Treatment of Hazardous Engineered Nanomaterials by Super

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Treatment of Hazardous Engineered Nanomaterials by Supermagnetized #-Cellulose Fibers of Renewable Paper-waste Origin Avinash A. Kadam, Saifullah Lone, Surendra Shinde, Jiwook Yang, Rijuta Ganesh Saratale, Ganesh Dattatraya Saratale, Jung-Suk Sung, Dae Young Kim, and Gajanan Sampatrao Ghodake ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05268 • Publication Date (Web): 01 Feb 2019 Downloaded from http://pubs.acs.org on February 3, 2019

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ACS Sustainable Chemistry & Engineering

Treatment of Hazardous Engineered Nanomaterials by Super-magnetized α-Cellulose Fibers of Renewable Paper-waste Origin Avinash A. Kadama, Saifullah Loneb, Surendra Shindec, Jiwook Yangc, Rijuta Ganesh Saratalea, Ganesh Dattatraya Sarataled, Jung-Suk Sunge, Dae Young Kimc, and Gajanan Ghodakec* a

Research Institute of Biotechnology & Medical Converged Science, Dongguk University-Seoul, 32, Dongguk-ro, Ilsandong-gu, Goyang-si, Gyonggido 10326, Republic of Korea b

Cogno-Mechatronics Engineering, Department of Optics and Mechatronics Engineering,

College of Nanoscience and Nanotechnology, Pusan National University, Busan 46241, South Korea c

Department of Biological and Environmental Science, College of Life Science and

Biotechnology, Dongguk University-Seoul, 32, Dongguk-ro, Ilsandong-gu, Goyang-si, Gyonggido 10326, South Korea d

Department of Food Science and Biotechnology, Dongguk University-Seoul, 32, Dongguk-ro, Ilsandong-gu, Goyang-si, Gyonggido 10326, Republic of Korea

e

Department of Life Science, College of Life Science and Biotechnology, Dongguk UniversitySeoul, 32, Dongguk-ro, Ilsandong-gu, Goyang-si, Gyonggido 10326, South Korea

Corresponding author: Gajanan Ghodake, Tel: +82-31-961-5159; Fax: +82-31-969-5122; Email: [email protected]

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ABSTRACT Engineered nanomaterials (ENMs) are posing detrimental ramifications to the human health in general and aquatic wildlife in particular. Herein, we report treatment of three types of ENMs namely CuO, CoO and ZnO by a magnetic composite (Fe3O4NPs) with α-cellulose fibers of paper-waste origin (PW-αCF). The removal efficiency of Fe3O4@PW-αCFs for (CuO), (CoO), and (ZnO) was obtained to be 850, 946, and 929 mg·g–1, respectively. The adsorption efficacy observed optimum at pH 6 to 7, thus, this system was based on hydroxyl groups of PW-αCFs. Also, to validate the real-world applications, the ENM removal capacity of Fe3O4@PW-αCFs was assessed in different water sources such as; a river, pond, and wastewater (spiked together with CuO, CoO, and ZnO). Furthermore, unprecedented energy dispersive spectrometric (EDS) mapping was employed to illustrate the ENMs loading on Fe3O4@PW-αCFs and to reveal the role of Fe3O4 NPs surface in the deposition of heavyweight aggregates of ENMs. The robust integration of ENMs onto Fe3O4@PW-αCF surfaces rules-out the ENMs leaching back into the aqueous media. Hence, abundant availability and their functionalities such as; hydroxyl groups, light-weight, high-surface area, and rapid magnetic separation, proved Fe3O4@PW-αCFs as an attractive bio-nanocomposite material for ENMs remediation and utilization in various applications.

KEYWORDS: paper waste; cellulose fibers, magnetic separation, Remediation of engineered nanomaterials, metal oxides


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INTRODUCTION ENMs employed in various industrial and wastewater treatment processes,1-2 eventually ends up in water (i.e., lakes, streams, rivers, and springs); as a result, it directly threatens the general public health and precious aquatic life.3-4 In last decade, the idea of using ENMs in water treatment plants to kill the pathogenic germs (e.g., bacteria, parasites, and viruses), remove heavy metal ions and organic pollutants, directed a significant rise in ENMs contaminantion.5-6 Regardless of the benefits, there is an immediate need to deploy sophisticated methods for monitoring, removing, and characterization of ENMs present in water samples. The effective removal (both physically as well as chemically) of hazardous colloidal pollutants from water bodies is a distinct challenge for researchers,7-8 driven by legislative pressures, health hazards, and environmental fate.9-10 Generally, ENMs have been removed from the wastewater stream using various methods including bioaccumulation, aggregation, precipitation, and flocculation.8, 11-12

Furthermore, it is vital to provide robust, sustainable, and inexpensive treatment alternative

to remediate and to remove ENMs under ambient temperature and smooth operations at the rapid pace. Cellulose fibers are the most abundant biopolymer on the earth and utilized in the production of papers and packaging materials. In recent times, PW recycling technologies have to become evident in the incorporation of recycled CFs in paper manufacturing; however, the industry is facing a constant downward burden to establish a balance between the paper quality and the production costs.13 Sustainable developments in the PW management demands taking care of both wastes generated and finding greener ways to convert it into value-added products.14-15 Waste-to-products of various kinds, modification of renewable cellulose fibers with



functional materials can be used to accelerate the circular-economy progress.16-17 PW recycling, in particular, will continue to rise due to financial interests and ecological advantages. Thus, the production of nano-, micro-fibrillated cellulose has instigated to take the shape of commercialization,18 and processing after that to develop various applications and so, most of the research fields for its claim. Relying on inherently fibrous nature and remarkably high mechanical strength, low-cost, biocompatible, and renewable resource; cellulose-based nanocomposites offer immense potential as a component for remediation of widespread pollutants in water.19 Modified cellulose materials have been extensively used as bioadsorbent for the remediation and recovery of metal ions and organic pollutants in a more concentrated form.20-22 Also, cellulose-based nanocomposites have also been proposed as a superior adsorbent for the preparation of environmentally friendly templates for catalysts, biofilters and pollutant sensors.23-24 As compared to the conventional adsorbents, the magnetized adsorbents are known for their unique separation capability and improved surface area ratio for rapid and highly effective removal of ENMs.25-26 The idea of separating adsorbent materials from the reaction medium is advantageous; it does not generate secondary waste or sludge as well as bioadsorbent can be recycled on an industrial scale and could be used for advanced applications.27-28 Therefore, in this work, a magnetic cellulose composite (Fe3O4@PW-αCFs) is fabricated to improve the aggregative adsorption of CuO, CoO, and ZnO from the water. The separation process is simple and straightforward from forming hazardous waste called sludge. The αCFs are first extracted from PW, magnetized by co-precipitation method, and then carefully characterized to reveal their unique properties. Fe3O4@PW-αCFs proved to be an extraordinary


