Enhanced Efficiency of Electron-Hole Separation in Bi2 O2 CO3 for Photocatalysis via Acid Treatment

Enhanced photocatalytic performance of Bi2O2CO3/Bi4O5Br2/reduced graphene oxide Z-schemehe terojunction via a one-pot room-temperature synthesis

Bi2O2CO3(BOC)/Bi4O5Br2(BOB)/reduced graphene oxide (rGO) Z-scheme heterojunction with promising photocatalytic properties was synthesized via a facile one-pot room-temperature method. Ultra-thin nanosheets of BOC and BOB were grown in situ on rGO. The formed 2D/2D direct Z-scheme heterojunction of BOC/BOB with oxygen vacancies (OVs) effectively leads to lower negative electron reduction potential of BOB as well as higher positive hole oxidation potential of BOC, showing improved reduction/oxidation ability. Particularly, rGO is an acceptor of the electrons from the conduction band of BOC. Its dual roles significantly improve the transfer performance of photo-induced charge carriers and accelerate their separation. With layered nanosheet structure, rich OVs, high specific surface area, and increased utilization efficiency of visible light, the multiple synergistic effects of BOC/BOB/rGO can achieve effective generation and separation of the electron-holes, thereby generating more •O2- and h+. The photocatalytic reduction efficiency of CO2 to CO (12.91 µmol/(g·hr)) is three times higher than that of BOC (4.18 µmol/(g·hr)). Moreover, it also achieved almost 100% removal of Rhodamine B and cyanobacterial cells within 2 hours.

Recent Development Strategies for Bismuth-Driven Materials in Sustainable Energy Systems and Environmental Restoration

Bismuth(Bi)-based materials have gained considerable attention in recent decades for use in a diverse range of sustainable energy and environmental applications due to their low toxicity and eco-friendliness. Bi materials are widely employed in electrochemical energy storage and conversion devices, exhibiting excellent catalytic and non-catalytic performance, as well as CO₂ /N₂ reduction and water treatment systems. A variety of Bi materials, including its oxides, chalcogenides, oxyhalides, bismuthates, and other composites, have been developed for understanding their physicochemical properties. In this review, a comprehensive overview of the properties of individual Bi material systems and their use in a range of applications is provided. This review highlights the implementation of novel strategies to modify Bi materials based on morphological and facet control, doping/defect inclusion, and composite/heterojunction formation. The factors affecting the development of different classes of Bi materials and how their control differs between individual Bi compounds are also described. In particular, the development process for these material systems, their mass production, and related challenges are considered. Thus, the key components in Bi compounds are compared in terms of their properties, design, and applications. Finally, the future potential and challenges associated with Bi complexes are presented as a pathway for new innovations.

Green Biosynthesis of Tin Oxide Nanomaterials Mediated by Agro-Waste Cotton Boll Peel Extracts for the Remediation of Environmental Pollutant Dyes

The sustainable synthesis of metal oxide materials provides an ecofriendly and more exciting approach in the domain of a clean environment. Besides, plant extracts to synthesize nanoparticles have been considered one of the more superior ecofriendly methods. This paper describes the biosynthetic preparation route of three different sizes of tetragonal structure SnO₂ nanoparticles (SNPs) from the agro-waste cotton boll peel aqueous extract at 200, 500, and 800 °C for 3 h and represents a low-cost and alternative preparation method. The samples were characterized by X-ray diffraction, Fourier transform infrared spectrophotometry, ultraviolet-visible absorption spectroscopy, high-resolution transmission electron microscopy (HR-TEM), and energy-dispersive X-ray spectroscopy. Surface area and porosity size distribution were identified by nitrogen adsorption-desorption isotherms and Brunauer-Emmett-Teller analysis. The photocatalytic properties of the SNP samples were studied against methylene blue (MB) and methyl orange (MO), and the degradation was evaluated with three different size nanomaterials of 3.97, 8.48, and 13.43 nm. Photocatalytic activities were carried out under a multilamp (125 W Hg lamps) photoreactor. The smallest size sample exhibited the highest MB degradation efficiency within 30 min than the most significant size sample, which lasted 80 min. Similarly, in the case of MO, the smallest sample showed a more superior degradation efficiency with a shorter period (40 min) than the large-size samples (100 min). Therefore, our studies suggested that the developed SNP nanomaterials could be potential, promising photocatalysts against the degradation of industrial effluents.

