Morphology regulated Bi2WO6 nanoparticles on TiO2 nanotubes by solvothermal Sb3+ doping as effective photocatalysts for wastewater treatment

Design of Bismuth Tungstate Bi2WO6 Photocatalyst for Enhanced and Environmentally Friendly Organic Pollutant Degradation

In this study, a chemical precipitation approach was adopted to produce a photocatalyst based on bismuth tungstate Bi2WO6 for enhanced and environmentally friendly organic pollutant degradation. Various tools such as X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), optical spectroscopy and X-ray photoelectron spectroscopy, were employed to assess the structural and morphological properties. Hence, the XRD profiles showed a well crystallized Bi2WO6 orthorhombic phase. The photocatalytic performance of the resulting photocatalyst was assessed by the decomposition of Rhodamine B (RhB) and methyl orange (MO) with a decomposition efficiency of 97 and 92%, along with the highest chemical oxygen demand of 82 and 79% during 120 min of illumination, respectively. The principal novelty of the present work is to focus on the changes in the crystalline structure, the morphology, and the optical and the photoelectrochemical characteristics of the Bi2WO6, by tuning the annealing temperature of the designed photocatalyst. Such physicochemical property changes in the as-prepared photocatalyst will affect in turn its photocatalytic activity toward the organic pollutant decomposition. The photocatalytic mechanism was elaborated based on electrochemical impedance spectroscopy, photocurrent analysis, photoluminescence spectroscopy, and radical trapping measurements. The overall data indicate that the superoxide O2•- and holes h+ are the principal species responsible for the pollutant photodegradation.

Construction of Z-scheme Bi2O3/CeO2 heterojunction for enhanced photocatalytic capacity of TiO2 NTs

Photocatalytic technology was recognized to be the effective strategy to overcome the obstacles of environment pollution and energy shortage, and the novel photocatalyst design/construction was the key point for photocatalytic performance improvement. In this paper, the Z-scheme Bi2O3 and CeO2 heterojunction was constructed on TiO2 nanotube arrays (TiO2 NTs) by the hydrothermal deposition method. The Bi2O3-CeO2 cosensitization not only extended the solar absorption region but also accelerated the photoelectron separation and transfer, finally enhanced the photocatalytic property. The photocatalysts exhibited the high RhB/MB photodegradation and Cr(VI) reduction, and the photoelectric conversion and photocatalytic H2 evolution were also preeminent. The Z-scheme heterojunction construction was recognized to be the reason for the high photoactivity, and O2- and OH radicals were formed and investigated as the main active species for the dye photodegradation. The work gives the simple method and idea to construct novel ternary Z-scheme heterojunctions with high photocatalytic capacity for environment remediation and new energy development.

Remediation of wastewater by biosynthesized manganese oxide nanoparticles and its effects on development of wheat seedlings

Introduction

Nanoparticles play a vital role in environmental remediation on a global scale. In recent years, there has been an increasing demand to utilize nanoparticles in wastewater treatment due to their remarkable physiochemical properties.

Methods

In the current study, manganese oxide nanoparticles (MnO-NPs) were synthesized from the Bacillus flexus strain and characterized by UV/Vis spectroscopy, X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy.

Results

The objective of this study was to evaluate the potential of biosynthesized MnO-NPs to treat wastewater. Results showed the photocatalytic degradation and adsorption potential of MnO-NPs for chemical oxygen demand, sulfate, and phosphate were 79%, 64%, and 64.5%, respectively, depicting the potential of MnO-NPs to effectively reduce pollutants in wastewater. The treated wastewater was further utilized for the cultivation of wheat seedlings through a pot experiment. It was observed that the application of treated wastewater showed a significant increase in growth, physiological, and antioxidant attributes. However, the application of treated wastewater led to a significant decrease in oxidative stress by 40%.

Discussion

It can be concluded that the application of MnO-NPs is a promising choice to treat wastewater as it has the potential to enhance the growth, physiological, and antioxidant activities of wheat seedlings.

Flexible, recoverable, and efficient photocatalysts: MoS2/TiO2 heterojunctions grown on amorphous carbon-coated carbon textiles

Most traditional powder photocatalysts are not easily recovered. Herein, we report a flexible and recoverable photocatalyst with superior photocatalytic activity, in which MoS2/TiO2 heterojunctions are grown on amorphous carbon-coated carbon textiles (CT@C-MoS2/TiO2). Recoverable CT@C-MoS2/TiO2 textile was used to degrade 10 mg L-1 rhodamine B, leading to a degradation rate of up to 98.8 % within 30 min. Such a degradation rate is much higher than that of most of the reported studies. A density functional theory (DFT) calculation results illustrate charge transfer mechanism inside TiO2-C, MoS2-C, and MoS2/TiO2 heterojunctions, which shows that CT@C-MoS2/TiO2 textile with three electron separation channels has a high photogenerated carrier separation rate, which remarkably enhances the photocatalytic activity. Our work provides a novel strategy to design an efficient and recoverable photocatalyst with high activity.

