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A novel tungsten disulfide-molybdenum copper oxide composite supported with graphene quantum dots (WM@GQDs) has been synthesized as a counter electrode (CE) for dye-sensitized solar cells (DSSCs) using a simple and low-cost ultrasonication method. The unique structure of WM@GQDs exhibits excellent power conversion efficiency due to its high catalytic activity and charge transport properties. In addition, the graphene quantum dots (GQDs) provide more active sites in the zero-dimensional materials for an I/I3- redox reaction which can improve the electrical and optical properties of the composite. The results indicate that the amount of GQDs in the composite affect the effectiveness of solar devices. When 0.9%wt of GQDs was used, the WM@GQDs composite achieved an efficiency of 10.38%, which is higher than that of the expensive platinum CE under the same conditions. The mechanism behind the improved power conversion efficiency (PCE) of the composite sample is also discussed in detail. Therefore, WM@GQDs can be an efficient material to replace platinum in DSSCs as a CE.

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A new mesoporous Cu-doped FeSn-G-SiO2 (CFSGS) based biosensor was developed for the detection of microalbumin in urine samples. The mechanically flexible FeSn modified sensor was fabricated at room temperature. These demonstrations highlight the unexplored potential of FeSn for developing novel biosensing devices. It is extremely sensitive and selective. Surfactant-aided self-assembly was used to synthesise the mesoporous CFSGS. The large surface area due to the mesopore presence in the CFSG surface that has been composited inside the mesoporous SiO2 boosted the electrochemical detection. The linear range and detection limit of microalbumin under optimum circumstances were 0.42 and 1 to 10 µL, respectively. This easily fabricated mesoporous CFSGS provided a fast response with high sensitivity, and good selectivity. The sensor's reusability and repeatability were also quite high, with just a 90 percent drop after 4 weeks of storage at ambient temperature. The biosensor also demonstrated high selectivity against typical potential interfering chemicals found in urine (ascorbic acid, urea, and sodium chloride). The good performance of the mesoporous CFSGS biosensor was validated by measuring microalbumin, and the findings indicated that this sensing device performed very well.

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Novel MoWO4 with ZnO nanoflowers was synthesized on multi-walled carbon nanotubes (MW-Z@MWCNTs) through a simple hydrothermal method, and this unique structure was applied as a counter electrode (CE) for dye-sensitized solar cells (DSSC) for the first time. The synergetic effect of ZnO nanoflowers and MoWO4 on MWCNTs was systematically investigated by different techniques. The amount of MWCNTs was optimized to achieve the best DSSC performance. It was found that the 1.5% MW-Z@MWCNTs composite structure had the highest power conversion efficiency of 9.96%, which is greater than that of traditional Pt CE. Therefore, MW-Z@MWCNTs-based CE can be used to replace traditional Pt-based electrodes in the future.

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The goal of this work was to use the pyrolysis process to synthesize graphene quantum dots doped with garlic extract (as N,S-GQDs) and simultaneously co-doped with iodine (as I-GQDs). XPS, HR-TEM, FE-SEM/EDX, FT-IR, fluorescence, and UV-visible absorption spectroscopy were used to characterize the N,S,I-GQDs and analyze their morphological images. The quantum yield of N,S,I-GQDs was found to be 45%, greater than that of undoped GQDs (31%). When stimulated at 363 nm, the N,S,I-GQDs display a strong fluorescence intensity at a maximum wavelength of 454 nm. Using N,S,I-GQDs as a fluorescence quenching sensor for screening tests with various metal ions, it was discovered that they are extremely selective towards Fe2+ over Fe3+ and other ions. Thus, solution pH, concentration of N,S,I-GQDs, quantity of garlic extract, EDTA and AgNO3 concentration as masking agents, reaction duration under ultrasonic aid, and tolerable limit of Fe3+ presence in the target analyte were all optimized for Fe2+ detection. A highly sensitive detection of Fe2+ was obtained using a linear curve with y = 141.34x + 5.5855, R 2 = 0.9961, LOD = 0.11 mg L-1, and LOQ = 0.35 mg L-1. The method precision, given as RSDs, was determined to be satisfactory at 1.04% for intra-day analysis and 3.22% for inter-day analysis, respectively. As a result, the selective determination of trace amounts of Fe2+ in real water samples using such labile multi-element doped GQDs in conjunction with garlic extract as a green chelating agent to maintain its enhanced sensitivity was successfully applied with good recoveries ranging from 89.16 to 121.45%.

