Light In Wavelength Range Research Articles

Red light enhances the antibacterial properties, biofabrication, and stability of Fagonia indica callus-based silver nanoparticles.

Plant-based nanoparticles can be tuned through the frequency of light for efficient synthesis, structural properties, and antibacterial applications. This research assessed the effect of material type (callus and whole-plant extract) and the interaction with a specific range of light wavelength on AgNP synthesis. All types of AgNPs were characterized by their size, shape, associated functional groups, and surface charge. Interestingly, the size of red light and callus-based AgNPs (RC-AgNPs) was smaller (6.32 nm) compared to 14.59 nm for Ultraviolet light and callus-based AgNPs (UV-C-AgNPs). Zeta potential analysis showed that RC-AgNPs had higher stability (-29.2 mV) compared to UV-C-AgNPs (-16.7 mV). Similarly, red light-based AgNPs had higher Oxidation reduction potential in both whole-plant-based and callus-based AgNPs, indicating a more oxidizing nature compared to those synthesized under UV light. This was confirmed by the lower total phenolic and flavonoid content associated with them and their lower antioxidant activity. The higher antibacterial activities and lower minimum inhibitory concentrations of red light-based AgNPs against highly resistant pathogenic bacteria demonstrated the role of red light in enhancing antibacterial activity. These results indicate that AgNPs synthesized in red light and callus extract are more active compared to those synthesized under other wavelengths and/or in whole-plant extracts.

The Mutating Effect of Microwave Irradiation on Spores and Crystal Protein Formation of Iraqi Bacillus thuringiensis kurstaki KS3

Alkhafaji, K.A., F.H. Nahar, S.A. Khlaywi, M.A. Abedallah, A.J. Feaath, A.A. Mezban. and S.A. Saleh. 2023. The Mutating Effect of Microwave Irradiation on Spores and Crystal Protein Formation of Iraqi Bacillus thuringiensis kurstaki KS3. Arab Journal of Plant Protection, 41(3): 285-291. https://doi.org/10.22268/AJPP-041.3.285291 Bacillus thuringiensis is the most important biological control agent that is used in fields and stores against insect pests of agricultural importance. This research was conducted to study the effect of microwave radiation on sporogenesis and crystal protein production by the Iraqi bacterium B. thuringiensis KS3 strain. The bacterium was enriched by Lauria bertani broth (LB) pH 7.0 for spore formation. Spore suspension was microwave irradiated at 1000 Watt for 5, 10 and 15 seconds. Spore inactivation rate for each time period of microwave treatment was calculated and the macroscopic differences were examined. Crystal protein and spore production were estimated for irradiated and nonirradiated bacterial cultures. Viable spores in the control treatment was 3×108 viable spores/ml, and decreased after 5, 10, and 15 s of microwave treatment to 3×107 , 2×106 and 2×104 viable spores/ml, respectively. The reduction of spore viability reached to 49.263% 15 seconds after treatment. The appearance of colonies on the top of nutrient agar (NA) were almost similar with the control, with no differences in color, margin and surface of treated colonies following the three time periods treatment. Colonies with dense color, smaller in size and with straight margin appeared on congo red culture for all treatments in contrast to the control. Microscopic examination showed that treated bacilli were similar regarding their shape, diameter and arrangement, however,smaller bacterial cell size following 15 s irradiation treatment was observed. Control culture after 72 h started to form spores, whereas after 24 h, irradiated spores for 5, 10 and 15 s formed 75, 90 and 90% viable spores, respectively. Crystal protein reached the highest concentration after 72 h in control culture, whereas it varied based on treatment period. The production of viable spores from microwave irradiated isolates increased about one logarithmic cycle compared with the control culture of B. thuringiensis KS3.The peak of the UV spectrum of Crystal protein extracts was recognized at 255-280 nm and the peak of the curve indicated the protein concentration at a given wavelength. Differences were recognized in the UV light wavelength range of 220-235 nm. Keywords: Sporogenesis, Physical effect, Delta toxin.

