Optical and AFM study of electrostatically assembled films of CdS and ZnS colloid nanoparticles

CdS and ZnS semiconducting colloid nanoparticles coated with the organic shell, containing either SO₃⁻ or NH₂⁺ groups, were prepared using the aqueous phase synthesis. The multilayer films of CdS (or ZnS) were deposited onto glass, quartz and silicon substrates using the technique of electrostatic self-assembly. The films produced were characterized with UV-vis spectroscopy, spectroscopic ellipsometry and atomic force microscopy. A substantial blue shift of the main absorption band with respect to the bulk materials was found for both CdS and ZnS films. The Efros equation in the effective mass approximation (EMA) theoretical model allowed the evaluation of the nanoparticle radius of 1.8 nm, which corresponds well to the ellipsometry results. AFM shows the formation of larger aggregates of nanoparticles on solid surfaces.     

Synthesis and characterization of CdS/PVA nanocomposite films

A series CdS/PVA nanocomposite films with different amount of Cd salt have been prepared by means of the in situ synthesis method via the reaction of Cd²⁺-dispersed poly vinyl-alcohol (PVA) with H₂S. The as-prepared films were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) absorption, photoluminescence (PL) spectra, Fourier transform infrared spectroscope (FTIR) and thermogravimetric analysis (TGA). The XRD results indicated the formation of CdS nanoparticles with hexagonal phase in the PVA matrix. The primary FTIR spectra of CdS/PVA nanocomposite in different processing stages have been discussed. The vibrational absorption peak of CdS bond at 405 cm⁻¹ was observed, which further testified the generation of CdS nanoparticles. The TGA results showed incorporation of CdS nanoparticles significantly altered the thermal properties of PVA matrix. The photoluminescence and UV-vis spectroscopy revealed that the CdS/PVA films showed quantum confinement effect.     

Silicon MIS diodes with Cr2O3 nanofilm: Optical, morphological/structural and electronic transport properties

In this work we report the optical, morphological and structural characterization and diode application of Cr₂O₃ nanofilms grown on p-Si substrates by spin coating and annealing process. X-ray diffraction (XRD), non-contact mode atomic force microscopy (NC-AFM), ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) spectroscopy were used for characterization of nanofilms. For Cr₂O₃ nanofilms, the average particle size determined from XRD and NC-AFM measurements was approximately 70 nm. Structure analyses of nanofilms demonstrate that the single phase Cr₂O₃ on silicon substrate is of high a crystalline structure with a dominant in hexagonal (1 1 0) orientation. The morphologic analysis of the films indicates that the films formed from hexagonal nanoparticles are with low roughness and uniform. UV-vis absorption measurements indicate that the band gap of the Cr₂O₃ film is 3.08 eV. The PL measurement shows that the Cr₂O₃ nanofilm has a strong and narrow ultraviolet emission, which facilitates potential applications in future photoelectric nanodevices. Au/Cr₂O₃/p-Si metal/interlayer/semiconductor (MIS) diodes were fabricated for investigation of the electronic properties such as current-voltage and capacitance-voltage. Ideality factor and barrier height for Au//Cr₂O₃/p-Si diode were calculated as 2.15 eV and 0.74 eV, respectively. Also, interfacial state properties of the MIS diode were determined. The interface-state density of the MIS diode was found to vary from 2.90 × 10¹³ eV⁻¹ cm⁻² to 8.45 × 10¹² eV⁻¹ cm⁻².     

Co-sensitized quantum dot solar cell based on ZnO nanowire

An efficient photoelectrode is fabricated by sequentially assembled CdS and CdSe quantum dots (QDs) onto a ZnO-nanowire film. As revealed by UV-vis absorption spectrum and scanning electron microscopy (SEM), CdS and CdSe QDs can be effectively adsorbed on ZnO-nanowire array. Electrochemical impedance spectroscopy (EIS) measured demonstrates that the electron lifetime for ZnO/CdS/CdSe (13.8 ms) is calculated longer than that of ZnO/CdS device (6.2 ms), which indicates that interface charge recombination rate is reduced by sensitizing CdSe QDs. With broader light absorption range and longer electron lifetime, a power conversion efficiency of 1.42% is achieved for ZnO based CdS/CdSe co-sensitized solar cell under the illumination of one Sun (AM 1.5G, 100 mW cm⁻²).     

