3D hierarchical graphene oxide-NiFe LDH composite with enhanced adsorption affinity to Congo red, methyl orange and Cr(VI) ions

3D hierarchical graphene oxide-NiFe LDH composite with enhanced adsorption affinity to Congo red, methyl orange and Cr(VI) ions

Journal of Hazardous Materials 369 (2019) 214–225 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.els...

8MB Sizes 0 Downloads 4 Views

Journal of Hazardous Materials 369 (2019) 214–225

Contents lists available at ScienceDirect

Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat

3D hierarchical graphene oxide-NiFe LDH composite with enhanced adsorption affinity to Congo red, methyl orange and Cr(VI) ions


Yingqiu Zhenga, Bei Chenga, Wei Youa, Jiaguo Yua,c, , Wingkei Hob, ⁎



State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Luoshi Road 122, Wuhan, 430070, PR China Department of Science and Environmental Studies and State Key Laboratory in Marine Pollution, The Education University of Hong Kong, Tai Po, N. T. Hong Kong, PR China c Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah, 21589, Saudi Arabia b




Keywords: Hierarchical GO LDH nanosheet Anionic pollutant Adsorption

Three-dimensional (3D) hierarchical graphene oxide-NiFe layered double hydroxide (GO-NiFe LDH) composite with sandwich-like structure is fabricated using a facile one-pot hydrothermal reaction. Electron microscopy images demonstrate that the GO-NiFe LDH composite possesses a highly porous and well-ordered structure. Both sides of the GO are fully covered by the LDH nanosheets, resulting in the sandwich-like architecture. The adsorption performance of the GO-NiFe LDH composite and pure NiFe LDH for three anionic pollutants, namely, Congo red (CR), methyl orange (MO) and hexavalent chromium ion [Cr(VI)] is systematically investigated. The presence of GO in the GONiFe LDH composite leads to the better adsorption capability and faster adsorption kinetics of this composite compared with the NiFe LDH microspheres. The pseudo-second-order kinetic model can well represent the adsorption kinetics, and the Langmuir isotherm model provides a better description for the adsorption isotherms. The GO-NiFe LDH composite demonstrates appreciable potential in alleviating anionic pollutants from the aquatic environment as shown by its excellent adsorption capability towards CR, MO and Cr(VI).

1. Introduction Environmental pollution has become increasingly serious because of

the rapid modern industrialisation. The pollution of water resources has adversely exacerbated the already scarce freshwater. Amongst the various water pollutants, pollution caused by synthetic organic dyes has

Corresponding author at: State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Luoshi Road 122, Wuhan, 430070, PR China. ⁎⁎ Corresponding author. E-mail addresses: [email protected] (J. Yu), [email protected] (W. Ho). ⁎

https://doi.org/10.1016/j.jhazmat.2019.02.013 Received 24 September 2018; Received in revised form 2 February 2019; Accepted 4 February 2019 Available online 06 February 2019 0304-3894/ © 2019 Elsevier B.V. All rights reserved.

Journal of Hazardous Materials 369 (2019) 214–225

Y. Zheng, et al.

recently been paid considerable attention. Colourful dyes can weaken the incident sunlight into the water body and impede the photosynthesis of aquatic plants. This phenomenon will seriously influence the survival of living creatures in the aquatic environment [1,2]. Moreover, synthetic dyes are poisonous to water creatures and human beings because of their inherent toxicity, mutagenicity and carcinogenicity [3–5]. These dyes are highly stable and hardly biodegradable. Although water coloration caused by some dyes can fade by biodegradation, the cleaved products and related aromatic amine compounds remain harmful to human health [6–8]. In addition to dye pollutions, inorganic pollutants in wastewater, especially the toxic metal ions, have become a significant problem and great concern. Chromium, which naturally possesses two main oxidation states [Cr(III) and Cr(VI)], has been listed as one of the most toxic contaminants. Amongst the two states, Cr(VI) displays strong oxidisability, and its toxicity is hundreds of times higher than that of Cr(III) [9,10]. Cr(VI) ions are quite harmful to organisms and associated with various carcinogenic and mutagenic diseases, such as dermatitis, chronic ulcers, liver inflammation and lung cancer [11,12]. Thereby, eliminating Cr(VI) in water is highly indispensable for human health and sustainable development. Numerous techniques have been employed to alleviate the pollution in aquatic environment. Adsorption is one of the most important methods to remove pollutants in effluents because of its remarkable easy operation, high efficiency, low cost and without secondary pollution [13–18]. Amongst the different adsorbents, layered double hydroxides (LDHs) are typical layered materials which have attracted great interest because of their large specific area, excellent ion exchange property, well-ordered layered structure, and high controllability in composition. A series of LDHs and their calcination products with different morphologies have been successfully fabricated and employed to effectively remove many organic and inorganic pollutants in wastewater, such as anionic dyes, heavy metal ions and fluoride [19–22]. Carbon materials are a large class of attractive materials with different allotropes and a variety of microstructures and morphologies, including carbon nanotubes, graphene, graphdiyne, mesoporous carbon, carbon nanospheres, cabon nanofibers, amorphous carbon, carbon black and carbon paper, etc., which have tremendous applications in environment and energy [23–30]. Among the multifarious carbon materials, graphene oxide (GO) is one of the most important carbon materials that has been extensively applied in photocatalysis, sensors, electrocatalysis and adsorption because of its unique physicochemical properties [31–34]. In addition to the large specific surface area of GO nanosheets, GO contain numerous oxygen-containing functional groups, such as hydroxyl (eOH), carbonyl (eC]Oe) and carboxyl (eCOOH) groups on its surface and edge. These groups contribute to the excellent adsorption capability towards various pollutants [35,36]. However, the fast and effective separation of pure GO from aqueous solution remains a challenge because of the strong hydrophilicity and fairly good dispersity of GO in water. The separation process usually involves an energy-intensive centrifugation and separation process. To facilitate the separation of GO from the liquid phase, LDHs have been applied as an efficient coagulation agent to remove GO because of the electrostatic interaction [37–39]. Therefore, the GO-LDH composite can be considered as an excellent adsorbent resulting from its remarkable adsorption performance and easy separation from aqueous solution [39–41]. Among various kinds of LDH, NiFe LDHs have been investigated and found to be a suitable adsorbent for anionic pollutants in water, including anionic organic dyes and Cr(VI) [21,42]. In addition, a starchNiFe LDH composite has been reported to exhibit better adsorption performance for MO compared with pure NiFe LDH [43]. Thus, it is desirable to further improve the adsorption capability of NiFe LDH through the combination with GO. Herein, we report the synthesis of hierarchical NiFe LDH and GO-NiFe LDH composite by a simple

Fig. 1. Synthesis of NiFe LDH microspheres (B) and GO-NiFe LDH composite (C).

hydrothermal process. The NiFe LDH was fabricated in the presence of trisodium citrate (TSC). Due to the strong affinity of citrate ions, the Ni (II) and Fe(II) in the solution are first complexed with the citrate ions. With increasing hydrothermal temperature, urea hydrolyzes and generates OH– and CO32–. Meanwhile, the unstable Fe(II) is oxidized to Fe (III). Finally, the Ni(II)-citrate and Fe(III)-citrate complexes react with the OH– and CO32– to form NiFe LDH [44,45]. We investigated the adsorption capability towards three anionic pollutants, namely, Congo red (CR), methyl orange (MO) and Cr(VI). The as-synthesised GO-NiFe LDH showed well-ordered porous structure and better adsorption capability for the anionic pollutants, compared with pure NiFe LDH. Thus, GO-NiFe LDH can be applied to alleviate the anionic pollutants in wastewater. 2. Experimental section GO was fabricated through a modified Hummer’s method as previously reported [46]. The hierarchical GO-NiFe LDH composite and NiFe LDH microspheres were fabricated through a one-step facile hydrothermal process (Fig. 1). Additional information on the experimentation and characterisation is provided in the Supporting Information. 3. Results and discussion 3.1. Crystal structure The crystal structure of the samples was identified by XRD, and the corresponding patterns of NiFe LDH and GO-NiFe LDH are displayed in