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To address the issues associated with traditional counter electrodes, a novel gamma-irradiated chitosan-doped reduced graphene-CuInS2 composite (Chi@RGO-CIS) was used as the counter electrode (CE). The system was fabricated following a simple hydrothermal method. The prepared Chi@RGO-CIS was characterized by various spectroscopic and microscopic techniques. The synergistic effect between chitosan, CuInS2, and reduced graphene oxide can help in producing a large surface area. It can also help in the generation of catalytic sites toward I-/I3-redox electrolytes. We used a composite (based on electrical considerations) to study the effect of the amount of graphene on the characteristics and photovoltaic efficiency of the Chi@RGO-CIS composites. The solar cell assembled with 1.5% Chi@RGO-CIS exhibited an efficiency of 12.21%. The efficiency was higher than that of a Pt-based device (9.96%) fabricated under the same conditions. Hence, Chi@RGO-CIS can be potentially used as the CE of dye-sensitized solar cells (DSSCs). It can be used as a substitute for Pt in DSSCs.

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This study aimed to synthesize dimethylglyoxime (DMG) (N-source)-doped graphene quantum dots (N-GQDs) via simultaneous pyrolysis of citric acid and 1.0% (w/v) DMG. The maximum excitation wavelength (λmax, ex = 380 nm) of the N-GQD solution (49% quantum yield (QY)) was a red shift with respect to that of bare GQDs (λmax, ex = 365 nm) (46% QY); at the same maximum emission wavelength (λmax, em = 460 nm), their resonance light scattering (RLS) intensity peak was observed at λmax, ex/em = 530/533 nm. FTIR, X-ray photoelectron spectroscopy, XRD, energy-dispersive X-ray spectroscopy, and transmission electron microscopy analyses were performed to examine the synthesized materials. The selective and sensitive detection of Ni2+ using the RLS intensity was performed at 533 nm under the optimum conditions consisting of both 25 mg L-1 N-GQDs and 2.5 mg L-1 DMG in the ammonium buffer solution of pH 9.0. The linearity of Ni2+ was 50.0-200.0 µg L-1 with a regression line, y = 5.031x - 190.4 (r 2 = 0.9948). The limit of detection (LOD) and the limit of quantitation (LOQ) were determined to be 20.0 and 60.0 µg L-1, respectively. The method precision expressed as % RSDs was 4.90 for intraday (n = 3 × 3) and 7.65 for interday (n = 5 × 3). This developed method afforded good recoveries of Ni2+ in a range of 85-108% when spiked with real water samples. Overall, this innovative method illustrated the identification and detection of Ni2+ as a DMG complex with N-GQDs, and the detection was highly sensitive and selective.

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This study aims to use graphene quantum dots (GQDs) as a fluorescence switching sensor (turn on-off) for the simultaneous detection of cyanide (CN-) and ferricyanide [Fe(CN)6]3- in wastewater samples. The GQDs were synthesized by pyrolyzing solid citric acid. The intrinsic blue color of the solution was observed under ultraviolet irradiation. The fluorescence spectrum was maximized at both excitation and emission wavelengths of 370 and 460 nm, respectively. The fluorescence intensity of GQDs decorated with Hg2+ (turn-off mode as the starting baseline) could be selectively turned on in the presence of CN- and once back to turn-off mode by [Fe(CN)6]3-. The fluorescence switching properties were used to develop a fluorescence turn-on-off sensor that could be used to detect trace amounts of CN- and [Fe(CN)6]3- in water samples. For highly sensitive detection under optimum conditions (Britton-Robinson buffer solution in the pH range of 8.0-9.0, linearity ranges of 5.0-15.0 µM (R 2 = 0.9976) and 10.0-50.0 µM (R 2 = 0.9994), respectively, and detection limits of 3.10 and 9.48 µM, respectively), good recoveries in the ranges of 85.89-112.66% and 84.88-113.92% for CN- and [Fe(CN)6]3-, respectively, were recorded. The developed methods were successfully used for the simultaneous and selective detection of CN- and [Fe(CN)6]3- in wastewater samples obtained from local municipal water reservoirs.

