Layer Of TiO2 Nanoparticles Research Articles

Improved charge generation and collection in dye-sensitized solar cells with modified photoanode surface

ZnO is considered as one of the most promising candidate photoanodes for dye-sensitized solar cells (DSCs) for its high electron mobility, suitable energy-band structure and excellent physical properties. However, the efficiency of ZnO based DSCs is quite low due to the poor chemical stability for dye solution and lots of surface defects for high charge recombination. This paper reports a facile surface modification for ZnO aggregates to achieve a significantly enhanced efficiency. This surface modification process introduce a thin layer of TiO2 nanoparticles on the surface of ZnO aggregates to reduce the charge recombination and increase the charge collection, at the same time, open the inner pores through in-situ selective etching of ZnO at the pore apertures. Collectively, the ZnO aggregates based DSCs exhibit an efficiency of 6.27%, which is much higher than that of the cells without modification (4.81%).

Photo-generated cathodic protection performance of electrophoretically Co-deposited layers of TiO2 nanoparticles and graphene nanoplatelets on steel substrate

In this work, electrophoretic deposition (EPD) was employed to deposit TiO2 nanoparticles and graphene nanoplatelets composite films onto stainless steel in order to fabricate a photo-generated cathodic protection layer. The colloidal suspension used for the EPD was characterized by the measurement of the zeta-potential of the solution using a dispersion optical analyzer. The surface morphology of the EPD layers was investigated using scanning electron microscopy (SEM), and the relative composition of the EPD layer was estimated from the peak intensities using an X-ray diffractometer (XRD) with the distinct peak at 2θ=26.5°. Moreover, the photo-generated cathodic protection abilities were characterized by measuring the open circuit potential (OCP) and the transient photo-generated current density response from the TiO2-graphene co-deposited samples with and without exposure to UV light. The TiO2-graphene EPD layer was found to be uniform, with no noticeable particle homo-aggregation. As a result of the OCP measurement, it was verified that the EPD layers efficiently provided photo-generated cathodic protection to the stainless steel because the potential of the photo-stimulated EPD layers was more negative than the corrosion potential of the stainless steel. When 10wt.% graphene (vs. TiO2 nanoparticles) was used in the EPD layer, the generated photo-current increased significantly from 0.08μA∙cm−2 to approximately 0.15mA∙cm−2 due to the efficient separation of the electron-hole pairs and the increased electron conductivity of the EPD film. However, it was found that the excessive incorporation of graphene nanoplatelets can impede the photocatalytic activation of the TiO2 by reducing its light absorption intensity in the UV range.

Influence of compact TiO2 layer on the photovoltaic characteristics of the organometal halide perovskite-based solar cells

A series of perovskite-based solar cells were fabricated wherein a compact layer (CL) of TiO2 of varying thickness (0–390nm) was introduced by spray pyrolysis deposition between fluorine-doped tin oxide (FTO) electrode and TiO2 nanoparticle layer in perovskite-based solar cells. Investigations of the CL thickness-dependent current density–voltage (J–V) characteristics, dark current, and open circuit voltage (Voc) decays showed a similar trend for thickness dependence. A CL thickness of 90nm afforded the perovskite-based solar cell with the maximum power conversion efficiency (η, 3.17%). Furthermore, two additional devices, perovskite-based solar cell omitting hole transporting materials layer and cell without the TiO2 nanoparticles, were designed and fabricated to study the influence of the CL thickness on different electron transport paths in perovskite-based solar cells. Solar cells devoid of TiO2 nanoparticles, but with perovskite and organic hole-transport materials (HTMs), exhibited sustained improvement in photovoltaic performances with increase in the thickness of CL, which is in contrast to the behavior of classical perovskite-based solar cell and common solid state solar cell which showed optimal photovoltaic performances when the thickness of CL is 90nm. These observations suggested that TiO2 nanoparticles play a significant role in electron transport in perovskite-based solar cells.

Enhanced dielectric and ferroelectric properties induced by TiO2@MWCNTs nanoparticles in flexible poly(vinylidene fluoride) composites

Flexible polymer based composites containing multi-walled carbon nanotubes (MWCNTs) have been reported to present high dielectric constant. However, the composites generally exhibit high dielectric loss and low dielectric breakdown strength, which prohibits their practical use in electronic and electric industry. MWCNTs were coated with a continuous layer of TiO2 nanoparticles (TiO2@MWCNTs) by a simple hydrothermal process and TiO2@MWCNTs/poly(vinylidene fluoride) (PVDF) composites were prepared by a solution casting method. Compared to the pristine MWCNTs/PVDF composites, the TiO2@MWCNTs/PVDF composites presented enhanced dielectric constant and lower dielectric loss. Additionally, the breakdown strength of the TiO2@MWCNTs/PVDF composites was also improved, which is favorable for enhanced ferroelectric properties in the composites.

