One-step preparation, characterization, and anticancer potential of ZnFe2O4/RGO nanocomposites.

Zinc ferrite nanoparticles (ZnFe2O4 NPs) have attracted extensive attention for their diverse applications including sensing, waste-water treatment, and biomedicine. The novelty of the present work is the fabrication of ZnFe2O4/RGO NCs by using a one-step hydrothermal process to assess the influence of RGO doping on the physicochemical properties and anticancer efficacy of ZnFe2O4 NPs. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy-dispersive X-ray(EDX), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), UV-vis spectroscopy, and Photoluminescence (PL) spectroscopy were employed to characterize prepared pure ZnFe2O4 NPs and ZnFe2O4/ RGO NCs. XRD results showed that the synthesized samples have high crystallinity. Furthermore, the average crystal sizes of ZnFe2O4 nanoparticles (NPs) and ZnFe2O4/RGO nanocomposites (NCs) were 51.08 nm and 54.36 nm, respectively. SEM images revealed that pure ZnFe2O4 NPs were spherical in shape with uniformly loaded on the surface of the RGO nanosheet. XPS and EDX analysis confirmed the elemental compositions of ZnFe2O4/RGO NCs. Elemental mapping of SEM shows that the elemental compositions (Zn, Fe, O, and C) were homogeneously distributed in ZnFe2O4/RGO NCs. The intensity of FT-IR spectra depicted that pure ZnFe2O4 NPs were successfully anchored into the RGO nanosheet. An optical study suggested that the band gap energy of ZnFe2O4/RGO NCs (1.61 eV) was lower than that of pure ZnFe2O4 NPs (1.96 eV). PL spectra indicated that the recombination rate of the ZnFe2O4/ RGO NCs was lower than ZnFe2O4 NPs. MTT assay was used to evaluate the anticancer performance of ZnFe2O4 /RGO NCs and pure ZnFe2O4NPs against human cancer cells. In vitro study indicates that ZnFe2O4 /RGO NCs have higher anticancer activity against human breast (MCF-7) and lung (A549) cancer cells as compared to pure form ZnFe2O4 NPs. This work suggests that RGO doping enhances the anticancer activity of ZnFe2O4NPs by tuning its optical behavior. This study warrants future research on potential therapeutic applications of these types of nanocomposites.

Band gap tuning and surface modification of carbon dots for sustainable environmental remediation and photocatalytic hydrogen production - A review.

Energy and water are the two major issues facing the modern mankind. Providing freshwater requires energy and producing energy uses water. In the present-day scenario, both these routes face growing problems and limitations. Energy crisis has risen due to the depletion of fossil fuels that cause pollution to water bodies making the water unusable for human consumption. In this regard, semiconductor nanocrystals with luminescent properties or carbon quantum dots (CQDs) are the newly developed nanomaterials whose distinctive photo-physical characteristics are focusing to a new generation of robust materials and sensors for sustainable development. In this review, advances in surface and band gap modification of CQDs to improve the activity of nanomaterials will be discussed with special reference to some specific CQDs exhibiting special optical properties for water treatment/splitting applications. Recent advances on CQDs nanocomposites including their applications in photodegradation of organic pollutants, sensing of heavy metal ions in water and water splitting are discussed critically to narrate the future prospects in this field. Challenges and limitations for further improvement are covered to provide smart choices for creating sustainability of benign environment and economic benefits.

Tailoring the Band Gap in 3D Hybrid Perovskites by Substitution of the Organic Cations: (CH3 NH3 )1-2y (NH3 (CH2 )2 NH3 )2y Pb1-y I3 (0≤y≤0.25).

Tuning the optical properties of MAPbI3 (MA=methylammonium) is a key requirement to increase the efficiency of perovskite solar cells (PSCs). Simple precipitation from solution allows the partial substitution of MA in MAPbI3 by H3 NCH2 CH2 NH3 (H2 en). Surprisingly, there is 1:1 exchange of the monovalent cation MA by the dication H2 en. The charge compensation results from a deficit of Pb2+ , leading to a series MA1-2y (H2 en)2y Pb1-y I3 with 0≤y≤0.25. This model has been supported by single-crystal measurements and NMR investigations. The substitution results in a continuous shift of the band gap from 1.51 to 2.1 eV and a color change from black to orange-red. The H2 en content stabilizes the cubic high-temperature (HT) form of MAPbI3 . There is a linear correlation between band gap and unit cell volume. The substitution enables controlled band gap tuning because the extent of substitution is closely related to the applied MA:H2 en ratio in solution.

