Edited by: Wenbo Wang, Lanzhou Institute of Chemical Physics (CAS), China
Reviewed by: Liang Bian, Southwest University of Science and Technology, China; Runliang Zhu, Guangzhou Institute of Geochemistry (CAS), China
This article was submitted to Green and Sustainable Chemistry, a section of the journal Frontiers in Chemistry
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Hexavalent chromium species, Cr(VI), which can activate teratogenic processes, disturb DNA synthesis and induce mutagenic changes resulting in malignant tumors. The detection and quantification of Cr(VI) is very necessary. One of the rapid and simple methods for contaminant analysis is fluorescence detection using organic dye molecules. Its application is limited owing to concentration quenching due to aggregation of fluorescent molecules. In this study, we successfully intercalated 7-amino-4-methylcoumarin (AMC) into the interlayer space of montmorillonite (MMT), significantly inhibited fluorescence quenching. Due to enhanced fluorescence property, the composite was fabricated into a film with chitosan to detect Cr(VI) in water. Cr(VI) can be detected in aqueous solution by instruments excellent, ranging from 0.005 to 100 mM with a detection limit of 5 μM.
Due to the high toxicity of heavy metals and bioaccumulation in human body through the food chain, will bring human health and environmental great issue. Cr is one of the most serious contaminants among various heavy metals (Soewu et al.,
Montmorillonite is a typical phyllosilicate of the smectite group of clay minerals (Ismadji et al.,
This research focused on the fabrication of a fluorescence material for Cr(VI) detection. To prevent quenching, the photoactive organic dye AMC was interposed into the interlining of MMT for maximal dye separation and minimum agminated (Yu et al.,
The montmorillonite was bought from Ningcheng, Inner Mongolia, China. Its CEC (Cation Exchange Capacity) was 9.8 mmolc/10 g which used Na+ as the staple commutable cationan exchange. The specific external surface area was 78 m2/g. AMC was purchased from Aladdin. The molecular structure (Nowakowska et al.,
Molecular structure of AMC studied. The all strains, C, gray; N, blue; O, red; H, white.
The effect of initial AMC concentrations on a performance of florescence were tested, 50 mL the original concentrations of AMC in water for 20, 50, 100, 200, 500, and 800 mg/L were blended with 0.25 g of MMT in every 100 mL centrifugal tube after shaking at 200 rotations per minute at indoor temperature for 8 h, respectively. The admixtures were centrifuged at 7,500 rotations per minute for 2 min. Afterwards, removing the supernatant, then at 60°C were dried the residues and pulverized the residues to powder as raw materials. This type of product was used for the AMC/MMT.
The chitosan film was prepared as follows: 0.25 g chitosan, 8 mL 0.1 M NaOH solution, 0.1 g AMC/MMT powder and two drops of 1 g/mL Polyvinyl Alcohol (PVA) solution were appended. The admixture was whipped for 30 min and then poured into a mold and air dried.
The followed solutions at a concentration of 0.1 M were originally screened for quenching of fluorescence in AMF: Al3+, Ca2+, Ba2+, Cr(VI), CTAB, K+, Na+, Ni3+, Pb2+, Fe3+, Imidazole, C2H5OH. Afterwards, they were dropped onto the AMF. Then, the fluorescence degrees were measured using a fluorescence spectrophotometer (Hitachi, F4600).
In order to estimate the Cr(VI) range of response, different concentrations of Cr(VI) solution were dropped onto the AMF. The Cr(VI) of original concentrations were the ranged of 5 μM to 100 mM.
Pictures of the AMF after in contact with Cr(VI) solutions were already obvious demonstration quenching of fluorescence effect by Cr(VI) and then measure the florescence intensions of AMF by fluorescence spectrophotometer (Hitachi, F4600).
Powder X-Ray Diffraction (XRD) was performed by a Rigaku D/max-IIIa diffractometer (Tokyo, Japan) with a Ni-filtered Cu Ka radiation at 40 kV and 40 mA. Prototypes were scanned the range of 3° to 70° at 8° per minute with a pace of 0.01° to research the particular changes in d001 separation distance of MMT as a function of original AMC concentrations. The changing of peak position proved the intercalation of AMC into the MMT was succeeded. The gallery heights were deduced from the (001) reflection of the composites using the Bragg's equation.
Fourier Transform Infrared Spectroscopy (FTIR) spectra were acquired on a Perkin Elmer Spectrum 100 Spectrometer. The spectra were obtained from 4,000 to 500 cm−1 by adding 256 scans in the resolution ratio of 4 cm−1.
Photoluminescence emission (PL) spectrum was obtained on a fluorescence spectrophotometer (Hitachi, F4600) at the scope of 400–600 nm with a photomultiplier tube handled at 800 volt. A 150 watt xenon lamp was served as the pumping source, at an excitation wavelength of 340 nm (Zamojć et al.,
Molecular mimicry was performed at the standard module “Forcite” of Materials Studio 6.0 software to research the structure of AMC in the interval of MMT. The unit lattice parameters were setted at a = 1.55 nm, b = 1.79 nm, c = 1.25 nm, α = γ = 90°, and β = 99°. A suite of 2 × 2 × 1 supercells were constructed of the interlayer spacing setting at 1.63 nm. Every circulation consisted of 106 steps, repeating three cycles.
The idea that interlayer cation was Na+ with a monolayer hydration was confirmed because the d001 value of pure MMT was 12.6 Å. The d001 spacing progressively increased from 12.6 to 16.3 Å with the initial AMC concentration increased (Figure
X-ray diffraction patterns of MMT was inserted with AMC in the interlayer, which was affected by initial AMC concentrations (mg/L).
FTIR spectra of MMT adsorbed with different amounts of AMC displayed both bands of raw MMT and AMC (Figure
FTIR spectra of AMC, and MMT with different amounts of AMC adsorption.
AMC powder was hardly used as a luminescent material just because the lack of strong luminescence (Wang et al.,
Fluorescence spectra of AMC/MMT was Influenced by initial concentrations of AMC.
The AMF was screened for response to various solutes (Figure
Fluorescence intensity of the AMF in response to a variety of aqueous solutions at a concentration of 0.1 M.
The mechanism of photoluminescence (PL) quenching of AFM was further investigated when the aqueous solution contains Cr(VI). Most importantly, an apparent decrease in fluorescence intensity was observed while the Cr(VI) concentration was increasing over the whole concentration ranges from 0.005 to 100 mM (Figure
Fluorescence spectra of the AMF in the presence of multifarious concentrations of Cr(VI)
Molecular mimicry was performed at the standard module “Forcite” of Materials Studio 6.0 software to research the structure of AMC between the interval of MMT. The interlayer spacing of MMT was directly influenced by the interlayer arrangement of AMC and the amount of AMC intercalation, this, on the other hand, would play an significant role in understanding the system structure and interaction forces (Krauss et al.,
Dynamic simulation of molecular interposition AMC into MMT at a different angle on account of the electric density and AMC loading distinction. The initial states were represented by
In this research, an organic dye (AMC) was resoundingly intercalated into the interlayer space of MMT, resulting in observably inhibition in quenching of fluorescence. The composite was fabricated into a film with chitosan to detect Cr(VI) in water with its enhanced fluorescent property. Cr(VI) can be detected in aqueous solution by instruments ranging from 0.005 to 100 mM with a detection limit of 5 μM.
YW and LM conceived the project. LM, GL, and LibL designed and performed the experiments. RL, ML, JW, and LinL analyzed the data. YW, ZL, and LM wrote the manuscript.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.