Waste Carton-Derived Nanocomposites for Efficient Removal of

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Waste carton-derived nanocomposites for efficient removal of hexavalent chromium Jie Han, Guilong Zhang, Linglin Zhou, Furu Zhan, Dongqing Cai, and Zhengyan Wu Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b00225 • Publication Date (Web): 11 May 2018 Downloaded from http://pubs.acs.org on May 13, 2018

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Waste carton-derived nanocomposites for efficient removal of hexavalent chromium Jie Han†,‡, Guilong Zhang†,§, Linglin Zhou†,‡, Furu Zhan*,†,§, Dongqing Cai*,†,§, Zhengyan Wu*,†,§

†

Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei

Institutes of Physical Science, Chinese Academy of Sciences, 350 Shushanhu Road, Hefei, Anhui 230031, People’s Republic of China ‡

University of Science and Technology of China, No. 96 Jinzhai Road, Hefei, Anhui

230026, People’s Republic of China §

Key Laboratory of Environmental Toxicology and Pollution Control Technology of

Anhui Province, Hefei Institutes of Physical Science, Chinese Academy of Sciences, 350 Shushanhu Road, Hefei, Anhui 230031, People’s Republic of China

*Corresponding authors. *F.Z. Tel.: +86-551-65593339. E-mail: [email protected]. *D.C. Tel.: +86-551-65595143. E-mail: [email protected]. *Z.W. Tel.: +86-551-65595012, Fax: +86-551-65595012. E-mail: [email protected].

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Abstract: A new nanocomposite (SCZ), micro spherical carbon (SC) loaded with nanoscale zero-valent iron (ZVI), was fabricated to efficiently remove hexavalent chromium (Cr(VI)) in water. Therein, SC was derived from waste carton through hydrothermal treatment after pretreatment of removing hemicellulose and lignin, and the optimal hydrothermal conditions (200oC, hydrothermal time of 12 h) for the preparation of SC were obtained. Subsequently, SC could effectively load ZVI nano particles which displayed high dispersion on the surface of SC and in the pores among SC particles owing to steric hindrance effect. The obtained SCZ displayed a high removal efficiency of 100% within 5 h on Cr(VI) (20 mg/L), and the resultant SCZ-Cr could be conveniently separated from water because of its magnetism. Importantly, SCZ could be loaded in cardboard and the obtained system could serve as a stable filter for removal of Cr(VI) in water. This work provides a cheap and effective method for Cr(VI) removal, which also greatly facilitates the recycling of waste carton. Keywords: waste carton; spherical carbon; zero-valent iron nanoparticles; Cr(VI); removal

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INTRODUCTION With the fast development of modern logistic industry, a large quantity of cartons made from wood were produced and widely used for packaging. After use, most of them were discarded, contributing to 40-45% of municipal solid waste,1 which not only caused a great consumption of wood resource, but also brought about serious environmental pollution.2 As such, it is essential to develop facile approaches to dispose and recycle waste carton, which was beneficial for saving wood resource and reducing environmental pollution. During the past few decades, a few methods have been used to promote the recycling of waste carton as composting,3 biomethane source,2,4 raw materials for production of lactic acid5 and bioplastics6 and so on. Although these approaches could promote the recycling of waste carton to a certain extent, they have several disadvantages including complex procedure, low commercial value, and secondary pollution, greatly limiting their wide application. Therefore, it was rather necessary to develop environmentally friendly approaches with simple procedure to improve physico-chemical property, enhance commercial value, broaden application field, and thus greatly facilitate the recycling of waste carton. In recent years, using waste carton as precursor to prepare carbon materials began to arouse the attention of scholars in environment and material fields. Wang et al fabricated a kind of carbon material using waste carton through calcination under N2 protection to be used for symmetric supercapacitor.7 This method provided a new route to enhance commercial value of waste carton, however it displayed a dominant 3