Ball-milled bismuth oxybromide/biochar composites with enhanced removal of reactive red owing to the synergy between adsorption and photodegradation

In this paper, bismuth oxybromide (BiOBr)/biochar composites were synthesized by a facile ball milling method for synergistic adsorption and photodegradation of Reactive red 120 (RR120). The characterizations show that ball milling changed the degree of crystallization, increased the surface area, and promoted the charge transfer ability of biochar. The 70% BiOBr/BC composite showed the best removal efficiency for RR120 removal with or without light illumination, which proves its enhanced removal ability by adsorption and photodegradation. The biochar is served as a support of BiOBr for preventing its aggregation and a transporter of charges for promoting the separation of photo-induced carriers in composites. BiOBr can release the adsorption sites on the surface of composites by degradation, which facilitated the RR120 removal and regenerated the photocatalyst for reusing. The strong interactions between BiOBr and biochar in composites resulted from ball milling were beneficial for the charge transfer and synergistic removal of adsorption and degradation. Findings of this work indicate that ball milling method is an effective method to prepare highly efficient biochar-based composites for RR120 removal through synergistic adsorption and photodegradation.

Template-free synthesis of Bi2O2CO3 hierarchical nanotubes self-assembled from ordered nanoplates for promising photocatalytic applications

In this study, we have adopted a one-step hydrothermal route to synthesize an interesting type of Bi₂O₂CO₃ hierarchical nanotubes self-assembled from ordered nanosheets. The effects of reaction time on the morphological and structural evolution, light absorption properties, photoelectrochemical performance, and photocatalytic performance of the prepared hierarchical nanotubes were investigated. Among the products synthesized at different reaction times, the 3-hour-derived Bi₂O₂CO₃ hierarchical nanotubes were identified to possess the highest photocatalytic performance. To promote the photocatalytic application of the as-synthesized Bi₂O₂CO₃ hierarchical nanotubes, their performance was systematically evaluated via the photodegradation of various organic pollutants (e.g., methyl orange (MO), rhodamine B (RhB), methylene blue (MB), ciprofloxacin (CIP), sulfamethoxazole (SMX) and tetracycline hydrochloride (TC)) and the photoreduction of Cr(VI) under simulated-sunlight irradiation. Furthermore, their photocatalytic performance was also evaluated by purifying simulated industrial wastewater (i.e., a MO/RhB/MB mixed solution) at different pH values and containing different inorganic anions. Based on the experimental data and density functional theory (DFT) calculations, the involved photocatalytic mechanism was discussed.

Visible light-driven photocatalytic rapid degradation of organic contaminants engaging manganese dioxide-incorporated iron oxide three dimensional nanoflowers

Water pollution via hazardous organic pollutants poses a high threat to the environment and globally imperils aquatic life and human health. Therefore, the elimination of toxic organic waste from water sources is vital to ensure a healthy green environment. In the current work, we synthesized α-MnO₂-Fe₃O₄ 3D-flower like structure using a two-step hydrothermal method and explored the combination in a visible-light-assisted photocatalytic degrdation of dyes. The attained high specific surface area of 82 m²/g with mesoporous nature of α-MnO₂ and Fe₃O₄ together can generate more active sites after exposure to visible light, leading to remarkable photodegradation performance. Significantly, twofold higher dye (methylene blue, MB (94.8%/120 min; crystal violet, CV (93.7%/120 min)) and drug (LVO 91%/90 min) photodegradations were observed with α-MnO₂-Fe₃O₄ as catalyst than pure α-MnO₂ and Fe₃O₄ at pH 6, respectively. This is attributed to the higher surface area and synergistic effect between Mn and Fe. More than 85% stability was observed with optimized catalysts employing MB and CV dyes, demonstrating the excellent reusability of the α-MnO₂-Fe₃O₄. The underlying mechanism indicates that the formation of reactive oxygen species predominantly plays a role in the photodegradation of dyes under visible light. Consequently, these new insights will shed light on the practical applications of the α-MnO₂-Fe₃O₄ 3D-flower-like spherical structure for eco-friendly remediation via wastewater treatment.

