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Chitosan-Montmorillonite microspheres: A sustainable fertilizer delivery system
Accepted Manuscript Title: Chitosan-Montmorillonite microspheres: A sustainable fertilizer delivery system Author: Bruna Rodrigues dos Santos Fabiana Britti Bacalhau Tamires dos Santos Pereira Claudinei Fonseca Souza Roselena Faez PII: DOI: Reference:
S0144-8617(15)00277-5 http://dx.doi.org/doi:10.1016/j.carbpol.2015.03.064 CARP 9806
To appear in: Received date: Revised date: Accepted date:
24-11-2014 16-2-2015 14-3-2015
Please cite this article as: Santos, B. R., Bacalhau, F. B., Pereira, T. S., Souza, C. F., and Faez, R.,Chitosan-Montmorillonite microspheres: a sustainable fertilizer delivery system, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.03.064 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Chitosan-Montmorillonite microspheres: a sustainable fertilizer delivery
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system
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Bruna Rodrigues dos Santosa, Fabiana Britti Bacalhaub, Tamires dos Santos
5
Pereiraa, Claudinei Fonseca Souzab, Roselena Faeza*
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cr
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a
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Federal de São Carlos, Campus Araras, Araras, Brazil.
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b
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Laboratório de Materiais Poliméricos e Biossorventes, Universidade
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Departamento de Recursos Naturais e Proteção Ambiental, Universidade
Federal de São Carlos, Campus Araras, Araras, Brazil.
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Corresponding author: [email protected]
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Abstract
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Controlled release fertilizers are efficient tools that increase the sustainability
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of agricultural practices. However, the biodegradability of the matrices and
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the determination of the release into soil still require some investigation. This
17
paper describes the preparation of potassium-containing microspheres
18
based on chitosan and montmorillonite clay and the in situ soil release. The
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chitosan-montmorillonite microspheres were prepared using a coagulation
20
method and different proportions of montmorillonite. The structural, thermal
21
and morphological properties as well the water swelling and fertilizer
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sorption capacity were evaluated. The best formulations were applied in soil,
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and the fertilizer release was monitored using time-domain reflectometry
24
(TDR). Montmorillonite clay provides better sorption properties than the
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chitosan microspheres because of the rough and porous surface. Due to
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these properties, high levels of fertilizer were sorbed onto the material.
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ChMMT33-containing potassium shows two specific periods of fertilizer
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release: the first one lasted approximately three days and was assigned to the external fertilizer on the microspheres. The second was assigned to the internal fertilizer. TDR is an important and fast tool and was used to determine the fertilizer release and the ion movement in the soil.
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Keywords:
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technique.
Chitosan,
controlled
release,
agricultural
practices,
TDR
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1. Introduction In recent decades, the production of food has increased due to the
39
growing population. According to the United Nations Food and Agriculture
40
Organization (FAO), the production of food will need to increase by 70% to
41
supply a population of nine billion people in 2050 (FAO, 2014). However, an
42
outstanding challenge is finding alternatives to increase the production of food
43
by optimizing the use of agricultural inputs, enabling economic benefits for
44
farmers and reducing the environmental impact of the activity. The use of
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alternative materials in agriculture has increased due to the need to enhance
46
the production systems with increasing productivity and cost savings
47
(Ghormade, Deshpande & Paknikar, 2011). Hydrogels are examples of
48
alternative materials that have the ability to significantly increase their size via
49
water absorption and gradually release their load into the medium where they
50
are inserted (Liang, Liu & Wu, 2007; Jin et al., 2011; Zhong et al, 2013). Some
51
polymers have been used to prepare hydrogels that increased water retention in
52
soil, reducing the required frequency of irrigation (Abedi-Koupaia, Sohrabb &
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Swarbrickc, 2008; Mendonça, Urbano, Peres & Souza, 2013). Nevertheless, the
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majority of these hydrogels are based on non-biodegradable materials, such as
55
polyacrylamide and polystyrene, and can leave residues in the soil, causing
56
salinization of the medium as their use becomes common (Mendonça et al.,
57
2013). In contrast, new studies have been performed using natural and
58
biodegradable polymers, which leave no residue after their application (Riyajan,
59
Sasithornsonti & Phinyocheep, 2012; Mulder, Gosselink, Vingerhoeds &
60
Harmsen, 2011). These materials can be used as soil conditioners because
61
they improve the availability of water and also act as an alternative for the
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controlled release of fertilizers. These uses ensure both economic and
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environment benefits by avoiding contamination of the ground water. The use of
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coated fertilizers is a promising alternative to improve many aspects of
65
fertilization based on the concept of controlled release (Chen, Xie, Zhuang,
66
Chen & Jing, 2008; Tomaszewska & Jarosiewicz, 2006). The main advantages
67
of using controlled release materials are regular and continuous delivery of
68
nutrients to the plants; a low frequency of fertilizer application to the soils; a
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reduction
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immobilization; elimination of damage to roots due to high salt concentrations;
71
easy handling of the fertilizer: a reduction in NO3 pollution; an increase in the
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eco-value of agricultural activity (less contamination of groundwater and surface
73
water); and a reduction in production costs (Liang et al., 2007). Chitosan has
74
been extensively explored as a coating material for preparing controlled release
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microspheres for a system where the rates of dissolution and release directly
76
depend on the characteristics of the material (Kumar, 2013; Kurita, 2008).
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Chitosan is a natural biopolymer extracted from the exoskeletons of insects and
78
crustaceans. It features good mechanical properties combined with the ability to
79
form fibers, films, gels, and microspheres. It is extremely attractive due to its
80
biodegradability, biocompatibility and non-toxicity (Kumar, 2013). In addition,
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the combination of inorganic and polymeric materials has been a successful
82
strategy in developing new properties, drawing attention the last few years due
83
to the attainment of materials with new or better properties than the pure
84
polymer (Kang et al., 2013; Park, Hwang, OH, Yang & Choy, 2013; Yasemin,
85
Gulten, Duygu & Ersin, 2009; Rui, Mingzhu & Lan, 2007). The addition of
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layered silicates, such as montmorillonite clay, is a promising alternative to
nutrient
losses
due
to
leaching,
volatilization
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and
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enhance certain properties, i.e., increasing the sorptive capacity for both water
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and chemical compounds. The use of clay minerals is justified due to ready
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availability, low cost and environmentally friendly nature, which make them
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interesting for applications in agriculture. Another interesting point is the
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necessity of monitoring fertilizer release in soil. Usually, the material is added
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to the soil, and at specified intervals, an aliquot of soil is treated and tested to
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determine the amount of fertilizer released, which requires time consuming and
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difficult experimental procedures. In contrast, the determination of ionic
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movement in the soil has been performed using the principle of electrical
96
conductivity. An efficient method to determine the electrical conductivity of a
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medium, such as soil, is the TDR (time-domain reflectometry) technique. This
98
technique estimates the electrical conductivity (EC) of medium using
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measurements in real time and without deforming the sample (Souza, Or &
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Matsura, 2004). Additionally, electrical conductivity is an effective parameter to
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monitor the release of the nutrients (fertilizer) into the soil. According to Queiroz
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et al. (Queiroz, Testezlaf & Matsura, 2005), the EC correlates with the total
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concentration of dissolved electrolytes (ions) in solution because pure water is
104
not a good electrical conductor. The TDR technique to determine the water
105
content and electrical conductivity of soil is becoming increasingly popular. Its
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outstanding advantages are its accuracy, speed, reproducibility, good
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theoretical basis, a well-defined and selected sampled volume, and the fact that
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the water content and salinity are measured in exactly the same sample (Souza
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& Folegatti, 2010; Topp, Davis, Annan, 1980). The method is based on the fact
110
that the speed of the propagation of microwave pulses in conductive cables
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inserted in the soil is very sensitive to its water content, which is the result of a
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large disparity between the dielectric permittivities of water (w= 81) and the
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other soil constituents, such as air (a= 1) and soil solid particles (s= 3-5)
114
(Noborio, 2001; Topp et al., 1980). Consequently, the bulk dielectric permittivity
115
(b) is dominated by the water phase. The soil b is determined from the travel
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time of a stepped electromagnetic pulse along a buried waveguide (TDR probe)
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(Zegelin, White & Jenkins, 1989; Topp, Davis & Annan, 1982). The use of TDR
118
to measure the soil EC was discovered by Dalton et al. (Dalton, Herkelrath,
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Rawlins & Rhoades, 1984) who proposed a “lumped circuit load” transmission
120
line as an analogy for EC measurements using TDR. The soil-probe system is
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assumed to be composed of a lumped circuit with load impedance at the end of
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the transmission line (typically a coaxial cable) of known characteristic
123
impedance (the cable impedance is typically 50 Ω). In this paper, a potassium-
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containing, controlled-release biodegradable material was prepared, and
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structural, thermal and morphological characterizations were performed.
