A novel thiourea derivative for preconcentration of copper(II), nickel(II), cadmium(II), lead(II) and iron(II) from seawater samples for Flame Atomic Absorption Spectrophotometry
Graphical abstract
Introduction
Natural bays or the water mass compartments in which water circulations were restricted can be easily polluted by anthropogenic inputs. Harbours, marinas, estuaries have circulation restricted water bodies which suffer from metal pollution (Abdulla and Naser, 2021; Adeleke et al., 2020; Balachandran et al., 2005; Birch et al., 2020; Cruz et al., 2020; González-Ortegón et al., 2019; Keshavarzi et al., 2015; Najamuddin et al., 2016; Nikulina and Dullo, 2009; Okoro et al., 2013; Şanlıer, 2018; Yılmaz and Sadikoglu, 2011; Zhang et al., 2019).
Although, natural heavy metal concentrations in unpolluted seawaters are at μg.L−1 level (Alonso Castillo et al., 2013; Baysal and Akman, 2018; Peng, 2015; Sverdrup et al., 1942; Wang et al., 2019) industrial marine areas have been polluted by heavy metal ions at high concentrations (A. Saleh et al., 2016; Baysal and Akman, 2018; Chiu et al., 2006; Gokkus and Berber, 2019). Aquatic flora and fauna which constitute food chain in the water ecosystems are effected by heavy metal pollutions along with other kind of pollutants and the consumption of aquatic products by humans leads to public health problems. For this reason, metal pollutions in waters should be under control.
Water vessels such as boats, ships, submarines and hovercrafts are exposed to physical and chemical effects of water and its components. The corrosion of metallic parts especially the steels in different compositions by seawater is the principal cause of water pollution. The vessels are protected by several kinds of applications on their hulls and topsides, including electrochemical protection (Bellezze et al., 2013; Gatto et al., 2018; Kim et al., 2016; Kramar et al., 2021; Turner, 2010).
In the shipyards several works are done during the ship constructions, maintenance, repair and painting. In all of the works, surface pretreatment is done following the surface preparation. Of the physical works, dry or wet sanding, dry or wet blasting wire brushing, scraping and chipping generate dust, chips and scrapes of metals, rusts, wastes of wooden and textile materials, plastics and paints (Kamal and Kutay, 2021; Şanlıer, 2020).
The chemical applications on the steel hull and on the wooden parts aims to clean the surface of the materials. The liquid spills and solid particulate matter are pollutant spreaders into the body of seawater where they react depending on the hydrological properties of the water (pH, dissolved oxygen, temperature, carbon dioxide, depth of the water column etc). Metal cations formed via oxidation or simply dissolution of metal bearing materials of the hulls of the ships exist in seawater mainly as chloro and/or organic complexes as well as free ions (Ferry and Carritt, 2002; Kiil et al., 2002; Nimisha Singh and Turner, 2009a).
Paint compositions differ regarding the applications made under or above the waterline of the vessels. Paints used for the surfaces under the waterline, contain biocidal agents which mainly have inorganic and organic copper and zinc compounds such as cuprous oxide, zinc oxide and zineb and the mixtures with other organic biocides. Old paint composite samples collected from different locations within the EU have been reported to contain up to about 30% Cu, 10% Zn, 0.18% Pb, 0.08% Ni and 0.008% Cd on dry weight basis (Nimisha Singh and Turner, 2009a; Turner, 2010). From the antifouling paints, the metals are released into water as dissolved metal cations, metal containing particles in nano and micro size which are further oxidized to give metal cations and metal complex ions such as CuCl2−, CuCl32−, CuCl42− and ZnCl42− (Adeleye et al., 2016; Ferry and Carritt, 2002; Kiil et al., 2002; Nimisha Singh and Turner, 2009a). Of the pyrithione complexes of Cu2+, Zn2+and Mn2+ which are used as biocides, Cu2+ complex is the most stable and widely used. However, the complexes can be photodegradated by 325–355 nm wavelengths of the UV spectrum or accumulated in the sediments from which the cations are continously leached into water (Maraldo and Dahllöf, 2004; Ohji et al., 2019; N. Singh and Turner, 2009b; Nimisha Singh and Turner, 2009a; Turner, 2010; Wang et al., 2019). Dissolved copper release rate from paints into the seawater of San Diego Bay has been reported 8 μg.cm−2.day−1 from hulls and 65 μg.cm−2.day−1 from painted steel panels (Valkirs et al., 2003). Pb containing chemicals such as Pb3O4, PbSO4, and PbCrO4 are used in dryers or paints for indoor and outdoor applications. Organotin compounds had been used in former applications.