Synergy of Oxygen Vacancies and Acid Sites on N-Doped WO3 Nanobelts for Efficient C-C Coupling Synthesis of Benzoin Isopropyl Ether

The surface property of a photocatalyst, including surface acid sites and oxygen vacancies, plays a pivotal role in photocatalytic organic synthesis reactions. Benzoin isopropyl ether (BIE) is usually produced via polycondensation of benzaldehyde and catalyzed with highly toxic cyanide. Here, we report a green photocatalytic approach for the selective synthesis of BIE over WO₃ driven by a green-light-emitting diode. The improved photocatalytic activity can be attributed to the synergy of oxygen vacancies (V_Os) and acid sites over N-doped WO₃ nanobelts. The results revealed that reactant molecules were predominantly adsorbed and activated on surface oxygen vacancies (V_OSs) and the Brønsted acid promoted the etherification reaction; the introduction of V_Os and nitrogen altered the band structure and electronic properties, resulting in improved photocatalytic activity. Our work provides an efficient approach to the selective photocatalytic synthesis of organics over photocatalysts with finely tuned surface properties and band structures via defect and doping engineering.

Synthesis and Characterization of Manganese-Modified Black TiO2 Nanoparticles and Their Performance Evaluation for the Photodegradation of Phenolic Compounds from Wastewater

The release of phenolic-contaminated treated palm oil mill effluent (TPOME) poses a severe threat to human and environmental health. In this work, manganese-modified black TiO₂ (Mn-B-TiO₂) was produced for the photodegradation of high concentrations of total phenolic compounds from TPOME. A modified glycerol-assisted technique was used to synthesize visible-light-sensitive black TiO₂ nanoparticles (NPs), which were then calcined at 300 °C for 60 min for conversion to anatase crystalline phase. The black TiO₂ was further modified with manganese by utilizing a wet impregnation technique. Visible light absorption, charge carrier separation, and electron–hole pair recombination suppression were all improved when the band structure of TiO₂ was tuned by producing Ti³⁺ defect states. As a result of the enhanced optical and electrical characteristics of black TiO₂ NPs, phenolic compounds were removed from TPOME at a rate of 48.17%, which is 2.6 times higher than P25 (18%). When Mn was added to black TiO₂ NPs, the Ti ion in the TiO₂ lattice was replaced by Mn, causing a large redshift of the optical absorption edges and enhanced photodegradation of phenolic compounds from TPOME. The photodegradation efficiency of phenolic compounds by Mn-B-TiO₂ improved to 60.12% from 48.17% at 0.3 wt% Mn doping concentration. The removal efficiency of phenolic compounds from TPOME diminished when Mn doping exceeded the optimum threshold (0.3 wt%). According to the findings, Mn-modified black TiO₂ NPs are the most effective, as they combine the advantages of both black TiO₂ and Mn doping.

4-Nitrophenol Efficient Photoreduction from Exfoliated and Protonated Phenyl-Doped Graphitic Carbon Nitride Nanosheets

The photoreduction of 4-nitrophenol to 4-aminophenol by means of protonated and exfoliated phenyl-doped carbon nitride is reported. Although carbon nitride-based materials have been recognized as efficient photocatalysts, the photoreduction of 4-nitrophenol to 4-aminophenol is not allowed because of the high recombination rate of the photogenerated electron–hole pairs. In this paper, we show the morphology effects on the photoactivity in phenyl-doped carbon nitride. Structural (TEM, XRD, Raman) and optical characterization (absorption, photoluminescence) of the protonated and exfoliated phenyl-doped carbon nitride (hereafter pePhCN) is reported. The increased photocatalytic efficiency, with respect to the bulk material, is underlined by the calculation of the kinetic constant of the photoreduction process (2.78 × 10⁻¹ min⁻¹ and 3.54 × 10⁻³ min⁻¹) for pePhCN and bulk PhCN, respectively. Finally, the detailed mechanism of the photoreduction process of 4-nitrophenol to 4-aminophenol by modified phenyl carbon nitride is proposed.

Synthesis, characterization and utilization of oxygen vacancy contained metal oxide semiconductors for energy and environmental catalysis

Developing novel functional materials with promising desired properties in enhancing energy conversion and lowering the catalytic reaction barriers is essential for the demand to solve the increasingly severe energy and environmental crisis nowadays. Metal oxide semiconductors (MOS) are widely used in the field of catalysis because of its excellent catalytic characteristics. Introduction of defects, in addition to the adjustment of composition and atomic arrangement in the materials can effectively improve the materials' catalytic performance. Especially, introducing oxygen vacancies (OVs) into the lattice structure of MOS has been developed as a facile route to improve MOS's optical and electronic transmission characteristics. And a large number of metal oxides with rich OVs have been served in oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO₂-RR) photo-degradation of organic pollutants, etc. This small review briefly outlines some preparation techniques to introduce OVs into MOS, and the characterization techniques to identify and quantify the OVs in MOS. The applications of OVs contained MOS especially in energy and environmental catalysis areas are also discussed. The effects of OVs types and concentrations on the catalytic performances are deliberated. Finally, the defective structure-catalytic property relationship is highlighted, and the future status and opportunities of MOS containing OVs in the catalytic field are suggested.

