Positively and Negatively Charged Double Shell with Au Sandwich for Protecting and Enhancing Photocatalytic Activity of TiO₂-Based Photocatalyst

Abstract

Enhancing selectivity and high affinity between a photocatalyst and target pollutants, preventing photocatalytic poisoning from degradation intermediates, and improving photocatalytic performance are three challenges for a heterogeneous photocatalyst that can be unlocked by a positively and negatively charged double shell with a Au sandwich. At pH 4.0, Ta 2 O 5 and TiO 2 shells are positively and negatively charged, respectively. Cationic dyes (Rhodamine B (RhB)) and double shelled Ta 2 O 5 @ Au@TiO 2 hollow spheres are chosen for a proof-of-concept study. The photocatalytic activity is in the order of double shelled Ta 2 O 5 @Au@TiO 2 hollow spheres > Ta 2 O 5 hollow spheres > TiO 2 hollow spheres. The photocatalytic performance of double shelled Ta 2 O 5 @Au@TiO 2 hollow spheres benefits from hollow spheres avoiding the reunion and more diverse heterophase junctions than Ta 2 O 5 , TiO 2 , and Au. Impressively, by electrostatic attraction and repulsion, cationic RhB is selectively enriched onto the negatively charged Ta 2 O 5 shell, and then, RhB and an intermediate are excluded into the positively charged inner TiO 2 shell, i.e., the poisoning on TiO 2 is avoided. Au is embedded in the middle to promote the transmission of photogenerated electrons, which is helpful to decompose the intermediates and RhB, so the poisoning on Ta 2 O 5 can be relieved.

Urchin-like, Surface-Positively Charged, Double-Shelled SnS2@TiO2 for Protecting and Enhancing Adsorption and Photocatalytic Activity to Remove High Concentrations of Anionic Pollutants

“…As shown in Figure g, the values of the BET specific surface areas of the as-synthesized products follow the order of hollow urchin-like TiO 2 @SnS 2 (55.82 m 2 /g) > TiO 2 hollow spheres (41.87 m 2 /g) > SnS 2 (21.77 m 2 /g). Remarkably, the excellent structural advantages (e.g., the large BET specific surface area, low mass density, and fast electronic transmission rate) of hollow composites not only can offer the high separation of electrons and holes but also provide abundant adsorption sites. , In order to analyze the optical absorption spectra of photocatalysts, the photocatalysts (SnS 2 , TiO 2 hollow spheres, and hollow urchin-like TiO 2 @SnS 2 ) are measured by the diffuse reflectance UV–vis spectra, as shown in Figure h. The absorption edge of TiO 2 hollow spheres is at approximately 387.5 nm in the UV region, corresponding to a band gap of ∼3.2 eV.…”

“…15 However, its applications are limited by the low utilization rate of sunlight, the high recombination rate of photogenerated electrons and holes, the poor affinity with pollutants, and a fatal defect of the poisoning from photodegradation intermediates. 16 Up to now, many methods have been proposed to protect and improve the photocatalytic performance of TiO 2 , including changing the morphology, 17,18 doping, 19,20 and surface coating. 21,22 SnS 2 as a CdI 2 -type structure semiconductor is reported to be a visiblelight-activated photocatalyst with nontoxicity, low cost, and good stability.…”

“…In addition, the morphology of photocatalysts has significant effects on the protection and improvement of their photocatalytic activities. 16 Hence, we construct hollow urchin-like SnS 2 @TiO 2 with high affinity with target pollutants as an efficient photocatalyst for photoreduction or photodegradation of target pollutants, and its advantages are listed as follows. First, the synthesis process is less dangerous, less time-consuming, and environmentally friendly because the production of SO 2 can be avoided at the reaction temperature.…”

“…TiO 2 is an excellent photocatalyst for its low cost, nontoxicity, semiconductivity, good thermal and chemical stability, and excellent biocompatibility . However, its applications are limited by the low utilization rate of sunlight, the high recombination rate of photogenerated electrons and holes, the poor affinity with pollutants, and a fatal defect of the poisoning from photodegradation intermediates . Up to now, many methods have been proposed to protect and improve the photocatalytic performance of TiO 2 , including changing the morphology, , doping, , and surface coating. , SnS 2 as a CdI 2 -type structure semiconductor is reported to be a visible-light-activated photocatalyst with nontoxicity, low cost, and good stability. − Nevertheless, the low photocatalytic efficiency of SnS 2 is a fatal weakness because of the slow transfer of photogenerated electrons (e – ) and holes (h + ).…”

“…Up to now, many methods have been proposed to protect and improve the photocatalytic performance of TiO 2 , including changing the morphology, , doping, , and surface coating. , SnS 2 as a CdI 2 -type structure semiconductor is reported to be a visible-light-activated photocatalyst with nontoxicity, low cost, and good stability. − Nevertheless, the low photocatalytic efficiency of SnS 2 is a fatal weakness because of the slow transfer of photogenerated electrons (e – ) and holes (h + ). In addition, the morphology of photocatalysts has significant effects on the protection and improvement of their photocatalytic activities …”