Photoelectrochemical Techniques Research Articles

Poly(amino acids) towards sensing pathogenic bacteria: A review

On the planet Earth, the living of numerous species has strongly depended on microorganisms, one of which is bacteria. Among various bacteria, the role of pathogenic bacteria in terms of prevalent diseases, environmental disasters, and even animal life are undeniable. Indeed, in the modern era, diagnosis of the spread of these bacteria in different settings including the human body, food matrix, and environment can able us to control them. Despite the advancement of sensing platforms, there is a huge shortage in the development of sensitive and selective sensing approaches. Hence, fabrication efficient sensing-assay can play an important role. Amino acids (AAs) are part of biocompatible materials that have attracted attention as a promising class in various biosensors as sensing probes. This review focuses on the application of poly(AAs) such as cysteine and poly (Cysteine), lysine and poly (Lysine), glutamic acid and poly (Glutamic acid), glycine and poly (Glycine) and other types of poly(AAs) in terms of pathogenic bacteria detection. In addition, the role of different nanomaterials along with biological factors in increasing the sensitivity and selectivity of these types of assays will be reviewed. To elaborate, the identification of pathogenic bacteria will be investigated using different diagnostic platforms such as electrochemiluminescence (ECL), optical, electrochemical (EC), and photoelectrochemical (PEC) techniques, which will pay special attention to the role of AA and poly AA. Finally, the existing technological and research gaps will be examined and criticized in order to solve them in the future. It should be noted the prepared study is the first comprehensive review of bacterial assay detection by using poly(AAs) in the construction of biosensors.

Effect of synthesis conditions on the photocatalytic behavior of ZnS-ZnO heterojunctions for the H2 generation

In the present work, the synthesis and photocatalytic performance for H2 production of ZnS-ZnO composites at different compositions of cubic sphalerite (ZnS-c), hexagonal wurtzite (ZnS-h) and zincite (ZnO) phases are shown. The synthesis was carried out by the solvothermal method using mono ethylene glycol and thiourea as solvent and sulfur source, respectively, for the partial sulfidation of ZnO at different temperatures (150 °C, 200 °C, and 250 °C). When the temperature is increased in the solvothermal process, the hexagonal phase grows at the expense of the cubic phase. The materials as powders were characterized by X-ray diffraction, scanning and transmission electron microscopy, UV–visible spectroscopy, X-ray photoelectron microscopy, N2 adsorption-desorption isotherms, and photoelectrochemical techniques. These materials were applied in H2 production as an alternative source of clean and sustainable energy generation. It was found that the most photoactive material was the one synthesized at 200 °C, this photocatalyst presented an H2 production rate of 580 µmol h−1 g−1. The enhancement of the photocatalytic activity is due to the optimization of the interfacial properties between ZnS-c/ZnS-h and ZnO as a model system for coupled photocatalysts.

Visual/Photoelectrochemical Off-On Sensor Based on Cu/Mn Double-Doped CeO2 and Branched Sheet Embedded Cu2O/CuO Nanocubes

An integrated dual-signal bioassay was devised to fulfil thrombin (TB) ultrasensitive detection by integrating visualization with the photoelectrochemical technique based on G-quadruplex/hemin. During the process, branched sheet embedded copper-based oxides prepared with illumination and alkaline condition play a vital role in obtaining the desirable photocurrent. The switchover of photoelectrochemical signal was realized by the adjustable distance between electron acceptor G-quadruplex/hemin and interface materials due to dissociation of the Cu/Mn double-doped cerium dioxide (CuMn@CeO2)/DNA caused by the addition of TB. Then, CuMn@CeO2 transferred onto visual zones triggered catalytic reactions under the existence of 3,3',5,5'-tetramethylbenzidine and hydrogen peroxide, making a variation in color recognized by the naked eye and providing visual prediction. Under optimized conditions, this bioassay protocol demonstrated wide linear ranges (0.0001-50 nM), high selectivity, stability, and reproducibility. More importantly, the proposed visual/photoelectrochemical transduction mechanism platform exhibits a lower background signal and more reliable detection results, which also offers an effective way for detecting other proteins and nucleic acids.

