A TEMPO-oxidized cellulose nanofibersMOFs hydrogel with temperature and pH responsiveness for fertilizers slow-release

Prévia do material em texto

International Journal of Biological Macromolecules 191 (2021) 483–491
Available online 23 September 2021
0141-8130/© 2021 Elsevier B.V. All rights reserved.
A TEMPO-oxidized cellulose nanofibers/MOFs hydrogel with temperature 
and pH responsiveness for fertilizers slow-release 
Xiangyu Lin a,1, Lizhen Guo a,1, Hiba Shaghaleh b, Yousef Alhaj Hamoud b, Xu Xu a,*, He Liu c,* 
a College of Chemical Engineering, Advanced Analysis and Testing Center, International Innovation Center for Forest Chemicals and Materials, Nanjing Forestry 
University, Jiangsu Provincial Key Lab for the Chemistry and Utilization of Agro-Forest Biomass, Jiangsu Key Lab of Biomass-Based Green Fuels and Chemicals, Nanjing 
210037, Jiangsu Province, China 
b College of Agricultural Science and Engineering, Hohai University, Nanjing 210098, China 
c Institute of Chemical Industry of Forestry Products, Chinese Academy of Forestry, Key Laboratory of Biomass Energy and Material, Co-Innovation Center of Efficient 
Processing and Utilization of Forest Resources, Key Lab. of Chemical Engineering of Forest Products, National Forestry and Grassland Administration, National 
Engineering Laboratory for Biomass Chemical Utilization, Nanjing 210042, Jiangsu Province, China 
A R T I C L E I N F O 
Keywords: 
Cellulose 
Hydrogel 
Slow-release 
A B S T R A C T 
In this work, a kind of MOF MIL-100(Fe)@CNFs hydrogel (MC) based on TEMPO-oxidized cellulose nanofibers 
(CNFs) for fertilizers slow-release was prepared by free-radical polymerization, where N-vinyl caprolactam 
(NVCL) and CNFs were involved to exhibit temperature and pH response, respectively. Particularly, porous MIL- 
100(Fe), a kind of metal organic frameworks (MOFs), was introduced to optimize the load and slow-release 
capabilities. The Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and 
thermogravimetric analysis were used to characterize. The swelling behaviors and water-retention capabilities of 
hydrogels were evaluated. Using urea as the model fertilizer, the slow-release mechanism was revealed. Wheat 
was used as the model crop to evaluate the practical growth status. Compared with MC-0% hydrogels, the MC- 
10% hydrogels exhibited a better swelling capacity (37 g/g), water-retention (22.78%) and slow-release per-
formance (40.84%). It also exhibited sensitivities to temperature and pH for regulating urea release. Besides, the 
number of tillers and leaves of wheat fertilized with MC hydrogels significantly increased, as did the photo-
synthetic rate. In conclusion, the MC-0% hydrogels had a positive influence on crops growth, and promoted the 
possible utilization of hydrogels in slow-release fertilizers. 
1. Introduction 
The efficient use of fertilizers and water resources can greatly in-
crease crops yields, and meet increased demands. However, the usage 
efficiencies of conventional fertilizers (urea) are generallyof the hydrogels was characterized by FT-IR, XRD, 
and SEM. The swelling ratio, urea release behavior, temperature- 
responsive nature, and pH-responsive properties of the MC hydrogel 
were investigated. Finally, the obtained MC hydrogels were applied in 
the growth of wheat. 
2. Materials and methods 
2.1. Materials 
2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO, 98%), 1,3,5- 
benzenetricarboxylic acid (H3BTC, 98%), ammonium persulfate (APS, 
98%), sodium hypochlorite (NaClO, 14%), N,N-dimethylacrylamide 
(DMAA, 98%), N-vinyl caprolactam (NVCL, 99%), and N,N-methyl-
enebisacrylamide (MBA, 99%) were purchased from Aladdin Chemical 
Co., Ltd. (Shanghai, China). Sodium hydroxide (NaOH, 97%), N,N- 
dimethylformamide (DMF, 99.5%), hydrochloric acid (HCl), sodium 
alginate (SA), and urea were purchased from Nanjing Chemical Reagent 
Co., Ltd. (Nanjing, China). Eucalyptus pulp was purchased from 
ARAUCO Co., Ltd. (Chile). 
2.2. Synthesis of the TEMPO-oxidized cellulose nanofibers (CNFs) 
NaBr (0.5 g) and TEMPO (0.08 g) were dissolved in deionized water 
(500 mL) and mechanically stirred in a three-neck round-bottomed flask 
(1000 mL). After adding the previously pulverized eucalyptus pulp (5 g), 
a solution of NaClO (8.5 mL, pH 10), whose pH value was adjusted using 
a 0.1 mol/L HCl solution, was slowly added to the flask at 25 ◦C. A 0.1 
mol/L NaOH solution was added at the same time to maintain the pH of 
the system at ~10. The CNFs were obtained via a suction filtration pu-
rification process, in which the CNFs were washed with deionized water 
until the conductivity of the washed solution wasout from the bottom, and the 
setup was weighted once again when there was no water seeping from 
the bottom (w1). The Hr (%) of the hydrogel in the soil was calculated as 
follows: 
Hr = (w1 − w0)/w0 × 100% (7) 
2.9. Slow-release behavior 
Load and release experiments were carried out on the MC-0% and 
MC-10% hydrogels using urea as a fertilizer model. To obtain hydrogels 
loaded with urea, the dried hydrogels were dipped into the aqueous urea 
solution (25 mg/mL) for 72 h at 25 ◦C. To investigate their urea release 
behaviors, hydrogels loaded with urea were placed in water at different 
temperatures and pH values. In each case, the soaking solution (1 mL) 
was collected at regular intervals, and the amount of urea released was 
characterized using UV–visible spectrophotometry. The cumulative 
release rate (%) of urea was calculated as follows: 
Cummulative release (%) = mt
/
m0 × 100% =
mt
m1
× 100% (8) 
where mt (g) and m0 (g) represent the quantity of urea released at a 
certain time and the urea loading, respectively. 