Effect of complexing agent on the photoelectrochemical properties of bath deposited CdS thin films

In the present paper photoelectrochemical (PEC) performance of bath deposited CdS thin films based on complexing agents i.e. ammonia and triethanolamine (TEA) has been discussed. Effect of annealing has also been analyzed. The as-deposited and annealed (at 523 K for 1 h in air) films were characterized by X-ray diffraction (XRD), ultraviolet-visible (UV-vis) absorption spectroscopy, SEM, electrochemical impedance spectroscopy (EIS), and PEC properties. XRD studies revealed that the films were nanocrystalline in nature with mixed hexagonal and cubic phases. TEA complex resulted in better crystallinity. Further improvement in the crystallinity of the films was observed after air annealing. The marigold flower-like structure, in addition to flakes morphology, was observed with TEA complex, whereas for ammonia complex only flakes morphology was observed. The UV-vis absorption studies revealed that the optical absorption edge for the films with ammonia and TEA complex was around 475 nm and 500 nm, respectively. Annealing of the films resulted in red shift in the UV-vis absorption. The PEC cell performance of CdS films was found to be strongly affected by crystallinity and morphology of the films resulted due to complexing agent and annealing. The air annealed film deposited using TEA complex showed maximum short circuit current density (J_sc) and open circuit voltage (V_oc) i.e. 99 μA/cm² and 376 mV respectively, under 10 mW/cm² of illumination. The films deposited using TEA complex showed good stability under PEC cell conditions.     

Static quenching of bovine serum albumin conjugated with small size CdS nanocrystalline quantum dots

The author reports on a strong fluorescence quenching of a model transport protein, bovine serum albumin BSA, when bioconjugated with CdS quantum dots QDs. The 4.4 nm size CdS QDs were synthesized using wet chemistry method and were characterized using UV-vis spectroscopy, scanning electron microscopy SEM and X-ray diffraction XRD techniques. It was found that the BSA fluorescence quenching increases linearly with increasing the CdS QDs concentrations in the range of 3×10⁻⁷-2.0×10⁻⁶ mol L⁻¹. This quenching is explained in terms of Stern-Volmer equation and is ascribed to static quenching with quenching constant 1.321×10⁴ L mol⁻¹ at 300 K.     

Synthesis and photoluminescence properties of aqueous CdWO4 quantum dots with WO6 luminescence center

Aqueous CdWO₄ QDs were synthesized by the reaction of CdCl₂ and Na₂WO₄ in the presence of mercaptoacetic acid (TGA) as capping reagent. The crystal morphology, particle size and its distribution of as-prepared products were characterized by transmission electron microscopy (TEM, SAED) atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), and photon correlation spectroscopy (PCS), respectively. Qualitative assays for functional groups on the QDs’ surface were measured by fourier transform infrared spectroscopy (FTIR). Photoluminescence properties of QDs were studied by photoluminescence spectroscopy (PL). The results showed that the single QD with diameter of about 8 ± 2 nm was single-crystal. The particle size distribution of QDs was normal. Infrared absorption bands of carboxylic group on the surface of CdWO₄ QDs were observed around 1610-1550 cm⁻¹ (nonsymmetrical vibration of -COO⁻) and 1400 cm⁻¹ (symmetric vibration of C-O). With reaction-time going, PL peak position shifted from 498 to 549 nm and intensity of PL increased first and then decreased. PL peak position of QDs was blue-shift compared with 570 nm WO₆⁶⁻ luminescence center of bulk CdWO₄.     

Third-order nonlinear optical properties of multiwalled carbon nanotubes modified by CdS nanoparticles

CdS nanoparticles were coated on the side wall of multiwalled carbon nanotubes (MWCNTs) by a wet chemical synthesis approach via noncovalent functionalization of MWCNTs with poly(diallyldimethylammonium chloride) (PDDA). The as-prepared material was characterized by X-ray diffraction (XRD), UV–vis absorption, fluorescence and transmission electron microscopy (TEM). The results indicated that CdS nanoparticles were uniformly coated on the surface of MWCNTs. Third-order optical nonlinearity of the as-prepared material was studied with the Z-scan technique with picosecond laser pulses at 532 nm. The Z-scan curve revealed that CdS nanoparticle-modified MWCNTs exhibited negative nonlinear refraction index and positive absorption coefficient. The real part and imaginary part of the third-order nonlinear susceptibility χ⁽³⁾ were calculated to be −4.9 × 10⁻¹² and 6.8 × 10⁻¹³ esu, respectively.     