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Additionally, the potassium concentration and swelling behavior in water were
127
determined. The best formulations of the composites were applied in soil
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samples, and the in situ determination of fertilizer release was performed using
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TDR.
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2. Experimental 2.1. Materials
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Chitosan with a deacetylation degree of 85 % was supplied by Polymar
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(97%, Brazil). The average molecular weight (Mw) was 1.8 105 g.mol-1 as
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determined by gel permeation chromatograph (Agilent 1100 chromatographic
136
system equipped with a refractive index detector). Sodium montmorillonite clay 6 Page 6 of 29
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(Brasgel Aço DS, Brazil), glacial acetic acid (Synth, 99%, Brazil), sodium
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hydroxide (Synth, 99%, Brazil), and fertilizer (Saltpetre Krista K (KNO3) Yara
139
Brazil Fertilizantes S.A.) were used without further purification.
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2.2. Preparation of Chitosan and Chitosan-MMt microspheres
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A chitosan solution of 40 g.L-1 was prepared by dissolving 4 g of chitosan
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flakes in 100 mL of acetic acid aqueous solution 5% (w/v) with mechanical
144
stirring overnight at 25°C. Afterwards, sodium montmorillonite clay (MMt-Na+)
145
was added to the chitosan solution at proportions of 6, 33 and 50 wt.% and the
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solution was mechanically stirred for 16 hours at 25°C. The microspheres were
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prepared by dripping the chitosan/clay solution into a 2 mol.L-1 sodium
148
hydroxide solution. The microspheres were filtered and washed with distilled
149
water until a neutral pH was reached, and they were subsequently added to a
150
fertilizer solution. For the structural, thermal and morphological characterization,
151
the microspheres were dried at 60°C for 30 minutes. The chitosan microspheres
152
(Ch) were prepared using the same methodology. The materials were called
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ChMMt6, ChMMt33 and ChMMt50, respectively, for Chitosan/MMt-Na+ with 6,
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33 and 50 wt.%.
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2.3. Preparation and characterization of potassium-containing microspheres The ChMMt33 microspheres were swelled in 1, 7, 15 and 30 g.L-1 KNO3
158
fertilizer solutions for 24 hours. After the potassium-containing ChMMt33
159
microspheres were dried at 60°C for 30 minutes, flame photometry (DM-62
160
Digimed, Brazil) was used to determine the KNO3 concentration.
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2.4. Structure,
thermal
and
morphological
characterization
of
the
microspheres FTIR spectra were recorded using a Shimadzu IR Prestige-21
165
spectrophotometer operating between 4000 and 400 cm-1. The samples were
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diluted in solid KBr before the spectrum recording. X-ray diffraction (XRD)
167
patterns of the powdered samples were recorded using a Rigaku diffractometer
168
model Miniflex using Cu-Kα radiation (1.541 Å, 30 kV and 15 mA).
169
Thermogravimetric
170
thermoanalyzer TA-60 under synthetic air with a flow of 200 cm3 min-1 and a
171
heating rate of 10 °C min-1. Scanning electron microscopy (SEM) images of the
172
microspheres were recorded using a JEOL field emission scanning electron
173
microscope model JSM 7401 F with an SEI detector.
performed
on
us
were
a
Shimadzu
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2.5. Microspheres water swelling
te
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(TGA)
an
analyses
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A pre-weighted dry microsphere (wi) was immersed into a certain amount
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of deionized water. At specific time intervals, the microspheres were removed
178
from the water and reweighed (wf). The swelling ratios (%SR) of the
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microspheres were calculated using equation 1:
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Equation 1
2.6. Release behavior of CHMMt33 containing potassium in the soil
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The potassium-containing microspheres were prepared at four fertilizer
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solution concentrations: 1, 7, 15 and 30 g.L-1 KNO3. ChMMt33 microspheres
186
containing KNO3 were placed in a 7.5-L container filled with soil (Typic 8 Page 8 of 29
dystrophic LVd). Table 1 shows the physical and chemical characteristics of
188
soil. Three replicates for each concentration were performed. The container was
189
prepared with a water drainage system consisting of a thin layer of gravel at the
190
bottom, which was followed by a geotextile fabric to prevent the loss of soil. The
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container was filled with soil (9 kg) in layers of 0.05 m to simulate the original
192
bulk density of 1.30 g.cm-3. Each container received 4 g of microspheres placed
193
at a single spot. They were placed at a depth of 10 cm. The fertilizer release
194
was monitored using three electromagnetic probes for TDR that consisted of
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three continuous metal rods of 20 cm, which were in contact with the material
196
and can be used to estimate the moisture and electrical conductivity. One probe
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was installed at the center of the container, which meant the rod was in contact
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with the microspheres in the soil. The other two probes were installed 5 cm from
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the central probe, and they were only in contact with the soil. Therefore, the
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purpose of these probes was to monitor the lateral displacement of the fertilizer
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from the microspheres in the soil.
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3. Results and Discussion 3.1. Structure,
thermal
and
morphological
characterization
of
the
microspheres
In
this
paper,
chitosan,
chitosan/clay
and
potassium-containing
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chitosan/clay materials were prepared as microspheres using a coagulation
208
method. The structural, thermal behavior and the morphology of the chitosan
209
and chitosan/clay were characterized using X-ray diffraction (XRD), Fourier
210
transform infrared (FTIR) spectroscopy, thermogravimetry (TG) and scanning
211
electron microscopy (SEM), respectively. The GPC results (not shown here)
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exhibit Mw ~1.8x105 g.mol-1 for net chitosan and its composites indicating no
213
degradation process during the microsphere preparation. The FTIR spectrum of
214
chitosan (Brugnerottoa et al., 2001) (Figure 1a) shows a broad band at 3440
215
cm−1 assigned to the overlapping of O-H and N-H stretching. The band at 1648
216
cm−1 was attributed to the C=O stretching (amide I) and a band of weak
217
intensity near 1550 cm−1 was assigned to the N-H bending (amide II). The
218
bands at 2872, 1157 and 1076 cm-1 are ascribed to the CH stretching, the anti-
219
symmetric stretching of C-O-C bridge and to the skeletal vibration involving C-O
220
stretching, respectively and are characteristic of the saccharide structure
221
(Monvisade & Siriphannon, 2009; Abdel-Fattah, Jiang, El-Bassyouni &
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Laurencin, 2007; Wang et al., 2005]. In addition, the bands assigned to the axial
223
deformation of the amide (CN) groups and the CN axial deformation of the
224
amino groups can be seen respectively at 1427 cm-1 and 1320-1380 cm-1. The
225
bands associated with chitosan remain unaltered in the FTIR spectra of the
226
chitosan-clay systems (Figures 1b-1d). However, the intensities of the bands
227
related to Si-O and Si-O-Si at 1060, 915, 793 and 521 cm-1 increase with the
228
clay content in the composite. The presence of KNO3 in the potassium-
229
containing microspheres is confirmed by the presence of the 1385 cm-1 band,
230
which is assigned to the NO3- symmetric stretching, Figure 1d.
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Figure 2 shows the XRD patterns of MMt-Na+ and microspheres of net
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chitosan and composites with different MMt concentrations. The XRD pattern of
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Ch presents two major peaks at about 210o and 20o ascribed to 020 (crystal
234
1) and 110 (crystal 2) reflections, respectively (Abdel-Fattah, Jiang, El-
235
Bassyouni & Laurencin, 2007; Wang et al., 2005). The XRD pattern of MMt-Na+
236
shows a reflection peak at 26.2° corresponding to a d001 basal spacing of 1.4 10 Page 10 of 29
nm. Comparing the XRD patterns of chitosan and its composites two main
238
aspects are observed. In the basal space region a d001 displacement to lower
239
2values and a broad peak at 24.9° are verified. The displacement of the
240
basal reflection is indicative of the formation of an intercalated structure
241
[Monvisade & Siriphannon, 2009). Taking into account the crystalline region of
242
chitosan (210°) a broadening peak and lower intensity is observed
243
confirming a decrease of the anhydrous crystal polymorph structure and the
244
degree of order of chitosan molecular structure (Wang et al., 2005). The peak at
245
220° (crystal 2) has increased sharpness since the crystal size has
246
increased. However, for ChMMt33-containing KNO3, the XRD curve shows a
247
broad peak in the d001 basal space due to the exfoliation-intercalation and the
248
presence of the KNO3 intense peaks at 218-20° which cover the chitosan
249
peaks in that region.
