One-pot self-assembled TiO2/graphene/poly(acrylamide) superporous hybrid for photocatalytic degradation of organic pollutants

We report the development of TiO₂/graphene/poly(acrylamide) superporous hybrid by a radical polymerization reaction and explore its environmental application as photocatalyst of organic pollutants. During the polymerization reaction, graphene nanosheets and TiO₂ nanoparticles homogeneously distribute on the hydrogel, in which TiO₂ nanoparticles with a uniform size are densely anchored onto graphene and self-assembled into different structures with various graphene contents. The resultant TiO₂/graphene/poly(acrylamide) superporous hybrid experiences tremendous adsorption toward dye pollution before photodegradation, and it also displays similar photodecomposition efficiency with pristine TiO₂. Moreover, the TiO₂/graphene/poly(acrylamide) superporous hybrid is recyclable, which demonstrates the potential of hybrid as an attractive photocatalyst for wastewater treatment. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47033.     

Improving the performance of dye-sensitized solar cells with TiO2/graphene/TiO2 sandwich structure

This study investigates the extent to which the TiO₂/graphene/TiO₂ sandwich structure improves the performance of dye-sensitized solar cells (DSSCs) over that of DSSCs with the traditional structure. Studies have demonstrated that the TiO₂/graphene/TiO₂ sandwich structure effectively enhances the open circuit voltage (V_oc), short-circuit current density (J_sc), and photoelectrical conversion efficiency (η) of DSSCs. The enhanced performance of DSSCs with the sandwich structure can be attributed to an increase in electron transport efficiency and in the absorption of light in the visible range. The DSSC with the sandwich structure in this study exhibited a V_oc of 0.6 V, a high J_sc of 11.22 mA cm^-2, a fill factor (FF) of 0.58, and a calculated η of 3.93%, which is 60% higher than that of a DSSC with the traditional structure.     

Synthesis of hybrid Pt/TiO2 (anatase)/MWCNTs nanomaterials by a combined sol–gel and polyol process

In the present study, hybrid Pt/TiO₂/MWCNTs nanomaterials are prepared successfully by a combined sol–gel and polyol process. The as-prepared nanomaterials are characterized by X-ray diffraction, high resolution transmission electron microscopy, and thermogravimetry analysis. In addition, its catalytic performance by converting CO into CO₂ is also evaluated. Experimental results show that the hybrid Pt/TiO₂/MWCNTs nanomaterials exhibit a mixture of anatase TiO₂ and Pt phases. Multi-wall carbon nanotubes serve as an excellent supporting material where anatase TiO₂ nanoparticles are decorated with well-distributed Pt nanoparticles. Excellent catalytic performance can be revealed for the hybrid Pt/TiO₂/MWCNTs nanomaterials. When compared with its Pt/TiO₂ counterparts where ～ 100% CO conversion occurred at 150 °C, almost 100% conversion of CO into CO₂ can be observed at a temperature ranged from 30 °C to 100 °C.     

The influence of anatase-rutile mixed phase and ZnO blocking layer on dye-sensitized solar cells based on TiO2nanofiberphotoanodes

High performance is expected in dye-sensitized solar cells (DSSCs) that utilize one-dimensional (1-D) TiO₂ nanostructures owing to the effective electron transport. However, due to the low dye adsorption, mainly because of their smooth surfaces, 1-D TiO₂ DSSCs show relatively lower efficiencies than nanoparticle-based ones. Herein, we demonstrate a very simple approach using thick TiO₂ electrospun nanofiber films as photoanodes to obtain high conversion efficiency. To improve the performance of the DSCCs, anatase-rutile mixed-phase TiO₂ nanofibers are achieved by increasing sintering temperature above 500°C, and very thin ZnO films are deposited by atomic layer deposition (ALD) method as blocking layers. With approximately 40-μm-thick mixed-phase (approximately 15.6?wt.% rutile) TiO₂ nanofiber as photoanode and 15-nm-thick compact ZnO film as a blocking layer in DSSC, the photoelectric conversion efficiency and short-circuit current are measured as 8.01% and 17.3?mA?cm^?2, respectively. Intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy measurements reveal that extremely large electron diffusion length is the key point to support the usage of thick TiO₂ nanofibers as photoanodes with very thin ZnO blocking layers to obtain high photocurrents and high conversion efficiencies.     

