Rajkumar Patel

Preparation of TiO2 spheres with hierarchical pores via grafting polymerization and sol–gel process for dye-sensitized solar cells

Titania (TiO2) nanoparticles were surface-modified via atom transfer radical polymerization (ATRP) with hydrophilic poly(oxyethylene) methacrylate (POEM), which can coordinate to the TiO2 precursor, titanium(IV) isopropoxide (TTIP). Following application of a sol–gel process and calcination at 450 °C, TiO2 nanospheres with hierarchical pores were generated, as confirmed by the shifting of conduction bands in TiO2 using UV-visible spectroscopy and X-ray photoelectron spectroscopy (XPS). The particle size and morphology of TiO2 were characterized using wide angle X-ray scattering (WAXS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Brunauer–Emmett–Teller (BET) analysis revealed bimodal distribution of TiO2 pore sizes with peaks at 6 nm and 50 nm to afford better penetration of polymer electrolyte, as confirmed by electrochemical impedance spectroscopy (EIS). Dye-sensitized solar cells (DSSC) made from TiO2 nanospheres with hierarchical pores exhibited improved photovoltaic efficiency (3.3% for low molecular weight (Mw) and 2.5% for high Mw polymer electrolytes), as compared to those from neat TiO2 nanoparticles (2.4% for low Mw and 1.3% for high Mw) at 100 mW/cm2, owing to the increased surface areas and light scattering.

Facile fabrication of vertically aligned TiO2 nanorods with high density and rutile/anatase phases on transparent conducting glasses: high efficiency dye-sensitized solar cells

We present a facile and effective method to prepare vertically aligned TiO2 nanorods (NRs) with a high density and rutile/anatase mixture phases on transparent conducting oxide (TCO) glasses. The anatase TiO2 nanoparticles grafted with hydrophilic poly(oxyethylene) methacrylate (POEM), which can coordinate with a TiO2 precursor such as Ti(BuO4), were introduced in the presence of glycine. Following application of a hydrothermal process and calcination at 450 °C, vertically well-aligned TiO2 NRs with diameters of 70 nm and lengths of 3 μm were generated, as confirmed by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The larger wavenumber shift observed with TiO2–POEM in FT-IR spectra suggests more favorable and stronger interactions that facilitate the nucleation and growth of NRs on the transparent conductive fluorine-doped tin oxide (FTO) substrates, resulting in increased NRs density. Dye-sensitized solar cells (DSSCs) fabricated using TiO2 NRs with a high density and rutile/anatase mixture phases exhibited improved energy conversion efficiency, irrespective of the type of electrolyte. When liquid electrolyte was used, the DSSCs exhibited an efficiency of 5.7% at 100 mW cm−2, which is the highest value for DSSCs fabricated with NRs directly grown on TCO substrates. High cell efficiencies of 4.5 and 3.7% were also obtained with quasi-solid-state and solid-state electrolytes, respectively, due to the reduced interfacial resistance of electrolyte/electrode and improved electron transport.

Preparation of TiO2 nanowires/nanotubes using polycarbonate membranes and their uses in dye-sensitized solar cells

Track-etched polycarbonate (PC) membranes were used as a soft template to synthesize mesoporous TiO(2) for use in dye-sensitized solar cells (DSSCs). The Ti precursor infiltrated into the cylindrical confined spaces of PC membranes. Upon calcination at 500 °C, TiO(2) nanowires (15TNW) were obtained from PC with a 15 nm pore diameter, whereas TiO(2) nanotubes (50TNT and 100TNT) were generated from PC with 50 and 100 nm diameter pores, respectively. TNW and TNT were used as photoelectrodes in DSSCs employing a polymer electrolyte. The ranking of the cell efficiencies of the 200 nm thick TiO(2) films was 50TNT (1.1%) > 15TNW (0.8%) ≅ 100TNT (0.7%), which was mostly attributed to different amounts of dye adsorption due to different surface areas. These TNW and TNT films were further coated with the graft copolymer-directed mesoporous TiO(2) and were used as interfacial layers between the FTO glass and the 4 μm thick nanocrystalline TiO(2) film. As a result, the order of energy conversion efficiency was 15TNW (5.0%) ≅ 50TNT (4.8%) > 100TNT (4.1%). The improved performance of 15TNW was due to a higher transmittance through the electrode and a longer electron lifetime for recombination. The DSSC performance was systematically investigated in terms of interfacial resistance and charge recombination using electrochemical impedance spectroscopy.

