Time-dependent Spectroscopy Research Articles

Spontaneous sieving of water from ethanol using angstrom-sized nanopores.

Ethanol is widely used as a precursor in products ranging from drugs to cosmetics. However, distillation of ethanol from aqueous solution is energy intensive and expensive. Here, we show that angstrom-sized nanopores with precisely controlled pore sizes can spontaneously remove water from ethanol-water mixtures through molecular sieving at room temperature and pressure. For small-diameter nanotubes, water-filling is observed, but ethanol is completely excluded, as evidenced by time-dependent density functional theory (TD-DFT) calculations and spectroscopy measurements. Potential of mean force calculations were performed to determine how the free energy barriers for water and ethanol-filling of the nanotubes change with increasing pore size. Water/ethanol selectivity ratio reaching as high as 6700 is observed with a (6,4) nanotube, which has a pore size of 0.204 nm. This selectivity vanishes as the pore size increases beyond 0.306 nm. These findings provide insights that may help realize energy efficient molecular sieving of ethanol and water.

A zinc-containing porphyrin aluminum MOF in sorption of diethyl sulfide vapor: mechanistic experimental and computational study.

We report a mechanistic study of the interactions in the sorption of volatile organic sulfur compound (VOSC) diethyl sulfide (DES) by zinc porphyrin aluminum MOF (actAl-MOF-TCPPZn) compound 3. First, interactions were studied under dynamic conditions with the vapor of DES in flowing air, using in situ time-dependent ATR-FTIR spectroscopy in a controlled atmosphere with a new facile spectroscopic mini-chamber. The first binding site includes μ(O-H) and COO- groups as detected by characteristic peak shifts. Control experiments with a model compound, which lacks porosity and these groups, show no peak shifts. An additional insight was obtained by DFT computations using small clusters. The kinetics of sorption of DES by compound 3 is of the Langmuir adsorption model and pseudo-first order with rate constant robs = 0.442 ± 0.056 min-1. Sorption of DES under static conditions in saturated vapor results in stoichiometric adsorption complex [Al-MOF-TCPPZn]1(DES)4 characterized by spectroscopic, structural and gravimetric methods; the adsorbed amount is very high (381 mg g-1 sorbent). The repetitive sorption and desorption of DES are conducted, with facile regeneration. Finally, the mechanistic details were determined by Raman and photoluminescence (PL) spectroscopy using a confocal Raman microscope. Photoexcitation of compound 3 at 405 nm into the Soret band of the metalloporphyrin linker shows the characteristic PL peaks of Q-bands: the purely electronic Q(0-0) and first vibronic Q(0-1) bands. Upon interaction with DES, preferential quenching of PL from the Q(0-0) band occurs with a significant increase of the signal of the vibronic Q(0-1) band, reflecting bonding to the metalloporphyrin ring. Compound 3 is of interest to mechanistic studies of VOSCs, their removal from air, and optical chemo-sensing.

Thickness- and Twist-Angle-Dependent Interlayer Excitons in Metal Monochalcogenide Heterostructures.

Interlayer excitons, or bound electron-hole pairs whose constituent quasiparticles are located in distinct stacked semiconducting layers, are being intensively studied in heterobilayers of two-dimensional semiconductors. They owe their existence to an intrinsic type-II band alignment between both layers that convert these into p-n junctions. Here, we unveil a pronounced interlayer exciton (IX) in heterobilayers of metal monochalcogenides, namely, γ-InSe on ε-GaSe, whose pronounced emission is adjustable just by varying their thicknesses given their number of layers dependent direct band gaps. Time-dependent photoluminescense spectroscopy unveils considerably longer interlayer exciton lifetimes with respect to intralayer ones, thus confirming their nature. The linear Stark effect yields a bound electron-hole pair whose separation d is just (3.6 ± 0.1) Å with d being very close to dSe = 3.4 Å which is the calculated interfacial Se separation. The envelope of IX is twist-angle-dependent and describable by superimposed emissions that are nearly equally spaced in energy, as if quantized due to localization induced by the small moiré periodicity. These heterostacks are characterized by extremely flat interfacial valence bands making them prime candidates for the observation of magnetism or other correlated electronic phases upon carrier doping.

Insights into Cationic Transference Number Values and Solid Electrolyte Interphase Growth in Liquid/Solid Electrolytes for Potassium Metal Batteries.

