Designing a hybrid nanomaterial based on Cr-containing polyoxometalate and graphene oxide as an electrocatalyst for the hydrogen evolution reaction.

A new polyoxometalate (POM)-based hybrid nanomaterial (denoted as PMo11-Cr-mGO) was designed via covalent interaction between the Cr(acac)3 complex and [PMo11O39]7- followed by immobilization on the surface of modified graphene oxide (mGO). The prepared nanomaterial was characterized using a series of physicochemical techniques. X-ray diffraction (XRD), Raman analysis, transmission electron microscopy (TEM), and FE-SEM-EDS revealed the preservation of layered GO during the formation of the desired hybrid nanomaterial. Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and elemental analysis confirmed the immobilization of POM (PMo11-Cr) on the surface of mGO and the formation of PMo11-Cr-mGO. In order to evaluate the performance of PMo11-Cr-mGO in the hydrogen evolution reaction (HER), electrochemical measurements were also performed. The resulting PMo11-Cr-mGO exhibited excellent HER activities with a low overpotential of 153 mV at 10 mA cm-2 and good durability in acidic media, thus emerging as one of the most efficient POM-based electrocatalysts.

Design, characterization and green synthesis of samarium-decorated magnetic Fe3O4 nanoparticles: cytotoxicity and DNA binding studies.

In this study, we have successfully synthesized magnetic Fe3O4 nanoparticles adorned with samarium (Sm-MNPs) utilizing ginger extract for the very first time. Furthermore, a comprehensive characterization of the nanoparticles along with an exploration of their physicochemical attributes was conducted. The biological functionalities of the synthesized nanoparticles were investigated through a thorough examination of their interaction with calf thymus DNA (ctDNA) using diverse spectroscopic techniques encompassing ultraviolet-visible (UV-Vis) and fluorescence spectroscopy at varying temperatures. Subsequently, we evaluated the cytotoxicity of the magnetic nanoparticles using a colorectal cancer cell model (HCT116 cells) and a tetrazolium colorimetric assay (MTT assay). The characterization of the ginger extract-coated magnetic nanoparticles (ginger-Sm-MNPs) revealed their superparamagnetic nature, nanocrystalline structure, spherical morphology, hydrodynamic size of 155 nm, and uniform distribution. The outcomes from UV-Vis and fluorescence spectroscopy affirmed the binding of ginger-Sm-MNPs with ctDNA. Additionally, the MTT assay demonstrated that the cytotoxicity of ginger-Sm-MNPs surpassed that of both magnetite nanoparticles and ginger extract. Notably, the inhibitory concentrations (IC50) for the green-synthesized nanoparticles after 24 and 48 h of incubation were determined as 198.1 and 135.8 µg/mL, respectively. In conclusion, our study findings suggest the potential utility of ginger-Sm-MNPs as a promising candidate for various biomedical applications.Communicated by Ramaswamy H. Sarma.

Photo-Fenton degradation of tetracycline antibiotic over MIL-101(Cr)/FeOOH nanocomposite as stable and efficient visible light responsive photocatalyst.

Designing an inexpensive, easily synthesized, stable and efficient photocatalyst is a major challenge in photocatalysis area, especially when photo-reaction is performed in aquatic medium to degrade organic pollutants. To this aim, nano-sized MIL-101(Cr) (MIL = Materials Institute Lavoisier), as chemically tolerant metal-organic framework (MOF), was simply prepared via HF-free hydrothermal synthesis procedure. In order to decorate amorphous FeOOH quantum dots (QDs) on the surface of this MOF, various amounts of FeOOH QDs (i.e., 5, 10, 15 and 20 wt%) were synthesized in the presence of MIL-101(Cr) to prepare MIL-101(Cr)/FeOOH(x%) nanocomposites. Decoration of such iron oxide quantum dots on the surface of MIL-101(Cr) and investigation of its activity in photo-Fenton degradation of tetracycline (TC) antibiotic is reported here for the first time. Among the synthesized nanocomposites, MIL-101(Cr)/FeOOH(15%) demonstrated superior photo-Fenton activity in degradation of TC (80%) at short reaction time under optimum reaction condition using the energy-efficient white LED lamps as visible light source. It was observed that the synergy between any component of this photo-Fenton system such as nanocomposite, hydrogen peroxide and visible light is the main reason for enhancement of TC removal over time. Also, neither MIL-101(Cr) nor FeOOH QDs exhibited poor degradation efficiency, which implies the positive role of the coupling of these materials. Furthermore, the stability and recoverability of MIL-101(Cr)/FeOOH(15%) nanocomposite was investigated in four photo-Fenton cycles, which no significant decrease in TC degradation performance was observed.

