Construction of Hollow Co3O4@ZnIn2S4 p-n Heterojunctions for Highly Efficient Photocatalytic Hydrogen Production

Abstract

Photocatalysts derived from semiconductor heterojunctions for water splitting have bright prospects in solar energy conversion. Here, a Co3O4@ZIS p-n heterojunction was successfully created by developing two-dimensional ZnIn2S4 on ZIF-67-derived hollow Co3O4 nanocages, realizing efficient spatial separation of the electron-hole pair. Moreover, the black hollow structure of Co3O4 considerably increases the range of light absorption and the light utilization efficiency of the heterojunction avoids the agglomeration of ZnIn2S4 nanosheets and further improves the hydrogen generation rate of the material. The obtained Co3O4(20) @ZIS showed excellent photocatalytic H2 activity of 5.38 mmol g−1·h−1 under simulated solar light, which was seven times more than that of pure ZnIn2S4. Therefore, these kinds of constructions of hollow p-n heterojunctions have a positive prospect in solar energy conversion fields.

An Efficient p–n Heterojunction Copper Tin Sulfide/g-C3N4 Nanocomposite for Methyl Orange Photodegradation

“…It can be seen that, in the CTS/CN composite, the E fb of CTS shifted upward to a less positive value (+1.24 V vs NHE) while that of CN shifted downward (−0.22 V vs NHE) along with the CB and VB positions relative to the pristine materials, resulting in the directional migration of photoinduced electrons from CB of CTS to CB of CN and photoinduced holes from VB of CN to VB of CTS, leading to enhanced charge separation. This finding is consistent with those reported for composites made of n- and p-type materials. − …”

“…The bandgaps of the synthesized materials were determined from the UV–vis absorption spectra by employing Tauc equation (eq ) and plotting (α h ν) n vs h ν through extrapolation of the linear region of the plot to the x -intercept. false( α h ν ) n = A false( h ν − E g false) where α, h , ν, and A represent the absorption coefficient, the Planck constant, the frequency of light absorbed, and a constant, respectively. The value of n depends on the type of optical transition . As shown in Tauc’s plots (insets of Figure a–c), the bandgap ( E g ) values of CTS, 50CTS/CN, and CN were calculated to be 1.72, 2.23, and 2.75 eV, respectively.…”

“…Accordingly, graphitic carbon nitride (g-C 3 N 4, denoted as carbon nitride (CN)) is a promising metal-free 2D semiconductor material that has been used as a visible light photoresponsive catalyst for the degradation of dyes and can be considered an excellent alternative due to its simple synthesis procedure, low toxicity, and robust chemical and photostability. , Unfortunately, CN is not as efficient as other photocatalysts due to its poor absorption of visible light, wider bandgap (2.75 eV), higher carrier recombination rate, and low electrical conductivity. − This limitation can be overcome by forming a p-n heterojunction composite with a narrow bandgap semiconductor such as CTS. The coupling of p- and n-type semiconductors has been shown to enhance photocatalytic activity due to the buildup of an internal electric field across the junction which helps minimize the recombination of charge carriers by promoting the directional flow of photoinduced electrons and holes. − Recently, the synthesis of CTS (Cu 3 SnS 4 , Cu 2 SnS 3 ), a p-type semiconductor, has been fascinating as an emerging material in the fields of photovoltaics , and photocatalysis − owing to its high visible light absorption coefficient (∼10 4 cm –1 ), , excellent electrical conductivity (with a hole density reaching up to ∼10 22 cm –3 ), narrow bandgap (<1.8 eV), , layered morphology, and reliable chemical and photostability. , In addition, CTS is composed of elements that are less toxic and more abundant in the Earth’s crust, making it a viable candidate for economic and environmental scale-up. In recent years, several studies have demonstrated the photocatalytic activity of CTS compounds for the degradation of methyl orange (MO) dye with promising results, with Cu 3 SnS 4 exhibiting the highest performance. ,− …”

“…The coupling of p- and n-type semiconductors has been shown to enhance photocatalytic activity due to the buildup of an internal electric field across the junction which helps minimize the recombination of charge carriers by promoting the directional flow of photoinduced electrons and holes. 25 − 27 Recently, the synthesis of CTS (Cu 3 SnS 4 , Cu 2 SnS 3 ), a p-type semiconductor, has been fascinating as an emerging material in the fields of photovoltaics 28 , 29 and photocatalysis 30 − 38 owing to its high visible light absorption coefficient (∼10 4 cm –1 ), 35 , 39 excellent electrical conductivity (with a hole density reaching up to ∼10 22 cm –3 ), 36 narrow bandgap (<1.8 eV), 35 , 36 layered morphology, and reliable chemical and photostability. 32 , 33 In addition, CTS is composed of elements that are less toxic and more abundant in the Earth’s crust, making it a viable candidate for economic and environmental scale-up.…”

Active Sites Formed on InVO4/Co3O4 S‐Scheme Heterostructure for Photocatalytic Hydrogen Production

“…Compared with the solid structure catalyst, the hollow structure has a thin shell, which makes the transfer path of photogenerated carriers shorter. In addition, there are multiple reflections and scattering of light in the hollow structure, which is helpful in enhancing the absorption and utilization of light [16–18] …”