Origin of Modified Luminescence Response in Reduced Graphitic Carbon Nitride Nanosheets

We report on the tuning of luminescence response of few layered graphitic carbon nitride (g-C₃N₄) nanosheets by reducing the functional groups though chemical reduction. The nanosheets of g-C₃N₄ have been obtained from its bulk counterpart through liquid phase exfoliation, while the attached functional groups have been removed through sodium borohydride treatment. X-ray photoelectron and micro Raman studies indicate the improved aromatization through the removal of the functional groups, while structural defect formation has been realized at higher reduction levels. It has been found that the increase in sp² C–N cluster size as a result of improved aromatization leads to the enhanced absorption through π → π* transition. Consequently, the luminescence response has been found to increase at the lower reduction level. On the other hand, near-ultraviolet emission and suppressed visible emission has been witnessed at higher reduction levels. The improvement in near-ultraviolet emission originates from the modified density of states which favors the transitions involving δ* and N lone pair states. Better understanding of the reduction mechanism can lead to the fabrication of prototype flexible light emitting devices that can emit light in the ultraviolet as well as the visible region of the spectrum

Chemically Reduced Graphene Oxide for Ammonia Detection at Room Temperature

Chemically reduced graphene oxide (RGO) has recently attracted growing interest in the area of chemical sensors because of its high electrical conductivity and chemically active defect sites. This paper reports the synthesis of chemically reduced GO using NaBH₄ and its performance for ammonia detection at room temperature. The sensing layer was synthesized on a ceramic substrate containing platinum electrodes. The effect of the reduction time of graphene oxide (GO) was explored to optimize the response, recovery, and response time. The RGO film was characterized electrically and also with atomic force microscopy and X-ray photoelectron spectroscopy. The sensor response was found to lie between 5.5% at 200 ppm (parts per million) and 23% at 2800 ppm of ammonia, and also resistance recovered quickly without any application of heat (for lower concentrations of ammonia). The sensor was exposed to different vapors and found to be selective toward ammonia. We believe such chemically reduced GO could potentially be used to manufacture a new generation of low-power portable ammonia sensors

Engineering Hierarchical Self-Assembled PANI-/1T@2H MoS₂ Nanostructure toward Ultrahigh Performance Supercapacitor Electrodes

Layered transition metal dichalcogenides (TMDCs) such as molybdenum disulfide (MoS2) with mixed phases (1T and 2H) have attracted huge attention as a promising supercapacitor electrode material attributing to their unique physical and electrical properties, abundant catalytically active sites with metallic edges, and high surface area. However, to enhance the electrochemical performance of 1T@2H MoS2 and to overcome the limitations of the stacking between the MoS2 layers, phase engineering and functionalization of MoS2 with polyaniline (PANI) simultaneously are a promising yet challenging way. Herein, we report the tubular uniform growth of PANI on 1T@2H MoS2 templates, where ascorbic acid plays a pivotal role in self-assembling the PANI molecules among themselves. The optimized PANI-/1T@2H MoS2 hybrid functionalized with l-ascorbic acid (L-AA), denoted as PM2, delivers a high specific capacitance of 618 F/g at a current density of 1 A/g and a good rate retention up to 73% with the increase in current density from 1 to 10 A/g in a three-electrode system. Interestingly, the symmetric supercapacitor (SSC) integrated using the PM2 hybrid delivers efficient capacitive property (160 F/g at 0.3 A/g), energy, and power density (8 Wh/kg and 6.1 kW/kg). It has been evidenced that the PM2 hybrid exhibits excellent electrochemical properties as a supercapacitor electrode material, having capacitive retention up to 98.1% even after completing 8000 cycles at a current density of 2 A/g. Additionally, PM2 SSCs possess an excellent degree of mechanical properties and flexibility, and they are able to power a red LED successfully when connected in series. Furthermore, the experimentally observed results are compared and justified with the theoretical findings. Our strategy of growing PANI onto L-AA functionalized 1T@2H MoS2 provides a possible pathway to enhance the electrochemical performance of PANI/MoS2-based hybrid materials for the design of future-generation energy storage devices

Self-Assembly of a Nine-Residue Amyloid-Forming Peptide Fragment of SARS Corona Virus E‑Protein: Mechanism of Self Aggregation and Amyloid-Inhibition of hIAPP

Molecular self-assembly, a phenomenon widely observed in nature, has been exploited through organic molecules, proteins, DNA, and peptides to study complex biological systems. These self-assembly systems may also be used in understanding the molecular and structural biology which can inspire the design and synthesis of increasingly complex biomaterials. Specifically, use of these building blocks to investigate protein folding and misfolding has been of particular value since it can provide tremendous insights into peptide aggregation related to a variety of protein misfolding diseases, or amyloid diseases (e.g., Alzheimer’s disease, Parkinson’s disease, type-II diabetes). Herein, the self-assembly of TK9, a nine-residue peptide of the extra membrane C-terminal tail of the SARS corona virus envelope, and its variants were characterized through biophysical, spectroscopic, and simulated studies, and it was confirmed that the structure of these peptides influences their aggregation propensity, hence, mimicking amyloid proteins. TK9, which forms a beta-sheet rich fibril, contains a key sequence motif that may be critical for beta-sheet formation, thus making it an interesting system to study amyloid fibrillation. TK9 aggregates were further examined through simulations to evaluate the possible intra- and interpeptide interactions at the molecular level. These self-assembly peptides can also serve as amyloid inhibitors through hydrophobic and electrophilic recognition interactions. Our results show that TK9 inhibits the fibrillation of hIAPP, a 37 amino acid peptide implicated in the pathology of type-II diabetes. Thus, biophysical and NMR experimental results have revealed a molecular level understanding of peptide folding events, as well as the inhibition of amyloid-protein aggregation are reported