Exploring the novel PES/malachite mixed matrix membrane to remove organic matter for water purification

Highlights

• MLC NPs were successfully incorporated in PES membrane via H-bond interaction.

• The MMMs with MLC NPs of 0.1 wt.% exhibited the best water flux and breaking strength.

• Increased MLC NPs enhanced organic carbon removal rate from 20.8% to 26.3%.

• Optical methods demonstrated the preferential removal of aromatic compounds by MMMs.

• Enhanced aromatic fractions were removed by MMMs at increased MLC NPs.

Abstract

This study presents a greener approach to fabricate mixed matrix membranes (MMMs) by introducing malachite nanoparticles (MLC NPs) synthesized from copper sulfate, a toxic waste from many industrial applications, into polyethersulfone (PES) membrane to remove organic matter for water reclamation. The PES/MLC MMMs were characterized by XRD, FTIR, SEM(EDX), Raman Spectroscopy, Photoluminescence Spectrometry, and Contact angle measurements. Results showed that the incorporation of MLC NPs into PES altered the membrane morphology, and made the membrane more hydrophilic. At the optimal amount of 0.1 wt.% MLC NPs, PES/MLC showed the best water flux of 931.1 L/(m² h) (LMH) with the highest breaking stability of 5.06 ± 0.33 MPa. The membrane also exhibited enhanced adsorption of organic foulants with a corresponding flux recovery rate of 0.55 ± 0.03%. The inevitable agglomeration of MLC NPs witnessed at MLC NP dosage of 1 wt.% compromised either the throughput or the mechanical integrity. The elevated NP loading rate from 0 to 1 wt.% enhanced the removal rate of organic carbon (C) from 20.8 ± 1.7% to 26.3 ± 2.3%, respectively. Optical methods demonstrated the preferential rejection of aromatic constituents by the fabricated membranes suggests their potential applicability of optical methods, particularly the fluorescence spectrometry for better prediction of treated water quality by membrane filtration.

Introduction

Urbanization, climate change, and overpopulation have driven water reclamation to be the core of sustainable alternatives to address global water scarcity. Recycled water can be utilized in an array of fields, including agricultural irrigation, toilet flushing, industrial processing, as well as replenishing sources for drinking water (Michael-Kordatou et al., 2015). The accomplishment of desired water quality requires a certain degree of removal of contaminants from the water sources. Of the water treatment technologies, polymeric membranes have soared as a most effective and reliable practice widely used in biological and chemical wastewater/water treatment and/or pretreatment for the nanofiltration and reverse osmosis modes (Ahmad et al., 2013, Ly et al., 2018b, Zhang et al., 2017), due to the absolute separation of impurities, stable water filtration, compact design and low chemical addition (Ahmad et al., 2013).

Interest in polymeric ultrafiltration (UF) membrane materials continues to rise in using polyethersulfone (PES), accredited to its excellent physical and chemical properties (Shen et al., 2012). However, the hydrophobic nature of PES leads to easy fouling, and hinders the permeability with increasing chemical and energy consumption, and shorten membrane lifespan (Sutzkover-Gutman et al., 2010). In recent decades, the incorporation of inorganic nanoparticles (NPs) in polymer matrices has developed beyond expectation, most notably for titanium (Ti) (Li et al., 2009, Razmjou et al., 2011, Vatanpour et al., 2012, Wu et al., 2008, Yang and Wang, 2006), silica (Si) (Yu et al., 2009), silver (Ag) (Basri et al., 2011, Li et al., 2013), and zirconium (Zr) (Rajabi et al., 2015, Shen et al., 2012). Such synthesis has been reported to be a promising route to enhance permeability, selectivity, physicochemical and mechanical stability of the pristine membranes (Dlamini et al., 2019). For example, Li et al. (2009) stated that introducing TiO₂ NPs into the PES membrane can either make the hybrid membrane more water permeable or increase the tensile strength using the optimal dose of 1–2 wt.%. Noted in other literature when using Zr-based NPs it was found that much smaller weights of approximately 0.2–0.4 wt.% is required to obtain exceptional performance of the nanocomposite PES membrane (Shen et al., 2012).

In this context, the incorporation of copper (Cu) NPs into membranes has also attracted much attention (Akar et al., 2013, Ben-Sasson et al., 2014, García et al., 2018, Nasrollahi et al., 2018). A very recent study fabricated the PES/CuO membrane and reported that a nanocomposite membrane blended with 0.2 wt.% CuO NPs approximately doubled the flux in comparison to the pristine PES membrane (Nasrollahi et al., 2019). The Cu NPs can be synthesized from the chemical reduction of Cu-based inorganic salts using a basic reduction procedure. Cu-based salts are essential materials for a myriad of industrial, agricultural, or mining applications (Bilal et al., 2013, Jančula and Maršálek, 2011). CuSO₄, for instance, is considered to be the most known algaecide and herbicide used in agriculture (Jančula and Maršálek, 2011). As such, their existence in the waste solid or wastewater effluent is inevitable and problematic, because exposure to excessive Cu²⁺ cation is well documented to cause severe detrimental health effects such as nausea, respiratory impairment, liver and kidney failure (Bilal et al., 2013). Another copper compound, malachite Cu₂(OH)₂CO₃ (MLC) is a natural mineral, extensively applicable in jewelry, artwork, fertilizer, wood preservative and electronic devices (Molchan et al., 2008, Saha and Das, 2009, Srivastava et al., 2015). Besides, MLC and its nano-sized forms have been proven to be far less toxic than the CuSO₄ (Arnold et al., 2003, Lee et al., 2016, Wang et al., 2014). As such, this merit suggests the possibility of being capable of recovering the potential toxic Cu ion waste into more useful MLC NPs that can be incorporated into the PES polymer matrix. To date, the physicochemical characteristics of the mixed matrix Cu-based nanocomposite membranes have not been fully explored as yet, and thus, deserve further investigation.

Aside from the matrix structure, the successful membrane application is mostly dependent upon the degree of fouling. Among these reported fouling factors, organic constituents in water are highlighted as critical components responsible for membrane fouling (Ly and Hur, 2018, Sutzkover-Gutman et al., 2010). Additionally, the removal of natural organic matter (NOM) is of great importance because of its catastrophic reservoir for carcinogenic disinfection byproducts (DBP) upon chlorination (Yang et al., 2008). Dissolved organic carbon (DOC) is widely adopted as a foremost parameter to determine the rejection and fouling potential of organic matters quantitatively. The major drawback of this technique lies in the fact that it is not sensitive and provides no information on chemical compositions (Ly et al., 2019). Recently, special attention has been paid to optical methods, such as ultraviolet–visible absorbance (UV–Vis) and fluorescence spectroscopy, of which the powerful credits are rapid, highly sensitive and robust (Henderson et al., 2009) and yet to the best of our knowledge their applications on evaluation of NOM rejection using different tailored nanocomposite membranes have not been explored. Consequently, this study is directed by having two primary objectives, that are: (1) to fabricate and to examine the nanocomposite PES/MLC MMMs properties, and (2) to evaluate the fouling potential, adsorption, and rejection of organic matter by the novel MMMs.