Study of Photophysical Properties of Thiol-capped CdS Quantum Dots Doped with Gold Nanoparticles.

In this study, CdS quantum dots (QDs) capped with benzyl mercaptan (thiol) were prepared by microwave irradiation technique. The shape, size, morphology, and spectral properties of thiol-capped CdS QDs were characterized with transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV-vis absorption, and photoluminescence (PL) spectrometry. The photophysical properties of synthesized thiol-capped CdS QDs in the presence of different amounts of gold nanoparticles (AuNPs) have been investigated, exhibiting strong PL quenching. The amount of fluorescence quenching was found to be dependent on the concentration of metal nanoparticles. A Stern-Volmer kinetics model was used to analyze the observed quenching mechanism as a function of the quencher (AuNPs) concentration. The Stern-Volmer plot along with the absorption spectra of thiol-capped CdS QDs in the absence and presence of AuNPs suggest the dynamic (collision) nature of quenching and rule out the possibility of static quenching. The energy transfers from QDs to Au NPs, and hence the quenching of QDs emissions provides new insight into designing novel optical-based materials and the development of FRET-based bionanosensors and phototherapeutic applications.

Photocatalytic activity of green synthesized cadmium sulfide quantum dots on the removal of RhB dye and its cytotoxicity and antibacterial studies.

Presence of inorganic pollutants in water reservoirs is the treating factor for human health and environment. Semiconductor quantum dots (QDs) has been regarded as one of the most efficient nanoparticles for their enhanced photocatalytic activity. Medicinal plants are the safe sources to provide green template for biosynthesis of inorganic nanoparticles such as quantum dots. In order to determine the photocatalytic and biological application of cadmium sulfide quantum dots (CdS QDs), a biosynthesis approach was employed using saffron (Crocus sativus L.) stigma extract as the green reaction substrate. The biosynthesis process was evaluated at different pH condition to obtain the most efficient CdS QDs. Characterization of prepared CdS QDs were determined through UV-vis and fluorescence spectroscopy, FTIR and TEM analysis. The obtained results showed well dsispersed and uniform QDs during green synthesis at the optimum condition. The absorption and electrical properties of green synthesized CdS QDs showed the lowest energy bandgap of 2.4 at pH 11. Photocatalytic activity of CdS QDs on Rhodamine B degradation showed 92% degradation after 80 min under UV light irradiation. The antibacterial and cell cytotoxicity of green synthesized CdS QDs were assayed by disk diffusion and MTT assays respectively. Obtained results showed significant antibacterial effect of CdS QDs against gram-positive and gram-negative bacteria includingB. subtilis(90%) andE. coli(96%) respectively. Moreover, cytotoxicity of prepared CdS Qds through MTT assay indicated 79% apoptosis induction on MCF-7 breast cancer cells.

Flexible photoelectrochemical sensor for highly sensitive chloramphenicol detection based on M-TiO2-CdTe QDs/CdS QDs composite.

Chloramphenicol (CAP) is widely used in the food industry and animal husbandry due to its effective antibiotic effect active against gram-positive and gram-negative microorganisms. However, research shows that it can cause serious adverse reactions and side effects in the human body. In order to effectively monitor the residues of CAP, a novel and simple photoelectrochemical (PEC) sensor for sensitive detection of CAP is fabricated based on M-TiO2-CdTe QDs/CdS QDs composite. The results show that the prepared M-TiO2 not only retains the original morphology and structure of MIL-125(Ti), but also exhibits more abundant pore structure and good photoelectrochemical properties. Compared with M-TiO2, the as-prepared M-TiO2-CdTe QDs/CdS QDs composite exhibits excellent PEC performances including about ninefold enhancement of photocurrent intensity, which is ascribed to the large surface of M-TiO2 and the introduction of CdTe QDs and CdS QDs. Based on the selective inhibitory effect of CAP in the photocurrent intensity of the M-TiO2-CdTe QDs/CdS QDs PEC system, a novel PEC sensor for CAP concentration determination is constructed. The designed PEC sensor demonstrates a linear range from 1 to 140 nmol L-1 with a detection limit of 0.14 nmol L-1 (S/N = 3). Moreover, the method is applied to real milk samples to quantify the CAP residues with spiked recoveries in the range of 96.3-106%, and the possible detection mechanism of the M-TiO2-CdTe QDs/CdS QDs PEC system is also discussed.