Liquid/solid battery electrolytes make separators dispensable and enable a high cationic transference number with liquid-like room temperature ionic conductivity. This work gives insights into electrochemical behavior (galvanostatic polarization and time-dependent impedance spectroscopy) of liquid/solid electrolytes containing potassium salts in battery cells enclosing potassium metal anodes. Very high potassium transference numbers (t K = 0.88) are observed in carbonate-based electrolytes, linked with long-term mechanical instability of the solid electrolyte interphase on the potassium anode. In the case of glyme-based electrolytes, electrochemical behavior indicates the existence of the highly porous solid electrolyte interphase and additional surface porosity of the potassium electrode.

ZnO/Zn(OH)2 nanoparticles and self-cleaning coatings for the photocatalytic degradation of organic pollutants

Zinc oxide (ZnO) nanostructures have emerged as efficient heterogeneous photocatalysts for the degradation of organic pollutants in aqueous solutions and industrial wastewaters. In this work, a simple and effective method is reported for the synthesis of zinc oxide/zinc hydroxide (ZnO/Zn(OH)2) hybrid nanoparticles using a mineral acid to enhance the photocatalytic activity of ZnO. Infrared spectroscopy reveals the presence of hydroxyl groups in ZnO/Zn(OH)2 nanoparticles. X-ray diffraction shows the formation of hexagonal wurtzite ZnO nanoparticles, which retain their wurtzite structure after acid treatment but additional diffractions for Zn(OH)2 are also recorded. The optical bandgap of resulting ZnO and ZnO/Zn(OH)2 nanoparticles is reduced to 3.05 and 3.08 eV, respectively. In the initial photocatalysis experiments, ZnO/Zn(OH)2 nanoparticles exhibit 3.5-times improved degradation and removal of sunset yellow dye, a model organic pollutant, from deionized water compared to pristine ZnO nanoparticles. Hence, for further studies, ZnO/Zn(OH)2 coatings are fabricated on glass slides with a uniform surface morphology as shown by the atomic force microscopy. The time-dependent UV-visible spectroscopy reveals the photocatalytic degradation of sunset yellow over the surface of ZnO/Zn(OH)2 coatings. The degradation reaction follows the pseudofirst-order mechanism with a rate constant of 2.9 × 10–2 min−1. The recyclability and stability experiments reveal the retention of appreciable photocatalytic activity of ZnO/Zn(OH)2 coatings (with >92% degradation efficiency after six successive cycles). The results are compared with recent examples from the pertinent literature. The surface hydroxyl groups on ZnO/Zn(OH)2 nanoparticles and bandgap lowering enhance the anchoring of dye molecules and electron transfer reactions.

Graphene/SOI-based self-powered Schottky barrier photodiode array

We have fabricated a four-element graphene/silicon on insulator (SOI) based Schottky barrier photodiode array (PDA) and investigated its optoelectronic device performance. In our device design, monolayer graphene is utilized as a common electrode on a lithographically defined linear array of n-type Si channels on a SOI substrate. As revealed by wavelength resolved photocurrent spectroscopy measurements, each element in the PDA structure exhibited a maximum spectral responsivity of around 0.1 A/W under a self-powered operational mode. Time-dependent photocurrent spectroscopy measurements showed excellent photocurrent reversibility of the device with ∼1.36 and ∼1.27 μs rise time and fall time, respectively. Each element in the array displayed an average specific detectivity of around 1.3 × 1012 Jones and a substantially small noise equivalent power of ∼0.14 pW/Hz−1/2. The study presented here is expected to offer exciting opportunities in terms of high value-added graphene/Si based PDA device applications such as multi-wavelength light measurement, level metering, high-speed photometry, and position/motion detection.

Thinfilm Hybrid Nanostructures: A Perspective to Subcycle Opto-Electronics and Coherent Control

In this article we present a theoretical investigation of gold-silica-silver nanostructures and their optical properties with respect to ultrafast electronic applications and coherent control by tailored optical fields. We found a remarkable sensitive behavior to the carrier envelope phase (CEP) of the driving laser pulses in the coupling of surface and bulk plasmons leading to a superposition of distinct modes with a time-dependent amplitude structure. Furthermore, we show a rather complex temporal evolution of plasmonic surface modes. Our results suggest the potential for coherent control of the time-dependent resonant coupling between surface and volume modes by tailored laser pulses and foster the field of time-dependent spectroscopy of thinfilm hybrid nanostructures with single layer thickness down to the two-dimensional limit.