Preparation of a novel metal-free polypyrrole-red phosphorus adsorbent for efficient removal of Cr(VI) from aqueous solution

The toxicity and carcinogenicity of Cr(VI) makes it a major threat to the health of animals and people. However, how to efficiently remove Cr(VI) still faces important challenges. In this study, a new metal-free polypyrrole-red phosphorus (PPy-RP) composite is successfully synthesized by in-situ oxidation polymerization for Cr(VI) removal from wastewater. The maximum adsorption capacity (q_m) of Cr(VI) on PPy-RP-1 is 513.2 mg/g when the pH value is 2, which is far superior to RP nanosheets (207.8 mg/g) and PPy (294.9 mg/g). The improved q_m can be ascribe to the good dispersion and increased specific surface area of PPy-RP adsorbent. Encouragingly, PPy-RP adsorbent still exhibits excellent stability after 7 cycles tests without a significant decline in removal efficiency, and remain above 81.4%. Based on the fittings of adsorption isotherms and kinetics, the process conforms to the pseudo-first-order kinetic model and the single-layer adsorption of the Langmuir model with an R² value of 0.98533. The adsorption process is chemical and monolayer. The experimental result demonstrates that the PPy-RP can efficient removal Cr(VI) by electrostatic attraction and complexation reaction (formation of N-Cr(VI) bond) through the PPy on the surface. The results of this study indicate that PPy-RP is a promising adsorbent to remove the Cr(IV).

Hybrid Composite of Sn(IV)-Porphyrin and Mesoporous Structure for Enhanced Visible Light Photocatalytic Degradation of Organic Dyes

Two hybrid composites (SnP@MCM-41 and SnP@SiO₂) were fabricated by chemical adsorption of (trans-dihydroxo)(5,10,15,20-tetraphenylporphyrinato)tin(IV) (SnP) on mesoporous structured Mobil Composition of Matter No. 41 (MCM-41) and SiO₂ nanoparticles. These materials were characterized by Fourier-transform infrared spectroscopy, ultraviolet-visible spectroscopy, fluorescence spectroscopy, transmission electron microscopy, and field-emission scanning electron microscopy techniques. The incorporation of SnP into MCM-41 and SiO₂ supports efficient photocatalytic degradation of the anionic erioglaucine, cationic rhodamine B, and neutral m-cresol purple dyes under visible light irradiation in an aqueous solution. The performances of degradation of these dyes by these photocatalysts under visible light irradiation varied from 87 to 95%. The pseudo-first-order degradation rate constant of organic dyes for SnP@MCM-41 was higher than those of SnP@SiO₂ and SnP. These visible light photocatalysts showed remarkable stability and reliable reusability.

Design of an interface heating device based on polydivinylbenzene/SiO2/Bi2WO6 and its visible light response performance for water purification

Environmental pollution and the shortage of drinking water are the challenges that mankind is facing. Solar interface evaporation technology has been demonstrated as an important method for producing clean water, but its application to sewage still faces problems, mainly manifested in solubility and oily pollutants. Therefore, an evaporator device contains a superhydrophobic Bi₂WO₆ felt floating layer, a filter paper hydrophilic layer, and a copper foam/CuO photothermal layer, of which the water contact angle of the superhydrophobic felt can reach 159°. The floating layer not only has the ability to adsorb n-hexane but the Rh B degradation can also be realized under indoor/outdoor light conditions. The carrier life of Bi₂WO₆ is 28.8 ns. A copper foam/CuO photothermal layer prepared through a low-temperature treatment is combined with the floating and hydrophilic layer to obtain an evaporation rate of 1.53 kg m^-2 h^-1.