Heterogeneous Catalytic Systems for Carbon Dioxide Hydrogenation to Value-Added Chemicals.

Utilizing renewable energy to hydrogenate carbon dioxide into fuels eliminates massive CO2 emissions from the atmosphere and diminishes our need for using fossil fuels. This review presents the most recent developments for designing heterogeneous catalysts for the hydrogenation of CO2 to formate, methanol, and C2+ hydrocarbons. Thermodynamic challenges and mechanistic insights are discussed, providing a strong foundation to propose a suitable catalyst. The main body of this review focuses on nanostructured catalysts for constructing efficient heterogeneous systems. The most important factors affecting catalytic performance are highlighted, including active metals, supports and promoters that can potentially be used. The summary of the results and the outlook are presented in the final section. During the past few decades, heterogeneous CO2 hydrogenation has gained much attention and made tremendous progress. Thus, many highly efficient catalysts have been studied to discover their active sites and provide mechanistic insights. This paper summarizes recent advances in CO2 hydrogenation and its conversion into various hydrocarbons such as formate, methanol, and C2+ products. As for formate production, Au and Ru nanocatalysts show superior activity. However, considering the catalyst cost, Cu-based catalysts have an excellent prospect for methanol production, among other catalysts. Ultra-small nanoparticles and nanoclusters appear promising to provide highly active cost-effective catalysts. A growing number of researchers are investigating the possibility of directly synthesizing C2+ products through CO2 hydrogenation. The major challenge in producing heavy hydrocarbons is breaking the ASF limitations, which have been achieved over bifunctional catalysts using zeolites. Using suitable support and promoter can lead to a superior activity, ascribed to structural, electronic, and chemical promotional effects.

Preparation of Fe2(MoO4)3/graphene/Ti nanocomposite electrode for visible-light photoelectrocatalytic degradation of organic pollutants.

The massive emission of organic pollutants, specially organic dyes into water poses a serious threat to the environment and human health. Photoelectrocatalysis (PEC) has been regarded as an efficient, promising and green technology for organic pollution degradation and mineralization. Herein, Fe2(MoO4)3/graphene/Ti nanocomposite was synthesized and applied as a superior photoanode in a visible-light PEC process for degradation and mineralization of an organic pollutant. First, the Fe2(MoO4)3 was synthesized by the microemulsion-mediated method. Then, Fe2(MoO4)3 and graphene particles were simultaneously immobilized on a titanium plate by the electrodeposition technique. The prepared electrode was characterized by XRD, DRS, FTIR and FESEM analyses. The ability of the nanocomposite was investigated in the Reactive Orange 29 (RO29) pollutant degradation by the PEC. The Taguchi method was used for the visible-light PEC experiments design. The efficiency of RO29 degradation was enhanced with increasing bias potential, number of Fe2(MoO4)3/graphene/Ti electrodes, visible-light power and Na2SO4 (electrolyte) concentration. The pH of the solution was the most influential variable in the visible-light PEC process. Furthermore, the performance of the visible-light PEC was compared with photolysis, sorption, visible-light photocatalysis and electrosorption processes. The obtained results confirm the synergistic effect of these processes on RO29 degradation by the visible-light PEC.

Extending the visible light absorption of NH2-UiO-66 through diazotization reaction for photocatalytic chromium (VI) reduction.

The optical properties of NH2-UiO-66 as a visible light-active metal organic framework was further enhanced through the diazotization reaction with π-conjugated 1-naphthol reagent. Diffuse reflectance UV-Vis spectrum of diazotized MOF, named as Azo-UiO-66, exhibited a significant red shift compared to unfunctionalized NH2-UiO-66 due to the formation of diazo compound. Also, Tauc calculations indicated considerable decrease in band gap energy from 2.68 to 1.7 eV, resulting in improvement of visible light harvesting. Furthermore, other physicochemical techniques, e.g., X-ray diffraction (XRD), N2 adsorption-desorption analysis, thermogravimetric analysis (TGA), energ-dispersive X-ray (EDX), and CHN elemental analyses demonstrated the successful MOF diazotization with 1-naphthol and preservation of NH2-UiO-66 framework upon post-modification process. The reduction of hexavalent chromium, Cr(VI), as a serious contaminant in wastewater to less toxic Cr(III) was performed over prepared photocatalyst, which demonstrated the positive role of ligand functionalization and enhancement of visible light absorption on overall photocatalytic performance of Azo-UiO-66.