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shortcoming of demanding of rigorous condition, which was unfavorable for its huge application. More importantly, it was a big challenge to fabricate waste carton-based carbon materials with regular shapes such as sphere, fiber and so on which could well fulfill the special demand of several fields.8 Hexavalent chromium (Cr(VI)), a typical heavy metal ion, showed a high risk of inducing cancer and gene-mutation for human beings.9 Until now, a number of approaches including electrochemical precipitation,10 membrane separation,11 ion exchange,12 photocatalysis13 and etc. were used to remove Cr(VI) in water. Recently, using nanomaterials in removal of Cr(VI) has received considerable attention because of their outstanding properties and high efficiencies.14-16 Therein, using nano scale zero-valent iron (ZVI) to remove Cr(VI) has become a hot topic, because of its multi-functions of adsorption, reduction, and convenient separation abilities at the same time.17 Nevertheless, due to interparticle interactions like magnetic interaction and Van der Waals forces, ZVI nanoparticles tended to aggregate, resulting in significant decrease of adsorption and reduction capabilities.18,19 Hence, developing approaches with simple procedure to prevent aggregation of ZVI becomes a primary demand for promoting the wide application of ZVI in environment. In recent years, spherical carbon (SC) has been widely used as carrier material of catalyst because of its excellent dispersion, good chemical stability, and high mechanical strength.20,21 Herein, we attempted to use SC as a carrier for ZVI to prevent aggregation of ZVI. In this study, waste carton was used as precursor to prepare uniformly micron-sized SC through hydrothermal treatment. Afterward, ZVI nanoparticles could 4


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be easily loaded on the surface of SC and in the pores among SC particles, displaying a high dispersion. The removal performance of the obtained nanocomposite (named as SCZ) on Cr(VI) from water was investigated under different temperature and pH conditions. Additionally, the removal ability of a filter, fabricated through loading of SCZ powders in internal channels of carton, on Cr(VI) was also investigated. Importantly, a pot test was performed to study the inhibition effect of SCZ on the uptake of Cr by plant. The interactions among Cr(VI), SC, and ZVI were studied to obtain the mechanism. This work not only developed a new route for recycling of waste carton, but also an efficient means for removal of Cr(VI) in water, which would present a high application value. EXPERIMENTAL Materials. Reagents (K2Cr2O7, NaOH, HNO3, NaClO2, NaBH4, FeSO4•7H2O) and other chemicals with analytical grade were provided by Sinopharm Chemical Reagent Company (Shanghai, China). Deionized water was used in all the experiments. Pretreatment of waste carton. Waste carton was ground to be powders (100-200 mesh) which (20 g) was then added to 800 mL of NaOH (50 mg/L) aqueous solution. Then the mixture was continuously stirred at 200 rpm under 100oC to remove hemicellulose in waste carton. After 2 h of stirring, the precipitate was obtained through centrifugation at 12000 rpm and washed by deionized water until a neutral pH was achieved. Then the resulting sample was added to a solution which was prepared via adding concentrated nitric acid (1 mL) dropwise to 800 mL of 5


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NaClO2 aqueous solution with concentration of 20 mg/L. Afterwards, the system was continuously stirred at 200 rpm under 100oC to remove lignin from waste carton. After 2 h of stirring, modified waste carton (MWC) with a dominant component of cellulose was obtained after filtering and drying at 60oC for 20 h. Preparation of SC by hydrothermal treatment. Based on previous studies,8,22,23 SC was fabricated with several modified parameters. MWC aqueous solution with concentrations of 5, 20, or 30 mg/L was placed in a 150 mL of teflon-lined stainless steel autoclave respectively and the resulting system was kept at 160, 180, and 200oC for a given time. After that, the precipitate was obtained through centrifugation at 12000 rpm and washed with deionized water twice and subsequently ethanol for three times. Finally, SC powders (100-200 mesh) were obtained after vacuum-drying (60 oC) for 12 h and grinding. Loading ZVI nanoparticles on SC. ZVI was prepared by the borohydride reduction method.24-26 SC (1 g) and FeSO4•7H2O with a given amount were mixed in a three-neck ﬂask with 200 mL of oxygen-free deionized water and then stirred (200 rpm) for 30 min. Then 10 mL of NaBH4 (n(FeSO4•7H2O):n(NaBH4)=1:5) was added dropwise to the mixture and the reduction process of the whole system was carried out under nitrogen atmosphere. After another 30 min stirring (200 rpm), SC/ZVI composites with weight ratios (WSC:WZVI) of 2:1, 1:1, and 1:2 respectively were obtained after magnetic separation, washing with deionized water twice and ethanol for three times, and subsequently vacuum-drying at 60oC for 12 h. Cr(VI) removal efficiency of SC/ZVI in aqueous solution. SC, ZVI or SC/ZVI 6


