Efficient entrapment and separation of anionic pollutants from aqueous solutions by sequential combination of cellulose nanofibrils and halloysite nanotubes
Graphical abstract
Introduction
Clays are naturally occurring inorganics, composed primarily of phyllosilicate minerals such as kaolinite and montmorillonite [1]. The atoms in phyllosilicates are arranged in tetrahedral and octahedral sheets that typically form layered and bulky platelets. Tubules, fibers, and laths of various sizes also exist [1]. Halloysite nanotubes (HNTs) are two-layered clay mineral particles with a chemical composition [Al2Si2O5(OH)4·nH2O] similar to that of kaolinite [Al2Si2O5(OH)4] [2]. However, in contrast to platy kaolinite, HNTs typically have a hollow tubular morphology [2]. The tube walls of HNTs comprise ~15–20 aluminosilicate layers, with a spacing ranging from 1.0 nm (in hydrated form, n = 2) to 0.7 nm (in dehydrated form, n = 0) [3]. HNTs are polydisperse in size, typically having an outer diameter of 50–70 nm, lumen diameter of 10–20 nm, and length ranging from 0.5 to 1.5 µm [3]. The external surface and the inner lumen of HNTs carry different charges at pH 2–8 in water [4], the former comprising negatively charged silica (SiO2, ζ-potential ~ −50 mV) [5] and the latter comprising positively charged alumina (Al2O3, ζ-potential ~ +20 mV) [5]. The experimentally determined ζ-potential of HNTs in water at pH 4–8 is ~ −30 mV, which reflects the charge difference of these two layers [5]. Besides being abundant and inexpensive, HNTs have low in vitro [6] and in vivo [7] toxicity.
HNTs are versatile materials that can interact with and adsorb many different substances, thanks to the charge difference between the inner and outer surfaces. Driven by cationic electrostatic interactions, neutral and anionic substances can be loaded into the lumen of HNTs [3], [8], [9]. In addition, cationic substances can be adsorbed on the external surface of the tube [3], [9]. Sometimes substances can even be intercalated between the layers of the tubes’ walls [10]. Currently, HNTs are widely studied for biomedical purposes [11], [12], [13], but their potential for environmental applications has hitherto been underexplored. HNTs have been shown to adsorb e.g. anionic and cationic dyes [14], [15], [16], metal ions [17], [18], [19] and pharmaceuticals [20], [21]. Therefore, one potential environmental application of HNTs is the treatment of various kinds of polluted waters [22], [23]. The separation of nano-sized clay particles from water after the treatment and the hindered water flux in the packed column structures is often a challenge [24], although approaches, such as magnetic HNT adsorbents [25], [26], [27], have emerged.
To overcome these drawbacks, HNTs have often been combined with natural or synthetic polymers to form, for instance, beads [28], [29], [30], [31], sponges [32] or membranes [33], [34], [35], [36], [37]. However, these methods typically require a significant amount of time and the use of additional chemicals. In a more straightforward approach, clay minerals have simply been mixed with a polymer to yield clay-polymer nanocomposites, which are then directly used for wastewater purification [38], [39]. In another study, pristine HNTs were combined with a synthetic cationic polymer for the removal of a cationic dye, basic blue 7, from water [24]. The mixing of HNTs with the polymer resulted in aggregation [40] and the formation of a HNT–polymer hybrid material, which was used as a matrix in column filtration of a dye solution. Although the hybrid was easily separated from water and transferred to a column, its dye removal performance was not optimum, as the cationic polymer covered the anionic surface of the HNTs, suggesting that better performance may be obtained if the HNTs are added to the treated mixture before the polymer is added.