A New Photoelectrocatalyst for Water Oxidation: A Polyoxometalate-Graphitic Carbon Nitride Hybrid Nanomaterial.

A new photoelectrocatalyst for the water oxidation process is designed by immobilizing [CoW12O40]6- (CoW12) heteropolyanions on the surface of covalently modified graphitic carbon nitride nanosheets (g-C3N4). For this purpose, g-C3N4 is first modified with cysteamine hydrochloride through the well-known thiol-ene click reaction. Afterward, [CoW12O40]6- heteropolyanions are immobilized on the surface of modified g-C3N4 nanosheets with electrostatic interaction with ammonium groups. After confirming the preparation of CoW12/clicked g-C3N4 with various physicochemical methods, its photoelectrocatalytic activity is evaluated in the oxygen evolution reaction. The CoW12/clicked g-C3N4 exhibits a low onset potential of 1.32 V versus NHE and a low overpotential of 230 mV at 10 mA cm-2 with a low Tafel slope of 67 mV dec-1 under visible light illumination. Moreover, the stability of the catalyst is investigated through the chronoamperometric measurements.

Charge separation effect in the nanocomposites of Co3O4-QDs: visible light photocatalytic dye degradation in aqueous solutions.

Photo-treatment of water is a promising environmentally friendly process that provides clean water and makes wastewater reusable in industry. Thus, efforts toward finding highly efficient photocatalysts have gained a huge attention to remove the organic contaminants in water. Quantum dots (QDs) are extensively utilized for photocatalytic remediation regarding their prominent optical, electrical, and chemical properties. Herein, we report the highly efficient and environmentally friendly synthesis of Co3O4-QDs-based graphene quantum dots (GQDs) and infinite coordination polymer comprising Zn nodes (Zn-ICP) nanocomposites as active and robust photocatalysts for photo-assisted water treatment. The pristine Co3O4-QDs, GQDs, and Zn-ICP showed lower activity under visible light. However, after functionalization of GQDs and Zn-ICP with Co3O4-QDs, the activity increased, and more photocatalytic efficiency was achieved. For instance, Zn-ICP, GQDs, Co3O4-QDs, Co3O4-QDs/Zn-ICP, and Co3O4-QDs/GQD degraded 21, 19, 52, 73, and 83% of rhodamine B (RhB) and 34, 46, 50, 73, and 76% of methylene blue (MB) after 60 min. The high photocatalytic efficiency was ascribed to the conjugation of Co3O4-QDs with GQDs and Zn-ICP which causes efficient absorption of visible light. The existence of Co3O4-QDs was found to be essential not only for effective charge separation but also widening the region of light absorption followed by increase in photocatalytic performances. Charge separation in photocatalytic reactions, energy levels of nanocomposites, and mechanism of the photocatalytic process were investigated by photoluminescence spectra (PL), Mott-Schottky, electrochemical impedance (EIS), and diffuse reflectance UV-Vis spectroscopy (DRS).

Ultrafine and well-dispersed Pd-Ni bimetallic catalyst stabilized by dendrimer-grafted magnetic graphene oxide for selective reduction of toxic nitroarenes under mild conditions.

A facile and efficient strategy is introduced for growing a dendrimer structure on the surface of magnetic graphene oxide by using thiol-ene click reaction. The as-synthesized dendrimer-grafted magnetic graphene oxide was used as a suitable support for bimetallic Pd-Ni nanoparticles. The prepared nanocomposite was utilized for the reduction of toxic nitroarenes to aminoarenes by using sodium borohydride in aqueous medium at room temperature. Various nitroarenes with functional groups like nitrile, halogen, carbonyl, hydroxyl, acid, and heterocycles were converted to their corresponding anilines with good to excellent yields. The enhanced performance of the catalyst could be attributed to the synergistic effect between Ni and Pd which causes the reaction to proceed more efficiently. Moreover, the catalyst could be readily isolated from the reaction mixture by utilizing an external magnet and reused till 5th cycles with marginal loss of activity.

Improving the photocatalytic activity of NH2-UiO-66 by facile modification with Fe(acac)3 complex for photocatalytic water remediation under visible light illumination.