Fig. 2. XRD patterns of pure NiFe LDH (a) and GO-NiFe LDH composite (b). 215

Journal of Hazardous Materials 369 (2019) 214–225

Y. Zheng, et al.

intercalated anionic ions in the interlayer. The similarity in the diffractions in curves (a) and (b) demonstrates the existence of NiFe LDH in the composite. Compared with curve (a), the broader peak at ca. 11.3° in curve (b), which is related to the (003) plane of LDH, implies the lower crystallinity of the NiFe LDH nanosheets in the composite. No GO signal can be observed in curve (b), possibly because the growth of LDH nanosheets on the surface of GO nanosheets results in the exfoliation of GO. This process leads to the destruction of the lamellar structure of the GO nanosheets [47]. 3.2. Raman spectra Raman spectroscopy is extremely sensitive to carbon materials with well-ordered structure. Thus, this technique was performed to examine the existence of GO in the composite. Two conspicuous adsorption bands appear at approximately 1336 and 1593 cm–1 in the Raman spectrum of GO (Fig. 3). These bands can be ascribed to the breathing mode of the κ-point phonons induced by the defects and disordered structure (D band) and the in-plane vibration of the sp2 C atoms arranged in the graphitic lattice (G band), respectively, which is typical characteristic of carbon materials [48]. The Raman spectrum of GONiFe LDH displays the same D and G bands as GO, but no obvious peaks can be detected for the spectrum of NiFe LDH within the wavenumber range in Fig. 3. This result indicates the existence of GO in the GO-NiFe LDH hybrid.

Fig. 3. Raman spectra of the NiFe LDH microspheres, GO-NiFe LDH composite and GO.

Fig. 2. Curve (a) reveals several peaks that can be indexed to the nickel iron hydrotalcite (NiFe LDH) with rhombohedral structure (JCPDS No. 40–0215) [42]. In addition, the slight shift of the diffraction peaks compared with that in the PDF card mainly results from the different

Fig. 4. FESEM images of the NiFe LDH microspheres (a and b) GO-NiFe LDH (c and d); TEM images of GO-NiFe LDH (e and f).


Journal of Hazardous Materials 369 (2019) 214–225

Y. Zheng, et al.

3.3. Morphology and microstructure

Table 1 Pore characteristics for NiFe LDH and GO-NiFe LDH.

The FESEM images of NiFe LDH are shown in Fig. 4a and b. The samples have hierarchically microspheric morphology formed by the assembly of numerous small nanosheets. The microspheres are irregular in size and tend to agglomerate, forming larger aggregates of several micrometres in size. Further magnification of the NiFe LDH microspheres (Fig. 4b) reveals that the nanosheets on the microspheres are ultrathin, with average thickness of less than 10 nm. The GO-NiFe LDH composite exhibits a hierarchically well-ordered structure as shown in the FESEM images in Fig. 4c and d. Both sides of the GO are fully covered by the LDH nanosheets, resulting in a sandwich-like architecture. Closer observation reveals the corrugated and scroll-like edge of the sandwich-like architecture, which inherits the crumpled characteristic of the GO nanosheets. The small-sized LDH nanosheets are interconnected. Thus, a three-dimensional (3D) porous network is developed. This characteristic is quite beneficial for the adsorbate molecules to diffuse rapidly in the samples. Compared with the morphology of individual NiFe LDH, the LDH nanosheets are arranged uniformly on the GO surface rather than being assembled into microspheres. This phenomenon implies that the introduction of GO nanosheets in the composite prevents the aggregation of LDH nanosheets into microspheres. Nevertheless, the growth of NiFe LDH nanosheets on the GO surface can hinder the restacking of GO nanosheets and lead to the exfoliation of GO nanosheets. This result is consistent with the XRD patterns. The TEM images of the GO-NiFe LDH (Fig. 4e and f) manifest that the LDH nanosheets are loosely assembled over the surface of the micron-sized GO nanosheets. Thus, a highly porous structure is developed. Furthermore, the curled edge of the GO-NiFe LDH composite reveals that the LDH nanosheets are almost perpendicularly anchored onto both sides of the GO nanosheets. This phenomenon shows the formation of a sandwich-like structure. The TEM image with higher magnification (Fig. 4f) demonstrates that the thickness of the LDH nanosheets is 3–4 nm, revealing ultrathin structure.


SBET (m2 g–1)

Vp (cm3 g–1)

dp (nm)


136 145

0.34 0.53

10.1 14.6

loops are a combination of type H2 and H3 loops [50]. At relative pressure of 0.4–0.9, the hysteresis loops are of type H2, corresponding to the ink-bottle shaped mesopores originating from the primary LDH nanoparticles within the nanosheets. The loops at relative pressure of 0.9–1.0 demonstrate the characteristic of type H3 hysteresis loop. This result implies the existence of mesopores with narrow-slit shape produced by the assembling of NiFe LDH nanosheets. The isotherms of GONiFe LDH composite display characteristics similar to those of NiFe LDH, revealing similar pore structures and porosities. The pore size distribution curves (inset in Fig. 5) demonstrate that the two samples exhibit bimodal distributions in the range of 2 nm to more than 200 nm. The peak at 2–3 nm for the NiFe LDH microsphere is related to the smaller mesopores generated through the intra-aggregated nanoparticles within the nanosheets. By contrast, the peak at approximately 10 nm can be associated with larger mesopores produced through the self-assembly of the LDH nanosheets. These results are in agreement with the above analysis of the isotherms. The GO-NiFe LDH composite exhibits a bimodal pore size distribution similar to that of NiFe LDH. The two peaks located at ca. 2.5 nm and 40 nm imply that larger mesopores formed between the interconnected nanosheets on the GO. Both samples possess pores with different sizes, ranging from small mesopores, large mesopores, and macropores. Thus, the two samples exhibit hierarchical pore structures, which contribute to the effective adsorption towards pollutants in water. Table 1 lists the specific surface areas (SBET), total pore volumes (Vp) and average pore diameters (dp) calculated using the N2 adsorption–desorption isotherms and pore size distributions. GO-NiFe LDH composite exhibits slightly higher SBET (145 m2 g–1) than pure NiFe LDH (136 m2 g–1), whilst the dp and Vp of GO-NiFe LDH composite are markedly larger than that of NiFe LDH. Higher SBET can generally provide more adsorption sites, whilst larger pore size and pore volume contribute to faster diffusion and better adsorption capacity for the adsorbates. The existence of GO in the composite enlarged the specific surface area, total pore volume and pore size, which is conducive to the excellent adsorption capability.

