In the last century, pollution caused by urbanization and industrialization has threatened surface and underground water sources [1, 2]. Heavy metals are ecological toxic materials that are widely used in industries and can affect the humans, animals, and plants health [3, 4]. If the wastewater polluted by heavy metals do not treated properly, it make a great threat to human health, thus heavy metal removal from wastewater is of great importance [5]. One of the harmful elements is arsenic, which has four valencies of -3, 0, 3 and 5 [6], among which only As5+ (arsenate) and As3+ (arsenite) are drinking water pollutants [7]. The concentration of arsenic in contaminated groundwater is 0.5–2.5 ppm and much higher (usually > 100 ppm) in industrial wastewaters [8]. Based on World Health Organization (WHO) suggestion, the arsenic ions concentration of drinking water should be less than 10 ppm [3]. Even studies indicate that long-term consumption of drinking water containing arsenic in concentrations of 0.05 ppm and higher can increase the risk of kidney, skin and bladder cancer [9–11]. Hence, arsenic is classified as a first priority toxic substance by the World Health Organization [12]. The results have shown that the absorption process is an effective process in removing arsenic from drinking water, and this method can easily achieve the amount recommended by the World Health Organization and the American Environmental Protection Agency (0.01 ppm) [13, 14].
Out of all the techniques used to remove arsenic from water, like coagulation and filtration, researchers are especially interested in adsorption because it's efficient, affordable, and easy to use [6]. Figure 1 illustrates various methods for removing heavy metals from polluted water. However, traditional materials used for adsorption often have limited capacity [15]. This is why choosing the right absorbent is crucial. Recently, a new type of material called metal-organic frameworks (MOFs) has shown promise as an effective absorbent for removing harmful heavy metals from water [16].
MOFs have attracted attention due to their porosity and high surface area, chemically tunable nature, reusability, structural features and performance, and are being evaluated for use in a variety of absorption applications [17]. However, many MOFs are unstable in the presence of water, which severely limits their usefulness, but the UiO-66 sample is a common form of Zr-MOFs that shows good absorption performance with good thermal stability (< 500°C) and water resistance [18–20]. UiO-66 is a special type of material called a Metal-Organic Framework (MOF). Its core building block is a cage-like structure made of zirconium and oxygen atoms (Zr6O4(OH)4 cluster). An important property of UiO-66 is its exceptional stability. The strong chemical bonds between zirconium and oxygen make it resistant to acidic and alkaline environments. This stability is a key reason why UiO-66 is considered promising for water purification applications [21].
Several factors influence how well adsorption removes pollutants from water. These factors include the type of pollutant and its concentration, the properties of the material used for adsorption (the adsorbent), and the conditions during the process like pH, temperature, and how long the pollutant is in contact with the adsorbent. Researchers have improved the effectiveness of UiO-66, a metal-organic framework (MOF), for removing heavy metals from water. For example, Fu et al. modified UiO-66 to remove lead (Pb) more selectively, achieving a capacity of 189.9 milligrams of lead per gram of adsorbent at a pH of 4 [22]. Other studies have shown success in using UiO-66 to remove other heavy metals like cadmium, chromium, and mercury. Such as Farhad et al. [23] were tested to enhance the treatment of Pb (II) using two amine ligands possessed by ethylenediamine (EDA) as a ligand to graft UiO-66, they achieved an adsorption capacity of 243.90 mg/g for Pb (II) and also, Saleem et al. [24] had modified the UiO-66 adsorbent for heavy metal treatment and improved the Cd2+ ,Cr2+ ,Pb2+ and Hg2+ ions adsorption removal efficiency, respectively to adsorption capacities of 49, 117, 232 and 769 mg/g. Additionally, researchers have explored alternative MOFs for arsenic removal. Zhang et al. demonstrated a cerium-based MOF that can rapidly remove almost all arsenic from water within 10 minutes [25]. Ren et al. [26] used a composite of magnetic core @ Shell Fe3O4 @ polypyrrole @ sodium dodecyl sulfate for relective removal of five dyestuffs and heavy metal ions from complex wastewater. They reached a removal efficiency above 90% after five desorption–adsorption cycles and confirmed that their adsorbent composite is a promising candidate for dyestuffs and heavy metal removal.
In this study, we compared the effectiveness of different materials for removing arsenic from synthetic wastewater. We tested UiO-66, acid and base-treated zeolite, and silicon dioxide nanoparticles (SiO2). We identified the best performing material and evaluated its effectiveness under various conditions. Finally, we compared the performance of the two best materials under the five most favorable conditions identified in our study.