Answering old questions with new techniques: Understanding performance-limiting factors in transition metal dichalcogenide photoelectrochemical solar cells

In the late 1970s and early 1980s, several research groups reported high-efficiency and stable photoelectrochemical solar cells based on transition metal dichalcogenides (TMDS; e.g., MoS 2 , WSe 2 , and MoSe 2 ) immersed in iodide/tri-iodide electrolytes. A consensus emerged that smooth crystals were necessary for high efficiency based on significant evidence that rough crystals with exposed edge sites produced lower photocurrents and fill factors. However, anecdotal observations in the literature hinted at significant performance variation among apparently smooth crystals with the possibility of highly active “hot” edge sites. This mini-review article is a case study on how spatially resolved photoelectrochemical techniques developed in the 2020s are answering old questions regarding the origin of performance variation in high efficiency n-type TMD|I – ,I 3 – |Pt photoelectrochemical solar cells.

Deep Eutectic Solvent-Mediated Synthesis of Ni3V2O8/N-Doped RGO for Visible-Light-Driven H2 Evolution and Simultaneous Degradation of Dyes

Photochemical hydrogen evolution and the degradation of synthetic dyes in water are the two key ways to unravel the issues associated with the energy and environmental sectors for sustainability. The present work deals with the use of a deep eutectic solvent for the synthesis of Ni3V2O8/N-doped reduced graphene oxide (NiV/NR hybrid). The NiV/NR hybrid, NRGO, and NiV were characterized using XRD, SEM, TEM, UV-DRS, XPS, and other photo-electrochemical techniques. The NiV/NR hybrid exhibited high efficiency towards light-driven hydrogen evolution (12,546 µmol)) compared to pristine NiV (6453 µmol) and NRGO (1935 µmol). Among the various sacrificial agents examined, TEOA showed better activity in H2 evolution. The photocatalytic degradation of anionic (Methyl orange; MO) and cationic dyes (crystal violet; CV) were evaluated and the reaction conditions were carefully optimized to attain the utmost efficiency. The efficiency of the NiV/NR hybrid was higher under visible light irradiation than UV light and able to degrade 94.6 and 96.7% of MO and CV, respectively. The results of the simultaneous degradation of dyes and total organic carbon (TOC) removal were good. Based on the obtained bandgap and Mott–Schottky plots, the mechanism of photocatalysis in the NiV/NR hybrid is discussed in detail. The reusability and stability of the NiV/NR hybrid in both H2 evolution experiments and degradation studies are excellent. The fabricated NiV/NR hybrid material could be used for multiple applications in energy and environmental applications.

Kinetic Difference in Water Photooxidation between TiO2 and WO3 Electrodes by Rate Law Analysis

The photocarrier interfacial kinetics is often considered to be a bottleneck for water photooxidation on semiconductors and has attracted extensive attention in recent years. Although tremendous efforts have been devoted into the kinetic study for a certain semiconductor, there are few works focused on the dynamic differences in water oxidation between various kinds of semiconductors. In this study, the kinetics of water oxidation on WO3 and TiO2 electrodes was investigated by a combination of photoelectrochemical techniques and then compared using the electrodes’ rate law. It was found that the water oxidation on WO3 is faster than the that of TiO2 electrodes under the same surface hole density and the basic origin for this kinetic difference is attributed to greater charger transfer rate constant (kct). The greater kct is due to the fact that the WO3 electrodes have a smaller Helmholtz layer capacitance (CH), a larger space charge layer capacitance (CSC), and a greater charge transfer rate constant at flatband potential (kct0). These finding provide a better understanding of the photocarrier transfer dynamics and may enlighten rational design on exploiting the metal oxide semiconductors to achieve a higher solar conversion efficiency.

