Elsevier

Sensors and Actuators B: Chemical

Volume 203, November 2014, Pages 854-863
Sensors and Actuators B: Chemical

Functionalized novel mesoporous adsorbent for selective lead(II) ions monitoring and removal from wastewater

https://doi.org/10.1016/j.snb.2014.07.063Get rights and content

Highlights

  • Novel ligand was used for preparing a new type mesoporous adsorbent.

  • Selective monitoring and removal of Pb(II) ions from multi-ion mixtures were evident.

  • Adsorbent was shown reusability in many cycles without significant deterioration.

Abstract

An efficient material is needed to develop selective and effective sensing/removal systems with high flexibility, and low capital cost for control the capturing of toxic ions. In this study, we designed ligand immobilized mesoporous adsorbent for ultra-trace Pb(II) monitoring and removal from wastewater. The adsorbent was synthesized by indirect immobilization of 4-tert-octyl-4-((phenyl)diazenyl)phenol onto inorganic mesoporous silica. This adsorbent exhibited the large surface area-to-volume ratios and uniformly shaped pores in case cavities, and its active sites kept open functionality to taking up Pb(II). The applicability of the adsorbent for Pb(II) detection and removal was assessed, and the efficient parameters such as solution pH, contacting time, initial Pb(II) concentration and ionic strength of competing ions were measured. The effective pH range for detection and removal systems was at the neutral region. The data revealed that the adsorbent was able to detect the ultra-trace Pb(II) ions with high sensitivity and selectivity by charge transfer (intense π–π transition) transduction mechanism. Then the adsorbent proved to have an efficient ability for continuous Pb(II) monitoring and removal even on-site and in situ chemical analyses. The maximum sorption capacity and limit of detection were 200.80 mg/g and 0.12 μg/L, respectively. The adsorbent was reused in several cycles without significant deterioration after elution with a suitable eluent (0.10 M HCl). Therefore, the design of mesoporous adsorbent has a great potentiality to be used in selective Pb(II) detection/removal from wastewater. Large-scale studies are recommended to confirm these promising results from the laboratory scale.

Introduction

Annually, industrial activity generates tons of heavy metals leading to contaminated bodies of water all over the world. However, heavy metals are a class of pollutants that require extensive treatment before being discharged into water bodies due to their harmful effect on humans, animals and living creatures. The low-level contaminants on public health have drawn the attention of researchers for developing effective means to identify and remove toxic pollutants from drinking water and wastewater. Lead (Pb(II)) is an element which can be regarded as a longstanding environmental contaminant and adversely affects human health [1], [2]. The potential sources of Pb(II) come from paints, pigment, batteries, metal products, the petroleum refining industry, electrodes in electrochemistry and chemical industries and ceramic glazes [3]. Pb(II) is a very toxic element, causing brain damage, kidney damage, delayed physical and mental developmental in infants and children, and gastrointestinal distress to humans at short-term exposure [4], [5]. However, chronic exposure can affect the central nervous system, renal system, cause convulsions and lead to kidney damage and death and mental retardation in children [6]. In some regions, the presence of lead in drinking water is a serious problem because of its high levels, much greater than the maximum tolerable limit. The maximal permissible limit in drinking water is set to 0.015 mg/L (15 ppb) [7], [8]. Therefore, monitoring and removal of Pb(II) in the environment with high sensitivity and selectivity is an important and essential aspect to safeguard the public health.

Several methods such as atomic absorption spectrometry (AAS), ICP-AES/OES, colorimetric assay, electrochemistry methods, biosensors, nuclear magnet resonance, and inductively coupled plasma mass spectrometry (ICP-MS) have been reported for Pb(II) detection [9], [10], [11], [12]. However, the AAS and ICP-MS are widely used instrumental techniques for Pb(II) ion detection [13], [14]. Although these sophisticated techniques are capable of absolute identification with low detection limits for metal ions, they are rather expensive and unsuitable for in situ analysis because of complicated instruments that prevent their widespread use, especially in developing countries. Therefore, low-cost and innovative methods have been increasingly based on being simple, robust, easy-to-use and with efficient sensitivity and selectivity. There is a growing demand worldwide to develop optical materials for accurate and rapid detection and for selective recognition of pollutant species [15], [16], [17], [18]. Colorimetric assays based on ligand immobilized nanomaterials are gaining increasing attention due to the advantages of simplicity, along with the additional benefits of cost-effectiveness, naked-eye observation and without the requirement of highly sophisticated instrumentation [19]. Therefore, the design of high-performance adsorbents for environmental cleanup and heavy-metal ion removal has attracted considerable attention.

There are many techniques used for Pb(II) separation and removal from water such as ion exchange, coagulation, chemical precipitation, solvent extraction, complexions, distillation, reverse osmosis and adsorption [20], [21], [22], [23], [24]. However, several drawbacks are listed including incomplete metal removal, high reagent and energy requirements and generation of toxic sludge [22], [25], [26]. Adsorption process, on the other hand, is cost-effective and efficient even at trace quantity of Pb(II) ions from the environmental samples. At low concentration, removal of pollutants is more effective by nanomaterials based adsorbents with operation simplicity and cost effectiveness. Therefore, major research has been encouraged to develop new sensitive, selective and cost-effective adsorbents for efficient Pb(II) monitoring and removal from water.