Oxygen Vacancy Enhanced Two-Dimensional Lithium Titanate for Ultrafast and Long-Life Bifunctional Lithium Storage

Boosting sufficient Li⁺ ion mobility in Li₄Ti₅O₁₂ (LTO) is crucial for high-rate performance lithium storage. Here, an ultrafast charge storage oxygen vacancy two-dimensional (2D) LTO nanosheet was successfully fabricated through a one-pot hydrothermal method. The selectively doped Al³⁺ into octahedron Li⁺/Ti⁴⁺ 16d sites not only provide bulk oxygen vacancy and appropriate distorted TiO₆ octahedra to facilitate Li⁺ ions diffusion, but also serve as a "pillar" to stabilize the Ti-O framework. The oxygen vacancy lowers Li⁺ ion diffusion energy barrier. Moreover, the 2D structure provides open diffusion channels for fast Li⁺ ion transport. As a result, the sample shows excellent electrochemical performance for bifunctional lithium storage. As a lithium-ion battery anode, the capacity retention reaches 112.8 mA h g^-1 after 5000 cycles at 40 C with a fading rate of 0.288% per 100 cycles. Meanwhile, as a lithium-ion capacitor anode, it exhibits an excellent rate capacity of 120 mA h g^-1 after 5000 cycles at 500 C with nearly 100% Coulombic efficiency. The produced LTO shows much higher rate capacity and longer lifetime than the reported LTO. Density functional theory calculations also demonstrate that oxygen vacancy can facilitate Li⁺ ion diffusion kinetics. The relationship between oxygen vacancy content and Li⁺ ions diffusion energy barrier in LTO is quantified. This work pioneers a defect engineering strategy for synthesized high-performance electrode materials.

Bi metal/oxygen-deficient BiO2-x with tetrahedral morphology and high photocatalytic activity

Vacancy-rich materials with high photocatalytic activity are of great interest for pollutants removal and play a significant role in green chemistry. Herein, we successfully synthesized Bi/BiO_2-x composite through hydrothermal route. In this case, the surface plasmon resonance effect of Bi and oxygen vacancies of BiO_2-x collectively increase the removal rate of pollutants. More importantly, the Bi/BiO_2-x composites have enhanced activity in the degradation of RhB, MO, BPA and CIP, and the reduction of Cr(VI) and PNA. Besides, an enhanced photocatalytic activity is due to the main reactive species of ·[Formula: see text] and h⁺ that is confirmed by trapping experiments and ESR analyses. The electronic structure and visible light harvesting of photocatalysts were measured and also theoretically calculated by using density functional theory and finite difference time domain calculations, DRS, VB x-ray photoelectron spectroscopy and Mott-Schottky plots, which allowed to propose a possible photocatalytic mechanism for the degradation process.

Photocatalytic inactivation of airborne bacteria in a polyurethane foam reactor loaded with a hybrid of MXene and anatase TiO2 exposing {0 0 1} facets

A hybrid of TiO2 exposing {0 0 1} facets and monolayer Ti3C2Tx nanosheet (MXene) was synthesized, characterized and used as a photocatalyst in this study. The introduction of MXene (3.4 wt%) helped to reduce the recombination of photo-induced electrons and holes, and thus enhanced the photocatalytic activity by 30%. A continuous flow-through reactor loaded with the as-prepared photocatalyst coated onto polyurethane foam was developed to inactivate airborne bacteria. The photocatalytic inactivation efficiency of airborne Escherichia coli (E. coli) achieved 3.4 lg order under ultraviolet (UV) irradiation at 254 (UV254), which was superior to that using UV254-only treatment with 2.5 lg order under the same operating condition (95% relative humidity and retention time of 4.27 s). The effect of humidity and bacteria species on inactivation performance was also investigated. The thick cell membrane could protect bacteria from photocatalytic oxidation while high humidity increased the photocatalytic inactivation efficiency by generating more reactive oxygen species. The phenomena of photo reactivation and dark repair of airborne E. coli using UV254-only treatment was observed. However, no reactivation occurred after UV photocatalytic inactivation, and even a continuous decline under visible light. These results suggested a different inactivation mechanism between UV irradiation and UV photocatalysis that the former inactivated bacteria by damaging their DNA, whereas photocatalysis physically damaged their cell structure.

