Solution-Processed Ultrathin SnS2-Pt Nanoplates for Photoelectrochemical Water Oxidation

Direct Z-Scheme Heterostructure of Vertically Oriented SnS2 Nanosheet on BiVO4 Nanoflower for Self-Powered Photodetectors and Water Splitting

The construction of nanostructured Z-scheme heterostructure is a powerful strategy for realizing high-performance photoelectrochemical (PEC) devices such as self-powered photodetectors and water splitting. Considering the band structure and internal electric field direction, BiVO4 is a promising candidate to construct SnS2 -based heterostructure. Herein, the direct Z-scheme heterostructure of vertically oriented SnS2 nanosheet on BiVO4 nanoflower is rationally fabricated for efficient self-powered PEC photodetectors. The Z-scheme heterostructure is identified by ultraviolet photoelectron spectroscopy, photoluminescence spectroscopy, PEC measurement, and water splitting. The SnS2 /BiVO4 heterostructure shows a superior photodetection performance such as excellent photoresponsivity (10.43 mA W-1 ), fast response time (6 ms), and long-term stability. Additionally, by virtue of efficient Z-scheme charge transfer and unique light-trapping nanostructure, the SnS2 /BiVO4 heterostructure also displays a remarkable photocatalytic hydrogen production rate of 54.3 µmol cm-2 h-1 in Na2 SO3 electrolyte. Furthermore, the synergistic effect between photo-activation and bias voltage further improves the PEC hydrogen production rate of 360 µmol cm-2 h-1 at 0.8 V, which is an order of magnitude above the BiVO4 . The results provide useful inspiration for designing direct Z-scheme heterostructures with special nanostructured morphology to signally promote the performance of PEC devices.

Constructing NCuS Interface Chemical Bonds over SnS2 for Efficient Solar-Driven Photoelectrochemical Water Splitting

The restricted charge transfer and slow oxygen evolution reaction (OER) dynamics tremendously hamper the realistic implementation of SnS₂ photoanodes for photoelectrochemical (PEC) water splitting. Here, a novel strategy is developed to construct interfacial NCuS bonds between NC skeletons and SnS₂ (CuNC@SnS₂ ) for efficient PEC water splitting. Compared with SnS₂ , the PEC activity of CuNC@SnS₂ photoelectrode is tremendously heightened, obtaining a current density of 3.40 mA cm² at 1.23 V_RHE with a negatively shifted onset potential of 0.04 V_RHE , which is 6.54 times higher than that of SnS₂ . The detailed experimental characterizations and theoretical calculation demonstrate that the interfacial NCuS bonds enhance the OER kinetic, reduce the surface overpotential, facilitate the separation of photon-generated carriers, and provide a fast transmission channel for electrons. This work presents a new approach for modulating charge transfer by interfacial bond design in heterojunction photoelectrodes toward promoting PEC performance and solar energy application.

Colorimetric and Photocurrent-Polarity-Switching Photoelectrochemical Dual-Mode Sensing Platform for Highly Selective Detection of Mercury Ions Based on the Split G-Quadruplex-Hemin Complex

Mercury ion (Hg²⁺) is one of the most harmful heavy metal ions with the greatest impact on public health. Herein, based on the excellent catalytic activity toward 3,3',5,5'-tetramethylbenzidine (TMB) and the strong photocurrent-polarity-switching ability to SnS₂ photoanode of the split G-quadruplex-hemin complex, the magnetic NiCo₂O₄@SiO₂-NH₂ sphere-assisted colorimetric and photoelectrochemical (PEC) dual-mode sensing platform was developed for the Hg²⁺ assay. First, the amino-labelled single-stranded DNA1 (S1) was immobilized on NiCo₂O₄@SiO₂-NH₂ and then partly hybridized with another single-stranded DNA2 (S2). When Hg²⁺ was present, the thymine-Hg²⁺-thymine base pairs between S1 and S2 were formed, causing the formation of the split G-quadruplex in the presence of K⁺. After addition of hemin, the split G-quadruplex-hemin complex was obtained and effectually catalyzed the H₂O₂-mediated oxidation of TMB. Thus, the color and absorbance intensity of the TMB solution were changed, resulting in the visual and colorimetric detection of Hg²⁺. The linear response range is 10 pM to 10 nM, and the detection limit is 3.8 pM. Meanwhile, the above G-quadruplex-hemin complex effectively switched the photocurrent polarity of SnS₂-modified indium tin oxide electrode, leading to the sensitive and selective PEC assay of Hg²⁺ with a linear response range of 5 pM to 500 nM and a detection limit of 2.3 pM. Moreover, the developed dual-mode sensing platform provided mutual authentication of detection results in different modes, effectively improving the assay accuracy and confidence, and may have a good potential application in highly sensitive, selective, and accurate determination of Hg²⁺ in environmental fields.

