Кафедра биофизики

Ag₂MoO₄ shows low photocatalytic activity under visible light. It would be interesting to develop Ag₂MoO₄-based composite/heterojunction photocatalysts working efficiently under visible light. Herein, novel Ag/AgCl/Ag₂MoO₄ composites were obtained via photoreduction of AgCl/Ag₂MoO₄ composites prepared by sequential precipitation. The composition, morphologies, and optical properties of the samples were studied via various characterization techniques. Photocatalytic degradation of rhodamine B (RhB), methylene blue (MB), methyl orange (MO), norfloxacin (NOF), and tetracycline hydrochloride (TC) solutions was conducted under visible-light irradiation. An optimal Ag/AgCl/Ag₂MoO₄ catalyst showed much higher photocatalytic activity than Ag₂MoO₄, and it also showed reasonably fine recyclability. Through radical-capturing experiments, photogenerated holes (h⁺) were determined to be the main active species whereas hydroxyl radicals (OH) were found to play a secondary role in photocatalysis. Possible photocatalytic mechanisms were proposed.

Ag/AgCl/Ag₂MoO₄ heterojunctions are effective photocatalysts.

Ciprofloxacin (CIP) is a widely used third generation fluoroquinolone antibiotics, and has been often detected in wastewater treatment plants. Finding an effective way to remove them from wastewater is of great concern. Ultraviolet (UV)/chlorine advanced oxidation process (AOP) has many advantages in micropollutant removal. In this study, CIP degradation in UV/chlorine process was investigated. Only 41.2% of CIP was degraded by UV photolysis and 30.5% by dark chlorination in 30 min, while 98.5% of CIP was degraded by UV/chlorine process in 9 min. HCO₃⁻ had markedly inhibition, NO₃⁻ and SO₄^2- had slight inhibition, and Cl⁻ had a marginal inhibition on CIP degradation in UV/chlorine system. The degradation of CIP in UV/chlorine process was mainly attributed to the attack of reactive species. The relative contributions of hydrated electrons (e_aq), hydroxyl radicals (HO), chlorine atoms (Cl), and UV photolysis were investigated. Under neutral condition in aqueous solution, CIP degradation had highest pseudo first-order reaction rate constant, in which e_aq had the highest contribution, followed by Cl, HO, and UV photolysis. The intermediates and byproducts were identified and the degradation pathway was proposed. The total organic chlorine (TOCl) and biotoxicity were further assessed. CIP and natural organic matters (NOMs) were removed efficiently in real water. UV/chlorine showed the potential for the wastewater treatment containing CIP.

Due to clinical importance, detection of dopamine by using easy and rapid method is still ongoing challenge. Here we present a simple and quite efficient method for dopamine (DA) detection in alkalescent medium using in situ prepared Ru(II) complex and sodium dodecyl benzyl sulfonate (SDBS) as highly luminescent luminophore. The luminescence enhancement in the Ru(II) complex (Ru-CIP) has been observed in the miceller medium formed by SDBS. The capability to successively quench the luminescence intensity has been tested for variety of molecules and only dopamine as analyte found to be able to quench luminescence effectively. Hence selective quenching of luminescence by dopamine was used as a tool to detect dopamine and two linear concentration ranges has been established from 0.1 μM to 1μM and from 2 μM to 10 μM with limit of detection (LOD) is 6.6 nM (S/N = 3). Spectral evidence showed that luminescence quenching mechanism arose via Forster resonance energy transfer (FRET) among oxidized DA (i.e. DA quinone) and in situ generated Ru-CIP and SDBS assembly. Due to ultra sensitivity and high selectivity of the prescribed (Ru-CIP-SDBS) luminescent probe has a strong potential for practical analytical application in clinical diagnosis.