TiNF and Related Analogues of TiO2 : A Combined Experimental and Theoretical Study.

Aliovalent anion substitution in inorganic materials brings about marked changes in properties, as exemplified by N,F-codoped metal oxides. Recently, complete substitution of oxygen in ZnO by N and F was carried out to generate Zn2 NF. In view of the important properties of TiO2 , we have attempted to prepare TiNF by employing an entirely new procedure involving the reaction of TiN with TiF4 . While the reaction at low temperature (450 °C) yields TiNF in the anatase phase, reaction at a higher temperature (600 °C) yields TiNF in the rutile phase. This is interesting since the anatase phase of TiO2 also transforms to the rutile phase on heating. The lattice parameters of TiNF are close to those of the parent oxide. Partial substitution of oxygen in TiO2 by N and F reduces the band gap, but complete substitution increases the value comparable to that of the oxide. We have examined properties of N,F-codoped TiO2 , and more interestingly N,F-codoped Ti3 O5 , both with lower band gaps than the parent oxides. A detailed first-principles calculations has been carried out on structural and electronic properties of N,F-TiO2 and the TiNF phases. This has enabled us to understand the effects of N,F substitution in TiO2 in terms of the crystal structure, electronic structure and optical properties.

Bandgap Tuning of Silicon Quantum Dots by Surface Functionalization with Conjugated Organic Groups.

The quantum confinement and enhanced optical properties of silicon quantum dots (SiQDs) make them attractive as an inexpensive and nontoxic material for a variety of applications such as light emitting technologies (lighting, displays, sensors) and photovoltaics. However, experimental demonstration of these properties and practical application into optoelectronic devices have been limited as SiQDs are generally passivated with covalently bound insulating alkyl chains that limit charge transport. In this work, we show that strategically designed triphenylamine-based surface ligands covalently bonded to the SiQD surface using conjugated vinyl connectivity results in a 70 nm red-shifted photoluminescence relative to their decyl-capped control counterparts. This suggests that electron density from the SiQD is delocalized into the surface ligands to effectively create a larger hybrid QD with possible macroscopic charge transport properties.

Tuning Nanographene-Enhanced Raman Scattering for Rapid Label-Free Detection of Amino Acids.

The rapid and sensitive detection of amino acids is important not only for fundamental studies but also for the establishment of a healthy society. However, conventional detection methods have been hampered by the difficulties of low sensitivity, long sampling and detection times, and expensive operation and instruments. Here, we report the plasma engineering of bioresource-derived graphene quantum dots (GQDs) as surface-enhanced Raman scattering (SERS)-active materials for the rapid and sensitive detection of amino acids. Surface-functionalized GQDs with tuned structures and band gaps were synthesized from earth-abundant bioresources by using reactive microplasmas under ambient conditions. Detailed microscopy and spectroscopy studies indicate that the SERS properties of the synthesized GQDs can be tuned by controlling the band gaps of synthesized GQDs. The plasma-synthesized metal-free GQDs with surface functionalities showed improved SERS properties for rapid amino acid detection with low detection limits of 10-5 M for tyrosine and phenylalanine. Theoretical calculations suggest that charge transfer between GQDs and amino acids can enhance the SERS response of the GQDs. Our work provides insights into the controlled engineering of SERS-active nanographene-based materials using the plasma-enhanced method.

A Review on Photocatalysis Used For Wastewater Treatment: Dye Degradation.

