silica nanocomposites by altering the content of quaternary ammonium groups grafted into softwood kraft lignin

Industrial Crops & Products 144 (2020) 112039

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Structural regulation of lignin/silica nanocomposites by altering the content of quaternary ammonium groups grafted into softwood kraft lignin

T

Wenlong Xionga,d, Dongjie Yangb, Md. Asraful Alama, Jingliang Xua,d,*, Yuanyuan Lic, Huan Wangb, Xueqing Qiub,* a

School of Chemical Engineering, Zhengzhou University, Zhengzhou 450001, China School of Chemistry and Chemical Engineering, Guangdong Provincial Engineering Research Center for Green Fine Chemicals, South China University of Technology, Guangzhou 510640, China c College of Pharmacy, Henan University of Chinese Medicine, 156 Jinshui East Road, Zhengzhou 450046, China d Henan Center for Outstanding Overseas Scientists, Zhengzhou, China b

A R T I C LE I N FO

A B S T R A C T

Keywords: Lignin Silica Quaternary ammonium groups Structural regulation

In this work, cationic lignin derivatives were synthesized by grafting reaction of lignin and 3-chloro-2-hydroxypropyltrimethylammonium chloride. Then the synthesized cationic lignins were used to prepare lignin/silica nanocomposites (LSNCs) via a green co-precipitation method. The following characterizations, particle size distribution, SEM, TEM, XRD, FT-IR, XPS, static contact angle, specific surface area, and pore size distribution, were employed to understand the dispersity, morphology, crystal structure, and textural property of different LSNCs. The results showed that lignin with low content of cationic quaternary ammonium (QA) groups couldn’t support the formation of uniform LSNCs, while lignin with moderate content of QA groups leaded to the formation of uniform LSNCs with a core-shell structure, lignin/silica hybrids in inner side and thin layer of lignin on surface. When the content of QA groups in lignin was high, the prepared LSNCs presented porous strawberry-like structure, lignin/silica hybrids at inside and coating layer of silica nanoparticles within 10 nm on surface.

1. Introduction Lignin, the second most abundant lignocellulosic biomass resource accounting for approximately 30 % of the non-fossil organic carbon on Earth, is the only large-volume renewable feedstock consisting of aromatic monomers (Doherty et al., 2011; Tuck et al., 2012; Upton and Kasko, 2016; Xiong et al., 2016; Wang et al., 2019). 50–70 million tons of industrial lignin is annually produced from paper industry and various current biorefinery processes (Laurichesse and Avérous, 2014; Kai et al., 2016; Lievonen et al., 2016; Aro and Fatehi, 2017). However, only less than 5 % of industrial lignin is upgrading to commercial products, including additives, adhesives, dispersants, and surfactants (Laurichesse and Avérous, 2014; Kai et al., 2016; Lievonen et al., 2016; Aro and Fatehi, 2017). The remaining 95 % are burned as boiler fuel or discarded as a waste material, which is low-value utilization with high capital cost and responsible for environmental problems such as CO2 emissions and global warming (Upton and Kasko, 2016; Kai et al., 2016; Lievonen et al., 2016). Therefore, recent years researchers are focusing on developing novel methods for high value-added utilization of lignin aiming to contribute considerably for economic, social and

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environmental benefits. Various new applications of lignin have been reported in last decades such as multifunctional colloidal lignin nanospheres and lignin nanoparticles (Qian et al., 2014; Nair et al., 2014; Deng et al., 2016; Li et al., 2017; Qian et al., 2017; Tang et al., 2018), lignin-based UV-absorbent additives (Liu et al., 2014; Qian et al., 2015a, b; Wang et al., 2018), lignin-based green sorbents (Li et al., 2015; Klapiszewski et al., 2017; Supanchaiyamat et al., 2019), lignin-based antibacterial materials (Dong et al., 2011; Richter et al., 2015), and lignin-based multifunctional composites (Thakur et al., 2014; Thakur and Thakur, 2015; Thakur et al., 2017; Huang et al., 2019), are extremely valuable applications of lignin. In addition, lignin can be used as a green and sustainable modifier to prepare lignin/silica nanocomposites (LSNCs), a novel multifunctional material (Jesionowski et al., 2014a, 2014b; Klapiszewski et al., 2015a, 2015b; Xiong et al., 2015, 2017; Jedrzak et al., 2018). Previous studies presented the use of rice husk (Qu et al., 2010), rice straw pulping (Zhang et al., 2013), and cellulosic ethanol residue (Tian et al., 2017) to synthesize LSNCs via acid-precipitation. These raw materials have a common feature of containing lignin interconnected with silica simultaneously. However, the limiting factor

Corresponding authors. E-mail addresses: [email protected] (J. Xu), [email protected] (X. Qiu).

https://doi.org/10.1016/j.indcrop.2019.112039 Received 17 June 2019; Received in revised form 17 October 2019; Accepted 9 December 2019 0926-6690/ © 2019 Elsevier B.V. All rights reserved.

