The NiO-CNT and NiO-Fe-CNT composites that have been prepared from waste high density polyethylene plastic and their carbon nanotube (CNT) quality-dependent supercapacitance tuning have been reported here. Multiwalled CNT (MWCNT) formation has been confirmed from TEM and Raman spectra with an I_D/I_G ratio of 0.77, which stands for high graphitization. The specific surface area (SSA) of MWCNTs in the NiO-Fe-CNT composite was 87.8 m²/g, while in the NiO-CNT composite, it was 25 m²/g. NiO-Fe-CNT displayed higher specific capacitance and energy density (1360 Fg^-1 and 1180 W h kg^-1) than NiO-CNT (1250 Fg^-1 and 1000 W h kg^-1), which may be due to the presence of higher-quality MWCNTs in the NiO-Fe-CNT composite. NiO-Fe-CNT displayed higher contributions of electric double-layer capacitor (59%) behavior compared to NiO-CNT (38%) and represented a hybrid supercapacitor. NiO-Fe-CNT also displayed a capacitive retention of 96% after 1000 charge-discharge cycles. Furthermore, studies in acidic electrolytes revealed higher performance of NiO-Fe-CNT than NiO-CNT, displaying specific capacitances of NiO-Fe-CNT to be 1147 Fg^-1 in 2 M H₂SO₄ and 943 Fg^-1 in 2 M HCl. It has been qualitatively explored that the quality of CNTs, SSA, and quantum confinement effects in the composites may be the factors responsible for the performance difference in NiO-Fe-CNT and NiO-CNT. The present work is geared toward the low-cost fabrication of high-quality CNT composites for supercapacitors and energy storage applications. The present work also contributes quantitatively to the understanding of CNT quality as an important parameter for the performance of CNT-composite-based supercapacitors.

Paper-based sensors or paper-based analytical devices (PADs) have recently emerged as the cost-efficient, and portable, on-site detection tools for various biological and environmental analytes.

Population explosion and increasing living standard of people resulted in generation of more than a Giga ton of waste per annum worldwide. Hence waste is one of the global problems in 21st century and expected that waste generation continues in future also. Every human activity is left with some waste. There are some major sectors for waste generation, such as manufacturing sector, agricultural sector (in the form of biomass) and municipality waste etc. These wastes are having minimal value or even negative values and creating problem or burden to the environment, human health etc. Therefore, it is utmost important to process and manage those wastes properly. The existing waste management processes involves: recycling, dumping and landfilling, incineration/combustion etc., which are neither sufficient to nullify the adverse effect of the waste nor economic process. These management processes involve human intervention and thereby resulting huge expenses. Nowadays, there is a paradigm shift from management of waste into conversion of waste producing fertilizer, fuel, energy as well as carbon materials etc. In this review, effort is given exclusively to summarize the different processes of waste conversion into functional carbon material such as activated carbon, porous carbon, carbon nanotube, graphene, carbon dot, carbon fibre etc. It has been discussed with the help of illustrative examples from the literatures.