Porous fibrous bacterial cellulose/La(OH)3 membrane for superior phosphate removal from water

Carbohydrate Polymers 298 (2022) 120135

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Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol

Porous fibrous bacterial cellulose/La(OH)3 membrane for superior
phosphate removal from water
Liping Tan a, b, 1, Weihua Zhang a, 1, Xiaoguang Zhu a, Yue Ru a, Wenbo Yi a, Bo Pang c, *,
Tongjun Liu a, *
a

Shandong Provincial Key Laboratory of Microbial Engineering, Department of Bioengineering, Qilu University of Technology, Shandong Academy of Sciences, Jinan
250353, China
Guangxi Key Laboratory of Clean Pulp & Papermaking and Pollution Control, College of Light Industry and Food Engineering, Guangxi University, Nanning 530004,
China
c
Department of Materials and Environmental Chemistry, Stockholm University, Stockholm 10691, Sweden
b

A R T I C L E I N F O

A B S T R A C T

Keywords:
Adsorption
Bacterial cellulose
Lanthanum hydroxide nanoparticles
Phosphate removal

Lanthanum (La)-based nanoparticles (NPs) are promising candidates for phosphate removal owing to their
inherently high affinity towards phosphate. However, significant challenges remain to be addressed before their
practical deployment, especially the problems associated with their aggregation. Herein, we fabricated a highefficient sorbent for phosphate removal through in-situ synthesizing La(OH)3 NPs on a natural support, bacte­
rial cellulose (BC), which is pre-modified with polyethyleneimine. The resultant La(OH)3 NPs-immobilized BC
with different La contents (BPLa-X) exhibited a highly fibrous porous structure, in which BPLa-3 was selected for
further phosphate adsorption studies. BPLa-3 demonstrated a high adsorption capacity of 125.5 mg P g− 1, and
high adsorption selectivity due to the large surface area and abundant exposed active adsorption sites for
phosphate. Additionally, BPLa-3 also displayed high reusability and still possessed high adsorption capacity after
four consecutive cycles of adsorption-desorption. Therefore, the present adsorbent is believed to be a promising
candidate for practical phosphate removal.

1. Introduction
Phosphorus (P) being a structural and functional component of
nucleic acids, phosphor-proteins and enzymes is an essential element of
various living organisms (Adam, Peplinski, Michaelis, Kley, & Simon,
2009; Correll, 1998; Paytan & McLaughlin, 2007). However, excessive
amounts of such a crucial element in water bodies can cause serious
environmental problems, for example, eutrophication and major eco­
nomic losses (Conley et al., 2009; Li, Chen, Zhao, & Zhang, 2015).
Removing and recovering P from water/wastewater has been recog­
nized as one of the most promising approaches to addressing these
challenges. To date, various approaches including chemical precipita­
tion (Gaterell, Gay, Wilson, Gochin, & Lester, 2000), biological treat­
ment (Lv, Yuan, Chen, Liu, & Luo, 2014), adsorption (Chen et al., 2018),
and/or combinations of these technologies have been developed for P
removal and recovery in the field of agricultural, industrial or domestic
wastewater treatment (Chen et al., 2018; Mino, Van Loosdrecht, &

˘uz, Gürses, & Canpolat, 2003; Qu et al., 2022). Bio­
Heijnen, 1998; Og

logical treatment generally exhibits high efficiency with reduced
chemical costs but is highly sensitive to pollution loading variations and
influent flow (Oehmen et al., 2007; Yeoman, Stephenson, Lester, &
Perry, 1988). Although chemical precipitation has been recognized as an
effective and low-cost method, secondary pollution may occur due to
excessive amounts of waste disposals and undesired chemicals gener­
ated during such processes (Chen et al., 2018). Compared with these
methods, adsorption approaches relying on the utilization of functional
materials with high affinity for P are preferred owing to various merits
such as high efficiency, low cost, and high practicability (Zhang et al.,
2022).
Lanthanum, an abundant rare-earth element considered to be envi­
ronmentally friendly, has inherently high affinity for phosphate and can
form complexes with phosphate of low concentrations (Yang et al.,
2011; Yang et al., 2012). Note: P exists in nature dominantly in the form
of phosphate, which is also the only form of P that can be directly

* Corresponding authors.
E-mail addresses: (B. Pang), (T. Liu).
1
Equally contributed first-authors
/>Received 10 July 2022; Received in revised form 13 September 2022; Accepted 18 September 2022
Available online 21 September 2022
0144-8617/© 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( />