Oxygen-Deficient Cobalt-Based Oxides for Electrocatalytic Water Splitting

An apparent increased interest has been recently devoted towards the previously untrodden path for anionic point defect engineering of electrocatalytic surfaces. The role of vacancy engineering in improving photo- and electrocatalytic activities of transition metal oxides (TMOs) has been widely reported. In particular, oxygen vacancy modulation on electrocatalysts of cobalt-based TMOs has seen a fresh spike of research work due to the substantial improvements they have shown towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Oxygen vacancy engineering is an effective scheme to quintessentially tune the electronic structure and charge transport, generate secondary active surface phases, and modify the surface adsorption/desorption behavior of reaction intermediates during water splitting. Based on contemporary efforts for inducing oxygen vacancies in a variety of cobalt oxide types, this work addresses facile and environmentally benign synthesis strategies, characterization techniques, and detailed insight into the intrinsic mechanistic modulation of electrocatalysts. It is our foresight that appropriate utilization of the principles discussed herein will aid researchers in rationally designing novel materials that can outperform noble metal-based electrocatalysts. Ultimately, future electrocatalysis implementation for selective seawater splitting is believed to depend on regulating the surface chemistry of active and stable TMOs.

Co3O4@NiCo2O4 double-shelled nanocages with hierarchical hollow structure and oxygen vacancies as efficient bifunctional electrocatalysts for rechargeable Zn-air batteries

Highly efficient bifunctional oxygen electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucially important for the rechargeable Zn-air battery, a potential power source for applications in electric vehicles and grid-scale stationary storage systems. Herein, Co3O4@NiCo2O4 double-shelled nanocages (Co3O4@NiCo2O4 DSNCs) with hierarchical hollow structure and oxygen vacancies were designed and synthesized via annealing metal-organic frameworks. Co3O4@NiCo2O4 DSNCs with large specific surface area and three-dimensional interconnected mesopores and cavity not only provide more reaction sites, but also offer an efficient transport environment for reactants. Moreover, oxygen vacancies on the surfaces improve the capture of oxygen species to enhance the reactivity of the catalyst. Consequently, Co3O4@NiCo2O4 DSNCs displayed excellent bifunctional electrocatalytic performance, with a positive half-wave potential of 0.81 V (vs. reversible hydrogen electrode, RHE) for ORR (approaching the potential of commercial Pt/C catalyst) and a low potential of 1.65 V at 10 mA cm-2 for OER (exceeding Pt/C). In a practical demonstration, the Zn-air battery using Co3O4@NiCo2O4 DSNCs as the cathode delivered a satisfactory power density of 102.1 mW cm-2, comparable to the Zn-air battery with a Pt/C cathode, and exhibited much longer cycling stability.

Defect Engineering Enhances the Charge Separation of CeO2 Nanorods toward Photocatalytic Methyl Blue Oxidation

Defect-rich photocatalytic materials with excellent charge transfer properties are very popular. Herein, Sm-doped CeO₂ nanorods were annealed in a N₂ atmosphere to obtain the defective Sm-doped CeO₂ photocatalysts (Vo–Sm–CeO₂). The morphology and structure of Vo–Sm–CeO₂ were systematically characterized. The Vo–Sm–CeO₂ nanorods demonstrated an excellent photodegradation performance of methyl blue under visible light irradiation compared to CeO₂ nanorods and Sm–CeO₂. Reactive oxygen species including OH, ·O₂⁻, and h⁺ were confirmed to play a pivotal role in the removal of pollutants via electron spin resonance spectroscopy. Doping Sm enhances the conductivity of CeO₂ nanorods, benefiting photogenerated electrons being removed from the surface reactive sites, resulting in the superior performance.

