Visible Light Excitation Research Articles

Visible-frequency plasmonic enhancement at the edge of graphene/h-BN heterostructures on silicon substrate

Heterostructures of graphene and hexagonal boron nitride (G/h-BN) have been widely studied for controlling and utilizing graphene electronic properties. Here we characterize specific optical and electronic properties of G/h-BN heterostructures made of a high-quality single layer chemical vapor deposition (CVD) graphene laid over h-BN flakes, with focus on plasmonic effects. We compare the G/h-BN properties on Si and SiO2 substrates by micro-Raman spectroscopy mapping, Kelvin probe force microscopy, optical and atomic force microscopy. We observe highly enhanced Raman intensity (up to 280 %) from Si as well as graphene along the G/h-BN edge. It is attributed to localized concentration of electrons in graphene and suitable perpendicular orientation of plasmonic vibrations at the edge. The plasmonic Raman enhancement occurs under a visible light excitation (532 nm) and the effect can be tuned by the h-BN flake thickness (10–150 nm). The enhancement is specific to G/h-BN/Si structures, on G/h-BN/SiO2 structures the Raman signal is suppressed while I2D/IG ratio is increased. Vice versa, change of surface potential under visible light illumination (photovoltage) is on G/h-BN/Si negligible (within 10 mV) compared to the G/h-BN/SiO2 structures. These results open new prospects for broad utilization of localized visible plasmonic effects in graphene.

Designing of multifunctional graphene quantum dot-polyvinyl alcohol-polyglycerol luminescent film for fluorescence detection of pH in sweat

BackgroundWound infection, skin disease, renal failure, cancer, cystic fibrosis, and other pathologies may induce obvious pH changes in sweat. Thus, tracking skin pH changes can help monitor human health in a convenient manner. Owing to their biocompatibility, easy preparation, and sensitive response to pH changes, graphene quantum dots (GQDs) have received increased attention in the optical detection of pH changes. However, their poor luminescent efficiency under visible light excitation and lack of functional diversification limit their application in skin pH monitoring. Therefore, the development of GQDs with excellent ultraviolet protection ability and antibacterial and luminescence performance is essential. ResultsFolic acid-, histidine-, and serine-functionalized boron-doped graphene quantum dots (FHSB-GQDs) were designed and synthesized via thermal treatment. The resulting FHSB-GQDs exhibit strong yellow fluorescence emission under excitation with 490-nm visible light and sensitive pH responsiveness. The peak fluorescence intensity linearly decreases with increasing pH from 4 to 9. Furthermore, the FHSB-GQDs were integrated with polyvinyl alcohol and polyglycerol to form a luminescent film via hydrogen bond interactions. The film exhibits high transparency, mechanical flexibility, ultraviolet protection ability, and antibacterial activity. The presence of polyvinyl alcohol and polyglycerol restricts the free movement of the FHSB-GQDs and improves fluorescence behavior. The film was successfully applied in an intelligent pH-sensing system for monitoring pH changes in human sweat. SignificanceThe graphene quantum dot–polyvinyl alcohol–polyglycerol luminescent film offers excellent transparency, mechanical flexibility, ultraviolet protection ability, antibacterial activity, and luminescence performance. It was successfully applied in an intelligent pH sensing system for the detection of pH changes in human sweat. This study provides a new strategy for the design and construction of wearable sensing systems for health monitoring, facial masks, and medical dressings.

A novel dual-model photoelectrochemical/electrochemical sensor based on Z-scheme TiO2 disks/methylene blue for kanamycin detection.

Herein, a new dual-model photoelectrochemical (PEC)/electrochemical (EC) sensor based on Z-scheme titanium dioxide (TiO2) disk/methylene blue (MB) sensibilization for the detection of kanamycin (Kana) was developed. Metal-organic framework-derived porous TiO2 disks were synthesized and exhibited excellent anodic photocurrent under visible light excitation. Subsequently, amino-labeled double-stranded DNA (dsDNA) was introduced into the modified electrode. Photocurrent was enhanced with MB embedded in dsDNA to form Z-scheme TiO2/MB sensibilization. When the target, Kana, was present, it specifically bound to the aptamer in the dsDNA, leading to the disruption of the dsDNA structure and the release of MB. This release of MB and the increase in target spatial resistance resulted in a significant weakening of PEC signal and a decreased oxidation peak current of MB. The PEC sensor successfully detected Kana in the range of 2-1000 pM with an LOD of 0.17 pM. Meanwhile, the EC sensor for Kana detection showed a linear range of 5-500 pM with an LOD of 1.8 pM. Additionally, the sensor exhibited excellent selectivity, reproducibility, stability, and good recoveries when applied to milk and honey samples. As a result, this method has the potential for application in ensuring food safety through the rapid determination of antibiotics in food.