Synthesis and photocatalytic performance of PVA/TiO2/graphene‐MWCNT nanocomposites for dye removal

TiO₂/graphene‐MWCNT nanocomposite was prepared using solvothermal reaction for the effective distribution of TiO₂ nanoparticles on carbonaceous materials. TiO₂/graphene‐MWCNT nanocomposite was immobilized in poly(vinyl alcohol) (PVA) matrix for a convenient recovery after wastewater purification. MWCNT was incorporated in a nanocomposite not only to prevent the restacking of graphene but also to increase the electron transfer from TiO₂. The detailed characterization of the nanocomposite was performed using SEM, EDX, XRD, XPS, and FTIR. The photocatalytic performance of PVA/TiO₂/graphene‐MWCNT nanocomposite was investigated by UV spectroscopy on the basis of degradation of organic pollutants. PVA/TiO₂/graphene‐MWCNT nanocomposite showed improved photocatalytic decomposition of more than 70% of residual dye left in case of using PVA/TiO₂/graphene nanocomposite due to the improved electron transfer and the higher adsorption of organic pollutants. PVA/TiO₂/graphene‐MWCNT nanocomposite was suitable as a promising material for the recyclable photocatalytic wastewater purification system. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40715.     

Effect of carbonaceous counter electrodes on the performance of ZnO-graphene nanocomposites based dye sensitized solar cells

With many advantages like low-cost preparation, excellent electrical properties, and high catalytic activity; carbon allotropes are the most expected carbon materials to substitute the expensive Platinum (Pt) as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). In the present study, the photovoltaic behaviors of DSSCs fabricated with graphene, multiwalled carbon nanotubes (MWCNTs), and Pt films CEs, respectively, were compared. The graphene and MWCNTs CEs films were prepared by doctor blading the graphene and MWCNTs pastes on Indium tin oxides (ITOs) glass substrates. The structural, morphological, and compositional properties of these carbon CEs viz. graphene and MWCNTs were investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and energy dispersive X-ray (EDX), respectively. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed for the examination of electrochemical and catalytic properties of Pt as well as carbonaceous CEs. These low-cost graphene and MWCNTs CEs were employed in the sandwich-structured DSSCs having ZnO-graphene nanocomposite films as photoanodes. The photoconversion efficiency (η) values of as prepared DSSCs were measured under AM 1.5 illumination (100?mW?cm^?2). The DSSCs with graphene CE and MWCNTs CE performed with efficiency values of 2.26% and 2.04%, respectively. The performance of these carbonaceous CEs are comparative to that of Pt CE which indicates the practicability of carbon based nanomaterials in DSSCs as low cost alternatives to the expensive Pt.     

The effect of dye-sensitized solar cell based on the composite layer by anodic TiO2 nanotubes

TiO₂ nanotube arrays are very attractive for dye-sensitized solar cells (DSSCs) owing to their superior charge percolation and slower charge recombination. Highly ordered, vertically aligned TiO₂ nanotube arrays have been fabricated by a three-step anodization process. Although the use of a one-dimensional structure provides an enhanced photoelectrical performance, the smaller surface area reduces the adsorption of dye on the TiO₂ surface. To overcome this problem, we investigated the effect of DSSCs constructed with a multilayer photoelectrode made of TiO₂ nanoparticles and TiO₂ nanotube arrays. We fabricated the novel multilayer photoelectrode via a layer-by-layer assembly process and thoroughly investigated the effect of various structures on the sample efficiency. The DSSC with a four-layer photoelectrode exhibited a maximum conversion efficiency of 7.22% because of effective electron transport and enhanced adsorption of dye on the TiO₂ surface.     

The photovoltaic efficiency of dye sensitized solar cell assembled using carbon capsulated TiO2 electrode

Carbon-encapsulated TiO₂ was synthesized and its applications to dye-sensitized solar cells (DSSCs) were evaluated. When carbon-encapsulated TiO₂ was applied to DSSCs as a scattering material, the efficiency was enhanced considerably compared to that using only double-layered, nanometer-sized pure TiO₂. The photovoltaic efficiency of the carbon-encapsulated TiO₂-DSSCs was approximately 3.59%, while it was 2.87% for the pure TiO₂-DSSCs. The quantum efficiencies evaluated from IPCE spectroscopy were better on the carbon-encapsulated TiO₂-DSSCs compared to of a TiO₂-DSSCs. PL spectroscopy showed that the rate of recombination between the holes and electrons on the carbon-encapsulated TiO₂ were lower than that on pure TiO₂.     

