Eco-Friendly Sustainable Fluorescent Carbon Dots for the Adsorption of Heavy Metal Ions in Aqueous Environment.

The materials and substances required for sustainable water treatment by adsorption technique, are still being researched widely by distinguished classes of researchers. Thus, the need to synthesize substances that can effectively clean up pollutants from the environment cannot be overemphasized. So far, materials in bulk forms that are rich in carbon, such as biochar and varieties of activated carbon have been used for various adsorptive purposes. The use of bulk materials for such purposes are not efficient due to minimal surface areas available for adsorption. This study explores the adsorption task at nano dimension using carbon dots (CDs) from tapioca. The properties of carbon structure and its influence on the adsorptive efficacy of carbon nanoparticles were investigated by energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), high resolution transmission electron microscopy (HrTEM), and atomic force microscopy (AFM). The results implied carbon present in CDs are good adsorbents for effective adsorption of heavy metal ions (lead) with removal efficiency of 80.6% in aqueous environment. The adsorption process as explored by both Langmuir and Freundlich isotherms have proven favorability of the adsorption process. Langmuir form two and three have correlation coefficients R2 at 0.9922 and 0.9912, respectively. The Freundlich isotherm confirms CDs as having defined surface heterogeneity and the exponential distribution of active sites. The adsorption of lead unto CDs obeyed the second order kinetic model with coefficient of determination, R2 of 0.9668 and 0.9996 at an initial lead concentration of 20 mg/L and 100 mg/L, respectively. The findings validated the efficiency of CDs derived from tapioca as an excellent material for further utilization in the environmental fields of wastewater pollution detection and clean up, bio-imaging, and chemical sensing applications.

Application of polypyrrole multi-walled carbon nanotube composite layer for detection of mercury, lead and iron ions using surface plasmon resonance technique.

Polypyrrole multi-walled carbon nanotube composite layers were used to modify the gold layer to measure heavy metal ions using the surface plasmon resonance technique. The new sensor was fabricated to detect trace amounts of mercury (Hg), lead (Pb), and iron (Fe) ions. In the present research, the sensitivity of a polypyrrole multi-walled carbon nanotube composite layer and a polypyrrole layer were compared. The application of polypyrrole multi-walled carbon nanotubes enhanced the sensitivity and accuracy of the sensor for detecting ions in an aqueous solution due to the binding of mercury, lead, and iron ions to the sensing layer. The Hg ion bonded to the sensing layer more strongly than did the Pb and Fe ions. The limitation of the sensor was calculated to be about 0.1 ppm, which produced an angle shift in the region of 0.3° to 0.6°.

Multi-wavelength generation by self-seeded four-wave mixing.

A cost effective method of generating multi-wavelength based on the cascaded four wave mixing effect is experimentally demonstrated. The proposed scheme is free from external tunable laser sources and pump modulators, resulting from the use of a broadened linewidth tunable dual wavelength erbium-doped fiber laser as intracavity pump. In this configuration, the number of four wave mixing cascades becomes larger in tandem with the increment of erbium-doped fiber amplifier output power. When its output power is set at 20.57 dBm, six waves having optical signal to noise ratio larger than 10 dB are generated. The six waves are stable with peak power fluctuations less than 1 dB within 30 minutes period and tunable with wavelength spacing ranging from 1.03 nm to 11.31 nm.