Introduction
Without taking into account any specific substance or class, the term “antibiotic” is used to refer to any class of organic molecules that hinder or annihilate germs by targeted interactions [1]. The goal of antibiotic synthesis is to kill or inhibit other microbes and their offshoots. Antibiotics are made to work very well even at very low doses, and if administered intravenously, they are meant to be eliminated from the body within a short time [2, 3]. In the cattle and aquaculture industries, antibiotics are frequently utilized because they help prevent bacterial illness and foster animal growth [4]. The unique biodegradability of natural antibiotics, which come from bacterial and fungal bioprocesses, gives them great value. These antibiotics are complex molecules with numerous different functional groups that give rise to a wide variety of chemical configurations [5]. Additionally, due to the distinct functional groups present, antibiotics exhibit variable dissociation constants (pKa) in the pH range of 1.5 to 9.5. Therefore, depending on the pH level over this threshold, they can live as positively or negatively charged molecules or as neutral entities adopting a zwitterion form [6]. While some antibiotics, such as penicillin, dissolve naturally in the environment, others, such as sulfadiazine, tetracycline, quinolones, ciprofloxacin [7], and sulfonamide, survive due to their resistance to degradation. Their extended lifespan in the environment, combined with poor disposal techniques, is a major worry. Microbes could persist due to the slow breakdown of antibiotics, necessitating treatment to be administered at levels below their minimal inhibitory concentrations (MICs). Indeed, the MIC is critical for antibiotic perseverance and their continued synthesis in the environment. When antibiotics are present in quantities lower than the MIC, this circumstance can promote the formation of antibiotic-resistant bacteria, emphasizing the importance of the MIC as a crucial parameter [4]. One of the most pressing environmental issues of our time revolves around the management and treatment of wastewater [8, 9]. Even trace levels of antibiotics in groundwater, surface water, and wastewater constitute a serious and concerning problem [10, 11]. To address this issue, a slew of antibiotic removal technologies for effluents have been developed and implemented.
It is commonly acknowledged that conventional biological wastewater treatment plants have difficulty in properly removing antibiotic residues [12, 13]. Coagulation-sedimentation [14], oxidation [15], distillation [16], adsorption [17–21], photocatalysis [22–27], electrocoagulation [28], and electrolysis [29] have all been explored as wastewater treatment technologies for antibiotic removal. Adsorption stands out among these due to its simplicity, cost-effectiveness, and ease of operation [30–33]. The main issue, however, is to create a reusable adsorbent with a wide surface area and significant binding affinity for pollutants. Another notable technology is photocatalysis with nanocomposites, which has gained popularity due to its capacity to effectively break down antibiotic residues in many circumstances [34–37]. In this context, zeolites stand out as a highly promising and cost-effective alternative approach for removing antibiotics efficiently [38–40]. Zeolites are low-cost crystalline aluminosilicate with a high surface area and a negative charge, making them ideal for adsorption and photocatalysis [40–42].
Zeolites are crystalline minerals that can be found naturally or synthesized. They have a characteristic framework made up of interlinked SiO4 and AlO4 tetrahedra joined by oxygen atoms and encasing cations within their structure [43]. These crystalline alumino-silicates have complicated three-dimensional networks with nano-sized channels and gaps that nearly resemble small organic molecules. These microporous structures serve as locations for selective adsorption and chemical reactions, with configurable selectivity and reactivity via structural and compositional changes. The nanoscale channels and cages seen in zeolites contribute to their high porosity and surface area. Notably, they have the extraordinary capacity to selectively adsorb molecules based on the geometry of their internal pore structure, a phenomenon known as molecular sieving, effectively rejecting bigger molecules [44]. Zeolite has been extensively used in removing antibiotics from wastewater through adsorption. In the context of antibiotic removal, zeolites, particularly Y and mordenite, have extraordinary efficacy in rapidly removing persistent sulfonamide antibiotics from water, highlighting their potential as effective remediation agents [45]. Although zeolites excel at adsorbing cationic species, surface modifications such as cationic surfactant treatment are required to promote the adsorption of anions and organic molecules (antibiotics), resulting in surfactant-modified zeolite (SMZ) adsorbents with increased capacity for these species [46]. Due to their distinctive structural characteristics and chemical composition, such as their high surface area, high adsorption and condensation properties, abundant acid, and base sites that can reduce the recombination of electron-hole pairs, low cost, and adjustable surface properties, zeolites have been widely regarded as promising candidates for hybrid adsorbent-photocatalyst applications. Numerous studies have used zeolite (as a supporting material) and its composite as an adsorptional photocatalyst for the removal of antibiotics [47–49].
The manufacture and engineering of various zeolites for the adsorption and degradation of antibiotic contaminants are covered in detail in this article. We dig into the serious topic of antibiotic pollution in the environment in this detailed analysis, examining its sources and the attendant risks for both the environment and human health. Then, we acquaint with zeolites as prospective remediation agents, discussing their kinds, synthesis processes, and prominent applications in water remediation, with a particular emphasis on antibiotic elimination. Our analysis includes a case study that highlights successful antibiotic removal as well as the mechanisms underlying antibiotic exclusion. Finally, we discuss the future prospects of this crucial field of research.
Antibiotics in the Environment
In terms of chemotherapeutic medicines, antibiotics are those that stop or prevent the growth of microorganisms (bacteria, fungi, protozoa, or viruses) even at very low doses [50]. The various types of antibiotics can be categorized according to their chemical makeup, mode of action, range of effects, and route of administration. The most prevalent classification among them is based on their mode of action and chemical or molecular makeup (Fig. 1), and the following are the most typical groups: quinolones, fluoroquinolones, aminoglycosides, glycopeptides, lincomycin, macrolides, polypeptides, polyenes, sulfonamides, monobactams, carbapenems, tetracyclines, oxazolidinones, and chloramphenicol [50–53].
2.1. Sources and Occurrence of Antibiotic Pollution
Antibiotics are a class of secondary metabolites produced by microorganisms that were originally derived from common natural substances. These chemicals were found through careful laboratory screening. Over time, scientists used this information to create semi-synthetic antibiotics, boosting the arsenal of medications available to battle diseases. When antibiotics were first produced, their effluents started to infiltrate the environment. Antibiotic contamination has been noted in plants, sediment, sludge, groundwater, wastewater, tap water, surface water (lakes, streams, rivers, and the sea), and aquatic animals [50]. Also, their pollution in water occurs from a variety of sources, with ciprofloxacin and sulfamethoxazole being frequent. These antibiotics are resistant to degradation, particularly quinolones [51]. Antibiotics such as erythromycin, amoxicillin, norfloxacin, ciprofloxacin, levofloxacin, ofloxacin, trimethoprim, tinidazole, sulfamethoxazole, tetracycline, and others are regularly found in groundwater and surface water, typically in toxic quantities [54]. Contamination sources include hospital and household waste, widespread antibiotic usage in medicine, antibiotics from fertilizers, sewage treatment plant sludge, and veterinary use in aquaculture. Improper drug disposal, such as flushing and tossing, aggravates the problem. Antibiotic levels in drug manufacturing plant effluents might surpass therapeutic values, as reported near Hyderabad, India [55]. Antibiotics are introduced into the water through sewage systems and biosolids land application, adding to worldwide antibiotic presence and resistance concerns. Fig. 2, given below, shows different pathways of antibiotic addition into the environment.