Clays in general have been shown to adsorb, for instance, natural organic matter (NOM), thus converting it to an insoluble form, which can then be removed by coagulation–flocculation processes using a cationic polymer [41]. The polymer itself also participates in the purification process by partly adsorbing NOM and forming precipitates [41]. However, there is a lack of studies expanding this concept for the removal of dissolved molecules (e.g., micropollutants) from water, possibly because the conventional coagulation–flocculation treatment has previously been declared inefficient for simultaneous micropollutant removal [42]. In addition, new and effective bio-based materials are needed to replace older synthetic polymers. One promising candidate is cellulose nanofibrils (CNFs), which are elongated and flexible nanomaterials originating from, for example, the mechanical refining of wood pulp or a combination of chemical/enzymatic treatments and mechanical force [43]. Depending on the raw material and the production method, the width of CNFs is typically 5–60 nm, and the length is a few micrometers [44]. In addition, the CNFs be functionalized with e.g. anionic carboxylic groups [45], [46], [47], [48] or cationic groups [49], [50], [51], [52], [53], [54], [55]. These functionalized CNFs can be designed using green solvent systems, such as recyclable deep eutectic solvents (DESs) [49].
In this study, we present a novel sequential approach that combines nanostructured clay and cellulose materials for the removal of small, anionically charged dye molecules from water. HNTs were first loaded with dye molecules and then aggregated using CNFs to enable their efficient separation through sedimentation. CNFs also played a role in the removal of dye molecules through adsorption. The cationic CNFs were produced through sequential periodate oxidation and DES-mediated functionalization from cellulose and combined with HNTs for the enhanced removal of aqueous anionic dye chrome azurol S (CAS). Kaolin clay was used as a reference material in adsorption experiments. The effects of CNF dose, pH and mixing time on the dye and turbidity removal were investigated. The chemical characteristics, sizes, and morphologies of the HNTs, CNFs, and kaolin were analyzed using polyelectrolyte titration, diffuse reflectance infrared transform spectroscopy (DRIFT), wide-angle X-ray diffraction (WAXD), laser diffraction (LS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).
Section snippets
Raw materials and chemicals
Commercial softwood dissolving pulp (cellulose 96.2%, hemicelluloses 3.5%, total lignin < 0.5%, acetone soluble extractives 0.17%; Domsjö Fabriker AB, Sweden) was used as the cellulose raw material. The dry sheets were disintegrated in deionized water before use. LiCl (Reag. Ph. Eur.; VWR, Belgium), sodium metaperiodate (<99.8%; Honeywell/Fluka, USA), glycerol (Reag. Ph. Eur.; VWR, Belgium), aminoguanidine hydrochloride (>98%; TCI, Japan), and ethanol (96%; VWR, France) were used in the
Effect of CNF dose on the combined dye removal process
A significant difference was observed between HNTs and kaolin in CAS removal at pH 7 (Fig. 1). Combining 25 mg CNFs with 1 g HNTs (i.e., CNF dose 25 mg/g) resulted in maximum CAS removal of 80% (qe 19 mg/g), whereas with kaolin only 43% (qe 11 mg/g) removal was achieved. Interestingly, HNTs alone removed 42% of CAS (qe 10 mg/g), but kaolin alone removed only 7% of CAS (qe 2 mg/g). As the CNF dose increased from 2.5 to 25 mg/g, the trend of removal was almost linear, indicating that complete
Conclusions
The sequential combination HNTs and CNFs resulted in significantly improved removal of anionic dye compared with using either of them alone. The size and morphology of the clay mineral had a clear impact on the outcome, as the nano-sized HNTs performed better than the micro-sized kaolin. The demonstrated concept is simple and requires no chemical pretreatments of the clay mineral (e.g., tube etching) or heavy energy usage (e.g., drying, vacuum). Moreover, both nanomaterials are abundantly
Acknowledgements
Ms. Eveliina Kuorikoski is acknowledged for her assistance in the laboratory experiments and Mr. Panpan Li is acknowledged for his advice in the preparation of CNFs. We would also like to thank Mr. Jarno Karvonen for performing the LS measurements, Mrs. Kaisu Ainassaari for performing the BET analysis, Mr. Marcin Selent from the Center of Microscopy and Nanotechnology at the University of Oulu for performing the XRD measurements, and Mr. Jens Kling for performing the high-resolution TEM imaging
Funding
This work was supported by the Advanced Materials Doctoral Program of the University of Oulu Graduate School and the Bionanochemicals project of the Academy of Finland [grant number 298295].
References (82)
- et al.
Chapter 1 general introduction: clays, clay minerals, and clay science
- et al.