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with amount of 20 mg was placed in 30 mL of Cr(VI) (10, 20, 40, 60, 80, or 100 mg/L) aqueous solution respectively and then continuously shaken at 20, 30, 40, and 50°C under varying pH conditions (2.0 to 10.0). After different intervals, the remaining Cr(VI) concentration in the solution was measured by diphenylcarbazine (DPCI) method.27 All experiments were carried out in triplicate. The Cr(VI) RE was obtained on the basis of equation (1): RE (%)=(C0-Ct)/C0×100%

(1)

Where C0 and Ct are the initial and remaining concentrations (mg/L) of Cr(VI) respectively. Through the RE investigation on Cr(VI), the optimal SC/ZVI (WSC:WZVI=1:2) was named as SCZ. RE of cardboard/SCZ (CB/SCZ) on Cr(VI). To make full use of carton, cardboard cut from the waste carton was used as a carrier to load SCZ, and the obtained CB/SCZ was used as a filter to remove Cr(VI) through filtration. SCZ powders (1 g) were loaded in the internal channels of a piece of circular cardboard (radius of 4.5 cm) with approximately 50 holes with diameter of 0.5 mm on both sides to obtain CB/SCZ. Then the CB/SCZ was used as a filter in a Buchner funnel with diameter of 9 cm. Every 20 min, Cr(VI) (10 mg/L) aqueous solution with 10 mL was dropped evenly onto the top of CB/SCZ, making the leachate flow into a beaker. After that, the Cr(VI) concentration remained in the leachate was determined. The RE on Cr(VI) after filtering through CB/SCZ was obtained on the basis of equation (2): RE (%)=(C0-Ct)/C0×100%

(2)

Where C0 and Ct are the initial and resulting concentrations (mg/L) of Cr(VI) 7


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respectively. Pot experiment. Firstly, SCZ (1 g) was placed in a plastic box (10×25×12 cm) with 500 mL of Cr(VI) aqueous solution (10 mg/L). Then, 12 pieces of water spinach (length of 5-10 cm, diameter of approximately 1 cm) evenly carried by a rectangle foam board (10×20 cm) were placed on the surface of the resulting solution. After that, the box was kept in a greenhouse at 25oC. After 7 days, the chlorophyll content in the water spinach leaves was measured. After that, the water spinach was dried at 60oC for 20 h, the amount of Cr in water spinach was measured using an inductively coupled plasma optical emission spectroscopy (ICP−OES, ICAP 7200, Thermo Fisher Scientiﬁc, USA) after digestion.28 Characterization. The morphologies, and composition were measured using a scanning electron microscope (SEM) with an energy dispersive X-ray spectrometer (EDX) (Sirion 200, FEI Co., USA). The chemical status was analyzed on an X-ray photoelectron spectroscope (XPS, ESCALAB 250, Thermo-VG Scientific Co., USA) and a TTR-III X-ray diffractometer (XRD, Rigaku Co., Japan). The concentration of Cr(VI) was determined on an ultraviolet-visible (UV-vis) spectrophotometer (UV Lambda 365, PerkinElmer Co., USA) at 540 nm. RESULTS AND DISCUSSION Fabrication of SC and morphology observation. Generally, carton mainly consisted of hemicellulose, lignin, and cellulose, wherein hemicellulose and lignin displayed a lower chemical activity and thus were more difficult to be carbonized through chemical method such as hydrothermal treatment compared with cellulose.29 8