Dynamic tuning of optical absorbance and structural color of VO2-based metasurface

Abstract Vanadium dioxide (VO2) is an attractive thermal-control material exhibiting low thermal hysteresis and excellent temperature cycling performance. However, the deficiencies including weak spectral shift and narrow-band absorption during insulating-metallic transitions hinder its application in optoelectronics. The transition metal dichalcogenides (TMDs) can provide a promising solution with their high dielectric properties and robust optical coupling. Here, we report a MoS2/VO2/Au/Si metasurface and investigate the dynamic tunability of its optical absorbance and structural color upon heating via spectroscopic ellipsometry measurements and numerical simulations. The first-principles calculations reveal that the dielectric absorptions of metallic and insulating VO2 oppositely response to temperature, closely related to the difference in the transitions of O-2p states. Finite-element simulations reveal that the introduction of MoS2 nanostructure induces more absorption peaks by 2∼3 and achieves strong absorption in the full wavelength range of visible light. The Fabry–Perot (F–P) resonance is the critical factor for the optimized optical absorption. The structural color is sensitive to environmental perturbations at high-ε state of VO2, lower oblique incidence angles, and heights of MoS2. This work seeks to facilitate the spectral modulation of phase change metamaterials and can be extended to photoelectric detection and temperature sensing applications.

Perovskite quantum dots modulating upconversion nanomaterials for cancer early detections

The accurate diagnosis and treatment of cancer cell lesions need a high standard of detection technology. Fluorescent probes to perform cancer biomarker detection have become a popular research issue. However, fluorescent probes still face enormous challenges of complex design and difficult detection. In this work, we propose a novel composite material UCNP@SiO2 + QDs based on the combination of rare earth upconversion (UCNPs) and perovskite quantum dots (QDs) and design a new fluorescent probe MB-UCNP@SiO2 + QDs with molecular beacon (MB) as the carrier, that can be excited by near-infrared light, emitted in the visible wavelength, specifically identified and highly sensitive. Under the excitation of 980 nm near-infrared light, the UCNPs and QDs in the composite produced the maximum efficiency of energy transfer through fluorescence resonance, and the multi-emission light of UCNPs synergistically excited the re-emission of QDs, and the energy transfer efficiency is 70.6%. By changing the doping ratio of QDs halogen elements in UCNP@SiO2 + QDs, it is possible to modulate the precise luminescence of UCNP@SiO2 + QDs in the entire wavelength range of visible light at different positions. The novel fluorescent probe is obtained using UCNP@SiO2 + QDs and Black Hole Quencher-1 (BHQ1) quenching groups linked to the two respective sides of MB, selecting as the target of detection the myeloma cancer biomarker miRNA-155, a difficult diagnostic and complex developmental type, and have achieved specific recognition and low concentration of miRNA-155 and a detection limit of 73.5 pM. This fluorescent probe design can provide new ideas for the early diagnosis and treatment of cancer, tumors, and cardiovascular diseases.Graphical

Quantitative Optical and Structural Comparison of 3D and (2+1)D Colloidal Photonic Crystals.

Colloidal crystals are excellent model systems to study self-assembly and structural coloration because their periodicities coincide with the wavelength range of visible light. Different assembly methods inherently introduce characteristic defects and irregularities, even with nearly monodisperse colloidal particles. Here, we investigate how these imperfections influence the structural coloration by comparing two techniques to obtain colloidal crystals. 3D colloidal crystals produced by convective assembly are well-ordered and periodically arranged but show microscopic cracks. (2+1)D colloidal crystals fabricated by stacking individual monolayers show a decreased hexagonal order and limited crystal registration between single monolayers in the z-direction. We investigate the optical properties of both systems by comparing identical numbers of layers using correlative microspectroscopy. These measurements show that the less ordered (2+1)D colloidal crystals exhibit higher reflected light intensities. Macroscopic reflection integrating all angles shows that the reflected light intensity levels out with an increasing number of layers, whereas incoherent scattering increases. Although both types of colloidal crystal show similar angle-dependent color shifts in specular reflection, the less-ordered structure of the (2+1)D colloidal crystal scatters light within a larger angular range under diffusive illumination. Our results suggest that structural coloration is surprisingly robust toward local defects and irregularities.

