Bimetallic Ce-UiO-66-NH2/diatomite (CUD) self-assembled membrane simultaneously with synergetic effect of phase equilibrium and rate separation

https://doi.org/10.1016/j.memsci.2019.117730Get rights and content

Highlights

  • Bimetallic Ce-UiO-66-NH2/diatomite (CUD) particles were first successfully prepared.

  • CUD self-assembled membrane exhibits the characteristics of rate and phase equilibrium separation.

  • CUD self-assembled membrane performs high separation efficiency and selective adsorption properties.

  • CUD self-assembled membrane is promising alternative for oily wastewater treatment.

Abstract

To efficiently clean oily wastewater with the linear anion polyacrylamide (APAM), selective adsorption strategy belonging to phase equilibrium separation is introduced into the membrane separation. Herein, bimetallic Ce-UiO-66-NH2/diatomite (CUD) were first synthesized by a one-step hydrothermal method and then employed as a functional layer to form CUD self-assembled membrane (CSA-membrane). CUD particles were characterized by FT-IR, XRD and SEM, and CSA-membrane was observed by SEM. The separation and the selective adsorption properties of CSA-membrane formed under the optimum conditions for APAM in oily wastewater were investigated. The results demonstrate that the size of CUD particles with proper sphericity is mainly 20 μm. Furthermore, CSA-membrane simultaneously exhibits fascinating separation and selective adsorption properties for cleaning oily wastewater, namely the concentration of oil decreases from 78.1 mg L-1 to 6.8 mg L-1, and flux of CSA-membrane reaches 789.5 L m-2 h-1. Remarkably, the adsorption capacity of CSA-membrane for APAM is 161.5 mg g-1, while showing the APAM removal rate of 51.3%. Therefore, CSA-membrane with the synergetic effect of phase equilibrium and rate separation is promising alternative for cleaning oily wastewater with APAM.

Graphical abstract

To efficiently clean oily wastewater with the linear anion polyacrylamide (APAM), selective adsorption strategy belonging to phase equilibrium separation is introduced into the membrane separation. Herein, bimetallic Ce-UiO-66-NH2/diatomite (CUD) particles were first synthesized by a one-step hydrothermal method and then employed as a functional layer to form CUD self-assembled membrane (CSA-membrane). CSA-membrane simultaneously exhibits fascinating separation and selective adsorption properties for cleaning oily wastewater. By joint effort of static interaction and hydrogen bonding, APAM is adsorbed to promote the separation effect of oily wastewater. Therefore, CSA-membrane benefiting from synergistic effect of phase equilibrium and rate separation has promising application prospects in effectively cleaning oily wastewater.

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Introduction

Mass transfer separation is a significant process widely used in many areas, such as chemical engineering, pharmaceutical engineering, environmental protection and food industry [[1], [2], [3], [4]]. Based on physical and chemical principles, mass transfer separation is divided into two categories, namely phase equilibrium separation and rate separation [5]. Phase equilibrium separation comprises adsorption, absorption, crystallization, distillation, extraction, drying, etc. It is made possible by the distribution difference between the two phases in equilibrium system [6]. In contrast, the rate separation process includes membrane separation and field separation, and mainly depends on the different movement rate of each component in the system under a certain driving force. Although the phase equilibrium separation processes show better selectivity, some unit operations are associated with high energy consumption and complicated operation. Whereas, the membrane separation belonging to rate separation shows energy-saving capabilities and low operating costs, and its limited selectivity caused by just size sieving is indeed impeded in high selective separation domain [7,8]. Therefore, a key challenge is the combination of membrane separation technology with phase equilibrium separation for improving the efficiency of mass transfer separation.

Ultrafiltration (UF) membrane technology belonging to the rate separation has attracted extensive attention for its moderate operating conditions, low energy consumption, without phase change and chemical additives, etc. [9]. Colloids, granules and macromolecular organic matters in wastewater are retained within specific membrane channels [10]. Inversely, some dissolved matter or linear substances are prone to pass easily through UF membranes causing environmental pollution because of their smaller sizes such as phosphate and anion polyacrylamide (APAM) [[11], [12], [13]]. To improve the separation performance of UF membrane without increasing energy consumption, it is a viable strategy to make UF membrane simultaneously have the characteristics of phase equilibrium (selective adsorption) and rate separation (size sieving). Recently, some researchers constructed molecular recognition sites on the membrane, thus perfectly matching the target molecules in space and binding sites [[14], [15], [16]]. For example, Zhang et al. [17] synthesized membranes with molecule recognition performance via molecular template, showing a high selectivity factor of 14.1 for the separation between luteolin and rutin. Wang et al. [18] fabricated multilayered molecularly imprinted membrane through an in situ activator for artemisinin separation, which indicated the as-prepared membrane possessed desirable adsorption ability and permselectivity. Although molecular imprinting technology significantly improves the selectivity of the membrane, its selectivity is achieved through channels and spatial sites, thus depending on the type of material and inevitably causing large mass transfer resistance. Hence, a novel membrane technology that introduces a phase equilibrium process, especially selective adsorption need to be further investigated.