Preparation and characterization of SnO2 nanoparticles using high power pulsed laser

Tin dioxide (SnO₂) nanoparticles having 3 nm size were synthesized by irradiating pure tin metal using high power Nd:YAG laser in deionized water. Formation of nano-SnO₂ crystallites was confirmed by X-ray diffraction (XRD) and AFM study. UV-vis absorption spectral studies showed a peak at 240 nm. FTIR spectrum showed a band in the range of 400-700 cm⁻¹ which was assigned to Sn-O antisymmetric vibrations. Photoluminescence spectrum of synthesized SnO₂ nanoparticles showed peak corresponding to 3.175, 2.901 and 2.613 eV respectively.     

pH dependent interaction of biofunctionalized CdS nanoparticles with nucleobases and nucleotides: A fluorimetric study

The interaction of DNA bases and corresponding nucleotides with CdS nanoparticles (NPs), biofunctionalized by cysteine, has been investigated by absorption and fluorescence spectroscopy. Unique enhancement effect of adenine, in contrast to other nucleobases, on the luminescence of cysteine capped CdS (cys-CdS) NPs at both pH 7.5 and 10.5 was found, the extent of enhancement being much higher at pH 10.5. At the latter pH, the difference optical absorption spectra show development of new peak at 278 nm with corresponding decrease in the absorption of adenine at 260 nm, which is attributed to binding of adenine anion to the CdS surface through N7 of the purine ring. Appearance of a new band at 478 cm⁻¹ and concomitant shift in the C₈-N₇ vibrations to 1610 cm⁻¹ in the FTIR spectra of cys-CdS NPs with adenine also suggest Cd-N7 binding on the particle surface. Amongst various nucleotides, ATP exhibited maximum luminescence enhancement on CdS NPs for a given change in concentration in the micro-molar range at physiological pH. A quantitative correlation between ATP concentration and PL enhancement of CdS NPs has been established, a step which in future might assist in developing new protocols for fluorescence sensing of adenine nucleotides under certain pathological conditions.     

Swift heavy ion induced modifications in cobalt doped ZnO thin films: Structural and optical studies

Modifications in the structural and optical properties of 100 MeV Ni⁷⁺ ions irradiated cobalt doped ZnO thin films (Zn_1−xCo_xO, x = 0.05) prepared by sol-gel route were studied. The films irradiated with a fluence of 1 × 10¹³ ions/cm² were single phase and show improved crystalline structure with preferred C-axis orientation as revealed from XRD analysis. Effects of irradiation on bond structure of thin films were studied by FTIR spectroscopy. The spectrum shows no change in bonding structure of Zn-O after irradiation. Improved quality of films is further supported by FTIR studies. Optical properties of the pristine and irradiated samples have been determined by using UV-vis spectroscopic technique. Optical absorption spectra show an appreciable red shift in the band gap of irradiated Zn_1−xCo_xO thin film due to sp-d interaction between Co²⁺ ions and ZnO band electrons. Transmission spectra show absorption band edges at 1.8 eV, 2.05 eV and 2.18 eV corresponding to d-d transition of Co²⁺ ions in tetrahedral field of ZnO. The AFM study shows a slight increase in grain size and surface roughness of the thin films after irradiation.     

Interactions between CdSe/CdS quantum dots and DNA through spectroscopic and electrochemical methods

The interaction of CdSe/CdS quantum dots (QDs) with Herring sperm-DNA (hs-DNA) has been studied by UV-vis spectroscopy and electrochemical method. Cu(phen)₂^2+/1+ (phen = 1, 10-phenanthroline) was used as an indicator for electroactive dsDNA or ssDNA. The apparent association constant has been deduced (4.94 × 10³ M⁻¹ and 2.39 × 10² M⁻¹) from the absorption spectral changes of the dsDNA-QDs and ssDNA-QDs. The results of dissociation method suggest that Cu(phen)₂^2+/1+ is more easily dissociated from dsDNA or ssDNA modified gold electrode (dsDNA/Au or dsDNA/Au) in presence of QDs. The dissociation rate constant (k) of Cu(phen)₂^2+/1+ on dsDNA/Au is 4.48 times higher than that in absence of QDs, while k is 2.34 times higher than that in absence of QDs on ssDNA/Au in Tris buffer with low ionic strength (pH 7.0, 0.5 mM NaCl). The results illuminate that hs-DNA has high affinity for QDs due to electrostatic force, hydrogen bonds, and van der Waals interactions, and the binding force of QDs with dsDNA is stronger than ssDNA.     