An "off-on" electrochemiluminescence aptasensor for determination of lincomycin based on CdS QDs/carboxylated g-C3N4.

A novel electrochemiluminescence (ECL) aptasensor for the determination of lincomycin (LIN) was developed based on CdS QDs/carboxylated g-C3N4 (CdS QDs/C-g-C3N4). CdS QDs/C-g-C3N4 served as the substrate of the aptasensor, and then CdS QDs/C-g-C3N4-modified electrode was incubated with aptamer DNA (Apt-DNA). When the non-specific sites of the electrode surface was blocked by 6-mercaptohexanol, the ferrocene-labeled probe (Fer-DNA) was assembled onto the electrode surface through base complementation with Apt-DNA. In the absence of LIN, the ECL signal was quenched effectively by Fer-DNA and a decreased ECL emission (off state) was acquired. On the contrary, LIN was specifically bond with Apt-DNA, and Fer-DNA was detached from the aptasensor surface because of the deformation of Apt-DNA, resulting in an effectively enhanced ECL signal (on state). The constructed ECL aptasensor exhibited a wide detection range for LIN determination (0.05 ng mL-1-100 µg mL-1) with a low detection limit (0.02 ng mL-1). Importantly, the proposed ECL aptasensor showed outstanding accuracy and specificity for LIN determination, and also provided a potential strategy for other antibiotic determinations.

Excellent fluorescence detection of Cu2+in water system using N-acetyl-L-cysteines modified CdS quantum dots as fluorescence probe.

View of the negative influence of metal ions on natural environment and human health, fast and quantitative detection of metals ions in water systems is significant. Ultra-small grain size CdS quantum dots (QDs) modified with N-acetyl-L-cysteines (NALC) (NALC-CdS QDs) are successfully prepared via a facile hydrothermal route. Based on the changes of fluorescence intensity of NALC-CdS QDs solution after adding metal ions, the fluorescence probe made from the NALC-CdS QDs is developed to detect metal ions in water systems. Among various metal ions, the fluorescence of NALC-CdS QDs effectively quenched by the addition of Cu2+, the probe shows high sensitivity and selectivity for detecting Cu2+in other interferential metal ions coexisted system. Importantly, the fluorescence intensity of NALC-CdS QDs changes upon the concentration of Cu2+, the probe displays an excellent linear relationship between the fluorescence quenching rate and the concentration of Cu2+in ranging from 1 to 25µM. Besides, the detected limitation of the probe towards Cu2+as low as 0.48µM. The measurement of Cu2+in real water sample is also carried out using the probe. The results indicate that NALC-CdS QDs fluorescence probe may be a promising candidate for quantitative Cu2+detection in practical application.

Glutathione Modified Fluorescent CdS QDs Synthesized Using Environmentally Benign Pathway for Detection of Mercury Ions in Aqueous Phase.

An adept, rapid and novel water-soluble glutathione functionalized CdS quantum dots (GSH@CdS QDs) were fabricated using green pathway for sensing of heavy metal contamination prevalent in industrial wastewater. GSH@CdS QDs were facilely synthesized in an aqueous phase reaction and were effectively characterized using FT-IR, XRD, FESEM, HRTEM and EDX techniques. The distinct fluorescence characteristics of GSH@CdS QDs were explored and the QDs showed selective sensitivity towards mercury ions with a low limit of detection of 0.54 nM under optimal conditions. The detailed interaction between GSH@CdS QDs and Hg2+ and the probable fluorescence quenching mechanism were established in this study. In comparison to already reported fluorescent probes, GSH@CdS QDs showed high sensitivity, biocompatibility, long fluorescence stability and convenient removal of mercury ions. Graphical Abstract Facile green route for the fabrication of glutathione capped CdS quantum dots for fluorescence-based detection of toxic Hg2+ ions.

Thioglycolic Acid-Capped CdS Quantum Dots Conjugated to α-Amylase as a Fluorescence Probe for Determination of Starch at Low Concentration.