Shipyard activities contaminate the seawater, sediments and soil (Chang et al., 2010; de La Fayette, 2000). Aquatic organisms from fito- and zooplanktons to fishes accumulate heavy metals as well as other pollutants by which the food chain becomes contaminated (Alkan et al., 2016; Baltas et al., 2017; Karsli, 2021; Özer Meyancı and Aydın, 2010; Podgurskaya et al., 2004; Nimisha Singh and Turner, 2009a; Turner et al., 2009). In the mid-Black Sea region of Turkish coast the metal ion concentrations in zooplanktons were reported 2902, 375, 52, 210 and 1.1 mg.kg−1 dry weight for Fe(II), Zn(II), Cu(II), Pb(II) and Cd(II), respectively (Bat et al., 2016; Makedonski et al., 2017).
The European Union (EU) Directives of 2008/105/EC and its amendment 2013/39/EU of the European Parliament and of the Council have established annual average concentrations (AA) and maximum allowable concentrations (MAC) of cadmium, nickel and lead in waters as quality standards, in which Cd was identified as priority hazardous substance (Annex X) (EU Directives, 2013). The AA concentrations in outland surface waters were given for Cd, Pb and Ni as 0.20, 1.3 and 8.6 μg L−1. MAC values were given for Cd, Pb and Ni as ≤0.45, 14 and 34 μg L−1. The World Health Organization (WHO) established the drinking water maximum permissible limits of metals much lower than the limits given by EU Directives for surface outland waters. The limits in drinking waters for Cd(II), Pb(II), Cu(II) and Fe(II) were given as 0.005, 0.05, 0.05 and 0.30 μg L−1, respectively. The Ni limit has not been given (World Health Organization (WHO), 2017).
Atomic spectroscopy which uses a number of techniques with different detection and determination limits is an efficient and easily usable tool for metal analysis in trace amounts. The atomic absorption and emission spectroscopies need to preconcentrate trace amounts of heavy metals in waters including seawater to improve the reliability and the LOD and LOQ values of the analyses. Some of the preconcentration methods are ion-exchange (Narin et al., 2001; Narin and Soylak, 2003; Soylak et al., 2003), co-precipitation (Aydin Urucu and Aydin, 2015), liquid-liquid extraction (Gherrou et al., 2002; Jalili et al., 2020), electroanalytical techniques (Ratajczak et al., 1975), solid-phase extraction (Çetinkaya and Aydın, 2017; Krawczyk and Jeszka-Skowron, 2016; Mahmoud et al., 2003; Montoro-Leal et al., 2020; Zhang et al., 1998). Preconcentration with solid phase extraction (SPE) has been widely used not only for heavy metals but also for selective adsorptions of some chemicals especially pollutants.
The major constituents of seawater interfere with heavy metal ions during direct analysis by atomic spectroscopy and it is needed to diminish their concentration and preconcentration of metal ions. Although flame atomic spectroscopy is the cheapest application technique, preconcentration of the metal ions is helpful to improve its limit of detection value and precision in the other techniques (Y. Sohrin and Bruland, 2011).
In solid phase extraction technique several solid phase materials are used. Some of them are thiourea and its derivatives and they have been used as selective ligands for most of the heavy metals including precious metals (Aydin et al., 2001; Becker et al., 1983; Groenewald, 1976). They are also used being supported on an adsorbent or on an inert material (Zhang et al., 2019). A novel thiourea derivative 3-phenyl-1-(2-pyridyl)thiourea (PPTU) was synthesized and investigated in the preconcentration of metal ions Cu(II), Ni(II), Cd(II), Pb(II) and Fe(II) for FAAS analysis.
The preparation of thioureas is simple and performed via the reaction between an amine and an isothiocyanate compound (Aydin et al., 2001; Kong et al., 2012; West et al., 1999). The electron donating atoms such as sulfur (S) and nitrogen (N) of the thiourea moiety take a role in the complexation of heavy metals. Depending on the alkyl or aryl substituents on nitrogens the thione form of the thiourea moiety is tautomerized to give thiol forms in different extents (Fig. 1). The metal complexes are formed through coordination with thiolate and other electron donating atoms of the molecule in which thiourea part also acts as bridging group to yield polynuclear formations (Hollmann et al., 2017).