3.4. Nitrogen adsorption–desorption analysis N2 adsorption–desorption isotherms reflect the porosity of a sample. These isotherms can be used to obtain the specific surface area and pore size distributions. Fig. 5 illustrates these isotherms for the NiFe LDH and GO-NiFe LDH samples, along with the corresponding pore size distribution curves obtained through the BJH method. Hysteresis loops can be detected in the two isotherms, and these loops are typical characteristics of type IV isotherm. Thus, mesopores exist in the two samples [49]. Apparently, step-wise desorption can be observed at the desorption branch in the isotherms of NiFe LDH. Thus, the hysteresis

3.5. Zeta potential measurement The zeta potential was measured at neutral condition to determine

Fig. 5. N2 adsorption–desorption isotherms and corresponding pore size distribution curves (inset) of NiFe LDH microspheres and GO-NiFe LDH composite.

Fig. 6. Zeta potential distributions for NiFe LDH (a), GO-NiFe LDH microspheres (b) and GO (c) in aqueous solution. 217

Journal of Hazardous Materials 369 (2019) 214–225

Y. Zheng, et al.

Fig. 7. XPS survey spectra (a). High-resolution X-ray photoelectron spectra of Ni 2p regions (b), Fe 2p regions (c), and C 1s regions (d) in the NiFe LDH microspheres and GO-NiFe LDH composite.

the charge on the surface of the samples when dispersed in water. Fig. 6 displays the distribution curves of the zeta potential for GO, NiFe LDH and GO-NiFe LDH, with measured average values of −50.5, 28.1 and 19.6 mV, respectively. The isoelectric point (IEP) of GO has been reported to be 3–4 [51], thus the abundant oxygen-containing groups on its surface and edge exhibit inclination to deprotonate. Consequently, the surface of GO is negatively charged at pH 7 [52]. By contrast, as a class of materials with positively-charged host layers, the IEP of LDH materials is greater than 7. Therefore, the surface of NiFe LDH carries positive charges at neutral condition. For the GO-NiFe LDH sample, smaller sized LDH nanosheets cannot completely cover the whole surface of GO. Accordingly, GO-NiFe LDH exhibits a less positive value than pure NiFe LDH at pH 7 because of the negative charges on the surface of GO. With the surface carrying net positive charges, both NiFe LDH and GO-NiFe LDH samples can attract anionic ions through electrostatic interaction, which is quite conducive to the adsorption of anionic pollutants [53].

3.6. XPS analysis XPS was conducted to investigate the chemical status and elemental composition on the surface of NiFe LDH microspheres and GO-NiFe LDH composite. The recorded spectra are presented in Fig. 7. The survey spectra of the two as-prepared samples reveal the existence of O, C, Ni and Fe elements (Fig. 7a). In addition, compared with the survey spectrum of NiFe LDH, the relative intensity of C 1s increases after hybridising with GO. Fig. 7b demonstrates the comparison of the highresolution regions of Ni 2p for the as-synthesised NiFe LDH and GONiFe LDH samples. Four peaks are observed in the Ni 2p region of NiFe LDH. Two peaks located at 855.9 and 873.4 eV are derived from the Ni 2p3/2 and Ni 2p1/2 core levels, whilst the other two peaks at 861.7 and 879.9 eV are associated with their satellites, respectively, which suggest the nickel element in NiFe LDH is in divalent form [42,54]. The two peaks at 712.2 and 724.9 eV can be associated with Fe 2p3/2 and Fe 2p1/ 2 orbitals, respectively (Fig. 7c). This result implies that trivalent iron

Fig. 8. FTIR spectra of the pristine GO-NiFe LDH sample, after the adsorption of CR and MO, pure MO and CR (a) and FTIR difference spectrum after the adsorption of Cr(VI) (b). 218

Journal of Hazardous Materials 369 (2019) 214–225

Y. Zheng, et al.

Fig. 9. Effect of pH on adsorption of CR, MO and Cr(VI) onto GO-NiFe LDH.

Fig. 10. Effect of initial concentration on adsorption of CR, MO and Cr(VI) onto GO-NiFe LDH.

ions exist in LDH [42,54]. The binding energy for the Ni 2p and Fe 2p regions in GO-NiFe LDH composite positively shifted compared with those of pure NiFe LDH (Fig. 7b and c). This phenomenon suggests the interaction between GO and NiFe LDH. Fig. 7d presents the high-resolution spectra of C 1s for NiFe LDH and GO-NiFe LDH. The three regions at approximately 284.6, 286.2 and 288.5 eV in the C 1s region for the GO-NiFe LDH composite can be attributed to the non-oxygenated ring C (C]C), CeO and C]O species, respectively [55]. Similarly, the C 1s region of NiFe LDH microspheres is composed of three parts, in which one peak located at 284.6 eV originates from the adventitious hydrocarbon. The other two at approximately 286.0 and 288.8 eV can be associated with the CeO and C]O groups which originate from the carbonate ions intercalated into the interlayers in the LDH. Moreover, the binding energy of CeO in NiFe LDH is up-shifted from 286.0 eV to 286.2 eV after the hybridisation with GO. By contrast, the peak of C]O shifts downward by 0.3 eV. This phenomenon further confirms the interaction between GO and NiFe LDH [41].

Fig. 11. Relationship between the adsorption quantity and time for CR (a), MO (b) and Cr(VI) (c) adsorption by NiFe LDH and GO-NiFe LDH composite.

1559 cm–1 and the eOH bending mode at 1636 cm–1 [56,57]. Moreover, the adsorption peak at 1357 cm–1 is derived from the carbonate ions in the interlayers of LDH, whilst the weaker peak at 1086 cm–1 indicates the sulphate ions [58,59]. Furthermore, the adsorption peaks within 550–800 cm–1 are assigned to the MeO bonds in the lattice of LDH [60]. After the adsorption of CR, three new adsorption peaks at approximately 1039, 1170 and 1220 cm–1 appeared in the spectrum. These peaks overlap the peak related to the SO42– at 1086 cm–1, which originates from the stretching mode of S]O in the sulfonate group (–SO3−) [61]. In addition, the peak of the adsorption band at 1500–1700 cm–1 shifted to 1606 cm–1. This phenomenon originates from the stretching vibration of the C]C bonds in the CR molecules. This result further confirms the successful adsorption of CR onto the sample [61]. The same shift occurs on the FTIR spectrum after MO

3.7. FTIR spectra FTIR spectroscopy was conducted to investigate the interaction between the GO-NiFe LDH and the adsorbates. The corresponding FTIR spectra are shown in Fig. 8. For the FTIR spectrum of pure GO-NiFe LDH in Fig. 8a, the broad peak at ca. 3383 cm–1 is attributable to the stretching mode of the −OH groups in the surface water molecules [56]. The broad band at approximately 1500–1700 cm–1 is an overlap of two peaks, namely, the asymmetric stretching mode of COO at 219

Journal of Hazardous Materials 369 (2019) 214–225

Y. Zheng, et al.

Fig. 12. Fitted results for CR, MO and Cr(VI) adsorption onto GO-NiFe LDH and NiFe LDH by linearised pseudo-first-order (a, b and c) and pseudo-second-order kinetic models (d, e and f).

adsorption. Moreover, four peaks are detected at approximately 1004, 1029, 1117 and 1166 cm–1 after the adsorption of MO. Amongst these new bands, the sharp peak at 1004 cm–1 is related to the in-plane bending vibration of CeH, whilst the other three peaks are ascribed to the stretching vibration of the sulfonate groups in the MO molecules adsorbed onto the GO-NiFe LDH [62–64]. The FTIR signal of inorganic Cr(VI) is not as strong as those of MO and CR. Thus, the difference in the FTIR spectra of GO-NiFe LDH before and after Cr(VI) adsorption was recorded to further investigate the adsorption process. Fig. 8b shows that the three adsorption peaks at 917, 876 and 820 cm–1 can be ascribed to the asymmetric and symmetric stretching vibrations of Cr–O in the CrO42– tetrahedral. This result is consistent with the previous literature [65,66]. Hence, Cr(VI) is successfully absorbed by the sample. The negative peaks at 1362 and 1080 cm–1 corresponding to the carbonate and sulphate ions imply the decrease in carbonate and sulphate ions whilst adsorbing Cr(VI). This result suggests the ion-exchange behaviour during adsorption.