In the present research, water soluble thioglycolic acid-capped CdS quantum dots (QDs) were synthesized by chemical precipitation method. The characteristics of prepared quantum dots were determined using X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The obtained results revealed that CdS QDs have 5.60 nm crystallite size, hexagonal wurtzite structure and spherical morphology with less than 10 nm diameter. The photoluminescence (PL) spectroscopy was performed in order to study the effect of the presence of starch solutions. Blue emission peaks were positioned at 488 nm and its intensity quenched by increasing the concentration of starch solutions. The result of PL quenches in range of studied concentrations (0-100 ppm) was best described by Michaelis-Menten model. The amount of Michaelis constant (Km) for immobilized α-amylase in this system was about 68.08 ppm which showed a great tendency of enzyme to hydrolyze the starch as substrate. Finally, the limit of detection (LOD) was found to be about 2.24 ppm.

The MTT and Crystal Violet Assays: Potential Confounders in Nanoparticle Toxicity Testing.

The toxicological effects of nanoparticles (NPs) on humans, animals, and environment are largely unknown. Assessment of NPs cytotoxicity depends on the choice of the test system. Due to NPs optical activity and absorption values, they can influence the classical cytotoxicity assay. Eight NPs were spiked in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and crystal violet assays and tested with HaCaT human skin cells. The MTT assay standard curve optical density (OD) measurements were altered by the presence of trisilanol phenyl and trisilanol isooctyl polyhedral oligomeric silsesquioxane particles. The crystal violet standard curve OD measurements were significantly shifted by gold NPs, but they did not affect the MTT assay. Carbon black decreased ODs in the MTT and crystal violet assays and was localized in the cell cytoplasm. These findings strongly indicate that a careful choice of in vitro viability systems is required to avoid flawed measurement of NPs toxicity.

Molecular spectroscopic studies on the interactions of rhein and emodin with thioglycolic acid-capped core/shell CdTe/CdS quantum dots and their analytical applications.

Water-soluble thioglycolic acid (TGA)-capped core/shell CdTe/CdS quantum dots (QDs) were synthesized. The interactions of rhein and emodin with TGA-CdTe/CdS QDs were evaluated by fluorescence and ultraviolet-visible absorption spectroscopy. Experimental results showed that the high fluorescence intensity of TGA-CdTe/CdS QDs could be effectively quenched in the presence of rhein (or emodin) at 570 nm, which may have resulted from an electron transfer process from excited TGA-CdTe/CdS QDs to rhein (or emodin). The quenching intensity was in proportion to the concentration of both rhein and emodin in a certain range. Under optimized conditions, the linear ranges of TGA-CdTe/CdS QDs fluorescence intensity versus the concentration of rhein and emodin were 0.09650-60 µg/mL and 0.1175-70 µg/mL with a correlation coefficient of 0.9984 and 0.9965, respectively. The corresponding detection limits (3σ/S) of rhein and emodin were 28.9 and 35.2 ng/mL, respectively. This proposed method was applied to determine rhein and emodin in human urine samples successfully with remarkable advantages such as high sensitivity, short analysis time, low cost and easy operation. Based on this, a simple, rapid and highly sensitive method to determine rhein (or emodin) was proposed.

Fluorescence quenching investigation on the interaction of glutathione-CdTe/CdS quantum dots with sanguinarine and its analytical application.

Water-soluble glutathione (GSH)-capped core/shell CdTe/CdS quantum dots (QDs) were synthesized. In pH5.4 sodium phosphate buffer medium, the interaction between GSH-CdTe/CdS QDs and sanguinarine (SA) was investigated by spectroscopic methods, including fluorescence spectroscopy and ultraviolet-visible absorption spectroscopy. Addition of SA to GSH-CdTe/CdS QDs results in fluorescence quenching of GSH-CdTe/CdS QDs. Quenching intensity was in proportion to the concentration of SA in a certain range. Investigation of the quenching mechanism, proved that the fluorescence quenching of GSH-CdTe/CdS QDs by SA is a result of electron transfer. Based on the quenching of the fluorescence of GSH-CdTe/CdS QDs by SA, a novel, simple, rapid and specific method for SA determination was proposed. The detection limit for SA was 3.4 ng/mL and the quantitative determination range was 0.2-40.0 µg/mL with a correlation coefficient of 0.9988. The method has been applied to the determination of SA in synthetic samples and fresh urine samples of healthy human with satisfactory results.

Development of reusable electrochemiluminescence sensing microchip for detection of vomitoxin.