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The TGA of Ch and ChMMt composites with a heating rate of 10°C min−1
251
under synthetic air between 25 and 800°C are given in Figure 3. Three major
252
stages of mass loss of neat chitosan are observed and calculated to be
253
approximately 17, 46, and 37%, which are assigned to water loss,
254
decomposition
255
degradation of the final waste of the polymer, respectively. ChMMt composites
256
also show three stages for mass loss. However, the decomposition of
257
montmorillonite clay is not complete until 800°C. Based on the TG curve
258
residue, the amount of clay in the composite was calculated and the smaller
259
values compared with the theoretical value are in agreement with the
260
experimental observation because there are losses of clay during the dripping
261
process, Table 2. Additionally, the ChMMt33-containing KNO3 shows higher
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of
the
polymer
via
deacetylation-depolymerization
and
11 Page 11 of 29
values for the residues than ChMMt33 due to the presence of KNO3. When
263
including the decomposition of the KNO3 salt (the residue is K2O), which is
264
taken into account to deduce the total KNO3 in the material, the amount of KNO3
265
from the TG curves (28%) is similar to the photometrically determined value
266
(32%) when the microspheres were added to the 15 gL KNO3 solution.
267
Additionally, based on the thermogravimetric results the final amount of polymer
268
content in the microspheres is 78, 59 and 46% for ChMMt-6, ChMMt-33 and
269
CHMMt-50, respectively.
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The SEM images of Ch and ChMMt show a spherical material but
271
deformations are observed at the breakpoint of the drops (Figure 4a). The
272
dispersed clay phase in the chitosan matrix and the interface region describes
273
the compatibilization of the phases. The fracture region, shown in Figure 4f,
274
shows a rough and porous surface for the ChMMt composite, which provides
275
better sorption of fertilizer, as demonstrate by the sorption-desorption results
276
shown in Figure 8. Figure 5 shows the morphology of the fracture regions and
277
the EDS (energy dispersive spectrometry) results for ChMMt33 in the sorption
278
and desorption processes, Figures 5a and 5b, respectively. A decrease in the K
279
intensity after the desorption process confirms the release of fertilizer, which is
280
in agreement with the TDR results, Figure 8.
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3.2. Swelling behavior of microspheres in water
283
Figure 6 shows the swelling behavior of the microspheres in water. In the
284
first hour, the microspheres increase in size, and a swelling degree in the range
285
of 150 to 200% is observed. Pure chitosan presents a higher value (200%) than
286
ChMMt33 (150%). The lower values of water sorption for the composites are
12 Page 12 of 29
due to the intercalation of the polymer into the clay galleries, which decreases
288
the ability of both materials (clay and chitosan) to swell. Furthermore, the
289
crystallinity increases for composites provide a swelling reduction. These results
290
were consistent with Qu and coauthors (Qu, Wirsén & Albertesson, 2000) since
291
they observe the higher crystalline material inhibited the water diffusion.
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Microspheres containing KNO3
Montmorillonite clay affects the amount of sorbed-desorbed KNO3, and
295
the presence of exfoliated or intercalated polymer phases influences the
296
sorption behavior, Figure 7a. The ChMMt33 composite shows a higher value for
297
potassium in the sorb-desorb process, which agrees with the morphological and
298
structural properties. Because ChMMt33 demonstrates the best characteristics,
299
the influence of the initial KNO3 concentration (1, 7, 15 or 30 g.L-1) was used to
300
swell the microspheres, Figure 7b. A higher value for the initial concentration
301
reflects a larger amount of potassium in the microspheres because the fertilizer
302
covers the microspheres in the 30 g.L-1 KNO3 sample, as shown in the images
303
in Figure 7b. Furthermore, ChMMt33 microspheres with 1, 7, 15 and 30 g.L-1 of
304
KNO3 were placed in soil samples, and TDR was used to evaluate the fertilizer
305
release for 60 days, Figure 8. TDR evaluates the changes in the soil
306
conductivity; however, we can correlate the ionic conductivity with the ion
307
concentration using equation 2 (Souza, Folegatti, Matsura & OR, 2006).
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Equation 2
308
309 310
C – Concentration of potassium nitrate (mmol L-1);
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CES – Electrical conductivity of the solution (dS m-1); The fertilizer release was estimated based on the electrical conductivity of the
313
central and lateral probes, and the data were related to the concentration of
314
potassium ions in the soil. According to the potassium release profile of the
315
central probes, Figure 8a, higher fertilizer release occurs for the first three days,
316
reaching 7.5, 5.3 and 3.1 g.L-1 for ChMMt33 with 30, 15 and 7 g.L-1,
317
respectively. This initial release represents the amount of fertilizer on the
318
surfaces of the microspheres (the central probes are in contact with the
319
microspheres). Over the course of the experiment, the potassium concentration
320
decreases until a constant value is reached. Then, the fertilizer in the inside of
321
the microspheres begins to escape. Figure 8b shows the continuum of the
322
fertilizer release, which supports ion movement because the K concentration at
323
the lateral probes increases with time.
324
326
Conclusion
The present study demonstrates an easy process for synthesizing a
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material with controlled fertilizer release combined with the direct determination
328
of the nutrients in soil. Clay provides a porous surface, increasing the KNO3
329
sorption. TDR shows an increase in the KNO3 release until the third day. This
330
behavior is due to the fertilizer on the outsides of the microspheres. The
331
fertilizer concentration decreases until a constant concentration is reached. The
332
lateral probes indicate that the ions diffuse through the soil because an increase
333
in the concentration near the lateral probes is observed after three days. The
334
TDR technique used to determine the fertilizer release will be useful for
14 Page 14 of 29
determining the real profile of nutrient release in soil and help in the design of
336
the best fertilizer release formulations.
337
Acknowledgments
338
Thanks are due to FAPESP (process number: 2014/06566-9) for financial
339
support and Bentonit União for supplying the clay.
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cr
340
References
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Jin, S., Yue, G., Feng, L., Han, Y., Yu, X., & Zhang, Z. (2011). Preparation and
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properties of a coated slow-release and water retention biuret phosphoramide
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fertilizer with superabsorbent. J.Agric. Food Chem., 59, 322–327.
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Kang, Z., Zuan-Tao, L., Xi-Liang, Z., Gang-Biao, J., Yu-Sheng, F., Xiao-Yun,
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M., & Zong Yen, L. (2013). Starch derivative-based superabsorbent with
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integration of water-retaining and controlled-release fertilizers. Carbohyd.
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Polym., 92, 1367-1376.
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Kumar, M.N.V.R. (2000). A review of chitin and chitosan applications. React.
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Funct. Polym., 46, 1-27.
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Kurita, K. (2008). Chitin and Chitosan: Functional Biopolymers from Marine
371
Crustaceans. Mar. Biotechnol., 8(3), 203-226.
372
Liang, R., Liu, M., & Wu, L. (2007). Controlled release NPK compound fertilizer
373
with the function of water retention. React. Funct. Polym., 67, 769–779.
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Mendonça, T.G., Urbano, V.R., Peres, J.G., & Souza, C.F. (2013). Hydrogel as
375
an alternative to increase water storage capacity of soil. Water Resources and
376
Irrigation Management, 2, 87-92.
377
Monvisade, P. & Siriphannon, P. (2009). Chitosan intercalated montmorillonite:
378
Preparation, characterization an cationic dye adsorption. Appl. Clay Sci., 42,
379
427-431.
380
Mulder, W.J., Gosselink, R.J.A., Vingerhoeds, M.H., Harmsen, P.F.H., &
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Eastham, D. (2011). Lignin based controlled release coatings. Industrial Crops
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and Products., 34, 915– 920.
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Noborio, K. (2001). Measurement of soil water content and electrical
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conductivity by time domain reflectometry: a review. Comput. Electron. Agr., 31,
385
213 – 237.
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Park, D.-H., Hwang, S.-J., OH, J.-M., Yang, J.-H., & Choy, J.-H. (2013).