interaction between GO-NiFe LDH and the adsorbates. When the solution pH is below the IEP of the GO-NiFe LDH, the surface of GO-NiFe LDH is positively charged and can attract the anionic species of CR, MO and Cr(VI) in the solution. As the pH of the solution increases, the positive charges on the surface of GO-NiFe LDH decrease and the negative charges increase. Accordingly, the electrostatic attraction between adsorbent and adsorbates weakens gradually with increasing pH, thus leading to the decrease of the adsorption efficiency. 3.9. Effect of initial concentration The effect of initial concentration on adsorption efficiency was studied. The adsorption efficiency of GO-NiFe LDH varies with the initial concentration of CR, MO and Cr(VI) are displayed in Fig. 10. Obviously, the removal percentage of CR, MO and Cr(VI) all decreases with increasing initial concentration. This is due to the limited adsorption sites of the fixed dosage of the adsorbent. Therefore, it is not surprising that the higher the initial concentration, the lower the adsorption efficiency.

3.8. Effect of pH The solution pH can significantly affect the adsorption performance. Therefore, the experiments of pH-dependent uptake of CR, MO and Cr (VI) on GO-NiFe LDH were conducted within the pH range of 3–10 and the corresponding curves are shown in Fig. 9. It is noted the removal efficiency of CR, MO and Cr(VI) all decreased continually with the pH changing from 3 to 10. This result can be explained by the electrostatic

3.10. Adsorption kinetics Kinetic experiments were performed to evaluate the adsorption rate of the three anionic pollutants by the two samples. Fig. 11 displays the kinetic curves for CR, MO and Cr(VI) adsorption. All six kinetic curves reveal that the uptake rate is quite fast at the initial stage of contact and 220

Journal of Hazardous Materials 369 (2019) 214–225

Y. Zheng, et al.

Table 2 Parameters in the two kinetic models for CR, MO and Cr(VI) adsorption by NiFe LDH microspheres and GO-NiFe LDH composite. Pollutants




qe,exp (mg g–1)

186.5 236.6 94.4 171.9 30.3 42.7

Pseudo-first-order model

Pseudo-second-order model 2

k1 (min–1)

qe,cal (mg g–1)


k2 (g mg–1· min–1)

qe,cal (mg g–1)


0.015 0.017 0.017 0.020 0.020 0.019

126.1 95.1 61.6 71.2 8.1 5.7

0.982 0.976 0.985 0.957 0.944 0.923

2.66 × 10–4 5.09 × 10–4 5.18 × 10–4 6.33 × 10–4 0.007 0.012

195.7 239.2 100.2 177.3 30.7 43.0

0.998 0.999 0.999 0.999 0.999 0.999

then decreases gradually with prolonging time, and eventually the adsorption reaches equilibrium. This is because there are a large number of vacant adsorption sites available at the initial period of adsorption, and then the residual vacant sites become fewer with increasing adsorption time. The adsorption equilibriums of CR, MO and Cr(VI) adsorption were reached at ca. 225, 135 and 84 min for GO-NiFe LDH composite, and 285, 225 and 134 min for NiFe LDH, respectively. GONiFe LDH composite apparently exhibits higher equilibrium adsorption quantity and reaches adsorption equilibrium much faster than NiFe LDH towards all three kinds of anionic pollutants. Table 1 shows that the GO-NiFe LDH composite possesses higher SBET, larger average pore size and total pore volume. Larger SBET and pore volume are generally correlated to more adsorption sites and higher adsorption capacity. Thus, the enhancement in adsorption quantity at equilibrium for GONiFe LDH composite is partially attributed to larger SBET and pore volume than pure NiFe LDH microspheres. Furthermore, abundant oxygen-containing functional groups exist on the surfaces and edges of the GO nanosheets. These groups contribute to the adsorption potential, because they can interact with the adsorbate molecules. Therefore, the better adsorption performance for GO-NiFe LDH composite is derived from the larger SBET and pore volume and the interactions between GO and adsorbates. For the adsorption rate, although both samples possess hierarchical porous structures, the average pore width of the GO-NiFe LDH composite is larger than that of the NiFe LDH microspheres. The larger pore size of the composite is more conducive to the diffusion of the adsorbates [67]. Hence, compared with the NiFe LDH microspheres, less time is consumed by the GO-NiFe LDH composite to reach adsorption equilibrium towards the three pollutants. The data from the adsorption kinetics were analysed by pseudofirst-order and pseudo-second-order kinetic models to further elucidate the adsorption process. The two kinetic models in linearised form are expressed by Equations 5 and 6 in Table S1 [68,69]. The applicability of the two kinetic models was examined using the fitted plots (see Fig. 12) and the corresponding parameters for the two samples towards the three anionic pollutants were listed in Table 2. Fig. 12 shows that all straight lines fitted by the pseudo-second-order model present a better match with the adsorption kinetics data than the lines referred to the pseudo-first-order model. In terms of the parameters presented in Table 2, the R2 values of the six lines corresponding to the pseudo-second-order kinetic model are greater than 0.99, which are closer to 1 compared with the lines fitted by the pseudo-first-order kinetic model. Moreover, the values of qe,cal, which is the calculated adsorption quantity at equilibrium, for the pseudo-second-order model is closer to the experimental values than the values calculated from the pseudo-first-order model. Hence, the pseudo-second-order kinetic model is more appropriate in interpreting the adsorption kinetics towards the three pollutants. 3.11. Adsorption isotherms

Fig. 13. CR, MO and Cr(VI) adsorption isotherms for the GO-NiFe LDH composite and NiFe LDH microspheres.

The relationship between the adsorption quantity of adsorbates onto adsorbents and the concentration of adsorbates in the aqueous phase at 221

Journal of Hazardous Materials 369 (2019) 214–225

Y. Zheng, et al.

Table 3 Parameters of the Langmuir, Freundlich and Liu isotherm models for CR, MO and Cr(VI) adsorption onto the NiFe LDH microspheres and GO-NiFe LDH composite. CR