Heterostructured Bi2O2CO3/rGO/PDA photocatalysts with superior activity for organic pollutant degradation: Structural characterization, reaction mechanism and economic assessment

Compared with conventional methods for organic pollutant degradation, photocatalysis is a promising treatment technology with broad application prospects. Bi₂O₂CO₃ is often used for organic pollutants degradation but greatly restricted by having drawbacks of large band gap and high electron-hole recombination rate. Herein, heterostructured Bi₂O₂CO₃ (BOC)/reduced graphene oxide (rGO)/polydopamine (PDA) (BGP) photocatalysts were first designed through a green chemical method. By incorporating rGO and PDA in BOC, the kinetic constant of BGP to catalytically degrade methyl orange (MO) was significantly increased; over fourfold elevated rather than that of BOC (k_app/BOC = 0.0019, k_app/BGP = 0.0089) due to the high electron transfer capability of rGO and superior adhesive force and semiconducting properties of PDA. DRS and photoelectrochemical results confirmed the improvement of the light absorption range and charge transfer capability because of the synergistic effect of rGO and PDA. Results of trapping experiment and ESR unraveled the catalytic mechanism that both holes (h⁺) and superoxide radicals (•O₂^-) were the main oxidative species for MO degradation. Economic assessment results demonstrated that Bi₂O₂CO₃/rGO/PDA heterojunctions have great potentials in the field of organic wastewater purification. This study developed a low-cost and highly efficient BGP material and provided a deep understanding of the structure-performance relationships of materials for organic pollutant degradation.

Biomass derived the V-doped carbon/Bi2O3 composite for efficient photocatalysts

This work focused on the utilization of biological extract for the preparation of lignin-based carbon composites materials and used in the field of photocatalysis. A straightforward one-step carbonization way has been developed to prepare vanadium-doped lignin-based carbon/Bi₂O₃ composites photocatalyst by using sodium lignosulfonate as the carbon source and catalyst. The application of lignin as the carbon source to form photocatalyst support tends to control the uniform distribution. At the same time, sodium lignosulfonate as the catalyst could break down the BiVO₄ during carbonization process. A series of characterizations demonstrated the BiVO₄ was transformed into Bi₂O₃ and vanadium-doped lignin-based carbon. The possible synthesis process was proposed. Moreover, the novel V-doped carbon/Bi₂O₃ composites photocatalyst displayed higher photocatalytic activity than bare BiVO₄. A possible photocatalytic mechanism was also discussed. This work provided new insight into the lignin-based carbon materials.

An overview of photocatalysis facilitated by 2D heterojunctions

Two-dimensional (2D) photocatalysts have attracted considerable research interest in the past decades due to their unique optical, physical and chemical properties. Constructing 2D/2D heterojunctions with large interface area has been considered as an effective approach to enhance the transfer rate and the separation efficiency of the charge carriers, leading to dramatic increase in the photocatalytic performance of the photocatalysts. Here, the state-of-the-art progress on heterojunctions based on 2D materials is reviewed, including the photocatalysis principles using 2D heterojunctions, the categories of 2D heterojunctions and their application in different photocatalytic reactions, and the theoretical studies of the 2D heterojunctions. Moreover, the advantages and disadvantages of the 2D heterojunctions are also discussed. Finally, the ongoing challenges and opportunities for the future development of 2D photocatalysts with built-in heterojunctions are proposed.

Oxygen vacancy-engineered Fe2O3 nanoarrays as free-standing electrodes for flexible asymmetric supercapacitors

The charge storage performance of Fe₂O₃ nanoarrays (NAs) as negative electrodes are limited by their poor conductivity and rate capability. Herein, we have reported the delicate interfacial engineering on carbon cloth (CC) fibers and oxygen vacancy (V_O) generation on Fe₂O₃ nanorod arrays to boost the capacitive performance. Polydopamine-derived nitrogen-doped carbon layers were fabricated on CC fibers to govern the growth of FeOOH NAs. Rich V_Os were generated in Fe₂O₃ NAs to construct a unique heterostructure with a crystalline core and amorphous shell via successive N₂ thermal treatment and chemical reduction. Optimized by 2 h chemical reduction, the V_O-rich Fe₂O₃ NA electrode, featuring a charged voltage of -1.10 V, exhibited a high areal specific capacitance of 2.63 F cm^-2 at 0.5 mA cm^-2 and 0.12 F cm^-2 even at 60 mA cm^-2. Impressively, 86.7% specific capacitance was retained after 10 000 cycles at 10 mA cm^-2. The flexible asymmetric supercapacitor by assembling free-standing CN-Fe₂O₃-2 h (negative electrode) and MnO₂ (positive electrode) showed an energy density of 1.33 mW h cm^-3 at 15.4 mW cm^-3. To the best of our knowledge, these results are the record performance for Fe₂O₃-based electrodes. The two-step interfacial engineering reported in this study may open a new door in the design of high energy-density electrodes for advanced energy storage.

