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Dithiocarbamate-modiﬁed cellulose-basedsorbents with high storage stability for selective
removal of arsenite and hazardous heavy metals†
Futo Morita,‡a Keisuke Nakakubo, ‡a Koki Yunoshita,‡a Masaru Endo, ab
Foni B. Biswas, ac Tatsuya Nishimura, a Asami S. Mashio, a
Hiroshi Hasegawa, *a Tsuyoshi Taniguchi *a and Katsuhiro Maeda *ad
A series of cellulose derivatives bearing dialkyl dithiocarbamate (DTC) groups were synthesized. Their ability

Received 26th June 2020
Accepted 6th August 2020of sorption of arsenite (As(III)) and heavy metals and their storage stability in the solid state were investigated.
Among them, DTC-modiﬁed cellulose derived from L-proline showed the highest sorption capacity for

DOI: 10.1039/d0ra05573e

As(III) and heavy metals to selectively remove them from aqueous media. It also showed exellent storage

rsc.li/rsc-advances

stability in air at 40  C.

Introduction
Compounds having a dithiocarbamate (DTC) group work as
good chelating agents to capture heavy metals because the DTC
group is a so Lewis base that has strong aﬃnity toward soLewis acids such as heavy metals to form stable complexes
according to the HSAB rule.1,2 Several small organic molecules
having a DTC group, such as sodium diethyldithiocarbamate,have been industrially used as sorbents for the removal ofhazardous heavy metals from aqueous or organic media.3,4 Suchsmall molecule-based sorbents are readily available, but further
treatment is oen required for the eﬃcient removal of theresultant complexes from aqueous media due to the diﬃculty inprecipitation of the heavy metal complexes.5 Polymer-basedsorbents carrying a DTC group are potential materials for theremoval of heavy metals from aqueous media because they canwork as heterogeneous sorbents for solid–liquid extraction andcan be easily recovered from water.6 However, typical polymerbased sorbents are synthesized from petroleum-based chemical materials, and the production of a large amount of wasteacid solutions poses serious problem for the environment.7
Cellulose is the world's most abundant natural polymericraw material with a fascinating structure and properties.8 This
polysaccharide is capable of being chemically modied throughthe hydroxyl groups in order to develop eco-friendly and costeﬀective biosorbents for wastewater treatment. Recently, ourgroup synthesized a DTC-modied cellulose material 1 withexcellent ability as a selective sorbent for highly toxic arsenite,which is an inorganic As(III) compound, from aqueous media(Fig. 1).9,10
It is generally believed that DTC compounds are stable in thesolid state. During the course of the above study, however, wefound that the sorption capacity of compound 1 for As(III)signicantly decreased with time when it was stored even in thesolid state under ambient conditions, probably due to decomposition of the DTC groups by moisture or oxygen. Althoughdegradation behaviors of polymer-based sorbents having DTC
groups in the solid state have not been investigated in detail,degradation might be a general problem for DTC-modiedaGraduate School of Natural Science and Technology, Kanazawa University,
Kakuma-machi, Kanazawa 920-1192, Japan. E-mail: hhiroshi@se.kanazawa-u.ac.jp;
tsuyoshi@p.kanazawa-u.ac.jp; maeda@se.kanazawa-u.ac.jpbc

Daicel Corporation, 1239 Shinzaike, Aboshi-ku, Himeji, Hyogo 671-1283, Japan

Department of Chemistry, University of Chittagong, Chittagong 4331, BangladeshdNano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kakuma-machi,
Kanazawa 920-1192, Japan† Electronic supplementary
10.1039/d0ra05573e

information(ESI)‡ These authors contributed equally.

30238 | RSC Adv., 2020, 10, 30238–30244

available.

See

DOI:

DTC-modiﬁed cellulose-based sorbents for the selective
removal of As(III).