A new and cost-effective photocatalyst was prepared via a facile modification of NH2-UiO-66 with an iron (III) complex i.e. Fe(acac)3, in order to enhance the optical properties and charge separation efficiency of pristine MOF. According to the results of UV-Vis DRS and Tauc plot calculations, the band gap value decreased from 2.7 eV to 2.46 eV for final Fe-UiO-66 photocatalyst, showing the improvement of light absorption in the visible region. Moreover, the photoluminescence (PL) and electrochemical impedance spectroscopies (EIS) confirmed the efficient separation of electron-hole carriers after introduction of Fe(acac)3 into the MOF structure. The photo-Fenton reaction was carried out in the presence of photocatalyst and hydrogen peroxide under white LED illumination for degradation of organic dyes (methyl violet 2B, rhodamine B, malachite green, and methylene blue) and tetracycline (TC) as the examples of water pollutants. A significant dye and TC removal up to 92% and 85% were obtained in photo-Fenton system containing Fe-UiO-66 photocatalyst, respectively. The trap experiment using isopropyl alcohol (IPA) and Na2EDTA demonstrated that the major active species for pollutants degradation are hydroxyl radicals (•OH) and photo-generated holes (h+), respectively. Besides, the transfer of photo-generated electron (e-) to Fe(acac)3 complex resulted in the reduction of Fe3+ to Fe2+ and acceleration of the photo-Fenton reaction. Also, the photocatalyst was found to be very stable during the photo-Fenton reaction according to physicochemical analyses, and it can be reused four times without remarkable decrease in activity.

New Water Oxidation Electrocatalyst Based on the Cobalt-Containing Polyoxometalate-Reduced Graphene Oxide Hybrid Nanomaterial.

A new hybrid nanomaterial based on the immobilization of cobalt-containing polyoxometalate (CoPOM) on the surface of reduced graphene oxide (rGO) was designed for an efficient electrocatalytic water splitting reaction. First, the surface of rGO was functionalized with aminopropylsilyl groups and protonated with hydrochloric acid to produce ammonium groups. Then, the electrostatic interaction of positively charged rGO-supported ammonium groups with anionic CoPOM produced a CoPOM-APTS-rGO hybrid nanomaterial. The achieved hybrid nanomaterial exhibited a low overpotential of 128 mV versus NHE at a current density of 10 mA cm-2 in the electrocatalytic water oxidation at pH 7. In addition, a fast reaction kinetic with a Tafel slope of 74 mV dec-1 was seen in the presence of the prepared hybrid nanomaterial. Linear sweep voltammetry analysis revealed the long-term stability and activity of CoPOM-APTS-rGO for water oxidation in neutral conditions.

Boric acid modified S and N co-doped graphene quantum dots as simple and inexpensive turn-on fluorescent nanosensor for quantification of glucose.

A new fluorescent nanosensor based on S and N co-doped graphene quantum dots (S,N-GQDs) modified by boric acid was designed for glucose detection. First, the S,N-GQDs was prepared via one pot hydrothermal process utilizing citric acid and thiourea as precursors. Then, S,N-GQDs was modified by boric acid to fabricate (B)/S,N-GQDs. The excitation dependent photoluminescence spectra of (B)/S,N-GQDs confirmed the heteroatom (S,N) dopant effect on GQDs emission. FT-IR and energy dispersive X-ray (EDX) spectroscopies confirmed the modification of S,N-GQDs with boric acid. The optical and electrochemical band gaps of the obtained (B)/S,N-GQDs were found to be 2.7 and 2.5 eV, respectively. The boric acid functionalized S,N-GQDs exhibited fluorescent enhancement at 455 nm upon addition of glucose. Such fluorescence response was used for glucose quantification with a detection limit of 5.5 µM which is comparable with previous boronic acid based fluorescent sensing systems. However, compared with earlier reported expensive boronic acid based glucose sensors, this modified system is simpler, more economical, and efficient. A mechanism was proposed for fluorescence enhancement based on the reaction of cis-diol units of glucose with the boric acid groups of (B)/S,N-GQDs which creates rigid (B)/S,N-GQDs-glucose structures, restricting the non-radiative intramolecular motions and results in the fluorescent enhancement.

CdS quantum dots encapsulated within the mesopores of MCM-41 and interlayers of montmorillonite as photocatalysts for rhodamine-B degradation in aqueous solution.