Concerning the notable usage of antibiotics, it’s worth noting that, in Europe, circa 1997; antibiotic consumption was substantial, with an estimated 10,000 tons per year being utilized [56]. This usage was evenly split between medical applications and animal health, as reported by FEDESA (European Federation of Animal Health) data. In 2017, data on the utilization of systemic antibiotics within the primary care sector across Europe revealed varying consumption levels, measured in Defined Daily Doses (DHD). Central-southern European countries exhibited a consumption range of 19,317 to 32,148 DHD. These countries could be categorized into three distinct blocks: the first block, encompassing countries like Italy, fell within the range of 19,317 to 23,594 DHD. The second block, including nations such as Spain and France, exhibited consumption levels ranging from 23,594 to 27,871 DHD. Finally, the third block, comprising countries like Greece and Romania, recorded consumption rates ranging from 27,871 to 32,148 DHD [57].
Conversely, in northern European nations such as England, Sweden, Norway, Denmark, and Germany, the consumption of systemic antibiotics in primary care settings remained lower, with a range of 10,763 to 19,317 DHD [57]. Numerous research endeavors in China have focused on the presence of antibiotics in wastewater treatment plants (WWTPs). Among these investigations, a notable study encompassed the examination of 45 WWTPs across 23 cities in China. Within this scope, quinolones emerged as the predominant antibiotic class, with concentrations peaking at an astonishing 29,647 μg/kg in the domestic sludge of Shanxi Province [58].
Spanish rivers, including Jarma, Manzanares, Guadarrama, Henares, and Tagus, have been documented to contain various antibiotics such as ciprofloxacin, clarithromycin, erythromycin, metronidazole, norfloxacin, ofloxacin, sulfamethoxazole, tetracycline, Azithromycin, and trimethoprim. Median concentrations of these antibiotics were approximately 3, 235, 320.5, 1195.5, 10, 179, 326, 23, 120 and 424 ng/L, respectively [59].
Research in Dalian province, China, examined antibiotics in seawater, sediment, and aquatic organisms. Tetracycline levels in seawater ranged from 2.11 to 9.23 ng/L, while sulfonamides dominated sediments (1.42–71.32 μg/kg) and aquatic organisms (2.18– 63.87 μg/kg), suggesting potential bioaccumulation of specific antibiotics [60]. Table 1 given below represents various studies for the concentration of antibiotics detected in water.
Table 1 presents concentrations (ng/L) of various antibiotics detected in different water sources including surface water, wastewater, hospital effluent, sewage, and rivers. The most commonly detected antibiotics across the sources are Sulfamethoxazole, Ciprofloxacin, and Trimethoprim (based on the data mentioned in Table 1). Their concentrations vary widely across different water sources, indicating potential environmental contamination and the need for monitoring and management strategies.
2.2. Environmental and Human Health Concerns
Antibiotic residues pose significant risks to consumer health, leading to direct toxicity, allergic reactions, hepatotoxicity, and destruction of intestinal flora, mutagenicity, reproductive disorders, teratogenicity, and carcinogenicity. These residues, found in water and food, can induce various adverse effects such as skin rashes, hepatitis, gastrointestinal disturbances, and increased mutation frequency. Moreover, antibiotic resistance, driven by these residues, presents a grave threat to public health, potentially causing millions of deaths annually by 2050 according to WHO estimates [80]. Antibiotic overuse has resulted in the fast emergence of antibiotic resistance, posing substantial health hazards to people. However, there is a lack of a quantitative approach to completely quantifying these hazards. Concerns about antibiotic residues in the environment include the possibility that ingested residues will alter the human microbiome, promoting bacterial resistance within the human body and creating selection pressures on the environmental microbiome, resulting in antibiotic resistance reservoirs. To address these issues, a comprehensive approach to assessing health risks associated with environmental antibiotic residues is required, with a focus on hazard identification, exposure assessment, dose-response assessment, and risk characterization. Unfortunately, there is a lack of data to characterize these risks, emphasizing the need for standardized monitoring of antibiotic residues and resistance, understanding the relationship between antibiotic levels and resistance development, and establishing dose-response relationships for pathogenic antibiotic-resistant bacteria. Collaboration among clinicians, engineers, and environmental scientists, as well as support from governmental agencies around the world, is critical to effectively address these environmental and human health concerns and develop long-term solutions to combat antibiotic resistance in both water systems and medical practice [81, 82].
Zeolites as Remediation Agent and its Physicochemical Properties
3.1. Introduction to Zeolites
The name “zeolite,” which is derived from the Greek words “zein” (boil) and “lithos” (rock), was first used in 1758 by the Swedish mineralogist Alex Fredrick Cronsted to describe a mineral that expanded when heated [83]. Zeolites are microporous crystalline aluminosilicates that are commonly referred to as “molecular sieves [84].” Their basic building units (BBU) are TO4-type tetrahedrons, where T stands for silicon and/or aluminum atoms [85]. The difference in valence between silicon (+4) and aluminum (+3) causes an excess of negative charge in the crystal structure, which is balanced by compensation cations, which are often alkali metal or alkaline earth metal elements. Zeolites have three-dimensional structures built up of interconnected networks of [SiO4]4− and [AlO4]5−-tetrahedra linked together by oxygen atoms. Cages are created by joining pore openings in tetrahedral structures that have specific diameters (between 0.3 and 1.0 nm), depending on the structural type. To create a neutral structure, the positive charge of the cations must balance out the negative charge on the lattice [86]. A zeolite’s typical chemical formula is Ma/b [(AlO2)a (SiO2)y]. cH2O, where M is an alkali or alkaline earth metal cation, b is its valence, c is the water content per unit cell, and a and y indicate the total number of [SiO4]4− and [AlO4]5−-tetrahedra in a unit cell, respectively [87]. Zeolites exhibit a rich array of physicochemical properties owing to their unique structural characteristics. Featuring channels and chambers within their skeletal framework, zeolites possess surface-active centers with acid-base or oxidation-reduction properties, which contribute to their exceptional adsorption and catalytic activity. One distinctive feature is the presence of micro-pores, typically ranging from 0.3 to 1.0 nm in diameter, alongside a micro-pore volume spanning from 0.10 to 0.35 cm3g−1 [88]. Classified based on pore size, zeolites can be grouped into categories of small, medium, large, and very large pore sizes. Moreover, their physicochemical behavior is intricately linked to the molar ratio of silicon to aluminum (Si/Al), which influences properties such as thermal stability, acidity, ion exchange capacity, and hydrophilicity. As the Si/Al ratio increases, so does the thermal stability and acidity of the zeolite, while ion exchange capacity tends to decrease. Zeolites exhibit a vast internal surface area, typically several hundred square meters per gram, coupled with a considerable cation exchange capacity [88]. Zeolites are classified into three categories depending on their Si/Al molar ratio: low silica (Si/Al ≤ 2), intermediate silica (2 < Si/Al < 5), and high silica (Si/Al ≥ 5). Because of their high ion exchange capability, low-silica zeolites excel at removing ammonium and heavy metals in environmental remediation. Because of their enhanced hydrophobic characteristics, high-silica zeolites are chosen for removing organic pollutants. These properties make zeolites versatile materials, finding applications in diverse industries ranging from environmental protection to agriculture, highlighting their significance in various technological and scientific endeavors. Fig. 3 depicts two-dimensional representation of the framework structure of zeolite [89].
