Visible Absorption Properties Research Articles

Effects of vacancy defects on the electronic, mechanical, and optical properties of penta-B2C4

The synthesis of two-dimensional (2D) pentagonal structures has sparked interest in further research on this class of materials. Here, the effects of intrinsic point vacancy defects on the electronic, mechanical, and optical properties of Penta-B2C4 were systematically investigated. The research indicates that three types of point vacancy defects (VB, VC and VBC) cause varying degrees of upward shift in the Fermi level of Penta-B2C4, ultimately leading to its transformation from p-type semiconductor to n-type semiconductor. The VB defect disrupts the mechanical stability of Penta-B2C4 while VC and VBC defects still maintain excellent mechanical properties, exhibiting flexibility even superior to graphene. The three vacancy defects also improve the visible optical absorption properties of Penta-B2C4, but the reflectance and refractive index in the same environment decrease. The research findings provide theoretical support for the application of Penta-B2C4 in flexible devices, mechanical engineering, and optoelectronic devices.

Tuning Excited State Character in Iridium(III) Photosensitizers and Its Influence on TTA-UC.

A series of mixed ligand, photoluminescent organometallic Ir(III) complexes have been synthesized to incorporate substituted 2-phenyl-1H-naphtho[2,3-d]imidazole cyclometalating ligands. The structures of three example complexes were categorically confirmed using X-ray crystallography each sharing very similar structural traits including evidence of interligand hydrogen bond contacts that account for the shielding effects observed in the 1H NMR spectra. The structural iterations of the cyclometalated ligand provide tuning of the principal electronic transitions that determine the visible absorption and emission properties of the complexes: emission can be tuned in the visible region between 550 and 610 nm and with triplet lifetimes up to 10 μs. The nature of the emitting state varies across the series of complexes, with different admixtures of ligand-centered and metal-to-ligand charge transfer triplet levels evident. Finally, the use of the complexes as photosensitizers in triplet-triplet annihilation energy upconversion (TTA-UC) was investigated in the solution state. The study showed that the complexes possessing the longest triplet lifetimes showed good viability as photosensitizers in TTA-UC. Therefore, the use of an electron-withdrawing group on the 2-phenyl-1H-naphtho[2,3-d]imidazole ligand framework can be used to rationally promote TTA-UC using this class of complex.

Mn3O4/ZnO-Al2O3-CeO2 mixed oxide catalyst derived from Mn-doped Zn-(Al/Ce)-LDHs: efficient visible light photodegradation of clofibric acid in water.

Mn3O4/ZnO-Al2O3-CeO2 catalyst was synthesized through a solid-state process from a 3% Mn-doped Zn-(Al/Ce) layered double hydroxide structure. Detailed structural and optical characterization using XRD, FTIR, UV-visible DRS, and TEM was conducted. By investigating clofibric acid (CA) degradation in aqueous solution, Mn3O4/ZnO-Al2O3-CeO2 photocatalytic activity was evaluated. The results show that the heterostructure mixed oxide catalyst has excellent CA photodegradation performance. Further, the characterization reveals that such photocatalytic efficiency can be attributed to two facts that are summarized in the optical properties and the synergic effect between Mn and Ce elements. The sample demonstrated a narrow band gap of 2.34 eV based on DRS. According to the experimental results of the photodegradation, after 120 min of irradiation, the photocatalyst exhibited the highest photocatalytic activity, with a degradation efficiency of 93.6%. Optimization outcomes indicated that maximum degradation efficiency was attained under the following optimum conditions: catalyst dose of 0.3 g/L, initial dye concentration of 20 mg/L, pH 3.86, and 120 min of reaction time. The quenching test demonstrates that photogenerated electrons and superoxide radicals are the most powerful reactive species. The catalyst could be useful in decreasing the photogenerated charges recombination, which offers more redox cycles simultaneously during the catalytic process. The strong Ce-Mn interaction and the formation of their different oxidation states offer a high degradation efficiency by facilitating electron-hole transfer. The introduction of Mn3O4 in the catalyst can effectively improve the visible absorption properties, which are beneficial in the photocatalytic process by reaching a high catalytic efficiency at a low cost.

