Structure and Electronic Properties of Small Silver–Gold Clusters on Titania Photocatalysts for H₂O₂ Production: An Investigation with Density Functional Theory

Abstract

Ag4–n –Au n (n = 1–3) clusters deposited on the surface of TiO2(101) are more efficient than titania as photocatalysts. The mechanisms of this enhancement are, however, unclear. In this study, density functional theory was applied with the Hubbard correction to investigate the atomic and electronic structure of Ag4–n –Au n (n = 1–3)@TiO2(101). The band gap of TiO2 in the presence of Ag3Au, Ag2Au2, and AgAu3 decreased to 1.00, 1.24, and 1.40 eV, respectively. The band edges of all systems satisfy the requirement for H2O2 production. H2O2 adsorption energies and O–O bond lengths have shown that Ag3Au@TiO2(101) and Ag2Au2@TiO2(101) systems are good candidates for H2O2 production without poisoning of the catalyst surface and H2O2 dissociation. The results show that Ag3Au and Ag2Au2 can produce midgap states at the top of the valence band from the direct Au–Ti bonds. The midgap state in Ag2Au2@TiO2(101) has a suitable position for H2O2 formation, thereby boosting the photoresponse of the system in visible and infrared light by improving the charge separation.

Ternary chalcogenides XGaS2 (X = Ag or Cu) for photocatalytic hydrogen generation from water splitting under irradiation of visible light

“…Moreover, the large calculation cost of the hybrid functional for many layer slabs presents challenges. The method proposed by Xu et al provides a helpful method for evaluating the positions of band edges for bulk structures; the method has been adopted by additional high‐credibility references . Here, we calculated the absolute band edges of the XGaS 2 according to the following equations proposed by Xu et al: where E VBM and E CBM represent the absolute potentials of VBM and CBM; E g is the calculated band energy gap of present structures based on the first principles calculation; and χ is the electronegativity of the semiconductors and is estimated as follows: where χ n and n represent the absolute electronegativities of the constituent atoms and the number of atomic species, whereas s, t, p, and q represent the number of individual atoms.…”

“…The method proposed by Xu et al [48] provides a helpful method for evaluating the positions of band edges for bulk structures; the method has been adopted by additional highcredibility references. [49,50] Here, we calculated the absolute band edges of the XGaS 2 according to the following equations proposed by Xu et al [48] :…”

Inorganic Metal‐Oxide Photocatalyst for H2O2 Production

“…Goliaei and Seriani conducted a density functional theory (DFT) calculation of H 2 O 2 production and decomposition over Ag 4−n −Au n (n = 1−3) clusters deposited on TiO 2 (101) to provide mechanistic insights. [47] With the deposition of Ag 3 Au, Ag 2 Au 2 , and AgAu 3 nanoclusters, the bandgap of TiO 2 decreased from 3.0 to 1.00, 1.24, and 1. 40 [69,73] however, Pt/TiO 2 could alternatively photogenerate H 2 O 2 via the 2e − WOR route.…”

“…The CB of TiO 2 is around −0.19 V (vs NHE) at pH 0, [46] more negative than the potential for the concerted 2e − ORR pathway. However, H 2 O 2 yield over pristine TiO 2 is merely at the micromolar level due to several restrictions: i) TiO 2 has large band gaps (≈3 eV) [47] and is only photoresponsive to UV radiation (<400 nm), which makes up 4-5% of the whole solar spectrum; ii) rapid electron-hole recombination causes tremendous loss of photogenerated carriers; [48] iii) the H 2 O 2 product interacts with surface Ti−OH groups on TiO 2 and readily decomposes when induced by UV or visible light; [49] iv) O 2 reduction on TiO 2 often undergoes the two-step one-electron ORR (Equations ( 3)-( 5)) instead of the concerted 2e − ORR pathway (Equation ( 1)); v) water oxidation by photogenerated holes is inherently a slow process, leading to accumulation of holes at the VB of TiO 2 and a higher rate for electron-hole recombination.…”

Нанокластеры Серебра В Биохимии И Медицине (Обзор)

“… òî aeå âðåìÿ áèìåòàëëè÷åñêèå êëàñòåðû Ag 4-n -Au n (n = 1 -3), íàõîäÿùèåñÿ íà ïîâåðõíîñòè TiO 2 , ìîaeíî ãîðàçäî áîëåå ýôôåêòèâíî, ÷åì äâóîêèñü òèòàíà, ïîïóëÿðíîãî ïîëóïðîâîäíèêà, ïðèìåíÿòü â êà÷åñòâå ôîòîêàòàëèçàòîðîâ -å¸ïîðîãîâûé óðîâåíü â ðÿäó êëàñòåðîâ Ag 3 Au, Ag 2 Au 2 è AgAu 3 çàìåòíî ñíèaeåí äî 1,00, 1,24 è 1,40 ýÂ, ñîîòâåòñòâåííî; íàèëó÷øèìè êàíäèäàòàìè äëÿ ïîëó÷åíèÿ H 2 O 2 ñåé÷àñ ïðèçíàíû ñèñòåìû Ag 3 Au@TiO 2 è Ag 2 Au 2 @TiO 2 , èáî îíè çàìåòíî ñòèìóëèðóþò ôîòîñèãíàë ñèñòåìû â âèäèìîé è èíôðàêðàñíîé îáëàñòè ñïåêòðà, óëó÷øàÿ, òàêèì îáðàçîì, ðàçäåëåíèå çàðÿäà [55]. Èçãîòîâëåí áèî÷èï, êîòîðûé âêëþ-÷àåò ñåðåáðî è ãèäðîôîáíûé ìàòåðèàë, è, èãðàÿ ðîëü âûêëþ÷àòåëÿ ñ 2 àâòîìàòè÷åñêèìè ïîëîaeåíèÿìè, ãåíåðèðóåò îäíîçíà÷íûé êîëè÷åñòâåííûé îòâåò íà ïîÿâëåíèå â êîíòðîëèðóåìîé ñèñòåìå H 2 O 2 [56].…”