Shape memory and underwater superelastic mof@cellulose aerogels for rapid and large-capacity adsorption of metal ions

Cellulose aerogels have been used in widespread areas, such as absorbents, thermal insulation material and medical material. Herein, we propose an effective strategy to fabricate elastic cellulose aerogels by combining cellulose nanofibers with polyvinyl alcohol (PVA) “glue”. The CA not only had a robust chemical-bond cross-link network, but also had a strong H-bond, which enhanced underwater mechanical properties. Moreover, the compressible CA provided a large number of nucleation sites for the growth of Metal–organic framework nanoparticles (ZIF-67 and ZIF-8) through interface self-assemble. The obtained aerogels with a low density of 9.8–11.2 mg cm−3 and highly porous of 99.4–99.5% possessed excellent elasticity both in air and underwater. The adsorption capacities of the MOF@CA for Pb2+ and Cu2+ are up to 123 mg g−1 and 70.53 mg g−1, respectively. The novel MOF@CA adsorbents with excellent mechanical properties display application prospects in the removal of heavy metals from wastewater.


Introduction
With the development of industry, environmental pollution becomes an increasingly serious issue (Ali and Khan 2017). As one of the most common pollutants, heavy metals accumulate in aquatic organisms and human bodies, causing great harm to public health and environmental health (Ali et al. 2019). The removal of these heavy metals such as Hg 2+ , Ni 2+ , Cd 2+ , Cr 5+ , Pb 2+ and Cu 2+ from polluted wastewater had become the focus of environmental problems in the world. Generally speaking, the methods for removing heavy metal ions from water included chemical precipitation, ion exchange, membrane filtration, flocculation, and adsorption. The adsorption as the preferred method can remove multiple ions simultaneously because it does not require complex chemical reactions, which is considered to be one of the most promising treatment methods (Jia et al. 2002). To date, various absorbent materials had been used for water treatment including zeolites (Fei et al. 2012), clays (Chan et al. 2015), polystyrene (Tran et al. 2020), activated carbon (Chen and Lin 2001), Abstract Cellulose aerogels have been used in widespread areas, such as absorbents, thermal insulation material and medical material. Herein, we propose an effective strategy to fabricate elastic cellulose aerogels by combining cellulose nanofibers with polyvinyl alcohol (PVA) "glue". The CA not only had a robust chemical-bond cross-link network, but also had a strong H-bond, which enhanced underwater mechanical properties. Moreover, the compressible CA provided a large number of nucleation sites for the growth of Metal-organic framework nanoparticles (ZIF-67 and ZIF-8) through interface self-assemble. The obtained aerogels with a low density of 9.8-11.2 mg cm −3 and highly porous of 99.4-99.5% possessed excellent elasticity both in air and underwater. The adsorption capacities of the MOF@CA for Pb 2+ and Cu 2+ are up to 123 mg g −1 and 70.53 mg g −1 , respectively. The novel MOF@ etc. Nevertheless, these absorbent materials were difficult to be widely used because of the poor adsorption capacity, non-degradation and expensive cost.
Cellulose is one of the most abundant polymers in nature, which is biocompatible, economical and biodegradable (Zhao et al. 2020). Cellulose aerogels (CA) are prepared from cellulose solution or nanocellulose as the substrate, which have the advantages of high porous and low density, and have broad application prospects in many fields of adsorption, catalysis, drug loading and so on (Wang et al. 2017). However, the poor underwater mechanical properties of CA have greatly limited its application in the fields of adsorption (Huang et al. 2020). This was ascribed to the weak hydrogen bond forces between CA molecular chains, where irreversible damage may occur during deformation. To overcome the weakness of CA, a number of materials such as graphene (Ge et al. 2018), PVA (Chhajed et al. 2019), polyurethane (Huang et al. 2022) and styrene acrylic (Gong et al. 2021) had been tried to improve the mechanical performance. Among them, PVA is a non-toxic, watersoluble and biodegradable polymer. PVA molecular chains have a large number of hydroxyl groups, which can form strong hydrogen bonding between hydroxyl and carboxyl groups with other polymers (Xiao and Yang 2006). Hence, PVA acts like "glue" to produce hydrogen bond with -OH of cellulose to improve the mechanical properties of cellulose aerogel.
Metal-organic frameworks (MOF) are emerging porous materials consisting of metal-containing nodes and organic ligands connected by coordination bonds, which have a large specific surface area and have been used as adsorbents for the removal of contaminants from the aqueous environment (Furukawa et al. 2013). Although MOFs have many unique properties, including abundant pore structures and a variety of functional ligands, their applied performance is still limited by intrinsic fragility and powdered crystalline state, as well as unsatisfied stability and processability (Wang et al. 2019a, b). Recently, several reports on the composite of MOF nanoparticles with cellulose had been published (Zhou et al. 2019, Da Silva Pinto et al. 2012, Bo et al. 2018. The composite from MOF and cellulose had excellent adsorption properties, with better removal of organic dye molecules and heavy metal ions from contaminated aqueous solution. However, due to the weak interaction between particles and the inherent rigidity of MOFs, the composite aerogels also lack sufficient flexibility and robustness. Hence, it is still a huge challenge for the fabrication of flexible and shape controllable MOF@cellulose aerogels. Here, we reported a new strategy to fabricate the CA by using crosslinking PVA chains as "glue" to bond cellulose nanofibers together. The abundant active sites of CA provided nucleation sites of MOF (ZIF-67 and ZIF-8) nanoparticles. The prepared MOF@CA showed excellent water absorption, shape recovery property under the water and high adsorption property. We had characterized the morphology, chemical and mechanical properties of the aerogels both in the air and under the water. Besides, the adsorption and desorption properties of the aerogels were evaluated. By using Pb 2+ and Cu 2+ as model contaminants, the adsorption performance, as well as its selectivity and reusability, were investigated by batch adsorption experiments. Furthermore, the adsorption mechanism was explored by fitting the experimental data of adsorption kinetics and isotherms to different adsorption models. This study provides a new prospect for eco-friendly and sustainable adsorption materials and developing a new way for the development and utilization of cellulose.