Strong thickness dependence in thin film photocatalytic heterojunctions: the ZnO-Bi2O3 case study.

Semiconductor heterojunctions are an effective way to achieve efficient photocatalysts, as they can provide an adequate redox potential with visible light excitation. Several works have reported synergistic effects with nanoparticle semiconductor materials. The question is still open for thin film heterojunctions formed by stacked layers, as photocatalysis is considered a surface phenomenon. To investigate if the internal layer really affects or modifies the photocatalytic properties of the external material, we analyze the thin film heterojunction with ZnO and Bi2O3 semiconductors deposited by spray pyrolysis in two configurations: substrate/ZnO/Bi2O3 and substrate/Bi2O3/ZnO. Microstructural analysis was performed to verify the formation of the physical junction of the materials and discard new ternary phases. The photocatalytic activity was analyzed as a function of the thickness of the layers under blue light irradiation. We determined the conduction and valence bands positions, the carrier concentrations, mobilities, Fermi levels, etc. that allowed us to distinguish two reaction mechanisms depending on the configuration. There is a strong compromise between the order and thickness of the layers with the photocatalytic activity. The internal electric field produced in the interface defines the route of the photogenerated charges, and therefore the photocatalytic response. Thus, well-designed thin film heterojunctions can indeed improve the photocatalytic activity of the surface layer.

Bio-inspired synthesis of N-doped TiO2/C nanocrystals using jellyfish mucus with high visible-light photocatalytic efficiency.

Non-metal doping of titanium dioxide (TiO2) has been widely investigated, because it can facilely improve the optical response of TiO2 under visible light excitation in environmental pollution treatments. In the ongoing efforts, however, little consideration has been given to the use of harmful marine organisms as dopants. Here, we employed the natural mucus proteins of the large harmful jellyfish Aurelia coerulea and Nemopilema nomurai, which have frequently bloomed in East Asian marginal seas in recent decades, to synthesize mesoporous nitrogen-doped TiO2 nanocrystals modified with carbon (N-TiO2/C) by a simple hydrothermal method. These nanocrystals were composed of predominantly anatase phase and a small amount of brookite phase TiO2. Their mesoporous structures changed with the variation of the volume ratio of jellyfish mucus added to tetrabutyl titanate (TBT). At the same ratio, larger surface area and pore volume but smaller pore size were observed in N-TiO2/C nanocrystals from N. nomurai rather than A. coerulea. Nitrogen was determinately doped into the lattice of the prepared nanocrystals and the carbon species were modified on their surfaces, which narrowed the band gap, facilitated the separation of photogenerated electron-hole pairs and favored the absorption of visible light, thus improving their visible light photocatalytic activity. The photocatalytic degradation efficiency of Rhodamine B (RhB) under visible light irradiation first increased and then decreased with the gradual increase of the volume ratio of jellyfish mucus proteins to TBT. The maximum reached 97.52% in 20 min from N-TiO2/C nanocrystals synthesized using N. nomurai mucus at the volume ratio of 4 : 1, which showed a remarkably strong visible light absorption, lower band gap energy and smaller electron transfer resistance. These N-TiO2/C nanocrystals also had a relatively stable crystal structure in multiple degradation reactions. The main active species including superoxide radicals (˙O2 -), photogenerated holes (h+) and hydroxyl radicals (˙OH) were found to play a major role in the degradation process of RhB. This study highlights the potential high-value reapplication of harmful jellyfish mucus as a natural organic matrix in fabricating advanced materials with optimized functional properties.

A photoelectrochemical capacitor using polyoxometalates coupled with semiconductor nanocrystals as the photosensitizer.

