Synthesis of α-Bi2Mo3O12/TiO2 Nanotube Arrays for Photoelectrochemical COD Detection Application

Red and near-infrared light-activated photoelectrochemical nanobiosensors for biomedical target detection

Photoelectrochemical (PEC) nanobiosensors integrate molecular (bio)recognition elements with semiconductor/plasmonic photoactive nanomaterials to produce measurable signals after light-induced reactions. Recent advancements in PEC nanobiosensors, using light-matter interactions, have significantly improved sensitivity, specificity, and signal-to-noise ratio in detecting (bio)analytes. Tunable nanomaterials activated by a wide spectral radiation window coupled to electrochemical transduction platforms have further improved detection by stabilizing and amplifying electrical signals. This work reviews PEC biosensors based on nanomaterials like metal oxides, carbon nitrides, quantum dots, and transition metal chalcogenides (TMCs), showing their superior optoelectronic properties and analytical performance for the detection of clinically relevant biomarkers. Furthermore, it highlights the innovative role of red light and NIR-activated PEC nanobiosensors in enhancing charge transfer processes, protecting them from biomolecule photodamage in vitro and in vivo applications. Overall, advances in PEC detection systems have the potential to revolutionize rapid and accurate measurements in clinical diagnostic applications. Their integration into miniaturized devices also supports the development of portable, easy-to-use diagnostic tools, facilitating point-of-care (POC) testing solutions and real-time monitoring.

A novel electrochemical sensor for the detection of fipronil and its toxic metabolite fipronil sulfone using TiO2-polytriazine imide submicrostructured composite as an efficient electrocatalyst

For the first time, a simple and sensitive electrochemical sensor based on a screen printed electrode (SPE) modified with titanium dioxide (TiO₂) and polytriazine imide submicrostructured composite (TiO₂-PTI) has been developed for the simultaneous detection of fipronil (FIP) and its toxic metabolite fipronil sulfone (FIP-S). The submicrostructured composite material based on TiO₂ and PTI was obtained by simple hydrothermal treatment of the Ti peroxocomplexes in the presence of pristine. This carbon nitride allotrope has better crystallinity and conductivity than its graphitic analog. It was found that the TiO₂-PTI submicrostructured composite enhanced the electrochemical sensing of the SPE electrode towards FIP and its metabolite FIP-S in 0.1 M Britton-Robinson buffer (pH 10) at the oxidation potentials of 0.82 V and 0.94 V, respectively. In addition, it showed good stability and reproducibility for the determination of both analytes. Under optimal conditions, the peak currents by square wave voltammetry were found to vary linearly with FIP and FIP-S concentrations in the range from 0.01 to 10 μM and from 10 to 50 μM, with a detection limit of 8.42 nM, 3.6 μg/kg for FIP and 9.72 nM, 4.04 μg/kg for FIP-S. This sensor was successfully used to detect FIP and FIP-S in eggs and water samples with good recoveries of 90%-106.6%.

Rational Regulation of Surface Free Radicals on TiO2 Nanotube Arrays via Ag2O-AgBiO3 towards Enhanced Selective Photoelectrochemical Detection

Due to integrated advances in photoelectrochemical (PEC) functionalities for environment detection applications, one-dimensional (1D) TiO2 nanostructures provide a new strategy (PEC sensors) towards organics detection in wastewater. However, the unidealized selectivity to the oxidation of water and organics limits the PEC detection performance. Herein, we designed a ternary photoanode consisting of Ag2O-AgBiO3/TiO2 nanotube arrays (NTAs) to solve this issue by using a facile one-step precipitation reaction. High oxidation capacity for organics is achieved by regulating the surface free radicals properly through the heterostructure formed between the interface of TiO2 and AgBiO3. More importantly, as a trap for electron capture, Ag2O in this ternary system could not only further improve the separation efficiency of charge carriers, but also capture electrons transferred to the TiO2 conduction band, thus reducing the electrons transferred to the external circuit and the corresponding background photocurrent when detecting organics. As a result, the reconstructed TiO2 NTAs decrease their photocurrent response to water and enhance their response to organics, thus presenting lower oxidation activity to water and higher activity to organics, that is, highly selective oxidation characteristics. This work provides more insights into the impact of charge transfer and surface free radicals on developing promising and efficient PEC sensors for organics.

Synergetic Ag2S and ZnS quantum dots as the sensitizer and recognition probe: A visible light-driven photoelectrochemical sensor for the "signal-on" analysis of mercury (II)

A visible-light-driven photoelectrochemical (PEC) sensor has been developed for the "signal-on" analysis of Hg²⁺ by the synergetic combination of low-bandgap Ag₂S and wide-bandgap ZnS quantum dots (QDs). Ag₂S QDs were synthesized with bead-chain-like structure by the self-assembly route and further covalently bound with ZnS QDs to be coated onto the indium tin oxide (ITO) electrodes. It was discovered that the ZnS@Ag₂S-modified electrodes could display the visible-light-driven PEC behavior, of which Ag₂S and ZnS QDs could act as the PEC sensitizer and Hg²⁺-recognition probe, respectively. More importantly, the photocurrent responses of the developed electrodes could be specifically turned on in the presence of Hg²⁺ under the visible-light irradiation, presumably due to that Hg²⁺ might conduct a Zn-to-Hg exchange on ZnS QDs to trigger the formation of HgS/ZnS@Ag₂S heterojunction towards the enhanced electron-hole separation. The as-prepared PEC sensor could facilitate the detection of Hg²⁺ with concentrations ranging from 0.010-1000 nM, with a detection limit of about 1.0 pM. Besides, the feasibility of practical applications of the developed PEC analysis strategy was verified by probing Hg²⁺ in environmental water samples. Such a visible-light-driven PEC detection platform with the unique "turn-on" signal output may promise for the extensive applications for Hg²⁺ evaluation.

