Halloysite nanotubes (HNTs) have been proposed as a potential support to immobilize enzymes. Improving enzyme loading on HNTs is critical to their practical applications. Herein, we reported a simple method on the preparation of high-enzyme-loading support by modification with dopamine on the surface of HNTs. The modified HNTs were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analyses. The results showed that dopamine could self-polymerize to adhere to the surface of HNTs and form a thin active coating. While the prepared hybrid nanotubes were used to immobilize enzyme of laccase, they exhibited high loading ability of 168.8 mg/g support, which was greatly higher than that on the pristine HNTs (11.6 mg/g support). The immobilized laccase could retain more than 90% initial activity after 30 days of storage and the free laccase only 32%. The immobilized laccase could also maintain more than 90% initial activity after five repeated uses. In addition, the immobilized laccase exhibited a rapid degradation rate and high degradation efficiency for removal of phenol compounds. These advantages indicated that the new hybrid material can be used as a low-cost and effective support to immobilize enzymes.

The spectra and dynamics of photogenerated electrons and holes in excited hematite (a-Fe 2 O 3 ) electrodes are investigated by transient absorption (from visible to infrared and from femto-to microseconds), bias-dependent differential absorption and Stark spectroscopy. Comparison of results from these techniques enables the assignment of the spectral signatures of photogenerated electrons and holes. Under the pulse illumination conditions of transient absorption (TA) measurement, the absorbed photon to electron conversion efficiency (APCE) of the films at 1.43 V (vs. reversible hydrogen electrode, RHE) is 0.69%, significantly lower than that at AM 1.5. TA kinetics shows that under these conditions, >98% of the photogenerated electrons and holes have recombined by 6 ms. Although APCE increases with more positive bias (from 0.90 to 1.43 V vs. RHE), the kinetics of holes up to 6 ms show negligible change, suggesting that the catalytic activity of the films is determined by holes with longer lifetimes.

Hot carrier and multiple exciton extractions from lead salt quantum dots (QDs) to TiO(2) single crystals have been reported. Implementing these ideas on practical solar cells likely requires the use of nanocrystalline TiO(2) thin films to enhance the light harvesting efficiency. Here, we report 6.4 ± 0.4 fs electron transfer time from PbS QDs to TiO(2) nanocrystalline thin films, suggesting the possibility of extracting hot carriers and multiple excitons in solar cells based on these materials.

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The water oxidation half-reaction is considered to be a bottleneck for achieving highly efficient solar-driven water splitting due to its multiproton-coupled four-electron process and sluggish kinetics. Herein, a triadic photoanode consisting of dual-sized CdTe quantum dots (QDs), Co-based layered double hydroxide (LDH) nanosheets, and BiVO4 particles, that is, QD@LDH@BiVO4, was designed. Two sets of consecutive Type-II band alignments were constructed to improve photogenerated electron-hole separation in the triadic structure. The efficient charge separation resulted in a 2-fold enhancement of the photocurrent of the QD@LDH@BiVO4 photoanode. A significantly enhanced oxidation efficiency reaching above 90% in the low bias region (i.e., E < 0.8 V vs RHE) could be critical in determining the overall performance of a complete photoelectrochemical cell. The faradaic efficiency for water oxidation was almost 90%. The conduction band energy of QDs is ∼1.0 V more negative than that of LDH, favorable for the electron injection to LDH and enabling a more efficient hole separation. The enhanced photon-to-current conversion efficiency and improved water oxidation efficiency of the triadic structure may result from the non-negligible contribution of hot electrons or holes generated in QDs. Such a band-matching and multidimensional triadic architecture could be a promising strategy for achieving high-efficiency photoanodes by sufficiently utilizing and maximizing the functionalities of QDs.

A multi-functional layered double hydroxide (LDH)-modified BiVO4 photoanode exhibits a tremendous cathodic shift of the onset potential and more than 2-fold enhancement in the oxidation efficiency and IPCE value.

Selective oxidation to produce target chemicals usually need activation of O 2 at high temperature and/or pressure, which have largely restricted its practical operation and application. Here, we put forward a radical relay strategy coupling photoelectrochemical (PEC) water oxidation toward efficiently selective conversion of benzyl alcohol (BA) to benzaldehyde (BAD). An illuminated BiVO 4 (BVO) photoanode covered with an ultrathin (∼3 nm) hydrothermally synthesized layered double hydroxide (U-LDH) catalyst and graphene (G) exhibited >99% selectivity to BAD (1.2 V vs. RHE). Mechanistic studies and DFT calculation verified that the hydroxyl radicals (•OH) generated from the oxidation of water are bound to the surface of U-LDH through hydrogen-bonding interactions and the energy is lowered. Fourier transform infrared spectroscopy showed that BA is adsorbed to the U-LDH catalyst, but BAD is not. Thus, the selectivity is favored not only by the controlled oxidation capacity of •OH radicals but the desorption of the desired product from the catalyst before further oxidation occurs. This work introduces an alternative PEC way to achieve mild and selective oxidation of BA derivatives based on ternary G@ U-LDH@BVO catalysts.

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