To investigate their release behaviors in soil, the urea-loaded 
hydrogels (1 g) were buried in dry sand (800 g) at a depth of approxi-
mately 5–6 cm below the surface for 30 d at room temperature. During 
the experiment, distilled water (200 mL) was irrigated every 5 d. Three 
sets of experiments were performed in parallel. Samples of the soil (1.5 
g) were removed at different periods (1, 3, 5, 7, 10, 15, 20, 25, and 30 d) 
and the cumulative amount of urea released was calculated using the 
Kjeldahl method, which can indicate the total nitrogen content present 
in the soil. The cumulative release rate (%) of urea was calculated using 
Eq. (8). 
To elucidate the urea release mechanism in soil, four kinetic math-
ematical models (i.e., the zero-order, first-order, Higuchi, and 
Korsmeyer-Peppas models) were used to fit and analyze the data ob-
tained [4,41,42]: 
①Zero − order release kinetics model : Mt/M∞ = k0t (9) 
②First − order release kinetics model : Mt
/
M∞ = 1 − e− k1t (10) 
③The Higuchi model : Mt
/
M∞ = kHt1/2 (11) 
④The Korsmeyer − Peppas model : Mt
/
M∞ = kkptn (12) 
where M∞ and Mt represent the mass of urea at the release equilibrium 
and a different release time ‘t’, respectively. k0, k1, kH and kkp represent 
the diffusional kinetic constant, the release constant, the dissolution 
constant, and the rate constant, respectively. ‘n’ is a diffusional expo-
nent, and according to its value, one of three diffusion mechanisms can 
be identified. The diffusion mechanism is Fickian if ‘n’ is ≤0.43, while 
where 0.43con-
taining MIL-100(Fe)) showed an irregular micropore structure (Fig. 4d). 
Moreover, the results of EDAX analysis (Fig. S4) indicated that MIL- 
100(Fe) distributed homogeneously in the hydrogels. Thus, to verify 
whether MOF MIL-100(Fe) can function properly in hydrogels, the BET 
adsorption-desorption isotherms were obtained (Fig. 4f and Table S3). 
As indicated, the MC-10% hydrogel exhibited a type II adsorption 
isotherm, as did MOF MIL-100(Fe) (Fig. S5). The MC-10% hydrogel also 
possessed a higher specific surface area, thereby suggesting that the 
combination of MOF MIL-100(Fe) with hydrogels was beneficial to 
enhance the adsorption of fertilizers and water. 
3.2. Swelling behavior and the swelling dynamic mechanism at room 
temperature 
As a controlled release carrier for fertilizers and water, the swelling 
behavior and dynamic swelling mechanism should be explored in a 
Fig. 2. Schematic of the preparation process for CNFs a, MIL-100 (Fe) b and 
MOF MIL-100(Fe)@CNFs hydrogels c d. 
Fig. 3. a FTIR spectra of CNFs, MIL-100 (Fe), NVCL, MC-0% hydrogel and MC- 
10% hydrogel, and b MC hydrogels with different MIL-100 (Fe) contents. c XRD 
spectra and d XPS spectra of CNFs, SA, MIL-100 (Fe), MC-0% and MC- 
10% hydrogels. 
X. Lin et al. 
International Journal of Biological Macromolecules 191 (2021) 483–491
487
hydrogel. During the swelling process, the free adsorption of water 
occurred initially [43], as indicated in Fig. 5, where the swelling be-
haviors of the different hydrogels at room temperature were shown. The 
swelling rates of all MC hydrogels increased rapidly during the initial 6 
h, and then increased slowly until equilibrium was reached. This was 
attributed to the expansion of the 3D network structure due to repulsion 
between the carboxylate groups in the hydrogels, which promoted the 
penetration of water into the 3D structure, and improved the swelling 
ratio. Compared with the MC-0% hydrogel, the MC-10% hydrogel 
showed the maximum increase in swelling capacity, i.e., from 27 to 37 
g/g (Fig. 5b). This was due to the inhibiting of the physical entanglement 
of the CNFs and the SA chains by MOF MIL-100(Fe), which led to a 
reduction in the hydrogel cross-linking density and an increased 
swelling ratio. However, as the content of MOF MIL-100(Fe) was 
increased further (i.e., in the case of the MC-20% hydrogel), the swelling 
rate decreased. It was likely due to increased cross-linking, which 
limited expansion of the network structure and hindered the infiltration 
of water molecules. Fig. 5f showed the results of the hydrogel reuse 
experiment, from which their good ability to absorb and release water 
repeatedly can be clearly observed. 
To explore the dynamic swelling mechanism of MC hydrogels in the 
initial stage, the Korsmeyer-Peppas model (Eq. (13)) and Schott's 
second-order swelling kinetics model (Eq. (14)) were introduced [41]. 