L. Tan et al.

Carbohydrate Polymers 298 (2022) 120135

assimilated by algae, microorganisms and many other planktons. Until

now, various types of lanthanum-containing materials, especially
lanthanum-based micro/nanoparticles such as La(OH)3 and La2O3 have
been developed for removing and recovering phosphate (Razanajatovo
et al., 2021; Zhi et al., 2020). However, similar to many other kinds of
micro/nanoparticles, La-based micro/nanoparticles (La-M/NPs) also
tend to form aggregates due to their high surface energy, which will
inhibit the efficient utilization of the inner regions of the resulting ag­
gregates (Cumbal & SenGupta, 2005; Tesh & Scott, 2014; Zhang, Xu,
et al., 2022). In addition, these La-based particles are not easy to be
recycled from the water environment after use. Loading La-based micro/
nanoparticles onto suitable supporting materials has been reported to be
a promising method to reduce their aggregation and improve the
operation process, thus improving their adsorption efficiency towards
phosphate (Tesh & Scott, 2014; Zhang, Xu, et al., 2022). Many types of
supporting polymer-based materials including polyacrylonitrile (PAN)
nanofibers, poly(vinylidene fluoride) membranes, and porous carbons,
have been employed to immobilize La-based micro/nanoparticles (Chen
et al., 2018; He et al., 2015; Liu, Zong, et al., 2018). However, most of
these materials suffer from various disadvantages such as tedious syn­
thetic steps (ex. electrospinning, phase separation), low biocompati­
bility and high cost. Therefore, loading La-based micro/nanoparticles
onto suitable supporting materials using simple methods is highly
desirable and of great significance.
Bacterial cellulose (BC) is considered to be the purest form of cel­
lulose that is free from hemicellulose, lignin and extractives. It generally
exists in the form of hydrogel with a three-dimensional (3D) network
structure possessing excellent biocompatibility, biodegradability,
excellent structure stability and high specific surface area (Klemm et al.,
2011). These features combined with numerous functionalizable surface
hydroxyl groups make BC a promising candidate for supporting various

types of particles, such as gold nanoparticles, silver nanoparticles, and
palladium nanoparticles (Kamal, Ahmad, Khan, & Asiri, 2019; Lv et al.,
2018; Xie et al., 2019). However, combinations of BC with La-based
micro/nanoparticles have been less reported, let alone their deploy­
ment as adsorbent for P removal and recovery.
In this study, we prepared a highly effective La(OH)3 nanoparticles
(NPs)-based adsorbent for P removal by employing BC as the natural
supporting material. PEI grafted BC was first synthesized via a glutar­
aldehyde crosslinking reaction between the hydrogel groups of BC and
the amine groups of PEI. The introduced large number of amine groups
has high affinity towards La(III), facilitating the subsequent in situ for­
mation of La(OH)3 NPs on the PEI-grafted BC (BPLa). The prepared BPLa
adsorbents demonstrated fast adsorption kinetics and high removal ef­
ficiency. Considering the simplicity of the fabrication method, the
excellent phosphate removal performance and the environmental
benign nature of the adsorbent, we believe the present material have
great potential for practical removal and recovery of P.

butanol was renewed every 60 min. Compared with water, tert-butanol
with a higher freezing point and a lower surface tension can lead to a
decline in capillary force, thus reducing the damage to the gel network
structure during the following freeze-drying process. The obtained BC
membrane (0.1 g) was then added to 500 mL of 0.5 % PEI aqueous so­
lution and stirred at room temperature for 300 min. After that, 1 mL of
25 % glutaraldehyde solution was pipetted into the system and stirred
for further 120 min. The PEI-modified BC hydrogel was then thoroughly
washed with abundant Milli-Q water. Afterward, the obtained BC
hydrogel was soaked into 500 mL of lanthanum chloride solution with
different initial concentrations (0.01 mol L− 1, 0.025 mol L− 1, 0.05 mol
L− 1 and 0.1 mol L− 1) at room temperature for 300 min. These four

samples were named as BPLa-1, BPLa-2, BPLa-3 and BPLa-4, respec­
tively. Subsequently, the BC hydrogels were immersed into 500 mL of
sodium hydroxide solution (0.1 mol L− 1) for 300 min. After reaction, the
La(OH)3 NPs-immobilized BC hydrogels were rinsed with plenty of
water. Finally, La(OH)3 NPs-immobilized BC aerogel membranes were
obtained by freeze drying after solvent exchange of water by tertbutanol.