Ultrahighly Sensitive Sandwich-Type Electrochemical Immunosensor for Selective Detection of Tumor Biomarkers

Herein, a novel sandwich-type immunosensor was designed using Pt nanoparticle-decorated SnS₂ nanoplates (Pt@SnS₂) as a matrix and N,B-doped Eu MOF (N,B-Eu MOF) nanospheres as a signal amplifier. In Pt@SnS₂, Pt nanoparticles (NPs) enhance the surface electron transport capability and electrochemiluminescence (ECL) performance of SnS₂ nanoplates. The dual "antenna" effect of 5-boronoisophthalic acid (5-bop) and 5-nitroisophthalic acid (5-nop) enables the N,B-Eu MOFs to show very good ECL performance at the cathode. In the presence of the target carcinoembryonic antigen (CEA), the sandwich-type immunosensor provides specific immune responses, and the ECL signal of the immunosensor is greatly amplified by the signal probe N,B-Eu MOFs. In view of the above, the immunosensor was successfully applied for highly sensitive and selective detection of CEA with a detection limit of 0.06 pg·mL^-1. This sensor exhibits high sensitivity and specificity, excellent stability, good reproducibility, and good practicability in real human serum.

Electrochemical Conversion of Alcohols into Acidic Commodities on Nickel Sulfide Nanoparticles

The electrocatalytic oxidation of alcohols is a potentially cost-effective strategy for the synthesis of valuable chemicals at the anode while simultaneously generating hydrogen at the cathode. For this approach to become commercially viable, high-activity, low-cost, and stable catalysts need to be developed. Herein, we demonstrate an electrocatalyst based on earth-abundant nickel and sulfur elements. Experimental investigations reveal the produced NiS displays excellent electrocatalytic performance associated with a higher electrochemical surface area (ECSA) and the presence of sulfate ions on the formed NiOOH surface in basic media. The current densities reached for the oxidation of ethanol and methanol at 1.6 V vs reversible hydrogen electrode (RHE) are up to 175.5 and 145.1 mA cm^-2, respectively. At these high current densities, the Faradaic efficiency of methanol to formate conversion is 98% and that of ethanol to acetate is 81%. Density functional theory calculations demonstrate the presence of the generated sulfate groups to modify the electronic properties of the NiOOH surface, improving electroconductivity and electron transfer. Besides, calculations are used to determine the reaction energy barriers, revealing the dehydrogenation of ethoxy groups to be more favorable than that of methoxy on the catalyst surface, which explains the highest current densities obtained for ethanol oxidation.

Contactless Photoelectrochemical Biosensor Based on the Ultraviolet-Assisted Gas Sensing Interface of Three-Dimensional SnS2 Nanosheets: From Mechanism Reveal to Practical Application

