
removal of arsenic and selenium using naturally prepared adsorbent materials. Int. J.
Environ. Sci. Technol. 11 (6), 1723–1732. https://doi.org/10.1007/s13762-0130374-1.
Mandal, S., Mayadevi, S., Kulkarni, B.D., 2009. Adsorption of aqueous selenite [Se(IV)]
species on synthetic layered double hydroxide materials. Ind. Eng. Chem. Res. 48
(17), 7893–7898. https://doi.org/10.1021/ie900136s.
Mosangi, D., Kesavan Pillai, S., Moyo, L., Ray, S.S., 2016. Inorganic layered double
hydroxides as a 4-hexyl resorcinol delivery system for topical applications. RSC Adv.
6 (81), 77709–77716. https://doi.org/10.1039/C6RA19195A.
Ouyang, H., Chen, N., Chang, G., Zhao, X., Sun, Y., Chen, S., Zhang, H., Yang, D., 2018.
Selective capture of toxic selenite anions by bismuth-based metal-organic
frameworks. Angew. Chem. Int. Ed. 57 (40), 13197–13201. https://doi.org/
10.1002/anie.v57.4010.1002/anie.201807891.
Plant, J.A., Bone, J., Voulvoulis, N., Kinniburgh, D.G., Smedley, P.L., Fordyce, F.M.,
Klinck, B., 2014. Arsenic and selenium. In: Holland, H.D., Turekain, K.K. (Eds.),
Environmental Geochemistry. Elsevier, Oxford, pp. 13–57.
Ramírez-Llamas, L.A., Leyva-Ramos, R., Jacobo-Azuara, A., Martínez-Rosales, J.M.,
Isaacs-Paez, E.D., 2015. Adsorption of fluoride from aqueous solution on calcined
and uncalcined layered double hydroxide. Adsorpt. Sci. Technol. 33 (4), 393–410.
https://doi.org/10.1260/0263-6174.33.4.393.
CRediT authorship contribution statement
B.A. Jiménez-López: Data curation, Formal analysis, Methodology,
Investigation, Writing – original draft, Visualization. R. Leyva-Ramos:
Conceptualization, Funding acquisition, Investigation, Project adminis­
tration, Supervision, Methodology, Writing – review & editing. J.J.
Salazar-Rábago: Data curation, Investigation, Visualization. A.
Jacobo-Azuara: Methodology. Antonio Aragon Piña: Methodology,
Formal analysis, Software.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgements
This study was financially supported by Fondo de Apoyo a la
Investigación (FAI)-Universidad Autonoma de San Luis Potosi (UASLP),
through grant No.: C20-FAI-10-27.27.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.enmm.2021.100580.
References
Abdolmohammad-Zadeh, H., Jouyban, A., Amini, R., Sadeghi, G., 2013. Nickelaluminum layered double hydroxide as a nano-sorbent for the solid phase extraction
of selenium, and its determination by continuous flow HG-AAS. Microchim. Acta.
180 (7-8), 619–626. https://doi.org/10.1007/s00604-013-0967-x.
Abukhadra, M.R., AlHammadi, A., El-Sherbeeny, A.M., Salam, M.A., El-Meligy, M.A.,
Awwad, E.M., Luqman, M., 2020. Enhancing the removal of organic and inorganic
selenium ions using and exfoliated kaolinite/cellulose fibres nanocomposite.
Carbohydr. Polym. 252, 117163 https://doi.org/10.1016/j.carbpol.2020.117163.
Braterman, P.S., Xu, Z.P., Yarberry, F., 2004. Layered double hydroxides (LDHs). In:
Auerbach, S.M., Carrado, K.A., Dutt, P.K. (Eds.), Handbook of Layered Materials.
Marcel Dekker Inc., New York, pp. 373–474.
Cai, J., Zhang, Y., Pan, B., Zhang, W., Lv, L., Zhang, Q., 2016. Efficient defluoridation of
water using reusable nanocrystalline layered double hydroxides impregnated
polystyrene anion exchanger. Water Res. 102, 109–116. https://doi.org/10.1016/j.
watres.2016.06.030.