Degradation of Dye Wastewater by a Novel mBT-MPR Visible Light Photocatalytic System

The high efficiency and low consumption green wastewater treatment technology has important practical significance for the recycling of printing and dyeing wastewater. The efficiency of visible light catalytic degradation of organics is greatly affected by the performance of the catalyst and the photo reactor. Therefore, Bi₂WO₆/TiO₂/Fe₃O₄ (mBT) visible light photocatalyst was accurately prepared by the ammonia iron double drop method. In order to improve the photodegradation efficiency, a tubular magnetic field-controlled photocatalytic reactor (MPR) was developed. The novel mBT-MPR visible light photocatalytic system was proposed to treat RhB simulated wastewater. The experimental results showed that when the dosage of mBT catalyst was 1 g/L and visible light was irradiated for 60 min, the average removal rate of rhodamine B (RhB) with initial an concentration of 10 mg/L in the simulated wastewater for four times was 91.7%. The mBT-MPR visible light photocatalysis system is a green and efficient treatment technology for organic pollutants in water with simple operation, low energy consumption, and no need for catalyst separation.

Advances in Bi2WO6-Based Photocatalysts for Degradation of Organic Pollutants

With the rapid development of modern industries, water pollution has become an urgent problem that endangers the health of human and wild animals. The photocatalysis technique is considered an environmentally friendly strategy for removing organic pollutants in wastewater. As an important member of Bi-series semiconductors, Bi₂WO₆ is widely used for fabricating high-performance photocatalysts. In this review, the recent advances of Bi₂WO₆-based photocatalysts are summarized. First, the controllable synthesis, surface modification and heteroatom doping of Bi₂WO₆ are introduced. In the respect of Bi₂WO₆-based composites, existing Bi₂WO₆-containing binary composites are classified into six types, including Bi₂WO₆/carbon or MOF composite, Bi₂WO₆/g-C₃N₄ composite, Bi₂WO₆/metal oxides composite, Bi₂WO₆/metal sulfides composite, Bi₂WO₆/Bi-series composite, and Bi₂WO₆/metal tungstates composite. Bi₂WO₆-based ternary composites are classified into four types, including Bi₂WO₆/g-C₃N₄/X, Bi₂WO₆/carbon/X, Bi₂WO₆/Au or Ag-based materials/X, and Bi₂WO₆/Bi-series semiconductors/X. The design, microstructure, and photocatalytic performance of Bi₂WO₆-based binary and ternary composites are highlighted. Finally, aimed at the existing problems in Bi₂WO₆-based photocatalysts, some solutions and promising research trends are proposed that would provide theoretical and practical guidelines for developing high-performance Bi₂WO₆-based photocatalysts.

Engineering hierarchical FeS2/TiO2 nanotubes on Ti mesh as a tailorable flow-through catalyst belt for all-day-active degradation of organic pollutants and pathogens

The increasing organic and microbiological pollutions in fresh water caused by human activities and industrial development have become a global concern nowadays. In this study, three-dimensional (3D) hierarchical FeS₂/TiO₂ structures with nanotube geometries were grown on a Ti mesh (M-TNTAs-FeS₂). Benefitting from the abundant available reactive sites on the open 3D micro/nanoporous structures, excellent photocatalytic activity of FeS₂/TiO₂ heterostructure in solar light, and satisfactory Fenton activity of FeS₂, the obtained M-TNTAs-FeS₂ exhibits outstanding performance as an all-day-active catalyst. Importantly, flexible meshes can be easily tailored and enveloped into fluorinated ethylene propylene (FEP) pockets in a series as a flow-through belt for large-capacitance applications (998 L m^-2 at a flow rate of 417 L m^-2 h^-1 for a four-pockets belt), as indicated by the degradation of azo dyes, antibiotics, pesticides, and pathogens. This study may inspire a new tailorable catalyst design for a promising point-of-use purification device.

Construction of Z-scheme CdS/Ag/TiO2 NTs photocatalysts for photocatalytic dye degradation and hydrogen evolution

The ternary CdS/Ag/TiO₂ NTs photocatalysts with indirect Z-scheme heterojunctions were synthesized by the photoreduction deposition of Ag and successive ionic layer adsorption and reaction (SILAR) of CdS on TiO₂ nanotube arrays (TiO₂ NTs). The elemental composition, microstructure, photoresponse and photoelectrochemical property of the photocatalyst were systematically characterized. The results proved that compared with binary heterojunction, the light absorption range of the ternary CdS/Ag/TiO₂ NTs photocatalyst was significantly extended, and the photoelectron transportation efficiency was improved. Under sunlight irradiation, the photocatalytic capacity was verified by investigating the photodegradation of MB and RhB dyes. The CdS/Ag/TiO₂ NTs exhibited the optimal photocatalytic performance with the degradation efficiency of 82.24% for RhB and 100% for MB. The synthesized CdS/Ag/TiO₂ NTs had high photocatalytic hydrogen evolution capacity and stability, and the hydrogen production reached 806.33 μmol·cm^-2. Based on the results of electron spin resonance spectroscopy (ESR) and free radical trapping, the photocatalytic reaction mechanism was explained. The synthesis of ternary CdS/Ag/TiO₂ NTs provides a practical reference and guidance for designing high-efficient photocatalysts with Z-scheme heterojunctions toward solar energy development for H₂ generation, pollutant remediation and photoelectric conversion.