Water pollution is a global issue as a consequence of rapid industrialization and urbanization. Organic compounds which are generated from various industries produce problematic pollutants in water. Recently, metal oxide (TiO2, SnO2, CeO2, ZrO2, WO3, and ZnO)-based semiconductors have been explored as excellent photocatalysts in order to degrade organic pollutants in wastewater. However, their photocatalytic performance is limited due to their high band gap (UV range) and recombination time of photogenerated electron-hole pairs. Strategies for improving the performance of these metal oxides in the fields of photocatalysis are discussed. To improve their photocatalytic activity, researchers have investigated the concept of doping, formation of nanocomposites and core-shell nanostructures of metal oxides. Rare-earth doped metal oxides have the advantage of interacting with functional groups quickly because of the 4f empty orbitals. More precisely, in this review, in-depth procedures for synthesizing rare earth doped metal oxides and nonocomposites, their efficiency towards organic pollutants degradation and sources have been discussed. The major goal of this review article is to propose high-performing, cost-effective combined tactics with prospective benefits for future industrial applications solutions.

Deposition of Sol-Gel ZnO:Mg Films and Investigation of Their Structural and Optical Properties.

This work presents a facile sol-gel method for the deposition of ZnO and ZnO:Mg films. The films are spin coated on silicon and quartz substrates. The impact of magnesium concentrations (0, 0.5, 1, 2 and 3 wt%) and post-annealing treatments (300-600 °C) on the film's structural, vibrational and optical properties is investigated. Undoped ZnO films crystallize in the wurtzite phase, with crystallite sizes ranging from 9.1 nm (300 °C) to 29.7 nm (600 °C). Mg doping deteriorates the film crystallization and shifting of 002 peak towards higher diffraction angles is observed, indicating the successful incorporation of Mg into the ZnO matrix. ZnO:Mg films (2 wt%) possess the smallest crystallite size, ranging from 6.2 nm (300 °C) to 25.2 nm (600 °C). The highest Mg concentration (3 wt%) results into a segregation of the MgO phase. Lattice constants, texture coefficients and Zn-O bond lengths are discussed. The diminution of the c lattice parameter is related to the replacement of Zn2+ by Mg2+ in the ZnO host lattice. The vibrational properties are studied by Fourier transform infrared (FTIR) spectroscopy. IR lines related to Mg-O bonds are found for ZnO:Mg films with dopant concentrations of 2 and 3 wt%. The optical characterization showed that the transmittance of ZnO:Mg thin films increased from 74.5% (undoped ZnO) to about 89.1% and the optical band gap energy from 3.24 to 3.56 eV. Mg doping leads to a higher refractive index compared to undoped ZnO films. The FESEM (field emission scanning electron microscopy) technique is used for observation of the surface morphology modification of ZnO:Mg films. The doped ZnO films possess a smoother grained surface structure, opposite to the wrinkle-type morphology of undoped sol-gel ZnO films. The smoother surface leads to improved transparency of ZnO:Mg films.

Exploring the Influence of Synthesis Parameters on the Optical Properties for Various CeO2 NPs.

Cerium oxide (CeO2) nanoparticles were synthesized with a chemical precipitation method in different experimental conditions using cerium nitrate hexahydrate (Ce(NO3)3·6H2O) as a precursor, modifying the solution pH, the reaction time, and Co atoms as dopants, in order to tune the band gap energy values of the prepared samples. The physical characteristics of the synthesized ceria nanoparticles were evaluated by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis analyses and photoluminescence measurements. XRD data revealed a pure cubic fluorite structure of CeO2 NPs, the estimation of crystallite sizes by Scherrer's formula indicates the formation of crystals with dimensions between 11.24 and 21.65 nm. All samples contain nearly spherical CeO2 nanoparticles, as well as cubic, rhomboidal, triangular, or polyhedral nanoparticles that can be identified by TEM images. The optical investigation of CeO2 samples revealed that the band gap energy values are between 3.18 eV and 2.85 eV, and, after doping with Co atoms, the Eg of samples decreased to about 2.0 eV. In this study, we managed to obtain CeO2 NPs with Eg under 3.0 eV by only modifying the synthesis parameters. In addition, by doping with Co ions, the band gap energy value was lowered to 2.0 eV. This aspect leads to promising results that provide an encouraging approach for future photocatalytic investigations.

Exploration of structural, thermal stability and band-gap tunability of organic and inorganic mixed cation (MA)1-xCsxPbBr3perovskite harvester via ultrasonication synthesis route.