3.2. Sources, Synthetic and Natural Zeolites
Zeolites occur naturally, but they can also be built in a laboratory setting. Based on source zeolites, are divided into two main categories: natural zeolite and synthetic zeolite. There are currently over 200 different varieties of zeolites. These are calculated using the silica-alumina ratio. According to the International Zeolite Association (IZA), there are currently 235 species of zeolites that are classified into 133 different crystalline forms [85, 90]. Zeolites’ structural characteristics are mostly governed by their framework. A framework type’s unique channel and frame structure is what it represents, and it has the biggest influence on how well pharmaceuticals are absorbed. Fig. S1(a–f), given below, provides a few significant zeolite frameworks.
3.2.1. Natural zeolite
There have been numerous natural zeolites discovered around the world. Clinoptilolite, analcime, mordenite, laumontite, phillipsite, stilbite, and chabazite are the most abundant minerals, while offretite, paulingite, barrerite, and mazzite are rarer. Clinoptilolite is the most abundant natural zeolite and is widely utilized around the world [91]. Natural zeolites are mostly found in the voids of volcanic lava flows, necessitating mining. They are the product of diagenetic rock-water processes that modify sedimentary rocks during their formation. Zeolites originate in certain “zeolite zones” or strata within volcanic debris, which are governed by elements such as the form of the volcanic materials and the type of water involved (marine, fresh, or saline). These mineral formations develop as a result of low-grade metamorphism caused by geothermal systems, burial metamorphism, or basalt hydrothermal alteration. They can also occur in a variety of habitats, including alkaline lakes, deep-sea sediments, and hydrothermal-geothermal systems, typically resulting in relatively pure deposits [89]. Natural zeolite ores can be discovered among rocks close to extinct or active volcanoes in various regions of the world. Asia, Australia, and Europe provide the majority of the world’s supply, with the United States providing only 1% of it [92]. Natural zeolites, porous minerals with distinct characteristics, are becoming increasingly important in environmental applications (cation exchange, molecular sieving, adsorption, and catalysis), particularly water treatment. Because of their excellent adsorption characteristics, they are potential remediation agents for successfully washing and purifying water and wastewater around the world. The chemical composition and structural details of a few significant natural zeolites [90, 91] are shown in Table S1 (inset in Fig. S1).
3.2.2. Synthetic zeolite
The primary raw elements used to make zeolites, silica, and alumina, are the most plentiful natural mineral components on Earth. SiO2 and Al2O3 from chemical reagents, clay minerals, red mud, waste materials like coal fly ash [93], and industrial byproducts like cupola slag and exhausted fluid cracking catalysts can all be used to make synthetic zeolites. Under hydrothermal conditions in alkaline circumstances, these silicon- and aluminum-rich materials can easily be converted into zeolites. Depending on the nature of the starting material, several zeolites such as NaA, NaX, NaP1, ZSM-48, Linde F, and ZSM-5 can be produced. Even municipal solid waste, such as non-recyclable glass and aluminum scrap, can be used as silicon and aluminum feedstock in zeolite production. For certain materials, this strategy provides both technological feasibility and an environmentally friendly disposal option. The chemical composition and structural details of a few significant synthetic zeolites [90] are shown in Table S2 (inset in Fig. S1). Compared to natural zeolite, because of the cost of manufacturing and purchasing, the synthesis of zeolites utilizing SiO2 and Al2O3 from chemical reagents is an expensive procedure. However, using waste products for synthesis is one approach to lowering synthesis costs. Depending on the crystallographic direction, natural zeolites typically have smaller pores with different-sized openings [94]. Contrarily, a key feature of synthetic zeolites is their uniformity and bigger pore width, regardless of the crystallographic direction, which subsequently boosts their effectiveness in some applications.
3.3. Modification-Synthesis of Zeolites, and Incorporation of Nanomaterials to Form Composites
According to the source, zeolites are classified as natural zeolites or synthetic zeolites. Natural zeolites are often affordable and widely available; however, they contain minerals, metals, quartz, and other contaminants. The adsorption characteristics of zeolites are determined by their Si/Al ratio, cation type, quantity, and location. To modulate these qualities, acid/base treatment and ion exchange with surfactants are utilized, boosting separation efficiency for different ions or organics by changing hydrophilic/hydrophobic traits [91].