Hierarchical Bi2WO6/TiO2-nanotube composites derived from natural cellulose for visible-light photocatalytic treatment of pollutants

A series of Bi2WO6/TiO2-nanotube (Bi2WO6/TiO2-NT) heterostructured composites were prepared by utilizing natural cellulose (e.g., laboratory filter paper) as the structural template. The obtained nanoarchitectonics, namely Bi2WO6/TiO2-NT nanocomposites, displayed three-dimensionally interwoven structures which replicated the initial cellulose template. The composite Bi2WO6/TiO2-NT nanotubes were formed by TiO2 nanotubes that uniformly anchored with Bi2WO6 nanoparticles of various densities on the surface. The composites exhibited improved photocatalytic activities toward the reduction of Cr(VI) and degradation of rhodamine B under visible light (λ > 420 nm), which were attributed to the uniform anchoring of Bi2WO6 nanoparticles on TiO2 nanotubes, as well as strong mutual effects and well-proportioned formation of heterostructures in between the Bi2WO6 and TiO2 phases. These improvements arose from the cellulose-derived unique structures, leading to an enhanced absorption of visible light together with an accelerated separation and transfer of the photogenerated electron-hole pairs of the nanocomposites, which resulted in increased effective amounts of photogenerated carriers for the photocatalytic reactions. It was demonstrated that the photoinduced electrons dominated the photocatalytic reduction of Cr(VI), while hydroxyl radicals and reactive holes contributed to the photocatalytic degradation of rhodamine B.

Debunking the essential effect of temperature and voltage on the current curve and the nanotube morphology

The formation mechanism of anodic TiO2 nanotubes remains to be unclear till now. Many researchers study the influence of temperatures above 0 °C instead of below 0 °C. Few papers before have explained the relationship between the current-time curve and the morphology of the nanotubes. In this study, the innovative 'oxygen bubble model' and the ionic current and electronic current theories were introduced to explain the growth of nanotubes below 0 °C. The length of anodic TiO2 nanotubes at 15 °C, 0 °C, -10 °C were 1.28 μm, 0.93 μm and 0.21 μm, respectively, but the diameter of anodic TiO2 nanotubes was almost the same, at about 164 nm. When the temperature was low, the magnitude of electronic current and the ionic current was small, the mold effect was weak and nanotubes could not be formed. At the same time, this study shows that the dissolution reaction of the field-assisted solution theory has no electron gain or loss, and it has nothing to do with the current, which negates the field-assisted dissolution theory. A novel two-step anodization was used to verify the conclusion. It was found that nanotubes could be obtained when the anodizing current was decreasing or increasing. Also, ginseng-shaped nanotubes are formed at a particular voltage sequence. Based on the 'oxygen bubble model' and the ionic current and electronic current theories, the formation process of nanotubes of two-step anodization is explained clearly.

Hybrid Inorganic-Organic Visible-Light-Driven Microrobots Based on Donor-Acceptor Organic Polymer for Degradation of Toxic Psychoactive Substances

Light-driven microrobots based on organic semiconductors have received tremendous attention in the past few years due to their unique properties, such as ease of reactivity tunability, band-gap modulation, and low cost. However, their fabrication with defined morphologies is a very challenging task that results in amorphous microrobots with poor motion efficiencies. Herein, we present hybrid inorganic-organic photoactive microrobots with a tubular shape and based on the combination of a mesoporous silica template with an active polymer containing thiophene and triazine units (named as Tz-Th microrobots). Owing to their well-defined tubular structure, such Tz-Th microrobots showed efficient directional motion under fuel-free conditions. Depending on the accumulation of the polymer coating, these microdevices also exhibited stand-up and rotation motion. As a proof-of-concept, we use these hybrid microrobots for the capture and degradation of toxic psychoactive drugs commonly found in wastewater effluents such as methamphetamine derivatives. We found that the microrobots were able to decompose the drug into small organic fragments after 20 min of visible light irradiation, reaching total intermediates removal after 2 h. Therefore, this approach represents a versatile and low-cost strategy to fabricate structured organic microrobots with efficient directional motion by using inorganic materials as the robot chassis, thereby maintaining the superior photocatalytic performance usually associated with such organic polymers.