Chawla, R., Filippini, T., Loomba, R., Cilloni, S., Dhillon, K.S., Vinceti, M., 2020.
Exposure to a high selenium environment in Punjab, India: biomarkers and health
conditions. Sci. Total Env. 719, 134541. https://doi.org/10.1016/j.
scitotenv.2019.134541.
Chen, M.L., An, M.I., 2012. Selenium adsorption and speciation with Mg-FeCO3 layered
double hydroxides loaded cellulose fibre. Talanta. 95, 31–35. https://doi.org/
10.1016/j.talanta.2012.03.038.
Chubar, N., Gerda, V., Megantari, O., Mičušík, M., Omastova, M., Heister, K., Man, P.,
Fraissard, J., 2013. Applications versus properties of Mg-Al layered double
hydroxides provided by their synthesis methods: Alkoxide and alkoxide-free sol-gel
syntheses and hydrothermal precipitation. Chem. Eng. J. 234, 284–299. https://doi.
org/10.1016/j.cej.2013.08.097.
Chubar, N., 2014. EXAFS and FTIR studies of selenite and selenate sorption by alkoxidefree sol-gel generated Mg-Al-CO3 layered double hydroxide with very labile
interlayer anions. J. Mater. Chem. A. 2 (38), 15995–16007. https://doi.org/
10.1039/C4TA03463E.
Cowan, C.E., Zachara, J.M., Resch, C.T., 1990. Solution ion effects on the surface
exchange of selenite on calcite. Geochim. Cosmochim. Acta. 54 (8), 2223–2234.
https://doi.org/10.1016/0016-7037(90)90047-O.
Das, N.N., Konar, J., Mohanta, M.K., Srivastava, S.C., 2004. Adsorption of Cr(VI) and Se
(IV) from their aqueous solutions onto Zr4+ -substituted ZnAl/MgAl-layered double
hydroxides: effect of Zr4+ substitution in the layer. J. Colloid Interface Sci. 270 (1),
1–8. https://doi.org/10.1016/S0021-9797(03)00400-4.
9
B.A. Jiménez-López et al.
Environmental Nanotechnology, Monitoring & Management 16 (2021) 100580
Rouquerol, F., Rouquerol, J., Sing, K.S.W., Llewellyn, P., Maurin, G., 2014. Adsorption by
Powders and Porous Solids: Principles, Methodology and Applications, 2nd ed.
Elsevier, Oxford.
Santamaría, L., Devred, F., Gaigneaux, E.M., Vicente, M.A., Korili, S.A., Gil, A., 2020.
Effect of the surface properties of Me2+/Al layered double hydroxides synthesized
from aluminum saline slag wastes on the adsorption removal of drugs. Micropor.
Mesopor. Mat. 309, 110560. https://doi.org/10.1016/j.micromeso.2020.110560.
Sharma, U., Tyagi, B., Jasra, R.V., 2008. Synthesis and characterization of Mg-Al-CO3
layered double hydroxide for CO2 adsorption. Ind. Eng. Chem. Res. 47 (23),
9588–9595. https://doi.org/10.1021/ie800365t.
Sun, M., Xiao, Y., Zhang, L., Gao, X., Yan, W., Wang, D., Su, J., 2015. High uptake of Cu2
+
, Zn2+ or Ni2+ on calcined MgAl hydroxides from aqueous solutions: Changing
adsorbent structures. Chem. Eng. J. 272, 17–27. https://doi.org/10.1016/j.
cej.2015.03.009.
Theiss, F.L., Couperthwaite, S.J., Ayoko, G.A., Frost, R.L., 2014. A review of the removal
of anions and oxyanions of the halogen elements from aqueous solution by layered
double hydroxides. J. Colloid Interface Sci. 417, 356–368. https://doi.org/10.1016/
j.jcis.2013.11.040.
Thommes, M., Kaneko, K., Neimark, A.V., Olivier, J.P., Rodriguez-Reinoso, F.,
Rouquerol, J., Sing, K.S., 2015. Physisorption of gases, with special reference to the
evaluation of surface area and pore size distribution (IUPAC Technical Report). Pure
Appl. Chem. 87, 1051–1069. https://doi.org/10.1515/pac-2014-1117.