3.3.1. Modification of natural zeolite
Modification of natural zeolite can be done by simple acid washing, which improves cation removal by removing pore obstructions and increasing pore size, allowing more cations to enter, and is called H-zeolite. Researchers discovered that ion exchange with H+ enhances microporosity and specific surface area in zeolites treated with HCl. Ammonium exchange followed by calcination (which maintains stability) and direct ion exchange with dilute acid (which results in dealumination and reduced thermal stability) are the two basic ways for generating proton-exchanged zeolites [91, 95]. The removal of oxytetracycline (OTC) from swine wastewater was greatly improved by acid-modified zeolite, which achieved a 90% removal efficiency compared to less than 20% with natural zeolite. OTC elimination was most successful in acidic circumstances (90%) compared to alkaline settings (20–35%) with effectiveness decreasing as ionic strength increased and a beneficial impact from dissolved humic acid and raised temperature [96]. Fluoroquinolone antibiotics (moxifloxacin and norfloxacin) were removed from contaminated water using natural zeolite and acid-treated natural zeolite. It is explained that the improved adsorption capacity of acid-treated zeolite can be due to modification-induced changes in pore diameters and the accompanying increased surface area, which makes it an efficient adsorbent [97]. Fig. 4a shows the scheme of acid treatment of zeolite. Surfactants are commonly used to improve the adsorption capacities of raw natural zeolites, which typically have a net negative charge and a limited affinity for anions and organics in water. Tetramethylammonium, cetyltrimethylammonium (CTMA), octadecyldimethylbenzyl ammonium (ODMBA), hexadecyltrimethylammonium (HDTMA) [98], and other cationic surfactants have been used to modify zeolite surfaces. These surfactants form a bilayer-like structure (Fig. 4b) on the zeolite surface, allowing it to adsorb anionic species and nonpolar organics without altering the chemical structure of the zeolite. The degree of surfactant adsorption determines whether monolayers or bilayers form at or above their critical micelle concentration. As a result, surfactant-modified zeolites have a wide range of functional groups for positively charged exchange sites, making them useful for anion sorption as well as cation exchange in wastewater treatment [95]. It is reported that the addition of organic surfactants such as HDTMA-Br and benzylhexadecyl dimethyl ammonium chloride (BCDMA-Cl) to natural zeolitic tuffs resulted in materials capable of adsorbing organic compounds and promoting the exchange of both inorganic cations and anions [99–101]. Dávila-Estrada et al. [102] discovered that an HDTMAmodified Clinoptilolite could sorb ceftriaxone and paracetamol, with maximal sorption capacities of 0.7288 mg/g and 0.0058 mg/g, respectively. Furthermore, Gamboa et al. [103] observed diclofenac sorption by an HDTMA-modified Clinoptilolite with a maximum sorption capacity of 0.880±0.012 mg/g.
3.3.2. Synthesis of synthetic zeolites
Synthesis of synthetic zeolites are frequently manufactured and utilized to obtain zeolites with excellent uniformity, purity, and better surface area. The properties of zeolites can be adjusted by modifying synthesis parameters such as temperature, raw material ratio, reaction duration, activation method, and aging period. Hydrothermal synthesis is, in fact, one of the most widely used processes for producing synthetic zeolites. The hydrothermal synthesis of zeolites is divided into two stages: 1) Formation of hydrated aluminosilicate gel; and 2) Crystallization, which includes four steps: condensation of anions, nucleation, nucleus growth, and zeolite crystal growth. Amorphous reactants, including silica and alumina, are initially combined in a basic (high pH) solution with a cation source in a typical hydrothermal zeolite synthesis. After that, the aqueous mixture is heated in a sealed autoclave, and the first amorphous phase remains over an induction period. Following that, crystalline zeolite products emerge, eventually replacing the amorphous material. Filtration, washing, and drying are used to recover these zeolite crystals, which are rich in Si-O-Al connections (Fig. S2(a)). Notably, the process has a minimal overall free energy change, indicating that it is primarily kinetically regulated, with the composition of the precursor oxides closely mirroring that of the final zeolite product [104, 105]. Zeolite X powder was efficiently produced utilizing environmentally friendly hydrothermal processes, with low-grade diatomite serving as the principal source of Si and a partial source of Al. This resulted in pure crystalline Zeolite X, which has a dual meso-microporous structure, excellent thermal resistance, a significant calcium ion exchange capacity of 248 mg/g, and a generous surface area of 453 m2/g [106]. This Zeolite X holds significant promise for a wide range of industrial, catalytical, and adsorption technology applications. Ionothermal synthesis for zeolite utilizes low-vapor pressure ionic liquids (Fig. S2(a)) acting as both a solvent and a structural template to form solid materials such as zeolite [107]. Solvothermal synthesis includes a variety of solvents for zeolite formation, with the relevance of water leading to the term “hydrothermal.” A variety of organic solvents, including alcohols, ethylene glycol, hydrocarbons, and pyridine, have also been used to successfully synthesize zeolites (Figure 6a), [87]. Lithosite (−LIT) aluminosilicate zeolites were successfully produced by solvothermal treatment of low-silica zeolite powders in an alcohol-KOH solution at 200–250°C for 15–120 hours without stirring [108]. In the alkali fusion method (Fig. S2(b)), silica- or alumina-rich materials are decomposed in the presence of alkali, catalyzing the generation of soluble aluminate and silicate salts in zeolite synthesis. In the alkali-fusion process, the raw material is typically melted with an alkali, such as NaOH, followed by further hydrothermal treatment [109]. The alkali fusion method (Fig. S3(i)) at temperatures ranging from 45 to 95°C was used to create Zeolite X and Zeolite 4A from coal fly ash (CFA2 and CFA1), differentiated through SEM and XRD patterns (Fig. S3(ii–iii)). As a solvent, coal mine water (CW) outperformed tap water (TP), producing zeolites with superior granular size and fewer carbon impurities. This research presents a simple hydrothermal method for repurposing coal fly ash and remediating toxic coal mine water into effective adsorbent materials for environmental purposes [93].
Alkali leaching (Fig. S2(c)) is an alternate process for zeolite synthesis that involves selectively extracting components with a solution such as NaOH while keeping the desired silica-alumina ratio in the resulting leachate [110]. The microwave heating method in zeolite synthesis is quick and energy-efficient, using microwave radiation to create heat via resonance or relaxation mechanisms, resulting in shorter reaction times and the generation of high-purity, fine-particle zeolites [111]. The ultrasonic method, with frequencies ranging from 20 kHz to 2 MHz, is an important component of sonochemistry, and it is widely used in synthetic chemistry operations [112]. Pal et al. used the ultrasound method to demonstrate the fast and ambient-temperature production of NaP zeolite nanocrystals [113]. The sol-gel (Fig. S2(d)) method is another typical approach for producing zeolites. The sol-gel method involves forming an inorganic sol and then gelating it to create a three-dimensional network structure, offering precise control over particle size and enhancing porosity [87]. Ali MM et al. used wheat straw ash as a silica precursor to synthesize NaY zeolite by a sol-gel technique, providing a high-surface-area adsorbent with 657.44 m2/g BET surface area and 0.341 cm3/g total pore volume, which was efficiently used for tetracycline pollution remediation [114].
