Dyes are extensively used in textile, dyeing, printing, leather, paper, pharmaceuticals, food, and plastic industries for various purposes. To date, more than ten thousand synthetic dyes are existing in the market. Dyes are categorized into several groups based on their nature, chemical composition, chemical structure, and their application. Among them, azo dyes have gained great prominence as they are available in a wide range of colors, easy to manufacture, and inexpensive. These dyes can be easily applied to various materials including cotton, wool, synthetic fibers, and silk. However, they are toxic and carcinogenic. According to several reports, azo dyes contribute to 50– 70% of the dye market (Hossain and Hossain, 2020; Paździor et al., 2019; Prabhakaran et al., 2020; Yaseen and Scholz, 2019).
Due to the rapidly growing dye-related industries, an enormous amount of dye effluent has regularly been discharged into freshwater without being properly treated (Cheng et al., 2020). The discharge of dye-contaminated wastewater, even at smaller volumes, causes inconceivable damage to natural resources (Cai et al., 2019; Kumari et al., 2022; Mekki et al., 2021; Paździor et al., 2019). It leads to eutrophication, aesthetic pollution, and disruptions of aquatic life. According to the literature, nearly 15% of the dyestuffs are lost in industrial (Routoula and Patwardhan, 2020). Azo dyes are popularly known to be toxic, carcinogenic, and mutagenic. Their presence in wastewater is a major environmental concern (Said et al., 2020).
Various methods including physical, chemical, and biological methods, have been developed to eliminate azo dyes from wastewater (Falalu, 2017; Kumari et al., 2022; Tripathi and Rawat Ranjan, 2015; Zazou et al., 2019). However, they are inefficient in removing dyes completely from the water matrix. Chemical oxidation and coagulation require a large quantity of chemicals and may produce harmful byproducts (Falalu, 2017; Vijayanand and Divyashree, 2015). Adsorption has a problem of regeneration/disposal of adsorbent materials which is again a threat to the environment (Nawaz and Sengupta, 2019). Recently, advanced oxidation processes (AOPs) such as electrochemical oxidation, ozonation, Fenton reagent, cavitation, and photocatalysis have acquired attention for dye removal from water due to their numerous notable advantages, including lower operating costs, higher performances, simplicity, and environmental friendliness (Ghatak, 2013; Malkapuram et al., 2023b; Paździor et al., 2019). Thus, many industries have adopted these techniques, including sewage treatment, the pharmaceutical industry, food processing, brackish water treatment, and desalination (Asghar et al., 2015; Nidheesh et al., 2018). However, AOPs are found to be not viable at an industrial scale due to technological limitations, and higher operating and material costs. Importantly, AOPs cannot eliminate dyes from water completely (Abdel-Karim et al., 2021; Nawaz et al., 2022). Thus, the treated water textile effluent is increasingly being treated using membrane technologies. Treatment of dye effluent by low-pressure membrane procedures such as microfiltration (MF) and ultrafiltration (UF) are economically advantageous (Dasgupta et al., 2015; Donkadokula et al., 2020).
Various polymers such as polyacrylonitrile (PAN) (Modi et al., 2022), polyether sulfone (PSF) (Yurekli, 2016), polyvinylidene fluoride (PVDF), bromo methylated polyphenylene oxide, etc. (Gui et al., 2015) have been extensively used for dye removal purposes. Cellulose acetate (CA) is considered one of the best materials for membrane production due to its excellent film-forming properties, ease of manufacture, low cost, and environmental friendliness. It is well-known for its intrinsic antifouling and antioxidant properties (Abdel-Karim et al., 2021; Kumar et al., 2021; Yang et al., 2021). However, CA-based membranes have less mechanical strength and fouling affinity. Most importantly, the CA-based membranes are hydrophobic (Abdel-Karim et al., 2021). With the development of nanotechnology, extensive studies have been conducted to use the benefits of different nanomaterials in polymeric membranes to overcome their disadvantages (Elgarahy et al., 2021). This type of membrane is widely known as a mixed matrix membrane (MMM) (Cong et al., 2020). Recently, several studies have reported on the incorporation of various nanomaterials, metal oxides (Ronquim et al., 2020; Teow et al., 2021), metal-organic frameworks (MOFs) (Malkapuram et al., 2023a), and various composites (Ganjali et al., 2020; Wen et al., 2019) into the CA polymer matrix.
Abdel-Karim et al. have developed Ag-TiO2 nanoparticle and α-aminophosphonate modified montmorillonite incorporated MMM were fabricated using CA polymer matrix for textile effluent treatment. The incorporation of additives has shown enhanced hydrophilicity, pollutant rejection performance, and mechanical stability of the membrane (Abdel-Karim et al., 2021). Yang, Shujuan, et al. have also reported improved pore structure, permeability, antifouling property, and mechanical strength of the membrane when additives like lignocellulose nanofibrils were incorporated in CA matrix that has exhibited an excellent antibacterial property by rejecting over 90% E.coli (Yang et al., 2021). Similarly, Malkapuram et al. have incorporated sonochemically synthesized ZIF-8 into CA polymer matrix and observed enahanced antifouling, hydrophilic, and dye rejection properties (Malkapuram et al., 2023a).
This study aims to incorporate silica nanoparticles in the CA matrix to develop an MMM (CA/SiO2). MMMs with nanoparticle additives are esteemed for their multifaceted advantages, such as heightened hydrophilicity, improved solute rejection, augmented mechanical strength, and enhanced chemical and thermal stability (Abdel-Karim et al., 2021). The intrinsic hydrophilicity of silicon dioxide (SiO2) nanoparticles, facilitated by the presence of silanol groups (Si-OH), in combination with their substantial porosity and expansive surface area, makes them an optimal strengthening filler for polymer matrices (Muhamad et al., 2015). This substantially enhances the structural integrity of membranes. Various characterization studies have been carried out to study its morphology, crystallinity, chemical composition, hydrophilicity, and thermal properties. Consequently, the membrane performance was evaluated on the removal of Safranin-O (Sf-O) dye from simulated wastewater.