Fast photoelectro-reduction of CrVI over MoS2@TiO2 nanotubes on Ti wire

Insights into the electron activation mechanisms at the micro level by nano zero-valent iron supported by molybdenum disulfide (nZVI@MD) from preparation to application

Both molybdenum disulfide (MoS2) and nano zero-valent iron (nZVI) exhibit excellent adsorption abilities. However, the constrained conductivity of MoS2 and the lack of selectivity of nZVI for electron transfer still pose challenges. In this study, we designed a series of novel nano zero-valent iron supported by molybdenum disulfide composites (nZVI@MD) with multiple electron-rich active sites, including iron dopant replacement, iron atom intercalation and exposed Mo4+, for effective removal of Cr(VI). Results showed that preparation temperature and the amount of MoS2 added were identified as the two most significant factors affecting the reduction properties of nZVI@MD. Systematic experiments revealed that the nZVI@MD exhibited good anti-interference performance, stability and reusability due to its excellent electron selectivity. Characterization results exhibited that iron atoms replaced the sulfur vacancies in MoS2 and inserted into an intercalation of MoS2 during the preparation process. The mechanisms underlying the uptake of Cr(VI) by nZVI@MD can be proposed as follows: (i) electrostatic interactions, (ii) reduction reaction, and (iii) co-precipitation involving Fe-O-Cr. Furthermore, nZVI@MD exhibited excellent electron activity, hydrophilicity and oxidation resistance, confirmed by density functional theory (DFT) calculations. This work provided new strategies and mechanistic insights for the rational design of adsorbents.

Efficient removal of pefloxacin from aqueous solution by acid-alkali modified sludge-based biochar: adsorption kinetics, isotherm, thermodynamics, and mechanism

In this paper, one kind of acid-alkali modified sludge-based biochar (ASBC) was synthesized, characterized, and employed as adsorbent for the removal of pefloxacin. The characterization results showed that the specific surface area (SSA) of ASBC (53.381 m²/g) was significantly higher than that of SBC (24.411 m²/g). ASBC had a rougher surface, larger particle distribution, lower zero point charge, and richer functional groups (e.g., C-O and O-H) than SBC. The adsorption capacity of ASBC was 1.82 times than that of SBC. After 8 adsorption cycles in reuse experiment, the adsorption capacity of ASBC for pefloxacin still reached 144.08 mg/L, indicating that ASBC has good reusability. Static experiments showed that the optimal pH value was 6.0 in the adsorption of pefloxacin on SBC and ASBC. The result of adsorption kinetics indicated that the pseudo-second-order model could describe well the adsorption process. The Freundlich model was better than the Langmuir model to describe the adsorption of pefloxacin by ASBC, indicating that the adsorption process was mainly multilayer adsorption. Thermodynamic result showed that the adsorption of pefloxacin by ASBC was spontaneous and endothermic. The removal mechanism of pefloxacin by ASBC is mainly the substitution reaction and π-π EDA interaction. In summary, acid-alkali modified biochar is an effective adsorbent for pefloxacin in aqueous solution, and has great application prospects.

Effective stabilization of atomic hydrogen by Pd nanoparticles for rapid hexavalent chromium reduction and synchronous bisphenol A oxidation during the photoelectrocatalytic process

Atomic hydrogen (H*) plays a vital role in the synchronous redox of metallic ions and organic molecules. However, H* is extremely unstable as it is easily converted to hydrogen. Herein, we designed a novel strategy for the effective stabilization of H* to enhance its utility. The synthesized Pd nanoparticles grown on the defective MoS₂ (DMS) of TiO₂ nanowire arrays (TNA) (TNA/DMS/Pd) photocathode exhibited rapid Cr(VI) reduction (~95% in 10 min) and bisphenol A (BPA) oxidation (~97% in 30 min), with the kinetic constants almost 24- and 6-fold higher than those of the TNA photocathode, respectively. This superior performances could be attributed to: (i) the generated interface heterojunctions between TNA and DMS boosted the separation efficiencies of photogenerated electrons, thereby supplying abundant valance electrons to lower the overpotential to create a suitable microenvironment for H* generation; (ii) the stabilization of H* by Pd nanoparticles resulted in a significant increase in the yield of hydroxyl radical (•OH). This research provides a new strategy for the effective utilization of H* toward rapid reduction of heavy metals and synchronous oxidation of the refractory organics.