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(Guangdong Guanghua Sci-Tech Co., Ltd., China) and sulfuric acid (Guangzhou Chemical Reagent Factory, China), were of analytical grade.

for the promotion of these methods is the scarce of raw materials. These methods are not suitable for preparing LSNCs by using the abundant industrial lignin, especially alkali lignin (e.g., kraft lignin, soda lignin, etc.) and enzymatic hydrolysis lignin due to weaker interaction with silica. Meanwhile, these lignins are extremely agglomerated during acid-precipitation. Up to now, the most reported studies on the preparation of LSNCs using alkali lignin were focused on multistep methods (Saad and Hawari, 2013; Klapiszewski et al., 2013; Jesionowski et al., 2014a, 2014b; Klapiszewski et al., 2015a, 2015b; Xiong et al., 2015; Jedrzak et al., 2018). Typically the silica was first prepared and modified with expensive and toxic chemicals (e.g., tetraethoxysilane, nonylphenylpolyoxyethylene-glycol ethers, cyclohexane, unsaturated fatty alcohol). Then the modified silicas were combined with silylated or oxidized lignin to prepare the LSNCs, respectively. The preparation process of LSNCs is complicated as well as not economic and environmentally friendly. In contrast, a simple, low cost and eco-friendly one-pot method for the preparation of LSNCs was proposed in our previous study (Xiong et al., 2017). It was found that uniform LSNCs were successfully prepared by a facile coprecipitation of sodium silicate and cationic lignin in an aqueous solution. In this work, the structural change of LSNCs was studied by altering the content of cationic quaternary ammonium (QA) groups grafted into the lignin molecules. The QA groups were derived from the modifiers, 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTMAC). This is a continuous study of our previous work, which fixes the content of QA groups in lignin as a constant (Xiong et al., 2017). We found that enough QA groups could be grafted into lignin when the initial mass ratio of CHPTMAC to lignin was 50 wt.%, and then uniform LSNCs were prepared. The prepared LSNCs based on this synthesized cationic lignin was amorphous and their surfaces mainly consisted of cationic lignin. However, if the initial mass ratio of CHPTMAC to lignin reaches to 60 wt.% or even higher to 80 wt.%, we found that the prepared LSNCs based on these synthesized cationic lignins were also amorphous, while the surface of them were coated by many silica nanoparticles with particle size of ∼10 nm. Best of our knowledge, this special morphology of LSNCs has never been reported in the earlier published papers (Jesionowski et al., 2014a, 2014b; Klapiszewski et al., 2015a, 2015b; Xiong et al., 2017; Jedrzak et al., 2018; Qu et al., 2010; Zhang et al., 2013; Tian et al., 2017; Saad and Hawari, 2013; Klapiszewski et al., 2013; Budnyak et al., 2018). The difference in the surface composition of LSNCs will lead to different physicochemical properties for LSNCs, which helps select the appropriate application fields for LSNCs. This study is beneficial to achieve the high value-added utilization of lignin.

2.2. Synthesis of quaternized kraft lignin (QKL) The aqueous solution (25 wt.%) of KL was heated up to 85 °C in a reactor flask, and CHPTMAC was added dropwise, and then the reaction was continued for 4 h. The pH was monitored and certain amount of aqueous sodium hydroxide was added during the addition of CHPTMAC to ensure that the solution pH was above 11. The condensate of QKL was obtained according to the above procedures. QKL powder was purified via dialysis (dialysis bag) with a cutoff molecular weight of 1000 Da and then dried in an ALPHA1-2 LD plus freeze dryer (Christ Corp., Germany) after vacuum rotary evaporation (Xiong et al., 2017). Four QKL samples, named as QKL30, QKL50, QKL60, and QKL80, were prepared based on the different initial mass ratios of CHPTMAC to lignin, 30 wt.%, 50 wt.%, 60 wt.%, and 80 wt.%, respectively. 2.3. Characterization of QKL The percentage composition of carbon, hydrogen, nitrogen and sulfur of the QKL samples were analyzed by an Elementar Vario EL cube instrument (Elementar Corp., Germany). The phenolic hydroxyl content of QKL samples were detected by FC method. The FT-IR spectra was measured on a Thermo NicoLet 380 Fourier transform infrared spectrometer (Thermo Fisher Corp., USA) based on KBr pellets technique. The FT-IR pattern was available in Supporting Information (Fig. S1). The zeta potential vs. pH was measured by a Zeta potential and laser particle size analyzer (Brookhaven Corp., USA). The measurements were performed in a 0.001 M solution of NaCl and the different pH values were adjusted by HCl (20 wt.%) or NaOH (20 wt.%). The pattern was available in Supporting Information (Fig. S2). 2.4. Preparation of lignin/silica nanocomposites (LSNCs) Na2SiO3·5H2O was dissolved in an ethanol-water mixture (the volume ratio of absolute ethanol to deionized water was 1:6) to form a 0.4 M solution. Then, a certain amount of KL or QKL sample (QKL30, QKL50, QKL60, or QKL80) was added to the solution and the mixture was stirred for 30 min at 35 °C. Subsequently, the pH value of the mixture was adjusted to 10.5 using aqueous ammonium chloride solution (2 M) and then stirred for 3 h. After that, the mixture was adjusted to a pH of 7.0 using aqueous sulfuric acid (20 wt.%) and then stirred for 30 min. After completing the reaction the mixture was kept at 40 °C for 1 h. Finally, the samples were collected by centrifugation, washed several times with neutral deionized water and dried in an oven (Xiong et al., 2017). Five LSNCs, named KL/SiO2, QKL30/SiO2, QKL50/SiO2, QKL60/SiO2, and QKL80/SiO2, were prepared based on the different used lignin samples, AL, QKL30, QKL50, QKL60, and QKL80, respectively.