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adsorbent for the removal of all tested ENMs. Afterwards to examine the adsorption behavior and performance of Fe3O4@PW-αCFs; the removal of ENMs from aqueous solution is followed by investigating operational parameters viz. adsorption-time, initial concentration, types of ENMs, and pH. Hence, this versatile method can be successfully used to remove a significant amount of ENMs as a result, it provides sustainable growth of both nanotechnology and waste management practices.

EXPERIMENTAL SECTION Chemicals and reagents. Ammonia (25%) was obtained from a Wako pure chemical industry (Osaka, Japan). Standard solution of NaOH and HCl, as well as FeCl3.6H2O and FeCl2.4H2O solutions were procured from Dae Jung chemicals, South Korea. Spherical shaped cobalt (II, III) oxide (CoO, 5 to 20 nm) and anisotropic shaped zinc oxide (ZnO, 20 to 200 nm) NMs were purchased and used as received from Sigma Aldrich Chemicals, South Korea. CuO was freshly prepared by ammonia-based co-precipitation was performed under nitrogen-rich environment by heating the solution at 60 oC for 20 min. A black precipitate of CuO nanosheets was then rinsed with distilled (DI) water and further dried at -80 oC and 5 mTorr vaccum using lyophilizer (Ilshin Biobase FD-8508). Extraction of PW-αCFs. A4 size office paper was used as a source of PW-αCFs. The small pieces of paper (50 g) were crushed in the blender and soaked in the water at 90 oC to produce a white pulp. In brief, 10 gm of paper pulp was placed in a 500 mL beaker and treated for 45 min at 50 °C in an ultrasonic bath with 250 mL of sodium hydroxide (10% (w/v)). The sample was then filtered and rinsed with DI water before being placed in a fresh beaker containing 17%



(w/v) sodium hydroxide and finally subjected to an ultrasonic bath for a further 45 min at 50 oC. The extracted PW-αCFs were then removed from the beaker and repeatedly washed until the solution pH reached up to 6.8 which are indicative of the complete removal of residual sodium hydroxide. Finally, a snow-colored soft powder of PW-αCFs was lyophilized (lshin Biobase, FD8508). This procedure allows, to separate PW-αCFs from the other components includes hemicellulose, adhesives, ink binders, and chemicals as reported previously.29-30 Preparation of Fe3O4@PW-αCFs. 3 g of PW-αCFs powder was mixed in 500 mL of DI water and dispersed for 1 h by bath sonication (Power Sonics 520). The well-dissolved solutions of FeCl2.4H2O and FeCl3.6H2O were prepared on the magnetic stirrer with a ratio of about 2:1 (in terms %) and kept overnight on the magnetic stirrer at ambient temperature. The dispersed PWαCFs were transferred to 1000 mL clean and dry beaker and kept on the heating plate with fine control over operational temperature (60 °C) under shaking condition of about 200 rpm with constant supply of nitrogen gas. First, FeCl3.6H2O was added drop-wise into the PW-αCFs mixture and then FeCl2.4H2O in the presence of nitrogen gas. Later, drop-wise addition of ammonia solution (40 mL, 25 %) was carried out to facilitate the crystal growth and impregnate Fe3O4 NPs onto the PW-αCF surface. The obtained co-precipitate product of Fe3O4@PW-αCFs was further incubated at 60 °C for 15 min. The freshly prepared bio-adsorbent was then removed from the reaction mixture by applying external magnet and further washed thoroughly with DI water. The obtained Fe3O4@PW-αCF was lyophilized at -80 oC and 5 mTorr vacuum using lyophilizer (Ilshin Biobase FD-8508) and further used in ENMs remediation experiments. Characterization of Fe3O4@PW-αCFs. The hysteresis magnetization curve of Fe3O4@PWαCFs was recorded using vibrating sample magnetometer (VSM) (Lakeshore, Model: 7407). The


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thermal stability properties of samples were characterized with a thermogravimetric analyzer (TGA) (TA Instruments, Q-600). The X-ray diffraction (XRD) patterns of thin films were obtained by using a Rigaku Ultima IV X-ray diffractometer. Fourier-transform infrared spectroscopy (FT-IR) spectroscopic studies of powdered PW-αCFs and Fe3O4@PW-αCFs samples were carried out after mixing and drying KBR pellets by Thermo Electron Nicolet 6700. Freeze-dried samples of PW-αCFs, Fe3O4@PW-αCFs, Fe3O4@PW-αCF-ENMs were placed on a sample holder containing the carbon tape coated with few nanometer-thin platinum layer using sputter coater for 50 s. Sputter coated samples were examined on Hitachi S-4800 field emission scanning electron microscopy (FE-SEM). Freeze-dried samples of Fe3O4@PW-αCFs, Fe3O4@PW-αCF-ENMs were placed onto the carbon coated copper grids, and excess samples were removed. Size, shape, and EDS mapping of ENMs aggregates as well as selected area electron diffraction (SAED) pattern of Fe3O4@PW-αCFs were performed using transmission electron microscope (TEM) (Tecnai-G2). ENMs removal. In this report, Fe3O4@PW-αCFs was used to remove ENMs; CuO, CoO, and ZnO from aqueous solution. The model ENMs; CuO, CoO, and ZnO solutions were freshly prepared in DI water to form a stock solution (1000 mg·L–1), exposed to bath sonication for 60 min and used freshly. In a typical removal experiment; 1 mg of Fe3O4@PW-αCFs was added into 8 mL DI water containing 1 mL solution from well dispersed each ENMs stock solutions (1000 mg·L–1). After the removal process, the ENMs adsorbed Fe3O4@PW-αCFs was removed magnetically, and the resulting supernatant measured spectrophotometrically at respective absorption maxima. With a similar method, the different removal experiments such as; effect of increasing shaking time, the effect of pH (4 to 9) and impact of increasing concentrations of ENMs (100, 150, 200, 250 and 300 mg·L–1) were studied, respectively. ENMs adsorption