2. Materials and methods

Qe = (C0 − Ce )V/m

2.3. The phosphate adsorption performance of the BPLa-X samples
The adsorption capacity of BPLa-X was studied in batch with phos­
phate solution. Briefly, 10 mg adsorbent was added into 20 mL of
phosphate solutions with various concentrations and stirred (150 rpm)
for 360 min to ensure the adsorption equilibrium. The adsorption
isotherm experiments for BPLa-X were tested in different initial con­
centrations of phosphate solution ranging from 5 to 350 mg P L− 1, and
the adsorption kinetic experiments were studied at the time interval of
0.5–160 min with an initial concentration of 30 mg P L− 1. To examine
the effect of pH on phosphate adsorption of BPLa samples, 10 mg
adsorbent and 20 mL 100 mg P L− 1 phosphate solution were shaken at
25 ◦ C for 4 h with an initial pH between 3.0 and 10.0. To test the in­
fluence of coexisting ionic strength on phosphate removal of the sam­
ples, a mixture phosphate solution (150 mg P L− 1) was prepared with
200 mg L− 1 coexisting anions by dissolving different salts of Na2SO4,
NaCl, NaNO3, NaHCO3, Mg(NO3)2 and Ca(NO3)2. After reaching the
adsorption equilibrium, the concentration of phosphate in the solution
was quantitatively determined by Inductively Coupled Plasma Atomic
Emission Spectrometry (ICP-AES). Then the P loaded adsorbents were

regenerated with 1 M NaOH solution and desorbed continuously for 240
min at room temperature. Finally, the reusable adsorbent was continu­
ously cleaned with deionized water for the adsorbent to be reused in
further experiment. Each measurement was repeated three times in the
experiment.
The adsorption capacity (per unit weight of adsorbent Qe (mg g− 1))
of the samples towards phosphate was calculated using the following
expression:
(1)

where C0 (mg L− 1) is the initial concentration of phosphate; Ce (mg L− 1)
is the equilibrium concentration of phosphate in solution; V (mL) is the
solution volume and m (g) is the weight of the used adsorbent mass.
The adsorption thermodynamic analysis is usually evaluated by
three important thermodynamic parameters, including the standard
entropy change (ΔS◦ ), standard enthalpy change (ΔH◦ ) and standard
free energy change (ΔG◦ ). ΔH◦ , ΔG◦ and ΔS◦ for BPLa-3 were calculated
using following equations (Qu, Wei, et al., 2022; Qu et al., 2022),
( )
◦
(2)
ΔG = − RTln K0e

2.1. Materials
BC was purchased from Beijing Guanlan Technology Co., Ltd. PEI,
glutaraldehyde and lanthanum hydroxide were received from Shanghai
Aladdin Biochemical Technology Co., Ltd. Sodium dihydrogen phos­
phate was bought from Shenggong Bioengineering Co., Ltd. Lanthanum
chloride was obtained from Shanghai McLean Biochemical Technology
Co., Ltd. tert-Butanol and sodium hydroxide were purchased from Xilong

Science Co., Ltd. Filter membrane (pore size, 0.22 μm) was purchased
from Jinteng Experimental Equipment Co., Ltd.

◦

◦

2.2. Synthesis of BPLa-X

( ) ΔS ΔH
ln K0e =
−
R
RT

The exchange of water to tert-butanol was first conducted by placing
BC hydrogel into tert-butanol and stirring for 300 min. Note that the tert-

where K0e is the adsorption distribution coefficient and R represents the
universal gas constant (8.314 J mol− 1 K− 1).
2

(3)


L. Tan et al.

Carbohydrate Polymers 298 (2022) 120135

2.4. Characterization

3. Results and discussion

Fourier transform infrared spectroscopy (FTIR) was performed on a
nicolettm ISTM 50 (Thermo Fisher, USA) spectrometer. X-ray diffraction
(XRD) analysis was performed on Bruker D8 advanced diffractometer
(Bruker, Germany). The specific surface area was measured by nitrogen
adsorption isotherm method by quantachrome autosorb IQ (quantach­
rome, USA) surface analyzer. Images of surface morphology were taken
with Regulus 8220 scanning electron microscope (SEM) (Hitachi, Japan)
at different magnifications. Prior to SEM observation, the samples were
sputtered with a layer of gold by E-1010 ion sputtering instrument
(Hitachi, Japan) to improve the conductivity of the material. X-ray
photoelectron spectroscopy (XPS) spectra were identified by a Thermo
Scientific K-Alpha spectrometer (USA). Thermogravimetric spectra were
performed on a TGA 4000 thermogravimetric analyzer (PerkinElmer,
USA). Mechanical properties were tested by a universal testing machine
(CMT6503, MTS Industrial Systems Co., Ltd., China) with a speed of 2
mm min− 1. In this test, all the samples were cut into a rectangular shape,
and at least five specimens were tested for each sample. After adsorp­
tion, the solution is filtrated with 0.22 μm filter membrane, and the
phosphate concentration in the solution was determined quantitatively
by ICP-AES (Optima 2000dv, PerkinElmer).

