Fast Electron-hole Recombination Research Articles

Facile construction of ZnWO4/g-C3N4 heterojunction for the improved photocatalytic degradation of MB, RhB and mixed dyes

This study presents the construction of binary ZnWO4/g-C3N4 nanocomposite via a facile hydrothermal approach to enhance the photocatalytic performance under the visible light irradiation. The proposed ZnWO4/g-C3N4 nanocomposite photocatalyst shows excellent photodegradation towards organic dyes, such as methylene blue (MB) and rhodamine B (RhB). The optimal loading of ZnWO4 and g-C3N4 leads to the synergistic effect which plays a predominant role in inhibiting the fast electron-hole pairs recombination rate at the interface of ZnWO4/g-C3N4 photocatalyst. The degradation rates of MB and RhB is achieved around 92.9 % and 88.8 % under the visible light irradiation for 120 min. According to our findings, the radical quenching experiments suggested that the ●OH radicals played a positive impact in the photodegradation process. Since, our proposed photocatalyst exhibit superior photocatalytic activity towards the individual MB and RhB degradation. The ZnWO4/g-C3N4 photocatalyst were further applied to demonstrate the degradation of mixed dyes (MB and RhB) at an irradiation time of 180 min. In the mixed dye solution, the ZnWO4/g-C3N4 photocatalyst achieved a highest reaction rate of 0.010 min−1 for MB and 0.012 min−1 for RhB with the degradation rate of 87.8 % and 83.3 % for RhB and MB, respectively. For the mixed dyes, the radical quenching experiments confirmed that the ●OH radicals are responsible for the fast photodegradation. Additionally, the practicality of the proposed ZnWO4/g-C3N4 photocatalyst towards the degradation of MB, RhB and the mixed dyes were examined in the tap water samples. Furthermore, the plausible photodegradation mechanism of ZnWO4/g-C3N4 photocatalyst was proposed in detail. This study provides a new insight for the simultaneous degradation of mixed chemical pollutants using our proposed ZnWO4/g-C3N4 photocatalyst.

Ultra-fast photocatalytic degradation of Rhodamine B exploiting oleate-stabilized zinc oxide nanoparticles

Rhodamine B (RhB) is a harmful dye released by industrial wastewaters, thus necessitating its urgent removal. Advanced oxidation processes constitute promising strategies to purify polluted water. Among others, photocatalysis relies on reactive oxygen species (ROS) produced by photocatalytic particles, typically semiconductors like titania or zinc oxide (ZnO), excited by solar or UV–Vis light. However, their wide band gap limits their catalytic capabilities within the absorption of the UV spectrum and causes fast electron–hole recombination. This study presents novel strategies to overcome these limitations: (i) doping semiconductors to increase photocatalytic efficiency; (ii) sensitization-mediated photocatalysis for visible light activation using chemical moieties to trap dye molecules; (iii) nanosizing the photocatalysts to enhance the surface area. ZnO nanoparticles, doped with iron or gadolinium and capped with oleic acid are here synthesized and tested in RhB dye solutions. Remarkably, the results demonstrate an ultra-fast RhB degradation, driven by oleic acid having crucial role in dye adsorption. The degradation mechanisms, including ROS-induced N-deethylation and xanthene group cleavage, are also unraveled. These findings underscore the efficacy of the proposed semiconductor photocatalyst design, highlighting a significant advancement with extensive potential applications in wastewater remediation. This innovative approach paves the way for more efficient and practical solutions to combat industrial dye pollution.Graphical abstract

Tailoring the morphology and charge transfer pathways of ultrathin Cd0.8Zn0.2S nanosheets via ionic liquid-modified Ti3C2 MXenes towards remarkable photocatalytic hydrogen evolution