Solar energy storage technology ensures a sustainable and reliable energy supply. Herein, we show that electrons generated in semiconductor nanocrystals (NCs) of CsPbBr3 by visible light excitation can be stored in polyoxometalates (POMs) of W10O32, and extracted as an electric current using a photoelectrochemical cell.

Photoinduced isomerization mechanism of isatin N<sup>2</sup>-diphenylhydrazones molecular switch

Hydrazone molecular switches have significant application value in supramolecular chemistry. A new type of hydrazone molecular switch, named isatin N<sup>2</sup>-diphenylhydrazone, has been synthesized. Owing to its cis-trans isomerization characteristics under visible light excitation, ease of synthesizing of derivatives, and sensitivity to external stimuli, it has important application value in the field of biochemistry. Because of its forward and backward visible light excitation characteristics, it is considered a class of compound that is very suitable for molecular switches, and it has a wide application value in fields such as biotechnology. In addition, the derivatives compound exhibits strong interactions with negative ions, which enhances its function as a molecular switch, making it a four-state molecular switch that can be achieved by a single molecule. However, the photo-induced isomerization mechanism of these new molecular switches is not yet clear, and whether there are novel phenomena in the isomerization process is also unknown. In this work, a semi empirical OM2/MRCI based trajectory surface hopping dynamics method is adopted to systematically study a photo induced isomerization mechanism based on the E-Z isomerization process of the isatin N<sup>2</sup>-diphenylhydrazones molecular switch. Optimization configuration and the average lifetime of the first excited S<sub>1</sub> state are obtained by using the semi-empirical OM2/MRCI method of molecular switch. It is found that the average lifetime of the S<sub>1</sub> excited state of the E-configuration molecular switch is about 107 fs, and the quantum yield of E-Z isomerization of the molecular switch is 16.01%. By calculating the photo induced isomerization process of the molecular switch, two different isomerization mechanisms of the molecular switch are identified. In addition to the traditional molecular switch isomerization mechanism revolving around the C=N bond, a new isomerization mechanism, i.e. the face-to-face twisting of the molecular switch rotor part is elucidated. By calculating the time-resolved fluorescence radiation spectrum, it is predicted that there may be a very fast fluorescence quenching phenomenon occurring in about 75 fs in the isomerization process, slightly faster than the S<sub>1</sub> average decay events (107 fs). The information about wavelength-resolved attenuation at different times is also calculated, which reflects the ultrafast fluorescence quenching process accompanied by fluorescence red shift, ranging from 2.1 × 10<sup>4</sup> cm<sup>–1</sup> to 3.4 × 10<sup>4</sup> cm<sup>–1</sup>. By comparing the calculated fluorescence spectra with the average lifetime of excited states, the existence of “dark states” is proposed, and possible explanations for the existence of “dark states” are provided, and those “dark states” may be related to lower quantum yields. The research results can provide theoretical guidance for the design and application of new molecular switches. The ease of synthesis and sensitivity to external stimuli of its derivatives make those compounds extremely valuable in molecular switching and light measurement applications.

Multi-resonance emitters with room-temperature phosphorescence in amorphous state and excited by visible light.

Unlike boron, nitrogen-containing multi-resonance emitters with thermally activated delayed fluorescence, here we report boron, sulfur (B, S)-based multi-resonance emitters with room-temperature phosphorescence (RTP) by inserting thiophene into a 5,9-dithia-13b-boranaphtho[3,2,1-de]anthracene skeleton that simultaneously realizes large singlet-triplet energy splitting and strong spin-orbital coupling, leading to efficient room-temperature phosphorescence in an amorphous state. Unlike most RTP emitters with ultraviolet excitation, the multi-resonance RTP emitters exhibit strong phosphorescence under daily-use blue/white LED lamps owing to their intense absorption in the visible-light region (400-486 nm). Meanwhile, such RTP behavior can be tuned by the number and fusing pattern of the thiophene moieties, with the emitters containing thiophene linked to boron atoms via α-positions exhibiting bathochromatically shifted emissions and longer phosphorescence lifetimes (47.7-119.4 ms) than those with β-position linkages. Given these features, amorphous RTP films with different emission colors and lifetimes are fabricated by dispersing the emitters in a poly(methyl methacrylate) matrix, and their applications in multi-color anti-counterfeiting are presented. These findings thus open a way to develop multi-resonance emitters as a new family of pure organic RTP materials that can work in an amorphous state and under visible-light excitation.

