Low Dye Loading Research Articles

Multiphasic titania photoanode: A facile phase assisted approach to enhance the photoelectrochemical and photovoltaic performance

A facile low-temperature method has been proposed and utilized to synthesize pristine and multiphasic titania. Increasing reactant acid content led to the phase transition of titania from pristine anatase to triphasic anatase-rutile-brookite mixed phase; then to biphasic anatase-rutile mixed phase and ultimately pristine rutile. Morphological differences between the samples led to different dye loading on the Dye Sensitized Solar Cell (DSSC) photoanodes, with anatase showing highest loading. However, the Electrochemical Impedance Spectroscopic (EIS) analyses revealed that the triphasic titania photoanode showed superior charge transport ability as evidenced by the lowest charge transfer resistance and highest carrier lifetime. This led to the triphasic DSSC showing a photoconversion efficiency of 4.23 % which is 45 % greater than the reference DP25 DSSC and 72 % better than that of the anatase DSSC despite having a 24 % lower dye loading. These factors suggest that the charge transport properties precede the dye loading capability of the photoanode in determining the DSSC performance. The intimate ternary interfacial junction between the anatase, rutile and brookite phases may be responsible for the enhanced charge transport properties of the triphasic titania. Thus, it is essential to ensure superior photoanode charge transport characteristics to enhance the DSSC performance.

Red-light photoswitching of indigos in polymer thin films.

Through simple synthetic derivatisation, the parent indigo dye becomes a red-light E-Z photoswitch exhibiting negative photochromism and tuneable thermal isomerisation kinetics. These attributes make indigo derivatives extremely attractive for applications related to materials and living systems. However, there is a lack of knowledge in translating indigo photoswitching dynamics from solution to solid state - the environment crucial for most applications. Herein, we study the photoswitching performance of six structurally distinct indigo derivatives in five polymers of varying rigidity. Three key strategies are identified to enable efficient photoswitching under red (660 nm) light: (i) choosing a soft polymer matrix to minimise its resistance toward the isomerisation, (ii) creating free volume around the indigo molecules through synthetic modifications, and (iii) applying low dye loading (<1% w/w) to inhibit aggregation. These strategies are shown to improve both photostationary state distributions and the thermal stability of the Z isomer. When all three strategies are implemented, the isomerisation performance (>80% Z form in the photostationary state) is nearly identical to that in solution. These findings thus pave the way for designing new red-light photochromic materials based on indigos.

Aquananotechnology: oriented-sawdust waste valorization into magnetic nanocellulosic particles for Synozol Red K-HL sorption prospect

High loaded textile dying effluents should undergo for treatment prior to final disposal into the environment. The current study aimed to apply naturally abundant and cheap by-product material namely sawdust (SWD) to develop magnetized cellulosic nano-adsorbent based on magnetite nanoparticles for reactive dye removal namely Synozol Red K-HL (R K-HL). The powder of SWD, which is available through various industries, was modified via pre-treatment with acid hydrolysis and bleaching before blending them with magnetite particles which is synthesized via co-precipitation route. Sawdust (SWD) conjugated with Fe3O4 at different weight percentages (wt%), i.e. SF-(1:1), SF-(2:1), SF-(3:1), SF-(5:1) and SF-(1:2), then subjected to microwave technique, and then characterized by X-ray diffraction spectroscopy (XRD); transmission electron microscope (TEM); Fourier transform infrared (FTIR). Thereafter, the effects of system parameters on adsorption capability, i.e. pH, temperature and dye loading were studied using the modified adsorbents. The SF-(2:1) adsorbent showed the highest affectivity which achieved the highest (21.71 mg g−1) adsorption uptake with a catalyst dosage of 1 g L−1. Moreover, a complete dye removal (100%) was attained at low initial dye loading in the aqueous medium. Langmuir, Freundlich, Temkin and Dubinin–Radushkevich (D-R) isotherm models and their corresponding constants were calculated and discussed. The experimental results showed that the Langmuir isotherm model is well expressed in the experimental data. The kinetics of R K-HL dye removal was found to depend on operational temperature. A study of three kinetic models has been made, and the Bangham’s kinetic model was found to describe the adsorption of dye R K-HL on all the adsorbents applied. The adsorption of reactive R K-HL onto magnetized sawdust adsorbents was spontaneous and exothermic in nature as concluded from thermodynamic assays. Experimental results verified that dye R K-HL could be successfully eliminated feasibly from the aqueous stream in economic way.