3.3.3. Synthesis of zeolite based composites
Zeolite-based composites boost zeolite functioning for applications such as pollutant adsorption and photocatalytic degradation. Composites take advantage of various material advantages, collaborating with zeolites to increase their efficacy in removing organic contaminants and other pollutants. Multiple approaches to developing zeolite-based nanocomposite adsorbents and photocatalysts are published in the scientific literature, such as hydrothermal [115], sol-gel [116], precipitation [117], co-precipitation [118], ultrasonication [119], oxidative polymerization, solvothermal, and others [41]. Fukahori et al. [47] used a sol-gel process to create a composite material composed of TiO2 and high-silica zeolite in their investigation. This composite material was successfully used to remove sulfamethazine (SMT), an antibiotic, from water. The Cdots@zeolite (CDZ) nanocomposites were created utilizing a hydrothermal technique with different weight ratios (1:1, 1:3, 1:5, 5:1, 1:7) to aid in the breakdown of organic molecules [34]. An ultrasonic approach is utilized to fabricate a ZIF-8/Zeolite composite that is efficient for antibiotic removal [120]. A high-activity Ag-C3N4-Clinoptilolite nano-photocatalyst was produced using ultrasonic radiation and used in the photocatalytic removal of tetracycline from aqueous solutions [121].
Application and Recent Advances of Zeolites in Antibiotic Remediation
Antibiotics are commonly removed from wastewater using zeolites. The investigations on antibiotic elimination using zeolites include adsorption and photocatalytic methods as an efficient strategy.
4.1. Adsorption, Isotherms, and Kinetics
Adsorption is the adhesion of fluid molecules to a solid surface caused by physical forces (such as van der Waals attractions or hydrogen bonds) or chemical bonding. Adsorption is often a reversible process, with desorption taking place when the adsorbent releases the bound molecules. Adsorption is classified into two types: physical adsorption, which is driven by physical forces, and chemical adsorption, which is driven by chemical bonding. Various interactions considered for the adsorption of antibiotics onto zeolite and its composite surface are electrostatic, pi-pi, hydrophobic, chelation, H-bonding, and Vander Waal forces of interaction [122]. It is well known that zeolite is extensively studied for the adsorption of pollutants from wastewater. Zeolites with low or intermediate Si/Al ratios have hydrophilic characteristics that successfully remove heavy metals and radioactive chemicals, mostly by ion exchange [44], but not organic pollutants (antibiotics). Zeolites with a high Si/Al ratio are hydrophobic and can be used for adsorption purposes, such as the adsorption of antibiotics from wastewater. ZSM-5 zeolite as a hydrophobic adsorbent is an excellent alternative for studying ciprofloxacin elimination [123]. Y faujasite hydrophobic zeolite is notable for its amazing ability to selectively adsorb large amounts of sulfonamide antibiotics within its cavities while exhibiting highly favorable kinetics [44].
Antibiotic uptake on the zeolite surface is primarily determined by the adsorption capacity Qt, which is defined as the amount of adsorbate per unit mass. Mathematically qt is given below in Eq. (1):
where C0 and Ct (mg/g) are the initial and final concentration of adsorbate (antibiotic) removed, m as adsorbent (zeolite) mass (mg), and V as adsorbate volume (mg/L) [123].
Kinetics is critical in determining how zeolite surfaces interact with antibiotics and the rate of adsorption. To assess the adsorption kinetics or rate-determining processes for the removal of antibiotics, several models have been presented, such as the pseudo-first-order, pseudo-second-order, intra-particle-diffusion model [124, 125], and the Elovich model [17, 126, 127]. Pseudo-second order is typically used for chemical adsorption, while pseudo-first order is typically used for physical adsorption and the Elovich model posits multilayer chemisorption and external-mass-transfer on a heterogeneous substrate surface [128]. The expressions for these kinetic models are given below in Eq. (2–5):
where Qe = adsorption-capacity of the adsorbent at equilibrium (mg/g), k1 = rate constant of pseudo-first-order adsorption (1/min), k2 = rate constant of pseudo-second-order adsorption (g/mg min), Kd = rate constant of the intra-particle diffusion kinetic model (mg/g min1/2), C = a constant, a = the initial adsorption rate (mg/g min), and b = the desorption constant (g/mg).
Various isotherm models have been used to characterize the equilibrium state of adsorbent-(zeolite)/adsorbate-(antibiotics) systems at constant temperature or to determine maximum adsorption capacity, including Freundlich, Langmuir, Redlich-Peterson, Jovanovic, Temkin, Sips, and others [129]. The Langmuir model assumes monolayer adsorption with uniformly distributed active sites on the adsorbent surface [130], whereas the Freundlich model is commonly utilized for heterogeneous surfaces. The Redlich-Peterson model has elements from both the Langmuir and Freundlich-isotherms. The Jovanovic model is almost identical to the Langmuir model. Because of adsorbent-adsorbate interactions, the Temkin-isotherm assumes a linear reduction in the heat of adsorption with increasing sorption coverage [131–133]. The equations for the most generally used isotherms, Langmuir and Freundlich [134], are presented below as Eq. (6–7):
where Ce = concentration of adsorbate at equilibrium (mg/L), Qe = adsorption capacity of the adsorbent at equilibrium (mg/g), KL = Langmuir constant (L/mg), qm = the maximum adsorption capacity ((mg/g) · (L/mg)1/n), KF = Freundlich constant (L/mg), and n = Freundlich parameters.
4.2. Case Study of Zeolite and Zeolite Based Composites for Antibiotic Removal via Adsorption
4.2.1. Tetracycline removal
Tetracyclines (TC) are a broad-spectrum antibiotic family that is widely utilized in veterinary and human medicine. Tetracycline antibiotics are widely used and improperly disposed of, posing substantial environmental and health concerns. In one study [135], Fe(III)-modified synthetic zeolite 13X was used to improve the removal of tetracycline, a common antibiotic pollutant in aquatic settings. The results show that removal efficiency has increased significantly, with a maximum adsorption capacity of around 200 mg/g. The fitting of the Langmuir isotherm shows selective monolayer adsorption via chemical bonding. The kinetics is governed by a second-order model, and diffusion analysis highlights the importance of both external mass transfer and intra-particle diffusion. The study goes into several critical aspects, such as pH, initial tetracycline concentration, and contact time. Notably, the findings highlight the importance of pH, with optimal adsorption capacity achieved around pH=6 due to the amphoteric functional groups of tetracycline and the surface properties of the zeolite-iron composite. The work highlights zeolite’s efficiency in removing antibiotics, which could have consequences for managing antibiotic pollution in industrial wastewater. Another innovative method employs MoS2@Zeolite [122] to remove TC with great efficiency (396.70 mg/g at 35°C). The hydrophilicity of modified zeolite is increased, MoS2 development is controlled, and key adsorption sites are exposed. The TC adsorption capability of MoS2@Zeolite-5 was shown to be pH-dependent. The optimal pH for TC removal was 4, with an adsorption capacity of 44.66 mg/g. Surprisingly, MoS2@Zeolite-5 performed consistently within the pH range of 3 to 6, indicating its acidic stability. These data emphasize the importance of electrostatic interactions, and H-bonding in the adsorption process, demonstrating the adaptability of this new adsorbent. The work demonstrates outstanding stability and reusability, confirming MoS2@Zeolite’s promise as a strong adsorbent for dealing with TC contamination in pharmaceutical wastewater as well as demonstrating zeolite’s performance in antibiotic removal.