Heterojunctions for Photocatalytic Wastewater Treatment: Positive Holes, Hydroxyl Radicals and Activation Mechanism under UV and Visible Light

Forming heterojunctions by coupling two or more semiconductors is an important strategy to develop stable and efficient photocatalysts able to operate both under near-UV and visible light. Five novel heterojunction systems were synthesized in the present study, using a modified sol-gel method: Bi2Mo3O12/TiO2, ZnFe2O4/TiO2, FeTiO3/TiO2, WO3(US)/TiO2 and WO3/TiO2. These heterojunction semiconductors were characterized by using XRD, SEM and EDX, UV–Vis diffuse reflectance spectroscopy and BET. Their photocatalytic activities were evaluated using methyl orange (MO) degradation under both near-UV and visible light. From the various heterojunctions developed, the WO3(US)/TiO2 photocatalyst was the one that showed the highest photocatalytic efficiency with this being assigned to the formation of a double heterojunction involving anatase, rutile and monoclinic WO3 phases. On this basis, a photocatalyst activation mechanism applicable to near-UV and visible light irradiation was proposed. This mechanism explains how the photogenerated electrons (e–) and positive holes (h+) can be transferred to the various phases. As a result, and given the reduced holes and electron recombination surface, hydroxyl radicals found were more abundant. To confirm this assumption, hole formation in the valence band was studied, using hole-scavenging reactions involving ion iodine (I–), while hydroxyl radical production used fluorescence spectroscopy.

In situ electrochemical oxidation of electrodeposited Ni-based nanostructure promotes alkaline hydrogen production

Highly active and stable electrocatalysts based on non-precious metals for hydrogen evolution reaction (HER) in alkaline solution are urgently required for enabling mass production of clean hydrogen in industry. Herein, core-shell NiOOH/Ni nanoarchitectures supported on the conductive carbon cloth have been successfully prepared by a facile electrodeposition process of Ni, and a subsequent in situ electrochemical oxidation. When explored as an alkaline HER electrocatalyst, the as-synthesized NiOOH/Ni nanoarchitecture requires only a low overpotential of ∼111 mV to attain a current density of -10 mA cm^-2, demonstrating its strong catalytic capability of hydrogeneration. The excellent HER activity could well be attributed to the decreasing charge transfer resistance and competitive electrochemical active area of the amorphous NiOOH, compared with inactive Ni substrate. The feasible methodology established in this study can be easily expanded to obtain a series of nano-sized metal oxyhydroxide materials for various energy conversion and storage applications, where Ni-based nanomaterials are among the highly active ones.

Enhanced Gas-Sensing Properties for Trimethylamine at Low Temperature Based on MoO3/Bi2Mo3O12 Hollow Microspheres

Most reported trimethylamine (TMA) sensors have to operate at high temperature, which will consume energy highly. To detect TMA at low temperature, it is necessary to modify the existing materials or develop new materials. In this paper, the sensor based on MoO₃/Bi₂Mo₃O₁₂ hollow microspheres can work at low operating temperature of 170 °C, which were prepared via a simple solvothermal route. The phase and morphology of the product were characterized by an X-ray diffraction meter, a scanning electron microscope and a transmission electron microscope. The surface chemistry of the MoO₃/Bi₂Mo₃O₁₂ sensor was studied with an X-ray photoelectron spectroscope to investigate the TMA sensing mechanism. The MoO₃/Bi₂Mo₃O₁₂ sensor ( S = 25.8) had a higher response to 50 ppm TMA than those of MoO₃ hollow spheres ( S = 10.8) and Bi₂Mo₃O₁₂ sensors ( S = 4.8) at 170 °C. In contrast to the pure MoO₃ and Bi₂Mo₃O₁₂ sensors, the MoO₃/Bi₂Mo₃O₁₂ sensor exhibited an obviously enhanced gas-sensing property for TMA, which might be due to the heterostructure formed between MoO₃ and Bi₂Mo₃O₁₂ and the hollow morphology. It is the first time for MoO₃/Bi₂Mo₃O₁₂ to apply in gas sensors, which might take an important step in the application of MoO₃/Bi₂Mo₃O₁₂ or Bi₂Mo₃O₁₂ in the field of gas sensing.

Localization and Stabilization of Photogenerated Electrons at TiO2 Nanoparticle Surface by Oxygen at Ambient Temperature

Understanding the mechanism by which oxygen adsorption influences the separation behavior of charge carriers is important in photocatalytic removal of air pollutants. In this study, we performed steady-state surface photovoltage and surface photocurrent spectroscopy combined with an atmosphere control system to determine the effect of oxygen on the charge separation behavior at the surface of anatase TiO₂ nanoparticles at ambient temperature. Results showed that photogenerated electrons were movable in N₂ atmosphere but were localized in O₂ atmosphere. O₂ obviously enhanced the stabilization of the localized photogenerated electrons when the surface defects of TiO₂ were fully occupied by adsorbed O₂. Moreover, O₂ adsorption increased the energy demand for exciting electrons from the valence band to localized surface defect states and reduced the density of band tail states. These findings suggest us that the effect of gaseous species on the mobility and stability of charge carriers should be considered to understand the photocatalytic degradation of air pollutants.