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Polymer-Inorganic supramolecular nanohybrids for red, white, green and blue
388
applications. Prog. Poly. Sci., 38, 1442-1486.
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Queiroz, S.O.P., Testezlaf, R., & Matsura, E.E. (2005). Evaluation of
390
equipments for soil electric conductivity determination. Irriga., 10(3), 279-287.
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Qu, X., Wirsén, A., & Albertsson, A.-C. (2000). Novel pH-sensitive hydrogles:
392
swelling behavior and states of water. Poly., 41, 4589-4598.
393
Riyajan, S.-A., Sasithornsonti, Y., & Phinyocheep, P. (2012). Green natural
394
rubber-g-modified starch for controlling urea release. Carbohyd. Polym., 89,
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251-258.
396
Rui, L., Mingzhu, L., & Lan, W. (2007). Controlled release NPK compound
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fertilizer with the function of water retention. React. Funct. Polym., 67, 769-799.
398
Souza, C.F., & Folegatti, M.V. (2010). Spatial and temporal characterization of
399
water and solute distribution patterns. Scient. Agr., 67, 09-15.
400
Souza, C.F., Folegatti, M.V., & Matsura, E.E.; OR, D. (2006). Time Domain
401
Reflectometry (TDR) calibration for estimating soil solution concentration.
402
Engenh. Agr.,26, 282-291.
403
Souza, C.F., Or, D., & Matsura, E.E. (2004). A variable-volume multi-wire TDR
404
probe for measuring water content distribution in large soil volumes. Soil Sci.
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Soc. Am. J., 68(1), 25-31.
406
Tomaszewska, M., & Jarosiewicz, (2006). A. Encapsulation of mineral fertilizer
407
by polysulfone using a spraying method. Desalination., 198, 346–352.
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17 Page 17 of 29
Topp, G.C., Davis, J.L., & Annan, A.P. (1980). Electromagnetic determination of
409
soil water content: measurements in coaxial transmission lines. Water Resour.
410
Res., 16, 574 – 582.
411
Topp, G.C., Davis, J.L., & Annan, A.P. (1982). Electromagnetic determination of
412
soil water content using TDR. II. Evaluation of installation and configuration of
413
parallel transmission lines. Soil Sci. Soc. Am. J., 46, 678 – 684.
414
Wang, S.F., Shen, L., Tong, Y.J., Chen, L., Phang, I.Y., Lim, P.Q., & Liu, T.X.
415
(2005). Biopolymer chitosanmontmorillonite nanocomposites: Preparation and
416
characterization. Polym. Degrad. Stab., 90, 123-131.
417
Yasemin, B., Gulten, A., Duygu, E. I., & Ersin, S. (2009). Synthesis of clay-
418
based superabsorbent composite and its sorption capability. J. Hazard Mater.,
419
171, 717-723.
420
Zegelin, S.J., White, I., & Jenkins, D.R. (1989). Improved field probes for soil
421
water content and electrical conductivity measurement using Time Domain
422
Reflectometry. Water Resour. Res., 25, 2367-2376.
423
Zhong, K., Lin, Z-T., Zheng, X.-L., Jiang, G.-B., Fang, Y.-S., Mao, X.Y., & Liao,
424
Z.W. (2013). Starch derivative-based superabsorbent with integration of water-
425
retaining and controlled-release fertilizers. Carbohyd. Polym., 92 (2), 1367-
426
1376.
428
cr
us
an
M
d
te
Ac ce p
427
ip t
408
429 430 431 432
18 Page 18 of 29
433 434 435
-C=O (amide I) -N-H (amide II)
(a)
us
(c)
an
(d)
(e)
3500
3000
M
Absorbance (a.u.)
(b)
4000
ip t
Figures
cr
436
2500
2000
NO31500
1000
500
-1
438
Figure 1: FTIR spectra of chitosan (a) and chitosan containing (b) 6, (c) 33 and
439
(d) 50% MMt and (e) ChMMt33 containing KNO3.
441 442 443 444 445
te
Ac ce p
440
d
437
wavenumber (cm )
446 447 448 449 19 Page 19 of 29
450 451
ip t
452
us
Intensity (a.u.)
(b)
cr
(a)
(c)
an
(d)
(f)
d
M
(e)
453
te
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
2(degree)
Figure 2: XRD diffraction patterns of (a) pristine clay (MMt-Na+) and (b) net
455
chitosan and of the phases produced by chitosan containing (c) 6, (d) 33 and
456
(e) 50wt.% MMt and (f) ChMMt33 containing KNO3.
457 458 459
Ac ce p
454
460 461 462 463
20 Page 20 of 29
464 465
100
ip t
90 80
50
(d)
cr
60
(e)
40
us
Mass (%)
70
(c)
30 20 10 0 0
100
200
300
400
an
(b)
500
600
700
(a) 800
900
Temperature (°C)
M
466
Figure 3: TG curves of chitosan (a) and chitosan containing (b) 6, (c) 33 and (d)
468
50wt.% of MMt and (e) ChMMt33-containing KNO3.
471 472 473 474 475
te
470
Ac ce p
469
d
467
476 477
21 Page 21 of 29
(d)
(c)
cr
(e)
an
us
(b)
M
ip t
(a)
478 479 480 481
Ac ce p
te
d
(f)
Figure 4: FEG-SEM images of (a-b) Ch and (d-e) ChMMt33 microspheres and (c) Ch and (d) ChMMt33 fracture region.
482
22 Page 22 of 29
ip t cr us an M
Figure 5: SEM/EDS of the fracture regions of ChMMt33-KNO3 in a sorption (a)
484
and desorption (b) process.
487 488 489 490
te
486
Ac ce p
485
d
483
23 Page 23 of 29
240
180
ip t
150 240
90
Ch ChMMt6 ChMMt33 ChMMt50
30
180 150 120 90 60 30 0
0
1
0 0
20
40
60
80
100
Time (hours)
491
500 501 502 503
160
180
te Ac ce p
499
140
d
495
498
120
M
494
497
5
Figure 6: Swelling rate of the microspheres in water.
493
496
4
an
492
2 3 Time (hours)
us
60
210
cr
120 H2O swelling degree/%
H2O swelling degree (%)
210
504
24 Page 24 of 29
70
Amount sorbed Amount dessorbed
60 50
ip t
30 20 10 0 ChMMt6
ChMMt33
Microspheres
(a)
506
M
30
25
d
20
te
15
10
Ac ce p
amount of sorbed KNO3 (g/L))
an
505
ChMMt50
us
Ch
cr
+
K (%)
40
5
0
0
507 508
5
10
15
20
25
30
35
[KNO3] (g/L) in the initial solution
(b)
509
Figure 7: (a) Amount of K+ sorbed-desorbed after the immersed microspheres in
510
a 15 g.L-1 KNO3 solution; (b) Effect of the initial concentration on the K-content
511
microspheres.
512 513 514 25 Page 25 of 29
8
a
7 6
+
-1
4 3
ip t
[K ] g.L 1 7 15 30
+
[ K ] g/L
5
2
cr
1 0 0
5
10
15
20
25
30
35
516
(a)
3 days -1
d
+
[ K ] g.L
1,0
0,0
5
10
Ac ce p
0
te
0,5
518
50
55
60
b
M
1,5
517
45
an
2,0
40
us
515
days
15
20
25
+
-1
[k ] g.L 1 7 15 30 30
35
40
45
50
55
60
days
(b)
519
Figure 8: Determination of the potassium concentration release in the soil using
520
TDR (a) central and (b) lateral probes.
521 522 523 524 525 526 527
26 Page 26 of 29
528
Table 1. Physical and chemical characteristics of soil layers from 0 to 0.20 m.
ip t
Physical characteristics CC PMP p Ds Dp VIB Sand Lime Clay m3 m-3 g cm-3 cm h-1 % 0.33 0.17 0.51 1.30 2.65 13.20 15 31 54 Chemical characteristics pH P OM H+Al K Ca Mg SB CEC V -3 -3 CaCl2 mg dm % mmol dm % 4.60 10 18 50 2.90 14 6 23.10 73.10 32
cr
CC = Field capacity, PMP = Permanent wilting point, p = Porosity, Ds = Soil density , Dp = Particle density, VIB = Steady state infiltration rate, pH = Potential hydrogen, P = Phosphorus, OM = Organic matter, H + Al = Potential acidity, K = potassium, Ca = calcium, Mg = Magnesium, SB = Sum of bases, CEC = Cation exchange capacity, V = Percentage of Base saturation
us
529 530
Table 2: Theoretical and TG values of MMt in the composite and d001 values
532
from the XRD patterns.