4.2.2. Doxycycline removal
It is a type of antibiotic in the tetracyclines category. It is highly effective against both gram-positive and gram-negative bacteria. It has significant residual toxicity in surface and groundwater due to its complex structure and more soluble nature [136]. NaY zeolite produced from wheat straw successfully eliminates doxycycline (DC) contaminants, displaying chemisorption with Langmuir isotherm fit. The adsorption process is endothermic and spontaneous. The mechanism research verified that there are other rate-regulating processes besides intraparticle diffusion. It shows promise in DC removal, with a maximum absorption of 269.75 mg/g at 50°C, making it a powerful adsorbent for treating antibiotic contaminants like DC in wastewater [134].
4.2.3. Diclofenac and ibuprofen removal
Al-Rimawi et al. [137] used natural zeolite Jordanate to remove sodium diclofenac and ibuprofen, discovering unique pH optima at 2 for ibuprofen and 6 for sodium diclofenac. At low concentrations, ibuprofen’s carboxylic group and oxygen atoms produced robust connections with silicon and aluminum components, while sodium diclofenac engaged in electrostatic interactions by penetrating zeolite pores at pH 6. Maximum removal efficiency was reached in 10 minutes; however, for optimal outcomes, a longer contact period of 80 minutes was chosen. Furthermore, at larger initial pharmaceutical concentrations, the zeolite’s removal capability improved, owing to enhanced mass transfer and strengthened interactions between the zeolite and the pharmaceuticals. The adsorption capacity for sodium diclofenac (Langmuir isotherm) was 4.8 mg/g and 1.23 mg/g for ibuprofen (Freundlich isotherm), demonstrating the zeolite’s efficacy in pharmaceutical elimination.
4.2.4. Azithromycin removal
A ZIF-8/Zeolite composite was produced utilizing the sonochemical approach for azithromycin-removal [120], and its extraordinary potential as an adsorbent was comprehensively investigated. The adsorption capabilities of individual zeolites, ZIF-8, and the composite ZIF-8/Zeolite were 22.37 mg/g, 235.3 mg/g, and 131 mg/g, respectively, according to comparative analysis. Equilibrium was quickly attained at pH 8, confirming the composite’s effectiveness. The adsorption process followed Langmuir isotherms, indicating monolayer adsorption, whereas kinetic analyses were consistent with pseudo-second-order kinetics. Furthermore, the adsorption process was endothermic, spontaneous, and entropically favorable. The composite demonstrated outstanding stability and reusability, maintaining 85% removal efficiency after ten cycles. This study emphasizes the composite’s performance in drug removal, providing a long-term and potent solution for a variety of aquatic settings. Fig. S4(a) depicts the complicated adsorption mechanism that governs azithromycin’s interaction with the ZIF-8/Zeolite composite. The pH-dependent adsorption capacity highlights the importance of electrostatic interactions as a driving force. Aside from electrostatics, the structural properties of both the medication and the adsorbent are critical. The hydroxyl groups (OH) in the zeolite’s structural makeup align with the amino groups in ZIF-8. Simultaneously, the complex structure of azithromycin, which contains acidic functional groups (−CH3, COOH), results in a rich interplay of acid-base interactions and hydrogen bonding. This multimodal process demonstrates the ZIF-8/Zeolite composite’s adaptability and efficacy in azithromycin adsorption.
4.2.5. Levofloxacin removal
In the study, a novel magnetic zeolite@-cyclodextrin-gum Arabic (MZ@-CD-GA) nanocomposite [138] is introduced as an efficient adsorbent for levofloxacin (LEV) removal from water. Adsorption kinetics followed pseudo-second-order and Elovich models, although Langmuir and Sips isotherms established monolayer chemisorption (Ea > 20 kJ/mol). According to the Langmuir model, the maximal adsorption capacity is 145 mg/g. MZ@-CD-GA reported removal efficiency ranging from 86% to 99% in actual water samples. Furthermore, its reusability for up to five cycles, ease of separation using an external magnet, and low cost make it an appealing adsorbent for practical antibiotic decontamination applications.
The adsorption mechanisms guiding the removal of levofloxacin (LEV) by the MZ@-CD-GA nanocomposite are complicated and may be divided into four separate processes: electrostatic interactions, hydrogen bonding, complexation, and potential fluoride mechanisms. The spectroscopic investigation, which included FTIR and XPS spectra, highlights the presence of electron-rich zeolitic components, carboxylate, and hydroxyl groups in the adsorbent material. These electron-rich functional groups are critical in promoting electrostatic interactions with the zwitterion form of LEV (Fig. S4(b)). Furthermore, the MZ@-CD-GA nanocomposites terminal hydroxyl and carboxylic groups create hydrogen bonds with the LEV zwitterion molecule, notably with its protonated amine group, producing an extra layer of adsorption mechanism.
The comparative analysis of various studies on antibiotic removal using zeolites and zeolite-based composites reveals diverse trends in adsorption efficiency and mechanisms. For instance, the adsorption capacities varied significantly depending on the antibiotic and the adsorbent used. In studies focusing on tetracycline removal, Fe (III)-modified synthetic zeolite 13X demonstrated a high adsorption capacity of 200 mg/g, while MoS2@zeolite exhibited an even higher capacity of 396.70 mg/g. Similarly, NaY zeolite derived from wheat straw displayed a notable adsorption capacity of 230.69 mg/g for doxycycline. The adsorption isotherms varied across studies, with Langmuir, Freundlich, and Sips isotherms being commonly observed, indicating monolayer or heterogeneous adsorption behavior. Moreover, the pH dependency of adsorption capacity was evident, with optimal pH values ranging from 2 to 8, depending on the specific adsorbent and antibiotic. The kinetic studies predominantly followed pseudo-second-order kinetics, highlighting the significance of chemical bonding and surface interactions in the adsorption process. Furthermore, the composite materials, such as ZIF-8/Zeolite and MZ@β-CD-GA nanocomposite, demonstrated excellent stability and reusability, making them promising candidates for practical applications. Overall, the data underscore the versatility and efficacy of zeolites and their composites in removing various antibiotics from aqueous environments, offering a potential solution to antibiotic contamination in wastewater treatment.