Photocatalytic degradation of glyphosate using Ce/N co-doped TiO2 with oyster shell powder as carrier under the simulated fluorescent lamp

Glyphosate is currently one of the most used organophosphorus herbicides in the world and its accumulation and translocation in soil and wave causes environmental pollution and biological health problems. A new approach to the problem is provided by the preparation of cerium and nitrogen co-doped titanium dioxide composite nano-photocatalysts loaded on modified oyster shell powder (CeNT@Oys) by a simple hydrothermal synthesis. The physicochemical and optoelectronic properties are analyzed using SEM, BET, XRD, Raman, FTIR, UV-vis DRS, XPS characterization techniques and a range of photoelectrochemical techniques. The results show that the addition of modified oyster shell powder increases its specific surface area, while Ce-N-TiO2 is an anatase crystal composed of Ce doped in the form of interstitial and surface, interstitial form of N, and the co-doping of Ce and N elements gives it the property of being excited by visible light. The photocatalytic activity of the different catalysts was evaluated by degrading 50 mg/L glyphosate solution under simulated sunlight. The catalyst was determined to be reusable by five repeated degradation experiments. Based on quenching experiments and the electron paramagnetic resonance tests, the effective active species of glyphosate degraded by the catalyst was determined and the mechanism of glyphosate degradation by photocatalyst was proposed. Finally, the degradation pathway for the photocatalytic degradation of PMG by CeNT@Oys was determined by HPLC-MS/MS determine of the intermediate products.

Preparation of surface-modified electrode of copper(ii) oxide mixed with the molecularly imprinted polymer for enhancement of melamine detection with photoelectrochemical technique.

Melamine contamination in food and beverages affects short- and long-term health. In this work, enhanced sensitivity and selectivity in photoelectrochemical determination for melamine detection was achieved using copper(ii) oxide (CuO) combined with a molecularly imprinted polymer (MIP). A CuO nanomaterial was used to achieve MIP surface modification via co-precipitation synthesis. An MIP film was deposited by polymerizing the methacrylic acid monomer and a melamine template. The properties of the CuO nanomaterials, such as the surface morphology, chemical oxidation state, and crystalline structure, were characterized using field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction patterns (XRD), respectively. The diffuse reflection spectroscopy technique was applied to evaluate the optical properties of the CuO nanoparticles. The results indicated that the synthesized CuO nanomaterials had a monoclinic structure with an optical bandgap of 1.49 eV, which corresponds to absorbance in the visible light region. CPE electrodes with surface-modified CuO/MIP were measured using the photoelectrochemical techniques of cyclic voltammetry, differential pulse voltammetry (DPV), and amperometry. The modified CuO/MIP electrode for melamine detection in 7.4 pH PBS buffer solution exhibited a high sensitivity of 0.332 nA nM-1, with a linear range of 5.0-75.0 nM and a limit of detection of 2.45 nM. Moreover, real samples of various kinds of milk were applied to evaluate the sensing response of the prepared CuO/MIP electrode. The modified CuO/MIP electrodes could be reused seven times with good reproducibility and high selectivity for melamine detection.

Optimizing the performance of Auy/Nix/TiO2NTs photoanodes for photoelectrochemical water splitting.

Water splitting using photoelectrochemical (PEC) techniques is thought to be a potential method for creating green hydrogen as a sustainable energy source. How to create extremely effective electrode materials is a pressing concern in this area. In this work, a series of Nix/TiO2 anodized nanotubes (NTs) and Auy/Nix/TiO2NTs photoanodes were prepared by electrodeposition via cyclic voltammetry and UV-photoreduction, respectively. The photoanodes were characterized by several structural, morphological, and optical techniques and their performance in PEC water-splitting for oxygen evolution reaction (OER) under simulated solar light was investigated. The obtained results revealed the nanotubular structure of TiO2NTs was preserved after deposition of NiO and Au nanoparticles while the band gap energy was reduced allowing for effective utilization of solar light with lower charge recombination rate. The PEC performance was monitored and it was found that the photocurrent densities of Ni20/TiO2NTs and Au30/Ni20/TiO2NTs were 1.75-fold and 3.25-fold that of pristine TiO2NTs, respectively. It was confirmed that the performance of the photoanodes depends on the number of electrodeposition cycles and duration of photoreduction of gold salt solution. The observed enhanced OER activity of Au30/Ni20/TiO2NTs could be attributed to the synergism between the local surface plasmon resonance (LSPR) effect of nanometric gold which increased solar light harvesting and the p-n heterojunction formed at the NiO/TiO2 interface which led to better charge separation and transportation suggesting its potential application as an efficient and stable photoanode in PEC water splitting for H2 production.