Fluorescent carbon quantum dots with controllable physicochemical properties fantastic for emerging applications: A review

AbstractCarbon quantum dots (CQDs) have emerged as prominent contenders in the realm of luminescent nanomaterials over the past decade owing to their tunable optical properties, robust photostability, versatile surface functionalization and doping potential, low toxicity, and straightforward synthesis utilizing environmentally friendly precursors. In this review, we commence with a concise introduction, presenting both top‐down and bottom‐up strategies for the eco‐friendly synthesis of CQDs. Subsequently, we delve into a comprehensive examination of CQDs' structure and optical characteristics, encompassing their ultraviolet–visible absorption properties, surface confinement effects, and surface state emissions contributing to room‐temperature photoluminescence (PL). This review proceeds to elucidate recent advancements in modification strategies for CQDs, specifically focusing on surface oxidation, passivation, and the incorporation of heteroatoms. These strategies serve to afford control over the physicochemical properties, facilitating the enhancement of PL through the decoration of highly visible‐responsive CQDs. This enhancement is achieved by suppressing the nonradiative recombination of electron‐hole pairs, enabling red/blue shifts in CQDs for the generation of a full‐color emission spectrum, and regulating the band‐gap and surface states to broaden the photoabsorption range. Finally, we offer an overview of the most recent developments in the applications of fluorescent CQDs, emphasizing their utility in biomedicine, fluorescent sensors, lighting, and displays, as well as photocatalysis.

Study on interface engineering and chemical bonding of the ReS2@ZnO heterointerface for efficient charge transfer and nonlinear optical conversion efficiency.

Rhenium sulfide (ReS2) has emerged as a promising two-dimensional material, demonstrating broad-spectrum visible absorption properties that make it highly relevant for diverse optoelectronic applications. Manipulating and optimizing the pathway of photogenerated carriers play a pivotal role in enhancing the efficiency of charge separation and transfer in novel semiconductor composites. This study focuses on the strategic construction of a semiconductor heterostructure by synthesizing ZnO on vacancy-containing ReS2 (VRe-ReS2) through chemical bonding processes. The ingeniously engineered built-in electric field within the heterostructure effectively suppresses the recombination of photogenerated electron-hole pairs. A direct and well-established interfacial connection between VRe-ReS2 and ZnO is achieved through a robust Zn-S bond. This distinctive bond configuration leads to enhanced nonlinear optical conversion efficiency, attributed to shortened carrier migration distances and accelerated charge transfer rates. Furthermore, theoretical calculations unveil the superior chemical interactions between Re vacancies and sulfide moieties, facilitating the formation of Zn-S bonds. The photoluminescence (PL) intensity is increased by the formation of VRe-ReS2 and ZnO heterostructure and the PL quantum yield of VRe-ReS2 is improved. The intricate impact of the Zn-S bond on the nonlinear absorption behavior of the VRe-ReS2@ZnO heterostructure is systematically investigated using femtosecond Z-scan techniques. The charge transfer from ZnO to ReS2 defect levels induces a transition from saturable absorption to reverse saturable absorption in the VRe-ReS2@ZnO heterostructure. Transient absorption measurements further confirm the presence of the Zn-S bond between the interfaces, as evidenced by the prolonged relaxation time (τ3) in the VRe-ReS2@ZnO heterostructure. This study offers valuable insights into the rational construction of heterojunctions through tailored interfacial bonding and surface/interface charge transfer pathways. These endeavors facilitate the modulation of electron transfer dynamics, ultimately yielding superior nonlinear optical conversion efficiency and effective charge regulation in optoelectronic functional materials.

