Shape-Controlled Hematite: An Efficient Photoanode for Photoelectrochemical Water Splitting

2,3-Dihydroxynaphthalene invoked surface oxygen vacancy effect on Fe2O3 nanorods for photoanodic signal transduction tactic

The state-of-art signal transduction mechanism of anodic photoelectrochemistry is constrained to the hole oxidation reaction, which greatly hinders its application for prospective biosensing applications. Herein, we present an innovative strategy for signal transduction by exploiting the in situ formation of surface oxygen vacancies (V_Os) on Fe₂O₃ nanorods (NRs) through the self-coordination of 2,3-dihydroxynaphthalene (2,3-DHN) on their surfaces. The 2,3-DHN was connected with Fe(Ⅲ) on the surface of Fe₂O₃ NRs vis the formation of the five-membered ring structures accompanied by the generation of V_Os. And the generated V_Os introduced a new defect energy level for trapping the photogenerated holes, which enhanced the charge separation and realized the enhancement of photocurrent signal. The developed signal transduction strategy was validated by the first photoelectrochemical (PEC) sensing platform for β-glucoside (β-Glu) and lipase (LPS), which can catalyze the hydrolysis of 3-hydroxy-2-naphthalenyl-β-D-glucoside and naphthalene-2,3-diol diacetate, respectively, to produce 2,3-DHN for signal stimuli. The β-Glu and LPS were detected with linear ranges of 0.01-10.0 U/mL and 0.001-5.0 mg/mL, respectively. Detection limits of 3.3 × 10^-3 U/mL and 0.32 μg/mL (S/N = 3) were achieved, for β-Glu and LPS, respectively. The present study not only provides a new strategy for spontaneous induction of V_Os in situ for n-type semiconductors, but also innovates the anodic PEC signal transduction strategy with broadened biosensing applications.

Morphology-Controlled Synthesis of α-Fe2O3 Nanocrystals Impregnated on g-C3N4-SO3H with Ultrafast Charge Separation for Photoreduction of Cr (VI) Under Visible Light

Surface functionalization and shape modifications are the key strategies being utilized to overcome the limitations of semiconductors in advanced oxidation processes (AOP). Herein, the uniform α-Fe₂O₃ nanocrystals (α-Fe₂O₃-NCs) were effectively synthesized via a simple solvothermal route. Meanwhile, the sulfonic acid functionalization (SAF) and the impregnation of α-Fe₂O₃-NCs on g-C₃N₄ (α-Fe₂O₃-NCs@CN-SAF) were achieved through complete solvent evaporation technique. The surface functionalization of the sulfonic acid group on g-C₃N₄ accelerates the faster migration of electrons to the surface owing to robust electronegativity. The incorporation of α-Fe₂O₃-NCs with CN-SAF significantly enhances the optoelectronic properties, ultrafast spatial charge separation, and rapid charge transportation. The α-Fe₂O₃-HPs@CN-SAF and α-Fe₂O₃-NPs@CN-SAF nanocomposites attained 97.41% and 93.64% of Cr (VI) photoreduction in 10 min, respectively. The photocatalytic efficiency of α-Fe₂O₃-NCs@CN-SAF nanocomposite is 2.4 and 2.1 times higher than that of pure g-C₃N₄ and α-Fe₂O₃, respectively. Besides, the XPS, PEC and recycling experiments confirm the excellent photo-induced charge separation via Z-scheme heterostructure and cyclic stability of α-Fe₂O₃-NCs@CN-SAF nanocomposites.

Type-II Heterostructure of ZnO and Carbon Dots Demonstrates Enhanced Photoanodic Performance in Photoelectrochemical Water Splitting

Hydrogen evolution through ecofriendly photoelectrochemical (PEC) water splitting is considered to be one of the most cost-effective and desirable methods for meeting ever-growing energy demands. However, the low photoconversion efficiency limits the practical applicability of PEC water splitting. To develop an efficient photoelectrode, here the morphology of ZnO is tuned from 0D to 3D. It is observed that vertically grown 2D nanosheets outperform other morphologies in PEC water splitting by generating nearly 0.414 mA cm^-2 at 0 V vs Ag/AgCl. Furthermore, these perpendicularly developed 2D nanosheets of ZnO are sensitized by metal-free carbon (C) dots to improve the photoconversion efficiency of ZnO. The prepared ZnO/C dots work as an effective photoanode, which can produce a 0.831 mA cm^-2 photocurrent density upon application of 0 V vs Ag/AgCl under constant illumination, which is 2 times higher than that of bare ZnO. The enhanced PEC performance of ZnO/C dots is confirmed by the photoconversion efficiency (η). The ZnO/C dots exhibit a 2-fold-higher photoconversion efficiency (η) compared to that of ZnO. Additionally, the enhancement in PEC activity of ZnO/C dots is attributed to the higher carrier concentrations in the heterostructure. Bare ZnO has a 1.77 × 10²⁰ cm^-3 carrier density, which becomes 3.70 × 10²⁰ cm^-3 after sensitization with C dots. Enhanced carrier density successively leads to higher PEC water splitting efficiency. Band alignments of ZnO and C dots indicate the creation of the type-II heterostructure, which facilitates successful charge transportation among C dots and ZnO, producing a charge-carrier separation. Two-dimensional sheets of ZnO and ZnO/C dots exhibit appreciable stability under continuous illumination for 1 and 2 h, respectively.

Nanoporous BiVO4 nanoflake array photoanode for efficient photoelectrochemical water splitting

A high-quality nanoporous BiVO₄ nanoflake array photoanode was prepared by using an in situ transformation approach, which exhibited an excellent photoelectrochemical activity.

Band gap tuning to improve the photoanodic activity of ZnInxSy for photoelectrochemical water oxidation

Elemental doping and band gap tuning of ZnIn_xS_y result in enhanced photoelectrochemical water splitting activity.