In this work, a reusable DNA sensing microchip was developed for detection of vomitoxin (deoxynivalenol, DON) in sorghum using Cd-based core-shell CdSe@CdS quantum dots (QDs) as promising electrochemiluminescence (ECL) emitter. The size-adjustable aqueous phase CdSe@CdS QDs were prepared through homogeneous method, exhibiting strong cathodic ECL emission with a central wavelength of 520 nm in S2O82- coreactant. And gold nanoparticles-modified iron cobalt cyanide hydrate (Fe-Co-Au) was introduced as an accelerator to amplify the ECL signal. ECL signal was quenched after the formation of a double-stranded (dsDNA) S1-S2 by generating an electron transfer system between the emitter and ferrocene (Fc), which are modified on the aptamer (ssDNA S1) and its complement sequence (ssDNA S2), respectively. When the target DON is presence, the aptamer ssDNA S1 will bind to the DON and trigger the unbinding of double strands DNA and the release of the ssDNA S2, thus the signal can be generated. This approach offers a feasible method for the detection of DON within the range of 1 ng/mL to 200 ng/mL.

The important role of EPS in mediated biosynthesis of CdS QDs: Comparative study of EPS-intact and EPS-free.

In this study, we investigated the adsorption of Cd(II) and the biosynthesis of CdS quantum dots (QDs) mediated by cells of sulfate-reducing bacteria before and after the removal of EPS to determine whether EPS or the cell wall plays a major role. Potentiometric titration revealed that the concentration of proton-active binding sites on cells with EPS (EPS-intact) was notably higher than that on cells without EPS (EPS-free) and that the sites were predominantly carboxyl, phosphoryl, hydroxyl, and amine groups. The protein content in EPS-intact cells was higher, and thus the Cd(II) adsorption capacity was stronger. The CdS QDs biosynthesized using EPS-intact possessed better properties, including uniform size distribution, good crystallinity, small particle size, high fluorescence, and strong antimicrobial activity, and the yields were significantly higher than those of EPS-free by a factor of about 1.5-3.7. Further studies revealed that alkaline amino acids in EPS play a major role and serve as templates in the biosynthesis of QDs, whereas they were rarely detected in the cell wall. This study emphasizes the important role of EPS in the bacterial binding of metals and efficient recycling of hazardous waste in water.

Near zero background noise photoelectrochemical sensor based on sensitized signal probe CdS QDs-Dox intercalating double-stranded DNA for PEDV detection.

The highly sensitive detection method for porcine epidemic diarrhea virus (PEDV) is crucial for promptly identify infected pigs and effectively control the spread of the virus. In this study, the sensitization enhancement of organic photoactive material was combined with near zero background noise strategy for PEDV sensitive detection. A novel sensitized signal probe CdS quantum dots-doxycycline complex (CdS QDs-Dox) was prepared serving as a photoelectrochemical (PEC) probe embedded in dsDNA. Subsequently, a thiol-modified upstream inner primer (SH-FIP) was immobilized on the surface of electrode modified with gold nanoparticles (Au NPs) via Au-S bonding, enabling the loop-mediated isothermal amplification (LAMP) of PEDV on the electrode surface. The PEC probe (CdS QDs-Dox) embedded in the amplified dsDNA groove showed an increasing photocurrent signal with the rise of PEDV concentration, establishing a near-zero background LAMP-PEC sensing platform for PEDV detection. Under optimized conditions, the photocurrent intensity of this platform exhibited a good linear relationship with PEDV concentrations ranging from 0.0005 pg/µL to 10 pg/µL, achieving a detection limit as low as 0.17 fg/µL. This platform demonstrates outstanding specificity and sensitivity, thereby enabling precise quantitative detection of diverse pathogens.

Mediated biosynthesis of CdS QDs by EPS from Desulfovibrio desulfuricans sub sp. under carbon source-induced reinforcement.

