key: cord-0702976-v3vsgm98 authors: Qi, Pengfei; Zeng, Jianqiang; Tong, Xiaohua; Shi, Junjie; Wang, Yan; Sui, Kunyan title: Bioinspired synthesis of fiber-shaped silk fibroin-ferric oxide nanohybrid for superior elimination of antimonite date: 2020-09-11 journal: J Hazard Mater DOI: 10.1016/j.jhazmat.2020.123909 sha: f6a63b9abebe8e0363ba6f1cbbd49586fcba6b90 doc_id: 702976 cord_uid: v3vsgm98 Bioinspired fibrous materials have emerged as a unique class of matrix for fabrication of fiber-shaped nanomaterial assemblies. Here, we report a novel functional fiber-shaped nanohybrid for efficient removal of antimonite via in situ synthesis of ferric oxides anchored to silk nanofibril. The silk nanofibril matrix played important roles in the growth of ferric oxides via metal-ligand interactions. The achieved nanocomposites had high surface areas and activity with more functional groups, contributing to superior antimonite elimination. The nanocomposite achieved a maximum removal capacity of 159.9 mg/g toward antimonite. And the common interfering ions of SO(4)(2-), NO(3)-, CO(3)(2-), PO(4)(3-) and SiO(3)(2-) exhibited negligible influence on antimonite removal. The mechanism study point that two factors are closely involved: surface complexation and hydrogen bonding. Benefiting from the low cost and environmental-friendly nature of silk fibroin as well as excellent removal capacity and high selectivity, it suggests that the nanohybrids might be promising for antimonite extraction from contaminated water. and harsh living conditions, for example, the proliferating Novel Coronavirus around the whole world in 2020. As the source of life, safe and clean drinking water is crucial for human life and health, however, the water quality is deteriorated due to natural processes and anthropological activities. Thus, this is especially urgent to capture the highly toxic heavy metals which are easy to migrate and accumulate in organisms such as antimonite. Antimonite, generally existed as Sb(OH)3, is the most toxic species of antimony. Among the existing removal technologies, adsorption is still one of the most intriguing methods for antimony removal involving strong practicality, simplicity and high efficiency [1] . However, the removal efficiency is still not satisfying. Thus, the development of environmental-friendly and low-cost materials with high antimonite loading capacity are highly desirable. Recently, various kinds of nano materials have been developed for antimony removal, including metal organic frameworks [2] [3] [4] , titanate nanotube [5, 6] and nanosized metal (hydro)oxides such as iron, zirconium and manganese oxides [7] [8] [9] . The most representative of nanostructured ferric oxides have attracted significant attention for capturing of antimonite due to the properties of low cost, high abundance, large surface area and high reactivity [10] . However, the natural nanostructured ferric oxides may instable and transfer to other types of iron oxides with good crystallinity, leading to a lower surface area and lower reactivity. Manipulating the structure and morphology of the ferric oxide using templates could be reasonable to enhance the removal capacity for antimonite. For example, iron oxide was loaded on the biochar fiber to prepare a nanoneedle type of composite with high adsorption capacity for As(V) [11] . The hydrated ferric oxide nanoparticles encapsulated inside porous matrixes such as resins and granular activated carbon had a stronger binding ability with Cu(II) ions than the pure hydrated ferric oxides [12] . Among these templates, natural fibers could exhibit special properties due to their large surface areas and high surface-volume ratio. And it could be feasible to enhance the removal capacity of antimonite by the functional nanohybrid combining the properties of natural fibers and ferric oxides. Silk fibroin (SF) is a natural polymer extracted from Bombyx mori silkworm containing J o u r n a l P r e -p r o o f abundant amino acid residues and deserving unique hierarchical structures [13, 14] . The silk fibroin has unique sequence self-assembly behaviors with abundant hydrophilic moieties such as hydroxyl groups, carboxyl groups, amino groups and acylamino groups, which are prone to assemble with metal ions and small molecular to design novel nanohybrids such as Fe3O4/SF nanoparticles [15, 16] , hematite [17] , copper oxide [18] , hydroxyapatite [19] , SF/silver nanowire composite [20] and Au nanoparticles@SF hybrid materials [21] . Also, the various amine-based functional groups are beneficial in the removal of heavy metals [22] . Nowadays, the silk nanofibril was usually obtained by dissolving the silk fibroin in high concentrated salt solution or in a ternary organic/inorganic solvent and then dialyzing it, however, the silk nanofibrils obtained by the strong degradation methods are not easy to control and could generate random coils. More unfortunately, there has been no study reported on the capture of antimonite by the ferric-based nanocomposite using the SNF as templates obtained by weak dissolution methods. Herein, we firstly used a modified gentle enzymatical degradation method consisting of urea