Mechanistic Study of Visible-Light-Induced Photodegradation of 4-Chlorophenol by TiO<sub>2−<i>x</i></sub>N<i><sub>x</sub></i>with Low Nitrogen Concentration (2011)

TiO<sub >2−<i>x </i></sub>N<i ><sub>x</sub></i> powders with low N-doping concentrations (<svg style="vertical-align:-0.30096pt;width:117.825px;" id="M1" height="11.0625" version="1.1" viewBox="0 0 117.825 11.0625" width="117.825" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,11.0625)"> <g transform="translate(72,-63.15)"> <text transform="matrix(1,0,0,-1,-71.95,63.5)"> <tspan style="font-size: 12.50px; " x="0" y="0">0</tspan> <tspan style="font-size: 12.50px; " x="6.2515001" y="0">.</tspan> <tspan style="font-size: 12.50px; " x="9.3772497" y="0">0</tspan> <tspan style="font-size: 12.50px; " x="15.62875" y="0">2</tspan> <tspan style="font-size: 12.50px; " x="21.880251" y="0">1</tspan> <tspan style="font-size: 12.50px; " x="31.595081" y="0"><</tspan> <tspan style="font-size: 12.50px; " x="43.635471" y="0">𝑥</tspan> <tspan style="font-size: 12.50px; " x="53.987953" y="0"><</tspan> <tspan style="font-size: 12.50px; " x="66.028343" y="0">0</tspan> <tspan style="font-size: 12.50px; " x="72.279846" y="0">.</tspan> <tspan style="font-size: 12.50px; " x="75.405594" y="0">0</tspan> <tspan style="font-size: 12.50px; " x="81.657089" y="0">4</tspan> <tspan style="font-size: 12.50px; " x="87.908592" y="0">9</tspan> </text> </g> </g> </svg>) were prepared by annealing commercial TiO<sub >2</sub> (P-25) under an NH<sub >3</sub> flow at 550°C. Regardless of UV or visible case, the photoactivities of the samples decreased as <i >x</i> increased, and TiO<sub >1.979</sub>N<sub >0.021</sub> showed the highest activity for the 4-chlorophenol (4-CP) decomposition under the visible-light irradiation. The visible-light response for N-doped TiO<sub >2</sub> could arise from an N-induced midgap level, formed above the valence band (O 2p). Electron spin resonance (ESR) measurements and the radical scavenger technologies gave the combined evidence that the active species (<svg style="vertical-align:-0.17554pt;width:30.862499px;" id="M2" height="10.9125" version="1.1" viewBox="0 0 30.862499 10.9125" width="30.862499" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,10.9125)"> <g transform="translate(72,-63.27)"> <text transform="matrix(1,0,0,-1,-71.95,63.5)"> <tspan style="font-size: 12.50px; " x="0" y="0">•</tspan> <tspan style="font-size: 12.50px; " x="6.5390692" y="0">O</tspan> <tspan style="font-size: 12.50px; " x="15.566235" y="0">H</tspan> </text> </g> </g> </svg> and <svg style="vertical-align:-3.13504pt;width:33.787498px;" id="M3" height="14.6" version="1.1" viewBox="0 0 33.787498 14.6" width="33.787498" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,14.6)"> <g transform="translate(72,-60.32)"> <text transform="matrix(1,0,0,-1,-71.95,63.5)"> <tspan style="font-size: 12.50px; " x="0" y="0">O</tspan> </text> <text transform="matrix(1,0,0,-1,-62.92,60.37)"> <tspan style="font-size: 8.75px; " x="0" y="0">2</tspan> </text> <text transform="matrix(1,0,0,-1,-58.05,63.5)"> <tspan style="font-size: 12.50px; " x="0" y="0">•</tspan> </text> <text transform="matrix(1,0,0,-1,-51.51,68.5)"> <tspan style="font-size: 8.75px; " x="0" y="0">−</tspan> </text> </g> </g> </svg>) are responsible for the photodecomposition of 4-CP over TiO<sub >2−<i>x</i></sub>N<i ><sub>x</sub></i> under the visible irradiation. A possible photocatalytic mechanism was discussed in detail.