Photocatalytic Hydrogen Production over Chromium Doped Layered Perovskite Sr₂TiO₄

Abstract

Layered semiconductor photocatalysts have been found to exhibit promising performance levels, probably linked to their interlayer framework that facilitates separation of charge carriers and the reduction/oxidation reactions. Layered titanates, however, generally demonstrate activities under UV irradiation, and therein lies the strong desire to extend their activity into the visible light region. Here, we investigated a series of layered perovskite by doping Sr2TiO4 with Cr and/or La in the hope to improve their visible light responses. Their crystal structures and other physicochemical properties were systematically explored. Our results show that La and Cr can be successfully accommodated in the layered structure and Cr is an efficient dopant for the extension of visible light absorbance. Much enhanced photocatalytic hydrogen evolution was observed after doping and was found to be composition-dependent. The highest hydrogen production rate approaches 97.7 μmol/h for Sr2Ti0.95Cr0.05O4-δ under full range irradiation (λ ≥ 250 nm) and 17 μmol/h for Sr2Ti0.9Cr0.1O4-δ under visible light irradiation (λ ≥ 400 nm), corresponding to an apparent quantum efficiency of 0.16% and 0.05%, respectively. Theoretical calculation reveals that the improved optical and photocatalytic properties are owing to a newly formed spin-polarized valence band from Cr 3d orbitals. The decreased unit cell parameters, reduced band gaps as well as anisotropic properties of layered architectures are likely the reasons for a better activity. Nevertheless, instability of these compounds in the presence of moisture and CO2 was also noticed, suggesting that protective atmospheres are needed for the storage of these photocatalysts.

Efficient Photocatalytic Oxygen Production over Nitrogen‐Doped Sr4Nb2O9 under Visible‐Light Irradiation

“…The latter peak is reported frequently as the O 1s state of many metal oxides and is assigned to lattice oxygen state (O 2− ) . The former peak, however, is probably caused by surface OH − groups . Therefore, the surface of Sr 4 Nb 2 O 9 and its nitridized counterpart are highly hydrophilic, particularly for the samples prepared at low nitridation temperatures (900 and 1000 °C) for which the peak for the O 2− state is completely indiscernible.…”

“…[22] The former peak, however, is probably caused by surface OH À groups. [3] Therefore, the surfaceo fS r 4 Nb 2 O 9 and its nitridized counterpart are highly hydrophilic, particularly for the samples prepareda tl ow nitridation temperatures (900 and 1000 8C) for which the peak for the O 2À state is completely indiscernible.H owever,t he N1s state only displays av ery weak peak aroundB E = 395 eV, which indicates that the surface has few Ns pecies. The surface atomicc omposition was then analyzed quantitativelyb yX PS ( Table 2).…”

“…Photocatalytic water splitting into hydrogen and oxygen using solar energy is ap romising approacht oc ope with our evergrowingd emand for renewable energy sourcesa nd to minimize the negative impact towards the environment as ar esult of energy consumption. [1][2][3] The successful application of this technique hinges on the fundamental improvement of photocatalytic materials in terms of the efficient absorption of solar photonsa nd the concomitant progress of chemical reactions. [4] Such improvement, however,i sl imited to af ew materials or systemsa nd most semiconductor photocatalysts still suffer from al ow quantum efficiency.…”

Layered lithium niobium (III) oxide—LiNbO2 as a visible-light-driven photocatalyst for H2 evolution

“…Such a simple energy conversion process is very tempting, yet only a few materials were found be to photocatalytically active for hydrogen production without sacrificial elements, let alone an appreciable conversion efficiency under visible light radiation [7][8][9][10]. A number of layered compounds have been found to exhibit interesting photocatalytic activity [9,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Their activity seems to be associated with the peculiar layered crystal structures that promote separation of charges and reactions [11,13,26,27].…”

Quinary wurtzite Zn-Ga-Ge-N-O solid solutions and their photocatalytic properties under visible light irradiation

“…Ideally, such a process includes a simple uphill reaction that water molecules are split into hydrogen and oxygen at the surface of a semiconductor, driven solely by incoming photons. Materials suitable for this reaction have to be light sensitive and catalytically active simultaneously, which by far is subject to only a few compounds or systems 1 2 3 4 5 6 7 8 9 10 . In particular, complete water splitting using visible light photons (λ ≥ 400 nm) is only reported in some metal oxides/oxynitrides containing elements with d 10 electronic configurations 11 12 13 and an organic semiconductor g-C 3 N 4 with carbon nanodots 14 .…”