Melanin-embedded materials effectively remove hexavalent chromium (CrVI) from aqueous solution

An Manh Cuong,Ly Bich Thuy,Nguyen Lai Thanh,Nguyen Thi Le Na,Pham Nhat Thang,Nguyen Dinh Thang,Trinh Ngoc Diep

doi:10.1186/s12199-018-0699-y

Abstract

BackgroundCurrently, it is recognized that water polluted with toxic heavy metal ions may cause serious effects on human health. Therefore, the development of new materials for effective removal of heavy metal ions from water is still a widely important area. Melanin is being considered as a potential material for removal of heavy metal from water.MethodsIn this study, we synthesized two melanin-embedded beads from two different melanin powder sources and named IMB (Isolated Melanin Bead originated from squid ink sac) and CMB (Commercial Melanin Bead originated from sesame seeds). These beads were of globular shape and 2–3 mm in diameter. We investigated and compared the sorption abilities of these two bead materials toward hexavalent-chromium (CrVI) in water. The isotherm sorption curves were established using Langmuir and Freundlich models in the optimized conditions of pH, sorption time, solid/liquid ratio, and initial concentration of CrVI. The FITR analysis was also carried out to show the differences in surface properties of these two beads.ResultsThe optimized conditions for isotherm sorption of CrVI on IMB/CMB were set at pH values of 2/2, sorption times of 90/300 min, and solid-liquid ratios of 10/20 mg/mL. The maximum sorption capacities calculated based on the Langmuir model were 19.60 and 6.24 for IMB and CMB, respectively. However, the adsorption kinetic of CrVI on the beads fitted the Freundlich model with R2 values of 0.992 for IMB and 0.989 for CMB. The deduced Freundlich constant, 1/n, in the range of 0.2–0.8 indicated that these beads are good adsorption materials. In addition, structure analysis data revealed great differences in physical and chemical properties between IMB and CMB. Interestingly, FTIR analysis results showed strong signals of –OH (3295.35 cm− 1) and –C=O (1608.63 cm− 1) groups harboring on the IMB but not CMB. Moreover, loading of CrVI on the IMB caused a shift of broad peaks from 3295.35 cm− 1 and 1608.63 cm− 1 to 3354.21 cm− 1 and 1597.06 cm− 1, respectively, due to –OH and –C=O stretching.ConclusionsTaken together, our study suggests that IMB has great potential as a bead material for the elimination of CrVI from aqueous solutions and may be highly useful for water treatment applications.

Highlights

It is recognized that water polluted with toxic heavy metal ions may cause serious effects on human health
Our study shows that Isolated Melanin Bead (IMB) is a highly effective material for removing Hexavalent chromium (CrVI) in water
The results indicated that the adsorption of CrVI on the surface of IMB may have caused a shift of the broad peaks at 3296 cm− 1 and 1608 cm− 1 to 3354 cm− 1 and 1597 cm− 1, respectively, due to –OH and –C=O stretching (Fig. 8b)

Summary

Introduction

It is recognized that water polluted with toxic heavy metal ions may cause serious effects on human health. There are many types of materials which have been being used to remove heavy metals from aqueous effluents; these include activated carbon, plantleaf materials, chitosan gel, and hydrotalcite [3, 4]. These materials are not fully effective nor cost efficient. Chromium is considered to be one of the key contaminants in the wastewaters of many industries, such as plating-electroplating, dying-pigmenting, film-photography, leathering and mining Both hexavalent chromium (CrVI) and trivalent chromium (CrIII) are predominant species in industrial effluents, the CrVI is more toxic than CrIII. The CrVI is considered as a mutagenic agent, which may cause adverse public health problems [1, 5]

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