Capping agent-free CdS quantum dots (CdS-QDs) were synthesized within the mesopores of MCM-41 and interlayers of montmorillonite (MMT), using a safe manner by a facile ion exchange-precipitation protocol. The mesopores of MCM-41 and interlayers of MMT controlled the growth of CdS-QDs. The obtained CdS-QDs@MCM-41 and CdS-QDs/MMT were characterized by X-ray diffraction (XRD) analysis, energy-dispersive X-ray (EDX), diffuse reflectance UV-Vis, and photoluminescence spectroscopies. Photodegradation of rhodamine-B (RhB) over these embedded CdS-QDs was investigated under UV-Vis light irradiation. The influences of some parameters on the photodegradation of RhB such as pH, temperature, and UV-Vis irradiation time were investigated. The results showed that the CdS-QDs/MMT and CdS-QDs@MCM-41 have high efficiencies for RhB photodegradation under UV-Vis illumination.

Pd supported on clicked cellulose-modified magnetite-graphene oxide nanocomposite for C-C coupling reactions in deep eutectic solvent.

Cellulose-modified magnetite-graphene oxide nanocomposite was prepared via click reaction and utilized for immobilization of palladium (Pd) nanoparticles without using additional reducing agent. The abundant OH groups of cellulose provided the uniform dispersion and high stability of Pd nanoparticles, while magnetite-graphene oxide as a supporting material offered high specific surface area and easy magnetic separation. The as-prepared nanocomposite served as a heterogeneous catalyst for the Heck and Sonogashira coupling reactions in various hydrophilic and hydrophobic deep eutectic solvents (DESs) as sustainable and environmentally benign reaction media. Among the fifteen DESs evaluated for coupling reactions, the hydrophilic DES composed of dimethyl ammonium chloride and glycerol exhibited the best results. Due to the low miscibility of catalyst and DES in organic solvents, the separated aqueous phase containing both of the catalyst and DES can be readily recovered by evaporating water and retrieved eight times with negligible loss of catalytic performance.

Designing a New Efficient Photocatalyst Based on Functionalization of Zn-Infinite Coordination Polymer with Ru(acac)3 Complex for Dye Degradation in Aqueous Solutions: Charge Separation Effect.

A new Zn-containing infinite coordination polymer, Zn-ICP, functionalized with Ru(acac)3 complex was designed and utilized as an efficient visible light photocatalyst for dye degradation in aqueous solutions. Incorporation of Ru(acac)3 not only extended the light absorption of the Zn-ICP to the visible region but also led to electron-hole separation. Upon visible light illumination, photoinduced electron transfer from excited state of Zn-ICP to Ru(acac)3 occurred, resulting in electron-hole separation as indicated by photoluminescence and electrochemical impedance spectroscopy. The obtained Ru-Zn-ICP revealed enhanced visible light photocatalytic activity in degradation of organic pollutants compared to pristine Zn-ICP owing to photoinduced electron transfer in the Ru-Zn-ICP system and efficient separation of photogenerated electron-hole pairs. The prepared Ru-Zn-ICP photocatalyst was readily recycled without major loss of activity in the successive cycles.

Microemulsion-mediated preparation of Ce2(MoO4)3 nanoparticles for photocatalytic degradation of crystal violet in aqueous solution.

Preparation of Ce2(MoO4)3 nanoparticles is reported via the microemulsion method by using two different surfactants, i.e., cationic surfactant, cetyltrimethylammonium bromide (CTAB), and nonionic surfactant, Triton X-100. The water pools produced in the microemulsion systems behave as nanoreactors for reaction of the cerium (3+) and molybdate ions to produce Ce2(MoO4)3 nanoparticles. The structure and morphology of the products were characterized by using Fourier-transform infrared (FT-IR) spectroscopy, energy-dispersive X-ray analysis (EDX), UV-Vis spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA-DTA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The prepared Ce2(MoO4)3 nanoparticles were successfully utilized as photocatalysts to remove crystal violet from aqueous solution in which the maximum percentage of dye degradation was about 89% after 5 h under the visible light irradiation. Also, kinetic study of the photocatalytic degradation revealed that pseudo-second order model is the best one for describing kinetic of the reaction.

Molecularly imprinted polymer containing fluorescent graphene quantum dots as a new fluorescent nanosensor for detection of methamphetamine.