Fig. 1This journal is © The Royal Society of Chemistry 2020

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Fig. 2

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Synthesis of DTC-modiﬁed cellulose derivatives 5a–d.

polymer-based sorbents. This drawback would greatly limit theapplicability of the material because manufacturing andtransport of materials with poor storage stability areproblematic.
We therefore decided to develop DTC-modied cellulosematerials with good storage stability that are capable of eﬃciently removing toxic As(III) and heavy metals from aqueous
media. Since monoalkyl DTC compounds (R–NH–C(]S)S; R ¼
alkyl group) have several competitive decomposition pathways
based on the N–H group,11 they do not have suﬃcient stability

Table 1

Sorption capacity of 1 and 5a–d for As(III)Amounts of adsorbed As(III) (mmol g1)a

Entry

Sorbent

As isAer 2 weeksb

1
2
3
4
5

1
5a
5b
5c
5d

595.3  5.1
480.6  20.9
332.1  2.6
489.5  40.9
618.8  17.6

66.5  6.2 (89%)
430.2  7.6 (11%)
184.0  2.4 (45%)
464.8  1.5 (5%)595.2  11.7 (4%)aConditions: [As(III)] ¼ 2 mmol L1 at pH 3. b Under air at 40  C.
Percentage values in parentheses show a rate of decrease in thesorption capacity.

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compared with the stability of dialkyl DTC compounds. In thisstudy, we synthesized a series of dialkyl DTC-modied (–R1–N(R2)–C(]S)S; R1 and R2 ¼ alkyl group) cellulose materials andevaluated their ability for sorption of As(III) and other heavy
metals as well as their storage stability. As a result, we identieda novel biopolymer material derived from cellulose and Lproline as a potential sorbent with excellent storage stability forselective sorption of As(III) and other heavy metals (Fig. 1).

Results and discussion
We began our study with the design and synthesis of four new
DTC-modied cellulose compounds 5a–d (Fig. 2). First,
commercially available microcrystalline cellulose was converted
to the corresponding cellulose esters 3a–d by condensation
between acyclic and cyclic N-protected amino acid derivatives
2a–d in the presence of 1-ethyl-3-(3-dimethylaminopropyl)
carbodiimide hydrochloride (EDC-HCl) and 4-(N,N-dimethylamino)pyridine (DMAP). Compounds 3a–d were readily soluble
in organic solvents, and 1H NMR and elemental analyses of
3a–d indicated that the degree of substitution (DS) was almost
3. Next, the tert-butoxycarbonyl group of 3a–d was removed bytreatment with triuoroacetic acid (TFA) to give secondary
ammonium salts 4a–d. Finally, treatment of 4a–d with CS2 andtetramethylammonium hydroxide provided the corresponding

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Removal percentages of metals from 5 mg L1 multi metal solution at pH 3 using 5d.

dialkyl DTC-modied cellulose compounds 5a–d as white
powders in good yields.§ Since compounds 5a–d were slightly
soluble in water or acetic acid, 1H NMR analysis of thesecompounds could be performed unlike in our previous study.9
Although 1H NMR spectra of 5a–d showed rather broadened
signals, they clearly indicated the existence of each side chain
and tetramethylammonium cation (see ESI†). IR spectra of 5a–
d showed a typical and strong band at around 1730–1740 cm1
based on C]O stretching of ester groups. The spectra also
displayed characteristic bands at around 1375–1485 cm1 and
1155–1185 cm1, which correspond to N–C(S) and C]Sstretching of DTC groups, respectively. The N–C(S) vibration
characteristically shied to a lower value in the order of acyclic
5a (1485 cm1) > 6-membered cyclic 5b (1410 cm1) > 5membered cyclic 5c (1384 cm1) and 5d (1375 cm1) (see ESI†).
Next, we evaluated the sorption ability of the obtained dialkyl
DTC-modied cellulose compounds 5a–d for As(III) (Table 1).
Our previous study showed that the monoalkyl DTC-modiedcellulose 1 had high capacity for sorption of As(III) in acidic
and neutral conditions (#pH 7) because As(III) exists asa neutral form over a wide pH range (pKa1 ¼ 9.2),9 and Ascontaining wastewater such as mining and smelting wastewater is usually acidic.12 Therefore, we tentatively compared thesorption capacities of compounds 5a–d for As(III) at pH 3.
Compound 5a, which is an N-methylated analogue of 1, showeda lower sorption capacity than 1 (Table 1, entries 1 and 2). The
sorption capacity of compound 5b having a piperidine ring was
also not good (Table 1, entry 3). Compound 5c having§ An appropriate caution (e.g., the use of safety glass and glove) should be paid forthe use of potentially toxic reagents such as DMAP and Me4NOH. In addition, theuse of hazardous CS2 as a reagent is unavoidable for the synthesis of DTC
compounds, but reacted CS2 is essentially incorporated to the material asa stable DTC group.