Spectroscopic and theoretical study of novel copper(II) complexes based on phenothiazine ligands: UV–Visible absorption and photoinduced electron transfer

This study presents three novel copper (II) complexes based on phenothiazine ligands that were synthesized and revealed their structures by spectral and analytical measurements. The synthesized complexes offered potential opportunities to explore their UV–visible absorption properties and photoinduced electron transfer with triethylamine. We performed density functional theory (DFT) calculations for Cu(II) (HL1)2 compounds and studied their frontier molecular orbitals in different environments. The calculations were done by using PBE1PBE functional and 6-31G(d)/Lanl2dz basis sets. We applied the LANL2DZ basis set for Cu. The treatment of all the other atoms was done by a 6-31G(d) basis set. For the calculation of the electronic structure, the basis set 6–31 + G(d)/Lanl2dz and SMD solvation model with MeCN and DMF were employed. We computed the frequencies to confirm the stability of the structures. Theoretical calculations can help explain the experimental findings, provide insights into the electronic transitions responsible for UV–visible absorption, and elucidate the photoinduced electron transfer processes involved.

First Principles Study of the Photoelectric Properties of Alkaline Earth Metal (Be/Mg/Ca/Sr/Ba)-Doped Monolayers of MoS2.

The energy band structure, density of states, and optical properties of monolayers of MoS2 doped with alkaline earth metals (Be/Mg/Ca/Sr/Ba) are systematically studied based on first principles. The results indicate that all the doped systems have a great potential to be formed and structurally stable. In comparison to monolayer MoS2, doping alkaline earth metals results in lattice distortions in the doped system. Therefore, the recombination of photogenerated hole-electron pairs is suppressed effectively. Simultaneously, the introduction of dopants reduces the band gap of the systems while creating impurity levels. Hence, the likelihood of electron transfer from the valence to the conduction band is enhanced, which means a reduction in the energy required for such a transfer. Moreover, doping monolayer MoS2 with alkaline earth metals increases the static dielectric constant and enhances its polarizability. Notably, the Sr-MoS2 system exhibits the highest value of static permittivity, demonstrating the strongest polarization capability. The doped systems exhibit a red-shifted absorption spectrum in the low-energy region. Consequently, the Be/Mg/Ca-MoS2 systems demonstrate superior visible absorption properties and a favorable band gap, indicating their potential as photo-catalysts for water splitting.

Nano‐SH‐MOF@Self‐Assembling Hollow Spherical g‐C3N4 Heterojunction for Visible‐Light Photocatalytic Nitrogen Fixation

AbstractMetal‐organic frameworks (MOFs)@g‐C3N4 heterojunctions are widely investigated as one of the most potential photocatalysts for N2 fixation owing to the visible absorption and effective photocatalytic properties. It is still a huge challenge to synthesize hollow spherical C3N4 coated with Nano‐MOF layers towards efficient visible photocatalytic activity on N2 fixation. In this work, the paramagnetic hollow spherical C3N4 (H‐C3N4) are coated with free radical MOF with sulfhydryl ligand (Nano‐SH‐MOF)[Zn2(DSBDC)] by self‐assemble method. The C8 M2 samples (the mass ratio of H‐C3N4 to Nano‐SH‐MOF is 8 : 2) exhibited an improved photocatalytic activity, which is almost 5.4 times higher than the pure H‐C3N4. The improved photocatalytic activity is also discussed in this work. It can be imagined that this work may be helpful for the hollow spherical C3N4 based heterojunction and MOF‐based heterojunction photocatalysts with effective photocatalytic nitrogen fixation.

Novel chalcone scaffolds of benzothiophene as an efficient real time hydrazine sensor: Synthesis and single crystal XRD studies

Continue to our on-going research, this article demonstrate the design and development of an efficient real time hydrazine sensor. A series of novel chalcone scaffolds are synthesised by the reaction of benzothiophene-3-aldehyde with various aromatic poly-nuclear hetero-aryl ketones. Theorized molecules are synthesised via the classical Claisen Smidt condensation. This condensation is illustrated by use of KOH and pyrrolidine as a catalyst to develop two different protocols with competitive studies. The obtained results suggest KOH as a quick catalyst however pyrrolidine as an efficient catalyst. Structure of prepared molecules are confirmed by various spectral analysis and single crystal XRD studies. Solvent screening study shows methanol as more appropriate solvent for UV–Visible absorption and fluorescence emission properties. Based on this study, an effecient real-time hydrazine sensing protocol is established with selected one molecule. A detailed process with working pH range, sensing selectivity among other analytes, soil sample test is developed and demonstrated. The studied chalcone has shown good working pH range and excellent selectivity for hydrazine. The possible mechanism for the detection of hydrazine is also confirmed by spectral analysis and discussed here. We are looking forward to fabricate the prototype devise for hydrazine detection in real life applications.