Extensive investigation over the last few years has been done on halide based perovskite light harvester due to higher power conversion efficiency but the thermal stability with organic cation i.e. methylamine is challenging for the commercialization. Therefore, for improved structural and thermal stability, it is significant to develop a mixed cation base perovskite compound. To improve the thermal and structural stability of the material and easy synthesis method for industrialization of the material, we have demonstrated the compositional engineering of MA/CsPbBr3perovskite material via ultrasonication synthesis process. The x-ray diffraction, transmission electron microscope, diffuse reflectance spectrometer and simultaneous thermal analyzer (STA) analysis were performed in order to understand the impact of the Cs+into MAPbBr3perovskite structure. Structural study reveals that up to 40% Cs+incorporation into MAPbBr3has purePm-3mcubic phase of perovskite compound with continuously increase in micro strain and lattice contraction. On the other hand, with increasing the concentration of Cs+than MA+, optical band gap slightly increases. The thermodynamic behavior and thermal stability of the sample was studied with STA (differential scanning calorimetry/thermogravimetry). For the new generation optoelectronics with admirable stability, we believe that pure phase MA0.60Cs0.40PbBr3perovskite compound may be a promising candidate.

High-Voltage, High-Current Electrical Switching Discharge Synthesis of ZnO Nanorods: A New Method toward Rapid and Highly Tunable Synthesis of Oxide Semiconductors in Open Air and Water for Optoelectronic Applications.

A novel method of oxide semiconductor nanoparticle synthesis is proposed based on high-voltage, high-current electrical switching discharge (HVHC-ESD). Through a subsecond discharge in the HVHC-ESD method, we successfully synthesized zinc oxide (ZnO) nanorods. Crystallography and optical and electrical analyses approve the high crystal-quality and outstanding optoelectronic characteristics of our synthesized ZnO. The HVHC-ESD method enables the synthesis of ZnO nanorods with ultraviolet (UV) and visible emissions. To demonstrate the effectiveness of our prepared materials, we also fabricated two UV photodetectors based on the ZnO nanorods synthesized using the subsecond HVHC-ESD method. The UV-photodetector test under dark and UV light irradiation also had a promising result with a linear ohmic current-voltage output. In addition to the HVHC-ESD method's excellent tunability for ZnO properties, this method enables the rapid synthesis of ZnO nanorods in open air and water. The results demonstrate the preparation, highlight the synthesis of fine hexagonal-shaped nanorods under a second with controlled oxygen vacancies, and point defects for a wide range of applications in less than a second.

Effect of copper concentration and sulfur vacancies on electronic properties of MoS2 monolayer: a computational study.

We investigated the geometrical and electronic properties of copper-doped MoS2 by first principles calculations. The doping is done by Cu substitution with Mo (1 to 4 atoms) accompanied by study of S vacancies. Our outcomes show that the concentration of doping and vacancy of S leads to determine and finely tune the band gap in the range of 0.16 to 1.95 eV. This fine tuning of band gap results due to variation in concentration of impurity, changing dopant site, and production of S vacancies. The resulting arrangements show significant charge redistribution on replacement of local atoms with foreign atoms dictated by electronegativity determined from the Bader analysis. In addition, bonding mechanism occurring due to substitution of foreign elements is discussed. These results give pleasing data regarding fine desired value of the band gap of the MoS2 which helps its utilization in semiconductor and other opto-electronic devices in addition to understanding the electrical conductivity.

Monocrystalline InP Thin Films with Tunable Surface Morphology and Energy Band gap.

InP is currently being used in various (opto)electronic and energy device applications. However, the high cost of InP substrates and associated epitaxial growth techniques has been huge impediments for its widespread use. Here, large-area monocrystalline InP thin films are demonstrated via a convenient cracking method, and the InP thin films show material properties identical to their bulk counterparts. Furthermore, the same substrate can be reused for the production of additional InP thin films. This cracking technique is also shown to be a versatile tool to form an ultrasmooth surface or a microscale periodic triangular grating structure on the surface, depending on the orientation of the donor substrate used. Strain-induced band gap energy shift is also observed in localized regions of the thin film with a grating structure. The simplicity of this technique, which does not require any sophisticated equipment and complex fabrication process, is promising to reduce the cost of InP thin-film devices.

