Novel nanostructured dendrimer based on 1,3-bis(4,6-dichloro-1,3,5-triazine-2-yl)urea as an excellent adsorbent for Pb²⁺, Ni²⁺, Co²⁺ and Zn²⁺ metal ions

Highlights

• A novel hydroxyl-terminated dendrimer was successfully synthesized using a divergent approach.

• Developed dendrimer used as an adsorbent for metal ions: Pb²⁺, Ni²⁺, Co²⁺ and Zn²⁺.

• The impact of various parameters on adsorption capacity was investigated.

Abstract

Human health is seriously harmed by the consumption of poor-quality water. Due to high toxicity and water solubility, heavy metals are present in wastewater discharged from numerous industries. In the environmental realm, metal-containing water must be treated before being released. A dendrimer is a superior adsorbent for the removal of heavy metal ions due to its nanostructure and hydrophilic end group. In this work, a novel triazine-based hydroxy-terminated dendrimer up to generation three is designed employing a carbamide core. The dendrimer's structure was explored using FT-IR and ¹H NMR studies. Full generation dendrimers UG1.0, UG2.0, and UG3.0 were utilized as an adsorbent for Pb²⁺, Ni²⁺, Co²⁺ and Zn²⁺ metal ion removal from water in a series of tests. The ability of dendrimers to uptake Pb²⁺, Ni²⁺, Co²⁺ and Zn²⁺ metal ions was investigated under various pH, time interval and dendrimer generation parameters. The presence of metal in the dendrimer was confirmed by FT-IR studies of dendrimer-metal complexes. The overall results show that Pb²⁺, Ni²⁺, Co²⁺ and Zn²⁺ metal ions uptake increases with the generation, time, and pH.

Introduction

The most crucial component of life on earth is water. It has no flavour, color and odour if it is at its purest form [1]. Water resource pollution is on the rise, making it harder for humanity to provide clean, safe drinking water. Globalization, industrialization, and other processes like climate change are all thought to be significant water stressors that aggravate the global shortage of clean water for drinking and other domestic uses. In both industrialized developing nations, a variety of contaminants are making their way into fresh water sources; these contaminants include heavy metals, medications and personal care items, pesticides, and micro-pollutants [2].

Industrial effluent discharge has increased the amount of pollutants in aquatic environments, which has raised water demand for domestic and industrial use [1]. Toxic heavy metal pollution of the environment is a global problem. In effluents from several industries, such as metal processing, mining, rubber, plastic, leather, and microelectronics, heavy metal pollutants are released. Nickel, zinc, mercury, copper, and lead are the most prevalent harmful heavy metal ions, and they stand out from other pollutants due to their capacity to accumulate in living things [3,4]. The kidneys, liver, and reproductive system, as well as essential cellular activities and brain functions, can all suffer significant and varied harm from chronic exposure to high levels of heavy metals. Additionally, coma, death, high blood pressure, anaemia, sleeplessness, headache, dizziness, irritability, weakness of the muscles, hallucinations, and renal impairment might be included among the most serious effects. Metal-containing water must be treated before being released into the environment in order to safeguard the environment [5].

The hematologic, neurologic, gastrointestinal, renal, and cardiovascular systems are only a few of the numerous body systems that are affected by Pb(II), which is categorised as a non-essential ubiquitous hazardous metal ion and serious environmental health problems. One of the most poisonous and stable ions in aquatic ecosystems is lead, which manifests a strong propensity to accumulate in a variety of organs of aquatic organisms as Pb(II). The primary human-caused sources of Pb(II) in aquatic ecosystems include urban sewage and industrial effluents released by various businesses that produce batteries, pigments, cables, pipelines, ceramics, gasoline, tobacco, steel, food packaging glasses, and pesticides [[6], [7], [8]]. Wastewater contains hazardous heavy metal ion nickel, which cannot biodegrade. Constipation, nausea, vomiting, abdominal pain, and diarrhoea are gastrointestinal symptoms of acute nickel intoxication. Additionally, nickel has an impact on the immune system, liver, and blood. Teratogenic and carcinogenic effects on mammals are caused by metallic nickel [9]. A well-known hazardous metal ion called zinc(II) has the potential to positively affect human life by bioaccumulating in the food chain. Zinc (II) is commonly detected in the effluents, released from various industries like electroplating, pigment manufacture, battery manufacturing, mining, metallurgy, and municipal wastewater treatment facilities. The World Health Organization recommends 5.0 mg/L of zinc as the highest permissible level in drinking water [10]. Cobalt is an essential component of vitamin B12 and is required for human growth. Cobalt is, therefore, a less toxic element than other metals; however, higher concentrations may be hazardous to humans. A toxic concentration of more than 1 mg/kg (1 ppm) of bodyweight could be considered. In contrast, the USSR recommended a permissible limit of 1.0 mg/L (1.0 ppm) cobalt metal ion concentration in water in 1990. The higher concentration of cobalt ion is considered a toxic heavy metal ion and is responsible for a variety of health problems such as nausea, low blood pressure, heart disease, vomiting, vision sterility, thyroid damage, hair loss, problems, bleeding, bone defects, diarrhoea, and, in rare cases, animal mutations [11]. Cr(VI) and Cd are highly toxic heavy metals that have the potential to be extremely hazardous to humans and the environment. It has been linked to lung, kidney, and liver cancer, as well as gastric damage. In drinking water, the chromium concentration should not exceed 0.05 mg/L. The upper limit level for cadmium in drinkable water should be 0.01 mg/L or less. Long-term impacts of cadmium (II) poisoning include kidney problems and variations in bone, liver, and blood constitution, according to toxicological studies. Nausea, vomiting, diarrhoea, and cramps are some of the short-term side effects. As a result, reducing the production of toxic waste and heavy metals is considered one of the world's most pressing environmental challenges nowadays [12].