Preparation of the TEMPO-oxide cellulose nanofibers (TOCN)
TOCN was prepared by oxidizing pulp according to our previous work (Wang et al. 2019a, b). In brief, the softwood kraft pulp was thoroughly washed with deionized water and dried in the oven at 100 °C for 12 h. TEMPO (0.032 g) and NaBr (0.2 g) were dissolved in softwood kraft pulp suspension (1wt%, 200 mL). The TEMPO-mediated oxidation was initiated by adding the desired amount of the NaClO solution (10 mmol) and stirred at room temperature. The pH was maintained at 10 by adding 0.5 M NaOH using a pH meter until no NaOH consumption was observed. After stirring for 10 h, the suspension was thoroughly washed with water via centrifugation. Then the TEMPO-oxidized cellulose suspension was fibrillated by a high-pressure homogenizer at 100 MPa for 5 cycles. The carboxylate content of the nanofibers was examined using an electric conductivity titration process and found to be 0.052 mmol/g.

Fabrication of TOCN/PVA aerogels (TPA)
PVA (0.1 g, 0.2 g, 0.3 g) was dissolved in TOCN suspensions (0.5 wt%, 100 mL) using a magnetic stirrer at 90 °C for 2 h. Then the suspensions were cooled down to room temperature. Subsequently, CCA (1.2 g) and 1.2 mL (H 3 PO 4 ) were added to the suspension with continuous stirring for 1 h. The suspensions were added to a plastic beaker and put in liquid nitrogen for 5 min. After the complete freeze, the samples were freeze-dried at a freezer dryer to obtain the aerogel. Consequently, the aerogels were heated in an oven at 60 °C for 2 h to achieve the crosslinking reaction between PVA and CCA. Then the samples were washed thoroughly with deionized water and dried at room temperature. The obtained TOCN/PVA aerogel was named TPA.

Fabrication of MOF self-growing aerogels
The TPA was immersed in the corresponding solutions of ligand precursors in alcohol for the growth of ZIF-8 and ZIF-67 under specific experimental. In detail, the prepared TPA were soaked in 40 mL methanol containing 0.8 g Zn(NO 3 ) 2 6H 2 O solution for 10 min, and then 40 mL methanol containing 1.76 g 2-methylimidazole was slowly added into the above solution. Then the aerogels were squeezed repeatedly until the two solutions were well mixed. Subsequently, the mixture was aged at room temperature for 12 h to grow ZIF-8 particles. The sample was obtained after being washed with ethanol and freezedried (-56 °C, < 20 Pa) at a freeze dryer. Similarly, the ZIF-67 particles were grown onto the surface of TPA by simple impregnation. In brief, the TPA was immersed in 40 mL methanol containing 0.416 g Co(NO 3 ) 2 6H 2 O solution for 10 min, and 40 mL methanol containing 2.0 g 2-methylimidazole was slowly added into the above solution. The mixture was aged at room temperature for 12 h and freezedried to obtain the aerogel. The resulting ZIF-8@ TPA and ZIF-67@TPA were abbreviated as TPAZ-8 and TPAZ-67, respectively.

