Shaping Sulfur Precursors to Low Dimensional (0D, 1D and 2D) Sulfur Nanomaterials: Synthesis, Characterization, Mechanism, Functionalization, and Applications

Room temperature, ultrafast and one-step synthesis of highly fluorescent sulfur quantum dots probe and their logic gate operation

The direct and rapid conversion of abundant and cheap elemental sulfur into fluorescent sulfur quantum dots (SQDs) at room temperature is a critical and urgent challenge. Conventional synthesis methods require high temperatures, high pressures, or specific atmospheric conditions, making them complex and impractical for real applications. Herein, we propose a simple method for synthesizing SQDs simply by adding H2O2 to an elemental sulfur-ethylenediamine (S-EDA) solution at room temperature. Remarkably, within a mere 10 min, SQDs with a photoluminescence quantum yield of 23.6 % can be obtained without the need for additional steps. A comprehensive analysis of the mechanism has demonstrated that H2O2 is capable of converting Sx2- ions generated in the S-EDA solution into zero-valent sulfur atoms through oxidation. The obtained SQDs can be utilized as a fluorescent probe for detection of tetracycline (TC) and Ca2+ ions with the limit of detection (LOD) of 0.137 μM and 0.386 μM respectively. Moreover, we have developed a sensitive logic gate sensor based on SQDs, harnessing the activated cascade effect to create an intelligent probe for monitoring trace levels of TC and Ca2+ ions. This paper not only presents a viable approach for ultrafast and scalable synthesis of SQDs at room temperature, but also contributes to the efficient utilization of elemental sulfur resources.

Fabrication of highly luminescent and thermally stable composites of sulfur nanodots through surface modification and assembly

Sulfur nanodots (S-dots) have emerged as a promising luminescent material to excel over traditional heavy metal-based quantum dots. However, their relatively low emission efficiency and poor thermal stability in the solid state have limited their wide applications in photoelectric devices. In this work, highly luminescent, with a photoluminescence quantum yield higher than 50%, and thermally stable composites of S-dots were produced through modulating their surface states and aggregation behaviors by introducing pyromellitic dianhydride (PMDA) and benzoyleneurea (BEU), respectively. PMDA eliminated the relatively short-lived surface states and defects on the surface of S-dots and BEU regulated the aggregation states and facilitated the energy transfer from BEU to S-dots. The as-obtained composites also showed significantly improved thermal stability compared to S-dots, aided by the hydrophobic chemical groups and dense matrix of PMDA and BEU, which extended their applications in fabricating light-emitting diodes. Our presented results provide a new approach to produce highly luminescent S-dots, which widen their applications in the fields of bioimaging, sensing, photoelectric devices, and environmental science.

Breaking Radial Dipole Symmetry in Planar Macrocycles Modulates Edge-to-Edge Packing and Disrupts Cofacial Stacking

Dipolar interactions are ever-present in supramolecular architectures, though their impact is typically revealed by making dipoles stronger. While it is also possible to assess the role of dipoles by altering their orientations by using synthetic design, doing so without altering the molecular shape is not straightforward. We have now done this by flipping one triazole unit in a rigid macrocycle, tricarb. The macrocycle is composed of three carbazoles (2 Debye) and three triazoles (5 Debye) defining an array of dipoles aligned radially but organized alternately in and out. These dipoles are believed to dictate edge-to-edge tiling and face-to-face stacking. We modified our synthesis to prepare isosteric macrocycles with the orientation of one triazole dipole rotated 40°. The new dipole orientation guides edge-to-edge contacts to reorder the stability of two surface-bound 2D polymorphs. The impact on dipole-enhanced π stacking, however, was unexpected. Our stacking model identified an unchanged set of short-range (3.4 Å) anti-parallel dipole contacts. Despite this situation, the reduction in self-association was attributed to long-range (~6.4 Å) dipolar repulsions between π-stacked macrocycles. This work highlights our ability to control the build-up and symmetry of macrocyclic skeletons by synthetic design, and the work needed to further our understanding of how dipoles control self-assembly.

Thiol ligand-mediated exfoliation of bulk sulfur to nanosheets and nanodots: applications in antibacterial activity

Reducing bulk materials to layers or dots results in profound alterations in their physiochemical and optoelectronic properties, leading to a wide array of applications, spanning from device manufacturing to biomedicine. In this regard, the preparation of sulfur nanomaterials has garnered significant attention due to their low toxicity. Traditional methods for sulfur nanomaterial synthesis often involve harsh reaction conditions, leaving a gap for convenient approaches to create nanomaterials, such as nanosheets (NSs) and nanodots (NDs). Herein, the mechanical exfoliation of bulk sulfur using a surfactant thiol ligand with probe sonication is reported, making a unique contribution to existing methods. In the reported method, the thiol group binds to sulfur surfaces, facilitating exfoliation and stabilization, while the hydrophilic ends provide functional groups for exfoliated nanomaterials. Exfoliation can yield either nanosheets or nanodots, depending on the thiol ligand and exfoliation time. This approach offers the opportunity to exfoliate bulk sulfur using bioactive thiol ligands. With this goal in mind, bulk sulfur was exfoliated with 4-mercaptophenylboronic acid (BA) to target Gram-positive bacteria. This innovative exfoliation strategy of bulk sulfur using thiol ligands holds immense promise for synthesizing functionalized sulfur nanomaterials with wide-ranging applications, particularly in biomedicine.

Post-functionalization of sulfur quantum dots and their aggregation-dependent antibacterial activity

Sulfur quantum dots (SQDs) have emerged as an intriguing class of luminescent nanomaterial due to their exceptional physiochemical and optoelectronic properties. However, their biomedical application is still in its infancy due to the limited scope of their surface functionalization. Herein, we explored the surface functionalization of SQDs through different thiol ligands with tuneable functionality and tested their antibacterial efficacy. Notably, very high antibacterial activity of functionalized SQDs (10-25 ng ml-1) was noted, which is 105 times higher compared to that of nonfunctionalized SQDs. Moreover, a rare phenomenon of the reverse trend of antibacterial activity through surface modification was observed, with increasing surface hydrophobicity of various nanomaterials as the antibacterial activity increased. However, we also noted that as the surface hydrophobicity increased, the SQDs tended to exhibit a propensity for aggregation, which consequently decreased their antibacterial efficacy. This identical pattern was also evident in in vivo assessments. Overall, this study illuminates the importance of surface modifications of SQDs and the role of surface hydrophobicity in the development of antibacterial agents.

Synthesis of Single Crystal 2D Cu2FeSnS4 Nanosheets with High-Energy Facets (111) as a Pt-Free Counter Electrode for Dye-Sensitized Solar Cells

Two-dimensional Cu₂FeSnS₄ (CFTS) nanosheets with exposed high-energy facets (111) have been synthesized by a facile, scalable, and cost-effective one-pot heating process. The CFTS phase formation is confirmed by both X-ray diffraction and Raman spectroscopy. The formation mechanism of exposed high-energy facet CFTS growth is proposed and its electrochemical and photoelectrochemical properties are investigated in detail to reveal the origin of the anisotropic effect of the high-energy facets. Dye-sensitized solar cells (DSSC) achieve a favorable power conversion efficiency of 5.92% when employing CFTS thin film as a counter electrode, suggesting its potential as a cost-effective substitute for Pt in DSSCs.