Green sol–gel route for selective growth of 1D rutile N–TiO₂: a highly active photocatalyst for H₂ generation and environmental remediation under natural sunlight

Abstract

We report selective growth of N-TiO 2 1D nanorods using a green aqueous sol-gel method followed by hydrothermal treatment. Titanium tetraisopropoxide, diethanolamine, and H 2 O 2 were used as precursors for preparing an aqueous gel. Trifluoroacetic acid (TFA) was used as a growth regulator for selective growth of desired structure and morphology. Effects of TFA on the structure and morphology of N-TiO 2 were studied by varying concentration of TFA between 1-10% by volume. Structural characterization using XRD confirmed formation of a specific rutile phase with slight crystal disorder with N-doped TiO 2 samples. FESEM and HRTEM analysis showed formation of 1D rice grain shaped N-TiO 2 in the presence of 1% TFA solution. One directional growth along the (211) A. IntroductionAmong transition metal oxide photocatalysts, titania (TiO 2 ) has been an intensively investigated candidate within the ambit of various potential applications such as photocatalytic water splitting, 1-3 organic pollutant degradation, 4-7 supercapacitors, 8 dye sensitized solar cells (DSSC), 9-12 Li-ion battery photo anodes, 13,14gas-sensors, 15,16 and super-hydrophilicity. 17 This can be ascribed to its fascinating electronic and optical properties, namely, favourable electronic band structure, non-toxicity, biocompatibility, long term chemical stability towards photo-corrosion, and, importantly, commercial cost-effectiveness.18,19 However, photocatalytic quantum efficiency of TiO 2 in solar applications is still limited due to its broad bandgap (3.0 and 3.2 eV for rutile and anatase phases, respectively) responding to UV radiation only (l < 387 nm).20 But, UV radiation accounts for merely 5% of solar photons. Subsequently, another important drawback with TiO 2 is a high recombination rate of photogenerated electron-hole pairs. To compensate for the above challenges, many attempts have been made to decrease the threshold energy of TiO 2 or photo-excitation by red-shiing its photo-response to visible light having a wavelength (l) range between 400-800 nm.

Recent Progress on Titanium Dioxide Nanomaterials for Photocatalytic Applications

“…[98][99][100] Sol-geli sasimple technique,a si tc an be performed atl ow temperatures. [104] The authors use titaniumt etraisopropoxide, diethanolamine, and H 2 O 2 as precursors to prepare an aqueous gel. The reaction can be accelerated by the addition of an acidic (e.g.,H Cl) or basic (e.g.,N aOH) catalyst.…”

“…The reaction can be accelerated by the addition of an acidic (e.g.,H Cl) or basic (e.g.,N aOH) catalyst. [104] Sol-gel is av ersatile method, as it allows good controlo ft he structure, including the porosity and particle size. The size, shape, and crystalline phase of TiO 2 can be controlled by the pH, solvent, alkoxide, and catalyst.…”

“…[100][101][102][103] Recently,K hore et al have reported on the growth of N-doped TiO 2 1D nanorods by using an aqueous sol-gelm ethod followed by hydrothermal treatment. [104] The authors use titaniumt etraisopropoxide, diethanolamine, and H 2 O 2 as precursors to prepare an aqueous gel. They use trifluoroacetic acid (TFA) as ag rowth regulator and study its effect on the structure and morphologyo fN -dopedT iO 2 .T he FESEM images in Figure 5e,f show that uniformally shaped nanorods are obtained upon treating N-doped TiO 2 with 1%TFA.…”

“…Ndoped TiO 2 with 1% TFAs hows excellent photocatalytic activity for the degradation of methyl orange and forH 2 generation under sunlight. [104] Sol-gel is av ersatile method, as it allows good controlo ft he structure, including the porosity and particle size. This technique ensures good homogeneity andh igh purity,b ecause mixing is performed at the molecular level.…”

“…in which r is the degradationr ate of the reagent, k represents the kinetic reactionc onstant, K is the adsorption equilibrium Electrodeposition -low costing -low-temperaturef eature -low deposition rate -limited usable substrates [58] electrospinning -cost effective -industrial applications -formationofn anofibers with highsurface areas -larges tandard deviations of the nanofiber's diameter -restricted fiber mat purity [146] hydrothermal -low energy consumption -simple equipment -chemical homogeneity -long reaction times -non-uniform particle sizes [87] electrochemical anodization -low costing -longest tube length -formationoft ubes with high surface areas -not suitable for massproduction -long process [91] template assisted -control of nanotube dimensions -yields dense arrays of uniform nanotubes -complicated process -limitation of nanotube's dimensions by the geometric parameters of the membrane [97] sol-gel -control of porosity and particle size -good homogeneity and high purity -low energy consumption -high cost of precursors -long process [104] spin coating -easy control of film thickness -uniform films -lackofm aterial efficiency -not suitable for massproduction [147] dip coating -low costing -easy process -not able to produce densified and uniform coatings [148] CVD -low depositiontemperature -uniformcoating in the micrometer range -not able to produce conformal films in the nanoscale range [ 126] ALD -deposition of conformal thin films in ap recise mannerin the nanoscalerange -low energy consumption -long depositiontime -not suitable for massproductionf or large-scale application [149,150] ChemSusChem 2018, 11,3023 -3047 www.chemsuschem.org 2018 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim constant, and C is the concentration of the reagent in the aqueous medium. In general,L angmuir-Hinshelwood-type behavior is observed.…”