Carbon Quantum Dots In Environmental Remediation
Atefeh Rahnama1and Zahra Ramezani2*
1Student Research Committee, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran
2Nanotechnology Research Center, Medicinal Chemistry Department, Faculty of Pharmacy, Ahvaz Jundishapur University of Medical sciences, Ahvaz, Iran
Submission: March 26, 2018; Published: May 01, 2018
*Corresponding author: Zahra Ramezani, Nanotechnology research center, Medicinal Chemistry Department, Faculty of Pharmacy, Ahvaz Jundishapur University of Medical sciences, Ahvaz, Iran, Tel: +986133738379; Email: zramezani@ajums.ac.ir
How to cite this article: Atefeh R, Zahra R. Carbon Quantum Dots In Environmental Remediation. Int J Environ Sci Nat Res. 2018; 10(4): 555794. DOI: 10.19080/IJESNR.2018.09.555794.
Abstract
Carbon quantum dots (CQD), is highly stable, biocompatible, and low toxic fluorescence nonomaterial that extensively used in different scientific disciplines such as design and construction of low-cost chemical and biological sensors, cell imaging, clinical diagnosing, and drug loading. Due to their optoelectronic properties, they have recently used in remediation studies as an alternative to or mixed with metal semiconductors. Having used CQD, an economic and green technique in environmental pollution remediation is introduced. Remediation happens through the ability of CQD composites in adsorption of pollutants or using its photo catalytic action. Herein, some recent applications in the environmental pollutant remediation are reviewed.
Introduction
CQDs are a new type of carbon nanomaterial accidentally found in 2004 through purification of single-wall carbon nano tubes [1]. They have attracted much scientific attention since they are stable photoluminescence particles with high chemical stability, low toxicity, and biocompatible as well as having optoelectronic properties. They are produced by different chemical or natural carbon rich precursors in one pot process by different heating methods [1-4]. The CQDs properties have tuned by surface modification through different synthetic protocols and using different chemical reagents [5] for a vast variety of applications since 2004. CQDs have strong and stable luminescence, and have been used in chemical sensors, optoelectronics [6-8] bacterial detection [9], cancer diagnosis [10], cell imaging [11] and drug loading [12].
Exposure of CQDs with photons of energy equal or higher than its band gap leads to the transfer of the electron from the valence band to the conduction band, producing an electron-hole. Both electron and hole on the surface of the CQDs gives it the ability to act as both electron donor and acceptor, and promote oxidation-reduction on the surface of the dots [13]. Doping CQD with dozens of elements like N, P, and S have induced a shift in the photoluminescence wavelength, and suggest its applications as an efficient catalyst. Photo catalytic degradation of organic pollutions and microorganism is extensively reported in the literature using semiconductors [13].The high photo activity of the catalyst has a vital role in the oxidation or reduction of the pollutants. Photo catalytic activity of CQDs improved by incorporating elements such as nitrogen on the surface, and preparation of a composite with other semiconductors such as TiO2. Pollutant remediation using CQDs is mainly due to the photo catalytic properties. But adsorption of the pollutants on the surface of CQDs composites is another strategy has rarely been used up to now. However, the application of CQDs in the pollutant remediation is briefly discussed and listed. Photocatalytic Degradation of Pollutants is an Title CQDs under photon irradiation generate electron-hole and acts as the visible light photo catalyst in environmental remediation and energy transfer reactions. A few reports on the application of CQDs for adsorption of environmental pollutants are available in the literature. Some recent application of CQDs, doped CQDs, and their composites with other nano particles, in environmental remediation, is reported in (Table 1) and discussed. Photo catalytic conversion of CO2 to organic acids by nitrogen doped CQD (NCQDs) with visible light irradiation was more efficient than colloidal TiO2 under UV radiations [5]. Martin et al [13] also synthesized nitrogen doped CQD by hydrothermal irradiation using glycerol as the carbon source and 4,7,10 trioxa-1,13- tridecanediamine for nitrogen doping. They prepared NCQD/ TiO2 nano composite and showed that photo catalytic activity of nano composite for methylene blue and NO remediation is higher than those for TiO2. Super paramagnetic nitrogen doped CQD /magnetite nano composites (Fe3O4@NCQD) [14,15] were used for removal of methyl blue from polluted water samples. They used lemon juice as a green carbon precursor and ethylene amine as the nitrogen source for CQD surface functionalization.