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In order to fabricate uniform micro/nano carbon materials based on waste carton, we developed a facile pretreating method to remove hemicellulose and lignin from waste carton through immersion in NaOH and then NaClO2 aqueous solutions at 100oC (Figure 1). After such a pretreatment, the obtained modified waste carton (MWC) consisted of mainly cellulose and thus could easily be transformed to SC through hydrothermal treatment, and the resulting SC could be used a carrier to load ZVI nano particles to obtain SC/ZVI. In the following, this will be discussed in detail. The morphologies of MWC products after hydrothermal treatment at different temperatures (160, 180, and 200oC) for 12 h were observed compared with raw waste carton. As shown in Figure 2a, after hydrothermal treatment at 200oC, waste carton displayed an irregular aggregate morphology rather than regularly-shaped carbon materials, which was probably because of the existence of chemically inactive hemicellulose and lignin in waste carton. As for MWC, it possessed a fibrous morphology with width of approximately 20 µm (Figure 2b), suggesting that cellulose was the dominant component of MWC. After hydrothermal treatment at 160oC, most of the MWC fibers disappeared and changed to a compact film with several small fibers on the surface (Figure 2d and 2g), wherein SC was not found, demonstrating that hydrothermal treatment at 160oC could just decompose the cellulose of MWC to small molecules rather than carbonization. While, after the hydrothermal treatment at 180oC, MWC displayed a porous network structure with a certain amount of micro SC on the surface (Figure 2e and 2h), exhibiting that hydrothermal treatment at 180oC could make a part of MWC carbonize to form SC. When the temperature increased to 9


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200oC, almost all the MWCs were transformed to SC with diameters of 0.2-2 µm (Figure 2c, 2f, and 2i). This result indicated that both the pretreatment and hydrothermal temperature displayed great effects in the fabrication of SC based on MWC, and 200oC was the optimal temperature. Besides, the influence of the time of hydrothermal treatment at 200oC on the morphology of SC was investigated to obtain the growth process of SC. As illustrated in Figure 3a and 3b, at hydrothermal time of 2 h, the MWC fibers illustrated a rather rough surface with several large defects in some parts of MWC, while SC was not generated. When the hydrothermal time was prolonged to 4 h, MWC displayed a much more irregular morphology because a large part of the fibers became short and thin ones, wherein several SC appeared on the surface (Figure 3c). After hydrothermal treatment for 6 h, all the fibers disappeared and changed to abundant SC particles and other small irregular particles (Figure 3d). When the hydrothermal time increased to 12 h, almost all the MWCs were converted to intact SC (diameter of 0.2-2 µm) accompanying with a few irregular particles (Figure 3e). However, after hydrothermal treatment for 24 h, the number of SC decreased while the number of irregular particles increased, suggesting that a part of SC were destroyed and transformed to irregular particles (Figure 3f). The morphology changes of MWC after hydrothermal treatment for different time could be interpreted that, during the initial 4 h, cellulose was gradually converted to monomers through hydrolysis and then converted to soluble organic compounds through dehydration, decarboxylation, and fragmentation. Afterwards (from 4 to 12 h), polymerization of these compounds occurred, leading to 10


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the formation of SC particles.30 After 12 h, some of the obtained SC particles were decomposed to be irregular small fragments. Therefore, 12 h was the optimum hydrothermal treatment time for synthesis of SC. Additionally, the effect of concentrations (5, 20, and 30 mg/L) of MWC on the morphologies of the hydrothermal (200oC and 12 h) products was also studied to get the optimum concentration of MWC. It was displayed in Figure 4a-d that plenty of smooth and intact SCs with few impurities were generated at MWC concentration of 20 mg/L rather than 5 mg/L, which was probably because the polymerization processes of the hydrothermal compounds occurred and meanwhile SC formed at a sufficient concentration of MWC. Nevertheless, when the MWC concentration increased to 30 mg/L, just a few SCs with rough surface were formed, exhibiting that over-dose of MWC was unfavorable for the fabrication of SC. Based on the preceding studies, the optimal hydrothermal conditions for the preparation of SC using MWC were selected as 200oC, hydrothermal time of 12 h, MWC concentration of 20 mg/L. Fabrication of SCZ. Subsequently, the as-prepared SC was used as the carrier to load ZVI nanoparticles in order to fabricate SC/ZVI nanocomposite. To obtain the optimum WSC:WZVI, the influence of weight ratios (WSC:WZVI) of 2:1, 1:1, and 1:2 at a certain concentration of SC on the morphology of SC/ZVI was studied as exhibited in Figure 5a, after the loading of ZVI on SC with WSC:WZVI of 2:1, only a small amount of ZVI particles with size of approximately 200 nm distributed on the SC surface and the pores among SC particles, resulting in a low loading efficiency. As for the SC/ZVI with WSC:WZVI of 1:1, more ZVI nanoparticles with a lower dispersion 11