The photovoltaic performance of alloyed CdTexS1−x quantum dots sensitized solar cells

The photovoltaic performance of alloyed CdTexS1−x quantum dots (QDs) sensitized solar cells (QDSSCs) as a function of tuning the band gap of alloyed CdTexS1−x QDs is studied. The tuning of band gap was carried out through controlling the molar ratio (x) of QDs. Presynthesized alloyed CdTexS1−x QDs of different x values (0, 0.2, 0.4, 0.6, 0.8, and 1) were deposited by direct adsorption (DA) technique onto a layer of TiO2 nanoparticles (NPs) to serve as sensitizers for the solar cells. The characteristic parameters of the assembled QDSSCs were measured under AM 1.5 sun illumination, and show that CdTexS1−x QDs has better photovoltaic performance than pure CdTe QDs or CdS QDs. The maximum values of Jsc (1.54mA/cm2) and η (0.31%) were obtained for x=0.6. However, The open circuit voltages (Voc) approximately constant (0.46±0.02V) for all alloyed CdTexS1−x QDSSCs. It is only dictated by the conduction band (CB) level of TiO2 nanoparticles (NPs) and the valance band (VB) of the electrolyte.

Photonic bandgap extension of surface-disordered 3D photonic crystals based on the TiO2 inverse opal architecture.

A photonic bandgap (PBG) extension of surface-disordered 3D photonic crystals (PCs) based on the TiO2 inverse opal (TiO2-IO) architecture has been demonstrated. By using a liquid phase deposition (LPD) process based on the controlled hydrolysis of ammonium hexafluorotitanate and boric acid, an extra layer of TiO2 nanoparticles were deposited onto the internal surface of the air voids in the TiO2-IOs to increase their surface roughness, thereby introducing surface disorder in the 3D order structures. The PBG relative width of surface-disordered TiO2-IOs has been broadened significantly, and, compared to the original TiO2-IO, its largest rate of increase (27%) has been obtained. It was found that the PBG relative width increased rapidly at first and then to a much slower rate of change with increase of the duration of the LPD time. A possible cause for this finding is discussed in this Letter.

PREPARATION OF NOVEL THIN-FILM COMPOSITE NANOFILTRATION MEMBRANES FOR SEPARATION OF AMOXICILLIN

Several novel composite membranes were prepared to separate and recycle amoxicillin from pharmaceutical wastewater via nanofiltration process. The synthesis of these membranes included three stages: 1- preparation of polysulfone ultrafiltration membranes as a support via phase separation process, 2- modification of its surface by interfacial polymerization as a selective layer (polyamide), and 3- self-assembly of TiO2 nanoparticles on the selective layer as an anti-fouling agent. The rejection of all nanofiltration membranes was more than 99% and only its flux was changed proportional to different conditions. In the presence and absence of TiO2 nanoparticles, the pure water flux of polyamide thin-film membrane also obtained 44.4 and 38.4 L/h.m2 at 4 bar pressure, respectively. These were equal to 34 L/h.m2 for amoxicillin solutions. The results showed that TiO2 nanoparticles increased hydrophilicity of polyamide selective layer and therefore, nanoparticles decreased the fouling level. SEM images illustrated the excellent establishment of polyamide layer and distribution of TiO2 nanoparticles on the selective layer. The properties of membrane surface were taken into consideration by using AFM, indicating the increment of surface roughness with interfacial polymerization and TiO2 nanoparticles self-assembly. The pore size of membranes was in the nanoscale (2.653 and 2.604 nm without and with TiO2 nanoparticles self-assembly, respectively)

Improved performance of metal foil-based dye-sensitized solar cells with low porosity and short length of TiO2 nanotube underlayer

In the present study, we propose low porosity and short length of TiO2 nanotubes (NTs) as underlayer in dye-sensitized solar cells (DSSCs). Photovoltaic characteristics of DSSCs with and without TiO2 NT underlayer are compared using various electrochemical analyses. Low porosity by small pore diameter, thick walled NT geometry and short length of NT underlayer help efficient charge transfer and reduced recombination at the interface of TiO2 nanoparticles (NPs)/Ti substrate. As a result, we can achieve a conversion efficiency of 6.89% for DSSCs with TiO2 NT underlayer, which is about 20% higher than that obtained from DSSCs with only a TiO2 NPs layer.