An assembly of organic-inorganic composites using halloysite clay nanotubes
Curr. Opin. Coll. Interface Sci.
(2018) - et al.
Colloidal stability of halloysite clay nanotubes
Ceram. Int.
(2019) - et al.
Study on the adsorption of Neutral Red from aqueous solution onto halloysite nanotubes
Water Res.
(2010) - et al.
Adsorption behavior of methylene blue on halloysite nanotubes
Micropor. Mesopor. Mater.
(2008) High removal capacity of silver ions from aqueous solution onto Halloysite nanotubes
Appl. Clay Sci.
(2014)- et al.
Kinetics of release and antibacterial activity of salicylic acid loaded into halloysite nanotubes
Appl. Clay Sci.
(2018) - et al.
A review on halloysite-based adsorbents to remove pollutants in water and wastewater
J. Mol. Liq.
(2018) - et al.
Fabrication of β-cyclodextrin conjugated magnetic HNT/iron oxide composite for high-efficient decontamination of U(VI)
Chem. Eng. J.
(2013) - et al.
Magnetic halloysite nanotubes/iron oxide composites for the adsorption of dyes
Chem. Eng. J.
(2011)
Core@double-shell structured magnetic halloysite nanotube nano-hybrid as efficient recyclable adsorbent for methylene blue removal
Chem. Eng. J.
The removal of dye from aqueous solution using alginate-halloysite nanotube beads
Chem. Eng. J.
Adsorption of dyes in aqueous solutions by chitosan–halloysite nanotubes composite hydrogel beads
Micropor. Mesopor. Mater.
Alginate/PAMAM dendrimer – halloysite beads for removal of cationic and anionic dyes
Int. J. Biol. Macromol.
Alginate gel beads filled with halloysite nanotubes
Appl. Clay Sci.
Chitosan based nano composite adsorbent—Synthesis, characterization and application for adsorption of binary mixtures of Pb(II) and Cd(II) from water
Carbohydr. Polym.
Efficient treatment of hazardous reactive dye effluents through antifouling polyetherimide hollow fiber membrane embedded with functionalized halloysite nanotubes
J. Taiwan Inst. Chem. Eng.
Fabrication of polyetherimide nanocomposite membrane with amine functionalised halloysite nanotubes for effective removal of cationic dye effluents
J. Taiwan Inst. Chem. Eng.
Application of dopamine-modified halloysite nanotubes/PVDF blend membranes for direct dyes removal from wastewater
Chem. Eng. J.
Novel polyvinylidene fluoride nanofiltration membrane blended with functionalized halloysite nanotubes for dye and heavy metal ions removal
J. Hazard. Mater.
Clarification of olive mill and winery wastewater by means of clay–polymer nanocomposites
Sci. Total Environ.
Cationic polymer and clay or metal oxide combinations for natural organic matter removal
Water Res.
Occurrence and removal of pharmaceuticals and hormones through drinking water treatment
Water Res.
Recent advances in surface-modified cellulose nanofibrils
Prog. Polym. Sci.
A simple approach to prepare carboxycellulose nanofibers from untreated biomass
Biomacromolecules
Recyclable deep eutectic solvent for the production of cationic nanocelluloses
Carbohydr. Polym.
Synthesis of highly cationic water-soluble cellulose derivative and its potential as novel biopolymeric flocculation agent
Carbohydr. Polym.
Cationization of lignocellulosic fibers with betaine in deep eutectic solvent: facile route to charge stabilized cellulose and wood nanofibers
Carbohydr. Polym.
Cationic nanofibrillar cellulose with high antibacterial properties
Carbohydr. Polym.
Periodate oxidation of cellulose at elevated temperatures using metal salts as cellulose activators
Carbohydr. Polym.
Flocculation performance of a cationic biopolymer derived from a cellulosic source in mild aqueous solution
Bioresour. Technol.
Fabrication of cationic cellulosic nanofibrils through aqueous quaternization pretreatment and their use in colloid aggregation
Carbohydr. Polym.
Rapid uptake of pharmaceutical salbutamol from aqueous solutions with anionic cellulose nanofibrils: the importance of pH and colloidal stability in the interaction with ionizable pollutants
Chem. Eng. J.