For Korsmeyer-Peppas model, wt and we denoted the weight of water 
absorbed at any time t and at theoretical equilibrium respectively; K was 
a constant that describes the characteristic of hydrogels and n was the 
exponent that described the type of diffusion. Both K and n can be 
calculated from the plots of log(F) versus log(t). For Schott's second- 
order swelling kinetics model, SR and ESR denoted the swelling ratios 
at any time t and at equilibrium respectively, and k represented the 
swelling rate constant. 
F =
wt
we
= Ktn (13) 
Fig. 4. a Photograph of (i) MC-0%, (ii) MC-10%. SEM images of b MIL-100 (Fe), c MC-0% hydrogel and d e MC-10% hydrogel at different magnifications. f Nitrogen 
adsorption-desorption isotherms of MC-0% and MC-10% at 77 K. 
Fig. 5. a Swelling ratios and b equilibrium swelling ratios of different hydro-
gels in distilled water at 25 ◦C. c Photograph of hydrogels before and after 
swelling equilibrium. d Korsmeyer-Peppas model and e Schott's second-order 
kinetic model for different hydrogels in water. f The reusable swelling and 
deswelling behaviors of different hydrogels. 
Fig. 6. a ESR of different hydrogels in distilled water at different temperature. 
b Cycle analysis for swelling ratios at different temperatures. c Swelling ratios 
at different pH values under 25 ◦C. d Cycle analysis for swelling ratios at 
different pH. 
X. Lin et al. 
International Journal of Biological Macromolecules 191 (2021) 483–491
488
t
SR
=
1
kESR2 +
1
ESR
t (14) 
As shown in Fig. 5d, good linear correlation coefficients were ob-
tained (R2 > 0.95) for the Korsmeyer-Peppas model, and the values of n, 
K, and R2 were given in Table S4. According to the obtained values of n 
(0.43 0.99, thereby indicating that this model was 
suitable for describing the MC hydrogel swelling behaviors. Moreover, 
the values of ESRcal matched well with the experimental values (ESRexp) 
(Table S4). 
3.3. Temperature- and pH-responsive behaviors 
It is well known that the conformations of the thermosensitive 
monomer NVCL chains in hydrogels change when the temperature is 
lower or higher than the low critical solution temperature (LCST), and 
this effect leads to the volume-phase transition of hydrogels [44]. More 
specifically, when the temperature is above the LCST, the hydrogels 
shrink rapidly. Thus, the prepared MC hydrogels were swollen in 
deionized water at various temperatures, and their equilibrium swelling 
ratios were calculated. As shown in Fig. 6a, the equilibrium swelling 
ratios of the MC hydrogels decreased as the temperature was increased, 
indicating that these MC hydrogels exhibited a high temperature 
response performance. In addition, the hydrogels were found to absorb 
water easily at temperatures below the LCST (25 ◦C). It can therefore be 
interpreted that the PNVCL chains showed great hydrophilicity at tem-
peratures below the LCST, but collapsed into a hydrophobic structure 
above the LCST [45] (Fig. S6a). 
In the context of actual application, it is essential for hydrogels to 
achieve repeatable shrinkage and swelling. Therefore, the cycling 
properties of the different MC hydrogels in terms of their swelling and 
shrinking behaviors were investigated at 25 ◦C (below the LCST) and at 
55 ◦C (above the LCST). As shown in Fig. 6b, all of the examined MC 
hydrogels exhibited good repeatable shrinkage and swelling behaviors, 
and showed a slightly consecutive reduction over time. 
The pH-responsive behaviors of the MC hydrogels were subsequently 
evaluated by investigating the swelling ratios at various pH values. As 
shown in Fig. 6c, the swelling ratios of all hydrogels increased with the 
pH increasing from 3 to 11. From this result, it can be interpreted as that 
the –COOH groups dissociated into –COO¡ groups under alkaline con-
ditions, thereby leading to an increase in the hydrophilicity and the 
electrostatic repulsion of the structure [46], and resulting in the 
observed improved water absorption ability (Fig. S6b). As shown in 
Fig. 6d, the examined MC hydrogels also exhibited good repeatable 
shrinkage and swelling behaviors at pH = 3 and pH = 11, presenting 
pleasuring pH-responsiveness. 
Fig. 7a showed the water-retention capabilities of the different MC 
hydrogels in distilled water at 55 ◦C (above the LCST). As shown, the 
introduction of MOF MIL-100(Fe) increased the water-retention of the 
hydrogelsfrom 60.28% (MC-0%) to 77.53% (MC-10%). Moreover, the 
maximum water-holding capacity of MC-10% was found to be higher 
than that of MC-0% in a soil environment (Fig. S7). Besides, the sample 
mixed with MC-10% (1.0 g) presented the greatest water-retention ca-
pacity of the various samples examined (Fig. 7b), which still remained 
22.78% in soil on day 30. For all the other samples, the water-retention 
reached to zero on day 30 or earlier. These observations suggested that 
the application of MC-10% hydrogels in agricultural production was a 
good choice to provide a suitable growth environment for crops. 
3.4. Urea release behaviors of the MC hydrogels 
To evaluate the application potentials of MC hydrogels in the field of 
slow-release fertilizers, the urea release behaviors of our prepared 
hydrogels were studies at different pH values and temperatures. Thus, 
Fig. S8 showed the FTIR spectra of MC hydrogels loaded with urea, and 
Fig. 8 showed the effects of pH and temperature on the cumulative 
release of urea. Overall, the obtained results illustrated a general trend 
wherein urea was released rapidly in the initial 3 h, followed by the 
subsequent slower release due to the fact that the urea loaded on the 
hydrogel surface was more easily released than that inside the hydrogel. 