Small-sized CdxZn1–xS solid solution nanomaterial is an important candidate for efficient photocatalytic hydrogen evolution (PHE), but it still suffers from easy agglomeration, severe photo corrosion, and fast photogenerated electron-hole recombination. To tackle these issues, herein, we propose a new strategy to modify CdxZn1–xS nanoreactors by the simultaneous utilization of ionic-liquid)-assisted morphology engineering and MXene-incorporating method. That is, we designed and synthesized a novel hierarchical Cd0.8Zn0.2S/Ti3C2 Schottky junction composite through the in-situ deposition of ultrathin Cd0.8Zn0.2S nanosheets on unique IL-modified Ti3C2 MXenes by a one-pot solvothermal method for efficiently PHE. The unique construction strategy tailors the thickness of ultrathin Cd0.8Zn0.2S nanosheets and prevents them from stacking and agglomeration, and especially, optimizes their charge transfer pathways during the photocatalytic process. Compared with pristine Cd0.8Zn0.2S nanosheets, Cd0.8Zn0.2S/Ti3C2 has abundant photogenerated electrons available on the Ti3C2 surface for proton reduction reaction, owing to the absence of deep-trapped electrons, suppression of electron-hole recombination in Cd0.8Zn0.2S and high-efficiency charge separation at the Cd0.8Zn0.2S/Ti3C2 Schottky junction interface. Moreover, the hydrophilicity, electrical conductivity, visible-light absorption capacity, and surficial hydrogen desorption of Cd0.8Zn0.2S/Ti3C2 heterostructure are significantly improved. As a result, the heterostructure exhibits outstanding photocatalytic stability and super high apparent quantum efficiency, being rendered as one of the best noble-metal-free Cd-Zn-S-based photocatalysts. This work illustrates the mechanisms of morphology control and heterojunction construction in controlling the catalytic behavior of photocatalysts and highlights the great potential of the IL-assisted route in the synthesis of high-performance MXene-based heterostructures for photocatalytic hydrogen evolution.

Organic pollutants photodegradation increment with use of TiO2 nanotubes decorated with transition metals after pulsed laser treatment

Among various titanium(IV) oxide (TiO2, titania) structures, 1D nanotubes (TiO2 NTs) produced during the two-electrode anodization process, are extensively utilized in sensors or supercapacitors as well as in photo(electro)catalytic water splitting. However, due to wide bandgap and fast electron-hole recombination additional modifications, mostly concerned on materials surface, are required. According to the recent research, TiO2 NTs photo(electro)catalytic characteristic were markedly improved by the combination of surface decoration with transition metal nanoparticles further treated with the laser beam. Nevertheless, until recently, the photocatalytic ability of laser-treated TiO2 NTs for recalcitrant chemicals degradation were hardly described. In this regard, our work focuses on obtaining long, about 7.3 μm TiO2 NTs (L-TiO2 NTs), together with their photoactivity and physicochemical characteristics, as well as their alterations following surface modification utilizing transition metals (tungsten, chromium and nickel) together with laser treatment. Obtained L-TiO2 NTs are characterized by over 13.5 times larger BET surface area in comparison to reference spaced TiO2 NTs with approximately 2 μm length (0.61 m2 g−1 and 0.05 m2 g−1, respectively). This allowed for increasing of the materials photocatalytic activity in both UV–vis and vis light. Additionally, phenol photodegradation reached up to 34% (0.21·10−2 min−1) for tungsten-modified titania after laser annealing at 20 mJ cm2 fluence. The reaction mechanism research revealed that reduction of organic pollutants concentration was primarily caused by superoxide radical anions •O2−. Furthermore, obtained modified L-TiO2 NTs showed remarkable durability without losing their initial activity over ten photocatalytic cycles.

Amphi-Luminescent MoS2 nanostructure for photocatalytic splitting of water and removal of Methylene Blue