As introduced above, BC generally exists in the form of 3D network
structure, which is composed of ultrafine nanofibers being around
10–1000 nm in length and 10–50 nm in diameter (Fig. S1) (Wang,
Tavakoli, & Tang, 2019). To introduce amine groups on the surface of
these nanofibers, PEI was grafted onto BC by crosslinking via glutaral­
dehyde. No obvious morphological change was observed for the PEIgrafted BC, as can be seen from Fig. 1b. The introduced amine groups

with strong affinity for metal ions facilitate the subsequent in-situ growth
of La(OH)3 NPs onto the PEI-grafted BC. As is shown in Fig. 1c–f, Labased NPs were homogeneously deposited onto the PEI-modified cel­
lulose nanofibers without obvious aggregation, which was also
confirmed by the elemental analysis mapping (Figs. 1h–j & S2). As can
be seen, the morphology of the composite membrane remained the
porous fibrous network of the native BC with different La contents. In
comparison, the synthesized La(OH)3 without BC support was aggre­
gated into large particles, which is not desirable for the further
adsorption process towards P.
The structure changes during the treatment for preparing BPLa-X
were characterized by FTIR spectroscopy (Fig. 2a). It is obvious that
the peak at 3340 cm− 1 is attributed to the hydroxyl groups. After
chemically cross-linking with PEI, the peaks at 2908 and 2853 cm− 1
were attributed to enhanced C–H stretching vibrations due to the large
amount of -CH2 from PEI (Song, Liu, Zhu, & Li, 2019). The peak at 1569

Fig. 1. (a) Schematic diagram of BPLa synthesis. SEM images of (b) BC/PEI, (c) BPLa-1, (d) BPLa-2, (e) BPLa-3, (f) BPLa-4 and (g) La(OH)3. (h–j) Elemental mapping
of BPLa-3.
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L. Tan et al.

Carbohydrate Polymers 298 (2022) 120135

Fig. 2. (a) FTIR spectra. (b) XRD patterns. (c) BET isotherms. (d) Stress-strain curve of BPLa-3 in dry and wet conditions.

ăkila
ă, Willfo
ăr, & Xu,

cm− 1 is assigned to amine group (Zhang, Wang, Ma
2022). These results strongly indicate the successful grafting of PEI
chains onto BC. After the introduction of La(OH)3, the peak at 3340
cm− 1 decreased dramatically, and the new absorption bands at 1495
cm− 1 was assigned to the asymmetric stretching mode of the CO2−
3
group, which is relevant to CO2 on the surface of La(OH)3 (SalavatiNiasari, Hosseinzadeh, & Davar, 2011). The changes of FTIR results
indicated that the BPLa-X were successfully prepared. We further
employed X-ray diffraction (XRD) method to determine the crystalline
structure of the as-synthesized La-based nanoparticles (Fig. 2b). Five
distinct peaks at 2θ = 16.2◦ , 27.6◦ , 39.8◦ , 47.8◦ and 55.2◦ corresponding
to the (100), (101), (201), (300) and (112) plane of the cubic phase of La
(OH)3 were observed for BPLa-3 (He et al., 2015; Zong et al., 2017).
Moreover, from Fig. 2b, we can conclude that La(OH)3 NPs synthesized
according to the same procedures without using PEI-grafted BC as sup­
porting material displayed the same reflections with the La(OH)3 NPs
immobilized on the BC nanofibers, indicating that the existence of PEIgrafted BC has no significant effect on the crystal phase of La(OH)3.
Note: Three main peaks at 2θ = 14.8◦ , 16.8◦ and 22.5◦ assigned to dif­
fractions from the (110), (110), and (200) planes of cellulose I were
observed for both pristine BC and PEG-grafted BC. This could be
explained by the fact that the PEI modification occurred on the surface
of BC nanofibers, which would not destroy the crystalline structure of
cellulose.
Generally, the porous structure and surface area of a porous adsor­
bent available for adsorption play crucial roles in determining its
adsorption capacity. Therefore, the N2 adsorption-desorption isotherms
were measured to determine the specific surface area (SSA) of the assynthesized samples. As can be seen from Fig. 2c, typical type III hys­
teresis loops were observed for pristine BC, BP, BPLa-3 as well as La
(OH)3 NPs, indicating the presence of mesoporous structures in these
samples and the occurrence of capillary condensation. Interestingly, the