Implications of Quenching‐to‐Dequenching Switch in Quantitative Cell Uptake and Biodistribution of Dye‐Labeled Nanoparticles

AbstractA general strategy to carry out cell uptake and biodistribution studies is to label nanoparticles (NPs) with a fluorescent dye. However, the comparative study of different dye‐loaded NPs remains difficult owing to uncontrolled dye quenching and de‐quenching. Here we compared two types of dye‐labeled NPs and demonstrated their distinct properties. NPs with dye molecules at a solid state suffer from dye quenching, so the dye release and/or NP degradation in biological environments leads to a several‐fold increase of fluorescence intensity despite the same amount of NPs, owing to the state switch from quenching to de‐quenching. In contrast, NPs with dye molecules at a soluble state exhibit no quenching effect. To standardize the comparative study, we propose two possible solutions: using lower dye loading or using medium analysis for quantifying cell uptake of NPs. This work provides valuable insights into selecting valid quantification methods for bio‐nano studies.

Implications of Quenching‐to‐Dequenching Switch in Quantitative Cell Uptake and Biodistribution of Dye‐Labeled Nanoparticles

AbstractA general strategy to carry out cell uptake and biodistribution studies is to label nanoparticles (NPs) with a fluorescent dye. However, the comparative study of different dye‐loaded NPs remains difficult owing to uncontrolled dye quenching and de‐quenching. Here we compared two types of dye‐labeled NPs and demonstrated their distinct properties. NPs with dye molecules at a solid state suffer from dye quenching, so the dye release and/or NP degradation in biological environments leads to a several‐fold increase of fluorescence intensity despite the same amount of NPs, owing to the state switch from quenching to de‐quenching. In contrast, NPs with dye molecules at a soluble state exhibit no quenching effect. To standardize the comparative study, we propose two possible solutions: using lower dye loading or using medium analysis for quantifying cell uptake of NPs. This work provides valuable insights into selecting valid quantification methods for bio‐nano studies.

High Quantum Yield Water‐Dispersed Near‐Infrared In(Zn)As–In(Zn)P–GaP–ZnS Quantum Dots with Robust Stability for Bioimaging

AbstractFluorescent dyes with a high photoluminescence quantum yield (PLQY) and photostability are favored in bioimaging as they offer better imaging signals at lower dye loading, circumventing issues of cytotoxicity and biological pathway interference. Quantum dots (QDs) are efficient emitters with narrow spectral line‐widths, but often employ toxic heavy‐metals, and show significantly diminished PLQY and poor stability after phase‐transfer into aqueous media. Here, the preparation of nontoxic, water‐dispersed giant‐shell In(Zn)As–In(Zn)P–GaP–ZnS QDs that emit in the near‐infrared (NIR) at 828 nm is demonstrated. The QDs exhibit a remarkable PLQY of 75% when initially synthesized in a hydrophobic medium, and retains a high PLQY of 60% after ligand‐exchange and phase‐transfer into water. The water‐dispersed QDs show robust photostability with negligible photoluminescence (PL) attenuation after 3 h of laser irradiation, suggesting that the giant shell is effective in reducing nonradiative recombination that may be caused by photoinduced defects. The water‐dispersed QDs also exhibit high aqueous colloidal stability, retaining a high PLQY of 53% without QD agglomeration after 14 months of storage at 4 °C at a high loading concentration of 20 mg mL−1. The QDs are also successfully incorporated into HeLa cells for confocal bioimaging with no practical signs of cytotoxicity.