Characterization
The TOCN were collected using carbon film-covered copper grids and observed using transmission electron microscopy (TEM, Talos F200X) at an accelerator voltage of 80 kV. The surface morphology of the samples was observed by scanning electron microscopy (SEM, Hitachi S4800) at an accelerator voltage of 15 kV. The chemical structures of the samples were studied by a Fourier-transform infrared (FTIR) spectrometer (Nicolet 5700, Thermo Fisher, America). The nitrogen adsorption and desorption isotherms were recorded with a Micrometrics ASAP 2020 analyzer. Pore size distribution and specific surface area were calculated via Barrett-Joyner-Halenda (BJH) and Brunauer-Emmett-Teller (BET) methods, respectively. The X-ray diffraction (XRD) measurement was performed using a D8-Advance with Nifiltered Cu-Kα radiation (λ = 0.15406 nm), with a sweeping range of 10 ∼ 50° and scanning speed of 2° min −1 . Raman spectra analysis was conducted by a Renishaw in Via Reflex Raman Spectrometer. X-ray photoelectron spectroscopy (XPS) analysis was performed with an ESCALAB 250 Xiphotoelectron spectroscopy using a monochromic Al X-ray source.

Mechanical properties
The mechanical characterizations (uniaxial compression) of aerogels were measured using an electronic universal testing machine (UTM6530, Shenzhen Suns Technology Co., Ltd). The cylindrical samples were put on the platform and examined at a speed of 50 mm/min.

Adsorption evaluation of the aerogels
The Pb 2+ and Cu 2+ were used to evaluate the adsorption capacity of the aerogels in aqueous solution. First of all, the Pb(NO 3 ) 2 and Cu(NO 3 )·3H 2 O were dissolved in deionized water to prepare a 200 mg L −1 solution, and the pH of the solution was measured to be 5.0 ± 0.2 for Pb 2+ and 5.2 ± 0.2 for Cu 2+ , respectively. The aerogels (3 mg) were incubated in 5 mL of metal ion solutions in a shaker at 25 °C. The concentrations of metal ions were measured with Sequential Plasma Spectrometer (iCAP PRO ICP-OES Duo) at wavelengths of 220.351 and 327.396 nm for Pb 2+ and Cu 2+ , respectively.

Desorption experiment of aerogels
The deionized water, methanol, 0.1 M HNO 3 , and 0.1 M HCl were used as an eluent to treat the adsorbed saturated aerogels. The saturated aerogels (3 mg) with 50 mL of aqueous solutions were oscillated in a shaker at 25 °C for 2 h. Then the samples were washed with deionized water until neutral and dried at 50 °C for adsorption experiments. The regeneration rate calculation (R) formula is as follow: where q t (mg g −1 ) is adsorption capacity after regeneration t times (t), q 0 (mg g −1 ) is adsorption capacity before regeneration.