Chemical dyes used in the textile industries are one of the major pollutants in water. Methylene blue (MB) is a commonly seen dye that creates hazardous health problems. In this article the photocatalytic degradation of MB by the nanocatalyst MoS2 (Nano-MoS2) and carbon dot (C Dots) incorporated MoS2 (Nano-CD-MoS2) is reported. The photocatalytic degradation of MB is analyzed based on the electron-hole recombination rate of the catalyst. Photoluminescence emission exhibited by the catalyst is used as a key indicator to probe the electron-hole recombination rate. Nano-MoS2 was synthesized hydrothermally at 180 0C for 8 h from ammonium tetra thiomolybdate (ATTM). C Dot was prepared following a green root from ash guard extract which later mixed with Nano-MoS2 and kept in an autoclave at a temperature 140 °C for 4 h to get Nano-CD-MoS2. The photoluminescence (PL) and photocatalytic behavior of Nano-MoS2 and Nano-CD-MoS2 and their application for water splitting and water purification are reported. The incorporation of graphene and artificial C Dot into MoS2 nanostructures are reported to increase the conductivity and active edge sites of MoS2 that enhances the photocatalytic action. Since green C Dots are eco-friendly and easily synthesizable than artificial C Dots, as a novel study, this article investigated the influence of green C Dots on the PL and photocatalytic performance of nanosized MoS2. Nano-MoS2 and Nano-CD-MoS2 exhibited both upconversion and downconversion PL; accordingly the nanostructures were termed as amphi-luminescent. The amphi-luminescence property widens the photon absorption range and hence enhances the catalytic degradation of dyes. Nano-MoS2 which exhibited lesser intensity of amphi-luminescence emission compared to Nano-CD-MoS2 showed better results in degradation of MB. C Dots may bind with the valence band electrons of MoS2, resulting in the reduction of dangling bonds. Dangling bonds can trap photo-induced excitons to hinder the rate of electron-hole recombination. So, fast electron-hole recombination occurs in Nano-CD-MoS2 than Nano-MoS2. Fast electron-hole recombination supports radiative electron-hole recombination while suppresses the non-radiative energy transfer of electrons and causes high PL intensity. However, according to the energy level diagram, Nano-MoS2 with minimal electron-hole recombination rate is more favorable for O2/O2–,.OH/ OH– and.OH/H2O reactions that facilitate MB degradation. Photocatalytic activity of catalysts were confirmed by measuring the photocurrent from a simple custom-made two-electrode water photolysis cell where the nanocatalysts were dispersed in electrolyte. Lead and steel rods were used as electrodes. Multimeter was used to measure current. Nano-MoS2 exhibited better performance with a maximum photocurrent of 141 µA. Influence of green C Dots in energy levels, PL and photocatalysis of MoS2 and mechanisms of PL and degradation of MB are thoroughly investigated in this article.

COF-Topological Quantum Material Nano-heterostructure for CO2 to Syngas Production under Visible Light.

Efficient solar-driven syngas production (CO+H2 mixture) from CO2 and H2O with a suitable photocatalyst and fundamental understanding of the reaction mechanism are the desired approach towards the carbon recycling process. Herein, we report the design and development of an unique COF-topological quantum material nano-heterostructure, COF@TI with a newly synthesized donor-acceptor based COF and two dimensional (2D) nanosheets of strong topological insulator (TI), PbBi2Te4. The intrinsic robust metallic surfaces of the TI act as electron reservoir, minimising the fast electron-hole recombination process, and the presence of 6s2 lone pairs in Pb2+ and Bi3+ in the TI helps for efficient CO2 binding, which are responsible for boosting overall catalytic activity. In variable ratio of acetonitrile-water (MeCN : H2O) solvent mixture COF@TI produces syngas with different ratios of CO and H2. COF@TI nano-heterostructure enables to produce higher amount of syngas with more controllable ratios of CO and H2 compared to pristine COF. The electron transfer route from COF to TI was realized from Kelvin probe force microscopy (KPFM) analysis, charge density difference calculation, excited state lifetime and photoelectrochemical measurements. Finally, a probable mechanistic pathway has been established after identifying the catalytic sites and reaction intermediates by in situ DRIFTS study and DFT calculation.

