Synthesis of carbon dots based on corn cobs as heavy metal ion sensors using the microwave method

Carbon dots (CDots) are nanomaterials that can be applied as a heavy metal ion sensor. CDotss ware synthesized from corncobs which are abundant and underutilized. This study aims to determine the effect of variations in the concentration of corncobs on optical properties of CDots and their application as  Fe3+ ion sensors. CDots were synthesized with variations of corncobs’ mass 5, 10, 15, and 20 g and variations in metal ion concentrations 10-7, 10-6, 10-5, 10-4, and 10-3 M. The success of CDots synthesis was indicated by luminescence green when exposed to UV light. UV-Vis characterization showed that the greater the concentration of CDots could cause a shift in the absorbance peak towards longer wavelengths and peaks at wavelengths of 290, 291, 295, 298, and 323 nm, respectively. Photoluminescence (PL) characterization showed CDots emission peaks at 511, 504, 503, and 495 nm. The greater the concentration of CDots can cause a shift in the emission peak towards a shorter wavelength and increase the intensity. The PL characterization can identify the presence of Fe3+ metal ions with a wavelength shift that indicates a change in the CDots structure. The synthesis of CDots from corncobs have great potential to be applied as sensors

Oxygen Reduction Reaction (ORR) of Pt/C Standard in Different Electrolyte Solutions and Terbium(III) Monoporphyrinato Complex

Electrocatalytic parameters of a Pt/C standard and a sample of terbium(III) monoporphyrinato were investigated in different solutions. N electron transfer, Tafel slope, Eonset, and overpotential of the catalyst of Pt/C in different solutions were calculated and analyzed using a rotating ring disk electrode (RRDE) in 0.5 M H2SO4, 0.1 M HClO4 and 0.1 M NaOH. In the RRDE measurements, a bipotentiostat at a potential range of 1.03 to 0.05 V vs RHE (Ering = 1.2 V vs RHE) with a scan rate of 5 mV/s and rotation rates of 200, 400, 900, 1600 and 2500 rpm was used. Hereafter, the test of terbium(III) monoporphyrinato compound formulated in [Tb(TPP)(cyclen)]Cl (TPP = 5,10,15,20-tetraphenylporphyrinato; cyclen = 1,4,7,10-tetraazacyclododecane) as a candidate material for ORR electrocatalyst was also done. The results showed that the measurement of Pt/C standards was satisfactory according to the literature for all parameters with the n electron transfer close to 4 in all electrolytes media. [Tb(TPP)(cyclen)]Cl had an n electron transfer value of 2.38, suggesting that the [Tb(TPP)(cyclen)]Cl compound has less potential for ORR catalysts