Results and discussion
Fabrication and structure characterization The fabrication process of TPAs was illustrated in Fig. 1a. The TOCN and PVA suspensions containing CCA were freeze-dried to obtain the aerogels. The freshly obtained aerogels with some viscosity were difficult to recover to their original shape after compression because of the weak hydrogen bonds among TOCN and PVA molecular chains and CCA. Subsequently, the resulting aerogels were heated in the air (60 °C for 2 h) to realize the robust crosslinking (1) R = q t q 0 * 100% Fig.1 Schematic illustrations of the fabrication process of TPAZ esterification among TOCN, PVA, and CCA. At last, the aerogels were immersed in the ions and organic ligands solution for growing the MOF particles uniformly (Fig. S1). The obtained aerogels with a low density of 9.8-11.2 mg cm −3 could steadily stand on the soft grass. As shown in Fig. 2a, the original cellulose was oxide by TEMPO and the hydroxyl group of C6 was oxidized to the carboxyl group (Isogai et al. 2011). After homogeneous, the TOCN possesses a high aspect ratio with a diameter of 5-15 nm and a length of 0.5-1.5 μm. Mostly cellulose nanofibers were woven together to form a network, which can form a robust aerogels skeleton (Wang et al. 2017). As illustrated in Fig. 2b, the TPA aerogels have a rich porous structure with a diameter of 10-20 μm, which was ascribed to the sublimation of ice crystals in the aerogel during the freeze-drying process. Furthermore, there is no single TOCN that can be seen in the SEM image because of the crosslinking of the PVA, TOCN and CCA. As illustrated in Fig. 2g, the TOCN, PVA and CCA may form these ester bonds during the heating process. When the aerogels were immersed in metal ions (Zn 2+ , Co 2+ ) solution, the metal ions with positive charge rapidly interacted with the carboxyl groups on the surface of aerogels by electrostatic action. Then the ZIF-8 or ZIF-67 were nucleated at the surface of the aerogels by interface self-growing. As shown in Fig. 2c and d, the ZIF-8 nanoparticles with a diameter of 100 nm were adhered to aerogels' surface via hydrogen bonding and ionic interactions, while the ZIF-67 grows on the surface of aerogel in  (Zhu et al. 2018). The ZIF-67 nanoparticles with a diameter of 100 ~ 150 nm were evenly distributed on the aerogel surface ( Fig. 2e and f). The load capacity of MOF in TPA is 30wt% and the loading mass of crystals within the aerogels can be easily adjusted from 10-50% by controlling the initial concentration of ions and organic ligands.
As shown in Fig. S2, the N 2 uptake at high relative pressures of TPA was dramatically increased and an obvious hysteresis loop was observed, revealing that there were abundant mesopores and macropores in the aerogels. These mesopores and macropores were derived from the cellulose aerogels after the ice crystal sublimation, which provided plenty of locations for the growth of MOF nanoparticles. N 2 adsorption-desorption isotherms and the corresponding pore size distribution of the TPAZ-8 and TPAZ-67 were shown in Fig. 3. After the growth of MOF nanoparticles, the aerogels possess three types of pore structure including micropores, mesopores and macropores. The specific surface area of TPA is 43.63 m −2 g −1 , and the TPAZ-8 and TPAZ-67 are up to 90.21 m −2 g −1 and 220.57 m −2 g −1 , respectively. The increase of specific surface area of TPAZ mainly comes from porous MOF particles. The open multi-pore structure, high surface area and abundant hydroxyl are beneficial for the rapid entry of wastewater into the pores and the adsorption of metal ions.
The chemical structure and possible interaction of TPA, TPAZ-8, and TPAZ-67 were investigated by FT-IR, XPS, and XRD. The FT-IR spectra showed the expected signals from all the components within the aerogels. As shown in Fig. 4a, the TOCN/ PVA mixture exhibits several absorption bands at  (Ha et al. 2015). Besides, character peaks appearing at 2912 cm −1 and 1420 cm −1 correspond to the C-H stretching and bending of the -CH 2 groups of cellulose, respectively (Zhang et al. 2015). The carboxyl (1733 cm −1 ) mainly came from C6 of TEMPO oxide cellulose (Isogai et al. 2011). After heating, the intensity of the ester bond (1600 cm −1 and 1733 cm −1 ) of TPA was remarkably strengthened, indicating that a large number of ester bonds were formed during the heating process (Fig. 2g). Moreover, a slight shift of the hydroxyl peak was observed at 3305 cm −1 , which might attribute to forming intermolecular hydrogen bonding among the TOCN, PVA and CCA. After the growth of ZIF-8, a sharp peak at 1140 cm −1 was formed, which was identified as C-N bonds in ZIF-8 (Hu et al. 2011). Similarly, after the growth of ZIF-67, new peaks at 1576 cm −1 appeared, corresponding to C = N vibrations of ZIF-67, respectively (Yang et al. 2018a, b). The formation of the MOF nanoparticles was confirmed by the existence of all the peaks related to ZIF-8 and ZIF-67 in its FT-IR spectrum.
As shown in Fig. S3, the TOCN displayed three diffraction peaks at 14.7°, 16.8° and 22.7°, which corresponded to the (1-10), (110) and (200) planes of cellulose I, respectively (Oh et al. 2005). After heating, the diffraction peaks of PVA (11.5,19.6,22.5 and 40.2°) nearly disappeared, which indicated that the CCA strongly interacted with the hydroxide radical of PVA (Fig. 4b). The characteristic peaks of ZIF-8 (Park and Oh 2017) and ZIF-67 (Pan et al. 2011) in the XRD pattern of aerogels again confirm the formation of MOF in the aerogels. Moreover, the XPS results provided the surface chemistry of the TPA, TPAZ-8 and TPAZ-67. As shown in Fig. 4c, TPA has two peaks at 285 and 532 eV corresponding to C 1 s and O 1 s. Compared to TPA, the TPAZ-8 has a peak at 400 and 1023 eV, corresponding to N 1 s and Zn 2p from ZIF-8. There are two major peaks of Co 2p 3/2 (781.2 eV) and Co 2p 1/2 (796.4 eV) in the TPAZ-67, which corresponded to the characteristic of ZIF-67 (Yang et al. 2018a, b).