A universal dual-channel ratiometric photoelectrochemical sensing platform with integrated ionic liquid-sensitized In2S3@BiOBr0.8I0.2/PEDOT photoanode and Cu@Cu2O photocathode

The generation, separation and interfacial reaction of photogenerated carriers are crucial to realize efficient photoelectrochemical (PEC) detection. However, fast electron-hole recombination and slow interfacial reaction dynamics remain challenges for constructing advanced PEC platforms. Herein, ionic liquids (i.e. 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm]BF4) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm]PF6)) are introduced as morphology modulator and supporting electrolyte into the synthesis of Cu@Cu2O and the heterogeneous combination of In2S3@BiOBr0.8I0.2 with electrochemically polymerized 3,4-ethylenedioxythiophene (PEDOT), for constructing a PEC sensing platform. As their unique microstructure, the formed p-n junction and the doped ionic liquids benefit the charge separation/transfer, the resulted [BMIm]BF4 − In2S3@BiOBr0.8I0.2/ [BMIm]PF6 − PEDOT/AuNPs (i.e. Au nanoparticles) photoanode material and [BMIm]PF6 − Cu@Cu2O photocathode material show enhanced interfacial reaction dynamics and photo-conversion efficiency. In order to improve the accuracy and reliability of PEC detection, the potentially responsive photocathode and photoanode materials are integrated on the same indium tin oxide electrode for potential-resolved two-channel ratiometric PEC detection. By tuning the bias voltage, the cathode and anode currents can be well distinguished, and dual signals can be obtained during a single detection run and used as reference for each other. Then, a biometric sensing platform for vascular endothelial growth factor and epithelial cell adhesion factor is constructed by combining with aptamers and it demonstrates excellent analytical performance. Compared with the traditional PEC biosensors, the platform can effectively eliminate the detection errors caused by the fluctuation of excitation light intensity and preparation conditions. In addition, the platform is universal, by changing the recognition element, it can be applied to the detection of a variety of biomarkers.

Effect of Codoping Zinc Oxide Nanoparticles with Sulfur and Nitrogen on Its Energy Bandgap, Antioxidant Properties, and Antibacterial Activity

Zinc oxide nanoparticles (ZnO-NPs) are used in various fields such as industrial, environmental remediation, catalytic, and antibacterial applications. However, their ability to absorb visible light is limited due to their high-energy bandgap and fast electron-hole recombination, which restricts their use. To enhance the efficiency of ZnO-NPs in medical and other applications, surface functionality can be modified through doping. Here, we investigated the effects of S and N doping on the energy bandgap of ZnO-NP and their antimicrobial and antioxidant activities. The results showed that the optical bandgap energy of pure ZnO-NPs was 2.98 eV while that of 6% N-ZnO, 4% S-ZnO, and S4-N6-ZnO was 2.78, 2.69, and 2.63 eV, respectively. The energy bandgap reduction is attributed to the changes in the electronic level of zinc oxide as the result of doping. The crystal size of pure ZnO-NPs, 6% N-ZnO, 4% S-ZnO, and S4-N6-ZnO was 29.06, 27.05, 29.02, and 25.06 nm, respectively, as calculated from XRD data using FWHM. Following the bandgap and particle size reduction, the antimicrobial activities of the dual-doped ZnO-NPs surpassed that of the pure ZnO-NPs. Moreover, dual doping improved the antioxidant activity of ZnO-NPs from 52.45% to 88.89% for the optimized concentration. Therefore, incorporating S and N as dual dopants can enhance the functionality and efficiency of ZnO-NPs in various fields.

Synthesis and photocatalytic activity of cation-doped titanium oxynitrides (Ti2.85-xMxO4N, M = Zn, Co, Cu).

The utilization of visible light in photocatalytic semiconductors is restricted by the presence of a wide energy bandgap and fast electron-hole pair recombination. This study aims to address this limitation by synthesizing nitrogen- and cation-doped Cs0.68Ti1.83O4 at varying temperatures and subsequently analyzing the photocatalytic performance and mechanism. The optical experimental findings indicate that the co-doping of N/M (where M represents Zn, Co, or Cu) can considerably decrease the energy bandgap of Cs0.68Ti1.83O4 by regulating the energy band position and effectively suppressing the recombination of photogenerated carriers. Notably, at a temperature of 600 °C, the N/Cu co-doped Cs0.68Ti1.83O4 exhibits the smallest energy bandgap of 1.98 eV, thereby demonstrating superior photocatalytic performance. The photocatalytic degradation test of pollutants shows that the degradation efficiency of methylene blue solution in 120 minutes under light was 84%, which is the result of the interaction between ˙OH and ˙O2-. This study provides new possibilities for the study of co-doped modified photocatalytic materials.