2D/2D heterojunction of Ti3C2/g-C3N4 nanosheets for enhanced photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution from water has received enormous attention due to its ability to address a number of global environmental and energy-related issues. Here, we synthesize 2D/2D Ti3C2/g-C3N4 composites by electrostatic self-assembly technique and demonstrate their use as photocatalysts for hydrogen evolution under visible light irradiation. The optimized Ti3C2/g-C3N4 composite exhibited a 10 times higher photocatalytic hydrogen evolution performance (72.3 μmol h-1 gcat-1) than that of pristine g-C3N4 (7.1 μmol h-1 gcat-1). Such enhanced photocatalytic performance was due to the formation of 2D/2D heterojunctions in the Ti3C2/g-C3N4 composites. The intimate contact between the monolayer Ti3C2 and g-C3N4 nanosheets promotes the separation of photogenerated charge carriers at the Ti3C2/g-C3N4 interface. Furthermore, the ultrahigh conductivity of Ti3C2 and the Schottky junction formed between g-C3N4/MXene interfaces facilitate the photoinduced electron transfer and suppress the recombination with photogenerated holes. This work demonstrates that the 2D/2D Ti3C2/g-C3N4 composites are promising photocatalysts thanks to the ultrathin MXenes as efficient co-catalysts for photocatalytic hydrogen production.

Ultrafine Bi3TaO7 Nanodot-Decorated V, N Codoped TiO2 Nanoblocks for Visible-Light Photocatalytic Activity: Interfacial Effect and Mechanism Insight

Bi₃TaO₇ is a potential photocatalyst because of its high chemical stability, defective fluorite-type structure, and superior mobility of photoinduced holes. However, few studies have focused on the interfacial effects of Bi₃TaO₇-based photocatalysts. In this work, 0D Bi₃TaO₇ nanodot-hybridized 3D V and N codoped TiO₂ nanoblock (B/VNT) composites were first synthesized for the photocatalytic removal of oxytetracycline hydrochloride, 2,4,6-trichlorophenol, and tetrabromobisphenol A. The fabricated B/VNT had a photocatalytic performance superior to that of pristine components, and probable degradation pathways were proposed according to the primary intermediates identified by a gas chromatography-mass spectrometer. Interestingly, on B/VNT, the transfer of interfacial electrons was observed from V/N-TiO₂ to Bi₃TaO₇, and the formed built-in electronic field led to a direct Z-scheme structure, rather than type II, as confirmed by the generated ^•OH and ^•O₂^- radicals and band structures from the density functional theory calculation. Therefore, the strong interfacial electronic interaction on the B/VNT was significant, which drove faster photogenerated charge transfer, more visible-light adsorption, and active ^•OH and ^•O₂^- generation, thus improving the photocatalytic activity.

Effects of engine load and biodiesel content on performance and regulated and unregulated emissions of a diesel engine using contour-plot map

This experimental study was conducted to explore the favorable and unfavorable conditions which promote or reduce the performance and emissions in a diesel engine, based on six engine loads (5% to 95% load) and five biodiesel contents including B0 (0% waste cooking oil biodiesel and 100% diesel, by volume %), B20, B50, B75 and B100 (pure biodiesel), at a constant engine speed of 1920 rpm. According to the results, the maximum brake specific fuel consumption was recorded at the lowest engine load (5% load) using B100; while the highest brake thermal efficiency was obtained at 80% load for B100. In regard to regulated emissions, the highest engine load (95% load) with diesel fuel was the condition for the formation of maximum CO, smoke opacity, PM mass, total particle number concentration and geometric mean diameter. The 95% load with B100 was the condition for maximum CO₂ and NO_X. The 60% load with diesel fuel was the condition for maximum THC. For unregulated emissions, low engine load with B100 was the condition for maximum formaldehyde, acetaldehyde, ethene and propene. The maximum 1,3-butadiene was observed for B100 at 80% load. The highest benzene emission was recorded at 40% load for B100. The maximum toluene and xylene emissions were found at 5% load for diesel fuel. In addition, the conditions which lead to produce the minimum emissions are also extensively discussed in the present study.

