Anodic TiO2 nanotube layer directly formed on the inner surface of Ti pipe for a tubular photocatalytic reactor

• TiO2 nanotube layer on Ti pipe is successfully employed in fabricating a continuous-flow photocatalytic reactor.
• The TiO2 nanotube layer is electrochemically anodized and its photocatalytic activity is optimized and evaluated for the degradation of organic substrates.
• TiO2 nanotube layer shows a superior photocatalytic activity than a compact TiO2 layer.
• The tubular TiO2 nanotube reactor exhibits promising performance for water purification.

We demonstrated the successful water treatment performance of a continuous-flow tubular TiO2 nanotube reactor made of Ti pipe where a TiO2 nanotube (TNT) layer was directly formed on the inner wall by an electrochemical anodization process. A cylindrical UV lamp was inserted into the pipe to irradiate the inner TNT surface as a light source. To optimize the thickness of TNT layer on Ti pipe, TNT layers with 1, 5 and 10 μm thickness were prepared and their photocatalytic activities were tested for the degradation of various organic substrates (acid orange 7 (AO7), dichloroacetate (DCA), and 4-chlorophenol (4-CP)) under UV illumination. The TNT layer with 10 μm thickness showed the highest photocatalytic activity, with first-order removal rate constants (k:min−1) of 0.019, 0.039, and 0.025 for AO7, 4-CP, and DCA, respectively. The directly formed TNTs (10 μm thickness) on Ti pipes in the continuous-flow tubular TNT reactor, having a strong adhesiveness and a high surface area, enabled the successful degradation of organic compounds and to have kept the activity without decrease during the repeated cycles and long-term experiments. The photocatalytic performance of the tubular TNT reactor was tested with a higher concentration, smaller volume ([4-CP]0 = 100 μM, solution vol. = 15 mL) and a lower concentration, larger volume ([4-CP]0 = 20 μM, solution vol. = 100 mL) in the circulation-flow mode (20 mL min−1). A good performance was achieved under the low intensity UV illumination (≈2 mW cm−2) with a half-life of ca. 50 min and ca. 11 h with 80% and 79% removal of TOC for the above two test conditions, respectively. The proposed tubular TNT reactor can be an effective option in the design of continuous flow-type photocatalytic reactors for practical water purification.

A tubular photocatalytic reactor made of Ti pipes with vertically well-aligned TiO2 nanotube (TNT) layer was successfully fabricated and evaluated for water purification activity. The TNT layers directly formed on Ti pipes have strong adhesiveness and high surface area with showing high activity and stability.Figure optionsDownload high-quality image (113 K)Download as PowerPoint slide