30240 | RSC Adv., 2020, 10, 30238–30244

a pyrrolidine ring showed better sorption capacity than 5a or 5b,
but its sorption capacity was still lower than that of 1 (Table 1,entry 4). Finally, we found that the sorption capacity ofcompound 5d having a L-proline side chain is superior to thatof 1 (Table 1, entry 5). The impact of reaction time in the
introduction of DTC groups to 4d does not seem to be signicant because 5d synthesized from 4d in a prolonged reaction
time (7 h / 24 h) did not show improved sorption capacity for
As(III) (503.6  65.8 mmol g1).
We investigated the change in sorption capacity ofcompounds 1 and 5a–d aer they had been stored in air at 40  C
for 2 weeks (Table 1). The sorption capacity of compound 1
having an N–H group was signicantly decreased by about 89%aer 2 weeks (Table 1, entry 1), and this was consistent with thegradual degradation observed in the course of storage underambient conditions as mentioned in the introduction section.
On the other hand, the sorption capacity of N-substituted DTC
derivatives 5a–d did not decrease as much as that of compound
1 even aer 2 weeks (Table 1, entries 2–5). Notably, the sorption
capacity of 5c and 5d having a pyrrolidine moiety was hardly
changed aer 2 weeks (Table 1, entries 4 and 5), indicating thatthese sorbents are suﬃciently stable to be stored for a long time
under ambient conditions.{ Consequently, 5d having a Lproline side chain was identied as a practical DTC-modiedcellulose-based sorbent with both high sorption capacity andexcellent storage stability. These good properties of 5d might bedue to the high nucleophilicity of a pyrrolidine moiety, which
could strongly ligate CS2.13,14 However, it is unclear why thesorption capacity of 5d is diﬀerent.
Finally, we preliminary tested the eﬃciency of compound 5dfor the removal of other metal ions using aqueous solutions{ Aer exposing the materials to air at 40  C for 2 weeks, the IR spectrum of 1
greatly changed whereas those of 5d hardly changed (Fig. S1 and S2†).

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containing 21 representative metal ions together with As(III) as
shown in Fig. 3. Compound 5d adsorbed heavy metals,
including V(IV), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ga(III), Cd(II),In(III), Pb(II) and Bi(III), with high eﬃciency.1,9 In contrast,
compound 5d hardly adsorbed alkaline earth metal ions, which
are hard metals. This trend is very similar to that of 1 and isconsistent with the HSAB rule.2 Exceptionally, Ti(IV), which isa hard acid, was eﬃciently adsorbed by 5d, and this might bebecause Ti(IV) could form a stable multidentate complex with
DTC groups like other heavy metals.15 Thus, 5d is a potential
sorbent for the selective and eﬃcient removal of As(III) and otherhazardous heavy metals from natural water or wastewater withhigh concentrations of hard metal ions such as alkaline earth
metal ions.

Conclusions
We have developed a new dialkyl DTC-modied biomass-basedsorbent 5d derived from cellulose and L-proline. This sorbent isa potential material for the selective removal of toxic As(III) andother heavy metals from aqueous media because it has highcapacity for As(III) and other hazardous heavy metals but hardly
adsorbs alkaline earth metal ions. The sorption capacity andstability was maintained even aer exposure to air at 40  C for 2
weeks, indicating its excellent storage stability for practical use.
In contrast, a signicant decrease in the sorption capacity for
As(III) was observed for monoalkyl DTC-modied compound 1,
suggesting that monoalkyl DTC-modied polymer-basedsorbents might have poor storage ability, and caution is therefore required for the practical use of such materials. The present
study demonstrated development of an improved sorbent forthe selective removal of As(III) and other heavy metals based ona solid molecular design with biopolymer. Studies for further
improvement and practical applications of the material areongoing in our laboratory.