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and size of approximately 100-200 nm generated and distributed mainly in the pores among SC particles (Figure 5b), which was unfavorable for the reduction capacity of ZVI. When the ZVI concentration further increased to WSC:WZVI of 1:2, abundant ZVI nanoparticles generated with a larger size of approximately 400 nm and a significantly higher dispersion, and distributed evenly on the surface of SC and in the pores among SC particles (Figure 5c), which could facilitate the reduction performance of ZVI. This result indicated that SC could be an ideal carrier for loading of ZVI particles and greatly promoted the dispersion of ZVI particles through steric hindrance effect. As such, WSC:WZVI of 1:2 was the optimal weight ratio for fabrication of SC/ZVI which was designated as SCZ. The crystal structure of SCZ was investigated by XRD measurement. As illustrated in Figure 5d, SC displayed a broad XRD peak at approximately 22o, demonstrating that SC was a typical amorphous carbon.31 Additionally, SCZ displayed a significantly characteristic peak at 44.5-45.0o ascribed to Fe0,32 proving the success loading of ZVI in SC, which was consistent with the XPS studies in Figure 5e. Notably, the peak of SC at 22o was not found in the spectrum of SCZ, which was because of the significantly higher XRD activity of crystal-structured ZVI compared with amorphous-structured SC. In addition, N2 adsorption-desorption isotherm and pore size distributions of SC and SCZ were also measured. It could be seen in Figure 5f that the specific surface area of SCZ (59.65 m2/g) was obviously larger than that of SC (11.64 m2/g) because SC greatly promoted the dispersion of ZVI. Figure 5g showed that SCZ owned a 12


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small quantity of mes/macro pores (4-100 nm) and mespores (2-3.5 nm). The mes/macro pores were probably formed by SC and ZVI particles, and the mespores were likely attributed to the unoccupied pores in SC by ZVI. While SC possessed only a few mespores (2-4 nm) likely because of the smooth surface and regular structure. Cr(VI) removal performance of SCZ. The Cr(VI) removal efficiencies of SC, ZVI, and SC/ZVI with WSC:WZVI of 2:1, 1:1, and 1:2 were studied. It can be seen in Figure 6a that SC exhibited a slow and low RE of 22% for Cr(VI) because there were some pores in SC and a small amount of oxygen groups (-OH) on the surface of SC. While SC/ZVI displayed a significantly higher RE for Cr(VI) than SC, likely because of the reduction effect of ZVI carried by SC. The RE of SC/ZVI on Cr(VI) showed a great increase with the increase of ZVI amount, demonstrating the key role of ZVI in Cr(VI) removal. Therein, the maximal Cr(VI) RE of 100% within 5 h was obtained by SC/ZVI with WSC:WZVI of 1:2 (actually SCZ), which mainly attributed to the highest dispersion of ZVI (Figure 5c). Noteworthily, SCZ displayed a higher RE than ZVI alone (approximately 80%), suggesting that SC as a carrier could efficiently promote the removal ability of ZVI for Cr(VI). On one hand, SC could effectively enhance the dispersion of ZVI, on the other hand, SC could adsorb Cr(VI) onto the surface, which greatly favored the reduction of Cr(VI) by ZVI. Besides, the RE of SCZ with different initial Cr(VI) concentrations were studied. It can be seen in Figure 6b, with the increase of initial Cr(VI) concentration, that the removal capacity of SCZ increased gradually and reached 65.5 mg/g at 100 mg/L of 13


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Cr(VI), likely attributed to the increase of contact probability between Cr(VI) ions and SCZ. Additionally, the RE on Cr(VI) decreased with the increasing initial concentration of Cr(VI). Figure 6c showed the RE of SCZ for Cr(VI) at different temperature (20-50oC). With the increase of temperature, the RE of SCZ showed a significant increase, indicating that the adsorption of SCZ was an endothermic process.33 This was because the Brownian movement of SCZ could be boosted at higher temperature and the contact probability between Cr(VI) ions and SCZ also increased. In addition, the REs of SCZ under varying pH conditions were also studied. Figure 6d illustrated that the RE of Cr(VI) decreased obviously from 100% (pH=2.0) to 17% (pH=10.0) with the increasing pH, which indicated that pH played an important role in the removal of Cr(VI) by SCZ. This was because the chemical state of Cr(VI) was greatly affected by pH, and HCrO4- was the dominant form under acid condition while CrO42- was dominant under neutral and alkaline conditions.34 Therein, HCrO4- possessed a higher oxidation capacity compared with CrO42-, therefore HCrO4- was more active to SCZ than CrO42-. Meanwhile, ZVI was also more active to reduce Cr(VI) under acid condition according to reaction (1): Cr2O72- + 14H+ + 3Fe → 2Cr3+ + 7H2O + 3Fe2+