amount (qe mg·g–1) by using Fe3O4@PW-αCFs were determined as per the equation given in earlier report.25 Stability assessment of the ENMs adsorbed on Fe3O4@PW-αCFs. Stability assessment of ENMs loaded on Fe3O4@PW-αCFs (Fe3O4@PW-αCFs-ENMs) was performed at broad pH range and ambient temperature. After the removal process, the Fe3O4@PW-αCFs-ENMs were powdered and used for leaching experiments. The solutions of Fe3O4@αCF-ENMs (100 mg·L–1) were made in pH solution (1-10) using lyophilized powder and agitated for 72 h by a shakerincubator at 200 rpm. The concentration of ENMs leached in water was measured at maximum absorbance wavelengths. Treatment of ENMs-spiked water samples. To prepare ENMs-spiked synthetic water, 1 mL from each stock solutions of CuO, CoO, and ZnO NMs (1000 mg·L–1) was added into 24 mL real-world water samples collected from the local river (RW), pond (PW), and wastewater (WW) treatment plant and used after filtration using Whatman paper. Following the addition of ENMs, synthetic wastewater was sonicated using a bath sonication (Power sonic-520) for 60 min to allow complete dispersion. Further, 3 mL of Fe3O4@PW-CFs (1000 mg·L–1) was added to the ENMs-spiked synthetic waters and kept at 200 rpm and room temperature for 12 h. The ENMs firmly adsorbed on the Fe3O4@PW-αCFs were separated by applying an external magnet, and supernatant solutions were used for the measurement of residual ENMs concentrations. Finally, imaging, EDS, and EDS mapping of Fe3O4@αCF-ENMs mixture were performed using the SEM and TEM analyzes.

Results and discussion


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Extraction of αCFs and preparation of Fe3O4@PW-αCFs. The increase in paper production and consumption has been continuously creating a staggering amount of PW, without a doubt it contributes globally about 20-40%, particularly to the municipal solid waste.31 The share of recycled fiber is relatively high in the newspaper about 50%, hygiene papers about 65%, wrapping paper about 86% and cart boards about 52% according to the recently published report.32 Recycled cellulose fibers from PW is an abundant resource, and the making of it is not an expensive or complicated process. Recycling paper waste and utilizing for making various value-added products would be useful to conserve forest resources and to reduce the environment related problem. In this study, the PW was processed into high-yield αCFs, combined with both mechanical and chemical treatments were used in pulping and bleaching. In brief, recycled PW pulp was treated chemically in the ultrasonic bath to isolate individual αCFs and remove hemicelluloses, lignins, and other noncellulosic substances. In chemical treatment, NaOH was used as the major active ingredient for impregnation and delignification. Hemicellulose is useful materials for environmental applications; however, its content in paper waste is minor, and it is also required additional steps to purify from other components present in the solution. The extracted and freeze-dried PW-αCF was white colored, floppy in nature and insoluble in the water. The structure of PW-αCFs was stable under sonication as well as shaking conditions due to excellent mechanical and physical properties. In this report, office PW is successfully used to isolate PW-αCFs with yield about 58.78% (w/w) and modified magnetically to explore bioadsorption of ENMs. Interest to extract PW-αCFs was driven from the previous report, which recommended PW fibers are the purest form of natural cellulose-containing PWαCFs more than 60% of its dry weight.33 Cellulose delignification was reported for various bioresources, giant reed, pennisetum, and corn stalk under aqueous NaOH conditions.34 The



effect of ultrasonic cavitation combined with NaOH treatments was reported for improvement of physical properties of regenerated αCFs.35 PW containing high cellulose content is the promising low-cost renewable source for producing regenerated αCFs, and other types of value-added products and chemicals.15, 36 Fe3O4 NPs were extensively used for developing various biomedication and environmental applications, however, its susceptible to dipole interactions that can lead to significant particle agglomeration. Herein, PW-αCFs was utilized for the loading of Fe3O4 NPs. PW-αCFs was characterized and identified as a raw material to fabricate Fe3O4@PW-αCFs nanocomposite. In the initial step, the iron ions (Fe3+ and Fe2+) were chelated by hydroxyl groups abundantly available on the surface of the PW-αCFs. In a next step, under the N2 gas conditions, the PW-αCFs surface chelated iron ions (Fe3+ and Fe2+) were reacted to the (OH-) ions from precipitant (NH4OH), and lead to the formation of the Fe3O4 NPs over the surface of the PWαCFs. The N2 gas conditions were used to avoid unnecessary oxidation reactions and products of Fe(OH)3 or Fe2O3. The schematic representation of the PW-αCFs magnetization was shown in Figure S1. The detailed schematic presentation of stepwise synthesis of Fe3O4@PW-αCFs for ENMs remediation was illustrated in the TOC graphic. Characterization of PW-αCFs and Fe3O4@PW-αCFs. The PW-αCFs was characterized using four independent techniques, zeta potential measurements, TGA, SEM, and FT-IR. The zeta potential values of the paper pulp, PW-αCFs (after NaOH treatment), and Fe3O4@PW-αCFs (after Fe3O4 NPs treatment) were determined as about -15.77, -8.59, and -1.45, respectively (data not shown). The obtained results indicate that the paper pulp and PW-αCFs were deprotonated and contains negatively charged hydroxyl groups; thus, resulted in electrostatic repulsion and led