Amplifying dual-visible-light photoswitching in aqueous media via confinement promoted triplet-triplet energy transfer.

Achieving visible-light photochromism is a long-term goal of chemists keen to exploit the opportunities of molecular photoswitches in multi-disciplinary research studies. Triplet-sensitization offers a flexible approach to building diverse visible-light photoswitches using existing photochromic scaffolds, circumventing the need for sophisticated molecular design and synthesis. Unfortunately, distance-dependence and environment-sensitivity of triplet-excited species remain as key challenges that severely impair sensitization efficiency and limit their practical availability. We present herein a nature-inspired nanoconfinement strategy in which a triplet-sensitized visible-light photoswitch/sensitizer system is assembled into nanoconfined micelles (d ∼ 40 nm). A ca. 10-fold efficiency increase of triplet-triplet energy transfer for photochromism as well as an amplified fluorescence on/off contrast upon bi-directional visible-light excitation (470/560 nm) was achieved in full aqueous media. By virtue of this, the hybrid photoswitchable system is successfully applied for both flash information encryption and multiple dynamic cell imaging assays, further proving its versatility in materials and life science.

Modulation of Fe–MOF via second-transition metal ion doping (Ti, Mn, Zn, Cu) for efficient visible-light driven CO2 reduction to CH4

This study developed metal–organic frameworks (MOFs) with enhanced properties for CO2 conversion by doping second- transition metal ions (Ti, Mn, Zn, and Cu) into Fe–MOF, which resulted in Fe-M−MOF (M = Ti, Mn, Zn, or Cu). The selection of different metal species in the metal cluster nodes of the MOFs significantly impacted the CO2 conversion efficiency. Among the different combinations, the Fe–Cu bimetallic cluster node was identified as the most optimal node. In addition, we investigated various variables and preparation conditions for determining the optimal synthesis conditions for Fe–Cu-MOFs. We observed that a synthesis temperature, time, and pH of 130 °C, 15 h, and 3.2, respectively, yielded the best results. The 13CO2 isotope labeling method confirmed that the carbon source of CO and CH4 were derived from CO2. Under simulated visible-light irradiation (λ ≥ 420 nm), Fe–Cu-T130 exhibited the highest photocatalytic activity, with a CH4 generation rate of up to 444.2 μmol g−1 h−1. This high activity was attributed to several factors. First, the presence of Fe2+, Fe3+, and Cu2+ on the surface of Fe–Cu-T130 resulted in photogenerated electrons and holes under visible-light excitation. Fe2+ accepted electrons to reduce CO2, whereas Fe3+ and Cu2+ oxidized H2O through holes. Second, the polycrystalline structure of Fe–Cu-T130 with abundant surface oxygen vacancies enhanced the chemical reactivity. Finally, the low conduction band position and narrower bandgap of Fe–Cu-T130 facilitated the excitation of electrons into the conduction band, thereby promoting the CO2 reduction reaction. This study successfully demonstrated the enhanced photocatalytic activity of Fe–Cu-T130 for CO2 conversion under visible light. The findings provide insight into the development of MOFs with improved properties for the sustainable and efficient utilization of CO2.

(Invited) Surface and Structural Dependent Reactivity of Alkylphosphonic Acids-Modified Titanium Oxide Nanostructures with 2-Chloroethyl Ethyl Sulfide Under Visible Light Excitation

