Prawit Nuengmatcha

A fluorescence switching sensor based on graphene quantum dots decorated with Hg2+ and hydrolyzed thioacetamide for highly Ag+-sensitive and selective detection

A selective fluorescent sensor based on graphene quantum dots (GQDs) was developed for the determination of silver ions (Ag+). The GQDs were prepared by the citric acid pyrolysis method. In the presence of mercury ions (Hg2+), the fluorescence intensity of the GQDs decreased linearly and it was fully recovered by the hydrolysis of thioacetamide (TAA), giving hydrogen sulfide in the reaction system. This research study was aimed at using the fluorescence turn-off sensor for the selective determination of Ag+. Upon the addition of Ag+, the fluorescence intensity of the generated sulfide-(Hg2+ quenched GQDs) decreased as a linear function of the Ag+ concentration. Then, the acquired GQDs showed steady, selective, and highly sensitive detection of Ag+. The experimental parameters affecting the fluorescence turn-on/off sensor were investigated and optimized. The optimum conditions included 4 μM Hg2+ concentration, 70 μM TAA concentration, solution pH of 7 and a 5 min reaction time. Under the optimized conditions, the working linear concentration range, limit of detection and limit of quantification for Ag+ were 0.5–10.0, 0.18 and 0.60 μM, respectively. The proposed method was successfully applied for the selective determination of trace amounts of Ag+ in five real water samples with satisfying levels of recovery (89.31–114.08%).

Electrolyte-assisted microemulsion breaking in vortex-agitated solidified floating organic drop microextraction for preconcentration and analysis of Sudan dyes in chili products

For the extraction and determination of trace amounts of Sudan I–IV dyes in chili product samples, a simple and efficient liquid phase microextraction technique was developed using electrolyte-assisted microemulsion breaking in vortex-agitated solidified floating organic drop microextraction (VA-SFODME-EAMB) and high performance liquid chromatography. Under optimal conditions, 5.0 mL of sample solution yielded a pre-concentration factor of 62. Linearity (0.5–2500 ng mL−1, R2 > 0.99), the limit of detection (0.16–0.24 ng mL−1), and the limit of quantification (0.53–0.80 ng mL−1) were used to validate this method. The precision, expressed as relative standard deviation (% RSD), was calculated using seven and five experiments with mixed Sudan dyes at a concentration of 500 ng mL−1. Intra- and inter-day analyses validated the % RSD precision data (<3.5 and 7.0%, respectively). For the analyzed real samples, the recoveries of these dyes ranged between 90.1% and 109%. This newly proposed method is simple, rapid, and environmentally friendly without using both a disperser solvent and a centrifugation step to separate the aqueous and organic phases. In particular, it is applicable for food analysis as a useful screening test of illegal adulteration with Sudan dyes.

Feasibility of hard acid–base affinity for the pronounced adsorption capacity of manganese(II) using amino-functionalized graphene oxide

The present study reveals the feasibility of using graphene oxide (GO) functionalized with 3-mercaptopropyl-trimethoxysilane (APTMS) for the removal of Mn(II) from aqueous solution. The APTMS bound on GOs surface was successfully confirmed by FTIR and EDX. For an optimal adsorption study, the effects of pH (pH 1–6), incubation time (5–80 min), temperature (30–60 °C) and initial concentration of Mn(II) (0.1–60 mg L−1) were investigated in association with Mn measurement by AAS. The optimum conditions for Mn(II) removal included a 20 mg L−1 initial concentration with 0.02 mg adsorbent at pH 5.5, and complete adsorption equilibrium was reached within 50 min. Their adsorption models are well described by both Langmuir and Freundlich isotherms. The maximum adsorption capacity of GO-NH2 for Mn(II) was 161.29 mg g−1, about 10 and 4 times higher than those of GP (16.45 mg g−1) and GO (41.67 mg g−1) according to their relevant functional groups. For the GO-NH2 adsorbent, the adsorption process of Mn(II) follows a pseudo-second-order kinetics model, indicating that the overall rate of Mn(II) uptake is controlled by external mass transfer at the initial stage of the adsorption. Later, the driving forces that control the adsorption rate are attributable to an intra-particle diffusion. A thermodynamic adsorption process reveals mainly an exothermic spontaneous reaction. Therefore, the present study provides an excellent adsorbent for Mn(II) from aqueous solution. This adsorbent can also potentially be used for wastewater treatment.

