A uniformly decorated and photostable polydopamine-organic semiconductor to boost the photoelectrochemical water splitting performance of CdS photoanodes

Screening Cobalt-based Catalysts on Multicomponent CdSe@CdS Nanorods for Photocatalytic Hydrogen Evolution in Aqueous Media

We present CdSe@CdS nanorods coated with a redox-active polydopamine (PDA) layer functionalized with cobaloxime-derived photocatalysts for efficient solar-driven hydrogen evolution in aqueous environments. The PDA-coating provides reactive groups for the functionalization of the nanorods with different molecular catalysts, facilitates charge separation and transfer of electrons from the excited photosensitizer to the catalyst, and reduces photo-oxidation of the photosensitizer. X-ray photoelectron spectroscopy (XPS) confirms the successful functionalization of the nanorods with cobalt-based catalysts, whereas the catalyst loading per nanorod is quantified by total reflection X-ray fluorescence spectrometry (TXRF). A systematic comparison of different types of cobalt-based catalysts was carried out, and their respective performance was analyzed in terms of the number of nanorods and the amount of catalyst in each sample [turnover number, (TON)]. This study shows that the performance of these multicomponent photocatalysts depends strongly on the catalyst loading and less on the specific structure of the molecular catalyst. Lower catalyst loading is advantageous for increasing the TON because the catalysts compete for a limited number of charge carriers at the nanoparticle surface. Therefore, increasing the catalyst loading relative to the absolute amount of hydrogen produced does not lead to a steady increase in the photocatalytic activity. In our work, we provide insights into how the performance of a multicomponent photocatalytic system is determined by the intricate interplay of its components. We identify the stable attachment of the catalyst and the ratio between the catalyst and photosensitizer as critical parameters that must be fine-tuned for optimal performance.

Synergistic effects of nano-structured WO3-Se heterojunction decorated by organic Nafion layer on improving photoelectrochemical performance

Exploration of high-performance photoanodes is considered as an essential challenge in photoelectrochemical (PEC) water splitting due to the complex four-electron reaction in water oxidation. Herein, the nano-structured WO₃-Se heterojunction decorated by organic Nafion layer is designed. The optimized WO₃-Se200-0.05Nafion photoanode shows a remarkable photocurrent of 1.40 mA cm^-2at 1.23 V versus reversible hydrogen electrode, which is 2.5-fold higher than that of pure WO₃nanosheets (WO₃NS) photoelectrode. Remarkably, the photocurrent increments of WO₃-Se200-0.05Nafion is larger than the increment sum of WO₃-Se200 and WO₃-0.05Nafion, which affirming the synergistic effect of Se nanospheres and Nafion layer. The improved PEC performances are attributed to the quick charge separation and transfer, the increased electric conductivity, and the excellent kinetics of oxygen evolution, which is derived from the strong interaction among WO₃, Se and Nafion. Meanwhile, the better visible-light harvesting from Se nanospheres as photosensitizer and the induction of transparent Nafion as a passivation layer can explain this synergy. It hopes this heterostructure design with organic Nafion decoration can inspire to exploit outstanding performance photoanodes for PEC water splitting.

P3HT-PbS nanocomposites with mimicking enzyme as bi-enhancer for ultrasensitive photocathodic biosensor

Photocathodic biosensor has great capability in anti-interference from reductive substances, however, the low signal intensity of photoactive species with inferior detection sensitivity restricts its wide application. In this work, the P3HT-PbS nanocomposites were synthesized as signal tags, by integrating with target-trigger generated hemin/G-quadruplex nanotail as bi-enhancer to significantly apmplify the photocurrent, an ultrasensitive photocathodic biosensor was proposed for detection of β2-microglobulin (β2-MG). Impressively, P3HT with cathode signal is an attractive polymer consisted of substantial thiophene groups with high absorption coefficient and mobility of photo-generated holes, which could anchor with the PbS dots as sensitizer, providing a high charge mobility and strong photosensitivity. More importantly, target-trigger generated hemin/G-quadruplexes could accept the electron from illuminated photoactive species through the conversion of Fe(III)/Fe(II) in hemin, effectively reducing charge recombination rate as well as accelerating the generation of electron acceptor O₂ in the assistant of H₂O₂. Moreover, hemin/G-quadruplexes inherited the HRP mimicking catalytic capability that further improved the produce of plentiful O₂. As a result, PEC cathode signal was significantly enhanced for sensitive analysis of β2-MG protein with a good detection range of 0.1 pg/mL to 100 ng/mL. It would provide a path for establishing PEC platform with excellent anti-interference ability and extend the application of photoelectrochemical (PEC) biosensor in bioanalysis and early disease diagnosis.

Rhodium-Complex-Functionalized and Polydopamine-Coated CdSe@CdS Nanorods for Photocatalytic NAD+ Reduction

We report on a photocatalytic system consisting of CdSe@CdS nanorods coated with a polydopamine (PDA) shell functionalized with molecular rhodium catalysts. The PDA shell was implemented to enhance the photostability of the photosensitizer, to act as a charge-transfer mediator between the nanorods and the catalyst, and to offer multiple options for stable covalent functionalization. This allows for spatial proximity and efficient shuttling of charges between the sensitizer and the reaction center. The activity of the photocatalytic system was demonstrated by light-driven reduction of nicotinamide adenine dinucleotide (NAD⁺) to its reduced form NADH. This work shows that PDA-coated nanostructures present an attractive platform for covalent attachment of reduction and oxidation reaction centers for photocatalytic applications.

The strong interfacial coupling effect of Nafion between LaFeO3/electrolyte for efficient photoelectrochemical water reduction

Insufficient reduction capability and scanty active substance limit the application of LaFeO₃(LFO) in the field of photoelectrochemical (PEC) water splitting. This work demonstrates a judicious combination of LFO/Nafion composite to improve the PEC performance by a unique dip-coating method on the FTO. The photocurrent density of the LFO electrode coated with two layers Nafion increased to -23.9μA cm^-2at 0.47 V versus RHE, which is 4.1 times that of the pristine LFO. Based on the experimental data and theoretical analysis, the improvement of the PEC properties is attributed to the construction of organic/inorganic units, which would enable strong electronic coupling and favor interfacial charge transfer, resulting in a 30 mV downward shift of its flat band potential. Thus, the conduction band gets closer to the proton reduction potential of H⁺to H₂after decoration with Nafion, resulting in a stronger photogenerated electron reduction ability. Our study provides insights that organic materials modify semiconductor photoelectrodes for accelerating charge kinetics.

Polydopamine Films with 2D-like Layered Structure and High Mechanical Resilience

Highly oriented, layered, and mechanically resilient films of polydopamine (PDA) have been synthesized from the air/water interface. The films show a unique layered structure, as shown by scanning and transmission electron studies (SEM/TEM) and X-ray diffraction analysis (XRD), which resemble that of 2D layered materials. The films exhibit a composition typical of PDA-based materials, as evidenced by X-ray photoelectron spectroscopy (XPS); moreover, the samples present the distinctive resonance modes of PDA-based nanomaterials in Raman and infrared spectroscopy (FTIR) experiments. The presence of highly ordinated 3-4 protomolecule stacking, taking place at the air/water interface, with a unique eumelanin-like supramolecular arrangement is presented. Moreover, the films show superior mechanical resilience with E = 13 ± 4 GPa and H = 0.21 ± 0.03 GPa, as revealed by nanoindentation experiments, making them highly resilient and easily transferable. Finally, the ordering induced by the interface opens many possibilities for further studies, including those regarding the supramolecular structure on PDA due to their similarity to 2D layered materials.