Highly ordered porous ZnO inverse opal (ZnO-IO) was manufactured via an auto-forced impregnation approach using self-assembled polystyrene (PS) spheres as colloidal crystal templates. ZnO-IO with deposited silver nanoparticles (Ag/ZnO-IO) was successfully fabricated based on a simple yet efficient photoassisted reduction route using an AgNO₃ ethanol-water mixed solution at room temperature and characterized properly by various analytical techniques. Upon visible-light irradiation, the Ag/ZnO-IO composite catalyst exhibited higher photocatalytic activity than pristine ZnO-IO regarding the decolorization of rhodamine B (RhB) in aqueous solution. Such a significant photoactivity improvement was predominantly attributed to surface plasmon resonance (SPR) effect of metallic silver nanoparticles, which could enhance the harvesting of visible light and improve the segregation and transfer of photoinduced charge carriers. The stability of the Ag/ZnO-IO photocatalyst was also investigated with respect to the decomposition of RhB. Furthermore, a plausible degradation mechanism of the Ag/ZnO-IO sample in the course of photocatalytic oxidation of organic pollutants was tentatively put forward from active species trapping experiments. The work reported here may help further progress in design and construction of promising visible-light-induced photocatalysts.

CdS quantum dots modified g-C₃N₄/ZnO nanorods core/shell structured photoanode has been designed and hydrothermally grown on electrically conductive fluorine-doped tin oxide substrate (FTO). The CdS/g-C₃N₄/ZnO heterojunction is sequentially fabricated by one-step hydrothermal method in the g-C₃N₄ aqueous solution and successive ionic layer adsorption-reaction method. It has been shown that the interface of ternary semiconductors plays a key role in enhancement of photoelectrochemical activity for water splitting under simulated sunlight illumination. The increase of photocurrent is attributed to the redshift of absorption edge of CdS/g-C₃N₄/ZnO towards visible light in comparison with CdS/ZnO, g-C₃N₄/ZnO and pristine ZnO. Moreover, the heterojunction between CdS, g-C₃N₄ and ZnO can significantly enhance the separation efficiency of photogenerated charge carriers. In addition, g-C₃N₄ can serve as holes receptor of CdS and act as a protective layer which will reduce the photocorrosion of CdS and improve the stability of photoanode. The optimized of photoanode exhibits an improved PEC performance under visible light irradiation. This work provides a promising strategy for developing ternary photoanode with high stability and efficiency.

In this work, the synthesis of ATiO₃ (A = Zn, Cd, Pb) perovskite materials by solid-state (SS) and solvo-combustion (SC) reactions were performed in order to investigate the influence of the physicochemical properties obtained by the use of different preparation method on the photocatalytic performance for hydrogen generation. The photocatalytic water splitting reaction experiments were carried out with deionized water and the prepared materials under UV light (254 nm) illumination. A series of photoelectrochemical measurements were performed to obtain information about the charge recombination process, the response of the (photo)electrocatalytic activity and the information related to the partial stability of the synthesized materials. The open circuit potential (OCP) and the transient photocurrents revealed the characteristic n-type semiconductor behavior for ZnTiO₃ and p-type for CdTiO₃ and PbTiO₃. The CdTiO₃ and PbTiO₃ materials prepared by solid-state reaction exhibited superior photocatalytic activity compared to the samples prepared by solvo-combustion reaction. This behavior is associated to uniform particle size which allowed a better photogenerated charge transfer as it was corroborated by photoluminescence and Nyquist analysis. In the case of ZnTiO₃ material, the sample synthesized by the solvo-combustion method showed the highest photocatalytic activity (94 μmol H₂) that is associated to the traces of TiO₂ acting as a co-catalyst, for an enhanced charge transfer and decreasing the electron-hole recombination favorable for hydrogen evolution.

Polymers are extensively applied to protect fluorescent molecules and nanomaterials against photooxidation. However, the chemical conjugation of nanomaterials such as semiconductor quantum dots to polymers is important for long-term stability, avoiding aggregation, and finding device application of polymer-nanomaterial hybrids. The chemical conjugation of polymers provides quantum dots with superior physical stability than those prepared by physical blending. Here, we report a single step conjugation of an environment-friendly, biocompatible polymer to the surface of CdSe/ZnS core shell quantum dots. The direct conjugation of a polymer to the quantum dot surface helps us to avoid phase segregation of quantum dots and the polymer host, without adversely affecting the photoluminescence properties of quantum dots. Here, N-isopropyl acrylamide-maleic anhydride random copolymer is directly attached to the core-shell quantum dots through the amide linkage. The amino-functionalized quantum dots are employed in the conjugation reaction with maleic anhydride units in the polymer. Quantum dots in the resultant conjugate retain resistance to photooxidation in the solution phase or film state. The properties of the conjugate, including photostability, are studied using fluorescence spectroscopy and microscopy methods.