Solvent-Free Mechanochemical Synthesis of a Systematic Series of Pure-Phase Mixed-Halide Perovskites MAPb(Ix Br1-x )3 and MAPb(Brx Cl1-x )3 for Continuous Composition and Band-Gap Tuning.

Hybrid perovskites have recently received much attention in optoelectronic applications. However, hybrid perovskites are unstable in a humid environment. Mixed halide perovskites (MHPs) show enhanced stability and band-gap tunability upon engineering of their halide composition. Here, MHPs are prepared through a solvent-free mechanochemical synthesis (MCS) route that allows superior control over halide compositions than the solvent synthesis routes (SS). The MCS route eliminates the problem in the preparation of MAPb(Ix Br1-x )3 with continuously varying x, while maintaining the material properties and suppressing phase segregation present in SS routes. UV-vis absorption and X-ray diffraction patterns confirm the production of the desired pure-phase MHPs. For MAPb(Ix Br1-x )3 (0≤x≤1), with increased ratio of halide (x), the cubic phase gradually transforms into the tetragonal phase and band-gap tunability is accomplished. The MCS route for the preparation of MHPs is a very promising and efficient technique for superior control in optoelectronic properties, leading to improved control in fabrication approaches.

Sulfur-Alloying Effects on Cu(In,Ga)(S,Se)2 Solar Cell Fabricated Using Aqueous Spray Pyrolysis.

We fabricated Cu(In,Ga)(S,Se)2 (CIGSSe) solar cells using aqueous spray based deposition, which is inexpensive and covers a large area. To apply the sprayed film to a photoabsorber of a solar cell, post-sulfo-selenization was carried out. Through the sulfo-selenization process, we were able to fabricate various S-alloyed CIGSSe films from S/(S + Se) = 0 (S-0.0) to S/(S + Se) = 0.4 (S-0.4). CIGSSe solar cells were made with the S-alloyed CIGSSe absorbers. Power conversion efficiency of CIGSSe solar cell was found to be increased with S-alloying up to S-0.3, and the best efficiency of 10.89% was obtained with the S-0.3 CIGSSe absorber. Comparison study of S-alloyed CIGSSe solar cells showed that enhanced efficiency in S-0.3 solar cell is due to the increased open-circuit voltage and an improved fill factor, which is induced by S-alloying. In addition, admittance spectroscopy revealed that the defect density of the deep level was developed in the S-alloyed S-0.3 CIGSSe absorber. However, the defect density was observed to be rather reduced. Details of characterization and analysis results are discussed in this paper.

Gas-Induced Confinement-Deconfinement Interplay in Organic-Inorganic Hybrid Perovskite Thin Film Results in Systematic Band Modulation.

Gas-induced growth of organic-inorganic hybrid perovskites, especially methylammonium lead iodide (MAPbI3), has shown interesting properties and applications in the area of optoelectronics. In this report, we introduce a method of gas-induced band gap engineering of thin films of MAPbI3 due to systematic dimensional confinement-deconfinement along the crystallographic c axis of growing MAPbI3. Interestingly, such a restricted growth phenomenon was observed when the hexylammonium lead iodide (two-dimensional hybrid perovskite) film was exposed to methylamine gas instead of the conventional PbI2 film-methylamine gas precursor pair. Hexylamine, formed due to the cation exchange reaction, interacts selectively with the Pb centers of growing MAPbI3 crystals, and this induces an enormous restriction in the growth of MAPbI3 along the crystallographic c direction, leading to a unique sheet-type MAPbI3 film having a much higher band gap (2.18 eV) compared to conventional bulk MAPbI3. However, careful control of exposure timing gradually evaporates the hexylamine, leading to systematic dimensional deconfinement, enabling modulation of the band gap from 2.18 to 1.69 eV. An interplay of adsorption and desorption of hexylamine is also utilized for generating patterns of two different fluorescent hybrid perovskite materials in a single pixel. This new mechanistic investigation highlighting gas-induced interplay of dimensional confinement-deconfinement associated with band gap tuning provides smooth thin films, which can be used to develop optoelectronic devices.