Oxygen vacancy BiO2-x/Bi2WO6 synchronous coupling with Bi metal for phenol removal via visible and near-infrared light irradiation

The introduction of oxygen-defects has been a versatile strategy to enhance photocatalysis efficiency. In this work, a 2D/3D Bi/BiO_2-x/Bi₂WO₆ heterojunction photocatalyst with rich oxygen-defective was in sequence prepared through a facile solvothermal method, which displays favorable photocatalytic activity towards organic contaminants under visible-NIR light irradiation. The enhancement in photocatalytic performance can be attributed to the synergistic effect between oxygen-vacancy-rich heterojunction and the localized surface plasmon resonance induced by metallic Bi. The functional group interaction, surface morphology, crystal structure, element composition, and tuned bandgap were investigated by FT-IR, SEM, Raman shift, ICP-MS, and XPS technique. The spectrum response performance of the photocatalyst was verified by UV-visible DRS analysis. Results of photodegradation experiments toward organic contaminants showed that the prepared photocatalyst can degrade 90% of phenol in 20 mins under visible-NIR light irradiation, both Z-scheme heterojunction and the introduction of Bi metal contribute to the enhancement in the photocatalytic activity. The results of the DFT calculation suggest that the valence band-edge hybridization within BiO_2-x and Bi₂WO₆ can effectively enhance the photocatalytic performance by increasing the migration efficiencies of electron-hole pairs. Moreover, a possible mechanism was proposed on the results of EIS, ESR and GC-MS tests. This work offers a novel insight for synthesizing efficient visible-NIR light photocatalysis by activating the semiconductors with Bi metal.

Mechanistic insights into 2,4-D photoelectrocatalytic removal from water with TiO2 nanotubes under dark and solar light irradiation

Removal of recalcitrant pollutants from water is a major challenge, to which the photoelectrocatalytic processes may be a solution. Applied potential plays a key role in the photocatalytic activity of the semiconductor. This paper investigated the effect of applied potential on the photoelectrocatalytic oxidation of 2,4-Dichlorophenoxyacetic acid (2,4-D) with TiO₂ nanotubular anodes under solar light irradiation. The process was investigated at constant potentials in different regions of the polarization curve: the ohmic region, the saturation region and in the region of the Schottky barrier breakdown. PEC tests were performed in aqueous solutions of 2,4-D, and in the presence of methanol or formic acid, as scavengers of OH^• radicals and holes. Results showed the main mechanism is oxidation by OH^• radicals from water oxidation, while runs with hole scavenger revealed a second mechanism of direct oxidation by holes photogenerated at the electrode surface, with high removal rates due to current doubling effect.

Simultaneously removal of Cr(VI) and Cd(II) from water using a flower-like primary battery nanosystem

In this study, a new flower-like primary battery nanosystem termed "Zn/CCP/ZIF-8" was prepared by depositing conductive carbon paint (CCP) and zeolitic imidazolate framework-8 (ZIF-8) on a zinc plate (Zn). Therein, CCP had good conductivity performance and adhesiveness, ZIF-8 and Zn/CCP/ZIF-8 possessed BET specific surface areas of 1909.5 and 1265.4 m²/g respectively. The results showed that the Zn/CCP/ZIF-8 nanosystem could effectively simultaneously adsorb hexavalent chromium (Cr(VI)) and bivalent cadmium (Cd(II)) from water. The system could promote the transfer of electrons from Zn to Cr(VI) and Cd(II) which were effectively reduced to trivalent chromium (Cr(III)) and cadmium (Cd), respectively. The resultant Zn/CCP/ZIF-8/Cr/Cd composite was then easily separated from water. The adsorption isotherm, kinetics, and thermodynamics of the prepared Zn/CCP/ZIF-8 for Cr(VI) and Cd(II) were investigated. An electrochemistry performance test proved that the Zn/CCP/ZIF-8 system was a primary battery. Notably, the Zn/CCP/ZIF-8 system substantially reduced the amounts of Cr(VI) and Cd(II) absorbed by zebrafish and water spinach, thus increasing food safety. The results of a rat test indicated that the Zn/CCP/ZIF-8 system possessed a high biosafety. This study provides a promising, eco-friendly, and facile method for the simultaneously treatment of Cr(VI) and Cd(II) contamination of water.