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to dispersion in the water.37-38 These results reveal that the negative charge must be originated from the deprotonation from PW-αCFs, similar to the previous report.39 Further, the treatment of PW-αCFs with Fe3O4 followed with thorough washing increased zeta potential value from -8.59 to -1.45. The negative charge present on Fe3O4@PW-αCFs was found to be lower than that of bare PW-αCFs due to increased protonation of hydroxyl groups in the process of magnetization and washing. However, Fe3O4@PW-αCFs powder dispersed in DI water reached almost neutral pH, and thus, it was very suitable for effective removal of ENMs. Therefore, the overall zeta potential study gave information regarding the surface charge of studied materials. To understand the magnetic characteristics, the facile synthesized Fe3O4@PW-αCFs was examined by VSM data shown in Figure 1a. The obtained VSM profile revealed a characteristic magnetic-hysteresis curve, having almost zero remanence and coercivity values. The saturation magnetization of Fe3O4@PW-αCFs was observed to be 20.40 emu/g. Thus, the obtained VSM profile corroborated a super-magnetic nature of Fe3O4@PW-αCFs. Representative photographs of Fe3O4@PW-αCFs kept in the vicinity of the magnet were shown in Figure 1a. Fe3O4@PWαCFs after a vigorous shake was separated quickly by using an external magnetic field (Figure 1a inset). This photograph strongly suggests super-magnetic nature of Fe3O4@PW-αCFs and ease of separation from the reaction solution. These results indicate that the Fe3O4@PW-αCFs is highly appropriate for environmental applications and rapid separation under the applied magnetic field. Magnetic Fe3O4 NPs have been widely used to ease separation and adsorption of pollutants from water, owing to their important properties such as strong magnetism, small size, functional groups, and biocompatibility.40-41



Figure 1b showed TGA data of PW-αCFs and Fe3O4@PW-αCFs in which, the initial weight loss of αCFs and Fe3O4@PW-αCF was observed within a temperature range of 25 to 250 °C attributes to the water/moisture loss. Second, the breakdown of the basic cellulosic structure started as increase in temperature from 250 to 380 °C. Third, the PW-αCFs exhibited complete weight loss between 390 °C, to 530 °C temperature range. Nonetheless, the Fe3O4@PW-αCF remained stable with a 23 weight % between 350 °C to 800 °C temperature. Hence, these results signify that Fe3O4@PW-αCFs have higher thermal stability as compared to the PW-αCFs. The variations caused in the difference of TGA curve and the crystallinity added to the PW-αCFs (amorphous) is from the crystalline nature of Fe3O4 NPs. Noticeably, Fe3O4 NPs have contained most of the incremental residual char in Fe3O4@PW-αCF, indicating Fe3O4 NPs were deeply embedded in PW-αCFs matrices. The regenerated cellulose is known to show lower onset temperature for decomposition than that of an original dissolved pulp; likewise, this sample also gives rise to a higher char yield, exhibited by a high residual mass.42 Crystalline structure analysis of PW-αCFs and Fe3O4@PW-αCFs were performed using XRD patterns shown in Figure 1c. The characteristic XRD peaks for cellulose were appeared at 22.48° and 34.31° for the crystal plane of the (002) and (040), respectively.29 However, the characteristic XRD peaks of Fe3O4 (2θ = 22.2°, 35.6°, 44.5°, 57.5°, and 63.2° are allocated to the characteristic planes (111), (311), (400), (511), and (440) of Fe3O4 crystals were clearly appeared in the Fe3O4@PW-αCFs sample. The characteristic Fe3O4 peaks were seen in Fe3O4@PW-αCF, indicates that the PW-αCF surfaces were well covered with Fe3O4 NPs, resulted in a clear diffraction peak with strong intensity (Figure 1c). Therefore, the obtained XRD spectra’s for PW-αCFs and Fe3O4@PW-αCFs suggests the combination of PW-αCFs and Fe3O4 made


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changes in some crystal, signifying that the Fe3O4 had been effectively coated onto the surface of PW-αCFs. XRD peaks were accountable with the previous report.43 Compared with the FTIR spectra of PW-αCFs and Fe3O4@PW-αCF, specific bands were remained identical changed concerning transmittance and wavenumber as shown in Figure 1d. The broad OH bending after bounding with water was seen at 1630–1666 cm−1 with two distinct peaks at 1637 and 1655 cm−1. In Figure 1d, peaks were evident in 1320, and 1380 cm−1 were identified for C-H stretching of CH2 of PW-αCFs. The peaks at ∼1110, 1337, and 2900 cm−1 corroborates for C–O stretching, –OH in-plane stretching and stretching vibrations of C–H, respectively.44 The maximum transmittance of hydrogen bonded (–OH) stretching was observed at wavenumber 3340 to 3375 cm−1, is in agreement with O(3)H⋯O(5) intramolecular hydrogen bonding of cellulose at 3340 to 3375 cm−1.45-46 The characteristic bands at 430, 588 and 670 cm−1 wavenumber which are recognized for the metal–oxygen (Fe–O) bonding,33, 47 demonstrating that Fe3O4 were embedded in PW-αCFs. TEM imaging and EDS analysis also confined the Fe3O4 loading onto the surface of PWαCFs. The TEM images clearly showed a long PW-αCF, and well-decorated Fe3O4 NPs were visible in Figure S2a. TEM images reveal that PW-αCFs provides sites for nucleation and in-situ growth of Fe3O4 NPs. Meanwhile, the PW-αCFs template acts as “spacer”, thus could avoid agglomeration of Fe3O4 NPs and promoted their even dispersion along the PW-αCFs. The sizes of the Fe3O4 NPs were distributed between 5 and 10 nm (Figure S2a inset). Fe3O4 NPs were uniformly distributed, allowed to improve surface to volume area of Fe3O4@PW-αCFs, and desirability of adsorbent materials. The EDS spectrum was helped to confirm the synthesis of Fe3O4@PW-αCFs with high purity (Figure S2b). The copper signal observed in the EDS