Synthesizing novel TiO2 nanomaterials are valuable for heterogeneous reactivity to address toxic chemical remediation. Titanium oxide nanoflowers (comprising assemblies of nanorods) and nanowires have been synthesized in which photocatalytic reactivity with 2-chloroethyl ethyl sulfide (2-CEES) has been significantly enhanced under visible light (1000 nm > λ > 400 nm) excitation. Enhancement of photooxidation with reaction rates of 99 and 168 µmol/g/h (quantum yields of 5.07 x 10-4 and 8.58 x 10-4 molecules/photon) were observed for TiO2 synthesized in the presence of two different alkylphosphonic acids (C14H29PO3H2 and C9H19PO3H2). Additionally, H2Ti2O5‧H2O nanowires were synthesized and capable of highly efficient hydrolysis of the carbon-chlorine (C-Cl) bond of 2-CEES without light at a reaction rate of 279.2 µmol/g/h due to high surface area and chemical nature of the titanate structure. These observations are correlated with: 1) generation of new surface defects/states (i.e. oxygen vacancies) as a result of TiO2 grafting by alkyl phosphonic acid that may serve as reaction active sites; 2) better light absorption by assemblies of nanorods in comparison to individual nanorods, 3) surface area differences, and 4) the exclusion of OH groups due to the formation surface functionalization with alkylphosphonic acids via Ti-O-P bonds on the TiO2. These robust materials can be used for highly efficient surface decontamination.

Visible-light-excited high efficiency multicolor room temperature phosphorescence of carbon dots in boric acid matrix

Visible light is safer for health and deeper penetrable than ultraviolet light, yet the development of room temperature afterglow (RTA) materials with visible-light-excitation remains an enormous challenge. A universal approach to acquire the activation of color-tunable carbon dots (CDs)-based RTA composites (CDs/BA) with excitation-dependent feature under visible light excitation with the highest quantum efficiency up to 54.27 % and long lifetime of 530 ms, surpassing most of nonmetallic afterglow materials under excitation of Vis-light. Meanwhile, CDs/BA exhibit color-tunable RTA properties from cyan to red at excitation of 420 nm via alteration in carbon source types. Benefiting by these excellent properties, CDs/BA composites were applied in advanced information security and anti-counterfeiting fields. Such a strategy provides an important way for the development of high-efficiency visible-light-excited RTA materials with color-tunability.

The Photoelectric Synaptic Device with Sensing‐Memory‐Computing Function Regulated by All‐Optical Pulse

AbstractThe photoelectric synaptic devices with the bidirectional optical response and multilevel nonvolatile all‐optical pulse control are the basis for constructing the sensing‐memory‐computing hardware network. However, the current all‐optical‐pulse‐regulated photoelectric synaptic devices cannot realize the bidirectional and multistage nonvolatile regulation of photocurrent responsivity under the detection light excitation. Here, p‐Si/n‐ZnO heterojunction synaptic devices are constructed, and the bidirectional, nonvolatile control of the synaptic device under visible light excitation is realized with up to 60 states of photocurrent responsivity by ultraviolet (UV) and near‐infrared (NIR) irradiation. Based on the performance of the synaptic device, the artificial feedback network can be built to realize the classification and recognition of colored handwritten digits. The recognition accuracy for optical handwritten digits at 415, 530, and 970 nm is 78.1 ± 1.2%, 79.4 ± 1.9% and 79.0 ± 1.6%, respectively. Additionally, the 3 × 3 convolution kernel constructed by the synaptic device can realize image‐processing functions like mean filtering, Gaussian filtering, and edge enhancement. The development of sensing‐storage‐computing all‐optical control artificial vision hardware networks can be greatly aided by the new approach to bidirectional and multistage nonvolatile all‐optical pulse regulation of photoelectric synaptic devices that is proposed in this paper.

Noble metal-free 0D-1D CoOx/Mn0.3Cd0.7S nanocomposites for efficient visible-light hydrogen production

Here, a series of MnxCd1-xS sosoloid composite photocatalysts with visible-light activity were first prepared by a solvothermal process. The element ratio of Cd2+ to Mn2+ was optimized to be Mn0.3Cd0.7S in MnxCd1-xS sosoloid on account of its photocatalytic activity for H2 evolution from H2O in response to visible light excitation. And on this basis, the CoOx nanopariticles were loaded on the surface of Mn0.3Cd0.7S sosoloid composite to obtain a binary p-n heterojunction of CoOx/Mn0.3Cd0.7S composite through a facile impregnation process and a high temperature sintering procedure. Benefitting from the synergistic effect of the built-in electric field, binary p-n heterojunction structure, and rearrange of the Fermi level equilibrium, the as-synthesized CoOx/Mn0.3Cd0.7S composite presents a highly enhanced photocatalytic activity for hydrogen production from H2O in response to visible light excitation, which is demonstrated to be 53.4 and 4.0 times higher than that of the primitive CdS and Mn0.3Cd0.7S, respectively. Furthermore, after 4 times circles of photocatalytic H2 production tests, the CoOx/Mn0.3Cd0.7S composite still keeps 92.0 % of the original photocatalytic activity. Considering its reasonable photochemistry stability and excellent photocatalytic activity for hydrogen evolution from H2O under with visible light excitation, the as-synthesized CoOx/Mn0.3Cd0.7S composite has potential applications in solar hydrogen production areas.