2. Materials and methods 2.1. Materials Kraft pulping black liquor was supplied by Tiger forest & paper group Co., Ltd. (Hunan province, China). The filter cake of purified kraft lignin (KL) was obtained from the black liquor by following steps: adjusted the pH value of black liquor to 3 with aqueous sulfuric acid (20 wt.%), continuously stirred the suspension for 2 h at 50 °C to facilitate lignin precipitation, after that collected the precipitates by a Büchner funnel and washed several times with deionized water. Some of the filter cake were dried to obtain the KL powder for characterization and the remaining cakes were used to prepared an aqueous solution (25 wt. %) of KL using deionized water and sodium hydroxide (Xiong et al., 2015). The reagents, such as sodium metasilicate pentahydrate (Tianjin Kemiou Chemical Reagent Co., Ltd., China), 60 wt.% 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTMAC) aqueous solution (Shanghai Aladdin Industrial Corp., China), ammonium chloride (Guangzhou Chemical Reagent Factory, China), sodium hydroxide

2.5. Characterization of LSNCs The particle size distributions of LSNCs were achieved by Mastersizer 2000 instruments (Malvern Instruments Ltd., UK). The measurement was conducted on 0.1 wt% suspension, which was prepared by dispersing the LSNCs in ethanol using an ultrasonic cell disruption processor (BILON98-IIIDLG, Shanghai Bilon Instrument Co., Ltd., China) for 5 min. The morphologies of the prepared LSNCs were studied using a field emission scanning electron microscopy (Merlin, Zeiss Corp., Germany) at 5 kV, respectively. The analysis was conducted on suspensions of the samples (0.05 wt%). The samples were suspended in ethanol as the same method described for the test of particle size distribution, and 2

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drops of the suspension were dried on polished silicon wafers and sputter-coated with Au to provide adequate conductivity. High-resolution transmission electron microscopy (TEM, JEM-2100 F, JEOL, Japan) was employed to further characterize the structure of the prepared LSNCs. The phase structures of the prepared LSNCs were characterized by a powder X-ray diffraction (XRD, conducted on a D8 Advance, BrukerAXS) instrument equipped with a Cu Kα radiation source in the 2θ range of 5°–90° with intervals of 0.02°, respectively. The results were presented in Supporting Information (Fig. S3). The FT-IR spectra of LSNCs were measured with the same instrument and method used for the FT-IR test of QKL samples. The pattern was shown in Supporting Information (Fig. S4). X-ray photoelectron spectroscopy (XPS) (ESCALAB 250Xi, Thermo Fisher Corp., UK) was used to confirm the surface compositions of different LSNCs. The pattern was shown in Supporting Information (Fig. S5). The hydrophilicity of LSNCs was evaluated by testing the contact angle of deionized water on LSNCs using a Power Each JC2000C1 static contact angle measurement instrument (Shanghai Zhongchen Digital Technic Apparatus Co., Ltd., China). All samples were successively pressed at 10 MPa to form them into disks before measurement. The specific surface area and pore size distributions of LSNCs were measured on a Tristar II 3020 automated surface area and pore size analyzer (Micromeritics Corp., USA). Specifically, the specific surface area was calculated using Brunauer-Emmett-Teller (BET) equation at P/ P0 < 0.3 (Brunauer et al., 1938; Lin and Haynes, 2010). The BET equation was defined as follows (Brunauer et al., 1938; Ambroz et al., 2018),

Table 1 Essential parameters of KL and the synthesized QKL samples. Samples

KL QKL30 QKL50 QKL60 QKL80

Phenolic hydroxyl content (mmol/g)

3.28 1.70 1.54 1.21 0.90

Elemental content (%)

Isoelectric point (pHi.e.p.)