This paper describes a unique molecular mechanism for the EPS-mediated synthesis of CdS QDs by sulfate-reducing bacteria (SRB) under carbon source-induced reinforcement. Under the induced by carbon sources (HCOONa, CH3COONa and C6H12O6), there was a significant increase in EPS production of SRB, particularly in protein, and the capacity of Cd(II) adsorption was further enhanced. CdS QDs were extracellularly synthesized by adding S2- after Cd(II) adsorption. The results showed that CdS QDs were wrapped or adhered by EPS, and the most significant increase in Arg and Lys among basic amino acids in EPS after HCOONa-induced was 133.34% and 63.89%, respectively. This may serve as a biological template for QD synthesis, producing protein gels with a large number of microcavities and controlling the nucleation of CdS QDs. The highest yield of HCOONa-CdS was achieved after induction, with 23.59 g/g biomass per unit strain, which was 447.34% higher than that before induction and was at a high level in previous studies. The synthesized CdS QDs were uniform in size distribution and had higher luminescence activity and a larger specific surface area than those synthesized by the chemical synthesis route, provides a new idea for EPS treatment of heavy metal wastewater and metal biorecovery.

Architecture design of TiO2 with Co-doped CdS quantum dots photoelectrode for water splitting.

Photoelectrochemical hydrogen production is a critical key to solving the carbon-zero goal of countries due to renewable sources of solar light and combustion products of hydrogen-only water. Here, an architecture design for an n-type nano rosettes-rod TiO2 (RT) surface using CdS and Co-doped CdS quantum dots (QDs) is carried out utilizing the SILAR (simple ionic layer adsorption and reaction) method. Furthermore, the photocatalytic behaviour of Co-doped CdS QDs SILAR cycles deposition is investigated in various cycles, including 5, 8, 10, and 12. The FESEM, Raman XRD, Uv-Vis spectrometer, and vibration modes are used to evaluate the photoelectrode surface structure, crystal structure, and solar light absorption, respectively. FESEM images and XRD pattern revealed successive CdS QDS and Co-doped CdS QDs deposition on the RT boundary and rising SILAR cycles of Co-doped CdS QDs lead to further coverage of RT surface. UV-vis spectrometer indicated shifting solar light absorption to the visible region by applying more SILAR cycles of Co-doped CdS QDs deposition. The electrochemical parameters obtained from EIS showed total polarization resistance (Rp) of the RT electrode dramatically decreased with 10 SILAR cycle Co-doped CdS QDs deposition (5093 Ω cm2 and 617 Ω cm2). Linear sweep voltammetry (LSV) and chronoamperometric photocatalytic performance measurements indicated Co-doped CdS QDs on RT extremely enhanced photoresponse under solar irradiation and 10 SILAR cycle Co-doped CdS QDs improved photocurrent density about fourfold according to blank RT electrode.

T4PPVB-COP composite-driven innovative electrochemiluminescence aptasensor for ultra-sensitive detection of chlorpyrifos.

Herein, an enhanced electrochemiluminescence (ECL) aptasensor driven by a complex (T4PPVB-COP@CdS QDs) with large specific surface area and high stability was constructed for highly sensitive detection of chlorpyrifos (CPF), using electrostatic interactions and signal amplification techniques. In the presence of CPF, the specific binding between the aptamer and CPF caused partial detachment of the aptamer from the sensor, thus restoring the ECL signal. Notably, gold nanoparticles functionalized with streptavidin (SA) as signal enhancers further amplified the ECL signal in specific interactions with aptamers, thereby improving the sensitivity of the assay. Based on this, the proposed ECL aptasensor demonstrated significant detection performance for CPF with a linear range of 1-107 pg/mL and a LOD of 0.34 pg/mL. Furthermore, the feasibility of the ECL aptasensor was validated by the detection and analysis of CPF in real samples, which also provided a broad reference value for bioanalysis.

Design an efficient photoelectrochemical aptasensor for PCB72 based on CdTe@CdS core@shell quantum dots-decorated TiO2 nanotubes.

In this work, an efficient and novel photoelectrochemical (PEC) aptasensor for 2,3',5,5'-tetrachlorobiphenyl (PCB72) was constructed based on CdTe@CdS core@shell quantum dots (CdTe@CdS QDs)-decorated TiO2 nanotubes (TiO2 NTs). CdTe@CdS QDs were prepared by the combination of CdTe and CdS with a proper lattice mismatch. Due to their large band offsets, core@shell QDs can reduce undesirable carrier recombination, significantly improving their charge separation efficiency. Then the synthesized CdTe@CdS QDs were modified on TiO2 NTs (CdTe@CdS QDs/TiO2 NTs) through electrostatic adsorption method. The as-prepared composites exhibit a wide visible light absorption range, good PEC activity and high photoelectric conversion efficiency. Also, the PEC aptasensor prepared via the immobilization of anti-PCB72 aptamer on the composites exhibits outstanding analytical performance with high sensitivity and specificity for PCB72 under visible-light irradiation, achieving a detection limit as low as 0.03 ng/L. It was also applied to detect PCB72 in four different real environmental samples with satisfactory results.