Investigation of charge collection layers for thin film rhenium sulfide solar cells

Rhenium sulfide (ReS2) is an exciting two-dimensional (2D) material employed in various optoelectronic applications due to panchromatic visible absorption properties. However, unlike other transition-metal dichalcogenides (TMDs) such as Mo(S/Se)2 and W(S/Se)2, ReS2 has not been explored for solar energy conversion applications. In this work, ReS2 nanolayers are employed as photoabsorber in both liquid and solid-state dye-sensitized type solar cells, in combination with TiO2 and SnO2 as electron transporting layers (ETLs). Various devices with compact/mesoporous TiO2 and mesoporous SnO2 ETLs were tested for photovoltaic performance with spiro-OMeTAD hole conductor as well as with different redox mediators. While no photovoltaic response was seen for mesoporous TiO2 (both liquid and solid-state), a clear photovoltaic performance was observed for mesoporous SnO2 solid-state devices. This was attributed to the energy level alignments unsuitable for charge carrier injection from ReS2 to ETL in the former and suitable in the latter cases. In the case of only compact layer TiO2 ETL, devices in both solid and liquid-state configurations exhibited photovoltaic response with latter showing higher photocurrent than the former, due to additional role played by the energy level of redox mediator. While impedance measurements revealed limitations in conductivity of ReS2 photoabsorber, presence of photovoltaic response in them indicate the significant role played by the energy level alignment of individual components. The presence of photovoltaic effect for compact layer TiO2 devices, in spite of unsuitable energy level alignment seen for TiO2, is attributed to the charge carrier injection assisted by the trap states.

Zinc(II) and copper(II) complexes with benzothiadiazole Schiff-base ligands

The ligand (2-[4-(2,1,3-benzothiadiazole)imino]methyl-phenol) HL1 containing the electron poor benzothiadiazole (BTD) unit, conveniently prepared by condensation of 4-amino-2,1,3-benzothiadiazole and salicylaldehyde, has been structurally characterized by single crystal X-ray diffraction. Two energy minima have been determined, by DFT calculations, for HL1 and for its ortho-vanillin analogue HL2, corresponding either to the conformer observed in the solid state or to the chelating tridentate form. TD-DFT calculations have been performed on HL1 and HL2 in order to assign their experimental UV–visible absorption bands. Reaction of HL1 and HL2 with copper (II) hexafluoroacetylacetonate (hfac), zinc (II) hexafluoroacetylacetonate or zinc (II) acetate provided the neutral complexes [Cu(L1)(hfac)] (1), [Zn(L1)2] (2), [Cu(L2)2] (3) and [Zn(L2)2] (4) which were structurally characterized, with a focus on the coordination sphere of the metal centre and on the intermolecular interactions. The UV–visible absorption properties of the Zn(II) complexes 2 and 4 have been experimentally and theoretically investigated and compared to those of the ligands. Finally, the cryomagnetic study of 1 and 3 in the temperature range 2.0–295.0 K reveals a Curie-Weiss law behaviour with very weak intermolecular antiferromagnetic interactions in the low temperature region.