A novel PEC and ECL bifunctional aptasensor based on V2CTx MXene-derived MOF embedded with silver nanoparticles for selectively aptasensing miRNA-126.

A novel photoelectrochemical (PEC) and electrochemiluminescence (ECL) bifunctional aptasensor has been established for the detection of miRNA-126 using V2CTx MXene-derived porphyrin-based metal-organic framework embedded with Ag nanoparticles (Ag NPs) (denoted as AgNPs@V-PMOF) as a robust bioplatform. Due to the presence of V nodes in V2CTx MXene nanosheets, V-based MOF was prepared using tetrakis(4-carboxyphenyl)porphyrin as ligand, followed by the incorporation of Ag+ ions to form the AgNPs@V-PMOF Schottky heterojunction. Benefiting from the fast electron transfer of the V2CTx substrate and well-matched band-edge energy level of the photosensitive Ag NPs and V-PMOF, the constructed AgNPs@V-PMOF Schottky heterojunction exhibited the promoted transfer of the photogenerated carriers, showing superior PEC and ECL performances. Moreover, a large number of the complementary DNA strand of miRNA-126 can be immobilized over AgNPs@V-PMOF in view of the combined interaction of π-π stacking, van der Waals force, and Ag-N coordination between AgNPs@V-PMOF. Consequently, the developed AgNPs@V-PMOF-based aptasensor illustrated extremely low detection limits of 0.78 and 0.53 fM within a wide range from 1.0 fM to 1.0 nM of miRNA-126 detected by PEC and ECL techniques, respectively, superior to most reported miRNA aptasensors. Also, the provided bifunctional aptasensor demonstrated high selectivity, good stability, fine reproducibility, and acceptable regenerability, as well as promising potential for the analysis of miRNA-126 from living cancer cells. This work puts forward the development of aptasensors for the early and accurate diagnosis of cancer markers and extends the application of MOF in the biosensing field.

Dual Direct Z-Scheme Heterojunction with Stable Electron Supply to a Au/PANI Photocathode for Ultrasensitive Photoelectrochemical and Electrochromic Visualization Detection of Ofloxacin in a Microfluidic Sensing Platform.

A novel dual-mode microfluidic analytical device integrating self-powered photoelectrochemical (PEC) sensing with electrochromic visualization analysis was developed for ultrasensitive ofloxacin (OFL) detection. First, an advanced dual direct Z-scheme BiVO4@Ni-ZnIn2S4/Bi2S3 (BVZIS) heterojunction was designed as a photoanode matrix to steadily provide electrons. The dual Z-scheme structure formed in photoactive BVZIS composites greatly accelerated the migration of electrons. In addition, the doping of Ni in ZnIn2S4 markedly enhanced the optical absorption and promoted the separation of the photocarrier. Second, electrochromic material polyaniline-modified Au (Au/PANI) was first electrodeposited on the photocathode for immobilizing aptamers and realizing visualized readout. On the one hand, Au/PANI with excellent conductivity could receive electrons from the photoanode without external energy supply. On the other hand, PANI would be rapidly reduced by the received electrons and change its color from blue to green obviously. With the increase in OFL, the increased steric hindrance resulted in the significant decline in the PEC signal and RGBgreen value. Third, wide linear ranges of PEC (0.05 pg/mL to 150 ng/mL) and electrochromic technique (0.1 pg/mL to 100 ng/mL) as well as low detection limits of PEC (18 fg/mL) and electrochromic (30 fg/mL) sensors could achieve the ultrasensitive detection of OFL in milk and river water.