Energy harvesting of dye-sensitized solar cells assisted with Ti-mesh and phosphor materials

We used the Ti-meshes for both the photoanode and counter electrode of the dye-sensitized solar cells (DSSCs) to improve the flexibility and conductivity of electrodes. This mesh type electrode showed good transparency and high bendability when subjected to an external force. The overall efficiency of the best cells was approximately 5.3% under standard air mass 1.5 global (AM 1.5 G) solar condition. We also modified the TiO2 nanoparticle based dye-sensitized solar cells (DSSCs) by depositing a layer of long-persistent phosphor SrAl2O4:Eu2+, Dy3+ on top of the TiO2 nanoparticle layer to prepare working electrodes of DSSCs. SrAl2O4:Eu2+, Dy3+ red-shifted short UV wavelengths into the main absorption range of the dye commonly used in DSSCs. The SrAl2O4:Eu2+, Dy3+ layer also acted as a light-scattering layer to reduce the loss of visible light. An overall 13% improvement in the conversion efficiency of modified DSSCs was achieved due to the presence of the phosphor layer.

Influence of TiO2 coating thickness on energy conversion efficiency of dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) were synthesized using a 0.25 cm2 area TiO2 nanoparticle/nanorod layer as an electrode and platinum (Pt) as a counter electrode. The TiO2 nanoparticle/nanorod layer was prepared by spin coating and spray coating on fluorine-doped tin oxide glass, respectively. The Pt counter electrode and the ruthenium dye anchored electrode were then assembled as a function of thickness of the TiO2 nanorod layer in a range of 8 to 30 µm. The best photovoltaic performance was observed in the case of a DSSC consisting of a 600 nm thick TiO2 nanoparticle layer and a 20 µm thick TiO2 nanorod layer: a short circuit current density of 11.54 mA·cm−2, open circuit voltage of 0.72V, fill factor of 61.2%, and energy conversion efficiency of 5.07%. A TiO2 nanorod/nanoparticle electrode layer with good adhesion was successfully fabricated.

Functional Modification with TiO2 Nanoparticles and Simultaneously Dyeing of Wool Fibers in a One-Pot Hydrothermal Process

Wool fibers are treated with titanate tetrabutyl in the presence of C. I. Reactive Blue 69 dye in a one-pot process under hydrothermal conditions. The fiber structure and as-prepared particles are characterized. The properties of percentage of exhaustion, K/S value, color fastness to light, tension, photocatalytic activity, and diffuse reflectance spectrum are investigated. The experimental results indicate that after treatment the wool fiber surfaces are evenly immobilized with a thin layer of anatase phase TiO2 nanoparticles. The TiO2 nanocrystals are grafted onto wool fibers via the C–Ti4+, S–Ti4+(Ti2+), and N–Ti4+ bonds. The thermal stability of wool fibers changes a little. The capability of wool fibers to protect against ultraviolet radiation is improved. The tensile properties decrease. The photocatalytic activity to decolorize methylene blue dye is endowed. A high degree of percentage of exhaustion and high K/S value are obtained by adding a certain amount of acetic acid in the precursor solution.

Fabrication of mechanically robust films with high transmittance and durable superhydrophilicity by precursor-derived one-step growth and post-treatment

In this study, we developed a novel approach to the fabrication of mechanically robust films with high transmittance and durable superhydrophilicity. First, precursor-derived one-step growth (POG) was used to fabricate ordered nanoporous silica films, and the thin film surface was then coated with one layer of SiO2 nanoparticles and one layer of TiO2 nanoparticles by dip-coating. After calcination at 550 °C and hardening at 720 °C, the obtained films exhibited not only high transmittance and low reflectivity, but also durable superhydrophilicity and good mechanical robustness. The maximum transmittance of the coated substrates reached as high as 97.8%, while the control glass substrate achieved only 91.4%. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used to observe the morphology and structure of the nanoparticles and coating surfaces. Optical properties were characterized by a UV-visible-near IR spectrophotometer. Surface wettability was studied by a contact angle/interface system. The current approach may open a new avenue to practical applications in windshields, eyeglasses, swimming goggles, periscopes, lenses in laparoscopes, windows of high rise buildings and solar cells, etc.