spectrum was from the Cu coated grid. The SAED pattern of the synthesized Fe3O4@PW-αCFs was evidenced that the Fe3O4 NPs are highly crystalline as presented in Figure S2b inset. The number of strong diffraction rings observed in the SAED patent were scattered due to the (111), (311), (400), (511), and (440) reflections from the Fe3O4 NPs cubic structures.33 This SAED observations are in agreement with XRD results (Figure 1c) CuO nanosheets were prepared and used for various applications such as highperformance supercapacitors,48 electrochemical reductions of carbon dioxide,49 and aqueous conductive ink.50 The TEM image of the freshly prepared CuO nanosheets using aqueous ammonia based precipitation methods is shown in Figure S3a. It can be observed that the welldefined fringe-like structures span a large distance, revealing the formation of CuO nanosheets and, then used for redispersion and sonication in water. Similarly, CoO and ZnO NMs obtained from Sigma Chemicals were directly used as received for TEM imaging, dispersion, and sonication and remediation experiments. TEM results suggest that both ZnO and CoO NMs were having particulate in nature and the size and morphology presented in Figure S3b,c. The TEM image clearly shows the presence of small-sized and spherical shaped CoO NMs (Figure S3b). These ENMs were having a size in the range of 5 to 20 nm. The TEM image of ZnO clearly shows the presence of nanorod-like morphology, and these nanorods having a diameter of 20 to 200 nm (Figure S3c). Removal of ENMs. The PW-αCFs modified with Fe3O4 NPs were used for removal of the ENMs from water samples. As a model ENMs, this study chose an industrially important oxide NMs; CuO, CoO, and ZnO, which were already reported as a serious environmental threat. UVvis spectroscopy was employed to observe the number of residual ENMs in the solution, and the


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residual concentration of CuO, CoO, and ZnO was calculated by using equation.1 Absorbance wavelength at the maximum absorption mentioned in UV-vis spectra was selected for further measurements (Figure 2a). Unless specified otherwise, the concentration of CuO, CoO, and ZnO in the solution was determined after 12 h treatment by measuring absorbance intensity at 340, 400 and 365 nm, respectively (Figure 2b) (UV-vis spectroscopy, Optizen-2120). Real-time ENMs removal. The real-time course of ENMs removal using both using PW-αCFs and Fe3O4@PW-αCFs were performed at ambient temperature. First, the effect of increasing contact time for PW-αCFs from 1 to 48 h, showed the CoO and ZnO was removed rapidly up to 898 mg·g–1 in the first 4 to 6 h, however, CuO was demonstrated a linear response (Figure 2c). This might be due to the nanosheet structure of CuO (Figure S3a) and hence its removal from water was kept on increasing linearly, rather reaching to the certain saturation stage. Conversely, the equilibrium of CoO and ZnO removal for PW-αCFs was reached at about 12 h. The adsorption of ENMs onto surfaces of PW-αCFs increases with increase of contact time, but a plateau stage was observed after 12 h. To test removal, 12 h was chosen here for ENMs, of which 850 of CuO, 946 CoO and 929 of ZnO (mg·g–1) were removed, respectively (Figure 2c). The removal of CuO, CoO, and ZnO was also investigated using super-magnetic Fe3O4@PW-αCFs as a function of time, and data was presented in Figure 2d. Removal of ENMs increases with increase in time, and adsorption saturation was reached from 12 to 24 h. It can be seen that the removal of ZnO was about 879 mg·g–1 observed at 6 h and then eventually a slower rate found after equilibrium is achieved at 12 h (Figure 2d). The removal of CoO linearly proportional to exposure time about 869 mg·g–1 was observed at 12 h and then finally reached 932 mg·g–1 at 24 h (Figure 2d). As represented in Figure 2d, the quantity of CuO per a



Fe3O4@PW-αCFs mass at 12 h was 870 mg·g–1, elevated further up to 934 mg·g–1 within 48 h at 25 °C representing, the overall rate for CuO was lower than that of CoO and ZnO (Figure 2d). However, the difference in removal capacity of Fe3O4@PW-αCFs towards studied ENMs was not significant, and the sequence was found as ZnO> CoO > CuO, typically from initial time 1 h to 24 h of exposure time. The removal of ZnO can be reached up to 879 mg·g–1 within 6 h and in same time frame CoO removal was achieved about 869 mg·g–1 (Figure 2d). The result suggests that the removal rate for both CoO and ZnO NMs in the initial time was a little bit higher than that of CuO. The reason behind this result is both CoO and ZnO NMs were particulate in nature and thus more accessible to the PW-CFs as compared to the CuO having nanosheet-like structure. As compared, the removal rate of PW-αCFs was found rapid in initial time (1 to 2 h) for CuO, CoO, and ZnO and then eventually set similar rate as with Fe3O4@PW-αCFs, due to saturation of functional groups stabilizes removal rate. A large number of free functional groups were readily available onto PW-αCFs for the adsorptive aggregation of ENMs as compared to Fe3O4@PW-αCFs. Therefore, through the time-resolved spectrophotometric analysis and transmission electron microscopy of ENM aggregates, it was found that, the metal oxides existed in the water were firmly adsorbed and transformed into large aggregates. The removal efficiency of PW-αCFs for all tested oxide NMs was competitive as a function of contact time, however practical application of such bioadsorbents is limited, and separation is too tricky and energyintensive.51 Effect of static and shaking conditions. ENMs removal experiments were carried at both static and shaking conditions at ambient temperature. Figure 3a shows the results of shaking and static conditions for ENMs removal by Fe3O4@PW-αCFs. It can be seen that the ENMs removal onto Fe3O4@PW-αCFs is a fast process at shaking conditions (200 rpm). Removal at static almost


