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The current work demonstrates the controlled synthesis of graphitic carbon nitride grafted silver (g-C3N4-g-Ag) doped tin oxide (SnO2) quantum dots (QDs) using the co-precipitation method. This research aimed to decrease the charge recombination rate of SnO2 and enhance their multifunctional effectiveness as catalysts and antibacterial agents with molecular docking analysis. The doping of g-C3N4-g-Ag increased the charge separation efficacy and number of active sites, resulting in the enhancement of catalytic and antibacterial activities. 6 mL of g-C3N4-g-Ag doped SnO2 QDs indicated remarkable dye removal activity of over 97.7%, which signifies its potential application in various environmental settings. Furthermore, the doped QDs demonstrated the 4.05 ± 0.08 mm inhibition area contrary to multiple drug resistant (MDR) Staphylococcus aureus (S. aureus). The inhibitory effect of g-C3N4-g-Ag doped SnO2 QDs on DNA gyraseS. aureus and tyrosyl-tRNA synthetaseS. aureus was elucidated using molecular docking analysis, supporting their bactericidal activity. [ABSTRACT FROM AUTHOR]

Bi2S3 is a narrow bandgap (1.2 eV) semiconductor of interest for the construction of solar cells and photoelectrodes. While many researchers have reported on the use of Bi2S3 as a sensitizer for photoelectrodes, the photoelectrochemical (PEC) properties of pure Bi2S3 films are less documented. Here, phase pure Bi2S3 films (Bi/S elemental ratio of 0.66) were grown on FTO, ITO, Au, Mo substrates by electrochemical deposition of bismuth, followed by sulfurization in a single-zone tube furnace. The nanostructured Bi2S3 films are 5 ± 1 μm thick and crystallize in an orthorhombic Stibnite type structure. They have a bandgap of ∼1.24 eV based on UV-Vis diffuse reflectance and are n-type based on a negative surface photovoltage (SPV) signal. X-ray photoelectron spectroscopy (XPS) places the Fermi level at 0.95–0.91 eV above the valence band edge. According to X-ray diffraction the substrates have no influence on the crystallographic properties of the Bi2S3 films. However, the PEC properties of Bi2S3 films in 0.5 M Na2S(aq) are sensitively controlled by the Bi2S3/substrate interface. Under 100 mW cm−2 simulated solar (AM 1.5) illumination and 1.23 VRHE applied bias, Bi2S3 photoelectrodes produce anodic photocurrents of 9.3 mA cm−2, 6.1, 3.6 and 1.8 mA cm−2 for FTO, Mo, Au and ITO substrates, respectively, and photovoltages of 0.9–0.25 V. For FTO, the photocurrent reported here is among the best reported for phase pure Bi2S3 photoanodes. The lower performance of the other substrates is due to a Schottky barrier at the Bi2S3/substrate interface, which retards electron transfer. These findings explain why FTO is a preferred substrate for Bi2S3 photoanodes and they highlight the importance of matching substrate workfunction to the Bi2S3 Fermi level for efficient majority carrier extraction. Lastly, the work demonstrates the use of electrochemical deposition combined with single-zone furnace-based sulfurization as a pathway to form high-quality Bi2S3 films for solar energy conversion. [ABSTRACT FROM AUTHOR]

Application of photocatalysts that strongly absorb within the visible range is a common strategy to improve the efficiency of photoelectrochemical (PEC) systems; this may translate to high photocurrents, but it is not always the case. Here, we show that nitrogen doping enhances visible light absorption of TiO2; however, it does not necessarily result in improved PEC performance. Depending on the applied external potential, N-doping can improve, or degrade, PEC performance either under water oxidation conditions or via hole scavenging (Na2S/Na2SO3). In this work, we developed a holistic approach to evaluate the true impact of N doping in TiO2 on PEC performance. Interstitial and substitutional N doping are experimentally explored for the first time through a simple and novel PEC approach which complemented X-ray photoelectron analyses. Using this approach, we show that interstitial N doping of anatase TiO2 dominates up to 400 °C and substitutional doping up to ca. 600 °C, without rutile formation. This reveals that the bottleneck for doping higher N-concentrations in TiO2 is the direct transformation to thermodynamically favorable N-rich phases, such as TiN/Ti2N at 700 °C, inhibiting the formation of rutile phase. Transmission electron microscopy revealed that N doping proceeds mainly from the inner to the outer tube walls via nitridation and follows a preferential pathway from interstitial to substitutional doping. Direct PEC experimental evidence on visible light activation of N doped TiO2, and the location of interband states, showed acceptor levels of 1.0 eV for substitutional and 0.7 eV for interstitial doping above the TiO2 valence band maximum. In addition, due to O vacancies and Ti3+ species, donor levels below the conduction band minimum were also created. These levels act as trapping/recombination centers for charge carriers and, therefore, the gain in the visible range due to N doping does not translate to an improved PEC performance by these structural defects. Ultimately, we show that whilst there is a benefit of visible light absorption through N doping in TiO2, the PEC performance of the samples only surpasses pristine TiO2 at relatively high biasing (>0.3 V vs. Ag/AgCl). [ABSTRACT FROM AUTHOR]