Optimization of titanium dioxide decorated by graphene quantum dot as a light scatterer for enhanced dye-sensitized solar cell performance

Titanium dioxide (TiO 2 ) as a photoanode in dye-sensitized solar cells (DSSCs) has some drawbacks that reduce its photovoltaic performances i.e. low dye loading capacity and low light-harvesting efficiency. Therefore, TiO 2 decorated by graphene quantum dot (GQD) as a light scatterer has been successfully fabricated via electrodeposition and drop-casting. The response surface methodology/central composite design was successfully utilized to optimize the preparation of photoanode with TiO 2 -GQD as a light scattering layer (LSL). A reduced quadratic model was successfully designed to predict the power conversion efficiency (PCE) accurately up to 97% with a 3% residual standard error. The TiO 2 -GQD LSL depicted a cluster of spherical nanoparticles on top of the photoanode that not only enhanced the light scattering effect but also improved the light-harvesting range from visible light to ultraviolet and near-infrared range. The resultant TiO 2 nanoparticles with TiO 2 -GQD LSL showed vast enhancement of PCE up to 66% from 3.06% to 5.01% due to a good synergistic effect. • TiO 2 -GQD as light scattering layer (LSL) was optimized using response surface methodology • The reduced quadratic model displays a low residual standard error. • TiO 2 nanoparticles with TiO 2 -GQD LSL displays enhanced efficiency up to 66%.

Anatase TiO2 nanowires with nanoscale whiskers for the improved photovoltaic performance in dye-sensitized solar cells

TiO2 as an efficient electron transfer material has been widely utilized in dye-sensitized solar cells (DSSCs), and the morphology of TiO2 plays a decisive role in the performance of DSSCs. However, one-dimensional TiO2 nanowires, which are generally used as the efficient electron transport layers, have small specific surface area and low dye loading. Here, we introduce an effective and reproducible one-step hydrothermal method to prepare TiO2 nanowire with nanoscale whiskers. The synthetic sample was characterized by the field emission scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction. TiO2 nanowire with nanoscale whiskers has a high light scattering performance and high dye loading capacity. This novel TiO2 nanowire show a power conversion efficiency (PCE) of 4.12%, which is close to the benchmark of P25 nanoparticle usually used in DSSC fabrication. The PCE of DSSC-3 using TiO2 nanowire with nanoscale whiskers and commercial P25 double-layer photoanode has a PCE of 5.98%, showing an increase of 11.98% when compared with DSSC-2 based on pure P25 photoanode.

Comparative Study on the Photoanode Nanoarchitectures for Photovoltaic Application

Vertically-aligned TiO2 nanotube (NT) arrays prepared by electrochemical anodization are considered promising alternatives to the conventional nanoparticle (NP)-based electrodes for photovoltaic devices. Recently, such NT arrays have been employed in dye-sensitized solar cells (DSSCs) by transferring them onto NP-based electrodes, to obtain multi-layered nanoelectrodes. Here, we comparatively evaluate the photovoltaic and photoelectrochemical properties of TiO2 NP-only electrodes and multi-layered electrodes comprising NP and NT arrays at the same thickness of 15 μm. Although the multi-layered electrodes have a smaller surface area compared to the NP-only electrodes, they show much higher transmittance. In addition, impedance studies reveal that the multi-layered electrodes have lower charge recombination with the electrolyte as well as enhanced electrolyte diffusion when applied as a photoanode in DSSCs. As a result, the multi-layered electrodes exhibit a photovoltaic conversion efficiency (η = 5.37%) comparable to that of the NP-only electrodes (η = 5.80%), despite 36.6% lower dye loading.

Highly Photostable and Fluorescent Microporous Solids Prepared via Solid-State Entrapment of Boron Dipyrromethene Dyes in a Nascent Metal-Organic Framework.

