In this study, a label-free “turn off” fluorescent sensor has been resoundingly fabricated using carbon dots (CDs) for ultrasensitive detection of copper ions (Cu 2+ ). CDs are prepared by solid phase carbonization method using p-toluidine and l -cysteine as the precursors. The synthesized CDs exhibited the highest fluorescence intensity with excitation and emission wavelengths set at 300 nm and 400 nm, respectively. The CDs were selective and sensitive to Cu 2+ due to the static quenching mechanism. The concentration of CDs, and solution pH and incubation time were important parameters for the developed sensor. The experimental results showed that 20 mgL −1 was enough for the analysis. As the solution pH was concerned, it was apparent that the sensor was endowed with an excellent response signal to Cu 2+ and provided high sensitivity at pH 12. The interaction occurred very quickly, and the incubation time could be set at 1 min. The sensor provided a two-stage calibration curve to Cu 2+ in the range of 0.05–0.7 and 0.7–4 μM with a limit of detection of 47 nM. The obtained results clearly demonstrated that this facile method was fast, reliable and selective for detecting Cu 2+ , which would explore a prospective strategy for developing effective and low-cost sensors for monitoring metal ions in aqueous environments.
Chao Zhu,Zarak Mahmood,Abdul Saboor Arshad,Jia Liu,Hongrui Ma
Wastewater treatment has become a major global issue due of undegradable pollutants. As toxic water pollutants , namely o-toluidine and p-toluidine are difficult to treat, this study uses the silicon rubber technology to treat them. A pair of modules having single tabular nonporous silicon rubber tube and HCl stripping solution were set up to extract o-toluidine and p-toluidine from high-saline wastewater. Reaction quotient ( Q C ) was calculated after every 12 h intervals to evaluate the equilibrium reaction. The effect of concentration, pH, temperature, ionic strength, and flow rate on the permeability (P) and removal efficiency ( η ) were investigated to illustrate the process parameters and mechanisms of recovery of both elements from wastewater. The results showed that the recovery efficiency was more than 96% with concentration of 2–10g/L. When pH of the extraction solution was 2 or less, the pollutant permeability efficiency was nearly 95%. Moreover, when the salting strength was over 10%, the recovery efficiency increased quickly to some extent. Permeability, which mainly influenced by membrane resistance and desorption rate, initially increased and then decreased when the water flow increased from 2 and 20 mL/min. Aging of silicon rubber tube was also studied with respect to salinity , temperature, and acidity. Acidity and temperature was found to have a significant effect on the tube, permeability increased with an increase in aging, and aging had a minor effect on the elastic properties of the silicon rubber tube. Absorption and diffusion of water in silicon rubber tubes decreased when salinity increased more than 10%, which increased separation of p-toluidine and water. Due to this, there is no need of desalination before membrane extraction in treatment of p-toluidine wastewater with high saline. Thus, this study demonstrates that membrane extraction is a highly energy-efficient process for the effective recovery of o-toluidine and p-toluidine from wastewater with high salinity.
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