Rational design direct Z-scheme β-GeSe/HfS2 heterostructure by interfacial engineering: Efficient photocatalyst for overall water splitting in the wide solar spectrum

The direct Z-scheme van der Waals (vdW) heterostructures that mimic the natural photosynthesis in plants raise a tremendous concern for photocatalysis applications. Herein, we propose a novel two-dimensional (2D) heterostructure comprised of HfS2 and β-GeSe monolayers. The most stable stacking configuration of the β-GeSe/HfS2 heterostructure is identified by using formation energy and molecular dynamic simulations. The direct Z-scheme photocatalytic property of the β-GeSe/HfS2 heterostructure was identified from band alignment, charge transfer, and built-in electric field. The β-GeSe/HfS2 heterostructure has a robust and excellent visible and ultraviolet optical absorption property (up to 105 cm−1). Moreover, the overall decomposition of water can proceed simultaneously and spontaneously on the surface of β-GeSe/HfS2 heterostructure when pH in the ranges from 7 to 12, without additional overpotential and co-catalyst. The highest solar-to-hydrogen (STH) efficiency of the heterostructure reaches 37.95%. This work not only provides a stepping stone into the design of high efficient Z-scheme photocatalyst but also demonstrates the enormous possibilities in two-dimensional heterostructures.

Synthesis and Photoelectrocatalytic Applications of TiO2/ZnO/Diatomite Composites

ZnO and TiO2 are semiconductor nanomaterials that are widely used in photocatalysis. However, the relatively high recombination rate and low quantum yield of photogenerated electron–hole pairs limit their practical applications. In this study, a series of TiO2/ZnO/diatomite composites with various compositions were successfully prepared via a two-step precipitation method. They exhibited stronger UV–visible absorption properties and substantially lower fluorescence intensities than those of ZnO and ZnO/diatomite, which was mainly due to the low recombination rate of the photogenerated electron–hole pairs in the composite system. The reaction intermediates of methylene blue were detected by liquid chromatography–mass spectrometry, and the degradation process was determined. The best composite catalyst was used for the degradation of gaseous methylbenzene and gaseous acetone. The gaseous acetone degradation product was determined to be acetaldehyde via gas chromatography–mass spectrometry. The results show that the composite catalyst exhibited a good photocatalytic degradation of both liquid pollutants and harmful volatile gases. When applied to the hydrogen and oxygen evolution reactions, the composite catalyst retained a good photoresponsivity and electrolytic efficiency.

A novel BiOX photocatalyst for the “green” degradation of polymers used in oilfields

The wastes from functional polymers (polyanionic cellulose, polyacrylamide, potassium polyacrylamide, and hydroxyethyl cellulose) generated during oil and gas exploration and development are harmful to biodiversity and human health. However, most traditional treatments are inefficient in degradation and cause secondary pollution. In this paper, BiOBr0.5Cl0.5 a 3D flower-like solid solution with in-situ deposition of elementary substance Bi and surface oxygen vacancies was synthesized by the hydrolysis and the redox methods. The chemical compositions, the morphologies, and the UV–visible absorption properties of Bi/BiOBr0.5Cl0.5 were characterized. Moreover, the photocatalytic activity of Bi/BiOBr0.5Cl0.5 and the kinetic behavior of the RhB photocatalytic degradation were investigated. The photocatalytic degradation of RhB followed a pseudo-first-order kinetic reaction, and Bi/BiOBr0.5Cl0.5-0.3 demonstrated the highest photocatalytic activity: The RhB degradation efficiency of Bi/BiOBr0.5Cl0.5-0.3 was 85%, and the COD removal rate of the functional polymers conducted by Bi/BiOBr0.5Cl0.5-0.3 was greater than 80%. The exciton photocatalytic processes of Bi/BiOBr0.5Cl0.5 was found through the electron spin resonance (ESR) and the active-species trapping analyses of the photocatalytic degradations of RhB by Bi/BiOBr0.5Cl0.5. In summary, in this paper, the synthesis methods of Bi/BiOBr0.5Cl0.5 photocatalyst and the photocatalytic activity of the Bi/BiOBr0.5Cl0.5 on the degradations of polymers used in oilfields were reported, addressing the shortcomings of the existing treatments for polymer waste fluids that are incorporated into the oil and gas exploration and development process.