534 535 536 537 538 539 540
M
d001 (nm) ------1.8 1.8 1.6 1.8** 1.4
*Microspheres added to a 15 g.L-1 initial KNO3 solution. **Broad peak (exfoliated-intercalated material)
Ac ce p
533
d
Chitosan ChMMt6 ChMMt33 ChMMt50 ChMMt33_KNO3 MMt
% of MMt in the composite theoretical TG dates 0 0 6 5.4 33 26 50 42 33 26 (28% KNO3)* 100 100
te
Microspheres
an
531
541 542 543 544 545 27 Page 27 of 29
546
Graphical Abstract
6 TDR Probes Central Lateral
5
3
ip t
+
2 1 0 0
5
10 15 20 25 30 35 40 45 50 55 60
an
us
days
cr
[ K ] g/L
4
547
Ac ce p
te
d
M
548
28 Page 28 of 29
548
Highlights
549
Chitosan-montmorillonite microspheres were prepared as controlled release
551
fertilizer; Chitosan-clay composites demonstrate to be an efficient sorbent to
552
potassium fertilizer in a sorption-dessorption process; in situ determination of the
553
potassium-containing material was monitored by an electromagnetic technique.
cr
ip t
550
554
us
555
Ac ce p
te
d
M
an
556
29 Page 29 of 29
S0144-8617(15)00277-5 http://dx.doi.org/doi:10.1016/j.carbpol.2015.03.064 CARP 9806
To appear in: Received date: Revised date: Accepted date:
24-11-2014 16-2-2015 14-3-2015
Please cite this article as: Santos, B. R., Bacalhau, F. B., Pereira, T. S., Souza, C. F., and Faez, R.,Chitosan-Montmorillonite microspheres: a sustainable fertilizer delivery system, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.03.064 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
Chitosan-Montmorillonite microspheres: a sustainable fertilizer delivery
2
system
3
Bruna Rodrigues dos Santosa, Fabiana Britti Bacalhaub, Tamires dos Santos
5
Pereiraa, Claudinei Fonseca Souzab, Roselena Faeza*
ip t
4
cr
6 7
a
8
Federal de São Carlos, Campus Araras, Araras, Brazil.
9
b
us
Laboratório de Materiais Poliméricos e Biossorventes, Universidade
an
Departamento de Recursos Naturais e Proteção Ambiental, Universidade
Federal de São Carlos, Campus Araras, Araras, Brazil.
11
Corresponding author: [email protected]
M
10
Ac ce p
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d
12
1 Page 1 of 29
12
Abstract
14
Controlled release fertilizers are efficient tools that increase the sustainability
15
of agricultural practices. However, the biodegradability of the matrices and
16
the determination of the release into soil still require some investigation. This
17
paper describes the preparation of potassium-containing microspheres
18
based on chitosan and montmorillonite clay and the in situ soil release. The
19
chitosan-montmorillonite microspheres were prepared using a coagulation
20
method and different proportions of montmorillonite. The structural, thermal
21
and morphological properties as well the water swelling and fertilizer
22
sorption capacity were evaluated. The best formulations were applied in soil,
23
and the fertilizer release was monitored using time-domain reflectometry
24
(TDR). Montmorillonite clay provides better sorption properties than the
25
chitosan microspheres because of the rough and porous surface. Due to
26
these properties, high levels of fertilizer were sorbed onto the material.
27
ChMMT33-containing potassium shows two specific periods of fertilizer
29 30 31 32
cr
us
an
M
d
te
Ac ce p
28
ip t
13
release: the first one lasted approximately three days and was assigned to the external fertilizer on the microspheres. The second was assigned to the internal fertilizer. TDR is an important and fast tool and was used to determine the fertilizer release and the ion movement in the soil.
33
Keywords:
34
technique.
Chitosan,
controlled
release,
agricultural
practices,
TDR
35 36
2 Page 2 of 29
36 37
1. Introduction In recent decades, the production of food has increased due to the
39
growing population. According to the United Nations Food and Agriculture
40
Organization (FAO), the production of food will need to increase by 70% to
41
supply a population of nine billion people in 2050 (FAO, 2014). However, an
42
outstanding challenge is finding alternatives to increase the production of food
43
by optimizing the use of agricultural inputs, enabling economic benefits for
44
farmers and reducing the environmental impact of the activity. The use of
45
alternative materials in agriculture has increased due to the need to enhance
46
the production systems with increasing productivity and cost savings
47
(Ghormade, Deshpande & Paknikar, 2011). Hydrogels are examples of
48
alternative materials that have the ability to significantly increase their size via
49
water absorption and gradually release their load into the medium where they
50
are inserted (Liang, Liu & Wu, 2007; Jin et al., 2011; Zhong et al, 2013). Some
51
polymers have been used to prepare hydrogels that increased water retention in
52
soil, reducing the required frequency of irrigation (Abedi-Koupaia, Sohrabb &
53
Swarbrickc, 2008; Mendonça, Urbano, Peres & Souza, 2013). Nevertheless, the
54
majority of these hydrogels are based on non-biodegradable materials, such as
55
polyacrylamide and polystyrene, and can leave residues in the soil, causing
56
salinization of the medium as their use becomes common (Mendonça et al.,
57
2013). In contrast, new studies have been performed using natural and
58
biodegradable polymers, which leave no residue after their application (Riyajan,
59
Sasithornsonti & Phinyocheep, 2012; Mulder, Gosselink, Vingerhoeds &
60
Harmsen, 2011). These materials can be used as soil conditioners because
61
they improve the availability of water and also act as an alternative for the
Ac ce p
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38
3 Page 3 of 29
controlled release of fertilizers. These uses ensure both economic and
63
environment benefits by avoiding contamination of the ground water. The use of
64
coated fertilizers is a promising alternative to improve many aspects of
65
fertilization based on the concept of controlled release (Chen, Xie, Zhuang,
66
Chen & Jing, 2008; Tomaszewska & Jarosiewicz, 2006). The main advantages
67
of using controlled release materials are regular and continuous delivery of
68
nutrients to the plants; a low frequency of fertilizer application to the soils; a
69
reduction
70
immobilization; elimination of damage to roots due to high salt concentrations;
71
easy handling of the fertilizer: a reduction in NO3 pollution; an increase in the
72
eco-value of agricultural activity (less contamination of groundwater and surface
73
water); and a reduction in production costs (Liang et al., 2007). Chitosan has
74
been extensively explored as a coating material for preparing controlled release
75
microspheres for a system where the rates of dissolution and release directly
76
depend on the characteristics of the material (Kumar, 2013; Kurita, 2008).