Experimental
1. General remarks
1.1. For synthetic experiments. All reactions were performed in oven-dried glassware. All reagents purchasedcommercially were used without further purication unlessotherwise noted. Dehydrated solvents were purchased from
Kanto Chemical Co., Inc. Cellulose (Avicel, DP: ca. 200) was
purchased from Merck. N-(tert-Butoxycarbonyl)-N-Me-b-alanine(2a) was prepared by methylation of commercially available N(tert-butoxycarbonyl)-b-alanine with iodomethane.16 2-(1-(tertButoxycarbonyl)piperidin-4-yl)acetic
acid
(2b),
1-(tertbutoxycarbonyl)pyrrolidine-3-carboxylic acid (2c), (tert-butoxycarbonyl)-L-proline (2d) and tetramethylammonium hydroxide(Me4NOH, 10% in methanol) were purchased from Tokyo
Chemical Industry Co., Ltd. (TCI). Lithium chloride, 1-ethyl-3(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCHCl), N,N-dimethyl-4-aminopyridine (DMAP), triuoroacetic
acid (TFA), and carbon disulde were purchased from Wako
Pure Chemical. DTC-modied cellulose 1 was preparedaccording to the procedure previously reported.9

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1

H NMR spectra were recorded on Bruker Avance 400 and
JEOL JNM-ECA 500 spectrometers at 20  C unless otherwise
noted. Chemical shis (d) are quoted relative to tetramethylsilane (1H NMR, d 0 ppm) or a solvent residual peak (D2O:
d 4.79 ppm; CD3CO2D: d 2.04 ppm) as the internal standard.
Coupling constants (J) are given in Hz. Multiplicities are indicated as follows: s (singlet), d (doublet), t (triplet), q (quartet), m(multiplet), or br (broadened). IR spectra were recorded witha JASCO Fourier Transform IR-4700 spectrophotometer.
Elemental analyses were performed by the Research Institutefor Instrumental Analysis of Advanced Science Research Center,
Kanazawa University or by the Research Initiative Center, Tottori University.
1.2. For batch sorption experiments. All laboratory wares
were soaked in an alkaline detergent (Scat 20X-PF; Nacalai
Tesque) overnight, and then rinsed with deionized water.
Subsequently, they were soaked in 3 mol L1 HCl overnight, andthen washed again with deionized water. As(III) standard solution (1000 mg L1), sodium hydroxide (NaOH), nitric acid
(HNO3, 60%) and acetic acid (AcOH, 99%) were purchased from
Kanto Chemical. Sodium acetate (AcONa) was purchased from
Nacalai Tesque. ICP multi-element standard solution IV containing 21 elements (Al, Ba, Be, Bi, Ca, Cd, Co, Cu, Fe, Ga, In, K,
Li, Mg, Mn, Na, Ni, Pb, Sr, Y, Zn) was purchased from GL
science.
The metal concentrations were quantied with inductively
coupled plasma optical emission spectrometry (ICP-OES; iCAP
6300; Thermo Fisher Scientic). For pH measurements, a pH
meter (Navi F-52; Horiba Instruments) was used. In order toprepare deionized water with a resistivity of > 18.2 MU cm, an
Arium Pro water purication system (Sartorius Stedium BiotechGmbH) was used. A natural incubator (NIB-82; Iwaki Asahi
Techno Glass) was used for heating.
2. Experimental details
2.1. Synthetic experiments
2.1.1. Synthesis of 3a–d (esterication). Aer cellulose (1equiv.) was dried for 2 h at 90  C in vacuo (0.1 mmHg), DMA(5.4 mL mmol1) was added, and the resultant slurry was stirred
for 20 h at 90  C. LiCl (ca. 7–8 equiv.) was added to the slurry
precooled to room temperature, and the mixture was stirred for
1 h at room temperature. 2a–d (6 equiv.), DMAP (6 equiv.) and
EDC-HCl (6 equiv.) were added to the resultant solution at 0  C,
and the mixture was stirred for 24 h at room temperature. The
reaction mixture was poured into an excess amount of MeOH/
H2O (70/30–80/20, v/v) under stirring. The formed precipitate
was collected by centrifugation, washed with MeOH/H2O (80/20,v/v), and dried in vacuo to give 3a–d. The product was oencontaminated with small amounts of waste based on reagentsused in the reaction, but those could be used for the next step
without further purication. For identication, the purer
product could be obtained by repeating precipitation andwashing with MeOH/H2O.
3a. Cellulose (301 mg, 1.86 mmol), DMA (20 mL), LiCl
(642 mg, 15.1 mmol), 2a (2.29 g, 11.3 mmol), DMAP (1.38 g, 11.3mmol) and EDC-HCl (2.16 g, 11.3 mmol) were used for the