Langmuir qmax (mg g–1) KL (L mg–1) R2

287 0.419 0.974

450 0.466 0.987

211 0.029 0.988

403 0.049 0.992

35.9 0.362 0.997

51.7 0.443 0.991

Freundlich KF (mg g–1) (L mg–1)1/n n R2

128.2 4.978 0.939

190.1 4.391 0.928

30.37 2.898 0.959

77.21 3.189 0.952

16.37 4.871 0.885

23.68 4.681 0.910

Liu qmax (mg g–1) Kg (L mg–1) n R2

323 0.311 0.660 0.994

489 0.378 0.753 0.996

230 0.0232 0.849 0.990

438 0.0408 0.833 0.993

35.5 0.366 1.047 0.997

53.6 0.418 0.878 0.994

the adsorption equilibriums is shown by the adsorption isotherms. Fig. 13 displays the isotherm curves for the CR, MO and Cr(VI) adsorption by NiFe LDH and GO-NiFe LDH composite. The GO-NiFe LDH composite exhibits larger equilibrium adsorption capacity towards the three anionic pollutants. This result follows the same tendency with the adsorption kinetics. Hence, the GO-NiFe LDH composite possesses higher adsorption capability than the NiFe LDH microspheres. The adsorption isotherms were further investigated using the Langmuir, Freundlich and Liu isotherm models. For more intuitive comparison, the experimental data for the adsorption isotherms were analysed through fitting using the Langmuir, Freundlich and Liu isotherm equations (Table S1) [70–72]. As displayed in Fig. 13, the plots fitted by Liu isotherm model match best the experimental data. In addition, the R2 for the Liu model is larger than the Langmuir and Freundlich isotherm models (Table 3). Thus, the Liu isotherm model better represents the adsorption isotherms. According to the Liu isotherm model, the calculated maximal adsorption quantities of the GO-NiFe LDH composite towards CR, MO and Cr(VI) are 489, 438 and 53.6 mg g–1, which are better than those of the NiFe LDH microspheres. This result indicates that the GO-NiFe LDH composite is a markedly superior adsorbent towards the three anionic pollutants. Furthermore, the adsorption capacities of GO-NiFe LDH towards CR, MO and Cr(VI) are higher than or comparable with that of many other related adsorbents reported previously (Table 4).

nature of the adsorption. The parameters of thermodynamics are obtained through calculation according to Eqs. 8–9 (Table S1) [79]. Ke° can be calculated by K e0 =

1000 × K g × molecule weight of adsorbate×standard concentration of adsorbate activity coefficient of adsorbate

The calculated values of ΔG°, ΔH° and ΔS° are presented in Table 5. It is noted that all the ΔG° presents negative values, which indicates the spontaneity nature of the CR, MO and Cr(VI) adsorption onto GO-NiFe LDH and NiFe LDH. The negative values of ΔH° for CR, MO adsorption reveal the exothermic nature of CR and MO adsorption, whereas the positive ΔH° for Cr(VI) suggests the Cr(VI) adsorption is an endothermic process. The positive values of ΔS° imply the increase in randomness after the adsorption of CR, MO and Cr(VI). 3.13. Adsorption mechanisms As revealed in Fig. 9, the adsorption efficiency of CR and MO decreases with increasing the pH, revealing the electrostatic attraction exists between the anionic dye molecules (CR and MO) and the positively charged surface of GO-NiFe LDH. Moreover, due to the intrinsic ion exchange property of LDH, the adsorption of CR and MO can also be achieved through the ions exchange with the anionic ions in the interlayers of the LDH. In addition to the electrostatic attraction and ions exchange, the benzene rings in the molecules of CR and MO can interact with the GO through π–π stacking, thus contributing to the anionic dyes adsorption. Furthermore, for the adsorption of CR, there are –NH2 groups exist in the CR molecules, which can form hydrogen bonding with the eOH groups in the GO-NiFe LDH composite. Therefore,

3.12. Adsorption thermodynamics The adsorption thermodynamics was studied to obtain information about the inherent energy change and understand the spontaneity

Table 4 Comparison of adsorption capacities of GO-NiFe LDH composite towards CR, MO and Cr(VI) with another adsorbents. Samples

3D hierarchical GO-NiFe LDH Hierarchical porous NiFe-LDO NiO/graphene nanosheets α-FeOOH nanorods NiO nanoparticles Calcined GO/NiAl LDH hybrid Starch-NiFe-LDH composites NiFe layered double hydroxide Fe3O4/GO composite [email protected] α-FeOOH/carbon microspheres NiO nanosheets

T (°C)

30 30 25 27 ± 3 30 25 25 — 4.5 30 30 25



Adsorption capacity (mg g–1)

6–7 — 7 6.5 — neutral 3 — 20 5.6 3.0 —




489 330 124 160





189 211 388 206

26.8 32.33 27.2 55.4 49.0

This work [42] [73] [74] [75] [18] [43] [21] [12] [76] [77] [78]

Journal of Hazardous Materials 369 (2019) 214–225

Y. Zheng, et al.

Table 5 Parameters of adsorption thermodynamics for CR, MO and Cr(VI) adsorption onto GO-NiFe LDH and NiFe LDH. Samples


T (K)

Kg (L mg–1)


ΔG° (kJ mol–1)

ΔH° (kJ mol–1)

ΔS° (kJ mol–1 K–1)



293 298 303 308 313 293 298 303 308 313 293 298 303 308 313 293 298 303 308 313 293 298 303 308 313 293 298 303 308 313

0.532 0.459 0.379 0.314 0.282 0.0555 0.0460 0.0408 0.0346 0.0308 0.353 0.382 0.418 0.458 0.508 0.397 0.362 0.311 0.286 0.255 0.0297 0.0271 0.0232 0.0201 0.0182 0.308 0.336 0.366 0.394 0.418

370904.44 319448.04 263894.49 218844.10 196118.67 18167.38 15069.55 13345.57 11309.33 10066.35 18353.56 19849.90 21752.03 23838.04 26404.97 276471.59 252080.18 216370.85 198934.29 177316.49 9736.91 8870.36 7609.72 6593.69 5972.86 16001.33 17463.87 19130.82 20468.61 21756.02

−31.25 −31.42 −31.46 −31.50 −31.73 −23.90 −23.85 −23.94 −23.91 −24.00 −23.93 −24.53 −25.17 −25.82 −26.51 −30.54 −30.83 −30.96 −31.26 −31.47 −22.38 −22.53 −22.53 −22.53 −22.64 −23.59 −24.21 −24.85 −25.43 −26.00



















electrostatic attraction, ions exchange and π–π interaction are the main adsorption mechanism of CR and MO adsorption, and hydrogen bonding interaction also contributes to the CR adsorption. Like CR and MO, Cr(VI) ions in aqueous solution exist in the form of anionic species, thus the adsorption of Cr(VI) ions can also occur through electrostatic attraction and ions exchange. Furthermore, as shown by the FTIR spectrum in Fig. 8b, the adsorption bands appeared after the adsorption of Cr(VI) ions, which are different from the aqueous species of chromate, revealing the surface complexation between the GO-NiFe LDH composite and Cr(VI) ions [65]. Thus, the adsorption mechanism of the Cr(VI) ions involves in electrostatic attraction, ions exchange and surface complexation. 3.14. Regeneration and reusability Reusability is significant for the practical use of the adsorbents. The recycle experiments were conducted to evaluate the recoverability of the GO-NiFe LDH composite. To regenerate GO-NiFe LDH sample, the adsorbent after MO adsorption was eluted by methanol, and the adsorbed CR and Cr(VI) were desorbed by 0.5 M NaOH solution. As displayed in Fig. 14, after four cycles, the removal efficiency for CR, MO and Cr(VI) decreased from 98.5, 97.0 and 93.5% to 74.2, 81.3 and 80.7%, respectively, suggesting the fair reusability of the GO-NiFe LDH composite.

Fig. 14. The removal efficiency of CR, MO and Cr(VI) for GO-NiFe LDH in recycle adsorption experiments.

responsible for the enhanced adsorption performance. The results from the adsorption kinetics indicated that the sandwich-like GO-NiFe LDH composite exhibited markedly faster adsorption kinetics and higher adsorption capacity than NiFe LDH. Thus, the well-constructed hierarchical sandwich-like GO-NiFe LDH composite can be an adsorbent for eliminating anionic pollutants from wastewater as shown by its excellent adsorption capability towards the three anionic pollutants.