Donor–Acceptor Stenhouse Adduct‐Polydimethylsiloxane‐Conjugates for Enhanced Photoswitching in Bulk Polymers

Donor-acceptor Stenhouse adducts (DASAs) are a rapidly emerging class of visible light-activated photochromes and DASA-functionalized polymers hold great promise as biocompatible photoresponsive materials. However, the photoswitching performance of DASAs in solid polymer matrices is often low, particularly in materials below their glass transition temperature. To overcome this limitation, DASAs are conjugated to polydimethylsiloxanes which have a glass transition temperature far below room temperature and which can create a mobile molecular environment around the DASAs for achieving more solution-like photoswitching kinetics in bulk polymers. The dispersion of DASAs conjugated to such flexible oligomers into solid polymer matrices allows for more effective and tunable DASA photoswitching in stiff polymers, such as poly(methyl methacrylate), without requiring modifications of the matrix. The photoswitching of conjugates with varying polymer molecular weight, linker type, and architecture is characterized via time-dependent UV-vis spectroscopy in organic solvents and blended into polymethacrylate films. In addition, DASA-functionalized polydimethylsiloxane networks, accessible via the same synthetic route, provide an alternative solution for achieving fast and efficient DASA photoswitching in the bulk owing to their intrinsic softness and flexibility. These findings may contribute to the development of DASA-functionalized materials with better tunable, more effective, and more reversible modulation of their optical properties.

Static and Dynamic Disorder of Charge Transfer States Probed by Optical Spectroscopy

AbstractSince the key role of charge transfers (CT) states has been identified for organic solar cells (OSCs), research into their properties is a timely topic. Conventionally, their absorption and emission spectra are described in terms of Marcus’ electron transfer theory. This is a single site approach with the essential parameter being the reorganization energy. Thus, it ignores ensemble effects, notably the role of static disorder that is inevitably present in a spin‐coated OSC film. Here time dependent photoluminescence spectroscopy is applied on blends of the polymeric donor MeLPPP with either the non‐fullerene acceptor SF‐PDI2 or with PC61BM within a temperature range from 295 to 5 K. The authors monitor how initially excited singlet states are converted to emissive CT states. Concomitantly, emission from residual singlets on the acceptor is observed rather than hybrid CT‐states. The role of spectral diffusion in this process is discussed. From the temperature and time dependent linewidths of absorption, fluorescence, and CT emission, the static and dynamic contributions to the total disorder are inferred. In both blends, at 295 K, the contribution of static disorder is comparable to the dynamic disorder.

Porphyrin aluminum MOF with ultra-high water sorption capacity: In-situ time-dependent ATR-FTIR spectroscopy and gravimetry to study mechanism of water bonding and desorption

Porphyrin-based aluminum metal-organic framework Al-MOF-TCPPH2 compound 1 is synthesized and activated to obtain compound 2. Its purity is demonstrated by ATR-FTIR spectroscopy, and spectral assignments of specific functional groups within the TCPP linker are provided as potential binding sites for adsorbate. Compound 2 reversibly sorbs and desorbs the significant amount of water (up to 50 wt. %) from humidified air and it forms the hydrated compound 3. Compound 3 contains as many as up to 25 water molecules bonded to several distinct groups in structural unit of Al-MOF-TCPPH2. In compound 3 water exists as small ice-like nanoclusters, in which water molecules are three-coordinated to other water molecules and the fourth bond is coordination of the surface water molecules d-H via their H atoms to functional groups in Al-MOF-TCPPH2. Further, water is bonded to the framework via the NH group, the carboxylate anion −COO−, phenyl group of the linker and the μ−OH group. Compound 3 facilely loses most of its water to air at moderate ambient relative humidity 45 %. During water loss, small ice-like nanoclusters with d-H waters are progressively transformed to those with four-coordinated waters denoted s-4. Chemical kinetics of water loss (desorption) by compound 3 has been investigated by in-situ time-dependent gravimetric method under ambient conditions. Kinetics of reaction of water desorption follows the pseudo-first order rate law with rate constant. The in-situ time-dependent ATR-FTIR spectroscopy demonstrates the capability to facilely identify multiple sorption sites of adsorbate to the MOF. Moreover, the combination of in-situ time-dependent ATR-FTIR spectroscopy and gravimetry forms a new unique experimental approach with significant potential. This approach can be facilely and successfully utilized in studies of mechanisms of reactions of sorption and desorption, determination of stoichiometry of complexes of sorbents with adsorbate, and studies of chemical kinetics of various solid-gas reactions under ambient and controlled environments.

Uniform supersonic flow sampling for detection by chirped-pulse rotational spectroscopy.

Chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy is a powerful near-universal detection method finding application in many areas. We have previously coupled it with supersonic flows (CPUF) to obtain product branching in reaction and photodissociation. Because chirped-pulse microwave detection requires monitoring the free induction decay on the timescale of microseconds, it cannot be employed with good sensitivity at the high densities achieved in some uniform supersonic flows. For application to low-temperature kinetics studies, a truly uniform flow is required to obtain reliable rate measurements and enjoy all the advantages that CP-FTMW has to offer. To this end, we present a new setup that combines sampling of uniform supersonic flows using an airfoil-shaped sampling device with chirped-pulse mmW detection. Density and temperature variations in the airfoil-sampled uniform flow were revealed using time-dependent rotational spectroscopy of pyridine and vinyl cyanide photoproducts, highlighting the use of UV photodissociation as a sensitive diagnostic tool for uniform flows. The performance of the new airfoil-equipped CPUF rotational spectrometer was validated using kinetics measurements of the CN + C2H6 reaction at 50K with detection of the HCN product. Issues relating to product detection by rotational spectroscopy and airfoil sampling are discussed. We show that airfoil sampling enables direct measurements of low temperature reaction kinetics on a microsecond timescale, while rotational spectroscopic detection enables highly specific simultaneous detection of reactants and products.

Visualizing spinon Fermi surfaces with time-dependent spectroscopy

Quantum simulation experiments have started to explore regimes that are not accessible with exact numerical methods. To probe these systems and enable new physical insights, the need for measurement protocols arises that can bridge the gap to solid-state experiments, and at the same time make optimal use of the capabilities of quantum simulation experiments. Here we propose applying time-dependent photoemission spectroscopy, an established tool in solid-state systems, in cold atom quantum simulators. Concretely, we suggest combining the method with large magnetic field gradients, unattainable in experiments on real materials, to drive Bloch oscillations of spinons, the emergent quasiparticles of spin liquids. We show in exact diagonalization simulations of the one-dimensional $t\text{\ensuremath{-}}J$ model with a single hole that the spinons start to populate previously unoccupied states in an effective band structure, thus allowing us to visualize states invisible in the equilibrium spectrum. The dependence of the spectral function on the time after the pump pulse reveals collective interactions among spinons. In numerical simulations of small two-dimensional systems, spectral weight appears at the ground-state energy at momentum $\mathbf{q}=(\ensuremath{\pi},\ensuremath{\pi})$, where the equilibrium spectral response is strongly suppressed up to higher energies, indicating a possible route toward solving the mystery of the Fermi arcs in the cuprate materials.

Growth Dynamics of Colloidal Silver-Gold Core-Shell Nanoparticles Studied by In Situ Second Harmonic Generation and Extinction Spectroscopy.

The in situ growth dynamics of colloidal silver–gold core–shell (Ag@Au CS) nanoparticles (NPs) in water are monitored in a stepwise synthesis approach using time-dependent second harmonic generation (SHG) and extinction spectroscopy. Three sequential additions of chloroauric acid, sodium citrate, and hydroquinone are added to the silver nanoparticle solution to grow a gold shell around a silver core. The first addition produces a stable urchin-like surface morphology, while the second and third additions continue to grow the gold shell thickness as the surface becomes more smooth and uniform, as determined using transmission electron microscopy. The extinction spectra after each addition are compared to finite-difference time-domain (FDTD) calculations, showing large deviations for the first and second additions due to the bumpy surface morphology and plasmonic hotspots while showing general agreement after the third addition reaches equilibrium. The in situ SHG signal is dominated by the NP surface, providing complementary information on the growth time scales due to changes to the surface morphology. This combined approach of synthesis and characterization of Ag@Au CS nanoparticles with in situ SHG spectroscopy, extinction spectroscopy, and FDTD calculations provides a detailed foundation for investigating complex colloidal nanoparticle growth mechanisms and dynamics in developing enhanced plasmonic nanomaterial technologies.