We report a strategy to synthesize highly emissive, photostable, microporous materials by solid-state entrapment of boron dipyrromethene (BODIPY) fluorophores in a metal-organic framework. Solvent-free mechanochemistry or accelerated aging enabled quantitative capture and dispersal of the PM605 dye within the ZIF-8 framework starting from inexpensive, commercial materials. While the design of emissive BODIPY solids is normally challenged by quenching in a densely packed environment, herein reported PM605@ZIF-8 materials show excellent emissive properties and to the best of our knowledge an unprecedented ∼10-fold enhancement of BODIPY photostability. Time-resolved and steady-state fluorescence studies of PM605@ZIF-8 show that interchromophore interactions are minimal at low dye loadings, but at higher ones lead to through-pore energy transfer between chromophores and to aggregate species.

Bay Annulated Indigo as a New Chromophore for p‐type Dye‐Sensitized Solar Cells

AbstractA prototype bay‐annulated indigo (BAI) dye has been synthesised and applied in p‐type dye‐sensitized solar cells (pDSC). The dye produced a broad spectral response up to 700 nm and an encouraging photocurrent (Jsc=1.13 mA cm−2, IPCE of 6.8 %) was recorded. These results have highlighted several challenges for integrating BAI dyes into pDSCs, including: low dye loading, a tendency to aggregate and lack of built‐in charge‐transfer character, which can be overcome by simple modifications to the dye structure.

Effects of Dye Surface Concentration on the Molecular Aggregation of Xanthene Dye in Colloidal Dispersions of Montmorillonite

AbstractThe molecular aggregation of organic dyes onto clay mineral particles is a very complex phenomenon including dye adsorption, the migration of dye molecules, rearrangement of initially formed aggregates, etc. Some details of this complex process are not yet fully understood. The objective of the present study was to understand the influence of dye surface concentration on the dynamic processes in dye molecular aggregation. A stopped-flow rapid mixing device was used for accurate measurements of the molecular aggregation of the cationic dye rhodamine 123 (R123) in montmorillonite (MntK) colloidal dispersions. The influence of dye surface concentration, which was changed by altering the ratio of the amount of R123 to the mass of MntK (nR123/mMntK), was examined in detail. Chemometric analysis was used to reconstruct the spectral matrix to obtain linearly uncorrelated spectral profiles of the major components and their concentrations at the respective reaction times. The conversion of isolated R123 cations into oblique J-aggregates (head-to-tail molecular assemblies) was observed over time and the existence of a J-dimers intermediate was hypothesized. The reaction kinetics followed a biphasic exponential function. An unexpected effect of dye surface concentration on R123 aggregation was observed: the initial formation of the molecular aggregates increased significantly with dye surface concentration, but an inverse trend was observed after longer reaction times. While dye aggregates were formed slowly at low dye loadings, systems with high R123/MntK ratios (nR123/mMntK) reached spectral stability after the first few seconds of the reaction. After longer reaction times, the greatest degree of dye aggregation was achieved in the dispersion of the lowest dye loading. Such a phenomenon is described for the first time. The results presented here are important for understanding the complex processes occurring in systems based on organic cations and clay minerals, and should be considered in the development of functional hybrid materials of dyes and nanoparticles with a layered structure.

Factors Affecting the Power Conversion Efficiency in ZnO DSSCs: Nanowire vs. Nanoparticles

A comparative assessment of nanowire versus nanoparticle-based ZnO dye-sensitized solar cells (DSSCs) is conducted to investigate the main parameters that affect device performance. Towards this aim, the influence of film morphology, dye adsorption, electron recombination and sensitizer pH on the power conversion efficiency (PCE) of the DSSCs is examined. Nanoparticle-based DSSCs with PCEs of up to 6.2% are developed and their main characteristics are examined. The efficiency of corresponding devices based on nanowire arrays (NW) is considerably lower (0.63%) by comparison, mainly due to low light harvesting ability of ZnO nanowire films. The dye loading of nanowire films is found to be approximately an order of magnitude lower than that of nanoparticle-based ones, regardless of their internal surface area. Inefficient anchoring of dye molecules on the semiconductor surface due to repelling electrostatic forces is identified as the main reason for this low dye loading. We propose a method of modifying the sensitizer solution by altering its pH, thereby enhancing dye adsorption. We report an increase in the PCE of nanowire DSSCs from 0.63% to 1.84% as a direct result of using such a modified dye solution.