Anodic TiO2 Nanotubes on 3D-Printed Titanium Meshes for Photocatalytic Applications

In this work, large 3D Ti meshes fabricated by direct ink writing were wirelessly anodized for the first time to prepare highly photocatalytically active TiO₂ nanotube (TNT) layers. The use of bipolar electrochemistry enabled the fabrication of TNT layers within the 3D Ti meshes without the establishment of an electrical contact between Ti meshes and the potentiostat, confirming its unique ability and advantage for the synthesis of anodic structures on metallic substrates with a complex geometry. TNT layers with nanotube diameters of up to 110 nm and thicknesses of up to 3.3 μm were formed. The TNT-layer-modified 3D Ti meshes showed a superior performance for the photocatalytic degradation of methylene blue in comparison to TiO₂-nanoparticle-decorated and nonanodized Ti meshes (with a thermal oxide layer), resulting in multiple increases in the dye degradation rate. The results presented here open new horizons for the employment of anodized 3D Ti meshes in various flow-through (photo)catalytic reactors.

Review on application of perylene diimide (PDI)-based materials in environment: Pollutant detection and degradation

Environment pollution is getting serious and various poisonous contaminants with chemical durability, biotoxicity and bioaccumulation have been widespreadly discovered in municipal wastewaters and surface water. The detection and removal of pollutants show great significance for the protection of human health and other organisms. Due to its distinctive physical and chemical properties, perylene diimide (PDI) has received widespread attention from different research fields, especially in the area of environment. In this review, a comprehensive summary of the development of PDI-based materials in fluorescence detection and advanced oxidation technology for environment was introduced. Firstly, we chiefly presented the recent progress about the synthesis of PDI and PDI-based nanomaterials. Then, their application in fluorescence detection for environment was presented and categorized, principally including the detection of heavy metal ions, harmful anions and organic contaminants in the environment. In addition, the application of PDI and PDI-based materials in different advanced oxidation technologies for environment, such as photocatalysis, photoelectrocatalysis, Fenton and Fenton-like reaction and persulfate activation, was also summarized. At last, the challenges and future prospects of PDI-based materials in environmental applications were discussed. This review focuses on presenting the practical applications of PDI and PDI-based materials as fluorescent probes or catalysts (especially photocatalysts) in the detection of hazardous substances or catalytic elimination of organic contaminants. The contents are aimed at supplying the researchers with a deeper understanding of PDI and PDI-based materials and encouraging their further development in environmental applications.

Preparation and application of BiOBr-Bi2S3 heterojunctions for efficient photocatalytic removal of Cr(VI)

Recently, the photocatalytic reduction of Cr(VI) has been extensively studied. Herein, we successfully prepared the BiOBr-Bi₂S₃ heterojunctions with high photocatalytic Cr(VI) reduction performance using an ion exchange method. The optimal BiOBr-Bi₂S₃ heterojunction (prepared with BiOBr, pH of 6.0, 2 mmol Na₂S₂O₃·5H₂O,) achieved 100% removal of Cr(VI) within 12 min. The performance of photo-reduced Cr(VI) was about 28.9 and 184.6 times higher than that of pure Bi₂S₃ and BiOBr, respectively. Besides, BiOBr-Bi₂S₃ heterojunctions had a good adsorption efficiency for Cr(III), suggesting that they could be applied as bifunctional photocatalyst. The formation process and photoelectric properties of the BiOBr-Bi₂S₃ heterojunctions were revealed by a series of characterizations. In conclusion, this work reported the synergistic effect of adsorption and photocatalysis of the BiOBr-Bi₂S₃ heterojunctions for Cr removal for the first time, suggesting that the BiOBr-Bi₂S₃ heterojunctions could act as a novel photocatalytic adsorbent to treat the Cr(VI)-containing wastewater.

