Facile synthesis of lanthanum hydroxide doped graphene oxide for scavenged of radioactive and heavy elements from water
Introduction
Heavy metals and radionuclides contaminated drinking water has become a global environmental issue. The existence of these metal ions in aqueous environments is detrimental to living organisms, including human beings. In fact, excess U(VI) and Pb(II) ions in drinking water leads to health issues associated with human beings [1], [2], [3], [4]. There is a necessity to treat the above metal ions from water samples. Conventional methods including ion-exchange, electrodialysis, chemical precipitation, and adsorption processes have been employed to remove excess heavy metals and radionuclides from drinking water to reduce their environmental impact [5], [6]. However, adsorption process is a potential technique for scavenging of both heavy metals and radionuclides because of its ergonomics, simplicity and selectivity [7]. The adsorption ability depends on the texture, shape, and surface of the adsorbent. Therefore, many researchers have focused on developing and exploring efficient adsorbents to treat effluent pollutants.
Graphene oxide (GO) have a great interest in the area of water treatment due to it has a high surface area, active surface functional groups and good affinity for removal of pollutants from water. Various GO-based adsorbents have been employed for treatment of heavy metals and radionuclides contaminated water [8]. In recent years, metal oxide-doped GO-based composites have been applied widely for the wastewater treatment [9], [10], [11], [12], [13], [14]. This literature study found that an interesting phenomena, the loading of inorganic oxides onto GO, leads to a high adsorptive removal capacity and easy separation of adsorbent from aqueous solutions through simple filtration or using external magnetic field. Its means that the issue of separation/recovery of highly dispersed GO from aqueous solution can be overcome by loading of metal oxide onto GO.
Nowadays, many researchers are exploring rare-earth oxides due to their interesting physical-chemical properties [15]. La is an interesting rare earth due to its strong bonding ability of oxygen containing functional groups (soft-soft interactions). Consequently, La is used as a dopant for porous composites are used for water treatments [10], [13], [16], [17], [18], [19], [20]. Moreover, due to relatively low toxicity and excellent catalytic properties of La ions have been used to remedy environmental issues [21]. Similarly, in our previous studies developed La-F-doped GO-based composites for arsenic removal from water and achieved high adsorption of arsenic [21], although fluoride leaked into the aqueous solution during the adsorption process. In consideration of this issue, a facile spindle shaped porous La loaded GO-based composite having porous surface morphology was developed for the adsorptive scavenging of U(VI) and Pb(II) in this study.
The development of an efficient adsorbent, lathanum hydroxide loaded GO-based composite, analysis of its physical and chemical properties, and evaluation of its application in view to the treatment of radioactive (U(VI)), and heavy metals (Pb(II)) contaminated water are the major objectives of this study. In addition, the factors including reaction time, pH, and initial concentrations effects on the adsorptive removal ability of the composite (GO-La(OH)3) are investigated. The development of the adsorption mechanism, stability analysis of the adsorbent, and re-usability studies are also performed to test the real-field applicability of the adsorbent. The results suggest that the developed GO-La(OH)3 can be applied in the adsorptive removal of heavy metals and radionuclides at WHO standard levels (0.03 mL−1 for U(VI) and 0.01/0.015 mg L−1 for Pb(II)) in drinking water and achieved below the above standards. The main and novel observations from the loaded of La onto GO are the alteration of the GO adsorption efficiency, adsorbent separation rate from aqueous solutions, and the stability of the composite. Moreover, quite interestingly, the adsorption capacity increased with increasing reaction temperature. In conclusion, the developed materials can overcome the separation and stability issues associated with bare GO in addition to exhibiting reliable adsorption capacity toward radioactive and heavy metals when used for water treatment. The comparable adsorption capacity with reported method and 5 time re-usability of GO-La(OH)3 without loss of its efficacy indicated that the feasibility of adsorbent.
Section snippets
GO-La(OH)3 composite preparation
Fig. 1. shows a schematic preparation of the GO-La(OH)3 composite. According to Fig. 1, 100 mg of GO powder, which has been prepared from graphite flakes using well known Hummers oxidation process [22] was added into 100 mL of water. Succeeded by ultrasonication for 1 h to complete dispersion of GO. To this dispersed GO solution, added lanthanum nitrate (500 mg) solution by dropwise with continuous magnetic agitation. Subsequently, the pH of the reaction mixture was adjusted to 10 using an
Structural analysis
XPS was used to analyze the elemental chemical compositions and their states in the prepared GO-La(OH)3 composite. The XPS spectrum of GO (Fig. 2a) showed two peaks at binding energies peaks of 284.56 and 532.23 eV ascribed to the C1s and O1s simulations, respectively. However, the La doped GO (GO-La(OH)3) XPS spectrum (Fig. 2a) showed La 3d (835–860 eV) and La 4d (~120 eV) peaks along with C1s and O1s peaks (associated with GO). The La 3d spectrum shows two peaks at the binding energies of
Conclusions
La-composite (such as La oxide and La(OH)3) nanoparticles loaded graphene oxide composite was prepared via a sol–gel method and the prepared material exhibited mesoporous structure. Meanwhile, GO-La(OH)3 exhibited excellent up take of both metal ions, U(VI) and Pb(II). Moreover, the adsorptive removal of U(VI) and Pb(II) were significantly dependent on the initial concentration, contact time, pH, and temperature. According to the isotherms data, both metal ions were well obeyed the Langmuir
CRediT authorship contribution statement
Lakshmi Prasanna Lingamdinne and Janardhan Reddy Koduru conceived and designed the experiments. Lakshmi Prasanna Lingamdinne and Suhyun Lee contributed to conducting experiments and contributed analysis tools. Lakshmi Prasanna Lingamdinne and Janardhan Reddy Koduru analyzed the data and wrote the manuscript. Janardhan Reddy Koduru, Yoon-Young Chang and Jae-Kyu Yang reviewed and edited the manuscript.
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.
Acknowledgments
The authors very much thankful to the National Research Foundation of Korea for the supported of this research (Research grant number: 2016R1D1A1B03930879); and Korea Environment Industry & Technology Institute (Research grant number: 2020002470002), Republic of Korea. Also the authors are grateful to the Kwangwoon University, Seoul, Korea for the partially supported of this research through a Kwangwoon University Research Grant-2020.
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