Resonance energy transfer between dye molecules in hybrid films of a layered silicate, including the effect of dye concentration thereon

Abstract Rhodamine 6G (R6G) and Oxazine 4 (Ox4), considered a “Forster Resonance Energy Transfer” (FRET) pair due to the significant overlap between the fluorescence of R6G (as energy donor, ED) and the absorption band of Ox4 (as energy acceptor, EA), were intercalated into an expandable layered silicate, saponite (Sap). Several films with different dyes/Sap loadings were prepared with the aim of studying the energy transfer process between both dyes at variable concentrations in the solids. The films were characterized by spectral methods in the visible spectral range. A theoretical model of FRET efficiency was proposed for hybrid solid materials, built around the construction of probability density functions of the intermolecular distances in the solids. The theoretical results were compared with FRET efficiencies determined experimentally using steady-state and time-resolved fluorescence spectroscopy. Considering the very high sensitivity of the FRET efficiency to the intermolecular distances between ED and EA, the theoretical model could predict experimental data relatively well only for low dye loadings (

Ensemble and Single Particle Fluorescence Characterization of Dye-Labeled Cellulose Nanocrystals.

Cellulose nanocrystals (CNCs) have been covalently labeled with both fluorescein and rhodamine and studied by a combination of UV-vis absorption spectroscopy and ensemble and single molecule fluorescence spectroscopy. For all samples, the fluorescence anisotropy and lifetimes were consistent with effects expected for covalently bound dye molecules. Low dye loading levels (∼0.1 dye/particle) were estimated for the fluorescein-labeled CNC which coupled with the strong pH dependence make this a less suitable fluorophore for most applications. Rhodamine-labeled CNCs were prepared from both sulfated and carboxylated CNCs and had loading levels that varied from 0.25 to ∼15 dye molecules/CNC. For the sulfated samples, the absorption due to (nonfluorescent) dimeric dye increased with dye loading; in contrast, the carboxylated sample, which had the highest rhodamine content, had a low dimer yield. Single particle fluorescence studies for two of the rhodamine-labeled CNCs demonstrated that individual particles are readily detected by their stepwise blinking/bleaching behavior and by polarization effects. Overall, the results indicate the importance of understanding the effects of loading on dye photophysics to select an optimal dye concentration to maximize sensitivity while minimizing the effect of the dye on the CNC behavior. The results also demonstrate that CNCs with relatively low dye loadings (e.g., ∼1 dye/particle) are readily detectable by fluorescence and should be adequate for use in fluorescence-based biological assays or to probe the distribution of CNCs in composite materials.

Microspectrophotometric analysis of yellow polyester fiber dye loadings with chemometric techniques

Microspectrophotometry is a quick, accurate, and reproducible method to compare colored fibers for forensic purposes. Applying chemometric techniques to spectroscopic data can provide valuable information, especially when looking at a complex dataset. In this study, background subtracted and normalized visible spectra from ten yellow polyester exemplars dyed with different concentrations of the same dye ranging from 0.1% to 3.5% (w/w), were analyzed by agglomerative hierarchical clustering (AHC), principal component analysis (PCA), and discriminant analysis (DA). Systematic changes in the wavelength of maximum absorption, peak shape and signal-to-background ratio were noted as dye loading increased. In general, classifying the samples into ten groups (one for each exemplar) had poor accuracy (i.e., 51%). However, classification was much more accurate (i.e., 96%) using three classes of fibers that were identified by AHC as having low (0.10–0.20wt%), medium (0.40–0.75wt%), and high (1.5–3.5wt%) dye loadings. An external validation with additional fibers and data generated by independent analysts confirmed these findings. Lastly, it was also possible to discriminating pairs of exemplars with small differences in dye loadings as a simulation of questioned (Q) versus known (K) comparisons.