SSA of pristine BC, BP and La(OH)3 were calculated to be around 98.80,
111.95 and 6.94 m2 g− 1, while the BPLa-X samples had higher SSA of
117.47, 120.18, 123.90 and 128.19 m2 g− 1 for BPLa-1, BPLa-2, BPLa-3
and BPLa-4 (Fig. S3), respectively. The stability of the adsorbents in

water was also an important factor that should be considered for their
practical application in phosphate removal from wastewater. Fig. 2d
presented the stress-strain curve of BPLa-3 in dry and wet conditions.
The sample BPLa-3 at 50 % RH had a tensile strength and an elongation
at break of 19.1 MPa and 3.3 %. When the sample was wetted with
water, it still presented excellent mechanical properties with tensile
strength and an elongation at break of 12.1 MPa and 6.8 %, which is
even comparable to synthetic polymer-based porous membrane (Ge
et al., 2022; Issa, Al-Maadeed, Mrlík, & Luyt, 2016; Rianjanu, Kusu­
maatmaja, Suyono, & Triyana, 2018; Shi et al., 2012).
The adsorption performance of the different samples towards P in
water was investigated. Fig. 3a showed the comparison of the phosphate
adsorption capacity of aggregated La(OH)3 powders, BPLa-X samples,
pristine BC and BP. As expected, pristine BC demonstrated no adsorption
performance towards phosphate, which is mainly due to the absence of
effective adsorption sites for phosphate on BC. Compared to the pristine
BC, BP showed slightly improved adsorption capacity for phosphate of
around 16.5 ± 1.1 mg P g− 1. This result is in line with previous study
suggesting that PEI-modified ethyl cellulose can be employed for
phosphate removal, with phosphate adsorption capacity of 15.53 mg P
g− 1 (Zong et al., 2021). It is worth noting that PEI, as a polymeric amine
with a large amount of -NH and -NH2 groups, has a zero-potential point
at a high pH value (Barick, Prasad Saha, Mitra, & Joshi, 2015). Thus, PEI
is positively charged at acid, neutral and even weak basic surroundings,
which is beneficial for the removal of many anion pollutants, for

example, phosphate owing to the electrostatic interactions. Compared
with powder La(OH)3, pristine BC and BP, all the BPLa-X samples,
namely BPLa-1, BPLa-2, BPLa-3 and BPLa-4, exhibited superior
adsorption tendency for phosphate with adsorption capacities of 57 ±
2.2, 80 ± 2.5, 106 ± 4.5 and 108 ± 6.3 mg P g− 1, respectively. The
observed increase in the adsorption capacities of BPLa-X samples were
mainly ascribed to the increase of the La content. As displayed in Fig. S4,
the La contents of BPLa-1, BPLa-2, BPLa-3 and BPLa-4 were calculated to
be 14.7 %, 29.5 %, 34.5 % and 35.4 %. Considering the fact that com­
parable phosphate adsorption capacities were observed for BPLa-3 and
BPLa-4, BPLa-3 was chosen for further studies including the adsorption
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L. Tan et al.

Carbohydrate Polymers 298 (2022) 120135

Fig. 3. (a) Phosphate adsorption capacities of the
prepared samples. (b) Adsorption kinetic
modeling of phosphate on BPLa-3 using pseudo
first-order, pseudo second-order, and Avrami
fractional-order models (initial phosphate con­
centrations: 30 mg P L− 1, adsorbent dosage: 0.5 g
L− 1, pH: 6, temperature: 25 ◦ C). (c) Adsorption
isotherms fitting of phosphate on BPLa-3 at
different temperatures. (Initial phosphate con­
centrations: 5–350 mg P L− 1, adsorbent dosage:
0.5 g L− 1, pH: 6, temperature: 10 ◦ C, 25 ◦ C, 40 ◦ C
and contact time: 4 h.)