Mechanical properties
As shown in Fig. 5a, 5g and Movie S1, the TPA showed excellent compressible property, which can completely recover to its original height at 70% compression strain in the air after the stress was removed. The TPA was subject to cyclic compression tests at different strains (50%, 60%, 70%). As illustrated in Fig. 5b, the loading stress-strain curve can be divided into three regions, which is typical tree-region curves of traditional foam materials. In an elastic region (ε < 30%), the stress was increased linearly with the compressive stress. In the following yield region Compression and release process of the TPA g in the air and h under the water (30% < ε < 60%), the compressive stress gradually increased with the strain because of the elastic bending of the skeleton of the aerogels. The last densification region (ε > 60%) was marked by a rapid increase of compressive stress, owing to the densification of the pore. Moreover, the stress-strain curve at 10th almost coincided with the 1st (Fig. 5c), showing excellent fatigue-resistant property. After the growth of MOF, the compress stress increased under the same strain (Fig. 5e), which was ascribed to the adhesion of a layer of rigid MOF particles on the surface of TPA. Furthermore, both the TPAZ-67 and TPAZ-8 had excellent compressible performance, which can recover to its original height at 70% strain (Fig. 5e).
Even underwater, the TPA still exhibits excellent elasticity and fatigue resistance. As shown in Movie S2, the TPA was immersed in a glass of water, and mostly absorbed water could be easily removed by simple squeezing methods. Once the squeezed TPA was in contact with water, it could reabsorb water instantaneously and return to the original shape in a very short time of 1.5 s, showing excellent water-activated shape recovery. This may ascribe to the functional crosslinked PVA polymer that could be acted as the glue which could effectively bond the TOCN to endow the TPA with high mechanical elastic. As shown in Fig. 5h and Movie S3, the TPA was subject to cyclic compression tests at different strains under the water. The stress-strain curves of the TPA underwater are similar to the compression process in air, which can be divide into three regions. However, the TPA showed better compressibility (80%) and fatigue resistance (80%, 100 cycles) than in the air ( Fig. 5c and d). After the growth of MOF, the excellent mechanical properties are still preserved in the TPAZ-8 and TPAZ-67 (Fig. 5f). Furthermore, both TPAZ-8 and TPAZ-67 were highly stable underwater and retained volume integrity even after a week in water. As shown in Fig. S4, TPAZ-8 and TPAZ-67 could still return to their initial shape at 80% strain after seven days of immersion in water, but the stress became smaller, which is mainly due to hydrogen bonds in aerogel were replaced by hydrogen bonds between cellulose and water (Ma et al. 2018).
Adsorption property and adsorption mechanism of the aerogels Pb 2+ and Cu 2+ are common heavy metal ions in wastewater. Here, Pb 2+ and Cu 2+ were used as a model cationic adsorbate to investigate the static adsorption property. As shown in Table S1, with the increase of the load capacity of MOF, the adsorption capacity of TPAZ increases gradually, but the aerogels became more brittle, so we selected aerogel with 30wt% loading capacity as the sample for our adsorption experiment. As illustrated in Fig. 6, the adsorption capacity of Pb 2+ for the TPA, TPAZ-8 and TPAZ-67 were 42.3 mg g −1 , 105.21 mg g −1 and 123 mg g −1 , respectively. For Cu 2+ , the adsorption of TPA, TPAZ-8 and TPAZ-67 were 20.12 mg g −1 , 54.78 mg g −1 and 70.53 mg g −1 , respectively. Such high adsorption capacity and distribution coefficient surpassed those of most of the previous absorbent materials (Chen et al. 2009(Chen et al. , 2010Gurgel et al. 2008). Moreover, all the samples showed a high adsorption rate at the initial stage of adsorptions (0-30 min), which may be due to the high wettability and porosity of the aerogels. The TPAZ-8 and TPAZ-67 showed more efficient adsorption than TPA, which was ascribed to the high porousness of ZIF-8 and ZIF-67.