77
Chitosan is a natural biopolymer extracted from the exoskeletons of insects and
78
crustaceans. It features good mechanical properties combined with the ability to
79
form fibers, films, gels, and microspheres. It is extremely attractive due to its
80
biodegradability, biocompatibility and non-toxicity (Kumar, 2013). In addition,
81
the combination of inorganic and polymeric materials has been a successful
82
strategy in developing new properties, drawing attention the last few years due
83
to the attainment of materials with new or better properties than the pure
84
polymer (Kang et al., 2013; Park, Hwang, OH, Yang & Choy, 2013; Yasemin,
85
Gulten, Duygu & Ersin, 2009; Rui, Mingzhu & Lan, 2007). The addition of
86
layered silicates, such as montmorillonite clay, is a promising alternative to
nutrient
losses
due
to
leaching,
volatilization
us
the
and
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d
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an
of
cr
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4 Page 4 of 29
enhance certain properties, i.e., increasing the sorptive capacity for both water
88
and chemical compounds. The use of clay minerals is justified due to ready
89
availability, low cost and environmentally friendly nature, which make them
90
interesting for applications in agriculture. Another interesting point is the
91
necessity of monitoring fertilizer release in soil. Usually, the material is added
92
to the soil, and at specified intervals, an aliquot of soil is treated and tested to
93
determine the amount of fertilizer released, which requires time consuming and
94
difficult experimental procedures. In contrast, the determination of ionic
95
movement in the soil has been performed using the principle of electrical
96
conductivity. An efficient method to determine the electrical conductivity of a
97
medium, such as soil, is the TDR (time-domain reflectometry) technique. This
98
technique estimates the electrical conductivity (EC) of medium using
99
measurements in real time and without deforming the sample (Souza, Or &
100
Matsura, 2004). Additionally, electrical conductivity is an effective parameter to
101
monitor the release of the nutrients (fertilizer) into the soil. According to Queiroz
102
et al. (Queiroz, Testezlaf & Matsura, 2005), the EC correlates with the total
103
concentration of dissolved electrolytes (ions) in solution because pure water is
104
not a good electrical conductor. The TDR technique to determine the water
105
content and electrical conductivity of soil is becoming increasingly popular. Its
106
outstanding advantages are its accuracy, speed, reproducibility, good
107
theoretical basis, a well-defined and selected sampled volume, and the fact that
108
the water content and salinity are measured in exactly the same sample (Souza
109
& Folegatti, 2010; Topp, Davis, Annan, 1980). The method is based on the fact
110
that the speed of the propagation of microwave pulses in conductive cables
111
inserted in the soil is very sensitive to its water content, which is the result of a
Ac ce p
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d
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5 Page 5 of 29
large disparity between the dielectric permittivities of water (w= 81) and the
113
other soil constituents, such as air (a= 1) and soil solid particles (s= 3-5)
114
(Noborio, 2001; Topp et al., 1980). Consequently, the bulk dielectric permittivity
115
(b) is dominated by the water phase. The soil b is determined from the travel
116
time of a stepped electromagnetic pulse along a buried waveguide (TDR probe)
117
(Zegelin, White & Jenkins, 1989; Topp, Davis & Annan, 1982). The use of TDR
118
to measure the soil EC was discovered by Dalton et al. (Dalton, Herkelrath,
119
Rawlins & Rhoades, 1984) who proposed a “lumped circuit load” transmission
120
line as an analogy for EC measurements using TDR. The soil-probe system is
121
assumed to be composed of a lumped circuit with load impedance at the end of
122
the transmission line (typically a coaxial cable) of known characteristic
123
impedance (the cable impedance is typically 50 Ω). In this paper, a potassium-
124
containing, controlled-release biodegradable material was prepared, and
125
structural, thermal and morphological characterizations were performed.
126
Additionally, the potassium concentration and swelling behavior in water were
127
determined. The best formulations of the composites were applied in soil
128
samples, and the in situ determination of fertilizer release was performed using
129
TDR.
131 132
cr
us
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M
d
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Ac ce p
130
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112
2. Experimental 2.1. Materials
133
Chitosan with a deacetylation degree of 85 % was supplied by Polymar
134
(97%, Brazil). The average molecular weight (Mw) was 1.8 105 g.mol-1 as
135
determined by gel permeation chromatograph (Agilent 1100 chromatographic
136
system equipped with a refractive index detector). Sodium montmorillonite clay 6 Page 6 of 29
137
(Brasgel Aço DS, Brazil), glacial acetic acid (Synth, 99%, Brazil), sodium
138
hydroxide (Synth, 99%, Brazil), and fertilizer (Saltpetre Krista K (KNO3) Yara
139
Brazil Fertilizantes S.A.) were used without further purification.
141
2.2. Preparation of Chitosan and Chitosan-MMt microspheres
ip t
140
A chitosan solution of 40 g.L-1 was prepared by dissolving 4 g of chitosan
143
flakes in 100 mL of acetic acid aqueous solution 5% (w/v) with mechanical
144
stirring overnight at 25°C. Afterwards, sodium montmorillonite clay (MMt-Na+)
145
was added to the chitosan solution at proportions of 6, 33 and 50 wt.% and the
146
solution was mechanically stirred for 16 hours at 25°C. The microspheres were
147
prepared by dripping the chitosan/clay solution into a 2 mol.L-1 sodium
148
hydroxide solution. The microspheres were filtered and washed with distilled
149
water until a neutral pH was reached, and they were subsequently added to a
150
fertilizer solution. For the structural, thermal and morphological characterization,
151
the microspheres were dried at 60°C for 30 minutes. The chitosan microspheres
152
(Ch) were prepared using the same methodology. The materials were called
153
ChMMt6, ChMMt33 and ChMMt50, respectively, for Chitosan/MMt-Na+ with 6,
154
33 and 50 wt.%.
156 157
us
an
M
d
te
Ac ce p
155
cr
142
2.3. Preparation and characterization of potassium-containing microspheres The ChMMt33 microspheres were swelled in 1, 7, 15 and 30 g.L-1 KNO3
158
fertilizer solutions for 24 hours. After the potassium-containing ChMMt33
159
microspheres were dried at 60°C for 30 minutes, flame photometry (DM-62
160
Digimed, Brazil) was used to determine the KNO3 concentration.
161
7 Page 7 of 29
162 163
2.4. Structure,
thermal
and
morphological
characterization
of
the
microspheres FTIR spectra were recorded using a Shimadzu IR Prestige-21
165
spectrophotometer operating between 4000 and 400 cm-1. The samples were
166
diluted in solid KBr before the spectrum recording. X-ray diffraction (XRD)
167
patterns of the powdered samples were recorded using a Rigaku diffractometer
168
model Miniflex using Cu-Kα radiation (1.541 Å, 30 kV and 15 mA).
169
Thermogravimetric
170
thermoanalyzer TA-60 under synthetic air with a flow of 200 cm3 min-1 and a
171
heating rate of 10 °C min-1. Scanning electron microscopy (SEM) images of the
172
microspheres were recorded using a JEOL field emission scanning electron
173
microscope model JSM 7401 F with an SEI detector.
performed
on
us
were
a
Shimadzu
M
d
174
2.5. Microspheres water swelling
te
175
(TGA)
an
analyses
cr
ip t
164
A pre-weighted dry microsphere (wi) was immersed into a certain amount
177
of deionized water. At specific time intervals, the microspheres were removed
178
from the water and reweighed (wf). The swelling ratios (%SR) of the
179
microspheres were calculated using equation 1:
180 181 182 183
Ac ce p
176
Equation 1
2.6. Release behavior of CHMMt33 containing potassium in the soil
184
The potassium-containing microspheres were prepared at four fertilizer
185
solution concentrations: 1, 7, 15 and 30 g.L-1 KNO3. ChMMt33 microspheres
186
containing KNO3 were placed in a 7.5-L container filled with soil (Typic 8 Page 8 of 29
dystrophic LVd). Table 1 shows the physical and chemical characteristics of
188
soil. Three replicates for each concentration were performed. The container was
189
prepared with a water drainage system consisting of a thin layer of gravel at the
190
bottom, which was followed by a geotextile fabric to prevent the loss of soil. The
191
container was filled with soil (9 kg) in layers of 0.05 m to simulate the original
192
bulk density of 1.30 g.cm-3. Each container received 4 g of microspheres placed
193
at a single spot. They were placed at a depth of 10 cm. The fertilizer release
194
was monitored using three electromagnetic probes for TDR that consisted of
195
three continuous metal rods of 20 cm, which were in contact with the material
196
and can be used to estimate the moisture and electrical conductivity. One probe
197
was installed at the center of the container, which meant the rod was in contact
198
with the microspheres in the soil. The other two probes were installed 5 cm from
199
the central probe, and they were only in contact with the soil. Therefore, the
200
purpose of these probes was to monitor the lateral displacement of the fertilizer
201
from the microspheres in the soil.