As-prepared Fe3O4@NCQD adsorbs 90.84% methyl blue from aqueous solutions in 20 min. Particles were separated from the solution by a magnet, methyl blue has been desorbed by hydrochloric acid, and the recovered particles were used five times without any considerable changes in the removal efficiency. CQD/nitrogen-doped ZnO (CQD/N-ZnO) composite was prepared and used for photo catalytic degradation of three commercial dyes, malachite green, methylene blue and fluoresce in under daylight irradiation. The composite removes all three dyes within 30-45 minutes [16]. CQDs-TiO2nanosheet (CQDs- TNS) composites were prepared and used in photo catalytic degradation of rhodamine B under visible light irradiation [17].
It was reported that photo catalytic activity of CQDs-TNS was higher than CQDs/TiO2 and pure TNS. Catalytic H2 production using highly crystalline CQDs on 2D C3N4nanosheets was reported [18]. Hydrogen peroxide produced during the reaction promotes bisphenol a removal. Excellent photo catalytic activity was observed for ternary mixture of CQDs/Ag/Ag2O [19]. The ternary photo catalyst removed methylene blue and Rhodamine B from aqueous solution. Composite of CQDs with g-C3N4nanosheet was also reported as an excellent photo catalyst for the degradation of rhodamine B and tetracycline hydrochloride (TC-HCl) under visible light irradiation [20]. Tetracycline mineralization by the composite of Ag+-CDs-Bi2WO6 [21] via photo catalytic reactions under visible light is also reported. The Ag+-CDs-Bi2WO6 has excellent stability even when recycled and reused for several times. Fe (III)-functionalized carbon dots (Fe(III)-CQDs) was used for remediation of hydrogen peroxide as well as olefin hydrogenation with high selectivity [22]. A green approach applied to the synthesis of La/Cu/Zr/CQDs tri metallic nano composites as both adsorptive and catalytic agent for pollutant remediation [23]. It has been observed that 96% ampicillin antibiotic and 86% of malachite green were degraded in 4 h. The prepared Bi2O3/ CQDs photo catalysts [24] showed the best photo catalytic activity in rhodamine B elimination. A new CQDs/ Bi2WO6 were applied in the remediation of methyl orange and bisphenol A in aqueous solution [25]. A novel ternary photo catalyst of single atom-dispersed silver and carbon quantum dots co-loaded with ultrathin g-C3N4 (Ag-CQDs- gC3N4) was synthesized [26]. Environment-Friendly CQDs/ ZnFe2O4 photo catalyst was synthesized and introduced as a biocompatible catalyst for NO removal in the atmosphere [27]. The catalyst has low cytotoxicity and is a good candidate for air purification. Application of CQDs was extended to the removal of microorganism from aqueous solution. Recently, multiwall carbon nano tube fiber incorporated CQDs (MWCNT-F/CQDs) composite has been proved as highly efficient material for bacterial removal from aqueous solution and inhibition of their activity [28]. In this study, the inhibitory rates for E. coli were 94.21% on the MWCNT filter surfaces coated with 0.2 mg CQDs.
Conclusion
To sum up, CQDs are introduced recently as the visible light photo catalyst for environmental remediation. The catalytic activity of CQDs increases by metals doping or making composites with the other semiconductor. Adsorption ability of CQDs for environmental pollutants are not well investigated. Another outstanding action of CQDs is in bacterial growth inhibition and removal from aqueous solution. Overall, CQDs is a green and biocompatible material for treatment and purification of water and atmosphere
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