Efficient removal of methyl orange and ciprofloxacin by reusable Eu-TiO2/PVDF membranes with adsorption and photocatalysis methods.

The presence of methyl orange (MO) and ciprofloxacin (CIP) in wastewater poses a serious threat to the environment and human health. Titanium dioxide nanoparticles (TiO2 NPs) are widely studied as photocatalysts for wastewater treatment. However, TiO2 NPs have the drawbacks of high energy required for activation, fast electron-hole pair recombination and difficulty in recovering from water. To overcome these problems, europium decorated titanium dioxide/poly(vinylidene fluoride) (Eu-TiO2/PVDF) membranes were successful prepared in this work by combining the modified sol-gel method and the immersion phase inversion method. The Eu-TiO2/PVDF membranes obtained with the increase of Eu-TiO2 NPs content during the preparation process were named M1, M2 and M3, respectively. The pure PVDF membrane without the addition of Eu-TiO2 NPs was named M0, which was prepared by the immersion phase inversion method and served as a reference. The prepared Eu-TiO2/PVDF membranes could not only adsorb MO, but also degrade CIP under visible-light irradiation. Moreover, the Eu-TiO2/PVDF membranes exhibited adsorption-photocatalytic activity towards a mixture of MO and CIP under visible-light irradiation. Last but not the least, the Eu-TiO2/PVDF membranes exhibited excellent recyclability and reusability, opening the avenue for a possible use of these membranes in sewage-treatment plants.

Surface plasmon resonance effect of silver decorated on BiOCl and its enhanced sunlight-active photodegradation of rhodamine B (RhB) dye and ofloxacin (OFL) antibiotic

Fast electron-hole recombination rate is the major problem concerning low photocatalytic performance of the UV-active BiOCl photocatalyst. To overcome this drawback, decoration of noble metals on the surface of semiconducting photocatalysts can be regarded as one of the promising strategies to improve the photoactivity due to a synergy of heterojunction formation and surface plasmon resonance effect. However, the huge dosage (larger than 10 wt%) of the noble metal incorporated on photocatalyst surface causes high cost in production of the final product. In this work, solvothermally grown BiOCl photocatalyst was decorated with low silver metal loading of 2.5–10 wt%. The tetragonal 2.5 wt%Ag/BiOCl photocatalyst exhibited complete photodegradation of Rhodamin B (RhB) dye and ofloxacin (OFL) antibiotic under natural solar light. The enhancement of the resultant photocatalytic efficiency is possibly due to increasing of charge carrier separation efficiency at the interface together with the formation of the Schottky barrier at the Ag/BiOCl interface so that an improvement in quantum efficiency and an increase in the photocatalytic activity are expected. In addition, well dispersion of silver on BiOCl also leads to red shift in the absorption of light toward visible regime. This is due to the local surface plasmon resonance (LSPR) effect of Ag on BiOCl surface. The synthesized Ag/BiOCl photocatalyst displays enhanced photocatalytic activity with great structural stability after five times of use indicating its excellent cycling ability. The present finding offers a new pathway to create a silver decorated BiOCl for complete removal of harmful dye and antibiotic in aqueous solution. The treatment of toxic organic pollutants in the natural water can be done very easily by utilization of the green technology based on photocatalytic method with the beneficial of abundant solar energy.

Synergistic doping with Ag, CdO, and ZnO to overcome electron-hole recombination in TiO2 photocatalysis for effective water photo splitting reaction.