This work reports a contactless photoelectrochemical biosensor based on an ultraviolet-assisted gas sensor (UV-AGS) with a homemade three-dimensional (3D)-SnS₂ nanosheet-functionalized interdigitated electrode. After rigorous examination, it was found that the gas responsiveness accelerated and the sensitivity increased using the UV irradiation strategy. The effects of the interlayer structure and the Schottky heterojunction on the gas-sensitive response of O₂ and NH₃ under UV irradiation were further investigated theoretically by 3D electrostatic field simulations and first-principles density functional theory to reveal the mechanism. Finally, a UV-AGS device was developed to quantify the blood ammonia bioassay in a small-volume whole blood sample by alkalizing blood to release gas-phase ammonia with a linear range of 25-5000 μM with a limit of detection (LOD) of 29.5 μM. The device also enables a rapid immunoassay of human cardiac troponin I (cTnI) with a linear range of 0.4-25.6 ng/mL and an LOD of 0.37 ng/mL using a urease-labeled antibody as the immune recognition molecule. Both analyses showed satisfying specificity and stability, suggesting that the device can be applied to practical assays and is of great potential to increase the value of gas-sensitive sensors in chemical biosensing.

2D/2D Heterojunction of TiO2 Nanoparticles and Ultrathin G-C3N4 Nanosheets for Efficient Photocatalytic Hydrogen Evolution

Photocatalytic hydrogen evolution is considered one of the promising routes to solve the energy and environmental crises. However, developing efficient and low-cost photocatalysts remains an unsolved challenge. In this work, ultrathin 2D g-C₃N₄ nanosheets are coupled with flat TiO₂ nanoparticles as face-to-face 2D/2D heterojunction photocatalysts through a simple electrostatic self-assembly method. Compared with g-C₃N₄ and pure TiO₂ nanosheets, 2D/2D TiO₂/g-C₃N₄ heterojunctions exhibit effective charge separation and transport properties that translate into outstanding photocatalytic performances. With the optimized heterostructure composition, stable hydrogen evolution activities are threefold and fourfold higher than those of pure TiO_2, and g-C₃N₄ are consistently obtained. Benefiting from the favorable 2D/2D heterojunction structure, the TiO₂/g-C₃N₄ photocatalyst yields H₂ evolution rates up to 3875 μmol·g⁻¹·h⁻¹ with an AQE of 7.16% at 380 nm.

Sulfide-Based Photocatalysts Using Visible Light, with Special Focus on In2S3, SnS2 and ZnIn2S4

Sulfides are frequently used as photocatalysts, since they absorb visible light better than many oxides. They have the disadvantage of being more easily photocorroded. This occurs mostly in oxidizing conditions; therefore, they are commonly used instead in reduction processes, such as CO2 reduction to fuels or H2 production. Here a summary will be presented of a number of sulfides used in several photocatalytic processes; where appropriate, some recent reviews will be presented of their behaviour. Results obtained in recent years by our group using some octahedral sulfides will be shown, showing how to determine their wavelength-dependent photocatalytic activities, checking their mechanisms in some cases, and verifying how they can be modified to extend their wavelength range of activity. It will be shown here as well how using photocatalytic or photoelectrochemical setups, by combining some enzymes with these sulfides, allows achieving the photo-splitting of water into H2 and O2, thus constituting a scheme of artificial photosynthesis.

Heterostructures between a tin-based intermetallic compound and a layered semiconductor for gas sensing

SnS2 nanoplates are used as sacrificial templates to facilitate the in situ growth of intermetallic compound Pt3Sn nanoparticles. The Pt3Sn/SnS2 heterostructures show promise for selective NO2 sensing due to the favored gas adsorption and gas-solid charge transfer on Pt3Sn, combined with the optimized film conductance and formation of ohmic-type Pt3Sn/SnS2 heterointerfaces.

Atomic Sandwiched p-n Homojunctions

Semiconductor p-n junctions have been explored and applied in photoelectrochemical (PEC) water splitting, but serious carrier recombination and sluggish oxygen evolution reaction (OER) dynamics have demanded further progress in p-n junction photoelectrode design. Here, via a controllable NH₃ treatment, we construct sandwiched p-n homojunctions in three-unit-cells n-type SnS₂ (n-SnS₂ ) nanosheet arrays using nitrogen (N) as acceptor dopants. The optimal N-doped n-SnS₂ (pnp-SnS₂ ) with such unique structure achieves a record photocurrent density of 3.28 mA cm^-2 , which is 21 times as high as that of n-SnS₂ and the highest value among all the SnS₂ photoanodes reported so far. Moreover, the stoichiometric O₂ and H₂ evolution from water was achieved with Faradaic efficiencies close to 100 %. The superior performance could be attributed to the facilitated electron-hole separation/transfer, accelerated surface OER kinetics, prolonged carrier lifetime, and improved structural stability.