Hybrid metal-organic framework nanomaterials with enhanced carbon dioxide and methane adsorption enthalpy by incorporation of carbon nanotubes

Two hybrid materials composed of metal-organic framework (JUC-32) nanoparticles and carboxyl-modified multi-wall carbon nanotubes (MWCNTs) were synthesised successfully in situ and characterized by TEM, PXRD, and TGA. The gas adsorption properties of these two hybrid materials were compared with the original JUC-32 material and a physical mixture of JUC-32 and MWCNTs. The results indicated that the composite materials absorbed larger amounts of CO₂ and CH₄ per specific surface area than the original materials, and that the adsorption enthalpies of CO₂ and CH₄ had significantly increased.     

Dye-sensitized solar cells based on double-layered TiO2 composite films and enhanced photovoltaic performance

Dye-sensitized solar cells (DSSCs) are fabricated based on double-layered composite films of TiO₂ nanoparticles and hollow spheres. The photoelectric conversion performances of DSSCs based on nanoparticles/nanoparticles (PP), hollow spheres/hollow spheres (HH), hollow spheres/nanoparticles (HP), and nanoparticles/hollow spheres (PH) double-layered films are investigated, and their photo-electric conversion efficiencies are 4.33, 4.72, 4.93 and 5.28%, respectively. The enhanced performance of TiO₂ nanoparticles/hollow spheres double-layered composite film solar cells can be attributed to the combined effect of following factors. The light scattering of overlayer hollow spheres enhances harvesting light of the DSSCs and the underlayer TiO₂ nanoparticle layer ensures good electronic contact between film electrode and the F-doped tin oxide (FTO) glass substrate. Furthermore, the high surface areas and pore volume of TiO₂ hollow spheres are respectively beneficial to adsorption of dye molecules and transfer of electrolyte solution.     

A natural tomato slurry as a photosensitizer for dye-sensitized solar cells with TiO2/CuO composite thin films

We have studied the performance of dye-sensitized solar cells by employing natural dye “anthocyanins” extracted from the tomato slurry as a sensitizer for the TiO₂/CuO photoanode. The extracts were anchored on TiO₂/CuO films deposited on an ITO substrate which was used as a photoanode. The dye adsorbed TiO₂/CuO films electrode, the copper plate as a counter electrode, and iodolyte as an electrolyte were assembled into DSSCs. The conversion efficiency of the DSSCs was found to be 2.96% with a V_OC of 0.615 V, J_SC of 6.6 mA/cm², and an FF of 0.73. This work highlights the use of contribution of the tomato slurry as a natural sensitizer to enhance the efficiency of DSSCs.     

Charge transfer properties and photoelectrocatalytic activity of TiO2/MWCNT hybrid

The vertically aligned multiwalled carbon nanotube (MWCNT) arrays on tantalum foils were successfully coated with TiO₂ nanoparticles by a hydrothermal process. The prepared TiO₂/MWCNT hybrid was characterized by scanning electron microscopy and transmission electron microscopy. The charge transfer properties and photocatalytic degradation of rhodamine B with and without bias potential under UV irradiation were investigated. The MWCNTs promoted the separation of photoinduced carriers in the TiO₂, thus enhanced photocatalytic activity. Applying bias potential on the photoanode further enhanced its catalytic activity. The efficient charge transportation and high photoelectrocatalytic activity towards degradation of rhodamine B made this hybrid material promising for photocatalyst and for the development of photoelectrical devices.     

Enhancement of the photoelectric performance of dye-sensitized solar cells using Ag-doped TiO<Subscript>2</Subscript> nanofibers in a TiO<Subscript>2</Subscript> film as electrode

For high solar conversion efficiency of dye-sensitized solar cells [DSSCs], TiO₂ nanofiber [TN] and Ag-doped TiO₂ nanofiber [ATN] have been extended to be included in TiO₂ films to increase the amount of dye loading for a higher short-circuit current. The ATN was used on affected DSSCs to increase the open circuit voltage. This process had enhanced the exit in dye molecules which were rapidly split into electrons, and the DSSCs with ATN stop the recombination of the electronic process. The conversion efficiency of TiO₂ photoelectrode-based DSSCs was 4.74%; it was increased to 6.13% after adding 5 wt.% ATN into TiO₂ films. The electron lifetime of DSSCs with ATN increased from 0.29 to 0.34 s and that electron recombination was reduced.     