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We report a novel method for the synthesis of 3-mercaptopropyl trimethoxysilane-modified hydroxyapatite (FHAP-SH) derived from fish-scale residues by using ultrasound irradiation. Scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy were used for the FHAP-SH characterization. Then, the organic dye adsorption on the FHAP-SH was monitored through an ultrasound process. After the dye removal optimization, significant improvements were observed in the maximum adsorption capacities for Congo Red (CR, 500 mg g-1), Coomassie Brilliant Blue G 250 (CB, 235 mg g-1), and Malachite Green (MG, 625 mg g-1). The adsorption behaviors of these dyes were fitted by using the Langmuir isotherm model with a high coefficient of determination values ranging from 0.9985 to 0.9969. The adsorption of the three dyes onto FHAP-SH was an endothermic process based on the adsorption thermodynamics model, while the adsorption kinetics analysis of the dyes presented a good alignment with the pseudo-second-order kinetics. The FHAP-SH exhibits a remarkably high adsorption capacity, is inexpensive, and fulfills the ecofriendly requirements of dye wastewater treatment, especially in the textile industry.

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A novel nanohybrid of graphene-based Cu2ZnNiSe4 with WO3 nanorods (G-CZNS@W) was successfully synthesized via a simple hydrothermal method to use as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). The characterization technique confirmed the structural and morphologies of the G-CZNS@W nanohybrid, which could show rapid electrons transfer pathway through the WO3 nanorods. Moreover, the as-fabricated G-CZNS@W nanohybrid exhibited synergetic effect between G-CZNS and a WO3 nanorod, which could affect the electrocatalytic activity towards triiodide reaction. The nanohybrid exhibits an excellent photovoltaic performance of 12.16%, which is higher than that of the standard Pt electrode under the same conditions. The G-CZNS@W nanohybrid material as CE thus offers a promising low-cost Pt-free counter electrode for DSSC.

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Novel Cadmium Oxide-Graphene Nanocomposite Grown on Mesoporous Silica have been successfully prepared using a self-assembly method under the catering of cetyltrimethylammonium bromide (CTAB) as the surfactant template at ambient conditions. The structural and optical properties of the obtained nanocomposites were investigated by many different techniques. The results of photocatalytic measurements revealed that almost 100% of MB organic dye was removed with the presence of SiO2/CdO-graphene composite under visible light irradiation. Moreover, the initial pH also plays an important role in the photodegradation processes. On the other hand, this work opens a way to enhance the photocatalytic activity of gallic acid at ambient conditions without any further different oxidation processes. From the evolutionary aspect, SiO2/CdO-graphene composite revealed better H2 generation than that of binary photocatalyst (CdO-graphene nanocomposite). The results of characterization and photodegradation suggest that SiO2/CdO-graphene material constitutes a new photocatalyst for the degradation of organic contaminants, as well as the development of an efficient hetero-system for hydrogen production.

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To develop counter electrodes (CEs) for dye-sensitized solar cells (DSSCs), band gap energy of quaternary semiconductor materials is of great interest. In the present study, a novel graphene sheet based on Mg2CuSnCoO6-Gallic acid nanomaterials (G/MCS@Gallic) was modified with a new Joule heating method, and a laser was applied for measuring band gap energy. Synergistic effect between graphene and Mg2CuSnCoO6-Gallic ensured excellent electron transport through the electrode and low band gap energy. The large surface area of the hybrid graphene materials rivaled the catalytic capability for iodide reduction. DSSCs achieved a maximum photoelectric conversion efficiency of 13.30% based on the 10% G/MCS@Gallic CE, which was higher than the platinum conversion efficiency. Thus, G/MCS@Gallic provides a novel, inexpensive, high-performance, and flexible cathode for solar cell applications.

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Currently, the development of sensitized solar cells (DSSCs) with high power conversion efficiency and low cost is a major challenge in the academic and industrial fields. In order to enhance the current efficiency of dye-sensitized solar cells (DSSCs), a perovskite graphene-La2CuNiO6-ZnSe (G-LCN-ZS) as a counter electrode (CE) was introduced in this study via a conventional microwave treatment. A DSSC with 15% G-LCN-ZS CE achieved a high-power conversion efficiency up to 11.05% under AM 1.5G solar simulation, which is one of the highest reported efficiencies for ternary oxide-based graphene DSSCs. The G-LCN-ZS CE nanocomposites exhibit excellent catalytic activity towards the I3-/I- redox couple due to the positive synergistic effect between LCN-ZS nanoparticles and graphene sheets. Moreover, the graphene-based materials can provide a fast diffusion pathway for the electrolyte. In this paper, we have shown that alternative materials with high energy conversion efficiency can be used in future applications.