Sunlight photocatalytic activity of CdS modified TiO2 loaded on activated carbon fibers

To improve the photocatalytic application performances of TiO₂, in this work, firstly CdS modified Degussa P25 TiO₂ (CdS/TiO₂) composites were prepared by two methods, sol-gel method and precipitation method. Next they, sol-gel-CdS/TiO₂ (sg-CdS/TiO₂) and precipitation-CdS/TiO₂ (pp-CdS/TiO₂), were loaded on activated carbon fibers (ACFs) by dip-coating method using the sodium carboxymethyl cellulose as adhesives. The composites were characterized by XRD, UV-vis absorbance spectra, SEM, EDS and BET. The photocatalytic activities under sunlight were investigated by the degradation of methylene blue. The results showed that CdS/TiO₂ composites were mainly composed of anatase-TiO₂ and little CdS cubic phases. The absorption wavelengths of sg-CdS/TiO₂ and pp-CdS/TiO₂ composites were extended to 590 nm and 740 nm, respectively. The absorption edge had a pronounced ‘red shift’. From EDS analysis, the elemental contents of CdS/TiO₂ were mainly Ti and O and a small quantity of S and Cd. CdS/TiO₂ loaded on ACFs were in the form of small clusters, but not very uniform; compared with the original ACFs, the surface area and pore volume of CdS/TiO₂/ACFs decreased slightly, respectively, while the average pore diameter was not changed. The photodegradation rate of methylene blue under sunlight with CdS/TiO₂/ACFs composites was markedly higher than that of P25-TiO₂/ACFs, and the effect of pp-CdS/TiO₂/ACFs composites was better than that of sg-CdS/TiO₂/ACFs, when irradiated for 180 min, and the photodegradation rate of methylene blue reached to 90.1%. The photodegradation kinetics of the methylene blue fitted with the Langmuir-Hinshelwood equation. The apparent reaction rate constants of sg-CdS/TiO₂/ACFs and pp-CdS/TiO₂ were 0.0105 min⁻¹ and 0.0146 min⁻¹, respectively, which were about 1.3-1.7 times as large as that of P25-TiO₂/ACFs.     

CdSe quantum dots decorated by mercaptosuccinic acid as fluorescence probe for Cu

Water-soluble CdSe quantum dots (QDs) were synthesized using mercaptosuccinic acid (MSA) as a stabilizer. The growth process and characterization of CdSe quantum dots were determined by transmission electron microscopy (TEM), X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, Ultraviolet-visible (UV-vis) spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy. Results demonstrated the MSA-capped CdSe QDs were highly crystalline and possessed good optical properties. Further, the resulting products could be used as fluorescent probes to detect Cu²⁺ ions in physiological buffer solution. The response was linearly proportional to the concentration of Cu²⁺ ion in the range 2×10⁻⁸- 3.5×10⁻⁷ mol L⁻¹ with a detection limit of 3.4 nmol L⁻¹.     

Electrical and optical properties of thermally-evaporated thin films from A2[TiO(C2O4)2] (A = K, PPh4) and 1,8-dihydroxyanthraquinone

In this work, the synthesis of molecular materials formed from A₂[TiO(C₂O₄)₂] (A = K, PPh4) and 1,8 dihydroxyanthraquinone is reported. The synthesized materials were characterized by atomic force microscopy (AFM), infrared (IR) and ultraviolet-visible (UV-vis) spectroscopy. IR spectroscopy showed that the molecular-material thin-films, deposited by vacuum thermal evaporation, exhibit the same intra-molecular vibration modes as the starting powders, which suggests that the thermal evaporation process does not alter the initial chemical structures. Electrical transport properties were studied by dc conductivity measurements. The electrical activation energies of the complexes, which were in the range of 0.003-1.16 eV, were calculated from Arrhenius plots. Optical absorption studies in the wavelength range of 190-1090 nm at room temperature showed that the optical band gaps of the thin films were around 1.9-2.3 eV for direct transitions Eg_d. The cubic NLO effects were substantially enhanced for materials synthesized from K₂[TiO(C₂O₄)₂], where χ⁽³⁾ (−3ω; ω, ω, ω) values in the promising range of 10⁻¹² esu have been evaluated.     