Vanadyl Naphthalocyanine-Doped Polymer Dots for Near-Infrared Light-Induced Nitric Oxide Release and Bactericidal Effects

The development of efficient antibacterial agents is important for public health. To completely damage bacteria in situ, light has been used as an external stimulus, but the wavelength range of light is limited up to visible light at which the antimicrobial activity is incomplete. Here, we report on our investigation of the bactericidal effect of heat and nitric oxide (NO) generated simultaneously by near-infrared (NIR) light using vanadyl naphthalocyanine-doped polymer dots (P-dots). P-dots co-doped with vanadyl naphthalocyanine and N-nitroso compounds generated heat and released NO upon NIR light irradiation. The amount of NO released was dramatically enhanced owing to the ease of bond dissociation in N-nitroso compounds in the presence of generated heat. The anti-bacterial effect of P-dots on Staphylococcus epidermidis and Pseudomonas aeruginosa was clearly caused by heat and NO, demonstrating the potential use of P-dots as antimicrobial agents.

Optical absorption performance of CZTS/ZnO thin film solar cells comprising anti-reflecting coating of texturing configuration.

This paper introduces a novel design of a thin-film solar cell based on CZTS and ZnO composite materials with the help of ITO as the front contact layer. This study primarily focuses on how the cells' optical absorbance at visible wavelengths can be improved. COMSOL Multiphysics is employed as a powerful tool for the investigation of the numerical simulation. The numerical findings showed that the optimum thicknesses of the ITO and ZnO are 80 and 350 nm, respectively. In this regard, with a normal incidence, a wide range of incoming light wavelengths from 450 nm to 800 nm might result in optical absorption of the examined cell of above 0.9. However, this value decreased significantly to reach less than 0.75 when the angle of incidence increased to 50°. To minimize this reduction, on the top surface of the cell, a texture-designed anti-reflective coating designed from a single period of well-known one-dimensional photonic crystals is deposited. The findings demonstrated that the cell's absorption at normal incidence could reach over 0.96 through the overall incident wavelengths. Therefore, CZTS/ZnO thin-film solar cells with an anti-reflecting coating of texturing configuration showed enormous potential for manufacturing effective solar cells.

Preparation and photoelectric property of large scale monolayer MoS<sub>2</sub>

Transition metal dichalcogenide (TMDC) monolayers exhibit enhanced electrical and optoelectrical properties, which are promising for next-generation optoelectronic devices. However, large-scale and uniform growth of TMDC monolayers with large grain size is still a considerable challenge. Presented in this work is a simple and effective approach to fabricating largescale molybdenum (MoS<sub>2</sub>) disulfide monolayers by chemical vapor deposition (CVD) method. It is found that MoS<sub>2</sub> grows from single crystal into thin film with the increase of oxide precursor proportion. The photodetector of large scale monolayer layer MoS<sub>2</sub> film is fabricated by depositing metal electrodes on the interdigital electrode mask through using thermal evaporation coating. Finally, the highly stable and repeatable photoelectric responses under the conditions of different voltages and different laser power are characterized under 405-nm laser excitation, with response time decreasing down to the order of milliseconds (ms). In addition, the photodetector achieves a wide spectral detection range from 405 nm to 830 nm, that is, from visible light to near-infrared light wavelength range, with optical response (<i>R</i>) of 291.7 mA/W and optical detection rate (<i>D</i><sup>*</sup>) of 1.629×10<sup>9</sup> Jones. The monolayer MoS<sub>2</sub> thin film photodetector demonstrated here has the advantages of low cost, feasibility of large-scale preparation, and good stability and repeatability in the wide spectrum range from visible light to near infrared light wavelength, providing the possibilities for future applications of electronic and optoelectronic devices .