Due to the pH responsiveness, the hydrogels exhibited lower fertilizer 
release rates in alkaline environments (Fig. 8a and b), so as to ensure a 
better fertilizer utilization efficiency in the environment (pH is around 
7.5) where crops are suitable for growth. Similarly, a higher temperature 
(around 30 ◦C) is beneficial to crops growth. Because of the temperature 
responsiveness, the hydrogels exhibited higher fertilizer release rates at 
the higher temperature (Fig. 8c and d), which also ensured sufficient 
nutrients for crops to sustain their growth. Overall, the MC-10% 
hydrogels presented the greatest slow-release performance under a 
range of conditions, and this was attributed to the fact that the MC-10% 
hydrogels possessed an abundant microporous structure and a tortuous 
diffusion path provided by MOF MIL-100(Fe) in the network, which 
inhibited the diffusion of urea, and improved its slow-release. To 
examine the release of urea in soil samples (Fig. S9), the cumulative 
release rates of MC-0% and MC-10% were determined, i.e., 49.74 and 
40.84% on day 30, respectively, which indicated that MC-10% exhibited 
a better sustained release performance. Moreover, the measured nitro-
gen contents in the soil samples also confirmed the better slow-release 
capacities of the MC-10% hydrogels (Fig. S10). 
The data displayed in Table 1 revealed the mechanisms involved in 
Fig. 7. a Water-retention behaviors of different hydrogels in distilled water at 
55 ◦C. b Water-retention behaviors of (1) soil only, (2) soil mixed with 0.5 g 
MC-0%, (3) soil mixed with 1.0 g MC-0%, (4) soil mixed with 0.5 g MC-10% 
and (5) soil mixed with 1.0 g MC-10%. 
Fig. 8. The urea release curves of different hydrogels in pH = 3 a and pH = 11 
b solution and in solution at 25 ◦C c and 45 ◦C d. 
X. Lin et al. 
International Journal of Biological Macromolecules 191 (2021) 483–491
489
the above release behaviors. According to the linear correlation coeffi-
cient (R2), the Higuchi model showed a good fit to the release data. In 
addition, based on the Korsmeyer-Peppas model and the calculated n 
values, as described above, the release mechanisms of the MC-0% and 
MC-10% hydrogels were determined to be non-Fickian and skeleton 
dissolution, respectively. 
3.5. Practical applications 
To explore the effect of the MC-10% hydrogel on the seed germina-
tion rates and nitrogen nutrition statuses of plants, wheat was used as a 
model crop to study the growth status under different fertilization 
methods. Thus, Fig. 9a showed the growth of wheat treated with 
different fertilization methods, from which it can be seen that the 
samples treated with the MC-10% and MC-0% hydrogels were signifi-
cantly healthier than those treated with either no urea or free urea. In 
particular, the sample treated with the MC-10% hydrogel was more 
luxuriant than that treated with the MC-0% hydrogel. These results 
confirmed that the MC-10% hydrogel exhibited pleasuring water and 
fertilizer retention properties, and that its 3D structure and porous MIL- 
100(Fe) component were beneficial to the growth of crops. Finally, we 
calculated the release percent of urea and its exhaustion of MC-10% 
hydrogels by measuring the remaining N content. During the whole 
process of wheat growth, the overall release percent of urea and its 
amount of exhaustion was 80%. 
As previously reported, the amide structure, which is the main 
chemical structure of nitrogen in plants, can be divided into amide I and 
amide II groups [47]. The spectral region of amide II is in the range of 
1500–1600 cm− 1, and the signals in this region correspond to the C–N 
stretching vibrations and the N–H bending vibrations. The spectral 
region of amide I is 1600–1700 cm− 1, and the signals in this region 
correspond to the C––O stretching vibration of the peptide bond. Thus, 
the nitrogen content of wheat can be assessed by examination of the 
Table 1 
Corresponding release kinetic parameters obtained from different models. 
Sample Zero-order First-order Higuchi Korsmeyer-Peppas 
R2 k0 R2 k1 R2 kH R2 k n 
MC-0% 0.810 1.540 0.873 − 0.0220 0.958 9.781 0.927 6.658 0.652 
MC-10% 0.819 1.373 0.867 − 0.0183 0.953 8.660 0.882 3.568 0.823 
Fig. 9. a Growth status of wheat treated with different fertilization methods: (I) 
MC-10%, (II) MC-0%, (III) Free-urea, (IV) No-urea. Deconvolution fitting curves 
of wheat leaves treated with different fertilization methods: b MC-10%, c MC- 
0%, d Free-urea, e No-urea. 
Table 2 
Various parameters of different materials reported in the relevant studies. 