Improved phenol decomposition and simultaneous regeneration of granular activated carbon by the addition of a titanium dioxide catalyst under a dielectric barrier discharge plasma

A catalytic method using titanium dioxide (TiO₂) under a dielectric barrier discharge (DBD) plasma was studied to improve the decomposition of phenol adsorbed on granular activated carbon (GAC) and the simultaneous regeneration of the saturated GAC. The TiO₂–GAC hybrid was fabricated by an impregnation-desiccation method and characterised by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, nitrogen adsorption isotherms and Boehm titration to investigate its adsorption and catalytic characteristics before and after the adsorption and DBD processes. The adsorption experiments showed that the GAC and TiO₂–GAC both followed pseudo-second-order kinetic models with adsorption isotherms that were well represented by the Langmuir model. TiO₂–GAC exhibited remarkable catalytic activity, increasing the phenol degradation by 19% and TOC removal by 8.7% relative to GAC in DBD treatment. TiO₂–GAC also exhibited better regeneration efficiency than GAC, and the reusability of the hybrid material was examined over four consecutive adsorption-regeneration cycles. The above results may be due to the enhanced generation of active species, such as hydroxyl radicals and hydrogen peroxide, on TiO₂–GAC relative to GAC during the discharge process, and the main intermediate products were analysed to explore the mechanisms involved in DBD plasma.     

Enhancement of photoelectric conversion by high-voltage electric field assisted crystallization of a novel ternary-encapsulated spherical TiO2 aggregate for solar cells

A novel ternary-encapsulated spherical TiO₂ aggregate (TES-TiO₂) with submicron particle sizes was formed by blending commercial P25 TiO₂ and two different sizes of TiO₂ particles (synthesized by modified sol-gel and hydrothermal methods). A double-layered TiO₂ electrode for dye-sensitized solar cells (DSSCs) was fabricated by depositing TES-TiO₂ particles onto nanocrystalline mesoporous TiO₂ (Meso-TiO₂)-coated FTO glass by a cathodic electrophoresis technique and then calcined at 450 °C for 30 min. Compared to double-layered Meso-TiO₂/P25 electrodes, the energy conversion efficiency (η) of DSSCs from the obtained Meso-TiO₂/TES-TiO₂ electrode was improved by 9.3%, from 5.94% to 6.49%. When the prepared double-layered Meso-TiO₂/TES-TiO₂ electrode was calcined at high temperature, a high-voltage electric field (HVEF) was introduced to assist crystallization. As a result, η was further enhanced by 8.6%, from 6.49% to 7.05%. Notably, compared to typical 20 nm TiO₂ nanocrystallites applied in the active layer of DSSCs, the prepared loosely porous TES-TiO₂ with submicron size increased the light-scattering effect and promoted dye molecule adsorption and the diffusion of electrolytes. In addition, introduction of the HVEF provided better connection among TiO₂ particles, which facilitated electron transport and avoided charge recombination.     

Fabrication of graphene films on TiO2 nanotube arrays for photocatalytic application

Graphene film was formed on the surface of titanium dioxide nanotube (TiO₂ NT) arrays through in situ electrochemical reduction of a graphene oxide dispersion by cyclic voltammetry. The residual oxygen-containing groups and other structural defects such as sp³-hybridized carbons in the electrodeposited graphene were further removed by photo-assisted reduction of the underlying TiO₂ NTs, thus achieving the maximum restoration of π-conjugation in the graphene planes. Spectroscopic, electrochemical, and photoelectrochemical techniques were used to characterize the graphene films, and the use of the resulting graphene–TiO₂ NT material in photocatalysis was investigated. The results showed that the graphene–TiO₂ NT material exhibited a greatly improved photocatalytic activity compared with unmodified TiO₂ NTs.     