There are a number of procedures that can be used to get rid of the heavy metals that are present in industrial effluents, including precipitation, adsorption, electrodepositing, electrocoagulation, cementation, membrane separation, liquid extraction, ion exchanges, etc. For massive alkaline sludge precipitation to be reliable, large settling tanks and post-treatment are needed. Ion exchange has the benefit of allowing metallic ions to be recovered, but it is also expensive and complicated [13,14]. There are some drawbacks, including limited efficiency, high energy consumption, harmful material precipitation etc. As a result, research is being done to identify affordable and effective materials. Processes like adsorption are being looked into as a way to overcome these drawbacks because of how much of an influence they have on the bioavailability and transport of hazardous metals. It is an effective and affordable method for removing heavy metals from waste water. Adsorption processes are frequently reversible, which gives them the further benefit of allowing the adsorbent to be recycled. The effectiveness of adsorbents is influenced by a variety of variables, including temperature, pH, starting concentration, contact time, and rotation speed [15]. Due to its high effectiveness, low cost, and simplicity of use, adsorption appears to be one of the most suitable approaches. For the adsorption-based removal of heavy metals, a variety of adsorbents have been used, including carbon foam, activated carbon, zeolite, clay minerals, organic polymers, and biochar, as well as numerous waste products, including fly ash, biomass, reused sanding wastes, and water treatment residuals (WTRs). Due to its high effectiveness, low cost, and simplicity of use, adsorption appears to be one of the most suitable approaches [16].

Currently, dendrimers are employed as an adsorbent in environmental clean-up processes, particularly when it comes to the elimination of heavy metal ions from water [17]. A dendrimer is a unique kind of polymer with a readily changeable surface and a highly branching structure. They are defined as molecular weight, three-dimensional, hyperbranched molecules with the capacity to confine both hosts and guests. Due to their characteristics like their nano dimensions, spherical structure, high highly branched, uniformly composition, monodispersed, biocompatibility, rising water solubility, lack of immunogenicity, precise molecular weight, hydrophilic, terminal group, and available internal cavities, dendrimers would make excellent delivery vehicles [18,19]. Diallo et al. reported the discovery of the first dendrimer for the removal of metal ions from water [20]. Lead ions were reported to be removed from water using a silica-supported polyamidoamine dendrimer by Niu et al. [21] The PAMAM coating of silica demonstrated great complexation affinity for Zn and equally excellent metal ion absorption efficiency for Zn²⁺, Mn²⁺, Ni²⁺, Co²⁺, Cd²⁺, Fe³⁺and U (IV) [22].

We introduce the newly developed dendrimer in this paper. In which the building block for the formation of dendrimers is 1,3-bis(4,6-Dichloro-1,3,5-triazine-2-yl)urea (UG0.5). Dendrimer was created utilizing a divergent technique up to generation three, employing diethanolamine and triazine trichloride as linkers. Dendrimers of the entire generation G1(OH)₈, G2(OH)₃₂, and G3(OH)₁₂₈ had their corresponding hydroxyl groups substituted with 8, 32, and 128. Dendrimer development and generation were studied using ¹H NMR and infrared spectroscopy. We investigated the adsorption behaviour of novel hydroxy-terminated full generation dendrimer for removal of heavy metal ions (Pb²⁺, Ni²⁺, Co²⁺, Zn²⁺). By using complexometric titration, we examined the effects of pH, time, and generation number on the adsorption behaviour of synthesized dendrimers. FT-IR was used to identify dendrimers that included metal.