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Fe3O4-graphene/ZnO@mesoporous-SiO2 (MGZ@SiO2) nanocomposites was synthesized via a simple one pot hydrothermal method. The as-obtained samples were investigated using various techniques, as follows: scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and specific surface area (BET) vibrating sample magnetometer (VSM), among others. The sonocatalytic activities of the catalysts were tested according to the oxidation for the removal of methylene blue (MB), methyl orange (MO), and rhodamine B (RhB) under ultrasonic irradiation. The optimal conditions including the irradiation time, pH, dye concentration, catalyst dosage, and ultrasonic intensity are 60min, 11, 50mg/L, 1.00g/L, and 40W/m2, respectively. The MGZ@SiO2 showed the higher enhanced sonocatalytic degradation from among the three dyes; furthermore, the sonocatalytic-degradation mechanism is discussed. This study shows that the MGZ@SiO2 can be applied asa novel-design catalyst for the removal of organic pollutants from aqueous solutions.

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Fe3O4/hydroxyapatite/graphene quantum dots (Fe3O4/HAP/GQDs) nanocomposite was synthesized and used as a novel magnetic adsorbent. This nanocomposite was characterized using scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and magnetization property. The Fe3O4/HAP/GQDs was applied to pre-concentrate copper residues in Thai food ingredients (so-called "Tom Yum Kung") prior to determination by inductively coupled plasma-atomic emission spectrometry. Based on ultrasound-assisted extraction optimization, various parameters affecting the magnetic solid-phase extraction, such as solution pH, amount of magnetic nanoparticles, adsorption and desorption time, and type of elution solvent and its concentration were evaluated. Under optimal conditions, the linear range was 0.05-1500ngmL-1 (R2>0.999), limit of detection was 0.58ngmL-1, and limit of quantification was 1.94ngmL-1. The precision, expressed as the relative standard deviation of the calibration curve slope (n=5), for intra-day and inter-day analyses was 0.87% and 4.47%, respectively. The recovery study of Cu for real samples was ranged between 83.5% and 104.8%. This approach gave the enrichment factor of 39.2, which guarantees trace analysis of Cu residues. Therefore, Fe3O4/HAP/GQDs can be a potential and suitable candidate for the pre-concentration and separation of Cu from food samples. It can easily be reused after treatment with deionized water.

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This study describes the preparation, characterization, and application of a new magnetic chitosan-graphene quantum dots (Fe3O4@Chi-GQDs) nanocomposite as an adsorbent for the preconcentration of Cu(II) in Thai food recipes or the so-called "Som Tam" (green papaya salad) prior to determination by inductively coupled plasma-optical emission spectrometry. The spectroscopic and magnetic properties along with the morphology and thermal property were analyzed using FTIR, EDX, XRD, TGA, VSM, and TEM. Preconcentration optimizations including pH, dosage of adsorbent, adsorption-desorption time, concentration and volume of elution solvent, sample volume and enrichment factor, and reusing time were investigated. Good linearity was obtained ranging from 0.05 to 1500µgL-1 with correlation coefficient of 0.999. Limit of detection was 0.015µgL-1. Relative recoveries of 85.4-107.5% were satisfactorily obtained. This Fe3O4@Chi-GQDs has high potential to be used as preconcentration method and can be reused 7times with high extraction efficiency.

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A novel core-shell magnetic surface molecularly imprinted polymer with folic acid as a template was successfully synthesized by the sol-gel method. To generate Lewis acid sites in the silica matrix for the interaction of the metal coordinate with the template, 3-aminopropyltriethoxysilane was used as a functional monomer, tetraethyl orthosilicate as a cross-linker, and aluminum ions as a dopant. The magnetite encapsulated by the silica shell plays an important role as a magnetic-coated polymer. The synthesized product was characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and FTIR and UV/Vis spectroscopy. The powder X-ray diffraction patterns, FTIR and UV/Vis spectra confirmed the characteristics of the as-prepared silica coated magnetite and folic acid molecularly imprinted polymer. It was successfully applied for magnetic solid-phase extraction prior to the determination of folates in tomato samples using high-performance liquid chromatography with photodiode array detection. The detection limit of the proposed method was 1.67 µg/L, and results were satisfactory, with a relative standard deviation of < 3.94%.

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