Z. Tian et al.
Journal of Physics and Chemistry of Solids 141 (2020) 109408
were complex and costly.
3 2
solution was prepared by dissolving Pb(NO ) in deionized water.
Sodium alginate (SA) is biodegradable and non-toxic. There are rich
SA resources in the world. Sodium alginate possesses a large number of
carboxylic groups capable of adsorbing heavy metal ions in water, and is
a promising material as a flocculant for removing heavy metal ions
Simulated wastewater containing HA was prepared by dissolving
sodium-HA in deionized water, and the pH adjusted using 1 mol/L
NaOH and 1 mol/L HCl solutions. All flocculation experiments were
carried out on a temperature-controlled rotary shaker (Model DKY-I,
Shanghai Duke Automation Equipment Co. Ltd., China). Briefly, a
certain amount of flocculant solution was added into wastewater solu-
tion and the mixture was rocked for 30 min at 110 r/min. In the floc-
[
19–21].
In order to simplify synthesis of flocculants, enhance flocculating
efficiency and expand the application scope of alginate, in this study a
novel amphoteric flocculant was synthesized based on SA. The cationic
2
culation for HA, CaCl was added as coagulant using the same amount of
þ
groups of –N (CH
3
)
3
were introduced into molecular chains of SA
mass as the flocculant, with continuous stirring for 10 min. The mixture
was kept motionless for 30 min, yielding a precipitate, which was then
through reaction of SA with 3-chloro-2-hydroxypropyltrimethyl
ammonium chloride (CTA) under alkaline conditions. The prepared
amphoteric flocculants demonstrated excellent flocculation efficiency
filtered. The Pb2 concentration in the solution was measured by atomic
absorption spectrophotometry (AA-220/220Z, Brookhaven Company,
USA). The HA concentration was determined by spectrophotometry
þ
for removing Pb2 and HA in wastewater. The amphoteric flocculant
had advantages of simple operation under mild conditions, and easy
post-treatment.
þ
(UV-2300 Shimadzu) [22]. The removal rate (Rr %) of Pb2 and HA was
þ
calculated using the following formula [23]:
Rr (%) ¼ (C
o
–C) ꢁ 100/C
o
(1)
2
. Materials and methods
and C are concentrations of Pb2 (or HA) (mg/L) before and
þ
where C
0
2
.1. Materials
after flocculation, respectively.
The SA (analytical grade, viscosity � 0.02 Pa s in an aqueous solution
3
. Results and discussion
ꢀ
of 1.0 wt %, 25 C), Pb(NO
3
)
2
, CaCl2, Hg(NO
3
)
2
⋅H
2
O, CuSO
4
2
⋅5H O,
2
ZnCl (analytical grade) and anhydrous ethanol were purchased from
3
.1. Preparation of SA–CTA amphoteric flocculants
Sinopharm Chemical Reagent Co. Ltd; CTA (60% aqueous solution) and
sodium-HA (analytical grade) were purchased from Aladdin Biochem-
ical Limited by Share Ltd. All raw materials were used as received
without further purification. We prepared the simulated wastewater
used in the experiment by dissolving pollutants in deionized water.
The mechanism of preparation was divided into two steps: first,
intramolecular etherification between chlorine atoms and hydroxyl
groups took place under alkaline conditions, producing 2,3-epoxy pro-
pyl trimethyl ammonium chloride [24]; then a ring-opening reaction
between the hydroxyl group of SA and the epoxy group of 2,3-epoxy
propyl trimethyl ammonium chloride was carried out under alkaline
conditions, giving a amphoteric flocculant product, containing both
2
.2. Preparation of amphoteric alginate flocculants
In a flask with magnetic stirring apparatus, 5.0 g of SA powder was
þ
À
cationic groups –N (CH
3
)
3
and anion groups –COO , denoted SA–CTA
dissolved in 200 mL of deionized water and 5 mL of NaOH (1 mol/L).
