Defect engineering using surface linkage modification is an efficient method to tailor solar-to-chemical energy conversion performance of a metal−organic framework (MOF), albeit the nature and impact of the defects remain unexplored. The present study explored that the alteration of electronic and morphological properties due to linkage modification augments the intrinsic charge transfer in MOF but is not reflected in the overall hydrogen production activity when integrated with a cocatalyst. This is illustrated with the simply prepared judicious bulk heterostructure between defect-regulated NH 2 -MIL-125 and Co 3 O 4 . The study further demonstrates that the subtle use of the photosensitizer can multi-fold improve the activity while anchored onto a semiconductor surface. Several analytical methods including X-ray absorption spectroscopy revealed the unique anchoring of Co 3 O 4 on the MOF surface that pertains to its catalytic activity. The composite Co 3 O 4 @PANI@NH 2 -MIL-125, without defects, showed significant spatial separation of the excited-state charge carriers thereby improving the rate of H 2 evolution reaction (∼1208 μmol h −1 g −1 ), with apparent quantum yield of ∼3% under simulated visible-light irradiation. The separation of photogenerated charge carriers at the MOF/cocatalyst interface was unequivocally confirmed by the time-dependent emission spectra and steady-state electrochemical measurements. The photocatalytic activity is correlated with the compatible charge transfer kinetics and density functional theory calculation on the Co 3 O 4 @NH 2 -MIL-125 heterostructure. Further, femtosecond transient absorption spectroscopy studies revealed the initial photoexcited charge transfer from polyaniline (PANI) to hybrid PANI@NH 2 -MIL-125, which favorably occurs in picoseconds time scale to boost the photocatalytic activity of the system. This investigation will bestow a beneficial blueprint for structural design on MOF to precisely manipulate cocatalyst morphology and structural positions for developing an efficient photocatalyst.
In this study, we garnered three important factors simultaneously, namely, wormhole mesoporosity of TiO 2 with welldesigned interfaces for effective charge transfers, precise loading of MoS 2 for plasmon induction, and increased surface area with exposed surface atoms and active sites. The controlled loading of MoS 2 on porous TiO 2 (MPT) forms a heterojunction that effectively modulates the interface engineering and thereby greatly enhances hydrogen evolution. The synthesis of a photocatalyst is based on a simple hydrothermal process that is well characterized. The resulting composite materials were tested for hydrogen evolution reactions. At optimum loading, MPT 10 induced a maximum hydrogen evolution rate of 1376 μmol h −1 g −1 with 2.28% apparent quantum yield (AQY), which was 10-fold higher compared to the MCT 10 (MoS 2 -commercial TiO 2 ) H 2 evolution rate of 138 μmol h −1 g −1 with 0.23% AQY under similar reaction conditions. The shorter decay component, lower emission intensity, and higher estimated lifetime of MPT 10 suggest its superiority over other materials. Density functional theory (DFT) calculations have further revealed the active sites of MPT and hierarchical porous TiO 2 (HPT) to support the experimental hydrogen evolution reaction (HER). This study suggests an avenue to design an efficient noble-metal-free photocatalyst for solar fuel productions.
Hydrogen evolution from water splitting is considered to be an important renewable clean energy source and alternative to fossil fuels for future energy sustainability. The photocatalytic and electrocatalytic water splitting...
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