Halloysite nanotubule clay for efficient water purification
J. Colloid Interface Sci.
Flocculation and dewatering of kaolin suspensions in the presence of polyacrylamide and surfactants
Int. J. Miner. Process.
Selective loading of 5-fluorouracil in the interlayer space of methoxy-modified kaolinite for controlled release
Appl. Clay Sci.
Surfactant adsorption to soil components and soils
Adv. Colloid Interface Sci.
Synthesis and antimicrobial activity of polymeric guanidine and biguanidine salts
Polymer
A study of crystallinity changes in oxidised celluloses
Polym. Degrad. Stab.
Orientation of charged clay nanotubes in evaporating droplet meniscus
J. Colloid Interface Sci.
Trapping characteristic of halloysite lumen for methyl orange
Appl. Surf. Sci.
Cited by (18)
Functionally modified halloysite nanotubes for personalized bioapplications
2023, Advances in Colloid and Interface ScienceCitation Excerpt :The typical tubular morphology and structure are shown in Fig. 1B. The particle size distribution of HNTs ranges from submicron to micron, and the ζ-potential (zeta potential) of HNTs remains negative (∼ −30 mV) at pH 4–8 [57], with the surface charge in the tube lumen is positive and opposite on the external surface which allows for the selective loading of negatively charged molecules inside the HNTs lumen and positively charged molecules bonded on the external surface (Fig. 1C) [58]. For water solubility, HNTs are often hydrophilic in nature because of the hydrophilic Si-OH groups of the clay surface [59].
A review of nanocellulose adsorptive membrane as multifunctional wastewater treatment
2022, Carbohydrate PolymersSeparation of halloysite/kaolinite mixtures in water controlled by sucrose addition: The influence of the attractive forces on the sedimentation behavior
2022, Colloids and Surfaces A: Physicochemical and Engineering AspectsCitation Excerpt :Inner and outer surfaces can be selectively modified by exploiting covalent and supramolecular interactions [15–18]. Accordingly, halloysite nanotubes have been developed as carriers for controlled release of active agents [19–32], as fillers for polymers [33–39] and for decontamination purposes [40–45]. Due to its high specific surface, halloysite was used as catalytic support for technological applications [46–54].
Adsorption modeling of microcrystalline cellulose for pharmaceutical-based micropollutants
2022, Journal of Hazardous MaterialsCitation Excerpt :For example, Balasubramani et al. (2020) developed a graphene oxide/cellulose nanogel composite to adsorb a drug flupentixol, wherein the role of cellulose was to sandwich the graphene oxide. Selkala et al. (2018, 2019) prepared tubular halloysite nanotubes and flexible cellulose nanofibrils to remove anionic micropollutants. In addition, to improve the adsorption properties of cellulose for pollutants, their chemical structure was modified or the cellulose was carbonized (Phan et al., 2006).
Dispersion Properties of Nanocellulose: A Review
2020, Carbohydrate PolymersCitation Excerpt :Traditional mechanical methods consume significant energy due to the large number of surface hydroxyl groups that generate vast hydrogen bond interactions among nanofibrils. To overcome this problem, some biological or chemical pretreatments have be adopted during the process of mechanical treatment (Mittal et al., 2018; Rol, Belgacem, Gandini, & Bras, 2019; Selkälä et al., 2019). Most CNFs have lengths in the micron scale and widths ranging from 10 to a few hundred nanometers (Habibi, 2014)().
Synthesis of porous activated carbon powder formation from fruit peel and cow dung waste for modified electrode fabrication and application
2020, Biomass and BioenergyCitation Excerpt :Waste polymer plastic bottles were carbonized and activated using KOH or NaOH to develop porous carbons materials and they studied the activity of prepared carbon materials for CO2 storage applications [12]. The potential use of agricultural waste sources with additional treatment for the removal of anionic pollutants such as chlorides, fluorides etc., from water was examined [14–16]. In another related study, ultrasonic method is adopted to prepare the porous carbon materials derived from agricultural waste and tested their activity for electro chemical super capacitor application [17,18].