Fabrication of Dandelion-like p-p Type Heterostructure of Ag2O@CoO for Bifunctional Photoelectrocatalytic Performance

A novel three-dimensional purple dandelion-like hierarchical Ag₂O@CoO heterojunction with an appropriate redox potential was constructed by chemical precipitation of Ag₂O nanoparticle on flower-like CoO. By feat of this hierarchical structure, the Ag₂O@CoO photocathode showed significantly high photoelectroreduction activities toward p-nitrophenol (p-NP) and Cr(VI). The high performance of Ag₂O@CoO was mainly attributed to the specific structural characteristics and synergistic effect of each chemical component. This hierarchical structure could effectively increase the specific surface area, provide more exposed active edges, and be beneficial for multiple light reflection/scattering channels and light utilization efficiency. The introduction of Ag₂O optimized the composition and further improved the band structure, resulting in an improved separation of photogenerated electrons and holes. The unique photocathode achieves a removal efficiency of 86% for photoelectrocatalytic p-NP degradation after 120 min and 95% for Cr(VI) after 40 min under visible light irradiation with excellent stability. This research provided a simple way for the synthesis of photoelectrocatalytic material with potential applications in the field of environmental governance with visible light illumination.

A reclaimed piezoelectric catalyst of MoS2@TNr composites as high-performance anode materials for supercapacitors

A piezoelectric catalyst of the MoS2@TNr composite (MoS2 nanosheets composited with TiO2 nanorods) was synthesized by a two-step hydrothermal method, and can be recycled and reused as an advanced anode material for supercapacitors. In the dark, the MoS2@TNr composite exhibited ultra-fast piezoelectric catalytic performance and good cycle stability on dye degradation; within 10 min, nearly all rhodamine B (50 mL, 20 ppm) was removed from the solution with the assistance of magnetic stirring. After the 5 cycle degradation reaction, the catalyst was reclaimed and applied to electrochemical testing, which showed better supercapacitor capacitance properties than the fresh catalyst due to the introduction of oxygen vacancies generated from the piezoelectric degradation process. The reclaimed catalyst demonstrated an excellent specific capacitance of 249 F g-1 at 1 A g-1, and 92% capacitance retention after 10 000 cycles. Furthermore, as the current density increased to 30 A g-1, the capacitance could maintain 58% of the initial value. Thus, it can be concluded that the abandoned catalysts may serve as a potential electrode material for energy storage; simultaneously, the reutilization could eliminate secondary pollution and decrease the energy consumption in efficiency.

Dual light-induced in situ antibacterial activities of biocompatibleTiO2/MoS2/PDA/RGD nanorod arrays on titanium

Prevention of bacterial infection and promotion of osseointegration are two important issues for titanium (Ti) implants in medical research.

One-step hydrothermal fabrication of SrMoO4/MoS2 composites with strong interfacial contacts for efficient photoreduction removal of Cr(vi)

In situ growth of MoS₂ nanosheets on bulk SrMoO₄ has been achieved by a one-step hydrothermal strategy. Strong interfacial contacts in 8%-SrMoO₄/MoS₂ composites endow them with superior photocatalytic performance.

2D MoS2 nanosheets on 1D anodic TiO2 nanotube layers: an efficient co-catalyst for liquid and gas phase photocatalysis

One-dimensional TiO₂ nanotube layers with different dimensions were homogeneously decorated with 2D MoS₂ nanosheets via atomic layer deposition and employed for liquid and gas phase photocatalysis. The 2D MoS₂ nanosheets revealed a high amount of exposed active edge sites and strongly enhanced the photocatalytic performance of TiO₂ nanotube layers.

Ultrahigh sorption and reduction of Cr(VI) by two novel core-shell composites combined with Fe3O4 and MoS2

In this investigation, two novel magnetic core-shell Fe₃O₄@MoS₂ (F@M) and MoS₂@Fe₃O₄ (M@F) composites were synthesized and exploited for Cr(VI) elimination. Eco-friendly preparation methods were applied for the synthesis of Fe₃O₄ and MoS₂ composites. The experimental results showed that both F@M and M@F have high saturation magnetization values (43.2 emu/g for F@M and 49.9 emu/g for M@F), excellent maximum sorption capacities of Cr(VI) at pH 5.0 and 298 K (324.3 mg/g for F@M, 290.2 mg/g for M@F), remarkable Cr(VI) removal efficiencies (Cr(VI) sorption equilibrium by both F@M and M@F can be reached in 90 min) and nice regeneration properties (the sorption capabilities of F@M and M@F decreased slightly after five consecutive sorption/desorption cycles). Chemical reduction of Cr(VI) to Cr(III) occurred on the surface of F@M and M@F, and the synergetic reduction of sulfur and ferrous ions made F@M an outstanding material for Cr(VI) removal. This paper highlights F@M and M@F as potential, eco-friendly and ultrahigh-efficiency materials for Cr(VI) pollution cleanup.