kinetics, recyclability, etc.
To better understand the adsorption process of the BPLa-3 towards
phosphate in water, the pseudo-first-order adsorption model, pseudosecond-order adsorption model and Avrami fraction-order model were
studied (Qu et al., 2022), and the kinetic parameters were shown in
Fig. 3b and Table S1. As demonstrated in Fig. 3b, the adsorption amount
of BPLa-3 for phosphate increased rapidly within 30 min, and reached
the plateau after 75 min. Moreover, the serviceability of each model was
assessed by using the adjusted determination coefficient (R2adj) and the
standard deviation (SD) (Qu, Dong, et al., 2022). Generally, higher R2adj
and lower SD indicate the better applicability of the corresponding ki­
netic model. Fig. 3b and Table S1 indicate that the adsorption process of
the BPLa-3 towards phosphate obeys the pseudo-second-order kinetics,
which is mainly controlled by chemical adsorption. Furthermore, the
Langmuir, Freundlich and Sips isotherm models were also investigated
to study the adsorption mechanism. From the adsorption isotherms and
parameters shown in Fig. 3c and Table S2, the phosphate adsorption
process was better fitted with the Langmuir isotherm model with a
higher correlation coefficient (R2adj = 0.9710) and lower SD (11.52)
than other models at 25 ◦ C, suggesting that the adsorption behavior is
monolayer adsorption process at room temperature. According to the
Langmuir equation, the maximum phosphate adsorption ability of BPLa3 was high to 125.5 mg P g− 1, which is 3.5 times higher than that of the
prepared La(OH)3 (35 mg P g− 1). However, under other conditions, such
as 10 ◦ C and 40 ◦ C, the phosphate adsorption process was better fitted
with the Sips isotherm model, which is a combination of Langmuir and
Freundlich models. When the concentration of adsorbate is high, Sips
model can predict the maximum unit adsorption of monolayer as
Langmuir model; when the concentration of adsorbate is low, Sips model
can describe the adsorption behavior of adsorbent as Freundlich model
(Zhang, Qu, et al., 2022). In addition, the thermodynamics were also

analyzed to study the phosphate adsorption process. As shown in
Table S3, ΔG◦ and ΔH◦ are negative at all temperatures, indicating that
the phosphate adsorption process of BPLa-3 is spontaneous and
exothermic. In the studied temperature range, the amplitude of ΔG◦
value decreases with the increase of temperature, which may correspond
to the decrease of spontaneity at the elevated temperature. In addition,
the value of ΔG◦ greater than − 20 kJ mol− 1 and less than − 80 kJ mol− 1
demonstrated that the adsorption process includes both physical

adsorption and chemical adsorption (Ahmed, Okoye, Hummadi, &
Hameed, 2019). The value of ΔS◦ is positive, indicating that the
randomness of the solid-liquid interface increases during the adsorption
process. Notably, BPLa-3 presented a high adsorption capacity (127 mg
P g− 1) for P (glyphosate) (Fig. S5). The excellent adsorption perfor­
mance of BPLa-3 for P removal is mainly because of the porous fibrous
structure and the homogeneously distributed La(OH)3 NPs on the sur­
face of BC nanofibers. The pH value is an important factor influencing
the adsorption performance of the adsorbent (Qu, Wu, et al., 2022). As is
shown in Fig. 4a, the adsorption capacity could reach up to 116.6 mg P
L− 1 at pH 3 and then decreased with increasing the pH value from 3 to
10. In this pH range, H2PO−4 and HPO2−
4 are the dominant species in the
solutions (Zong et al., 2018), and the zeta potential of the adsorbent
decreased dramatically with increasing the pH value (Fig. S6). There­
fore, the decrease in the adsorption capacity is probably due to the
weakening of the electrostatic attraction between the adsorbent,
H2PO4− and HPO2−
4 .
In addition, many other anions generally co-exist with phosphate in
practical water and/or wastewater may also influence the adsorption

performance. Thus, a desirable adsorbent should possess high adsorp­
tion selectivity towards phosphate. In this work, to evaluate the
adsorption selectivity towards phosphate, the adsorption studies of
BPLa-3 were conducted in the presence of various competing anions
including chloride, carbonate, sulfate, nitrate, and mixtures of these
anions. According to the results shown in Fig. 4b, it can be concluded
that these competing ions have a negligible effect on the adsorption
selectivity for phosphate of BPLa-3. This result is in good agreement
with previous studies on phosphate adsorption by La-based adsorbents
(Zhang, Xu, et al., 2022; Zong et al., 2018).
The reusability of an adsorbent is an important index in assessing its
practical applicability. In this work, BPLa-3 was firstly immersed in
phosphate solution with the initial concentration of 150 mg P L− 1. After
being immersed for 160 min, BPLa-3 was picked up, squeezed and then
immersed in 1 M NaOH solution for 240 min. After that, BPLa-3 was
separated from NaOH solution and washed with deionized water until
neutral pH. The regenerated BPLa-3 was then employed for the subse­
quent cycle of adsorption. As seen in Fig. 4c, after four consecutive cy­
cles of adsorption-desorption, the adsorption capacity of phosphate by
BPLa-3 was maintained at 101.7 mg P g− 1, which is comparable or