Dynamic membranes represent a promising alternative to conventional membrane technology for its high flux, convenient operation and brilliant separation efficiency [19,20]. However, dynamic membranes face certain difficulties in broadening the application field owing to the absence of designability, limited material types, the uncontrollable morphology and scale of material. As an emerging technology, layer-by-layer (LbL) assembly technology with tunableness and controllability has stimulated interests [21,22]. This technology provides a reliable approach for generating desirable self-assembled membranes sustained by intermolecular forces like electrostatic interactions and van der Waals forces between each layer. Furthermore, compared with conventional membrane, self-assembled membrane with regular curved channels could perform the turbulent diffusion process, conspicuously facilitating mass transfer and enhancing efficiency in phase equilibrium separation. In addition, self-assembled membrane could be controllably formed on the porous support layer via regulating a feed solution containing fine particles [23]. According to the formation process, it normally consists of three layers: porous support, support layer and functional layer. In general, functional layer plays an important role in determining the membrane performance. Particles assembled into functional layers could achieve selective adsorption in phase equilibrium separation and accuracy sieve separation in rate separation. Progress has been made on functional layers of self-assembled membranes in recent years. For instance, Cai et al. [24] prepared dense MnO2 membrane to treat oil refinery wastewater and the results showed that turbidity removal rate was 98%. Zhang et al. [25] formed phosphorylated YxSi1-xO2/Al2O3 (PYSA) self-assembled membrane for oily wastewater cleaning, which displayed oil retention rate of 86.32%. When treating oily wastewater, linear APAM molecules along with its carried oil droplets and some dissolved matters readily pass through membrane channels, so permeate water quality of membrane cannot satisfy the standard of recycle and discharge [26,27]. However, γ-Al2O3 with a small specific surface area in PYSA is utilized to adsorb APAM, which results in a poor adsorption capacity and weaken the effect of phase equilibrium separation. In addition, hydrophilicity of PYSA self-assembled membranes is restrained due to limited Lewis acid sites and hydroxyls, which declines the oil separation efficiency. Therefore, it is crucial to further investigate new functional materials with good selective adsorption capacity and high hydrophilicity to facilitate phase equilibrium and rate separation of self-assembled membranes.

Metal-organic frameworks (MOFs) are newly emerged promising sorbent materials in light of their large specific surface area, flexible structure and tunable porosity [[28], [29], [30]]. Especially, Zr-based MOFs of UiO-66-NH2 constructed with 2-aminoterephthalic acid ligands and Zr6O4(OH)4 clusters, has attracted much attention with inherent hydrophilicity and adsorption capacity [[31], [32], [33], [34]]. In order to improve intrinsic properties of MOFs, incorporating new secondary metal nodes into the frameworks appears to be an appealing strategy [35,36]. Cerium (Ce) is a suitable candidate for introduction into UiO-66-NH2 [37]. On the one hand, introduction of Ce3+ ions could provide more coordinatively unsaturated sites of metal clusters and organic ligands to create defects [38,39] inside the framework, exposing rich adsorption sites. Hence, positively charged MOFs have electrostatic interactions with anionic APAM. Furthermore, owing to abundant –NH2 as well as –OH, the H-bond also contribute to selective adsorption. On the other hand, the hydrophilicity of Zr-based bimetallic MOFs could be facilitated, because the coordinatively unsaturated metal ions can more readily coordinate with water molecules compared to those organic molecules with lower polarity and larger size, achieving the large flux and good separation efficiency of membrane. With its proper size, diatomite is selected as the substrate for its high rigidity, good sphericity and abundant pores [40]. If Ce-UiO-66-NH2 could be deposited on diatomite composites and then employed as the functional layer to form self-assembled membrane, membrane performance would be improved.

In this paper, to efficiently treat oily wastewater containing APAM, bimetallic Ce-UiO-66-NH2/diatomite (CUD) particles were first synthesized by a one-step hydrothermal method and then employed as a functional layer to form CSA-membrane with characteristics of phase equilibrium and rate separation. Moreover, CUD particles and CSA-membranes were characterized. Finally, CSA-membranes were used to treat oily wastewater and the permeate water quality was also studied.