(1)

Cr(VI) removal mechanism. The removal mechanism of SCZ for Cr(VI) was studied through XPS analyses. In the full spectrum of SCZ-Cr (Figure 7a), the characteristic peaks of Cr could be seen, indicating that Cr was adsorbed in SCZ. In addition, the obvious peak (576.8 eV) in the Cr2p spectrum of SCZ-Cr (Figure 7b) 14


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was consistent with the binding energy of Cr(III), proving that the Cr(VI) was reduced to Cr(III) which was then adsorbed in SCZ.35 As shown in Figure 7c, the peaks (710.8, 719.0, and 724.8 eV) corresponding to the oxide compounds of iron could be seen in Fe2p spectrum of SCZ-Cr, indicating that ZVI was oxidized during the Cr(VI) treatment.36 Based on the analyses above, the Cr(VI) removal mechanism of SCZ was obtained and displayed in Figure 7d. Firstly, Cr(VI) ions were adsorbed in SCZ, wherein a large amount of Cr(VI) ions were reduced to Cr(III) by ZVI. At the same time, the ZVI converted to oxide compounds of iron. Other Cr(VI) ions were reduced to Cr(III) by -OH on SC. Finally, the obtained Cr(III) and a small number of remaining Cr(VI) ions were adsorbed on the surface or in pores of SCZ. Then the final SCZ-Cr could be removed easily from water using a magnetic (0.1 T) (Figure 7e). RE of CB/SCZ on Cr(VI) through filtration. To promote the application of SCZ and make full use of carton, SCZ powders were evenly loaded in the internal channel of a piece of circular cardboard (radius of 4.5 cm) to obtain CB/SCZ (Figure 8a). Afterwards, the Cr(VI) solution was filtered through a Buchner funnel using a piece of CB/SCZ as the filter. As shown in Figure 8b, after filtering for 15 times, the CB/SCZ still exhibited a high RE (>65%) for Cr(VI), indicating the reuse property and high stability of CB/SCZ. During the process of filtration, Cr(VI) could be adsorbed in CB/SCZ and subsequently reduced to Cr(III). Meanwhile, the obtained Cr(III) remained in CB/SCZ, resulting in clean leachate. It can be seen in Figure 8c 15


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that, after the filtering, Cr distributed evenly in the internal channel of CB/SCZ, indicating the effective adsorption of Cr (mainly Cr(III)) in CB/SCZ. Noteworthily, the Fe and C also distributed evenly in CB/SCZ-Cr, which demonstrated the stable existence of SCZ particles in the internal channel of CB. This result indicated that waste carton could be used as not only a good precursor to fabricate SC but also an ideal support for SCZ to construct a high-performance filter for Cr(VI) removal. Effect of SCZ on plant growth. A large amount of Cr in growing environment of plant results in imbalance of nutrient, top wilting, chlorosis in young leaves, and then inhibition on plant growth.37 Cr is easily absorbed by crops and then mankind, bringing about various diseases. The effect of SCZ on growth and Cr absorption of water spinach, a typical vegetable growing in water, in Cr(VI)-contaminated water was investigated. As seen in Figure 9, SCZ has a significantly positive effect on the growth of water spinach, including smaller area of yellow leaves, larger height, higher chlorophyll content in leaves (Figure 9b), and lower Cr concentration in water spinach (Figure 9c) compared with that without treatment. This result presented that the addition of SCZ to Cr(VI)-contaminated water could effectively promote the growth of water spinach, inhibit the uptake of Cr, and improve the bio-safety of plants. CONCLUSION In conclusion, waste carton was used as precursor to fabricate SC and the optimal condition was investigated. The as-prepared SC was used as a carrier to load ZVI for improving the dispersity of ZVI. The obtained SCZ could efficiently remove Cr(VI) in water through adsorption and reduction. After Cr(VI) treatment, the resulting 16