This manuscript is dedicated to a comprehensive exploration of the multifaceted challenge of fast electron-hole recombination in titanium dioxide photocatalysis, with a primary focus on its critical role in advancing the field of water photo splitting. To address this challenge, three prominent approaches-Schottky barriers, Z-scheme systems, and type II heterojunctions-were rigorously investigated for their potential to ameliorate TiO2's photocatalytic performance toward water photo splitting. Three distinct dopants-silver, cadmium oxide, and zinc oxide-were strategically employed. This research also delved into the dynamic interplay between these dopants, analyzing the synergetic effects that arise from binary and tertiary doping configurations. The results concluded that incorporation of Ag, CdO, and ZnO dopants effectively countered the fast electron-hole recombination problem in TiO2 NPs. Ag emerged as a critical contributor at higher temperatures, significantly enhancing photocatalytic performance. The photocatalytic system exhibited a departure from Arrhenius behavior, with an optimal temperature of 40°C. Binary doping systems, particularly those combining CdO and ZnO, demonstrated exceptional photocatalytic activity at lower temperatures. However, the ternary doping configuration involving Ag, CdO, and ZnO proved to be the most promising, surpassing many functional materials. In sum, this study offers valuable insights into how Schottky barriers, Z-scheme systems, and type II heterojunctions, in conjunction with specific dopants, can overcome the electron-hole recombination challenge in TiO2-based photocatalysis. The results underscore the potential of the proposed ternary doping system to revolutionize photocatalytic water splitting for efficient green hydrogen production, significantly advancing the field's understanding and potential for sustainable energy applications.

ZnO-Bi2O3 Heterostructured Composite for the Photocatalytic Degradation of Orange 16 Reactive Dye: Synergistic Effect of UV Irradiation and Hydrogen Peroxide

The development of semiconductor photocatalysts has recently witnessed notable momentum in the photocatalytic degradation of organic pollutants. ZnO is one of the most widely used photocatalysts; however, its activity is limited by the inefficient absorption of visible light and the fast electron–hole recombination. The incorporation of another metal or semiconductor with ZnO boosts its performance. In this present study, a heterostructured ZnO-Bi2O3 composite was synthesized via a simple co-precipitation method and was investigated for the UV-driven photocatalytic degradation of the Reactive Orange 16 (RO16), a model textile dye. The successful fabrication of ZnO-Bi2O3 microstructures with crystalline nature was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX). The discoloration of the dye solution was quantified using UV–Vis spectroscopy to determine the photocatalytic efficiency. The photocatalytic activity results demonstrated that the photodegradation at ZnO-Bi2O3 heterojunction was more efficient and 300 and 33% faster than individual Bi2O3 and ZnO catalysts, respectively, an effect that is indicative of a synergistic effect. In the presence of ZnO-Bi2O3 particles, the UV light-driven activity for RO16 degradation was twice as high as in its absence. The influence of adding the oxidant H2O2 on the UV-induced photocatalytic degradation was investigated and the results revealed a two-time increase in the photocatalytic activity of ZnO-Bi2O3 compared to UV irradiation alone, which could be ascribed to a summative degradative effect between UV and H2O2. Hence, this approach holds the potential for environmentally friendly wastewater treatment.

Constructing C-doped TiO2/β-Bi2O3 hybrids Z-scheme heterojunction for enhanced CO2 photoreduction

Rational fabricating advanced photocatalysts to recycle CO2 into solar fuel is one of the most promising approaches to simultaneously address energy shortages and global warming. TiO2 has been widely used in photocatalytic CO2 reduction due to its abundant reserves, non-toxicity and harmlessness etc. However, it remains significantly challenging for practical applications due to the fast electron-hole recombination. Herein, we design a direct TiO2 based Z-Scheme heterojunction by self-assembly of C-doped TiO2 nanoparticles on 3D hierarchical petal of flower-like β-Bi2O3 (C-TiO2/β-Bi2O3). In situ electron paramagnetic resonance tests, in situ X-ray photoelectron spectroscopy and theoretical calculations reveal that electrons are transferred from β-Bi2O3 to C-TiO2 due to the formation of Z-Scheme heterojunction, which greatly accelerates the separation of photogenerated carriers to promote efficient CO2 photoreduction. Ultimately, the optimal heterojunction shows significantly enhanced photocatalytic activity for CO2 reduction to CO (31.07 μmol g–1 h−1) compared to the pure TiO2 (3.28 μmol g–1 h−1) without using any photosensitizers and sacrificial agents. This work provides a unique insight to design direct Z-Scheme heterojunctions and delivers a promising photocatalyst for overcoming global warming and energy-supply issues.