and guanidine hydrochloride to extract the silk fibroin [23] . The nanocomposite was then designed by in situ synthesis of ferric oxides anchored to silk fibroin. The structure and morphology of the nanocomposite was characterized, and the performance for elimination of antimonite was evaluated. Finally, deep insights were focused on the antimonite binding mechanism. All chemicals used in this study were of analytical grade. Sodium carbonate (Na2CO3), First, Bombyx mori cocoons were degummed twice in a boiling solution of 0.5 wt% Na2CO3, and the obtained silk fibroin was washed by distilled water for several times and dried at 50 °C for 24 h. Then, the silk fibroin was hydrolyzed and degraded by a mixture of urea and guanidine hydrochloride according to the mothed modified from previous study [23] , then followed washing and filtration by distilled water. The exfoliated tofukasu-like materials were then dispersed in water with a weight ratio of 1:250 under vigorous stirring. The silk nanofibril solution was obtained after the above suspension was sonicated and centrifuged. Finally, a certain amount of 0.1 M FeCl3 was added to silk nanofibril solution and stirred for half an hour, then 1M NaOH was introduced to the suspensions drop by drop. The mixture was incubated at room temperature for two days, and then filtered, washed and dried for further use and characterization. The batch experiments were carried out to evaluate the removal performance of antimonite, including the effect of SF ligand, the effect of pH, selectivity and maximum removal capacity. Firstly, a series of nanohybrids were prepared to study the effect of SF ligand on the removal performance by adding different quantity of SNF to react with iron ions. The effect of pH was investigated in a broad pH ranging at 3, 5, 7, 9 and 11, and the pH values were adjusted by adding either HCl or NaOH solutions. The The morphologies of nano silk fibroin and silk fibroin-ferric oxide nanohybrid were studied using a transmission electron microscopy (TEM, JEM-1200EX electron microscope, JEOL, Japan), respectively. The crystal structure of the as-prepared silk fibril/ferric oxide nanocomposites were confirmed by X-ray diffraction measurements. And the element compositions of the silk fibril/ferric oxide nanocomposites were analyzed using scanning electron microscope (SEM) together with elemental mapping. The specific surface areas of the samples were examined by the Brunauer-Emmett-Teller (BET) N2 adsorption/desorption method, and the pore size distribution was determined by the Brunauer-Joyner-Hallenda (BJH) method using desorption data. The structures and interactions of the samples before and after antimonite loading were monitored using a Fourier transform infrared spectrometer (FTIR) and an X-ray photoelectron spectroscope (XPS). The main steps involved in the synthesis of silk fibroin-ferric oxide nanohybrids are summarized in Figure 1a . The silk sericin was first wiped off by heating silkworms in Na2CO3 solutions for half an hour. A gel state material was then obtained by degrading the silk fibroin using the mixture of urea and guanidine hydrochloride ( Figure S1 ). After washing by deionized water and filtered, the obtained tofukasu-like materials were then re-dispersed in water. The silk nanofibril (SNF) was finally obtained after the above re-dispersed solution was stirring vigorously and centrifuged Due to the contribution of large length-diameter ratio of the fiber-shaped nanohybrids, The mechanism about the metal-ligand binding interactions between iron ions and silk fibroin was employed by FTIR spectrum (Figure 2b) . A sharp peak at 3276 cm -1 was ascribed to the stack stretching vibration of N-H and O-H. The characteristic peaks responsible for the secondary structures of SF at around1624 and 1520 cm -1 were J o u r n a l P r e -p r o o f assigned to β-sheets, amide Ⅰ band and amide Ⅱ band [26, 27] . In the spectra of SNF/ferric oxide nanohybrid, the N-H stretching shifted to left, and the intensity of the amide Ⅱ band peaks at 1624 and 1520 cm -1 decreased, suggesting a lower β-sheet content after chelating with iron ions. Additionally, the new peaks found at around 1336.3, 879.8 and 786.5 cm -1 were corresponding to Fe-O stretching [28, 29] . The results indicated that the SF was successfully coated with ferric oxide. The The content of SNF could influence the performance of the nanohybrids. A series of experiments were carried out by varying the SNF solution volumes to explore the positive influences of the ligand SNF on capturing of antimonite. And the ferric oxides without the addition of silk fibroin were obtained as a control. As shown in Figure 3a , the optimal removal capacity for antimonite by the nanohybrid appeared with addition of 8 mL SNF, which was higher than the pristine ferric oxides. It demonstrated more active surface sites were available for antimonite via surface complexation after ferric oxides assembly with SNF, and the abundant amino groups could enhance the removal capacity synergistically. While the removal capacity of the nanohybrid appeared a decline with more addition of SNF. It could be ascribed that the excess of SNF