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reaction to give 3a (1.17 g, 84% yield) as a white solid. 1H NMR(500 MHz, CDCl3, 55  C): d 5.05 (br, 1H), 4.73 (br, 1H), 4.55 (br,1H), 4.48 (br, 1H), 4.07 (br, 1H), 3.33–3.70 (m, 8H), 2.82–2.87 (m,9H), 2.43–2.56 (m, 6H), 1.43 (s, 27H); IR (KBr, cm1): 1745, 1691.
Anal. calcd for C33H55N3O14$H2O: C, 53.87; H, 7.81; N, 5.71.
Found: C, 54.12; H, 7.58; N, 5.70.
3b. Cellulose (1.00 g, 6.17 mmol), DMA (31 mL), LiCl (1.96 g,
46.3 mmol), 2b (9.00 g, 37.0 mmol), DMAP (4.52 g, 37.0 mmol)and EDC-HCl (7.09 g, 37.0 mmol) were used for the reaction to
give 3b (3.87 g, 75% yield) as a white solid. 1H NMR (500 MHz,CDCl3, 55  C): d 5.06 (br, 1H), 4.68 (br, 1H), 4.53 (br, 1H), 4.34
(br, 1H), 3.93–4.20 (m, 7H), 3.76 (br, 1H), 3.51 (br, 1H), 2.72 (br,6H), 2.10–2.30 (m, 6H), 1.55–1.95 (br, 9H), 1.45 (s, 27H), 1.00–
1.25 (m, 6H); IR (KBr, cm1): 1747, 1691. Anal. calcd for
C42H67N3O14: C, 60.20; H, 8.06; N, 5.01. Found: C, 59.81; H,
8.22; N, 5.04.
3c. Cellulose (253 mg, 1.56 mmol), DMA (9.4 mL), LiCl
(528 mg, 12.5 mmol), 2c (2.03 g, 9.43 mmol), DMAP (1.17 g, 9.56mmol) and EDC-HCl (1.79 g, 9.35 mmol) were used for thereaction to give 3c (1.15 g, 98% yield) as a white solid. 1H NMR(500 MHz, CDCl3, 55  C): d 5.07 (br, 1H), 4.00–4.72 (m, 3H),
2.70–3.90 (m, 18H), 1.90–2.30 (m, 6H), 1.45 (s, 27H); IR(KBr, cm1): 1751, 1691. Anal. calcd for C36H55N3O14$0.5H2O: C,
56.68; H, 7.40; N, 5.51. Found: C, 56.68; H, 7.33; N, 5.55.
3d. Cellulose (1.25 g, 7.71 mmol), DMA (42 mL), LiCl (2.60 g,
61.4 mmol), 2d (10.0 g, 46.6 mmol), DMAP (5.72 g, 46.8 mmol)and EDC-HCl (9.00 g, 47.0 mmol) were used for the reaction to
give 3d (4.82 g, 82% yield) as a white solid. 1H NMR (500 MHz,CDCl3, 55  C): d 3.20–5.20 (br, 16H), 1.58–2.40 (br, 12H), 1.43
(br, 27H); IR (KBr, cm1): 1755, 1709. Anal. calcd for C36H55N3O14$H2O: C, 56.02; H, 7.44; N, 5.44. Found: C, 55.92; H,
7.31; N, 5.45.
2.1.2. Synthesis of 4a–d (deprotection). TFA (5 mL mmol1)
was added to 3a–d, and the mixture was stirred for 7 h at room
temperature. The reaction mixture was poured into an excess
amount of Et2O under stirring. The formed precipitate wascollected by centrifugation, washed with Et2O, and dried invacuo to give 4a–d.
4a. TFA (7.8 mL) and 3a (1.17 g, 1.63 mmol) were used for thereaction to give 4a (1.08 g, 92% yield) as a white solid. 1H NMR(500 MHz, D2O, 80  C): d 5.71 (br, 1H), 4.10–5.40 (m, 6H,partially overlapped with a water signal), 3.85 (br, 6H), 3.20–3.55(m, 15H), the signal based on NH2 was not observed due to H-D
exchange; IR (KBr, cm1): 1750, 1681. Anal. calcd for C24H34N3O14F9$2H2O: C, 36.23; H, 4.81; N, 5.28. Found: C, 36.32; H,
4.43; N, 5.22.
4b. TFA (8.0 mL) and 3b (1.36 g, 1.62 mmol) were used for thereaction to give 4b (1.37 g, 96% yield) as a white solid. 1H NMR(500 MHz, D2O): d 5.09 (br, 1H), 4.30–4.80 (m, 5H, partiallyoverlapped with a water signal), 3.75 (br, 1H), 3.42 (br, 6H), 2.98
(br, 6H), 1.80–2.50 (m, 15H), 1.30–1.50 (m, 6H), the signal basedon NH2 was not observed due to H-D exchange; IR (KBr, cm1):
1745, 1689. Anal. calcd for C33H46N3O14F9$2H2O: C, 43.28; H,
5.50; N, 4.59. Found: C, 42.84; H, 5.07; N, 4.51.