Optimization of the ultraviolet–visible absorption properties of nano‐particle TiO2: Influence of milling, surface area and surfactants on particle‐size distribution, and stability of isocyanate/acrylic paints

AbstractThe ultraviolet–visible (UV–Vis) absorption properties of a range of nano‐particle titanium dioxides have been optimized and interrelated to the effects of the nature of calcination versus wet milling methodologies. Different inorganic and organic surfactants and surface treatments were also assessed. The TiO2 particles as prepared were characterized using X‐Ray diffraction spectrometry (XRD), transmission electron microscopy (TEM), BET, UV/Vis spectroscopy, and CPS disk centrifuge. Data are related to their spectral absorption properties and weathering stability in an isocyanate‐acrylic coating via gloss retention and weight loss. The choice of particle size is a compromise between UVA absorption, UVB absorption, visible transmission, and photoactivity. It is demonstrated that TiO2 with a crystallite size of 25 nm yields a product with the optimum properties. A method using UV/visible absorption spectroscopy has been developed and found to give excellent sensitivity to particle size was shown with CPS (disk centrifuge). It is shown to be a useful way to assess nano‐TiO2 dispersions. The wet milling of the base TiO2 before surface treatment was also optimized utilizing different dispersants. It was shown that using the ratio of absorbance at 300:550 nm is a good approximation for the ratio of the whole area under the curve in the UV spectrum to that in the visible region. This was used as an indication of the generation of smaller fragments generated by milling the larger aggregates. The particle‐size distribution and nature of the wet‐milling process significantly influenced the subsequent accelerated ATLAS weathering performance of the titania particles in an isocyanate‐acrylic coating.

Annealing temperature enhanced visible absorption and magnetic properties of (Cu, Cr) co-doped ZnO diluted magnetic semiconductors

Cu and Cr co-doped ZnO nanopowder (Zn0.96Cu0.02Cr0.02O) had been synthesized by co-precipitation method and the nanopowders were annealed at 400 ˚C (S1), 600 ˚C (S2), and 800 ˚C (S3). The sample S2 had better crystallization with a lesser amount of defects and imperfections. However, the presence of impurities and imperfection in sample S1 and lattice distortion due to the thermal expansion of lattice in sample S3 were noticed in the XRD pattern. All the samples had wide absorption and emission bands in the UV/violet, blue and green regions due to the d-d transition of metal ions. The Cr3+ ions in the tetrahedral environment undergo crystal field splitting. The violet band centered at 435 nm, blue emission centered at 478 nm, and green emission centered at 520 nm are ascribed due to the transition from 4T1(4P) to 4A2(4F), 4T1(4F) to 4A2(4F), and 4T2(F) to 4A2(4F) respectively. The visible absorption and emission of the nanopowders had been enhanced by annealing. All the samples had room-temperature ferromagnetism (RTFM) and the sample S2 had maximum saturation magnetization among others.

Ligand effects on the dimensionality of cyclophosphazene-based mercury(II) coordination polymers: Structures, UV–Visible absorption and thermal properties

Herein, we have presented a new cyclotriphosphazene-functionalized molecular building block and its two new one-dimensional (1D) Hg(II) coordination polymers. Firstly, the hexakis(5-hydroxy-2-methylpyridyloxy) cyclotriphosphazene (MeHPCP) ligand was prepared and its structure was characterised by 31P{H}, 13C and 1H NMR spectroscopies, mass and FT-IR analysis. Also, its structure was determined by the single crystal X-ray diffraction technique. Next, 1D Hg(II) coordination polymers were successfully synthesized with MeHPCP using HgX2 (X = Cl, I) metal salts. The isolated white crystalline 1D Hg(II) coordination polymers, namely {[Hg(MeHPCP)(Cl)2]}n (1) and {[Hg(MeHPCP)(I)2]}n (2), were structurally characterized by elemental analysis, FT-IR spectroscopy and single crystal X-ray crystallography. Crystallographic analysis revealed that isostructural Hg(II) complexes 1 and 2 crystallize in the triclinic crystal system with the P-1 space group. In complexes 1 and 2, MeHPCP exhibited the κ2N coordination binding mode with the divalent Hg ions to form zig-zag 1D chain structures. The central Hg(II) atoms in complexes 1 and 2 have a distorted seesaw coordination geometry. The UV–Vis properties and the thermal stability of MeHPCP and its complexes (1 and 2) were also investigated. According to the thermogravimetric analysis (TGA), MeHPCP shows a higher thermal stability than 1 and 2.