Preparation of Ru-loaded CdS/Al-HMS nanocomposites and production of hydrogen by photocatalytic degradation of formic acid

The composite of aluminum-substituted mesoporous silica (Al-HMS) molecular sieve coupled with CdS (CdS/Al-HMS) was prepared by template, ion exchange and sulfurization reactions. The result of low angle XRD patterns showed that the low content of 2.5 wt% CdS is incorporated inside Al-HMS channels. The results of diffuse reflectance UV-visible spectra and fluorescence emission spectra exhibited that the absorption edge and photoluminescence peak for CdS/Al-HMS are blue-shifted about 75 nm and 40 nm in comparison to bulk CdS, respectively. The activities of hydrogen production by photocatalytic degradation of formic acid were evaluated under visible light irradiation (λ ≥ 420 nm) and the CdS/Al-HMS loaded 0.07 wt% Ru showed the highest H₂ evolution at a rate of 3.7 mL h⁻¹ with an apparent quantum yield of 1.2% at 420 nm.     

Preparation and characterization of CdS/Si coaxial nanowires

CdS/Si coaxial nanowires were fabricated via a simple one-step thermal evaporation of CdS powder in mass scale. Their crystallinities, general morphologies and detailed microstructures were characterized by using X-ray diffraction, scanning electron microscope, transmission electron microscope and Raman spectra. The CdS core crystallizes in a hexagonal wurtzite structure with lattice constants of a=0.4140 nm and c=0.6719 nm, and the Si shell is amorphous. Five Raman peaks from the CdS core were observed. They are 1LO at 305 cm⁻¹, 2LO at 601 cm⁻¹, A₁-TO at 212 cm⁻¹, E₁-TO at 234 cm⁻¹, and E₂ at 252 cm⁻¹. Photoluminescence measurements show that the nanowires have two emission bands around 510 and 590 nm, which originate from the intrinsic transitions of CdS cores and the amorphous Si shells, respectively.     

A green synthetic approach to graphene nanosheets for hydrogen adsorption

A green and facile strategy of preparing graphene by reducing exfoliated graphite oxide (GO) with glucose was developed in this study. The as-prepared samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Atomic force microscopy (AFM). The characterization results indicated that the graphene sheets (GS) were of high quality with smooth surface, rich pore structure and few layer graphene. The samples have a BET specific surface area of 1205.8 m² g⁻¹ measured by N₂ adsorption at 77 K. The hydrogen storage capacity of 2.7 wt.% at 298 K and 25 bar demonstrated that the as-prepared graphene employing glucose as reductant is supposed to be a promising material with outstanding property for hydrogen storage.     

Synthesis, characterizations, photocatalytic and sensing studies of ZnO nanocapsules

ZnO nanocapsules have been synthesized hydrothermally. The structural and morophological properties were investigated using X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), FTIR, Raman, EDS and UV-vis absorption spectroscopy. For the first time chemical sensing properties of the synthesized ZnO nanocapsules have been investigated by I-V technique, where chloroform is used as a target compound. The chloroform sensors show good sensitivity (0.478 μA cm⁻² mM⁻¹), lower detection limit (6.67 μM), and large linear dynamic range (LDR, 12.0 μM-12.0 mM) with good linearity (R, 0.8523) in short response time. Additionally, photocatalytic activity of the prepared capsule shaped ZnO photocatalyst was evaluated by the degradation of acridine orange. Prepared ZnO nanocapsules posses high photocatalytic activity when compared with TiO₂-UV100.     

Interaction of the docetaxel with human serum albumin using optical spectroscopy methods

Docetaxel is a semi-synthetic product derived from the needles of the European yew. It is an antineoplastic agent belonging to the taxoid family. The interaction between docetaxel and human serum albumin (HSA) has been investigated systematically by the fluorescence quenching technique, synchronous fluorescence spectroscopy, ultraviolet (UV)-vis absorption spectroscopy, circular dichroism (CD) spectroscopy and Fourier transform infrared (FT-IR) under physiological conditions. Our fluorescence data showed that HSA had only one docetaxel binding site and the binding process was a static quenching procedure. According to the Van’t Hoff equation, the thermodynamic parameters standard enthalpy (ΔH⁰) and standard entropy (ΔS⁰) were calculated to be −41.07 KJ mol⁻¹ and −49.72 J mol⁻¹ K⁻¹. These results suggested that hydrogen bond was the predominant intermolecular force stabling the docetaxel-HSA complex. The data from the CD, FT-IR and UV-vis spectroscopy supported the change in the secondary structure of protein caused by the interaction of docetaxel with HSA.