Multifunctional all-TiO2Bragg stacks based on blocking layer-assisted spin coating

Multifunctional all-TiO2 Bragg stacks displaying structural color are fabricated by sequentially spin coating two TiO2 nanoparticles of different shapes and sizes. We find that Bragg stacks generated by simple sequential deposition of the two nanoparticles have poor reflective properties compared to what would be expected based on the optical properties of individual TiO2 nanoparticle layers. This poor photonic property is due to the cross-contamination of neighboring layers during the deposition process; that is, small TiO2 nanoparticles infiltrate the pre-existing TiO2 nanoparticle layers, changing their optical properties. A sacrificial polymer-blocking layer is added between the low- and high-refractive-index layers to prevent their cross-contamination upon fabrication, which, in turn, significantly improves the overall photonic performance of these all-TiO2 Bragg stacks. All-TiO2 Bragg stacks exhibit excellent superhydrophilicity and self-cleaning properties, due to the porosity of the stacked structure and the photocatalytic nature of TiO2 nanoparticles, respectively, enabling patterning of wettability in these multilayer structures. Additionally, we demonstrate that the high quality photonic properties of these all-TiO2 multilayer structures render them ideal for use in enhancing the energy conversion efficiency of dye-sensitized solar cells (DSSCs).

Extraction of light trapped due to total internal reflection using porous high refractive index nanoparticle films.

TiO₂ nanoparticle layers composed of columnar TiO₂ nanoparticle piles separated with nanoscale pores were fabricated on the bottom surface of the hemispherical glass prism by performing gas phase cluster beam deposition at glancing incidence. The porosity as well as the refractive index of the nanoparticle layer was precisely tuned by the incident angle. Effective extraction of the light trapped in the substrate due to total internal reflection with the TiO₂ nanoparticle layers was demonstrated and the extraction efficiency was found to increase with the porosity. An enhanced Rayleigh scattering mechanism, which results from the columnar aggregation of the nanoparticles as well as the strong contrast in the refractive index between pores and TiO₂ nanoparticles in the nanoporous structures, was proposed. The porous TiO₂ nanoparticle coatings were fabricated on the surface of GaN LEDs to enhance their light output. A nearly 92% PL enhancement as well as a 30% EL enhancement was observed. For LED applications, the enhanced light extraction with the TiO₂ nanoparticle porous layers can be a supplement to the microscale texturing process for light extraction enhancement.

Double-Sided Brush-Shaped TiO2 Nanostructure Assemblies with Highly Ordered Nanowires for Dye-Sensitized Solar Cells

We describe a seeded hydrothermal process for the growth of unique double-sided brush-shaped (DSBS) TiO2 nanostructure assemblies consisting of highly ordered rutile nanowires vertically aligned around an annealed TiO2 nanoparticle layer. The annealed TiO2 nanoparticle layer seeds the nanowire growth and also supports the DSBS structure. The morphology of the DSBS TiO2 nanostructure depends on the hydrothermal reaction time. The diameter of the nanowires is about 6.6 nm, and with increasing reaction time from 1 to 8 h the nanowire length increases from 0.6 to 6.2 μm, whereas the thickness of the nanoparticle layer decreases from 4.3 to 2.8 μm. These free-standing nanowire arrays provide large internal surface area, which is essential for minimizing carrier recombination in high performance photovoltaic devices. Furthermore, the nanowire architecture can help increase the rate of charge transport as compared to particulate films because of lower concentration of grain boundaries. The power conversion efficiency of backside (DSBS TiO2/FTO photoanode) illuminated dye-sensitized solar cells fabricated using the DSBS TiO2 nanostructure assembly is found to be depended on the nanowire length. A cell fabricated using 15.2 μm thick nanostructures sensitized by N719 has a short-circuit current density of 12.18 mA cm(-2), 0.78 V open circuit potential, and a 0.59 filling factor, yielding a maximum power conversion efficiency of 5.61% under AM 1.5 illumination.

Double layered nanoarchitecture based on anodic TiO2 nanotubes for dye-sensitized solar cells

Based on the TiO2 nanotube (TONT) with three different thicknesses (10, 18, 28 μm) prepared by electrochemical anodization, a double layered electrode consisting of TONT and TiO2 nanoparticles (TONPs) with a size of approximately 20 nm was developed. The anodic TONT electrode has been actively investigated due to its beneficial properties such as a favorable electron transport rate and light scattering ability. However, the small specific surface area caused by the large pores and vacant space between 1-D NTs impedes the fabrication of high efficient DSSCs. Hence, the TONP layer with a thickness of 10 μm is additionally deposited on the top surface of the TONT film to offer a sufficient surface area for large dye loading. Compared to a single TONT electrode, the double layered TONT/NP electrodes provide a high short-circuit current density (Jsc) and fill factor (FF) while maintaining a constant open-circuit voltage (Voc), finally disclosing a higher conversion efficiency (η), attributed to the high loading of dye molecules, light scattering ability, low resistance in the photoanode/electrolyte interface, and longer electron lifetimes. In particular, the optimal η was attained with the TONT/NP (18 μm) electrode having a Voc of 0.80 V, a Jsc of 7.80 mA/cm2, a FF of 62.7%, and a η of 3.93%. Incidentally, when using a longer TONT film (28 μm), η decreases steadily due to the fast charge recombination process. A more detailed discussion is included below.