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remains constant from initial time. The removal mode at the static condition limits exposure of Fe3O4@PW-αCF thus has a low removal ratio, which was about 278, 176 and 197 mg·g–1 for CuO, CoO, and ZnO, respectively (Figure 3a). The ENMs removal of Fe3O4@PW-αCFs for shaking condition was much higher than that of static, it was noted about 859, 854, and 891 mg·g–1 for CuO, CoO, and ZnO at 12 h, respectively (Figure 3a). Experimental results suggest that the ENMs removal at shaking conditions was accelerated through improved exposure and contact of individual oxide NMs with Fe3O4@PW-αCFs. Effects of the initial ENMs concentration. The impacts of various concentrations (100 to 300 mg L–1) of CuO, CoO, and ZnO on PW-αCFs and Fe3O4@PW-αCFs removal efficiency were investigated at 12 h of incubation (Figure 3b-d). The maximum removal capacities of PW-αCFs for CuO, CoO, and ZnO were about 1568, 1808, and 1586 mg·g–1, respectively at the initial concentration of 300 mg L–1 (Figure 3b-d). When the concentration was 150 mg L–1, the removal capacities of PW-αCFs was observed about 1335, 1305, and 1339 mg·g–1 for CuO, CoO, and ZnO, respectively after12 h of incubation (Figure 3b-d). This obtained results corroborated that PW-αCFs is suitable to employ for remediation of ENMs contaminated water, however, the formation of solid sludge a secondary waste cannot be avoided. The solid waste that results in the wastewater treatment plants contain concentrated levels of pollutants in the wastewater. A great deal of concern is that these solids must be appropriately handled and disposed to protect environmental water bodies. Considering the loss of valuable nanomaterials in sludge, the toxicity of nanomaterial’s, and the cost of handling as well as disposing of such solid waste is not sustainable or appropriate for the environment. The efficiency of PW-αCFs in the removal of ENMs from water is the remarkable and increasing use of Fe3O4 NPs in the environmental



application is reasonably noticeable. To avoid these issues of solid sludge, rapidly-separable magnetic nano-composite Fe3O4@PW-αCFs were fabricated and applied ENMs removal At 150 mg L–1 concentration of CuO, CoO, and ZnO, the removal efficiency by Fe3O4@PW-αCFs was observed to be 1381, 1330, and 1367 mg·g–1, respectively, (Figure 3b-d). In case of CuO and CoO; the adsorption efficiency was found higher about 150 mg·g–1 than that observed for ZnO at the high initial concentration (300 mg L–1). An increase in initial concentrations from 100

to 300 mg L–1, the removal efficiency of Fe3O4@PW-αCFs was

enhanced, the values of removal were observed as, for CuO from 958 to 1753 mg·g–1, for CoO from 917 to 1973 mg·g–1, and ZnO from 965 to 1673 mg·g–1, respectively (Figure 3b-d). The foregoing result suggests that Fe3O4@PW-αCFs were most effective than that of bare PW-αCFs regarding removal efficiency particularly at high initial concentrations of ENMs. The acquired results could be described by the occurrence of Fe3O4 NPs in the matrix of PW-αCFs, which supports improving surface aspect ratio and aggregation of ENMs nucleating onto the Fe3O4 NPs. The bare PW-αCFs surfaces modified with smaller sized Fe3O4 NPs (10 nm); thus, provided nanoscale surface feature and additional adsorption sites for aggregative deposition of ENMs. Additionally, zoomed TEM image (inset of Figure S2a) clearly evident the distribution Fe3O4 NPs on PW-αCFs was not dense, and more space available in between the two Fe3O4 nanoparticles, therefore, both the hydroxyl groups from PW-αCFs and Fe3O4 NPs played a role in increased ENMs removal by Fe3O4@PW-αCFs. The ENMs removal efficiency of by both PW-αCFs and Fe3O4@PW-αCFs found to be increasing with the increase in initial concentration and saturation was observed at 250 mg L–1, indicating aggregative deposition is a vital factor in the adsorptive removal of ENMs. The most important finding should be described in this context is that the lightweight of PW-αCFs is significantly appropriate for adsorptive removal of


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heavyweight aggregates of ENMs. Thus, the presence of Fe3O4 NPs might provide additional support to PW-αCFs, with the intention of persuading aggregation of ENMs, mainly via random attachment and agglomeration into heavyweight aggregates. Minor adsorption of ENMs onto experimental tube surfaces was observed and all the reported values are calculated by considering adsorption error at identical conditions. This result suggests bioadsorbent based on the Fe3O4 NPs and PW-αCFs are effective to explore practical remediation of ENMs contaminated water and magnetic separation to use in various applications.52-54 Effect of pH on ENMs removal. The results of CuO, CoO, and ZnO removal by Fe3O4@PWCFs was investigated at a pH (4-9). The removal tests were performed using Fe3O4@PW-αCFs (100 mg L–1) at ambient temperature for 12 h. The results of the blank test exhibited that varying the pH of ENMs solution had a minor effect on their ƛmax wavelength (data not shown). The minimum removal of CoO, CuO, and ZnO at pH 4 were 532.5, 616.2, and 763.9 mg·g–1, respectively (Figure 4a). The removal of ZnO onto Fe3O4@PW-αCFs was satisfactory at pH 5; however it was slowed after reaching pH 8, as it can be seen in Figure 4a. It was found that the removal of CoO on the on Fe3O4@PW-αCFs was maximum at pH 6–7, and then similar to ZnO, the removal of CoO slightly slowed from pH 8. The removal of CuO on the on Fe3O4@PWαCFs was improved significantly at pH 6–7, and become stable at pH 8–9 with 904.7 mg·g–1 removal. The maximum removal of CoO and ZnO were observed at pH 7 were 856.2 and 938.5 mg·g–1, respectively. These results were proved that an increase in pH of the solution increases the negative charge density available on Fe3O4@PW-αCFs surfaces, thereby serves as an adsorption center, and strengthens the interactions among positively charged oxide NMs and leads to their aggregations. However, in the acidic solution of pH 4, Fe3O4@PW-αCFs was remained protonated; thus, an excessive H+ ions of Fe3O4@PW-αCF surfaces compete with



ENMs for adsorption, resulting in the low removal in the sequence of CoO> CuO> ZnO at the pH 4. In the alkaline solution, the Fe3O4@PW-αCFs become deprotonated, and increased electrostatic interaction between Fe3O4@PW-αCFs and ENMs, resulting in higher removal efficiency.55 Thus, these observations revealed the obtained ENMs removal was strongly based on the hydroxyl groups. The CFs have highly dense hydroxyl-groups, and might be modified using various functional-groups,56 and can be also be used as the template for the adsorption of pollutants, includes, metal ions,57-58 organic pollutants,59 and particulate matter.60-61 Treatment of ENMs-spiked water samples. The rising concentration of nanomaterials in wastewater, considerable toxicity and long-term persistence in a real-world environment is of serious concern.62-63 A standard wastewater treatment procedures used for remediation of various pollutants appears to be poorly suitable to the remove of ENMs from wastewater.64 Thus, individual NMs in real-world water can change their behavior regarding aggregation, agglomeration, and sedimentation of oxide particles