A novel fluorescent nanosensor based on graphene quantum dots embedded within molecularly imprinted polymer (GQDs@MIP) was developed for detection and determination of methamphetamine (METH). The resulting GQDs@MIP nanocomposite exhibited higher methamphetamine selectivity in comparison with corresponding non-imprinted polymer (GQDs@NIP). Characterization of the GQDs@MIP nanocomposite was done by nitrogen adsorption and desorption analysis (BET method), transmission electron microscopy (TEM), photoluminescence (PL), ultraviolet-visible (UV-Vis), and Fourier transform infrared (FT-IR) spectroscopies. The fluorescence intensity of GQDs@MIP was efficiently quenched in the presence of methamphetamine template molecules while no quenching was observed in the presence of other analytes such as amphetamine, ibuprofen, codeine, and morphine. Using this method, the detection limit of 1.7 µg/L was obtained for methamphetamine determination.

CdTe0.5S0.5/ZnS Quantum Dots Embedded in a Molecularly Imprinted Polymer for the Selective Optosensing of Dopamine.

This work describes the preparation of molecularly imprinted polymer (MIP)-modified core/shell CdTe0.5S0.5/ZnS quantum dots (QDs). The QDs@MIP particles were used for the selective and sensitive detection of dopamine (DA). Acrylamide, which is able to form hydrogen bonds with DA, and ethylene glycol dimethylacrylate (EGDMA) as cross-linker were used for the preparation of the MIP. Highly cross-linked polymer particles with sizes up to 1 µm containing the dots were obtained after the polymerization. After the removal of the DA template, MIP-modified QDs (QDs@MIP) exhibit a high photoluminescence (PL) with an intensity similar to that of QDs embedded in the nonimprinted polymer (NIP). A linear PL decrease was observed upon addition of DA to QDs@MIP and the PL response was in the linear ranges from 2.63 µM to 26.30 µM with a limit of detection of 6.6 nM. The PL intensity of QDs@MIP was quenched selectively by DA. The QDs@MIP particles developed in this work are easily prepared and of low cost and are therefore of high interest for the sensitive and selective detection of DA in biological samples.

Surface Functionalization of Magnetite Nanoparticles with Sulfonic Acid and Heteropoly Acid: Efficient Magnetically Recoverable Solid Acid Catalysts.

New magnetically recoverable solid acid catalysts for acid-catalyzed reactions were designed via the surface chemical functionalization of silica-coated magnetite nanoparticles (SCMNPs) with sulfonic acid groups. First, the SCMNPs were covalently functionalized with 3-aminopropyl groups to achieve Amp-SCMNPs. Then, reaction of the Amp-SCMNPs with 1,4-butane sultone followed by acidification with phosphotungstic acid (HPW) or diluted sulfuric acid produced magnetically recoverable solid acid catalysts, HPW-ampsul-SCMNPs and H-ampsul-SCMNPs, respectively. Both catalysts were characterized by various physicochemical analyses such as Fourier transform infrared (FT-IR) and inductively coupled plasma-optical emission (ICP-OES) spectroscopies, vibrating sample magnetometry (VSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) analyses. Finally, the catalytic activities of the prepared catalysts were examined in the esterification of acetic acid with butanol and acetalization of benzaldehyde with ethylene glycol. Excellent catalytic efficiencies were obtained in both cases. The catalysts were consecutively recovered and reused five times without significant loss of their activities.

Design and photophysical insights on graphene quantum dots for use as nanosensor in differentiating methamphetamine and morphine in solution.

Fluorescent graphene quantum dots (GQDs) were prepared and utilized as nanosensor for differentiation and determination of two most common narcotic drugs i.e. morphine and methamphetamine. The microstructure and optical properties of the GQDs were investigated by various physicochemical methods. XRD analysis indicated low crystalline nature, demonstrating the graphitic nature of the GQDs. According to the Tauc plot derived from UV-Vis spectrum, the optical band gap of the GQDs was determined to ~4.98 eV, assigned to the n-π* transitions. Cyclic voltammetry analysis of the GQDs determined electrochemical band gap of ~4.88 eV with HOMO and LUMO energies equal to -6.83 eV and -1.95 eV, respectively. The GQDs were employed as fluorescent sensing probe for determination of morphine and methamphetamine. The blue fluorescence of the prepared GQDs under the excitation at 362 nm was quenched in the presence of methamphetamine and enhanced in the presence of morphine. The detection limits of 1.48 and 0.5 µg/ml were found for methamphetamine and morphine, respectively. This inexpensive sensing system shows some advantages such as short response time (t < 1 min) and low detection limit as well as nontoxicity.