C

H

N

S

63.21 63.99 65.72 64.92 66.35

5.60 6.72 7.47 7.57 7.91

0.18 1.93 2.47 2.74 2.95

3.22 2.38 2.01 2.35 2.20

– ∼4.7 ∼7.5 ∼9.1 ∼10.0

The representative parameters of different QKL samples, elemental content, phenolic hydroxyl content, and isoelectric point (pHi.e.p.), are listed in Table 1. The phenolic hydroxyl content of different QKL samples (from QKL30 to QKL80) decreased and the content of nitrogen in different QKL samples (from QKL30 to QKL80) increased, showing that the amount of QA groups grafted into KL increased. The negative phenolic hydroxyl groups were consumed, which decreased the electronegativity of lignin molecules. Meanwhile, the increasing amount of grafted QA groups increased the electropositivity of lignin molecules. This dual function leaded to the occurrence of isoelectric point (pHi.e.p.) of QKL. According to Supporting Information (Fig. S2), the pHi.e.p. of QKL30, QKL50, QKL60, and QKL80 were approximately 4.7, 7.5 (Li et al., 2017), 9.1, and 10.0, respectively. This indicated that QKL samples with different content of QA groups were synthesized successfully because the raw material, KL, had no pHi.e.p. (Klapiszewski et al., 2013). 3.2. Structures of the prepared LSNCs

P ∕P0 1 C−1 (P ∕P0) = + n (1 − P ∕P0 ) nm C nm C

3.2.1. Particles size distribution and morphology The particle size distributions and SEM images (low and high magnification) of KL/SiO2, QKL30/SiO2, QKL50/SiO2, QKL60/SiO2, and QKL80/SiO2 are presented in Fig. 1. The particle size of KL/SiO2 was within the range of 0.3−30 μm and 30−300 μm and the big aggregates (circled by the red frame in the SEM image with high magnification) were found in SEM images of KL/SiO2. This meant that it was impracticable to prepare uniform LSNCs by the co-precipitation of KL and sodium metasilicate in aqueous solution. The similar phenomenon also had been found by Saad and Hawari (Saad and Hawari, 2013). The main reason was that the interaction between KL and precipitated silica was too weak and the KL molecules were extremely easy to form agglomerates during acid precipitation. As for QKL30/SiO2, there still have some micron-sized aggregates and irregular particles (circled by the blue frame in the SEM image with high magnification), although the interaction between KL and precipitated silica increased via the introduction of electrostatic force. This suggested that uniform LSNCs also couldn’t be prepared based on the co-precipitation of QKL with low degree of quaternization and sodium metasilicate in aqueous solution. When the degree of quaternization of KL was further increased, uniform LSNCs were successfully prepared, as evidenced by the homogeneous particle size distributions of QKL50/SiO2 (0.3−5 μm), QKL60/SiO2 (0.1−3 μm), and QKL80/SiO2 (0.15−3 μm), respectively. Moreover, the SEM images of QKL50/SiO2, QKL60/SiO2, and QKL80/ SiO2 also provided the corresponding evidences. This demonstrated that strong electrostatic force not only enhance the interaction between KL and precipitated silica but also prevented the self-aggregation of QKL molecules during acid precipitation. According to the SEM images of QKL50/SiO2, QKL60/SiO2, and QKL80/SiO2, there were distinct differences between the morphologies among them. QKL50/SiO2 presented the morphology of homogeneous and spherical particles, while QKL60/ SiO2 and QKL80/SiO2 presented the morphology of spherical particles with many nanoparticles on their surfaces. This kind of special morphology had not been presented in the previous publications (Klapiszewski et al., 2013; Jesionowski et al., 2014a, 2014b; Klapiszewski et al., 2015a, 2015b; Xiong et al., 2015; Xiong et al., 2017;

where P is the pressure, P0 is the saturation pressure of a substance being adsorbed at the adsorption temperature, n is the specific amount of the adsorbed gas at the relative pressure P/P0, nm is the monolayer capacity of the adsorbed gas, and C is the BET constant which is exponentially related to the energy of monolayer adsorption. The pore size distribution was calculated from the branch of the desorption isotherm using a Barrett-Joyner-Halenda (BJH) method. The total pore volume was determined at P/P0 = 0.99 (Brunauer et al., 1938; Lin and Haynes, 2010). 3. Results and discussion 3.1. Essential parameters of the synthesized QKL samples The FT-IR spectra of KL and QKL samples is shown in supporting information (Fig. S1). The reactive site, phenolic hydroxyl in lignin molecules, is responsible for the grafted quaternarization of lignin. Compared with the spectra of KL, the spectra of QKL samples revealed the presence of the characteristic bond CeN (1406 cm−1) (Pal et al., 2005; Fan et al., 2012), which indicated the successful grafted quaternarization. The characteristic peaks of non-conjugated C]O (1705 cm−1) and aromatic ring stretching vibrations (1609 cm−1) shifted to the right (lower wavenumber), while CeH asymmetric deformations (1456 cm−1) in −CH3 and −CH2 shifted to the left (higher wavenumber) after grafted quaternarization occurred. Meanwhile, the characteristic peaks of CeH stretching vibrations in −CH3 and −CH2 (2936 cm−1), C–H stretching vibration in −OCH3 (2849 cm−1), nonconjugated C]O (1705 cm−1), aromatic ring stretching vibrations (1609 and 1508 cm−1), guaiacyl ring breathing with CeO stretching vibration (1269 cm−1), and CeO stretching vibrations of phenolic hydroxyl and phenolic ether (1219 cm−1) were weakened after the grafted quaternarization. It requires additional characterizations to distinguish the different QKL samples because their spectra are similar. 3