Fig. 4. Effect of (a) pH, (b) anions and (c) adsorption-desorption cycles (c) on the adsorption performance of BPLa-3.
5


Carbohydrate Polymers 298 (2022) 120135

L. Tan et al.

superior to many other La-based adsorbents (Table 1). A slight decrease

in the adsorption capacity should be mainly ascribed to the inevitable
lanthanum leaching (Fig. S7).
Compared to many other La-based adsorbents previously reported
for phosphate removal, BPLa-3 showed much higher adsorption capacity
and faster adsorption kinetics (Table 1). For instance, Chen et al. re­
ported the in-situ preparation of La(OH)3-poly(vinylidene fluoride)
composite filtration membrane for phosphate removal. Although a high
permeability was achieved, the membrane had an adsorption capacity of
only 13.86 mg P g− 1, which is much lower than that of BPLa-3. The
difference in the adsorption performance between BPLa samples and
these sorbents and membranes can be explained from the two main
factors, the La content and the specific surface area. Obviously, higher
La content can provide more adsorption sites for phosphate, enabling
the sorbents with higher adsorption capacity. As for the as-prepared
BPLa samples, the La content could reach up to around 35 %. Addi­
tionally, the introduced amine groups also work as phosphate adsorp­
tion sites, also contributing to the excellent adsorption performance of
BPLa samples. The microstructure of the sorbent is also an important
factor that determines their adsorption performance. In this work, the insitu synthesis of La(OH)3 NPs on the nanofibers of porous BC efficiently
prevented the aggregation of these NPs, thus providing more exposed
phosphate adsorption sites. Note: Studies revealed that lanthanum hy­
droxide generally can offer more adsorption sites, for example, surface
hydroxyl groups, than lanthanum oxide. Thus, the BPLa-X samples also
possess higher adsorption capacity than that of many La-based adsor­
bents (Table 1).
In order to probe the possible adsorption mechanism of phosphate
onto BPLa adsorbent, a series of characterization experiments were
carried out in this study. As shown in Fig. 5a, the O-P-O bond bending
− 1
vibration in PO3−

4 groups can be observed at 608 and 534 cm , indi­
cating that phosphate is successfully adsorbed on BPLa-3. It also can be
seen that after phosphate adsorption, the stretching vibration peak of
La–O at 845 cm− 1 decreased, which means that La–O bond partici­
pates in the adsorption with phosphate (Li et al., 2021). Moreover, XPS
spectra were also performed to explore the adsorption mechanism of
phosphate by BPLa-3 (Qu, Yuan, et al., 2022). The wide scan XPS spectra
of BPLa-3 before and after phosphate adsorption indicated the presence
of C, O, La and P elements (shown in Fig. 5b). The presence of a
distinguished peak centered at ~133.4 eV indicated the appearance of
phosphorus after the phosphate adsorption. The P 2p spectrum from
standard samples are located at ~134.0 eV and ~0.6 eV to lower energy

levels after phosphate adsorption, indicating a strong affinity between
phosphate and BPLa-3 (Liu et al., 2022).
As shown in Fig. 5c, the representative satellite peaks of La 3d5/2 and
La 3d3/2 in BPLa-3 are concentrated at ~835.8 eV and ~851.8 eV,
respectively. The shift of the peak to higher energy is usually observed in
La-based compounds, which can be explained by the transfer of elec­
trons from the valence band of the ligand atom (Lu et al., 2021). Obvi­
ously, the absorption peaks of La 3d5/2 and La 3d3/2 shift to higher
binding energies after phosphate adsorption, indicating the formation of
new La-O-P complexes. In addition, the binding types of O elements on
BPLa-3 surface before and after phosphate adsorption were analyzed by
high-resolution XPS scanning. As shown in Fig. 5d–e, the O 1s spectrum
is divided into three overlapping peaks, corresponding to C–O (~532.8
eV), La-OH (~531.4 eV) and La–O (~529.9 eV) derived from the BPLa
adsorbent, respectively. After phosphate adsorption, the area ratio of the
peak attributed to the percentage of La–O increased from 6.06 % to
7.24 %, while the relative area ratio of the peak of La-OH decreased from