In recent years, zeolites and their composite materials have received a lot of attention as excellent tools for removing antibiotics like Ofloxacin, Sulfamethoxazole, Roxithromycin, Norfloxacin, Ciprofloxacin, Ceftazidime, and other antibiotics from diverse environmental matrices. Table 2 below summarizes a recent study on the use of zeolites and their composites for antibiotic adsorption removal:
Table 2 presents a comprehensive overview of studies investigating the efficacy of zeolites and zeolite-based composites in removing various antibiotics from aqueous environments through adsorption. Different types of zeolites, such as FAU, NaY, zeolite-hydroxyapatite-activated oil palm ash composite, and zeolite analcime, have been explored for their adsorption capacities against antibiotics like tetracycline, azithromycin, doxycycline, and levofloxacin. The adsorption capacities varied significantly across studies, with values ranging from as low as 1.56 mg/g for clindamycin to as high as 454.55 mg/g for tetracycline. The choice of adsorption isotherm varied depending on the antibiotic and zeolite type, with Langmuir, Freundlich, and Sips isotherms being commonly used. Kinetic studies predominantly followed pseudo-second-order kinetics, indicating the involvement of chemical bonding and surface interactions in the adsorption process. Furthermore, the studies demonstrate the potential of zeolite-based composites, such as MoS2@zeolite and magnetic zeolite@β-cyclodextrin-gum Arabic nanocomposite, in achieving high adsorption capacities and efficient removal of antibiotics from water. Overall, the findings underscore the versatility and promising application of zeolites and their composites in mitigating antibiotic pollution in wastewater treatment processes. However, further research is needed to optimize adsorption conditions and scale up these techniques for practical implementation.
4.3. Photocatalytic Degradation, Adsorptional Photocatalysis and Mechanism
Photocatalytic degradation uses photon energy to build electron (e−) and hole (h+) pairs within the catalyst, thereby commencing primary radical production. These initial radicals then hydrolyze water molecules, producing a variety of secondary radicals that aid in antibiotic removal. The steps listed below are being considered for photocatalytic antibiotic breakdown using a photocatalyst [164], presented in Eq. (8–15):
However, some of the primary radicals may recombine with the catalyst’s surface, reducing its total photocatalytic efficiency [165]. Because photocatalytic systems have limits (in terms of efficiency, time, surface area, and band gap), numerous support materials have been introduced to improve their efficiency. These support materials help to overcome these limits and improve overall photocatalytic performance. Zeolites are highly regarded as excellent photocatalytic support materials. Their distinct structural characteristics, such as a wide surface area and an abundance of acid/base sites, minimize electron-hole pair recombination, improving photocatalytic efficiency. The superior adsorption and condensation properties of zeolites concentrate organic molecules on the catalyst surface, enabling photodegradation. Zeolites are versatile options for hybrid adsorbent-photocatalyst systems, boosting environmental remediation technologies due to their adjustable surface features [47, 166]. Clinoptilolite is an exquisite zeolite whose use in expanding the surface area of photocatalysts has received much attention [167, 168]. H-MOR zeolite has also been identified as a viable photocatalyst template due to the oxygen vacancy in its structure and enhanced activity in UV-region [169]. The percentage degradation or removal efficiency [48] was calculated using the following Eq. (16):
where De represents degradation rate, C0 (mg/L) and Ct (mg/L) represents the initial concentration and concentration at time t of the pollutant, respectively.
In the realm of zeolite-based photocatalysts, the process of adsorption and photocatalytic degradation typically encompasses three fundamental steps: (1) organic compound (antibiotics) adsorption and diffusion on the surface of the zeolite-based photocatalyst; (2) degradation of adsorbed molecular pollutants by photocatalysis (above-mentioned mechanism steps); (3) degradation products and intermediates are decomposed-desorbed [166]. Adsorption and photocatalytic degradation on the surface of zeolite-based composites are depicted schematically in Fig. 5.
4.4. A Case Study of Antibiotic Degradation via Photocatalysis
4.4.1. Tetracycline degradation
It is a widely used antibiotic in people as well as animals. Excessive tetracycline use has polluted the environment, prompting the exploration of zeolite-based photocatalysts for effective tetracycline removal. Liu and colleagues described a new CoS2/MoS2/zeolite composite for tetracycline elimination in the presence of visible light. Surprisingly, it had the highest photocatalytic efficacy, eliminating 96.71% of TC in 2 hours, which can be attributed to increased active sites and efficient electron-hole pair separation. The inclusion of a hydrophilic zeolite increased tetracycline adsorption considerably, addressing MoS2’s hydrophobicity and limited catalytic activity. Furthermore, under acidic conditions, the amphoteric characteristics of zeolite promoted tetracycline adsorption on its negatively charged surface, promoting closeness to the photocatalyst and increasing photocatalytic activity [48]. In another study, TiO2 was modified with Fe ions and immobilized on beta (BEA) zeolite support to achieve successful photocatalytic treatment of tetracycline-contaminated water. Under blue LED illumination, the resultant Fe-TiO2/BEA catalyst achieved total TC elimination (100%) in 90 minutes, outperforming TiO2 alone (80%). This higher performance was ascribed to the increased surface area enabled by TiO2 immobilization on BEA zeolite and the band gap lowering of TiO2 by Fe3+ ions, which enabled visible light absorption while limiting charge carrier recombination [170].
4.4.2. Amoxicillin degradation
A beta-lactam antibiotic commonly used as human as well as animal medicine. Amoxicillin (AMX) is difficult to completely break down, and its hydrolyzed and metabolized byproducts can be found in both urine and feces. TiO2-zeolite-based integrated photocatalytic adsorbents (IPA) successfully removed AMX via a unique surface structure containing TiO2 clusters, allowing adsorption and degradation. After 240 minutes of irradiation, LC-MS analysis confirmed the full elimination of AMX and its metabolites. This method combines zeolite adsorption, acid-catalyzed hydrolysis, and TiO2 photocatalysis for effective pharmaceutical ingredient degradation and catalyst recovery [171]. In both UV and visible light, the Au-TiO2/Zeolite Y photocatalyst can convert amoxicillin into compounds with substantially reduced toxicity [172].
4.4.3. Cefazolin degradation
A beta-lactam antibiotic is frequently prescribed to prevent postoperative infections and is considered a non-biodegradable pollutant. CdS/CaFe2O4 supported on Clinoptilolite zeolite was prosperously prepared and showed degradation of CFZ (Cefazolin) under visible light irradiation. Optimized conditions, including a catalyst concentration of 0.6 g/L, an initial CFZ concentration of 15 mg/L, a pH of 7, and a reaction period of 90 minutes, resulted in over 86% CFZ degradation. Mechanistic investigations identified °O2 and h+ as the principal active species in the Z-scheme photocatalyst, while kinetic experiments verified a pseudo-first-order, endothermic reaction [173].