Well-organized meso-macroporous TiO2/SiO2 film derived from amphiphilic rubbery comb copolymer.

We report the facile synthesis of a well-organized meso-macroporous TiO2/SiO2 thin film with high porosity and good interconnectivity from a binary mixture (i.e., titania precursor and polymer template). Our process is based on self-assembly of the amphiphilic rubbery comb copolymer, poly(dimethylsiloxane)-g-poly(oxyethylene methacrylate) (PDMS-g-POEM) with titanium tetraisopropoxide (TTIP). SiO2 is self-provided by thermal oxidation of PDMS chains during calcination under air. The selective, preferential interaction between TTIP and the hydrophilic POEM chains was responsible for the formation of well-organized TiO2/SiO2 films, as supported by transmission electron microscopy, scanning electron microscopy, X-ray photospectroscopy, and X-ray diffraction analyses. We investigated in detail the effect of precursor content, solvent type, and polymer concentration on thin film morphology. Photodegradation of methyl orange by the well-organized meso-macroporous TiO2/SiO2 film was greater than that of a dense TiO2 film prepared without PDMS-g-POEM as well as a SiO2-etched TiO2 film. These results indicate that the well-organized structure and SiO2 doping of the TiO2 film play a pivotal role in enhancing its photocatalytic properties.

Bioinert membranes prepared from amphiphilic poly(vinyl chloride)-g-poly(oxyethylene methacrylate) graft copolymers

Poly(vinyl chloride) (PVC) membrane was hydrophilically modified by grafting with poly(oxyethylene methacrylate) (POEM) using atom transfer radical polymerization (ATRP). The successful grafting of PVC main chain by POEM was characterized by Fourier transform infrared spectroscopy (FT-IR). The molecular weight and hydrophilicity of membranes increased with the amount of POEM grafting, as characterized by gel permeation chromatography (GPC) and contact angle measurement, respectively. Transmission electron microscope (TEM) and small angle X-ray scattering (SAXS) analysis revealed the microphase-separated structure of PVC-g-POEM and the domain spacing increased from 59.3 to 86.1 nm with increasing grafting degree. Scanning electron microscopy (SEM) was used for the direct visualization of the mouse embryonic fibroblast (MEF) cell and bacteria adhesion on the membrane surface. Protein adsorption and eukaryotic and prokaryotic cell adhesion tests showed that the bioinert properties of membranes were significantly increased with POEM content.

Antibacterial behaviour of quaternized poly(vinyl chloride)-g-poly(4-vinyl pyridine) graft copolymers

Amphiphilic graft copolymers consisting of poly(vinyl chloride) (PVC) main chains and poly(4-vinyl pyridine) (P4VP) side chains were synthesized via atom transfer radical polymerization (ATRP) using direct initiation of chlorine atoms. The successful synthesis of PVC-g-P4VP graft copolymers was confirmed by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H-NMR). Transmission electron microscope (TEM) and small angle X-ray scattering (SAXS) analysis showed that PVC-g-P4VP exhibited microphase-separated, ordered structure with 37.6 nm of domain spacing, which was not observed in neat PVC. For antibacterial applications, the tertiary nitrogen atoms of PVC-g-P4VP was quaternized using 1-bromohexane, as confirmed by FTIR measurements. Bacteria including Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Bacillus cereus (B. cereus), and Pseudomonas aeruginosa (P. aeruginosa) were completely killed in 24 h on the quaternized PVC-g-P4VP (46% grafting) surface, indicating its excellent antibacterial behavior while it showed to be cytotoxic to mammalian cell.

Preparation of Porous TiO 2 Thin Films by Poly(vinyl chloride)-graft-poly(N-vinyl pyrrolidone) and Their Applications to Dye-sensitized Solar Cells

Mesoporous titanium dioxide () thin films were prepared using poly(vinyl chloride)-graft-poly(N-vinyl pyrrolidone) (PVC-g-PVP) as a templating agent via sol-gel process. Grafting of PVC chains from PVC backbone was done by atom transfer radical polymerization (ATRP) technique. The successful grafting of PVP to synthesize PVC-g-PVP was checked by fourier-transform infrared spectroscopy (FT-IR) and gel permeation chromatography (GPC). The carbonyl group interaction of PVC-g-PVP graft copolymer with was confirmed by FT-IR. The porous morphologies of the films genereated after calcination at was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The mesoporous films with 580 nm in thickness were used as a photoelectrode for solid state dye sensitized solar cell (DSSC) and showed an energy conversion efficiency of 1.05% at 100 .