Photoelectrochemistry-driven ambient nitrogen reduction to ammonia: Materials’ design insights

Agriculture, industrialization, and fossil fuel consumption lead to a significant imbalance and redistribution of nitrogen-containing resources. Alternative sustainable approaches are required to avoid the CO2 footprint related to nitrogen-containing commodities. Haber-Bosch (HB) process mediated commercial NH3 synthesis suffers from excess CO2 emission, therefore electrochemical/ photochemical methods to bring the N2 to NH3 under milder conditions depicts an alternative pathway. Recently, a growing number of studies on individual electrochemical (EC) photochemical (PC) along with photoelectrochemical (PEC) techniques have attracted extensive attention. Among them PEC method comes with the hurdles of materials’ design complexity as in PEC, it is vital to consider maximum solar light absorption along with the catalytic active site for nitrogen adsorption and inert N≡N activation. Here we provide an overview of the latest progress and current state of knowledge on photoelectrochemical NRR catalysts and challenges. The study is supplemented by the material design and understanding of the hetero-material interfaces' role in PEC-NRR. Nevertheless, suppressive techniques for NRR competitor H2 evolution is also discussed. Finally, an initial blueprint of PEC-NRR catalyst performance has been presented, along with its future prospects.

Hydrothermally modified ZnO-NiSe heterostructure as promising photoelectrocatalyst in hydrogen evolution reaction

Water splitting through electrolysis is the standard and efficient method to generate hydrogen on a large scale. The efficiency of this method can be increased using the photoelectrochemical technique by using an effective photoelectrocatalyst. This work demonstrates ZnO-NiSe@NF as a potential photoelectrocatalyst for hydrogen evolution reactions (HER). The heterostructure is synthesized by hydrothermal method, and the electrochemical and photoelectrochemical analyses are done in an acidic medium using a 0.5 M H2SO4 solution. In electrochemical measurements, ZnO-NiSe@NF shows excellent performance with a lower overpotential (-0.081 V) and low Tafel slope of 80.01 mV/dec. The photoelectrochemical linear sweep voltammetry measurements show an enhancement in HER performance, with the positive shift of overpotential to −0.065 V. Mott-Schottky analysis demonstrates n-type behavior for the composite where the electrons are the primary charge carrier. The possible mechanism of the reaction has been discussed.

Identification of Photoacidic Behavior Using AC and Open-Circuit Photoelectrochemical Techniques

Photoacids are molecules whose acidity increases through absorption of light. When the excited-state lifetime of a photoacid is sufficiently long, proton transfer from its thermally equilibrated electronic excited state results in a transient change in pH and/or pOH, which is commonly detected using spectroscopic techniques. Herein we expand this measurement toolkit by introducing alternating AC and open-circuit photoelectrochemical techniques that characterize photoacidic behavior from a model photoacid, the sodium salt of 8-hydroxypyrene-1,3,6-trisulfonate, dissolved in aqueous solutions in a thin-pathlength two-electrode cell. Continuous illumination of protonated photoacids in their electronic ground state results in significant and reproducible changes in low-frequency impedance and open-circuit potential. When these molecules are made to be non-acidic, via deprotonation using more alkaline pH conditions or methoxylation via synthesis, electrochemical data measured in the dark and under illumination are nearly identical. Best fits of AC electrochemical data to a simplified equivalent circuit support that photoelectrochemical responses are likely due to changes in local proton concentration at the electrode∣electrolyte interface, and not changes in proton flux due to mass transfer, as previously suggested. Collectively, our results provide further insight into the utility of these photoelectrochemical techniques to probe photoacidic behavior.

Recent trends on electrochemical determination of antibiotic Ciprofloxacin in biological fluids, pharmaceutical formulations, environmental resources and foodstuffs: Direct and indirect approaches.