Literatures Materials Stimulus response Swelling 
capacity 
(g/g) 
Fertilizer slow- 
release 
in soil 
Water- 
retention 
in soil 
Model crops 
This study Cellulose 
/MOFs/DMAA 
pH and temperature 
response 
37.0 
(3 d) 
40.84% 
(30 d) 
22.78% 
(30 d) 
Wheat 
Reference [4] CMC/Acrylamide 
/Acrylic acid /HNTs 
No 110.2 
(12 d) 
98.7% 
(6 d) 
30.6% 
(6 d) 
No 
Reference 
[23] 
Methylcellulose /Hydroxypropyl 
methylcellulose 
/K2SO4 
pH and temperature 
response 
~20.0 
(8 h) 
47.5% 
(500 min) 
31.3% 
(30 d) 
Chinese 
cabbage 
Reference 
[24] 
N, N-dimethyl-aminoethyl methacrylate 
/Dopamine 
pH and temperature 
response 
No 54. 13% 
(30 d) 
No No 
Reference 
[31] 
SA/Acrylamide/ 
Acrylic acid/HNTs 
No 107.9 
(3 d) 
79.5% 
(4 d) 
14.4% 
(10 d) 
No 
Reference 
[42] 
Starch/HNTs No 71.90 
(70 h) 
97% 
(5 d) 
21.6% 
(6 d) 
No 
Reference 
[49] 
Cellulose-g-poly (acrylic acid-co- 
acrylamide) 
No 420.0 
(70 h) 
~100% 
(10 d) 
7.2% 
(25 d) 
No 
Reference 
[50] 
Collagen/Acrylic acid /Maleic anhydride No 2208 70% 
(30 d) 
No No 
Reference 
[51] 
Attapulgite clay/ 
CMC/HEC 
No 76 
(1 h) 
95% 
(20 d) 
15.5% 
(28 d) 
No 
Reference 
[52] 
Cellulose/SA/ 
MOFs/DMAA 
pH response 100 
(pH = 11) 
50% 
(30 d) 
~0 
(30 d) 
Wheat 
X. Lin et al. 
International Journal of Biological Macromolecules 191 (2021) 483–491
490
absorption bands belonging to amide I and amide II. Relative study has 
reported that the intensity ratio of amide II to amide I can well reflect the 
total N of the leaves [48]. Photoacoustic spectroscopy was then used to 
investigate the absorption intensities of thesesignals in the crop leaves, 
and their corresponding ratios were calculated (Fig. 9b–e). As shown, 
the amide II/amide I ratio of the sample treated with the MC-10% 
hydrogel (0.72) was clearly the highest among the various samples, 
which was consistent with the wheat growth results discussed above. 
The germination rate, tiller number, photosynthetic rate, and chlo-
rophyll content of wheat were also tested for each sample, as outlined in 
Table S5. Compared with other groups, all values for the above prop-
erties were higher for the wheat treated with the MC-10% hydrogel, 
again indicating that the MC-10% hydrogel was beneficial in terms of 
continuously providing fertilizer and water to seeds, as well as pro-
moting the growth of crops. In addition, the comparison of various pa-
rameters between this study and the relevant literature studies has been 
supplied as Table 2. Although the swelling capacity in this work was 
inferior, the water-retention and fertilizer slow-release performance of 
this study both performed well, especially the slow-release of fertilizer, 
which was also the reason for the use of MOFs. The fertilizers slow- 
release performance in soil of this study (40.84%) was better than that 
reported in other literature. Besides, the water-retention in soil of this 
study was also a level in the forefront (22.78%). 
4. Conclusion 
In summary, we developed a kind of hydrogel to enhance the utili-
zation rate of fertilizers and water by integrating MOF MIL-100(Fe) and 
cellulose-based hydrogels with temperature- and pH-responsiveness. 
Owing to the microporous structure of MOF MIL-100(Fe), the pre-
pared MC-10% hydrogels exhibited higher water-retention and better 
urea slow-release performance. The water-retention increased from 
60.28% (MC-0%) to 77.53% (MC-10%) in deionized water after 12 h, 
and the cumulative release rates of MC-10% hydrogels reached to 
40.84% in soil on day 30. Also, NVCL and CNFs provided temperature- 
and pH-sensitivities for regulating urea release. For the wheat sample 
treated with the MC-10% hydrogel, germination rate, tiller number, 
photosynthetic rate, and chlorophyll content were significantly 
increased. 
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. 
Acknowledgments 
We gratefully acknowledge the Fundamental Research Funds of CAF 
(CAFYBB2020QC003) and the Opening Project of Guangxi Key Labo-
ratory of Forest Products Chemistry and Engineering (GXFK2008) for 
financial support of this research. 
Appendix A. Supplementary data 
Supplementary data to this article can be found online at https://doi. 
org/10.1016/j.ijbiomac.2021.09.075. 
References 
[1] C.O. Dimkpa, J. Fugice, U. Singh, T.D. Lewis, Development of fertilizers for 
enhanced nitrogen use efficiency - trends and perspectives, Sci. Total Environ. 731 
(2020), 139113. 
[2] M.Y. Naz, S.A. Sulaiman, Slow release coating remedy for nitrogen loss from 
conventional urea: a review, J. Control. Release 225 (2016) 109–120. 
[3] S. Fertahi, M. Ilsouk, Y. Zeroual, A. Oukarroum, A. Barakat, Recent trends in 
organic coating based on biopolymers and biomass for controlled and slow release 
fertilizers, J. Control. Release 330 (2021) 341–361. 
[4] Y. Shen, H. Wang, Z. Liu, W. Li, Y. Liu, J. Li, H. Wei, H. Han, Fabrication of a water- 
retaining, slow-release fertilizer based on nanocomposite double-network 
hydrogels via ion-crosslinking and free radical polymerization, J. Ind. Eng. Chem. 
93 (2021) 375–382. 
[5] A. Di Martino, Y.A. Khan, S. Durpekova, V. Sedlarik, O. Elich, J. Cechmankova, 
Ecofriendly renewable hydrogels based on whey protein and for slow release of 
fertilizers and soil conditioning, J. Clean. Prod. 285 (2021), 124848. 
[6] X. Liu, Y. Li, Y. Meng, J. Lu, Y. Cheng, Y. Tao, H. Wang, Pulping black liquor-based 
polymer hydrogel as water retention material and slow-release fertilizer, Ind. Crop. 