203 204 205 206
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187
3. Results and Discussion 3.1. Structure,
thermal
and
morphological
characterization
of
the
microspheres
In
this
paper,
chitosan,
chitosan/clay
and
potassium-containing
207
chitosan/clay materials were prepared as microspheres using a coagulation
208
method. The structural, thermal behavior and the morphology of the chitosan
209
and chitosan/clay were characterized using X-ray diffraction (XRD), Fourier
210
transform infrared (FTIR) spectroscopy, thermogravimetry (TG) and scanning
211
electron microscopy (SEM), respectively. The GPC results (not shown here)
9 Page 9 of 29
exhibit Mw ~1.8x105 g.mol-1 for net chitosan and its composites indicating no
213
degradation process during the microsphere preparation. The FTIR spectrum of
214
chitosan (Brugnerottoa et al., 2001) (Figure 1a) shows a broad band at 3440
215
cm−1 assigned to the overlapping of O-H and N-H stretching. The band at 1648
216
cm−1 was attributed to the C=O stretching (amide I) and a band of weak
217
intensity near 1550 cm−1 was assigned to the N-H bending (amide II). The
218
bands at 2872, 1157 and 1076 cm-1 are ascribed to the CH stretching, the anti-
219
symmetric stretching of C-O-C bridge and to the skeletal vibration involving C-O
220
stretching, respectively and are characteristic of the saccharide structure
221
(Monvisade & Siriphannon, 2009; Abdel-Fattah, Jiang, El-Bassyouni &
222
Laurencin, 2007; Wang et al., 2005]. In addition, the bands assigned to the axial
223
deformation of the amide (CN) groups and the CN axial deformation of the
224
amino groups can be seen respectively at 1427 cm-1 and 1320-1380 cm-1. The
225
bands associated with chitosan remain unaltered in the FTIR spectra of the
226
chitosan-clay systems (Figures 1b-1d). However, the intensities of the bands
227
related to Si-O and Si-O-Si at 1060, 915, 793 and 521 cm-1 increase with the
228
clay content in the composite. The presence of KNO3 in the potassium-
229
containing microspheres is confirmed by the presence of the 1385 cm-1 band,
230
which is assigned to the NO3- symmetric stretching, Figure 1d.
cr
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Ac ce p
231
ip t
212
Figure 2 shows the XRD patterns of MMt-Na+ and microspheres of net
232
chitosan and composites with different MMt concentrations. The XRD pattern of
233
Ch presents two major peaks at about 210o and 20o ascribed to 020 (crystal
234
1) and 110 (crystal 2) reflections, respectively (Abdel-Fattah, Jiang, El-
235
Bassyouni & Laurencin, 2007; Wang et al., 2005). The XRD pattern of MMt-Na+
236
shows a reflection peak at 26.2° corresponding to a d001 basal spacing of 1.4 10 Page 10 of 29
nm. Comparing the XRD patterns of chitosan and its composites two main
238
aspects are observed. In the basal space region a d001 displacement to lower
239
2values and a broad peak at 24.9° are verified. The displacement of the
240
basal reflection is indicative of the formation of an intercalated structure
241
[Monvisade & Siriphannon, 2009). Taking into account the crystalline region of
242
chitosan (210°) a broadening peak and lower intensity is observed
243
confirming a decrease of the anhydrous crystal polymorph structure and the
244
degree of order of chitosan molecular structure (Wang et al., 2005). The peak at
245
220° (crystal 2) has increased sharpness since the crystal size has
246
increased. However, for ChMMt33-containing KNO3, the XRD curve shows a
247
broad peak in the d001 basal space due to the exfoliation-intercalation and the
248
presence of the KNO3 intense peaks at 218-20° which cover the chitosan
249
peaks in that region.
d
M
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us
cr
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237
The TGA of Ch and ChMMt composites with a heating rate of 10°C min−1
251
under synthetic air between 25 and 800°C are given in Figure 3. Three major
252
stages of mass loss of neat chitosan are observed and calculated to be
253
approximately 17, 46, and 37%, which are assigned to water loss,
254
decomposition
255
degradation of the final waste of the polymer, respectively. ChMMt composites
256
also show three stages for mass loss. However, the decomposition of
257
montmorillonite clay is not complete until 800°C. Based on the TG curve
258
residue, the amount of clay in the composite was calculated and the smaller
259
values compared with the theoretical value are in agreement with the
260
experimental observation because there are losses of clay during the dripping
261
process, Table 2. Additionally, the ChMMt33-containing KNO3 shows higher
Ac ce p
te
250
of
the
polymer
via
deacetylation-depolymerization
and
11 Page 11 of 29
values for the residues than ChMMt33 due to the presence of KNO3. When
263
including the decomposition of the KNO3 salt (the residue is K2O), which is
264
taken into account to deduce the total KNO3 in the material, the amount of KNO3
265
from the TG curves (28%) is similar to the photometrically determined value
266
(32%) when the microspheres were added to the 15 gL KNO3 solution.
267
Additionally, based on the thermogravimetric results the final amount of polymer
268
content in the microspheres is 78, 59 and 46% for ChMMt-6, ChMMt-33 and
269
CHMMt-50, respectively.
us
cr
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262
The SEM images of Ch and ChMMt show a spherical material but
271
deformations are observed at the breakpoint of the drops (Figure 4a). The
272
dispersed clay phase in the chitosan matrix and the interface region describes
273
the compatibilization of the phases. The fracture region, shown in Figure 4f,
274
shows a rough and porous surface for the ChMMt composite, which provides
275
better sorption of fertilizer, as demonstrate by the sorption-desorption results
276
shown in Figure 8. Figure 5 shows the morphology of the fracture regions and
277
the EDS (energy dispersive spectrometry) results for ChMMt33 in the sorption
278
and desorption processes, Figures 5a and 5b, respectively. A decrease in the K
279
intensity after the desorption process confirms the release of fertilizer, which is
280
in agreement with the TDR results, Figure 8.
282
M
d
te
Ac ce p
281
an
270
3.2. Swelling behavior of microspheres in water
283
Figure 6 shows the swelling behavior of the microspheres in water. In the
284
first hour, the microspheres increase in size, and a swelling degree in the range
285
of 150 to 200% is observed. Pure chitosan presents a higher value (200%) than
286
ChMMt33 (150%). The lower values of water sorption for the composites are
12 Page 12 of 29
due to the intercalation of the polymer into the clay galleries, which decreases
288
the ability of both materials (clay and chitosan) to swell. Furthermore, the
289
crystallinity increases for composites provide a swelling reduction. These results
290
were consistent with Qu and coauthors (Qu, Wirsén & Albertesson, 2000) since
291
they observe the higher crystalline material inhibited the water diffusion.
ip t
287
293
cr
292
Microspheres containing KNO3
Montmorillonite clay affects the amount of sorbed-desorbed KNO3, and
295
the presence of exfoliated or intercalated polymer phases influences the
296
sorption behavior, Figure 7a. The ChMMt33 composite shows a higher value for
297
potassium in the sorb-desorb process, which agrees with the morphological and
298
structural properties. Because ChMMt33 demonstrates the best characteristics,
299
the influence of the initial KNO3 concentration (1, 7, 15 or 30 g.L-1) was used to
300
swell the microspheres, Figure 7b. A higher value for the initial concentration
301
reflects a larger amount of potassium in the microspheres because the fertilizer
302
covers the microspheres in the 30 g.L-1 KNO3 sample, as shown in the images
303
in Figure 7b. Furthermore, ChMMt33 microspheres with 1, 7, 15 and 30 g.L-1 of
304
KNO3 were placed in soil samples, and TDR was used to evaluate the fertilizer
305
release for 60 days, Figure 8. TDR evaluates the changes in the soil
306
conductivity; however, we can correlate the ionic conductivity with the ion
307
concentration using equation 2 (Souza, Folegatti, Matsura & OR, 2006).
Ac ce p
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M
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294
Equation 2
308
309 310
C – Concentration of potassium nitrate (mmol L-1);
13 Page 13 of 29
311
CES – Electrical conductivity of the solution (dS m-1); The fertilizer release was estimated based on the electrical conductivity of the
313
central and lateral probes, and the data were related to the concentration of
314
potassium ions in the soil. According to the potassium release profile of the
315
central probes, Figure 8a, higher fertilizer release occurs for the first three days,
316
reaching 7.5, 5.3 and 3.1 g.L-1 for ChMMt33 with 30, 15 and 7 g.L-1,
317
respectively. This initial release represents the amount of fertilizer on the
318
surfaces of the microspheres (the central probes are in contact with the
319
microspheres). Over the course of the experiment, the potassium concentration
320
decreases until a constant value is reached. Then, the fertilizer in the inside of
321
the microspheres begins to escape. Figure 8b shows the continuum of the
322
fertilizer release, which supports ion movement because the K concentration at
323
the lateral probes increases with time.
324
326
Conclusion
The present study demonstrates an easy process for synthesizing a
Ac ce p
325
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d
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cr
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312
327
material with controlled fertilizer release combined with the direct determination
328
of the nutrients in soil. Clay provides a porous surface, increasing the KNO3
329
sorption. TDR shows an increase in the KNO3 release until the third day. This
330
behavior is due to the fertilizer on the outsides of the microspheres. The
331
fertilizer concentration decreases until a constant concentration is reached. The
332
lateral probes indicate that the ions diffuse through the soil because an increase
333
in the concentration near the lateral probes is observed after three days. The
334
TDR technique used to determine the fertilizer release will be useful for
14 Page 14 of 29
determining the real profile of nutrient release in soil and help in the design of
336
the best fertilizer release formulations.