Atomic spectroscopy which uses a number of techniques with different detection and determination limits is an efficient and easily usable tool for metal analysis in trace amounts. The major constituents of seawater interfere with the determination of trace metals even if powerful techniques such as high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) are applied.
Section snippets
Chemicals
The chemicals were in analytical grade and purchased from Merck (Germany) and Aldrich (USA). The inorganic chemicals (CuSO4.5H2O; FeSO4.7H2O; Ni(NO3)2.H2O; Cd(NO3)2.4H2O; Pb(NO3)2, Ca(NO3)2.4H2O; Mg(NO3)2.6H2O; Na2SO4; NaCl; NaNO3, K2SO4, CH3COONa.3H2O) and tetrahydrofuran (THF) were purchased from E. Merck (Darmstadt, Germany). 2-Aminopyridine and phenyl isothiocyanate from Aldrich Chem.Co., (USA) and Acros Organics (Geel, Belgium) respectively.
All the glassware were plunged into 10% nitric
Sampling
The proposed SPE method was applied to the tap water and seawater samples to analyse Cu(II), Ni(II), Pb(II), Cd(II) and Fe(II) ions. Seawater samples with salinity of 19‰ were collected from the 50 cm depth of the surface waters of the shipyard. The samples were filtered from 0,45 μm PTFE membrane, acidified to 1% with nitric acid and kept in polyethylene bottles.
Adsorption experiments
Adsorption capabilities of the ligand 3-Phenyl-1-(2-pyridyl)thiourea (PPTU) were studied for the cations Cu(II), Ni(II), Cd(II) and Pb(II). The batch procedure was applied in the work. Metal adsorption/removal efficiency (%) and adsorption capacity (qe, mg.g−1) were calculated from the equations given below:where Co and Ce are the metal ion concentrations (mg.L−1) before and after the adsorption, V is the volume of solution (L) and WL is the mass of the
Characterization of 3-Phenyl-1-(2-pyridyl)thiourea (PPTU)
In addition to the elemantal analysis, chemical structure of the PPTU was elucidated by FT-IR, 1H NMR, 13C NMR and Mass spectral data. Fig. 2 shows the FT-IR spectra of the starting chemicals and the product the PPTU. The bands at 3213 cm−1and 3173 cm−1 were assigned to the NH stretching bands of the urea moiety. The four thiourea bands υ(CN) + δ(NH) (Thioamide I bands), υ(CN) + υ(C=S) (Thioamide II and III bands), υ(C=S)(Thioamide IV band) appeared at 1549, 1267, 1187 and 861 cm−1,
Proposed method for the preconcentration of Cu(II), Cd(II), Ni(II), Pb(II) and Fe(II) using the PPTU in the seawater
pH of the one liter seawater is adjusted according to the appropriate pH for interested metal (pH 5 for Pb(II), pH 5.5 for Cu(II) and Ni(II), pH 6 for Fe(II) and pH 8.5 for Cd(II)) using 0.1 N acid or base solution. The volume of acid or base solution is recorded. The dilution is regarded in calculations.
In the batch process, following the pH adjustment, to the water sample is added 6 g PPTU and the suspension is mixed well for an hour in a water bath at 25 °C. For Fe(II) the suspension is
Conclusions
PPTU was proposed as an adsorbent for Cu(II), Ni(II), Cd(II), Pb(II) and Fe(II) to concentrate their working solutions to use in FAAS analyses. The relative standard deviations were less than 2% and 3% in intraday and interday works, respectively. The PPTU is very useful in preconcentrating target metal ions in fresh and seawaters with overall RSDs lower than 2%. The preparation of PPTU is simple and one-step synthesis without need of complicated and time consuming laboratory work. The proposed
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
CRediT authorship contribution statement
Şengül Şanlier Uçak: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing. Adnan Aydin: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Supervision.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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2023, Journal of Environmental Chemical EngineeringCitation Excerpt :Chronic conditions like liver and brain damage, irritability, sleeplessness, nausea, and diarrhoea can be caused by an excessive amount of Cu(II) accumulating in the body [7]. According to reports, wastewater with an excess of Fe(II) is carcinogenic, damages the intestinal tract, and irritates the respiratory system [8]. In addition, asthma, dermatitis, lung fibrosis, headaches, liver damage, brain haemorrhage, cardiac arrest, and carcinogenicity are all severe outcomes of prolonged exposure to nickel [9].