Dye Sensitized Solar Cells Based on Different Solvents: Comparative Study

Solution of Z907 dye in two different solvents, namely ethanol (EtOH) and chloroform (CHCl3) are prepared and utilized in dye-sensitized solar cells (DSSCs). The effects of dye solvents on the performance of these cells have been investigated and the results are represented. The DSSCs that used EtOH as a dye-adsorption solvent showed an improved solar cell efficiency relative to the DSSCs that used CHCl3. For dye-adsorption solvents, the highest conversion efficiency of 1.40% is achieved using CHCl3 and 0.15% for EtOH, respectively. Photo- and electrochemical tests of Z907 dye in ethanol, adsorbed on the TiO2 surface showed low dye loading and coverage on the surface, shorter electron lifetime and the greater resistance in the TiO2/dye/electrolyte interface, publicized to the dye aggregation at the TiO2 surface, which decreased the solar cell performance of the DSSCs.

The Role of Hole Transport between Dyes in Solid-State Dye-Sensitized Solar Cells

In dye-sensitized solar cells (DSSCs) photogenerated positive charges are normally considered to be carried away from the dyes by a separate phase of hole-transporting material (HTM). We show that there can also be significant transport within the dye monolayer itself before the hole reaches the HTM. We quantify the fraction of dye regeneration in solid-state DSSCs that can be attributed to this process. By using cyclic voltammetry and transient anisotropy spectroscopy, we demonstrate that the rate of interdye hole transport is prevented both on micrometer and nanometer length scales by reducing the dye loading on the TiO2 surface. The dye regeneration yield is quantified for films with high and low dye loadings (with and without hole percolation in the dye monolayer) infiltrated with varying levels of HTM. Interdye hole transport can account for >50% of the overall dye regeneration with low HTM pore filling. This is reduced to about 5% when the infiltration of the HTM in the pores is optimized in 2 μm th...

Improvement of light harvesting and device performance of dye-sensitized solar cells using rod-like nanocrystal TiO2 overlay coating on TiO2 nanoparticle working electrode

Novel TiO2 single crystalline nanorods were synthesized by electrospinning and hydrothermal treatment. The role of the TiO2 nanorods on TiO2 nanoparticle electrode in improvement of light harvesting and photovoltaic properties of dye-sensitized solar cells (DSSCs) was examined. Although the TiO2 nanorods had lower dye loading than TiO2 nanoparticle, they showed higher light utilization behaviour. Electron transfer in TiO2 nanorods received less resistance than that in TiO2 nanoparticle aggregation. By just applying a thin layer of TiO2 nanorods on TiO2 nanoparticle working electrode, the DSSC device light harvesting ability and energy conversion efficiency were improved significantly. The thickness of the nanorod layer in the working electrode played an important role in determining the photovoltaic property of DSSCs. An energy conversion efficiency as high as 6.6% was found on a DSSC device with the working electrode consisting of a 12 μm think TiO2 nanoparticle layer covered with 3 μm thick TiO2 nanorods. The results obtained from this study may benefit further design of highly efficient DSSCs.

Micrometer-sized fluorine doped tin oxide as fast electron collector for enhanced dye-sensitized solar cells.

Titanium dioxide (TiO2)-layered fluorine doped tin oxide (FTO) powder was synthesized and applied as the photoanode in dye-sensitized solar cells (DSSCs). FTO powders are connected to form a direct electron pathway for the efficient extract of injected electrons, while the TiO2 layer serves as an energy barrier prohibiting the charge combination with oxidized dye or I3(-). The electrochemical impedance spectroscopy (EIS) analyses suggest that electrons have a longer combination lifetime (τe = 233 ms) than that of the electron in the DSSCs using traditional P25 photoanodes (τe = 28 ms). The DSSCs using 5 μm thick TiO2@FTO as photoanodes eventually give a respectable and long-term stable photovoltaic performance with a current density of 23.8 mA/cm(2), an open circuit voltage of 0.69 V, and power conversion efficiency of 7.4%. The results are received on a low dye loading level (0.25 × 10(-7) mol/cm(2)), which is (1)/10 of that for traditional photoanode (2.79 × 10(-7) mol/cm(2)).