Another solution containing 7.90 g of CTA and 20 mL of NaOH (1 mol/L)
was added dropwise to the above SA solution under stirring in a water
[
25]. The preparation scheme is shown in Fig. 1.
Four samples with different conjugation rate (CR) were prepared
using varied feed ratios of CTA to SA, and the results are shown in
Table 1. The CR was defined as follows:
ꢀ
ꢀ
bath at 45 C. Then the temperature was raised to 70 C, and the reaction
continued for 10 h. Afterwards, the reacted mixture was cooled to room
temperature, and excess anhydrous ethanol was added for precipitation
of the product. After filtration, the product was redissolved in deionized
water, and precipitated again by anhydrous ethanol. After three cycles,
the unreacted CTA was removed. Finally, the product was freeze dried.
Four samples of amphoteric SA flocculants with different group con-
version rates were prepared by using varied feeds of CTA to SA.
CR (%) ¼ (m
1
À m
0
)/m
0
ꢁ 100
(2)
where m and m
0
1
are the weights of alginate before and after conjuga-
tion with CTA, respectively. The CR increased with the increase of CTA
dosage (Table 1).
The reactant CTA was soluble in water and ethanol; however, the
final product SA–CTA flocculant was soluble in water, but insoluble in
ethanol. When the reaction was completed, the raw product solution
was poured into anhydrous ethanol for precipitation; after filtration the
product was redissolved in deionized water and precipitated again by
anhydrous ethanol. After three cycles, the unreacted CTA was removed.
2
.3. Characterizations of the SA–CTA flocculants
Fourier transform infrared (FTIR) spectra were produced using an
attenuated total reflectance method scanning in a range of 400–4000
À 1
cm (ATR-FTIR, Nicolet 6700, USA). A nuclear magnetic resonance
.2. 1H NMR analysis spectra
3
(
NMR) instrument (Bruker AVANCE III HD 400 MHz) was used for 1
H
NMR. Thermal analysis was performed on a thermo-gravimetric analysis
The 1H NMR spectra of the flocculants are shown in Fig. 2. A new
(
TGA) instrument (SDTA 851e Mettler Toledo, 1100SF, Switzerland;
peak at δ ¼ 3.2 ppm in the spectra of amphoteric flocculants (SA–CTA1
ꢀ
nitrogen atmosphere flow rate of 50 mL/min, heating rate of 10 C/min
þ
to SA–CTA4) was attributed to protons in –N (CH
3 3
) [26,27], and this
ꢀ
and temperature range of 25–600 C). Zeta potentials of the flocculants
peak was not present in SA. Three new peaks at 3.35, 3.43 and 3.47 ppm
were ascribed to the protons attached to C , C and C next to quaternary
were measured with a nanometer particle size analyzer (ZetaPALS, US
Brookhaven Company). Flocculant morphology was observed by scan-
ning electron microscope (SEM, Hitachi, S-4800). The binding energy
1
2
3
ammonium groups in CTA, respectively [28]. This fact showed that CTA
was successfully introduced into SA. Additionally, the signals of the
peaks gradually became stronger with the increase in CTA content,
indicating that the CR rose with the increase of CTA content in the feeds.
changes for some atomic orbits of the flocculants and Pb2 before and
þ
after flocculation were determined by X-ray photoelectron spectroscopy
(
XPS; AXIS SUPRA, Kratos Analytical).
1
In the H NMR of SA, the chemical shift at δ ¼ 4.7 ppm was the proton
peak of residual H
2
O in the sample. The peak ranging within 3.65–3.86
2
.4. Flocculation property test for SA–CTA
ppm was due to the resonance of C
alginate.
1
–C
5
protons in the sugar rings of
An aqueous solution containing 1 wt% of flocculant was prepared by
2
þ
dissolving SA–CTA flocculant in deionized water. A 1000 mg/L Pb
2