Constructing a CdS QDs/silica gel composite with high photosensitivity and prolonged recyclable operability for enhanced visible-light-driven NADH regeneration.

Visible-light-driven nicotinamide adenine dinucleotide (NADH) regeneration is one of the most effective measures, and cadmium sulfide (CdS) materials are typically used as low-cost photocatalysts. The CdS photocatalysts, however, still suffer from low regeneration efficiency and poor cycle stability. In this work, the CdS quantum dots (QDs) less than 10 nm embedded onto silica gel (CdS QDs/Silica gel) were constructed for visible-light-driven NADH regeneration by a successive ionic layer adsorption reaction and ball milling method. Results demonstrate that the photosensitivity of the CdS QDs/Silica gel composite was 31 times higher than that of the bulk CdS. Moreover, the conduction band (CB) edge of the CdS QDs/Silica gel composite is -1.34 eV, which is more negative 0.5 eV than that of the bulk CdS. The obtained CdS QDs/Silica gel composites showed the highest NADH regeneration yields of 68.8% under visible-light (LED, 420 nm) illumination and can be reused for over 40 cycles. Finally, the bioactivity of NADH toward enzyme catalysis is further confirmed by the hydrogenation of benzaldehyde to benzyl alcohol catalyzed with an alcohol dehydrogenase as enzyme catalysis.

Ultrathin MXene nanosheet-based TiO2/CdS heterostructure as a photoelectrochemical sensor for detection of CEA in human serum samples.

To develop highly accurate and ultrasensitive strategies is of great importance for the clinical measurement, in particular, the detection of cancer biomarkers. Herein, we synthesized an ultrasensitive TiO2/MXene/CdS QDs (TiO2/MX/CdS) heterostructure as a photoelectrochemical immunosensor, which favors energy levels matching and fast electron transfer from CdS to TiO2 in the help of ultrathin MXene nanosheet. Dramatic photocurrent quenching can be observed upon incubation of the TiO2/MX/CdS electrode by Cu2+ solution from 96-well microplate, which caused by the formation of CuS and subsequent CuxS (x = 1, 2), reducing the absorption of light and boosting the electron-hole recombination upon irradiation. As a result, the as-prepared biosensor demonstrates a linearly increased photocurrent quenching percentage (Q%) value with CEA concentration ranging from 1 fg/mL to 10 ng/mL, as well as a low detection limit of 0.24 fg/mL. Benefit from its excellent stability, high selectivity and good reproducibility of as-prepared PEC immunosensor, we believe that this proposed strategy might provide new opportunities for clinical diagnosis of CEA and other tumor markers.

Designing and fabricating a CdS QDs/Bi2MoO6 monolayer S-scheme heterojunction for highly efficient photocatalytic C2H4 degradation under visible light.

Achieving efficient photocatalytic degradation of atmospheric volatile organic compounds (VOCs) under sun-light is still a significant challenge for environmental protection. The S-scheme heterojunction with its unique charge migration route, high charge separation rate and strong redox ability, has great potential. However, how to regulate interfacial charge transfer of the S-scheme heterojunction is of significant importance. Here, density functional theory (DFT) calculations were first conducted and predicted that an S-scheme heterojunction could be formed in the CdS quantum dots/Bi2MoO6 monolayer system. Subsequently, this novel heterojunction is constructed by in-situ hydrothermal synthesis of CdS quantum dots on monolayer Bi2MoO6. Under visible-light, this novel S-scheme system gives a high-efficiency photocatalytic degradation rate (6.04 × 10-2 min-1) towards C2H4, which is 30.3 times higher than that of pure CdS (1.99 × 10-3 min-1) and 41.7 times higher than pure Bi2MoO6 (1.45 × 10-3 min-1). Strong evidence for the S-scheme charge transfer path is provided by in-situ XPS, PL, TRPL and EPR.