Photoelectrochemical degradation of TMAH by green synthesized silver modified titanate nanotube arrays

In this study, titanate nanotube arrays (TNAs) were prepared by using electrochemical anodization, and the silver nanoparticles were deposited on a titanate dioxide nanotube array (Ag/TNAs) by green synthesis methods. The Ag/TNAs was further applied to degrade tetramethylammonium hydroxide (TMAH) in a photoelectrochemical (PEC) system. SEM results showed that the diameter and length were 121.7 nm and about 3.45 & mu;m, respectively, for TNAs. The deposited silver nanoparticles showed spherical and flaky shapes depending on using tea and coffee as green reducing agents, respectively. XPS showed that the atomic percentage of silver in Ag/TNAs-CTC5 and Ag/TNAs-CGA2.5 was 6.60% and 1.76%, individually. Results of UV-vis analyses indicated that the absorbance edge of TNAs red-shifts to a more extended wavelength region after silver modification. The pho-tocurrents of Ag/TNAs-CTC5 (5.03 mA/cm2) and Ag/TNAs-CGA2.5 (3.63 mA/cm2) were 51% and 32% higher than that of TNAs (2.45 mA/cm2), illustrating that the photocatalytic ability of TNAs was significantly enhanced after silver nanoparticles modifying. Electrochemical impedance analysis (EIS) results confirmed that the elec-tron lifetime of Ag/TNA-CTC and Ag/TNAs-CGA was 6.6 and 1.82 times longer than that of the TNA in the PEC system. Mott-Schottky analyses indicated that TNAs, Ag/TNAs-CTC5, and Ag/TNAs-CGA2.5 are n-type semi-conductors with a density of dopants of 3.16 x 1019, 1.42 x 1020, and 9.49 x 1019 cm-3. The results of TMAH degradation showed that Ag/TNAs-CTC5 performed the highest efficiency at pH= 3 in the PEC system. EPR analyses of TNAs and Ag/TNAs-CTC5 showed a peak intensity of 1:2:2:1 which represented the characteristic DMPO-OH, revealing the dominant oxidants of the PEC system.