4.4.4. Metronidazole degradation
The Cdots@zeolite nanocomposites were utilizing a hydrothermal technique with different weight ratios (1:1, 1:3, 1:5, 5:1, 1:7). Maximum degradation (79%) was obtained for MET at an optimal catalyst dosage of 0.2 g/L and pH 4. The improved surface area, pore volume, low recombination rate, and favorable band gap energy of the 1:5 CDZ composite resulted in increased photodegradation efficiency. The study also indicated that visible light was the most effective at decomposing MET, with hydroxyl radicals playing an important role [34].
The studies discussed highlight the diverse approaches to degrading various antibiotics using zeolite-based photocatalysts. For tetracycline (TC) degradation, the CoS2/MoS2/zeolite composite and Fe-TiO2/BEA catalyst demonstrated remarkable efficiency, achieving high removal percentages within relatively short reaction times. The CoS2/MoS2/zeolite composite utilized visible light to enhance tetracycline elimination through increased active sites and efficient electron-hole pair separation, while the Fe-TiO2/BEA catalyst capitalized on TiO2 immobilization on BEA zeolite to enhance surface area and lower the band gap, allowing for efficient photocatalytic degradation under blue LED illumination. Similarly, for antibiotics like amoxicillin and cefazolin, TiO2-zeolite-based integrated photocatalytic adsorbents and CdS/CaFe2O4 supported on Clinoptilolite zeolite exhibit efficient degradation under both UV and visible light irradiation, offering promising solutions for antibiotic removal. Moreover, the utilization of Cdots@zeolite nanocomposites for metronidazole degradation underscores the importance of optimizing catalyst composition to achieve enhanced photodegradation efficiency. Overall, these studies demonstrate the versatility and effectiveness of zeolite-based photocatalysts in addressing antibiotic pollution, laying the groundwork for the development of sustainable water treatment strategies. However, further research is needed to optimize catalyst synthesis and operational parameters for practical application in real-world wastewater treatment systems.
Table 3 given below represents various recent examples of zeolite-based materials exhibiting photocatalytical degradation.
The presented studies showcase the effectiveness of zeolite-based materials in the photocatalytic degradation of various antibiotics under different light sources. Notably, the Ag-C3N4-Clinoptilolite composite and Fe-TiO2/BEA zeolite demonstrates exceptional removal efficiencies of tetracycline under solar light and blue LED irradiation, respectively, highlighting the versatility of zeolite composites for antibiotic degradation. Furthermore, Ag2O/Y-Zeolite and CdS/PbS/Clinoptilolite exhibit significant degradation percentages for ranitidine and Cefotaxime under blue LED and Hg lamp irradiation, respectively, emphasizing the importance of selecting appropriate light sources for enhancing photocatalytic activity. Additionally, the CdS-CaFe2O4-clinoptilolite composite effectively degrades cefazolin under visible light, showcasing the potential of zeolite-based photocatalysts for antibiotic removal in diverse environmental conditions. Moreover, novel materials like Cdots@zeolite and Zeolitic-octahedral-metal-oxide-based-on-niobate (ZOMO-NbOx) demonstrate promising degradation efficiencies for metronidazole and ciprofloxacin, respectively, indicating the continuous advancement of zeolite-based photocatalysts in addressing antibiotic pollution. Overall, these studies underscore the importance of tailored zeolite composite design and optimized photocatalytic conditions for achieving efficient antibiotic degradation, paving the way for the development of sustainable water treatment solutions.
Conclusions and Future Prospectives
5.1. Conclusions
The utilization of zeolites and their composites as novel remediation agents for antibiotic removal presents promising solutions to the growing environmental concerns associated with antibiotic pollution. Through adsorptional and photocatalytic mechanisms, these materials demonstrate significant efficacy in eliminating various antibiotics from wastewater and other environmental matrices. The review highlights the diverse range of zeolite-based materials employed for antibiotic removal, including Fe (III)-modified synthetic zeolite 13X, MoS2@Zeolite, NaY zeolite produced from wheat straw, and natural zeolite Jordanate. These materials exhibit impressive adsorption capacities, with maximum adsorption capacities ranging from 1.23 mg/g to 454.55 mg/g, depending on the specific zeolite and antibiotic. Moreover, photocatalytic degradation studies demonstrate the effectiveness of zeolite-based materials in eliminating antibiotics under different light sources. For instance, Fe-TiO2/BEA zeolite achieved total tetracycline elimination (100%) in 90 minutes under blue LED illumination, while Ag2O/Y-Zeolite achieved 97.51% removal of ranitidine under 50 W blue LED light. Zeolites have been classified on the basis of the Si/Al ratio and sources. Different types of natural (Clinoptilolite, Mordenite, Chabazite, and Erionite) and synthetic zeolite (X, Y, ZSM-5, and beta) frameworks have been provided. A detailed description of the synthesis and modification procedures has been provided, which included acid and surfactant treatment of natural zeolite as well as various methods to synthesize synthetic zeolite such as hydrothermal, alkali-fusion, alkali leaching, sol-gel, microwave, and ultrasonic methods. Methods for creating zeolite composites have also been described. Zeolite’s current developments in antibiotic removal and the mechanisms of antibiotic adsorption, isotherm, kinetics, and photocatalysis of zeolite and zeolite-based composites are also provided. Antibiotic adsorption on zeolites and their composites mostly follows second-order kinetics and follows the Langmuir isotherm, showing chemisorptive, and monolayer adsorption behavior, based on the current findings.
5.2. Future Perspectives
Development of affordable technologies: Future research should focus on developing affordable and scalable technologies for the effective removal of new antibiotics, particularly those constantly introduced into wastewater streams.
Stricter concentration restrictions: Implementation of strict concentration restrictions for pharmaceutical pollutants in aquatic habitats is crucial to reducing pharmaceutical pollution and its impact on ecosystems.
Accurate drug detection techniques: There is a need to develop accurate drug detection techniques, especially in rapidly industrializing countries, to monitor and mitigate the effects of pharmaceuticals on the environment.
Exploration of granulation techniques: Further exploration into granulation techniques for zeolite-based materials is necessary to improve column flow examinations and enhance material stability.
Research on regeneration methods: Investigation of regeneration methods for zeolite-based adsorbents is essential to ensure material reusability without sacrificing sorption capacity and selectivity.
Advancement of photocatalytic Effectiveness: Research efforts should be directed towards improving the photocatalytic effectiveness of zeolite-based materials, particularly in sunlight, to enhance their efficiency in antibiotic degradation.
Cost-effective production technologies: Attention must be paid to developing cost-effective and environmentally acceptable production technologies for zeolite-based materials, ensuring their practical applicability in environmental remediation.
In conclusion, zeolites and their composites offer promising avenues for the removal of antibiotics from environmental matrices, with significant adsorption capacities and photocatalytic degradation capabilities. Future research should focus on addressing key challenges and exploring innovative strategies to further enhance the efficiency and applicability of these materials in antibiotic pollution control.
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