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4c. TFA (32 mL) and 3c (4.80 g, 6.37 mmol) were used for thereaction to give 4c (4.73 g, 93% yield) as a white solid. 1H NMR(500 MHz, D2O): d 5.19 (br, 1H), 3.303.80–4.80 (m, 6H, partiallyoverlapped with a water signal), 3.30–3.70 (m, 12H), 1.70–2.50(m, 9H), the signal based on NH2 was not observed due to H-D
exchange; IR (KBr, cm1): 1747, 1679. Anal. calcd for C27H34N3O14F9$H2O: C, 39.86; H, 4.46; N, 5.16. Found: C, 39.49; H,
4.28; N, 5.15.
4d. TFA (32 mL) and 3d (4.82 g, 6.40 mmol) were used for thereaction to give 4d (4.09 g, 80% yield) as a white solid. 1H NMR(500 MHz, D2O): d 5.42 (br, 1H), 4.55–5.20 (m, 5H, partiallyoverlapped with a water signal), 3.80–4.40 (m, 4H), 3.50 (br, 6H),
1.85–2.70 (m, 12H), the signal based on NH2 was not observed
due to H-D exchange; IR (KBr, cm1): 1755, 1678. Anal. calcd for
C27H34N3O14F9$H2O: C, 39.86; H, 4.46; N, 5.16. Found: C, 39.55;
H, 4.54; N, 4.97.
2.1.3. Synthesis of 5a–d (dithiocarbamation). To a solution of
4a–d in DMSO (5 mL mmol1) was added CS2 (15 equiv.) and
10% Me4NOH solution in MeOH (ca. 6–7 equiv.) at 0  C, and theresultant suspension was stirred at room temperature. The
reaction mixture became almost homogeneous in 7–48 h. The
reaction mixture was poured into an excess amount of MeOH
(for 4a and 4b) or EtOH (for 4c and 4d) under stirring. The
formed precipitate was collected by centrifugation, washed with
MeOH (for 4a and 4b) or EtOH (for 4c and 4d), and dried invacuo to give 5a–d.
5a. 4a (1.55 g, 2.04 mmol), DMSO (10 mL), CS2 (1.84 mL, 30.5mmol) and 10% Me4NOH solution in MeOH (14 mL, 13.9mmol) were used for the reaction (7 h) to give 5a (605 mg, 34%
yield) as a white solid. 1H NMR (500 MHz, D2O): d 3.90–5.50 (m,7H, partially overlapped with a water signal), 3.45 (br, 6H), 3.18
(br, 9H), 3.16 (s, 36H); IR (KBr, cm1): 1741, 1485, 1156. The
value observed by elemental analysis was signicantly diﬀerent
from the theoretical value because the sample contained
a signicant amount of water or because the side chain waspartially degraded by hydrolysis (for example, Anal. calcd for
C33H64N6O8S6: C, 45.81; H, 7.46; N, 9.71. Found: C, 41.42; H,
7.13; N, 8.14).
5b. 4b (507 mg, 0.576 mmol), DMSO (2.8 mL), CS2 (0.52 mL,
8.61 mmol) and 10% Me4NOH solution in MeOH (3.7 mL, 3.66mmol) were used for the reaction (48 h) to give 5b (496 mg, 87%
yield) as a white solid. 1H NMR (500 MHz, CD3CO2D): d 3.70–
5.50 (m, 7H), 3.54 (br, 6H), 3.22 (s, 36H), 3.09 (br, 6H), 1.80–2.50(br, 15H, partially overlapped with a solvent signal), 1.40–1.70(m, 6H); IR (KBr, cm1): 1741, 1410, 1174. The value observed byelemental analysis was signicantly diﬀerent from the theoretical value because the sample contained a signicant amount ofwater or because the side chain was partially degraded byhydrolysis (for example, Anal. calcd for C42H76N6O8S6: C, 51.19;
H, 7.77; N, 8.53. Found: C, 47.76; H, 6.69; N, 6.43).
5c. 4c (421 mg, 0.529 mmol), DMSO (2.7 mL), CS2 (0.49 mL,
8.12 mmol) and 10% Me4NOH solution in MeOH (3.7 mL, 3.66mmol) were used for the reaction (48 h) to give 5c (404 mg, 83%
yield) as a white solid. 1H NMR (500 MHz, D2O): d 5.27 (br, 1H),This journal is © The Royal Society of Chemistry 2020