Two-Phase Room-Temperature Multiferroic Nanocomposite with BiMnO3-Tilted Nanopillars in the Bi2W1-xMnxO6 Matrix.

Single-phase multiferroics are scarce because of the fact that the coexistence of magnetism (spin order) and ferroelectricity (electric dipole order) in a single-phase material may be limited. Taking advantage of the nanocomposite design, combining a ferroelectric phase and a ferromagnetic phase presents enormous opportunities in multiferroic material exploration. In this work, a new 2D-layered framework of Bi2W1-xMnxO6-BiMnO3 (BWMO-BMO) in the nanocomposite thin-film form has been demonstrated and shows obvious room-temperature multiferroic properties, that is, ferroelectric and ferromagnetic at room temperature. The BMO phase forms a unique tilted domain structure in the BWMO matrix, and both phases are of excellent epitaxial quality. The ferroelectric response originates from the layered Aurivillius phase of the BWMO matrix, and the ferromagnetic properties mainly arise from the BMO nanodomains. Moreover, the band gap of the BWMO-BMO nanocomposite is effectively tuned to 3.10 eV from its original 3.75 eV of BWO. This study demonstrates a new design of nanocomposite using layered oxides toward future multifunctional oxides for nanoscale devices.

Tuning Band Alignments and Charge-Transport Properties through MoSe2 Bridging between MoS2 and Cadmium Sulfide for Enhanced Hydrogen Production.

Transition-metal dichalcogenide materials play a major role in the state-of-the-art innovations for energy conversion because of potential applications resulting from their unique properties. These materials additionally show inordinate potential toward the progress of hygienic power sources to deal with increasing environmental disputes at the time of skyrocketing energy demands. Herein, we report earth-abundant, few-layered, MoSe2-bridged MoS2/cadmium sulfide (CdS) nanocomposites, which reduce photogenerated electron and hole recombination by effectively separating charge carriers to achieve a high photocatalytic efficiency. Accordingly, the MoSe2-bridged MoS2/CdS system produced effective hydrogen (193 µmol·h-1) as that of water using lactic acid as a hole scavenger with the irradiation of solar light. The presence of few-layered MoSe2 bridges in MoS2/CdS successfully separates photogenerated charge carriers, thereby enhancing the shuttling of electrons on the surface to active edge sites. To the best of our knowledge, this few-layered MoSe2-bridged MoS2/CdS system exhibits the most effective concert among altogether-reported MoS2-based CdS composites. Notably, these findings with ample prospective for the development of enormously real photocatalytic systems are due to their economically viable and extraordinary efficiency.

Graphitic Nitrogen Triggers Red Fluorescence in Carbon Dots.

Carbon dots (CDs) are a stable and highly biocompatible fluorescent material offering great application potential in cell labeling, optical imaging, LED diodes, and optoelectronic technologies. Because their emission wavelengths provide the best tissue penetration, red-emitting CDs are of particular interest for applications in biomedical technologies. Current synthetic strategies enabling red-shifted emission include increasing the CD particle size (sp2 domain) by a proper synthetic strategy and tuning the surface chemistry of CDs with suitable functional groups (e.g., carboxyl). Here we present an elegant route for preparing full-color CDs with well-controllable fluorescence at blue, green, yellow, or red wavelengths. The two-step procedure involves the synthesis of a full-color-emitting mixture of CDs from citric acid and urea in formamide followed by separation of the individual fluorescent fractions by column chromatography based on differences in CD charge. Red-emitting CDs, which had the most negative charge, were separated as the last fraction. The trend in the separation, surface charge, and red-shift of photoluminescence was caused by increasing amount of graphitic nitrogen in the CD structure, as was clearly proved by XPS, FT-IR, Raman spectroscopy, and DFT calculations. Importantly, graphitic nitrogen generates midgap states within the HOMO-LUMO gap of the undoped systems, resulting in significantly red-shifted light absorption that in turn gives rise to fluorescence at the low-energy end of the visible spectrum. The presented findings identify graphitic nitrogen as another crucial factor that can red-shift the CD photoluminescence.