Prod. 165 (2021), 113445. 
[7] S. Liu, Q. Wu, X. Sun, Y. Yue, B. Tubana, R. Yang, H.N. Cheng, Novel alginate- 
cellulose nanofiber-poly(vinyl alcohol) hydrogels for carrying and delivering 
nitrogen, phosphorus and potassium chemicals, Int. J. Biol. Macromol. 172 (2021) 
330–340. 
[8] H. Li, M. Eddaoudi, M. O'Keeffe, O.M. Yaghi, Design and synthesis of an 
exceptionally stable and highly porous metal-organic framework, Nature 402 
(6759) (1999) 276–279. 
[9] L.N. Rosi, Hydrogen storage in microporous metal-organic frameworks, Science 
300 (5622) (2003) 1127–1129. 
[10] D. Desantis, J.A. Mason, B.D. James, C. Houchins, J.R. Long, M. Veenstra, Techno- 
economic analysis of metal-organic frameworks for hydrogen and natural gas 
storage, Energy Fuel 31 (2) (2017) 2024–2032. 
[11] P. Horcajada, S. Surble, C. Serre, D.Y. Hong, Y.K. Seo, J.S. Chang, J.M. Greneche, 
I. Margiolaki, G. Ferey, Synthesis and catalytic properties of MOF MIL-100(Fe), an 
iron(III) carboxylate with large pores, Chem. Commun. (Camb.) (27) (2007) 
2820–2822. 
[12] A.U. Czaja, N. Trukhan, U. Muller, Industrial applications of metal-organic 
frameworks, Chem. Soc. Rev. 38 (5) (2009) 1284–1293. 
[13] J. Nie, H. Xie, M. Zhang, J. Liang, S. Nie, W. Han, Effective and facile fabrication of 
MOFs/cellulose composite paper for air hazards removal by virtue of in situ 
synthesis of MOFs/chitosan hydrogel, Carbohydr. Polym. 250 (2020), 116955. 
[14] H. Lima, C. Silva, V.L. Kupfer, J. Rinaldi, A.W. Rinaldi, Synthesis of resilient hybrid 
hydrogels using UiO-66 MOFs and alginate (hydroMOFs) and their effect on 
mechanical and matter transport properties, Carbohydr. Polym. 251 (2020), 
116977. 
[15] Y. Cui, B. Chen, G. Qian, Lanthanide metal-organic frameworks for luminescent 
sensing and light-emitting applications, Coord. Chem. Rev. 273–274 (2014) 76–86. 
[16] L. Wang, H. Xu, J. Gao, J. Yao, Q. Zhang, Recent progress in metal-organic 
frameworks-based hydrogels and aerogels and their applications, Coord. Chem. 
Rev. 398 (2019), 213016. 
[17] P.H. Corkhill, C.J. Hamilton, B.J. Tighe, Synthetic hydrogels VI Hydrogel 
composites as wound dressings and implant materials, Biomaterials 10 (1) (1989) 
3–10. 
[18] X. Li, Q. Li, X. Xu, Y. Su, Q. Yue, B. Gao, Characterization, swelling and slow- 
release properties of a new controlled release fertilizer based on wheat straw 
cellulose hydrogel, J. Taiwan Inst. Chem. Eng. 60 (2016) 564–572. 
[19] L. Sun, Z. Mo, Q. Li, D. Zheng, X. Qiu, X. Pan, Facile synthesis and performance of 
pH/temperature dual-response hydrogel containing lignin-based carbon dots, Int. 
J. Biol. Macromol. 175 (2021) 516–525. 
[20] N. Jommanee, C. Chanthad, K. Manokruang, Preparation of injectable hydrogels 
from temperature and pH responsive grafted chitosan with tuned gelation 
temperature suitable for tumor acidic environment, Carbohydr. Polym. 198 (2018) 
486–494. 
[21] R. Yoshida, Y. Kaneko, K. Sakai, A. Kikuchi, Y. Sakurai, T. Okano, K. Uchida, Comb- 
type grafted hydrogels with rapid deswelling response to temperature changes, 
Nature 374 (6519) (1995) 240–242. 
[22] T. Li, S. Lu, J. Yan, X. Bai, C. Gao, M. Liu, An environment-friendly fertilizer 
prepared by layer-by-layer self-assembly for pH-responsive nutrient release, ACS 
Appl. Mater. Interfaces 11 (11) (2019) 10941–10950. 
[23] Y.C. Chen, Y.H. Chen, Thermo and pH-responsive methylcellulose and 
hydroxypropyl methylcellulose hydrogels containing K2SO4 for water retention 
and a controlled-release water-soluble fertilizer, Sci. Total Environ. 655 (2019) 
958–967. 
[24] C. Feng, S. Lü, C. Gao, X. Wang, X. Xu, X. Bai, N. Gao, M. Liu, L. Wu, “Smart” 
fertilizer with temperature- and pH-responsive behavior via surface-initiated 
polymerization for controlled release of nutrients, ACS Sustain. Chem. Eng. 3 (12) 
(2015) 3157–3166. 
[25] H. Du, W. Liu, M. Zhang, C. Si, X. Zhang, B. Li, Cellulose nanocrystals and cellulose 
nanofibrils based hydrogels for biomedical applications,Carbohydr. Polym. 209 
(2019) 130–144. 
[26] B. Wang, Q. Peng, Y. Yan, Y. Ding, Z. Wang, Biomimetic, strong, and tough 
hydrogels by integrating cellulose nanocrystals into polymer networks, Ind. Crop. 