The adsorption model is an important tool to describe the adsorption behavior and mechanism. In this study, two typical kinetic models, pseudo-firstorder (Eq. 2) and pseudo-second-order models (Eq. 3), were used for fitting adsorption kinetic curves.
The pseudo-first-order model: The pseudo-second-order kinetic model: The Langmuir isotherm model: The Freundlich isotherm model: where q e (mg g −1 ) and q t (mg g −1 ) are the adsorption equilibrium and the adsorption amount at time t, (2) ln q e − q t = ln q e − k 1 t (5) ln q e = 1 n ln Ce + ln K F respectively; k 1 (min −1 ) and k 2 (g mg −1 min −1 ) are the pseudo-first-order and pseudo-second-order rate constants, respectively; C e is the equilibrium concentration of metal ions in aqueous solution (mg•L −1 ); q m and K L (L mg −1 ) are the Langmuir constants related to qe for a complete monolayer and energy of adsorption, respectively; K F (mg g −1 ) and n are the Freundlich constants that indicate the adsorption capacity and adsorption intensity, respectively. As shown in Table S2 and Fig. S5, values of R 2 are generally higher than R 1 , indicating the pseudosecond-order model fitted the experimental data of all samples better compared to the pseudo-first-order model. This further illustrates that the adsorption process was mainly controlled by the chemical adsorption mechanism (Yan et al. 2015).
As shown in Fig. 7a, the elution efficiency of different eluents for TPAZ-8 and TPAZ-67 were tested. The elution efficiency of the TPAZ-8 and TPAZ-67 is about 10% in water, while is about 90% in 0.1 M of HCl. Therefore, 1 M HCl was selected as the eluent and the cyclic adsorption capacity as illustrated in Fig. 7b. After five times of adsorption-desorption, the adsorption efficiency of TPAZ-8 and TPAZ-67 were still maintained at 80% and 83%, respectively, indicating that the aerogels had excellent repeatability and potential application in the field of adsorption.
The aerogels possess shape-controllably, fast recovery, and rapid adsorption kinetics, which provides convenience for many special cases. As shown  Fig. 8a and Movies S4, the cylindrical aerogels were packed into syringes to filter contaminants from water. After three suction and extrusion at a flow rate of 6 L h −1 , the concentration of Cu 2+ was reduced by 85% (Fig. 8b). Furthermore, in contrast with other aerogels, the solution in the resulting aerogels can be squeezed sufficiently accelerating the discharge of the filtrate. Moreover, the strong interaction between MOF and cellulose aerogels ensured minimal MOF loss during repeated adsorption, showing excellent adsorption stability.

Conclusion
In this study, ultralight and under-water elastic cellulose aerogels were successfully fabricated through esterification crosslink of the cellulose nanofiber with PVA. The aerogels not only offered excellent mechanical flexibility and high porosity, but also provided abundant nucleation sites for growing MOF crystals. The resulting MOF@ cellulose aerogels with high porosity up to 90% and a low density of 9.8-11.2 mg cm −3 , showing high adsorption capacity for metal ions and rapid adsorption kinetics. The adsorption capacities of TPAZ-8 for Pb 2+ and Cu 2+ are up to 105.21 mg g −1 and 54.78 mg g −1 , while the TPAZ-67 is 123 mg g −1 and 70.53 mg g −1 . Among them, the adsorption capacity of TPAZ-67 is better than that of TPAZ-8, because of the larger specific surface area and rational pore size distribution of TPAZ-67. The kinetic studies show that the absorption of Pb 2+ and Cu 2+ on TPAZ can be described by the pseudo-second-order model. Moreover, the shapecontrollable and high elasticity of TPAZ-67 make it a special filter device for water purification applications. In brief, these remarkable properties make it have high potential application value in wastewater treatment and adsorption fields.