A new approach to study the long-term urban heat island evolution using time-dependent spectroscopy

This study presents a new approach to study long-term temperature and urban heat island intensity (UHII) evolution based on the method of time-depended spectroscopy on the example of Moscow megacity. In contrast to standard spectroscopy, this method allows analyzing the changes of the amplitude Fourier spectrum of the time series along the study period. Applying the novel method to the air temperature series for the period of 1977-2020, we demonstrate that ongoing changes of the mean temperature and UHII are accompanied by the changes of their spectra, including the spectral amplitudes corresponding to diurnal, annual and synoptic-scale oscillations. Such changes are complex, often non-linear, and seasonally asymmetric. Steady upward trends are found for summer season, for the spectral amplitudes of diurnal temperature and UHII oscillations, and synoptic-scale UHII oscillations. Spectral amplitudes of annual temperature and UHII oscillations experiences V-shaped dynamics with an increase since 1990th. For UHII such pattern reflects a switch between regimes with wintertime or summertime UHI maximum. Presented results provides an evidence that observed intensification of Moscow's UHI is forced not only by urban growth, but also by changing background meteorological conditions, which are becoming more favorable to UHI appearance in summer and less favorable in winter.

Photo-Induced Cluster-to-Cluster Transformation of [Au37-xAgx(PPh3)13Cl10]3+ into [Au25-yAgy(PPh3)10Cl8]+: Fragmentation of a Trimer of 8-Electron Superatoms by Light.

We present the photoinduced size/structure transformation of [Au37-xAgx(PPh3)13Cl10]3+ (M37) into [Au25-yAgy(PPh3)10Cl8]+ (M25) cluster. Single-crystal X-ray diffraction revealed that M37 has a tri-icosahedron M36 metal core assembled via the fusion of three Au7Ag6 icosahedrons in a cyclic fashion and that the M36 core is further protected by phosphine and chloride ligands. The M37 cluster is found to be highly sensitive toward ambient light, and the M37 → M25 transition is observed with 530 nm irradiation, monitored by time-dependent UV-vis spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and femtosecond transient absorption spectroscopy. Linear-response time-dependent DFT calculations indicated that the strong absorption of the M37 cluster close to 500 nm induces an antibonding-type configuration in the induced electron density within the plane of the three 8-electron systems, possibly promoting dissociation of one of the 8-electron superatoms. This theoretical result supports the experimental observation of the sensitivity of the M37 → M25 transition to 530 nm irradiation.

Hygroscopic metal-organic framework MIL-160(Al): In-situ time-dependent ATR-FTIR and gravimetric study of mechanism and kinetics of water vapor sorption

Metal-organic frameworks (MOFs) are advanced highly porous coordination polymers of high interest to separations, environmental remediation, catalysis, and biomedicine. While many MOFs are unstable in water and aqueous solutions, aluminum MOFs (Al-MOFs) offer an unprecedented stability. First, we synthesize unusual highly hygroscopic Al-MOF MIL-160(Al), purify it and assign FTIR peaks to specific groups as potential water binding sites. Further, we introduce a novel method of in-situ time-dependent ATR-FTIR spectroscopy to detect specific binding sites in MIL-160(Al) and investigate the progress of reaction. Specifically, we combine in-situ time-dependent ATR-FTIR spectroscopy with using water as “spectroscopic probe” to determine binding sites in MIL-160(Al) and their evolution during the reaction. The in-situ time-dependent ATR-FTIR spectra provide evidence of water bonding to: the μ-OH group, the carboxylate anion COO– in 2,5-FDCA2- linker, oxygen atom in the furan ring of the linker, and the C–C and C–H bonds of the furan ring of the linker. Then, we conduct mechanistic and kinetic study of sorption of water vapor on MIL-160(Al) in air using the combination of two complementary in-situ time-dependent methods: the ATR-FTIR spectroscopy and gravimetric analysis. Water vapor sorption on MIL-160(Al) results in the solid-state adsorption complex with up to four water molecules per unit of MIL-160(Al). Chemical kinetics of water sorption on MIL-160(Al) follows a pseudo-first order rate law and it is consistent with dynamics and timescale revealed by in-situ time-dependent ATR-FTIR. The combination of two in-situ time-dependent methods, the ATR-FTIR spectroscopy and gravimetry, forms a new powerful experimental approach to facilely study mechanisms, stoichiometry and chemical kinetics of various solid–gas reactions in the ambient and controlled environments.