Two dimensional cubic boron nitride nanosheets converted from hexagonal boron nitride bilayers: electrical conductivity, magnetism and visible absorption properties

The development of novel structure, fabrication methods, formation mechanisms, and versatile applicability of boron nitride (BN) nanomaterials is still one of the research hotspots. In this report, we developed a novel two dimensional cubic boron nitride nanosheets (2D c-BNNSs) based on the first principles calculations. This structure is converted from hexagonal BN (h-BN) bilayers induced by hydroxyl (OH) radical and fluoride (F) atom codoping. The geometrical, electronic, and optical properties of the novel 2D OH radical and F atom codoped c-BNNSs (OH-F-c-BNNSs) have been systematically investigated. The results reveal that the unpaired electrons appear due to the electronegativity difference between OH radical and F atoms, resulting in the excellent electrical and magnetic properties of OH-F-c-BNNSs. In addition, OH-F-c-BNNSs also exhibit a strong response to the visible light with an absorption range covering the whole visible light region. More importantly, when the doping positions of OH radical and F atom are exchanged (F-OH-c-BNNSs), the F-OH-c-BNNS will have only electrical conductivity, which will make us to regulate the intrinsic properties of c-BNNSs for different applications only by adjusting the element doping positions. This work can provide a theoretical and experimental basis/support for designing and fabricating new types of 2D c-BN nanomaterials for different applications.

Paramagnetism and Relaxation Dynamics in Melanin Biomaterials.

Spectroscopical characterization of melanins is a prior requirement for the efficient tailoring of their radical scavenging, ultraviolet-visible radiation absorption, metal chelation, and natural pigment properties. Electron paramagnetic resonance (EPR), exploiting the common persistent paramagnetism of melanins, represents the elective standard for the structural and dynamical characterization of their constituting radical species. Although melanins are mainly investigated using X-band (9.5 GHz) continuous wave (CW)-EPR, an integration with the application of Q-band (34 GHz) in CW and pulse EPR for the discrimination of melanin pigments of different compositions is presented here. The longitudinal relaxation times measured highlight faster relaxation rates for cysteinyldopa melanin, compared to those of the most common dopa melanin pigment, suggesting pulse EPR spin-lattice relaxation time measurements as a complementary tool for characterization of pigments of interest for biomimetic materials engineering.

Electrospinning technique for the fabrication of poly(styrene-co-methyl methacrylate) nanofibers and the effect of fiber diameter on UV–Visible absorption and thermal properties

Nanofibers are gaining much importance in research field owing to its versatile applications and unique properties. Eventhough different methods are there to fabricate nanofibers; electrospinning is of great interest due to its added advantages in terms of cost effectiveness and wide applicability. Among different materials electrospun polymers are more preferred because of no post-processing requisites. The major challenge associated with electrospinning is to optimize the parameters determining the fineness of surface morphology of electrospun fibers. In the present study an attempt is made to investigate the effect of solution parameters such as concentration of the polymer solution, nature and ratio of solvent type and the processing parameters like applied voltage on the fineness of fiber surface morphology of copolymer poly(styrene-co-methyl methacrylate) fibers. The effect of fiber diameter on thermal degradation is monitored. The concentration studies were done by varying the concentration from 3% (w/v) to 20% (w/v) and for solvent studies varying proportions of THF and DMF were chosen. Voltage studies were carried out by varying the applied voltage from 15 kV to 25 kV. The characterization techniques include SEM, TGA UV–Visible Spectroscopy and FTIR analyses. The results showed that by adjusting the applied voltage, concentration of the polymer and solvent ratio, a good control over the fineness of surface morphology can be accomplished. From the TGA analysis it is found the degradation property of nanofibers varied as a function of fiber diameter.