Fluorometric Sensing of Metal Ions by Carbon Nano Dots - A Review

abstract: Contamination from heavy metal ions is a rising problem. It has direct and indirect impacts on human health, the environment, and aquatic life. Thus, detecting trace amounts of these elements presents significant challenges. It is important to develop effective, affordable, accurate, fast sensing monitoring systems. A new field of sensing techniques has emerged with the discovery of bio-compatible fluorescent carbon nanodots. Although the study of heavy metal ion detection using carbon nanodots and fluorometric sensing techniques is relatively new and developing, it holds great potential for aiding scientists in the development of environmentally friendly sensing systems. This article focuses on the utilization of carbon nanodots in fluorescencebased detection of metal ions in various media. The ability to emit fluorescence across the entire visible spectrum under UV and visible light excitation offers fluorescent quenching or fluorescent enhancement phenomena in the presence of trace amount of metal ions. The present work discusses different fluorometric sensing phenomena, its mechanism and applications of carbon dots on it. It covers the recent progress in carbon-nano dots for bio-based synthesis, physical properties, and application in heavy metal sensing.

Photocatalytic activity of Fe3O4–Fe2O3 particles supported on mordenite under visible light exposure for methylene blue degradation

Dyes pollution is a serious environmental problem and heterogeneous catalysis has been proposed as a remediation method. In this study, a set of catalysts of synthetic mordenite with iron oxides was synthesized by a simple chemical co-precipitation method assisted by subsequent thermal treatment with an oxidation process. Physicochemical characterization of prepared materials was performed by a variety of techniques, including XRD, SEM, EDS, SBET, UV–Vis DR, and XPS. Photocatalytic methylene blue (MB) degradation by the synthesized catalyst was evaluated with visible light excitation. From the studied set of catalysts, the sample prepared with a thermal treatment at 100 °C in air atmosphere for 3 h was capable of degrading ~ 90% of MB after 120 min with visible light of λ = 420 nm exposition and a small portion of H2O2 added. The catalyst used three processes to degrade MB: (1) adsorption of organic residues in the mordenite matrix support for electrostatic interactions, (2) photocatalysis heterogeneous reaction with visible light and (3) Fenton reaction catalyst with a small portion to H2O2 by Fe3O4–Fe2O3 presence. The catalytic efficiency to dye degradation was improved by a simple and economical thermal treatment without changing reaction conditions like pH, temperature, dose, or other. Studied mordenite iron oxide catalysts can be retrieved and reused at least five times without noticeable degradation, taking advantage of their magnetic properties. These catalysts could be proposed an economical, simple, and non-toxic alternative for eliminating organic dye pollution using visible light or solar irradiation in wastewater remediation related to textile, food, and pharmaceutical industries.

Composites of W18O49 Nanowires with g-C3N4/RGO Nanosheets for Broadband Light-Driven Photocatalytic Wastewater Purification.

Developing a photocatalyst that can effectively utilize the full solar spectrum remains a high-priority objective in the ongoing pursuit of efficient light-to-chemical energy conversion. Herein, the ternary nanocomposite g-C3N4/RGO/W18O49 (CN/RGO/WO) was constructed and characterized by a variety of techniques. Remarkably, under the excitation of photon energies ranging from the ultraviolet (UV) to the near-infrared (NIR) region, the photocatalytic performance of the CN/RGO/WO nanocomposite exhibited a significant enhancement compared with single component g-C3N4 or W18O49 nanosheets for the degradation of methyl orange (MO). The MO photodegradation rate of the optimal CN/1.0 wt% RGO/45.0 wt% WO catalyst reached 0.816 and 0.027 min-1 under UV and visible light excitation, respectively. Even under low-energy NIR light, which is not sufficient to excite g-C3N4, the MO degradation rate can still reach 0.0367 h-1, exhibiting a significant enhancement than pure W18O49. The outstanding MO removal rate and stability were demonstrated by CN/RGO/WO nanocomposites, which arise from the synergistic effect of localized surface plasmon resonance effect induced by W18O49 under vis-NIR excitation and the Z-scheme nanoheterojunction of W18O49 and g-C3N4. In this work, we have exploited the great potential of integrating nonmetallic plasmonic nanomaterials and good conductor RGO to construct high-performance g-C3N4-based full-solar spectral broadband photocatalysts.