Fabrication of visible light responsive nitrogen-doped carbon quantum dots/MIL-101(Cr) composites for enhanced photodegradation of Rhodamine B

In this study, an environmentally friendly hydrothermal process was successfully utilized for the fabrication of MIL-101(Cr) (MIL-Cr) and nitrogen-doped carbon quantum dots (N-CQDs) without employing toxic and hazardous hydrofluoric acid and organic solvents. Then, a simple solvent-deposition technique was used to prepare MIL-Cr/N-CQDs(x) composites without requiring specialized equipment. To assess the photocatalytic capabilities of the synthesized materials, Rhodamine B (RhB) was chosen as one of the wastewater toxic organic dye pollutants for photo-degradation experiments. The optimum amount of N-CQDs in composite structure was determined by mixing different volumes of N-CQDs with MIL-Cr, in which MIL-Cr/N-CQDs(2) composite exhibited the highest photocatalytic performance (95%) under visible light illumination. Also, all composites showed better photocatalytic activity in comparison with pristine MOF and N-CQDs individually because N-CQDs can operate as electron acceptors when coupled with MOF, which can prevent the fast electron-hole recombination and increase the visible light absorption. Based on the results of the kinetic investigation, the MIL-Cr/N-CQDs(2) depicted the highest kinetic rate, which is 2.63 and 9.5 times larger than pristine MIL-Cr and N-CQDs under the same experimental conditions. Furthermore, a photocatalytic mechanism was postulated through reactive species scavenging experiments, and it was found that •OH and photo-generated h+ were crucial to the degradation process.

Atmospheric Pressure Plasma Deposition of Hybrid Nanocomposite Coatings Containing TiO2 and Carbon-Based Nanomaterials

Among the different applications of TiO2, its use for the photocatalytic abatement of organic pollutants has been demonstrated particularly relevant. However, the wide band gap (3.2 eV), which requires UV irradiation for activation, and the fast electron-hole recombination rate of this n-type semiconductor limit its photocatalytic performance. A strategy to overcome these limitations relies on the realization of a nanocomposite that combines TiO2 nanoparticles with carbon-based nanomaterials, such as rGO (reduced graphene oxide) and fullerene (C60). On the other hand, the design and realization of coatings formed of such TiO2-based nanocomposite coatings are essential to make them suitable for their technological applications, including those in the environmental field. In this work, aerosol-assisted atmospheric pressure plasma deposition of nanocomposite coatings containing both TiO2 nanoparticles and carbon-based nanomaterials, as rGO or C60, in a siloxane matrix is reported. The chemical composition and morphology of the deposited films were investigated for the different types of prepared nanocomposites by means of FT-IR, FEG-SEM, and TEM analyses. The photocatalytic activity of the nanocomposite coatings was evaluated through monitoring the photodegradation of methylene blue (MB) as a model organic pollutant. Results demonstrate that the nanocomposite coatings embedding rGO or C60 show enhanced photocatalytic performance with respect to the TiO2 counterpart. In particular, TiO2/C60 nanocomposites allow to achieve 85% MB degradation upon 180 min of UV irradiation.

G-C3N4/MnFe2O4 p-n hollow stratified heterojunction to improve the photocatalytic CO2 reduction activity

Graphite carbon nitride (g-C3N4) is considered as a promising photocatalyst for CO2 reduction. However, they have problems such as small surface area and fast electron hole recombination rate, so how to improve the photocatalytic efficiency of g-C3N4 remains a great challenge. In this paper, g-C3N4/MnFe2O4 p-n heterojunction composites were synthesized successfully, and their photocatalytic activity for CO2 reduction was tested. We constructed g-C3N4 nanotubes to increase its specific surface area and increase the active sites available for reaction. The structure of p-n heterojunction promotes electron hole separation. The results indicate that under visible light irradiation, CO yield of g-C3N4/MnFe2O4 composite can reach 1136.8 μmol h−1 g−1 when the molar ratio of g-C3N4 microtubules to MnFe2O4 is 10:3, which is 14 times of g-C3N4 microtubules and 29 times of g-C3N4. This study provides some guidance for the design of g-C3N4 based heterojunction.

