Zinc oxide (ZnO) has been considered as one of the potential materials in solar cell applications, owing to its relatively high conductivity, electron mobility, stability against photo-corrosion and availability at low-cost.

One of the emerging challenges in tackling environmental issues is to treat electronic waste, with fast-growing battery waste as a notable threat to the environment. Proper recycling processes, particularly the conversion of waste to useful & value-added materials, are of great importance but not readily available. In this work, we report a facile and fast production of graphene from graphite extracted from spent Zn–C batteries. The graphene flakes are produced by electrochemically exfoliating graphite under varying DC voltages in poly(sodium 4-styrenesulfonate) (PSS) solution of different concentrations. The exfoliation takes place via the insertion of PSS into the interlayers of graphite to form C–S bonds as confirmed by FTIR and XPS studies. Under an applied voltage of 5 V and in 0.5 M PSS, high quality graphene flakes are obtained in a good yield, giving an I_D/I_G ratio of about 0.86 in Raman spectroscopy. The transparent conductive film prepared from the dispersion of high quality graphene flakes shows great promise due to its low sheet resistance (R_s) of 1.1 kΩ sq⁻¹ and high transmittance of 89%. This work illustrates an effective and low-cost method to realize large scale production of graphene from electronic waste.

Uric acid (UA) is the primary waste product from purine metabolism in humans. Excessive UA levels in the body will accumulate in joints and form crystals that cause a wide range of health problems. An enzymatic electrochemical biosensor for UA based on the transition metal complex-incorporated polyaniline PANI-RC functionalized with both urate oxidase (UOx) as a specific bioreceptor and horseradish peroxidase (HRP) as a signal enhancer was developed. The transition metal complex being used herein is the commonly used redox couple (RC) in electrochemical biosensors, [Fe(CN)₆]^3−/4−, which plays the pivotal role of electron acceptors. This PANI-RC platform then becomes a conducive environment not only for enzyme immobilization but also for signal transfer improvement. The synergistic combination of HRP near UOx and RC anchored on the backbone of PANI helps in electron transfer from the enzymatic reaction to the current collector. The resulting PANI-RC-based UA sensor demonstrates high sensitivity with a detection limit of 11.4 μM, wide linear range, good stability, and excellent selectivity even in the presence of the most problematic interference in UA assays (e.g., ascorbic acid and urea). The recovery tests using artificial biofluid-spiked UA samples also showed promising results for practical usage of the PANI-RC-based UA sensor.