Prod. 158 (2020), 112973. 
[27] S. Mishra, N. Thombare, M. Ali, S. Swami, Applications of biopolymeric gels in 
agricultural sector, Polym. Gels (2018) 185–228. 
[28] W. Lan, M. Liu, Preparation and properties of chitosan-coated NPK compound 
fertilizer with controlled-release and water-retention, Carbohydr. Polym. 72 (2) 
(2008) 240–247. 
[29] Z. Mohammadbagheri, A. Rahmati, P. Hoshyarmanesh, Synthesis of a novel 
superabsorbent with slow-release urea fertilizer using modified cellulose as a 
grafting agent and flexible copolymer, Int. J. Biol. Macromol. 182 (2021) 
1893–1905. 
X. Lin et al. 
https://doi.org/10.1016/j.ijbiomac.2021.09.075
https://doi.org/10.1016/j.ijbiomac.2021.09.075
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951273535
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951273535
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951273535
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951281128
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951281128
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951291283
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951291283
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951291283
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951300515
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951300515
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951300515
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951300515
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951308533
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951308533
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951308533
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201947175107
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201947175107
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201947175107
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951320509
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951320509
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951320509
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951320509
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951330196
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951330196
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951330196
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201947182488
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201947182488
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951338168
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951338168
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951338168
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201947470316
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201947470316
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201947470316
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201947470316
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951344888
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951344888
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951363631
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951363631
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951363631
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201947523213
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201947523213
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201947523213
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201947523213
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201948072698
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201948072698
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951371192
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951371192
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951371192
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950299341
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950299341
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950299341
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951379762
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951379762
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951379762
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951388634
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951388634
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951388634
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951400576
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951400576
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951400576
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951400576
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950317658
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950317658
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950317658
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951410932
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951410932
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951410932
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951418325
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951418325
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951418325
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951418325
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951428033
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951428033
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951428033
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951428033
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951438309
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951438309
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951438309
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950333228
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950333228
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950333228
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950468275
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950468275
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950486175
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950486175
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950486175
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951456121
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951456121
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951456121
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951456121
International Journal of Biological Macromolecules 191 (2021) 483–491
491
[30] Y. Wang, M. Sun, D. Qiao, J. Li, Y. Wang, W. Liu, C. Bunt, H. Liu, J. Liu, X. Yang, 
Graft copolymer of sodium carboxymethyl cellulose and polyether polyol (CMC-g- 
TMN-450) improves the crosslinking degree of polyurethane for coated fertilizers 
with enhanced controlled release characteristics, Carbohydr. Polym. 272 (2021), 
118483. 
[31] Y. Shen, H. Wang, W. Li, Z. Liu, Y. Liu, H. Wei, J. Li, Synthesis and characterization 
of double-network hydrogels based on sodium alginate and halloysite for slow 
release fertilizers, Int.J. Biol. Macromol. 164 (2020) 557–565. 
[32] M. Bhattacharya, M.M. Malinen, P. Lauren, Y.R. Lou, S.W. Kuisma, L. Kanninen, 
M. Lille, A.C. Orlu, C. Guguen-Guillouzo, O. Ikkala, Nanofibrillar cellulose 
hydrogel promotes three-dimensional liver cell culture, J. Control. Release 164 (3) 
(2012) 291–298. 
[33] D. Klemm, B. Heublein, H.P. Fink, A. Bohn, Cellulose: fascinating biopolymer and 
sustainable raw material, Angew. Chem. Int. Ed. 44 (22) (2005) 3358–3393. 
[34] X.M. Cai, Y. Lin, X. Chen, X. Chen, F. Wang, Linker regulation: synthesis and 
electrochemical properties of ferrocene-decorated cellulose, J. Inorg. Organomet. 
Polym. Mater. 30 (9) (2020) 3771–3780. 
[35] X.M. Cai, X. Chen, X. Chen, Y. Li, F. Wang, A luminescent cellulose ether with a 
regenerated crystal form obtained in tetra(n-butyl)ammonium hydroxide/dimethyl 
sulfoxide, Carbohydr. Polym. 230 (2020), 115649. 
[36] J. Wei, Y. Chen, H. Liu, C. Du, H. Yu, J. Ru, Z. Zhou, Effect of surface charge 
content in the TEMPO-oxidized cellulose nanofibers on morphologies and 
properties of poly( N -isopropylacrylamide)-based composite hydrogels, Ind. Crop. 
Prod. 92 (2016) 227–235. 
[37] T.H.M. Nguyen, C. Abueva, H.V. Ho, S.-Y. Lee, B.-T. Lee, In vitro and in vivo acute 
response towards injectable thermosensitive chitosan/TEMPO-oxidized cellulose 
nanofiber hydrogel, Carbohydr. Polym. 180 (2018) 246–255. 
[38] S. Durkut, Y.M. Elçin, Synthesis and characterization of thermosensitive poly(N- 
vinyl caprolactam)-grafted-aminated alginate hydrogels, Macromol. Chem. Phys. 
221 (2) (2020) 1900412. 
[39] A. Mignon, G.J. Graulus, D. Snoeck, J. Martins, N.D. Belie, P. Dubruel, S. 
V. Vlierberghe, pH-sensitive superabsorbent polymers: a potential candidate 
material for self-healing concrete, J. Mater. Sci. 50 (2) (2015) 970–979. 
[40] C. Wu, Y. Dan, D. Tian, Y. Zheng, S. Wei, D. Xiang, Facile fabrication of MOF(Fe) 
@alginate aerogel and its application for a high-performance slow-release N- 
fertilizer, Int. J. Biol. Macromol. 145 (2020) 1073–1079. 