Section snippets

Materials and reagents

Zirconium chloride (ZrCl4, 98%) and N, N′-Dimethylformamide (DMF, 99.5%) were purchased from Aladdin. Amino-terephthalic acid (H2BDC-NH2, 98.0%) was supplied by Tianjin Guangfu Fine Chemical Co., Ltd. Cerium trichloride heptahydrate (CeCl3·7H2O, 98%) was purchased from Sinopharm Chemical Reagent Co., Ltd. Anhydrous methanol (CH3OH, 99.5%) were bought from Real & Lead chemical Co., Ltd. Diatomite was obtained from Qingdao Sanxing Diatomite Co., Ltd. APAM was obtained from Daqing, China. All

The optimum preparation conditions of CUD particles

In order to confirm the optimal preparation conditions of CUD particles, CUD particles with different molar ratio of Ce/Zr were employed to form CSA-membranes to treat oily wastewater. The initial oil concentration of oily wastewater is 78.1 mg L-1 (Table 1). It can be seen from Fig. 2(a), as the adding amount of Ce increases, oil concentrations in permeate gradually decline and then slowly rise. When the molar ratio of Ce/Zr is 1:5, oil concentration reaches a minimum of 6.8 mg L-1, satisfying

Conclusion

In this work, to efficiently clean oily wastewater with the linear anion polyacrylamide (APAM), selective adsorption strategy belonging to phase equilibrium separation is introduced into the membrane separation. Bimetallic Ce-UiO-66-NH2/diatomite (CUD) were first prepared by a one-step hydrothermal method and then employed as a functional layer to form CSA-membrane. CSA-membrane formed under the optimum conditions for oily wastewater purification achieves an attractive separation performance

CRediT authorship contribution statement

Jiaqi Wang: Conceptualization, Investigation. Yuqing Zhang: Methodology, Supervision. Ying Wang: Validation. Shuai Sun: Writing - review & editing.

Acknowledgment

This project is supported by National Natural Science Foundation of China (No. 21676180, 21076143), by the key technologies R & D program of Tianjin (15ZCZDSF00160).

References (46)

  • Y. Zhang et al.

    Study on composite membranes with high selective permeance properties

    J. Membr. Sci.

    (2010)
  • C. Zhu et al.

    Highly efficient extraction of lead ions from smelting wastewater, slag and contaminated soil by two-dimensional montmorillonite-based surface ion imprinted polymer absorbent

    Chemosphere

    (2018)
  • J.L. Xiong et al.

    Self-adaptive dynamic membrane module with a high flux and stable operation for the municipal wastewater treatment

    J. Membr. Sci.

    (2014)
  • Y. Zhang et al.

    YxSi1-x O2 -SO3 H self-assembled membrane formed on phosphorylated YxSi1-x O2/Al2O3 for oily seawater partial desalination and deep cleaning

    J. Membr. Sci.

    (2018)
  • X.S. Yi et al.

    Factorial design applied to flux decline of anionic polyacrylamide removal from water by modified polyvinylidene fluoride ultrafiltration membranes

    Desalination

    (2011)
  • Y. Zhang et al.

    Formation of phosphorylated ZrxSi1−xO2/Al2O3 self-assembled membrane for cleaning oily seawater

    J. Membr. Sci.

    (2017)
  • J. Koo et al.

    Hollowing out MOFs: hierarchical micro- and mesoporous MOFs with tailorable porosity via selective acid etching

    Chem. Sci.

    (2017)
  • S. Zhuang et al.

    Adsorption of diclofenac from aqueous solution using UiO-66-type metal-organic frameworks

    Chem. Eng. J.

    (2019)
  • H.J. An et al.

    Water adsorption/desorption over metal-organic frameworks with ammonium group for possible application in adsorption heat transformation

    Chem. Eng. J.

    (2019)
  • B. Galzerano et al.

    Design of sustainable porous materials based on 3D-structured silica exoskeletons, Diatomite : chemico-physical and functional properties

    Mater. Des.

    (2018)
  • G. Zhang et al.

    Novel polysulfone hybrid ultrafiltration membrane prepared with TiO2-g-HEMA and its antifouling characteristics

    J. Membr. Sci.

    (2013)
  • N. Tien-Binh et al.

    In-situ cross interface linking of PIM-1 polymer and UiO-66-NH2 for outstanding gas separation and physical aging control

    J. Membr. Sci.

    (2018)
  • M.A. Khraisheh et al.

    Effect of OH and silanol groups in the removal of dyes from aqueous solution using diatomite

    Water Res.

    (2005)
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