A Direct Z-Scheme for the Photocatalytic Hydrogen Production from a Water Ethanol Mixture on CoTiO3/TiO2 Heterostructures

Photocatalytic H₂ evolution from ethanol dehydrogenation is a convenient strategy to store solar energy in a highly valuable fuel with potential zero net CO₂ balance. Herein, we report on the synthesis of CoTiO₃/TiO₂ composite catalysts with controlled amounts of highly distributed CoTiO₃ nanodomains for photocatalytic ethanol dehydrogenation. We demonstrate these materials to provide outstanding hydrogen evolution rates under UV and visible illumination. The origin of this enhanced activity is extensively analyzed. In contrast to previous assumptions, UV-vis absorption spectra and ultraviolet photoelectron spectroscopy (UPS) prove CoTiO₃/TiO₂ heterostructures to have a type II band alignment, with the conduction band minimum of CoTiO₃ below the H₂/H⁺ energy level. Additional steady-state photoluminescence (PL) spectra, time-resolved PL spectra (TRPLS), and electrochemical characterization prove such heterostructures to result in enlarged lifetimes of the photogenerated charge carriers. These experimental evidence point toward a direct Z-scheme as the mechanism enabling the high photocatalytic activity of CoTiO₃/TiO₂ composites toward ethanol dehydrogenation. In addition, we probe small changes of temperature to strongly modify the photocatalytic activity of the materials tested, which could be used to further promote performance in a solar thermophotocatalytic reactor.

Novel Self-Powered Photodetector with Binary Photoswitching Based on SnSx/TiO2 Heterojunctions

Binary photoresponse characteristics can help realize optical signal processing and logic operations. UV photodetectors (PDs) with SnS_x nanoflakes and TiO₂ nanorod arrays (NRs) show a novel binary photoswitching behavior (change in current from positive to negative) by manipulating the light wavelength without an external power source, utilizing the interfacial recombination of the photogenerated carriers in the type-I SnS_x/TiO₂ heterojunctions. The enhanced responsivity (R*), detectivity (D^*), and fast photoresponse time for self-powered SnS_x/TiO₂PDs can be achieved by adjusting the phase ratio of SnS and SnS₂ nanoflakes. The binary photoswitching in the self-powered UV PDs can be applied in the encrypted optical signal processing and imaging in some special conditions without external bias.

Photo-responsive chitosan/Ag/MoS2 for rapid bacteria-killing

Bacterial infection is a serious problem threatening human health. The chitosan (CS)-modified MoS₂ coating loaded with silver nanoparticles (Ag NPs) was designed on the surface of titanium (Ti) to kill bacteria rapidly and efficiently under 660 nm visible light. Ag/MoS₂ exhibited high photocatalytic activity due to the rapid transfer of photo-inspired electrons from MoS₂ to Ag NPs, resulting in higher yields of radical oxygen species (ROS) to kill bacteria. The covering of CS made the composite coating positively charged to further enhance the antibacterial property of the coating. In addition, CS/Ag/MoS₂-Ti also showed a certain photothermal effect. in vitro results showed that the antibacterial efficiency of the coating on Staphylococcus aureus and Escherichia coli was 98.66% and 99.77% respectively, when the coating was irradiated by 660 nm visible light for 20 min. Cell culture tests showed that CS/Ag/MoS₂-Ti had no adverse effects on cell growth. Hence, this surface system will be a very promising strategy for eliminating bacterial infection on biomedical device and implants safely and effectively within a short time.

A novel approach to photoelectrochemical immunoassay for procalcitonin on the basis of SnS2/CdS

A label-free photoelectrochemical (PEC) immunoassay system based on the one-step synthesis of SnS₂/CdS nanocomposites is successfully constructed for sensitively analyzing procalcitonin (PCT).