[41] Hans Schott, Swelling kinetics of polymers, J. Macromol. Sci. Part B Phys. 31 (1) 
(1992) 1–9. 
[42] H. Wei, H. Wang, H. Chu, J. Li, Preparation and characterization of slow-release 
and water-retention fertilizer based on starch and halloysite, Int. J. Biol. Macromol. 
133 (2019) 1210–1218. 
[43] C.G.D. Kruif, S.G. Anema, C. Zhu, P. Havea, C. Coker, Water holding capacity and 
swelling of casein hydrogels, Food Hydrocoll. 44 (2015) 372–379. 
[44] H. Feil, Y.H. Bae, J. Feijen, S.W. Kim, Effect of comonomer hydrophilicity and 
ionization on the lower critical solution temperature of N-isopropylacrylamide 
copolymers, Macromolecules 26 (10) (1993) 2496–2500. 
[45] X. Yang, Z. Li, H. Liu, L. Ma, X. Huang, Z. Cai, X. Xu, S. Shang, Z. Song, Cellulose- 
based polymeric emulsifier stabilized poly(N-vinylcaprolactam) hydrogel with 
temperature and pH responsiveness, Int. J. Biol. Macromol. 143 (2020) 190–199. 
[46] N. Masruchin, B.-D. Park, V. Causin, Dual-responsive composite hydrogels based on 
TEMPO-oxidized cellulose nanofibril and poly(N-isopropylacrylamide) for model 
drug release, Cellulose 25 (1) (2017) 485–502. 
[47] S. Sharma, A.K. Singh, M.K. Tiwari, K.N. Uttam, Prompt screening of the 
alterations in biochemical and mineral profile of wheat plants treated with 
chromium using attenuated total reflectance fourier transform infrared 
spectroscopy and X-ray fluorescence excited by synchrotron radiation, Anal. Lett. 
53 (3) (2020) 482–508. 
[48] K. Wu, C. Du, F. Ma, Y. Shen, D. Liang, J. Zhou, Rapid diagnosis of nitrogen status 
in rice based on fourier transform infrared photoacoustic spectroscopy (FTIR-PAS), 
Plant Methods 15 (1) (2019) 94. 
[49] Y. Zhang, X. Liang, X. Yang, H. Liu, J. Yao, An eco-friendly slow-release urea 
fertilizer based on waste mulberry branches for potential agriculture and 
horticulture applications, ACS Sustain. Chem. Eng. 2 (7) (2014) 1871–1878. 
[50] Z.-Y. Hu, G. Chen, S.-H. Yi, Y. Wang, Q. Liu, R. Wang, Multifunctional porous 
hydrogel with nutrient controlled-release and excellent biodegradation, J. Environ. 
Chem. Eng. 9 (5) (2021), 106146. 
[51] B. Ni, M. Liu, S. Lü, L. Xie, Y. Wang, Environmentally friendly slow-release nitrogen 
fertilizer, J. Agric. Food Chem. 59 (18) (2011) 10169–10175. 
[52] Y. Wang, H. Shaghaleh, Y.A. Hamoud, S. Zhang, P. Li, X. Xu, H. Liu, Synthesis of a 
pH-responsive nano-cellulose/sodium alginate/MOFs hydrogel and its application 
in the regulation of water and N-fertilizer, Int. J. Biol. Macromol. 187 (2021) 
262–271. 
X. Lin et al. 
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951467377
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951467377
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951467377
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951467377
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951467377
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951479538
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951479538
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951479538
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951087653
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951087653
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951087653
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951087653
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951493148
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951493148
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950494309
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950494309
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950494309
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951517665
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951517665
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951517665
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950505995
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950505995
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950505995
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950505995
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951521305
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951521305
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951521305
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951536016
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951536016
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951536016
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950514730
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950514730
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950514730
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951540516
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951540516
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951540516
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952123670
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952123670
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952135179
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952135179
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952135179
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951227968
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201951227968
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952145106
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952145106
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952145106http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952154139
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952154139
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952154139
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950524729
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950524729
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201950524729
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952158038
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952158038
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952158038
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952158038
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952158038
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952167677
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952167677
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952167677
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952173942
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952173942
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952173942
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952284984
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952284984
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952284984
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952293242
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952293242
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952303466
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952303466
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952303466
http://refhub.elsevier.com/S0141-8130(21)01996-6/rf202109201952303466
	A TEMPO-oxidized cellulose nanofibers/MOFs hydrogel with temperature and pH responsiveness for fertilizers slow-release
	1 Introduction
	2 Materials and methods
	2.1 Materials
	2.2 Synthesis of the TEMPO-oxidized cellulose nanofibers (CNFs)
	2.3 Synthesis of MOF MIL-100(Fe)
	2.4 Synthesis of the MC hydrogels
	2.5 Material characterization
	2.6 Swelling behavior
	2.7 Temperature and pH responsiveness
	2.8 Water-retention behavior
	2.9 Slow-release behavior
	2.10 Application in growth of crops
	3 Results and discussion
	3.1 Characterization of the CNFs, MOF MIL-100(Fe), and the MC hydrogels
	3.2 Swelling behavior and the swelling dynamic mechanism at room temperature
	3.3 Temperature- and pH-responsive behaviors
	3.4 Urea release behaviors of the MC hydrogels
	3.5 Practical applications
	4 Conclusion
	Declaration of competing interest
	Acknowledgments
	Appendix A Supplementary data
	References