The DNA targeting nature of thiosemicarbazone based Schiff bases has provided a great platform for synthesis of its novel derivatives and their progressive exploitation as therapeutic agents. The present work embodies the synthesis of a potential bioactive pharmacophore thiosemicarbazone Schiff base derivative viz. (E)-1-(4-(diethylamino)-2-hydroxybenzylidene)-4,4-dimethyl-thiosemicarbazide (DAHTS) along with its structural characterisation by ¹H NMR, FT-IR, mass spectrometry and single crystal X-ray diffraction analysis. Identification of ground and excited state geometries of the synthesized DAHTS molecule, with possibility of solvent dependent excited state intramolecular proton transfer (ESIPT) reaction have also been unveiled using electronic absorption, steady state and time resolve fluorescence spectroscopic techniques. The ESIPT process has further been validated by Density functional theory (DFT) and Time-dependent density functional theory (TD-DFT) based quantum chemical calculations. Spectral and single crystal XRD analysis indicate existence of intramolecular H-bonding between phenolic hydrogen and azomethine nitrogen in DAHTS molecule that stabilises the normal enol-imine (E) form in the ground state of DAHTS molecule. The synthesised molecule exhibits dual emission in non-polar hexane. On photoexcitation, DAHTS possibly undergoes excited state intramolecular proton transfer (ESIPT) reaction to produce keto-amine species (K) in nonpolar solvents. Frontier molecular orbital (FMO) analysis indicates that although intramolecular proton transfer reaction possibly might not occur in ground state of DAHTS but it may become feasible in the lowest singlet excited state of enol-imine form (E^*) to produce its excited tautomer (K^*). The lower energy difference (1.17 kcal/mol) between excited enol-imine (E^*) and keto-amine (K^*)form, obtained from Potential energy curve (PEC) corroborates the observed dual emission of the synthesised fluorophore. DFT and TD-DFT studies also aid in visualization of electronic charge displacement inside the molecular framework of DAHTS; which in turn suggests partial increase of Mulliken charge of azomethine nitrogen that further makes way for intramolecular proton transfer in the excited state. The amalgamated spectroscopic and theoretical research described herein, delivers enormous information about comprehensive synthetic and photophysical aspects of potential bioactive thiosemicarbazone derivatives for further utilization in medicinal chemistry research.

The paper considers novel behavior of molecule photodissociation probability under the influence of electromagnetic pulses in the femtosecond range. The study considers as examples the photodissociation of methane, ethylene and water molecules. The probability of photodissociation under radiation is calculated as a function of pulse duration for different values of the carrier frequency. In the limit of long pulses, the process probability, as expected, increases linearly with pulse duration. However, the dependence of photodissociation probability on pulse duration for the pulses in the femto- and sub-femtosecond ranges exhibits strong nonlinearity. The nonmonotonic effects occur at carrier pulse frequencies corresponding to the minimum values of the photodissociation cross-section. It is remarkable that the observed nonlinearity is described in the frame of the first order of perturbation theory for relatively small field amplitude and unrelated to the strong field effects. The proposed method of describing photodissociation is quite general and suitable for studying such processes under the influence of electromagnetic pulses of any duration.

Efficient and cost-effective SnO₂/g-C₃N₄ photocatalysts have been developed via simple wet chemical method using urea as a g-C₃N₄ precursor. The effect of different mass ratios (SnO₂: g-C₃N₄ = 1-5:5-1) on the synthesized photocatalysts was investigated. XRD, SEM/EDS, FE-SEM, HR-TEM and XPS analysis techniques were used for the characterization of adsorbents which also confirmed the strong bonding of SnO₂ with g-C₃N₄. The photocatalytic degradation process has been chosen for the treatment of synthetic wastewater containing organic and textile dyes (Rhodamine-B, RhB, and Remazol Brilliant Red X-3BS, RbX).The synthesized photocatalysts exhibited excellent degradation efficiency for the pollutants due to the synergistic effect of g-C₃N₄ and SnO₂. Kinetic studies for RhB degradation revealed the highest rate constant (0.0485 min⁻¹) for the SnO₂/g-C₃N₄-1:1 catalyst, which was ca. 33 times higher than that of pure g-C₃N₄. Furthermore, photocatalysts exhibited high durability and stability during five recycling experiments. In addition, a mechanism for the photocatalytic degradation of pollutants over SnO₂/g-C₃N₄ via photocatalysis has also been explained.