Enhanced H2 sensing performance of Pd-modified ZnO nanorods under visible light excitation

High-performance room-temperature hydrogen (H2) sensors are the optimal choice for practical applications. Light excitation, especially visible light, is safer and requires less power compared to ultraviolet (UV) light. This makes it an effective method for achieving room temperature operation. In this study, different mass ratios of Pd-modified ZnO nanorods were synthesized using a combination of hydrothermal and impregnation methods, and their sensing performance to H2 under visible light excitation was investigated. Material characterization results demonstrated that the localized surface plasmon resonance (LSPR) effect of Pd broadened the absorption in the visible light region, increasing the generation of high-energy hot electrons. Notably, the 2.5 wt% Pd/ZnO exhibited excellent sensing performance towards 5000 ppm H2 at room temperature under visible light excitation, with a high response value of 5906.78. The LSPR effect and the catalytic activity of Pd nanoparticles significantly enhance the sensing performance of H2. Based on our current knowledge, there have been no explicit reports on the detection of H2 using visible light excitation with Pd/ZnO, thus highlighting a new direction for the study of room temperature H2 sensors.

Plasmonic-Assisted Water–Gas Shift Reaction of Gold Particles on TiO2

The Localized Surface Plasmon (LSP) effect of 5 nm mean size Au particles deposited on TiO2 P25 was investigated during the photo-thermal water gas shift reaction (WGSR). The effects of CO concentration, excitation light flux and energy, and molecular oxygen addition during the reaction were investigated. The photocatalytic WGSR rate under light excitation with wavelengths extending from 320 to 1100 nm was found to be higher than the thermal reaction alone at the same temperature (85 °C). A H2/CO2 ratio of near unity was found at high concentrations of CO. The addition of molecular oxygen during the reaction resulted in a slight decrease in molecular hydrogen production, while the rates of CO2 formation and CO consumption changed by one order of magnitude. More importantly, it was found that the WGSR rates were still high under only visible light excitation (600–700 nm). The results prove that Au LSP alone triggers this chemical reaction without requiring the excitation of the semiconductor on which they are deposited.

Construction of oxygen vacancy-rich MoO3-x and NiFe-LDH p-n heterojunction for enhanced carrier separation to promote photoelectrochemical oxidation of pollutants and hydrogen precipitation

In this work, a novel portable photoanode consisting of MoO3-x/NiFe@NF with excellent photoelectrochemical (PEC) performance and multifunctional applications was synthesized using a simple hydrothermal and electrodeposition method. In a visible-light-driven PEC system, the photoanode was able to simultaneously promote the degradation of tetracycline and the generation of hydrogen. The degradation efficiency of MoO3-x/NiFe@NF for TC (20 mg/L) was up to 99.9 %. The production of hydrogen (H2) at the cathode could be at most 32.07 μmol cm−2 within 100 min. In addition, the MoO3-x/NiFe@NF photoanode exhibited a positive bactericidal effect against Gram-negative bacteria (E. coli) which could be completely removed within 20 min under the synergistic effect of visible light and voltage. The improved photoelectrocatalytic efficiency is attributed to the built-in electric field resulting from the formation of a p-n heterojunction between MoO3-x and NiFe-LDH. Under the excitation of visible light, the built-in electric field is able to promote the separation and transmission of the photogenerated carriers. A possible mechanism of MoO3-x/NiFe@NF p-n heterojunction was proposed and discussed based on DRS, Mott-Schottky, UPS characterization and DFT theoretical calculations. Furthermore, the electrode's reusability and stability were evaluated through cycling experiments. This work provides a novel p-n heterojunction synthesis method with significant potential for wastewater treatment and future applications in ship ballast water treatment.