65

. Existing purification methods used to

treat ENMs wastewater often failed to address this problem adequately. This scenario created a new demand for removal of ENMs from various types of water samples using novel and efficient materials. In this study, removal of ENMs-spiked real water samples was also tested for the first time using Fe3O4@PW-αCFs, without any interference from pollutants towards the removal efficiency. The results observed for WW samples treated in a one-step process using Fe3O4@PW-αCFs suggests that the removal efficiency can be achieved about 964.7 for CuO, 838.9 for CoO, and 925.2 for ZnO (mg·g–1) at ambient temperature, respectively (Figure 4b). Similarly, results observed for RW and PW water-spiked samples also showed excellent removal efficiency of Fe3O4@PW-αCFs at ambient temperature (Figure 4b). CuO, CuO, and ZnO were successfully removed from the synthetic wastewater within 12 h of treatment using Fe3O4@PW-


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αCFs at shaking conditions (200 rpm). The Fe3O4@PW-αCFs was thus successfully used for the effective removal of CuO, CoO, and ZnO real-world water samples (Figure 4b). Thus, this report strongly corroborates the significance of Fe3O4@PW-αCFs for removal of ENMs mixtures from WW, RW and PW, and therefore, greatly encouraged for the application in the remediation of several other ENMs from water. Comparative account for previous available reports for ENMs removal was presennted in Table 1. This comparison also concludes Fe3O4@PW-αCFs potential for ENMs remediation . Stability assessments of adsorbed ENMs. The stability was tested by shaking the ENMs adsorbed Fe3O4@PW-αCFs (Fe3O4@PW-αCFs-ENMs) up to 72 h in water. The leaching of either Fe3O4 or adsorbed ENMs were not observed, and the released concentrations of CuO, CoO, and ZnO were less than that of the detectable limit (Data not shown). The observations suggest that the adsorption of CuO, CoO, and ZnO onto the surface of Fe3O4@PW-αCFs was most stable. ENMs desorption was almost insignificant even at pH 4. It corroborated the extraordinary bonding capacity of the Fe3O4@PW-αCFs surface over three different ENMs. Furthermore, there is no need to dispose or regenerate the used Fe3O4@PW-αCF, but it can be reused as an adsorbent, catalyst, or antibacterial agents for the further sustainable application.66-68 Imaging, EDS, and mapping. The detailed characterization of the final products and adsorption mechanism was performed to validate Fe3O4@PW-αCFs as a super-adsorbent and to reveal the reasons behind the effective removal of ZnO and CuO or CoO. FE-SEM performed the surface morphology examination of Fe3O4@PW-αCFs, results showed numerous cylindrical shaped micro-fibers of PW-αCFs were not aggregated (Figure S4a). The size of PW-αCFs fibers in its native state was in agreement with DLS measurements (data not shown). Magnified SEM images



of Fe3O4@PW-αCFs surface loaded with CuO, CoO, and ZnO was clearly demonstrated by the respective ENM removal (Figure S4b-c). The SEM images of clearly exhibited aggregates of sheet-like structures of CuO (Figure S4b). Meanwhile, CoO was also observed to form a large aggregate (Figure S4c), in contrast to Fe3O4 that were significantly small in size. The SEM images of the Fe3O4@PW-αCFs prepared after removal of ZnO are shown in Figure S4d. In high magnification SEM images, ZnO aggregate structures were clearly evident onto the surface of fibers. Therefore, these respective surface observations under SEM strongly corroborated an adsorptive aggregation of ENMs. Figure 5a shows the STEM image of the Fe3O4@PW-αCFs exposed to an equal amount of CuO, CoO, and ZnO. More interestingly, the adsorbed ENMs were not distributed uniformly on the surface of the Fe3O4@PW-αCFs. Figure 5a depicts the shape and sizes observed in the STEM image allow differentiating in between CoO and ZnO were much smaller than those of CuO. Additionally, the CuO were well organized side to side and formed sheet-like structures and at some places it seemed as flower-like structures. The randomly distributed structures of CuO, CoO, and ZnO might give rise to elevated surface to volume area and adsorption sites to each other, thus assisted adsorption and aggregation markedly, as seen in Figure 5a. Furthermore, the EDS and elemental mapping of the Fe3O4@αCF-ENMs was shown in Figure 5b-f. The EDS spectra of Fe3O4@PW-αCFs-ENMs shown in Figure 5b revealed the presence of only Cu, Co, Zn, Fe, O and C elements. The obtained results corroborated the successful loading of ENMs onto the Fe3O4@PW-αCFs surface. Additionally, the obtained EDS results also gave strong validation of ENMs removal capacities shown by Fe3O4@PW-αCFs. EDS elemental mapping revealed the existence of Fe, Cu, Co, and Zn onto surface of the


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Fe3O4@PW-αCFs-ENMs. Figure 5c-f shows the corresponding Fe, Cu, Co, and Zn TEM-EDS maps, as the main constituent metals of Fe3O4@PW-αCFs-ENMs. ENMs adsorptive removal suggests ENMs underwent extensive aggregation to form large aggregates as can be seen in TEM imaging under standard operational conditions. The mapping data show that the Fe3O4 NPs were found spread around the PW-αCFs surface (Figure 5c). Remarkably, the Fe3O4 NPs were uniformly arranged on the surface of the PW-αCFs as shown in Figure 5a. TEM mapping suggests, matrix of PW-αCFs also acts as a spacer to avoid agglomeration of Fe3O4 NMs and promote their dispersion onto the PW-αCFs (Figure 5c). Figure 5d, f shows an overlay arrangement for Cu and Zn distribution; thus, Cu nanosheets were scattered around the surface of the ZnO NMs. It can be noticed that the distribution of CoO on the Fe3O4@PW-αCFs was somewhat heterogeneous (Figure 5e). These results demonstrate that the ENMs together forms heavyweight aggregates and covers the surfaces of Fe3O4@PW-αCFs and also confirms the successful removal of a mixture of Cu, Co, and Zn oxides from the real-world water (Figure 5df). This aggregative adsorption of studied ENMs onto Fe3O4@PW-αCFs surface can be an alternative “green” solution to the present methods used for ENMs treatment.