Interaction with low molecular weight organic acids affects the electron shuttling of biochar for Cr(VI) reduction

Biochar can act as "electron shuttle" in soil redox reactions. It is possible that biochar accepts the electrons from low molecular weight organic acids (LMWOAs) in soil and then transfer them to the acceptors, e.g., Cr(VI). This study evaluated the interaction between seven soil LMWOAs and peanut shell biochar (BC) as well as its effect on the electron shuttling of biochar for Cr(VI) reduction. Both redox reactions and sorption process occurred during the interaction of biochar and LMWOAs, which altered the contents of Cr(VI) reduction-relevant groups (i.e., CO and CO) on the surface of biochar. The redox reactions were more important to the electron transfer between biochar produced at 400℃ (BC400) and LMWOAs due to the repeated cycle of reduction-oxidation of surface functional groups. The reduction rate of Cr(VI) by LMWOAs mediated by BC400 was 1.10-7.09 × 10^-3 h^-1, among which tartaric acid had the best reduction efficiency due to its highest reducing capability. For biochar produced at 700℃ (BC700), the sorption process of LMWOAs was the key factor to the direct electron shuttling process through the conjugated structure of biochar. The reduction rate of Cr(VI) by LMWOAs mediated by BC700 was significantly higher and ranged 7.40-864 × 10^-3 h^-1, with the oxalic acid having the best reduction efficiency due to its highest sorption capacity by BC700. The results obtained from this study can help to establish the linkage between biochar and LMWOAs in soil electron network, which better explains the multifunctional roles of biochar during the redox processes such as Cr(VI) reduction in soil.

Wafer-Scale Sulfur Vacancy-Rich Monolayer MoS2 for Massive Hydrogen Production

As one of the promising low-cost and high-efficiency catalysts for the electrochemical hydrogen evolution reaction (HER), it is well-known that there are both tiny exposed catalytic active edge sites and large-area inert basal planes in two-dimensional MoS₂ structures. For enhancing its HER activity, extensive work has been done to activate the inert basal plane of MoS₂. In this article, wafer-scale (2 in.) continuous monolayer MoS₂ films with substantial in situ generated sulfur vacancies are fabricated by employing the laser molecular beam epitaxy process benefitting from ultrahigh vacuum growth condition and high substrate temperature. The intrinsic sulfur vacancies throughout the wafer-scale basal plane present an ideal electrocatalytic platform for massive hydrogen production. The fabricated vacancy-rich monolayer MoS₂ can achieve a current density of -10 mA/cm² at an overpotential of -256 mV. The wafer-scale fabrications of sulfur vacancy-rich monolayer MoS₂ provide great leaps forward in the practical application of MoS₂ for massive hydrogen production.

Structural defects in 2D MoS2 nanosheets and their roles in the adsorption of airborne elemental mercury

In this research, ab initio calculations and experimental approach were adopted to reveal the mechanism of Hg⁰ adsorption on MoS₂ nanosheets that contain various types of defects. The ab initio calculation showed that, among different structural defects, S vacancies (Vs) in the MoS₂ nanosheets exhibited outstanding potential to strongly adsorb Hg⁰. The MoS₂ material was then prepared in a controlled manner under conditions, such as temperature, concentration of precursors, etc., that were determined by adopting the new method developed in this study. Characterisation confirmed that the MoS₂ material is of graphene-like layered structure with abundant structural defects. The integrated dynamic and steady state (IDSS) testing demonstrated that the Vs-rich nanosheets showed excellent Hg⁰ adsorption capability. In addition, ab initial calculation on charge density difference, PDOS, and adsorption pathways revealed that the adsorption of Hg⁰ on the Vs-rich MoS₂ surface is non-activated chemisorption.