4. Conclusions In summary, a simple one-pot hydrothermal process was employed to fabricate the 3D hierarchical sandwich-like GO-NiFe LDH composite. The presence of GO nanosheets in the composite prevented the LDH nanosheets from aggregating into microspheres, which in reverse led to the simultaneous exfoliation of GO nanosheets. Thus, a well-ordered 3D structure was constructed. The hybridisation with GO nanosheets formed GO-NiFe LDH composite with higher SBET and larger pore size and pore volume. This result suggests a more porous structure, which is

Acknowledgements The research was partially supported by the National Natural Science Foundation of China (U1705251 and 21573170), and Self-determined and Innovative Research Funds of SKLWUT (2017-ZD-4). 223

Journal of Hazardous Materials 369 (2019) 214–225

Y. Zheng, et al.

Appendix A. Supplementary data

Small 14 (2018) 1702407. [27] Y. Wang, N. Xiao, Z. Wang, Y. Tang, H. Li, M. Yu, C. Liu, Y. Zhou, J. Qiu, Ultrastable and high-capacity carbon nanofiber anodes derived from pitch/polyacrylonitrile for flexible sodium-ion batteries, Carbon 135 (2018) 187–194. [28] Q. Xu, B. Cheng, J. Yu, G. Liu, Making co-condensed amorphous carbon/g-C3N4 composites with improved visible-light photocatalytic H2-production performance using Pt as cocatalyst, Carbon 118 (2017) 241–249. [29] Y. Wang, A. Du Pasquier, D. Li, P. Atanassova, S. Sawrey, M. Oljaca, Electrochemical double layer capacitors containing carbon black additives for improved capacitance and cycle life, Carbon 133 (2018) 1–5. [30] Z. He, Y. Jiang, Y. Li, J. Zhu, H. Zhou, W. Meng, L. Wang, L. Dai, Carbon layerexfoliated, wettability-enhanced, SO3H-functionalized carbon paper: a superior positive electrode for vanadium redox flow battery, Carbon 127 (2018) 297–304. [31] Q. Li, X. Li, S. Wageh, A.A. Al-Ghamdi, J. Yu, CdS/graphene nanocomposite photocatalysts, Adv. Energy Mater. 5 (2015) 1500010. [32] H. Zhao, S. Fan, Y. Chen, Z. Feng, H. Zhang, W. Pang, D. Zhang, M. Zhang, Oxygen plasma-treated graphene oxide surface functionalization for sensitivity enhancement of thin-film piezoelectric acoustic gas sensors, ACS Appl. Mater. Interfaces 9 (2017) 40774–40781. [33] H. Zou, B. He, P. Kuang, J. Yu, K. Fan, NixSy Nanowalls/nitrogen-doped graphene foam is an efficient trifunctional catalyst for unassisted artificial photosynthesis, Adv. Funct. Mater. 28 (2018) 1706917. [34] W. Xu, Y. Song, K. Dai, S. Sun, G. Liu, J. Yao, Novel ternary nanohybrids of tetraethylenepentamine and graphene oxide decorated with MnFe2O4 magnetic nanoparticles for the adsorption of Pb(II), J. Hazard. Mater. 358 (2018) 337–345. [35] Z. Cheng, J. Liao, B. He, F. Zhang, F. Zhang, X. Huang, L. Zhou, One-Step Fabrication of graphene oxide enhanced magnetic composite gel for highly efficient dye adsorption and catalysis, ACS Sustain. Chem. Eng. 3 (2015) 1677–1685. [36] D. Zhao, X. Gao, C. Wu, R. Xie, S. Feng, C. Chen, Facile preparation of amino functionalized graphene oxide decorated with Fe3O4 nanoparticles for the adsorption of Cr(VI), Appl. Surf. Sci. 384 (2016) 1–9. [37] Y. Zou, X. Wang, Y. Ai, Y. Liu, J. Li, Y. Ji, X. Wang, Coagulation behavior of graphene oxide on nanocrystallined Mg/Al layered double hydroxides: batch experimental and theoretical calculation study, Environ. Sci. Technol. 50 (2016) 3658–3667. [38] Y. Zou, X. Wang, Z. Chen, W. Yao, Y. Ai, Y. Liu, T. Hayat, A. Alsaedi, N.S. Alharbi, X. Wang, Superior coagulation of graphene oxides on nanoscale layered double hydroxides and layered double oxides, Environ. Pollut. 219 (2016) 107–117. [39] W. Yao, J. Wang, P. Wang, X. Wang, S. Yu, Y. Zou, J. Hou, T. Hayat, A. Alsaedi, X. Wang, Synergistic coagulation of GO and secondary adsorption of heavy metal ions on Ca/Al layered double hydroxides, Environ. Pollut. 229 (2017) 827–836. [40] W. Linghu, H. Yang, Y. Sun, G. Sheng, Y. Huang, One-Pot synthesis of LDH/GO composites as highly effective adsorbents for decontamination of U(VI), ACS Sustain. Chem. Eng. 5 (2017) 5608–5616. [41] J. Wang, X. Wang, L. Tan, Y. Chen, T. Hayat, J. Hu, A. Alsaedi, B. Ahmad, W. Guo, X. Wang, Performances and mechanisms of Mg/Al and Ca/Al layered double hydroxides for graphene oxide removal from aqueous solution, Chem. Eng. J. 297 (2016) 106–115. [42] C. Lei, M. Pi, P. Kuang, Y. Guo, F. Zhang, Organic dye removal from aqueous solutions by hierarchical calcined Ni-Fe layered double hydroxide: isotherm, kinetic and mechanism studies, J. Colloid Interface Sci. 496 (2017) 158–166. [43] M. Zubair, N. Jarrah, A. Ihsanullah, M.S. Khalid, T.S. Manzar, M.A. Kazeem, AlHarthi, Starch-NiFe-layered double hydroxide composites: efficient removal of methyl orange from aqueous phase, J. Mol. Liq. 249 (2018) 254–264. [44] Y. Han, Z.-H. Liu, Z. Yang, Z. Wang, X. Tang, T. Wang, L. Fan, K. Ooi, Preparation of Ni2+-Fe3+ layered double hydroxide material with high crystallinity and well-defined hexagonal shapes, Chem. Mater. 20 (2008) 360–363. [45] T. Xiao, Y.W. Tang, Z.Y. Jia, D.W. Li, X.Y. Hu, B.H. Li, L.J. Luo, Self-assembled 3D flower-like Ni2+-Fe3+ layered double hydroxides and their calcined products, Nanotechnology 20 (2009) 475603. [46] M. Liu, J. Xu, B. Cheng, W. Ho, J. Yu, Synthesis and adsorption performance of Mg (OH)2 hexagonal nanosheet–graphene oxide composites, Appl. Surf. Sci. 332 (2015) 121–129. [47] J. Xu, S. Gai, F. He, N. Niu, P. Gao, Y. Chen, P. Yang, A sandwich-type three-dimensional layered double hydroxide nanosheet array/graphene composite: fabrication and high supercapacitor performance, J. Mater. Chem. A Mater. Energy Sustain. 2 (2014) 1022–1031. [48] J. Xu, D. Xu, B. Zhu, B. Cheng, C. Jiang, Adsorptive removal of an anionic dye Congo red by flower-like hierarchical magnesium oxide (MgO)-graphene oxide composite microspheres, Appl. Surf. Sci. 435 (2018) 1136–1142. [49] M. Thommes, K. Kaneko, A.V. Neimark, J.P. Olivier, F. Rodriguez-Reinoso, J. Rouquerol, K.S.W. Sing, Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report), Pure Appl. Chem. 87 (2015) 1051–1069. [50] B. Cheng, Y. Le, W. Cai, J. Yu, Synthesis of hierarchical Ni(OH)2 and NiO nanosheets and their adsorption kinetics and isotherms to Congo red in water, J. Hazard. Mater. 185 (2011) 889–897. [51] R. Lin, W. Yue, F. Niu, J. Ma, Novel strategy for the preparation of graphene-encapsulated mesoporous metal oxides with enhanced lithium storage, Electrochim. Acta 205 (2016) 85–94. [52] B. Zhu, P. Xia, W. Ho, J. Yu, Isoelectric point and adsorption activity of porous gC3N4, Appl. Surf. Sci. 344 (2015) 188–195. [53] C. Lei, X. Zhu, B. Zhu, J. Yu, W. Ho, Hierarchical NiO-SiO2 composite hollow microspheres with enhanced adsorption affinity towards Congo red in water, J. Colloid Interface Sci. 466 (2016) 238–246. [54] F. Ning, M. Shao, S. Xu, Y. Fu, R. Zhang, M. Wei, D.G. Evans, X. Duan, TiO2/

Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jhazmat.2019.02.013. References [1] J.A. González, M.E. Villanueva, L.L. Piehl, G.J. Copello, Development of a chitin/ graphene oxide hybrid composite for the removal of pollutant dyes: adsorption and desorption study, Chem. Eng. J. 280 (2015) 41–48. [2] L.A. Kafshgari, M. Ghorbani, A. Azizi, Fabrication and investigation of MnFe2O4/ MWCNTs nanocomposite by hydrothermal technique and adsorption of cationic and anionic dyes, Appl. Surf. Sci. 419 (2017) 70–83. [3] P. Jha, R. Jobby, N.S. Desai, Remediation of textile azo dye acid red 114 by hairy roots of Ipomoea carnea Jacq. and assessment of degraded dye toxicity with human keratinocyte cell line, J. Hazard. Mater. 311 (2016) 158–167. [4] S. Adhikari, S. Mandal, D. Sarkar, D.-H. Kim, G. Madras, Kinetics and mechanism of dye adsorption on WO3 nanoparticles, Appl. Surf. Sci. 420 (2017) 472–482. [5] C. Lei, M. Pi, B. Cheng, C. Jiang, J. Qin, Fabrication of hierarchical porous ZnO/NiO hollow microspheres for adsorptive removal of Congo red, Appl. Surf. Sci. 435 (2018) 1002–1010. [6] K.T. Chung, Azo dyes and human health: a review, J. Environ. Sci. Health Care 34 (2016) 233–261. [7] S. Vahidhabanu, A. Abideen Idowu, D. Karuppasamy, B. Ramesh Babu, M. Vineetha, Microwave initiated facile formation of sepiolite-poly(dimethylsiloxane) nanohybrid for effective removal of Congo red dye from aqueous solution, ACS Sustain. Chem. Eng. 5 (2017) 10361–10370. [8] C. Lei, X. Zhu, Y. Le, B. Zhu, J. Yu, W. Ho, Hierarchically porous NiO–Al2O3 nanocomposite with enhanced Congo red adsorption in water, RSC Adv. 6 (2016) 10272–10279. [9] W. Qi, Y. Zhao, X. Zheng, M. Ji, Z. Zhang, Adsorption behavior and mechanism of Cr (VI) using Sakura waste from aqueous solution, Appl. Surf. Sci. 360 (2016) 470–476. [10] M. Gheju, I. Balcu, G. Mosoarca, Removal of Cr(VI) from aqueous solutions by adsorption on MnO2, J. Hazard. Mater. 310 (2016) 270–277. [11] C. Liu, R.-N. Jin, X.-k. Ouyang, Y.-G. Wang, Adsorption behavior of carboxylated cellulose nanocrystal—polyethyleneimine composite for removal of Cr(VI) ions, Appl. Surf. Sci. 408 (2017) 77–87. [12] M. Liu, T. Wen, X. Wu, C. Chen, J. Hu, J. Li, X. Wang, Synthesis of porous Fe3O4 hollow microspheres/graphene oxide composite for Cr(VI) removal, Dalton Trans. 42 (2013) 14710–14717. [13] F. Budiman, N. Bashirom, W.K. Tan, K.A. Razak, A. Matsuda, Z. Lockman, Rapid nanosheets and nanowires formation by thermal oxidation of iron in water vapour and their applications as Cr(VI) adsorbent, Appl. Surf. Sci. 380 (2016) 172–177. [14] C. Santhosh, E. Daneshvar, P. Kollu, S. Peräniemi, A.N. Grace, A. Bhatnagar, Magnetic [email protected] nanoparticles decorated on graphene oxide as efficient adsorbents for the removal of anionic pollutants from water, Chem. Eng. J. 322 (2017) 472–487. [15] Q. Liu, Q. Liu, B. Liu, T. Hu, W. Liu, J. Yao, Green synthesis of tannin-hexamethylendiamine based adsorbents for efficient removal of Cr(VI), J. Hazard. Mater. 352 (2018) 27–35. [16] C. Lei, M. Pi, D. Xu, C. Jiang, B. Cheng, Fabrication of hierarchical porous ZnOAl2O3 microspheres with enhanced adsorption performance, Appl. Surf. Sci. 426 (2017) 360–368. [17] H. Chen, Y. Zheng, B. Cheng, J. Yu, C. Jiang, Chestnut husk-like nickel cobaltite hollow microspheres for the adsorption of Congo red, J. Alloys Compd. 735 (2018) 1041–1051. [18] Z. Yang, S. Ji, W. Gao, C. Zhang, L. Ren, W.W. Tjiu, Z. Zhang, J. Pan, T. Liu, Magnetic nanomaterial derived from graphene oxide/layered double hydroxide hybrid for efficient removal of methyl orange from aqueous solution, J. Colloid Interface Sci. 408 (2013) 25–32. [19] M.A. Teixeira, A.B. Mageste, A. Dias, L.S. Virtuoso, K.P.F. Siqueira, Layered double hydroxides for remediation of industrial wastewater containing manganese and fluoride, J. Clean. Prod. 171 (2018) 275–284. [20] W. Zhou, W. Zhang, Z. Chen, Universal biomimetic preparation and immobilization of layered double hydroxide films and adsorption behavior, Appl. Surf. Sci. 392 (2017) 153–161. [21] Y. Lu, B. Jiang, L. Fang, F. Ling, J. Gao, F. Wu, X. Zhang, High performance NiFe layered double hydroxide for methyl orange dye and Cr(VI) adsorption, Chemosphere 152 (2016) 415–422. [22] C. Lei, X. Zhu, B. Zhu, C. Jiang, Y. Le, J. Yu, Superb adsorption capacity of hierarchical calcined Ni/Mg/Al layered double hydroxides for Congo red and Cr(VI) ions, J. Hazard. Mater. 321 (2017) 801–811. [23] L. Qin, W. Lv, W. Wei, F. Kang, D. Zhai, Q.-H. Yang, Oxygen-enriched carbon nanotubes as a bifunctional catalyst promote the oxygen reduction/evolution reactions in Li-O2 batteries, Carbon 141 (2019) 561–567. [24] P.Y. Kuang, B.C. Zhu, Y.L. Li, H.B. Liu, J.G. Yu, K. Fan, Graphdiyne: a superior carbon additive to boost the activity of water oxidation catalysts, Nanoscale Horiz. 3 (2018) 317–326. [25] Z.U. Ahmad, B. Chao, M.I. Konggidinata, Q. Lian, M.E. Zappi, D.D. Gang, Molecular simulation and experimental validation of resorcinol adsorption on Ordered Mesoporous Carbon (OMC), J. Hazard. Mater. 354 (2018) 258–265. [26] T. Liu, L. Zhang, W. You, J. Yu, Core–shell nitrogen-doped carbon hollow spheres/ Co3O4 nanosheets as advanced electrode for high-performance supercapacitor,