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Fig. 1. Particle size distributions and SEM images (low and high magnification) of KL/SiO2, QKL30/SiO2, QKL50/SiO2, QKL60/SiO2, and QKL80/SiO2.

amorphous and homogeneous particles (image b1 and b2), which indicated QKL60 and SiO2 form into hybrid particles during acid precipitation. As for QKL80/SiO2, it seemed that one large hybrid particle consisted of many nanoparticles within 10 nm (image c1 and c2). Hence, the surface roughness of QKL80/SiO2 particle was the highest. The process of recombining nanoparticles to form larger particles should be regulated and controlled by the three-dimensional structure of QKL80 and abundant QA groups in QKL80 providing strong electrostatic interaction. According to the TEM analysis, it could be concluded that moderate degree of quaternization only ensured that QKL and SiO2

Jedrzak et al., 2018). Obviously, the degree of quaternization of KL has significant effect on the formation of LSNCs. 3.2.2. Analyses of micromorphology TEM and XRD are employed to characterize the micromorphology of the uniform LSNCs, QKL50/SiO2, QKL60/SiO2, and QKL80/SiO2. The results are shown in Fig. 2 and supporting information (Fig. S3). According to image a1 and a2, it was found that QKL50/SiO2 consisted of amorphous particles with a homogeneous inner core, QKL/silica hybrids, and a thin outer shell, QKL. QKL60/SiO2 only consisted of

Fig. 2. TEM images of QKL50/SiO2 (a1, a2), QKL60/SiO2 (b1, b2), and QKL80/SiO2 (c1, c2). 4

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could hybridize with each other, but high degree of quaternization supported the hybridization of QKL and SiO2 and control of the growth of SiO2 particles simultaneously. Furthermore, XRD results also showed that QKL50/SiO2, QKL60/SiO2, and QKL80/SiO2 were amorphous materials (Fig. S3, supporting information). 3.2.3. FT-IR, XPS and static contact angle The presence of desired functional groups in QKL50/SiO2, QKL60/ SiO2 and QKL80/SiO2 were confirmed by FT-IR (Fig. S4). Their spectra revealed the presence of the characteristic bonds Si-O-Si (νs: 1091 cm−1, νas: 800 cm−1), Si−OH (νs: 962 cm−1) and Si-O (δ: 466 cm−1), where νs and νas stand for the symmetric and asymmetric stretching vibrations, while δ is the bending vibration (Klapiszewski et al., 2013). Meanwhile, the characteristic peaks from QKL, C–H stretching vibrations in −CH3 and −CH2 (2936 cm−1), CeH stretching vibration in eOCH3 (2849 cm−1), aromatic ring stretching vibrations (1508 cm−1), CeH bending vibration in −CH3 and −CH2 (1468 cm−1) and CeN stretching vibration (1406 cm−1), were also presented in their spectra. The characteristic peaks from QKL were more distinct in the spectra of QKL60/SiO2 and QKL80/SiO2 compared to that of QKL50/SiO2. The results of FT-IR confirmed the successful preparation of LSNCs (QKL50/ SiO2, QKL60/SiO2 and QKL80/SiO2) combined with the results of SEM and TEM. According to the results of SEM and TEM, the surfaces of QKL50/ SiO2, QKL60/SiO2 and QKL80/SiO2 were different from each other. XPS was used to analyze the elemental compositions of these different surfaces of LSNCs. The results are presented in Table 2 and supporting information (Fig. S5). The content of carbon decreased significantly, while the contents of oxygen and silicon increased dramatically with the increasing amount of grafted QA groups. Meanwhile, the content of nitrogen also increased gradually. Based on the results of SEM, TEM and XPS, the regulation process of the formation of LSNCs by changing the content of QA groups grafted into KL was as follows: the electrostatic force provided by QKL50 with moderate content of QA groups only could support the in situ growth of silica and hybridization of silica and QKL50, resulting in a morphology of spherical composite particles; however, when the strong electrostatic force was provided by QKL with high content of QA groups, the in situ hybridization of silica and QKL80 was still going on, while the in situ growth of silica was suppressed. The primary small QKL/SiO2 hybrid particles were reconstructed into large QKL/SiO2 nanocomposite particles with particle size in the range of 100−300 nm. This process was the result of dual function of strong electrostatic interaction between QKL80 and primary silica nanoparticles and regulation by the three-dimensional structure of QKL80. In addition, the increased value of Si/C indicated that the surface of LSNCs contained more silica with increased amount of grafted QA groups. This leaded the increase in hydrophilicity of LSNCs, which was evidenced by the gradually decrease in the value of static contact angle presented in Supporting Information (Fig. S6).

