Plasmochemical Approach to Template‐Free Synthesis of Highly Crystalline Mesoporous TiO₂ within Milliseconds

Abstract

A plasmochemical synthetic strategy for the template-free and one-step preparation of highly crystalline mesoporous TiO 2 from oxidation of titanium tetraisopropoxide (TTIP) aerosol by gliding arc plasma in a vortex air flow within milliseconds is reported. The scanning electron microscopy, high-resolution transmission electron microscopy, and nitrogen sorption characterizations confirm the wormhole-like mesoporous structures. The highly crystalline mesoporous TiO 2 has an optimized anatase/rutile weight ratio of about 80/20 for photocatalytic applications, exhibiting superior thermal stability and good photocatalytic activity.TiO 2 has attracted considerable attentions due to its stability, non-toxicity, and inexpensiveness, and promising photocatalytic applications in degrading pollutants, energy conversion and chemical synthesis. [1] TiO 2 with high specific surface area, large porosity and tunable morphologies is often in demand to achieve the high photocatalytic efficiency. Therefore, mesoporous TiO 2 has aroused increasing interests. [2] For the mesoporous TiO 2 , the preparing techniques are of great concern with its characteristics. The synthesis of mesoporous TiO 2 generally requires soft templates (surfactants and block polymers) and hard templates (e. g., porous silica, polystyrene spheres, porous carbon). [2] Normally, the processes of sol-gel, [2a,3] hydrothermal chemistry, [4] microwave [5] and sonochemistry [6] are widely and employed. However, these synthesis processes inevitably require the costly surfactants and are comparatively complicated and time consuming. [2d] Calcination is the necessary step to remove the template and to obtain crystalline structure. However, the shrinkage of mesoporous structure and agglomeration of the particles will be caused by calcination. [2b,d,7] Recently, the important applications of plasmas for catalyst preparation have been reported increasingly. [8] Herein, we report a plasmochemical synthetic strategy for the templatefree and one-step preparation of highly crystalline mesoporous TiO 2 within milliseconds.In this plasmochemical synthetic strategy, a vortex-flow gliding arc plasma is employed. The plasma features a fast transition from a quasi-thermal stage to a non-thermal stage, providing high electron density (10 13 -10 14 cm À3 ) and gas temperature of over 2000 K in the quasi-thermal stage and high level of non-equilibrium (electron temperature @ gas temperature) in the non-thermal stage. [9] As shown in the left of Figure 1, titanium tetraisopropoxide (TTIP, J&K Scientific, 98%) aerosol as the Ti precursor is generated from an ultrasonic atomizer and carried by 100 mL/min N 2 into the specially designed plasma reactor. The air with a flow rate of 5 L/min enters via two tangential gas inlets of the plasma reactor to generate gliding arc plasma under an input power of 100 W (the middle of Figure 1). The TTIP aerosol is rapidly oxidized by the air plasma and a highly crystalline mesoporous TiO 2 is directly produced (the right of Figure 1), expe...

Mesoporous TiO2 electrocatalysts synthesized by gliding arc plasma for oxygen evolution reaction

“…The detailed method for catalyst synthesis is shown elsewhere, in our more recent work [25]. Using titanium tetraisopropoxide (TTIP, J&K Scientific, 98%) as precursor that was atomized by ultrasonic atomizer and nitrogen (purity > 99.999%) of 0.1 l min −1 as carrier gas to deliver the formed TTIP aerosol (in a water bath of 318 K) to the bottom of gliding arc plasma reactor (designed and made by our laboratory), under exact control by mass flow controller.…”

“…Using titanium tetraisopropoxide (TTIP, J&K Scientific, 98%) as precursor that was atomized by ultrasonic atomizer and nitrogen (purity > 99.999%) of 0.1 l min −1 as carrier gas to deliver the formed TTIP aerosol (in a water bath of 318 K) to the bottom of gliding arc plasma reactor (designed and made by our laboratory), under exact control by mass flow controller. The gliding arc reactor was described in our previous work [25], which consists of a powered electrode, a grounded electrode, a quartz tube and tangential inlets. To initiate the reaction for catalyst synthesis, the gliding arc plasma is generated between powered and grounded electrodes and driven by an alternating-current high voltage power supply (CTP-2000X, Nanjing Suman Electronics, China).…”

“…The waveforms of discharge voltage and current were obtained by a digital oscilloscope (DPO4104B, Tektronix). The assynthesized sample of mesoporous TiO 2 under the input power of 100 W, was marked as mT-1, and that with post calcination at 550 • C for mT-2 [25]. Herein, it is denoted mT and mTc (instead of mT-1 and mT-2) for our synthesized catalysts, and cT for commercial TiO 2 (P25, Deggusa) for easy comparison, respectively.…”

“…Under the optimal conditions of input power of 100 W and air (with TTIP) flow rate of 5 l min −1 , the mesoporous TiO 2 (mT) in nanopowder in the gliding arc plasma reactor was achieved, followed by that of calcination (mTc). See the images for the apparatus in our previous work [25] with cover feature (see the link). The resulting material features mesopores surrounded by a continuous (inverse) phase of nanoscale semiconductor, which could be interesting for exploring fundamental triple phase boundaries for photo-or electro-catalysis.…”

A 3D Hierarchical Ti3C2Tx/TiO2 Heterojunction for Enhanced Photocatalytic CO2 Reduction

“…In particular, photocatalytic reduction of CO 2 is a promising way and has been widely studied, because it can directly convert CO 2 into hydrocarbons through a photocatalyst under light irradiation [3–6] . Among numerous photocatalysts, TiO 2 is still one of the best candidates due to its favorable stability, high activity, nontoxicity and low price [7–11] . Nevertheless, electron‐hole pairs recombine too fast and no more than 5% of solar energy can be utilized in a single‐component TiO 2 , restricting its real application [12–14] .…”