Two-Terminal Perovskite Tandem Solar Cells: from Design to Commercial Prospect

Tandem Solar Cells (TSCs) with multi-junction are capable to break the SQ limit and achieve high PCE through absorbing larger range of light wavelength by multiple absorber layers with different band gaps. Perovskite solar cells are ideal light absorbing materials for TSC because of its high PCE, high suitability with other absorbers, low cost and easy fabrication. Perovskite-based TSCs have so far outperformed single-junction devices in PCE, garnering considerable interest from both academia and material industry. In this review, the basic science of perovskite Tandem Solar Cells (PTSCs) is presented, as well as the construction and properties of PSC as a top cell. Then three main types of PTSCs are introduced: Perovskite/Si, Perovskite/CIGS, and Perovskite/Perovskite including their design, challenges and fabrication methods. Finally, the current status and future prospects for commercialization of PTSCs are also discussed. According to recent developments, PTSCs are considered to be one of the most promising solar cells. Research on PTSCs could contribute to the development of desirable clean energy sources in order to solve the energy crisis and environmental problems of human beings.

Green-Lighting the Sub-Band Gap Excitation in Two-Dimensional Zinc Oxide.

Solar spectrum and sensitivity of human eyes peak at green wavelength range of visible light, and the materials that can respond to a larger part of the visible spectrum are highly sought after. Two-dimensional graphene-like zinc oxide (gZnO) is a wide band gap semiconductor, but photogeneration of electron-hole pairs in it at visible wavelengths has not been achieved so far. Here, the sub-band gap excitation in 2D zinc oxide layers covered with gold nanoparticles is reported. The sub-band gap excitation and corresponding emission are correlated with oxygen interstitials introduced by AuNP deposition in the gZnO lattice. Attachment of AuNPs on gZnO also leads to increased electron availability at oxygen sites of the gZnO lattice, which translates into greater electron availability for sub-band gap excitation. The plasmonically enhanced trap level to conduction band transition constitutes sub-band gap excitation and manifests itself in local surface potential measurements carried out using a Kelvin probe force microscope.

γ-MnO2-deposited photonic crystal fiber: Novel photonic devices for multi-state solitons generation

Transition metal oxides, especially MnO2 nanoparticles, are often used as cathode of dry batteries and catalysts. They are also promising materials for ultrafast laser applications due to their strong absorption in visible light and near-infrared wavelength range. In this work, high-concentration MnO2 nanoparticles dispersions embedded in the hole cladding of dual-hole photonic crystal fiber is fabricated as a saturable absorber with a modulation depth of 4 % and a saturation intensity of 25 MW/cm2. Strong MnO2-light interaction occurs due to enhanced evanescent-field strength (over 10 cm) of the SA could enable stable mode locking operation at 1.55 μm region. By inserting a Sagnac fiber filter in the cavity, multi-state solitons are experimentally demonstrated with identical layout, respectively, which greatly improves the versatility of this laser. This study proves that MnO2 nanoparticles possess excellent nonlinear optical properties in the near-infrared band. The simple in-line structure of the proposed nanoparticles-deposited device could pave a way for high power and all-fiber applications of photonics.

Characterizing the efficiency of low-cost LED lights for conducting laboratory studies to investigate polycyclic aromatic hydrocarbon photodegradation processes

Polycyclic aromatic hydrocarbons (PAHs) are common contaminants ubiquitously present in various waste products such as biosolids (e.g. wastewater sludges), oil spill residues (e.g. tarballs), road asphalts, and combustion byproducts. In this study, the photodegradation of PAHs is investigated under natural sunlight (cloudy and sunny/clear weather conditions), and using two types of artificial LED light sources. This is the first study to investigate the relative efficiency of low-cost LED light sources for conducting laboratory-scale PAH photodegradation experiments and directly comparing the results against those obtained using natural sunlight. Two types of LED light sources are investigated in this study: a light source with a full-spectrum range (380 nm–780 nm) that can cover the broad wavelength range of solar light reaching the Earth's surface, and a light source with a UV-A range (365 nm) that covers the UV range of the solar spectrum reaching the Earth's surface. The results show that the degradation of high molecular weight (HMW) PAHs is primarily due to photodegradation, and other lighter PAHs are degraded by both photodegradation and evaporation processes. HMW PAH photodegradation reactions follow the first-order degradation kinetics. The degradation rate constants of different PAHs are used to compare the relative efficiency of the light sources. The data show that the full-spectrum LED induced PAH photodegradation rates are similar to the natural sunlight induced rates. Furthermore, when the values of the rate constants are normalized to respective irradiance levels, the normalized rates for HMW PAH photodegradation under both full-spectrum LED light and natural sunlight are almost identical. However, the normalized photodegradation rate constants of HMW PAHs under the UV-A LED light are about two to three orders of magnitude higher than the sunlight as well as the full-spectrum-LED values. Therefore, the UV-A LED light is the optimal low-cost light source for studying PAH photodegradation processes under laboratory conditions.