Integrated adsorption and photocatalytic degradation of volatile organic compounds (VOCs) using carbon-based nanocomposites: A critical review

Volatile organic compounds (VOCs) are harmful for human and surrounding ecosystem, and a great number of VOC abatement technologies have been developed during the past few decades. However, the single method has some problems such as high energy consumption, unfriendly environment, and low removal efficiency. Recently, the integration of adsorption and photocatalytic degradation of VOCs is considered as a promising one. Carbon material, with large surface area, high adsorption capacity, and fast electron transfer ability, is widely used in integrated adsorptive-photocatalytic removal of VOCs. It is thus crucial to digest and summarize recent research advances in carbon-based nanocomposites as the adsorbent-photocatalyst for VOC removal. To satisfy this need, this work provides a critical review of the related literature with focuses on: (1) the advantages and disadvantages of various carbon-based nanocomposites for the applications of VOC adsorption and photocatalytic degradation; (2) models and mechanisms of adsorptive-photocatalytic removal of VOCs according to the material properties; and (3) major factors controlling adsorption-photocatalysis processes of VOCs. The review is aimed to establish the "structure-property-application" relationships for the development of innovative carbon-supported nanocomposites and to promote future research on the integrated adsorptive and photocatalytic removal of VOCs.

Efficient Hydrogen Evolution Activity and Overall Water Splitting of Metallic Co4N Nanowires through Tunable d-Orbitals with Ultrafast Incorporation of FeOOH

Cobalt nitride electrocatalysts have been investigated and proven to show excellent oxygen evolution reaction activity owing to their excellent metallic properties, but their hydrogen evolution reaction (HER) properties are rarely reported because of their unsatisfactory molecular energy level, especially the d-orbital. Herein, taking Co₄N as a case study, we tune the d-orbital of metallic Co₄N nanowires via rapid formation of iron oxyhydroxide (FeOOH). Experimental analyses show that FeOOH@Co₄N/SSM exhibits excellent HER catalytic activity with considerable low onset overpotential (22 mV), small Tafel slope (34 mV dec^-1), and excellent stability at current densities ranging from 20 to 100 mA cm^-2. Additionally, theoretical assessments display that the hybridization of Co₄N with FeOOH is beneficiary for optimizing and promoting the free energy of H adsorption due to the tuning of d-orbital. An overall water-splitting device assembled based on bifunctional FeOOH@Co₄N/SSM delivers an onset potential of 1.48 V with excellent stability up to 4 days. This shows a new strategy for designing a high-performance water-splitting device based on cobalt-based electrocatalysts.

Heterostructural design of I-deficient BiOI for photocatalytic decoloration and catalytic CO2 conversion

I⁻ vacancies in BiOI play a major role in governing the photocatalysis and catalysis.

Polyethylene glycol-doped BiZn2VO6 as a high-efficiency solar-light-activated photocatalyst with substantial durability toward photodegradation of organic contaminations

In this study, we focus on a simple, low-priced, and mild condition hydrothermal route to construct BiZn₂VO₆ nanocompounds (NCs) as a novel photocatalyst with strong solar light absorption ability for environmental purification using solar energy. NCs were further doped with polyethylene glycol (PEG) to improve their photocatalytic efficiency for photodegradation processes through inhibition of fast charge carrier recombination rates and higher charge separation efficiency. Surface morphology, phase structure, optical characteristics, and band structure of the as-prepared samples were analyzed using XRD, EDX, XPS, SEM, UV-vis spectroscopy, CL, and BET techniques. PEG-doped BiZn₂VO₆ NCs were applied as effective materials to degrade various kinds of organic pollutants including cationic and anionic types, and these NCs exhibited excellent photocatalytic efficiency as compared to traditional photocatalysts. In particular, the PEG-doped BiZn₂VO₆ (0.10% w/v) photocatalyst exhibited highly enhanced photocatalytic performance with improvements of about 46.4, 28.3, and 7.23 folds compared with PEG-doped ZnO nanorods (NRs), pristine BiVO₄, and BiZn₂VO₆ samples, respectively, for the decomposition of congo red (CR) dye. After 40 minutes of sunlight irradiation, 97.4% of CR was decomposed. In this study, scavenging experiments indicated that both hydroxyl radicals and holes play dominant roles in CR photodegradation under simulated solar light irradiation. Meanwhile, the optimal photocatalyst demonstrated good reproducibility and stability for successive cycles of photocatalysis.