Journal of Hazardous Materials 369 (2019) 214–225

Y. Zheng, et al.

[55] [56] [57] [58]

[59] [60] [61] [62] [63] [64] [65] [66] [67]

graphene/NiFe-layered double hydroxide nanorod array photoanodes for efficient photoelectrochemical water splitting, Energy Environ. Sci. 9 (2016) 2633–2643. J. Cao, C. Wang, Multifunctional surface modification of silk fabric via graphene oxide repeatedly coating and chemical reduction method, Appl. Surf. Sci. 405 (2017) 380–388. R. Chen, J. Yu, W. Xiao, Hierarchically porous MnO2 microspheres with enhanced adsorption performance, J. Mater. Chem. A 1 (2013) 11682–11690. D. Zhao, Q. Zhang, H. Xuan, Y. Chen, K. Zhang, S. Feng, A. Alsaedi, T. Hayat, C. Chen, EDTA functionalized Fe3O4/graphene oxide for efficient removal of U(VI) from aqueous solutions, J. Colloid Interface Sci. 506 (2017) 300–307. X. Wu, J.-G. Li, Q. Zhu, W. Liu, J. Li, X. Li, X. Sun, Y. Sakka, One-step freezing temperature crystallization of layered rare-earth hydroxide (Ln2(OH)5NO3·nH2O) nanosheets for a wide spectrum of Ln (Ln = Pr–Er, and Y), anion exchange with fluorine and sulfate, and microscopic coordination probed via photoluminescence, J. Mater. Chem. C 3 (2015) 3428–3437. A. Guzmán-Vargas, E. Lima, G.A. Uriostegui-Ortega, M.A. Oliver-Tolentino, E.E. Rodríguez, Adsorption and subsequent partial photodegradation of methyl violet 2B on Cu/Al layered double hydroxides, Appl. Surf. Sci. 363 (2016) 372–380. S. Nayak, L. Mohapatra, K. Parida, Visible light-driven novel g-C3N4/NiFe-LDH composite photocatalyst with enhanced photocatalytic activity towards water oxidation and reduction reaction, J. Mater. Chem. A 3 (2015) 18622–18635. Y. Zheng, B. Zhu, H. Chen, W. You, C. Jiang, J. Yu, Hierarchical flower-like nickel (II) oxide microspheres with high adsorption capacity of Congo red in water, J. Colloid Interface Sci. 504 (2017) 688–696. Y. Jiang, B. Liu, J. Xu, K. Pan, H. Hou, J. Hu, J. Yang, Cross-linked chitosan/βcyclodextrin composite for selective removal of methyl orange: adsorption performance and mechanism, Carbohydr. Polym. 182 (2018) 106–114. L. Deng, Z. Shi, X. Peng, S. Zhou, Magnetic calcinated cobalt ferrite/magnesium aluminum hydrotalcite composite for enhanced adsorption of methyl orange, J. Alloys Compd. 688 (2016) 101–112. Y. Liu, Y. Tian, C. Luo, G. Cui, S. Yan, One-pot preparation of a MnO2–graphene–carbon nanotube hybrid material for the removal of methyl orange from aqueous solutions, New J. Chem. 39 (2015) 5484–5492. C.P. Johnston, M. Chrysochoou, Investigation of chromate coordination on ferrihydrite by in situ ATR-FTIR spectroscopy and theoretical frequency calculations, Environ. Sci. Technol. 46 (2012) 5851–5858. C.P. Johnston, M. Chrysochoou, Mechanisms of chromate adsorption on hematite, Geochim. Cosmochim. Acta 138 (2014) 146–157. Y. Zheng, H. Wang, B. Cheng, W. You, J. Yu, Fabrication of hierarchical bristle-

[68] [69] [70] [71] [72]

[73] [74] [75] [76] [77] [78] [79]


grass-like NH4Al(OH)[email protected](OH)2 core-shell structure and its enhanced Congo red adsorption performance, J. Alloys Compd. 750 (2018) 644–654. C. Lei, M. Pi, C. Jiang, B. Cheng, J. Yu, Synthesis of hierarchical porous zinc oxide (ZnO) microspheres with highly efficient adsorption of Congo red, J. Colloid Interface Sci. 490 (2017) 242–251. D. Ma, B. Zhu, B. Cao, J. Wang, J. Zhang, Fabrication of the novel hydrogel based on waste corn stalk for removal of methylene blue dye from aqueous solution, Appl. Surf. Sci. 422 (2017) 944–952. H.M.F. Freundlich, Uber die adsorption in losungen, J. Phys. Chem. 57 (1916) 385–470. I. Langmuir, The adsorption of gases on plane surfaces of glass, mica and platinum, J. Am. Chem. Soc. 40 (1918) 1361–1403. P.S. Thue, M.A. Adebayo, E.C. Lima, J.M. Sieliechi, F.M. Machado, G.L. Dotto, J.C.P. Vaghetti, S.L.P. Dias, Preparation, characterization and application of microwave-assisted activated carbons from wood chips for removal of phenol from aqueous solution, J. Mol. Liq. 223 (2016) 1067–1080. X. Rong, F. Qiu, J. Qin, H. Zhao, J. Yan, D. Yang, A facile hydrothermal synthesis, adsorption kinetics and isotherms to Congo Red azo-dye from aqueous solution of NiO/graphene nanosheets adsorbent, J. Ind. Eng. Chem. 26 (2015) 354–363. D. Maiti, S. Mukhopadhyay, P.S. Devi, Evaluation of mechanism on selective, rapid, and superior adsorption of Congo red by reusable mesoporous α-Fe2O3 nanorods, ACS Sustain. Chem. Eng. 5 (2017) 11255–11267. A.A.A. Darwish, M. Rashad, H.A. Al-Aoh, Methyl orange adsorption comparison on nanoparticles: isotherm, kinetics, and thermodynamic studies, Dyes Pigm. 160 (2019) 563–571. M. Su, Y. Fang, B. Li, W. Yin, J. Gu, H. Liang, P. Li, J. Wu, Enhanced hexavalent chromium removal by activated carbon modified with micro-sized goethite using a facile impregnation method, Sci. Total Environ. 647 (2019) 47–56. L. Zhang, F. Fu, B. Tang, Adsorption and redox conversion behaviors of Cr(VI) on goethite/carbon microspheres and akaganeite/carbon microspheres composites, Chem. Eng. J. 356 (2019) 151–160. J. Zhao, Y. Tan, K. Su, J. Zhao, C. Yang, L. Sang, H. Lu, J. Chen, A facile homogeneous precipitation synthesis of NiO nanosheets and their applications in water treatment, Appl. Surf. Sci. 337 (2015) 111–117. E.C. Lima, A. Hosseini-Bandegharaei, J.C. Moreno-Piraján, I. Anastopoulos, A critical review of the estimation of the thermodynamic parameters on adsorption equilibria. Wrong use of equilibrium constant in the Van’t Hoof equation for calculation of thermodynamic parameters of adsorption, J. Mol. Liq. 273 (2019) 425–434.