Intercalation of Bi2O3/Bi2S3 nanoparticles into highly expanded MoS2 nanosheets for greatly enhanced gas sensing performance at room temperature

Synthesizing a gas sensor based on heterostructured nanomaterials (NMs) via a controllable morphology by a facile hydrothermal method is an area of frontier research. In the present work, we designed a facile strategy to synthesize a controllable morphology and composition for three component heterojunctions (MoS₂-Bi₂O₃-Bi₂S₃) NMs using different hydrothermal reaction times. The Bi₂S₃ easily form as an intermediate phase due to the strong interaction of the Bi₂O₃ with MoS₂ nanosheets (NSs). The as fabricated heterojunctions MB-5 NMs exhibited a sensitive response to NO_x gas (R_a/R_g = 10.7 at 50 ppm), with an ultra-fast response time of only 1 s (s) at room temperature (RT) in air. The detection limit was predicted to be as low as 50 ppb. This sensational behaviour of the sensor reveals the outstanding morphological structure and synergistic effect of the MoS₂ NSs with Bi₂O₃ nanoparticles (NPs), which was realized by the flow of electrons across MoS₂-Bi₂O₃-Bi₂S₃ interfaces through band energy alignment.

Research on the sustainable efficacy of g-MoS2 decorated biochar nanocomposites for removing tetracycline hydrochloride from antibiotic-polluted aqueous solution

Antibiotic concentrations in surface waters far exceed the pollution limit due to the abuse of pharmaceuticals, resulting in an urgent need for an approach with potential efficiency, sustainability and eco-friendliness to remove antibiotic pollutants. A novel biochar-based nanomaterial was synthesized by hydrothermal synthesis and was investigated for its removal potential for tetracycline hydrochloride (TC) from both artificial and real wastewater. The associative facilitation between biochar and g-MoS₂ nanosheets was proposed, revealing the favorable surface structures and adsorption properties of the composite. The related adsorption kinetics, isotherms and thermodynamics were studied by several models with adsorption experimental data, turning out that biochar decorated by g-MoS₂ exhibited optimum TC removal with adsorption capacity up to 249.45 mg/g at 298 K. The adsorption behavior of TC molecules on g-MoS₂-BC can be interpreted well by three-step process, and it is dominated by several mechanisms containing pore-filling, electrostatic force, hydrogen bond and π-π interaction. In addition, the cost-effective g-MoS₂-BC nanocomposites demonstrated excellent adsorption and recycling performance in TC-contaminated river water, which might provide the underlying insights needed to guide the design of promising approach for contaminant removal on a large scale in practical application.

Titania-Based Hybrid Materials with ZnO, ZrO₂ and MoS₂: A Review

Titania has properties that enable it to be used in a variety of applications, including self-cleaning surfaces, air and water purification systems, hydrogen evolution, and photoelectrochemical conversion. In order to improve the properties of titanium dioxide, modifications are made to obtain oxide/hybrid systems that are intended to have the properties of both components. In particular, zinc oxide, zirconia and molybdenum disulfide have been proposed as the second component of binary systems due to their antibacterial, electrochemical and photocatalytic properties. This paper presents a review of the current state of knowledge on the synthesis and practical utility of TiO₂-ZnO and TiO₂-ZrO₂ oxide systems and TiO₂-MoS₂ hybrid materials. The first part focuses on the hydrothermal method; then a review is made of the literature on the synthesis of the aforementioned materials using the sol-gel method. In the last section, the literature on the electrospinning method of synthesis is reviewed. The most significant physico-chemical, structural and dispersive-morphological properties of binary hybrid systems based on TiO₂ are described. A key aim of this review is to indicate the properties of TiO₂-ZnO, TiO₂-ZrO₂ and TiO₂-MoS₂ hybrid systems that have the greatest importance for practical applications. The variety of utilities of titania-based hybrid materials is emphasized.