Tian, N., Zhou, Z., Tian, X., Yang, C., Li, Y., 2017. Superior capability of MgAl2O4 for
selenite removal from contaminated groundwater during its reconstruction of
layered double hydroxides. Sep. Purif. Technol. 176, 66–72. https://doi.org/
10.1016/j.seppur.2016.11.062.
Villela-Martínez, D.E., Leyva-Ramos, R., Aragon-Piña, A., Navarro-Tovar, R., 2020.
Arsenic elimination from water solutions by adsorption on bone char. Effect of
operating conditions and removal from actual drinking water. Water, Air, & Soil
Pollution 231 (221), 1–13. https://doi.org/10.1007/s11270-020-04596-w.
Wang, Q., Tay, H.H., Guo, Z., Chen, L., Liu, Y., Chang, J., Zhong, Z., Luo, J., Borgna, A.,
2012. Morphology and composition controllable synthesis of Mg-Al-CO3
hydrotalcites by tuning the synthesis pH and the CO2 capture capacity. Appl. Clay
Sci. 55, 18–26. https://doi.org/10.1016/j.clay.2011.07.024.
Wang, R., Xu, H., Zhang, K., Wei, S., Deyong, W., 2019. High-quality Al@Fe-MOF
prepared using Fe-MOF as a micro-reactor to improve adsorption performance for
selenite. J. Hazard. Mater. 364, 272–280. https://doi.org/10.1016/j.
jhazmat.2018.10.030.
Wei, J., Zhang, W., Pan, W., Li, C., Sun, W., 2018. Experimental and theoretical
investigations on Se(IV) and Se(VI) adsorption to UiO-66-based metal-organic
frameworks. Environ. Sci. Nano. 5, 1441–1453. https://doi.org/10.1039/
C8EN00180D.
Xin, Y.u., Gu, P., Long, H., Meng, M., Yaseen, M., Su, H., 2021. Fabrication of
ferrihydrite-loaded magnetic sugar cane bagasse charcoal adsorbent for the
adsorptive removal of selenite from aqueous solution. Colloids Surf. A Physicochem.
Eng. Asp. 614, 126131. https://doi.org/10.1016/j.colsurfa.2020.126131.
Yang, L.i., Shahrivari, Z., Liu, P.K.T., Sahimi, M., Tsotsis, T.T., 2005. Removal of trace
levels of arsenic and selenium from aqueous solutions by calcined and uncalcined
layered double hydroxides (LDH). Ind. Eng. Chem. Res. 44 (17), 6804–6815. https://
doi.org/10.1021/ie049060u.
Yang, Y., Yang, M., Zheng, Z., Zhang, X., 2020. Highly effective adsorption removal of
perfluorooctanoic acid (PFOA) from aqueous solution using calcined layer-like MgAl hydrotalcites nanosheets. Environ. Sci. Pollut. Res. 27 (12), 13396–13408.
https://doi.org/10.1007/s11356-020-07892-4.
You, Y., Vance, G.F., Zhao, H., 2001. Selenium adsorption on Mg-Al and Zn-Al layered
double hydroxides. Appl. Clay Sci. 20 (1-2), 13–25. https://doi.org/10.1016/S01691317(00)00043-0.
Yu, S., Yin, L., Pang, H., Wu, Y., Wang, X., Zhang, P., Hub, B., Chen, Z., Wang, X., 2018.
Constructing sphere-like cobalt-molybdenum-nickel ternary hydroxide and calcined
ternary oxide nanocomposites for efficient removal of U(VI) from aqueous solutions.
Chem. Eng. J. 352 (2018), 360–370. https://doi.org/10.1016/j.cej.2018.07.033.
Yun, Z., Qingze, J. Evans D.G., Xue, D., 2002. Mechanism of pore formation and
structural characterization for mesoporous Mg-Al composite oxides. Sc. China, Ser.
B: Chem. 45, 37-45. https://doi.org/10.1360/02yb9006.
10