Bio-Template Mediated In Situ Phosphate Transfer to Hierarchically Porous TiO₂ with Localized Phosphate Distribution and Enhanced Photoactivities

Abstract

A localized phosphate distribution (LPD) was introduced for the first time into a porous TiO 2 nanostructure by using a biotemplate synthetic strategy, that is, Staphylococcus aureus (S. aureus)-assisted in situ phosphate transfer. The resulting novel nanostructures have shown remarkable enhancement of photoactivities for both selective dye degradation and photoelectrochemical water reduction. Mechanistic understanding reveals that improved separation, directional transport, and less limited interface transfer of the photogenerated electron and hole may be achieved simultaneously within the LPD-modified TiO 2 nanostructures because of the existence of the confined negative surface electrostatic field (NSEF) and the spatially oriented upward band bending (UBB). On the contrary, a homogeneous phosphate distribution (HPD) will greatly increase electron interface transfer resistance, which will cause the increase of recombination in bulk. The most important inspiration we can obtain herein is that a comprehensive consideration of the influence of nanostructure on all of the critical aspects of the carrier's dynamics is needed during the rational design and construction of the advanced nanostructured photocatalyst systems. Considering the available resources for the synthesis and strong covalent interaction of phosphate with many other transition metal cations, the authors think that the novel strategy for a simultaneous optimization of the dynamic processes of the charge pairs by introducing LPD is promising for several applications including photocatalysis, photoelectrochemical hydrogen production, and solar cell.

Electron trapping induced electrostatic adsorption of cations: a general factor leading to photoactivity decay of nanostructured TiO2

“…The nanoparticulate films on FTO substrates are prepared through the common "doctor blade" processing and sintering procedure, the raw materials are anatase TiO 2 nanoparticles prepared through a dialysis procedure 24 (the film is called D-TiO 2 ). X-ray diffraction (XRD, Shimadzu-6100 diffractometer with a Cu Kα radiation) and scanning electron microscopy (SEM, HITACHI S-4800 FE-SEM) techniques are applied to give structural and morphological characterizations of the films.…”

“…1050 cm -1 in IR spectra (Figure 4d). 24,25,36 It has been proven that the hydrolysis of Ti-O-P connections can only occur in alkaline solution but cannot in neutral or acidic solution. 37 IR spectra indicate the dissociation of the covalent Ti-O-P connection after a phosphate-modified TiO 2 electrode is subjected to the electron trapping experiment, further confirming the occurrence of the ETPU process (see Figure s3 for more details).…”

Conformal Titanyl Phosphate Surface Passivation for Enhancing Photocatalytic Activity

“…The negative electrostatic field also can activate the formation of hydrogen bond between phosphate anion and water molecule. This promotes the adsorption of water molecules at the surface of photocatalysts and the generation of hydroxyl radical, resulting in high efficient photocatalytic properties [20,22,23]. Moreover, the charge recombination was suppressed since the charge trap states of TiO 2 were ameliorated by the surface titanyl phosphate passivation layer.…”

“…In recent years, numerous efforts have been conducted to enhance the photocatalytic activity of TiO 2 nanoparticles by modifying their surface properties with phosphate anion (PO 4 3-) [18][19][20][21][22].…”

“…This preferred surface electrostatic field facilitates the efficient charge separation and prolongs the photo-induced charge migration [20,22]. In addition, the negative electrostatic field can activate the formation of hydrogen bonds between phosphate anions and water molecules.…”