Low temperature synthesis of NbC/C nano-composites as visible light photoactive catalyst

A facile carbothermal route was adopted to obtain niobium carbide nanoparticles (NPs) embedded in carbon network from Nb2O5 to study photocatalytic behavior. Optimization of synthesis parameters to obtain single phase NbC NPs has been successfully done. The phase identification, morphology and nature of carbon were determined with the help of X-ray diffraction, transmission electron microscopy (TEM) and Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) suggested the presence of multiple oxidation states of Nb associated to NbC and NbCxOy centers on the surface of NPs. Due to the presence of NbCxOy on the surface of NPs, absorption under visible region of EM spectrum has been observed by UV-visible spectroscopy. Different organic dyes (RhB, MB and MO) were used to study the effect of holding time on the photocatalytic performance of as-synthesized samples. RhB dye was found to be the most sensitive organic molecule among all the considered dyes and degraded 78% in 120 min.

TiO₂ Nanotubes/Ag/MoS₂ Meshy Photoelectrode with Excellent Photoelectrocatalytic Degradation Activity for Tetracycline Hydrochloride

A novel type of TiO₂ nanotubes (NTs)/Ag/MoS₂ meshy photoelectrode was fabricated with highly oriented TiO₂ nanotube arrays grown from a Ti mesh supporting Ag nanoparticles and three-dimensional MoS₂ nanosheets. In this structure, Ag nanoparticles act as bridges to connect MoS₂ and TiO₂ and pathways for electron transfer, ensuring the abundant production of active electrons, which are the source of •O₂⁻. The TiO₂ NTs/Ag/MoS₂ mesh can be used as both photocatalyst and electrode, exhibiting enhanced photoelectrocatalytic efficiency in degrading tetracycline hydrochloride under visible light irradiation (λ ≥ 420 nm). Compared to unmodified TiO₂ NTs, the improved photoelectrocatalytic activity of the TiO₂ NTs/Ag/MoS₂ arise from the formation of Z-scheme heterojunctions, which facilitate the efficient separation of photogenerated electron-hole pairs through the Schottky barriers at the interfaces of TiO₂ NTs–Ag and Ag–MoS₂.

Photoelectrochemical CdSe/TiO2 nanotube array microsensor for high-resolution in-situ detection of dopamine

A photoelectrochemical wire microelectrode was constructed based on the use of a TiO₂ nanotube array with electrochemically deposited CdSe semiconductor. A strongly amplified photocurrent is generated on the sensor surface. The microsensor has a response in the 0.05-20 μM dopamine (DA) concentration range and a 16.7 μM detection limit at a signal-to-noise ratio of 3. Sensitivity, recovery and reproducibility of the sensor were validated by detecting DA in spiked human urine, and satisfactory results were obtained. Graphical abstract Schematic of a sensitive photoelectrochemical microsensor based on CdSe modified TiO₂ nanotube array. The photoelectrochemical microsensor was successfully applied to the determination of dopamine in urine samples.

Preparation of MoS2/TiO2 based nanocomposites for photocatalysis and rechargeable batteries: progress, challenges, and perspective

The rapidly increasing severity of the energy crisis and environmental degradation are stimulating the rapid development of photocatalysts and rechargeable lithium/sodium ion batteries. In particular, MoS₂/TiO₂ based nanocomposites show great potential and have been widely studied in the areas of both photocatalysis and rechargeable lithium/sodium ion batteries due to their superior combination properties. In addition to the low-cost, abundance, and high chemical stability of both MoS₂ and TiO₂, MoS₂/TiO₂ composites also show complementary advantages. These include the strong optical absorption of TiO₂vs. the high catalytic activity of MoS₂, which is promising for photocatalysis; and excellent safety and superior structural stability of TiO₂vs. the high theoretic specific capacity and unique layered structure of MoS₂, thus, these composites are exciting as anode materials. In this review, we first summarize the recent progress in MoS₂/TiO₂-based nanomaterials for applications in photocatalysis and rechargeable batteries. We highlight the synthesis, structure and mechanism of MoS₂/TiO₂-based nanomaterials. Then, advancements and strategies for improving the performance of these composites in photocatalytic degradation, hydrogen evolution, CO₂ reduction, LIBs and SIBs are critically discussed. Finally, perspectives on existing challenges and probable opportunities for future exploration of MoS₂/TiO₂-based composites towards photocatalysis and rechargeable batteries are presented. We believe the present review would provide enriched information for a deeper understanding of MoS₂/TiO₂ composites and open avenues for the rational design of MoS₂/TiO₂ based composites for energy and environment-related applications.