Fig. 3. (a) N2 adsorption-desorption isotherms and (b) pore volume curves of different LSNCs.

3.2.4. BET analysis The surface areas of different LSNCs (QKL50/SiO2, QKL60/SiO2 and QKL80/SiO2) were determined by measuring N2 adsorption-desorption isotherms and application of BET modeling, and those corresponding pore volume distributions were analyzed by Barrett–Joyner–Halenda (BJH) method using desorption isotherm data. As shown in Fig. 3a, a

hysteresis loop was found in the adsorption-desorption isotherm of each LSNCs, which resembled type IV of Brunauer’s classification (Brunauer et al., 1938). This type of adsorption-desorption isotherm meant the presence of mesopores and the different hysteresis loops were related to different textural properties. The adsorption-desorption isotherm of QKL50/SiO2 was similar to those of LSNCs in the previous works (Qu et al., 2010; Tian et al., 2017). This indicated that LSNCs with correspondingly smooth surfaces showed similar textural properties. However, the adsorption-desorption isotherms of QKL60/SiO2 and QKL80/ SiO2 were different from the normal shape of reported LSNCs. It was found that their adsorption-desorption isotherms also presented rapid increase in amount of nitrogen adsorption at high relative pressure (P/ P0 > 0.95) except containing a hysteresis loop. This suggested that LSNCs with rough surface like QKL60/SiO2 and QKL80/SiO2 produced more large pores due to the particle packing. According to the pore volume curves in Fig. 3b, QKL50/SiO2 had mesopores within the range of 2−10 nm and most of them is 2−3 nm. For QKL60/SiO2 and QKL80/SiO2, they had little amount of mesopores within the range of 2−4 nm and large amount of mesopores within the range of 4−20 nm. The size of most mesopores in QKL60/SiO2 and QKL80/SiO2 is 6−8 nm and 7−10 nm, respectively, which were larger than that of QKL50/SiO2. The higher value in BET surface area of QKL50/SiO2 was due to the higher ratio of micropore, according to the summary presented in Supplementary Table S1.

Table 2 Elemental composition from XPS analysis.

4. Conclusions

Samples

QKL50/SiO2 QKL60/SiO2 QKL80/SiO2

Atomic content (%)

Si / C

C

O

Si

N

64.99 53.61 48.75

26.35 32.86 35.55

5.53 10.42 12.42

2.95 3.10 3.28

With QKL as a structure directing reagent and sodium metasilicate as a source of silica, LSNCs with different structures were prepared via a green co-precipitation method. The structural change of LSNCs depended on the degree of quaternization of lignin. Only the lignins with moderate and high degree of quaternization ensured the formation of uniform LSNCs. When the lignin with moderate degree of

0.085 0.194 0.255

5

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quaternization (QKL50) was used, the LSNCs presented spherical particles with core-shell structure, most particle size of 100−400 nm, and most mesopore size of 2−3 nm. However, the LSNCs prepared from lignin with high degree of quaternization (QKL80) presented spherical particles with strawberry-like structure, most particle size of 100−300 nm, and most mesopore size of 7−10 nm. These LSNCs with different structures have potential application of UV-absorbent additives, green sorbents, electrode additives for batteries, etc.