4-Hydroxyl-oxoisoaporphine, one small molecule as theranostic agent for simultaneous fluorescence imaging and photodynamic therapy as type II photosensitizer

Oxoisoaporphine (OA) is a plant phototoxin isolated from Menispermaceae, however, its weak fluorescence and low water solubility impede it for theranostics. We developed here 4-hydroxyl-oxoisoaporphine (OHOA), which has good singlet oxygen-generating ability (0.06), strong fluorescence (0.72) and improved water solubility. OHOA displays excellent fluorescence for cell imaging and exhibits light-induced cytotoxicity against cancer cell. In vitro model of human cervical carcinoma (HeLa) cell proved that singlet oxygen generated by OHOA triggered photosensitized oxidation reactions and exert toxic effect on tumor cells. The MTT assay using HeLa cells verified the low cytotoxicity of OHOA in the dark and high phototoxicity. Confocal experiment indicates that OHOA mainly distributes in mitochondria and western blotting demonstrated that OHOA induces cell apoptosis via the mitochondrial pathway in the presence of light. Our molecule provides an alternative choice as a theranostic agent against cancer cells which usually are in conflict with each other for most traditional theranostic agents.

Solvothermal preparation of Ti3+ self-doped TiO2-x nanotube arrays for enhanced photoelectrochemical performance

Ti³⁺ self-doped TiO_2-x nanotube arrays (TiO_2-x NTs) were prepared by solvothermal treatment in KBH₄ ethanol solution followed by calcination, and were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis diffusion reflection spectroscopy (DRS). The photoelectrochemical properties of TiO_2-x NTs prepared in different KBH₄ concentrations were investigated. The TiO_2-x NTs exhibited high visible light response, visible light photocurrent and photoelectrocatalytic activities. The active species and photocatalytic mechanism for the dye degradation were proposed, and the improved photoelectrochemical performance was attributed to the synergistic effect of the narrowed energy gap and enhanced electron transportation. The ability to improve the photoelectrochemical properties of TiO_2-x electrode materials should open up new opportunities for high-performance solar cells and photocatalysts.

Promoting superoxide generation in Bi2WO6 by less electronegative substitution for enhanced photocatalytic performance: an example of Te doping

Doping with elements with lower electronegativity, like Te, shifts the band potentials of Bi2WO6 to the point that superoxide radical generation is feasible. As a result, an optimum of 2.5 at% Te doping improves the activity of Bi2WO6 by 48 times.

Tuning wall thickness of TiO2 microtubes for an enhanced photocatalytic activity with thickness-dependent charge separation efficiency

TiO₂ microtubes with tunable wall thickness have been synthesized by a one-step electrospinning method linked with a calcination process. The wall thickness of TiO₂ microtubes can be easily tuned by altering the dosage of liquid paraffin. The influence of the thickness on the light-harvesting ability and separation efficiency of the photogenerated carriers was studied using ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, photoluminescence emission spectroscopy, and photocurrent density measurements. Results show that TiO₂ microtubes with an appropriate thickness exhibit enhanced light scattering effect, UV-vis light-harvesting ability, charge separation efficiency, and photocatalytic performance. The degradation rates of rhodamine B and 2,4-dinitrophenol by using TiO₂ microtubes synthesized at a dosage of 0.14 g/mL liquid paraffin are 99.9% within 60 min and 97.8% within 40 min, respectively, which are higher than most of the reported values. All these results suggest that our work provides an ideal strategy for adjusting the wall thickness of TiO₂ microtubes and new approach to enhance the photocatalytic performance of TiO₂.

Highly Efficient Photoelectrochemical Synthesis of Ammonia Using Plasmon-Enhanced Black Silicon under Ambient Conditions

Although photoelectrochemical synthesis of NH₃ is considered as an eco-friendly and sustainable process under ambient conditions, stable and highly efficient catalysts for the N₂ reduction reaction are still lacking because of the chemically inert nature of the triple bonds in elemental nitrogen and the competitive reaction of water reduction. In this paper, a photoelectrochemical N₂ reduction reaction route is proposed through combining black silicon and Ag nanoparticles using a simple deposition method. The synergetic effect of Ag nanoparticles and black Si significantly enhances the activity for the ammonia evolution reaction. The obtained Ag/bSi photocathode reaches a high Faraday efficiency of 40.6% and an NH₃ yield of 2.87 μmol h^-1 cm^-2 at -0.2 V versus the reversible hydrogen electrode in 0.1 M Na₂SO₄.