A New Synthetic Methodology in the Preparation of Bimetallic Chalcogenide Clusters via Cluster-to-Cluster Transformations

A decanuclear silver chalcogenide cluster, [Ag10(Se){Se2P(OiPr)2}8] (2) was isolated from a hydride-encapsulated silver diisopropyl diselenophosphates, [Ag7(H){Se2P(OiPr)2}6], under thermal condition. The time-dependent NMR spectroscopy showed that 2 was generated at the first three hours and the hydrido silver cluster was completely consumed after thirty-six hours. This method illustrated as cluster-to-cluster transformations can be applied to prepare selenide-centered decanuclear bimetallic clusters, [CuxAg10-x(Se){Se2P(OiPr)2}8] (x = 0–7, 3), via heating [CuxAg7−x(H){Se2P(OiPr)2}6] (x = 1–6) at 60 °C. Compositions of 3 were accurately confirmed by the ESI mass spectrometry. While the crystal 2 revealed two un-identical [Ag10(Se){Se2P(OiPr)2}8] structures in the asymmetric unit, a co-crystal of [Cu3Ag7(Se){Se2P(OiPr)2}8]0.6[Cu4Ag6(Se){Se2P(OiPr)2}8]0.4 ([3a]0.6[3b]0.4) was eventually characterized by single-crystal X-ray diffraction. Even though compositions of 2, [3a]0.6[3b]0.4 and the previous published [Ag10(Se){Se2P(OEt)2}8] (1) are quite similar (10 metals, 1 Se2−, 8 ligands), their metal core arrangements are completely different. These results show that different synthetic methods by using different starting reagents can affect the structure of the resulting products, leading to polymorphism.

Sustainable synthesis of silver nanoparticles using Alstonia scholaris for enhanced catalytic degradation of methylene blue

The present work described a simple, green, and fast approach for the synthesis of silver nanoparticles using an aqueous fruit extract of Alstonia scholaris(AS-AgNPs). The role of plant extract was identified as both reducing as well as capping agent in the synthesis of AS-AgNPs. The formation of AS-AgNPs was confirmed through the visible color change from pale yellow to brown and the respective surface plasmon resonance (SPR) peak observed at 426 nm in the UV-Visible (UV-Vis) spectrum. Further, the synthesized AS-AgNPs were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy with Energy dispersive spectrum (SEM with EDS), High resolution transmission electron microscopy (HR-TEM), and Dynamic light scattering (DLS) with Zeta potential. The DLS derived average particle size and poly dispersion index (PDI) of AS-AgNPs are about 50 nm and 0.664 with Zeta potential of -22.4 mV, suggested the presence of mono and polydispersive AS-AgNPs with good stability. The synthesized AS-AgNPs were mainly distributed (56 %) as a quasi-spherical shape with size ranges from 5 to 50 nm revealed by SEM and TEM images. Moreover, the catalytic reduction of methylene blue (MB) by AS-AgNPs has been accessed via time-dependent UV-Vis spectroscopy. The UV-Vis results suggested that AS-AgNPs show enhanced catalytic activity on the reduction of MB by aqueous sodium borohydride with pseudo first-order kinetics and the calculated rate constant was about 0.7 × 10−3 s−1. Overall, the green synthesized AS-AgNPs have a great catalytic potential in the degradation of MB in water.

Electron capture and emission dynamics of self-assembled quantum dots far from equilibrium with the environment

The electron transfer dynamics between self-assembled quantum dots and their environment are measured under nonequilibrium conditions by time-dependent capacitance spectroscopy. The quantum dots are embedded in a wide spacer, which inhibits elastic tunneling to or from the reservoirs. At certain bias voltages, electron capture and emission are both significant. A rate equation model is used to determine the corresponding transfer rates and the average occupation numbers of the dots as a function of the bias voltage.

Fabrication of reusable polymer nanocomposite films made of thermoplastic polyurethane and modified BiVO4 for photodegradation of Malachite Green

Semiconducting BiVO4, is successfully prepared by solid-state route and attempts are taken to dope vanadium sites by titanium ions to produce BiV1-xTixO4 (x = 5%, 10% and 15%). The products are analyzed using powder X-ray diffraction, Raman spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. The average particle sizes are in the range of 71-82 nm. Using diffuse reflectance spectroscopy, the band gaps are estimated and fall in visible range (2.11-2.41 eV). These nanomaterials are investigated for the photodegradation of malachite green dye solution that can find application in wastewater treatment and their efficiencies are investigated by time-dependent UV-Visible spectroscopy. 15% titanium doped BiVO4 (BVO-15) showed the highest efficiency by completely degrading malachite green in 180 min under visible light irradiation. In such heterogenous processes, separation of the used nanocatalysts remain a challenge. To address this, reusable polymer nanocomposite films are prepared using thermoplastic polyurethane (TPU) to immobilize BVO-15. The polymer nanocomposite film with 0.10 g of catalyst in 1 g of TPU showed maximum efficiency (~ 96%). The powder and film catalysts are investigated for three cycles and found to be effective. Thus, they show remarkable photocatalytic activity, stability and reusability that make them suitable for the wastewater treatment.