CONCLUSIONS This study represent a facile, cost-effective, and practically-viable wastewater treatment by utilizing renewable Fe3O4@PW-αCFs as a super-magnetic bioadsorbent for the removal of large quantities of ENMs, such as CuO, CoO, and ZnO from various real-world wastewater samples. The advantage of hydroxyl functional groups on PW-αCFs and the careful magnetization of this biopolymer provide a new surface platform technology that could be



efficiently used to target various ENMs from the water. Fe3O4@PW-αCFs also assisted the removal of high concentrations of ENMs from the WW, RW and PW. Fe3O4@PW-αCFs not only prevents the ENMs leaching into the water but also inhibits the dispersion of attached-Fe3O4 into the water. As demonstrated, the ease of preparation, magnetization, and separation together with low-cost, light-weight, and high-performance in ENMs removal suggests possibilities in practical applications. Raw material used in preparation of PW-αCF is abundantly available and renewable; thus, the theme of proposed bio-adsorbent follows green chemistry principle called ‘use of renewable feedstock’. Therefore, Fe3O4@PW-αCF based bio-adsorbents might become the best choice for laboratory water and commercial level wastewater treatment. Furthermore, Fe3O4@PW-αCFs will also blow as a new bioadsorbents having useful properties and for diverse applications.

ACKNOWLEDGMENTS National Research Foundation of South Korea supported this research under Project No. 2017R1C1B-5017360. This work is also supported by a grant (2017001970003) from the Ministry of Environment, South Korea. This research work was endorsed by Dongguk University-Seoul, South Korea Research Fund 2017-2020. Supporting Information: The supporting information is available free of charge on the ACS Publications website at DOI: The schematic representation of the PW-αCFs magnetization, characterization of ENMs and Fe3O4@PW-αCFs, SEM imaging of the Fe3O4@PW-αCFs and Fe3O4@PW-αCF-ENMs.


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Table 1 Comparison with other methods in the removal of various ENMs. Removal Method

Type of ENM

Removal

Reference

capacity Simulated Wastewater ZnO

5 mg L−1

69

70

Treatment Activated Carbon

ZnO

9.3 mg/g

Membrane Filtration

ZnO

10 mg/L

Bacterial Adsorption

CuO

5 mg/L

71

Coagulation

Cadmium telluride

12.2 mg/L

72

Coagulation

Fe2O3,

ZnO,

oxide,

and

Nickel ~7-8 mg/L

73

Titanium

dioxide nanopowder Filtration

Silver NPs, Titanium 1 to 3 mg/L

74

dioxide, and ZnO Coagulation

nC60

Coagulation

Multi

0.3 to 1 mg/L walled

carbon 2 to 4 mg/L

75 76

nanotubes Adsorption Adsorption, separation

CoO

85 mg/L

magnetic Cuo, Zno, and CoO 90 mg/L NPs


77

This study

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Figure Legends: Figure 1. (a) VSM analysis of Fe3O4@PW-αCFs, (b) TGA analysis of PW-αCFs and Fe3O4@PW-αCFs, (c) XRD spectrum of PW-αCFs and Fe3O4@PW-αCFs, (d) FTIR analysis of PW-αCFs and Fe3O4@PW-αCFs. Figure 2. (a) UV-vis spectra of CuO, CoO, and ZnO, (b) UV-vis spectra of CuO, CoO, and ZnO after treatment with Fe3O4@PW-αCFs, (Inset shows the color of solutions), (c) Real-time removal of CuO, CoO, and ZnO at 100 mg/L using PW-αCFs, (d) Real-time removal of CuO, CoO, and ZnO at 100 mg/L using Fe3O4@PW-αCFs. Figure 3. (a) Effect of static and shaking conditions on removal efficiency of PW-αCFs and Fe3O4@PW-αCFs at 100 mg/L, Effect of initial concentration from 100 to 300 mg L–1 of (b) CuO, (c) CoO, and (d) ZnO on removal efficiency of PW-αCFs and Fe3O4@PW-αCFs. Figure 4. (a) Effect of pH on the adsorption capacity of Fe3O4@PW-αCFs against ENMs, CuO, CoO, and ZnO at 100 mg/L, (b) Treatment of three different synthetic wastewater prepared using addition of CuO, CoO, ZnO 100 mg/L using Fe3O4@PW-αCFs. (WW: Waste Water, RW: River Water, PW: Pond Water). Figure 5. TEM imaging, EDS and elemental mapping of the ENMs mixture (CuO, CoO, ZnO) at 100 mg/L treated Fe3O4@PW-αCFs, (a) STEM image, (b) EDS spectrum, an elemental map of (c) Fe, (d) Cu, (e) Co, (f) Zn.



120

(b)

(a)

20

PW-CFs Fe3O4@PW-CFs

10 Weight (%)

Magnetic saturation (emu/g)

100

Fe3O4@PW-CFs 0

80 60 40

-10 20 -20 -15000

-10000

-5000

0

5000

10000

15000

0

200

400

600

800

Temperature ( oC) 800


(d)


(c)

%Transmittance

600 Intensity (cps)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 37

400

200

0 20

30

40

50

60

70

80

1000

2000

3000

Wavenumber (cm -1)

2 Theta

Figure 1.


4000

Page 33 of 37

(a)

(b)

1000

1000

(c)

(d) 900

900 CuO CoO ZnO

700 600

qe (mg/g)

800

800

qe (mg/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


CuO CoO ZnO

700 600 500

500

400

400

300

1

2

4

6

12

24

48

1

Time (h)

2

4

6

Time (h)

Figure 2.


12

24

48


Page 34 of 37

(a)

(b)

(c)

(d)

Figure 3.


Page 35 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4.



(a)

(b)

(c)

(d)

(e)

(f)

Figure 5.


Page 36 of 37

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TOC graphic:

Synopsis: Paper waste derived α-cellulose fibers super-magnetized and their applications in remediation of engineered nanomaterials from water are discussed.


Treatment of Hazardous Engineered Nanomaterials by Super

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