47.42 % to 20.41 %, which confirmed that the hydroxyl groups on the
surface of BPLa adsorbent played a major role in phosphate adsorption,
thus leading to the substitution of hydroxyl groups by phosphate during
the adsorption process (Zong et al., 2018). The XRD patterns of BPLa-3
before and after phosphate adsorption were recorded in Fig. 5f.
Compared with the original BPLa-3, it is obvious that the range, in­
tensity and properties of the peaks are greatly different from those of the
original adsorbent after phosphate adsorption. Additionally, the char­
acteristic diffraction peaks at 28.7◦ , 31.2◦ and 42.0◦ indicated that the
adsorption of phosphate by BPLa sample could result in the formation of
LaPO4 via a ligand exchange mechanism between P ions and La-OH
(Huang, Zhu, et al., 2014).
4. Conclusions
In this work, a high-efficient adsorbent for phosphate removal was
facilely constructed by in-situ synthesizing La(OH)3 NPs on PEI-modified
BC. The resultant porous fibrous sample BPLa-3 demonstrated high
adsorption capacity of 125.5 mg P g− 1, fast adsorption kinetics of ~75
min and high adsorption selectivity towards phosphate in the presence
of various anions at room temperature. Moreover, BPLa-3 can be easily
regenerated by simple immersion in NaOH solution, and a high
adsorption capacity of 101.7 mg P g− 1 was still maintained even after
four consecutive cycles of adsorption-desorption. Considering these
merits of such an adsorbent, BPLa is believed to be a promising

Table 1
Comparison of phosphate adsorption capacities of different La-based materials.
Adsorbents

Equilibrium time
(min)

Qm (mg P
g− 1)

Qm (mg P g−
content)

La/Al pillared
clays
La/carbon fiber

300

13.02

120

La-silica spheres
La-vermiculites
La/CNC
La-zeolite

1

La) (La

Specific surface
area (m2g)

Average pore

diameter (nm)

Pore volume
(cm3/g)

Ref.

–

–

–

–

29.44

155.11 (18.98 %)

–

–

–

1440
2880
180
–

47.89
79.6
47.28
17.2

213.41 (22.44 %)
252.54 (31.52 %)
256.82 (18.41 %)
227.81 (7.55 %)

420.38
39.1
136
52.75

2.46
20.74
6.71
5.78

0.23
0.17
0.36
0.076

La/Fe3O4

240

45.45

–

–

–

–

La/lignin
La/PVDF
La/chitosan
La/Fe3O4/lignin
La-iron oxide
La/biochar
La-hydrogel
La/graphene
La/BC
membrane

60
200
10
360
180
480
120
1000
75

65.79
13.86
57.84
60.36
88.6
37.37
105.72
76.85
125.5

229.71 (28.64 %)
256.6 (5.4 %)
98.60 (58.66 %)
–
–
–
335.62 (31.5 %)
–
363.35 (34.54 %)

85.78
–
12.47
208
131.92
–
11.32
158.9
123.90

–
–
–
–
–
–
10.83
4.5
0.31

0.44
–
–
0.46
–
–
0.03
–
1.004

(Tian, Jiang, Ning, & Su,
2009)
(Liu, Zhou, Chen, Zhang, &
Chang, 2013)
(Huang et al., 2014)
(Huang et al., 2014)
(Zheng et al., 2016)
(He, Lin, Dong, & Wang,
2017)
(Liu, Chen, Wang, Zheng, &

Yang, 2018)
(Zong et al., 2018)
(Chen et al., 2018)
(Liu et al., 2020)
(Li, Li, et al., 2021)
(Lu et al., 2021)
(Liu et al., 2022)
(Zhou et al., 2022)
(Wang et al., 2022)
This work

6


L. Tan et al.

Carbohydrate Polymers 298 (2022) 120135

Fig. 5. (a) FTIR analysis of the BPLa-3 before or after phosphate adsorption. (b) XPS survey scan of BPLa-3 before and after phosphate adsorption. (c) La spectra
before and after phosphate adsorption. (d) O1s spectra of pristine BPLa-3. (e) O1s spectra of BPLa-3 after phosphate adsorption. (f) XRD analysis of the BPLa-3 before
or after phosphate adsorption.

candidate for phosphate removal in practical applications.

org/10.1016/j.carbpol.2022.120135.

CRediT authorship contribution statement

References

Liping Tan: Conceptualization, Methodology, Writing – original
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Yue Ru: Methodology, Investigation. Wenbo Yi: Methodology, Inves­
tigation. Bo Pang: Conceptualization, Writing – review & editing, Su­
pervision. Tongjun Liu: Writing – review & editing, Supervision, Project
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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.
Data availability
No data was used for the research described in the article.
Acknowledgment
The project supported by the foundation (No. 2021KF27) of Guangxi
Key Laboratory of Clean Pulp and Papermaking and Pollution Control,
College of Light Industry and Food Engineering, Guangxi University.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
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8