Enhanced photocatalytic H2 production performance of Au@Cu2O-Ta3N5 discrete ternary core-shell spheres

Ta3N5 owns a theoretical band structure for photocatalytic H2 production. However, the practical production performance is unsatisfactory, which is probably attributed to fast electron-hole recombination. In this study, we design novel Au@Cu2O-Ta3N5 discrete core-shell ternary nanospheres for highly efficient photocatalytic H2 production by splitting water. This catalyst is prepared by coating Cu2O on the Au nanoparticles of Au-Ta3N5 nanospheres via an illumination method. The core-shell structure irradiated for 2 h (Au@Cu2O-Ta3N5 2 h) shows higher photocatalytic H2 production rate (65.78 μmol·g−1·h−1) than Au-Ta3N5 (0.5% Au-Ta3N5, 22.43 μmol·g−1·h−1), Au-Cu2O-Ta3N5 (32.24 μmol·g−1·h−1), and fully covered Au@Cu2O-Ta3N5 5 h sample (51.27 μmol·g−1·h−1). The enhanced performance is attributed to the unique discrete core-shell structure, designed appropriate band structure, low charge transfer resistance, and high electron-hole separation ability. This study provides a novel Ta3N5-based ternary core-shell structure for high-performance H2 production.

Investigations of Carrier Transport Mechanisms in Perovskite Solar Cells with Different Types of ZnO Layer

The interfacial mechanisms of carrier transport in perovskite solar cells with different types of zinc oxide (hydrothermal solution method (ZnOHT) and sol–gel method (ZnOSG)) are investigated. Power conversion efficiencies of the devices with ZnOHT and ZnOSG layers are 18.66% and 13.39%, respectively, which are significantly varied by the rates of photoelectron injection and electron–hole recombination. The space‐charge‐limited current and electrochemical impedance measurements both show that the device utilizing ZnOHT layer exhibits fewer internal defects compared to that with ZnOSG layer. Via transient absorption spectroscopy, faster injection of photoelectrons from the active layer to the transport layer occurs at ≈3.8 ps in the devices with ZnOHT layer, which is half of the value observed in devices with ZnOSG layer and benefits the device performance. Moreover, a faster electron–hole recombination in devices with ZnOSG degrades device performance due to the trap states in high‐defect‐density devices. Both device performances stably maintain a level higher than 98% of the initial value after over 600 h without encapsulation in glove box. Finally, the structural and electronic properties of charge transport layer can be controlled by the methods of preparation and ZnOHT shows great promise in enhancing perovskite solar cell efficiency with relatively low‐temperature process.

Ab Initio Nonadiabatic Molecular Dynamics of Ultrafast Demagnetization in Iron.

Ultrafast demagnetization in magnetic metals is the key to spintronics devices. Taking iron as a prototypical system, we investigate the demagnetization mechanism by simulating the charge and spin dynamics using nonadiabatic molecular dynamics in the presence of explicit spin-orbit coupling (SOC). Strong SOC drives ultrafast spin-flip of electrons and holes, which trigger demagnetization and remagnetization, respectively. Their confrontation decreases the demagnetization ratio and finishes the demagnetization within 167 fs, agreeing with the experimental time scale. The joint spin-flip of electrons and holes correlated with the electron-phonon coupling-induced fast electron-hole recombination further decreases the maximum demagnetization ratio, below 5% of experimental value. Although the Elliott-Yafet electron-phonon scattering model can rationalize the ultrafast spin-flip process, it fails to reproduce the experimental maximum demagnetization ratio. The study suggests the key role of SOC on spin dynamics and emphasizes the interplay between SOC and electron-phonon interactions on the ultrafast demagnetization.