Photocatalytic activity of TiO2 supported on multi-walled carbon nanotubes under simulated solar irradiation

TiO₂ particles supported on multi-walled carbon nanotubes (MWCNTs) were prepared using a sol–gel method to investigate their photocatalytic activity under simulated solar irradiation for the degradation of methyl orange (MO) in aqueous solution. The prepared composites were analyzed using XRD, SEM, EDS and UV–vis absorption spectroscopy. The results of this study indicated that there was little difference in the shape and structure of MWCNTs/TiO₂ composite and pure TiO₂ particles. The composite exhibited enhanced absorption properties in the visible light range compared to pure TiO₂. The degradation of MO by MWCNTs/TiO₂ composite photocatalysts was investigated under irradiation with simulated solar light. The results of this study indicated that MWCNTs played a significant role in improving photocatalytic performance. Different amounts of MWCNTs had different effects on photodegradation efficiency, and the most efficient MO photodegradation was observed for a 2% MWCNT/TiO₂ mass ratio. Photocatalytic reaction kinetics were described using the Langmuir–Hinshelwood (L–H) model. The photocatalyst was reused for eight cycles, and it retained over 95.2% photocatalytic degradation efficiency. Possible decomposition mechanisms were also discussed. The results of this study indicated that photocatalytic reactions with TiO₂ particles supported on MWCNTs under simulated solar light irradiation are feasible and effective for degrading organic dye pollutants.     

Preparation of TiO<Subscript>2</Subscript> nanotube/nanoparticle composite particles and their applications in dye-sensitized solar cells

Efficiency of dye-sensitized solar cells [DSSCs] was enhanced by combining the use of TiO₂ nanotubes [TNTs] and nanoparticles. TNTs were fabricated by a sol-gel method, and TiO₂ powders were produced through an alkali hydrothermal transformation. DSSCs were constructed using TNTs and TiO₂ nanoparticles at various weight percentages. TNTs and TiO₂ nanoparticles were coated onto FTO glass by the screen printing method. The DSSCs were fabricated using ruthenium(II) (N-719) and electrolyte (I₃/I₃ ^-) dyes. The crystalline structure and morphology were characterized by X-ray diffraction and using a scanning electron microscope. The absorption spectra were measured using an UV-Vis spectrometer. The incident photocurrent conversion efficiency was measured using a solar simulator (100 mW/cm²). The DSSCs based on TNT/TiO₂ nanoparticle hybrids showed better photovoltaic performance than cells made purely of TiO₂ nanoparticles.     

Influence of MWCTs and nanometal oxide/MWCTs hybrids on the thermal conduction of their acrylic-based nanocomposites

In this study, acrylic-based nanocomposites containing different contents of multi-walled carbon nanotubes (MWCNTs) and metal oxide nanoparticles (i.e., TiO₂, CuO and Fe₂O₃) were fabricated by solvent mixing method. The thermal conductivity of these samples was evaluated. The results indicated that the thermal conductivity of all fabricated samples was significantly improved even at small loading of MWCNTs. It was found that the thermal conductivity was enhanced by increase in MWCNTs content up to 5 wt%. Similarly, the metal oxide nanoparticles caused up to 75 % increment in thermal conductivity at 1.5 wt% of their loading in acrylic film. Contrary to expectations, the thermal conductivity of acrylic film was more increased by nanometal oxides (i.e., TiO₂, CuO and Fe₂O₃) than MWCNTs. The effect of hybridizing of nanometal oxide particles (1.5 wt%) and MWCNTs (1.5 wt%) on thermal conduction was investigated as well. It was found that hybridizing improved thermal conductivities by about 85, 94 and 97 % for Fe₂O₃, TiO₂ and CuO, respectively. Finally, the effects of TiO₂ pigment and CaCO₃ extender on the thermal conductivity of acrylic polymer and nano-TiO₂ acrylic composites were studied. It was found that TiO₂ could increase considerably thermal conduction of its acrylic films and acrylic nanocomposites.     

Flexible free-standing graphene–TiO2 hybrid paper for use as lithium ion battery anode materials

Flexible and binder-free graphene–TiO₂ paper was prepared by a simple route. A unique 3-D nano-structure was achieved with nano-sized TiO₂ intercalated between graphene layers as pillars, significantly increasing the Li-ion insertion/extraction rate. At a current rate of 2 Ag⁻¹, the specific capacity can reach 122 mAhg⁻¹ after 100 charge/discharge cycles. More remarkably, the flexible graphene/TiO₂ hybrid paper shows an excellent stability when the rates decrease from 4 Ag⁻¹ back to 200 mAg⁻¹ with the retained capacity of 175 mAhg⁻¹.