2D/1D MoS2 /TiO2 Heterostructure Photocatalyst with a Switchable CO2 Reduction Product.

Regulating the transfer pathway of charge carriers in heterostructure photocatalysts is of great importance for selective CO2 photoreduction. Herein, the charge transfer pathway and in turn the redox potential succeeded to regulate in 2D MoS2 /1D TiO2 heterostructure by varying the light wavelength range. Several in situ measurements and experiments confirm that charge transfer follows either an S-scheme mechanism under simulated solar irradiation or a heterojunction approach under visible light illumination, elucidating the switchable property of the MoS2 /TiO2 heterostructure. Replacing the simulated sunlight irradiation with the visible light illumination switches the photocatalytic CO2 reduction product from CO to CH4. 13 CO2 isotope labeling confirms that CO2 is the source of carbon for CH4 and CO products. The photoelectrochemical H2 generation further supports the switching property of MoS2 /TiO2 . Unlike previous studies, density functional theory calculations are used to investigate the band structure of Van der Waals MoS2 /TiO2 S scheme after contact, allowing to propose accurate charge transfer pathways, in which the theoretical results are well matched with the experimental results. This work opens the opportunity to develop photocatalysts with switchable charge transport and tunable redox potential for selective artificial photosynthesis.

Site-Selective Occupancy Control of Cr Ions toward Ultrabroad-Band Infrared Luminescence with a Spectral Width up to 419 nm.

Infrared-emitting phosphor-converted light-emitting diodes (LEDs) are desirable light sources for a very wide range of applications such as spectroscopy analysis, nondestructive monitoring, covert information identification, and night-vision surveillance. The most important aspect of infrared emitters for spectroscopy is to cover the widest possible wavelength range of emitted light. However, developing ultrabroad-band infrared emitters based on converter technology is still a challenging task due to the lack of suitable phosphor materials that emit in a wide wavelength range upon excitation from blue-emitting chips. Herein, this work demonstrates Cr3+-activated Mg2SiO4 infrared phosphors with a super wide infrared spectral range of 600 to 1400 nm and high internal quantum yield up to 80.4% upon 460 nm excitation. Site-selective occupancy of Cr3+ emitters in two different Mg sites in the Mg2SiO4 lattice results in two distinct broad emission bands peaking at 760 and 970 nm, both of which contribute to the ultrabroad-band infrared luminescence with a full width at half maximum (FWHM) of 419 nm. This is by far the broadest infrared emission to the best of our knowledge. On this basis, an ultrabroad-band infrared LED prototype has been fabricated by the combination of the Mg2SiO4:Cr3+ phosphor with a blue LED chip, which shows great potential for imaging and sensing applications. This work demonstrates that site-selective occupancy control of Cr ions is an effective strategy for developing ultrabroad-band Cr3+-doped phosphors.

Research on achromatic Risley prism in normal tracing angle measurement system

The normal tracing angle measurement system based on Risley prisms can eliminate the influence of aberrations other than the dispersion of Risley prisms on the angle measurement accuracy. Although the traditional dispersion optimization method based on the extreme point can make the beam directions of different wavelengths more consistent after passing through the Risley prisms, the light intensity distribution that deviates from the extreme point wavelength causes the spot centroid to deviate from the target position, thus introducing the angle measurement error. In this paper, we propose a highly symmetry-glued achromatic Risley prisms optimization method for the needs of a normal tracing angle measurement system. Our method not only realizes the beam direction as closely as possible after the deflection of the Risley prisms but also compensates for the centroid error caused by the beam deviating from the central wavelength. ZEMAX simulation shows that, in the normal tracing angle measurement system, within the angle measurement range of ±700 ″ and the light source wavelength range of 600 to 700 nm, the angle measurement error introduced by the dispersion of the optimized Risley prisms is not >0.01 ″ .