In the last few decades, pharmaceuticals, credited with saving millions of lives, have emerged as a new class of environmental contaminants. These compounds can have both chronic and acute harmful effects on aquatic ecosystems and consequently on human health. Therefore, there is an urgent need for the development of extremely sensitive, portable, and low-cost devices to perform analysis. In the present review article, recent reports on the application of various voltammetric and photo-electrochemical techniques using different electrode materials for the determination of antibiotic Ciprofloxacin (CIPRO) are reported. This review provides an insight into direct and indirect electrochemical approaches as well as the photoelectrochemical methods used for the determination of CIPRO. Emphasis is put on the applications of unmodified and modified carbon-based electrodes considering the modifier, supporting electrolytes, analytical method, concentration range, limit of detection, and real matrices. Carbon-based electrodes are the most used materials attributed to their commercial availability, reduced cost, high chemical stability, and non-toxicity.

3D/2D Heterojunction Fabricated from RuS2 Nanospheres Encapsulated in Polymeric Carbon Nitride Nanosheets for Selective Photocatalytic CO2 Reduction to CO.

Micro/nanostructure control of heterostructures is still a challenge for achieving high efficiency and selectivity of photocatalytic CO2 conversion. In this work, a new three-dimensiona/two-dimensional (3D/2D) heterostructure is fabricated by encapsulating RuS2 nanospheres in the interlayer of mesoporous polymeric carbon nitride (PCN) nanosheets based on an in situ growth and polymerization strategy. The unique microstructure of the obtained 3D/2D RuS2/PCN heterojunction can effectively improve the transfer and separation efficiency of photogenerated charge carriers, reduce the mass transfer resistance of CO2 toward active sites, and provide a confined reaction space, thus propelling the photocatalytic CO2 reduction to CO with high selectivity. The CO yield over the optimal 5%-RuS2/PCN sample reaches 4.2 and 2.8 times as high as that of single PCN and RuS2 within 4 h, respectively. Furthermore, the plausible charge transfer mechanism and CO2 reduction path are revealed by time-dependent in situ Fourier transform infrared (FT-IR) spectra combined with photophysical, electrochemical, and photoelectrochemical techniques and density functional theory (DFT) calculations. This work develops the microstructural engineering design strategy of PCN-based heterojunctions for selective photocatalytic CO2 fuel conversion.

Fabrication of visible-light-driven bimetallic MOF-derived Ag/NiOx/N-TiO2: Photocatalytic hydrogen production mechanism and methanol transformation pathway

A novel bimetallic metal–organic framework (MOF)-derived Ag/NiOx/N-TiO2 photocatalyst with a Z-scheme system was successfully synthesized for photocatalytic hydrogen production. The as-prepared photocatalysts were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscope, X-ray photoelectron spectroscopy, UV–vis spectroscopy, photoluminescence, and photoelectrochemical techniques. Compared to N-TiO2, the Ag/NiOx/N-TiO2 composite material with a wider light absorption range exhibited outstanding photocatalytic hydrogen production using methanol as a sacrificial agent. The optimum Ag/NiOx ratio (5 wt%) results in a hydrogen production rate of 1240 μmol·g−1·h−1 in a 50 v/v% methanol solution. According to the results of the durability test, the synthesized photocatalyst demonstrates good stability. Consequently, a possible mechanism of the photocatalysts and the transformation pathway of methanol have been reported. The Z-scheme system of NiOx and N-TiO2 can effectively separate the electron-hole pairs. The surface plasmon resonance effect of Ag0 enhanced the visible light response. This study provides a valuable reference for the synthesis of MOF-derived photocatalytic technologies and the mechanism of rapid and efficient hydrogen production.

Synergistic Interaction of MoS2 Nanoflakes on La2Zr2O7 Nanofibers for Improving Photoelectrochemical Nitrogen Reduction.