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SCZ-Cr could be removed conveniently from water using a magnet. Importantly, SCZ could be conveniently loaded in the internal channel of cardboard to obtain a stable filter (CB/SCZ) for removal of Cr(VI) through filtering. Therefore, this work not only develops a new route to effectively recycle the disposed waste carton, but also provides a high-performance composite to remediate Cr(VI)-contaminated water, which would present a high application value. AUTHOR INFORMATION Corresponding Authors *F.Z. Tel.: +86-551-65593339. E-mail: [email protected]. *D.C. Tel.: +86-551-65595143. E-mail: [email protected]. *Z.W. Tel.: +86-551-65595012, Fax: +86-551-65595012. E-mail: [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS The authors acknowledge financial support from the Youth Innovation Promotion Association of Chinese Academy of Sciences (No. 2015385), the National Natural Science Foundation of China (No. 21407151), the Environmental Protection Department of Anhui Province (No. 2017-04), the Science and Technology Major Project of Anhui Province (No. 17030701051), the Science and Technology Service Programs of Chinese Academy of Sciences (Nos. KFJ-STS-ZDTP-002 and KFJ-SW-STS-143), and the Key Program of Chinese Academy of Sciences (No. KSZD-EW-Z-022-05). 17


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Figure captions Figure 1. Schematic diagram of synthesis of SCZ. Figure 2. SEM images: (a) waste carton (20 mg/L) after hydrothermal treatment at 200oC for 12 h, (b) MWC (20 mg/L) and its products after hydrothermal treatment at (d, g) 160, (e, h) 180, and (f, i) 200oC for 12 h. (c) Particle size distribution of SC obtained by hydrothermal treatment at 200oC for 12 h. Figure 3. SEM images of products of MWC (20 mg/L) after hydrothermal treatment at 200oC for (a) 0, (b) 2, (c) 4, (d) 6, (e) 12, and (f) 24 h. Figure 4. SEM images of products of MWC with different concentrations of (a, b) 5, (c, d) 20, and (e, f) 30 mg/L after hydrothermal treatment at 200oC for 12 h. Figure 5. (a-c) SEM images of SC/ZVI with WSC:WZVI of 2:1, 1:1, and 1:2 at a certain SC

concentration

of

5

g/L.

(d-g)

XRD

patterns,

XPS

spectra,

N2

adsorption-desorption isotherms, and pore size distributions of SC and SCZ. Figure 6. (a) RE of Cr(VI) (20 mg/L) in water by different samples; (b) RE of SCZ on Cr(VI) with different initial concentrations; (c, d) RE of SCZ for Cr(VI) (40 mg/L) under different temperatures and pH. (Error bars indicate standard deviation (n=3)) Figure 7. (a-c) XPS spectra (full range, Cr2p, and Fe2p) of SCZ-Cr; (d) Schematic diagram of Cr(VI) removal mechanism by SCZ; (e) Digital photos of solutions of (I) Cr(VI), SCZ-Cr (II) before and (III) after magnetic separation by a magnet (0.1 T). Figure 8. (a) Schematic diagram of CB/SCZ filtration system for Cr(VI) removal; (b) RE of CB/SCZ on Cr(VI) with filtering times (Error bars indicate standard deviation (n=3)); (c) SEM image of the marked rectangular region of CB/SCZ after Cr(VI) 24


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treatment and the distribution maps of C, Fe, and Cr in CB/SCZ-Cr. Figure 9. (a) Photos, (b) chlorophyll content of water spinach leaves, and (c) Cr content of water spinach treated with (I) Cr(VI) and (II) Cr(VI)/SCZ. (Error bars indicate standard deviation (n=3))

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Figures

Figure 1

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Figure 2

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Figure 3

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Figure 4

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Figure 5

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Figure 6

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Figure 7

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Figure 8

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Figure 9

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Waste carton-derived nanocomposites for efficient removal of hexavalent chromium Jie Han, Guilong Zhang, Linglin Zhou, Furu Zhan*, Dongqing Cai*, Zhengyan Wu*

TOC Spherical carbon derived from waste carton was used as a carrier for zero-valent iron nanoparticles to efficiently remove Cr(VI).

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Waste Carton-Derived Nanocomposites for Efficient Removal of

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