Rational design and fabrication of optically transparent broadband microwave absorber with multilayer structure based on indium tin oxide

A multilayer metamaterial absorber (MMA) with optically transparent and broadband microwave absorption characteristics based on Indium Tin Oxide ( ITO) and polymethyl methacrylate (PMMA) was designed and fabricated. The microwave absorption properties can be regulated by the resistance of ITO and the structural parameters of the unit cell. In the frequency range of 2.64–18 GHz, more than 90 % microwave absorption can be achieved. The microwave attenuation mechanism was investigated through equivalent electromagnetic parameters, impedance matching, electric and magnetic field distribution, power loss density and layer electric current at special frequencies. The microwave absorption performance at different incident angles under TE and TM polarization models was investigated to explore the angle-sensitive properties. The average transmittance of the absorber in the visible light wavelength range (400–800 nm) was also measured. The experimental and simulated microwave absorption rates are in accordance, indicating the potential application of the proposed absorber in the field of transparent microwave absorption. • Visible light transparent metamaterial absorber is fabricated. • The microwave absorbance over 90 % can be achieved within 2.64–18 GHz. • The metamaterial absorber has polarization insensitive and wide-angle stability properties. • Microwave attenuation mechanisms were investigated by surface electric current.

Design Simulation and Optimization of Germanium-Based Solar Cells with Micro-Nano Cross-Cone Absorption Structure

In this paper, germanium-based solar cells were designed based on germanium (Ge) materials, and the cross-cone (CC) nanostructures were used as the absorber layer of the solar cells. The optical path inside the absorber layer was increased by microstructure reflection, thereby increasing the absorption efficiency of the germanium-based solar cell. The reflectivity, transmittance, electric field and magnetic field of the corresponding position of the device were simulated and calculated by the finite difference time domain (FDTD) method. By simulating doping and simulating the external potential difference, the short-circuit current density (JSC), open-circuit voltage (VOC), output power and photoelectric conversion efficiency (η) of the device were calculated. The study found that for the entire study wavelength range (300–1600 nm), the transmittance of the device was close to none, and the average light absorption rate under air mass 1.5 global (AM1.5G) was 94.6%. In the light wavelength range from 310 nm to 1512 nm with a width of 1201 nm, the absorption rate was greater than 90%, which is in line with the high absorption of the broadband. Among them, the absorption rate at 886 nm reached 99.84%, the absorption rate at 1016 nm reached 99.89%, and the absorption rate at 1108 nm reached 99.997%, which is close to full absorption. By exploring the electrical performance of the device under different Ge nanostructure parameters, a germanium-based solar cell device under the nanocross-cone absorption structure array with both high-efficiency light absorption and excellent electrical performance was finally obtained. The study shows that the VOC of its single-junction cell was 0.31 V, JSC reached 45.5 mA/cm2, and it had a fill factor (FF) of 72.7% and can achieve a photoelectric conversion efficiency of 10.3%, surpassing the performance of most Ge solar cells today.

Study on microstructure and extinction characteristics of particulate matter in diesel engine fueled with different biodiesels.

Biodiesel combustion particulate matter (PM) is different from diesel combustion PM in terms of microscopic morphology, which directly affects the optical properties of PM. To investigate the effect of the microstructure of biodiesel PM on the extinction characteristics, an experiment was performed on a high-pressure common rail diesel engine to collect PM from three kinds of biodiesel (the main raw materials were soybean oil methyl eater (SME), palm oil methyl eater (PME), and waste cooking oil methyl eater (WME), respectively). The particle size distribution, micro morphology, and extinction characteristics of biodiesel PM were analyzed. Results show that combustion biodiesel reduces PM emissions by up to 84.2%. Compared to PM from diesel, biodiesel PM has a smaller particle size and a higher aggregation degree, which results in weaker light absorption capacity. With the iodine number of biodiesel decreasing, the number concentration of biodiesel PM decreases and the fractal dimension increases, which leads to producing a more complex agglomerate and a consequent reduction in extinction coefficient. The average particle sizes of PM from SME, PME, and WME are 5.1%, 6.7%, and 13.9% lower than that of diesel PM. Compared with diesel combustion PM, the peak absorption coefficients of SME, WME, and PME combustion PM decrease by 8.4%, 11.4%, and 13.3%, respectively. The extinction properties of particles decrease with increasing fractal dimension within the wavelength range of visible light.

