Band Gap Engineering of ZnO using Core/Shell Morphology with Environmentally Benign Ag₂S Sensitizer for Efficient Light Harvesting and Enhanced Visible-Light Photocatalysis

Band gap engineering offers tunable optical and electronic properties of semiconductors in the development of efficient photovoltaic cells and photocatalysts. Our study demonstrates the band gap engineering of ZnO nanorods to develop a highly efficient visible-light photocatalyst. We engineered the band gap of ZnO nanorods by introducing the core/shell geometry with Ag₂S sensitizer as the shell. Introduction of the core/shell geometry evinces great promise for expanding the light-harvesting range and substantial suppression of charge carrier recombination, which are of supreme importance in the realm of photocatalysis. To unveil the superiority of Ag₂S as a sensitizer in engineering the band gap of ZnO in comparison to the Cd-based sensitizers, we also designed ZnO/CdS core/shell nanostructures having the same shell thickness. The photocatalytic performance of the resultant core/shell nanostructures toward methylene blue (MB) dye degradation has been studied. The results imply that the ZnO/Ag₂S core/shell nanostructures reveal 40- and 2-fold enhancement in degradation constant in comparison to the pure ZnO and ZnO/CdS core/shell nanostructures, respectively. This high efficiency is elucidated in terms of (i) efficient light harvesting owing to the incorporation of Ag₂S and (ii) smaller conduction band offset between ZnO and Ag₂S, promoting more efficient charge separation at the core/shell interface. A credible photodegradation mechanism for the MB dye deploying ZnO/Ag₂S core/shell nanostructures is proposed from the analysis of involved active species such as hydroxyl radicals (OH^•), electrons (e^–_CB), holes (h^<b>+</b>_VB), and superoxide radical anions (O₂^•–) in the photodegradation process utilizing various active species scavengers and EPR spectroscopy. The findings show that the MB oxidation is directed mainly by the assistance of hydroxyl radicals (OH^•). The results presented here provide new insights for developing band gap engineered semiconductor nanostructures for energy-harvesting applications and demonstrate Ag₂S to be a potential sensitizer to supersede Cd-based sensitizers for eco-friendly applications

Biosensing Test-Bed Using Electrochemically Deposited Reduced Graphene Oxide

The development of an efficient test-bed for biosensors requires stable surfaces, capable of interacting with the functional groups present in bioentities. This work demonstrates the formation of highly stable electrochemically reduced graphene oxide (ERGO) thin films reproducibly on indium tin oxide (ITO)-coated glass substrates using a reliable technique through 60 s chronoamperometric reduction of a colloidal suspension maintained at neutral pH containing graphene oxide in deionized water. Structural optimization and biocompatible interactions of the resulting closely packed and uniformly distributed ERGO flakes on ITO surfaces (ERGO/ITO) are characterized using various microscopic and spectroscopic tools. Lipase enzyme is immobilized on the ERGO surface in the presence of ethyl-3-[3-(dimethylamino)­propyl]­carbodimide and <i>N</i>-hydroxysuccinimide for the detection of triglyceride in a tributyrin (TBN) solution. The ERGO/ITO surfaces prepared using the current technique indicate the noticeable detection of TBN, a source of triglycerides, at a sensitivity of 37 pA mg dL^–1 cm^–2 in the linear range from 50 to 300 mg dL^–1 with a response time of 12 s. The low apparent Michaelies–Menten constant of 0.28 mM suggests high enzyme affinity to TBN. The currently developed fast, simple, highly reproducible, and reliable technique for the formation of an ERGO electrode could be routinely utilized as a test bed for the detection of clinically active bioentities