could hinder the active sites of ferric oxides after the saturated metal-ligand binding interactions between iron ions and silk nanofibril. The pH-dependent antimonite removal properties by the SNF/ferric nanohybrids were tested at pH values ranging from 3.0 to 11.0 (Figure 3b) . The results showed that the SNF/ferric nanohybrids exhibited superior antimonite removal capacities at a wide pH range from 5.0 to 9.0 after contacting for 24 h, while having a minor decline at a very acidic or basic condition (Figure 3b ). This is distinguishing to the reported previous works that the removal of antimonite species was generally independent on pH values due to the low electrostatic interactions involving the neutral form of H3SbO3 [2, 7, 30] . The decline of the removal capacity was due to the possible hydrolysis reactions for part of the amino and carboxyl groups onto silk fibroins at a relatively acid or alkaline conditions. It is crucial to estimate the removal selectivity for antimonite purification in real practical applications, due to the ubiquitous anionic species in the aqueous environment. The effect of common anions including SO4 2-, NO3 -, CO3 2-, SiO3 2and J o u r n a l P r e -p r o o f PO4 3on the elimination of antimonite were determined. As shown in Figure 3c , the ferric nanocomposite displays high selectivity toward antimonite at the presence of SO4 2-, NO3 -, CO3 2-, SiO3 2and PO4 3-, in which the removal capacity was as high as that without these interfering ions even when the concentrations of interfering ions are triple higher than antimonite. Although these coexisting anions could also be adsorbed on the nanocomposite by hydrogen bonding, the removal capacity for antimonite was still not significantly affected by the anions. This is mainly due to that the synergistic effect of silk fibroin and iron oxides contributed to the superior removal ability of antimonite. The removal ability for antimonite by silk fibroin was also studied as shown in Figure S4 Benefiting from the successful binding of silk nanofibril and iron oxides, the fiber-shaped nanocomposite with fascinating length-to-diameter ratio exhibited a larger surface area than the neat iron oxides. And more functional groups such as amino and carboxyl groups ascribed to silk fibroin were available on the nanocomposite, thus the silk fibroin-ferric oxide nanocomposite could present an intriguing removal capacity for antimonite. The kinetic studies were firstly performed at a predetermined time interval. The removal capacity toward antimonite remarkably increased at the initial contact stage, and reached equilibrium then followed a platform after 2 h ( Figure S5 ). The maximum removal capacity for antimonite was then further evaluated by adsorption isotherms, which were carried out at neutral pH value with J o u r n a l P r e -p r o o f the antimonite concentration ranging from 2 to 60 mg/L. As illustrated in Figure 2d , the removal of antimonite was preferred by the Langmuir model with the correlation coefficient R 2 > 0.96 (Table S1 ), suggesting that the adsorption procedure is monolayer. The theoretical maximum adsorption capacity calculated by Langmuir model was 159.9 mg/g. The high removal capacity was ascribed to the increment of the specific surface area provided during the self-assembly process of ferric oxide and silk fibroin, as well as the substantial functional groups available on silk fibroin. To our knowledge, this SNF-ferric oxide nanocomposite showed relatively better removal capacity than most of the recent reported nanocomposite materials, including porous MOFs, nanofiber-based materials and magnetic nanocomposites ( Figure 4) [2, 3, 7, [31] [32] [33] [34] [35] [36] . In particular, except for the high removal capacity and selectivity, both silk fibroin and iron oxide are environmental-friendly. To gain further insights into the removal mechanism, X-ray photoelectron J o u r n a l P r e -p r o o f spectroscopy (XPS) were performed to analyze the chemical binding energy of SNF-ferric oxide nanohybrid before and after antimonite loading. The C1s, N1s, O1s and Fe 2p were existed in the survey scan spectrum of the nanocomposite as shown in Figure S6 , in which N1s was obviously from the SNF components. A much stronger and distinct peak located at around 540 eV was observed for antimonite-loaded samples, resulting from the contribution of O1s and the adsorbed antimonite (at these two peaks are very close). It suggests successful antimonite scavenge by the nanocomposite. The Sb 3d speaks of the nanocomposite after adsorption display two representative peaks centering at about 540 eV (Sb 3d3/2) and 530.2 eV (Sb 3d5/2) (the inset in Figure 5b ), which demonstrates the presence of antimonate (higher binding energy) and antimonite (lower binding energy), respectively [37] . The observed two typical peaks corresponding to Sb3d3/2 and Sb3d5/2 suggest partial oxidation of antimonite to antimonate. The deconvolution of O1s and C1s spectra was further explored, respectively. The In summary, we developed a novel fiber-shaped nanohybrid by anchoring ferric oxides on silk nanofibril. The exfoliated SNF possessed uniform fiber diameter after enzymatic degradation. The ferric oxide in situ grew along the silk nanofibril via metal-ligand binding interaction, and the obtained nanohybrids inherited both the functions of ferric oxide and silk nanofibril. The as-prepared nanohybrids achieved an excellent antimonite removal capacity of 159.9 mg/g, which was superior than most reported kinds of materials to our knowledge. Moreover, the nanohybrid showed high selectivity in the presence of anionic species of SO4 2-, NO3 -, CO3 2-, SiO3 2and PO4 3-. The over consideration of high adsorption capacity, environmental-friendly and high selectivity, the novel fiber-shaped silk fibroin-ferric oxide nanohybrid developed in this study would be promising materials for antimonite extraction from water. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Selective and Efficient Removal of Fluoride from Water Fibril/ZrO2 Hybrid Membranes Development of a magnetic core-shell Fe3O4@TA@UiO-66 microsphere for removal of arsenic(III) and antimony(III) from aqueous solution Screening of zirconium-based metal-organic frameworks for efficient simultaneous removal of antimonite (Sb(III)) and antimonate (Sb(V)) from aqueous solution Metalorganic framework-based materials: superior adsorbents for the capture of toxic and radioactive metal ions Efficient removal of both antimonite (Sb(iii)) and antimonate (Sb(v)) from environmental water using titanate nanotubes and nanoparticles Electroactive modified carbon nanotube filter for simultaneous detoxification and sequestration of Sb(III) Chitosan functionalized iron nanosheet for enhanced removal of As(III) and Sb(III): Synergistic effect and mechanism Antimony removal from aqueous solution using novel α-MnO2 nanofibers: equilibrium, kinetic, and density functional theory studies Biosorption of antimony(V) onto Fe(III)-treated aerobic granules Arsenic and antimony in water and wastewater: Overview of removal techniques with special reference to latest advances in adsorption Efficient removal of arsenic from groundwater using iron oxide nanoneedle array-decorated biochar fibers J o u r n a l P r e -p r o o f with high Fe utilization and fast adsorption kinetics Stability of hydrous ferric oxide nanoparticles encapsulated inside porous matrices: Effect of solution and matrix phase Materials fabrication from Bombyx mori silk fibroin Design, fabrication, and function of silk-based nanomaterials One-step synthesis of biocompatible magnetite/silk fibroin core-shell nanoparticles Biomimetic magnetic silk scaffolds Hematite nanostructures synthesized by a silk fibroin-assisted hydrothermal method Synthesis of hierarchical three-dimensional copper oxide nanostructures through a biomineralization-inspired approach Structure and properties of various hybrids fabricated by silk nanofibrils and nanohydroxyapatite Bioinspired Unidirectional Silk Fibroin-Silver Compound Nanowire Composite Scaffold via Interface-Mediated In Situ Synthesis Primary and Secondary Mesoscopic Hybrid Materials of Au Nanoparticles@Silk Fibroin and Applications Progress in silk materials for integrated water treatments: Fabrication, modification and applications Controllable exfoliation of natural silk fibers into nanofibrils by protein denaturant deep eutectic solvent: nanofibrous strategy for multifunctional membranes In situ bioinspired synthesis of silver chloride nanocrystals on silk fibroin fibers Radiolytic formation of Fe3O4 nanoparticles: influence of radiation dose on structure and magnetic properties Self-Assembled Regenerated Silk Fibroin Microsphere-Embedded Fe3O4 Magnetic Nanoparticles for Immobilization of Zymolyase Study on the blends of silk fibroin and sodium alginate: Hydrogen bond formation, structure and properties Polysulfone/hydrous ferric oxide ultrafiltration mixed matrix membrane: Preparation, characterization and its adsorptive removal of lead(II) from aqueous solution Preparation and evaluation of iron-chitosan composites for removal of As(III) and As(V) from arsenic contaminated real life groundwater Sb(III) removal from aqueous solution by a novel nano-modified chitosan (NMCS) Efficient removal of antimony(III, V) from contaminated water by amino modification of zirconium metal-organic framework with mechanism study Removal of antimonite and antimonate from water using Fe-based metal-organic frameworks: the relationship between framework structure and adsorption performance Three-dimensional reduced graphene oxide coupled with Mn3O4 for highly efficient removal of Sb(III) and Sb(V) from water Simultaneous removal of Sb(III) and Cd(III) in water by adsorption onto a MnFe2O4-biochar nanocomposite Antimony removal from aqueous solution using novel α-MnO2 nanofibers: equilibrium, kinetic, and density functional theory studies Preparation of a novel Fe3O4/HCO composite adsorbent and the mechanism for the removal of antimony(III) from aqueous solution Antimonate adsorption onto Mg-Fe layered double hydroxides in aqueous solutions at different pH values: Coupling surface complexation modeling with solid-state analyses This research was supported by Natural science foundation of Shandong Province (ZR2019QD019), and Program for Taishan Scholar of Shandong Province.