Enhanced Sunlight Harvesting of Dye-Sensitized Solar Cells Assisted with Long Persistent Phosphor Materials

TiO2 nanoparticle-based dye-sensitized solar cells (DSSCs) were modified by depositing a layer of a long-persistent phosphor, SrAl2O4:Eu2+,Dy3+, on top of the TiO2 nanoparticle layer to prepare working electrodes of the DSSCs. SrAl2O4:Eu2+,Dy3+ red-shifted the short UV wavelengths into the main absorption range of the dye commonly used in DSSCs. The SrAl2O4:Eu2+,Dy3+ layer also acted as a light-scattering layer to reduce the loss of visible light. Incident photon to current conversion efficiency measurements showed that the application of such phosphor materials enhanced light-harvesting. The open-circuit voltage was found to be higher in the modified DSSCs. The electrons produced by the SrAl2O4:Eu2+,Dy3+ particles contribute to the reduction of I3– to I–, leading to a lower I3– concentration in the electrolyte. This reduces the recapture of electrons injected in the conduction band of TiO2 by triiodide ions and promotes the open circuit voltage. The performance of the modified DSSC device was improved compared with the cell using a working electrode without this phosphor layer. An overall 13% improvement in conversion efficiency of modified DSSCs was achieved due to the presence of the phosphor layer.

TiO2 supported on silica nanolayers derived from vermiculite for efficient photocatalysis

Various TiO2 composite photocatalysts were synthesized by immobilizing TiO2 nanoparticles onto the surface of silica nanolayers (SNLs) derived from vermiculite via a simple reaction between titanium hydrate and SNLs by varying Ti/SNLs ratios and using different acidic media (HCl, HNO3 and H2SO4). As-obtained composites were characterized by means of XRD, SEM and BET analytical techniques. The photocatalytic activities of photocatalysts were evaluated using methylene blue (MB) as a model pollutant in aqueous solution. It was found that the acidic media HCl and HNO3 favored the formation of tri-crystalline and flat spongy-like thin layers of TiO2 nanoparticles with large specific surface area giving excellent photocatalytic activity; while H2SO4 medium resulted in the single-phase of anatase TiO2 with ball-like aggregates on the TiO2 thin layer, giving relatively low photocatalytic activity. The excellent performance of the composites obtained using proper SNLs content and suitable acidic medium can be mainly ascribed to the mixed-phase structures with an optimum ratio and large specific surface area, as well as the facile immobilization of TiO2 on the support, which will be beneficial to their separation from water treatment system in practical application.

Modification and Photocatalytic Activity of TiO<SUB>2</SUB> Inverse Opal Membranes

The surface of TiO2 inverse opal material was modified by Liquid Phase Deposition(LPD) method, and a layer of TiO2 nanoparticles was deposited on the inverse opal framework in order to increase the specific surface area. The photo-catalytical degradation of Rhodamine B was used as the probe-reaction to investigate the photocatalysis ac- tivity of the TiO2 inverse opal membranes, and the influences of boric acid concentration of the LPD solution on surface morphology and photocatalysis activity of TiO2 inverse opal membranes were investigated. The results showed that the photocatalysis activity of TiO2 inverse opal membrane modified by LPD method was improved which was about 6 times higher than that of the unmodified TiO2 inverse opal when the boric acid concentration of PLD solution was 0.0183 g/mL.

Patterning of wettability for controlling capillary-driven flow in closed channels

Glass capillaries are prepared with well-defined regions of tuneable wettability on the interior walls using an inexpensive and simple approach. A homogeneous layer of hydrophilic TiO2 nanoparticles is adsorbed on the capillary wall and chemically hydrophobized using octadecyltrihydrosilane (OTHS). The hydrophobic OTHS monolayer is then patterned by spatially-selective removal of the OTHS via TiO2-catalysed decomposition by ultraviolet irradiation. By patterning the capillaries with hydrophilic-hydrophobic rings, modulated penetration of a liquid (glycerol, in this study) can be achieved. For given wettability contrast, the penetration dynamics and equilibrium rise heights are very sensitive to the characteristic length-scale of the pattern, and may offer greater, time-dependent sampling control in fluidic devices.