Biointerfaces 134, 220–228. Klapiszewski, Ł., Siwińska-Stefańska, K., Kołodyńska, D., 2017. Development of lignin based multifunctional hybrid materials for Cu(II) and Cd(II) removal from the aqueous system. Chem. Eng. J. 330, 518–530. Laurichesse, S., Avérous, L., 2014. Chemical modification of lignins: towards biobased polymers. Prog. Polym. Sci. 39, 1266–1290. Li, Y., Qiu, X., Qian, Y., Xiong, W., Yang, D., 2017. pH-responsive lignin-based complex micelles: preparation, characterization and application in oral drug delivery. Chem. Eng. J. 327, 1176–1183. Li, Z., Kong, Y., Ge, Y., 2015. Synthesis of porous lignin xanthate resin for Pb2+ removal from aqueous solution. Chem. Eng. J. 270, 229–234. Lievonen, M., Valle-Delgado, J.J., Mattinen, M.-L., Hult, E.-L., Lintinen, K., Kostiainen, M.A., Paananen, A., Szilvay, G.R., Setälä, H., Österberg, M., 2016. A simple process for lignin nanoparticle preparation. Green Chem. 18, 1416–1422. Lin, Y.-S., Haynes, C.L., 2010. Impacts of mesoporous silica nanoparticle size, pore ordering, and pore integrity on hemolytic activity. J. Am. Chem. Soc. 132, 4834–4842. Liu, X., Wang, J., Li, S., Zhuang, X., Xu, Y., Wang, C., Chu, F., 2014. Preparation and properties of UV-absorbent lignin graft copolymer films from lignocellulosic butanol residue. Ind. Crops Prod. 52, 633–641. Nair, S.S., Sharma, S., Pu, Y., Sun, Q., Pan, S., Zhu, J.Y., Deng, Y., Ragauskas, A.J., 2014. High shear homogenization of lignin to nanolignin an thermal stability of nanoligninpolyvinyl alcohol blends. ChemSusChem 7, 3513–3520. Pal, S., Mal, D., Singh, R.P., 2005. Cationic starch: an effective flocculating agent. Carbohyd. Polym. 59, 417–423. Qian, Y., Deng, Y., Qiu, X., Li, H., Yang, D., 2014. Formation of uniform colloidal spheres from lignin, a renewable resource recovered from pulping spent liquor. Green Chem. 16, 2156–2163. Qian, Y., Qiu, X., Zhong, X., Zhang, D., Deng, Y., Yang, D., Zhu, S., 2015a. Lignin reverse micelles for UV-Absorbing and high mechanical performance thermoplastics. Ind. Eng. Chem. Res. 54, 12025–12030. Qian, Y., Qiu, X., Zhu, S., 2015b. Lignin: a nature-inspired sun blocker for broadspectrum sunscreens. Green Chem. 17, 320–324. Qian, Y., Zhong, X., Li, Y., Qiu, X., 2017. Fabrication of uniform lignin colloidal spheres for developing natural broad-spectrum sunscreens with high sun protection factor. Ind. Crops Prod. 101, 54–60. Qu, Y., Tian, Y., Zou, B., Zhang, J., Zheng, Y., Wang, L., Li, Y., Rong, C., Wang, Z., 2010. A novel mesoporous lignin/silica hybrid from rice husk produced by a sol-gel method. Bioresour. Technol. 101, 8402–8405. Richter, A.P., Brown, J.S., Bharti, B., Wang, A., Gangwal, S., Houck, K., Hubal, E.A.C., Paunov, V.N., Stoyanov, S.D., Velev, O.D., 2015. An environmentally benign antimicrobial nanoparticle based on a silver-infused lignin core. Nature Nanotech. 10, 817–824. Saad, R., Hawari, J., 2013. Grafting of lignin onto nanostructured silica SBA-15: preparation and characterization. J. Porous Mater. 20, 227–233. Supanchaiyamat, N., Jetsrisuparb, K., Knijnenburg, J.T.N., Tsang, D.C.W., Hunt, A.J., 2019. Lignin materials for adsorption: current trend, perspectives and opportunities. Bioresour. Technol. 272, 570–581. Tang, Q., Zhou, M., Li, Y., Qiu, X., Yang, D., 2018. Formation of uniform colloidal spheres based on lignosulfonate, a renewable biomass resource recovered from pulping spent liquor. ACS Sustainable Chem. Eng. 6, 1379–1386. Thakur, S., Govender, P.P., Mamo, M.A., Tamulevicius, S., Mishra, Y.K., Thakur, V.K., 2017. Progress in lignin hydrogels and nanocomposites for water purification: future perspectives. Vacuum 146, 342–355. Thakur, V.K., Thakur, M.K., 2015. Recent advances in green hydrogels from lignin: a review. Int. J. Biol. Macromol. 72, 834–847. Thakur, V.K., Thakur, M.K., Raghavan, P., Kessler, M.R., 2014. Progress in green polymer composites from lignin for multifunctional applications: a review. ACS Sustainable Chem. Eng. 2, 1072–1092. Tian, W., Li, H., Zhou, J., Guo, Y., 2017. Preparation, characterization and the adsorption characteristics of lignin/silica nanocomposites from cellulosic ethanol residue. RSC Adv. 7, 41176–41181. Tuck, C.O., Pérez, E., Horváth, I.T., Sheldon, R.A., Poliakoff, M., 2012. Valorization of biomass: deriving more value from waste. Science 337, 695–699. Upton, B.M., Kasko, A.M., 2016. Strategies for the conversion of lignin to high-value polymeric materials: review and perspective. Chem. Rev. 116, 2275–2306. Wang, H., Lin, W., Qiu, X., Fu, F., Zhong, R., Liu, W., Yang, D., 2018. In situ synthesis of flowerlike lignin/ZnO composite with excellent UV-absorption properties and its application in polyurethane. ACS Sustainable Chem. Eng. 6, 3696–3705. Wang, H., Pu, Y., Ragauskas, A., Yang, B., 2019. From lignin to valuable products–strategies, challenges, and prospects. Bioresour. Technol. 271, 449–461. Xiong, W., Qiu, X., Yang, D., Zhong, R., Qian, Y., Li, Y., Wang, H., 2017. A simple one-pot method to prepare UV-absorbent lignin/silica hybrids based on alkali lignin from pulping black liquor and sodium metasilicate. Chem. Eng. J. 326, 803–810. Xiong, W., Qiu, X., Zhong, R., Yang, D., 2016. Characterization of the adsorption properties of a phosphorylated kraft lignin-based polymer at the solid/liquid interface by the QCM-D approach. Holzforschung 70, 937–945. Xiong, W., Yang, D., Zhong, R., Li, Y., Zhou, H., Qiu, X., 2015. Preparation of lignin-based silica composite submicron particles from alkali lignin and sodium silicate in aqueous solution using a direct precipitation method. Ind. Crops Prod. 74, 285–292. Zhang, X., Zhao, Z., Ran, G., Liu, Y., Liu, S., Zhou, B., Wang, Z., 2013. Synthesis of ligninmodified silica nanoparticles from black liquor of rice straw pulping. Powder Technol. 246, 664–668.