Nano-engineering inorganic materials have received considerable public interest in the last two decades because of their uniform and tunable pores [27], [28]. These materials have been recently used as appropriate carriers for potential applications in water treatment technology. In addition, inorganic nanomaterials have not been widely used directly for precise applications, as they have no functional groups suitable for environmental conjugations. Therefore, the present work aims to develop novel ligand immobilized mesoporous adsorbent for ultra-trace Pb(II) monitoring and removal from wastewater. It is also noted that the conventional ligands suffer from lack of selectivity toward Pb(II) ions in the presence of diverse competing ions.

In the present study, the organic ligand of 4-tert-octyl-4-((phenyl)diazenyl)phenol (TPDP) was functionalized onto mesoprous inorganic silica for selective and sensitive monitoring and removal of Pb(II) ions in environmental samples. The TPDP was associated to mesoporous silica based on non-covalent interactions (hydrogen bonding) and reversible covalent bonds. The experimental studies were carried out by batch approaches. The influence of various parameters was optimized and the analytical performance using the novel sensor ensemble adsorbent was systematically evaluated. The objective of the present investigation is to develop a novel, simple, sensitive and efficient method for monitoring and removal of Pb(II) in wastewater samples. The main advantages of this mesoporous adsorbent are: Pb(II) can be monitored in ultra-trace level with high sensitivity; Pb(II) can also be removed from water with extreme high selectivity; the adsorbent would be cost-effective due to the reversibility and reusability performances.

Section snippets

Materials

All materials and chemicals were of analytical grade and used as purchased without further purification. Tetramethylorthosilicate (TMOS) and the triblock copolymers of poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) as Pluronic F108, designated as F108 (EO141PO44EO141) were obtained from Sigma–Aldrich Company Ltd. USA. The standard Pb(II) and other metal ions solutions were prepared from their corresponding AAS grade (1000 μg/mL) solutions and purchased from Wako Pure Chemicals, Osaka,

Characterization of mesoporous inorganic silica and optical adsorbent

The N2 isotherms show a typical type IV adsorption behavior with a hysteresis loop as shown in Fig. 1. The adsorption branches were significantly shifted toward lower relative pressure (P/P0). Also, desorption occurs from the mesopores by evaporation and usually takes place in the lower pressure region than that of capillary condensation resulting in a hysteresis loop. The location of the hysteresis loop in the N2 isotherm can be used to determine whether the material possesses a regular

Conclusions

This work was an investigation of Pb(II) monitoring and removal from wastewater using a new class mesoporous adsorbent as a potential alternative to traditional techniques of toxic metal capturing systems. The design of mesoporous adsorbent was prepared based on 4-tert-octyl-4-((phenyl)diazenyl)phenol (TPDP) ligand onto mesoporous silica by indirect immobilization. The ability of the adsorbent for enabling in monitoring and removal responses according to [Pb(II)-TPDP]n+ binding events by a

Acknowledgments

This research was partially supported by the Grant-in-Aid for Research Activity Start-up (24860070) from the Japan Society for the Promotion of Science. The authors also wish to thank the anonymous reviewers and editor for their helpful suggestions and enlightening comments. The authors are also greatly acknowledged to Christopher Paul Taylor for his selfless English language editing.

Md. Rabiul Awual received his bachelor (Hons) and M.Sc. from the Department of Applied Chemistry and Chemical Technology, University of Dhaka, Bangladesh. He obtained the Ph.D. degree in industrial and environmental science and engineering in 2008 (Kumamoto University, Japan). In 2009, he was appointed as an analytical manager in Bureau Veritas Consumers Products Services (BD) Ltd. He also worked as visiting scientist in Pukyong National University, South Korea. In 2010, he awarded NIMS

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Md. Rabiul Awual received his bachelor (Hons) and M.Sc. from the Department of Applied Chemistry and Chemical Technology, University of Dhaka, Bangladesh. He obtained the Ph.D. degree in industrial and environmental science and engineering in 2008 (Kumamoto University, Japan). In 2009, he was appointed as an analytical manager in Bureau Veritas Consumers Products Services (BD) Ltd. He also worked as visiting scientist in Pukyong National University, South Korea. In 2010, he awarded NIMS Researcher fellowship and conducted the research successfully for two years. He is the author of dozens of scientific articles published in reputed international journals. He is currently appointed a fixed-term researcher at Japan Atomic Energy Agency (JAEA), Japan. His research activity has covered a wide range of novel material preparation and coordination with metals ions specifically lanthanide and actinide, adsorbent materials for specific functional groups and environmental applications.

Md. Munjur Hasan is studying in Medical Science at Shaheed Ziaur Rahman Medical College, Bogra, Bangladesh. He is interested for ion toxicity to human health and remediation the toxicity to safeguard the public health.

Ahmed Shahat received his Ph.D. degree in 2007 from Chemistry Department, Faculty of Science, Suez Canal University, Egypt in major of Inorganic chemistry. He worked at National Institute for materials Science (NIMS) as post-doctoral fellow for two years. He is now an Associate Professor in Suez University, Egypt. His research interest is focusing in inorganic–organic nanomaterials synthesis for environmental applications.

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