GSH-doped GQDs using citric acid rich-lime oil extract for highly selective and sensitive determination and discrimination of Fe3+ and Fe2+ in the presence of H2O2 by a fluorescence “turn-off” sensor

Synthesis and characterization of graphene quantum dots (GQDs) simultaneously doped with 1% glutathione (GSH-GQDs) by pyrolysis using citric acid rich-lime oil extract as a starting material. The excitation wavelength (λmax = 337 nm) of the obtained GSH-GQD solution is blue shifted from that of bare GQDs (λmax = 345 nm), with the same emission wavelength (λmax = 430 nm) indicating differences in the desired N and S matrices decorating the carbon based nanoparticles, without any background effect of both ionic strength and masking agent. For highly Fe3+-sensitive detection under optimum conditions, acetate buffer at pH 4.0 in the presence of 50 μM H2O2, the linearity range was 1.0–150 μM (R2 = 0.9984), giving its calibration curve: y = 34.934x + 169.61. The LOD and LOQ were found to be 0.10 and 0.34 μM, respectively. The method’s precisions expressed in terms of RSDs for repeatability (n = 3 × 3 for intra-day analysis) were 2.03 and 3.17% and for reproducibility (n = 5 × 3 for inter-day analysis) were 3.11 and 4.55% for Fe2+ and Fe3+, respectively. The recoveries of the method expressed as the mean percentage (n = 3) were found in the ranges of 100.1–104.1 and 98.08–102.7% for Fe2+ and Fe3+, respectively. The proposed method was then implemented satisfactorily for trace determination of iron speciation in drinking water.

The use of S2O82− and H2O2 as novel specific masking agents for highly selective “turn-on” fluorescent switching recognition of CN− and I− based on Hg2+–graphene quantum dots

In this study, we report that both CN− and I− can enhance the fluorescent intensity of Hg2+–graphene quantum dots (Hg2+–GQDs). However, the selectivity of the sensor was poor. Accordingly, simple specific masking agents can be directly used to solve this problem. Here, for the first time, we report the use of persulfate ion (S2O82−) as a turn-on fluorescent probe of Hg2+–GQDs for selective CN− detection, while hydrogen peroxide (H2O2) was selected for its sensing ability towards I− ion detection. Interestingly, the signal was immediately measured after addition of the masking agent to Hg2+–GQDs and the sample because its interaction was very fast and efficient. The method had a linear response in the concentration ranges of 0.5–8 μM (R2 = 0.9994) and 1–12 μM (R2 = 0.9998) with detection limits of 0.17 and 0.20 μM for CN− and I−, respectively. The sensor was successfully used for the dual detection of both CN− and I− in real water samples with satisfactory results. In conclusion, the specific masking agents in a Hg2+–GQDs system appeared to be good candidates for fluorometric “turn-on” sensors for CN− and I− with excellent selectivity over other ions.

Resonance light scattering sensor of the metal complex nanoparticles using diethyl dithiocarbamate doped graphene quantum dots for highly Pb(II)-sensitive detection in water sample

This study was aimed to detect Pb2+ using diethyl dithiocarbamate-doped graphene quantum dots (DDTC-GQDs) based pyrolysis of citric acid. The excitation maximum wavelength (λmax, ex = 337 nm) of the DDTC-GQDs solution was blue shift from bare GQDs (λmax, ex = 365 nm), with the same emission maximum wavelength (λmax, em = 459 nm) indicating differences in the desired N, S matrices decorating in the nanoparticles. Their resonance light scattering intensities were peaked at the same λmax, ex/em = 551/553 nm without any background effect of both ionic strength and masking agent. Under optimal conditions, the linear range was 1.0-10.0 μg L-1 (R2 = 0.9899), limit of detection was 0.8 μg L-1 and limit of quantification was 1.5 μg L-1. The precision, expressed as the relative standard deviations, for intra-day and inter-day analyses was 0.87% and 4.47%, respectively. The recovery study of Pb2+ for real water samples was ranged between 80.8% and 109.5%. The proposed method was also proved with certified water sample containing 60 μg L-1 Pb2+ giving an excellent accuracy and was then implied satisfactorily for ultra-trace determination of Pb2+ in drinking water and tap water samples.