Declaration of Competing Interest All the authors declare no competing financial interest. Acknowledgments This research is financially supported by the National Natural Science Foundation of China (21908205, 21878114, 21690083), Natural Science Foundation of Guangdong Province of China (2018B030311052, 2017B090903003), Program of Processing and Efficient Utilization of Biomass Resources of Henan Center for Outstanding Overseas Scientists (GZS2018004). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.indcrop.2019.112039. References Ambroz, F., Macdonald, T.J., Martis, V., Parkin, I.P., 2018. Evaluation of the BET theory for the characterization of meso and microporous MOFs. Small Methods 2, 1800173. Aro, T., Fatehi, P., 2017. Production and application of lignosulfonates and sulfonated lignin. ChemSusChem 10, 1861–1877. Brunauer, S., Emmett, P.H., Teller, E., 1938. Adsorption of gases in multimolecular layers. J. Am. Chem. Soc. 60, 309–319. Budnyak, T.M., Aminzadeh, S., Pylypchuk, I.V., Riazanova, A.V., Tertykh, V.A., Lindström, M.E., Sevastyanova, O., 2018. Peculiarities of synthesis and properties of lignin-silica nanocomposites prepared by sol-gel method. Nanomaterials 8, 950. Deng, Y., Zhao, H., Qian, Y., Lü, L., Wang, B., Qiu, X., 2016. Hollow lignin azo colloids encapsulated avermectin with high anti-photolysis and controlled release performance. Ind. Crops Prod. 87, 191–197. Doherty, W.O.S., Mousavioun, P., Fellows, C.M., 2011. Value-adding to cellulosic ethanol: lignin polymers. Ind. Crops Prod. 33, 259–276. Dong, X., Dong, M., Lu, Y., Turley, T., Jin, T., Wu, C., 2011. Antimicrobial and antioxidant activities of lignin from residue of corn stover to ethanol production. Ind. Crops Prod. 34, 1629–1634. Fan, L., Cao, M., Gao, S., Wang, W., Peng, K., Tan, C., Wen, F., Tao, S., Xie, W., 2012. Preparation and characterization of a quaternary ammonium derivative of pectin. Carbohyd. Polym. 88, 707–712. Huang, S., Su, S., Gan, H., Wu, L., Lin, C., Xu, D., Zhou, H., Lin, X., Qin, Y., 2019. Facile fabrication and characterization of highly stretchable lignin-based hydroxyethyl cellulose self-healing hydrogel. Carbohyd. Polym. 223, 115080. https://doi.org/10. 1016/j.carbpol.2019.115080. Jedrzak, A., Rębiś, T., Klapiszewski, Ł., Zdarta, J., Milczarek, G., Jesionowski, T., 2018. Carbon paste electrode based on functional GOx/silica-lignin system to prepare an amperometric glucose biosensor. Sens. Actuators B Chem. 256, 176–185. Jesionowski, T., Klapiszewski, Ł., Milczarek, G., 2014a. Kraft lignin and silica as precursors of advanced composite materials and electroactive blends. J. Mater. Sci. 49, 1376–1385. Jesionowski, T., Klapiszewski, Ł., Milczarek, G., 2014b. Structural and electrochemical properties of multifunctional silica/lignin materials. Mater. Chem. Phys. 147, 1049–1057. Kai, D., Tan, M.J., Chee, P.L., Chua, Y.K., Yap, Y.L., Loh, X.J., 2016. Towards lignin-based functional materials in a sustainable world. Green Chem. 18, 1175–1200. Klapiszewski, Ł., Bartczak, P., Wysokowski, M., Jankowska, M., Kabat, K., Jesionowski, T., 2015a. Silica conjugated with kraft lignin and its use as a novel ‘green’ sorbent for hazardous metal ions removal. Chem. Eng. J. 260, 684–693. Klapiszewski, Ł., Nowacka, M., Milczarek, G., Jesionowski, T., 2013. Physicochemical and electrokinetic properties of silica/lignin biocomposites. Carbohyd. Polym. 94, 345–355. Klapiszewski, Ł., Rzemieniecki, T., Krawczyk, M., Malina, D., Norman, M., Zdarta, J., Majchrzak, I., Dobrowolska, A., Czaczyk, K., Jesionowski, T., 2015b. Kraft lignin/ silica–AgNPs as a functional material with antibacterial activity. Colloids Surf. B

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