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3.30–5.00 (m, 18H, partially overlapped with a water signal),
3.20 (s, 36H), 1.90–2.70 (br, 9H).; IR (KBr, cm1): 1740, 1384,
1165. The value observed by elemental analysis was signicantly
diﬀerent from the theoretical value because the sample contained a signicant amount of water or because the side chain
was partially degraded by hydrolysis (for example, Anal. calcd
for C36H64N6O8S6: C, 47.97; H, 7.15; N, 9.32. Found: C, 44.32; H,
7.34; N, 8.51).

Conﬂicts of interest

5d. 7 h: 4d (1.00 g, 1.26 mmol), DMSO (6.3 mL), CS2 (1.14 mL,
18.9 mmol) and 10% Me4NOH solution in MeOH (8.7 mL, 8.61mmol) were used for the reaction (7 h) to give 5d (915 mg, 81%
yield) as a white solid. 24 h: 4d (504 mg, 0.633 mmol), DMSO
(3.1 mL), CS2 (0.57 mL, 9.44 mmol) and 10% Me4NOH solution
in MeOH (4.3 mL, 4.27 mmol) were used for the reaction (24 h)
to give 5d (519 mg, 91% yield) as a white solid. 1H NMR (500
MHz, D2O): d 5.04 (br, 3H, partially overlapped with a water
signal), 3.90 (br, 6H), 3.17 (s, 36H), 1.70–2.60 (br, 12H), signals
based on the cellulose moiety (7H) were obscure due to broadening; IR (KBr, cm1): 1737, 1375, 1183. The value observed byelemental analysis was signicantly diﬀerent from the theoretical value because the sample contained a signicant amount ofwater or because the side chain was partially degraded byhydrolysis (for example, Anal. calcd for C36H64N6O8S6: C, 47.97;
H, 7.15; N, 9.32. Found: C, 42.50; H, 7.40; N, 7.81).
2.2. Batch sorption experiments. The durability of thesorbents was investigated by comparing the sorption capacities
of As(III) before and aer keeping them at 40  C for fortnight.
Sorption tests were conducted in 50 mL centrifuge tubes containing 0.02 g of sorbent and 10 mL of 2 mmol L1 As(III)solutions by agitating the tubes for 20 minutes at 25  C and
200 rpm. Then, the solutions were collected by ltratingsuspensions through a 0.45 mm membrane lter. Subsequently,
the metal concentrations in the solutions were determined with
ICP-OES. The sorption capacities of As(III) (qe) were calculated
according to the equation shown below:

This work was nancially supported by Daicel Corporation and
JSPS KAKENHI (Grant-in-Aid for Scientic Research (C), No.
18K04723).

qe ¼

ðCi  Ce Þ
V
m

(1)

where qe (mmol g1) represents the sorption capacity of As(III), Ci
and Ce (mmol L1) refer to initial and equilibrium concentrations of As(III), m (g) is the weight of the sorbent, and V (L) is thesolution volume.
The removal eﬃciency of various elements was examinedusing polymer 5d. The solution containing 21 elements was
prepared by diluting the desired amount of the ICP multielement standard solution with deionized water so that theconcentrations became 5 mg L1. Then, the pH was adjusted to
pH 3 using 0.1 mol L1 HNO3 or NaOH solution, and sorption
tests were carried out according to the procedure mentioned
above. The removed metal percentages (%) were calculated
from the following equation:

Removed metalð%Þ ¼

ðCi  Ce Þ
 100
Ci

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The authors declare the following conict of interest(s): Kanazawa University and Daicel Corporation hold or have a ledpatent related to this work (Patent Application No. PCT/JP2020/
21903).

Acknowledgements

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