337
Acknowledgments
338
Thanks are due to FAPESP (process number: 2014/06566-9) for financial
339
support and Bentonit União for supplying the clay.
ip t
335
cr
340
References
342
Abdel-Fattah, W. I., Jiang, T., El-Bassyouni, G. E.-T., & Laurencin, C. T. (2007).
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Chen, L., Xie, Z., Zhuang, X., Chen, X., & Jing, X. (2008). Controlled release of
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Jin, S., Yue, G., Feng, L., Han, Y., Yu, X., & Zhang, Z. (2011). Preparation and
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Kang, Z., Zuan-Tao, L., Xi-Liang, Z., Gang-Biao, J., Yu-Sheng, F., Xiao-Yun,
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Kumar, M.N.V.R. (2000). A review of chitin and chitosan applications. React.
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Kurita, K. (2008). Chitin and Chitosan: Functional Biopolymers from Marine
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Liang, R., Liu, M., & Wu, L. (2007). Controlled release NPK compound fertilizer
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Topp, G.C., Davis, J.L., & Annan, A.P. (1982). Electromagnetic determination of
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parallel transmission lines. Soil Sci. Soc. Am. J., 46, 678 – 684.
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Wang, S.F., Shen, L., Tong, Y.J., Chen, L., Phang, I.Y., Lim, P.Q., & Liu, T.X.
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characterization. Polym. Degrad. Stab., 90, 123-131.
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based superabsorbent composite and its sorption capability. J. Hazard Mater.,
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171, 717-723.
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Zegelin, S.J., White, I., & Jenkins, D.R. (1989). Improved field probes for soil
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water content and electrical conductivity measurement using Time Domain
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Reflectometry. Water Resour. Res., 25, 2367-2376.
423
Zhong, K., Lin, Z-T., Zheng, X.-L., Jiang, G.-B., Fang, Y.-S., Mao, X.Y., & Liao,
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Z.W. (2013). Starch derivative-based superabsorbent with integration of water-
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1376.
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d
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Ac ce p
427
ip t
408
429 430 431 432
18 Page 18 of 29
433 434 435
-C=O (amide I) -N-H (amide II)
(a)
us
(c)
an
(d)
(e)
3500
3000
M
Absorbance (a.u.)
(b)
4000
ip t
Figures
cr
436
2500
2000
NO31500
1000
500
-1
438
Figure 1: FTIR spectra of chitosan (a) and chitosan containing (b) 6, (c) 33 and
439
(d) 50% MMt and (e) ChMMt33 containing KNO3.
441 442 443 444 445
te
Ac ce p
440
d
437
wavenumber (cm )
446 447 448 449 19 Page 19 of 29
450 451
ip t
452
us
Intensity (a.u.)
(b)
cr
(a)
(c)
an
(d)
(f)
d
M
(e)
453
te
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
2(degree)
Figure 2: XRD diffraction patterns of (a) pristine clay (MMt-Na+) and (b) net
455
chitosan and of the phases produced by chitosan containing (c) 6, (d) 33 and
456
(e) 50wt.% MMt and (f) ChMMt33 containing KNO3.
457 458 459
Ac ce p
454
460 461 462 463
20 Page 20 of 29
464 465
100
ip t
90 80
50
(d)
cr
60
(e)
40
us
Mass (%)
70
(c)
30 20 10 0 0
100
200
300
400
an
(b)
500
600
700
(a) 800
900
Temperature (°C)
M
466
Figure 3: TG curves of chitosan (a) and chitosan containing (b) 6, (c) 33 and (d)
468
50wt.% of MMt and (e) ChMMt33-containing KNO3.
471 472 473 474 475
te
470
Ac ce p
469
d
467
476 477
21 Page 21 of 29
(d)
(c)
cr
(e)
an
us
(b)
M
ip t
(a)
478 479 480 481
Ac ce p
te
d
(f)
Figure 4: FEG-SEM images of (a-b) Ch and (d-e) ChMMt33 microspheres and (c) Ch and (d) ChMMt33 fracture region.
482
22 Page 22 of 29
ip t cr us an M
Figure 5: SEM/EDS of the fracture regions of ChMMt33-KNO3 in a sorption (a)
484
and desorption (b) process.
487 488 489 490
te
486
Ac ce p
485
d
483
23 Page 23 of 29
240
180
ip t
150 240
90
Ch ChMMt6 ChMMt33 ChMMt50
30
180 150 120 90 60 30 0
0
1
0 0
20
40
60
80
100
Time (hours)
491
500 501 502 503
160
180
te Ac ce p
499
140
d
495
498
120
M
494
497
5
Figure 6: Swelling rate of the microspheres in water.
493
496
4
an
492
2 3 Time (hours)
us
60
210
cr
120 H2O swelling degree/%
H2O swelling degree (%)
210
504
24 Page 24 of 29
70
Amount sorbed Amount dessorbed
60 50
ip t
30 20 10 0 ChMMt6
ChMMt33
Microspheres
(a)
506
M
30
25
d
20
te
15
10
Ac ce p
amount of sorbed KNO3 (g/L))
an
505
ChMMt50
us
Ch
cr
+
K (%)
40
5
0
0
507 508
5
10
15
20
25
30
35
[KNO3] (g/L) in the initial solution
(b)
509
Figure 7: (a) Amount of K+ sorbed-desorbed after the immersed microspheres in
510
a 15 g.L-1 KNO3 solution; (b) Effect of the initial concentration on the K-content
511
microspheres.
512 513 514 25 Page 25 of 29
8
a
7 6
+
-1
4 3
ip t
[K ] g.L 1 7 15 30
+
[ K ] g/L
5
2
cr
1 0 0
5
10
15
20
25
30
35
516
(a)
3 days -1
d
+
[ K ] g.L
1,0
0,0
5
10
Ac ce p
0
te
0,5
518
50
55
60
b
M
1,5
517
45
an
2,0
40
us
515
days
15
20
25
+
-1
[k ] g.L 1 7 15 30 30
35
40
45
50
55
60
days
(b)
519
Figure 8: Determination of the potassium concentration release in the soil using
520
TDR (a) central and (b) lateral probes.
521 522 523 524 525 526 527
26 Page 26 of 29
528
Table 1. Physical and chemical characteristics of soil layers from 0 to 0.20 m.
ip t
Physical characteristics CC PMP p Ds Dp VIB Sand Lime Clay m3 m-3 g cm-3 cm h-1 % 0.33 0.17 0.51 1.30 2.65 13.20 15 31 54 Chemical characteristics pH P OM H+Al K Ca Mg SB CEC V -3 -3 CaCl2 mg dm % mmol dm % 4.60 10 18 50 2.90 14 6 23.10 73.10 32
cr
CC = Field capacity, PMP = Permanent wilting point, p = Porosity, Ds = Soil density , Dp = Particle density, VIB = Steady state infiltration rate, pH = Potential hydrogen, P = Phosphorus, OM = Organic matter, H + Al = Potential acidity, K = potassium, Ca = calcium, Mg = Magnesium, SB = Sum of bases, CEC = Cation exchange capacity, V = Percentage of Base saturation
us
529 530
Table 2: Theoretical and TG values of MMt in the composite and d001 values
532
from the XRD patterns.
534 535 536 537 538 539 540
M
d001 (nm) ------1.8 1.8 1.6 1.8** 1.4
*Microspheres added to a 15 g.L-1 initial KNO3 solution. **Broad peak (exfoliated-intercalated material)
Ac ce p
533
d
Chitosan ChMMt6 ChMMt33 ChMMt50 ChMMt33_KNO3 MMt
% of MMt in the composite theoretical TG dates 0 0 6 5.4 33 26 50 42 33 26 (28% KNO3)* 100 100
te
Microspheres
an
531
541 542 543 544 545 27 Page 27 of 29
546
Graphical Abstract
6 TDR Probes Central Lateral
5
3
ip t
+
2 1 0 0
5
10 15 20 25 30 35 40 45 50 55 60
an
us
days
cr
[ K ] g/L
4
547
Ac ce p
te
d
M
548
28 Page 28 of 29
548
Highlights
549
Chitosan-montmorillonite microspheres were prepared as controlled release
551
fertilizer; Chitosan-clay composites demonstrate to be an efficient sorbent to
552
potassium fertilizer in a sorption-dessorption process; in situ determination of the
553
potassium-containing material was monitored by an electromagnetic technique.
cr
ip t
550
554
us
555
Ac ce p
te
d
M
an
556
29 Page 29 of 29