Ammonia is a suitable hydrogen carrier with each molecule accounting for up to 17.65% of hydrogen by mass. Among various potential ammonia production methods, we adopt the photoelectrochemical (PEC) technique, which uses solar energy as well as electricity to efficiently synthesize ammonia under ambient conditions. In this article, we report MoS2@La2Zr2O7 heterostructures designed by incorporating two-dimensional (2D)-MoS2 nanoflakes on La2Zr2O7 nanofibers (MoS2@LZO) as photoelectrocatalysts. The MoS2@LZO heterostructures are synthesized by a facile hydrothermal route with electrospun La2Zr2O7 nanofibers and Mo precursors. The MoS2@LZO heterostructures work synergistically to amend the drawbacks of the individual MoS2 electrocatalysts. In addition, the harmonious activity of the mixed phase of pyrochlore/defect fluorite-structured La2Zr2O7 nanofibers generates an interface that aids in increased electrocatalytic activity by enriching oxygen vacancies in the system. The MoS2@LZO electrocatalyst exhibits an enhanced Faradaic efficiency and ammonia yield of approximately 2.25% and 10.4 μg h-1 cm-2, respectively, compared to their corresponding pristine samples. Therefore, the mechanism of improving the PEC ammonia production performance by coupling oxygen-vacant sites to the 2D-semiconductor-based electrocatalysts has been achieved. This work provides a facile strategy to improve the activity of PEC catalysts by designing an efficient heterostructure interface for PEC applications.

A sol-gel route to prepare CeOx dot-decorated TiO2 pigment with improved weatherability

Conventional surface treatment of TiO2 pigment aims at depositing uniform and continuous inorganic shells on the surface of TiO2 nanoparticles via precipitation methods, however, requiring strictly controlled conditions. Here we demonstrate the preparation of the CeOx dot-decorated TiO2 pigment via a sol-gel route. The CeOx dots were directly deposited onto TiO2 particles by adding CeOx sol solution into TiO2 slurry, which has been proved to improve both the weatherability and dispersibility in the water of the TiO2 pigment. Besides, the suppression mechanism of the TiO2 photoactivity by CeOx was investigated in detail using photoelectrochemical techniques. CeOx has been found to passivate surface states of TiO2 and hinder the hole transport rather than hole interfacial transfer. Moreover, an extra SiO2 layer was subsequently deposited onto the CeOx dot-decorated TiO2, further enhancing the weatherability and pigment properties of the product.

CuO Nanozymes as Multifunctional Signal Labels for Efficiently Quenching the Photocurrent of ZnO/Au/AgSbS2 Hybrids and Initiating a Strong Fluorescent Signal in a Dual-Mode Microfluidic Sensing Platform.

A novel dual-mode microfluidic sensing platform based on CuO nanozymes as a photoelectrochemical (PEC)-fluorescent (FL) multifunctional signal label was developed for ultrasensitive neuron specific enolase (NSE) detection. Herein, ZnO/Au/AgSbS2 hybrids, possessing excellent PEC properties, were first exploited as a sensing matrix to provide a stable photocurrent. The controlled synthesis of photoactive ZnO nanoflowers (NFs) was successfully conducted using a microfluidic reactor in the scale of seconds. Furthermore, the photocurrent of ZnO NFs decorated by Au and AgSbS2 nanoparticles significantly improved, owing to the local surface plasma resonance effect of Au and matching band structure between ZnO and AgSbS2. A strategy of catalytic oxidation ascorbic acid (AA) by CuO nanozymes was proposed to quench the PEC signals and initiate FL signals. CuO nanoparticles growing on conductive carbon spheres (CuO@CSs) as secondary antibodies' labels could efficiently catalyze the oxidation of AA to achieve a PEC "signal-off" state. Then, the produced dehydroascorbic acid reacting with o-phenylenediamine opportunely generated a strong FL signal. Importantly, wide linear ranges of 0.0001-150 ng/mL for the PEC technique and 0.001-150 ng/mL for the FL method with a low detection limit of 0.028 and 0.25 pg/mL, respectively, could guarantee the sensitive detection of NSE.