The surface modification with a proper amount of phosphate accelerates the dynamic decay of photogenerated electrons in the nanocrystalline anatase TiO(2) film in the presence of O(2), consequently prolonging greatly the lifetime of photogenerated holes so as to improve the charge separation of TiO(2) and then its photocatalytic activity for degrading gas-phase acetaldehyde and liquid-phase phenol mainly based on the transient absorption spectra and the measurements of electrochemical O(2) reduction and the produced hydroxyl radical amount. The acceleration effects are attributed to the increased amount of adsorbed O(2) by means of the curves of O(2) temperature-programmed desorption.
It is highly desired to effectively trap photogenerated holes for efficient photoelectrochemical (PEC) water oxidation to evolve O2 on oxide semiconductors. Herein, it is found for the first time mainly based on the time-resolved- and atmosphere-controlled- surface photovoltage responses that the modified chloride would effectively trap photogenerated holes so as to prolong the charge lifetime and hence promote charge separation of single-crystal rutile TiO2 nanorods. Its strong capacity to trap holes, comparable to the widely-used methanol and Co(II) phosphate, is well responsible for the exceptional photoactivities for PEC water oxidation to evolve O2 on rutile nanorods with a proper amount of chloride modified, about 2.5-time high as that on the resulting anatase nanoparticles, even 10-time if the surface area is considered. Moreover, it is suggested that the hole trapping role of chemically-adsorbed chloride is related to its lonely-pair electrons, and to the subsequently-produced intermediate Cl atoms with proper electronegativity for evolving O2. Interestingly, this finding is also applicable to the chloride-modified anatase TiO2. This work will provide a feasible strategy to design high-activity nanostructured semiconductor photoanodes for PEC water oxidation, even for overall water splitting.
The promotion of O2 adsorption on semiconductor surfaces for effectively capturing photogenerated electrons in the photocatalytic degradation of pollutants is highly desired. In this study, the targeted co-modification of residual chlorine rutile TiO2 nanorods with phosphoric and boric acids has been accomplished for the first time by simple wet chemical processes. The key to targeted co-modification is to connect -P-OH and -B-OH to the Cl-residual TiO2 surfaces by -Ti-OH and -Ti-Cl, respectively, consequently forming -Ti-O-P-OH and -Ti-Cl:B-OH ends. By means of the atmosphere-controlled surface photovoltage spectroscopy, the degrees for capturing photogenerated electrons by the adsorbed O2 as receptors on the resulting TiO2 nanorods are quantitatively analyzed. It is confirmed that the targeted co-modification could greatly promote the capture of the photogenerated electrons compared to the phosphate and borate modification alone. This is attributed to increased amounts of adsorbed O2 based on electrochemical O2 reduction and O2 temperature-programmed desorption measurements, further leading to the enhanced separation of photogenerated charges, characterized by an increase in the amount of produced hydroxyl radicals. This is responsible for the obviously enhanced photocatalytic activity of TiO2 nanorods towards the degradation of colorless gas-phase acetaldehyde and liquid-phase phenol. This work would provide us a feasible route for the co-modification with inorganic acids to synthesize efficient nanosized TiO2-based photocatalysts.
In this work, commercial P25 TiO2 is modulated by post‐treatments with different acidic substances, and the effects of residual acidic substances on the photogenerated charge separation of TiO2 and its photocatalytic activity are investigated in detail. It is demonstrated by means of atmosphere‐controlled surface photovoltage spectroscopy that an increase in acid surface modification is favorable for improving the photogenerated charge separation of TiO2. As a result, its photocatalytic activity for the degradation of gas‐phase acetaldehyde is enhanced greatly. On the basis of measurements of O2 temperature‐programmed desorption of untreated and treated TiO2, it is confirmed that an increased amount of acid surface modification promotes the adsorption of O2 on TiO2. Hence, it is suggested for the first time that an increase in surface acidity through post‐treatment with an appropriate amount of acidic substance leads to a clear enhancement of the photocatalytic activity of TiO2 by promoting O2 adsorption, and thus, improving the photogenerated charge separation of TiO2. This work provides a feasible route for the synthesis of high‐activity oxide‐based semiconductor photocatalysts through surface modification with stable inorganic acids.
In general, an increase in O2 adsorption is highly desirable for efficient photocatalysis. Herein, commercial P25 TiO2 is modified with an F127‐containing SiO2 sol, and post‐treated with phosphoric acid. It is confirmed, on the basis of O2 temperature‐programmed desorption measurements, that the O2 adsorption of commercial P25 TiO2 is greatly promoted through its modification with porous SiO2, especially in the phosphate‐treated case. The promotion of O2 adsorption is attributed to the introduction of SiOH and POH as surface ends, and to the slightly increased surface area. Interestingly, it is concluded that the promotion of O2 adsorption is favorable for the separation of photogenerated charge carriers, as seen from the steady‐state surface photovoltage spectra, transient‐state surface photovoltage responses, and measurements of the hydroxyl radicals produced. This is responsible for the clear enhancement in the photocatalytic activity of modified TiO2 for the degradation of gas‐phase acetaldehyde and liquid‐phase phenol as colorless pollutants. This work provides a feasible route for improving the photocatalytic activity of TiO2.
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