The
disposal of organic waste materials such as polymers is a serious
problem to natural ecosystems as some of them can be non-biodegradable
and potentially toxic. Thus,
there is immense interest in developing processes that convert waste
polystyrene into useable carbon. In this work, we developed a unique
approach for obtaining graphitic carbon from waste polystyrene as
a raw carbon source. The conversion process is catalyzed using the
Ni-butanethiolate ink in ultralow quantities under an optimized temperature
(800 °C) in the presence of 5% hydrogen in nitrogen. Interestingly,
macroporous sugar cubes are used as a soft template to hold polystyrene
and the catalyst together during decomposition, eliminating the need
for a high-pressure source for retaining carbon for graphitization
at high temperatures. An additional step of hydrogen annealing for
pyrolyzed carbon nullifies the surface effects and improves the graphitization,
reduces the point defects, and enhances the crystallinity of carbon
and electrical conductivity specifically required for an electric
double-layer capacitor (EDLC). The SPC8H-based graphitic carbon electrode
exhibits perfect rectangular cyclic voltammetry characteristics with
a symmetric triangular charge–discharge curve and a specific
capacitance of ∼158 F/g at 1 A/g. The two-electrode EDLC device
demonstrated excellent cyclic stability with a capacitance retention
of ∼90% even after 10,000 cycles. This study reveals that the
trashed polystyrene waste could be transformed into highly crystalline,
graphitic carbon electrodes for energy storage devices. This indeed
offers an alternative and sustainable approach with a low price to
high-performance ratio that can probably manage the issue of white
pollution at a commercial scale.
2D metal oxide-based nanomaterials have emerged as an exciting area of research owing to their rich electrochemical properties and diverse applications, including biosensors. In this work, we have synthesized ultra-thin Co 3 O 4 , NiO, and NiCo 2 O 4 nanostructures supported on a carbon cloth and printed graphite/Kapton substrates following thermal reduction of self-assembled metal alkanethiolates. These nanostructures act as a sensing platform for simultaneous detection of dopamine (DA) and uric acid (UA), important biological molecules in physiological and pathological tests. The ultrathin 2D nanoplates of NiCo 2 O 4 spinel formed in this study exhibit high electrochemical activity than pristine NiO and Co 3 O 4 . The electrochemical character-ization studies indicate that NiCo 2 O 4 possesses a high potential for DA and UA with a peak separation of ~140 mV, high sensitivity, and excellent selectivity. The low-cost and disposable, single-shot probe biosensors fabricated in this work possess a wide working range of 0.001-1000 μM with detection limits of 0.33 and 0.49 nM for DA and UA, respectively, with a practically achievable limit of quantification of ~1 nM. Multiple sensing electrodes are printed on graphite/Kapton all at once following this method with improved reproducibility for DA and UA sensing further extending the scope of work towards mass fabrication and practical usage.
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