Effluent degradation followed hydrogen production using near-infrared sensitized nanocomposite of reduced nanographene oxide under visible light.

The purpose of this research work is to synthesize near-infrared dye-sensitized nanocomposites with core-shell nanostructures of titanium dioxide/reduced nanographene oxide (TiO2/r-NGO) to be an effective photocatalyst for effluent degradation followed hydrogen generation under visible light irradiation. The generation of hydrogen using photocatalysts has been intensely researched for the effective utilization of hydrogen in a controlled way. The mechanistic pathway for both hydrogen generation and effluent degradation utilizes the electrons generated through photoexcitation during dye sensitization. For this reason, the squaraine dyes were synthesized by the C-H-direct arylation method and made the nanocomposites with self-assembled core/shell nanocomposites (r-NGOT), where TiO2 serves as the core and r-NGO as the shell. Due to the lack of anchoring groups, VJ-Q was only adsorbed on the surface of r-NGOT through π-π stacking, which is confirmed by Fourier transformed-infrared spectroscopy, X-ray photoelectron spectroscopy, high resolution-transmission electron microscopy, and electron energy loss spectroscopy. The optical absorption spectra of VJ-Q/r-NGOT nanocomposites measured with diffuse reflectance UV/visible absorption spectroscopy covers the whole range of visible light wavelengths up to 800nm. During the photocatalytic activity, VJ-Q/r-NGOT/Pt followed a ligand-to-metal-charge transfer (LMCT) type mechanism for the electron transfer to the core-shell nanostructure. This mechanistic pathway is utilized for the effluent dye degradation followed hydrogen generation through water splitting. The photocatalytic efficiency of the nanocomposite with adsorbed dye is superior to that of dye-TiO2 due to the large surface area provided by r-NGO and the prevention of dye aggregation. The work is significant due to the limited research works that are carried under dye-sensitized nanocomposites that have been utilized for both dye degradation and hydrogen generation.

A comparative study on the photocatalytic activity and formation mechanism of nanostructured Cu2ZnSnS4 prepared by thermal and mechano-thermal methods

In this paper, a nanostructured Cu2ZnSnS4 (CZTS) was synthesized from elemental constituents through two simple methods: thermal and mechano-thermal. The thermal analysis was applied to determine the appropriate heat treatment conditions. Wet ball milling was employed in mechano-thermal synthesis to obtain a uniform activated powder, and the optimum conditions were investigated. The X-ray diffraction (XRD) and Raman results confirmed the formation of kesterite structure CZTS after annealing the mixture at 550 °C for 1 h in thermal synthesis, while the annealing temperature for CZTS formation is reduced to 410 °C in mechano-thermal synthesis. For mechano-thermally synthesized sample, the scanning electron microscopy (SEM) and the transmission electron microscopy (TEM) results showed the agglomerated powders with average particle sizes of 123 and 139 nm, respectively. The surface and optical properties of samples were compared through Brunauer-Emmett-Teller (BET), diffusion reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. DRS results demonstrated considerable absorbance over the entire range of visible light wavelengths with bandgap energies of about 1.48–1.51 eV. The photocatalytic activities of synthesized samples, degradation kinetics and mechanisms, and the effect of SnO2 phase formation have been investigated through photodegradation of methylene blue (MB) dye under visible light irradiation. The optimum mechano-thermally synthesized sample as the photocatalyst led to 94% degradation after 120 min. Mechanism explained by scavenger studies revealed that holes were the main reactive radicals responsible for the degradation process.